Table of contents

The tunneling method for stationary black holes in the Hamilton-Jacobi variant is reconsidered in the light of some critiques that have been moved against. It is shown that once the tunneling trajectories have been correctly identified the method is free from internal inconsistencies, it is manifestly covariant, it allows for the extension to spinning particles and it can even be used without solving the Hamilton-Jacobi equation. These conclusions borrow support on a simple analytic continuation of the classical action of a pointlike particle, made possible by the unique assumption that it should be analytic in the complexified Schwarzschild or Kerr-Newman space-time. A more general version of the Parikh-Wilczek method will also be proposed along these lines.

We analyze multipartite entanglement in systems of spin-½ particles from a relativistic perspective. General conditions which have to be met for any classification of multipartite entanglement to be Lorentz invariant are derived, which contributes to a physical understanding of entanglement classification. We show that quantum information in a relativistic setting requires the partition of the Hilbert space into particles to be taken seriously. Furthermore, we study exemplary cases and show how the spin and momentum entanglement transforms relativistically in a multipartite setting.

Adiabatic Z_Q invariants by quantized Berry phases are defined for gapped electronic systems in d-dimensions (Q=d+1). This series includes Polyacetylene, Kagome and Pyrochlore lattice, respectively for d=1, 2 and 3. The invariants are quantum Q-multimer order parameters to characterize the topological phase transitions by the multimerization. This fractional quantization is protected by the global Z_Q equivalence even with particle-particle interaction. As for the chiral symmetric case, a topological form of the Z₂ invariant is explicitly given as well.

We study how quantum correlations survive at large scales in spite of their exposition to stochastic backgrounds of gravitational waves. We consider Einstein-Podolski-Rosen (EPR) correlations built up on the polarizations of photon pairs and evaluate how they are affected by the cosmic gravitational wave background (CGWB). We evaluate the quantum decoherence of the EPR correlations in terms of a reduction of the violation of the Bell inequality as written by Clauser, Horne, Shimony and Holt (CHSH). We show that this decoherence remains small and that EPR correlations can in principle survive up to the largest cosmic scales.

We investigate a three-terminal heat pump through classical molecular dynamics simulations. It is reported an asymmetrical structure is necessary for the molecular heat pump. There exists an optimum pumping efficiency by controlling the asymmetry and the average temperature of the heat pump. The efficiency increases with the decreasing of the temperature difference between the hot and cold heat baths.

We examine the non-extensive approach to the statistical mechanics of Hamiltonian systems with H=T+V, where T is the classical kinetic energy. Our analysis starts from the basics of the formalism by applying the standard variational method for maximizing the entropy subject to the average energy and normalization constraints. The analytical results show i) that the non-extensive thermodynamics formalism should be called into question to explain experimental results described by extended exponential distributions exhibiting long tails, i.e.q-exponentials with q > 1, and ii) that in the thermodynamic limit the theory is only consistent in the range 0 ⩽ q ⩽ 1 where the distribution has finite support, thus implying that configurations with, e.g., energy above some limit have zero probability, which is at variance with the physics of systems in contact with a heat reservoir. We also discuss the (q-dependent) thermodynamic temperature and the generalized specific heat.

We show that extremal linear dilaton black holes in Einstein-Maxwell-dilaton-axion (EMDA) gravity have a hidden conformal symmetry. In this regard, we consider the wave equation of a massless scalar field propagating in this spacetime and find that in the "near region", the wave equation in the extremal limit can be written in terms of the SL(2, R) quadratic Casimir operator. Moreover, we obtain the microscopic entropy of the extremal linear EMDA spacetimes also we calculate the correlation function of a near-region scalar field and find perfect agreement with the dual 2D CFT.

We discuss non-equilibrium extensions of the Casimir force (due to electromagnetic fluctuations), where the objects as well as the environment are held at different temperatures. While the formalism we develop is quite general, we focus on a sphere in front of a plate, as well as two spheres, when the radius is small compared to separation and thermal wavelengths. In this limit the forces can be expressed analytically in terms of the lowest-order multipoles, and corroborated with results obtained by diluting parallel plates of vanishing thickness. Non-equilibrium forces are generally stronger than their equilibrium counterpart, and may oscillate with separation (at a scale set by material resonances). For both geometries we obtain stable points of zero net force, while two spheres may have equal forces in magnitude and direction resulting in a self-propelling state.

All experimental evidence for violation of discrete spacetime symmetries: Parity and Time reversal and the related Charge conjugation/Parity combination (P, T and CP, respectively) has been obtained on Earth in a gravitational potential that is P and T anisotropic. It is suggested that the origin of the observed CP violation is the scalar field equal to the frame dragging term dϕdt in the Kerr metric of a spinning massive body. The Galaxy would be the largest such source. Indirect evidence of such an effect would be anisotropic decay products when plotted in a reference frame defined by the fixed stars. As a consequence, CP violation would be very much greater near compact astrophysical objects with large angular momentum.

Various scintillation devices are used in many countries and wide scientific fields. Key elements that determine the performance of a scintillation device are the number of photons emitted per incident radiation event and the emission of easy-to-measure blue photons. It is generally known that only materials with very complex compositions perform well as scintillators. However, we demonstrated that the scintillation performance of a newly developed plastic such as 100 percent pure polyethylene naphthalate exceeds that of conventional organic scintillators. By measuring the light output spectra and emission spectra of several samples, we revealed that the plastic emits a high number of photons per incident radiation event (∼10500 photons/MeV), and, surprisingly, deep-blue photons (425 nm). Even though the plastic has a simple composition, it could replace the expensive organic scintillators that have been used in many applications.

Our micromechanical experiments show that viscoelastic features of type-I collagen fibril at physiological temperatures display essential dependence on the frequency and speed of heating. For temperatures of 20–30 ^°C the internal friction has a sharp maximum for a frequency less than 2 kHz. Upon heating the internal friction displays a peak at a temperature T_soft(v) that essentially depends on the speed of heating v: T_soft≈70^°C for v=1^°C/min, and T_soft≈25^°C for v=0.1^°C/min. At the same temperature T_soft(v) Young's modulus passes through a minimum. All these effects are specific for the native state of the fibril and disappear after heat-denaturation. Taken together with the known facts that the fibril is axially ordered as quasicrystal, but disordered laterally, we interpret our findings as indications of a glassy state, where T_soft is the softening transition.

In the present letter we propose a robust method to optimize the conventional heterogeneous patching (HP) method of controlling pattern formation in oscillatory systems. Normal heterogeneous patch controllers always leave visible imprints making the final patterns imperfect. Our optimal HP method uses normal wave (antiwave) media as the patched controllers to control dynamics of antiwave (normal wave) media. With properly selected and patched controllers, this method can modulate systems to desired patterns with the controllers themselves entirely hidden in homogeneous wave patterns. This favorable dynamics is due to the mechanism of interface selected waves (ISWs), which are found recently (Cui Xiaohua et al., Phys. Rev. E, 78 (2008) 026202). Moreover, utilizing the characteristics of ISWs, we are able to flexibly realize rich delicately designed spatiotemporal patterns by jointly using multiple oscillatory media with normal waves and antiwaves.

We address light propagation in segmented waveguide arrays where the refractive index is longitudinally modulated with an out-of-phase modulation in adjacent waveguides, so that the coupling strength varies along the propagation direction. Thus in resonant segments coupling may be inhibited hence light remains localized, while in detuned segments coupling results in complex switching scenarios that may be controlled by stacking several resonant and nonresonant segments. By tuning the modulation frequency and lengths of the waveguide segments one may control the distribution of light among the output guides, including localizing all light in the selected output channel.

The influences of intense coherent laser fields on the transport properties of a single-layer graphene are investigated by solving the time-dependent Dirac equation numerically. Under an intense laser field, the valence band and conduction band states mix via the optical Stark effect. The chiral symmetry of Dirac electrons is broken and the perfect chiral tunneling is strongly suppressed. These properties might be useful in the fabrication of an optically controlled field-effect transistor.

The propagation of light incident upon a 1D photonic superlattice consisting of successive stacking of alternate layers of a right-handed nondispersive material and a metamaterial, arranged to form a Cantor-like fractal, is considered. Plasmon-polariton excitations are thoroughly investigated within the transfer-matrix approach and shown to strongly depend on the Cantor step number N. More specifically, the number of plasmon-polariton bands corresponds to the number 2^N− 1 of metamaterial layers within the unit cell.

We present a parametric study of a nonlinear diffusion equation which generalises Leith's model of a turbulent cascade to an arbitrary cascade having a single conserved quantity. There are three stationary regimes depending on whether the Kolmogorov exponent is greater than, less than or equal to the equilibrium exponent. In the first regime, the large-scale spectrum scales with the Kolmogorov exponent. In the second regime, the large-scale spectrum scales with the equilibrium exponent so the system appears to be at equilibrium at large scales. Furthermore, in this equilibrium-like regime, the amplitude of the large-scale spectrum depends on the small-scale cut-off. This is interpreted as an analogue of cascade nonlocality. In the third regime, the equilibrium spectrum acquires a logarithmic correction. An exact analysis of the self-similar, nonstationary problem shows that time-evolving cascades have direct analogues of these three regimes.

It is perhaps appropriate that, in a year marking the 90th anniversary of Meghnad Saha seminal paper (1920), new developments should call fresh attention to the problem of ionization equilibrium in gases. It is established that, according to the identity principle, the "physical" model with only one chemical potential for all electrons in the system should be used, in contrast with the Saha "chemical" approach. Ionization equilibrium is considered in the simplest "physical" model for an electronic subsystem of matter in a rarefied state, consisting of one localized electronic state in each nucleus and delocalized electronic states considered as free ones. It is shown that, despite the qualitative agreement, there is a significant quantitative difference from the results of the application of the Saha formula to the degree of ionization and chemical potential. This is caused by the fact that the Saha formula corresponds to the "chemical" model of matter.

Quasielastic neutron scattering (QENS) has been used to investigate microscopic dynamics in the glass-forming Ni₈₀P₂₀, Pd₄₀Ni₄₀P₂₀ and Pd₄₃Ni₁₀Cu₂₇P₂₀ melts. These melts are characterized by a high-packing fraction that is similar at their liquidus temperatures. Increasing the number of components in these melts increases the viscosity at their liquidus temperature. However, the fragility of these melts did not show a composition dependence. Atomic dynamics in these liquids agree well with mode-coupling theory (MCT) predictions. From the MCT analysis of the QENS data the critical packing fractions for the microscopic glass-transition (φ_c) were obtained. The values obtained for φ_c are well within the MCT theoretical predictions for hard-sphere liquids.

We have investigated the isothermal and non-isothermal crystallization kinetics in molecular glasses in the system Ag₂O-SeO₂-MoO₃ with different modifier (Ag₂O) contents. We have observed a change from two-dimensional to three-dimensional crystallization with the increase of the modifier content. We have shown that John-Mehl-Avrami and Sestak-Berggren models give the best description of the isothermal and non-isothermal crystallization kinetics respectively for the glass-crystal transformation.

Using a generic model of a current-carrying molecular junction we discuss, for the first time, correlations between Raman flux and electrical conductance. A mechanism alternative to molecular motion is proposed for these experimentally detected correlations. Numerical simulations based on realistic estimates of molecular junction parameters suggest that the effect should be observable.

Rocksalt-structured GeSbTe (GST) phase-change materials contain significant amounts of intrinsic vacancies at one sublattice. On the basis of ab initio total energy calculations, we have shown that the so-called intrinsic vacancies result from geometrical voids that originate from packing spaces for lone pairs of electrons tightly bound to specific Te layers where a weak bonding exists. The existence of such geometrical voids is concomitant with a narrow band gap. The present results will shed new insights on the intrinsic vacancies in rocksalt-structured GST.

For bipartite honeycomb lattices, we show that the Berry phase depends not only on the shape of the system but also on the hopping couplings. Using the entanglement entropy spectra obtained by diagonalizing the block Green's function matrices, the maximally entangled states with the eigenvalue λ_m=1/2 of the reduced density matrix are shown to have one-to-one correspondences to the zero-energy states of the lattice with open boundaries. The existence of these states depends on the Berry phase. For systems with finite bearded edges along the x-direction, we show that new maximally entangled states (zero-energy states) appear pair-by-pair when one increases the hopping coupling h over the critical values h_c's.

Many high-temperature superconductors are highly polarizable ionic lattices where the Fröhlich electron-phonon interaction (EPI) with longitudinal optical phonons creates an effective attraction of doped carriers virtually equal to their Coulomb repulsion. The general multi-polaron theory is given with both interactions being strong compared with the carrier kinetic energy so that the conventional BCS-Eliashberg approximation is inapplicable. The many-electron system is described by the polaronic t-J_p Hamiltonian with reduced hopping integral, t, allowed double on-site occupancy, large phonon-induced antiferromagnetic exchange, J_p≫t, and a high-temperature superconducting state of small superlight bipolarons protected from clustering.

We study the time-dependent transmission of entanglement entropy through an out-of-equilibrium model interacting device in a quantum transport set-up. The dynamics is performed via the Kadanoff-Baym equations within many-body perturbation theory. The double occupancy , needed to determine the entanglement entropy, is obtained from the equations of motion of the single-particle Green's function. A remarkable result of our calculations is that can become negative, thus not permitting to evaluate the entanglement entropy. This is a shortcoming of approximate, and yet conserving, many-body self-energies. Among the tested perturbation schemes, the T-matrix approximation stands out for two reasons: it compares well to exact results in the low-density regime and it always provides a non-negative . For the second part of this statement, we give an analytical proof. Finally, the transmission of entanglement across the device is diminished by interactions but can be amplified by a current flowing through the system.

Accurate retrieval of spin-axis orientation at the antiferromagnetic (AFM) surface requires involved consideration of the crystal field effect in X-ray magnetic linear dichroism (XMLD), which was neglected until recently. Here, we present a unique determination of surface spin-axes of the prototype antiferromagnet NiO(100) from detailed angular-dependent measurements using different polarizations of incident light by considering the recently developed angular dependence of the XMLD effect. The bulk twin domains terminating on the (100) surface have also been determined from the angular dependence of the experimental contrast at the oxygen K edge. The effect of Fe deposition on the AFM domain pattern was followed in situ and the interfacial exchange coupling of as-deposited Fe/NiO(100) has been explored using the recent formalism of XMLD. Unlike Co/NiO(100), we realize only the rough perpendicular coupling between Fe moments and compensated Ni spin-axes. The uncompensated spins (UCS) at the interface were also characterized and a mechanism of interfacial coupling is suggested.

We consider an electron-hole bilayer in the limit of extreme density imbalance, where a single particle in one layer interacts attractively with a Fermi liquid in the other parallel layer. Using an appropriate variational wave function for the dressed exciton, we provide strong evidence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in electron-hole bilayers with a large density imbalance. Furthermore, within this unusual limit of FFLO, we find that a dilute gas of minority particles forms excitons that condense into a two-dimensional "supersolid".

We show that high-resolution Resonant Inelastic X-ray Scattering (RIXS) provides direct, element-specific and momentum-resolved information on the electron-phonon (e-p) coupling strength. Our theoretical analysis indicates how the e-p coupling can be extracted from RIXS spectra by determining the differential phonon scattering cross-section. An alternative manner to extract the coupling is to use the one- and two-phonon loss ratio, which is governed by the e-p coupling strength and the core-hole lifetime. This allows the determination of the e-p coupling on an absolute energy scale.

By in situ X-ray photon correlation spectroscopy and small-angle X-ray scattering we quantify the evolution of dynamics and structure during the formation of a cross-linked polymer gel. A fast, non-ergodic relaxation stemming from localized motions of polymer clusters indicates a stiffening network on the nano-scale as a signature of the gelation. A second, much slower relaxation that restores ergodicity is due to the dynamics of the gel network. As the gelation proceeds the reinforcement of the cross-linked network is accompanied by a slowing-down of this second relaxation that also changes line shape during the reaction. Spatial anisotropy develops in the network dynamics but without any signs of dynamical heterogeneity. This distinguishes the observed dynamics from that of typical jammed systems where dynamical heterogeneity is a hallmark.

We synthesized sp³-rich crystalline tubular structures, referred to as diamond nanotubes (DNTs), by hot-filament chemical vapor deposition and characterized them using SEM, TEM, EELS, and Raman spectroscopy. The images and spectra indicate the formation of DNTs with internal diameter of about 7–10 nm and external diameter of about 20–30 nm. During the fabrication process, CNTs form first and give way to the synthesis of DNTs. The DNTs show good field emission properties and enhanced temporal stability as compared to CNTs.

A comparative simulation study of polymer brushes formed by grafting at a planar surface either flexible linear polymers (chain length N_L) or (non-catenated) ring polymers (chain length N_R=2N_L) is presented. Two distinct off-lattice models are studied, one by Monte Carlo methods, the other by molecular dynamics, using a fast implementation on graphics processing units (GPUs). It is shown that the monomer density profiles ρ(z) in the z-direction perpendicular to the surface for rings and linear chains are practically identical, ρ_R(2N_L,z)=ρ_L(N_L, z). The same applies to the pressure, exerted on a piston at height z, as well. While the gyration radii components of rings and chains in the z-direction coincide, too, and increase linearly with N_L, the transverse components differ, even with respect to their scaling properties: R_gxy^(L)∝N_L^1/2, R_gxy^(R)∝N_L^0.4. These properties are interpreted in terms of the statistical properties known for ring polymers in dense melts.

Catalytically active particles suspended in a liquid can move due to self-phoresis by generating solute gradients via chemical reactions of the solvent occurring at parts of their surface. Such particles can be used as carriers at the micro-scale. As a simple model for a carrier-cargo system we consider a catalytically active particle connected by a thin rigid rod to a catalytically inert cargo particle. We show that the velocity of the composite strongly depends on the relative orientation of the carrier-cargo link. Accordingly, there is an optimal configuration for the linkage. The subtlety of such carriers is underscored by the observation that a spherical particle completely covered by catalyst, which is motionless when isolated, acts as a carrier once attached to a cargo.

We study the robustness of scale-free networks against attack with grey information, which means that one can obtain the information of all nodes, but the attack information may be imprecise. The known random failure and intentional attack are two extreme scenarios of our robustness model. By introducing two attack information parameters α and β, where α governs negative deviation of one's observation while β governs positive deviation of the observation, we demonstrate tunable equilibrium of degree, which accommodates abundant observation mechanisms. We derive the exact solution of the critical removal fraction of nodes for the disintegration of networks. Increasing the precision of attack information can reduce the robustness of scale-free networks. Our main finding is that the attack robustness of scale-free networks is more sensitive to the parameter α than to the parameter β. Moreover, if α and β for a node having degree k are proportional to k^γ, where −∞<γ<+∞, we find that increasing γ enhances the robustness of scale-free networks when γ> 0 and that the network seems rather fragile for any γ<0. Our model provides insight into the investigation of attack and defence strategies of complex networks.

We study the storage of multiple phase-coded patterns as stable dynamical attractors in recurrent neural networks with sparse connectivity. To determine the synaptic strength of existent connections and store the phase-coded patterns, we introduce a learning rule inspired to the spike-timing–dependent plasticity (STDP). We find that, after learning, the spontaneous dynamics of the network replays one of the stored dynamical patterns, depending on the network initialization. We study the network capacity as a function of topology, and find that a small-world–like topology may be optimal, as a compromise between the high wiring cost of long-range connections and the capacity increase.

We investigate the multifractal random walk (MRW) model, popular in the modelling of stock fluctuations in the financial market. The exact probability distribution function (PDF) is derived by employing methods proposed in the derivation of correlation functions in string theory, including the analytical extension of Selberg integrals. We show that the recent results by Y. V. Fyodorov, P. Le Doussal and A. Rosso obtained with the logarithmic Random Energy Model (REM) model are sufficient to derive exact formulas for the PDF of the log returns in the MRW model.

In recent years it has been argued that the tension parameter driving the fluctuations of fluid membranes, differs from the imposed lateral stress, the "frame tension". In particular, stress-free membranes were predicted to have a residual fluctuation tension. In the present paper, this argument is reconsidered and shown to be inherently inconsistent —in the sense that a linearized theory, the Monge model, is used to predict a nonlinear effect. Furthermore, numerical simulations of one-dimensional stiff membranes are presented, which clearly demonstrate, first, that the internal "intrinsic" stress in membranes indeed differs from the frame tension as conjectured, but second, that the fluctuations are nevertheless driven by the frame tension. With this assumption, the predictions of the Monge model agree excellently with the simulation data for stiffness and tension values spanning several orders of magnitude.