In situ measurements of ion-exchange processes in single polymer particles: laser trapping microspectroscopy and confocal fluorescence microspectroscopy

Ion-exchange processes of a cationic dye (Rhodamine B; RhB) were studied for individual polymer particles (diameter of 16-20 μm) by laser trapping microspectroscopy and confocal fluorescence laser microspectroscopy. The absorbance of RhB at 565 nm adsorbed on a cation-exchange particle increased linearly with the concentration of RhB in the aqueous phase, while it was independent of the particle diameter. Fluorescence intensity profile measurements of RhB along the particle diameter by confocal fluorescence microspectroscopy directly proved that ion exchange took place in the surface layer (～2-μm thickness) of the particle in the initial stage (1 h). Diffusion of RhB in the particle was very slow, and ion exchange proceeded gradually to the inner volume in the order of days. The ion-exchange processes were analyzed on the basis of simulation of the time course of the concentration profile of RhB in the particle, and the diffusion coefficient of RhB was determined to be (2-4) × 10(-11) cm(2)·s(-1).     

Growth technique for producing high quality superconducting YBa2Cu3O7-δ single crystals

High quality single crystals of YBa₂Cu₃O_7- (YBCO) have been grown in yttria-stabilized zirconia crucibles by using a flux method. This method yields crystals with area 3 to 4 times larger than a previous method, and 3 to 5 times more crystals. Several crystals as large as 3×4mm² in thea-b plane are routinely obtained from each crucible. The samples typically range from 10 to 60 m thick. The superconductivity transition temperatureT _c of the crystals, measured by magnetic susceptibility, falls in the range 92.5 to 93 K and the smallest transition width (10 to 90%) is less than 0.25 K. Compared with the previous method, the surface is generally smoother, with less flux, and larger untwinned regions of 1 x 1 mm² are usually found.     

Spin correlations for an Anderson impurity in conventional and unconventional superconductors

We present a theoretical study of the spin-spin correlation functionC(r) in a superconductor, whereC(r) = S · s(r);S is an impurity spin operator, ands(r) is the conduction electron spin density operator. We model the impurity using the Anderson Hamiltonian, and use the U , 1/N expansion to do the calculations. In addition to conventional superconductors, we consider unconventional superconductors, in which the order parameter (k) has a lower rotational symmetry, and has vanishing angular average. Of particular interest is the way that the behavior ofC(r) reflects two length scales, the Kondo length _k and the superconducting coherence length, ₀, and the way that its behavior is affected by the angular dependence of unconventional gaps.     

Thermal conductivity of CVD diamond films

Diamond films 60 and 170 µm in thickness were grown by PACVD (plasma-assisted chemical vapor deposition) under similar conditions. The thermal diffusivity of these freestanding films was measured between 100 and 300 K using AC calorimetry. Radiation heat loss from the surface was estimated by analyzing both the amplitude and the phase shift of a lock-in amplifier signal. Thermal conductivity was calculated using the specific heat data of natural diamond. At room temperature, the thermal conductivity of the 60 and 170 m films is 9 and 16 W-cm^–1. K^–1 respectively, which is 40–70% that of natural diamond, The temperature dependence of thermal conductivity of the CVD diamond films is similar to that of natural diamond, Phonon scattering processes are considered using the Debye model, The microsize of the grain boundary has a significant effect on the mean free path of phonons at low temperatures. The grain in CVD diamond film is grown as a columnar structure, Thus, the thicker film has the larger mean grain size and the higher thermal conductivity. Scanning electron microscopy (SEM) and Raman spectroscopy were used to study the microstructure of the CVD diamond films. In this experiment, we evaluated the quality of CVD diamond film of the whole sample by measuring the thermal conductivity.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Study on the solidification cracking behaviour of high strength aluminum alloy welds: Effects of alloying elements and solidification behaviours

The solidification cracking susceptibility of the 7000 series Al-Zn-Mg high strength aluminum alloy has been studied. The cracking behaviour of the specimens were evaluated by a Tig-a-Ma-Jig Varestraint test process under various augmented strain conditions. It has been experimentally observed that the addition of copper decreased the solidification cracking resistivity of the high strength aluminum alloy weld metal by increasing the total crack length (TCL). The effect of the addition of manganese on the solidification cracking behaviour is found to be beneficial by markedly decreasing the solidification cracking susceptibility as the manganese content increases from 0.3 to 0.7%. This enhancement by manganese is understood to be attributed to the reduction of the mushy zone size during the solidification process. The effects of chromium and zirconium additions are also investigated. The weld metal containing zirconium is less sensitive to the solidification cracking than the weld metal containing chromium. In addition, the solidification behaviours of the tested alloys are also investigated and it is found that as the solidification temperature range (T) becomes narrow, the solidified structure becomes more dendritic in its features which is believed to create higher solidification cracking resistance.     

Characterization of centrifugally atomized Al-12Si-5Fe-3Cu-1Mg(wt%) alloy powder and extruded rod

The Al-12Si-5Fe-3Cu-1Mg(wt%) alloy was rapidly solidified by centrifugal atomization. The microstructural characteristics of rapidly solidified powder and the microstructure changes with heat treatment were investigated in terms and related to powder size. The microstructures of the powder consisted of dendritic -Al, eutectic phase, Cu-rich phase, and needle-like intermetallic compounds. These phases were much finer than that of ingot cast structure and the size decreased with increasing cooling rate. The X-ray diffraction of the atomized powders revealed the presence of non-equilibrium 3-(AlFeSi) intermetallic phase. This phase appeared to transform to an equilibrium -(AlFeSi) phase by heating at temperatures above 470°C. The extruded rod which was hot extruded at 360°C with an extrusion ratio of 40:1 also revealed the presence of the -(AIFeSi) intermetallic phase. Using DSC, the exothermic peak due to precipitation from the supersaturated -Al matrix was observed in the range of 200–250°C during continuous heating of atomized powder, and the size of the peaks increased with decreasing powder size.     

Preparation of beta-alumina powder from kaolin-derived aluminium sulphate solution

The synthesis of beta-alumina powder from kaolin-derived aluminium sulphate solution is described. A homogeneous mixture of Al₂(SO₄)₃·18H₂O and Na₂SO₄·10H₂O was precipitated by dropping the mixed solution of the kaolin-derived aluminium sulphate and sodium hydroxide into ethanol with agitation by stirring. The preparation conditions - mixing mole ratio of Na₂O/Al₂O₃ in the solution and calcination temperature of the resultant precipitate — were experimentally determined for obtaining the beta-alumina powder with a structure consisting of - and -alumina and a well crystallized state.     

Surface modification of polyetherurethaneureas and their antithrombogenicity

Polyetherurethaneurea (PU) films were treated by oxygen plasma discharge followed by acrylic acid (AA) grafting. The carboxyl groups of the AA-grafted PU (PU-AA) surface were coupled with bovine serum albumin and heparin via water soluble carbodiimide. Surface characterization of the modified PUs was carried out by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The amount of immobilized albumin and heparin on the PU surface was 1.8 and 1.5 g/cm², respectively, as determined by the dye interaction method. Interactions between the surface-modified PUs and blood components such as plasma proteins and platelets were investigated to evaluate the blood compatibility of the samples. Plasma recalcification time (PRT) and activated partial thromboplastin time (APTT) of the albumin-immobilized PU (PU-Al) were almost the same as those of PU, while platelets were less adhered on the PU-Al than on PU. On the other hand, PRT and APTT of the PU-He were significantly longer than those of the PU, PU-AA, and PU-Al. Moreover, adhesion of platelets was effectively suppressed on the PU-He, leading to good in vitro blood compatibility.     

Microstructural evolution of potassium titanate whiskers during the synthesis by the calcination and slow-cooling method

K₂Ti₆O₁₃ whisker was synthesized by the calcination and slow-cooling method, and the microstructural evolution of whiskers, and the relations between the phase and the layer structure, were investigated. The amount of K₂O in the starting powder mixture played a key role in forming a layer structure, which can be obtained by addition of excess K₂O. During calcination, rod-like K₂Ti₆O₁₃ particles with a layer structure were formed by reactions between K₂O and TiO₂. During slow-cooling, the K₂O-rich liquid phase reacted with K₂Ti₆O₁₃ layers near the boundary and k₂Ti₄O₉ whiskers were produced by the splitting of layers within rod-like k₂T₆O₁₃ particles. k₂Ti₄O₉ whiskers were reformed into k₂T₆O₁₃ whiskers by treatment in boiling water and reheating. The synthesized k₂T₆O₁₃ whiskers had a clean surface and a length exceeding 100 m.     

A study of a new data association and track initiation method with normalized distance squared ordering

In an underwater environment, measurements regarding true targets and false targets (clutter) can be made. Therefore, a suitable data association method to exactly detect and track a target and an efficient track initiation method for judging tracks formed by the target should be selected in this environment. This paper attempts to propose a new data association method and track initiation method to detect and track targets more effectively. Also, the performance of the new method is tested in a series of Monte Carlo simulation runs and is compared with the existing data association and track initiation methods in a cluttered environment.