Multistage impaction

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

There are several different approaches that are commonly used to determine particle size distributions in air. One of them, impaction, has been discussed earlier. Multistage impactors with different cut points are used extensively to obtain both mass and chemical composition data as a function of size for particles with diameters > 0.2 /xm. Others, including methods based on optical properties, electrical or aerodynamic mobility, and diffusion speeds, are described briefly in the following section. The condensation particle counter (CPC) is used as a detector in combination with some of these size-sorting methods. 

Vacuum annealing leads to a higher ductility and impact toughness of alloy T110. Its multistage heat treatment provides the best combination of strength and ductility values. Annealing at 750°C is the simplest type of heat treatment and provides the required level of mechanical properties. 

None of these principal gravity-dependent and gravity-independent processes have been investigated in multistage electrophoresis, which is designed to minimize the impact of these processes on separation quality. All of these processes have been studied in the past in applications to other forms of free electrophoresis as reviewed by Todd [34,41]. 

Dynamic decision making occurs in a changing environment, in which the results of earlier decisions impact future decisions. The decisions made in such settings often make use of feedback and are multistage in nature. For example, a decision to take a medical test almost always requires a subsequent decision regarding what to do after receiving the test results. Dynamic decision making is represented at the lowest level of the model by the presence of two feedback loops, which show how the action taken and its effects can feedforward to the assessment of a new decision or feedback to the reassessment of the current decision. 

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