Boundary element analysis of a plate on elastic foundations

The objective of this study is to examine the applicability of the boundary element method to analysing a plate on elastic foundation. The fundamental solution of the problem is presented as a Fourier-Bessel integral. For the computation of the values of the fundamental solution an algorithm was developed in which the Fourier-Bessel integral was decomposed into an alternative convergent sequence. Equations based on the direct and indirect boundary element method were derived for a plate situated on a one- or two-parametric elastic foundation. According to the theory presented, computer programs based on the direct and indirect boundary element method were developed. These programs can be used for examining the behaviour of a smooth-boundary plate on a one- or two-parametric elastic foundation. The computer programs were tested by several examples. The results obtained by using a small number of boundary elements compared favourably to the results obtained by a fine finite element mesh. The study shows that the boundary element method is applicable to the analysis of a plate on elastic foundation.     

Hot-rolling simulation and modelling using Gleeble 1500

Using the Gleeble 1500, incremental and continuous hot compression tests, simulating hot rolling, were performed on C-Mn, Nb-T, and Nb steels with test temperatures varying between 875 and 1100°C and strain rates between 0.5 and 20 s^?1. Four models are proposed. The stress peak model allows the prediction of continuous stress-strain curves from incremental curves and vice versa through the use of stress restoration index K. Variation in K for Nb-T₁, C-Mn and Nb steels at strain rates of 3, 12 and 20 s^?1 was found to be negligible. The predicted stress strain curve corresponds to experimental stress strain curve at same temperature and strain rate. The strain history model predicts continuous strain-time curves from incremental stress-strain curves using ‘constant’ ‘negative strain’ restoration index. At 950°C, with holding time 2 s and strain rate 12 s^?1, strain time decay curves obtained for C-Mn, Nb and Nb-T, steels were ε = 1.5e^?05t, ε = 1.2e^?0.36t and ε = e^?0.3t, respectively. The creep model analysis relates creep strain rate to the testing strain rate. For Nb steel at 875°C, and test strain rate of 12 s^?1, ?_creep was found to be 9.5 s^?1. The stress history model predicts continuous stress-time curves from incremental stress-time curves. Stress decay curve for C-Mn steel at 1100°C and ? = 3s^?1 was found to be σ = 181e^?0.04t. Hot rolling characteristics of steels can be accurately predicted using hot compression tests and proposed models.     

ASYMPTOTIC PROPERTIES OF SOME PRELIMINARY ESTIMATORS FOR AUTOREGRESSIVE MOVING AVERAGE TIME SERIES MODELS

Abstract. Some simple preliminary estimators for the coefficients of mixed autoregressive moving average time series models are considered. As the first step the estimators require the fitting of a long autoregression to the data. The first two methods of the paper are non-iterative and generally inefficient. The estimators are Yule-Walker type modifications of the least squares estimators of the coefficients in auxiliary linear regression models derived, respectively, for the coefficients of the long autoregression and for the coefficients of the corresponding long moving average approximation of the model. Both of these estimators are shown to be strongly consistent and their asymptotic distributions are derived. The asymptotic distributions are used in studying the loss in efficiency and in constructing the third estimator of the paper which is an asymptotically efficient two-step estimator. A numerical illustration of the third estimator with real data is given.     

Effect of Austenite Pancaking on the Microstructure,Texture, and Bendability of an Ultrahigh-Strength Strip Steel

The effect of austenite pancaking in the non-recrystallization regime on microstructure and texture evolution and thereby on bendability was investigated in an ultrahigh-strength strip steel with a martensitic-bainitic microstructure. The results indicate that an increase in rolling reduction (R _tot) below the non-recrystallization temperature, which improves the strength and toughness properties, increases the intensities of the ~{554}〈225〉 _α and ~{112}〈110〉 _α texture components along the strip centerline and of the ~{112}〈111〉 _α component at the surface region. Even with the highest R _tot of 79 pct, the bendability along the rolling direction was good, but the preferred alignment of rod-shaped MA constituents along the rolling direction led to a dramatic decrease in the bendability transverse to the rolling direction, with severe cracking occurring even at small bending angles. The early cracking is attributed to localization of the strain in narrow shear bands. It is concluded that the R_tot value has to be limited to guarantee successful bendability.     

Strength retention of drawn self-reinforced polyglycolide rods and fixation properties of the distal femoral osteotomies with these rods. An experimental study on rats

Drawn self-reinforced polyglycolide (SR-PGA) rods, Ø 2 mm and 26 mm long, were implanted in the dorsal subcutaneus tissue of 16 rats. Osteotomies of the distal femur were fixed with SR-PGA rods (2 mm by 15 mm) in another 38 rats. The follow-up times varied from one week to one year. After sacrifice, three-point bending and shear tests were performed for subcutaneously placed rods. Radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies of osteotomized and intact control femora were also performed. At three weeks the flexural strength of the rods was 50% of the initial value, and the flexural modulus was 46% of the initial value. Five osteotomy specimens had to be excluded due to dislocation or non-union. One of the 33 evaluated osteotomy specimens showed signs of postoperative infection. Thirty-two osteotomies healed uneventfully. No gross signs of inflammatory or foreign-body reaction were observed. The amount of osteoid surface and active osteoid formation surface reached their highest value in the histomorphometrical analysis at 24 weeks. The present investigation demonstrated that the mechanical strength and fixation properties of the drawn SR-PGA rods are suitable for fixation of cancellous bone osteotomies in rats. The present article is the first report on the successful application of drawn SR-PGA rods for fixation of cancellous bone osteotomies.     

Cardiac status and cardiovascular risk factors among Finnish sea pilots

The present study investigated the expressed number of CR1 on erythrocytes (E) in relationship of the CR1 density genotype from 46 patients with systemic lupus erythematosus (SLE) and 47 healthy volunteers. The CR1 genotype was determined by a method based on polymerase chain reaction (PCR) amplification of the genomic DNA fragment of 1.8 kb separated by HindIII endonuclease digestion and agarose gel electrophoresis. Our data supported the earlier results that the number of binding sites/E for monoclonal anti-CR1 decreased among SLE patients compared with normal individuals having the same alleles for the CR1/E density. At the same time the novelty of our recent results was that the decreased expression of CR1 on E correlated significantly with kidney involvement in patients homozygous for the CR1/E high density allele (HH). These data suggest that the deficiency of the detectable number of CR1 on erythrocytes is acquired in this SLE population.     

Reliability Growth and Duane Learning Curves

This paper examines Duane learning curves for reliability improvement between successive reliability tests. A constant failure rate ratio between successive tests gives curved lines on a Duane plot. Gordon's observation that dominant failures appear exponentially with test time leads to exponential failure rate ratio models. These models, although not the only possible ones, give results that agree well with observations from practice.     

Fixation of distal femoral osteotomies with self-reinforced poly(L/DL)lactide 70 : 30/bioactive glass composite rods. An experimental study on rats

Self-reinforced poly(L/DL)lactide 70:30/bioactive glass [SR-P(L/DL)LA/bioactive glass] composite rods, 2 mm in diameter and 36 mm in length, were implanted into the dorsal subcutaneous tissue of 16 rats. Osteotomies of the distal femur were fixed with these rods (2 x 15 mm) in 64 other rats. The follow-up times varied from one week to one year. After sacrifice, three-point bending and shear tests, and molecular weight measurements were performed for subcutaneously placed rods. Radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies of the osteotomized and intact control femora were performed. At 24 weeks the mechanical properties had decreased significantly. Thirty-nine osteotomies healed uneventfully. One of the 64 evaluated osteotomies showed signs of infection at six weeks, and there were 19 non-unions and six delayed unions. In 20 operations the fixation was loose and out of these 14 non-unions were observed. No gross signs of inflammatory or foreign-body reactions were observed. The present investigation showed that the mechanical strength and fixation properties of SR-P(L/DL)LA/bioactive glass composite rods are suitable for fixation of cancellous bone osteotomies in rats as long as the operative technique is correct. The present article is the first report on the application of SR-P(L/DL)LA/bioactive glass composite rods for fixation of cancellous bone osteotomies.     

Multilinear model for spatial pattern analysis of the Measurement of Haze and Visual Effects project

A multilinear model was developed for the analysis of the spatial patterns and possible sources affecting haze and its visual effects in the southwestern United States. The data from the project Measurement of Haze and Visual Effects (MOHAVE) collected during the late winter and mid-summer of 1992 at the monitoring sites in four states (i.e., California, Arizona, Nevada and Utah) were used in the study. The three-way data array was analyzed by a four-product-term model. This study makes a direct effort to include wind patterns as a component in the model in order to obtain the information of the spatial patterns of source contributions. The solution is computed using the conjugate gradient algorithm with applied non-negativity constraints. For the winter data set, reasonable solutions contained six sources and six wind patterns. The analysis of summer data required seven sources and seven wind patterns. The ME results are compared to the prior single-species empirical orthogonal function analysis results--and prior work describing the transport pathways.