Electric Current Path Research Articles

Enhancement of photocurrent of polymer‐gelled dye‐sensitized solar cell by incorporation of exfoliated montmorillonite nanoplatelets

AbstractPoly(n‐isopropylacrylamide) (PNIPAAm) and its nanocomposite with exfoliated montmorillonite (MMT) were prepared by soap‐free emulsion polymerization and individually applied to gel the electrolyte systems for the dye‐sensitized solar cells (DSSCs). Each exfoliated MMT nanoplatelet had a thickness of ∼ 1 nm, carried ∼ 1.8 cation/nm2, and acted like a two‐dimensional electrolyte. The DSSC with the LiI/I2/tertiary butylpyridine electrolyte system gelled by this polymer nanocomposite had higher short‐circuit current density (Jsc) compared to that gelled by the neat PNIPAAm. The former has a Jsc of 12.6 mA/cm2, an open circuit voltage (Voc) of 0.73 V, and a fill factor (FF) of 0.59, which harvested 5.4% electricity conversion efficiency (η) under AM 1.5 irradiation at 100 mW/cm2, whereas the latter has Jsc = 7.28 mA/cm2, Voc = 0.72 V, FF = 0.60, and η = 3.17%. IPCE of the nanocomposite‐gelled DSSC were also improved. Electrochemical impedance spectroscopy of the DSSCs revealed that the nanocomposite‐gelled electrolytes significantly decreased the impedances in three major electric current paths of DSSCs, that is, the resistance of electrolytes and electric contacts, impedance across the electrolytes/dye‐coated TiO2 interface, and Nernstian diffusion within the electrolytes. The results were also consistent with the increased molar conductivity of nanocomposite‐gelled electrolytes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 47–53, 2008

Integrated Preconcentration SDS−PAGE of Proteins in Microchips Using Photopatterned Cross-Linked Polyacrylamide Gels

The potential of integration of functions in microfluidic chips is demonstrated by implementing on-chip preconcentration of proteins prior to on-chip protein sizing by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Two polymeric elements-a thin (approximately 50 microm) size exclusion membrane for preconcentration and a longer (approximately cm) porous monolith for protein sizing-were fabricated in situ using photopolymerization. Contiguous placement of the two polymeric elements in the channels of a microchip enabled simple and zero dead volume integration of the preconcentration with SDS-PAGE. The size exclusion membrane was polymerized in the injection channel using a shaped laser beam, and the sizing monolith was cast by photolithography using a mask and UV lamp. Proteins injected electrophoretically were trapped on the upstream side of the size exclusion membrane (MW cutoff approximately 10 kDa) and eluted off the membrane by reversing the electric field. Subsequently, the concentrated proteins were separated in a cross-linked polyacrylamide monolith that was patterned contiguous to the size exclusion membrane. The extent of protein preconcentration is easily tuned by varying the voltage during injection or by controlling the sample volume loaded. Electric fields applied across the nanoporous membrane resulted in a concentration polarization effect evidenced by decreasing current over time and irreproducible migration of proteins during sizing. To minimize the concentration polarization effect, sieving gels were polymerized only on the separation side of the membrane, and an alternate electrical current path was employed, bypassing the membrane, for most of the elution and separation steps. Electrophoretically sweeping a fixed sample volume against the membrane yields preconcentration factors that are independent of protein mobility. The volume sweeping method also avoids biased protein loading from concentration polarization and sample matrix variations. Mobilities of the concentrated proteins were log-linear with respect to molecular weight, demonstrating the suitability of this approach for protein sizing. Proteins were concentrated rapidly (<5 min) over 1000-fold followed by high-resolution separation in the sieving monolith. Proteins with concentrations as low as 50 fM were detectable with 30 min of preconcentration time. The integrated preconcentration-sizing approach facilitates analysis of low-abundant proteins that cannot be otherwise detected. Moreover, the integrated preconcentration-analysis approach employing in situ formation of photopatterned polymeric elements provides a generic, inexpensive, and versatile method to integrate functions at chip level and can be extended to lowering of detection limits for other applications such as DNA analysis and clinical diagnostics.

Field-Scale Compositional Simulation of a CO2 Flood in the Fractured Midale Field

Abstract A stimulation test using electric heating was conducted on a single oil production well in the Schoonebeek reservoir in The Netherlands during 1989 and 1990. The performance of the test and its interpretation is described. The Bentheim reservoir sands are 31 m thick with a porosity of 0.3 and a permeability in the range 0.2 - 4 µm2; the oil has an in-situ viscosity at 160 mPa.s and is waxy with a cloud point very close to the reservoir temperature of 40 °C. The reservoir pressure of about 7000 kPa is supported by a strong edge aquifer. The objective of the test was to stimulate oil production with heat and, particularly, to melt wax that was suspected to be present either near the wellbore or uniformly throughout the reservoir. Prior to stimulation the oil production rate was 13 m3/d at a water cut of 35%. As the surface power dissipated was increased above 60 kW, the oil production rate increased abruptly to 30 m3/d with a bottomhole temperature in the range 54 to 60 °C; at higher power levels no further increase of production rate was observed. Analytical methods proved very useful for understanding the electric healing process, particularly for tracing the electric current flow path in the reservoir and for modelling the heat distribution and production response. Numerical simulations of the well's performance showed that the observed abrupt increase of oil production rate was compatible with the melting 01 wax at 60 °C and partial removal of a skin (of approximately 27) but not of a wax deposited uniformly throughout the reservoir. Introduction Though electrical heating has been used to stimulate well productivity al various times over the last 25 years, it is not widely applied. A lest of the stimulation method was recently completed on Well SCH-280 in the RW2-E area of the Schoonebeek oil reservoir of The Netherlands (see Figs. 1 and 2) by the Nederlandse Aardolle Maatschappij B. V. (NAM). In this paper we describe the properties of the Schoonebeek reservoirand the characteristics of Well SCH-280 and review the objectives, test programme and actual performance of the electric heating stimulation (EHS) test. In several respects, the information required to interpret the test unambiguously was not available. To circumvent these limitations, methods were developed for inferring the electric current flow path and heat distribution in the reservoir, Using both analytical and numerical simulation methods, a broadly consistent interpretation of the test was developed and this is described herein. FIELD PERFORMANCE OF OTHER ELECTRIC HEATING TESTS Over the last 25 years there have been a number of reports in the literature of planned or executed field tests of the electric heating process, mostly based on the ohmic dissipation of electric energy in the formation. Electrothermic Co., for example, stimulated four wells of the Little Tom field in South Texas. The reservoir there contains 8 - 12 °API gravity oil with a high pour point [1,2].

Validation strategies of HIMAG in interfacial flow computation for fusion applications

HIMAG, a 3-D incompressible MHD free surface code developed by HyPerComp Inc., in a joint research project with UCLA has been successfully applied for APEX [M.A. Abdou, A. Ying, N. Morley, et al., On the exploration of innovative concepts for fusion chamber technology, APEX Interim Report Overview, Fusion Eng. Des. 54 (2001) 181–247] and fusion relevant cases [R. Munipalli, V. Shankar, M.-J. Ni, N. Morley, et al., Development of a 3-D incompressible free surface MHD computational environment for arbitrary geometries: HIMAG DOE phase-II SBIR, period of performance: June 2001–June 2003, Final Report, June 2003; N. Morley, S. Smolentsev, N. Munipalli, M.-J. Ni, D. Gao, M. Abdou, Progress on the modeling of liquid metal, free surface, MHD flows for fusion liquid walls, Fusion Eng. Des. 72 (2004) 3–34] including LIMITS and NSTX. This unique code was developed to model multiple solid and liquid phase materials with arbitrary geometry. The inclusion of complex-geometry, electrically conducting walls and nozzles are essential since electric current closure paths are typically through these solid structures. In HIMAG, a second-order variable density projection method is used to simulate incompressible Navier–Stokes equations and the level set method is used to capture free surfaces. HIMAG is developed on unstructured grids, and can be run in parallel across multiple processors, and is thus able to efficiently solve large complex problems. HIMAG has already been validated for steady and unsteady single-fluid flow with/without MHD effects. In this paper, we demonstrate some validation cases for interfacial flows using HIMAG.

Numerical analysis of projection welding on auto-body sheet metal using a coupled finite element method

A comprehensive finite element method employing a subroutine to link up submodules of commercial code ANSYS is proposed to perform analysis of projection welding in quantitative detail. In order to solve the complexity due to dynamic changes in heat and electrical current flow paths, as well as temperature-dependent material properties, information about contact interfaces and the geometry of the projection areas have been taken into account. By updating parameter information among these submodules in an incremental manner, a truly thermal-electrical-mechanical coupled numerical analysis is realized for projection welding simulation. A case study of an automotive door assembly welding process is carried out and a series of experiments is conducted to confirm the validity of the newly developed method. The agreement between the experimental and numerical results is satisfactory, indicating that the incrementally coupled finite element method may be suitable for projection welding research. Finally, future work to extend this method in optimizing projection welding process design is also presented.

Bipolar radiofrequency ablation of liver metastases during laparotomy. First clinical experiences with a new multipolar ablation concept

Radiofrequency ablation (RFA) is a promising method for local treatment of liver malignancies. Currently available systems for radiofrequency ablation use monopolar current, which carries the risk of uncontrolled electrical current paths, collateral damages and limited effectiveness. To overcome this problem, we used a newly developed internally cooled bipolar application system in patients with irresectable liver metastases undergoing laparotomy. The aim of this study was to clinically evaluate the safety, feasibility and effectiveness of this new system with a novel multipolar application concept. Patients with a maximum of five liver metastases having a maximum diameter of 5 cm underwent laparotomy and abdominal exploration to control resectability. In cases of irresectability, RFA with the newly developed bipolar application system was performed. Treatment was carried out under ultrasound guidance. Depending on tumour size, shape and location, up to three applicators were simultaneously inserted in or closely around the tumour, never exceeding a maximum probe distance of 3 cm. In the multipolar ablation concept, the current runs alternating between all possible pairs of consecutively activated electrodes with up to 15 possible electrode combinations. Post-operative follow-up was evaluated by CT or MRI controls 24-48 h after RFA and every 3 months. In a total of six patients (four male, two female; 61-68 years), ten metastases (1.0-5.5 cm) were treated with a total of 14 RF applications. In four metastases three probes were used, and in another four and two metastases, two and one probes were used, respectively. During a mean ablation time of 18.8 min (10-31), a mean energy of 48.8 kJ (12-116) for each metastases was applied. No procedure-related complications occurred. The patients were released from the hospital between 7 and 12 days post-intervention (median 9 days). The post-interventional control showed complete tumour ablation in all cases. Bipolar radiofrequency using the novel multipolar ablation concept permits a safe and effective therapy for the induction of large volumes of coagulation in the local treatment of liver metastases.

Electric field in hard superconductors with arbitrary cross section and general critical current law

The induced electric field E(x) during magnetic flux entry in superconductors with arbitrary cross section Ω and general critical current law, has been evaluated by integration along the vortex penetration paths. Nontrivial flux motion streamlines are obtained from a variational statement of the critical state, which takes the form of an optimization problem on the finite element discretization of Ω. The generality of the theory allows one to deal with physical conditions not considered before. In particular, it is shown that the boundary condition to be used for determining E is the knowledge of the locus E=0 within the sample. This is emphasized for anisotropic materials in which the electric field is not parallel to the surface. Both numerical and analytical evaluations are presented for homogeneous materials with different geometries: convex and concave contours, samples with holes, variable curvature contours, and for anisotropic samples. In the isotropic case, discontinuities in the electric current paths are shown to be related to changing curvature of the sample’s surface. Anisotropic samples display the same kind of discontinuities, even for constant surface curvature.

Magneto-optical observation of the latchup effect in CMOS ICs induced by uniform and local irradiation

A new application of garnet films with high Faraday rotation—the first direct observation of latchup effect in serially produced complementary metal-oxide-semiconductor integrated circuits (CMOS ICs)—is reported. The visualization method based on the formation of straight domain walls inside magneto-optical films along electrical current path in ICs is used. The influence of spatially uniform or focused laser irradiation on the latchup configuration and thresholds is discussed.

Models of electron transport through organic molecular monolayers self-assembled on nanoscale metallic contacts

We propose a model of electrical conduction through self-assembled monolayers (SAM's) of organic molecules that bridge the gap between a pair of nanoscale metallic contacts. In this model each molecule bonds chemically to only one of the contacts. For dense SAM's the dominant electric current path is through two overlapping molecules each bonded to a different metal contact whereas for dilute SAM's the current flows through a single molecule. The model accounts quantitatively for the experimental data of M. A. Reed et al. [Science 278, 252 (1997)] on gold break junctions containing benzene-dithiol (BDT) SAM's, including the magnitude of the measured differential conductance. It also accounts for the striking differences between the data on the Au/BDT system and the recent measurements of J. Reichert et al. [cond-mat/0106219, 2001 (unpublished)] on a somewhat different system, namely, the strong asymmetry of the current-voltage characteristic and the larger size of the differential conductance found in latter experiments. We also present calculations of electron transport through dense and dilute SAM's of ${\mathrm{SC}}_{6}{\mathrm{H}}_{4}\mathrm{S}\ensuremath{-}{\mathrm{CH}}_{3}$ molecules. Experiments on these systems should test the validity of the proposed model.

Analysis of piezoresistive properties of CVD-diamond films on silicon

The piezoresistive properties of CVD-diamond are still very much in discussion since not only the materials energy band structure properties have to be considered but also the grain boundaries and internal stress distribution. Here, the experimental piezoresistive properties of CVD-diamond-on-silicon layers for free standing structures have been investigated comprehensively. The longitudinal gauge factor k l has been extracted using freestanding diamond cantilevers on silicon. The piezoresistors have been grown selectively onto the surface of diamond cantilevers near the mechanical suspension and doped with boron (acceptor). The electrical contacts are based on the tunneling mechanism with a silicon-based multilayer metalization leading to a linear IV-characteristic. Gauge factor values, k l, have been extracted on various structures with different doping concentrations and diamond film quality (highly oriented and textured, textured, randomly oriented), depending on temperature (room temperature, −350°C) and intrinsic stress. Highly oriented and textured films with grain sizes between 3 and 10 μm have been used to realize ‘single grain’ resistor structures enabling the investigation of grain boundaries in the electrical current path of the piezoresistor. Raman measurements have been performed to measure the intrinsic stress in the diamond grains. Gauge factors, k l of between 4 and 28 have been extracted. Largest k l values were observed on piezoresistors on highly oriented and textured diamond (HOD) films. Results of this work have been used in piezoresistive sensor applications.

Distribution of electric current path and temperature in spark sintering: H.Watanabe et al. (Kagawa Industrial Technology Centre, Takamoto, Japan.) J. Jpn Soc. Powder Powder Metall., vol 44, no 10, 1997, 974–979. (In Japanese.)

Distribution of electric current path and temperature in spark sintering: H.Watanabe et al. (Kagawa Industrial Technology Centre, Takamoto, Japan.) J. Jpn Soc. Powder Powder Metall., vol 44, no 10, 1997, 974–979. (In Japanese.)

A numerical investigation of three-dimensional magnetoconvection in rectangular cavities

In this paper the influence of stationary magnetic fields of arbitrary direction on three-dimensional natural convection in liquid metals is investigated. The liquid metal is confined in electrically insulating rectangular cavities. The convection is driven by horizontal or vertical temperature gradients. A second-order finite-difference method is employed to solve the basic dimensionless equations. Electric current paths and the effect of resulting Lorentz forces on the organisation of flow and heat transport are studied. Electric currents often close within the fluid without short circuiting through Hartmann layers. Typical flow patterns show excessive intensities in regions close to corners.

抵抗シーム溶接性に及ぼす通電領域の影響

抵抗シーム溶接性に及ぼす通電領域の影響

放電焼結における通電経路とモールド内部の温度分布

In spark sintering copper powder and alumina one with a graphite and insulated dies under a constant pressure and a constant electric current, electric voltage between electrodes and temperature distributions of die, punch and specimen were measured. And, we considered effect of the electric current paths on the spark sintering.In the first case of sintering the copper powder with the graphite die, during initial electricity, almost all the electric current went through the specimen. During sequential electricity, the electric current went through both the graphite die and the specimen. Therefore, fluctuation of temperature distribution in the specimen was decreased as the discharged time was spent.In the second case of sintering the copper powder with the insulated die, the electric current went through the graphite punch and the specimen. The fluctuation of temperature distribution in the specimen was larger than that of the case which the graphite die was used, for the specimen was not heated by the graphite die.In the third case of sintering of alumina powder with the graphite die, the electric current went through the graphite punch and the graphite die. Therefore, the temperature distribution of both the graphite mold and the specimen was considerably different from that of the case of the copper powder with the graphite die.

Magnetohydrodynamic flow in a right-angle bend in a strong magnetic field

The magnetohydrodynamic (MHD) flow through sharp 90° bends of rectangular cross-section, in which the flow turns from a direction almost perpendicular to the magnetic field to a direction almost aligned with the magnetic field, is investigated experimentally for high values of the Hartmann number M and of the interaction parameter N. The bend flow is characterized by strong three-dimensional effects causing a large pressure drop and large deformations in the velocity profile. Since such bends are basic elements of fusion reactors, the scaling laws of magnetohydrodynamic bends flows with the main flow parameters such as M and N as well as the sensitivity to small magnetic field inclinations are of major importance. The obtained experimental results are compared to those of an asymptotic theory.In the case where one branch of the bend is perfectly aligned with the magnetic field good agreement between the results obtained by the asymptotic model and by the experiments was found at high M ≈ 8 × 10 and N ≈ 105 for pressure as well as for electric potentials on the duct surface. At lower values of N a significant influence of inertia has been detected. The pressure drop due to inertial effects was found to scale with N−1/3. The same – 1/3-power dependency on N has been found in the vicinity of the bend for the electric potentials at walls aligned with the magnetic field. At walls with a significant normal component of the field an influence neither of the Hartmann number nor of the interaction parameter has been found. This suggests that the inertial part of the pressure drop arises from inertial side layers, whereas the core flow remains inertialess and inviscid. A variation of the Hartmann number is of negligible influence compared to inertia effects with respect to pressure drop and surface potential distribution. The viscous part of the pressure drop scales with M−½.Changes of the magnetic field orientation with respect to the bend lead in general to different flow patterns in the duct, because the electric current paths are changed. The inertia–electromagnetic interaction determines the magnitude of the inertial part of the pressure drop, which scales with N−1/3 for any magnetic field orientation. The dependence of the pressure drop on M remains proportional to M−½. With increasing M and N the measured data tend to those predicted by the asymptotic model. Local measurements within the liquid metal exhibit discrepancies with the model predictions for which no adequate explanation has been found. But they show that below a critical interaction parameter flow regions exist in which the flow is time dependent. These regions are highly localized, whereas the flow in the rest of the bend remains steady.

Electrical current paths in acute pericarditis

The electrocardiographic changes accompanying pericarditis consist of ST elevation in most of the leads of the 12-lead electrocardiogram. The source of this ST elevation is thought to be local inflammatory changes in the epicardium underlying the inflamed pericardium. The current from this area of ST elevation must return to some unaffected region of the heart and this should be associated with a region of ST depression. This current path from the external epicardial surface has been postulated to flow back into the endocardium through the great vessels and atria. To test this hypothesis, 18 patients with pericarditis were studied by body surface potential mapping and inverse epicardial potential distributions were computed. The resultant maps were compared to those of normal people and patients with acute anterior infraction. Epicardial maps from patients with pericarditis showed a region of current flow into the heart over the great vessels and atria in all 18 patients. This pattern was not seen in normal patients or infarction patients and was consistent with the mechanism resulting in ST elevation in pericarditis being one of current flowing from the epicardium out into the thorax and black into the heart through the great vessels and atria.

Transport of fluid and electric current through a single fracture

One expects the hydraulic and electrical conductivities of rock to be related, since there is an analogy between the differential equations describing each process. Fractures in rock are commonly described by the parallel plate model, where the fracture surfaces are smooth and parallel with a separation or aperture of d. For this model the hydraulic conductivity is proportional to d3, whereas the electrical conductivity is proportional to d. Deviations from the parallel plate model are expected, since real fracture surfaces are rough and in partial contact. Computer simulations of fluid flow and conduction of electricity were performed on simulated fractures composed of rough surfaces generated with a fractal algorithm. The finite difference method was used to calculate the volume flow rate and electric current. This solution was used in the parallel plate model to get an effective hydraulic aperture dh and electric aperture de. The electric and hydraulic apertures are nearly the same when the surfaces are widely separated. However, de is always smaller than dh, with the difference increasing as the fracture closes. Additionally, the local directions of fluid flow and electric current are not the same. Thus contrary to the common assumption, the actual path length of a fluid particle as measured by the tortuosity is different for each process. The results of these simulations are consistent with the “equivalent channel model,” which shows that by introducing the tortuosity of the fluid flow or electric current paths, one can relate the microscopic physics of the transport properties to the macroscopic behaviors described by Darcy's and Ohm's laws.

Mathematical modelling and computer simulation of continuous free flow isotachophoresis

A mathematical model of continuous free flow isotachophoresis (ITP) is developed which describes the movement of the boundary between the zones of the leading and terminating electrolytes (or sample) in a free-flow electrophoretic cell of rectangular cross-section operating under a constant voltage and a hydrodynamic counterflow regime. Although not considering some disturbances of a real process (diffusion, electroosmosis, thermoconvection, parabolic velocity profile), the model predicts important parameters of the process, e.g., the coordinates of the boundary between the zones of the leading and terminating electrolytes (or sample), the intensity of the electric field, electric current, Joule heat, electromigration velocity and effective separation path. Based on this model, a computer program was developed which makes possible simulation of a continuous free flow ITP process and its optimization.

The Shattering Effect of Lightning-Pressure from Heating of Air by Stroke Current

The shattering effect attributed to lightning is due to lightning's secondary effect-the pressure impulse of air heated by the lightning. At distances over a few tens of feet, we know this as thunder, but at less than 10-20 ft, this pressure can be great enough to destroy many man-made structures. By combining results from several sources, it is possible to determine the intensity of this pressure from the stroke current magnitude and the distance from the stroke terminal to the susceptible structure. From this it becomes apparent the lightning-protection systems need to take into account this pressure aspect as well as the electrical current path to earth, as presently specified.

Direct Observation for the Effect of Electric Current on Contact Interface

The conditions of the contact interface affect contact resistance characteristics. Therefore, information of the contact interface is very important for the study of contact performance. However, a real contact area, which carries the electric current path, is quite small. If the area can be observed directly, much information of the contact interface will be obtained. Such an investigation has not been performed for electric contacts energized by current. The experimental and technical realization of the equipment for measuring and directly observing the characteristics of contact interface energized by current is described. It is composed of an automatically contact-making apparatus, conductive transparent electrodes, and an inverted type metallurgical microscope. Investigations were carried out for various kinds of contact materials from the viewpoint of how the flowing current affects the interface of real contact area. The real contact area increases markedly by Joule heating when the temperature in the area rises to the recrystallization temperature peculiar to metals. The softening temperature agrees with the recrystallization temperature. Sulfide films deform due to softening. This softening of the films causes !ow contact resistance characteristics.