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At least 1,693 records · Page 94Linked to original sources
PubMed2002

Natural causes of the tundra-taiga boundary.

The tundra-taiga interface is characterized by a change in tree cover or density, tree size and shape, tree growth, and reproduction. Generally, trees get denser, taller, and less damaged as one moves from the tundra into the taiga proper. The environmental covariates and possible mechanisms resulting in these patterns are addressed in the paper. Low seed rain density, lack of safe sites caused by microclimatic variation, low surface substrate moisture, and low soil nutrient availability may limit the density of the tree species. Tree growth may be limited by a short growing season and further diminished, by shoot and root damage reducing carbon and nutrient stores as well as by reducing carbon and nutrient uptake capacities. Positive and negative feedbacks of tree density on tree growth exist at treeline. Increased tree density leads to increased air temperature and decreased wind damage, but also to lower soil temperature, reduced nutrient availability, and greater nutrient competition.

Arctic Regions↗
PubMed2002

How can the dynamics of the tundra-taiga boundary be remotely monitored?

This paper discusses some of the difficulties in establishing the location of the Arctic treeline and forest line on a circumpolar basis, and the contribution that remote sensing, particularly from spaceborne platforms, can make in resolving them. Spaceborne techniques can provide spatial resolutions as fine as a few meters, although the requirements for regional or global coverage are likely to limit the resolution to 30 to 100 m. Since this will preclude the identification of individual trees, the definition of the treeline will be based on statistical parameters estimated from satellite images. The optimum criteria for these parameters remain to be determined. Most remote-sensing observations that are suited to the measurement of the distribution of vegetation, and identification of its type, are based on the visible and near-infrared (VIR) parts of the electromagnetic spectrum, although there is increasing interest in the use of active microwave (radar) techniques. We discuss the basis of both types of approach and the techniques that follow from them, and present 3 case studies from the Russian Arctic.

Arctic Regions↗
PubMedDate not supplied

Alaska outreach.

Bringing dental hygiene and dental education to a remote section of far northern Alaska provides both challenges and rewards.

Alaska↗
PubMed2002

[Gastroduodenal ulcer hemorrhage under conditions of Extreme North (Yakut)].

Under analysis there were results of treatment of 431 patients with duodenal ulcer bleedings. The authors note that the duodenal ulcer bleedings under conditions of Extreme North (Yakutia) are observed more often in those who come (not in residents). Among specific features of the clinical course of the ulcer disease the authors note a short case history, continuous and severe exacerbation, short remission, frequent development of complications. The authors use in their work active individualized surgical methods and make organ-saving operations aimed at saving the patient's life.

Adult↗
PubMed1970

Multiplication of certain soil micro-organisms under simulated Martian conditions.

According to earlier observations, severe UV irradiation kills all micro-organisms in a chamber with simulated Martian conditions. However, even a thin soil layer protects buried micro-organisms from UV irradiation. The chief limiting factor for microbial multiplication under simulated Martian conditions seems to be soil humidity. Several micro-organisms were isolated from harsh environments (e.g., from Arctic, Antarctic desert and high-mountain soil samples). A strain of an oligonitrophilic mycococcus, isolated from Dixon Island, proved to be most resistant to low humidity. It multiplied in a mixture of limonite (maximal hygroscopical humidity 3.8%) + 2% (w/w) garden soil kept in a chamber simulating Martian conditions. Total cell count increased 7.6-fold and, in some experiments, 26-fold in 14 days. The oligonitrophilic mycococcus was able to grow even at a humidity level of 2.5%, that is less than maximal hygroscopical (3.8%). Under these conditions cell count increased 10-fold in 36 days. Thus, it was shown that even in Earth soils there are xerophytic micro-organisms which are able to multiply in limonite of low humidity. These data might correct our current concepts concerning microbial water requirements. One might speculate that Martian micro-organisms belong to xerophytic species.

Actinomycetales↗
PubMed2003

[Study on sperm quality of males living in cold area].

OBJECTIVE: To investigate the effects on male reproductive function working under cold area. METHODS: After on site investigation, advanced molecular lab analysis-single-cell gel electrophoresis (SCGE) and sperm chromatin structure assay (SCSA) which are combined with semen routine analysis were used to evaluate semen quality and sperm sub-clinical injury. RESULTS: Semen routine analysis showed that the semen parameters of the males working in cold area were within normal range, but level I comet cell percentage in SCGE increased significantly, which was 4.4%, compared to the contrast group (1.9%) with significant difference. During sperm chromatin structure assay parameters, comp alpha t increased, with an average value of 22.26%. The two kinds of results both showed single and double strand breakages in sperm. CONCLUSION: Long-term exposure to cold could induce sperm DNA injury, but not affect sperm quality. The results suggested that it was important to reinforce the reproductive care in males working in cold areas.

Adult↗
PubMed1992

Accidents in the Arctic. A psychological point of view.

The aim of this paper is to discuss the influence of arctic conditions on the occurrence of accidents especially from the point of view of the interaction between environment, activity and man. Special attention is paid to risk assessment, risk taking and risk compensation. According to the danger factor theory frostbites should be extremely common in arctic regions, but in reality serious frostbites appear rarely in accident statistics. This finding supports the interactive accident theories. Instead cold can be a contributing factor in accident and injury causation and the effect of cold is most often indirect. Frostbites can occur e.g. as a result of an accident, losing one's way because of darkness, snow storm etc., wet clothes, unexpected temperature changes, disease attack, alcohol-induced reasons such as immobility or excess risk taking etc. Temperatures below and above +20 degrees C increase unsafe behavior. In the Arctic it is impossible to remove all the potentially dangerous factors, because many typical features of working and living conditions are regulated by natural forces, the seasons etc. This makes accurate risk assessment and prediction especially important in accident prevention. If the person does not recognize the situations in which the risk factors exist, he/she cannot implement precautionary steps at the right moment and hence cannot avoid risks. Moreover, if better and safer machines, equipment and tools get people to take greater risks, the accident situation can even become worse.

Accident Prevention↗
PubMed1992

Ergonomic design of machinery for use in the cold. A review based on the literature and original research.

The main purpose of this paper is to identify some important problems associated with ergonomics of the human-machine-task-environment system under cold conditions. Practical examples of stress, strain and accident risks based on the literature and original research are given, and needs and possibilities for improving the ergonomic design of machinery are described. The awareness of designers to the demands set by cold conditions should be increased. Both the need for better operability and the need for better maintainability of machinery in the cold argue for the development of a new, systematic engineering design methodology.

Accidents, Occupational↗
PubMed1992

Work in the cold--an information and research program in occupational health.

Hundreds of thousands of employees work in the cold. The problems concerning cold are, to a great extent, well known. There are also good suggestions about how to deal with these problems. This project deals with: Cold stress, as an important risk factor for medical illness; the problems concerning clothing and equipment; how to change the snowmobile into a modern low risk piece of equipment: international standardization usable in the field; different approaches for information to reach and be used by the workers and their chiefs.

Cold Climate↗
PubMed1992

Protective clothing against cold--performance standards as method for preventive measures.

Survival, function and comfort in the cold are dependent on a rational and cautious use of protective measures to reduce and control heat losses. International standards are now available for establishing a basis for the rational assessment of protection requirements and the subsequent selection of appropriate clothing. Protection requirements may be readily calculated by the IREQ-index (ISO/TR-11079), which specifies required resultant clothing insulation for given conditions. Performance of selected clothing ensemble can be tested by measuring the insulation value on a moveable, thermal manikin according to prEN-342. Similarly, performance of protective gloves against cold may be tested with a heated hand model (prEN-511). It is important to emphasize that the outlined procedure should only be applied as a guide-line for action. Due to considerable individual variation in capacities, preference and demand, room must be available for behavioral adjustments, as well as clothing must be flexible enough to accommodate these adjustments.

Cold Climate↗
PubMed1992

Fat metabolism, exercise, and the cold.

Whereas short-term cold exposure depletes glycogen reserves, repeated and prolonged moderate exercise in a cold environment creates an energy deficit that is satisfied by an increased metabolism of depot fat. Factors contributing to the fat loss include an exercise-induced hypertrophy of lean tissue, a loss of energy through a cold-induced ketonuria, a stimulation of resting metabolism, increases in the energy cost of movement, and a lower yield of energy per litre of oxygen consumed. Biochemical explanations of the enhanced lipolysis include increased catecholamine secretion, altered sensitivity of catecholamine receptors, and decreases of circulating insulin. The enhanced fat loss with combinations of cold and exercise may be helpful in the therapy of obesity, although the response seems less well developed in women than in men. Moreover, there may be other objections to cold exposure in an older obese population. Short-term glycogen depletion has negative implications for the endurance competitor. Cold acclimation, by favoring an insulative response to cold, reduces glycogen depletion; endurance training may supplement this effect by enhancing the activity of fat-metabolizing enzymes.

Acclimatization↗