Contact Bridges Research Articles

Study of the biocompatibility of porous 3D-TiNi implants in vivo

Introduction. Porous TiNi alloys are widely used in medicine as osteoreplacement implants due to their unique properties of superelasticity and biocompatibility, but their clinical use is severely limited by time-consuming manual fabrication and the inability to create precise geometries. Reconstructive surgery for the replacement of bone defects requires biocompatible endoprostheses of individual shape and complex geometry. The use of porous 3D-TiNi implants can be a solution to many problems in traumatology and bone oncology.Aim: To evaluate the possibility of using porous 3D-TiNi implants in osteoplastic surgery based on a study of the structure and biocompatibility of the material under in vivo conditions.Material and Methods. Porous samples in the form of cones and a single implant for maxillofacial surgery were prepared from TiNi powder by selective laser melting. To print an individual implant for maxillofacial surgery, the personal data of the patient at the Oncology Research Institute were used. The macrostructure, elemental and phase composition of porous titanium nickelide samples were investigated using scanning microscopy and X-ray diffraction analysis. The biocompatibility of porous cone-shaped samples was evaluated in vivo using guinea pigs whose condition was analysed by CT scanning.Results. Structural studies of porous titanium nickelide samples showed that selective laser melting can be used to obtain a continuous porous structure with strong contact bridges between particles of a three-phase powder. In vivo testing of the cone-shaped implants showed no local inflammatory changes, rejection or deformation of the hind limb axes of the experimental animals. The basic feasibility of fabricating a custom implant of complex geometry from TiNi powder using selective laser melting according to a patient’s MSCT data was demonstrated.Conclusions. Porous 3D-TiNi implants obtained by selective laser melting showed high biocompatibility under in vivo conditions. An experimental study confirmed the efficacy and ease of use of 3D TiNi implants, their excellent self-fixation in bone tissue, and bone tissue augmentation at the interface with the implant. The macrostructure, chemical and phase composition of the implant material was found to be close to traditional porous TiNi alloys. It was shown that the method of selective laser melting makes it possible to create complex geometric defects in bone tissue from TiNi.

Universal design method for bright quantum light sources based on circular Bragg grating cavities.

We theoretically develop an efficient and universal design scheme of quantum light sources based on hybrid circular Bragg grating (CBG) cavity with and without electrical contact bridges. As the proposed design scheme strongly alleviates the computational cost of numerical simulation, we present high-performance CBG designs based on the GaAs/SiO2/Au material system for emission wavelengths ranging from 900 nm to 1600 nm, covering the whole telecom O-band and C-band. All designs achieve remarkable Purcell factors surpassing a value of 26 and extraction efficiencies (into a numerical aperture of 0.8) exceeding 92% without contact bridges and 86% with contact bridges. Additionally, we show that our design approach easily deals with realistic structural constraints, such as preset thicknesses of a semiconductor membrane or SiO2 layers or with a different material system. The high design flexibility greatly supports the experimental deterministic fabrication approaches, allowing one to perform in-situ design adaptation and to integrate single quantum emitters of an inhomogeneously broadened ensemble on the same chip into wavelength-adapted structures without spectral constraints, which highly increase the yield of quantum device fabrication.

IMPROVED DESIGN TECHNIQUE FOR CONDUCTING PARTS OF ELECTROMAGNETIC CONTACTORS

The existing design techniques for the conductive parts of the main circuit of electromagnetic contactors are based on two assumptions: the infinite length of the conductor and the absence of its heating, which is determined by the contact resistance. This can lead to significant errors in the design of conductors of finite length, primarily in the design of conductive parts with contact bridges, which contain almost all modern electromagnetic contactors. For a more efficient determination of the geometric parameters of the conductive parts, it is proposed to use an improved technique without the above assumptions. The technique uses a model of a contact formed by overlapping the ends of two rectangular conductors and containing a contact piece as a design one. A key feature of the technique is the use in the calculations of the temperature distribution constant along the length of the conductor, introduced for the first time, which determines the nature of the change in its heating temperature. The main stages of calculation and an example of determining the geometric dimensions of the conductive parts by this method for ABB contactors for different rated currents are given.

Multi-Physics Calculation and Contact Degradation Mechanism Evolution of GIB Connector Under Daily Cyclic Loading

A 3-D electromagnetic-thermal-mechanical coupling finite element model of a gas-insulated bus plug-in connector is proposed in this paper with a subsequent analysis for the contact fatigue mechanism. Special attention has been paid to the contact degradation mechanism under normal cyclic operation conditions, which is important for the optimal designing and condition monitoring of the equipment. The current constriction effect and the contact resistance are considered through modeling the equivalent contact bridges between contact interfaces, and the current densities derived from the electromagnetic field are applied as load inputs in a electrical-thermal-mechanical analysis where varying of friction coefficient is considered. The validity of the calculation model has been demonstrated by temperature rise and relative motion experiments, and the influence of daily changing current and environmental temperature on the thermal and mechanical characteristics of plug-in connector has been analyzed. Analysis results show that the temperature rise among different contact fingers of plug-in connector is not the same with different contact forces, and the plastic deformation can be induced on contact spots. The insert depth of connector can be changed under the action of alternating thermal loading induced by daily change of current and environmental temperature, leading to contact degradation and overheating fault of plug-in connector.

Incorporation of spatial interactions in location networks to identify critical geo-referenced routes for assessing disease control measures on a large-scale campus.

Respiratory diseases mainly spread through interpersonal contact. Class suspension is the most direct strategy to prevent the spread of disease through elementary or secondary schools by blocking the contact network. However, as university students usually attend courses in different buildings, the daily contact patterns on a university campus are complicated, and once disease clusters have occurred, suspending classes is far from an efficient strategy to control disease spread. The purpose of this study is to propose a methodological framework for generating campus location networks from a routine administration database, analyzing the community structure of the network, and identifying the critical links and nodes for blocking respiratory disease transmission. The data comes from the student enrollment records of a major comprehensive university in Taiwan. We combined the social network analysis and spatial interaction model to establish a geo-referenced community structure among the classroom buildings. We also identified the critical links among the communities that were acting as contact bridges and explored the changes in the location network after the sequential removal of the high-risk buildings. Instead of conducting a questionnaire survey, the study established a standard procedure for constructing a location network on a large-scale campus from a routine curriculum database. We also present how a location network structure at a campus could function to target the high-risk buildings as the bridges connecting communities for blocking disease transmission.

Cardiac Myocyte Diversity and a Fibroblast Network in the Junctional Region of the Zebrafish Heart Revealed by Transmission and Serial Block-Face Scanning Electron Microscopy

The zebrafish has emerged as an important model of heart development and regeneration. While the structural characteristics of the developing and adult zebrafish ventricle have been previously studied, little attention has been paid to the nature of the interface between the compact and spongy myocardium. Here we describe how these two distinct layers are structurally and functionally integrated. We demonstrate by transmission electron microscopy that this interface is complex and composed primarily of a junctional region occupied by collagen, as well as a population of fibroblasts that form a highly complex network. We also describe a continuum of uniquely flattened transitional cardiac myocytes that form a circumferential plate upon which the radially-oriented luminal trabeculae are anchored. In addition, we have uncovered within the transitional ring a subpopulation of markedly electron dense cardiac myocytes. At discrete intervals the transitional cardiac myocytes form contact bridges across the junctional space that are stabilized through localized desmosomes and fascia adherentes junctions with adjacent compact cardiac myocytes. Finally using serial block-face scanning electron microscopy, segmentation and volume reconstruction, we confirm the three-dimensional nature of the junctional region as well as the presence of the sheet-like fibroblast network. These ultrastructural studies demonstrate the previously unrecognized complexity with which the compact and spongy layers are structurally integrated, and provide a new basis for understanding development and regeneration in the zebrafish heart.

Evaluation of stress-controlled coal swelling processes

Stress-controlled swelling tests are normally conducted in the laboratory to characterize the evolution of coal permeability under the influence of gas sorption. Typically reductions in permeability are observed from gas-sorption-induced swelling even where effective stresses remain constant. This behavior remains enigmatic as the permeability of the porous coal is determined by the effective stress only. When these observations were interpreted, a matchstick or cubic coal model was assumed. Under this assumption, matrix swelling would not affect coal permeability because of the complete separation between matrix blocks caused by through-going fractures. This is why current coal permeability models have little success in explaining this inconsistency. It is generally believed that the reason for the failure is the inconsistency between the experimental conditions and the model assumptions. However, in this paper, it is considered that the reason may be the internal actions between coal fractures and matrixes have not been taken into consideration. In this study, a model capable of replicating this apparently anomalous behavior is developed. We consider the interactions of the fractured coal mass where cleats do not create a full separation between adjacent matrix blocks but where solid rock bridges are present. We accommodate the role of swelling strains both over contact bridges that hold cleat faces apart but also over the non-contacting span between these bridges. The effects of swelling act competitively over these two components: increasing porosity and permeability due to swelling of the bridging contacts but reducing porosity and permeability due to the swelling of the intervening free-faces. Under these conditions, a new permeability model is formulated. The new model is the key cross link that couples the multiphysics of coal–gas interactions. The formulation and incorporation of this permeability model into the multiphysics simulation of coal–gas interactions are presented in this paper.

Fabrication of high power RF MEMS switches

High power RF MEMS switches have been designed and fabricated. The switches are composed of a matrix of ohmic contact cantilevers and bridges. Optimized fabrication processes have been developed to improve planarization on contact surface and reduce residual stress in switch beams, which ensure a reasonable flat and smooth cantilever and membrane bridge for operation at high RF power and low actuation voltage.

An Analytical Model for Simulation of Heat Flow in Plasma-Sprayed Thermal Barrier Coatings

Numerical (finite difference) and analytical models have been developed for the simulation of heat flow through plasma-sprayed coatings, allowing the effective thermal conductivity to be predicted as a function of microstructural parameters. The structure is assumed to be composed of lamellar material (splats), separated by (thin) pores, within which there are areas of contact (bridges). The analytical model is based on dividing the material into two regimes, within which the heat flow occurs either by unidirectional serial flow through lamellae and pores or by being funneled through the regions of the lamellae above and below the bridges. The validity of this model is demonstrated by a comparison of the predictions obtained from it and those obtained from the numerical model. The effects of pore geometry on conductive and radiative heat transfer within the coating have been investigated over a range of temperatures and gas pressures. It is shown that the main factor controlling the conductivity is the intersplat bridge area. Comparisons are also presented with experimental conductivity data, for cases in which some attempt has been made to characterize the key microstructural features. The study is oriented toward thermal barrier coatings, based on zirconiayttria top coats. It is noted that the effect of microstructural sintering, which tends to occur in these coatings under service conditions, can be predicted using this model.

A Model for the Calculation of the Volume Fraction of Glass Binder in Abrasive Ceramic Tools

A model for the calculation of the volume fraction of glass binder in abrasive ceramic tools is proposed, assuming the glass interlayers between abrasive grains to be spherical particles and the grain shape is approximated by various bodies of revolution: spheres, cylinders, and two paraboloids joined along a circumference The use of the model makes it possible to estimate the minimum content of glass binder, with which no contact bridges are formed between the grains, and also the thickness of the glass interlayers between the grains.

Membrane microextension: a possible mechanism for establishing molecular contact in electrofusion

True cell membrane contact is an essential condition for electro-pulsed cell fusion, but initial morphological perturbation leading to true contact is still not clear. Dielectrophoresis mediated compression and fusogenic pulse induced compaction of cells led to rapid merger of tight membranes, and deprived direct microscopic view of surface membrane perturbation. Freely suspending cells with large and different cell–cell gaps may proceed to electrofusion with perturbed membrane and initiates fusion events at different time. These pulsed exposed cells can be used for capturing changes in the membrane surface and early electrofusion events. Early stage of fusion of freely suspended intact human erythrocytes exposed to single exponential decay pulse was studied by scanning electron microscopy (SEM). Field pulse induces small membrane bumps. Interaction of bumps on adjacent membranes lead to true membrane contact and form bridges between the membranes as microextension, combining both membranes into a topologically single structure. Some fusion products showed expanded fusion zones, which suggest indication of open lumen at contact area.

Structural changes during sintering of powder of the metastable alloy Al-5% Cu prepared by centrifugal atomization of melt

The formation of liquid-phase interlayers between particles of rapidly cooled powder of the alloy Al-5% Cu during sintering was studied by the methods of complex thermal analysis and electron-scanning metallography. It was found that fluctuations of the chemical potential which arise as a result of the decomposition of the solid solution and excess grain-boundary energy drive the sintering process. Contact bridges between the particles are formed as a result of extrusion of melt to the particle surface during grain growth.

Macroscopic mechanism of formation of interparticle contact in electric current sintering of powders

We proposed the mechanism of electric discharge sintering which consists of three stages: the first stage is the formation of the initial contact frame, the second stage is the preferential destruction of a specific volume of the contact frame, and the third stage is the formation of a short-circuited core or of interparticle discrete bridges which close up the interparticle gaps, the increase of the perfection of the contact bridges as a result of consolidation of the central part of the contact bridge, and filling of the resultant voids by the finest particles of electroerosion origin.

Sensory hair fusion in vestibular sensory cells after gentamycin exposure. A transmission and scanning electron microscope study.

Scanning and transmission electron microscopic studies were performed on the crista ampullaris epithelium of gentamycin treated guinea pigs. 200 μl of a 0.3% solution of the antibiotic was injected once a day through a polythene tube into the middle ear. After seven daily injections various stages of sensory hair degeneration could be observed on the crista surface. The central part of the crista was most severely damaged whereas the periphery of the sides of the crista, as well as the area close to the planum semilunatum, showed less change. The sensory cells of type I were more severely damaged than those of type II. The sensory hairs showed successive stages of fusion. Initially multiple points of contact between neighbouring sensory hairs appeared. Later the plasma membrane disappeared at the points of contact and protoplasmic bridges were formed between the hairs. These bridges increased in length and width until a complete fusion occured between two or more neighbouring hairs. Thus giant hairs were formed. The fusion started close to the cuticle and progressed distally. Balloon-shaped protrusions were then formed into which protoplasm containing cell organelles damaged, to varying extent, was pushed out from the cell. Finally the sensory cell disintegrated and disappeared.

Surface Heating by Friction and Abrasion by Thermal Decomposition

Abstract In this research, an attempt is made at determining the frictional temperatures which may occur in tires under various driving conditions. This is based on phenomenological theories of heat conduction. Since these temperature pulses are to be traced back to heat current pulses which may last in the neighborhood of 10−2 second, the resulting warming will be localized in boundary layers of the order of 10−2 cm. From the estimated values of the temperatures, it is concluded that the abrasion which occurs under normal driving conditions is purely mechanical. Only under extreme conditions, such as in very rapid acceleration, or in case of locked wheels—particularly at what we call “contact bridges” or surface elevations—may we expect high frictional temperatures, which lie far above the decomposition temperature of rubber.

The formation and rupture of molten metal bridges in electrical contacts

The bridge of molten metal which is formed between the electrodes of an electrical contact is of considerable interest from a fundamental physical point of view. It is also of practical importance as the cause of erosion and failure of such contacts, which is due to the transfer of metals from one electrode to the other after repeated operations of the contact. The theory of the formation, development and rupture of contact bridges is discussed, and an experimental study of the properties of bridges between slowly opening contacts is described. Observations have been made on bridges in the ordinary atmosphere andin vacuo. The method of producing bridges for visual examination in air andin vacuo has been applied to an investigation of bridges of the noble metals, and of the readily oxidizable base metals. The temperature in a bridge can reach very high values, approaching the boiling point of the metal, with a potential difference of only one to two volts between the electrodes. Theoretical predictions of the shape of molten metal bridges as controlled by the temperature distribution and by surface tension and electrodynamic forces are compared with the shapes actually observed. Photographs of bridges showing the agreement between theory and experiment are given. The potential difference between the electrodes when the rupture of the bridge takes place, — the rupture voltage, has been measured for a number of metals: Pt, Pd, Ag, Au, Cu, Fe, Ni, W, Mo and Sn. The results are discussed in relation to theories of the cause and the mode of rupture and to the electrical and thermal properties of metals at high temperatures.