Dipole Separation Research Articles

Analysis of direct current resistivity data using continuous wavelet transform

We have developed a new method for the direct current resistivity interpretation, based on the continuous wavelet transform (CWT) of electric potential-difference data. It exploits the main properties of the CWT, such as stability versus noise, and does not require a starting model or other a priori information such as a model weighting function or constraints. Because the approximate integral equation of the resistivity problem has the same form as the forward problem for potential fields, the authors analyze geoelectric data (with dipole-dipole configuration) using the wavelets belonging to the Poisson kernel semigroup. They find that the CWT analysis of the measured electric potential difference is able to identify buried bodies, defining their depth, position, and extent. Such parameters are estimated with no prior knowledge of the resistivity contrast between the bodies and the background. We consider several synthetic models, such as dikes, compact bodies, and contacts. In general, the depth and the lateral thickness of the buried bodies are estimated with good accuracy, using a diagram relating the singular point estimations to the different values of the dipole separation factor n. Thanks to the good results obtained from synthetic data, we test the method with data generated during laboratory experiments. In two laboratory-scale models, our method displays a better precision compared with smoothness-constrained least-squares inversion in identifying the exact position of the edges of a buried body. Finally, we find that combining CWT and inversion is advantageous: after constraining the inverse problem with a priori information from the CWT analysis, we obtain an improved inverse model.

Controlling surface dipole via applying current through conductive polyurethane-based organic/inorganic film to prohibit biofouling

We develop a new type of antifouling platform via the hybridization of conductive materials – carbon black (Ketchen black) and polypyrrole in inductively separated manner – and a non-conducting polyurethane, which was realized upon casting a coating with three components mixed in 1-methyl-2-pyrrolidone. The antifouling performance of the platforms was controlled by applying current on their surfaces. The antifouling performance was analyzed in terms of the removal efficacy of sticky mucin from the platforms that showed electrical conductivity. The optimized platforms were empirically established with varying mixing weight ratio of three components in the coatings, which were cast into films on glass Petri dishes. In the best antifouling performance condition, the carbon black phases would be well formulated on top of films that were interpreted based on Lifshitz–van der Waals and Lewis Acid–Base. The conductivity of carbon black accumulated on top of the surface enabled effective dipole separation at the surface upon current application, finally resulting in the removal of the surface-attached sticky mucin moiety.

A calibration and imaging strategy at 300 MHz with the Murchison Widefield Array (MWA)

AbstractAt relatively high frequencies, highly sensitive grating sidelobes occur in the primary beam patterns of low frequency aperture arrays (LFAA) such as the Murchison Widefield Array (MWA). This occurs when the observing wavelength becomes comparable to the dipole separation for LFAA tiles, which for the MWA occurs at${\sim}300$MHz. The presence of these grating sidelobes has made calibration and image processing for 300 MHz MWA observations difficult. This work presents a new calibration and imaging strategy which employs existing techniques to process two example 300 MHz MWA observations. Observations are initially calibrated using a new 300 MHz sky-model which has been interpolated from low frequency and high frequency all-sky surveys. Using this 300 MHz model in conjunction with the accurate MWA tile primary beam model, we perform sky-model calibration for the two example observations. After initial calibration a self-calibration loop is performed by all-sky imaging each observation. We mask the main lobe of the all-sky image, and perform a sky-subtraction by estimating the masked image visibilities. We then image the main lobe of the sky-subtracted visibilities, which results in high dynamic range images of the two example observations. These images have been convolved with a Gaussian to a resolution of$2.4$arcminutes, with a maximum sensitivity of${{\sim}}31\,\textrm{mJy/beam}$. The calibration and imaging strategy demonstrated in this work opens the door to performing science at 300 MHz with the MWA, which was previously an inaccessible domain. With this paper we release the code described below and the cross-matched catalogue along with the code to produce a sky-model in the range 70–1 400 MHz.

Low-power wavelength modulation in size-controlled Si nanocrystals using quantum confined Stark effect

We report on the quantum confined Stark effect coupled with a permanent built-in electric dipole moment in size-controlled Si nanocrystals (SiNCs) investigated under steady state conditions by photoluminescence spectroscopy. The study was conducted on samples with SiNC layer thicknesses between 2 nm and 5 nm. The emission spectra of the samples subjected to electric field magnitudes of up to 5 × 108 V/m were analyzed in terms of the dependency of the spectral shift on field magnitude and SiNC size. A clear trend of red shift along with increasing dipole separation was observed with increasing SiNC size. Experimental results show a high degree of accuracy to the model based on the time independent perturbation theory approximation for a biased quantum well. We propose a potential application for size-controlled SiNCs in photon detection in the near infrared band based on the studied phenomena as well as the use of SiNCs as a model platform for further study of the Stark effect in quantum confined structures as a whole.

Directional dipole radiations and long-range quantum entanglement mediated by hyperbolic metasurfaces.

In the vicinity of two-dimensional structures, the excitation of deep subwavelength polaritonic modes can be realized owing to the presence of free-carrier motion. Here we consider the launching of surface plasmonics in hyperbolic metasurfaces and theoretically demonstrate that the radiation energy of quantum emitter channels along specific directions was determined by the conductivity tensor of the surface. While the propagating length of the suface plasmon field supported by isotropic surfaces is normally limited on the scale of subwavelength to several vacuum wavelengths, it may be largely amplified when hyperbolic metasurfaces have been applied. Based on these exciting properties, prominent super- and subradiant behaviors between two distant quantum emitters are observed by engineering the anisotropy of the metasurfaces. Further investigations show that the directional collective interactions supported by the metasurfaces enable the generation of quantum entanglement over macroscopic dipole separations, with large values of concurrence, and allow remarkable revivals from sudden death. Our proposal can easily be extended to systems that include multiple quantum emitters interacting through hyperbolic metasurfaces and thus may have potential applications in on-chip science that aims at quantum information processing and quantum networks.

Assessment of Internal Stresses Using Dislocation Dipole Heights in Cyclically Deformed [001] Copper Single Crystals

There have been a number of studies on dipole separations in cyclically deformed FCC single crystals in single slip while there are no such studies in multiple slip. The dipole heights provide insight into the presence of long-range internal stresses (LRIS). In this study, we investigated how LRIS compare with the single slip studies through measuring the dislocation of dipole heights. [001] oriented copper single crystals were cyclically deformed in strain-control to saturation at ambient temperature. Transmission electron microscopy (TEM) confirms a labyrinth dislocation microstructure with high dislocation density walls and low dislocation density channels. The maximum dipole heights under the saturation stress were approximately independent of location, being nearly equal in the walls and within the channels. This, by itself, supports a uniform stress across the microstructure and low long-range internal stresses. The maximum value for dipole heights suggests dipole strengths (local stresses) that are about a factor of 2.4 higher than the applied stress based on the usual athermal equations. Considering the small “extra” stress that may be provided by tripoles or small dislocation pile-ups, a nearly homogenous stress distribution with only small internal stresses may be present, which is consistent with the observation of uniform dipole height across the heterogeneous dislocation microstructure. This observation that the stress state appears to be homogenous and higher than the applied stress has also been reported in the case of cyclically deformed metals in single slip.

A Wideband Absorber of Load Dipoles on a Dielectric Substrate with Inductive Ground Plane

AbstractA planar array of dipoles with matched loads in air backed by a ground plane at a quarter wavelength would become an absorber with a −10‐dB bandwidth of about 10%. Obviously, if the air substrate behind the dipoles is replaced by a dielectric substrate, the physical thickness of the absorber, saying a quarter wavelength, can be reduced. Meanwhile, as the incident waves illuminate on the absorber, the reflections are mainly from three ways, which are the air‐dielectric interface, the back scattering of the loaded dipole as a receiving antenna, and the ground plane. This paper shows that with the combination of the three reflections and a suitable dielectric constant together with its dipole separations, the −10‐dB bandwidth of the absorber increases to 20% and beyond. To further decrease the thickness of the dipole‐based absorber, inductive ground plane is introduced to replace the normal ground; phase analyses of the dipole‐based absorber with inductive ground is also given to explain the feasibility of the proposed technique. Both simulations and measurement results show that, with the proposed technique above, not only the thickness of the dipole‐based absorber can be decreased from a quarter wavelength to less than fifth wavelength, but also the −10‐dB bandwidth of the reflection can be enhanced from 20% to 48% or so.

Separation of Elastic and Plastic Timescales in a Phase Field Crystal Model.

A consistent small-scale description of plasticity and dislocation motion in a crystalline solid is presented based on the phase field crystal description. By allowing for independent mass motion and lattice distortion, the crystal can maintain elastic equilibrium on the timescale of plastic motion. We show that the singular (incompatible) strains are determined by the phase field crystal density, while the smooth distortions are constrained to satisfy elastic equilibrium. A numerical implementation of the model is presented and used to study a benchmark problem: the motion of an edge dislocation dipole in a triangular lattice. The time dependence of the dipole separation agrees with continuum elasticity with no adjustable parameters.

Using Electrical Resistivity Tomography (ERT) to Delineate Subsurface Structures at Siloam Hot Spring in the Soutpansberg Basin, South Africa

Electrical resistivity tomography (ERT) was used to delineate subsurface structures at Siloam hot spring in the Soutpansberg Basin of South Africa. The spring water was reported to be hottest in South Africa. Groundwater with temperature ranging between 63.3 °C and 67.5°C was observed flowing from the spring. Relatively wet areas were noted to the south and north of the spring. Electrical resistivity arrays with Dipole-dipole and Wenner-Schlumberger configurations were used. Current injection and potential dipole separations of 5 m and 10 m were applied across the spring. Inversion results for arrays with the shorter dipole separation of 5 m had better resolution. Resistivity sections were generated from inversion of ERT data. The resistivity values for the low and high resistive zones were ρa < 10 and ρa > 70 Ωm respectively. Sub-horizontal resistivity zones were obtained from the inversion of Wenner-Schlumberger array survey data. High resistivity zones associated with dykes or sills were delineated on Dipole-dipole derived depth sections. Near vertical structures associated with water bearing faults or fractures were delineated at the Siloam hot spring.

Dipolar Relaxation in Functionalized Poly-p-phenylenes Bearing Ultrastrong Dipoles Perpendicular to the Backbone

Local polymer dynamics are studied in polymers bearing dipoles rigidly attached to the backbone. The compounds are based on cyano-substituted dihydrobenzimidazoles bearing ultrastrong dipole moments (∼12 D per repeat unit) incorporated in a poly-p-phenylene backbone, giving rise to polymers with rigid dipoles perpendicular to the chain. They belong to type B polymers according to the Stockmayer classification. They are ideal model systems for studying rotational isomers in the gas phase and the self-assembly and local dynamics in the solid state. Gas phase calculations (DFT) provided the dipole moments, the energetic barriers, and the backbone conformation as a function of the dipole strength and dipole separation. Calculated dipole moments show an odd–even effect as a function of dipole separation. Specific rotational isomers that maximize the dipole moment are obtained. In the solid state, dielectric spectroscopy and site-specific NMR techniques revealed that packing through intermolecular forces such as van der Waals, π–π, and dipole–dipole interactions dictates the dynamics. Dielectric spectroscopy further identified two modes, both with Arrhenius temperature dependence and activation energies of 20–23 kcal/mol. Combined results attribute the faster process to a libration motion of the highly polar group reorienting only the nonplanar five-membered ring and the slower process to larger amplitude and/or correlated motions of the polar groups. These dynamic results are in agreement with structural investigations (X-ray diffraction) demonstrating that type B polymers in the bulk have rigid backbones.

Comparison of different sets of array configurations for multichannel 2D ERT acquisition

Traditional electrode arrays such Wenner-Schlumberger or dipole-dipole are still widely used thanks to their well-known properties but the array configurations are generally not optimized for multi-channel resistivity measures.Synthetic datasets relating to four different arrays, dipole-dipole (DD), pole-dipole (PD), Wenner-Schlumberger (WS) and a modified version of multiple gradient (MG), have been made for a systematic comparison between 2D resistivity models and their inverted images. Different sets of array configurations generated from simple combinations of geometric parameters (potential dipole lengths and dipole separation factors) were tested with synthetic and field data sets, even considering the influence of errors and the acquisition velocity. The purpose is to establish array configurations capable to provide reliable results but, at the same time, not involving excessive survey costs, even linked to the acquiring time and therefore to the number of current dipoles used.For DD, PD and WS arrays a progression of different datasets were considered increasing the number of current dipoles trying to get about the same amount of measures. A multi-coverage MG array configuration is proposed by increasing the lateral coverage and so the number of current dipoles. Noise simulating errors both on the electrode positions and on the electric potential was added.The array configurations have been tested on field data acquired in the landfill site of Bellolampo (Palermo, Italy), to detect and locate the leachate plumes and to identify the HDPE bottom of the landfill.The inversion results were compared using a quantitative analysis of data misfit, relative model resolution and model misfit. The results show that the trends of the first two parameters are linked on the array configuration and that a cumulative analysis of these parameters can help to choose the best array configuration in order to obtain a good resolution and reliability of a survey, according to generally short acquisition times.

Optimal dipole planar antenna array design for different UHF band applications using cuckoo search algorithm

This article presents the cuckoo search algorithm (CSA) for the optimum design of a 4 × 4 dipole planar antenna array (DPAA) taking mutual coupling into account. The CSA is employed to optimise the input parameters such as lengths of each dipole elements and separation distance between the dipole elements of the DPAA in order to achieve higher directivity with low half power beam width and high front to side lobe level with less computational time. The optimal input parameters at 300 MHz are obtained using a multi-objective fitness function. The array is simulated using method of moments codes using MATLAB and verified using MININEC software. Finally, the optimised results are compared with the results of other antenna arrays obtained using several other popular optimisation techniques to evaluate the performance of our proposed DPAA. The optimum design procedure can be used to design similar DPAAs at other operating frequencies in the UHF band.

A DPIV study on the effects of separation distance upon the vortical behaviour of jet–cylinder impingements

An experimental investigation based on laser-induced fluorescence (LIF) and digital particle image velocimetry (DPIV) was conducted to provide a better understanding into the effects of jet–cylinder separation distance on the vortical structures and dynamic behaviour resulting from jet impingements upon convex cylinders. Separation distances of 1, 2 and 4 jet diameters were investigated, while cylinder–jet diameter ratio was maintained at 2 throughout. LIF and DPIV results show that jet ring-vortex initiation, wall-separated vortex initiation, vortex dipole formation and vortex separation occur further away from the impingement point as the separation distance decreases. Varying the separation distance also influences the recirculating wake region size at the cylinder lee sides, as well as producing two distinct flow modes between adjacent vortex dipoles along the cylinder straight edges. Mean and instantaneous skin friction coefficient distributions determined from DPIV results not only showcase the different effects of separation distance on the wall shear stress, but also illustrate how the flow dynamics influence the local wall shear stress levels. On the other hand, wall-separated vortex initiation, vortex dipole formation and separation events incur little distinctive changes upon the local wall shear stress distributions that may ease their unique identification.

Resolving electrolayers from VES: A contribution from modeling the electrical response of a tightly constrained alluvial stratigraphy

The reliability of the hydrostratigraphic interpretation of electrostratigraphy derived from ground based, Direct Current resistivity methods is analyzed through the forward modeling of synthetically derived electrostratigraphic layering in a tightly constrained alluvial framework. To this purpose, a high-resolution stratigraphic model of the horizontally-stratified, alluvial aquifers hosted by the Quaternary regressive cycle of the Po plain in Lombardy was elaborated for a small area (1ha) by correlation of borehole lithostratigraphic data down to 160m below the ground surface. The stratigraphic model was used to compute 1-D synthetic electrostratigraphy based on the petrophysical relationship linking the bulk electrical resistivity of porous sediments to the coarse-to-fine litho-textural ratio and to the average pore-water electrical conductivity. A synthetic apparent resistivity curve was computed for the 1-D synthetic electrostratigraphy and for a traditional Vertical Electrical Sounding with Schlumberger array and a maximum dipole separation of 300m. A good agreement was observed with the experimental apparent resistivity curve obtained with a Vertical Electrical Sounding collected in the study area. The comparison of the 1-D synthetic electrostratigraphy with the results obtained by inversion of the experimental data with the linear-digital filter method, under the assumption of electrically homogeneous layers and no lateral resistivity transition, was used to estimate the hydrostratigraphic resolving power of ground-based resistivity data at various depths. Stratigraphic units of different hierarchic orders can be resolved by Direct Current methods at different depths and at different sites. In this specific case study, Vertical Electrical Sounding resolution was comparable to the hierarchy of the genetic depositional systems, corresponding to the rank of the hydrostratigraphic systems.

Electrically charged one-and-a-half monopole solution

Recently, we have discussed the coexistence of a finite energy one-half monopole and a ’t Hooft–Polyakov monopole of opposite magnetic charges. In this paper, we would like to introduce electric charge into this new monopoles configuration, thus creating a one-and-a-half dyon. This new dyon possesses finite energy, magnetic dipole moment, and angular momentum and is able to precess in the presence of an external magnetic field. Similar to the other dyon solutions, when the Higgs self-coupling constant, \(\lambda \), is nonvanishing, this new dyon solution possesses critical electric charge, total energy, magnetic dipole moment, and dipole separation as the electric charge parameter, \(\eta \), approaches 1. The electric charge and total energy increase with \(\eta \) to maximum critical values as \(\eta \rightarrow 1\) for all nonvanishing \(\lambda \). However, the magnetic dipole moment decreases with \(\eta \) when \(\lambda \ge 0.1\) and the dipole separation decreases with \(\eta \) when \(\lambda \ge 1\) to minimum critical values as \(\eta \rightarrow 1\).

The one and a half monopoles solution of the SU(2) Yang–Mills–Higgs field theory

Recently we have reported on the existence of finite energy SU(2) Yang–Mills–Higgs particle of one-half topological charge. In this paper, we show that this one-half monopole can co-exist with a ’t Hooft–Polyakov monopole. The magnetic charge of the one-half monopole is of opposite sign to the magnetic charge of the ’t Hooft–Polyakov monopole. However the net magnetic charge of the configuration is zero due to the presence of a semi-infinite Dirac string along the positive z-axis that carries the other half of the magnetic monopole charge. The solution possesses gauge potentials that are singular along the z-axis, elsewhere they are regular. The total energy is found to increase with the strength of the Higgs field self-coupling constant λ. However the dipole separation and the magnetic dipole moment decrease with λ. This solution is non-BPS even in the BPS limit when the Higgs self-coupling constant vanishes.

Mechanical separation of chiral dipoles by chiral light

We calculate optical forces and torques exerted on a chiral dipole by chiral light fields and reveal genuine chiral forces in combining the chiral contents of both light field and dipolar matter. Here, the optical chirality is characterized in a general way through the definition of optical chirality density and chirality flow. We show, in particular, that both terms have mechanical effects associated, respectively, with reactive and dissipative components of the chiral forces. Remarkably, these chiral force components are directly related to standard observables: optical rotation for the reactive component and circular dichroism for the dissipative one. As a consequence, the resulting forces and torques are dependent on the enantiomeric form of the chiral dipole. This suggests promising strategies for using chiral light forces to mechanically separate chiral objects according to their enantiomeric form.

Modelling and Simulation Radial and Tangential Dipoles of Human Head Local Field Potentials

The mathematical tangential and radial dipole models were constructed. Dipoles can be use to answer if any special electrical and magnetic patterns exist in human head, and also use them to reveal many other magic phenomena of head nero-system. Construct of a mathematical models of the electric potentials. Use validation of the mathematical model and interrogation of the validated model to determine what sort of dipole separation would produce patterns. Our models were simulated by using MATLAB. Simulation clearly show that those tangential and radial dipole models reflected real dipoles physical and electrical characteristic of them. Those models show that even with spatial filtering, the electrode array can not be more than 4.5 mm above the surface of the cortex for the sorts of patterns we are looking for to be resolved.

Quantum mechanical study of the solvent-dependence of electronic energy transfer rates in a Bodipy closely-spaced dyad

The ability of Förster theory to describe electronic energy transfer rates, and their solvent-dependence, have been studied theoretically in a series of 15 solvents of varying degrees of polarity for a rigid closely-spaced dyad, constituted by two boron dipyrromethene dyes, which was recently studied experimentally by Harriman & Ziessel, Photochem. Photobiol. Sci., 2010, 9, 960. We use time-dependent density functional theory calculations coupled to the polarizable continuum model to analyse the solvent-dependence of the spectroscopic and energy transfer properties of the system. This methodology allows us to examine the impact of the solvent on both electronic (solvent screening) and structural (dipole separation and orientation) factors by consistently incorporating solvent effects in the determination of molecular geometries, transition densities, and electronic couplings. In addition, we analyse the impact of bridge-mediated contributions to the electronic interaction between the dyes. We are therefore able to assess whether a Förster-type point-dipole approximation is valid for the molecular system studied.

Molecular Characterization of Agonists That Bind to an Insect GABA Receptor

Ionotropic GABA receptors are widely distributed throughout the vertebrate and invertebrate central nervous system (CNS) where they mediate inhibitory neurotransmission. One of the most widely studied insect GABA receptors is constructed from RDL (resistance to dieldrin) subunits from Drosophila melanogaster. The aim of this study was to determine critical features of agonists binding to RDL receptors using in silico and experimental data. Partial atomic charges and dipole separation distances of a range of GABA analogues were calculated, and the potency of the analogues was determined using RDL receptors expressed in Xenopus oocytes. These data revealed functional agonists require an ammonium group and an acidic group with an optimum separation distance of ∼5 Å. To determine how the agonists bind to the receptor, a homology model of the extracellular domain was generated and agonists were docked into the binding site. The docking studies support the requirements for functional agonists and also revealed a range of potential interactions with binding site residues, including hydrogen bonds and cation−π interactions. We conclude that the model and docking procedures yield a good model of the insect GABA receptor binding site and the location of agonists within it.