Disk rotation speed

With disk diameters above 5.25 in., all parameters, eg, water absorption and thermal expansion, become more critical which aggravates the expansion or warp of disks. If in the future disk rotation speeds have to be increased significantly to boost data transfer rates, higher demands will be placed on warp (tilt angle) and modulus to avoid creeping (ie, irreversible elongation in radial direction). A survey of the requirement profile for the substrate material of optical disks is given in Table 5 (182,186,187,189). 

Therefore, the final equation is relatively simple despite the fact that the derivation is complex. Equation (145) shows that the intrinsic dissolution rate depends on the diffusion coefficient and solubility of the drug, disk rotational speed, and the viscosity of the dissolution medium. The amount of drug dissolving per unit area is the same everywhere on the disk s surface. This makes the disk a powerful experimental tool in drug discovery and development. 

Objective function. The objective function is to maximize the total extraction rate for constant disk rotation speed subject to the inequality and equality constraints ... 

The mass transfer boundary layer thickness, d, on a rotating disk electrode can be estimated by d = 1.6/J V a) where D is the substrate diffusion coefficient, v is the solution viscosity, and CO is the disk rotation speed. 

Figures 1 through 4 illustrate the effect of Hamaker s constant, disk rotation speed, ionic strength, surface potentials, and particle radius on the rate of deposition of particles onto a rotating disk as computed from Eqs. [lj and [23. For this set of figures, the interaction energy profiles (%) were evaluated from Eqs. 41 5], and 9].

Electrochemical dissolution depends on many factors such as applied anode potential, electrolyte, temperature, interelectrode distance, disk rotation speed. 

The rotating disk electrode, described in Section 11.6, has the advantage that the fluid flow is well defined emd that the system is compact and simple to use. The rotation of the disk imposes a centrifugal flow that in turn causes a radially uniform flow toward the disk. If the reaction on the disk is mass-transfer controlled, the associated current density is imiform, which greatly simplifies the mathematical description. As discussed in sections 5.6.1 and 8.1.3, the current distribution below the mass-transfer-limited current is not uniform. The distribution of current and potential associated with the disk geometry has been demonstrated to cause a frequency dispersion in impedance results. The rotating disk is therefore ideally suited for experiments in which the disk rotation speed is modulated while im-der the mass-transfer limited condition. Such experiments yield another t)q)e of impedance known as the electrohydrodynamic impedance, discussed in Chapter 15. 

The techniques presented here each involve analysis of data collected as a function of a system parameter such as temperature, potential, or disk rotation speed. 

Graphical methods can be used to extract information concerning mass transfer if the data are collected under well-controlled hydrodynamic conditions. The systems described in Chapter 11 that are imiformly accessible with respect to convective diffusion would be appropriate. The analysis would apply to data collected on a rotating disk electrode as a function of disk rotation speed, or an impinging jet as a function of jet velocity. 

FIGURE 26.25 Composition of a NiFe film plated on a rotating disk electrode as a function of the total plating current for different disk rotation speeds at 25°C. Solution composition was 0.2 M NiCl2, 0.4 M H3BO3, and 0.5 M NaCl (pH = 3). Data from [106]. (Reproduced by permission of ECS—The Electrochemical Society.)... 

Fig. 111.18. Apparatus for application of dust to plates (1) frame (2) electric motor (3) disk for plates (4) plates (5) rubber membrane (6) bell jar (7) screen (8) transformer for adjusting disk rotating speed (9) rubber tube with bulb.

On some devices, it is possible for the sample holder to rotate in either the same direction as the disk or in the opposite direction. These modes are referred to as complementary rotation and counterrotation, respectively. Counterrotation yields a higher removal rate, which can be especially advantageous in planar grinding. With complementary rotation, a mediiun disk rotational speed (150-200 rpm) will allow the surface to be processed gently and uniformly. For this reason, the use of complementary rotation predominates. 

Like the CD-ROM drives, the CD-R drives have relatively low performance (when compared with optical or hard drives). The seek times are on the order of a few hundred miUiseconds, whereas the maximum data rate for a 4X speed drive is about 600 kilobytes/s. The seek time is slow because the CD-R drives spin the disks in constant linear velocity (CLV) mode as defined in the Red Book standards. Constant linear velocity means that the disk rotation speed varies with the radius at which the read head is positioned in such a way as to ensure that the linear velocity is constant with radius. 

Repetition rate (Hz) Disk rotation speed (m/ s) Laser beam size (pm) X-ray beam size (pm) Number of repetition for one disk... 

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