A New Approach for Evaluating Flexible Working Hours

Recent studies on flexible working hours show at least some of these working time arrangements seem to be associated with impairing effects of health and well-being. According to available evidence, variability of working hours seems to play an important role. The question, however, is how this variability can be assessed and used to explain or predict impairments. Based on earlier methods used to assess shift-work effects, a time series analysis approach was applied to the matter of flexible working hours. Data on the working hours of 4 week's length of 137 respondents derived from a survey on flexible work hours involving 15 companies of different production and service sectors in Germany were converted to time series and analyzed by spectral analysis. A cluster analysis of the resulting power spectra yielded 5 clusters of flexible work hours. Analyzing these clusters for differences in reported impairments showed that workers who showed suppression of circadian and weekly rhythms experienced severest impairments, especially in circadian controlled functions like sleep and digestion. The results thus indicate that analyzing the periodicity of flexible working hours seems to be a promising approach for predicting impairments which should be investigated further in the future.     

The power of modified instrumental variables tests for unit roots

In this paper we investigate the power of Hall's (1989) instrumentalvariables tests for unit roots. A slight modification is madeto Hall's t statistic so that the modified t statistic can beapplied directly without encountering the possible negativestandard error problem of Hall's original t statistic. The majorfinding is that the power curves of the instrumental variablestests are not monotonic functions of the autoregressive coefficientof the unit root models when there is a negative moving averagecomponent.     

Time perception,emotions and mood disorders

In this review, we describe recent internal clock models accounting for time perception and look at how they try to explain the time distortions produced by emotion. We then discuss the results of studies of patients suffering from affective disorders (depression) who experience the feeling of time slowing down. A distinction is thus made between time perception and explicit awareness of the passage of time. We conclude that the feeling that time is passing slowly is not systematically associated with a disruption in the basic mechanisms underlying time perception.     

CICLOGRAMA: A TOOL FOR DETECTION OF RHYTHMICITIES IN SLEEP/WAKE CYCLES

The Fourier spectral analysis of binary time series (or rectangular signals) causes methodological problems, due to the fact that it is based on sinusoidal functions. We propose a new tool for the detection of periodicities in binary time series, focusing on sleep/wake cycles. This methodology is based on a weighted histogram of cycle durations. In this paper, we compare our methodology with the Fourier spectral analysis on the basis of simulated and real binary data sets of various lengths. We also provide an approach to statistical validation of the periodicities determined with our methodology. Furthermore, we analyze the discriminating power of both methods in terms of standard deviation. Our results indicate that the Ciclograma is much more powerful than Fourier analysis when applied on this type of time series.     

Decoupled time-marching schemes in computational cardiac electrophysiology and ECG numerical simulation

This work considers the approximation of the cardiac bidomain equations, either isolated or coupled with the torso, via first order semi-implicit time-marching schemes involving a fully decoupled computation of the unknown fields (ionic state, transmembrane potential, extracellular and torso potentials). For the isolated bidomain system, we show that the Gauss-Seidel and Jacobi like splittings do not compromise energy stability; they simply alter the energy norm. Within the framework of the numerical simulation of electrocardiograms (ECG), these bidomain splittings are combined with an explicit Robin-Robin treatment of the heart-torso coupling conditions. We show that the resulting schemes allow a fully decoupled (energy) stable computation of the heart and torso fields, under an additional hyperbolic-CFL like condition. The accuracy and convergence rate of the considered schemes are investigated numerically with a series of numerical experiments.     

Long-term changes in metapopulation genetic structure: a quarter-century retrospective study on low-Arctic rock pool Daphnia

Population genetic surveys approximately 25 years apart examined the distribution and abundance of asexual clones of the freshwater zooplankter Daphnia pulex complex in rock pools near Churchill, Manitoba, Canada. In 1984–1985, melanic members of this species complex were present in 131 rock pools at this site, but were only detected in 90 of these pools in 2007–2008. Allozymic surveys conducted during these two time periods revealed that 59 per cent of these populations showed unchanged clonal composition. Total clonal replacement occurred in 8 per cent of the populations, while the others (33%) included a mixture of ‘resident’ clones and new ‘colonists’. We discuss these changes in light of shifts in biotic and abiotic factors. We also discuss the use of rock pool habitats as ‘sentinel’ systems for examining long-term environmental changes in the ecological genetics of aquatic organisms in the Arctic.     

The importance of the reinforcer as a time marker

Shifts in the psychometric function in the Free Operant Psychophysical Procedure (FOPP) have traditionally been explained by suggesting the pacemaker rate is proportional to the reinforcement rate (Behavioral Theory of Timing; BeT), or by direct associative competition between the two responses (Learning to Time; LeT). The application of these models assumes that the stimulus onset is the relevant time marker. Head-entries were reinforced in the second half of a stimulus (s1) and in the first half of a different stimulus (s2). During extinction, response times shifted earlier in s2 only, contrary to BeT. Competition between responses is an unlikely cause of the shift, contrary to LeT. We found a single-cycle correlation between the last food delivery and the time the rat stopped responding on s2. This correlation was also present in FOPP data. These results are consistent with the interpretation that the reinforcer, more than the stimulus onset, acted as the relevant time marker on this task.     

ARIMA与SVM组合模型在害虫预测中的应用

害虫发生是一种复杂、 动态时间序列数据, 单一预测模型都是基于线性或非线性数据, 不能同时捕捉害虫发生的线性和非线性规律, 很难达到理想的预测精度。本研究首先采用差分自回归移动平均模型对昆虫发生时间序列进行线性建模, 然后采用支持向量机对非线性部分进行建模, 最后得到两种模型的组合预测结果。将组合模型应用到松毛虫Dendrolimus punctatus发生面积的预测, 实验结果表明组合模型的预测精度明显优于单一模型, 发挥了两种模型各自的优势。组合模型是一种切实可行的害虫预测预报方法。     

无量山西黑冠长臂猿二重唱的声谱结构和时间特征

2003年3月—2004年3月对无量山大寨子3群西黑冠长臂猿的二重唱的时间特征进行了监测。于2007年3月和2008年3月利用Sony TC-D5 Pro2录音机、Sony C-76指向性话筒和Sony录音磁带对其二重唱进行了录音,对录音效果最好的5个声音用Signal/RTS 4.0软件进行声谱分析。对无量山西黑冠长臂猿二重唱的声谱结构和时间特征的研究结果表明,雄性西黑冠长臂猿的声音由起始音节、简单的重复音节和调节音节组成。根据频率变化的强度,可以将调节音节分为弱调节音节和强调节音节。强调节音节的特征是第二个音节具有非常明显的频率变化,有时第三个音节有类似变化,变频时的最高频率可达到5 828 Hz。雌性长臂猿一般只会发出一种类型的声音,即固定而刻板的激动鸣叫。根据激动鸣叫是否完整可以分为成功的激动鸣叫和失败的激动鸣叫。典型的西黑冠长臂猿二重唱通常由成年雄性发起,并占主导地位,且一般由雄性结束。雌性激动鸣叫结束后,雄性马上发出调节音节与之配合,雄性调节音节与雌性激动鸣叫的时间间隔平均为2.7 s。平均每个群体的鸣叫频次为53%。如果发生鸣叫,一个群体平均每天鸣叫1.09次。91.5%的鸣叫发生在日出前0.5 h至日出后3 h之间,其中48.6%的鸣叫发生在日出后1 h内。在一次鸣叫中,雌性平均发出成功的激动鸣叫4.6次,两次成功的激动鸣叫之间的时间间隔平均为115 s。群体间均未显示鸣叫频次和持续时间上的差异,但激动鸣叫次数和激动鸣叫时间间隔具有显著差异。     

Design and Analysis of Crossover Trials for Absorbing Binary Endpoints

Summary The crossover is a popular and efficient trial design used in the context of patient heterogeneity to assess the effect of treatments that act relatively quickly and whose benefit disappears with discontinuation. Each patient can serve as her own control as within‐individual treatment and placebo responses are compared. Conventional wisdom is that these designs are not appropriate for absorbing binary endpoints, such as death or HIV infection. We explore the use of crossover designs in the context of these absorbing binary endpoints and show that they can be more efficient than the standard parallel group design when there is heterogeneity in individuals' risks. We also introduce a new two‐period design where first period “survivors” are rerandomized for the second period. This design combines the crossover design with the parallel design and achieves some of the efficiency advantages of the crossover design while ensuring that the second period groups are comparable by randomization. We discuss the validity of the new designs and evaluate both a mixture model and a modified Mantel–Haenszel test for inference. The mixture model assumes no carryover or period effects while the Mantel–Haenszel approach conditions out period effects. Simulations are used to compare the different designs and an example is provided to explore practical issues in implementation.