Fringe element reconstruction for front tracking for three‐dimensional incompressible flow analysis

Fringe element reconstruction technique for tracking the free surface in three‐dimensional incompressible flow analysis was developed. The flow field was calculated by the mixed formulation based on a four‐node tetrahedral element with a bubble function at the centroid (P1+/P1). Since an Eulerian approach was employed in this study, the flow front interface was advected by the flow through a fixed mesh. For accurate modelling of interfacial movement, a fringe element reconstruction method developed can provide not only an accurate treatment of material discontinuity but also surface tension across the interface. The effect of surface tension was modelled by imposing tensile stress directly on the constructed surface elements at the flow front interface. To verify the numerical approach developed, the developed algorithm was applied to two examples whose solutions are available in references. Good agreement was obtained between the simulation results and these solutions. Copyright © 2005 John Wiley & Sons, Ltd.     

Exposure of defects in GaN by plasma etching

The effect of plasma exposure to n-type GaN surfaces has been examined. Etch pits are formed as a result of preferential sputtering at the sites of threading dislocations. Dark spots which are visible before plasma exposure can be attributed to screw dislocations, while those that emerge after plasma exposure are edge dislocations. The optimum condition for revealing defects clearly is derived, and has been adopted for the study of dislocations in a series of GaN epilayers grown under different conditions. A distinct trend in the dislocation density can be observed as the dopant concentration of the film varies. PACS 61.72.Ff; 68.37.Tj     

First-principles study on the electronic structures of iron phthalocyanine monolayer

The electronic band structure and magnetic properties of iron phthalocyanine (FePc) monolayer were investigated by using the first-principles all-electron full-potential linearized augmented plane wave energy band method. It is found that the ferromagnetic FePc monolayer is energetically more stable than the paramagnetic one. The exchange interaction, which splits the majority and minority bands, influences strongly on the electronic structure near the Fermi level (E_F). Magnetic moment of the central Fe atom is calculated to 1.95 μ_B. The range of the positive polarization of Fe site is larger in the out-of-plane than in the in-plane direction. The FePc ligand remains paramagnetic. The presence of states at E_F indicates the metallic character of FePc monolayer both for the paramagnetic and ferromagnetic states. However, the large density of states at E_F of the majority spins in the ferromagnetic state is expected to cause a phase transition to insulating antiferromagnetic state from the metallic ferromagnetic one.     

Gaps of operators

We construct examples which distinguish clearly the classes of p-hyponormal operators for 0<p?∞. In addition, we show that those examples classify the classes of w-hyponormal, absolute-p-paranormal, and normaloid operators on the complex Hilbert space. Only a few examples of p-hyponormal operators have been examined. Our technique can provide many examples related to the above operators.     

Spin-Hall effect: Back to the beginning at a higher level

The phenomena of the spin-Hall effect, initially proposed over three decades ago in the context of asymmetric Mott skew scattering, was revived recently by the proposal of a possible intrinsic spin-Hall effect originating from a strongly spin-orbit coupled band structures. This new proposal has generated an extensive debate and controversy over the past 2 years. On August 2006 the first workshop on the spin-Hall effect was held at the Asian Pacific Center for Theoretical Physics. Its purpose was to bring together many of the leading groups in this field to resolve such issues and identify future challenges. We offer this short summary to clarify formerly controversial issues now settled and help refocus the research efforts in new and important avenues.     

ESR study of rare-earth ions with the effective spin of 1/2 in LiNbO3 crystals

Rare-earth ions of Nd³⁺ and Er³⁺ in nearly stoichiometric and MgO-doped LiNbO₃ crystals, respectively, have been investigated by employing an X-band electron spin resonance (ESR) spectrometer. The grown crystal was heated in Li-rich powder at 1100°C in order to make it nearly stoichiometric by the vapor transport equilibrium technique. Due to the fact that the ESR linewidth is much narrower in the stoichiometric crystal than in the congruent LiNbO₃, we were able to determine the hyperfine constants of¹⁴³Nd and¹⁴⁵Nd at 4 K. By codoping MgO into LiNbO₃, a new Er³⁺ center has been observed with a differentg-tensor. We propose that the new Er³⁺ center in Mg-doped LiNbO₃ occupies the niobium site due to the local excessive Mg²⁺ ion at the lithium site, whereas Nd³⁺ and Er³⁺ in congruent crystals reside at the lithium site. The proposal is consistent with theg-value anisotropy.     

Synthesis and photoluminescence study of benz[f]indene derivatives

The synthesis and optical properties of a series of benz[f]indenes as new building blocks for electronic and optoelectronic materials are described.     

Electron paramagnetic resonance of deep boron acceptors in 4H-SiC and 3C-SiC crystals

EPR spectra of deep boron in 4H-SiC and 3C-SiC crystals have been observed and studied. Two sites in 4H-SiC produced deep-boron EPR signals, quasi-cubic k and hexagonal h. In both cases the deep-boron center symmetry is close to axial along the c crystal axis, and the g factor anisotropy is about an order of magnitude larger than that for shallow boron centers. In the 3C-SiC crystal, the deep-boron symmetry is also close to axial along one of the four 〈111〉 directions. The model proposed for the deep boron center with acceptor properties is B_Si-v _C, where B_Si is the boron substituting for silicon, and v _C is the carbon vacancy, with the B_Si-v _C direction coinciding in 4HSiC with the hexagonal axis of the crystal for both k and h positions. In the cubic 3C-SiC crystal, there are four equivalent deep boron centers, which represent B_Si-v _C pairs with the bond directed along one of the four 〈111〉 crystal directions. Fiz. Tverd. Tela (St. Petersburg) 40, 36–40 (January 1998)     

Anomalous drift of resonant particles in a buffer medium under pressure of light

We study theoretically the drift of resonant particles in a buffer medium when a traveling light wave impinges on the medium, with allowance for the velocity dependence of the transport collision rate. When the pressure of light dominates over the light-induced drift (low pressure of the buffer gas or the drift of conduction electrons in semiconductors), we discover a new sudden transformation of the spectral dependence of the drift velocity of the resonant particles: Instead of the ordinary bell-shaped function representing the velocity spectrum we have a double-humped curve with deep dip at the center of the absorption line. We show that the largest transformation of the drift velocity spectrum occurs in the atmosphere of a heavy buffer gas in the case of Coulomb interaction between the resonant and buffer particles. The transformation effect is caused by the variation of the transport rate of the collisions of the resonant and buffer particles due to the recoil effect in the absorption of radiation. Zh. éksp. Teor. Fiz. 112, 856–868 (September 1997)