Permeability and stiffness of sands at very low effective stresses

Loose saturated sandy soils may undergo liquefaction under cyclic loading, generating positive excess pore pressures due to their contractile nature and inability to dissipate pore pressures rapidly during earthquake loading. These liquefied soils have a near-zero effective stress state, and hence have very low strength and stiffness, causing severe damage to structures founded upon them. The duration for which this near-zero effective stress state persists is a function of the rate of reconsolidation of the liquefied soil, which in turn is a function of the permeability and stiffness of the soil at this very low effective stress. Existing literature based on observation of physical model tests suggests that the consolidation coefficient C v associated with this reconsolidation of liquefied sand is significantly lower than that of the same soil at moderate stress levels. In this paper, the results of a series of novel fluidisation tests in which permeability k and coefficient of consolidation C v were independently measured will be presented. These results allow calculation of the variation of stiffness E 0 and permeability k with effective stress. It is shown that while permeability increases markedly at very low effective stresses, the simultaneous drop in stiffness measured results in a decrease in consolidation coefficient and hence an increase in the duration for which the soil remains liquefied.

Very low-pressure VLP-CVD growth of high quality gamma-Al2O3 films on silicon by multi-step process

gamma-Al2O3 films were grown on Si (10 0) substrates using the sources of TMA (AI(CH3)(3)) and O-2 by very low-pressure chemical vapor deposition. The effects of temperature control on the crystalline quality, surface morphology, uniformity and dielectricity were investigated. It has been found that the,gamma-Al2O3 film prepared at a temperature of 1000degreesC has a good crystalline quality, but the surface morphology, uniformity and dielectricity were poor due to the etching reaction between 0, and Si substrate in the initial growth stage. However, under a temperature-varied multi-step process the properties Of gamma-Al2O3 film were improved. The films have a mirror-like surface and the dielectricity was superior to that grown under a single-step process. The uniformity of gamma-Al2O3 films for 2-in epi-wafer was <5%, it is better than that disclosed elsewhere. In order to improve the crystalline quality, the gamma-Al2O3 films were annealed for I h in O-2 atmosphere. (C) 2002 Elsevier Science B.V. All rights reserved.

Very low hysteresis organic thin-film transistors

Very low hysteresis vanadyl-phthalocyanine/para-sexiphenyl thin-film transistors (TFTs) have been fabricated using benzocyclobutenone (BCBO) derivatives/tantalum pentoxide (Ta2O5)/BCBO triple gate dielectrics. The field effect mobility, on/off current ratio and threshold voltage of organic TFTs are 0.45 cm(2) V-1 s(-1), 3.5 x 10(4) and -6.8 V, respectively. To clarify the mechanism of hysteresis, devices with different dielectrics have been studied. It is found that the bottom BCBO derivatives (contact with a gate electrode) block the electron injection from a gate electrode to dielectrics.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with a matrix of carbon nanotubes for the analysis of low-mass compounds in environmental samples

The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for environmental analysis has been mainly focused on qualitative analysis of high-mass molecules, such as toxins, humic acid, and microorganisms. Herein,we describe a novel MALDI-TOF-MS method with a matrix of oxidized carbon nanotubes for analysis of low-mass compounds in environmental samples. A number of chemicals in the environment were qualitatively analyzed by the present method, and it was found that most of them, especially the highly polar chemicals, were measurable with high sensitivity. With the intrinsic ability to measure high-mass chemicals, this method can compensate for the current shortage of methods for environmental analysis for the measurement of highly polar or high-mass chemicals. For sample analysis, arsenic speciation in Chinese traditional medicines was qualified and diphenylolpropane in water samples was quantified. With the relatively high tolerance of the method to interfering molecules, a simple pretreatment or even no pretreatment could be employed before MS detection. Furthermore, this method can be employed in a high-throughput format.

Interpolation formula between very low and intermediate-to-high damping Kramers escape rates for single-domain ferromagnetic particles

It is shown that the Mel'nikov-Meshkov formalism for bridging the very low damping (VLD) and intermediate-to-high damping (IHD) Kramers escape rates as a function of the dissipation parameter for mechanical particles may be extended to the rotational Brownian motion of magnetic dipole moments of single-domain ferromagnetic particles in nonaxially symmetric potentials of the magnetocrystalline anisotropy so that both regimes of damping, occur. The procedure is illustrated by considering the particular nonaxially symmetric problem of superparamagnetic particles possessing uniaxial anisotropy subject to an external uniform field applied at an angle to the easy axis of magnetization. Here the Mel'nikov-Meshkov treatment is found to be in good agreement with an exact calculation of the smallest eigenvalue of Brown's Fokker-Planck equation, provided the external field is large enough to ensure significant departure from axial symmetry, so that the VLD and IHD formulas for escape rates of magnetic dipoles for nonaxially symmetric potentials are valid.

The massive neutron star or low-mass black hole in 2S 0921-630

We report on the optical spectroscopy of the eclipsing halo low-mass X-ray binary 2S 0921-630, which reveals the absorption-line radial velocity curve of the K0 III secondary star with a semiamplitude K-2=92.89+/-3.84 km s(-1), a systemic velocity gamma=34.9+/-3.3 km s(-1), and an orbital period P-orb of 9.0035+/-0.0029 days (1 sigma). Given the quality of the data, we find no evidence for the effects of X-ray irradiation. Using the previously determined rotational broadening of the mass donor and applying conservative limits on the orbital inclination, we constrain the compact object mass to be 2.0-4.3 M-circle dot (1 sigma), ruling out a canonical neutron star at the 99% level. Since the nature of the compact object is unclear, this mass range implies that the compact object is either a low-mass black hole with a mass slightly higher than the maximum possible neutron star mass (2.9 M-circle dot) or a massive neutron star. If the compact object is a black hole, it confirms the prediction of the existence of low-mass black holes, while if the object is a massive neutron star, its high mass severely constrains the equation of state of nuclear matter.