Polyphasic sleep strategies improve prolonged sustained performance: A field study on 99 sailors

In situations where continuous prolonged work demands exist, the habitual nocturnal monophasic (6-8h duration) sleep pattern can rarely be accomplished, and performance effectiveness may sometimes be severely compromised by accumulation of sleep debt. Several studies have shown that naps can be disproportionately effective in recovering functioning during continuous work (CW).

In this study, sleep-wake patterns and their relationship to performance were studied for 99 sailors involved in solo and double-handed ocean sailing races (a model of a highly demanding CW situation). Most sailors spontaneously adopted multiple nap sleep-wake schedules and adapted without major difficulties to such polyphasic patterns. 66.5% had mean sleep episode durations (SEDs) ranging from 20 min to 2h. Overall mean Total Sleep Time (TST) per 24h was reduced from a baseline of 7.5 to 6.3h. Race performance correlated negatively and significantly with mean SEDs and TSTs. Best performance results were obtained by those sleeping for periods of between 20 min and 1 h and for a total of 4.5 to 5.5h of sleep per day.

The results are discussed together with several chronobiological, phylogenetic and experimental studies and issues, all of which suggest that adult humans may have a damped polyphasic sleep-wake tendency. It is also proposed that polyphasic sleep schedules could become promising and feasible solutions for the management of sleep requirements under prolonged CW situations.     

New Zealand Consumption Equivalence Scales From Quasi-unit Record Data

This paper uses quasi-unit record data on expenditures and incomes of New Zealand households of different demographic profiles to estimate consumption equivalence scales which measure the relative levels of spending required by households of different composition to attain given levels of utility. The equivalence scales with respect to specific items of consumption, as well as total consumption, have been obtained from the parameters of the preference-consistent Extended Linear Expenditure System and a few alternative versions of a rank 3 complete demand system with demand shifters. Among the demographic variables included in the models, the type of housing tenure and the actual age of children have special relevance. For the sake of comparison, a few heuristic scales are also computed. The results are largely in line with those found in similar studies of Australia and New Zealand. The analysis is developed within the framework of hypothesized utility-maximizing behaviour of households.     

Bird in hand: How experience makes nature

It is almost a truism that nature is social, but by what means is nature made social at the level of the interactional encounter? While the transformation of society/nature relationships is often approached through the problematic of distance, and at the scale of macro-historical transformation, this article uses a conflict between American birdwatchers and ornithologists over scientific “collecting” (literally, the killing of birds) to examine the processes through which individuals come to know nature, and come to know it so differently. With John Dewey’s (1958 [1925]) “experience” as the unit of analysis, I trace changes in each group’s experience with birds over the past century; the phenomenology of the resulting encounters; and the understanding that emerges from each in order to understand (1) how, empirically, these two very different loves of birds are formed, and (2) knowledge of nature as an affective sensibility shaped by experiences of closeness.     

Attachment and adaptive skills in children of international adoption

The attachment pattern of a sample of 168 internationally adopted children was explored in this study using the semi‐structured Friends and Family Interview. The pattern was analysed in relation to the development of adaptive skills as an expression of the children's resilience. The secure attachment pattern rates were slightly lower and the insecure attachment patterns were considerably higher than those of normative samples from the previous studies. The children from Eastern Europe demonstrated a more insecure attachment pattern (odds ratio [OR]= 2.46; confidence interval [CI]= 1.23–3.94), and their scores on the adaptive skills scales were lower than the scores of children from other countries (OR = 2.62; 95% CI = 1.02–6.72). These results help to identify the groups at risk of failing to develop secure attachment patterns and appropriate adaptive skills, and should provide valuable information for designing effective interventions.     

A new rank correlation measure

A new rank correlation measure β _n is proposed, so as to develop a nonparametric test of independence for two variables. β _n is shown to be the symmetrized version of a measure earlier proposed by Borroni and Zenga (Stat Methods Appl 16:289–308, 2007). More specifically, β _n is built so that it can take the opposite sign, without changing its absolute value, when the ranking of one variable is reversed. Further, the meaning of the population equivalent of β _n is discussed. It is pointed out that this latter association measure vanishes not only at independence but, more generally, at indifference, that is when the two variables do not show any “tendency” to positive or negative dependence. The null distribution of β _n needs an independent study: hence, the finite null variance and a table of critical values are determined. Moreover, the asymptotic null distribution of β _n is derived. Finally, the performance of the test based on β _n is evaluated by simulation. β _n is shown to be a good competitor of some classical tests for the same problem.     

Pivotal Quantities Based on Sequential Data: A Bootstrap Approach

A bootstrap algorithm is provided for obtaining a confidence interval for the mean of a probability distribution when sequential data are considered. For this kind of data the empirical distribution can be biased but its bias is bounded by the coefficient of variation of the stopping rule associated with the sequential procedure. When using this distribution for resampling the validity of the bootstrap approach is established by means of a series expansion of the corresponding pivotal quantity. A simulation study is carried out using Wang and Tsiatis type tests and considering the normal and exponential distributions to generate the data. This study confirms that for moderate coefficients of variation of the stopping rule, the bootstrap method allows adequate confidence intervals for the parameters to be obtained, whichever is the distribution of data.     

Large Deviation Results for Wave Governed Random Motions Driven by Semi-Markov Processes

In this article, we present large deviation results for a model {ξ₁ + … + ξ _n : n ≥ 1} which is close to a random walk. More precisely, we consider independent random variables {ξ _n : n ≥ 1} such that {ξ _n : n ≥ 2} are i.i.d. and a different distribution for ξ₁ is allowed. We prove large deviation estimates for P(N _x  ≤ xT) and P(N _x < ∞) as x → ∞, where N _x : = inf {n ≥ 1: ξ₁ + … + ξ _n  ≥ x}. Moreover, we provide an asymptotically efficient simulation law for the estimation of P(N _x  ≤ xT) and P(N _x < ∞) by Monte Carlo simulation based on the importance sampling technique. These results will be adapted to wave governed random motions driven by semi-Markov processes and we present some simulations. Finally, we study the convergence of some large deviation rates for standard wave governed random motions based on a scaling presented in the literature (see Kac, 1974 Kac , M. ( 1974 ). A stochastic model related to the telegrapher's equation . Rocky Mountain Journal of Mathematics 4 : 497 – 509 .[Crossref] , [Google Scholar]; Orsingher, 1990 Orsingher , E. ( 1990 ). Probability law, flow function, maximum distribution of wave governed random motions and their connections with Kirchoff's laws . Stochastic Processes and their Applications 34 ( 1 ): 49 – 66 . [Google Scholar]).     

Agricultural policy modelling under imperfect competition

This study evaluates the role of imperfect competition in determining the agri-food policies impact assessment outcomes. In most impact studies, the supply chain between agricultural production and final consumption is modelled in a perfectly competitive framework. However, there is a growing attention of stakeholders for the presence of imperfectly competitive markets, with the retail sector often being under investigation. This issue is empirically analysed with an application to the dairy industry. First, the degree of market power is estimated using a multi-output demand and price transmission equation system. Then, this model is used for policy simulation with the perfect competition outcome taken as a benchmark to evaluate the impact of imperfect competition. Results show a significant degree of market power in the dairy industry with implications on the projected policy scenarios. Moreover, the imperfect competition model alters the price transmission mechanisms, generating more flexible price trends.     

Assessment of physical workload in boiler operations

The use of boiler wood-fired is fairly common equipment utilized in steam generation for energy production in small industries. The boiler activities are considered dangerous and heavy, mainly due to risks of explosions and the lack of mechanization of the process. This study assessed the burden of physical labor that operators of boilers are subjected during the workday. Assessment of these conditions was carried out through quantitative and qualitative measurements. A heart rate monitor, a wet-bulb globe thermometer (WBGT), a tape-measure and a digital infrared camera were the instruments used to collect the quantitative data. The Nordic Questionnaire and the Painful Areas Diagram were used to relate the health problems of the boiler operator with activity. With study, was concluded that the boiler activity may cause pains in the body of intensity different, muscle fatigue and diseases due to excessive weight and the exposure to heat. The research contributed to improve the boiler operator's workplace and working conditions.     

Contributions of ergonomics to the construction of bus drivers health and excellence in public transport and at work

This article is the product of research that analyzed the work of bus drivers of a public transportation company that is considered a benchmark reference in its field of operations, in which it strives to achieve operating excellence. Within this context, the authors sought to understand how such a company has managed to maintain a policy that is capable of reconciling quality public transport while also providing working conditions compatible with the professional development, comfort and health of its workers. Ergonomic work analysis and activity analysis were the guiding elements used in this study. Initial analyses indicate that the activity of drivers includes serving a population and providing mobility for it, which depends on driving the vehicle itself and on relationships with colleagues, users, pedestrians, drivers and others.