Charge Perturbation Research Articles

Electronic response of graphene to linelike charge perturbations

The problem of electrostatic screening of a charged line by undoped or weakly doped graphene is treated beyond the linear-response theory. The induced electron density is found to be approximately doping independent, n(x)~(log x)^2/x^2, at intermediate distances x from the charged line. At larger x, twin p-n junctions may form if the external perturbation is repulsive for graphene charge carriers. The effect of such inhomogeneities on conductance and quantum capacitance of graphene is calculated. The results are relevant for transport properties of graphene grain boundaries and for local electrostatic control of graphene with ultrathin gates.

Accurate evaluation of charge asymmetry in aqueous solvation.

Charge hydration asymmetry (CHA)-a characteristic dependence of hydration free energy on the sign of the solute charge-quantifies the asymmetric response of water to electric field at microscopic level. Accurate estimates of CHA are critical for understanding hydration effects ubiquitous in chemistry and biology. However, measuring hydration energies of charged species is fraught with significant difficulties, which lead to unacceptably large (up to 300%) variation in the available estimates of the CHA effect. We circumvent these difficulties by developing a framework which allows us to extract and accurately estimate the intrinsic propensity of water to exhibit CHA from accurate experimental hydration free energies of neutral polar molecules. Specifically, from a set of 504 small molecules we identify two pairs that are analogous, with respect to CHA, to the K(+) /F(-) pair-a classical probe for the effect. We use these "CHA-conjugate" molecule pairs to quantify the intrinsic charge-asymmetric response of water to the microscopic charge perturbations: the asymmetry of the response is strong, ∼50% of the average hydration free energy of these molecules. The ability of widely used classical water models to predict hydration energies of small molecules correlates with their ability to predict CHA.

Stability of highly-charged Reissner-Nordström black holes to charged scalar perturbations

It is shown that highly-charged Reissner-Nordstr\"om black holes in the charge interval $8/9<{(Q/M)}^2<1$ are stable to charged scalar perturbations.

Chiral magnetic wave in an expanding QCD fluid

As a consequence of the chiral anomaly, the hydrodynamics of hot QCD matter coupled to QED allows for a long-wavelength mode of chiral charge density, the chiral magnetic wave (CMW), that provides for a mechanism of electric charge separation along the direction of an external magnetic field. Here, we investigate the efficiency of this mechanism for values of the time-dependent magnetic field and of the energy density attained in the hot QCD matter of ultra-relativistic heavy ion collisions. To this end, we derive the CMW equations of motion for expanding systems by treating the CMW as a charge perturbation on top of an expanding Bjorken-type background field in the limit of small chemical potential. Both, approximate analytical and full numerical solutions to these equations of motion indicate that for the lifetime and thermodynamic conditions of ultra-relativistic heavy ion collisions, the efficiency of CMW-induced electric charge separation decreases with increasing center of mass energy and that the effect is numerically very small. We note, however, that if sizable oriented asymmetries in the axial charge distribution (that are not induced by the CMW) are present in the early fluid dynamic evolution, then the mechanism of CMW-induced electric charge separation can be much more efficient.

Testable constraint on near-tribimaximal neutrino mixing

General lowest order perturbations to hermitian squared mass matrices of leptons are considered away from the tribimaximal (TBM) limit in which a weak flavor basis with mass diagonal charged leptons is chosen. The three measurable TBM deviants are expressed linearly in terms of perturbation induced dimensionless coefficients appearing in the charged lepton and neutrino flavor eigenstates. With unnatural cancellations assumed to be absent and the charged lepton perturbation contributions to their flavor eigenstates argued to be small, we analytically derive the following result. Within lowest order perturbations, a deviation from maximal atmospheric neutrino mixing and the amount of CP violation in neutrino oscillations cannot both be large (i.e. $12$-$17 \% $), posing the challenge of verification to forthcoming experiments at the intensity frontier.

Greybody factors of massive charged fermionic fields in a charged two-dimensional dilatonic black hole

We study massive charged fermionic perturbations in the background of a charged two-dimensional dilatonic black hole, and we solve the Dirac equation analytically. Then, we compute the reflection and transmission coefficients and the absorption cross section for massive charged fermionic fields, and we show that the absorption cross section vanishes at the low and high frequency limits. However, there is a range of frequencies where the absorption cross section is not null. Furthermore, we study the effect of the mass and electric charge of the fermionic field over the absorption cross section.

Label-Free Detection of DNA Hybridization by Using Charge Perturbation on Poly(thionine)-Modified Glassy Carbon and Gold Electrodes

Simple and label-free electrochemical sensors for the detection of DNA hybridization were developed based on charge perturbation of poly(thionine)-modified glassy carbon and gold electrodes (PTH/GCE and PTH/Au). Probe DNA (pDNA) was immobilized on PTH films via covalent bonds between the amine (-NH2) group of the PTH and the phosphate (PO43−) group at the 5′ end of the pDNA. The immobilized single-strand pDNA decreased the oxidation current of [Fe(CN)6]4− as a result of electrostatic repulsion by the negatively charged PO43- backbone of the pDNA. The current was further decreased subsequent to duplex formation by the hybridization of target complementary DNA (cDNA) due to increased electrostatic repulsion. Both sensors demonstrated excellent selectivity, stability, and the sensitivity of 1.27 and 58.6 μA·cm−2·pM−1 with detection limits of 0.47 and 0.20 pM, respectively, for cDNA hybridization.

Dihydrogen Bonding in Compressed Ammonia Borane and Its Roles in Structural Stability

Theoretical structure prediction calculations have revealed that the conformation of ammonia borane (NH3BH3) in the crystalline state can be modified by pressure, changing from the staggered configuration at low pressure to an eclipsed geometry at high pressure. At low pressure, the crystalline structure is stabilized by the charge transfer N—Hδ+···δ−H—B dihydrogen interactions. In the high pressure polymorphs, the NH3BH3 is predicted to form a layered structure. The N—Hδ+···δ−H—B bonding is still predominant within the layer. The stacking of the layers, however, is determined by the occurrence of additional homopolar B—Hδ−···δ−H—B interaction unprecedented in NH3BH3 and facilitated by the eclipsed conformation. This bonding is shown to be the result of secondary interactions between BH3 groups from molecules of adjacent layers. Topological analysis of the charge density and perturbation calculations on the molecule fragments show unambiguously that the B—Hδ−···δ−H—B interaction is covalent in nature with the bond strength comparable to a conventional hydrogen bond.

Superradiant instability of charged scalar field in stringy black hole mirror system

It has been shown that the mass of the scalar field in the charged stringy black hole is never able to generate a potential well outside the event horizon to trap the superradiant modes. This is to say that the charged stringy black hole is stable against the massive charged scalar perturbation. In this paper we will study the superradiant instability of the massless scalar field in the background of charged stringy black hole due to a mirror-like boundary condition. The analytical expression of the unstable superradiant modes is derived by using the asymptotic matching method. It is also pointed out that the black hole mirror system becomes extremely unstable for a large charge $q$ of scalar field and the small mirror radius $r_m$.

Publisher’s Note: Stability of Reissner-Nordström black hole in de Sitter background under charged scalar perturbation [Phys. Rev. D90, 044042 (2014)

Publisher’s Note: Stability of Reissner-Nordström black hole in de Sitter background under charged scalar perturbation [Phys. Rev. D<b>90</b>, 044042 (2014)

Stability of Reissner-Nordström black hole in de Sitter background under charged scalar perturbation

We find a new instability in the four-dimensional Reissner-Nordstr\"om--de Sitter black holes against charged scalar perturbations with vanishing angular momentum, $l=0$. We show that such an instability is caused by superradiance. The instability does not occur for a larger angular index, as explicitly proved for $l=1$. Our results are obtained from a numerical investigation of the time-domain profiles of the perturbations.

Charge Transport in Amorphous Organic Semiconductors: Effects of Disorder, Carrier Density, Traps, and Scatters

AbstractIn real devices, organic semiconductors are largely amorphous. Because accurate molecular packing in them cannot be obtained, the relationship between the molecular structure and the material properties can be difficult to understand. Nevertheless, knowing the charge transport processes is essential to material and device engineering. In amorphous organic semiconductors, charge transport is often apprehended as a hopping process that can be described using the Marcus or MillerAbrahams equations. The intrinsic disorder and frequently present traps have a great influence on the charge mobility. Carrier density, which would affect the effective density of states and create spacecharge perturbations, is also one important factor in the charge transport process. Herein, recent advances in the charge transport mechanism in amorphous organic semiconductors are summarized. The influences of disorder, carrier density, traps, and scatters are discussed in detail.

Dirac quasinormal modes of two-dimensional charged dilatonic black holes

We study charged fermionic perturbations in the background of two-dimensional charged Dilatonic black holes, and we present the exact Dirac quasinormal modes. Also, we study the stability of these black holes under charged fermionic perturbations.

Identification and Characterization of Noncovalent Interactions That Drive Binding and Specificity in DD-Peptidases and β-Lactamases.

Bacterial resistance to standard (i.e., β-lactam-based) antibiotics has become a global pandemic. Simultaneously, research into the underlying causes of resistance has slowed substantially, although its importance is universally recognized. Key to unraveling critical details is characterization of the noncovalent interactions that govern binding and specificity (DD-peptidases, antibiotic targets, versus β-lactamases, the evolutionarily derived enzymes that play a major role in resistance) and ultimately resistance as a whole. Herein, we describe a detailed investigation that elicits new chemical insights into these underlying intermolecular interactions. Benzylpenicillin and a novel β-lactam peptidomimetic complexed to the Stremptomyces R61 peptidase are examined using an arsenal of computational techniques: MD simulations, QM/MM calculations, charge perturbation analysis, QM/MM orbital analysis, bioinformatics, flexible receptor/flexible ligand docking, and computational ADME predictions. Several key molecular level interactions are identified that not only shed light onto fundamental resistance mechanisms, but also offer explanations for observed specificity. Specifically, an extended π–π network is elucidated that suggests antibacterial resistance has evolved, in part, due to stabilizing aromatic interactions. Additionally, interactions between the protein and peptidomimetic substrate are identified and characterized. Of particular interest is a water-mediated salt bridge between Asp217 and the positively charged N-terminus of the peptidomimetic, revealing an interaction that may significantly contribute to β-lactam specificity. Finally, interaction information is used to suggest modifications to current β-lactam compounds that should both improve binding and specificity in DD-peptidases and their physiochemical properties.

Electrostatic shielding in plasmas and the physical meaning of the Debye length

This paper examines the electrostatic shielding in plasmas, and resolves inconsistencies about what the Debye length really is. Two different interpretations of the Debye length are currently used: (1) The potential energy approximately equals the thermal energy, and (2) the ratio of the shielded to the unshielded potential drops to 1/e. We examine these two interpretations of the Debye length for equilibrium plasmas described by the Boltzmann distribution, and non-equilibrium plasmas (e.g. space plasmas) described by kappa distributions. We study three dimensionalities of the electrostatic potential: 1-D potential of linear symmetry for planar charge density, 2-D potential of cylindrical symmetry for linear charge density, and 3-D potential of spherical symmetry for a point charge. We resolve critical inconsistencies of the two interpretations, including: independence of the Debye length on the dimensionality; requirement for small charge perturbations that is equivalent to weakly coupled plasmas; correlations between ions and electrons; existence of temperature for non-equilibrium plasmas; and isotropic Debye shielding. We introduce a third Debye length interpretation that naturally emerges from the second statistical moment of the particle position distribution; this is analogous to the kinetic definition of temperature, which is the second statistical moment of the velocity distribution. Finally, we compare the three interpretations, identifying what information is required for theoretical/experimental plasma-physics research: Interpretation 1 applies only to kappa distributions; Interpretation 2 is not restricted to any specific form of the ion/electron distributions, but these forms have to be known; Interpretation 3 needs only the second statistical moment of the positional distribution.

Rapid and Sensitive Detection of Nano-fluidically Trapped Protein Biomarkers

ABSTRACTIn this work, we demonstrate the label-free and ultrasensitive detection of troponin-T, cardiac biomarker using nanoporous membrane integrated on a microelectrode sensor platform. The nanoporous membrane allows for spatial confinement of the protein molecules. Antigen interaction with thiol immobilized antibody perturbs the electrical double layer. Charge perturbations are recorded as impedance change at low frequency using the principle of electrochemical impedance spectroscopy (EIS). The measured impedance change is used to quantitatively determine the concentration of troponin-T in tested sample. We have shown that sensitivity of sensor for troponin-T to be 1pg/mL. The accuracy and reliability of this sensor was tested by comparing the experimental troponin-T concentration values with a commercially available electrochemiluminescence assay measured with Roche Elecsys analyzer. Using this technique we were successful in detecting protein biomarkers in whole blood, human serum, and ionic buffers. This technology provides a robust analytical platform for rapid and sensitive detection of protein biomarkers, thus establishing this technology as an ideal candidate for biomarker screening in clinical settings.

Stability of charged black holes in string theory under charged massive scalar perturbations

Similar to the superradiant effect in Reissner-Nordstr\"{o}m black hole, a charged scalar field can be amplified when impinging on the charged black hole in string theory. According to the black-hole bomb mechanism,the mass term of the incident field can works as the reflecting mirror, which may trigger the instability of black hole. We study the possible instability triggered by superradiant effect and demonstrate that the charged black hole in string theory is stable against the massive charged scalar perturbation. The reason is that there is no trapping potential well in the black hole exterior which is separated from the horizon by a potential barrier and there is no bound states in the superradiant regime.

Polycation-π Interactions Are a Driving Force for Molecular Recognition by an Intrinsically Disordered Oncoprotein Family

Molecular recognition by intrinsically disordered proteins (IDPs) commonly involves specific localized contacts and target-induced disorder to order transitions. However, some IDPs remain disordered in the bound state, a phenomenon coined “fuzziness”, often characterized by IDP polyvalency, sequence-insensitivity and a dynamic ensemble of disordered bound-state conformations. Besides the above general features, specific biophysical models for fuzzy interactions are mostly lacking. The transcriptional activation domain of the Ewing's Sarcoma oncoprotein family (EAD) is an IDP that exhibits many features of fuzziness, with multiple EAD aromatic side chains driving molecular recognition. Considering the prevalent role of cation-π interactions at various protein-protein interfaces, we hypothesized that EAD-target binding involves polycation- π contacts between a disordered EAD and basic residues on the target. Herein we evaluated the polycation-π hypothesis via functional and theoretical interrogation of EAD variants. The experimental effects of a range of EAD sequence variations, including aromatic number, aromatic density and charge perturbations, all support the cation-π model. Moreover, the activity trends observed are well captured by a coarse-grained EAD chain model and a corresponding analytical model based on interaction between EAD aromatics and surface cations of a generic globular target. EAD-target binding, in the context of pathological Ewing's Sarcoma oncoproteins, is thus seen to be driven by a balance between EAD conformational entropy and favorable EAD-target cation-π contacts. Such a highly versatile mode of molecular recognition offers a general conceptual framework for promiscuous target recognition by polyvalent IDPs.

The Reduced Hartree–Fock Model for Short-Range Quantum Crystals with Nonlocal Defects

In this article, we consider quantum crystals with defects in the reduced Hartree–Fock framework. The nuclei are supposed to be classical particles arranged around a reference periodic configuration. The perturbation is assumed to be small in amplitude, but need not be localized in a specific region of space or have any spatial invariance. Assuming Yukawa interactions, we prove the existence of an electronic ground state, solution of the self-consistent field equation. Next, by studying precisely the decay properties of this solution for local defects, we are able to expand the density of states of the nonlinear Hamiltonian of a system with a random perturbation of Anderson–Bernoulli type, in the limit of low concentration of defects. One important step in the proof of our results is the analysis of the dielectric response of the crystal to an effective charge perturbation.

Superradiance without event horizons in general relativity

Superradiant scattering processes are studied in general relativistic systems which, unlike rotating and/or charged black holes, do not exhibit an event horizon. Inspired by Zel'dovich's seminal works on the amplification of waves by a rotating cylinder, we analyse, in the context of General Relativity, the possibility of superradiance for electromagnetic waves reflecting off a rotating star and for charged scalar perturbations impinging on a charged sphere. The role of energy dissipation in these systems is analysed and compared with the role of the event horizon in black hole superradiance.