Humidity fluctuations

Figure 3.24 depicts a piezoelectric sensor consisting of two oscillator circuits a detector crystal oscillator and a reference crystal oscillator. The two are identical except for the fact that the reference oscillator is not coated with biological material and is intended to correct for temperature and humidity fluctuations, as well as other interfering effects. The two oscillator frequencies are fed to a mixer that provides the difference in frequency between the two crystals. In order to use the piezoelectric effect to detect a target dissolved substrate it should be reacted with a suitable biocatalyst immobilized on the crystal by entrapment (deposition from an acrylamide solution), cross-linking, irradiation or pre-coating. 

The properties of tablets are also influenced by temperature and humidity fluctuations, e.g., during storage. Is it possible to select excipient compositions that minimize the effect of temperature and humidity fluctuations on the quality of tablets These questions are raised and treated in a small example in Chapter 2 and extensively in Chapter 8. 

As a first step toward data collection with little human interference, an automatic hygrothermograph interfaced with a minicomputer was developed in our laboratory to study the internal climate of the tomb. This instrument can take temperature and humidity measurements every 33 min for 1 year and store the data in a computer memory. Its sensitivity to humidity fluctuation exceeds that of conventional chart hygrothermographs by a factor of 5. Therefore, the instrument has an important advantage over a clockwork hygrothermograph because it provides information on long-term climatic fluctuations in the tomb. 

As an example of the error that may be induced in NIR measurements by failure to control humidity, fluctuations in the concentration of atmospheric water vapor generated by an air conditioner were identified as a source of noise in NIR spectrometers in a 1987 paper [3]. 

In the case of a diffusion-limited reaction, hydrodynamic factors, such as turbulent flow, may influence the dissolution process. Humidity fluctuations also may alter the solute concentrations in the moisture film at the rock surface, and they may result in the dissolution and recrystallization, not only of the carbonates, but also of the secondary minerals, such as calcium sulfate. Wetting and drying cycles may lead to measureable changes in fluid composition at the stone surface. 

Testing allows isolation of the individual parameters, a useful feature if the application involves a complex and varied environment or if the behavior of the prototype is not predictable. Accelerated simulation of in-service conditions is often feasible by applying environmental factors that are most influential in product lifetime, such as stresses, strains, temperature, and humidity fluctuations sunlight exposure and attack by solvents. 

Temperature or humidity fluctuations can be accelerated only to the point of maintaining uniform penetration that is likely in the end use environment. If creep or vibration is expected in service, time-temperature superposition may often be applied to accelerate laboratory testing. This technique mathematically predicts the material s response in service, based on laboratory characterization of the material over a... 

Lafontaine, R. H., Wood, P. A. (1982). The stabilization of ivory against relative humidity fluctuations. Studies in Conservation, 27, 109-117. 

Easter RC, Peters LK. Binary homogeneous nucleation temperature and relative humidity fluctuations, nonlinearity, and aspects of new particle production in the atmosphere. J Appl Meteorol 1994 33 775-784. 

Figure 4.2 shows the sample chamber for monitoring the spreading drop over porous layers and dynamic contact angles. A porous wafer 1 (Figure 4.2) is placed in a thermostated and hermetically closed chamber 2 with a fixed humidity and temperature. The chamber was made of brass to prevent temperature and humidity fluctuations. In the chamber walls, several channels were drilled to enable pumping of a thermostating liquid. The chamber is equipped with a fan. The temperature is monitored by a thermocouple. Droplets of liquid 3 are placed onto the wafer by a dosator 4 (Figure 4.2). The volume of drops is set by the diameter of the separable capillary of the dosator.

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