Unitary Charges Research Articles

Scanning Probe Microscopies for Characterizations of 2D Materials.

2D materials are intriguing due to their remarkably thin and flat structure. This unique configuration allows the majority of their constituent atoms to be accessible on the surface, facilitating easier electron tunneling while generating weak surface forces. To decipher the subtle signals inherent in these materials, the application of techniques that offer atomic resolution (horizontal) and sub-Angstrom (z-height vertical) sensitivity is crucial. Scanning probe microscopy (SPM) emerges as the quintessential tool in this regard, owing to its atomic-level spatial precision, ability to detect unitary charges, responsiveness to pico-newton-scale forces, and capability to discern pico-ampere currents. Furthermore, the versatility of SPM to operate under varying environmental conditions, such as different temperatures and in the presence of various gases or liquids, opens up the possibility of studying the stability and reactivity of 2D materials in situ. The characteristic flatness, surface accessibility, ultra-thinness, and weak signal strengths of 2D materials align perfectly with the capabilities of SPM technologies, enabling researchers to uncover the nuanced behaviors and properties of these advanced materials at the nanoscale and even the atomic scale.

Direct Measurement of the Topological Charge in Elliptical Beams Using Diffraction by a Triangular Aperture

We introduce a simple method to characterize the topological charge associated with the orbital angular momentum of a m-order elliptic light beam. This method consists in the observation of the far field pattern of the beam carrying orbital angular momentum, diffracted from a triangular aperture. We show numerically and experimentally, for Mathieu, Ince–Gaussian, and vortex Hermite–Gaussian beams, that only isosceles triangular apertures allow us to determine in a precise and direct way, the magnitude m of the order and the number and sign of unitary topological charges of isolated vortices inside the core of these beams.

Twelve years of scottish school public private partnerships: Are they better value for money?

This research evaluates the value-for-money (VFM) obtained from public-private partnership (PPP) schools in Scotland, based on headteachers questionnaires, local authority interviews and Scottish School Estate Statistics. The period covered is 2000-2012, when 395 new schools were commissioned. The PPPs were better in building condition and maintenance standards and conventionally-financed schools were better in terms of teacher access and improvement in staff morale. There was transfer of knowledge whereby the high standards of the PPPs then became the new standards for the conventionally-financed schools. Concerns about PPP VFM relates to the high cost of unitary charges and contract inflexibilities. A higher percentage of headteachers of conventionally-financed schools (63.64%) considered their new schools resulted in good VFM compared to PPP schools (42.86%).

Chloride Anions Regulate Kinetics but Not Voltage-Sensor Qmax of the Solute Carrier SLC26a5

In general, SLC26 solute carriers serve to transport a variety of anions across biological membranes. However, prestin (SLC26a5) has evolved, now serving as a motor protein in outer hair cells (OHCs) of the mammalian inner ear and is required for cochlear amplification, a mechanical feedback mechanism to boost auditory performance. The mechanical activity of the OHC imparted by prestin is driven by voltage and controlled by anions, chiefly intracellular chloride. Current opinion is that chloride anions control the Boltzmann characteristics of the voltage sensor responsible for prestin activity, including Qmax, the total sensor charge moved within the membrane, and Vh, a measure of prestin’s operating voltage range. Here, we show that standard narrow-band, high-frequency admittance measures of nonlinear capacitance (NLC), an alternate representation of the sensor’s charge-voltage (Q-V) relationship, is inadequate for assessment of Qmax, an estimate of the sum of unitary charges contributed by all voltage sensors within the membrane. Prestin’s slow transition rates and chloride-binding kinetics adversely influence these estimates, contributing to the prevalent concept that intracellular chloride level controls the quantity of sensor charge moved. By monitoring charge movement across frequency, using measures of multifrequency admittance, expanded displacement current integration, and OHC electromotility, we find that chloride influences prestin kinetics, thereby controlling charge magnitude at any particular frequency of interrogation. Importantly, however, this chloride dependence vanishes as frequency decreases, with Qmax asymptoting at a level irrespective of the chloride level. These data indicate that prestin activity is significantly low-pass in the frequency domain, with important implications for cochlear amplification. We also note that the occurrence of voltage-dependent charge movements in other SLC26 family members may be hidden by inadequate interrogation timescales, and that revelation of such activity could highlight an evolutionary means for kinetic modifications within the family to address hearing requirements in mammals.

Effects of the internal structure of spheroidal divalent ions on the charge density profiles of the electric double layer

In this work, the effects of the internal structure of charge for ions are analyzed by means of Monte Carlo simulations within a modified primitive model of electric double layer with spheroidal ions. The simulation results are compared to those obtained from a generalized Poisson-Boltzmann theory, where the separation of the charges within the spheroidal ions is considered. The spheroidal divalent ions have finite dimensions and two identical unitary charges separated by a distance of one diameter. Two structurally equivalent but oppositely charged ionic species are considered: coions and counterions. In the simulation, the number of particles is not fixed and the grand canonical ensemble is employed to reach the thermodynamic equilibrium. Meanwhile, the variational theory is applied to the analytical density functional. The fixed separation between charges within the spheroidal ions causes the orientational ordering of the spheroidal ions (with quadrupolar charge distributions) leading to very different charge distributions than those of the regular divalent ions from the primitive model of electrolyte. The internal structure of ions could be dramatically relevant for the modelling of large molecules, which are known to posses complex charge distributions.

Nanoscale Quantitative Measurement of the Potential of Charged Nanostructures by Electrostatic and Kelvin Probe Force Microscopy: Unraveling Electronic Processes in Complex Materials

In microelectronics and biology, many fundamental processes involve the exchange of charges between small objects, such as nanocrystals in photovoltaic blends or individual proteins in photosynthetic reactions. Because these nanoscale electronic processes strongly depend on the structure of the electroactive assemblies, a detailed understanding of these phenomena requires unraveling the relationship between the structure of the nano-object and its electronic function. Because of the fragility of the structures involved and the dynamic variance of the electric potential of each nanostructure during the charge generation and transport processes, understanding this structure-function relationship represents a great challenge. This Account discusses how our group and others have exploited scanning probe microscopy based approaches beyond imaging, particularly Kelvin probe force microscopy (KPFM), to map the potential of different nanostructures with a spatial and voltage resolution of a few nanometers and millivolts, respectively. We describe in detail how these techniques can provide researchers several types of chemical information. First, KPFM allows researchers to visualize the photogeneration and splitting of several unitary charges between well-defined nano-objects having complementary electron-acceptor and -donor properties. In addition, this method maps charge injection and transport in thin layers of polycrystalline materials. Finally, KPFM can monitor the activity of immobilized chemical components of natural photosynthetic systems. In particular, researchers can use KPFM to measure the electric potential without physical contact between the tip and the nanostructure studied. These measurements exploit long-range electrostatic interactions between the scanning probe and the sample, which scale with the square of the probe-sample distance, d. While allowing minimal perturbation, these long-range interactions limit the resolution attainable in the measurement of potentials. Although the spatial resolution of KPFM is on the nanometer scale, it is inferior to that of other related techniques such as atomic force or scanning tunneling microscopy, which are based on short-range interactions scaling as d(-7) or e(-d), respectively. To overcome this problem, we have recently devised deconvolution procedures that allow us to quantify the electric potential of a nano-object removing the artifacts due to its nanometric size.

New Development: The PFI: Scotland's Plan for Expansion and its Implications

The public expenditure implications of PFI projects in Scotland's NHS are substantial. This article compares PFI capital expenditure with projected unitary charges, examines the annual cost of existing PFI schemes and looks at future costs arising from the planned expansion of PFI. Unless the new Scottish National Party-led administration applies the breaks, the annual cost of PFI to Scotland's NHS is to increase almost five-fold, from £107.1 million in 2005/06 to £500 million by the early part of the next decade.

Ca 2+- and Voltage-Dependent Gating of Ca 2+- and ATP-Sensitive Cationic Channels in Brain Capillary Endothelium

Biophysical properties of the Ca 2+-activated nonselective cation channel expressed in brain capillaries were studied in inside-out patches from primary cultures of rat brain microvascular endothelial cells. At −40 mV membrane potential, open probability ( P o) was activated by cytosolic [Ca 2+] > 1 μM and was half-maximal at ∼20 μM. Increasing [Ca 2+] stimulated opening rate with little effect on closing rate. At constant [Ca 2+], P o was voltage-dependent, and effective gating charge corresponded to 0.6 ± 0.1 unitary charges. Depolarization accelerated opening and slowed closing, thereby increasing apparent affinity for Ca 2+. Within ∼1 min of excision, P o declined to a lower steady state with decreased sensitivity toward activating Ca 2+ when studied at a fixed voltage, and toward activating voltage when studied at a fixed [Ca 2+]. Deactivated channels opened ∼5-fold slower and closed ∼10-fold faster. The sulfhydryl-reducing agent dithiotreitol (1 mM) completely reversed acceleration of closing rate but failed to recover opening rate. Single-channel gating was complex; distributions of open and closed dwell times contained at least four and five exponential components, respectively. The longest component of the closed-time distribution was markedly sensitive to both [Ca 2+] and voltage. We conclude that the biophysical properties of gating of this channel are remarkably similar to those of large-conductance Ca 2+-activated K + channels.

Characterization and structural study of the complex of Al(III) with 2,4-dihydroxy-benzophenone. Ionic strength and solvent effects

The complexation reaction between AlCl 3 and 2,4-dihydroxy-benzophenone with varying permittivity and ionic strength of the reaction medium was investigated by theoretical and experimental procedures, namely, density functional (DFT) and UV–vis spectroscopic methods, respectively. The stoichiometric composition of the complex formed, which was determined by means of the molar ratio method, is 1:1. The molar absorptivity and stability constant of the complex were determined using a method designed by the authors. It was observed that the stoichiometric composition of the complex does not change with the used solvents and that the stability constant in methanol is higher than ethanol. Kinetic experiments in solutions with different ionic strength were also performed. The results obtained permit to conclude that the complex is formed through of a mechanism whose rate-determining step is a reaction between two ions with opposite unitary charges. In the theoretical study performed at the B3LYP/6-31G(d) level of theory using Tomasi's model, it was proposed that the formation of the complex involves one simple covalent bond between the aluminum atom and the oxygen atom of o-hydroxyl group of the ligand and a stronger coulombic attraction (or a second covalent bond) between the central atom and the carbonyl oxygen atom of 2,4-dihydroxy-benzophenone. Using the calculated magnitudes, it was predicted that the complex formed has higher thermodynamic stability in methanol than ethanol. It was also concluded that the planarity of the chelate ring favors a greater planarity of 4-hydroxy-benzoyl group of the complex with respect to the ligand, which agrees with the observed batochromic shifts. The formulated theoretical conclusions satisfactorily match the experimental determinations performed.

Unitary cardiac Na+, Ca2+ exchange current magnitudes determined from channel-like noise and charge movements of ion transport

The cardiac Na+, Ca2+ exchanger (NCX1) is thought to achieve a high turnover rate, but all estimates to date are indirect. Two new strategies demonstrate that maximum unitary exchange currents are about 1 fA (6000 unitary charges per s) and that they fluctuate between on and off levels similar to ion channel currents. First, exchange current noise has been identified in small cardiac patches with properties expected for a gated transport process. Noise power density spectra correlate well with exchanger inactivation kinetics, and the noise has a predicted bell-shaped dependence on the activation states of the exchanger. From the magnitudes of exchange current noise, maximum unitary exchange currents are estimated to be 0.6-1.3 fA. Second, charge movements with rates of approximately 5000 s-1 have been isolated for the transport of both Na+ and Ca2+ in giant membrane patches using nonsaturating ion concentrations. The Na+ transport reactions are disabled or "immobilized" by exchanger inactivation reactions, thus confirming that inactivation generates fully inactive exchanger states.

Generalized graphs and unitary irrational central charge in the superconformal master equation

For each magic basis of Lie g, it is known that the Virasoro master equation on affine g contains a generalized graph theory of conformal level-families. In this paper, it is found that the superconformal master equation on affine g×SO(dim g) similarly contains a generalized graph theory of superconformal level-families for each magic basis of g. The superconformal level-families satisfy linear equations on the generalized graphs, and the first exact unitary irrational solutions of the superconformal master equation are obtained on the sine-area graphs of g=SU(n), including the simplest unitary irrational central charges c=6nx/(nx+8 sin2(rsπ/n)) yet observed in the program.

IX. A dynamical theory of the electric and luminiferous medium.— Part III. relations with material media

1. In two previous memoirs* it has been explained, that the various hypotheses involved in the theory of electric and optical phenomena, which has been developed by F araday and Maxwell, can be systematized by assuming the aether to be a continuous, homogeneous, and incompressible medium, endowed with inertia and with elasticity purely rotational. In this medium unitary electric charges, or electrons, exist as point-singularities, or centres of intrinsic strain, which can move about under their mutual actions ; while atoms of matter are in whole or in part aggregations of electrons in stable orbital motion. In particular, this scheme provides a consistent foundation for the electrodynamic laws, and agrees with the actual relations between radiation and moving matter.