Fibrous hydroxyapatite grown in the gel system: effects of pH of the solution on the growth rate and morphology

In the preparation of fibrous hydroxyapatite (HAp), using the gel system consisting of agar gel containing calcium nitrate and over-layered (NH₄)₂HPO₄ solution, the pH of the solution was found to greatly influence the growth rate and morphology of the resultant products. In particular, a pH value of about 9–10 produced straight fibrous HAp in the shortest time. Also, the Ca/P molar ratio of the product increased with the pH value of the starting solution. The growth rate and morphology of the product were correlated to the ion species present in the solution at different pHs.     

Preferential changes in hepatosplanchnic hemodynamics in patients with borderline hypertension

The purpose of this study was to gather data from first-year medical students prior to their taking gross anatomy and again at the end of the course to determine if changes occur regarding death anxiety and detached concern toward patients. Chi-square and t-tests were used to assess statistical significance. From the 84 students for whom we had data both prior to and after gross anatomy, only the sociodemographic variable of sex was consistently related to the two dependent variables. Women reported more death anxiety prior to and after the gross anatomy course and were more likely to disagree with the need for detached concern.     

Foam processing and cellular structure of polypropylene/clay nanocomposites

Polypropylene (PP)/clay nanocomposites (PPCNs) were autoclave‐foamed in a batch process. Foaming was performed using supercritical CO₂ at 10 MPa, within the temperature range from 130.6°C to 143.4°C, i.e., below the melting temperature of either PPCNs or maleic anhydride‐modified PP (PP‐MA) matrix without clay. The foamed PP‐MA and PPCN2 (prepared at 130.6°C and containing 2 wt% clay) show closed cell structures with pentagonal and/or hexagonal faces, while foams of PPCN4 and PPCN7.5 (prepared at 143.4°C, 4 and 7.5 wt% clay) had spherical cells. Scanning electron microscopy confirmed that foamed PPCNs had high cell density of 10⁷–10⁸ cells/mL, cell sizes in the range of 30–120 μm, cell wall thicknesses of 5–15 μm, and low densities of 0.05–0.3 g/mL. Interestingly, transmission electron microscopic observations of the PPCNs' cell structure showed biaxial flow‐induced alignment of clay particles along the cell boundary. In this paper, the correlation between foam structure and rheological properties of the PPCNs is also discussed.     

Some classes of automata as partially ordered sets

A class of automata is considered as a partially ordered set by homomorphism relation. We show first that some classes of automata. e.g., quasiperfect automata, perfect automata and strongly cofinal automata, are lattices, and other classes, e.g., strongly connected automata, cyclic automata and cofinal automata, are not lattices. At the same time, we give algorithms for computing the least upper bound and the greatest lower bound of given two elements in each class which forms a lattice.     

A sensitive test to evaluate antioxidants in oils and fatty esters

Efficacy of common lipid antioxidants was evaluated by use of sesamol dimer and hemoglobin (SD method), and the method was compared with traditional peroxide value (POV) method. There were good correlations between the increases in SD and POV values, with different substrate oils and with the different antioxidants. While the POV method requires 500 mg of the substrate oil, the SD method requires less than 10 mg of the oil. The SD method is useful to estimate the potency of antioxidants with a small amount of oils and fatty esters.     

Enforcing logical delays in DNA computing systems

DNA computing has the potential to create powerful devices, but, in the context of well-mixed systems, sequentiality of operations is hard to achieve. To enforce such sequentiality, we propose a generic delay gate that can be interfaced with virtually any DNA system. Since it is system-independent, our delay gate can be used as an off-the-shelf library to accelerate the design of increasingly complex systems. Additionally, we checked the feasibility of our design by testing various in vitro implementations. We also present a theoretical proof of concept of its applicability by using it to complement an existing DNA module library, the DNA toolbox, to design new systems.     

Damage to cement concrete pavements due to exposure to organic compounds in a cold region

Pop-out and disaggregation of aggregate in a 1-year old cement concrete pavement originally mixed with air-entraining (AE) water-reducing agent was observed after the pavement had been exposed to ethylene glycol based snow-melting agent on the surface in the winter. The study used: gas chromatography–mass spectrometry (GC–MS) tests, ¹H Nuclear Magnetic Resonance (NMR) tests, X-ray fluorescence analysis, emission spectral analysis (ICP), elution tests in anion type surfactant solution conducted for mortar and aggregate taken from the cement concrete where pop-out had occurred, as well as samples made by cement paste in the laboratory. Tests of the tensile strength, thermal-stress, and three-dimensional crack analysis by micro-focus computerized tomography (CT) scanner were conducted for specimens (2.5 × 2.5 × 10 cm) taken from the cement concrete where pop-out had occurred and with cement concrete samples made in the laboratory. Microscope observations and Electron Probe Micro Analyzer (EPMA) analysis were conducted for thin samples (2.5 × 2.5 cm and 20 μm thick) taken from the cement concrete where pop-out had occurred. The tests results showed that organic compounds contained in the cement reacted with the cement during the hardening process, generating cracks and gel in the cement paste. It was established that these caused the pop-out of the aggregate, together with the effects of the ethylene glycol based snow-melting agent that the cement concrete had been exposed to. No pop-out or disaggregation of aggregate were found in cement concrete at a repaired section, at the same location, with aggregate of low absorbing water ratio in this cold region and in place for 2 years.     

Boundary shape determination of steady‐state heat‐conduction fields

In this paper, a practical method of numerical analysis for the boundary shape design of steady‐state heat‐conduction fields to control the temperature distribution to a prescribed distribution is presented. Reshaping was accomplished by the traction method proposed by one of the authors as a solution to domain optimization problems in which elliptic boundary value problems were defined. In this study, we formulated a temperature square error norm minimization problem between the prescribed distribution and the actual distribution on prescribed boundaries and theoretically derived a shape gradient function for this problem. We developed a convenient numerical method using a general‐purpose FEM program for the temperature prescribed problem. The successful results for the two‐dimensional problems of an erosion surface on a blast furnace hearth and a coolant flow passage in a wing demonstrate the validity of the presented method. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 245–258, 2001     

Generation,growth, shrinkage,and dispersion of Au agglomerates in Si during the annealing of supersaturated substitutional Au

Si samples homogeneously pre-indiffused with Au atoms at a concentration 7.5 × 10¹⁶ atoms/cm³ were heat treated at 900 °C for 22.5, 90, 360, and 1,440 h to generate Au agglomerates during the out-diffusion process of supersaturated high-temperature substitutional Au. The number of Au atoms in all of the agglomerates in the regions 8–22, 22–36, 36–50, and 50–64 μm from the surface were measured by secondary ion mass spectrometry, and the change of their distributions during annealing was obtained. As a result, agglomerates containing (1–3) × 10⁵ Au atoms were initially generated with a concentration of 1.1 × 10¹⁰ agglomerates/cm³ at a short annealing time. The generated agglomerates grow, shrink, and disperse with the decrease of the supersaturation of the surrounding Au concentration, that is, with increase of annealing time. The boundary Au concentration for changing from growth to shrinkage of the agglomerates is (3–5) × 10¹⁵ atoms/cm³. The agglomerates grow and contain until about 2.3 × 10⁶ atoms. The agglomerates disperse and finally disappear as the surrounding Au concentration decreases to its thermal equilibrium value with continued annealing. It is difficult to explain the continuous generation, growth, shrinkage, and dispersion of the agglomerates during annealing using the usual theoretical treatment of agglomeration of supersaturated solutes in solids.