DISCRETE HUYGENS' MODELLING APPROACH TO WAVE PROPAGATIONS IN A HOMOGENEOUS ELASTIC FIELD

The application of the discrete Huygens' modelling has been discussed for acoustic wave propagation problems, in which the scalar wave field problems have been focused. The present paper extends the application of the modelling to the elastic wave propagation in a homogeneous elastic medium in which two types of waves, the longitudinal wave and the shear wave, are independent except at the boundary. Each wave can be treated like a scalar wave until the two waves reach the boundary where they couple so as to satisfy the displacement or stress boundary condition. We propose the approach confining ourselves to the two-dimensional field. Some examples are demonstrated, whose solutions are compared with the vectorial wave modelling and finite difference modelling solutions whenever they are available.     

Shear response of Fe-bearing MgSiO3 post-perovskite at lower mantle pressures

We investigate the shear response of possible slip systems activated in pure and Fe-bearing MgSiO₃ post-perovskite (PPv) through ab initio generalized stacking fault (GSF) energy calculations. Here we show that the [100](001) slip system has the easiest response to plastic shear among ten possible slip systems investigated. Incorporation of Fe²⁺ decreases the strength of all slip systems but does not change the plastic anisotropy style. Therefore, pure and Fe-bearing MgSiO₃ PPv should demonstrate similar LPO patterns with a strong signature of the [100](001) slip system. An aggregate with this deformation texture is expected to produce a V_SH > V_SV type polarization anisotropy, being consistent with seismological observations.     

New vibrational assignments in the Ā1 Au-[Xtilde] 1Σ+ g electronic transition of acetylene,C2H2: the v′1 frequency

New laser-induced fluorescence spectra of supersonic jet cooled acetylene (C₂H₂) in the wavelength region 230–205 nm have led to an improved understanding of the vibrational structure of the A ¹A_u state. Among the new bands observed are two weak perturbed bands at 46008 cm^?1 and 46116 cm^?1. Rotational analyses of these bands, together with the corresponding ‘hot’ bands arising from the ground state v4 fundamental, have shown that the upper states have asymmetric top K structure that is unaffected by a axis Coriolis coupling; this means that they do not involve overtones of the low frequency bending vibrations and therefore must be combinations of a_g vibrational normal modes. From their positions in the manifold, their vibrational assignments can only be 2² ₀3¹ ₀; and 1¹ ₀;3¹ ₀. These assignments lead to values of x ₂₂, x₁₃, and a revised value for the symmetric CH stretching frequency, ν₁ = 2880.5cm^?1; this revised value is 160cm^?1 lower than the previously accepted value, but consistent with new ab initio calculations that we performed at the EOM-CCSD level using a TZ2P (triple-zeta plus double polarization) basis set.     

Circadian clock-controlled diurnal oscillation of Ras/ERK signaling in mouse liver

Accumulating evidence indicates that ERK MAP kinase signaling plays an important role in the regulation of the circadian clock, especially in the clock-resetting mechanism in the suprachiasmatic nucleus (SCN) in mammals. Previous studies have also shown that ERK phosphorylation exhibits diurnal variation in the SCN. However, little is known about circadian regulation of ERK signaling in peripheral tissues. Here we show that the activity of Ras/ERK signaling exhibits circadian rhythms in mouse liver. We demonstrate that Ras activation, MEK phosphorylation, and ERK phosphorylation oscillate in a circadian manner. As the oscillation of ERK phosphorylation is lost in Cry1/Cry2 double-knockout mice, Ras/ERK signaling should be under the control of the circadian clock. Furthermore, expression of MAP kinase phosphatase-1 (Mkp-1) shows diurnal changes in liver. These results indicate that Ras/ERK signaling is strictly regulated by the circadian clock in liver, and suggest that the circadian oscillation of the activities of Ras, MEK, and ERK may regulate diurnal variation of liver function and/or homeostasis.     

FINITE ELEMENT AND BOUNDARY ELEMENT MODELLING FOR THE ACOUSTIC WAVE TRANSMISSION IN MEAN FLOW MEDIUM

The frequency characteristics of the acoustic wave transmission in a medium with mean flow are considered. One approach is to solve the Helmholtz equation with mean flow medium in original co-ordinates, which is directly discretized for the one-dimensional and the axisymmetric FEM. Another approach is to transform the equation into the standard Helmholtz equation, which is discretized for the axisymmetric FEM and the three-dimensional BEM. The numerical models are examined first for a straight circular duct. The solutions by the numerical approaches are compared with the analytical solution. The examination is then extended to the case when the mean flow is locally present in the muffler with expansion chamber. To model the spatial mean flow in the BEM model, the partitioned domain approach is also developed. No shear effect between the two regions are included.