Two theorems concerning recognizable N-subsets of σ1

It is proved that the family of recognizable N-subsets is not closed under the operation sup, and that there exists even a DOL length sequence x₀, x₁, … such that, for any k,x_i ? x_i+1 ? … ? x_i+k holds true for some i and the cardinality of the set {n ∈ N|x_n > x_n+1} is infinite.     

Size-Fractionating Aerosol Generator

An aerosol generator has been developed and evaluated for applications where the aerosol concentration and size distribution need to be tailored to specific needs. In this device, a modified Wright nebulizer generates the primary aerosol whose concentration and, to a limited degree, size distribution are adjusted through selection of the pressure drop and the gas-to-liquid flow rate ratio. Further modification of the size distribution is achieved through virtual and solid-plate impaction so that specific aerosol concentration in specific size ranges can be chosen as the aerosol output.     

Remarks on commutative n-rational series

Commutative N-rational formal power series are considered. Series giving polynomial functions as their coefficients are characterized, and a monotonicity result for commutative series is proved. As an application the division problem for N-rational formal power series is solved.     

A new heart rate variability-based method for the estimation of oxygen consumption without individual laboratory calibration: application example on postal workers

Traditionally, the estimation of oxygen consumption (VO2) at work using heart rate (HR) has required the determination of individual HR/VO2 calibration curves in a separate exercise test in a laboratory (VO2-TRAD). Recently, a new neural network-, and heart rate variability-based method has been developed (Firstbeat PRO heartbeat analysis software) for the estimation of VO2 without individual calibration (VO2-HRV). In the present study, the VO2-values by the VO2-HRV were compared with the values by VO2-TRAD in 22 postal workers. Within individuals the correlation between the two methods was high (range 0.80-0.99). The VO2-TRAD gave higher values of VO2 compared to VO2-HRV (19%) especially during low physical activity work when non-metabolic factors may increase HR. When assessed in different HR categories, the smallest difference (11%), and highest correlations (range 0.83-0.99) in VO2 between the methods were observed at higher HR levels. The results indicate that the VO2-HRV is a potentially useful method to estimate VO2 in the field without laboratory calibration.     

Modelling local bubble size distributions in agitated vessels

Photography and capillary suction probe were used to measure local bubble size distributions (BSDs) from Rushton turbine agitated (14/200 L) air-tap water and CO₂-n-butanol dispersions. A multiblock stirred tank model with population balances (PBs) for bubbles was created to describe local BSDs in agitated vessels. Unknown parameters in breakage and coalescence models were adjusted by comparing the predicted and measured local BSDs. The BSDs from both investigated systems and varying vessel-operating conditions were included simultaneously to the fitting. The adjusted models were incorporated to MUSIG PB model in CFX-5.7 and tested for the laboratory stirred tanks. The multiblock model showed to be an optimal trade-off between the accuracy and CPU time for the investigation of gas-liquid hydrodynamics and validation of closure models. As a result of fitting, the adjusted model seems to describe local BSDs more accurately in agitated vessels than the model of Lehr et al. [2002. Bubble-size distributions and flow fields in bubble columns. A.I.Ch.E. Journal 48, 2426-2443], which has been successful in bubble column studies. This shows that phenomenological breakage and coalescence closures need experimental validation for various flow environments.     

Workload and physical capacity among ageing municipal employees—a 16-year follow-up study

The main purpose of this study was to ascertain musculoskeletal and cardiovascular capacity among ageing employees in relation to workload over a period of 16 years. As the more specific aims were to find out firstly if the physical capacity was different among subjects who had high workload compared with subjects who had low workload and secondly if the changes in physical capacity during the follow-up period were different between subjects with high workload than among subjects with low workload

The data were obtained by physical capacity tests and field measurements (assessments of musculoskeletal and cardiovascular load). The study group consisted of 95 middle-aged subjects who were on average 51.9 years old at the beginning of the follow-up in 1981 and they were all employed. In 1997 they were 67.3 years and 93 of the subjects had retired. The sample represented workers who were employed in municipal occupations in different regions of Finland.

During the 16-year follow-up period age-related decline in physical capacity was observed. In general the subjects with low workload had better physical capacity than the subjects with high workload, especially among women. The improvements in physical capacity were more common than declines among subjects with low physical workload over the follow-up period. Among subjects with high physical workload the situation was mostly vice versa. However, the declines in isometric trunk extension strength and in aerobic capacity were more common among subjects with physically low workload than among subjects with high workload. The differences between high and low workload groups in physical capacity were larger among women than among men. It was concluded that physical workload seems to have more wearing effects than training effects on ageing workers.

Relevance to industry

Physically heavy work may have no training effect on physical capacity among aged workers. The physically heavy work has to be individually adjusted to correspond to a worker's physical capacity, bearing in mind age-related decline of physical capacity, and thereby preventing the overload of the worker.     

Elevated temperature thermal conductivities of some as-cast and austempered cast irons

The aim of this study was to provide insight on thermal conductivity of three cast iron groups, namely lamellar, compacted and spheroidal graphite irons at elevated temperatures up to 673?K (400°C) in as-cast and austempered states. Austempering treatments increased mechanical properties of all the studied materials while decreasing thermal conductivity across the line. The effects of austempering on conductivity were lower for grey and compacted graphite iron than for spheroidal graphite irons. The results indicate that heat treating can be a viable option in increasing cast iron performance in thermally stressed applications. One ferritic low-silicon spheroidal graphite iron surpassed lamellar graphite iron in conductivity at elevated temperatures, while high-silicon spheroidal graphite irons exhibited low conductivities.     

A benchmark study of reduced‐strain shell finite elements: quadratic schemes

We study experimentally the accuracy and reliability of some low‐order shell finite element schemes based on modifying the standard displacement formulation by reduced‐strain expressions. We focus on quadrilateral elements with a quadratic displacement approximation. Three benchmark problems with different asymptotic behaviour in the limit of zero shell thickness is used in the experiments. Following the error analysis of a reduced‐strain scheme, we study two components of the total error, the approximation error and the consistency error. We demonstrate that the performance of the methods is both case and mesh dependent. When a bending dominated problem is solved, none of the methods studied can avoid the usual worst‐case locking effect of the approximation error on general meshes. For a membrane dominated problem the total error is typically dominated by the consistency error which often convergences slowly. Copyright © 2000 John Wiley & Sons, Ltd.