Parallel interfaces

The thickness of thin film layers separated by uniform, parallel interfaces can be determined from optical interference patterns that result. These measurements can be made from about 400 nm out through the visible spectrum and on into the near-infrared (NIR) region. Since film thickness measurements rely not on the absolnte magnitude of the reflected light, but on the variation of that signal with wavelength, the choice of nnits is less important. Typically %R is used, but in some cases raw intensity is also satisfactory. We will treat thickness determinations in more detail in the applications section of this chapter. 

When two emulsion drops or foam bubbles approach each other, they hydrodynamically interact which generally results in the formation of a dimple [10,11]. After the dimple moves out, a thick lamella with parallel interfaces forms. If the continuous phase (i.e., the film phase) contains only surface active components at relatively low concentrations (not more than a few times their critical micellar concentration), the thick lamella thins on continually (see Fig. 6, left side). During continuous thinning, the film generally reaches a critical thickness where it either ruptures or black spots appear in it and then, by the expansion of these black spots, it transforms into a very thin film, which is either a common black (10-30 nm) or a Newton black film (5-10 nm). The thickness of the common black film depends on the capillary pressure and salt concentration [8]. This film drainage mechanism has been studied by several researchers [8,10-12] and it has been found that the classical DLVO theory of dispersion stability [13,14] can be qualitatively applied to it by taking into account the electrostatic, van der Waals and steric interactions between the film interfaces [8]. 

At this point, both in the case of coherent [(2.8) and (2.9)] and incoherent [(2.11) and (2.12)] 1Z and T spectra, numerical inversion of the corresponding equations delivers n if the thickness is known. The model is easily extended to several flat and parallel interfaces, as in the case of a multilayer deposited on a substrate [21,22], In this case, as the thickness of the layers and h for the substrate are known, numerical inversion of the corresponding equations yields n for the unknown layer [38-41]. The critical feature of this procedure is the accurate determination of the thickness (tens to hundreds of nanometres) of the different layers. This is what limits uncertainty in the determination of n. 

The deviations from parallel interfaces induced by the roughness were calculated in the manner illustrated in the inlet of Fig. 4 the tangent of the inclination angle is equal to the first derivative of the geometrical profile z = z(x), where z is the vertical coordinate and x the lateral one. The total deviation S from parallel surfaces, defined as the difference between the inclination angle of the upper and the lower interface (5 = c+pper — (flower), turned out to be smaller than one degree, which assured practically uniform electrical fields between the electrodes. 

Fig. 4 Angle of deviation S from parallel interfaces. Inlet, the calculation of the inclination angle a from the measured geometrical profile...

Two-way parallel interfaces. These involve a two-way dynamic transfer of information between two simulations running in parallel at two different modelling levels. An example includes running both an MM and CG simulation of a system and using replica exchange ° moves to exchange coordinates between the two levels. 

If you ve ever used a really fast disk drive, you know that the Commodore 1541 drive leaves something to be desired— namely, speed. True, it s much faster than a normal Datassette, but it s still annoyingly slow compared with other floppy disk drives with high-speed parallel interfaces. 

The most popular type of interface available on computers today is the parallel interface. Parallel communications take the interstate approach to data communications. Everyone knows that interstate travel is faster, normally. This is mainly because you can fit multiple cars going the same direction on the same highway by using multiple lanes. On the return trip, you take a similar path, but on a completely separate road. The parallel interface (an example of one is shown in Figure 2.20) transfers data eight bits at a time over eight separate transmit wires inside a parallel cable (one bit per wire). Normal parallel interfaces use a DB-25 female connector on the computer to transfer data to peripherals. 

The most common use of the parallel interface is printer communication, and there are three major types standard, bidirectional, and enhanced parallel ports. Let s look at the differences between the three. 

Centronics parallel interface A standard 36-pin interface in the PC world for the exchange of information between the PC and a peripheral, such as a printer, originally developed by the printer manufacturer Centronics, Inc. The standard defines eight parallel data lines, plus additional lines for status and control information. 

SCSI Acronym for small computer system interface. A high-speed, system-level parallel interface defined by the ANSI X3T9.2 committee. SCSI is used to connect a personal computer to several peripheral devices using just one port. Devices connected in this way are said to be daisy-chained together, and each device must have a unique identifier or priority number. 

There are various cases of particle-interface interactions, which require separate theoretical treatment. The simpler case is the hydrodynamic interaction of a solid particle with a solid interface. Other cases are the interactions of fluid particles (of tangentially mobile or immobile interfaces) with a solid surface in these cases, the hydrodynamic interaction is accompanied by deformation of the particle. On the other hand, the colloidal particles (both solid and fluid) may hydrodynamically interact with a fluid interface, which thereby undergoes a deformation. In the case of fluid interfaces, the effects of surfactant adsorption, surface diffusivity, and viscosity affect the hydrodynamic interactions. A special class of problems concerns particles attached to an interface, which are moving throughout the interface. Another class of problems is related to the case when colloidal particles are confined in a restricted space within a narrow cylindrical channel or between two parallel interfaces (solid and/or fluid) in the latter case, the particles interact simultaneously with both film surfaces. 

Reflectivity from a System with Two Parallel Interfaces... 

Fig. 11.20 (a) Analogue section of an automated PSA Instrument. The operational amplifiers are NS LF 336. The digital panel meter and the differentiating amplifier are optional, (b) Block diagram of the instrument. PI, parallel interface IRQ, interrupt request. Only 4 kb worth of the PROH capacity is used. Bus transceivers are not shown. (Reproduced from [95] with permission of Elsevier). 

Suppose that there are two parallel interfaces which divide a space into three parts as shown in Fig. 5.1. The vertical magnetic dipole is placed at the origin of the cylindrical system of coordinates and its moment is oriented along the z-axis. 

To make calculations more efficient, the particle codes are usually run on multiprocessor systems in broad variety of computer architectures and parallel interfaces. In this section, we present basic issues exploited in construction of a typical discrete-particle code based on the FPM. 

Time-distance graphs for a theoretical single-layer problem, with parallel interface. With non-parallel interfaces, both forward and reverse profiles must be surveyed. 

The constructive interference found for the reflection of light from plane-parallel interfaces between two regions with different refractive indices can be utilized to produce highly reflecting, essentially absorption-free mirrors. The improved technology of such dielectric mirrors has greatly supported the development of visible and ultraviolet laser systems. 

The use of a serial data interface reduees the number of required FPGA pins and inereases signal integrity. For instance, the number of FPGA pins required is reduced by a faetor of 16 for each transmitting channel by using a serial interface DAC rather than a 16-bit parallel interface DAC. The characteristics of the serial and parallel interfaces are compared in Table 1. 

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