Deriving heart rate variability indices from cardiac monitoring—An indicator of driver sleepiness

Objective: Driver fatigue is considered to be a major contributor to road traffic crashes. Cardiac monitoring and heart rate variability (HRV) analysis is a candidate method for early and accurate detection of driver sleepiness. This study has 2 objectives: to evaluate the (1) suitability of different preprocessing strategies for detecting and removing outlier heartbeats and spectral transformation of HRV signals and their impact of driver sleepiness assessment and (2) relation between common HRV indices and subjective sleepiness reported by a large number of drivers in real driving situations, for the first time.

Methods: The study analyzed >3,500 5-min driving epochs from 76 drivers on a public motorway in Sweden. The electrocardiograph (ECG) data were recorded in 3 studies designed to evaluate the physiological differences between awake and sleepy drivers. The drivers reported their perceived level of sleepiness according to the Karolinska Sleepiness Scale (KSS) every 5?min. Two standard methods were used for identifying outlier heartbeats: (1) percentage change (PC), where outliers were defined as interbeat intervals deviating >30% from the mean of the four previous intervals and (2) standard deviation (SD), where outliers were defined as interbeat interval deviating >4 SD from the mean interval duration in the current epoch. Three standard methods were used for spectral transformation, which is needed for deriving HRV indices in the frequency domain: (1) Fourier transform; (2) autoregressive model; and (3) Lomb-Scargle periodogram. Different preprocessing strategies were compared regarding their impact on derivation of common HRV indices and their relation to KSS data distribution, using box plots and statistical tests such as analysis of variance (ANOVA) and Student’s t test.

Results: The ability of HRV indices to discriminate between alert and sleepy drivers does not differ significantly depending on which outlier detection and spectral transformation methods are used. As expected, with increasing sleepiness, the heart rate decreased, whereas heart rate variability overall increased. Furthermore, HRV parameters representing the parasympathetic branch of the autonomous nervous system increased. An unexpected finding was that parameters representing the sympathetic branch of the autonomous nervous system also increased with increasing KSS level. We hypothesize that this increment was due to stress induced by trying to avoid an incident, because the drivers were in real driving situations.

Conclusions: The association of HRV indices to KSS did not depend on the preprocessing strategy. No preprocessing method showed superiority for HRV association to driver sleepiness. This was also true for combinations of methods for frequency domain HRV indices. The results prove clear relationships between HRV indices and perceived sleepiness. Thus, HRV analysis shows promise for driver sleepiness detection.     

基于不同强度等级混凝土的动力学特性研究

基于TAW-2000D电液伺服岩石三轴仪和直径75 mm的霍普金森压杆试验装置,得到了C25,C35和C45混凝土在静、动载荷作用下的应力-应变曲线,探讨了混凝土强度等级、动态峰值强度、峰值应变和应变率之间的变化规律。结果表明:混凝土准静态应力-应变曲线和动态应力-应变曲线在形态上存在明显差异,动态应力-应变曲线的峰值点随应变率的增大向右上方移动,线弹性阶段各曲线斜率变化不明显;动态峰值应力、动态弹性模量和峰值应变均存在不同程度的率相关性,并且混凝土材料的应变率敏感性随其强度等级的提高而增强;混凝土C45的各力学指标对应变率的敏感性最强,C35次之,C25的应变率敏感性最弱;推导了应变率与强度等级和冲击速率之间的经验公式,三者之间存在非线性变化规律。     

加卸荷条件下岩石力学特性与声发射特征

为了探究真三轴复杂应力变化条件下岩石强度及破坏模式,通过真三轴卸荷扰动测试系统对砂岩试件进行不同第二主应力加卸荷试验,讨论在加卸荷过程中岩石的力学特性及声发射特征。试验结果表明:第二主应力的增加对试件的承载能力起到先增强后弱化的效果;不同第二主应力加卸荷声发射能量及累计振铃计数变化趋势大体一致,耗散能量比在载荷达到岩石损伤强度时突增;声发射能量峰值提前于试件轴向应力跌落,声发射能量和累计振铃计数大幅突增可作为岩石破坏的前兆;在低载荷下岩石中活动主要是裂隙压密与发育,在达到岩石损伤强度后岩石中的活动主要是裂纹贯通形成破裂面,砂岩试件声发射定位点集中区域与试件主要破裂面基本吻合。     

我国特种劳动防护用品产业分布特点分析

为了解我国特种劳动防护用品产业分布特点和产业市场集中程度,基于生产企业统计数据,估算我国特种劳动防护用品产业市场集中度;对比2017年和2010年数据,统计分析我国特种劳动防护用品产业的区域、产品种类、企业注册资金规模和企业从业人员数量的分布和变化,分析总结了产业发展呈现的特点,提出了加快我国特种劳动防护用品产业发展的相应建议。结果表明:当前我国特种劳动防护用品产业市场结构尚属于低集中竞争型;各区域生产企业数量按照东部、中部、西部和东北的顺序依次递减,东部生产企业占据全国企业总数的65%以上;一半以上企业的注册资金均大于1 000万元;以从业人员数量看,80%以上企业属于小型企业规模;与2010年相比,2017年我国特种劳动防护用品生产企业从业人员数量增加了6.67%,企业从业人员规模分布变化不明显,企业注册资金规模已由约7成企业在500万元以下转变为近7成超过500万元,产品种类增加了40%。研究结果可为我国劳动防护用品产业和安全产业的发展提供科学参考。     

微量Fe3+对过氧化氢异丙苯热稳定性影响研究

为研究微量铁离子（Fe³⁺）对过氧化氢异丙苯（CHP）热稳定性的影响,采用绝热加速量热仪（ARC）对CHP及含4种不同浓度Fe3+的CHP进行了绝热分解测试,测试分析了5个样品在绝热条件下的起始分解温度（To,s）、绝热温升（ΔTad,s）、最大温升速率（mm,s）和最大温升速率到达时间（θm,s）等参数,并利用热惰性因子Φ对实验数据进行了修正。研究结果表明:在绝热条件下,微量Fe3+的存在对CHP分解的To,s,ΔTad,s,mm,s和θm,s均有较大影响,且浓度不同对各参数的影响不一样;Fe³⁺的存在增加了CHP分解的剧烈程度,且浓度越大,CHP分解越剧烈,其热分解失控可能性越大,危险性越高;储存运输CHP时要避免与高浓度的Fe³⁺接触。研究结果可为CHP的热稳定性安全提供一定参考。     

稻田甲烷排放通量与农业管理措施的关系

1990至1992年对北京地区的麦后稻区及单季稻区进行了三年的稻田甲烷排放通量的测定,麦后稻区的甲烷排放通量约17.5mg/m~2·h;单季稻小区约在8.5-10mg/m~2·h。有机底肥的用量是影响甲烷排放通量的首要因素,旱直播及仅使用化肥可降低甲烷排放通量。在一定量有机底肥的条件下,采用间歇灌溉的方法既可保持或提高水稻的产量,又可抑制或降低甲烷的排放通量,但也观测到干干湿湿的状态下温室气体N_2O的排放通量有所增加。     

水分调节材料对牛粪堆肥氨气挥发的影响

利用通风式堆肥发酵方式研究了牛粪堆制过程中氨气的挥发特征和锯末、稻壳、稻草等不同水分调节材料对氨气挥发的影响。结果表明,牛粪堆制过程中主要在前期,尤其是在最初的2周内释放氨气;堆肥期间挥发的氨态氮约为牛粪总含氮量的17%～50%。不同水分调节材料都可以在一定程度上抑制氨气的挥发,但锯末抑制氨气挥发效果最好,其次是稻壳,稻草抑制氨气挥发的效果较小。因此,为了减少氮素损失,应采取适当措施抑制氨挥发或回收挥发的氨气。     

生物质燃烧释放N2O的测定及其分布

本文报导了实验室规模的生物质封闭燃烧系统及稻草、玉米秸、麦杆燃烧过程中Ｎ２Ｏ排放因子的测定结果，测定结果表明：稻草、麦杆及玉米秸燃烧排气中Ｎ２Ｏ的排放因子分析是８４．４ｇ／ｔ，２７．３ｇ／ｔ，１３２ｇ／ｔ。用Ｎ２Ｏ－Ｎ占生物全氮的百分含量表示，稻草及玉米秸分别上０．５９％，０．８７％。用实验得到的Ｎ２Ｏ的排放因子计算出了生物质燃烧产生Ｎ２Ｏ在全国各省、直辖市、县的年排放量，并作出了全国年排放的分布     

中国农田N_2O排放量的估算

排放量估算是温室效应气体研究的重要内容。本文论述了影响农田Ｎ２Ｏ排放量估算准确性的因素，讨论如何提高农田Ｎ２Ｏ排放量估算的准确性，并估算了中国农田Ｎ２Ｏ排放总量。     

Power-law behaviour and parametric models for the size-distribution of forest fires

This paper examines the distribution of areas burned in forest fires. Empirical size distributions, derived from extensive fire records, for six regions in North America are presented. While they show some commonalities, it appears that a simple power-law distribution of sizes, as has been suggested by some authors, is too simple to describe the distributions over their full range. A stochastic model for the spread and extinguishment of fires is used to examine conditions for power-law behaviour and deviations from it. The concept of the extinguishment growth rate ratio (EGRR) is developed. A null model with constant EGRR leads to a power-law distribution, but this does not appear to hold empirically for the data sets examined. Some alternative parametric forms for the size distribution are presented, with a four-parameter ‘competing hazards’ model providing the overall best fit.