Parametric investigation of load-induced structure remodeling in the proximal femur

The process of adaptive bone remodeling can be simulated with a self-optimizing finite element method. The basic remodeling rules attempt to obtain a constant value for the strain energy per unit bone mass, by adapting density. The precise solution is dependent on the loads, initial conditions, and the parameters of the remodeling rule. While there are several investigations on developing algorithms leading to the bone density distribution in the proximal femur, these algorithms often require a large number of iterations. The aim of this study was to develop a more efficient adaptive bone remodeling algorithm, and to identify how the bone density distribution of the proximal femur was affected by parameters that govern the remodeling process. The forces at different phases of the gait cycle were applied as boundary conditions. The bone density distributions from these forces were averaged to estimate the density distribution in the proximal femur. The effect of varying the initial bone density, spatial influence function, non-linear order of the adaptive algorithm, and the influence range on the converged solution were investigated. The proposed procedure was shown to converge in a fewer number of iterations and requiring less computational time, while still generating a realistic bone density distribution. It was also shown that varying the identified parameters within reasonable upper and lower bounds had very little impact on the qualitative form of the converged solution. In contrast, the convergence rate was affected to a greater degree by variation of these parameters. In all cases, the solutions obtained are comparable with the actual density in the proximal femur, as measured by Dual-energy X-ray absorptiometry (DEXA) scans.     

A comparison of recently developed correction procedures for electron probe microanalysis

Three recently developed absorption and atomic number correction procedures have been investigated with regard to possible improvements and to the performance of these improved models, which has been studied depending on different values of the absorption correction factor. The test file includes 655 measurements of elements with Z > 10 and 258 B-, C-, and N-measurements. The results show that the models of Bastin and Heijligers and of Sewell, Love, and Scott generally are substantially better than the one of Tan-uma and Nagashima or the established ZAF approach.     

A comparison of different algorithms for circularity evaluation

The measurement and evaluation of circularity of cylindrical components is very important for the majority of cylindrical workpieces used in precision engineering. Further, since the measurement and evaluation of cylindricity is more complex and time consuming, only circularity is evaluated for most applications.The evaluation of circularity from a circularity graph and/or from digital data requires a suitable algorithm. The most commonly used criterion for this has been the least squares criterion, though it is known that this does not necessarily give the best solution. Hence, an attempt has been made in this paper to propose different algorithms and compare them. The algorithms considered are based on the methods of least squares, intuition, general second-degree equation for a circle, best-fit ellipse and simplex search. A comparison of these methods is presented.     

A comparison of two sampling procedures for stereological analysis of cell pellets

Electron micrographs of macrophages within pellets of rat peritoneal exudate cells were analysed by the morphometric point-counting technique to compare the volumetric and surface-to-volume parameters obtained by two distinct sampling procedures. The distinction between the two sampling procedures was dependent upon the nature of the cell profile recorded on the micrographs. The two types of profile compared were (1) equatorial profiles (each containing a substantial nuclear component to facilitate cell identification) and (2) mixed profiles (a random mixture of equatorial profiles, anucleate profiles and cell profile fragments). Exudate cells were obtained from normal animals and from animals stimulated 5 days previously by a single intraperitoneal injection of Freund's Complete Adjuvant in Hank's solution. Volumetric data for intracyto-plasmic organelles were found to be in excellent agreement when the two sampling procedures were compared. In addition, the results gave satisfactory consistency for the recorded decrease in the surface-to-volume estimate of the stimulated macrophage. It is concluded that equatorial profile analysis, in which cell identification is facilitated by virtue of the presence of the nucleus, is suitable for comparative morphometric cytology in the present study and that the biased sampling procedure may have a wide applicability.     

A recommended method for evaluation of international comparison results

A method for the evaluation of international comparison results is demonstrated by consideration of the CCL-K2 key comparison of long gauge block calibration. CCL-K2 is selected for this illustrative example because the comparison measurand is a geometrically simple case of the gauge block central length, and challenging measurement issues often encountered in international comparison exercises are present and can be discussed.     

不同手术方案治疗精索静脉曲张症疗效比较

目的 :比较不同手术方案治疗精索静脉曲张症的疗效、安全性与经济性。方法 :2011年5月—2015年5月收治的78例精索静脉曲张症患者,按照患者意愿将其纳入开放组(n=22)、腹腔镜组(n=38)、显微镜组(n=18),分别实施开放手术、腹腔镜下、显微镜下精索静脉结扎,比较3组患者手术、恢复情况、并发症发生情况及手术前后睾丸血流动力学参数变化。结果 :腹腔镜组、显微镜组术后2 h VAS评分、出院至恢复工作时间、治疗费用均低于开放组,腹腔镜组、开放组、显微镜组手术时间依次增加,腹腔镜组、显微镜组、开放组住院时间依次增加;腹腔镜组、显微镜组并发症发生率低于开放组,差异有统计学意义(P<0.05)。3组患者术后6个月精子密度、前向运动、EDV均较术前升高,PSV、RI、PR均较术前降低,腹腔镜组、显微镜组变化更为明显,差异有统计学意义(P<0.05)。结论 :与传统开放手术相比,腹腔镜、显微镜下精索静脉结扎能够在保证治疗效果的基础上降低术后并发症发生风险,鉴于显微镜技术手术时间较长、操作稍显复杂的弊端,腹腔镜术式可作为精索静脉曲张症的首选方案。     

A three-dimensional morphometrical study of the distal human femur.

The objective of this paper is to present a method to describe the three-dimensional variations of the geometry of the three portions forming the distal part of the human femur: the medial and lateral femoral condyles and the intercondylar fossa. The contours of equally spaced sagittal slices were digitized on the distal femur to determine its surface topography. Data collection was performed using a digitizer system which utilizes low-frequency, magnetic field technology to determine the position and orientation of a magnetic field sensor in relation to a specified reference frame. The generalized reduced gradient optimization method was used to reconstruct the profile of each slice utilizing two primitives: straight-line segments and circular arcs. The profile of each slice within the medial femoral condyle was reconstructed using two circular arcs: posterior and distal. The profile of each slice within the lateral femoral condyle was reconstructed using three circular arcs: posterior, distal and anterior. Finally, the profile of each slice within the intercondylar fossa was reconstructed using two circular arcs: proximal-posterior and anterior, and a distal-posterior straight-line segment tangent to the proximal-posterior circular arc. Combining the data describing the profiles of the different slices forming the distal femur, the posterior portions of each of the medial and lateral femoral condyles were modelled using parts of spheres having an average radius of 20 mm. The anterior portion of the lateral condyle was approximated to a right cylinder having its circular base parallel to the sagittal plane with an average radius of 26 mm. The anterior portion of the intercondylar fossa was modelled using an oblique cylinder having its circular base parallel to the sagittal plane with an average radius of 22 mm. Furthermore, it is suggested that the distal portion of the lateral femoral condyle could be modelled using parts of two oblique cones while the distal portion of the medial femoral condyle could be modelled using a part of a single oblique cone, all cones having their circular bases parallel to the sagittal plane. It is also suggested that the posterior portion of the intercondylar fossa could be modelled using two oblique cones: a proximal cone having its base parallel to the sagittal plane and a distal cone having its base parallel to the frontal plane.     

Combustion stability characteristics of the model chamber with various configurations of triplet impinging-jet injectors

Combustion stability characteristics in actual full-scale combustion chamber of a rocket engine are investigated by experimental tests with the model (sub-scale) chamber. The present hot-fire tests adopt the combustion chamber with three configurations of triplet impinging-jet injectors such as F-O-O-F, F-O-F, and O-F-O configurations. Combustion stability boundaries are obtained and presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio. From the experimental tests, two instability regions are observed and the pressure oscillations have the similar patterns irrespective of injector configuration. But, the O-F-O injector configuration shows broader upper-instability region than the other configurations. To verify the instability mechanism for the lower and upper instability regions, air-purge acoustic test is conducted and the photograph of the flames is taken. As a result, it is found that the pressure oscillations in the two regions can be characterized by the first impinging point of hydraulic jets and pre-blowout combustion, respectively.     

A technique for advanced manufacturing systems capability evaluation and comparison (ACEC)

This paper proposes a generic technique for the evaluation and comparison of the capability of manufacturing systems as a decision-making aid. It provides a methodical approach for extracting key capability factors (CF) and their degree of fulfilment by the institutes. The capability factors and their priorities are determined by experts in the related industry. By adopting this approach, a “capability index” for each institute will be derived. This will be the basis for capability comparison. The proposed method applies fuzzy relations and analytic hierarchy process (AHP) techniques to calculate capability indices. The case study discussed in this paper is the result of a project commissioned by a prominent UK based company (UBC) to consolidate its EU operations. The results illustrate the effectiveness and flexibility of the proposed methodology for a wide range of applications.     

Cross-sectional geometry of the human femur in the mid-third region.

The design of a medical implant requires that the geometry and anatomy of the host region is fully understood. For any prosthesis to be located in the mid-third of the human femur it is therefore vitally important that an in-depth understanding of this region is obtained. This study focuses on the geometry of the medulla and the cortex and the relationship between them in the diaphyseal region of the human femur. Sixteen femora obtained from the Human Biology Department of the University of Leeds were sectioned at 10 mm intervals along the shaft and scaled photographs of each section were taken. These photographs then provided the raw data to enable the variation in long bone cross-sectional geometry to be evaluated. The results show that the medulla is almost cylindrical in the mid-third region, being most cylindrical between 35 and 50 per cent of the total bone length. The medullary width is found to be greater in the antero-posterior direction (> 90 per cent maximum diameter) than in the medio-lateral direction (78-88 per cent maximum diameter) along the studied femoral length. The cortex is also analysed and it is found that the mean cortical thickness on the anterior side is significantly smaller than the medial cortex and the lateral cortex, with the posterior cortex being the thickest. All the above findings suggest that the medulla does not lie centrally within the femur but is positioned slightly anteriorly. Anatomical characteristics such as this can have profound effects on the design of prostheses to be implanted in this region.     

A comparison between micro-CT and histology for the evaluation of cortical bone: effect of polymethylmethacrylate embedding on structural parameters

Cortical bone microstructure is an important parameter in the evaluation of bone strength. The aim of this study was to validate the characterization of human cortical bone microarchitecture using microcomputed tomography. In order to do this, microcomputed tomography structural measurements were compared with those obtained through histological examination (the gold standard). Moreover, to calculate structural parameters, microcomputed tomography images have to be binarized with the separation between bone and nonbone structures throughout a global thresholding. As the effect of the surrounding medium on the threshold value is not clear, an easy procedure to find the global uniform threshold for a given acquisition condition is applied. This work also compared the structural parameters of microcomputed tomography cortical sample scan in air or embedded in polymethylmethacrylate; histology was used as a reference. For each acquisition condition, a fixed threshold value was found and was applied on the corresponding microcomputed tomography image for the parameters assessment. Twenty cortical bone samples were collected from human femur and tibia diaphyses. All samples were microcomputed tomography scanned in air, embedded in polymethylmethacrylate, rescanned by microcomputed tomography, examined by histology and finally compared. A good correspondence between the microcomputed tomography images and the histological sections was found. Paired comparisons in cortical porosity, Haversian canal diameter and Haversian canal separation between histological sections and microcomputed tomography cross sections, first in air and then embedded in PolyMethylMethAcrylate, were made: no significant differences were found. None of the comparisons showed significant differences for cortical porosity, Haversian canal diameter and Haversian separation over a three-dimensional volume of interest, between microcomputed tomography scans in air and with samples embedded in PolyMethylMethAcrylate. The very good correlation between bone structural measures obtained from microcomputed tomography datasets and from two-dimensional histological sections confirms that microcomputed tomography may be an efficient tool for the characterization of cortical bone microstructure. Moreover, when the corresponding threshold value for each condition is used, structural parameters determined by microcomputed tomography are not affected by the surrounding medium (PolyMethylMethAcrylate).     

A heuristic algorithm for the loading problem in flexible manufacturing systems

The paper considers the loading problem in flexible manufacturing systems (FMSs). This problem involves the assignment to the machine tools of all operations and associated cutting tools required for part types that have been selected to be produced simultaneously. The loading problem is first formulated as a linear mixed 0–1 program with the objective to minimize the greatest workload assigned to each machine. A heuristic procedure is presented in which an assignment of operations to machine tools is obtained by solving a parameterized generalized assignment problem with an objective function that approximates the use of tool slots required by the operations assigned to the machines. The algorithm is coded in FORTRAN and tested on an IBM-compatible personal computer. Computational results are presented for different test problems to demonstrate the efficiency and effectiveness of the suggested procedure.     

Network localization procedures for experimental evaluation of mobile spatial coordinate measuring system (MScMS)

Large scale metrology refers to dimensional measurement of objects or features of perhaps a ten of meters or more in size. Alternatively, large scale metrology could be said to apply to any dimensional measurement where the metrology instrument has to be brought to the object rather than vice versa. Recent approaches seem to turn their attention towards distributed metrology systems made of multiple components with small dimensions spread around the measuring area. In general, these components are able to form a wireless network of sensors that allows rapid dimensional measurements to be performed in relation to large-size objects, with typical dimensions of several decametres. The portability, flexibility, and ease of installation of wireless sensor networks (WSNs) make these systems attractive for many industries manufacturing large scale products. This paper proposes different WSN localization procedures designed for the mobile spatial coordinate measuring system, a distributed metrology system developed at the industrial metrology and quality laboratory of DISPEA—Politecnico di Torino.     

A method for measuring the various constituents of the human hair follicle

Hair follicles from scalp biopsies (temporal and parietal regions) were isolated by microdissection. This technique allows preservation of the whole structure of the follicle in its fibrous sheath, or isolation of certain elements: bulb and dermal papilla. Each follicle is examined by transmission optical microscopy and its image is digitized into sixty-four grey levels by an image analyser. Follicle images are memorized on a hard disc, then recalled individually for measurement. The image analysis consists of thresholding, interactive selecting, then measurement of the following elements: diameter of the hair follicle, volume of the bulb, height of the keratogenous zone, mean diameter of the hair and size of the dermal papilla. These parameters were related to a clinical classification (terminal, dystrophic, vellus). This morphometric study constitutes an objective approach which is different from, but complementary, to the classic trichogram (telogen/anagen).     

A finite strip method for the buckling of plate structures under arbitrary loading

A finite strip method is presented for the stability analysis of prismatic thin walled structures under arbitrary loading. Sample problems are analysed and the economy of the method compared with the finite element method is demonstrated.     

The elastic-plastic analysis of a thick spherical shell under thermal loading—A comparison of three numerical procedures

The elastic-plastic response of a thick spherical shell subjected to thermal loading is predicted by three independent numerical analyses. Heat radiation from the inner face of a sufficiently large hollow cylinder is applied to an initially unloaded hollow sphere having a thickness equal to the inner radius of the sphere. Solutions obtained by a finite difference program and two independent finite element programs compare well with an exact elastic solution before yielding occurs. The post yield analyses of the three programs follow a consistent pattern.     

Measuring error and sampling variation in stereology: comparison of the efficiency of various methods for planar image analysis

An evaluation is made of the relative efficiency (precision of the final estimate per unit time of measurement on a given set of sections) of different methods for planar analysis aimed at estimating aggregate, overall stereological parameters (such as V_v, S_v). The methods tested are point-counting with different densities of test points (4 ≤ P_T ≤ 900 per picture), semiautomatic computer image analysis with MOP and automatic image analysis with Quantimet, for obtaining V_v and S_v estimates. One biological sample as well as three synthetic model structures with known coefficients of variation between sections are used. The standard error of an estimate is mainly determined by the coefficient of variation between sampling units (= sections in the present paper) so that measuring each sample unit with a very high precision is not necessary. Automatic image analysis and point-counting with a 100-point grid were the most efficient methods for reducing the relative standard errors of the V_v and S_v estimates to equivalent levels in the synthetic models. Using a 64-point grid was as precise, and about 11 times faster than using a tracing device for obtaining the estimate of V_v in the biological sample.     

A research on the effect of different measuring configurations in Network RTK applications

The aim of this article is to try to determine whether there’s a statistically significant difference between coordinates obtained under different elevation angles and measuring epochs through different correction methods in Network Real Time Kinematic Applications. For this purpose, analysis of variance was used. When the statistical data obtained according to different variables are compared, the accuracy seems to be less in the direction of h coordinate axis. There is no a statistically significant difference among the values obtained according to different epoch numbers in all directions of the coordinate axes. The subsets formed according to satellite elevation angles show similar characteristics along Y and h coordinate axes while they differ 30° according to other angles in the direction of X coordinate axis. Based on the correction methods, while FKP and VRS method show different characteristics with respect to each other, MAC method shows similar characteristics compared to other methods.     

A novel dynamic model for multiple configurations of machine tools using a coordinate transformation method

Virtual machine tools have been used widely for simulating designs in computer environments to determine optimal design parameters without the need for manufacturing prototypes. Machine tools include different multiple configurations that are designed to be suitable for the differing requirements of production. To date, studies on dynamic analysis have been limited to a few-axis machine tools of a specific configuration, such as a 3-axis milling machine or a 4-axis grinding machine. Here, we propose a novel method to focus on the dynamic analyses of multi-axis machines with differing multiple configurations. The motion equations for multiple degrees of freedom of linear and rotary axes are established by a Lagrange energy method, equilibrium equations, and Newton’s second law. This technique formulates the motion equations for each axis, and then further develops them for a multi-axis machine through a combination process and a transformation matrix. The library includes five dynamic model components, built to simulate 1236 different configurations of a machine tool. A dynamic analysis was applied to a control system to simulate the control signals of a virtual machine, which include stepped, ramped, curved, sinusoidal, and circular responses, and frequency response functions. The simulated and experimental results demonstrated that the method has high accuracy and reliability for one-, two-, and four-axis machine tools. Thus, this method can simulate the dynamic analyses of multi-axis machines and different multi-configurations without the need to build a specific configuration for each machine. It is recommended for selecting optimal motors, design parameters, and control parameters of the multiple configurations in a machine tool.