Symmetric Contacts Research Articles

Fast High-Resolution Simulation of the Gross Slip Wear of Axially Symmetric Contacts

ABSTRACTIn the present article, we study the development of a wear profile in an axially symmetric contact under conditions of gross slip and assumption of the Reye-Archard wear criterion. Simulations are carried out using the method of dimensionality reduction and a full finite element method (FEM) formulation. The calculation time of the proposed model is several orders lower than that of FEM-based models and allows for much higher spatial resolution.

Functional Central Limit Theorem for the Interface of the Symmetric Multitype Contact Process

We study the interface of the symmetric multitype contact process on Z. In this process, each site of Z is either empty or occupied by an individual of one of two species. Each individual dies with rate 1 and attempts to give birth with rate 2R lambda; the position for the possible new individual is chosen uniformly at random within distance R of the parent, and the birth is suppressed if this position is already occupied. We consider the process started from the configuration in which all sites to the left of the origin are occupied by one of the species and all sites to the right of the origin by the other species, and study the evolution of the region of interface between the two species. We prove that, under diffusive scaling, the position of the interface converges to Brownian motion.

Simulation of the influences of surface topography of deposited layer on arc shape and state in arc based additive forming

The stacking deposition and the overlapping deposition are usually employed in arc based additive forming process, which will result in different surface topographies of deposited layer. Consequently, the shape and state, heat and mass transfer of electric arc will be affected by the surface topography of deposited layer. A three-dimensional numerical model of electric arc based on magnetic fluid dynamics, local thermodynamic equilibrium and optical thin assumption for arc based additive forming process with pure argon shielding gas is presented. Simultaneously, four kinds of deposited layer model with different surface topographies are established, which are the deposited layer models of planar substrate, namely the substrate without weld bead, deposited layer model of single-pass single-layer, deposited layer model of single-pass two-layers, and deposited layer model of overlapping. The numerical calculation is performed on condition that deposition current and the distance between the electrodes are constant. And the simulation results include the profile of electric arc, corresponding temperature field, flow field, current density, electromagnetic force, and the arc pressure distribution. The temperature field of planar substrate accords well with other researcher's experimental result, and the profiles of electric arc are in good agreement with images captured by high-speed camera. Surface topography of deposited layer plays a decisive role in determining the profile of electric arc under the same process conditions. The comparison of evolvement among the distributions on specified paths shows that the electric arc of planar substrate has higher temperature, velocity, current density and pressure in the arc center, arising from completely symmetrical deposition layer model and smaller contact area between the arc and the substrate; the number of layers of single-pass multi-layer deposited layer has little influence on various parameters of electric arc, but because the deposited layer height changes, the temperature and pressure on the outside of deposited layer have small deviation; asymmetric arc profile will form when the overlapping deposition is performed. There is a relatively low temperature in the arc center, resulting from larger contact area between the arc and the surface of deposited layer. In addition, the distributions of current density, electromagnetic force and pressure deflect to the deposited layer. The above conclusions can provide a theoretical basis for basic research and process decision of arc based additive forming, and it can also provide the parameters for the subsequent weld pool dynamics and metal transfer simulation.

Solid state carbon nanotube device for controllable trion electroluminescence emission.

Semiconducting carbon nanotubes (CNTs) have a direct chirality-dependent bandgap and reduced dimensionality-related quantum confinement effects, which are closely related to the performance of optoelectronic devices. Here, taking advantage of the large energy separations between neutral singlet excitons and charged excitons, i.e. trions in CNTs, we have achieved for the first time all trion electroluminescence (EL) emission from chirality-sorted (8,3) and (8,4) CNT-based solid state devices. We showed that strong trion emission can be obtained as a result of localized impact excitation and electrically injected holes, with an estimated efficiency of ∼5 × 10(-4) photons per injected hole. The importance of contact-controlled carrier injection (including symmetric and asymmetric contact configurations) and EL spectral stability for gradually increasing bias were also investigated. The realization of electrically induced pure trion emission opens up a new opportunity for CNT film-based optoelectronic devices, providing a new degree of freedom in controlling the devices to extend potential applications in spin or magnetic optoelectronics fields.

Existence Theory for the Radially Symmetric Contact Lens Equation

In this paper we present a variational formulation of the problem of determining the elastic stresses in a contact lens on an eye and the induced suction pressure distribution in the tear film between the eye and the lens. This complements the force-balance derivation that we used in earlier work [K. L. Maki and D. S. Ross, J. Bio. Sys., 22 (2014), pp. 235--248]. We investigate the existence of solutions of the relevant boundary value problem for the singular, second-order Euler--Lagrange equation. We prove that, for lenses of constant thickness, solutions exist. We present an example to show that in some cases in which the lens thickness increases with distance from the lens center no solution exists.

Finite Elements Approach to Predicting Impedance Response of Geometrically Convoluted Samples

Capacitance and resistance are extensive variables that depend on the geometry of a sample. Therefore, to obtained a normalized value, attributable to the material and not the sample shape and dimension, the geometry has to be taken into account. While with certain geometric forms simple division of multiplication, based on length and cross-section can be applied, with more convoluted forms this is not as straightforward. Ideal measurement will be done on samples geometrically simple. However, with awkward shapes or irregular electrode placements, measurements are still done and the geometry effect can be corrected after the fact. As an example is a ceramic disc with grain and boundary resistance and capacitance, that could be encountered in studies of advanced high temperature materials, e.g., for sensors of high-temperature fuel cells. The disks prepared by various methods of synthesis are contacted on their flat sides to the impedance analyzer circuitry. Our study correlates the (simulated) measured data to data that would be expected if perfectly symmetrical all-covering contacts were used.

Manufacturing technologies for photovoltaics and possible means of their development in Russia (Review): Part 2. Modification of production technologies for photoelectric converters, development of contact structures, and choice of promising technologies for expansion of FEC production in Russia

As the development of the first part of the review of modern industrial technologies for manufacture of photoelectric converters (PECs) of solar power, the present paper considers modifications of technologies for manufacture of PECs, including various thin-film techniques. Main tendencies in the advancement of contact structures of PECs are described. Formulation and substantiation are made for promising, in the authors' opinion, lines of the development of industry of PECs in Russia based on the upcoming implementation of 1.5 GW network photovoltaic power plants to 2020, which are developed with the national support under conditions of the fulfillment of rigid requirements to manufacture localization. As the most prospective technology for development of the competitive manufacture of photoelectric converters subject to the Russian scientific and engineering groundwork, the authors recommend the technology based on single-crystal silicon of the n type with the passivation of the frontal and rear sides and symmetrical contacts (n-PASHa), which provides the possibility to produce double-faced solar modules also.

Nanoparticulated hydrophobic CdO coatings deposited by microwave procedure

A novel and inexpensive way to deposit nanostructured cadmium oxide (CdO) coatings is described. Metallic Cd is evaporated by heating a silicon carbide crucible, via microwave radiation at standard atmosphere conditions. The Cd vapour rises from the crucible and reacts with the atmospheric oxygen depositing on a glass substrate. CdO coating is homogeneously distributed above the glass surface and it presents a well-defined cubic-shaped nanostructure. The as-deposited CdO coatings showed good hydrophobic properties and achieved symmetric contact angles of 112°. The hydrophobic behaviour was lost after a 75 min of heat treatment at 723 K.

Investigation of load carrying capacity of asymmetric high contact ratio spur gear based on load sharing using direct gear design approach

The Direct Gear Design® approach is one of the many gear designing methods available to improve load carrying capacity of the gear pairs. For customized gear pairs, the direct gear design approach is more advantageous over conventional design. In this paper, a parametric study is carried out for asymmetric high contact ratio spur gears based on load sharing method to determine the improvement in load carrying capacity. A finite element model for multi-pair contact is adopted to determine the non-dimensional fillet and contact stresses which quantify the load carrying capacity of the gear pairs. The results of direct designed symmetric and asymmetric high contact ratio spur gears are compared with the conventional symmetric high contact ratio spur gears. Also, the influence of gear parameters such as addendum pressure angle, gear ratio, teeth number and backup ratio of non-dimensional stresses is analyzed in detail. The results show significant improvement in gear pair performance for all parameters analyzed.

Finite Elements Approach to Predicting Impedance Response of Geometrically Convoluted Samples

The geometry of a sample is of utmost importance in interpretation of impedance measurements and correlating them to the properties of the studied material. The first, always considered, issue is inclusion of the geometrical dimensions, so that capacitance and resistance of a sample can be interpreted and reported for proper comparison based on values per unit dimensions. In ideal measurements the samples prepared are a prioriprepared in simple geometries, allowing proper electric contact connections so that the calculations are simplified and measurements in a single laboratory, even without data interpretation, lend themselves to quick visual side-by-side comparison. However, such arrangement is not always possible and therefore we investigated, by method of computer simulation, dependence of impedance results on geometry of a sample and location of electrode connection. As an example is a ceramic disc with grain and boundary resistance and capacitance, that could be encountered in studies of advanced high temperature materials, e.g.,for sensors of high-temperature fuel cells. The disks prepared by various methods of synthesis are contacted on their flat sides to the impedance analyzer circuitry. Our study correlates the (simulated) measured data to data that would be expected if perfectly symmetrical all-covering contacts were used. While in part the correlation reveals that a simple multiplication factor can be used in some cases to correct for the geometry of the electrode placement, under conditions of more extreme electrode placements the response is such, that equivalent modeling of the obtained impedance data is not adequately described only by RC circuits. Instead, a constant phase element has to be introduced. The simulation for this work was done using the ANSYS software package. The figure shows the geometric layout used for simulation. In this case a sample disk of a 30-mm diameter, thickness 7 mm is connected to the measurement circuit by two symmetrical, centrally placed metal circular electrodes of diameter 14 mm. In the process of simulations the size of the electrodes and their placement vs. the centerr of the sample was varied. For the data fitting to the suitable equivalent circuits was used the ZView package from Scribner Associates. This work was supported by the project “CEITEC - Central European Institute of Technology” (CZ.1.05/1.1.00/02.0068) from European Regional Development Fund. Figure 1

Schottky Biristor: A Metal-Semiconductor–Metal Bistable Resistor

In this brief, we report a novel metal-semiconductor-metal-based bistable resistor, called the Schottky biristor, whose performance is superior to the existing bipolar junction transistor-based biristors. The proposed device can be realized by joining symmetrical Schottky contacts back to back. Apart from being free of the thermal budgets involved in the fabrication of p-n junctions in a biristor, the Schottky biristor also has much lower latch voltages (latch-up voltage of 1.62 V and latch-down voltage of 1.18 V) and a reasonable latch window (0.44 V) as demonstrated by our simulation results.

Spin polarization of the asymmetric quantum point contact and conductance anomalies in the case of resonances

We study spin polarization and conductance of the asymmetric quantum point contact. We consider both Rashba coupling and lateral spin–orbit interaction induced by laterally asymmetric confinement potential. We show that in longitudinally symmetric quantum point contact, the spin polarization is not accompanied by the appearance of the conductance plateau at 0.5G0(G0=2e2/h). In longitudinally asymmetric quantum point contact the above plateau arises due to the presence of resonant states within the using one-electron approximation. An explanation of the experimental fact that the plateau exists only for a limited range of variation of the gate voltage is given.

Two-dimensional symmetric double contacts of elastically similar materials

The two-dimensional contact problem for an elastic body indenting an elastically similar half plane resulting in double contacts is important for various applications. In this paper, a generic quasi-static two-dimensional symmetric double contact problem with nonsingular end points between two elastically similar half planes, under the constant normal and oscillatory tangential loading, is analyzed. The classical singular integral equations approach is utilized to extract the pressure and shear functions in the contact zones; subsequently boundary conditions at end points are applied and a new side condition is derived and titled “the consistency condition” for symmetric double contacts. This condition is necessary for determining the extent of the contact and stick zones. Next, this analytical approach is applied to the symmetric indentation of a flat surface by two rigidly interconnected wedge-shaped punches.

Highly efficient piezotronic strain sensors with symmetrical Schottky contacts on the monopolar surface of ZnO nanobelts.

Piezotronic strain sensors have drawn a lot of attention since the piezotronic theory was established. In this work, we developed a flexible piezotronic strain sensor based on an indium-doped ZnO nanobelt, of which the top surface was the monopolar surface. By connecting two electrodes with the two ends of the top surface of the nanobelt, the strain sensor was constructed. Compared with a nanorod/nanowire based strain sensor, this monopolar surface device avoids the need to identify the polar direction. Under strain, a static potential with the same value and polarity was generated by the coupling effect of the piezoelectric effect and the Poisson effect. This induced piezopotential influenced the Schottky barrier heights at the interfaces of both the source and drain electrodes, resulting in current changes with the same trend at forward and reverse biases. By applying a series of periodical strains, the sensor showed clear, fast and accurate current responses. The gauge factor achieved for compressive strain was 4036. This type of piezotronic strain sensor with a polar surface facing upward presented a high performance and easier fabrication, showing promise for applications in electrical mechanical sensors and MEMS.

Arc-Erosion Behavior of Boric Oxide-Reinforced Silver-Based Electrical Contact Materials Produced by Mechanical Alloying

This study investigated the effect of the boric oxide (B2O3) content on the arc-erosion performance of silver (Ag)-based composite electrical contact materials, produced by powder metallurgy combined with mechanical alloying. Pure Ag and B2O3 powders were milled in a high-energy planetary-type ball mill for 5 h, to obtain a powder mixture that would be used in manufacturing the composites. Powder mixtures containing 5, 10, and 15 vol.% B2O3 were drawn separately into a cylindrical die, pressed, and sintered at 200 MPa and 800°C. For each composition, a symmetrical contact pair configuration was created. Arc-erosion experiments were performed under the following testing conditions: operating voltage of 220 V, AC switching mode, frequency of 50 Hz, switching current of 5 A, and switching frequency of 60 operations/min. The relationship between the weight loss of the contacts and the number of cycles was investigated. Contact surfaces were examined by scanning electron microscopy (SEM). Chemical compositions near the arc were determined by energy-dispersive x-ray spectroscopy. The weight loss decreased with increasing B2O3 content up to 10 vol.%, indicating that the optimal arc-erosion performance (minimum weight loss) was obtained with 10 vol.% B2O3. Excessive B2O3 caused much more worn debris and increased the weight loss. SEM examinations of the contact surfaces showed that the size of the arc-affected zones generally increased with an increasing number of cycles.

Photocurrent imaging of semiconducting carbon nanotube devices with local mirrors

Photocurrent spectroscopy has recently been used by several research groups to study the light–matter interaction in carbon nanotubes. To achieve this, long‐channel devices with symmetric metallic contacts are typically used, where photocurrent of opposite sign is generated at the two contacts. However, in short‐channel devices (<1 µm) the diffraction‐limited laser spot results in simultaneous excitation of both metal–nanotube contacts and leads to partial cancellation of the photocurrent. In this work, we avoid simultaneous excitation of both metal–nanotube contacts by fabricating an isolated metallic mirror over one of the contacts. With the use of (6,5) carbon nanotubes we demonstrate a unipolar photocurrent signal, that is consistent with the second order interband absorption of a (6,5) nanotube.

Self-sustaining charging of identical colliding particles.

Recent experiments have demonstrated that identical material samples can charge one another after being brought into symmetric contact. The mechanism for this charging is not known. In this article, we use a simplified one-dimensional lattice model to analyze charging in the context of agitated particles. We find that the electric field from a single weakly polarized grain can feed back on itself by polarizing its neighbors, leading to an exponential growth in polarization. We show that, by incorporating partial neutralization between neighboring polarized particles, either uniform alignment of dipoles or complex charge and polarization waves can be produced. We reproduce a polarized state experimentally using identical colliding particles and raise several issues for future study.

Current and Noise Properties of InAs Nanowire Transistors With Asymmetric Contacts Induced by Gate Overlap

Nanowire transistors are typically fabricated as geometrically symmetrical devices, with metal/semiconductor source and drain contacts rather than a graduated doping profile. While the source and drain contacts are nominally identical, contact asymmetry can arise when the gate contact is not centered over the nanowire, leaving uneven access regions with no gate coverage on one or both sides of the channel. Measuring the characteristics of devices with symmetric and asymmetric contact geometries allows contact effects to be studied. In this paper, indium arsenide nanowire transistors were fabricated with symmetric and asymmetric gate coverage. It is shown that devices with highly asymmetric gate coverage can exhibit a factor of 10 change in current and a shift in threshold of up to 0.5 V upon reversing the source-drain orientation. Devices with highly asymmetric properties show nearly identical channel-generated noise yet a significant difference in contact-generated noise levels when the contact orientation is reversed. Fully symmetric devices show higher current levels, lower threshold voltages, and lower contact-generated noise than asymmetric devices with either source or drain gated, but channel-generated noise levels are similar.

Development of generalized Iwan model to simulate frictional contacts with variable normal loads

Most friction models are originally proposed to predict restoring forces in mechanical contacts with constant normal load. In practice the contact interface kinematics may involve normal motion in addition to the tangential displacements, leading to variation of the contact normal load. This phenomenon is observed most strongly in contacts with high lateral vibration amplitudes and is known as slap. The current study establishes a general friction model to account for variation in the normal load and enables one to predict the behavior of a contact more precisely. Iwan model (1966) [5] is a suitable candidate for contact interface modeling and is able to represent the stick-micro/macro slip behavior involved in a friction contact. This physical based model is employed in the current work and its physical parameters are generalized to include the normal load variation effects. The model is characterized by a slippage distribution density function and a linear stiffness at stick state. Both these parameters, defined in presence of constant normal load in the original model, are derived considering normal load variation leading to generalization of the contact model. Conventional models with constant normal loads produce symmetric contact interface hysteresis loops, but the developed generalized Iwan model is capable of generating asymmetric hysteresis loops similar to those frequently seen in experiments. The generalized contact model is employed to simulate the measured behavior of a beam with frictional support observed in an experimental test set-up. The contact slippage distribution function is first identified in a constant normal load condition. Next in low levels of contact preloads where variation of the normal load is significant, the identified distribution function in generalized form is employed to predict the experimental observations.

An Unusual Presentation of Nickel‐Associated “School Chair Sign”

Symmetric sources of exposure generally result in symmetric contact dermatitis, but patient habits may distort or modify exposures in ways that may obscure clinical relevance. We present a variant of "school chair sign" consistent with the child's usual habit of sitting obliquely with her right leg crossed over her left leg.