Dissipative Abelian Sandpiles and Random Walks

We show that the dissipative Abelian sandpile on a graph L can be related to a random walk on a graph which consists of L extended with a trapping site. From this relation it can be shown, using exact results and a scaling assumption, that the dissipative sandpiles' correlation length exponent \nu always equals 1/d_w, where d_w is the fractal dimension of the random walker. This leads to a new understanding of the known results that \nu=1/2 on any Euclidean lattice. Our result is however more general and as an example we also present exact data for finite Sierpinski gaskets which fully confirm our predictions.Comment: 10 pages, 1 figur

Association of treatment satisfaction and psychopathological sub-syndromes among involuntary patients with psychotic disorders

Publisher's version: http://www.springerlink.com/content/rx24036274667t10

2,2′-(Disulfanedi­yl)dibenzoic acid–2,9-dimethyl­phenanthroline–tetra­hydro­furan (1/2/1)

The asymmetric unit of the title co-crystal solvate, C14H10O4S2·2C14H12N2·C4H8O, comprises a 2,2′-(disulfanedi­yl)dibenzoic acid mol­ecule, two mol­ecules of 2,9-dimethyl­phenanthroline and a tetra­hydro­furan (THF) solvent mol­ecule. Each end of the twisted diacid [dihedral angle between the benzene rings = 74.33 (17)°] forms a strong O—H⋯N hydrogen bond with a 2,9-dimethyl­phenanthroline mol­ecule, forming a trimeric aggregate. The crystal structure comprises layers of acid and THF mol­ecules, and layers of 2,9-dimethyl­phenanthroline mol­ecules that alternate along the a axis, the main connections between them being of the type C—H⋯O

2,2′-(Disulfanedi­yl)dibenzoic acid–N,N′-bis­(4-pyridyl­meth­yl)ethane­dithio­amide (1/1)

The asymmetric unit of the title co-crystal, C14H14N4S2·C14H10O4S2, comprises a twisted 2,2′-(disulfanedi­yl)dibenzoic acid mol­ecule [dihedral angle between the benzene rings = 83.53 (14)°] and a U-shaped mol­ecule of N,N′-bis­(4-pyridyl­meth­yl)ethane­dithio­amide in which intra­molecular N—H⋯S hydrogen bonds are observed. Two mol­ecules of each form a centrosymmetric ring, with an extended chair conformation, mediated by carbox­yl–pyridine O—H⋯N hydrogen bonds between the carboxylic acid groups of two 2,2′-(disulfanediyl)dibenzoic acid molecules and pyridine-N atoms of two N,N’-bis(4-pyridylmethyl)ethanedithioamide molecules. The tetra­meric aggregates are linked into a supra­molecular chain along the b axis via amide–carbonyl N—H⋯O hydrogen bonds

Boundary effects in a random neighbor model of earthquakes

We introduce spatial inhomogeneities (boundaries) in a random neighbor version of the Olami, Feder and Christensen model [Phys. Rev. Lett. 68, 1244 (1992)] and study the distributions of avalanches starting both from the bulk and from the boundaries of the system. Because of their clear geophysical interpretation, two different boundary conditions have been considered (named free and open, respectively). In both cases the bulk distribution is described by the exponent $\tau \simeq {3/2}$. Boundary distributions are instead characterized by two different exponents $\tau ' \simeq {3/2}$ and $\tau ' \simeq {7/4}$, for free and open boundary conditions, respectively. These exponents indicate that the mean-field behavior of this model is correctly described by a recently proposed inhomogeneous form of critical branching process.Comment: 6 pages, 2 figures ; to appear on PR

Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Comment: 27 pages, 8 figures and 3 table

2-(4-Chloro­phen­yl)acetic acid–2-{(E)-[(E)-2-(2-pyridyl­methyl­idene)hydrazin-1-yl­idene]meth­yl}pyridine (1/1)

In the crystal of the title 1:1 adduct, C8H7ClO2·C12H10N4, the components are linked by an O—H⋯N hydrogen bond between the carb­oxy­lic acid and one of the pyridine N atoms. In the acid, the carb­oxy­lic acid group is approximately normal to [dihedral angle = 72.9 (2)°] but twisted with respect to the plane through the benzene ring [C—C—C—O torsion angle = 25.4 (5)°]. The base is roughly planar [dihedral angle between rings = 12.66 (15)°; r.m.s. deviation of the 16 non-H atoms = 0.107 Å] and the conformations about both imine bonds are E. The dimeric aggregates are linked into a supra­molecular layer in the ab plane by C—H⋯O inter­actions

Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 $< p_{\rm{T}, assoc} < p_{\rm{T}, trig} <$ 5.0 GeV/$c$ is examined, to include correlations induced by jets originating from low momen\-tum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta|<0.9$. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton--parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/161

How self-organized criticality works: A unified mean-field picture

We present a unified mean-field theory, based on the single site approximation to the master-equation, for stochastic self-organized critical models. In particular, we analyze in detail the properties of sandpile and forest-fire (FF) models. In analogy with other non-equilibrium critical phenomena, we identify the order parameter with the density of ``active'' sites and the control parameters with the driving rates. Depending on the values of the control parameters, the system is shown to reach a subcritical (absorbing) or super-critical (active) stationary state. Criticality is analyzed in terms of the singularities of the zero-field susceptibility. In the limit of vanishing control parameters, the stationary state displays scaling characteristic of self-organized criticality (SOC). We show that this limit corresponds to the breakdown of space-time locality in the dynamical rules of the models. We define a complete set of critical exponents, describing the scaling of order parameter, response functions, susceptibility and correlation length in the subcritical and supercritical states. In the subcritical state, the response of the system to small perturbations takes place in avalanches. We analyze their scaling behavior in relation with branching processes. In sandpile models because of conservation laws, a critical exponents subset displays mean-field values ($\nu=1/2$ and $\gamma = 1$) in any dimensions. We treat bulk and boundary dissipation and introduce a new critical exponent relating dissipation and finite size effects. We present numerical simulations that confirm our results. In the case of the forest-fire model, our approach can distinguish between different regimes (SOC-FF and deterministic FF) studied in the literature and determine the full spectrum of critical exponents.Comment: 21 RevTex pages, 3 figures, submitted to Phys. Rev.

Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider

Measurements of multi-particle azimuthal correlations (cumulants) for charged particles in p-Pb and Pb-Pb collisions are presented. They help address the question of whether there is evidence for global, flow-like, azimuthal correlations in the p-Pb system. Comparisons are made to measurements from the larger Pb-Pb system, where such evidence is established. In particular, the second harmonic two-particle cumulants are found to decrease with multiplicity, characteristic of a dominance of few-particle correlations in p-Pb collisions. However, when a $|\Delta \eta|$ gap is placed to suppress such correlations, the two-particle cumulants begin to rise at high-multiplicity, indicating the presence of global azimuthal correlations. The Pb-Pb values are higher than the p-Pb values at similar multiplicities. In both systems, the second harmonic four-particle cumulants exhibit a transition from positive to negative values when the multiplicity increases. The negative values allow for a measurement of $v_{2}\{4\}$ to be made, which is found to be higher in Pb-Pb collisions at similar multiplicities. The second harmonic six-particle cumulants are also found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find $v_{2}\{4\} \simeq v_{2}\{6\}\neq 0$ which is indicative of a Bessel-Gaussian function for the $v_{2}$ distribution. For very high-multiplicity Pb-Pb collisions, we observe that the four- and six-particle cumulants become consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and Pb-Pb are measured. These are found to be similar for overlapping multiplicities, when a $|\Delta\eta| > 1.4$ gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87