Physics Measurements

Studies of Subcritical Lattices with Distributed Neutron Absorber by Means of the Pulsed-Neutron Source Technique / Hettry E. Bliss, D. D, Lammtg, Joseph Harrington, I. Kaplan, B. K. Malaviya, T. J. Thompson (MIT) 

Pulsed neutron measurements have been made on sub-crttlcal uranium heavy-water lattices with and without distributed neutron absorbers leading to a determination of the amount of absorber necessary to reduce the prompt infinite multiplication factor to unity. A value of I , has also been obtained for each lattice studied. 

The prompt-neutron fundamental-mode decay constant for a bare, homc eneous. multiplying medium can be expressed in terms of the medium s nuclear parameters  

Value of k and the Leaat-Squares Coetficlenta m. n and q In Subcritical Lattices With and Without Absorber 

An initial set of experiments has been performed in the MIT Lattice Facility on a lattice consisting of 0.25-In.-diara, 1.143% enriched-uranium metal rods located on a 2.50-in. triangular pitch and immersed in 99.50 mole% heavy water. Copper in the form of thin rods served as a thermal absorber. Three lattices were studied, 1) the clean core with no copper, 2) a lattice with one 0.144-in.-diam copper rod per fuel rod, and 3) a lattice with two such rods per fuel rod. 

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Now let us use the wavepackets just discussed to extract the physically measurable infomration about our problem, namely, the probabilities of reflection and transmission. As long as the wavepackets do not spread much during the collision, these probabilities are given by the general definition ... 

Note that the sums are restricted to the portion of the frill S matrix that describes reaction (or the specific reactive process that is of interest). It is clear from this definition that the CRP is a highly averaged property where there is no infomiation about individual quantum states, so it is of interest to develop methods that detemiine this probability directly from the Scln-ddinger equation rather than indirectly from the scattering matrix. In this section we first show how the CRP is related to the physically measurable rate constant, and then we discuss some rigorous and approximate methods for directly detennining the CRP. Much of this discussion is adapted from Miller and coworkers [44, 45]. 

The presence of the half-odd quantum number j in Eq. (69) is potentially a physically measurable consequence of geomehic phase, which was first claimed to have been detected in the spectrum of Naa [16]. The situation is, however, quite complicated and the first unambiguous evidence for geometric phase in Nas was reported only in 1999 [17],... 

Data any observation provides data, which could be the result of a physical measurement, a yes/no answer to whether a reaction occurs or not, or the determination of a biological activity. 

Quantum Mechanics Describes Matter in Terms of Wavefunctions and Energy Levels. Physical Measurements are Described in Terms of Operators Acting on Wavefunctions... 

Each physically measurable quantity has a corresponding operator. The eigenvalues of the operator tell the values of the corresponding physical property that can be observed... 

Quantum mechanics has a set of rules that link operators, wavefunctions, and eigenvalues to physically measurable properties. These rules have been formulated not in some arbitrary manner nor by derivation from some higher subject. Rather, the rules were designed to allow quantum mechanics to mimic the experimentally observed facts as revealed in mother nature s data. The extent to which these rules seem difficult to... 

Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN. The specific gravity of iridium is only very slightly lower than osmium, which is generally credited as the heaviest known element. Calculations of the densities of iridium and osmium from the space lattices give values of 22.65 and 22.61 g/cm 3, respectively. These values may be more reliable than actual physical measurements. At present, therefore, we know that either iridium or osmium is the densest known element, but the data do not yet allow selection between the two. 

Until this time alkyl cations were considered only transient species. Their existence had been indirectly inferred from kinetic and stereochemical studies, but no reliable spectroscopic or other physical measurements of simple alkyl cations in solution or in the solid state were obtained. 

Molecular nitric acid is the main species present in this medium, but physical measurements demonstrate the existence of significant concentrations of other species. 

Measurements usually consist of a unit and a number expressing the quantity of that unit. Unfortunately, many different units may be used to express the same physical measurement. For example, the mass of a sample weighing 1.5 g also may be expressed as 0.0033 lb or 0.053 oz. For consistency, and to avoid confusion, scientists use a common set of fundamental units, several of which are listed in Table 2.1. These units are called SI units after the Systeme International d Unites. Other measurements are defined using these fundamental SI units. For example, we measure the quantity of heat produced during a chemical reaction in joules, (J), where... 

Ultrasonic Microhardness. A new microhardness test using ultrasonic vibrations has been developed and offers some advantages over conventional microhardness tests that rely on physical measurement of the remaining indentation size (6). The ultrasonic method uses the DPH diamond indenter under a constant load of 7.8 N (800 gf) or less. The hardness number is derived from a comparison of the natural frequency of the diamond indenter when free or loaded. Knowledge of the modulus of elasticity of the material under test and a smooth surface finish is required. The technique is fast and direct-reading, making it useful for production testing of similarly shaped parts. 

The PLM can be used in a reflection or a transmission mode. With either mode, light of various wavelengths from ultraviolet to infrared, polarized or unpolarized, is used to yield a wide variety of physical measurements. With just ordinary white light, a particle or any object detail down to about 0.5 p.m (500 nm) in diameter can be observed to detect shape, size, color, refractive index, melting point, and solubiUty in a group of solvents, all nondestmetively. Somewhat larger particles yield UV, visible, or IR absorption spectra. 

In Vivo Biosensing. In vivo biosensing involves the use of a sensitive probe to make chemical and physical measurements in living, functioning systems (60—62). Thus it is no longer necessary to decapitate an animal in order to study its brain. Rather, an electrochemical biosensor is employed to monitor interceUular or intraceUular events. These probes must be small, fast, sensitive, selective, stable, mgged, and have a linear response. 

Pressure is defined as force per unit of area. The International System of Units (SI) pressure unit is the pascal (Pa), defined as 1.0 N /m. Conversion factors from non-SI units to pascal are given in Table 1 (see also Units and conversion factors front matter). An asterisk after the sixth decimal place indicates that the conversion factor is exact and all subsequent digits are 2ero. Relationships that are not followed by an asterisk are either the results of physical measurements or are only approximate. The factors are written as numbers greater than 1 and less than 10, with 6 or fewer decimal places (1). 

Future Trends. Methods of laser cooling and trapping are emerging as of the mid-1990s that have potential new analytical uses. Many of the analytical laser spectroscopies discussed herein were first employed for precise physical measurements in basic research. AppHcations to analytical chemistry occurred as secondary developments from 10 to 15 years later. 

C2S2, is a red Hquid (mp —0.5° C, bp 60—70°C at 1.6 kPa (12 mm Hg)) produced by the action of an electric arc on carbon disulfide (1 4). The stmcture has been shown to be S=C=C=C=S on the basis of its reactions to form malonic acid derivatives and on the basis of physical measurements. It is unstable and decomposes ia a few weeks at room temperature it decomposes explosively when heated rapidly at 100—120°C with formation of a black polymeric substance (C2S2) (5,6). Dilute solutions ia CS2 are fairly stable, but photochemical polymerisation to (C2S2) occurs. 

Several requirements must be met in developing a stmcture. Not only must elementary analysis and other physical measurements be consistent, but limitations of stmctural organic chemistry and stereochemistry must also be satisfied. Mathematical expressions have been developed to test the consistency of any given set of parameters used to describe the molecular stmcture of coal and analyses of this type have been reported (4,6,19,20,29,30). 

The other physical measurements (4,6), except for diamagnetic susceptibiUty (4) and possibly density (4), are primarily of interest for determining chemical stmctural properties of coal. 

Zinc coatings are covered by an ASTM specification (143). Because of the varying purity of 2inc deposits from chloride and 2incate baths, some thickness measuring methods can vary considerably (39). Methods based on physical measurement of magnetic methods (144,145) are used for best accuracy. 

There are also physical measurements that can give evidence of aromaticity. The... 

It would be worthwhile making theoretical calculations to evaluate the effect of defects on the nanotube properties. The chemistry might be affected, although to a lesser degree because nanotubes, like graphite, are chemically quite inert. If at all possible, nanotubes should be annealed (if not also purified) before physical measurements are made. Only then are the results likely to be consistent and unambiguous. 

The only statistical techniques which need control are those used to determine the acceptability of a product or service or the capability of a process that produces the product or service. Any activity where you rely on statistical evidence rather than physical measurement is an activity which should be governed by these requirements. The use of recognized techniques is important to the confidence one has in the result. It is similar to the use of measuring equipment that has been calibrated against known standards of accuracy. Unless you actually check every product, measure every attribute or variable you cannot be 100% certain. But that is costly and you can be 99.99% certain by using statistical techniques 99.99% may be sufficiently accurate for your needs. 

In Section 2.2, the stress-strain relations (generalized Hooke s law) for anisotropic and orthotropic as well as isotropic materials are discussed. These relations have two commonly accepted manners of expression compliances and stiffnesses as coefficients (elastic constants) of the stress-strain relations. The most attractive form of the stress-strain relations for orthotropic materials involves the engineering constants described in Section 2.3. The engineering constants are particularly helpful in describing composite material behavior because they are defined by the use of very obvious and simple physical measurements. Restrictions in the form of bounds are derived for the elastic constants in Section 2.4. These restrictions are useful in understanding the unusual behavior of composite materials relative to conventional isotropic materials. Attention is focused in Section 2.5 on stress-strain relations for an orthotropic material under plane stress conditions, the most common use of a composite lamina. These stress-strain relations are transformed in Section 2.6 to coordinate systems that are not aligned with the principal material... 

Chemical kinetics involves the study of reaction rates and the variables tliat affect these rates. It is a topic that is critical for the analysis of reacting systems. The objective in tliis sub-section is to develop a working understanding of tliis subject that will penuit us to apply chemical kinetics principles in tlie tu ea of safety. The topic is treated from an engineering point of view, tliat is, in temis of physically measurable quantities. 

Once an approximation to the wavefunction of a molecule has been found, it can be used to calculate the probable result of many physical measurements and hence to predict properties such as a molecular hexadecapole moment or the electric field gradient at a quadrupolar nucleus. For many workers in the field, this is the primary objective for performing quantum-mechanical calculations. But from... 

Many of the properties oj -hydroxypyridines are typical of phenols. It was long assumed that they existed exclusively in the hydroxy form, and early physical measurements seemed to confirm this. For example, the ultraviolet spectrum of a methanolic solution of 3-hydroxypyridine is very similar to that of the 3-methoxy analog, and the value of the dipole moment of 3-hydroxypyridine obtained in dioxane indicates little, if any, zwitterion formation. However, it has now become clear that the hydroxy form is greatly predominant only in solvents of low dielectric constant. Comparison of the pK values of 3-hydroxypyridine with those of the alternative methylated forms indicated that the two tautomeric forms are of comparable stability in aqueous solution (Table II), and this was confirmed using ultraviolet spectroscopy. The ratios calculated from the ultraviolet spectral data are in good agreement with those de-... 

Various physical measurements yield data from which one can... 

Quinoxalin-2 one (70) is in mobile tautomeric equilibrium with 2-hydroxyquinoxaline (71), but physical measurements fail to demonstrate the presence of the hydroxy form (see following). 

Quinoxalin-2-ones are in tautomeric equilibrium with 2-hydroxy-quinoxalines, but physical measurements indicate that both in solution and in the solid state they exist as cyclic amides rather than as hydroxy compounds. Thus quinoxalin-2-one and its A -methyl derivative show practically identical ultraviolet absorption and are bases of similar strength. In contrast, the ultraviolet spectra of quinoxalin-2-one and its 0-methyl derivative (2-methoxyquinoxaIine) are dissimilar. The methoxy compound is also a significantly stronger base (Table II). Similar relationships also exist between the ultraviolet absorption and ionization properties of 3-methylquinoxalin-2-one and its N- and 0-methyl derivatives. The infrared spectrum of 3- (p-methoxy-benzyl)quinoxalin-2-one (77) in methylene chloride shows bands at 3375 and 1565 cm" which are absent in the spectrum of the deuterated... 

Note that from Table 4-128 the very large volumes that can dissolve in oil-base muds. For the water-base muds, 0.6 to 0.9% of gas will dissolve and not appreciably change the density or compressibility of the mud. It will be difficult to detect these low concentrations with downhole physical measurements. Free gas will be easily detected as shown hereafter. For the oil-base muds we will assume no free gas is present at bottomhole and the mud properties are changed only due to the dissolved gas. The detection will be more difficult than with free gas. 

This can be a real problem for baghouses that rely on automatic timers to control cleaning frequency. The use of a timing function to control cleaning frequency is not recommended unless the dust load is known to be consistent. A better approach is to use differential-pressure gages to physically measure the pressure drop across the filter media to trigger the cleaning process based on preset limits. 

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