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To study the effects of co-ions on iodide ion transport through a novel anion exchange paper membrane containing trimethylhydroxypropylammonium groups with approximately 0.30 meq. g−1 dry-membrane ion exchange capacity, transmembrane potential, membrane conductance and ionic fluxes were measured in the concentration-cell system for seven kinds of iodine salts (1:1-electrolytes) at 10−3 to 10−1 mol dm−3. For analysis of ion transport, the electroconductive membrane permeability, representing the solution/membrane ion distribution due to electrostatic effects, and the diffusional membrane permeability, representing the migration speed of ions within the membrane phase, concerning ion pair diffusion, and increasing with co-ion penetration and diffusion, were introduced in terms of linear phenomenological equations. Electroconductive membrane permeabilities of iodide ions were found to increase linearly with increasing hydrated co-ion radii; r2=0.855, while diffusional membrane permeabilities of iodide ions increased linearly with increasing crystal co-ion radii; r2=0.899. These results for a paper membrane differ from those of synthetic amphoteric membrane and nanoporus membranes in which ions of both charges penetrate equally, in which membrane permeabilities decreased with increasing co-ion radii. This suggests that iodide ion transport may be partially controlled by co-ion transport dependent on surface cationic charge density rather than ion radii in the anion exchange paper membrane, as the pores are large enough for ions to freely permeate within membrane matrix. [Copyright &y& Elsevier]

Abstract: Latent fingermarks were deposited onto white office paper samples containing writing or printing from several media (for example, ballpoint pens and laser printers). Fingermarks were deposited both before and after writing/printing. The marks were then treated with appropriate latent fingermark development techniques. Once treated, they were examined with standard techniques applied in document examination (filtered light analysis, electrostatic detection device and Raman spectroscopy) to determine the sequence of application. The results suggested that the sequence of laser printing and latent marks could be determined via electrostatic detection device examination of undeveloped and Ninhydrin developed samples. [Copyright &y& Elsevier]

Abstract: To produce bioactive papers, i.e. papers incorporating biomolecules that are useful for analyte detection, adequate immobilization strategies should be devised. In this article, the physical immobilization behavior and activity of the enzyme horseradish peroxidase (HRP) on various papermaking substrates were studied. The papermaking substrates included amorphous and crystalline cellulose, calcium carbonate, styrene butadiene latex, polystyrene, and both negatively charged rayon and rayon with a positively charged layer. It was found that HRP adsorption improves as the hydrophobicity of the substrate increases; however, excessive hydrophobicity produces enzyme deactivation. HRP–calcium carbonate binding was weak and the enzyme loading was scant. These results provided a possible explanation for the poor analytical signals observed in pigment-coated papers when used as bioactive paper supports. Electrostatic effects played a minor role in HRP adsorption behavior. [Copyright &y& Elsevier]

Variable stiffness surgical robots are capable of adapting to different surgical scenarios, providing enhanced stability during minimally-invasive surgeries. Prevalent methods for achieving variable stiffness, such as lockable mechanisms, granular jamming, and phase transition materials, have inherent weaknesses including difficulties in downsizing and issues related to excessive temperatures. In this paper, a novel lockable mechanism based on electrostatics is proposed, along with a tendon-driven surgical robot prototype that utilizes this locking mechanism to achieve variable stiffness. The proposed mechanism involves the installation of graphite electrode sheets at each joint, with silica gel being used as the dielectric material. By applying a high voltage to the electrode sheets, adjacent joints automatically absorb and restrict relative sliding, effectively preventing joint rotation and ensuring complete joint locking. An electrostatic adhesive braking force model for the robot is presented. Simulations and experiments conducted based on the robot prototype have been carried out to validate the locking capability of the proposed mechanism and the accuracy of the electrostatic adhesive braking force model. [ABSTRACT FROM AUTHOR]

• Multi-scale fusion neural network is proposed to solve the elliptical interface problem. • Multi-scale fusion neural network can better capture "sharp turns" on the interface. • Solutions by multi-scale fusion neural network can better preserve the C 0 continuity while keeping the flux jumps. • We apply multi-scale fusion neural network to calculate the electrostatic potential of immersed biomolecules. In this paper, we construct a novel multi-scale fusion network as a new deep learning structure to solve the elliptic interface problem. Compared with the results of the fully connected neural network and ResNet, the new multi-scale fusion network is shown to be able to better capture "sharp turns", leading to the improved accuracy. Furthermore, its numerical solutions can preserve the C 0 continuity of the solution while keeping the flux jumps passing through different interfaces, thus maintaining the physics of the differential equation. Then, as an application, the new method is applied to solve the three-dimensional Poisson-Boltzmann equations to calculate the electrostatic potential of immersed biomolecules. Numerical experiments demonstrate the effectiveness of our new method compared to the results obtained by the finite element method. [ABSTRACT FROM AUTHOR]

In this paper, the local and nonlocal Poisson–Boltzmann equations are studied on their linear and nonlinear models with spherical symmetry. In particular, the exact solutions of the linear and nonlinear modes are obtained in either analytical expressions or simplified boundary value problems, whose solutions can be found easily via the Maple procedure dsolve for example. Numerical results confirm the derived solution properties, and show that the two new linear models proposed in this paper can have higher accuracy than the two conventional linear models in approximation to the local and nonlocal nonlinear models, respectively. [ABSTRACT FROM AUTHOR]

Abstract The electrostatically controlled deployable membrane antenna (ECDMA) is expected to become one of the next generation spaceborne antennas due to its lightweight, large-aperture and high-precision advantages. However, form-finding of the ECDMA is a challenge that related to the cable-membrane structure and electrostatic force. This paper presents an extended force density method (EFDM) that identifying the equivalent cable force density to replace the orthotropic membrane element stress by the virtual work principle. Then the force density equilibrium equations of the cable-membrane electrode structure and the membrane reflective surface of the ECDMA are deduced based on the EFDM and the corresponding form-finding strategies are given, respectively. Simulations and experiments show that the EFDM presented in this paper is effective for the form-finding design of the ECDMA. Highlights • The EFDM is applicable to the form-finding of orthotropic membrane structure. • The form-finding design of the cable-membrane electrode structure and the membrane surface need different strategies. • The parabolic membrane reflective surface wrinkling is worth of study. [ABSTRACT FROM AUTHOR]

• FWVM module has 2 stages of Cock-Croft Walton voltage multiplier circuit. • The FWVM unit is fed by a center tapped, 20 kHz high voltage transformer. • The maximum ground fault current is 50 A as per simulation results. • The 100 kV, 100 mA FWVM module is designed, fabricated and tested at 100 kV. The 100 kV, 100 mA DC full-wave voltage multiplier (FWVM) modular unit is being developed for accelerator power supply and other plasma applications at Institute for Plasma Research (IPR). The high voltage engineering design involved in fabrication architecture and assembly of 100 kV, 100 mA DC FWVM module is the main focus of this paper. This FWVM module has 2 stages of Cock-Croft Walton voltage multiplier circuit considering the required optimum number of stages for final 500 kV voltage output. The FWVM unit is fed by a center tapped High Voltage High Frequency (HVHF) transformer. Electrical circuit simulations have been carried out to ensure the electrical performance parameters. The maximum value of the fault current during ground fault is 50 A as per simulation results. The 100 kV, 100 mA FWVM module is designed, fabricated and tested at 100 kV. Simulation Results, fabrication details, engineering design details and test results have been presented in this paper. [ABSTRACT FROM AUTHOR]

• A holistic assessment of EHD technologies, fundamentals, limitations, and prospects. • Introducing a theoretical tool to assess EHD's effectiveness window. • EHD technologies cannot induce pressures above 300 Pa in gases. • EHD technologies cannot induce pressures above 300 kPa in liquids. • None of the EHD applications has reached to final technology readiness level yet. Electrohydrodynamics (EHD) refers to the interaction of electrical forces with fluids, whether liquids or gases. EHD has established itself as an energy-efficient, highly versatile, and effective tool to influence fluids without moving mechanical parts. Therefore, it has found applications in various fields of science and engineering. This review paper categorizes the most notable applications of EHD into five areas, grouping them based on their shared operational principles. The first application area includes electrospinning, electrospraying, and EHD jet printing. The other application areas are EHD-based heat and mass transfer, active airflow control, air filtration or so-called electrostatic precipitators, and EHD-based pumps, thrusters, and blowers. For each application, the fundamental theories are presented, and a summary of the recent advances is discussed. Moreover, a critical analysis of their current limitations and their envisaged future is provided. Finally, the overall application areas status is analyzed using indicators such as technology readiness level (TRL), scalability, and effectiveness compared to similar technologies in their respective fields. The analysis across the five technology areas indicates that electrostatic precipitators are mature and effective, while EHD-based pumps, thrusters, and blowers are in the early stages of development. Electrospinning, electrospraying, and EHD jet printing show promise with moderate technology readiness, while EHD-based heat and mass transfer and EHD-based airflow control fall within a mid-range, reflecting ongoing development. As many reviews on EHD focus on specific applications, the contribution of this review is to draw a comprehensive map of different applications, illustrate their similarities and differences, integrate current knowledge, and highlight areas for further investigation. This interdisciplinary perspective enables researchers to identify various capabilities of EHD and benefit from advances made by other established applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding the behavior and properties of spherical polyelectrolyte brushes (SPEBs), which are polyelectrolyte brushes grafted to a spherical core, is fundamental to many applications in biomedical, chemical and petroleum engineering as well as in pharmaceutics. In this paper, we study the pH-responsive electrostatics of such SPEBs in the decoupled regime. In the first part of the paper, we derive the scaling conditions in terms of the grafting density of the PEs on the spherical core that ensure that the analysis can be performed in the decoupled regime. In such a regime the elastic and the excluded volume effects of polyelectrolyte brushes (PEBs) can be decoupled from the electrostatic effects associated with the PE charge and the induced EDL. As a consequence the PE brush height, assumed to be dictated by the balance of the elastic and excluded volume effects, can be independent of the electrostatic effects. In the second part, we quantify the pH-responsive electrostatics of the SPEBs – we pinpoint that the radial monomer distribution for a given brush molecule exhibit a non-unique cubic distribution that decays away from the spherical core. Such a monomer distribution ensures that the hydrogen ion concentration is appropriately accounted for in the description of the SPEB thermodynamics. We anticipate that the present analysis, which provides possibly one of the first models for probing the electrostatics of pH-responsive SPEBs in a thermodynamically-consistent framework, will be vital for understanding the behavior of a large number of entities ranging from PE-coated NPs and stealth liposomes to biomolecules like bacteria and viruses. [ABSTRACT FROM AUTHOR]

Guidance-plate-covered electrostatic precipitators (GPC-ESPs), which are ESPs with perforated guidance plates that cover their collecting electrodes, have been experimentally proven to have higher collection efficiencies than their traditional counterparts. The key to the GPC-ESP׳s success in high collection efficiency is that particles that enter the gaps between the guidance plate and the collecting electrode have lower chances of returning to the environment. This paper presents the characteristics of the GPC-ESPs, and discusses how the parameters of interest affect collection efficiency. The numerical model is carried out by modeling the particle transport, flow field, and electric field. Results show that when the diameters of the holes on the guidance plate are larger, the flow recirculation is stronger and allows for more particles to easily enter the gaps through these holes. The electrical characteristics are dependent on the repelling voltage and the diameter of the holes. The collection efficiency is also discussed in terms of two dimensionless parameters: the Stokes numbers (the ratio of inertia force to viscous drag force) and the electrostatic numbers (the ratio of electrostatic force to viscous drag force). Results show that a lower Stokes number and a higher electrostatic number results in a higher collection efficiency. The collection efficiency remains numerically unchanged when the electrostatic number stays the same. This paper also demonstrates a set of simulations to simulate particle re-entrainment. Results show that when particle re-entrainment happens at the collecting electrode, none of the particles reenter the environment through the holes of the guidance plate. When particle re-entrainment happens at the guidance plate, some of the particles escape the collector, but most of the particles enter the gaps and are recaptured at the collecting electrode, due to either flow recirculation or induced electrostatic forces. [ABSTRACT FROM AUTHOR]

In this paper, we analyze and give experimental evidence of the efficiency of pulsed-mode actuation for the characterization of capacitive MEMS resonators. In particular, we show how to process the output signal in pulsed mode to eliminate parasitic feedthrough effects and characterize the resonator. We test our approach on a pressure sensor, developed by THALES Avionics, used for avionics applications. Contrary to the existing state-of-the-art techniques, the method described in this paper can be used to characterize an electrostatic MEMS without a spectrum analyzer or high-performance ADC. [ABSTRACT FROM AUTHOR]

Abstract: This survey paper describes NCLab (Network Computing Laboratory), a novel cloud computing service that is pioneering free web browser access to finite element simulations. Presently, these include general second-order linear partial differential equations, linear elasticity problems, and electrostatics problems (all in two spatial dimensions). The modeling process consists of geometry definition in the web browser, mesh generation on a remote server, specification of material parameters and boundary conditions in the web browser, computation on a remote server, and visualization in the web browser. The module supports curvilinear elements and higher-order finite element discretizations. In this paper we present the modeling process using a sample electrostatics problem. Numerical results are provided. [Copyright &y& Elsevier]

Abstract: This paper explores the concept of using electrostatic forces for deployment of gossamer space structures. The Electrostatically Inflated Membrane Structure (EIMS) uses two conducting membranes that are interconnected through membrane ribs. An absolute electrostatic charge is applied to the structure through active charge emission. This causes repulsion between layers of lightweight membranes that inflates the EIMS system and tensions the membranes. Assuming positive tensions, the EIMS system is modeled as a rigid system. Typical orbital perturbations are considered such as solar radiation pressure, differential gravity, and atmospheric drag which may compress the structure leading to shape destabilization. Restricting the analysis in this paper to flat membranes, the minimum potentials required to exactly compensate for the worst case scenario of differential solar radiation pressure at geostationary altitudes are estimated to be on the order of hundreds of volts. In low Earth orbit, voltage magnitudes of several kilovolts are required to reach an inflation pressure to offset the normal compressive drag pressure. [Copyright &y& Elsevier]

Abstract: ASME Technical Paper ES2010-90396 “Solute Ion Coulomb Force Monopole Motor and Solute Ion Linear Alignment Propulsion” by the author describes a motor that is based on an arrangement of solute ion electric field monopoles.[1] That is, through a process called capacitive deionization, sodium and chlorine ions in salt water are captured and confined by an electrically conductive material to form electric field monopoles. At least four of the like charged monopoles (all negative or all positive) can be arranged on a disc. At least one stationary monopole of the same charge is placed adjacent to the disc and positioned so that a repulsive electric field is formed between the stationary monopole and at least one of the monopoles positioned on the disc so that the disc is then forced to rotate a shaft at the center of the disc. This paper analyzes the behavior of the dielectric materials forming part of the monopoles to show that the net torque on the motor is greater than zero and also illustrates a novel effect of polarization of a dielectric material positioned between two like-charged monopoles as occurs in the configuration of the monopole motor and a deficiency in the conventional closed path analysis for work performed during movement of electric charges that emit electrostatic fields by failing to consider the effects of dielectric materials in shielding the electrostatic fields. The monopole motor connected to an to electrical generator can provide continuous on-board electrical power to electrical loads for local and deep space applications including power to electrode assemblies designed for linear alignment of like-charged solute ions as a means of propulsion and particle acceleration as described in the ES2010-90396 paper. Details of the monopole motor and the propulsion are available in WO 2008/024927 A2 (and US2010/0199632 A1) “Solute Ion Coulomb Force Acceleration and Electric Field Monopole Passive Voltage Source” by the author Ref.[2]. [Copyright &y& Elsevier]

Abstract: This paper deals with the study of parametric oscillation of an electrostatically actuated microbeam using variational iteration method. The paper considers a micro-beam suspended between two conductive micro-plates, subjected to a same actuation voltage. The nonlinear governing differential equation of motion about static equilibrium position using calculus of variation theory and Taylor series expansion has been linearized and implementing a Galerkin based reduced order model a Mathieu type equation has been obtained. By improving variational iteration method combining with method of strained parameters transition curves, separating stable from unstable regions have been obtained. The results of variational iteration method, perturbation and direct numerical integration methods for some cases selected from different regions (stable and unstable regions) have been compared. [Copyright &y& Elsevier]

• Gold and silica nanoparticles interact differently with the plasma membrane. • Variation in nanoparticle-membrane van der Waals interactions causes the difference. • This difference affects the specific and non-specific adhesion of the nanoparticles. • Choice of the ligands and the nanoparticle cytotoxicity effects are also affected. Making a nanoparticle (NP) approach and interact with a plasma membrane (PM) through the receptor-ligand interaction is key for applications like targeted drug delivery, cellular imaging, and theranostics. In this paper, we show that the van der Waals (vdW) interactions dominate the electrostatics ensuring that a gold NP approached the PM more spontaneously as compared to a silica NP. The negative σ (charge density) of a PM induces a negative electrostatic potential at the surface of the approaching gold NP and the silica NP; however, there is very little difference between these induced values due to a small electric double layer at the physiological salt concentration (c ∞). Hence there is very little difference in the electrostatic repulsion between the two cases, while the PM-NP vdW attraction is much more for the gold NP as a result of a larger Hamaker constant. Therefore, in comparison to the gold NP, the silica NP would (a) undergo a promotion of the specific adhesion and a prevention of the non-specific adhesion simultaneously for a larger σ − c ∞ phase space including the physiological conditions, (b) necessitate a larger length of the ligands to trigger spontaneous receptor-ligand interactions, and (c) require a larger driving force for force-driven receptor-ligand interactions. [ABSTRACT FROM AUTHOR]

Abstract Due to the complex and harsh operation conditions, like corrosion, aging cable and static electricity, of electrical traction drive system, ground fault will generate large short circuit current to harm the key components. Effective fault diagnosis is important, but also challenging. The conventional method used for ground fault detection only takes advantage of voltage measurements of DC-link. Other measurements onboard are also available, which are correlated with the voltage measurements. Taking the correlation into account will improve the detection performance. To this end, this paper presents a data-driven solution, which makes full use of the correlation between the voltage measurements with other measurements onboard. The proposed method consists of two components: (1) a canonical correlation analysis-based fault detection method, which takes into account the correlation within measurements; (2) a fault isolation method by means of the fault direction, which can be obtained with the available faulty data stored in the long-term operation. The developed method is applied to a traction drive system. It is shown that the proposed approach is able to improve the fault detection and isolation performance significantly with respect to three performance indicators, namely fault detection rate, detection delay and correct isolation rate, in comparison with the conventional method, which only uses the voltage measurements of DC-link. Highlights • Introduce characteristics of typical ground faults in the electrical traction system. • An CCA solution is proposed using the correlation between the measurements onboard. • A fault isolation method is proposed using the residual and fault direction info. [ABSTRACT FROM AUTHOR]

Abstract This study presents a novel control scheme for voltage regulation of a negative output cascade ultra-lift Luo converter (NOCULLC). Due to the complicated high order model of the converter, its performance is degraded against large load variations, input voltage changes and parametric uncertainties. In order to enhance the converter behavior, a PI compensator and a sliding mode current controller are combined to control the fourth order NOCULLC worked in a wide range of operating conditions. Because of the non-minimum phase structure of the converter, the output voltage of the converter is indirectly regulated by enforcing the input inductor current to track its reference signal. The sliding mode current controller improves the dynamic and static performances of the converter by minimizing the inrush current of the input inductor of the converter and also, the PI controller eliminates the steady state error of the output voltage of the converter. The closed loop system stability is demonstrated by using sliding mode theory. Furthermore, this paper proposes a systematic procedure to compute the gains of the controller based on the stability constraints which guarantees robustness of the developed controller. The experimental results show the robustness and effectiveness of the proposed controller against parametric variations and uncertainties of the converter. Also, a comprehensive comparison of the general aspects of the properties between the developed method and other existed controllers is provided. Highlights • Operation analysis of a NOCULL converter. • A PI and HM sliding mode current controller is designed for converter. • Experimental results of the converter under the proposed controller are illustrated. • Comparison between the proposed controller and a simple controller is presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the use of the electrostatic layer-by-layer (LbL) technique for the preparation of bioanodes with potential application in ethanol/O2 biofuel cells. More specifically, the LbL technique was employed for immobilization of dehydrogenase enzymes and polyamidoamine (PAMAM) dendrimers onto carbon paper support. Both mono (anchoring only the enzyme alcohol dehydrogenase, ADH) and bi-enzymatic (anchoring both ADH and aldehyde dehydrogenase, AldDH) systems were tested. The amount of ADH deposited onto the Toray® paper was 95ngcm−2 per bilayer. Kinetic studies revealed that the LbL technique enables better control of enzyme disposition on the bioanode, as compared with the results obtained with the bioanodes prepared by the passive adsorption technique. The power density values achieved for the mono-enzymatic system as a function of the enzyme load ranged from 0.02 to 0.063mWcm−2 for the bioanode containing 36 ADH bilayers. The bioanodes containing a gas diffusion layer (GDL) displayed enhanced performance, but their mechanical stability must be improved. The bi-enzymatic system generated a power density of 0.12mWcm−2. In conclusion, the LbL technique is a very attractive approach for enzyme immobilization onto carbon platform, since it enables strict control of enzyme disposition on the bioanode surface with very low enzyme consumption. [ABSTRACT FROM AUTHOR]

In many industrial processes, electrostatic charges are inevitable and affect the hydrodynamic behavior and heat transfer ability of chemical equipment. A comprehensive study of the electrostatic effect on bubble behavior, particle fluctuation velocity and heat transfer coefficient in the fluidized bed with a central jet has been evaluated in this paper by Eulerian-Eulerian two-fluid model coupled with electrostatic model and energy model. The simulated voidage profiles at different positions, bubble detachment time and initial bubble diameter are compared with experimental results from the literature without charge. The bubble behaviors including bubble frequency and bubble numbers, combined with particle fluctuation parameters are analyzed in both charged and uncharged system. The electrostatic effect on two kinds of heat transfer coefficients is quantitatively compared, namely bubble to emulsion phase heat transfers based on the gas throughflow velocity and gas-solid local heat transfer coefficient. Simulation results show that electrostatic charges decrease bubble numbers and granular temperature, whereas the averaged heat transfer coefficients are enhanced. Overall, the electrostatic effect on the hydrodynamic and heat transfer characteristics can be revealed. [ABSTRACT FROM AUTHOR]

Abstract This paper deals with the mathematical and numerical analysis of a nonlinear 2D transient magnetic model when the source data are given in terms of the voltage drop excitations in conductors and the remanent magnetic flux for permanent magnets. The formulation consists of a distributed nonlinear magnetostatic model with time appearing as a parameter, and a circuit equation linking currents and voltage drops. This last equation is used to express the problem as an implicit ODE system whose operator involves the resolution of the distributed model. The model is spatially discretized using a finite element method and an implicit Euler scheme is employed for time discretization. We perform the mathematical analysis of the problem at both the continuous and discrete levels and obtain an error estimate that is illustrated with some numerical results. [ABSTRACT FROM AUTHOR]

Highlights • A nonlinear pedal like FGM microresonator under electrostatic actuation is modeled. • Both softening-type and hardening-type behaviors are observed in the system. • Pull-in voltages are calculated for various FG material profiles and gap distances. • Internal resonance of 1:2 ratio between the two modes of the system is studied. • Using FG material provides a wider frequency bandwidth during design process. Abstract In this paper a nonlinear pedal like microresonator made of Functionally Graded material is introduced and modeled. Using Lagrangian formulation nonlinear equations of motion of the system are derived and the natural frequencies and mode shapes are extracted by linear analysis. The effects of various parameters such as geometry, FG material index and DC voltages on the natural frequencies and mode shapes are investigated. Static pull-in voltages of the system are obtained and it is found that depending on the type of actuation, both softening and hardening behaviors can be observed in the system. The results are compared with previous studies and finite element method where a good agreement is achieved. A two-mode reduced order model along with first-order averaging technique is implemented to derive the asymptotic dynamic equations of motion. The effects of different parameters including AC actuation level, damping and material power index on the dynamic response of the system are studied around resonance conditions. It is observed that when the system parameters are adjusted properly, the directly excited in-plane mode, in turn excites the out-of-plane torsional mode of the structure through internal resonance of 1:2 ratio within a specific frequency bandwidth. A wide range of frequency will be available by changing only the power index of the material and the system can be manipulated to be used in various MEMS applications such as mass sensors and RF filter-mixer devices. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

This paper takes a detailed look at the operation of the electrostatic soot sensor and its potential use to monitor motor vehicle particulate matter emissions. Charged soot particles entering the sensor are trapped and grow into dendritic soot structures aligned with the electric field. Above a critical length, the electrostatic force fractures the dendrites, producing fragments that carry sufficient charge between the electrodes to generate nanoamp level currents. While proportional to soot concentration, this current also responds to flow variations, which limits the sensor's application in areas such as motor vehicle on-board diagnostics. The present work demonstrates that this flow dependence is closely related to the sensor's response to variations in electric field. The measured response to step changes in applied voltage agrees very well with a kinetic model of electric field induced dendrite growth and fragmentation. Variations in flow induce fluctuations in sensor current as dendrites reorient in response to the drag force and find themselves above or below the critical length for fragmentation. This mechanism qualitatively fits the experimental data. In engine exhaust applications, variation of exhaust flow with engine operation interferes with time resolved soot measurement. This interference partially cancels out when averaged over time, rendering the electrostatic soot sensor a potentially viable means to distinguish diesel particulate filter performance. [ABSTRACT FROM AUTHOR]

Abstract: In a series of seminal papers, Thomas J. Stieltjes (1856–1894) gave an elegant electrostatic interpretation for the zeros of classical families of orthogonal polynomials, such as Jacobi, Hermite and Laguerre polynomials. More generally, he extended this approach to the zeros of polynomial solutions of certain second-order linear differential equations (Lamé equations), the so-called Heine–Stieltjes polynomials. In this paper, a class of electrostatic equilibrium problems in , where the free unit charges are in presence of a finite family of “attractors” (i.e., negative charges) , is considered and its connection with certain class of Lamé-type equations is shown. In addition, we study the situation when both and , by analyzing the corresponding (continuous) equilibrium problem in presence of a certain class of external fields. [ABSTRACT FROM AUTHOR]

Abstract: This paper is dedicated to studying dynamic effects in thin liquid films (TLF) containing ionic surfactants. The standard theory of TLF drainage has been developed without considering the electrical double layer (EDL) in the hydrodynamic equations, although EDL always exists. In addition, it has been found that this theory very well describes the drainage of TLF containing non-ionic surfactants in the presence of electrolytes. The inclusion of EDL into the hydrodynamics of TLF complicates the theory, producing additional dynamic effects during film drainage. For example, a gradient of electrostatic disjoining pressure across the film arises, thus causing non-uniform electrostatic repulsion between the film surfaces. This paper analyzes the hydrodynamics of TLF with EDL. A new equation of drainage was derived. This equation accounts for the non-uniform distribution of surface charges during the films drainage, which is coupled with non-uniform electrostatic repulsion between the film surfaces and results in faster film drainage. The theory was tested with drainage experiments on TLF with ionic surfactants. Foam films containing sodium dodecyl sulfate (SDS) in the presence and in the absence of added electrolyte were studied and the experimental data compared to the theoretical predictions. The experimental results, however, disagree with the theory. For example, the kinetic equation predicted faster film drainage for foam films at low ionic strength; at high ionic strength the theory tends to “Reynolds drainage”. Inversely, the experiment exhibited slower drainage than predicted by the Reynolds equation in both cases of low and high ionic strengths. Numerical simulations yielded . In addition, cases of “positive” and “negative” velocity of film surfaces were shown. Despite the sign of the velocity the dependence remained. The analysis showed similarity between the experimental data and the prediction of the Manev–Tsekov–Radoev (MTR) drainage model at . The analysis showed rather complex dynamics of the film drainage. The paper calls upon further development on this topic. [Copyright &y& Elsevier]

Abstract: In this paper we investigate the behavior of a fluidized bed of silica nanoparticles under the influence of externally applied vibrations and an electrostatic field. We have observed that the application of these fields separately has opposite effects on bed expansion. On one hand, vertical vibrations enhance bed expansion as the vibration intensity is increased up to a critical value. On the other hand, an electrostatic field applied in the horizontal direction, hinders bed expansion. In previous research papers, it has been suggested that the size of nanoparticle agglomerates could be affected either by vibration or by the action of the electric field. Using the modified Richardson–Zaki method to analyze our experimental data we find that vertical vibration tends to decrease the average agglomerate size in agreement with previous research. However, in this work we look further into the physical mechanisms which affect the response of the fluidized bed. Our results suggest that both vibration and the electric field produce a significant perturbation to the flow of agglomerates within the fluidized bed. Vibration transmits a vertical motion to the agglomerates that enhances bed expansion until the vibration velocity becomes of the order of the expected rising velocity of macroscopic bubbles. At this critical point, bubble growth is stimulated by vibration. A horizontal electrostatic field produces a drift of the charged agglomerates toward the walls that gives rise to fluidization heterogeneity and bed collapse. When both fields are simultaneous applied, these opposed effects can be practically compensated. [Copyright &y& Elsevier]

Abstract: This paper presents a new topology optimization scheme for nonlinear electrostatic systems actuated by Coulomb’s forces. For successful optimization, computational issues such as (i) alternating governing equations with respect to spatially defined design variables, (ii) imposing interaction boundary conditions between insulator (air) and conductor (solid) and (iii) control of minimum geometrical feature sizes must be addressed. To address the first two issues, the paper presents a monolithic formulation based on continuum mechanics theory which simultaneously calculates the electric potential and structural displacements. To interpolate between insulator and conductor with continuous design variables, the monolithic approach distinguishes between the permittivity value of the electric Poisson’s equation and that of Maxwell’s stress tensor. For the optimization, standard material interpolations are used for Young’s modulus and permittivity values. Moreover, a recently developed morphology filter is applied to control electrode gaps and other geometrical features. [Copyright &y& Elsevier]

Abstract: The electrostatic process for imaging indentations on documents using the ESDA device is investigated under controlled experimental settings. An in-house modified commercial xerographic developer housing is used to control the uniformity and volume of toner deposition, allowing for reproducible image development. Along with this novel development tool, an electrostatic voltmeter and fixed environmental conditions facilitate an optimization process. Sample documents are preconditioned in a humidity cabinet with microprocessor control, and the significant benefit of humidification above 70% RH on image quality is verified. Improving on the subjective methods of previous studies, image quality analysis is carried out in an objective and reproducible manner using the PIAS-II. For the seven commercial paper types tested, the optimum ESDA operating point is found to be at an electric potential near −400V at the Mylar surface; however, for most paper types, the optimum operating regime is found to be quite broad, spanning relatively small electric potentials between −200 and −550V. At −400V, the film right above an indented area generally carries a voltage which is 30–50V less negative than the non-indented background. In contrast with Seward''s findings [G.H. Seward, Model for electrostatic imaging of forensic evidence via discharge through Mylar–paper path, J. Appl. Phys. 83 (3) (1998) 1450–1456; G.H. Seward, Practical implications of the charge transport model for electrostatic detection apparatus (ESDA), J. Forensic Sci. 44 (4) (1999) 832–836], a period of charge decay before image development is not required when operating in this optimal regime. A brief investigation of the role played by paper-to-paper friction during the indentation process is conducted using our optimized development method. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the mixing and residence time distribution behaviour of an experimental electrically enhanced column contactor in which electrically charged drops of water were fed into an organic liquid phase of sunflower oil across which a non-linear electrical field was maintained. The effects of electrical field strength upon mixing in the continuous phase were determined and a significant increase in mixing was observed as the field strength was increased. A quantitative theoretical development describing the observed behaviour is also presented. The mixing is described by simultaneous consideration of the movement of the drop phase and the continuous liquid phase. The drop motion, after formation at the charged nozzle and during the subsequent trajectory motion under the influence of the non-linear electric field, is analysed. The interaction between the drop motion and the velocity field of the continuous phase is thus described. The paper describes theoretical prediction of the interactions between charged drops and the electrodes. These interactions can exert a strong influence on the overall residence time of drops passing through the column, and potentially on the velocity profile of the continuous phase. Description of both sets of interactions is used to predict mixing patterns in the continuous phase as a function of applied field strength. The predicted mixing patterns are compared with experimentally recorded images of tracer movement in the continuous phase obtained under the same conditions. The calculated patterns compare favourably with those measured by experiment. The modelling methodology was used afterwards with success for predicting the residence time distribution in the form of the normalised concentration (proportional to the exit function) versus time. [Copyright &y& Elsevier]

• The novel Modified-Extended Pitzer-Debye-Hückel term is applied with the UNIversal QUAsi-Chemical model in aqueous ionic liquids. • Three developments of the Pitzer-Debye-Hückel equation are tested and compared. • Binary interaction parameters are systematically reduced keeping comparable modeling performance. Recently an improved long-range model for electrolyte solutions was developed that is applicable from infinite dilution to pure salt. This paper tests this claim for the first time applying it to the calculation of liquid-liquid equilibria for mixtures of different ionic liquids (ILs) and water. The conventional Pitzer-Debye-Hückel (PDH) equation is compared to two of its new, thermodynamically consistent extensions. Both development stages, the extended PDH term and the modified-extended PDH, account for concentration dependent mixture properties instead of using solvent properties. The latter one additionally introduces a modified parameter of closest approach which improves the overall performance of the model for high electrolyte concentrations in systems with variable or low permittivities. To account for the short-range interactions, these long-range models are coupled with the UNIversal QUAsi-Chemical (UNIQUAC) model. Three modeling strategies were tested for the short-range contribution. First, the UNIQUAC parameters were adjusted to each system individually, then the binary interaction parameters were the same for each binary interaction type for all the systems and lastly a linear function of the carbon number was used where possible. For all systems and all modeling strategies tested, the predictive performance increased from PDH to E-PDH and then to ME-PDH. Overall, an introduction of concentration dependent properties and the modification added to ME-PDH enhanced modeling performance when describing these systems, showing the general applicability of this novel long-range term. [ABSTRACT FROM AUTHOR]

In this paper, we review the importance of long-range zeolite framework interactions in theoretical predictions for a variety of zeolite-catalyzed processes, and we show why such interactions must be determined accurately in order to reproduce experimentally measured adsorption and activation energies. We begin with an overview of the different strategies that have been used to account for long-range coulombic and dispersive interactions of zeolite framework atoms with species adsorbed at an active site. These methods include full periodic-DFT calculations and multi-layer hybrid techniques. Electrostatic interactions are observed to have a more significant impact than dispersive interactions on the geometries of ion-pair transition states and adsorbed species. Stabilization of the TS relative to reactant complexes is also dictated by electrostatic interactions. Dispersion effects are found to significantly stabilize both transition and reactant states for adsorbed species, especially those which have dimensions that provide good fits within the zeolite pore or cavity. We also show that the relevance of particular active site configurations can be missed, if the effects of long-range interactions are neglected. As a case in point, we demonstrate that a site previously considered inactive for ethane dehydrogenation, [GaH 2 ] + may in fact be more active than previously thought, when the impact of long-range interactions on the predicted activation energy is taken into account. Finally, the use of hybrid quantum mechanics/molecular mechanics approaches on extended, finite zeolite clusters has emerged as an accurate, highly cost-effective, and versatile alternative towards overcoming some of the present-day limitations of periodic calculations. [ABSTRACT FROM AUTHOR]

The size-modified Poisson–Boltzmann equation (SMPBE) is one important variant of the popular dielectric model, the Poisson–Boltzmann equation (PBE), to reflect ionic size effects in the prediction of electrostatics for a biomolecule in an ionic solvent. In this paper, a new SMPBE hybrid solver is developed using a solution decomposition, Schwartz’s overlapped domain decomposition, finite element, and finite difference. It is then programmed as a software package in C , Fortran , and Python based on the state-of-the-art finite element library DOLFIN from the FEniCS project. This software package is well validated on a Born ball model with analytical solution and a dipole model with known physical properties. Numerical results on six proteins with different net charges demonstrate its high performance. Finally, this new SMPBE hybrid solver is shown to be numerically stable and convergent in the calculation of electrostatic solvation free energy for 216 biomolecules and binding free energy for a DNA-drug complex. [ABSTRACT FROM AUTHOR]

Carbonaceous materials served as functional units have trigged tremendous fundamental and practical interest in preparing electronic composites especially in meta-composites. In this paper, carbon functional nano-units were built by electrostatic self-assembly of carbon nanotubes (CNTs) and carbon black (CB). Three-dimension carbon networks hosted in CaCu 3 Ti 4 O 12 (CCTO) matrix were constructed by randomizing CNTs/CB nano-units. Negative permittivity was observed when increasing CNTs/CB nano-units contents exceeded the percolation threshold. The negative permittivity behavior considered as deriving from the low frequency plasma oscillation of delocalized electrons in carbon networks was analyzed by Drude model and equivalent circuit model. Besides, the electrical properties influenced by percolating phenomenon including ac conductivity, dielectric loss, and impedance were investigated. This work presents a novel meta-composites with negative permittivity built by CNTs/CB nano-units filling in low-temperature sintering CCTO matrix which extends the fields of meta-composites and will greatly facilitate its practical applications. [ABSTRACT FROM AUTHOR]

In this paper, an electrostatic vibration energy harvester is proposed and fabricated with both broad bandwidth and high normalized power density (NPD, harvested power/volume/acceleration 2 ). The device is made up of two parts, top movable plate and bottom fixed plate, both of which are fabricated from silicon wafers using advanced micro-electro-mechanical system (MEMS) technology. A CYTOP polymer layer is spray coated for an electret material as well as an adhesive layer for low temperature wafer bonding. The air damping effect in energy harvesting has been investigated. At a low pressure of 3 Pa in a vacuum chamber, maximum power output of 4.95 μW has been harvested at low vibration amplitude of 0.09 g, resulting in a bandwidth of 12 Hz and NPD of 3 mW/cm 3 /g 2 , which outperforms most of the previous harvesters. A high harvester effectiveness of 67.9% is therefore achieved. The response on random vibrations is also tested. An average output power of 2.22 μW is harvested when random vibration is applied at a frequency range of 160 ± 12.5 Hz with RMS acceleration of 10.5 m/s 2 . The excellent overall performance gives promising application for energy harvesting from random sources and multi-device stack for wireless sensor networks. [ABSTRACT FROM AUTHOR]

In this paper, a size-dependent model of clamped-clamped composite laminated electrostatic Euler–Bernoulli microbeams with piezoelectric layers attached was proposed based on a new modified couple stress theory for anisotropic elasticity. With the aid of Hamilton's principle, the nonlinear differential governing equation was established and solved by utilizing the generalized differential quadrature method. The present model, which can be reduced to the isotropic beam model takes the residual stresses, fringing effects and midplane stretching effects into consideration. A good agreement exists between numerical results of the present reduced model and those of available literature. Numerical analysis reveals that the size effect is significant when geometry sizes of a beam are comparable to the internal material length scale parameter (hereafter referred to as MLSP). Furthermore, the pull-in voltage dependence of the residual stress, midplane stretching, MLSP as well as the voltage applied to the piezoelectric layers are also investigated. The present model can accurately predict the static behavior and guide the design of composite laminated micro-beam actuated by both the electrostatic and piezoelectric forces. [ABSTRACT FROM AUTHOR]

The Ion Source of the ITER Heating Neutral Beam Injector (HNB) is polarized at −1MVdc to ground. A large-1MVdc air-insulated Faraday cage (12.5 m (L) × 8.4 m (W) × 9.6 m (H)), called High Voltage Deck 1 (HVD1), hosts the Ion Source and Extractor Power Supplies (ISEPS) and the associated HNB diagnostics; the HVD1 is interfaced with a SF 6 insulated Transmission Line (connecting the main power supplies to the HNB) through a High Voltage (HV) Bushing Assembly (HVBA) carrying inside ISEPS power conductors and diagnostics. The HVD1 and HVBA are unique devices for size, electrostatic and mechanical features. This paper presents the main design choices adopted to comply with the challenging technical requirements and the supporting electrostatic, seismic and thermal analyses. Finally, next procurement steps and definition of special tests to verify the key design choices are also reported. [ABSTRACT FROM AUTHOR]

This paper reports a turn-on theranostic fluorescent nanoprobe P-CDs/HA-Dox obtained by electrostatic assembly of polyethylenimine (PEI)-modified carbon dots (P-CDs) and Hyaluronic acid (HA)-conjugated doxorubicin (Dox) for hyaluronidase (HAase) detection, self-targeted imaging and drug delivery. P-CDs/HA-Dox show weak emission in a physiological environment. By utilizing the high affinity of HA to CD44 receptors overexpressed on many cancer cells, P-CDs/HA-Dox are capable of targeting and penetrating into cancer cells, where they are activated by HAase. As a result, HA-Dox can be digested into small fragments, causing the release of Dox and thereby restoring the fluorescence of P-CDs. The theranostic fluorescent nanoprobe can effectively distinguish cancer cells from normal cells. The as-prepared nanoprobe achieves a sensitive assay of HAase with a detection limit of 0.65 U mL −1 . Furthermore, upon Dox release, the Dox could efficiently induce apoptosis in HeLa cells, as confirmed by MTT assay. The design of such a turn-on theranostic fluorescent probe provides a new strategy for self-targeted and image-guided chemotherapy. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic pull-in instability and bifurcation characteristics of circular nanoplate subjected to electrostatic and Casimir forces are studied. Surface effect originates from high surface/volume ratio of nanostructures, where atoms at a free surface experience distinct local environments with respect to those in the bulk material. Thus, the surface free energy being negligible in classical elastic theory, becomes significant in dynamic behaviors of nanostructures. Based on Eringen's nonlocal elasticity and Gurtin-Murdoch surface model, the nonlinear governing equation of electrically actuated circular nanoplate is derived in polar coordinate. The closed-form solution of dynamic frequency and electrostatic voltage is obtained by utilizing the homotopy perturbation method (HPM). Furthermore, the coupling effects of nonlocal parameter and surface characteristics on the dynamic pull-in instability of circular nanoplate are investigated, and the nonlinear dynamics behaviors, time histories and phase diagrams of electrically actuated circular nanoplate are discussed. Some new results obtained in this work could be helpful in design of 2-D circular nanoplate-type actuator considering size-dependency and quantum vacuum fluctuation effects. [ABSTRACT FROM AUTHOR]

In this paper we prove the Liouville type theorem for stable solution of the p -Laplace equation (0.1) − Δ p u = f ( x ) | u | q − 1 u , x ∈ R N , where f ( x ) is a continuous and nonnegative function in R N ∖ { 0 } such that f ( x ) ≥ a 0 | x | a as | x | ≥ R 0 > 0 , where a > − p and a 0 > 0 . The results hold true for 1 ≤ p − 1 < q = q c ( p , N , a ) . Here q c is a new exponent, which is infinity in low dimension and is always larger than the classical critical one. [ABSTRACT FROM AUTHOR]

This paper resolves an ostensible inconsistency in the literature in calculating the evaporation rate for sessile drops in a quiescent environment. The earlier models in the literature have shown that adapting the evaporation flux model for a suspended spherical drop to calculate the evaporation rate of a sessile drop needs a correction factor; the correction factor was shown to be a function of the drop contact angle, i.e. f ( θ ). However, there seemed to be a problem as none of the earlier models explicitly or implicitly mentioned the evaporation flux variations along the surface of a sessile drop. The more recent evaporation models include this variation using an electrostatic analogy, i.e. the Laplace equation (steady-state continuity) in a domain with a known boundary condition value, or known as the Dirichlet problem for Laplace's equation. The challenge is that the calculated evaporation rates using the earlier models seemed to differ from that of the recent models (note both types of models were validated in the literature by experiments). We have reinvestigated the recent models and found that the mathematical simplifications in solving the Dirichlet problem in toroidal coordinates have created the inconsistency. We also proposed a closed form approximation for f ( θ ) which is valid in a wide range, i.e. 8 ° ≤ θ ≤ 131°. Using the proposed model in this study, theoretically, it was shown that the evaporation rate in the CWA (constant wetted area) mode is faster than the evaporation rate in the CCA (constant contact angle) mode for a sessile drop. [ABSTRACT FROM AUTHOR]

A rotating circular disk with variable thickness under thermal environment is investigated in this paper. The circular disk is made of functionally graded magneto-electro-elastic (FGMEE) material, which is a mixture of piezoelectric (PE) and piezomagnetic (PM) materials, and the material properties are assumed to vary along the radius of the disk exponentially. In order to study the thermo-magneto-electro-elastic behavior of the FGMEE circular disk, equations of heat conduction, electrostatics and magnetostatics are established, and the governing equation expressed by displacement is finally solved utilizing a semi-analytical method. Numerical results separately show the effect of material properties, material components, geometric shapes and rotating speeds on the thermo-magneto-electro-elastic behaviors of the FGMEE circular disk. In the discussions of influences of various parameters to the results, material property parameters are the temperature change index and functionally graded index, material component parameter is the volume fraction of PE material, and geometric parameters are the inner-outer thickness ratio, thickness change index and inner-outer radius ratio. Results in this study may be useful for the optimal design of rotating FGMEE circular disks with variable thickness. [ABSTRACT FROM AUTHOR]

A helicopter flying through an atmosphere containing particulates may accumulate high electrostatic charges which can challenge its operational safety. In this paper we elaborate and validate a triboelectric charging model to predict the electrification experienced by a helicopter while hovering in dusty air. We employed Large Eddy simulations to describe the turbulent structures inherent in the flow around the rotorcraft. The dust particles were tracked individually in a Lagrangian framework. A model accounting for the triboelectric charge transfer when a particle hits the helicopter was introduced. The results demonstrate the accuracy of the proposed approach and allow a detailed analysis of the location of the charge accumulation. [ABSTRACT FROM AUTHOR]

In this paper, the distribution of 210 Po after high temperature processes in six units of coal-fired power plants (CFPs) were evaluated. The coal, bottom ashes, fly ashes from electrostatic precipitators (ESP), and flue gases from stacks were sampled from four CFPs and analyzed for 210 Po contents. The results showed that 210 Po was mainly captured by the ESP, with little left in the bottom ash, and a small fraction of 210 Po was directly discharged into the environment through the stacks, accounting for 0.06%–0.6%, which was consistent with the reported data. It was also found that part of the 210 Po could not be accounted for in the mass balance analysis for the whole combustion process in CFPs, which was also in line with the reported data. The results obtained in this study provided essential basic data for environmental radiological risk analysis for CFPs. [ABSTRACT FROM AUTHOR]

Viscoelastic phenomena widely exist in MEMS materials, which may have certain effects on quasi-static behaviors and transition mechanism of nonlinear jumping phenomena. The static and dynamic behaviors of a doubly clamped viscoelastic microbeam actuated by one sided electrode are investigated in detail, based on a modified couple stress theory. The governing equation of motion is introduced here, which is essentially nonlinear due to its midplane stretching effect and electrostatic force. Through quasi-static analysis, the equilibrium position, pull-in voltage and pull-in location of the system are obtained with differential quadrature method and finite element method. The equivalent geometric nonlinear parameter is presented to explain the influence of the scale effect on the pull-in location. Different from elastic material, there are two kinds of pull-in voltages called as instantaneous pull-in voltage and the durable pull-in voltage in viscoelastic system. Then, Galerkin discretization and the method of multiple scales are applied to determine the response and stability of the system for small vibration amplitude. A new perturbation method to deal with viscoelastic term is presented. Theoretical expressions about the parameter spaces of linear-like vibration, hardening-type vibration and softening-type vibration are then deduced. The influence of viscoelasticity and scale effect on nonlinear dynamic behavior is studied. Results show that the viscoelasticity can reduce the effective elastic modulus and make the system tend to softening-type vibration; the scale effect can increase effective elastic modulus and make the system tend to hardening-type vibration. And most of all, simulation results of case studies are used to realize parameter optimization. Then parameter conditions of linear-like vibration, which is desired for many applications, are obtained. In this paper, the results of multi-physical field coupling simulation are used to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

A generalized formulation for coagulation of charged particles is presented in this paper. The governing equations can be solved semi-implicitly for a number of discrete size and charge bins. The computationally efficient mechanism gives volume and charge conserved solution with time. A distinct way of handling electrostatic dispersion in dynamic model has been used in this work. The scheme has been tested for charged, nebulized aerosol particles by model studies and also compared with experimental observations. The model simulated results show that charge can significantly affect the coagulation dynamics if charge level is higher than the Boltzmann equilibrium charge limit for less than 1 μm particles. It was found that for the bipolar charge case, there was a significant effect on the enhancement of the coagulation process. For the case of unipolar charge, electrostatic dispersion was seen to play a role in the depletion of number concentration. The model was then validated against results of six controlled experiments in which electrical low pressure impactor (ELPI) was used for measurement of charge and number size distribution. Our model results were found to be in reasonable agreement with observed values. The developed model is fast (independent of time step) and numerically stable. It can be used for several applications involving coagulation dynamics of charged aerosol particles. [ABSTRACT FROM AUTHOR]

Electrons injected into the build envelope during powder bed electron-beam additive manufacturing can accumulate on the irradiated particles and cause them to repel each other. Under certain conditions, these electrostatic forces can grow so large that they drive the particles out of the build envelope in a process known as “smoking”. In the present work, we investigate the causes of powder bed charging and smoking during electron-beam additive manufacturing. In the first part of the paper, we characterize the surface chemistry of a common feedstock material—gas-atomized Ti-6Al-4V powder—and find that a thick, electrically insulating oxide overlayer encapsulates the particles. Based on these experimental results, we then formulate an analytical model of powder bed charging in which each particle is approximated as a capacitor, where the particle and its substrate are the electrodes and the oxide overlayer is the dielectric. Using this model, we estimate the charge distribution in the powder bed, the electrostatic forces acting on the particles, and the conditions under which the powder bed will smoke. It is found that the electrical resistivity of the oxide overlayer strongly influences the charging behavior of the powder bed and that a high resistivity promotes charge accumulation and consequent smoking. This analysis suggests new quality control and process design measures that can help suppress smoking. [ABSTRACT FROM AUTHOR]

The paper reports a simple electrostatic self-assembly method to fabricate the gold nanoparticles/graphene oxide (Au NPs@GO) films which present superior SERS activity. The Au NPs@GO films with different layers construction and surface compositions (with Au NPs or GO as the outer layer) are obtained simply by changing the self-assembly cycles. Results indicate that the film with two assembly cycles (F-2 film) exhibits the best SERS activity towards R6G molecules compared with that of one assembly cycle (F-1 film) and three assembly cycles (F-3 film) due to the high loadings of the absorbed Au NPs exposed on the surface of the film. Meanwhile, the Raman enhancement effect of the F-2 film with the outer layer of Au NPs is better than that of the outer layer covering with GO sheets (F-2-GO) possibly owing to the optimal synergetic effect of Au NPs and GO. Furthermore, our fabricated Au NPs@GO films present favorable reproducibility and high stability, which are significant for the practical application of these SERS substrates. [ABSTRACT FROM AUTHOR]

Thus far, Computational Fluid Dynamics (CFD) simulations fail to predict the electrostatic charging of particle–gas flows reliably. The lack of a predictive tool leads to powder operations prone to deposits and discharges, making chemical plants unsustainable and prime candidates for explosions. This paper reviews the rapid progress of numerical models in recent years, their limitations, and outlines future research. In particular, the discussion includes CFD models for the physics and chemistry of particle electrification. The condenser model is most popular today in CFD simulations of powder flow electrification but fails to predict most of its features. New experiments led to advanced models, such as the non-uniform charge model, which resolves the local charge distribution on non-conductive particle surfaces. Further, models relying on the surface state theory predicted bipolar charging of polydisperse particles made of the same material. While these models were usually implemented in CFD tools using an Eulerian–Lagrangian strategy, recently Eulerian methods successfully described powder charging. The Eulerian framework is computationally efficient when handling complete powders; thus, Eulerian methods can pave the way from academic studies to application, simulating full-scale powder processing units. Overall, even though CFD models for powder flow charging improved, major hurdles toward a predictive tool remain. • Simulating powder flow charging is an unsolved multi-scale and -physics problem. • Highly resolved Lagrangian simulations reveal the particle charging dynamics. • The particle charging model is the largest contributor to the simulation error. • New experiments and nano-scale models capture same-material and bipolar charging. • Eulerian simulations can cover complete conveyors but struggle with polydispersity. [ABSTRACT FROM AUTHOR]

The dynamic response of a MEMS accelerometer can be influenced by several multi-physics effects, especially if the gaps between the shuttle and the stator attain sub-micrometric values. The present paper aims at tackling the aforementioned issues by means of a suitable experimental procedure, which has been purposely devised for the problem at hand, and through the execution of numerical analyses (based on the Finite Element Model). The effect of parasitic electrostatic forces and hydrodynamic forces is clearly demonstrated. [ABSTRACT FROM AUTHOR]