Regular Series

Vol. 43 (2012), No. 11, pp. 2037 – 2146

Nonequilibrium Phase Transition in the Kinetic Ising Model: Absence of Tricritical Behaviour in Presence of Impurities

Acta Phys. Pol. B 43, 2041 (2012)

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abstract

The nonequilibrium dynamic phase transition, in the two dimensional site diluted kinetic Ising model in presence of an oscillating magnetic field, has been studied by Monte Carlo simulation. The projections of dynamical phase boundary surface are drawn in the planes formed by the dilution and field amplitude and the plane formed by temperature and field amplitude. The tricritical behaviour is found to be absent in this case which was observed in the pure system.

Tsallis Fits to $p_{\mathrm T}$ Spectra for $pp$ Collisions at the LHC

Acta Phys. Pol. B 43, 2047 (2012)

page 2047 •

abstract

Phenomenological Tsallis fits to the CMS and ATLAS transverse spectra of charged particles were found to extend for $p_{\mathrm T}$ from 0.5 to 181 GeV in $pp$ collisions at the LHC at $\sqrt {s}=7$ TeV, and for $p_{\mathrm T}$ from 0.5 to 31 GeV at $\sqrt {s}=0.9$ TeV. The simplicity of the Tsallis parametrization and the large range of the fitting transverse momentum raise questions on the physical meaning of the degrees of freedom that enter into the Tsallis distribution or $q$-statistics.

On the Anomalous $t$-quark Charge Asymmetry and Noncontractibility of the Physical Space

Acta Phys. Pol. B 43, 2055 (2012)

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abstract

Heavy flavour production at hadron colliders represents a very promising field to test perturbative QCD. The integrated forward–backward asymmetry of the top–antitop quark production is particularly sensitive to any deviation from the standard QCD calculations. The two Tevatron collaborations, CDF and D0, reported a much larger $t$-quark charge asymmetry than predicted by the theory. We show that the QCD in noncontractible space, where the minimal distance is fixed by weak interactions, enhances the asymmetry by more than a factor of 3 (5) at the parton level in leading order of the coupling for the Tevatron (LHC) center-of-mass energies. This result should not be a surprise since the asymmetry observable directly explores the far ultraviolet sector of the spacelike domain of the Minkowski spacetime.

NLO Corrections to Hard Process in QCD Shower — Proof of Concept

Acta Phys. Pol. B 43, 2067 (2012)

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abstract

The concept of new methodology of adding QCD NLO corrections in the initial state Monte Carlo parton shower (hard process part) is tested numerically using, as an example, the process of the heavy boson production at hadron–hadron colliders such as LHC. In spite of the use of a simplified model of the process, all presented numerical results prove convincingly that the basic concept of the new methodology works correctly in practice, that is, in the numerical environment of the Monte Carlo parton shower event generator. The differences with the other well established methods, like MC@NLO and POWHEG, are briefly discussed and future refinements of the implementation of the new method are also outlined.

Bose Gas in Power-like Spherically Symmetric Potential in Arbitrary Spatial Dimensionality

Acta Phys. Pol. B 43, 2089 (2012)

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abstract

Temperature of the Bose–Einstein condensation and the temperature behavior of the chemical potential and other thermodynamical functions of the ideal Bose gas are found for the arbitrary power-like spherical-symmetric potential at an arbitrary space dimension. It is shown that the recently observed Bose–Einstein condensation of photons in the cavity is the phase transition of the third kind.

Tracking Scaling Effects in Mutual Funds Return Time Series

Acta Phys. Pol. B 43, 2103 (2012)

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abstract

Data coming from many fields of science and technology, ranging from hydrology through network traffic to economics, show long range dependence and self-similarity. These properties result in significant consequences and usually require a redefinition of well grounded assumptions and theories. In the case of financial markets, the classical models which often assume that the dynamics of economic time series is described by the random walk, may incorrectly evaluate the investment risk. Therefore, it is important to understand the dynamics of returns generated by different financial instruments. In this work, we tested fifteen different mutual funds investing in stocks through a stock exchange. We found that the distribution of funds daily returns cannot be described by the random walk. Furthermore, using several different method, we provide empirical evidence, that the daily returns of the analysed funds may exhibit long-range correlations and fractal behaviour.

Modeling Hysteresis Observed in the Human Erythrocyte Voltage-dependent Cation Channel

Acta Phys. Pol. B 43, 2117 (2012)

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abstract

The non-selective voltage-activated cation channel from human red cells, which is activated at depolarizing potentials, has been shown to exhibit counter-clockwise gating hysteresis. Here, we analyze this phenomenon with the simplest possible phenomenological models. Specifically, the hysteresis cycle, including its direction, is reproduced by a model with $2 \times 2$ discrete states: the normal open/closed states and two different states of “gate tension”. Rates of transitions between the two branches of the hysteresis curve are modeled with single-barrier kinetics by introducing a real-valued “reaction coordinate” parametrizing the protein’s conformational change between the two states of gate tension. The resulting scenario suggests a reanalysis of former experiments with NSVDC channels.

Estimating Masses of Keplerian Disk Systems: the Case of AGN in NGC 4258

Acta Phys. Pol. B 43, 2141 (2012)

page 2141 •

abstract

The Keplerian motion of accretion disks in Active Galactic Nuclei (AGN) is usually believed to be generated by a heavy central mass. We investigate accreting disk systems with polytropic gas in Keplerian rotation and obtain a phenomenological formula that relates the Keplerian angular frequency to the ratio of disk and central masses. Central mass approaches the Keplerian value, if the inner boundary of a disk is close to the minimal stable orbit of a black hole. These results are applied to NGC 4258, the unique AGN with a finely measured Keplerian rotation curve of the central disk, with the conclusion that its rotation curve is, in fact, determined by the central black hole. The mass of the accretion disk exceeds $100\,M_{\odot }$.

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