[en] In this paper, we propose a stochastic Cellular Automata (CA) model to study traffic flow at a single-lane urban roundabout (resp. traffic circle) of N entry points (resp. exit points), the entry points are controlled by rates α_1 and α_2 while the removal rates from the exit points are denoted by β. The traffic is controlled by a self-organized scheme. Based on computer simulation, density profiles, global density and current are calculated in terms of rates. Furthermore, the phase diagrams for roundabout as well as traffic circle are constructed. It has turned out that the phase diagrams consist essentially of two phases namely free flow and jamming. It is noted that the typology of the phase diagrams of the roundabout is not similar to it in the traffic circle. Furthermore, we have compared the performance of the two systems in terms of the geometrical properties and the number of entry points. - Highlights: • Simulations are conducted to study traffic flow at a single-lane urban roundabout as well as traffic circle. • Phase diagrams for roundabout as well as traffic circle are constructed. • The performance of the two systems are compared in terms of the geometrical properties and the number of entry points

[en] The effect of a variable surface transverse magnetic field Ω_s, on the order-disorder layering transitions of an Ising spin-((1)/(2)) model is investigated using mean field theory (MF) and finite cluster approximation (FC). For a film with finite thickness formed with N layers, each layer z transits at a fixed temperature from the ordered to the disordered phase, under the effect of the transverse magnetic field Ω(z)=Ω_s/z^α, (z=1, triple dot, N). These order-disorder layering transitions are absent for α=0 even if increasing the temperature and/or the surface transverse magnetic field. On the other hand, the dependency of longitudinal and transverse magnetisations on temperature and surface transverse magnetic field are illustrated for a fixed value of the exponent α

[en] The magnetic order-disorder layering transitions of a spin-1 Ising model are investigated, under the effect of a variable surface crystal field Δ_s, using the mean-field theory. Each layer k, of the film formed with N layers, disorders at a finite surface crystal field distributed according to the law Δ_k=Δ_s/k^α, k=1,2,...,N and α being a positive constant. We have established the temperature-crystal field phase diagrams and found a constant tricritical point and a reentrant phenomenon for the first k₀ layers. This reentrant phenomenon is absent for the remaining N-k₀ layers, but the cricritical points subsist and depend not only on the film thickness but also on the exponent α. On the other hand, the thermal behaviour of the surface magnetisation for a fixed value of the surface crystal field Δ_s and selected values of the parameter α are established

[en] The cationic substitutions effects at different concentrations, within the Zn_xCd_1-xCr₂Se₄ lattice (0.35≤x≤0.58), on the electronic transfer in chromium's ion are investigated. For this purpose, after taking into account the exchange integrals, we use the Anderson-Kanamori theory of superexchange to determine the transfer integrals b_σσ and b_πσ. Using the conventional molecular orbital model, the covalency-mixing parameters λ_σ and λ_π, the electron spin transfer coefficients f_i(i=σ, π, s) and the total charge C are evaluated. The b_σσ and b_σπ variation with x, agrees with the passage of the system from ferromagnetic to antiferromagnetic order. For the compound presenting re-entrant behaviour (0.45≤x≤0.58), f_s exhibits anomalies. The C increasing with x is consistent with the expected decrease in covalency of the non-magnetic cation in a tetrahedral site

[en] New types of renormalization group theory using the generalized Callen identities are exploited in the study of the Ising model. Another type of two-step renormalization is proposed. Critical couplings and critical exponents y_T and y_H are calculated by these methods for square and simple cubic lattices, using different size clusters. (author). 17 refs, 2 tabs

[en] The influence of frustration on the phase transitions of a semi-infinite three-dimensional Ising model is investigated. Temperature-concentration phase diagrams for fixed values of the ratio of surface and bulk interactions can exhibit five different types of phase transition. (author). 6 refs, 1 fig

[en] Using the finite cluster approximation, phase diagrams of bond and site diluted three-dimensional simple cubic Ising models with a random field have been determined. The resulting phase diagrams have the same general features for both bond and site dilution. (author). 7 refs, 4 figs

[en] The three dimensional spin-1 Ising model with crystal field interactions exhibit tri-critical behaviour. Using an expansion technique for cluster identities of spin-1 localized spin systems, we study the influence of transverse magnetic field on this behaviour. Temperature-crystal-field phase diagrams is investigated for different values of transverse field. The longitudinal and transverse magnetizations, the quadrupolar moments are calculated. General formulae, applicable to structures with arbitrary coordination number N, are given. (author). 19 refs, 5 figs

[en] We study the phase diagram and magnetic properties of a transverse spin-1 Ising model with random longitudinal crystal field interactions within an expansion technique for cluster identities of spin-1 localized spin systems. The partially ordered phases appear for a particular two valued distribution P(D_i) = 1/2[δ(D_i-(1+α)D)+δ(D_i-(1-α)D)], and for sufficiently small transverse field Ω. The longitudinal and transverse magnetizations, the quadrupolar moments are calculated. General formulae applicable to structures with arbitrary coordination number, are given. (author). 19 refs, 3 figs

[en] The magnetic properties of ferrimagnetic mixed-spin Ising model in the checkerboard lattice are studied using Monte Carlo simulations. The variation of total magnetization and magnetic susceptibility with the crystal field has been established. A transition from an order to a disordered phase has been obtained in some critical value of the physical variables. The reduced transition temperature is obtained for different exchange interactions. The magnetic hysteresis cycles have been established. The multiples hysteresis cycle in checkerboard lattice are obtained. The multiples hysteresis cycle have been established. The ferrimagnetic mixed-spin Ising model in checkerboard lattice is very interesting from the experimental point of view. The mixed spins system have many technological applications such as in domain opto-electronics, memory, nanomedicine and nano-biological systems. The obtained results show that that crystal field induce long-range spin–spin correlations even bellow the reduced transition temperature