Analysis of the asymmetrically loaded spine by means of a continuum beam model

A continuum beam model of the human spine, proposed by Hjalmars (Proceedings of the Fourth International Conference on Continuum Models of Discrete Systems, 1981), and earlier used by the present author as a tool for the analysis of mild functional scoliosis, is here used for the study of a spine, asymmetrically loaded in the frontal plane. In order to validate the theoretical predictions of the model, preliminary experiments are carried out, which show that the model fairly well describes the lateral curvatures that occur when, for various loading conditions, the spine is adjusted into a muscle-relaxed state of equilibrium. Values of the flexural rigidity estimated from the experiments are found to be in reasonable agreement with values, estimated from earlier observations on dead material, reported in the literature. The experiments also indicate that the model may be developed to a tool for estimations of the effective flexural rigidity of the spine in vivo.     

A reduced-order model of the spine to study pediatric scoliosis

Biomechanics and Modeling in Mechanobiology - The S-shaped curvature of the spine has been hypothesized as the underlying mechanical cause of adolescent idiopathic scoliosis. In earlier work, we...     

Three-dimensional mathematical model of the human spine structure

A method is presented for constructing discrete-parameter type three-dimensional mathematical models and governing equations of motion of the spine structure. The anatomic structure is represented by any combination of rigid bodies, springs, and dashpots in space. These are positioned, orientated, and connected in a manner to represent the true mechanical function of the structure. The rigid bodies are of any shape and have 6 degrees-of-freedom, allowing three-dimensional motion. The springs and dashpots may have up to twenty-one stiffness and damping coefficients respectively to precisely represent the three-dimensional coupled behavior. The method is straightforward and simple to apply. The governing equations are in the matrix form and are easily generated and solved by computer techniques.     

用电子束加速器固定蛋白酶

俄罗斯科学院的技术人员完成了用电子束将蛋白酶固定在聚乙烯氧化物上,从而获得多用途活性生物聚合物的研究,被固定的蛋白酶热稳定性（80℃）比游离酶（60℃）高,PH适用范围大,且不含过氧化物和长命自由基。     

A viscoelastic anisotropic hyperelastic constitutive model of the human cornea

A constitutive model based on the continuum mechanics theory has been developed which represents interlamellar cohesion, regional variation of collagen fibril density, 3D anisotropy and both age-related viscoelastic and hyperelastic stiffening behaviour of the human cornea. Experimental data gathered from a number of previous studies on 48 ex vivo human cornea (inflation and shear tests) enabled calibration of the constitutive model by numerical analysis. Wide-angle X-ray scattering and electron microscopy provided measured data which quantify microstructural arrangements associated with stiffness. The present study measures stiffness parallel to the lamellae of the cornea which approximately doubles with an increase in strain rate from 0.5 to 5%/min, while the underlying stromal matrix provides a stiffness 2–3 orders of magnitude lower than the lamellae. The model has been simultaneously calibrated to within 3% error across three age groups ranging from 50 to 95 years and three strain rates across the two loading scenarios. Age and strain-rate-dependent material coefficients allow numerical simulation under varying loading scenarios for an individual patient with material stiffness approximated by their age. This present study addresses a significant gap in numerical representation of the cornea and has great potential in daily clinical practice for the planning and optimisation of corrective procedures and in preclinical optimisation of diagnostic procedures.     

An inhomogeneous and anisotropic constitutive model of human dentin

Dentin constitutes the major part of human tooth. It is composed of a large number of tubules with both variational radii and radially parallel pattern. In addition, peritubular dentin surrounds each tubule lumen and has a higher elastic modulus than the matrix of dentin, i.e. intertubular dentin. Considering the above microstructural characteristics, a micromechanics model is used in this paper to evaluate the overall elastic properties of dentin. Five independent effective elastic parameters in transverse isotropic elasticity matrix can be expressed analytically by the material parameters of peri- and intertubular dentin and the volume fraction of tubules. To determine the effectivity of this theoretical model, a finite element (FE) model simulating a longitudinal tooth slice in moire fringe testing of Wang and Weiner (J. Biomech. 31 (1998) 135) was performed. Furthermore, the FE model was developed incorporate modeling of variation of tubule's diameter and softer characteristic of intertubular dentin near the dentin-enamel junction and around the pulp chamber. It turned out that the isoline figure of longitudinal displacement by FE calculation has very similar patterns to the moire fringe results. However, the FE results of displacement by traditional stress-strain models which regard dentin as a homogeneous and isotropic material show an obviously different strain distributions as compared to published moire fringes results. Thus the inhomogeneous and anisotropic model developed in this paper more accurately reflects the true physical nature of human dentin.     

Analysis of the non-stationary EEG by means of an approximate canonical expansion

The mathematical framework of the canonical expansion of a random time function has been applied to the analysis of the electroencephalogram. The proposed method has been adapted for a computersuited algorithm by using an orthogonalization concept of the vector space theory. The offered solution avoids the mathematical difficulties of the rigorous theory of Karhunen-Loeve expansion. Moreover, the results of the analysis highlight new aspects of the physical properties of the electroencephalogram. Suggestions with regard to the non-linear character of the oscillators generating electrical activity seem to be valid.     

A three-dimensional model of the human cervical spine for impact simulation

A three-dimensional analytical model of the cervical spine is described. The cervical vertebrae and the head are modeled as rigid bodies which are interconnected by deformable elements representing the intervertebral disks, facet joints, ligaments and muscles. A special pentahedral continuum element for representing the articular facets is described which effectively maintains stability of the cervical spine in both lateral and frontal plane accelerations, which is very difficult with multi-spring models of the facets. A simplified representation is used for the spine and body below the level of T1. The neck musculature is modeled by over 100 muscle elements representing 22 major muscle groups in the neck. The model has been validated for frontal and sideways impact accelerations by simulating published experimental data. Results are also presented to show the effects of the stretch reflex response on the dynamics of the head and neck under moderate acceleration.     

Specimen-specific multi-scale model for the anisotropic elastic constants of human cortical bone

The anisotropic elastic constants of human cortical bone were predicted using a specimen-specific micromechanical model that accounted for structural parameters across multiple length scales. At the nano-scale, the elastic constants of the mineralized collagen fibril were estimated from measured volume fractions of the constituent phases, namely apatite crystals and Type I collagen. The elastic constants of the extracellular matrix (ECM) were predicted using the measured orientation distribution function (ODF) for the apatite crystals to average the contribution of misoriented mineralized collagen fibrils. Finally, the elastic constants of cortical bone tissue were determined by accounting for the measured volume fraction of Haversian porosity within the ECM. Model predictions using the measured apatite crystal ODF were not statistically different from experimental measurements for both the magnitude and anisotropy of elastic constants. In contrast, model predictions using common idealized assumptions of perfectly aligned or randomly oriented apatite crystals were significantly different from the experimental measurements. A sensitivity analysis indicated that the apatite crystal volume fraction and ODF were the most influential structural parameters affecting model predictions of the magnitude and anisotropy, respectively, of elastic constants.     

Monitoring of cross-country skiers by means of an expert model of potential performance

On the basis of expert knowledge, an expert model of potential performance covering the motor, morphological, psychological, and sociological subspace was constructed (MMPS). The scores of variables were obtained by application of the computer program Sport Measurement Management System (SMMS). In the subjects included in measurements, trends of the obtained average scores of variables were established through various competition categories and age periods. The sample of subjects consisted of 48 cross-country skiers in three competition categories. Fluctuations in development in individual age periods are larger in the motor and morphological subspace. In the psychological subspace, an upward trend of average scores can be noticed, while the sociological subspace is not subjected to any essential changes in different age and competition categories. Monitoring of cross-country skiers across all three competition categories showed that in these age categories there are periods which owing to laws of development do not allow uniform progress. Therefore, the principle of individuality must be taken into account especially in planning the transformation process.     

Reduction of biological properties by means of functional sub-types

The general aim of this paper is to propose a reductionist strategy to higher-level property types. Starting from a common ground in the philosophy of science, I shall elaborate on possible realizer differences of higher-level property types. Because of the realizer types' causal heterogeneity, an introduction of functional subtypes of higher-level properties will be suggested. Each higher-level functional sub-type corresponds to one realizer type. This means that there is the theoretical possibility to reach some kind of type-identity and this opens up the way for theory reduction in a more complete manner. This kind of type-identity will go beyond the common ground of the identity of tokens and their reductive explanation. In the second part of the paper, this reductionist strategy will be applied to a specific debate in the philosophy of biology--the reductionist approach to classical genetics from a molecular point of view.     

Fluorescent location of human colonic tumour cells by means of an enzyme-inhibitor complex

We studied the enzymic status of the tumour cell surface protease, guanidinobenzoatase (GB) in frozen sections of a human colonic tumour grown in nude mice and also in human colons. Active enzyme was demonstrated by the binding of a synthetic fluorescent probe for the active centre of guanidinobenzoatase (GB). It was observed that tissue derived inhibitors of GB blocked the binding of this fluorescent probe and that enzyme inhibitor complex formation could be controlled by lowering the pH of the medium with lactic acid. The presence of an inhibitor of GB in the mouse tumour extract was taken advantage of by making two fluorescent derivatives of this inhibitor; both of which located GB on colonic tumour cells in frozen sections of human colon.     

Quantitative description of the adaptation of vagal effects by means of an electromechanical coupling model]

A four compartments model describes the electrotropic and the inotropic vagal effect time courses during long time stimulation. The model realises electro-mechanical coupling. A differential equation for the coupling model is developed, solutions are given and a numerical treatment is described. The model shows the essential properties of effect adaptation: time delay and smaller extent of electrotropic effect adaptation.     

Twente spine model: A complete and coherent dataset for musculo-skeletal modeling of the lumbar region of the human spine

Musculo-skeletal modeling can greatly help in understanding normal and pathological functioning of the spine. For such models to produce reliable muscle and joint force estimations, an adequate set of musculo-skeletal data is necessary. In this study, we present a complete and coherent dataset for the lumbar spine, based on medical images and dissection measurements from one embalmed human cadaver. We divided muscles into muscle-tendon elements, digitized their attachments at the bones and measured morphological parameters. In total, we measured 11 muscles from one body side, using 96 elements. For every muscle element, we measured three-dimensional coordinates of its attachments, fiber length, tendon length, sarcomere length, optimal fiber length, pennation angle, mass, and physiological cross-sectional area together with the geometry of the lumbar spine. Results were consistent with other anatomical studies and included new data for the serratus posterior inferior muscle. The dataset presented in this paper enables a complete and coherent musculo-skeletal model for the lumbar spine and will improve the current state-of-the art in predicting spinal loading.