Optical method

Several other non-optical methods have been described in the literature.  

Optical Methods. Optical methods may conveniently be considered in three categories, (a) Methods suitable up to 10 to 20 MPa in which the coexisting liquid and vapour phases at predetermined pressures and temperatures are analysed. Such methods combine the advantages of the optical and analytical methods, (b) Methods suitable up to 10 to 20 MPa in which the composition of the mixture studied is controlled by the filling of the cell at the outset of the experiment, (c) Methods suitable for high-pressure studies above 10 MPa in which the composition of the mixture studied is controlled by the filling of the cell at the outset of the experiment. Such methods are suitable for studying either or both liquid-liquid or so-called gas-gas immiscibility. 

McCurdy and Katz have described a simple visual cell for measuring vapour-liquid equilibrium. The equilibrium cell had a volume of 92 cm , was fitted with double glass windows and could be rocked to agitate the fluid phases and thus bring them into equilibrium. The sample was confined over mercury. To sample the gas phase, mercury was driven into the cell at the bottom at the same rate as gas sample was removed from the top. The liquid phase was sampled by completely removing the vapour sample and then the liquid sample by injection of mercury into the bottom of the cell. The gas and liquid samples were analysed by chemical gas absorption methods. 

Roof and co-workers have designed a pressure vessel which has internal windows. Basically the vessel consists of thick-walled glass tube of about 1 cm internal diameter contained in a metal cell. The sample is confined in an annular space between the outside of the glass tube and the metal cell. The contents of the cell are viewed by a periscope which can be moved up and down inside the glass tube. The design is attractive in that it enables visual observation at pressures up to 50 to 60 MPa without the need for carefully ground optical 

Most optical cells for studying phase behaviour at pressures in excess of 10 MPa do not use glass for the optical portion. While glass capillary tubes can 

In the following, various optical methods will be described along with discussions of their capabilities and limitations. 

A holographic method is basically a two-step imaging process that captures in permanent form the sizes and locations of 

It is also feasible to measure both droplet size and velocity simultaneously with the holographic method. Such a measurement system has been developed by Murakami and Ishikawa. 65()l They used two pulse lasers of different wavelengths to record two holograms on two different films, separated by an appropriate time interval. The displacements of moving particles were measured on a superimposed picture of the two films to determine the velocities of the particles. 

In the large off-axis light scatter detection method, the droplet size can be related, for example, to the phase shift of the light scattered by refraction in the off-axis forward direction as  

Phase-Doppler Anemometry. Theoretical analyses on dualbeam light scattering with off-axis detection 670 showed that the spatial frequency of the scattered interference fringe pattern is 

Labelling with an enzyme that catalyses chemiluminescent reactions gives rise to signals that can be detected optically with the help of an 

In fluorescence microscopy (FM) a small amount of a fluorescent dye is added to the mono-layer. To be incorporated into the monolayer the dye must be amphiphilic. The film is illuminated and the lateral distribution of the fluorescent molecules is observed with an optical microscope [589], Depending on the phase condition of the monolayer, the fluorescent molecules distribute unevenly or have a different quantum yield. Usually the dyes are expelled from condensed liquid and solid phases. With this technique the coexistence of different phases in monolayers on water was demonstrated for the first time [590,591], 

Example 13.3 demonstrates that phospholipids can form domains of distinct two-dimensional shapes on liquid surfaces. It has been found that the domain shape mainly depends on the chemical composition of the monolayer and the conditions such as temperature, pH, and ionic concentration. Domain structures can usually be understood by taking two competing interactions into account an attractive dispersive van der Waals force and a repulsive dipole-dipole 

The presence of undissolved gas and of cavitation bubbles affects the transparency and refractive index of a liquid. Thus when a sonicated liquid is irradiated with light, X-rays, y-rays, or even high-frequency ultrasound, the attenuation and (or) refraction of the wave can be used to detect both the cavitation threshold and bubble density, and their variation with time. This is possible even within a very short period of the order of one ultrasonic cycle [138,139]. 

These methods have several advantages over the methods previously described including (a) the absence of distortions of the ultrasonic field which might be engendered by an invasive probe system (b) they can be used in a wide range of frequency and ultrasonic power, below or above the cavitation threshold and (c) they can even be used with solid materials by studying the reflected beam at the surface of the material [140]. 

The main drawback to systems which use optical methodologies is that they require somewhat sophisticated equipment and a complex mathematical treatment of the data [141], Naturally they also require that a transparent pathway is available through the walls of the sonicated cell and that the medium itself should be transparent to the diffracted wave. 

Observation of the Cherenkov radiation from irradiated reactor fuel assemblies is used to obtain qualitative confirmation (attribute testing) of the presence of spent fuel in storage by scanning rows of assemblies from the pool bridge. Characteristic patterns formed by the arrangements of rods and holes in fuel assemblies have to be observed to ensure a valid verification. A well-trained inspector can easily detect the presence of an inactive dummy assembly surrounded by highly active neighbors. 

ICVD cannot be used when fuel is stored in canisters. Furthermore, absorption and reflection of the Cherenkov light caused by additives or particles in the water and its turbulence in spent fuel ponds may result in failure to verify the spent fuel. It is also difficult to see fuel assemblies that are double-stacked in the storage pool. 

The optical fiber radiation probe system (OFPS) is used to verify irradiated bundles in the spent fuel bay of CANDU stations (Rim et al. 2006). The OFPS consists of a scanning actuator, an optical fiber scintillator coupled to a flexible optical liber, data acquisition electronics, and a PC. 

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Often industry requires fast techniques to measure movements, deformations, etc. The optics methods, between them those based in speckle K gives quick solutions to this problems. 

Optical Methods for On Line Surface Wire Testing. 

The exact values of E and 5E / 5n are in general unknown and the Kirchhoff or physical optics method consists in approximating the values of these two quantities on the surface and then evaluating the Helmholtz integral. We shall approximate the field at any point of the surface by the field that would be present on a tangent plane at the point. With this approximation, the field on the surface and its normal derivative are... 

We present two optical methods for characterizing wire surfaces. These methods allow us to measure the roughness and the correlation length of the surface. It is also possible to identify qualitatively, at a glance, the variations of the roughness along a wire or among its different zones. 

The absolute measurement of the distance, D, between the surfaces is central to the SFA teclmique. In interferometric SFAs, it is realized tluough an optical method called multiple beam interferometry (MBI), which has been described by Tolansky [47]. 

B1.22 Surface characterization and structural determination optical methods... 

The first half of this section discusses the use of the crossed beams method for the study of reactive scattering, while the second half describes the application of laser-based spectroscopic metliods, including laser-mduced fluorescence and several other laser-based optical detection teclmiques. Furtlier discussion of both non-optical and optical methods for the study of chemical reaction dynamics can be found in articles by Lee [8] and Dagdigian [9]. 

The most widely employed optical method for the study of chemical reaction dynamics has been laser-induced fluorescence. This detection scheme is schematically illustrated in the left-hand side of figure B2.3.8. A tunable laser is scanned tlnough an electronic band system of the molecule, while the fluorescence emission is detected. This maps out an action spectrum that can be used to detemiine the relative concentrations of the various vibration-rotation levels of the molecule. 

Dagdigian P J 1988 Reactive scattering II optical methods Atomic and Molecular Beam Methods vol 1, ed G Scoles et al (New York Oxford University Press) pp 596-629... 

Some of the most interesting recent work in the optical properties of nanocrystals involves the study of single nanocrystals rather than ensembles, using near-field optical teclmiques. These relatively new optical methods can... 

Even though the rates of initiation span almost a 10-fold range, the values of k, show a standard deviation of only 4%, which is excellent in view of experimental errors. Note that the rotating sector method can be used in high-pressure experiments and other unusual situations, a characteristic it shares with many optical methods in chemistry. 

We can imagine measuring experimental curves equivalent to those in Fig. 9.11 by, say, scanning the length of the diffusion apparatus by some optical method for analysis after a known diffusion time. Such results are then interpreted by rewriting Eq. (9.85) in the form of the normal distribution function, P(z) dz. This is accomplished by defining a parameter z such that... 

The most recent approach to reductive nanofabrication that can indeed constmct nanoscale stmctures and devices uses microscopic tools (local probes) that can build the stmctures atom by atom, or molecule by molecule. Optical methods using laser cooling (optical molasses) are also being developed to manipulate nanoscale stmctures. 

Analysis of Surface Molecular Composition. Information about the molecular composition of the surface or interface may also be of interest. A variety of methods for elucidating the nature of the molecules that exist on a surface or within an interface exist. Techniques based on vibrational spectroscopy of molecules are the most common and include the electron-based method of high resolution electron energy loss spectroscopy (hreels), and the optical methods of ftir and Raman spectroscopy. These tools are tremendously powerful methods of analysis because not only does a molecule possess vibrational modes which are signatures of that molecule, but the energies of molecular vibrations are extremely sensitive to the chemical environment in which a molecule is found. Thus, these methods direcdy provide information about the chemistry of the surface or interface through the vibrations of molecules contained on the surface or within the interface. 

Chemical Gas Detection. Spectral identification of gases in industrial processing and atmospheric contamination is becoming an important tool for process control and monitoring of air quaUty. The present optical method uses the ftir (Fourier transform infrared) interference spectrometer having high resolution (<1 cm ) capabiUty and excellent sensitivity (few ppb) with the use of cooled MCT (mercury—cadmium—teUuride) (2) detectors. 

Optics. Good optical properties and low thermal resistance make poly(methyl methacrylate) polymers well suited for use as plastic optical fibers. The manufacturing methods and optical properties of the fibers have been reviewed (124) (see Fiber optics). Methods for the preparation of Fresnel lenses and a Fresnel lens film have been reported (125,126). Compositions and methods for the industrial production of cast plastic eyeglass lenses are available (127). 

In spectroscopic analysis, species are identified by the frequencies and stmctures of absorption, emission, or scatteting features, and quantified by the iatensities of these features. The many appHcations of optical methods to chemical analysis rely on just a few basic mechanisms of light—matter iateraction. 

I. M. Kolthoff, P. J. Elving, and E. J. Meehan, Optical Methods ofMnaljsis, Vol. 8, Treatise on Analytical Chemisty, Part I, John Wiley Sons, Inc., New York, 1986. 

The reduction of dimensions also reduces volumes which are accessible to the detector. Thus, detection principles related to geometric dimensions of the detector cell ai e not ideally suited for coupling to microsystems, whereas surface sensitive principles, such as electrochemical methods or optical methods utilizing the evanescent field of a waveguide, or methods which can be focussed on a small amount of liquid, such as electrochemiluminescence (ECE), ai e better suited. This is why electrochemiluminescence detectors ai e combined to microsystems. Moreover ECE has found wide applications in biochemistry because of its high sensitivity, relatively simplicity and feasibility under mild conditions. 

Magnesium anodes are usually built into the object to be protected through isolating sockets or holes (see Fig. 20-6) and joined to them with cables. They must be readily accessible and easily exchangeable for convenient control [4]. The directions for use have to indicate the necessity for an inspection after 2 years of operation. During operation, control can be exercised by electrical measurements (current, resistance). In addition, acoustic and optical methods exist to determine the amount of anode consumption [4]. The life of the anodes is usually more than 5 years (see Section 6.6). 

List the advantages and disadvantages of remote sensing techniques by optical methods. 

Basically, the optical method uses equipment such as alignment telescopes, jig transits, and sight levels. Instruments with built-in optical micrometers for measuring displacements from a referenced line of sight enable an accurate determination of target movements, which are mounted on the machine. 

For SFM, maintaining a constant separation between the tip and the sample means that the deflection of the cantilever must be measured accurately. The first SFM used an STM tip to tunnel to the back of the cantilever to measure its vertical deflection. However, this technique was sensitive to contaminants on the cantilever." Optical methods proved more reliable. The most common method for monitoring the defection is with an optical-lever or beam-bounce detection system. In this scheme, light from a laser diode is reflected from the back of the cantilever into a position-sensitive photodiode. A given cantilever deflection will then correspond to a specific position of the laser beam on the position-sensitive photodiode. Because the position-sensitive photodiode is very sensitive (about 0.1 A), the vertical resolution of SFM is sub-A. 

Band gaps in semiconductors can be investigated by other optical methods, such as photoluminescence, cathodoluminescence, photoluminescence excitation spectroscopy, absorption, spectral ellipsometry, photocurrent spectroscopy, and resonant Raman spectroscopy. Photoluminescence and cathodoluminescence involve an emission process and hence can be used to evaluate only features near the fundamental band gap. The other methods are related to the absorption process or its derivative (resonant Raman scattering). Most of these methods require cryogenic temperatures. 

Independent of depth profiling considerations, SNMS provides a powerful bulk analysis method that is sensitive and accurate for all elements, from major to trace element levels. Since SNMS is universally sensitive, it offers obvious advantages over elementally selective optical methods. 

Inductively Coupled Plasma-Optical (ICP-optical) methods and ICPMS are extremely sensitive elemental survey techniques that also are described in this volume. ICP methods, however, require a solution for analysis, so that the direct... 

From a practical sense, MOKE is a versatile technique it is an optical method the polarization measurement is fairly easy to do the necessary optical components are common and relatively inexpensive and it has no intrinsic vacuum requirements. 

The number of measurable layers of a stack is limited only by the optical contrast between the different layers. In practice stacks of ten layers and more can be analyzed by ellipsometry. Further advantages of ellipsometry compared with other metrological methods are the non-invasive and non-destructive character of the optical method, the low energy entry into the sample, the direct measurement of the dielectric function of materials, and the possibility of making the measurement in any kind of optical transparent environment. 

In view of this apparent contradictory outcome from the transport and magnetic properties, we were motivated to investigate the dynamics of the charge excitation spectrum by optical methods. In fact, the optical measurement is a powerful contactless experimental tool which should in principle allow to unfold the disagreement between and p(7 since the optical response of a metal... 

A. Kastler (Paris) discovery and development of optical methods for studying hertzian resonances in atoms. 

Draw ratio X-ray method IR spectroscopy method Absorption Absorption band 898 band 1368 cm cm Optical method Fluorescent polarization method D R S D F method s... 

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