Crystallizers sampling systems

In conclusion, the fundamental features of various methods for obtaining high strength systems from flexible-chain polymers should also be mentioned. Since the presence of ECC leads to an increase in the fraction of tie chains in crystallized samples (their number can be increased by other methods not related to a direct formation of ECC, e.g. by orientational drawing investigated by Marikhin and Myasnikova4)), the main tech-... 

It should be noted that the fraction of ECC in samples obtained by other methods described in Sect. 2 is approximately as small as that of the framework in the orientation-ally crystallized samples. These methods differ in details but depend on the mechanical treatment of the crystallizing system and are therefore given the common name stress-induced crystallization . Although the structure of the samples obtained by these methods has some features in common with that of orientationally crystallized samples, the thermodynamics and kinetics of orientational crystallization are fundamentally different from the mechanism of stress-induced crystallization. 

In systems from which only a polycrystalline or an amorphous sample can be obtained, NMR becomes the method of choice since the diffraction technique requires single crystal samples. 

Constant use of this liquid nitrogen delivery system requires control of the environment within the X-ray enclosure to eliminate condensation of water on the phase separator located above the crystal sample. If this water were to reach the sample, the crystal would experience a temporary increase in temperature that can result in loss of crystallinity. Dehumidification of the hutch eliminates this potential problem. Removal of ambient humidity has the added benefit of reducing the formation of ice on all components that use liquid nitrogen, particularly the dewars used to store crystals before and after X-ray analysis. 

In short, a Ti Sapphire laser system in combination with two four-pass OPAs were used to create the femtosecond pump and probe pulses at variable wavelengths. The wavelength of the pump laser was chosen to be 530 nm for all experiments presented in the following. For the probe laser we used the fundamental output at 800 nm as well as wavelengths between 300 and 400 nm. The light scattered from the oriented single crystal samples was analyzed by a monochromator equipped with a photomultiplier tube. A more detailed description of the experimental setup is given in ref. 1. 

Piezoelectric hygrometers (Fig. 6.S6) These consist of a quartz crystal with a hygroscopic coating (Fig. 6.S60 and Section 6.3.3). Two crystals are usually employed and the wet gas (sample) and dry gas (reference) are passed over them alternately (normally every 30s—Fig. 6.566). The crystals absorb and desorb. The difference in angular frequency Am is proportional to the concentration of water vapour by volume. Capable of high precision. Can monitor moisture contents of the order of 1 to 3000 ppm by volume. Usually measures up to dewpoint of 310 K. Fast response but expensive. Sample must be dean to avoid contamination of the crystals. Complex sampling system. Suitable for on-line use. 

The effluent from the column was sprayed on to the surface of the crystal, the solvent was evaporated and the mass of the residual solute was determined from the change in frequency of the crystal. This system was not in continuous use since sampling was carried... 

The specific heat at constant pressure, Cpf of the HIP-treated sample with nominal composition LaVg 25 0,7504 was measured over the temperature range 4-400 K by the heat pulse method in a calorimeter that incorporates a feedback system to regulate the temperature of concentric radiation shields surrounding the sample (9). The Cp values are accurate to within 1%, as determined by calibration runs using a polycrystalline copper sample and a sapphire single crystal sample. 

Fig. 13. The magnetization vs. applied magnetic field at T = 5 K for single-crystal samples of the LaMnj xGax03 system. The full hysteresis loop is shown for the x = 0.5 sample the inset is the detail in low fields, after Zhou et al.

Figure 7 shows the screen display of measurements made using the Vernier LabPro system in the development of a liquid crystal experiment for this text (Exp. 15). Tabulated and plotted versus time are the temperature and the (amplified) photomultiplier voltage as a liquid crystal sample was heated through the nematic to isotropic phase change and then cooled back down. The temperature probe is a calibrated thermistor contained in a metal... 

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