Test sets and checking words for homomorphism equivalence

Given a language L over an alphabet Σ and two homomorphisms g and h, defined on $\text{Σ}{}^1$, we want to decide whether or not g and h are equivalent on L, i.e., whether or not g(w) = h(w) holds for all words w in L. We prove the following results' for the case where Σ consists of two letters. Every language L possesses a finite subset L, such that, for any pair (g, h), g and h are equivalent on L if and only if they are equivalent on L₁. For every language L (with the exception of some trivial cases), there is a word w (not necessarily in L) such that, for any pair (g, h), g and h are equivalent on L if and only if g(w) = h(w). Our constructions are, in general, noneffective. Also some related notions are discussed in the paper.     

Multi-criteria evaluation of residential energy supply systems

In this paper, we consider the selection of a residential energy supply system as a multi-criteria decision-making problem, which involves both financial and environmental issues. Specifically, we compare micro-CHP (micro-cogeneration) heating with traditional heating systems through an evaluation that accounts for: (i) the decision-makers’ subjective preferences, (ii) uncertainties in the performance of micro-CHP heating systems (which are partly caused by the lack of long-term operational experiences) and (iii) the context-dependency of life-cycle costs and environmental burdens of heating systems. Motivated by these considerations, we employ the PAIRS multi-criteria decision-making methodology that captures incomplete information by way of interval-valued parameters and provides support for sensitivity analyses, too. Our comparative analysis of alternative heating systems suggests that micro-CHP is a reasonable alternative to traditional systems, particularly from the environmental point of view.     

Estimating the environmental burdens of residential energy supply systems through material input and emission factors

This paper introduces a method and application for the assessment of environmental burdens due to the construction and operation of a residential energy supply system. The methodology encompasses energy and environmental impact analyses with sensitivity analysis. Here, natural resource consumption is assessed through material input factors. Global warming and acidification potentials are estimated by way of CO₂− and SO₂− equivalents. A simple optimization scheme is established to capture uncertainties related to preferential treatment between natural resource categories. A computational study on the energy supply of a group of low-energy single-family houses in Finland is presented. Specifically, the potential of micro-cogeneration is evaluated with respect to traditional options based on grid electricity, district heat and natural gas. The energy analysis suggests that the operation of a heating system causes a major part of environmental burdens and that no more than 1000 W on-site generated electrical power per one household would result in minimum thermal losses and thus environmental burdens. On the basis of environmental impact analysis, the use of state-of-the-art micro-cogeneration may decrease the annual use of abiotic resources and water to some extent, but for practical applications, further improvement of system efficiency is still required.     

Physical, chemical and microbiological water characteristics associated with the occurrence of Legionella in cooling tower systems

The occurrence of Legionella in water of 30 cooling tower systems was studied, as well as the relationship of its occurrence with the physical, chemical and microbiological characteristics of the waters. The samples were concentrated by membrane filtration and one part of the concentrate was acid washed. Three types of culture media, MWY, CCVC and BCYEα were used. Fourteen (47%) of the cooling systems were Legionella-positive. Numbers of Legionella in the positive systems varied between 50 and 490,000 cfu/l. Legionella pneumophila was the dominant isolate, and the serogroups 6 and 1 were the commonest ones. There was no statistically significant difference in mean water temperature between the Legionella-positive (27°C) and -negative (24°C) systems. The total number of bacteria (AODC) was lower in the Legionella-positive than in the negative systems. Also the nutrient concentrations were generally lower in the Legionella-positive cooling systems. The results suggest that different factors regulate the occurrence of Legionella than that of overall bacterial populations in the cooling tower systems.     

Muscle activity patterns and spinal shrinkage in office workers using a sit–stand workstation versus a sit workstation

Reducing sitting time by means of sit–stand workstations is an emerging trend, but further evidence is needed regarding their health benefits. This cross-sectional study compared work time muscle activity patterns and spinal shrinkage between office workers (aged 24–62, 58.3% female) who used either a sit–stand workstation (Sit–Stand group, n = 10) or a traditional sit workstation (Sit group, n = 14) for at least the past three months. During one typical workday, muscle inactivity and activity from quadriceps and hamstrings were monitored using electromyography shorts, and spinal shrinkage was measured using stadiometry before and after the workday. Compared with the Sit group, the Sit–Stand group had less muscle inactivity time (66.2 ± 17.1% vs. 80.9 ± 6.4%, p = 0.014) and more light muscle activity time (26.1 ± 12.3% vs. 14.9 ± 6.3%, p = 0.019) with no significant difference in spinal shrinkage (5.62 ± 2.75 mm vs. 6.11 ± 2.44 mm). This study provides evidence that working with sit–stand workstations can promote more light muscle activity time and less inactivity without negative effects on spinal shrinkage.

Practitioner Summary: This cross-sectional study compared the effects of using a sit–stand workstation to a sit workstation on muscle activity patterns and spinal shrinkage in office workers. It provides evidence that working with a sit–stand workstation can promote more light muscle activity time and less inactivity without negative effects on spinal shrinkage.     

Sampling and dilution of nanoparticles at high temperature

Sampling and dilution of flame-generated, fractal-like ZrO₂ aerosols is investigated by aerosol mass/mobility measurements and microscopy. Two broadly used sampler configurations, a straight-tube (ST) and a hole-in-a-tube (HiaT), at three different in-flow orientations and hole diameters are evaluated. The mobility size distributions, mass-mobility exponent, D_fm, prefactor, k_fm, and average primary particle diameter are obtained at 10–60 cm height above the burner (HAB) of fuel-rich (hot) and fuel-lean (cold) spray flames by differential mobility analyzer (DMA) and aerosol particle mass (APM) measurements using a recent power law for fractal-like particles. The primary particle diameter, agglomerate size distributions, and corresponding standard deviations from aerosol measurements are compared to those by counting images of particles collected by thermophoretic sampling along the flame centerline. Once new particle formation is completed in the flame, both sampler configurations result in nearly identical particle size distributions. Furthermore, all HiaT samplers result in similar mobility size distributions at all orientations, regardless of hole size. Sampling using a downstream in-flow hole orientation results in slightly larger Sauter mean diameters than those obtained by upstream or sidestream ones, especially for the cold flame. Additionally, a correlation is developed by Discrete Element Modeling (DEM) for the agglomerate D_fm evolution to its asymptotic value of 2.2 as function of the average number of primary particles per agglomerate, n_va, or the relative particle density with pre-exponential constant k_fm = 1.18, regardless of primary particle size. This is in good agreement with an experimentally obtained correlation in terms of relative particle density as well as with experimental data for ZrO₂, Ag, and Cu nanoparticles.

© 2016 American Association for Aerosol Research     

Preparation of barium hexaferrite coatings using atmospheric plasma spraying

Thick coatings of barium hexaferrite with the compositions BaFe₁₂O₁₉ and BaCoTiFe₁₀O₁₉ were prepared using atmospheric plasma spraying (APS) technology. The coatings were prepared from pre-reacted powders of the desired composition. The as-deposited coatings were poorly crystallized, but their crystallinity was improved with a subsequent annealing. The crystallization mechanism of the sprayed hexaferrites was studied during annealing up to 1300 °C, using X-ray powder diffraction combined with thermal analysis and with electron microscopy including microanalysis. Single-phase coatings were obtained after annealing treatments at 1100–1300 °C. Their magnetic properties showed that they would be suitable for absorbers at microwave and mm-wave frequencies, depending on the coating phase's composition, the crystallinity and the thicknesses.     

Emissions from large-scale medium-speed diesel engines: 1. Influence of engine operation mode and turbocharger

The operation of four – stroke diesel engines in either propulsion or generator mode application has a strong influence on gaseous, smoke (soot) and particulates emissions. Tests were made with a supercharged after-cooled large-scale diesel engine (mean speed  500 rpm, power per cylinder  1 MW) burning mainly heavy fuel oil. Gaseous emissions (NOx, CO, HC) were measured according to the IMO technical code, smoke (soot) emissions were determined optically and particulate matter (PM) was measured using a gravimetric impactor for five size fractions. Impact on gaseous emissions, smoke (soot) and PM was found when analysing the effects of the engine operating mode, fuel nozzle, start of injection (SOI), and load (speed). Results show that the exhaust emission was also highly dependent on the engine turbocharger system, especially the by-pass control, but was not affected by waste gate control. The gaseous and soot emissions were less for the generator mode in the total load region, decreasing with the load. PM emissions were found to decrease with the load for the propulsion mode, while showing an increase with the load for the generator mode.