AESOP: A Python Library for Investigating Electrostatics in Protein Interactions.

Science.gov (United States)

Harrison, Reed E S; Mohan, Rohith R; Gorham, Ronald D; Kieslich, Chris A; Morikis, Dimitrios

2017-05-09

Electric fields often play a role in guiding the association of protein complexes. Such interactions can be further engineered to accelerate complex association, resulting in protein systems with increased productivity. This is especially true for enzymes where reaction rates are typically diffusion limited. To facilitate quantitative comparisons of electrostatics in protein families and to describe electrostatic contributions of individual amino acids, we previously developed a computational framework called AESOP. We now implement this computational tool in Python with increased usability and the capability of performing calculations in parallel. AESOP utilizes PDB2PQR and Adaptive Poisson-Boltzmann Solver to generate grid-based electrostatic potential files for protein structures provided by the end user. There are methods within AESOP for quantitatively comparing sets of grid-based electrostatic potentials in terms of similarity or generating ensembles of electrostatic potential files for a library of mutants to quantify the effects of perturbations in protein structure and protein-protein association. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Efficient Algorithms for Electrostatic Interactions Including Dielectric Contrasts

Directory of Open Access Journals (Sweden)

Christian Holm

2013-10-01

Full Text Available Coarse-grained models of soft matter are usually combined with implicit solvent models that take the electrostatic polarizability into account via a dielectric background. In biophysical or nanoscale simulations that include water, this constant can vary greatly within the system. Performing molecular dynamics or other simulations that need to compute exact electrostatic interactions between charges in those systems is computationally demanding. We review here several algorithms developed by us that perform exactly this task. For planar dielectric surfaces in partial periodic boundary conditions, the arising image charges can be either treated with the MMM2D algorithm in a very efficient and accurate way or with the electrostatic layer correction term, which enables the user to use his favorite 3D periodic Coulomb solver. Arbitrarily-shaped interfaces can be dealt with using induced surface charges with the induced charge calculation (ICC* algorithm. Finally, the local electrostatics algorithm, MEMD(Maxwell Equations Molecular Dynamics, even allows one to employ a smoothly varying dielectric constant in the systems. We introduce the concepts of these three algorithms and an extension for the inclusion of boundaries that are to be held fixed at a constant potential (metal conditions. For each method, we present a showcase application to highlight the importance of dielectric interfaces.

Coarse-grained electrostatic interactions of coronene: Towards the crystalline phase

Energy Technology Data Exchange (ETDEWEB)

Heinemann, Thomas, E-mail: thomas.heinemann@tu-berlin.de; Klapp, Sabine H. L., E-mail: klapp@physik.tu-berlin.de [Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Palczynski, Karol, E-mail: karol.palczynski@helmholtz-berlin.de; Dzubiella, Joachim, E-mail: joachim.dzubiella@helmholtz-berlin.de [Institut für Physik, Humboldt Universität zu Berlin, Newtonstraße 15, 12489 Berlin (Germany); Institut für Weiche Materie und Funktionale Materialen, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner Platz 1, 14109 Berlin (Germany)

2015-11-07

In this article, we present and compare two different, coarse-grained approaches to model electrostatic interactions of disc-shaped aromatic molecules, specifically coronene. Our study builds on our previous work [T. Heinemann et al., J. Chem. Phys. 141, 214110 (2014)], where we proposed, based on a systematic coarse-graining procedure starting from the atomistic level, an anisotropic effective (Gay-Berne-like) potential capable of describing van der Waals contributions to the interaction energy. To take into account electrostatics, we introduce, first, a linear quadrupole moment along the symmetry axis of the coronene disc. The second approach takes into account the fact that the partial charges within the molecules are distributed in a ring-like fashion. We then reparametrize the effective Gay-Berne-like potential such that it matches, at short distances, the ring-ring potential. To investigate the validity of these two approaches, we perform many-particle molecular dynamics simulations, focusing on the crystalline phase (karpatite) where electrostatic interaction effects are expected to be particularly relevant for the formation of tilted stacked columns. Specifically, we investigate various structural parameters as well as the melting transition. We find that the second approach yields consistent results with those from experiments despite the fact that the underlying potential decays with the wrong distance dependence at large molecule separations. Our strategy can be transferred to a broader class of molecules, such as benzene or hexabenzocoronene.

Coarse-grained electrostatic interactions of coronene: Towards the crystalline phase

International Nuclear Information System (INIS)

Heinemann, Thomas; Klapp, Sabine H. L.; Palczynski, Karol; Dzubiella, Joachim

2015-01-01

In this article, we present and compare two different, coarse-grained approaches to model electrostatic interactions of disc-shaped aromatic molecules, specifically coronene. Our study builds on our previous work [T. Heinemann et al., J. Chem. Phys. 141, 214110 (2014)], where we proposed, based on a systematic coarse-graining procedure starting from the atomistic level, an anisotropic effective (Gay-Berne-like) potential capable of describing van der Waals contributions to the interaction energy. To take into account electrostatics, we introduce, first, a linear quadrupole moment along the symmetry axis of the coronene disc. The second approach takes into account the fact that the partial charges within the molecules are distributed in a ring-like fashion. We then reparametrize the effective Gay-Berne-like potential such that it matches, at short distances, the ring-ring potential. To investigate the validity of these two approaches, we perform many-particle molecular dynamics simulations, focusing on the crystalline phase (karpatite) where electrostatic interaction effects are expected to be particularly relevant for the formation of tilted stacked columns. Specifically, we investigate various structural parameters as well as the melting transition. We find that the second approach yields consistent results with those from experiments despite the fact that the underlying potential decays with the wrong distance dependence at large molecule separations. Our strategy can be transferred to a broader class of molecules, such as benzene or hexabenzocoronene

Non-specific interactions are sufficient to explain the position of heterochromatic chromocenters and nucleoli in interphase nuclei

NARCIS (Netherlands)

Nooijer, de S.; Wellink, J.; Mulder, B.; Bisseling, T.

2009-01-01

The organization of the eukaryote nucleus into functional compartments arises by self-organization both through specific protein–protein and protein–DNA interactions and non-specific interactions that lead to entropic effects, such as e.g. depletion attraction. While many specific interactions have

Electrostatic double-layer interaction between stacked charged bilayers

Science.gov (United States)

Hishida, Mafumi; Nomura, Yoko; Akiyama, Ryo; Yamamura, Yasuhisa; Saito, Kazuya

2017-10-01

The inapplicability of the DLVO theory to multilayered anionic bilayers is found in terms of the co-ion-valence dependence of the lamellar repeat distance. Most of the added salt is expelled from the interlamellar space to the bulk due to the Gibbs-Donnan effect on multiple bilayers with the bulk. The electrostatic double-layer interaction is well expressed by the formula recently proposed by Trefalt. The osmotic pressure due to the expelled ions, rather than the van der Waals interaction, is the main origin of the attractive force between the bilayers.

Electrostatic interactions between immunoglobulin (IgG) molecules and a charged sorbent

NARCIS (Netherlands)

Bremer, M.G.E.G.; Duval, J.; Norde, Willem; Lyklema, J.

2004-01-01

The influence of electrostatic interactions on the adsorption of IgG is examined both theoretically and experimentally. The long-range interaction between IgG and the charged sorbent surface is treated in terms of the DLVO theory taking into account the possibility of charge- and potential

Enhanced Cycling Stability of Lithium–Sulfur batteries by Electrostatic-Interaction

International Nuclear Information System (INIS)

Ma, Zhaoling; Huang, Xiaobing; Jiang, Qianqian; Huo, Jia; Wang, Shuangyin

2015-01-01

Highlights: • Electrostatic interaction is utilized to hinder the shuttling of polysulfides. • Directly functionalizing SG can better prolong the cycle life of Li–S batteries. • SG/PDDA showed significantly improved capacity retention. - Abstract: Lithiums–sulfur battery is considered as one of the most promising energy storage devices to replace the current Li ion batteries because of its high theoretical capacity of 1675 mA h g −1 . However, the poor cycle stability hinders the further development of this battery system. In order to improve the stability of Li–S batteries, the diffusion of polysulfides from electrodes into electrolyte should be suppressed. Herein, we utilize a positively charged polyelectrolyte to functionalize the electrode materials with the aim to hamper the polysulfides dissolution via electrostatic interaction between strong positively charged polyelectrolyte and negatively charged polysulfides anion. The effect of the functionalization quantity of poly(diallyl dimethylammonium) chloride (PDDA) and functionalization sequence on cycling performances is investigated in detail. It is found that the sulfur–graphene composite (SG) directly functionalized with 10 times PDDA exhibited best cycling stability. At a discharge current density of 0.2 C, much higher capacity retention was realized on the functionalized electrodes than the unfunctionalized (81% vs. 47.3%) after 120 cycles. The as-observed results demonstrate that the electrostatic interaction can effectively prolong the cycling life of Li–S batteries, which provides a new promising strategy for improving the electrochemical performance of Li–S batteries.

Electrostatic Charging and Particle Interactions in Microscopic Insulating Grains

Science.gov (United States)

Lee, Victor

In this thesis, we experimentally investigate the electrostatic charging as well as the particle interactions in microscopic insulating grains. First, by tracking individual grains accelerated in an electric field, we quantitatively demonstrate that tribocharging of same-material grains depends on particle size. Large grains tend to charge positively, and small ones tend to charge negatively. Theories based on the transfer of trapped electrons can explain this tendency but have not been validated. Here we show that the number of trapped electrons, measured independently by a thermoluminescence technique, is orders of magnitude too small to be responsible for the amount of charge transferred. This result reveals that trapped electrons are not responsible for same-material tribocharging of dielectric particles. Second, same-material tribocharging in grains can result in important long-range electrostatic interactions. However, how these electrostatic interactions contribute to particle clustering remains elusive, primarily due to the lack of direct, detailed observations. Using a high-speed camera that falls with a stream charged grains, we observe for the first time how charged grains can undergo attractive as well as repulsive Kepler-like orbits. Charged particles can be captured in their mutual electrostatic potential and form clusters via multiple bounces. Dielectric polarization effects are directly observed, which lead to additional attractive forces and stabilize "molecule-like" arrangements of charged particles. Third, we have developed a new method to study the charge transfer of microscopic particles based on acoustic levitation techniques. This method allows us to narrow the complex problem of many-particle charging down to precise charge measurements of a single sub-millimeter particle colliding with a target plate. By simply attaching nonpolar groups onto glass surfaces, we show that the contact charging of a particle is highly dependent on

The role of electrostatics in protein-protein interactions of a monoclonal antibody.

Science.gov (United States)

Roberts, D; Keeling, R; Tracka, M; van der Walle, C F; Uddin, S; Warwicker, J; Curtis, R

2014-07-07

Understanding how protein-protein interactions depend on the choice of buffer, salt, ionic strength, and pH is needed to have better control over protein solution behavior. Here, we have characterized the pH and ionic strength dependence of protein-protein interactions in terms of an interaction parameter kD obtained from dynamic light scattering and the osmotic second virial coefficient B22 measured by static light scattering. A simplified protein-protein interaction model based on a Baxter adhesive potential and an electric double layer force is used to separate out the contributions of longer-ranged electrostatic interactions from short-ranged attractive forces. The ionic strength dependence of protein-protein interactions for solutions at pH 6.5 and below can be accurately captured using a Deryaguin-Landau-Verwey-Overbeek (DLVO) potential to describe the double layer forces. In solutions at pH 9, attractive electrostatics occur over the ionic strength range of 5-275 mM. At intermediate pH values (7.25 to 8.5), there is a crossover effect characterized by a nonmonotonic ionic strength dependence of protein-protein interactions, which can be rationalized by the competing effects of long-ranged repulsive double layer forces at low ionic strength and a shorter ranged electrostatic attraction, which dominates above a critical ionic strength. The change of interactions from repulsive to attractive indicates a concomitant change in the angular dependence of protein-protein interaction from isotropic to anisotropic. In the second part of the paper, we show how the Baxter adhesive potential can be used to predict values of kD from fitting to B22 measurements, thus providing a molecular basis for the linear correlation between the two protein-protein interaction parameters.

Effect of electrostatic interactions on the formation of proton transfer ...

Indian Academy of Sciences (India)

WINTEC

We report here a theoretical study on the effect of electrostatic interactions on the formation .... has also been noted in the case of the mutant Lys- ... we outline the theoretical method used. ... The starting point of our analysis is a high-reso-.

A hybrid parallel architecture for electrostatic interactions in the simulation of dissipative particle dynamics

Science.gov (United States)

Yang, Sheng-Chun; Lu, Zhong-Yuan; Qian, Hu-Jun; Wang, Yong-Lei; Han, Jie-Ping

2017-11-01

In this work, we upgraded the electrostatic interaction method of CU-ENUF (Yang, et al., 2016) which first applied CUNFFT (nonequispaced Fourier transforms based on CUDA) to the reciprocal-space electrostatic computation and made the computation of electrostatic interaction done thoroughly in GPU. The upgraded edition of CU-ENUF runs concurrently in a hybrid parallel way that enables the computation parallelizing on multiple computer nodes firstly, then further on the installed GPU in each computer. By this parallel strategy, the size of simulation system will be never restricted to the throughput of a single CPU or GPU. The most critical technical problem is how to parallelize a CUNFFT in the parallel strategy, which is conquered effectively by deep-seated research of basic principles and some algorithm skills. Furthermore, the upgraded method is capable of computing electrostatic interactions for both the atomistic molecular dynamics (MD) and the dissipative particle dynamics (DPD). Finally, the benchmarks conducted for validation and performance indicate that the upgraded method is able to not only present a good precision when setting suitable parameters, but also give an efficient way to compute electrostatic interactions for huge simulation systems. Program Files doi:http://dx.doi.org/10.17632/zncf24fhpv.1 Licensing provisions: GNU General Public License 3 (GPL) Programming language: C, C++, and CUDA C Supplementary material: The program is designed for effective electrostatic interactions of large-scale simulation systems, which runs on particular computers equipped with NVIDIA GPUs. It has been tested on (a) single computer node with Intel(R) Core(TM) i7-3770@ 3.40 GHz (CPU) and GTX 980 Ti (GPU), and (b) MPI parallel computer nodes with the same configurations. Nature of problem: For molecular dynamics simulation, the electrostatic interaction is the most time-consuming computation because of its long-range feature and slow convergence in simulation space

Limits of applicability of the quasilinear approximation to the electrostatic wave-plasma interaction

Science.gov (United States)

Zacharegkas, Georgios; Isliker, Heinz; Vlahos, Loukas

2016-11-01

The limitation of the Quasilinear Theory (QLT) to describe the diffusion of electrons and ions in velocity space when interacting with a spectrum of large amplitude electrostatic Langmuir, Upper and Lower hybrid waves, is analyzed. We analytically and numerically estimate the threshold for the amplitude of the waves above which the QLT breaks down, using a test particle code. The evolution of the velocity distribution, the velocity-space diffusion coefficients, the driven current, and the heating of the particles are investigated, for the interaction with small and large amplitude electrostatic waves, that is, in both regimes, where QLT is valid and where it clearly breaks down.

Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy–magnetic force microscopy combination

Directory of Open Access Journals (Sweden)

Miriam Jaafar

2011-09-01

Full Text Available The most outstanding feature of scanning force microscopy (SFM is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sample that could be interpreted as a magnetic interaction. To distinguish clearly the origin of the tip–sample forces we propose to use a combination of Kelvin probe force microscopy (KPFM and MFM. The KPFM technique allows us to compensate in real time the electrostatic forces between the tip and the sample by minimizing the electrostatic contribution to the frequency shift signal. This is a great challenge in samples with low magnetic moment. In this work we studied an array of Co nanostructures that exhibit high electrostatic interaction with the MFM tip. Thanks to the use of the KPFM/MFM system we were able to separate the electric and magnetic interactions between the tip and the sample.

I-DIRT, a general method for distinguishing between specific and nonspecific protein interactions.

Science.gov (United States)

Tackett, Alan J; DeGrasse, Jeffrey A; Sekedat, Matthew D; Oeffinger, Marlene; Rout, Michael P; Chait, Brian T

2005-01-01

Isolation of protein complexes via affinity-tagged proteins provides a powerful tool for studying biological systems, but the technique is often compromised by co-enrichment of nonspecifically interacting proteins. We describe a new technique (I-DIRT) that distinguishes contaminants from bona fide interactors in immunopurifications, overcoming this most challenging problem in defining protein complexes. I-DIRT will be of broad value for studying protein complexes in biological systems that can be metabolically labeled.

Computational Methods for Biomolecular Electrostatics

Science.gov (United States)

Dong, Feng; Olsen, Brett; Baker, Nathan A.

2008-01-01

An understanding of intermolecular interactions is essential for insight into how cells develop, operate, communicate and control their activities. Such interactions include several components: contributions from linear, angular, and torsional forces in covalent bonds, van der Waals forces, as well as electrostatics. Among the various components of molecular interactions, electrostatics are of special importance because of their long range and their influence on polar or charged molecules, including water, aqueous ions, and amino or nucleic acids, which are some of the primary components of living systems. Electrostatics, therefore, play important roles in determining the structure, motion and function of a wide range of biological molecules. This chapter presents a brief overview of electrostatic interactions in cellular systems with a particular focus on how computational tools can be used to investigate these types of interactions. PMID:17964951

Surface charges promote nonspecific nanoparticle adhesion to stiffer membranes

Science.gov (United States)

Sinha, Shayandev; Jing, Haoyuan; Sachar, Harnoor Singh; Das, Siddhartha

2018-04-01

This letter establishes the manner in which the electric double layer induced by the surface charges of the plasma membrane (PM) enhances the nonspecific adhesion (NSA) of a metal nanoparticle (NP) to stiffer PMs (i.e., PMs with larger bending moduli). The NSA is characterized by the physical attachment of the NP to the membrane and occurs when the decrease in the surface energy (or any other mechanism) associated with the attachment process provides the energy for bending the membrane. Such an attachment does not involve receptor-ligand interactions that characterize the specific membrane-NP adhesion. Here, we demonstrate that a significant decrease in the electrostatic energy caused by the NP-attachment-induced destruction of the charged-membrane-electrolyte interface is responsible for providing the additional energy needed for bending the membrane during the NP adhesion to stiffer membranes. A smaller salt concentration and a larger membrane charge density augment this effect, which can help to design drug delivery to cells with stiffer membranes due to pathological conditions, fabricate NPs with biomimetic cholesterol-rich lipid bilayer encapsulation, etc.

Electrostatic interactions in protein adsorption probed by comparing lysozyme and succinylated lysozyme

NARCIS (Netherlands)

Veen, van der M.; Norde, W.; Cohen Stuart, M.A.

2004-01-01

The influence of electrostatic interactions on protein adsorption was studied by comparing the adsorption of lysozyme and succinylated lysozyme at silica surfaces. The succinylation affects the charge of the protein, but also the stability. Although changes in stability can have an influence on

Transferability of polarizable models for ion-water electrostatic interaction

International Nuclear Information System (INIS)

Masia, Marco

2009-01-01

Studies of ion-water systems at condensed phase and at interfaces have pointed out that molecular and ionic polarization plays an important role for many phenomena ranging from hydrogen bond dynamics to water interfaces' structure. Classical and ab initio Molecular Dynamics simulations reveal that induced dipole moments at interfaces (e.g. air-water and water-protein) are usually high, hinting that polarizable models to be implemented in classical force fields should be very accurate in reproducing the electrostatic properties of the system. In this paper the electrostatic properties of three classical polarizable models for ion-water interaction are compared with ab initio results both at gas and condensed phase. For Li + - water and Cl - -water dimers the reproducibility of total dipole moments obtained with high level quantum chemical calculations is studied; for the same ions in liquid water, Car-Parrinello Molecular Dynamics simulations are used to compute the time evolution of ionic and molecular dipole moments, which are compared with the classical models. The PD2-H2O model developed by the author and coworkers [Masia et al. J. Chem. Phys. 2004, 121, 7362] together with the gaussian intermolecular damping for ion-water interaction [Masia et al. J. Chem. Phys. 2005, 123, 164505] showed to be the fittest in reproducing the ab initio results from gas to condensed phase, allowing for force field transferability.

Distinct binding interactions of HIV-1 Gag to Psi and non-Psi RNAs: Implications for viral genomic RNA packaging

OpenAIRE

Webb, Joseph A.; Jones, Christopher P.; Parent, Leslie J.; Rouzina, Ioulia; Musier-Forsyth, Karin

2013-01-01

The mechanism underlying the selective packaging of genomic RNA into HIV-1 virions is not known. This paper provides important new biophysical insights into the nature of protein–RNA interactions responsible for HIV-1 genome packaging by quantifying the electrostatic and hydrophobic contributions to specific and nonspecific RNA.

Effect of electrostatic Interactions on the Percolation Concentration of Fibrillar ß-Lactoglobuline Gels

NARCIS (Netherlands)

Veerman, C.; Ruis, H.G.M.; Sagis, L.M.C.; Linden, van der E.

2002-01-01

The effect of electrostatic interactions on the critical percolation concentration (cp) of fibrillar -lactoglobulin gels at pH 2 was investigated using rheological measurements, transmission electron microscopy (TEM), and performing conversion experiments. A decreasing cp with increasing ionic

One-dimensional Brownian motion of charged nanoparticles along microtubules: a model system for weak binding interactions.

Science.gov (United States)

Minoura, Itsushi; Katayama, Eisaku; Sekimoto, Ken; Muto, Etsuko

2010-04-21

Various proteins are known to exhibit one-dimensional Brownian motion along charged rodlike polymers, such as microtubules (MTs), actin, and DNA. The electrostatic interaction between the proteins and the rodlike polymers appears to be crucial for one-dimensional Brownian motion, although the underlying mechanism has not been fully clarified. We examined the interactions of positively-charged nanoparticles composed of polyacrylamide gels with MTs. These hydrophilic nanoparticles bound to MTs and displayed one-dimensional Brownian motion in a charge-dependent manner, which indicates that nonspecific electrostatic interaction is sufficient for one-dimensional Brownian motion. The diffusion coefficient decreased exponentially with an increasing particle charge (with the exponent being 0.10 kBT per charge), whereas the duration of the interaction increased exponentially (exponent of 0.22 kBT per charge). These results can be explained semiquantitatively if one assumes that a particle repeats a cycle of binding to and movement along an MT until it finally dissociates from the MT. During the movement, a particle is still electrostatically constrained in the potential valley surrounding the MT. This entire process can be described by a three-state model analogous to the Michaelis-Menten scheme, in which the two parameters of the equilibrium constant between binding and movement, and the rate of dissociation from the MT, are derived as a function of the particle charge density. This study highlights the possibility that the weak binding interactions between proteins and rodlike polymers, e.g., MTs, are mediated by a similar, nonspecific charge-dependent mechanism. Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Limiting assumptions in molecular modeling: electrostatics.

Science.gov (United States)

Marshall, Garland R

2013-02-01

Molecular mechanics attempts to represent intermolecular interactions in terms of classical physics. Initial efforts assumed a point charge located at the atom center and coulombic interactions. It is been recognized over multiple decades that simply representing electrostatics with a charge on each atom failed to reproduce the electrostatic potential surrounding a molecule as estimated by quantum mechanics. Molecular orbitals are not spherically symmetrical, an implicit assumption of monopole electrostatics. This perspective reviews recent evidence that requires use of multipole electrostatics and polarizability in molecular modeling.

Dependence of Interaction Free Energy between Solutes on an External Electrostatic Field

Directory of Open Access Journals (Sweden)

Pei-Kun Yang

2013-07-01

Full Text Available To explore the athermal effect of an external electrostatic field on the stabilities of protein conformations and the binding affinities of protein-protein/ligand interactions, the dependences of the polar and hydrophobic interactions on the external electrostatic field, −Eext, were studied using molecular dynamics (MD simulations. By decomposing Eext into, along, and perpendicular to the direction formed by the two solutes, the effect of Eext on the interactions between these two solutes can be estimated based on the effects from these two components. Eext was applied along the direction of the electric dipole formed by two solutes with opposite charges. The attractive interaction free energy between these two solutes decreased for solutes treated as point charges. In contrast, the attractive interaction free energy between these two solutes increased, as observed by MD simulations, for Eext = 40 or 60 MV/cm. Eext was applied perpendicular to the direction of the electric dipole formed by these two solutes. The attractive interaction free energy was increased for Eext = 100 MV/cm as a result of dielectric saturation. The force on the solutes along the direction of Eext computed from MD simulations was greater than that estimated from a continuum solvent in which the solutes were treated as point charges. To explore the hydrophobic interactions, Eext was applied to a water cluster containing two neutral solutes. The repulsive force between these solutes was decreased/increased for Eext along/perpendicular to the direction of the electric dipole formed by these two solutes.

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

Science.gov (United States)

Yigit, Cemil; Heyda, Jan; Dzubiella, Joachim

2015-08-14

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

Electrostatic interactions drive native-like aggregation of human alanine:glyoxylate aminostransferase.

Science.gov (United States)

Dindo, Mirco; Conter, Carolina; Cellini, Barbara

2017-11-01

Protein aggregate formation is the basis of several misfolding diseases, including those displaying loss-of-function pathogenesis. Although aggregation is often attributed to the population of intermediates exposing hydrophobic surfaces, the contribution of electrostatic forces has recently gained attention. Here, we combined computational and in vitro studies to investigate the aggregation process of human peroxisomal alanine:glyoxylate aminotransferase (AGT), a pyridoxal 5'-phosphate (PLP)-dependent enzyme involved in glyoxylate detoxification. We demonstrated that AGT is susceptible to electrostatic aggregation due to its peculiar surface charge anisotropy and that PLP binding counteracts the self-association process. The two polymorphic mutations P11L and I340M exert opposite effects. The P11L substitution enhances the aggregation tendency, probably by increasing surface charge anisotropy, while I340M plays a stabilizing role. In light of these results, we examined the effects of the most common missense mutations leading to primary hyperoxaluria type I (PH1), a rare genetic disorder associated with abnormal calcium oxalate precipitation in the urinary tract. All of them endow AGT with a strong electrostatic aggregation propensity. Moreover, we predicted that pathogenic mutations of surface residues could alter charge distribution, thus inducing aggregation under physiological conditions. A global model describing the AGT aggregation process is provided. Overall, the results indicate that the contribution of electrostatic interactions in determining the fate of proteins and the effect of amino acid substitutions should not be underestimated and provide the basis for the development of new therapeutic strategies for PH1 aimed at increasing AGT stability. © 2017 Federation of European Biochemical Societies.

The first step in layer-by-layer deposition: Electrostatics and/or non-electrostatics?

NARCIS (Netherlands)

Lyklema, J.; Deschênes, L.

2011-01-01

A critical discussion is presented on the properties and prerequisites of adsorbed polyelectrolytes that have to function as substrates for further layer-by-layer deposition. The central theme is discriminating between the roles of electrostatic and non-electrostatic interactions. In order to

Electrostatic fluctuations in soap films

International Nuclear Information System (INIS)

Dean, D.S.; Horgan, R.R.

2002-01-01

A field theory to describe electrostatic interactions in soap films, described by electric multilayers with a generalized thermodynamic surface-charging mechanism, is studied. In the limit where the electrostatic interactions are weak, this theory is exactly soluble. The theory incorporates in a consistent way, the surface-charging mechanism and the fluctuations in the electrostatic field that correspond to the zero-frequency component of the van der Waals force. It is shown that these terms lead to a Casimir-like attraction that can be sufficiently large to explain the transition between the common black film to a Newton black film

Specific Electrostatic Molecular Recognition in Water

DEFF Research Database (Denmark)

Li, Ming; Hoeck, Casper; Schoffelen, Sanne

2016-01-01

The identification of pairs of small peptides that recognize each other in water exclusively through electrostatic interactions is reported. The target peptide and a structure-biased combinatorial ligand library consisting of ≈78 125 compounds were synthesized on different sized beads. Peptide......-bead binding assay and by 2D NMR spectroscopy. Molecular dynamics (MD) studies revealed a putative mode of interaction for this unusual electrostatic binding event. High binding specificity occurred through a combination of topological matching and electrostatic and hydrogen-bond complementarities. From MD...

The electrostatic interaction of two point charges in equilibrium plasmas within the Debye approximation

International Nuclear Information System (INIS)

Filippov, A V

2015-01-01

This paper is devoted to a careful study of two charge interaction in an equilibrium plasma within the Debye approximation. The effect of external boundary conditions for the electric field strength and potential on the electrostatic force is studied. The problem is solved by the method of potential decomposition into Legendre polynomials up to the fifth multipole term included. It is shown that the effect of attraction of identically charged macroparticles is explained by the influence of the external boundary. When the size of a calculation cell is increased the attraction effect disappears and the electrostatic force is well described by the screened Debye-Hückel potential. (paper)

Understanding and Manipulating Electrostatic Fields at the Protein-Protein Interface Using Vibrational Spectroscopy and Continuum Electrostatics Calculations.

Science.gov (United States)

Ritchie, Andrew W; Webb, Lauren J

2015-11-05

Biological function emerges in large part from the interactions of biomacromolecules in the complex and dynamic environment of the living cell. For this reason, macromolecular interactions in biological systems are now a major focus of interest throughout the biochemical and biophysical communities. The affinity and specificity of macromolecular interactions are the result of both structural and electrostatic factors. Significant advances have been made in characterizing structural features of stable protein-protein interfaces through the techniques of modern structural biology, but much less is understood about how electrostatic factors promote and stabilize specific functional macromolecular interactions over all possible choices presented to a given molecule in a crowded environment. In this Feature Article, we describe how vibrational Stark effect (VSE) spectroscopy is being applied to measure electrostatic fields at protein-protein interfaces, focusing on measurements of guanosine triphosphate (GTP)-binding proteins of the Ras superfamily binding with structurally related but functionally distinct downstream effector proteins. In VSE spectroscopy, spectral shifts of a probe oscillator's energy are related directly to that probe's local electrostatic environment. By performing this experiment repeatedly throughout a protein-protein interface, an experimental map of measured electrostatic fields generated at that interface is determined. These data can be used to rationalize selective binding of similarly structured proteins in both in vitro and in vivo environments. Furthermore, these data can be used to compare to computational predictions of electrostatic fields to explore the level of simulation detail that is necessary to accurately predict our experimental findings.

Probing lipid membrane electrostatics

Science.gov (United States)

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 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

The role of electrostatic interactions in the Streptococcus thermophilus adhesion on human erythrocytes in media with different 2:1 electrolyte concentration

Directory of Open Access Journals (Sweden)

О. І. Гордієнко

2015-10-01

Full Text Available In the two-stage sorption model at the first stage is mostly reversible attachment, while at the second irreversible stage molecular and cellular adhesion processes take place. An important factor, influencing the adhesion processes, is physical-chemical characteristics of the medium, in particular, the presence of divalent cations therein. The aim of this work is to assess the role of electrostatic component of the intercellular interactions in media with different 2:1 electrolyte concentration at the first reversible stage of adhesion and probability of further occurrence of specific binding. Electrostatic interactions play a decisive role in intercellular adhesion process. The obtained experimental results and theoretical calculations of the electrostatic interaction parameters once again confirmed the acceptability of a two-stage model of sorption and DLVO theory to describe a cell-cell adhesion.

Electrostatic interactions in aqueous solutions of polyelectrolyte

International Nuclear Information System (INIS)

Belloni, Luc

1982-01-01

In this study, the structure, equilibrium and transport properties of poly-electrolytes solutions are reported. These dissymmetric systems are studied in the context of a primitive model (Charged hard spheres and rods in a solvent continuum). The first phenomenon studied is the strong electrostatic attractive interaction of counterions on the poly-ion surface. The model used considers the poly-ions on a matrix and the different concentrations are calculated using the P.B. equation. Auto-diffusion coefficients obtained give a good description of experimental slowing down of the counterions. The model allows a correlation between the theoretical limits represented by Bjerrum's and Manning's models and gives a physical significance to the concept of condensation. In the second part, the complete structure is calculated using only slightly restrictive H.N.C. approximation. This theory enables all the pair correlation functions to be calculated as well as thermodynamic data and structure factors. The last part of this study treats transport phenomena. Quasi-elastic light scattering gives information on the autocorrelation function of the scattered light intensity. Analysis using cumulants leads to an effective diffusion coefficient which is theoretically related to the structure factor and the hydrodynamic interactions. A crude approximation of the last contribution allows to fit the experimental data. (author) [fr

Electrostatic tuning of permeation and selectivity in aquaporin water channels

DEFF Research Database (Denmark)

Jensen, Mogens O Stibius; Tajkhorshid, E.; Schulten, K.

2003-01-01

Water permeation and electrostatic interactions between water and channel are investigated in the Escherichia coli glycerol uptake facilitator GlpF, a member of the aquaporin water channel family, by molecular dynamics simulations. A tetrameric model of the channel embedded in a 16:0/ 18:1c9...... with the protein electrostatic fields enforce a bipolar water configuration inside the channel with dipole inversion at the NPA motifs. At the NPA motifs water-protein electrostatic interactions facilitate this inversion. Furthermore, water-water electrostatic interactions are in all regions inside the channel...... stronger than water-protein interactions, except near a conserved, positively charged Arg residue. We find that variations of the protein electrostatic field through the channel, owing to preserved structural features, completely explain the bipolar orientation of water. This orientation persists despite...

The impact of electrostatic interactions on ultrafast charge transfer at Ag 29 nanoclusters–fullerene and CdTe quantum dots–fullerene interfaces

KAUST Repository

Ahmed, Ghada H.

2015-11-09

A profound understanding of charge transfer (CT) at semiconductor quantum dots (QDs) and nanoclusters (NCs) interfaces is extremely important to optimize the energy conversion efficiency in QDs and NCs-based solar cell devices. Here, we report on the ground- and excited-state interactions at the interface of two different bimolecular non-covalent donor-acceptor (D-A) systems using steady-state and femtosecond transient absorption (fs-TA) spectroscopy with broadband capabilities. We systematically investigate the electrostatic interactions between the positively charged fullerene derivative C60-(N,N dimethylpyrrolidinium iodide) (CF) employed as an efficient molecular acceptor and two different donor molecules: Ag29 nanoclusters (NCs) and CdTe quantum dots (QDs). For comparison purposes, we also monitor the interaction of each donor molecule with the neutral fullerene derivative C60-(malonic acid)n, which has minimal electrostatic interactions. Our steady-state and time-resolved data demonstrate that both QDs and NCs have strong interfacial electrostatic interactions and dramatic fluorescence quenching when the CF derivative is present. In other words, our results reveal that only CF can be in close molecular proximity with the QDs and NCs, allowing ultrafast photoinduced CT to occur. It turned out that the intermolecular distances, electronic coupling and subsequently CT from the excited QDs or NCs to fullerene derivatives can be controlled by the interfacial electrostatic interactions. Our findings highlight some of the key variable components for optimizing CT at QDs and NCs interfaces, which can also be applied to other D-A systems that rely on interfacial CT. © The Royal Society of Chemistry 2016.

Tuning of electrostatic vs. depletion interaction in deciding the phase behavior of nanoparticle-polymer system

Energy Technology Data Exchange (ETDEWEB)

Kumar, Sugam, E-mail: sugam@barc.gov.in; Aswal, V. K. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Kohlbrecher, J. [Laboratory for Neutron Scattering, Paul Scherrer Institut, H-5232 PSI Villigen (Switzerland)

2015-06-24

Nanoparticle-polymer system interestingly show a re-entrant phase behavior where charge stabilized silica nanoparticles (phase I) undergo particle clustering (phase II) and then back to individual particles (phase I) as a function of polymer concentration. Such phase behavior arises as a result of dominance of various interactions (i) nanoparticle-nanoparticle electrostatic repulsion (ii) polymer induced attractive depletion between nanoparticles and (iii) polymer-polymer repulsion, at different concentration regimes. Small-angle neutron scattering (SANS) has been used to study the evolution of interaction during this re-entrant phase behavior of nanoparticles by contrast-marching the polymer. The SANS data have been modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The degree of both of these parts has been separately tuned by varying the polymer concentration and ionic strength of the solution. Both of these parts are found to have long-range nature. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the strength of depletion leading to re-entrant phase behavior. The clusters formed under depletion attraction are found to have surface fractal morphology.

Tuning of electrostatic vs. depletion interaction in deciding the phase behavior of nanoparticle-polymer system

International Nuclear Information System (INIS)

Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

2015-01-01

Nanoparticle-polymer system interestingly show a re-entrant phase behavior where charge stabilized silica nanoparticles (phase I) undergo particle clustering (phase II) and then back to individual particles (phase I) as a function of polymer concentration. Such phase behavior arises as a result of dominance of various interactions (i) nanoparticle-nanoparticle electrostatic repulsion (ii) polymer induced attractive depletion between nanoparticles and (iii) polymer-polymer repulsion, at different concentration regimes. Small-angle neutron scattering (SANS) has been used to study the evolution of interaction during this re-entrant phase behavior of nanoparticles by contrast-marching the polymer. The SANS data have been modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The degree of both of these parts has been separately tuned by varying the polymer concentration and ionic strength of the solution. Both of these parts are found to have long-range nature. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the strength of depletion leading to re-entrant phase behavior. The clusters formed under depletion attraction are found to have surface fractal morphology

Direct electron and ion fluid computation of high electrostatic fields in dense inhomogeneous plasmas with subsequent nonlinear optical and dynamical laser interaction

International Nuclear Information System (INIS)

Lalousis, P.

1984-01-01

Nonthermal direct electrodynamic interaction between laser energy and a fully ionized plasma was studied. The particular emphasis is on the action of nonlinear forces, in which the optical electromagnetic fields act on the plasma electrons which then transfer their energy to the ions electrostatically. Instead of the usual single fluid model, the plasma is treated as two separate conducting fluids for electrons and ions, coupled by momentum and Coulomb interactions. The equations governing the two fluids are derived from first principles, and numerical algorithms for computing these equations are developed, enabling the plasma oscillatons to be resolved and studied. Fully ionized plasma expansion without laser irradiation is studied first numerically. Remarkable damping mechanisms by coupling to ion oscillations have been observed. Inhomogeneities in densities of the two fluids result in large electrostatic fields and double layers are generated. There is quite close agreement between numerically calculated electrostatic fields and analytical solutions. Laser interaction with fully ionized plasma is also studied numerically. The generation of cavitons is numerically observed, and it is inferred that laser plasma interactions produce very high electrostatic fields in the vicinity of cavitons. It is further shown that charge neutrality is not necessarily maintained in a caviton

Loop electrostatics modulates the intersubunit interactions in ferritin.

Science.gov (United States)

Bernacchioni, Caterina; Ghini, Veronica; Pozzi, Cecilia; Di Pisa, Flavio; Theil, Elizabeth C; Turano, Paola

2014-11-21

Functional ferritins are 24-mer nanocages that self-assemble with extended contacts between pairs of 4-helix bundle subunits coupled in an antiparallel fashion along the C2 axes. The largest intersubunit interaction surface in the ferritin nanocage involves helices, but contacts also occur between groups of three residues midway in the long, solvent-exposed L-loops of facing subunits. The anchor points between intersubunit L-loop pairs are the salt bridges between the symmetry-related, conserved residues Asp80 and Lys82. The resulting quaternary structure of the cage is highly soluble and thermostable. Substitution of negatively charged Asp80 with a positively charged Lys in homopolymeric M ferritin introduces electrostatic repulsions that inhibit the oligomerization of the ferritin subunits. D80K ferritin was present in inclusion bodies under standard overexpressing conditions in E. coli, contrasting with the wild type protein. Small amounts of fully functional D80K nanocages formed when expression was slowed. The more positively charged surface results in a different solubility profile and D80K crystallized in a crystal form with a low density packing. The 3D structure of D80K variant is the same as wild type except for the side chain orientations of Lys80 and facing Lys82. When three contiguous Lys groups are introduced in D80KI81K ferritin variant the nanocage assembly is further inhibited leading to lower solubility and reduced thermal stability. Here, we demonstrate that the electrostatic pairing at the center of the L-loops has a specific kinetic role in the self-assembly of ferritin nanocages.

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

Science.gov (United States)

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.

Influence of nanoparticle-membrane electrostatic interactions on membrane fluidity and bending elasticity.

Science.gov (United States)

Santhosh, Poornima Budime; Velikonja, Aljaž; Perutkova, Šarka; Gongadze, Ekaterina; Kulkarni, Mukta; Genova, Julia; Eleršič, Kristina; Iglič, Aleš; Kralj-Iglič, Veronika; Ulrih, Nataša Poklar

2014-02-01

The aim of this work is to investigate the effect of electrostatic interactions between the nanoparticles and the membrane lipids on altering the physical properties of the liposomal membrane such as fluidity and bending elasticity. For this purpose, we have used nanoparticles and lipids with different surface charges. Positively charged iron oxide (γ-Fe2O3) nanoparticles, neutral and negatively charged cobalt ferrite (CoFe2O4) nanoparticles were encapsulated in neutral lipid 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine and negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine lipid mixture. Membrane fluidity was assessed through the anisotropy measurements using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Though the interaction of both the types of nanoparticles reduced the membrane fluidity, the results were more pronounced in the negatively charged liposomes encapsulated with positively charged iron oxide nanoparticles due to strong electrostatic attractions. X-ray photoelectron spectroscopy results also confirmed the presence of significant quantity of positively charged iron oxide nanoparticles in negatively charged liposomes. Through thermally induced shape fluctuation measurements of the giant liposomes, a considerable reduction in the bending elasticity modulus was observed for cobalt ferrite nanoparticles. The experimental results were supported by the simulation studies using modified Langevin-Poisson-Boltzmann model. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Interaction between two point-like charges in nonlinear electrostatics

Energy Technology Data Exchange (ETDEWEB)

Breev, A.I. [Tomsk State University, Tomsk (Russian Federation); Tomsk Polytechnic University, Tomsk (Russian Federation); Shabad, A.E. [P.N. Lebedev Physical Institute, Moscow (Russian Federation); Tomsk State University, Tomsk (Russian Federation)

2018-01-15

We consider two point-like charges in electrostatic interaction within the framework of a nonlinear model, associated with QED, that provides finiteness of their field energy. We find the common field of the two charges in a dipole-like approximation, where the separation between them R is much smaller than the observation distance r: with the linear accuracy with respect to the ratio R/r, and in the opposite approximation, where R >> r, up to the term quadratic in the ratio r/R. The consideration proposes the law a + bR{sup 1/3} for the energy, when the charges are close to one another, R → 0. This leads to the singularity of the force between them to be R{sup -2/3}, which is weaker than the Coulomb law, R{sup -2}. (orig.)

Interaction between two point-like charges in nonlinear electrostatics

Science.gov (United States)

Breev, A. I.; Shabad, A. E.

2018-01-01

We consider two point-like charges in electrostatic interaction within the framework of a nonlinear model, associated with QED, that provides finiteness of their field energy. We find the common field of the two charges in a dipole-like approximation, where the separation between them R is much smaller than the observation distance r : with the linear accuracy with respect to the ratio R / r, and in the opposite approximation, where R≫ r, up to the term quadratic in the ratio r / R. The consideration proposes the law a+b R^{1/3} for the energy, when the charges are close to one another, R→ 0. This leads to the singularity of the force between them to be R^{-2/3}, which is weaker than the Coulomb law, R^{-2}.

Electrostatic similarities between protein and small molecule ligands facilitate the design of protein-protein interaction inhibitors.

Directory of Open Access Journals (Sweden)

Arnout Voet

Full Text Available One of the underlying principles in drug discovery is that a biologically active compound is complimentary in shape and molecular recognition features to its receptor. This principle infers that molecules binding to the same receptor may share some common features. Here, we have investigated whether the electrostatic similarity can be used for the discovery of small molecule protein-protein interaction inhibitors (SMPPIIs. We have developed a method that can be used to evaluate the similarity of electrostatic potentials between small molecules and known protein ligands. This method was implemented in a software called EleKit. Analyses of all available (at the time of research SMPPII structures indicate that SMPPIIs bear some similarities of electrostatic potential with the ligand proteins of the same receptor. This is especially true for the more polar SMPPIIs. Retrospective analysis of several successful SMPPIIs has shown the applicability of EleKit in the design of new SMPPIIs.

Biomolecular electrostatics and solvation: a computational perspective.

Science.gov (United States)

Ren, Pengyu; Chun, Jaehun; Thomas, Dennis G; Schnieders, Michael J; Marucho, Marcelo; Zhang, Jiajing; Baker, Nathan A

2012-11-01

An understanding of molecular interactions is essential for insight into biological systems at the molecular scale. Among the various components of molecular interactions, electrostatics are of special importance because of their long-range nature and their influence on polar or charged molecules, including water, aqueous ions, proteins, nucleic acids, carbohydrates, and membrane lipids. In particular, robust models of electrostatic interactions are essential for understanding the solvation properties of biomolecules and the effects of solvation upon biomolecular folding, binding, enzyme catalysis, and dynamics. Electrostatics, therefore, are of central importance to understanding biomolecular structure and modeling interactions within and among biological molecules. This review discusses the solvation of biomolecules with a computational biophysics view toward describing the phenomenon. While our main focus lies on the computational aspect of the models, we provide an overview of the basic elements of biomolecular solvation (e.g. solvent structure, polarization, ion binding, and non-polar behavior) in order to provide a background to understand the different types of solvation models.

Multipolar electrostatics for proteins: atom-atom electrostatic energies in crambin.

Science.gov (United States)

Yuan, Yongna; Mills, Matthew J L; Popelier, Paul L A

2014-02-15

Accurate electrostatics necessitates the use of multipole moments centered on nuclei or extra point charges centered away from the nuclei. Here, we follow the former alternative and investigate the convergence behavior of atom-atom electrostatic interactions in the pilot protein crambin. Amino acids are cut out from a Protein Data Bank structure of crambin, as single amino acids, di, or tripeptides, and are then capped with a peptide bond at each side. The atoms in the amino acids are defined through Quantum Chemical Topology (QCT) as finite volume electron density fragments. Atom-atom electrostatic energies are computed by means of a multipole expansion with regular spherical harmonics, up to a total interaction rank of L = ℓA+ ℓB + 1 = 10. The minimum internuclear distance in the convergent region of all the 15 possible types of atom-atom interactions in crambin that were calculated based on single amino acids are close to the values calculated from di and tripeptides. Values obtained at B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels are only slightly larger than those calculated at HF/6-31G(d,p) level. This convergence behavior is transferable to the well-known amyloid beta polypeptide Aβ1-42. Moreover, for a selected central atom, the influence of its neighbors on its multipole moments is investigated, and how far away this influence can be ignored is also determined. Finally, the convergence behavior of AMBER becomes closer to that of QCT with increasing internuclear distance. Copyright © 2013 Wiley Periodicals, Inc.

Electrostatic Phenomena on Planetary Surfaces

Science.gov (United States)

Calle, Carlos I.

2017-02-01

The diverse planetary environments in the solar system react in somewhat different ways to the encompassing influence of the Sun. These different interactions define the electrostatic phenomena that take place on and near planetary surfaces. The desire to understand the electrostatic environments of planetary surfaces goes beyond scientific inquiry. These environments have enormous implications for both human and robotic exploration of the solar system. This book describes in some detail what is known about the electrostatic environment of the solar system from early and current experiments on Earth as well as what is being learned from the instrumentation on the space exploration missions (NASA, European Space Agency, and the Japanese Space Agency) of the last few decades. It begins with a brief review of the basic principles of electrostatics.

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

Science.gov (United States)

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

Instability of nanocantilever arrays in electrostatic and van der Waals interactions

Energy Technology Data Exchange (ETDEWEB)

Ramezani, Asghar [Department of Automotive Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Alasty, Aria, E-mail: aramezani@iust.ac.i, E-mail: aalasti@sharif.ed [Center of Excellence in Design, Robotics, and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

2009-11-21

The structural instability of an array of cantilevers, each of which interacts with two neighbouring beams through electrostatic and van der Waals forces, is studied. Distributed and lumped parameter modelling of the array result in a set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations, respectively. These coupled nonlinear systems are solved numerically for different numbers of beams in the array to obtain the pull-in parameters. The pull-in parameters converge to constant values with an increase in the number of beams in the array. These constants, which are important in the design of cantilever arrays, are compared for the distributed and lumped parameter models.

Manipulation and Investigation of Uniformly-Spaced Nanowire Array on a Substrate via Dielectrophoresis and Electrostatic Interaction

Directory of Open Access Journals (Sweden)

U Hyeok Choi

2018-06-01

Full Text Available Directed-assembly of nanowires on the dielectrics-covered parallel electrode structure is capable of producing uniformly-spaced nanowire array at the electrode gap due to dielectrophoretic nanowire attraction and electrostatic nanowire repulsion. Beyond uniformly-spaced nanowire array formation, the control of spacing in the array is beneficial in that it should be the experimental basis of the precise positioning of functional nanowires on a circuit. Here, we investigate the material parameters and bias conditions to modulate the nanowire spacing in the ordered array, where the nanowire array formation is readily attained due to the electrostatic nanowire interaction. A theoretical model for the force calculation and the simulation of the induced charge in the assembled nanowire verifies that the longer nanowires on thicker dielectric layer tend to be assembled with a larger pitch due to the stronger nanowire-nanowire electrostatic repulsion, which is consistent with the experimental results. It was claimed that the stronger dielectrophoretic force is likely to attract more nanowires that are suspended in solution at the electrode gap, causing them to be less-spaced. Thus, we propose a generic mechanism, competition of dielectrophoretic and electrostatic force, to determine the nanowire pitch in an ordered array. Furthermore, this spacing-controlled nanowire array offers a way to fabricate the high-density nanodevice array without nanowire registration.

Protein-protein interactions in paralogues: Electrostatics modulates specificity on a conserved steric scaffold.

Directory of Open Access Journals (Sweden)

Stefan M Ivanov

Full Text Available An improved knowledge of protein-protein interactions is essential for better understanding of metabolic and signaling networks, and cellular function. Progress tends to be based on structure determination and predictions using known structures, along with computational methods based on evolutionary information or detailed atomistic descriptions. We hypothesized that for the case of interactions across a common interface, between proteins from a pair of paralogue families or within a family of paralogues, a relatively simple interface description could distinguish between binding and non-binding pairs. Using binding data for several systems, and large-scale comparative modeling based on known template complex structures, it is found that charge-charge interactions (for groups bearing net charge are generally a better discriminant than buried non-polar surface. This is particularly the case for paralogue families that are less divergent, with more reliable comparative modeling. We suggest that electrostatic interactions are major determinants of specificity in such systems, an observation that could be used to predict binding partners.

Protein-protein interactions in paralogues: Electrostatics modulates specificity on a conserved steric scaffold.

Science.gov (United States)

Ivanov, Stefan M; Cawley, Andrew; Huber, Roland G; Bond, Peter J; Warwicker, Jim

2017-01-01

An improved knowledge of protein-protein interactions is essential for better understanding of metabolic and signaling networks, and cellular function. Progress tends to be based on structure determination and predictions using known structures, along with computational methods based on evolutionary information or detailed atomistic descriptions. We hypothesized that for the case of interactions across a common interface, between proteins from a pair of paralogue families or within a family of paralogues, a relatively simple interface description could distinguish between binding and non-binding pairs. Using binding data for several systems, and large-scale comparative modeling based on known template complex structures, it is found that charge-charge interactions (for groups bearing net charge) are generally a better discriminant than buried non-polar surface. This is particularly the case for paralogue families that are less divergent, with more reliable comparative modeling. We suggest that electrostatic interactions are major determinants of specificity in such systems, an observation that could be used to predict binding partners.

Electrostatics, structure prediction, and the energy landscapes for protein folding and binding.

Science.gov (United States)

Tsai, Min-Yeh; Zheng, Weihua; Balamurugan, D; Schafer, Nicholas P; Kim, Bobby L; Cheung, Margaret S; Wolynes, Peter G

2016-01-01

While being long in range and therefore weakly specific, electrostatic interactions are able to modulate the stability and folding landscapes of some proteins. The relevance of electrostatic forces for steering the docking of proteins to each other is widely acknowledged, however, the role of electrostatics in establishing specifically funneled landscapes and their relevance for protein structure prediction are still not clear. By introducing Debye-Hückel potentials that mimic long-range electrostatic forces into the Associative memory, Water mediated, Structure, and Energy Model (AWSEM), a transferable protein model capable of predicting tertiary structures, we assess the effects of electrostatics on the landscapes of thirteen monomeric proteins and four dimers. For the monomers, we find that adding electrostatic interactions does not improve structure prediction. Simulations of ribosomal protein S6 show, however, that folding stability depends monotonically on electrostatic strength. The trend in predicted melting temperatures of the S6 variants agrees with experimental observations. Electrostatic effects can play a range of roles in binding. The binding of the protein complex KIX-pKID is largely assisted by electrostatic interactions, which provide direct charge-charge stabilization of the native state and contribute to the funneling of the binding landscape. In contrast, for several other proteins, including the DNA-binding protein FIS, electrostatics causes frustration in the DNA-binding region, which favors its binding with DNA but not with its protein partner. This study highlights the importance of long-range electrostatics in functional responses to problems where proteins interact with their charged partners, such as DNA, RNA, as well as membranes. © 2015 The Protein Society.

Recurrent activity in higher order, modality non-specific brain regions

DEFF Research Database (Denmark)

Lou, Hans Olav Christensen; Joensson, Morten; Biermann-Ruben, Katja

2011-01-01

It has been proposed that the workings of the brain are mainly intrinsically generated recurrent neuronal activity, with sensory inputs as modifiers of such activity in both sensory and higher order modality non-specific regions. This is supported by the demonstration of recurrent neuronal activity...... in the visual system as a response to visual stimulation. In contrast recurrent activity has never been demonstrated before in higher order modality non-specific regions. Using magneto-encephalography and Granger causality analysis, we tested in a paralimbic network the hypothesis that stimulation may enhance...... causal recurrent interaction between higher-order, modality non-specific regions. The network includes anterior cingulate/medial prefrontal and posterior cingulate/medial parietal cortices together with pulvinar thalami, a network known to be effective in autobiographic memory retrieval and self...

Modulation of electrostatic interactions to improve controlled drug delivery from nanogels

Energy Technology Data Exchange (ETDEWEB)

Mauri, Emanuele; Chincarini, Giulia M.F.; Rigamonti, Riccardo; Magagnin, Luca; Sacchetti, Alessandro, E-mail: alessandro.sacchetti@polimi.it; Rossi, Filippo, E-mail: filippo.rossi@polimi.it

2017-03-01

The synthesis of nanogels as devices capable to maintain the drug level within a desired range for a long and sustained period of time is a leading strategy in controlled drug delivery. However, with respect to the good results obtained with antibodies and peptides there are a lot of problems related to the quick and uncontrolled diffusion of small hydrophilic molecules through polymeric network pores. For these reasons research community is pointing toward the use of click strategies to reduce release rates of the linked drugs to the polymer chains. Here we propose an alternative method that considers the electrostatic interactions between polymeric chains and drugs to tune the release kinetics from nanogel network. The main advantage of these systems lies in the fact that the carried drugs are not modified and no chemical reactions take place during their loading and release. In this work we synthesized PEG-PEI based nanogels with different protonation degrees and the release kinetics with charged and uncharged drug mimetics (sodium fluorescein, SF, and rhodamine B, RhB) were studied. Moreover, also the effect of counterion used to induce protonation was taken into account in order to build a tunable drug delivery system able to provide multiple release rates with the same device. - Highlights: • The design of nanogels as drug delivery systems based on electrostatic interaction among drug and polymers is proposed. • Nanogels can be synthetized tuning their positive charge density, according to the protonation of PEI at different pH. • No biorthogonal chemistry strategies are applied to the polymers or drugs. • Drug release is efficiently modulated by charge density of PEI chains. • The effect of counterion on nanogel synthesis is investigated and allows controlling the drug release.

Nonlinear Dynamics of Carbon Nanotubes Under Large Electrostatic Force

KAUST Repository

Xu, Tiantian; Younis, Mohammad I.

2015-01-01

Because of the inherent nonlinearities involving the behavior of CNTs when excited by electrostatic forces, modeling and simulating their behavior is challenging. The complicated form of the electrostatic force describing the interaction

Geometry-Dependent Electrostatics near Contact Lines

International Nuclear Information System (INIS)

Chou, Tom

2001-01-01

Long-ranged electrostatic interactions in electrolytes modify contact angles on charged substrates in a scale and geometry-dependent manner. For angles measured at scales smaller than the typical Debye screening length, the wetting geometry near the contact line must be explicitly considered. Using variational and asymptotic methods, we derive new transcendental equations for the contact angle as functions of the electrostatic potential only at the three phase contact line. Analytic expressions are found in certain limits and compared with predictions for contact angles measured with lower resolution. An estimate for electrostatic contributions to line tension is also given

Electrostatic screening in classical Coulomb fluids: exponential or power-law decay or both? An investigation into the effect of dispersion interactions

International Nuclear Information System (INIS)

Kjellander, Roland

2006-01-01

It is shown that the nature of the non-electrostatic part of the pair interaction potential in classical Coulomb fluids can have a profound influence on the screening behaviour. Two cases are compared: (i) when the non-electrostatic part equals an arbitrary finite-ranged interaction and (ii) when a dispersion r -6 interaction potential is included. A formal analysis is done in exact statistical mechanics, including an investigation of the bridge function. It is found that the Coulombic r -1 and the dispersion r -6 potentials are coupled in a very intricate manner as regards the screening behaviour. The classical one-component plasma (OCP) is a particularly clear example due to its simplicity and is investigated in detail. When the dispersion r -6 potential is turned on, the screened electrostatic potential from a particle goes from a monotonic exponential decay, exp(-κr)/r, to a power-law decay, r -8 , for large r. The pair distribution function acquire, at the same time, an r -10 decay for large r instead of the exponential one. There still remains exponentially decaying contributions to both functions, but these contributions turn oscillatory when the r -6 interaction is switched on. When the Coulomb interaction is turned off but the dispersion r -6 pair potential is kept, the decay of the pair distribution function for large r goes over from the r -10 to an r -6 behaviour, which is the normal one for fluids of electroneutral particles with dispersion interactions. Differences and similarities compared to binary electrolytes are pointed out

Bounding the electrostatic free energies associated with linear continuum models of molecular solvation.

Science.gov (United States)

Bardhan, Jaydeep P; Knepley, Matthew G; Anitescu, Mihai

2009-03-14

The importance of electrostatic interactions in molecular biology has driven extensive research toward the development of accurate and efficient theoretical and computational models. Linear continuum electrostatic theory has been surprisingly successful, but the computational costs associated with solving the associated partial differential equations (PDEs) preclude the theory's use in most dynamical simulations. Modern generalized-Born models for electrostatics can reproduce PDE-based calculations to within a few percent and are extremely computationally efficient but do not always faithfully reproduce interactions between chemical groups. Recent work has shown that a boundary-integral-equation formulation of the PDE problem leads naturally to a new approach called boundary-integral-based electrostatics estimation (BIBEE) to approximate electrostatic interactions. In the present paper, we prove that the BIBEE method can be used to rigorously bound the actual continuum-theory electrostatic free energy. The bounds are validated using a set of more than 600 proteins. Detailed numerical results are presented for structures of the peptide met-enkephalin taken from a molecular-dynamics simulation. These bounds, in combination with our demonstration that the BIBEE methods accurately reproduce pairwise interactions, suggest a new approach toward building a highly accurate yet computationally tractable electrostatic model.

Bounding the electrostatic free energies associated with linear continuum models of molecular solvation.

Energy Technology Data Exchange (ETDEWEB)

Bardhan, J. P.; Knepley, M. G.; Anitescu, M. (Biosciences Division); ( MCS); (Rush Univ.)

2009-03-01

The importance of electrostatic interactions in molecular biology has driven extensive research toward the development of accurate and efficient theoretical and computational models. Linear continuum electrostatic theory has been surprisingly successful, but the computational costs associated with solving the associated partial differential equations (PDEs) preclude the theory's use in most dynamical simulations. Modern generalized-Born models for electrostatics can reproduce PDE-based calculations to within a few percent and are extremely computationally efficient but do not always faithfully reproduce interactions between chemical groups. Recent work has shown that a boundary-integral-equation formulation of the PDE problem leads naturally to a new approach called boundary-integral-based electrostatics estimation (BIBEE) to approximate electrostatic interactions. In the present paper, we prove that the BIBEE method can be used to rigorously bound the actual continuum-theory electrostatic free energy. The bounds are validated using a set of more than 600 proteins. Detailed numerical results are presented for structures of the peptide met-enkephalin taken from a molecular-dynamics simulation. These bounds, in combination with our demonstration that the BIBEE methods accurately reproduce pairwise interactions, suggest a new approach toward building a highly accurate yet computationally tractable electrostatic model.

Lipid bilayers driven to a wrong lane in molecular dynamics simulations by subtle changes in long-range electrostatic interactions

NARCIS (Netherlands)

Patra, M.; Karttunen, M.E.J.; Hyvönen, M.T.; Falck, E.; Vattulainen, I.

2004-01-01

We provide compelling evidence that different treatments of electrostatic interactions in molecular dynamics simulations may dramatically affect dynamic properties of lipid bilayers. To this end, we consider a fully hydrated pure dipalmitoylphosphatidylcholine bilayer through 50-ns molecular

Electrostatic energy and screened charge interaction near the surface of metals with different Fermi surface shape

Science.gov (United States)

Gabovich, A. M.; Il'chenko, L. G.; Pashitskii, E. A.; Romanov, Yu. A.

1980-04-01

Using the Poisson equation Green function for a self-consistent field in a spatially inhomogeneous system, expressions for the electrostatic energy and screened charge interaction near the surface of a semi-infinite metal and a thin quantizing film are derived. It is shown that the decrease law and Friedel oscillation amplitude of adsorbed atom indirect interaction are determined by the electron spectrum character and the Fermi surface shape. The results obtained enable us to explain, in particular, the submonolayer adsorbed film structure on the W and Mo surfaces.

Interactions of a zwitterionic thiophene-based conjugated polymer with surfactants

DEFF Research Database (Denmark)

Costa, Telma; De Azevedo, Diego; Stewart, Beverly

2015-01-01

In this paper we investigate the optical and structural properties of a zwitterionic poly[3-(N-(4-sulfonato-1-butyl)-N,N-diethylammonium)hexyl-2,5-thiophene] (P3SBDEAHT) conjugated polyelectrolyte (CPE) and its interaction in water with surfactants, using absorption, photoluminescence (PL......), electrical conductivity, molecular dynamics simulations (MDS) and small-angle X-ray scattering (SAXS). Different surfactants were studied to evaluate the effect of the head group and chain length on the self-assembly. PL data emphasize the importance of polymer-surfactant electrostatic interactions...... in the formation of complexes. Nevertheless, conductivity and MDS data have shown that nonspecific interactions also play an important role. These seem to be responsible for the spatial position of the surfactant tail in the complex and, eventually, for breaking-up P3SBDEAHT aggregates. SAXS measurements on P3...

Predicting the influence of long-range molecular interactions on macroscopic-scale diffusion by homogenization of the Smoluchowski equation

Energy Technology Data Exchange (ETDEWEB)

Kekenes-Huskey, P. M., E-mail: pkekeneshuskey@ucsd.edu [Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0636 (United States); Gillette, A. K. [Department of Mathematics, University of Arizona, Tucson, Arizona 85721-0089 (United States); McCammon, J. A. [Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0636 (United States); Department of Chemistry, Howard Hughes Medical Institute, University of California San Diego, La Jolla, California 92093-0636 (United States)

2014-05-07

The macroscopic diffusion constant for a charged diffuser is in part dependent on (1) the volume excluded by solute “obstacles” and (2) long-range interactions between those obstacles and the diffuser. Increasing excluded volume reduces transport of the diffuser, while long-range interactions can either increase or decrease diffusivity, depending on the nature of the potential. We previously demonstrated [P. M. Kekenes-Huskey et al., Biophys. J. 105, 2130 (2013)] using homogenization theory that the configuration of molecular-scale obstacles can both hinder diffusion and induce diffusional anisotropy for small ions. As the density of molecular obstacles increases, van der Waals (vdW) and electrostatic interactions between obstacle and a diffuser become significant and can strongly influence the latter's diffusivity, which was neglected in our original model. Here, we extend this methodology to include a fixed (time-independent) potential of mean force, through homogenization of the Smoluchowski equation. We consider the diffusion of ions in crowded, hydrophilic environments at physiological ionic strengths and find that electrostatic and vdW interactions can enhance or depress effective diffusion rates for attractive or repulsive forces, respectively. Additionally, we show that the observed diffusion rate may be reduced independent of non-specific electrostatic and vdW interactions by treating obstacles that exhibit specific binding interactions as “buffers” that absorb free diffusers. Finally, we demonstrate that effective diffusion rates are sensitive to distribution of surface charge on a globular protein, Troponin C, suggesting that the use of molecular structures with atomistic-scale resolution can account for electrostatic influences on substrate transport. This approach offers new insight into the influence of molecular-scale, long-range interactions on transport of charged species, particularly for diffusion-influenced signaling events

The dust acoustic wave in a bounded dusty plasma with strong electrostatic interactions between dust grains

International Nuclear Information System (INIS)

Shukla, Nitin; Shukla, P.K.

2011-01-01

The dispersion relation for the dust acoustic wave (DAW) in an unmagnetized dusty plasma cylindrical waveguide is derived, accounting for strong electrostatic interactions between charged dust grains. It is found that the boundary effect limits the radial extent of the DAW. The present result should be helpful for understanding the frequency spectrum of the DAW in a dusty plasma waveguide with strongly coupled charged dust grains. - Highlights: → We study the dust acoustic wave (DAW) in a bounded plasma. → We account for interactions between dust grains. → The boundary effect limits the radial extent of the DAW.

Nonlocal electrostatics in ionic liquids: The key to an understanding of the screening decay length and screened interactions

Science.gov (United States)

Kjellander, Roland

2016-09-01

Screened electrostatic interactions in ionic liquids are investigated by means of exact statistical mechanical analysis combined with physical arguments that enhance the transparency and conceptual accessibility of the analysis and results. The constituent ions and immersed particles in the liquid can have arbitrary shapes and any internal charge distributions. The decay of the screened electrostatic potential and the free energy of interaction in ionic liquids can be exponentially damped oscillatory (like in molten simple salts) as well as plain exponential and long-ranged (like in dilute electrolyte solutions). Both behaviors are in agreement with the exact statistical mechanical analysis and reasons for their appearances are investigated. Exact but surprisingly simple expressions for the decay parameter κ of the screened electrostatics are obtained, which replace the classical expression for the Debye-Hückel parameter κDH (the reciprocal Debye length). The expressions are applicable both for cases with plain exponential and oscillatory behaviors. The key importance of nonlocal electrostatics is thereby demonstrated explicitly. Dielectric properties of ionic liquids and other electrolytes are investigated, in particular the static dielectric function ɛ ˜ ( k ) and some effective relative permittivities ( Er eff and Er ∗ ), which take roles that the dielectric constant ɛr has for polar liquids consisting of electroneutral molecules. The dielectric constant in the latter case, which is the limit of ɛ ˜ ( k ) when the wave number k → 0, can be expressed solely in terms of dipolar features of the molecules. In contrast to this, the effective dielectric permittivities of ionic liquids have contributions also from quadrupolar, octupolar, and higher multipolar features of the constituent ions. The "dielectric constant" of electrolytes does not exist since ɛ ˜ ( k ) → ∞ when k → 0, a well-known effect of perfect screening. The effective relative

Toward transferable interatomic van der Waals interactions without electrons: The role of multipole electrostatics and many-body dispersion

International Nuclear Information System (INIS)

Bereau, Tristan; Lilienfeld, O. Anatole von

2014-01-01

We estimate polarizabilities of atoms in molecules without electron density, using a Voronoi tesselation approach instead of conventional density partitioning schemes. The resulting atomic dispersion coefficients are calculated, as well as many-body dispersion effects on intermolecular potential energies. We also estimate contributions from multipole electrostatics and compare them to dispersion. We assess the performance of the resulting intermolecular interaction model from dispersion and electrostatics for more than 1300 neutral and charged, small organic molecular dimers. Applications to water clusters, the benzene crystal, the anti-cancer drug ellipticine—intercalated between two Watson-Crick DNA base pairs, as well as six macro-molecular host-guest complexes highlight the potential of this method and help to identify points of future improvement. The mean absolute error made by the combination of static electrostatics with many-body dispersion reduces at larger distances, while it plateaus for two-body dispersion, in conflict with the common assumption that the simple 1/R 6 correction will yield proper dissociative tails. Overall, the method achieves an accuracy well within conventional molecular force fields while exhibiting a simple parametrization protocol

Toward transferable interatomic van der Waals interactions without electrons: The role of multipole electrostatics and many-body dispersion

Energy Technology Data Exchange (ETDEWEB)

Bereau, Tristan, E-mail: bereau@mpip-mainz.mpg.de [Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany and Department of Chemistry, University of Basel, 4056 Basel (Switzerland); Lilienfeld, O. Anatole von [Department of Chemistry, Institute of Physical Chemistry, University of Basel, 4056 Basel, Switzerland and Argonne Leadership Computing Facility, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2014-07-21

We estimate polarizabilities of atoms in molecules without electron density, using a Voronoi tesselation approach instead of conventional density partitioning schemes. The resulting atomic dispersion coefficients are calculated, as well as many-body dispersion effects on intermolecular potential energies. We also estimate contributions from multipole electrostatics and compare them to dispersion. We assess the performance of the resulting intermolecular interaction model from dispersion and electrostatics for more than 1300 neutral and charged, small organic molecular dimers. Applications to water clusters, the benzene crystal, the anti-cancer drug ellipticine—intercalated between two Watson-Crick DNA base pairs, as well as six macro-molecular host-guest complexes highlight the potential of this method and help to identify points of future improvement. The mean absolute error made by the combination of static electrostatics with many-body dispersion reduces at larger distances, while it plateaus for two-body dispersion, in conflict with the common assumption that the simple 1/R{sup 6} correction will yield proper dissociative tails. Overall, the method achieves an accuracy well within conventional molecular force fields while exhibiting a simple parametrization protocol.

Rational redesign of inhibitors of furin/kexin processing proteases by electrostatic mutations.

Science.gov (United States)

Cai, Xiao-hui; Zhang, Qing; Ding, Da-fu

2004-12-01

To model the three-dimensional structure and investigate the interaction mechanism of the proprotein convertase furin/kexin and their inhibitors (eglin c mutants). The three-dimensional complex structures of furin/kexin with its inhibitors, eglin c mutants, were generated by modeller program using the newly published X-ray crystallographical structures of mouse furin and yeast kexin as templates. The electrostatic interaction energy of each complex was calculated and the results were compared with the experimentally determined inhibition constants to find the correlation between them. High quality models of furin/kexin-eglin c mutants were obtained and used for calculation of the electrostatic interaction energies between the proteases and their inhibitors. The calculated electrostatic energies of interaction showed a linear correlation to the experimental inhibition constants. The modeled structures give good explanations of the specificity of eglin c mutants to furin/kexin. The electrostatic interactions play important roles in inhibitory activity of eglin c mutants to furin/kexin. The results presented here provided quantitative structural and functional information concerning the role of the charge-charge interactions in the binding of furin/kexin and their inhibitors.

A closed form for the electrostatic interaction between two rod-like charged objects

International Nuclear Information System (INIS)

Askari, M; Abouie, J

2011-01-01

We have calculated the electrostatic interaction between two rod-like charged objects with arbitrary orientations in three dimensions. We obtained a closed-form formula expressing the interaction energy in terms of the separation distance between the centers of the two rod-like objects, r, their lengths (denoted by 2l 1 and 2l 2 ) and their relative orientations (indicated by θ and φ). When the objects have the same length (2l 1 = 2l 2 = l), for particular values of separations, i.e. for r ≤ 0.8l, two types of minimum appear in the interaction energy with respect to θ. By employing the closed-form formula and introducing a scaled temperature t, we have also studied the thermodynamic properties of a 1D system of rod-like charged objects. For different separation distances, the dependence of the specific heat of the system to the scaled temperature has been studied. It is found that, for r < 0.8l, the specific heat has a maximum.

The impact of electrostatic interactions on ultrafast charge transfer at Ag 29 nanoclusters–fullerene and CdTe quantum dots–fullerene interfaces

KAUST Repository

Ahmed, Ghada H.; Parida, Manas R.; Tosato, Alberto; AbdulHalim, Lina G.; Usman, Anwar; Alsulami, Qana; Banavoth, Murali; Alarousu, Erkki; Bakr, Osman; Mohammed, Omar F.

2015-01-01

investigate the electrostatic interactions between the positively charged fullerene derivative C60-(N,N dimethylpyrrolidinium iodide) (CF) employed as an efficient molecular acceptor and two different donor molecules: Ag29 nanoclusters (NCs) and CdTe quantum

A theoretical study of complexes formed between cations and curved aromatic systems: electrostatics does not always control cation-π interaction.

Science.gov (United States)

Carrazana-García, Jorge A; Cabaleiro-Lago, Enrique M; Rodríguez-Otero, Jesús

2017-04-19

The present work studies the interaction of two extended curved π-systems (corannulene and sumanene) with various cations (sodium, potassium, ammonium, tetramethylammonium, guanidinium and imidazolium). Polyatomic cations are models of groups found in important biomolecules in which cation-π interaction plays a fundamental role. The results indicate an important size effect: with extended π systems and cations of the size of potassium and larger, dispersion is much more important than has been generally recognized for cation-π interactions. In most of the systems studied here, the stability of the cation-π complexes is the result of a balanced combination of electrostatic, induction and dispersion contributions. None of the systems studied here owes its stability to the electrostatic interaction more than 42%. Induction dominates stabilization in complexes with sodium, and in some of the potassium and ammonium complexes. In complexes with large cations and with flat cations dispersion is the major stabilizing contribution and can provide more than 50% of the stabilization energy. This implies that theoretical studies of the cation-π interaction involving large or even medium-size fragments require a level of calculation capable of properly modelling dispersion. The separation between the cation and the π system is another important factor to take into account, especially when the fragments of the cation-π complex are bound (for example, to a protein backbone) and cannot interact at the most favourable distance.

Electrostatic study of Alanine mutational effects on transcription: application to GATA-3:DNA interaction complex.

Science.gov (United States)

El-Assaad, Atlal; Dawy, Zaher; Nemer, Georges

2015-01-01

Protein-DNA interaction is of fundamental importance in molecular biology, playing roles in functions as diverse as DNA transcription, DNA structure formation, and DNA repair. Protein-DNA association is also important in medicine; understanding Protein-DNA binding kinetics can assist in identifying disease root causes which can contribute to drug development. In this perspective, this work focuses on the transcription process by the GATA Transcription Factor (TF). GATA TF binds to DNA promoter region represented by `G,A,T,A' nucleotides sequence, and initiates transcription of target genes. When proper regulation fails due to some mutations on the GATA TF protein sequence or on the DNA promoter sequence (weak promoter), deregulation of the target genes might lead to various disorders. In this study, we aim to understand the electrostatic mechanism behind GATA TF and DNA promoter interactions, in order to predict Protein-DNA binding in the presence of mutations, while elaborating on non-covalent binding kinetics. To generate a family of mutants for the GATA:DNA complex, we replaced every charged amino acid, one at a time, with a neutral amino acid like Alanine (Ala). We then applied Poisson-Boltzmann electrostatic calculations feeding into free energy calculations, for each mutation. These calculations delineate the contribution to binding from each Ala-replaced amino acid in the GATA:DNA interaction. After analyzing the obtained data in view of a two-step model, we are able to identify potential key amino acids in binding. Finally, we applied the model to GATA-3:DNA (crystal structure with PDB-ID: 3DFV) binding complex and validated it against experimental results from the literature.

Diminish electrostatic in piezoresponse force microscopy through longer or ultra-stiff tips

Science.gov (United States)

Gomez, A.; Puig, T.; Obradors, X.

2018-05-01

Piezoresponse Force Microscopy is a powerful but delicate nanoscale technique that measures the electromechanical response resulting from the application of a highly localized electric field. Though mechanical response is normally due to piezoelectricity, other physical phenomena, especially electrostatic interaction, can contribute to the signal read. We address this problematic through the use of longer ultra-stiff probes providing state of the art sensitivity, with the lowest electrostatic interaction and avoiding working in high frequency regime. In order to find this solution we develop a theoretical description addressing the effects of electrostatic contributions in the total cantilever vibration and its quantification for different setups. The theory is subsequently tested in a Periodically Poled Lithium Niobate (PPLN) crystal, a sample with well-defined 0° and 180° domains, using different commercial available conductive tips. We employ the theoretical description to compare the electrostatic contribution effects into the total phase recorded. Through experimental data our description is corroborated for each of the tested commercially available probes. We propose that a larger probe length can be a solution to avoid electrostatic forces, so the cantilever-sample electrostatic interaction is reduced. Our proposed solution has great implications into avoiding artifacts while studying soft biological samples, multiferroic oxides, and thin film ferroelectric materials.

Non-specific immunization against babesiosis

International Nuclear Information System (INIS)

Cox, F.E.G.

1980-01-01

The rodent babesias, Babesia rodhaini and the less virulent B. microti, are useful models with which to study immunity to and immunization against babesiosis. In contrast with the difficulty in inducing specific immunity to these parasites it is comparatively easy to induce non-specific immunity by prior exposure to related and unrelated intra-erythrocytic protozoa, micro-organisms such as Mycobacterium bovis (BCG) and Corynebacterium parvum, microbial extracts and muramyl dipeptide. This non-specific immunity is long lasting and extremely effective. It is characterized by the facts that (a) it occurs early in the infection at the height of the first peak of parasitaemia, and (b) it involves the intra-erythrocytic death of the parasites. After the primary parasitaemia has resolved, some parasites continue to persist at a low level and when introduced into clean mice produce only low-level 'attenuated' infections in these. Non-specific immunity is not equally effective in all strains of mice. It is suggested that immunity to babesiosis, and infections caused by other intra-erythrocytic protozoa, involves two mechanisms, the first non-specific and the second specific. The actual balance between these two mechanisms varies from parasite to parasite and from host to host. An effective vaccine would have to be based on an understanding of the roles of non-specific immunity in the actual disease under consideration, and would ideally combine an adjuvant that would also stimulate non-specific immunity and an attenuated strain of parasite that would induce a specific response. (author)

Electrostatic atomization--Experiment, theory and industrial applications

Science.gov (United States)

Okuda, H.; Kelly, Arnold J.

1996-05-01

Experimental and theoretical research has been initiated at the Princeton Plasma Physics Laboratory on the electrostatic atomization process in collaboration with Charged Injection Corporation. The goal of this collaboration is to set up a comprehensive research and development program on the electrostatic atomization at the Princeton Plasma Physics Laboratory so that both institutions can benefit from the collaboration. Experimental, theoretical and numerical simulation approaches are used for this purpose. An experiment consisting of a capillary sprayer combined with a quadrupole mass filter and a charge detector was installed at the Electrostatic Atomization Laboratory to study fundamental properties of the charged droplets such as the distribution of charges with respect to the droplet radius. In addition, a numerical simulation model is used to study interaction of beam electrons with atmospheric pressure water vapor, supporting an effort to develop an electrostatic water mist fire-fighting nozzle.

3D RISM theory with fast reciprocal-space electrostatics

Energy Technology Data Exchange (ETDEWEB)

Heil, Jochen; Kast, Stefan M., E-mail: stefan.kast@tu-dortmund.de [Physikalische Chemie III, Technische Universität Dortmund, Otto-Hahn-Str. 6, 44227 Dortmund (Germany)

2015-03-21

The calculation of electrostatic solute-solvent interactions in 3D RISM (“three-dimensional reference interaction site model”) integral equation theory is recast in a form that allows for a computational treatment analogous to the “particle-mesh Ewald” formalism as used for molecular simulations. In addition, relations that connect 3D RISM correlation functions and interaction potentials with thermodynamic quantities such as the chemical potential and average solute-solvent interaction energy are reformulated in a way that calculations of expensive real-space electrostatic terms on the 3D grid are completely avoided. These methodical enhancements allow for both, a significant speedup particularly for large solute systems and a smoother convergence of predicted thermodynamic quantities with respect to box size, as illustrated for several benchmark systems.

3D RISM theory with fast reciprocal-space electrostatics.

Science.gov (United States)

Heil, Jochen; Kast, Stefan M

2015-03-21

The calculation of electrostatic solute-solvent interactions in 3D RISM ("three-dimensional reference interaction site model") integral equation theory is recast in a form that allows for a computational treatment analogous to the "particle-mesh Ewald" formalism as used for molecular simulations. In addition, relations that connect 3D RISM correlation functions and interaction potentials with thermodynamic quantities such as the chemical potential and average solute-solvent interaction energy are reformulated in a way that calculations of expensive real-space electrostatic terms on the 3D grid are completely avoided. These methodical enhancements allow for both, a significant speedup particularly for large solute systems and a smoother convergence of predicted thermodynamic quantities with respect to box size, as illustrated for several benchmark systems.

3D RISM theory with fast reciprocal-space electrostatics

International Nuclear Information System (INIS)

Heil, Jochen; Kast, Stefan M.

2015-01-01

The calculation of electrostatic solute-solvent interactions in 3D RISM (“three-dimensional reference interaction site model”) integral equation theory is recast in a form that allows for a computational treatment analogous to the “particle-mesh Ewald” formalism as used for molecular simulations. In addition, relations that connect 3D RISM correlation functions and interaction potentials with thermodynamic quantities such as the chemical potential and average solute-solvent interaction energy are reformulated in a way that calculations of expensive real-space electrostatic terms on the 3D grid are completely avoided. These methodical enhancements allow for both, a significant speedup particularly for large solute systems and a smoother convergence of predicted thermodynamic quantities with respect to box size, as illustrated for several benchmark systems

Stray capacitances in the watt balance operation: electrostatic forces

DEFF Research Database (Denmark)

Quagliotti, Danilo; Mana, G.

2014-01-01

In a watt balance, stray capacitances exist between the coil and the magnet. Since the electric current flowing in the coil creates a difference in electric potentials between the coil and magnet, their electrostatic interactions must be taken into account. This paper reports the results of a fin......In a watt balance, stray capacitances exist between the coil and the magnet. Since the electric current flowing in the coil creates a difference in electric potentials between the coil and magnet, their electrostatic interactions must be taken into account. This paper reports the results...

Efficiency determination of an electrostatic lunar dust collector by discrete element method

Science.gov (United States)

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

2012-07-01

Lunar grains become charged by the sun's radiation in the tenuous atmosphere of the moon. This leads to lunar dust levitation and particle deposition which often create serious problems in the costly system deployed in lunar exploration. In this study, an electrostatic lunar dust collector (ELDC) is proposed to address the issue and the discrete element method (DEM) is used to investigate the effects of electrical particle-particle interactions, non-uniformity of the electrostatic field, and characteristics of the ELDC. The simulations on 20-μm-sized lunar particles reveal the electrical particle-particle interactions of the dust particles within the ELDC plates require 29% higher electrostatic field strength than that without the interactions for 100% collection efficiency. For the given ELDC geometry, consideration of non-uniformity of the electrostatic field along with electrical interactions between particles on the same ELDC geometry leads to a higher requirement of ˜3.5 kV/m to ensure 100% particle collection. Notably, such an electrostatic field is about 103 times less than required for electrodynamic self-cleaning methods. Finally, it is shown for a "half-size" system that the DEM model predicts greater collection efficiency than the Eulerian-based model at all voltages less than required for 100% efficiency. Halving the ELDC dimensions boosts the particle concentration inside the ELDC, as well as the resulting field strength for a given voltage. Though a lunar photovoltaic system was the subject, the results of this study are useful for evaluation of any system for collecting charged particles in other high vacuum environment using an electrostatic field.

Electrostatics at the membrane define MscL channel mechanosensitivity and kinetics.

Science.gov (United States)

Zhong, Dalian; Blount, Paul

2014-12-01

The bacterial mechanosensitive channel of large conductance (MscL) serves as a biological emergency release valve, preventing the occurrence of cell lysis caused by acute osmotic stress. Its tractable nature allows it to serve as a paradigm for how a protein can directly sense membrane tension. Although much is known of the importance of the hydrophobicity of specific residues in channel gating, it has remained unclear whether electrostatics at the membrane plays any role. We studied MscL chimeras derived from functionally distinct orthologues: Escherichia coli and Staphylococcus aureus. Dissection of one set led to an observation that changing the charge of a single residue, K101, of E. coli (Ec)-MscL, effects a channel phenotype: when mutated to a negative residue, the channel is less mechanosensitive and has longer open dwell times. Assuming electrostatic interactions, we determined whether they are due to protein-protein or protein-lipid interactions by performing site-directed mutagenesis elsewhere in the protein and reconstituting channels into defined lipids, with and without negative head groups. We found that although both interactions appear to play some role, the primary determinant of the channel phenotype seems to be protein-lipid electrostatics. The data suggest a model for the role of electrostatic interactions in the dynamics of MscL gating. © FASEB.

Effect of the size of charged spherical macroparticles on their electrostatic interaction in an equilibrium plasma

Energy Technology Data Exchange (ETDEWEB)

Filippov, A. V., E-mail: fav@triniti.ru; Derbenev, I. N. [State Research Center of the Russian Federation, Troitsk Institute for Innovation and Fusion Research (Russian Federation)

2016-12-15

The effect of the size of two charged spherical macroparticles on their electrostatic interaction in an equilibrium plasma is analyzed within the linearized Poisson–Botzmann model. It is established that, under the interaction of two charged dielectric macroparticles in an equilibrium plasma, the forces acting on each particle turn out to be generally unequal. The forces become equal only in the case of conducting macroparticles or in the case of dielectric macroparticles of the same size and charge. They also turn out to be equal when the surface potentials of the macroparticles remain constant under the variation of interparticle distances. Formulas are proposed that allow one to calculate the interaction force with a high degree of accuracy under the condition that the radii of macroparticles are much less than the screening length, which is usually satisfied in experiments with dusty plasmas.

Non-specific immunization against parasites

International Nuclear Information System (INIS)

Cox, F.E.G.

1981-01-01

Non-specific resistance to tumours can be induced by pretreating animals with micro-organisms, microbial extracts or various synthetic substances. Mycobacterium bovis, Corynebacterium parvum and a number of other micro-organisms also protect mice against rodent piroplasms and there is evidence that they are also protective against other parasites including Schistosoma mansoni. The actual mechanisms of non-specific immunity are still unclear but it is influenced by both the genetic make-up of the host and the nature of the parasite. Non-specific immunization may be a possible alternative to specific immunization and may avoid many of the potential immunopathological changes induced during parasite infections. Irradiated vaccines (Dictyocaulus viviparus, schistomiasis) are mentioned marginally only

Orientation of KRb molecules in a switched electrostatic field

International Nuclear Information System (INIS)

Huang Yun-Xia; Xu Shu-Wu; Yang Xiao-Hua

2013-01-01

We theoretically investigate the orientation of the cold KRb molecules induced in a switched electrostatic field by numerically solving the full time-dependent Schrödinger equation. The results show that the periodic field-free molecular orientation can be realized for the KRb molecules by rapidly switching off the electrostatic field. Meanwhile, by varying the switching times of the electrostatic field, the adiabatic and nonadiabatic interactions of the molecules with the applied field can be realized. Moreover, the influences of the electrostatic field strength and the rotational temperature to the degree of the molecular orientation are studied. The investigations show that increasing the electrostatic field will increase the degree of the molecular orientation, both in the constant-field regime and in the field-free regime, while the increasing of the rotational temperature of the cold molecules will greatly decrease the degree of the molecular orientation. (atomic and molecular physics)

Fluorine Gauche Effect Explained by Electrostatic Polarization Instead of Hyperconjugation: An Interacting Quantum Atoms (IQA) and Relative Energy Gradient (REG) Study.

Science.gov (United States)

Thacker, Joseph C R; Popelier, Paul L A

2018-02-08

We present an interacting quantum atoms (IQA) study of the gauche effect by comparing 1,2-difluoroethane, 1,2-dichloroethane, and three conformers of 1,2,3,4,5,6-hexafluorocyclohexane. In the 1,2-difluoroethane, the gauche effect is observed in that the gauche conformation is more stable than the anti, whereas in 1,2-dichloroethane the opposite is true. The analysis performed here is exhaustive and unbiased thanks to using the recently introduced relative energy gradient (REG) method [ Thacker , J. C. R. ; Popelier , P. L. A. Theor. Chem. Acc . 2017 , 136 , 86 ], as implemented in the in-house program ANANKE. We challenge the common explanation that hyperconjugation is responsible for the gauche stability in 1,2-difluoroethane and instead present electrostatics as the cause of gauche stability. Our explanation of the gauche effect is also is seen in other molecules displaying local gauche conformations, such as the recently synthesized "all-cis" hexafluorocyclohexane and its conformers where all the fluorine atoms are in the equatorial positions. Using our extension of the traditional IQA methodology that allows for the partitioning of electrostatic terms into polarization and charge transfer, we propose that the cause of gauche stability is 1,3 C···F electrostatic polarization interactions. In other words, if a number of fluorine atoms are aligned, then the stability due to polarization of nearby carbon atoms is increased.

Combining crystallographic information and an aspherical-atom data bank in the evaluation of the electrostatic interaction energy in an enzyme–substrate complex: influenza neuraminidase inhibition

Energy Technology Data Exchange (ETDEWEB)

Dominiak, Paulina M., E-mail: pdomin@chem.uw.edu.pl [Department of Chemistry, State University of New York at Buffalo, NY 14260 (United States); Department of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warszawa (Poland); Volkov, Anatoliy; Dominiak, Adam P. [Department of Chemistry, State University of New York at Buffalo, NY 14260 (United States); Jarzembska, Katarzyna N. [Department of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warszawa (Poland); Coppens, Philip, E-mail: pdomin@chem.uw.edu.pl [Department of Chemistry, State University of New York at Buffalo, NY 14260 (United States)

2009-05-01

The electrostatic component of the enzyme/inhibitor interaction of a wide range influenza neuraminidases and inhibitors has been analyzed using transferable aspherical-atom densities from a recently compiled databank. Results are subdivided into the contributions of individual active-site residues and different functional groups of the inhibitors, and the effect of the Arg292→Lys mutation is considered. Although electrostatic interactions contribute only a part of the interaction energies between macromolecules, unlike dispersion forces they are highly directional and therefore dominate the nature of molecular packing in crystals and in biological complexes and contribute significantly to differences in inhibition strength among related enzyme inhibitors. In the reported study, a wide range of complexes of influenza neuraminidases with inhibitor molecules (sialic acid derivatives and others) have been analyzed using charge densities from a transferable aspherical-atom data bank. The strongest interactions of the residues are with the acidic group at the C2 position of the inhibitor (∼−300 kJ mol{sup −1} for —COO{sup −} in non-aromatic inhibitors, ∼−120–210 kJ mol{sup −1} for —COO{sup −} in aromatic inhibitors and ∼−450 kJ mol{sup −1} for —PO{sub 3}{sup 2−}) and with the amino and guanidine groups at C4 (∼−250 kJ mol{sup −1}). Other groups contribute less than ∼100 kJ mol{sup −1}. Residues Glu119, Asp151, Glu227, Glu276 and Arg371 show the largest variation in electrostatic energies of interaction with different groups of inhibitors, which points to their important role in the inhibitor recognition. The Arg292→Lys mutation reduces the electrostatic interactions of the enzyme with the acidic group at C2 for all inhibitors that have been studied (SIA, DAN, 4AM, ZMR, G20, G28, G39 and BCZ), but enhances the interactions with the glycerol group at C6 for inhibitors that contain it. This is in agreement with the lower level

Pattern Formation in Langmuir Monolayers Due to Long-Range Electrostatic Interactions

Science.gov (United States)

Fischer, Thomas M.; Lösche, Mathias

A distinctive characteristic of Langmuir monolayers that bears important consequences for the physics of structure formation within membranes is the uniaxial orientation of the constituent dipolar molecules, brought about by the symmetry break which is induced by the surface of the aqueous substrate. The association of oriented molecular dipoles with the interface leads to the formation of image dipoles within the polarizeable medium - the subphase - such that the effective dipole orientation of every of the individual molecules is strictly normal to the surface, even within molecularly disordered phases. As a result, dipole-dipole repulsions play an eminently important role for the molecular interactions within the system - independent of the state of phase (while the dipole area density does of course depend on the state of phase) - and control the morphogenesis of the phase boundaries in their interplay with the one-dimensional (1D) line tension between coexisting phases. The physics of these phenomena is only now being explored and is particularly exciting for systems within a three-phase coexistence region where complete or partial wetting, as well as dewetting between the coexisting phases may be experimentally observed by applying fluorescence microscopy to the monolayer films. It is revealed that the wetting behavior depends sensitively on the details of the electrostatic interactions, in that the apparent contact angles observed at three-phase contact points depends on the sizes of the coexisting phases. This is in sharp contrast to the physics of wetting in conventional 3D systems where the contact angle is a materials property, independent of the local details. In 3D systems, this leads to Youngs equation - which has been established more than two centuries ago. We report recent progress in the understanding of this unusual and rather unexpected behavior of a quasi-2D system by reviewing recent experimental results from optical microscopy on equilibrium

Ionic fluids with r-6 pair interactions have power-law electrostatic screening

International Nuclear Information System (INIS)

Kjellander, Roland; Forsberg, Bjoern

2005-01-01

The decay behaviour of radial distribution functions for large distances r is investigated for classical Coulomb fluids where the ions interact with an r -6 potential (e.g. a dispersion interaction) in addition to the Coulombic and the short-range repulsive potentials (e.g. a hard core). The pair distributions and the density-density (NN), charge-density (QN) and charge-charge (QQ) correlation functions are investigated analytically and by Monte Carlo simulations. It is found that the NN correlation function ultimately decays like r -6 for large r, just as it does for fluids of electroneutral particles interacting with an r -6 potential. The prefactor is proportional to the squared compressibility in both cases. The QN correlations decay in general like r -8 and the QQ correlations like r -10 in the ionic fluid. The average charge density around an ion decays generally like r -8 and the average electrostatic potential like r -6 . This behaviour is in stark contrast to the decay behaviour for classical Coulomb fluids in the absence of the r -6 potential, where all these functions decay exponentially for large r. The power-law decays are, however, the same as for quantum Coulomb fluids. This indicates that the inclusion of the dispersion interaction as an effective r -6 interaction potential in classical systems yields the same decay behaviour for the pair correlations as in quantum ionic systems. An exceptional case is the completely symmetric binary electrolyte for which only the NN correlation has a power-law decay but not the QQ correlations. These features are shown by an analysis of the bridge function

Electrostatic atomization emdash Experiment, theory and industrial applications

International Nuclear Information System (INIS)

Okuda, H.; Kelly, A.J.

1996-01-01

Experimental and theoretical research has been initiated at the Princeton Plasma Physics Laboratory on the electrostatic atomization process in collaboration with Charged Injection Corporation. The goal of this collaboration is to set up a comprehensive research and development program on the electrostatic atomization at the Princeton Plasma Physics Laboratory so that both institutions can benefit from the collaboration. Experimental, theoretical and numerical simulation approaches are used for this purpose. An experiment consisting of a capillary sprayer combined with a quadrupole mass filter and a charge detector was installed at the Electrostatic Atomization Laboratory to study fundamental properties of the charged droplets such as the distribution of charges with respect to the droplet radius. In addition, a numerical simulation model is used to study interaction of beam electrons with atmospheric pressure water vapor, supporting an effort to develop an electrostatic water mist fire-fighting nozzle. copyright 1996 American Institute of Physics

Long range Debye-Hückel correction for computation of grid-based electrostatic forces between biomacromolecules

International Nuclear Information System (INIS)

Mereghetti, Paolo; Martinez, Michael; Wade, Rebecca C

2014-01-01

Brownian dynamics (BD) simulations can be used to study very large molecular systems, such as models of the intracellular environment, using atomic-detail structures. Such simulations require strategies to contain the computational costs, especially for the computation of interaction forces and energies. A common approach is to compute interaction forces between macromolecules by precomputing their interaction potentials on three-dimensional discretized grids. For long-range interactions, such as electrostatics, grid-based methods are subject to finite size errors. We describe here the implementation of a Debye-Hückel correction to the grid-based electrostatic potential used in the SDA BD simulation software that was applied to simulate solutions of bovine serum albumin and of hen egg white lysozyme. We found that the inclusion of the long-range electrostatic correction increased the accuracy of both the protein-protein interaction profiles and the protein diffusion coefficients at low ionic strength. An advantage of this method is the low additional computational cost required to treat long-range electrostatic interactions in large biomacromolecular systems. Moreover, the implementation described here for BD simulations of protein solutions can also be applied in implicit solvent molecular dynamics simulations that make use of gridded interaction potentials

Structure of DNA toroids and electrostatic attraction of DNA duplexes

International Nuclear Information System (INIS)

Cherstvy, A G

2005-01-01

DNA-DNA electrostatic attraction is considered as the driving force for the formation of DNA toroids in the presence of DNA condensing cations. This attraction comes from the DNA helical charge distribution and favours hexagonal toroidal cross-sections. The latter is in agreement with recent cryo-electron microscopy studies on DNA condensed with cobalt hexammine. We treat the DNA-DNA interactions within the modern theory of electrostatic interaction between helical macromolecules. The size and thickness of the toroids is calculated within a simple model; other models of stability of DNA toroids are discussed and compared

Collapse of Electrostatic Waves in Magnetoplasmas

DEFF Research Database (Denmark)

Shukla, P. K.; Yu, M. Y.; Juul Rasmussen, Jens

1984-01-01

The two-fluid model is employed to investigate the collapse of electrostatic waves in magnetized plasmas. It is found that nonlinear interaction of ion cyclotron, upper-, and lower-hybrid waves with adiabatic particle motion along the external magnetic field can cause wave-field collapse....

Electrostatic ion thrusters - towards predictive modeling

Energy Technology Data Exchange (ETDEWEB)

Kalentev, O.; Matyash, K.; Duras, J.; Lueskow, K.F.; Schneider, R. [Ernst-Moritz-Arndt Universitaet Greifswald, D-17489 (Germany); Koch, N. [Technische Hochschule Nuernberg Georg Simon Ohm, Kesslerplatz 12, D-90489 Nuernberg (Germany); Schirra, M. [Thales Electronic Systems GmbH, Soeflinger Strasse 100, D-89077 Ulm (Germany)

2014-02-15

The development of electrostatic ion thrusters so far has mainly been based on empirical and qualitative know-how, and on evolutionary iteration steps. This resulted in considerable effort regarding prototype design, construction and testing and therefore in significant development and qualification costs and high time demands. For future developments it is anticipated to implement simulation tools which allow for quantitative prediction of ion thruster performance, long-term behavior and space craft interaction prior to hardware design and construction. Based on integrated numerical models combining self-consistent kinetic plasma models with plasma-wall interaction modules a new quality in the description of electrostatic thrusters can be reached. These open the perspective for predictive modeling in this field. This paper reviews the application of a set of predictive numerical modeling tools on an ion thruster model of the HEMP-T (High Efficiency Multi-stage Plasma Thruster) type patented by Thales Electron Devices GmbH. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Compact electrostatic comb actuator

Science.gov (United States)

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

2000-01-01

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

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

International Nuclear Information System (INIS)

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

2010-01-01

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

Effect of electrostatic interaction between fluoxetine and lipid membranes on the partitioning of fluoxetine investigated using second derivative spectrophotometry and FTIR.

Science.gov (United States)

Do, Tien T T; Dao, Uyen P N; Bui, Huong T; Nguyen, Trang T

2017-10-01

The interaction between a drug molecule and lipid bilayers is highly important regarding the pharmaceutical activity of the drug. In this study, the interaction of fluoxetine, a well-known selective serotonin reuptake inhibitor antidepressant and lipid bilayers composed of 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was studied from the aspect of electrostatics using second derivative spectrophotometry and Fourier transform infrared spectroscopy (FTIR) in order to provide insights into the drug behavior. Changing pH from 7.4 to 9.5 to increases the neutral state of fluoxetine, the partitioning of fluoxetine into the zwitterionic DPPC large unilamellar vesicles (LUVs) was increased whereas it was reduced into the negatively charged DPPG LUVs. Fluoxetine was found to exhibit a disordering effect on the acyl chains of DPPC and DPPG bilayers upon its partitioning. In addition, increasing concentration of NaCl lessened the binding of fluoxetine into DPPG bilayers due to the reduction in electrostatic attraction between positively charged fluoxetine and negatively charged DPPG LUVs. In addition, the FTIR study revealed that increasing the NaCl concentration could trigger the shift to higher frequency of the CH 2 stretching as well as the notable blue shift in the PO 2 - regions of DPPG, indicating that fluoxetine had deeper penetration into DPPG LUVs. The differences in the NaCl concentration showed a negligible effect on the incorporation of fluoxetine into the zwitterionic DPPC LUVs. In summary, the electrostatic interaction plays an important role on the partitioning of a cationic amphiphilic SSIR drug into the lipid bilayers and the drug partitioning induces the lipids' conformational change. These imply a possible influence on the drug pharmacology. Copyright © 2017 Elsevier B.V. All rights reserved.

Optics elements for modeling electrostatic lenses and accelerator components: III. Electrostatic deflectors

International Nuclear Information System (INIS)

Brown, T.A.; Gillespie, G.H.

2000-01-01

Ion-beam optics models for simulating electrostatic prisms (deflectors) of different geometries have been developed for the envelope (matrix) computer code TRACE 3-D as a part of the development of a suite of electrostatic beamline element models which includes lenses, acceleration columns, quadrupoles and prisms. The models for electrostatic prisms are described in this paper. The electrostatic prism model options allow the first-order modeling of cylindrical, spherical and toroidal electrostatic deflectors. The application of these models in the development of ion-beam transport systems is illustrated through the modeling of a spherical electrostatic analyzer as a component of the new low-energy beamline at the Center for Accelerator Mass Spectrometry. Although initial tests following installation of the new beamline showed that the new spherical electrostatic analyzer was not behaving as predicted by these first-order models, operational conditions were found under which the analyzer now works properly as a double-focusing spherical electrostatic prism

Tight ceramic UF membrane as RO pre-treatment: the role of electrostatic interactions on phosphate rejection.

Science.gov (United States)

Shang, Ran; Verliefde, Arne R D; Hu, Jingyi; Zeng, Zheyi; Lu, Jie; Kemperman, Antoine J B; Deng, Huiping; Nijmeijer, Kitty; Heijman, Sebastiaan G J; Rietveld, Luuk C

2014-01-01

Phosphate limitation has been reported as an effective approach to inhibit biofouling in reverse osmosis (RO) systems for water purification. The rejection of dissolved phosphate by negatively charged TiO2 tight ultrafiltration (UF) membranes (1 kDa and 3 kDa) was observed. These membranes can potentially be adopted as an effective process for RO pre-treatment in order to constrain biofouling by phosphate limitation. This paper focuses on electrostatic interactions during tight UF filtration. Despite the larger pore size, the 3 kDa ceramic membrane exhibited greater phosphate rejection than the 1 kDa membrane, because the 3 kDa membrane has a greater negative surface charge and thus greater electrostatic repulsion against phosphate. The increase of pH from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. At pH 8.5, the maximum phosphate rejections achieved by the 1 kDa and 3 kDa membrane were 75% and 86%, respectively. A Debye ratio (ratio of the Debye length to the pore radius) is introduced in order to evaluate double layer overlapping in tight UF membranes. Threshold Debye ratios were determined as 2 and 1 for the 1 kDa and 3 kDa membranes, respectively. A Debye ratio below the threshold Debye ratio leads to dramatically decreased phosphate rejection by tight UF membranes. The phosphate rejection by the tight UF, in combination with chemical phosphate removal by coagulation, might accomplish phosphate-limited conditions for biological growth and thus prevent biofouling in the RO systems. Copyright © 2013 Elsevier Ltd. All rights reserved.

Pitch-angle diffusion coefficients from resonant interactions with electrostatic electron cyclotron harmonic waves in planetary magnetospheres

Directory of Open Access Journals (Sweden)

A. K. Tripathi

2011-02-01

Full Text Available Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH waves in the magnetospheres of Earth, Jupiter, Saturn, Uranus and Neptune. Calculations have been performed at two radial distances of each planet. It is found that observed wave electric field amplitudes in the magnetospheres of Earth and Jupiter are sufficient to put electrons on strong diffusion in the energy range of less than 100 eV. However, for Saturn, Uranus and Neptune, the observed ECH wave amplitude are insufficient to put electrons on strong diffusion at any radial distance.

Optics Elements for Modeling Electrostatic Lenses and Accelerator Components: III. Electrostatic Deflectors

International Nuclear Information System (INIS)

Brown, T.A.; Gillespie, G.H.

1999-01-01

Ion-beam optics models for simulating electrostatic prisms (deflectors) of different geometries have been developed for the computer code TRACE 3-D. TRACE 3-D is an envelope (matrix) code, which includes a linear space charge model, that was originally developed to model bunched beams in magnetic transport systems and radiofrequency (RF) accelerators. Several new optical models for a number of electrostatic lenses and accelerator columns have been developed recently that allow the code to be used for modeling beamlines and accelerators with electrostatic components. The new models include a number of options for: (1) Einzel lenses, (2) accelerator columns, (3) electrostatic prisms, and (4) electrostatic quadrupoles. A prescription for setting up the initial beam appropriate to modeling 2-D (continuous) beams has also been developed. The models for electrostatic prisms are described in this paper. The electrostatic prism model options allow the modeling of cylindrical, spherical, and toroidal electrostatic deflectors. The application of these models in the development of ion-beam transport systems is illustrated through the modeling of a spherical electrostatic analyzer as a component of the new low energy beamline at CAMS

Large electrostatic accelerators

International Nuclear Information System (INIS)

Jones, C.M.

1984-01-01

The paper is divided into four parts: a discussion of the motivation for the construction of large electrostatic accelerators, a description and discussion of several large electrostatic accelerators which have been recently completed or are under construction, a description of several recent innovations which may be expected to improve the performance of large electrostatic accelerators in the future, and a description of an innovative new large electrostatic accelerator whose construction is scheduled to begin next year

Role of Electrostatics in Protein-RNA Binding: The Global vs the Local Energy Landscape.

Science.gov (United States)

Ghaemi, Zhaleh; Guzman, Irisbel; Gnutt, David; Luthey-Schulten, Zaida; Gruebele, Martin

2017-09-14

U1A protein-stem loop 2 RNA association is a basic step in the assembly of the spliceosomal U1 small nuclear ribonucleoprotein. Long-range electrostatic interactions due to the positive charge of U1A are thought to provide high binding affinity for the negatively charged RNA. Short range interactions, such as hydrogen bonds and contacts between RNA bases and protein side chains, favor a specific binding site. Here, we propose that electrostatic interactions are as important as local contacts in biasing the protein-RNA energy landscape toward a specific binding site. We show by using molecular dynamics simulations that deletion of two long-range electrostatic interactions (K22Q and K50Q) leads to mutant-specific alternative RNA bound states. One of these states preserves short-range interactions with aromatic residues in the original binding site, while the other one does not. We test the computational prediction with experimental temperature-jump kinetics using a tryptophan probe in the U1A-RNA binding site. The two mutants show the distinct predicted kinetic behaviors. Thus, the stem loop 2 RNA has multiple binding sites on a rough RNA-protein binding landscape. We speculate that the rough protein-RNA binding landscape, when biased to different local minima by electrostatics, could be one way that protein-RNA interactions evolve toward new binding sites and novel function.

Theory of electrostatics and electrokinetics of soft particles

Directory of Open Access Journals (Sweden)

Hiroyuki Ohshima

2009-01-01

Full Text Available We investigate theoretically the electrostatics and electrokinetics of a soft particle, i.e. a hard particle covered with an ion-penetrable surface layer of polyelectrolytes. The electric properties of soft particles in an electrolyte solution, which differ from those of hard particles, are essentially determined by the Donnan potential in the surface layer. In particular, the Donnan potential plays an essential role in the electrostatics and electrokinetics of soft particles. Furthermore, the concept of zeta potential, which is important in the electrokinetics of hard particles, loses its physical meaning in the electrokinetics of soft particles. In this review, we discuss the potential distribution around a soft particle, the electrostatic interaction between two soft particles, and the motion of a soft particle in an electric field.

Electrostatic forces on grains near asteroids and comets

Directory of Open Access Journals (Sweden)

Hartzell Christine

2017-01-01

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

Negative adsorption due to electrostatic exclusion of micelles.

Science.gov (United States)

Somasundaran, P; Ananthapadmanabhan, K P; Deo, Puspendu

2005-10-15

Interactions of surfactants with solid substrates are important in the controlling of processes such as flotation, coating, flocculation and sedimentation. These interactions usually lead to adsorption on solids, but can also result in an exclusion of the reagents with dire consequences. In this work electrostatic exclusion of negatively charged dodecylbenzene sulfonate micelles from quartz/water, Bio-Sil/water and alumina/water interfaces has been investigated as a function of pH and ionic strength. Measurable negative adsorption of these surfactants from similarly charged solid/liquid interface was observed in the micellar region. In the case of porous samples with large surface area, comparison of pore size with the micelle size is necessary to avoid any erroneous conclusions regarding the role of electrostatic exclusion in a given system. A theoretical model for the electrostatic exclusion of micelles is developed and used to calculate the adsorption of negatively charged dodecylbenzene sulfonate on negatively charged quartz (pH 7), silica (Bio-Sil A, pH 3) and alumina (pH 11) in the micellar concentration region. The micellar exclusion values calculated using the model are in excellent agreement with the experimental results.

Electrostatic Interactions between Elongated Monomers Drive Filamentation of Drosophila Shrub, a Metazoan ESCRT-III Protein

Directory of Open Access Journals (Sweden)

Brian J. McMillan

2016-08-01

Full Text Available The endosomal sorting complex required for transport (ESCRT is a conserved protein complex that facilitates budding and fission of membranes. It executes a key step in many cellular events, including cytokinesis and multi-vesicular body formation. The ESCRT-III protein Shrub in flies, or its homologs in yeast (Snf7 or humans (CHMP4B, is a critical polymerizing component of ESCRT-III needed to effect membrane fission. We report the structural basis for polymerization of Shrub and define a minimal region required for filament formation. The X-ray structure of the Shrub core shows that individual monomers in the lattice interact in a staggered arrangement using complementary electrostatic surfaces. Mutations that disrupt interface salt bridges interfere with Shrub polymerization and function. Despite substantial sequence divergence and differences in packing interactions, the arrangement of Shrub subunits in the polymer resembles that of Snf7 and other family homologs, suggesting that this intermolecular packing mechanism is shared among ESCRT-III proteins.

Systemic sclerosis with normal or nonspecific nailfold capillaroscopy.

Science.gov (United States)

Fichel, Fanny; Baudot, Nathalie; Gaitz, Jean-Pierre; Trad, Salim; Barbe, Coralie; Francès, Camille; Senet, Patricia

2014-01-01

In systemic sclerosis (SSc), a specific nailfold videocapillaroscopy (NVC) pattern is observed in 90% of cases and seems to be associated with severity and progression of the disease. To describe the characteristics of SSc patients with normal or nonspecific (normal/nonspecific) NVC. In a retrospective cohort study, clinical features and visceral involvements of 25 SSc cases with normal/nonspecific NVC were compared to 63 SSc controls with the SSc-specific NVC pattern. Normal/nonspecific NVC versus SSc-specific NVC pattern was significantly associated with absence of skin sclerosis (32 vs. 6.3%, p = 0.004), absence of telangiectasia (47.8 vs. 17.3%, p = 0.006) and absence of sclerodactyly (60 vs. 25.4%, p = 0.002), and less frequent severe pulmonary involvement (26.3 vs. 58.2%, p = 0.017). Normal/nonspecific NVC in SSc patients appears to be associated with less severe skin involvement and less frequent severe pulmonary involvement. © 2014 S. Karger AG, Basel.

Electrostatics in Chemistry

Indian Academy of Sciences (India)

Electrostatics in Chemistry. 3. Molecular Electrostatic Potential: Visualization and Topography. Shridhar R Gadre and Pravin K Bhadane. 1 1. Basic Principles, Resona- nce, Vol.4, No.2, 11-19, 1999. 2. Electrostatic Potentials of. Atoms, Ions and Molecules,. Resonance, Vol.4, No.5, 40-51,. 1999. Topographical features of the ...

Histidine in Continuum Electrostatics Protonation State Calculations

Science.gov (United States)

Couch, Vernon; Stuchebruckhov, Alexei

2014-01-01

A modification to the standard continuum electrostatics approach to calculate protein pKas which allows for the decoupling of histidine tautomers within a two state model is presented. Histidine with four intrinsically coupled protonation states cannot be easily incorporated into a two state formalism because the interaction between the two protonatable sites of the imidazole ring is not purely electrostatic. The presented treatment, based on a single approximation of the interrelation between histidine’s charge states, allows for a natural separation of the two protonatable sites associated with the imidazole ring as well as the inclusion of all protonation states within the calculation. PMID:22072521

Rational design of viscosity reducing mutants of a monoclonal antibody: hydrophobic versus electrostatic inter-molecular interactions.

Science.gov (United States)

Nichols, Pilarin; Li, Li; Kumar, Sandeep; Buck, Patrick M; Singh, Satish K; Goswami, Sumit; Balthazor, Bryan; Conley, Tami R; Sek, David; Allen, Martin J

2015-01-01

High viscosity of monoclonal antibody formulations at concentrations ≥100 mg/mL can impede their development as products suitable for subcutaneous delivery. The effects of hydrophobic and electrostatic intermolecular interactions on the solution behavior of MAB 1, which becomes unacceptably viscous at high concentrations, was studied by testing 5 single point mutants. The mutations were designed to reduce viscosity by disrupting either an aggregation prone region (APR), which also participates in 2 hydrophobic surface patches, or a negatively charged surface patch in the variable region. The disruption of an APR that lies at the interface of light and heavy chain variable domains, VH and VL, via L45K mutation destabilized MAB 1 and abolished antigen binding. However, mutation at the preceding residue (V44K), which also lies in the same APR, increased apparent solubility and reduced viscosity of MAB 1 without sacrificing antigen binding or thermal stability. Neutralizing the negatively charged surface patch (E59Y) also increased apparent solubility and reduced viscosity of MAB 1, but charge reversal at the same position (E59K/R) caused destabilization, decreased solubility and led to difficulties in sample manipulation that precluded their viscosity measurements at high concentrations. Both V44K and E59Y mutations showed similar increase in apparent solubility. However, the viscosity profile of E59Y was considerably better than that of the V44K, providing evidence that inter-molecular interactions in MAB 1 are electrostatically driven. In conclusion, neutralizing negatively charged surface patches may be more beneficial toward reducing viscosity of highly concentrated antibody solutions than charge reversal or aggregation prone motif disruption.

DNA-inspired hierarchical polymer design: electrostatics and hydrogen bonding in concert.

Science.gov (United States)

Hemp, Sean T; Long, Timothy E

2012-01-01

Nucleic acids and proteins, two of nature's biopolymers, assemble into complex structures to achieve desired biological functions and inspire the design of synthetic macromolecules containing a wide variety of noncovalent interactions including electrostatics and hydrogen bonding. Researchers have incorporated DNA nucleobases into a wide variety of synthetic monomers/polymers achieving stimuli-responsive materials, supramolecular assemblies, and well-controlled macromolecules. Recently, scientists utilized both electrostatics and complementary hydrogen bonding to orthogonally functionalize a polymer backbone through supramolecular assembly. Diverse macromolecules with noncovalent interactions will create materials with properties necessary for biomedical applications. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Role of Subunit Exchange and Electrostatic Interactions on the Chaperone Activity of Mycobacterium leprae HSP18

Science.gov (United States)

Nandi, Sandip Kumar; Panda, Alok Kumar; Chakraborty, Ayon; Ray, Sougata Sinha; Biswas, Ashis

2015-01-01

Mycobacterium leprae HSP18, a major immunodominant antigen of M. leprae pathogen, is a small heat shock protein. Previously, we reported that HSP18 is a molecular chaperone that prevents aggregation of different chemically and thermally stressed client proteins and assists refolding of denatured enzyme at normal temperature. We also demonstrated that it can efficiently prevent the thermal killing of E. coli at higher temperature. However, molecular mechanism behind the chaperone function of HSP18 is still unclear. Therefore, we studied the structure and chaperone function of HSP18 at normal temperature (25°C) as well as at higher temperatures (31–43°C). Our study revealed that the chaperone function of HSP18 is enhanced significantly with increasing temperature. Far- and near-UV CD experiments suggested that its secondary and tertiary structure remain intact in this temperature range (25–43°C). Besides, temperature has no effect on the static oligomeric size of this protein. Subunit exchange study demonstrated that subunits of HSP18 exchange at 25°C with a rate constant of 0.018 min-1. Both rate of subunit exchange and chaperone activity of HSP18 is found to increase with rise in temperature. However, the surface hydrophobicity of HSP18 decreases markedly upon heating and has no correlation with its chaperone function in this temperature range. Furthermore, we observed that HSP18 exhibits diminished chaperone function in the presence of NaCl at 25°C. At elevated temperatures, weakening of interactions between HSP18 and stressed client proteins in the presence of NaCl results in greater reduction of its chaperone function. The oligomeric size, rate of subunit exchange and structural stability of HSP18 were also found to decrease when electrostatic interactions were weakened. These results clearly indicated that subunit exchange and electrostatic interactions play a major role in the chaperone function of HSP18. PMID:26098662

Role of Subunit Exchange and Electrostatic Interactions on the Chaperone Activity of Mycobacterium leprae HSP18.

Science.gov (United States)

Nandi, Sandip Kumar; Panda, Alok Kumar; Chakraborty, Ayon; Sinha Ray, Sougata; Biswas, Ashis

2015-01-01

Mycobacterium leprae HSP18, a major immunodominant antigen of M. leprae pathogen, is a small heat shock protein. Previously, we reported that HSP18 is a molecular chaperone that prevents aggregation of different chemically and thermally stressed client proteins and assists refolding of denatured enzyme at normal temperature. We also demonstrated that it can efficiently prevent the thermal killing of E. coli at higher temperature. However, molecular mechanism behind the chaperone function of HSP18 is still unclear. Therefore, we studied the structure and chaperone function of HSP18 at normal temperature (25°C) as well as at higher temperatures (31-43°C). Our study revealed that the chaperone function of HSP18 is enhanced significantly with increasing temperature. Far- and near-UV CD experiments suggested that its secondary and tertiary structure remain intact in this temperature range (25-43°C). Besides, temperature has no effect on the static oligomeric size of this protein. Subunit exchange study demonstrated that subunits of HSP18 exchange at 25°C with a rate constant of 0.018 min(-1). Both rate of subunit exchange and chaperone activity of HSP18 is found to increase with rise in temperature. However, the surface hydrophobicity of HSP18 decreases markedly upon heating and has no correlation with its chaperone function in this temperature range. Furthermore, we observed that HSP18 exhibits diminished chaperone function in the presence of NaCl at 25°C. At elevated temperatures, weakening of interactions between HSP18 and stressed client proteins in the presence of NaCl results in greater reduction of its chaperone function. The oligomeric size, rate of subunit exchange and structural stability of HSP18 were also found to decrease when electrostatic interactions were weakened. These results clearly indicated that subunit exchange and electrostatic interactions play a major role in the chaperone function of HSP18.

Molecular printboards as a general platform for protein immobilization: A supramolecular solution to nonspecific adsorption

NARCIS (Netherlands)

Ludden, M.J.W.; Mulder, A.; Tampe, Robert; Reinhoudt, David; Huskens, Jurriaan

2007-01-01

Be specific: A supramolecular adsorbate consisting of an adamantyl group (red) and an oligo(ethylene glycol) chain has been designed to prevent nonspecific protein adsorption at cyclodextrin molecular printboards. The adamantyl group allows specific and reversible interactions. Specific

Effect of electrostatic interaction on thermochemical behavior of 12-crown-4 ether in various polar solvents

International Nuclear Information System (INIS)

Barannikov, Vladimir P.; Guseynov, Sabir S.; Vyugin, Anatoliy I.

2010-01-01

The enthalpies of solution of 12-crown-4 ether have been measured in chloroform, ethyl acetate, acetone, pyridine, acetonitrile and methanol at 298.15 K. The values of enthalpy of solvation and solute-solvent interaction were determined from the obtained results and similar literature data for 12-crown-4 in solvents of various polarities. It was shown that the certain correlation is observed between the enthalpy of solute-solvent interaction and the squared dipole moment of the solvent molecules for solutions in tetrachlormethane, ethyl acetate, pyridine, acetonitrile, DMF, DMSO and propylene carbonate. This means that the electrostatic interaction of 12-crown-4 with polar solvent molecules contributes significantly to the exothermic effect of solvation. The understated negative value was found for the enthalpy of interaction of 12-crown-4 with acetone that can be connected with domination of low polar conformer of the crown ether in acetone medium. The most negative values of enthalpy of solvation are observed for solutions in chloroform and water because of hydrogen bonding between O-atoms of crown ether and molecules of the indicated solvents. This effect is not observed for methanol. The negative coefficient of pairwise solute-solute interaction in methanol indicates that the effects of solvophobic solute-solute interaction and H-bonding of the ether molecule with chain associates of methanol are not evinced in the thermochemical behavior of 12-crown-4.

Electrostatic Origin of the Red Solvatochromic Shift of DFHBDI in RNA Spinach.

Science.gov (United States)

Bose, Samik; Chakrabarty, Suman; Ghosh, Debashree

2017-05-11

Interactions with the environment tune the spectral properties of biological chromophores, e.g., fluorescent proteins. Understanding the relative contribution of the various types of noncovalent interactions in the spectral shifts can provide rational design principles toward developing new fluorescent probes. In this work, we investigate the origin of the red shift in the absorption spectra of the difluoro hydroxybenzylidene dimethyl imidazolinone (DFHBDI) chromophore in RNA spinach as compared to the aqueous solution. We systematically decompose the effects of various components of interactions, namely, stacking, hydrogen bonding, and long-range electrostatics, in order to elucidate the relative role of these interactions in the observed spectral behavior. We find that the absorption peak of DFHBDI is red-shifted by ∼0.35 eV in RNA relative to the aqueous solution. Earlier proposals from Huang and co-workers have implicated the stacking interactions between DFHBDI and nucleic acid bases to be the driving force behind the observed red shift. In contrast, our findings reveal that the long-range electrostatic interactions between DFHBDI and negatively charged RNA make the most significant contribution. Moreover, we notice that the opposing electrostatic fields due to the RNA backbone and the polarized water molecules around the RNA give rise to the resultant red shift. Our results emphasize the effect of strong heterogeneity in the various environmental factors that might be competing with each other.

Structural and electrostatic regularities in interactions of homeodomains with operator DNA

International Nuclear Information System (INIS)

Chirgadze, Yu.N.; Ivanov, V.V.; Polozov, R.V.; Zheltukhin, E.I.; Sivozhelezov, V.S.

2008-01-01

Interfaces of five DNA-homeodomain complexes, selected by similarity of structures and patterns of contacting residues, were compared. The long-range stage of the recognition process was characterized by electrostatic potentials about 5 Angstroem away from molecular surfaces of both protein and DNA. For proteins, clear positive potential is displayed only at the side contacting DNA, while grooves of DNA display a strong negative potential. Thus, one functional role of electrostatics is guiding the protein into the DNA major groove. At the close-range stage, neutralization of the phosphate charges by positively charged residues is necessary for decreasing the strong electrostatic potential of DNA, allowing nucleotide bases to participate in formation of protein-DNA atomic contacts in the interface. The protein's recognizing α-helix was shown to form both invariant and variable contacts with DNA by means of the certain specific side groups, with water molecules participating in some of the contacts. The invariant contacts included the highly specific Asn-Ade hydrogen bonds, nonpolar contacts of hydrophobic amino acids serving as barriers for fixing the protein on DNA, and interface water molecule cluster providing local mobility necessary for the dissociation of the protein-DNA complex. One of the water molecules is invariant and located at the center of the interface. Invariant contacts of the proteins are mostly formed with the TAAT motive of promoter DNA's forward strand. They distinguish the homeodomain family from other DNA-binding proteins. Variable contacts are formed with the reverse strand and are responsible for the binding specificity within the homeodomain family

Experimental investigation of the impact of compound-specific dispersion and electrostatic interactions on transient transport and solute breakthrough

DEFF Research Database (Denmark)

Muniruzzaman, Muhammad; Rolle, Massimo

2017-01-01

. The experimental results show that compound-specific effects and charge-induced Coulombic interactions are important not only at low velocities and/or for steady state plumes but also for transient transport under high flow velocities. Such effects can lead to a remarkably different behavior of measured....... The latter is based on the multicomponent formulation of coupled diffusive/dispersive fluxes and was used to describe and explain the electrostatic effects of charged species. Furthermore, we determined experimentally the temporal profiles of the flux-related dilution index. This metric of mixing, used...

The impact of base stacking on the conformations and electrostatics of single-stranded DNA.

Science.gov (United States)

Plumridge, Alex; Meisburger, Steve P; Andresen, Kurt; Pollack, Lois

2017-04-20

Single-stranded DNA (ssDNA) is notable for its interactions with ssDNA binding proteins (SSBs) during fundamentally important biological processes including DNA repair and replication. Previous work has begun to characterize the conformational and electrostatic properties of ssDNA in association with SSBs. However, the conformational distributions of free ssDNA have been difficult to determine. To capture the vast array of ssDNA conformations in solution, we pair small angle X-ray scattering with novel ensemble fitting methods, obtaining key parameters such as the size, shape and stacking character of strands with different sequences. Complementary ion counting measurements using inductively coupled plasma atomic emission spectroscopy are employed to determine the composition of the ion atmosphere at physiological ionic strength. Applying this combined approach to poly dA and poly dT, we find that the global properties of these sequences are very similar, despite having vastly different propensities for single-stranded helical stacking. These results suggest that a relatively simple mechanism for the binding of ssDNA to non-specific SSBs may be at play, which explains the disparity in binding affinities observed for these systems. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Embedding beyond electrostatics

DEFF Research Database (Denmark)

Nåbo, Lina J.; Olsen, Jógvan Magnus Haugaard; Holmgaard List, Nanna

2016-01-01

We study excited states of cholesterol in solution and show that, in this specific case, solute wave-function confinement is the main effect of the solvent. This is rationalized on the basis of the polarizable density embedding scheme, which in addition to polarizable embedding includes non-electrostatic...... repulsion that effectively confines the solute wave function to its cavity. We illustrate how the inclusion of non-electrostatic repulsion results in a successful identification of the intense π → π∗ transition, which was not possible using an embedding method that only includes electrostatics....... This underlines the importance of non-electrostatic repulsion in quantum-mechanical embedding-based methods....

Improving the treatment of coarse-grain electrostatics: CVCEL

Energy Technology Data Exchange (ETDEWEB)

Ceres, N.; Lavery, R., E-mail: richard.lavery@ibcp.fr [Bioinformatics: Structures and Interactions, Institut de Biologie et Chimie des Protéines, BMSSI UMR CNRS 5086/Université Lyon I, 7 Passage du Vercors, Lyon 69367 (France)

2015-12-28

We propose an analytic approach for calculating the electrostatic energy of proteins or protein complexes in aqueous solution. This method, termed CVCEL (Circular Variance Continuum ELectrostatics), is fitted to Poisson calculations and is able to reproduce the corresponding energies for different choices of solute dielectric constant. CVCEL thus treats both solute charge interactions and charge self-energies, and it can also deal with salt solutions. Electrostatic damping notably depends on the degree of solvent exposure of the charges, quantified here in terms of circular variance, a measure that reflects the vectorial distribution of the neighbors around a given center. CVCEL energies can be calculated rapidly and have simple analytical derivatives. This approach avoids the need for calculating effective atomic volumes or Born radii. After describing how the method was developed, we present test results for coarse-grain proteins of different shapes and sizes, using different internal dielectric constants and different salt concentrations and also compare the results with those from simple distance-dependent models. We also show that the CVCEL approach can be used successfully to calculate the changes in electrostatic energy associated with changes in protein conformation or with protein-protein binding.

Improving the treatment of coarse-grain electrostatics: CVCEL

International Nuclear Information System (INIS)

Ceres, N.; Lavery, R.

2015-01-01

We propose an analytic approach for calculating the electrostatic energy of proteins or protein complexes in aqueous solution. This method, termed CVCEL (Circular Variance Continuum ELectrostatics), is fitted to Poisson calculations and is able to reproduce the corresponding energies for different choices of solute dielectric constant. CVCEL thus treats both solute charge interactions and charge self-energies, and it can also deal with salt solutions. Electrostatic damping notably depends on the degree of solvent exposure of the charges, quantified here in terms of circular variance, a measure that reflects the vectorial distribution of the neighbors around a given center. CVCEL energies can be calculated rapidly and have simple analytical derivatives. This approach avoids the need for calculating effective atomic volumes or Born radii. After describing how the method was developed, we present test results for coarse-grain proteins of different shapes and sizes, using different internal dielectric constants and different salt concentrations and also compare the results with those from simple distance-dependent models. We also show that the CVCEL approach can be used successfully to calculate the changes in electrostatic energy associated with changes in protein conformation or with protein-protein binding

Improving the treatment of coarse-grain electrostatics: CVCEL.

Science.gov (United States)

Ceres, N; Lavery, R

2015-12-28

We propose an analytic approach for calculating the electrostatic energy of proteins or protein complexes in aqueous solution. This method, termed CVCEL (Circular Variance Continuum ELectrostatics), is fitted to Poisson calculations and is able to reproduce the corresponding energies for different choices of solute dielectric constant. CVCEL thus treats both solute charge interactions and charge self-energies, and it can also deal with salt solutions. Electrostatic damping notably depends on the degree of solvent exposure of the charges, quantified here in terms of circular variance, a measure that reflects the vectorial distribution of the neighbors around a given center. CVCEL energies can be calculated rapidly and have simple analytical derivatives. This approach avoids the need for calculating effective atomic volumes or Born radii. After describing how the method was developed, we present test results for coarse-grain proteins of different shapes and sizes, using different internal dielectric constants and different salt concentrations and also compare the results with those from simple distance-dependent models. We also show that the CVCEL approach can be used successfully to calculate the changes in electrostatic energy associated with changes in protein conformation or with protein-protein binding.

G-mode magnetic force microscopy: Separating magnetic and electrostatic interactions using big data analytics

Energy Technology Data Exchange (ETDEWEB)

Collins, Liam; Belianinov, Alex; Kalinin, Sergei V.; Jesse, Stephen [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Proksch, Roger [Asylum Research, An Oxford Instruments Company, Santa Barbara, California 93117 (United States); Zuo, Tingting [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Deptarment of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996-2200 (United States); Zhang, Yong [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Liaw, Peter K. [Deptarment of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996-2200 (United States)

2016-05-09

In this work, we develop a full information capture approach for Magnetic Force Microscopy (MFM), referred to as generalized mode (G-Mode) MFM. G-Mode MFM acquires and stores the full data stream from the photodetector, captured at sampling rates approaching the intrinsic photodiode limit. The data can be subsequently compressed, denoised, and analyzed, without information loss. Here, G-Mode MFM is implemented and compared to the traditional heterodyne-based MFM on model systems, including domain structures in ferromagnetic Yttrium Iron Garnet and the electronically and magnetically inhomogeneous high entropy alloy, CoFeMnNiSn. We investigate the use of information theory to mine the G-Mode MFM data and demonstrate its usefulness for extracting information which may be hidden in traditional MFM modes, including signatures of nonlinearities and mode-coupling phenomena. Finally, we demonstrate detection and separation of magnetic and electrostatic tip-sample interactions from a single G-Mode image, by analyzing the entire frequency response of the cantilever. G-Mode MFM is immediately implementable on any atomic force microscopy platform and as such is expected to be a useful technique for probing spatiotemporal cantilever dynamics and mapping material properties, as well as their mutual interactions.

Electrostatics-Driven Hierarchical Buckling of Charged Flexible Ribbons.

Science.gov (United States)

Yao, Zhenwei; Olvera de la Cruz, Monica

2016-04-08

We investigate the rich morphologies of an electrically charged flexible ribbon, which is a prototype for many beltlike structures in biology and nanomaterials. Long-range electrostatic repulsion is found to govern the hierarchical buckling of the ribbon from its initially flat shape to its undulated and out-of-plane twisted conformations. In this process, the screening length is the key controlling parameter, suggesting that a convenient way to manipulate the ribbon morphology is simply to change the salt concentration. We find that these shapes originate from the geometric effect of the electrostatic interaction, which fundamentally changes the metric over the ribbon surface. We also identify the basic modes by which the ribbon reshapes itself in order to lower the energy. The geometric effect of the physical interaction revealed in this Letter has implications for the shape design of extensive ribbonlike materials in nano- and biomaterials.

Electrostatic Effects in Phase Transitions of Biomembranes between Cubic Phases and Lamellar Liquid-Crystalline (Lα) phase

Science.gov (United States)

Masum, Shah Md.; Li, Shu Jie; Tamba, Yukihiro; Yamashita, Yuko; Yamazaki, Masahito

2004-04-01

Elucidation of the mechanisms of transitions between cubic phase and liquid-crystalline (Lα) phase, and between different IPMS cubic phases, are essential for understanding of dynamics of biomembranes and topological transformation of lipid membranes. Recently, we found that electrostatic interactions due to surface charges of lipid membranes induce transition between cubic phase and Lα phase, and between different IPMS cubic phases. As electrostatic interactions increase, the most stable phase of a monoolein (MO) membrane changes: Q224 ⇒ Q229 ⇒ Lα. We also found that a de novo designed peptide partitioning into electrically neutral lipid membrane changed the phase stability of the MO membranes. As peptide-1 concentration increased, the most stable phase of a MO membrane changes: Q224 ⇒ Q229 ⇒Lα. In both cases, the increase in the electrostatic repulsive interaction greatly reduced the absolute value of spontaneous curvature of the MO monolayer membrane. We also investigated factors such as poly (L-lysine) and osmotic stress to control structure and phase stability of DOPA/MO membranes. Based on these results, we discuss the mechanism of the effect of electrostatic interactions on the stability of cubic phase.

Dynamics of Quasi-Electrostatic Whistler waves in Earth's Radiation belts

Science.gov (United States)

Goyal, R.; Sharma, R. P.; Gupta, D. N.

2017-12-01

A numerical model is proposed to study the dynamics of high amplitude quasi-electrostatic whistler waves propagating near resonance cone angle and their interaction with finite frequency kinetic Alfvén waves (KAWs) in Earth's radiation belts. The quasi-electrostatic character of whistlers is narrated by dynamics of wave propagating near resonance cone. A high amplitude whistler wave packet is obtained using the present analysis which has also been observed by S/WAVES instrument onboard STEREO. The numerical simulation technique employed to study the dynamics, leads to localization (channelling) of waves as well as turbulent spectrum suggesting the transfer of wave energy over a range of frequencies. The turbulent spectrum also indicates the presence of quasi-electrostatic whistlers and density fluctuations associated with KAW in radiation belts plasma. The ponderomotive force of pump quasi-electrostatic whistlers (high frequency) is used to excite relatively much lower frequency waves (KAWs). The wave localization and steeper spectra could be responsible for particle energization or heating in radiation belts.

Electrostatics promotes molecular crowding and selects the aggregation pathway in fibril-forming protein solutions

International Nuclear Information System (INIS)

Raccosta, S.; Martorana, V.; Manno, M.; Blanco, M.; Roberts, C.J.

2016-01-01

The role of intermolecular interaction in fibril-forming protein solutions and its relation with molecular conformation are crucial aspects for the control and inhibition of amyloid structures. Here, we study the fibril formation and the protein-protein interactions for two proteins at acidic ph, lysozyme and α-chymotrypsinogen. By using light scattering experiments and the Kirkwood-Buff integral approach, we show how concentration fluctuations are damped even at moderate protein concentrations by the dominant long-ranged electrostatic repulsion, which determines an effective crowded environment. In denaturing conditions, electrostatic repulsion keeps the monomeric solution in a thermodynamically metastable state, which is escaped through kinetically populated conformational sub-states. This explains how electrostatics acts as a gatekeeper in selecting a specific aggregation pathway.

Theeffectivenessofginger compress on non-specific low back pain ...

African Journals Online (AJOL)

Theeffectivenessofginger compress on non-specific low back pain. ... for a total of ten sessions and control group (n=7) did not received any treatment. ... in pain relief and reduces functional disability in patients with non-specific low back pain.

NONLINEAR DYNAMICS OF CARBON NANOTUBES UNDER LARGE ELECTROSTATIC FORCE

KAUST Repository

Xu, Tiantian

2015-06-01

Because of the inherent nonlinearities involving the behavior of CNTs when excited by electrostatic forces, modeling and simulating their behavior is challenging. The complicated form of the electrostatic force describing the interaction of their cylindrical shape, forming upper electrodes, to lower electrodes poises serious computational challenges. This presents an obstacle against applying and using several nonlinear dynamics tools typically used to analyze the behavior of complicated nonlinear systems undergoing large motion, such as shooting, continuation, and integrity analysis techniques. This works presents an attempt to resolve this issue. We present an investigation of the nonlinear dynamics of carbon nanotubes when actuated by large electrostatic forces. We study expanding the complicated form of the electrostatic force into enough number of terms of the Taylor series. Then, we utilize this form along with an Euler-Bernoulli beam model to study for the first time the dynamic behavior of CNTs when excited by large electrostatic force. The geometric nonlinearity and the nonlinear electrostatic force are considered. An efficient reduced-order model (ROM) based on the Galerkin method is developed and utilized to simulate the static and dynamic responses of the CNTs. Several results are generated demonstrating softening and hardening behavior of the CNTs near their primary and secondary resonances. The effects of the DC and AC voltage loads on the behavior have been studied. The impacts of the initial slack level and CNT diameter are also demonstrated.

Nonlinear Dynamics of Carbon Nanotubes Under Large Electrostatic Force

KAUST Repository

Xu, Tiantian

2015-06-01

Because of the inherent nonlinearities involving the behavior of CNTs when excited by electrostatic forces, modeling and simulating their behavior is challenging. The complicated form of the electrostatic force describing the interaction of their cylindrical shape, forming upper electrodes, to lower electrodes poises serious computational challenges. This presents an obstacle against applying and using several nonlinear dynamics tools typically used to analyze the behavior of complicated nonlinear systems undergoing large motion, such as shooting, continuation, and integrity analysis techniques. This works presents an attempt to resolve this issue. We present an investigation of the nonlinear dynamics of carbon nanotubes when actuated by large electrostatic forces. We study expanding the complicated form of the electrostatic force into enough number of terms of the Taylor series. Then, we utilize this form along with an Euler-Bernoulli beam model to study for the first time the dynamic behavior of CNTs when excited by large electrostatic force. The geometric nonlinearity and the nonlinear electrostatic force are considered. An efficient reduced-order model (ROM) based on the Galerkin method is developed and utilized to simulate the static and dynamic responses of the CNTs. Several results are generated demonstrating softening and hardening behavior of the CNTs near their primary and secondary resonances. The effects of the DC and AC voltage loads on the behavior have been studied. The impacts of the initial slack level and CNT diameter are also demonstrated.

Electrostatics and the assembly of an RNA virus

NARCIS (Netherlands)

Schoot, van der P.P.A.M.; Bruinsma, R.

2005-01-01

Electrostatic interactions play a central role in the assembly of single-stranded RNA viruses. Under physiological conditions of salinity and acidity, virus capsid assembly requires the presence of genomic material that is oppositely charged to the core proteins. In this paper we apply basic polymer

A new application of scanning electrochemical microscopy for the label-free interrogation of antibody-antigen interactions

Energy Technology Data Exchange (ETDEWEB)

Holmes, Joanne L.; Davis, Frank; Collyer, Stuart D. [Cranfield Health, Cranfield University, Cranfield, MK43 0AL (United Kingdom); Higson, Seamus P.J., E-mail: s.p.j.higson@cranfield.ac.uk [Cranfield Health, Cranfield University, Cranfield, MK43 0AL (United Kingdom)

2011-03-18

Within this work we present a 'proof of principle' study for the use of scanning electrochemical microscopy (SECM) to detect and image biomolecular interactions in a label-free assay as a potential alternative to current fluorescence techniques. Screen-printed carbon electrodes were used as the substrate for the deposition of a dotted array, where the dots consist of biotinylated polyethyleneimine. These were then further derivatised, first with neutravidin and then with a biotinylated antibody to the protein neuron specific enolase (NSE). SECM using a ferrocene carboxylic acid mediator showed clear differences between the array and the surrounding unmodified carbon. Imaging of the arrays before and following exposure to various concentrations of the antigen showed clear evidence for specific binding of the NSE antigen to the antibody derivatised dots. Non-specific binding was quantified. Control experiments with other proteins showed only non-specific binding across the whole of the substrate, thereby confirming that specific binding does occur between the antibody and antigen at the surface of the dots. Binding of the antigen was accompanied by a measured increase in current response, which may be explained in terms of protein electrostatic interaction and hydrophobic interactions to the mediator, thereby increasing the localised mediator flux. A calibration curve was obtained between 500 fg mL{sup -1} to 200 pg mL{sup -1} NSE which demonstrated a logarithmic relationship between the current change upon binding and antigen concentration without the need for any labelling of the substrate.

Optimization of key factors of the electrostatic separation for crushed PCB wastes using roll-type separator

International Nuclear Information System (INIS)

Wu Jiang; Li Jia; Xu Zhenming

2008-01-01

For the electrostatic separation process, the separator is most crucial. As a classical one, the roll-type corona-electrostatic separator has some advantages in recycle of waste electrical and electronic equipment (WEEE). Some researches have been done in this field and shown that there was a complex correlation between its configuration and the efficiency of the separation. In this paper, a fractional factorial design (2 v 1-5 ) was built and 32 tests were performed on a roll-type corona-electrostatic separator. The sample of granular mixture got from crushed PCB wastes (size 0.3-0.45 mm, containing 25% metal and 75% nonmetal). The experimental data were discussed and used to analyze the factors' main effect, interaction and optimization of the process. Three liner-interaction mathematical models were derived to describe the mass of middling fraction (M), conductor fraction (C) and Nonconductor fraction (NC), respectively. The results show that the efficiency of the PCB waste electrostatic separation process has a significant correlation with not only factors' main effects, but also the interaction between them

Large electrostatic accelerators

Energy Technology Data Exchange (ETDEWEB)

Jones, C.M.

1984-01-01

The increasing importance of energetic heavy ion beams in the study of atomic physics, nuclear physics, and materials science has partially or wholly motivated the construction of a new generation of large electrostatic accelerators designed to operate at terminal potentials of 20 MV or above. In this paper, the author briefly discusses the status of these new accelerators and also discusses several recent technological advances which may be expected to further improve their performance. The paper is divided into four parts: (1) a discussion of the motivation for the construction of large electrostatic accelerators, (2) a description and discussion of several large electrostatic accelerators which have been recently completed or are under construction, (3) a description of several recent innovations which may be expected to improve the performance of large electrostatic accelerators in the future, and (4) a description of an innovative new large electrostatic accelerator whose construction is scheduled to begin next year. Due to time and space constraints, discussion is restricted to consideration of only tandem accelerators.

Large electrostatic accelerators

International Nuclear Information System (INIS)

Jones, C.M.

1984-01-01

The increasing importance of energetic heavy ion beams in the study of atomic physics, nuclear physics, and materials science has partially or wholly motivated the construction of a new generation of large electrostatic accelerators designed to operate at terminal potentials of 20 MV or above. In this paper, the author briefly discusses the status of these new accelerators and also discusses several recent technological advances which may be expected to further improve their performance. The paper is divided into four parts: (1) a discussion of the motivation for the construction of large electrostatic accelerators, (2) a description and discussion of several large electrostatic accelerators which have been recently completed or are under construction, (3) a description of several recent innovations which may be expected to improve the performance of large electrostatic accelerators in the future, and (4) a description of an innovative new large electrostatic accelerator whose construction is scheduled to begin next year. Due to time and space constraints, discussion is restricted to consideration of only tandem accelerators

Proton emission with a screened electrostatic barrier

Energy Technology Data Exchange (ETDEWEB)

Budaca, R. [Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele (Romania); Academy of Romanian Scientists, Bucharest (Romania); Budaca, A.I. [Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele (Romania)

2017-08-15

Half-lives of proton emission for Z ≥ 51 nuclei are calculated within a simple analytical model based on the WKB approximation for the barrier penetration probability which includes the centrifugal and overlapping effects besides the electrostatic repulsion. The model has a single free parameter associated to a Hulthen potential which emulates a Coulomb electrostatic interaction only at short distance. The agreement with experimental data is very good for most of the considered nuclei. Theoretical predictions are made for few cases with uncertain emitting state configuration or incomplete decay information. The model's assignment of the proton orbital momentum is in agreement with the differentiation of the experimental data by orbital momentum values realized with a newly introduced correlation formula. (orig.)

A Solvatochromic Model Calibrates Nitriles’ Vibrational Frequencies to Electrostatic Fields

Science.gov (United States)

Bagchi, Sayan; Fried, Stephen D.; Boxer, Steven G.

2012-01-01

Electrostatic interactions provide a primary connection between a protein’s three-dimensional structure and its function. Infrared (IR) probes are useful because vibrational frequencies of certain chemical groups, such as nitriles, are linearly sensitive to local electrostatic field, and can serve as a molecular electric field meter. IR spectroscopy has been used to study electrostatic changes or fluctuations in proteins, but measured peak frequencies have not been previously mapped to total electric fields, because of the absence of a field-frequency calibration and the complication of local chemical effects such as H-bonds. We report a solvatochromic model that provides a means to assess the H-bonding status of aromatic nitrile vibrational probes, and calibrates their vibrational frequencies to electrostatic field. The analysis involves correlations between the nitrile’s IR frequency and its 13C chemical shift, whose observation is facilitated by a robust method for introducing isotopes into aromatic nitriles. The method is tested on the model protein Ribonuclease S (RNase S) containing a labeled p-CN-Phe near the active site. Comparison of the measurements in RNase S against solvatochromic data gives an estimate of the average total electrostatic field at this location. The value determined agrees quantitatively with MD simulations, suggesting broader potential for the use of IR probes in the study of protein electrostatics. PMID:22694663

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

International Nuclear Information System (INIS)

Kato, Tsunehiko N.; Takabe, Hideaki

2010-01-01

A two-dimensional electromagnetic particle-in-cell simulation with the realistic ion-to-electron mass ratio of 1836 is carried out to investigate the electrostatic collisionless shocks in relatively high-speed (∼3000 km s -1 ) plasma flows and also the influence of both electrostatic and electromagnetic instabilities, which can develop around the shocks, on the shock dynamics. It is shown that the electrostatic ion-ion instability can develop in front of the shocks, where the plasma is under counterstreaming condition, with highly oblique wave vectors as was shown previously. The electrostatic potential generated by the electrostatic ion-ion instability propagating obliquely to the shock surface becomes comparable with the shock potential and finally the shock structure is destroyed. It is also shown that in front of the shock the beam-Weibel instability gradually grows as well, consequently suggesting that the magnetic field generated by the beam-Weibel instability becomes important in long-term evolution of the shock and the Weibel-mediated shock forms long after the electrostatic shock vanished. It is also observed that the secondary electrostatic shock forms in the reflected ions in front of the primary electrostatic shock.

An expanded genetic code for probing the role of electrostatics in enzyme catalysis by vibrational Stark spectroscopy.

Science.gov (United States)

Völler, Jan-Stefan; Biava, Hernan; Hildebrandt, Peter; Budisa, Nediljko

2017-11-01

To find experimental validation for electrostatic interactions essential for catalytic reactions represents a challenge due to practical limitations in assessing electric fields within protein structures. This review examines the applications of non-canonical amino acids (ncAAs) as genetically encoded probes for studying the role of electrostatic interactions in enzyme catalysis. ncAAs constitute sensitive spectroscopic probes to detect local electric fields by exploiting the vibrational Stark effect (VSE) and thus have the potential to map the protein electrostatics. Mapping the electrostatics in proteins will improve our understanding of natural catalytic processes and, in beyond, will be helpful for biocatalyst engineering. This article is part of a Special Issue entitled "Biochemistry of Synthetic Biology - Recent Developments" Guest Editor: Dr. Ilka Heinemann and Dr. Patrick O'Donoghue. Copyright © 2017 Elsevier B.V. All rights reserved.

The two sides of complement C3d: evolution of electrostatics in a link between innate and adaptive immunity.

Science.gov (United States)

Kieslich, Chris A; Morikis, Dimitrios

2012-01-01

The interaction between complement fragment C3d and complement receptor 2 (CR2) is a key aspect of complement immune system activation, and is a component in a link between innate and adaptive immunities. The complement immune system is an ancient mechanism for defense, and can be found in species that have been on Earth for the last 600 million years. However, the link between the complement system and adaptive immunity, which is formed through the association of the B-cell co-receptor complex, including the C3d-CR2 interaction, is a much more recent adaptation. Human C3d and CR2 have net charges of -1 and +7 respectively, and are believed to have evolved favoring the role of electrostatics in their functions. To investigate the role of electrostatics in the function and evolution of human C3d and CR2, we have applied electrostatic similarity methods to identify regions of evolutionarily conserved electrostatic potential based on 24 homologues of complement C3d and 4 homologues of CR2. We also examine the effects of structural perturbation, as introduced through molecular dynamics and mutations, on spatial distributions of electrostatic potential to identify perturbation resistant regions, generated by so-called electrostatic "hot-spots". Distributions of electrostatic similarity based on families of perturbed structures illustrate the presence of electrostatic "hot-spots" at the two functional sites of C3d, while the surface of CR2 lacks electrostatic "hot-spots" despite its excessively positive nature. We propose that the electrostatic "hot-spots" of C3d have evolved to optimize its dual-functionality (covalently attaching to pathogen surfaces and interaction with CR2), which are both necessary for the formation B-cell co-receptor complexes. Comparison of the perturbation resistance of the electrostatic character of the homologues of C3d suggests that there was an emergence of a new role of electrostatics, and a transition in the function of C3d, after the

The two sides of complement C3d: evolution of electrostatics in a link between innate and adaptive immunity.

Directory of Open Access Journals (Sweden)

Chris A Kieslich

Full Text Available The interaction between complement fragment C3d and complement receptor 2 (CR2 is a key aspect of complement immune system activation, and is a component in a link between innate and adaptive immunities. The complement immune system is an ancient mechanism for defense, and can be found in species that have been on Earth for the last 600 million years. However, the link between the complement system and adaptive immunity, which is formed through the association of the B-cell co-receptor complex, including the C3d-CR2 interaction, is a much more recent adaptation. Human C3d and CR2 have net charges of -1 and +7 respectively, and are believed to have evolved favoring the role of electrostatics in their functions. To investigate the role of electrostatics in the function and evolution of human C3d and CR2, we have applied electrostatic similarity methods to identify regions of evolutionarily conserved electrostatic potential based on 24 homologues of complement C3d and 4 homologues of CR2. We also examine the effects of structural perturbation, as introduced through molecular dynamics and mutations, on spatial distributions of electrostatic potential to identify perturbation resistant regions, generated by so-called electrostatic "hot-spots". Distributions of electrostatic similarity based on families of perturbed structures illustrate the presence of electrostatic "hot-spots" at the two functional sites of C3d, while the surface of CR2 lacks electrostatic "hot-spots" despite its excessively positive nature. We propose that the electrostatic "hot-spots" of C3d have evolved to optimize its dual-functionality (covalently attaching to pathogen surfaces and interaction with CR2, which are both necessary for the formation B-cell co-receptor complexes. Comparison of the perturbation resistance of the electrostatic character of the homologues of C3d suggests that there was an emergence of a new role of electrostatics, and a transition in the function of C3

Construction and Self-Assembly of Single-Chain Polymer Nanoparticles via Coordination Association and Electrostatic Repulsion in Water.

Science.gov (United States)

Zhu, Zhengguang; Xu, Na; Yu, Qiuping; Guo, Lei; Cao, Hui; Lu, Xinhua; Cai, Yuanli

2015-08-01

Simultaneous coordination-association and electrostatic-repulsion interactions play critical roles in the construction and stabilization of enzymatic function metal centers in water media. These interactions are promising for construction and self-assembly of artificial aqueous polymer single-chain nanoparticles (SCNPs). Herein, the construction and self-assembly of dative-bonded aqueous SCNPs are reported via simultaneous coordination-association and electrostatic-repulsion interactions within single chains of histamine-based hydrophilic block copolymer. The electrostatic-repulsion interactions are tunable through adjusting the imidazolium/imidazole ratio in response to pH, and in situ Cu(II)-coordination leads to the intramolecular association and single-chain collapse in acidic water. SCNPs are stabilized by the electrostatic repulsion of dative-bonded block and steric shielding of nonionic water-soluble block, and have a huge specific surface area of function metal centers accessible to substrates in acidic water. Moreover, SCNPs can assemble into micelles, networks, and large particles programmably in response to the solution pH. These unique media-sensitive phase-transformation behaviors provide a general, facile, and versatile platform for the fabrication of enzyme-inspired smart aqueous catalysts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of dielectric inhomogeneity on electrostatic twist rigidity of a helical biomolecule in Debye-Hückel regime

Science.gov (United States)

Rezaie-Dereshgi, Amir; Mohammad-Rafiee, Farshid

2018-04-01

The electrostatic interactions play a crucial role in biological systems. Here we consider an impermeable dielectric molecule in the solvent with a different dielectric constant. The electrostatic free energy in the problem is studied in the Debye-Hückel regime using the analytical Green function that is calculated in the paper. Using this electrostatic free energy, we study the electrostatic contribution to the twist rigidity of a double stranded helical molecule such as a DNA and an actin filament. The dependence of the electrostatic twist rigidity of the molecule to the dielectric inhomogeneity, structural parameters, and the salt concentration is studied. It is shown that, depending on the parameters, the electrostatic twist rigidity could be positive or negative.

SIMION, Electrostatic Lens Analysis and Design

International Nuclear Information System (INIS)

Dahl, David A.

2001-01-01

1 - Description of program or function: SIMION is an electrostatic lens analysis and design program. In SIMION an electrostatic lens is defined as a two-dimensional electrostatic potential array containing both electrode and non-electrode points. The potential array is refined using over-relaxation methods allowing voltage contours and ion trajectories to be computed and plotted. Planar and cylindrical symmetry assumptions allow the two-dimensional fields to support three-dimensional ion trajectory calculations. In addition, the user has the option of writing simple programs which can among other actions control field scale factors, dynamically adjust electrodes, and define explicit three-dimensional field functions (e.g. a quadrupole) used in lieu of array fields in specified portions of the potential array. Magnetic fields can be specified for computing ion trajectories in many electrostatic and magnetic field environments. An interactive graphics interface that uses a high resolution color display and mouse allows the user to view electrodes, trajectories, and contours on the screen prior to plotting, and a memory zoom feature permits expansion of selected areas in the current view. The mouse can be operated to edit the potential array, initialize voltage gradients, or resize the potential array. 2 - Method of solution: SIMION is designed to model the electrostatic fields and forces created by a collection of shaped electrodes given certain symmetry assumptions. The electrostatic fields are modeled as boundary value problem solutions of a Laplace elliptical partial differential equation. A finite difference technique called dynamically self-adjusting over-relaxation is applied to the two-dimensional potential array of points representing electrode and non-electrode regions to obtain a best estimate of the voltages for those points within the array that depict non-electrode regions. A standard fourth-order Runge-Kutta method is used for numerical integration of

Magnetosheath electrostatic turbulence

International Nuclear Information System (INIS)

Rodriguez, P.

1979-01-01

By using measurements with the University of Iowa plasma wave experiment on the Imp 6 satellite a study has been conducted of the spectrum of electrostatic plasma waves in the terrestrial magnetosheath. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz to 70 kHz) rms field intensities typically 0.01--1.0 mV m -1 . Peak intensities of about 1.0 mV m -1 near the electron plasma frequency (30--60 kHz) have been detected occasionally. Two or three components can usually be identified in the spectrum of magnetosheath electrostatic turbulence: a high-frequency (> or =30kHz) component peaking at the electron plasma frequency f/sub p/e, a low-frequency component with a broad intensity maximum below the nominal ion plasma frequency f/sub p/i (approx. f/sub p/e/43), and a less well defined intermediate component in the range f/sub p/i < f< f/sub p/e. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low-frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath. Electrostatic waves below 1 kHz are polarized along the magnetic field direction, a result consistent with the polarization of electrostatic waves at the shock. The high- and intermediate-frequency components are features of the magnetosheath spectrum which are not characteristic of the shock spectrum but are often detected in the upstream solar wind. The intensity distribution of electrostatic turbulence at the magnetosheath plasma frequency has no apparent correlation with the shock, indicating that electron plasma oscillations are a general feature of the magnetosheath. The plasma wave noise shows a tendency to decrease toward the dawn and dusk regions, consistent with a general decrease in turbulence away from the subsolar magnetosheath

Electrostatics in Chemistry

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education; Volume 4; Issue 7. Electrostatics in Chemistry - Molecular Electrostatic Potential: Visualization and Topography. Shridhar R Gadre Pravin K Bhadane. Series Article Volume 4 Issue 7 July 1999 pp 14-23 ...

Probing the electrostatics of active site microenvironments along the catalytic cycle for Escherichia coli dihydrofolate reductase.

Science.gov (United States)

Liu, C Tony; Layfield, Joshua P; Stewart, Robert J; French, Jarrod B; Hanoian, Philip; Asbury, John B; Hammes-Schiffer, Sharon; Benkovic, Stephen J

2014-07-23

Electrostatic interactions play an important role in enzyme catalysis by guiding ligand binding and facilitating chemical reactions. These electrostatic interactions are modulated by conformational changes occurring over the catalytic cycle. Herein, the changes in active site electrostatic microenvironments are examined for all enzyme complexes along the catalytic cycle of Escherichia coli dihydrofolate reductase (ecDHFR) by incorporation of thiocyanate probes at two site-specific locations in the active site. The electrostatics and degree of hydration of the microenvironments surrounding the probes are investigated with spectroscopic techniques and mixed quantum mechanical/molecular mechanical (QM/MM) calculations. Changes in the electrostatic microenvironments along the catalytic environment lead to different nitrile (CN) vibrational stretching frequencies and (13)C NMR chemical shifts. These environmental changes arise from protein conformational rearrangements during catalysis. The QM/MM calculations reproduce the experimentally measured vibrational frequency shifts of the thiocyanate probes across the catalyzed hydride transfer step, which spans the closed and occluded conformations of the enzyme. Analysis of the molecular dynamics trajectories provides insight into the conformational changes occurring between these two states and the resulting changes in classical electrostatics and specific hydrogen-bonding interactions. The electric fields along the CN axes of the probes are decomposed into contributions from specific residues, ligands, and solvent molecules that make up the microenvironments around the probes. Moreover, calculation of the electric field along the hydride donor-acceptor axis, along with decomposition of this field into specific contributions, indicates that the cofactor and substrate, as well as the enzyme, impose a substantial electric field that facilitates hydride transfer. Overall, experimental and theoretical data provide evidence for

Contemporary NMR Studies of Protein Electrostatics.

Science.gov (United States)

Hass, Mathias A S; Mulder, Frans A A

2015-01-01

Electrostatics play an important role in many aspects of protein chemistry. However, the accurate determination of side chain proton affinity in proteins by experiment and theory remains challenging. In recent years the field of nuclear magnetic resonance spectroscopy has advanced the way that protonation states are measured, allowing researchers to examine electrostatic interactions at an unprecedented level of detail and accuracy. Experiments are now in place that follow pH-dependent (13)C and (15)N chemical shifts as spatially close as possible to the sites of protonation, allowing all titratable amino acid side chains to be probed sequence specifically. The strong and telling response of carefully selected reporter nuclei allows individual titration events to be monitored. At the same time, improved frameworks allow researchers to model multiple coupled protonation equilibria and to identify the underlying pH-dependent contributions to the chemical shifts.

Teaching Electrostatics and Entropy in Introductory Physics

Science.gov (United States)

Reeves, Mark

Entropy changes underlie the physics that dominates biological interactions. Indeed, introductory biology courses often begin with an exploration of the qualities of water that are important to living systems. However, one idea that is not explicitly addressed in most introductory physics or biology courses is important contribution of the entropy in driving fundamental biological processes towards equilibrium. I will present material developed to teach electrostatic screening in solutions and the function of nerve cells where entropic effects act to counterbalance electrostatic attraction. These ideas are taught in an introductory, calculus-based physics course to biomedical engineers using SCALEUP pedagogy. Results of student mastering of complex problems that cross disciplinary boundaries between biology and physics, as well as the challenges that they face in learning this material will be presented.

At technique for visualizing electrostatic fields based on their topological structures

International Nuclear Information System (INIS)

Handa, Susumu

2004-01-01

In molecular science, visualization techniques based on computer graphics are now well established as a tool to interpret simulation results, since molecules are complicated in the structures and mutual interactions. As a probe to study such molecular interactions, electrostatic fields are considered to be useful. However, since they are given as 3D vector fields having complicated distributions, conventional drawing techniques are inadequate. In this article, a new approach based on topological structures in vector fields is presented to visualize the electrostatic fields of molecules. The scheme is to select regions of interest only from the topological structures of the fields. An example in applications to chemical reactions of an amino acid complex is presented to show how the scheme is used. (author)

Continuum Electrostatics Approaches to Calculating pKas and Ems in Proteins

Energy Technology Data Exchange (ETDEWEB)

Gunner, Marilyn R.; Baker, Nathan A.

2016-06-20

Proteins change their charge state through protonation and redox reactions as well as through binding charged ligands. The free energy of these reactions are dominated by solvation and electrostatic energies and modulated by protein conformational relaxation in response to the ionization state changes. Although computational methods for calculating these interactions can provide very powerful tools for predicting protein charge states, they include several critical approximations of which users should be aware. This chapter discusses the strengths, weaknesses, and approximations of popular computational methods for predicting charge states and understanding their underlying electrostatic interactions. The goal of this chapter is to inform users about applications and potential caveats of these methods as well as outline directions for future theoretical and computational research.

Numerical simulation of electrostatic waves in plasmas

International Nuclear Information System (INIS)

Erz, U.

1981-08-01

In this paper the propagation of electrostatic waves in plasmas and the non-linear interactions, which occur in the case of large wave amplitudes, are studied using a new numerical method for plasma simulation. This mathematical description is based on the Vlasov-model. Changes in the distribution-function are taken into account and thus plasma kinetic effects can be treated. (orig./HT) [de

Electrostatics of spherical metallic particles in cylinder electrostatic separators/sizers

International Nuclear Information System (INIS)

Lu Hongzhou; Li Jia; Guo Jie; Xu Zhenming

2006-01-01

This paper presents a theoretical analysis of the dynamics of spherical metallic particles in electrostatic separators/sizers (ESSs). A computational algorithm is employed to depict the cylinder-type electrode arrangements applied in some electrostatic processes generating non-uniform electric fields. The ESS consists of a pair of conducting cylinders. The upper cylinder is energized by HVdc, while the lower one is grounded and mounted horizontally on a revolvable axis. The aim of this paper is to present a new electrode configuration and demonstrate the usefulness of numerical techniques for the evaluation of the particle's motion. A computer program was employed for analysing the behavior of spherical particles in a two-dimensional electrode arrangement that models the actual electric field configuration of cylinder-type electrostatic separators/sizers. The analysis is needed for the development of any new application of this cylinder-type electrode arrangement as an electrostatic separation method. The results reveal that the particle's motion depends on its radius and density and amplitude of the applied voltage. The actual granular mixtures with different specific mass and radius could be separated applying this cylinder-type electrostatic separation method; the lift voltage is an important parameter for separation. With a program for two-dimensional analysis of the electric field, the computational procedure presented in this paper could be employed for any particle shapes

Electrostatic coupling of ion pumps.

Science.gov (United States)

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

1992-01-01

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

Optimized Baxter model of protein solutions : Electrostatics versus adhesion

NARCIS (Netherlands)

Prinsen, P.; Odijk, T.

2004-01-01

A theory is set up of spherical proteins interacting by screened electrostatics and constant adhesion, in which the effective adhesion parameter is optimized by a variational principle for the free energy. An analytical approach to the second virial coefficient is first outlined by balancing the

Using carboxylated cellulose nanofibers to enhance mechanical and barrier properties of collagen fiber film by electrostatic interaction.

Science.gov (United States)

Wang, Wenhang; Zhang, Xiuling; Li, Cong; Du, Guanhua; Zhang, Hongjie; Ni, Yonghao

2018-06-01

Collagen-based films including casings with a promising application in meat industry are still needed to improve its inferior performance. In the present study, the reinforcement of carboxylated cellulose nanofibers (CNF) for collagen film, based on inter-/intra- molecular electrostatic interaction between cationic acid-swollen collagen fiber and anionic carboxylated CNF, was investigated. Adding CNF decreased the zeta-potential but increased particle size of collagen fiber suspension, with little effect on pH. Furthermore, CNF addition led to a higher tensile strength but a lower elongation, and the water vapor and oxygen barrier properties were improved remarkably. Because the CNF content was 50 g kg -1 or lower, the films had a homogeneous interwoven network, and CNF homogeneously embedded into collagen fiber matrix according to the scanning electron microscopy and atomic force microscopy analysis. Additionally, CNF addition increased film thickness and opacity, as well as swelling rate. The incorporation of CNF endows collagen fiber films good mechanical and barrier properties over a proper concentration range (≤ 50 g kg -1 collagen fiber), which is closely associated with electrostatic reaction of collagen fiber and CNF and, subsequently, the form of the homogenous, compatible spatial network, indicating a potential applications of CNF in collagenous protein films, such as edible casings. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

New Distributed Multipole Methods for Accurate Electrostatics for Large-Scale Biomolecular Simultations

Science.gov (United States)

Sagui, Celeste

2006-03-01

An accurate and numerically efficient treatment of electrostatics is essential for biomolecular simulations, as this stabilizes much of the delicate 3-d structure associated with biomolecules. Currently, force fields such as AMBER and CHARMM assign ``partial charges'' to every atom in a simulation in order to model the interatomic electrostatic forces, so that the calculation of the electrostatics rapidly becomes the computational bottleneck in large-scale simulations. There are two main issues associated with the current treatment of classical electrostatics: (i) how does one eliminate the artifacts associated with the point-charges (e.g., the underdetermined nature of the current RESP fitting procedure for large, flexible molecules) used in the force fields in a physically meaningful way? (ii) how does one efficiently simulate the very costly long-range electrostatic interactions? Recently, we have dealt with both of these challenges as follows. In order to improve the description of the molecular electrostatic potentials (MEPs), a new distributed multipole analysis based on localized functions -- Wannier, Boys, and Edminston-Ruedenberg -- was introduced, which allows for a first principles calculation of the partial charges and multipoles. Through a suitable generalization of the particle mesh Ewald (PME) and multigrid method, one can treat electrostatic multipoles all the way to hexadecapoles all without prohibitive extra costs. The importance of these methods for large-scale simulations will be discussed, and examplified by simulations from polarizable DNA models.

The dependency of adhesion and friction on electrostatic attraction

Science.gov (United States)

Persson, B. N. J.

2018-04-01

I develop a general mean-field theory for the influence of electrostatic attraction between two solids on the contact mechanics. I assume elastic solids with random surface roughness. I consider two cases, namely, with and without an electrically insulating layer between the conducting solids. The former case is important for, e.g., the finger-touch screen interaction. I study how the electrostatic attraction influences the adhesion and friction. For the case of an insulating layer, I find that when the applied nominal contact pressure is relatively small, as the applied voltage increases, there is a sharp increase in the contact area, and hence in the friction, at a critical voltage.

Homogeneous and label-free electrochemiluminescence aptasensor based on the difference of electrostatic interaction and exonuclease-assisted target recycling amplification.

Science.gov (United States)

Ni, Jiancong; Yang, Weiqiang; Wang, Qingxiang; Luo, Fang; Guo, Longhua; Qiu, Bin; Lin, Zhenyu; Yang, Huanghao

2018-05-15

The difference of electrostatic interaction between free Ru(phen) 3 2+ and Ru(phen) 3 2+ embedded in double strand DNA (dsDNA) to the negatively charged indium tin oxide (ITO) electrode has been applied to develop a homogeneous and label-free electrochemiluminescence (ECL) aptasensor for the first time. Ochratoxin A (OTA) has been chosen as the model target. The OTA aptamer is first hybridized with its complementary single strand DNA (ssDNA) to form dsDNA and then interacted with Ru(phen) 3 2+ via the grooves binding mode to form dsDNA-Ru(phen) 3 2+ complex, which remains negatively charged feature as well as low diffusion capacity to the negatively charged ITO electrode surface owing to the electrostatic repulsion. Meanwhile, the intercalated Ru(phen) 3 2+ in the grooves of dsDNA works as an ECL signal reporter instead of the labor-intensive labeling steps and can generate much more ECL signal than that from the labeling probe. In the presence of target, the aptamer prefers to form an aptamer-target complex in lieu of dsDNA, which induces the releasing of Ru(phen) 3 2+ from the dsDNA-Ru(phen) 3 2+ complex into the solution. With the assistance of RecJ f exonuclease (a ssDNA specific exonuclease), the released ssDNA and the aptamer in the target-complex were digested into mononucleotides. In the meantime, the target can be also liberated from OTA-aptamer complex and induce target cycling and large amount of free Ru(phen) 3 2+ present in the solution. Since Ru(phen) 3 2+ contains positive charges, which can diffuses easily to the ITO electrode surface because of electrostatic attraction, causing an obviously enhanced ECL signal detected. Under the optimal conditions, the enhanced ECL of the system has a linear relationship with the OTA concentration in the range of 0.01-1.0 ng/mL with a detection limit of 2 pg/mL. This innovative system not only expands the immobilization-free sensors in the electrochemiluminescent fields, but also can be developed for the

Electrostatic septum, SPS

CERN Multimedia

CERN PhotoLab

1978-01-01

To minimize losses during slow extraction towards N- and W-Area, electrostatic septa in long straight sections 2 and 6 precede the magnetic septa. This picture shows such an electrostatic septum in its tank. See 7501120X, 7501199 and 7501201 for more detailed pictures.

Accurate potentiometric determination of lipid membrane-water partition coefficients and apparent dissociation constants of ionizable drugs: electrostatic corrections.

Science.gov (United States)

Elsayed, Mustafa M A; Vierl, Ulrich; Cevc, Gregor

2009-06-01

Potentiometric lipid membrane-water partition coefficient studies neglect electrostatic interactions to date; this leads to incorrect results. We herein show how to account properly for such interactions in potentiometric data analysis. We conducted potentiometric titration experiments to determine lipid membrane-water partition coefficients of four illustrative drugs, bupivacaine, diclofenac, ketoprofen and terbinafine. We then analyzed the results conventionally and with an improved analytical approach that considers Coulombic electrostatic interactions. The new analytical approach delivers robust partition coefficient values. In contrast, the conventional data analysis yields apparent partition coefficients of the ionized drug forms that depend on experimental conditions (mainly the lipid-drug ratio and the bulk ionic strength). This is due to changing electrostatic effects originating either from bound drug and/or lipid charges. A membrane comprising 10 mol-% mono-charged molecules in a 150 mM (monovalent) electrolyte solution yields results that differ by a factor of 4 from uncharged membranes results. Allowance for the Coulombic electrostatic interactions is a prerequisite for accurate and reliable determination of lipid membrane-water partition coefficients of ionizable drugs from potentiometric titration data. The same conclusion applies to all analytical methods involving drug binding to a surface.

Multipolar electrostatics.

Science.gov (United States)

Cardamone, Salvatore; Hughes, Timothy J; Popelier, Paul L A

2014-06-14

Atomistic simulation of chemical systems is currently limited by the elementary description of electrostatics that atomic point-charges offer. Unfortunately, a model of one point-charge for each atom fails to capture the anisotropic nature of electronic features such as lone pairs or π-systems. Higher order electrostatic terms, such as those offered by a multipole moment expansion, naturally recover these important electronic features. The question remains as to why such a description has not yet been widely adopted by popular molecular mechanics force fields. There are two widely-held misconceptions about the more rigorous formalism of multipolar electrostatics: (1) Accuracy: the implementation of multipole moments, compared to point-charges, offers little to no advantage in terms of an accurate representation of a system's energetics, structure and dynamics. (2) Efficiency: atomistic simulation using multipole moments is computationally prohibitive compared to simulation using point-charges. Whilst the second of these may have found some basis when computational power was a limiting factor, the first has no theoretical grounding. In the current work, we disprove the two statements above and systematically demonstrate that multipole moments are not discredited by either. We hope that this perspective will help in catalysing the transition to more realistic electrostatic modelling, to be adopted by popular molecular simulation software.

DelPhiForce web server: electrostatic forces and energy calculations and visualization.

Science.gov (United States)

Li, Lin; Jia, Zhe; Peng, Yunhui; Chakravorty, Arghya; Sun, Lexuan; Alexov, Emil

2017-11-15

Electrostatic force is an essential component of the total force acting between atoms and macromolecules. Therefore, accurate calculations of electrostatic forces are crucial for revealing the mechanisms of many biological processes. We developed a DelPhiForce web server to calculate and visualize the electrostatic forces at molecular level. DelPhiForce web server enables modeling of electrostatic forces on individual atoms, residues, domains and molecules, and generates an output that can be visualized by VMD software. Here we demonstrate the usage of the server for various biological problems including protein-cofactor, domain-domain, protein-protein, protein-DNA and protein-RNA interactions. The DelPhiForce web server is available at: http://compbio.clemson.edu/delphi-force. delphi@clemson.edu. Supplementary data are available at Bioinformatics online. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com

Contribution of electrostatics to the binding of pancreatic-type ribonucleases to membranes.

Science.gov (United States)

Sundlass, Nadia K; Eller, Chelcie H; Cui, Qiang; Raines, Ronald T

2013-09-17

Pancreatic-type ribonucleases show clinical promise as chemotherapeutic agents but are limited in efficacy by the inefficiency of their uptake by human cells. Cellular uptake can be increased by the addition of positive charges to the surface of ribonucleases, either by site-directed mutagenesis or by chemical modification. This observation has led to the hypothesis that ribonuclease uptake by cells depends on electrostatics. Here, we use a combination of experimental and computational methods to ascertain the contribution of electrostatics to the cellular uptake of ribonucleases. We focus on three homologous ribonucleases: Onconase (frog), ribonuclease A (cow), and ribonuclease 1 (human). Our results support the hypothesis that electrostatics are necessary for the cellular uptake of Onconase. In contrast, specific interactions with cell-surface components likely contribute more to the cellular uptake of ribonuclease A and ribonuclease 1 than do electrostatics. These findings provide insight for the design of new cytotoxic ribonucleases.

Collisionless electrostatic shocks

DEFF Research Database (Denmark)

Andersen, H.K.; Andersen, S.A.; Jensen, Vagn Orla

1970-01-01

An attempt was made in the laboratory to observe the standing collisionless electrostatic shocks in connection with the bow shock of the earth......An attempt was made in the laboratory to observe the standing collisionless electrostatic shocks in connection with the bow shock of the earth...

Emission shaping in fluorescent proteins: role of electrostatics and π-stacking.

Science.gov (United States)

Park, Jae Woo; Rhee, Young Min

2016-02-07

For many decades, simulating the excited state properties of complex systems has been an intriguing but daunting task due to its high computational cost. Here, we apply molecular dynamics based techniques with interpolated potential energy surfaces toward calculating fluorescence spectra of the green fluorescent protein (GFP) and its variants in a statistically meaningful manner. With the GFP, we show that the diverse electrostatic tuning can shape the emission features in many different ways. By computationally modulating the electrostatic interactions between the chromophore phenoxy oxygen and its nearby residues, we demonstrate that we indeed can shift the emission to the blue or to the red side in a predictable manner. We rationalize the shifting effects of individual residues in the GFP based on the responses of both the adiabatic and the diabatic electronic states of the chromophore. We next exhibit that the yellow emitting variant, the Thr203Tyr mutant, generates changes in the electrostatic interactions and an additional π-stacking interaction. These combined effects indeed induce a red shift to emit the fluorescence into the yellow region. With the series of demonstrations, we suggest that our approach can provide sound rationales and useful insights in understanding different responses of various fluorescent complexes, which may be helpful in designing new light emitting proteins and other related systems in future studies.

Modulation of electrostatic interactions to improve controlled drug delivery from nanogels.

Science.gov (United States)

Mauri, Emanuele; Chincarini, Giulia M F; Rigamonti, Riccardo; Magagnin, Luca; Sacchetti, Alessandro; Rossi, Filippo

2017-03-01

The synthesis of nanogels as devices capable to maintain the drug level within a desired range for a long and sustained period of time is a leading strategy in controlled drug delivery. However, with respect to the good results obtained with antibodies and peptides there are a lot of problems related to the quick and uncontrolled diffusion of small hydrophilic molecules through polymeric network pores. For these reasons research community is pointing toward the use of click strategies to reduce release rates of the linked drugs to the polymer chains. Here we propose an alternative method that considers the electrostatic interactions between polymeric chains and drugs to tune the release kinetics from nanogel network. The main advantage of these systems lies in the fact that the carried drugs are not modified and no chemical reactions take place during their loading and release. In this work we synthesized PEG-PEI based nanogels with different protonation degrees and the release kinetics with charged and uncharged drug mimetics (sodium fluorescein, SF, and rhodamine B, RhB) were studied. Moreover, also the effect of counterion used to induce protonation was taken into account in order to build a tunable drug delivery system able to provide multiple release rates with the same device. Copyright © 2016 Elsevier B.V. All rights reserved.

Electrostatics effects in granular materials

Science.gov (United States)

Sarkar, Saurabh; Chaudhuri, Bodhisattwa

2013-06-01

This purpose of this study is to investigate the role of physiochemical properties and operational conditions in determining the electrostatic interactions between two species on a surface under typical industrial conditions. The variables considered for the study were particle type, particle size and shape, loading mass, surface type, angle of inclination of chute, nature and concentration of additive. Triboelectrification of simple and binary mixtures in a simple hopper and chute geometry was observed to be strongly linked to work function and moisture content of the powdered material.

Long-pore Electrostatics in Inward-rectifier Potassium Channels

Science.gov (United States)

Robertson, Janice L.; Palmer, Lawrence G.; Roux, Benoît

2008-01-01

Inward-rectifier potassium (Kir) channels differ from the canonical K+ channel structure in that they possess a long extended pore (∼85 Å) for ion conduction that reaches deeply into the cytoplasm. This unique structural feature is presumably involved in regulating functional properties specific to Kir channels, such as conductance, rectification block, and ligand-dependent gating. To elucidate the underpinnings of these functional roles, we examine the electrostatics of an ion along this extended pore. Homology models are constructed based on the open-state model of KirBac1.1 for four mammalian Kir channels: Kir1.1/ROMK, Kir2.1/IRK, Kir3.1/GIRK, and Kir6.2/KATP. By solving the Poisson-Boltzmann equation, the electrostatic free energy of a K+ ion is determined along each pore, revealing that mammalian Kir channels provide a favorable environment for cations and suggesting the existence of high-density regions in the cytoplasmic domain and cavity. The contribution from the reaction field (the self-energy arising from the dielectric polarization induced by the ion's charge in the complex geometry of the pore) is unfavorable inside the long pore. However, this is well compensated by the electrostatic interaction with the static field arising from the protein charges and shielded by the dielectric surrounding. Decomposition of the static field provides a list of residues that display remarkable correspondence with existing mutagenesis data identifying amino acids that affect conduction and rectification. Many of these residues demonstrate interactions with the ion over long distances, up to 40 Å, suggesting that mutations potentially affect ion or blocker energetics over the entire pore. These results provide a foundation for understanding ion interactions in Kir channels and extend to the study of ion permeation, block, and gating in long, cation-specific pores. PMID:19001143

Nonlinear Electrostatic Steepening of Whistler Waves: The Guiding Factors and Dynamics in Inhomogeneous Systems

Science.gov (United States)

Agapitov, O.; Drake, J. F.; Vasko, I.; Mozer, F. S.; Artemyev, A.; Krasnoselskikh, V.; Angelopoulos, V.; Wygant, J.; Reeves, G. D.

2018-03-01

Whistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The efficiency of wave-particle resonant interactions is defined by whistler wave properties which have been described by the approximation of plane linear waves propagating through the cold plasma of the inner magnetosphere. However, recent observations of extremely high-amplitude whistlers suggest the importance of nonlinear wave-particle interactions for the dynamics of the outer radiation belt. Oblique chorus waves observed in the inner magnetosphere often exhibit drastically nonsinusoidal (with significant power in the higher harmonics) waveforms of the parallel electric field, presumably due to the feedback from hot resonant electrons. We have considered the nature and properties of such nonlinear whistler waves observed by the Van Allen Probes and Time History of Events and Macroscale Interactions define during Substorms in the inner magnetosphere, and we show that the significant enhancement of the wave electrostatic component can result from whistler wave coupling with the beam-driven electrostatic mode through the resonant interaction with hot electron beams. Being modulated by a whistler wave, the electron beam generates a driven electrostatic mode significantly enhancing the parallel electric field of the initial whistler wave. We confirm this mechanism using a self-consistent particle-in-cell simulation. The nonlinear electrostatic component manifests properties of the beam-driven electron acoustic mode and can be responsible for effective electron acceleration in the inhomogeneous magnetic field.

Development of an Electrostatically Clean Solar Array Panel

Science.gov (United States)

Stern, Theodore G.; Krumweide, Duane; Gaddy, Edward; Katz, Ira

2000-01-01

The results of design, analysis, and qualification of an Electrostatically Clean Solar Array (ECSA) panel are described. The objective of the ECSA design is to provide an electrostatic environment that does not interfere with sensitive instruments on scientific spacecraft. The ECSA design uses large, ITO-coated coverglasses that cover multiple solar cells, an aperture grid that covers the intercell areas, stress-relieved interconnects for connecting the aperture grid to the coverglasses, and edge clips to provides an electromagnetically shielded enclosure for the solar array active circuitry. Qualification coupons were fabricated and tested for photovoltaic response, conductivity, and survivability to launch acoustic and thermal cycling environments simulating LEO and GEO missions. The benefits of reducing solar panel interaction with the space environment are also discussed.

Edutainment Science: Electrostatics

Science.gov (United States)

Ahlers, Carl

2009-01-01

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

Roles of electrostatics and conformation in protein-crystal interactions.

Directory of Open Access Journals (Sweden)

Paul V Azzopardi

2010-02-01

Full Text Available In vitro studies have shown that the phosphoprotein osteopontin (OPN inhibits the nucleation and growth of hydroxyapatite (HA and other biominerals. In vivo, OPN is believed to prevent the calcification of soft tissues. However, the nature of the interaction between OPN and HA is not understood. In the computational part of the present study, we used molecular dynamics simulations to predict the adsorption of 19 peptides, each 16 amino acids long and collectively covering the entire sequence of OPN, to the {100} face of HA. This analysis showed that there is an inverse relationship between predicted strength of adsorption and peptide isoelectric point (P<0.0001. Analysis of the OPN sequence by PONDR (Predictor of Naturally Disordered Regions indicated that OPN sequences predicted to adsorb well to HA are highly disordered. In the experimental part of the study, we synthesized phosphorylated and non-phosphorylated peptides corresponding to OPN sequences 65-80 (pSHDHMDDDDDDDDDGD and 220-235 (pSHEpSTEQSDAIDpSAEK. In agreement with the PONDR analysis, these were shown by circular dichroism spectroscopy to be largely disordered. A constant-composition/seeded growth assay was used to assess the HA-inhibiting potencies of the synthetic peptides. The phosphorylated versions of OPN65-80 (IC(50 = 1.93 microg/ml and OPN220-235 (IC(50 = 1.48 microg/ml are potent inhibitors of HA growth, as is the nonphosphorylated version of OPN65-80 (IC(50 = 2.97 microg/ml; the nonphosphorylated version of OPN220-235 has no measurable inhibitory activity. These findings suggest that the adsorption of acidic proteins to Ca2+-rich crystal faces of biominerals is governed by electrostatics and is facilitated by conformational flexibility of the polypeptide chain.

Development of coaxial speaker-like non-contact electrostatic sensor for aviation engine exhaust electrostatic character research

Directory of Open Access Journals (Sweden)

Du Zhaoheng

2015-01-01

Full Text Available Electrostatic sensor is the most important equipment in aero-engine exhaust electrostatic character research. By comparing a variety of sensor test programs, the coaxial speaker-like noncontact electrostatic sensor program is proposed. Numerical simulation analysis indicates the electric field distribution of electrostatic sensor, the influence principle of gap width, outer diameter, center diameter, angle and other factors on the sensor capacitance values which identify the key indicators of electrostatic sensor. The experiment test shows that the simulation analysis is in good agreement with the experimental results.

Continuum Electrostatics Approaches to Calculating pKas and Ems in Proteins.

Science.gov (United States)

Gunner, M R; Baker, N A

2016-01-01

Proteins change their charge state through protonation and redox reactions as well as through binding charged ligands. The free energy of these reactions is dominated by solvation and electrostatic energies and modulated by protein conformational relaxation in response to the ionization state changes. Although computational methods for calculating these interactions can provide very powerful tools for predicting protein charge states, they include several critical approximations of which users should be aware. This chapter discusses the strengths, weaknesses, and approximations of popular computational methods for predicting charge states and understanding the underlying electrostatic interactions. The goal of this chapter is to inform users about applications and potential caveats of these methods as well as outline directions for future theoretical and computational research. © 2016 Elsevier Inc. All rights reserved.

A new non-specificity measure in evidence theory based on belief intervals

Institute of Scientific and Technical Information of China (English)

Yang Yi; Han Deqiang; Jean Dezert

2016-01-01

In the theory of belief functions, the measure of uncertainty is an important concept, which is used for representing some types of uncertainty incorporated in bodies of evidence such as the discord and the non-specificity. For the non-specificity part, some traditional measures use for reference the Hartley measure in classical set theory;other traditional measures use the simple and heuristic function for joint use of mass assignments and the cardinality of focal elements. In this paper, a new non-specificity measure is proposed using lengths of belief intervals, which represent the degree of imprecision. Therefore, it has more intuitive physical meaning. It can be proved that our new measure can be rewritten in a general form for the non-specificity. Our new measure is also proved to be a strict non-specificity measure with some desired properties. Numerical examples, simulations, the related analyses and proofs are provided to show the characteristics and good properties of the new non-specificity definition. An example of an application of the new non-specificity measure is also presented.

Precise Placement of Metallic Nanowires on a Substrate by Localized Electric Fields and Inter-Nanowire Electrostatic Interaction

Directory of Open Access Journals (Sweden)

U Hyeok Choi

2017-10-01

Full Text Available Placing nanowires at the predetermined locations on a substrate represents one of the significant hurdles to be tackled for realization of heterogeneous nanowire systems. Here, we demonstrate spatially-controlled assembly of a single nanowire at the photolithographically recessed region at the electrode gap with high integration yield (~90%. Two popular routes, such as protruding electrode tips and recessed wells, for spatially-controlled nanowire alignment, are compared to investigate long-range dielectrophoretic nanowire attraction and short-range nanowire-nanowire electrostatic interaction for determining the final alignment of attracted nanowires. Furthermore, the post-assembly process has been developed and tested to make a robust electrical contact to the assembled nanowires, which removes any misaligned ones and connects the nanowires to the underlying electrodes of circuit.

Electrostatic Interactions Govern "Odd/Even" Effects in Water-Induced Gemini Surfactant Self-Assembly.

Science.gov (United States)

Mantha, Sriteja; McDaniel, Jesse G; Perroni, Dominic V; Mahanthappa, Mahesh K; Yethiraj, Arun

2017-01-26

Gemini surfactants comprise two single-tailed surfactants connected by a linker at or near the hydrophilic headgroup. They display a variety of water-concentration-dependent lyotropic liquid crystal morphologies that are sensitive to surfactant molecular structure and the nature of the headgroups and counterions. Recently, an interesting dependence of the aqueous-phase behavior on the length of the linker has been discovered; odd-numbered linker length surfactants exhibit characteristically different phase diagrams than even-numbered linker surfactants. In this work, we investigate this "odd/even effect" using computer simulations, focusing on experimentally studied gemini dicarboxylates with Na + counterions, seven nonterminal carbon atoms in the tails, and either three, four, five, or six carbon atoms in the linker (denoted Na-73, Na-74, Na-75, and Na-76, respectively). We find that the relative electrostatic repulsion between headgroups in the different morphologies is correlated with the qualitative features of the experimental phase diagrams, predicting destabilization of hexagonal phases as the cylinders pack close together at low water content. Significant differences in the relative headgroup orientations of Na-74 and Na-76 compared to those of Na-73 and Na-75 surfactants lead to differences in linker-linker packing and long-range headgroup-headgroup electrostatic repulsion, which affects the delicate electrostatic balance between the hexagonal and gyroid phases. Much of the fundamental insight presented in this work is enabled by the ability to computationally construct and analyze metastable phases that are not observable in experiments.

A Study of Electrostatic Charge on Insulating Film by Electrostatic Force Microscopy

International Nuclear Information System (INIS)

Kikunaga, K; Toosaka, K; Kamohara, T; Sakai, K; Nonaka, K

2011-01-01

Electrostatic charge properties on polypropylene film have been characterized by atomic force microscopy and electrostatic force microscopy. The measurements have been carried out after the polypropylene film was electrified by contact and separation process in an atmosphere of controlled humidity. The negative and positive charge in concave surface has been observed. The correlation between concave surface and charge position suggests that the electrostatic charges could be caused by localized contact. On the other hand, positive charge on a flat surface has been observed. The absence of a relationship between surface profile and charge position suggests that the electrostatic charge should be caused by discharge during the separation process. The spatial migration of other positive charges through surface roughness has been observed. The results suggest that there could be some electron traps on the surface roughness and some potentials on the polypropylene film.

Electrostatic accelerators

CERN Document Server

Hinterberger, F

2006-01-01

The principle of electrostatic accelerators is presented. We consider Cockcroft– Walton, Van de Graaff and Tandem Van de Graaff accelerators. We resume high voltage generators such as cascade generators, Van de Graaff band generators, Pelletron generators, Laddertron generators and Dynamitron generators. The speci c features of accelerating tubes, ion optics and methods of voltage stabilization are described. We discuss the characteristic beam properties and the variety of possible beams. We sketch possible applications and the progress in the development of electrostatic accelerators.

Clustering of HIV-1 Subtypes Based on gp120 V3 Loop electrostatic properties

International Nuclear Information System (INIS)

López de Victoria, Aliana; Kieslich, Chris A; Rizos, Apostolos K; Krambovitis, Elias; Morikis, Dimitrios

2012-01-01

The V3 loop of the glycoprotein gp120 of HIV-1 plays an important role in viral entry into cells by utilizing as coreceptor CCR5 or CXCR4, and is implicated in the phenotypic tropisms of HIV viruses. It has been hypothesized that the interaction between the V3 loop and CCR5 or CXCR4 is mediated by electrostatics. We have performed hierarchical clustering analysis of the spatial distributions of electrostatic potentials and charges of V3 loop structures containing consensus sequences of HIV-1 subtypes. Although the majority of consensus sequences have a net charge of +3, the spatial distribution of their electrostatic potentials and charges may be a discriminating factor for binding and infectivity. This is demonstrated by the formation of several small subclusters, within major clusters, which indicates common origin but distinct spatial details of electrostatic properties. Some of this information may be present, in a coarse manner, in clustering of sequences, but the spatial details are largely lost. We show the effect of ionic strength on clustering of electrostatic potentials, information that is not present in clustering of charges or sequences. We also make correlations between clustering of electrostatic potentials and net charge, coreceptor selectivity, global prevalence, and geographic distribution. Finally, we interpret coreceptor selectivity based on the N 6 X 7 T 8 |S 8 X 9 sequence glycosylation motif, the specific positive charge location according to the 11/24/25 rule, and the overall charge and electrostatic potential distribution. We propose that in addition to the sequence and the net charge of the V3 loop of each subtype, the spatial distributions of electrostatic potentials and charges may also be important factors for receptor recognition and binding and subsequent viral entry into cells. This implies that the overall electrostatic potential is responsible for long-range recognition of the V3 loop with coreceptors CCR5/CXCR4, whereas the charge

Clustering of HIV-1 Subtypes Based on gp120 V3 Loop electrostatic properties

Directory of Open Access Journals (Sweden)

López de Victoria Aliana

2012-02-01

Full Text Available Abstract Background The V3 loop of the glycoprotein gp120 of HIV-1 plays an important role in viral entry into cells by utilizing as coreceptor CCR5 or CXCR4, and is implicated in the phenotypic tropisms of HIV viruses. It has been hypothesized that the interaction between the V3 loop and CCR5 or CXCR4 is mediated by electrostatics. We have performed hierarchical clustering analysis of the spatial distributions of electrostatic potentials and charges of V3 loop structures containing consensus sequences of HIV-1 subtypes. Results Although the majority of consensus sequences have a net charge of +3, the spatial distribution of their electrostatic potentials and charges may be a discriminating factor for binding and infectivity. This is demonstrated by the formation of several small subclusters, within major clusters, which indicates common origin but distinct spatial details of electrostatic properties. Some of this information may be present, in a coarse manner, in clustering of sequences, but the spatial details are largely lost. We show the effect of ionic strength on clustering of electrostatic potentials, information that is not present in clustering of charges or sequences. We also make correlations between clustering of electrostatic potentials and net charge, coreceptor selectivity, global prevalence, and geographic distribution. Finally, we interpret coreceptor selectivity based on the N6X7T8|S8X9 sequence glycosylation motif, the specific positive charge location according to the 11/24/25 rule, and the overall charge and electrostatic potential distribution. Conclusions We propose that in addition to the sequence and the net charge of the V3 loop of each subtype, the spatial distributions of electrostatic potentials and charges may also be important factors for receptor recognition and binding and subsequent viral entry into cells. This implies that the overall electrostatic potential is responsible for long-range recognition of the V3

Electrostatics in Chemistry

Indian Academy of Sciences (India)

characteristics and applications of the electrostatic potential of many-electron atoms, ions and molecules are discussed. Electrostatic Potential of Atoms and Singly. Charged ..... [6] R K Pathak and S R Gadre,J. Chat. Phys., 93, 1770, 1990. [7] S R Gadre, S A Kalkarni and I H Shrivastava,J. Chern. Phys., 96,52;3,. 1992. ~ .1.

Role of electrostatic interactions on the transport of druglike molecules in hydrogel-based articular cartilage mimics

DEFF Research Database (Denmark)

Ye, Fengbin; Baldursdottir, Stefania G.; Hvidt, Søren

2016-01-01

In the field of drug delivery to the articular cartilage, it is advantageous to apply artificial tissue models as surrogates of cartilage for investigating drug transport and release properties. In this study, artificial cartilage models consisting of 0.5% (w/v) agarose gel containing 0.5% (w...... to the pure agarose gel. The decrease in apparent diffusivity of the cationic compounds was not caused by a change in the gel structure since a similar reduction in apparent diffusivity was not observed for the net negatively charged protein α-lactalbumin. The apparent diffusivity of the cationic compounds...... the electrostatic nature of their interactions. The results obtained from the UV imaging diffusion studies are important for understanding the effect of drug physicochemical properties on the transport in articular cartilage. The extracted information may be useful in the development of hydrogels for in vitro...

Lunar electrostatic effects and protection

International Nuclear Information System (INIS)

Sun, Yongwei; Yuan, Qingyun; Xiong, Jiuliang

2013-01-01

The space environment and features on the moon surface are factors in strong electrostatic electrification. Static electricity will be produced in upon friction between lunar soil and detectors or astronauts on the lunar surface. Lunar electrostatic environment effects from lunar exploration equipment are very harmful. Lunar dust with electrostatic charge may enter the equipment or even cover the instruments. It can affect the normal performance of moon detectors. Owing to the huge environmental differences between the moon and the earth, the electrostatic protection technology on the earth can not be applied. In this paper, we review the electrostatic characteristics of lunar dust, its effects on aerospace equipment and moon static elimination technologies. It was concluded that the effect of charged lunar dust on detectors and astronauts should be completely researched as soon as possible.

Effects of RNA branching on the electrostatic stabilization of viruses

NARCIS (Netherlands)

Erdemci-Tandogan, Gonca; Wagner, Jef; Schoot, Paul van der|info:eu-repo/dai/nl/102140618; Podgornik, Rudolf; Zandi, Roya

2016-01-01

Many single-stranded (ss) RNA viruses self assemble from capsid protein subunits and the nucleic acid to form an infectious virion. It is believed that the electrostatic interactions between the negatively charged RNA and the positively charged viral capsid proteins drive the encapsidation, although

Study of receptor-chaperone interactions using the optical technique of spectroscopic ellipsometry.

Science.gov (United States)

Kriechbaumer, Verena; Tsargorodskaya, Anna; Mustafa, Mohd K; Vinogradova, Tatiana; Lacey, Joanne; Smith, David P; Abell, Benjamin M; Nabok, Alexei

2011-07-20

This work describes a detailed quantitative interaction study between the novel plastidial chaperone receptor OEP61 and isoforms of the chaperone types Hsp70 and Hsp90 using the optical method of total internal reflection ellipsometry (TIRE). The receptor OEP61 was electrostatically immobilized on a gold surface via an intermediate layer of polycations. The TIRE measurements allowed the evaluation of thickness changes in the adsorbed molecular layers as a result of chaperone binding to receptor proteins. Hsp70 chaperone isoforms but not Hsp90 were shown to be capable of binding OEP61. Dynamic TIRE measurements were carried out to evaluate the affinity constants of the above reactions and resulted in clear discrimination between specific and nonspecific binding of chaperones as well as differences in binding properties between the highly similar Hsp70 isoforms. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

PCE: web tools to compute protein continuum electrostatics

Science.gov (United States)

Miteva, Maria A.; Tufféry, Pierre; Villoutreix, Bruno O.

2005-01-01

PCE (protein continuum electrostatics) is an online service for protein electrostatic computations presently based on the MEAD (macroscopic electrostatics with atomic detail) package initially developed by D. Bashford [(2004) Front Biosci., 9, 1082–1099]. This computer method uses a macroscopic electrostatic model for the calculation of protein electrostatic properties, such as pKa values of titratable groups and electrostatic potentials. The MEAD package generates electrostatic energies via finite difference solution to the Poisson–Boltzmann equation. Users submit a PDB file and PCE returns potentials and pKa values as well as color (static or animated) figures displaying electrostatic potentials mapped on the molecular surface. This service is intended to facilitate electrostatics analyses of proteins and thereby broaden the accessibility to continuum electrostatics to the biological community. PCE can be accessed at . PMID:15980492

Non-Specific Reactions during Immunomagnetic Separation of Listeria

Directory of Open Access Journals (Sweden)

Iveta Zachová

2005-01-01

Full Text Available Problems occurring during the immunomagnetic separation (IMS of Listeria using immunomagnetic particles Dynabeads® anti-Listeria (Dynal Biotech, Norway were specified. Characteristics of these particles were compared with anti-Listeria spp. magnetite particles (Quantum Magnetics, USA. Pure cultures of Listeria innocua, Arthrobacter spp., Bacillus subtilis, Citrobacter braakii, Escherichia coli, Enterobacter aerogenes, Enterobacter cloacae and Staphylococcus aureus were used to evaluate non-specific reactions during IMS. Gram-positive microorganisms, especially Staphylococcus aureus and Arthrobacter spp., were found to be responsible for non-specific reactions in most cases. The capacity of Dynabeads® anti-Listeria particles was determined to be about 10 % of the initial pure cultures of Listeria spp., after 10 min of incubation. Non-specific reactions during IMS of Listeria were examined on the artificially inoculated food samples in which Gram-positive bacteria showed the highest percentage of capture. Influence of washing in two buffers was also studied.

Investigation of electrostatic behavior of a lactose carrier for dry powder inhalers.

Science.gov (United States)

Chow, Keat Theng; Zhu, Kewu; Tan, Reginald B H; Heng, Paul W S

2008-12-01

This study aims to elucidate the electrostatic behavior of a model lactose carrier used in dry powder inhaler formulations by examining the effects of ambient relative humidity (RH), aerosolization air flow rate, repeated inhaler use, gelatin capsule and tapping on the specific charge (nC/g) of bulk and aerosolized lactose. Static and dynamic electrostatic charge measurements were performed using a Faraday cage connected to an electrometer. Experiments were conducted inside a walk-in environmental chamber at 25 degrees C and RHs of 20% to 80%. Aerosolization was achieved using air flow rates of 30, 45, 60 and 75 L/min. The initial charges of the bulk and capsulated lactose were a magnitude lower than the charges of tapped or aerosolized lactose. Dynamic charge increased linearly with aerosolization air flow rate and RH. Greater frictional forces at higher air flow rate induced higher electrostatic charges. Increased RH enhanced charge generation. Repeated inhaler use significantly influenced electrostatic charge due to repeated usage. This study demonstrated the significance of interacting influences by variables commonly encountered in the use DPI such as variation in patient's inspiratory flow rate, ambient RH and repeated inhaler use on the electrostatic behavior of a lactose DPI carrier.

Dynamical chaos of plasma ions in electrostatic waves

International Nuclear Information System (INIS)

Fasoli, A.; Kleiber, R.; Tran, M.Q.; Paris, P.J.; Skiff, F.

1992-09-01

Chaos generated by the interaction between charged particles and electrostatic plasma waves has been observed in a linear magnetized plasma. The macroscopic wave properties, the kinetic ion dielectric response and the microscopic heating mechanisms have been investigated via optical diagnostic techniques based on laser induced fluorescence. Observations of test-particle dynamical evolution indicate an exponential separation of initially close ion trajectories. (author) 5 figs., 20 refs

Effect of electrostatic interactions on phase stability of cubic phases of biomembranes.

Science.gov (United States)

Li, Shu Jie; Masum, Shah Md; Yamashita, Yuko; Tamba, Yukihiro; Yamazaki, Masahito

2002-06-01

We investigated effect of electrostatic interactions due to surfacecharges on structures and stability of cubic phases of monoolein (MO)membrane using the small-angle X-ray scattering method. Firstly, wechanged the surface charge density of the membrane by usingdioleoylphosphatidic acid (DOPA). As increasing DOPA concentration in themembrane at 30 wt % lipid concentration, a Q(224) to Q(229) phasetransition occurred at 0.6 mol % DOPA, and at and above 25 mol %, DOPA/MOmembranes were in the L(α) phase. NaCl in the bulk phase reduced theeffect of DOPA. These results indicate that as the electrostaticinteractions increase, the most stable phase changes as follows: Q(224)⇒ Q(229) ⇒ L(α). The increase in DOPAconcentration reduced the absolute value of spontaneous curvature of themembrane, | H(0) |. Secondly, we changed the surface charge of themembrane by adding a de novo designed peptide, which has netpositive charges and a binding site on the electrically neutral membraneinterface. The peptide-1 (WLFLLKKK) induced a Q(224) to Q(229)phase transition in the MO membrane at low peptide concentration. As NaClconcentration increases, the MO/peptide-1 membrane changed from Q(229)to Q(224) phase. The increase in peptide-1 concentration reduced |H(0) |. Based on these results, the stability of the cubic phases and themechanism of phase transition between cubic phase and L(α) phase arediscussed.

Ion sources for electrostatic accelerators

International Nuclear Information System (INIS)

Hellborg, R.

1998-01-01

Maybe the most important part of an electrostatic accelerator system, and also often the most tricky part is the ion source. There has been a rapid growth in activity in ion-source research and development during the last two to three decades. Some of these developments have also been of benefit to electrostatic accelerator users. In this report some of the different types of ion sources used in electrostatic accelerators are described. The list is not complete but more an overview of some of the more commonly used sources. The description is divided into two groups; positive ion sources for single stage electrostatic accelerators and negative ion sources for two stages (i.e. tandem) accelerators

A strong focussing cylindrical electrostatic quadrupole

International Nuclear Information System (INIS)

Sheng Yaochang

1986-01-01

The construction and performance of small cylindrical electrostatic quadrupole, which is installed in JM-400 pulse electrostatic accelerator, are described. This electrostatic quadrupole is not only used in neutron generator, but also suitable for ion injector as well as for low energy electron accelerator

Association of hypovitaminosis Dwith persistent non-specific musculoskeletal pains

International Nuclear Information System (INIS)

Alam, H.M.A.; Kamran, M.; Rehman, S.U.; Khan, D.A.; Hussain, K.

2017-01-01

The study was conducted in Pakistani population to find association of vitamin D deficiency with persistent non-specific musculoskeletal pains by comparing with pain free controls. Study Design: Case control study. Material and Methods: Patients aged 12 years or more presenting to Medical OPD with persistent nonspecific musculoskeletal pains for more than 3 months were selected as cases, while healthy individuals served as controls Results: A total of 60 cases (patients with persistent non-specific pains) presenting to medical outpatients department at Military Hospital Rawalpindi and 60 controls were studied. Mean age of cases was 43.9 +- 14.0 years and amongst controls were 33.2 +- 17.8 years. Mean serum vitamin D level of 32.8 nmol/L was reported in cases whereas mean serum vitamin D level amongst controls was 26.7 +- 17.8 nmol/L. Hypovitaminosis D amongst cases and controls was 86.6% and 95% respectively. The proportion of vitamin D deficiency did not differ significantly as compared to controls. There was non-significant difference in proportion of deficiency amongst cases and controls. Conclusion: Overall there was no association between persistent non-specific musculoskeletal pains and vitamin D deficiency. (author)

Electrostatic Detumble of Space Objects

Data.gov (United States)

National Aeronautics and Space Administration — Electrostatic Tractor Technology research explores the harmony of physics and engineering to develop and test electrostatic actuation methods for touchless detumble...

Molecular electrostatic potential and "atoms-in-molecules" analyses of the interplay between π-hole and lone pair···π/X-H···π/metal···π interactions.

Science.gov (United States)

Bauzá, Antonio; Seth, Saikat Kumar; Frontera, Antonio

2018-04-05

Using ab initio calculations, we analyze the interplay between π-hole interactions involving the nitro group of 1,4-dinitrobenzene and lone pair···π (lp···π), C-H···π or metal(M)···π noncovalent interactions. Moreover, we have also used 1,4-phenylenebis(phosphine dioxide) for comparison purposes. Interesting cooperativity effects are found when π-hole (F···N,P) and lp···π/C-H···π/M···π interactions coexist in the same supramolecular assembly. These effects are studied theoretically in terms of energetic and geometric features of the complexes, which are computed by ab initio methods (RI-MP2/def2-TZVP). A charge density analysis using the Bader's theory of "atoms in molecules" is carried out to characterize the interactions and to analyze their strengthening or weakening depending on the variation of charge density at critical points. The importance of electrostatic effects on the mutual influence of the interaction is studied by means of molecular electrostatic potential calculations. By taking advantage of these computational tools, the present study examines interplay of these interactions. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Interaction and dynamics of ambient water adlayers on graphite probed using AFM voltage nanolithography and electrostatic force microscopy

International Nuclear Information System (INIS)

Gowthami, T; Raina, Gargi; Kurra, Narendra

2014-01-01

In this work, we report the impact of the interaction and dynamics of increasing ambient water adlayers on etch patterns on a hydrophobic highly oriented pyrolytic graphite (HOPG) surface obtained using atomic force microscopy (AFM) voltage nanolithography in contact mode by applying a positive bias to the sample. The changes in the dimensions of the etch patterns were investigated as a function of the increasing number of water adlayers present on the HOPG, which is varied by changing the time interval since HOPG cleavage. Changes in the width of the etch patterns and the surrounding water droplets were monitored with time, using intermittent-contact-mode AFM. Electrostatic force microscopy (EFM) has been employed to study the charged nature of the etch patterns and the neighboring water film with time. The width of the etch patterns made on freshly cleaved HOPG shows an increase of ∼33% over 48 h, whereas nine-day-old cleaved HOPG shows a 79% increase over the same period. No changes in the dimensions are observed while imaging in a nitrogen atmosphere soon after lithography. In ambient conditions, the EFM phase shift of the patterns shows a large change of ∼84–88% over 30 h. This study demonstrates the effect of the stored electrostatic energy of a polarized ice-like water adlayer, resulting in changes in the dimensions of the etch patterns long after lithography, whereas liquid-like water droplets do not affect the etch patterns. (paper)

Effective electrostatic interactions among charged thermo-responsive microgels immersed in a simple electrolyte

Energy Technology Data Exchange (ETDEWEB)

González-Mozuelos, P. [Departamento de Física, Cinvestav del I. P. N., Av. Instituto Politécnico Nacional 2508, Mexico, Distrito Federal, C. P. 07360 (Mexico)

2016-02-07

This work explores the nature and thermodynamic behavior of the effective electrostatic interactions among charged microgels immersed in a simple electrolyte, taking special interest in the effects due to the thermally induced variation of the microgel size while the remaining parameters (microgel charge and concentration, plus the amount of added salt) are kept constant. To this end, the rigorous approach obtained from applying the precise methodology of the dressed ion theory to the proper definition of the effective direct correlation functions, which emerge from tracing-out the degrees of freedom of the microscopic ions, is employed to provide an exact description of the parameters characterizing such interactions: screening length, effective permittivity, and renormalized charges. A model solution with three components is assumed: large permeable anionic spheres for the microgels, plus small charged hard spheres of equal size for the monovalent cations and anions. The two-body correlations among the components of this model suspension, used as the input for the determination of the effective interaction parameters, are here calculated by using the hyper-netted chain approximation. It is then found that at finite microgel concentrations the values of these parameters change as the microgel size increases, even though the ionic strength of the supporting electrolyte and the bare charge of the microgels remain fixed during this process. The variation of the screening length, as well as that of the effective permittivity, is rather small, but still interesting in view of the fact that the corresponding Debye length stays constant. The renormalized charges, in contrast, increase markedly as the microgels swell. The ratio of the renormalized charge to the corresponding analytic result obtained in the context of an extended linear response theory allows us to introduce an effective charge that accounts for the non-linear effects induced by the short

Electrostatic Levitator Layout

Science.gov (United States)

1998-01-01

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

Electrostatic potential map modelling with COSY Infinity

International Nuclear Information System (INIS)

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

2016-01-01

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

Perspectives on electrostatics and conformational motions in enzyme catalysis.

Science.gov (United States)

Hanoian, Philip; Liu, C Tony; Hammes-Schiffer, Sharon; Benkovic, Stephen

2015-02-17

CONSPECTUS: Enzymes are essential for all living organisms, and their effectiveness as chemical catalysts has driven more than a half century of research seeking to understand the enormous rate enhancements they provide. Nevertheless, a complete understanding of the factors that govern the rate enhancements and selectivities of enzymes remains elusive, due to the extraordinary complexity and cooperativity that are the hallmarks of these biomolecules. We have used a combination of site-directed mutagenesis, pre-steady-state kinetics, X-ray crystallography, nuclear magnetic resonance (NMR), vibrational and fluorescence spectroscopies, resonance energy transfer, and computer simulations to study the implications of conformational motions and electrostatic interactions on enzyme catalysis in the enzyme dihydrofolate reductase (DHFR). We have demonstrated that modest equilibrium conformational changes are functionally related to the hydride transfer reaction. Results obtained for mutant DHFRs illustrated that reductions in hydride transfer rates are correlated with altered conformational motions, and analysis of the evolutionary history of DHFR indicated that mutations appear to have occurred to preserve both the hydride transfer rate and the associated conformational changes. More recent results suggested that differences in local electrostatic environments contribute to finely tuning the substrate pKa in the initial protonation step. Using a combination of primary and solvent kinetic isotope effects, we demonstrated that the reaction mechanism is consistent across a broad pH range, and computer simulations suggested that deprotonation of the active site Tyr100 may play a crucial role in substrate protonation at high pH. Site-specific incorporation of vibrational thiocyanate probes into the ecDHFR active site provided an experimental tool for interrogating these microenvironments and for investigating changes in electrostatics along the DHFR catalytic cycle

APBSmem: a graphical interface for electrostatic calculations at the membrane.

Directory of Open Access Journals (Sweden)

Keith M Callenberg

2010-09-01

Full Text Available Electrostatic forces are one of the primary determinants of molecular interactions. They help guide the folding of proteins, increase the binding of one protein to another and facilitate protein-DNA and protein-ligand binding. A popular method for computing the electrostatic properties of biological systems is to numerically solve the Poisson-Boltzmann (PB equation, and there are several easy-to-use software packages available that solve the PB equation for soluble proteins. Here we present a freely available program, called APBSmem, for carrying out these calculations in the presence of a membrane. The Adaptive Poisson-Boltzmann Solver (APBS is used as a back-end for solving the PB equation, and a Java-based graphical user interface (GUI coordinates a set of routines that introduce the influence of the membrane, determine its placement relative to the protein, and set the membrane potential. The software Jmol is embedded in the GUI to visualize the protein inserted in the membrane before the calculation and the electrostatic potential after completing the computation. We expect that the ease with which the GUI allows one to carry out these calculations will make this software a useful resource for experimenters and computational researchers alike. Three examples of membrane protein electrostatic calculations are carried out to illustrate how to use APBSmem and to highlight the different quantities of interest that can be calculated.

Biomechanical aspects of nonspecific back pain

Directory of Open Access Journals (Sweden)

Ridwan Harrianto

2010-12-01

Full Text Available Low back pain (LBP is a common problem in adult life, since despite its benign nature it is commonly associated with incapacity, productivity loss due to sick leave, and correspondingly high costs to the individual worker. Psychosocial and lifestyle factors and work-place exposures have been implicated in the onset of symptoms. Heavy physical work, static work postures, frequent bending and twisting, lifting and postural movements, repetitive work, and whole body vibrations are occupational factors associated with LBP. The usual classification of LBP is related to the duration of the complaints (acute, subacute, and chronic. However, these terms fail to take into account several clinically important aspects of the course of LBP, which is frequently recurrent and thus neither acute nor chronic. More realistically, LBP should be classified as specific and nonspecific. Approximately 90% of LBP cases have no identifiable cause and is designated nonspecific LBP. However, despite its high prevalence, the etiology and nature of nonspecific LBP are not yet well understood. Its pathophysiology remains complex and multifaceted. Multiple anatomic structures and elements of the lumbar spine (e.g. bones, ligaments, tendons, discs, and muscles are all suspected of playing a role. Many of these components of the lumbar spine have sensory innervations that can generate nociceptive signals in response to tissue-damaging stimuli. Other causes could be neuropathic (e.g. sciatica. Some cases of LBP most likely involve mixed nociceptive and neuropathic etiologies.

Advances in electrostatic accelerators

International Nuclear Information System (INIS)

Wegner, H.E.

1975-01-01

Advances in the design and performance of electrostatic accelerators since 1969 are reviewed with special emphasis on the ''forefront'' accelerators that are currently leading in voltage capability. A comparison of the acceleration tube design offered by the National Electrostatics Corporation and the High Voltage Engineering Corporation is also made. Other methods of increasing heavy ion energy by means of dual foil stripping are discussed as well as the performance of a newly developed sputter ion source for the production of negative heavy ions with reliability and flexibility that greatly exceeds all other present systems. Finally, new developments in terms of both booster systems and very high voltage electrostatic accelerators (25 to 60 MV) are discussed. (U.S.)

Electrostatics of DNA-DNA juxtapositions: consequences for type II topoisomerase function

International Nuclear Information System (INIS)

Randall, Graham L; Pettitt, B Montgomery; Buck, Gregory R; Zechiedrich, E Lynn

2006-01-01

Type II topoisomerases resolve problematic DNA topologies such as knots, catenanes, and supercoils that arise as a consequence of DNA replication and recombination. Failure to remove problematic DNA topologies prohibits cell division and can result in cell death or genetic mutation. Such catastrophic consequences make topoisomerases an effective target for antibiotics and anticancer agents. Despite their biological and clinical importance, little is understood about how a topoisomerase differentiates DNA topologies in a molecule that is significantly larger than the topoisomerase itself. It has been proposed that type II topoisomerases recognize angle and curvature between two DNA helices characteristic of knotted and catenated DNA to account for the enzyme's preference to unlink instead of link DNA. Here we consider the electrostatic potential of DNA juxtapositions to determine the possibility of juxtapositions occurring through Brownian diffusion. We found that despite the large negative electrostatic potential formed between two juxtaposed DNA helices, a bulk counterion concentration as small as 50 mM provides sufficient electrostatic screening to prohibit significant interaction beyond an interhelical separation of 3 nm in both hooked and free juxtapositions. This suggests that instead of electrostatics, mechanical forces such as those occurring in anaphase, knots, catenanes, or the writhe of supercoiled DNA may be responsible for the formation of DNA juxtapositions

Driving electrostatic transducers

DEFF Research Database (Denmark)

Nielsen, Dennis; Knott, Arnold; Andersen, Michael A. E.

2013-01-01

Electrostatic transducers represent a very interesting alternative to the traditional inefficient electrodynamic transducers. In order to establish the full potential of these transducers, power amplifiers which fulfill the strict requirements imposed by such loads (high impedance, frequency...... depended, nonlinear and high bias voltage for linearization) must be developed. This paper analyzes power stages and bias configurations suitable for driving an electrostatic transducer. Measurement results of a 300 V prototype amplifier are shown. Measuring THD across a high impedance source is discussed...

Zymosan-induced immune challenge modifies the stress response of hypoxic air-breathing fish (Anabas testudineus Bloch): Evidence for reversed patterns of cortisol and thyroid hormone interaction, differential ion transporter functions and non-specific immune response.

Science.gov (United States)

Simi, S; Peter, Valsa S; Peter, M C Subhash

2017-09-15

Fishes have evolved physiological mechanisms to exhibit stress response, where hormonal signals interact with an array of ion transporters and regulate homeostasis. As major ion transport regulators in fish, cortisol and thyroid hormones have been shown to interact and fine-tune the stress response. Likewise, in fishes many interactions have been identified between stress and immune components, but the physiological basis of such interaction has not yet delineated particularly in air-breathing fish. We, therefore, investigated the responses of thyroid hormones and cortisol, ion transporter functions and non-specific immune response of an obligate air-breathing fish Anabas testudineus Bloch to zymosan treatment or hypoxia stress or both, to understand how immune challenge modifies the pattern of stress response in this fish. Induction of experimental peritonitis in these fish by zymosan treatment (200ngg -1 ) for 24h produced rise in respiratory burst and lysozomal activities in head kidney phagocytes. In contrast, hypoxia stress for 30min in immune-challenged fish reversed these non-specific responses of head kidney phagocytes. The decline in plasma cortisol in zymosan-treated fish and its further suppression by hypoxia stress indicate that immune challenge suppresses the cortisol-driven stress response of this fish. Likewise, the decline in plasma T 3 and T 4 after zymosan-treatment and the rise in plasma T 4 after hypoxia stress in immune-challenged fish indicate a critical role for thyroid hormone in immune-stress response due to its differential sensitivity to both immune and stress challenges. Further, analysis of the activity pattern of ion-dependent ATPases viz. Na + /K + -ATPase, H + /K + -ATPase and Na + /NH 4 + -ATPase indicates a functional interaction of ion transport system with the immune response as evident in its differential and spatial modifications after hypoxia stress in immune-challenged fish. The immune-challenge that produced differential

Electrical operation of electrostatic precipitators

CERN Document Server

Parker, Ken

2003-01-01

The electrostatic precipitator remains on of the most cost effective means of controlling the emission of particulates from most industrial processes. This book will be of interest to both users and suppliers of electrostatic precipitators as well as advanced students on environmental based courses. The author identifies the physical and engineering basis for the development of electrical equipment for electrostatic precipitators and thoroughly explores the technological factors which optimize the efficiency of the precipitator and hence minimize emissions, as well as future developments in th

Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties.

Science.gov (United States)

Doktorova, Milka; Heberle, Frederick A; Kingston, Richard L; Khelashvili, George; Cuendet, Michel A; Wen, Yi; Katsaras, John; Feigenson, Gerald W; Vogt, Volker M; Dick, Robert A

2017-11-07

Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Interaction of particles with complex electrostatic structures and 3D clusters

International Nuclear Information System (INIS)

Antonova, Tetyana

2007-01-01

Particles of micrometer size externally introduced in plasmas usually find their positions of levitation in the plasma sheath, where the gravity force is compensated by the strong electric field. Here due to electrostatic interaction they form different structures, which are interesting objects for the investigation of strongly coupled systems and critical phenomena. Because of the low damping (e.g. in comparison to colloidal suspension) it is possible to measure the dynamics up to the relevant highest frequency (e.g. Einstein frequency) at the most elementary level of single particle motion. The task of this work was to analyze the three dimensional structure, dynamical processes and the limit of the cooperative behavior in small plasma crystals. In addition to the study of the systems formed, the immersed particles themselves may be used for diagnostics of the plasma environment: estimation of parameters or monitoring of the processes inside plasma. The laboratory experiments are performed in two radio-frequency (RF) plasma reactors with parallel plate electrodes, where the lower electrode is a so-called ''adaptive electrode''. This electrode is segmented into 57 small ''pixels'' independently driven in DC (direct current) and/or RF voltage. When RF voltage is applied to one of these pixels, a bright localized glow, ''secondary plasma ball'', appears above. Three dimensional dust crystals with less than 100 particles are formed inside this ''plasma ball'' - the ideal conditions for the investigation of the transition from cluster systems to collective systems. The investigation of the particle interactions in crystals is performed with an optical diagnostic, which allows determination of all three particle coordinates simultaneously with time resolution of 0.04 sec. The experimental results are: 1. The binary interaction among particles in addition to the repelling Coulomb force exhibits also an attractive part, which is experimentally determined for the first

Interaction of particles with complex electrostatic structures and 3D clusters

Energy Technology Data Exchange (ETDEWEB)

Antonova, Tetyana

2007-10-16

Particles of micrometer size externally introduced in plasmas usually find their positions of levitation in the plasma sheath, where the gravity force is compensated by the strong electric field. Here due to electrostatic interaction they form different structures, which are interesting objects for the investigation of strongly coupled systems and critical phenomena. Because of the low damping (e.g. in comparison to colloidal suspension) it is possible to measure the dynamics up to the relevant highest frequency (e.g. Einstein frequency) at the most elementary level of single particle motion. The task of this work was to analyze the three dimensional structure, dynamical processes and the limit of the cooperative behavior in small plasma crystals. In addition to the study of the systems formed, the immersed particles themselves may be used for diagnostics of the plasma environment: estimation of parameters or monitoring of the processes inside plasma. The laboratory experiments are performed in two radio-frequency (RF) plasma reactors with parallel plate electrodes, where the lower electrode is a so-called 'adaptive electrode'. This electrode is segmented into 57 small 'pixels' independently driven in DC (direct current) and/or RF voltage. When RF voltage is applied to one of these pixels, a bright localized glow, 'secondary plasma ball', appears above. Three dimensional dust crystals with less than 100 particles are formed inside this 'plasma ball' - the ideal conditions for the investigation of the transition from cluster systems to collective systems. The investigation of the particle interactions in crystals is performed with an optical diagnostic, which allows determination of all three particle coordinates simultaneously with time resolution of 0.04 sec. The experimental results are: 1. The binary interaction among particles in addition to the repelling Coulomb force exhibits also an attractive part, which is

Defining the contributions of permanent electrostatics, Pauli repulsion, and dispersion in density functional theory calculations of intermolecular interaction energies

Energy Technology Data Exchange (ETDEWEB)

Horn, Paul R., E-mail: prhorn@berkeley.edu; Mao, Yuezhi; Head-Gordon, Martin, E-mail: mhg@cchem.berkeley.edu [Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division Lawrence Berkeley National Laboratory Berkeley, California 94720 (United States)

2016-03-21

In energy decomposition analysis of Kohn-Sham density functional theory calculations, the so-called frozen (or pre-polarization) interaction energy contains contributions from permanent electrostatics, dispersion, and Pauli repulsion. The standard classical approach to separate them suffers from several well-known limitations. We introduce an alternative scheme that employs valid antisymmetric electronic wavefunctions throughout and is based on the identification of individual fragment contributions to the initial supersystem wavefunction as determined by an energetic optimality criterion. The density deformations identified with individual fragments upon formation of the initial supersystem wavefunction are analyzed along with the distance dependence of the new and classical terms for test cases that include the neon dimer, ammonia borane, water-Na{sup +}, water-Cl{sup −}, and the naphthalene dimer.

Nonspecific Arm Pain

Directory of Open Access Journals (Sweden)

Ali Moradi

2013-12-01

Full Text Available Nonspecific activity-related arm pain is characterized by an absence of objective physical findings and symptoms that do not correspond with objective pathophysiology. Arm pain without strict diagnosis is often related to activity, work-related activity in particular, and is often seen in patients with physically demanding work. Psychological factors such as catastrophic thinking, symptoms of depression, and heightened illness concern determine a substantial percentage of the disability associated with puzzling hand and arm pains. Ergonomic modifications can help to control symptoms, but optimal health may require collaborative management incorporating psychosocial and psychological elements of illness.

Nonspecific Arm Pain

Directory of Open Access Journals (Sweden)

Ali Moradi

2013-12-01

Full Text Available   Nonspecific activity-related arm pain is characterized by an absence of objective physical findings and symptoms that do not correspond with objective pathophysiology. Arm pain without strict diagnosis is often related to activity, work-related activity in particular, and is often seen in patients with physically demanding work. Psychological factors such as catastrophic thinking, symptoms of depression, and heightened illness concern determine a substantial percentage of the disability associated with puzzling hand and arm pains. Ergonomic modifications can help to control symptoms, but optimal health may require collaborative management incorporating psychosocial and psychological elements of illness.

Evaluating the effects of cutoffs and treatment of long-range electrostatics in protein folding simulations.

Directory of Open Access Journals (Sweden)

Stefano Piana

Full Text Available The use of molecular dynamics simulations to provide atomic-level descriptions of biological processes tends to be computationally demanding, and a number of approximations are thus commonly employed to improve computational efficiency. In the past, the effect of these approximations on macromolecular structure and stability has been evaluated mostly through quantitative studies of small-molecule systems or qualitative observations of short-timescale simulations of biological macromolecules. Here we present a quantitative evaluation of two commonly employed approximations, using a test system that has been the subject of a number of previous protein folding studies--the villin headpiece. In particular, we examined the effect of (i the use of a cutoff-based force-shifting technique rather than an Ewald summation for the treatment of electrostatic interactions, and (ii the length of the cutoff used to determine how many pairwise interactions are included in the calculation of both electrostatic and van der Waals forces. Our results show that the free energy of folding is relatively insensitive to the choice of cutoff beyond 9 Å, and to whether an Ewald method is used to account for long-range electrostatic interactions. In contrast, we find that the structural properties of the unfolded state depend more strongly on the two approximations examined here.

The Effects of Noncellulosic Compounds on the Nanoscale Interaction Forces Measured between Carbohydrate-Binding Module and Lignocellulosic Biomass.

Science.gov (United States)

Arslan, Baran; Colpan, Mert; Ju, Xiaohui; Zhang, Xiao; Kostyukova, Alla; Abu-Lail, Nehal I

2016-05-09

The lack of fundamental understanding of the types of forces that govern how cellulose-degrading enzymes interact with cellulosic and noncellulosic components of lignocellulosic surfaces limits the design of new strategies for efficient conversion of biomass to bioethanol. In a step to improve our fundamental understanding of such interactions, nanoscale forces acting between a model cellulase-a carbohydrate-binding module (CBM) of cellobiohydrolase I (CBH I)-and a set of lignocellulosic substrates with controlled composition were measured using atomic force microscopy (AFM). The three model substrates investigated were kraft (KP), sulfite (SP), and organosolv (OPP) pulped substrates. These substrates varied in their surface lignin coverage, lignin type, and xylan and acetone extractives' content. Our results indicated that the overall adhesion forces of biomass to CBM increased linearly with surface lignin coverage with kraft lignin showing the highest forces among lignin types investigated. When the overall adhesion forces were decoupled into specific and nonspecific component forces via the Poisson statistical model, hydrophobic and Lifshitz-van der Waals (LW) forces dominated the binding forces of CBM to kraft lignin, whereas permanent dipole-dipole interactions and electrostatic forces facilitated the interactions of lignosulfonates to CBM. Xylan and acetone extractives' content increased the attractive forces between CBM and lignin-free substrates, most likely through hydrogen bonding forces. When the substrates treated differently were compared, it was found that both the differences in specific and nonspecific forces between lignin-containing and lignin-free substrates were the least for OPP. Therefore, cellulase enzymes represented by CBM would weakly bind to organosolv lignin. This will facilitate an easy enzyme recovery compared to other substrates treated with kraft or sulfite pulping. Our results also suggest that altering the surface hydrophobicity

Electrostatic septum, SPS

CERN Multimedia

1975-01-01

To minimize losses during slow extraction towards N- and W-Areas, electrostatic septa in long straight sections 2 an 6 precede the magnetic septa. The 2 electrode plates, visible at the entrance to the septum, provide a vertical electric field to remove the ions created by the circulating beam in the residual gas. Here we see one of the electrostatic septa being assembled by Faustin Emery (left) and Jacques Soubeyran (right), in the clean room of building 867. See also 7501199, 7501201, 7801286 and further explanations there.

Explosion safety in industrial electrostatics

Science.gov (United States)

Szabó, S. V.; Kiss, I.; Berta, I.

2011-01-01

Complicated industrial systems are often endangered by electrostatic hazards, both from atmospheric (lightning phenomenon, primary and secondary lightning protection) and industrial (technological problems caused by static charging and fire and explosion hazards.) According to the classical approach protective methods have to be used in order to remove electrostatic charging and to avoid damages, however no attempt to compute the risk before and after applying the protective method is made, relying instead on well-educated and practiced expertise. The Budapest School of Electrostatics - in close cooperation with industrial partners - develops new suitable solutions for probability based decision support (Static Control Up-to-date Technology, SCOUT) using soft computing methods. This new approach can be used to assess and audit existing systems and - using the predictive power of the models - to design and plan activities in industrial electrostatics.

Influence of electrostatic interactions on the morphology and properties of blends containing perfluorinated ionomers

Science.gov (United States)

Taylor, Eric Paul

2002-01-01

The first goal of this research project was to investigate the influence of the electrostatic interactions within the ion-containing domains of Nafion RTM perfluorosulfonate ionomer (PFSI) on the morphology and resultant properties of blend systems with poly(propylene imine) dendrimers of a variety of generational sizes and poly(vinylidene fluoride) (PVDF). Perfluorosulfonate ionomers (PFSIs) are a commercially successful class of semi-crystalline, ion-containing polymers whose most extensive application is in use as a polymer electrolytic membrane in fuel cell applications. NafionRTM was blended and high temperature solution processed with poly(propylene imine) dendrimer as the minor component in order to increase the efficiency of direct methanol fuel cells by decreasing methanol crossover without significant loss of protonic conductivity. The preferential insertion of the dendrimer into the ionic cluster due to proton transfer reactions and the creation of ammonium-sulfonate ion pairs served to alter the transport properties through the ionic network of the membrane. In the second major system investigated, blends of poly(vinylidene fluoride) (PVDF) with NafionRTM, a perfluorosulfonate ionomer, have been prepared and examined in terms of the crystallization kinetics and crystal morphology of the PVDF component in the blend. DSC analysis showed faster rates of bulk crystallization when PVDF was crystallized in the presence of Na+-form NafionRTM suggesting a high degree of phaseseparation in this blend system and an increase in the nucleation density. NafionRTM neutralized with alkylammonium-form counterions display an increase in blend compatibility with PVDF with an increase in the alkylammonium counterion size. As the alkylammonium counterion size increases, the strength of the electrostatic network within the ionic domains of Nafion RTM decrease resulting in a reduction in the driving force for ionic aggregation. Thus, a decrease is observed in the crystal

Risk factors of non-specific spinal pain in childhood.

Science.gov (United States)

Szita, Julia; Boja, Sara; Szilagyi, Agnes; Somhegyi, Annamaria; Varga, Peter Pal; Lazary, Aron

2018-05-01

Non-specific spinal pain can occur at all ages and current evidence suggests that pediatric non-specific spinal pain is predictive for adult spinal conditions. A 5-year long, prospective cohort study was conducted to identify the lifestyle and environmental factors leading to non-specific spinal pain in childhood. Data were collected from school children aged 7-16 years, who were randomly selected from three different geographic regions in Hungary. The risk factors were measured with a newly developed patient-reported questionnaire (PRQ). The quality of the instrument was assessed by the reliability with the test-retest method. Test (N = 952) and validity (N = 897) datasets were randomly formed. Risk factors were identified with uni- and multivariate logistic regression models and the predictive performance of the final model was evaluated using the receiver operating characteristic (ROC) method. The final model was built up by seven risk factors for spinal pain for days; age > 12 years, learning or watching TV for more than 2 h/day, uncomfortable school-desk, sleeping problems, general discomfort and positive familiar medical history (χ 2  = 101.07; df = 8; p < 0.001). The probabilistic performance was confirmed with ROC analysis on the test and validation cohorts (AUC = 0.76; 0.71). A simplified risk scoring system showed increasing possibility for non-specific spinal pain depending on the number of the identified risk factors (χ 2  = 65.0; df = 4; p < 0.001). Seven significant risk factors of non-specific spinal pain in childhood were identified using the new, easy to use and reliable PRQ which makes it possible to stratify the children according to their individual risk. These slides can be retrieved under Electronic Supplementary Material.

Nonspecific eating disorders - a subjective review.

Science.gov (United States)

Michalska, Aneta; Szejko, Natalia; Jakubczyk, Andrzej; Wojnar, Marcin

2016-01-01

The aim of this paper was to characterise nonspecific eating disorders (other than anorexia nervosa and bulimia nervosa). The Medline database was searched for articles on nonspecific eating disorders. The following disorders were described: binge eating disorder (BED), pica, rumination disorder, avoidant/restrictive food intake disorder, night eating syndrome (NES), sleep-related eating disorder (SRED), bigorexia, orthorexia, focusing on diagnosis, symptoms, assessment, comorbidities, clinical implications and treatment. All of the included disorders may have dangerous consequences, both somatic and psychological. They are often comorbid with other psychiatric disorders. Approximately a few percent of general population can be diagnosed with each disorder, from 0.5-4.7% (SRED) to about 7% (orthorexia). With the growing literature on the subject and changes in DSM-5, clinicians recognise and treat those disorders more often. More studies have to be conducted in order to differentiate disorders and treat or prevent them appropriately.

Preconceptual design for the electrostatic enclosure

International Nuclear Information System (INIS)

Meyer, L.C.

1992-09-01

This report presents a preconceptual design (design criteria and assumptions) for electrostatic enclosures to be used during buried transuranic waste recovery operations. These electrostatic enclosures (along with the application of dust control products) will provide an in-depth contamination control strategy. As part of this preconceptual design, options for electrostatic curtain design are given including both hardwall and fabric enclosures. Ventilation systems, doors, air locks, electrostatic curtains, and supporting systems also are discussed. In addition to the conceptual design, engineering scale tests are proposed to be run at the Test Reactor Area. The planned engineering scale tests will give final material specifications for full-scale retrieval demonstrations

Interdomain electron transfer in cellobiose dehydrogenase is governed by surface electrostatics.

Science.gov (United States)

Kadek, Alan; Kavan, Daniel; Marcoux, Julien; Stojko, Johann; Felice, Alfons K G; Cianférani, Sarah; Ludwig, Roland; Halada, Petr; Man, Petr

2017-02-01

Cellobiose dehydrogenase (CDH) is a fungal extracellular oxidoreductase which fuels lytic polysaccharide monooxygenase with electrons during cellulose degradation. Interdomain electron transfer between the flavin and cytochrome domain in CDH, preceding the electron flow to lytic polysaccharide monooxygenase, is known to be pH dependent, but the exact mechanism of this regulation has not been experimentally proven so far. To investigate the structural aspects underlying the domain interaction in CDH, hydrogen/deuterium exchange (HDX-MS) with improved proteolytic setup (combination of nepenthesin-1 with rhizopuspepsin), native mass spectrometry with ion mobility and electrostatics calculations were used. HDX-MS revealed pH-dependent changes in solvent accessibility and hydrogen bonding at the interdomain interface. Electrostatics calculations identified these differences to result from charge neutralization by protonation and together with ion mobility pointed at higher electrostatic repulsion between CDH domains at neutral pH. In addition, we uncovered extensive O-glycosylation in the linker region and identified the long-unknown exact cleavage point in papain-mediated domain separation. Transition of CDH between its inactive (open) and interdomain electron transfer-capable (closed) state is shown to be governed by changes in the protein surface electrostatics at the domain interface. Our study confirms that the interdomain electrostatic repulsion is the key factor modulating the functioning of CDH. The results presented in this paper provide experimental evidence for the role of charge repulsion in the interdomain electron transfer in cellobiose dehydrogenases, which is relevant for exploiting their biotechnological potential in biosensors and biofuel cells. Copyright © 2016 Elsevier B.V. All rights reserved.

The role of non-specific interactions in nuclear organization

NARCIS (Netherlands)

Nooijer, de S.

2010-01-01

The most important organelle in eukaryotic cells is the nucleus. Many processes occurring within the nucleus depend on spatial organization of the nucleus. The spatial organization of the eukaryotic nucleus derives from interactions between its constituents. Both specific interactions, for instance

Role of DNA conformation & energetic insights in Msx-1-DNA recognition as revealed by molecular dynamics studies on specific and nonspecific complexes.

Science.gov (United States)

Kachhap, Sangita; Singh, Balvinder

2015-01-01

In most of homeodomain-DNA complexes, glutamine or lysine is present at 50th position and interacts with 5th and 6th nucleotide of core recognition region. Molecular dynamics simulations of Msx-1-DNA complex (Q50-TG) and its variant complexes, that is specific (Q50K-CC), nonspecific (Q50-CC) having mutation in DNA and (Q50K-TG) in protein, have been carried out. Analysis of protein-DNA interactions and structure of DNA in specific and nonspecific complexes show that amino acid residues use sequence-dependent shape of DNA to interact. The binding free energies of all four complexes were analysed to define role of amino acid residue at 50th position in terms of binding strength considering the variation in DNA on stability of protein-DNA complexes. The order of stability of protein-DNA complexes shows that specific complexes are more stable than nonspecific ones. Decomposition analysis shows that N-terminal amino acid residues have been found to contribute maximally in binding free energy of protein-DNA complexes. Among specific protein-DNA complexes, K50 contributes more as compared to Q50 towards binding free energy in respective complexes. The sequence dependence of local conformation of DNA enables Q50/Q50K to make hydrogen bond with nucleotide(s) of DNA. The changes in amino acid sequence of protein are accommodated and stabilized around TAAT core region of DNA having variation in nucleotides.

Motions and electrostatic interactions in natural and semisynthetic myoglobins: a carbon-13 nuclear magnetic resonance study

International Nuclear Information System (INIS)

Maskalick, D.G.

1984-01-01

It is expected that the internal motions of amino acid side chains and protein backbone segments influence and are in turn affected by charge-charge and related interactions, steric constraints, hydrophobic forces, and hydrogen bonding. As an initial test of this theory 13 C-enriched glycine, alanine, and isoleucine have been substituted for the amino terminal valine of sperm whale myoglobin using semisynthetic techniques. 13 C-NMR has been used to analyze the motions of the side chain and the protonation state of the alpha amino group as a function of pH. The addition of a single methyl group to the side chain can alter the alpha amino pK value by as much as 0.3 pH units indicating a delicately balanced set of change-charge interactions between the alpha amino group and the rest of the protein. Further evidence in support of the state theory was found upon examination of the internal motions of seven of nine isoleucine vectors. These motions were extracted from natural abundance 13 C-NMR relaxation data. The results suggest a strong possibility that concerted motions are important. Also, an increase in temperature from 32 0 C to 52 0 C leads to an electrostatically driven tightening of the myoglobin structure as evidenced by no significant increase in motion amplitude of most of the vectors

Electrostatic energy of KHF2

NARCIS (Netherlands)

Gool, W. van; Bruinink, J.; Bottelberghs, P.H.

1972-01-01

Electrostatic lattice energies are calculated in KHF2. Fractional charges occurring in the complex anions are treated with a general procedure and the results are compared to a specialized approach reported earlier. Interstitial potentials are calculated to obtain the electrostatic field through

GroPBS: Fast Solver for Implicit Electrostatics of Biomolecules

Directory of Open Access Journals (Sweden)

Franziska eBertelshofer

2015-11-01

Full Text Available Knowledge about the electrostatic potential on the surface of biomolecules or biomembranes under physiological conditions is an important step in the attempt to characterize the physico-chemical properties of these molecules and in particular also their interactions with each other. Additionally, knowledge about solution electrostatics may guide also the design of molecules with specified properties. However, explicit water models come at a high computational cost, rendering them unsuitable for large design studies or for docking purposes. Implicit models with the water phase treated as a continuum require the numerical solution of the Poisson-Boltzmann Equation (PBE. Here, we present a new flexible program for the numerical solution of the PBE, allowing for different geometries, and the explicit and implicit inclusion of membranes. It involves a discretization of space and the computation of the molecular surface. The PBE is solved using finite differences, the resulting set of equations is solved using a Gauss-Seidel method. It is shown for the example of the sucrose transporter ScrY that the implicit inclusion of a surrounding membrane has a strong effect also on the electrostatics within the pore region and thus need to be carefully considered e.g. in design studies on membrane proteins.

Reducing detrimental electrostatic effects in Casimir-force measurements and Casimir-force-based microdevices

Science.gov (United States)

Xu, Jun; Klimchitskaya, G. L.; Mostepanenko, V. M.; Mohideen, U.

2018-03-01

It is well known that residual electrostatic forces create significant difficulties in precise measurements of the Casimir force and the wide use of Casimir-operated microdevices. We experimentally demonstrate that, with the help of Ar-ion cleaning of the surfaces, it is possible to make electrostatic effects negligibly small compared to the Casimir interaction. Our experimental setup consists of a dynamic atomic force microscope supplemented with an Ar-ion gun and argon reservoir. The residual potential difference between the Au-coated surfaces of a sphere and those of a plate was measured both before and after in situ Ar-ion cleaning. It is shown that this cleaning decreases the magnitude of the residual potential by up to an order of magnitude and makes it almost independent of the separation. The gradient of the Casimir force was measured using ordinary samples subjected to Ar-ion cleaning. The obtained results are shown to be in good agreement both with previous precision measurements using specially selected samples and with theoretical predictions of the Lifshitz theory. The conclusion is made that the suggested method of in situ Ar-ion cleaning is effective in reducing the electrostatic effects and therefore is a great resource for experiments on measuring the Casimir interaction and for Casimir-operated microdevices.

Discrete Pathophysiology is Uncommon in Patients with Nonspecific Arm Pain.

Science.gov (United States)

Kortlever, Joost T P; Janssen, Stein J; Molleman, Jeroen; Hageman, Michiel G J S; Ring, David

2016-06-01

Nonspecific symptoms are common in all areas of medicine. Patients and caregivers can be frustrated when an illness cannot be reduced to a discrete pathophysiological process that corresponds with the symptoms. We therefore asked the following questions: 1) Which demographic factors and psychological comorbidities are associated with change from an initial diagnosis of nonspecific arm pain to eventual identification of discrete pathophysiology that corresponds with symptoms? 2) What is the percentage of patients eventually diagnosed with discrete pathophysiology, what are those pathologies, and do they account for the symptoms? We evaluated 634 patients with an isolated diagnosis of nonspecific upper extremity pain to see if discrete pathophysiology was diagnosed on subsequent visits to the same hand surgeon, a different hand surgeon, or any physician within our health system for the same pain. There were too few patients with discrete pathophysiology at follow-up to address the primary study question. Definite discrete pathophysiology that corresponded with the symptoms was identified in subsequent evaluations by the index surgeon in one patient (0.16% of all patients) and cured with surgery (nodular fasciitis). Subsequent doctors identified possible discrete pathophysiology in one patient and speculative pathophysiology in four patients and the index surgeon identified possible discrete pathophysiology in four patients, but the five discrete diagnoses accounted for only a fraction of the symptoms. Nonspecific diagnoses are not harmful. Prospective randomized research is merited to determine if nonspecific, descriptive diagnoses are better for patients than specific diagnoses that imply pathophysiology in the absence of discrete verifiable pathophysiology.

Electrostatic correlations: from plasma to biology

International Nuclear Information System (INIS)

Levin, Yan

2002-01-01

Electrostatic correlations play an important role in physics, chemistry and biology. In plasmas they result in thermodynamic instability similar to the liquid-gas phase transition of simple molecular fluids. For charged colloidal suspensions the electrostatic correlations are responsible for screening and colloidal charge renormalization. In aqueous solutions containing multivalent counterions they can lead to charge inversion and flocculation. In biological systems the correlations account for the organization of cytoskeleton and the compaction of genetic material. In spite of their ubiquity, the true importance of electrostatic correlations has come to be fully appreciated only quite recently. In this paper, we will review the thermodynamic consequences of electrostatic correlations in a variety of systems ranging from classical plasmas to molecular biology

Non-specific Effects of Vaccines and Stunting: Timing May Be Essential

Directory of Open Access Journals (Sweden)

Mike L.T. Berendsen

2016-06-01

Conclusions: We found a general time-dependent pattern of non-specific effects of vaccination, with positive associations for vaccinations given early in life and negative associations for vaccinations given later in infancy. If confirmed in further research, our findings may provide a new perspective on the non-specific effects of vaccination.

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

International Nuclear Information System (INIS)

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

2015-01-01

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

Simple and cooperative electrostatic binding of amonium ions to phosphate-polyions: NMR, infrared and theoretical study

Czech Academy of Sciences Publication Activity Database

Kříž, Jaroslav; Dybal, Jiří

2004-01-01

Roč. 108, č. 26 (2004), s. 9306-9314 ISSN 1520-6106 R&D Projects: GA AV ČR KSK4050111 Institutional research plan: CEZ:AV0Z4050913 Keywords : cooperative interactions * electrostatic binding * hydrophobic interactions Subject RIV: CD - Macromolecular Chemistry Impact factor: 3.834, year: 2004

Electrostatic analogy for symmetron gravity

Science.gov (United States)

Ogden, Lillie; Brown, Katherine; Mathur, Harsh; Rovelli, Kevin

2017-12-01

The symmetron model is a scalar-tensor theory of gravity with a screening mechanism that suppresses the effect of the symmetron field at high densities characteristic of the Solar System and laboratory scales but allows it to act with gravitational strength at low density on the cosmological scale. We elucidate the screening mechanism by showing that in the quasistatic Newtonian limit there are precise analogies between symmetron gravity and electrostatics for both strong and weak screening. For strong screening we find that large dense bodies behave in a manner analogous to perfect conductors in electrostatics. Based on this analogy we find that the symmetron field exhibits a lightning rod effect wherein the field gradients are enhanced near the ends of pointed or elongated objects. An ellipsoid placed in a uniform symmetron gradient is shown to experience a torque. By symmetry there is no gravitational torque in this case. Hence this effect unmasks the symmetron and might serve as the basis for future laboratory experiments. The symmetron force between a point mass and a large dense body includes a component corresponding to the interaction of the point mass with its image in the larger body. None of these effects have counterparts in the Newtonian limit of Einstein gravity. We discuss the similarities between symmetron gravity and the chameleon model as well as the differences between the two.

Research on electrostatic electrification during jet kerosene spraying

International Nuclear Information System (INIS)

Liu, Quanzhen; Li, Yipeng; Zhang, Wentian; Sun, Keping

2013-01-01

Multiple electrostatic electrifications during aircraft fuelling process may cause a fire disaster or explosion, so study on the protection measure for electrostatic electrification is very important for the security of aircraft fuelling. This paper investigated the electrostatic voltage and charge of the fuel nozzle and metal parts during the fuel spraying by self-designed jet kerosene spraying electrostatic electrification test system. The experimental results indicate that the voltage on the fuel nozzle and metal parts is very dangerous for electrostatic safety if they are not reliably grounded.

Charging and absorption characteristics of small particulates under alternative and electrostatic voltages in an electrostatic precipitator

International Nuclear Information System (INIS)

Jiang Xue-Dong; Xu He; Wang Xin

2014-01-01

The charge quantity of small particulates such as PM2.5 plays a key role in the collection efficiency of an electrostatic precipitator (ESP). Under a single electrostatic voltage, it is difficult to charge and absorb small particulates. A new method of superimposing an alternative voltage on the electrostatic voltage is provided in this paper. Characteristics of small particulates are analyzed under alternative and electrostatic voltages. It is demonstrated that an alternative voltage can significantly improve the collection efficiency in three aspects: preventing anti-corona, increasing the charge quantity of small particulates, and increasing the median particulate size by electric agglomeration. In addition, practical usage with the superposition of alternative voltage is provided, and the results are in agreement with the theoretical analysis. (physics of gases, plasmas, and electric discharges)

Electrostatics in pharmaceutical aerosols for inhalation.

Science.gov (United States)

Wong, Jennifer; Chan, Hak-Kim; Kwok, Philip Chi Lip

2013-08-01

Electrostatics continues to play an important role in pharmaceutical aerosols for inhalation. Despite its ubiquitous nature, the charging process is complex and not well understood. Nonetheless, significant advances in the past few years continue to improve understanding and lead to better control of electrostatics. The purpose of this critical review is to present an overview of the literature, with an emphasis on how electrostatic charge can be useful in improving pulmonary drug delivery.

SMPBS: Web server for computing biomolecular electrostatics using finite element solvers of size modified Poisson-Boltzmann equation.

Science.gov (United States)

Xie, Yang; Ying, Jinyong; Xie, Dexuan

2017-03-30

SMPBS (Size Modified Poisson-Boltzmann Solvers) is a web server for computing biomolecular electrostatics using finite element solvers of the size modified Poisson-Boltzmann equation (SMPBE). SMPBE not only reflects ionic size effects but also includes the classic Poisson-Boltzmann equation (PBE) as a special case. Thus, its web server is expected to have a broader range of applications than a PBE web server. SMPBS is designed with a dynamic, mobile-friendly user interface, and features easily accessible help text, asynchronous data submission, and an interactive, hardware-accelerated molecular visualization viewer based on the 3Dmol.js library. In particular, the viewer allows computed electrostatics to be directly mapped onto an irregular triangular mesh of a molecular surface. Due to this functionality and the fast SMPBE finite element solvers, the web server is very efficient in the calculation and visualization of electrostatics. In addition, SMPBE is reconstructed using a new objective electrostatic free energy, clearly showing that the electrostatics and ionic concentrations predicted by SMPBE are optimal in the sense of minimizing the objective electrostatic free energy. SMPBS is available at the URL: smpbs.math.uwm.edu © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Modeling multicomponent ionic transport in groundwater with IPhreeqc coupling: Electrostatic interactions and geochemical reactions in homogeneous and heterogeneous domains

DEFF Research Database (Denmark)

Muniruzzaman, Muhammad; Rolle, Massimo

2016-01-01

is coupled with the geochemical code PHREEQC-3 by utilizing the IPhreeqc module, thus enabling to perform the geochemical calculations included in the PHREEQC's reaction package. The multicomponent reactive transport code is benchmarked with different 1-D and 2-D transport problems. Successively...... the electrostatic interactions during transport of charged ions in physically and chemically heterogeneous porous media. The modeling approach is based on the local charge balance and on the description of compound-specific and spatially variable diffusive/dispersive fluxes. The multicomponent ionic transport code......, conservative and reactive transport examples are presented to demonstrate the capability of the proposed model to simulate transport of charged species in heterogeneous porous media with spatially variable physical and chemical properties. The results reveal that the Coulombic cross-coupling between dispersive...

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

Science.gov (United States)

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.

Self-consistent treatment of electrostatics in molecular DNA braiding through external forces.

Science.gov (United States)

Lee, Dominic J

2014-06-01

In this paper we consider a physical system in which two DNA molecules braid about each other. The distance between the two molecular ends, on either side of the braid, is held at a distance much larger than supercoiling radius of the braid. The system is subjected to an external pulling force, and a moment that induces the braiding. In a model, developed for understanding such a system, we assume that each molecule can be divided into a braided and unbraided section. We also suppose that the DNA is nicked so that there is no constraint of the individual linking numbers of the molecules. Included in the model are steric and electrostatic interactions, thermal fluctuations of the braided and unbraided sections of the molecule, as well as the constraint on the braid linking (catenation) number. We compare two approximations used in estimating the free energy of the braided section. One is where the amplitude of undulations of one molecule with respect to the other is determined only by steric interactions. The other is a self-consistent determination of the mean-squared amplitude of these undulations. In this second approximation electrostatics should play an important role in determining this quantity, as suggested by physical arguments. We see that if the electrostatic interaction is sufficiently large there are indeed notable differences between the two approximations. We go on to test the self-consistent approximation-included in the full model-against experimental data for such a system, and we find good agreement. However, there seems to be a slight left-right-handed braid asymmetry in some of the experimental results. We discuss what might be the origin of this small asymmetry.

The role of electrostatic interactions in the Streptococcus thermophilus adhesion on human erythrocytes in media with different 1:1 electrolyte concentration

Directory of Open Access Journals (Sweden)

О. І. Гордієнко

2015-10-01

Full Text Available The process of bacterial adhesion is usually discussed in terms of the two-stage sorption model. According to the model, at the first stage the bacteria fastly attaches to the surface by weak physical interactions, while at the second stage irreversible molecular and cellular adhesion process takes place. An important factor, influencing the adhesion processes, is physical-chemical characteristics of the medium, in particular, the presence of monovalent cations therein. The aim of this work is to assess the role of electrostatic component of the intercellular interactions at the first reversible stage of adhesion. Comparison of experimental data of adhesion of lactobacilli S. thermophilus on human erythrocytes and theoretical definition of the Debye radius and the erythrocytes surface potential in the experimental solutions showed that with decreasing ionic strength of the solution the change in the adhesion index in our experiments is fully in line with the theory DLVO predictions.

Depth profile analysis of non-specific fluorescence and color of tooth tissues after peroxide bleaching.

Science.gov (United States)

Klukowska, Malgorzata; Götz, Hermann; White, Donald J; Zoladz, James; Schwarz, Björn-Olaf; Duschner, Heinz

2013-02-01

To examine laboratory changes of endogenous non-specific fluorescence and color throughout subsurface of tooth structures prior to and following peroxide bleaching. Extracted human teeth were cross sectioned and mounted on glass slides. Cross sections were examined for internal color (digital camera) and nonspecific fluorescence (microRaman spectroscopy) throughout the tooth structure at specified locations. Surfaces of sections were then saturation bleached for 70 hours with a gel containing 6% hydrogen peroxide. Cross sections were reexamined for color and non-specific fluorescence changes. Unbleached enamel, dentin-enamel junction and dentin exhibit different CIELab color and non-specific fluorescence properties. Bleaching of teeth produced significant changes in color of internal cross sections and substantial reductions of non-specific fluorescence levels within enamel dentin and DEJ. Enamel and dentin non-specific fluorescence were reduced to common values with bleaching with enamel and the DEJ showing larger reductions than dentin.

Electrostatic effect for the collisionless tearing mode

International Nuclear Information System (INIS)

Hoshino, M.

1987-01-01

Electron dynamics has not been self-consistently considered in collisionless tearing mode theories to date because of the mathematical complexity of the Vlasov-Maxwell equations. We have found using computer simulations that electrostatic fields play an important role in the tearing mode. Vlasov theory, including the electrostatic field, is investigated for topologies with both antiparallel and nonantiparallel magnetic field lines. The electrostatic field influences the resonant current in the neutral sheet which is a non-MHD effect, and modifies the linear growth rate. At the magnetopause, where the field lines are not antiparallel, the electrostatic effect acts to raise the linear growth rate of the tearing mode. On the other hand, in the magnetotail, where magnetic field lines are antiparallel, the electrostatic effect reduces the tearing mode growth rate. copyright American Geophysical Union 1987

The electrostatic atomization of hydrocarbons

Energy Technology Data Exchange (ETDEWEB)

Kelly, A J

1984-06-01

Exploitation of the unique and potentially beneficial characteristics of electrostatic atomization in combustion systems has foundered upon the inability of two element, diode devices to operate at flow rates that are larger than a fraction of a millilitre per second. This restriction has been attributed to the high innate electrical resistivity of hydrocarbon fuels. A discussion of proposed electrostatic fuel atomizers and their limitations is presented from the vantage of a recently developed theory of electrostatic spraying. Comparison of theory and experiment reveals the existence of a 'constant of spraying' and the presence of an operational regime in which low charge density droplet development is possible. Operation with hydrocarbons in this regime occurs when the mean droplet size is greater than or equal to 10 ..mu..m and fluid viscosity is below about 250 cp. The resulting spray has a mean droplet size that is functionally dependent only upon the free charge density level of the fluid. Consequently there is no theoretical impediment to the attainment of high flow rate electrostatic atomization with fluids of arbitrary conductivity. Implementation is achieved by a general class of electrostatic spray devices which employ direct charge injection. The Spray Triode, a submerged field-emission electron gun, represents a particularly simple member of this new class of atomizer. Among the Spray Triode operational characteristics to be discussed is insensitivity to spray fluid properties and flow rate.

Dissecting electrostatic interactions in Bacillus circulans xylanase through NMR-monitored pH titrations

Energy Technology Data Exchange (ETDEWEB)

McIntosh, Lawrence P., E-mail: mcintosh@chem.ubc.ca; Naito, Daigo; Baturin, Simon J.; Okon, Mark; Joshi, Manish D. [University of British Columbia, Department of Biochemistry and Molecular Biology, Department of Chemistry, and Michael Smith Laboratories, Life Sciences Centre (Canada); Nielsen, Jens E. [University College Dublin, School of Biomolecular and Biomedical Science, Centre for Synthesis and Chemical Biology, UCD Conway Institute (Ireland)

2011-09-15

NMR-monitored pH titration curves of proteins provide a rich source of structural and electrostatic information. Although relatively straightforward to measure, interpreting pH-dependent chemical shift changes to obtain site-specific acid dissociation constants (pK{sub A} values) is challenging. In order to analyze the biphasic titrations exhibited by the side chain {sup 13}C{sup {gamma}} nuclei of the nucleophilic Glu78 and general acid/base Glu172 in Bacillus circulans xylanase, we have revisited the formalism for the ionization equilibria of two coupled acidic residues. In general, fitting NMR-monitored pH titration curves for such a system will only yield the two macroscopic pK{sub A} values that reflect the combined effects of both deprotonation reactions. However, through the use of mutations complemented with ionic strength-dependent measurements, we are able to extract the four microscopic pK{sub Ai} values governing the branched acid/base equilibria of Glu78 and Glu172 in BcX. These data, confirmed through theoretical calculations, help explain the pH-dependent mechanism of this model GH11 xylanase by demonstrating that the kinetically determined pK{sub A} values and hence catalytic roles of these two residues result from their electrostatic coupling.

Dissecting electrostatic interactions in Bacillus circulans xylanase through NMR-monitored pH titrations

International Nuclear Information System (INIS)

McIntosh, Lawrence P.; Naito, Daigo; Baturin, Simon J.; Okon, Mark; Joshi, Manish D.; Nielsen, Jens E.

2011-01-01

NMR-monitored pH titration curves of proteins provide a rich source of structural and electrostatic information. Although relatively straightforward to measure, interpreting pH-dependent chemical shift changes to obtain site-specific acid dissociation constants (pK A values) is challenging. In order to analyze the biphasic titrations exhibited by the side chain 13 C γ nuclei of the nucleophilic Glu78 and general acid/base Glu172 in Bacillus circulans xylanase, we have revisited the formalism for the ionization equilibria of two coupled acidic residues. In general, fitting NMR-monitored pH titration curves for such a system will only yield the two macroscopic pK A values that reflect the combined effects of both deprotonation reactions. However, through the use of mutations complemented with ionic strength-dependent measurements, we are able to extract the four microscopic pK Ai values governing the branched acid/base equilibria of Glu78 and Glu172 in BcX. These data, confirmed through theoretical calculations, help explain the pH-dependent mechanism of this model GH11 xylanase by demonstrating that the kinetically determined pK A values and hence catalytic roles of these two residues result from their electrostatic coupling.

Electrostatics in biomolecular simulations : where are we now and where are we heading?

NARCIS (Netherlands)

Karttunen, M.E.J.; Rottler, J.; Vattulainen, I.; Sagui, C.

2008-01-01

Chapter 2. In this review, we discuss current methods and developments in the treatment of electrostatic interactions in biomolecular and soft matter simulations. We review the current ‘work horses’, namely, Ewald summation based methods such the Particle-Mesh Ewald, and others, and also newer

Laser spectroscopy with an electrostatic ConeTrap

Energy Technology Data Exchange (ETDEWEB)

Kelly, S., E-mail: sam.kelly@postgrad.manchester.ac.uk; Campbell, P. [University of Manchester, Nuclear Physics Group, Schuster Laboratory, Brunswick Street (United Kingdom); Cheal, B., E-mail: Bradley.Cheal@Liverpool.ac.uk [University of Liverpool, Oliver Lodge Laboratory (United Kingdom); Eronen, T.; Geldhof, S.; Jokinen, A.; Moore, I. D.; Penttilä, H.; Pohjalainen, I.; Rinta-Antila, S.; Sonnenschein, V.; Voss, A. [JYFL, University of Jyväskylä (Finland)

2017-11-15

A compact electrostatic trap has been designed and installed as part of the recent upgrades to the IGISOL IV facility. The ConeTrap provides an in vacuo optical pumping site for low energy (800 eV) ionic ensembles available for interaction periods of 10-100 ms. At present, 6.7(3) % of injected mass A=98 ions can be trapped, stored for 5 ms, extracted and transported to a laser-ion interaction region. This fraction represents those ions for which no perturbation to total energy or energy spread is observed. Proposed enhancements to the trap are designed to improve the trapping efficiency by up to a factor of 5. Differential pumping and reduction in background pressure below the present 10{sup −6} mbar will extend storage times beyond 100 ms.

PREFACE: Electrostatics 2015

Science.gov (United States)

Matthews, James

2015-10-01

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

Electrostatic curtain studies

International Nuclear Information System (INIS)

Meyer, L.C.

1992-05-01

This report presents the results of experiments using electrostatic curtains (ESCS) as a transuranic (TRU) contamination control technique. The TRU contaminants included small (micrometer to sub micrometer) particles of plutonium and americium compounds associated with defense-related waste. Three series of experiments were conducted. The first was with uncontaminated Idaho National Engineering Laboratory (INEL) soil, the second used contaminated soil containing plutonium-239 (from a mixture of Rocky Flats Plant contaminated soil and INEL uncontaminated soil), and the third was uncontaminated INEL soil spiked with plutonium-239. All experiments with contaminated soil were conducted inside a glove box containing a dust generator, low volume cascade impactor (LVCI), electrostatic separator, and electrostatic materials. The data for these experiments consisted of the mass of dust collected on the various material coupons, plates, and filters; radiochemical analysis of selected samples; and photographs, as well as computer printouts giving particle size distributions and dimensions from the scanning electron microscope (SEM). The following results were found: (a) plutonium content (pCi/g) was found to increase with smaller soil particle sizes and (b) the electrostatic field had a stronger influence on smaller particle sizes compared to larger particle sizes. The SEM analysis indicated that the particle size of the tracer Pu239 used in the spiked soil experiments was below the detectable size limit (0.5 μm) of the SEM and, thus, may not be representative of plutonium particles found in defense-related waste. The use of radiochemical analysis indicated that plutonium could be found on separator plates of both polarities, as well as passing through the electric field and collecting on LVCI filters

Electrostatic Levitator Electrode Layout

Science.gov (United States)

1998-01-01

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

Continuous electrodeionization through electrostatic shielding

International Nuclear Information System (INIS)

Dermentzis, Konstantinos

2008-01-01

We report a new continuous electrodeionization cell with electrostatically shielded concentrate compartments or electrochemical Faraday cages formed by porous electronically and ionically conductive media, instead of permselective ion exchange membranes. Due to local elimination of the applied electric field within the compartments, they electrostatically retain the incoming ions and act as 'electrostatic ion pumps' or 'ion traps' and therefore concentrate compartments. The porous media are chemically and thermally stable. Electrodeionization or electrodialysis cells containing such concentrate compartments in place of ion exchange membranes can be used to regenerate ion exchange resins and produce deionized water, to purify industrial effluents and desalinate brackish or seawater. The cells can work by polarity reversal without any negative impact to the deionization process. Because the electronically and ionically active media constituting the electrostatically shielded concentrate compartments are not permselective and coions are not repelled but can be swept by the migrating counterions, the cells are not affected by the known membrane associated limitations, such as concentration polarization or scaling and show an increased current efficiency

Surface electrostatics: theory and computations

KAUST Repository

Chatzigeorgiou, G.

2014-02-05

The objective of this work is to study the electrostatic response of materials accounting for boundary surfaces with their own (electrostatic) constitutive behaviour. The electric response of materials with (electrostatic) energetic boundary surfaces (surfaces that possess material properties and constitutive structures different from those of the bulk) is formulated in a consistent manner using a variational framework. The forces and moments that appear due to bulk and surface electric fields are also expressed in a consistent manner. The theory is accompanied by numerical examples on porous materials using the finite-element method, where the influence of the surface electric permittivity on the electric displacement, the polarization stress and the Maxwell stress is examined.

Introduction to numerical electrostatics using MATLAB

CERN Document Server

Dworsky, Lawrence N

2014-01-01

The first of its kind uniquely devoted to the field of computational electrostatics, this book dives headfirst into the actual problems that engineers are expected to solve using method of moment (MoM), finite difference, and finite element techniques. Readers are guided step by step through specific problems and challenges, covering all aspects of electrostatics with an emphasis on numerical procedures. Focusing on practical examples, mathematical equations, and common issues with algorithms, this is an ideal text for students in engineering, physics, and electrostatics-and working engineers

On calculation of the electrostatic potential of a phosphatidylinositol phosphate-containing phosphatidylcholine lipid membrane accounting for membrane dynamics.

Directory of Open Access Journals (Sweden)

Jonathan C Fuller

Full Text Available Many signaling events require the binding of cytoplasmic proteins to cell membranes by recognition of specific charged lipids, such as phosphoinositol-phosphates. As a model for a protein-membrane binding site, we consider one charged phosphoinositol phosphate (PtdIns(3P embedded in a phosphatidylcholine bilayer. As the protein-membrane binding is driven by electrostatic interactions, continuum solvent models require an accurate representation of the electrostatic potential of the phosphoinositol phosphate-containing membrane. We computed and analyzed the electrostatic potentials of snapshots taken at regular intervals from molecular dynamics simulations of the bilayer. We observe considerable variation in the electrostatic potential of the bilayer both along a single simulation and between simulations performed with the GAFF or CHARMM c36 force fields. However, we find that the choice of GAFF or CHARMM c36 parameters has little effect on the electrostatic potential of a given configuration of the bilayer with a PtdIns(3P embedded in it. From our results, we propose a remedian averaging method for calculating the electrostatic potential of a membrane system that is suitable for simulations of protein-membrane binding with a continuum solvent model.

Application of electrostatic prevention technology on polyethylene silos

International Nuclear Information System (INIS)

Gong, Hong; Liu, Quanzhen; Tan, Fenggui; Zhang, Yunpeng

2013-01-01

The main reasons of static electric explosion accidents in polyolefin plant silos were analyzed in this paper, and the study finds that the reasons include control failure of flammable gas content in the feed, high electrification caused by the wind supply, and frequent electrostatic discharge in silos. The electrostatic-reducing technologies of polyolefin powder were introduced, and its application performance in polyolefin plant silos was also clarified. In addition, the methods including FDCS and DGES for evaluation of electrostatic explosion in polyolefin plant silo were proposed. In the end, the risk of electrostatic explosion in PE plant blended silo was evaluated before and after application of electrostatic reducing technology.

Contribution of Electrostatics in the Fibril Stability of a Model Ionic-Complementary Peptide.

Science.gov (United States)

Owczarz, Marta; Casalini, Tommaso; Motta, Anna C; Morbidelli, Massimo; Arosio, Paolo

2015-12-14

In this work we quantified the role of electrostatic interactions in the self-assembly of a model amphiphilic peptide (RADA 16-I) into fibrillar structures by a combination of size exclusion chromatography and molecular simulations. For the peptide under investigation, it is found that a net charge of +0.75 represents the ideal condition to promote the formation of regular amyloid fibrils. Lower net charges favor the formation of amorphous precipitates, while larger net charges destabilize the fibrillar aggregates and promote a reversible dissociation of monomers from the ends of the fibrils. By quantifying the dependence of the equilibrium constant of this reversible reaction on the pH value and the peptide net charge, we show that electrostatic interactions contribute largely to the free energy of fibril formation. The addition of both salt and a charged destabilizer (guanidinium hydrochloride) at moderate concentration (0.3-1 M) shifts the monomer-fibril equilibrium toward the fibrillar state. Whereas the first effect can be explained by charge screening of electrostatic repulsion only, the promotion of fibril formation in the presence of guanidinium hydrochloride is also attributed to modifications of the peptide conformation. The results of this work indicate that the global peptide net charge is a key property that correlates well with the fibril stability, although the peptide conformation and the surface charge distribution also contribute to the aggregation propensity.

A view on thermodynamics of concentrated electrolytes: Modification necessity for electrostatic contribution of osmotic coefficient

Science.gov (United States)

Sahu, Jyoti; Juvekar, Vinay A.

2018-05-01

Prediction of the osmotic coefficient of concentrated electrolytes is needed in a wide variety of industrial applications. There is a need to correctly segregate the electrostatic contribution to osmotic coefficient from nonelectrostatic contribution. This is achieved in a rational way in this work. Using the Robinson-Stokes-Glueckauf hydrated ion model to predict non-electrostatic contribution to the osmotic coefficient, it is shown that hydration number should be independent of concentration so that the observed linear dependence of osmotic coefficient on electrolyte concentration in high concentration range could be predicted. The hydration number of several electrolytes (LiCl, NaCl, KCl, MgCl2, and MgSO4) has been estimated by this method. The hydration number predicted by this model shows correct dependence on temperature. It is also shown that the electrostatic contribution to osmotic coefficient is underpredicted by the Debye-Hückel theory at concentration beyond 0.1 m. The Debye-Hückel theory is modified by introducing a concentration dependent hydrated ionic size. Using the present analysis, it is possible to correctly estimate the electrostatic contribution to the osmotic coefficient, beyond the range of validation of the D-H theory. This would allow development of a more fundamental model for electrostatic interaction at high electrolyte concentrations.

Nonspecific effects of neonatal and infant vaccination

DEFF Research Database (Denmark)

Aaby, Peter; Kollmann, Tobias R; Benn, Christine Stabell

2014-01-01

Vaccines can have nonspecific effects through their modulation of responses to infections not specifically targeted by the vaccine. However, lack of knowledge about the underlying immunological mechanisms and molecular cause-and-effect relationships prevent use of this potentially powerful early-...

The Molecular Basis of Polyunsaturated Fatty Acid Interactions with the Shaker Voltage-Gated Potassium Channel.

Directory of Open Access Journals (Sweden)

Samira Yazdi

2016-01-01

Full Text Available Voltage-gated potassium (KV channels are membrane proteins that respond to changes in membrane potential by enabling K+ ion flux across the membrane. Polyunsaturated fatty acids (PUFAs induce channel opening by modulating the voltage-sensitivity, which can provide effective treatment against refractory epilepsy by means of a ketogenic diet. While PUFAs have been reported to influence the gating mechanism by electrostatic interactions to the voltage-sensor domain (VSD, the exact PUFA-protein interactions are still elusive. In this study, we report on the interactions between the Shaker KV channel in open and closed states and a PUFA-enriched lipid bilayer using microsecond molecular dynamics simulations. We determined a putative PUFA binding site in the open state of the channel located at the protein-lipid interface in the vicinity of the extracellular halves of the S3 and S4 helices of the VSD. In particular, the lipophilic PUFA tail covered a wide range of non-specific hydrophobic interactions in the hydrophobic central core of the protein-lipid interface, while the carboxylic head group displayed more specific interactions to polar/charged residues at the extracellular regions of the S3 and S4 helices, encompassing the S3-S4 linker. Moreover, by studying the interactions between saturated fatty acids (SFA and the Shaker KV channel, our study confirmed an increased conformational flexibility in the polyunsaturated carbon tails compared to saturated carbon chains, which may explain the specificity of PUFA action on channel proteins.

Excitation of electrostatic ion cyclotron wave in electron beam plasma system

International Nuclear Information System (INIS)

Fukumura, Takashi; Takamoto, Teruo

1984-01-01

The electrostatic ion cyclotron waves excited in an electron beam plasma system was investigated. The excitation condition of the waves was calculated by using Harris type dispersion relation under some assumption, and its comparison with the experimental result was made. Beam plasma discharge is a kind of RF discharge, and it is caused by the waves generated by the interaction of electron beam with plasma. It was shown that electrostatic ion cyclotron waves seemed to be the most probable as excited waves. But the excitation mechanism of these waves has not been concretely investigated. In this study, the excitation condition of electrostatic ion cyclotron waves was calculated as described above. The experimental apparatus and the results of potential, electric field and ion saturation current in beam plasma, electron drift motion in azimuthal direction and the waves excited in beam plasma are reported. The frequency of oscillation observed in beam plasma corresponds to the harmonics or subharmonics of ion cyclotron frequency. The calculation of Harris type dispersion relation, the numerical calculation and the comparison of the experimental result with the calculated result are described. (Kako, I.)

Molecular modeling of nucleic Acid structure: electrostatics and solvation.

Science.gov (United States)

Bergonzo, Christina; Galindo-Murillo, Rodrigo; Cheatham, Thomas E

2014-12-19

This unit presents an overview of computer simulation techniques as applied to nucleic acid systems, ranging from simple in vacuo molecular modeling techniques to more complete all-atom molecular dynamics treatments that include an explicit representation of the environment. The third in a series of four units, this unit focuses on critical issues in solvation and the treatment of electrostatics. UNITS 7.5 & 7.8 introduced the modeling of nucleic acid structure at the molecular level. This included a discussion of how to generate an initial model, how to evaluate the utility or reliability of a given model, and ultimately how to manipulate this model to better understand its structure, dynamics, and interactions. Subject to an appropriate representation of the energy, such as a specifically parameterized empirical force field, the techniques of minimization and Monte Carlo simulation, as well as molecular dynamics (MD) methods, were introduced as a way of sampling conformational space for a better understanding of the relevance of a given model. This discussion highlighted the major limitations with modeling in general. When sampling conformational space effectively, difficult issues are encountered, such as multiple minima or conformational sampling problems, and accurately representing the underlying energy of interaction. In order to provide a realistic model of the underlying energetics for nucleic acids in their native environments, it is crucial to include some representation of solvation (by water) and also to properly treat the electrostatic interactions. These subjects are discussed in detail in this unit. Copyright © 2014 John Wiley & Sons, Inc.

Clustering of carboxylated magnetite nanoparticles through polyethylenimine: Covalent versus electrostatic approach

Energy Technology Data Exchange (ETDEWEB)

Tóth, Ildikó Y., E-mail: Ildiko.Toth@chem.u-szeged.hu [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary); Nesztor, Dániel [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary); Novák, Levente [Department of Colloid and Environmental Chemistry, University of Debrecen, Egyetem square 1, Debrecen (Hungary); Illés, Erzsébet; Szekeres, Márta; Szabó, Tamás [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary); Tombácz, Etelka, E-mail: tombacz@chem.u-szeged.hu [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary)

2017-04-01

Carboxylated magnetite nanoparticles (MNPs) are frequently used to develop materials with enhanced properties for MRI and hyperthermia. The controlled clustering of MNPs via covalent or electrostatic approaches provides opportunity to prepare high quality materials. MNPs were prepared by co-precipitation and coated by poly(acrylic acid-co-maleic acid) (PAM@MNP). The clusters were synthesized from purified PAM@MNPs and polyethylenimine (PEI) solution via electrostatic interaction and covalent bond formation (ES-cluster and CB-cluster, respectively). The electrostatic adhesion (–NH{sub 3}{sup +} and –COO{sup –}) and the formed amide bond were confirmed by ATR-FTIR. The averaged area of CB-clusters was about twice as large as that of ES-cluster, based on TEM. The SAXS results showed that the surface of MNPs was smooth and the nanoparticles were close packed in both clusters. The pH-dependent aggregation state and zeta potential of clusters were characterized by DLS and electrophoresis measurements, the clusters were colloidally stable at pH>5. In hyperthermia experiments, the values of SAR were about two times larger for the chemically bonded cluster. The MRI studies showed exceptionally high transversion relaxivities, the r{sub 2} values are 457 mM{sup −1} s{sup −1} and 691 mM{sup −1} s{sup −1} for ES-cluster and CB-cluster, respectively. Based on these results, the chemically clustered product shows greater potential for feasible biomedical applications. - Highlights: • Chemically bonded clusters (CB-cluster) were prepared from PEI and PAM-coated MNPs. • The electrostatically clustered units (ES-cluster) are smaller and more compact. • The electrostatic adhesion and the amide bond formation were confirmed by ATR-FTIR. • CB-cluster dispersions are colloidally stable under physiological conditions. • CB-cluster shows great potential for application in MRI and hyperthermia.

Increasing the reactivity of an artificial dithiol-disulfide pair through modification of the electrostatic milieu

DEFF Research Database (Denmark)

Hansen, Rosa E; Østergaard, Henrik; Winther, Jakob R

2005-01-01

K(a) value of Cys149, as well as favorable electrostatic interactions with the negatively charged reagents. The results presented here show that the electrostatic milieu of cysteine thiols in proteins can have substantial effects on the rates of the thiol-disulfide exchange reactions.......The thiol-disulfide exchange reaction plays a central role in the formation of disulfide bonds in newly synthesized proteins and is involved in many aspects of cellular metabolism. Because the thiolate form of the cysteine residue is the key reactive species, its electrostatic milieu is thought...... surface. We have studied properties of vicinal cysteine residues in proteins using a model system based on redox-sensitive yellow fluorescent protein (rxYFP). In this system, the formation of a disulfide bond between two cysteines Cys149 and Cys202 is accompanied by a 2.2-fold decrease in fluorescence...

Significance of non-specific complaints in asymptomatic cerebral infarction. Approach based on the cerebral circulation

Energy Technology Data Exchange (ETDEWEB)

Sakayori, Osamu; Kitamura, Shin; Nagazumi, Atsushi; Terashi, Akirou [Nippon Medical School, Tokyo (Japan)

1997-10-01

Seventy-three cases with asymptomatic cerebral infarction detected by MR scanning and 80 cases of past stroke patients were evaluated. The regional cerebral blood flow (CBF) using the SPECT, idoine-123-IMP autoradiography (ARG) method was measured. Twenty-two patients with non-specific complaints (dizziness, numbness of the extremities, headache, etc.) without cerebrovascular risk factors were also examined as controls. Fifty-two percent of the asymptomatic infarction cases had non-specific complaints. The regional CBF in all cerebral non-specific complaints showed significantly lower values as compared to the controls. There was no difference in CBF values between the asymptomatic infarction cases with non-specific complaints and the past stroke patients. Among the asymptomatic infarction patients, cases with both non-specific complaints and hypertension displayed significantly lower CBF values, especially in the frontal and temporal cortical regions, than did cases without non-specific complaints or hypertension. These findings suggest that the patient`s complaints should be taken into consideration when determining the clinical treatment of asymptomatic infarction. (author)

Construction of iron-polymer-graphene nanocomposites with low nonspecific adsorption and strong quenching ability for competitive immunofluorescent detection of biomarkers in GM crops.

Science.gov (United States)

Yin, Kaifei; Liu, Anran; Shangguan, Li; Mi, Li; Liu, Xu; Liu, Yuanjian; Zhao, Yuewu; Li, Ying; Wei, Wei; Zhang, Yuanjian; Liu, Songqin

2017-04-15

We developed a new immunofluorescent biosensor by utilizing a novel nanobody (Nb) and iron-polymer-graphene nanocomposites for sensitive detection of 5-enolpyruvylshikimate-3-phosphate synthase from Agrobacdterium tumefaciens strain CP4 (CP4-EPSPS), which considered as biomarkers of genetically modified (GM) crops. Specifically, we prepared iron doped polyacrylic hydrazide modified reduced graphene nanocomposites (Fe@RGO/PAH) by in-situ polymerization approach and subsequent a one-pot reaction with hydrazine. The resulting Fe@RGO/PAH nanocomposites displayed low nonspecific adsorption to analytes (11% quenching caused by nonspecific adsorption) due to electrostatic, energetic and steric effect of the nanocomposites. After Nb immobilizing, the as-prepared Fe@RGO/PAH/Nbs showed good selectivity and high quenching ability (92% quenching) in the presence of antigen (Ag) and polyethylene glycol (PEG) modified CdTe QDs (Ag/QDs@PEG), which is a nearly 4 fold than that of the unmodified GO in same condition. The high quenching ability of Fe@RGO/PAH/Nbs can be used for detection of CP4-EPSPS based on competitive immunoassay with a linearly proportional concentration range of 5-100ng/mL and a detection limit of 0.34ng/mL. The good stability, reproducibility and specificity of the resulting immunofluorescent biosensor are demonstrated and might open a new window for investigation of fluorescent sensing with numerous multifunctional graphene based materials. Copyright © 2016 Elsevier B.V. All rights reserved.

Electrostatic design and beam transport for a folded tandem electrostatic quadrupole accelerator facility for accelerator-based boron neutron capture therapy

International Nuclear Information System (INIS)

Thatar Vento, V.; Bergueiro, J.; Cartelli, D.; Valda, A.A.; Kreiner, A.J.

2011-01-01

Within the frame of an ongoing project to develop a folded Tandem-Electrostatic-Quadrupole (TESQ) accelerator facility for Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT), we discuss here the electrostatic design of the machine, including the accelerator tubes with electrostatic quadrupoles and the simulations for the transport and acceleration of a high intensity beam.

Structural study of surfactant-dependent interaction with protein

Energy Technology Data Exchange (ETDEWEB)

Mehan, Sumit; Aswal, Vinod K., E-mail: vkaswal@barc.gov.in [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Kohlbrecher, Joachim [Laboratory for Neutron Scattering, Paul Scherrer Institut, CH-5232 PSI Villigen (Switzerland)

2015-06-24

Small-angle neutron scattering (SANS) has been used to study the complex structure of anionic BSA protein with three different (cationic DTAB, anionic SDS and non-ionic C12E10) surfactants. These systems form very different surfactant-dependent complexes. We show that the structure of protein-surfactant complex is initiated by the site-specific electrostatic interaction between the components, followed by the hydrophobic interaction at high surfactant concentrations. It is also found that hydrophobic interaction is preferred over the electrostatic interaction in deciding the resultant structure of protein-surfactant complexes.

The cation-π interaction.

Science.gov (United States)

Dougherty, Dennis A

2013-04-16

The chemistry community now recognizes the cation-π interaction as a major force for molecular recognition, joining the hydrophobic effect, the hydrogen bond, and the ion pair in determining macromolecular structure and drug-receptor interactions. This Account provides the author's perspective on the intellectual origins and fundamental nature of the cation-π interaction. Early studies on cyclophanes established that water-soluble, cationic molecules would forego aqueous solvation to enter a hydrophobic cavity if that cavity was lined with π systems. Important gas phase studies established the fundamental nature of the cation-π interaction. The strength of the cation-π interaction (Li(+) binds to benzene with 38 kcal/mol of binding energy; NH4(+) with 19 kcal/mol) distinguishes it from the weaker polar-π interactions observed in the benzene dimer or water-benzene complexes. In addition to the substantial intrinsic strength of the cation-π interaction in gas phase studies, the cation-π interaction remains energetically significant in aqueous media and under biological conditions. Many studies have shown that cation-π interactions can enhance binding energies by 2-5 kcal/mol, making them competitive with hydrogen bonds and ion pairs in drug-receptor and protein-protein interactions. As with other noncovalent interactions involving aromatic systems, the cation-π interaction includes a substantial electrostatic component. The six (four) C(δ-)-H(δ+) bond dipoles of a molecule like benzene (ethylene) combine to produce a region of negative electrostatic potential on the face of the π system. Simple electrostatics facilitate a natural attraction of cations to the surface. The trend for (gas phase) binding energies is Li(+) > Na(+) > K(+) > Rb(+): as the ion gets larger the charge is dispersed over a larger sphere and binding interactions weaken, a classical electrostatic effect. On other hand, polarizability does not define these interactions. Cyclohexane is

Electrostatic behavior of the charge-regulated bacterial cell surface.

Science.gov (United States)

Hong, Yongsuk; Brown, Derick G

2008-05-06

The electrostatic behavior of the charge-regulated surfaces of Gram-negative Escherichia coli and Gram-positive Bacillus brevis was studied using numerical modeling in conjunction with potentiometric titration and electrophoretic mobility data as a function of solution pH and electrolyte composition. Assuming a polyelectrolytic polymeric bacterial cell surface, these experimental and numerical analyses were used to determine the effective site numbers of cell surface acid-base functional groups and Ca(2+) sorption coefficients. Using effective site concentrations determined from 1:1 electrolyte (NaCl) experimental data, the charge-regulation model was able to replicate the effects of 2:1 electrolyte (CaCl(2)), both alone and as a mixture with NaCl, on the measured zeta potential using a single Ca(2+) surface binding constant for each of the bacterial species. This knowledge is vital for understanding how cells respond to changes in solution pH and electrolyte composition as well as how they interact with other surfaces. The latter is especially important due to the widespread use of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in the interpretation of bacterial adhesion. As surface charge and surface potential both vary on a charge-regulated surface, accurate modeling of bacterial interactions with surfaces ultimately requires use of an electrostatic model that accounts for the charge-regulated nature of the cell surface.

Antidepressants for non-specific low back pain

NARCIS (Netherlands)

Urquhart, D. M.; Hoving, J. L.; Assendelft, W. W. J. J.; Roland, M.; van Tulder, M. W.

2008-01-01

BACKGROUND: Antidepressants are commonly used in the management of low-back pain. However, their use is controversial. OBJECTIVES: The aim of this review was to determine whether antidepressants are more effective than placebo for the treatment of non-specific low-back pain. SEARCH STRATEGY:

The establishment and application of direct coupled electrostatic-structural field model in electrostatically controlled deployable membrane antenna

Science.gov (United States)

Gu, Yongzhen; Duan, Baoyan; Du, Jingli

2018-05-01

The electrostatically controlled deployable membrane antenna (ECDMA) is a promising space structure due to its low weight, large aperture and high precision characteristics. However, it is an extreme challenge to describe the coupled field between electrostatic and membrane structure accurately. A direct coupled method is applied to solve the coupled problem in this paper. Firstly, the membrane structure and electrostatic field are uniformly described by energy, considering the coupled problem is an energy conservation phenomenon. Then the direct coupled electrostatic-structural field governing equilibrium equations are obtained by energy variation approach. Numerical results show that the direct coupled method improves the computing efficiency by 36% compared with the traditional indirect coupled method with the same level accuracy. Finally, the prototype has been manufactured and tested and the ECDMA finite element simulations show good agreement with the experiment results as the maximum surface error difference is 6%.

Specifying the non-specific components of acupuncture analgesia

Science.gov (United States)

Vase, Lene; Baram, Sara; Takakura, Nobuari; Yajima, Hiroyoshi; Takayama, Miho; Kaptchuk, Ted J.; Schou, Søren; Jensen, Troels Staehelin; Zachariae, Robert; Svensson, Peter

2014-01-01

It is well known that acupuncture has pain-relieving effects, but the contribution of specific and especially non-specific factors to acupuncture analgesia is less clear. One hundred and one patients who developed pain ≥ 3 on a visual analog scale (VAS, 0-10) following third molar surgery were randomized to receive active acupuncture, placebo acupuncture, or no treatment for 30 min with acupuncture needles with potential for double-blinding. Patients’ perception of the treatment (active or placebo), and expected pain levels (VAS) were assessed prior to and halfway through the treatment. Looking at actual treatment allocation, there was no specific effect of active acupuncture (P = 0.240), but a large and significant non-specific effect of placebo acupuncture (P acupuncture (P acupuncture had significantly lower pain levels than those who believed they received placebo acupuncture. Expected pain levels accounted for significant and progressively larger amounts of the variance in pain ratings following both active and placebo acupuncture (up to 69.8%), This is the first study to show that under optimized blinding conditions non-specific factors such as patients’ perception of and expectations toward treatment are central to the efficacy of acupuncture analgesia and that these factors may contribute to self-reinforcing effects in acupuncture treatment To obtain an effect of acupuncture in clinical practice it may, therefore, be important to incorporate and optimize these factors. PMID:23707680

Relative importance of driving force and electrostatic interactions in the reduction of multihaem cytochromes by small molecules.

Science.gov (United States)

Quintas, Pedro O; Cepeda, Andreia P; Borges, Nuno; Catarino, Teresa; Turner, David L

2013-06-01

Multihaem cytochromes are essential to the energetics of organisms capable of bioremediation and energy production. The haems in several of these cytochromes have been discriminated thermodynamically and their individual rates of reduction by small electron donors were characterized. The kinetic characterization of individual haems used the Marcus theory of electron transfer and assumed that the rates of reduction of each haem by sodium dithionite depend only on the driving force, while electrostatic interactions were neglected. To determine the relative importance of these factors in controlling the rates, we studied the effect of ionic strength on the redox potential and the rate of reduction by dithionite of native Methylophilus methylotrophus cytochrome c″ and three mutants at different pH values. We found that the main factor determining the rate is the driving force and that Marcus theory describes this satisfactorily. This validates the method of the simultaneous fitting of kinetic and thermodynamic data in multihaem cytochromes and opens the way for further investigation into the mechanisms of these proteins. Copyright © 2013 Elsevier B.V. All rights reserved.

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

International Nuclear Information System (INIS)

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

2013-01-01

An electrostatic chuck (ESC) is a type of reversible dry adhesive which clamps objects by means of electrostatic force. Currently an ESC is used only for objects having flat surfaces because the attractive force is reduced for rough surfaces. An ESC that can handle objects with rough surfaces will expand its applications to MEMS (micro electro mechanical system) or optical parts handling. An ESC consisting of compliant electrostatic inductive fibers which conform to the profile of the surface has been proposed for such use. This paper aims at furthering previous research by observing the attractive force/pressure generated, both theoretically and experimentally, through step-by-step fabrication and analysis. Additionally, how the proposed fiber ESC behaves toward rough surfaces is also observed. The attractive force/pressure of the fiber ESC is theoretically investigated using a robust mechano-electrostatic model. Subsequently, a prototype of the fiber ESC consisting of ten fibers arranged at an angle is employed to experimentally observe its attractive force/pressure for objects with rough surfaces. The attractive force of the surface which is modeled as a sinusoidal wave with various amplitudes is observed, through which the feasibility of a fiber ESC is justified. (paper)

An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

International Nuclear Information System (INIS)

Pyzer-Knapp, Edward O.; Thompson, Hugh P. G.; Day, Graeme M.

2016-01-01

An empirically parameterized intermolecular force field is developed for crystal structure modelling and prediction. The model is optimized for use with an atomic multipole description of electrostatic interactions. We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%

Interdomain electron transfer in cellobiose dehydrogenase is governed by surface electrostatics

Czech Academy of Sciences Publication Activity Database

Kádek, Alan; Kavan, Daniel; Marcoux, J.; Stojko, J.; Felice, A.K.G.; Cianférani, S.; Ludwig, R.; Halada, Petr; Man, Petr

2017-01-01

Roč. 1861, č. 2 (2017), s. 157-167 ISSN 0304-4165 R&D Projects: GA ČR GAP206/12/0503; GA MŠk(CZ) ED1.1.00/02.0109; GA MŠk(CZ) LQ1604 Institutional support: RVO:61388971 Keywords : Cellobiose dehydrogenase * Direct electron transfer * Electrostatic interaction Subject RIV: CE - Biochemistry OBOR OECD: Biochemistry and molecular biology Impact factor: 4.702, year: 2016

Allele mining in barley genetic resources reveals genes of race-nonspecific powdery mildew resistance

Directory of Open Access Journals (Sweden)

Annika eSpies

2012-01-01

Full Text Available Race-nonspecific, or quantitative, pathogen resistance is of high importance to plant breeders due to its expected durability. However, it is usually controlled by multiple quantitative trait loci (QTL and therefore difficult to handle in practice. Knowing the genes that underlie race-nonspecific resistance would allow its exploitation in a more targeted manner. Here, we performed an association-genetic study in a customized worlwide collection of spring barley accessions for candidate genes of race-nonspecific resistance to the powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh and combined data with results from QTL-mapping- as well as functional-genomics approaches. This led to the idenfication of 11 associated genes with converging evidence for an important role in race-nonspecific resistance in the presence of the Mlo-gene for basal susceptibility. Outstanding in this respect was the gene encoding the transcription factor WRKY2. The results suggest that unlocking plant genetic resources and integrating functional-genomic with genetic approaches accelerates the discovery of genes underlying race-nonspecific resistance in barley and other crop plants.

Returnable packaging for non-specific building materials

NARCIS (Netherlands)

Gassel, van F.J.M.

1998-01-01

A certain amount of construction waste comes from disposable packaging and this waste is ecologically damaging, one solution would be to reduce the disposable by using returnable packaging for non-specific construction products. To find out if this solution is feasible a study has been carried out

Electrostatic hazards

CERN Document Server

Luttgens, Günter; Luttgens, Gnter; Luttgens, G Nter

1997-01-01

In the US, UK and Europe there is in excess of one notifiable dust or electrostatic explosion every day of the year. This clearly makes the hazards associated with the handling of materials subject to either cause or react to electrostatic discharge of vital importance to anyone associated with their handling or industrial bulk use. This book provides a comprehensive guide to the dangers of static electricity and how to avoid them. It will prove invaluable to safety managers and professionals, as well as all personnel involved in the activities concerned, in the chemical, agricultural, pharmaceutical and petrochemical process industries. The book makes extended use of case studies to illustrate the principles being expounded, thereby making it far more open, accessible and attractive to the practitioner in industry than the highly theoretical texts which are also available. The authors have many years' experience in the area behind them, including the professional teaching of the content provided here. Günte...

Mechanical behavior analysis on electrostatically actuated rectangular microplates

Science.gov (United States)

Li, Zhikang; Zhao, Libo; Jiang, Zhuangde; Ye, Zhiying; Dai, Lu; Zhao, Yulong

2015-03-01

Microplates are widely used in various MEMS devices based on electrostatic actuation such as MEMS switches, micro pumps and capacitive micromachined ultrasonic transducers (CMUTs). Accurate predictions for the mechanical behavior of the microplate under electrostatic force are important not only for the design and optimization of these electrostatic devices but also for their operation. This paper presents a novel reduced-order model for electrostatically actuated rectangular and square microplates with a new method to treat the nonlinear electrostatic force. The model was developed using Galerkin method which turned the partial-differential equation governing the microplates into an ordinary equation system. Using this model and cosine-like deflection functions, explicit expressions were established for the deflection and pull-in voltage of the rectangular and square microplates. The theoretical results were well validated with the finite element method simulations and experimental data of literature. The expressions for the deflection analysis are able to predict the deflection up to the pull-in position with an error less than 5.0%. The expressions for the pull-in voltage analysis can determine the pull-in voltages with errors less than 1.0%. Additionally, the method to calculate the capacitance variation of the electrostatically actuated microplates was proposed. These theoretical analyses are helpful for design and optimization of electrostatically actuated microdevices.

Conservation and Role of Electrostatics in Thymidylate Synthase.

Science.gov (United States)

Garg, Divita; Skouloubris, Stephane; Briffotaux, Julien; Myllykallio, Hannu; Wade, Rebecca C

2015-11-27

Conservation of function across families of orthologous enzymes is generally accompanied by conservation of their active site electrostatic potentials. To study the electrostatic conservation in the highly conserved essential enzyme, thymidylate synthase (TS), we conducted a systematic species-based comparison of the electrostatic potential in the vicinity of its active site. Whereas the electrostatics of the active site of TS are generally well conserved, the TSs from minimal organisms do not conform to the overall trend. Since the genomes of minimal organisms have a high thymidine content compared to other organisms, the observation of non-conserved electrostatics was surprising. Analysis of the symbiotic relationship between minimal organisms and their hosts, and the genetic completeness of the thymidine synthesis pathway suggested that TS from the minimal organism Wigglesworthia glossinidia (W.g.b.) must be active. Four residues in the vicinity of the active site of Escherichia coli TS were mutated individually and simultaneously to mimic the electrostatics of W.g.b TS. The measured activities of the E. coli TS mutants imply that conservation of electrostatics in the region of the active site is important for the activity of TS, and suggest that the W.g.b. TS has the minimal activity necessary to support replication of its reduced genome.

ON THE RELATIVE IMPORTANCE OF SPECIFIC AND NONSPECIFIC APPROACHES TO ORAL MICROBIAL ADHESION

NARCIS (Netherlands)

BUSSCHER, HJ; COWAN, MM; VANDERMEI, HC

In this paper, it is suggested that specificity and non-specificity in (oral) microbial adhesion are different expressions for the same phenomena. It is argued that the same basic, physicochemical forces are responsible for so-called 'non-specific' and 'specific' binding and that from a

A comparison between activities for non-specific esterases and esterproteases

DEFF Research Database (Denmark)

Kirkeby, S; Moe, D

1988-01-01

Electrophoretic separation of non-specific esterases and esterproteases from kidney, lung, and liver have been carried out in polyacrylamide gels. By use of zone electrophoresis, isoelectric focusing, and 2-dimensional electrophoresis it was found that most of the esterprotease bands had the same...... localization in the gels as non-specific esterase bands. A number of esterase bands showed no activity towards the esterprotease substrates and a single kidney band possessed esterprotease activity only. Isozymes of the ES-6 and ES-9 zones showed sex dependent esterprotease reactions. In sections esterase...

Electrostatics with Computer-Interfaced Charge Sensors

Science.gov (United States)

Morse, Robert A.

2006-01-01

Computer interfaced electrostatic charge sensors allow both qualitative and quantitative measurements of electrostatic charge but are quite sensitive to charges accumulating on modern synthetic materials. They need to be used with care so that students can correctly interpret their measurements. This paper describes the operation of the sensors,…

Electrostatic Climber for Space Elevator and Launcher

OpenAIRE

Bolonkin, A.

2007-01-01

Author details research on the new, very prospective, electrostatic Space Elevator climber based on a new electrostatic linear engine previously offered at the 42nd Joint Propulsion Conference (AIAA-2006-5229) and published in AEAT, Vol.78, No.6, 2006, pp. 502-508. The electrostatic climber discussed can have any speed (and braking), the energy for climber movement is delivered by a lightweight high-voltage line into a Space Elevator-holding cable from Earth electric generator. This electric ...

Electrostatic instabilities, turbulence and fast ion interactions in the TORPEX device

Energy Technology Data Exchange (ETDEWEB)

Fasoli, A; Burckel, A; Federspiel, L; Furno, I; Gustafson, K; Iraji, D; Labit, B; Loizu, J; Plyushchev, G; Ricci, P; Theiler, C [Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom-Confederation Suisse, CH-1015 Lausanne (Switzerland); Diallo, A; Podesta, M [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Mueller, S H [Center for Energy Research, University of California, San Diego, CA 92093 (United States); Poli, F [Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL (United Kingdom)

2010-12-15

Electrostatic turbulence, related structures and their effect on particle, heat and toroidal momentum transport are investigated in TORPEX simple magnetized plasmas using high-resolution diagnostics, control parameters, linear fluid models and nonlinear numerical simulations. The nature of the dominant instabilities is controlled by the value of the vertical magnetic field, B{sub v}, relative to that of the toroidal field, B{sub T}. For B{sub v}/B{sub T} > 3%, only ideal interchange instabilities are observed. A critical pressure gradient to drive the interchange instability is experimentally identified. Interchange modes give rise to blobs, radially propagating filaments of enhanced plasma pressure. Blob velocities and sizes are obtained from electrostatic probe measurements using pattern recognition methods. The observed values span a wide range and are described by a single analytical expression, from the small blob size regime in which the blob velocity is limited by cross-field ion polarization currents, to the large blob size regime in which the limitation to the blob velocity comes from parallel currents to the sheath. As a first attempt at controlling the blob dynamical properties, limiter configurations with varying angles between field lines and the conducting surface of the limiter are explored. Mach probe measurements clearly demonstrate a link between toroidal flows and blobs. To complement probe data, a fast framing camera and a movable gas puffing system are installed. Density and light fluctuations show similar signatures of interchange activity. Further developments of optical diagnostics, including an image intensifier and laser-induced fluorescence, are under way. The effect of interchange turbulence on fast ion phase space dynamics is studied using movable fast ion source and detector in scenarios for which the development from linear waves into blobs is fully characterized. A theory validation project is conducted in parallel with TORPEX

Design space of electrostatic chuck in etching chamber

International Nuclear Information System (INIS)

Sun Yuchun; Cheng Jia; Lu Yijia; Hou Yuemin; Ji Linhong

2015-01-01

One of the core semiconductor devices is the electrostatic chuck. It has been widely used in plasma-based and vacuum-based semiconductor processing. The electrostatic chuck plays an important role in adsorbing and cooling/heating wafers, and has technical advantages on non-edge exclusion, high reliability, wafer planarity, particles reduction and so on. This article extracts key design elements from the existing knowledge and techniques of electrostatic chuck by the method proposed by Paul and Beitz, and establishes a design space systematically. The design space is composed of working objects, working principles and working structures. The working objects involve electrostatic chuck components and materials, classifications, and relevant properties; the working principles involve clamping force, residual force, and temperature control; the working structures describe how to compose an electrostatic chuck and to fulfill the overall functions. The systematic design space exhibits the main issues during electrostatic chuck design. The design space will facilitate and inspire designers to improve the design quality and shorten the design time in the conceptual design. (paper)

Interaction of cationic drugs with liposomes.

Science.gov (United States)

Howell, Brett A; Chauhan, Anuj

2009-10-20

Interactions between cationic drugs and anionic liposomes were studied by measuring binding of drugs and the effect of binding on liposome permeability. The measurements were analyzed in the context of a continuum model based on electrostatic interactions and a Langmuir isotherm. Experiments and modeling indicate that, although electrostatic interactions are important, the fraction of drug sequestered in the double-layer is negligible. The majority of drug enters the bilayer with the charged regions interacting with the charged lipid head groups and the lipophilic regions associated with the bilayer. The partitioning of the drug can be described by a Langmuir isotherm with the electrostatic interactions increasing the sublayer concentration of the drug. The binding isotherms are similar for all tricyclic antidepressants (TCA). Bupivacaine (BUP) binds significantly less compared to TCA because its structure is such that the charged region has minimal interactions with the lipid heads once the BUP molecule partitions inside the bilayer. Conversely, the TCAs are linear with distinct hydrophilic and lipophilic regions, allowing the lipophilic regions to lie inside the bilayer and the hydrophilic regions to protrude out. This conformation maximizes the permeability of the bilayer, leading to an increased release of a hydrophilic fluorescent dye from liposomes.

Effects of salts on protein-surface interactions: applications for column chromatography.

Science.gov (United States)

Tsumoto, Kouhei; Ejima, Daisuke; Senczuk, Anna M; Kita, Yoshiko; Arakawa, Tsutomu

2007-07-01

Development of protein pharmaceuticals depends on the availability of high quality proteins. Various column chromatographies are used to purify proteins and characterize the purity and properties of the proteins. Most column chromatographies require salts, whether inorganic or organic, for binding, elution or simply better recovery and resolution. The salts modulate affinity of the proteins for particular columns and nonspecific protein-protein or protein-surface interactions, depending on the type and concentration of the salts, in both specific and nonspecific manners. Salts also affect the binding capacity of the column, which determines the size of the column to be used. Binding capacity, whether equilibrium or dynamic (under an approximation of a slow flow rate), depends on the binding constant, protein concentration and the number of the binding site on the column as well as nonspecific binding. This review attempts to summarize the mechanism of the salt effects on binding affinity and capacity for various column chromatographies and on nonspecific protein-protein or protein-surface interactions. Understanding such salt effects should also be useful in preventing nonspecific protein binding to various containers. Copyright 2007 Wiley-Liss, Inc.

Electrostatic design and beam transport for a folded tandem electrostatic quadrupole accelerator facility for accelerator-based boron neutron capture therapy.

Science.gov (United States)

Vento, V Thatar; Bergueiro, J; Cartelli, D; Valda, A A; Kreiner, A J

2011-12-01

Within the frame of an ongoing project to develop a folded Tandem-Electrostatic-Quadrupole (TESQ) accelerator facility for Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT), we discuss here the electrostatic design of the machine, including the accelerator tubes with electrostatic quadrupoles and the simulations for the transport and acceleration of a high intensity beam. Copyright © 2011 Elsevier Ltd. All rights reserved.

Electrostatic interactions in finite systems treated with periodic boundary conditions: application to linear-scaling density functional theory.

Science.gov (United States)

Hine, Nicholas D M; Dziedzic, Jacek; Haynes, Peter D; Skylaris, Chris-Kriton

2011-11-28

We present a comparison of methods for treating the electrostatic interactions of finite, isolated systems within periodic boundary conditions (PBCs), within density functional theory (DFT), with particular emphasis on linear-scaling (LS) DFT. Often, PBCs are not physically realistic but are an unavoidable consequence of the choice of basis set and the efficacy of using Fourier transforms to compute the Hartree potential. In such cases the effects of PBCs on the calculations need to be avoided, so that the results obtained represent the open rather than the periodic boundary. The very large systems encountered in LS-DFT make the demands of the supercell approximation for isolated systems more difficult to manage, and we show cases where the open boundary (infinite cell) result cannot be obtained from extrapolation of calculations from periodic cells of increasing size. We discuss, implement, and test three very different approaches for overcoming or circumventing the effects of PBCs: truncation of the Coulomb interaction combined with padding of the simulation cell, approaches based on the minimum image convention, and the explicit use of open boundary conditions (OBCs). We have implemented these approaches in the ONETEP LS-DFT program and applied them to a range of systems, including a polar nanorod and a protein. We compare their accuracy, complexity, and rate of convergence with simulation cell size. We demonstrate that corrective approaches within PBCs can achieve the OBC result more efficiently and accurately than pure OBC approaches.

Nature and strength of defect interactions in cubic stabilized zirconia

International Nuclear Information System (INIS)

Bogicevic, A.; Wolverton, C.

2003-01-01

The intrinsic ordering tendencies that limit ionic conduction in doped zirconia electrolytes are fully elucidated using first-principles calculations. A detailed analysis of nearly 300 yttria- and scandia-stabilized cubic-zirconia-ordered vacancy compounds reveals a delicate balance between competing elastic and electrostatic interactions. These results explain several outstanding experimental observations and provide substantial insight needed for improving ionic conduction and enabling low-temperature operation of zirconia-based electrolytes. We show that the surprising vacancy ordering in dilute solid solutions is a consequence of repulsive electrostatic and attractive elastic interactions that balance at third-neighbor vacancy separations. In contrast, repulsive elastic vacancy-dopant interactions prevail over electrostatic attraction at all probed defect separations in YSZ and lead to very weak ordering preferences in ScSZ. The total electronic contribution to the defect interactions is shown to be strongly dominated by simple point-charge electrostatics, leaving speciation of defect ordering for a given class of aliovalent dopants to the elastic term. Thus, ion size becomes a critical parameter in controlling the ionic conductivity of doped oxide electrolytes

Theoretical study of H3AXH3 and H3AYH2 (A = B, Al, Ga; X = N, P, As and Y = O, S, and Se), electrostatic and hyperconjugative interactions roles

International Nuclear Information System (INIS)

El Guerraze, Abdelaali; El-Nahas, Ahmed M.; Jarid, Abdellah; Serrar, Chafiq; Anane, Hafid; Esseffar, M'hamed

2005-01-01

H 3 AXH n (A = B, Al, and Ga; XH n = NH 3 , PH 3 , AsH 3 , H 2 O, SH 2 and SeH 2 ) donor-acceptor complexes are studied from conformational and coordination-mode points of view at B3LYP/6-311+G(3df,2p) and CCSD(T)/6-311+G(3df,2p) levels of theory. The metallic character of gallium atom is responsible of the irregular structural and coordination mode trends in free and complexed gallane (GaH 3 ). The intuitive staggered conformation is not adopted by all compounds because there is, in some cases, competition between H(donor)-H(acceptor) electrostatic interaction and hyperconjugative electronic delocalisation. All H 3 AXH 3 (X = N, P, and As) complexes are staggered. In accordance with Pophristic-Goodman's study (V. Pophristic, L. Goodman, Nature 411 (2001) 565), hyperconjugation is behind this geometrical preference. For the H 3 AYH 2 series, the H 3 BOH 2 staggered conformation is also favoured by this interaction. Nevertheless, H 3 AlOH 2 and H 3 GaOH 2 are curiously eclipsed and not favoured by the hyperconjugation. This paradox is clarified by both electrostatic and energetic delocalisation interactions analysis. The coordination mode is horizontally and vertically discussed in N and O groups of the periodic table within these complex sets

Inertial Electrostatic Confinement (IEC) devices

International Nuclear Information System (INIS)

Nebel, R.A.; Turner, L.; Tiouririne, T.N.; Barnes, D.C.; Nystrom, W.D.; Bussard, R.W.; Miley, G.H.; Javedani, J.; Yamamoto, Y.

1994-01-01

Inertial Electrostatic Confinement (IEC) is one of the earliest plasma confinement concepts, having first been suggested by P. T. Farnsworth in the 1950s. The concept involves a simple apparatus of concentric spherical electrostatic grids or a combination of grids and magnetic fields. An electrostatic structure is formed from the confluence of electron or ion beams. Gridded IEC systems have demonstrated neutron yields as high as 2 * 10 10 neutrons/sec. These systems have considerable potential as small, inexpensive, portable neutron sources for assaying applications. Neutron tomography is also a potential application. Atomic physics effects strongly influence the performance of all of these systems. Important atomic effects include elastic scattering, ionization, excitation, and charge exchange. This paper discusses how an IEC system is influenced by these effects and how to design around them. Theoretical modeling and experimental results are presented

Sensitivity of core-level spectroscopy to electrostatic environments of nitrile groups: An ab initio study

Directory of Open Access Journals (Sweden)

Abid Hussain

2017-09-01

Full Text Available Ab initio quantum chemistry calculations have been performed to probe the influence of hydrogen bonding on the electronic structure of hydrogen cyanide (HCN. Our calculations determine the origin of nitrogen-specific Raman spectral features from resonant inelastic X-ray scattering occurring in the presence of a water molecule and an electric dipole field. The similarity of the two interactions in altering the electronic structure of the nitrogen atom differs only in the covalent contributions from the water molecule. The CN stretching mode as a structural probe was also investigated to study the electronic origin of the anomalous frequency shift of the nitrile group when subjected to hydrogen bonding and an electrostatic dipole field. The major changes in the electronic structure of HCN are electrostatic in nature and originate from dipole-dipole interactions. The relative shifts of the CN stretching frequency are in good agreement with those experimentally observed.

Mechanical behavior analysis on electrostatically actuated rectangular microplates

International Nuclear Information System (INIS)

Li, Zhikang; Zhao, Libo; Jiang, Zhuangde; Ye, Zhiying; Zhao, Yulong; Dai, Lu

2015-01-01

Microplates are widely used in various MEMS devices based on electrostatic actuation such as MEMS switches, micro pumps and capacitive micromachined ultrasonic transducers (CMUTs). Accurate predictions for the mechanical behavior of the microplate under electrostatic force are important not only for the design and optimization of these electrostatic devices but also for their operation. This paper presents a novel reduced-order model for electrostatically actuated rectangular and square microplates with a new method to treat the nonlinear electrostatic force. The model was developed using Galerkin method which turned the partial-differential equation governing the microplates into an ordinary equation system. Using this model and cosine-like deflection functions, explicit expressions were established for the deflection and pull-in voltage of the rectangular and square microplates. The theoretical results were well validated with the finite element method simulations and experimental data of literature. The expressions for the deflection analysis are able to predict the deflection up to the pull-in position with an error less than 5.0%. The expressions for the pull-in voltage analysis can determine the pull-in voltages with errors less than 1.0%. Additionally, the method to calculate the capacitance variation of the electrostatically actuated microplates was proposed. These theoretical analyses are helpful for design and optimization of electrostatically actuated microdevices. (paper)

Specific and non-specific match effects in negative priming.

Science.gov (United States)

Labossière, Danielle I; Leboe-McGowan, Jason P

2018-01-01

The negative priming effect occurs when withholding a response to a stimulus impairs generation of subsequent responding to a same or a related stimulus. Our goal was to use the negative priming procedure to obtain insights about the memory representations generated by ignoring vs. attending/responding to a prime stimulus. Across three experiments we observed that ignoring a prime stimulus tends to generate higher identity-independent, non-specific repetition effects, owing to an overlap in the coarse perceptual form of a prime distractor and a probe target. By contrast, attended repetition effects generate predominantly identity-specific sources of facilitation. We use these findings to advocate for using laboratory phenomena to illustrate general principles that can be of practical use to non-specialists. In the case of the negative priming procedure, we propose that the procedure provides a useful means for investigating attention/memory interactions, even if the specific cause (or causes) of negative priming effects remain unresolved. Copyright © 2017 Elsevier B.V. All rights reserved.

An Electrostatic Funnel in the GABA-Binding Pathway.

Directory of Open Access Journals (Sweden)

Timothy S Carpenter

2016-04-01

Full Text Available The γ-aminobutyric acid type A receptor (GABAA-R is a major inhibitory neuroreceptor that is activated by the binding of GABA. The structure of the GABAA-R is well characterized, and many of the binding site residues have been identified. However, most of these residues are obscured behind the C-loop that acts as a cover to the binding site. Thus, the mechanism by which the GABA molecule recognizes the binding site, and the pathway it takes to enter the binding site are both unclear. Through the completion and detailed analysis of 100 short, unbiased, independent molecular dynamics simulations, we have investigated this phenomenon of GABA entering the binding site. In each system, GABA was placed quasi-randomly near the binding site of a GABAA-R homology model, and atomistic simulations were carried out to observe the behavior of the GABA molecules. GABA fully entered the binding site in 19 of the 100 simulations. The pathway taken by these molecules was consistent and non-random; the GABA molecules approach the binding site from below, before passing up behind the C-loop and into the binding site. This binding pathway is driven by long-range electrostatic interactions, whereby the electrostatic field acts as a 'funnel' that sweeps the GABA molecules towards the binding site, at which point more specific atomic interactions take over. These findings define a nuanced mechanism whereby the GABAA-R uses the general zwitterionic features of the GABA molecule to identify a potential ligand some 2 nm away from the binding site.

Electrostatics in Chemistry

Indian Academy of Sciences (India)

fundamental concepts of electrostatics as applied to atoms and molecules. The electric ... chemistry, the chemistry of the covalent bond, deals with the structures ..... the position of an asteroid named Ceres ... World Scientific. Singapore, 1992.

The cellular prion protein interacts with the tissue non-specific alkaline phosphatase in membrane microdomains of bioaminergic neuronal cells.

Directory of Open Access Journals (Sweden)

Myriam Ermonval

Full Text Available BACKGROUND: The cellular prion protein, PrP(C, is GPI anchored and abundant in lipid rafts. The absolute requirement of PrP(C in neurodegeneration associated to prion diseases is well established. However, the function of this ubiquitous protein is still puzzling. Our previous work using the 1C11 neuronal model, provided evidence that PrP(C acts as a cell surface receptor. Besides a ubiquitous signaling function of PrP(C, we have described a neuronal specificity pointing to a role of PrP(C in neuronal homeostasis. 1C11 cells, upon appropriate induction, engage into neuronal differentiation programs, giving rise either to serotonergic (1C11(5-HT or noradrenergic (1C11(NE derivatives. METHODOLOGY/PRINCIPAL FINDINGS: The neuronal specificity of PrP(C signaling prompted us to search for PrP(C partners in 1C11-derived bioaminergic neuronal cells. We show here by immunoprecipitation an association of PrP(C with an 80 kDa protein identified by mass spectrometry as the tissue non-specific alkaline phosphatase (TNAP. This interaction occurs in lipid rafts and is restricted to 1C11-derived neuronal progenies. Our data indicate that TNAP is implemented during the differentiation programs of 1C11(5-HT and 1C11(NE cells and is active at their cell surface. Noteworthy, TNAP may contribute to the regulation of serotonin or catecholamine synthesis in 1C11(5-HT and 1C11(NE bioaminergic cells by controlling pyridoxal phosphate levels. Finally, TNAP activity is shown to modulate the phosphorylation status of laminin and thereby its interaction with PrP. CONCLUSION/SIGNIFICANCE: The identification of a novel PrP(C partner in lipid rafts of neuronal cells favors the idea of a role of PrP in multiple functions. Because PrP(C and laminin functionally interact to support neuronal differentiation and memory consolidation, our findings introduce TNAP as a functional protagonist in the PrP(C-laminin interplay. The partnership between TNAP and PrP(C in neuronal cells may

Electrostatic coating technologies for food processing.

Science.gov (United States)

Barringer, Sheryl A; Sumonsiri, Nutsuda

2015-01-01

The application of electrostatics in both powder and liquid coating can improve the quality of food, such as its appearance, aroma, taste, and shelf life. Coatings can be found most commonly in the snack food industry, as well as in confectionery, bakery, meat and cheese processing. In electrostatic powder coating, the most important factors influencing coating quality are powder particle size, density, flowability, charge, and resistivity, as well as the surface properties and characteristics of the target. The most important factors during electrostatic liquid coating, also known as electrohydrodynamic coating, include applied voltage and electrical resistivity and viscosity of the liquid. A good understanding of these factors is needed for the design of optimal coating systems for food processing.

Electrostatic micromotor based on ferroelectric ceramics

Science.gov (United States)

Baginsky, I. L.; Kostsov, E. G.

2004-11-01

A new electrostatic micromotor is described that utilizes the electromechanical energy conversion principle earlier described by the authors. The electromechanical energy conversion is based on reversible electrostatic rolling of thin metallic films (petals) on a ferroelectric surface. The motor's active media are layers of ferroelectric ceramics (about 100 µm in thickness). The characteristics of the electrostatic rolling of the petals on different ceramic surfaces are studied, as well as the dynamic characteristics of the micromotors. It is shown that the use of antiferroelectric material allows one to reach a specific energy capacitance comparable to that of the micromotors based on ferroelectric films and to achieve a specific power of 30-300 µW mm-2.

Friction coefficient dependence on electrostatic tribocharging.

Science.gov (United States)

Burgo, Thiago A L; Silva, Cristiane A; Balestrin, Lia B S; Galembeck, Fernando

2013-01-01

Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro- and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro- and nanoscale friction coefficients in PTFE and probably in other insulating polymers.

Investigating ESD sensitivity in electrostatic SiGe MEMS

International Nuclear Information System (INIS)

Sangameswaran, Sandeep; De Coster, Jeroen; Linten, Dimitri; Scholz, Mirko; Thijs, Steven; Groeseneken, Guido; De Wolf, Ingrid

2010-01-01

The sensitivity of electrostatically actuated SiGe microelectromechanical systems to electrostatic discharge events has been investigated in this paper. Torsional micromirrors and RF microelectromechanical systems (MEMS) actuators have been used as two case studies to perform this study. On-wafer electrostatic discharge (ESD) measurement methods, such as the human body model (HBM) and machine model (MM), are discussed. The impact of HBM ESD zap tests on the functionality and behavior of MEMS is explained and the ESD failure levels of MEMS have been verified by failure analysis. It is demonstrated that electrostatic MEMS devices have a high sensitivity to ESD and that it is essential to protect them.

Including diverging electrostatic potential in 3D-RISM theory: The charged wall case

Science.gov (United States)

Vyalov, Ivan; Rocchia, Walter

2018-03-01

Although three-dimensional site-site molecular integral equations of liquids are a powerful tool of the modern theoretical chemistry, their applications to the problem of characterizing the electrical double layer originating at the solid-liquid interface with a macroscopic substrate are severely limited by the fact that an infinitely extended charged plane generates a divergent electrostatic potential. Such potentials cannot be treated within the standard 3D-Reference Interaction Site Model equation solution framework since it leads to functions that are not Fourier transformable. In this paper, we apply a renormalization procedure to overcome this obstacle. We then check the validity and numerical accuracy of the proposed computational scheme on the prototypical gold (111) surface in contact with water/alkali chloride solution. We observe that despite the proposed method requires, to achieve converged charge densities, a higher spatial resolution than that suited to the estimation of biomolecular solvation with either 3D-RISM or continuum electrostatics approaches, it still is computationally efficient. Introducing the electrostatic potential of an infinite wall, which is periodic in 2 dimensions, we avoid edge effects, permit a robust integration of Poisson's equation, and obtain the 3D electrostatic potential profile for the first time in such calculations. We show that the potential within the electrical double layer presents oscillations which are not grasped by the Debye-Hückel and Gouy-Chapman theories. This electrostatic potential deviates from its average of up to 1-2 V at small distances from the substrate along the lateral directions. Applications of this theoretical development are relevant, for example, for liquid scanning tunneling microscopy imaging.

Electrostatic assembly/disassembly of nanoscaled colloidosomes for light-triggered cargo release

KAUST Repository

Li, Song

2015-04-27

Colloidosome capsules possess the potential for the encapsulation and release of molecular and macromolecular cargos. However, the stabilization of the colloidosome shell usually requires an additional covalent crosslinking which irreversibly seals the capsules, and greatly limits their applications in large-cargos release. Herein we report nanoscaled colloidosomes designed by the electrostatic assembly of organosilica nanoparticles (NPs) with oppositely charged surfaces (rather than covalent bonds), arising from different contents of a bridged nitrophenylene-alkoxysilane [NB; 3-nitro-N-(3-(triethoxysilyl)propyl)-4-(((3-(triethoxysilyl)propyl)-amino)methyl)benzamid] derivative in the silica. The surface charge of the positively charged NPs was reversed by light irradiation because of a photoreaction in the NB moieties, which impacted the electrostatic interactions between NPs and disassembled the colloidosome nanosystems. This design was successfully applied for the encapsulation and light-triggered release of cargos. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of Electrostatic Tactile Feedback on Accuracy and Efficiency of Pan Gestures on Touch Screens.

Science.gov (United States)

Liu, Guohong; Sun, Xiaoying; Wang, Dangxiao; Liu, Yue; Zhang, Yuru

2018-01-01

Recently, many studies examined electrostatic tactile feedback on touch screens to enrich interaction experience. However, it is unclear as to whether added tactile feedback during a sliding process increases the accuracy of pan gestures with velocity constraints. In this study, a custom-designed electrostatic tactile display was considered. Initially, the accuracy and efficiency of pan gestures were compared under two conditions, namely with and without electrostatic tactile feedback. This was followed by exploring the evolution of completion time (CT) with different indices of difficulties (ID). Experimental results with 12 participants indicated that the accuracy and completion time of pan gestures with added tactile feedback significantly exceeded those without tactile feedback. Furthermore, the relationship between CT and ID satisfied Fitts' Law with a correlation coefficient exceeding 0.9. Based on the findings, a "Tactile Fruit Sorting" game was designed, and subjective and objective evaluations were conducted. The results confirmed that the added tactile feedback enhanced both user performance and interest with respect to the game.

Nonlinear dynamics of resistive electrostatic drift waves

DEFF Research Database (Denmark)

Korsholm, Søren Bang; Michelsen, Poul; Pécseli, H.L.

1999-01-01

The evolution of weakly nonlinear electrostatic drift waves in an externally imposed strong homogeneous magnetic field is investigated numerically in three spatial dimensions. The analysis is based on a set of coupled, nonlinear equations, which are solved for an initial condition which is pertur......The evolution of weakly nonlinear electrostatic drift waves in an externally imposed strong homogeneous magnetic field is investigated numerically in three spatial dimensions. The analysis is based on a set of coupled, nonlinear equations, which are solved for an initial condition which...... polarity, i.e. a pair of electrostatic convective cells....

Magnetic and electrostatic confinement of plasma with tuning of electrostatic field

Science.gov (United States)

Rostoker, Norman [Irvine, CA; Binderbauer, Michl [Irvine, CA; Qerushi, Artan [Irvine, CA; Tahsiri, Hooshang [Irvine, CA

2008-10-21

A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

Intermolecular interactions

International Nuclear Information System (INIS)

Kaplan, I.G.; Rodimova, O.B.; AN SSSR, Tomsk. Inst. Optiki Atmosfery)

1978-01-01

The present state of the intermolecular interaction theory is described. The general physical picture of the molecular interactions is given, the relative contributions of interactions of different types are analyzed (electrostatic, resonance, induction, dispersion, relativistic, magnetostatic and exchange), and the main ones in each range of separations are picked out. The methods of the potential curve calculations are considered, specific for definite separations between the interacting systems. The special attention is paid to the analysis of approximations used in different theoretical calculation methods

Hazard of electrostatic generation in a pneumatic conveying system: electrostatic effects on the accuracy of electrical capacitance tomography measurements and generation of spark

International Nuclear Information System (INIS)

Zhang, Yan; Wang, Chi-Hwa; Liang, Yung Chii

2008-01-01

The study of the hazard of electrostatic generation in pneumatic conveying systems was attempted by examining the sensitivity of electrical capacitance tomography (ECT) and the phenomena of spark generation due to strong electrostatics. The influence on ECT measurement accuracy of an electrostatic charge was analysed with reference to a switch capacitor configuration model. Consequently, it was found that the electrostatic charge introduced at the bend with sharp angles influenced the ECT results most significantly in pneumatic conveying systems, especially for the cases where a spark was generated. The investigation of spark generation indicated that a strong electrostatic charge can cause major discharges inside or outside the pipeline to damage the experimental instrument in severe cases

Threshold separation distance for attractive interaction between dust particles

International Nuclear Information System (INIS)

Jabdaraghi, R. Najafi; Sobhanian, S.

2008-01-01

Interaction between dust grains in a dusty plasma could be both repulsive and attractive. The Coulomb interaction between two negatively charged dust particulates and the electrostatic force between them are repulsive, while the shadowing force affecting them is attractive. We show in this paper that in some experimental conditions, there is some grain separation zone for which the attractive shadowing force is larger than the repulsive forces between them. In experimental conditions, for the grains separation distance r = 0.4 cm the shadowing force is almost equal to the electrostatic force between them and for r>0.4 cm the shadowing force exceeds the electrostatic force. So the resultant interaction force will be attractive. The possibility of dust crystal formation in this zone and also the motion of dust particles in the resultant potential of the form V = -(a/r)+(b/r 2 ) will be discussed. This form of potential comes from the combination electrostatic (F es (c/r 3 )) and shadowing (F shadow = -(d/r 2 )) forces.

Attitude stabilization of a spacecraft equipped with large electrostatic protection screens

Science.gov (United States)

Nikitin, D. Yu.; Tikhonov, A. A.

2018-05-01

A satellite with a system of three electrostatic radiation protection (ERP) screens is under consideration. The screens are constructed as electrostatically charged toroidal shields with characteristic size of order equal to 100 m. The interaction of electric charge with the Earth's magnetic field (EMF) give rise to the Lorentz torque acting upon a satellite attitude motion. As the sizes of ERP system are large, we derive the Lorentz torque taking into account the complex form of ERP screens and gradient of the EMF in the screen volume. It is assumed that the satellite center of charge coincides with the satellite mass center. The EMF is modeled by the straight magnetic dipole. In the paper we investigate the usage of Lorentz torque for passive attitude stabilization for satellite in a circular equatorial orbit. Mathematical model for attitude dynamics of a satellite equipped with ERP interacting with the EMF is derived and first integral of corresponding differential equations is constructed. The straight equilibrium position of the satellite in the orbital frame is found. Sufficient conditions for stability of satellite equilibrium position are constructed with the use of the first integral. The gravity gradient torque is taken into account. The satellite equilibrium stability domain is constructed.

Electrostatic pickup station

CERN Multimedia

CERN PhotoLab

1982-01-01

Electrostatic pickup station, with 4 interleaved electrodes, to measure beam position in the horizontal and vertical plane. This type is used in the transfer lines leaving the PS (TT2, TT70, TTL2). See also 7904075.

Electrostatic beneficiation of coal

Energy Technology Data Exchange (ETDEWEB)

Mazumder, M.K.; Tennal, K.B.; Lindquist, D.

1994-10-01

Dry physical beneficiation of coal has many advantages over wet cleaning methods and post combustion flue gas cleanup processes. The dry beneficiation process is economically competitive and environmentally safe and has the potential of making vast amounts of US coal reserves available for energy generation. While the potential of the electrostatic beneficiation has been studied for many years in laboratories and in pilot plants, a successful full scale electrostatic coal cleaning plant has not been commercially realized yet. In this paper the authors review some of the technical problems that are encountered in this method and suggest possible solutions that may lead toward its full utilization in cleaning coal.

High-energy capacitance electrostatic micromotors

Science.gov (United States)

Baginsky, I. L.; Kostsov, E. G.

2003-03-01

The design and parameters of a new electrostatic micromotor with high energy output are described. The motor is created by means of microelectronic technology. Its operation is based on the electromechanic energy conversion during the electrostatic rolling of the metallic films (petals) on the ferroelectric film surface. The mathematical simulation of the main characteristics of the rolling process is carried out. The experimentally measured parameters of the petal step micromotors are shown. The motor operation and its efficiency are investigated.

Dissection of specific binding of HIV-1 Gag to the 'packaging signal' in viral RNA.

Science.gov (United States)

Comas-Garcia, Mauricio; Datta, Siddhartha Ak; Baker, Laura; Varma, Rajat; Gudla, Prabhakar R; Rein, Alan

2017-07-20

Selective packaging of HIV-1 genomic RNA (gRNA) requires the presence of a cis -acting RNA element called the 'packaging signal' (Ψ). However, the mechanism by which Ψ promotes selective packaging of the gRNA is not well understood. We used fluorescence correlation spectroscopy and quenching data to monitor the binding of recombinant HIV-1 Gag protein to Cy5-tagged 190-base RNAs. At physiological ionic strength, Gag binds with very similar, nanomolar affinities to both Ψ-containing and control RNAs. We challenged these interactions by adding excess competing tRNA; introducing mutations in Gag; or raising the ionic strength. These modifications all revealed high specificity for Ψ. This specificity is evidently obscured in physiological salt by non-specific, predominantly electrostatic interactions. This nonspecific activity was attenuated by mutations in the MA, CA, and NC domains, including CA mutations disrupting Gag-Gag interaction. We propose that gRNA is selectively packaged because binding to Ψ nucleates virion assembly with particular efficiency.

Reduction of the non-specific binding of DNA to gamma-globulin in Farr radioimmunoassay by addition of dextran sulfate and calcium chloride

Energy Technology Data Exchange (ETDEWEB)

Wakizaka, A; Okuhara, E [Akita Univ. (Japan)

1979-01-23

The effect of non-specific binding caused by the interaction between gamma-globulin and denatured DNA was markedly reduced by addition of dextran sulfate or CaCl/sub 2/ at alkaline pH. This method was shown to be applicable in the detection of anti-DNA antibodies in sera from cases of human systemic lupus erythematosus.

Continuum electrostatics for ionic solutions with non-uniform ionic sizes

International Nuclear Information System (INIS)

Li Bo

2009-01-01

This work concerns electrostatic properties of an ionic solution with multiple ionic species of possibly different ionic sizes. Such properties are described by the minimization of an electrostatic free-energy functional of ionic concentrations. Bounds are obtained for ionic concentrations with low electrostatic free energies. Such bounds are used to show that there exists a unique set of equilibrium ionic concentrations that minimizes the free-energy functional. The equilibrium ionic concentrations are found to depend sorely on the equilibrium electrostatic potential, resembling the classical Boltzmann distributions that relate the equilibrium ionic concentrations to the equilibrium electrostatic potential. Unless all the ionic and solvent molecular sizes are assumed to be the same, explicit formulae of such dependence are, however, not available in general. It is nevertheless proved that in equilibrium the ionic charge density is a decreasing function of the electrostatic potential. This determines a variational principle with a convex functional for the electrostatic potential

On the representation of the electric charge distribution in ethane for calculations of the molecular quadrupole moment and intermolecular electrostatic energy

DEFF Research Database (Denmark)

Hansen, Flemming Yssing; Alldredge, G. P.; Bruch, L. W.

1985-01-01

and gives a repulsive rather than an attractive electrostatic interaction at typical intermolecular distances. In the local multipole model, the atom-site dipoles give the largest contribution to both the molecular quadrupole moment and the intermolecular interaction. The Journal of Chemical Physics...

Harvesting electrostatic energy using super-hydrophobic surfaces

Science.gov (United States)

Pociecha, Dominik; Zylka, Pawel

2016-11-01

Almost all environments are now being extensively populated by miniaturized, nano-powered electronic sensor devices communicated together through wireless sensor networks building Internet of Things (IoT). Various energy harvesting techniques are being more and more frequently proposed for battery-less powering of such remote, unattended, implantable or wearable sensors or other low-power electronic gadgets. Energy harvesting relays on extracting energy from the ambient sources readily accessible at the sensor location and converting it into electrical power. The paper exploits possibility of generating electric energy safely accessible for nano-power electronics using tribo-electric and electrostatic induction phenomena displayed at super-hydrophobic surfaces impinged by water droplets. Mechanism of such interaction is discussed and illustrated by experimental results.

Genetic variations in non-specific immune response to ...

African Journals Online (AJOL)

Non-specific immune response in three strains of Heterobranchus bidorsalis challenged with the bacterium Aeromonas hydrophilia was evaluated. The study was undertaken in three strains of H. bidorsalis from different ecological zones in Nigeria and the percentage cumulative mortality was lowest and significantly ...

Nonspecific effect of BCG vaccination at birth on early childhood infections

DEFF Research Database (Denmark)

Kjærgaard, Jesper; Birk, Nina Marie; Nissen, Thomas N

2016-01-01

BACKGROUND: Childhood infections are common and Bacillus Calmette-Guérin (BCG) vaccination at birth may prevent these via nonspecific effects. METHODS: A randomized, clinical multicenter trial. All women planning to give birth (n = 16,521) at the three study sites were invited during the recruitm......BACKGROUND: Childhood infections are common and Bacillus Calmette-Guérin (BCG) vaccination at birth may prevent these via nonspecific effects. METHODS: A randomized, clinical multicenter trial. All women planning to give birth (n = 16,521) at the three study sites were invited during...... during the first 3 mo....

An efficient numerical approach to electrostatic microelectromechanical system simulation

International Nuclear Information System (INIS)

Pu, Li

2009-01-01

Computational analysis of electrostatic microelectromechanical systems (MEMS) requires an electrostatic analysis to compute the electrostatic forces acting on micromechanical structures and a mechanical analysis to compute the deformation of micromechanical structures. Typically, the mechanical analysis is performed on an undeformed geometry. However, the electrostatic analysis is performed on the deformed position of microstructures. In this paper, a new efficient approach to self-consistent analysis of electrostatic MEMS in the small deformation case is presented. In this approach, when the microstructures undergo small deformations, the surface charge densities on the deformed geometry can be computed without updating the geometry of the microstructures. This algorithm is based on the linear mode shapes of a microstructure as basis functions. A boundary integral equation for the electrostatic problem is expanded into a Taylor series around the undeformed configuration, and a new coupled-field equation is presented. This approach is validated by comparing its results with the results available in the literature and ANSYS solutions, and shows attractive features comparable to ANSYS. (general)

Mathematical analysis of the boundary-integral based electrostatics estimation approximation for molecular solvation: exact results for spherical inclusions.

Science.gov (United States)

Bardhan, Jaydeep P; Knepley, Matthew G

2011-09-28

We analyze the mathematically rigorous BIBEE (boundary-integral based electrostatics estimation) approximation of the mixed-dielectric continuum model of molecular electrostatics, using the analytically solvable case of a spherical solute containing an arbitrary charge distribution. Our analysis, which builds on Kirkwood's solution using spherical harmonics, clarifies important aspects of the approximation and its relationship to generalized Born models. First, our results suggest a new perspective for analyzing fast electrostatic models: the separation of variables between material properties (the dielectric constants) and geometry (the solute dielectric boundary and charge distribution). Second, we find that the eigenfunctions of the reaction-potential operator are exactly preserved in the BIBEE model for the sphere, which supports the use of this approximation for analyzing charge-charge interactions in molecular binding. Third, a comparison of BIBEE to the recent GBε theory suggests a modified BIBEE model capable of predicting electrostatic solvation free energies to within 4% of a full numerical Poisson calculation. This modified model leads to a projection-framework understanding of BIBEE and suggests opportunities for future improvements. © 2011 American Institute of Physics

Electrostatics in Chemistry

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education; Volume 4; Issue 2. Electrostatics in Chemistry - Basic Principles. Shridhar R Gadre Pravin K Bhadane. Series Article Volume 4 Issue 2 February 1999 pp 8-19. Fulltext. Click here to view fulltext PDF. Permanent link:

Electrostatic pickup station

CERN Multimedia

CERN PhotoLab

1979-01-01

Electrostatic pickup station, with 4 electrodes, to measure beam position in the horizontal and vertical plane. This type is used in the transfer lines leaving the PS (TT2, TTL2, TT70). See also 8206063, where the electrode shapes are clearly visible.

Friction coefficient dependence on electrostatic tribocharging

Science.gov (United States)

Burgo, Thiago A. L.; Silva, Cristiane A.; Balestrin, Lia B. S.; Galembeck, Fernando

2013-01-01

Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro- and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro- and nanoscale friction coefficients in PTFE and probably in other insulating polymers. PMID:23934227

Evaluation of Electrostatic Force on Bipolar Charged Electret

International Nuclear Information System (INIS)

Sonoda, K; Minami, K; Miwatani, N; Fujita, T; Kanda, K; Maenaka, K

2014-01-01

This paper presents an evaluation of an electrostatic vibration energy harvester with the bipolar charged electret. The energy harvester with the size of 13 × 12 × 1.2 mm 3 was fabricated. The output power of the bipolar charged with ±250 V harvester was 9 μW when the acceleration was 1.4 g at 352 Hz with 0.9 MΩ load resistance. The effectiveness against the velocity-damped resonant-generator (VDRG) limit was 2.5%. The electrostatic forces of the actual device with DC bias, which simulates charged electret with monopolar and bipolar were experimentally and numerically verified. We estimated the electrostatic force by measuring the vibration amplitude versus applied acceleration of the electret mass. As a result, we investigated the bipolar charged device can reduce the effect of electrostatic force as low as no bias condition. The numerical model of the energy harvester considering the electrostatic force by FEM static analysis was also established. The comparison between the numerical model and the measurement results showed a similar inclination

Manufacture of electrostatic septum for extracting particle beam

International Nuclear Information System (INIS)

Tokumoto, Shuichi

1979-01-01

In the main ring of National Laboratory for High Energy Physics, fast and slow extractions of accelerated proton beam are carried out by using electrostatic septa. The electrostatic septum is an apparatus to deflect beam by an electrostatic field, basically composed of a couple of parallel plate electrodes installed in a vacuum chamber. The electrostatic septum is required to satisfy the following two conditions: it must be very thin and flat to reduce the loss of extracted beam, and sufficiently high electric field must be generated to deflect beam in a limited length. The structure and manufacture of electrostatic septa are described. The manufacturing is explained by dividing a septum into an anode and a cathode, terminals introducing high voltage, a vacuum chamber, and high voltage circuit. The performance is also described on the experiments for no-beam condition and beam extraction. Beam extraction has been carried out over 1500 hours thus far, the average beam intensity being 1 x 10 12 ppp, and extraction efficiency more than 90%. There have been no serious failure to affect the performance nor metal wire breakage. They have satisfied their purposes, being used for both fast and slow extractions. Presently, lengthening of the electrostatic field region is being planned to increase the length of the septa to 1.5 m per unit. (Wakatsuki, Y.)

General theory of the ionization of an atom by an electrostatic field

International Nuclear Information System (INIS)

Fonda, L.

1981-05-01

The ionization of an atom by an external electrostatic field is reconsidered by taking into account the interactions of the system with the measuring apparatus. The experimental ionization rate is drastically different from the expression obtained when no measurements are present. A dependence on the mean frequency of measurements is found. This fact can be used to determine this quantity once the ionization rate is determined experimentally. (author)

Remarks on “A new non-specificity measure in evidence theory based on belief intervals”

Directory of Open Access Journals (Sweden)

Joaquín ABELLÁN

2018-03-01

Full Text Available Two types of uncertainty co-exist in the theory of evidence: discord and non-specificity. From 90s, many mathematical expressions have arisen to quantify these two parts in an evidence. An important aspect of each measure presented is the verification of a coherent set of properties. About non-specificity, so far only one measure verifies an important set of those properties. Very recently, a new measure of non-specificity based on belief intervals has been presented as an alternative measure that quantifies a similar set of properties (Yang et al., 2016. It is shown that the new measure really does not verify two of those important properties. Some errors have been found in their corresponding proofs in the original publication. Keywords: Additivity, Imprecise probabilities, Non-specificity, Subadditivity, Theory of evidence, Uncertainty measures

Electrostatics Control Actin Filament Nucleation and Elongation Kinetics*

Science.gov (United States)

Crevenna, Alvaro H.; Naredi-Rainer, Nikolaus; Schönichen, André; Dzubiella, Joachim; Barber, Diane L.; Lamb, Don C.; Wedlich-Söldner, Roland

2013-01-01

The actin cytoskeleton is a central mediator of cellular morphogenesis, and rapid actin reorganization drives essential processes such as cell migration and cell division. Whereas several actin-binding proteins are known to be regulated by changes in intracellular pH, detailed information regarding the effect of pH on the actin dynamics itself is still lacking. Here, we combine bulk assays, total internal reflection fluorescence microscopy, fluorescence fluctuation spectroscopy techniques, and theory to comprehensively characterize the effect of pH on actin polymerization. We show that both nucleation and elongation are strongly enhanced at acidic pH, with a maximum close to the pI of actin. Monomer association rates are similarly affected by pH at both ends, although dissociation rates are differentially affected. This indicates that electrostatics control the diffusional encounter but not the dissociation rate, which is critical for the establishment of actin filament asymmetry. A generic model of protein-protein interaction, including electrostatics, explains the observed pH sensitivity as a consequence of charge repulsion. The observed pH effect on actin in vitro agrees with measurements of Listeria propulsion in pH-controlled cells. pH regulation should therefore be considered as a modulator of actin dynamics in a cellular environment. PMID:23486468

Electrostatics control actin filament nucleation and elongation kinetics.

Science.gov (United States)

Crevenna, Alvaro H; Naredi-Rainer, Nikolaus; Schönichen, André; Dzubiella, Joachim; Barber, Diane L; Lamb, Don C; Wedlich-Söldner, Roland

2013-04-26

The actin cytoskeleton is a central mediator of cellular morphogenesis, and rapid actin reorganization drives essential processes such as cell migration and cell division. Whereas several actin-binding proteins are known to be regulated by changes in intracellular pH, detailed information regarding the effect of pH on the actin dynamics itself is still lacking. Here, we combine bulk assays, total internal reflection fluorescence microscopy, fluorescence fluctuation spectroscopy techniques, and theory to comprehensively characterize the effect of pH on actin polymerization. We show that both nucleation and elongation are strongly enhanced at acidic pH, with a maximum close to the pI of actin. Monomer association rates are similarly affected by pH at both ends, although dissociation rates are differentially affected. This indicates that electrostatics control the diffusional encounter but not the dissociation rate, which is critical for the establishment of actin filament asymmetry. A generic model of protein-protein interaction, including electrostatics, explains the observed pH sensitivity as a consequence of charge repulsion. The observed pH effect on actin in vitro agrees with measurements of Listeria propulsion in pH-controlled cells. pH regulation should therefore be considered as a modulator of actin dynamics in a cellular environment.

Stability, Nonlinearity and Reliability of Electrostatically Actuated MEMS Devices

Directory of Open Access Journals (Sweden)

Di Chen

2007-05-01

Full Text Available Electrostatic micro-electro-mechanical system (MEMS is a special branch with a wide range of applications in sensing and actuating devices in MEMS. This paper provides a survey and analysis of the electrostatic force of importance in MEMS, its physical model, scaling effect, stability, nonlinearity and reliability in detail. It is necessary to understand the effects of electrostatic forces in MEMS and then many phenomena of practical importance, such as pull-in instability and the effects of effective stiffness, dielectric charging, stress gradient, temperature on the pull-in voltage, nonlinear dynamic effects and reliability due to electrostatic forces occurred in MEMS can be explained scientifically, and consequently the great potential of MEMS technology could be explored effectively and utilized optimally. A simplified parallel-plate capacitor model is proposed to investigate the resonance response, inherent nonlinearity, stiffness softened effect and coupled nonlinear effect of the typical electrostatically actuated MEMS devices. Many failure modes and mechanisms and various methods and techniques, including materials selection, reasonable design and extending the controllable travel range used to analyze and reduce the failures are discussed in the electrostatically actuated MEMS devices. Numerical simulations and discussions indicate that the effects of instability, nonlinear characteristics and reliability subjected to electrostatic forces cannot be ignored and are in need of further investigation.

Electrostatic models of electron-driven proton transfer across a lipid membrane

Energy Technology Data Exchange (ETDEWEB)

Smirnov, Anatoly Yu; Nori, Franco [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Mourokh, Lev G [Department of Physics, Queens College, The City University of New York, Flushing, NY 11367 (United States)

2011-06-15

We present two models for electron-driven uphill proton transport across lipid membranes, with the electron energy converted to the proton gradient via the electrostatic interaction. In the first model, associated with the cytochrome c oxidase complex in the inner mitochondria membranes, the electrostatic coupling to the site occupied by an electron lowers the energy level of the proton-binding site, making proton transfer possible. In the second model, roughly describing the redox loop in a nitrate respiration of E. coli bacteria, an electron displaces a proton from the negative side of the membrane to a shuttle, which subsequently diffuses across the membrane and unloads the proton to its positive side. We show that both models can be described by the same approach, which can be significantly simplified if the system is separated into several clusters, with strong Coulomb interaction inside each cluster and weak transfer couplings between them. We derive and solve the equations of motion for the electron and proton creation/annihilation operators, taking into account the appropriate Coulomb terms, tunnel couplings, and the interaction with the environment. For the second model, these equations of motion are solved jointly with a Langevin-type equation for the shuttle position. We obtain expressions for the electron and proton currents and determine their dependence on the electron and proton voltage build-ups, on-site charging energies, reorganization energies, temperature, and other system parameters. We show that the quantum yield in our models can be up to 100% and the power-conversion efficiency can reach 35%.

Electrostatic models of electron-driven proton transfer across a lipid membrane

International Nuclear Information System (INIS)

Smirnov, Anatoly Yu; Nori, Franco; Mourokh, Lev G

2011-01-01

We present two models for electron-driven uphill proton transport across lipid membranes, with the electron energy converted to the proton gradient via the electrostatic interaction. In the first model, associated with the cytochrome c oxidase complex in the inner mitochondria membranes, the electrostatic coupling to the site occupied by an electron lowers the energy level of the proton-binding site, making proton transfer possible. In the second model, roughly describing the redox loop in a nitrate respiration of E. coli bacteria, an electron displaces a proton from the negative side of the membrane to a shuttle, which subsequently diffuses across the membrane and unloads the proton to its positive side. We show that both models can be described by the same approach, which can be significantly simplified if the system is separated into several clusters, with strong Coulomb interaction inside each cluster and weak transfer couplings between them. We derive and solve the equations of motion for the electron and proton creation/annihilation operators, taking into account the appropriate Coulomb terms, tunnel couplings, and the interaction with the environment. For the second model, these equations of motion are solved jointly with a Langevin-type equation for the shuttle position. We obtain expressions for the electron and proton currents and determine their dependence on the electron and proton voltage build-ups, on-site charging energies, reorganization energies, temperature, and other system parameters. We show that the quantum yield in our models can be up to 100% and the power-conversion efficiency can reach 35%.

Molecular Effects of Concentrated Solutes on Protein Hydration, Dynamics, and Electrostatics.

Science.gov (United States)

Abriata, Luciano A; Spiga, Enrico; Peraro, Matteo Dal

2016-08-23

Most studies of protein structure and function are performed in dilute conditions, but proteins typically experience high solute concentrations in their physiological scenarios and biotechnological applications. High solute concentrations have well-known effects on coarse protein traits like stability, diffusion, and shape, but likely also perturb other traits through finer effects pertinent at the residue and atomic levels. Here, NMR and molecular dynamics investigations on ubiquitin disclose variable interactions with concentrated solutes that lead to localized perturbations of the protein's surface, hydration, electrostatics, and dynamics, all dependent on solute size and chemical properties. Most strikingly, small polar uncharged molecules are sticky on the protein surface, whereas charged small molecules are not, but the latter still perturb the internal protein electrostatics as they diffuse nearby. Meanwhile, interactions with macromolecular crowders are favored mainly through hydrophobic, but not through polar, surface patches. All the tested small solutes strongly slow down water exchange at the protein surface, whereas macromolecular crowders do not exert such strong perturbation. Finally, molecular dynamics simulations predict that unspecific interactions slow down microsecond- to millisecond-timescale protein dynamics despite having only mild effects on pico- to nanosecond fluctuations as corroborated by NMR. We discuss our results in the light of recent advances in understanding proteins inside living cells, focusing on the physical chemistry of quinary structure and cellular organization, and we reinforce the idea that proteins should be studied in native-like media to achieve a faithful description of their function. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

An experimental study on anti-electrostatic gauge rulers

International Nuclear Information System (INIS)

Lou, Renjie; Dai, Liping; Sun, Hong

2013-01-01

The process of oil filling will produce electrostatic phenomena which may cause fire accidents. There were no reports about research on the danger of static electricity generation in the process of gauging operation to date. This paper presents an experiment on charge transferring quantity of gauge rulers, and calculates the charge transferring quantity of an anti-electrostatic gauge ruler and a metal one, respectively. The results indicate that the charge transferring quantity can be more than 0.1 μC for a metal gauge ruler, while it is less than 0.1 μC for an antistatic gauge ruler. Therefore, this experimental research proves that using an anti-electrostatic gauge ruler is safer than using a metal one. This study also provides some theoretical and experimental evidence for making anti-electrostatic gauge rulers.

Numerical study of droplet evaporation in coupled high-temperature and electrostatic fields

Directory of Open Access Journals (Sweden)

Ziwen Zuo

2015-03-01

Full Text Available The evaporation of a sessile water droplet under the coupled electrostatic and high-temperature fields is studied numerically. The leaky dielectric model and boiling point evaporation model are used for calculating the electric force and heat mass transfer. The free surface is captured using the volume of fluid method accounting for the variable surface tension and the transition of physical properties across the interface. The flow behaviors and temperature evolutions in different applied fields are predicted. It shows that in the coupled fields, the external electrostatic field restrains the flow inside the droplet and keeps a steady circulation. The flow velocity is reduced due to the interaction between electric body force and the force caused by temperature gradient. The heat transfer from air into the droplet is reduced by the lower flow velocity. The evaporation rate of the droplet in the high-temperature field is decreased.

Evidences of Changes in Surface Electrostatic Charge Distribution during Stabilization of HPV16 Virus-Like Particles.

Directory of Open Access Journals (Sweden)

Juan F Vega

Full Text Available 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.

Long-range interaction between heterogeneously charged membranes.

Science.gov (United States)

Jho, Y S; Brewster, R; Safran, S A; Pincus, P A

2011-04-19

Despite their neutrality, surfaces or membranes with equal amounts of positive and negative charge can exhibit long-range electrostatic interactions if the surface charge is heterogeneous; this can happen when the surface charges form finite-size domain structures. These domains can be formed in lipid membranes where the balance of the different ranges of strong but short-ranged hydrophobic interactions and longer-ranged electrostatic repulsion result in a finite, stable domain size. If the domain size is large enough, oppositely charged domains in two opposing surfaces or membranes can be strongly correlated by the electrostatic interactions; these correlations give rise to an attractive interaction of the two membranes or surfaces over separations on the order of the domain size. We use numerical simulations to demonstrate the existence of strong attractions at separations of tens of nanometers. Large line tensions result in larger domains but also increase the charge density within the domain. This promotes correlations and, as a result, increases the intermembrane attraction. On the other hand, increasing the salt concentration increases both the domain size and degree of domain anticorrelation, but the interactions are ultimately reduced due to increased screening. The result is a decrease in the net attraction as salt concentration is increased. © 2011 American Chemical Society

Chlamydia trachomatis in non-specific urethritis.

Science.gov (United States)

Terho, P

1978-01-01

Chlamydia trachomatis was isolated from 58.5% of 159 patients with non-specific urethritis (NSU) using irradiated McCoy cell cultures. Patients with persistent Chlamydia-positive NSU remained Chlamydia-positive each time they were examined before treatment and patients with Chlamydia-negative NSU remained Chlamydia-negative during the course of the illness. Neither the duration of symptoms of urethritis nor a history of previous urethritis affected the chlamydial isolation rate significantly. Of 40 patients with severe discharge 30 (75%) harboured C. trachomatis. One-third of the Chlamydia-positive patients had a severe urethral discharge, while this was present in only 15% of Chlamydia-negative patients. Complications--such as conjunctivitis, arthritis, and epididymitis--were more severe in men with Chlamdia-positive NSU than in those with Chlamydia-negative NSU. Of 64 men matched for sexual promiscuity but without urethritis, none harboured C. trachomatis in his urethra. This differs significantly (P less than 0.001) when compared with patients with NSU. C. trachomatis was isolated from the urogenital tract in 24 (42%) out of 57 female sexual contacts of patients with NSU. The presence of C. trachomatis in the women correlated significantly (P less than 0.001) with the isolation of the agent from their male contacts. These findings give further evidence for the aetiological role of C. trachomatis in non-specific urethritis and its sexual transmission. PMID:678958

Electrostatic Deposition of Large-Surface Graphene

Directory of Open Access Journals (Sweden)

Charles Trudeau

2018-01-01

Full Text Available This work describes a method for electrostatic deposition of graphene over a large area using controlled electrostatic exfoliation from a Highly Ordered Pyrolytic Graphite (HOPG block. Deposition over 130 × 130 µm2 with 96% coverage is achieved, which contrasts with sporadic micro-scale depositions of graphene with little control from previous works on electrostatic deposition. The deposition results are studied by Raman micro-spectroscopy and hyperspectral analysis using large fields of view to allow for the characterization of the whole deposition area. Results confirm that laser pre-patterning of the HOPG block prior to cleaving generates anchor points favoring a more homogeneous and defect-free HOPG surface, yielding larger and more uniform graphene depositions. We also demonstrate that a second patterning of the HOPG block just before exfoliation can yield features with precisely controlled geometries.

Energy Balance in an Electrostatic Accelerator

OpenAIRE

Zolotorev, Max S.; McDonald, Kirk T.

2000-01-01

The principle of an electrostatic accelerator is that when a charge e escapes from a conducting plane that supports a uniform electric field of strength E_0, then the charge gains energy e E_0 d as it moves distance d from the plane. Where does this energy come from? We that the mechanical energy gain of the electron is balanced by the decrease in the electrostatic field energy of the system.

Electrostatic Levitation Furnace for the ISS

Science.gov (United States)

Murakami, Keiji; Koshikawa, Naokiyo; Shibasaki, Kohichi; Ishikawa, Takehiko; Okada, Junpei; Takada, Tetsuya; Arai, Tatsuya; Fujino, Naoki; Yamaura, Yukiko

2012-01-01

JAXA (Japan Aerospace Exploration Agency) has just started the development of Electrostatic Levitation Furnace to be launched in 2014 for the ISS. This furnace can control the sample position with electrostatic force and heat it above 2000 degree Celsius using semiconductor laser from four different directions. The announcement of Opportunity will be issued soon for this furnace. In this paper, we will show the specifications of this furnace and also the development schedule

Embedding beyond electrostatics-The role of wave function confinement.

Science.gov (United States)

Nåbo, Lina J; Olsen, Jógvan Magnus Haugaard; Holmgaard List, Nanna; Solanko, Lukasz M; Wüstner, Daniel; Kongsted, Jacob

2016-09-14

We study excited states of cholesterol in solution and show that, in this specific case, solute wave-function confinement is the main effect of the solvent. This is rationalized on the basis of the polarizable density embedding scheme, which in addition to polarizable embedding includes non-electrostatic repulsion that effectively confines the solute wave function to its cavity. We illustrate how the inclusion of non-electrostatic repulsion results in a successful identification of the intense π → π(∗) transition, which was not possible using an embedding method that only includes electrostatics. This underlines the importance of non-electrostatic repulsion in quantum-mechanical embedding-based methods.

Acute non-specific low back pain in primary care

African Journals Online (AJOL)

Treatment of non-specific low back pain typically results in a significant improvement ... and the potential benefits and risks associated with drug treatment, have been ... South African Family Practice 2014; 56(6):10-14. Open Access article ...

Competing processes of whistler and electrostatic instabilities in the magnetosphere

International Nuclear Information System (INIS)

Omura, Y.; Matsumoto, H.

1987-01-01

Competing processes of whistler mode and electrostatic mode instabilities induced by an electron beam are studied by a linear growth rate analysis and by an electromagnetic particle simulation. In addition to a background cold plasma we assumed an electron beam drifting along a static magnetic field. We studied excitation of whistler and electrostatic mode waves in the direction of the static magnetic field. We first calculated linear growth rates for the whistler mode and electrostatic mode instabilities, assuming various possible parameters in the equatorial magnetosphere. We found that the growth rate for the electrostatic instability is always larger than that of the whistler mode instability. A short simulation run with a monoenergetic electron beam demonstrates that a monoenergetic beam can hardly give energy to whistler mode waves as a result of competition with faster growing electrostatic waves, because the beam electrons are trapped and diffused by the electrostatic waves, and hence the growth rates for whistler mode waves become very small. A long simulation run starting with a warm electron beam demonstrates that whistler mode waves are excited in spite of the small growth rates and the coexisting quasi-linear electrostatic diffusion process

Geometrical optics, electrostatics, and nanophotonic resonances in absorbing nanowire arrays.

Science.gov (United States)

Anttu, Nicklas

2013-03-01

Semiconductor nanowire arrays have shown promise for next-generation photovoltaics and photodetection, but enhanced understanding of the light-nanowire interaction is still needed. Here, we study theoretically the absorption of light in an array of vertical InP nanowires by moving continuously, first from the electrostatic limit to the nanophotonic regime and then to the geometrical optics limit. We show how the absorption per volume of semiconductor material in the array can be varied by a factor of 200, ranging from 10 times weaker to 20 times stronger than in a bulk semiconductor sample.

Electrostatic septum, SPS

CERN Multimedia

CERN PhotoLab

1975-01-01

To minimize losses during slow extraction towards N- and W-Area, electrostatic septa in long straight sections 2 and 6 precede the magnetic septa. This picture is a detail of 7501199, and shows the suspension of the wires. 7801286 shows a septum in its tank. See also 7501120X.

A small-gap electrostatic micro-actuator for large deflections

Science.gov (United States)

Conrad, Holger; Schenk, Harald; Kaiser, Bert; Langa, Sergiu; Gaudet, Matthieu; Schimmanz, Klaus; Stolz, Michael; Lenz, Miriam

2015-01-01

Common quasi-static electrostatic micro actuators have significant limitations in deflection due to electrode separation and unstable drive regions. State-of-the-art electrostatic actuators achieve maximum deflections of approximately one third of the electrode separation. Large electrode separation and high driving voltages are normally required to achieve large actuator movements. Here we report on an electrostatic actuator class, fabricated in a CMOS-compatible process, which allows high deflections with small electrode separation. The concept presented makes the huge electrostatic forces within nanometre small electrode separation accessible for large deflections. Electrostatic actuations that are larger than the electrode separation were measured. An analytical theory is compared with measurement and simulation results and enables closer understanding of these actuators. The scaling behaviour discussed indicates significant future improvement on actuator deflection. The presented driving concept enables the investigation and development of novel micro systems with a high potential for improved device and system performance. PMID:26655557

Electrostatic solitons in unmagnetized hot electron-positron-ion plasmas

International Nuclear Information System (INIS)

Mahmood, S.; Ur-Rehman, H.

2009-01-01

Linear and nonlinear electrostatic waves in unmagnetized electron-positron-ion (e-p-i) plasmas are studied. The electrons and positrons are assumed to be isothermal and dynamic while ions are considered to be stationary to neutralize the plasma background only. It is found that both upper (fast) and lower (slow) Langmuir waves can propagates in such a type of pair (e-p) plasma in the presence of ions. The small amplitude electrostatic Korteweg-de Vries (KdV) solitons are also obtained using reductive perturbation method. The electrostatic potential hump structures are found to exist when the temperature of the electrons is larger than the positrons, while the electrostatic potential dips are obtained in the reverse temperature conditions for electrons and positrons in e-p-i plasmas. The numerical results are also shown for illustration. The effects of different ion concentration and temperature ratios of electrons and positrons, on the formation of nonlinear electrostatic potential structures in e-p-i plasmas are also discussed.

Investigation of plasma–surface interaction effects on pulsed electrostatic manipulation for reentry blackout alleviation

International Nuclear Information System (INIS)

Krishnamoorthy, S; Close, S

2017-01-01

The reentry blackout phenomenon affects most spacecraft entering a dense planetary atmosphere from space, due to the presence of a plasma layer that surrounds the spacecraft. This plasma layer is created by ionization of ambient air due to shock and frictional heating, and in some cases is further enhanced due to contamination by ablation products. This layer causes a strong attenuation of incoming and outgoing electromagnetic waves including those used for command and control, communication and telemetry over a period referred to as the ‘blackout period’. The blackout period may last up to several minutes and is a major contributor to the landing error ellipse at best, and a serious safety hazard in the worst case, especially in the context of human spaceflight. In this work, we present a possible method for alleviation of reentry blackout using electronegative DC pulses applied from insulated electrodes on the reentry vehicle’s surface. We study the reentry plasma’s interaction with a DC pulse using a particle-in-cell (PIC) model. Detailed models of plasma–insulator interaction are included in our simulations. The absorption and scattering of ions and electrons at the plasma–dielectric interface are taken into account. Secondary emission from the insulating surface is also considered, and its implications on various design issues is studied. Furthermore, we explore the effect of changing the applied voltage and the impact of surface physics on the creation and stabilization of communication windows. The primary aim of this analysis is to examine the possibility of restoring L- and S-band communication from the spacecraft to a ground station. Our results provide insight into the effect of key design variables on the response of the plasma to the applied voltage pulse. Simulations show the creation of pockets where electron density in the plasma layer is reduced three orders of magnitude or more in the vicinity of the electrodes. These pockets extend to

Orbital dynamics in a storage ring with electrostatic bending

International Nuclear Information System (INIS)

Mane, S.R.

2008-01-01

A storage ring where electrostatic fields contribute to the bending and focusing of the orbital motion has some novel features because, unlike a magnetostatic field, an electrostatic field can change the kinetic energy of the particles. I present analytical formulas to calculate the linear focusing gradient, dispersion, momentum compaction and natural chromaticity for a storage ring with a radial electrostatic field. I solve the formulas explicitly for a weak focusing model.

A Direct Driver for Electrostatic Transducers

DEFF Research Database (Denmark)

Nielsen, Dennis; Knott, Arnold; Andersen, Michael A. E.

2014-01-01

Electrostatic transducers represent a very interesting alternative to the traditional inefficient electrodynamic transducers. In order to establish the full potential of these transducers, power amplifiers which fulfill the strict requirements imposed by such loads (high impedance, frequency...... depended, nonlinear and high bias voltage for linearization) must be developed. This paper analyzes a power stage suitable for driving an electrostatic transducer under biasing. Measurement results of a ±400 V prototype amplifier are shown. THD below 1% is reported....

Electrostatic accelerators

OpenAIRE

Hinterberger, F

2006-01-01

The principle of electrostatic accelerators is presented. We consider Cockcroft– Walton, Van de Graaff and Tandem Van de Graaff accelerators. We resume high voltage generators such as cascade generators, Van de Graaff band generators, Pelletron generators, Laddertron generators and Dynamitron generators. The speci c features of accelerating tubes, ion optics and methods of voltage stabilization are described. We discuss the characteristic beam properties and the variety of possible beams. We ...

Acoustic effects of single electrostatic discharges

International Nuclear Information System (INIS)

Orzech, Łukasz

2015-01-01

Electric discharges, depending on their character, can emit different types of energy, resulting in different effects. Single electrostatic discharges besides generation of electromagnetic pulses are also the source of N acoustic waves. Their specified parameters depending on amount of discharging charge enable determination of value of released charge in a function of acoustic descriptor (e.g. acoustic pressure). Presented approach is the basics of acoustic method for measurement of single electrostatic discharges, enabling direct and contactless measurement of value of charge released during ESD. Method for measurement of acoustic effect of impact of a single electrostatic discharge on the environment in a form of pressure shock wave and examples of acoustic descriptors in a form of equation Q=f(p a ) are described. The properties of measuring system as well as the results of regression static analyses used to determine the described relationships are analysed in details. (paper)

The Role of Non-specific and Specific Immune Systems in Poultry against Newcastle Disease

Directory of Open Access Journals (Sweden)

Dyah Ayu Hewajuli

2015-09-01

Full Text Available Newcastle disease (ND is caused by avian paramyxovirus-1 which belong to Avulavirus genus and Paramyxoviridae family. The birds have abnormalities in humoral (bursa fabricius and cellular (thymus and spleen lymphoid organs. Lesions decrease the immune system. Immune system consists of non-specific and specific immune systems. The main components of non-specific immunity are physical and chemical barrier (feather and skin or mucosa, phagocytic cells (macrophages and natural killer, protein complement and the mediator of inflammation and cytokines. Interferons (IFNs belong to a group of cytokines that play a major role in the nonspecific or innate (natural immunity. The virulent ND virus encodes protein of V gene can be suppressed IFN type I. This leads to non-specific immune system fail to respond to the virulent strains resulting in severe pathogenicity. The defense mechanism of the host is replaced by specific immunity (adaptive immunity when natural immunity fails to overcome the infection. The specific immune system consists of humoral mediated immunity (HMI and cell-mediated immunity (CMI. The cells of immune system that react specifically with the antigen are B lymphocytes producing the antibodies, T lymphocytes that regulate the synthesis of antibodies and T cells as effector or the direct cytotoxic cells. Both non-specific and specific immunities are complementary against the invasion of ND virus in the birds. The objective of this article is to discuss the role of non specific and specific immune system in ND.

Molecular dynamics simulation of liquid structure for undercooled Zr-Nb alloys assisted with electrostatic levitation experiments

Science.gov (United States)

Yang, S. J.; Hu, L.; Wang, L.; Wei, B.

2018-06-01

The liquid structures of undercooled Zr90Nb10, Zr70Nb30 and Zr50Nb50 alloys were studied by molecular dynamics simulation combined with electrostatic levitation experiments. The densities of three alloys were measured by electrostatic levitation to modify the Zr-Nb potential functions by adjusting parameters in potential functions. In simulation, the atomic packing in Zr-Nb alloys was more ordered at lower temperatures. The Voronoi tessellation analyses indicated Nb-centered clusters were easier to form than Zr-centered clusters although the Nb content was less than 50%. The partial pair distribution functions showed that the interactions among Zr atoms are quite different to that among Nb atoms.

Revised electrostatic model of the LISA Pathfinder inertial sensor

Energy Technology Data Exchange (ETDEWEB)

Brandt, Nico [Astrium GmbH, 88039 Friedrichshafen (Germany); Fichter, Walter, E-mail: nico.brandt@astrium.eads.ne [iFR, Universitaet Stuttgart, Pfaffenwaldring 7a, 70569 Stuttgart (Germany)

2009-03-01

A comprehensive electrostatic finite-element (FE) analysis of the LISA Pathfinder Inertial Sensor (IS) has been carried out at Astrium GmbH. Starting with a detailed geometrical model of the IS housing and test mass (TM) flight units, FE results were derived from multiple analyses runs applying the Maxwell 3D field simulation software. The electrostatic forces and torques on the TM in 6DoF, as well as all non-negligible capacitances between the TM, the 18 electrodes, and the housing, have been extracted for different TM translations and rotations. The results of the FE analyses were expected to confirm the existing IS electrostatic model predictions used for performance analysis, simulations, and on-board algorithms. Major discrepancies were found, however, between the results and the model used so far. In general, FE results give considerably larger capacitance values than the equivalent infinite non-parallel plate estimates. In contrast, the FE derived forces and torques are in general significantly lower compared to the analytic IS electrostatic model predictions. In this paper, these results are discussed in detail and the reasons for the deviations are elaborated. Based on these results, an adapted analytic IS electrostatic model is proposed that reflects the electrostatic forces, torques, and stiffness values in the LISA Pathfinder IS significantly more accurate.

Revised electrostatic model of the LISA Pathfinder inertial sensor

International Nuclear Information System (INIS)

Brandt, Nico; Fichter, Walter

2009-01-01

A comprehensive electrostatic finite-element (FE) analysis of the LISA Pathfinder Inertial Sensor (IS) has been carried out at Astrium GmbH. Starting with a detailed geometrical model of the IS housing and test mass (TM) flight units, FE results were derived from multiple analyses runs applying the Maxwell 3D field simulation software. The electrostatic forces and torques on the TM in 6DoF, as well as all non-negligible capacitances between the TM, the 18 electrodes, and the housing, have been extracted for different TM translations and rotations. The results of the FE analyses were expected to confirm the existing IS electrostatic model predictions used for performance analysis, simulations, and on-board algorithms. Major discrepancies were found, however, between the results and the model used so far. In general, FE results give considerably larger capacitance values than the equivalent infinite non-parallel plate estimates. In contrast, the FE derived forces and torques are in general significantly lower compared to the analytic IS electrostatic model predictions. In this paper, these results are discussed in detail and the reasons for the deviations are elaborated. Based on these results, an adapted analytic IS electrostatic model is proposed that reflects the electrostatic forces, torques, and stiffness values in the LISA Pathfinder IS significantly more accurate.

Versatile electrostatic trap

NARCIS (Netherlands)

van Veldhoven, J.; Bethlem, H.L.; Schnell, M.; Meijer, G.

2006-01-01

A four electrode electrostatic trap geometry is demonstrated that can be used to combine a dipole, quadrupole, and hexapole field. A cold packet of ND315 molecules is confined in both a purely quadrupolar and hexapolar trapping field and additionally, a dipole field is added to a hexapole field to

Analysis of fast boundary-integral approximations for modeling electrostatic contributions of molecular binding

Science.gov (United States)

Kreienkamp, Amelia B.; Liu, Lucy Y.; Minkara, Mona S.; Knepley, Matthew G.; Bardhan, Jaydeep P.; Radhakrishnan, Mala L.

2013-01-01

We analyze and suggest improvements to a recently developed approximate continuum-electrostatic model for proteins. The model, called BIBEE/I (boundary-integral based electrostatics estimation with interpolation), was able to estimate electrostatic solvation free energies to within a mean unsigned error of 4% on a test set of more than 600 proteins—a significant improvement over previous BIBEE models. In this work, we tested the BIBEE/I model for its capability to predict residue-by-residue interactions in protein–protein binding, using the widely studied model system of trypsin and bovine pancreatic trypsin inhibitor (BPTI). Finding that the BIBEE/I model performs surprisingly less well in this task than simpler BIBEE models, we seek to explain this behavior in terms of the models’ differing spectral approximations of the exact boundary-integral operator. Calculations of analytically solvable systems (spheres and tri-axial ellipsoids) suggest two possibilities for improvement. The first is a modified BIBEE/I approach that captures the asymptotic eigenvalue limit correctly, and the second involves the dipole and quadrupole modes for ellipsoidal approximations of protein geometries. Our analysis suggests that fast, rigorous approximate models derived from reduced-basis approximation of boundary-integral equations might reach unprecedented accuracy, if the dipole and quadrupole modes can be captured quickly for general shapes. PMID:24466561

Electrostatic-Dipole (ED) Fusion Confinement Studies

Science.gov (United States)

Miley, George H.; Shrestha, Prajakti J.; Yang, Yang; Thomas, Robert

2004-11-01

The Electrostatic-Dipole (ED) concept significantly differs from a "pure" dipole confinement device [1] in that the charged particles are preferentially confined to the high-pressure region interior of the dipole coil by the assistance of a surrounding spherical electrostatic grid. In present ED experiments, a current carrying coil is embedded inside the grid of an IEC such as to produce a magnetic dipole field. Charged particles are injected axisymmetrically from an ion gun (or duo-plasmatron) into the center of the ED confinement grid/dipole ring where they oscillate along the magnetic field lines and pass the peak field region at the center of the dipole region. As particles begin accelerating away from the center region towards the outer electrostatic grid region, they encounter a strong electrostatic potential (order of 10's of kilovolts) retarding force. The particles then decelerate, reverse direction and re-enter the dipole field region where again magnetic confinement dominates. This process continues, emulating a complex harmonic oscillator motion. The resulting pressure profile averaged over the field curvature offers good plasma stability in the ED configuration. The basic concept and results from preliminary experiments will be described. [1] M.E. Mauel, et al. "Dipole Equilibrium and Stability," 18th IAEA Conference of Plasma Phys. and Control. Nuclear Fusion, Varenna, Italy 2000, IAEA-F1-CN-70/TH

Innovative Electrostatic Adhesion Technologies

Science.gov (United States)

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

2015-01-01

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

TIARA electrostatic accelerator facility

International Nuclear Information System (INIS)

Tajima, Satoshi; Takada, Isao; Mizuhashi, Kiyoshi; Uno, Sadanori; Ohkoshi, Kiyonori; Nakajima, Yoshinori; Saitoh, Yuichi; Ishii, Yasuyuki; Kamiya, Tomihiro

1996-07-01

In order to promote the Advanced Radiation Technology Project, Japan Atomic Energy Research Institute constructed TIARA facility composed of four ion accelerators at Takasaki Radiation Chemistry Research Establishment for the period from 1988 to 1993. A 3MV tandem accelerator and an AVF cycrotron were completed in 1991 as the first phase of the construction, and a 3MV single-ended accelerator and a 400kV ion implanter were completed in 1993 as the second phase. Three electrostatic accelerators, the tandem, the single-ended and the implanter, were installed in the Multiple-beam facility of TIARA and have been operated for various experiments with using single, dual and triple beams without any serious trouble. This report describes the constructive works, machine performances, control systems, safety systems and accessory equipments of the electrostatic accelerators. (author)

IAE pulsed electrostatic accelerator

International Nuclear Information System (INIS)

Afanas'ev, V.P.; Ganzhelyuk, M.L.; Kozlov, L.D.; Koltypin, E.A.; Molchanov, Yu.D.; Otroshchenko, G.A.; Yan'kov, G.B.

1976-01-01

The modernized pulse electrostatic accelerator using the klystron ion grouping and the beam interruption system prior to acceleration is described. The accelerator is modernized in order to improve parameters of a current pulse and to decrease the background in the measurement room. The ion beam of needed dimensions is obtained with the help of a high-frequency source and a beam grouping and deflection system. The general view of the beam grouping and deflection system is shown. The ion beam forming process is considered in detail. The modernized electrostatic accelerator permits to obtain a pulse current with a pulse length of 1.5 ns and an amplitude of 1.5 - 2 μA. With the repetition frequency of 2 MHz, the average target current is about 6 μA

Nonspecific Verbal Cues Alleviate Forgetting by Young Children

Science.gov (United States)

Morgan, Kirstie; Hayne, Harlene

2007-01-01

Verbal reminders play a pervasive role in memory retrieval by human adults. In fact, relatively nonspecific verbal information (e.g. "Remember the last time we ate at that restaurant?") will often cue vivid recollections of a past event even when presented outside the original encoding context. Although research has shown that memory retrieval by…

Control of Electrostatic Interactions Between F-Actin And Genetically Modified Lysozyme in Aqueous Media

International Nuclear Information System (INIS)

Sanders, L.K.; Xian, W.; Guaqueta, C.; Strohman, M.; Vrasich, C.R.; Luijten, E.; Wong, G.C.L.

2009-01-01

The aim for deterministic control of the interactions between macroions in aqueous media has motivated widespread experimental and theoretical work. Although it has been well established that like-charged macromolecules can aggregate under the influence of oppositely charged condensing agents, the specific conditions for the stability of such aggregates can only be determined empirically. We examine these conditions, which involve an interplay of electrostatic and osmotic effects, by using a well defined model system composed of F-actin, an anionic rod-like polyelectrolyte, and lysozyme, a cationic globular protein with a charge that can be genetically modified. The structure and stability of actin-lysozyme complexes for different lysozyme charge mutants and salt concentrations are examined by using synchrotron x-ray scattering and molecular dynamics simulations. We provide evidence that supports a structural transition from columnar arrangements of F-actin held together by arrays of lysozyme at the threefold interstitial sites of the actin sublattice to marginally stable complexes in which lysozyme resides at twofold bridging sites between actin. The reduced stability arises from strongly reduced partitioning of salt between the complex and the surrounding solution. Changes in the stability of actin-lysozyme complexes are of biomedical interest because their formation has been reported to contribute to the persistence of airway infections in cystic fibrosis by sequestering antimicrobials such as lysozyme. We present x-ray microscopy results that argue for the existence of actin-lysozyme complexes in cystic fibrosis sputum and demonstrate that, for a wide range of salt conditions, charge-reduced lysozyme is not sequestered in ordered complexes while retaining its bacterial killing activity.

Review on the Modeling of Electrostatic MEMS

Directory of Open Access Journals (Sweden)

Wan-Chun Chuang

2010-06-01

Full Text Available Electrostatic-driven microelectromechanical systems devices, in most cases, consist of couplings of such energy domains as electromechanics, optical electricity, thermoelectricity, and electromagnetism. Their nonlinear working state makes their analysis complex and complicated. This article introduces the physical model of pull-in voltage, dynamic characteristic analysis, air damping effect, reliability, numerical modeling method, and application of electrostatic-driven MEMS devices.

Preliminary tests of the electrostatic plasma accelerator

Science.gov (United States)

Aston, G.; Acker, T.

1990-01-01

This report describes the results of a program to verify an electrostatic plasma acceleration concept and to identify those parameters most important in optimizing an Electrostatic Plasma Accelerator (EPA) thruster based upon this thrust mechanism. Preliminary performance measurements of thrust, specific impulse and efficiency were obtained using a unique plasma exhaust momentum probe. Reliable EPA thruster operation was achieved using one power supply.

Relativistic ion acceleration by ultraintense laser interactions

International Nuclear Information System (INIS)

Nakajima, K.; Koga, J.K.; Nakagawa, K.

2001-01-01

There has been a great interest in relativistic particle generation by ultraintense laser interactions with matter. We propose the use of relativistically self-focused laser pulses for the acceleration of ions. Two dimensional PIC simulations are performed, which show the formation of a large positive electrostatic field near the front of a relativistically self-focused laser pulse. Several factors contribute to the acceleration including self-focusing distance, pulse depletion, and plasma density. Ultraintense laser-plasma interactions are capable of generating enormous electrostatic fields of ∼3 TV/m for acceleration of protons with relativistic energies exceeding 1 GeV

Meta-analysis: exercise therapy for nonspecific low back pain

NARCIS (Netherlands)

Hayden, J.A.; van Tulder, M.; Malmivaara, A.V.; Koes, B.W.

2005-01-01

BACKGROUND: Exercise therapy is widely used as an intervention in low back pain. OBJECTIVE: To evaluate the effectiveness of exercise therapy in adult nonspecific acute, subacute, and chronic low back pain versus no treatment and other conservative treatments. DATA SOURCES: MEDLINE, EMBASE,

Electrostatic mode coupling at 2ω/sub UH/: a generation mechanism for auroral kilometric radiation

International Nuclear Information System (INIS)

Barbosa, D.D.

1976-01-01

The instability of a low density, electron beam drifting along a magnetic field to nearly perpendicular propagating electrostatic waves near the upper hybrid frequency is investigated for application to an auroral environment. It was found that 4 to 10 KeV beams can interact significantly with the background plasma through anomalous cyclotron resonances which extend the range of unstable parallel wave numbers over a large region of wave number space. This region can include a nonconvective hot spot where the group velocity of the unstable waves approaches zero. Positive slope in the total distribution function is not a necessary requirement for instability; the broken symmetry along the field can allow the transfer of beam drift energy to electrostatic wave turbulence. Using Gurnett's (1974) polar ionospheric model for a representative auroral field line modeled as dipolar (L = 8), one infers that certain heights favor generation of enhanced, beamdriven electrostatic turbulence. Those regions are in the vicinity of where ω/sub UH//Ω/sub c/ approx. 3/2 with an excursion from this value depending on beam parameters. We speculate that electrostatic turbulence will heat the background electrons to a limiting temperature such that the instability becomes marginally effective. This limiting temperature is estimated for auroral beam-plasma conditions as 1 to 6 eV. Quasi-linear beam moment equations are developed to compute an upper bound to electrostatic wave amplitudes that can be maintained by the beam. We find that energy densities approaching E 2 /8πnT approx. 1 over auroral scale lengths can result in effective energy transfer from the beam to the plasma

Electrostatic beam-position monitor

CERN Multimedia

CERN PhotoLab

1969-01-01

Electrostatic beam-position monitor installed in its final location (bake-out cover removed). The ISR will contain about 110 of these monitors. Their accuracy is better than 1 mm, their band width about 1 MHz.

Inertial electrostatic confinement I(IEC) neutron sources

International Nuclear Information System (INIS)

Nebel, R.A.; Barnes, D.C.; Caramana, E.J.; Janssen, R.D.; Nystrom, W.D.; Tiouririne, T.N.; Trent, B.C.; Miley, G.H.; Javedani, J.

1995-01-01

Inertial Electrostatic Confinement (IEC) is one of the earliest plasma confinement concepts, having first been suggested by P.T. Farnsworth in the 1950s. The concept involves a simple apparatus of concentric spherical electrostatic grids or a combination of grids and magnetic fields. An electrostatic structure is formed from the confluence of electron or ion beams. Gridded IEC systems have demonstrated neutron yields as high as 2*10 [10]. neutrons/sec in steady state. These systems have considerable potential as small, inexpensive, portable neutron sources for assaying applications. Neutron tomography is also a potential application. This paper discusses the IEC concept and how it can be adapted to a steady-state assaying source and an intense pulsed neutron source. Theoretical modeling and experimental results are presented

A Novel Electrostatic/Microstructured Adhesive with Dust Mitigation Capabilities

Data.gov (United States)

National Aeronautics and Space Administration — This work will develop a novel electrostatic/gecko-like adhesive that will demonstrate an order-of-magnitude improvement of electrostatic adhesion pressure coupled...

Role of electrostatics in the assembly pathway of a single-stranded RNA virus.

Science.gov (United States)

Garmann, Rees F; Comas-Garcia, Mauricio; Koay, Melissa S T; Cornelissen, Jeroen J L M; Knobler, Charles M; Gelbart, William M

2014-09-01

We have recently discovered (R. D. Cadena-Nava et al., J. Virol. 86:3318-3326, 2012, doi:10.1128/JVI.06566-11) that the in vitro packaging of RNA by the capsid protein (CP) of cowpea chlorotic mottle virus is optimal when there is a significant excess of CP, specifically that complete packaging of all of the RNA in solution requires sufficient CP to provide charge matching of the N-terminal positively charged arginine-rich motifs (ARMS) of the CPs with the negatively charged phosphate backbone of the RNA. We show here that packaging results from the initial formation of a charge-matched protocapsid consisting of RNA decorated by a disordered arrangement of CPs. This protocapsid reorganizes into the final, icosahedrally symmetric nucleocapsid by displacing the excess CPs from the RNA to the exterior surface of the emerging capsid through electrostatic attraction between the ARMs of the excess CP and the negative charge density of the capsid exterior. As a test of this scenario, we prepare CP mutants with extra and missing (relative to the wild type) cationic residues and show that a correspondingly smaller and larger excess, respectively, of CP is needed for complete packaging of RNA. Cowpea chlorotic mottle virus (CCMV) has long been studied as a model system for the assembly of single-stranded RNA viruses. While much is known about the electrostatic interactions within the CCMV virion, relatively little is known about these interactions during assembly, i.e., within intermediate states preceding the final nucleocapsid structure. Theoretical models and coarse-grained molecular dynamics simulations suggest that viruses like CCMV assemble by the bulk adsorption of CPs onto the RNA driven by electrostatic attraction, followed by structural reorganization into the final capsid. Such a mechanism facilitates assembly by condensing the RNA for packaging while simultaneously concentrating the local density of CP for capsid nucleation. We provide experimental evidence of

Charge sniffer for electrostatics demonstrations

Science.gov (United States)

Dinca, Mihai P.

2011-02-01

An electronic electroscope with a special design for demonstrations and experiments on static electricity is described. It operates as an electric charge sniffer by detecting slightly charged objects when they are brought to the front of its sensing electrode. The sniffer has the advantage of combining high directional sensitivity with a logarithmic bar display. It allows for the identification of electric charge polarity during charge separation by friction, peeling, electrostatic induction, batteries, or secondary coils of power transformers. Other experiments in electrostatics, such as observing the electric field of an oscillating dipole and the distance dependence of the electric field generated by simple charge configurations, are also described.

Frequency-dependent electrostatic actuation in microfluidic MEMS.

Energy Technology Data Exchange (ETDEWEB)

Zavadil, Kevin Robert; Michalske, Terry A.; Sounart, Thomas L.

2003-09-01

Electrostatic actuators exhibit fast response times and are easily integrated into microsystems because they can be fabricated with standard IC micromachining processes and materials. Although electrostatic actuators have been used extensively in 'dry' MEMS, they have received less attention in microfluidic systems probably because of challenges such as electrolysis, anodization, and electrode polarization. Here we demonstrate that ac drive signals can be used to prevent electrode polarization, and thus enable electrostatic actuation in many liquids, at potentials low enough to avoid electrochemistry. We measure the frequency response of an interdigitated silicon comb-drive actuator in liquids spanning a decade of dielectric permittivities and four decades of conductivity, and present a simple theory that predicts the characteristic actuation frequency. The analysis demonstrates the importance of the native oxide on silicon actuator response, and suggests that the actuation frequency can be shifted by controlling the thickness of the oxide. For native silicon devices, actuation is predicted at frequencies less than 10 MHz, in electrolytes of ionic strength up to 100 mmol/L, and thus electrostatic actuation may be feasible in many bioMEMS and other microfluidic applications.

Waferscale Electrostatic Quadrupole Array for Multiple Ion Beam Manipulation

OpenAIRE

Vinayakumar, K. B.; Persaud, A.; Seidl, P. A.; Ji, Q.; Waldron, W. L.; Schenkel, T.; Ardanuc, S.; Lal, A.

2018-01-01

We report on the first through-wafer silicon-based Electrostatic Quadrupole Array (ESQA) to focus high energy ion beams. This device is a key enabler for a wafer based accelerator architecture that lends itself to orders-of-magnitude reduction in cost, volume and weight of charged particle accelerators. ESQs are a key building block in developing compact Multiple Electrostatic Quadrupole Array Linear Accelerator (MEQALAC) [1]. In a MEQALAC electrostatic forces are used to focus ions, and elec...

Factors affecting the electrostatic charge of ceramic powders

International Nuclear Information System (INIS)

Lorite, I.; Romero, J.; Fernandez, J. F.

2011-01-01

The phenomenon of electrostatic charge in ceramic powders takes place when the particle surfaces enter in contact between them or with the containers. The accumulation of electrostatic charge is of relevance in ceramic powders in view of their insulating character and the risk of explosions during the material handling. In this work the main factors that affect the appearance of intrinsic charge and tribo-charge in ceramic powder have been studied. In ceramic powders of alumina it has been verified that the smallest particle sizes present an increase of the electrostatic charge of negative polarity. A correlation has been observed between the nature of the OH -surface groups and the electrostatic charge. The intrinsic charge and the tribocharge in ceramic powders can be diminished by compensating the surface groups that support the charge. The dry dispersion of nanoparticles on microparticles allows surface charge compensation with a noticeable modification of the powder agglomeration. (Author) 19 refs.

A versatile electrostatic trap with open optical access

Science.gov (United States)

Li, Sheng-Qiang; Yin, Jian-Ping

2018-04-01

A versatile electrostatic trap with open optical access for cold polar molecules in weak-field-seeking state is proposed in this paper. The trap is composed of a pair of disk electrodes and a hexapole. With the help of a finite element software, the spatial distribution of the electrostatic field is calculated. The results indicate that a three-dimensional closed electrostatic trap is formed. Taking ND3 molecules as an example, the dynamic process of loading and trapping is simulated. The results show that when the velocity of the molecular beam is 10 m/s and the loading time is 0.9964 ms, the maximum loading efficiency reaches 94.25% and the temperature of the trapped molecules reaches about 30.3 mK. A single well can be split into two wells, which is of significant importance to the precision measurement and interference of matter waves. This scheme, in addition, can be further miniaturized to construct one-dimensional, two-dimensional, and three-dimensional spatial electrostatic lattices.

Nonlinear Electrostatic Wave Equations for Magnetized Plasmas

DEFF Research Database (Denmark)

Dysthe, K.B.; Mjølhus, E.; Pécseli, Hans

1984-01-01

The lowest order kinetic effects are included in the equations for nonlinear electrostatic electron waves in a magnetized plasma. The modifications of the authors' previous analysis based on a fluid model are discussed.......The lowest order kinetic effects are included in the equations for nonlinear electrostatic electron waves in a magnetized plasma. The modifications of the authors' previous analysis based on a fluid model are discussed....

The Use of Breathing Exercises in the Treatment of Chronic, Nonspecific Low Back Pain.

Science.gov (United States)

Anderson, Barton E; Bliven, Kellie C Huxel

2017-09-01

Clinical Scenario: Research has shown a link between poor core stability and chronic, nonspecific low back pain, with data to suggest that alterations in core muscle activation patterns, breathing patterns, lung function, and diaphragm mechanics may occur. Traditional treatment approaches for chronic, nonspecific low back pain focus on exercise and manual therapy interventions, however it is not clear whether breathing exercises are effective in treating back pain. Focused Clinical Question: In adults with chronic, nonspecific low back pain, are breathing exercises effective in reducing pain, improving respiratory function, and/or health related quality of life? Summary of Key Findings: Following a literature search, 3 studies were identified for inclusion in the review. All reviewed studies were critically appraised at level 2 evidence and reported improvements in either low back pain or quality of life following breathing program intervention. Clinical Bottom Line: Exercise programs were shown to be effective in improving lung function, reducing back pain, and improving quality of life. Breathing program frequencies ranged from daily to 2-3 times per week, with durations ranging from 4 to 8 weeks. Based on these results, athletic trainers and physical therapists caring for patients with chronic, nonspecific low back pain should consider the inclusion of breathing exercises for the treatment of back pain when such treatments align with the clinician's own judgment and clinical expertise and the patient's preferences and values. Strength of Recommendation: Grade B evidence exists to support the use of breathing exercises in the treatment of chronic, nonspecific low back pain.

Direct Determination of Chitosan–Mucin Interactions Using a Single-Molecule Strategy: Comparison to Alginate–Mucin Interactions

Directory of Open Access Journals (Sweden)

Kristin E. Haugstad

2015-01-01

Full Text Available Aqueous chitosan possesses attractive interaction capacities with various molecular groups that can be involved in hydrogen bonds and electrostatic and hydrophobic interactions. In the present paper, we report on the direct determination of chitosan–mucin molecular pair interactions at various solvent conditions as compared to alginate–mucin interactions. Two chitosans of high molecular weight with different degrees of acetylation—thus possessing different solubility profiles in aqueous solution as a function of pH and two alginates with different fractions of α-guluronic acid were employed. The interaction properties were determined through a direct unbinding assay at the single-molecular pair level using an atomic force microscope. When probed against immobilized mucin, both chitosans and alginates revealed unbinding profiles characteristic of localized interactions along the polymers. The interaction capacities and estimated parameters of the energy landscapes of the pairwise chitosan–mucin and alginate–mucin interactions are discussed in view of possible contributions from various fundamental forces. Signatures arising both from an electrostatic mechanism and hydrophobic interaction are identified in the chitosan–mucin interaction properties. The molecular nature of the observed chitosan–mucin and alginate–mucin interactions indicates that force spectroscopy provides fundamental insights that can be useful in understanding the surface binding properties of other potentially mucoadhesive polymers.

Electrostatic Transport and Manipulation of Lunar Soil and Dust

International Nuclear Information System (INIS)

Kawamoto, Hiroyuki

2008-01-01

Transport and manipulation technologies of lunar soil and dust are under development utilizing the electrostatic force. Transport of particles is realized by an electrostatic conveyer consisting of parallel electrodes. Four-phase traveling electrostatic wave was applied to the electrodes to transport particles upon the conveyer and it was demonstrated that particles were efficiently transported under conditions of low frequency, high voltage, and the application of rectangular wave. Not only linear but also curved and closed transport was demonstrated. Numerical investigation was carried out with a three-dimensional hard-sphere model of the Distinct Element Method to clarify the mechanism of the transport and to predict performances in the lunar environment. This technology is expected to be utilized not only for the transport of bulk soil but also for the cleaning of a solar panel and an optical lens. Another technology is an electrostatic manipulation system to manipulate single particle. A manipulator consisted of two parallel pin electrodes. When voltage was applied between the electrodes, electrophoresis force generated in non-uniform electrostatic field was applied to the particle near the tip of the electrode. The particle was captured by the application of the voltage and released from the manipulator by turning off the voltage. It was possible to manipulate not only insulative but also conductive particles. Three-dimensional electrostatic field calculation was conducted to calculate the electrophoresis force and the Coulomb force

Club cells surviving influenza A virus infection induce temporary nonspecific antiviral immunity.

Science.gov (United States)

Hamilton, Jennifer R; Sachs, David; Lim, Jean K; Langlois, Ryan A; Palese, Peter; Heaton, Nicholas S

2016-04-05

A brief window of antigen-nonspecific protection has been observed after influenza A virus (IAV) infection. Although this temporary immunity has been assumed to be the result of residual nonspecific inflammation, this period of induced immunity has not been fully studied. Because IAV has long been characterized as a cytopathic virus (based on its ability to rapidly lyse most cell types in culture), it has been a forgone conclusion that directly infected cells could not be contributing to this effect. Using a Cre recombinase-expressing IAV, we have previously shown that club cells can survive direct viral infection. We show here not only that these cells can eliminate all traces of the virus and survive but also that they acquire a heightened antiviral response phenotype after surviving. Moreover, we experimentally demonstrate temporary nonspecific viral immunity after IAV infection and show that surviving cells are required for this phenotype. This work characterizes a virally induced modulation of the innate immune response that may represent a new mechanism to prevent viral diseases.

A small jab - a big effect: nonspecific immunomodulation by vaccines.

Science.gov (United States)

Benn, Christine S; Netea, Mihai G; Selin, Liisa K; Aaby, Peter

2013-09-01

Recent epidemiological studies have shown that, in addition to disease-specific effects, vaccines against infectious diseases have nonspecific effects on the ability of the immune system to handle other pathogens. For instance, in randomized trials tuberculosis and measles vaccines are associated with a substantial reduction in overall child mortality, which cannot be explained by prevention of the target disease. New research suggests that the nonspecific effects of vaccines are related to cross-reactivity of the adaptive immune system with unrelated pathogens, and to training of the innate immune system through epigenetic reprogramming. Hence, epidemiological findings are backed by immunological data. This generates a new understanding of the immune system and about how it can be modulated by vaccines to impact the general resistance to disease. Copyright © 2013 Elsevier Ltd. All rights reserved.

Field distribution in a coaxial electrostatic wiggler

Directory of Open Access Journals (Sweden)

Shi-Chang Zhang

2010-09-01

Full Text Available The field distribution in a coaxial electrostatic wiggler corresponds to the special solution of a Laplace equation in a cylindrical coordinate system with a boundary value problem of sinusoidal ripples. This paper is devoted to the physical and mathematical treatment for an analytical solution of the field distribution in the coaxial electrostatic wiggler. The explicit expression of the solution indicates that the field distribution in the coaxial electrostatic wiggler varies according to a periodic function in the longitudinal direction, and is related to the first and second kinds of modified Bessel functions in the radial direction, respectively. Comparison shows excellent agreement between the analytical formula and the computer simulation technology (CST results. The physical application of the considered system and its analytical solution are discussed.

Cervico-ocular Reflex Is Increased in People With Nonspecific Neck Pain.

Science.gov (United States)

de Vries, Jurryt; Ischebeck, Britta K; Voogt, Lennard P; Janssen, Malou; Frens, Maarten A; Kleinrensink, Gert-Jan; van der Geest, Jos N

2016-08-01

Neck pain is a widespread complaint. People experiencing neck pain often present an altered timing in contraction of cervical muscles. This altered afferent information elicits the cervico-ocular reflex (COR), which stabilizes the eye in response to trunk-to-head movements. The vestibulo-ocular reflex (VOR) elicited by the vestibulum is thought to be unaffected by afferent information from the cervical spine. The aim of the study was to measure the COR and VOR in people with nonspecific neck pain. This study utilized a cross-sectional design in accordance with the STROBE statement. An infrared eye-tracking device was used to record the COR and the VOR while the participant was sitting on a rotating chair in darkness. Eye velocity was calculated by taking the derivative of the horizontal eye position. Parametric statistics were performed. The mean COR gain in the control group (n=30) was 0.26 (SD=0.15) compared with 0.38 (SD=0.16) in the nonspecific neck pain group (n=37). Analyses of covariance were performed to analyze differences in COR and VOR gains, with age and sex as covariates. Analyses of covariance showed a significantly increased COR in participants with neck pain. The VOR between the control group, with a mean VOR of 0.67 (SD=0.17), and the nonspecific neck pain group, with a mean VOR of 0.66 (SD=0.22), was not significantly different. Measuring eye movements while the participant is sitting on a rotating chair in complete darkness is technically complicated. This study suggests that people with nonspecific neck pain have an increased COR. The COR is an objective, nonvoluntary eye reflex and an unaltered VOR. This study shows that an increased COR is not restricted to patients with traumatic neck pain. © 2016 American Physical Therapy Association.

Nonspecific Chronic Low Back Pain Patients Are Deconditioned and Have An Increased Body Fat Percentage

Science.gov (United States)

Hodselmans, Audy P.

2010-01-01

The aim of this cross-sectional study was to compare data on the level of aerobic capacity and body composition of nonspecific chronic low back pain (CLBP) patients with normative data matched for sex, age and level of sporting activity. The study population consisted of 101 outpatients with nonspecific CLBP who had entered a rehabilitation…

Engineering Design of Electrostatic Quadrupole for ISOL Beam Lines

International Nuclear Information System (INIS)

Kim, H. S.; Kwon, H. J.; Cho, Y. S.

2014-01-01

In the ISOL system, the RI beam should be transported from the target ion source to post accelerator through various analyzing and charge-breeding systems such as PS (pre-seperator), HRMS (High Resolution Mass Seperator), RF cooler and A/q separator. A reference particle for the beam dynamics calculation is 132 Sn 1+ . After charge breeder system, the charge state is boosted from +1 to +19 with ECR charge breeder and to +33 with EBIS charge breeder. Because the beam energy is as low as 50 keV, the electrostatic optics was adopted rather than the magnetic optics. The electrostatic quadrupole triplets were used for the beam focusing and the electrostatic bender is used for 90-degree bending. In this paper, the design procedure and engineering design of the electrostatic quadrupole are presented

Nonspecific microvascular vasodilation during iontophoresis is attenuated by application of hyperosmolar saline.

Science.gov (United States)

Asberg, A; Holm, T; Vassbotn, T; Andreassen, A K; Hartmann, A

1999-07-01

Iontophoretic administration of acetylcholine chloride (ACh) and sodium nitroprusside (SNP) combined with laser Doppler skin blood perfusion measurements are used for determination of endothelial-dependent and -independent vasodilation. However, the method is biased by nonspecific vasodilation. The primary aim of this study was to investigate if iontophoresis-induced nonspecific vasodilation may be attenuated by addition of high molar concentrations of NaCl to the iontophoresis solutions. Secondary we investigated the applicability of 5 mol/liter NaCl solution as vehicle for ACh and SNP in this method. Skin perfusion changes were determined for iontophoresis of pure vehicles, deionized water and 5 mol/liter NaCl solution, in 12 healthy volunteers. Responses in skin perfusion to iontophoresis of ACh and SNP dissolved in both vehicles were also investigated. Addition of 5 mol/liter NaCl to deionized water significantly attenuated the nonspecific vasodilation and lowered the potential applied over the skin. The inter- and intraindividual coefficients of variation to ACh and SNP responses became, however, higher using hyperosmolar vehicle. During iontophoresis of SNP (in deionized water) we were unable to distinguish between SNP and vehicle effects. This study shows that the nonspecific vasodilation induced by iontophoresis can be attenuated by addition of 5 mol/liter NaCl, possibly due to lower electrical potential over the skin. However, the variability of the method was not improved. When deionized water was used as vehicle the effect of SNP could not be differentiated from that of the vehicle. This was not the case for ACh. Copyright 1999 Academic Press.

Quantum chemical analysis explains hemagglutinin peptide-MHC Class II molecule HLA-DRβ1*0101 interactions

International Nuclear Information System (INIS)

Cardenas, Constanza; Villaveces, Jose Luis; Bohorquez, Hugo; Llanos, Eugenio; Suarez, Carlos; Obregon, Mateo; Patarroyo, Manuel Elkin

2004-01-01

We present a new method to explore interactions between peptides and major histocompatibility complex (MHC) molecules using the resultant vector of the three principal multipole terms of the electrostatic field expansion. Being that molecular interactions are driven by electrostatic interactions, we applied quantum chemistry methods to better understand variations in the electrostatic field of the MHC Class II HLA-DRβ1*0101-HA complex. Multipole terms were studied, finding strong alterations of the field in Pocket 1 of this MHC molecule, and weak variations in other pockets, with Pocket 1 >> Pocket 4 > Pocket 9 ∼ Pocket 7 > Pocket 6. Variations produced by 'ideal' amino acids and by other occupying amino acids were compared. Two types of interactions were found in all pockets: a strong unspecific one (global interaction) and a weak specific interaction (differential interaction). Interactions in Pocket 1, the dominant pocket for this allele, are driven mainly by the quadrupole term, confirming the idea that aromatic rings are important in these interactions. Multipolar analysis is in agreement with experimental results, suggesting quantum chemistry methods as an adequate methodology to understand these interactions

quinolinium iodide in suppression of protein–protein interactions

Indian Academy of Sciences (India)

In searching for alternative ways to reduce protein–protein interactions or to inhibit the amyloid formation, the inhibitory effects ..... ing the exposure of hydrophobic surfaces mirrors the ... is well-supported by electrostatic interactions between.

Revaccination with Live Attenuated Vaccines Confer Additional Beneficial Nonspecific Effects on Overall Survival

DEFF Research Database (Denmark)

Benn, Christine S; Fisker, Ane B; Whittle, Hilton C

2016-01-01

BACKGROUND: Live vaccines against measles (MV), tuberculosis (BCG), polio (OPV) and smallpox reduce mortality more than explained by target-disease prevention. The beneficial nonspecific effects (NSEs) of MV are strongest when MV is given in presence of maternal antibodies. We therefore hypothesi......BACKGROUND: Live vaccines against measles (MV), tuberculosis (BCG), polio (OPV) and smallpox reduce mortality more than explained by target-disease prevention. The beneficial nonspecific effects (NSEs) of MV are strongest when MV is given in presence of maternal antibodies. We therefore...

Electrostatics and Flexibility Drive Membrane Recognition and Early Penetration by Antimicrobial Peptide Dendrimer bH1

Energy Technology Data Exchange (ETDEWEB)

Ravi, Harish Kumar; Stach, Michaela; Soares, Thereza A.; Darbre, Tamis; Reymond, Jean-Louis; Cascella, Michele

2013-08-01

Molecular dynamics simulation of polycationic antimicrobial peptide dendrimer bH1 (Leu)8(DapLeu)4(DapPhe)2DapLys- NH2 binding to membranes suggest that electrostatic 10 interactions with the polyanionic lipopolysaccharide (LPS) and conformational flexibility of the 2,3-diaminopropanoic acid (Dap) branching units drive its selective insertion into microbial membranes.

Non-specific Inflammatory Disease Showed Abnormal FDG Uptake in Lower Extremities

International Nuclear Information System (INIS)

Chun, Kyung Ah; Kong, Eun Jung; Cho, Ihn Ho; Hong, Young Hoon; Lee, Choong Ki

2008-01-01

Including malignancy, various disease can show abnormal uptake in bone marrow. 1,2) We report a case of non-specific inflammatory FDG uptake in bone marrow mimicking malignancy. A 35-year old woman with fever of unknown origin (FUO) underwent 18 F-FDG PET/CT to find out fever focus and unknown malignancy. 18 F-FDG was injected and imaged 1hr after injection with Discovery ST (GE, USA). 18 F-FDG PET/CT whole body image showed abnormal uptake in lower extremities. MRI and biopsy was also done in the sites of abnormal uptake. PET and MRI suspect malignancy, but biopsy result was non-specific inflammatory process. The patient was improved her clinical condition after antibiotics therapy

Ion-Beam-Excited Electrostatic Ion Cyclotron Waves

DEFF Research Database (Denmark)

Michelsen, Poul; Pécseli, Hans; Juul Rasmussen, Jens

1976-01-01

Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field.......Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field....

Electrostatic shielding of transformers

Energy Technology Data Exchange (ETDEWEB)

De Leon, Francisco

2017-11-28

Toroidal transformers are currently used only in low-voltage applications. There is no published experience for toroidal transformer design at distribution-level voltages. Toroidal transformers are provided with electrostatic shielding to make possible high voltage applications and withstand the impulse test.

Frontier applications of electrostatic accelerators

Science.gov (United States)

Liu, Ke-Xin; Wang, Yu-Gang; Fan, Tie-Shuan; Zhang, Guo-Hui; Chen, Jia-Er

2013-10-01

Electrostatic accelerator is a powerful tool in many research fields, such as nuclear physics, radiation biology, material science, archaeology and earth sciences. Two electrostatic accelerators, one is the single stage Van de Graaff with terminal voltage of 4.5 MV and another one is the EN tandem with terminal voltage of 6 MV, were installed in 1980s and had been put into operation since the early 1990s at the Institute of Heavy Ion Physics. Many applications have been carried out since then. These two accelerators are described and summaries of the most important applications on neutron physics and technology, radiation biology and material science, as well as accelerator mass spectrometry (AMS) are presented.

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

Science.gov (United States)

Zhou, S.

2017-12-01

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.

Evaluation of the release characteristics of covalently attached or electrostatically bound biocidal polymers utilizing SERS and UV-Vis absorption

Directory of Open Access Journals (Sweden)

G. N. Mathioudakis

2016-09-01

Full Text Available In this work, biocidal polymers with antimicrobial quaternized ammonium groups introduced in the polymer biocidal chains either through covalent attachment or electrostatic interaction have been separately incorporated in a poly (methyl methacrylate polymer matrix. The objective of present study was to highlight the release characteristics of biocidal polymers, primarily in saline but also in water ethanol solutions, utilizing UV-Vis absorption and Surface Enhanced Raman Scattering (SERS. It is shown that through the combination of UV-Vis and SERS techniques, upon the release process, it is possible the discrimination of the polymeric backbone and the electrostatically bound biocidal species. Moreover, it is found that electrostatically bound and covalently attached biocidal species show different SERS patterns. The long term aim is the development of antimicrobial polymeric materials containing both ionically bound and covalently attached quaternary ammonium thus achieving a dual functionality in a single component polymeric design.

Electrostatic potentials of the S-locus F-box proteins contribute to the pollen S specificity in self-incompatibility in Petunia hybrida.

Science.gov (United States)

Li, Junhui; Zhang, Yue; Song, Yanzhai; Zhang, Hui; Fan, Jiangbo; Li, Qun; Zhang, Dongfen; Xue, Yongbiao

2017-01-01

Self-incompatibility (SI) is a self/non-self discrimination system found widely in angiosperms and, in many species, is controlled by a single polymorphic S-locus. In the Solanaceae, Rosaceae and Plantaginaceae, the S-locus encodes a single S-RNase and a cluster of S-locus F-box (SLF) proteins to control the pistil and pollen expression of SI, respectively. Previous studies have shown that their cytosolic interactions determine their recognition specificity, but the physical force between their interactions remains unclear. In this study, we show that the electrostatic potentials of SLF contribute to the pollen S specificity through a physical mechanism of 'like charges repel and unlike charges attract' between SLFs and S-RNases in Petunia hybrida. Strikingly, the alteration of a single C-terminal amino acid of SLF reversed its surface electrostatic potentials and subsequently the pollen S specificity. Collectively, our results reveal that the electrostatic potentials act as a major physical force between cytosolic SLFs and S-RNases, providing a mechanistic insight into the self/non-self discrimination between cytosolic proteins in angiosperms. © 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.

Interaction between synthetic lecithin and various sulfur-containing radioprotectors

International Nuclear Information System (INIS)

Rix-Montel, M.A.; Kranck, H.; Vasilescu, D.

1981-01-01

Interaction of the synthetic lecithin dipalmitoylphosphatidylcholine (DPPC) smectic mesophases with sulfur-containing radioprotectors was investigated by means of spectrophotometric and dielectric measurements. Electrical conductivity behavior indicated in all cases that an electrostatic interaction occurs between DPPC and the antiradiation drugs. This interaction is very strong in the case of the WR 2721 molecule. Thermal transitions of DPPC studied by spectrophotometry and conductivity Arrhenius diagrams showed that although the radio-protectors investigated (except WR 2721) delete the pretransition of the lipid phase, the principal transition is not modified. The observed electrostatic interactions are discussed with regard to ionized sites of the phosphatidylcholine lipid head and those of the radioprotectors. The special cases of WR 2721 and its metabolite, WR 1065, are examined

On the relationship between pain intensity and postural sway in patients with non-specific neck pain

DEFF Research Database (Denmark)

Ruhe, Alexander; Fejer, René; Walker, Bruce

2013-01-01

Increased center of pressure excursions are well documented in patients with non-specific neck pain. While a linear relationship between pain intensity and postural sway has been described in low back pain patients, no such investigation has been conducted in adults with non-specific neck pain....

Fabrication and characterization of an electrostatic contraction beams micromotor

NARCIS (Netherlands)

Sarajlic, Edin; Berenschot, Johan W.; Tas, Niels Roelof; Fujita, H.; Krijnen, Gijsbertus J.M.; Elwenspoek, Michael Curt

2006-01-01

We report on fabrication and experimental characterization of an electrostatic contraction beams motor that exhibits both reliable operation and high performance haracteristics. This electrostatic linear stepper micromotor is fabricated in a single polysilicon layer combining vertical trench

Electromechanical coupling in electrostatic micro-power generators

International Nuclear Information System (INIS)

Mahmoud, M A E; El-Saadany, E F; Mansour, R R; Abdel-Rahman, E M

2010-01-01

Electrostatic micro-power generators (MPGs) are modeled and analyzed with particular emphasis on electromechanical coupling and its impact on the system dynamics. We identify two qualitatively different regimes in the MPG response, dubbed slow and fast. A linearized electromechanically coupled model of an electrostatic MPG and two simplified linear models are used to study the response of the MPG. Linear models are found adequate to represent the dynamic response of fast MPGs but inadequate to represent the response of slow and mixed domain MPGs. A nonlinear model is developed and validated to describe the response of those MPGs under moderately large excitations. On the basis of this analysis, we describe a method and provide design rules for realizing wideband electrostatic MPGs, and develop closed-form formulae for the extracted power for MPGs under moderately large excitations

AN ANALYSIS ON KNOWLEDGE AND ATTITUDE OF SHIPPING PORT WORKERS TOWARD NONSPECIFIC BACK PAIN

Directory of Open Access Journals (Sweden)

Izham Zain

2015-08-01

Full Text Available Background: Nonspecific back pain can be defined as pain and discomfort, localized over below the costal margin and above the inferior gluteal folds. Such disorder are known to be a major cause of reduced work capabilities and causing substantial financial consequences and poor productivity. Occupational related nonspecific back pain is the common disorder affecting those workers performing high physical demanding task. The shipping port workers were exposed to hazardous working nature and known to be affected. Numerous study indicate that knowledge and attitude towards safety were contributing factors to occupational related back pain. Currently no study was conducted to determine the relationship between knowledge, attitude and occupational related back pain among them. The objective of this study is to evaluate the prevalence of nonspecific back pain and determine the difference between knowledge and attitude toward such incident. Methods: The respondents were workers known to have nonspecific back pain. The data collection is carry out through a set of questionnaire consists of knowledge, attitudes and Nordic questionnaire on area of back pain. Results: Majority of respondents (n=70 involve in driving and maneuver terminal crane cargo. The mean of knowledge score is 7.49 (±1.20, attitude score is 5.72 (±1.33 and were ranked in good and moderate respectively. There is no statistical difference between knowledge, attitudes with workers job nature, academic qualification and years of working experience. Conclusion: A preventive intervention should be introduced to enhance workers attitudes and curb the nonspecific back pain incidents. Employee positive involvement, strongly supported by employer and active engagement of healthcare provider able to curb occupational related back pain at work place.

Creation of Magnetic Fields by Electrostatic and Thermal Fluctuations

International Nuclear Information System (INIS)

Saleem, Hamid

2009-01-01

It is pointed out that the electrostatic and thermal fluctuations are the main source of magnetic fields in unmagnetized inhomogeneous plasmas. The unmagnetized inhomogeneous plasmas can support a low frequency electromagnetic ion wave as a normal mode like Alfven wave of magnetized plasmas. But this is a coupled mode produced by the mixing of longitudinal and transverse components of perturbed electric field due to density inhomogeneity. The ion acoustic wave does not remain electrostatic in non-uniform plasmas. On the other hand, a low frequency electrostatic wave can also exist in the pure electron plasmas and it couples with ion acoustic wave when ions are dynamic. These waves can become unstable when density and temperature gradients are parallel to each other as can be the case of laser plasmas and is the common situation in stellar cores. The main instability condition for the electrostatic and electromagnetic modes is the same (2/3)κ n T (where κ n and κ T are inverse of the scale lengths of gradients of density and electron temperature, respectively). This indicates that the electrostatic and magnetic field fluctuations are strongly coupled in unmagnetized nonuniform plasmas.

Characterizing low affinity epibatidine binding to α4β2 nicotinic acetylcholine receptors with ligand depletion and nonspecific binding

Directory of Open Access Journals (Sweden)

Person Alexandra M

2011-11-01

Full Text Available Abstract Background Along with high affinity binding of epibatidine (Kd1≈10 pM to α4β2 nicotinic acetylcholine receptor (nAChR, low affinity binding of epibatidine (Kd2≈1-10 nM to an independent binding site has been reported. Studying this low affinity binding is important because it might contribute understanding about the structure and synthesis of α4β2 nAChR. The binding behavior of epibatidine and α4β2 AChR raises a question about interpreting binding data from two independent sites with ligand depletion and nonspecific binding, both of which can affect equilibrium binding of [3H]epibatidine and α4β2 nAChR. If modeled incorrectly, ligand depletion and nonspecific binding lead to inaccurate estimates of binding constants. Fitting total equilibrium binding as a function of total ligand accurately characterizes a single site with ligand depletion and nonspecific binding. The goal of this study was to determine whether this approach is sufficient with two independent high and low affinity sites. Results Computer simulations of binding revealed complexities beyond fitting total binding for characterizing the second, low affinity site of α4β2 nAChR. First, distinguishing low-affinity specific binding from nonspecific binding was a potential problem with saturation data. Varying the maximum concentration of [3H]epibatidine, simultaneously fitting independently measured nonspecific binding, and varying α4β2 nAChR concentration were effective remedies. Second, ligand depletion helped identify the low affinity site when nonspecific binding was significant in saturation or competition data, contrary to a common belief that ligand depletion always is detrimental. Third, measuring nonspecific binding without α4β2 nAChR distinguished better between nonspecific binding and low-affinity specific binding under some circumstances of competitive binding than did presuming nonspecific binding to be residual [3H]epibatidine binding after

Characterizing low affinity epibatidine binding to α4β2 nicotinic acetylcholine receptors with ligand depletion and nonspecific binding

Science.gov (United States)

2011-01-01

Background Along with high affinity binding of epibatidine (Kd1≈10 pM) to α4β2 nicotinic acetylcholine receptor (nAChR), low affinity binding of epibatidine (Kd2≈1-10 nM) to an independent binding site has been reported. Studying this low affinity binding is important because it might contribute understanding about the structure and synthesis of α4β2 nAChR. The binding behavior of epibatidine and α4β2 AChR raises a question about interpreting binding data from two independent sites with ligand depletion and nonspecific binding, both of which can affect equilibrium binding of [3H]epibatidine and α4β2 nAChR. If modeled incorrectly, ligand depletion and nonspecific binding lead to inaccurate estimates of binding constants. Fitting total equilibrium binding as a function of total ligand accurately characterizes a single site with ligand depletion and nonspecific binding. The goal of this study was to determine whether this approach is sufficient with two independent high and low affinity sites. Results Computer simulations of binding revealed complexities beyond fitting total binding for characterizing the second, low affinity site of α4β2 nAChR. First, distinguishing low-affinity specific binding from nonspecific binding was a potential problem with saturation data. Varying the maximum concentration of [3H]epibatidine, simultaneously fitting independently measured nonspecific binding, and varying α4β2 nAChR concentration were effective remedies. Second, ligand depletion helped identify the low affinity site when nonspecific binding was significant in saturation or competition data, contrary to a common belief that ligand depletion always is detrimental. Third, measuring nonspecific binding without α4β2 nAChR distinguished better between nonspecific binding and low-affinity specific binding under some circumstances of competitive binding than did presuming nonspecific binding to be residual [3H]epibatidine binding after adding a large concentration of

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

Science.gov (United States)

Bernardino, Kalil; de Moura, André F

2015-10-13

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

Method of electrostatic filtration

International Nuclear Information System (INIS)

Devienne, F.M.

1975-01-01

Electrostatic filtration of secondary ions of mass m in a given mass ratio with a primary ion of mass M which has formed the secondary ions by fission is carried out by a method which consists in forming a singly-charged primary ion of the substance having a molecular mass M and extracting the ion at a voltage V 1 with respect to ground. The primary ion crosses a potential barrier V 2 , in producing the dissociation of the ion into at least two fragments of secondary ions and in extracting the fragment ion of mass m at a voltage V 2 . Filtration is carried out in an electrostatic analyzer through which only the ions of energy eV'' are permitted to pass, detecting the ions which have been filtered. The mass m of the ions is such that (M/m) = (V 1 - V 2 )/(V'' - V 2 )

Characterizing the Performance of the Wheel Electrostatic Spectrometer

Science.gov (United States)

Johansen, Michael R.; Mackey, P. J.; Holbert, E.; Calle, C. I.; Clements, J. S.

2013-01-01

Insulators need to be discharged after each wheel revolution. Sensor responses repeatable within one standard deviation in the noise of the signal. Insulators may not need to be cleaned after each revolution. Parent Technology- Mars Environmental Compatibility Assessment/Electrometer Electrostatic sensors with dissimilar cover insulators Protruding insulators tribocharge against regolith simulant Developed for use on the scoop for the 2001 Mars Odyssey lander Wheel Electrostatic Spectrometer Embedded electrostatic sensors in prototype Martian rover wheel If successful, this technology will enable constant electrostatic testing on Mars Air ionizing fan used to neutralize the surface charge on cover insulators . WES rolled on JSClA lunar simulant Control experiment -Static elimination not conducted between trials -Capacitor discharged after each experiment Charge neutralization experiment -Static elimination conducted between trials -Capacitor discharged after each experiment. Air ionizing fan used on insulators after each wheel revolution Capacitor discharged after each trial Care was taken to roll WES with same speed/pressure Error bars represent one standard deviation in the noise of e ach sensor

Managing patients with acute and chronic non-specific neck pain

DEFF Research Database (Denmark)

Brockhusen, Simon Sidenius; Bussières, André; French, Simon David

2017-01-01

was mainly reserved for chronic patients. Danish chiropractors' compliance with guidelines for neck-pain patients was low, but is neither worse nor better than what is seen for other complaints or health disciplines. Our findings suggest a need for active knowledge translation strategies and robust......Background: Non-specific neck pain represents a quarter of all chiropractic patient visits in Denmark. Evidence informed practice can help ensure providers use best available treatment, speed up patient recovery rate and reduce healthcare utilization. It is generally believed that Danish...... chiropractors treat according to best practice, but we do not know if this is true for management of neck-pain. The objective of this study was to investigate how Danish chiropractors treat patients with acute and chronic non-specific neck pain and determine if management is compliant with recent Canadian...

Females have stronger neurogenic response than males after non-specific nasal challenge in patients with seasonal allergic rhinitis.

Science.gov (United States)

Tomljenovic, Dejan; Baudoin, Tomislav; Megla, Zeljka Bukovec; Geber, Goran; Scadding, Glenis; Kalogjera, Livije

2018-07-01

Epidemiological studies show female predominance in the prevalence of non- allergic rhinitis (NAR) and local allergic rhinitis (LAR). Experimental studies show female patients with allergic rhinitis (AR) demonstrate higher levels of sensitivity to irritants and airway hyperresponsiveness than males. Bronchial asthma shows female predominance in post-puberty patients, and gender interaction with severe asthma endotypes. Fibromyalgia, chronic fatigue syndrome, migraine and chronic cough, syndromes, which are commonly related to neurokinin substance P (SP) in the literature, also show strong female predominance. Studies have demonstrated that sex hormones, primarily oestrogens, affect mast cell activation. Mast cell proteases can amplify neurogenic inflammatory responses including the release of SP. Based on human epidemiological data and animal experimental data we hypothesized that female patients have different interaction between mast cell activation and neurogenic inflammation, i.e. substance P release, resulting in a different nasal symptom profile. To test the hypothesis we performed allergen and non-specific nasal challenges in patients with seasonal allergic rhinitis (SAR) out of season and looked for gender differences in subjective and objective responses. The interaction between subjective and objective reactivity was evaluated through the comparison of subjective symptom scores, concentrations of neurokinin substance P (SP) and cellular markers in nasal lavages after low doses of nasal allergen challenges. Female allergic subjects tended to have higher substance P (SP) concentrations both before and after non-specific challenges. The difference between post-allergen and post - hypertonic saline (HTS) challenge was highly significant in female patients (p = 0.001), while insignificant in male subjects (p = 0.14). Female patients had significantly stronger burning sensation after HTS challenge than male. These data indicate difference in the

Realistic electrostatic potentials in a neutron star crust

International Nuclear Information System (INIS)

Ebel, Claudio; Mishustin, Igor; Greiner, Walter

2015-01-01

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

21 CFR 20.50 - Nonspecific and overly burdensome requests.

Science.gov (United States)

2010-04-01

... policy reasons justifying the requests. A decision on the processing of such a request for information... PUBLIC INFORMATION Procedures and Fees § 20.50 Nonspecific and overly burdensome requests. The Food and... operations of the Food and Drug Administration, the person making the request will be asked to be more...

Nonspecific abdominal pain is a safe diagnosis.

Science.gov (United States)

Pennel, David John Laurie; Goergen, Nina; Driver, Chris P

2014-11-01

The aim of this study is to assess if a clinical diagnosis of nonspecific abdominal pain (NSAP) is safe and if patients with this initial diagnosis are likely to require further investigation or surgical intervention. 3323 patients admitted with NSAP from July 1990 to September 2012 utilizing a prospective database of all surgical admissions were included. Readmission over the period of the study and specifically within 30 days of their initial presentation was identified together with any invasive investigation or surgical intervention. 319 children (9.6%) were subsequently readmitted with abdominal pain at some point during the study period. Of these, 78 (2.3%) were readmitted within 30 days. 118 (3.5%) children subsequently had an operation or invasive investigation some point following their initial admission. Of these 33 (0.6%) had the procedure within 3 months of the initial admission. 13 patients had an appendicectomy within 3 months of the initial presentation. Of these histology confirmed appendicitis in 8 patients. This gives an overall incidence of "missed" appendicitis of 0.2 % (8/3323). This study confirms that a clinical diagnosis of nonspecific abdominal pain (NSAP) is safe in a pediatric population and the risk of "missing" appendicitis is only 0.2%. Patients and/or parents can be confidently reassured that the risk of missing organic pathology is very low. Copyright © 2014 Elsevier Inc. All rights reserved.

Bone growth, limb proportions and non-specific stress in archaeological populations from Croatia.

Science.gov (United States)

Pinhasi, R; Timpson, A; Thomas, M; Slaus, M

2014-01-01

The effect of environmental factors and, in particular, non-specific stress on the growth patterns of limbs and other body dimensions of children from past populations is not well understood. This study assesses whether growth of mediaeval and post-mediaeval children aged between 0-11.5 years from Adriatic (coastal) and continental Croatia varies by region and by the prevalence and type of non-specific stress. Dental ages were estimated using the Moorrees, Fanning and Hunt (MFH) scoring method. Growth of long bone diaphyses (femur, tibia, humerus, radius and ulna) was assessed by using a composite Z-score statistic (CZS). Clavicular length was measured as a proxy for upper trunk width, distal metaphyseal width of the femur was measured as a proxy for body mass and upper and lower intra-limb indices were calculated. Differences between sub-sets sampled by (a) region and (b) active vs healed non-specific stress indicators and (c) intra-limb indices were tested by Mann--Whitney U-tests and Analysis of Covariance (ANCOVA). Adriatic children attained larger dimensions-per-age than continental children. Children with healed stress lesions had larger dimensions-per-age than those with active lesions. No inter-regional difference was found in intra-limb indices. These findings highlight the complexity of growth patterns in past populations and indicate that variation in environmental conditions such as diet and differences in the nature of non-specific stress lesions both exert a significant effect on long bone growth.

The Effect of Residual Stress on the Electromechanical Behavior of Electrostatic Microactuators

Directory of Open Access Journals (Sweden)

Ming-Hung Hsu

2008-01-01

Full Text Available This work simulates the nonlinear electromechanical behavior of different electrostatic microactuators. It applies the differential quadrature method, Hamilton's principle, and Wilson-θ integration method to derive the equations of motion of electrostatic microactuators and find a solution to these equations. Nonlinear equation difficulties are overcome by using the differential quadrature method. The stresses of electrostatic actuators are determined, and the residual stress effects of electrostatic microactuators are simulated.

PREFACE: 7th International Conference on Applied Electrostatics (ICAES-2012)

Science.gov (United States)

Li, Jie

2013-03-01

ICAES is an important conference organized every four years by the Committee on Electrostatics of the Chinese Physical Society, which serves as a forum for scientists, educators and engineers interested in the fundamentals, applications, disasters and safety of electrostatics, etc. In recent years, new techniques, applications and fundamental theories on electrostatics have developed considerably. ICAES-7, held in Dalian, China, from 17-19 September 2012, aimed to provide a forum for all scholars to report the newest developments in electrostatics, to probe the questions that scholars faced and to discuss fresh ideas related to electrostatics. ICAES-7 was co-organized and hosted by Dalian University of Technology, and was sponsored by the Ministry of Education of China, the National Natural Science Foundation of China, Dalian University of Technology, Nanjing Suman Electronics Co. Ltd (Suman, China), Shekonic (Yangzhou Shuanghong, China) Electric/Mechanical Co. Ltd, and Suzhou TA&A Ultra Clean Technology Co. Ltd. (China). On behalf of the organizing committee of ICAES-7, I express my great appreciation for their support of the conference. Over 160 scholars and engineers from many countries including Croatia, The Czech Republic, D.P.R. Korea, Germany, Japan, Malaysia, Poland, Russia, the United States of America, China attended ICAES-7, and the conference collected and selected 149 papers for publication. The subjects of those papers cover the fundamentals of electrostatics, electrostatic disaster and safety, and electrostatic application (e.g. precipitation, pollutant control, biological treatment, mixture separation and food processing, etc). I cordially thank all authors and attendees for their support, and my appreciation is also given to the conference honorary chair, the organizing committee and advisory committee, and the conference secretaries for their hard work. ICAES-7 is dedicated to the memory of Professor Jen-Shih Chang (professor emeritus in the

Electrostatic interactions between polyglutamic acid and polylysine yields stable polyion complex micelles for deoxypodophyllotoxin delivery

Directory of Open Access Journals (Sweden)

Wang Y

2017-10-01

indicated that the interaction of anionic and cationic charged polyionic segments could be an effective strategy to control drug release and to improve the stability of polymer-based nanocarriers. Keywords: polyion complex micelles, electrostatic interaction, oligopeptide, stability, pharmacokinetics

Biological risk indicators for recurrent non-specific low back pain in adolescents.

Science.gov (United States)

Jones, M A; Stratton, G; Reilly, T; Unnithan, V B

2005-03-01

A matched case-control study was carried out to evaluate biological risk indicators for recurrent non-specific low back pain in adolescents. Adolescents with recurrent non-specific low back pain (symptomatic; n = 28; mean (SD) age 14.9 (0.7) years) and matched controls (asymptomatic; n = 28; age 14.9 (0.7) years) with no history of non-specific low back pain participated. Measures of stature, mass, sitting height, sexual maturity (Tanner self assessment), lateral flexion of the spine, lumbar sagittal plane mobility (modified Schober), hip range of motion (Leighton flexometer), back and hamstring flexibility (sit and reach), and trunk muscle endurance (number of sit ups) were performed using standardised procedures with established reliability. Backward stepwise logistic regression analysis was performed, with the presence/absence of recurrent low back pain as the dependent variable and the biological measures as the independent variables. Hip range of motion, trunk muscle endurance, lumbar sagittal plane mobility, and lateral flexion of the spine were identified as significant risk indicators of recurrent low back pain (plow back pain in a group of adolescents. These risk indicators identify the potential for exercise as a primary or secondary prevention method.

High density hydrogen storage in nanocavities: Role of the electrostatic interaction

Energy Technology Data Exchange (ETDEWEB)

Reguera, L. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada del IPN, Legaria 694, Mexico D.F (Mexico); Facultad de Quimica, Universidad de La Habana, La Habana (Cuba); Roque, J. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada del IPN, Legaria 694, Mexico D.F (Mexico); Hernandez, J. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada del IPN, Legaria 694, Mexico D.F (Mexico); Universidad de Pinar del Rio, Pinar del Rio (Cuba); Reguera, E. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada del IPN, Legaria 694, Mexico D.F (Mexico); Instituto de Ciencia y Tecnologia de Materiales, Universidad de La Habana, La Habana (Cuba)

2010-12-15

High pressure H{sub 2} adsorption isotherms at N{sub 2} liquid temperature were recorded for the series of cubic nitroprussides, Ni{sub 1-x}Co{sub x}[Fe(CN){sub 5}NO] with x = 0, 0.5, 0.7, 1. The obtained data were interpreted according to the effective polarizing power for the metal found at the surface of the cavity. The cavity volume where the hydrogen molecules are accumulated was estimated from the amount of water molecules that are occupying that available space in the as-synthesized solids considering a water density of 1 g/cm{sup 3}. The calculated cavity volume was then used to obtain the density of H{sub 2} storage in the cavity. For the Ni-containing material the highest storage density was obtained, in a cavity volume of 448.5 A{sup 3} up to 10.4 hydrogen molecules are accumulated, for a local density of 77.6 g/L, above the density value corresponding to liquid hydrogen (71 g/L). Such high value of local density was interpreted as related to the electrostatic contribution to the adsorption potential for the hydrogen molecule within the cavity. (author)

Development and Application Prospects of Pneumatic Electrostatic Sprayer in Orchard

OpenAIRE

Zhou, Yan; Qi, Li-jun; Jia, Shou-xing; Zheng, Xuan; Meng, Xiang-jin; Tang, Zhi-hui; Shen, Cong-ju

2012-01-01

We firstly introduce existing situations of development of electrostatic spraying technology both at home and abroad. On the basis of such problems as serious drift, loss and deterioration of environment during orchard spraying in Xinjiang, we design and develop a new electrostatic sprayer which can effectively reduce the pesticide, improve the adhesion rate of pesticide in the target, and reduce pollution on human body and environment. Using electrostatic induction principle, this electrosta...

"EGM" (Electrostatics of Granular Matter): A Space Station Experiment to Examine Natural Particulate Systems

Science.gov (United States)

Marshall, J.; Sauke, T.; Buehler, M.; Farrell, W.; Green, R.; Birchenough, A.

1999-09-01

A granular-materials experiment is being developed for a 2002 launch for Space Station deployment. The experiment is funded by NASA HQ and managed through NASA Lewis Research Center. The experiment will examine electrostatic aggregation of coarse granular materials with the goals of (a) obtaining proof for an electrostatic dipole model of grain interactions, and (b) obtaining knowledge about the way aggregation affects the behavior of natural particulate masses: (1) in unconfined dispersions (clouds such as nebulae, aeolian dust palls, volcanic plumes), (2) in semi-confined, self-loaded masses as in fluidized flows (pyroclastic surges, avalanches) and compacted regolith, or (3) in semi-confined non-loaded masses as in dust layers adhering to solar cells or space suits on Mars. The experiment addresses both planetary/astrophysical issues as well as practical concerns for human exploration of Mars or other solar system bodies. Additional information is contained in the original.

Ballistic Jumping Drops on Superhydrophobic Surfaces via Electrostatic Manipulation.

Science.gov (United States)

Li, Ning; Wu, Lei; Yu, Cunlong; Dai, Haoyu; Wang, Ting; Dong, Zhichao; Jiang, Lei

2018-02-01

The ballistic ejection of liquid drops by electrostatic manipulating has both fundamental and practical implications, from raindrops in thunderclouds to self-cleaning, anti-icing, condensation, and heat transfer enhancements. In this paper, the ballistic jumping behavior of liquid drops from a superhydrophobic surface is investigated. Powered by the repulsion of the same kind of charges, water drops can jump from the surface. The electrostatic acting time for the jumping of a microliter supercooled drop only takes several milliseconds, even shorter than the time for icing. In addition, one can control the ballistic jumping direction precisely by the relative position above the electrostatic field. The approach offers a facile method that can be used to manipulate the ballistic drop jumping via an electrostatic field, opening the possibility of energy efficient drop detaching techniques in various applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of buffer at nanoscale molecular recognition interfaces - electrostatic binding of biological polyanions.

Science.gov (United States)

Rodrigo, Ana C; Laurini, Erik; Vieira, Vânia M P; Pricl, Sabrina; Smith, David K

2017-10-19

We investigate the impact of an over-looked component on molecular recognition in water-buffer. The binding of a cationic dye to biological polyanion heparin is shown by isothermal calorimetry to depend on buffer (Tris-HCl > HEPES > PBS). The heparin binding of self-assembled multivalent (SAMul) cationic micelles is even more buffer dependent. Multivalent electrostatic molecular recognition is buffer dependent as a result of competitive interactions between the cationic binding interface and anions present in the buffer.

Theoretical assessment of the disparity in the electrostatic forces between two point charges and two conductive spheres of equal radii

Science.gov (United States)

Kolikov, Kiril

2016-11-01

The Coulomb's formula for the force FC of electrostatic interaction between two point charges is well known. In reality, however, interactions occur not between point charges, but between charged bodies of certain geometric form, size and physical structure. This leads to deviation of the estimated force FC from the real force F of electrostatic interaction, thus imposing the task to evaluate the disparity. In the present paper the problem is being solved theoretically for two charged conductive spheres of equal radii and arbitrary electric charges. Assessment of the deviation is given as a function of the ratio of the distance R between the spheres centers to the sum of their radii. For the purpose, relations between FC and F derived in a preceding work of ours, are employed to generalize the Coulomb's interactions. At relatively short distances between the spheres, the Coulomb force FC, as estimated to be induced by charges situated at the centers of the spheres, differ significantly from the real force F of interaction between the spheres. In the case of zero and non-zero charge we prove that with increasing the distance between the two spheres, the force F decrease rapidly, virtually to zero values, i.e. it appears to be short-acting force.

Wall Climbing Robot Using Electrostatic Adhesion Force Generated by Flexible Interdigital Electrodes

Directory of Open Access Journals (Sweden)

Rong Liu

2013-01-01

Full Text Available Electrostatic adhesion technology has broad application prospects on wall climbing robots because of its unique characteristics compared with other types of adhesion technologies. A double tracked wall climbing robot based on electrostatic adhesion technology is presented including electrode panel design, mechanical structure design, power supply system design and control system design. A theoretical adhesion model was established and the electrostatic potential and field were expressed by series expansions in terms of solutions of the Laplace function. Based on this model, the electrostatic adhesion force was calculated using the Maxwell stress tensor formulation. Several important factors which may influence the electrostatic adhesion force were analysed and discussed by both FEM simulation and theoretical calculation. In addition, experiments on the adhesion performance of the electrode panel and the climbing performance of the robot on various wall materials were carried out. Both the simulation and experiment results verify the feasibility of electrostatic adhesion technology being applied on wall climbing robots. The theoretical model and calculation method for the electrostatic adhesion force proposed in this paper are also justified.

Ion-Flow-Induced Excitation of Electrostatic Cyclotron Mode in Magnetized Dusty Plasma

Science.gov (United States)

Bezbaruah, P.; Das, N.

2018-05-01

The stability of electrostatic cyclotron mode is investigated in a flowing magnetized dusty plasma in the presence of strong ion-neutral collisions. In the high magnetic field limit, when the dust magnetization becomes important, it is expected that the collective behavior of magnetized dust grains suspended in the near-sheath region substantially influences the dispersion properties of electrostatic modes. The growth/damping of the collective excitation is significantly controlled by such parameters as the ion-neutral collision frequency, Mach number, and magnetic field strength. In our case, the explicit dependence of the Mach number on the magnetic field and collision frequency has been taken into account and possible implications on the stability of the mode is analyzed. Streaming instability of cyclotron modes may be important to understand issues related to the interaction mechanism between dust grains and other associated phenomena like Coulomb crystallization, phase behavior, transport properties, etc., in the relatively strong magnetic field limit, which is currently accessible in the DPD (Kiel University) and MDPX (PSL, Auburn University) experiments.

On-Orbit 3-Dimensional Electrostatic Detumble for Generic Spacecraft Geometries

Science.gov (United States)

Bennett, Trevor J.

In recent years, there is a growing interest in active debris removal and on-orbit servicing of Earth orbiting assets. The growing need for such approaches is often exemplified by the Iridium-Kosmos collision in 2009 that generated thousands of debris fragments. There exists a variety of active debris removal and on-orbit servicing technologies in development. Conventional docking mechanisms and mechanical capture by actuated manipulators, exemplified by NASA's Restore-L mission, require slow target tumble rates or more aggressive circumnavigation rate matching. The tumble rate limitations can be overcome with flexible capture systems such nets, harpoons, or tethers yet these systems require complex deployment, towing, and/or interfacing strategies to avoid servicer and target damage. Alternatively, touchless methods overcome the tumble rate limitations by provide detumble control prior to a mechanical interface. This thesis explores electrostatic detumble technology to touchlessly reduce large target rotation rates of Geostationary satellites and debris. The technical challenges preceding flight implementation largely reside in the long-duration formation flying guidance, navigation, and control of a servicer spacecraft equipped with electrostatic charge transfer capability. Leveraging prior research into the electrostatic charging of spacecraft, electrostatic detumble control formulations are developed for both axisymmetric and generic target geometries. A novel relative position vector and associated relative orbit control approach is created to manage the long-duration proximity operations. Through detailed numerical simulations, the proposed detumble and relative motion control formulations demonstrate detumble of several thousand kilogram spacecraft tumbling at several degrees per second in only several days. The availability, either through modeling or sensing, of the relative attitude, relative position, and electrostatic potential are among key concerns

Optical klystron FELs based on tandem electrostatic accelerators

International Nuclear Information System (INIS)

Gover, A.; Friedman, A.

1989-01-01

The operation of tandem electrostatic accelerator FELs in an optical klystron configuration makes it possible to take advantage of the high quality (low emittance and low energy spread) of the electron beam in electrostatic accelerators. With evolving microwiggler technology, state-of-the-art moderate energy (6-14-MeV) tandem electrostatic accelerators may be used for the development of highly coherent tunable radiation sources in the entire IR region. The authors present the general design considerations and the predicted operating characteristics of such devices and refer in specifics to a design of a 10-1000-μm FEL based on the parameters of a 5-6-MeV high current tandem accelerator. The operating wavelength of FELs is determined by the Doppler shift formula

Nonlinear electrostatic wave equations for magnetized plasmas - II

DEFF Research Database (Denmark)

Dysthe, K. B.; Mjølhus, E.; Pécseli, H. L.

1985-01-01

For pt.I see ibid., vol.26, p.443-7 (1984). The problem of extending the high frequency part of the Zakharov equations for nonlinear electrostatic waves to magnetized plasmas, is considered. Weak electromagnetic and thermal effects are retained on an equal footing. Direction dependent (electrosta......For pt.I see ibid., vol.26, p.443-7 (1984). The problem of extending the high frequency part of the Zakharov equations for nonlinear electrostatic waves to magnetized plasmas, is considered. Weak electromagnetic and thermal effects are retained on an equal footing. Direction dependent...... (electrostatic) cut-off implies that various cases must be considered separately, leading to equations with rather different properties. Various equations encountered previously in the literature are recovered as limiting cases....

Electrostatics of Pharmaceutical Aerosols for Pulmonary Delivery.

Science.gov (United States)

Lip Kwok, Philip Chi

2015-01-01

This paper provides a review on key research findings in the rapidly developing area of pharmaceutical aerosol electrostatics. Solids and liquids can become charged without electric fields, the former by contact or friction and the latter by flowing or spraying. Therefore, charged particles and droplets carrying net charges are produced from pharmaceutical inhalers (e.g. dry powder inhalers, metered dose inhalers, and nebulisers) due to the mechanical processes involved in aerosolisation. The charging depends on many physicochemical factors, such as formulation composition, solid state properties, inhaler material and design, and relative humidity. In silico, in vitro, and limited in vivo studies have shown that electrostatic charges may potentially influence particle deposition in the airways. However, the evidence is not yet conclusive. Furthermore, there are currently no regulatory requirements on the characterisation and control of the electrostatic properties of inhaled formulations. Besides the need for further investigations on the relationship between physicochemical factors and charging characteristics of the aerosols, controlled and detailed in vivo studies are also required to confirm whether charges can affect particle deposition in the airways. Since pharmaceutical aerosol electrostatics is a relatively new research area, much remains to be explored. Thus there is certainly potential for development. New findings in the future may contribute to the advancement of pharmaceutical aerosol formulations and respiratory drug delivery.

Holes in magneto electrostatic traps

International Nuclear Information System (INIS)

Jones, R.

1996-01-01

We observe that in magneto electrostatic confinement (MEC) devices the magnetic surfaces are not always equipotentials. The lack of symmetry in the equipotential surfaces can result in holes in MEC plasma traps. (author)

Nucleotide insertion initiated by van der Waals interaction during ...

Indian Academy of Sciences (India)

renormalized van der Waals (vdW) interaction of a stronger type, the ..... can be used to determine the electrostatic dipole–dipole, .... water molecule and a surface oxygen atom. ..... understand proteins electronic interaction.54 Here, we.

Low-frequency electrostatic dust-modes in a non-uniform

Indian Academy of Sciences (India)

A self-consistent and general description of obliquely propagating low-frequency electrostatic dust-modes in a non-uniform magnetized dusty plasma system has been presented. A number of different situations, which correspond to different low-frequency electrostatic dust-modes, namely, dust-acoustic mode, dust-drift ...

Electrostatic afocal-zoom lens design using computer optimization technique

Energy Technology Data Exchange (ETDEWEB)

Sise, Omer, E-mail: omersise@gmail.com

2014-12-15

Highlights: • We describe the detailed design of a five-element electrostatic afocal-zoom lens. • The simplex optimization is used to optimize lens voltages. • The method can be applied to multi-element electrostatic lenses. - Abstract: Electron optics is the key to the successful operation of electron collision experiments where well designed electrostatic lenses are needed to drive electron beam before and after the collision. In this work, the imaging properties and aberration analysis of an electrostatic afocal-zoom lens design were investigated using a computer optimization technique. We have found a whole new range of voltage combinations that has gone unnoticed until now. A full range of voltage ratios and spherical and chromatic aberration coefficients were systematically analyzed with a range of magnifications between 0.3 and 3.2. The grid-shadow evaluation was also employed to show the effect of spherical aberration. The technique is found to be useful for searching the optimal configuration in a multi-element lens system.

Fabrication of graphene/polyaniline composite multilayer films by electrostatic layer-by-layer assembly

Science.gov (United States)

Cong, Jiaojiao; Chen, Yuze; Luo, Jing; Liu, Xiaoya

2014-10-01

A novel graphene/polyaniline composite multilayer film was fabricated by electrostatic interactions induced layer-by-layer self-assembly technique, using water dispersible and negatively charged chemically converted graphene (CCG) and positively charged polyaniline (PANI) as building blocks. CCG was achieved through partly reduced graphene oxide, which remained carboxyl group on its surface. The remaining carboxyl groups not only retain the dispersibility of CCG, but also allow the growth of the multilayer films via electrostatic interactions between graphene and PANI. The structure and morphology of the obtained CCG/PANI multilayer film are characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Ultraviolet-visible absorption spectrum (UV-vis), scanning electron microscopy (SEM), Raman spectroscopy and X-Ray Diffraction (XRD). The electrochemical properties of the resulting film are studied using cyclic voltammetry (CV), which showed that the resulting CCG/PANI multilayer film kept electroactivity in neutral solution and showed outstanding cyclic stability up to 100 cycles. Furthermore, the composite film exhibited good electrocatalytic ability toward ascorbic acid (AA) with a linear response from 1×10-4 to 1.2×10-3 M with the detect limit of 5×10-6 M. This study provides a facile and effective strategy to fabricate graphene/PANI nanocomposite film with good electrochemical property, which may find potential applications in electronic devices such as electrochemical sensor.

A non-electrostatic spacer for aerosol delivery

DEFF Research Database (Denmark)

Bisgaard, H; Anhøj, J; Klug, B

1995-01-01

to 6 years, suspected to have asthma the non-electrostatic spacer delivered a mean total dose of budesonide aerosol of 39% of the nominal dose, which was significantly higher than the Babyhaler (28%), the Nebuhaler (21%), and the AeroChamber (19%). These differences were most pronounced in children......A pear shaped non-electrostatic spacer, composed of steel with a volume of 250 ml and equipped with a facemask containing integrated inlet and outlet valves for inspiration and expiration, was compared with three plastic spacers. The plastic spacers were primed with repeated puffs from a budesonide...... was 27 seconds and independent of the use of p-MDI. In vitro the maximum dose of budesonide from a p-MDI, expressed as a percentage of the nominal dose, was 56% from the non-electrostatic spacer, 61% from the Nebuhaler, 45% from the Babyhaler, and 30% from the AeroChamber. In 124 children, age 6 months...

A non-electrostatic spacer for aerosol delivery

DEFF Research Database (Denmark)

Bisgaard, H; Anhøj, J; Klug, B

1995-01-01

A pear shaped non-electrostatic spacer, composed of steel with a volume of 250 ml and equipped with a facemask containing integrated inlet and outlet valves for inspiration and expiration, was compared with three plastic spacers. The plastic spacers were primed with repeated puffs from a budesonide...... pressurised metered dose inhaler (p-MDI) to minimise the electrostatic charge on the plastic. The procedure prolonged the half life (t1/2) of the aerosol in the Nebuhaler from nine to 32 seconds. A normal cleaning procedure reduced the aerosol t1/2 back to baseline. The t1/2 of the aerosol in the metal spacer...... was 27 seconds and independent of the use of p-MDI. In vitro the maximum dose of budesonide from a p-MDI, expressed as a percentage of the nominal dose, was 56% from the non-electrostatic spacer, 61% from the Nebuhaler, 45% from the Babyhaler, and 30% from the AeroChamber. In 124 children, age 6 months...

Imaging latex–carbon nanotube composites by subsurface electrostatic force microscopy

International Nuclear Information System (INIS)

Patel, Sajan; Petty, Clayton W.; Krafcik, Karen Lee

2016-01-01

Electrostatic modes of atomic force microscopy have shown to be non-destructive and relatively simple methods for imaging conductors embedded in insulating polymers. Here we use electrostatic force microscopy to image the dispersion of carbon nanotubes in a latex-based conductive composite, which brings forth features not observed in previously studied systems employing linear polymer films. A fixed-potential model of the probe-nanotube electrostatics is presented which in principle gives access to the conductive nanoparticle's depth and radius, and the polymer film dielectric constant. Comparing this model to the data results in nanotube depths that appear to be slightly above the film–air interface. Furthermore, this result suggests that water-mediated charge build-up at the film–air interface may be the source of electrostatic phase contrast in ambient conditions.

Reintroducing electrostatics into macromolecular crystallographic refinement: application to neutron crystallography and DNA hydration.

Science.gov (United States)

Fenn, Timothy D; Schnieders, Michael J; Mustyakimov, Marat; Wu, Chuanjie; Langan, Paul; Pande, Vijay S; Brunger, Axel T

2011-04-13

Most current crystallographic structure refinements augment the diffraction data with a priori information consisting of bond, angle, dihedral, planarity restraints, and atomic repulsion based on the Pauli exclusion principle. Yet, electrostatics and van der Waals attraction are physical forces that provide additional a priori information. Here, we assess the inclusion of electrostatics for the force field used for all-atom (including hydrogen) joint neutron/X-ray refinement. Two DNA and a protein crystal structure were refined against joint neutron/X-ray diffraction data sets using force fields without electrostatics or with electrostatics. Hydrogen-bond orientation/geometry favors the inclusion of electrostatics. Refinement of Z-DNA with electrostatics leads to a hypothesis for the entropic stabilization of Z-DNA that may partly explain the thermodynamics of converting the B form of DNA to its Z form. Thus, inclusion of electrostatics assists joint neutron/X-ray refinements, especially for placing and orienting hydrogen atoms. Copyright © 2011 Elsevier Ltd. All rights reserved.

Immunological Links to Nonspecific Effects of DTwP and BCG Vaccines on Infant Mortality

Directory of Open Access Journals (Sweden)

Mogens Helweg Claesson

2011-01-01

Full Text Available A number of mainly observational studies suggest that many African females below the age of one year die each year from the nonspecific effects of vaccination with diphtheria-tetanus toxoids and killed (whole-cell Bordetella pertussis (DTwP. In contrast, similar studies suggest that many African females and males may have their lives saved each year by the nonspecific immunological benefits of Bacillus Calmette-Guerin (BCG vaccination. From an immunological point of view, we hypothesise that the adverse effects of DTwP vaccine may occur because of the Th2-polarising effect of the aluminium phosphate adjuvant in the vaccine and because intramuscular administration of the vaccine may cause chronic inflammation at the site of injection. However, the Th1-polarising effect of BCG is likely to be beneficial. Sexual dimorphism affecting immune functions and vitamin A supplementation may influence both the deleterious and beneficial nonspecific effects of immunisation.

Effects of electrostatic trapping on neoclassical transport in an impure plasma

International Nuclear Information System (INIS)

Hazeltine, R.D.; Ware, A.A.

1976-01-01

Contamination of a toroidally confined plasma by highly charged impurity ions can produce substantial variation of the electrostatic potential within a magnetic surface. The resulting electrostatic trapping and electrostatic drifts, of hydrogen ions and electrons, yields significant alterations in neoclassical transport theory. A transport theory which includes these effects is derived from the drift-kinetic equation, with an ordering scheme modeled on the parameters of recent tokamak experiments. The theory self-consistently predicts that electrostatic trapping should be fully comparable to magnetic trapping, and provides transport coefficients which, depending quadratically upon the temperature and pressure gradients, differ markedly from the standard neoclassical coefficients for a pure plasma