Nonconducting Regions Research Articles

'Trapped re-entry' as source of acute focal atrial arrhythmias.

Diseased atria are characterized by functional and structural heterogeneities, adding to abnormal impulse generation and propagation. These heterogeneities are thought to lie at the origin of fractionated electrograms recorded during sinus rhythm (SR) in atrial fibrillation (AF) patients and are assumed to be involved in the onset and perpetuation (e.g. by re-entry) of this disorder. The underlying mechanisms, however, remain incompletely understood. Here, we tested whether regions of dense fibrosis could create an electrically isolated conduction pathway (EICP) in which re-entry could be established via ectopy and local block to become 'trapped'. We also investigated whether this could generate local fractionated electrograms and whether the re-entrant wave could 'escape' and cause a global tachyarrhythmia due to dynamic changes at a connecting isthmus. To precisely control and explore the geometrical properties of EICPs, we used light-gated depolarizing ion channels and patterned illumination for creating specific non-conducting regions in silico and in vitro. Insight from these studies was used for complementary investigations in virtual human atria with localized fibrosis. We demonstrated that a re-entrant tachyarrhythmia can exist locally within an EICP with SR prevailing in the surrounding tissue and identified conditions under which re-entry could escape from the EICP, thereby converting a local latent arrhythmic source into an active driver with global impact on the heart. In a realistic three-dimensional model of human atria, unipolar epicardial pseudo-electrograms showed fractionation at the site of 'trapped re-entry' in coexistence with regular SR electrograms elsewhere in the atria. Upon escape of the re-entrant wave, acute arrhythmia onset was observed. Trapped re-entry as a latent source of arrhythmogenesis can explain the sudden onset of focal arrhythmias, which are able to transgress into AF. Our study might help to improve the effectiveness of ablation of aberrant cardiac electrical signals in clinical practice.

Heterogeneity in La Distribution in Highly La-Doped SrTiO3 Crystals

Our paper is focused on the investigation of the dopant distribution in lanthanum-doped strontium titanate (LSTO) single crystals with a 5 wt.% doping level of La. Using X-ray diffraction analysis and pycnometric density measurement, we have found a discrepancy between the theoretical density and the experimentally determined value. The origin of this behavior could be either the creation of the voids in the matrix or the intergrowth of secondary phases with La surplus in the crystal. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and selected area diffraction (SAD) microscopic investigation have confirmed the second hypothesis, namely, that in different regions of LSTO, the local concentration of La shows a substantial variation on the micro- and nanoscopic scale. In order to study the influence of the La dopants on the electronic structure and, therefore, on the electrical conductivity, we have used the local conductivity atomic force microscopy (LCAFM) method as a local electrical probe to map the in-plane electrical conductivity of the La-doped crystal’s surface. The LCAFM conductivity maps reveal heterogeneous conductivity (here in the form of the bands with higher conductivity than the surroundings), related to band-like inhomogeneities of the La distribution. Using LCAFM measurements with atomic resolution obtained between the conducting and nonconducting regions, we analyzed the spreading (spatial expansion) of doping on the undoped or low-doped part of the STO crystal. The found limitation of the doping effect of La on the dielectric part of the STO crystal to 4–5 lattice constants was in good correlation with ab initio studies from the literature.

Investigation of Interface Discharge Characteristics for Cable Accessories After Moisture Penetration Into the XLPE–SiR Interface

For cable accessories, environmental moisture inevitably gradually diffuses into the XLPE-SiR composite interface. The penetrated moisture always causes interface insulation degradation and failure. In this paper, to investigate the discharge characteristics at the interface insulation, a composite interface discharge experimental unit is performed, and the insulation deterioration when the interface remains dry or becomes damped are discussed and analyzed. Combined with optical tests, discharge signal tests, SEM and EDS tests, the interface discharge characteristics are studied. In addition, several analysis models are established, and the discharge processes of the interface insulation are discussed in detail. Moreover, several field cases are discussed and compared to better understand the interface discharge. It is found that the discharge trace is mainly concentrated in one channel when the insulation remains dry. Moisture-induced early deterioration of the interface insulation is characterized by the emergence of non-conductive regions and weak dendritic discharge. As the interfacial water content increases, weak dendritic discharge turns into a macroscopic one. The occurrence and development of discharge after interface wetting can be attributed to two main factors. On one hand, interface discharge is related to the interface electric field distribution and interface contact morphology. On the other hand, the discharge performance is strongly influenced by the electric field distortion caused by water droplets, size of the dry area between water droplets, and increase in electrical losses ascribed to the invading moisture. The ultimate damage to the interface insulation takes two forms: continuous thermal breakdown that erodes the insulation, and instantaneous arc breakdown at the interface.

Explainable Machine Learning to Predict Anchored Reentry Substrate Created by Persistent Atrial Fibrillation Ablation in Computational Models.

Background Postablation arrhythmia recurrence occurs in ~40% of patients with persistent atrial fibrillation. Fibrotic remodeling exacerbates arrhythmic activity in persistent atrial fibrillation and can play a key role in reentrant arrhythmia, but emergent interaction between nonconductive ablation-induced scar and native fibrosis (ie, residual fibrosis) is poorly understood. Methods and Results We conducted computational simulations in pre- and postablation left atrial models reconstructed from late gadolinium enhanced magnetic resonance imaging scans to test the hypothesis that ablation in patients with persistent atrial fibrillation creates new substrate conducive to recurrent arrhythmia mediated by anchored reentry. We trained a random forest machine learning classifier to accurately pinpoint specific nonconductive tissue regions (ie, areas of ablation-delivered scar or vein/valve boundaries) with the capacity to serve as substrate for anchored reentry-driven recurrent arrhythmia (area under the curve: 0.91±0.03). Our analysis suggests there is a distinctive nonconductive tissue pattern prone to serving as arrhythmogenic substrate in postablation models, defined by a specific size and proximity to residual fibrosis. Conclusions Overall, this suggests persistent atrial fibrillation ablation transforms substrate that favors functional reentry (ie, rotors meandering in excitable tissue) into an arrhythmogenic milieu more conducive to anchored reentry. Our work also indicates that explainable machine learning and computational simulations can be combined to effectively probe mechanisms of recurrent arrhythmia.

A comprehensive and biophysically detailed computational model of the whole human heart electromechanics

While ventricular electromechanics is extensively studied in both physiological and pathological conditions, four-chamber heart models have only been addressed recently; most of these works however neglect atrial contraction. Indeed, as atria are characterized by a complex anatomy and a physiology that is strongly influenced by the ventricular function, developing computational models able to capture the physiological atrial function and atrioventricular interaction is very challenging. In this paper, we propose a biophysically detailed electromechanical model of the whole human heart that considers both atrial and ventricular contraction. Our model includes: (i) an anatomically accurate whole-heart geometry; (ii) a comprehensive myocardial fiber architecture; (iii) a biophysically detailed microscale model for the active force generation; (iv) a 0D closed-loop model of the circulatory system, fully-coupled with the mechanical model of the heart; (v) the fundamental interactions among the different core models, such as the mechano-electric feedback or the fibers-stretch and fibers-stretch-rate feedbacks; (vi) specific constitutive laws and model parameters for each cardiac region. Concerning the numerical discretization, we propose an efficient segregated-intergrid-staggered scheme that includes a computationally efficient strategy to handle the non-conductive regions. We also propose extending recent stabilization techniques – regarding the circulation and the fibers-stretch-rate feedback – to the whole heart, demonstrating their cruciality for obtaining a stable formulation in a four-chamber scenario. We are able to reproduce the healthy cardiac function for all the heart chambers, in terms of pressure–volume loops, time evolution of pressures, volumes and fluxes, and three-dimensional cardiac deformation, with volumetric indexes within reference ranges for cardiovascular magnetic resonance. We also show the importance of considering atrial contraction, fibers-stretch-rate feedback and the proposed stabilization techniques, by comparing the results obtained with and without these features in the model. In particular, we show that the fibers-stretch-rate feedback, often neglected due to the numerical challenges that it entails, plays a fundamental role in the regulation of the blood flux ejected by ventricles. The proposed model represents the state-of-the-art electromechanical model of the iHEART ERC project – an Integrated Heart Model for the Simulation of the Cardiac Function – and is a fundamental step toward the building of physics-based digital twins of the human heart.

Fabrication of Nonconductive Microscale Patterns on Ion Exchange Membrane by Laser Process

The electroconvection generated on the surface of an ion exchange membrane (IEM) is closely related to the electrical/chemical characteristics or topology of the IEM. In particular, when non-conductive regions are mixed on the surface of the IEM, it can have a great influence on the transfer of ions and the formation of nonlinear electroconvective vortices, so more theoretical and experimental studies are necessary. Here, we present a novel method for creating microscale non-conductive patterns on the IEM surface by laser ablation, and successfully visualize microscale vortices on the surface modified IEM. Microscale (~300 µm) patterns were fabricated by applying UV nanosecond laser processing to the non-conductive film, and were transferred to the surface of the IEM. In addition, UV nanosecond laser process parameters were investigated for obvious micro-pattern production, and operating conditions were optimized, such as minimizing the heat-affected zone. Through this study, we found that non-conductive patterns on the IEM surface could affect the generation and growth of electroconvective vortices. The experimental results provided in our study are expected to be a good reference for research related to the surface modification of IEMs, and are expected to be helpful for new engineering applications of electroconvective vortices using a non-conductive patterned IEM.

Improved RF power performance of AlGaN/GaN HEMT on silicon with planar distributed channel

AlGaN/GaN HEMTs with planar distributed channel were fabricated on a silicon substrate. With a standard ion implantation isolation process, the area between the ohmic contacts was divided into conductive and non-conductive regions. Compared to a conventional HEMT, simulations and experimental results indicate the decreased channel temperature and improved RF power performance in the distributed channel device, while there is no significant degradation in small signal characteristics. The fabricated multi-finger distributed channel devices with 0.65-mm gate periphery demonstrated a decrease in channel temperature from 186 °C to 162 °C, accompanied by a 15.6 % increase (from 3.2 W/mm to 3.7 W/mm) in output power density, and an 8 % increase (from 42.0 % to 50.0 %) in drain efficiency at 3.5 GHz.

Three-dimensional Analytical Modeling of Axial Flux Permanent Magnets Maglev Motor

The three-dimensional(3D) analytical model of the magnetic field in an Axial Flux Permanent Magnets Maglev Motor(AFPMMM) is proposed and investigated the influence of the structural parameters on electromagnetic characteristics. Firstly, the topology and working principle of the AFPMMM is introduced, and the model is transferred into a mathematical model in 3D cartesian coordinate. Then, the volume integral method and equivalent current sheets model is applied to find the 3D magnetic field distribution function of Halbach rotor. A unified form expression can be obtained by two dimensional discrete fourier transform (2-D DFT) is applied on the 3D magnetic field distribution function. Thirdly, the conductive and nonconductive regions of AFPMMM will be formulated by the second order vector potential (SOVP) to built the 3D analytic model. The expression of the lift force, torque and power losses was derived. Besides, the relationship between electromagnetic characteristics and structural parameters of the AFPMMM were analyzed based on 3D analytic model and validated using the 3D finite element analysis(FEA). Finally, the experiments based on a small scale prototype are carried out to verify the analytical results.

The structural and magnetic features of perovskite oxides La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) depending on the strontium doping content and heat treatment

Sr-doped (0<x < 0.2) ceramic samples of the lanthanum manganite oxides were obtained via sol-gel method to investigate the influence of doping on structural, magnetic end electronic responses, and their correlations. Synthesized samples of non-stoichiometric compositions are rhombohedral single-phase. After annealing the formation of a phase-separated system as a mixture of orthorhombic phases was found. The R-3c and PnmaI, PnmaII* and PnmaII phases have been studied using Mössbauer spectroscopy, XRD, SEM analysis and magnetic measurements. The magnetic temperature-concentration phase diagram of La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) was obtained.The Jahn-Teller effect or the orbital order breaking, as well as the competition between Mn3+–O2—Mn4+ double- and Mn3+–O2-–Mn3+ superexchange interaction was demonstrated under the effect of cation doping compound and interstitial oxygen value (δ). The relaxation character of the Mössbauer spectra and the type of magnetization dependences revealed nanosized magnetic clusters with fluctuation of their magnetic moment in all perovskite phases. Results are interpreted in terms of matrix – clusters: regions of sample with ferromagnetic type of ordering (cluster) exist in antiferromagnetically or ferromagnetically (with different exchange parameter) ordered matrix. Exchange interaction frustrations of the cluster with the matrix can lead to relaxation behavior of the magnetic moment of the cluster. The clusters size vary from about 3.9 to 5.7 nm. All samples are characterized by the presence of particles agglometates with a typical size about 0.4–0.8 μm; for annealed samples additional non-conducting regions with 80–220 nm in size were found. It is shown that the annealing time significantly affects the production of materials with determined properties and be useful in the applied field in technological processes.

Combined Normal and Disruption, Electromagnetic Transient, Thermal, and Structural Analysis of COMPASS Upgrade

COMPASS Upgrade is a replacement for the COMPASS device at the Institute of Plasma Physics (IPP) of the Czech Academy of Sciences. It is a cryogenic copper machine with a major radius of 0.89 m, with 5 T at the plasma centerline and 2-MA plasma current. It is intended to develop ITER relevant plasma densities and high power fluxes in the divertor region. The entire vacuum vessel is planned to reach 500°C. The COMPASS-U TF coil is a bitter plate-like design with radial conductor plates that extend the width of the TF inner leg. Currents redistribute radially based on resistive and inductive effects. This necessitates an electromagnetic (EM) transient analysis of the coil current distribution. For copper coils like COMPASS Upgrade, the solution must be coupled with a thermal solution to properly include the temperature-dependent resistive effects. The EM transient solution includes the TF magnetic loads, and a stress pass on the results produces in-plane loads. The EM solution chosen requires inclusion of all the conducting and nonconducting regions surrounding the TF coil. With the TF current distribution solved, the addition of the poloidal coils and resulting background fields allows the determination of the out-of-plane loads. Integration of the Joule heating produced from the EM solution produces temperature distributions throughout the shot, which can be read in to a structural pass to include thermal stresses in the evaluation. This is true of both TF and PF temperature prediction with appropriate packing fractions. Currents in the PF coils, with computed background fields, produce Lorentz loads. Time transients of the PF currents produce startup eddy currents in the structures included in the model; inclusion of the vessel and other passive structures allows these to be included in a stress pass. The EM transient solution includes all the elements needed for a disruption analysis with prescribed motions and quench of the plasma. From a model originally intended to simulate current diffusion in the TF coil, the analysis can be refined to be used to predict the performance of most of the components of the tokamak or provide boundary conditions for more detailed submodels. In this article, the use of the current diffusion model for bounding assessments of the COMPASS Upgrade TF, PF, vessel, external structure, and disruption analyses will be presented.

Estimation of local conductivity of disordered carbon in a natural carbon-mineral composite using a model of intragranular currents

The mechanism of high dynamic conductivity of disordered carbon in shungite determines high shielding properties of shungite materials in the microwave range is analyzed. We presented an algorithm for calculating such conducting characteristics of disordered carbon as local conductivity of these regions and conductivity of a bulk sample from the measured reflection coefficient of microwave waves. Anomalously high local dynamic conductivity was found at medium and low carbon content in the samples. We showed that the mechanism of intragranular currents, due to the high local dynamic conductivity of isolated regions of carbon, played a key role in the reflection and conductivity of shungites, when the sizes of the conducting sections were many times smaller than the sizes of the non-conducting regions. We presented the key role of ordering the carbon structure on contacts with minerals for increasing local conductivity.

Analysis of Mo Sidewall Ohmic Contacts to InGaAs Fins

We present a novel test structure for the study of sidewall ohmic contacts to III–V fins for FinFETs. We apply it to the characterization of the impact of digital etch (DE), used to trim the fin width, and thermal annealing on the contact resistivity of Mo/ $\text{n}^{+}$ -InGaAs fin sidewall contacts. To obtain sidewall contacts, we leave in place the etch mask that is used to define the fins in a reactive ion etching process and deposit conformal Mo around them. We present a model that describes well the electrical characteristics of the test structure. In our results, we find that the specific acid that is used for DE or the number of DE cycles that are performed have a minor impact on contact resistivity. Thermal annealing is found to significantly improve the sidewall contact resistivity, with the best value of $3.7~ \pm ~0.2~ {\Omega } \cdot {\mu } \text{m}^{{2}}$ obtained after annealing at 400 °C. This is about three times higher than the reported contact resistivity for this contact technology with the contact wrapping around the top and the sidewall surfaces of fins, about $1.3~ {\Omega } \cdot {\mu }\text{m}^{{2}}$ . Also, we find that the width of the non-conductive region under the sidewall surface of Mo contact, which we term “deadzone,” can be significantly mitigated by thermal annealing. Our work highlights the importance of understanding sidewall ohmic contact formation for future high-performance InGaAs FinFETs.

Efficient Modeling of High-Temperature Superconductors Surrounded by Magnetic Components Using a Reduced H–$\phi$ Formulation

Although the H-formulation has proven to be one of the most versatile formulations used to accurately model superconductors in the finite element method, the use of vector-dependent variables in nonconducting regions leads to unnecessarily long computation times. Additionally, in some applications of interest, the combination of multiple magnetic components interacting with superconducting bulks and/or tapes leads to large domains of simulation. In this article, we separate the magnetic field into a source and reaction field and use the H-Φ formulation to efficiently simulate a superconductor surrounded by magnetic bodies. We model a superconducting cube between a pair of Helmholtz coils and a permanent magnet levitating above a superconducting pellet. In both cases, we find excellent agreement with the H-formulation while the computation times are reduced by factors of nearly three and four in 2-D and 3-D, respectively. Finally, we show that the H-Φ formulation is more accurate and efficient than the H-A formulation in 2-D.

On the Role of Ionic Modeling on the Signature of Cardiac Arrhythmias for Healthy and Diseased Hearts

Computational cardiology is rapidly becoming the gold standard for innovative medical treatments and device development. Despite a worldwide effort in mathematical and computational modeling research, the complexity and intrinsic multiscale nature of the heart still limit our predictability power raising the question of the optimal modeling choice for large-scale whole-heart numerical investigations. We propose an extended numerical analysis among two different electrophysiological modeling approaches: a simplified phenomenological one and a detailed biophysical one. To achieve this, we considered three-dimensional healthy and infarcted swine heart geometries. Heterogeneous electrophysiological properties, fine-tuned DT-MRI -based anisotropy features, and non-conductive ischemic regions were included in a custom-built finite element code. We provide a quantitative comparison of the electrical behaviors during steady pacing and sustained ventricular fibrillation for healthy and diseased cases analyzing cardiac arrhythmias dynamics. Action potential duration (APD) restitution distributions, vortex filament counting, and pseudo-electrocardiography (ECG) signals were numerically quantified, introducing a novel statistical description of restitution patterns and ventricular fibrillation sustainability. Computational cost and scalability associated with the two modeling choices suggests that ventricular fibrillation signatures are mainly controlled by anatomy and structural parameters, rather than by regional restitution properties. Finally, we discuss limitations and translational perspectives of the different modeling approaches in view of large-scale whole-heart in silico studies.

Scalable Fabrication of Scratch-Proof Transparent Al/F-SnO2 Hybrid Electrodes with Unusual Thermal and Environmental Stability.

Fabrication protocols of transparent conducting electrodes (TCEs), including those which produce TCEs of high values of figure of merit, often fail to address issues of scalability, stability, and cost. When it comes to working with high-temperature stable electrodes, one is left with only one and that too, an expensive choice, namely, fluorine-doped SnO2 (FTO). It is rather difficult to replace FTO with a low-cost TCE due to stability issues. In the present work, we have shown that an Al nanomesh fabricated employing the crack template method exhibits extreme thermal stability in air even at 500 °C, compared with that of FTO. In order to fill in the non-conducting island regions present in between the mesh wires, a moderately conducting material SnO2 layer was found adequate. The innovative step employed in the present work relates to the SnO2 deposition without damaging the underneath Al, which is a challenge in itself, as the commonly used precursor, SnCl2 solution, is quite corrosive toward Al. Optimization of spray coating of the precursor while the Al mesh on a glass substrate held at an appropriate temperature was the key to form a stable hybrid electrode. The resulting Al/SnO2 electrode exhibited an excellent transparency of ∼83% at 550 nm and a low sheet resistance of 5.5 Ω/□. SnO2 coating additionally made the TCE scratch-proof and mechanically stable, as the adhesion tape test showed only 8% change in sheet resistance after 1000 cycles. Further, to give FTO-like surface finish, the SnO2 surface was fluorinated by treating with a Selectfluor solution. As a result, the Al/F-SnO2 hybrid film exhibited one order higher surface conductivity with negligible sensitivity toward humidity and volatile organics, while becoming robust toward neutral electrochemical environments. Finally, a custom-designed projection lithography technique was used to pixelate the Al/SnO2 hybrid film for optoelectronic device applications.

Magnetic Induction Tomography Sensors for Quantitative Visualization of Liquid Metal Flow Shape

This letter proposes magnetic induction tomography (MIT) sensors for liquid metal visualization. Design aspect and performance evaluation, which by far were overlooked, are presented to quantify the shape of conductive substance against a nonconductive region. Portable MIT sensors have been constructed and tested on GaInSn in the submerged entry nozzle model. Reconstruction result shows applicability for liquid metal imaging. This feature meets the need to observe flow regime and phase distribution of steel in continuous casting. There are challenging flow regimes that cannot yet fully be recovered, which are also investigated here.

Unstructured PEEC method with the use of surface impedance boundary condition

PurposeThis paper aims to study unstructured-partial element equivalent circuit (PEEC) method for modelling electromagnetic regions with surface impedance condition (SIBC) is proposed. Two coupled circuits representations are used for solving both electric and/or magnetic effects in thin regions discretized by a finite element surface mesh. The formulation is applied in the context of low frequency problems with volumic magnetic media and coils. Non simply connected regions are treated with fundamental branch independent loop matrices coming from the circuit representation.Design/methodology/approachBecause of the use of Whitney face elements, two coupled circuits representations are used for solving both electric and/or magnetic effects in thin regions discretized by a finite element surface mesh. The air is not meshed.FindingsThe new surface impedance formulation enables the modeling of volume conductive regions to efficiently simulate various devices with only a surface mesh.Research limitations/implicationsThe propagation effects are not taken into account in the proposed formulation.Originality/valueThe formulation is original and is efficient for modeling non simply connected conductive regions with the use of SIBC. The unstructured PEEC SIBC formulation has been validated in presence of volume magnetic nonconductive region and compared with a SIBC FEM approach. The computational effort is considerably reduced in comparison with volume approaches.

Appearance of Conducting Behavior in a One Dimensional Nano Resistor Identical to a Semiconductor Diode

The present work deals with the simulation of electronic transport through a single dimensional carbon atoms chain device coupled to Graphene nanoribbons (GNR) electrodes. In order to observe electron transport in a more specific manner, applied voltage is regulated across an eight atoms long carbon chain resistor sandwiched between two identical semi-infinite semiconducting Armchair Graphene nanoribbon (AGNR) electrodes. The entire device is 2.06nm in length consisting of a 0.93nm long monoatomic carbon chain with eight carbon atoms coupled with two 1.13nm wide 7-AGNR electrodes. Nonequilibrium green's function (NEGF) technique coupled with density functional theory (DFT) generally used to simulate electronic transport in such systems is employed. The experimental realization of stable carbon chain and 7-AGNR observed in past studies motivated us to link these two experimentally obtained carbon based materials and construct a device in order to investigate electron transport properties theoretically. Meanwhile, the continuous advancement in nanotechnology realization of such devices experimentally may be anticipated in near future, with which the authenticity of the present and other similar reported simulated results may be validated. In this device the current is calculated as a function of potential difference within the 0.0-2.5V range. The I-V curve exhibits a nonconducting region upto 0.81V, followed by steep rise in current magnitude to a maximum value 13.0 ¹A as in semiconductor diodes, involving non-linear characteristic curve displaying a sharp negative differential resistance (NDR) pattern, which is the main focus of our study. Nano devices displaying such unusual I/V characteristics have been considered for developing application oriented futuristic miniaturized devices.

Electrochemiluminescence Waveguide in Single Crystalline Molecular Wires.

Here we report the first observation of active waveguide of electrochemiluminescence (ECL) in single crystalline molecular wires self-assembled from cyclometalated iridium(III) complexes, namely tris(1-phenylisoquinoline-C2 , N) (Ir(piq)3 ). Under dark conditions, the molecular wires deposited on the electrode surface can act as both ECL emitters and active waveguides. As revealed by ECL microscopy, they exhibit the typical characteristics of optical waveguides, transmitting ECL and generating much brighter ECL emission at their terminals. Moreover, self-generated ECL can be confined inside the molecular wire and propagates along the longitudinal direction as far as ≈100 μm to the terminal out of touch with the electrode. Therefore, this one-dimensional crystalline molecular wire-based waveguide offers the opportunity to switch the electrochemically generated ECL to remote light emission in non-conductive regions and is promising for contactless electrochemical analysis and study of (bio)chemical systems.

An a posteriori Error Estimate for Scanning Electron Microscope Simulation with Adaptive Mesh Refinement.

The intensity variation in a scanning electron microscope is a complex function of sample topography and composition. Measurement accuracy is improved when an explicit accounting for the relationship between signal and measurand is made. Because the determinants of the signal are many, the theoretical understanding usually takes the form of a simulator. For samples with nonconducting regions that charge, one phase of the simulation is finite element analysis to compute the electric field. The size of the finite element mesh, and consequently computation time, can be reduced through the use of adaptive mesh refinement. We present a new a posteriori local error estimator and adaptive mesh refinement algorithm for the scanning electron microscope simulation. This error estimate is designed to minimize the error in the electron trajectories, rather than the energy norm of the error that traditional error estimators minimize. Using a test problem with a known exact solution, we show that the adaptive mesh can achieve the same error in electron trajectories as a carefully designed hand-graded mesh while using 3.5 times fewer vertices and 2.25 times less computation time.