Net Electric Charge Research Articles

Magnetic branes supported by a nonlinear electromagnetic field

Considering the nonlinear electromagnetic field coupled to Einstein gravity in the presence of a cosmological constant, we obtain a new class of d-dimensional magnetic brane solutions. This class of solutions yields a spacetime with a longitudinal nonlinear magnetic field generated by a static source. These solutions have no curvature singularity and no horizons but have a conic geometry with a deficit angle δϕ. We investigate the effects of nonlinearity on the metric function and deficit angle and also find that for the special range of the nonlinear parameter, the solutions are not asymptotic AdS. We generalize this class of solutions to the case of spinning magnetic solutions and find that when one or more rotation parameters are nonzero, the brane has a net electric charge which is proportional to the magnitude of the rotation parameters. Then, we use the counterterm method and compute the conserved quantities of these spacetimes. Finally, we obtain a constraint on the nonlinear parameter, such that the nonlinear electromagnetic field is conformally invariant.

Enhanced polarizability of aromatic molecules placed in the vicinity of silverclusters

We use a charge–dipole interaction model to study the polarizability of aromaticmolecules that are placed between two silver clusters. In particular we examine theenhancement in polarizability induced by the clusters at plasmon-like resonantfrequencies of the cluster–molecule–cluster system. The model used for thesesimulations relies on representation of the atoms by both a net electric charge and adipole. By relating the time variation of the atomic charges to the currents thatflow through the bonds of the structures considered, a least-action principle canbe formulated that enables the atomic charges and dipoles to be determined.We consider benzene, naphthalene and anthracene for this study, comparing thepolarizability of these aromatic molecules when placed in the middle between twoAg120 clusters, with their polarizability as isolated molecules. We find that the polarizability ofthese molecules is enhanced by the clusters, and this increases the electromagnetic couplingbetween the two clusters. This results in significant red-shifting (by up to 0.8 eV) of the lowestenergy optical transition in the cluster–molecule–cluster system compared to plasmon-likeexcitation in the cluster–cluster system. The resulting resonant polarizability enhancementleads to an electromagnetic enhancement in surface-enhanced Raman scattering of over106.

Magnetic string coupled to nonlinear electromagnetic field

We introduce a class of rotating magnetically charged string solutions of the Einstein gravity with a nonlinear electrodynamics source in four dimensions. The present solutions has no curvature singularity and no horizons but has a conic singularity and yields a spacetime with a longitudinal magnetic field. Also, we investigate the effects of nonlinearity on the properties of the solutions and find that for the special range of the nonlinear parameter, the solutions are not asymptotic AdS. We show that when the rotation parameter is nonzero, the spinning string has a net electric charge that is proportional to the magnitude of the rotation parameter. Finally, we use the counterterm method inspired by AdS/CFT correspondence and calculate the conserved quantities of the solutions.

How Flexible Polymers Interact with Proteins and Its Relationship with the Protein Separation Method by Protein–Polymer Complex Formation

Bovine serum albumin was selected as a model protein to study the molecular mechanism of interaction between flexible polymer with net negative electrical charge (polyvinylsulphonate and polyacrylic acid) and a non-charged polymer such as poly(ethylene) poly(propylene) oxide (molecular mass 8,400) by using spectroscopies techniques combination: fluorescence emission and circular dichroism. Polyvinylsulphonate and polyacrylic acid interact with the protein due to the coulombic interaction between positive charged protein groups such as amine of lysine and histidine. The poly(ethylene)-poly(propylene) oxide increased the hydrophobic microenvironment around the tryptophan residues. This polymer preserved the secondary and tertiary structure of the protein and did not induce any significant modification in the protein surface area exposed to the solvent.

A charge–dipole interaction model for the frequency-dependent polarizability of silverclusters

We present a charge–dipole interaction model for the calculation of the frequency-dependentpolarizability of silver clusters. The model relies on the representation of silver atoms byboth a net electric charge and a dipole. Time variations of the atomic charges are related tothe currents that flow through the bonds of the structures considered and theatomic charges and dipoles are eventually determined from the application of aleast-action principle. After a generalization that enables the bonds of the bulkand surface atoms to have specific resistances, the model is parameterized ondata obtained by the time-dependent density functional theory for tetrahedralAg20,Ag84 andAg120 clusters. We then study the polarization properties of dimers of silver clusters. We comparein particular the polarizability of the dimers with that of the isolated clusters, for a rangeof gap distances and frequencies. We also consider the field enhancements one can achievewith these systems. The results are in good agreement with reference data and enable anextension of these data to a wider range of situations. They show that significant fieldenhancements are achieved at frequencies associated with resonant polarization along theaxis of the dimer.

Imaging with polarized neutrons

Neutrons have zero net electrical charge and can thus penetrate deeply into matter, but their intrinsic magnetic moment makes them highly sensitive to magnetic fields. These properties have been combined with radiographic (2D) and tomographic (3D) imaging methods to provide a unique technique to probe macroscopic magnetic phenomena both within and around bulk matter. Based on the spin-rotation of a polarized neutron beam as it passes through a magnetic field, this method allows the direct, real-space visualization of magnetic field distributions. It has been used to investigate the Meissner effect in a type I (Pb) and a type II (YBCO) superconductor, flux trapping in a type I (Pb) superconductor, and the electromagnetic field associated with a direct current flowing in a solenoid. The latter results have been compared to predictions calculated using the Biot–Savart law and have been found to agree well.

Solar radiation pressure and deviations from Keplerian orbits

Newtonian gravity and general relativity give exactly the same expression for the period of an object in circular orbit around a static central mass. However, when the effects of the curvature of spacetime and solar radiation pressure are considered simultaneously for a solar sail propelled satellite, there is a deviation from Kepler's third law. It is shown that solar radiation pressure affects the period of this satellite in two ways: by effectively decreasing the solar mass, thereby increasing the period, and by enhancing the effects of other phenomena, potentially rendering some of them detectable. In particular, we consider deviations from Keplerian orbits due to spacetime curvature, frame dragging from the rotation of the sun, the oblateness of the sun, a possible net electric charge of the sun, and a very small positive cosmological constant.

Polarized neutron imaging at the CONRAD instrument at Helmholtz Centre Berlin

Neutrons are highly sensitive to magnetic fields because of their intrinsic magnetic moment. At the same time, their zero net electrical charge allows them to penetrate thick layers of matter. In combination with standard radiographic and tomographic imaging techniques, these properties have been exploited to visualize magnetic fields in free space and within the bulk of solid, massive, opaque samples. In this paper, the basic principle of this new technique and its realization at the CONRAD instrument at the Helmholtz Centre Berlin (formerly Hahn-Meitner Institute Berlin) are explained. Two application examples will be given: the visualization of the magnetic field around a permanent magnet and the investigation of the displacement of the current density from the core of a conductor to the surface (the skin effect).

Wormhole solutions in Gauss–Bonnet–Born–Infeld gravity

A new class of solutions which yields an (n + 1)-dimensional spacetime with a longitudinal nonlinear magnetic field is introduced. These spacetimes have no curvature singularity and no horizon, and the magnetic field is non singular in the whole spacetime. They may be interpreted as traversable wormholes which could be supported by matter not violating the weak energy conditions. We generalize this class of solutions to the case of rotating solutions and show that the rotating wormhole solutions have a net electric charge which is proportional to the magnitude of the rotation parameter, while the static wormhole has no net electric charge. Finally, we use the counterterm method and compute the conserved quantities of these spacetimes.

Magnetic dilaton strings in anti-de Sitter spaces

With an appropriate combination of three Liouville-type dilaton potentials, we construct a new class of spinning magnetic dilaton string solutions which produces a longitudinal magnetic field in the background of anti-de Sitter spacetime. These solutions have no curvature singularity and no horizon, but have a conic geometry. We find that the spinning string has a net electric charge which is proportional to the rotation parameter. We present the suitable counterterm which removes the divergences of the action in the presence of dilaton potential. We also calculate the conserved quantities of the solutions by using the counterterm method.

Magnetic branes in third order Lovelock-Born-Infeld gravity

Considering both the nonlinear invariant terms constructed by the electromagnetic field and the Riemann tensor in gravity action, we obtain a new class of $(n+1)$-dimensional magnetic brane solutions in third order Lovelock-Born-Infeld gravity. This class of solutions yields a spacetime with a longitudinal nonlinear magnetic field generated by a static source. These solutions have no curvature singularity and no horizons but have a conic geometry with a deficit angle $\ensuremath{\delta}$. We find that, as the Born-Infeld parameter decreases, which is a measure of the increase of the nonlinearity of the electromagnetic field, the deficit angle increases. We generalize this class of solutions to the case of spinning magnetic solutions and find that, when one or more rotation parameters are nonzero, the brane has a net electric charge which is proportional to the magnitude of the rotation parameters. Finally, we use the counterterm method in third order Lovelock gravity and compute the conserved quantities of these spacetimes. We found that the conserved quantities do not depend on the Born-Infeld parameter, which is evident from the fact that the effects of the nonlinearity of the electromagnetic fields on the boundary at infinity are wiped away. We also find that the properties of our solution, such as deficit angle, are independent of Lovelock coefficients.

Aromaticity at the Water-Hydrocarbon Core Interface of the Membrane: Consequences on the Nicotinic Acetylcholine Receptor

Almost all lipid-exposed transmembrane domains of integral proteins contain aromatic residues flanking the hydrophobic segment of the domains. These residues generally reside close to the carbonyl region of the membrane, and several structural and functional roles have been associated to these residues. Although the roles and physicochemical reasons for aromatic preference have been extensively studied using model systems, few studies have been done in a native membrane system. To gain insight about the mechanistic implication for this aromatic preference, we selected position αF426 of the muscle-type nicotinic acetylcholine receptor (nAChR). αF426 is a lipid-exposed residue at the extracellular segment of the αM4 transmembrane domain and is highly conserved among different nAChR subunits and species. We used site-directed mutagenesis, α-Bungarotoxin-binding assay, and two-electrodes voltage clamp in Xenopus laevis oocytes to characterize mutations at position αF426, which impart different physicochemical properties like volume, polarity, hydrogen bonds, aromaticity, and net electrical charge. All mutations except the aromatic residues resulted in a significant reduction of the nAChR cell-surface levels and the macroscopic currents to acetylcholine. These results suggest that position αF426 contributes to structural stability and open-close transitions of the nAChR. Finally, the present study also provides information about how intermolecular interactions at position α426 modulate open-close transitions of the nAChR.

Anomalously high aggregation level of the polyene antibiotic amphotericin B in acidic medium: Implications for the biological action

Amphotericin B (AmB) is a polyene antibiotic used to treat deep-seated mycoses. Both the therapeutic action and the toxic side effects of this drug are dependent on its molecular organization. AmB appears as a zwitterion at neutral pH owing to NH 3 + and COO − groups. The results obtained with electronic absorption, fluorescence, resonance light scattering and infrared absorption spectroscopic analyses show that in the aqueous medium at pH above 10 AmB appears in the monomeric form owing to the negative net electric charge of the molecule. On the contrary, anomalously high aggregation level has been observed at pH below 2, despite the positive net electric charge. The effect is interpreted in terms of the permanent polarization of the polyene chain at low pH, associated with relative rotational freedom of the charged mycosamine fragment of the molecule. The pH-dependent aggregation of AmB is discussed in aspect of pharmacological action of the drug.

Sulphur dioxide plasma modification on poly(methyl methacrylate) for fluidic devices

Abstract We developed a sulphur dioxide plasma modification on a poly(methyl methacrylate) (PMMA) material for fluidic electrophoresis devices. The inner surface of the PMMA channel of a chip was modified by using sulphur dioxide plasma treatment. Contact angle measurements indicated that the buffer solutions were able to fill the capillary because of the hydrophilic property of the internal surface of the chip. XPS analysis indicated that the sulphur dioxide plasma treatment introduced a negative charge originating from the dissociation of the hydrogen atoms of sulphonic groups. Since this introduced a negative charge originating from strong acid sulphonic groups onto the surface of the channel, the electroosmotic flow (EOF) was observed to be large (∼7 × 10−4 m2 V−1 s−1) and stable over a wide range of pH (4–10). The chip was fabricated by using plastic injection moulding methods for enabling the mass fabrication and disposable use of chips. The separation method is based on the net electric charge of the material, which enables the separation of identical samples on the basis of both isoelectric points and molecular weight. Two synthetic peptides with similar isoelectric points and molecular weights but different net charges were selected as model protein samples for the separation. The sample peptides were detected under fluorescence microscopy. The resulting electropherograms obtained by using the sulphur dioxide plasma-treated PMMA chip demonstrated that the two peptides were separated and that the migration time of the peptides was correlated with the net charge.

Spin current studies in Fe∕Ag,Au∕Fe by ferromagnetic resonance and time-resolved magneto-optics

A precessing magnetization within a magnetic double layer acts as a peristaltic spin pump which transports spin momentum but no net electric charge. Crystalline Fe single layers Au∕12Fe∕GaAs(001) and double layers Fe12∕(Au,Ag)∕Fe16∕GaAs(001) were prepared by molecular beam epitaxy, where the integers represent the number of Fe atomic layers, and (Au,Ag) represents a set of gold and silver layers of different thicknesses. Ferromagnetic resonance (FMR) was used to investigate spin diffusion in thick Au layers in Au∕12Fe∕GaAs(001) samples. Time-resolved magneto-optical Kerr effect (TRMOKE) measurements are an ideal tool for investigating the propagation of spin currents in these structures. Spin currents generated by the bottom 16Fe layer propagated across the normal metal spacer and resulted in rf excitations in the top 12Fe film. Landau-Lifshitz-Gilbert equations of motion modified by spin pump and spin sink effects were used to interpret the FMR and TRMOKE measurements. The spin diffusion lengths in Au were Ag were found 34 and 170nm, respectively.

Modification of the Thermal Unfolding Pathways of Myoglobin upon Drug Interaction in Different Aqueous Media

In this work, we have analyzed the influence of two structurally related phenothiazine drugs, promazine and triflupromazine hydrochlorides, when bound to myoglobin, a model protein, and how the drug concentration and solution conditions may affect the denaturation process of this protein. In this manner, we derive the thermodynamic quantities of the unfolding process by using a spectroscopic technique such as UV-vis spectroscopy at different drugs concentrations and at pH 2.5, 5.5, and 9.0. To do this, a thermodynamic model was used which included experimental data corresponding to the pre- and post-transition into the observable transition. It has been found that both drugs play a destabilizing role for the protein, at least at low concentrations. In addition, at acidic pH and higher drug concentrations, a stabilizing effect can be observed, which may be related to the formation of some type of protein refolding, subsequent aggregation, or both. The reason for this behavior has been suggested to be the different protein conformations at acidic pH, the increase of solvent-exposed hydrophobic and hydrophilic residues after denaturation and/or binding, and the different strength of drug-protein interactions when changing the solution conditions. For this reason, thermodynamic quantities such as Gibbs energies, DeltaG, and entropies of unfolding, DeltaS(m), increase as the solution pH increases provided that additional solvent-exposed hydrophobic residues are present, which were previously buried at room temperature. Moreover, the larger binding affinity at pH 9.0 due to enhanced electrostatic interactions between protein and drug molecules (drug and protein differ in their net electrical charge) additionally collaborates to this residue exposition to solvent as a consequence of the alteration of protein conformation as due to drug binding. Comparison of thermodynamic data between promazine and triflupromazine hydrochlorides also shows that drug-protein affinity and hydrophobicity also affect the thermodynamic denaturation parameters.

Magnetic strings in Einstein–Born–Infeld-dilaton gravity

A class of spinning magnetic string in 4-dimensional Einstein-dilaton gravity with Liouville type potential which produces a longitudinal nonlinear electromagnetic field is presented. These solutions have no curvature singularity and no horizon, but have a conic geometry. In these spacetimes, when the rotation parameter does not vanish, there exists an electric field, and therefore the spinning string has a net electric charge which is proportional to the rotation parameter. Although the asymptotic behavior of these solutions are neither flat nor (A)dS, we calculate the conserved quantities of these solutions by using the counterterm method. We also generalize these four-dimensional solutions to the case of (n+1)-dimensional rotating solutions with k⩽[n/2] rotation parameters, and calculate the conserved quantities and electric charge of them.

Shape instabilities in adsorbed polymer condensates

AbstractA polymer chain in a poor solvent collapses to a spherical globule. If this globule is subsequently deformed, either by stretching it or if it has some non‐zero net electric charge, it will become unstable to sinusoidal perturbations leading to novel final states. When such globules are imaged by direct methods such as atomic force microscopy the substrate on which they adsorb can affect the final morphological state. We therefore investigate strongly adsorbed polymers in poor solvents. We demonstrate that the real‐space, Self‐Consistent Field method is an ideal numerical tool in predicting equilibrium morphologies. New structures are predicted, which support previous explicit free energy calculations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3327–3337, 2007

Time resolved secretion of chloride from a monolayer of mucin-secreting epithelial cells

Short-circuit current (Isc) measurement is used to quantify transepithelial ion flux. This technique provides a direct measure of net charge transport across a cell monolayer. Isc however, lacks chemical selectivity. Chemically resolved ion fluxes may be much greater than Isc, and differ in different biological processes. This work describes a novel experimental approach and deconvolution method to obtain temporally resolved ion fluxes at epithelial cell monolayers. HT29-Cl.16E cells, a sub clone of the human colonic cancer cell line HT29 was used as a model cell line to validate this approach in the context of epithelial transport studies. This cell line is known to secrete chloride in response to purinergic stimulation. Changes in chloride concentration after stimulation with 1 mM ATP plus 50 nM phorbol-myristate acetate (PMA) are recorded with a chloride ion-selective electrode (ISE) at a short distance (approximately 50 microm) from the monolayer. The recorded concentrations are transformed to corresponding chloride flux across the monolayer using a deconvolution algorithm for extracellular mass transport based on minimization of the shape error function (Nair and Gratzl in Anal Chem 77:2875-2888, 2005). Simultaneous voltage clamp yields the associated net electrical charge flux (Isc). The dynamics of Cl(-) flux did correlate with that of the electrical flux, but was found to be greater in amplitude. This suggests that Cl(-) may not be the only ion secreted. The method of simultaneously assessing ionic and electrical fluxes with a temporal resolution of seconds provides unique information about the dynamics of solute fluxes across the apical membrane.

Spacetimes with longitudinal and angular magnetic fields in third order Lovelock gravity

We obtain two new classes of magnetic solutions in third order Lovelock gravity. The first class of solutions yields an (n+1)-dimensional spacetime with a longitudinal magnetic field generated by a static source. We generalize this class of solutions to the case of spinning magnetic strings with one or more rotation parameters. These solutions have no curvature singularity and no horizons, but have a conic geometry. For the spinning string, when one or more rotation parameters are nonzero, the string has a net electric charge which is proportional to the magnitude of the rotation parameters, while the static string has no net electric charge. The second class of solutions yields a spacetime with an angular magnetic field. These solutions have no curvature singularity, no horizon, and no conical singularity. Although the second class of solutions may be made electrically charged by a boost transformation, the transformed solutions do not present new spacetimes. Finally, we use the counterterm method in third order Lovelock gravity and compute the conserved quantities of these spacetimes.