Nonzero Potential Research Articles

COLD BLACK HOLES AND CONFORMAL CONTINUATIONS

We study Einstein gravity minimally coupled to a scalar field in a static, spherically symmetric space–time in four dimensions. Black hole solutions are shown to exist for a phantom scalar field whose kinetic energy is negative. These "scalar black holes" have an infinite horizon area and zero Hawking temperature and are termed "cold black holes" (CBHs). The relevant explicit solutions are well known in the massless case (the so-called anti-Fisher solution), and we have found a particular example of a CBH with a nonzero potential V(ϕ). All CBHs with V(ϕ) ≢ 0 are shown to behave near the horizon, quite similarly to those with a massless field. The above solutions can be converted by a conformal transformation to Jordan frames of a general class of scalar–tensor theories of gravity, but CBH horizons in one frame are in many cases converted to singularities in the other, which gives rise to a new type of conformal continuation.

Aqueous Electrolytes near Hydrophobic Surfaces: Dynamic Effects of Ion Specificity and Hydrodynamic Slip

We demonstrate, using molecular-dynamics computer simulations, the strong influence of surface wettability on the equilibrium structure of the electrical double layer at solid interfaces and on electrokinetic transport in aqueous electrolytes due to the effects of interfacial ion specificity and hydrodynamic slip. In particular, we show that anomalous electrokinetic effects such as nonzero zeta potentials for uncharged surfaces are general features of electro-osmotic flow in hydrophobic channels for electrolytes with substantial cation/anion size asymmetry, as a result of the stronger attraction of the larger ion to the "vapor-liquid-like" interface induced by a hydrophobic surface. We establish that the simulated velocity profiles obey continuum hydrodynamics on the nanoscopic length scales studied and show that the anomalous flow profiles can be accurately predicted by using a modified Poisson-Boltzmann description for the ion density distributions that incorporates an ion-size-dependent hydrophobic solvation energy as a crucial component. We also demonstrate that, counterintuitively, the flow for a charge-neutral fluid is independent of the solid-fluid friction coefficient.

Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite

Nanostructures can form on mineral surfaces through reactions with H2O or O2 in the natural environment. In this study, nanostructures on the (1014) surfaces of calcite and rhodochrosite are characterized by their surface potentials using Kelvin probe force microscopy. Water-induced nanostructures on calcite have a topographic height of 1.1 (+/-0.6) nm and an excess surface potential of 126 (+/-31) mV at 45% relative humidity. The corresponding values for oxygen-induced nanostructures on rhodochrosite at the same RH are 1.3 (+/-0.7) nm and 271 (+/-14) mV, respectively. For increasing relative humidity on calcite, the topographic height of the nanostructures increases while their excess surface potential remains unchanged. In comparison, on rhodochrosite thetopographic height remains unchanged for increasing relative humidity but excess surface potential decreases. The nonzero excess surface potentials indicate that the nanostructures have compositions different from their parent substrates. The surface-potential heterogeneity associated with the distributed nanostructures has important implications for reactivity in both gaseous and aqueous environments. Taking into consideration such heterogeneities, which are not included in state-of-the-art models, should improve the accuracy of the predictions of contaminantfate and transport in natural environments.

Ion-Specific Anomalous Electrokinetic Effects in Hydrophobic Nanochannels

We show with computer simulations that anomalous electrokinetic effects, such as ion specificity and nonzero zeta potentials for uncharged surfaces, are generic features of electro-osmotic flow in hydrophobic channels. This behavior is due to the stronger attraction of larger ions to the "vapor-liquidlike" interface induced by a hydrophobic surface. We propose an analytical model involving a modified Poisson-Boltzmann description for the ion density distributions that quantitatively predicts the anomalous flow profiles. This description includes as a crucial component an ion-size-dependent hydrophobic solvation energy. These results provide an effective framework for predicting ion-specific effects, with potentially important implications for biological modeling.

GRAVITATIONAL COLLAPSE OF A SELF-INTERACTING SCALAR FIELD

We construct and study here a class of collapsing scalar field models with a nonzero potential. The weak energy condition is satisfied by the collapsing configuration and it is shown that the end state of collapse could be either a black hole or a naked singularity. It is seen that physically it is the rate of collapse that governs these outcomes of the dynamical evolution. The implications for the cosmic censorship conjecture are discussed.

Haemophilus influenzae Outer Membrane Protein P5 Is Associated with Inorganic Polyphosphate and Polyhydroxybutyrate

Outer membrane protein P5 of nontypeable (acapsulate) Haemophilus influenzae (NTHi P5) forms large pores in planar lipid bilayers between symmetric solutions that unpredictably display a nonzero reversal potential. Moreover, NTHi P5 has a high theoretical isoelectric point, calculated as 9.58, which is not in agreement with the experimental isoelectric point, determined as 6.3–6.8, or with its preference for cations, disproportionately strong at one side. These anomalous results intimate that NTHi P5 is associated with a polyanion. Chemical and immunological analyses revealed the presence of inorganic polyphosphate (polyP), and the amphiphilic, solvating polyester, poly-(R)-3-hydroxybutyrate, frequently associated with polyP. A sharp reduction in cation selectivity was observed after addition of Saccharomyces cerevisiae exopolyphosphatase X to the bilayer, providing functional evidence for the involvement of polyP in selectivity. The results suggest that NTHi P5 associates with polyP and poly-(R)-3-hydroxybutyrate to create large, cation-selective pores in the outer membrane of H. influenzae.

Influence of bimolecular recombination on xerographic discharge process

The photoinduced decay of surface potential, known as xerographic discharge, is analyzed as a method of determination of photogeneration quantum yield taking into account the recombination processes. The effects of slowing down the surface potential decay with time of illumination and nonzero residual potential are usually explained by trapping of the charge carriers in the bulk of the photoconductor. However, these effects can be explained also by bimolecular recombination in the illuminated thin surface layer occurring simultaneously with the photogeneration. In this work it is assumed that as a result of the illumination the mobile positive charge carriers and immobile negative recombination centers are generated. The critical value of the recombination cross section is determined for which the nonzero residual surface potential appears. This analysis allows also to determine an influence of the accumulated recombination centers on the photocurrent decay and build up of the residual potential in a series of subsequent xerographic discharge experiments.

Gauss-Bonnet dark energy

We propose the Gauss-Bonnet dark energy model inspired by string/M-theory where standard gravity with scalar contains additional scalar-dependent coupling with Gauss-Bonnet invariant. It is demonstrated that effective phantom (or quintessence) phase of late universe may occur in the presence of such term when the scalar is phantom or for non-zero potential (for canonical scalar). However, with the increase of the curvature the GB term may become dominant so that phantom phase is transient and $w=-1$ barrier may be passed. Hence, the current acceleration of the universe may be caused by mixture of scalar phantom and (or) potential/stringy effects. It is remarkable that scalar-Gauss-Bonnet coupling acts against the Big Rip occurence in phantom cosmology.

Langmuir and Langmuir–Blodgett Films Containing a Porphyrin–Ruthenium Complex

The fabrication of supramolecular structures from the tetraruthenated porphyrin-containing phosphines, {TPyP[RuCl3(dppb)]4}, RuTPyP, is demonstrated with Langmuir and Langmuir-Blodgett films. The surface pressure-molecular area isotherms (pi-A) point to an edge-on arrangement for the RuTPyP molecules in the condensed state. Weak aggregation in the Langmuir films was indicated by non-zero surface potentials at large areas per molecule and a slight red shift in the ultraviolet-visible absorption spectrum in comparison to the spectrum in solution. Further aggregation occurs in the Z-type Langmuir-Blodgett films, which was confirmed with ultraviolet-visible spectroscopy of the deposited films. Fourier transform infrared and Raman spectroscopic data for powder and Langmuir-Blodgett films indicate that the RuTPyP molecules are chemically stable in Langmuir-Blodgett films regardless of the contact with water during film fabrication. The nanostructured nature of the Langmuir-Blodgett films was manifested in cyclic voltammetry due to the high sensitivity of the metallic centers in RuTPyP. Electrodes modified with Langmuir-Blodgett films exhibit an anodic peak at 100 mV and a cathodic peak at 7 mV, which is assigned to RuIII/RuII redox processes. Furthermore, Langmuir-Blodgett films from RuTPyP showed electrocatalytic activity for oxidation of benzyl alcohol, illustrated by a large shift of 100 mV in the anodic peak at 400 mV, while electropolymerized and cast films of the same compound displayed smaller and no activities, respectively.

Generalization of the Langmuir–Blodgett laws for a nonzero potential gradient

The Langmuir–Blodgett laws for cylindrical and spherical diodes and the Child–Langmuir law for planar diodes repose on the assumption that the electric field at the emission surface is zero. In the case of ion beam extraction from a plasma, the Langmuir–Blodgett relations are the typical tools of study, however, their use under the above assumption can lead to significant error in the beam distribution functions. This is because the potential gradient at the sheath/beam interface is nonzero and attains, in most practical ion beam extractors, some hundreds of kilovolts per meter. In this paper generalizations to the standard analysis of the spherical and cylindrical diodes to incorporate this difference in boundary condition are presented and the results are compared to the familiar Langmuir–Blodgett relation.

Formulae and equations for finding scattering data from the Dirichlet-to-Neumann map with nonzero background potential

For the Schrödinger equation at fixed energy with a potential supported in a bounded domain we give formulae and equations for finding scattering data from the Dirichlet-to-Neumann map with nonzero background potential. For the case of zero background potential these results were obtained in (Novikov 1988 Multidimensional inverse spectral problem for the equation −Δψ + (v(x) − Eu(x))ψ = 0 Funkt. Anal. Ego Pril. 22 (4) 11–22).

Competition between the Effects of Asymmetries in Ion Diameters and Charges in an Electrical Double Layer Studied by Monte Carlo Simulations and Theories

The electrical double layer near a charged electrode formed by a binary electrolyte in which the cations and anions have different diameters varying between 1.5 and 4.25 Å is studied by Monte Carlo (MC) simulation. Our emphasis is on small electrode charge, where new phenomena may be expected. As one would expect, there is a nonzero potential at the point of zero charge (PZC). Such an effect is outside the popular Gouy−Chapman theory, although it can be introduced. It arises naturally in the mean spherical approximation (MSA). A comparison of the simulation results is made with the linearized modified Gouy−Chapman (LMGC) and MSA. Surprisingly, for monovalent ions, the LMGC theory yields more reliable electrode potentials than does the MSA. In the case when the cations and anions have different charge, a nonzero PZC potential results, even if the diameters of the ions are equal. This phenomenon is not reproduced by either of the theories but is predicted by the modified Poisson−Boltzmann (MPB5) theory. Results are presented for the competition of the effects resulting from the size and charge asymmetries of the ions. A comparison of the density and potential profiles, as obtained from MC and LMGC calculations, is reported.

Biologically inspired learning in a layered neural net

A feed-forward neural net with adaptable synaptic weights and fixed, zero or non-zero threshold potentials is studied, in the presence of a global feedback signal that can only have two values, depending on whether the output of the network in reaction to its input is right or wrong. It is found, on the basis of four biologically motivated assumptions, that only two forms of learning are possible, Hebbian and Anti-Hebbian learning. Hebbian learning should take place when the output is right, while there should be Anti-Hebbian learning when the output is wrong. For the Anti-Hebbian part of the learning rule a particular choice is made, which guarantees an adequate average neuronal activity without the need of introducing, by hand, control mechanisms like extremal dynamics. A network with realistic, i.e., non-zero threshold potentials is shown to perform its task of realizing the desired input–output relations best if it is sufficiently diluted, i.e., if only a relatively low fraction of all possible synaptic connections is realized.

Computer Simulations of a Monolayer of Like-charged Particles Condensed on an Oppositely-charged Flat Area

A non-traditional approach to the computer simulation study of a class of quasi-two-dimensional Coulomb systems (charged particles confined to a layer near a charged planar surface) is presented. The essence of the approach lies in exploiting the fact that the charged confinement is of finite dimensions. The main consequence of such a finiteness is a non-zero potential gradient along the finite charged area that includes a non-zero tangential component of the electric field. A system of like-charged spherical particles confined by the planar surface that includes an oppositely charged squared area is considered as an example. We find that the like-charged particles, independent of their concentration, all become confined on the oppositely charged area, if the surface charge balances the total charge carried by the particles, and if the electrostatic coupling is sufficiently large. The local density of the particles above the charged area is not homogeneous; near the boundaries of the charged square a clear tendency of layer formation along the square sides is observed.

Bubble-free electrokinetic pumping

Bubble-free electroosmotic flow (fr-EOF) of aqueous electrolytes in microfluidic channels with integrated electrodes is demonstrated. Undesirable electrolytic bubble formation is avoided by applying a periodic, zero net charge current to generate a nonzero average potential between the electrodes. Electrokinetic pressure generated in this active segment of the microchannel drives now upstream and downstream where electric field is absent. Flow rates commensurate with theoretical predictions for EOF driven by a dc voltage equivalent to the average net potential have been measured. By significantly reducing driving potentials and liquid exposure time to strong electric fields, fr-EOF opens the way for fully integrated, versatile micro total analysis systems (/spl mu/TAS).

Cosmic strings in a braneworld theory with metastable gravitons

If the graviton possesses an arbitrarily small (but nonvanishing) mass, perturbation theory implies that cosmic strings have a nonzero Newtonian potential. Nevertheless in Einstein gravity, where the graviton is strictly massless, the Newtonian potential of a cosmic string vanishes. This discrepancy is an example of the van Dam--Veltman--Zakharov (VDVZ) discontinuity. We present a solution for the metric around a cosmic string in a braneworld theory with a graviton metastable on the brane. This theory possesses those features that yield a VDVZ discontinuity in massive gravity, but nevertheless is generally covariant and classically self-consistent. Although the cosmic string in this theory supports a nontrivial Newtonian potential far from the source, one can recover the Einstein solution in a region near the cosmic string. That latter region grows as the graviton's effective linewidth vanishes (analogous to a vanishing graviton mass), suggesting the lack of a VDVZ discontinuity in this theory. Moreover, the presence of scale dependent structure in the metric may have consequences for the search for cosmic strings through gravitational lensing techniques.

VACUUM RESPONSE TO ELECTROMAGNETIC BACKGROUNDS

We investigate the vacuum state of a charged scalar field [Formula: see text] coupled to two different electromagnetic (EM) backgrounds on two different spaces. (i) [Formula: see text] is first defined on cylindrical space E2 × S1 with compact direction z ∈ S1 having circumference L3. This spatial compactification enables (but does not compel) an EM vacuum density j3 to flow around the spatial cylinder, parallel to z. However, a nonzero gauge potential A3 prefers one direction around z over the other, causing j3 to become nonzero. We analyze this situation for A3 = A3 (y) an arbitrary function of coordinate y, with A0,1,2 = 0. (ii) [Formula: see text] is next defined on Minkowski spacetime in the presence of a background EM plane wave of arbitrary shape and amplitude. As the plane wave sweeps through the charged virtual particle sea at the speed of light it locally excites or churns the sea, making the vacuum nonstationary (without producing vacuum pairs). This nonstationary excitation of the vacuum is nondissipative. A summary of recent calculations is presented. These two examples clearly display that, in gauge theory, potentials are more fundamental then fields.

Ginzburg-Landau free energy functional of color superconductivity at weak coupling

We derive the Ginzburg-Landau free energy functional of color superconductivity in terms of the thermal diagrams of QCD in its perturbative region. The zero mode of the quadratic term coefficient yields the same transition temperature, including the pre-exponential factor, as the one obtained previously from the Fredholm determinant of the two quark scattering amplitude. All coefficients of the free energy can be made identical to those of a BCS model by setting the Fermi velocity of the latter equal to the speed of light. We also calculate the induced symmetric color condensate near $T_c$ and find that it scales as the cubic power of the dominant antisymmetric color component. We show that in the presence of an inhomogeneity and a nonzero gauge potential, while the color-flavor locked condensate dominates in the bulk, the unlocked condensate, the octet, emerges as a result of a simultaneous color-flavor rotation in the core region of a vortex filament or at the junction of super and normal phases.

Scanning electric potential microscopy imaging of polymers: electrical charge distribution in dielectrics

Scanning electric potential images of polymer surfaces are presented and compared to standard non-contact AFM images. Samples used were a latex film with a well-known distribution of chemical constituents and thus of ionic electrical charges, as well as finished industrial products. Topography and electric potential images show a variable degree of correlation, thus evidencing the independence of topographic and electrical features of the samples, in the micro- and nanoscopic scales. Domains with non-zero negative or positive electric potentials are observed, extending for a few tenths of a micron and creating an electric mosaic in the otherwise neutral polymers. Large electric potential gradients are observed, e.g. in a HDPE film.

Use of universal correlations to predict some thermophysical properties of alternative refrigerants

The necessary replacement of refrigerants with non-zero ozone depletion potential has generated in recent years a significant amount of theoretical and experimental work about the thermophysical properties of alternative refrigerants, pure compounds, mixtures or blends, with zero ozone depletion potential. However, the amount of data necessary for the engineering design for refrigeration and air-conditioning units requires the development of reliable procedures for the estimation of liquid phase properties, based on reliable and simple-to-use equations of state. An overall view is presented of work done in the use of universal reduced equations to predict the vapour pressure and the density of pure, binary, and ternary mixtures of hydrofluorocarbons, including methane, ethane, and propane derivatives. Some hints devised to extend the correlations obtained to fluoroethers are also discussed.