Table of contents

Relativistic thermodynamics is constructed from the point of view of special relativistic hydrodynamics. A relativistic four-current for heat and a general treatment of thermal equilibrium between moving bodies are presented. The different temperature transformation formulas of Planck and Einstein, Ott, Landsberg and Doppler appear upon particular assumptions about internal heat current.

There exists a large class of generally covariant metric Lagrangians that contain only local terms and describe two propagating degrees of freedom. Trivial examples can be be obtained by applying a local field redefinition to the Lagrangian of general relativity, but we show that the class of two propagating degrees of freedom Lagrangians is much larger. Thus, we exhibit a large family of non-local field redefinitions that map the Einstein-Hilbert Lagrangian into ones containing only local terms. These redefinitions have origin in the topological shift symmetry of BF theory, to which GR is related in Plebański formulation, and can be computed order by order as expansions in powers of the Riemann curvature. At its lowest non-trivial order such a field redefinition produces the (Riemann)³ invariant that arises as the two-loop quantum gravity counterterm. Possible implications for quantum gravity are discussed.

The question as to whether or not quantum mechanics is applicable to the macroscopic scale has motivated efforts to generate superposition states of macroscopic numbers of particles and to determine their effective size. Superpositions of circulating current states in flux qubits constitute candidate states that have been argued to be at least mesoscopic. We present a microscopic analysis that reveals the number of electrons participating in these superpositions to be surprisingly but not trivially small, even though differences in macroscopic observables are large.

We report the observation of high-order resonances of the quantum δ-kicked accelerator using a BEC kicked by a standing wave of light. The signature of these resonances is the existence of quantum accelerator modes. For the first time quantum accelerator modes were seen near 1/2, 2/3 and 1/3 of the half-Talbot time. Using a BEC enabled the internal momentum state structure of the modes and resonances to be studied for the first time. This structure has many similarities to that present in the fractional Talbot effect. We present a theory for this system based on rephasing of momentum orders and apply it to predict the behavior of the accelerator modes around a resonance of any order.

We study the response of a granular system at rest to an instantaneous input of energy in a localised region. We present scaling arguments that show that, in d dimensions, the radius of the resulting disturbance increases with time t as t^α, and the energy decreases as t^-αd, where the exponent α=1/(d+1) is independent of the coefficient of restitution. We support our arguments with an exact calculation in one dimension and event-driven molecular-dynamics simulations of hard-sphere particles in two and three dimensions.

We investigate the properties of packings of frictionless non-spherical particles utilizing a dynamic particle expansion technique. We employ superquadric particles (superellipsoids), which allows us to explore how a broad range of particle shapes affect both the macroscopic and the local configurational properties of the system. We smoothly transition from spherical particles possessing only translational degrees of freedom to large aspect ratio non-spherical grains where rotational degrees of freedom are highly important. We demonstrate that the degree of anisotropy and local surface curvature of the particles have a profound effect on their packing properties, determining whether a random or an ordered packing is readily formed.

Suspensions of small anisotropic particles, "rheoscopic fluids", are used for flow visualisation. By illuminating the fluid with light of three different colours, it is possible to determine Poincaré indices for vector fields formed by the longest axis of the particles. Because this vector field is non-oriented, half-integer Poincaré indices are possible, and are observed experimentally. An exact solution for the direction vector appears to preclude the existence of topological singularities. However, we show that upon averaging over the random initial orientations of particles, singularities with half-integer Poincaré index appear. We describe their normal forms.

Ultrashort laser pulse filaments in dispersive nonlinear Kerr media induce a moving refractive index perturbation which modifies the spacetime geometry as seen by co-propagating light rays. We study the analogue geometry induced by the filament and show that one of the most evident features of filamentation, namely conical emission, may be precisely reconstructed from the geodesics. We highlight the existence of favorable conditions for the study of analogue black hole kinematics and Hawking-type radiation.

It will be shown that barotropic magnetohydrodynamics is equivalent to a four-function field theory, reducing the number of equations and variables needed to describe the theory from seven (the magnetic field the velocity field and the density ρ) to four. This field theory possesses a novel double infinite symmetry group.

The energy densities, the heat capacities and the diffusion constants in two- and three-dimensional non-ideal dissipative systems of particles interacting with the screened Coulomb potential are studied. A simple semi-empirical expression for the energy density is considered. New analytical relations between the diffusion constants and the energy density in strongly coupled systems are proposed. Comparison of theoretical results and numerical simulations is presented.

The ground state of a two-dimensional ionic mixture at zero pressure composed of oppositely charged spheres is determined as a function of the size asymmetry by using a penalty method. The cascade of stable structures includes square, triangular and rhombic crystals as well as "empty" crystals made up of dipoles and chains, which have a vanishing number density. Thereby we confirm the square structure, found experimentally on charged granulates, and predict new phases detectable in experiments on granular and colloidal matter.

We show that the introduction of slippage has a profound effect on instabilities induced by electric field or contact forces in soft solid elastic films. The critical force required to initiate these instabilities is markedly reduced because of slippage, and is lowest when the slippage arises from an intercalating viscous layer between the elastic film and its rigid substrate. Remarkably, unlike in rigidly bonded elastic films, the length scale of instabilities can be tuned by changing the film thicknesses, material properties of the films, and the strength of the destabilizing force of the bilayers. This feature can be potentially exploited in meso-patterning applications.

Semi-crystalline fibers, such as nylon, orlon, and spectra, play a crucial role in modern society in applications including clothing, medical devices, and aerospace technology. These applications rely on the enhanced properties that are generated in these fibers through the orientation and deformation of the constituent molecules of a molten liquid undergoing flow prior to crystallization; however, the atomistic mechanisms of flow-induced crystallization are not understood, and macroscopic theories that have been developed in the past to describe this behavior are semi-empirical. We present here the results of the first successful simulation of flow-induced crystallization at constant temperature using a nonequilibrium Monte Carlo algorithm for a short-chain polyethylene liquid. A phase transition between the liquid and crystalline phases was observed at a critical flow rate in elongational flow. The simulation results quantitatively matched experimental X-ray diffraction data of the crystalline phase. Examination of the configurational temperature generated under flow confirmed for the first time the hypothesis that flow-induced stresses within the liquid effectively raised the crystallization temperature of the liquid.

When studying the condensation of vapor to liquid drops on solid hydrophobic surfaces the volume of drops V is found to increase linearly with time, V∝t. Constant-contact-angle evaporation studies showed that drop volumes decrease according to V∝t^3/2. Since both processes are diffusion limited, one would expect the same kinetics. Here, we demonstrate experimentally, theoretically and by finite-element simulations that the spacing between condensing or evaporating drops affects the growth. The volume of single, isolated drops changes according to V∝t^3/2. For a dense array of drops each individual drop will grow or shrink linearly, V∝t.

We show that the classical Langevin dynamics for a charged particle on a closed curved surface in a time-independent magnetic field leads to the canonical distribution in the long time limit. Thus the Bohr-van Leeuwen theorem holds even for a finite system without any boundary and the average magnetic moment is zero. This is contrary to the recent claim by Kumar and Kumar (EPL, 86 (2009) 17001), obtained from numerical analysis of Langevin dynamics, that a classical charged particle on the surface of a sphere in the presence of a magnetic field has a nonzero average diamagnetic moment. We extend our analysis to a many-particle system on a curved surface and show that the nonequilibrium fluctuation theorems also hold in this geometry.

Carrier interactions on graphene are studied. The study shows that besides the well-known Coulomb repulsion between carriers, there also exist four-fermion interactions associated with the U-process, one of which attracts carriers in different valleys. We then calculate the contributions to the valley magnetic moment from vertex corrections and from four-fermion corrections explicitly. The relative contributions are - 18% and 3%, respectively. Lastly we point out that we can mimic the heavy-quarkonium system by carrier interactions in graphene.

The novel method for fabricating magnetic dots reported in this work exploits the dependence of the magnetic anisotropy of an ultrathin Co film on its thickness and on the type of the buffer layer. A patterned buffer prepared as self-assembled Au islands with a lateral size of several hundred nanometres grown on a Mo film surface induces mono-domain dots magnetized perpendicularly to the film plane in the epitaxial Co layer. Polar magneto-optical Kerr magnetometry and magnetic force microscopy have been used to investigate the magnetization reversal of the dots. Nucleation of the reversed magnetic domain followed by the unpinned movement of domain walls is discussed as a possible mechanism responsible for magnetization switching.

We calculate the transverse magnetoresistance in layered electronic systems at nonquantizing magnetic fields parallel and perpendicular to the layer plane and discuss the effect of the relationship between the Fermi level and the mini-band width, and also the direction and magnitude of the magnetic field on the transverse magnetoresistance and its sign. We show that the transverse magnetoresistance of a degenerate quasi–three-dimensional electron gas in the fields parallel to the layer plane is negative in weak fields and is positive in strong fields.

In the present heterostructure of YBa₂Cu₃O_7−δ/La_0.67Sr_0.33MnO₃ (YBCO/LSMO), a paramagnetic moment is observed, increasing monotonically with enhancing applied-field strength during the field-cooled (FC) magnetization process. Such a paramagnetic effect, however, emerges only in those samples where manganite layers are magnetically inhomogeneous, probably arising from the flux compression in the FC process. It is supposed that the flux compression occurs as a result of the strong magnetic pinning, caused by the stress-induced ferromagnetic/antiferromagnetic (FM/AFM) phase separation in the constituent layer of LSMO.

The iron arsenide Sr₂CrO₃FeAs with the tetragonal Sr₂GaO₃CuS-type structure was synthesized and its crystal structure re-determined by neutron powder diffraction. In contrast to previous X-ray crystallographic studies, a mixed occupancy of chromium and iron was found within the FeAs_4/4 layer (93±1%Fe:7±1%Cr). We suggest that the partial Cr-doping at the Fe site is the reason for the absence of a spin-density-wave anomaly and superconductivity in this compound. Additional experiments via neutron polarization analysis revealed short-range spin correlations below ∼100 K and long-range antiferromagnetic ordering below T_N=36 K with a magnetic propagation vector of ). The Cr³⁺-ions form a collinear magnetic structure of the C-type in the magnetic space group C_Pmma' (a'=a-b, b'=a+b, c'=c), where Cr³⁺-ions occupy the 4g () Wyckoff position. The magnetic moments are aligned along the orthorhombic a'-axis. At 3.5 K, an ordered magnetic moment of 2.75±0.05 μ_B for the Cr³⁺-sublattice was refined.

Non-local, inhomogeneous and retarded response similar to that observed in experiments is studied theoretically by introducing the Inhomogeneous Momentum Average (IMA) approximation for single-polaron problems with disorder in the on-site potential and/or spatial variations of the electron-phonon couplings and/or phonon frequencies. We show that the electron-phonon coupling gives rise to an additional inhomogeneous, strongly retarded potential. This potential describes essential physics ignored by "instanteneous" approximations. The accuracy of IMA is demonstrated by comparison with single-impurity results from the approximation-free Diagrammatic Monte Carlo (DMC) method. Its simplicity allows for easy study of many problems that were previously unaccessible.

In the present paper, by applying the Lang-Firsov canonical transformation and the so-called noncrossing-approximation technique, we investigate the effect of the electron-phonon interaction on the transport of a quantum dot (QD) system in the Kondo regime. The numerical results show that the zero-frequency shot noise and Fano factor are always enhanced significantly due to the electron-phonon interaction. The well-known peak structure around the Kondo temperature in the S-V curve exhibits a probe of the electron-phonon coupling strength λ. In addition, the enhancement of the Fano factor due to the electron-phonon interaction is attributed to the reduction of the Kondo-enhanced density-of-state and transmission probability in a quantum dot. The results may be informative for future experimental measurements.

We introduce a new distributed algorithm for aligning graphs or finding substructures within a given graph. It is based on the cavity method and is used to study the maximum-clique and the graph-alignment problems in random graphs. The algorithm allows to analyze large graphs and may find applications in fields such as computational biology. As a proof of concept we use our algorithm to align the similarity graphs of two interacting protein families involved in bacterial signal transduction, and to predict actually interacting protein partners between these families.

We study with ARPES the electronic structure of CoO₂ slabs, stacked with rock-salt (RS) layers exhibiting a different (misfit) periodicity. Fermi surfaces (FS) in phases with different doping and/or periodicities reveal the influence of the RS potential on the electronic structure. We show that these RS potentials are well ordered, even in incommensurate phases, where STM images reveal broad stripes with width as large as 80 Å. The anomalous evolution of the FS area at low dopings is consistent with the localization of a fraction of the electrons. We propose that this is a new form of electronic ordering, induced by the potential of the stacked layers (RS or Na in Na_xCoO₂) when the FS becomes smaller than the Brillouin Zone of the stacked structure.

The influence of geometry fluctuations on lateral diffusions is investigated numerically on a simple 1D problem which presents the same kind of non-linearities as fully 2D situations. It is found that geometry fluctuations influence diffusions at all scales, including scales much larger than the characteristic scales of fluctuations. The effective large-scale description of these diffusions is also investigated and the possibility of introducing a renormalized diffusion coefficient is discussed.

Scale-free networks have strong tolerance against random failures yet are fragile under intentional attacks. Existing results show that the network robustness can also be affected by its correlation profile. Specifically, scale-free networks with larger assortativity coefficients generally tend to be more robust against intentional attack. In this letter, we reveal some interesting different observations. By proposing a simple rewiring method which does not change any nodal degree, we show that network robustness can be steadily enhanced at a slightly decreased assortativity coefficient. The tolerance against random failures meanwhile remains largely unaffected. Such observations demonstrate the more complicated relationship between network robustness and its assortativity level, as well as some new possibilities of network enhancement and protection.

How to efficiently design a communication network is a paramount task for network designing and engineering. It is, however, not a single objective optimization process as perceived by most previous researches, i.e., to maximize its transmission capacity, but a multi-objective optimization process, with lowering its cost to be another important objective. These two objectives are often contradictive in that optimizing one objective may deteriorate the other. After a deep investigation of the impact that network topology, node capability scheme and routing algorithm as well as their interplays have on the two objectives, this letter presents a systematic approach to achieve a cost-effective design by carefully choosing the three designing aspects. Only when routing algorithm and node capability scheme are elegantly chosen can BA-like scale-free networks have the potential of achieving good tradeoff between the two objectives. Random networks, on the other hand, have the built-in character for a cost-effective design, especially when other aspects cannot be determined beforehand.

The electrodeformation of giant vesicles is studied as a function of their radii and the frequency of the applied AC field. At low frequency the shape is prolate, at sufficiently high frequency it is oblate and at some frequency, f_c, the shape changes from prolate to oblate. A linear dependence of the prolate-to-oblate transition inverse frequency, 1/f_c, on the vesicle radius is found. The nature of this phenomenon does not change with the variation of both the solution conductivity, σ, and the type of the fluid enclosed by the lipid membrane (water, sucrose or glucose aqueous solution). When σ increases, the value of f_c increases while the slope of the line 1/f_c(r) decreases. For vesicles in symmetrical conditions (the same conductivity of the inner and the outer solution) a linear dependence between σ and the critical frequency, f_c, is obtained for conductivities up to σ=114 μS/cm. For vesicles with sizes below a certain minimum radius, depending on the solution conductivity, no shape transition could be observed.

We study jammed configurations of polydisperse colloidal hard spheres with a well-defined temperature (constant kinetic energy) as a function of compression speed and size polydispersity. To this end, we employ event-driven molecular-dynamics simulations at fixed temperature, using an algorithm that strictly prohibits particle overlaps. We find a strong dependence of the jamming density on the compression rate that cannot be explained by crystallization. Additionally, we find that during the compression, the pressure follows the metastable liquid branch until the system gets kinetically arrested. Our results show that further compression yields jammed configurations that can be regarded as the infinite-pressure limit of glassy states and that different glasses can jam at different jamming densities depending on the compression rate. We present accurate data for the jamming density as a function of compression rate and size polydispersity.

Usually, we expect large particles to sediment faster than small ones of the same material. Contrary to this intuition, we report a dynamical competition between sedimentation and phase ordering which leads to smaller particles settling faster than larger ones. We access this phenomenon using suspensions of polymers and two colloidal species which we image with confocal microscopy. Polymers mediate attractions between colloids, leading to phase separation and crystallisation. We find that the dynamical interplay between sedimentation, phase separation and crystal nucleation underlie this phenomenon. Furthermore, under certain conditions we find a kinetic pathway leading to an apparent coexistence between a one-component crystal and a binary fluid of equal buoyancy. These findings may be relevant to the basic understanding of sedimentation-induced zone formation in nature and industrial applications.

The non-scientific event of a soccer match is analysed on a strictly scientific level. The analysis is based on the recently introduced concept of a team fitness (Eur. Phys. J. B, 67 (2009) 445) and requires the use of finite-size scaling. A uniquely defined function is derived which quantitatively predicts the expected average outcome of a soccer match in terms of the fitness of both teams. It is checked whether temporary fitness fluctuations of a team hamper the predictability of a soccer match. To a very good approximation scoring goals during a match can be characterized as independent Poissonian processes with pre-determined expectation values. Minor correlations give rise to an increase of the number of draws. The non-Poissonian overall goal distribution is just a consequence of the fitness distribution among different teams. The limits of predictability of soccer matches are quantified. Our model-free classification of the underlying ingredients determining the outcome of soccer matches can be generalized to different types of sports events.

In this work we study the excursions, defined as the number of beats to return to a local mean value, in heartbeat interval time series from healthy subjects and patients with congestive heart failure (CHF). First, we apply the segmentation procedure proposed by Bernaola-Galván et al. (Phys. Rev. Lett., 87 (2001) 168105), to nonstationary heartbeat time series to identify stationary segments with a local mean value. Next, we identify local excursions around the local mean value and construct the distributions to analyze the time organization and memory in the excursions sequences from the whole time series. We find that the cumulative distributions of excursions are consistent with a stretched exponential function given by g(x)∼e^−aτb, with a=1.09±0.15 (mean value±SD) and b=0.91±0.11 for healthy subjects and a=1.31±0.23 and b=0.77±0.13 for CHF patients. The cumulative conditional probability G(τ|τ₀) is considered to evaluate if τ depends on a given interval τ₀, that is, to evaluate the memory effect in excursion sequences. We find that the memory in excursions sequences under healthy conditions is characterized by the presence of clusters related to the fact that large excursions are more likely to be followed by large ones whereas for CHF data we do not observe this behavior. The presence of correlations in healthy data is confirmed by means of the detrended fluctuation analysis (DFA) while for CHF records the scaling exponent is characterized by a crossover, indicating that for short scales the sequences resemble uncorrelated noise.

Many epidemic processes in networks spread by stochastic contacts among their connected vertices. There are two limiting cases widely analyzed in the physics literature, the so-called contact process (CP) where the contagion is expanded at a certain rate from an infected vertex to one neighbor at a time, and the reactive process (RP) in which an infected individual effectively contacts all its neighbors to expand the epidemics. However, a more realistic scenario is obtained from the interpolation between these two cases, considering a certain number of stochastic contacts per unit time. Here we propose a discrete-time formulation of the problem of contact-based epidemic spreading. We resolve a family of models, parameterized by the number of stochastic contact trials per unit time, that range from the CP to the RP. In contrast to the common heterogeneous mean-field approach, we focus on the probability of infection of individual nodes. Using this formulation, we can construct the whole phase diagram of the different infection models and determine their critical properties.

The polymerization of actin filaments is coupled to the hydrolysis of adenosine triphosphate (ATP), which involves both the cleavage of ATP and the release of inorganic phosphate. We describe hydrolysis by a reduced two-state model with a cooperative cleavage mechanism, where the cleavage rate depends on the state of the neighboring actin protomer in a filament. We obtain theoretical predictions of experimentally accessible steady-state quantities such as the size of the ATP-actin cap, the size distribution of ATP-actin islands, and the cleavage flux for cooperative cleavage mechanisms.

In this paper we provide a new analysis of the system of partial differential equations describing the radial and vertical equilibria of the plasma in accretion disks. In particular, we show that the partial differential system can be separated once a definite oscillatory (or hyperbolic) form for the radial dependence of the relevant physical quantities is assumed. The system is thus reduced to an ordinary differential system in the vertical dimensionless coordinate. The resulting equations can be integrated analytically in the limit of small magnetic pressure. We complete our analysis with a direct numerical integration of the more general case. The main result is that a ring-like density profile (i.e., radial oscillations in the mass density) can appear even in the limit of small magnetic pressure.

Evidence for superluminal radiation in γ-ray burst (GRB) spectra is pointed out. The spectral maps of GRB 941017, GRB 990123, and GRB 990104 are analyzed. The superluminal radiation modes are generated by the shock-heated ultra-relativistic source plasma. The tachyonic radiation field is a real Proca field with negative mass-square, coupled to the electron gas by a frequency-dependent fine-structure constant. At GeV energies, the coupling constant approaches a limit value, so that the radiation field is minimally coupled to the electron current. In the soft γ-ray band, the interaction with the GRB plasma becomes nonlocal, due to the varying coupling strength depending on the energy of the radiated modes. The spectral fitting with tachyonic flux densities generated by nonlocal plasma currents is explained. Estimates of the tachyonic luminosity, temperature, and internal energy of the electronic source plasma are obtained from the spectral fits.