Effects of Discrete Charge Clustering in Simulations of Charged Interfaces.

PubMed

Grime, John M A; Khan, Malek O

2010-10-12

A system of counterions between charged surfaces is investigated, with the surfaces represented by uniform charged planes and three different arrangements of discrete surface charges - an equispaced grid and two different clustered arrangements. The behaviors of a series of systems with identical net surface charge density are examined, with particular emphasis placed on the long ranged corrections via the method of "charged slabs" and the effects of the simulation cell size. Marked differences are observed in counterion distributions and the osmotic pressure dependent on the particular representation of the charged surfaces; the uniformly charged surfaces and equispaced grids of discrete charge behave in a broadly similar manner, but the clustered systems display a pronounced decrease in osmotic pressure as the simulation size is increased. The influence of the long ranged correction is shown to be minimal for all but the very smallest of system sizes.

Modulating interactions between ligand-coated nanoparticles and phase-separated lipid bilayers by varying the ligand density and the surface charge.

PubMed

Chen, Xiaojie; Tieleman, D Peter; Liang, Qing

2018-02-01

The interactions between nanoparticles and lipid bilayers are critical in applications of nanoparticles in nanomedicine, cell imaging, toxicology, and elsewhere. Here, we investigate the interactions between nanoparticles coated with neutral and/or charged ligands and phase-separated lipid bilayers using coarse-grained molecular dynamics simulation. Both penetration and adsorption processes as well as the final distribution of the nanoparticles can be readily modulated by varying the ligand density and the surface charge of the nanoparticles. Completely hydrophobic (neutral) nanoparticles with larger size initially preferentially penetrate into the liquid-disordered region of the lipid bilayer and finally transfer into the liquid-ordered region; partially hydrophilic nanoparticles with low or moderate surface charge tend to either distribute in the liquid-disordered region or be adsorbed on the surface of the lipid bilayer, while strongly hydrophilic nanoparticles with high surface charge always reside on the surface of the lipid bilayer. Interactions of the nanoparticles with the lipid bilayers are affected by the surface charge of nanoparticles, hydrophobic mismatch, bending of the ligands, and the packing state of the lipids. Insight in these factors can be used to improve the efficiency of designing nanoparticles for specific applications.

Distribution of electron density in charged Li@C60 complexes

NASA Astrophysics Data System (ADS)

Sadlej-Sosnowska, Nina; Mazurek, Aleksander P.

2013-08-01

The Letter is an expanded commentary to the paper 'Fullerene as an electron buffer: charge transfer in Li@C60', by Pavanello and co-authors [8]. We calculated the electron density distribution in the space inside and outside the fullerene cage in Li@C60 complexes differing in total charge, based on Gauss's law. It allowed us to determine the charges contained inside surfaces isomorphic with the fullerene cage and contracted or enlarged with respect to the latter. For every complex, a surface was found in the vicinity of the central Li atom such that the charge enclosed within it was equal to +1.

Adhesion of osteoblasts to a nanorough titanium implant surface

PubMed Central

Gongadze, Ekaterina; Kabaso, Doron; Bauer, Sebastian; Slivnik, Tomaž; Schmuki, Patrik; van Rienen, Ursula; Iglič, Aleš

2011-01-01

This work considers the adhesion of cells to a nanorough titanium implant surface with sharp edges. The basic assumption was that the attraction between the negatively charged titanium surface and a negatively charged osteoblast is mediated by charged proteins with a distinctive quadrupolar internal charge distribution. Similarly, cation-mediated attraction between fibronectin molecules and the titanium surface is expected to be more efficient for a high surface charge density, resulting in facilitated integrin mediated osteoblast adhesion. We suggest that osteoblasts are most strongly bound along the sharp convex edges or spikes of nanorough titanium surfaces where the magnitude of the negative surface charge density is the highest. It is therefore plausible that nanorough regions of titanium surfaces with sharp edges and spikes promote the adhesion of osteoblasts. PMID:21931478

High-energy Electron Scattering and the Charge Distributions of Selected Nuclei

DOE R&D Accomplishments Database

Hahn, B.; Ravenhall, D. G.; Hofstadter, R.

1955-10-01

Experimental results are presented of electron scattering by Ca, V, Co, In, Sb, Hf, Ta, W, Au, Bi, Th, and U, at 183 Mev and (for some of the elements) at 153 Mev. For those nuclei for which asphericity and inelastic scattering are absent or unimportant, i.e., Ca, V, Co, In, Sb, Au, and Bi, a partial wave analysis of the Dirac equation has been performed in which the nuclei are represented by static, spherically symmetric charge distributions. Smoothed uniform charge distributions have been assumed; these are characterized by a constant charge density in the central region of the nucleus, with a smoothed-our surface. Essentially two parameters can be determined, related to the radium and to the surface thickness. An examination of the Au experiments show that the functional forms of the surface are not important, and that the charge density in the central regions is probably fairly flat, although it cannot be determined very accurately.

Exact solutions to model surface and volume charge distributions

NASA Astrophysics Data System (ADS)

Mukhopadhyay, S.; Majumdar, N.; Bhattacharya, P.; Jash, A.; Bhattacharya, D. S.

2016-10-01

Many important problems in several branches of science and technology deal with charges distributed along a line, over a surface and within a volume. Recently, we have made use of new exact analytic solutions of surface charge distributions to develop the nearly exact Boundary Element Method (neBEM) toolkit. This 3D solver has been successful in removing some of the major drawbacks of the otherwise elegant Green's function approach and has been found to be very accurate throughout the computational domain, including near- and far-field regions. Use of truly distributed singularities (in contrast to nodally concentrated ones) on rectangular and right-triangular elements used for discretizing any three-dimensional geometry has essentially removed many of the numerical and physical singularities associated with the conventional BEM. In this work, we will present this toolkit and the development of several numerical models of space charge based on exact closed-form expressions. In one of the models, Particles on Surface (ParSur), the space charge inside a small elemental volume of any arbitrary shape is represented as being smeared on several surfaces representing the volume. From the studies, it can be concluded that the ParSur model is successful in getting the estimates close to those obtained using the first-principles, especially close to and within the cell. In the paper, we will show initial applications of ParSur and other models in problems related to high energy physics.

Direct Observation of Charge Transfer at a MgO(111) Surface

NASA Astrophysics Data System (ADS)

Subramanian, A.; Marks, L. D.; Warschkow, O.; Ellis, D. E.

2004-01-01

Transmission electron diffraction (TED) combined with direct methods have been used to study the √(3)×√(3)R30° reconstruction on the polar (111) surface of MgO and refine the valence charge distribution. The surface is nonstoichiometric and is terminated by a single magnesium atom. A charge-compensating electron hole is localized in the next oxygen layer and there is a nominal charge transfer from the oxygen atoms to the top magnesium atom. The partial charges that we obtain for the surface atoms are in reasonable agreement with empirical bond-valence estimations.

Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: a Monte Carlo simulation study in the Debye-Hückel approximation.

PubMed

Truzzolillo, D; Bordi, F; Sciortino, F; Sennato, S

2010-07-14

We study the effective interaction between differently charged polyelectrolyte-colloid complexes in electrolyte solutions via Monte Carlo simulations. These complexes are formed when short and flexible polyelectrolyte chains adsorb onto oppositely charged colloidal spheres, dispersed in an electrolyte solution. In our simulations the bending energy between adjacent monomers is small compared to the electrostatic energy, and the chains, once adsorbed, do not exchange with the solution, although they rearrange on the particles surface to accommodate further adsorbing chains or due to the electrostatic interaction with neighbor complexes. Rather unexpectedly, when two interacting particles approach each other, the rearrangement of the surface charge distribution invariably produces antiparallel dipolar doublets that invert their orientation at the isoelectric point. These findings clearly rule out a contribution of dipole-dipole interactions to the observed attractive interaction between the complexes, pointing out that such suspensions cannot be considered dipolar fluids. On varying the ionic strength of the electrolyte, we find that a screening length kappa(-1), short compared with the size of the colloidal particles, is required in order to observe the attraction between like-charged complexes due to the nonuniform distribution of the electric charge on their surface ("patch attraction"). On the other hand, by changing the polyelectrolyte/particle charge ratio xi(s), the interaction between like-charged polyelectrolyte-decorated particles, at short separations, evolves from purely repulsive to strongly attractive. Hence, the effective interaction between the complexes is characterized by a potential barrier, whose height depends on the net charge and on the nonuniformity of their surface charge distribution.

Molecular dynamics investigation of the ionic liquid/enzyme interface: application to engineering enzyme surface charge.

PubMed

Burney, Patrick R; Nordwald, Erik M; Hickman, Katie; Kaar, Joel L; Pfaendtner, Jim

2015-04-01

Molecular simulations of the enzymes Candida rugosa lipase and Bos taurus α-chymotrypsin in aqueous ionic liquids 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium ethyl sulfate were used to study the change in enzyme-solvent interactions induced by modification of the enzyme surface charge. The enzymes were altered by randomly mutating lysine surface residues to glutamate, effectively decreasing the net surface charge by two for each mutation. These mutations resemble succinylation of the enzyme by chemical modification, which has been shown to enhance the stability of both enzymes in ILs. After establishing that the enzymes were stable on the simulated time scales, we focused the analysis on the organization of the ionic liquid substituents about the enzyme surface. Calculated solvent charge densities show that for both enzymes and in both solvents that changing positively charged residues to negative charge does indeed increase the charge density of the solvent near the enzyme surface. The radial distribution of IL constituents with respect to the enzyme reveals decreased interactions with the anion are prevalent in the modified systems when compared to the wild type, which is largely accompanied by an increase in cation contact. Additionally, the radial dependence of the charge density and ion distribution indicates that the effect of altering enzyme charge is confined to short range (≤1 nm) ordering of the IL. Ultimately, these results, which are consistent with that from prior experiments, provide molecular insight into the effect of enzyme surface charge on enzyme stability in ILs. © 2015 Wiley Periodicals, Inc.

Altering surface charge nonuniformity on individual colloidal particles.

PubMed

Feick, Jason D; Chukwumah, Nkiru; Noel, Alexandra E; Velegol, Darrell

2004-04-13

Charge nonuniformity (sigmazeta) was altered on individual polystyrene latex particles and measured using the novel experimental technique of rotational electrophoresis. It has recently been shown that unaltered sulfated latices often have significant charge nonuniformity (sigmazeta = 100 mV) on individual particles. Here it is shown that anionic polyelectrolytes and surfactants reduce the native charge nonuniformity on negatively charged particles by 80% (sigmazeta = 20 mV), even while leaving the average surface charge density almost unchanged. Reduction of charge uniformity occurs as large domains of nonuniformity are minimized, giving a more random distribution of charge on individual particle surfaces. Targeted reduction of charge nonuniformity opens new opportunities for the dispersion of nanoparticles and the oriented assembly of particles.

Silver nanoparticles as a key feature of a plasma polymer composite layer in mitigation of charge injection into polyethylene under dc stress

NASA Astrophysics Data System (ADS)

Milliere, L.; Maskasheva, K.; Laurent, C.; Despax, B.; Boudou, L.; Teyssedre, G.

2016-01-01

The aim of this work is to limit charge injection from a semi-conducting electrode into low density polyethylene (LDPE) under dc field by tailoring the polymer surface using a silver nanoparticles-containing layer. The layer is composed of a plane of silver nanoparticles embedded in a semi-insulating organosilicon matrix deposited on the polyethylene surface by a plasma process. Size, density and surface coverage of the nanoparticles are controlled through the plasma process. Space charge distribution in 300 μm thick LDPE samples is measured by the pulsed-electroacoustic technique following a short term (step-wise voltage increase up to 50 kV mm-1, 20 min in duration each, followed by a polarity inversion) and a longer term (up to 12 h under 40 kV mm-1) protocols for voltage application. A comparative study of space charge distribution between a reference polyethylene sample and the tailored samples is presented. It is shown that the barrier effect depends on the size distribution and the surface area covered by the nanoparticles: 15 nm (average size) silver nanoparticles with a high surface density but still not percolating form an efficient barrier layer that suppress charge injection. It is worthy to note that charge injection is detected for samples tailored with (i) percolating nanoparticles embedded in organosilicon layer; (ii) with organosilicon layer only, without nanoparticles and (iii) with smaller size silver particles (<10 nm) embedded in organosilicon layer. The amount of injected charges in the tailored samples increases gradually in the samples ranking given above. The mechanism of charge injection mitigation is discussed on the basis of complementary experiments carried out on the nanocomposite layer such as surface potential measurements. The ability of silver clusters to stabilize electrical charges close to the electrode thereby counterbalancing the applied field appears to be a key factor in explaining the charge injection mitigation effect.

Electron-beam-charged dielectrics: Internal charge distribution

NASA Technical Reports Server (NTRS)

Beers, B. L.; Pine, V. W.

1981-01-01

Theoretical calculations of an electron transport model of the charging of dielectrics due to electron bombardment are compared to measurements of internal charge distributions. The emphasis is on the distribution of Teflon. The position of the charge centroid as a function of time is not monotonic. It first moves deeper into the material and then moves back near to the surface. In most time regimes of interest, the charge distribution is not unimodal, but instead has two peaks. The location of the centroid near saturation is a function of the incident current density. While the qualitative comparison of theory and experiment are reasonable, quantitative comparison shows discrepancies of as much as a factor of two.

Effective Electrostatic Interactions Between Two Overall Neutral Surfaces with Quenched Charge Heterogeneity Over Atomic Length Scale

NASA Astrophysics Data System (ADS)

Zhou, S.

2017-12-01

Using Monte Carlo results as a reference, a classical density functional theory ( CDFT) is shown to reliably predict the forces between two heterogeneously charged surfaces immersed in an electrolyte solution, whereas the Poisson-Boltzmann ( PB) theory is demonstrated to deteriorate obviously for the same system even if the system parameters considered fall within the validity range of the PB theory in the homogeneously charged surfaces. By applying the tested CDFT, we study the effective electrostatic potential of mean force ( EPMF) between two face-face planar and hard surfaces of zero net charge on which positive and negative charges are separated and considered to present as discontinuous spots on the inside edges of the two surfaces. Main conclusions are summarized as follows: (i) strength of the EPMF in the surface charge separation case is very sensitively and positively correlated with the surface charge separation level and valency of the salt ion. Particularly, the charge separation level and the salt ion valency have a synergistic effect, which makes high limit of the EPMF strength in the surface charge separation case significantly go beyond that of the ideal homogeneously charged surface counterpart at average surface charge density similar to the average surface positive or negative charge density in the charge separation case. (ii) The surface charge distribution patterns mainly influence sign of the EPMF: symmetrical and asymmetrical patterns induce repulsive and attractive (at small distances) EPMF, respectively; but with low valency salt ions and low charge separation level the opposite may be the case. With simultaneous presence of both higher valency cation and anion, the EPMF can be repulsive at intermediate distances for asymmetrical patterns. (iii) Salt ion size has a significant impact, which makes the EPMF tend to become more and more repulsive with the ion diameter regardless of the surface charge distribution patterns and the valency of the salt ion; whereas if the 1:1 type electrolyte and the symmetrical patterns are considered, then the opposite may be the case. All of these findings can be explained self-consistently from several perspectives: an excess adsorption of the salt ions (induced by the surface charge separation) serving to raise the osmotic pressure between the plates, configuration fine-tuning in the thinner ion adsorption layer driven by the energy decrease principle, direct Coulombic interactions operating between charged objects on the two face-to-face plates involved, and net charge strength in the ion adsorption layer responsible for the net electrostatic repulsion.

Electromagnetic Field Redistribution in Metal Nanoparticle on Graphene.

PubMed

Li, Keke; Liu, Anping; Wei, Dapeng; Yu, Keke; Sun, Xiaonan; Yan, Sheng; Huang, Yingzhou

2018-04-25

Benefiting from the induced image charge on metal film, the light energy is confined on a film surface under metal nanoparticle dimer, which is called electromagnetic field redistribution. In this work, electromagnetic field distribution of metal nanoparticle monomer or dimer on graphene is investigated through finite-difference time-domain method. The results point out that the electromagnetic field (EM) redistribution occurs in this nanoparticle/graphene hybrid system at infrared region where light energy could also be confined on a monolayer graphene surface. Surface charge distribution was analyzed using finite element analysis, and surface-enhanced Raman spectrum (SERS) was utilized to verify this phenomenon. Furthermore, the data about dielectric nanoparticle on monolayer graphene demonstrate this EM redistribution is attributed to strong coupling between light-excited surface charge on monolayer graphene and graphene plasmon-induced image charge on dielectric nanoparticle surface. Our work extends the knowledge of monolayer graphene plasmon, which has a wide range of applications in monolayer graphene-related film.

The Review on the Charge Distribution on the Conductor Surface

ERIC Educational Resources Information Center

Matehkolaee, M. Jafari; Asrami, A. Naderi

2013-01-01

In this paper we have a full review on the surface charge density at disordered conductor surfaces. Basically, reading text books does not resolve ambiguities in this field. As far as is possible, we have tried to the concepts easier to turn. In fact we will answer two questions. One of them is that why do charges tend to go where the curvature is…

Charge-Spot Model for Electrostatic Forces in Simulation of Fine Particulates

NASA Technical Reports Server (NTRS)

Walton, Otis R.; Johnson, Scott M.

2010-01-01

The charge-spot technique for modeling the static electric forces acting between charged fine particles entails treating electric charges on individual particles as small sets of discrete point charges, located near their surfaces. This is in contrast to existing models, which assume a single charge per particle. The charge-spot technique more accurately describes the forces, torques, and moments that act on triboelectrically charged particles, especially image-charge forces acting near conducting surfaces. The discrete element method (DEM) simulation uses a truncation range to limit the number of near-neighbor charge spots via a shifted and truncated potential Coulomb interaction. The model can be readily adapted to account for induced dipoles in uncharged particles (and thus dielectrophoretic forces) by allowing two charge spots of opposite signs to be created in response to an external electric field. To account for virtual overlap during contacts, the model can be set to automatically scale down the effective charge in proportion to the amount of virtual overlap of the charge spots. This can be accomplished by mimicking the behavior of two real overlapping spherical charge clouds, or with other approximate forms. The charge-spot method much more closely resembles real non-uniform surface charge distributions that result from tribocharging than simpler approaches, which just assign a single total charge to a particle. With the charge-spot model, a single particle may have a zero net charge, but still have both positive and negative charge spots, which could produce substantial forces on the particle when it is close to other charges, when it is in an external electric field, or when near a conducting surface. Since the charge-spot model can contain any number of charges per particle, can be used with only one or two charge spots per particle for simulating charging from solar wind bombardment, or with several charge spots for simulating triboelectric charging. Adhesive image-charge forces acting on charged particles touching conducting surfaces can be up to 50 times stronger if the charge is located in discrete spots on the particle surface instead of being distributed uniformly over the surface of the particle, as is assumed by most other models. Besides being useful in modeling particulates in space and distant objects, this modeling technique is useful for electrophotography (used in copiers) and in simulating the effects of static charge in the pulmonary delivery of fine dry powders.

Characterization of trapped charges distribution in terms of mirror plot curve.

PubMed

Al-Obaidi, Hassan N; Mahdi, Ali S; Khaleel, Imad H

2018-01-01

Accumulation of charges (electrons) at the specimen surface in scanning electron microscope (SEM) lead to generate an electrostatic potential. By using the method of image charges, this potential is defined in the chamber's space of such apparatus. The deduced formula is expressed in terms a general volumetric distribution which proposed to be an infinitesimal spherical extension. With aid of a binomial theorem the defined potential is expanded to a multipolar form. Then resultant formula is adopted to modify a novel mirror plot equation so as to detect the real distribution of trapped charges. Simulation results reveal that trapped charges may take a various sort of arrangement such as monopole, quadruple and octuple. But existence of any of these arrangements alone may never be take place, rather are some a formations of a mix of them. Influence of each type of these profiles depends on the distance between the incident electron and surface of a sample. Result also shows that trapped charge's amount of trapped charges can refer to a threshold for failing of point charge approximation. Copyright © 2017 Elsevier B.V. All rights reserved.

The Flexible Faraday Cage

NASA Astrophysics Data System (ADS)

Gluck, Paul

2004-03-01

The Faraday ice-pail experiment is performed when studying the distribution of charges in conductors: Inside a hollow conductor the net charge is zero, and any excess charge resides on the outside surface.

The Charging Events in Contact-Separation Electrification.

PubMed

Musa, Umar G; Cezan, S Doruk; Baytekin, Bilge; Baytekin, H Tarik

2018-02-06

Contact electrification (CE)-charging of surfaces that are contacted and separated, is a common phenomenon, however it is not completely understood yet. Recent studies using surface imaging techniques and chemical analysis revealed a 'spatial' bipolar distribution of charges at the nano dimension, which made a paradigm shift in the field. However, such analyses can only provide information about the charges that remained on the surface after the separation, providing limited information about the actual course of the CE event. Tapping common polymers and metal surfaces to each other and detecting the electrical potential produced on these surfaces 'in-situ' in individual events of contact and separation, we show that, charges are generated and transferred between the surfaces in both events; the measured potential is bipolar in contact and unipolar in separation. We show, the 'contact-charges' on the surfaces are indeed the net charges that results after the separation process, and a large contribution to tribocharge harvesting comes, in fact, from the electrostatic induction resulting from the generated CE charges. Our results refine the mechanism of CE providing information for rethinking the conventional ranking of materials' charging abilities, charge harvesting, and charge prevention.

Material identification based on electrostatic sensing technology

NASA Astrophysics Data System (ADS)

Liu, Kai; Chen, Xi; Li, Jingnan

2018-04-01

When the robot travels on the surface of different media, the uncertainty of the medium will seriously affect the autonomous action of the robot. In this paper, the distribution characteristics of multiple electrostatic charges on the surface of materials are detected, so as to improve the accuracy of the existing electrostatic signal material identification methods, which is of great significance to help the robot optimize the control algorithm. In this paper, based on the electrostatic signal material identification method proposed by predecessors, the multi-channel detection circuit is used to obtain the electrostatic charge distribution at different positions of the material surface, the weights are introduced into the eigenvalue matrix, and the weight distribution is optimized by the evolutionary algorithm, which makes the eigenvalue matrix more accurately reflect the surface charge distribution characteristics of the material. The matrix is used as the input of the k-Nearest Neighbor (kNN)classification algorithm to classify the dielectric materials. The experimental results show that the proposed method can significantly improve the recognition rate of the existing electrostatic signal material recognition methods.

Real-space measurement of potential distribution in PECVD ONO electrets by Kelvin probe force microscopy.

PubMed

Emmerich, F; Thielemann, C

2016-05-20

Multilayers of silicon oxide/silicon nitride/silicon oxide (ONO) are known for their good electret properties due to deep energy traps near the material interfaces, facilitating charge storage. However, measurement of the space charge distribution in such multilayers is a challenge for conventional methods if layer thickness dimensions shrink below 1 μm. In this paper, we propose an atomic force microscope based method to determine charge distributions in ONO layers with spatial resolution below 100 nm. By applying Kelvin probe force microscopy (KPFM) on freshly cleaved, corona-charged multilayers, the surface potential is measured directly along the z-axis and across the interfaces. This new method gives insights into charge distribution and charge movement in inorganic electrets with a high spatial resolution.

Protein adsorption at charged surfaces: the role of electrostatic interactions and interfacial charge regulation.

PubMed

Hartvig, Rune A; van de Weert, Marco; Østergaard, Jesper; Jorgensen, Lene; Jensen, Henrik

2011-03-15

The understanding of protein adsorption at charged surfaces is important for a wide range of scientific disciplines including surface engineering, separation sciences and pharmaceutical sciences. Compared to chemical entities having a permanent charge, the adsorption of small ampholytes and proteins is more complicated as the pH near a charged surface can be significantly different from the value in bulk solution. In this work, we have developed a phenomenological adsorption model which takes into account the combined role of interfacial ion distribution, interfacial charge regulation of amino acids in the proximity of the surface, electroneutrality, and mass balance. The model is straightforward to apply to a given set of experimental conditions as most model parameters are obtained from bulk properties and therefore easy to estimate or are directly measurable. The model provides a detailed understanding of the importance of surface charge on adsorption and in particular of how changes in surface charge, concentration, and surface area may affect adsorption behavior. The model is successfully used to explain the experimental adsorption behavior of the two model proteins lysozyme and α-lactalbumin. It is demonstrated that it is possible to predict the pH and surface charge dependent adsorption behavior from experimental or theoretical estimates of a preferred orientation of a protein at a solid charged interface.

Miniaturized ultrafine particle sizer and monitor

NASA Technical Reports Server (NTRS)

Qi, Chaolong (Inventor); Chen, Da-Ren (Inventor)

2011-01-01

An apparatus for measuring particle size distribution includes a charging device and a precipitator. The charging device includes a corona that generates charged ions in response to a first applied voltage, and a charger body that generates a low energy electrical field in response to a second applied voltage in order to channel the charged ions out of the charging device. The corona tip and the charger body are arranged relative to each other to direct a flow of particles through the low energy electrical field in a direction parallel to a direction in which the charged ions are channeled out of the charging device. The precipitator receives the plurality of particles from the charging device, and includes a disk having a top surface and an opposite bottom surface, wherein a predetermined voltage is applied to the top surface and the bottom surface to precipitate the plurality of particles.

Electroosmotic flow in a microcavity with nonuniform surface charges.

PubMed

Halpern, David; Wei, Hsien-Hung

2007-08-28

In this work, we theoretically explore the characteristics of electroosmostic flow (EOF) in a microcavity with nonuniform surface charges. It is well known that a uniformly charged EOF does not give rise to flow separation because of its irrotational nature, as opposed to the classical problem of viscous flow past a cavity. However, if the cavity walls bear nonuniform surface charges, then the similitude between electric and flow fields breaks down, leading to the generation of vorticity in the cavity. Because this vorticity must necessarily diffuse into the exterior region that possesses a zero vorticity set by a uniform EOF, a new flow structure emerges. Assuming Stokes flow, we employ a boundary element method to explore how a nonuniform charge distribution along the cavity surface affects the flow structure. The results show that the stream can be susceptible to flow separation and exhibits a variety of flow structures, depending on the distributions of zeta potentials and the aspect ratio of the cavity. The interactions between patterned EOF vortices and Moffatt eddies are further demonstrated for deep cavities. This work not only has implications for electrokinetic flow induced by surface imperfections but also provides optimal strategies for achieving effective mixing in microgrooves.

Charge renormalization and inversion of a highly charged lipid bilayer: effects of dielectric discontinuities and charge correlations.

PubMed

Taheri-Araghi, Sattar; Ha, Bae-Yeun

2005-08-01

We reexamine the problem of charge renormalization and inversion of a highly charged surface of a low dielectric constant immersed in ionic solutions. To be specific, we consider an asymmetrically charged lipid bilayer, in which only one layer is negatively charged. In particular, we study how dielectric discontinuities and charge correlations (among lipid charges and condensed counterions) influence the effective charge of the surface. When counterions are monovalent (e.g., Na+), our mean-field approach implies that dielectric discontinuities can enhance counterion condensation. A simple scaling picture shows how the effects of dielectric discontinuities and surface-charge distributions are intertwined: Dielectric discontinuities diminish condensation if the backbone charge is uniformly smeared out while counterions are localized in space; they can, however, enhance condensation when the backbone charge is discrete. In the presence of asymmetric salts such as CaCl2 , we find that the correlation effect, treated at the Gaussian level, is more pronounced when the surface has a lower dielectric constant, inverting the sign of the charge at a smaller value of Ca2+ concentration.

A submicron device to rectify a square-wave angular velocity.

PubMed

Moradian, A; Miri, M F

2011-02-01

We study a system composed of two thick dielectric disks separated by a thin layer of an electrolyte solution. Initially both plates have the same surface charge distribution. The surface charge distribution has no rotational symmetry. We show that the top plate experiences a torque [Formula: see text]([Formula: see text]) if it rotates about its axis by an angle [Formula: see text] . The torque can be controlled by varying the electrolyte concentration, the separation and the surface charge density of the plates. For a specific example of charged rods attached to the plates, we find [Formula: see text]([Formula: see text]) [Formula: see text] sin(4[Formula: see text]) . We also study the dynamics of the system. We consider the case where the angular velocity of the bottom disk is a square-wave signal. We find that the average angular velocity of the top disk is not zero.

Surface charge dynamics and OH and H number density distributions in near-surface nanosecond pulse discharges at a liquid / vapor interface

NASA Astrophysics Data System (ADS)

Winters, Caroline; Petrishchev, Vitaly; Yin, Zhiyao; Lempert, Walter R.; Adamovich, Igor V.

2015-10-01

The present work provides insight into surface charge dynamics and kinetics of radical species reactions in nanosecond pulse discharges sustained at a liquid-vapor interface, above a distilled water surface. The near-surface plasma is sustained using two different discharge configurations, a surface ionization wave discharge between two exposed metal electrodes and a double dielectric barrier discharge. At low discharge pulse repetition rates (~100 Hz), residual surface charge deposition after the discharge pulse is a minor effect. At high pulse repetition rates (~10 kHz), significant negative surface charge accumulation over multiple discharge pulses is detected, both during alternating polarity and negative polarity pulse trains. Laser induced fluorescence (LIF) and two-photon absorption LIF (TALIF) line imaging are used for in situ measurements of spatial distributions of absolute OH and H atom number densities in near-surface, repetitive nanosecond pulse discharge plasmas. Both in a surface ionization wave discharge and in a double dielectric barrier discharge, peak measured H atom number density, [H] is much higher compared to peak OH number density, due to more rapid OH decay in the afterglow between the discharge pulses. Higher OH number density was measured near the regions with higher plasma emission intensity. Both OH and especially H atoms diffuse out of the surface ionization wave plasma volume, up to several mm from the liquid surface. Kinetic modeling calculations using a quasi-zero-dimensional H2O vapor / Ar plasma model are in qualitative agreement with the experimental data. The results demonstrate the experimental capability of in situ radical species number density distribution measurements in liquid-vapor interface plasmas, in a simple canonical geometry that lends itself to the validation of kinetic models.

Effect of Surfaces on Amyloid Fibril Formation

PubMed Central

Moores, Bradley; Drolle, Elizabeth; Attwood, Simon J.; Simons, Janet; Leonenko, Zoya

2011-01-01

Using atomic force microscopy (AFM) we investigated the interaction of amyloid beta (Aβ) (1–42) peptide with chemically modified surfaces in order to better understand the mechanism of amyloid toxicity, which involves interaction of amyloid with cell membrane surfaces. We compared the structure and density of Aβ fibrils on positively and negatively charged as well as hydrophobic chemically-modified surfaces at physiologically relevant conditions. We report that due to the complex distribution of charge and hydrophobicity amyloid oligomers bind to all types of surfaces investigated (CH3, COOH, and NH2) although the charge and hydrophobicity of surfaces affected the structure and size of amyloid deposits as well as surface coverage. Hydrophobic surfaces promote formation of spherical amorphous clusters, while charged surfaces promote protofibril formation. We used the nonlinear Poisson-Boltzmann equation (PBE) approach to analyze the electrostatic interactions of amyloid monomers and oligomers with modified surfaces to complement our AFM data. PMID:22016789

Electron gun controlled smart structure

DOEpatents

Martin, Jeffrey W.; Main, John Alan; Redmond, James M.; Henson, Tammy D.; Watson, Robert D.

2001-01-01

Disclosed is a method and system for actively controlling the shape of a sheet of electroactive material; the system comprising: one or more electrodes attached to the frontside of the electroactive sheet; a charged particle generator, disposed so as to direct a beam of charged particles (e.g. electrons) onto the electrode; a conductive substrate attached to the backside of the sheet; and a power supply electrically connected to the conductive substrate; whereby the sheet changes its shape in response to an electric field created across the sheet by an accumulation of electric charge within the electrode(s), relative to a potential applied to the conductive substrate. Use of multiple electrodes distributed across on the frontside ensures a uniform distribution of the charge with a single point of e-beam incidence, thereby greatly simplifying the beam scanning algorithm and raster control electronics, and reducing the problems associated with "blooming". By placing a distribution of electrodes over the front surface of a piezoelectric film (or other electroactive material), this arrangement enables improved control over the distribution of surface electric charges (e.g. electrons) by creating uniform (and possibly different) charge distributions within each individual electrode. Removal or deposition of net electric charge can be affected by controlling the secondary electron yield through manipulation of the backside electric potential with the power supply. The system can be used for actively controlling the shape of space-based deployable optics, such as adaptive mirrors and inflatable antennae.

Octanol-water distribution of engineered nanomaterials.

PubMed

Hristovski, Kiril D; Westerhoff, Paul K; Posner, Jonathan D

2011-01-01

The goal of this study was to examine the effects of pH and ionic strength on octanol-water distribution of five model engineered nanomaterials. Distribution experiments resulted in a spectrum of three broadly classified scenarios: distribution in the aqueous phase, distribution in the octanol, and distribution into the octanol-water interface. Two distribution coefficients were derived to describe the distribution of nanoparticles among octanol, water and their interface. The results show that particle surface charge, surface functionalization, and composition, as well as the solvent ionic strength and presence of natural organic matter, dramatically impact this distribution. Distributions of nanoparticles into the interface were significant for nanomaterials that exhibit low surface charge in natural pH ranges. Increased ionic strengths also contributed to increased distributions of nanoparticle into the interface. Similarly to the octanol-water distribution coefficients, which represent a starting point in predicting the environmental fate, bioavailability and transport of organic pollutants, distribution coefficients such as the ones described in this study could help to easily predict the fate, bioavailability, and transport of engineered nanomaterials in the environment.

Surface Charging in the Auroral Zone on the DMSP Spacecraft in LEO

NASA Astrophysics Data System (ADS)

Anderson, Phillip C.

1998-11-01

A recent anomaly on the DMSP F13 spacecraft was attributed to an electrical malfunction caused by an electrostatic discharge on the vehicle associated with surface charging. It occurred during an intense energetic electron precipitation event (an auroral arc) within a region of very low plasma density in the auroral zone. A study of 1.5 year's worth of DMSP data from three satellites acquired during the recent minimum in the solar cycle has shown that such charging was a common occurrence with 704 charging events found. This is the result of significantly reduced background plasma densities associated with the solar minimum; smaller than ever previously experienced by the DMSP spacecraft. At times, the spacecraft charged for periods of 10s of seconds as they skimmed along an auroral arc instead of cutting across it. We show examples of the observed plasma density and the precipitating electron and ion spectra associated with the charging, and the MLT distribution and the seasonal distribution of the events. The preponderance of events occurred in the premidnight and morning sectors with two types of electron spectra being observed: a sharply peaked distribution indicative of field-aligned acceleration in the premidnight sector and a very hard distribution in the morning sector.

Influence of the shell thickness and charge distribution on the effective interaction between two like-charged hollow spheres.

PubMed

Angelescu, Daniel G; Caragheorgheopol, Dan

2015-10-14

The mean-force and the potential of the mean force between two like-charged spherical shells were investigated in the salt-free limit using the primitive model and Monte Carlo simulations. Apart from an angular homogeneous distribution, a discrete charge distribution where point charges localized on the shell outer surface followed an icosahedral arrangement was considered. The electrostatic coupling of the model system was altered by the presence of mono-, trivalent counterions or small dendrimers, each one bearing a net charge of 9 e. We analyzed in detail how the shell thickness and the radial and angular distribution of the shell charges influenced the effective interaction between the shells. We found a sequence of the potential of the mean force similar to the like-charged filled spheres, ranging from long-range purely repulsive to short-range purely attractive as the electrostatic coupling increased. Both types of potentials were attenuated and an attractive-to-repulsive transition occurred in the presence of trivalent counterions as a result of (i) thinning the shell or (ii) shifting the shell charge from the outer towards the inner surface. The potential of the mean force became more attractive with the icosahedrally symmetric charge model, and additionally, at least one shell tended to line up with 5-fold symmetry axis along the longest axis of the simulation box at the maximum attraction. The results provided a basic framework of understanding the non-specific electrostatic origin of the agglomeration and long-range assembly of the viral nanoparticles.

Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: A Monte Carlo simulation study

NASA Astrophysics Data System (ADS)

Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

2014-05-01

Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations.

Profiling charge complementarity and selectivity for binding at the protein surface.

PubMed

Sulea, Traian; Purisima, Enrico O

2003-05-01

A novel analysis and representation of the protein surface in terms of electrostatic binding complementarity and selectivity is presented. The charge optimization methodology is applied in a probe-based approach that simulates the binding process to the target protein. The molecular surface is color coded according to calculated optimal charge or according to charge selectivity, i.e., the binding cost of deviating from the optimal charge. The optimal charge profile depends on both the protein shape and charge distribution whereas the charge selectivity profile depends only on protein shape. High selectivity is concentrated in well-shaped concave pockets, whereas solvent-exposed convex regions are not charge selective. This suggests the synergy of charge and shape selectivity hot spots toward molecular selection and recognition, as well as the asymmetry of charge selectivity at the binding interface of biomolecular systems. The charge complementarity and selectivity profiles map relevant electrostatic properties in a readily interpretable way and encode information that is quite different from that visualized in the standard electrostatic potential map of unbound proteins.

The Thomas-Fermi model in the theory of systems of charged particles above the surface of liquid dielectrics

NASA Astrophysics Data System (ADS)

Lytvtnenko, D. M.; Slyusarenko, Yu. V.; Kirdin, A. I.

2012-10-01

A consistent theory of equilibrium states of same sign charges above the surface of liquid dielectric film located on solid substrate in the presence of external attracting constant electric field is proposed. The approach to the development of the theory is based on the Thomas-Fermi model generalized to the systems under consideration and on the variational principle. The using of self-consistent field model allows formulating a theory containing no adjustable constants. In the framework of the variational principle we obtain the self-consistency equations for the parameters describing the system: the distribution function of charges above the liquid dielectric surface, the electrostatic field potentials in all regions of the system and the surface profile of the liquid dielectric. The self-consistency equations are used to describe the phase transition associated with the formation of spatially periodic structures in the system of charges on liquid dielectric surface. Assuming the non-degeneracy of the gas of charges above the surface of liquid dielectric film the solutions of the self-consistency equations near the critical point are obtained. In the case of the symmetric phase we obtain the expressions for the potentials and electric fields in all regions of the studied system. The distribution of the charges above the surface of liquid dielectric film for the symmetric phase is derived. The system parameters of the phase transition to nonsymmetric phase - the states with a spatially periodic ordering are obtained. We derive the expression determining the period of two-dimensional lattice as a function of physical parameters of the problem - the temperature, the external attractive electric field, the number of electrons per unit of the flat surface area of the liquid dielectric, the density of the dielectric, its surface tension and permittivity, and the permittivity of the solid substrate. The possibility of generalizing the developed theory in the case of degenerate gas of like-charged particles above the liquid dielectric surface is discussed.

Effect of the charge surface distribution on the flow field induced by a dielectric barrier discharge actuator

NASA Astrophysics Data System (ADS)

Cristofolini, Andrea; Neretti, Gabriele; Borghi, Carlo A.

2013-08-01

The Electro-Hydro-Dynamics (EHD) interaction induced by a surface dielectric barrier discharge in the aerodynamic boundary layer at one atmosphere still air has been investigated. Three different geometrical configurations of the actuator have been utilized. In the first configuration, an electrode pair separated by a 2 mm dielectric sheet has been used. The second and the third configurations have been obtained by adding a third electrode on the upper side of the dielectric surface. This electrode has been placed downstream of the upper electrode and has been connected to ground or has been left floating. Three different dielectric materials have been utilized. The high voltage upper electrode was fed by an a.c. electric tension. Measurements of the dielectric surface potential generated by the charge deposition have been done. The discharge has been switched off after positive and negative phases of the plasma current (the current phase was characterized by a positive or a negative value, respectively). The measurements have been carried out after both phases. The charge distribution strongly depended on the switching off phase and was heavily affected by the geometrical configuration. A remarkable decrease of the charge deposited on the dielectric surface has been detected when the third electrode was connected to ground. Velocity profiles were obtained by using a Pitot probe. They showed that the presence of the third electrode limits the fluid dynamics performance of the actuator. A relation between the charge surface distribution and the EHD interaction phenomenon has been found. Imaging of the plasma has been done to evaluate the discharge structure and the extension of the plasma in the configurations investigated.

The application of diffusion theory to the analysis of hydrogen desorption data at 25 deg C

NASA Technical Reports Server (NTRS)

Danford, M. D.

1985-01-01

The application of diffusion theory to the analysis of hydrogen desorption data (coulombs of H2 desorbed versus time) has been studied. From these analyses, important information concerning hydrogen solubilities and the nature of the hydrogen distributions in the metal has been obtained. Two nickel base alloys, Rene' 41 and Waspaloy, and one ferrous alloy, 4340 steel, are studied in this work. For the nickel base alloys, it is found that the hydrogen distributions after electrolytic charging conforms closely to those which would be predicted by diffusion theory. For Waspaloy samples charged at 5,000 psi, it is found that the hydrogen distributions are essentially the same as those obtained by electrolytic charging. The hydrogen distributions in electrolytically charged 4340 steel, on the other hand, are essentially uniform in nature, which would not be predicted by diffusion theory. A possible explanation has been proposed. Finally, it is found that the hydrogen desorption is completely explained by the nature of the hydrogen distribution in the metal, and that the fast hydrogen is not due to surface and sub-surface hydride formation, as was originally proposed.

Dissociation and recombination of positive holes in minerals

NASA Technical Reports Server (NTRS)

Freund, Friedemann; Batllo, Francois; Freund, Minoru M.

1990-01-01

The formation mechanisms are described of positive holes - electronic defects in the O2 sublattice - with attention given to detecting the positive surface charge of minerals with these holes. Charge distribution analysis (CDA) is presented which measures dielectric polarization in an inhomogeneous field. CDA can be applied to the detection of the peroxide/superoxide functionality caused by positive holes on the surface. It is demonstrated with obsidian that the measurements provide data on O(-) mobility as a function of surface-charge carrier density and on O(-) generation as a function of temperature.

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

PubMed Central

2017-01-01

High-resolution atomic force microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl2 concentration. Using DLVO theory with charge regulation, we determine from the measured force–distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7 and negatively charged at pH above 7. Investigations in CaCl2 at pH 6 show that the surface charge on the gibbsite facet increases for concentration up to 10 mM CaCl2 and starts to decrease upon further increasing the salt concentration to 50 mM. The increase of surface charge at low concentration is explained by Ca2+ ion adsorption, while Cl– adsorption at higher CaCl2 concentrations partially neutralizes the surface charge. Atomic resolution imaging and density functional theory calculations corroborate these observations. They show that hydrated Ca2+ ions can spontaneously adsorb on the gibbsite facet of the kaolinite particle and form ordered surface structures, while at higher concentrations Cl– ions will co-adsorb, thereby changing the observed ordered surface structure. PMID:29140711

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

PubMed

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

2017-12-19

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

Numerical modelling of needle-grid electrodes for negative surface corona charging system

NASA Astrophysics Data System (ADS)

Zhuang, Y.; Chen, G.; Rotaru, M.

2011-08-01

Surface potential decay measurement is a simple and low cost tool to examine electrical properties of insulation materials. During the corona charging stage, a needle-grid electrodes system is often used to achieve uniform charge distribution on the surface of the sample. In this paper, a model using COMSOL Multiphysics has been developed to simulate the gas discharge. A well-known hydrodynamic drift-diffusion model was used. The model consists of a set of continuity equations accounting for the movement, generation and loss of charge carriers (electrons, positive and negative ions) coupled with Poisson's equation to take into account the effect of space and surface charges on the electric field. Four models with the grid electrode in different positions and several mesh sizes are compared with a model that only has the needle electrode. The results for impulse current and surface charge density on the sample clearly show the effect of the extra grid electrode with various positions.

Charge Storage, Conductivity and Charge Profiles of Insulators as Related to Spacecraft Charging

NASA Technical Reports Server (NTRS)

Dennison, J. R.; Swaminathan, Prasanna; Frederickson, A. R.

2004-01-01

Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination. Conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping centers; and radiation-induced conductivity. Our experiments also show that "Malter" electron emission occurs for hours after turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects Program.

Profiling Charge Complementarity and Selectivity for Binding at the Protein Surface

PubMed Central

Sulea, Traian; Purisima, Enrico O.

2003-01-01

A novel analysis and representation of the protein surface in terms of electrostatic binding complementarity and selectivity is presented. The charge optimization methodology is applied in a probe-based approach that simulates the binding process to the target protein. The molecular surface is color coded according to calculated optimal charge or according to charge selectivity, i.e., the binding cost of deviating from the optimal charge. The optimal charge profile depends on both the protein shape and charge distribution whereas the charge selectivity profile depends only on protein shape. High selectivity is concentrated in well-shaped concave pockets, whereas solvent-exposed convex regions are not charge selective. This suggests the synergy of charge and shape selectivity hot spots toward molecular selection and recognition, as well as the asymmetry of charge selectivity at the binding interface of biomolecular systems. The charge complementarity and selectivity profiles map relevant electrostatic properties in a readily interpretable way and encode information that is quite different from that visualized in the standard electrostatic potential map of unbound proteins. PMID:12719221

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

Self-consistent simulation of radio frequency multipactor on micro-grooved dielectric surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Libing; Wang, Jianguo, E-mail: wanguiuc@mail.xjtu.edu.cn; Northwest Institute of Nuclear Technology, Xi'an, Shaanxi 710024

2015-02-07

The multipactor plays a key role in the surface breakdown on the feed dielectric window irradiated by high power microwave. To study the suppression of multipactor, a 2D electrostatic PIC-MCC simulation code was developed. The space charge field, including surface deposited charge and multipactor electron charge field, is obtained by solving 2D Poisson's equation in time. Therefore, the simulation is self-consistent and does not require presetting a fixed space charge field. By using this code, the self-consistent simulation of the RF multipactor on the periodic micro-grooved dielectric surface is realized. The 2D space distributions of the multipactor electrons and spacemore » charge field are presented. From the simulation results, it can be found that only half slopes have multipactor discharge when the slope angle exceeds a certain value, and the groove presents a pronounced suppression effect on the multipactor.« less

FY04 LDRD Final Report: Interaction of Viruses with Membranes and Soil Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaldach, C M

2005-02-08

The influence of ionic strength on the electrostatic interaction of viruses with environmentally relevant surfaces was determined for three viruses, MS2, Q{beta} and Norwalk. The environmental surface is modeled as charged Gouy-Chapman plane with and without a finite atomistic region (patch) of opposite charge. The virus is modeled as a particle comprised of ionizable amino acid residues in a shell surrounding a spherical RNA core of negative charge, these charges being compensated for by a Coulomb screening due to intercalated ions. Surface potential calculations for each of the viruses show excellent agreement with electrophoretic mobility and zeta potential measurements asmore » a function of pH. The results indicate that the electrostatic interaction between the virus and the planar surface, mitigated by the ionic strength of the solute, is dependent upon the spatial distribution of the amino acid residues in the different viruses. Specifically, the order of interaction energies with the patch (MS2 greatest at 5 mM; Norwalk greatest at 20 mM) is dependent upon the ionic strength of the fluid as a direct result of the viral coat amino acid distributions. We have developed an atomistic-scale method of calculation of the binding energy of viruses to surfaces including electrostatic, van der Waals, electron-overlap repulsion, surface charge polarization (images), and hydrophobic effects. The surface is treated as a Gouy-Chapman plane allowing inclusion of pH and ionic strength effects on the electrostatic potential at each amino acid charge. Van der Waals parameters are obtained from the DREIDING force field and from Hamaker constant measurements. We applied this method to the calculation of the Cowpea Mosaic Virus (CPMV), a negatively charged virus at a pH of 7.0, and find that the viral-gold surface interaction is very long range for both signs of surface potential, a result due to the electrostatic forces. For a negative (Au) surface potential of -0.05 volts, a nearly 4 eV barrier must be overcome to reach 1 nm from the surface.« less

Model simulations of the adsorption of statherin to solid surfaces: Effects of surface charge and hydrophobicity

NASA Astrophysics Data System (ADS)

Skepö, M.

2008-11-01

The structural properties of the salivary protein statherin upon adsorption have been examined using a coarse-grained model and Monte Carlo simulation. A simple model system with focus on electrostatic interactions and short-ranged attractions among the uncharged amino acids has been used. To mimic hydrophobically modified surfaces, an extra short-ranged interaction was implemented between the amino acids and the surface. It has been shown that the adsorption and the thickness of the adsorbed layer are determined by (i) the affinity for the surface, i.e., denser layer with an extrashort-ranged potential, and (ii) the distribution of the charges along the chain. If all the amino acids have a high affinity for the surface, the protein adsorbs in a train conformation, if the surface is negatively charged the protein adsorbs in a tail-train conformation, whereas if the surface is positively charged the protein adsorbs in a loop conformation. The latter gives rise to a more confined adsorbed layer.

Effects of Acids, Bases, and Heteroatoms on Proximal Radial Distribution Functions for Proteins.

PubMed

Nguyen, Bao Linh; Pettitt, B Montgomery

2015-04-14

The proximal distribution of water around proteins is a convenient method of quantifying solvation. We consider the effect of charged and sulfur-containing amino acid side-chain atoms on the proximal radial distribution function (pRDF) of water molecules around proteins using side-chain analogs. The pRDF represents the relative probability of finding any solvent molecule at a distance from the closest or surface perpendicular protein atom. We consider the near-neighbor distribution. Previously, pRDFs were shown to be universal descriptors of the water molecules around C, N, and O atom types across hundreds of globular proteins. Using averaged pRDFs, a solvent density around any globular protein can be reconstructed with controllable relative error. Solvent reconstruction using the additional information from charged amino acid side-chain atom types from both small models and protein averages reveals the effects of surface charge distribution on solvent density and improves the reconstruction errors relative to simulation. Solvent density reconstructions from the small-molecule models are as effective and less computationally demanding than reconstructions from full macromolecular models in reproducing preferred hydration sites and solvent density fluctuations.

X-ray Reflectivity Characterization of Ion Distribution at Biomimetic Membrane Surfaces

NASA Astrophysics Data System (ADS)

Krüger, Peter; Pittler, Jens; Vaknin, David; Lösche, Mathias

2003-03-01

Ions at cell membrane surfaces may control the function and conformation of nearby biomolecules, thus playing an important role in inter- and intracellular transport as well as in biorecognition processes. Moreover, charge patterns at membrane surfaces may direct the growth of inorganic crystals in biomineralization. Langmuir monolayers are widely employed as model systems for studying charge distribution and growth processes at the organic/inorganic interface. We present a novel x-ray reflectivity technique that provides detailed information on ion distribution at biomembrane surfaces by using monochromatic x-rays at various energies at and away from the ion x-ray absorption edges. As a model, the interaction of Ba^2+ with DMPA^- (dimyristoyl phosphatidic acid) monolayers at the aqueous surface was studied. We find an unexpectedly large concentration of the cations near the interface where they form a Stern layer of bound ions. These studies have been complemented with conventional x-ray reflectivity measurements and extended to other anionic lipid species (DMPS, DMPG) and cations (Ca^2+).

Experimental evidence of beam-foil plasma creation during ion-solid interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Prashant, E-mail: prashant@iuac.res.in; Nandi, Tapan

2016-08-15

Charge state evolution of the energetic projectile ions during the passage through thin carbon foils has been revisited using the X-ray spectroscopy technique. Contributions from the bulk and the solid surface in the charge changing processes have been segregated by measuring the charge state distribution of the projectile ions in the bulk of the target during the ion–solid interaction. Interestingly, the charge state distribution measured in the bulk exhibits Lorentzian profile in contrast to the well-known Gaussian structure observed using the electromagnetic methods and the theoretical predictions. The occurrence of such behavior is a direct consequence of the imbalance betweenmore » charge changing processes, which has been seen in various cases of the laboratory plasma. It suggests that the ion-solid collisions constitute high-density, localized plasma in the bulk of the solid target, called the beam-foil plasma. This condensed beam-foil plasma is similar to the high-density solar and stellar plasma which may have practical implementations in various fields, in particular, plasma physics and nuclear astrophysics. The present work suggests further modification in the theoretical charge state distribution calculations by incorporating the plasma coupling effects during the ion–solid interactions. Moreover, the multi-electron capture from the target exit surface has been confirmed through comparison between experimentally measured and theoretically predicted values of the mean charge state of the projectile ions.« less

On the physics of both surface overcharging and charge reversal at heterophase interfaces.

PubMed

Wang, Zhi-Yong; Zhang, Pengli; Ma, Zengwei

2018-02-07

The conventional paradigm for characterizing surface overcharging and charge reversal is based on the so-called Stern layer, in which surface dissociation reaction and specific chemical adsorption are assumed to take place. In this article, a series of Monte Carlo simulations have been applied to obtain useful insights into the underlying physics responsible for these two kinds of anomalous phenomena at the interface of two dielectrics, with special emphasis on the case of divalent counterions that are more relevant in natural and biological environments. At a weakly charged surface, it is found that independent of the type of surface charge distribution and the dielectric response of the solution, the overcharging event is universally driven by the ion size-asymmetric effect. Exceptionally, the overcharging still persists when the surface is highly charged but is only restricted to the case of discrete surface charge in a relatively low dielectric medium. As compared to the adsorption onto the homogeneously smeared charge surface that has the same average affinity for counterions, on the other hand, charge reversal under the action of a dielectric response can be substantially enhanced in the discrete surface charge representation due to strong association of counterions with interfacial groups, and the degree of enhancement depends in a nontrivial way on the reduction of the medium dielectric constant and the steric effects of finite ion size. Rather interestingly, the charge reversal is of high relevance to the overcharging of interfaces because the overwhelming interfacial association forces the coions closer to the surface due to their smaller size than the counterions. Upon the addition of a monovalent salt to the solution, the interfacial association with divalent counterions makes surface overcharging and charge reversal widely unaffected, in contrast to the prevailing notion that screening of surface charge of a homogeneous nature is determined by the competitive effects between size-exclusion effects and energetic contributions. Overall, the present work highlights that the complex interplay between the electrostatic and steric interactions should be coupled to the realistic character of surface charge to establish a faithful description of the overcharging and charge reversal at heterophase interfaces.

Model improvements to simulate charging in SEM

NASA Astrophysics Data System (ADS)

Arat, K. T.; Klimpel, T.; Hagen, C. W.

2018-03-01

Charging of insulators is a complex phenomenon to simulate since the accuracy of the simulations is very sensitive to the interaction of electrons with matter and electric fields. In this study, we report model improvements for a previously developed Monte-Carlo simulator to more accurately simulate samples that charge. The improvements include both modelling of low energy electron scattering and charging of insulators. The new first-principle scattering models provide a more realistic charge distribution cloud in the material, and a better match between non-charging simulations and experimental results. Improvements on charging models mainly focus on redistribution of the charge carriers in the material with an induced conductivity (EBIC) and a breakdown model, leading to a smoother distribution of the charges. Combined with a more accurate tracing of low energy electrons in the electric field, we managed to reproduce the dynamically changing charging contrast due to an induced positive surface potential.

Charging properties of cassiterite (alfa-SnO2) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenqvist, Jorgen K; Machesky, Michael L.; Vlcek, L.

The acid-base properties of cassiterite (alfa-SnO2) surfaces at 10 50 C were studied using potentiometric titrations of powder suspensions in aqueous NaCl and RbCl media. The proton sorption isotherms exhibited common intersection points in the pH-range 4.0 to 4.5 at all conditions and the magnitude of charging was similar but not identical in NaCl and RbCl. The hydrogen bonding configuration at the oxide-water interface, obtained from classical Molecular Dynamics (MD) simulations, was analyzed in detail and the results were explicitly incorporated in calculations of protonation constants for the reactive surface sites using the revised MUSIC model. The calculations indicated thatmore » the terminal SnOH2 group is more acidic than the bridging Sn2OH group, with protonation constants (log KH) of 3.60 and 5.13 at 25 C, respectively. This is contrary to the situation on the isostructural alfa-TiO2 (rutile), apparently due to the difference in electronegativity between Ti and Sn. MD simulations and speciation calculations indicated considerable differences in the speciation of Na+ and Rb+, despite the similarities in overall charging. Adsorbed sodium ions are almost exclusively found in bidentate surface complexes, while adsorbed rubidium ions form comparable amounts of bidentate and tetradentate complexes. Also, the distribution of adsorbed Na+ between the different complexes shows a considerable dependence on surface charge density (pH), while the distribution of adsorbed Rb+ is almost independent of pH. A Surface Complexation Model (SCM) capable of accurately describing both the measured surface charge and the MD predicted speciation of adsorbed Na+/Rb+ was formulated. According to the SCM, the deprotonated terminal group (SnOH-0.40) and the protonated bridging group (Sn2OH+0.36) dominate the surface speciation over the entire pH-range (2.7 10), illustrating the ability of positively and negatively charged surface groups to coexist. Complexation of the medium cations increases significantly with increasing negative surface charge and at pH 10 roughly 40 percent of the terminal sites are predicted to form cation complexes, while anion complexation is minor throughout the studied pH-range.« less

Electrostatic interaction between stereocilia: I. Its role in supporting the structure of the hair bundle.

PubMed

Dolgobrodov, S G; Lukashkin, A N; Russell, I J

2000-12-01

This paper provides theoretical estimates for the forces of electrostatic interaction between adjacent stereocilia in auditory and vestibular hair cells. Estimates are given for parameters within the measured physiological range using constraints appropriate for the known geometry of the hair bundle. Stereocilia are assumed to possess an extended, negatively charged surface coat, the glycocalyx. Different charge distribution profiles within the glycocalyx are analysed. It is shown that charged glycocalices on the apical surface of the hair cells can support spatial separation between adjacent stereocilia in the hair bundles through electrostatic repulsion between stereocilia. The charge density profile within the glycocalyx is a crucial parameter. In fact, attraction instead of repulsion between adjacent stereocilia will be observed if the charge of the glycocalyx is concentrated near the membrane of the stereocilia, thereby making this type of charge distribution unlikely. The forces of electrostatic interaction between stereocilia may influence the mechanical properties of the hair bundle and, being strongly non-linear, contribute to the non-linear phenomena that have been recorded from the periphery of the auditory and vestibular systems.

Characterization of millimetre magnitude atmospheric pressure streamer discharge in pin-to-plane dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Xu, S. J.; Zhang, Y. H.; Yu, Z.; Yao, J.; Zhang, Z. T.

2013-03-01

The streamer regime of pin-to-plane dielectric barrier discharge in air was studied by means of fast photography, electrical measurement and photoelectricity. The fast photographs of positive streamer were obtained by CCD camera with micro lens. The exposure time is one microseconds. The images illustrate that the streamer is non-axisymmetric because of some random factors, such as surface charge position, space charge distribution, gas liquidity and so on. In fact, the streamer propagates along bend discharge channel. The bending degree increases with the electric field strengthen. By surveying a mass of images, the diameter of streamer, height of surface charge effect and scope of surface charge was estimate used to describe the shape of streamer.

On the design of composite protein-quantum dot biomaterials via self-assembly.

PubMed

Majithia, Ravish; Patterson, Jan; Bondos, Sarah E; Meissner, Kenith E

2011-10-10

Incorporation of nanoparticles during the hierarchical self-assembly of protein-based materials can impart function to the resulting composite materials. Herein we demonstrate that the structure and nanoparticle distribution of composite fibers are sensitive to the method of nanoparticle addition and the physicochemical properties of both the nanoparticle and the protein. Our model system consists of a recombinant enhanced green fluorescent protein-Ultrabithorax (EGFP-Ubx) fusion protein and luminescent CdSe-ZnS core-shell quantum dots (QDs), allowing us to optically assess the distribution of both the protein and nanoparticle components within the composite material. Although QDs favorably interact with EGFP-Ubx monomers, the relatively rough surface morphology of composite fibers suggests EGFP-Ubx-QD conjugates impact self-assembly. Indeed, QDs templated onto EGFP-Ubx film post-self-assembly can be subsequently drawn into smooth composite fibers. Additionally, the QD surface charge impacts QD distribution within the composite material, indicating that surface charge plays an important role in self-assembly. QDs with either positively or negatively charged coatings significantly enhance fiber extensibility. Conversely, QDs coated with hydrophobic moieties and suspended in toluene produce composite fibers with a heterogeneous distribution of QDs and severely altered fiber morphology, indicating that toluene severely disrupts Ubx self-assembly. Understanding factors that impact the protein-nanoparticle interaction enables manipulation of the structure and mechanical properties of composite materials. Since proteins interact with nanoparticle surface coatings, these results should be applicable to other types of nanoparticles with similar chemical groups on the surface.

Parallel tempering Monte Carlo simulations of lysozyme orientation on charged surfaces

NASA Astrophysics Data System (ADS)

Xie, Yun; Zhou, Jian; Jiang, Shaoyi

2010-02-01

In this work, the parallel tempering Monte Carlo (PTMC) algorithm is applied to accurately and efficiently identify the global-minimum-energy orientation of a protein adsorbed on a surface in a single simulation. When applying the PTMC method to simulate lysozyme orientation on charged surfaces, it is found that lysozyme could easily be adsorbed on negatively charged surfaces with "side-on" and "back-on" orientations. When driven by dominant electrostatic interactions, lysozyme tends to be adsorbed on negatively charged surfaces with the side-on orientation for which the active site of lysozyme faces sideways. The side-on orientation agrees well with the experimental results where the adsorbed orientation of lysozyme is determined by electrostatic interactions. As the contribution from van der Waals interactions gradually dominates, the back-on orientation becomes the preferred one. For this orientation, the active site of lysozyme faces outward, which conforms to the experimental results where the orientation of adsorbed lysozyme is co-determined by electrostatic interactions and van der Waals interactions. It is also found that despite of its net positive charge, lysozyme could be adsorbed on positively charged surfaces with both "end-on" and back-on orientations owing to the nonuniform charge distribution over lysozyme surface and the screening effect from ions in solution. The PTMC simulation method provides a way to determine the preferred orientation of proteins on surfaces for biosensor and biomaterial applications.

An in vivo study of electrical charge distribution on the bacterial cell wall by atomic force microscopy in vibrating force mode

NASA Astrophysics Data System (ADS)

Marlière, Christian; Dhahri, Samia

2015-05-01

We report an in vivo electromechanical atomic force microscopy (AFM) study of charge distribution on the cell wall of Gram+ Rhodococcus wratislaviensis bacteria, naturally adherent to a glass substrate, under physiological conditions. The method presented in this paper relies on a detailed study of AFM approach/retract curves giving the variation of the interaction force versus distance between the tip and the sample. In addition to classical height and mechanical (as stiffness) data, mapping of local electrical properties, such as bacterial surface charge, was proved to be feasible at a spatial resolution better than a few tens of nanometers. This innovative method relies on the measurement of the cantilever's surface stress through its deflection far from (>10 nm) the repulsive contact zone: the variations of surface stress come from the modification of electrical surface charge of the cantilever (as in classical electrocapillary measurements) likely stemming from its charging during contact of both the tip and the sample electrical double layers. This method offers an important improvement in local electrical and electrochemical measurements at the solid/liquid interface, particularly in high-molarity electrolytes when compared to techniques focused on the direct use of electrostatic force. It thus opens a new way to directly investigate in situ biological electrical surface processes involved in numerous practical applications and fundamental problems such as bacterial adhesion, biofilm formation, microbial fuel cells, etc.We report an in vivo electromechanical atomic force microscopy (AFM) study of charge distribution on the cell wall of Gram+ Rhodococcus wratislaviensis bacteria, naturally adherent to a glass substrate, under physiological conditions. The method presented in this paper relies on a detailed study of AFM approach/retract curves giving the variation of the interaction force versus distance between the tip and the sample. In addition to classical height and mechanical (as stiffness) data, mapping of local electrical properties, such as bacterial surface charge, was proved to be feasible at a spatial resolution better than a few tens of nanometers. This innovative method relies on the measurement of the cantilever's surface stress through its deflection far from (>10 nm) the repulsive contact zone: the variations of surface stress come from the modification of electrical surface charge of the cantilever (as in classical electrocapillary measurements) likely stemming from its charging during contact of both the tip and the sample electrical double layers. This method offers an important improvement in local electrical and electrochemical measurements at the solid/liquid interface, particularly in high-molarity electrolytes when compared to techniques focused on the direct use of electrostatic force. It thus opens a new way to directly investigate in situ biological electrical surface processes involved in numerous practical applications and fundamental problems such as bacterial adhesion, biofilm formation, microbial fuel cells, etc. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00968e

Lattice Boltzmann Simulation of Electroosmotic Micromixing by Heterogeneous Surface Charge

NASA Astrophysics Data System (ADS)

Tang, G. H.; Wang, F. F.; Tao, W. Q.

Microelectroosmotic flow is usually restricted to low Reynolds number regime, and mixing in these microfluidic systems becomes problematic due to the negligible inertial effects. To gain an improved understanding of mixing enhancement in microchannels patterned with heterogeneous surface charge, the lattice Boltzmann method has been employed to obtain the electric potential distribution in the electrolyte, the flow field, and the species concentration distribution, respectively. The simulation results show that heterogeneous surfaces can significantly disturb the streamlines leading to apparently substantial improvements in mixing. However, the introduction of such a feature can reduce the mass flow rate in the channel. The reduction in flow rate effectively prolongs the available mixing time when the flow passes through the channel and the observed mixing enhancement by heterogeneous surfaces partly results from longer mixing time.

Surface correlation effects in two-band strongly correlated slabs.

PubMed

Esfahani, D Nasr; Covaci, L; Peeters, F M

2014-02-19

Using an extension of the Gutzwiller approximation for an inhomogeneous system, we study the two-band Hubbard model with unequal band widths for a slab geometry. The aim is to investigate the mutual effect of individual bands on the spatial distribution of quasi-particle weight and charge density, especially near the surface of the slab. The main effect of the difference in band width is the presence of two different length scales corresponding to the quasi-particle profile of each band. This is enhanced in the vicinity of the critical interaction of the narrow band where an orbitally selective Mott transition occurs and a surface dead layer forms for the narrow band. For the doped case, two different regimes of charge transfer between the surface and the bulk of the slab are revealed. The charge transfer from surface/center to center/surface depends on both the doping level and the average relative charge accumulated in each band. Such effects could also be of importance when describing the accumulation of charges at the interface between structures made of multi-band strongly correlated materials.

Analysis of microscopic parameters of surface charging in polymer caused by defocused electron beam irradiation.

PubMed

Liu, Jing; Zhang, Hai-Bo

2014-12-01

The relationship between microscopic parameters and polymer charging caused by defocused electron beam irradiation is investigated using a dynamic scattering-transport model. The dynamic charging process of an irradiated polymer using a defocused 30 keV electron beam is conducted. In this study, the space charge distribution with a 30 keV non-penetrating e-beam is negative and supported by some existing experimental data. The internal potential is negative, but relatively high near the surface, and it decreases to a maximum negative value at z=6 μm and finally tend to 0 at the bottom of film. The leakage current and the surface potential behave similarly, and the secondary electron and leakage currents follow the charging equilibrium condition. The surface potential decreases with increasing beam current density, trap concentration, capture cross section, film thickness and electron-hole recombination rate, but with decreasing electron mobility and electron energy. The total charge density increases with increasing beam current density, trap concentration, capture cross section, film thickness and electron-hole recombination rate, but with decreasing electron mobility and electron energy. This study shows a comprehensive analysis of microscopic factors of surface charging characteristics in an electron-based surface microscopy and analysis. Copyright © 2014 Elsevier Ltd. All rights reserved.

Rover wheel charging on the lunar surface

NASA Astrophysics Data System (ADS)

Jackson, Telana L.; Farrell, William M.; Zimmerman, Michael I.

2015-03-01

The environment at the Moon is dynamic, with highly variable solar wind plasma conditions at the lunar dayside, terminator, and night side regions. Moving objects such as rover wheels will charge due to contact electrification with the surface, but the degree of charging is controlled by the local plasma environment. Using a dynamic charging model of a wheel, it is demonstrated herein that moving tires will tribocharge substantially when venturing into plasma-current starved regions such as polar craters or the lunar nightside. The surface regolith distribution and the overall effect on charge accumulation of grains cohesively sticking to the rover tire has been incorporated into the model. It is shown that dust sticking can limit the overall charge accumulated on the system. However charge dissipation times are greatly increased in shadowed regions and can present a potential hazard to astronauts and electrical systems performing extra-vehicular activities. We show that dissipation times change with wheel composition and overall system tribocharging is dependent upon wheel velocity.

Competitive Adsorption and Ordered Packing of Counterions near Highly Charged Surfaces: From Mean-Field Theory to Monte Carlo Simulations

PubMed Central

Wen, Jiayi; Zhou, Shenggao; Xu, Zhenli; Li, Bo

2013-01-01

Competitive adsorption of counterions of multiple species to charged surfaces is studied by a size-effect included mean-field theory and Monte Carlo (MC) simulations. The mean-field electrostatic free-energy functional of ionic concentrations, constrained by Poisson’s equation, is numerically minimized by an augmented Lagrangian multiplier method. Unrestricted primitive models and canonical ensemble MC simulations with the Metropolis criterion are used to predict the ionic distributions around a charged surface. It is found that, for a low surface charge density, the adsorption of ions with a higher valence is preferable, agreeing with existing studies. For a highly charged surface, both of the mean-field theory and MC simulations demonstrate that the counterions bind tightly around the charged surface, resulting in a stratification of counterions of different species. The competition between mixed entropy and electrostatic energetics leads to a compromise that the ionic species with a higher valence-to-volume ratio has a larger probability to form the first layer of stratification. In particular, the MC simulations confirm the crucial role of ionic valence-to-volume ratios in the competitive adsorption to charged surfaces that had been previously predicted by the mean-field theory. The charge inversion for ionic systems with salt is predicted by the MC simulations but not by the mean-field theory. This work provides a better understanding of competitive adsorption of counterions to charged surfaces and calls for further studies on the ionic size effect with application to large-scale biomolecular modeling. PMID:22680474

Competitive adsorption and ordered packing of counterions near highly charged surfaces: From mean-field theory to Monte Carlo simulations.

PubMed

Wen, Jiayi; Zhou, Shenggao; Xu, Zhenli; Li, Bo

2012-04-01

Competitive adsorption of counterions of multiple species to charged surfaces is studied by a size-effect-included mean-field theory and Monte Carlo (MC) simulations. The mean-field electrostatic free-energy functional of ionic concentrations, constrained by Poisson's equation, is numerically minimized by an augmented Lagrangian multiplier method. Unrestricted primitive models and canonical ensemble MC simulations with the Metropolis criterion are used to predict the ionic distributions around a charged surface. It is found that, for a low surface charge density, the adsorption of ions with a higher valence is preferable, agreeing with existing studies. For a highly charged surface, both the mean-field theory and the MC simulations demonstrate that the counterions bind tightly around the charged surface, resulting in a stratification of counterions of different species. The competition between mixed entropy and electrostatic energetics leads to a compromise that the ionic species with a higher valence-to-volume ratio has a larger probability to form the first layer of stratification. In particular, the MC simulations confirm the crucial role of ionic valence-to-volume ratios in the competitive adsorption to charged surfaces that had been previously predicted by the mean-field theory. The charge inversion for ionic systems with salt is predicted by the MC simulations but not by the mean-field theory. This work provides a better understanding of competitive adsorption of counterions to charged surfaces and calls for further studies on the ionic size effect with application to large-scale biomolecular modeling.

Controlling the Local Electronic Properties of Si(553)-Au through Hydrogen Doping

NASA Astrophysics Data System (ADS)

Hogan, C.; Speiser, E.; Chandola, S.; Suchkova, S.; Aulbach, J.; Schäfer, J.; Meyer, S.; Claessen, R.; Esser, N.

2018-04-01

We propose a quantitative and reversible method for tuning the charge localization of Au-stabilized stepped Si surfaces by site-specific hydrogenation. This is demonstrated for Si(553)-Au as a model system by combining density functional theory simulations and reflectance anisotropy spectroscopy experiments. We find that controlled H passivation is a two-step process: step-edge adsorption drives excess charge into the conducting metal chain "reservoir" and renders it insulating, while surplus H recovers metallic behavior. Our approach illustrates a route towards microscopic manipulation of the local surface charge distribution and establishes a reversible switch of site-specific chemical reactivity and magnetic properties on vicinal surfaces.

Molecular charge distribution and dispersion of electronic states in the contact layer between pentacene and Cu(119) and beyond

NASA Astrophysics Data System (ADS)

Annese, E.; Fujii, J.; Baldacchini, C.; Zhou, B.; Viol, C. E.; Vobornik, I.; Betti, M. G.; Rossi, G.

2008-05-01

The interaction of pentacene molecules in contact with the Cu(119) stepped surface has been directly imaged by scanning tunneling microscopy and analyzed by angle resolved photoemission spectroscopy. Interacting molecules, which are in contact with copper, generate dispersive electronic states associated with a perturbed electron charge density distribution of the molecular orbitals. In contrast, the electron charge density of molecules of the pentacene on top of the first layer, which is not in direct contact with the Cu surface, shows an intramolecular structure very similar to that of the free molecule. Our results indicate that the delocalization of the molecular states in the pentacene/Cu system is confined to the very first molecular layer at the interface.

Fibronectin module FN(III)9 adsorption at contrasting solid model surfaces studied by atomistic molecular dynamics.

PubMed

Kubiak-Ossowska, Karina; Mulheran, Paul A; Nowak, Wieslaw

2014-08-21

The mechanism of human fibronectin adhesion synergy region (known as integrin binding region) in repeat 9 (FN(III)9) domain adsorption at pH 7 onto various and contrasting model surfaces has been studied using atomistic molecular dynamics simulations. We use an ionic model to mimic mica surface charge density but without a long-range electric field above the surface, a silica model with a long-range electric field similar to that found experimentally, and an Au {111} model with no partial charges or electric field. A detailed description of the adsorption processes and the contrasts between the various model surfaces is provided. In the case of our model silica surface with a long-range electrostatic field, the adsorption is rapid and primarily driven by electrostatics. Because it is negatively charged (-1e), FN(III)9 readily adsorbs to a positively charged surface. However, due to its partial charge distribution, FN(III)9 can also adsorb to the negatively charged mica model because of the absence of a long-range repulsive electric field. The protein dipole moment dictates its contrasting orientation at these surfaces, and the anchoring residues have opposite charges to the surface. Adsorption on the model Au {111} surface is possible, but less specific, and various protein regions might be involved in the interactions with the surface. Despite strongly influencing the protein mobility, adsorption at these model surfaces does not require wholesale FN(III)9 conformational changes, which suggests that the biological activity of the adsorbed protein might be preserved.

Suppression of surface charge accumulation on Al{sub 2}O{sub 3}-filled epoxy resin insulator under dc voltage by direct fluorination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Boya; Zhang, Guixin, E-mail: guixin@mail.tsinghua.edu.cn; Li, Chuanyang

2015-12-15

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al{sub 2}O{sub 3}-filled epoxy resin were surface fluorinated using a F{sub 2}/N{sub 2} mixture (12.5% F{sub 2}) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on themore » fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the surface physicochemical properties. These structure changes, especially the physical defects reduced the depth of charge traps in the surface layer, which was verified by the measurement of energy distributions of the electron and hole traps based on the isothermal current theory. The results in this paper demonstrate that fluorination can be a promising and effective method to suppress surface charge accumulation on epoxy insulators in gas insulated devices.« less

Strong coupling electrostatics for randomly charged surfaces: antifragility and effective interactions.

PubMed

Ghodrat, Malihe; Naji, Ali; Komaie-Moghaddam, Haniyeh; Podgornik, Rudolf

2015-05-07

We study the effective interaction mediated by strongly coupled Coulomb fluids between dielectric surfaces carrying quenched, random monopolar charges with equal mean and variance, both when the Coulomb fluid consists only of mobile multivalent counterions and when it consists of an asymmetric ionic mixture containing multivalent and monovalent (salt) ions in equilibrium with an aqueous bulk reservoir. We analyze the consequences that follow from the interplay between surface charge disorder, dielectric and salt image effects, and the strong electrostatic coupling that results from multivalent counterions on the distribution of these ions and the effective interaction pressure they mediate between the surfaces. In a dielectrically homogeneous system, we show that the multivalent counterions are attracted towards the surfaces with a singular, disorder-induced potential that diverges logarithmically on approach to the surfaces, creating a singular but integrable counterion density profile that exhibits an algebraic divergence at the surfaces with an exponent that depends on the surface charge (disorder) variance. This effect drives the system towards a state of lower thermal 'disorder', one that can be described by a renormalized temperature, exhibiting thus a remarkable antifragility. In the presence of an interfacial dielectric discontinuity, the singular behavior of counterion density at the surfaces is removed but multivalent counterions are still accumulated much more strongly close to randomly charged surfaces as compared with uniformly charged ones. The interaction pressure acting on the surfaces displays in general a highly non-monotonic behavior as a function of the inter-surface separation with a prominent regime of attraction at small to intermediate separations. This attraction is caused directly by the combined effects from charge disorder and strong coupling electrostatics of multivalent counterions, which dominate the surface-surface repulsion due to the (equal) mean charges on the two surfaces and the osmotic pressure of monovalent ions residing between them. These effects can be quite significant even with a small degree of surface charge disorder relative to the mean surface charge. The strong coupling, disorder-induced attraction is typically much stronger than the van der Waals interaction between the surfaces, especially within a range of several nanometers for the inter-surface separation, where such effects are predicted to be most pronounced.

Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiemstra, T.; Riemsdijk, W.H. van

1999-02-01

An important challenge in surface complexation models (SCM) is to connect the molecular microscopic reality to macroscopic adsorption phenomena. This study elucidates the primary factor controlling the adsorption process by analyzing the adsorption and competition of PO{sub 4}, AsO{sub 4}, and SeO{sub 3}. The authors show that the structure of the surface-complex acting in the dominant electrostatic field can be ascertained as the primary controlling adsorption factor. The surface species of arsenate are identical with those of phosphate and the adsorption behavior is very similar. On the basis of the selenite adsorption, The authors show that the commonly used 1pKmore » models are incapable to incorporate in the adsorption modeling the correct bidentate binding mechanism found by spectroscopy. The use of the bidentate mechanism leads to a proton-oxyanion ratio and corresponding pH dependence that are too large. The inappropriate intrinsic charge attribution to the primary surface groups and the condensation of the inner sphere surface complex to a point charge are responsible for this behavior of commonly used 2pK models. Both key factors are differently defined in the charge distributed multi-site complexation (CD-MUSIC) model and are based in this model on a surface structural approach. The CD-MUSIC model can successfully describe the macroscopic adsorption phenomena using the surface speciation and binding mechanisms as found by spectroscopy. The model is also able to predict the anion competition well. The charge distribution in the interface is in agreement with the observed structure of surface complexes.« less

Electron beam charging of insulators: A self-consistent flight-drift model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Touzin, M.; Goeuriot, D.; Guerret-Piecourt, C.

2006-06-01

Electron beam irradiation and the self-consistent charge transport in bulk insulating samples are described by means of a new flight-drift model and an iterative computer simulation. Ballistic secondary electron and hole transport is followed by electron and hole drifts, their possible recombination and/or trapping in shallow and deep traps. The trap capture cross sections are the Poole-Frenkel-type temperature and field dependent. As a main result the spatial distributions of currents j(x,t), charges {rho}(x,t), the field F(x,t), and the potential slope V(x,t) are obtained in a self-consistent procedure as well as the time-dependent secondary electron emission rate {sigma}(t) and the surfacemore » potential V{sub 0}(t). For bulk insulating samples the time-dependent distributions approach the final stationary state with j(x,t)=const=0 and {sigma}=1. Especially for low electron beam energies E{sub 0}<4 keV the incorporation of mainly positive charges can be controlled by the potential V{sub G} of a vacuum grid in front of the target surface. For high beam energies E{sub 0}=10, 20, and 30 keV high negative surface potentials V{sub 0}=-4, -14, and -24 kV are obtained, respectively. Besides open nonconductive samples also positive ion-covered samples and targets with a conducting and grounded layer (metal or carbon) on the surface have been considered as used in environmental scanning electron microscopy and common SEM in order to prevent charging. Indeed, the potential distributions V(x) are considerably small in magnitude and do not affect the incident electron beam neither by retarding field effects in front of the surface nor within the bulk insulating sample. Thus the spatial scattering and excitation distributions are almost not affected.« less

Characterization of electrical conductivity of carbon fiber reinforced plastic using surface potential distribution

NASA Astrophysics Data System (ADS)

Kikunaga, Kazuya; Terasaki, Nao

2018-04-01

A new method of evaluating electrical conductivity in a structural material such as carbon fiber reinforced plastic (CFRP) using surface potential is proposed. After the CFRP was charged by corona discharge, the surface potential distribution was measured by scanning a vibrating linear array sensor along the object surface with a high spatial resolution over a short duration. A correlation between the weave pattern of the CFRP and the surface potential distribution was observed. This result indicates that it is possible to evaluate the electrical conductivity of a material comprising conducting and insulating regions.

Charge-induced secondary atomization in diffusion flames of electrostatic sprays

NASA Technical Reports Server (NTRS)

Gomez, Alessandro; Chen, Gung

1994-01-01

The combustion of electrostatic sprays of heptane in laminar counterflow diffusion flames was experimentally studied by measuring droplet size and velocity distributions, as well as the gas-phase temperature. A detailed examination of the evolution of droplet size distribution as droplets approach the flame shows that, if substantial evaporation occurs before droplets interact with the flame, an initially monodisperse size distribution becomes bimodal. A secondary sharp peak in the size histogram develops in correspondence of diameters about one order of magnitude smaller than the mean. No evaporation mechanism can account for the development of such bimodality, that can be explained only in terms of a disintegration of droplets into finer fragments of size much smaller than that of the parent. Other evidence in support of this interpretation is offered by the measurements of droplet size-velocity correlation and velocity component distributions, showing that, as a consequence of the ejection process, the droplets responsible for the secondary peak have velocities uncorrelated with the mean flow. The fission is induced by the electric charge. When a droplet evaporates, in fact, the electric charge density on the droplet surface increases while the droplet shrinks, until the so-called Rayleigh limit is reached at which point the repulsion of electric charges overcomes the surface tension cohesive force, ultimately leading to a disintegraton into finer fragments. We report on the first observation of such fissions in combustion environments. If, on the other hand, insufficient evaporation has occurred before droplets enter the high temperature region, there appears to be no significant evidence of bimodality in their size distribution. In this case, in fact, the concentration of flame chemi-ions or, in the case of positively charged droplets, electrons may be sufficient for them to neutralize the charge on the droplets and to prevent disruption.

Scattered Ion Energetics for H atoms Impinging a Copper Surface

NASA Astrophysics Data System (ADS)

Defazio, J. N.; Stephen, T. M.; Peko, B. L.

2002-05-01

The energy loss and charge state of atomic hydrogen scattered from surfaces is important in a broad range of scientific endeavors. These include the charging of spacecraft, the detection of low energy neutrals in the space environment, energy transfer from magnetically confined plasmas and the modeling of low energy electric discharges. Measurements of scattered ions resulting from low energy (20 - 1000 eV) atomic hydrogen impacting a copper surface have been accomplished. Differential energy distributions and yields for H- and H+ resulting from these collisions are presented. The data show that the energy distributions develop a universal dependence, when scaled by the incident energy. These results are compared with studies involving incident hydrogen ions. For incident energies less than 100eV, there are obvious differences in the scattered ion energy distributions resulting from impacting atoms when compared to those resulting from ions.

Image method for induced surface charge from many-body system of dielectric spheres

NASA Astrophysics Data System (ADS)

Qin, Jian; de Pablo, Juan J.; Freed, Karl F.

2016-09-01

Charged dielectric spheres embedded in a dielectric medium provide the simplest model for many-body systems of polarizable ions and charged colloidal particles. We provide a multiple scattering formulation for the total electrostatic energy for such systems and demonstrate that the polarization energy can be rapidly evaluated by an image method that generalizes the image methods for conducting spheres. Individual contributions to the total electrostatic energy are ordered according to the number of polarized surfaces involved, and each additional surface polarization reduces the energy by a factor of (a/R)3ɛ, where a is the sphere radius, R the average inter-sphere separation, and ɛ the relevant dielectric mismatch at the interface. Explicit expressions are provided for both the energy and the forces acting on individual spheres, which can be readily implemented in Monte Carlo and molecular dynamics simulations of polarizable charged spheres, thereby avoiding costly computational techniques that introduce a surface charge distribution that requires numerical solution.

IImage method for induced surface charge from many-body system of dielectric spheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Jian; de Pablo, Juan J.; Freed, Karl F.

2016-09-28

Charged dielectric spheres embedded in a dielectric medium provide the simplest model for many-body systems of polarizable ions and charged colloidal particles. We provide a multiple scattering formulation for the total electrostatic energy for such systems and demonstrate that the polarization energy can be rapidly evaluated by an image method that generalizes the image methods for conducting spheres. Individual contributions to the total electrostatic energy are ordered according to the number of polarized surfaces involved, and each additional surface polarization reduces the energy by a factor of (a/R)(3) epsilon, where a is the sphere radius, R the average inter-sphere separation,more » and. the relevant dielectric mismatch at the interface. Explicit expressions are provided for both the energy and the forces acting on individual spheres, which can be readily implemented in Monte Carlo and molecular dynamics simulations of polarizable charged spheres, thereby avoiding costly computational techniques that introduce a surface charge distribution that requires numerical solution.« less

Measurements of charge distributions of the fragments in the low energy fission reaction

NASA Astrophysics Data System (ADS)

Wang, Taofeng; Han, Hongyin; Meng, Qinghua; Wang, Liming; Zhu, Liping; Xia, Haihong

2013-01-01

The measurement for charge distributions of fragments in spontaneous fission 252Cf has been performed by using a unique style of detector setup consisting of a typical grid ionization chamber and a ΔΕ-Ε particle telescope, in which a thin grid ionization chamber served as the ΔΕ-section and the E-section was an Au-Si surface barrier detector. The typical physical quantities of fragments, such as mass number and kinetic energies as well as the deposition in the gas ΔΕ detector and E detector were derived from the coincident measurement data. The charge distributions of the light fragments for the fixed mass number A2* and total kinetic energy (TKE) were obtained by the least-squares fits for the response functions of the ΔΕ detector with multi-Gaussian functions representing the different elements. The results of the charge distributions for some typical fragments are shown in this article which indicates that this detection setup has the charge distribution capability of Ζ:ΔΖ>40:1. The experimental method developed in this work for determining the charge distributions of fragments is expected to be employed in the neutron induced fissions of 232Th and 238U or other low energy fission reactions.

First-Principles Molecular Dynamics Study on the Electric-double layer Capacitance of Water-MXene interfaces

NASA Astrophysics Data System (ADS)

Ando, Yasunobu; Otani, Minoru

MXenes are a new, large family of layered materials synthesized from MAX phases by simple chemical treatments. Due to their enormous variations, MXenes have attracted great attention as promising candidates as anode materials for next-generation secondary batteries. Unfortunately, the specific capacitance of MXenes supercapacitors is lower than that of active-carbon ones. Theoretical investigation of the electric-double layer (EDL) at electrode interfaces is necessary to improve their capacitance. First-principles molecular dynamics (FPMD) simulation based on the density functional theory (DFT) is performed to estimate the EDL capacitance from a potential profile V(z) and a charge distribution q(z) induced by the ions at water-Ti2CTx (T =O, F) interfaces. Potential profiles V(z) of both Ti2CO2 and Ti2CF2 decrease about 1.0 eV steeply in a region of only 3 Å from a Ti layer, which is the same profile at the platinum interfaces. On the other hand, induced charge distribution q(z) depends on the species of surface termination. Induced electrons are introduced at Ti layers in the case of O surface termination. However, Ti2CF2 is not capable to store electrons at Ti layers because it is mono-valence anions. It indicates that effective surface-position of MXenes depends on the surface terminations. Our results are revealed that small induced charge leads the low EDL capacitance at MXene interfaces. This is because interface polarization due to strong interaction between water and Ti2CTx induces net charge. The surface net charge hinders the introduction of ion-induced charges.

Effects of Acids, Bases, and Heteroatoms on Proximal Radial Distribution Functions for Proteins

PubMed Central

Nguyen, Bao Linh; Pettitt, B. Montgomery

2015-01-01

The proximal distribution of water around proteins is a convenient method of quantifying solvation. We consider the effect of charged and sulfur-containing amino acid side-chain atoms on the proximal radial distribution function (pRDF) of water molecules around proteins using side-chain analogs. The pRDF represents the relative probability of finding any solvent molecule at a distance from the closest or surface perpendicular protein atom. We consider the near-neighbor distribution. Previously, pRDFs were shown to be universal descriptors of the water molecules around C, N, and O atom types across hundreds of globular proteins. Using averaged pRDFs, a solvent density around any globular protein can be reconstructed with controllable relative error. Solvent reconstruction using the additional information from charged amino acid side-chain atom types from both small models and protein averages reveals the effects of surface charge distribution on solvent density and improves the reconstruction errors relative to simulation. Solvent density reconstructions from the small-molecule models are as effective and less computationally demanding than reconstructions from full macromolecular models in reproducing preferred hydration sites and solvent density fluctuations. PMID:26388706

Electrokinetic flow in a capillary with a charge-regulating surface polymer layer.

PubMed

Keh, Huan J; Ding, Jau M

2003-07-15

An analytical study of the steady electrokinetic flow in a long uniform capillary tube or slit is presented. The inside wall of the capillary is covered by a layer of adsorbed or covalently bound charge-regulating polymer in equilibrium with the ambient electrolyte solution. In this solvent-permeable and ion-penetrable surface polyelectrolyte layer, ionogenic functional groups and frictional segments are assumed to distribute at uniform densities. The electrical potential and space charge density distributions in the cross section of the capillary are obtained by solving the linearized Poisson-Boltzmann equation. The fluid velocity profile due to the application of an electric field and a pressure gradient through the capillary is obtained from the analytical solution of a modified Navier-Stokes/Brinkman equation. Explicit formulas for the electroosmotic velocity, the average fluid velocity and electric current density on the cross section, and the streaming potential in the capillary are also derived. The results demonstrate that the direction of the electroosmotic flow and the magnitudes of the fluid velocity and electric current density are dominated by the fixed charge density inside the surface polymer layer, which is determined by the regulation characteristics such as the dissociation equilibrium constants of the ionogenic functional groups in the surface layer and the concentration of the potential-determining ions in the bulk solution.

Adsorption of hydrophobin on different self-assembled monolayers: the role of the hydrophobic dipole and the electric dipole.

PubMed

Peng, Chunwang; Liu, Jie; Zhao, Daohui; Zhou, Jian

2014-09-30

In this work, the adsorptions of hydrophobin (HFBI) on four different self-assembled monolayers (SAMs) (i.e., CH3-SAM, OH-SAM, COOH-SAM, and NH2-SAM) were investigated by parallel tempering Monte Carlo and molecular dynamics simulations. Simulation results indicate that the orientation of HFBI adsorbed on neutral surfaces is dominated by a hydrophobic dipole. HFBI adsorbs on the hydrophobic CH3-SAM through its hydrophobic patch and adopts a nearly vertical hydrophobic dipole relative to the surface, while it is nearly horizontal when adsorbed on the hydrophilic OH-SAM. For charged SAM surfaces, HFBI adopts a nearly vertical electric dipole relative to the surface. HFBI has the narrowest orientation distribution on the CH3-SAM, and thus can form an ordered monolayer and reverse the wettability of the surface. For HFBI adsorption on charged SAMs, the adsorption strength weakens as the surface charge density increases. Compared with those on other SAMs, a larger area of the hydrophobic patch is exposed to the solution when HFBI adsorbs on the NH2-SAM. This leads to an increase of the hydrophobicity of the surface, which is consistent with the experimental results. The binding of HFBI to the CH3-SAM is mainly through hydrophobic interactions, while it is mediated through a hydration water layer near the surface for the OH-SAM. For the charged SAM surfaces, the adsorption is mainly induced by electrostatic interactions between the charged surfaces and the oppositely charged residues. The effect of a hydrophobic dipole on protein adsorption onto hydrophobic surfaces is similar to that of an electric dipole for charged surfaces. Therefore, the hydrophobic dipole may be applied to predict the probable orientations of protein adsorbed on hydrophobic surfaces.

Computer Modeling of High-Intensity Cs-Sputter Ion Sources

NASA Astrophysics Data System (ADS)

Brown, T. A.; Roberts, M. L.; Southon, J. R.

The grid-point mesh program NEDLab has been used to computer model the interior of the high-intensity Cs-sputter source used in routine operations at the Center for Accelerator Mass Spectrometry (CAMS), with the goal of improving negative ion output. NEDLab has several features that are important to realistic modeling of such sources. First, space-charge effects are incorporated in the calculations through an automated ion-trajectories/Poissonelectric-fields successive-iteration process. Second, space charge distributions can be averaged over successive iterations to suppress model instabilities. Third, space charge constraints on ion emission from surfaces can be incorporate under Child's Law based algorithms. Fourth, the energy of ions emitted from a surface can be randomly chosen from within a thermal energy distribution. And finally, ions can be emitted from a surface at randomized angles The results of our modeling effort indicate that significant modification of the interior geometry of the source will double Cs+ ion production from our spherical ionizer and produce a significant increase in negative ion output from the source.

Surface charge accumulation of particles containing radionuclides in open air

DOE PAGES

Kim, Yong-ha; Yiacoumi, Sotira; Tsouris, Costas

2015-05-01

Radioactivity can induce charge accumulation on radioactive particles. But, electrostatic interactions caused by radioactivity are typically neglected in transport modeling of radioactive plumes because it is assumed that ionizing radiation leads to charge neutralization. The assumption that electrostatic interactions caused by radioactivity are negligible is evaluated here by examining charge accumulation and neutralization on particles containing radionuclides in open air. Moreover, a charge-balance model is employed to predict charge accumulation on radioactive particles. It is shown that particles containing short-lived radionuclides can be charged with multiple elementary charges through radioactive decay. The presence of radioactive particles can significantly modify themore » particle charge distribution in open air and yield an asymmetric bimodal charge distribution, suggesting that strong electrostatic particle interactions may occur during short- and long-range transport of radioactive particles. Possible effects of transported radioactive particles on electrical properties of the local atmosphere are reported. Our study offers insight into transport characteristics of airborne radionuclides. Results are useful in atmospheric transport modeling of radioactive plumes.« less

Design of asymmetric particles containing a charged interior and a neutral surface charge: comparative study on in vivo circulation of polyelectrolyte microgels.

PubMed

Chen, Kai; Xu, Jing; Luft, J Christopher; Tian, Shaomin; Raval, Jay S; DeSimone, Joseph M

2014-07-16

Lowering the modulus of hydrogel particles could enable them to bypass in vivo physical barriers that would otherwise filter particles with similar size but higher modulus. Incorporation of electrolyte moieties into the polymer network of hydrogel particles to increase the swelling ratio is a straightforward and quite efficient way to decrease the modulus. In addition, charged groups in hydrogel particles can also help secure cargoes. However, the distribution of charged groups on the surface of a particle can accelerate the clearance of particles. Herein, we developed a method to synthesize highly swollen microgels of precise size with near-neutral surface charge while retaining interior charged groups. A strategy was employed to enable a particle to be highly cross-linked with very small mesh size, and subsequently PEGylated to quench the exterior amines only without affecting the internal amines. Acidic degradation of the cross-linker allows for swelling of the particles to microgels with a desired size and deformability. The microgels fabricated demonstrated extended circulation in vivo compared to their counterparts with a charged surface, and could potentially be utilized in in vivo applications including as oxygen carriers or nucleic acid scavengers.

Modeling of spacecraft charging

NASA Technical Reports Server (NTRS)

Whipple, E. C., Jr.

1977-01-01

Three types of modeling of spacecraft charging are discussed: statistical models, parametric models, and physical models. Local time dependence of circuit upset for DoD and communication satellites, and electron current to a sphere with an assumed Debye potential distribution are presented. Four regions were involved in spacecraft charging: (1) undisturbed plasma, (2) plasma sheath region, (3) spacecraft surface, and (4) spacecraft equivalent circuit.

Investigation of surface charge density on solid-liquid interfaces by modulating the electrical double layer.

PubMed

Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

2015-05-20

A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid-liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid-liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid-liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid-liquid interfaces.

Charging Properties of Cassiterite (alpha-SnO2) surfaces in NaCl and RbCl Ionic Media.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenqvist, Jorgen K; Machesky, Michael L.; Vlcek, Lukas

2009-01-01

The acid-base properties of cassiterite (alpha-SnO2) surfaces at 10-50 degrees C were studied using potentiometric titrations of powder suspensions in aqueous NaCl and RbCl media. The proton sorption isotherms exhibited common intersection points in the pH range of 4.0-4.5 under all conditions, and the magnitude of charging was similar but not identical in NaCl and RbCl. The hydrogen bonding configuration at the oxide-water interface, obtained from classical molecular dynamics (MD) simulations, was analyzed in detail, and the results were explicitly incorporated in calculations of protonation constants for the reactive surface sites using the revised MUSIC model. The calculations indicated thatmore » the terminal SnOH2 group is more acidic than the bridging Sn2OH group, with protonation constants (log KH) of 3.60 and 5.13 at 25 degrees C, respectively. This is contrary to the situation on the isostructural alpha-TiO2 (rutile), apparently because of the difference in electronegativity between Ti and Sn. MD simulations and speciation calculations indicated considerable differences in the speciation of Na+ and Rb+, despite the similarities in overall charging. Adsorbed sodium ions are almost exclusively found in bidentate surface complexes, whereas adsorbed rubidium ions form comparable numbers of bidentate and tetradentate complexes. Also, the distribution of adsorbed Na+ between the different complexes shows a considerable dependence on the surface charge density (pH), whereas the distribution of adsorbed Rb+ is almost independent of pH. A surface complexation model (SCM) capable of accurately describing both the measured surface charge and the MD-predicted speciation of adsorbed Na+/Rb+ was formulated. According to the SCM, the deprotonated terminal group (SnOH(-0.40)) and the protonated bridging group (Sn2OH+0.36) dominate the surface speciation over the entire pH range of this study (2.7-10). The complexation of medium cations increases significantly with increasing negative surface charge, and at pH 10, roughly 40% of the terminal sites are predicted to form cation complexes, whereas anion complexation is minor throughout the studied pH range.« less

Constrained Surface Complexation Modeling: Rutile in RbCl, NaCl, and NaCF 3SO 3 Media to 250 °C

DOE PAGES

Machesky, Michael L.; Předota, Milan; Ridley, Moira K.; ...

2015-06-01

In this paper, a comprehensive set of molecular-level results, primarily from classical molecular dynamics (CMD) simulations, are used to constrain CD-MUSIC surface complexation model (SCM) parameters describing rutile powder titrations conducted in RbCl, NaCl, and NaTr (Tr = triflate, CF 3SO 3 –) electrolyte media from 25 to 250 °C. Rb + primarily occupies the innermost tetradentate binding site on the rutile (110) surface at all temperatures (25, 150, 250 °C) and negative charge conditions (-0.1 and -0.2 C/m 2) probed via CMD simulations, reflecting the small hydration energy of this large, monovalent cation. Consequently, variable SCM parameters (Stern-layer capacitancemore » values and intrinsic Rb + binding constants) were adjusted relatively easily to satisfactorily match the CMD and titration data. The larger hydration energy of Na + results in a more complex inner-sphere distribution, which shifts from bidentate to tetradentate binding with increasing negative charge and temperature, and this distribution was not matched well for both negative charge conditions, which may reflect limitations in the CMD and/or SCM approaches. Finally, in particular, the CMD axial density profiles for Rb + and Na + reveal that peak binding distances shift toward the surface with increasing negative charge, suggesting that the CD-MUSIC framework may be improved by incorporating CD or Stern-layer capacitance values that vary with charge.« less

Constrained Surface Complexation Modeling: Rutile in RbCl, NaCl, and NaCF 3SO 3 Media to 250 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Machesky, Michael L.; Předota, Milan; Ridley, Moira K.

In this paper, a comprehensive set of molecular-level results, primarily from classical molecular dynamics (CMD) simulations, are used to constrain CD-MUSIC surface complexation model (SCM) parameters describing rutile powder titrations conducted in RbCl, NaCl, and NaTr (Tr = triflate, CF 3SO 3 –) electrolyte media from 25 to 250 °C. Rb + primarily occupies the innermost tetradentate binding site on the rutile (110) surface at all temperatures (25, 150, 250 °C) and negative charge conditions (-0.1 and -0.2 C/m 2) probed via CMD simulations, reflecting the small hydration energy of this large, monovalent cation. Consequently, variable SCM parameters (Stern-layer capacitancemore » values and intrinsic Rb + binding constants) were adjusted relatively easily to satisfactorily match the CMD and titration data. The larger hydration energy of Na + results in a more complex inner-sphere distribution, which shifts from bidentate to tetradentate binding with increasing negative charge and temperature, and this distribution was not matched well for both negative charge conditions, which may reflect limitations in the CMD and/or SCM approaches. Finally, in particular, the CMD axial density profiles for Rb + and Na + reveal that peak binding distances shift toward the surface with increasing negative charge, suggesting that the CD-MUSIC framework may be improved by incorporating CD or Stern-layer capacitance values that vary with charge.« less

Propagation of electromagnetic wave in dusty plasma and the influence of dust size distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Hui; China Research Institute of Radio Wave Propagation; Wu, Jian

The effect of charged dust particle and their size distribution on the propagation of electromagnetic wave in a dusty plasma is investigated. It is shown that the additional collision mechanism provided by charged dust particles can significantly alter the electromagnetic properties of a plasma, leading to the appearance of attenuation of electromagnetic wave through dusty plasma. The attenuation coefficient mainly depends on the dust density, radius, and the charge numbers on the dust surface. The results described here will be used to enhance understanding of electromagnetic wave propagation processed in space and laboratory dusty plasma.

The role of charged surface residues in the binding ability of small hubs in protein-protein interaction networks

PubMed Central

Patil, Ashwini; Nakamura, Haruki

2007-01-01

Hubs are highly connected proteins in a protein-protein interaction network. Previous work has implicated disordered domains and high surface charge as the properties significant in the ability of hubs to bind multiple proteins. While conformational flexibility of disordered domains plays an important role in the binding ability of large hubs, high surface charge is the dominant property in small hubs. In this study, we further investigate the role of the high surface charge in the binding ability of small hubs in the absence of disordered domains. Using multipole expansion, we find that the charges are highly distributed over the hub surfaces. Residue enrichment studies show that the charged residues in hubs are more prevalent on the exposed surface, with the exception of Arg, which is predominantly found at the interface, as compared to non-hubs. This suggests that the charged residues act primarily from the exposed surface rather than the interface to affect the binding ability of small hubs. They do this through (i) enhanced intra-molecular electrostatic interactions to lower the desolvation penalty, (ii) indirect long – range intermolecular interactions with charged residues on the partner proteins for better complementarity and electrostatic steering, and (iii) increased solubility for enhanced diffusion-controlled rate of binding. Along with Arg, we also find a high prevalence of polar residues Tyr, Gln and His and the hydrophobic residue Met at the interfaces of hubs, all of which have the ability to form multiple types of interactions, indicating that the interfaces of hubs are optimized to participate in multiple interactions. PMID:27857564

The role of charged surface residues in the binding ability of small hubs in protein-protein interaction networks.

PubMed

Patil, Ashwini; Nakamura, Haruki

2007-01-01

Hubs are highly connected proteins in a protein-protein interaction network. Previous work has implicated disordered domains and high surface charge as the properties significant in the ability of hubs to bind multiple proteins. While conformational flexibility of disordered domains plays an important role in the binding ability of large hubs, high surface charge is the dominant property in small hubs. In this study, we further investigate the role of the high surface charge in the binding ability of small hubs in the absence of disordered domains. Using multipole expansion, we find that the charges are highly distributed over the hub surfaces. Residue enrichment studies show that the charged residues in hubs are more prevalent on the exposed surface, with the exception of Arg, which is predominantly found at the interface, as compared to non-hubs. This suggests that the charged residues act primarily from the exposed surface rather than the interface to affect the binding ability of small hubs. They do this through (i) enhanced intra-molecular electrostatic interactions to lower the desolvation penalty, (ii) indirect long - range intermolecular interactions with charged residues on the partner proteins for better complementarity and electrostatic steering, and (iii) increased solubility for enhanced diffusion-controlled rate of binding. Along with Arg, we also find a high prevalence of polar residues Tyr, Gln and His and the hydrophobic residue Met at the interfaces of hubs, all of which have the ability to form multiple types of interactions, indicating that the interfaces of hubs are optimized to participate in multiple interactions.

Electrokinetic Response of Charge-Selective Nanostructured Polymeric Membranes

NASA Astrophysics Data System (ADS)

Schiffbauer, Jarrod; Li, Diya; Gao, Feng; Phillip, William; Chang, Hsueh-Chia

2017-11-01

Nanostructured polymeric membranes, with a tunable pore size and ease of surface molecular functionalization, are a promising material for separations, filtration, and sensing applications. Recently, such membranes have been fabricated wherein the ion selectivity is imparted by self-assembled functional groups through a two-step process. Amine groups are used to provide a positive surface charge and acid groups are used to yield a negative charge. The membranes can be fabricated as either singly-charged or patterned/mosaic membranes, where there are alternating regions of amine- lined or acid-lined pores. We demonstrate that such membranes, in addition to having many features in common with other charge selective membranes (i.e. AMX or Nafion), display a unique single-membrane rectification behavior. This is due to the asymmetric distribution of charged functional groups during the fabrication process. We demonstrate this rectification effect using both dc current-voltage characteristics as well as dc-biased electrical impedance spectroscopy. Furthermore, surface charge changes due to dc concentration polarization and generation of localized pH shifts are monitored using electrical impedance spectroscopy. (formerly at University of Notre Dame).

Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators

NASA Technical Reports Server (NTRS)

Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.

2007-01-01

A recently introduced phenomenological model to simulate flow control applications using plasma actuators has been further developed and improved in order to expand its use to complicated actuator geometries. The new modeling approach eliminates the requirement of an empirical charge density distribution shape by using the embedded electrode as a source for the charge density. The resulting model is validated against a flat plate experiment with quiescent environment. The modeling approach incorporates the effect of the plasma actuators on the external flow into Navier Stokes computations as a body force vector which is obtained as a product of the net charge density and the electric field. The model solves the Maxwell equation to obtain the electric field due to the applied AC voltage at the electrodes and an additional equation for the charge density distribution representing the plasma density. The new modeling approach solves the charge density equation in the computational domain assuming the embedded electrode as a source therefore automatically generating a charge density distribution on the surface exposed to the flow similar to that observed in the experiments without explicitly specifying an empirical distribution. The model is validated against a flat plate experiment with quiescent environment.

Electrostatic dust transport on the surfaces of airless bodies

NASA Astrophysics Data System (ADS)

Wang, X.; Schwan, J.; Hsu, H. W.; Horanyi, M.

2015-12-01

The surfaces of airless bodies are charged due to the exposure to solar wind plasma and UV radiation. Dust particles on the regolith of these surfaces can become charged, and may move and even get lofted due to electrostatic force. Electrostatic dust transport has been a long-standing problem that may be related to many observed phenomena on the surfaces of airless planetary bodies, including the lunar horizon glow, the dust ponds on asteroid Eros, the spokes in Saturn's rings, and more recently, the collection of dust particles ejected off Comet 67P, observed by Rosetta. In order to resolve these puzzles, a handful of laboratory experiments have been performed in the past and demonstrated that dust indeed moves and lifts from surfaces exposed to plasma. However, the exact mechanisms for the mobilization of dust particles still remain a mystery. Current charging models, including the so-called "shared charge model" and the charge fluctuation theory, will be discussed. It is found that neither of these models can explain the results from either laboratory experiments or in-situ observations. Recently, single dust trajectories were captured with our new dust experiments, enabling novel micro-scale investigations. The particles' initial launch speeds and size distributions are analyzed, and a new so-called "patched charge model" is proposed to explain our findings. We identify the role of plasma micro-cavities that are formed in-between neighboring dust particles. The emitted secondary or photo- electrons are proposed to be absorbed inside the micro-cavities, resulting in significant charge accumulation on the exposed patches of the surfaces of neighboring particles. The resulting enhanced Coulomb force (repulsion) between particles is likely the dominant force to mobilize and lift them off the surface. The role of other properties, including surface morphology, cohesion and photoelectron charging, will also be discussed.

A Monte Carlo modeling on charging effect for structures with arbitrary geometries

NASA Astrophysics Data System (ADS)

Li, C.; Mao, S. F.; Zou, Y. B.; Li, Yong Gang; Zhang, P.; Li, H. M.; Ding, Z. J.

2018-04-01

Insulating materials usually suffer charging effects when irradiated by charged particles. In this paper, we present a Monte Carlo study on the charging effect caused by electron beam irradiation for sample structures with any complex geometry. When transporting in an insulating solid, electrons encounter elastic and inelastic scattering events; the Mott cross section and a Lorentz-type dielectric function are respectively employed to describe such scatterings. In addition, the band gap and the electron–long optical phonon interaction are taken into account. The electronic excitation in inelastic scattering causes generation of electron–hole pairs; these negative and positive charges establish an inner electric field, which in turn induces the drift of charges to be trapped by impurities, defects, vacancies etc in the solid, where the distributions of trapping sites are assumed to have uniform density. Under charging conditions, the inner electric field distorts electron trajectories, and the surface electric potential dynamically alters secondary electron emission. We present, in this work, an iterative modeling method for a self-consistent calculation of electric potential; the method has advantages in treating any structure with arbitrary complex geometry, in comparison with the image charge method—which is limited to a quite simple boundary geometry. Our modeling is based on: the combination of the finite triangle mesh method for an arbitrary geometry construction; a self-consistent method for the spatial potential calculation; and a full dynamic description for the motion of deposited charges. Example calculations have been done to simulate secondary electron yield of SiO2 for a semi-infinite solid, the charging for a heterostructure of SiO2 film grown on an Au substrate, and SEM imaging of a SiO2 line structure with rough surfaces and SiO2 nanoparticles with irregular shapes. The simulations have explored interesting interlaced charge layer distribution underneath the nanoparticle surface and the mechanism by which it is produced.

ELECTROSTATIC FORCES IN WIND-POLLINATION: PART 2: SIMULATIONS OF POLLEN CAPTURE

EPA Science Inventory

During fair-weather conditions, a 100 V m^-1 electric field exists between positive charge suspended in the air and negative charge distributed on the surfaces of plants and on the ground. The fields surrounding plants are highly complex reaching magnitudes up to 3x106 ...

Proceedings of the Spacecraft Charging Technology Conference: Executive Summary

NASA Technical Reports Server (NTRS)

Pike, C. P.; Whipple, E. C., Jr.; Stevens, N. J.; Minges, M. L.; Lehn, W. L.; Bunn, M. H.

1977-01-01

Aerospace environments are reviewed in reference to spacecraft charging. Modelling, a theoretical scheme which can be used to describe the structure of the sheath around the spacecraft and to calculate the charging currents within, is discussed. Materials characterization is considered for experimental determination of the behavior of typical spacecraft materials when exposed to simulated geomagnetic substorm conditions. Materials development is also examined for controlling and minimizing spacecraft charging or at least for distributing the charge in an equipotential manner, using electrical conductive surfaces for materials exposed to space environment.

FAST TRACK COMMUNICATION: Inhomogeneous charge redistribution in Xe clusters exposed to an intense extreme ultraviolet free electron laser

NASA Astrophysics Data System (ADS)

Iwayama, H.; Sugishima, A.; Nagaya, K.; Yao, M.; Fukuzawa, H.; Motomura, K.; Liu, X.-J.; Yamada, A.; Wang, C.; Ueda, K.; Saito, N.; Nagasono, M.; Tono, K.; Yabashi, M.; Ishikawa, T.; Ohashi, H.; Kimura, H.; Togashi, T.

2010-08-01

The emission of highly charged ions from Xe clusters exposed to intense extreme ultraviolet laser pulses (λ ~ 52 nm) from the free electron laser in Japan was investigated using ion momentum spectroscopy. With increasing average cluster size, we observed multiply charged ions Xez + up to z = 3. From kinetic energy distributions, we found that multiply charged ions were generated near the cluster surface. Our results suggest that charges are inhomogeneously redistributed in the cluster to lower the total energy stored in the clusters.

Reactivity of etoricoxib based on computational study of molecular orbitals, molecular electrostatic potential surface and Mulliken charge analysis

NASA Astrophysics Data System (ADS)

Sachdeva, Ritika; Soni, Abhinav; Singh, V. P.; Saini, G. S. S.

2018-05-01

Etoricoxib is one of the selective cyclooxygenase inhibitor drug which plays a significant role in the pharmacological management of arthritis and pain. The theoretical investigation of its reactivity is done using Density Functional Theory calculations. Molecular Electrostatic Potential Surface of etoricoxib and its Mulliken atomic charge distribution are used for the prediction of its electrophilic and nucleophilic sites. The detailed analysis of its frontier molecular orbitals is also done.

Measurement of surface charges on the dielectric film based on field mills under the HVDC corona wire

NASA Astrophysics Data System (ADS)

Donglai, WANG; Tiebing, LU; Yuan, WANG; Bo, CHEN; Xuebao, LI

2018-05-01

The ion flow field on the ground is one of the significant parameters used to evaluate the electromagnetic environment of high voltage direct current (HVDC) power lines. HVDC lines may cross the greenhouses due to the restricted transmission corridors. Under the condition of ion flow field, the dielectric films on the greenhouses will be charged, and the electric fields in the greenhouses may exceed the limit value. Field mills are widely used to measure the ground-level direct current electric fields under the HVDC power lines. In this paper, the charge inversion method is applied to calculate the surface charges on the dielectric film according to the measured ground-level electric fields. The advantages of hiding the field mill probes in the ground are studied. The charge inversion algorithm is optimized in order to decrease the impact of measurement errors. Based on the experimental results, the surface charge distribution on a piece of quadrate dielectric film under a HVDC corona wire is studied. The enhanced effect of dielectric film on ground-level electric field is obviously weakened with the increase of film height. Compared with the total electric field strengths, the normal components of film-free electric fields at the corresponding film-placed positions have a higher effect on surface charge accumulation.

Transmission of low-energy negative ions through insulating nanocapillaries

NASA Astrophysics Data System (ADS)

Zhang, Qi; Liu, Zhonglin; Li, Pengfei; Jin, Bo; Song, Guangyin; Jin, Dingkun; Niu, Ben; Wei, Long; Ha, Shuai; Xie, Yiming; Ma, Yue; Wan, Chengliang; Cui, Ying; Zhou, Peng; Zhang, Hongqiang; Chen, Ximeng

2018-04-01

A simulation is performed to study the transmission of low-energy C l- ions through A l2O3 nanocapillaries. For the trajectory simulations, there are several processes involved: the image forces induced by the projectile; the electrostatic force from the deposited charges; the scattering from the inner surface and charge exchange. The simulation reproduces the main features of the experiments; i.e., the double peak structure in the transmitted angular distribution and the transmitted fractions of C l- , C l+ , and C l0 were found in the charge state distribution. The transmitted C l- ions are centered around the beam direction while the transmitted fractions of C l0 and C l+ are centered around the tilt angles. The role of the deposited charge is also studied by simulations. With the deposited charge, it is found that C l- is dominant in the transmission and the majority of the ions, centered around the tilt angle, are mainly from the single deflection by the negative charge patches on the inner surfaces of the capillaries, and only a few directly transmitted C l- ions are centered around the incident direction. There are also a few transmitted fractions of C l0 and C l+ from close surface scatterings. In the case that there are no negative charge patches, the simulation agrees with the experiment in detail: The majority of the directly transmitted C l- ions are centered around the incident direction while only a few scattered C l- ions are centered around the tilt angle from the single close collisions with the inner surfaces of the capillaries. There is a portion, comparable to the transmitted fraction of C l- , of the transmitted fractions of C l0 and C l+ , centered around the tilt angle, from the single scatterings with the inner surfaces of the capillaries. This confirms that at the present experimental conditions there are most probably no negative charge patches formed to guide the negative ions through insulating A l2O3 nanocapillaries.

Surface charge accumulation of particles containing radionuclides in open air.

PubMed

Kim, Yong-Ha; Yiacoumi, Sotira; Tsouris, Costas

2015-05-01

Radioactivity can induce charge accumulation on radioactive particles. However, electrostatic interactions caused by radioactivity are typically neglected in transport modeling of radioactive plumes because it is assumed that ionizing radiation leads to charge neutralization. The assumption that electrostatic interactions caused by radioactivity are negligible is evaluated here by examining charge accumulation and neutralization on particles containing radionuclides in open air. A charge-balance model is employed to predict charge accumulation on radioactive particles. It is shown that particles containing short-lived radionuclides can be charged with multiple elementary charges through radioactive decay. The presence of radioactive particles can significantly modify the particle charge distribution in open air and yield an asymmetric bimodal charge distribution, suggesting that strong electrostatic particle interactions may occur during short- and long-range transport of radioactive particles. Possible effects of transported radioactive particles on electrical properties of the local atmosphere are reported. The study offers insight into transport characteristics of airborne radionuclides. Results are useful in atmospheric transport modeling of radioactive plumes. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spatial variation of permittivity of an electrolyte solution in contact with a charged metal surface: a mini review

PubMed Central

Gongadze, E.; van Rienen, U.; Kralj-Iglič, V.; Iglič, A.

2012-01-01

Contact between a charged metal surface and an electrolyte implies a particular ion distribution near the charged surface, i.e. the electrical double layer. In this mini review, different mean-field models of relative (effective) permittivity are described within a simple lattice model, where the orientational ordering of water dipoles in the saturation regime is taken into account. The Langevin-Poisson-Boltzmann (LPB) model of spatial variation of the relative permittivity for point-like ions is described and compared to a more general Langevin-Bikerman (LB) model of spatial variation of permittivity for finite-sized ions. The Bikerman model and the Poisson-Boltzmann model are derived as limiting cases. It is shown that near the charged surface, the relative permittivity decreases due to depletion of water molecules (volume-excluded effect) and orientational ordering of water dipoles (saturation effect). At the end, the LPB and LB models are generalised by also taking into account the cavity field. PMID:22263808

Charge Transfer Effect on Raman and Surface Enhanced Raman Spectroscopy of Furfural Molecules.

PubMed

Wan, Fu; Shi, Haiyang; Chen, Weigen; Gu, Zhaoliang; Du, Lingling; Wang, Pinyi; Wang, Jianxin; Huang, Yingzhou

2017-08-02

The detection of furfural in transformer oil through surface enhanced Raman spectroscopy (SERS) is one of the most promising online monitoring techniques in the process of transformer aging. In this work, the Raman of individual furfural molecules and SERS of furfural-M x (M = Ag, Au, Cu) complexes are investigated through density functional theory (DFT). In the Raman spectrum of individual furfural molecules, the vibration mode of each Raman peak is figured out, and the deviation from experimental data is analyzed by surface charge distribution. In the SERS of furfural-M x complexes, the influence of atom number and species on SERS chemical enhancement factors (EFs) are studied, and are further analyzed by charge transfer effect. Our studies strengthen the understanding of charge transfer effect in the SERS of furfural molecules, which is important in the online monitoring of the transformer aging process through SERS.

Charge Transfer Effect on Raman and Surface Enhanced Raman Spectroscopy of Furfural Molecules

PubMed Central

Wan, Fu; Shi, Haiyang; Chen, Weigen; Gu, Zhaoliang; Du, Lingling; Wang, Pinyi; Wang, Jianxin

2017-01-01

The detection of furfural in transformer oil through surface enhanced Raman spectroscopy (SERS) is one of the most promising online monitoring techniques in the process of transformer aging. In this work, the Raman of individual furfural molecules and SERS of furfural-Mx (M = Ag, Au, Cu) complexes are investigated through density functional theory (DFT). In the Raman spectrum of individual furfural molecules, the vibration mode of each Raman peak is figured out, and the deviation from experimental data is analyzed by surface charge distribution. In the SERS of furfural-Mx complexes, the influence of atom number and species on SERS chemical enhancement factors (EFs) are studied, and are further analyzed by charge transfer effect. Our studies strengthen the understanding of charge transfer effect in the SERS of furfural molecules, which is important in the online monitoring of the transformer aging process through SERS. PMID:28767053

Molecular dynamics studies of water deposition on hematite surfaces

NASA Astrophysics Data System (ADS)

Kvamme, Bjørn; Kuznetsova, Tatiana; Haynes, Martin

2012-12-01

The interest in carbon dioxide for enhanced oil recovery is increasing proportional to the decrease in naturally driven oil production and also due to the increasing demand for reduced emission of carbon dioxide to the atmosphere. Transport of carbon dioxide in offshore pipelines involves high pressure and low temperatures which may lead to the formation of hydrate between residual water dissolved in carbon dioxide. The critical question is whether the water at some condition of temperature and pressure will drop out as liquid droplets or as water adsorbed on the surfaces of the pipeline and then subsequently form hydrates heterogeneously. In this work we have used the 6-311G basis set with B3LYP to estimate the charge distribution of different sizes of hematite crystals. The obtained surface charge distribution were kept unchanged while the inner charge distribution where scaled so as to result in an overall neutral crystal. These rust particles were embedded in water and chemical potential for adsorbed water molecules were estimated through thermodynamic integration and compared to similar estimates for same size water cluster. Estimated values of water chemical potentials indicate that it is thermodynamically favorable for water to adsorb on hematite, and that evaluation of potential carbon dioxide hydrate formation conditions and kinetics should be based this sequence of processes.

Measurements of the electrical resistance and the hydrogen depth distribution for Ni 60Nb 20Zr 20 amorphous alloy before and after hydrogen charging

NASA Astrophysics Data System (ADS)

Nakano, Sumiaki; Ohtsu, Naofumi; Nagata, Shinji; Yamaura, Shin-ichi; Uchinashi, Sakae; Kimura, Hisamichi; Shikama, Tatsuo; Inoue, Akihisa

2005-02-01

A Ni 60Nb 20Zr 20 amorphous alloy was prepared by the single-roller melt-spinning technique. The change in the electrical resistance of the alloy after electrochemical hydrogen charging in 6 N KOH solution was investigated. The change in the hydrogen depth distribution in the alloy was also investigated by elastic recoil detection. As a result, we found that the electrical resistance of the alloy increases with increasing the hydrogen content in the alloy and that a large number of hydrogen atoms are remained in the surface area of the hydrogen-charged alloy.

Space charge characteristics of fluorinated polyethylene: Different effects of fluorine and oxygen

NASA Astrophysics Data System (ADS)

Zhao, Ni; Nie, Yongjie; Li, Shengtao

2018-04-01

Direct fluorination are proved having obvious effect on space charge characteristics of polyethylene. It is believed that fluorine has a positive effect on suppressing space charge injection while oxygen impurity has a negative effect. However, the mechanism for the opposite effect of fluorine and oxygen is still not clear. In this paper, the different effects of fluorine and oxygen on space charge characteristics of fluorinated low density polyethylene (LDPE) are investigated on the basis of dielectric property, chemical constitutes and trap performance of surface fluorinated layers. The results show that direct fluorination has obvious effect on chemical constitutes and dielectric properties of surface fluorinated layer. Introduced fluorine is the main factor for suppressing charge injection from the electrodes, because it seriously changes the chemical constitutes and further the trap properties of the surface fluorinated layer. While introduction of oxygen results in heterocharges and makes space charge distribution complex, due to the ionization of generated small groups like C=O containing groups. Moreover, direct fluorination will result in cleavage of some LDPE molecules whatever there is oxygen impurity or not.

Surface-charge-governed electrolyte transport in carbon nanotubes

NASA Astrophysics Data System (ADS)

Xue, Jian-Ming; Guo, Peng; Sheng, Qian

2015-08-01

The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes (CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid-liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results, we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work. Project supported by the National Natural Science Foundation of China (Grant Nos. 11375031 and 11335003).

Crystal structure of the DNA polymerase III β subunit (β-clamp) from the extremophile Deinococcus radiodurans.

PubMed

Niiranen, Laila; Lian, Kjersti; Johnson, Kenneth A; Moe, Elin

2015-02-27

Deinococcus radiodurans is an extremely radiation and desiccation resistant bacterium which can tolerate radiation doses up to 5,000 Grays without losing viability. We are studying the role of DNA repair and replication proteins for this unusual phenotype by a structural biology approach. The DNA polymerase III β subunit (β-clamp) acts as a sliding clamp on DNA, promoting the binding and processivity of many DNA-acting proteins, and here we report the crystal structure of D. radiodurans β-clamp (Drβ-clamp) at 2.0 Å resolution. The sequence verification process revealed that at the time of the study the gene encoding Drβ-clamp was wrongly annotated in the genome database, encoding a protein of 393 instead of 362 amino acids. The short protein was successfully expressed, purified and used for crystallisation purposes in complex with Cy5-labeled DNA. The structure, which was obtained from blue crystals, shows a typical ring-shaped bacterial β-clamp formed of two monomers, each with three domains of identical topology, but with no visible DNA in electron density. A visualisation of the electrostatic surface potential reveals a highly negatively charged outer surface while the inner surface and the dimer forming interface have a more even charge distribution. The structure of Drβ-clamp was determined to 2.0 Å resolution and shows an evenly distributed electrostatic surface charge on the DNA interacting side. We hypothesise that this charge distribution may facilitate efficient movement on encircled DNA and help ensure efficient DNA metabolism in D. radiodurans upon exposure to high doses of ionizing irradiation or desiccation.

Kinesin motor protein as an electrostatic ratchet machine

NASA Astrophysics Data System (ADS)

Tsironis, George; Ciudad, Aleix; Sancho, Jose Maria

2008-03-01

Kinesin and related motor proteins utilize ATP fuel to propel themselves along the external surface of microtubules in a processive and directional fashion. We show that the observed step-like motion is possible through time varying charge distributions furnished by the ATP hydrolysis circle while the static charge configuration on the microtuble provides the guide for motion. Thus, while the chemical hydrolysis energy induces appropriate local conformational changes, the motor translational energy is fundamentally electrostatic. Numerical simulations of the mechanical equations of motion show that processivity and directionality are direct consequences of the ATP-dependent electrostatic interaction between the different charge distributions of kinesin and microtubule. Treating proterins as continuous dielectric media and using a Green's function formalism we find analytical expressions for the electrostatic energy in the vicinity of the protein surfaces. We calculate the Bjerrum length in the interior of the protein and analyze its dependence on the charge proximity to the protein interface. We apply these results to kinesin and estimate the pure electrostatic ATP-ADP interaction to be larger than 2k T.

Basic surface properties of mononuclear cells from Didelphis marsupialis.

PubMed

Nacife, V P; de Meirelles, M de N; Silva Filho, F C

1998-01-01

The electrostatic surface charge and surface tension of mononuclear cells/monocytes obtained from young and adult marsupials (Didelphis marsupialis) were investigated by using cationized ferritin and colloidal iron hydroxyde, whole cell electrophoresis, and measurements of contact angles. Anionic sites were found distributed throughout the entire investigated cell surfaces. The results revealed that the anionic character of the cells is given by electrostatic charges corresponding to -18.8 mV (cells from young animals) and -29.3 mV (cells from adult animals). The surface electrostatic charge decreased from 10 to 65.2% after treatment of the cells with each one of trypsin, neuraminidase and phospholipase C. The hydrophobic nature of the mononuclear cell surfaces studied by using the contact angle method revealed that both young and adult cells possess cell surfaces of high hidrofilicity since the angles formed with drops of saline water were 42.5 degrees and 40.8 degrees, respectively. Treatment of the cells with trypsin or neuraminidase rendered their surfaces more hydrophobic, suggesting that sialic acid-containing glycoproteins are responsible for most of the hydrophilicity observed in the mononuclear cell surfaces from D. marsupialis.

Complex interaction of subsequent surface streamers via deposited charge: a high-resolution experimental study

NASA Astrophysics Data System (ADS)

Hoder, T.; Synek, P.; Chorvát, D.; Ráhel', J.; Brandenburg, R.; Černák, M.

2017-07-01

The coplanar barrier discharge in synthetic air at 30 kPa pressure was studied by time-correlated single photon counting enhanced optical emission spectroscopy, far-field microscopy enhanced intensified CCD camera and sensitive current measurements. The discharge operated in a regime where two subsequent microdischarges appeared within the same voltage half-period. The electrical analysis of the barrier discharge setup enabled us to quantify charge transfer and the effective electric field development. During the second microdischarge the positive surface streamers follow the interface (triple-line) between the area of deposited charge from the previous one and the area of uncharged dielectric surface. It is shown that additional branching and flashes of surface streamers are responsible for the increased spatial complexity of the deposited surface charges at high overvoltage. A suppressed streamer propagating over the area of deposited surface charge was tracked and the evidence of surface streamer reconnection is presented. A spatiotemporal distribution (resolution of 120 ps and 100 μm) of the reduced electric field strength was obtained for both microdischarges from the recorded luminosities of the molecular nitrogen. The reduced electric field of positive streamers in the first microdischarge reached 1200 Td. For the second one, the electric field values for the streamer at the triple-line are slightly lower than that, while for the suppressed streamers are even higher.

Supercharging of the Lunar Surface by Solar Wind Halo Electrons

NASA Astrophysics Data System (ADS)

Stubbs, T. J.; Farrell, W. M.; Collier, M. R.; Halekas, J. S.; Delory, G. T.; Holland, M. P.; Vondrak, R. R.

2007-12-01

Lunar surface potentials can reach several kilovolts negative during Solar Energetic Particle (SEPs) events, as indicated by recent analysis of data from the Lunar Prospector Electron Reflectometer (LP/ER). The lunar surface- plasma interactions that result in such extreme surface potentials are poorly characterized and understood. Extreme lunar surface charging, and the associated electrostatic discharges and transport of charged dust, will likely present significant hazards to future human explorers. This is of particular concern near the terminator and polar regions, such as the South Pole/Aiken Basin site planned for NASA's manned outpost. It is the flux of electrons from the ambient plasma that charges the surface of the Moon to negative potentials. In the solar wind, the electron temperature is typically ~10 eV which tends to charge the lunar surface to ~100 V negative in shadow. However, during space weather events the solar wind electrons are often better described by the sum of two Maxwellian distributions, referred to as the "core" and "halo" components. The core electrons are relatively cool and dense (e.g., ~10 eV and ~10/cc), whereas the halo electrons are hot and tenuous (e.g., ~100 eV and ~0.1/cc). Despite, the tenuous nature of the halo electrons, our surface charging model - using core and halo electron data derived from the Solar Wind Experiment (SWE) aboard the Wind spacrcraft - predicts that they are capable of "supercharging" the lunar surface to kilovolt potentials during space weather events, which could explain the LP/ER observations.

Charging Properties of Cassiterite (alpha-SnO2) Surfaces in NaCl and RbCl Ionic Media.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenqvist, Jorgen K; Machesky, Michael L.; Vlcek, Lukas

2009-01-01

The acid-base properties of cassiterite ({alpha}-SnO{sub 2}) surfaces at 10-50 C were studied using potentiometric titrations of powder suspensions in aqueous NaCl and RbCl media. The proton sorption isotherms exhibited common intersection points in the pH range of 4.0-4.5 under all conditions, and the magnitude of charging was similar but not identical in NaCl and RbCl. The hydrogen bonding configuration at the oxide-water interface, obtained from classical molecular dynamics (MD) simulations, was analyzed in detail, and the results were explicitly incorporated in calculations of protonation constants for the reactive surface sites using the revised MUSIC model. The calculations indicated thatmore » the terminal SnOH{sub 2} group is more acidic than the bridging Sn{sub 2}OH group, with protonation constants (log K{sub H}) of 3.60 and 5.13 at 25 C, respectively. This is contrary to the situation on the isostructural {alpha}-TiO{sub 2} (rutile), apparently because of the difference in electronegativity between Ti and Sn. MD simulations and speciation calculations indicated considerable differences in the speciation of Na{sup +} and Rb{sup +}, despite the similarities in overall charging. Adsorbed sodium ions are almost exclusively found in bidentate surface complexes, whereas adsorbed rubidium ions form comparable numbers of bidentate and tetradentate complexes. Also, the distribution of adsorbed Na{sup +} between the different complexes shows a considerable dependence on the surface charge density (pH), whereas the distribution of adsorbed Rb{sup +} is almost independent of pH. A surface complexation model (SCM) capable of accurately describing both the measured surface charge and the MD-predicted speciation of adsorbed Na{sup +}/Rb{sup +} was formulated. According to the SCM, the deprotonated terminal group (SnOH{sup -0.40}) and the protonated bridging group (Sn{sub 2}OH{sup +0.36}) dominate the surface speciation over the entire pH range of this study (2.7-10). The complexation of medium cations increases significantly with increasing negative surface charge, and at pH 10, roughly 40% of the terminal sites are predicted to form cation complexes, whereas anion complexation is minor throughout the studied pH range.« less

Simulation of multipactor on the rectangular grooved dielectric surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Libing; Wang, Jianguo, E-mail: wanguiuc@mail.xjtu.edu.cn; Northwest Institute of Nuclear Technology, Xi'an, Shaanxi 710024

2015-11-15

Multipactor discharge on the rectangular grooved dielectric surface is simulated self-consistently by using a two-and-a-half dimensional (2.5 D) electrostatic particle-in-cell (PIC) code. Compared with the electromagnetic PIC code, the former can give much more accurate solution for the space charge field caused by the multipactor electrons and the deposited surface charge. According to the rectangular groove width and height, the multipactor can be divided into four models, the spatial distributions of the multipactor electrons and the space charge fields are presented for these models. It shows that the rectangular groove in different models gives very different suppression effect on themore » multipactor, effective and efficient suppression on the multipactor can only be reached with a proper groove size.« less

Electrophoresis of a charged soft particle in a charged cavity with arbitrary double-layer thickness.

PubMed

Chen, Wei J; Keh, Huan J

2013-08-22

An analysis for the quasi-steady electrophoretic motion of a soft particle composed of a charged spherical rigid core and an adsorbed porous layer positioned at the center of a charged spherical cavity filled with an arbitrary electrolyte solution is presented. Within the porous layer, frictional segments with fixed charges are assumed to distribute uniformly. Through the use of the linearized Poisson-Boltzmann equation and the Laplace equation, the equilibrium double-layer potential distribution and its perturbation caused by the applied electric field are separately determined. The modified Stokes and Brinkman equations governing the fluid flow fields outside and inside the porous layer, respectively, are solved subsequently. An explicit formula for the electrokinetic migration velocity of the soft particle in terms of the fixed charge densities on the rigid core surface, in the porous layer, and on the cavity wall is obtained from a balance between its electrostatic and hydrodynamic forces. This formula is valid for arbitrary values of κa, λa, r0/a, and a/b, where κ is the Debye screening parameter, λ is the reciprocal of the length characterizing the extent of flow penetration inside the porous layer, a is the radius of the soft particle, r0 is the radius of the rigid core of the particle, and b is the radius of the cavity. In the limiting cases of r0 = a and r0 = 0, the migration velocity for the charged soft sphere reduces to that for a charged impermeable sphere and that for a charged porous sphere, respectively, in the charged cavity. The effect of the surface charge at the cavity wall on the particle migration can be significant, and the particle may reverse the direction of its migration.

On the mechanism of pattern formation in glow dielectric barrier discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, Yajun; Li, Ben; Ouyang, Jiting, E-mail: jtouyang@bit.edu.cn

2016-01-15

The formation mechanism of pattern in glow dielectric barrier discharge is investigated by two-dimensional fluid modeling. Experimental results are shown for comparison. The simulation results show that the non-uniform distribution of space charges makes the discharge be enhanced in the high-density region but weakened in its neighborhood, which is considered as an activation-inhibition effect. This effect shows through during a current pulse (one discharge event) but also in a certain period of time after discharge that determines a driving frequency range for the non-uniformity of space charges to be enhanced. The effects of applied voltage, surface charge, electrode boundary, andmore » external field are also discussed. All these factors affect the formation of dielectric-barrier-discharge pattern by changing the distribution or the dynamics of space charges and hence the activation-inhibition effect of non-uniform space charges.« less

Effect of surface charge on the colloidal stability and in vitro uptake of carboxymethyl dextran-coated iron oxide nanoparticles

PubMed Central

Ayala, Vanessa; Herrera, Adriana P.; Latorre-Esteves, Magda; Torres-Lugo, Madeline

2013-01-01

Nanoparticle physicochemical properties such as surface charge are considered to play an important role in cellular uptake and particle–cell interactions. In order to systematically evaluate the role of surface charge on the uptake of iron oxide nanoparticles, we prepared carboxymethyl-substituted dextrans with different degrees of substitution, ranging from 38 to 5 groups per chain, and reacted them using carbodiimide chemistry with amine–silane-coated iron oxide nanoparticles with narrow size distributions in the range of 33–45 nm. Surface charge of carboxymethyl-substituted dextran-coated nano-particles ranged from −50 to 5 mV as determined by zeta potential measurements, and was dependent on the number of carboxymethyl groups incorporated in the dextran chains. Nanoparticles were incubated with CaCo-2 human colon cancer cells. Nanoparticle–cell interactions were observed by confocal laser scanning microscopy and uptake was quantified by elemental analysis using inductively coupled plasma mass spectroscopy. Mechanisms of internalization were inferred using pharmacological inhibitors for fluid-phase, clathrin-mediated, and caveola-mediated endocytosis. Results showed increased uptake for nanoparticles with greater negative charge. Internalization patterns suggest that uptake of the most negatively charged particles occurs via non-specific interactions. PMID:24470787

The effects of plasma inhomogeneity on the nanoparticle coating in a low pressure plasma reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pourali, N.; Foroutan, G.

2015-10-15

A self-consistent model is used to study the surface coating of a collection of charged nanoparticles trapped in the sheath region of a low pressure plasma reactor. The model consists of multi-fluid plasma sheath module, including nanoparticle dynamics, as well as the surface deposition and particle heating modules. The simulation results show that the mean particle radius increases with time and the nanoparticle size distribution is broadened. The mean radius is a linear function of time, while the variance exhibits a quadratic dependence. The broadening in size distribution is attributed to the spatial inhomogeneity of the deposition rate which inmore » turn depends on the plasma inhomogeneity. The spatial inhomogeneity of the ions has strong impact on the broadening of the size distribution, as the ions contribute both in the nanoparticle charging and in direct film deposition. The distribution width also increases with increasing of the pressure, gas temperature, and the ambient temperature gradient.« less

Critical review of electrical conductivity measurements and charge distribution analysis of magnesium oxide

NASA Technical Reports Server (NTRS)

Freund, Friedemann; Freund, Minoru M.; Batllo, Francois

1993-01-01

The electrical conductivity sigma of MgO single crystals shows a sharp increase at 500-800 C, in particular of sigma surface, generally attributed to surface contamination. Charge Distribution Analysis (CDA), a new technique providing information on fundamental properties that was previously unavailable, allows for the determination of surface charges, their sign and associated internal electric field. Data on 99.99% purity, arc-fusion grown MgO crystals show that mobile charge carriers start to appear in the bulk of the MgO crystals between 200 and 400 C when sigma (measured by conventional techniques) is in t he 10(exp -14) to 10(exp -16) /omega/cm range. Above 500 C, as sigma increases to 10(exp -6) to 10(exp -7)/omega/cm, more charges appear giving rise to a strong positive surface charge supported by a strong internal field. This indicates that charges are generated in the bulk and diffuse to the surface by an internally controlled process. On the basis of their positive sign they are identified as holes (defect electrons). Because of the low cation content of these very pure MgO crystals, theses holes cannnot be associated with transition metal impurties. Instead, they are associated with the O(2-) sublattice, e.g. consist of O(-) states or positive holes. This conclusion is supported by magnetic susceptibility data showing the appearance of 1000 +/- 500 ppm paramagnetic species between 200-500 C. The magnetic data are consistent with strongly coupled, diamagnetic O(-) pairs below 200-500 C, chemically equivalent to peroxy anions, O2(2-), and probably associated with cation vacancies in the MgO matrix. The formation of O2(2-) in arc-fusion grown MgO crystals is very unexpected because of the highly reducing growth conditions. Their presence implies an internal redox reaction involving dissolved 'water' by which OH(-) pairs convert to O2(2-) plus H2 molecules. This redox conversion is supported by mass spectroscopic measurements of the H2 release from highly OH(-)-doped, finely divided MgO and by wet-chemical analysis of its oxidant concentration.

Analyte preconcentration in nanofluidic channels with nonuniform zeta potential

NASA Astrophysics Data System (ADS)

Eden, A.; McCallum, C.; Storey, B. D.; Pennathur, S.; Meinhart, C. D.

2017-12-01

It is well known that charged analytes in the presence of nonuniform electric fields concentrate at locations where the relevant driving forces balance, and a wide range of ionic stacking and focusing methods are commonly employed to leverage these physical mechanisms in order to improve signal levels in biosensing applications. In particular, nanofluidic channels with spatially varying conductivity distributions have been shown to provide increased preconcentration of charged analytes due to the existence of a finite electric double layer (EDL), in which electrostatic attraction and repulsion from charged surfaces produce nonuniform transverse ion distributions. In this work, we use numerical simulations to show that one can achieve greater levels of sample accumulation by using field-effect control via wall-embedded electrodes to tailor the surface potential heterogeneity in a nanochannel with overlapped EDLs. In addition to previously demonstrated stacking and focusing mechanisms, we find that the coupling between two-dimensional ion distributions and the axial electric field under overlapped EDL conditions can generate an ion concentration polarization interface in the middle of the channel. Under an applied electric field, this interface can be used to concentrate sample ions between two stationary regions of different surface potential and charge density. Our numerical model uses the Poisson-Nernst-Planck system of equations coupled with the Stokes equation to demonstrate the phenomenon, and we discuss in detail the driving forces behind the predicted sample enhancement. The numerical velocity and salt concentration profiles exhibit good agreement with analytical results from a simplified one-dimensional area-averaged model for several limiting cases, and we show predicted amplification ratios of up to 105.

Ionic strength independence of charge distributions in solvation of biomolecules

NASA Astrophysics Data System (ADS)

Virtanen, J. J.; Sosnick, T. R.; Freed, K. F.

2014-12-01

Electrostatic forces enormously impact the structure, interactions, and function of biomolecules. We perform all-atom molecular dynamics simulations for 5 proteins and 5 RNAs to determine the dependence on ionic strength of the ion and water charge distributions surrounding the biomolecules, as well as the contributions of ions to the electrostatic free energy of interaction between the biomolecule and the surrounding salt solution (for a total of 40 different biomolecule/solvent combinations). Although water provides the dominant contribution to the charge density distribution and to the electrostatic potential even in 1M NaCl solutions, the contributions of water molecules and of ions to the total electrostatic interaction free energy with the solvated biomolecule are comparable. The electrostatic biomolecule/solvent interaction energies and the total charge distribution exhibit a remarkable insensitivity to salt concentrations over a huge range of salt concentrations (20 mM to 1M NaCl). The electrostatic potentials near the biomolecule's surface obtained from the MD simulations differ markedly, as expected, from the potentials predicted by continuum dielectric models, even though the total electrostatic interaction free energies are within 11% of each other.

Intrinsic Charge Trapping Observed as Surface Potential Variations in diF-TES-ADT Films.

PubMed

Hoffman, Benjamin C; McAfee, Terry; Conrad, Brad R; Loth, Marsha A; Anthony, John E; Ade, Harald W; Dougherty, Daniel B

2016-08-24

Spatial variations in surface potential are measured with Kelvin probe force microscopy for thin films of 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophenes (diF-TES-ADT) grown on SiO2 and silane-treated SiO2 substrates by organic molecular beam deposition. The variations are observed both between and within grains of the polycrystalline organic film and are quantitatively different than electrostatic variations on the substrate surfaces. The skewness of surface potential distributions is larger on SiO2 than on HMDS-treated substrates. This observation is attributed to the impact of substrate functionalization on minimizing intrinsic crystallographic defects in the organic film that can trap charge.

Unraveling the Agglomeration Mechanism in Charged Block Copolymer and Surfactant Complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borreguero, Jose M.; Pincus, Philip A.; Sumpter, Bobby G.

Here, we report a molecular dynamics simulation investigation of self-assembly and complex formation of charged-neutral double hydrophilic and hydrophobic-hydrophilic block copolymers (BCP) with oppositely charged surfactants. Furthermore, the structure of the surfactant micelles and the BCP aggregation on the micelle surface is systematically studied for five different BCP volume fractions that also mimics a reduction of the surfactant concentration. The local electrostatic interactions between the oppositely charged species encourage the formation of core-shell structures between the surfactant micelles where the surfactants form the cores and the charged blocks of the BCP form the corona. The emergent morphologies of these aggregatesmore » are contingent upon the nature of the BCP neutral blocks. The hydrophilic neutral blocks agglomerate with the micelles as hairy colloidal structures while the hydrophobic neutrals agglomerate in lamellar structures with the surfactant micelles. The distribution of counterion charges along the simulation box show a close-to-normal density distribution for the hydrophilic neutral blocks and a binodal distribution for hydrophobic neutral blocks. No specific surfactant concentration dependent scaling relation is observed as opposed to the simpler case of homo-polyelectrolytes.« less

Unraveling the Agglomeration Mechanism in Charged Block Copolymer and Surfactant Complexes

DOE PAGES

Borreguero, Jose M.; Pincus, Philip A.; Sumpter, Bobby G.; ...

2017-01-27

Here, we report a molecular dynamics simulation investigation of self-assembly and complex formation of charged-neutral double hydrophilic and hydrophobic-hydrophilic block copolymers (BCP) with oppositely charged surfactants. Furthermore, the structure of the surfactant micelles and the BCP aggregation on the micelle surface is systematically studied for five different BCP volume fractions that also mimics a reduction of the surfactant concentration. The local electrostatic interactions between the oppositely charged species encourage the formation of core-shell structures between the surfactant micelles where the surfactants form the cores and the charged blocks of the BCP form the corona. The emergent morphologies of these aggregatesmore » are contingent upon the nature of the BCP neutral blocks. The hydrophilic neutral blocks agglomerate with the micelles as hairy colloidal structures while the hydrophobic neutrals agglomerate in lamellar structures with the surfactant micelles. The distribution of counterion charges along the simulation box show a close-to-normal density distribution for the hydrophilic neutral blocks and a binodal distribution for hydrophobic neutral blocks. No specific surfactant concentration dependent scaling relation is observed as opposed to the simpler case of homo-polyelectrolytes.« less

A model for calculating the vertical distribution of the atmospheric electric potential in the exchange layer in a maritime clean atmosphere

NASA Astrophysics Data System (ADS)

Kulkarni, M. N.; Kamra, A. K.

2012-11-01

A theoretical model is developed for calculating the vertical distribution of atmospheric electric potential in exchange layer of maritime clean atmosphere. The transport of space charge in electrode layer acts as a convective generator in this model and plays a major role in determining potential distribution in vertical. Eddy diffusion is the main mechanism responsible for the distribution of space charge in vertical. Our results show that potential at a particular level increases with increase in the strength of eddy diffusion under similar conditions. A method is suggested to estimate columnar resistance, the ionospheric potential and the vertical atmospheric electric potential distribution in exchange layer from measurements of total air-earth current density and surface electric field made over oceans. The results are validated and found to be in very good agreement with the previous aircraft measurements. Different parameters involved in the proposed methodology can be determined either theoretically, as in the present work, or experimentally using the near surface atmospheric electrical measurements or using some other surface-based measurement technique such as LIDAR. A graphical relationship between the atmospheric eddy diffusion coefficient and height of exchange layer obtained from atmospheric electrical approach, is reported.

Enhancement in ion adsorption rate and desalination efficiency in a capacitive deionization cell through improved electric field distribution using electrodes composed of activated carbon cloth coated with zinc oxide nanorods.

PubMed

Laxman, Karthik; Myint, Myo Tay Zar; Bourdoucen, Hadj; Dutta, Joydeep

2014-07-09

Electrodes composed of activated carbon cloth (ACC) coated with zinc oxide (ZnO) nanorods are compared with plain ACC electrodes, with respect to their desalination efficiency of a 17 mM NaCl solution at different applied potentials. Polarization of the ZnO nanorods increased the penetration depth and strength of the electric field between the electrodes, leading to an increase in the capacitance and charge efficiency at reduced input charge ratios. Uniform distribution of the electric field lines between two electrodes coated with ZnO nanorods led to faster ion adsorption rates, reduced the electrode saturation time, and increased the average desalination efficiency by ∼45% for all applied potentials. The electrodes were characterized for active surface area, capacitance from cyclic voltammetry, theoretical assessment of surface area utilization, and the magnitude of electric field force acting on an ion of unit charge for each potential.

Extended hierarchical solvent perturbations from curved surfaces of mesoporous silica particles in a deep eutectic solvent.

PubMed

Hammons, Joshua A; Zhang, Fan; Ilavsky, Jan

2018-06-15

Many applications of deep eutectic solvents (DES) rely on exploitation of their unique yet complex liquid structures. Due to the ionic nature of the DES components, their diffuse structures are perturbed in the presence of a charged surface. We hypothesize that it is possible to perturb the bulk DES structure far (>100 nm) from a curved, charged surface with mesoscopic dimensions. We performed in situ, synchrotron-based ultra-small angle X-ray scattering (USAXS) experiments to study the solvent distribution near the surface of charged mesoporous silica particles (MPS) (≈0.5 µm in diameter) suspended in both water and a common type of DES (1:2 choline Cl-:ethylene glycol). A careful USAXS analysis reveals that the perturbation of electron density distribution within the DES extends ≈1 μm beyond the particle surface, and that this perturbation can be manipulated by the addition of salt ions (AgCl). The concentration of the pore-filling fluid is greatly reduced in the DES. Notably, we extracted the real-space structures of these fluctuations from the USAXS data using a simulated annealing approach that does not require a priori knowledge about the scattering form factor, and can be generalized to a wide range of complex small-angle scattering problems. Copyright © 2018 Elsevier Inc. All rights reserved.

Structural, vibrational spectroscopic and quantum chemical studies on indole-3-carboxaldehyde

NASA Astrophysics Data System (ADS)

Premkumar, R.; Asath, R. Mohamed; Mathavan, T.; Benial, A. Milton Franklin

2017-05-01

The potential energy surface (PES) scan was performed for indole-3-carboxaldehyde (ICA) and the most stable optimized conformer was predicted using DFT/B3LYP method with 6-31G basis set. The vibrational frequencies of ICA were theoretically calculated by the DFT/B3LYP method with cc-pVTZ basis set using Gaussian 09 program. The vibrational spectra were experimentally recorded by Fourier transform-infrared (FT-IR) and Fourier transform-Raman spectrometer (FT-Raman). The computed vibrational frequencies were scaled by scaling factors to yield a good agreement with observed vibrational frequencies. The theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of potential energy distribution (PED) calculation using VEDA 4.0 program. The molecular interaction, stability and intramolecular charge transfer of ICA were studied using frontier molecular orbitals (FMOs) analysis and Mulliken atomic charge distribution shows the distribution of the atomic charges. The presence of intramolecular charge transfer was studied using natural bond orbital (NBO) analysis.

Capillary electrophoresis of covalently functionalized single-chirality carbon nanotubes.

PubMed

He, Pingli; Meany, Brendan; Wang, Chunyan; Piao, Yanmei; Kwon, Hyejin; Deng, Shunliu; Wang, YuHuang

2017-07-01

We demonstrate the separation of chirality-enriched single-walled carbon nanotubes (SWCNTs) by degree of surface functionalization using high-performance CE. Controlled amounts of negatively charged and positively charged functional groups were attached to the sidewall of chirality-enriched SWCNTs through covalent functionalization using 4-carboxybenzenediazonium tetrafluoroborate or 4-diazo-N,N-diethylaniline tetrafluoroborate, respectively. Surfactant- and pH-dependent studies confirmed that under conditions that minimized ionic screening effects, separation of these functionalized SWCNTs was strongly dependent on the surface charge density introduced through covalent surface chemistry. For both heterogeneous mixtures and single-chirality-enriched samples, covalently functionalized SWCNTs showed substantially increased peak width in electropherogram spectra compared to nonfunctionalized SWCNTs, which can be attributed to a distribution of surface charges along the functionalized nanotubes. Successful separation of functionalized single-chirality SWCNTs by functional density was confirmed with UV-Vis-NIR absorption and Raman scattering spectroscopies of fraction collected samples. These results suggest a high degree of structural heterogeneity in covalently functionalized SWCNTs, even for chirality-enriched samples, and show the feasibility of applying CE for high-performance separation of nanomaterials based on differences in surface functional density. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microporous nano-MgO/diatomite ceramic membrane with high positive surface charge for tetracycline removal.

PubMed

Meng, Xian; Liu, Zhimeng; Deng, Cheng; Zhu, Mengfu; Wang, Deyin; Li, Kui; Deng, Yu; Jiang, Mingming

2016-12-15

A novel microporous nano-MgO/diatomite ceramic membrane with high positive surface charge was prepared, including synthesis of precursor colloid, dip-coating and thermal decomposition. Combined SEM, EDS, XRD and XPS studies show the nano-MgO is irregularly distributed on the membrane surface or pore walls and forms a positively charged nano coating. And the nano-MgO coating is firmly attached to the diatomite membrane via SiO chemical bond. Thus the nano-MgO/diatomite membrane behaves strong electropositivity with the isoelectric point of 10.8. Preliminary filtration tests indicate that the as-prepared nano-MgO/diatomite membrane could remove approximately 99.7% of tetracycline in water through electrostatic adsorption effect. The desirable electrostatic property enables the nano-MgO/diatomite membrane to be a candidate for removal of organic pollutants from water. And it is convinced that there will be a great application prospect of charged ceramic membrane in water treatment field. Copyright © 2016 Elsevier B.V. All rights reserved.

Beyond the continuum: how molecular solvent structure affects electrostatics and hydrodynamics at solid-electrolyte interfaces.

PubMed

Bonthuis, Douwe Jan; Netz, Roland R

2013-10-03

Standard continuum theory fails to predict several key experimental results of electrostatic and electrokinetic measurements at aqueous electrolyte interfaces. In order to extend the continuum theory to include the effects of molecular solvent structure, we generalize the equations for electrokinetic transport to incorporate a space dependent dielectric profile, viscosity profile, and non-electrostatic interaction potential. All necessary profiles are extracted from atomistic molecular dynamics (MD) simulations. We show that the MD results for the ion-specific distribution of counterions at charged hydrophilic and hydrophobic interfaces are accurately reproduced using the dielectric profile of pure water and a non-electrostatic repulsion in an extended Poisson-Boltzmann equation. The distributions of Na(+) at both surface types and Cl(-) at hydrophilic surfaces can be modeled using linear dielectric response theory, whereas for Cl(-) at hydrophobic surfaces it is necessary to apply nonlinear response theory. The extended Poisson-Boltzmann equation reproduces the experimental values of the double-layer capacitance for many different carbon-based surfaces. In conjunction with a generalized hydrodynamic theory that accounts for a space dependent viscosity, the model captures the experimentally observed saturation of the electrokinetic mobility as a function of the bare surface charge density and the so-called anomalous double-layer conductivity. The two-scale approach employed here-MD simulations and continuum theory-constitutes a successful modeling scheme, providing basic insight into the molecular origins of the static and kinetic properties of charged surfaces, and allowing quantitative modeling at low computational cost.

Dust particles investigation for future Russian lunar missions.

NASA Astrophysics Data System (ADS)

Dolnikov, Gennady; Horanyi, Mihaly; Esposito, Francesca; Zakharov, Alexander; Popel, Sergey; Afonin, Valeri; Borisov, Nikolay; Seran, Elena; Godefroy, Michel; Shashkova, Inna; Kuznetsov, Ilya; Lyash, Andrey; Vorobyova, Elena; Petrov, Oleg; Lisin, Evgeny

One of the complicating factors of the future robotic and human lunar landing missions is the influence of the dust. Meteorites bombardment has accompanied by shock-explosive phenomena, disintegration and mix of the lunar soil in depth and on area simultaneously. As a consequence, the lunar soil has undergone melting, physical and chemical transformations. Recently we have the some reemergence for interest of Moon investigation. The prospects in current century declare USA, China, India, and European Union. In Russia also prepare two missions: Luna-Glob and Luna-Resource. Not last part of investigation of Moon surface is reviewing the dust condition near the ground of landers. Studying the properties of lunar dust is important both for scientific purposes to investigation the lunar exosphere component and for the technical safety of lunar robotic and manned missions. The absence of an atmosphere on the Moon's surface is leading to greater compaction and sintering. Properties of regolith and dust particles (density, temperature, composition, etc.) as well as near-surface lunar exosphere depend on solar activity, lunar local time and position of the Moon relative to the Earth's magneto tail. Upper layers of regolith are an insulator, which is charging as a result of solar UV radiation and the constant bombardment of charged particles, creates a charge distribution on the surface of the moon: positive on the illuminated side and negative on the night side. Charge distribution depends on the local lunar time, latitude and the electrical properties of the regolith (the presence of water in the regolith can influence the local distribution of charge). On light side of Moon near surface layer there exists possibility formation dusty plasma system. Altitude of levitation is depending from size of dust particle and Moon latitude. The distribution dust particle by size and altitude has estimated with taking into account photoelectrons, electrons and ions of solar wind, solar emission. Dust analyzer instrument PmL for future Russian lender missons intends for investigation the dynamics of dusty plasma near lunar surface. PmL consist of three blocks: Impact Sensor and two Electric Field Sensors. Dust Experiment goals are: 1) Impact sensor to investigate the dynamics of dust particles near the lunar surface (speed, charge, mass, vectors of a fluxes) a) high speed micrometeorites b) secondary particles after micrometeorites soil bombardment c) levitating dust particles due to electrostatic fields PmL instrument will measure dust particle impulses. In laboratory tests we used - min impulse so as 7•10-11 N•c, by SiO2 dust particles, 20-40 µm with velocity about 0,5 -2,5 m/c, dispersion 0.3, and - max impulse was 10-6 N•c with possibility increased it by particles Pb-Sn 0,7 mm with velocity 1 m/c, dispersion ±0.3. Also Impact Sensor will measure the charge of dust particle as far as 10-15 C ( 1000 electrons). In case the charge and impulse of a dust particle are measured we can obtain velocity and mass of them. 2) Electric field Sensor will measure the value and dynamics of the electric fields the lunar surface. Two Electric Field Sensors both are measured the concentration and temperature of charged particles (electrons, ions, dust particles). Uncertainty of measurements is 10%. Electric Field Sensors contain of Lengmure probe. Using Lengmure probe to dark and light Moon surface we can obtain the energy spectra photoelectrons in different period of time. PmL instrument is developing, working out and manufacturing in IKI. Simultaneously with the PmL dust instrument to study lunar dust it would be very important to use an onboard TV system adjusted for imaging physical properties of dust on the lunar surface (adhesion, albedo, porosity, etc), and to collect dust particles samples from the lunar surface to return these samples to the Earth for measure a number of physic-chemical properties of the lunar dust, e.g. a quantum yield of photoemission, what is very important for modeling physical processes in the lunar exosphere.

Active species delivered by dielectric barrier discharge filaments to bacteria biofilms on the surface of apple

NASA Astrophysics Data System (ADS)

Cheng, He; Liu, Xin; Lu, Xinpei; Liu, Dawei

2016-07-01

The atmospheric pressure non-equilibrium plasma has shown a significant potential as a novel food decontamination technology. In this paper, we report a computational study of the intersection of negative streamer produced by air dielectric barrier discharge with bacteria biofilm on an apple surface. The structure, conductivities, and permittivities of bacteria biofilm have been considered in the Poisson's equations and transportation equations of charge and neutral species to realize self-consistent transportation of plasma between electrode and charging surfaces of apple. We find that the ionization near the biofilm facilitates the propagation of negative streamer when the streamer head is 1 mm from the biofilm. The structure of the biofilm results in the non-uniform distribution of ROS and RNS captured by flux and time fluence of these reactive species. The mean free path of charged species in μm scale permitted the plasma penetrate into the cavity of the biofilm, therefore, although the density of ROS and RNS decrease by 6-7 order of magnitude, the diffusion results in the uniform distribution of ROS and RNS inside the cavity during the pulse off period.

Electrification of particulate entrained fluid flows-Mechanisms, applications, and numerical methodology

NASA Astrophysics Data System (ADS)

Wei, Wei; Gu, Zhaolin

2015-10-01

Particulates in natural and industrial flows have two basic forms: liquid (droplet) and solid (particle). Droplets would be charged in the presence of the applied electric field (e.g. electrospray). Similar to the droplet charging, particles can also be charged under the external electric field (e.g. electrostatic precipitator), while in the absence of external electric field, tribo-electrostatic charging is almost unavoidable in gas-solid two-phase flows due to the consecutive particle contacts (e.g. electrostatic in fluidized bed or wind-blown sand). The particle charging may be beneficial, or detrimental. Although electrostatics in particulate entrained fluid flow systems have been so widely used and concerned, the mechanisms of particulate charging are still lack of a thorough understanding. The motivation of this review is to explore a clear understanding of particulate charging and movement of charged particulate in two-phase flows, by summarizing the electrification mechanisms, physical models of particulate charging, and methods of charging/charged particulate entrained fluid flow simulations. Two effective methods can make droplets charged in industrial applications: corona charging and induction charging. The droplet charge to mass ratio by corona charging is more than induction discharge. The particle charging through collisions could be attributed to electron transfer, ion transfer, material transfer, and/or aqueous ion shift on particle surfaces. The charges on charged particulate surface can be measured, nevertheless, the charging process in nature or industry is difficult to monitor. The simulation method might build a bridge of investigating from the charging process to finally charged state on particulate surface in particulate entrained fluid flows. The methodology combining the interface tracking under the action of the applied electric with the fluid flow governing equations is applicable to the study of electrohydrodynamics problems. The charge distribution and mechanical behaviors of liquid surface can be predicted by using this method. The methodology combining particle charging model with Computational Fluid Dynamics (CFD) and Discrete element method (DEM) is applicable to study the particle charging/charged processes in gas-solid two phase flows, the influence factors of particle charging, such as gas-particle interaction, contact force, contact area, and various velocities, are described systematically. This review would explore a clear understanding of the particulate charging and provide theoretical references to control and utilize the charging/charged particulate entrained fluid system.

Using supramolecular binding motifs to provide precise control over the ratio and distribution of species in multiple component films grafted on surfaces: demonstration using electrochemical assembly from aryl diazonium salts.

PubMed

Gui, Alicia L; Yau, Hon Man; Thomas, Donald S; Chockalingam, Muthukumar; Harper, Jason B; Gooding, J Justin

2013-04-16

Supramolecular interactions between two surface modification species are explored to control the ratio and distribution of these species on the resultant surface. A binary mixture of aryl diazonium salts bearing oppositely charged para-substituents (either -SO3(-) or -N(+)(Me)3), which also reduce at different potentials, has been examined on glassy carbon surfaces using cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Striking features were observed: (1) the two aryl diazonium salts in the mixed solution undergo reductive adsorption at the same potential which is distinctively less negative than the potential required for the reduction of either of the two aryl diazonium salts alone; (2) the surface ratio of the two phenyl derivatives is consistently 1:1 regardless of the ratio of the two aryl diazonium salts in the modification solutions. Homogeneous distribution of the two oppositely charged phenyl species on the modified surface has also been suggested by XPS survey spectra. Diffusion coefficient measurements by DOSY NMR and DFT based computation have indicated the association of the two aryl diazonium species in the solution, which has led to changes in the molecular orbital energies of the two species. This study highlights the potential of using intermolecular interactions to control the assembly of multicomponent thin layers.

Controlling the Charge State and Redox Properties of Supported Polyoxometalates via Soft Landing of Mass Selected Ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunaratne, Kalupathirannehelage Don D.; Johnson, Grant E.; Andersen, Amity

2014-12-04

We investigate the controlled deposition of Keggin polyoxometalate (POM) anions, PMo12O403- and PMo12O402-, onto different self-assembled monolayer (SAM) surfaces via soft landing of mass-selected ions. Utilizing in situ infrared reflection absorption spectroscopy (IRRAS), ex situ cyclic voltammetry (CV) and electronic structure calculations, we examine the structure and charge retention of supported multiply-charged POM anions and characterize the redox properties of the modified surfaces. SAMs of alkylthiol (HSAM), perfluorinated alkylthiol (FSAM), and alkylthiol terminated with NH3+ functional groups (NH3+SAM) are chosen as model substrates for soft landing to examine the factors which influence the immobilization and charge retention of multiply chargedmore » anionic molecules. The distribution of charge states of POMs on different SAM surfaces are determined by comparing the IRRAS spectra with vibrational spectra calculated using density functional theory (DFT). In contrast to the results obtained previously for multiply charged cations, soft landed anions are found to retain charge on all three SAM surfaces. This charge retention is attributed to the substantial electron binding energy of the POM anions. Investigation of redox properties by CV reveals that, while surfaces prepared by soft landing exhibit similar features to those prepared by adsorption of POM from solution, the soft landed POM2- has a pronounced shift in oxidation potential compared to POM3- for one of the redox couples. These results demonstrate that ion soft landing is uniquely suited for precisely controlled preparation of substrates with specific electronic and chemical properties that cannot be achieved using conventional deposition techniques.« less

Mechanisms of Polyelectrolyte Enhanced Surfactant Adsorption at the Air-Water Interface

PubMed Central

Stenger, Patrick C.; Palazoglu, Omer A.; Zasadzinski, Joseph A.

2009-01-01

Chitosan, a naturally occurring cationic polyelectrolyte, restores the adsorption of the clinical lung surfactant Survanta to the air-water interface in the presence of albumin at much lower concentrations than uncharged polymers such as polyethylene glycol. This is consistent with the positively charged chitosan forming ion pairs with negative charges on the albumin and lung surfactant particles, reducing the net charge in the double-layer, and decreasing the electrostatic energy barrier to adsorption to the air-water interface. However, chitosan, like other polyelectrolytes, cannot perfectly match the charge distribution on the surfactant, which leads to patches of positive and negative charge at net neutrality. Increasing the chitosan concentration further leads to a reduction in the rate of surfactant adsorption consistent with an over-compensation of the negative charge on the surfactant and albumin surfaces, which creates a new repulsive electrostatic potential between the now cationic surfaces. This charge neutralization followed by charge inversion explains the window of polyelectrolyte concentration that enhances surfactant adsorption; the same physical mechanism is observed in flocculation and re-stabilization of anionic colloids by chitosan and in alternate layer deposition of anionic and cationic polyelectrolytes on charged colloids. PMID:19366599

Mechanisms of polyelectrolyte enhanced surfactant adsorption at the air-water interface.

PubMed

Stenger, Patrick C; Palazoglu, Omer A; Zasadzinski, Joseph A

2009-05-01

Chitosan, a naturally occurring cationic polyelectrolyte, restores the adsorption of the clinical lung surfactant Survanta to the air-water interface in the presence of albumin at much lower concentrations than uncharged polymers such as polyethylene glycol. This is consistent with the positively charged chitosan forming ion pairs with negative charges on the albumin and lung surfactant particles, reducing the net charge in the double-layer, and decreasing the electrostatic energy barrier to adsorption to the air-water interface. However, chitosan, like other polyelectrolytes, cannot perfectly match the charge distribution on the surfactant, which leads to patches of positive and negative charge at net neutrality. Increasing the chitosan concentration further leads to a reduction in the rate of surfactant adsorption consistent with an over-compensation of the negative charge on the surfactant and albumin surfaces, which creates a new repulsive electrostatic potential between the now cationic surfaces. This charge neutralization followed by charge inversion explains the window of polyelectrolyte concentration that enhances surfactant adsorption; the same physical mechanism is observed in flocculation and re-stabilization of anionic colloids by chitosan and in alternate layer deposition of anionic and cationic polyelectrolytes on charged colloids.

The Limitations of an Exclusively Colloidal View of Protein Solution Hydrodynamics and Rheology

PubMed Central

Sarangapani, Prasad S.; Hudson, Steven D.; Migler, Kalman B.; Pathak, Jai A.

2013-01-01

Proteins are complex macromolecules with dynamic conformations. They are charged like colloids, but unlike colloids, charge is heterogeneously distributed on their surfaces. Here we overturn entrenched doctrine that uncritically treats bovine serum albumin (BSA) as a colloidal hard sphere by elucidating the complex pH and surface hydration-dependence of solution viscosity. We measure the infinite shear viscosity of buffered BSA solutions in a parameter space chosen to tune competing long-range repulsions and short-range attractions (2 mg/mL ≤ [BSA] ≤ 500 mg/mL and 3.0 ≤ pH ≤ 7.4). We account for surface hydration through partial specific volume to define volume fraction and determine that the pH-dependent BSA intrinsic viscosity never equals the classical hard sphere result (2.5). We attempt to fit our data to the colloidal rheology models of Russel, Saville, and Schowalter (RSS) and Krieger-Dougherty (KD), which are each routinely and successfully applied to uniformly charged suspensions and to hard-sphere suspensions, respectively. We discover that the RSS model accurately describes our data at pH 3.0, 4.0, and 5.0, but fails at pH 6.0 and 7.4, due to steeply rising solution viscosity at high concentration. When we implement the KD model with the maximum packing volume fraction as the sole floating parameter while holding the intrinsic viscosity constant, we conclude that the model only succeeds at pH 6.0 and 7.4. These findings lead us to define a minimal framework for models of crowded protein solution viscosity wherein critical protein-specific attributes (namely, conformation, surface hydration, and surface charge distribution) are addressed. PMID:24268154

Material influence on hot spot distribution in the nanoparticle heterodimer on film

NASA Astrophysics Data System (ADS)

Chen, Fang; Huang, Yingzhou; Wei, Hua; Wang, Shuxia; Zeng, Xiping; Cao, Wenbin; Wen, Weijia

2018-04-01

The metal nanoparticle aggregated on film, as an effective plasma enhancement pathway, has been widely used in various surface plasmon-related fields. In this study, the hot spots on the metal nanoparticle dimer composed of different materials (Agsbnd Au, Agsbnd Pd, and Agsbnd Cu) on metal (Au) film were investigated with finite element method. Based on the results, the hot spot distribution affected by the material can be confirmed by the electric field distribution of the metal nanoparticle dimer on the film. The aggregation effects of Au and Ag nanoparticles in Ausbnd Ag dimer system are not significant. However, for the Pdsbnd Ag dimer system, the hot spot aggregation effect is slightly larger than that of the Pd nanoparticle under the Ag nanoparticle. Besides, the non-uniform hot spots would bring about the light focusing phenomenon that the light intensity under Ag nanoparticle is almost 100 times greater than that under Cu nanoparticle in Agsbnd Cu dimer system. These results were further confirmed by the surface charge distribution, and analyzed based on the plasmonic hybridization theory. The data about the nanoparticle dimer on the dielectric (Si) film demonstrate the importance of induced image charges on the film surface in such a light focusing phenomenon. Our findings can enhance the understanding of the surface plasmon coupling in different materials, which may have great application prospects in surface plasmon-related fields, such as SERS, plasmonic enhanced solar cell, and plasmonic sensoring, etc.

Numerical investigation of the spatiotemporal distribution of chemical species in an atmospheric surface barrier-discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, M. I.; Walsh, J. L., E-mail: jlwalsh@liverpool.ac.uk

Using a one dimensional time dependent convection-reaction-diffusion model, the temporal and spatial distributions of species propagating downstream of an atmospheric pressure air surface barrier discharge was studied. It was found that the distribution of negatively charged species is more spatially spread compared to positive ions species, which is attributed to the diffusion of electrons that cool down and attach to background gas molecules, creating different negative ions downstream of the discharge region. Given the widespread use of such discharges in applications involving the remote microbial decontamination of surfaces and liquids, the transport of plasma generated reactive species away from themore » discharge region was studied by implementing mechanical convection through the discharge region. It was shown that increased convection causes the spatial distribution of species density to become uniform. It was also found that many species have a lower density close to the surface of the discharge as convection prevents their accumulation. While for some species, such as NO{sub 2}, convection causes a general increase in the density due to a reduced residence time close to the discharge region, where it is rapidly lost through reactions with OH. The impact of the applied power was also investigated, and it was found that the densities of most species, whether charged or neutral, are directly proportional to the applied power.« less

Investigation of ultrahigh sensitivity in GaInAsP nanolaser biosensor

NASA Astrophysics Data System (ADS)

Saijo, Yoshito; Watanabe, Takumi; Hasegawa, Yu; Nishijima, Yoshiaki; Baba, Toshihiko

2018-02-01

We have developed GaInAsP semiconductor photonic crystal nanolaser biosensor and demonstrated the detection of ultralow-concentration (fM to aM) proteins and deoxyribonucleic acids (DNAs) adsorbed on the device surface. In general, this type of photonic sensors exploiting optical resonance has been considered to detect the refractive index of biomolecules via the wavelength shift. However, this principle cannot explain the detection of such ultralowconcentration. Therefore, we investigated another candidate principle, i.e., ion sensitivity. We consider such a process that 1) the electric charge of biomolecules changes the nanolaser's surface charge, 2) the Schottky barrier near the semiconductor surface is increased or decreased, 3) the distribution of photopumped carriers is modified by the barrier, 4) the refractive index of the semiconductor is changed by the carrier effects, and 5) the laser wavelength shifts. To confirm this process, we electrochemically measured the zeta and flatband potentials when charged electrolyte polymers were adsorbed in water. We clearly observed that these potentials temporally behaved consistently with that of the laser wavelength, which suggests that polymers significantly acted on the Schottky barrier. The same behaviors were also observed for the adsorption of 1 fM DNA. We consider that a limited number of charged DNA changed the surface functional group of the entire device surface. Such charge effects will be the key that achieves the ultrahigh sensitivity in the nanolaser biosensor.

The structure and properties of a simple model mixture of amphiphilic molecules and ions at a solid surface

NASA Astrophysics Data System (ADS)

Pizio, O.; Sokołowski, S.; Sokołowska, Z.

2014-05-01

We investigate microscopic structure, adsorption, and electric properties of a mixture that consists of amphiphilic molecules and charged hard spheres in contact with uncharged or charged solid surfaces. The amphiphilic molecules are modeled as spheres composed of attractive and repulsive parts. The electrolyte component of the mixture is considered in the framework of the restricted primitive model (RPM). The system is studied using a density functional theory that combines fundamental measure theory for hard sphere mixtures, weighted density approach for inhomogeneous charged hard spheres, and a mean-field approximation to describe anisotropic interactions. Our principal focus is in exploring the effects brought by the presence of ions on the distribution of amphiphilic particles at the wall, as well as the effects of amphiphilic molecules on the electric double layer formed at solid surface. In particular, we have found that under certain thermodynamic conditions a long-range translational and orientational order can develop. The presence of amphiphiles produces changes of the shape of the differential capacitance from symmetric or non-symmetric bell-like to camel-like. Moreover, for some systems the value of the potential of the zero charge is non-zero, in contrast to the RPM at a charged surface.

Determination of trap distributions from current characteristics of pentacene field-effect transistors with surface modified gate oxide

NASA Astrophysics Data System (ADS)

Scheinert, Susanne; Pernstich, Kurt P.; Batlogg, Bertram; Paasch, Gernot

2007-11-01

It has been demonstrated [K. P. Pernstich, S. Haas, D. Oberhoff, C. Goldmann, D. J. Gundlach, B. Batlogg, A. N. Rashid, and G. Schitter, J. Appl. Phys. 96, 6431 (2004)] that a controllable shift of the threshold voltage in pentacene thin film transistors is caused by the use of organosilanes with different functional groups forming a self-assembled monolayer (SAM) on the gate oxide. The observed broadening of the subthreshold region indicates that the SAM creates additional trap states. Indeed, it is well known that traps strongly influence the behavior of organic field-effect transistors (OFETs). Therefore, the so-called "amorphous silicon (a-Si) model" has been suggested to be an appropriate model to describe OFETs. The main specifics of this model are transport of carriers above a mobility edge obeying Boltzmann statistics and exponentially distributed tail states and deep trap states. Here, approximate trap distributions are determined by adjusting two-dimensional numerical simulations to the experimental data. It follows from a systematic variation of parameters describing the trap distributions that the existence of both donorlike and acceptorlike trap distributions near the valence band, respectively, and a fixed negative interface charge have to be assumed. For two typical devices with different organosilanes the electrical characteristics can be described well with a donorlike bulk trap distribution, an acceptorlike interface distribution, and/or a fixed negative interface charge. As expected, the density of the fixed or trapped interface charge depends strongly on the surface treatment of the dielectric. There are some limitations in determining the trap distributions caused by either slow time-dependent processes resulting in differences between transfer and output characteristics, or in the uncertainty of the effective mobility.

Studies in electron phenomena in MOS structures: The pulsed C-V method. M.S. Thesis. Abstract Only

NASA Technical Reports Server (NTRS)

Kaplan, G.

1983-01-01

The pulse hysteresis capacitance voltage (C-V) provides a straight forward technique for measuring the change of various charges in MOS structures and a tool for investigating the kinetics of various electron phenomena is developed and described. The method can be used for measuring the energy distribution and kinetics of surface states with the resolution of about 1/5 x 10 to the -9 power cm eV. Some transients in an MOS structure, particularly, the thermal generation of minority charge carriers via surface states and the relaxation of minority charge carriers supplied from the inversion layer outside the MOS structure are theoretically investigated. Analytical expressions which clearly present the physics of those electron phenomena are derived.

Investigation of dust particles with future Russian lunar missions: achievements of further development of PmL instrument.

NASA Astrophysics Data System (ADS)

Kuznetsov, Ilya; Zakharov, Alexander; Afonin, Valeri; Seran, Elena; Godefroy, Michel; Shashkova, Inna; Lyash, Andrey; Dolnikov, Gennady; Popel, Sergey; Lisin, Evgeny

2016-07-01

One of the complicating factors of the future robotic and human lunar landing missions is the influence of the dust. Meteorites bombardment has accompanied by shock-explosive phenomena, disintegration and mix of the lunar soil in depth and on area simultaneously. As a consequence, the lunar soil has undergone melting, physical and chemical transformations. Recently we have the some reemergence for interest of Moon investigation. The prospects in current century declare USA, China, India, and European Union. In Russia also prepare two missions: Luna-Glob and Luna-Resource. Not last part of investigation of Moon surface is reviewing the dust condition near the ground of landers. Studying the properties of lunar dust is important both for scientific purposes to investigation the lunar exosphere component and for the technical safety of lunar robotic and manned missions. The absence of an atmosphere on the Moon's surface is leading to greater compaction and sintering. Properties of regolith and dust particles (density, temperature, composition, etc.) as well as near-surface lunar exosphere depend on solar activity, lunar local time and position of the Moon relative to the Earth's magneto tail. Upper layers of regolith are an insulator, which is charging as a result of solar UV radiation and the constant bombardment of charged particles, creates a charge distribution on the surface of the moon: positive on the illuminated side and negative on the night side. Charge distribution depends on the local lunar time, latitude and the electrical properties of the regolith (the presence of water in the regolith can influence the local distribution of charge). On the day side of Moon near surface layer there exists possibility formation dusty plasma system. Altitude of levitation is depending from size of dust particle and Moon latitude. The distribution of dust particles by size and altitude has estimated with taking into account photoelectrons, electrons and ions of solar wind, solar emission. Dust analyzer instrument PmL for future Russian lander missions intends for investigation the dynamics of dusty plasma near lunar surface. PmL consists of three parts in the case of Luna-Glob: Impact Sensor and two Electric Field Sensors (EFC). There are 9 parts of PmL instrument for Luna-Resource mission: two Impact Sensors, 5 EFC (three on the Boom and two on the lander) and 2 Solar Wind and Dust Analyzers. These days the engineering model of PmL for LG-mission is finished. We obtained first practical results from the simulating chambers with dust particles injectors and plasma inside. All the important achievements are presented in this report as well as the roadmap for further development of PmL instruments in both of Russian lunar missions.

Ion transport in a pH-regulated nanopore.

PubMed

Yeh, Li-Hsien; Zhang, Mingkan; Qian, Shizhi

2013-08-06

Fundamental understanding of ion transport phenomena in nanopores is crucial for designing the next-generation nanofluidic devices. Due to surface reactions of dissociable functional groups on the nanopore wall, the surface charge density highly depends upon the proton concentration on the nanopore wall, which in turn affects the electrokinetic transport of ions, fluid, and particles within the nanopore. Electrokinetic ion transport in a pH-regulated nanopore, taking into account both multiple ionic species and charge regulation on the nanopore wall, is theoretically investigated for the first time. The model is verified by the experimental data of nanopore conductance available in the literature. The results demonstrate that the spatial distribution of the surface charge density at the nanopore wall and the resulting ion transport phenomena, such as ion concentration polarization (ICP), ion selectivity, and conductance, are significantly affected by the background solution properties, such as the pH and salt concentration.

Impact of local electrostatic field rearrangement on field ionization

NASA Astrophysics Data System (ADS)

Katnagallu, Shyam; Dagan, Michal; Parviainen, Stefan; Nematollahi, Ali; Grabowski, Blazej; Bagot, Paul A. J.; Rolland, Nicolas; Neugebauer, Jörg; Raabe, Dierk; Vurpillot, François; Moody, Michael P.; Gault, Baptiste

2018-03-01

Field ion microscopy allows for direct imaging of surfaces with true atomic resolution. The high charge density distribution on the surface generates an intense electric field that can induce ionization of gas atoms. We investigate the dynamic nature of the charge and the consequent electrostatic field redistribution following the departure of atoms initially constituting the surface in the form of an ion, a process known as field evaporation. We report on a new algorithm for image processing and tracking of individual atoms on the specimen surface enabling quantitative assessment of shifts in the imaged atomic positions. By combining experimental investigations with molecular dynamics simulations, which include the full electric charge, we confirm that change is directly associated with the rearrangement of the electrostatic field that modifies the imaging gas ionization zone. We derive important considerations for future developments of data reconstruction in 3D field ion microscopy, in particular for precise quantification of lattice strains and characterization of crystalline defects at the atomic scale.

Brownian Dynamics Simulations of Polyelectrolyte Adsorption in Shear Flow

NASA Astrophysics Data System (ADS)

Panwar, Ajay

2005-03-01

The adsorption of polyelectrolytes onto charged surfaces often occurs in microfludic devices and can influence their operation. We employ Brownian dynamics simulations to investigate the effect of a simple shear flow on the adsorption of an isolated polyelectrolyte molecule onto an oppositely charged surface. The polyelectrolyte is modeled as a freely-jointed bead-rod chain where the total charge is distributed uniformly among all the beads, and the beads are allowed to interact with one another and the charged surface through screened Coulombic interactions. The simulations are performed by placing the chain some distance above the surface, and the adsorption behavior is studied as a function of the screening length. Specifically, we look at the components of the radius of gyration, normal and parallel to the adsorbing surface, as functions of the screening length, both in the absence and presence of the flow. We find that in the absence of flow, the chain lies flat and stretched on the adsorbing surface in the limit of weak screening, but attains free solution behavior in the limit of strong screening. In the presence of a shear flow, the chain orientation in the direction of the flow increases with increasing Weissenberg number over the entire range of screening lengths studied. We also find that increasing the strength of the shear flow leads to an increased contact of the chain with the surface compared to the case when no flow is present.

Electrohydrodynamic simulation of an electrospray in a colloid thruster

NASA Astrophysics Data System (ADS)

Jugroot, Manish; Forget, Martin; Malardier-Jugroot, Cecile

2012-02-01

A precise understanding of electrosprays is highly interesting as the complexity of micro-technology (such as nano-material processing, spacecraft propulsion and mass-spectrometers) systems increases. A multi-component CFD-based model coupling fluid dynamics, charged species dynamics and electric field is developed. The simulations describe the charged fluid interface with emphasis on the Taylor cone formation and cone-jet transition under the effect of a electric field. The goal is to recapture this transition from a rounded liquid interface into a Taylor cone from an initial uniform distribution, without making assumptions on the behaviour, geometry or charge distribution of the system. The time evolution of the interface highlights the close interaction among space charge, coulombic forces and the surface tension, which appear as governing and competing processes in the transition. The results from the coupled formalism provide valuable insights on the physical phenomena and will be applied to a colloid thruster for small spacecrafts.

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.

The influence of the breakdown electric field in the configuration of lightning corona sheath on charge distribution in the channel

NASA Astrophysics Data System (ADS)

Ignjatovic, Milan; Cvetic, Jovan; Heidler, Fridolin; Markovic, Slavoljub; Djuric, Radivoje

2014-11-01

A model of corona sheath that surrounds the thin core of the lightning channel has been investigated by using a generalized traveling current source return stroke model. The lightning channel is modeled by a charged corona sheath that stretches around a highly conductive central core through which the main current flows. The channel core with the negatively charged outer channel sheath forms a strong electric field, with an overall radial orientation. The return stroke process is modeled as the negative leader charge in the corona sheath being discharged by the positive charge coming from the channel core. Expressions that describe how the corona sheath radius evolves during the return stroke are obtained from the corona sheath model, which predicts charge motion within the sheath. The corona sheath model, set forth by Maslowski and Rakov (2006), Tausanovic et al. (2010), Marjanovic and Cvetic (2009), Cvetic et al. (2011) and Cvetic et al. (2012), divides the sheath onto three zones: zone 1 (surrounding the channel core with net positive charge), zone 2 (surrounding zone 1 with negative charge) and zone 3 (the outer zone, representing uncharged virgin air). In the present study, we have assumed a constant electric field inside zone 1, as suggested by experimental research of corona discharges in coaxial geometry conducted by Cooray (2000). The present investigation builds upon previous studies by Tausanovic et al. (2010) and Cvetic et al. (2012) in several ways. The value of the breakdown electric field has been varied for probing its effect on channel charge distribution prior and during the return stroke. With the aim of investigating initial space charge distribution along the channel, total electric field at the outer surface of the channel corona sheath, just before the return stroke, is calculated and compared for various return stroke models. A self-consistent algorithm is applied to the generalized traveling current source return stroke model, so that the boundary condition for total electric field is fulfilled. The new density of space charge and the new radius of channel corona envelope, immediately before the return stroke stage, are calculated. The obtained results indicate a strong dependence of channel charge distribution on the breakdown electric field value. Among the compared return stroke models, transmission-line-type models have exhibited a good agreement with the predictions of the Gauss' law regarding total breakdown electric field on the corona sheath's outer surface. The generalized lightning traveling current source return stroke model gives similar results if the adjustment of the space charge density inside the corona sheath is performed.

Coverage Dependent Charge Reduction of Cationic Gold Clusters on Surfaces Prepared Using Soft Landing of Mass-selected Ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Grant E.; Priest, Thomas A.; Laskin, Julia

2012-11-29

The ionic charge state of monodisperse cationic gold clusters on surfaces may be controlled by selecting the coverage of mass-selected ions soft landed onto a substrate. Polydisperse diphosphine-capped gold clusters were synthesized in solution by reduction of chloro(triphenylphosphine)gold(I) with borane tert-butylamine in the presence of 1,3-bis(diphenylphosphino)propane. The polydisperse gold clusters were introduced into the gas phase by electrospray ionization and mass selection was employed to select a multiply charged cationic cluster species (Au11L53+, m/z = 1409, L = 1,3-bis(diphenylphosphino)propane) which was delivered to the surfaces of four different self-assembled monolayers on gold (SAMs) at coverages of 1011 and 1012 clusters/mm2.more » Employing the spatial profiling capabilities of in-situ time-of-flight secondary ion mass spectrometry (TOF-SIMS) it is shown that, in addition to the chemical functionality of the monolayer (as demonstrated previously: ACS Nano, 2012, 6, 573) the coverage of cationic gold clusters on the surface may be used to control the distribution of ionic charge states of the soft-landed multiply charged clusters. In the case of a 1H,1H,2H,2H-perfluorodecanethiol SAM (FSAM) almost complete retention of charge by the deposited Au11L53+ clusters was observed at a lower coverage of 1011 clusters/mm2. In contrast, at a higher coverage of 1012 clusters/mm2, pronounced reduction of charge to Au11L52+ and Au11L5+ was observed on the FSAM. When soft landed onto 16- and 11-mercaptohexadecanoic acid surfaces on gold (16,11-COOH-SAMs), the mass-selected Au11L53+ clusters exhibited partial reduction of charge to Au11L52+ at lower coverage and additional reduction of charge to both Au11L52+ and Au11L5+ at higher coverage. The reduction of charge was found to be more pronounced on the surface of the shorter (thinner) C11 than the longer (thicker) C16-COOH-SAM. On the surface of the 1-dodecanethiol (HSAM) monolayer, the most abundant charge state was found to be Au11L52+ at lower coverage and Au11L5+ at higher coverage, respectively. A coverage-dependent electron tunneling mechanism is proposed to account for the observed reduction of charge of mass-selected multiply charged gold clusters soft landed on SAMs. The results demonstrate that one of the critical parameters that influence the chemical and physical properties of supported metal clusters, ionic charge state, may be controlled by selecting the coverage of charged species soft landed onto surfaces.« less

Formulation design space for stable, pH sensitive crystalline nifedipine nanoparticles.

PubMed

Jog, Rajan; Unachukwu, Kenechi; Burgess, Diane J

2016-11-30

Enteric coated formulations protect drugs from degrading in the harsh environment of the stomach (acidic pH and enzymes), and promotes drug delivery to and absorption into the duodenum and/or later parts of the intestine. Four DoE models were applied to optimize formulation parameters for the preparation of pH sensitive nifedipine nanoparticles. Stability studies were performed on the optimized formulations to monitor any possible variation in particle size distribution, homogeneity index, surface charge and drug release (pH 1.2 and pH 6.8). Stability studies were performed for 3 months at 4°C, 25°C and 40°C. A combination of Eudragit ® L 100-55 and polyvinyl alcohol was determined to be the most effective in stabilizing the nanoparticle suspension. The average particle size distribution, polydispersity index and surface charge of the optimized pH sensitive nifedipine nanoparticles were determined to be 131.86±8.21nm, 0.135±0.008 and -7.631±0.146mV, respectively. Following three months storage, it was observed that the formulations stored at 4°C were stable in terms of particle size distribution, polydispersity index, surface charge, drug loading and drug release, whereas those stored at 25°C and 40°C were relatively unstable. A predictive model to prepare stable pH sensitive nifedipine nanoparticles, was successfully developed using multiple linear regression analysis. Copyright © 2016 Elsevier B.V. All rights reserved.

Self-organizing layers from complex molecular anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warneke, Jonas; McBriarty, Martin E.; Riechers, Shawn L.

Ions are promising building blocks for tunable self-organizing materials with advanced technological applications. However, because of strong Coulomb attraction with counterions, the intrinsic properties of ions are difficult to exploit for preparation of bulk materials. Here, we report the precisely-controlled preparation of macroscopic surface layers by soft landing of mass selected complex anions which determine the self organization of the layers with their molecular properties. The family of halogenated dodecaborates [B12X12]2- (X = F, Cl, Br, I), in which the internal charge distribution between core and shell regions of the molecular ions systematically vary, was deposited on different self assembledmore » monolayer surfaces (SAMs) on gold at high coverage. Layers of anions were found to be stabilized by accumulation of neutral molecules. Different phases, self-organization mechanisms and optical properties were observed to depend upon the internal charge distribution of the deposited anions, the underlying surface and the coadsorbed molecules. This demonstrates rational control of the properties of anion based layers.« less

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides

NASA Astrophysics Data System (ADS)

Giocondi, Jennifer Lynn

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Electrochemical properties of polycrystalline TiO/sub 2/ electrodes prepared by anodic oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nogami, G.; Ogawa, V.; Nishiyama, Y.

1988-12-01

Polycrystalline TiO/sub 2/ electrodes were characterized by electroluminescence and capacitance-voltage measurements. The intensity of electroluminescence in a polycrystalline TiO/sub 2/ was about two orders of magnitude larger than that in a single crystalline TiO/sub 2/. Due to the intensive light emission which could be seen with the naked eye, a spectroscopic analysis by using a monochromator was possible. The emission spectrum showed a broad band peaked at 570 nm, which was assigned to a radiation recombination of a hole injected from the electrolyte with an electron on the surface state, the distribution of which was estimated from the C-V measurements.more » Mott-Schottky plots for a polycrystalline TiO/sub 2/ showed little frequency dispersion. Cole-Cole plots could be fitted by two semicircles. Through the analysis of relaxation times, charging and discharging process at the electrode surface could be clarified. The analysis of the impedance data have revealed that the surface state is distributed from the conduction bandage to the midgap in the forbidden gap. The surface-state density falls with energy from the conduction band. It has been concluded that the dynamic electron distribution of the surface states, which is determined by the competitive charge transfer process of electrons and holes injected from the electrolyte and from the semiconductor determines the luminescence characteristics of this material.« less

Charge Behaviors around Oxide Device/Pseudo-Physiological Solution Interface with Molecular Dynamic Simulations

NASA Astrophysics Data System (ADS)

Maekawa, Yuki; Shibuta, Yasushi; Sakata, Toshiya

2013-12-01

In this study, we investigated the charge behaviors of ions and water molecules at the oxide device/pseudo-physiological solution interface by use of molecular dynamics (MD) simulations because the detection principle of semiconductor-based biosensors is based on the detection of charge density changes at the oxide sensing surface in physiological environments. In particular, we designed an alpha-quartz (100) surface with some charges corresponding to pH=5.5 so that the ionic behaviors for 500 mM each of Na+ and Cl- around the interface were calculated under the surface condition with charges, considering a real system. As a result of the simulation, we defined the region of Debye length from the calculated potential distribution, in which some parameters such as diffusion coefficient and the vibration of water molecules around the interface differed from those of the bulk solution. The elucidation of the solid/liquid interfacial behaviors by the simulation technique should deepen our understanding of the detection principle of semiconductor-based biosensors and will give guidelines for the design of a bio-interface in the field of biosensing technology, because they cannot be demonstrated experimentally.

Humidity-Induced Charge Leakage and Field Attenuation in Electric Field Microsensors

PubMed Central

Zhang, Haiyan; Fang, Dongming; Yang, Pengfei; Peng, Chunrong; Wen, Xiaolong; Xia, Shanhong

2012-01-01

The steady-state zero output of static electric field measuring systems often fluctuates, which is caused mainly by the finite leakage resistance of the water film on the surface of the electric field microsensor package. The water adsorption has been calculated using the Boltzmann distribution equation at various relative humidities for borosilicate glass and polytetrafluoroethylene surfaces. At various humidities, water film thickness has been calculated, and the induced charge leakage and field attenuation have been theoretically investigated. Experiments have been performed with microsensors to verify the theoretical predictions and the results are in good agreement. PMID:22666077

(abstract) Satellite Physical Oceanography Data Available From an EOSDIS Archive

NASA Technical Reports Server (NTRS)

Digby, Susan A.; Collins, Donald J.

1996-01-01

The Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory archives and distributes data as part of the Earth Observing System Data and Information System (EOSDIS). Products available from JPL are largely satellite derived and include sea-surface height, surface-wind speed and vectors, integrated water vapor, atmospheric liquid water, sea-surface temperature, heat flux, and in-situ data as it pertains to satellite data. Much of the data is global and spans fourteen years.There is email access, a WWW site, product catalogs, and FTP capabilities. Data is free of charge.

Dusty Plasmas on the Lunar Surface

NASA Astrophysics Data System (ADS)

Horanyi, M.; Andersson, L.; Colwell, J.; Ergun, R.; Gruen, E.; McClintock, B.; Peterson, W. K.; Robertson, S.; Sternovsky, Z.; Wang, X.

2006-12-01

The electrostatic levitation and transport of lunar dust remains one of the most interesting and controversial science issues from the Apollo era. This issue is also of great engineering importance in designing human habitats and protecting optical and mechanical devices. As function of time and location, the lunar surface is exposed to solar wind plasma, UV radiation, and/or the plasma environment of our magnetosphere. Dust grains on the lunar surface collect an electrostatic charge; alter the large-scale surface charge density distribution, ?and subsequently develop an interface region to the background plasma and radiation. There are several in situ and remote sensing observations that indicate that dusty plasma processes are likely to be responsible for the mobilization and transport of lunar soil. These processes are relevant to: a) understanding the lunar surface environment; b) develop dust mitigation strategies; c) to understand the basic physical processes involved in the birth and collapse of dust loaded plasma sheaths. This talk will focus on the dusty plasma processes on the lunar surface. We will review the existing body of observations, and will also consider future opportunities for the combination of in situ and remote sensing observations. Our goals are to characterize: a) the temporal variation of the spatial and size distributions of the levitated/transported dust; and b) the surface plasma environment

Experimental-Theoretical Approach to the Adsorption Mechanisms for Anionic, Cationic, and Zwitterionic Surfactants at the Calcite-Water Interface.

PubMed

Durán-Álvarez, Agustín; Maldonado-Domínguez, Mauricio; González-Antonio, Oscar; Durán-Valencia, Cecilia; Romero-Ávila, Margarita; Barragán-Aroche, Fernando; López-Ramírez, Simón

2016-03-22

The adsorption of surfactants (DTAB, SDS, and CAPB) at the calcite-water interface was studied through surface zeta potential measurements and multiscale molecular dynamics. The ground-state polarization of surfactants proved to be a key factor for the observed behavior; correlation was found between adsorption and the hard or soft charge distribution of the amphiphile. SDS exhibits a steep aggregation profile, reaching saturation and showing classic ionic-surfactant behavior. In contrast, DTAB and CAPB featured diversified adsorption profiles, suggesting interplay between supramolecular aggregation and desorption from the solid surface and alleviating charge buildup at the carbonate surface when bulk concentration approaches CMC. This manifests as an adsorption profile with a fast initial step, followed by a metastable plateau and finalizing with a sharp decrease and stabilization of surface charge. Suggesting this competition of equilibria, elicited at the CaCO3 surface, this study provides atomistic insight into the adsorption mechanism for ionic surfactants on calcite, which is in accordance with experimental evidence and which is a relevant criterion for developing enhanced oil recovery processes.

2D Thermoluminescence imaging of dielectric surface long term charge memory of plasma surface interaction in DBD discharges

NASA Astrophysics Data System (ADS)

Ambrico, Paolo F.; Ambrico, Marianna; Schiavulli, Luigi; De Benedictis, Santolo

2014-07-01

The charge trapping effect due to the exposure of alumina surfaces to plasma has been studied in a volume dielectric barrier discharge (DBD) in Ar and He noble gases. The long lasting charge trapping of alumina dielectric plates, used as barriers in DBDs, is evidenced by an ex situ thermoluminescence (TL) experiment performed with a standard and a custom two-dimensional (2D)-TL apparatus. The spatial density of trapped surface charges is found to be strongly correlated to the plasma morphology, and the surface spatial memory lasted for several minutes to hours after plasma exposure. In the case of Ar, the plasma channel impact signature on the surface shows a higher equivalent radiation dose with respect to the surface plasma wave and the post-discharge species signature. As a consequence, for the development of discharges, inside the dielectric surface the availability of lower energy trapped electrons is larger in the first region of plasma impact. The reported spatial memory increases the likelihood of the occurrence of plasma filaments in the same position in different runs. In He plasmas, the dielectric barrier shows an almost uniform distribution of trapped charges, meaning that there is no preferred region for the development of the discharge. In all cases a slight asymmetry was shown in the direction of the gas flow. This can be interpreted as being due to the long-living species moving in the direction of the gas flow, corresponding with the TL side experiment on the sample exposed to the plasma afterglow. The maximum values and the integral of the 2D-TL images showed a linear relation with the total charge per ac cycle, corresponding with findings for the TL glow curve. In conclusion, 2D-TL images allow the retrieval of information regarding the plasma surface interaction such as the plasma morphology, trap sites and their activation temperature.

Solute location in a nanoconfined liquid depends on charge distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey, Jacob A.; Thompson, Ward H., E-mail: wthompson@ku.edu

2015-07-28

Nanostructured materials that can confine liquids have attracted increasing attention for their diverse properties and potential applications. Yet, significant gaps remain in our fundamental understanding of such nanoconfined liquids. Using replica exchange molecular dynamics simulations of a nanoscale, hydroxyl-terminated silica pore system, we determine how the locations explored by a coumarin 153 (C153) solute in ethanol depend on its charge distribution, which can be changed through a charge transfer electronic excitation. The solute position change is driven by the internal energy, which favors C153 at the pore surface compared to the pore interior, but less so for the more polar,more » excited-state molecule. This is attributed to more favorable non-specific solvation of the large dipole moment excited-state C153 by ethanol at the expense of hydrogen-bonding with the pore. It is shown that a change in molecule location resulting from shifts in the charge distribution is a general result, though how the solute position changes will depend upon the specific system. This has important implications for interpreting measurements and designing applications of mesoporous materials.« less

Influence of aspartic acid and lysine on the uptake of gold nanoparticles in rice.

PubMed

Ye, Xinxin; Li, Hongying; Wang, Qingyun; Chai, Rushan; Ma, Chao; Gao, Hongjian; Mao, Jingdong

2018-02-01

The interactions between plants and nanomaterials (NMs) can shed light on the environmental consequences of nanotechnology. We used the major crop plant rice (Oryza sativa L.) to investigate the uptake of gold nanoparticles (GNPs) coated with either negatively or positively charged ligands, over a 5-day period, in the absence or presence of one of two amino acids, aspartic acid (Asp) or lysine (Lys), acting as components of rice root exudates. The presence of Asp or Lys influenced the uptake and distribution of GNPs in rice, which depended on the electrical interaction between the coated GNPs and each amino acid. When the electrical charge of the amino acid was the same as that of the surface ligand coated onto the GNPs, the GNPs could disperse well in nutrient solution, resulting in increased uptake of GNPs into rice tissue. The opposite was true where the charge on the surface ligand was different from that on the amino acid, resulting in agglomeration and reduced Au uptake into rice tissue. The behavior of GNPs in the hydroponic nutrient solution was monitored in terms of agglomeration, particle size distribution, and surface charge in the presence and absence of Asp or Lys, which depended strongly on the electrostatic interaction. Results from this study indicated that the species of root exudates must be taken into account in assessing the bioavailability of nanomaterials to plants. Copyright © 2017 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, He; Liu, Xin; Lu, Xinpei

The atmospheric pressure non-equilibrium plasma has shown a significant potential as a novel food decontamination technology. In this paper, we report a computational study of the intersection of negative streamer produced by air dielectric barrier discharge with bacteria biofilm on an apple surface. The structure, conductivities, and permittivities of bacteria biofilm have been considered in the Poisson's equations and transportation equations of charge and neutral species to realize self-consistent transportation of plasma between electrode and charging surfaces of apple. We find that the ionization near the biofilm facilitates the propagation of negative streamer when the streamer head is 1 mm frommore » the biofilm. The structure of the biofilm results in the non-uniform distribution of ROS and RNS captured by flux and time fluence of these reactive species. The mean free path of charged species in μm scale permitted the plasma penetrate into the cavity of the biofilm, therefore, although the density of ROS and RNS decrease by 6–7 order of magnitude, the diffusion results in the uniform distribution of ROS and RNS inside the cavity during the pulse off period.« less

Hysteresis in Carbon Nanotube Transistors: Measurement and Analysis of Trap Density, Energy Level, and Spatial Distribution.

PubMed

Park, Rebecca Sejung; Shulaker, Max Marcel; Hills, Gage; Suriyasena Liyanage, Luckshitha; Lee, Seunghyun; Tang, Alvin; Mitra, Subhasish; Wong, H-S Philip

2016-04-26

We present a measurement technique, which we call the Pulsed Time-Domain Measurement, for characterizing hysteresis in carbon nanotube field-effect transistors, and demonstrate its applicability for a broad range of 1D and 2D nanomaterials beyond carbon nanotubes. The Pulsed Time-Domain Measurement enables the quantification (density, energy level, and spatial distribution) of charged traps responsible for hysteresis. A physics-based model of the charge trapping process for a carbon nanotube field-effect transistor is presented and experimentally validated using the Pulsed Time-Domain Measurement. Leveraging this model, we discover a source of traps (surface traps) unique to devices with low-dimensional channels such as carbon nanotubes and nanowires (beyond interface traps which exist in today's silicon field-effect transistors). The different charge trapping mechanisms for interface traps and surface traps are studied based on their temperature dependencies. Through these advances, we are able to quantify the interface trap density for carbon nanotube field-effect transistors (∼3 × 10(13) cm(-2) eV(-1) near midgap), and compare this against a range of previously studied dielectric/semiconductor interfaces.

A comparative study on vibrational, conformational and electronic structure of 2-chloro-4-methyl-3-nitropyridine and 2-chloro-6-methylpyridine

NASA Astrophysics Data System (ADS)

Arjunan, V.; Saravanan, I.; Marchewka, Mariusz K.; Mohan, S.

Experimental FTIR and FT-Raman spectroscopic analysis of 2-chloro-4-methyl-3-nitropyridine (2C4M3NP) and 2-chloro-6-methylpyridine (2C6MP) have been performed. A detailed quantum chemical calculations have been carried out using B3LYP and B3PW91 methods with 6-311++G** and cc-pVTZ basis sets. Conformation analysis was carried for 2C4M3NP and 2C6MP. The temperature dependence of thermodynamic properties has been analysed. The atomic charges, electronic exchange interaction and charge delocalisation of the molecule have been performed by natural bond orbital (NBO) analysis. Molecular electrostatic surface potential (MESP), total electron density distribution and frontier molecular orbitals (FMOs) are constructed at B3LYP/6-311++G** level to understand the electronic properties. The charge density distribution and site of chemical reactivity of the molecules have been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach.

Directional mass transport in an atmospheric pressure surface barrier discharge.

PubMed

Dickenson, A; Morabit, Y; Hasan, M I; Walsh, J L

2017-10-25

In an atmospheric pressure surface barrier discharge the inherent physical separation between the plasma generation region and downstream point of application reduces the flux of reactive chemical species reaching the sample, potentially limiting application efficacy. This contribution explores the impact of manipulating the phase angle of the applied voltage to exert a level of control over the electrohydrodynamic forces generated by the plasma. As these forces produce a convective flow which is the primary mechanism of species transport, the technique facilitates the targeted delivery of reactive species to a downstream point without compromising the underpinning species generation mechanisms. Particle Imaging Velocimetry measurements are used to demonstrate that a phase shift between sinusoidal voltages applied to adjacent electrodes in a surface barrier discharge results in a significant deviation in the direction of the plasma induced gas flow. Using a two-dimensional numerical air plasma model, it is shown that the phase shift impacts the spatial distribution of the deposited charge on the dielectric surface between the adjacent electrodes. The modified surface charge distribution reduces the propagation length of the discharge ignited on the lagging electrode, causing an imbalance in the generated forces and consequently a variation in the direction of the resulting gas flow.

Secondary electron emission from lunar soil by solar wind type ion impact: Laboratory measurements

NASA Astrophysics Data System (ADS)

Dukes, Catherine; Bu, Caixia; Baragiola, Raul A.

2015-11-01

Introduction: The lunar surface potential is determined by time-varying fluxes of electrons and ions from the solar wind, photoelectrons ejected by UV photons, cosmic rays, and micrometeorite impacts. Solar wind ions have a dual role in the charging process, adding positive charge to the lunar regolith upon impact and ejecting negative secondary electrons (SE). Electron emission occurs when the energy from the impacting ion is transferred to the solid, ionizing and damaging the material; electrons with kinetic energy greater than the ionization potential (band gap + electron affinity) are ejected from the solid[1].Experiment: We investigate the energy distribution of secondary electrons ejected from Apollo soils of varying maturity and lunar analogs by 4 keV He+. Soils are placed into a shallow Al cup and compressed. In-situ low-energy oxygen plasma is used to clean atmospheric contaminants from the soil before analysis[2]. X-ray photoelectron spectroscopy ascertains that the sample surface is clean. Experiments are conducted in a PHI 560 system (<10-9 Torr), equipped with a double-pass, cylindrical-mirror electron energy analyzer (CMA) and μ-metal shield. The spectrometer is used to measure SE distributions, as well as for in situ surface characterization. A small negative bias (~5V) with respect to the grounded entrance grid of the CMA may be placed on the sample holder in order to expose the low energy cutoff.To measure SE energy distributions, primary ions rastered over a ~6 x 6 mm2 area are incident on the sample at ~40° relative to the surface normal, while SE emitted with an angle of 42.3°± 3.5° in a cone are analyzed.Results: The energy distribution of SE ejected from 4 keV He ion irradiation of albite with no bias applied shows positive charging of the surface. The general shape and distribution peak (~4 eV) are consistent with spectra for low energy ions on insulating material[1].Acknowledgements: We thank the NASA LASER program for support.References: [1]P. Riccardi, R. Baragiola et al. (2004); Surf. Science 57, L305-L310. [2]C.A. Dukes & R.A. Baragiola (2010) Surface Interface Anal. 42, 40-44.

Multiple Weyl points and the sign change of their topological charges in woodpile photonic crystals

NASA Astrophysics Data System (ADS)

Chang, Ming-Li; Xiao, Meng; Chen, Wen-Jie; Chan, C. T.

2017-03-01

We show that Weyl points with topological charges 1 and 2 can be found in very simple chiral woodpile photonic crystals and the distribution of the charges can be changed by changing the material parameters without altering space-group symmetry. The underlying physics can be understood through a tight-binding model. Gapless surface states and their backscattering immune properties also are demonstrated in these systems. Obtaining Weyl points in these easily fabricated woodpile photonic crystals will facilitate the realization of Weyl point physics in optical and IR frequencies.

Ultrafiltration and nanofiltration membrane fouling by natural organic matter: Mechanisms and mitigation by pre-ozonation and pH.

PubMed

Yu, Wenzheng; Liu, Teng; Crawshaw, John; Liu, Ting; Graham, Nigel

2018-08-01

The fouling of ultrafiltration (UF) and nanofiltration (NF) membranes during the treatment of surface waters continues to be of concern and the particular role of natural organic matter (NOM) requires further investigation. In this study the effect of pH and surface charge on membrane fouling during the treatment of samples of a representative surface water (Hyde Park recreational lake) were evaluated, together with the impact of pre-ozonation. While biopolymers in the surface water could be removed by the UF membrane, smaller molecular weight (MW) fractions of NOM were poorly removed, confirming the importance of membrane pore size. For NF membranes the removal of smaller MW fractions (800 Da-10 kDa) was less than expected from their pore size; however, nearly all of the hydrophobic, humic-type substances could be removed by the hydrophilic NF membranes for all MW distributions (greater than 90%). The results indicated the importance of the charge and hydrophilic nature of the NOM. Thus, the hydrophilic NF membrane could remove the hydrophobic organic matter, but not the hydrophilic substances. Increasing charge effects (more negative zeta potentials) with increasing solution pH were found to enhance organics removal and reduce fouling (flux decline), most likely through greater membrane surface repulsion. Pre-ozonation of the surface water increased the hydrophilic fraction and anionic charge of NOM and altered their size distributions. This resulted in a decreased fouling (less flux decline) for the UF and smaller pore NF, but a slight increase in fouling for the larger pore NF. The differences in the NF behavior are believed to relate to the relative sizes of ozonated organic fractions and the NF pores; a similar size of ozonated organic fractions and the NF pores causes significant membrane fouling. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Negative differential electrolyte resistance in a solid-state nanopore resulting from electroosmotic flow bistability.

PubMed

Luo, Long; Holden, Deric A; White, Henry S

2014-03-25

A solid-state nanopore separating two aqueous solutions containing different concentrations of KCl is demonstrated to exhibit negative differential resistance (NDR) when a constant pressure is applied across the nanopore. NDR refers to a decrease in electrical current when the voltage applied across the nanopore is increased. NDR results from the interdependence of solution flow (electroosmotic and pressure-engendered) with the distributions of K+ and Cl- within the nanopore. A switch from a high-conductivity state to a low-conductivity state occurs over a very narrow voltage window (<2 mV) that depends on the nanopore geometry, electrolyte concentration, and nanopore surface charge density. Finite element simulations based on a simultaneous solution of the Navier-Stokes, Poisson, and Nernst-Planck equations demonstrate that NDR results from a positive feedback mechanism between the ion distributions and electroosmotic flow, yielding a true bistability in fluid flow and electrical current at a critical applied voltage, i.e., the NDR "switching potential". Solution pH and Ca2+ were separately employed as chemical stimuli to investigate the dependence of the NDR on the surface charge density. The NDR switching potential is remarkably sensitive to the surface charge density, and thus to pH and the presence of Ca2+, suggesting possible applications in chemical sensing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yafyasov, A. M., E-mail: yafyasov@gmail.com; Bogevolnov, V. B.; Ryumtsev, E. I.

A semiconductor—organic-insulator system with spatially distributed charge is created with a uniquely low density of fast surface states (N{sub ss}) at the interface. A system with N{sub ss} ≈ 5 × 10{sup 10} cm{sup –2} is obtained for the example of n-Ge and the physical characteristics of the interface are measured for this system with liquid and metal field electrodes. For a system with an organic insulator, the range of variation of the surface potential from enrichment of the space-charge region of the semiconductor to the inversion state is first obtained without changing the mechanism of interaction between the adsorbedmore » layer and the semiconductor surface. The effect of enhanced polarization of the space-charge region of the semiconductor occurs due to a change in the spatial structure of mobile charge in the organic dielectric layer. The system developed in the study opens up technological opportunities for the formation of a new generation of electronic devices based on organic film structures and for experimental modeling of the electronic properties of biological membranes.« less

Formation mechanism of dot-line square superlattice pattern in dielectric barrier discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Weibo; Dong, Lifang, E-mail: donglfhbu@163.com, E-mail: pyy1616@163.com; Wang, Yongjie

We investigate the formation mechanism of the dot-line square superlattice pattern (DLSSP) in dielectric barrier discharge. The spatio-temporal structure studied by using the intensified-charge coupled device camera shows that the DLSSP is an interleaving of three different subpatterns in one half voltage cycle. The dot square lattice discharges first and, then, the two kinds of line square lattices, which form square grid structures discharge twice. When the gas pressure is varied, DLSSP can transform from square superlattice pattern (SSP). The spectral line profile method is used to compare the electron densities, which represent the amounts of surface charges qualitatively. Itmore » is found that the amount of surface charges accumulated by the first discharge of DLSSP is less than that of SSP, leading to a bigger discharge area of the following discharge (lines of DLSSP instead of halos of SSP). The spatial distribution of the electric field of the surface charges is simulated to explain the formation of DLSSP. This paper may provide a deeper understanding for the formation mechanism of complex superlattice patterns in DBD.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanjeewa, Hakmana; He Xiaochun; Cleven, Christopher

The Muon charge ratio at the Earth's surface has been studied with a Geant4 based simulation for two different geomagnetic locations: Atlanta and Lynn Lake. The simulation results are shown in excellent agreement with the data from NMSU-WIZARD/CAPRICE and BESS experiments at Lynn Lake, At low momentum, ground level muon charge ratios show latitude dependent geomagnetic effects for both Atlanta and Lynn Lake from the simulation. The simulated charge ratio is 1.20 {+-} 0.05 (without geomagnetic field), 1.12 {+-} 0.05 (with geomagnetic field) for Atlanta and 1.22 {+-} 0.04 (with geomagnetic field) for Lynn Lake. These types of studies aremore » very important for analyzing secondary cosmic ray muon flux distribution at Earth's surface and can be used to evaluate the parameter of atmospheric neutrino oscillations.« less

Charge, energy and LET spectra of high LET primary and secondary particles in CR-39 plastic nuclear track detectors of the P0006 experiment

NASA Technical Reports Server (NTRS)

Csige, I.; Frigo, L. A.; Benton, E. V.; Oda, K.

1995-01-01

We have measured the charge, energy and linear energy transfer (LET) spectra of about 800 high LET (LET(sub infinity) H2O greater than 50 keV/micron) particles in CR-39 plastic nuclear track detectors in the P0006 experiment of LDEF. Primary particles with residual range at the reference surface greater than about 2 microns and secondary particles produced in the detector material with total range greater than about 4 microns were measured. We have used a multi-etch technique and an internal calibration to identify and measure the energy of the particles at the reference surface. The LET spectrum was obtained from the charge and energy distribution of the particles.

Fabrication of polyamide thin-film nanocomposite membranes with enhanced surface charge for nitrate ion removal from water resources.

PubMed

Ghaee, A; Zerafat, M M; Askari, P; Sabbaghi, S; Sadatnia, B

2017-03-01

Exclusion due to membrane surface charge is considered as one of the main separation mechanisms occurring in charged membranes, which can be varied through various approaches to affect membrane rejection performance. In this study, thin-film composite (TFC) polyamide (PA) membranes were fabricated via interfacial polymerization of m-phenylenediamine (m-PDA) and 2,4-diaminobenzene sulfonic acid with trimesoyl chloride (TMC) on a polysulfone sub-layer. The ability of the prepared membrane to remove nitrate ions from water resources has been investigated. In order to improve membrane permeability, zeolite-PA thin film nanocomposite (TFN) membranes were fabricated by incorporating natural zeolite nanoparticles obtained through ball milling of an Iranian natural zeolite powder in the interfacial polymerization process. The size, morphology and specific surface area of the as-obtained nanozeolite were characterized using particle size analysis, FE-SEM and BET. The functional groups, morphology and surface charge of the membrane were characterized using ATR-FTIR, SEM and zeta potential analyses. Also, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) were used to determine the distribution of nanozeolite in TFN membranes. The influence of zeolite addition to surface roughness was accessed by atomic force microscopy. The performance of TFC and TFN membranes was evaluated in terms of pure water flux and nitrate rejection. The results showed that in case of sulfonated diamine, nitrate ions rejection was enhanced from 63% to 85% which could be attributed to surface charge enhancement. TFN permeability was almost doubled by the addition of nanozeolite.

Dispersing Zwitterions into Comb Polymers for Nonviral Transfection: Experiments and Molecular Simulation.

PubMed

Ghobadi, Ahmadreza F; Letteri, Rachel; Parelkar, Sangram S; Zhao, Yue; Chan-Seng, Delphine; Emrick, Todd; Jayaraman, Arthi

2016-02-08

Polymer-based gene delivery vehicles benefit from the presence of hydrophilic groups that mitigate the inherent toxicity of polycations and that provide tunable polymer-DNA binding strength and stable complexes (polyplexes). However, hydrophilic groups screen charge, and as such can reduce cell uptake and transfection efficiency. We report the effect of embedding zwitterionic sulfobetaine (SB) groups in cationic comb polymers, using a combination of experiments and molecular simulations. Ring-opening metathesis polymerization (ROMP) produced comb polymers with tetralysine (K4) and SB pendent groups. Dynamic light scattering, zeta potential measurements, and fluorescence-based experiments, together with coarse-grained molecular dynamics simulations, described the effect of SB groups on the size, shape, surface charge, composition, and DNA binding strength of polyplexes formed using these comb polymers. Experiments and simulations showed that increasing SB composition in the comb polymers decreased polymer-DNA binding strength, while simulations indicated that the SB groups distributed throughout the polyplex. This allows polyplexes to maintain a positive surface charge and provide high levels of gene expression in live cells. Notably, comb polymers with nearly 50 mol % SB form polyplexes that exhibit positive surface charge similarly as polyplexes formed from purely cationic comb polymers, indicating the ability to introduce an appreciable amount of SB functionality without screening surface charge. This integrated simulation-experimental study demonstrates the effectiveness of incorporating zwitterions in polyplexes, while guiding the design of new and effective gene delivery vectors.

Density functional theory study of defect energies and space charge distribution at a solid-oxide electrolyte surface

NASA Astrophysics Data System (ADS)

Han, Chu; Bongiorno, Angelo

2014-03-01

Yttrium-doped barium zirconate (BZY) is a proton conducting electrolyte forming a class of novel materials for new generation of solid oxide fuel cells, for hydrogen separation and purification, and for electrolysis of water. Here we use density functional theory calculations to compute the energy of protons and oxygen vacancies at the surface and in the bulk of lightly Y-doped BZY materials. We found that protons are energetically more stable at the surface termination than in the bulk of BZY by about 1 eV. In contrast, doubly-positively charged oxygen vacancies are found to form iso-energetic defects at both the terminal surface layer and in the bulk of BZY, while in the sub-surface region the defect energy raises by about 1 eV with respect to the value in the bulk. The energetic behavior of protons and oxygen vacancies in the near surface region of BZY is attributed to the competition of strain and electrostatic effects. Lattice model representations of BZY surfaces are then used in combination with Monte Carlo simulations to solve the Poisson-Boltzmann equation and investigate the implication of the results above on the structure of the space charge region at the surface of BZY materials.

Copper(II) adsorption on the kaolinite(001) surface: Insights from first-principles calculations and molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Kong, Xiang-Ping; Wang, Juan

2016-12-01

The adsorption behavior of Cu(II) on the basal hydroxylated kaolinite(001) surface in aqueous environment was investigated by first-principles calculations and molecular dynamics simulations. Structures of possible monodentate and bidentate inner-sphere adsorption complexes of Cu(II) were examined, and the charge transfer and bonding mechanism were analyzed. Combining the binding energy of complex, the radial distribution function of Cu(II) with oxygen and the extended X-ray absorption fine structure data, monodentate complex on site of surface oxygen with ;upright; hydrogen and bidentate complex on site of two oxygens (one with ;upright; hydrogen and one with ;lying; hydrogen) of single Al center have been found to be the major adsorption species of Cu(II). Both adsorption species are four-coordinated with a square planar geometry. The distribution of surface hydroxyls with ;lying; hydrogen around Cu(II) plays a key role in the structure and stability of adsorption complex. Upon the Mulliken population analysis and partial density of states, charge transfer occurs with Cu(II) accepting some electrons from both surface oxygens and aqua oxygens, and the bonding Cu 3d-O 2p state filling is primarily responsible for the strong covalent interaction of Cu(II) with surface oxygen.

Jovian Plasma Modeling for Mission Design

NASA Technical Reports Server (NTRS)

Garrett, Henry B.; Kim, Wousik; Belland, Brent; Evans, Robin

2015-01-01

The purpose of this report is to address uncertainties in the plasma models at Jupiter responsible for surface charging and to update the jovian plasma models using the most recent data available. The updated plasma environment models were then used to evaluate two proposed Europa mission designs for spacecraft charging effects using the Nascap-2k code. The original Divine/Garrett jovian plasma model (or "DG1", T. N. Divine and H. B. Garrett, "Charged particle distributions in Jupiter's magnetosphere," J. Geophys. Res., vol. 88, pp. 6889-6903,1983) has not been updated in 30 years, and there are known errors in the model. As an example, the cold ion plasma temperatures between approx.5 and 10 Jupiter radii (Rj) were found by the experimenters who originally published the data to have been underestimated by approx.2 shortly after publication of the original DG1 model. As knowledge of the plasma environment is critical to any evaluation of the surface charging at Jupiter, the original DG1 model needed to be updated to correct for this and other changes in our interpretation of the data so that charging levels could beproperly estimated using the Nascap-2k charging code. As an additional task, the Nascap-2k spacecraft charging tool has been adapted to incorporate the so-called Kappa plasma distribution function--an important component of the plasma model necessary to compute the particle fluxes between approx.5 keV and 100 keV (at the outset of this study,Nascap-2k did not directly incorporate this common representation of the plasma thus limiting the accuracy of our charging estimates). The updating of the DG1 model and its integration into the Nascap-2k design tool means that charging concerns can now be more efficiently evaluated and mitigated. (We note that, given the subsequent decision by the Europa project to utilize solar arrays for its baseline design, surface charging effects have becomeeven more of an issue for its mission design). The modifications and results of those modifications to the DG1 model to produce the new DG2 model presented here and the steps taken to integrate the DG2 predictions into Nascap-2k are described in this report

Jovian plasma modeling for mission design

NASA Technical Reports Server (NTRS)

Garrett, Henry B.; Kim, Wousik; Belland, Brent; Evans, Robin

2015-01-01

The purpose of this report is to address uncertainties in the plasma models at Jupiter responsible for surface charging and to update the jovian plasma models using the most recent data available. The updated plasma environment models were then used to evaluate two proposed Europa mission designs for spacecraft charging effects using the Nascap-2k code. The original Divine/Garrett jovian plasma model (or "DG1", T. N. Divine and H. B. Garrett, "Charged particle distributions in Jupiter's magnetosphere," J. Geophys. Res., vol. 88, pp. 6889-6903,1983) has not been updated in 30 years, and there are known errors in the model. As an example, the cold ion plasma temperatures between approx.5 and 10 Jupiter radii (Rj) were found by the experimenters who originally published the data to have been underestimated by approx.2 shortly after publication of the original DG1 model. As knowledge of the plasma environment is critical to any evaluation of the surface charging at Jupiter, the original DG1 model needed to be updated to correct for this and other changes in our interpretation of the data so that charging levels could beproperly estimated using the Nascap-2k charging code. As an additional task, the Nascap-2k spacecraft charging tool has been adapted to incorporate the so-called Kappa plasma distribution function--an important component of the plasma model necessary to compute the particle fluxes between approx.5 keV and 100 keV (at the outset of this study,Nascap-2k did not directly incorporate this common representation of the plasma thus limiting the accuracy of our charging estimates). The updating of the DG1 model and its integration into the Nascap-2k design tool means that charging concerns can now be more efficiently evaluated and mitigated. (We note that, given the subsequent decision by the Europa project to utilize solar arrays for its baseline design, surface charging effects have becomeeven more of an issue for its mission design). The modifications and results of those modifications to the DG1 model to produce the new DG2 model presented here and the steps taken to integrate the DG2 predictions into Nascap-2k are described in this report.

Real time quantitative imaging for semiconductor crystal growth, control and characterization

NASA Technical Reports Server (NTRS)

Wargo, Michael J.

1991-01-01

A quantitative real time image processing system has been developed which can be software-reconfigured for semiconductor processing and characterization tasks. In thermal imager mode, 2D temperature distributions of semiconductor melt surfaces (900-1600 C) can be obtained with temperature and spatial resolutions better than 0.5 C and 0.5 mm, respectively, as demonstrated by analysis of melt surface thermal distributions. Temporal and spatial image processing techniques and multitasking computational capabilities convert such thermal imaging into a multimode sensor for crystal growth control. A second configuration of the image processing engine in conjunction with bright and dark field transmission optics is used to nonintrusively determine the microdistribution of free charge carriers and submicron sized crystalline defects in semiconductors. The IR absorption characteristics of wafers are determined with 10-micron spatial resolution and, after calibration, are converted into charge carrier density.

Deep Dielectric Charging of Spacecraft Polymers by Energetic Protons

NASA Technical Reports Server (NTRS)

Green, Nelson W.; Dennison, J. R.

2007-01-01

The majority of research in the field of spacecraft charging concentrates on electron charging effects with little discussion of charging by protons. For spacecraft orbiting in the traditional LEO and GEO environments this emphasis on electrons is appropriate since energetic electrons are the dominant species in those orbits. But for spacecraft in orbits within the inner radiation belts or for interplanetary and lunar space probes, proton charging (center dot) effects may also be of concern. To examine bulk spacecraft charging effects in these environments several typical highly insulating spacecraft polymers were exposed to energetic protons (center dot) with energies from 1 Me V to lO Me V to simulate protons from the solar wind and from solar energetic proton events. Results indicate that effects in proton charged dielectrics are distinctly different than those observed due to electron charging. In most cases, the positive surface potential continued to increase for periods on the order of minutes to a day, followed by long time scale decay at rates similar to those observed for electron charging. All samples charged to positive potentials with substantially lower magnitudes than for equivalent electron doses. Possible explanations for the different behavior of the measured surface potentials from proton irradiation are discussed; these are related to the evolving internal charge distribution from energy dependent electron and proton transport, electron emission, charge migration due to dark current and radiation induced conductivity, and electron capture by embedded protons.

Predicting tensorial electrophoretic effects in asymmetric colloids

NASA Astrophysics Data System (ADS)

Mowitz, Aaron J.; Witten, T. A.

2017-12-01

We formulate a numerical method for predicting the tensorial linear response of a rigid, asymmetrically charged body to an applied electric field. This prediction requires calculating the response of the fluid to the Stokes drag forces on the moving body and on the countercharges near its surface. To determine the fluid's motion, we represent both the body and the countercharges using many point sources of drag known as Stokeslets. Finding the correct flow field amounts to finding the set of drag forces on the Stokeslets that is consistent with the relative velocities experienced by each Stokeslet. The method rigorously satisfies the condition that the object moves with no transfer of momentum to the fluid. We demonstrate that a sphere represented by 1999 well-separated Stokeslets on its surface produces flow and drag force like a solid sphere to 1% accuracy. We show that a uniformly charged sphere with 3998 body and countercharge Stokeslets obeys the Smoluchowski prediction [F. Morrison, J. Colloid Interface Sci. 34, 210 (1970), 10.1016/0021-9797(70)90171-2] for electrophoretic mobility when the countercharges lie close to the sphere. Spheres with dipolar and quadrupolar charge distributions rotate and translate as predicted analytically to 4% accuracy or better. We describe how the method can treat general asymmetric shapes and charge distributions. This method offers promise as a way to characterize and manipulate asymmetrically charged colloid-scale objects from biology (e.g., viruses) and technology (e.g., self-assembled clusters).

Interstitial distribution of charged macromolecules in the dog lung: a kinetic model.

PubMed

Parker, J C; Miniati, M; Pitt, R; Taylor, A E

1987-01-01

A mathematic model was constructed to investigate conflicting physiologic data concerning the charge effect of continuous capillaries to macromolecules in the lung. We simulated the equilibration kinetics of lactate dehydrogenase (MR 4.2 nM) isozymes LDH 1 (pI = 5.0) and LDH 5 (pI = 7.9) between plasma and lymph using previously measured permeability coefficients, lung tissue distribution volumes (VA) and plasma concentrations (CP) in lung tissue. Our hypothesis is that the fixed anionic charges in interstitium, basement membrane, and cell surfaces determine equilibration rather than charged membrane effects at the capillary barrier, so the same capillary permeability coefficients were used for both isozymes. Capillary filtration rates and protein fluxes were calculated using conventional flux equations. Initial conditions at baseline and increased left atrial pressures (PLA) were those measured in animal studies. Simulated equilibration of isozymes over 30 h in the model at baseline capillary pressures accurately predicted the observed differences in lymph/plasma concentration ratios (CL/CP) between isotopes at 4 h and equilibration of these ratios at 24 h. Quantitative prediction of isozyme CL/CP ratios was also obtained at increased PLA. However, an additional cation selective compartment representing the surface glycocalyx was required to accurately simulate the initial higher transcapillary clearances of cationic LDH 5. Thus experimental data supporting the negative barrier, positive barrier, and no charge barrier hypotheses were accurately reproduced by the model using only the observed differences in interstitial partitioning of isozymes without differences in capillary selectivity.

Conductorlike behavior of a photoemitting dielectric surface

NASA Technical Reports Server (NTRS)

De, B. R.

1979-01-01

It has been suggested in the past that a uniformly illuminated photoemitting dielectric surface of finite extent acquires in the steady state a surface charge distribution as if the surface were conducting (i.e., the surface becomes equipotential). In this paper an analytical proof of this conductorlike behavior is given. The only restrictions are that the photoelectron emission from the surface has azimuthal symmetry and that the photosheath may be assumed to be collisionless. It is tacitly assumed that a steady state is attainable, which means that the photoelectron spectrum has a high-energy cutoff.

Microcapsules with three orthogonal reactive sites

PubMed Central

Mason, Brian P.; Hira, Steven M.; Strouse, Geoffrey F.; McQuade, D. Tyler

2009-01-01

Polymeric microcapsules containing reactive sites on the shell surface and two orthogonally reactive polymers encapsulated within the interior are selectively labeled. The capsules provide three spatially separate and differentially reactive sites. Confocal fluorescence microscopy is used to characterize the distribution of labels. Polymers encapsulated are distributed homogeneously within the core and do not interact with the shell even when oppositely charged. PMID:19254010

Probing protein orientation near charged nanosurfaces for simulation-assisted biosensor design.

PubMed

Cooper, Christopher D; Clementi, Natalia C; Barba, Lorena A

2015-09-28

Protein-surface interactions are ubiquitous in biological processes and bioengineering, yet are not fully understood. In biosensors, a key factor determining the sensitivity and thus the performance of the device is the orientation of the ligand molecules on the bioactive device surface. Adsorption studies thus seek to determine how orientation can be influenced by surface preparation, varying surface charge, and ambient salt concentration. In this work, protein orientation near charged nanosurfaces is obtained under electrostatic effects using the Poisson-Boltzmann equation, in an implicit-solvent model. Sampling the free energy for protein G B1 D4' at a range of tilt and rotation angles with respect to the charged surface, we calculated the probability of the protein orientations and observed a dipolar behavior. This result is consistent with published experimental studies and combined Monte Carlo and molecular dynamics simulations using this small protein, validating our method. More relevant to biosensor technology, antibodies such as immunoglobulin G are still a formidable challenge to molecular simulation, due to their large size. With the Poisson-Boltzmann model, we obtained the probability distribution of orientations for the iso-type IgG2a at varying surface charge and salt concentration. This iso-type was not found to have a preferred orientation in previous studies, unlike the iso-type IgG1 whose larger dipole moment was assumed to make it easier to control. Our results show that the preferred orientation of IgG2a can be favorable for biosensing with positive charge on the surface of 0.05 C/m(2) or higher and 37 mM salt concentration. The results also show that local interactions dominate over dipole moment for this protein. Improving immunoassay sensitivity may thus be assisted by numerical studies using our method (and open-source code), guiding changes to fabrication protocols or protein engineering of ligand molecules to obtain more favorable orientations.

Probing protein orientation near charged nanosurfaces for simulation-assisted biosensor design

NASA Astrophysics Data System (ADS)

Cooper, Christopher D.; Clementi, Natalia C.; Barba, Lorena A.

2015-09-01

Protein-surface interactions are ubiquitous in biological processes and bioengineering, yet are not fully understood. In biosensors, a key factor determining the sensitivity and thus the performance of the device is the orientation of the ligand molecules on the bioactive device surface. Adsorption studies thus seek to determine how orientation can be influenced by surface preparation, varying surface charge, and ambient salt concentration. In this work, protein orientation near charged nanosurfaces is obtained under electrostatic effects using the Poisson-Boltzmann equation, in an implicit-solvent model. Sampling the free energy for protein G B1 D4' at a range of tilt and rotation angles with respect to the charged surface, we calculated the probability of the protein orientations and observed a dipolar behavior. This result is consistent with published experimental studies and combined Monte Carlo and molecular dynamics simulations using this small protein, validating our method. More relevant to biosensor technology, antibodies such as immunoglobulin G are still a formidable challenge to molecular simulation, due to their large size. With the Poisson-Boltzmann model, we obtained the probability distribution of orientations for the iso-type IgG2a at varying surface charge and salt concentration. This iso-type was not found to have a preferred orientation in previous studies, unlike the iso-type IgG1 whose larger dipole moment was assumed to make it easier to control. Our results show that the preferred orientation of IgG2a can be favorable for biosensing with positive charge on the surface of 0.05 C/m2 or higher and 37 mM salt concentration. The results also show that local interactions dominate over dipole moment for this protein. Improving immunoassay sensitivity may thus be assisted by numerical studies using our method (and open-source code), guiding changes to fabrication protocols or protein engineering of ligand molecules to obtain more favorable orientations.

Multipactor saturation in parallel-plate waveguides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sorolla, E.; Mattes, M.

2012-07-15

The saturation stage of a multipactor discharge is considered of interest, since it can guide towards a criterion to assess the multipactor onset. The electron cloud under multipactor regime within a parallel-plate waveguide is modeled by a thin continuous distribution of charge and the equations of motion are calculated taking into account the space charge effects. The saturation is identified by the interaction of the electron cloud with its image charge. The stability of the electron population growth is analyzed and two mechanisms of saturation to explain the steady-state multipactor for voltages near above the threshold onset are identified. Themore » impact energy in the collision against the metal plates decreases during the electron population growth due to the attraction of the electron sheet on the image through the initial plate. When this growth remains stable till the impact energy reaches the first cross-over point, the electron surface density tends to a constant value. When the stability is broken before reaching the first cross-over point the surface charge density oscillates chaotically bounded within a certain range. In this case, an expression to calculate the maximum electron surface charge density is found whose predictions agree with the simulations when the voltage is not too high.« less

Current rectification for transport of room-temperature ionic liquids through conical nanopores

DOE PAGES

Jiang, Xikai; Liu, Ying; Qiao, Rui

2016-02-09

Here, we studied the transport of room-temperature ionic liquids (RTILs) through charged conical nanopores using a Landau-Ginzburg-type continuum model that takes steric effect and strong ion-ion correlations into account. When the surface charge is uniform on the pore wall, weak current rectification is observed. When the charge density near the pore base is removed, the ionic current is greatly suppressed under negative bias voltage while nearly unchanged under positive bias voltage, thereby leading to enhanced current rectification. These predictions agree qualitatively with prior experimental observations, and we elucidated them by analyzing the different components of the ionic current and themore » structural changes of electrical double layers (EDLs) at the pore tip under different bias voltages and surface charge patterns. These analyses reveal that the different modifications of the EDL structure near the pore tip by the positive and negative bias voltages cause the current rectification and the observed dependence on the distribution of surface charge on the pore wall. The fact that the current rectification phenomena are captured qualitatively by the simple model originally developed for describing EDLs at equilibrium conditions suggests that this model may be promising for understanding the ionic transport under nonequilibrium conditions when the EDL structure is strongly perturbed by external fields.« less

Metal parts hydrosized by explosive force

NASA Technical Reports Server (NTRS)

1965-01-01

Large metal parts are sized by a charge exploded above a sealed container filled with evacuated die and water. Explosive hydrosizing achieves close dimensional tolerances, eliminates damage to the surface, and allows longer force application and more even pressure distribution.

The human peripheral subunit-binding domain folds rapidly while overcoming repulsive Coulomb forces

PubMed Central

Arbely, Eyal; Neuweiler, Hannes; Sharpe, Timothy D; Johnson, Christopher M; Fersht, Alan R

2010-01-01

Peripheral subunit binding domains (PSBDs) are integral parts of large multienzyme complexes involved in carbohydrate metabolism. PSBDs facilitate shuttling of prosthetic groups between different catalytic subunits. Their protein surface is characterized by a high density of positive charges required for binding to subunits within the complex. Here, we investigated folding thermodynamics and kinetics of the human PSBD (HSBD) using circular dichroism and tryptophan fluorescence experiments. HSBD was only marginally stable under physiological solvent conditions but folded within microseconds via a barrier-limited apparent two-state transition, analogous to its bacterial homologues. The high positive surface-charge density of HSBD leads to repulsive Coulomb forces that modulate protein stability and folding kinetics, and appear to even induce native-state movement. The electrostatic strain was alleviated at high solution-ionic-strength by Debye-Hückel screening. Differences in ionic-strength dependent characteristics among PSBD homologues could be explained by differences in their surface charge distributions. The findings highlight the trade-off between protein function and stability during protein evolution. PMID:20662005

Dusty Plasma Dynamics Near Surfaces in Space

NASA Technical Reports Server (NTRS)

Colwell, Joshua E.; Robertson, S.; Horanyi, M.; Nahra, Henry (Technical Monitor)

1998-01-01

The investigation 'Dusty Plasma Dynamics Near Surfaces in Space' is an experimental and theoretical study of the dynamics of dust particles on airless bodies in the solar system in the presence of a photoelectron sheath generated by solar ultraviolet light impinging on the surface. Solar UV illumination of natural and manmade surfaces in space produces photoelectrons which form a plasma sheath near the surface. Dust particles on the surface acquire a charge and may be transported by electric fields in the photoelectron sheath generated by inhomogeneities in the surface or the illumination (such as shadows). The sheath itself has a finite vertical extent leading to (at least) an electric field normal to the illuminated surface. If dust particles are launched from the surface by some other process, such as meteoroid impact, or spacecraft activity on the surface, these grains become charged and move under the influence of gravity and the electric field. This can give rise to suspension of the particles above the surface, loss from the parent body entirely (if accelerated beyond escape velocity), and a different distribution of dust ejecta from what would be expected with purely gravitational dynamics.

Surface charge-specific interactions between polymer nanoparticles and ABC transporters in Caco-2 cells

NASA Astrophysics Data System (ADS)

Bhattacharjee, Sourav; van Opstal, Edward J.; Alink, Gerrit M.; Marcelis, Antonius T. M.; Zuilhof, Han; Rietjens, Ivonne M. C. M.

2013-06-01

The surface charge-dependent transport of polymeric nanoparticles (PNPs) across Caco-2 monolayers grown on transwell culture systems as an in vitro model for intestinal transport was tested. The transport of well-characterized, monodisperse, and fluorescent tri-block copolymer nanoparticles (TCNPs/size 45 nm) and polystyrene nanoparticles (PSNPs/size 50 nm), with different surface charges (positive and negative), was quantified. The positive PNPs showed a higher intracellular uptake and flux across the Caco-2 monolayers than the negative PNPs. Multidrug resistance/P-glycoprotein (MDR1/P-gp), a specific ATP-binding cassette (ABC) transporter, was found to play a major role in the cellular efflux of positive PNPs, whereas the multidrug resistance protein 1 took part in the efflux of negative PNPs from Caco-2 cells. The positive PNPs also caused an increased cellular uptake and apical to basolateral transport of the carcinogen PhIP across the Caco-2 monolayer. The flavonoid quercetin, which is known to interact with ABC transporters, promoted the intracellular uptake of different PNPs and interfered with the normal distribution patterns of PNPs in the transwell system. These results indicate that PNPs display surface charge-specific interactions with ABC transporters and can even affect the bioavailability of toxic food-borne compounds (like pro-carcinogens).

On the physics of dispersive electron transport characteristics in SnO2 nanoparticle-based dye sensitized solar cells.

PubMed

Ashok, Aditya; Vijayaraghavan, S N; Unni, Gautam E; Nair, Shantikumar V; Shanmugam, Mariyappan

2018-04-27

The present study elucidates dispersive electron transport mediated by surface states in tin oxide (SnO 2 ) nanoparticle-based dye sensitized solar cells (DSSCs). Transmission electron microscopic studies on SnO 2 show a distribution of ∼10 nm particles exhibiting (111) crystal planes with inter-planar spacing of 0.28 nm. The dispersive transport, experienced by photo-generated charge carriers in the bulk of SnO 2 , is observed to be imposed by trapping and de-trapping processes via SnO 2 surface states present close to the band edge. The DSSC exhibits 50% difference in performance observed between the forward (4%) and reverse (6%) scans due to the dispersive transport characteristics of the charge carriers in the bulk of the SnO 2 . The photo-generated charge carriers are captured and released by the SnO 2 surface states that are close to the conduction band-edge resulting in a very significant variation; this is confirmed by the hysteresis observed in the forward and reverse scan current-voltage measurements under AM1.5 illumination. The hysteresis behavior assures that the charge carriers are accumulated in the bulk of electron acceptor due to the trapping, and released by de-trapping mediated by surface states observed during the forward and reverse scan measurements.

On the physics of dispersive electron transport characteristics in SnO2 nanoparticle-based dye sensitized solar cells

NASA Astrophysics Data System (ADS)

Ashok, Aditya; Vijayaraghavan, S. N.; Unni, Gautam E.; Nair, Shantikumar V.; Shanmugam, Mariyappan

2018-04-01

The present study elucidates dispersive electron transport mediated by surface states in tin oxide (SnO2) nanoparticle-based dye sensitized solar cells (DSSCs). Transmission electron microscopic studies on SnO2 show a distribution of ˜10 nm particles exhibiting (111) crystal planes with inter-planar spacing of 0.28 nm. The dispersive transport, experienced by photo-generated charge carriers in the bulk of SnO2, is observed to be imposed by trapping and de-trapping processes via SnO2 surface states present close to the band edge. The DSSC exhibits 50% difference in performance observed between the forward (4%) and reverse (6%) scans due to the dispersive transport characteristics of the charge carriers in the bulk of the SnO2. The photo-generated charge carriers are captured and released by the SnO2 surface states that are close to the conduction band-edge resulting in a very significant variation; this is confirmed by the hysteresis observed in the forward and reverse scan current-voltage measurements under AM1.5 illumination. The hysteresis behavior assures that the charge carriers are accumulated in the bulk of electron acceptor due to the trapping, and released by de-trapping mediated by surface states observed during the forward and reverse scan measurements.

Reactions of Microsolvated Organic Compounds at Ambient Surfaces: Droplet Velocity, Charge State, and Solvent Effects

NASA Astrophysics Data System (ADS)

Badu-Tawiah, Abraham K.; Campbell, Dahlia I.; Cooks, R. Graham

2012-06-01

The exposure of charged microdroplets containing organic ions to solid-phase reagents at ambient surfaces results in heterogeneous ion/surface reactions. The electrosprayed droplets were driven pneumatically in ambient air and then electrically directed onto a surface coated with reagent. Using this reactive soft landing approach, acid-catalyzed Girard condensation was achieved at an ambient surface by directing droplets containing Girard T ions onto a dry keto-steroid. The charged droplet/surface reaction was much more efficient than the corresponding bulk solution-phase reaction performed on the same scale. The increase in product yield is ascribed to solvent evaporation, which causes moderate pH values in the starting droplet to reach extreme values and increases reagent concentrations. Comparisons are made with an experiment in which the droplets were pneumatically accelerated onto the ambient surface (reactive desorption electrospray ionization, DESI). The same reaction products were observed but differences in spatial distribution were seen associated with the "splash" of the high velocity DESI droplets. In a third type of experiment, the reactions of charged droplets with vapor phase reagents were examined by allowing electrosprayed droplets containing a reagent to intercept the headspace vapor of an analyte. Deposition onto a collector surface and mass analysis showed that samples in the vapor phase were captured by the electrospray droplets, and that instantaneous derivatization of the captured sample is possible in the open air. The systems examined under this condition included the derivatization of cortisone vapor with Girard T and that of 4-phenylpyridine N-oxide and 2-phenylacetophenone vapors with ethanolamine.

Modulating protein behaviors on responsive surface by external electric fields: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Xie, Yun; Pan, Yufang; Zhang, Rong; Liang, Ying; Li, Zhanchao

2015-01-01

Molecular dynamics simulations were employed to investigate the modulation of protein behaviors on the electrically responsive zwitterionic phosphorylcholine self-assembled monolayers (PC-SAMs). Results show that PC-SAMs could sensitively respond to the applied electric fields and exhibit three states with different charge distributions, namely both the negatively charged phosphate groups and the positively charged choline groups are exposed to the solution in the absence of electric fields (state 1), phosphate groups exposed in the presence of positive electric fields (state 2), and choline groups exposed in the presence of negative electric fields (state 3). Under state 1, the adsorption of Cyt c on the PC-SAM is reversible and the orientations of Cyt c are randomly distributed. Under state 2, the adsorption of Cyt c is enhanced due to the electrostatic attractions between the exposed phosphate groups and the positively charged protein; when adsorbed on the PC-SAMs, Cyt c tends to adopt the orientation with the heme plane perpendicular to the surface plane, and the percentage of this orientation increases as the field strength rises up. Under state 3, the adsorption of Cyt c is retarded because of the electrostatic repulsions between the exposed choline groups and the protein; however, if the gaps between PC chains are large enough, Cyt c could insert into the PC-SAM and access the phosphate groups after overcoming a slight energy barrier. Under three states, the basic backbone structures of Cyt c are well kept within the simulation time since the conformation of Cyt c is mainly affected by the surface-generated electric fields, whose strengths are modulated by the external electric fields and are not strong enough to deform protein. The results indicate the possibility of regulating protein behaviors, including promoting or retarding protein adsorption and regulating protein orientations, on responsive surfaces by applying electric fields on the surfaces without worrying protein deformation, which may be helpful in the applications of protein separation and controlled drug delivery.

Electronic structure and partial charge distribution of Doxorubicin in different molecular environments.

PubMed

Poudel, Lokendra; Wen, Amy M; French, Roger H; Parsegian, V Adrian; Podgornik, Rudolf; Steinmetz, Nicole F; Ching, Wai-Yim

2015-05-18

The electronic structure and partial charge of doxorubicin (DOX) in three different molecular environments-isolated, solvated, and intercalated in a DNA complex-are studied by first-principles density functional methods. It is shown that the addition of solvating water molecules to DOX, together with the proximity to and interaction with DNA, has a significant impact on the electronic structure as well as on the partial charge distribution. Significant improvement in estimating the DOX-DNA interaction energy is achieved. The results are further elucidated by resolving the total density of states and surface charge density into different functional groups. It is concluded that the presence of the solvent and the details of the interaction geometry matter greatly in determining the stability of DOX complexation. Ab initio calculations on realistic models are an important step toward a more accurate description of the long-range interactions in biomolecular systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge regulation at semiconductor-electrolyte interfaces.

PubMed

Fleharty, Mark E; van Swol, Frank; Petsev, Dimiter N

2015-07-01

The interface between a semiconductor material and an electrolyte solution has interesting and complex electrostatic properties. Its behavior will depend on the density of mobile charge carriers that are present in both phases as well as on the surface chemistry at the interface through local charge regulation. The latter is driven by chemical equilibria involving the immobile surface groups and the potential determining ions in the electrolyte solution. All these lead to an electrostatic potential distribution that propagate such that the electrolyte and the semiconductor are dependent on each other. Hence, any variation in the charge density in one phase will lead to a response in the other. This has significant implications on the physical properties of single semiconductor-electrolyte interfaces and on the electrostatic interactions between semiconductor particles suspended in electrolyte solutions. The present paper expands on our previous publication (Fleharty et al., 2014) and offers new results on the electrostatics of single semiconductor interfaces as well as on the interaction of charged semiconductor colloids suspended in electrolyte solution. Copyright © 2014 Elsevier Inc. All rights reserved.

Spin relaxation measurements of electrostatic bias in intermolecular exploration

NASA Astrophysics Data System (ADS)

Teng, Ching-Ling; Bryant, Robert G.

2006-04-01

We utilize the paramagnetic contribution to proton spin-lattice relaxation rate constants induced by freely diffusing charged paramagnetic centers to investigate the effect of charge on the intermolecular exploration of a protein by the small molecule. The proton NMR spectrum provided 255 resolved resonances that report how the explorer molecule local concentration varies with position on the surface. The measurements integrate over local dielectric constant variations, and, in principle, provide an experimental characterization of the surface free energy sampling biases introduced by the charge distribution on the protein. The experimental results for ribonuclease A obtained using positive, neutral, and negatively charged small nitroxide radicals are qualitatively similar to those expected from electrostatic calculations. However, while systematic electrostatic trends are apparent, the three different combinations of the data sets do not yield internally consistent values for the electrostatic contribution to the intermolecular free energy. We attribute this failure to the weakness of the electrostatic sampling bias for charged nitroxides in water and local variations in effective translational diffusion constant at the water-protein interface, which enters the nuclear spin relaxation equations for the nitroxide-proton dipolar coupling.

Analysis of Static Spacecraft Floating Potential at Low Earth Orbit (LEO)

NASA Technical Reports Server (NTRS)

Herr, Joel L.; Hwang, K. S.; Wu, S. T.

1995-01-01

Spacecraft floating potential is the charge on the external surfaces of orbiting spacecraft relative to the space. Charging is caused by unequal negative and positive currents to spacecraft surfaces. The charging process continues until the accelerated particles can be collected rapidly enough to balance the currents at which point the spacecraft has reached its equilibrium or floating potential. In low inclination. Low Earth Orbit (LEO), the collection of positive ion and negative electrons. in a particular direction. are typically not equal. The level of charging required for equilibrium to be established is influenced by the characteristics of the ambient plasma environment. by the spacecraft motion, and by the geometry of the spacecraft. Using the kinetic theory, a statistical approach for studying the interaction is developed. The approach used to study the spacecraft floating potential depends on which phenomena are being applied. and on the properties of the plasma. especially the density and temperature. The results from kinetic theory derivation are applied to determine the charging level and the electric potential distribution at an infinite flat plate perpendicular to a streaming plasma using finite-difference scheme.

Positively charged microporous ceramic membrane for the removal of Titan Yellow through electrostatic adsorption.

PubMed

Cheng, Xiuting; Li, Na; Zhu, Mengfu; Zhang, Lili; Deng, Yu; Deng, Cheng

2016-06-01

To develop a depth filter based on the electrostatic adsorption principle, positively charged microporous ceramic membrane was prepared from a diatomaceous earth ceramic membrane. The internal surface of the highly porous ceramic membrane was coated with uniformly distributed electropositive nano-Y2O3 coating. The dye removal performance was evaluated through pressurized filtration tests using Titan Yellow aqueous solution. It showed that positively charged microporous ceramic membrane exhibited a flow rate of 421L/(m(2)·hr) under the trans-membrane pressure of 0.03bar. Moreover it could effectively remove Titan Yellow with feed concentration of 10mg/L between pH3 to 8. The removal rate increased with the enhancement of the surface charge properties with a maximum rejection of 99.6%. This study provides a new and feasible method of removing organic dyes in wastewater. It is convinced that there will be a broad market for the application of charged ceramic membrane in the field of dye removal or recovery from industry wastewater. Copyright © 2016. Published by Elsevier B.V.

The Electric Honeycomb; an investigation of the Rose window instability

NASA Astrophysics Data System (ADS)

Niazi, Muhammad Shaheer

2017-10-01

The Rose window instability is a little-explored electrohydrodynamic instability that manifests when a layer of low-conducting oil is placed in an electric field generated by corona discharge in a point-to-plane configuration. Above a critical voltage, the instability starts as a single dimple in the oil layer right below the point electrode and subsequently evolves into a characteristic pattern of polygonal cells. In this study, we experimentally explore governing parameters that guide the instability and document geometric attributes of the characteristic cellular pattern. The driving force for the instability has been attributed to the buildup of charged ions which in turn apply an electric pressure on the oil surface. We confirm the charged surface distribution using thermal imaging and demonstrate that the instability can be locally inhibited by preventing charge buildup under an ion shadow.

The Electric Honeycomb; an investigation of the Rose window instability

PubMed Central

2017-01-01

The Rose window instability is a little-explored electrohydrodynamic instability that manifests when a layer of low-conducting oil is placed in an electric field generated by corona discharge in a point-to-plane configuration. Above a critical voltage, the instability starts as a single dimple in the oil layer right below the point electrode and subsequently evolves into a characteristic pattern of polygonal cells. In this study, we experimentally explore governing parameters that guide the instability and document geometric attributes of the characteristic cellular pattern. The driving force for the instability has been attributed to the buildup of charged ions which in turn apply an electric pressure on the oil surface. We confirm the charged surface distribution using thermal imaging and demonstrate that the instability can be locally inhibited by preventing charge buildup under an ion shadow. PMID:29134066

Charge-carrier relaxation in sonochemically fabricated dendronized CaSiO3-SiO2-Si nanoheterostructures

NASA Astrophysics Data System (ADS)

Savkina, Rada; Smirnov, Aleksey; Kirilova, Svitlana; Shmid, Volodymyr; Podolian, Artem; Nadtochiy, Andriy; Odarych, Volodymyr; Korotchenkov, Oleg

2018-04-01

We present systematic studies of charge-carrier relaxation processes in sonochemically nanostructured silicon wafers. Impedance spectroscopy and transient photovoltage techniques are employed. It is found that interface potential in Si wafers remarkably increases upon their exposure to sonochemical treatments in Ca-rich environments. In contrast, the density of fast interface electron states remains almost unchanged. It is found that the initial photovoltage decay, taken before ultrasonic treatments, exhibits the involvement of shorter- and longer time recombination and trapping centers. The decay speeds up remarkably due to cavitation treatments, which is accompanied by a substantial quenching of the photovoltage magnitude. It is also found that, before the treatments, the photovoltage magnitude is markedly non-uniform over the wafer surface, implying the existence of distributed sites affecting distribution of photoexcited carriers. The treatments cause an overall broadening of the photovoltage distribution. Furthermore, impedance measurements monitor the progress in surface structuring relevant to several relaxation processes. We believe that sonochemical nanostructuring of silicon wafers with dendronized CaSiO3 may enable new promising avenue towards low-cost solar energy efficiency multilayered solar cell device structures.

Ionic Size Effects: Generalized Boltzmann Distributions, Counterion Stratification, and Modified Debye Length.

PubMed

Liu, Bo; Liu, Pei; Xu, Zhenli; Zhou, Shenggao

2013-10-01

Near a charged surface, counterions of different valences and sizes cluster; and their concentration profiles stratify. At a distance from such a surface larger than the Debye length, the electric field is screened by counterions. Recent studies by a variational mean-field approach that includes ionic size effects and by Monte Carlo simulations both suggest that the counterion stratification is determined by the ionic valence-to-volume ratios. Central in the mean-field approach is a free-energy functional of ionic concentrations in which the ionic size effects are included through the entropic effect of solvent molecules. The corresponding equilibrium conditions define the generalized Boltzmann distributions relating the ionic concentrations to the electrostatic potential. This paper presents a detailed analysis and numerical calculations of such a free-energy functional to understand the dependence of the ionic charge density on the electrostatic potential through the generalized Boltzmann distributions, the role of ionic valence-to-volume ratios in the counterion stratification, and the modification of Debye length due to the effect of ionic sizes.

Ionic Size Effects: Generalized Boltzmann Distributions, Counterion Stratification, and Modified Debye Length

PubMed Central

Liu, Bo; Liu, Pei; Xu, Zhenli; Zhou, Shenggao

2013-01-01

Near a charged surface, counterions of different valences and sizes cluster; and their concentration profiles stratify. At a distance from such a surface larger than the Debye length, the electric field is screened by counterions. Recent studies by a variational mean-field approach that includes ionic size effects and by Monte Carlo simulations both suggest that the counterion stratification is determined by the ionic valence-to-volume ratios. Central in the mean-field approach is a free-energy functional of ionic concentrations in which the ionic size effects are included through the entropic effect of solvent molecules. The corresponding equilibrium conditions define the generalized Boltzmann distributions relating the ionic concentrations to the electrostatic potential. This paper presents a detailed analysis and numerical calculations of such a free-energy functional to understand the dependence of the ionic charge density on the electrostatic potential through the generalized Boltzmann distributions, the role of ionic valence-to-volume ratios in the counterion stratification, and the modification of Debye length due to the effect of ionic sizes. PMID:24465094

Ion-source modeling and improved performance of the CAMS high-intensity Cs-sputter ion source

NASA Astrophysics Data System (ADS)

Brown, T. A.; Roberts, M. L.; Southon, J. R.

2000-10-01

The interior of the high-intensity Cs-sputter source used in routine operations at the Center for Accelerator Mass Spectrometry (CAMS) has been computer modeled using the program NEDLab, with the aim of improving negative ion output. Space charge effects on ion trajectories within the source were modeled through a successive iteration process involving the calculation of ion trajectories through Poisson-equation-determined electric fields, followed by calculation of modified electric fields incorporating the charge distribution from the previously calculated ion trajectories. The program has several additional features that are useful in ion source modeling: (1) averaging of space charge distributions over successive iterations to suppress instabilities, (2) Child's Law modeling of space charge limited ion emission from surfaces, and (3) emission of particular ion groups with a thermal energy distribution and at randomized angles. The results of the modeling effort indicated that significant modification of the interior geometry of the source would double Cs + ion production from our spherical ionizer and produce a significant increase in negative ion output from the source. The results of the implementation of the new geometry were found to be consistent with the model results.

Depth profile of halide anions under highly charged biological membrane

NASA Astrophysics Data System (ADS)

Sung, Woongmo; Wang, Wenjie; Lee, Jonggwan; Vaknin, David; Kim, Doseok

2015-03-01

Halide ion (Cl- and I-) distribution under a cationic Langmuir monolayer consisting of 1,2-dipalmitoyl-3 trimethylammonium-propane (DPTAP) molecules was investigated by vibrational sum-frequency generation (VSFG) and X-ray spectroscopy. From VSFG spectra, it was observed that large halide anions (I-) screen surface charge more efficiently so that interfacial water alignment becomes more randomized. On the other hand, number density of ions directly measured by X-ray fluorescence spectroscopy at grazing incidence angle reveals that the ion densities within 6 ~ 8 nm are the same for both I- and Cl-. Since the observed ion densities in both cases are almost equal to the charge density of the DPTAP monolayer, we propose that larger halide anions are attracted closer to the surface making direct binding with the charged headgroups of the molecules in the monolayer, accomplishing charge neutrality in short distance. This direct adsorption of anions also disturbs the monolayer structure both in terms of the conformation of alkyl chains and the vertical configuration of the monolayer, with iodine having the stronger effect. Our study shows that the length scale that ions neutralize a charged interface varies significantly and specifically even between monovalent ions.

Well behaved parametric class of relativistic charged fluid ball in general relativity

NASA Astrophysics Data System (ADS)

Pant, Neeraj

2011-04-01

The paper presents a class of interior solutions of Einstein-Maxwell field equations of general relativity for a static, spherically symmetric distribution of the charged fluid. This class of solutions describes well behaved charged fluid balls. The class of solutions gives us wide range of parameter K (0≤ K≤42) for which the solution is well behaved hence, suitable for modeling of super dense star. For this solution the mass of a star is maximized with all degree of suitability and by assuming the surface density ρ b =2×1014 g/cm3. Corresponding to K=2 and X=0.30, the maximum mass of the star comes out to be 4.96 M Θ with linear dimension 34.16 km and central redshift and surface redshift 2.1033 and 0.683 respectively. In absence of the charge we are left behind with the well behaved fourth model of Durgapal (J. Phys., A, Math. Gen. 15:2637, 1982).

Laboratory studies of magnetic anomaly effects on electric potential distributions near the lunar surface

NASA Astrophysics Data System (ADS)

Wang, X.; Robertson, S. H.; Horanyi, M.; NASA Lunar Science Institute: Colorado CenterLunar Dust; Atmospheric Studies

2011-12-01

The Moon does not have a global magnetic field, unlike the Earth, rather it has strong crustal magnetic anomalies. Data from Lunar Prospector and SELENE (Kaguya) observed strong interactions between the solar wind and these localized magnetic fields. In the laboratory, a configuration of a horseshoe permanent magnet below an insulating surface is used as an analogue of lunar crustal magnetic anomalies. Plasmas are created above the surface by a hot filament discharge. Potential distributions are measured with an emissive probe and show complex spatial structures. In our experiments, electrons are magnetized with gyro-radii r smaller than the distance from the surface d (r < d) and ions are un-magnetized with r > d. Unlike negative charging on surfaces with no magnetic fields, the surface potential at the center of the magnetic dipole is found close to the plasma bulk potential. The surface charging is dominated by the cold unmagnetized ions, while the electrons are shielded away. A potential minimum is formed between the center of the surface and the bulk plasma, most likely caused by the trapped electrons between the two magnetic mirrors at the cusps. The value of the potential minimum with respect to the bulk plasma potential decreases with increasing plasma density and neutral pressure, indicating that the mirror-trapped electrons are scattered by electron-electron and electron-neutral collisions. The potential at the two cusps are found to be more negative due to the electrons following the magnetic field lines onto the surface.

Multisite adsorption of cadmium on goethite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venema, P.; Hiemstra, T.; Riemsdijk, W.H. van

1996-11-10

Recently a new general ion adsorption model has been developed for ion binding to mineral surfaces (Hiemstra and van Riemsdijk, 1996). The model uses the Pauling concept of charge distribution (CD) and is an extension of the multi-site complexation (MUSIC) approach. In the CD-MUSIC model the charge of an adsorbing ion that forms an inner sphere complex is distributed over its ligands, which are present in two different electrostatic planes. In this paper the authors have applied the CD-MUSIC model to the adsorption of metal cations, using an extended data set for cadmium adsorbing on goethite. The adsorption of cadmiummore » and the cadmium-proton exchange ratio were measured as function of metal ion concentration, pH, and ionic strength. The data could be described well, taking into account the surface heterogeneity resulting from the presence of two different crystal planes (the dominant 110 face and the minor 021 face). The surface species used in the model are consistent with recent EXAFS data. In accordance with the EXAFS results, high-affinity complexes at the 021 face were used in the model.« less

Classical density functional theory and Monte Carlo simulation study of electric double layer in the vicinity of a cylindrical electrode

NASA Astrophysics Data System (ADS)

Zhou, Shiqi; Lamperski, Stanisław; Sokołowska, Marta

2017-07-01

We have performed extensive Monte-Carlo simulations and classical density functional theory (DFT) calculations of the electrical double layer (EDL) near a cylindrical electrode in a primitive model (PM) modified by incorporating interionic dispersion interactions. It is concluded that (i) in general, an unsophisticated use of the mean field (MF) approximation for the interionic dispersion interactions does not distinctly worsen the classical DFT performance, even if the salt ions considered are highly asymmetrical in size (3:1) and charge (5:1), the bulk molar concentration considered is high up to a total bulk ion packing fraction of 0.314, and the surface charge density of up to 0.5 C m-2. (ii) More specifically, considering the possible noises in the simulation, the local volume charge density profiles are the most accurately predicted by the classical DFT in all situations, and the co- and counter-ion singlet distributions are also rather accurately predicted; whereas the mean electrostatic potential profile is relatively less accurately predicted due to an integral amplification of minor inaccuracy of the singlet distributions. (iii) It is found that the layered structure of the co-ion distribution is abnormally possible only if the surface charge density is high enough (for example 0.5 C m-2) moreover, the co-ion valence abnormally influences the peak height of the first counter-ion layer, which decreases with the former. (iv) Even if both the simulation and DFT indicate an insignificant contribution of the interionic dispersion interaction to the above three ‘local’ quantities, it is clearly shown by the classical DFT that the interionic dispersion interaction does significantly influence a ‘global’ quantity like the cylinder surface-aqueous electrolyte interfacial tension, and this may imply the role of the interionic dispersion interaction in explaining the specific Hofmeister effects. We elucidate all of the above observations based on the arguments from the liquid state theory and at the molecular scale.

Imaging the Anomalous Charge Distribution Inside CsPbBr3 Perovskite Quantum Dots Sensitized Solar Cells.

PubMed

Panigrahi, Shrabani; Jana, Santanu; Calmeiro, Tomás; Nunes, Daniela; Martins, Rodrigo; Fortunato, Elvira

2017-10-24

Highly luminescent CsPbBr 3 perovskite quantum dots (QDs) have gained huge attention in research due to their various applications in optoelectronics, including as a light absorber in photovoltaic solar cells. To improve the performances of such devices, it requires a deeper knowledge on the charge transport dynamics inside the solar cell, which are related to its power-conversion efficiency. Here, we report the successful fabrication of an all-inorganic CsPbBr 3 perovskite QD sensitized solar cell and the imaging of anomalous electrical potential distribution across the layers of the cell under different illuminations using Kelvin probe force microscopy. Carrier generation, separation, and transport capacity inside the cells are dependent on the light illumination. Large differences in surface potential between electron and hole transport layers with unbalanced carrier separation at the junction have been observed under white light (full solar spectrum) illumination. However, under monochromatic light (single wavelength of solar spectrum) illumination, poor charge transport occurred across the junction as a consequence of less difference in surface potential between the active layers. The outcome of this study provides a clear idea on the carrier dynamic processes inside the cells and corresponding surface potential across the layers under the illumination of different wavelengths of light to understand the functioning of the solar cells and ultimately for the improvement of their photovoltaic performances.

Effects of different crystal faces on the surface charge of colloidal goethite (α-FeOOH) particles: an experimental and modeling study

NASA Astrophysics Data System (ADS)

Gaboriaud, Fabien; Ehrhardt, Jean-Jacques

2003-03-01

The surface charge of colloidal particles is usually determined by potentiometric titration. These acid-base titrations make it possible to measure the pH of point-of-zero charge (pzc) for oxide minerals. This macroscopic property is the most important parameter used in surface complexation modeling to reproduce experimental data. The pzc values of goethite reported in the literature vary between 7.0 and 9.5. Carbonate adsorption and/or surface morphology are thought to account for this wide range. We demonstrate a procedure for the removal of the carbonate ions that initially adsorb on goethite and strongly affect the titration curves and pzc determination. We also investigated the crystal-face-specific reactivity of two morphologically different goethites. The z-profiles obtained from atomic force microscopy (AFM) images showed that the goethite with the smallest specific surface area ( S = 49 m 2/g, denoted G49) exhibits 70% of the (001) face, whereas this value is only 30% for the goethite with largest specific surface area ( S = 95 m 2/g, denoted G95). This morphologic difference results in slightly different pzc values: 9.0 for G49 goethite and 9.1 for G95 geothite. These experimental pzc values have been correlated with multisite complexation calculations using both the full-site and the 1-pK approaches. We used the full-site approach to consider all of the configurations of hydrogen bond interactions with surface site. The resulting mean charges gave estimated pzc values of 8.9 and 9.2 for the (001) and (101) faces, respectively. Considering these theoretical pzc values for individual faces and the face distributions obtained from AFM analysis, the calculated pzc values are in full agreement with the experimental pzc values. However, this morphologic difference is more expressed in surface charge values than in the pzc values. Indeed, the surface charge of G49 goethite is much higher than that of G95 goethite, and the 1-pK calculations make it possible to fit the titration data satisfactorily.

New vistas in the determination of hydrogen in aerospace engine metal alloys

NASA Technical Reports Server (NTRS)

Danford, M. D.

1986-01-01

The application of diffusion theory to the analysis of hydrogen desorption data has been studied. From these analyses, important information concerning hydrogen solubilities and the nature of the hydrogen distributions in the metal has been obtained. Two nickel base alloys, Rene' 41 and Waspaloy, and one ferrous alloy, 4340 steel, were studied in this work. For the nickel base alloys, it was found that the hydrogen distributions after electrolytic charging conformed closely to those which would be predicted by diffusion theory. The hydrogen distributions in electrolytically charged 4340 steel, on the other hand, were essentially uniform in nature, which would not be predicted by diffusion theory. Finally, it has been found that the hydrogen desorption is completely explained by the nature of the hydrogen distribution in the metal, and that the 'fast' hydrogen is not due to surface and subsurface hydride formation, as was originally proposed.

The Importance of Accurate Secondary Electron Yields in Modeling Spacecraft Charging

DTIC Science & Technology

1986-05-01

Release; Distribution Unlimited AIR FORCE GEOPHYSICS LABORATORY AIR FORCE SYSTEMS COMMAND •IDTIC UNITED STATES AIR FORCE FLECTE HANSCOM AIR FORCE BASE...properties are taken to be those of solor cell rover slip model developed for NASCAP (MandeU et at, (1984)) since most of the exterior surface of the...Research 85, 1155, 1980. Garrett, H. B., "Spacecraft Charging: A Review", in Space Systems and Their Interactions with the Earth’. Space Environment, H

Electronic Interactions of Size-Selected Oxide Clusters on Metallic and Thin Film Oxide Supports

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Meng; Nakayama, Miki; Liu, Ping

The interfacial electronic structure of various size-selected metal oxide nanoclusters (M 3O x; M = Mo, Nb, Ti) on Cu(111) and a thin film of Cu 2O supports were investigated in this paper by a combination of experimental methods and density functional theory (DFT). These systems explore electron transfer at the metal–metal oxide interface which can modify surface structure, metal oxidation states, and catalytic activity. Electron transfer was probed by measurements of surface dipoles derived from coverage dependent work function measurements using two-photon photoemission (2PPE) and metal core level binding energy spectra from X-ray photoelectron spectroscopy (XPS). The measured surfacemore » dipoles are negative for all clusters on Cu(111) and Cu 2O/Cu(111), but those on the Cu 2O surface are much larger in magnitude. In addition, sub-stoichiometric or “reduced” clusters exhibit smaller surface dipoles on both the Cu(111) and Cu 2O surfaces. Negative surface dipoles for clusters on Cu(111) suggest Cu → cluster electron transfer, which is generally supported by DFT-calculated Bader charge distributions. For Cu 2O/Cu(111), calculations of the surface electrostatic potentials show that the charge distributions associated with cluster adsorption structures or distortions at the cluster–Cu 2O–Cu(111) interface are largely responsible for the observed negative surface dipoles. Changes observed in the XPS spectra for the Mo 3d, Nb 3d, and Ti 2p core levels of the clusters on Cu(111) and Cu 2O/Cu(111) are interpreted with help from the calculated Bader charges and cluster adsorption structures, the latter providing information about the presence of inequivalent cation sites. Finally, the results presented in this work illustrate how the combined use of different experimental probes along with theoretical calculations can result in a more realistic picture of cluster–support interactions and bonding.« less

Electronic Interactions of Size-Selected Oxide Clusters on Metallic and Thin Film Oxide Supports

DOE PAGES

Xue, Meng; Nakayama, Miki; Liu, Ping; ...

2017-09-13

The interfacial electronic structure of various size-selected metal oxide nanoclusters (M 3O x; M = Mo, Nb, Ti) on Cu(111) and a thin film of Cu 2O supports were investigated in this paper by a combination of experimental methods and density functional theory (DFT). These systems explore electron transfer at the metal–metal oxide interface which can modify surface structure, metal oxidation states, and catalytic activity. Electron transfer was probed by measurements of surface dipoles derived from coverage dependent work function measurements using two-photon photoemission (2PPE) and metal core level binding energy spectra from X-ray photoelectron spectroscopy (XPS). The measured surfacemore » dipoles are negative for all clusters on Cu(111) and Cu 2O/Cu(111), but those on the Cu 2O surface are much larger in magnitude. In addition, sub-stoichiometric or “reduced” clusters exhibit smaller surface dipoles on both the Cu(111) and Cu 2O surfaces. Negative surface dipoles for clusters on Cu(111) suggest Cu → cluster electron transfer, which is generally supported by DFT-calculated Bader charge distributions. For Cu 2O/Cu(111), calculations of the surface electrostatic potentials show that the charge distributions associated with cluster adsorption structures or distortions at the cluster–Cu 2O–Cu(111) interface are largely responsible for the observed negative surface dipoles. Changes observed in the XPS spectra for the Mo 3d, Nb 3d, and Ti 2p core levels of the clusters on Cu(111) and Cu 2O/Cu(111) are interpreted with help from the calculated Bader charges and cluster adsorption structures, the latter providing information about the presence of inequivalent cation sites. Finally, the results presented in this work illustrate how the combined use of different experimental probes along with theoretical calculations can result in a more realistic picture of cluster–support interactions and bonding.« less

Charge calculation studies done on a single walled carbon nanotube using MOPAC

NASA Astrophysics Data System (ADS)

Negi, S.; Bhartiya, Vivek Kumar; Chaturvedi, S.

2018-04-01

Dipole symmetry of induced charges on DWNTs are required for their application as a nanomotor. Earlier a molecular dynamics analysis was performed for a double-walled carbon-nanotube based motor driven by an externally applied sinusoidally varying electric field. One of the ways to get such a system is chemical or end functionalization, which promises to accomplish this specific and rare configuration of the induced charges on the surface of the carbon nanotube (CNT). CNTs are also a promising system for attaching biomolecules for bio-related applications. In an earlier work, ab initio calculations were done to study the electronic and structural properties of the groups -COOH, -OH, -NH2 and -CONH2 functionalized to an (8, 0) SWNT. The systems were shown to have a very stable interaction with the CNTs. The exterior surface of the SWNT is found to be reactive to NH2 (amidogen). In this work, charge calculations are done on a CNT using MOPAC, which is a semi empirical quantum chemistry software package. As a first step, we calculate the effect of NH2 functionalization to a (5,0) SWNT of infinite length. The symmetric charge distribution of the bare SWNT is observed to be disturbed on addition of a single NH2 in the close proximity of the SWNT. A net positive and opposite charge is observed to be induced on the opposite sides of the nanotube circumference, which is, in turn, imperative for the nanomotor applications. The minimum and maximum value of the charge on any atom is observed to increase from - 0.3 to 0.6 and from - 0.3 to - 1.8 electronic charge as compared to the bare SWNT. This fluctuation of the surface charge to larger values than bare CNT, can be attributed to the coulomb repulsion between NH2 and the rest of the charge on the surface which results into minimizing the total energy of the system. No such opposite polarity of charges are observed on adding NH2 to each ring of the SWNT implying addition of a single amidogen to be the most appropriate configuration to produce a DWNT configuration suited to act like a nanomotor.

Sensing Coulomb impurities with 1/f noise in 3D Topological Insulator

NASA Astrophysics Data System (ADS)

Bhattacharyya, Semonti; Banerjee, Mitali; Nhalil, Hariharan; Elizabeth, Suja; Ghosh, Arindam

2015-03-01

Electrical transport in the non-trivial surface states of bulk Topological Insulator (TI) reveal several intriguing properties ranging from bipolar field effect transistor action, weak antilocalization in quantum transport, to the recently discovered quantum anomalous Hall effect. Many of these phenomena depend crucially on the nature of disorder and its screening by the Dirac Fermions at the TI surface. We have carried out a systematic study of low-frequency 1/f noise in Bi1.6Sb0.4Te2Se1 single crystals, to explore the dominant source of scattering of surface electrons and monitor relative contributions of the surface and bulk channels. Our results reveal that while trapped coulomb impurities at the substrate-TI interface are dominating source of scattering for thin (10 nm) TI, charged crystal disorder contribute strongly in thick TI (110 nm) channels. An unexpected maximum at 25K in noise from thick TI devices indicate scattering of the surface states by a cooperative charge dynamics in the bulk of the TI, possibly associated with the Selenium vacancies. Our experiment demonstrates, for the first time, impact of the bulk charge distribution on the surface state transport in TIs that could be crucial to the implementation of these materials in electronic applications.

Modeling the Electrostatics of Hollow Shell Suspensions: Ion Distribution, Pair Interactions, and Many-Body Effects.

PubMed

Hallez, Yannick; Meireles, Martine

2016-10-11

Electrostatic interactions play a key role in hollow shell suspensions as they determine their structure, stability, thermodynamics, and rheology and also the loading capacity of small charged species for nanoreservoir applications. In this work, fast, reliable modeling strategies aimed at predicting the electrostatics of hollow shells for one, two, and many colloids are proposed and validated. The electrostatic potential inside and outside a hollow shell with a finite thickness and a specific permittivity is determined analytically in the Debye-Hückel (DH) limit. An expression for the interaction potential between two such hollow shells is then derived and validated numerically. It follows a classical Yukawa form with an effective charge depending on the shell geometry, permittivity, and inner and outer surface charge densities. The predictions of the Ornstein-Zernike (OZ) equation with this pair potential to determine equations of state are then evaluated by comparison to results obtained with a Brownian dynamics algorithm coupled to the resolution of the linearized Poisson-Boltzmann and Laplace equations (PB-BD simulations). The OZ equation based on the DLVO-like potential performs very well in the dilute regime as expected, but also quite well, and more surprisingly, in the concentrated regime in which full spheres exhibit significant many-body effects. These effects are shown to vanish for shells with small thickness and high permittivity. For highly charged hollow shells, we propose and validate a charge renormalization procedure. Finally, using PB-BD simulations, we show that the cell model predicts the ion distribution inside and outside hollow shells accurately in both electrostatically dilute and concentrated suspensions. We then determine the shell loading capacity as a function of salt concentration, volume fraction, and surface charge density for nanoreservoir applications such as drug delivery, sensing, or smart coatings.

Simulation of the dynamical transmission of several-hundred-keV protons through a conical capillary

NASA Astrophysics Data System (ADS)

Yang, A. X.; Zhu, B. H.; Niu, S. T.; Pan, P.; Han, C. Z.; Song, H. Y.; Shao, J. X.; Chen, X. M.

2018-05-01

The time evolution of the trajectories, angular distributions, and two-dimensional images of intermediate-energy protons being transmitted through a conical capillary was simulated. The simulation results indicate that the charge deposited in the capillary significantly enhances the probability of surface specular scattering and thus greatly enhances the transmission rate. Furthermore, this deposited-charge-assisted specular reflection causes the transmission rate to exhibit an energy dependence proportional to E-1, which is very consistent with the experimental data. After transmission at nonzero tilt angles, the angular distribution of several-hundred-keV protons is far from symmetric, unlike in the case of keV protons.

Comparison of Classical and Charge Storage Methods for Determining Conductivity of Thin Film Insulators

NASA Technical Reports Server (NTRS)

Swaminathan, Prasanna; Dennison, J. R.; Sim, Alec; Brunson, Jerilyn; Crapo, Eric; Frederickson, A. R.

2004-01-01

Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of charged particles, light, and plasma, with a metal electrode attached to the other side of the insulator. Data are obtained by capacitive coupling to measure both the resulting voltage on the open surface and emission of electrons from the exposed surface, as well monitoring currents to the electrode. Instrumentation for both classical and charge storage decay methods has been developed and tested at Jet Propulsion Laboratory (JPL) and at Utah State University (USU). Details of the apparatus, test methods and data analysis are given here. The JPL charge storage decay chamber is a first-generation instrument, designed to make detailed measurements on only three to five samples at a time. Because samples must typically be tested for over a month, a second-generation high sample throughput charge storage decay chamber was developed at USU with the capability of testing up to 32 samples simultaneously. Details are provided about the instrumentation to measure surface charge and current; for charge deposition apparatus and control; the sample holders to properly isolate the mounted samples; the sample carousel to rotate samples into place; the control of the sample environment including sample vacuum, ambient gas, and sample temperature; and the computer control and data acquisition systems. Measurements are compared here for a number of thin film insulators using both methods at both facilities. We have found that conductivity determined from charge storage decay methods is 102 to 104 larger than values obtained from classical methods. Another Spacecraft Charging Conference presentation describes more extensive measurements made with these apparatus. This work is supported through funding from the NASA Space Environments and Effects Program and the USU Space Dynamics Laboratory Enabling Technologies Program.

Investigation of Ion-Implanted Photosensitive Silicon Structures by Electrochemical Capacitance–Voltage Profiling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yakovlev, G. E., E-mail: geyakovlev@etu.ru; Frolov, D. S.; Zubkova, A. V.

2016-03-15

The method of electrochemical capacitance–voltage profiling is used to study boron-implanted silicon structures for CCD matrices with backside illumination. A series of specially prepared structures with different energies and doses of ion implantation and also with various materials used for the coating layers (aluminum, silicon oxide, and their combinations) is studied. The profiles of the depth distribution of majority charge carriers of the studied structures are obtained experimentally. Also, using the Poisson equation and the Fredholm equation of the first kind, the distributions of the charge-carrier concentration and of the electric field in the structures are calculated. On the basismore » of the analysis and comparison of theoretical and experimental concentration profiles, recommendations concerning optimization of the structures’ parameters in order to increase the value of the pulling field and decrease the effect of the surface potential on the transport of charge carriers are suggested.« less

Self-Consistent Approach to Global Charge Neutrality in Electrokinetics: A Surface Potential Trap Model

NASA Astrophysics Data System (ADS)

Wan, Li; Xu, Shixin; Liao, Maijia; Liu, Chun; Sheng, Ping

2014-01-01

In this work, we treat the Poisson-Nernst-Planck (PNP) equations as the basis for a consistent framework of the electrokinetic effects. The static limit of the PNP equations is shown to be the charge-conserving Poisson-Boltzmann (CCPB) equation, with guaranteed charge neutrality within the computational domain. We propose a surface potential trap model that attributes an energy cost to the interfacial charge dissociation. In conjunction with the CCPB, the surface potential trap can cause a surface-specific adsorbed charge layer σ. By defining a chemical potential μ that arises from the charge neutrality constraint, a reformulated CCPB can be reduced to the form of the Poisson-Boltzmann equation, whose prediction of the Debye screening layer profile is in excellent agreement with that of the Poisson-Boltzmann equation when the channel width is much larger than the Debye length. However, important differences emerge when the channel width is small, so the Debye screening layers from the opposite sides of the channel overlap with each other. In particular, the theory automatically yields a variation of σ that is generally known as the "charge regulation" behavior, attendant with predictions of force variation as a function of nanoscale separation between two charged surfaces that are in good agreement with the experiments, with no adjustable or additional parameters. We give a generalized definition of the ζ potential that reflects the strength of the electrokinetic effect; its variations with the concentration of surface-specific and surface-nonspecific salt ions are shown to be in good agreement with the experiments. To delineate the behavior of the electro-osmotic (EO) effect, the coupled PNP and Navier-Stokes equations are solved numerically under an applied electric field tangential to the fluid-solid interface. The EO effect is shown to exhibit an intrinsic time dependence that is noninertial in its origin. Under a step-function applied electric field, a pulse of fluid flow is followed by relaxation to a new ion distribution, owing to the diffusive counter current. We have numerically evaluated the Onsager coefficients associated with the EO effect, L21, and its reverse streaming potential effect, L12, and show that L12=L21 in accordance with the Onsager relation. We conclude by noting some of the challenges ahead.

Inner-sphere complexation of cations at the rutile-water interface: A concise surface structural interpretation with the CD and MUSIC model

NASA Astrophysics Data System (ADS)

Ridley, Moira K.; Hiemstra, Tjisse; van Riemsdijk, Willem H.; Machesky, Michael L.

2009-04-01

Acid-base reactivity and ion-interaction between mineral surfaces and aqueous solutions is most frequently investigated at the macroscopic scale as a function of pH. Experimental data are then rationalized by a variety of surface complexation models. These models are thermodynamically based which in principle does not require a molecular picture. The models are typically calibrated to relatively simple solid-electrolyte solution pairs and may provide poor descriptions of complex multi-component mineral-aqueous solutions, including those found in natural environments. Surface complexation models may be improved by incorporating molecular-scale surface structural information to constrain the modeling efforts. Here, we apply a concise, molecularly-constrained surface complexation model to a diverse suite of surface titration data for rutile and thereby begin to address the complexity of multi-component systems. Primary surface charging curves in NaCl, KCl, and RbCl electrolyte media were fit simultaneously using a charge distribution (CD) and multisite complexation (MUSIC) model [Hiemstra T. and Van Riemsdijk W. H. (1996) A surface structural approach to ion adsorption: the charge distribution (CD) model. J. Colloid Interf. Sci. 179, 488-508], coupled with a Basic Stern layer description of the electric double layer. In addition, data for the specific interaction of Ca 2+ and Sr 2+ with rutile, in NaCl and RbCl media, were modeled. In recent developments, spectroscopy, quantum calculations, and molecular simulations have shown that electrolyte and divalent cations are principally adsorbed in various inner-sphere configurations on the rutile 1 1 0 surface [Zhang Z., Fenter P., Cheng L., Sturchio N. C., Bedzyk M. J., Předota M., Bandura A., Kubicki J., Lvov S. N., Cummings P. T., Chialvo A. A., Ridley M. K., Bénézeth P., Anovitz L., Palmer D. A., Machesky M. L. and Wesolowski D. J. (2004) Ion adsorption at the rutile-water interface: linking molecular and macroscopic properties. Langmuir20, 4954-4969]. Our CD modeling results are consistent with these adsorbed configurations provided adsorbed cation charge is allowed to be distributed between the surface (0-plane) and Stern plane (1-plane). Additionally, a complete description of our titration data required inclusion of outer-sphere binding, principally for Cl - which was common to all solutions, but also for Rb + and K +. These outer-sphere species were treated as point charges positioned at the Stern layer, and hence determined the Stern layer capacitance value. The modeling results demonstrate that a multi-component suite of experimental data can be successfully rationalized within a CD and MUSIC model using a Stern-based description of the EDL. Furthermore, the fitted CD values of the various inner-sphere complexes of the mono- and divalent ions can be linked to the microscopic structure of the surface complexes and other data found by spectroscopy as well as molecular dynamics (MD). For the Na + ion, the fitted CD value points to the presence of bidenate inner-sphere complexation as suggested by a recent MD study. Moreover, its MD dominance quantitatively agrees with the CD model prediction. For Rb +, the presence of a tetradentate complex, as found by spectroscopy, agreed well with the fitted CD and its predicted presence was quantitatively in very good agreement with the amount found by spectroscopy.

inner-sphere complexation of cations at the rutile-water interface: A concise surface structural interpretation with the CD and MUSIC model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ridley, Mora K.; Hiemstra, T; Van Riemsdijk, Willem H.

Acid base reactivity and ion-interaction between mineral surfaces and aqueous solutions is most frequently investigated at the macroscopic scale as a function of pH. Experimental data are then rationalized by a variety of surface complexation models. These models are thermodynamically based which in principle does not require a molecular picture. The models are typically calibrated to relatively simple solid-electrolyte solution pairs and may provide poor descriptions of complex multicomponent mineral aqueous solutions, including those found in natural environments. Surface complexation models may be improved by incorporating molecular-scale surface structural information to constrain the modeling efforts. Here, we apply a concise,more » molecularly-constrained surface complexation model to a diverse suite of surface titration data for rutile and thereby begin to address the complexity of multi-component systems. Primary surface charging curves in NaCl, KCl, and RbCl electrolyte media were fit simultaneously using a charge distribution (CD) and multisite complexation (MUSIC) model [Hiemstra T. and Van Riemsdijk W. H. (1996) A surface structural approach to ion adsorption: the charge distribution (CD) model. J. Colloid Interf. Sci. 179, 488 508], coupled with a Basic Stern layer description of the electric double layer. In addition, data for the specific interaction of Ca2+ and Sr2+ with rutile, in NaCl and RbCl media, were modeled. In recent developments, spectroscopy, quantum calculations, and molecular simulations have shown that electrolyte and divalent cations are principally adsorbed in various inner-sphere configurations on the rutile 110 surface [Zhang Z., Fenter P., Cheng L., Sturchio N. C., Bedzyk M. J., Pr edota M., Bandura A., Kubicki J., Lvov S. N., Cummings P. T., Chialvo A. A., Ridley M. K., Be ne zeth P., Anovitz L., Palmer D. A., Machesky M. L. and Wesolowski D. J. (2004) Ion adsorption at the rutile water interface: linking molecular and macroscopic properties. Langmuir 20, 4954 4969]. Our CD modeling results are consistent with these adsorbed configurations provided adsorbed cation charge is allowed to be distributed between the surface (0-plane) and Stern plane (1-plane). Additionally, a complete description of our titration data required inclusion of outer-sphere binding, principally for Cl which was common to all solutions, but also for Rb+ and K+. These outer-sphere species were treated as point charges positioned at the Stern layer, and hence determined the Stern layer capacitance value. The modeling results demonstrate that a multi-component suite of experimental data can be successfully rationalized within a CD and MUSIC model using a Stern-based description of the EDL. Furthermore, the fitted CD values of the various inner-sphere complexes of the mono- and divalent ions can be linked to the microscopic structure of the surface complexes and other data found by spectroscopy as well as molecular dynamics (MD). For the Na+ ion, the fitted CD value points to the presence of bidenate inner-sphere complexation as suggested by a recent MD study. Moreover, its MD dominance quantitatively agrees with the CD model prediction. For Rb+, the presence of a tetradentate complex, as found by spectroscopy, agreed well with the fitted CD and its predicted presence was quantitatively in very good agreement with the amount found by spectroscopy.« less

Evolutionary conservativeness of electric field in the Cu,Zn superoxide dismutase active site. Evidence for co-ordinated mutation of charged amino acid residues.

PubMed

Desideri, A; Falconi, M; Polticelli, F; Bolognesi, M; Djinovic, K; Rotilio, G

1992-01-05

Equipotential lines were calculated, using the Poisson-Boltzmann equation, for six Cu,Zn superoxide dismutases with different protein electric charge and various degrees of sequence homology, namely those from ox, pig, sheep, yeast, and the isoenzymes A and B from the amphibian Xenopus laevis. The three-dimensional structures of the porcine and ovine superoxide dismutases were obtained by molecular modelling reconstruction using the structure of the highly homologous bovine enzyme as a template. The three-dimensional structure of the evolutionary distant yeast Cu,Zn superoxide dismutase was recently resolved by us, while computer-modelled structures are available for X. laevis isoenzymes. The six proteins display large differences in the net protein charge and distribution of electrically charged surface residues but the trend of the equipotential lines in the proximity of the active sites was found to be constant in all cases. These results are in line with the very similar catlytic rate constants experimentally measured for the corresponding enzyme activities. This analysis shows that electrostatic guidance for the enzyme-substrate interaction in Cu,Zn superoxide dismutases is related to a spatial distribution of charges, arranged so as to maintain, in the area surrounding the active sites, an identical electrostatic potential distribution, which is conserved in the evolution of this protein family.

Effects of Systematic Variation in Size and Surface Coating of Silver Nanoparticles on Their In Vitro Toxicity to Macrophage RAW 264.7 Cells.

PubMed

Makama, Sunday; Kloet, Samantha K; Piella, Jordi; van den Berg, Hans; de Ruijter, Norbert C A; Puntes, Victor F; Rietjens, Ivonne M C M; van den Brink, Nico W

2018-03-01

In literature, varying and sometimes conflicting effects of physicochemical properties of nanoparticles (NPs) are reported on their uptake and effects in organisms. To address this, small- and medium-sized (20 and 50 nm) silver nanoparticles (AgNPs) with specified different surface coating/charges were synthesized and used to systematically assess effects of NP-properties on their uptake and effects in vitro. Silver nanoparticles were fully characterized for charge and size distribution in both water and test media. Macrophage cells (RAW 264.7) were exposed to these AgNPs at different concentrations (0-200 µg/ml). Uptake dynamics, cell viability, induction of tumor necrosis factor (TNF)-α, ATP production, and reactive oxygen species (ROS) generation were assessed. Microscopic imaging of living exposed cells showed rapid uptake and subcellular cytoplasmic accumulation of AgNPs. Exposure to the tested AgNPs resulted in reduced overall viability. Influence of both size and surface coating (charge) was demonstrated, with the 20-nm-sized AgNPs and bovine serum albumin (BSA)-coated (negatively charged) AgNPs being slightly more toxic. On specific mechanisms of toxicity (TNF-α and ROS production) however, the AgNPs differed to a larger extent. The highest induction of TNF-α was found in cells exposed to the negatively charged AgNP_BSA, both sizes (80× higher than control). Reactive oxygen species induction was only significant with the 20 nm positively charged AgNP_Chit.

Analytical model of a corona discharge from a conical electrode under saturation

NASA Astrophysics Data System (ADS)

Boltachev, G. Sh.; Zubarev, N. M.

2012-11-01

Exact partial solutions are found for the electric field distribution in the outer region of a stationary unipolar corona discharge from an ideal conical needle in the space-charge-limited current mode with allowance for the electric field dependence of the ion mobility. It is assumed that only the very tip of the cone is responsible for the discharge, i.e., that the ionization zone is a point. The solutions are obtained by joining the spherically symmetric potential distribution in the drift space and the self-similar potential distribution in the space-charge-free region. Such solutions are outside the framework of the conventional Deutsch approximation, according to which the space charge insignificantly influences the shape of equipotential surfaces and electric lines of force. The dependence is derived of the corona discharge saturation current on the apex angle of the conical electrode and applied potential difference. A simple analytical model is suggested that describes drift in the point-plane electrode geometry under saturation as a superposition of two exact solutions for the field potential. In terms of this model, the angular distribution of the current density over the massive plane electrode is derived, which agrees well with Warburg's empirical law.

Influence of pH, layer charge location and crystal thickness distribution on U(VI) sorption onto heterogeneous dioctahedral smectite.

PubMed

Guimarães, Vanessa; Rodríguez-Castellón, Enrique; Algarra, Manuel; Rocha, Fernando; Bobos, Iuliu

2016-11-05

The UO2(2+) adsorption on smectite (samples BA1, PS2 and PS3) with a heterogeneous structure was investigated at pH 4 (I=0.02M) and pH 6 (I=0.2M) in batch experiments, with the aim to evaluate the influence of pH, layer charge location and crystal thickness distribution. Mean crystal thickness distribution of smectite crystallite used in sorption experiments range from 4.8nm (sample PS2), to 5.1nm (sample PS3) and, to 7.4nm (sample BA1). Smaller crystallites have higher total surface area and sorption capacity. Octahedral charge location favor higher sorption capacity. The sorption isotherms of Freundlich, Langmuir and SIPS were used to model the sorption experiments. The surface complexation and cation exchange reactions were modeled using PHREEQC-code to describe the UO2(2+) sorption on smectite. The amount of UO2(2+) adsorbed on smectite samples decreased significantly at pH 6 and higher ionic strength, where the sorption mechanism was restricted to the edge sites of smectite. Two binding energy components at 380.8±0.3 and 382.2±0.3eV, assigned to hydrated UO2(2+) adsorbed by cation exchange and by inner-sphere complexation on the external sites at pH 4, were identified after the U4f7/2 peak deconvolution by X-photoelectron spectroscopy. Also, two new binding energy components at 380.3±0.3 and 381.8±0.3eV assigned to AlOUO2(+) and SiOUO2(+) surface species were observed at pH 6. Copyright © 2016 Elsevier B.V. All rights reserved.

Using magnetic charge to understand soft-magnetic materials

NASA Astrophysics Data System (ADS)

Arrott, Anthony S.; Templeton, Terry L.

2018-04-01

This is an overview of what the Landau-Lifshitz-Gilbert equations are doing in soft-magnetic materials with dimensions large compared to the exchange length. The surface magnetic charges try to cancel applied magnetic fields inside the soft magnetic material. The exchange energy tries to reach a minimum while meeting the boundary conditions set by the magnetic charges by using magnetization patterns that have a curl but no divergence. It can almost do this, but it still pays to add some divergence to further lower the exchange energy. There are then both positively and negatively charged regions in the bulk. The unlike charges attract one another, but do not annihilate because they are paid for by the reduction in exchange energy. The micromagnetics of soft magnetic materials is about how those charges rearrange themselves. The topology of magnetic charge distributions presents challenges for mathematicians. No one guessed that they like to form helical patterns of extended multiples of charge density.

Study of solids by use of nonthermalized positrons

NASA Astrophysics Data System (ADS)

Nielsen, Bent; Lynn, K. G.; Chen, Yen-C.

1986-10-01

We have measured the energy distribution of positrons reemitted from the surfaces of solids after being implanted at low energy. It is shown that this provides a unique possibility to study energy losses of a charged particle down to near-thermal energy. Such measurements are used to estimate the positron thermalization time in Al. A dramatic change in this energy distribution was observed after oxidation of the Al surface. We attribute this to the band gap of the oxide. Trapping of epithermal positrons with a remarkably high cross section was observed for both Al and Cu.

Charge retention of soft-landed phosphotungstate Keggin anions on self-assembled monolayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunaratne, K. Don D.; Prabhakaran, Venkateshkumar; Andersen, Amity

Soft landing of mass-selected ions onto surfaces often results in partial loss of charge that may affect the structure and reactivity of deposited species. In this study, Keggin phosphotungstate anions in two selected charge states, PW12O403- (WPOM3-) and PW12O402- (WPOM2-), were soft-landed onto different self-assembled monolayer (SAM) surfaces and examined using in situ infrared reflection absorption spectroscopy (IRRAS) and density functional theory (DFT) calculations. Partial retention of the 3- charge was observed when WPOM3- was soft-landed onto the fluorinated SAM (FSAM), while the charge state distribution was dominated by the 2- charge after both WPOM3- and WPOM2- were deposited ontomore » a hydrophilic alkylthiol SAM terminated with cationic NH3+ functional groups (NH3+SAM). We found that during the course of the soft landing of WPOM3-, the relative abundance of WPOM3- on FSAM decreased while that of WPOM2- increased. We propose that the higher stability of immobilized WPOM2- in comparison with WPOM3- makes it the preferred charge state of WPOM on both the FSAM and NH3+SAM. We also observe weaker binding of WPOM anions to SAMs in comparison with phosphomolybdate ions (MoPOM) reported previously (J. Phys. Chem. C 2014, 118, 27611–27622). The weaker binding of WPOM to SAMs is attributed to the lower reactivity of WPOM reported in the literature. This study demonstrates that both the charge retention and the reactivity of deposited anionic POM clusters on surfaces are determined by the type of addenda metal atoms in the cluster.« less

Evaluation of reduced point charge models of proteins through Molecular Dynamics simulations: application to the Vps27 UIM-1-Ubiquitin complex.

PubMed

Leherte, Laurence; Vercauteren, Daniel P

2014-02-01

Reduced point charge models of amino acids are designed, (i) from local extrema positions in charge density distribution functions built from the Poisson equation applied to smoothed molecular electrostatic potential (MEP) functions, and (ii) from local maxima positions in promolecular electron density distribution functions. Corresponding charge values are fitted versus all-atom Amber99 MEPs. To easily generate reduced point charge models for protein structures, libraries of amino acid templates are built. The program GROMACS is used to generate stable Molecular Dynamics trajectories of an Ubiquitin-ligand complex (PDB: 1Q0W), under various implementation schemes, solvation, and temperature conditions. Point charges that are not located on atoms are considered as virtual sites with a nul mass and radius. The results illustrate how the intra- and inter-molecular H-bond interactions are affected by the degree of reduction of the point charge models and give directions for their implementation; a special attention to the atoms selected to locate the virtual sites and to the Coulomb-14 interactions is needed. Results obtained at various temperatures suggest that the use of reduced point charge models allows to probe local potential hyper-surface minima that are similar to the all-atom ones, but are characterized by lower energy barriers. It enables to generate various conformations of the protein complex more rapidly than the all-atom point charge representation. Copyright © 2013 Elsevier Inc. All rights reserved.

Calculation of ionized fields in DC electrostatic precipitators in the presence of dust and electric wind

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cristina, S.; Feliziani, M.

1995-11-01

This paper describes a new procedure for the numerical computation of the electric field and current density distributions in a dc electrostatic precipitator in the presence of dust, taking into account the particle-size distribution. Poisson`s and continuity equations are numerically solved by supposing that the coronating conductors satisfy Kaptzov`s assumption on the emitter surfaces. Two iterative numerical procedures, both based on the finite element method (FEM), are implemented for evaluating, respectively, the unknown ionic charge density and the particle charge density distributions. The V-I characteristic and the precipitation efficiencies for the individual particle-size classes, calculated with reference to the pilotmore » precipitator installed by ENEL (Italian Electricity Board) at its Marghera (Venice) coal-fired power station, are found to be very close to those measured experimentally.« less

High Current Ionic Diode Using Homogeneously Charged Asymmetric Nanochannel Network Membrane.

PubMed

Choi, Eunpyo; Wang, Cong; Chang, Gyu Tae; Park, Jungyul

2016-04-13

A high current ionic diode is achieved using an asymmetric nanochannel network membrane (NCNM) constructed by soft lithography and in situ self-assembly of nanoparticles with uniform surface charge. The asymmetric NCNM exhibits high rectified currents without losing a rectification ratio because of its ionic selectivity gradient and differentiated electrical conductance. Asymmetric ionic transport is analyzed with diode-like I-V curves and visualized via fluorescent dyes, which is closely correlated with ionic selectivity and ion distribution according to variation of NCNM geometries.

Orienting proteins by nanostructured surfaces: evidence of a curvature-driven geometrical resonance.

PubMed

Messina, Grazia M L; Bocchinfuso, Gianfranco; Giamblanco, Nicoletta; Mazzuca, Claudia; Palleschi, Antonio; Marletta, Giovanni

2018-04-26

Experimental and theoretical reports have shown that nanostructured surfaces have a dramatic effect on the amount of protein adsorbed and the conformational state and, in turn, on the performances of the related devices in tissue engineering strategies. Here we report an innovative method to prepare silica-based nanostructured surfaces with a reproducible, well-defined local curvature, consisting of ordered hexagonally packed arrays of curved hemispheres, from nanoparticles of different diameters (respectively 147 nm, 235 nm and 403 nm). The nanostructured surfaces have been made chemically homogeneous by partially embedding silica nanoparticles in poly(hydroxymethylsiloxane) films, further modified by means of UV-O3 treatments. This paper has been focused on the experimental and theoretical study of laminin, taken as a model protein, to study the nanocurvature effects on the protein configuration at nanostructured surfaces. A simple model, based on the interplay of electrostatic interactions between the charged terminal domains of laminin and the nanocurved charged surfaces, closely reproduces the experimental findings. In particular, the model suggests that nanocurvature drives the orientation of rigid proteins by means of a "geometrical resonance" effect, involving the matching of dimensions, charge distribution and spatial arrangement of both adsorbed molecules and adsorbent nanostructures. Overall, the results pave the way to unravel the nanostructured surface effects on the intra- and inter-molecular organization processes of proteins.

Optoelectronic properties and depth profile of charge transport in nanocrystal films

NASA Astrophysics Data System (ADS)

Aigner, Willi; Bienek, Oliver; Desta, Derese; Wiggers, Hartmut; Stutzmann, Martin; Pereira, Rui N.

2017-07-01

We investigate the charge transport in nanocrystal (NC) films using field effect transistors (FETs) of silicon NCs. By studying films with various thicknesses in the dark and under illumination with photons with different penetration depths (UV and red light), we are able to predictably change the spatial distribution of charge carriers across the films' profile. The experimental data are compared with photoinduced charge carrier generation rates computed using finite-difference time-domain (FDTD) simulations complemented with optical measurements. This enables us to understand the optoelectronic properties of NC films and the depth profile dependence of the charge transport properties. From electrical measurements, we extract the total (bulk) photoinduced charge carrier densities (nphoto) and the photoinduced charge carrier densities in the FETs channel (nphoto*). We observe that the values of nphoto and their dependence on film thickness are similar for UV and red light illumination, whereas a significant difference is observed for the values of nphoto*. The dependencies of nphoto and nphoto* on film thickness and illumination wavelength are compared with data from FDTD simulations. Combining experimental data and simulation results, we find that charge carriers in the top rough surface of the films cannot contribute to the macroscopic charge transport. Moreover, we conclude that below the top rough surface of NC films, the efficiency of charge transport, including the charge carrier mobility, is homogeneous across the film thickness. Our work shows that the use of NC films as photoactive layers in applications requiring harvesting of strongly absorbed photons such as photodetectors and photovoltaics demands a very rigorous control over the films' roughness.

Model for screened, charge-regulated electrostatics of an eye lens protein: Bovine gammaB-crystallin

PubMed Central

Wahle, Christopher W.; Martini, K. Michael; Hollenbeck, Dawn M.; Langner, Andreas; Ross, David S.; Hamilton, John F.; Thurston, George M.

2018-01-01

We model screened, site-specific charge regulation of the eye lens protein bovine gammaB-crystallin (γ B) and study the probability distributions of its proton occupancy patterns. Using a simplified dielectric model, we solve the linearized Poisson-Boltzmann equation to calculate a 54 × 54 work-of-charging matrix, each entry being the modeled voltage at a given titratable site, due to an elementary charge at another site. The matrix quantifies interactions within patches of sites, including γB charge pairs. We model intrinsic pK values that would occur hypothetically in the absence of other charges, with use of experimental data on the dependence of pK values on aqueous solution conditions, the dielectric model, and literature values. We use Monte Carlo simulations to calculate a model grand-canonical partition function that incorporates both the work-of-charging and the intrinsic pK values for isolated γB molecules and we calculate the probabilities of leading proton occupancy configurations, for 4 < pH < 8 and Debye screening lengths from 6 to 20 Å. We select the interior dielectric value to model γB titration data. At pH 7.1 and Debye length 6.0 Å, on a given γB molecule the predicted top occupancy pattern is present nearly 20% of the time, and 90% of the time one or another of the first 100 patterns will be present. Many of these occupancy patterns differ in net charge sign as well as in surface voltage profile. We illustrate how charge pattern probabilities deviate from the multinomial distribution that would result from use of effective pK values alone and estimate the extents to which γB charge pattern distributions broaden at lower pH and narrow as ionic strength is lowered. These results suggest that for accurate modeling of orientation-dependent γB-γB interactions, consideration of numerous pairs of proton occupancy patterns will be needed. PMID:29346981

Model for screened, charge-regulated electrostatics of an eye lens protein: Bovine gammaB-crystallin.

PubMed

Wahle, Christopher W; Martini, K Michael; Hollenbeck, Dawn M; Langner, Andreas; Ross, David S; Hamilton, John F; Thurston, George M

2017-09-01

We model screened, site-specific charge regulation of the eye lens protein bovine gammaB-crystallin (γB) and study the probability distributions of its proton occupancy patterns. Using a simplified dielectric model, we solve the linearized Poisson-Boltzmann equation to calculate a 54×54 work-of-charging matrix, each entry being the modeled voltage at a given titratable site, due to an elementary charge at another site. The matrix quantifies interactions within patches of sites, including γB charge pairs. We model intrinsic pK values that would occur hypothetically in the absence of other charges, with use of experimental data on the dependence of pK values on aqueous solution conditions, the dielectric model, and literature values. We use Monte Carlo simulations to calculate a model grand-canonical partition function that incorporates both the work-of-charging and the intrinsic pK values for isolated γB molecules and we calculate the probabilities of leading proton occupancy configurations, for 4

Model for screened, charge-regulated electrostatics of an eye lens protein: Bovine gammaB-crystallin

NASA Astrophysics Data System (ADS)

Wahle, Christopher W.; Martini, K. Michael; Hollenbeck, Dawn M.; Langner, Andreas; Ross, David S.; Hamilton, John F.; Thurston, George M.

2017-09-01

We model screened, site-specific charge regulation of the eye lens protein bovine gammaB-crystallin (γ B ) and study the probability distributions of its proton occupancy patterns. Using a simplified dielectric model, we solve the linearized Poisson-Boltzmann equation to calculate a 54 ×54 work-of-charging matrix, each entry being the modeled voltage at a given titratable site, due to an elementary charge at another site. The matrix quantifies interactions within patches of sites, including γ B charge pairs. We model intrinsic p K values that would occur hypothetically in the absence of other charges, with use of experimental data on the dependence of p K values on aqueous solution conditions, the dielectric model, and literature values. We use Monte Carlo simulations to calculate a model grand-canonical partition function that incorporates both the work-of-charging and the intrinsic p K values for isolated γ B molecules and we calculate the probabilities of leading proton occupancy configurations, for 4

Impact of GaN cap on charges in Al₂O₃/(GaN/)AlGaN/GaN metal-oxide-semiconductor heterostructures analyzed by means of capacitance measurements and simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ťapajna, M., E-mail: milan.tapajna@savba.sk; Jurkovič, M.; Válik, L.

2014-09-14

Oxide/semiconductor interface trap density (D{sub it}) and net charge of Al₂O₃/(GaN)/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with and without GaN cap were comparatively analyzed using comprehensive capacitance measurements and simulations. D{sub it} distribution was determined in full band gap of the barrier using combination of three complementary capacitance techniques. A remarkably higher D{sub it} (∼5–8 × 10¹²eV⁻¹ cm⁻²) was found at trap energies ranging from E C-0.5 to 1 eV for structure with GaN cap compared to that (D{sub it} ∼ 2–3 × 10¹²eV⁻¹ cm⁻²) where the GaN cap was selectively etched away. D{sub it} distributions were then used for simulation of capacitance-voltage characteristics. A good agreement betweenmore » experimental and simulated capacitance-voltage characteristics affected by interface traps suggests (i) that very high D{sub it} (>10¹³eV⁻¹ cm⁻²) close to the barrier conduction band edge hampers accumulation of free electron in the barrier layer and (ii) the higher D{sub it} centered about E C-0.6 eV can solely account for the increased C-V hysteresis observed for MOS-HEMT structure with GaN cap. Analysis of the threshold voltage dependence on Al₂O₃ thickness for both MOS-HEMT structures suggests that (i) positive charge, which compensates the surface polarization, is not necessarily formed during the growth of III-N heterostructure, and (ii) its density is similar to the total surface polarization charge of the GaN/AlGaN barrier, rather than surface polarization of the top GaN layer only. Some constraints for the positive surface compensating charge are discussed.« less

Calculations of the electrostatic potential adjacent to model phospholipid bilayers.

PubMed

Peitzsch, R M; Eisenberg, M; Sharp, K A; McLaughlin, S

1995-03-01

We used the nonlinear Poisson-Boltzmann equation to calculate electrostatic potentials in the aqueous phase adjacent to model phospholipid bilayers containing mixtures of zwitterionic lipids (phosphatidylcholine) and acidic lipids (phosphatidylserine or phosphatidylglycerol). The aqueous phase (relative permittivity, epsilon r = 80) contains 0.1 M monovalent salt. When the bilayers contain < 11% acidic lipid, the -25 mV equipotential surfaces are discrete domes centered over the negatively charged lipids and are approximately twice the value calculated using Debye-Hückel theory. When the bilayers contain > 25% acidic lipid, the -25 mV equipotential profiles are essentially flat and agree well with the values calculated using Gouy-Chapman theory. When the bilayers contain 100% acidic lipid, all of the equipotential surfaces are flat and agree with Gouy-Chapman predictions (including the -100 mV surface, which is located only 1 A from the outermost atoms). Even our model bilayers are not simple systems: the charge on each lipid is distributed over several atoms, these partial charges are non-coplanar, there is a 2 A ion-exclusion region (epsilon r = 80) adjacent to the polar headgroups, and the molecular surface is rough. We investigated the effect of these four factors using smooth (or bumpy) epsilon r = 2 slabs with embedded point charges: these factors had only minor effects on the potential in the aqueous phase.

Calculations of the electrostatic potential adjacent to model phospholipid bilayers.

PubMed Central

Peitzsch, R M; Eisenberg, M; Sharp, K A; McLaughlin, S

1995-01-01

We used the nonlinear Poisson-Boltzmann equation to calculate electrostatic potentials in the aqueous phase adjacent to model phospholipid bilayers containing mixtures of zwitterionic lipids (phosphatidylcholine) and acidic lipids (phosphatidylserine or phosphatidylglycerol). The aqueous phase (relative permittivity, epsilon r = 80) contains 0.1 M monovalent salt. When the bilayers contain < 11% acidic lipid, the -25 mV equipotential surfaces are discrete domes centered over the negatively charged lipids and are approximately twice the value calculated using Debye-Hückel theory. When the bilayers contain > 25% acidic lipid, the -25 mV equipotential profiles are essentially flat and agree well with the values calculated using Gouy-Chapman theory. When the bilayers contain 100% acidic lipid, all of the equipotential surfaces are flat and agree with Gouy-Chapman predictions (including the -100 mV surface, which is located only 1 A from the outermost atoms). Even our model bilayers are not simple systems: the charge on each lipid is distributed over several atoms, these partial charges are non-coplanar, there is a 2 A ion-exclusion region (epsilon r = 80) adjacent to the polar headgroups, and the molecular surface is rough. We investigated the effect of these four factors using smooth (or bumpy) epsilon r = 2 slabs with embedded point charges: these factors had only minor effects on the potential in the aqueous phase. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 PMID:7756540

Electronic structure, bonding, charge distribution, and x-ray absorption spectra of the (001) surfaces of fluorapatite and hydroxyapatite from first principles

NASA Astrophysics Data System (ADS)

Rulis, Paul; Yao, Hongzhi; Ouyang, Lizhi; Ching, W. Y.

2007-12-01

Fluorapatite (FAP) and hydroxyapatite (HAP) are two very important bioceramic crystals. The (001) surfaces of FAP and HAP crystals are studied by ab initio density functional calculations using a supercell slab geometry. It is shown that in both crystals, the O-terminated (001) surface is more stable with calculated surface energies of 0.865 and 0.871J/m2 for FAP and HAP, respectively. In FAP, the two surfaces are symmetric. In HAP, the orientation of the OH group along the c axis reduces the symmetry such that the top and bottom surfaces are no longer symmetric. It is revealed that the atoms near the surface and subsurface are significantly relaxed especially in the case of HAP. The largest relaxations occurred via the lateral movements of the O ions at the subsurface level. The electronic structures of the surface models in the form of layer-by-layer resolved partial density of states for all the atoms show systematic variation from the surface region toward the bulk region. The calculated Mulliken effective charge on each type of atom and the bond order values between cations (Ca, P) and anions (O, F) show different charge transfers and bond strength variations from the bulk crystal values. Electron charge density calculations show that the surfaces of both FAP and HAP crystals are mostly positively charged due to the presence of Ca ions at the surface. The positively charged surfaces have implications for the absorption on apatite surfaces of water and other organic molecules in an aqueous environment which are an important part of its bioactivity. The x-ray absorption near-edge structure (XANES) spectra ( Ca-K , O-K , F-K , P-K , and P-L3 edges) of both the surface models and the bulk crystals are calculated and compared. The calculations use a supercell approach which takes into account the electron-core-hole interaction. It is shown that the site-specific XANES spectra show significant differences between atoms near the surface and in the bulk and are very sensitive to the local atomic environment of each atom. This information will be very valuable for characterizing the apatite materials and in the interpretation of experimental data. Comparisons of several sets of experimental data with the weighted sums of the calculated spectra at different sites for the same element show very good agreement.

IONIZATION AND DUST CHARGING IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivlev, A. V.; Caselli, P.; Akimkin, V. V., E-mail: ivlev@mpe.mpg.de

2016-12-10

Ionization–recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance ofmore » the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.« less

Frequency and Distribution of Single-Nucleotide Polymorphisms within mprF in Methicillin-Resistant Staphylococcus aureus Clinical Isolates and Their Role in Cross-Resistance to Daptomycin and Host Defense Antimicrobial Peptides.

PubMed

Bayer, Arnold S; Mishra, Nagendra N; Chen, Liang; Kreiswirth, Barry N; Rubio, Aileen; Yang, Soo-Jin

2015-08-01

MprF is responsible for the lysinylation of phosphatidylglycerol (PG) to synthesize the positively charged phospholipid (PL) species, lysyl-PG (L-PG). It has been proposed that the single-nucleotide polymorphisms (SNPs) within the mprF open reading frame (ORF) are associated with a gain-in-function phenotype in terms of daptomycin resistance in Staphylococcus aureus. (Note that although the official term is daptomycin nonsusceptibility, we use the term daptomycin resistance in this paper for ease of presentation.) Using 22 daptomycin-susceptible (DAP(s))/daptomycin-resistant (DAP(r)) clinical methicillin-resistant S. aureus (MRSA) strain pairs, we assessed (i) the frequencies and distribution of putative mprF gain-in-function SNPs, (ii) the relationships of the SNPs to both daptomycin resistance and cross-resistance to the prototypical endovascular host defense peptide (HDP) thrombin-induced platelet microbicidal protein (tPMP), and (iii) the impact of mprF SNPs on positive surface charge phenotype and modifications of membrane PL profiles. Most of the mprF SNPs identified in our DAP(r) strains were clustered within the two MprF loci, (i) the central bifunctional domain and (ii) the C-terminal synthase domain. Moreover, we were able to correlate the presence and location of mprF SNPs in DAP(r) strains with HDP cross-resistance, positive surface charge, and L-PG profiles. Although DAP(r) strains with mprF SNPs in the bifunctional domain showed higher resistance to tPMPs than DAP(r) strains with SNPs in the synthase domain, this relationship was not observed in positive surface charge assays. These results demonstrated that both charge-mediated and -unrelated mechanisms are involved in DAP resistance and HDP cross-resistance in S. aureus. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

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

PubMed

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

1997-07-01

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.

Repulsion-based model for contact angle saturation in electrowetting

PubMed Central

2015-01-01

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results. PMID:25759748

Repulsion-based model for contact angle saturation in electrowetting.

PubMed

Ali, Hassan Abdelmoumen Abdellah; Mohamed, Hany Ahmed; Abdelgawad, Mohamed

2015-01-01

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results.

Diffuse sorption modeling.

PubMed

Pivovarov, Sergey

2009-04-01

This work presents a simple solution for the diffuse double layer model, applicable to calculation of surface speciation as well as to simulation of ionic adsorption within the diffuse layer of solution in arbitrary salt media. Based on Poisson-Boltzmann equation, the Gaines-Thomas selectivity coefficient for uni-bivalent exchange on clay, K(GT)(Me(2+)/M(+))=(Q(Me)(0.5)/Q(M)){M(+)}/{Me(2+)}(0.5), (Q is the equivalent fraction of cation in the exchange capacity, and {M(+)} and {Me(2+)} are the ionic activities in solution) may be calculated as [surface charge, mueq/m(2)]/0.61. The obtained solution of the Poisson-Boltzmann equation was applied to calculation of ionic exchange on clays and to simulation of the surface charge of ferrihydrite in 0.01-6 M NaCl solutions. In addition, a new model of acid-base properties was developed. This model is based on assumption that the net proton charge is not located on the mathematical surface plane but diffusely distributed within the subsurface layer of the lattice. It is shown that the obtained solution of the Poisson-Boltzmann equation makes such calculations possible, and that this approach is more efficient than the original diffuse double layer model.

Charge retention in scaled SONOS nonvolatile semiconductor memory devices—Modeling and characterization

NASA Astrophysics Data System (ADS)

Hu, Yin; White, Marvin H.

1993-10-01

A new analytical model is developed to investigate the influence of the charge loss processes in the retention mode of the SONOS NVSM device. The model considers charge loss by the following processes: (1) electron back-tunneling from the nitride traps to the Si conduction band, (2) electron back-tunneling from the nitride traps to the Si/SiO 2 interface traps and (3) hole injection from the Si valence band to the nitride traps. An amphoteric trap charge distribution is used in this model. The new charge retention model predicts that process (1) determines the short term retention, while processes (2) and (3) determine the long term retention. Good agreement has been reached between the results of analytical calculations and the experimental retention data on both surface channel and buried channel SONOS devices.

Agglutination of like-charged red blood cells induced by binding of beta2-glycoprotein I to outer cell surface.

PubMed

Lokar, Marusa; Urbanija, Jasna; Frank, Mojca; Hägerstrand, Henry; Rozman, Blaz; Bobrowska-Hägerstrand, Malgorzata; Iglic, Ales; Kralj-Iglic, Veronika

2008-08-01

Plasma protein-mediated attractive interaction between membranes of red blood cells (RBCs) and phospholipid vesicles was studied. It is shown that beta(2)-glycoprotein I (beta(2)-GPI) may induce RBC discocyte-echinocyte-spherocyte shape transformation and subsequent agglutination of RBCs. Based on the observed beta(2)-GPI-induced RBC cell shape transformation it is proposed that the hydrophobic portion of beta(2)-GPI molecule protrudes into the outer lipid layer of the RBC membrane and increases the area of this layer. It is also suggested that the observed agglutination of RBCs is at least partially driven by an attractive force which is of electrostatic origin and depends on the specific molecular shape and internal charge distribution of membrane-bound beta(2)-GPI molecules. The suggested beta(2)-GPI-induced attractive electrostatic interaction between like-charged RBC membrane surfaces is qualitatively explained by using a simple mathematical model within the functional density theory of the electric double layer, where the electrostatic attraction between the positively charged part of the first domains of bound beta(2)-GPI molecules and negatively charged glycocalyx of the adjacent RBC membrane is taken into account.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, Richard P.; Lott, James A.

1994-01-01

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, R.P.; Lott, J.A.

1994-09-27

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors. 5 figs.

Constructing irregular surfaces to enclose macromolecular complexes for mesoscale modeling using the discrete surface charge optimization (DISCO) algorithm.

PubMed

Zhang, Qing; Beard, Daniel A; Schlick, Tamar

2003-12-01

Salt-mediated electrostatics interactions play an essential role in biomolecular structures and dynamics. Because macromolecular systems modeled at atomic resolution contain thousands of solute atoms, the electrostatic computations constitute an expensive part of the force and energy calculations. Implicit solvent models are one way to simplify the model and associated calculations, but they are generally used in combination with standard atomic models for the solute. To approximate electrostatics interactions in models on the polymer level (e.g., supercoiled DNA) that are simulated over long times (e.g., milliseconds) using Brownian dynamics, Beard and Schlick have developed the DiSCO (Discrete Surface Charge Optimization) algorithm. DiSCO represents a macromolecular complex by a few hundred discrete charges on a surface enclosing the system modeled by the Debye-Hückel (screened Coulombic) approximation to the Poisson-Boltzmann equation, and treats the salt solution as continuum solvation. DiSCO can represent the nucleosome core particle (>12,000 atoms), for example, by 353 discrete surface charges distributed on the surfaces of a large disk for the nucleosome core particle and a slender cylinder for the histone tail; the charges are optimized with respect to the Poisson-Boltzmann solution for the electric field, yielding a approximately 5.5% residual. Because regular surfaces enclosing macromolecules are not sufficiently general and may be suboptimal for certain systems, we develop a general method to construct irregular models tailored to the geometry of macromolecules. We also compare charge optimization based on both the electric field and electrostatic potential refinement. Results indicate that irregular surfaces can lead to a more accurate approximation (lower residuals), and the refinement in terms of the electric field is more robust. We also show that surface smoothing for irregular models is important, that the charge optimization (by the TNPACK minimizer) is efficient and does not depend on the initial assigned values, and that the residual is acceptable when the distance to the model surface is close to, or larger than, the Debye length. We illustrate applications of DiSCO's model-building procedure to chromatin folding and supercoiled DNA bound to Hin and Fis proteins. DiSCO is generally applicable to other interesting macromolecular systems for which mesoscale models are appropriate, to yield a resolution between the all-atom representative and the polymer level. Copyright 2003 Wiley Periodicals, Inc. J Comput Chem 24: 2063-2074, 2003

Effects of surface roughening on the mass transport and mechanical properties of ionic polymer-metal composite

NASA Astrophysics Data System (ADS)

Chang, Longfei; Asaka, Kinji; Zhu, Zicai; Wang, Yanjie; Chen, Hualing; Li, Dichen

2014-06-01

Ionic Polymer-Metal Composite (IPMC) has been well-documented of being a promising functional material in extensive applications. In its most popular and traditional manufacturing technique, roughening is a key process to ensure a satisfying performance. In this paper, based on a lately established multi-physical model, the effect of roughening process on the inner mass transportation and the electro-active output of IPMC were investigated. In the model, the electro-chemical field was monitored by Poisson equation and a properly simplified Nernst-Planck equation set, while the mechanical field was evaluated on the basis of volume strain effect. Furthermore, with Ramo-Shockley theorem, the out-circuit current and accumulated charge on the electrode were bridged with the inner cation distribution. Besides, nominal current and charge density as well as the curvature of the deformation were evaluated to characterize the performance of IPMC. The simulation was implemented by Finite Element Method with Comsol Multi-physics, based on two groups of geometrical models, those with various rough interface and those with different thickness. The results of how the roughening impact influences on the performance of IPMC were discussed progressively in three aspects, steady-state distribution of local potential and mass concentration, current response and charge accumulation, as well as the curvature of deformation. Detailed explanations for the performance improvement resulted from surface roughening were provided from the micro-distribution point of view, which can be further explored for the process optimization of IPMC.

Subtle Change in the Charge Distribution of Surface Residues May Affect the Secondary Functions of Cytochrome c*

PubMed Central

Paul, Simanta Sarani; Sil, Pallabi; Haldar, Shubhasis; Mitra, Samaresh; Chattopadhyay, Krishnananda

2015-01-01

Although the primary function of cytochrome c (cyt c) is electron transfer, the protein caries out an additional secondary function involving its interaction with membrane cardiolipin (CDL), its peroxidase activity, and the initiation of apoptosis. Whereas the primary function of cyt c is essentially conserved, its secondary function varies depending on the source of the protein. We report here a detailed experimental and computational study, which aims to understand, at the molecular level, the difference in the secondary functions of cyt c obtained from horse heart (mammalian) and Saccharomyces cerevisiae (yeast). The conformational landscape of cyt c has been found to be heterogeneous, consisting of an equilibrium between the compact and extended conformers as well as the oligomeric species. Because the determination of relative populations of these conformers is difficult to obtain by ensemble measurements, we used fluorescence correlation spectroscopy (FCS), a method that offers single-molecule resolution. The population of different species is found to depend on multiple factors, including the protein source, the presence of CDL and urea, and their concentrations. The complex interplay between the conformational distribution and oligomerization plays a crucial role in the variation of the pre-apoptotic regulation of cyt c observed from different sources. Finally, computational studies reveal that the variation in the charge distribution at the surface and the charge reversal sites may be the key determinant of the conformational stability of cyt c. PMID:25873393

Space charge influence on the angle of conical spikes developing on a liquid-metal anode.

PubMed

Boltachev, G Sh; Zubarev, N M; Zubareva, O V

2008-05-01

The influence of the space charge of ions emitted from the surface of a conical spike on its shape has been studied. The problem of the calculation of the spatial distributions of the electric field, ion velocity field, and the space charge density near the cone tip has been reduced to the analysis of a system of ordinary differential equations. As a result of numerical solution of these equations, the criterion for the balance of the capillary and electrostatic forces on the conic surface of a liquid-metal anode has been determined. It has allowed us to relate the electrical current flowing through the system, the applied potential difference, and the cone angle. We have compared the results of our calculations with available experimental data concerning emission from the surface of pure liquid gallium, indium, tin, and some liquid alloys, such as Au+Si , Co+Ge , and Au+Ge . On the basis of the proposed model, explanations have been given for a number of specific features of the emissive behavior of different systems.

Beyond Poisson-Boltzmann: Fluctuation effects and correlation functions

NASA Astrophysics Data System (ADS)

Netz, R. R.; Orland, H.

2000-02-01

We formulate the exact non-linear field theory for a fluctuating counter-ion distribution in the presence of a fixed, arbitrary charge distribution. The Poisson-Boltzmann equation is obtained as the saddle-point of the field-theoretic action, and the effects of counter-ion fluctuations are included by a loop-wise expansion around this saddle point. The Poisson equation is obeyed at each order in this loop expansion. We explicitly give the expansion of the Gibbs potential up to two loops. We then apply our field-theoretic formalism to the case of a single impenetrable wall with counter ions only (in the absence of salt ions). We obtain the fluctuation corrections to the electrostatic potential and the counter-ion density to one-loop order without further approximations. The relative importance of fluctuation corrections is controlled by a single parameter, which is proportional to the cube of the counter-ion valency and to the surface charge density. The effective interactions and correlation functions between charged particles close to the charged wall are obtained on the one-loop level.

Detecting negative ions on board small satellites

NASA Astrophysics Data System (ADS)

Lepri, S. T.; Raines, J. M.; Gilbert, J. A.; Cutler, J.; Panning, M.; Zurbuchen, T. H.

2017-04-01

Recent measurements near comets, planets, and their satellites have shown that heavy ions, energetic neutral atoms, molecular ions, and charged dust contain a wealth of information about the origin, evolution, and interaction of celestial bodies with their space environment. Using highly sensitive plasma instruments, positively charged heavy ions have been used to trace exospheric and surface composition of comets, planets, and satellites as well as the composition of interplanetary and interstellar dust. While positive ions dominate throughout the heliosphere, negative ions are also produced from surface interactions. In fact, laboratory experiments have shown that oxygen released from rocky surfaces is mostly negatively charged. Negative ions and negatively charged nanograins have been detected with plasma electron analyzers in several different environments (e.g., by Cassini and Rosetta), though more extensive studies have been challenging without instrumentation dedicated to negative ions. We discuss an adaptation of the Fast Imaging Plasma Spectrometer (FIPS) flown on MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) for the measurement of negatively charged particles. MESSENGER/FIPS successfully measured the plasma environment of Mercury from 2011 until 2015, when the mission ended, and has been used to map multiple ion species (H+ through Na+ and beyond) throughout Mercury's space environment. Modifications to the existing instrument design fits within a 3U CubeSat volume and would provide a low mass, low power instrument, ideal for future CubeSat or distributed sensor missions seeking, for the first time, to characterize the contribution of negative particles in the heliospheric plasmas near the planets, moons, comets, and other sources.

Electric double layer at metal oxide surfaces:static properties of the cassiterite-water interface.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlcek, L.; Zhang, Z.; Machesky, M .L.

2007-03-24

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively chargedmore » variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).« less

Electric double layer at metal oxide surfaces: Static properties of the cassiterite - Water Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlcek, Lukas; Zhang, Zhan; Machesky, Michael L.

2007-01-01

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively chargedmore » variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).« less

Differential Effects of Monovalent Cations and Anions on Key Nanoparticle Attributes

EPA Science Inventory

Understanding the key particle attributes such as particle size, size distribution and surface charge of both the nano- and micron-sized particles is the first step in drug formulation as such attributes are known to directly influence several characteristics of drugs including d...

Vertical Distribution of VOCs in Soils from Groundwater to the Surface/Subslab

EPA Science Inventory

The U.S. Environmental Protection Agency (EPA) is charged by ongress with protecting the nation’s natural resources. Under the mandate of national environmental laws, the EPA strives to formulate and implement actions leading to a compatible balance between human activities and ...

Self-consistent field calculations of conductance through conjugated molecules at finite bias

NASA Astrophysics Data System (ADS)

Paulsson, Magnus; Stafström, Sven

2001-03-01

Conductance through conjugated molecules have previously been calculated for a large number of systems using the Landauer formula but only a few calculations have included charging effects. In this study we present calculations in the mean field approximation of the conductance of metal-molecule-metal systems using two different kinds of molecules for a large number of configurations and applied biases. The molecules are described in the Pariser-Parr Pople model. Current-voltage (I-V) characteristics and charge distribution of the molecule connected by one dimensional leads to reservoirs is solved within the Hartree-Fock approximation. Charging of the molecule occurs when the chemical potential of the reservoirs approach the resonant tunneling levels. The ensuing potential difference, due to the charging, shifts the tunneling peaks which affects the I-V curves considerably. Asymmetrical interaction with the metal leads, e.g. molecule on a metal surface contacted with an STM-tip, also give asymmetrical I-V curves where the potential of the molecule is shown to more closely follow the potential of the surface. Negative differential conductance is discussed in systems consisting of two weakly coupled molecules.

A multiscale model for charge inversion in electric double layers

NASA Astrophysics Data System (ADS)

Mashayak, S. Y.; Aluru, N. R.

2018-06-01

Charge inversion is a widely observed phenomenon. It is a result of the rich statistical mechanics of the molecular interactions between ions, solvent, and charged surfaces near electric double layers (EDLs). Electrostatic correlations between ions and hydration interactions between ions and water molecules play a dominant role in determining the distribution of ions in EDLs. Due to highly polar nature of water, near a surface, an inhomogeneous and anisotropic arrangement of water molecules gives rise to pronounced variations in the electrostatic and hydration energies of ions. Classical continuum theories fail to accurately describe electrostatic correlations and molecular effects of water in EDLs. In this work, we present an empirical potential based quasi-continuum theory (EQT) to accurately predict the molecular-level properties of aqueous electrolytes. In EQT, we employ rigorous statistical mechanics tools to incorporate interatomic interactions, long-range electrostatics, correlations, and orientation polarization effects at a continuum-level. Explicit consideration of atomic interactions of water molecules is both theoretically and numerically challenging. We develop a systematic coarse-graining approach to coarse-grain interactions of water molecules and electrolyte ions from a high-resolution atomistic scale to the continuum scale. To demonstrate the ability of EQT to incorporate the water orientation polarization, ion hydration, and electrostatic correlations effects, we simulate confined KCl aqueous electrolyte and show that EQT can accurately predict the distribution of ions in a thin EDL and also predict the complex phenomenon of charge inversion.

Prediction of purification of biopharmeceuticals with molecular dynamics

NASA Astrophysics Data System (ADS)

Ustach, Vincent; Faller, Roland

Purification of biopharmeceuticals remains the most expensive part of protein-based drug production. In ion exchange chromatography (IEX), prediction of the elution ionic strength of host cell and target proteins has the potential to reduce the parameter space for scale-up of protein production. The complex shape and charge distribution of proteins and pores complicates predictions of the interactions in these systems. All-atom molecular dynamics methods are beyond the scope of computational limits for mass transport regimes. We present a coarse-grained model for proteins for prediction of elution pH and ionic strength. By extending the raspberry model for colloid particles to surface shapes and charge distributions of proteins, we can reproduce the behavior of proteins in IEX. The average charge states of titratatable amino acid residues at relevant pH values are determined by extrapolation from all-atom molecular dynamics at pH 7. The pH specific all-atom electrostatic field is then mapped onto the coarse-grained surface beads of the raspberry particle. The hydrodynamics are reproduced with the lattice-Boltzmann scheme. This combination of methods allows very long simulation times. The model is being validated for known elution procedures by comparing the data with experiments. Defense Threat Reduction Agency (Grant Number HDTRA1-15-1-0054).

Electronic structure and partial charge distribution of doxorubicin under different molecular environments

NASA Astrophysics Data System (ADS)

Poudel, Lokendra

Doxorubicin (trade name Adriamycin, abbreviated DOX) is a well-known an- thracyclic chemotherapeutic used in treating a variety of cancers including acute leukemia, lymphoma, multiple myeloma, and a range of stomach, lung, bladder, bone, breast, and ovarian cancers. The purpose of the present work is to study electronic structure, partial charge distribution and interaction energy of DOX under different environments. It provides a framework for better understanding of bioactivity of DOX with DNA. While in this work, we focus on DOX -- DNA interactions; the obtained knowledge could be translated to other drug -- target interactions or biomolecular interactions. The electronic structure and partial charge distribution of DOX in three dierent molecular environments: isolated, solvated, and intercalated into a DNA complex,were studied by rst principles density functional methods. It is shown that the addition of solvating water molecules to DOX and the proximity and interaction with DNA has a signicant impact on the electronic structure as well as the partial charge distribution. The calculated total partial charges for DOX in the three models are 0.0, +0.123 and -0.06 electrons for the isolated, solvated, and intercalated state, respectively. Furthermore, by using the more accurate ab initio partial charge values on every atom in the models, signicant improvement in estimating the DOX-DNA interaction energy is obtained in conjunction with the NAnoscale Molecular Dynamics (NAMD) code. The electronic structure of the DOX-DNA is further elucidated by resolving the total density of states (TDOS) into dierent functional groups of DOX, DNA, water, co-crystallized Spermine molecule, and Na ions. The surface partial charge distribution in the DOX-DNA is calculated and displayed graphically. We conclude that the presence of the solvent as well as the details of the interaction geometry matter greatly in the determination of the stability of the DOX complexion. Ab initio calculations on realistic models are an important step towards a more accurate description of biomolecular interaction and in the eventual understanding of long-range interactions in biomolecular systems.

Mars Dust: Characterization of Particle Size and Electrostatic Charge Distribution

NASA Technical Reports Server (NTRS)

Mazumder, M. K.; Saini, D.; Biris, A. S.; Sriama, P. K.; Calle, C.; Buhler, C.

2004-01-01

Some of the latest pictures of Mars surface sent by NASA's Spirit rover in early January, 2004, show very cohesive, "mud-like" dust layers. Significant amounts of dust clouds are present in the atmosphere of Mars [1-4]. NASA spacecraft missions to Mars confirmed hypotheses from telescopic work that changes observed in the planet's surface markings are caused by wind-driven redistribution of dust. In these dust storms, particles with a wide range of diameters (less than 1 micrometer to 50 micrometers) are a serious problem to solar cells, spacecraft, and spacesuits. Dust storms may cover the entire planet for an extended period of time [5]. It is highly probable that the particles are charged electrostatically by triboelectrification and by UV irradiation.

Scaling laws and edge effects for polymer surface discharges

NASA Technical Reports Server (NTRS)

Balmain, K. G.

1979-01-01

Specimens of Mylar sheet were exposed to a 20 kV electron beam. The resulting surface discharge arcs were photographed and the discharge current into a metal backing plate measured as a function of time. The area of the Mylar sheet was defined by a round aperture in a close-fitting metal mask, and the current pulse characteristics were plotted against area on log-log paper. The plots appear as straight lines (due to power-law behavior) with slopes of 0.50 for the peak current, 1.00 for the charge released, 1.49 for the energy and 0.55 for the pulse duration. Evidence is presented for the occurrence of banded charge distributions near grounded edges, on both Teflon and Mylar.

Flight evidence of spacecraft surface contamination rate enhancement by spacecraft charging obtained with a quartz crystal microbalance

NASA Technical Reports Server (NTRS)

Clark, D. M.; Hall, D. F.

1980-01-01

The significance of the fraction of the mass outgassed by a negatively charged space vehicle which is ionized within the vehicle plasma sheath and electrostatically reattracted to the space vehicle was determined. The ML-12 retarding potential analyzer/temperature controlled quartz crystal microbalances (RPA/TQCMs) distinguishes between charged and neutral molecules and investigates contamination mass transport mechanism. Two long term, quick look flight data sets indicate that on the average a significant fraction of mass arriving at one RPA/TQCM is ionized. It is assumed that vehicle frame charging during these periods was approximately uniformly distributed in degree and frequency. It is shown that electrostatic reattraction of ionized molecules is an important contamination mechanism at and near geosynchronous altitudes.

Electrical activity of ferroelectric biomaterials and its effects on the adhesion, growth and enzymatic activity of human osteoblast-like cells

NASA Astrophysics Data System (ADS)

Vaněk, P.; Kolská, Z.; Luxbacher, T.; García, J. A. L.; Lehocký, M.; Vandrovcová, M.; Bačáková, L.; Petzelt, J.

2016-05-01

Ferroelectrics have been, among others, studied as electroactive implant materials. Previous investigations have indicated that such implants induce improved bone formation. If a ferroelectric is immersed in a liquid, an electric double layer and a diffusion layer are formed at the interface. This is decisive for protein adsorption and bioactive behaviour, particularly for the adhesion and growth of cells. The charge distribution can be characterized, in a simplified way, by the zeta potential. We measured the zeta potential in dependence on the surface polarity on poled ferroelectric single crystalline LiNbO3 plates. Both our results and recent results of colloidal probe microscopy indicate that the charge distribution at the surface can be influenced by the surface polarity of ferroelectrics under certain ‘ideal’ conditions (low ionic strength, non-contaminated surface, very low roughness). However, suggested ferroelectric coatings on the surface of implants are far from ideal: they are rough, polycrystalline, and the body fluid is complex and has high ionic strength. In real cases, it can therefore be expected that there is rather low influence of the sign of the surface polarity on the electric diffusion layer and thus on the specific adsorption of proteins. This is supported by our results from studies of the adhesion, growth and the activity of alkaline phosphatase of human osteoblast-like Saos-2 cells on ferroelectric LiNbO3 plates in vitro.

ELECTROSTATIC SURFACE STRUCTURES OF COAL AND MINERAL PARTICLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

It is the purpose of this research to study electrostatic charging mechanisms related to electrostatic beneficiation of coal with the goal of improving models of separation and the design of electrostatic separators. Areas addressed in this technical progress report are (a) electrostatic beneficiation of Pittsburgh #8 coal powders as a function of grind size and processing atmosphere; (b) the use of fluorescent micro-spheres to probe the charge distribution on the surfaces of coal particles; (c) the use of electrostatic beneficiation to recover unburned carbon from flyash; (d) the development of research instruments for investigation of charging properties of coal. Pittsburghmore » #8 powders were beneficiated as a function of grind size and under three atmosphere conditions: fresh ground in air , after 24 hours of air exposure, or under N2 atmosphere. The feed and processed powders were analyzed by a variety of methods including moisture, ash, total sulfur, and pyritic sulfur content. Mass distribution and cumulative charge of the processed powders were also measured. Fresh ground coal performed the best in electrostatic beneficiation. Results are compared with those of similar studies conducted on Pittsburgh #8 powders last year (April 1, 1997 to September 30, 1997). Polystyrene latex spheres were charged and deposited onto coal particles that had been passed through the electrostatic separator and collected onto insulating filters. The observations suggest bipolar charging of individual particles and patches of charge on the particles which may be associated with particular maceral types or with mineral inclusions. A preliminary investigation was performed on eletrostatic separation of unburned carbon particles from flyash. Approximately 25% of the flyash acquired positive charge in the copper tribocharger. This compares with 75% of fresh ground coal. The negatively charged material had a slightly reduced ash content suggesting some enrichment of carbonaceous material. There was also evidence that the carbon is present at a higher ratio in larger particles than in small particles. An ultraviolet photoelectron counter for use in ambient atmosphere is nearing completion. The counter will be used to measure work functions of different maceral and mineral types in the coal matrix. A Particle Image Analyzer for measuring size and charge of airborne particles is also under contruction and its current status is presented. A charged, monodisperse, droplet generator is also being constructed for calibration of the Particle Image Analyzer and other airborne particle analyzers in our labs.« less

Vertical motion of a charged colloidal particle near an AC polarized electrode with a nonuniform potential distribution: theory and experimental evidence.

PubMed

Fagan, Jeffrey A; Sides, Paul J; Prieve, Dennis C

2004-06-08

Electroosmotic flow in the vicinity of a colloidal particle suspended over an electrode accounts for observed changes in the average height of the particle when the electrode passes alternating current at 100 Hz. The main findings are (1) electroosmotic flow provides sufficient force to move the particle and (2) a phase shift between the purely electrical force on the particle and the particle's motion provides evidence of an E2 force acting on the particle. The electroosmotic force in this case arises from the boundary condition applied when faradaic reactions occur on the electrode. The presence of a potential-dependent electrode reaction moves the likely distribution of electrical current at the electrode surface toward uniform current density around the particle. In the presence of a particle the uniform current density is associated with a nonuniform potential; thus, the electric field around the particle has a nonzero radial component along the electrode surface, which interacts with unbalanced charge in the diffuse double layer on the electrode to create a flow pattern and impose an electroosmotic-flow-based force on the particle. Numerical solutions are presented for these additional height-dependent forces on the particle as a function of the current distribution on the electrode and for the time-dependent probability density of a charged colloidal particle near a planar electrode with a nonuniform electrical potential boundary condition. The electrical potential distribution on the electrode, combined with a phase difference between the electric field in solution and the electrode potential, can account for the experimentally observed motion of particles in ac electric fields in the frequency range from approximately 10 to 200 Hz.

Effect of replacing a hydroxyl group with a methyl group on arsenic (V) species adsorption on goethite (alpha-FeOOH).

PubMed

Zhang, J S; Stanforth, R S; Pehkonen, S O

2007-02-01

Arsenate and methylated arsenicals, such as dimethylarsinate (DMA) and monomethylarsonate (MMA), are being found with increasing frequency in natural water systems. The mobility and bioavailability of these arsenic species in the environment are strongly influenced by their interactions with mineral surface, especially iron and aluminum oxides. Goethite (alpha-FeOOH), one of the most abundant ferric (hydr)oxides in natural systems, has a high retention capacity for arsenic species. Unfortunately, the sorption mechanism for the species is not completely understood, which limits our ability to model their behavior in natural systems. The purpose of this study is to investigate the effect of replacing a hydroxyl group with a methyl group on the adsorption behaviors of arsenic (V) species using adsorption edges, the influence of the background electrolyte on arsenic adsorption, and their effect on the zeta potential of goethite. The affinity of the three species to the goethite surface decreases in the order of AsO4=MMA>DMA. The uptake of DMA and MMA is independent of the concentration of background electrolyte, indicating that both species form inner-sphere complexes on the goethite surface and the most charge of adsorbed DMA and MMA locates at the surface plane. Arsenate uptake increases with increasing concentrations of background electrolyte at pH above 4, possibly due to that the charge of adsorbed arsenate is distributed between the surface plane and another electrostatic plane. DMA and lower concentrations of MMA have small effect on the zeta potential, whereas the zeta potential of goethite decreases in the presence of arsenate. The small effect on zeta potential of DMA or MMA adsorption suggests that the sorption sites for the anions is not important in controlling the surface charge. This observation is inconsistent with most adsorption models that postulate a singly coordinated hydroxyls contributing to both the adsorption and the surface charge, but supports the thesis that the charge on the goethite surface comes primarily from protonation of the triply bound oxygen atoms on the surface.

Adsorption of transgenic insecticidal Cry1Ab protein to SiO2. 2. Patch-controlled electrostatic attraction.

PubMed

Madliger, Michael; Sander, Michael; Schwarzenbach, René P

2010-12-01

Adsorption governs the fate of Cry proteins from genetically modified Bt crops in soils. The effect of ionic strength (I) on the adsorption of Cry1Ab (isoelectric point IEP(Cry1Ab) ≈ 6) to negatively charged quartz (SiO(2)) and positively charged poly-L-lysine (PLL) was investigated at pH 5 to 8, using quartz crystal microbalance with dissipation monitoring and optical waveguide lightmode spectroscopy. Cry1Ab adsorbed via positively and negatively charged surface patches to SiO(2) and PLL, respectively. This patch controlled electrostatic attraction (PCEA) explains the observed increase in Cry1Ab adsorption to sorbents that carried the same net charge as the protein (SiO(2) at pH > IEP(Cry1Ab) and PLL at pH < IEP(Cry1Ab)) with decreasing I. In contrast, the adsorption of two reference proteins, BSA and HEWL, with different adsorption mechanism, were little affected by similar changes of I. Consistent with PCEA, Cry1Ab desorption from SiO(2) at pH > IEP(Cry1Ab) increased with increasing I and pH. Weak Cry1Ab-SiO(2) PCEA above pH 7 resulted in reversible, concentration dependent adsorption. Solution depletion experiments showed that PCEA also governed Cry1Ab adsorption to SiO(2) particles at environmentally relevant concentrations (a few ng mL(-1)). These results imply that models describing Cry1Ab adsorption to charged surfaces in soils need to account for the nonuniform surface charge distribution of the protein.

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory.

PubMed

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G

2011-08-28

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. © 2011 American Institute of Physics

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

PubMed Central

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

2011-01-01

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

Rb + adsorption at the quartz(101)-aqueous interface: comparison of resonant anomalous x-ray reflectivity with ab initio calculations

DOE PAGES

Bellucci, Francesco; Lee, Sang Soo; Kubicki, James D.; ...

2015-01-29

We study adsorption of Rb + to the quartz(101)–aqueous interface at room temperature with specular X-ray reflectivity, resonant anomalous X-ray reflectivity, and density functional theory. The interfacial water structures observed in deionized water and 10 mM RbCl solution at pH 9.8 were similar, having a first water layer at height of 1.7 ± 0.1 Å above the quartz surface and a second layer at 4.8 ± 0.1 Å and 3.9 ± 0.8 Å for the water and RbCl solutions, respectively. The adsorbed Rb + distribution is broad and consists of presumed inner-sphere (IS) and outer-sphere (OS) complexes at heights ofmore » 1.8 ± 0.1 and 6.4 ± 1.0 Å, respectively. Projector-augmented planewave density functional theory (DFT) calculations of potential configurations for neutral and negatively charged quartz(101) surfaces at pH 7 and 12, respectively, reveal a water structure in agreement with experimental results. These DFT calculations also show differences in adsorbed speciation of Rb + between these two conditions. At pH 7, the lowest energy structure shows that Rb + adsorbs dominantly as an IS complex, whereas at pH 12 IS and OS complexes have equivalent energies. The DFT results at pH 12 are generally consistent with the two site Rb distribution observed from the X-ray data at pH 9.8, albeit with some differences that are discussed. In conclusion, surface charge estimated on the basis of the measured total Rb + coverage was -0.11 C/m 2, in good agreement with the range of the surface charge magnitudes reported in the literature.« less

Simulation study on discrete charge effects of SiNW biosensors according to bound target position using a 3D TCAD simulator.

PubMed

Chung, In-Young; Jang, Hyeri; Lee, Jieun; Moon, Hyunggeun; Seo, Sung Min; Kim, Dae Hwan

2012-02-17

We introduce a simulation method for the biosensor environment which treats the semiconductor and the electrolyte region together, using the well-established semiconductor 3D TCAD simulator tool. Using this simulation method, we conduct electrostatic simulations of SiNW biosensors with a more realistic target charge model where the target is described as a charged cube, randomly located across the nanowire surface, and analyze the Coulomb effect on the SiNW FET according to the position and distribution of the target charges. The simulation results show the considerable variation in the SiNW current according to the bound target positions, and also the dependence of conductance modulation on the polarity of target charges. This simulation method and the results can be utilized for analysis of the properties and behavior of the biosensor device, such as the sensing limit or the sensing resolution.

Quantitative Analysis of Charge Injection and Discharging of Si Nanocrystals and Arrays by Electrostatic Force Microscopy

NASA Technical Reports Server (NTRS)

Bell, L. D.; Boer, E.; Ostraat, M.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.

2000-01-01

NASA requirements for computing and memory for microspacecraft emphasize high density, low power, small size, and radiation hardness. The distributed nature of storage elements in nanocrystal floating-gate memories leads to intrinsic fault tolerance and radiation hardness. Conventional floating-gate non-volatile memories are more susceptible to radiation damage. Nanocrystal-based memories also offer the possibility of faster, lower power operation. In the pursuit of filling these requirements, the following tasks have been accomplished: (1) Si nanocrystal charging has been accomplished with conducting-tip AFM; (2) Both individual nanocrystals on an oxide surface and nanocrystals formed by implantation have been charged; (3) Discharging is consistent with tunneling through a field-lowered oxide barrier; (4) Modeling of the response of the AFM to trapped charge has allowed estimation of the quantity of trapped charge; and (5) Initial attempts to fabricate competitive nanocrystal non-volatile memories have been extremely successful.

Amorphous titanium-oxide supercapacitors.

PubMed

Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko

2016-10-21

The electric capacitance of an amorphous TiO 2-x surface increases proportionally to the negative sixth power of the convex diameter d. This occurs because of the van der Waals attraction on the amorphous surface of up to 7 mF/cm 2 , accompanied by extreme enhanced electron trapping resulting from both the quantum-size effect and an offset effect from positive charges at oxygen-vacancy sites. Here we show that a supercapacitor, constructed with a distributed constant-equipment circuit of large resistance and small capacitance on the amorphous TiO 2-x surface, illuminated a red LED for 37 ms after it was charged with 1 mA at 10 V. The fabricated device showed no dielectric breakdown up to 1,100 V. Based on this approach, further advances in the development of amorphous titanium-dioxide supercapacitors might be attained by integrating oxide ribbons with a micro-electro mechanical system.

Amorphous titanium-oxide supercapacitors

NASA Astrophysics Data System (ADS)

Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko

2016-10-01

The electric capacitance of an amorphous TiO2-x surface increases proportionally to the negative sixth power of the convex diameter d. This occurs because of the van der Waals attraction on the amorphous surface of up to 7 mF/cm2, accompanied by extreme enhanced electron trapping resulting from both the quantum-size effect and an offset effect from positive charges at oxygen-vacancy sites. Here we show that a supercapacitor, constructed with a distributed constant-equipment circuit of large resistance and small capacitance on the amorphous TiO2-x surface, illuminated a red LED for 37 ms after it was charged with 1 mA at 10 V. The fabricated device showed no dielectric breakdown up to 1,100 V. Based on this approach, further advances in the development of amorphous titanium-dioxide supercapacitors might be attained by integrating oxide ribbons with a micro-electro mechanical system.

Numerical solution of a multi-ion one-potential model for electroosmotic flow in two-dimensional rectangular microchannels.

PubMed

Van Theemsche, Achim; Deconinck, Johan; Van den Bossche, Bart; Bortels, Leslie

2002-10-01

A new more general numerical model for the simulation of electrokinetic flow in rectangular microchannels is presented. The model is based on the dilute solution model and the Navier-Stokes equations and has been implemented in a finite-element-based C++ code. The model includes the ion distribution in the Helmholtz double layer and considers only one single electrical' potential field variable throughout the domain. On a charged surface(s) the surface charge density, which is proportional to the local electrical field, is imposed. The zeta potential results, then, from this boundary condition and depends on concentrations, temperature, ion valence, molecular diffusion coefficients, and geometric conditions. Validation cases show that the model predicts accurately known analytical results, also for geometries having dimensions comparable to the Debye length. As a final study, the electro-osmotic flow in a controlled cross channel is investigated.

Superior electric storage on an amorphous perfluorinated polymer surface

PubMed Central

Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko; Sueyoshi, Takashi

2016-01-01

Amorphous perfluoroalkenyl vinyl ether polymer devices can store a remarkably powerful electric charge because their surface contains nanometre-sized cavities that are sensitive to the so-called quantum-size effect. With a work function of approximately 10 eV, the devices show a near-vertical line in the Nyquist diagram and a horizontal line near the −90° phase angle in the Bode diagram. Moreover, they have an integrated effect on the surface area for constant current discharging. This effect can be explained by the distributed constant electric circuit with a parallel assembly of nanometre-sized capacitors on a highly insulating polymer. The device can illuminate a red LED light for 3 ms after charging it with 1 mA at 10 V. Further gains might be attained by integrating polymer sheets with a micro-electro mechanical system. PMID:26902953

Hα line shape in front of the limiter in the HT-6M tokamak

NASA Astrophysics Data System (ADS)

Wan, Baonian; Li, Jiangang; Luo, Jiarong; Xie, Jikang; Wu, Zhenwei; Zhang, Xianmei; HT-6M Group

1999-11-01

The Hα line shape in front of the limiter in the HT-6M tokamak is analysed by multi-Gaussian fitting. The energy distribution of neutral hydrogen atoms reveals that Hα radiation is contributed by Franck-Condon atoms, atoms reflected at the limiter surface and charge exchange. Multi-Gaussian fitting of the Hα spectral profile indicates contributions of 60% from reflection particles and 40% from molecule dissociation to recycling. Ion temperatures in central regions are obtained from the spectral width of charge exchange components. Dissociation of hydrogen molecules and reflection of particles at the limiter surface are dominant in edge recycling. Reduction of particle reflection at the limiter surface is important for controlling edge recycling. The measured profiles of neutral hydrogen atom density are reproduced by a particle continuity equation and a simplified one dimensional Monte Carlo simulation code.

Patterned-wettability-induced alteration of electro-osmosis over charge-modulated surfaces in narrow confinements.

PubMed

Ghosh, Uddipta; Chakraborty, Suman

2012-04-01

In the present study, we focus on alterations in flow physics as a consequence of interactions between patterned-wettability gradients on microfluidic substrates with modulated surface charge distributions, giving rise to an intricate electrohydrodynamic coupling over small scales. We demonstrate that by exploiting such intricate coupling, it may be possible to pattern vortices occurring in the fluidic confinement by exploiting an interplay between the Navier slip and electro-osmotic transport. Our studies do reveal that the resultant flow structure originating out of the spatially periodic variations in the surface charge and surface wettability may depend critically on several independently tunable controlling parameters, such as the amplitudes and frequencies of the respective patterning functions, the phase shift between the two, an asymmetry factor, and the channel height to Debye length ratio. We show that judicious choices with regard to the combinations of these parameters may result in significant augmentations in the corresponding mixing efficiency without any appreciable compromise in the net microfluidic throughput. Furthermore, our studies reveal an optimum patterning frequency, which results in the most efficient microfluidic mixing within the constraints of achieving a desired volumetric flow rate. Our results also demonstrate that the net flow rate is maximized when the surface wettability variation functions and surface charge-density functions are in phase, whereas mixing is best facilitated when they are in opposite phase. In practice, therefore, one may select an intermediate value of the phase angle depending on the extent of compromise necessary between flow rate and mixing characteristics, yielding far-ranging scientific and technological advances toward an improved design of miniaturized fluidic devices of practical relevance.

Color and chemistry on Triton

NASA Technical Reports Server (NTRS)

Thompson, W. Reid; Sagan, Carl

1990-01-01

The surface of Triton is very bright but shows subtle yellow to peach hues which probably arise from the production of colored organic compounds from CH4 + N2 and other simple species. In order to investigate possible relationships between chemical processes and the observed surface distribution of chromophores, the surface units are classified according to color/albedo properties, the rates of production of organic chromophores by the action of ultraviolet light and high-energy charged particles is estimated, and rates, spectral properties, and expected seasonal redistribution processes are compared to suggest possible origins of the colors seen on Triton's surface.

Adsorption of transgenic insecticidal Cry1Ab protein to silica particles. Effects on transport and bioactivity.

PubMed

Madliger, Michael; Gasser, Christoph A; Schwarzenbach, René P; Sander, Michael

2011-05-15

Bt crops are genetically modified to be resistant against insect pests by expressing insecticidal Cry proteins. The processes governing the fate and bioavailability of the expressed transgenic Cry proteins in soils are poorly understood. We studied adsorption of Cry1Ab to negatively charged silica (SiO(2)) particles, a major soil constituent and a model for negatively charged mineral surfaces, at pH 5 to 10 and ionic strengths I = 10 mM to 250 mM, both in solution depletion and saturated column transport experiments. Cry1Ab-SiO(2) interactions were dominated by patch-controlled electrostatic attraction (PCEA), as evident from increasing Cry1Ab attraction to SiO(2) with decreasing I at pH at which both Cry1Ab and SiO(2) were net negatively charged. Experimental and modeling evidence is provided that the surface heterogeneity of SiO(2) particles modulated PCEA, leading to a fraction of adsorption sites with slow Cry1Ab desorption kinetics. Desorption rates from these sites increased upon increasing the solution pH. In toxicity bioassays, we demonstrated that Cry1Ab retained insecticidal activity when adsorbed to SiO(2), suggesting high protein conformational stability during adsorption-desorption cycles. Models predicting Cry1A protein adsorption in soils therefore need to account for combined effects of the nonuniform protein surface charge distribution and of sorbent surface heterogeneity.

Quantification of surface charge density and its effect on boundary slip.

PubMed

Jing, Dalei; Bhushan, Bharat

2013-06-11

Reduction of fluid drag is important in the micro-/nanofluidic systems. Surface charge and boundary slip can affect the fluid drag, and surface charge is also believed to affect boundary slip. The quantification of surface charge and boundary slip at a solid-liquid interface has been widely studied, but there is a lack of understanding of the effect of surface charge on boundary slip. In this paper, the surface charge density of borosilicate glass and octadecyltrichlorosilane (OTS) surfaces immersed in saline solutions with two ionic concentrations and deionized (DI) water with different pH values and electric field values is quantified by fitting experimental atomic force microscopy (AFM) electrostatic force data using a theoretical model relating the surface charge density and electrostatic force. Results show that pH and electric field can affect the surface charge density of glass and OTS surfaces immersed in saline solutions and DI water. The mechanisms of the effect of pH and electric field on the surface charge density are discussed. The slip length of the OTS surface immersed in saline solutions with two ionic concentrations and DI water with different pH values and electric field values is measured, and their effects on the slip length are analyzed from the point of surface charge. Results show that a larger absolute value of surface charge density leads to a smaller slip length for the OTS surface.

Electronic structure, dielectric response, and surface charge distribution of RGD (1FUV) peptide.

PubMed

Adhikari, Puja; Wen, Amy M; French, Roger H; Parsegian, V Adrian; Steinmetz, Nicole F; Podgornik, Rudolf; Ching, Wai-Yim

2014-07-08

Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor.

Nanoporous carbon supercapacitors in an ionic liquid: a computer simulation study.

PubMed

Shim, Youngseon; Kim, Hyung J

2010-04-27

Supercapacitors composed of carbon nanotube (CNT) micropores in the room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI+BF4(-)) are studied via molecular dynamics (MD)computer simulations. It is found that the distribution of RTIL ions inside the micropore varies significantly with the pore size. Internal solvation of small (6,6) and (7,7) CNTs with an electrified interior wall is effected almost exclusively via counterions. Surprisingly, these counterions, even though they all have the same charge, lead to a charge density characterized by multiple layers with alternating signs. This intriguing feature is attributed to the extended nature of RTIL ion charge distributions, which result in charge separation through preferential orientation inside the electrified nanotubes. In the case of larger (10,10) and (15,15) CNTs, counterions and coions develop multilayer solvation structures. The specific capacitance normalized to the pore surface area is found to increase as the CNT diameter decreases from (15,15) to (7,7). As the pore size further reduces from (6,6) to(5,5), however, the specific capacitance diminishes rapidly. These findings are in excellent agreement with recent experiments with carbon-based materials. A theoretical model based on multiple charge layers is proposed to understand both the MD and experimental results.

Electronic structures of rutile (011)(2 × 1) surfaces: A many-body perturbation theory study.

PubMed

Liu, Guokui; Chen, Tingwei; Liu, Xiaobiao; Jin, Fan; Yuan, Shiling; Ma, Yuchen

2017-03-28

Using the GW method within many-body perturbation theory, we investigate the electronic properties of the rutile (011) surfaces with different reconstruction patterns. We find that keeping the Ti:O ratio on the reconstructedsurface to 1:2 enlarges the bandgap of the rutile (011) surface to ca. 4.0 eV. Increasing the content of O atoms in the surface can turn rutile into a semi-metal. For some surfaces, it is important to apply self-consistent GW calculation to get the correct charge distributions for the frontier orbitals, which are relevant to the photocatalytic behavior of TiO 2 .

Probing anode degradation in automotive Li-ion batteries

NASA Astrophysics Data System (ADS)

Kwon, Ou Jung

The lithium-ion battery is drawing attention as a power source for future clean and fuel-efficient vehicles. Although the Li-ion battery presently shows best performance for energy density and power density compared to other rechargeable batteries, some degradation problems still remain as key challenges for long-term durability in automotive applications. Among those problems, Li deposition is well known for causing permanent capacity loss. Fundamental mechanisms of Li deposition in the carbon anode are, however, not fully understood, especially at subzero temperature and/or under high rate charge. This dissertation introduces comprehensive study of Li deposition using automotive 18650 Li-ion cells. The mechanism and relevant diagnostic methods as well as preventive charging protocol are discussed. In part one, a new diagnostic tool is introduced utilizing 3-electrode cell system, which measures thermodynamic and kinetic parameters of cathode and anode, respectively, as a function of temperature and SOC (state of charge): open circuit potential (OCP); Li diffusion coefficient in active particles; and internal resistance. These data are employed to understand electrochemical reaction and its thermal interaction under charging conditions that result in Li deposition. Part two provides a threshold parameter for the onset of Li deposition, which is not commonly used anode potential but charge capacity, or more specifically the amount of Li+ ions participating in intercalation reaction without Li deposition at given charging circumstances. This is called the critical charge capacity in this thesis, beyond which capacity loss at normal operating condition is observed, which becomes more serious as temperature is lowered and/or charge C-rate increases. Based on these experimental results, the mechanism of Li deposition is proposed as the concept of anode particle surface saturation, meaning that once the anode particle surface is saturated with Li in any charging circumstances, no more Li+ ions can be intercalated but should be reduced to metallic form on the anode particle surface. This is validated by calculating the distribution of Li concentration inside the anode particle with electrochemical modeling. In part three, a novel pulse charge protocol is developed, which consists of two steps. First high current charge/discharge pulses increase the cell temperature from a subzero temperature up to above room temperature in a short time, and next, high current charge provides the net charge capacity. Sluggish Li diffusion at low temperature becomes fast thanks to cell temperature elevation by high current pulses (1st step), which plays a role of preventing surface saturation during high current charge (2nd step). Thus, this charge protocol is not only Li deposition-free but also leads to rapid charge at subzero temperatures.

Multifunctional nanoparticulate polyelectrolyte complexes.

PubMed

Hartig, Sean M; Greene, Rachel R; DasGupta, Jayasri; Carlesso, Gianluca; Dikov, Mikhail M; Prokop, Ales; Davidson, Jeffrey M

2007-12-01

Water-soluble, biodegradable, polymeric, polyelectrolyte complex dispersions (PECs) have evolved because of the limitations, in terms of toxicity, of the currently available systems. These aqueous nanoparticulate architectures offer a significant advantage for products that may be used as drug delivery systems in humans. PECs are created by mixing oppositely charged polyions. Their hydrodynamic diameter, surface charge, and polydispersity are highly dependent on concentration, ionic strength, pH, and molecular parameters of the polymers that are used. In particular, the complexation between polyelectrolytes with significantly different molecular weights leads to the formation of water-insoluble aggregates. Several PEC characteristics are favorable for cellular uptake and colloidal stability, including hydrodynamic diameter less than 200 nm, surface charge of >30 mV or <-30 mV, spherical morphology, and polydispersity index (PDI) indicative of a homogeneous distribution. Maintenance of these properties is critical for a successful delivery vehicle. This review focuses on the development and potential applications of PECs as multi-functional, site-specific nanoparticulate drug/gene delivery and imaging devices.

Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl3

NASA Astrophysics Data System (ADS)

Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

2016-12-01

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ~0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.

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

Surface electroluminescence phenomena correlated with trapping parameters of insulating polymers

NASA Astrophysics Data System (ADS)

Zhang, Guan-Jun; Yang, Kai; Dong, Ming; Zhao, Wen-Bin; Yan, Zhang

2007-12-01

Electroluminescence (EL) phenomena are closely linked to the space charge and degradation in insulating polymers, and dominated by the luminescence and trap centers. EL emission has been promising in defining the onset of electrical aging and in the investigation of dissipation mechanisms. Generally, polymeric degradation reveals the increment of the density of luminescence and trap centers, so a fundamental study is proposed to correlate the EL emission of insulating polymers and their trapping parameters. A sensitive photon counting system is constructed to detect the weak EL. The time- and phase-resolved EL characteristics from different polymers (LDPE, PP and PTFE) are investigated with a planar electrode configuration under stepped ac voltage in vacuum. In succession, each sample is charged with exposing to multi-needle corona discharge, and then its surface potential decay is continuously recorded at a constant temperature. Based on the isothermal relaxation current theory, the energy level and density of both electron and hole trap distribution in the surface layer of each polymer is obtained. It is preliminarily concluded that EL phenomena are strongly affected by the trap properties, and for different polymers, its EL intensity is in direct contrast to its surface trap density, and this can be qualitatively explained by the trapping and detrapping sequence of charge carriers in trap centers with different energy level.

Modeling salt-mediated electrostatics of macromolecules: the discrete surface charge optimization algorithm and its application to the nucleosome.

PubMed

Beard, D A; Schlick, T

2001-01-01

Much progress has been achieved on quantitative assessment of electrostatic interactions on the all-atom level by molecular mechanics and dynamics, as well as on the macroscopic level by models of continuum solvation. Bridging of the two representations-an area of active research-is necessary for studying integrated functions of large systems of biological importance. Following perspectives of both discrete (N-body) interaction and continuum solvation, we present a new algorithm, DiSCO (Discrete Surface Charge Optimization), for economically describing the electrostatic field predicted by Poisson-Boltzmann theory using a discrete set of Debye-Hückel charges distributed on a virtual surface enclosing the macromolecule. The procedure in DiSCO relies on the linear behavior of the Poisson-Boltzmann equation in the far zone; thus contributions from a number of molecules may be superimposed, and the electrostatic potential, or equivalently the electrostatic field, may be quickly and efficiently approximated by the summation of contributions from the set of charges. The desired accuracy of this approximation is achieved by minimizing the difference between the Poisson-Boltzmann electrostatic field and that produced by the linearized Debye-Hückel approximation using our truncated Newton optimization package. DiSCO is applied here to describe the salt-dependent electrostatic environment of the nucleosome core particle in terms of several hundred surface charges. This representation forms the basis for modeling-by dynamic simulations (or Monte Carlo)-the folding of chromatin. DiSCO can be applied more generally to many macromolecular systems whose size and complexity warrant a model resolution between the all-atom and macroscopic levels. Copyright 2000 John Wiley & Sons, Inc.

A smoothed particle hydrodynamics model for electrostatic transport of charged lunar dust on the moon surface

NASA Astrophysics Data System (ADS)

Mao, Zirui; Liu, G. R.

2018-02-01

The behavior of lunar dust on the Moon surface is quite complicated compared to that on the Earth surface due to the small lunar gravity and the significant influence of the complicated electrostatic filed in the Universe. Understanding such behavior is critical for the exploration of the Moon. This work develops a smoothed particle hydrodynamics (SPH) model with the elastic-perfectly plastic constitutive equation and Drucker-Prager yield criterion to simulate the electrostatic transporting of multiple charged lunar dust particles. The initial electric field is generated based on the particle-in-cell method and then is superposed with the additional electric field from the charged dust particles to obtain the resultant electric field in the following process. Simulations of cohesive soil's natural failure and electrostatic transport of charged soil under the given electric force and gravity were carried out using the SPH model. Results obtained in this paper show that the negatively charged dust particles levitate and transport to the shadow area with a higher potential from the light area with a lower potential. The motion of soil particles finally comes to a stable state. The numerical result for final distribution of soil particles and potential profile above planar surface by the SPH method matches well with the experimental result, and the SPH solution looks sound in the maximum levitation height prediction of lunar dust under an uniform electric field compared to theoretical solution, which prove that SPH is a reliable method in describing the behavior of soil particles under a complicated electric field and small gravity field with the consideration of interactions among soil particles.

Space charge deposition in tubular channel ferroelectrets: A combined fluorescence imaging/LIMM study with finite element analysis

NASA Astrophysics Data System (ADS)

Nepal, Neerajan; Altafim, Ruy Alberto Pisani; Mellinger, Axel

2017-06-01

Ferroelectrets, i.e., soft materials with electric charges deposited on the surfaces of internal voids, are well known for their potential in transducer applications and energy harvesting. Due to their regular geometry and optical transparency, tubular channel ferroelectrets (manufactured by laminating polymer films around a polytetrafluoroethylene template which is later removed) are well-suited for studying the process of charge deposition. Understanding how space charges are formed on the internal surfaces will lead to improvements in the charge density and in the piezoelectric performance of these films. In this work, the inception voltage for dielectric barrier discharges (and hence the onset of charge deposition) was measured using two independent techniques, fluorescence imaging and the laser intensity modulation method (LIMM). The results (around 1.4-1.7 kV, depending on the void height) are in agreement within ±50 V. The internal electric field distribution was calculated using finite element analysis (FEA). Combined with Paschen's law, these calculations explained the experimentally observed discharge patterns, starting from the channel edges in thick samples, but glowing more uniformly in films with void heights of 50 μm or less. A time-dependent FEA simulation of the LIMM measurement reproduced the observed thermoelastic resonances and their effect on the LIMM signal, and explained its seemingly erratic behavior. This approach has great potential for analyzing LIMM and thermal pulse data obtained in inhomogeneous materials.

Effect of sacrificial agents on the dispersion of metal cocatalysts for photocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Cao, Shaowen; Shen, Baojia; Huang, Qian; Chen, Zhe

2018-06-01

Surface photodeposition of noble metal cocatalyst has been regarded as an effective approach to facilitate the separation of charge carriers and reduce the over-potential of water reduction, thus to enhance the photocatalytic H2-production activities of semiconductor photocatalyst. Herein, the influences of sacrificial agents used in the photodeposition process on the dispersion of noble metal nanoparticles are investigated, via a series of technique of photocatalytic hydrogen evolution test, microstructure analysis and photoelectrochemical measurement. As a result, the sacrificial agents are found to show large impact on the loading amount, particle size and distribution of different metals on the surface of g-C3N4. The real loading amount of Pt and Au is higher in methanol solution than that in triethanolamine solution. Better distribution and smaller size of Pt nanoparticles are achieved in the presence of methanol; while better distribution and smaller size of Au nanoparticles are achieved in the presence of triethanolamine. As a result, quite different charge transfer ability is achieved for the synthesized Pt and Au decorated g-C3N4, which subsequently leads to disparate photocatalytic activities of the same g-C3N4 photocatalyst under various conditions. The finding in this work indicates that the valid deposition content, particle size and distribution of metal cocatalysts should be carefully taken into account when comparing the photocatalytic activities among various samples.

On deriving the Maxwell stress tensor method for calculating the optical force and torque on an object in harmonic electromagnetic fields

NASA Astrophysics Data System (ADS)

Ye, Qian; Lin, Haoze

2017-07-01

Though extensively used in calculating optical force and torque acting on a material object illuminated by laser, the Maxwell stress tensor (MST) method follows the electromagnetic linear and angular momentum balance that is usually derived in most textbooks for a continuous volume charge distribution in free space, if not resorting to the application of Noether’s theorem in electrodynamics. To cast the conservation laws into a physically appealing form involving the current densities of linear and angular momentum, on which the MST method is based, the divergence theorem is employed to transform a volume integral into a surface integral. When a material object of finite volume is put into the field, it brings about a discontinuity of field across its surface, due to the presence of induced surface charge and surface current. Ambiguity arises among students in whether the divergence theorem can still be directly used without any justification. By taking into account the effect of the induced surface charge and current, we present a simple pedagogical derivation for the MST method for calculating the optical force and torque on an object immersed in monochromatic optical field, without resorting to Noether’s theorem. Although the results turn out to be identical to those given in the standard textbooks, our derivation avoids the direct use of the divergence theorem on a discontinuous function.

Theoretical study for heterojunction surface of NEA GaN photocathode dispensed with Cs activation

NASA Astrophysics Data System (ADS)

Xia, Sihao; Liu, Lei; Wang, Honggang; Wang, Meishan; Kong, Yike

2016-09-01

For the disadvantages of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, new-type NEA GaN photocathodes with heterojunction surface dispensed with Cs activation are investigated based on first-principle study with density functional theory. Through the growth of an ultrathin n-type GaN cap layer on p-type GaN emission layer, a p-n heterojunction is formed on the surface. According to the calculation results, it is found that Si atoms tend to replace Ga atoms to result in an n-type doped cap layer which contributes to the decreasing of work function. After the growth of n-type GaN cap layer, the atom structure near the p-type emission layer is changed while that away from the surface has no obvious variations. By analyzing the E-Mulliken charge distribution of emission surface with and without cap layer, it is found that the positive charge of Ga and Mg atoms in the emission layer decrease caused by the cap layer, while the negative charge of N atom increases. The conduction band moves downwards after the growth of cap layer. Si atom produces donor levels around the valence band maximum. The absorption coefficient of GaN emission layer decreases and the reflectivity increases caused by n-type GaN cap layer.

An Analytical Model of Tribocharging in Regolith

NASA Astrophysics Data System (ADS)

Carter, D. P.; Hartzell, C. M.

2015-12-01

Nongravitational forces, including electrostatic forces and cohesion, can drive the behavior of regolith in low gravity environments such as the Moon and asteroids. Regolith is the 'skin' of solid planetary bodies: it is the outer coating that is observed by orbiters and the first material contacted by landers. Triboelectric charging, the phenomenon by which electrical charge accumulates during the collision or rubbing of two surfaces, has been found to occur in initially electrically neutral granular mixtures. Although charge transfer is often attributed to chemical differences between the different materials, charge separation has also been found to occur in mixtures containing grains of a single material, but with a variety of grain sizes. In such cases, the charge always separates according to grain size; typically the smaller grains acquire a more negative charge than the larger grains. Triboelectric charging may occur in a variety of planetary phenomena (including mass wasting and dust storms) as well as during spacecraft-surface interactions (including sample collection and wheel motion). Interactions between charged grains or with the solar wind plasma could produce regolith motion. However, a validated, predictive model of triboelectric charging between dielectric grains has not yet been developed. A model for such size-dependent charge separation will be presented, demonstrating how random collisions between initially electrically neutral grains lead to net migration of electrons toward the smaller grains. The model is applicable to a wide range of single-material granular mixtures, including those with unusual or wildly varying size distributions, and suggests a possible mechanism for the reversal of the usual size-dependent charge polarity described above. This is a significant improvement over existing charge exchange models, which are restricted to two discrete grains sizes and provide severely limited estimates for charge magnitude. We will also discuss the design of an experiment planned to test the charging estimates provided by the model presented and the potential implications for our understanding of regolith behavior.

Interaction of the Antimicrobial Peptide Aurein 1.2 and Charged Lipid Bilayer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rai, Durgesh K.; Qian, Shuo

Aurein 1.2 is a potent antimicrobial peptide secreted by frog Litoria aurea. As a short membrane-active peptide with only 13 amino acids in sequence, it has been found to be residing on the surface of lipid bilayer and permeabilizing bacterial membranes at high concentration. However, the detail at the molecular level is largely unknown. Here in this study, we investigated the action of Aurein 1.2 in charged lipid bilayers composed of DMPC/DMPG. Oriented Circular Dichroism results showed that the peptide was on the surface of lipid bilayer regardless of the charged lipid ratio. Only at a very high peptide-to-lipid ratiomore » (~1/10), the peptide became perpendicular to the bilayer, however no pore was detected by neutron in-plane scattering. To further understand how it interacted with charged lipid bilayers, we employed Small Angle Neutron Scattering to probe lipid distribution across bilayer leaflets in lipid vesicles. The results showed that Aurein 1.2 interacted strongly with negatively charged DMPG, causing strong asymmetry in lipid bilayer. At high concentration, while the vesicles were intact, we found additional structure feature on the bilayer. Finally, our study provides a glimpse into how Aurein 1.2 disturbs anionic lipid-containing membranes without pore formation.« less

Interaction of the Antimicrobial Peptide Aurein 1.2 and Charged Lipid Bilayer

DOE PAGES

Rai, Durgesh K.; Qian, Shuo

2017-06-16

Aurein 1.2 is a potent antimicrobial peptide secreted by frog Litoria aurea. As a short membrane-active peptide with only 13 amino acids in sequence, it has been found to be residing on the surface of lipid bilayer and permeabilizing bacterial membranes at high concentration. However, the detail at the molecular level is largely unknown. Here in this study, we investigated the action of Aurein 1.2 in charged lipid bilayers composed of DMPC/DMPG. Oriented Circular Dichroism results showed that the peptide was on the surface of lipid bilayer regardless of the charged lipid ratio. Only at a very high peptide-to-lipid ratiomore » (~1/10), the peptide became perpendicular to the bilayer, however no pore was detected by neutron in-plane scattering. To further understand how it interacted with charged lipid bilayers, we employed Small Angle Neutron Scattering to probe lipid distribution across bilayer leaflets in lipid vesicles. The results showed that Aurein 1.2 interacted strongly with negatively charged DMPG, causing strong asymmetry in lipid bilayer. At high concentration, while the vesicles were intact, we found additional structure feature on the bilayer. Finally, our study provides a glimpse into how Aurein 1.2 disturbs anionic lipid-containing membranes without pore formation.« less

Size effect in Quincke rotation: a numerical study.

PubMed

Peters, F; Lobry, L; Khayari, A; Lemaire, E

2009-05-21

This paper deals with the Quincke rotation of small insulating particles. This dc electrorotation of insulating objects immersed in a slightly conducting liquid is usually explained by looking at the action of the free charges present in the liquid. Under the effect of the dc electric field, the charges accumulate at the surface of the insulating particle which, in turn, acquires a dipole moment in the direction opposite to that of the field and begins to rotate in order to flip its dipole moment. In the classical Quincke model, the charge distribution around the rotor is supposed to be purely superficial. A consequence of this assumption is that the angular velocity does not depend on the rotor size. Nevertheless, this hypothesis holds only if the rotor size is much larger than the characteristic ion layer thickness around the particle. In the opposite case, we show thanks to numerical calculations that the bulk charge distribution has to be accounted for to predict the electromechanical behavior of the rotor. We consider the case of an infinite insulating cylinder whose axis is perpendicular to the dc electric field. We use the finite element method to solve the conservation equations for the positive and the negative ions coupled with Navier-Stokes and Poisson equations. Doing so, we compute the bulk charge distribution and the velocity field in the liquid surrounding the cylinder. For sufficiently small cylinders, we show that the smaller the cylinder is, the smaller its angular velocity is when submitted to a dc electric field. This size effect is shown to originate both in ion diffusion and electromigration in the charge layer. At last, we propose a simple analytical model which allows calculating the angular velocity of the rotor when electromigration is present but weak and diffusion can be neglected.

Size effect in Quincke rotation: A numerical study

NASA Astrophysics Data System (ADS)

Peters, F.; Lobry, L.; Khayari, A.; Lemaire, E.

2009-05-01

This paper deals with the Quincke rotation of small insulating particles. This dc electrorotation of insulating objects immersed in a slightly conducting liquid is usually explained by looking at the action of the free charges present in the liquid. Under the effect of the dc electric field, the charges accumulate at the surface of the insulating particle which, in turn, acquires a dipole moment in the direction opposite to that of the field and begins to rotate in order to flip its dipole moment. In the classical Quincke model, the charge distribution around the rotor is supposed to be purely superficial. A consequence of this assumption is that the angular velocity does not depend on the rotor size. Nevertheless, this hypothesis holds only if the rotor size is much larger than the characteristic ion layer thickness around the particle. In the opposite case, we show thanks to numerical calculations that the bulk charge distribution has to be accounted for to predict the electromechanical behavior of the rotor. We consider the case of an infinite insulating cylinder whose axis is perpendicular to the dc electric field. We use the finite element method to solve the conservation equations for the positive and the negative ions coupled with Navier-Stokes and Poisson equations. Doing so, we compute the bulk charge distribution and the velocity field in the liquid surrounding the cylinder. For sufficiently small cylinders, we show that the smaller the cylinder is, the smaller its angular velocity is when submitted to a dc electric field. This size effect is shown to originate both in ion diffusion and electromigration in the charge layer. At last, we propose a simple analytical model which allows calculating the angular velocity of the rotor when electromigration is present but weak and diffusion can be neglected.

Thermodynamics and Hawking radiation of five-dimensional rotating charged Goedel black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu Shuangqing; Peng Junjin; College of Science, Wuhan Textile University, Wuhan, Hubei 430074

2011-02-15

We study the thermodynamics of Goedel-type rotating charged black holes in five-dimensional minimal supergravity. These black holes exhibit some peculiar features such as the presence of closed timelike curves and the absence of a globally spatial-like Cauchy surface. We explicitly compute their energies, angular momenta, and electric charges that are consistent with the first law of thermodynamics. Besides, we extend the covariant anomaly cancellation method, as well as the approach of the effective action, to derive their Hawking fluxes. Both the methods of the anomaly cancellation and the effective action give the same Hawking fluxes as those from the Planckmore » distribution for blackbody radiation in the background of the charged rotating Goedel black holes. Our results further support that Hawking radiation is a quantum phenomenon arising at the event horizon.« less

Nanoparticles in natural systems II: The natural oxide fraction at interaction with natural organic matter and phosphate

NASA Astrophysics Data System (ADS)

Hiemstra, Tjisse; Antelo, Juan; van Rotterdam, A. M. D.(Debby); van Riemsdijk, Willem H.

2010-01-01

Information on the particle size and reactive surface area of natural samples and its interaction with natural organic matter (NOM) is essential for the understanding bioavailability, toxicity, and transport of elements in the natural environment. In part I of this series ( Hiemstra et al., 2010), a method is presented that allows the determination of the effective reactive surface area ( A, m 2/g soil) of the oxide particles of natural samples which uses a native probe ion (phosphate) and a model oxide (goethite) as proxy. In soils, the natural oxide particles are generally embedded in a matrix of natural organic matter (NOM) and this will affect the ion binding properties of the oxide fraction. A remarkably high variation in the natural phosphate loading of the oxide surfaces ( Γ, μmol/m 2) is observed in our soils and the present paper shows that it is due to surface complexation of NOM, acting as a competitor via site competition and electrostatic interaction. The competitive interaction of NOM can be described with the charge distribution (CD) model by defining a ≡NOM surface species. The interfacial charge distribution of this ≡NOM surface species can be rationalized based on calculations done with an evolved surface complexation model, known as the ligand and charge distribution (LCD) model. An adequate choice is the presence of a charge of -1 v.u. at the 1-plane and -0.5 v.u. at the 2-plane of the electrical double layer used (Extended Stern layer model). The effective interfacial NOM adsorption can be quantified by comparing the experimental phosphate concentration, measured under standardized field conditions (e.g. 0.01 M CaCl 2), with a prediction that uses the experimentally derived surface area ( A) and the reversibly bound phosphate loading ( Γ, μmol/m 2) of the sample (part I) as input in the CD model. Ignoring the competitive action of adsorbed NOM leads to a severe under-prediction of the phosphate concentration by a factor ˜10 to 1000. The calculated effective loading of NOM is low at a high phosphate loading ( Γ) and vice versa, showing the mutual competition of both constituents. Both constituents in combination usually dominate the surface loading of natural oxide fraction of samples and form the backbone in modeling the fate of other (minor) ions in the natural environment. Empirically, the effective NOM adsorption is found to correlate well to the organic carbon content (OC) of the samples. The effective NOM adsorption can also be linked to DOC. For this, a Non-Ideal Competitive adsorption (NICA) model is used. DOC is found to be a major explaining factor for the interfacial loading of NOM as well as phosphate. The empirical NOM-OC relation or the parameterized NICA model can be used as an alternative for estimating the effective NOM adsorption to be implemented in the CD model for calculation of the surface complexation of field samples. The biogeochemical impact of the NOM-PO 4 interaction is discussed.

Satellite Anomalies: Benefits of a Centralized Anomaly Database and Methods for Securely Sharing Information Among Satellite Operators

DTIC Science & Technology

2014-01-01

unprecedented efficiencies in global busi- ness collaboration through communication, information distribution, and fast electronic monetary transactions...tudes (which peaks in free electron density at 300–400 km but extends to just above 1,000 km). At GEO, surface charging occurs intermit - tently

Recent progress on RE2O3-Mo/W emission materials.

PubMed

Wang, Jinshu; Zhang, Xizhu; Liu, Wei; Cui, Yuntao; Wang, Yiman; Zhou, Meiling

2012-08-01

RE2O3-Mo/W cathodes were prepared by powder metallurgy method. La2O3-Y2O3-Mo cermet cathodes prepared by traditional sintering method and spark plasma sintering (SPS) exhibit different secondary emission properties. The La2O3-Y2O3-Mo cermet cathode prepared by SPS method has smaller grain size and exhibits better secondary emission performance. Monte carlo calculation results indicate that the secondary electron emission way of the cathode correlates with the grain size. Decreasing the grain size can decrease the positive charging effect of RE2O3 and thus is favorable for the escaping of secondary electrons to vacuum. The Scandia doped tungsten matrix dispenser cathode with a sub-micrometer microstructure of matrix with uniformly distributed nanometer-particles of Scandia has good thermionic emission property. Over 100 A/cm2 full space charge limited current density can be obtained at 950Cb. The cathode surface is covered by a Ba-Sc-O active surface layer with nano-particles distributing mainly on growth steps of W grains, leads to the conspicuous emission property of the cathode.

Spatial Variation in Mobility-Lifetime Product in Bulk TlBr and CZT

NASA Astrophysics Data System (ADS)

Phillips, David; Haegel, Nancy; Blaine, Kevin; Kim, Hadong; Ciampi, Guido; Cirignano, Len

2012-02-01

The energy resolution of a semiconductor radiation detector depends on the charge transport properties of the semiconductor, and the mobility-lifetime (μτ) product is a key figure of merit for charge transport. In this work, we investigate the effects of two impurities, Na and Cu, on the μτ product in bulk thallium bromide (TlBr) using cathodoluminescence (CL) and transport imaging. Transport imaging uses a scanning electron microscope to generate a line of charge carriers on the surface of a bulk sample, and the intensity and spatial distribution of the recombination luminescence are recorded. A Green's function approach is used to model the generation, diffusion, and recombination of charge carriers under steady-state conditions. The luminescence distribution is fit to the model to extract the ambipolar diffusion length and the μτ product, providing a high-resolution correlation between the luminescence variations due to dopants/defects and the quantitative transport behavior. The μτ product has been mapped across a 40 μm segment of TlBr at a resolution of 2 μm. Additionally, this approach has been used to locally map variations in ambipolar diffusion length and μτ product due to extended defects in cadmium zinc telluride (CZT).

Chromatin ionic atmosphere analyzed by a mesoscale electrostatic approach.

PubMed

Gan, Hin Hark; Schlick, Tamar

2010-10-20

Characterizing the ionic distribution around chromatin is important for understanding the electrostatic forces governing chromatin structure and function. Here we develop an electrostatic model to handle multivalent ions and compute the ionic distribution around a mesoscale chromatin model as a function of conformation, number of nucleosome cores, and ionic strength and species using Poisson-Boltzmann theory. This approach enables us to visualize and measure the complex patterns of counterion condensation around chromatin by examining ionic densities, free energies, shielding charges, and correlations of shielding charges around the nucleosome core and various oligonucleosome conformations. We show that: counterions, especially divalent cations, predominantly condense around the nucleosomal and linker DNA, unburied regions of histone tails, and exposed chromatin surfaces; ionic screening is sensitively influenced by local and global conformations, with a wide ranging net nucleosome core screening charge (56-100e); and screening charge correlations reveal conformational flexibility and interactions among chromatin subunits, especially between the histone tails and parental nucleosome cores. These results provide complementary and detailed views of ionic effects on chromatin structure for modest computational resources. The electrostatic model developed here is applicable to other coarse-grained macromolecular complexes. Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

A semi-grand canonical Monte Carlo simulation model for ion binding to ionizable surfaces: proton binding of carboxylated latex particles as a case study.

PubMed

Madurga, Sergio; Rey-Castro, Carlos; Pastor, Isabel; Vilaseca, Eudald; David, Calin; Garcés, Josep Lluís; Puy, Jaume; Mas, Francesc

2011-11-14

In this paper, we present a computer simulation study of the ion binding process at an ionizable surface using a semi-grand canonical Monte Carlo method that models the surface as a discrete distribution of charged and neutral functional groups in equilibrium with explicit ions modelled in the context of the primitive model. The parameters of the simulation model were tuned and checked by comparison with experimental titrations of carboxylated latex particles in the presence of different ionic strengths of monovalent ions. The titration of these particles was analysed by calculating the degree of dissociation of the latex functional groups vs. pH curves at different background salt concentrations. As the charge of the titrated surface changes during the simulation, a procedure to keep the electroneutrality of the system is required. Here, two approaches are used with the choice depending on the ion selected to maintain electroneutrality: counterion or coion procedures. We compare and discuss the difference between the procedures. The simulations also provided a microscopic description of the electrostatic double layer (EDL) structure as a function of pH and ionic strength. The results allow us to quantify the effect of the size of the background salt ions and of the surface functional groups on the degree of dissociation. The non-homogeneous structure of the EDL was revealed by plotting the counterion density profiles around charged and neutral surface functional groups. © 2011 American Institute of Physics

Simulating Donnan equilibria based on the Nernst-Planck equation

NASA Astrophysics Data System (ADS)

Gimmi, Thomas; Alt-Epping, Peter

2018-07-01

Understanding ion transport through clays and clay membranes is important for many geochemical and environmental applications. Ion transport is affected by electrostatic forces exerted by charged clay surfaces. Anions are partly excluded from pore water near these surfaces, whereas cations are enriched. Such effects can be modeled by the Donnan approach. Here we introduce a new, comparatively simple way to represent Donnan equilibria in transport simulations. We include charged surfaces as immobile ions in the balance equation and calculate coupled transport of all components, including the immobile charges, with the Nernst-Planck equation. This results in an additional diffusion potential that influences ion transport, leading to Donnan ion distributions while maintaining local charge balance. The validity of our new approach was demonstrated by comparing Nernst-Planck simulations using the reactive transport code Flotran with analytical solutions available for simple Donnan systems. Attention has to be paid to the numerical evaluation of the electrochemical migration term in the Nernst-Planck equation to obtain correct results for asymmetric electrolytes. Sensitivity simulations demonstrate the influence of various Donnan model parameters on simulated anion accessible porosities. It is furthermore shown that the salt diffusion coefficient in a Donnan pore depends on local concentrations, in contrast to the aqueous salt diffusion coefficient. Our approach can be easily implemented into other transport codes. It is versatile and facilitates, for instance, assessing the implications of different activity models for the Donnan porosity.

Upregulation of BMSCs Osteogenesis by Positively-Charged Tertiary Amines on Polymeric Implants via Charge/iNOS Signaling Pathway

PubMed Central

Zhang, Wei; Liu, Na; Shi, Haigang; Liu, Jun; Shi, Lianxin; Zhang, Bo; Wang, Huaiyu; Ji, Junhui; Chu, Paul K.

2015-01-01

Positively-charged surfaces on implants have a similar potential to upregulate osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs) as electromagnetic therapy approved for bone regeneration. Generally, their osteogenesis functions are generally considered to stem from the charge-induced adhesion of extracellular matrix (ECM) proteins without exploring the underlying surface charge/cell signaling molecule pathways. Herein, a positively-charged surface with controllable tertiary amines is produced on a polymer implant by plasma surface modification. In addition to inhibiting the TNF-α expression, the positively-charged surface with tertiary amines exhibits excellent cytocompatibility as well as remarkably upregulated osteogenesis-related gene/protein expressions and calcification of the contacted BMSCs. Stimulated by the charged surface, these BMSCs display high iNOS expressions among the three NOS isoforms. Meanwhile, downregulation of the iNOS by L-Can or siRNA inhibit osteogenic differentiation in the BMSCs. These findings suggest that a positively-charged surface with tertiary amines induces osteogenesis of BMSCs via the surface charge/iNOS signaling pathway in addition to elevated ECM protein adhesion. Therefore, creating a positively-charged surface with tertiary amines is a promising approach to promote osseointegration with bone tissues. PMID:25791957

Competitive adsorption in model charged protein mixtures: Equilibrium isotherms and kinetics behavior

NASA Astrophysics Data System (ADS)

Fang, F.; Szleifer, I.

2003-07-01

The competitive adsorption of proteins of different sizes and charges is studied using a molecular theory. The theory enables the study of charged systems explicitly including the size, shape, and charge distributions in all the molecular species in the mixture. Thus, this approach goes beyond the commonly used Poisson-Boltzmann approximation. The adsorption isotherms of the protein mixtures are studied for mixtures of two proteins of different size and charge. The amount of proteins adsorbed and the fraction of each protein is calculated as a function of the bulk composition of the solution and the amount of salt in the system. It is found that the total amount of proteins adsorbed is a monotonically decreasing function of the fraction of large proteins on the bulk solution and for fixed protein composition of the salt concentration. However, the composition of the adsorbed layer is a complicated function of the bulk composition and solution ionic strength. The structure of the adsorb layer depends upon the bulk composition and salt concentration. In general, there are multilayers adsorbed due to the long-range character of the electrostatic interactions. When the composition of large proteins in bulk is in very large excess it is found that the structure of the adsorb multilayer is such that the layer in contact with the surface is composed by a mixture of large and small proteins. However, the second and third layers are almost exclusively composed of large proteins. The theory is also generalized to study the time-dependent adsorption. The approach is based on separation of time scales into fast modes for the ions from the salt and the solvent and slow for the proteins. The dynamic equations are written for the slow modes, while the fast ones are obtained from the condition of equilibrium constrained to the distribution of proteins given by the slow modes. Two different processes are presented: the adsorption from a homogeneous solution to a charged surface at low salt concentration, and large excess of the large proteins in bulk. The second process is the kinetics of structural and adsorption change by changing the salt concentration of the bulk solution from low to high. The first process shows a large overshoot of the large proteins on the surface due to their excess in solution, followed by a surface replacement by the smaller molecules. The second process shows a very fast desorption of the large proteins followed by adsorption at latter stages. This process is found to be driven by large electrostatic repulsions induced by the fast ions from the salt approaching the surface. The relevance of the theoretical predictions to experimental system and possible directions for improvements of the theory are discussed.

Modulation of protein stability and aggregation properties by surface charge engineering.

PubMed

Raghunathan, Govindan; Sokalingam, Sriram; Soundrarajan, Nagasundarapandian; Madan, Bharat; Munussami, Ganapathiraman; Lee, Sun-Gu

2013-09-01

An attempt to alter protein surface charges through traditional protein engineering approaches often affects the native protein structure significantly and induces misfolding. This limitation is a major hindrance in modulating protein properties through surface charge variations. In this study, as a strategy to overcome such a limitation, we attempted to co-introduce stabilizing mutations that can neutralize the destabilizing effect of protein surface charge variation. Two sets of rational mutations were designed; one to increase the number of surface charged amino acids and the other to decrease the number of surface charged amino acids by mutating surface polar uncharged amino acids and charged amino acids, respectively. These two sets of mutations were introduced into Green Fluorescent Protein (GFP) together with or without stabilizing mutations. The co-introduction of stabilizing mutations along with mutations for surface charge modification allowed us to obtain functionally active protein variants (s-GFP(+15-17) and s-GFP(+5-6)). When the protein properties such as fluorescent activity, folding rate and kinetic stability were assessed, we found the possibility that the protein stability can be modulated independently of activity and folding by engineering protein surface charges. The aggregation properties of GFP could also be altered through the surface charge engineering.

Molecular simulation study of feruloyl esterase adsorption on charged surfaces: effects of surface charge density and ionic strength.

PubMed

Liu, Jie; Peng, Chunwang; Yu, Gaobo; Zhou, Jian

2015-10-06

The surrounding conditions, such as surface charge density and ionic strength, play an important role in enzyme adsorption. The adsorption of a nonmodular type-A feruloyl esterase from Aspergillus niger (AnFaeA) on charged surfaces was investigated by parallel tempering Monte Carlo (PTMC) and all-atom molecular dynamics (AAMD) simulations at different surface charge densities (±0.05 and ±0.16 C·m(-2)) and ionic strengths (0.007 and 0.154 M). The adsorption energy, orientation, and conformational changes were analyzed. Simulation results show that whether AnFaeA can adsorb onto a charged surface is mainly controlled by electrostatic interactions between AnFaeA and the charged surface. The electrostatic interactions between AnFaeA and charged surfaces are weakened when the ionic strength increases. The positively charged surface at low surface charge density and high ionic strength conditions can maximize the utilization of the immobilized AnFaeA. The counterion layer plays a key role in the adsorption of AnFaeA on the negatively charged COOH-SAM. The native conformation of AnFaeA is well preserved under all of these conditions. The results of this work can be used for the controlled immobilization of AnFaeA.

Spatially resolved surface valence gradient and structural transformation of lithium transition metal oxides in lithium-ion batteries.

PubMed

Liu, Hanshuo; Bugnet, Matthieu; Tessaro, Matteo Z; Harris, Kristopher J; Dunham, Mark J R; Jiang, Meng; Goward, Gillian R; Botton, Gianluigi A

2016-10-26

Layered lithium transition metal oxides are one of the most important types of cathode materials in lithium-ion batteries (LIBs) that possess high capacity and relatively low cost. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and not yet fully understood. We herein systematically investigate the chemical evolution and structural transformation of the LiNi x Mn y Co 1-x-y O 2 (NMC) cathode material in order to understand the battery performance deterioration driven by the cathode degradation upon cycling. Using high-resolution electron energy loss spectroscopy (HR-EELS) we clarify the role of transition metals in the charge compensation mechanism, particularly the controversial Ni 2+ (active) and Co 3+ (stable) ions, at different states-of-charge (SOC) under 4.6 V operation voltage. The cathode evolution is studied in detail from the first-charge to long-term cycling using complementary diagnostic tools. With the bulk sensitive 7 Li nuclear magnetic resonance (NMR) measurements, we show that the local ordering of transition metal and Li layers (R3[combining macron]m structure) is well retained in the bulk material upon cycling. In complement to the bulk measurements, we locally probe the valence state distribution of cations and the surface structure of NMC particles using EELS and scanning transmission electron microscopy (STEM). The results reveal that the surface evolution of NMC is initiated in the first-charging step with a surface reduction layer formed at the particle surface. The NMC surface undergoes phase transformation from the layered structure to a poor electronic and ionic conducting transition-metal oxide rock-salt phase (R3[combining macron]m → Fm3[combining macron]m), accompanied by irreversible lithium and oxygen loss. In addition to the electrochemical cycling effect, electrolyte exposure also shows non-negligible influence on cathode surface degradation. These chemical and structural changes of the NMC cathode could contribute to the first-cycle coulombic inefficiency, restrict the charge transfer characteristics and ultimately impact the cell capacity.

Molecular orbital imaging of cobalt phthalocyanine on native oxidized copper layers using STM.

PubMed

Guo, Qinmin; Huang, Min; Qin, Zhihui; Cao, Gengyu

2012-07-01

To observe molecular orbitals using scanning tunneling microscopy, well-ordered oxidized layers on Cu(001) were fabricated to screen the individual adsorbed cobalt phthalocyanine (CoPc) molecules from the electronic influence of the metal surface. Scanning tunneling microscope images of the molecule on this oxidized layer show similarities to the orbital distribution of the free molecule. The good match between the differential conductance mapping images and the calculated charge distribution at energy levels corresponding to the frontier orbitals of CoPc provides more evidence of the screening of the oxidized layer from interactions between the metal surface and supported molecules. Copyright © 2012 Elsevier B.V. All rights reserved.

Electrophoretic separation of kidney and pituitary cells on STS-8

NASA Technical Reports Server (NTRS)

Morrison, D. R.; Nachtwey, D. S.; Barlow, G. H.; Cleveland, C.; Lanham, J. W.; Farrington, M. A.; Hatfield, J. M.; Hymer, W. C.; Grindeland, R.; Lewis, M. L.

1984-01-01

Specific secretory cells were separated from suspensions of cultured primary human embryonic cells and rat pituitary cells in microgravity conditions, with an objective of isolating the subfractions of kidney cells that produce the largest amount of urakinase, and the subfractions of rat pituitary cells that secrete growth hormones (GH), prolactin (PRL), and other hormones. It is inferred from the experimental observations that the surface charge distributions of the GH-containing cells differ from those of the PRL-containing cells, which is explained by the presence of secretory products on the surface of pituitary cells. For kidney cells, the electrophoretic mobility distributions in flight experiments were spread more than the ground controls.

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 gain 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. Electrostatic forces are generally under-estimated for their role in causing agglomeration of dispersed grains in particulate clouds, or their role in affecting the internal frictional relationships in packed granular masses. We believe that electrostatic, in particular dipole-mediated processes, 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.

Effect of Experimental Parameters on Alginate/Chitosan Microparticles for BCG Encapsulation

PubMed Central

Caetano, Liliana A.; Almeida, António J.; Gonçalves, Lídia M.D.

2016-01-01

The aim of the present study was to develop novel Mycobacterium bovis bacille Calmette-Guérin (BCG)-loaded polymeric microparticles with optimized particle surface characteristics and biocompatibility, so that whole live attenuated bacteria could be further used for pre-exposure vaccination against Mycobacterium tuberculosis by the intranasal route. BCG was encapsulated in chitosan and alginate microparticles through three different polyionic complexation methods by high speed stirring. For comparison purposes, similar formulations were prepared with high shear homogenization and sonication. Additional optimization studies were conducted with polymers of different quality specifications in a wide range of pH values, and with three different cryoprotectors. Particle morphology, size distribution, encapsulation efficiency, surface charge, physicochemical properties and biocompatibility were assessed. Particles exhibited a micrometer size and a spherical morphology. Chitosan addition to BCG shifted the bacilli surface charge from negative zeta potential values to strongly positive ones. Chitosan of low molecular weight produced particle suspensions of lower size distribution and higher stability, allowing efficient BCG encapsulation and biocompatibility. Particle formulation consistency was improved when the availability of functional groups from alginate and chitosan was close to stoichiometric proportion. Thus, the herein described microparticulate system constitutes a promising strategy to deliver BCG vaccine by the intranasal route. PMID:27187418

Large transient nonproton ion movements in purple membrane suspensions are abolished by solubilization in Triton X-100.

PubMed Central

Marinetti, T; Mauzerall, D

1986-01-01

Light-induced release/uptake of both protons and other ions cause transient changes in conductivity in suspensions of purple membrane (PM) fragments (Marinetti, Tim, and David Mauzerall, 1983, Proc. Natl. Acad. Sci. USA, 80:178-180). We find that the release/uptake of nonproton ions with quantum yield greater than 1 is observed at most pHs and ionic strengths. Only at both low pH and low ionic strength is the conductivity transient mostly due to protons. Our hypothesis is that during the photocycle, changes occur in the PM's dense surface charge distribution that result in changes in the number of counterions bound or condensed at the membrane surface. To test this, the PM structure was perturbed with the nonionic detergent Triton X-100. Immediately after addition, Triton does not abolish the nonproton ion movements; in fact at low detergent concentrations (0.02% vol/vol) the signal amplitudes increased considerably. However, when PM is completely solubilized into monomers in Triton, the conductivity transients are due to protons alone, though at lower quantum yield compared with native PM. These results suggest that changes in the surface charge distribution in native PM's photocycle could contribute to proton transfer between the aqueous phase and bR itself. PMID:3019444

Constraints on the microphysics of Pluto's photochemical haze from New Horizons observations

NASA Astrophysics Data System (ADS)

Gao, Peter; Fan, Siteng; Wong, Michael L.; Liang, Mao-Chang; Shia, Run-Lie; Kammer, Joshua A.; Yung, Yuk L.; Summers, Michael E.; Gladstone, G. Randall; Young, Leslie A.; Olkin, Catherine B.; Ennico, Kimberly; Weaver, Harold A.; Stern, S. Alan; New Horizons Science Team

2017-05-01

The New Horizons flyby of Pluto confirmed the existence of hazes in its atmosphere. Observations of a large high- to low- phase brightness ratio, combined with the blue color of the haze (indicative of Rayleigh scattering), suggest that the haze particles are fractal aggregates, perhaps analogous to the photochemical hazes on Titan. Therefore, studying the Pluto hazes can shed light on the similarities and differences between the Pluto and Titan atmospheres. We model the haze distribution using the Community Aerosol and Radiation Model for Atmospheres assuming that the distribution is shaped by downward transport and coagulation of particles originating from photochemistry. Hazes composed of both purely spherical and purely fractal aggregate particles are considered. General agreement between model results and solar occultation observations is obtained with aggregate particles when the downward mass flux of photochemical products is equal to the column-integrated methane destruction rate ∼1.2 × 10-14 g cm-2 s-1, while for spherical particles the mass flux must be 2-3 times greater. This flux is nearly identical to the haze production flux of Titan previously obtained by comparing microphysical model results to Cassini observations. The aggregate particle radius is sensitive to particle charging effects, and a particle charge to radius ratio of 30 e-/μm is necessary to produce ∼0.1-0.2 μm aggregates near Pluto's surface, in accordance with forward scattering measurements. Such a particle charge to radius ratio is 2-4 times higher than those previously obtained for Titan. Hazes composed of spheres with the same particle charge to radius ratio have particles that are 4 times smaller at Pluto's surface. These results further suggest that the haze particles are fractal aggregates. We also consider the effect of condensation of HCN, C2H2, C2H4, and C2H6 on the haze particles, which may play an important role in shaping their altitude and size distributions.

Effect of Surface Hydration on Antifouling Properties of Mixed Charged Polymers.

PubMed

Leng, Chuan; Huang, Hao; Zhang, Kexin; Hung, Hsiang-Chieh; Xu, Yao; Li, Yaoxin; Jiang, Shaoyi; Chen, Zhan

2018-05-07

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water, and how such structures change while exposing to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property while other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.

Measurement of clay surface areas by polyvinylpyrrolidone (PVP) sorption and its use for quantifying illite and smectite abundance

USGS Publications Warehouse

Blum, A.E.; Eberl, D.D.

2004-01-01

A new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectite particles dispersed in aqueous solution. The sorption density of PVP-55K on a wide range of smectites, illites and kaolinites is ~0.99 mg/m2, which corresponds to ~0.72 g of PVP-55K per gram of montmorillonite. Polyvinylpyrrolidone sorption on smectites is independent of layer charge and solution pH. PVP sorption on SiO2, Fe2O3 and ZnO normalized to the BET surface area is similar to the sorption densities on smectites. γ-Al2O3, amorphous Al(OH)3 and gibbsite have no PVP sorption over a wide range of pH, and sorption of PVP by organics is minimal. The insensitivity of PVP sorption densities to mineral layer charge, solution pH and mineral surface charge indicates that PVP sorption is not localized at charged sites, but is controlled by more broadly distributed sorption mechanisms such as Van der Waals’ interactions and/or hydrogen bonding. Smectites have very large surface areas when dispersed as single unit-cell-thick particles (~725 m2/g) and usually dominate the total surface areas of natural samples in which smectites are present. In this case, smectite abundance is directly proportional to PVP sorption. In some cases, however, the accurate quantification of smectite abundance by PVP sorption may require minor corrections for PVP uptake by other phases, principally illite and kaolinite. Quantitative XRD can be combined with PVP uptake measurements to uniquely determine the smectite concentration in such samples.

Molecular insight into the electrostatic membrane surface potential by 14n/31p MAS NMR spectroscopy: nociceptin-lipid association.

PubMed

Lindström, Fredrick; Williamson, Philip T F; Gröbner, Gerhard

2005-05-11

Exploiting naturally abundant (14)N and (31)P nuclei by high-resolution MAS NMR (magic angle spinning nuclear magnetic resonance) provides a molecular view of the electrostatic potential present at the surface of biological model membranes, the electrostatic charge distribution across the membrane interface, and changes that occur upon peptide association. The spectral resolution in (31)P and (14)N MAS NMR spectra is sufficient to probe directly the negatively charged phosphate and positively charged choline segment of the electrostatic P(-)-O-CH(2)-CH(2)-N(+)(CH(3))(3) headgroup dipole of zwitterionic DMPC (dimyristoylphosphatidylcholine) in mixed-lipid systems. The isotropic shifts report on the size of the potential existing at the phosphate and ammonium group within the lipid headgroup while the chemical shielding anisotropy ((31)P) and anisotropic quadrupolar interaction ((14)N) characterize changes in headgroup orientation in response to surface potential. The (31)P/(14)N isotropic chemical shifts for DMPC show opposing systematic changes in response to changing membrane potential, reflecting the size of the electrostatic potential at opposing ends of the P(-)-N(+) dipole. The orientational response of the DMPC lipid headgroup to electrostatic surface variations is visible in the anisotropic features of (14)N and (31)P NMR spectra. These features are analyzed in terms of a modified "molecular voltmeter" model, with changes in dynamic averaging reflecting the tilt of the C(beta)-N(+)(CH)(3) choline and PO(4)(-) segment. These properties have been exploited to characterize the changes in surface potential upon the binding of nociceptin to negatively charged membranes, a process assumed to proceed its agonistic binding to its opoid G-protein coupled receptor.

Monitoring the degrafting of polyelectrolyte brushes by using surface gradients

NASA Astrophysics Data System (ADS)

Ko, Yeongun; Genzer, Jan

Polymer brushes comprise densely grafted polymer chains on surfaces, which possess high stability and high concentration of reactive centers per unit area compared to physisorbed polymer film. Polymer brushes are employed in many applications, including anti-fouling surfaces, cell adhesive surfaces, responsive surfaces, low-friction surfaces, etc. Recently, researchers reported that charged (or chargeable) polymer brushes can be degrafted from substrate while incubated in buffer solutions. Based on previous experiments conducted in our group and by others, we assume that chain degrafting results from the hydrolysis of Si-O groups in head-group of the initiator and/or the ester groups in main body of the initiator. The kinetic of hydrolysis is affected by mechanical forces acting on the initiator. Those forces depend on the molecular weight and the grafting density of the brush, and the concentration and distribution of charges along the macromolecule (tuned by pH - for weak electrolytes - and concentration of external salt). In this work, we study the stability of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes in two solvents (ethanol and water) at various pH values in water and under different levels of external salt concentration. National Science Foundation.

Energetics and kinetics of primary charge separation in bacterial photosynthesis.

PubMed

LeBard, David N; Kapko, Vitaliy; Matyushov, Dmitry V

2008-08-21

We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and charge-transfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair.

Vacuum phonon tunneling.

PubMed

Altfeder, Igor; Voevodin, Andrey A; Roy, Ajit K

2010-10-15

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

Numerical simulation of electroosmotic flow in rough microchannels using the lattice Poisson-Nernst-Planck methods

NASA Astrophysics Data System (ADS)

Kamali, Reza; Soloklou, Mohsen Nasiri; Hadidi, Hooman

2018-05-01

In this study, coupled Lattice Boltzmann method is applied to solve the dynamic model for an electroosmotic flow and investigate the effects of roughness in a 2-D flat microchannel. In the present model, the Poisson equation is solved for the electrical potential, the Nernst- Planck equation is solved for the ion concentration. In the analysis of electroosmotic flows, when the electric double layers fully overlap or the convective effects are not negligible, the Nernst-Planck equation must be used to find the ionic distribution throughout the microchannel. The effects of surface roughness height, roughness interval spacing and roughness surface potential on flow conditions are investigated for two different configurations of the roughness, when the EDL layers fully overlap through the microchannel. The results show that in both arrangements of roughness in homogeneously charged rough channels, the flow rate decreases by increasing the roughness height. A discrepancy in the mass flow rate is observed when the roughness height is about 0.15 of the channel width, which its average is higher for the asymmetric configuration and this difference grows by increasing the roughness height. In the symmetric roughness arrangement, the mass flow rate increases until the roughness interval space is almost 1.5 times the roughness width and it decreases for higher values of the roughness interval space. For the heterogeneously charged rough channel, when the roughness surface potential ψr is less than channel surface potential ψs , the net charge density increases by getting far from the roughness surface, while in the opposite situation, when ψs is more than ψr , the net charge density decreases from roughness surface to the microchannel middle center. Increasing the roughness surface potential induces stronger electric driving force on the fluid which results in larger velocities in the flow.

Surface waves generated by shallow underwater explosions

NASA Technical Reports Server (NTRS)

Falade, A.; Holt, M.

1978-01-01

Surface water waves generated by surface and near surface point explosions are calculated. Taking the impulse distribution imparted at the water surface by the explosion as the overriding mechanism for transferring energy of the explosive to surface wave motion, the linearized theory of Kranzer and Keller is used to obtain the wave displacement in the far field. The impulse distribution is obtained by integrating the pressure wave over an appropriate time interval on a horizontal surface just beneath the undisturbed water surface. For surface explosions, a modified form of the similarity method first used by Collins and Holt is used to obtain the flow field. In the case of submerged explosions, the flow field is estimated by making necessary modifications to Sedov's similarity solution to account for the venting that accompanies the interaction of the leading (blast) wave with the ocean surface. Surface waves generated by a charge at six depths of placement (0.15 m, 0.30 m, 0.61 m, 0.91 m, 1.37 m, 3.05 m) are considered in addition to surface explosions. The results seem to support the existence of an upper critical depth phenomenon (of the type already established for chemical explosions) for point (nuclear) explosions.

Studies of Surface Charging of Polymers by Indirect Triboelectrification

NASA Astrophysics Data System (ADS)

Mantovani, James; Calle, Carlos; Groop, Ellen; Buehler, Martin

2001-03-01

Charge is known to develop on the surface of an insulating polymer by frictional charging through direct physical contact with another material. We will present results of recent triboelectrification studies of polymer surfaces that utilized an indirect method of frictional charging. This method first involves placing a grounded thin metal foil in stationary contact over the polymer surface. The exposed metal foil is then rubbed with the surface of the material that generates the triboelectric charge. Data is presented for five types of polymers: fiberglass/epoxy, polycarbonate (Lexan), polytetraflouroethylene (Teflon), Rulon J, and polymethylmethacrylate (PMMA, Lucite). The amount of charge that develops on an insulator's surface is measured using the MECA Electrometer, which was developed jointly by NASA Kennedy Space Center and the Jet Propulsion Laboratory to study the electrostatic properties of soil on the surface of Mars. Even though the insulator's surface is electrically shielded from the rubbing material by the grounded metal foil, charge measurements obtained by the MECA Electrometer after the metal foil is separated from the insulator's surface reveal that the insulator's surface does accumulate charge by indirect frictional charging. A possible explanation of the observations will be presented based on a simple contact barrier model.

Current-voltage characteristics influenced by the nanochannel diameter and surface charge density in a fluidic field-effect-transistor.

PubMed

Singh, Kunwar Pal; Guo, Chunlei

2017-06-21

The nanochannel diameter and surface charge density have a significant impact on current-voltage characteristics in a nanofluidic transistor. We have simulated the effect of the channel diameter and surface charge density on current-voltage characteristics of a fluidic nanochannel with positive surface charge on its walls and a gate electrode on its surface. Anion depletion/enrichment leads to a decrease/increase in ion current with gate potential. The ion current tends to increase linearly with gate potential for narrow channels at high surface charge densities and narrow channels are more effective to control the ion current at high surface charge densities. The current-voltage characteristics are highly nonlinear for wide channels at low surface charge densities and they show different regions of current change with gate potential. The ion current decreases with gate potential after attaining a peak value for wide channels at low values of surface charge densities. At low surface charge densities, the ion current can be controlled by a narrow range of gate potentials for wide channels. The current change with source drain voltage shows ohmic, limiting and overlimiting regions.

Charge transportation and permittivity in electron beam irradiated polymethyl methacrylate

NASA Astrophysics Data System (ADS)

Zheng, Feihu; Zhang, Yewen; Xia, Junfeng; Xiao, Chun; An, Zhenlian

2009-09-01

The charging phenomenon in the insulating dielectrics often occurs in the radiative environments such as in the outer space and in the nuclear reactor. Both surface charging and bulk charging have various influences on the dielectric properties. Understanding electrical properties of e-beam irradiated dielectrics is of great significance in order to maintain the stability and reliability of the related operating system. In this work, the effect of electron beam irradiation on the permittivity of polymethyl methacrylate (PMMA) samples was investigated. It was found that the variance of permittivity in e-beam irradiated PMMA is mainly determined by two factors. One is the porosity of the material. The irradiating process could increase the porosity of PMMA due to the escape of the small molecule (e.g., CO, CO2, and CH4) produced during material degradation caused by e-beam irradiation. The enhanced higher porosity corresponds to lower permittivity. The distribution of the implanted charge is the other factor that influences the permittivity. When the distribution of electric field generated by the accumulating charge is asymmetric for the middle thickness of the sample, the PMMA sample with polar groups would be subjected to extra polarization by the field, which could lead to the increase in permittivity. Combining with the model of Wakino et al. [J. Am. Ceram. Soc. 76, 2588 (1993)] on permittivity of mixture materials, the Clausius-Mosotti equation was utilized to analyze the variation in permittivity in the e-beam irradiated PMMA samples.

Effect of electric charge on the adhesion of human blood platelets.

PubMed

Lowkis, B; Szymonowicz, M

1993-01-01

The paper presents the results of research into the effect of the size and depth of the implanted electric charge on the adhesion of human blood platelets. The experiments were carried out on polyethylene terephthalate PET foil of 36 microns thickness. The electret formation process was carried out in an electron-beam device. The electrization conditions were such that electrets with the excess electric charge accumulated at various depths were obtained. The selection of conditions was verified by investigating the space charge distribution with the use of the virtual electrode method. The microscopic observation of non-electrified foils and electrets as well as the quantitative examination of the adhesion of human blood platelets has explicitly confirmed the positive influence of the electret effect on the thrombogenesis of PET foil. This made it possible to define the optimum electrization conditions. The research has additionally indicated that the relationship between the amount of adherent blood platelets and the size of the electric charge is not a simple relation of the kind: the larger negative charge, the more thrombogenic material. The decisive and positive effect of the space charge has been confirmed by analysing the effectiveness of the surface and space charge.

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms

DOE PAGES

Zhou, Jun; Li, Junjie; Correa, Alfredo A.; ...

2014-10-24

We report the first systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which are escaping into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We alsomore » developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.« less

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Jun; Li, Junjie; Correa, Alfredo A.

We report the first systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which are escaping into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We alsomore » developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.« less

Rectification of nanopores at surfaces

PubMed Central

Sa, Niya

2011-01-01

At the nanoscale, methods to measure surface charge can prove challenging. Herein we describe a general method to report surface charge through the measurement of ion current rectification of a nanopipette brought in close proximity to a charged substrate. This method is able to discriminate between charged cationic and anionic substrates when the nanopipette is brought within distances from ten to hundreds of nanometers from the surface. Further studies of the pH dependence on the observed rectification support a surface-induced mechanism and demonstrate the ability to further discriminate between cationic and nominally uncharged surfaces. This method could find application in measurement and mapping of heterogeneous surface charges and is particularly attractive for future biological measurements, where noninvasive, noncontact probing of surface charge will prove valuable. PMID:21675734

Adsorption and Dissociation of Molecular Hydrogen on the (0001) Surface of DHCP Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Ray, Asok

2009-03-01

Hydrogen molecule adsorption on the (0001) surface of double hexagonal closed packed americium has been studied in detail within the framework of density functional theory. Weak molecular hydrogen adsorptions were observed. The most stable configuration corresponded to a Hor2 approach molecular adsorption at the one-fold top site where the molecule's approach is perpendicular to a lattice vector. Adsorption energies and adsorption geometries for different adsorption sites will be discussed. The change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the hydrogen molecule will be discussed. Reaction barrier for the dissociation of hydrogen molecule will be presented. The implications of adsorption on Am 5f electron localization-delocalization will be summarized.

The electrokinetic behavior of calcium oxalate monohydrate in macromolecular solutions

NASA Technical Reports Server (NTRS)

Curreri, P. A.; Onoda, G. Y., Jr.; Finlayson, B.

1988-01-01

Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chrondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for chemical adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopopolysacchrides have greater affinity for the COM surface than the proteins. The amount of proteins that can chemically adsorb appears to be limited to approximately one monomolecular layer. When the surface charge is high, an insufficient number of proteins can chemically adsorb to neutralize or reverse the surface charge. The remaining surface charge is balanced by proteins held near the surface by longer range electrostatic forces only. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein.

Crystal structure of the disintegrin heterodimer from saw-scaled viper (Echis carinatus) at 1.9 A resolution.

PubMed

Bilgrami, Sameeta; Yadav, Savita; Kaur, Punit; Sharma, Sujata; Perbandt, Markus; Betzel, Christian; Singh, Tej P

2005-08-23

Disintegrins constitute a family of potent polypeptide inhibitors of integrins. Integrins are transmembrane heterodimeric molecules involved in cell-cell and cell-extracellular matrix interactions. They are involved in many diseases such as cancer and thrombosis. Thus, disintegrins have a great potential as anticancer and antithrombotic agents. A novel heterodimeric disintegrin was isolated from the venom of saw-scaled viper (Echis carinatus) and was crystallized. The crystals diffracted to 1.9 A resolution and belonged to space group P4(3)2(1)2. The data indicated the presence of a pseudosymmetry. The structure was solved by applying origin shifts to the disintegrin homodimer schistatin solved in space group I4(1)22 with similar cell dimensions. The structure refined to the final R(cryst)/R(free) factors of 0.213/0.253. The notable differences are observed between the loops, (Gln39-Asp48) containing the important Arg42-Gly43-Asp44, of the present heterodimer and schistatin. These differences are presumably due to the presence of two glycines at positions 43 and 46 that allow the molecule to adopt variable conformations. A comparative analysis of the surface-charge distributions of various disintegrins showed that the charge distribution on monomeric disintegrins occurred uniformly over the whole surface of the molecule, while in the dimeric disintegrins, the charge is distributed only on one face. Such a feature may be important in the binding of two integrins to a single dimeric disintegrin. The phylogenetic analysis developed on the basis of amino acid sequence and three-dimensional structures indicates that the protein diversification and evolution presumably took place from the medium disintegrins and both the dimeric and short disintegrins evolved from them.

Charged particle detectors with active detector surface for partial energy deposition of the charged particles and related methods

DOEpatents

Gerts, David W; Bean, Robert S; Metcalf, Richard R

2013-02-19

A radiation detector is disclosed. The radiation detector comprises an active detector surface configured to generate charge carriers in response to charged particles associated with incident radiation. The active detector surface is further configured with a sufficient thickness for a partial energy deposition of the charged particles to occur and permit the charged particles to pass through the active detector surface. The radiation detector further comprises a plurality of voltage leads coupled to the active detector surface. The plurality of voltage leads is configured to couple to a voltage source to generate a voltage drop across the active detector surface and to separate the charge carriers into a plurality of electrons and holes for detection. The active detector surface may comprise one or more graphene layers. Timing data between active detector surfaces may be used to determine energy of the incident radiation. Other apparatuses and methods are disclosed herein.

An uptake of cationized ferritin by alveolar type I cells in airway-instilled goat lung: distribution of anionic sites on the epithelial surface.

PubMed

Atwal, O S; Viel, L; Minhas, K J

1990-07-01

The present study has investigated ultrastructural localization of anionic sites on the luminal surface of the alveolar epithelium of goat lung by direct airway instillation of cationized ferritin (CF) in the cranial lobe of the right lung through a bronchoscope. The cationic probe decorated preferentially the luminal plasmalemmal vesicles and plasmalemma proper of alveolar type I cell. This indicated the presence of highly charged anionic microdomains at these binding sites. The ligand was internalized in the free plasmalemmal vesicles of alveolar type I cell within 2 min. Heavy decoration of vesicles at 5 min of perfusion indicated that the amount of CF internalization increased with its concentration in the alveoli. It is suggested that exposure of alveolar surface to several gases of ruminal-origin induces changes in the surface charge of luminal plasmalemma of alveolar type I cells. The significance of these anionic plasmalemmal sites is discussed in relation to the adjustment of osmotic pressure gradient across the alveolar-capillary membrane of the ruminant lung.

The effect of surface functionality on cellular trafficking of dendrimers.

PubMed

Perumal, Omathanu P; Inapagolla, Rajyalakshmi; Kannan, Sujatha; Kannan, Rangaramanujam M

2008-01-01

Dendrimers are an emerging group of nanostructured, polymeric biomaterials that have potential as non-viral vehicles for delivering drugs and genetic material to intracellular targets. They have a high charge density with tunable surface functional groups, which can alter the local environment and influence cellular interactions. This can have a significant impact on the intracellular trafficking of dendrimer-based nanodevices. With the help of flow cytometry, fluorescence microscopy, and by using specific inhibitors, the influence of surface functionality on their uptake in A549 lung epithelial cells, and subsequent intracellular distribution was investigated. In this paper, we have shown that even though all the dendrimers are taken up by fluid-phase endocytosis, significant differences in uptake mechanisms exist. Anionic dendrimers appear to be mainly taken up by caveolae mediated endocytosis in A549 lung epithelial cells, while cationic and neutral dendrimers appear to be taken in by a non-clathrin, non-caveolae mediated mechanism that may be by electrostatic interactions or other non-specific fluid-phase endocytosis. These findings open up new possibilities of targeting therapeutic agents to specific cell organelles based on surface charge.

Luminescence evolution from alumina ceramic surface before flashover under direct and alternating current voltage in vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Guo-Qiang; Wang, Yi-Bo; Song, Bai-Peng

2016-06-15

The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under amore » higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.« less

Luminescence evolution from alumina ceramic surface before flashover under direct and alternating current voltage in vacuum

NASA Astrophysics Data System (ADS)

Su, Guo-Qiang; Wang, Yi-Bo; Song, Bai-Peng; Mu, Hai-Bao; Zhang, Guan-Jun; Li, Feng; Wang, Meng

2016-06-01

The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under a higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation.

PubMed

Eckenrode, Heather M; Jen, Shih-Hui; Han, Jun; Yeh, An-Gong; Dai, Hai-Lung

2005-03-17

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity.

Alkali-metal induced band structure deformation investigated by angle-resolved photoemission spectroscopy and first-principles calculations

NASA Astrophysics Data System (ADS)

Ito, S.; Feng, B.; Arita, M.; Someya, T.; Chen, W.-C.; Takayama, A.; Iimori, T.; Namatame, H.; Taniguchi, M.; Cheng, C.-M.; Tang, S.-J.; Komori, F.; Matsuda, I.

2018-04-01

Alkali-metal adsorption on the surface of materials is widely used for in situ surface electron doping, particularly for observing unoccupied band structures by angle-resolved photoemission spectroscopy (ARPES). However, the effects of alkali-metal atoms on the resulting band structures have yet to be fully investigated, owing to difficulties in both experiments and calculations. Here, we combine ARPES measurements on cesium-adsorbed ultrathin bismuth films with first-principles calculations of the electronic charge densities and demonstrate a simple method to evaluate alkali-metal induced band deformation. We reveal that deformation of bismuth surface bands is directly correlated with vertical charge-density profiles at each electronic state of bismuth. In contrast, a change in the quantized bulk bands is well described by a conventional rigid-band-shift picture. We discuss these two aspects of the band deformation holistically, considering spatial distributions of the electronic states and cesium-bismuth hybridization, and provide a prescription for applying alkali-metal adsorption to a wide range of materials.

Representation of the Geosynchronous Plasma Environment in Spacecraft Charging Calculations

NASA Technical Reports Server (NTRS)

Davis, V. A.; Mandell, M. J.; Thomsen, M. F.

2006-01-01

Historically, our ability to predict and postdict spacecraft surface charging has been limited by the characterization of the plasma environment. One difficulty lies in the common practice of fitting the plasma data to a Maxwellian or Double Maxwellian distribution function, which may not represent the data well for charging purposes. We use electron and ion flux spectra measured by the Los Alamos National Laboratory (LANL) Magnetospheric Plasma Analyzer (MPA) to examine how the use of different spectral representations of the charged particle environment in computations of spacecraft potentials during magnetospheric substorms affects the accuracy of the results. We calculate the spacecraft potential using both the measured fluxes and several different fits to these fluxes. These measured fluxes have been corrected for the difference between the measured and calculated potential. The potential computed using the measured fluxes and the best available material properties of graphite carbon, with a secondary electron escape fraction of 81%, is within a factor of three of the measured potential for 87% of the data. Potentials calculated using a Kappa function fit to the incident electron flux distribution function and a Maxwellian function fit to the incident ion flux distribution function agree with measured potentials nearly as well as do potentials calculated using the measured fluxes. Alternative spectral representations gave less accurate estimates of potential. The use of all the components of the net flux, along with spacecraft specific average material properties, gives a better estimate of the spacecraft potential than the high energy flux alone.

Atomic Charge Parameters for the Finite Difference Poisson-Boltzmann Method Using Electronegativity Neutralization.

PubMed

Yang, Qingyi; Sharp, Kim A

2006-07-01

An optimization of Rappe and Goddard's charge equilibration (QEq) method of assigning atomic partial charges is described. This optimization is designed for fast and accurate calculation of solvation free energies using the finite difference Poisson-Boltzmann (FDPB) method. The optimization is performed against experimental small molecule solvation free energies using the FDPB method and adjusting Rappe and Goddard's atomic electronegativity values. Using a test set of compounds for which experimental solvation energies are available and a rather small number of parameters, very good agreement was obtained with experiment, with a mean unsigned error of about 0.5 kcal/mol. The QEq atomic partial charge assignment method can reflect the effects of the conformational changes and solvent induction on charge distribution in molecules. In the second section of the paper we examined this feature with a study of the alanine dipeptide conformations in water solvent. The different contributions to the energy surface of the dipeptide were examined and compared with the results from fixed CHARMm charge potential, which is widely used for molecular dynamics studies.

Contributions of molecular size, charge distribution, and specific amino acids to the iron-binding capacity of sea cucumber (Stichopus japonicus) ovum hydrolysates.

PubMed

Sun, Na; Cui, Pengbo; Jin, Ziqi; Wu, Haitao; Wang, Yixing; Lin, Songyi

2017-09-01

This study investigated the contributions of molecular size, charge distribution and specific amino acids to the iron-binding capacity of sea cucumber (Stichopus japonicus) ovum hydrolysates (SCOHs), and further explored their iron-binding sites. It was demonstrated that enzyme type and degree of hydrolysis (DH) significantly influenced the iron-binding capacity of the SCOHs. The SCOHs produced by alcalase at a DH of 25.9% possessed the highest iron-binding capacity at 92.1%. As the hydrolysis time increased, the molecular size of the SCOHs decreased, the negative charges increased, and the hydrophilic amino acids were exposed to the surface, facilitating iron binding. Furthermore, the Fourier transform infrared spectra, combined with amino acid composition analysis, revealed that iron bound to the SCOHs primarily through interactions with carboxyl oxygen of Asp, guanidine nitrogen of Arg or nitrogen atoms in imidazole group of His. The formed SCOHs-iron complexes exhibited a fold and crystal structure with spherical particles. Copyright © 2017 Elsevier Ltd. All rights reserved.

Electronic Structure, Dielectric Response, and Surface Charge Distribution of RGD (1FUV) Peptide

PubMed Central

Adhikari, Puja; Wen, Amy M.; French, Roger H.; Parsegian, V. Adrian; Steinmetz, Nicole F.; Podgornik, Rudolf; Ching, Wai-Yim

2014-01-01

Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor. PMID:25001596

NASA charging analyzer program: A computer tool that can evaluate electrostatic contamination

NASA Technical Reports Server (NTRS)

Stevens, N. J.; Roche, J. C.; Mandell, M. J.

1978-01-01

A computer code, the NASA Charging Analyzer Program (NASCAP), was developed to study the surface charging of bodies subjected to geomagnetic substorm conditions. This program will treat the material properties of a surface in a self-consistent manner and calculate the electric fields in space due to the surface charge. Trajectories of charged particles in this electric field can be computed to determine if these particles enhance surface contamination. A preliminary model of the Spacecraft Charging At The High Altitudes (SCATHA) satellite was developed in the NASCAP code and subjected to a geomagnetic substorm environment to investigate the possibility of electrostatic contamination. The results indicate that differential voltages will exist between the spacecraft ground surfaces and the insulator surfaces. The electric fields from this differential charging can enhance the contamination of spacecraft surfaces.

Circular, confined distribution for charged particle beams

DOEpatents

Garnett, Robert W.; Dobelbower, M. Christian

1995-01-01

A charged particle beam line is formed with magnetic optics that manipulate the charged particle beam to form the beam having a generally rectangular configuration to a circular beam cross-section having a uniform particle distribution at a predetermined location. First magnetic optics form a charged particle beam to a generally uniform particle distribution over a square planar area at a known first location. Second magnetic optics receive the charged particle beam with the generally square configuration and affect the charged particle beam to output the charged particle beam with a phase-space distribution effective to fold corner portions of the beam toward the core region of the beam. The beam forms a circular configuration having a generally uniform spatial particle distribution over a target area at a predetermined second location.

Circular, confined distribution for charged particle beams

DOEpatents

Garnett, R.W.; Dobelbower, M.C.

1995-11-21

A charged particle beam line is formed with magnetic optics that manipulate the charged particle beam to form the beam having a generally rectangular configuration to a circular beam cross-section having a uniform particle distribution at a predetermined location. First magnetic optics form a charged particle beam to a generally uniform particle distribution over a square planar area at a known first location. Second magnetic optics receive the charged particle beam with the generally square configuration and affect the charged particle beam to output the charged particle beam with a phase-space distribution effective to fold corner portions of the beam toward the core region of the beam. The beam forms a circular configuration having a generally uniform spatial particle distribution over a target area at a predetermined second location. 26 figs.

Charge state distribution of 86Kr in hydrogen and helium gas charge strippers at 2.7 MeV /nucleon

NASA Astrophysics Data System (ADS)

Kuboki, H.; Okuno, H.; Hasebe, H.; Fukunishi, N.; Ikezawa, E.; Imao, H.; Kamigaito, O.; Kase, M.

2014-12-01

The charge state distributions of krypton (86Kr) with an energy of 2.7 MeV /nucleon were measured using hydrogen (H2 ) and helium (He) gas charge strippers. A differential pumping system was constructed to confine H2 and He gases to a thickness sufficient for the charge state distributions to attain equilibrium. The mean charge states of 86Kr in H2 and He gases attained equilibrium at 25.1 and 23.2, respectively, whereas the mean charge state in N2 gas at equilibrium was estimated to be less than 20. The charge distributions are successfully reproduced by the cross sections of ionization and electron capture processes optimized by a fitting procedure.

A family of well behaved charge analogues of Durgapal's perfect fluid exact solution in general relativity

NASA Astrophysics Data System (ADS)

Murad, Mohammad Hassan; Fatema, Saba

2013-02-01

This paper presents a new family of interior solutions of Einstein-Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with a particular form of charge distribution. This solution gives us wide range of parameter, K, for which the solution is well behaved hence, suitable for modeling of superdense star. For this solution the gravitational mass of a star is maximized with all degree of suitability by assuming the surface density equal to normal nuclear density, ρ nm=2.5×1017 kg m-3. By this model we obtain the mass of the Crab pulsar, M Crab, 1.36 M ⊙ and radius 13.21 km, constraining the moment of inertia > 1.61×1038 kg m2 for the conservative estimate of Crab nebula mass 2 M ⊙. And M Crab=1.96 M ⊙ with radius R Crab=14.38 km constraining the moment of inertia > 3.04×1038 kg m2 for the newest estimate of Crab nebula mass, 4.6 M ⊙. These results are quite well in agreement with the possible values of mass and radius of Crab pulsar. Besides this, our model yields moments of inertia for PSR J0737-3039A and PSR J0737-3039B, I A =1.4285×1038 kg m2 and I B =1.3647×1038 kg m2 respectively. It has been observed that under well behaved conditions this class of solutions gives us the overall maximum gravitational mass of super dense object, M G(max)=4.7487 M ⊙ with radius R_{M_{max}}=15.24 km, surface redshift 0.9878, charge 7.47×1020 C, and central density 4.31 ρ nm.

Central depression of nuclear charge density distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chu Yanyun; Ren Zhongzhou; Center of Theoretical Nuclear Physics, National Laboratory of Heavy-Ion Accelerator, Lanzhou 730000

The center-depressed nuclear charge distributions are investigated with the parametrized distribution and the relativistic mean-field theory, and their corresponding charge form factors are worked out with the phase shift analysis method. The central depression of nuclear charge distribution of {sup 46}Ar and {sup 44}S is supported by the relativistic mean-field calculation. According to the calculation, the valence protons in {sup 46}Ar and {sup 44}S prefer to occupy the 1d{sub 3/2} state rather than the 2s{sub 1/2} state, which is different from that in the less neutron-rich argon and sulfur isotopes. As a result, the central proton densities of {sup 46}Armore » and {sup 44}S are highly depressed, and so are their central charge densities. The charge form factors of some argon and sulfur isotopes are presented, and the minima of the charge form factors shift upward and inward when the central nuclear charge distributions are more depressed. Besides, the effect of the central depression on the charge form factors is studied with a parametrized distribution, when the root-mean-square charge radii remain constant.« less

Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl3

PubMed Central

Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

2016-01-01

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ≈0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface. PMID:27941761

Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl3.

PubMed

Ziatdinov, M; Banerjee, A; Maksov, A; Berlijn, T; Zhou, W; Cao, H B; Yan, J-Q; Bridges, C A; Mandrus, D G; Nagler, S E; Baddorf, A P; Kalinin, S V

2016-12-12

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl 3 . Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl 3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ≈0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl 3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.

Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl 3

DOE PAGES

Ziatdinov, Maxim A.; Banerjee, Arnab; Maksov, Artem B.; ...

2016-12-12

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, -RuCl3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of -RuCl3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at themore » nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of 0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual -RuCl3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.« less

Scale-invariant puddles in graphene: Geometric properties of electron-hole distribution at the Dirac point.

PubMed

Najafi, M N; Nezhadhaghighi, M Ghasemi

2017-03-01

We characterize the carrier density profile of the ground state of graphene in the presence of particle-particle interaction and random charged impurity in zero gate voltage. We provide detailed analysis on the resulting spatially inhomogeneous electron gas, taking into account the particle-particle interaction and the remote Coulomb disorder on an equal footing within the Thomas-Fermi-Dirac theory. We present some general features of the carrier density probability measure of the graphene sheet. We also show that, when viewed as a random surface, the electron-hole puddles at zero chemical potential show peculiar self-similar statistical properties. Although the disorder potential is chosen to be Gaussian, we show that the charge field is non-Gaussian with unusual Kondev relations, which can be regarded as a new class of two-dimensional random-field surfaces. Using Schramm-Loewner (SLE) evolution, we numerically demonstrate that the ungated graphene has conformal invariance and the random zero-charge density contours are SLE_{κ} with κ=1.8±0.2, consistent with c=-3 conformal field theory.

Influence of Molecular Orientation on Charge-Transfer Processes at Phthalocyanine/Metal Oxide Interfaces and Relationship to Organic Photovoltaic Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Hsiao-Chu; MacDonald, Gordon A.; Shi, Yanrong

2015-05-04

The effect of the molecular orientation distribution of the first monolayer of donor molecules at the hole-harvesting contact in an organic photovoltaic (OPV) on device efficiency was investigated. Two zinc phthalocyanine (ZnPc) phosphonic acids (PA) deposited on indium tin oxide (ITO) electrodes are compared: ZnPc(PA)4 contains PA linkers in all four quadrants, and ZnPcPA contains a PA linker in one quadrant. ZnPcPA monolayers exhibited a broad distribution of molecular orientations whereas ZnPc(PA)4 adsorption produced a monolayer with a narrower orientation distribution with the molecular plane more parallel to the ITO surface. We used potential-modulated attenuated total reflectance spectroelectrochemistry (PM-ATR) tomore » characterize the charge-transfer kinetics of these films and show that the highest rate constants correspond to ZnPc subpopulations that are oriented more parallel to the ITO surface plane. For ZnPc(PA)4, rate constants exceeded 104 s–1 and are among the highest ever reported for a surface-confined redox couple, which is attributable to both its orientation and the small ZnPc–electrode separation distance. The performance of OPVs with ITO hole-harvesting contacts modified with ZnPc(PA)4 was comparable to that achieved with highly activated bare ITO contacts, whereas for ZnPcPA-modified contacts, the OPV performance was similar to that observed with (hole-blocking) alkyl-PA modifiers. These results demonstrate the synergism between molecular structure, energetics, and dynamics at interfaces in OPVs.« less

Differential effects of DEAE negative mode chromatography and gel-filtration chromatography on the charge status of Helicobacter pylori neutrophil-activating protein

PubMed Central

Pan, Timothy; Tzeng, Huey-Fen

2017-01-01

Helicobacter pylori neutrophil-activating protein (HP-NAP) is involved in H. pylori-associated gastric inflammation. HP-NAP is also a vaccine candidate, a possible drug target, and a potential diagnostic marker for H. pylori-associated diseases. Previously, we purified recombinant HP-NAP by one-step diethylaminoethyl (DEAE) negative mode chromatography by collecting the unbound fraction at pH 8.0 at 4°C. It remains unclear why HP-NAP does not bind to DEAE resins at the pH above its isoelectric point during the purification. To investigate how pH affects the surface net charge of HP-NAP and its binding to DEAE resins during the purification, recombinant HP-NAP expressed in Escherichia coli was subjected to DEAE negative mode chromatography at pH ranging from 7.0 to 9.0 at 25°C and the surface charge of purified HP-NAP was determined by capillary electrophoresis. A minimal amount of HP-NAP was detected in the elution fraction of DEAE Sepharose resin at pH 8.5, whereas recombinant HP-NAP was detected in the elution fraction of DEAE Sephadex resin only at pH 7.0 and 8.0. The purified recombinant HP-NAP obtained from the unbound fractions was not able to bind to DEAE resins at pH 7.0 to 9.0. In addition, the surface charge of the purified HP-NAP was neutral at pH 7.0 to 8.0 and was either neutral or slightly negative at pH 8.5 and 9.0. However, recombinant HP-NAP purified from gel-filtration chromatography was able to bind to DEAE Sepharose resin at pH 7.0 to 9.0 and DEAE Sephadex resin at pH 7.0. At pH 8.5 and 9.0, only the negatively charged species of HP-NAP were found. Thus, recombinant HP-NAP with different charge status can be differentially purified by DEAE negative mode chromatography and gel-filtration chromatography. Furthermore, the charge distribution on the surface of HP-NAP, the presence of impure proteins, and the overall net charge of the resins all affect the binding of HP-NAP to DEAE resins during the negative purification. PMID:28328957

Differential effects of DEAE negative mode chromatography and gel-filtration chromatography on the charge status of Helicobacter pylori neutrophil-activating protein.

PubMed

Hong, Zhi-Wei; Yang, Yu-Chi; Pan, Timothy; Tzeng, Huey-Fen; Fu, Hua-Wen

2017-01-01

Helicobacter pylori neutrophil-activating protein (HP-NAP) is involved in H. pylori-associated gastric inflammation. HP-NAP is also a vaccine candidate, a possible drug target, and a potential diagnostic marker for H. pylori-associated diseases. Previously, we purified recombinant HP-NAP by one-step diethylaminoethyl (DEAE) negative mode chromatography by collecting the unbound fraction at pH 8.0 at 4°C. It remains unclear why HP-NAP does not bind to DEAE resins at the pH above its isoelectric point during the purification. To investigate how pH affects the surface net charge of HP-NAP and its binding to DEAE resins during the purification, recombinant HP-NAP expressed in Escherichia coli was subjected to DEAE negative mode chromatography at pH ranging from 7.0 to 9.0 at 25°C and the surface charge of purified HP-NAP was determined by capillary electrophoresis. A minimal amount of HP-NAP was detected in the elution fraction of DEAE Sepharose resin at pH 8.5, whereas recombinant HP-NAP was detected in the elution fraction of DEAE Sephadex resin only at pH 7.0 and 8.0. The purified recombinant HP-NAP obtained from the unbound fractions was not able to bind to DEAE resins at pH 7.0 to 9.0. In addition, the surface charge of the purified HP-NAP was neutral at pH 7.0 to 8.0 and was either neutral or slightly negative at pH 8.5 and 9.0. However, recombinant HP-NAP purified from gel-filtration chromatography was able to bind to DEAE Sepharose resin at pH 7.0 to 9.0 and DEAE Sephadex resin at pH 7.0. At pH 8.5 and 9.0, only the negatively charged species of HP-NAP were found. Thus, recombinant HP-NAP with different charge status can be differentially purified by DEAE negative mode chromatography and gel-filtration chromatography. Furthermore, the charge distribution on the surface of HP-NAP, the presence of impure proteins, and the overall net charge of the resins all affect the binding of HP-NAP to DEAE resins during the negative purification.

Development and characterisation of semi-crystalline composite granules: The effect of particle chemistry and the electrostatic charging

NASA Astrophysics Data System (ADS)

Haque, Syed N.; Hussain, Tariq; Chowdhry, Babur Z.; Douroumis, Dennis; Scoutaris, Nikolaos; Nokhodchi, Ali; Maniruzzaman, Mohammed

2017-12-01

This study investigated the surface of semi-crystalline composite granules produced via a novel mechano-chemical process and assessed the effect of electrostatic charging. Ibuprofen (IBU), a model drug with low solubility and known associated processing challenges was loaded in composite granules to improve its processibility and dissolution rates. Synthetic amorphous mesoporous magnesium alumina metasilicate (MAS) was co-processed with hydrophilic HPMC polymer in the presence of polyethylene glycol 2000 (PEG) and deionised water. The solid state analyses conducted by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) revealed the existence of semi-crystalline IBU in the complex composite structures. Dynamic vapour sorption (DVS) study showed the water sorption and desorption profiles of the manufactured composite granules as well as the effect of water on the solid-state stability of IBU in various formulations. Advanced surface analysis conducted via energy dispersive X-ray (EDS) revealed homogenous distribution of the drug/excipients on the surface of the granules while atomic force microscopy (AFM) complemented the findings. The electrostatic charge analysis showed variable charge property which is affected by the size of the particles/granules. As expected, the in vitro dissolution study showed about 5 fold increase in the release rates of IBU compared to that of the bulk drug. The mechanochemical processing has been demonstrated as an efficient technique to develop semi-crystalline composite granules with enhanced dissolution rates of water insoluble drugs.

Nanopipette delivery: influence of surface charge.

PubMed

Shi, Wenqing; Sa, Niya; Thakar, Rahul; Baker, Lane A

2015-07-21

In this report, transport through a nanopipette is studied and the interplay between current rectification and ion delivery for small pipettes is examined. First, surface charge dependence of concentration polarization effects in a quartz nanopipette was investigated. Electrical characterization was performed through current-potential (I-V) measurements. In addition, fluorescein (an anionic fluorescent probe) was utilized to optically map ion enrichment and ion depletion in the nanopipette tip. Bare nanopipettes and polyethylenimine (PEI)-modified nanopipettes were examined. Results confirm that concentration polarization is a surface charge dependent phenomenon and delivery can be controlled through modification of surface charge. The relationship between concentration polarization effects and voltage-driven delivery of charged electroactive species was investigated with a carbon ring/nanopore electrode fabricated from pyrolyzed parylene C (PPC). Factors such as surface charge polarity of the nanopipette, electrolyte pH, and electrolyte concentration were investigated. Results indicate that with modification of surface charge, additional control over delivery of charged species can be achieved.

The electronic and optical properties of Cs adsorbed GaAs nanowires via first-principles study

NASA Astrophysics Data System (ADS)

Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu; Lu, Feifei

2018-07-01

In this study, we investigate the Cs adsorption mechanism on (110) surface of zinc-blende GaAs nanowire. The adsorption energy, work function, dipole moment, geometric structure, Mulliken charge distribution, charge transfer index, band structures, density of state and optical properties of Cs adsorption structures are calculated utilizing first-principles method based on density function theory. Total-energy calculations show that all the adsorption energies are negative, indicating that Cs adsorption process is exothermic and Cs covered GaAs nanowires are stable. The work function of nanowire surface has an obvious decrease after Cs adsorption. Besides, the ionization of nanowire surface is enhanced as well. More importantly, Cs adsorption contributes to a lower side shift of bands near Fermi level, and the corresponding band gap disappears. Additionally, the absorption peak and energy loss function after Cs adsorption are far higher than those before adsorption, implying better light absorption characteristic of nanowire surface after Cs adsorption. These theoretical calculations can directly guide the Cs activation experiment for negative electron affinity GaAs nanowire, and also lay a foundation for the further study of Cs/O co-adsorption on the nanowire surface.

Balancing charge in the complementarity-determining regions of humanized mAbs without affecting pI reduces non-specific binding and improves the pharmacokinetics.

PubMed

Datta-Mannan, Amita; Thangaraju, Arunkumar; Leung, Donmienne; Tang, Ying; Witcher, Derrick R; Lu, Jirong; Wroblewski, Victor J

2015-01-01

Lowering the isoelectric point (pI) through engineering the variable region or framework of an IgG can improve its exposure and half-life via a reduction in clearance mediated through non-specific interactions. As such, net charge is a potentially important property to consider in developing therapeutic IgG molecules having favorable pharmaceutical characteristics. Frequently, it may not be possible to shift the pI of monoclonal antibodies (mAbs) dramatically without the introduction of other liabilities such as increased off-target interactions or reduced on-target binding properties. In this report, we explored the influence of more subtle modifications of molecular charge on the in vivo properties of an IgG1 and IgG4 monoclonal antibody. Molecular surface modeling was used to direct residue substitutions in the complementarity-determining regions (CDRs) to disrupt positive charge patch regions, resulting in a reduction in net positive charge without affecting the overall pI of the mAbs. The effect of balancing the net positive charge on non-specific binding was more significant for the IgG4 versus the IgG1 molecule that we examined. This differential effect was connected to the degree of influence on cellular degradation in vitro and in vivo clearance, distribution and metabolism in mice. In the more extreme case of the IgG4, balancing the charge yielded an ∼7-fold improvement in peripheral exposure, as well as significantly reduced tissue catabolism and subsequent excretion of proteolyzed products in urine. Balancing charge on the IgG1 molecule had a more subtle influence on non-specific binding and yielded only a modest alteration in clearance, distribution and elimination. These results suggest that balancing CDR charge without affecting the pI can lead to improved mAb pharmacokinetics, the magnitude of which is likely dependent on the relative influence of charge imbalance and other factors affecting the molecule's disposition.

Balancing charge in the complementarity-determining regions of humanized mAbs without affecting pI reduces non-specific binding and improves the pharmacokinetics

PubMed Central

Datta-Mannan, Amita; Thangaraju, Arunkumar; Leung, Donmienne; Tang, Ying; Witcher, Derrick R; Lu, Jirong; Wroblewski, Victor J

2015-01-01

Lowering the isoelectric point (pI) through engineering the variable region or framework of an IgG can improve its exposure and half-life via a reduction in clearance mediated through non-specific interactions. As such, net charge is a potentially important property to consider in developing therapeutic IgG molecules having favorable pharmaceutical characteristics. Frequently, it may not be possible to shift the pI of monoclonal antibodies (mAbs) dramatically without the introduction of other liabilities such as increased off-target interactions or reduced on-target binding properties. In this report, we explored the influence of more subtle modifications of molecular charge on the in vivo properties of an IgG1 and IgG4 monoclonal antibody. Molecular surface modeling was used to direct residue substitutions in the complementarity-determining regions (CDRs) to disrupt positive charge patch regions, resulting in a reduction in net positive charge without affecting the overall pI of the mAbs. The effect of balancing the net positive charge on non-specific binding was more significant for the IgG4 versus the IgG1 molecule that we examined. This differential effect was connected to the degree of influence on cellular degradation in vitro and in vivo clearance, distribution and metabolism in mice. In the more extreme case of the IgG4, balancing the charge yielded an ∼7-fold improvement in peripheral exposure, as well as significantly reduced tissue catabolism and subsequent excretion of proteolyzed products in urine. Balancing charge on the IgG1 molecule had a more subtle influence on non-specific binding and yielded only a modest alteration in clearance, distribution and elimination. These results suggest that balancing CDR charge without affecting the pI can lead to improved mAb pharmacokinetics, the magnitude of which is likely dependent on the relative influence of charge imbalance and other factors affecting the molecule's disposition. PMID:25695748

Airblast Simulator Studies.

DTIC Science & Technology

1984-02-01

RAREFACTION WAVE ELIMINATOR CONSIDERATIONS 110 5.1 FLIP CALCULATIONS 110 5.2 A PASSIVE/ACTIVE RWE 118 6 DISTRIBUTED FUEL AIR EXPLOSIVES 120 REFERENCES 123 TA...conventional and distributed-charge fuel- air explosive charges used in a study of the utility of distributed charge FAE systems for blast simulation. The...limited investigation of distributed charge fuel air explosive configurations for blast simulator applications. During the course of this study

Network based management for multiplexed electric vehicle charging

DOEpatents

Gadh, Rajit; Chung, Ching Yen; Qui, Li

2017-04-11

A system for multiplexing charging of electric vehicles, comprising a server coupled to a plurality of charging control modules over a network. Each of said charging modules being connected to a voltage source such that each charging control module is configured to regulate distribution of voltage from the voltage source to an electric vehicle coupled to the charging control module. Data collection and control software is provided on the server for identifying a plurality of electric vehicles coupled to the plurality of charging control modules and selectively distributing charging of the plurality of charging control modules to multiplex distribution of voltage to the plurality of electric vehicles.

Ion distributions, exclusion coefficients, and separation factors of electrolytes in a charged cylindrical nanopore: a partially perturbative density functional theory study.

PubMed

Peng, Bo; Yu, Yang-Xin

2009-10-07

The structural and thermodynamic properties for charge symmetric and asymmetric electrolytes as well as mixed electrolyte system inside a charged cylindrical nanopore are investigated using a partially perturbative density functional theory. The electrolytes are treated in the restricted primitive model and the internal surface of the cylindrical nanopore is considered to have a uniform charge density. The proposed theory is directly applicable to the arbitrary mixed electrolyte solution containing ions with the equal diameter and different valences. Large amount of simulation data for ion density distributions, separation factors, and exclusion coefficients are used to determine the range of validity of the partially perturbative density functional theory for monovalent and multivalent counterion systems. The proposed theory is found to be in good agreement with the simulations for both mono- and multivalent counterion systems. In contrast, the classical Poisson-Boltzmann equation only provides reasonable descriptions of monovalent counterion system at low bulk density, and is qualitatively and quantitatively wrong in the prediction for the multivalent counterion systems due to its neglect of the strong interionic correlations in these systems. The proposed density functional theory has also been applied to an electrolyte absorbed into a pore that is a model of the filter of a physiological calcium channel.

Point Charges Optimally Placed to Represent the Multipole Expansion of Charge Distributions

PubMed Central

Onufriev, Alexey V.

2013-01-01

We propose an approach for approximating electrostatic charge distributions with a small number of point charges to optimally represent the original charge distribution. By construction, the proposed optimal point charge approximation (OPCA) retains many of the useful properties of point multipole expansion, including the same far-field asymptotic behavior of the approximate potential. A general framework for numerically computing OPCA, for any given number of approximating charges, is described. We then derive a 2-charge practical point charge approximation, PPCA, which approximates the 2-charge OPCA via closed form analytical expressions, and test the PPCA on a set of charge distributions relevant to biomolecular modeling. We measure the accuracy of the new approximations as the RMS error in the electrostatic potential relative to that produced by the original charge distribution, at a distance the extent of the charge distribution–the mid-field. The error for the 2-charge PPCA is found to be on average 23% smaller than that of optimally placed point dipole approximation, and comparable to that of the point quadrupole approximation. The standard deviation in RMS error for the 2-charge PPCA is 53% lower than that of the optimal point dipole approximation, and comparable to that of the point quadrupole approximation. We also calculate the 3-charge OPCA for representing the gas phase quantum mechanical charge distribution of a water molecule. The electrostatic potential calculated by the 3-charge OPCA for water, in the mid-field (2.8 Å from the oxygen atom), is on average 33.3% more accurate than the potential due to the point multipole expansion up to the octupole order. Compared to a 3 point charge approximation in which the charges are placed on the atom centers, the 3-charge OPCA is seven times more accurate, by RMS error. The maximum error at the oxygen-Na distance (2.23 Å ) is half that of the point multipole expansion up to the octupole order. PMID:23861790

Poisson-Boltzmann theory of the charge-induced adsorption of semi-flexible polyelectrolytes.

PubMed

Ubbink, Job; Khokhlov, Alexei R

2004-03-15

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson-Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Angstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson-Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)]. (c) 2004 American Institute of Physics.

Electron capture into large-l Rydberg states of multiply charged ions escaping from solid surfaces

NASA Astrophysics Data System (ADS)

Nedeljković, N.; Nedeljković, Lj.; Mirković, M.

2003-07-01

We have investigated the electron capture into large-l Rydberg states of multiply charged ionic projectiles (e.g., the core charges Z=6, 7, and 8) escaping solid surfaces with intermediate velocities (v≈1 a.u.) in the normal emergence geometry. A model of the nonresonant electron capture from the solid conduction band into the moving large angular-momentum Rydberg states of the ions is developed through a generalization of our results obtained previously for the low-l cases (l=0, 1, and 2). The model is based on the two-wave-function dynamics of the Demkov-Ostrovskii type. The electron exchange process is described by a mixed flux through a moving plane (“Firsov plane”), placed between the solid surface and the ionic projectile. Due to low eccentricities of the large-l Rydberg systems, the mixed flux must be evaluated through the whole Firsov plane. It is for this purpose that a suitable asymptotic method is developed. For intermediate ionic velocities and for all relevant values of the principal quantum number n≈Z, the population probability Pnl is obtained as a nonlinear l distribution. The theoretical predictions concerning the ions S VI, Cl VII, and Ar VIII are compared with the available results of the beam-foil experiments.

Evidences of Changes in Surface Electrostatic Charge Distribution during Stabilization of HPV16 Virus-Like Particles

PubMed Central

Vega, Juan F.; Vicente-Alique, Ernesto; Núñez-Ramírez, Rafael; Wang, Yang; Martínez-Salazar, Javier

2016-01-01

The stabilization of human papillomavirus type 16 virus-like particles has been examined by means of different techniques including dynamic and static light scattering, transmission electron microscopy and electrophoretic mobility. All these techniques provide different and often complementary perspectives about the aggregation process and generation of stabilized virus-like particles after a period of time of 48 hours at a temperature of 298 K. Interestingly, static light scattering results point towards a clear colloidal instability in the initial systems, as suggested by a negative value of the second virial coefficient. This is likely related to small repulsive electrostatic interactions among the particles, and in agreement with relatively small absolute values of the electrophoretic mobility and, hence, of the net surface charges. At this initial stage the small repulsive interactions are not able to compensate binding interactions, which tend to aggregate the particles. As time proceeds, an increase of the size of the particles is accompanied by strong increases, in absolute values, of the electrophoretic mobility and net surface charge, suggesting enhanced repulsive electrostatic interactions and, consequently, a stabilized colloidal system. These results show that electrophoretic mobility is a useful methodology that can be applied to screen the stabilization factors for virus-like particles during vaccine development. PMID:26885635

Radiation measurement above the lunar surface by Kaguya gamma-ray spectrometer

NASA Astrophysics Data System (ADS)

Hasebe, Nobuyuki; Nagaoka, Hiroshi; Kusano, Hiroki; Hareyama, Matoko; Ideguchi, Yusuke; Shimizu, Sota; Shibamura, Eido

The lunar surface is filled with various ionizing radiations such as high energy galactic particles, albedo particles and secondary radiations of neutrons, gamma rays and other elementary particles. A high-resolution Kaguya Gamma-Ray Spectrometer (KGRS) was carried on the Japan’s lunar explorer SELENE (Kaguya), the largest lunar orbiter since the Apollo missions. The KGRS instrument employed, for the first time in lunar exploration, a high-purity Ge crystal to increase the identification capability of elemental gamma-ray lines. The Ge detector is surrounded by BGO and plastic counters as for anticoincidence shields. The KGRS measured gamma rays in the energy range from 200 keV to 13 MeV with high precision to determine the chemical composition of the lunar surface. It provided data on the abundance of major elements over the entire lunar surface. In addition to the gamma-ray observation by the KGRS, it successfully measured the global distribution of fast neutrons. In the energy spectra of gamma-rays observed by the KGRS, several saw-tooth- peaks of Ge are included, which are formed by the collision interaction of lunar fast neutrons with Ge atoms in the Ge crystal. With these saw-tooth-peaks analysis, global distribution of neutrons emitted from the lunara surface was successfully created, which was compared with the previous results obtained by Lunar Prospector neutron maps. Another anticoincidence counter, the plastic counter with 5 mm thickness, was used to veto radiation events mostly generated by charged particles. A single photomultiplier serves to count scintillation light from the plastic scintillation counter. The global map of counting rates observed by the plastic counter was also created, implying that the radiation counting rate implies the geological distribution, in spite that the plastic counter mostly measures high energy charged particles and energetic neutrons. These results are presented and discussed.

Structure and capacitance of an electric double layer of an asymmetric valency dimer electrolyte: A comparison of the density functional theory with Monte Carlo simulations

DOE PAGES

Henderson, Douglas; Silvestre-Alcantara, Whasington; Kaja, Monika; ...

2016-08-18

Here, the density functional theory is applied to a study of the structure and differential capacitance of a planar electric double layer formed by a valency asymmetric mixture of charged dimers and monomers. The dimer consists of two tangentially tethered hard spheres of equal diameters of which one is charged and the other is neutral, while the monomer is a charged hard sphere of the same size. The dimer electrolyte is next to a uniformly charged, smooth planar electrode. The electrode-particle singlet distributions, the mean electrostatic potential, and the differential capacitance for the model double layer are evaluated for amore » 2:1/1:2 valency electrolyte at a given concentration. Important consequences of asymmetry in charges and in ion shapes are (i) a finite, non-zero potential of zero charge, and (ii) asymmetric shaped 2:1 and 1:2 capacitance curves which are not mirror images of each other. Comparisons of the density functional results with the corresponding Monte Carlo simulations show the theoretical predictions to be in good agreement with the simulations overall except near zero surface charge.« less

Distributed charging of electrical assets

DOEpatents

Ghosh, Soumyadip; Phan, Dung; Sharma, Mayank; Wu, Chai Wah; Xiong, Jinjun

2016-02-16

The present disclosure relates generally to the field of distributed charging of electrical assets. In various examples, distributed charging of electrical assets may be implemented in the form of systems, methods and/or algorithms.

Modeling of Optical Waveguide Poling and Thermally Stimulated Discharge (TSD) Charge and Current Densities for Guest/Host Electro Optic Polymers

NASA Technical Reports Server (NTRS)

Watson, Michael D.; Ashley, Paul R.; Abushagur, Mustafa

2004-01-01

A charge density and current density model of a waveguide system has been developed to explore the effects of electric field electrode poling. An optical waveguide may be modeled during poling by considering the dielectric charge distribution, polarization charge distribution, and conduction charge generated by the poling field. These charge distributions are the source of poling current densities. The model shows that boundary charge current density and polarization current density are the major source of currents measured during poling and thermally stimulated discharge These charge distributions provide insight into the poling mechanisms and are directly related to E(sub A), and, alpha(sub r). Initial comparisons with experimental data show excellent correlation to the model results.

Lunar Surface Charging during Solar Energetic Particle Events

NASA Astrophysics Data System (ADS)

Halekas, Jasper S.; Delory, G. T.; Mewaldt, R. A.; Lin, R. P.; Fillingim, M. O.; Brain, D. A.; Lee, C. O.; Stubbs, T. J.; Farrell, W. M.; Hudson, M. K.

2006-09-01

The surface of the Moon, not protected by any substantial atmosphere, is directly exposed to the impact of both solar UV and solar wind plasma and energetic particles. This creates a complex lunar electrostatic environment, with the surface typically charging slightly positive in sunlight, and negative in shadow. Observations from the Apollo era and theoretical considerations strongly suggest that surface charging leads to dust electrification and transport, posing a potentially significant hazard for exploration. The most significant charging effects should occur when the Moon is exposed to high-temperature plasmas like those encountered in the terrestrial plasmasheet or in solar storms. We now present evidence for kilovolt-scale negative charging of the shadowed lunar surface during solar energetic particle (SEP) events, utilizing data from the Lunar Prospector Electron Reflectometer (LP ER). We find that SEP events are associated with the most extreme lunar surface charging observed during the LP mission - rivaled only by previously reported charging during traversals of the terrestrial plasmasheet. The largest charging event observed by LP is a 4 kV negative surface potential (as compared to typical values of V) during a SEP event in May 1998. We characterize lunar surface charging during several SEP events, and compare to energetic particle measurements from ACE, Wind, and SOHO in order to determine the relationship between SEP events and extreme lunar surface charging. Space weather events are already considered by NASA to be a significant hazard to lunar exploration, due to high-energy ionizing radiation. Our observations demonstrate that plasma interactions with the lunar surface during SEP events, causing extreme surface charging and potentially significant dust electrification and transport, represent an additional hazard associated with space weather.

Structure–activity relationships for biodistribution, pharmacokinetics, and excretion of atomically precise nanoclusters in a murine model†

PubMed Central

Wong, O. Andrea; Hansen, Ryan J.; Ni, Thomas W.; Heinecke, Christine L.; Compel, W. Scott; Gustafson, Daniel L.

2013-01-01

The absorption, distribution, metabolism and excretion (ADME) and pharmacokinetic (PK) properties of inorganic nanoparticles with hydrodynamic diameters between 2 and 20 nm are presently unpredictable. It is unclear whether unpredictable in vivo properties and effects arise from a subset of molecules in a nanomaterials preparation, or if the ADME/PK properties are ensemble properties of an entire preparation. Here we characterize the ADME/PK properties of atomically precise preparations of ligand protected gold nanoclusters in a murine model system. We constructed atomistic models and tested in vivo properties for five well defined compounds, based on crystallographically resolved Au25(SR)18 and Au102(SR)44 nanoclusters with different (SR) ligand shells. To rationalize unexpected distribution and excretion properties observed for several clusters in this study and others, we defined a set of atomistic structure–activity relationships (SAR) for nanoparticles, which includes previously investigated parameters such as particle hydrodynamic diameter and net charge, and new parameters such as hydrophobic surface area and surface charge density. Overall we find that small changes in particle formulation can provoke dramatic yet potentially predictable changes in ADME/PK. PMID:24057086

Atomistic and molecular effects in electric double layers at high surface charges

DOE PAGES

Templeton, Jeremy Alan; Lee, Jonathan; Mani, Ali

2015-06-16

Here, the Poisson–Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. In order to investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson–Boltzmann theories can model this limit if they are augmented with atomic packing densities providedmore » by MD. However, when the solvent is a highly polar molecule water an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential’s quadratic surface charge dependence is not obtained.« less

Surface charge mapping with a nanopipette.

PubMed

McKelvey, Kim; Kinnear, Sophie L; Perry, David; Momotenko, Dmitry; Unwin, Patrick R

2014-10-01

Nanopipettes are emerging as simple but powerful tools for probing chemistry at the nanoscale. In this contribution the use of nanopipettes for simultaneous surface charge mapping and topographical imaging is demonstrated, using a scanning ion conductance microscopy (SICM) format. When a nanopipette is positioned close to a surface in electrolyte solution, the direct ion current (DC), driven by an applied bias between a quasi-reference counter electrode (QRCE) in the nanopipette and a second QRCE in the bulk solution, is sensitive to surface charge. The charge sensitivity arises because the diffuse double layers at the nanopipette and the surface interact, creating a perm-selective region which becomes increasingly significant at low ionic strengths (10 mM 1:1 aqueous electrolyte herein). This leads to a polarity-dependent ion current and surface-induced rectification as the bias is varied. Using distance-modulated SICM, which induces an alternating ion current component (AC) by periodically modulating the distance between the nanopipette and the surface, the effect of surface charge on the DC and AC is explored and rationalized. The impact of surface charge on the AC phase (with respect to the driving sinusoidal signal) is highlighted in particular; this quantity shows a shift that is highly sensitive to interfacial charge and provides the basis for visualizing charge simultaneously with topography. The studies herein highlight the use of nanopipettes for functional imaging with applications from cell biology to materials characterization where understanding surface charge is of key importance. They also provide a framework for the design of SICM experiments, which may be convoluted by topographical and surface charge effects, especially for small nanopipettes.

Surface speciation of yttrium and neodymium sorbed on rutile: Interpretations using the charge distribution model

NASA Astrophysics Data System (ADS)

Ridley, Moira K.; Hiemstra, Tjisse; Machesky, Michael L.; Wesolowski, David J.; van Riemsdijk, Willem H.

2012-10-01

The adsorption of Y3+ and Nd3+ onto rutile has been evaluated over a wide range of pH (3-11) and surface loading conditions, as well as at two ionic strengths (0.03 and 0.3 m), and temperatures (25 and 50 °C). The experimental results reveal the same adsorption behavior for the two trivalent ions onto the rutile surface, with Nd3+ first adsorbing at slightly lower pH values. The adsorption of both Y3+ and Nd3+ commences at pH values below the pHznpc of rutile. The experimental results were evaluated using a charge distribution (CD) and multisite complexation (MUSIC) model, and Basic Stern layer description of the electric double layer (EDL). The coordination geometry of possible surface complexes were constrained by molecular-level information obtained from X-ray standing wave measurements and molecular dynamic (MD) simulation studies. X-ray standing wave measurements showed an inner-sphere tetradentate complex for Y3+ adsorption onto the (1 1 0) rutile surface (Zhang et al., 2004b). The MD simulation studies suggest additional bidentate complexes may form. The CD values for all surface species were calculated based on a bond valence interpretation of the surface complexes identified by X-ray and MD. The calculated CD values were corrected for the effect of dipole orientation of interfacial water. At low pH, the tetradentate complex provided excellent fits to the Y3+ and Nd3+ experimental data. The experimental and surface complexation modeling results show a strong pH dependence, and suggest that the tetradentate surface species hydrolyze with increasing pH. Furthermore, with increased surface loading of Y3+ on rutile the tetradentate binding mode was augmented by a hydrolyzed-bidentate Y3+ surface complex. Collectively, the experimental and surface complexation modeling results demonstrate that solution chemistry and surface loading impacts Y3+ surface speciation. The approach taken of incorporating molecular-scale information into surface complexation models (SCMs) should aid in elucidating a fundamental understating of ion-adsorption reactions.

Protein corona affects the relaxivity and MRI contrast efficiency of magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Amiri, Houshang; Bordonali, Lorenzo; Lascialfari, Alessandro; Wan, Sha; Monopoli, Marco P.; Lynch, Iseult; Laurent, Sophie; Mahmoudi, Morteza

2013-08-01

Magnetic nanoparticles (NPs) are increasingly being considered for use in biomedical applications such as biosensors, imaging contrast agents and drug delivery vehicles. In a biological fluid, proteins associate in a preferential manner with NPs. The small sizes and high curvature angles of NPs influence the types and amounts of proteins present on their surfaces. This differential display of proteins bound to the surface of NPs can influence the tissue distribution, cellular uptake and biological effects of NPs. To date, the effects of adsorption of a protein corona (PC) on the magnetic properties of NPs have not been considered, despite the fact that some of their potential applications require their use in human blood. Here, to investigate the effects of a PC (using fetal bovine serum) on the MRI contrast efficiency of superparamagnetic iron oxide NPs (SPIONs), we have synthesized two series of SPIONs with variation in the thickness and functional groups (i.e. surface charges) of the dextran surface coating. We have observed that different physico-chemical characteristics of the dextran coatings on the SPIONs lead to the formation of PCs of different compositions. 1H relaxometry was used to obtain the longitudinal, r1, and transverse, r2, relaxivities of the SPIONs without and with a PC, as a function of the Larmor frequency. The transverse relaxivity, which determines the efficiency of negative contrast agents (CAs), is very much dependent on the functional group and the surface charge of the SPIONs' coating. The presence of the PC did not alter the relaxivity of plain SPIONs, while it slightly increased the relaxivity of the negatively charged SPIONs and dramatically decreased the relaxivity of the positively charged ones, which was coupled with particle agglomeration in the presence of the proteins. To confirm the effect of the PC on the MRI contrast efficiency, in vitro MRI experiments at ν = 8.5 MHz were performed using a low-field MRI scanner. The MRI contrasts, produced by different samples, were fully in agreement with the relaxometry findings.Magnetic nanoparticles (NPs) are increasingly being considered for use in biomedical applications such as biosensors, imaging contrast agents and drug delivery vehicles. In a biological fluid, proteins associate in a preferential manner with NPs. The small sizes and high curvature angles of NPs influence the types and amounts of proteins present on their surfaces. This differential display of proteins bound to the surface of NPs can influence the tissue distribution, cellular uptake and biological effects of NPs. To date, the effects of adsorption of a protein corona (PC) on the magnetic properties of NPs have not been considered, despite the fact that some of their potential applications require their use in human blood. Here, to investigate the effects of a PC (using fetal bovine serum) on the MRI contrast efficiency of superparamagnetic iron oxide NPs (SPIONs), we have synthesized two series of SPIONs with variation in the thickness and functional groups (i.e. surface charges) of the dextran surface coating. We have observed that different physico-chemical characteristics of the dextran coatings on the SPIONs lead to the formation of PCs of different compositions. 1H relaxometry was used to obtain the longitudinal, r1, and transverse, r2, relaxivities of the SPIONs without and with a PC, as a function of the Larmor frequency. The transverse relaxivity, which determines the efficiency of negative contrast agents (CAs), is very much dependent on the functional group and the surface charge of the SPIONs' coating. The presence of the PC did not alter the relaxivity of plain SPIONs, while it slightly increased the relaxivity of the negatively charged SPIONs and dramatically decreased the relaxivity of the positively charged ones, which was coupled with particle agglomeration in the presence of the proteins. To confirm the effect of the PC on the MRI contrast efficiency, in vitro MRI experiments at ν = 8.5 MHz were performed using a low-field MRI scanner. The MRI contrasts, produced by different samples, were fully in agreement with the relaxometry findings. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00345k

Recombination-enhanced surface expansion of clusters in intense soft x-ray laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rupp, Daniela; Flückiger, Leonie; Adolph, Marcus

Here, we studied the nanoplasma formation and explosion dynamics of single large xenon clusters in ultrashort, intense x-ray free-electron laser pulses via ion spectroscopy. The simultaneous measurement of single-shot diffraction images enabled a single-cluster analysis that is free from any averaging over the cluster size and laser intensity distributions. The measured charge state-resolved ion energy spectra show narrow distributions with peak positions that scale linearly with final ion charge state. These two distinct signatures are attributed to highly efficient recombination that eventually leads to the dominant formation of neutral atoms in the cluster. The measured mean ion energies exceed themore » value expected without recombination by more than an order of magnitude, indicating that the energy release resulting from electron-ion recombination constitutes a previously unnoticed nanoplasma heating process. This conclusion is supported by results from semiclassical molecular dynamics simulations.« less

Vibrational studies of Thyroxine hormone: Comparative study with quantum chemical calculations

NASA Astrophysics Data System (ADS)

Borah, Mukunda Madhab; Devi, Th. Gomti

2017-11-01

The FTIR and Raman techniques have been used to record spectra of Thyroxine. The stable geometrical parameters and vibrational wave numbers were calculated based on potential energy distribution (PED) using vibrational energy distribution analysis (VEDA) program. The vibrational energies are assigned to monomer, chain dimer and cyclic dimers of this molecule using the basis set B3LYP/LANL2DZ. The computational scaled frequencies are in good agreements with the experimental results. The study is extended to calculate the HOMO-LUMO energy gap, Molecular Electrostatic Potential (MEP) surface, hardness (η), chemical potential (μ), Global electrophilicity index (ω) and different thermo dynamical properties of Thyroxine in different states. The calculated HOMO-LUMO energies show the charge transfer occurs within the molecule. The calculated Natural bond orbital (NBO) analysis confirms the presence of intra-molecular charge transfer as well as the hydrogen bonding interaction.

Recombination-enhanced surface expansion of clusters in intense soft x-ray laser pulses

DOE PAGES

Rupp, Daniela; Flückiger, Leonie; Adolph, Marcus; ...

2016-10-07

Here, we studied the nanoplasma formation and explosion dynamics of single large xenon clusters in ultrashort, intense x-ray free-electron laser pulses via ion spectroscopy. The simultaneous measurement of single-shot diffraction images enabled a single-cluster analysis that is free from any averaging over the cluster size and laser intensity distributions. The measured charge state-resolved ion energy spectra show narrow distributions with peak positions that scale linearly with final ion charge state. These two distinct signatures are attributed to highly efficient recombination that eventually leads to the dominant formation of neutral atoms in the cluster. The measured mean ion energies exceed themore » value expected without recombination by more than an order of magnitude, indicating that the energy release resulting from electron-ion recombination constitutes a previously unnoticed nanoplasma heating process. This conclusion is supported by results from semiclassical molecular dynamics simulations.« less

DNA mimic proteins: functions, structures, and bioinformatic analysis.

PubMed

Wang, Hao-Ching; Ho, Chun-Han; Hsu, Kai-Cheng; Yang, Jinn-Moon; Wang, Andrew H-J

2014-05-13

DNA mimic proteins have DNA-like negative surface charge distributions, and they function by occupying the DNA binding sites of DNA binding proteins to prevent these sites from being accessed by DNA. DNA mimic proteins control the activities of a variety of DNA binding proteins and are involved in a wide range of cellular mechanisms such as chromatin assembly, DNA repair, transcription regulation, and gene recombination. However, the sequences and structures of DNA mimic proteins are diverse, making them difficult to predict by bioinformatic search. To date, only a few DNA mimic proteins have been reported. These DNA mimics were not found by searching for functional motifs in their sequences but were revealed only by structural analysis of their charge distribution. This review highlights the biological roles and structures of 16 reported DNA mimic proteins. We also discuss approaches that might be used to discover new DNA mimic proteins.

High resolution printing of charge

DOEpatents

Rogers, John; Park, Jang-Ung

2015-06-16

Provided are methods of printing a pattern of charge on a substrate surface, such as by electrohydrodynamic (e-jet) printing. The methods relate to providing a nozzle containing a printable fluid, providing a substrate having a substrate surface and generating from the nozzle an ejected printable fluid containing net charge. The ejected printable fluid containing net charge is directed to the substrate surface, wherein the net charge does not substantially degrade and the net charge retained on the substrate surface. Also provided are functional devices made by any of the disclosed methods.

Particle size, charge and colloidal stability of humic acids coprecipitated with Ferrihydrite.

PubMed

Angelico, Ruggero; Ceglie, Andrea; He, Ji-Zheng; Liu, Yu-Rong; Palumbo, Giuseppe; Colombo, Claudio

2014-03-01

Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and other environmental conditions. Accordingly, with the present study we intend to assess the colloidal properties of Fe(II) coprecipitated with humic acids (HA) and their effect on Fe hydroxide crystallinity under abiotic oxidation and order of addition of both Fe(II) and HA. TEM, XRD and DRS experiments showed that Fe-HA consisted of Ferrihydrite with important structural variations. DLS data of Fe-HA at acidic pH showed a bimodal size distribution, while at very low pH a slow aggregation process was observed. Electrophoretic zeta-potential measurements revealed a negative surface charge for Fe-HA macromolecules, providing a strong electrostatic barrier against aggregation. Under alkaline conditions HA chains swelled, which resulted in an enhanced stabilization of the colloid particles. The increasing of zeta potential and size of the Fe-HA macromolecules, reflects a linear dependence of both with pH. The increase in the size and negative charge of the Fe-HA precipitate seems to be more affected by the ionization of the phenolic acid groups, than by the carboxylic acid groups. The main cause of negative charge generation of Fe/HA is due to increased dissociation of phenolic groups in more expanded structure. The increased net negative surface potential induced by coprecipitation with Ferrihydrite and the correspondent changes in configuration of the HA could trigger the inter-particle aggregation with the formation of new negative surface. The Fe-HA coprecipitation can reduce electrosteric repulsive forces, which in turn may inhibit the aggregation process at different pH. Therefore, coprecipitation of Ferrihydrite would be expected to play an important role in the carbon stabilization and persistence not only in organic soils, but also in waters containing dissolved organic matter. Copyright © 2013 Elsevier Ltd. All rights reserved.

Mapping disease-related missense mutations in the immunoglobulin-like fold domain of lamin A/C reveals novel genotype-phenotype associations for laminopathies.

PubMed

Scharner, Juergen; Lu, Hui-Chun; Fraternali, Franca; Ellis, Juliet A; Zammit, Peter S

2014-06-01

Mutations in A-type nuclear lamins cause laminopathies. However, genotype-phenotype correlations using the 340 missense mutations within the LMNA gene are unclear: partially due to the limited availability of three-dimensional structure. The immunoglobulin (Ig)-like fold domain has been solved, and using bioinformatics tools (including Polyphen-2, Fold X, Parameter OPtimized Surfaces, and PocketPicker) we characterized 56 missense mutations for position, surface exposure, change in charge and effect on Ig-like fold stability. We find that 21 of the 27 mutations associated with a skeletal muscle phenotype are distributed throughout the Ig-like fold, are nonsurface exposed and predicted to disrupt overall stability of the Ig-like fold domain. Intriguingly, the remaining 6 mutations clustered, had higher surface exposure, and did not affect stability. The majority of 9 lipodystrophy or 10 premature aging syndrome mutations also did not disrupt Ig-like fold domain stability and were surface exposed and clustered in distinct regions that overlap predicted binding pockets. Although buried, the 10 cardiac mutations had no other consistent properties. Finally, most lipodystrophy and premature aging mutations resulted in a -1 net charge change, whereas skeletal muscle mutations caused no consistent net charge changes. Since premature aging, lipodystrophy and the subset of 6 skeletal muscle mutations cluster tightly in distinct, charged regions, they likely affect lamin A/C -protein/DNA/RNA interactions: providing a consistent genotype-phenotype relationship for mutations in this domain. Thus, this subgroup of skeletal muscle laminopathies that we term the 'Skeletal muscle cluster', may have a distinct pathological mechanism. These novel associations refine the ability to predict clinical features caused by certain LMNA missense mutations. © 2013 Wiley Periodicals, Inc.

Cytochemical analysis of alkaline phosphatase and esterase activities and of lectin-binding and anionic sites in rat and mouse Peyer's patch M cells.

PubMed

Owen, R L; Bhalla, D K

1983-10-01

M cells in Peyer's patch follicle epithelium endocytose and transport luminal materials to intraepithelial lymphocytes. We examined (1) enzymatic characteristics of the epithelium covering mouse and rat Peyer's patches by using cytochemical techniques, (2) distribution of lectin-binding sites by peroxidase-labeled lectins, and (3) anionic site distribution by using cationized ferritin to develop a profile of M cell surface properties. Alkaline phosphatase activity resulted in deposits of dense reaction product over follicle surfaces but was markedly reduced over M cells, unlike esterase which formed equivalent or greater product over M cells. Concanavalin A, ricinus communis agglutinin, wheat germ agglutinin and peanut agglutinin reacted equally with M cells and with surrounding enterocytes over follicle surfaces. Cationized ferritin distributed in a random fashion along microvillus membranes of both M cells and enterocytes, indicating equivalent anionic site distribution. Staining for alkaline phosphatase activity provides a new approach for distinguishing M cells from enterocytes at the light microscopic level. Identical binding of lectins indicates that M cells and enterocytes share common glycoconjugates even though molecular groupings may differ. Lectin binding and anionic charge similarities of M cells and enterocytes may facilitate antigen sampling by M cells of particles and compounds that adhere to intestinal surfaces in non-Peyer's patch areas.

Luminescent systems based on the isolation of conjugated PI systems and edge charge compensation with polar molecules on a charged nanostructured surface

DOEpatents

Ivanov, Ilia N.; Puretzky, Alexander A.; Zhao, Bin; Geohegan, David B.; Styers-Barnett, David J.; Hu, Hui

2014-07-15

A photoluminescent or electroluminescent system and method of making a non-luminescent nanostructured material into such a luminescent system is presented. The method of preparing the luminescent system, generally, comprises the steps of modifying the surface of a nanostructured material to create isolated regions to act as luminescent centers and to create a charge imbalance on the surface; applying more than one polar molecule to the charged surface of the nanostructured material; and orienting the polar molecules to compensate for the charge imbalance on the surface of the nanostructured material. The compensation of the surface charge imbalance by the polar molecules allows the isolated regions to exhibit luminescence.

Modeling secondary electron emission from nanostructured materials in helium ion microscope

NASA Astrophysics Data System (ADS)

Ohya, K.; Yamanaka, T.

2013-11-01

Charging of a SiO2 layer on a Si substrate during helium (He) beam irradiation is investigated at an energy range relevant to a He ion microscope (HIM). A self-consistent calculation is performed to model the transport of the ions and secondary electrons (SEs), the charge accumulation in the layer, and the electric field below and above the surface. The calculated results are compared with those for gallium (Ga) ions at the same energy and 1 keV electrons corresponding to a low-voltage scanning electron microscope (SEM). The charging of thin layers (<250 nm) is strongly suppressed due to wide depth and lateral distributions of the He ions in the layer, the voltage of which is much lower than that for the Ga ions and the electrons, where the distributions are much more localized. When the irradiation approaches the edge of a 100-nm-high SiO2 step formed on a Si substrate, a sharp increase in the number of SEs is observed, irrespective of whether a material is charged or not. When the He ions are incident on the bottom of the step, the re-entrance of SEs emitted from the substrate into the sidewall is clearly observed, but it causes the sidewall to be charged negatively. At the positions on the SiO2 layer away from the step edge, the charging voltage becomes positive with increasing number of Ga ions and electrons. However, He ions do not induce such a voltage due to strong relaxation of positive and negative charges in the Si substrate and their recombination in the SiO2 layer.

Proximity charge sensing for semiconductor detectors

DOEpatents

Luke, Paul N; Tindall, Craig S; Amman, Mark

2013-10-08

A non-contact charge sensor includes a semiconductor detector having a first surface and an opposing second surface. The detector includes a high resistivity electrode layer on the first surface and a low resistivity electrode on the high resistivity electrode layer. A portion of the low resistivity first surface electrode is deleted to expose the high resistivity electrode layer in a portion of the area. A low resistivity electrode layer is disposed on the second surface of the semiconductor detector. A voltage applied between the first surface low resistivity electrode and the second surface low resistivity electrode causes a free charge to drift toward the first or second surface according to a polarity of the free charge and the voltage. A charge sensitive preamplifier coupled to a non-contact electrode disposed at a distance from the exposed high resistivity electrode layer outputs a signal in response to movement of free charge within the detector.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Y.H. Feng; X.X. Zhang; M.L. Wu

The coke descending behavior in a CDQ cooling shaft is studied experimentally by means of a tracing method with a digital camera. For three different blast-caps, the law of coke flow is studied under five conditions of coke charge. The experimental results show that, for the sake of the uniformity of the coke burden descending, a blast-cap with elliptical cross-section is a better choice than that with circular cross-section regardless of high or low placement. A coke charge pattern with a flat top burden surface is preferable to that with peak-valley surface, a double-peak superior to a one-peak. Trajectory andmore » average velocity distribution of coke behavior depend weakly on whether the coke is continuously fed or not as the discharging began. The blast-caps have local effects on the descending coke and hardly affect whether the cokes flow smoothly or not in the case of coke burden with enough depth.« less

Adsorption and Dissociation of Molecular Oxygen on the (0001) Surface of Double Hexagonal Close Packed Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Atta-Fynn, Raymond; Ray, Asok

2008-03-01

Oxygen molecule adsorption on (0001) surface of double hexagonal packed americium has been studied in detail within the framework of density functional theory using a full-potential all-electron linearized augmented plane wave plus local orbitals method. The most stable configuration corresponded to molecular dissociation with the oxygen atoms occupying neighboring three-fold hollow h3 sites. Chemisorption energies and adsorption geometries for the adsorbed species, and change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the oxygen molecule will be discussed. The effects of chemisorption on Am 5f electron localization-delocalization in the vicinity of the Fermi level and the reaction barrier calculation for the dissociation of oxygen molecule to the most stable h3 sites will be discussed.

A Density Functional Study of Atomic Hydrogen and Oxygen Chemisorptions on the (0001) Surface of Double Hexagonal Close Packed Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Atta-Fynn, Raymond; Ray, Asok

2008-03-01

Ab initio total energy calculations within the framework of density functional theory have been performed for atomic hydrogen and oxygen chemisorptions on the (0001) surface of double hexagonal packed americium using a full-potential all-electron linearized augmented plane wave plus local orbitals (FLAPW+lo) method. The three-fold hollow hcp site was found to be the most stable site for H adsorption, while the two-fold bridge adsorption site was found to be the most stable site for O adsorption. Chemisorption energies and adsorption geometries for different adsorption sites will be discussed. The change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the adatom will be discussed. The implications of chemisorption on Am 5f electron localization-delocalization will also be discussed.

Spectral probes of the holographic Fermi ground state: Dialing between the electron star and AdS Dirac hair

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cubrovic, Mihailo; Liu Yan; Schalm, Koenraad

2011-10-15

We argue that the electron star and the anti-de Sitter (AdS) Dirac hair solution are two limits of the free charged Fermi gas in AdS. Spectral functions of holographic duals to probe fermions in the background of electron stars have a free parameter that quantifies the number of constituent fermions that make up the charge and energy density characterizing the electron star solution. The strict electron star limit takes this number to be infinite. The Dirac hair solution is the limit where this number is unity. This is evident in the behavior of the distribution of holographically dual Fermi surfaces.more » As we decrease the number of constituents in a fixed electron star background the number of Fermi surfaces also decreases. An improved holographic Fermi ground state should be a configuration that shares the qualitative properties of both limits.« less

Abstractive dissociation of oxygen over Al(111): a nonadiabatic quantum model.

PubMed

Katz, Gil; Kosloff, Ronnie; Zeiri, Yehuda

2004-02-22

The dissociation of oxygen on a clean aluminum surface is studied theoretically. A nonadiabatic quantum dynamical model is used, based on four electronically distinct potential energy surfaces characterized by the extent of charge transfer from the metal to the adsorbate. A flat surface approximation is used to reduce the computation complexity. The conservation of the helicopter angular momentum allows Boltzmann averaging of the outcome of the propagation of a three degrees of freedom wave function. The dissociation event is simulated by solving the time-dependent Schrödinger equation for a period of 30 femtoseconds. As a function of incident kinetic energy, the dissociation yield follows the experimental trend. An attempt at simulation employing only the lowest adiabatic surface failed, qualitatively disagreeing with both experiment and nonadiabatic calculations. The final products, adsorptive dissociation and abstractive dissociation, are obtained by carrying out a semiclassical molecular dynamics simulation with surface hopping which describes the back charge transfer from an oxygen atom negative ion to the surface. The final adsorbed oxygen pair distribution compares well with experiment. By running the dynamical events backward in time, a correlation is established between the products and the initial conditions which lead to their production. Qualitative agreement is thus obtained with recent experiments that show suppression of abstraction by rotational excitation. (c) 2004 American Institute of Physics.

Single-molecule interfacial electron transfer dynamics in solar energy conversion

NASA Astrophysics Data System (ADS)

Dhital, Bharat

This dissertation work investigated the parameters affecting the interfacial electron transfer (ET) dynamics in dye-semiconductor nanoparticles (NPs) system by using single-molecule fluorescence spectroscopy and imaging combined with electrochemistry. The influence of the molecule-substrate electronic coupling, the molecular structure, binding geometry on the surface and the molecule-attachment surface chemistry on interfacial charge transfer processes was studied on zinc porphyrin-TiO2 NP systems. The fluorescence blinking measurement on TiO2 NP demonstrated that electronic coupling regulates dynamics of charge transfer processes at the interface depending on the conformation of molecule on the surface. Moreover, semiconductor surface charge induced electronic coupling of molecule which is electrostatically adsorbed on the semiconductor surface also predominantly alters the ET dynamics. Furthermore, interfacial electric field and electron accepting state density dependent ET dynamics has been dissected in zinc porphyrin-TiO2 NP system by observing the single-molecule fluorescence blinking dynamics and fluorescence lifetime with and without applied bias. The significant difference in fluorescence fluctuation and lifetime suggested the modulation of charge transfer dynamics at the interface with external electric field perturbation. Quasi-continuous distribution of fluorescence intensity with applied negative potential was attributed to the faster charge recombination due to reduced density of electron accepting states. The driving force and electron accepting state density ET dependent dynamics has also been probed in zinc porphyrin-TiO2 NP and zinc porphyrin-indium tin oxide (ITO) systems. Study of a molecule adsorbed on two different semiconductors (ITO and TiO2), with large difference in electron densities and distinct driving forces, allows us to observe the changes in rates of back electron transfer process reflected by the suppressed fluorescence blinking of molecule on ITO surface. Finally, the electric field effect on the interface properties has been probed by using surface-enhanced Raman spectroscopy and supported by density functional theory calculations in alizarin-TiO2 system. The perturbation, created by the external potential, has been observed to cause a shift and/or splitting interfacial bond vibrational mode, typical indicator of the coupling energy changes between alizarin and TiO2. Such splitting provides evidence for electric field-dependent electronic coupling changes that have a significant impact on the interfacial electron transfer dynamics.

Characterizing the surface charge of synthetic nanomembranes by the streaming potential method

PubMed Central

Datta, Subhra; Conlisk, A. T.; Kanani, Dharmesh M.; Zydney, Andrew L.; Fissell, William H.; Roy, Shuvo

2010-01-01

The inference of the surface charge of polyethylene glycol (PEG)-coated and uncoated silicon membranes with nanoscale pore sizes from streaming potential measurements in the presence of finite electric double layer (EDL) effects is studied theoretically and experimentally. The developed theoretical model for inferring the pore wall surface charge density from streaming potential measurements is applicable to arbitrary pore cross-sectional shapes and accounts for the effect of finite salt concentration on the ionic mobilities and the thickness of the deposited layer of PEG. Theoretical interpretation of the streaming potential data collected from silicon membranes having nanoscale pore sizes, with/without pore wall surface modification with PEG, indicates that finite electric double layer (EDL) effects in the pore-confined electrolyte significantly affect the interpretation of the membrane charge and that surface modification with PEG leads to a reduction in the pore wall surface charge density. The theoretical model is also used to study the relative significance of the following uniquely nanoscale factors affecting the interpretation of streaming potential in moderate to strongly charged pores: altered net charge convection by applied pressure differentials, surface-charge effects on ionic conduction, and electroosmotic convection of charges. PMID:20462592

Electronically shielded solid state charged particle detector

DOEpatents

Balmer, D.K.; Haverty, T.W.; Nordin, C.W.; Tyree, W.H.

1996-08-20

An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite. 1 fig.

Electronically shielded solid state charged particle detector

DOEpatents

Balmer, David K.; Haverty, Thomas W.; Nordin, Carl W.; Tyree, William H.

1996-08-20

An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite.

Morpho-chemical characterization and surface properties of carcinogenic zeolite fibers.

PubMed

Mattioli, Michele; Giordani, Matteo; Dogan, Meral; Cangiotti, Michela; Avella, Giuseppe; Giorgi, Rodorico; Dogan, A Umran; Ottaviani, Maria Francesca

2016-04-05

Erionite belonging to the zeolite family is a human health-hazard, since it was demonstrated to be carcinogenic. Conversely, offretite family zeolites were suspected carcinogenic. Mineralogical, morphological, chemical, and surface characterizations were performed on two erionites (GF1, MD8) and one offretite (BV12) fibrous samples and, for comparison, one scolecite (SC1) sample. The specific surface area analysis indicated a larger availability of surface sites for the adsorption onto GF1, while SC1 shows the lowest one and the presence of large pores in the poorly fibrous zeolite aggregates. Selected spin probes revealed a high adsorption capacity of GF1 compared to the other zeolites, but the polar/charged interacting sites were well distributed, intercalated by less polar sites (Si-O-Si). MD8 surface is less homogeneous and the polar/charged sites are more interacting and closer to each other compared to GF1. The interacting ability of BV12 surface is much lower than that found for GF1 and MD8 and the probes are trapped in small pores into the fibrous aggregates. In comparison with the other zeolites, the non-carcinogenic SC1 shows a poor interacting ability and a lower surface polarity. These results helped to clarify the chemical properties and the surface interacting ability of these zeolite fibers which may be related to their carcinogenicity. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of surface material on electrostatic charging of houseflies (Musca domestica L).

PubMed

McGonigle, Daniel F; Jackson, Chris W

2002-04-01

Houseflies (Musca domestica L) accumulated electrostatic charges when walking over clean, uncharged dielectric surfaces. The charges elicited on a walking housefly by a range of materials were quantified, allowing a triboelectric series to be determined relative to M domestica. This ranged from surfaces that charged individuals positively, e.g. Correx (corrugated polypropylene) [.1 (+/- 4.2)pC], to those that applied a negative charge, e.g. clear cast acrylic [-14.9 (+/- 2.9)pC]. Maximum positive and negative charges accumulated by individual M domestica were +73 and -27 pC. Replicate measurements on the same fly and surface showed little variation. Variation between individuals was not related to sex and was not consistent between surfaces. Different materials charged M domestica significantly differently and individual flies had significantly different charging properties. Variation in temperature between 21.3 degrees C and 24.7 degrees C and humidity between 24% and 41% RH significantly affected charge accumulated by M domestica on some surfaces, although further experimentation is needed to confirm this. The implications of this work are discussed in relation to insect trap design and pollination biology.

Ionic Structure at Dielectric Interfaces

NASA Astrophysics Data System (ADS)

Jing, Yufei

The behavior of ions in liquids confined between macromolecules determines the outcome of many nanoscale assembly processes in synthetic and biological materials such as colloidal dispersions, emulsions, hydrogels, DNA, cell membranes, and proteins. Theoretically, the macromolecule-liquid boundary is often modeled as a dielectric interface and an important quantity of interest is the ionic structure in a liquid confined between two such interfaces. The knowledge gleaned from the study of ionic structure in such models can be useful in several industrial applications, such as biosensors, lithium-ion batteries double-layer supercapacitors for energy storage and seawater desalination. Electrostatics plays a critical role in the development of such functional materials. Many of the functions of these materials, result from charge and composition heterogeneities. There are great challenges in solving electrostatics problems in heterogeneous media with arbitrary shapes because electrostatic interactions remains unknown but depend on the particular density of charge distributions. Charged molecules in heterogeneous media affect the media's dielectric response and hence the interaction between the charges is unknown since it depends on the media and on the geometrical properties of the interfaces. To determine the properties of heterogeneous systems including crucial effects neglected in classical mean field models such as the hard core of the ions, the dielectric mismatch and interfaces with arbitrary shapes. The effect of hard core interactions accounts properly for short range interactions and the effect of local dielectric heterogeneities in the presence of ions and/or charged molecules for long-range interactions are both analyzed via an energy variational principle that enables to update charges and the medium's response in the same simulation time step. In particular, we compute the ionic structure in a model system of electrolyte confined by two planar dielectric interfaces using molecular dynamics(MD) simulations and compared it with liquid state theory result. We explore the effects of high electrolyte concentrations, multivalent ions, and dielectric contrasts on the ionic distributions. We observe the presence of non-monotonous ionic density profiles leading to structure deformation in the fluid which is attributed to the competition between electrostatic and steric (entropic) interactions. We find that thermal forces that arise from symmetry breaking at the interfaces can have a profound effect on the ionic structure and can oftentimes overwhelm the influence of dielectric discontinuity. The combined effect of ionic correlations and inhomogeneous dielectric permittivity significantly changes the character of effective interaction between two interfaces. We show that, in concentrated electrolytes with confinement, it is imperative to take into account the finite-size of the ions as well as proper description of electrostatic interactions in heterogeneous media, which is not fully fulfilled by Poisson-Boltzmann based approaches. The effect of electric field at interface between two immiscible electrolyte solutions is studied as well. The classical Poisson-Boltzmann theory has been widely used to describe the corresponding ionic distribution, even though it neglects the polarization and ion correlations typical of these charged systems. Using Monte Carlo simulations, we provide an enhanced description of an oil-water interface in the presence of an electric field without needing any adjustable parameter, including realistic ionic sizes, ion correlations, and image charges. Our data agree with experimental measurements of excess surface tension for a wide range of electrolyte concentrations of LiCl and TBATPB (tetrabutylammonium-tetraphenylborate), contrasting with the result of the classical non-linear Poisson-Boltzmann theory. More importantly, we show that the size-asymmetry between small Li+ and large Cl- ions can significantly increase the electric field near the liquid interface, or can even reverse it locally, at high salt concentrations in the aqueous phase. These observations suggest a novel trapping/release mechanism of charged nanoparticles at oil-water interfaces in the vicinity of the point of zero charge. In addition, we study the effects of size asymmetry and charge asymmetry on ion distribution at a dielectric interface using coarse-grained MD based on an energy variational principle. The goal is to explore charge amplification with exact consideration of surface polarization. We find that both size asymmetry and charge asymmetry lead to charge separation at the interfaces. In addition, charge separation is enhanced by interface polarization. We are currently extending the research to charged interfaces that has broad applications such as batteries and supercapacitors for energy storage.

Critical Dipole Length for the Wetting Transition Due to Collective Water-dipoles Interactions

PubMed Central

Wang, Chunlei; Zhou, Bo; Tu, Yusong; Duan, Manyi; Xiu, Peng; Li, Jingye; Fang, Haiping

2012-01-01

The wetting behavior of water on the solid surfaces is fundamental to various physical, chemical and biological processes. Conventionally, the surface with charges or charge dipoles is hydrophilic, whereas the non-polar surface is hydrophobic though some exceptions were recently reported. Using molecular dynamics simulations, we show that there is a critical length of the charge dipoles on the solid surface. The solid surface still exhibited hydrophobic behavior when the dipole length was less than the critical value, indicating that the water molecules on the solid surface seemed not “feel” attractive interactions from the charge dipoles on the solid surface. Those unexpected observations result from the collective interactions between the water molecules and charge dipoles on the solid surface, where the steric exclusion effect between water molecules greatly reduces the water-dipole interactions. Remarkably, the steric exclusion effect is also important for surfaces with charge dipole lengths greater than this critical length. PMID:22496954

Multiple Surface Regions on the Niemann-Pick C2 Protein Facilitate Intracellular Cholesterol Transport.

PubMed

McCauliff, Leslie A; Xu, Zhi; Li, Ran; Kodukula, Sarala; Ko, Dennis C; Scott, Matthew P; Kahn, Peter C; Storch, Judith

2015-11-06

The cholesterol storage disorder Niemann-Pick type C (NPC) disease is caused by defects in either of two late endosomal/lysosomal proteins, NPC1 and NPC2. NPC2 is a 16-kDa soluble protein that binds cholesterol in a 1:1 stoichiometry and can transfer cholesterol between membranes by a mechanism that involves protein-membrane interactions. To examine the structural basis of NPC2 function in cholesterol trafficking, a series of point mutations were generated across the surface of the protein. Several NPC2 mutants exhibited deficient sterol transport properties in a set of fluorescence-based assays. Notably, these mutants were also unable to promote egress of accumulated intracellular cholesterol from npc2(-/-) fibroblasts. The mutations mapped to several regions on the protein surface, suggesting that NPC2 can bind to more than one membrane simultaneously. Indeed, we have previously demonstrated that WT NPC2 promotes vesicle-vesicle interactions. These interactions were abrogated, however, by mutations causing defective sterol transfer properties. Molecular modeling shows that NPC2 is highly plastic, with several intense positively charged regions across the surface that could interact favorably with negatively charged membrane phospholipids. The point mutations generated in this study caused changes in NPC2 surface charge distribution with minimal conformational changes. The plasticity, coupled with membrane flexibility, probably allows for multiple cholesterol transfer routes. Thus, we hypothesize that, in part, NPC2 rapidly traffics cholesterol between closely appositioned membranes within the multilamellar interior of late endosomal/lysosomal proteins, ultimately effecting cholesterol egress from this compartment. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

The trapping and distribution of charge in polarized polymethylmethacrylate under electron-beam irradiation

NASA Astrophysics Data System (ADS)

Song, Z. G.; Gong, H.; Ong, C. K.

1997-06-01

A scanning electron microscope (SEM) mirror-image method (MIM) is employed to investigate the charging behaviour of polarized polymethylmethacrylate (PMMA) under electron-beam irradiation. An ellipsoid is used to model the trapped charge distribution and a fitting method is employed to calculate the total amount of the trapped charge and its distribution parameters. The experimental results reveal that the charging ability decreases with increasing applied electric field, which polarizes the PMMA sample, whereas the trapped charge distribution is elongated along the direction of the applied electric field and increases with increasing applied electric field. The charges are believed to be trapped in some localization states, of activation energy and radius estimated to be about 19.6 meV and 0022-3727/30/11/004/img6, respectively.

LSI arrays for space stations

NASA Technical Reports Server (NTRS)

Gassaway, J. D.

1976-01-01

Two approaches have been taken to study CCD's and some of their fundamental limitations. First a numerical analysis approach has been developed to solve the coupled transport and Poisson's equation for a thorough analysis of charge transfer in a CCD structure. The approach is formulated by treating the minority carriers as a surface distribution at the Si-SiO2 interface and setting up coupled difference equations for the charge and the potential. The SOR method is proposed for solving the two dimensional Poisson's equation for the potential. Methods are suggested for handling the discontinuities to improve convergence. Second, CCD shift registers were fabricated with parameters which should allow complete charge transfer independent of the transfer electrode gap width. A test instrument was designed and constructed which can be used to test this, or any similar, three phase CCD shift register.

Ion association at discretely-charged dielectric interfaces: Giant charge inversion [Dielectric response controlled ion association at physically heterogeneous surfaces: Giant charge reversal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhi -Yong; Wu, Jianzhong

2017-07-11

Giant charge reversal has been identified for the first time by Monte Carlo simulation for a discretely charged surface in contact with a trivalent electrolyte solution. It takes place regardless of the surface charge density under study and the monovalent salt. In stark contrast to earlier predictions based on the 2-dimensional Wigner crystal model to describe strong correlation of counterions at the macroion surface, we find that giant charge reversal reflects an intricate interplay of ionic volume effects, electrostatic correlations, surface charge heterogeneity, and the dielectric response of the confined fluids. While the novel phenomenon is yet to be confirmedmore » with experiment, the simulation results appear in excellent agreement with a wide range of existing observations in the subregime of charge inversion. Lastly, our findings may have far-reaching implications to understanding complex electrochemical phenomena entailing ionic fluids under dielectric confinements.« less

Triboelectric, Corona, and Induction Charging of Insulators as a Function of Pressure

NASA Technical Reports Server (NTRS)

Hogue, Michael D.; Mucciolo, Eduardo R.; Calle, Carlos I.

2006-01-01

Theoretical and experimental research has been performed that shows that the surface charge on an insulator after triboelectric charging with another insulator is rapidly dissipated with lowered atmospheric pressure. This pressure discharge is consistent with surface ions being evaporated off the surface once their vapor pressure is attained. In this paper we will report on the results of three different charging techniques (triboelectric, corona, and induction) performed on selected polymers with varying atmospheric pressure. This data will show that ion exchange between the polymer samples is the mechanism responsible for most of the surface charge on the polymer surfaces.

Dusty plasmas over the Moon: theory research in support of the upcoming lunar missions

NASA Astrophysics Data System (ADS)

Popel, Sergey; Zelenyi, Lev; Zakharov, Alexander; Izvekova, Yulia; Dolnikov, Gennady; Dubinskii, Andrey; Kopnin, Sergey; Golub, Anatoly

The future Russian lunar missions Luna 25 and Luna 27 are planned to be equipped with instruments for direct detection of nano- and microscale dust particles and determination of plasma properties over the surface of the Moon. Lunar dust over the Moon is usually considered as a part of a dusty plasma system. Here, we present the main our theory results concerning the lunar dusty plasmas. We start with the description of the observational data on dust particles on and over the surface of the Moon. We show that the size distribution of dust on the lunar surface is in a good agreement with the Kolmogorov distribution, which is the size distribution of particles in the case of multiple crushing. We discuss the role of adhesion which has been identified as a significant force in the dust particle launching process. We evaluate the adhesive force for lunar dust particles with taking into account the roughness and adsorbed molecular layers. We show that dust particle launching can be explained if the dust particles rise at a height of about dozens of nanometers owing to some processes. This is enough for the particles to acquire charges sufficient for the dominance of the electrostatic force over the gravitational and adhesive forces. The reasons for the separation of the dust particles from the surface of the Moon are, in particular, their heating by solar radiation and cooling. We consider migration of free protons in regolith from the viewpoint of the photoemission properties of the lunar soil. Finally, we develop a model of dusty plasma system over the Moon and show that it includes charged dust, photoelectrons, and electrons and ions of the solar wind. We determine the distributions of the photoelectrons and find the characteristics of the dust which rise over the lunar regolith. We show that there are no significant constraints on the Moon landing sites for future lunar missions that will study dusty plasmas in the surface layer of the Moon. We discuss also waves in dusty plasmas over the lunar surface. This work was supported by the Presidium of the Russian Academy of Sciences (basic research program no. 22 “Fundamental Problems of Research and Exploration of the Solar System”) and by the Russian Foundation for Basic Research (project 12-02-00270-a).

Secondary atomization in the combustion of electrostatic sprays

NASA Technical Reports Server (NTRS)

Gomez, Alessandro; Chen, Gung

1993-01-01

The combustion of electrosprays in a laminar counterflow diffusion flame has been experimentally studied by measuring droplet size and velocity distributions and gas-phase temperature. Detailed examination of the evolution of droplet size distribution as droplets approach the flame shows that, if substantial evaporation occurs before droplets 'interact' with the flame, the size distribution becomes bimodal. A secondary, sharp peak, in fact, develops in correspondence of diameters about one order of magnitude smaller than the mean. No evaporation mechanism can account for the development of such bimodality, that can be explained only in terms of a disintegration of droplets into finer fragments of size much smaller than the parent ones. This fission is of electric nature and it occurs when the repulsion of electric charges overcomes the surface tension cohesive force ultimately leading to a disintegration into finer fragments at or about the so-called Rayleigh limit. We here report on the first observation in combustion environments of such 'explosions'. If, on the other hand, droplets enter the very high temperature region before exploding, there appears to be no evidence of bimodality in their size distribution. In this case, in fact, flame chemi-ions may neutralize the charge on the droplets and thus prevent disruption.

Modulating the fixed charge density in silicon nitride films while monitoring the surface recombination velocity by photoluminescence imaging

NASA Astrophysics Data System (ADS)

Bazilchuk, Molly; Haug, Halvard; Marstein, Erik Stensrud

2015-04-01

Several important semiconductor devices such as solar cells and photodetectors may be fabricated based on surface inversion layer junctions induced by fixed charge in a dielectric layer. Inversion layer junctions can easily be fabricated by depositing layers with a high density of fixed charge on a semiconducting substrate. Increasing the fixed charge improves such devices; for instance, the efficiency of a solar cell can be substantially increased by reducing the surface recombination velocity, which is a function of the fixed charge density. Methods for increasing the charge density are therefore of interest. In this work, the fixed charge density in silicon nitride layers deposited by plasma enhanced chemical vapor deposition is increased to very high values above 1 × 1013 cm-2 after the application of an external voltage to a gate electrode. The effect of the fixed charge density on the surface recombination velocity was experimentally observed using the combination of capacitance-voltage characterization and photoluminescence imaging, showing a significant reduction in the surface recombination velocity for increasing charge density. The surface recombination velocity vs. charge density data was analyzed using a numerical device model, which indicated the presence of a sub-surface damage region formed during deposition of the layers. Finally, we have demonstrated that the aluminum electrodes used for charge injection may be chemically removed in phosphoric acid without loss of the underlying charge. The injected charge was shown to be stable for a prolonged time period, leading us to propose charge injection in silicon nitride films by application of soaking voltage as a viable method for fabricating inversion layer devices.

Investigating the Role of Adducts in Protein Supercharging with Sulfolane

NASA Astrophysics Data System (ADS)

Douglass, Kevin Aart; Venter, Andre R.

2012-03-01

The supercharging effect of sulfolane on cytochrome c (cyt c) during electrospray ionization mass spectrometry (ESI-MS) in the absence of conformational effects was investigated. The addition of sulfolane on the order of 1 mM or greater to denaturing solutions of cyt c results in supercharging independent of protein concentration over the range of 0.1 to 10 μM. While supercharging was observed in the positive mode, no change in the charge state distribution was observed in the negative mode, ruling out polarity-independent factors such as conformational changes or surface tension effects. A series of sulfolane adducts observed with increasing intensity concurrent with increasing charge state suggests that a direct interaction between sulfolane and the charged sites of cyt c plays an important role in supercharging. We propose that charge delocalization occurring through large-scale dipole reordering of the highly polar supercharging reagent reduces the electrostatic barrier for proximal charging along the cyt c amino acid chain. Supporting this claim, supercharging was shown to increase with increasing dipole moment for several supercharging reagents structurally related to sulfolane.

Mean-force-field and mean-spherical approximations for the electric microfield distribution at a charged point in the charged-hard-particles fluid

NASA Astrophysics Data System (ADS)

Rosenfeld, Yaakov

1989-01-01

The linearized mean-force-field approximation, leading to a Gaussian distribution, provides an exact formal solution to the mean-spherical integral equation model for the electric microfield distribution at a charged point in the general charged-hard-particles fluid. Lado's explicit solution for plasmas immediately follows this general observation.

Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Kaur, Supreet; Sharma, Shobha; Kashyap, Hemant K.

2017-11-01

We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (Cd) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of Cd with positive and negative surface potentials.

Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study.

PubMed

Kaur, Supreet; Sharma, Shobha; Kashyap, Hemant K

2017-11-21

We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (C d ) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of C d with positive and negative surface potentials.

Entropy and charge in molecular evolution--the case of phosphate

NASA Technical Reports Server (NTRS)

Arrhenius, G.; Sales, B.; Mojzsis, S.; Lee, T.; Bada, J. L. (Principal Investigator)

1997-01-01

Biopoesis, the creation of life, implies molecular evolution from simple components, randomly distributed and in a dilute state, to form highly organized, concentrated systems capable of metabolism, replication and mutation. This chain of events must involve environmental processes that can locally lower entropy in several steps; by specific selection from an indiscriminate mixture, by concentration from dilute solution, and in the case of the mineral-induced processes, by particular effectiveness in ordering and selective reaction, directed toward formation of functional biomolecules. Numerous circumstances provide support for the notion that negatively charged molecules were functionally required and geochemically available for biopoesis. Sulfite ion may have been important in bisulfite complex formation with simple aldehydes, facilitating the initial concentration by sorption of aldehydes in positively charged surface active minerals. Borate ion may have played a similar, albeit less investigated role in forming charged sugar complexes. Among anionic species, oligophosphate ions and charged phosphate esters are likely to have been of even more wide ranging importance, reflected in the continued need for phosphate in a proposed RNA world, and extending its central role to evolved biochemistry. Phosphorylation is shown to result in selective concentration by surface sorption of compounds, otherwise too dilute to support condensation reactions. It provides protection against rapid hydrolysis of sugars and, by selective concentration, induces the oligomerization of aldehydes. As a manifestation of life arisen, phosphate already appears in an organic context in the oldest preserved sedimentary record.

Electric Vehicles Charging Scheduling Strategy Considering the Uncertainty of Photovoltaic Output

NASA Astrophysics Data System (ADS)

Wei, Xiangxiang; Su, Su; Yue, Yunli; Wang, Wei; He, Luobin; Li, Hao; Ota, Yutaka

2017-05-01

The rapid development of electric vehicles and distributed generation bring new challenges to security and economic operation of the power system, so the collaborative research of the EVs and the distributed generation have important significance in distribution network. Under this background, an EVs charging scheduling strategy considering the uncertainty of photovoltaic(PV) output is proposed. The characteristics of EVs charging are analysed first. A PV output prediction method is proposed with a PV database then. On this basis, an EVs charging scheduling strategy is proposed with the goal to satisfy EVs users’ charging willingness and decrease the power loss in distribution network. The case study proves that the proposed PV output prediction method can predict the PV output accurately and the EVs charging scheduling strategy can reduce the power loss and stabilize the fluctuation of the load in distributed network.

Influence of argon and oxygen on charge-state-resolved ion energy distributions of filtered aluminum arcs

NASA Astrophysics Data System (ADS)

Rosén, Johanna; Anders, André; Mráz, Stanislav; Atiser, Adil; Schneider, Jochen M.

2006-06-01

The charge-state-resolved ion energy distributions (IEDs) in filtered aluminum vacuum arc plasmas were measured and analyzed at different oxygen and argon pressures in the range of 0.5-8.0 mTorr. A significant reduction of the ion energy was detected as the pressure was increased, most pronounced in an argon environment and for the higher charge states. The corresponding average charge state decreased from 1.87 to 1.0 with increasing pressure. The IEDs of all metal ions in oxygen were fitted with shifted Maxwellian distributions. The results show that it is possible to obtain a plasma composition with a narrow charge-state distribution as well as a narrow IED. These data may enable tailoring thin film properties through selecting growth conditions that are characterized by predefined charge state and energy distributions.

Dust Dynamics Near Planetary Surfaces

NASA Astrophysics Data System (ADS)

Colwell, Joshua; Hughes, Anna; Grund, Chris

Observations of a lunar "horizon glow" by several Surveyor spacecraft in the 1960s opened the study of the dynamics of charged dust particles near planetary surfaces. The surfaces of the Moon and other airless planetary bodies in the solar system (asteroids, and other moons) are directly exposed to the solar wind and ionizing solar ultraviolet radiation, resulting in a time-dependent electric surface potential. Because these same objects are also exposed to bombardment by micrometeoroids, the surfaces are usually characterized by a power-law size distribution of dust that extends to sub-micron-sized particles. Individual particles can acquire a charge different from their surroundings leading to electrostatic levitation. Once levitated, particles may simply return to the surface on nearly ballistic trajectories, escape entirely from the moon or asteroid if the initial velocity is large, or in some cases be stably levitated for extended periods of time. All three outcomes have observable consequences. Furthermore, the behavior of charged dust near the surface has practical implications for planned future manned and unmanned activities on the lunar surface. Charged dust particles also act as sensitive probes of the near-surface plasma environment. Recent numerical modeling of dust levitation and transport show that charged micron-sized dust is likely to accumulate in topographic lows such as craters, providing a mechanism for the creation of dust "ponds" observed on the asteroid 433 Eros. Such deposition can occur when particles are supported by the photoelectron sheath above the dayside and drift over shadowed regions of craters where the surface potential is much smaller. Earlier studies of the lunar horizon glow are consistent with those particles being on simple ballistic trajectories following electrostatic launching from the surface. Smaller particles may be accelerated from the lunar surface to high altitudes consistent with observations of high altitude streams observed by Apollo astronauts and potentially also by the Clementine spacecraft. In addition to the Surveyor images of lunar horizon glow and the high altitude streamer measurements, the Apollo 17 Lunar Ejecta and Meteorite surface package detected signals consistent with the impact of relatively slow-moving dust particles that may have been charged dust electrostatically levitated from the surface. There is renewed interest in this near-surface dust environment with plans to return robotic landers and astronauts to the lunar surface. No Apollo-era instruments were specifically designed to detect or measure dust levitated off the lunar surface. One new experiment under study is the Autonomous Lunar Dust Observer (ALDO). ALDO is a high-sensitivity scanning lidar (laser radar) that autonomously maps and records its 3-D dust environment. Flexibility of programmable scan pattern enables ALDO to characterize the dust context in and around experiment sites. Repeated shallow angle scans in a vertical plane enable high vertical resolution studies of dust levitation near the ground. Single elevation angle sector or full azimuth scans enable large-area statistical surveys of the frequency and size of ejecta plumes from micrometeoroid impacts, and vertical or fixed-angle stares enable very high sensitivity dust profiles to extended ranges. It is estimated that backscatter from dust concentrations as low as 1/cm3 can be measured. The concept is equally applicable to surface and atmospheric studies of other airless bodies.

Wave processes in dusty plasma near the Moon’s surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozova, T. I.; Kopnin, S. I.; Popel, S. I., E-mail: popel@iki.rssi.ru

2015-10-15

A plasma—dust system in the near-surface layer on the illuminated side of the Moon is described. The system involves photoelectrons, solar-wind electrons and ions, neutrals, and charged dust grains. Linear and nonlinear waves in the plasma near the Moon’s surface are discussed. It is noticed that the velocity distribution of photoelectrons can be represented as a superposition of two distribution functions characterized by different electron temperatures: lower energy electrons are knocked out of lunar regolith by photons with energies close to the work function of regolith, whereas higher energy electrons are knocked out by photons corresponding to the peak atmore » 10.2 eV in the solar radiation spectrum. The anisotropy of the electron velocity distribution function is distorted due to the solar wind motion with respect to photoelectrons and dust grains, which leads to the development of instability and excitation of high-frequency oscillations with frequencies in the range of Langmuir and electromagnetic waves. In addition, dust acoustic waves can be excited, e.g., near the lunar terminator. Solutions in the form of dust acoustic solitons corresponding to the parameters of the dust—plasma system in the near-surface layer of the illuminated Moon’s surface are found. Ranges of possible Mach numbers and soliton amplitudes are determined.« less

The molecular shape and the field similarities as criteria to interpret SAR studies for fragment-based design of platinum(IV) anticancer agents. Correlation of physicochemical properties with cytotoxicity.

PubMed

Lorenzo, Julia; Montaña, Ángel M

2016-09-01

Molecular shape similarity and field similarity have been used to interpret, in a qualitative way, the structure-activity relationships in a selected series of platinum(IV) complexes with anticancer activity. MM and QM calculations have been used to estimate the electron density, electrostatic potential maps, partial charges, dipolar moments and other parameters to correlate the stereo-electronic properties with the differential biological activity of complexes. Extended Electron Distribution (XED) field similarity has been also evaluated for the free 1,4-diamino carrier ligands, in a fragment-based drug design approach, comparing Connolly solvent excluded surface, hydrophobicity field surface, Van der Waals field surface, nucleophilicity field surface, electrophilicity field surface and the extended electron-distribution maxima field points. A consistency has been found when comparing the stereo-electronic properties of the studied series of platinum(IV) complexes and/or the free ligands evaluated and their in vitro anticancer activity. Copyright © 2016 Elsevier Inc. All rights reserved.

Electric Double-Layer Interaction between Dissimilar Charge-Conserved Conducting Plates.

PubMed

Chan, Derek Y C

2015-09-15

Small metallic particles used in forming nanostructured to impart novel optical, catalytic, or tribo-rheological can be modeled as conducting particles with equipotential surfaces that carry a net surface charge. The value of the surface potential will vary with the separation between interacting particles, and in the absence of charge-transfer or electrochemical reactions across the particle surface, the total charge of each particle must also remain constant. These two physical conditions require the electrostatic boundary condition for metallic nanoparticles to satisfy an equipotential whole-of-particle charge conservation constraint that has not been studied previously. This constraint gives rise to a global charge conserved constant potential boundary condition that results in multibody effects in the electric double-layer interaction that are either absent or are very small in the familiar constant potential or constant charge or surface electrochemical equilibrium condition.

Bacterial attachment to RO membranes surface-modified by concentration-polarization-enhanced graft polymerization.

PubMed

Bernstein, Roy; Belfer, Sofia; Freger, Viatcheslav

2011-07-15

Concentration polarization-enhanced radical graft polymerization, a facile surface modification technique, was examined as an approach to reduce bacterial deposition onto RO membranes and thus contribute to mitigation of biofouling. For this purpose an RO membrane ESPA-1 was surface-grafted with a zwitterionic and negatively and positively charged monomers. The low monomer concentrations and low degrees of grafting employed in modifications moderately reduced flux (by 20-40%) and did not affect salt rejection, yet produced substantial changes in surface chemistry, charge and hydrophilicity. The propensity to bacterial attachment of original and modified membranes was assessed using bacterial deposition tests carried out in a parallel plate flow setup using a fluorescent strain of Pseudomonas fluorescens. Compared to unmodified ESPA-1 the deposition (mass transfer) coefficient was significantly increased for modification with the positively charged monomer. On the other hand, a substantial reduction in bacterial deposition rates was observed for membranes modified with zwitterionic monomer and, still more, with very hydrophilic negatively charged monomers. This trend is well explained by the effects of surface charge (as measured by ζ-potential) and hydrophilicity (contact angle). It also well correlated with force distance measurements by AFM using surrogate spherical probes with a negative surface charge mimicking the bacterial surface. The positively charged surface showed a strong hysteresis with a large adhesion force, which was weaker for unmodified ESPA-1 and still weaker for zwitterionic surface, while negatively charged surface showed a long-range repulsion and negligible hysteresis. These results demonstrate the potential of using the proposed surface- modification approach for varying surface characteristics, charge and hydrophilicity, and thus minimizing bacterial deposition and potentially reducing propensity biofouling.

Probing lipid membrane electrostatics

NASA Astrophysics Data System (ADS)

Yang, Yi

The electrostatic properties of lipid bilayer membranes play a significant role in many biological processes. Atomic force microscopy (AFM) is highly sensitive to membrane surface potential in electrolyte solutions. With fully characterized probe tips, AFM can perform quantitative electrostatic analysis of lipid membranes. Electrostatic interactions between Silicon nitride probes and supported zwitterionic dioleoylphosphatidylcholine (DOPC) bilayer with a variable fraction of anionic dioleoylphosphatidylserine (DOPS) were measured by AFM. Classical Gouy-Chapman theory was used to model the membrane electrostatics. The nonlinear Poisson-Boltzmann equation was numerically solved with finite element method to provide the potential distribution around the AFM tips. Theoretical tip-sample electrostatic interactions were calculated with the surface integral of both Maxwell and osmotic stress tensors on tip surface. The measured forces were interpreted with theoretical forces and the resulting surface charge densities of the membrane surfaces were in quantitative agreement with the Gouy-Chapman-Stern model of membrane charge regulation. It was demonstrated that the AFM can quantitatively detect membrane surface potential at a separation of several screening lengths, and that the AFM probe only perturbs the membrane surface potential by <2%. One important application of this technique is to estimate the dipole density of lipid membrane. Electrostatic analysis of DOPC lipid bilayers with the AFM reveals a repulsive force between the negatively charged probe tips and the zwitterionic lipid bilayers. This unexpected interaction has been analyzed quantitatively to reveal that the repulsion is due to a weak external field created by the internai membrane dipole moment. The analysis yields a dipole moment of 1.5 Debye per lipid with a dipole potential of +275 mV for supported DOPC membranes. This new ability to quantitatively measure the membrane dipole density in a noninvasive manner will be useful in identifying the biological effects of the dipole potential. Finally, heterogeneous model membranes were studied with fluid electric force microscopy (FEFM). Electrostatic mapping was demonstrated with 50 nm resolution. The capabilities of quantitative electrostatic measurement and lateral charge density mapping make AFM a unique and powerful probe of membrane electrostatics.

Programmable ion-sensitive transistor interfaces. III. Design considerations, signal generation, and sensitivity enhancement

NASA Astrophysics Data System (ADS)

Jayant, Krishna; Auluck, Kshitij; Rodriguez, Sergio; Cao, Yingqiu; Kan, Edwin C.

2014-05-01

We report on factors that affect DNA hybridization detection using ion-sensitive field-effect transistors (ISFETs). Signal generation at the interface between the transistor and immobilized biomolecules is widely ascribed to unscreened molecular charges causing a shift in surface potential and hence the transistor output current. Traditionally, the interaction between DNA and the dielectric or metal sensing interface is modeled by treating the molecular layer as a sheet charge and the ionic profile with a Poisson-Boltzmann distribution. The surface potential under this scenario is described by the Graham equation. This approximation, however, often fails to explain large hybridization signals on the order of tens of mV. More realistic descriptions of the DNA-transistor interface which include factors such as ion permeation, exclusion, and packing constraints have been proposed with little or no corroboration against experimental findings. In this study, we examine such physical models by their assumptions, range of validity, and limitations. We compare simulations against experiments performed on electrolyte-oxide-semiconductor capacitors and foundry-ready floating-gate ISFETs. We find that with weakly charged interfaces (i.e., low intrinsic interface charge), pertinent to the surfaces used in this study, the best agreement between theory and experiment exists when ions are completely excluded from the DNA layer. The influence of various factors such as bulk pH, background salinity, chemical reactivity of surface groups, target molecule concentration, and surface coatings on signal generation is studied. Furthermore, in order to overcome Debye screening limited detection, we suggest two signal enhancement strategies. We first describe frequency domain biosensing, highlighting the ability to sort short DNA strands based on molecular length, and then describe DNA biosensing in multielectrolytes comprising trace amounts of higher-valency salt in a background of monovalent saline. Our study provides guidelines for optimized interface design, signal enhancement, and the interpretation of FET-based biosensor signals.

Experimental study and simulation of space charge stimulated discharge

NASA Astrophysics Data System (ADS)

Noskov, M. D.; Malinovski, A. S.; Cooke, C. M.; Wright, K. A.; Schwab, A. J.

2002-11-01

The electrical discharge of volume distributed space charge in poly(methylmethacrylate) (PMMA) has been investigated both experimentally and by computer simulation. The experimental space charge was implanted in dielectric samples by exposure to a monoenergetic electron beam of 3 MeV. Electrical breakdown through the implanted space charge region within the sample was initiated by a local electric field enhancement applied to the sample surface. A stochastic-deterministic dynamic model for electrical discharge was developed and used in a computer simulation of these breakdowns. The model employs stochastic rules to describe the physical growth of the discharge channels, and deterministic laws to describe the electric field, the charge, and energy dynamics within the discharge channels and the dielectric. Simulated spatial-temporal and current characteristics of the expanding discharge structure during physical growth are quantitatively compared with the experimental data to confirm the discharge model. It was found that a single fixed set of physically based dielectric parameter values was adequate to simulate the complete family of experimental space charge discharges in PMMA. It is proposed that such a set of parameters also provides a useful means to quantify the breakdown properties of other dielectrics.

Improved charge breeding efficiency of light ions with an electron cyclotron resonance ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vondrasek, R.; Kutsaev, Sergey; Delahaye, P.

2012-11-15

The Californium Rare Isotope Breeder Upgrade is a new radioactive beam facility for the Argonne Tandem Linac Accelerator System (ATLAS). The facility utilizes a {sup 252}Cf fission source coupled with an electron cyclotron resonance ion source to provide radioactive beam species for the ATLAS experimental program. The californium fission fragment distribution provides nuclei in the mid-mass range which are difficult to extract from production targets using the isotope separation on line technique and are not well populated by low-energy fission of uranium. To date the charge breeding program has focused on optimizing these mid-mass beams, achieving high charge breeding efficienciesmore » of both gaseous and solid species including 14.7% for the radioactive species {sup 143}Ba{sup 27+}. In an effort to better understand the charge breeding mechanism, we have recently focused on the low-mass species sodium and potassium which up to present have been difficult to charge breed efficiently. Unprecedented charge breeding efficiencies of 10.1% for {sup 23}Na{sup 7+} and 17.9% for {sup 39}K{sup 10+} were obtained injecting stable Na{sup +} and K{sup +} beams from a surface ionization source.« less

Improved charge breeding efficiency of light ions with an electron cyclotron resonance ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vondrasek, R.; Delahaye, P.; Kutsaev, Sergey

2012-11-01

The Californium Rare Isotope Breeder Upgrade is a new radioactive beam facility for the Argonne Tandem Linac Accelerator System (ATLAS). The facility utilizes a 252Cf fission source coupled with an electron cyclotron resonance ion source to provide radioactive beam species for the ATLAS experimental program. The californium fission fragment distribution provides nuclei in the mid-mass range which are difficult to extract from production targets using the isotope separation on line technique and are not well populated by low-energy fission of uranium. To date the charge breeding program has focused on optimizing these mid-mass beams, achieving high charge breeding efficiencies ofmore » both gaseous and solid species including 14.7% for the radioactive species 143Ba27+. In an effort to better understand the charge breeding mechanism, we have recently focused on the low-mass species sodium and potassium which up to present have been difficult to charge breed efficiently. Unprecedented charge breeding efficiencies of 10.1% for 23Na7+ and 17.9% for 39K10+ were obtained injecting stable Na+ and K+ beams from a surface ionization source.« less

Monte Carlo simulations of polyelectrolytes inside viral capsids.

PubMed

Angelescu, Daniel George; Bruinsma, Robijn; Linse, Per

2006-04-01

Structural features of polyelectrolytes as single-stranded RNA or double-stranded DNA confined inside viral capsids and the thermodynamics of the encapsidation of the polyelectrolyte into the viral capsid have been examined for various polyelectrolyte lengths by using a coarse-grained model solved by Monte Carlo simulations. The capsid was modeled as a spherical shell with embedded charges and the genome as a linear jointed chain of oppositely charged beads, and their sizes corresponded to those of a scaled-down T=3 virus. Counterions were explicitly included, but no salt was added. The encapisdated chain was found to be predominantly located at the inner capsid surface, in a disordered manner for flexible chains and in a spool-like structure for stiff chains. The distribution of the small ions was strongly dependent on the polyelectrolyte-capsid charge ratio. The encapsidation enthalpy was negative and its magnitude decreased with increasing polyelectrolyte length, whereas the encapsidation entropy displayed a maximum when the capsid and polyelectrolyte had equal absolute charge. The encapsidation process remained thermodynamically favorable for genome charges ca. 3.5 times the capsid charge. The chain stiffness had only a relatively weak effect on the thermodynamics of the encapsidation.

A thundercloud electric field sounding - Charge distribution and lightning

NASA Technical Reports Server (NTRS)

Weber, M. E.; Few, A. A.; Stewart, M. F.; Christian, H. J.

1982-01-01

An instrumented free balloon measured electric fields and field changes as it rose through a thundercloud above Langmuir Laboratory, New Mexico. The variation of the electric field with altitude implied that the cloud contained negative space charge of density -0.6 to -4 nC/cu m between 5.5 and 8.0 km MSL. The environmental temperature at these levels ranged from -5 to -20 C. The measurements imply that the areal extent of this negative charge center was significantly greater than that of the cloud's intense precipitation shafts. At altitudes greater than 8 km, the instrument ascended past net positive charge. In addition, positive space charge adjacent to the earth's surface (concentration 0.6 nC/cu m and in the lowest portion of the cloud (1.0 nC/cu m) is inferred from the measurements. Electric field changes from intracloud lightning were interpreted by using a simple model for the developing streamer of the initial phase. Thunder source reconstructions provided estimates for the orientation of lightning channels. Seven 'streamers' so analyzed propagated on the average, at 50,000 m/s and carried a current of 390 A. The mean charge dissipated during a flash was 30 C.

Proceedings of the Spacecraft Charging Technology Conference Held in Monterey, California on 31 October - 3 November 1989. Volume 2

DTIC Science & Technology

1989-11-01

STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution unlimited 13. ABSTRACT (Maximum 200 words) The Spacecraft Charging... Distribution I D Availability Codes ’ Avail and/orDist Special VIvt PREFACE The Spacecraft Charging Technology conference was held at the Naval... distribution , the spacecraft will charge negatively during this time according to dV/dt = 47ta 2 Jth ev/° / C whose solution is V/0= - ln(l + t/t) "t = C 0

Charging of moving surfaces by corona discharges sustained in air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jun-Chieh, E-mail: junchwan@umich.edu; Kushner, Mark J., E-mail: mjkush@umich.edu; Zhang, Daihua, E-mail: dhzhang@tju.edu.cn

Atmospheric pressure corona discharges are used in electrophotographic (EP) printing technologies for charging imaging surfaces such as photoconductors. A typical corona discharge consists of a wire (or wire array) biased with a few hundred volts of dc plus a few kV of ac voltage. An electric discharge is produced around the corona wire from which electrons drift towards and charge the underlying dielectric surface. The surface charging reduces the voltage drop across the gap between the corona wire and the dielectric surface, which then terminates the discharge, as in a dielectric barrier discharge. In printing applications, this underlying surface ismore » continuously moving throughout the charging process. For example, previously charged surfaces, which had reduced the local electric field and terminated the local discharge, are translated out of the field of view and are replaced with uncharged surface. The uncharged surface produces a rebound in the electric field in the vicinity of the corona wire which in turn results in re-ignition of the discharge. The discharge, so reignited, is then asymmetric. We found that in the idealized corona charging system we investigated, a negatively dc biased corona blade with a dielectric covered ground electrode, the discharge is initially sustained by electron impact ionization from the bulk plasma and then dominated by ionization from sheath accelerated secondary electrons. Depending on the speed of the underlying surface, the periodic re-ignition of the discharge can produce an oscillatory charging pattern on the moving surface.« less

Adsorption of insulin peptide on charged single-walled carbon nanotubes: significant role of ordered water molecules.

PubMed

Shen, Jia-Wei; Wu, Tao; Wang, Qi; Kang, Yu; Chen, Xin

2009-06-02

Ordered hydration shells: The more ordered hydration shells outside the charged CNT surfaces prevent more compact adsorption of the peptide in the charged CNT systems [picture: see text], but peptide binding strengths on the charged CNT surfaces are stronger due to the electrostatic interaction.Studies of adsorption dynamics and stability for peptides/proteins on single-walled carbon nanotubes (SWNTs) are of great importance for a better understanding of the properties and nature of nanotube-based biosystems. Herein, the dynamics and mechanism of the adsorption of the insulin chain B peptide on different charged SWNTs are investigated by explicit solvent molecular dynamics simulations. The results show that all types of surfaces effectively attract the model peptide. Water molecules play a significant role in peptide adsorption on the surfaces of charged carbon nanotubes (CNTs). Compared to peptide adsorption on neutral CNT surfaces, the more ordered hydration shells outside the tube prevent more compact adsorption of the peptide in charged CNT systems. This shield effect leads to a smaller conformational change and van der Waals interaction between the peptide and surfaces, but peptide binding strengths on charged CNT surfaces are stronger than those on the neutral CNT surface due to the strong electrostatic interaction. The result of these simulations implies the possibility of improving the binding strength of peptides/proteins on CNT surfaces, as well as keeping the integrity of the peptide/protein conformation in peptide/protein-CNT complexes by charging the CNTs.

Effect of surface charge density on the affinity of oxide nanoparticles for the vapor-water interface.

PubMed

Brown, Matthew A; Duyckaerts, Nicolas; Redondo, Amaia Beloqui; Jordan, Inga; Nolting, Frithjof; Kleibert, Armin; Ammann, Markus; Wörner, Hans Jakob; van Bokhoven, Jeroen A; Abbas, Zareen

2013-04-23

Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si-O(-)) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.

Treatment of charge singularities in implicit solvent models.

PubMed

Geng, Weihua; Yu, Sining; Wei, Guowei

2007-09-21

This paper presents a novel method for solving the Poisson-Boltzmann (PB) equation based on a rigorous treatment of geometric singularities of the dielectric interface and a Green's function formulation of charge singularities. Geometric singularities, such as cusps and self-intersecting surfaces, in the dielectric interfaces are bottleneck in developing highly accurate PB solvers. Based on an advanced mathematical technique, the matched interface and boundary (MIB) method, we have recently developed a PB solver by rigorously enforcing the flux continuity conditions at the solvent-molecule interface where geometric singularities may occur. The resulting PB solver, denoted as MIBPB-II, is able to deliver second order accuracy for the molecular surfaces of proteins. However, when the mesh size approaches half of the van der Waals radius, the MIBPB-II cannot maintain its accuracy because the grid points that carry the interface information overlap with those that carry distributed singular charges. In the present Green's function formalism, the charge singularities are transformed into interface flux jump conditions, which are treated on an equal footing as the geometric singularities in our MIB framework. The resulting method, denoted as MIBPB-III, is able to provide highly accurate electrostatic potentials at a mesh as coarse as 1.2 A for proteins. Consequently, at a given level of accuracy, the MIBPB-III is about three times faster than the APBS, a recent multigrid PB solver. The MIBPB-III has been extensively validated by using analytically solvable problems, molecular surfaces of polyatomic systems, and 24 proteins. It provides reliable benchmark numerical solutions for the PB equation.

Treatment of charge singularities in implicit solvent models

NASA Astrophysics Data System (ADS)

Geng, Weihua; Yu, Sining; Wei, Guowei

2007-09-01

This paper presents a novel method for solving the Poisson-Boltzmann (PB) equation based on a rigorous treatment of geometric singularities of the dielectric interface and a Green's function formulation of charge singularities. Geometric singularities, such as cusps and self-intersecting surfaces, in the dielectric interfaces are bottleneck in developing highly accurate PB solvers. Based on an advanced mathematical technique, the matched interface and boundary (MIB) method, we have recently developed a PB solver by rigorously enforcing the flux continuity conditions at the solvent-molecule interface where geometric singularities may occur. The resulting PB solver, denoted as MIBPB-II, is able to deliver second order accuracy for the molecular surfaces of proteins. However, when the mesh size approaches half of the van der Waals radius, the MIBPB-II cannot maintain its accuracy because the grid points that carry the interface information overlap with those that carry distributed singular charges. In the present Green's function formalism, the charge singularities are transformed into interface flux jump conditions, which are treated on an equal footing as the geometric singularities in our MIB framework. The resulting method, denoted as MIBPB-III, is able to provide highly accurate electrostatic potentials at a mesh as coarse as 1.2Å for proteins. Consequently, at a given level of accuracy, the MIBPB-III is about three times faster than the APBS, a recent multigrid PB solver. The MIBPB-III has been extensively validated by using analytically solvable problems, molecular surfaces of polyatomic systems, and 24 proteins. It provides reliable benchmark numerical solutions for the PB equation.

Modeling quantum yield, emittance, and surface roughness effects from metallic photocathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrov, D. A.; Bell, G. I.; Smedley, J.

Here, detailed measurements of momentum distributions of emitted electrons have allowed the investigation of the thermal limit of the transverse emittance from metal photocathodes. Furthermore, recent developments in material design and growth have resulted in photocathodes that can deliver high quantum efficiency and are sufficiently robust to use in high electric field gradient photoinjectors and free electron lasers. The growth process usually produces photoemissive material layers with rough surface profiles that lead to transverse accelerating fields and possible work function variations, resulting in emittance growth. To better understand the effects of temperature, density of states, and surface roughness on themore » properties of emitted electrons, we have developed realistic three-dimensional models for photocathode materials with grated surface structures. They include general modeling of electron excitation due to photon absorption, charge transport, and emission from flat and rough metallic surfaces. The models also include image charge and field enhancement effects. We report results from simulations with flat and rough surfaces to investigate how electron scattering, controlled roughness, work function variation, and field enhancement affect emission properties. Comparison of simulation results with measurements of the quantum yield and transverse emittance from flat Sb emission surfaces shows the importance of including efficient modeling of photon absorption, temperature effects, and the material density of states to achieve agreement with the experimental data.« less

Modeling quantum yield, emittance, and surface roughness effects from metallic photocathodes

DOE PAGES

Dimitrov, D. A.; Bell, G. I.; Smedley, J.; ...

2017-10-26

Here, detailed measurements of momentum distributions of emitted electrons have allowed the investigation of the thermal limit of the transverse emittance from metal photocathodes. Furthermore, recent developments in material design and growth have resulted in photocathodes that can deliver high quantum efficiency and are sufficiently robust to use in high electric field gradient photoinjectors and free electron lasers. The growth process usually produces photoemissive material layers with rough surface profiles that lead to transverse accelerating fields and possible work function variations, resulting in emittance growth. To better understand the effects of temperature, density of states, and surface roughness on themore » properties of emitted electrons, we have developed realistic three-dimensional models for photocathode materials with grated surface structures. They include general modeling of electron excitation due to photon absorption, charge transport, and emission from flat and rough metallic surfaces. The models also include image charge and field enhancement effects. We report results from simulations with flat and rough surfaces to investigate how electron scattering, controlled roughness, work function variation, and field enhancement affect emission properties. Comparison of simulation results with measurements of the quantum yield and transverse emittance from flat Sb emission surfaces shows the importance of including efficient modeling of photon absorption, temperature effects, and the material density of states to achieve agreement with the experimental data.« less

Specific spacecraft evaluation: Special report. [charged particle transport from a mercury ion thruster to spacecraft surfaces

NASA Technical Reports Server (NTRS)

Sellen, J. M., Jr.

1978-01-01

Charged and neutral particle transport from an 8 cm mercury ion thruster to the surfaces of the P 80-1 spacecraft and to the Teal Ruby sensor and the ECOM-501 sensor of that spacecraft were investigated. Laboratory measurements and analyses were used to examine line-of-sight and nonline-of sight particle transport modes. The recirculation of Hg(+) ions in the magnetic field of the earth was analyzed for spacecraft velocity and Earth magnetic field vector configurations which are expected to occur in near Earth, circular, high inclination orbits. For these magnetic field and orbit conditions and for expected ion release distribution functions, in both angles and energies, the recirculation/re-interception of ions on spacecraft surfaces was evaluated. The refraction of weakly energetic ions in the electric fields of the thruster plasma plume and in the electric fields between this plasma plume and the material boundaries of the thruster, the thruster sputter shield, and the various spacecraft surfaces were examined. The neutral particle transport modes of interest were identified as sputtered metal atoms from the thruster beam shield. Results, conclusions, and future considerations are presented.

Relating saturation capacity to charge density in strong cation exchangers.

PubMed

Steinebach, Fabian; Coquebert de Neuville, Bertrand; Morbidelli, Massimo

2017-07-21

In this work the relation between physical and chemical resin characteristics and the total amount of adsorbed protein (saturation capacity) for ion-exchange resins is discussed. Eleven different packing materials with a sulfo-functionalization and one multimodal resin were analyzed in terms of their porosity, pore size distribution, ligand density and binding capacity. By specifying the ligand density and binding capacity by the total and accessible surface area, two different groups of resins were identified: Below a ligand density of approx. 2.5μmol/m 2 area the ligand density controls the saturation capacity, while above this limit the accessible surface area becomes the limiting factor. This results in a maximum protein uptake of around 2.5mg/m 2 of accessible surface area. The obtained results allow estimating the saturation capacity from independent resin characteristics like the saturation capacity mainly depends on "library data" such as the accessible and total surface area and the charge density. Hence these results give an insight into the fundamentals of protein adsorption and help to find suitable resins, thus limiting the experimental effort in early process development stages. Copyright © 2017 Elsevier B.V. All rights reserved.

Charge state distributions of oxygen and carbon in the energy range 1 to 300 keV/e observed with AMPTE/CCE in the magnetosphere

NASA Technical Reports Server (NTRS)

Kremser, G.; Stuedemann, W.; Wilken, B.; Gloeckler, G.; Hamilton, D. C.

1985-01-01

Observations of charge state distributions of oxygen and carbon are presented that were obtained with the charge-energy-mass spectrometer onboard the AMPTE/CCE spacecraft. Data were selected for two different local time sectors (apogee at 1300 LT and 0300 LT, respectively), three L-ranges (4-6, 6-8, and greater than 8), and quiet to moderately disturbed days (Kp less than or equal to 4). The charge state distributions reveal the existence of all charge states of oxygen and carbon in the magnetosphere. The relative importance of the different charge states strongly depends on L and much less on local time. The observations confirm that the solar wind and the ionosphere contribute to the oxygen population, whereas carbon only originates from the solar wind. The L-dependence of the charge state distributions can be interpreted in terms of these different ion sources and of charge exchange and diffusion processes that largely influence the distribution of oxygen and carbon in the magnetosphere.

The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria.

PubMed

Meschke, S; Smith, B D; Yost, M; Miksch, R R; Gefter, P; Gehlke, S; Halpin, H A

2009-04-01

A series of experiments were conducted to evaluate the effect of surface charge and air ionization on the deposition of airborne bacteria. The interaction between surface electrostatic potential and the deposition of airborne bacteria in an indoor environment was investigated using settle plates charged with electric potentials of 0, +/-2.5kV and +/-5kV. Results showed that bacterial deposition on the plates increased proportionally with increased potential to over twice the gravitational sedimentation rate at +5kV. Experiments were repeated under similar conditions in the presence of either negative or bipolar air ionization. Bipolar air ionization resulted in reduction of bacterial deposition onto the charged surfaces to levels nearly equal to gravitational sedimentation. In contrast, diffusion charging appears to have occurred during negative air ionization, resulting in an even greater deposition onto the oppositely charged surface than observed without ionization. Static charges on fomitic surfaces may attract bacteria resulting in deposition in excess of that expected by gravitational sedimentation or simple diffusion. Implementation of bipolar ionization may result in reduction of bacterial deposition. Fomitic surfaces are important vehicles for the transmission of infectious organisms. This study has demonstrated a simple strategy for minimizing charge related deposition of bacteria on surfaces.

Interaction of highly charged ions with carbon nano membranes

NASA Astrophysics Data System (ADS)

Gruber, Elisabeth; Wilhelm, Richard A.; Smejkal, Valerie; Heller, René; Facsko, Stefan; Aumayr, Friedrich

2015-09-01

Charge state and energy loss measurements of slow highly charged ions (HCIs) after transmission through nanometer and sub-nanometer thin membranes are presented. Direct transmission measurements through carbon nano membranes (CNMs) show an unexpected bimodal exit charge state distribution, accompanied by charge exchange dependent energy loss. The energy loss of ions in CNMs with large charge loss shows a quadratic dependency on the incident charge state, indicating charge state dependent stopping force values. Another access to the exit charge state distribution is given by irradiating stacks of CNMs and investigating each layer of the stack with high resolution imaging techniques like transmission electron microscopy (TEM) and helium ion microscopy (HIM) independently. The observation of pores created in all of the layers confirms the assumption derived from the transmission measurements that the two separated charge state distributions reflect two different impact parameter regimes, i.e. close collision with large charge exchange and distant collisions with weak ion-target interaction.

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

DOE PAGES

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

Biosafety evaluations of well-dispersed mesoporous silica nanoparticles: towards in vivo-relevant conditions

NASA Astrophysics Data System (ADS)

Liu, Tsang-Pai; Wu, Si-Han; Chen, Yi-Ping; Chou, Chih-Ming; Chen, Chien-Tsu

2015-04-01

This study aimed to investigate how mesoporous silica nanoparticles (MSNs), especially focussing on their surface functional groups, interacted with Raw 264.7 macrophages, as well as with zebrafish embryos. Upon introducing nanoparticles into a biological milieu, adsorption of proteins and biomolecules onto the nanoparticle surface usually progresses rapidly. Nanoparticles bound with proteins can result in physiological and pathological changes, but the mechanisms remain to be elucidated. In order to evaluate how protein corona affected MSNs and the subsequent cellular immune responses, we experimented in both serum and serum-deprived conditions. Our findings indicated that the level of p-p38 was significantly elevated by the positively charged MSNs, whereas negatively charged MSNs resulted in marked ROS production. Most significantly, our experiments demonstrated that the presence of protein efficiently mitigated the potential nano-hazard. On the other hand, strongly positively charged MSNs caused 94% of the zebrafish embryos to die. In that case, the toxicity caused by the quaternary ammonium ligands on the surface of those nanoparticles was exerted in a dose-dependent manner. In summary, these fundamental studies here provide valuable insights into the design of better biocompatible nanomaterials in the future.This study aimed to investigate how mesoporous silica nanoparticles (MSNs), especially focussing on their surface functional groups, interacted with Raw 264.7 macrophages, as well as with zebrafish embryos. Upon introducing nanoparticles into a biological milieu, adsorption of proteins and biomolecules onto the nanoparticle surface usually progresses rapidly. Nanoparticles bound with proteins can result in physiological and pathological changes, but the mechanisms remain to be elucidated. In order to evaluate how protein corona affected MSNs and the subsequent cellular immune responses, we experimented in both serum and serum-deprived conditions. Our findings indicated that the level of p-p38 was significantly elevated by the positively charged MSNs, whereas negatively charged MSNs resulted in marked ROS production. Most significantly, our experiments demonstrated that the presence of protein efficiently mitigated the potential nano-hazard. On the other hand, strongly positively charged MSNs caused 94% of the zebrafish embryos to die. In that case, the toxicity caused by the quaternary ammonium ligands on the surface of those nanoparticles was exerted in a dose-dependent manner. In summary, these fundamental studies here provide valuable insights into the design of better biocompatible nanomaterials in the future. Electronic supplementary information (ESI) available: TEM image, size distribution histogram of as-synthesized wn-R-MSN@PEG. TGA measurements. Cellular uptake efficiency. WST-1 analysis. Western blot assays. Confocal images and zebrafish mortality. See DOI: 10.1039/c4nr07421a

Thermionic noise measurements for on-line dispenser cathode diagnostics for linear beam microwave tubes

NASA Technical Reports Server (NTRS)

Holland, C.; Brodie, I.

1985-01-01

A test stand has been set up to measure the current fluctuation noise properties of B- and M-type dispenser cathodes in a typical TWT gun structure. Noise techniques were used to determine the work function distribution on the cathode surfaces. Significant differences between the B and M types and significant changes in the work function distribution during activation and life are found. In turn, knowledge of the expected work function can be used to accurately determine the cathode-operating temperatures in a TWT structure. Noise measurements also demonstrate more sensitivity to space charge effects than the Miram method. Full automation of the measurements and computations is now required to speed up data acquisition and reduction. The complete set of equations for the space charge limited diode were programmed so that given four of the five measurable variables (J, J sub O, T, D, and V) the fifth could be computed. Using this program, we estimated that an rms fluctuation in the diode spacing d in the frequency range of 145 Hz about 20 kHz of only about 10 to the -5 power A would account for the observed noise in a space charge limited diode with 1 mm spacing.

Electrostatic interaction between stereocilia: II. Influence on the mechanical properties of the hair bundle.

PubMed

Dolgobrodov, S G; Lukashkin, A N; Russell, I J

2000-12-01

This paper is based on our model [Dolgobrodov et al., 2000. Hear. Res., submitted for publication] in which we examine the significance of the polyanionic surface layers of stereocilia for electrostatic interaction between them. We analyse how electrostatic forces modify the mechanical properties of the sensory hair bundle. Different charge distribution profiles within the glycocalyx are considered. When modelling a typical experiment on bundle stiffness measurements, applying an external force to the tallest row of stereocilia shows that the asymptotic stiffness of the hair bundle for negative displacements is always larger than the asymptotic stiffness for positive displacements. This increase in stiffness is monotonic for even charge distribution and shows local minima when the negative charge is concentrated in a thinner layer within the cell coat. The minima can also originate from the co-operative effect of electrostatic repulsion and inter-ciliary links with non-linear mechanical properties. Existing experimental observations are compared with the predictions of the model. We conclude that the forces of electrostatic interaction between stereocilia may influence the mechanical properties of the hair bundle and, being strongly non-linear, contribute to the non-linear phenomena, which have been recorded from the auditory periphery.

Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer

NASA Astrophysics Data System (ADS)

Lee, Victor; James, Nicole M.; Waitukaitis, Scott R.; Jaeger, Heinrich M.

2018-03-01

Electrostatic charging of insulating fine particles can be responsible for numerous phenomena ranging from lightning in volcanic plumes to dust explosions. However, even basic aspects of how fine particles become charged are still unclear. Studying particle charging is challenging because it usually involves the complexities associated with many-particle collisions. To address these issues, we introduce a method based on acoustic levitation, which makes it possible to initiate sequences of repeated collisions of a single submillimeter particle with a flat plate, and to precisely measure the particle charge in situ after each collision. We show that collisional charge transfer between insulators is dependent on the hydrophobicity of the contacting surfaces. We use glass, which we modify by attaching nonpolar molecules to the particle, the plate, or both. We find that hydrophilic surfaces develop significant positive charges after contacting hydrophobic surfaces. Moreover, we demonstrate that charging between a hydrophilic and a hydrophobic surface is suppressed in an acidic environment and enhanced in a basic one. Application of an electric field during each collision is found to modify the charge transfer, again depending on surface hydrophobicity. We discuss these results within the context of contact charging due to ion transfer, and we show that they lend strong support to O H- ions as the charge carriers.

Use of anionic surfactants for selective polishing of silicon dioxide over silicon nitride films using colloidal silica-based slurries

NASA Astrophysics Data System (ADS)

Penta, Naresh K.; Amanapu, H. P.; Peethala, B. C.; Babu, S. V.

2013-10-01

Four different anionic surfactants, sodium dodecyl sulfate, dodecyl benzene sulfonic acid (DBSA), dodecyl phosphate and Sodium lauroyl sarcosine, selected from the sulfate, phosphate, and carboxylic family, were investigated as additives in silica dispersions for selective polishing of silicon dioxide over silicon nitride films. We found that all these anionic surfactants suppress the nitride removal rates (RR) for pH ≤4 while more or less maintaining the oxide RRs, resulting in high oxide-to-nitride RR selectivity. The RR data obtained as a function of pH were explained based on pH dependent distributions of surfactant species, change in the zeta potentials of oxide and nitride surfaces, and thermogravimetric data. It appears that the negatively charged surfactant species preferentially adsorb on the positively charged nitride surface below IEP through its electrostatic interactions and form a bilayer adsorption, resulting in the suppression of nitride RRs. In contrast to the surfactants, K2SO4 interacts only weakly with the nitride surface and hence cannot suppress its RR.

Stochastic many-particle model for LFP electrodes

NASA Astrophysics Data System (ADS)

Guhlke, Clemens; Gajewski, Paul; Maurelli, Mario; Friz, Peter K.; Dreyer, Wolfgang

2018-02-01

In the framework of non-equilibrium thermodynamics, we derive a new model for many-particle electrodes. The model is applied to LiFePO4 (LFP) electrodes consisting of many LFP particles of nanometer size. The phase transition from a lithium-poor to a lithium-rich phase within LFP electrodes is controlled by both different particle sizes and surface fluctuations leading to a system of stochastic differential equations. An explicit relation between battery voltage and current controlled by the thermodynamic state variables is derived. This voltage-current relation reveals that in thin LFP electrodes lithium intercalation from the particle surfaces into the LFP particles is the principal rate-limiting process. There are only two constant kinetic parameters in the model describing the intercalation rate and the fluctuation strength, respectively. The model correctly predicts several features of LFP electrodes, viz. the phase transition, the observed voltage plateaus, hysteresis and the rate-limiting capacity. Moreover we study the impact of both the particle size distribution and the active surface area on the voltage-charge characteristics of the electrode. Finally we carefully discuss the phase transition for varying charging/discharging rates.

Significance of Polarization Charges and Isomagnetic Surface in Magnetohydrodynamics

PubMed Central

Liang, Zhu-Xing; Liang, Yi

2015-01-01

From the frozen-in field lines concept, a highly conducting fluid can move freely along, but not traverse to, magnetic field lines. We discuss this topic and find that in the study of the frozen-in field lines concept, the effects of inductive and capacitive reactance have been omitted. When admitted, the relationships among the motional electromotive field, the induced electric field, the eddy electric current, and the magnetic field becomes clearer. We emphasize the importance of isomagnetic surfaces and polarization charges, and show analytically that whether a conducting fluid can freely traverse magnetic field lines or not depends solely on the magnetic gradient along the path of the fluid. If a fluid does not change its density distribution and shape (can be regarded as a quasi-rigid body) and moves along isomagnetic surface, it can freely traverse magnetic field lines without any magnetic drag, no matter how strong the magnetic field is. Besides theoretical analysis, we also present experimental results to support our analysis. The main purpose of this work is to correct a fallacy among some astrophysicists. PMID:26322894

The impacts of pore-scale physical and chemical heterogeneities on the transport of radionuclide-carrying colloids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ning

Independent of the methods of nuclear waste disposal, the degradation of packaging materials could lead to mobilization and transport of radionuclides into the geosphere. This process can be significantly accelerated due to the association of radionuclides with the backfill materials or mobile colloids in groundwater. The transport of these colloids is complicated by the inherent coupling of physical and chemical heterogeneities (e.g., pore space geometry, grain size, charge heterogeneity, and surface hydrophobicity) in natural porous media that can exist on the length scale of a few grains. In addition, natural colloids themselves are often heterogeneous in their surface properties (e.g.,more » clay platelets possess opposite charges on the surface and along the rim). Both physical and chemical heterogeneities influence the transport and retention of radionuclides under various groundwater conditions. However, the precise mechanisms how these coupled heterogeneities influence colloidal transport are largely elusive. This knowledge gap is a major source of uncertainty in developing accurate models to represent the transport process and to predict distribution of radionuclides in the geosphere.« less

Cell-polymer interactions of fluorescent polystyrene latex particles coated with thermosensitive poly(N-isopropylacrylamide) and poly(N-vinylcaprolactam) or grafted with poly(ethylene oxide)-macromonomer.

PubMed

Vihola, Henna; Marttila, Anna-Kaisa; Pakkanen, Jukka S; Andersson, Mirja; Laukkanen, Antti; Kaukonen, Ann Marie; Tenhu, Heikki; Hirvonen, Jouni

2007-10-01

Cell-polymer interactions of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) or poly(N-vinylcaprolactam) (PVCL) coated particles with RAW264.7 macrophages and intestinal Caco-2 cells were evaluated. Nanosized particles were prepared by modifying the surface of fluorescent polystyrene (FPS) particles with the thermosensitive polymer gels or with poly(ethylene oxide) (PEO)-macromonomer grafts. The particles were characterized by IR-spectroscopy for functional groups, light scattering for size distribution and zeta-potential for surface charge. Effects of temperature and polymer coating/grafting on the cellular interactions were evaluated by cell association/uptake and visualized by confocal scanning microscope. PEO and PNIPAM inhibited the polymer-cell contact by steric repulsion, evidenced by weak attachment of the particles. PVCL-coated FPS was adsorbed on the cells more strongly, especially at 37 degrees C, because of more hydrophobic nature at higher temperatures. The results suggest feasibility of the PNIPAM and PVCL for biotechnological/pharmaceutical applications, as the cell-particle interactions may be modified by size, surface charge, hydrophobicity, steric repulsion and temperature.

Colloid transport in model fracture filling materials

NASA Astrophysics Data System (ADS)

Wold, S.; Garcia-Garcia, S.; Jonsson, M.

2010-12-01

Colloid transport in model fracture filling materials Susanna Wold*, Sandra García-García and Mats Jonsson KTH Chemical Science and Engineering Royal Institute of Technology, SE-100 44 Stockholm, Sweden *Corresponding author: E-mail: wold@kth.se Phone: +46 8 790 6295 In colloid transport in water-bearing fractures, the retardation depends on interactions with the fracture surface by sorption or filtration. These mechanisms are difficult to separate. A rougher surface will give a larger area available for sorption, and also when a particle is physically hindered, it approaches the surface and enables further sorption. Sorption can be explained by electrostatics were the strongest sorption on minerals always is observed at pH below pHpzc (Filby et al., 2008). The adhesion of colloids to mineral surfaces is related to the surface roughness according to a recent study (Darbha et al., 2010). There is a large variation in the characteristics of water-bearing fractures in bedrock in terms of aperture distribution, flow velocity, surface roughness, mineral distributions, presence of fracture filling material, and biological and organic material, which is hard to implement in modeling. The aim of this work was to study the transport of negatively charged colloids in model fracture filling material in relation to flow, porosity, mineral type, colloid size, and surface charge distribution. In addition, the impact on transport of colloids of mixing model fracture filling materials with different retention and immobilization capacities, determined by batch sorption experiments, was investigated. The transport of Na-montmorillonite colloids and well-defined negatively charged latex microspheres of 50, 100, and 200 nm diameter were studied in either columns containing quartz or quartz mixed with biotite. The ionic strength in the solution was exclusively 0.001 and pH 6 or 8.5. The flow rates used were 0.002, 0.03, and 0.6 mL min-1. Sorption of the colloids on the model fracture minerals was studied prior to the transport experiments under the same conditions. By varying the amount of solid substrate, it was possible to determine an interaction constant from a linear expression. Complementary zeta potential measurements and scanning electron microscopy (SEM) imaging were performed to examine the mineral surfaces after exposure to colloids. In experiments with low flow rates the retention of the colloids in the transport experiments were attributed to the interaction constants including both physical filtration and sorption. At higher flow rate the interactions between colloids and mineral surfaces were also significant but not as pronounced. Immobilization and retardation of the colloids were reflected by the interaction constants, which included both an irreversible and a reversible component of physical filtration and sorption. References Darbha, G.K., Schaefer, T., Heberling, F., Lüttge, A. and Fisher, C. 2010. Retention of Latex Colloids on Calcite as a Function of Surface Roughness and Topography. Langmuir, 26(7), 4743-4752. Filby, A., Plaschke, M., Geckeis, H., Fanghänel, Th. 2008. Interaction of latex colloids with mineral surfaces and Grimsel granodiorite. J. Contam. Hydrol., 102, 273-284.

Spectroscopic Methodologies for Characterizing the Adsorption Behavior and Distribution of Silver Nanoparticles to Hydrated Mineral Surfaces

NASA Astrophysics Data System (ADS)

Brittle, S. W.; O'Neil, K. A.; Foose, D. P.; Stahler, A. C.; Johnson, J. K.; Higgins, S. R.; Sizemore, I. E.; Sikon, J.

2016-12-01

The expansive incorporation of silver nanoparticles (AgNPs) into over 400 consumer products has raised considerable concern about their eventual release into the environment. Although minerals make up a large component of soils, there has been limited research on their interactions with AgNPs. In this study, a representative nonsilicate mineral, corundum (α-Al2O3), was used in fused beaded form (specific surface area of 6-8 m2 g-1) as a model to study the interaction between minerals and negatively-charged, Creighton AgNPs. A concentration of 1 mg L-1 of AgNPs was selected in order to ensure sub-monolayer surface coverage and to surpass the maximum contaminant level (MCL) set by the U.S. Environmental Agency (EPA) for Ag+ in drinking water (0.1 mg L-1). Raman maps collected on the corundum particles exposed to AgNPs at environmentally relevant pH values (6-11) demonstrated AgNP adsorption onto the hydrated mineral surface through OH- moieties regardless of surface charge (i.e. no pH dependence). In addition, two other well-established analytical techniques were employed for supportive purposes. Namely, the AgNP-corundum interaction was also confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES) through the quantification of the total amount of AgNPs adsorbed onto α-Al2O3. It was found that approximately 75% of the available AgNPs had adsorbed to the mineral surface at all pH values. Atomic force microscopy (AFM), in intermittent contact mode, was also performed to map AgNPs surface distribution on polished and annealed flatter corundum windows. To further demonstrate the Raman analysis, the corundum were also imaged to observe AgNPs adsorption with less surface area and onto other minerals through the occurrence of molecular Ag- vibrations and/or the enhancement of a tracer compound dispensed on mineral surfaces with adsorbed AgNPs (i.e., Surface Enhanced Raman Spectroscopy hot-spots). Overall, this spectroscopic-based analysis promotes extrapolation to other studies as an effective way to observe the interactions between mineral surfaces and nanomaterials.

A Combined Model of Charging of the Surface and Bulk of a Dielectric Target by Electrons with the Energies 10-30 keV

NASA Astrophysics Data System (ADS)

Zykov, V. M.; Neiman, D. A.

2018-04-01

A physico-mathematical model of the processes of radiation-induced charging of dielectric materials with open surfaces, irradiated with monoenergetic electrons in the energy range 10-30 keV, is described. The model takes into account the relationship between the processes of surface and bulk charging for the given conditions of the experimental design, which accounts for the effect of anomalously long charging of dielectrics after the incident energy of primary electrons during charging is reduced to below the second critical energy for the secondary electronic emission coefficient. The initial fast phase of charging a high-resistivity dielectric material (Al2O3) is investigated. It is shown that as the incident electron energy is approaching the second critical energy during charging, the secondary electronic emission is partially suppressed due to negative charging of the open surface of the dielectric and formation of a near-surface inversion electrical field retarding the electronic emission yield.

Entropic contributions enhance polarity compensation for CeO2(100) surfaces

NASA Astrophysics Data System (ADS)

Capdevila-Cortada, Marçal; López, Núria

2017-03-01

Surface structure controls the physical and chemical response of materials. Surface polar terminations are appealing because of their unusual properties but they are intrinsically unstable. Several mechanisms, namely metallization, adsorption, and ordered reconstructions, can remove thermodynamic penalties rendering polar surfaces partially stable. Here, for CeO2(100), we report a complementary stabilization mechanism based on surface disorder that has been unravelled through theoretical simulations that: account for surface energies and configurational entropies; show the importance of the ion distribution degeneracy; and identify low diffusion barriers between conformations that ensure equilibration. Disordered configurations in oxides might also be further stabilized by preferential adsorption of water. The entropic stabilization term will appear for surfaces with a high number of empty sites, typically achieved when removing part of the ions in a polar termination to make the layer charge zero. Assessing the impact of surface disorder when establishing new structure-activity relationships remains a challenge.