Control of the physical stability

The polymer geometry also influences the importance of the diffusion in the control of the physical loss of a stabilizer. It was reported that the diffusion-controlled loss dominates in thick sections. From the point of view of the stabilising efficiency, a low diffusion rate for thin samples is desirable. A high diffusion rate may be of advantage for thick samples if chemical or physical depletion of deteriogens near the sample surface is required. 

Th. E. Tadros, Control and Assessment of the Physical Stability of Pesticidal Suspension Concentrates , Chem. Ind. (London), 1980, 211. 

The main drawback of O/W emulsions is the control of their physical stability, which needs to be controlled at various temperatures with adequate shelf life (usually a shelf life of 1-2 years is required at temperatures that can vary from —10° to 50 °C). This represents a challenge to the formulation chemist. 

The effective method for increasing thermal oxidation stability of polymers is control of the physical structure [7], The additive effect on the physical structure of PI film was studied with the help of X-ray structural analysis. The film possesses mesomorphous regularity, of which the presence of an intrachain order in the absence of interchain packing regulation is typical. As shown on the diffraction pattern, such structure manifests itself by a single narrow peak of the intrachain order (5-6 deg) and wide amorphous halo (Figure 19). Diffraction patterns show high intrachain orderliness of the stabilized sample. This difference is... 

The vesicle size is an important parameter not only for in-process control but particularly in quality assurance, because the physical stability of the vesicle dispersion depends on particle size and particle size distribution. An appropriate and particularly quick method is laser light scattering or diffraction. Laser light diffraction can be applied to particles > 1 pm and refers to the proportionality between the intensity of diffraction and the square of the particle diameter according to the diffraction theory of Fraunhofer. 

Physical Stabilization Process. Cellular polystyrene, the outstanding example polytvinyl chloride) copolymers of styrene and acrylonitrile (SAN copolymers) and polyethylene can be manufactured by this process, Chemical Stabilization Processes. This method is more versatile and thus has been used successfully for more materials than the physical stabilization process. Chemical stabilization is more adaptable for condensation polymers than for vinyl polymers because of the fast yet controllable curing reactions and the absence of atmospheric inhibition. Foamed plastics produced by these processes include polyurethane foams, polyisocyanurates. and polyphenols. 

Abstract. We present a frequency comparison and an absolute frequency measurement of two independent -stabilized frequency-doubled Nd YAG lasers at 532 nm, one set up at the Institute of Laser Physics, Novosibirsk, Russia, the other at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. The absolute frequency of the l2-stabilized lasers was determined using a CH4-stabilized He-Ne laser as a reference. This laser had been calibrated prior to the measurement by an atomic cesium fountain clock. The frequency chain linking phase-coherently the two frequencies made use of the frequency comb of a Kerr-lens mode-locked Ti sapphire femtosecond laser where the comb mode separation was controlled by a local cesium atomic clock. A new value for the R.(56)32-0 aio component, recommended by the Comite International des Poids et Mesures (CIPM) for the realization of the metre [1], was obtained with reduced uncertainty. Absolute frequencies of the R(56)32-0 and P(54)32-0 iodine absorp tion lines together with the hyperfine line separations were measured. 

Control of Drop Size w/o Emulsions. Although the control of the drift of herbicide sprays was the initial reason for renewed interest in water-in-oil emulsion sprays, there are other interesting and novel ways of applying pesticides. The physical properties of w/o emulsions are considerably different from those of more conventional types of spray liquids, and the emulsifiers required to form and stabilize w/o emulsions are different from the usual materials employed in oil-in-water and wettable powder sprays. These differences can affect all aspects of spray performance, and a thorough study is required to appreciate the advantages and disadvantages which w/o emulsions may possess over aqueous-based sprays. 

Sensor. The control of the exhaust composition was essential to maintain the air-to-fuel ratio close to stoichiometric for simultaneous conversion of all three pollutants. This control came about with the invention of the 02 sensor.21,22 The sensor head of this device was installed in the exhaust immediately at the inlet to the catalyst and was able to measure the 02 content instantly and precisely. It generates a voltage consistent with the Nemst equation in which the partial pressure of 02 (P02)exhaust in the exhaust develops a voltage (E) relative to a reference. The exhaust electrode was Pt deposited on a solid oxygen ion conductor of yttrium-stabilized zirconia (Zr02). The reference electrode, also Pt, was deposited on the opposite side of the electrolyte but was physically mounted outside the exhaust and sensed the partial pressure (P02)ref in the atmosphere. E0 is the standard state or thermodynamic voltage. R is the universal gas constant, T the absolute temperature, n the number of electrons transferred in the process, and F the Faraday constant. 

The droplet size of topical aerosol sprays does not need to be carefully controlled, and the dose usually is not metered as in inhalers. The spray may be used to apply the drug to the skin (topical aerosol) or mouth (lingual aerosol) and the functionality of the sprayer should be addressed. The drug product has no contact with the cap and short-term contact with the nozzle. A topical aerosol may be sterile or may conform to acceptance criteria for microbial limits. However, the physical stability of aerosols can lead to changes in total drug delivered per dose and total number of doses that may be obtained from the container. 

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