Net Electric Charge Research Articles

Magnetic branes in (n+1)-dimensional Einstein-Maxwell-dilaton gravity

We construct two new classes of spacetimes generated by spinning and traveling magnetic sources in ($n+1$)-dimensional Einstein-Maxwell-dilaton gravity with Liouville-type potential. These solutions are neither asymptotically flat nor (A)dS. The first class of solutions which yields a ($n+1$)-dimensional spacetime with a longitudinal magnetic field and $k$ rotation parameters have no curvature singularity and no horizons, but have a conic geometry. We show that when one or more of the rotation parameters are nonzero, the spinning branes have a net electric charge that is proportional to the magnitude of the rotation parameters. The second class of solutions yields a static spacetime with an angular magnetic field and has no curvature singularity, no horizons, and no conical singularity. Although one may add linear momentum to the second class of solutions by a boost transformation, one does not obtain a new solution. We find that the net electric charge of these traveling branes with one or more nonzero boost parameters is proportional to the magnitude of the velocity of the branes. We also use the counterterm method and calculate the conserved quantities of the solutions.

Experimental Study of the Electrophoretic Mobility and Effective Electric Charge of Polystyrene-Block-Poly(Methacrylic Acid) Micelles in Aqueous Media

Kinetically frozen polystyrene-block-poly(methacrylic acid) (PS-PMA) micelles were prepared by dialysis of reversible micelles from 1,4-dioxane-rich aqueous solutions in solvents with increasing content of water and finally in pure aqueous media. Dynamic light scattering (DLS) and capillary zone electrophoresis (CZE) were used to determine the hydrodynamic radius and electrophoretic mobility of micelles as functions of pH. The electrophoretic curves show broad and relatively fast moving micellar peaks, indicating fairly high electrophoretic mobility and a non-negligible net electric charge of micelles. The experiments show that CZE is a suitable technique for studying polyelectrolyte micelles.

Numeric simulation of relativistic stellar core collapse and the formation of Reissner-Nordström black holes

The time evolution of a set of $22{M}_{\ensuremath{\bigodot}}$ unstable charged stars that collapse is computed integrating the Einstein-Maxwell equations. The model simulates the collapse of a spherical star that had exhausted its nuclear fuel and has or acquires a net electric charge in its core while collapsing. When the charge-to-mass ratio is $Q/\sqrt{G}M\ensuremath{\ge}1$, the star does not collapse but spreads. On the other hand, a different physical behavior is observed with a charge-to-mass ratio of $1>Q/\sqrt{G}M>0.1$. In this case, the collapsing matter forms a bubble enclosing a lower density core. We discuss an immediate astrophysical consequence of these results that is a more efficient neutrino trapping during the stellar collapse and an alternative mechanism for powerful supernova explosions. The outer space-time of the star is the Reissner-Nordstr\"om solution that matches smoothly with our interior numerical solution; thus the collapsing models form Reissner-Nordstr\"om black holes.

Formulation in terms of normalized propagators of a charge-dipole model enabling the calculation of the polarization properties of fullerenes and carbon nanotubes

We present a model for the calculation of the polarization properties of fullerenes and carbon nanotubes. This model describes each atom by both a net electric charge and a dipole. Compared to dipole-only models, the consideration of electric charges enables one to account for the displacement of free electrons in structures subject to an external field. It also enables one to account for the accumulation of additional charges. By expressing the electrostatic interactions in terms of normalized propagators, the model achieves a better consistency as well as an improved stability. In its most elementary form, the model depends on a single adjustable parameter and provides an excellent agreement with other experimental and theoretical data. The technique is applied to a ${\mathrm{C}}_{720}$ fullerene and to open and closed (5,5) nanotubes. The simulations demonstrate the improved stability of our algorithm. In addition, they quantify the role of free charges in the polarization of these structures. The paper finally investigates the field-enhancement properties of open and closed (5,5) nanotubes.

Post-duplication charge evolution of phosphoglucose isomerases in teleost fishes through weak selection on many amino acid sites

BackgroundThe partitioning of ancestral functions among duplicated genes by neutral evolution, or subfunctionalization, has been considered the primary process for the evolution of novel proteins (neofunctionalization). Nonetheless, how a subfunctionalized protein can evolve into a more adaptive protein is poorly understood, mainly due to the limitations of current analytical methods, which can detect only strong selection for amino acid substitutions involved in adaptive molecular evolution. In this study, we employed a comparative evolutionary approach to this question, focusing on differences in the structural properties of a protein, specifically the electric charge, encoded by fish-specific duplicated phosphoglucose isomerase (Pgi) genes.ResultsFull-length cDNA cloning, RT-PCR based gene expression analyses, and comparative sequence analyses showed that after subfunctionalization with respect to the expression organ of duplicate Pgi genes, the net electric charge of the PGI-1 protein expressed mainly in internal tissues became more negative, and that of PGI-2 expressed mainly in muscular tissues became more positive. The difference in net protein charge was attributable not to specific amino acid sites but to the sum of various amino acid sites located on the surface of the PGI molecule.ConclusionThis finding suggests that the surface charge evolution of PGI proteins was not driven by strong selection on individual amino acid sites leading to permanent fixation of a particular residue, but rather was driven by weak selection on a large number of amino acid sites and consequently by steady directional and/or purifying selection on the overall structural properties of the protein, which is derived from many modifiable sites. The mode of molecular evolution presented here may be relevant to various cases of adaptive modification in proteins, such as hydrophobic properties, molecular size, and electric charge.

Baryon number and electric charge fluctuations in Pb+Pb collisions at relativistic energies

Event-by-event fluctuations of the net baryon number and electric charge in nucleus-nucleus collisions are studied in Pb+Pb at SPS energies within the Hadron-String Dynamics (HSD) transport model. We reveal an important role of the fluctuations in the number of target nucleon participants. They strongly influence all measured fluctuations even in the samples of events with rather rigid centrality trigger. This fact can be used to check different scenarios of nucleus-nucleus collisions by measuring the multiplicity fluctuations as a function of collision centrality in fixed kinematical regions of the projectile and target hemispheres. The HSD results for the event-by-event fluctuations of electric charge in central collisions at $20A,30A,40A,80A$, and $158A$ GeV are in a good agreement with the NA49 experimental data and considerably larger than expected in a quark-gluon plasma. This demonstrates that the distortions of the initial fluctuations by the hadronization phase and, in particular, by the final resonance decays dominate the observable fluctuations.

DYONS OF ONE-HALF MONOPOLE CHARGE

We would like to present some exact SU(2) Yang–Mills–Higgs dyon solutions of one-half monopole charge. These static dyon solutions satisfy the first order Bogomol'nyi equations and are characterized by a parameter, m. They are axially symmetric. The gauge potentials and the electromagnetic fields possess a string singularity along the negative z-axis and hence they possess infinite energy density along the line singularity. However the net electric charges of these dyons which varies with the parameter m are finite.

Homology modeling of tubulin: influence predictions for microtubule’s biophysical properties

Using comparative modeling, we have generated structural models of 475 alpha and beta tubulins. Using these models, we observed a global, structural similarity between the tubulin isotypes. However, a number of subtle differences in the isotypes physical properties, including net electric charges, solvent accessible surface areas, and electric dipole moments were also apparent. In order to examine the roles that these properties may play in microtubule (MT) assembly and stability, we have created a model to evaluate the dipole-dipole interaction energies of varying MT lattice conformations, using human tubulin isotypes as particularly important examples. We conclude that the dipole moments of each tubulin isotype may influence their functional characteristics within the cell, resulting in differences for MT assembly kinetics and stability.

Electrostatic Aggregation and Formation of Core−Shell Suprastructures in Binary Mixtures of Charged Metal Nanoparticles

Electrostatic aggregation of oppositely charged silver and gold nanoparticles leads to the formation of core-shell clusters in which the shell is formed by the nanoparticles, which are in excess. Arguments based on Debye screening of interactions between like-charged particles help explain why these clusters are stable despite possessing net electric charge. The core-shell aggregates exhibit unusual optical properties with the resonance absorption of the shell particles enhanced by the particles in the core and that of the core suppressed by the shell. Experimental UV-vis absorption spectra are faithfully reproduced by Mie theory. The modeling allows for estimation of the numbers of particles forming the shell and of the shell's effective thickness. These theoretical predictions are substantiated by experiments using nanoparticles covered with different combinations of charged groups and performed at different values of pH.

Charges and Fluxes in Maxwell Theory on Compact Manifolds with Boundary

We investigate the charges and fluxes that can occur in higher-order Abelian gauge theories defined on compact space-time manifolds with boundary. The boundary is necessary to supply a destination to the electric lines of force emanating from brane sources, thus allowing non-zero net electric charges, but it also introduces new types of electric and magnetic flux. The resulting structure of currents, charges, and fluxes is studied and expressed in the language of relative homology and de Rham cohomology and the corresponding abelian groups. These can be organised in terms of a pair of exact sequences related by the Poincaré-Lefschetz isomorphism and by a weaker flip symmetry exchanging the ends of the sequences. It is shown how all this structure is brought into play by the imposition of the appropriately generalised Maxwell’s equations. The requirement that these equations be integrable restricts the world-volume of a permitted brane (assumed closed) to be homologous to a cycle on the boundary of space-time. All electric charges and magnetic fluxes are quantised and satisfy the Dirac quantisation condition. But through some boundary cycles there may be unquantised electric fluxes associated with quantised magnetic fluxes and so dyonic in nature.

Electric birefringence and dichroism of DNA fragments in aqueous solution

A major task in this work is to study the mechanisms of orientation of DNA fragments in dilute solution in presence of an electric field. The DNA fragments are modeled as charged and polarizable bent rods. Considering the participation of electrophoresis and electric moments in the orientation of particles, we first obtain the Fokker–Planck equation for the system in the local coordinate system and finally arrive to the Smoluchowski equations for the steady state in the laboratory system. We here demonstrate that the solution of this equation, the orientational distribution function of molecules, is independent from the location of the origin of the molecule coordinate system. This property is based on the fact that the drift vector in the Fokker–Planck equation is also invariant to this change. This characteristic enables us to state that when the bent rods move by electrophoresis, wherever the bent rod coordinate system is located, the orientation of the ensemble always results in a translation–rotation coupling of particles with the origin of the molecule coordinate system in their center of charge. We analyze the orientation characteristics of the particles due to an electric moment m that appears when the origin of the coordinate system is located in a different point from its center of charge and we compare it with the electric dipole moment μ , originated by the charge distribution with null net electric charge.

Unified modeling of conductance kinetics for low- and high-conductance potassium ion channels

A kinetics model is proposed for the description of ion conductance of low- and high-conductance potassium ion channels. The model describes ion permeation through the selectivity filter, which is assumed to be the only conductance determining part of the open channel. The filter occupancy can vary from zero to three ions, affecting the ion entry and exit rates. Ion motion between the binding sites inside the filter is assumed fast compared to the latter rates allowing averaging the equilibrium entry and exit rate constants over the possible ion configurations in the filter with a particular occupancy. Averaged rate constants related to a pair of adjacent occupancy states characterize a particular ion permeation mechanism. An expression for the channel conductance as a function of the symmetrical external ion concentration is derived. It comprises a sum of concentration independent conductance amplitudes for different ion permeation mechanisms weighted by the equilibrium filter occupancy probabilities. It is shown that each amplitude (i.e., maximum contribution to the channel conductance from each conductance mechanism) is proportional to an averaged exit rate constant and to quantities characterizing the effect of the applied electric field on the rate constants and the equilibrium ion distribution in the filter. The conductance expression derived provides a good description of the experimentally observed conductance-concentration curves for low-conductance (e.g., Kir2.1) and high-conductance (e.g., KcsA) potassium channels. It enables one to obtain equilibrium ion binding constants at different filter occupancies and to calculate the average number of ions in the selectivity filter for a given external ion concentration. For KcsA this number (2.0 at 200 mM) is in a good agreement with the available experimental value (2.1 at 200 mM). For the high-conductance potassium channels the net negative electrical charge around the selectivity filter increases the ion binding constants, thereby causing the larger occupancy probabilities to occur at smaller external ion concentrations compared to the low-conductance channels. This substantially increases the contributions of the two- and three-ion permeation mechanisms, with the larger conductance amplitudes leading to increased channel conductance compared to the low-conductance channels.

Cationic lipid membranes—specific interactions with counter-ions

Lipids bearing net electric charges in their hydrophilic headgroups are ubiquitous inbiological membranes. Recently, the interest in cationic lipids has surged because of theirpotential as non-viral transfection vectors. In order to utilize cationic lipids in transfer ofnucleic acids and to elucidate the role of charged lipids in cellular membranes in general,their complex interactions within the membrane and with the molecules in thesurrounding media need to be thoroughly characterized. Yet, even interactions betweenmonovalent counter-ions and charged lipids are inadequately understood. We studiedthe interactions of the cationic gemini surfactant (2R,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide (RR-1) with chloride, bromide, fluoride, and iodideas counter-ions by differential scanning calorimetry and Langmuir balance. Chlorideinteracts avidly with RR-1, efficiently condensing the monolayer, decreasing the collapsepressure, and elevating the main transition temperature. With bromide and iodide clearlydifferent behaviour was observed, indicating specific interactions between RR-1 and thesecounter-ions. Moreover, with fluoride as a counter-ion and in pure water identical resultswere obtained, demonstrating inefficient electrostatic screening of the headgroups ofRR-1 and suggesting fluoride being depleted on the surface of RR-1 membranes.

Electrostatic Stability of a Large Collection of Charged Anisotropic Nanoparticles: A Monte Carlo Study Exploiting a Hierarchical Approach

We have performed Monte Carlo simulations of the self-organization of large collections of charged disks of various electric charges to probe the influence of electrostatic coupling on the structure and the mechanical stability of aqueous dispersions of charged anisotropic nanoparticles in the presence of salt. A hierarchical approach of the long-range Coulombic potential was used to perform such Monte Carlo simulations of a large number of charged species. By analyzing the influence of the net electric charge of the disks on their self-organization, we detected a negative contribution to the mean force potential resulting from their electrostatic coupling. In addition, it has been shown that the same electrostatic coupling restricts the spatial extend of locally ordered microdomains within dilute dispersions of charged anisotropic colloids.

The evolution of the structure of tubulin and its potential consequences for the role and function of microtubules in cells and embryos

This paper discusses the results of homology modeling and resulting calculation of key structural and physical properties for close to 300 tubulin sequences, including alpha, beta, gamma, delta and epsilon -tubulins. The basis for our calculations was the structure of the tubulin dimer published several years ago by Nogales et al. (1998), later refined to 3.5 resolution by Lowe et al. (2001). While, it appears that the alpha, beta and gamma-tubulins segregate into distinct structural families, we have found several differences in the physical properties within each group. Each of the alpha, beta and gamma- tubulin groups exhibit major differences in their net electric charge, dipole moments and dipole vector orientations. These properties could influence functional characteristics such as microtubule stability and assembly kinetics, due to their effects on the strength of protein-protein interactions. In addition to the general structural trends between tubulin isoforms, we have observed that the carboxy-termini of alpha and beta-tubulin exists in at least two stable configurations, either projecting away from the tubulin (or microtubule) surface, or collapsed onto the surface. In the latter case, the carboxy-termini form a lattice distinctly different from that of the well-known A and B lattices formed by the tubulin subunits. However, this C-terminal lattice is indistinguishable from the lattice formed when the microtubule-associated protein tau binds to the microtubule surface. Finally, we have discussed how tubulin sequence diversity arose in evolution giving rise to its particular phylogeny and how it may be used in cell- and tissue-specific expression including embryonal development.

Monitoring of flowing charges with an electrostatic voltmeter

This paper describes a simple method of monitoring the net electric charge of powders transported pneumatically through a dielectric pipe. An electrostatic voltmeter (ESVM) is used to measure the voltage induced on an isolated ring electrode placed on the outside surface of the pipe. An equivalent circuit model of the measurement system was constructed and experimentally verified using an electrophotographic toner and an aluminum oxide powder (Al/sub 2/O/sub 3/). Knowledge of the voltage induced by flowing charged particles on the electrode allows for the calculation of the total charge that flew through the pipe. However, in order to obtain an accurate voltage measurement, the input impedance of the instrument used for that purpose must be very high. The high impedance of an ESVM makes it uniquely suited for this application.

Hadronic fluctuations at the QCD phase transition

We discuss the properties of hadronic fluctuations, i.e., fluctuations of net quark and isospin numbers as well as electric charge, in the vicinity of the QCD transition in isospin-symmetric matter at vanishing quark chemical potential. We analyse second- and fourth-order cumulants of these fluctuations and argue that the ratio of quartic and quadratic cumulants reflects the relevant degrees of freedom that carry the quark number, isospin or charge, respectively. In the hadronic phase we find that an enhancement of charge fluctuations arises from contributions of doubly charged hadrons to the thermodynamics. The rapid suppression of fluctuations seen in the high-temperature phase suggests that in the QGP, net quark number and electric charge are predominantly carried by quasi-particles, with the quantum numbers of quarks.

Local repulsion in protein structures as revealed by a charge distribution analysis of allamino acid sequences from the Saccharomyces cerevisiae genome

The structures and physical properties of individual protein molecules have beenextensively studied, but the general features of all proteins in a cell have hardly beeninvestigated. The distribution of net electric charges of all proteins from the Saccharomycescerevisiae proteome agreed well with a Gaussian distribution. The shift in chargedistribution caused by protonation of histidine suggested that the proteins in a cell arebuffered against pH changes. A comparison between the amino acid sequences from theproteome and randomly generated sequences indicated that electric charges in the realsequences are clustered. Analysis of autocorrelation function of charged residues in thetotal proteome of S. cerevisiae showed a positive correlation of net charges inamino acid sequences with characteristic length as long as 81 residues, leadingto the conclusion that the interactions within proteins is repulsive on average.

Ion Implantation: Effect on Flux and Rejection Properties of NF Membranes

Nanofiltration (NF) membranes typically carry a net electric charge, enabling electrostatic interactions to play a pivotal role in the rejection of species such as metals, nitrates, and other charged contaminants. In this study, two types of polymeric NF membranes, polyamide and cellulose acetate, were modified by ion implantation to increase the effective surface charge of the membranes. The modified membranes contain implanted ions in the membrane matrix, inducing a discrete, permanent charge in the active membrane layer. The presence of a permanent charge in the membrane matrix allows for increased electrostatic repulsive forces throughout the entire pH range. Streaming potential measurements were conducted as a function of pH for the modified and unmodified membranes to determine the effect of ion implantation on the zeta potential of the membranes. Rejection experiments were performed in order to quantify the effect of increased electrostatic repulsion on ion rejection, and flux measurements quantified the effect of the modification on permeability. Results indicate that electrostatic interactions near the membrane surface can affect rejection; however, the extent of the effect of increased membrane charge depends on physical-chemical characteristics of the membrane. Increased negative zeta potential of the modified membranes resulted in slightly higher rejection of salts with divalent co-ions from the membrane, with less increase observed with salts of monovalent co-ions. Modified membranes were less permeable than the unmodified membranes. Results of this research hold implications in membrane synthesis and modification studies as well as choice of membranes for water treatment applications.

On the use of the MNDO-d semiempirical method for the structural study of chlorophyll b and anhydrous chlorophyll b dimer

Semiempirical MNDO-d molecular orbital calculations have been used for the structural study of chlorophyll b and anhydrous chlorophyll b dimer systems in their respective ground states. A model of chlorophyll b dimer has been considered whereby the magnesium atom is five-coordinate with an oxygen atom in the fifth coordination site. Total energies, net electric charges, and electronic dipole moments have been determined for the ground states of the above-mentioned molecules. The proposed models allow for the examination of distortions within the pyrroles and porphyrin macrocycles of these magnesium complexes. They also permit the estimate of changes in bond lengths, bond angles and dihedrals produced by dimerization via the acetyl oxygen of the carbometoxy group and the central magnesium atom, and changes in the π-electronic system of the chlorin systems. The results obtained are in good agreement with the experimental findings, and they reproduce many of the observed trends. In particular, neutron diffraction crystal structure, NMR and infrared spectra, provide experimental evidence in support of these theoretical predictions. Comparison with other theoretical results, shows that there is a good correlation between the DFT/B3LYP(6-31G*) and the MNDO-d, and also that the MNDO-d performs better than the HF/6-31G* and the PM5 in general.