International Journal of Modern Physics B

We examine features of intracellular networks that make errors less probable and beneficial responses more probable. In a false negative (F^-) error, a network does not respond to input. A network is reliable if it operates with a low probability of a F^- error. Features that promote reliability include fewer reactions in sequence, more alternative pathways, no side reactions and negative feedback. In a false positive (F⁺) error, a network produces output without input. Here, a network is specific if it has a low probability of a F⁺ error. Conjunctions of signals within or between pathways can improve specificity through sigmoid steady-state response curves, kinetic proofreading and checkpoints. Both reliability and specificity are important in networks that regulate the fate of a cell and in networks with hubs or modules, and this includes scale-free networks. Some networks discriminate among several inputs by responding to each input through a different combination of pathways.

Within a tight-binding Su–Schrieffer–Heeger model, the elementary excitations and optical absorption of a polyacene chain are investigated. The polyacene chain composed of a number of aromatic rings is considered as two strongly coupled polyacetylene chains with an open boundary condition. First of all we found an interchain-coupled neutral soliton in a pristine chain as a consequence of odd-number sites in each chain. There are two localized electronic states accompanying the soliton and appearing in the conduction and valence bands, respectively. Moreover, an injected electron or hole will induce a polaron-like deformation mixed with the interchain soliton, while two extra electrons or holes will result in three separate solitons, among which one is doubly charged and other two are neutral. The optical absorption due to these elementary excitations are obtained.

We have produced powders of nanostructured and amorphous alloys as well as bulk amorphous alloys with composition Zr₆₄Cu₁₈Ni₁₀Al₈ by mechanical alloying and by quenching arc melted melts in water cooled cooper dies, respectively. The alloys were investigated by X-ray diffraction as well as by thermal analysis in order to determine the structure and thermal properties. The mechanical alloyed amorphous powders and bulk amorphous cylinders show the same thermal and X-ray characteristics. For the amorphous powders, we find that the glass transition temperature T_g is 657 K and the crystallization temperature T_x is 752 K. For bulk amorphous alloys with the same composition prepard by arc melting and liquid quenching T_gis 655 K and the T_x is 725 K. Moreover for the bulk amorphous alloys the supercooled liquid region Δ T_xg is 70 K, the reduced glass transition temperature t_g is 0.557, the Lu–Liu parameter γ which represents the glass forming ability for bulk metallic glasses is 0.396 and experimentally the critical cooling rate R_c takes the value 7 K s^-1.

We use Lewis and Riesenfeld's quantum invariant theory to calculate the Lewis–Riesenfeld phases for a time-dependent frequency harmonic oscillator that is confined between a fixed boundary and a moving one. We also discuss the Berry phase for the system with a sinusoidally oscillating boundary.

The surfactant structures are approximately given by the zero-potential surfaces of A⁺ and B^- atoms in circle or sphere packings. The Dirichlet domains of A atoms are connected by T₁ channels to neighboring A domains in rod like structures with T₁ = 2, or layered structures at increased T₁ values. Micelles are usually isolated with T₁ = 0 or 1 channels. Layered or rod like structures are formed at A–A attraction while isolated micelles are formed at repulsive A–A interactions. The rod like structures are similar to polymer chains of A = carbon atoms with T₁ = 2 neighbors. The ordered micelle structures are observed for charged colloid particles A⁺.

The equilibrium structures and cohesive energies of small Cu_n clusters using the full-potential muffin-tin orbitals (FP-LMTO) based molecular dynamics (MD) have been studied for n ≤ 9. The results obtained have been compared with other chemical methods. We propose the FP-LMTO-MD technique to be a useful starting point of more empirical methods which can efficiently deals with larger cluster sizes relevant for nanoparticles.

AC susceptibility measurements as a function of temperature and amplitude of alternative magnetic field have been carried out on the samples (Bi,Pb)(Sr,Ba):2223 with Cu substituted by Zn at a concentration of x = 0.00, 0.02 and 0.05. The decrease of intergrain and intragrain critical temperatures with increasing x is in agreement with the increase of the residual resistivity. Using Muller critical state model and the linear dependence of T_p for the maximum of imaginary χ″(T) peak, as a function of AC field amplitude, the intergranular pining force density was obtained. The intergrain properties are more influenced than the intragrain ones.

The f and d electron density of states of the one-dimensional Falicov–Kimball model are studied in the weak-coupling limit by exact diagonalization calculations. The resultant behaviors are used to examine the d electron gap (Δ_d), the f electron gap (Δ_f), and the fd electron gap (Δ_fd) as functions of the f level energy E_f and hybridization V. It is shown that the spinless Falicov–Kimball model behaves fully differently for zero and finite hybridization between f and d states. At zero hybridization the energy gaps do not coincide (Δ_d ≠ Δ_f ≠ Δ_fd), and the activation gap Δ_fd vanishes discontinuously at some critical value of the f level energy E_fc. On the other hand, at finite hybridization all energy gaps coincide and vanish continuously at the insulator-metal transition point E_f = E_fc. The importance of these results for a description of real materials is discussed.

We use the double exchange (DE) model via degenerate orbitals and tight-binding approximation to study the magnetoconductivity of a canted A-phase of pseudo-cubic manganites. It is argued that the model is applicable in a broad concentration range for manganites A_{1 - x}B_xMnO₃ with the tolerance factor t close to one. As for the substitutional disorder, scattering on random Jahn–Teller distortions of MnO₆ octahedra is chosen. We emphasize an intimate correlation between the carrier concentration and resistivity value of metallic manganites. Magnetoresistance as a function of magnetization is calculated for a canted A-phase for both in-plane and out-of-plane current directions. A contact between two manganite phases is considered and structure of the transition region near the contact is discussed. Numerical calculations show charge re-distribution near the contact and a large screening length of the order of five inter-atomic distances. We employed our results to interpret data obtained in recent experiments on La_0.4Sr_0.6MnO₃/La_0.55Sr_0.45MnO₃ superlattices. We also briefly discuss the relative importance of the cooperative Jahn–Teller distortions, double exchange mechanism and super-exchange interactions for the formation of the A-phase at increasing Sr concentrations x > 0.45 in La_{1 - x}Sr_xMnO₃ which suggest that the Jahn–Teller contraction of octahedra, c/a < 1, plays a prevailing role.

The subject of the study are the thermodynamic characteristics of the phonon gas in the chains with heterogeneous mass distribution. The expressions for the internal energy, entropy and free energy of the system are evaluated both in the region of high and low temperature. It is shown that the mass heterogeneity is the source of the strong dissipation of the vibrational energy, which causes all thermodynamic functions of the chains to be quasi-periodic functions of the temperature.

By means of the measure of entanglement called "concurrence" we study the entanglement in Heisenberg dimer single molecular magnets V⁴⁺ with a strong magnetic field and find that thermal entanglement exits for both ferromagnetic (FM) and antiferromagnetic (AFM) cases. In FM case entanglement vanishes for anisotropic parameter λ = 0 while in AFM case, entanglement exits in the whole region of anisotropic parameter 0 ≤ λ ≤ 1. Entanglement variations with anisotropic parameter λ, magnetic field B and temperature T are evaluated. We find a critical magnetic field at which the concurrence changes sharply from zero to maximum entanglement.

The field theoretic renormalization group is applied to the stochastic Navier–Stokes equation that describes fully developed fluid turbulence in d > 2 dimensions. For the first time, the complete two-loop calculation of the renormalization constant, the β function, the fixed point and the ultraviolet correction exponent is performed. The Kolmogorov constant and the inertial-range skewness factor are expressed in terms of universal (in the sense of the theory of critical behavior) quantities, which allows one to construct for them a regular perturbative calculational scheme. The practical calculations are performed up to the second order of the ε-expansion (two-loop approximation). The results obtained are in a good agreement with the experiment. The large d behavior of these quantities is briefly discussed. The possibility of the extrapolation of the ε-expansion beyond the threshold where the sweeping effects become important is demonstrated by the example of a Galilean-invariant quantity, the equal-time pair correlation function of the velocity field.