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Different deterministic solution methods are being used to solve the criticality problem of the reflected systems with different anisotropic behaviours for both fission neutrons and neutrons undergoing scattering. In the present study, the criticality problem is simulated using the developed Monte Carlo algorithm. Different angular distributions, such as Inönü, Anlı–Güngör and tetra-anisotropic kernels are taken into account. For each anisotropic kernel, the sampling method of the direction cosine of either newborn fission neutrons or scattered neutrons is presented by extracting the required probability distribution function (PDF). The simulation starts with an initial guess and following the presented procedure, the criticality thickness of the system is estimated with a certain convergence criterion. Different variance reduction methods, such as implicit capture, Russian-roulette and splitting, are also implemented to get more precise results with a reasonable computational time cost. The validity of the presented method is verified by comparing with the results of different deterministic methods. Finally, using an exact scattering function, the three considered kernels are compared with each other. It is seen that the tetra-anisotropic kernel is the best among the considered kernels. [ABSTRACT FROM AUTHOR]

We review some ideas about the quantum physics of black hole information storage and processing in terms of a general phenomenon of quantum criticality. [ABSTRACT FROM AUTHOR]

leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil-Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements. [ABSTRACT FROM AUTHOR]

In the present paper, we study the relation between criticality and information transmission in the one-dimensional contact process with infection parameter $$\lambda .$$ We introduce a notion of sensitivity of the process to its initial condition and prove that it increases not only for values of $$\lambda < \lambda _c, $$ the value of the critical parameter, but keeps increasing even after $$ \lambda _c , $$ before finally starting to decrease for values of $$\lambda $$ sufficiently above $$\lambda _c.$$ This provides a counterexample to the common belief that associates maximal information transmission to criticality. [ABSTRACT FROM AUTHOR]

We show that the inclusion of higher curvature terms in the gravitational action can lead to phase transitions and critical behaviour for charged black branes. The higher curvature terms considered here belong to the recently constructed generalized quasi-topological class [], which possess a number of interesting properties, such as being ghost-free on constant curvature backgrounds and non-trivial in four dimensions. We show that critical behaviour is a generic feature of the black branes in all dimensions d ≥ 4, and contextualize the results with a review of the properties of black branes in Lovelock and quasi-topological gravity, where critical behaviour is not possible. These results may have interesting implications for the CFTs dual to this class of theories. [ABSTRACT FROM AUTHOR]

The Sachdev-Ye-Kitaev model is a (0 + 1)-dimensional model describing Majorana fermions or complex fermions with random interactions. This model has various interesting properties such as approximate local criticality (power law correlation in time), zero temperature entropy, and quantum chaos. In this article, we propose a higher dimensional generalization of the Sachdev-Ye-Kitaev model, which is a lattice model with N Majorana fermions at each site and random interactions between them. Our model can be defined on arbitrary lattices in arbitrary spatial dimensions. In the large N limit, the higher dimensional model preserves many properties of the Sachdev-Ye-Kitaev model such as local criticality in two-point functions, zero temperature entropy and chaos measured by the out-of-time-ordered correlation functions. In addition, we obtain new properties unique to higher dimensions such as diffusive energy transport and a 'butterfly velocity' describing the propagation of chaos in space. We mainly present results for a (1 + 1)-dimensional example, and discuss the general case near the end. [ABSTRACT FROM AUTHOR]

The specific features of calculation of the effective multiplication factor using the Monte Carlo method for weakly coupled and non-asymptotic multiplying systems are discussed. Particular examples are considered and practical recommendations on detection and Monte Carlo calculation of systems typical in numerical substantiation of nuclear safety for VVER fuel management problems are given. In particular, the problems of the choice of parameters for the batch mode and the method for normalization of the neutron batch, as well as finding and interpretation of the eigenvalue spectrum for the integral fission matrix, are discussed. [ABSTRACT FROM AUTHOR]

Pinch Analysis is an established method for enhancing the sustainability of industrial processes via efficient use of various resources. It is based on the principle of target identification followed by subsequent system design aided by a problem decomposition strategy based on the Pinch Point. This approach has recently been extended to apply to a broad range of structurally analogous problems in various domains, such as financial management and carbon-constrained energy planning. In this work, a novel graphical methodology for industrial safety risk and environmental management is proposed. In this method, it is assumed that a set of risk or pollution reduction measures is available, and that each measure is characterized by its implementation cost and the degree of benefit that it delivers. These data are then used to generate a source composite curve. Targeting can then be achieved by shifting this curve relative to a pre-defined sink composite curve, which represents the locus of the plant management's 'willingness to pay,' or budget relative to benefits with respect to risk or pollutant reduction. The methodology is then demonstrated on two case studies. The first case is based on the well-known Bhopal incident, while the second case focuses on the reduction of airborne fluoride emissions from brick firing plant. [ABSTRACT FROM AUTHOR]

A method of measuring the subcriticality of a reactor, according to which the reactor is transferred from a critical into a subcritical state twice by moving control rods with different velocities V and V, is substantiated. A correction to the indications of a reactivity meter for the spatial effect of reactivity is calculated according to detector signals which are recorded with each movement. The correction calculation does not require neutron-physical calculations. As an example this method is applied to water-moderated and -cooled reactors. [ABSTRACT FROM AUTHOR]

Criticality problem of nuclear tractors generally refers to an eigenvalue problem for the transport equations. In this paper, we deal with the eigenvalue of the anisotropic scattering transport equation in slab geometry. We propose a new discrete method which was called modified discrete ordinates method. It is constructed by redeveloping and improving discrete ordinates method in the space of L( X). Different from traditional methods, norm convergence of operator approximation is proved theoretically. Furthermore, convergence of eigenvalue approximation and the corresponding error estimation are obtained by analytical tools. [ABSTRACT FROM AUTHOR]

The discrete height abelian sandpile model was introduced by Bak, Tang, Wiesenfeld and Dhar as an example for the concept of self-organized criticality. When the model is modified to allow grains to disappear on each toppling, it is called bulk-dissipative. We provide a detailed study of a continuous height version of the abelian sandpile model, called the abelian avalanche model, which allows an arbitrarily small amount of dissipation to take place on every toppling. We prove that for non-zero dissipation, the infinite volume limit of the stationary measure of the abelian avalanche model exists and can be obtained via a weighted spanning tree measure. We show that in the whole non-zero dissipation regime, the model is not critical, i.e., spatial covariances of local observables decay exponentially. We then study the zero dissipation limit and prove that the self-organized critical model is recovered, both for the stationary measure and for the dynamics. We obtain rigorous bounds on toppling probabilities and introduce an exponent describing their scaling at criticality. We rigorously establish the mean-field value of this exponent for $$d > 4$$ . [ABSTRACT FROM AUTHOR]

Rare-earth (RE) elements are enablers for a wide range of technologies, including high-strength permanent magnets, energy-efficient lighting, high-temperature thermal barrier coatings, and catalysts. While direct material substitution is difficult in many of these applications because of the specific electronic, optical, or electrochemical properties imparted by the individual rare-earth elements, we describe an example from the aviation industry where supply chain optimization may be an option. Ceramic matrix composite engine components require environmental barrier coatings (EBCs) to protect them from extreme temperatures and adverse reactions with water vapor in the hot gas path. EBC systems based on rare-earth silicates offer a unique combination of environmental resistance, thermal expansion matching, thermal conductivity, and thermal stability across the service temperature window. Several pure rare-earth silicates and solid solutions have been demonstrated in EBC applications. However, all rely on heavy rare-earth elements (HREEs) for phase stability. This article considers the possibility of using separation tailings containing a mixture of HREEs as a source material in lieu of using the high-purity HREE oxides. This option arises because the desired properties of RE-silicate EBCs derive from the average cation size rather than the electronic properties of the individual rare-earth cations. Because separation tailings have not incurred the costs associated with the final stages of separation, they offer an economical alternative to high-purity oxides for this emerging application. [ABSTRACT FROM AUTHOR]

With no agreed-on definition of critical materials, product and process designers have been unable to systematically address the critical materials issue. Using a comprehensive methodology, we have determined the criticality of 62 metals and metalloids-approximately two-thirds of the periodic table. We illustrate how the analyses were performed, provide an overview of criticality at the global level for all elements, and then present examples of how the criticality information could be used in making material-related choices in product and process design. [ABSTRACT FROM AUTHOR]

The need to check the accuracy of evaluations of the constant component of the Doppler reactivity effect, which depends on cross sections, self-screening factors, and the neutron spectrum, is addressed. The problem of studying the Doppler effect of samples of reactor materials by perturbation of the criticality of assemblies, modeling a reactor core with different neutron spectra (the problem of studying the increments of reactivity effects during heating of the samples) with the assembly remaining cold (at room temperature) is formulated. The experiments were performed on two critical assemblies of the KoBRa stand, six assemblies of the BFS-1 stand and three assemblies of the BFS-2 stand. The experimental procedure, measurements, and an analysis of the Doppler reactivity effect for PuO and NpO samples on critical BFS assemblies are presented. [ABSTRACT FROM AUTHOR]

Disordered fibre networks are the basis of many man-made and natural materials, including structural components of living cells and tissue. The mechanical stability of such networks relies on the bending resistance of the fibres, in contrast to rubbers, which are governed by entropic stretching of polymer segments. Although it is known that fibre networks exhibit collective bending deformations, a fundamental understanding of such deformations and their effects on network mechanics has remained elusive. Here we introduce a lattice-based model of fibrous networks with variable connectivity to elucidate the roles of single-fibre elasticity and network structure. These networks exhibit both a low-connectivity rigidity threshold governed by fibre-bending elasticity and a high-connectivity threshold governed by fibre-stretching elasticity. Whereas the former determines the true onset of network rigidity, we show that the latter exhibits rich zero-temperature critical behaviour, including a crossover between various mechanical regimes along with diverging strain fluctuations and a concomitant diverging correlation length. [ABSTRACT FROM AUTHOR]

This paper reconsiders the Project Evaluation and Review Technique (PERT) scheduling problem when information about task duration is incomplete. We model uncertainty on task durations by intervals. With this problem formulation, our goal is to assert possible and necessary criticality of the different tasks and to compute their possible earliest starting dates, latest starting dates, and floats. This paper combines various results and provides a complete solution to the problem. We present the complexity results of all considered subproblems and efficient algorithms to solve them. [ABSTRACT FROM AUTHOR]

An activation method is used to measure and calculate the neutron spectrum inside a cylindrical caisson in the KVANT criticality test stand. This is compared with the neutron spectrum near the inner surface of the core housing of the test stand. [ABSTRACT FROM AUTHOR]

A long-standing question in the field of superconductivity is whether pairing of electrons can arise in some cases as a result of magnetic interactions instead of electron–phonon-induced interactions as in the conventional Bardeen–Cooper–Schrieffer theory. A major challenge to the idea of magnetically mediated superconductivity has been the dramatically different behaviour of the cerium and ytterbium heavy-fermion compounds. The cerium-based systems are often found to be superconducting, in keeping with a magnetic pairing scenario, but corresponding ytterbium systems, or hole analogues of the cerium systems, are not. Despite searches over two decades there has been no evidence of heavy-fermion superconductivity in an ytterbium system, casting doubt on our understanding of the electron–hole parallelism between the cerium and the ytterbium compounds. Here we present the first empirical evidence that superconductivity is indeed possible in an ytterbium-based heavy-fermion system. In particular, we observe a superconducting transition at Tc=80 mK in high-purity single crystals of YbAlB4 in the new structural β phase. We also observe a novel type of non-Fermi-liquid state above Tc that arises without chemical doping, in zero applied magnetic field and at ambient pressure, establishing β-YbAlB4 as a unique system showing quantum criticality without external tuning. [ABSTRACT FROM AUTHOR]

We present numerical investigations of the short-time dynamics at criticality in the 1D Potts model with power-law decaying interactions of the form 1/r1+σ. The scaling properties of the magnetization, autocorrelation function and time correlations of the magnetization are studied. The dynamical critical exponents θ' and z are derived in the cases q=2 and q=3 for several values of the parameter σ belonging to the nontrivial critical regime. [ABSTRACT FROM AUTHOR]

Avalanches, or Avalanche-like, events are often observed in the dynamical behaviour of many complex systems which span from solar flaring to the Earth's crust dynamics and from traffic flows to financial markets. Self-organized criticality (SOC) is one of the most popular theories able to explain this intermittent charge/discharge behaviour. Despite a large amount of theoretical work, empirical tests for SOC are still in their infancy. In the present paper we address the common problem of revealing SOC from a simple time series without having much information about the underlying system. As a working example we use a modified version of the multifractal random walk originally proposed as a model for the stock market dynamics. The study reveals, despite the lack of the typical ingredients of SOC, an avalanche-like dynamics similar to that of many physical systems. While, on one hand, the results confirm the relevance of cascade models in representing turbulent-like phenomena, on the other, they also raise the question about the current state of reliability of SOC inference from time series analysis. [ABSTRACT FROM AUTHOR]

Here I present a new approach to forecasting the effects of climate change on catastrophic events, based on the 'self-organised criticality' concept from statistical physics. In particular, I develop the 'self-organised critical fuel succession model' (SOCFUS), which deals with wildland fires. I show that there is good agreement between model and data for the response pattern of the whole fire size statistical distribution to weather fluctuations in a boreal forest region. I tentatively predict the fire regime in this region for an instance of possible climate change scenario. I show that the immediate response is sharper than usually thought, but part of the added burning rate might not persist indefinitely. A large fraction of the extra burning in the transition period is likely to be concentrated in a few 'climate change fires', much larger than the largest fires that could currently occur. I also suggest that the major fire events recently observed in some tropical rainforest regions belong to a qualitatively different, even more abrupt type of response, which is also predicted by the model. [ABSTRACT FROM AUTHOR]

We investigate numerically the Self Organized Criticality (SOC) properties of the dissipative Olami-Feder-Christensen model on small-world and scale-free networks. We find that the small-world OFC model exhibits self-organized criticality. Indeed, in this case we observe power law behavior of earthquakes size distribution with finite size scaling for the cut-off region. In the scale-free OFC model, instead, the strength of disorder hinders synchronization and does not allow to reach a critical state. [ABSTRACT FROM AUTHOR]

The effect of bulk dissipation on non critical sandpile models is studied using both multifractal and finite size scaling analyses. We show numerically that the local limited (LL) model exhibits a crossover from multifractal to self-similar behavior as the control parameters hext and epsilon turn towards their critical values, i.e. hext ?0+ and epsilon?epsilonc. The critical exponents are not universal and exhibit a continuous variation with epsilon. On the other hand, the finite size effects for the local unlimited (LU), non local limited (NLL), and non local unlimited (NLU) models are well described by the multifractal analysis for all values of dissipation rate epsilon. The space-time avalanche structure is studied in order to give a deeper understanding of the finite size effects and the origin of the crossover behavior. This result is confirmed by the calculation of the susceptibility. [ABSTRACT FROM AUTHOR]

We discuss sensitivity to initial conditions in a model for avalanches in granular media displaying self-organized criticality. We show that damage, due to a small perturbation in initial conditions, does not spread. The damage persists in a statistically time-invariant and scale-free form. We argue that the origin of this behavior is the Abelian nature of the model, which generalizes our results to all models with Abelian properties, including the BTW model and the Manna model. An ensemble average of the damage leads to seemingly time dependent damage spreading. Scaling arguments show that this numerical result is due to the time lag before avalanches reach the initial perturbation. [ABSTRACT FROM AUTHOR]

The results are given of an experimental investigation of fluctuation phenomena under conditions of electric arc discharge. Fluctuations are observed whose spectral density is inversely proportional to frequency (1/f noise). Power dependences are revealed of the fluctuation distribution functions. The behavior of spectral density and of distribution functions is associated with the simultaneous occurrence of various nonequilibrium phase transitions. Within the framework of the mean field theory, a mathematical model is suggested of interacting nonequilibrium phase transitions in a distributed system, which predicts the self-organization of the critical state and the generation of fluctuations with diverging spectral characteristics. An adequate agreement is observed between the suggested model and experimental data. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The field dependence of the magnetic moment of square (100×100) Josephson networks was examined with the use of a SQUID magnetometer. The field dependence of the magnetic moment was found to be regular with features corresponding to integer and half-integer numbers of flux quanta per cell. At temperatures below 5.8 K, jumps in the magnetization curves associated with the entry and exit of avalanches of tens and hundreds of fluxons were observed. It was shown that the probability distribution of these processes corresponded to the theory of self-organized criticality. An avalanche character of flux motion was observed at temperatures at which the size of the fluxons did not exceed the size of the cell, that is, when a discrete vortex structure occurred. © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The phenomenon of upper critical dimensionality d[sub c2] has been studied from the viewpoint of the scaling concepts. The Thouless number g(L) is not the only essential variable in scale transformations, because there is the second essential parameter connected with the off-diagonal disorder. The investigation of the resulting two-parameter scaling has revealed two scenarios, and switching from one to another scenario determines the upper critical dimensionality. The first scenario corresponds to the conventional one-parameter scaling and is characterized by the parameter g(L) invariant under scale transformations when the system is at the critical point. In the second scenario, the Thouless number g(L) grows at the critical point as L[sup d-d[sub c2]], which leads to a violation of the Wegner relation s=ν(d-2) between the critical exponents for conductivity s and localization radius ν, which takes the form s=ν(d[sub c2]-2). The resulting formulas for g(L) are in agreement with the symmetry theory suggested in a previous publication, I. M. Suslov, Zh. Éksp. Teor. Fiz. 108, 1686 (1995) [JETP 81, 925 (1995)]. A more rigorous version of Mott’s argument concerning localization due to topological disorder has been proposed. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The article discusses papers published within the issue, including one on a broad elemental study on criticality and its implications for product and process designers, and another on the evaluation of a substitute for high-purity rare-earth oxides.

The original publication of the article unfortunately contained a mistake in the first sentence of Theorem 1 and in the second part of the proof of Theorem 1. The corrected statement of Theorem as well as the corrected proof are given below. The full text of the corrected version is available at [ABSTRACT FROM AUTHOR]