Comparing maximal mean values on different scales

When computing the average speed of a car over different time periods from given GPS data, it is conventional wisdom that the maximal average speed over all time intervals of fixed length decreases if the interval length increases. However, this intuition is wrong. We investigate this phenomenon and make rigorous in which sense this intuition is still true

Non-innocent side-chains with dipole moments in organic solar cells improve charge separation

Providing sustainable energy is one of the biggest challenges nowadays. An attractive answer is the use of organic solar cells to capture solar energy. Recently a promising route to increase their efficiency has been suggested: developing new organic materials with a high dielectric constant. This solution focuses on lowering the coulomb attraction between electrons and holes, thereby increasing the yield of free charges. In here, we demonstrate from a theoretical point of view that incorporation of dipole moments in organic materials indeed lowers the coulomb attraction. A combination of molecular dynamics simulations for modelling the blend and ab initio quantum chemical calculations to study specific regions was performed. This approach gives predictive insight in the suitability of new materials for application in organic solar cells. In addition to all requirements that make conjugated polymers suitable for application in organic solar cells, this study demonstrates the importance of large dipole moments in polymer side-chains

Thermal conditions measurement

Thermal conditions measuremen

Temperature regulation, heat balance and climatic stress

This paper discusses human thermoregulation and how this relates to health problems during exposure to climatic stress. The heat exchange of the body with the environment is described in terms of the heat balance equation which determines whether the body heats up, remains at stable temperature, or cools. Inside the body the thermoregulatory control aims at creating the right conditions of heat loss to keep the body temperature stable. In the heat the main effector mechanism for this is sweating. The heat balance is affected by air temperature, radiant temperature, humidity and wind speed as climatic parameters and by activity rate, clothing insulation and sweat capacity as personal parameters. Heat tolerance is discussed in the light of personal characteristics (age, gender, fitness, acclimatisation, morphology and fat) indicating age and fitness as most important predictors. Heat related mortality and morbidity are strongly linked to age

Metabolic rate and clothing insulation data of children and adolescents during various school activities

Data on metabolic rates (n=81) and clothing insulation (n=96) of school children and adolescents (A, primary school: age 9-10; B, primary school: age 10-11 year; C, junior vocational (technical) education: age 13-16 (lower level); D, same as C but at advanced level; and E, senior vocational (technical) education, advanced level: age 16-18) were collected (Diaferometer, Oxylog, Heart Rate derivation) during theory-, practical- and physical education- lessons. Clothing insulation was calculated from clothing weight, covered body surface area, and the number of clothing layers worn. Clothing insulation was found to be similar to that expected for adults in the same (winter) season, with minimal variation with age or school type (0.9 to 1.0 clo; 1.38 clo where coverall was worn), but more variation within groups (coefficient of variation 6-12%). Metabolic rate values (W.m-2) were lower than expected from adult data for similar activities, but are supported by other child data. The results of this study can be used to establish design criteria for school climate control systems or as general data on energy expenditure for children and adolescents. The results emphasise the need for specific child data and shows the limited value of size-corrected adult data for use in children

Laboratory assessment of cold weather clothing

An overview of laboratory tests for cold weather clothing is provided starting from physical measurements on fabrics, and physical measurements on whole garments using thermal manikins. This is extended to human wear trials and climatic chamber experimentation. Insulation and vapour resistance are considered the most relevant parameters followed by wind and water proofness and moisture absorption properties. The use of test participants in wear trials is considered regarding the information provided by such tests. Tests for innovative fabrics (heated, variable insulation, phase change materials) are discussed. Finally testing of sleeping bags is considered

Moisture accumulation in sleeping bags at subzero temperatures - effect of semipermeable and impermeable covers

Because subzero temperatures are expected to affect the vapor resistance of micro porous membranes, the effect of using semipermeable and impermeable rain covers for sleeping bags on moisture accumulation in the bags during 6 days of use at -7°C is investigated. Moisture accumulation is related to the vapor resistance of the materials. The best semipermeable material gives the same moisture build-up as no cover. Semiperme able cover materials are effective at reducing moisture accumulation in sleeping bags at moderate subzero temperatures

Clothing heat exchange models for research and application

The regulated exchange of heat from the human body to the environment is essential in human survival. This exchange is adjusted by our physiological response mechanisms. We are able to sweat profusely to cool the body in exercise and heat exposure, and are able to fine-tune our body temperatures in moderate environments through variations in skin circulation. In slightly cool environments, we reduce blood flow to our extremities and skin and use our fat layer insulation to conserve central body temperature. We can increase our heat production by shivering and can create a small insulating air layer around our skin by pilo-erection. However, when temperature goes down further, we cannot sustain our body temperature in the long run without behavioural adjustments that include putting on clothing or using heated dwellings. In this context, clothing has allowed mankind to expand its habitat around the world and has had a positive influence on its development. Today, clothing is worn for various reasons. Apart from its functional aspects (insulation, protection), it has a strong cultural and social aspect as well. The latter are on occasion counterproductive in terms of the first. A business suit for instance is hardly functional in a tropical climate, nor is a ladies evening dress in a cold environment. Also, when the function of the clothing is not only protection against heat or cold, as e.g. is the case with chemical protective clothing, the barriers introduced in the clothing to achieve the required protection can cause a conflict between the protective function of the clothing and the thermal functioning of the body. These conflicts can lead to discomfort, but also to physical strain and in extreme cases can put the person at risk from heat or cold injury or illness

Temperature regulation and technology

The ability to thermoregulate typically decreases with age. This is strongly related to decreases in physical fitness and increases in the incidence of disabilities with ageing. The reduced thermoregulatory capacity leads to increased mortality and morbidity. Heat stroke, hypothermia, increased number of falls, and in home drowning are some of the problems that are identified to be associated with this reduced thermoregulatory capacity. As solution, using advanced technology in terms of full climate control is suggested as a short-term solution for the ill or infirm only. For longer-term solutions, limited climate control (taking away peak loads), improved housing design and proper use of modern clothing are proposed to alleviate the problems. For the clothing, better education of the elderly in the possible advantages of high tech clothing materials is proposed, as well as education to their proper way of use. Manufacturers should consider adjusting their marketing policies to include the elderly in their targeted groups