Investigation of phase transition of γ-alumina to α-alumina via mechanical milling method

In this research, the results obtained from studying the phase transition of γ-alumina (γ-Al₂O₃) to α-alumina (α-Al₂O₃) during intense mechanical activation in high-energy ball milling are presented. The powder samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric and Differential thermal analyses (TG-DTA). With respect to the results achieved from above analyses, the transition of γ → α-alumina through δ- and θ-phases, can be initiated. Also, it was found that the pure γ-alumina phase showed a great stability during high-energy ball milling and there was no transformation to any other phase after a long milling time (30 h). On the other hand, γ-alumina containing a small amount of the α-alumina seed, showed a gradual phase transition from γ-alumina to α-alumina in milling. The phase transition mechanism during milling is nucleation and growth, which is promoted by the α-alumina seed.     

Hopping conduction in Na-β-alumina

The frequency dependence of ionic conductivity, σ(ω), in Na-β-alumina is calculated on the basis of a simple hopping model of conduction. By comparing the calculated results with the experimental data on σ(ω), a possible potential energy-distance diagram is suggested.     

Discrete elliptic solitons in two-dimensional waveguide arrays

The fundamental properties of discrete elliptic solitons (DESs) in the two-dimensional waveguide arrays were studied. The DESs show nontrivial spatial structures in their parameters space due to the introduction of the new freedom of ellipticity, and their stability is closely linked to their propagation directions in the transverse plane.     

Ionic conduction in Sr hexa-aluminate with β-alumina structure

A new type of strontium β-alumina was developed by a single solid state reaction. Polycrystals of Sr β-alumina with the chemical formula of SrMgAl₁₀O₁₇ were prepared and examined by a conductivity. The values of ionic conductivity in the Sr β-alumina were 5 to 3 orders of magnitude lower than those of polycrystalline Na β-alumina between 773 and 1273 K. The ion exchange of Sr β-alumina for sodium was also examined, and the values of conductivity for the partially ion-exchanged samples increased with the increase of the excess amount of Na⁺ up to 0.5–0.6 in comparison with that of the ideal Na β-alumina.     

Thermal disordering near a Σ=3{111} twin boundary in Cu3Au

Symmetrical and asymmetrical configurations of a =3 (111) twin boundary in Cu₃Au are studied by means of energy minimization and Monte Carlo simulations of a rigid lattice, using an adapted n-body potential. We find that relaxation occurring in the neighborhood of the boundary is larger for asymmetrical than for the symmetrical minimum energy configurations. From energy minimization the latter are also shown to correspond to the lowest excess energy. For the asymmetrical twin structure, Monte Carlo calculations of the long-range order parameter on a local basis show the existence of prewetting effects, i.e., the appearance well below the critical temperature of several partially disordered layers at each side of the twin boundary. In contrast, the order is preserved in the symmetrical twin in the same temperature range. These results are consistent with experimental observations of wetting in =3 (111) twins in Cu₃Au, and it is found to occur at lower temperature in asymmetrical than in symmetrical boundaries.     

Prediction for α3(Mz) in a string-inspired model

We apply the Renormalisation Group Evolution (RGE) to analyse the phenomenological implications of an extended supersymmetric model, for the value of the unification scale and the strong coupling at the electroweak scale. The model we consider is predicted to exist in Calabi–Yau string compactifications with Wilson line mechanism for E₆ symmetry breaking, contains additional matter beyond the MSSM spectrum and avoids the “doublet-triplet” splitting problem in the Higgs sector. The calculation is analytical in two-loop order and includes the effects of the heavy thresholds due to the additional matter considered. The value of α₃(M_z) can be brought within the experimental limits without a significant change of the unification scale from the MSSM prediction.     

Intrinsic luminescence centers in γ- and θ-alumina nanoparticles

In this study, we investigate the photoluminescence(PL) properties of γ and θ-alumina nanoparticles synthesized by the chemical wet method followed by annealing. The obtained experimental results indicate the presence of some favorable near ultraviolet(NUV)-orange luminescent centers for usage in various luminescence applications, such as oxygen vacancies(F, F~+_2, F~(2+)_2, and F_2centers), OH related defects, cation interstitial centers, and some new luminescence bands attributed to trapped-hole centers or donor–acceptor centers. The energy states of each defect are discussed in detail. The defects mentioned could alter the electronic structure by producing some energy states in the band gap that result in the optical absorption in the middle ultraviolet(MUV) region. Spectra show that photoionazation of F and F_2 centers plays a crucial role in providing either free electrons for the conduction band, or the photoconversions of aggregated oxygen vacancies into each other, or mobile electrons for electrons-holes recombination process by the Shockley–Read–Hall(SRH)mechanism.     

Peptide arrays with designed α-helical structures for characterization of proteins from FRET fingerprint patterns

A practical high-throughput protein detection system is described, based on synthetic peptide arrays consisting of designed alpha-helical peptides, detected by fluorescence resonance energy transfer (FRET). Initially a model alpha-helical peptide known to interact with a structured protein, calmodulin, was selected to establish the strategy for high-throughput detection. In comparison to peptides with a single probe, a much higher FRET response has been observed with two fluorescent probes (7-diethylaminocoumarin-3-carboxylic acid and 5(6)-carboxy-fluorescein) at both termini of the synthetic peptides. To establish a reproducible high-throughput detection system, peptides were also immobilized onto a solid surface for detection of the target proteins. A small library of 112 different peptides was constructed, based on a model of the alpha-helical peptide with systematic replacement of residues carrying specific charges and/or hydrophobicities. The library was used to effectively characterize various proteins, giving their own 'protein fingerprint' patterns. The resulting 'protein fingerprints' correlate with the recognition properties of the proteins. The present microarray with designed synthetic peptides as the capturing agents is promising for the development of protein detection chips.     

On Bose–Einstein condensation in Josephson junctions star graph arrays

We report on the evidence of anomalous currents in graph-shaped arrays of Josephson junctions along peculiar branches of the networks. The specific case of a star-shaped array is considered and the evidence of the anomalies is achieved by comparing the current-voltage characteristics of the arrays embedded in the star structure with those of “reference” arrays which are fabricated by-side the network structure and are dc-isolated from these. The experimental data are consistent with the results of a theoretical model predicting gradients of the populations of Cooper pairs on the islands situated in proximity of the central superconductive island as a result of a Bose–Einstein condensation process.     

Zeeman effect in α-quartz

The helical crystal structure in α-quartz acts as the natural micro-solenoids for an electromagnetic wave passing through them, producing a longitudinal magnetic field in the direction of the optical axis. The longitudinal magnetic field further induces the Larmor frequency for the rotation of the bound electrons. The calculated Larmor frequency was experimentally confirmed by monitoring a line splitting of the infrared OH-band in the transmission spectra of α-quartz. A shift in the resonance frequency of the OH-band is equal to the Larmor frequency induced by the natural Zeeman effect.     

Topological Insulators in α-Graphyne

In this paper, we investigate topological phases of α-graphyne with tight-binding method. By calculating the topological invariant Z2 and the edge states, we identify topological insulators. We present the phase diagrams of α-graphyne with different filling fractions as a function of spin-orbit interaction and the nearest-neighbor hopping energy. We find there exist topological insulators in α-graphyne. We analyze and discuss the characteristics of topological phases of α-graphyne.     

Au diffusion in α-Ti

The solubility and diffusion of Au in -Ti have been studied in a 823–1023 K temperature range using the Rutherford backscattering technique. For this purpose we have implanted Au into -Ti samples. Our results show that the solubility of Au varies between 0.2 and 0.35 at.%. In addition, we found that the diffusion coefficients follow a normal Arrhenius behavior with Q=260 kJ/mol and D _o=1.9×10^–5 m²/s¹. These values are typical for a substitutional diffusion mechanism.     

Lead diffusion in α-Zr

Pb diffusion in α-Zr matrix between 823 and 1123 K was measured using heavy ion Rutherford backscattering spectrometry (HIRBS) technique. A deviation from the Arrhenius law was observed, with two different regions. At low temperatures the activation energy Q is close to the expected value for a substitutional diffuser but the pre-exponential factor D₀ is higher than expected. Close to the phase transition temperature the opposite occurs, with a low Q value. This behavior is similar to the one observed for Hf and self-diffusion in α-Zr. Received: 29 September 1998 / Accepted: 29 January 1999 / Published online: 28 April 1999     

Top rare decays t→cV in mirror twin Higgs models

The decay t→cV(V=γ,Z,g)processes in mirror twin Higgs models with colorless top partners are studied in this paper.We report that the branchi ng ratios of these decays can strongly affect the standard model expectations in some parameter spaces and may be detectable according to the current precision electroweak measurements.Thus,constraints on the model parameters may be obtained from the branching fraction of the decay processes,which may serve as a robust detection tool for this new physics model.     

Coupling-induced bipartite pointer states in arrays of electron billiards: quantum Darwinism in action?

We discuss a quantum system coupled to the environment, composed of an open array of billiards (dots) in series. Beside pointer states occurring in individual dots, we observe sets of robust states which arise only in the array. We define these new states as bipartite pointer states, since they cannot be described in terms of simple linear combinations of robust single-dot states. The classical existence of bipartite pointer states is confirmed by comparing the quantum-mechanical and classical results. The ability of the robust states to create "offspring" indicates that quantum Darwinism is in action.