Rheology of stimulated whole saliva in a typical pre-orthodontic sample population

The dynamic viscosity () of stimulated whole saliva in a typical pre-orthodontic sample population was characterized as a function of temperature (T). Samples were collected from 30 adolescents or young adults, after screening for factors that are known to have an effect on salivary viscosity. Using a cone and plate viscometer, 1.5 ml of stimulated whole saliva was evaluated at a constant shear rate of 450 s^-1 from T=20°C to T=40°C. Data from the -T plots showed a negative dependence of the form, =a–bT, over a range of from 1.08 to 2.45 centipoise (cps) at 34°C. Most of the samples fell into a narrow envelope, where the mean of the saliva samples ranged from 2.42±0.61 cps at 20°C to 1.57±0.32 cps at 37°C. With regard to sample stability, viscosity-time plots indicated that a small but predictable decrease in occurred during the 3 h period. The -T plots generated from fresh and frozen saliva samples demonstrated an appreciable change in as a result of refrigeration. With regard to sample reproducibility, viscometric data obtained from a typical pre-orthodontic patient over a 1-week period fluctuated within a fairly broad envelope of values.Presented, in part, at the 21st Annual Meeting and Exhibition of the A.A.D.R., Boston, Massachusetts, March, 1992.     

An animal study of c.p. titanium screws with different surface topographies

Sixty screw-shaped commercially pure (c.p.) titanium implants were inserted in the tibial and the femoral metaphyses of adult rabbits. The implants were divided into four groups with different surface roughnesses. The surface roughness was characterized before and after implant insertion. One group was left as-machined, this group had an initial R _a value of 0.4 m. Two groups were blasted with 25 m sized particles of TiO₂ and Al₂O₃, respectively; corresponding R _a values for these groups were 0.9 m and 0.8 m. One group was blasted with 250 m sized particles of Al₂O₃. The R _a value for this last group was 2.1 m. After a healing time of 12 weeks the torque necessary for implant removal and histomorphometric evaluations was evaluated. After removal of the implants the R _a values for the four above mentioned groups were 0.9, 1.3, 1.1 and 1.9 m, respectively. We found a better bone response for implants blasted with 25 m sized particles compared to an as-machined (turned) surface, but no differences between the implants blasted with 25 m particles and the implants blasted with 250 m sized particles.     

The Interpretation of Phase-Slip and Critical-Velocity Data from the Flow of Superfluid 4He through a 2 μm by 2 μm Aperture

An analysis has been made of phase-slip and critical-velocity data for both the ac and dc flow of superfluid ⁴ He through a 2 m by 2 m aperture in a 0.1-m-thick titanium foil between 0.36 and 2.10 K. Single-2 phase slips were resolvable over the entire range of temperature in the ac flow measurements, carried out between 10 and 20 Hz, making it possible to determine the width of the critical-velocity distribution throughout the temperature range from these measurements. These data have been interpreted in terms of the thermal nucleation of vortex half-rings at the walls of the aperture, involving a velocity- and temperature-dependent energy barrier. The barrier can be modeled with moderate success using an approach close to that of Avenel and Varoquaux and coworkers.     

A note on the μ-zeros of combinations of cross-product bessel functions

Summary In the problem of diffraction of elastic waves in annular circular, or cylindrical (doubly connected) domains, the zeros of complicated combinations of cross-products of cylinder functions as analytic functions of the index =n+i (in general complex) are required. In this note, the imaginary -zeros of two such combinations of cross-products of two identical doubly connected domains, however with two different boundary conditions on one boundary, are asymptotically computed and graphically displayed. It is shown that even for such a comparison of different boundary conditions, one can obtain with a minimum effort in mathematics asymptotic distributions and the relative dispositions of the respective -zeros. It is then rather simple to determine with a computer the exact positions of the -zeros.

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Zusammenfassung Bei der Behandlung des Beugungsproblems elastischer Wellen in kreisringförmigen oder zylindrischen (zweifach zusammenhängenden) Bereichen werden die Nullstellen komplizierter Produktkombinationen von Zylinderfunktionen benötigt, und zwar als analytische Funktionen ihrer im allgemeinen komplexen Ordnung =n+i . In dieser Arbeit werden die imaginären -Nullstellen zweier solcher Produktkombinationen in zwei identischen, zweifach zusammenhängenden Bereichen, jedoch mit an einem Rand verschiedenen Randbedingungen, asymptotisch berechnet und graphisch dargestellt. Es wird gezeigt, daß man selbst bei einem solchen Vergleich verschiedener Randbedingungen mit einem Minimum an mathematischem Aufwand asymptotische Verteilungen und die relativen Lagen der entsprechenden -Nullstellen erhalten kann. Es ist dann ziemlich einfach, mit Hilfe eines Rechners die exakten Lagen der -Nullstellen zu bestimmen.

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With 1 Figure     

Effect of Grain Size on the Modulus of Elasticity and Strength of Synthetic Graphites

The effect of the grain size of the filler on the mechanical properties (compressive, bending, and tensile strength and modulus of elasticity) of synthetic graphite is analyzed using data for commercial structural graphites. As the mean particle size of the filler (_av) decreases from 3000 to 1 m, the modulus of elasticity increases, on the average, from 10 to 15 GPa, and the compressive, bending, and tensile strength increases by about one order of magnitude. The Griffith equation is used to evaluate the size of defects that initiate fracture (c _c) in different types of graphites. It is shown that the factors determining the critical defect size depend on the particle size of the filler. For _av > 150 m, c _c is comparable to _av or _max. In the range 30 < _av < 150 m, c _c is equal to or greater than _max. In graphites with _av < 30 m, c _c far exceeds _max and, presumably, corresponds to the particle size of the molding powder.     

Characterization of silver-palladium submicronic powders

Various properties of submicronic silver-palladium powders (70/30 and 75/25 Ag/Pd % wt/wt), recently obtained by a new process of precipitation in aqueous solution, are described. These powders are intended to be used in the multilayer ceramic capacitor industry. The morphology of the particles has been analysed through various measurements, such as SEM images, tap density, BET surface area, and the size distribution by a sedimentation technique. The powders were found to be made of spherical shaped particles of mean diameter close to 0.3 m with a narrow size distribution. The individual grains were agglomerated only to a small extent. After being conditioned as a paste by blending with an organic binder, screen-printed and fired, the particles sintered into a conductive layer of low resistivity (15–30 Wcm for 2 m thickness) with only a few remaining voids, as observed by SEM. Thermal measurements indicated no melting of a pure silver phase at 960 °C, thus indicating that alloying was achieved before this temperature.     

Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility

We have measured the nuclear specific heat C_n and nuclear susceptibility _n of In nuclei (I=9/2, =5.5 _n) in the cubic intermetallic compound AuIn₂ (Korringa constant =0.11 Ksec) in the normal conducting state at 30K10mK and 2mTB115 mT. Our data show a positive nuclear Weiss temperature =+ 43 K and that the In nuclei undergo a nuclear ferromagnetic transition at T_c=35 K. The In nuclei experience an internal field of about 10 mT (obtained from C_n at T>T_c ). The nuclear ordering temperature T_c and the internal field increase with applied magnetic field. From the data we deduce exchange constants for the investigated system. The critical entropy reduction S(T_c)/S_max=8.6% and critical enthalpy E=0.28 RT_c are in reasonable agreement with the measured ordering temperature T_c,applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time calculated from the real and imaginary parts of _n is 10 msec at T>50 K, but drops to <1msec at T_c.This is the first observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T _nuclear =T _electron .     

Absorption Spectrum of ZnO Precipitates in ZnSe

The absorption spectrum of ZnO precipitates in ZnSe saturated with oxygen is studied in the spectral range 500–2000 cm^–1 and is shown to correlate with the transmission spectrum of single-crystal ZnO. Saturation of ZnSe with oxygen in the course of growth leads to ZnO precipitation during cooling. The precipitates give rise to narrow absorption bands in the range 5.8–7.1 m, which correlate with the components of the multiphonon absorption spectrum of ZnO, formed by combinations of LO and TO phonons. The 2LO mode defines the long-wavelength transmission edge of ZnO. In addition, the spectrum shows strong absorptions due to the LO + TO(10.2 m) and 2TO (11.3 and 12.7 m) modes. The possible role of SeO₂ is discussed. It is suggested that ZnO with a high carrier concentration may act as a gray filter in the spectral range 2–9 m.     

Nuclear ferromagnetic ordering of141Pr in the diluted Van Vleck paramagnets Pr1−x Y x Ni5

We report on the first investigation of the effect of magnetic dilution on nuclear magnetic spin interactions in metals; we studied this effect in the diluted Van Vleck paramagnets Pr_1–xY_xNi₅. In addition, we investigated the electronic magnetic properties of these intermetallic compounds. For this purpose, we have measured the nuclear and electronic susceptibilities of Pr_1–xY_xNi5 with x = 0 to 0.2 at 50K T 8 mK and at 2.2 K T 300 K. We observe a linear decrease of the electronic Van Vleck susceptibility and of the hyperfine enhancement factor by 13% (per mole Pr³⁺). The hyperfine-enhanced nuclear susceptibility decreases by about a factor of three when going fromx = 0 tox = 0.2. The samples show nuclear ferromagnetic transitions of¹⁴¹Pr with nuclear Curie temperatures T_c decreasing from 370 K to 100 K and Weiss temperatures decreasing from 218 K to 13 K in this concentration range. These data are compared with the results of mean-field calculations. In addition, we report on measurements of the nuclear spin relaxation time of these compounds, for which we find values of a few msec at millikelvin temperatures and a critical speeding-up at T_c. Our data give hints that for x > 0.2 the character of the nuclear magnetic transition may change, possibly to a nuclear spin glass freezing.     

Study of the lattice strain relaxation in the Ga1-X Al X Sb/GaSb system by x-ray topography and high resolution diffraction

High resolution x-ray diffraction and topographic methods have been used to study lattice strain relaxation in the Ga_1-X Al _X Sb/GaSb system. Samples with layer thickness ranging between 0.1 and 6 m and with Al concentration x=0.402±0.005 have been grown by molecular beam epitaxy at 550 °C on (0 0 1) oriented undoped GaSb LEC substrates. A first critical thickness (t _C1), related to the misfit dislocation generation, has been found to be between 0.16 < t _C1 < 0.20 m. Due to the weak sensitivity of the rocking curve to the onset of relaxation, this result has been obtained by means of a double crystal topographic technique. A plateau region in the curve of the residual strain versus thickness has been observed for t ranging between 0.2 and 0.5 m. The residual strain _res shows a dependence close to t^–0.5 above a second critical thickness value t _C2 slightly larger than 0.5 m. Finally, in the last region above a layer thickness of 3 m, strong dislocation interaction effects seem to affect the relaxation. A comparison with theoretical models has been made.     

Hydrothermal synthesis of barium titanate fine particles from amorphous and crystalline titania

Barium titanate fine particles of cubic system were synthesized hydrothermally from aqueous barium hydroxide solutions with fine particles of either amorphous or crystalline (rutile) titania in suspension. The mean size of barium titanate particles prepared from amorphous titania ranged from 0.03 m to 0.11 m, depending on hydrothermal conditions. The particle size approximately agreed with the crystallite size (0.04–0.09 m). On the other hand, the mean size of barium titanate particles prepared from rutile titania ranged from 0.2 to 0.7 m, which was about six times as large as the crystallite size. The difference of sizes of barium titanate particles prepared might be ascribed to the difference in dissolution rates of amorphous or crystalline titania particles.Nomenclature mean particle size, m - BT barium to titanium molar ratio - d crystallite size, m - K shape factor appearing in Equation 3 - half value breadth of diffraction peak - lattice strain - Bragg diffraction angle, degree - wave length of X-ray, urn - _g geometric standard deviation defined by 84.1%-size/50%-size in a log normal size distribution     

Deposition from the vapour phase during induction plasma treatment of alumina powders

A study was carried out of the induction plasma melting of alumina powders (particle mean diameter, ¯d _p=24.5 m), (Ar/H₂ or Ar/N₂ plasma, plate power, 40 kW) under reduced pressure conditions (400 torr). The results reveal that in the process, partial vaporization of the alumina powders takes place in the hot region of the discharge. As the molten particles cool down and solidify, the deposits from the vapour phase was formed with the spheroidized particles. In all treatments with the Ar/H₂ and Ar/N₂ plasmas, a condensate of ultrafine alumina fume (d _p<200 nm) was obtained. The fine particles consisted essentially of metastable -, - and -phases. Needle-like crystals(0.1–0.3 m diameter, by 5–15 m long) were observed when operating with an Ar/N₂ plasma at powder feed rates exceeding 10 g min^–1. Electron diffraction analysis revealed that the needles were whiskers, whose structure was very similar to - or -aluminas with an hexagonal close-packed oxygen lattice. The change of morphology is related to the degree of supersaturation in the vapour phase.     

Physicochemical Study of the Mechanism of Radionuclide Migration from the Shelter Object and Its Service Area to Groundwater

Radionuclide distribution over coarsely dispersed particles (>0.1 m), colloidal particles (0.01-0.1 m), and ionic species in water taken from the Shelter Object and in groundwater sampled from observation wells situated in the service area was studied. A new mechanism of radionuclide transfer from the soil surface to groundwater was suggested.     

Microstructure-property studies in friction-stir welded, Thixomolded magnesium alloy AM60

Thixomolded magnesium alloy AM60 plates joined by friction-stir welding were observed to be as strong or stronger than the unwelded base material. The thixotropic microstructures of the as-molded plates consisted of either 3% or 18% primary solid fraction of -Mg globules (45 m average size) in a eutectic mixture consisting of -Mg grains (10 m) surrounded by Mg₁₇Al₁₂ intermetallic grains in the -Mg grain boundaries (having an average size of 1–2 m). This complex, composite microstructure became a homogeneous (Mg + 6% Al)), recrystallized, equiaxed grain (10–15 m) microstructure in the weld zone.     

Effects of carbon content on microstructures and magnetic properties of annealed or solution treated Fe-Cr-Ni-C alloys

The correlations between microstructures and magnetic properties were studied in four Fe-17.5 mass%Cr-2.0 mass%Ni-Xmass%C (X = 0.3–0.6) alloys. Each alloy consisted of ferromagnetic and M₂₃C₆ carbide phases by step-annealing at 1053 K and 848 K. The number of the M₂₃C₆ carbide particles increased with the carbon content, and this microstructural variation caused a deterioration of the soft magnetic properties. On the other hand, the alloy with 0.3 mass% carbon content consisted of ferromagnetic and paramagnetic retained structures after solution treatment at 1473 K. The amount of the stable structure increased with the carbon content, while the amount of the structure decreased. This microstructural variation caused a decrease in the relative permeability, _r, and the stabilization of the paramagnetic property to low temperatures below room temperature. The temperature stability of the _r values was closely related to the martensite start temperature, M _s. From an equation for the estimation of M _s from the chemical compositions of the phase, the M _s's of the alloys with 0.3, 0.4, 0.5 and 0.6 mass%C were estimated to be 326, 289, 241 and 216 K respectively. These values were consistent with the M _s's expected from the microstructures and temperature dependences of the _r values.     

Effect of filler content and size to properties of composite resins on microwave curing

The effect of filler content and size to property of composite resin using high purity spherical silica particles on microwave curing was examined by mechanical means and electron microscope observation to develop microwave-curing composite resin inlay. Increasing filler content in three kinds of filler particles (0.45, 0.96 and 1.46 m) resulted in increasing compressive strength, diametral tensile strength and knoop hardness and indicated the highest values at the operative mixing limit. The effect of particle size was that the mechanical property of the 0.96 m filled resin was highest, followed by 1.46 m and 0.45 m on the same filler content. The 0.96 m filled resin had about the same knoop hardness on both surfaces of the cured sample, which means that uniform polymerization occurred in the cured sample.With electron microscope observation, the bubbles of about 1.0 m and the cracks between the fillers and the matrix were observed in each cured resin. This is caused by the excessive absorption of microwave energy in fillers and surface treatment materials of fillers. Therefore, improvement of the composition of filler and surface treatment material of filler are needed, which makes it harder to absorb the microwave energy. ©©1999©Kluwer Academic Publishers     

Ultrasonic spray pyrolysis for nanoparticles synthesis

This article presents new findings regarding the effects of precursor drop size and precursor concentration on product particle size and morphology in ultrasonic spray pyrolysis. Large precursor drops (diameter > 30 m) generated by ultrasonic atomization at 120 kHz yielded particles with holes due to high solvent evaporation rate, as predicted by the conventional one particle per drop mechanism. Precursor drops 6–9 m in diameter, generated by an ultrasonic nebulizer at 1.65 MHz and 23.5 W electric drive power, yielded uniform spherical particles 90 nm in diameter with proper control of precursor concentration and residence time. Moreover, air-assisted ultrasonic spray pyrolysis at 120 kHz and 2.3 W yielded spherical particles about 70% of which were smaller than those produced by the ultrasonic spray pyrolysis of the 6–9 m precursor drops, despite much larger precursor drop size (28 m peak diameter versus 7 m mean diameter). These particles are much smaller than predicted by the conventional one particle per drop mechanism, suggesting that a gas-to-particle conversion mechanism may also be involved in spray pyrolysis.     

Study on surface cracking of alumina scratched by single-point diamonds

Scratching experiments have been carried out on hot-pressed alumina by using single-point diamonds of conical shape (conical angle 85, 108, 128 and 65° and nose radius 1.6, 1.1, 1.9 and 45.0m, respectively). With an increase of the scratching depth, the material exhibits the following behaviour: macroscopic plastic deformation scale-like cracking cracking or chipping. Cracking or chipping is absent only if the groove depths are less than certain values which vary with the diamond shape. The crack penetration depth is approximately in proportion to the depth of cut. For a depth of cut less than 2m, the penetration depth of crack induced by the diamond of nose radius 45.0m is almost 8 times those produced by the other diamonds. For a depth of cut more than 2m, the former is more than twice the latter. The coefficients of pile-up increase as the depths of cut decrease.     

Adhesion of thermally sprayed hydroxyapatite–bond-coat systems measured by a novel peel test

Ti6Al4V foils, 100 m thick, were coated with thin (10–15 m) bond coats based on titania and zirconia, and subsequently coated with a thick (100–120 m) hydroxyapatite layer, using atmospheric plasma spraying. Peel adhesion tests of the coating systems performed on the foils showed that titania, and mixed titania/non-stabilized zirconia bond coats improved the adhesion of the ceramic layers to the metallic substrate in a statistically significant way, while a partially CaO-stabilized zirconia bond coat led to a decrease of the peel adhesion strength when compared to hydroxyapatite coatings without a bond coat.     

Flow of a heated ferrofluid over a stretching sheet in the presence of a magnetic dipole

Summary The flow of a viscous ferrofluid over a stretching sheet in the presence of a magnetic dipole is considered. The fluid momentum and thermal energy equations are fomulated as a five-parameter problem, and the influence of the magneto-thermomechanical coupling is explored numerically. It is concluded that the primary effect of the magnetic field is to decelerate the fluid motion as compared to the hydrodynamic case, thereby increasing the skin friction and reducing the heat transfer rate at the sheet.Nomenclature a distance - c constant - c _p specific heat at constant pressure - C _f wall friction coefficient - e 2.71828 ... - f dimensionless stream function - H magnetic field - k thermal conductivity - K constant - M magnetization - Nu _x local Nusselt number - p pressure - P dimensionless pressure - Pr Prandtl number, c _p/k - Re _x local Reynolds number, cx ²/ - T temperature - u velocity component along the sheet - v velocity component normal to the sheet - x coordinate along the sheet - y coordinate normal to the sheet - dimensionless distance - ferrohydrodynamic interaction parameter - constant - dimensionless Curie temperature - dimensionless coordinate - dimensionless temperature - viscous dissipation parameter - dynamic viscosity - ₀ permeability - dimensionless coordinate - density - shear stress - magnetic potential - stream function