Melting of Silica up to 7 GPa

Melting relations of SiO₂ were determined up to 7 GPa. The triple point of quartz-coesite-liquid is located at 4.5 GPa and 2450°C. The melting curve of coesite has a steep initial slope (150°C/GPa) and reaches about 2700°C at 7 GPa. Densities of the quenched glasses are also reported.     

Granular packings of cohesive elongated particles

We report numerical results of effective attractive forces on the packing properties of two-dimensional elongated grains. In deposits of non-cohesive rods in 2D, the topology of the packing is mainly dominated by the formation of ordered structures of aligned rods. Elongated particles tend to align horizontally and the stress is mainly transmitted from top to bottom, revealing an asymmetric distribution of local stress. However, for deposits of cohesive particles, the preferred horizontal orientation disappears. Very elongated particles with strong attractive forces form extremely loose structures, characterized by an orientation distribution, which tends to a uniform behavior when increasing the Bond number. As a result of these changes, the pressure distribution in the deposits changes qualitatively. The isotropic part of the local stress is notably enhanced with respect to the deviatoric part, which is related to the gravity direction. Consequently, the lateral stress transmission is dominated by the enhanced disorder and leads to a faster pressure saturation with depth.     

Impact of coronary artery calcification in hemodialysis patients: Risk factors and associations with prognosis

The risk factors of coronary artery calcification (CAC) and the impact of CAC on cardiovascular events, cardiovascular deaths, and all‐cause deaths in hemodialysis (HD) patients have not been fully elucidated. We examined the CAC score (CACS) in 74 HD patients using electron‐beam computed tomography. Fifty‐six patients underwent a second electron‐beam computed tomography after a 15‐month interval to evaluate CAC progression. We evaluated (1) the risk factors for CAC and its progression and (2) the impact of CAC on the prognosis. In the cross‐sectional study, HD vintage and high‐sensitive C‐reactive protein (hsCRP) were the independent risk factors for CAC. In the prospective cohort study, delta CACS (progression of CAC) was significantly correlated with hsCRP, fibrinogen, and serum calcium level in the univariate analysis. Stepwise multiple regression analysis revealed that only hsCRP was the independent risk factor for CAC progression in HD patients. Kaplan‐Meier survival analysis revealed that cardiovascular events (P<0.0001), cardiovascular deaths (P=0.039), and all‐cause deaths (P=0.026) were significantly associated with CACS. In conclusion, CAC had significantly progressed in HD patients during the 15‐month observation period. Microinflammation was the only independent risk factor for CAC progression in HD patients. The advanced CAC was a significant prognostic factor in HD patients, i.e., which was strongly associated with future cardiovascular events, cardiovascular deaths, and all‐cause deaths.     

New three-dimensional electrode structure for the lithium battery: Nano-sized γ-Fe2O3 in a mesoporous carbon matrix

A new electrode structure based on a three-dimensional mesoporous matrix was developed. Nanoparticles of γ-iron oxide (Fe₂O₃) were introduced into the mesopores of a carbon matrix (mesoporous carbon, CMK-3) by oxidizing metallic iron, which was electroplated in the matrix. The resulting structure was found to have a high charge-discharge capacity when used as the positive electrode of a lithium battery. The iron oxide nanoparticles bonded tightly to the electrically conductive electrode framework, and showed a high activity for the electrochemical reaction: Fe₂O₃ + 6Li → 3Li₂O + 2Fe.     

Thermo-mechanical stability of porous alumina: effect of sintering parameters

Recently, we proposed a two-step heating schedule involving pulse electric current sintering (PECS), a kind of pressure assisted vacuum sintering, and subsequent post-heat treatment in air to fabricate porous alumina support, using commercially available alumina and carbon powders [J. Mater. Res. 18 (2003) 751]. During pressure assisted vacuum sintering, Al₂O₃–C system of low porosity was obtained and in second stage, i.e. during post-heat treatment in air, carbon particles present in the Al₂O₃–C system burnt out to form highly porous Al₂O₃ support. Following our previous brief study, the effects of sintering parameters such as temperature, pressure, and heating rate on the properties of the porous alumina were investigated. The porosity varied between 28 and 38% depending on the sintering parameters. As desired, the pore size distribution did not change with post-heat treatment temperature and hence the mechanical properties as well. It was concurred from this present study that the sintering parameters of PECS greatly influenced pore characteristics and other properties of porous compacts. We admit that the initial composition ratio of powder mixture (Al₂O₃:C) also plays important role on properties such as porosity, pore size, etc. which is beyond the scope of this present study.     

Removal of arsenic from contaminated soils by microbial reduction of arsenate and quinone

We investigated bioremediation of As-contaminated soils by reductive dissolution of As using a dissimilatory As(V)-reducing bacterium (DARB), Bacillus selenatarsenatis SF-1. We also examined the effect of anthraquinone-2,6-disulfonate (AQDS), an extracellular electron-shuttling quinone, on the As extraction. When B. selenatarsenatis was incubated with As(V)-laden Al precipitates, no acceleration of As dissolution was observed in the presence of AQDS, even though the microbial reduction of AQDS occurred actively. In contrast, AQDS addition significantly enhanced the reductive dissolution of As and Fe in analogous experiments with As(V)-laden Fe(III) precipitates, whereas As dissolution did not occur in the absence of the As(V) reducer. These results indicate the dissolution of As was accelerated by indirect reduction of solid-phase Fe(III) following microbial AQDS reduction, although As(V) reduction is vital for As extraction. B. selenatarsenatis was able to extract As from two types of industrially contaminated soils through reduction of solid-phase As(V) and Fe(III). The copresence of AQDS with B. selenatarsenatis improved the removal efficiency of As from the contaminated soils, concomitantly releasing Fe(II), suggesting that simultaneous use of DARB and electron-shuttling compounds can be an effective strategy for remediation of As-contaminated soils.     

Metal--semiconductor transition in single-walled carbon nanotubes induced by low-energy electron irradiation

We report the effect of low-energy (1 keV) electron beam irradiation on gated, three-terminal devices constructed from metallic single-walled carbon nanotubes. Pristine devices, which exhibited negligible gate voltage response at room temperature and metallic single-electron transistor characteristics at low temperatures, when exposed to an electron beam, exhibited ambipolar field effect transistor (room temperature) and single-electron transistor (low temperature) characteristics. This metal-semiconductor transition is attributed to inhomogeneous electric fields arising from charging during electron irradiation.     

IR detectors using Pb(Mg1/3Nb2/3)O3 and Pb(Sc1/2Ta1/2)O3 ceramics under DC bias

Recently, one type of thermal-type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperature T_c for stable responsivity to temperature. Electric field induced-type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg_1/3Nb_2/3)O₃ (PMN) and Pb(Sc_1/2Ta_1/2)O₃ (PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor. This paper describes the sensor properties of electric field induced-type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high-response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced-type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher electric field.     

Application of the independent molecule model to the calculation of free energy and rigid-body motions of water hexamers

The stabilities of five water hexamers (cyclic, boat, book, prism and cage structure) in the gas phase were investigated with the independent molecule model. In this model, the position and orientation of each water molecule within the hexamer are characterized with a translational vector and Eulerian angles, and then each molecule can move freely as a rigid body with respect to the others. Force field energy minimization yielded structures for each hexamer. Normal mode analyses were done on the five hexamers. Hydrogen bond strength in the hexamer decreases in the order: boat, cyclic, book, cage and prism. Hydrogen bond lifetimes also decrease in this order. By estimating the internal energy and the vibrational entropy of rigid-body motions, we determined the temperature dependence of the free energy for each hexamer in the range 100–350 K. Free energy of the hexamers increases in the previously mentioned order also. The most stable hexamer is the boat, and the least stable is the prism. The stabilities of the boat and the cyclic are very similar. The more planar hexamers (cyclic and boat) are more stable than the three-dimensional hexamers (cage and prism). Although the experiments of Liu et al. [Nature 381 (1996) 501] were interpreted in terms of a cage cluster, our calculations indicate boat is more likely.