Showing papers by "National Institute of Standards and Technology published in 1973"

CRC Handbook of Chemistry and Physics

Abstract: CRC handbook of chemistry and physics , CRC handbook of chemistry and physics , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

The Lunar Laser Ranging Experiment: Accurate ranges have given a large improvement in the lunar orbit and new selenophysical information.

Abstract: The scientific objectives achievable through high-accuracy range measurements to lunar retroreflectors are considered. A specific study of design questions related to the operation of retroreflectors on the lunar surface indicated that a reflector panel containing a number of solid fused silica corner reflectors would be capable of maintaining essentially diffraction limited performance under direct solar illumination. Initial Apollo 11 observations are discussed together with the installation of additional lunar retroreflectors in connection with the Luna 17, Apollo 14, Apollo 15, and Luna 21 missions. Range measurements at the McDonald Observatory are considered along with new results from lunar range data, and prospects regarding future lunar ranging stations.

Molecular Theory of Atomic Collisions: Fine-Structure Transitions

Abstract: The theory of fine-structure transitions in atom-atom collisions is formulated in terms of the molecular states of the diatomic collision complex. The Born-Oppenheimer (BO) electronic wave functions are implicit functions of the interatomic coordinate $R$, and the molecular theory is analogous to the "perturbed-stationary-state" method. Expansion in molecular channel states incorporates the effects of polarization, exchange, and valence forces on the electronic portion of the scattering wave function and embodies the "adiabatic" contribution of the entire set of closed-channel excited states that are generated in the more usual asymptotic-atomic-state expansion. The channel states are expressed explicity in terms of the body-fixed molecular wave functions, and the resultant interaction matrix elements in the close-coupling scattering formalism are related to the molecular potentials. The theory is developed specifically for proton collisions with the fluorine atom in its ground $^{2}P_{j,\mathrm{mj}}$ state, with explicit account being taken of the spin-orbit splitting between the $j=\frac{3}{2}$ and $j=\frac{1}{2}$ multiplet states. Use is made of the accurate H${\mathrm{F}}^{+}$ ($^{2}\mathrm{II}$) and ${\mathrm{HF}}^{+}(^{2}\ensuremath{\Sigma})$ wave functions calculated by Wahl, Julienne, and Krauss. These molecular states asymptotically approach ${\mathrm{H}}^{+}$ +F($^{2}\mathrm{P}$), and accurate quadrupole and induced-dipole interaction parameters which describe the asymptotic interaction potentials are obtained from the calculations. Estimates are made of the BO coupling terms and they are found to be negligible compared to the spin-orbit couplings. In the following paper close-coupling calculations are made of the cross sections for the fine-structure transitions ($j,{m}_{j}\ensuremath{\rightarrow}{j}^{\ensuremath{'}},{m}_{j}$).

Molecular Basis of Flame Inhibition.

Abstract: The role played by inorganic chemical additives in fire retardancy and flame inhibition is considered. Particular attention is given to the molecular level aspects of commercially important systems containing compounds of antimony, halogens, and phosphorus. The flame inhibiting function of metal containing additives is also discussed.

Theory of Disclinations: IV. Straight Disclinations.

Abstract: The general theory of disclinations developed earlier is applied to the special case of a straight disclination line. First the geometrical fields are found, such as the defect loop densities which correspond to Mura's new concepts of "plastic distortion" and "plastic rotation," the basic plastic fields (strain and bend-twist), the defect densities (dislocation and disclination), the characteristic vectors (Burgers and Frank), and the incompatibility. Then the static fields are found for the isotropic case, such as the displacement, total distortion, basic elastic fields, and the stress. It is shown that the disclination axis is moved by adding a dislocation to the disclination line. All these special results for the straight disclination line are shown to satisfy the general equations of the theory. As corollaries the following topics are also treated: 1. The finite and infinitesimal straight disclination dipole, which can be biaxial or uniaxial. It resembles the straight dislocation line. 2. The dislocation models of the straight disclination line and of the finite disclination dipole. They are terminating dislocation walls (tilt and twist). 3. The compensated disclination line and the bent dislocation wall. 4. Finally we show analytically a special case of a dislocation ending on a disclination.

Effect of Electrolyte pH on Crack Propagation in Glass

Abstract: : Crack velocity studies were conducted in various acids, bases and neutral solutions using the double cantilever beam techniques. Results are explained in terms of crack tip pH, which is controlled by the electrolyte at low crack velocities and by the glass composition at high crack velocities. The crack velocity data are consistent with the known dependence of strength on pH for soda-lime silicate glass. Results also suggest that the slope of the universal fatigue curve should depend on surface pH. (Author)

Technical Note-Minimizing Average Flow Time with Parallel Machines

Abstract: This note shows that the assignment and sequencing of single-operation jobs in a parallel-machine environment can be formulated as an assignment problem. Means for reducing the size and computational difficulty of this problem are identified.

Theory of Disclinations: II. Continuous and Discrete Disclinations in Anisotropic Elasticity.

Abstract: A general theory of stationary disclinations for a linearly elastic, infinitely extended, homogeneous body is developed. Dislocation theory is extended in three different ways to include disclinations, i.e., from continuous distributions, discrete lines, and continuous distributions of infinitesimal loops. This leads to three independent definitions of the disclination, which can be uniquely related to each other. These interrelationships clarify Anthony and Mura's approaches to disclination theory, which at first appear to diverge from the present theory. Mura's "plastic distortion" and "plastic rotation" are identified as the dislocation and disclination loop densities. The clastic strain and bend-twist are derived as closed integrals in terms of the defect densities, and shown to be state quantities. The theory reduces to classical dislocation theory when the disclinations vanish. For every discrete disclination line, it is always possible to find a "dislocation model," which is a dislocation wall terminating on the line that gives exactly the same elastic strain and stress.

Failure Prediction in Structural Ceramics Using Acoustic Emission

Abstract: Crack propagation in a typical structural ceramic (porcelain) is accompanied by acoustic emission. Two types of emission are detected. The first type is caused by slow growth of the fracture-initiating flaw; the emission rate depends primarily on crack velocity. Failure prediction using this source of emission can be effective, however, only if low-level emission, which may be related exclusively to crack growth, can be detected. The second source of emission, which occurs during bulk stressing, is the cracking associated with second-phase particles (quartz particles in porcelain) as a result of the combined action of the applied stress and local thermal and mechanical stresses. An analysis for predicting emission rates is developed and forms the basis for using this source of acoustic emission in failure prediction.

Ferroelectricity in lead monohydrogen phosphate, PbHPO4, and the deuterated form, PbDPO4

Abstract: PbHPO4 and the deuterated form PbDPO4 are found to be ferroelectric at room temperature with space group Pc. Pyroelectric, dielectric and ferroelectric measurements as a function of temperature show the room temperature values of the spontaneous polarization Ps are 0.72 and 2.1 μC/cm2, for PbHPO4 and PbDPO4 respectively, and second order ferroelectric-paraelectric phase transitions occur at 37°C and 179°C, respectively. The ferroelectric behavior is discussed in terms of the crystal structure.

An idea whose time has come.

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Description, performance, and wavelengths of iodine stabilized lasers.

Abstract: A description is given of lasers stabilized to components of the 129I2 spectrum in the region of the 633-nm laser lines for 3He–20Ne and 3He–22Ne. Relationships between operational characteristics such as power output, peak size, and peak width are shown, along with their relationships to some of the controllable parameters such as excitation level, iodine absorption, and iodine pressure. We found an iodine pressure broadening of about 13 MHz/Torr with a 2.6-MHz zero-pressure intercept. The frequency shift associated with iodine pressure is roughly 2 × 10−9ν/Torr to the red. Power broadening and power shifts are small, about a 10% increase in width and about 2 × 10−11ν variation in frequency for a fivefold to sixfold increase in power. These lasers exhibit a frequency stability for 10-sec sampling time of about 2 × 10−12ν and a resetability of about 1 × 10−10ν. The absolute vacuum wavelength for one iodine component has been measured against the 86Kr standard—3He–20Ne:129I2, k λ = 632 991.2670 A 0.0009 pm. The wavelengths of several other iodine components have been determined by measuring the frequency difference between them and the 129I2, k component. Among these are 3He–22Ne:129I2, B λ = 632 990.0742 ± 0.0009 pm: and 3He–20Ne:127I2, i λ = 632 991.3954 ± 0.0009 pm. These results were obtained using the Rowley-Hamon model for asymmetry in the krypton line and assume that the defined value for the standard is associated with the center of gravity of the line profile. The indicated uncertainties are statistical. No allowance has been included for imperfect realization of the krypton standard or for uncertainty in the asymmetry model.

A Referee Method for the Determination of Total Calcium in Serum

Abstract: The first referee method of analysis (a method of known accuracy) in clinical chemistry has been developed through the cooperation of scientists from the National Bureau of Standards and eight clinical chemistry laboratories. Subject to some limitations discussed in the text, calcium in serum can be determined by the referee method to within ±2% of the "true or absolute" value. The complete protocol, based on an atomic absorption spectrometric procedure, is described in detail.

Solubility and Surface Properties of Finely Divided Hydroxyapatite.

Abstract: Synthetic hydroxyapatite (OHAp), Ca5(PO4)3OH, was prepared by slow addition of phosphoric acid to a boiling Ca(OH)2 suspension. The solid, precipitated at a pH of about 12, was stabilized by prolonged boiling. The Ca/P ratio of the product was 1.69 ± 0.04 and it had a specific surface area of 26 m2/g. Samples of OHAp were equilibrated with phosphoric acid solutions. Within the pH range studied, 5 to 7, the solubility product, (Ca)5(PO4)3(OH), was found to be 6.3 ± 2.1 × 10-59 at 25 °C. Substantial deviations of the overall dissolution reaction from OHAp stoichiometry were observed and are attributed to nonstoichiometric reactions occurring at the surface. A linear dependence of excessive phosphorus on the surface with decrease in pH was found. Estimates on the extent of deviation from stoichiometry caused by the surface reaction are given.

Effect of temperature on the fracture of sapphire

Abstract: At low temperatures, metastable crack growth dictates the environment free strength of sapphire. Plastic deformation by dislocation motion or twin formation and growth plays no role in the fracture process at temperatures below 400° C. These conclusions are supported both by crack growth studies and critical stress intensity factor measurements on sapphire crystals, and by transmission electron microscopy studies of arrested cracks in sapphire and alumina.

Contrasting Valence-Band Auger-Electron Spectra for Silver and Aluminum

Abstract: Measurements of the ${L}_{2,3}\mathrm{VV}$ ($V=\mathrm{valence}$) Auger spectrum of aluminum and the ${M}_{4,5}\mathrm{VV}$ Auger spectrum of silver cannot be simply related to the valence-band density of states. The data for Al indicate a strong energy variation of the transition probability. For silver, the position and shape of the Auger spectrum are associated with multiplet splitting of localized double-$d$-hole final states.

Crystallization of Random Copolymers.

Abstract: A theory of crystallization is formulated for random copolymers which crystallize with the non-crystallizable co-units incorporated into the crystalline lattice as defects. The appropriate melting point equation and other associated thermodynamic properties are derived for this model as a function of crystal thickness and comonomer concentration. The formation of lamellar type morphology is assumed to be a kinetically determined phenomena and nucleation theory is utilized accordingly. The isothermal lamella thickness is predicted to increase in a definitive manner as the noncrystallizable comonomer concentration X increases, while the associated isothermal growth rate is predicted to decrease. The variation of lamella thickness with X when the copolymer is quenched or cooled at a uniform rate is also qualitatively predicted. Under these conditions lamella thickness decreases with increasing X, which is in accord with previous experimental observations on random copolymers of tetrafluoroethylene and hexafluoropropylene as well as other random copolymers. Theory also suggests how the surface free energy parameters σ e and σ can be determined from isothermal crystallization experiments for a series of random copolymers of varying composition.

The Effect of Temperature and Pressure on the Refractive Index of Some Oxide Glasses.

Abstract: The change in refractive index with temperature has been determined for some oxide glasses from about -200 to 700 °C. The change in refractive index with applied hydrostatic pressure has been determined at room temperature from a pressure of 105 to 108 Pa. All measurements were made using the yellow spectral line of helium. A calcium aluminate glass, an aluminum magnesium phosphate glass, a binary barium borate glass and a multicomponent germanate glass were studied, as were four commercial specimens of fused silica. From the data at room temperature, it has been possible to calculate the change in electronic polarizability with temperature at constant volume. This parameter has been found to be very high for the glasses as compared to crystals, and this agrees with the results of earlier research on silica-based optical glasses. Furthermore, over the entire temperature range, the change of refractive index with temperature is shown to be due predominantly to the temperature dependence at constant volume of the electronic polarizability. The relevance of the data to the molecular scattering of light in glasses is discussed.

Rotational Constants for C 12 O 2 16 from Beats between Lamb-Dip—Stabilized Lasers

Abstract: New experimental measurements of the frequency separations of 30 pairs of $^{12}\mathrm{C}$$^{16}\mathrm{O}_{2}$ laser lines in the 10.4-\ensuremath{\mu}m band and 26 pairs in the 9.4-\ensuremath{\mu}m band have been made with Lamb-dip---stabilized lasers. The use of a Josephson junction as the frequency-mixing element simplified the measurements. Uncertainties in existing rotational constants for the laser vibrational levels were reduced 20 to 30 times and an additional rotational constant ${H}_{v}$ was determined for the first time.

Excited electronic states of O2

Abstract: Configuration interaction (CI) variational trial functions (which assure formally correct dissociation) and the single-configuration self-consistent-field approximation are applied to the calculation of the excited electronic states of the negatively charged oxygen molecule The energy curves and wave functions of these states are analyzed All the excited states are found to have equilibrium-internuclear separations at least 1 au larger than the ground state The two lowest energy states are characterized, respectively, as shape and valence Feshbach resonances

Biodegradation of Phenylmercuric Acetate by Mercury-Resistant Bacteria

Abstract: Selected cultures of mercury-resistant bacteria degrade the fungicide-slimicide phenylmercuric acetate. By means of a closed system incorporating a flameless atomic absorption spectrophotometer and a vapor phase chromatograph, it was demonstrated that elemental mercury vapor and benzene were products of phenylmercuric acetate degradation.

Strength Degradation by Projectile Impacts

Abstract: The impacting of ceramic components by small projectiles can lead to strength degradation caused by the formation of Hertzian cracks. The conditions which produce degradation are analyzed in terms of the momentum and elastic properties of the projectile. A critical momentum must be exceeded before strength loss can occur, and the critical condition depends on the surface condition of the ceramic. Comparison of the analytical predictions with data for SiC confirms the reliability of the analysis.