Titanium dental implants coated with Bonelike®: Clinical case report

The aim of the study was to evaluate the direct bone bonding and osteointegration of the commercial pure (cp Ti) implants coated with Bonelike® synthetic bone graft by plasma spraying. The Bonelike® coated implant was placed in the mandible of a 40-year-old patient and it was removed after a healing period of 3 months with a trephine of 6 mm diameter. The structure of the coating and new bone/implant interface of retrieved samples were evaluated using scanning electron microscopy (SEM) and histological analysis using light microscopy. In vivo microstructure observations of Bonelike® coated retrieved implants showed excellent bone remnants on its surface without any tissue and inflammatory signs observed. The reported Bonelike® coated (cp Ti) implants improved primary stability, which may increase the lifetime of the implant. Bonelike® coated dental implants proved to be highly bioactive with extensive new bone formation and strongly bonded to Bonelike® coating.     

Experimental studies on mechanical properties of cellular structures using Nomex® honeycomb cores

An experimental method is presented to obtain the effective in-plane compliance matrices of cellular structures using Nomex® honeycomb cores without a priori assumptions such as orthotropy. In this method, firstly, uni-axial tension tests are carried out for different material orientations. The independent variables in these experiments are the material orientation and displacement of the actuator, while the main dependent variables are positions of the marker points and the force acting on the specimens. Marker tracking technique is used to determine the marker positions which are processed to get strain of the measuring domain, while the stress is estimated through external loading and core geometry. The analysis is confined to the measuring domain under near homogeneous stress and strain fields. The experiment results are processed with transformation and least squares functions to obtain all effective in-plane elastic parameters, which are compared with analytical solution based on deformation of idealized cell structure. Through this comparison, the effects of geometrical parameters of cell structure are discussed in detail. By means of the introduced method, the problem of lack of experimental studies on the effective in-plane compliances of cellular structures in the literature is expected to be solved.     

Determination of in-situ fibre, matrix and interface properties in a composite using tensile tests and an extended shear-lag model

The strength and modulus values of the matrix and of the fibres as incorporated in a ceramic matrix composite (CMC) may differ from those obtained on the matrix and the fibres separately for a number of reasons. The same applies for the interfacial properties obtained from tests on specimens designed for that purpose, and their values in a real CMC. This paper outlines a methodology which allows the determination of the in-situ values of these parameters in the composite. It is based on an evaluation of the results of tensile tests in the light of a newly developed extended shear-lag model. Calibration of the five model parameters leads to the identification of the fibre and matrix moduli, as well as of the interfacial friction coefficient and the radial interface strength. The axial stress profiles obtained from the shear-lag model subsequently allow the determination of the fibre and matrix strength. The methodology is illustrated by application to a 2D woven CMC. In-situ properties at the level of individual tows, and on the level of individual fibres within a longitudinal tow are obtained.     

基于单自由度参数激励模型的车辆随机振动分析

包装件振动可靠性的分析和优化需要构建高效准确的车辆随机振动载荷分析模型.该研究将车辆建模为单自由度参数激励系统,分析车辆在平稳载荷下的加速度响应.基于Mathieu方程分析车辆动态响应特性,结果表明,车辆响应中出现少量的大幅振动响应的原因是参数激励系统中随机过程β(t)的波动引起了系统的失稳.分别构建车辆在稳态、失稳和...     

Vibration analysis of multi-walled carbon nanotubes using a spring–mass based finite element model

We report a study of the vibrational characteristics of multi-walled carbon nanotubes modeled exclusively using springs and lumped masses. Based on the atomic microstructure of the nanotube, three-dimensional nanoscale spring elements are utilized to simulate the dynamic behavior of each layer of the multi-walled carbon nanotubes. Appropriate spring elements are also developed to model the interlayer interactions and describe the van der Waals potentials between carbon atoms on different layers. Direct application of the physical variables of molecular mechanics theory to the springs is used to simulate the relative translations and rotations between atoms as well as the masses of the carbon atoms. The stiffness and mass matrices of the problem are used to construct the dynamic equilibrium equation. The natural modes of vibration and the corresponding natural frequencies are derived by solving the eigenvalue problem for different support conditions. The present method suggests novel basic modes of vibration, beyond those reported in the literature pertaining to multi-walled carbon nanotubes. The effects on the basic modes and natural frequencies created by van der Waals interactions and geometric parameters such as number of layers and aspect ratio are investigated in the context of elastic support conditions. Comparisons with other theoretical studies reveal very good correlations in terms of fundamental modes and frequencies.     

Biomechanical analyses of whiplash injuries using an experimental model

Neck pain and headaches are the two most common symptoms of whiplash. The working hypothesis is that pain originates from excessive motions in the upper and lower cervical segments. The research design used an intact human cadaver head-neck complex as an experimental model. The intact head-neck preparation was fixed at the thoracic end with the head unconstrained. Retroreflective targets were placed on the mastoid process, anterior regions of the vertebral bodies, and lateral masses at every spinal level. Whiplash loading was delivered using a mini-sled pendulum device. A six-axis load cell and an accelerometer were attached to the inferior fixation of the specimen. High-speed video cameras were used to obtain the kinematics. During the initial stages of loading, a transient decoupling of the head occurs with respect to the neck exhibiting a lag of the cranium. The upper cervical spine-head undergoes local flexion concomitant with a lag of the head while the lower column is in local extension. This establishes a reverse curvature to the head-neck complex. With continuing application of whiplash loading, the inertia of the head catches up with the neck. Later, the entire head-neck complex is under an extension mode with a single extension curvature. The lower cervical facet joint kinematics demonstrates varying local compression and sliding. While the anterior- and posterior-most regions of the facet joint slide, the posterior-most region of the joint compresses more than the anterior-most region. These varying kinematics at the two ends of the facet joint result in a pinching mechanism. Excessive flexion of the posterior upper cervical regions can be correlated to headaches. The pinching mechanism of the facet joints can be correlated to neck pain. The kinematics of the soft tissue-related structures explain the mechanism of these common whiplash associated disorders.     

Estimation of time‐to‐failure distribution derived from a degradation model using fuzzy clustering

Some life tests are terminated with few or no failures. In such cases, a recent approach is to obtain degradation measurements of product performance that may contain some useful information about product reliability. Generally degradation paths of products are modeled by a nonlinear regression model with random coefficients. If we can obtain the estimates of parameters under the model, then the time‐to‐failure distribution can be estimated. In some cases, the patterns of a few degradation paths are different from those of most degradation paths in a test. Therefore, this study develops a weighted method based on fuzzy clustering procedure to robust estimation of the underlying parameters and time‐to‐failure distribution. The method will be studied on a real data set. Copyright © 2000 John Wiley & Sons, Ltd.     

Unstable matrix equations and their relationship to measuring the emittance of an electron beam using beam position monitors

In general, the spatial distributions of electron beams from photoinjectors are unknown and are not well approximated by a Gaussian. Therefore, when measuring the emittance, it is important to make no assumptions about the beam's spatial distribution. An emittance diagnostic that fulfills this requirement uses beam position monitors to measure the second moment of the electron beam's image charge. This information, coupled with the beam line's transfer matrix, forms a set of linear equations. The least squares solution to these equations estimates the necessary beam parameters. More often than not, however, this solution is unstable and amplifies the errors in the second moment measurement. For this diagnostic to be viable, a stable implementation has to be found. Described here is an approach that accomplishes this task.     

On the constitutive relation of materials with microstructure using a potential-based cohesive model for interface interaction

Macroscopic constitutive relationship is estimated by considering the microscopic particle/matrix interfacial debonding. For the interfacial debonding, the PPR potential-based cohesive model is utilized. The extended Mori-Tanaka model is employed for micromechanics, while a finite element-based cohesive zone model is used for the computational model. Both models (theoretical and computational) agree well each other in representing the macroscopic constitutive relationship on the basis of the PPR model. The microscopic interfacial cohesive parameters of the PPR model are estimated from macroscopic composite material behavior. In addition, different microscopic debonding processes are observed with respect to different macroscopic constitutive relationships (e.g. hardening, softening, and snap-back).     

Simulation of perforation and penetration in metal matrix composite materials using coupled viscoplastic damage model

In the first part of the two companion papers, theoretical formulation of the multiscale micromechanical constitutive model that couples the anisotropic damage mechanism with the viscoplastic deformation is presented. In the second part of these companion papers the numerical simulation of the computational aspects of the theory are elaborated. The perforation and penetration problem of metal matrix composites (MMCs) due to high impact loading is simulated. In this sense, the computational aspects of the developed theory are elaborated here. First, the verification of the developed model is performed through its numerical implementation in order to test the model predictions of the material characteristic tests. This encompasses uniaxial monotonic loading and unloading under different strain rates, uniaxial cyclic loading, and uniaxial loading and relaxation. The verified material routine of the developed model is then implemented in the explicit finite element code ABAQUS via the user defined subroutine VUMAT at each integration point in order to analyze the projectile impact and penetration into laminated composite plates.     

Performance estimation of a Venturi scrubber using a computational model for capturing dust particles with liquid spray

A Venturi scrubber has dispersed three-phase flow of gas, dust, and liquid. Atomization of a liquid jet and interaction between the phases has a large effect on the performance of Venturi scrubbers. In this study, a computational model for the interactive three-phase flow in a Venturi scrubber has been developed to estimate pressure drop and collection efficiency. The Eulerian-Lagrangian method is used to solve the model numerically. Gas flow is solved using the Eulerian approach by using the Navier-Stokes equations, and the motion of dust and liquid droplets, described by the Basset-Boussinesq-Oseen (B-B-O) equation, is solved using the Lagrangian approach. This model includes interaction between gas and droplets, atomization of a liquid jet, droplet deformation, breakup and collision of droplets, and capture of dust by droplets. A circular Pease-Anthony Venturi scrubber was simulated numerically with this new model. The numerical results were compared with earlier experimental data for pressure drop and collection efficiency, and gave good agreements.     

Analysis of the sensitivity properties of a model of vector-borne bubonic plague.

Model sensitivity is a key to evaluation of mathematical models in ecology and evolution, especially in complex models with numerous parameters. In this paper, we use some recently developed methods for sensitivity analysis to study the parameter sensitivity of a model of vector-borne bubonic plague in a rodent population proposed by Keeling & Gilligan. The new sensitivity tools are based on a variational analysis involving the adjoint equation. The new approach provides a relatively inexpensive way to obtain derivative information about model output with respect to parameters. We use this approach to determine the sensitivity of a quantity of interest (the force of infection from rats and their fleas to humans) to various model parameters, determine a region over which linearization at a specific parameter reference point is valid, develop a global picture of the output surface, and search for maxima and minima in a given region in the parameter space.     

Evaluation of overload-induced fatigue crack growth retardation parameters using an exponential model

In this study, fatigue crack growth rate in mixed-mode overload (modes I and II) induced retardation zone has been predicted by using an “Exponential model”. The important parameter of this model is the specific growth rate. This has been correlated with various crack driving parameters such as stress intensity factor range, maximum stress intensity factor, equivalent stress intensity factor, and mode mixity, as well as material properties such as modulus of elasticity and yield stress. An equation has been formulated for specific growth rate which has been used to calculate crack growth rate under mixed-mode loading conditions. It has been observed that the crack growth rate predicted by the model is in good agreement with experimental results.     

Evaluation of the unavailability of a multistate-component system using a binary model

In this article, we discuss the problem of computing the unavailability of a multistate-component system. We propose the use of a Boolean model describing as much as possible about the system structure. A theorem of two-sided estimation of the approximation error enables us to check the calculation accuracy. An application of this method to a nuclear safety system is offered.     

Ice adhesion of an aqueous solution including a surfactant with stirring on cooling wall: ethylene glycol—a silane coupling agent aqueous solution

Ice adhesion to the cooling wall directly hinders continuous ice formation or system performance due to the increase of flow and thermal resistance. In order to obtain the basic characteristics of two- or three-component aqueous solutions with EG, SCA and water on freezing, the influence of component ratio and supercooling degree on those solutions was investigated through a batch type freezing process of the solutions. Moreover, the strength of ice adhesion was shown to vary by stirring power. Ice adhesion was suppressed when (1) the solution including the additive SCA at comparatively high concentration; (2) the solution had high initial concentration of EG or SCA; (3) the brine temperature was higher; (4) the supercooling degree was comparatively small in the lower concentrations. No ice adhesion occurred at the stirring power below 30 W. Furthermore, particle size of the ice slurry was smaller in higher concentrations.     

Synthesis of a simulation model for an electromagnetic flowmeter

The principles of constructing a simulation model for an electromagnetic flowmeter are considered by means of which it is possible to carry out research into the metrological characteristics of instruments. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 38–43, May, 2006.     

Simulation of mercury capture by sorbent injection using a simplified model

Mercury pollution by fossil fuel combustion or solid waste incineration is becoming the worldwide environmental concern. As an effective control technology, powdered sorbent injection (PSI) has been successfully used for mercury capture from flue gas with advantages of low cost and easy operation. In order to predict the mercury capture efficiency for PSI more conveniently, a simplified model, which is based on the theory of mass transfer, isothermal adsorption and mass balance, is developed in this paper. The comparisons between theoretical results of this model and experimental results by Meserole et al. [F.B. Meserole, R. Chang, T.R. Carrey, J. Machac, C.F.J. Richardson, Modeling mercury removal by sorbent injection, J. Air Waste Manage. Assoc. 49 (1999) 694–704] demonstrate that the simplified model is able to provide good predictive accuracy. Moreover, the effects of key parameters including the mass transfer coefficient, sorbent concentration, sorbent physical property and sorbent adsorption capacity on mercury adsorption efficiency are compared and evaluated. Finally, the sensitive analysis of impact factor indicates that the injected sorbent concentration plays most important role for mercury capture efficiency.     

A half-plane model for analysis of stress in the blade of a spade

The present work deals with the state of stress produced in the blade of a spade as a result of an external load acting around its middle. Such loadings can occur when the cutting edge of a spade encounters a hard obstacle such as a pebble or a boulder. It is shown that a half-plane model can simulate the situation. Stress distributions have been obtained corresponding to five types of external load, namely, concentrated normal, distributed normal, concentrated tangential, distributed tangential and combined normal and tangential. A discussion on the significance of the results is also included.     

基于温度突变模型的冷屏预冷时间计算

为了优化冷屏的预冷系统设计,引入了温度突变模型来分析冷屏的预冷问题。首先介绍了温度突变模型的基理,阐述了将冷屏简化成低温液体输运管的思想。然后对一个大型空间模拟环境试验舱的低温泵氦板预冷系统进行了研究,利用温度突变模型计算得到其理论预冷时间和实际测得的时间相吻合,证明了该模型是可行的。还提出为原始的温度突变模型添加一个修正系数的思想,以便让该模型更加适用于冷屏的预冷过程分析。