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PubMed2006

The influence of urban design on outdoor thermal comfort in the hot, humid city of Colombo, Sri Lanka.

The outdoor environment is deteriorating in many tropical cities due to rapid urbanization. This leads to a number of problems related to health and well-being of humans and also negatively affects social and commercial outdoor activities. The creation of thermally comfortable microclimates in urban environments is therefore very important. This paper discusses the influence of street-canyon geometry on outdoor thermal comfort in Colombo, Sri Lanka. Five sites with different urban geometry, ground cover, and distance from the sea were studied during the warmest season. The environmental parameters affecting thermal comfort, viz. air temperature, humidity, wind speed, and solar radiation, were measured, and the thermal comfort was estimated by calculating the physiologically equivalent temperature (PET). The thermal comfort is far above the assumed comfort zone due to the combination of intense solar radiation, high temperatures, and low wind speeds, especially on clear days. The worst conditions were found in wide streets with low-rise buildings and no shade trees. The most comfortable conditions were found in narrow streets with tall buildings, especially if shade trees were present, as well as in areas near the coast where the sea breeze had a positive effect. In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc. The opening up of the city's coastal strip would allow the sea breeze to penetrate further into the city.

Cities↗
PubMed1999

Applications of a universal thermal index: physiological equivalent temperature.

The physiological equivalent temperature, PET, is a thermal index derived from the human energy balance. It is well suited to the evaluation of the thermal component of different climates. As well as having a detailed physiological basis, PET is preferable to other thermal indexes like the predicted mean vote because of its unit ( degrees C), which makes results more comprehensible to urban or regional planners, for example, who are not so familiar with modern human-biometeorological terminology. PET results can be presented graphically or as bioclimatic maps. Graphs mostly display the temporal behaviour of PET, whereas spatial distribution is specified in bioclimatic maps. In this article, some applications of PET are discussed. They relate to the evaluation of the urban heat island in cities in both temperate climates and warm climates at high altitude. The thermal component of the microclimate in the trunk space of a deciduous forest is also evaluated by PET. As an example of the spatial distribution of PET, a bioclimatic map for Greece in July (Mediterranean climate) is presented.

Altitude↗
PubMed2003

Glomalin content of forest soils in relation to fire frequency and landscape position.

Low-intensity, dormant season fires were frequent and widespread in oak-hickory ( Quercus-Carya) forests of eastern North America until widespread fire suppression began in the mid-1900s. To assess how reintroduction of fire into such ecosystems might affect the activity of arbuscular mycorrhizal (AM) fungi and, thereby, predict the long-term responses of plants and soils to fire, we analyzed the content of the immunoreactive fractions of the AM-fungus-specific glycoprotein glomalin in soils taken in 1994 and 2000 from three forested watersheds in southern Ohio, USA. One watershed remained unburned, one was burned annually from 1996-1999 and one was burned twice, in 1996 and 1999. In addition, to account for the strong landscape-scale gradients of microclimate and soil that typify these watersheds, we stratified each watershed-scale treatment area into three microclimatic zones (=landscape positions) using a GIS-based integrated moisture index (IMI). In the unburned control, the concentrations of immunoreactive, easily-extractable glomalin (IREEG) and immunoreactive total glomalin (IRTG) did not change significantly over the 6-year interval between sampling times, either overall or within any of the three IMI classes. IRTG content was greatest in the mesic landscape positions and lowest in the relatively xeric landscape positions, but IREEG did not vary among landscape positions. Neither IREEG nor IRTG contents were affected by fire, nor were there significant interactions between fire and landscape position in glomalin content. Both correlation and regression analyses demonstrated significant linkages between soil glomalin content, the density/diversity of herbaceous plants, and soil N availability. Despite significant effects of fires on soil N availability and root growth, we resolved no effect of fire on AM fungal activity at this spatial scale.

Carya↗
PubMed2006

Microenvironmental preferences of oribatid mite species on the floor of a tropical rainforest.

The vertical distribution, microenvironmental preference, canopy cover, as well as monthly fluctuations of recently described species of three genera of macropyline oribatid mites, Mesoplophora, Bicyrthermannia and Nothrus and three genera of brachypyline mites, Scheloribates, Muliercula and Galumnella were investigated over a 9-month period in shaded and unshaded areas of a secondary regrowth forest floor in Ile Ife, Nigeria. Sampling was done monthly from August 2002 to April 2003 covering the two seasons of the annual cycle. There was an overwhelming predominance of mite populations in the 5 cm topsoil compared with the fermentation and litter layers. The preference of M. ifeana and B. nigeriana extracted from the topsoil for the shaded plot was attributed to highly conducive moisture conditions provided by the canopy. It is suggested that M. ifeana, B. nigeriana, N. lasebikani, S. mochlosimilaris, M. inexpectata and G. sonpona, that exhibited a single peak density in the wet season in this study, had similar ecological needs. The populations of M. ifeana and S. mochlosimilaris were relatively stable in the fermentation layer. The study concluded that canopy cover affected the sensitivity of soil dwelling mites on the floor of a secondary regrowth forest with regard to vertical gradients of light, microclimate and foliage quality in a complex way.

Animals↗
PubMed1982

The effect of the environment of human performance.

The performance of man, for a given level of ability, will be affected by his hygro-thermal, electro-ionic, visual and psychological microclimates. This paper presents the results of studies which demonstrate the effect of the hygro-thermal micro-climate on worker performance. The effects of the other micro-climates on worker performance are also discussed. For tasks with mainly physical activity performance depends upon metabolic heat. For tasks with mainly psychological activities there have, until now, been no specified criteria for determining the effects of the environment on performance. Consideration of the results of studies conducted in working environments clearly shows that environmental conditions can effect the efficiency of workers and hence that there are sound economic arguments for optimising working conditions.

Journal Article↗
PubMed1991

Clothing ventilation - update and applications.

The Environmental Ergonomics Unit at the P.O.W. provided a forum for the discussion and consolidation of ideas regarding the origins, current progress and the future development of the Clothing Ventilation Index. Crockford et al (1972) first developed the concept of clothing ventilation. The basic technique employs a trace gas dilution method for measuring the ventilation of the clothing microclimate. Ventilation is vital to the removal of sensible and insensible heat and, therefore, an important determinant of thermal comfort. Two techniques (Lotens and Havenith, 1986, 1988; Reischl et al, 1987) have subsequently been developed. The former method results in an average ventilation value for the total clothed-body surface area, whereas the latter method also takes into consideration regional changes in garment design as separate entities from the total ventilation, allowing for local modification in garment design. The Clothing Ventilation Index is a quantitative, relatively inexpensive, fast, reliable and repeatable technique. It can be used in context, in the working environment to predict the effectiveness, preference and suitability of garments and clothing assemblies; firstly, to ensure that protective clothing is worn and used correctly, and secondly, to improve performance by minimising heat strain, sweat retention and thermal discomfort. Further work on validating the techniques in terms of human responses to the thermal environment is required. Questions were also raised as to whether human beings or manikins should be used. The use of human beings in dynamic situations is of paramount importance; however, manikins could be used for purely physical measurements to test various assumptions in evaluating clothing ventilation. It is essential that body dimensions and posture are always specified. The seminar enabled researchers to identify with the proposed techniques, outline the advantages and importance of the Clothing Ventilation Index and focus future studies.

Journal Article↗
PubMed1993

The effects of season, climate, and air-conditioning on the prevalence of Dermatophagoides mite allergens in household dust.

BACKGROUND: Clinical evidence reveals a strong relationship between dust mite allergen levels and asthma. This study suggests the relative importance and interactions among factors that influence mite allergen levels in human dwellings. METHODS: Dermatophagoides pteronyssinus allergen (Der p I) and D. farinae allergen (Der f I) were measured in 536 dust samples collected from 424 homes across the United States. RESULTS: There were distinct seasonal fluctuations of Der p I and Der f I. Der p I rapidly increased to peak in July then gradually decreased through October. Der f I slowly rose to peak later, around September, before declining. Different climates in regions of the United States had no significant affect on the quantity of Der p I or Der f I. However, regional climate differences seemed to influence the prevalence of either D. pteronyssinus or D. farinae. Air-conditioning significantly reduced (p < 0.001) Der I mite allergens detected in the dust samples, and a tendency existed for Der f I to be higher than Der p I in air-conditioned homes. There was a significant (p < 0.01) interaction between air-conditioning and seasons. The most dramatic affect was observed during the summer months, the cooling season, from approximately May to September. CONCLUSIONS: These findings show that distinct seasonal fluctuations exist of D. pteronyssinus and D. farinae mite populations, and suggest that differences in the microclimate within homes may have a dramatic affect on Dermatophagoides mite populations.

Air Conditioning↗
PubMed1994

Suited crewmember productivity.

Analysis of the extravehicular activity (EVA) sortie experience gained in the former Soviet Union and physiologic hygienic aspect of space suit design and development shows that crewmember productivity is related to the following main factors: -space suit microclimate (gas composition, pressure and temperature); -limitation of motion activity and perception, imposed by the space suit; -good crewmember training in the ground training program; -level of crewmember general physical performance capabilities in connection with mission duration and intervals between sorties; -individual EVA experience (with accumulation) at which workmanship improves, while metabolism, physical and emotional stress decreases; -concrete EVA duration and work rate; -EVA bioengineering, including selection of tools, work station, EVA technology and mechanization.

Astronauts↗
PubMed1991

Factors influencing the performance of temporary skin substitutes.

Advances in our knowledge of the wound healing process has led to the development of various synthetic skin substitutes, which when applied to the wound surface provide a microclimate conducive to healing. The requirements of an ideal temporary skin substitute are presented. This review also provides an updated account of the preclinical evaluation procedures utilized to assess these demands, particularly important parameters such as water vapour permeability, adherence to excised wound surface, oxygen permeability, mechanical properties, microbial permeability and exudate soaking capacity.

Adhesiveness↗
PubMed1989

Yields of field-grown soybeans exposed to simulated acidic deposition.

Rainfall acidity response functions for crop yield and growth are necessary to predict the overall impacts on crop yields of ambient and/or anticipated levels of acidic rain. The experiment described herein was performed at Brookhaven National Laboratory during 1984 and 1985 to determine the effects of simulated rainfalls of pH 5.6, 4.4, 4.1 and 3.3 on seed yields of four cultivars of field-grown soybeans (Glycine max Merrill). Soybeans were chosen because previous results suggested that certain varieties of this crop are sensitive to rainfall acidity and because they are an economically important crop in the USA. Sixteen plots per treatment were used. Plants were grown using standard agronomic practices under automatically movable exclusion shelters which minimize changes in the plant's microclimate. Analysis of variance of seed yields of the four cultivars showed significant treatments for all four cultivars. For all cultivars, seed yields were lower when exposed to simulated rainfalls of pH 4.4, 4.1 and 3.3 compared with rainfalls of pH 5.6. Compared with pH 5.6 rainfall (controls), yields of Amsoy exposed to pH 4.4, 4.1 and 3.3 were lower by 13, 11 and 12%, respectively. The percentage yield reductions for Asgrow, Corsoy and Hobbit were not as great as those of Amsoy. Averaged over all cultivars tested, there was a 9% seed reduction for plants exposed to simulated rain at pH 4.1 (comparable to ambient) compared with pH 5.6.

Journal Article↗
PubMed1990

Epiphyte recolonization of oaks along a gradient of air pollution in South-East England, 1979-1990.

The abundances of epiphytes on free-standing oaks (Quercus robur) along a transect extending approximately 70 km SSW from Central London were redetermined annually from 1979 to 1990. During this period SO(2) levels in inner London fell to between one-quarter and one-seventh of levels occurring in the 1960s. The sample trees were also scored annually using Hawksworth and Rose's (1970) scale for predicting SO(2) levels from the epiphytes present. Little evidence was obtained for epiphyte recolinization of oaks at sites within the built-up area. At Epsom Common, on the urban fringe, cover of the pollution-tolerant lichen Lecanora conizaeoides fell, and in the inner suburbs, at Putney Heath, L. conizaeoides and Lepraria incana increased, while the alga Desmococcus viridis declined at this site. These changes might be due to a contraction inwards of zones of peak abundance of L. conizaeoides and D. viridis with decreasing SO(2) levels. However, it is also possible that the changes at Putney Heath resulted from scrub clearance activities and alteration to the microclimate. The cover of the moderately SO(2) tolerant foliose lichen Hypogymnia physodes remained low and static at Putney Heath during the 12-year period. Possible reasons for the poor recolinization of London's oaks by epiphytes are discussed. Particular emphasis is given to the highly acidic bark of oak in the London area (pH2.9-4.0) in comparison with other tree species and with oaks in unpolluted regions.

Journal Article↗
PubMed1990

Modeling the effects of ozone on soybean growth and yield.

A simple mechanistic model was developed based on an existing growth model in order to address the mechanisms of the effects of ozone on growth and yield of soybean [Glycine max. (L.) Merr. 'Davis'] and interacting effects of other environmental stresses. The model simulates daily growth of soybean plants using environmental data including shortwave radiation, temperature, precipitation, irrigation and ozone concentration. Leaf growth, dry matter accumulation, water budget, nitrogen input and seed growth linked to senescence and abscission of leaves are described in the model. The effects of ozone are modeled as reduced photosynthate production and accelerated senescence. The model was applied to the open-top chamber experiments in which soybean plants were exposed to ozone under two levels of soil moisture regimes. After calibrating the model to the growth data and seed yield, goodness-of-fit of the model was tested. The model fitted well for top dry weight in the vegetative growth phase and also at maturity. The effect of ozone on seen yield was also described satisfactorily by the model. The simulation showed apparent interaction between the effect of ozone and soil moisture stress on the seed yield. The model revealed that further work is needed concerning the effect of ozone on the senescence process and the consequences of alteration of canopy microclimate by the open-top chambers.

Journal Article↗
PubMed1995

Climate change: potential effects of increased atmospheric carbon dioxide (CO2), ozone (O3), and ultraviolet-B (UV-B) radiation on plant diseases.

Continued world population growth results in increased emission of gases from agriculture, combustion of fossil fuels, and industrial processes. This causes changes in the chemical composition of the atmosphere. Evidence is emerging that increased solar ultraviolet-B (UV-B) radiation is reaching the earth's atmosphere, due to stratospheric ozone depletion. Carbon dioxide (CO(2)), ozone (O(3)) and UV-B are individual climate change factors that have direct biological effects on plants. Such effects may directly or indirectly affect the incidence and severity of plant diseases, caused by biotic agents. Carbon dioxide may increase plant canopy size and density, resulting in a greater biomass of high nutritional quality, combined with a much higher microclimate relative humidity. This would be likely to promote plant diseases such as rusts, powdery mildews, leaf spots and blights. Inoculum potential from greater overwintering crop debris would also be increased. Ozone is likely to have adverse effects on plant growth. Necrotrophic pathogens may colonize plants weakened by O(3) at an accelerated rate, while obligate biotroph infections may be lessened. Ozone is unlikely to have direct adverse effects on fungal pathogens. Ozone effects on plant diseases are host plant mediated. The principal effects of increased UV-B on plant diseases would be via alterations in host plants. Increased flavonoids could lead to increased diseased resistance. Reduced net photosynthesis and premature ripening and senescence could result in a decrease in diseases caused by biotrophs and an increase in those caused by necrotrophs. Microbial plant pathogens are less likely to be adversely affected by CO(2), O(3) and UV-B than are their corresponding host plants. Changes in host plants may result in expectable alterations of disease incidence, depending on host plant growth stages and type of pathogen. Given the importance of plant diseases in world food and fiber production, it is essential to begin studying the effects of increased CO(2), O(3) and UV-B (and other climate change factors) on plant diseases. We know very little about the actual impacts of climate change factors on disease epidemiology. Epidemiologists should be encouraged to consider CO(2), O(3) and UV-B as factors in their field studies.

Journal Article↗
PubMed1988

Fermentation of polysaccharides and absorption of short chain fatty acids in the mammalian hindgut.

1. Hindgut volume varies considerably between carnivores, omnivores and herbivores. But a common feature in all mammals is an extensive microbial fermentation of polysaccharides in the hindgut. Large amounts of short chain fatty acids (SCFA) are produced. Total concentrations of SCFA are generally ca 100 mmol/l. SCFA metabolism contributes considerably to the energy metabolism of the animal. 2. In hindgut fermenting herbivores ileal outflow provides fluid and the buffering capacity essential for microbial metabolism. 3. SCFA are rapidly absorbed. Absorption is passive and, unexpectedly, nearly independent from luminal pH. This is attributed to the presence of a constant pH-microclimate at the epithelial surface. 4. The permeability of the proximal compared to the distal colon of guinea pig is higher for acetate, equal for propionate and lower for butyrate. This difference is due to partial absorption of SCFA in the dissociated form in the proximal segment. 5. Protons required for SCFA transport in the undissociated form may be partially explained by HCO3 accumulation or by Na-H exchange. Findings are controversial.

Animals↗
PubMed1988

Concentration- and pH-dependence of short-chain fatty acid absorption in the proximal and distal colon of guinea pig (Cavia porcellus).

1. Absorption of short-chain fatty acids (SCFA), acetate, propionate, and butyrate was studied in simultaneously perfused proximal and distal segments of the colon in anaesthetized guinea pigs. 2. Acetate absorption rates increased linearly with concentration in both segments, indicating passive transport. 3. SCFA-clearance was independent of bulk luminal pH between pH 6.2 and 8.1 in the proximal and distal colon. SCFA-clearance was slightly higher in both segments at pH values less than 6. 4. The unexpected pH-independence of SCFA-absorption is attributed to the existence of a constant pH-microclimate at the surface of the colonic epithelium. 5. Relative permeabilities to acetate:propionate:butyrate were estimated as 1:1.19 +/- 0.03:1.27 +/- 0.05 in the proximal colon and 1:2.31 +/- 0.39:3.50 +/- 0.61 in the distal colon. The significance of these findings with respect to the pH-partition hypothesis are discussed.

Acetates↗
PubMed1993

Epidemiology of Ostertagia in the Northwestern USA.

The two most significant environmental factors that influence the epidemiology of Ostertagia are temperature and moisture. These factors vary more in the west and northwest than in any other part of the USA because of extreme regional differences in climate, topography, and land use. Consequently, patterns of Ostertagia transmission and inhibition also vary widely from region to region and from year to year. Recent data require revisions of previously accepted concepts of northern/southern transmission and inhibition. In particular, the flaw of liberal extrapolation of information from one region to another has now been recognized. Inhibition may not occur along the coast of the Pacific Northwest. Although not completely delineated, the transition zone between northern and southern patterns of inhibition appears to be significantly wider and more variable than previously recognized; Oregon data suggest a possible indeterminate and variable band extending north of the 45th parallel and south of the 43rd parallel. Summer inhibition has now been documented in areas of Oregon and Montana. Other than the recent Oregon and Montana studies, data on this transition zone in the Rocky Mountain region and high plains are sparse to non-existent. In contrast to previously accepted doctrine, the fall rise in egg count generally exceeds the traditionally accepted spring rise in many areas. From the Pacific Northwest to the Midwest, year-round transmission patterns have been observed. The presence of geothermal ground water sources produces microclimates that favor larval survival in many areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The ecology of Haemonchus contortus in a winter rainfall climate in Australia: the survival of infective larvae on pasture.

At sites near Albany, on the south coast of Western Australia, sheep faecal pellets containing either eggs or infective larvae (L3) of Haemonchus contortus were deposited onto natural pasture plots at intervals over 3 years. Faecal and pasture samples were collected periodically and processed to detect L3. On annual pasture plots, L3 were recovered for from 10 to over 20 weeks from depositions made between autumn and early spring, at which time temperatures were mild or low, rainfall was frequent and the pasture was visibly green. During the hot and dry summer, when the pasture was completely dry, L3 often failed to develop or were recovered on only a single occasion, and the mean larval survival period on positive plots was less than 5 weeks. In contrast, L3 deposited on green perennial pasture plots in summer were recovered for up to 4 months in faecal pellets and on pasture. The longest periods of larval survival were associated with the lowest temperature and highest rainfall recordings, and with the greatest quantity of green plant material in the pasture. It is suggested that the poor survival of L3 during the dry summer period could be used in a strategic treatment programme to interrupt the transmission cycle of H. contortus in winter rainfall climates. However, areas of green pasture which persist in summer may provide a sufficiently moist microclimate to permit the survival of H. contortus L3 despite otherwise unfavourable environmental conditions.

Animals↗
PubMed1983

Multiple sclerosis: plaques caused by 2-step demyelination?

Selected studies concerning events at the contour of a progressive plaque are reviewed and an explanation of the subtle changes in periplaque white matter which various investigators have observed on autopsy or biopsy is presented. Recurrent exposure to toxic small molecular weight substances carried by arterial blood and capable of diffusing through the walls of blood vessels cause modification of protein or glycoprotein in the myelin sheath. These then act as allergens (modified native tissue considered as 'nonself' tissue by the immune system) which induce antibody formation (termed allo-auto-allergy). Phagocytosis of altered myelin, debris removal and cellular action to maintain homeostasis in the fluid surrounding neurons characterize the premorbid phase of multiple sclerosis. We suggest that the accumulation in the perivascular space of macrophages with large lysosomes digesting myelin debris (visible in electron micrographs) causes bottlenecks in the lymphatic channels serving the extracellular space near nodes of Ranvier. This changes the chemical microclimate and leads to the second step of demyelination and degeneration of the oligodendrocytes, i.e. plaque formation. Reference is made to outstanding problems. Research into the diffusion of small molecular weight substances into the extracellular spaces of white matter would aid in evaluating the hypothesis.

Astrocytes↗