Time constant vacuum

As our first example we shall define what is known as a gaussian Markov process. This process, as we shall see later, is a good model for thermal noise or vacuum-tube-generated noise that has been passed through an RC filter with time constant a 1. We begin by defining two functions / and Q as follows... 

The sampling of a suction lysimeter is initiated by applying a vacuum (approximately 40-50 cm of mercury) through the vacuum/pressure line with a hand pump or electric pump. The valve on the sampling line must be closed. A constant vacuum may be maintained on the lysimeter using an electric pump. The time required before collecting a sample from a lysimeter will depend on the method of vacuum application, the moisture content of the soil, and the soil type. 

Sometimes, to get data from 4 K up to room temperature, the simplest and more economical way is to let the cryostat warm if the thermal insulation is good and the vacuum chamber is kept under pumping, the warm-up time can be several days. If the experiment thermal time constant is much shorter, data at practically constant temperature can be recorded. 

The duration of each dosing experiment is about 15-50 minutes (depending on the sample and of the time constant of the calorimeter), which was long enough to yield well-resolved heat-flow peaks and a stable horizontal baseline of the microcalorimeter. For all catalysts presented here, adsorption always reached thermodynamic equilibrium. Prior to adsorption measurements, the samples were pretreated in the calorimetric cell by heating overnight under vacuum. 

The ratio V/Sgj, is generally designated as a time constant x. Thus the pump-down time of a vacuum chamber from atmospheric pressure to a pressure p is given by ... 

Time constants The time constant for a vacuum system is set by V... 

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