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2.
We propose a network model with a fixed number of nodes and links and with a dynamic which favors links between nodes differing in connectivity. We observe a phase transition and parameter regimes with degree distributions following power laws, P(k)∼k-γ, with γ ranging from 0.2 to 0.5, small-world properties, with a network diameter following D(N)∼logN and relative high clustering, following C(N)∼1/N and C(k)∼k-α, with α close to 3. We compare our results with data from real-world protein interaction networks. 相似文献
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Motivated by experiments in nanoscopic systems, we study a generalized Anderson, which consist of two spin degenerate doublets hybridized to a singlet by the promotion of an electron to two conduction bands, as a function of the energy separation δ between both doublets. For δ=0 or very large, the model is equivalent to a one-level SU(N) Anderson model, with N=4 and 2 respectively. We study the evolution of the spectral density for both doublets (ρ1σ(ω) and ρ2σ(ω)) and their width in the Kondo limit as δ is varied, using the non-crossing approximation (NCA). As δ increases, the peak at the Fermi energy in the spectral density (Kondo peak) splits and the density of the doublet of higher energy ρ2σ(ω) shifts above the Ferrmi energy. The Kondo temperature TK (determined by the half-width at half maximum of the Kondo peak in density of the doublet of lower energy ρ1σ(ω)) decreases dramatically. The variation of TK with δ is reproduced by a simple variational calculation. 相似文献
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Amovilli and March (2006) [8] used diffusion quantum Monte Carlo techniques to calculate the non-relativistic ionization potential I(Z) in He-like atomic ions for the range of (fractional) nuclear charges Z lying between the known critical value Zc=0.911 at which I(Z) tends to zero and Z=2. They showed that it is possible to fit I(Z) to a simple quadratic expression. Following that idea, we present here a semiempirical fine-tuning of Hartree–Fock ionization potentials for the isoelectronic series of He, Be, Ne, Mg and Ar-like atomic ions that leads to excellent estimations of Zc for these series. The empirical information involved is experimental ionization and electron affinity data. It is clearly demonstrated that Hartree–Fock theory provides an excellent starting point for determining I(Z) for these series. 相似文献
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The first principle calculations have been performed to study the influence of number of layers on the dielectric properties of dichalcogenides of Mo and W for in-plan (E⊥c) as well as out-of-plan polarization (E∥c). We have taken bulk, mono, bi, four and 6-layer setup for this study. The EELS shows significant red shift in the energies of π plasmons, while prominent red shift has been found for the energies of (π+σ) plasmons of all the studied materials by reducing the number of layers from bulk to monolayer limit. The ?s has been found to red shifted by 62.5% (66.3%), 48.5% (62.1%), 52.7% (66.2%), 61.7% (64.6%), 61.5% (66.7%) and 62.5% (70.5%) from bulk values of MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2 respectively for E⊥c(E∥c) as one goes from bulk to monolayer of these materials. The interband transitions are found to remain independent of the number of layers, however their intensity decreases with decrease in the number of layers. The dielectric functions are highly anisotropic in low energy range and becomes isotropic in high energy range. 相似文献
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We consider the Q-state Potts model in the random-cluster formulation, defined on finite two-dimensional lattices of size L×N with toroidal boundary conditions. Due to the non-locality of the clusters, the partition function Z(L,N) cannot be written simply as a trace of the transfer matrix TL. Using a combinatorial method, we establish the decomposition Z(L,N)=∑l,Dkb(l,Dk)Kl,Dk, where the characters Kl,Dk=i∑N(λi) are simple traces. In this decomposition, the amplitudes b(l,Dk) of the eigenvalues λi of TL are labelled by the number l=0,1,…,L of clusters which are non-contractible with respect to the transfer (N ) direction, and a representation Dk of the cyclic group Cl. We obtain rigorously a general expression for b(l,Dk) in terms of the characters of Cl, and, using number theoretic results, show that it coincides with an expression previously obtained in the continuum limit by Read and Saleur. 相似文献
8.
We introduce the curvature Ωk as a new free parameter in the Bayesian analysis using SNIa, BAO and CMB data, in a model with variable equation of state parameter w(z). We compare the results using both the Constitution and Union 2 data sets, and also study possible low redshift transitions in the deceleration parameter q(z). We found that, incorporating Ωk in the analysis, it is possible to make all the three observational probes consistent using both SNIa data sets. Our results support dark energy evolution at small redshift, and show that the tension between small and large redshift probes is ameliorated. However, although the tension decreases, it is still not possible to find a consensus set of parameters that fit all the three data set using the Chevalier–Polarski–Linder CPL parametrization. 相似文献
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In this Letter we show numerical existence of O(4) Dirac–Born–Infeld (DBI) Textures living in (N+1) dimensional spacetime. These defects are characterized by SN→S3 mapping, generalizing the well-known Hopf fibration into πN(S3), for all N>3. The nonlinear nature of DBI kinetic term provides stability against size perturbation and thus renders the defects having natural scale. 相似文献
12.
The particle in a symmetrical squared tangent potential well is studied by examining its Shannon information entropy and standard deviations. The position and momentum information entropy densities ρs(x), ρs(p) and probability densities ρ(x), ρ(p) are illustrated with different potential range L and potential depth U . We present analytical position information entropies Sx for the lowest two states. We observe that the sum of position and momentum entropies Sx and Sp expressed by Bialynicki-Birula–Mycielski (BBM) inequality is satisfied. Some eigenstates exhibit entropy squeezing in the position. The entropy squeezing in position will be compensated by an increase in momentum entropy. We also note that the Sx increases with the potential range L, while decreases with the potential depth U . The variation of Sp is contrary to that of Sx. 相似文献
13.
The large-n expansion is applied to the calculation of thermal critical exponents describing the critical behavior of spatially anisotropic d-dimensional systems at m -axial Lifshitz points. We derive the leading non-trivial 1/n correction for the perpendicular correlation-length exponent νL2 and hence several related thermal exponents to order O(1/n). The results are consistent with known large-n expansions for d -dimensional critical points and isotropic Lifshitz points, as well as with the second-order epsilon expansion about the upper critical dimension d?=4+m/2 for generic m∈[0,d]. Analytical results are given for the special case d=4, m=1. For uniaxial Lifshitz points in three dimensions, 1/n coefficients are calculated numerically. The estimates of critical exponents at d=3, m=1 and n=3 are discussed. 相似文献
14.
We consider the renormalization-group coupled equations for the effective potential V(?) and the field strength Z(?) in the spontaneously broken phase as a function of the infrared cutoff momentum k . In the k→0 limit, the numerical solution of the coupled equations, while consistent with the expected convexity property of V(?), indicates a sharp peaking of Z(?) close to the end points of the flatness region that define the physical realization of the broken phase. This might represent further evidence in favor of the non-trivial vacuum field renormalization effect already discovered with variational methods. 相似文献
15.
We determine the simple currents and fixed points of the orbifold theory CFT⊗CFT/Z2, given the simple currents and fixed point of the original CFT . We see in detail how this works for the SUk(2) WZW model, focusing on the field content (i.e. h -spectrum of the primary fields) of the theory. We also look at the fixed point resolution of the simple current extended orbifold theory and determine the SJ matrices associated to each simple current for SU2(2) and for the B1(n) and D1(n) series. 相似文献
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Magnetic properties of the bond and crystal field dilution spin-3/2 Blume–Capel model in an external magnetic field (h) on simple cubic lattice are studied by using the effective field theory. In the m−T plane, the degeneracy of the magnetization (m) is affected by the concentration of bond or crystal field dilution at low temperature (T). The magnetization curves can appear to fluctuate in certain regions of negative crystal field. In the m−h plane, the initial magnetization curve has an irregular behavior due to the introduction of bond dilution. The crystal field dilution has the influence on the process of magnetic domain displacement. In the χ−h plane, there exists one susceptibility (χ) shoulder and one step for different negative crystal field. The susceptibility curve takes on the feature of multi-peaks distribution under bond and crystal field dilution conditions. 相似文献
17.
Minos A. Neto J. Roberto Viana J. Ricardo de Sousa 《Journal of magnetism and magnetic materials》2012
In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter (Δ) and magnetic field (H ), where Δ=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N =4 spins (EFT-4). The staggered ms=(mA−mB)/2 and total m=(mA+mB)/2 magnetizations are numerically calculated, where in the limit of ms→0 the critical line TN(H,Δ) is obtained. The phase diagram in the T−H plane is discussed as a function of the parameter Δ for all values of H∈[0,Hc(Δ)], where Hc(Δ) correspond the critical field (TN=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=Hc(Δ)≥Hc(Δ=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of Δ∈[0,1]. This reentrant behavior increases with increase of the anisotropy parameter Δ. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. 相似文献
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Motivated by the necessity of discrete ZN symmetries in the MSSM to insure baryon stability, we study the origin of discrete gauge symmetries from open string sector U(1)?s in orientifolds based on rational conformal field theory. By means of an explicit construction, we find an integral basis for the couplings of axions and U(1) factors for all simple current MIPFs and orientifolds of all 168 Gepner models, a total of 32 990 distinct cases. We discuss how the presence of discrete symmetries surviving as a subgroup of broken U(1)?s can be derived using this basis. We apply this procedure to models with MSSM chiral spectrum, concretely to all known U(3)×U(2)×U(1)×U(1) and U(3)×Sp(2)×U(1)×U(1) configurations with chiral bi-fundamentals, but no chiral tensors, as well as some SU(5) GUT models. We find examples of models with Z2 (R-parity) and Z3 symmetries that forbid certain B and/or L violating MSSM couplings. Their presence is however relatively rare, at the level of a few percent of all cases. 相似文献
19.
Given an excess demand function of an economy, say Z(p), a stable price adjustment mechanism (SPAM) guarantees convergence of solution path p(t,p0) to an equilibrium peq solution of Z(p)=0. Besides, all equilibrium points of Z(p) are asymptotically stable. Some SPAMs have been proposed, including Newton and transpose Jacobian methods. Despite this powerful stability property of SPAMs, their acceptation in the economics community has been limited by a lack of interpretation. This paper focuses on this issue. Specifically, feedback control theory is used to link SPAMs and price dynamics models with control inputs, which match the economically intuitive Walrasian Hypothesis (i.e., prices change with excess demand sign). Under mild conditions, it is shown the existence of a feedback function that transforms the price dynamics into a desired SPAM. Hence, a SPAM is interpreted as a fundamental (e.g., Walrasian) price dynamics under the action of a feedback function aimed to stabilize the equilibrium set of the excess demand function. 相似文献
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The spin-glass q-state Potts model on d -dimensional diamond hierarchical lattices is investigated by an exact real space renormalization group scheme. Above a critical dimension dl(q) for q>2, the coupling constants probability distribution flows to a low-temperature strange attractor or to the high-temperature paramagnetic fixed point, according to the temperature is below or above the critical temperature Tc(q,d). The strange attractor was investigated considering four initial different distributions for q=3 and d=5 presenting strong robustness in shape and temperature interval suggesting a condensed phase with algebraic decay. 相似文献