Modeling the non-linear viscoelastic response of high temperature polyimides

A constitutive model is developed to predict the viscoelastic response of polyimide resins that are used in high temperature applications. This model is based on a thermodynamic framework that uses the notion that the ‘natural configuration’ of a body evolves as the body undergoes a process and the evolution is determined by maximizing the rate of entropy production in general and the rate of dissipation within purely mechanical considerations. We constitutively prescribe forms for the specific Helmholtz potential and the rate of dissipation (which is the product of density, temperature and the rate of entropy production), and the model is derived by maximizing the rate of dissipation with the constraint of incompressibility, and the reduced energy dissipation equation is also regarded as a constraint in that it is required to be met in every process that the body undergoes. The efficacy of the model is ascertained by comparing the predictions of the model with the experimental data for PMR-15 and HFPE-II-52 polyimide resins.     

Impact of perceptual treatments on lateral control during driving on crest vertical curves: a driving simulator study

Approximately 48% of all fatal collisions in Europe are classified as single-vehicle run-off-road or head-on collisions. These crashes relate to trajectory control (road departure) and represent a safety challenge. In France, single-vehicle run-off-road crashes represent 21% of all crashes and head-on collisions represent 11%. This study evaluated the effectiveness of four perceptual treatments (i.e., a painted center line, post-delineators, rumble strips on both sides of the center line and sealed shoulders) in supporting the driver to maintain lateral control; that is, to support the driver to keep in the center of his/her lane. Forty-three participants drove a fixed-base driving simulator, on a simulated straight 3 km rural road with two crest vertical curves (CVC). Four sections were chosen for analysis: a reference section (i.e., the first CVC), a test section (i.e., the second CVC), a pre-test section (i.e., immediately before the second CVC) and a post-test section (i.e., immediately after the second CVC). The results showed that drivers drive more at the center of their lane with the rumble strips on both sides of the center line and with the sealed shoulders than with the actual marking (here center line) or other treatments.     

Neural Networks in Applied Statistics

Artificial neural networks are computer algorithms or computer programs derived in part from attempts to model the activity of nerve cells. They have been applied to pattern recognition, classification, and optimization problems in the physical and chemical sciences, as well as in other fields. We introduce the principles of the multilayer feedforward network that is among the most commonly used neural networks in practical problems. The relevance of neural network models for the applied statistician is considered using a time series prediction problem as an example. The multilayer feedforward neural network uses a nonlinear function of the predictors to obtain predictions for future time series values. We illustrate the considerations involved in specifying a neural network model and evaluate the accuracy of neural network models relative to the accuracy obtained using other computer-intensive, nonmodel-based techniques.     

Dynamic modelling of time series data in nutritional metabonomics — A powerful complement to randomized clinical trials in functional food studies

Functional foods are foods or dietary ingredients that provide a health benefit beyond basic nutrition. A new legislation, known as the Nutrition and Health Claims Regulation, defines the legal framework for such claims within the European Union. Any claim about the nutritional or physiological effects of a product must be scientifically demonstrated. In this study, we have focused on the exploration of metabonomics as a complementary profiling technology to establish monitoring/data analysis procedures of randomized nutritional trials. More specifically, a combined intake of soybean and grapefruit in a human intervention study was analyzed with respect to both pharmacological and physiological effects. Resulting multivariate models showed a diet-induced decrease of lactate, cholesterols and triglycerides. The most drastically elevated metabolite, myo-inositol, was found to accompany a marked reduction of triglyceride levels. Suggestively, this is due to the biotransformation of myo-inositol to phosphatidylinositol, which results in a decrease of available precursors to form triglycerides. Strong inter-subject variation was present that required special attention. Dynamic modelling of collected time series data that provided the opportunity to identify slow, medium or fast responders as well as groups of subjects showing different response profiles, was also highlighted in the study. The applied strategy of time series data has proven to be a powerful complement to randomized nutritional studies adopting a clinical trial design.     

The impact of perceptual treatments on lateral control: A study using fixed-base and motion-base driving simulators

This research was carried out as part of the French national multidisciplinary research project, PREDIT-SARI. Using a driving simulator, it aimed to test the effectiveness of road treatments intended to inform drivers about the risk of losing control on rural roads with “crest vertical curves” (Landis et al., 2004). [Rosey, F., Auberlet, J.M., Bertrand, J., Plainchault, P., 2008. Impact of perceptual treatments on lateral control during driving on crest vertical curves: a driving simulator study. Accid. Anal. Prev. 40, 1515-1523, Scopus.] used a fixed-base driving simulator to test four perceptual treatments intended to help drivers maintain lateral control when driving on crest vertical curves and found that two of them, rumble strips on both sides of the centerline and sealed shoulders, were more effective than the others. This first study prompted us to ask if non-visual sensory cues (e.g., vestibular or proprioceptive perceptions) could influence driver perception and consequently lateral control. We therefore conducted a second study on a motion-base driving simulator, using the same virtual 3D database. The results showed that: (1) drivers drive closer to the center of their lane when there are rumble strips on both sides of the centerline, or when there are sealed shoulders, than they do with the current marking system (i.e., continuous lines), and (2) the impact of the two tested perceptual treatments was replicated on both types of driving simulator.     

Accounting for time-dependent covariates in driving simulator studies

Driving involves multiple cognitive processes that are influenced by a dynamic external environment and internal feedback loops. These processes are typically studied in a simulator environment to capture time-dependent driver performance measures. The primary objective of this research is to show that data analysis techniques that ignore or improperly treat time-dependent covariates will lead to erroneous estimates and conclusions. This is demonstrated with a driving simulator study that was used to test whether a significant decrease in performance occurs in the presence of auditory and visual distractions. A total of 28 drivers participated in a 2 (age)?×?7 (strategy) repeated measures experiment. The response variable—accelerator release time—was analysed with and without consideration of time-dependent covariates. Using the inverse headway distance as a time-dependent covariate corrected logically inconsistent results obtained when the covariate was ignored. This indicates that ignoring covariates can actually lead to inappropriate design or policy implications.     

Modeling study of migration-driven lateral instability in autocatalytic systems

The lateral stability of reaction fronts in simple autocatalytic models with the components carrying various charges is investigated when the system is exposed to an inhomogeneous electric field parallel to the direction of propagation. The enhanced migrational flux of the reactant destabilizes the planar front giving rise to a cellular structure because the electric field strength is greater on the reactant side of the reaction front. The onset of instability depends not only on the charge difference between the reactant and the autocatalyst but also on the variation of specific conductance in the course of the reaction, which results in a difference in electric field strength on the opposite sides of the reaction front.     

On the use of time series techniques in shape recognition applications

In this paper, a method for classifying objects based on the use of autoregressive model parameters which are obtained from a time series representation of shape boundaries in digital images of objects is presented. This technique is insensitive to size and is rotation invariant. The objects chosen are four types of aircraft from a digital photograph. Recognition accuracies of more than 90% were obtained for all the pattern classes. All pattern recognition problems involve two random variables, the pattern vector and the class to which it belongs. The interdependence of the two variables is given by the conditional probability density function. The degree of dependence between the pattern vector and the particular class is measured by the “distance”. A simple Bhattacharya distance classifier was used for the purpose.     

The endurance of the effects of the penalty point system in Spain three years after. Main influencing factors

In this work we have used ARIMA time series models to analyse the contribution of the penalty point system, the most important legislative measure for driving licences, in reducing the number of fatalities over 24 h on the roads in Spain during the study period (January 1995 to June 2009). In addition, because of this long period of analysis, other control variables were introduced to model the enactment of the Reform of the Penal Code in December 2007, together with other more specific effects needed to fit the model correctly. The ARIMA intervention models methodology combines the basic features of specific times series models: it controls the trend and seasonal variation in data that is present when modelling the structure through autoregressive and moving average parameters and allows for inserting step or impulse input variables for checking and evaluating the effects of deterministic measures, such as legislative changes which are the object of study in this work. This paper analyses the surveillance and control measures introduced in the periods before and after the implementation of the penalty point system and helps to partly explain its apparent endurance over time. The results show that the introduction of the penalty point system in Spain had a very positive effect in reducing the number of fatalities (over 24 h) on the road, and that this effect has endured up to the present time. This success may be due to the continuing increase in surveillance measures and fines as well the significantly growing interest shown by the news media in road safety since the measures were introduced. All this has led to positive changes in driver behaviour. It is, therefore, a combination of three factors: the penalty point system, the gradual stepping up of surveillance measures and sanctions, and the publicity given to road safety issues in the mass media would appear to be the key to success. The absence of any of these three factors would have predictably led to a far less positive evolution of the accident rate on Spanish roads.     

Alcohol and fatal accidents in the United States--a time series analysis for 1950-2002

AIMS: To estimate the association between per capita alcohol consumption and fatal accidents in the United States and to compare the outcome with findings from Europe and Canada. DATA AND METHOD: Yearly data on fatal accidents by gender and age were analysed in relation to per capita alcohol consumption for 1950-2002 using the Box-Jenkins technique for time series analysis. FINDINGS: A 1-L increase in per capita consumption was on average followed by 4.4 male deaths per 100,000 inhabitants, but had no significant effect on female accident mortality. Regarding specific categories of accidents, the effect on fatal motor vehicle accidents accounted for a large part of the overall effect for men and was also significant for women. With respect to fatal falling accidents and other accidents, the only significant effects were found among young males. As concerns women, the association with per capita consumption in the US was weak in comparison with Canada and Europe. The US effect estimate for overall male accidents was however equally strong as in Northern Europe (5.2) or Canada (5.9), and stronger than that found in Central and Southern Europe (2.1 and 1.6, respectively). With respect to alcohol and fatal motor vehicle accidents, the association for men of 3.2 was stronger than in Europe and more similar to the Canadian finding (3.6). CONCLUSIONS: Per capita alcohol consumption has at least partly been an explanation for the development of male fatal accidents and particularly motor vehicle accident rates in the post-war United States. High traffic density and relatively high legal limits for drunken driving blood alcohol concentration (BAC) are suggested to explain the strong association found between alcohol and fatal motor vehicle accidents. The results also suggest that a reduction in per capita consumption would have its most preventive impact on fatal accidents among younger males.     

并行工程环境下的产品质量监视系统

提出了一种在并行工程环境下用于小批量生产的质量反馈两层模型，能够准确，客观、在线动态地评价现行加工工序的状况和进行相应的加工过程质量仿真。     

Deep-level studies in GaN layers grown by epitaxial lateral overgrowth

The electrical properties, deep-level spectra, microcathodoluminescence (MCL) spectra and diffusion lengths of minority charge carriers were measured in GaN films grown by the epitaxial lateral overgrowth (ELOG) technique. The results are compared to the properties of GaN layers grown in a standard fashion without masking of the initial template. MCL and electron beam induced current (EBIC) imaging of the laterally overgrown regions revealed the presence of dark spots with density of 1-5 × 10⁶ cm^− 2 that are associated with individual dislocations. The concentration of deep electron and hole traps was found to be much higher in the standard material than in the ELOG material. Diffusion lengths of minority carriers determined from EBIC signal profiling gave values of 0.8-1 μm along the bright regions and 0.4-0.5 μm in the dark regions of the ELOG samples. Similar measurements on metal organic chemical vapor deposition templates gave a diffusion length of 0.4-0.5 μm, close to the diffusion length in the dark stripes of the ELOG samples.     

Forecast of trademark applications in Switzerland

Trademark offices which run according to principles of new management have an inherent need for dependable forecasting data in planning capacity and service levels. We wanted to find out whether there are factors which positively or negatively influence customers to register trademarks in Switzerland. Lacking literature on the idiosyncrasies of trademark filing behavior, we developed our own forecasting model adapted from those in other fields. It included timelines for trademark applications and corresponding classes over a 9-year period (1992–2001) and internal events which might possibly influence filing.The forecast is based on state space models with and without explanatory variables. We used a standard model with trend, season and random components, then added variables for external interventions and finally, added a model for regressors. The result was a statistical model which produced reliable forecasting over an 18-month period. It compares well to four other forecasting methods. Reliability was improved slightly by adding economic variables such as the Dow Jones Industrial Average, SPI, SMI and the Swiss Consumer Index.     

Efflorescence control in geopolymer binders based on natural pozzolan

This paper addresses methods to reduce efflorescence in a geopolymer binder based on a pumice-type natural pozzolanic material from Taftan, Iran. Geopolymer pastes samples are analyzed for compressive strength and efflorescence formation after curing at 95% humidity for 28 days. To reduce the extent of efflorescence, Al-rich mineral admixtures such as metakaolin, ground granulated blast-furnace slag, and three types of calcium aluminate cements are incorporated into the dry binder at a range of concentrations. Hydrothermal curing at elevated temperatures also shows a positive effect in efflorescence reduction. Calcium aluminate cements show the greatest effect in efflorescence reduction, which is attributed to their dissolution in alkaline media releasing high amounts of alumina into the aluminosilicate geopolymer gel. These results confirm that it is possible to develop a more reliable geopolymer binder with improved properties either by adding a suitable amount of active alumina to precursors such as natural pozzolan, or by manipulating the curing conditions to enhance alumina release from less-reactive precursor phases.     

Internal validation of near-crashes in naturalistic driving studies: A continuous and multivariate approach

Large naturalistic driving studies give extremely detailed insight into how traffic accidents happen and what causes them. However, even in very large studies there are only relatively few crashes. Hence one additionally selects and studies crash surrogates, so called “near-crashes”, i.e. situations when a crash almost happened. The selection procedures invariably entail severe risks of causing bias. In this paper we use extreme value statistics to develop two methods to study the extent and form of this bias. The methods are applied to a large naturalistic driving study, the 100-car study. Both methods identified a severe discrepancy between the rear-striking near-crashes and the rear-striking crashes. Perhaps surprisingly, one conclusion is that, for rear-striking and in this study, the crashes have little relevance for increasing traffic safety. We believe substantial efforts should be made to develop statistical methods for using near-crashes and crashes in future large naturalistic driving studies (such as the SHRP2 study).     

A Graphical Estimation of Mixed Weibull Parameters in Life-Testing of Electron Tubes

It is widely recognized that electron tube failures may be classified into two types: sudden and delayed. A mixture of two Weibull distributions, each representing one type of tube failure, is proposed, and a simple graphical method for estimating the parameters of the mixed Weibull distribution described.     

Missing Values in Response Surface Designs

The estimation of missing values for a general design is described and discussed. Formulae are provided for the estimation of missing values for two well-known, three factor, second order rotatable designs, with zero to six center points. A worked example illustrates the use of the formulae in the case of the cube plus octahedron plus one center point design.     

Modeling of rate-dependent phase transition in bacterial flagellar filament

Recent experiment of Darnton and Berg [34] showed that phase transition of bacterial flagellar filament is loading rate-dependent. The object of this paper is to describe the observed loading rate-dependent phase transition responses of the filament by using time dependent Ginzberg–Landau continuum model. We developed a finite element method (FEM) code to simulate the phase transition under a displacement-controlled loading condition (controlled helix-twist) by using viscosity-type kinetics. Our FEM simulation captures the main features of the rate-dependence: under slow loading (i.e., loading time ? the relaxation time) the filament phase transition is an equilibrium process and each phase grows via interface propagation on the Maxwell line; under rapid loading (i.e., loading time ? the relaxation time), the phase transition does not occur and the response is elastic. Our FEM model provides a tool to study the effects of loading-rate dependent phase transition for bio-filament with viscous kinetics.     

On statistical inference in time series analysis of the evolution of road safety

Data collected for building a road safety observatory usually include observations made sequentially through time. Examples of such data, called time series data, include annual (or monthly) number of road traffic accidents, traffic fatalities or vehicle kilometers driven in a country, as well as the corresponding values of safety performance indicators (e.g., data on speeding, seat belt use, alcohol use, etc.). Some commonly used statistical techniques imply assumptions that are often violated by the special properties of time series data, namely serial dependency among disturbances associated with the observations. The first objective of this paper is to demonstrate the impact of such violations to the applicability of standard methods of statistical inference, which leads to an under or overestimation of the standard error and consequently may produce erroneous inferences. Moreover, having established the adverse consequences of ignoring serial dependency issues, the paper aims to describe rigorous statistical techniques used to overcome them. In particular, appropriate time series analysis techniques of varying complexity are employed to describe the development over time, relating the accident-occurrences to explanatory factors such as exposure measures or safety performance indicators, and forecasting the development into the near future. Traditional regression models (whether they are linear, generalized linear or nonlinear) are shown not to naturally capture the inherent dependencies in time series data. Dedicated time series analysis techniques, such as the ARMA-type and DRAG approaches are discussed next, followed by structural time series models, which are a subclass of state space methods. The paper concludes with general recommendations and practice guidelines for the use of time series models in road safety research.