Quantum information processing in the wall of cytoskeletal microtubules

Microtubules (MT) are composed of 13 protofilaments, each of which is a series of two-state tubulin dimers. In the MT wall, these dimers can be pictured as "lattice" sites similar to crystal lattices. Based on the pseudo-spin model, two different location states of the mobile electron in each dimer are proposed. Accordingly, the MT wall is described as an anisotropic two-dimensional (2D) pseudo-spin system considering a periodic triangular "lattice". Because three different "spin-spin" interactions in each cell exist periodically in the whole MT wall, the system may be shown to be an array of three types of two-pseudo-spin-state dimers. For the above-mentioned condition, the processing of quantum information is presented by using the scheme developed by Lloyd.

The bipolar doping of ZnS via native defects and external dopants

By employing first-principle total-energy calculations, a systematic study of the dopability of ZnS to be both n- and p-types compared with that of ZnO is carried out. We find that all the attempted acceptor dopants, group V substituting on the S lattice site and group I and IB on the Zn sites in ZnS, have lower ionization energies than the corresponding ones in ZnO. This can be accounted for by the fact that ZnS has relative higher valence band maximum than ZnO. Native ZnS is weak p-type under S-rich condition, as the abundant acceptor V-Zn has rather large ionization energy. Self-compensations by the formation of interstitial donors in group I and IB-doped p-type ZnS can be avoided when sample is prepared under S-rich condition. In terms of ionization energies, Li-Zn and N-S are the preferred acceptors in ZnS. Native n- type doping of ZnS is limited by the spontaneous formation of intrinsic V-Zn(2-); high efficient n-type doping with dopants is harder to achieve than in ZnO because of the readiness of forming native compensating centers and higher ionization energy of donors in ZnS. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3103585]

Donor defect in P-diffused bulk ZnO single crystal

A high concentration of shallow donor defect is formed in P-diffused ZnO single crystals. X-ray photoelectron spectroscopy analysis indicates that P atom occupy different lattice site at different diffusion temperature. Nature of the donor defect has been discussed.

Luminescence spectroscopy of ion implanted AlN bulk single crystal

High concentrations of Si and Zn were implanted into (0001) AlN bulk crystal grown by the self-seeded physical vapor transport (PVT) method. Cathode luminescence (CL) and photoluminescence (PL) spectroscopy were used to investigate the defects and properties of the implanted AlN. PL spectra of the implanted AlN are dominated by a broad near-band luminescence peak between 200 and 254 nm. After high temperature annealing, implantation induced lattice damages are recovered and the PL intensity increases significantly, suggesting that the implanted impurity Si and Zn occupy lattice site of Al. CL results imply that a 457 nm peak is Al vacancy related. Resistance of the AlN samples is still very high after annealing, indicating a low electrical activation efficiency of the impurity in AlN single crystal.

Simulated morphological landscape of polymer single crystals by phase-field model

The novel phase field model with the "polymer characteristic" was established based on a nonconserved spatiotemporal Ginzburg-Landau equation (TDGL model A). Especially, we relate the diffusion equation with the crystal growth faces of polymer single crystals. Namely, the diffusion equations are discretized according to the diffusion coefficient of every lattice site in various crystal growth faces and the shape of lattice is selected based on the real proportion of the unit cell dimensions.

Synthesis, crystal structure, and density of (W1-xAlx)C

A new solid solution system of Al in WC, with the stoichiometry of (W1-xAlx)C (x = 0.10, 0.25, 0.50, 0.75, 0.86), has been synthesized by a solid-state reaction between W1-xAlx alloys and carbon at around 1673 K in vacuum. Environment scanning electron microscope, energy- dispersive analysis of X-ray, X-ray photoelectron spectroscopy, and inductively coupled plasma analyses are used to certify the formation of the products. The mechanism of the solid-state reaction is also discussed. (W1-xAlx)C is identified to crystallize in the hexagonal space group P6m2 (No. 187) and belongs to the WC structure type. The atoms of W and Al occupy the same lattice site (la site) in the cell of (W1-xAlx)C. The cell parameters for each specimen in the phase of W-AI-C are quite close to that of WC, while their densities are far lower than that of WC.

The luminescence of Eu2+ in mixed phase system

The dependence of the structure of the hosts on the M ion radius in MMgAl10O17 (M = Be, Mg, Ca, Sr, Ba, Pb, Eu, Mn, Fe, Co, Ni, Zn, Cd, Sn) system was studied and the luminescence of Eu2+ the mixed phase system was discussed. When M ion radius is less than 0.10 nm, the system MMgAl10O17 constructs by the mixed phases consisting of manegtoplumbite and spinel, alpha-alumina or spinel and alpha-alumina. In the mixed phase of manegtoplumbite and spinel and alpha-alumina, Eu2+ ion preferentially occupies lattice site of the cations in manegtoplumbite well matched with the radius and charge of Eu2+. There exists only d-->f transition emission of Eu2+ and no characteristic emission of Eu3+ occurs in those hosts. In the mixed phase of spinel and alpha-alumina, Eu2+ can enter the lattice site of Mg2+ ion or Al3+ ion and the d-->f and f-->f transition of Eu2+ can been observed respectively. Meanwhile, since the radius and charge of matrix lattice ions substituted by Eu2+ do not match with those of Eu2+, the valence state of Eu2+ is unstable. Eu2+ is partly changed into Eu3+ and the emission of Eu3+ is obviously observed even under the condition of reduction atmosphere. If reaction temperature is more than 1 150 degrees C, Al2O3 forms alpha-Al2O3 structure, the f-->f transition of Eu2+ appears. If reaction temperature is less than 1 150 degrees C, a mixed phase of alpha-Al2O3 and gamma-Al2O3 is formed, the f-->f transition of Eu2+ disappears and a new band emission from d-->f transition of Eu2+ occurs.

Theoretical investigation on the phase stability of Nd2Fe14B and site preference of V, Cr, Mn, Zr and Nb

The stability of the excellent permanent magnetic compound Nd2Fe14B and substitution of Fe in the compound by V, Cr, Mn, Zr and Nb are investigated by using interatomic pair potentials which are converted from lattice-inversion method. Calculation shows that the substitution always makes the cell volume larger, and the increase of the volume is almost linear with substituent concentration. The calculated cohesive energy shows that the preferential order of substitution of Fe is Nb, V, Cr, Mn, Zr. Nevertheless, all the five substituting elements should most preferentially replace Fe in the j(2)' site, which has the greatest space among all six Fe sites. (C) 2005 Elsevier B.V. All rights reserved.

Active site structure of NO decomposition on perovskite(-like) oxides: An investigation from experiment and density functional theory

Active site structure for NO decomposition carried out on perovskite-like oxides were discussed based on the N-2 yield measured from LaSrNi1-x,AlxO4 with different B-site cations and from La2-ySryCuO4 with different crystal phases. Results show that the active site contains two oxygen vacancies, two transition metals, and one lattice-oxygen, with the oxygen vacancy locating on the apex of MO6 octahedron, and the lattice oxygen locating between the two transition metals (i.e., M-O-M plane). Density functional theory (DFT) analysis to the structure shows that this new active site is the most active structure for NO adsorbing, and hence, for NO decomposition. The similar trend of the relative energies that are required for the formation of oxygen vacancies with f form (calculated from DFT), the amount of oxygen vacancies, and the activities (N-2 yield) certifies this result further.

Effects of chain flexibility on polymer conformation in dilute solution studied by lattice Monte Carlo simulation

Effects of chain flexibility on the conformation of homopolymers in good solvents have been investigated by Monte Carlo simulation. Bond angle constraint coupled with persistence length of polymer chains has been introduced in the modified eight-site bond fluctuation simulation model. The study about the effects of chain flexibility on polymer sizes reveals that the orientation of polymer chains under confinement is driven by the loss of conformation entropy. The conformation of polymer chains undergoing a gradual change from spherical iso-diametric ellipsoid to rodlike iso-diametric ellipsoid with the decrease of polymer chain flexibility in a wide region has been clearly illustrated from several aspects. Furthermore, a comparison of the freely jointed chain (FJC) model and the wormlike chain (WLC) model has also been made to describe the polymer sizes in terms of chain flexibility and quasi-quantitative boundary toward the suitability of the models.

Simple lattice Boltzmann model for traffic flows

A lattice Boltzmann model with 5-bit lattice for traffic flows is proposed. Using the Chapman-Enskog expansion and multi-scale technique, we obtain the higher-order moments of equilibrium distribution function. A simple traffic light problem is simulated by using the present lattice Boltzmann model, and the result agrees well with analytical solution.

Rossby Vortex Simulation on a Paraboloidal Coordinate System Using the Lattice Boltzmann Method

In this paper, we apply our compressible lattice Boltzmann model to a rotating parabolic coordinate system to simulate Rossby vortices emerging in a layer of shallow water flowing zonally in a rotating paraboloidal vessel. By introducing a scaling factor, nonuniform curvilinear mesh can be mapped to a flat uniform mesh and then normal lattice Boltzmann method works. Since the mass per unit area on the two-dimensional (2D) surface varies with the thickness of the water layer, the 2D flow seems to be "compressible" and our compressible model is applied. Simulation solutions meet with the experimental observations qualitatively. Based on this research, quantitative solutions and many natural phenomena simulations in planetary atmospheres, oceans, and magnetized plasma, such as the famous Jovian Giant Red Spot, the Galactic Spiral-vortex, the Gulf Stream, and the Kuroshio Current, etc,, can be expected.

Lattice Boltzmann方法模拟多孔介质Klinkenberg效应

格子Boltzmann数值模拟方法是研究复杂的多孔介质结构特别是Klinkenberg效应的有效方法之一，对处理复杂边值问题尤其有效。用格子Boltzmann方法研究了气流穿越多孔介质问题，并将数值计算结果与实验结果进行了比较，结果表明格子Boltzmann方法是数值模拟气流穿越多孔介质问题的有效方法之一。

A lattice Boltzmann method for KDV equation

We prepose a 5-bit lattice Boltzmann model for KdV equation. Using Chapman-Enskog expansion and multiscale technique, we obtained high order moments of equilibrium distribution function, and the 3rd dispersion coefficient and 4th order viscosity. The parameters of this scheme can be determined by analysing the energy dissipation.

Lattice Boltzmann method for compressible flows with high Mach numbers

In this paper we present a lattice Boltzmann model to simulate compressible flows by introducing an attractive force. This scheme has two main advantages: one is to soften sound speed effectively, which greatly raises the Mach number (up to 5); another is its relative simple procedure. Simulations of the March cone and the comparison between theoretical expectations and simulations demonstrate that the scheme is effective in the simulation of compressible flows with high Mach numbers, which would create many new applications.