Supervised hours requirements in graduated driver licensing: Effectiveness and parental awareness

Most states require teens to complete a certain number of hours of supervised driving practice to obtain a license to drive unsupervised. Although widely implemented, the effect of requiring supervised practice is largely unknown. Using auto-regressive integrated moving average (ARIMA) interrupted time-series analysis, we found no change in fatal and injury crash involvement of 16–17-year-old drivers in Minnesota following enactment of a 30 h supervised driving requirement. To supplement and provide insight into these findings, we conducted telephone interviews with parents of newly licensed teenage drivers in five states with varying amounts of required supervised driving, including Minnesota. Interviews revealed awareness of supervised driving requirements was limited. Only a third of parents (32%) overall could correctly identify the number of hours their state required. In Minnesota only 15% of parents could identify the amount of supervised driving their teen was required to complete. Awareness of the number of hours required was substantially higher (55%) in Maryland. Unlike the other states, Maryland requires submission of a driving log detailing the hours of supervised driving. The findings suggest states need to develop more effective mechanisms to ensure parents are aware of supervised hours requirements.     

Short-term effects of a teenage driver cell phone restriction

On December 1, 2006, North Carolina began prohibiting use of any mobile communication device by drivers younger than 18. The current study examined the effects of the law on teenage drivers’ cell phone use. Teenage drivers were observed at high schools in North Carolina 1-2 months before and approximately 5 months after the law took effect. The proportion of teenagers using cell phones did not change significantly (11.0% before the law took effect, 11.8% after). Cell phone use among teenage drivers at high schools in South Carolina, an adjacent state without a teenage driver phone ban, was stable at about 13%. Interviews were conducted with parents and teenagers in North Carolina both before and after the law took effect. In post-law interviews, teenagers were more likely than parents to say they knew about the cell phone restriction (64% vs. 39%), but support for the ban was greater among parents (95% vs. 74%). Only 22% of teenagers and 13% of parents believed the law was being enforced fairly often or a lot. Although the proportion of teenagers who reported using phones while driving declined somewhat following the law, about half admitted they used their phones, if they had driven, on the day prior to the interview. Overall, the findings suggest that North Carolina's cell phone restriction had little to no effect on teenage drivers’ use of cell phones shortly after the law took effect.     

双向搜索分层化的多约束路由启发式计算方法

提出一种多约束路由的双向搜索层次化计算方法,第一层分别从源和目的节点出发,计算到达各中间节点的可达路径,第二层在各可达路径中进行路径的筛选。可达路径是采用邻接矩阵变换方式获得的,筛选路径是根据非线性开销函数采用启发方式择优选取。当两方向搜索的节点数累计总和达到n-2后,则对接合并两方向到达中间节点的路径,获得多条经过不同中间节点的源到目的节点的路径,从中选择最佳路径作为路由输出。通过算例详细介绍了可达路径计算及启发式选优方法,论述了算法的正确性与合理性,分析了最坏时间杂性,简介了新算法具备并行运算特征。通过仿真实验评估,不仅更进一步验证了新算法的正确性,而且表明新算法在性能上要优于其他算法。     

Some numerical properties of explicit solutions to the one‐dimensional conservation equation

Abstract:

One‐dimensional unsteady‐state advection‐dispersion models are useful in practice for predicting time‐varying concentrations in streams for phenomena such as chemical spills or combined sewer overflows. The challenge in modeling such phenomena, which demonstrate sharp concentration gradients, is to ensure that the numerical dispersion, an artificial erroneous smearing of concentrations, not overshadow the true dispersion, which, while of significance due to sharp gradients, is ordinarily small compared to advection as a transport mechanism. This paper revisits stability criteria and numerical dispersion properties of explicit Lagrangian and Eulerian solutions of the one‐dimensional advection‐dispersion equation. It is shown that the Leith method of correcting for numerical dispersion (which was developed prior to the recent increase in popularity of Lagrangian methods) has similar stability restrictions on the step sizes as the latter when the zero‐overshoot criterion for stability is used. For uncorrected Eulerian formulations, the stable regions for Dx and Dt depend on the approximation of the advection term. For the forward and central difference approximations, the region is bounded, while for the backward difference formulation, Dx is unbounded. For Lagrangian formulations, the stable region has no upper bound, but has a lower bound on Dx. Correcting numerical dispersion in Eulerian formulations not only results in substantially better accuracy but changes the stable regions for Dx and Dt. The stable regions for corrected Eulerian formulations ‐ indeed, the formulations themselves ‐ are independent of the type of approximation of the first derivative, and are unbounded, although they become increasingly narrow as the true dispersion decreases. As the true dispersion approaches zero, the stable region approaches a line which corresponds to a Courant number of one. Thus, in the limit where the dispersion approaches zero, corrected Eulerian formulations, like Lagrangian formulations, must use a Courant number of one, but corrected Eulerian formulations do not have the lower bound on step size.     

Estimation of regression coefficients subject to exact linear restrictions when some observations are missing and quadratic error balanced loss function is used

This article considers a linear regression model when a set of exact linear restrictions binding the coefficients is available and some observations on the study variable are missing. Estimators for the vectors of regression coefficients are presented and their superiority properties with respect to the criteria of the variance covariance matrix and the risk under balanced loss functions are analyzed.     

粒子群优化算法的边界变异策略比较研究

为解决粒子群优化( PSO)算法中粒子越界和早熟收敛等问题,在比较国内外学者提出的边界变异策略基础上,提出一种新的边界变异策略———双重限制变异策略。针对粒子越界时速度和位置变异方向的不同情形,通过同时限制粒子的更新位置和更新速度,将粒子控制在搜索空间范围内。利用5种测试函数进行实验,结果表明,与其他4种边界变异策略相比,双重变异策略收敛速度快,在解决粒子越界问题上具有较好的效果。此外,通过实验测试显示粒子的最大速度和最大位置的比值与变异策略的好坏程度成反比,为边界变异策略的研究提供了一定依据。     

On thermo-electro-viscoelastic relaxation functions in a Green–Naghdi type theory

Abstract

We find restrictions on the relaxation functions of thermo-electro-viscoelastic materials. This is achieved within an extension of the Green–Naghdi theory for thermoelasticity, which uses the energy equation to exploit constitutive equations. These restrictions extend the results previously found for thermo-viscoelastic materials and for the classical infinitesimal theory of viscoelasticity.