Sharif Digital Repository

We have investigated the "weak chaos" exponent to see if it can be considered as a classification parameter of different sandpile models. Our simulation results show that the (Abelian) BTW sandpile model, the (non-Abelian) Zhang model, and the ("Abelian") Manna model possesses different "weak chaos" exponents, so they may belong to different universality classes. Finally, we show that getting off the critical point destroys this behavior in these models  

In this paper we investigate the effect of the number of dissipative sites in an Abelian sandpile model. The dissipative sites are considered to be in the bulk rather than in the boundary. In such systems, statistics of avalanches smaller than a certain size obey a power law. We have seen that the exponents associated with these power law behaviors change slightly as the number of dissipative sites is decreased. We have found that the zero dissipation limits of these exponents are independent of size. Therefore we suggest that the previously-seen dependence of the exponent on the system size is because of the number of dissipative sites rather than the system size. Also it is observed that... 

A numerical method based on the transfer matrix method is developed to calculate the critical temperature of two-layer Ising ferromagnet with a weak inter-layer coupling. The reduced internal energy per site has been accurately calculated for symmetric ferromagnetic case, with the nearest neighbor coupling K1 = K2 = K (where K1 and K2 are the nearest neighbor interaction in the first and second layers, respectively) with inter-layer coupling J. The critical temperature as a function of the inter-layer coupling ξ = J/K, is obtained for very weak inter-layer interactions, ξ < 0.1. Also a different function is given for the case of the strong inter-layer interactions (ξ > 1). The importance of... 

We investigate a new version of sandpile model which is very similar to Abelian Sandpile Model (ASM), but the height variables are continuous ones. With the toppling rule we define in our model, we show that the model can be mapped to ASM, so the general properties of the two models are identical. Yet the new model allows us to investigate some problems such as the effect of very small mass on the height probabilities, different boundary conditions  

A graph is equimatchable if all of its maximal matchings have the same size. A graph is claw-free if it does not have a claw as an induced subgraph. In this paper, we provide the first characterization of claw-free equimatchable graphs by identifying the equimatchable claw-free graph families. This characterization implies an efficient recognition algorithm. © 2018 Elsevier B.V  

Calculations of the frozen phonon for Ag Raman modes of the superconducting Y Ba2 Cu3 O7 and Y Ba2 Cu4 O8 systems have been carried out using the pseudopotential density functional theory in the local density approximation employing the VASP code. The eigenvalues and eigenvectors of the Ag Raman modes for the two systems have been calculated and compared with other experimental and computational studies. Electronic band structure and total density of states have been calculated for all the bare Ag modes for both systems. By calculating the changes in the bands intersecting the Fermi energy by ionic displacements, the ionic dependence of the electronic band structure in each of the Ag Raman... 

This comment concerns the mathematical errors in the recent work of Wang et al. (2016). The corrected equations are presented. Deflections and critical values of compressive force and forward speed are modified. © 2018 Elsevier Ltd  

A set S of vertices of a graph G = (V, E) is a connected dominating set if every vertex of V(G) S is adjacent to some vertex in S and the induced subgraph G[S] is connected. The connected domination number γc (G) is the minimum cardinality of a connected dominating set of G. The connected domination subdivision number sdγc(G) is the minimum number of edges that must be subdivided (each edge in G can be subdivided at most once) in order to increase the connected domination number. In this paper first we establish upper bounds on the connected domination subdivision number in terms of the order n of G or of its edge connectivity number K'(G). We also prove that γc(G) + sdγc(G) ≤ n - 1 with... 

For natural numbers n and k (n > 2k), a generalized Petersen graph P(n, k), is defined by vertex set {ui ui] and edge set {ui ui+1, ui ui, ui ui+k}; where i = 1, 2,..., n and subscripts are reduced modulo n. Here first, we characterize minimum vertex covers in generalized Petersen graphs. Second, we present a lower bound and some upper bounds for β(P(n, k)), the size of minimum vertex cover of P(n,k). Third, in some cases, we determine the exact values of β(P(n,k)). Our conjecture is that β(P(n, k)) < n+ [n/5], for all n and k  

The critical micelle concentration (CMC) of a set of 58 alkylsulfates, alkylsulfonates, alkyltrimethyl ammonium and alkylpyridinium salts were predicted using an artificial neural network (ANN). The multiple linear regression (MLR) technique was used to select the important descriptors that act as inputs for artificial neural network. These descriptors are Balaban index, heat of formation, maximum distance between the atoms in the molecule, Randic index and volume of the molecule. Designed artificial neural network is a fully connected back-propagation network that has a 5-5-1 architecture. The results obtained using neural network were compared with those obtained using MLR technique.... 

A critical set in an n×n array is a set C of given entries, such that there exists a unique extension of C to an n×n Latin square and no proper subset of C has this property. The cardinality of the largest critical set in any Latin square of order n is denoted by lcs(n). In 1978, Curran and van Rees proved that lcs(n)n 2-n. Here, we show that lcs(n)n 2-3n+3. © 2002 Elsevier Science B.V  

A new approach to measure the critical current density of bulk superconductors is presented in this paper. In the proposed technique, the characterization uses a pulsed current which passes through a small point contact at the middle of the bulk and distributes uniformly, while the other contact is a copper ring around the bulk. By increasing the pulsed current above a threshold current, a normal zone appears and develops into a semi-oblate spheroid forming around the contact point. By analyzing its size and shape, and electromagnetic fundamentals, the voltage-current relationship in the normal zone is obtainable. In addition, experimental works have been performed and the results are in... 

Ground-state fidelity (GSF) and quantum renormalization group (QRG) theory have proven to be useful tools in the study of quantum critical systems. Here we lay out a general, unified formalism of GSF and QRG; specifically, we propose a method for calculating GSF through QRG, obviating the need for calculating or approximating ground states. This method thus enhances the characterization of quantum criticality as well as scaling analysis of relevant properties with system size. We illustrate the formalism in the one-dimensional Ising model in a transverse field (ITF) and the anisotropic spin-1/2 Heisenberg (XXZ) model. Explicitly, we find the scaling behavior of the GSF for the ITF model in... 

Correct scheduling of the project is the necessary condition for the project success. In traditional models, the activities duration times are deterministic and known. In real world however, accurate calculation of time for performing each activity is not possible and is always faced with uncertainty. In this paper, the duration of each activity is estimated by the experts as linguistic variables and the said variables are represented in fuzzy numbers form using the fuzzy theory. Estimating the project accomplishment duration and determining the project critical path will be possible through resolving a fuzzy linear programming model. For solving model, Fuzzy Critical Path Method Algorithm... 

The polycarbonate (PC)/thermoplastic polyurethane (TPU) blend membranes were prepared by phase inversion process applied to membrane bioreactor (MBR) to investigate the fouling characteristics. The impact of TPU and poly (vinylpyrrolidone) PVP concentration in polymer dopes on membrane structure, morphology, and performance were studied. The flat sheet fabricated membranes were characterized by scanning electron microscope (SEM), water contact angle (WCA), membrane surface roughness measurements and mechanical strength. The membrane performance was investigated at subcritical operating conditions. Pure water and critical flux through the fabricated membranes were measured for better... 

Recent developments in the field of applied nanoscience and nanotechnology have heightened the need for categorizing various characteristics of nanostructures. In this regard, this paper establishes a novel method to investigate magnetic properties (phase diagram and spontaneous magnetization) of a cylindrical Ising nanotube. Using a two-layer Ising model and the core-shell concept, the interactions within nanotube has been modelled. In the model, both ferromagnetic and antiferromagnetic cases have been considered. Furthermore, the effect of nanotube's length on the critical temperature is investigated. The model has been simulated using cellular automata approach and phase diagrams were... 

The present mixed-methods research examined the identity and attitude of Iranian English language learners as a result of their participation in an online critical reflective course. The participants were 38 English language students who attended ten online sessions within a five-month English language course. Their online posts underwent inductive qualitative content analysis and subsequently five themes were extracted. In addition, the content of the first and last two sessions were analysed quantitatively. A validated questionnaire was also administered and 18 participants were interviewed. Qualitative and quantitative content analyses of the data revealed eight finalised codes. The... 

Nowadays, deliberate or unwanted fire incidents have created much attention to the behavior of structures against these types of events. Since the properties of structural members are influenced by the increase in the temperature of the members, it is more difficult to predict the general and local behavior of the structures during the fire. In this research, a method has been proposed to calculate the critical temperature in two-dimensional structures at its collapse with desirable accuracy. In this process, the upper-bound theory of plastic analysis is used. The plastic analysis is performed by applying the initial fire scenario to the structure, and its collapse load factor with the... 

Over centuries and across cultures, scholars have consistently highlighted the role of character for achieving personal and societal good. Yet we know little about how character matters for entrepreneurship. This study builds upon the theory of character strengths to extend our knowledge about personal antecedents of entrepreneurial thinking. Specifically, we examine how character strengths of valor, industriousness, and critical thinking can affect different dimensions of entrepreneurial alertness: scanning and search, association and connection, and evaluation and judgment. We use two samples of 412 students and 145 entrepreneurs to test the study’s hypotheses. The results shed light on...