Relative humidity and temperature

On being exposed to the environment, micro-organisms lose water molecules that are replaced during host infection or transfer to some other 

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Where highly poHshed surfaces are manufactured or stored for short intervals between different phases of processing, relative humidity and temperature are both maintained constant to minimise surface moisture films. If these surfaces are shipped or stored for extended intervals, protective coverings or coatings may be required. 

Adsorption. Wood is highly hygroscopic. The amount of moisture adsorbed depends mainly on the relative humidity and temperature (Fig. 1). Exceptions occur with species with high extractive contents (eg, redwood, cedar, and teak). The equihbtium moisture contents of such woods ate generally... 

The water-vapor transmission rate (WVTR) is another descriptor of barrier polymers. Strictly, it is not a permeabihty coefficient. The dimensions are quantity times thickness in the numerator and area times a time interval in the denominator. These dimensions do not have a pressure dimension in the denominator as does the permeabihty. Common commercial units for WVTR are (gmil)/(100 in. d). Table 2 contains conversion factors for several common units for WVTR. This text uses the preferred nmol/(m-s). The WVTR describes the rate that water molecules move through a film when one side has a humid environment and the other side is dry. The WVTR is a strong function of temperature because both the water content of the air and the permeabihty are direcdy related to temperature. Eor the WVTR to be useful, the water-vapor pressure difference for the value must be reported. Both these facts are recognized by specifying the relative humidity and temperature for the WVTR value. This enables the user to calculate the water-vapor pressure difference. Eor example, the common conditions are 90% relative humidity (rh) at 37.8°C, which means the pressure difference is 5.89 kPa (44 mm Hg). 

Thermohydrograph A mechanical or electrical device that records simultaneously the relative humidity and temperature of the air throughout the day. 

The effect of relative humidity and temperature on the physical and structural properties of the 1 1 isopropanol solvatomorph of warfarin has been studied [58], Below the critical relative humidity of 60-68% the solid is not hygroscopic, but becomes deliquescent at higher values of relative humidity without exchange of water for isopropanol. Storage of the solvate-morph at elevated temperatures causes formation of an amorphous solid owing to loss of isopropanol, which may proceed through an intermediate crystalline phase. 

Water evaporation occurs when the vapor pressure of the water at the surface, which is temperature dependent, is greater than the water pressure in the subsurface, which is dependent on relative humidity and temperature. The isothermal evaporation process is described by Stumm and Morgan (1996) via a reaction progress model, in which the effects of the initial reaction path are based on the concept of partial equilibrium. Stumm and Morgan (1996) describe partial equilibrium as a state in which a system is in equilibrium with respect to one reaction but out of equilibrium with respect to others. As an example, Stumm and Morgan (1996) indicate (Fig. 7.1) that water with a negative residual alkalinity (i.e.. 

Relative humidity and temperature are two variables which have influence on the chromatographic behavior of the solutes [2] but which can not always be set at desired levels. The relative humidity is expected to have a large influence, while temperature has a small influence. In reference [2] it is stated that a temperature change of 5 degrees seldom exceeds reproducibility limits of the standard working techniques. It is most feasible to discuss the effect of variation in relative humidity and temperature in terms of activity. Therefore in the following paragraphs first the concept of activity will be introduced. Then the concept will be applied in a short examination of the effect of relative humidity and temperature on the retention. 

For a Taguchi approach to robustness the solvent composition is varied in the inner array, and the relative humidity and temperature in the outer array. The response is the resolution of noscapine and quinine. The data used in this example is a subset of the data set which is collected for this paper. The inner array consists of seven design points, the outer array of three. The three responses obtained at each setting of the inner array are combined to form a so-called signal-to-noise ratio. For maximization of the responses the following equation is [11] ... 

A robust TLC separation of the seven alkaloids (strychnine, quinine, heroin, noscapine, caffeine, papaverine and narceine) is difficult to obtain. The solutes used have different properties and can therefore not be separated trustworthy for all possible values of relative humidity and temperature. 

Figure 9-2 High-precision CC-1 measurement cell for measurement of relative humidity and temperature including an ionic liquid as sensing electrolyte, as commercialized by Novasina S.A. (with permission of Novasina S.A.).

Calibrated Dickson relative humidity and temperature recorder... 

Fig. 77. The arrangement of layers of water molecules (dashed lines) in hydrated montmor-illonites and the corresponding interlayer spacings in (a) a one-layer clay (b) a two-layer clay (c) a three-layer clay. The spacing adopted by a particular montmorillonite depends on the nature of the silicate layer and on the exchangeable cation as well as on certain other conditions of intercalation (e.g., relative humidity and temperature) (470).

Emission rate studies are currently underway with a number of membrane materials. Early tests were very encouraging a number of more recent test results show variations in emission rate from lot to lot and as a function of ambient relative humidity and temperature. Tests have not yet started on long-term emission behavior,... 

Kett et al. [1.162] studied Tg in freeze-dried formulations containing sucrose as a function of relative humidity and temperature during storage by TMDSC and ther-mogravimetric analysis. Craig et al. [1.163] found it helpful to asses the relaxation behavior of freeze-dried amorphous lactose by MTDSC. Relaxation times were calculated from measurements of Tg, and the magnitude of the relaxation endotherm. Scannnig was performed at 2°C/min with a modulation amplitude of 0.3 °C and a period of 60 s. 

Critical environmental parameters that include, but are not limited to, relative humidity and temperature, must be maintained within the computer equipment manufacturer s requirements. In cases where there are a number of requirements, the most stringent should be utilized. 

Three items are important in the storage of admixtures, namely, the ease of identification, humidity and temperature at which they are stored. To avoid confusion between different admixtures, drums should be delivered clearly labeled as to the contents identification can be made easier by a colorant which has no influence on the concrete. Powdered admixtures are more sensitive to moisture and carbon dioxide than are Portland cements. The materials should, therefore, be packed in waterproofed bags and always stored in areas free of high relative humidity and temperature extremes to avoid condensation. Storage tanks should be vented properly, and fill nozzles and any other tank openings should be capped when not in use to avoid contamination. 

Another problem with these instruments is determination of mechanical properties of moisture sensitive materials (10-12). Such materials have tendency to gain moisture when subjected to mechanical excitation at constant relative humidity and temperature. This makes single frequency tests impractical for isomoisture studies over a range of frequencies. 

Mould overwinters in plant dehris (leaf stalks, mummified fruit). High relative humidity and temperatures of 15-20°C during flowering are conducive to the primary infection. Fruit becomes more susceptible with increasing ripeness. The disease can spread rapidly in wet weather. 

Environmental Factors. Moisture. Wood, which is a hygroscopic material, gains or loses moisture to equilibrate with its immediate environment. The equilibrium moisture content (EMC) is the steady-state level that wood achieves when subjected to a particular relative humidity and temperature. The eventual EMC of two similar specimens will differ if one approaches EMC under adsorbing... 

The effects of relative humidity and temperature on the moisture sorption and stability of sodium bicarbonate powder have been investigated. Sodium bicarbonate powder is stable below 76% relative humidity at 25°C and below 48% relative humidity at 40°C. At 54% relative humidity, the degree of pyrolytic decarboxylation of sodium bicarbonate should not exceed 4.5% in order to avoid detrimental effects on stability. ... 

Dey M. Enever R, Kraml M, ct al. The dissolution and bioavailability of etodolac from capsules exposed to conditions of high relative humidity and temperatures. Pharm Res 1993 10 1295-300. 

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