Seed scattering

In the paraelectric phase at T > Tm, where polar clusters vanish and beam-coupling is not possible because the polar macrostructure is no longer present, only the weak seed scattering is observed. Due to the drastic changes in the domain structure at the phase transition, the seed scattering at 130 °C differs from that at 28 °C both in the total amount and in the angular distribution. 

Figure 9.12 Seed scattering at refractive index modulations induced by localized internal random fields via the electro-optic effect. The internal fields are also responsible for the formation of a rich ferroelectric domain structure. Here, a periodic sequence of domains with lengths A d is shown. Note, that the grating period of the refractive index modulation As is equal to the lengths of the ferroelectric domains.

The diffraction of the pump beam from the (5n-perturbations associated with a large-scale domain structure results in small-angle seed scattering, while (5n-perturbations on the assemblies composed from small domains result in seed components propagating at large 9S (see Equation (9.11)). 

Applying Equation (9.12) to the results of our scattering hysteresis experiment, we receive the seed scattering amplitude Iso as functions of the scattering angle 6S and of the external field (Figure 9.13), respectively. 

Figure 9.9 (b) the seed scattering increases as a function of temperature, reaches a maximum and subsequently decreases. 

The light-scattering objects must track the flow accurately, ensuring that their velocity represents the fluid velocity with a high accuracy. The light-scattering objects are either in the flow as a natural impurity such as dust, or are artificially introduced into the airflow at an optimum concentration ( seeding ). 

If the light-scattering objects originally present in the airflow are unsuitable for LDA measurements due to insufficient concentration or incorrect estimated flow-tracking capability, the air must be seeded with oil smoke, tobacco smoke, or titanium dioxide tracer particles or droplets. A simple smoke candle is generally suitable for seeding, even if the enclosure is large and the air path is not closed as in several cases of industrial ventilation. 

Results Typical OCT images of dry barley seeds out of the control and GMF groups are shown in Figures 4a and 4b. A highly scattering layer with thickness of about 100 pm is clearly seen on the both images. No differences between the control and GMF seeds are observed. 

Figures 4e and 4f show OCT images of two control seeds after 60 minutes when turgescence has started. Similar to the GMF seeds, individual structural differences of the seeds are clearly visible here. However, after the same time period the heterogeneous absorption zones (Fig. 4f) are less expressed than in the GMF seeds (Fig. 4d). The bright area corresponding to highly scattering regions (Fig. 4d) is narrower (about 100 im) in the control than in GMF seeds (about 200 pm). Thus OCT imaging of barley seeds can distinctly visualize water absorption processes within the first hour, as well as, individual variations in different seeds. The variations reflect the phenomenon of biological variability of seeds at the tissue level.

Five minutes later, a well-structured water distribution becomes apparent in the OCT image of the flax seed. The upper bright layer is separated by a darker layer from a highly scattering area (about 50 pm). The darker layer has a thickness of (about 40 pm). Below there is a water absorption area... 

After 10 minutes Ten minutes after the water absorption has started, the process of differentiation of water absorbing layers is faster in GMF seeds (Fig. 6e) than in control seeds (Fig. 6f). The highly scattering layers are larger,... 

Using canes, mark out a grid to help you distribute the seed at the recommended rate, and scatter the seed evenly over the ground. 

PLIF or Mie scatter on seeded particles). The pairs of scalar images were combined by making use of phase locked imaging. By changing the phase angle of the laser with respect to the vortex roll up cycle the time evolution of the mixing... 

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