Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of gamma-LiAlO2

gamma-LiAlO2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 degrees C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190-1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398x10(-6)/degrees C to 16.5240x10(-6)/degrees C, and that for c axis drops from 10.7664x10(-6)/degrees C to 10.0786x10(-6)/degrees C.

Reflection and transmission properties of double submerged rectangular blocks

An analytic method is used to study the reflection and transmission coefficients of the double submerged rectangular blocks (DSRBs) in oblique waves.. The scattering potentials are obtained by means of the eigenfunction expansion method, and expressions for the reflection and transmission coefficients are determined. The boundary element method is employed to verify the correctness of the present analytical method. The DSRBs have better performance than the single submerged rectangular block (SSRB) in certain cases. The reflection and transmission properties of the DSRBs are investigated for some specific cases, and the influences of the geometric parameters are also presented.

Equivalent Model Of Expansion Of Cement Mortar Under Sulphate Erosion

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

Transmission Electron Microscopy Characterization of Laser Welding Cast Ni-Based Superalloy K418 Turbo Disk And Alloy Steel 42Crmo Shaft

Microstructure characterization is important for controlling the quality of laser welding. In the present work, a detailed microstructure characterization by transmission electron microscopy was carried out on the laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft and an unambiguous identification of phases in the weldment was accomplished. It was found that there are gamma-FeCrNiC austenite solid solution dendrites as the matrix, (Nb, Ti) C type MC carbides, fine and dispersed Ni-3 Al gamma' phase as well as Laves particles in the interdendritic region of the seam zone. A brief discussion was given for their existence based on both kinetic and thermodynamic principles. (c) 2007 Elsevier B.V. All rights reserved.

Size-Dependent Interface Phonon Transmission And Thermal Conductivity Of Nanolaminates

An analytical model for size-dependent interface phonon transmission and thermal conductivity of nanolaminates is derived based on the improved acoustic mismatch theory and the Lindemann melting theory by considering the size effect of phonon velocity and the interface lattice mismatch effect. The model suggests that the interface phonon transmission is dominant for the cross-plane thermal conductivity of nanolaminates and superlattices, and the intrinsic variety of size effect of thermal conductivity for different systems is proposed based on the competition mechanism of size effect of phonon transport between two materials constituting the interfaces. The model's prediction for thermal conductivity of nanolaminates agrees with the experimental results. (C) 2008 American Institute of Physics.

Derivation Of A Nonlinear Reynolds Stress Model Using Renormalization Group Analysis And Two-Scale Expansion Technique

Adopting Yoshizawa's two-scale expansion technique, the fluctuating field is expanded around the isotropic field. The renormalization group method is applied for calculating the covariance of the fluctuating field at the lower order expansion. A nonlinear Reynolds stress model is derived and the turbulent constants inside are evaluated analytically. Compared with the two-scale direct interaction approximation analysis for turbulent shear flows proposed by Yoshizawa, the calculation is much more simple. The analytical model presented here is close to the Speziale model, which is widely applied in the numerical simulations for the complex turbulent flows.

Control dynamics of severe acute respiratory syndrome transmission

Severe acute respiratory syndrome (SARS) is a serious disease with many puzzling features. We present a simple, dynamic model to assess the epidemic potential of SARS and the effectiveness of control measures. With this model, we analysed the SARS epidemic data in Beijing. The data fitting gives the basic case reproduction number of 2.16 leading to the outbreak, and the variation of the effective reproduction number reflecting the control effect. Noticeably, our study shows that the response time and the strength of control measures have significant effects on the scale of the outbreak and the lasting time of the epidemic.

An optimal theory for an expansion of flow quantities to capture the flow structures

An optimal theory on how database analysis to capture the flow structures has been developed in this paper, which include the POD method as its special case. By means of the remainder minimization method in the Sobolev space, for more general optimal conditions the new theory has the potential to overcome an inherent limitation of the POD method, i.e., it cannot be used to the situations in which the optimal condition is other than the inner product global one. As an example, using the new theory, the database of a two-dimensional flow over a backward-facing step is analyzed in detail, with velocity and vorticity bases.

Magnetostatic relations including fluctuation fields - the local expansion

Using the approach of local expansion, we analyze the magnetostatic relations in the case of conventional turbulence. The turbulent relations are obtained consisten tly for themomentum equation and induction equation of both the average and fluctuation relations.In comparison with the magnetostatic relations as discussed usually, turbulent fluctuationfields produce forces, one of which 1/(4π)(α1×B0)×B0 may have parallel and perpendicular components in the direction of magnetic field, the other of which 1/(4π)K×B0 is introduced by the boundary value of turbulence and is perpendicular to the magnetic field. In the case of 2-dimensional configuration of magnetic field, the basic equation will be reduced into a second-order elliptic equation, which includes some linear and nonlinear terms introduced by turbulent fluctuation fields. Turbulent fields may change the configuration of magnetic field and even shear it non-uniformly. The study on the influence of turbulent fields is significant since they are observed in many astrophysical environments.

Naive asymptotic expansion of the water wave generated by a slowly moving body

It is pointed out that the naive asymptotic expansion does not satisfy all the body boundary condition. A nonhomogeneous body boundary condition is obtained from this expansion. It is this condition that the additional wave term must satisfy. Moreover, because of this condition, the wave term must appear. It is pointed out that the zeroth approximation in the naive asymptotic expansion has weak singularity and the singularities become still stronger in the subsequent approximations.

The influence of fluctuation fields on the force-free field .2. The local expansion

In Paper I (Hu, 1982), we discussed the the influence of fluctuation fields on the force-free field for the case of conventional turbulence and demonstrated the general relationships. In the present paper, by using the approach of local expansion, the equation of average force-free field is obtained as (1+b)×B 0=(#x002B;a)B 0#x002B;a (1)×B 0#x002B;K. The average coefficientsa,a (1),b, andK show the influence of the fluctuation fields in small scale on the configurations of magnetic field in large scale. As the average magnetic field is no longer parallel to the average electric current, the average configurations of force-free fields are more general and complex than the usual ones. From the view point of physics, the energy and momentum of the turbulent structures should have influence on the equilibrium of the average fields. Several examples are discussed, and they show the basic features of the fluctuation fields and the influence of fluctuation fields on the average configurations of magnetic fields. The astrophysical environments are often in the turbulent state, the results of the present paper may be applied to the turbulent plasma where the magnetic field is strong.

EQUIVALENT MODEL OF EXPANSION OF CEMENT MORTAR UNDER SULPHATE EROSION

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

Size- And Temperature-Dependent Thermal Expansion Coefficient Of A Nanofilm

The thermal expansion coefficient (TEC) of an ideal crystal is derived by using a method of Boltzmann statistics. The Morse potential energy function is adopted to show the dependence of the TEC on the temperature. By taking the effects of the surface relaxation and the surface energy into consideration, the dimensionless TEC of a nanofilm is derived. It is shown that with decreasing thickness, the TEC can increase or decrease, depending on the surface relaxation of the nanofilm.

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the case of homonuclear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuclear clusters with larger sizes are required to achieve a greater neutron yield.

Transmission spectrum of a double quantum-dot-nanocavity system in photonic crystals

We investigate the optical transmission properties of a combined system which consists of two quantum-dot-nanocavity subsystems indirectly coupled to a waveguide in a planar photonic crystal. A Mollow-like triplet and the growth of sidebands are found, reflecting intrinsic optical responses in the complex microstructure.