Microsphere plate

A newer and less expensive alternative to the microchannel plate is the microsphere plate (MSP). As illustrated in Figure 3.6, this electron multiplier consists of glass beads with diameters from 20 to 100 pm that are sintered to form a thin plate with a thickness of 0.7 mm. This plate is porous with irregularly shaped channels between the planar faces. The surfaces of the beads are covered with an electron emissive material and the two sides of the plate are coated to make them conductive. The operating principle of this electron multiplier is similar to that of the microchannel plate. A potential difference of between 1.5 and 3.5 kV is applied across the plate, with the output side of the plate at the more positive potential. When particles hit the input side of the microsphere plate, they produce secondary electrons. These electrons are then accelerated by the electric field through the porous plate and collide with other beads. Secondary electron multiplication in the gaps occurs and finally a large number of secondary electrons are emitted from the output side of the plate. 

Microsphere plate detector and electron multiplication through the porous plate. Reproduced (modified) from El-Mul Technologies Ltd documentation, with permission. 

The microsphere plate offers some advantages over the microchannel plate. It is less expensive and its gain of 106-107 is higher. This higher amplification is due to the fact that nearly the entire surface of the input side is active and therefore emits secondary electrons that will be accelerated onto and through the plate to give the final signal. In comparison, the surface of the microchannel plate between the microchannels, which corresponds to about 50 % of the entire surface, is inactive. 

Porous (2) Packed bed Perforated plates stacked meshes, cloths, felts, foams Granules and flakes, microspheres, spheroids, fibers, rods, Raschig rings... 

Scanning Electron Microscope (SEM) examination was used to confirm that palladium did fill the inside of the PWHGMs. A sample of the filled and reduced microspheres was mounted on a sample stage and examined with the SEM. Micrographs were taken to record the appearances and locations of the individual microspheres. The same sample was then removed from the SEM and the microspheres cracked open to reveal their interior before the sample was put back into the SEM for further examination. The cracking was done by pressing the mounted sample with a metal plate using the... 

Fig. 8. Concentration dependence of ultrasound backscatter signal by plates coated with a layer of targeted microbubbles. Surface concentrations of microbubbles (as observed by bright-field optical microscopy, bottom) increase from left to right. Imaging performed using a fundamental frequency scheme. Samples placed on top of an ultrasound tissue phantom. Reprinted from Advanced Drug Delivery Reviews v. 37, A.L. Klibanov, Targeted delivery of gas-filled microspheres, contrast agents for ultrasound imaging, p. 145. Copyright, 1999, with permission from Elsevier Science...

The performance of a micro structured plate and fin heat exchanger (0.25 dm3 reactor volume), wash coated with 2.0 g of catalyst, was assessed in comparison with similar alternative technologies by Dudfield et al. [88], The first was a shell and tube heat exchanger filled with 4.66 g of catalyst microspheres (0.25 dm3 reactor... 

In another approach, ultrasonic acoustic flexural plate waves (or Lamb waves) were used to generate fluid mixing motion of microspheres in water in a Si device. A 10-pm-thick piezoelectric ZnO film was deposited on the back side of a Si wafer (see Figure 3.48). This thickness is an odd-multiple of the acoustic half-... 

Nakamura et al. ° studied the adhesion of water-soluble and neutral polymers, hydroxypropyl cellulose (HPC), xanthan gum (XG), tamarind gum (TG), and polyvinyl alcohol (PVA) to nasal mucosa in vitro and in vivo. The polymers, mixed with a dye, were applied as powders to the nasal cavity of rabbits, and the remaining dye residue was determined at 2, 4, and 6 h after nasal instillation with a thin fiberscope. The polymer XG showed the longest residence time of the dye in the cavity, followed by TG, HPC, and PVA in decreasing order. For the mixture XG and XG-PVA (2 8), some residue of dye could still be observed 6h after administration. The order of adhesion of these polymers to agar plates in vitro agreed with that of their mucoadhesion in vivo. Ilium et al. introduced bioadhesive microspheres for nasal delivery of poorly absorbable drugs. Radiolabelled microspheres made from diethylaminoethyl (DEAE)-dextran, starch microspheres, and albumin microspheres were administered to human volunteers and appeared to be cleared significantly slower than solutions or... 

Standard approaches with HPTLC in research and development are usually based on the former TLC methods developed for older products. Unfortunately, these official methods (pharmacopoeias or associations of analytical chemistry) were based on TLC plates and material. The development of HPTLC material (100- or 200-jam-thick plates, microspheres of 5 /im, etc.) should improve many of these methods as far as duration of elution, resolution, and quantification are concerned. Therefore, older methods may have to be completely reviewed before being fuUy adapted to newer techniques. 

Figure 1. Schematic of the parallel-plate plasma coater showing the location of the vibrating pan used to agitate the glass microspheres.

Table 4.1. Effect of glass microspheres on performance of positive plates [1].

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