Modern Physics Letters B

We propose three stages in protein folding, based on physical arguements involving the interplay between the hydrophobic effect and hydrogen bonding, and computer simulations using the CSAW (conditioned self-avoiding walk) model. These stages are characterized by universal exponents ν = 3/5, 3/7, 2/5 in the power law R ~ N^ν, where R is the radius of gyration and N is the number of residues. They correspond to the experimentally observed stages: unfolded, preglobule, molten globule.

In this letter, a new form of electromagnetic-quantum equations is proposed. The electric and magnetic potentials are expressed through a single Hertz vector, and the systems of quantum and Maxwell equations are transformed into more compact integro-differential ones. These new forms are given for the Schrödinger, Pauli, Dirac and Klein–Gordon equations, and a practical way to calculate them by available software tools is considered.

The presence of dopant ions in a high-temperature superconductor (HTSC) is accounted for by introducing an effective temperature of current carriers. It is shown that the BCS formalism, with a power law for the bandwidth and state density dependence on dopant concentration x and a temperature scale, yields a closed formula for T_c(x), which, in several cases, agrees well with experimental data on T_c(x) of HTSCs.

By adding 2 at.% Al element in Zr₅₀Cu₅₀ binary glass-forming alloy, we obtained Zr₅₀Cu₄₈Al₂ glassy rods with diameter larger than 3 mm. The reduced glass transition temperature, parameter γ and the critical section thickness obtained from the differential scanning calorimetry (DSC) traces indicate the better glass-forming ability (GFA) of Zr₅₀Cu₄₈Al₂ bulk metallic glass (BMG). The super-cooled liquid region and the continuous heating transformation diagram constructed from Vogel–Fulcher–Tammann fitting of crystallization temperature illustrate the enhanced thermal stability of the Zr₅₀Cu₄₈Al₂ BMG. The mechanism of effect of minor Al addition on GFA was investigated in more detail from Angell's fragility concept and from the thermodynamic point of view respectively.

We show the steady-state optical multistability (OM) behavior in a four-level atomic system inside a unidirectional ring cavity. We find that the intensity and the detunings of the fields can affect the optical multistability behavior dramatically, which can be used to control the transition from OM to OB or vice versa without the need to resort to the effect of spontaneously generated coherence (SGC). The effect of the atomic cooperation parameter on OM is also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.

The size effect of nano-grain BaTiO₃ ceramics has been studied in this paper. We assume that the surface charge does not fully compensate long-range Coulomb interaction, so that 180 degree nano-domains still exists in small BaTiO₃ particles. We have calculated the long-range interaction in BaTiO₃ nanocrystals with 180 degree nano-domains, and obtained the relationship between grain size and domain size. The relation between transition temperature and grain size is also obtained by incorporating the domain-wall energy into the Landau–Ginzburg free-energy density. The results show that with decreasing grain size the transition temperature of cubic-tetragonal phase decreases, while those of tetragonal-orthorhombic and orthorhombic-rhombohedral phases increase. Our model predicts that with further reduction of grain size, the structures of ferroelectric phase becomes unstable and gradually disappears, leaving only one stable structure of cubic phase. In addition, an interesting conclusion is that a quadruple phase point exists in the phase diagram of the transition temperature versus grain size. The results are compared with experimental data.

Theoretical calculation based on density function theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying the magnetic properties of nitrogen-doped ZnO. The results show that ferromagnetism (FM) coupling between N atoms is more stable for the majority of 11 geometrically distinct configurations, and N atoms in ZnO have a clear clustering tendency. In addition, the formation and ionization energy of native defects in ZnO is analyzed and discussed. The effect of native defects on FM properties of nitrogen-doped ZnO has also been investigated. It is found that FM state is more favored than the AFM state in the presence of zinc vacancy or oxygen interstitial. In the paper, we also analyze strain effect on FM of nitrogen-doped ZnO.

CrO₂ has a wide band gap for "down" spins and the Fermi level lies in the middle of the band gap. Calculations based on the local-spin density approximation (LSDA) has been performed to investigate the electronic and physical properties of CrO₂ in the rutile structure (P42/mnm). We considered the semicore electrons as valence electrons and found that CrO₂ appears to be half-metallic with a direct band gap of 1.8 eV in spin-down and has metallic behavior in spin-up configurations.

Cd²⁺ substituted Li–Zn ferrite with compositional formula Li_0.4-x/2Zn_0.2Cd_xFe_2.4-x/2O₄ with x = 0.02, 0.03 and 0.04 were prepared by the conventional double sintering ceramic technique. XRD technique confirmed the formation of single phase with spinel structure. The substitution causes an increase in the lattice constant, density and DC resistivity, while the Curie temperature and dielectric constant decreases with Cd²⁺ substitution. The mechanisms involved are discussed.