Active temperature fluctuations

Weathering The physical or chemical conversion of surface rocks into sediments, soils, and dissolved and suspended materials in water through exposure of the rocks to liquid water, oxygen, carbon dioxide, wind, acids, salts, ice, biological activity, temperature fluctuations, and/or other factors at and near the Earth s surface (compare with chemical and physical weathering). 

Biological activity from insects, lizards, snakes and rodents is limited as well, and mainly concentrates in the deeper soil layers where moisture remains relatively high and temperature fluctuations are reduced. 

The air temperature fluctuations at the Diavik site results in ground surface temperatures that vary as much as 10°C during a month. The active layer in the bedrock at the site is about 4 m, as the surface temperatures vary between -28 and 16.5°C throughout the year. At 10 m depth into the bedrock, the temperature is stable at -5°C. In the Type I and Type III test piles, an active layer ranges from approximately 5 to 10 m depth under the influence of surface temperatures. Below a depth of 5 m, the cooling rate of waste rock varies from 2 to 3°C per year. 

To minimize extreme ambient temperature fluctuations. If the laboratory and dew-point instrument temperatures fluctuate by as much as 5°C daily, water activity readings may vary by 0.01 aw. Often, this much uncertainty in sample aw is unacceptable, so there is a need for a temperature-controlled model. 

The accuracy of VPM measurements may depend upon the range of water activity being measured. Acott and Labuza (1975) gave an accuracy of 0.005 unit of aw for aw < 0.85 using this method. At higher values of aw the accuracy is no better than 0.02 units of aw because of temperature fluctuation (Labuza et al., 1976). 

In many cases, reactions in aqueous solutions are not at equilibrium. The failure to achieve equilibrium may be due to slow reaction kinetics, temperature fluctuations, biological activity, or open systems. For a reaction that is not at equilibrium, Equation 2.23 is not true ... 

A small change in cadmium temperature resulted in a slow continuous change in alloy weight corresponding to a linear relationship between activity and cadmium mole fraction. Such a relationship could be followed for days at a time. The nucleation of a new structure resulted in an easily recognized sharp departure in composition which was completed in about 1/2 hour. The system composition would reflect even the small temperature fluctuations associated with change of ambient conditions in the room. The effect tended to randomize the direction of approach to equilibrium for a particular point. 

In Figure 2 arrows have been drawn where transitions between curves were witnessed and also for some cases where it was known only that a transition had occurred between consecutive points. In these cases the arrow indicates only the extreme limit of composition-activity difference at which transition could have occurred. The transitions which occurred between consecutive points 278 and 279, 279 and 280, 282 and 283, and 286 and 287 have not been indicated. However, following (and very close to) point 278, during a period of less than an hour, the system was observed to undergo an excursion at nearly constant activity which is interpreted to be an attempt at a transition possibly to line Q, but it then returned to line P. This attempt at transition was doubtless prevented by temperature fluctuation, but it seems definite that the system was very close to the two-phase equilibrium region between two microphases. Also between points 278 and 279 the system was observed to be in the region of mole fraction 0.8220 and line U, but the next equilibrium point was 279 in the secondary family. Where the interfamily transitions have been indicated, dashed arrows have been used. 

Temperature Increase Dynamics after the First Cycle. As with the start up of the bed, subsequent temperature cycles resulted in the formation of a mild hot spot. The occurrence of this temperature fluctuation is undesirable since the past history of the catalyst may be altered. The adsorption of thiophene upon the active hydrogenation sites was assumed to be irreversible and therefore unaffected by temperature. However, as will become apparent later, the effect of temperature may have altered the poison coverage/or profile. Lyubarski, et. al [73 determined that, as a result of the hydrogenation of thiophene and subsequent hydrogenolysis to butane, the adsorption capacity of a suported Ni... 

Here A is the Arrhenius constant, p the mass density, nif, the mass fraction of the fuel, AH the enthalpy of reaction and E the activation energy. This approach yielded values for both the probability that an autoignition centre could be large enough to become critical and, if it was, the associated localized overpressure at the hot spot. Both the probability and the overpressure increased with temperature and AHpm/A, but decreased with the activation temperature, EIR. Just prior to criticality the hot-spot temperature was about 10% above that of the surrounding gas. Concentration fluctuations, particularly of active species, would have a similar effect. A strong localized explosion can cause knock, the intensity of which depends not only upon the localized overpressure, but on how the pressure pulse so created interacts with the remaining end gas. 

These values are model-dependent. In absolute terms, the variation of sticking with beam or surface temperature is very weak. No fundamental, molecular scale meaning is given to the separate activation energies for different coordinates or the width to each activation barrier. Fluctuating... 

To suppress sample temperature fluctuations a feedback stabilization circuit is employed (see above) Figure 5b shows the sample temperature fluctuations measured on a (Mg,Fe)Si03 sample heated at 29 GPa for 17-35 min when the feedback stabilization system was activated. In these long-term heating runs the peak-to-peak amplitude of the sample temperature fluctuations were kept below 5% of the average temperature. 

The activation energy is a parameter that has been used to characterize plastic packaging. Knowledge of the activation energy of the breath of product and packaging serves as an important tool to predict the effects of temperature fluctuations on the concentration of gases inside the package (Cameron et al., 1995). 

The 2009-2011 years vegetation seasons were considerably differed both between them and with mean mnltiannual values. Observed fluctuations of mean daily air temperatures were fiom+10.8°C (May) to +17.2 °C (July) in 2009, from +8.9°C (September) to +17.5 °C (Jnly)-in 2010 and from +10.8°C (May) to +18.0 °C (Jnne)-in 2011. Minimal daily temperatures were observed in May 2009 and 2011 and in September 2010 maximal temperatures-in July 2009 and 2010 and in June 2011. It is possible to characterize the years of the research as warm with sharp flnctuations of daily and monthly temperatures. The overage above multiannual data made in 2009-2.8 °C, in2010-0.5 °C, in 2011-3.2 °C. Snmof active temperatures was above the normal (1500-1700°C) at the average for the whole period on 219 °C and made 1977.4 °C in 2009, 1855.4 °C in 2010 and 1925.3 °C in 2011. 

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