A stiffness-varying model of human gait

We report on a conceptual two degrees of freedom (2 DOF) human gait model, which incorporates nonlinear joint stiffness as a stabilizing agent. Specifically, muscle spring-like property provides inherent stability during gait movement using a nonlinear angular spring and dash pot at each joint. The instability problem of the gait model in direct dynamic analysis is overcome by simulating the human co-contraction muscle function. By developing dynamic system stability requirements and hypothesizing a minimum joint stiffness criterion, we determine time-varying joint stiffness. Optimum joint stiffnesses are present for varying gait pattern, stride lengths and cadences. We conclude that nonlinear joint stiffness can be incorporated into gait models to overcome stability problems inherent in such linkage models.     

Male-female differences: A computer simulation.

Agrees with A. H. Eagly's (see record 1995-21141-001) contention that the use of easily understood metrics (binomial effects size display and the common language effect) are not entirely sufficient at showing a significant sex effect. The authors recommend the use of computer simulations as a tool for assessing the impact of sex differences. Results of a computer simulation regarding the effects of pyramid structure and initial performance ratings on limitations of the upward mobility of women in the workplace confirm Eagly's point that the effects of male–female differences are best determined not only by the magnitude of the effect but its consequences in natural settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A computer simulation of strength of metal matrix

The deformation and fracture behavior of metal matrix composites with a reaction layer at the fiber-matrix interface was studied by means of a computer simulation experiment, using a two-dimensional model, and the results of the simulation experiment were compared with the predictions based on the single fiber model, which has been proposed to describe the reduction of strength of composites due to a reaction layer. In the simulation experiment, the composite was regarded as an assembly of single fiber elements, in which, for each element, the reaction layer introduces a notch on the fiber surface when it is broken, which reduces the strength of the fiber if the thickness of the layer is thinner than a critical value, as has been studied by using the single fiber model. The strength of composites was reduced with increasing thickness of the reaction layer and the fracture mode became catastrophic. The strength values obtained by the simulation were equal to those based on the single fiber model only when the fracture of the fiber was caused by the extension of the notch having been introduced by premature fracture of the reaction layer. In other cases, the strength values of the simulation were lower than those predicted by the single fiber model, although the single fiber model gave approximate values.     

A computer simulation of jury decision making.

A computer simulation of jury decision making is described and evaluated in terms of its ability to account for findings in 2 empirical studies. The computer model is based on elementary assumptions about the effects of relative jury faction sizes and variability in juror resistance to persuasion. The model is used to simulate decision making in empirical studies based on a murder case and a rape case. In the simulation of the 1st study, the model's performance is compared to empirical results from 6- and 12-member juries using unanimous and nonunanimous decision rules. Criteria to evaluate the model's performance are distributions of verdicts, deliberation times, rates of juror vote changing, and reversals of 1st-ballot majorities. The evaluation results support the theory underlying the model. (61 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A computer simulation for teaching critical thinking skills

Telephone-based health services is a fast growing subspecialty of nursing practice. It is used in demand management and managed care organizations in a highly unregulated environment. The article presents background information and identifies the need for systematic studies of ethical implications inherent in telephone-based practice. Conclusions suggest that nurses need to become actively involved in ethical decision making related to this area of practice.     

A computer simulation on tensile strength of surface-Damaged fibers

The strength of surface-damaged fibers was studied by means of a computer simulation experiment based on the Monte-Carlo method using a simple model which assumes that the surface flaws can be regarded as mode I notches on fiber surfaces, the strength of undamaged fibers obeys the Weibull distribution function, and the largest flaw determines the strength of damaged fibers. Normal and exponential distribution functions were taken as the flaw size distribution function. By employing the present simulation method, the effects of average flaw size, coefficient of variation of flaw size, density of flaws, and gage length on average strength and its coefficient of variation were studied. It was found that the surface-damaged fibers can retain their full strength only when the average flaw size is small, the coefficient of variation of flaw size is small, density of flaw size is low, and gage length is short. Otherwise the average strength of damaged fibers was reduced seriously. It was emphasized that the scatter of size of flaws and density of flaws strongly affect the strength of fibers as well as flaw size and gage length.     

A computer algorithm for defining the group electromyographic profile from individual gait profiles

A computer algorithm was developed to determine the group electromyographic (EMG) profile for the soleus muscle during free speed level walking. Subjects consisted of 50 adults (21 male, 29 female) with no history of musculoskeletal disease. EMG was recorded from the soleus muscle with wire electrodes, and was normalized by maximum muscle test. Two algorithms (time-adjusted mean profile (TAMP) and mean intensity profile (MIP)) were implemented to construct a group profile from identical individual EMG profiles. In addition, a grand ensemble average (GEAV) of the same individual data was performed. A high positive correlation (omega 2 > .995) was found between MIP and GEAV of EMG data. A control group was established based on mean timing and relative intensity of the individual EMG profiles. The MIP and GEAV were shown to have earlier onsets, later cessations, and extended EMG duration in comparison to control values. No significant differences were observed comparing TAMP and mean values for any measure.     

A computer simulation study of cortical imaging from scalp potentials

In this paper, computer simulation studies were conducted to test the feasibility of imaging brain electrical activity from the scalp electroencephalograms. The inhomogeneous three-concentric-sphere head model was used to represent the head volume conductor. Closed spherical dipole layers, consisting of several thousand uniformly distributed dipoles, were used to reconstruct the cortical potential maps corresponding to neuronal sources located inside the brain. Simulation results indicate that the present procedure can image both cortical and deep sources, and for the cortical sources, a spatial resolution as high as 1.2 cm can be achieved.     

Functional evaluation of normal and pathologic knees during gait

The functional performance of the knee joints of 29 normal volunteers, 65 patients with degenerative joint disease and 30 patients with rheumatoid arthritis was studied according to clinical (historical, physical and roentgenographic) and biomechanical gait parameters. Temporal and distance gait factors (velocity, cadence and stride length) were significantly reduced in patients with diseased knees. Sagittal plane knee motion was markedly reduced, as was stance phase flexion, indicating poor tolerance of loading the flexed knee in the patient groups. There was no correlation between passive motion of the diseased knee and the amount of motion used during gait. Patients with rheumatoid arthritis generally showed more compromise of knee joint function than did patients with degenerative joint disease. Statistically, significant correlations between various clinical and biomechanical gait parameters suggest that the techniques used are an objective measurement of knee joint function and may be employed as a means of evaluating various treatment modalities for the diseased knee.     

Equity theory and career pay: A computer simulation approach.

Used computer simulation to convert E. Jaques's 1961 theory of equitable payment into the composites model utilized by the M. Haire et al's (see record 1967-14292-001) study of career pay. Salaries of 100 Ss were stochastically allocated for 25 time periods. A Markovian process model produced a set of pay parameters that more closely replicated past empirical findings than the parameters produced by an independent process model. Distributing pay increases according to differentially developing work capacity curves yielded pay increases distributed at random with respect to past salaries. Thus, Jaques's theory of equitable payment provides one explanation for the empirical findings generated by previous studies of career pay curves. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Imposed quotas and personnel selection: A computer simulation study.

A computer simulation program was used to assess a set of algorithms developed to predict the necessary recruitment and performance outcomes likely for organizations under different subgroup quota constraints. Results demonstrate the accuracy of the algorithms in predicting outcomes for a range of selection problems common in organizational practice. It is concluded that the joint probability of locating enough qualified applicants of a particular subgroup to meet a quota may result in certain consequences that have neither been considered nor intended by those advocating such quotas. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of the human respiratory system in hypoxic and anoxic hypoxia by analogue computer simulation

The goal of this work is to synthesise a model of an adaptive system of respiration control in man, which could be used for the prognosis of human performance under extreme conditions. The model was partly based on 428 experimental results from hypoxic and anoxic hypoxia. Simulation of the oxygen regulatory circuit was realised on the NADAC 100 and MEDA T 80 analogue computers with satisfactory results. Equations constituting a new version of the model are presented in some detail, together with the results of the simulation of ventilatory mechanics.     

Role of back-diffusion studied by computer simulation

The solidification of Fe-Cr-C alloys was simulated with a program that allowed realistic treatment of diffusion in the liquid and the primary solid phase. It interacts with a thermodynamic databank and can evaluate the heat extraction continuously. Solidification under a constant rate of heat extraction can be simulated. In agreement with previous experience, diffusion of carbon in the fcc phase was found to be very effective, and it can be approximated by an infinitely fast diffusion. The same holds for carbon and chromium in the liquid. The back-diffusion of chromium in the fcc phase was examined in detail. Three different geometries were tested: the planar and cylindrical cases, as well as a new model based on two coupled cylinders. The simulation program allowed the effect of back-diffusion after the end of solidification to be included, and it was found to be important for the segregation ratio.