Magnitude Of Temperature Fluctuations Research Articles

冰雪覆盖、气温和地下水流动对水迹排水的北极山坡融冻层热状态的影响

Permafrost in Arctic watersheds limits soil biological activity to a thin, seasonally thawed active layer that contributes water to streams. In many hillslopes, relatively wet drainage features called water tracks have distinct freeze-thaw patterns that affect groundwater flow and storage, and thus the export of heat and solutes to Arctic streams. This study uses groundwater flow and energy transport models to examine potential controls on the timing and duration of freeze–thaw conditions and the magnitude of temperature fluctuations within water tracks and their adjacent hillslopes. The simulated length of the active-layer thaw season varies by 1 month over the range of snow-cover and mean annual air-temperature scenarios simulated. The timing and duration of freezing is particularly sensitive to depth and duration of snow cover. Thus, the deeper snowpack covers that can accumulate in water tracks contribute to their more persistent thaw conditions and their ability to conduct groundwater downslope. A three-dimensional simulation shows that during the summer thaw season, the water track captures groundwater laterally from half way across the hillslope. The models presented here elucidate key mechanisms driving small-scale variation in the active-layer thermal regime of tundra hillslopes, which may be responsible for changes in drainage-network geometry and Arctic biogeochemical fluxes under a warming climate.

Shifts in temperature influence how Batrachochytrium dendrobatidis infects amphibian larvae.

Many climate change models predict increases in frequency and magnitude of temperature fluctuations that might impact how ectotherms are affected by disease. Shifts in temperature might especially affect amphibians, a group with populations that have been challenged by several pathogens. Because amphibian hosts invest more in immunity at warmer than cooler temperatures and parasites might acclimate to temperature shifts faster than hosts (creating lags in optimal host immunity), researchers have hypothesized that a temperature shift from cold-to-warm might result in increased amphibian sensitivity to pathogens, whereas a shift from warm-to-cold might result in decreased sensitivity. Support for components of this climate-variability based hypothesis have been provided by prior studies of the fungus Batrachochytrium dendrobatidis (Bd) that causes the disease chytridiomycosis in amphibians. We experimentally tested whether temperature shifts before exposure to Batrachochytrium dendrobatidis (Bd) alters susceptibility to the disease chytridiomycosis in the larval stage of two amphibian species–western toads (Anaxyrus boreas) and northern red legged frogs (Rana aurora). Both host species harbored elevated Bd infection intensities under constant cold (15° C) temperature in comparison to constant warm (20° C) temperature. Additionally, both species experienced an increase in Bd infection abundance after shifted from 15° C to 20° C, compared to a constant 20° C but they experienced a decrease in Bd after shifted from 20° C to 15° C, compared to a constant 15° C. These results are in contrast to prior studies of adult amphibians highlighting the potential for species and stage differences in the temperature-dependence of chytridiomycosis.

Quantification of temperature fluctuations in restaurant coolers and modelled Listeria monocytogenes growth


 Background: Coolers in food service establishments should ideally operate at 4°C or less. However in restaurant environments cooler doors are continually being opened and closed as food workers gather and store items. These actions may lead to temperature fluctuations in coolers which may pose a health risk towards the storage of potentially hazardous foods. This study measured and analyzed temperature fluctuations in coolers and quantified the risk they presented by modelling Listeria monocytogenes growth in response to these temperatures. Method: ACR Systems Inc. Smart Buttons were placed near the opening of restaurant coolers and recorded temperatures over a 1-week span. Food Spoilage and Safety Predictor (FSSP) was used to model L. monocytogenes growth in response to the collected cooler temperatures. Results: Coolers spend significantly less than 50% of the time above 4°C. The magnitude of temperature fluctuations during open business hours was found to be insignificant in comparison to fluctuations during closed business hours. However, fluctuations were significantly greater in reach-in coolers than in walk-in coolers. With respect to modeled L. monocytogenes growth, it was inconclusive on whether growth would be more or less than Health Canada’s 100cfu/g policy in smoked salmon. However growth was significantly less than this limit in ready-to-eat ham. Conclusions: More restaurant coolers need to be analyzed to confirm whether the defrost cycles of coolers have a greater impact on temperature fluctuations above 4°C than the daily activities of staff members. In addition, more coolers need to be analyzed to determine whether L. monocytogenes growth in smoked salmon stored in coolers for a week grow significantly more than 100cfu/g. However, it can be concluded L. monocytogenes growth will be significantly less than 100cfu/g in ready-to-eat ham and will pose a lower risk for listeriosis than smoked salmon.

Thermal convection with mixed thermal boundary conditions: effects of insulating lids at the top

The effects of insulating lids on the convection beneath were investigated experimentally using rectangular convection cells in the flux Rayleigh number range $2.3\times 10^{9}\leqslant Ra_{F}\leqslant 1.8\times 10^{11}$ and cylindrical cells in the range $1.4\times 10^{10}\leqslant Ra_{F}\leqslant 1.2\times 10^{12}$ with the Prandtl number $Pr$ fixed at 4.3. It is found that the presence of the insulating lids leads to reduction of the global heat transfer efficiency as expected, which primarily depends on the insulating area but is insensitive to the detailed insulating patterns. At the leading-order level, the magnitude of temperature fluctuations in the bulk fluid is, again, found to be insensitive to the insulating pattern and mainly depends on the insulating area; while the temperature probability density function in the bulk is essentially invariant with respect to both the insulating area and the spatial pattern of the lids. The flow dynamics, on the other hand, is sensitive to both the covering area and the spatial distribution of the lids. At fixed $Ra_{F}$, the flow strength is found to increase with increasing insulating area so as to transfer the same amount of heat through a smaller cooling area. Moreover, for a constant insulating area, a symmetric insulating pattern results in a symmetric flow pattern, i.e. double-roll structure; whereas an asymmetric insulating pattern leads to asymmetric flow, i.e. single-roll structure. It is further found that the symmetry breaking of the insulating pattern leads to a stronger flow that enhances the horizontal velocity more than the vertical velocity.

The thermal environment of the nest affects body and cell size in the solitary red mason bee (Osmia bicornis L.)

Many ectotherms grow larger at lower temperatures than at higher temperatures. This pattern, known as the temperature-size rule, is often accompanied by plastic changes in cell size, which can mechanistically explain the thermal dependence of body size. However, the theory predicts that thermal plasticity in cell size has adaptive value for ectotherms because there are different optimal cell-membrane-to-cell-volume ratios at different temperatures. At high temperatures, the demand for oxygen is high; therefore, a large membrane surface of small cells is beneficial because it allows high rates of oxygen transport into the cell. The metabolic costs of maintaining membranes become more important at low temperatures than at high temperatures, which favours large cells. In a field experiment, we manipulated the thermal conditions inside nests of the red mason bee, a solitary bee that does not regulate the temperature in its nests and whose larvae develop under ambient conditions. We assessed the effect of temperature on body mass and ommatidia size (our proxy of cell size). The body and cell sizes decreased in response to a higher mean temperature and greater temperature fluctuations. This finding is in accordance with predictions of the temperature-size rule and optimal cell size theory and suggests that both the mean temperature and the magnitude of temperature fluctuations are important for determining body and cell sizes. Additionally, we observed that males of the red mason bee tend to have larger ommatidia in relation to their body mass than females, which might play an important role during mating flight.

An integrated thermal and mechanical investigation of molten-salt thermocline energy storage

Thermal ratcheting is a critical phenomenon associated with the cyclic operation of dual-medium thermocline tanks in solar energy applications. Although thermal ratcheting poses a serious impediment to thermocline operation, this failure mode in dual-medium thermocline tanks is not yet well understood. To study the potential for the occurrence of ratcheting, a comprehensive model of a thermocline tank that includes both the heterogeneous filler region as well as the composite tank wall is formulated. The filler region consists of a rock bed with interstitial molten salt, while the tank wall is composed of a steel shell with two layers of insulation (firebrick and ceramic). The model accounts separately for the rock and molten-salt regions in view of their different thermal properties. Various heat loss conditions are applied at the external tank surface to evaluate the effect of energy losses to the surroundings. Hoop stresses, which are governed by the magnitude of temperature fluctuations, are determined through both a detailed finite-element analysis and simple strain relations. The two methods are found to yield almost identical results. Temperature fluctuations are damped by heat losses to the surroundings, leading to a reduction in hoop stresses with increased heat losses. Failure is prevented when the peak hoop stress is less than the material yield strength of the steel shell. To avoid ratcheting without incurring excessive energy loss, insulation between the steel shell and the filler region should be maximized.

Thermal characteristics of wild and captive Micronesian kingfisher nesting habitats

AbstractTo provide information for managing the captive population of endangered Guam Micronesian kingfishers (Halcyon cinnamomina cinnamomina), four biologically relevant thermal metrics were compared among captive facilities on the United States mainland and habitats used by wild Micronesian kingfishers on the island of Pohnpei (H. c. reichenbachii), Federated States of Micronesia. Additionally, aviaries where kingfishers laid eggs were compared to those in which birds did not attempt to breed. Compared to aviaries, habitats used by wild Pohnpei kingfishers had 3.2°C higher daily maximum and minimum temperatures and the proportion of time when temperatures were in the birds' thermoneutral zone was 45% greater. No differences were found in the magnitude of temperature fluctuation in captive and wild environments. In captive environments in which birds bred, daily maximum temperatures were 2.1°C higher and temperatures were within the thermoneutral zone 25% more often than in the aviaries where the kingfishers did not breed. No differences were found in the magnitude of temperature fluctuation or the daily minimum temperature. Results suggest that the thermal environment has the potential to influence reproduction, and that consideration should be given to increasing temperatures in captive breeding facilities to improve propagation of the endangered Micronesian kingfisher. Zoo Biol 23:301–308, 2004. Published 2004 Wiley‐Liss, Inc.

The application of temperature-modulated DSC to the glass transition region: II. Effect of a distribution of relaxation times

An analysis of temperature-modulated differential scanning calorimetry (TMDSC) in the glass transition region is presented. It extends an earlier and simpler model by introducing a distribution of relaxation times, characterised by a Kohlrausch–Williams–Watts (KWW) stretched exponential parameter β, in addition to the usual kinetic parameters of relaxation, namely the Tool–Narayanaswamy–Moynihan (TNM) non-linearity parameter x and the apparent activation energy Δ h ∗. The present model describes, more realistically than did its predecessor, all the characteristic features of TMDSC in the glass transition region, and it has been used to examine the effects of the important experimental variables, namely the period of modulation and the underlying cooling rate. It is shown that, for typical experimental conditions in practice, it is likely that there well be an interaction between the vitrification process, due to the underlying cooling rate, and the dynamic glass transition whereby the complex heat capacity C p ∗ shows a sigmoidal decrease in a temperature range dependent on the modulation frequency. Accordingly, care must be exercised in the quantitative evaluation of TMDSC data in the glass transition region, and suggestions are made regarding the optimum procedures in this respect. Also, by comparing the cooling rate and modulation period required to define the same transition temperature for conventional DSC and C p ∗ , respectively, a correspondence between them is obtained which allows the magnitude of temperature fluctuations in Donth’s fluctuation dissipation theorem to be evaluated. Finally, it is shown that β and x have similar effects on conventional DSC cooling curves, but have very different effects on C p ∗ , whereby there is little effect of x but a significant broadening of the transition as β decreases. It is argued that the breadth of the C p ∗ transition therefore provides a measurement of β independent of the value of x, thus resolving a problem that has existed for some years.

Transient high-Rayleigh-number thermal convection with large viscosity variations

The characteristics of thermal convection in a fluid whose viscosity varies strongly with temperature are studied in the laboratory. At the start of an experiment, the upper boundary of an isothermal layer of Golden Syrup is cooled rapidly and maintained at a fixed temperature. The fluid layer is insulated at the bottom and cools continuously. Rayleigh numbers calculated with the viscosity of the well-mixed interior are between 106 and 108 and viscosity contrasts are up to 106. Thermal convection develops only in the lower part of the thermal boundary layer, and the upper part remains stagnant. Vertical profiles of temperature are measured with precision, allowing deduction of the thickness of the stagnant lid and the convective heat flux. At the onset of convection, the viscosity contrast across the unstable boundary layer has a value of about 3. In fully developed convection, this viscosity contrast is higher, with a typical value of 10. The heat flux through the top of the layer depends solely on local conditions in the unstable boundary layer and may be written \[Q_{\rm s} = - CK_{\rm m} (\alpha g/\kappa \nu_{\rm m})^{\frac{1}{3}} \Delta T^{\frac{4}{3}}_{\rm v}\], where km and νm are thermal conductivity and kinematic viscosity at the temperature of the well-mixed interior, κ thermal diffusivity, α the coefficient of thermal expansion, g the acceleration due to gravity. ΔTv, is the ‘viscous’ temperature scale defined by \[\Delta T_{\rm v} = - \frac{\mu (T_{\rm m})}{({\rm d}\mu /{\rm d}T)(T_{\rm m})}\] where μ(T) is the fluid viscosity and Tm the temperature of the well-mixed interior. Constant C takes a value of 0.47 ± 0.03. Using these relations, the magnitude of temperature fluctuations and the thickness of the stagnant lid are calculated to be in excellent agreement with the experimental data. One condition for the existence of a stagnant lid is that the applied temperature difference exceeds a threshold value equal to (2ΔTv).

The oceans, the climate and people (with a view from mars)*

Abstract If the Earth is looked at as a planet, the first really significant influence that man has had is the increase in atmospheric CO2 which has occurred over the past Century. Models based on projected uses of fossil fuels and the behaviour of the ocean and the biosphere, in so far as they are understood, lead to predictions of a doubling of the atmospheric CO2 by the middle of the next Century and an increase by a factor of from five to eight within two centuries. Models of the climatic impact of such a CO2 increase predict an increase of surface temperature of about 2°C for doubling and 5 to 10°C for a factor of eight. 2°C is twice the magnitude of temperature fluctuations over the past Century, and 10°C is greater than the change between present conditions and a full ice age. Thus, increasing CO2 may very well dramatically affect mankind. However, there are many uncertainties in the models, in particular in the way in which the ocean is treated concerning both its ability to absorb CO2 and its res...

点溶接機電極の先端部の温度上昇の実測と計算

The maximum temperature rise in electrode tip is estimated from the measured heat input to the electrode during one spot welding. It reaches as high as about 700°C for ordinary spot welding conditions of steel plates of 0.8-3.2 mm thickness.For calculation the electrode cross section is assumed constant along the electrode length, and the effect of wave form of heat flow from the tip is investigated. Q in Table 1 is the measured heat input to each side of the electrode per one welding under the conditions shown in the table. θ2 in the table shows the calculated results using the equation (9) under the following assumption, i.e. the heat flow wave form is taken as Fig. 11(a), heat flow time TH is assumed as equal to current flow time T0 shown in the table, the cross section of the electrode is taken as S2 corresponding to the root diameter of the electrode.Fig.14 shows the temperature distribution curves along the length when a constant heat H=1000 cal/cm2 sec flows in from the electrode tip for the duration TH=0.25, 0.5, 1.0, 1.5sec. Curves A-D show the temperature rise when the distance x0 of cooling end from the tip is infinity and A, B'-E' for x0=1 cm. For the calculation of the effect of cooling water, it is assumed that equation (33) holds, according to the model shown in Fig. 13 (h is taken as 1 for Fig. 14 and 18).Heat flow time TH is divided into two parts as shown in Fig.17 and the temperature at the moment C is calculated as the sum of the parts. Temperature due to the part AB is calculated using equation (49), T1 being time constant defined as in equation (43) and the period of BC is chosen far longer than time constant T2.It is easily shown that the magnitude of temperature fluctuation at a point I cm distant from the tip is negligible when intermittent heat input cycle is less than 1 sec/spot and we see that the cooling effect of cooling water is only effective to reduce the average temperature rise in the electrode under intermittent welding.Table 3 shows the temperature rise at the tip for cyclic heat flow from the tip for various combinations of x0, h, TH and Tw (i.e. cyclic period). The value shows the temperature at the moment C in Fig. 19 for H=1000 cal/cm2 sec.Fig.2, 4 shows the oscillogram of the temperature rise at 2 mm distant from the tip (Fig.1). Electrode pressure is also shown in Fig.2.

Optical Image Quality in a Turbulent Atmosphere

Measurements of the time-average modulation transfer function of an optical system comprising an objective and a horizontal air path correlate with a parameter which characterizes the magnitude of temperature fluctuations in the lower layers of the atmosphere. Evidence is produced to support an exponential relationship between the transfer function and the atmospheric temperature structure function. The transfer function fluctuates rapidly about a mean; visual estimates of resolution limit agree more closely with the maxima than with the mean. The significance of these results is discussed in relation to the choice of conditions for good terrestrial and astronomical seeing.

Temperature fluctuations in the atmospheric boundary layer

A systematic analysis is made of published measurements of the magnitude of temperature fluctuations in the atmospheric boundary layer. These cover a wide range of height, wind speed, and thermal stratification. Within appropriate ranges of the variables, there is evidence for the existence of a dominantly forced convection régime, and also one wherein the predictions of the similarity theory of free convection are fairly closely approached. Subject to the limitations set by the recording systems used, regression relations are obtained for the magnitude of the fluctuations in terms of height and vertical temperature gradient or heat flux.