Upper trapezius muscle activity in healthy office workers: reliability and sensitivity of occupational exposure measures to differences in sex and hand dominance

Patterns of cervical muscle activity may contribute to overuse injuries in office workers. The purpose of this investigation was to characterise patterns of upper trapezius muscle activity in pain-free office workers using traditional occupational exposure measures and a modified Active Amplitude Probability Distribution Function (APDF), which considers only periods of active muscle contraction. Bilateral trapezius muscle activity was recorded in 77 pain-free office workers for 1–2 full days in their natural work environment. Mean amplitude, gap frequency, muscular rest and Traditional and Active APDF amplitudes were calculated. All measures demonstrated fair to substantial reliability. Dominant muscles demonstrated higher amplitudes of activity and less muscular rest compared to non-dominant, and women demonstrated less muscular rest with no significant difference in amplitude assessed by Active APDF compared to men. These findings provide normative data to identify atypical motor patterns that may contribute to persistence or recurrence of neck pain in office workers.

Practitioner Summary: Upper trapezius muscle activity was characterised in a large cohort of pain-free workers using electromyographic recordings from office environments. Dominant muscles demonstrated higher activity and less rest than non-dominant, and women demonstrated less rest than men. Results may be used to identify atypical trapezius muscle activity in office workers.     

Optimal allocation of change points in simple step-stress experiments under Type-II censoring

In simple step-stress experiments under Type-II censoring with the cumulative exposure model and exponentially distributed lifetimes, maximum likelihood estimates (MLE) of the expected lifetimes may not exist due to the absence of failure times either before or after the stress change point. For this reason, when planning a step-stress experiment, the change point could be chosen so as to minimize the probability of non-existence of the MLE. These non-existence probabilities are examined and compared in the one- as well as the two-sample situations. Moreover, the optimal allocations of the change points are discussed and the effects of the use of non-optimal choices for the change points are assessed.     

Extracting LiDAR indices to characterise multilayered forest structure using mixture distribution functions

Discrete Light Detection and Ranging (LiDAR) data is used to stratify a multilayered eucalyptus forest and characterise the structure of the vertical profile. We present a methodology that may prove useful for a very broad range of forest management applications, particularly for timber inventory evaluation and forest growth modelling. In this study, we use LiDAR data to stratify a multilayered eucalyptus forest and characterise the structure of specific vegetation layers for forest hydrology research, as vegetation dynamics influence a catchment's streamflow yield. A forest stand's crown height, density, depth, and closure, influence aerodynamic properties of the forest structure and the amount of transpiring leaf area, which in turn determine evapotranspiration rates. We present a methodology that produces canopy profile indices of understorey and overstorey vegetation using mixture models with a wide range of theoretical distribution functions. Mixture models provide a mechanism to summarise complex canopy attributes into a short list of parameters that can be empirically analysed against stand characteristics.Few studies have explored theoretical distribution functions to represent the vertical profile of vegetation structure in LiDAR data. All prior studies have focused on a Weibull distribution function, which is unimodal. In a complex native forest ecosystem, the form of the distribution of LiDAR points may be highly variable between forest types and age classes. We compared 44 probability distributions within a two component mixture model to determine the most suitable bimodal distributions for representing LiDAR density estimates of Mountain Ash forests in south-eastern Australia. An elimination procedure identified eleven candidate distributions for representing the eucalyptus component of the mixture model.We demonstrate the methodology on a sample of plots to predict overstorey stand volumes and basal area, and understorey basal area of 18-, 37-, and 70-year old Mountain Ash forest with variable density classes. The 70-year old forest has been subjected to a range of treatments including: thinning of the eucalyptus layer with two distinct retention rates, removal of the understorey, and clear felling of patches that have 37 year old regenerating forest. We demonstrate that the methodology has clear potential, as observed versus predicted values of eucalyptus basal area and stand volume were highly correlated, with bootstrap based r² ranging from 0.61 to 0.89 and 0.67 to 0.88 respectively. Non-eucalyptus basal area r² ranged from 0.5 to 0.91.     

基于Pareto最优和限制精英的多目标进化算法

在NSGA-II算法的基础上,提出了一种基于Pareto最优和限制精英的多目标进化算法(LEMOEA)。通过分布函数的引入,限制了精英选取的数量,从而更好地维护了种群多样性。同时给出了一种新的单点复合交叉算子,其不但增大了解的搜索区域,而且增强了算法对解的搜索能力。实验结果表明:LEMOEA比NSGA-II有更好的收敛效果和种群多样性。     

Effects of user experience,working posture and joint hardness on powered nutrunner torque reactions

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force and upper limb muscle activity (electromyography (EMG)) due to the effects of operator experience, working height and distance, type of tool and fastener joint hardness were measured in this study with 15 experienced and 15 novice nutrunner users. The results show that when pistol grip handles were used to work on a horizontal surface, experienced users allowed an average handle displacement of 7.9°, while novice users allowed 11.5°. Average EMG scaled by reference voluntary contraction (RVC) at forearm flexors, forearm extensors and biceps were greater for experienced users (318% RVC, 285% RVC, 143% RVC, respectively) than for novice users (246% RVC, 219% RVC, 113% RVC, respectively). Experienced users exerted more grip force than novice users when using right angle handles, but less force when using pistol grip handles. The results suggest that it is possible to minimize tool handle displacement by adapting the workplace layout to permit different working postures for each user group.     

银行信贷风险的测量与控制

信贷风险是银行资产业务中最直接、经常性的风险．本文分析了目前金融风险测量的主流技术VAR模型及其在信贷风险控制上的不足,从信贷风险产生的根源——企业破产深层次角度,对企业破产风险状态的识别及破产概率进行了研究,提出基于生存函数的信贷风险控制模型,并给出仿真计算案例．     

改进的粒子群优化算法求解车辆调度问题*

采用对基本粒子群优化算法引入遗传操作来提高种群多样性,这样虽能避免产生局部极小,但收敛速度会降低,通过加入收缩因子来达到两者的均衡。优化和仿真结果表明改进算法性能更优,能有效地解决公交车辆的智能排班问题。     

多维直方图联合概率分布的掩模矩阵降维算法

彩色图像的分量独立处理或感知彩色空间的强度分量处理,都能达到增强图像对比度的效果,但由于没有考虑各个分量之间的联系,不能开发完全的RGB色域。多通道直方图建模技术可以改善上述缺陷,就是通过求取多个分量的直方图联合概率密度函数和累积分布函数,从而得到彩色图像的像素灰度值映射函数,但计算联合直方图的过程也导致了过高的运算复杂度。为了降低计算量,提出了掩模降维的方法,将计算多维直方图的过程转化为了计算一维直方图,从而大大降低了运算复杂度,提高运算速度,增强对比度的效果。     

一种由粗到精的车标定位算法

简要描述了“识别系统”的技术结构,并在研究了经典定位算法后,提出了一种实用的由粗到精的车标定位算法,即根据相关的先验知识确定车标的大致范围,再运用边缘检测和形态算子确定较准确的车标位置,最后在极小的范围内用相关匹配算子得到车标的精确位置。实验结果表明,该算法在应用仿真中取得了良好的效果。     

Bicycle messengers: energy expenditure and exposure to air pollution

The purpose of the study was to determine the level of energy expenditure and exposure to air pollution for bicycle messengers. Relationships between heart rate (HR) and oxygen uptake, and between HR and pulmonary ventilation (VE) for each participant were established in laboratory tests. Air pollution and HR were measured during one working day. The total oxygen uptake was then described as the total energy expenditure in Joule (J) and in multiples of the energy expenditure at rest (MET). The mean energy expenditure during a working day (8 h) was 12 MJ, (4.8 MET). The level of air pollution exposure when cycling seemed to be comparable with the levels of exposure when sitting inside a vehicle. The VE during cycling was four times higher than resting value. Increased VE led to increased exposure to air pollution.     

多目标遗传算法在GPS动态车辆调度中的应用研究

围绕车辆调度问题多目标优化这一主题,依据企业现有的GPS定位系统,设计一种基于实数编码和精英保留策略,综合应用外部惩罚函数法的多目标遗传算法.并于其中创新性的引入基因校验算子,避免了重复车次的产生.程序使用Java语言编制,后台数据库使用oracle.实验结果表明,该算法能够充分满足系统硬约束条件,快速收敛于目标约束,完成车辆的优化调度,具有较强的实用价值.     

牵引负荷实测数据的分类

随着电气化铁路在铁路运输中的迅猛发展以及电压等级的不断提高,电气化铁路牵引负荷对电网的负序和谐波影响也随之增大。为了建立准确有效的电气化铁路牵引负荷模型以评估其对电网的影响程度,本文根据全国部分牵引变电所的实测数据,利用Matlab仿真软件对实测数据进行分析处理,得到其概率密度函数图以及对应的累积分布函数图。通过观察发现累积分布函数图之间存在一定规律,因此根据累积分布函数图,对牵引负荷实测数据进行分类整理,得到牵引负荷实测数据的分类。     

Inference for a simple step-stress model with competing risks for failure from the exponential distribution under time constraint

In reliability analysis, accelerated life-testing allows for gradual increment of stress levels on test units during an experiment. In a special class of accelerated life tests known as step-stress tests, the stress levels increase discretely at pre-fixed time points, and this allows the experimenter to obtain information on the parameters of the lifetime distributions more quickly than under normal operating conditions. Moreover, when a test unit fails, there are often more than one fatal cause for the failure, such as mechanical or electrical. In this article, we consider the simple step-stress model under time constraint when the lifetime distributions of the different risk factors are independently exponentially distributed. Under this setup, we derive the maximum likelihood estimators (MLEs) of the unknown mean parameters of the different causes under the assumption of a cumulative exposure model. Since it is found that the MLEs do not exist when there is no failure by any particular risk factor within the specified time frame, the exact sampling distributions of the MLEs are derived through the use of conditional moment generating functions. Using these exact distributions as well as the asymptotic distributions, the parametric bootstrap method, and the Bayesian posterior distribution, we discuss the construction of confidence intervals and credible intervals for the parameters. Their performance is assessed through Monte Carlo simulations and finally, we illustrate the methods of inference discussed here with an example.     

Two-sample tests of the equality of two cumulative incidence functions

Typically, differences in the effect of treatment on competing risks are compared by a weighted log-rank test. This test compares the cause-specific hazard rates between the groups. Often the test does not agree with impressions gained from plots of the cumulative incidence functions. Here, we discuss two-sample tests of the equality of two cumulative incidence functions. The first test, based on a suggestion of Lin [1997. Non-parametric inference for cumulative incidence functions in competing risks studies. Statist. Med. 16, 901-910], compares the maximum difference between the two cumulative incidence functions. A Monte Carlo method is used to find p-values for the test. The second test, based on a suggestion of Pepe [1991. Inference for events with dependent risks in multiple endpoint studies. J. Amer. Statist. Assoc. 86, 770-778], compares the integrated difference between the functions. A new variance estimator is proposed for this statistic. A small simulation study is used to compare the various tests. The methods are illustrated on a bone marrow transplant study.     

Optimal control of stable weakly regular linear systems

The paper extends quadratic optimal control theory to weakly regular linear systems, a rather broad class of infinite-dimensional systems with unbounded control and observation operators. We assume that the system is stable (in a sense to be defined) and that the associated Popov function is bounded from below. We study the properties of the optimally controlled system, of the optimal cost operatorX, and the various Riccati equations which are satisfied byX. We introduce the concept of an optimal state feedback operator, which is an observation operator for the open-loop system, and which produces the optimal feedback system when its output is connected to the input of the system. We show that if the spectral factors of the Popov function are regular, then a (unique) optimal state feedback operator exists, and we give its formula in terms ofX. Most of the formulas are quite reminiscent of the classical formulas from the finite-dimensional theory. However, an unexpected factor appears both in the formula of the optimal state feedback operator as well as in the main Riccati equation. We apply our theory to an extensive example.Part of the results reported here were obtained while the second author was visiting FUNDP Namur, under the Belgian Program on Inter-University Poles of Attraction initiated by the Belgian state, Prime Minister's Office, Science Policy Programming. The scientific responsibility is assumed by the authors.     

Stress-induced muscle effort as a cause of repetitive strain injury?

The influence of stress-induced muscle effort during computer utilization was tested in patients with repetitive strain injury (RSI). Twenty academic researchers with a formal medical diagnosis of RSI and 20 matched controls, randomly selected from a sample of 71 colleagues with and without RSI, typed after stress (induced via an intelligence/skill task under social pressure) and after relaxation. Results indicated that both groups had more electromyography (EMG) activity in the shoulder muscles during typing after stress than after relaxation, but that patients started with higher baseline muscle activity. Furthermore, EMG activity of different muscle groups during typing after stress correlated among controls, but not among patients. Finally, analysis of intake forms showed that patients scored higher than controls on neuroticism and alexithymia, but not on extraversion, openness, agreeableness and conscientiousness. It was concluded that deviations in muscle activity during computer utilization, as well as neuroticism and alexithymia, may be risk factors for RSI.     

Occupational noise exposure of fishermen aboard small and medium-scale fishing vessels

There is little information about occupational noise exposure of fishermen working on small and medium-scale fishing vessels, mainly because of the difficulty of conducting noise exposure surveillance in such occupations. The objective of the current study was to evaluate the exposure of this group of workers to occupational noise using a combined measurement and questionnaire approach. Sound pressure levels were measured aboard 24 fishing vessels at all working or resting locations and during speeding and slow-down moods of the engine. The average existence times of the crew at such locations were collected using a questionnaire. The average daily noise exposure levels (L_EP,d,8h) for engine mechanics in all vessel types (91.2–94.3 dBA) and the tiller operators in gill/trammel and purse seining vessels (84.7–88.4 dBA) exceeded the NIOSH recommended exposure limit of 85 dBA. Other crew members were found to be exposed, on average, to daily noise exposure levels slightly lower than the recommended one (81.6–83.5 dBA). However, direct personal dosimetry for five crew members revealed daily noise exposure levels 1.1–5.1 dBA higher than the calculated averages, which might be attributed, partly, to sources of uncertainty. The results of this study suggest that small and medium-scale vessels fishermen are at high risk of NIHL, calling for development and enforcement of suitable interventions for hearing protection of the workforce of this sector.     

关于离散空间中最优搜索策略的一些结果

研究关于N个位置的最优搜索问题.最优搜索问题是研究如何将用于搜索的资源(如时间等)分配到N个位置使得发现目标的概率为最大.以往人们在研究最优搜索问题时总是假设目标的分布函数是已知的,但实际情况往往不是这样.用拉格朗日算子理论来研究目标的分布函数是未知的情况下的最优搜索问题,得出了一系列新的结果,包括分布函数的近似方法和误差估计公式.最后给出了两个例子.     

无人驾驶车辆光学传感器自适应曝光算法研究

为保证无人驾驶车辆图像采集系统能够在光线强弱变化的环境中获取更为可靠的道路信息,提供更多的道路边界,提出一种自适应曝光算法.利用光学传感器特性,将采集图像转化为灰度值,并运行进行动态阁值比对处理,快速获取下一周期正确曝光点.在道路实际的测试中,该算法能够快速并有效获取道路信息,后续的边界处理较为清晰.