Electric Charge Distribution Research Articles

Particle beam deflection imaging for simultaneous characterization of aerosol particle size and charge

We present a novel method referred to as Particle Beam Deflection Imaging (PBDI) for the simultaneous characterization of the size and electric charge distribution of submicrometer (currently ∼200–800 nm) aerosol particles in real-time (currently ≤30 s). It combines aerodynamic and electrostatic particle deflection, providing two-dimensional information on size and charge in a single two-dimensional light scattering image. The image allows one to extract information on charge-averaged and charged-resolved particle size distributions, and on size-dependent bipolar charge distributions. The current prototype has a size resolution of <50 nm and can resolve individual charge states. Compared to Scanning Mobility Particles Sizers (SMPS), the PBDI offers the advantage of providing simultaneous size and charge information at higher size resolution in a significantly shorter measurement time, hence allowing real-time characterization of volatile aerosol particles.

Finite Element Modeling of the Combined Faradaic and Electrostatic Contributions to the Voltammetric Response of Monolayer Redox Films.

The voltammetric response of electrodes coated with a redox-active monolayer is computed by finite element simulations based on a generalized model that couples the Butler–Volmer, Nernst–Planck, and Poisson equations. This model represents the most complete treatment of the voltammetric response of a redox film to date and is made accessible to the experimentalist via the use of finite element modeling and a COMSOL-generated report. The model yields a full description of the electric potential and charge distributions across the monolayer and bulk solution, including the potential distribution associated with ohmic resistance. In this way, it is possible to properly account for electrostatic effects at the molecular film/electrolyte interface, which are present due to the changing charge states of the redox head groups as they undergo electron transfer, under both equilibrium and nonequilibrium conditions. Specifically, our numerical simulations significantly extend previous theoretical predictions by including the effects of finite electron-transfer rates (k0) and electrolyte conductivity. Distortion of the voltammetric wave due to ohmic potential drop is shown to be a function of electrolyte concentration and scan rate, in agreement with experimental observations. The commonly used Laviron analysis for the determination of k0 fails to account for ohmic drop effects, which may be non-negligible at high scan rates. This model provides a more accurate alternative for k0 determination at all scan rates. The electric potential and charge distributions across an electrochemically inactive monolayer and electrolyte solution are also simulated as a function of applied potential and are found to agree with the Gouy-Chapman-Stern theory.

Transverse charge and current densities in the nucleon from dispersively improved chiral effective field theory

Background: The transverse densities $\rho_{1, 2}(b)$ describe the distributions of electric charge and magnetic moment at fixed light-front time and connect the nucleon's elastic form factors with its partonic structure. The dispersive representation of the form factors $F_{1, 2}(t)$ expresses the densities in terms of exchanges of hadronic states in the $t$-channel and permits their analysis using hadronic physics methods. Purpose: Compute the densities at peripheral distances $b = \mathcal{O}(M_\pi^{-1})$, where they are generated predominantly by the two-pion states in the dispersive representation. Quantify the uncertainties. Methods: Dispersively improved chiral effective field theory (DI$\chi$EFT) is used to calculate the isovector spectral functions $\textrm{Im}\, F_{1, 2}(t)$ on the two-pion cut. The method includes $\pi\pi$ interactions ($\rho$ resonance) through elastic unitarity and provides realistic spectral functions up to $t \approx$ 1 GeV$^2$. Higher-mass states are parametrized by effective poles and constrained by sum rules (charges, radii, superconvergence relations). The densities $\rho_{1, 2}(b)$ are obtained from their dispersive representation. Uncertainties are quantified by varying the spectral functions. The method respects analyticity and ensures the correct $b \rightarrow \infty$ asymptotic behavior of the densities. Results: Accurate densities are obtained at all distances $b \gtrsim 0.5$ fm, with correct behavior down to $b \rightarrow 0$. The region of distances is quantified where transverse nucleon structure is governed by the two-pion state. The light-front current distributions in the polarized nucleon are computed and discussed. Conclusions: Peripheral nucleon structure can be computed from first principles using DI$\chi$EFT. The method can be extended to generalized parton distributions and other nucleon form factors.

Coulombic force contribution to nano scale aerosol capture by a wire grid: Quantitative comparison of experiments and simulations

Fibers of filter media and aerosol particles both typically have some distributions of electric charge. Attractive coulombic interactions between charged particles and fibers enhance aerosol filtration efficiency; however, these coulombic interactions are difficult to characterize due to the complex, nonuniform fiber charge, diameter and spacing of typical filter media. We develop an experimental filter assembly to control these coulombic interactions. The filter assembly consists of three sequential electrically isolated metallic grids—high voltage is applied to the middle grid and the adjacent outer grids are electrically grounded such that the electric potential distribution in the filter assembly is well-defined. We test this filter assembly with aerosols of controlled diameter (ranging between ∼70 and 500 nm) and electric charge (1e−), and systematically increase the applied voltage to the middle grid to enhance coulombic interactions and consequently the filter efficiency. We develop particle trajectory simulations to model our experimental filter assembly such that all parameters in the simulation have direct basis from the experimental system. We find excellent quantitative agreement between the filter efficiency measured in experiments and predicted from simulations without any fitting parameters. The precise control and accurate simulation of coulombic interactions demonstrated in this study indicate that the experimental and simulation methodologies developed here may be applied to uncover fundamental insights into the role of coulombic forces in more complex phenomena such as filter clogging.

Coexistence of circular dichroism and asymmetric transmission in Babinet-complementary metamaterials.

Chiral metamaterials with circular dichroism (CD) or asymmetric transmission (AT) draw enormous attention for their attractive applications in polarization transformers, circular polarizers, and biosensing. In this study, a feasible trilayer chiral metamaterials (TCM) is designed and investigated in theory and simulation. The proposed TCM is composed of a nanoslit layer and a Babinet-complementary nanorod layer separated by a nanoslit spacer. Owing to symmetry breaking by the tilted nanoslit in metal film, the TCM shows simultaneous CD and AT effects in the near-infrared region. The simulated electric charge distributions prove that the chirality arises from the excitation of asymmetric electric dipole resonant modes due to the coupling of adjacent unit cells. Moreover, CD and AT can be tuned by the tilted angle of the nanoslit and the thickness of the spacer, the fitting functions of which are consistent with the theoretical formulas based on transmittance matrix analysis. The proposed nanostructure offers a potential strategy for manipulating metamaterials with simultaneous CD and AT effects, allowing a multitude of exciting applications such as ultra-sensitive polarization transformer and biosensor.

Efficient and Accurate Modeling of the Surface Deflection of Thin Layers on Composite Substrates with Applications to Piezoelectric Parameter Measurements

The electrical and mechanical response of multilayered structures involving a piezoelectric layer and bull’s eye shaped electrodes is investigated. A boundary element method is employed based on spectral domain Green’s functions. With this method, the electric field distribution is determined first, and the local mechanical displacement in a second step. As will be shown, this allows us to exploit cylindrical symmetry for the electric surface charge distribution, but not for the vertical surface displacements. The effect of substrate bending due to in plane-stress, introduced by the piezoelectric constant d31, and the benefits of using bull’s eye electrode geometries with thick metallic backplates intended to reduce this effect are studied. A rigorous analysis and a largely simplified, but accurate approximation are compared. The application of this technique is demonstrated on a practical example for highly efficient and accurate determination of selected piezoelectric coefficients from surface topography measurements on such structures.

The Use of Excess Electric Charge for Highly Sensitive Protein Detection: Proof of Concept

In highly sensitive bioanalytical systems intended for the detection of protein biomarkers at low and ultra-low concentrations, the efficiency of capturing target biomolecules from the volume of the analyzed sample onto the sensitive surface of the detection system is a crucial factor. Herein, the application of excess electric charge for the enhancement of transport of target biomolecules towards the sensitive surface of a detection system is considered. In our experiments, we demonstrate that an uncompensated electric charge is induced in droplets of protein-free water owing to the separation of charge in a part of the Kelvin dropper either with or without the use of an external electric field. The distribution of an excess electric charge within a protein-free water droplet is calculated. It is proposed that the efficiency of protein capturing onto the sensitive surface correlates with the sign and the amount of charge induced per every single protein biomolecule. The effect described herein can allow one to make the protein capturing controllable, enhancing the protein capturing in the desired (though small) sensitive area of a detector. This can be very useful in novel systems intended for highly sensitive detection of proteins at ultra-low (≤10−15 M) concentrations.

Structure and Framework Association of Lewis Acid Sites in MOR Zeolite.

Zeolites, although key materials used in industrial processes, remain poorly understood on a molecular level despite their well-defined crystal lattices. In fact, obtaining a direct spectroscopic signatures and resolving the structure of Lewis acid sites (LAS) has remained a challenge. In this work, thanks to 1D and 2D 1H, 15N, and 27Al MAS NMR spectroscopy, carried out at different temperatures (from 298 down to 107 K), we were able to obtain the NMR spectroscopic signatures of LAS and Brønsted acid sites (BAS) in mordenite zeolite in the presence and the absence of adsorbed pyridine (Py). Combined with DFT modeling, this information enabled the structure of LAS to be revealed, namely (≡SiO)3Al sites interacting with pyridine, thus indicating that the corresponding base-free framework-associated sites are pseudo tricoordinated Al sites, namely tricoordinated Al sites interacting with an additional coordinated adjacent siloxane bridge. With this information in hand, we propose a molecular-level understanding on how the AlIV and AlVI framework and framework-associated sites evolve upon dehydration and exposure to Py into BAS and LAS, and their associated Py adducts. By measuring and analyzing the changes in quadrupolar coupling constants (CQ) that reflect electrical charge distribution around the nuclei, we further show that the lower CQ values observed at 298 K are due to residual dynamics that makes the electric field around aluminum nuclei more symmetric. Thus, NMR spectroscopic signatures of 27Al greatly vary with temperature; this information illustrates the importance of accounting for the temperature effect when confronting experimental and calculated CQ values of the corresponding aluminum sites in zeolites in order to obtain accurate structural assessment.

How does the electric field make a droplet exhibit the ejection and rebound behaviour on a superhydrophobic surface?

A droplet impinging on a superhydrophobic substrate in an electric field is an important process in droplet manipulation and electrostatic spraying. Here, the entire impinging dynamic of the droplet in a vertical electric field is studied by a visualization experiment and numerical simulation with OpenFOAM. We investigate the effect of an electrostatic force on droplet impact in depth, where four ejection modes and three rebound modes are found experimentally. In particular, the filamentous ejecting phenomenon occurs after a droplet impinging on a superhydrophobic substrate is first discovered. In the numerical simulation, the strong coupling between the dynamic distribution of the interface electric charge and the evolution of the droplet profile can lead to different ejection modes, and the different ejection behaviours are caused by the combined effects of electrostatic pressure, capillary pressure, dynamic pressure and static pressure on the droplet apex. A charge scaling law for the ejection droplets is proposed. Furthermore, a set of theoretical models is established, which can successfully predict the threshold electric capillary number for different droplet ejection modes. The results reveal some important characteristics for a droplet impinging on a superhydrophobic surface in an electric field, which could facilitate the design of electrically operated droplet equipment and guide the safe and stable operation of the device.

Effect of Loaded Glycyrrhizic Acid on PLGA Nano-particle on Treatment of Allergic Asthma.

Asthma is considered a complex disease of the respiratory system that is characterized by bronchoconstriction, airway inflammation, cough, dyspnea, and wheezing. Allergic reactions are the main reason behind asthma which is known as an important health problem with a high rate of morbidity and mortality in patients with respiratory diseases. Liquorice, the root of Glycyrrhiza, is primarily effective for asthma which is widely used in herbal medicine. In the present study, we designed nano-particles that carry Glycyrrhizic acid as the effective component of Liquorice. After Poly (D,L-lactide-co-glycolic acid) PLGA nanoparticle preparation and Glycyrrhizic acid loading, the morphology of the nanoparticle, the electric charge distribution, and drug-releasing ability were studied. Then the effect of Glycyrrhizic acid-PLGA on the animal model of allergic asthma was investigated. Glycyrrhizic acid-nanoparticle had a mean±SD size of 350±50 nm. about 67% of the effective component was released after 10 h. The interleukin (IL)-4, IL-5, IL-13, and IL-25 levels and the Muc5ac mRNA expression were decreased in the Glycyrrhizic acid-PLGA treated group. In addition, a significant decline was observed in goblet cell hyperplasia, mucus hyper-secretion, and eosinophilic inflammation around bronchi and vessels of the nano-drug treated group, compared with the asthmatic group. We found that Glycyrrhizic acid-PLGA nanoparticle had an anti-asthma effect which may be used as a new drug to cure asthma. It can prevent bronchial obstruction, breathlessness, and asthma attacks.

Electrically charged supermassive twin stars

By assuming that ultra dense hybrid neutron stars are endowed with a distribution of electric charge, we study the corresponding twin star solutions and their properties resulting from a sharp first order transition from confined hadronic to a deconfined quark phase. Two distinct quark matter equations of state with increasing stiffness are considered and the values for the maximum gravitational masses of the hadronic and hybrid twin configurations are obtained for different values of the total electric charge. Interestingly, our calculations indicate that sharp transitions make charged twin hybrid stars more massive than their neutral counterparts, and that the {2},{hbox {M}_{odot }} constraint from PSR J0740+6620 is surpassed for standard values of electric charge and can be considered stable only satisfying partial M/partial epsilon _0 > 0. In particular, our charged stellar models reach masses even higher than the unknown compact object measured in the GW190814 event.

The Effect of Fluorinated Solvents on the Physicochemical Properties, Ionic Association, and Free Volume of a Prototypical Solvate Ionic Liquid.

Solvate ionic liquid (SIL) synthesis and properties depend on a delicate balancing of cation-solvent and cation-anion interactions to produce materials containing only cation-solvent complexes and solvent-separated anions. Most SILs meeting these characteristics fall within the paradigm of oligomeric ethylene oxides (e.g. glymes and glycols) and lithium salts. Targeted functionalization of solvent molecules to achieve desired properties is a relatively unexplored avenue of research. Fluorinated solvents have significantly different electric charge distributions compared to their nonfluorinated analogs. We test the impact of solvent fluorination for a SIL created from equimolar mixtures of lithium bis(trifluoromethylsulfonyl)imide (LiNTf2 ) and triethylene glycol (TEG), hereafter [(TEG)1 Li]NTf2 . In the first experiment, TEG is partially substituted with 2,2,4,4,5,5,7,7-octafluoro-3,6-dioxaoctane-1,8-diol (FTEG). This leads to a precipitous decrease in ionic conductivity and larger quantities of ionically-associated Li(NTf2 )2 - species, as detected with vibrational spectroscopy. These observations suggest FTEG does not readily coordinate Li+ ions in a manner analogous to TEG. Computational studies reinforce this conclusion. Relative complex cation stabilities are ranked as [(FTEG)1 Li]+ >[(TEG)1 Li]+ . A second experiment adds FTEG as a diluent to [(TEG)1 Li]NTf2 . This places FTEG and TEG in competition to coordinate a limited number of Li+ ions. The resulting mixtures exhibit conductivity enhancement over the parent SIL and minimal changes in ion speciation due to the poor Li+ binding by FTEG compared to TEG. Positron annihilation lifetime spectroscopic studies point to increased amounts of free volume upon dilution of FTEG. This likely explains the origin of the conductivity and viscosity enhancements.

Electron-Positron Pair Production in Electro-Magnetic Field

At very high energies, pair production formation (γ + N → e+e-) exhibits a variety of intriguing properties. Analytically and quantitatively, the formation of Electron-Positron pairs in the Electro-Magnetic field of light nuclei has been calculated. In Ultra-Relativistic (UR) areas of incident photon energy, applying the resulting formulas to the energy distribution of the (e-, e+) operation. When we compare the results, we can observe that the Magnetic field of the target nucleus is more efficacious than the Electric field of the nucleus in the (e-, e+) operation. Furthermore, we can show that in Pair Production operation, the Differential Cross Section (DCS) owing to the target nucleus’s Electric Quadrupole (EQ) and Magnetic Octupole (MO) are bigger than the Differential Cross Section (DCS) attributable to the target nucleus’s Electric Charge (EC) distribution and Magnetic Dipole (MD).

Parametric Resonance in the Oscillations of a Charged Pendulum Inside a Uniformly Charged Circular Ring

We study the mechanical system consisting of the following variant of the planar pendulum. The suspension point oscillates harmonically in the vertical direction, with small amplitude $\varepsilon$, about the center of a circumference which is located in the plane of oscillations of the pendulum. The circumference has a uniform distribution of electric charges with total charge $Q$ and the bob of the pendulum, with mass $m$, carries an electric charge $q$. We study the motion of the pendulum as a function of three parameters: $\varepsilon$, the ratio of charges $\mu=\frac{q}{Q}$ and a parameter $\alpha$ related to the frequency of oscillations of the suspension point and the length of the pendulum. As the speed of oscillations of the mass $m$ are small magnetic effects are disregarded and the motion is subjected only to the gravity force and the electrostatic force. The electrostatic potential is determined in terms of the Jacobi elliptic functions. We study the parametric resonance of the linearized equations about the stable equilibrium finding the boundary surfaces of stability domains using the Deprit – Hori method.

Sudden discharge of young charged magnetars as a new model for FRBs

ABSTRACT We propose a new model for Fast Radio Bursts (FRBs) based on a sudden discharge of a charged young magnetar, caused by the short falling time-scale of oppositely charged particles on to the magnetar. In this scenario, curvature radiation is emitted by particles accelerated at relativistic by the strong electric fields produced by the disconnection and the subsequent reconnection of the magnetic field lines, a process triggered by the sudden discharge. We modelled the magnetars as charged neutron stars in the static approximation using the exterior metric by the Reissner–Nordström. We also adopted an electrical charge distribution proportional to the mass-energy density, although our results are not strongly sensitive to the specific star’s charge distribution, only to the total charge. Our calculations show that the discharge and emission time-scales are several milliseconds, compatible with the FRB phenomena for magnetars with a total charge of ∼1020 C and mass and radius in the range of 1.5–3.0 M⊙ and 10–45 km, respectively. Furthermore, the calculated total emitted power of a coherent pulse is $P_{\mathrm{ tot}}\sim 10^{42-43} \, \mathrm{erg\, s}^{-1}$, and the frequency range and time-scale are also consistent with FRBs astronomical observations. Finally, if the magnetar does not collapse after the discharge, the existence of FRB repeater sources cannot rule out the existence of a blast repetition after the time needed to magnetosphere recharges and produce a new discharge.

Electrostatics in a tortuous nanochannel in a newly developed curvilinear coordinate system

Although nanochannels in tortuous shape exhibit unusual transportational characteristics, the traditional theoretical analysis of nanofluidics in such kinds of systems remains challenging, partly due to their complicated boundary description. In this paper, by developing a curvilinear coordinate system for such tortuous nanochannels, we solve the electrostatic Poisson–Boltzmann equation analytically for a two-dimensional nanochannel, with its effectiveness confirmed through numerical calculation. The influences of the geometric profile on the distribution of electric potential, ionic concentration, and surface charge on channel walls are quantitatively evaluated in a facilitated way in terms of the curvilinear coordinates introduced. Such a technique can be widely applied to many nanofluidic systems in curved channels.

Error evaluation of defect shape identification using charge simulation method for static electricity

In this study, a numerical scheme for nondestructive inspection using static electricity is proposed. The relationship between the electric charges on the defect and the electric field at the observation points is described using the Fredholm integral equation for the first kind (IFK). A response function, which uses the relative coordinates between the electric charge and observation point as input variables, is derived. A system of linear equations, whose entries of the coefficient matrix are the kernels of IFK, is derived. Subsequently, an inverse algorithm is constructed to restore the electric charge distribution from the electric-field distribution. The Tikhonov regularization method is used to obtain the regularized solution because of the ill-posedness of the coefficient matrix. The optimal regularization parameter is determined using the L-curve criterion. The accuracy of the proposed method is verified through numerical experiments. The observable electric field is determined mathematically through forward analysis. A formula that quantitatively evaluates the error is then defined. It is confirmed that the inverse analysis result provides a more accurate solution than the raw data of the electric field.

Rearrangements in the conformational structure of polyampholytic polypeptides on the surface of a uniformly charged and polarized nanowire: Molecular dynamics simulation

Molecular dynamics has been employed to study electrically induced rearrangements in the conformational structure of polyampholytic polypeptides adsorbed on the surface of a gold nanowire with a uniform distribution of electric charges and on the surface of a transversely polarized nanowire. The angular and radial distributions have been calculated for the average densities of polypeptide atoms. On the uniformly charged surface of the nanowire, the macromolecular "fringe" consisted of three layers: two differently charged layers and a neutral layer that was located between them. On the surface of a transversely polarized nanowire, swelling of the macromolecular “fringe” has been observed in the direction of polarization. The thickness of the polyampholytic "fringe" on a uniformly charged nanowire and the ratio of the thickness of the "fringe" in the direction of polarization to the thickness in the orthogonal direction in the cross section turned out to be the greater, the greater the distance between the oppositely charged units in the polyampholyte.

A Magic Wand Selection Tool for Surface of 3D Model

Introduction: segmentation of 3d shapes is a fundamental problem in computer graphics and computer-aided design. It has received much plays attention in recent years. The analysis and research methods of 3d mesh models have established reliable mathematical foundations in graphics and geometric modeling. Compared with color and texture, shape features describe the shape information of objects from geometric structure features. And it an important role in a wide range of applications, including mesh parameterization, skeleton extraction, resolution modeling, shape retrieval, character recognitio,, robot navigation, and many others. Methods: The interactive selection surface of models is mainly used for shape segmentation. The common method is boundary-based selection, which requires user input some stokes near the edge of the selected or segmented region. Chen et al.introduced an approach to join the specified points form the boundaries for region segmentation on the surface. Funkhouser et al. improve the Dijkstra algorithm to find segmentation boundary contour. The graph cut algorithm use the distance between the surface and its convex hull as the growing criteria to decompose a shape into meaningful components. The watershed algorithm, widely used for image segmentation, is a region-growing algorithm with multiple seed points. Wu and Levine use simulated electrical charge distributions over the mesh to deal with the 3D part segmentation problem. Other methods using a watershed algorithm for surface decomposition. Results: We implemented our algorithm in C++ and Open MP and conducted the experiments on a PC with a 3.07 GHz Intel(R) Core(TM) i7 CPU and 6 GB memory. Our method can get a similar region under different interaction vertices in specific regions. Figure 6a and Figure 6b are the calculation results of tolerance region selection of this algorithm in a certain region of kitten model at two different interaction points, from which we can see the obtained regions are similar from different vertices in this region. Figure 6c and figure 6d are two different interactive points in the same region, and the region selection results are obtained by Region growing technique. Discussion: In this paper, we proposed a novel magic wand selection tool to interactive select surface of 3D model. The feature vector is constructed by extracting the HKS feature descriptor and means curvature of 3D model surface, which allows users to input the feature tolerance value for region selection and improves the self-interaction of users. Many experiments show that our algorithm has obvious advantages in speed and effectiveness. The interactive generation of region boundary is very useful for many applications including model segmentation. Conclusion: In consideration of a couple of requirements including user-friendliness and effectiveness in model region selection, we propose a novel magic wand selection tool to interactive selection surface of 3D models. First, we pre-compute the heat kernel feature and mean curvature of the surface, and then form the eigenvector of the model. Then we provide two ways for region selection. One is to select the region according to the feature of tolerance value. The other is to select the region that aligns with stroke automatically. Finally, we use the geometry optimization approach to improve the performance of the computing region con-tours. Extensive experimental results show that our algorithm is efficient and effective.

Simulation of bright–dark soliton solutions of the Lonngren wave equation arising the model of transmission lines

In this study, the auxiliary equation method is applied successfully to the Lonngren wave equation. Bright soliton, bright–dark soliton solutions are produced, which play an important role in the distribution and distribution of electric charge. In the conclusion and discussion section, the effect of nonlinearity term on wave behavior in bright soliton traveling wave solution is examined. The advantages and disadvantages of the method are discussed. While graphs representing the stationary wave are obtained, special values are given to the constants in the solutions. These graphs are presented as 3D, 2D and contour.