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At least 703 records · Page 39Linked to original sources
PubMed1964

FLUID INTAKE PATTERNS OF 6-YEAR-OLD CHILDREN IN A NORTHERN FLUORIDATED COMMUNITY.

The quantity of various fluids ingested in winter by 160 six-year-old children living in a northern climate (54 degrees N.) was surveyed as part of a study to determine whether the amount of dental decay was related to the amount of fluoridated water ingested. Only milk, water and fruit juices were found to be important sources of dietary fluid. Total fluids ingested ranged from 11.7 to 91.0 oz. per day, whereas milk intake varied from 3.1 to 52.0 oz. and water intake from 0 to 29.0 oz. per day. Twenty-four children did not drink water as such. The results, when compared with previous reports, indicate that a greater quantitative and qualitative variation in ingested fluids may occur in cool climates, possibly owing to the absence of a constant fluid demand imposed by evaporation for body cooling. Further elucidation of these differences could influence the vehicle and dosage of nutritional supplements to dietary fluids.

Animals↗
PubMed2003

C4 photosynthesis at low temperature. A study using transgenic plants with reduced amounts of Rubisco.

C(4) plants are rare in the cool climates characteristic of high latitudes and elevations, but the reasons for this are unclear. We tested the hypothesis that CO(2) fixation by Rubisco is the rate-limiting step during C(4) photosynthesis at cool temperatures. We measured photosynthesis and chlorophyll fluorescence from 6 degrees C to 40 degrees C, and in vitro Rubisco and phosphoenolpyruvate carboxylase activity from 0 degrees C to 42 degrees C, in Flaveria bidentis modified by an antisense construct (targeted to the nuclear-encoded small subunit of Rubisco, anti-RbcS) to have 49% and 32% of the wild-type Rubisco content. Photosynthesis was reduced at all temperatures in the anti-Rbcs plants, but the thermal optimum for photosynthesis (35 degrees C) did not differ. The in vitro turnover rate (kcat) of fully carbamylated Rubisco was 3.8 mol mol(-)(1) s(-)(1) at 24 degrees C, regardless of genotype. The in vitro kcat (Rubisco Vcmax per catalytic site) and in vivo kcat (gross photosynthesis per Rubisco catalytic site) were the same below 20 degrees C, but at warmer temperatures, the in vitro capacity of the enzyme exceeded the realized rate of photosynthesis. The quantum requirement of CO(2) assimilation increased below 25 degrees C in all genotypes, suggesting greater leakage of CO(2) from the bundle sheath. The Rubisco flux control coefficient was 0.68 at the thermal optimum and increased to 0.99 at 6 degrees C. Our results thus demonstrate that Rubisco capacity is a principle control over the rate of C(4) photosynthesis at low temperatures. On the basis of these results, we propose that the lack of C(4) success in cool climates reflects a constraint imposed by having less Rubisco than their C(3) competitors.

Carbon Dioxide↗
PubMed2005

Centennial-scale climate cooling with a sudden cold event around 8,200 years ago.

The extent of climate variability during the current interglacial period, the Holocene, is still debated. Temperature records derived from central Greenland ice cores show one significant temperature anomaly between 8,200 and 8,100 years ago, which is often attributed to a meltwater outflow into the North Atlantic Ocean and a slowdown of North Atlantic Deep Water formation--this anomaly provides an opportunity to study such processes with relevance to present-day freshening of the North Atlantic. Anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in Greenland. But the anomalies in many of these records span 400 to 600 years, start from about 8,600 years ago and form part of a repeating pattern within the Holocene. More sudden climate changes around 8,200 years ago appear superimposed on this longer-term cooling. The compounded nature of the signals implies that far-field climate anomalies around 8,200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of North Atlantic Deep Water formation, and the geographical extent of the rapid cooling event 8,200 years ago remains to be determined.

Journal Article↗
PubMed2000

The state and future of Mars polar science and exploration.

As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of approximately 10(6) km2 and total as much as 3-4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young--preserving a record of the seasonal and climatic cycling of atmospheric CO2, H2O, and dust over the past approximately 10(5)-10(8) years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet--documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason--providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding.

Atmosphere↗
PubMed2005

Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean.

The ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth. At present, this depth is approximately 4,500 m, with some variation between and within ocean basins. The calcite compensation depth is linked to ocean acidity, which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate. Geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the Eocene/Oligocene boundary (approximately 34 million years ago) when significant permanent ice sheets first appeared on Antarctica, but the relationship between these two events is poorly understood. Here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical Pacific Ocean that cover the Eocene/Oligocene boundary. We find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40,000 years each, synchronous with the stepwise onset of Antarctic ice-sheet growth. The glaciation was initiated, after climatic preconditioning, by an interval when the Earth's orbit of the Sun favoured cool summers. The changes in oxygen-isotope composition across the Eocene/Oligocene boundary are too large to be explained by Antarctic ice-sheet growth alone and must therefore also indicate contemporaneous global cooling and/or Northern Hemisphere glaciation.

Aluminum Silicates↗
PubMed2001

[Functionality of inhalation aerosols is inadequate or lost at low temperature].

Correct and safe performance of metered-dose inhalers are necessary for efficient treatment of asthma under all climatic conditions. The spray mechanism malfunctioned when canister temperature was below -15 degrees C. The range and propagation of the spray plume at canister temperatures below 10 degrees C deviated clearly from those at 20 degrees C. Also the composition and particle concentration of the spray plume at low temperatures differed from those at more normal temperatures. Information must be provided to the effect that a canister must not be cold when used.

Administration, Inhalation↗
PubMed2001

[Cold stress and its prophylaxis].

The authors present criteria of cold stress and their relationships with thermoregulatory strain, ability to work and some health state parameters. Findings are unfavorable influence of human cooling and adaptation to cold on vibration disease development. The article covers requirements to heat-proof properties of clothing set, to duration of exposure to cold in various climate areas of Russian Federation.

Cold Climate↗