Table of contents

A noncommutative BTZ black hole is constructed in three-dimensional anti-de Sitter space. In this black-hole model, the noncommutative smearing is obtained by replacing the point-like source term with a Lorentzian distribution. We mainly investigate the thermodynamical properties of this black hole, including Hawking temperature, entropy, heat capacity and free energy.

An experimental study is presented, about transitions between Non-Equilibrium Steady States (NESS) in a dissipative medium. The core device is a small rotating blade that imposes cycles of increasing and decreasing forcings to a granular gas, shaken independently. The velocity of this blade is measured, subject to the transitions imposed by the periodic torque variation. The Hatano-Sasa (HS) equality, that generalises the second principle of thermodynamics to NESS, is verified with a high accuracy (a few 10⁻³), at different variation rates. Besides, it is observed that the fluctuating velocity at fixed forcing follows a generalised Gumbel distribution. A rough evaluation of the mean free path in the granular gas suggests that it might be a correlated system, at least partially.

We demonstrate theoretically and experimentally that excitable systems can be built with autonomous Boolean networks. Their experimental implementation is realized with asynchronous logic gates on a reconfigurabe chip. When these excitable systems are assembled into time-delay networks, their dynamics display nanosecond time scale spike synchronization patterns that are controllable in period and phase.

Using the ABCD formalism of atom optics, the generating function method and the invariant operator method (Liouville-von Neumann picture), I show in this letter how the quantum time evolution of any wave packet can be entirely determined by a natural symplectic invariant, which provides both the (non-Hermitian) invariant operator and the adequate eigenvalue. Within this framework, the quantum propagator does not appear any more as the fundamental kernel of integration but merely as a particular property of this invariant operator. The symplectic invariant method is interpreted in terms of creation/annihilation operators of N-dimensional Hermite-Gaussian modes.

We introduce a method for the dissipative preparation of strongly correlated quantum states of ultracold atoms in an optical lattice via localized particle loss. The interplay of dissipation and interactions enables different types of dynamics. This ushers in a new line of experimental methods to maintain the coherence of a Bose-Einstein condensate or to deterministically generate macroscopically entangled quantum states.

We study how universality arises when computing Casimir interactions between arbitrary bodies by discretizing their boundaries into pointlike constraints viewed as pointlike inclusions. Introducing ad hoc cutoff and regularization for the field's correlation function, we find that universality arises when i) the separation δ between the pointlike inclusions is less than the cutoff Λ⁻¹, and ii) the bodies are much larger than the cutoff. A sharp transition from discrete to continuous boundaries occurs at δ = π/Λ in the thermodynamic limit for rods at large separation. We illustrate our findings in two dimensions with rodlike bodies and more complex bodies shaped as moons.

The origin of flavor mixings in the quark and lepton sectors is still a mystery, and the structure of flavor mixings in the lepton sector seems completely different from that of the quark sector. In this letter, we point out that the flavor mixing angles in the quark and lepton sectors could be unified at a high-energy scale, when neutrinos are degenerate. It means that a minimal flavor violation at a high-energy scale can induce a rich variety of flavor mixings in the quark and lepton sectors at a low-energy scale through quantum corrections.

We investigate the nonresonant three-body decays of the B meson to J/ψπ⁺π⁻ and J/ψπ⁺π⁰ final-states mesons. There are a tree and a penguin diagram for these decays modes in the naive factorization approach. The transition matrix element of $B\rightarrow J/\psi \pi \pi$ is factorized into a $B\rightarrow \pi \pi$ form factor multiplied by the J/ψ decay constant. We assume that the J/ψ meson remains stationary and the two pion mesons move back to back. We calculate the branching ratio of the $B^0\rightarrow J/\psi \pi ^+\pi ^-$ and $B^+\rightarrow J/\psi \pi ^+\pi ^0$ decays and obtain 1.09 × 10⁻⁵ and 5.45 × 10⁻⁶, respectively, while the experimental results are less than 1.2 × 10⁻⁵ and 7.3 × 10⁻⁶, respectively. The branching ratios obtained in our model, are compatible with the upper limits of the experimental results.

Relative cross-sections for double ionization and single ionization of targets under the impact of hydrogen anions were measured. Two systems were investigated, H⁻ projectiles with Kr and Xe targets. The energy region was 10–30 keV. Recoil ions originated from target (Kr⁺, Kr²⁺, Xe⁺, Xe²⁺) were detected in coincidence with projectiles in several final charge states (q = 0 and q = + 1). We compare the present results with the previous results of Ar. The results show that the cross-section ratios, taken between double and single ionization of Ar, Kr and X in the channels of single and double electron loss of H⁻, become larger and larger with the incident energy increasing, and that the cross-section ratios will cross at some certain energy for the two different electron loss channels. The crossing energy for Xe is about 23 keV.

We design a coherent perfect absorber (CPA) that can totally absorb the converging wave. Such a CPA is of subwavelength size and can be embedded in Maxwell's fish-eye lens and serve as a drain very well. Numerical simulations were performed to verify the functionalities.

A new concept of the development of plasma compressor for generation of extremely short, relativistically strong femtosecond pulses at a petawatt power level is proposed. The considered compression mechanism is based on the non-stationary self-focusing of a spatially confined wave packet in transparent plasma during the excitation of a plasma wake wave with a period exceeding the laser pulse duration. It is shown that by using appropriately shaped, strong short laser pulses even shorter pulses (with durations up to one optical cycle of the field) can be generated with intensities much greater (>10 times) than the incident pulse with a significant fraction (∼25%) of incident pulse energy.

In this paper, two side-coupled zero-index-metamaterial–based resonators that mimic the spontaneous-emission cancellation (SEC) effect are investigated numerically and experimentally. It is found that an interference-induced stopband as deep as −70 dB can be observed in a microstrip SEC structure whose size is even less than 0.5 cm². More simulations about the electrical-field distributions demonstrate intuitively the underlying physics, i.e., the destructive interference between two side-coupled zero-index-metamaterial–based resonators. Our method of realizing ultra-deep stopband properties in a miniaturized filter may find potential applications in both microwave and optical-communication systems.

We present here experimental results on the effect of a forest of cylinder obstacles (nails) on the stability of a granular layer over a rough incline, in a so-called "fakir plane" configuration. The nail forest is found to increase the stability of the layer, the more for the densest array, and such an effect is recovered by a simple model taking into account the additional friction force exerted by the pillar forest onto the granular layer.

By a comprehensive mathematical derivation, we show that the underlying physics of realizing a two-dimensional omnidirectional radiation from multiple sources via radially anisotropic zero-index metamaterials (RAZIM), as numerically and experimentally demonstrated in Cheng Q.et al., Phys. Rev. Lett., 108 (2012) 213903, lies in that the RAZIM shell confines all anisotropic cylindrical modes within the shell, while keeping transparent to isotropic cylindrical modes. From the illustrated underlying physics, it follows straightforwardly that it is impossible to use the RAZIM for generating perfectly coherent isotropic radiation in a three-dimensional free space, contrary to the claim made in the above-mentioned reference.

The structure of driven three-dimensional complex-plasma clusters was studied experimentally. The clusters consisted of around 60 glass microspheres that were suspended in a plasma of rf discharge in argon. The particles were confined in a glass box with conductive yet transparent coating on its four side walls. This allowed manipulating the particle cluster by biasing the confining walls in a certain sequence and direct imaging of the cluster. In this work, a rotating electric field was used to drive the clusters. Depending on the field frequency, the clusters rotated (10⁴–10⁷ times slower than the rotating field) or remained stationary. The cluster structure was neither that of nested spherical shells nor a simple chain structure. Strings of various lengths were found consisting of 2 to 5 particles, their spatial and temporal correlations were studied. The results are compared to recent simulations.

Due to the extreme plasma conditions in Hall thrusters, such as electron temperature anisotropy and non-Maxwellian electron distribution function (EDF), understanding the plasma-wall interaction is a very challenging task. This letter is attempting to study this issue with a two-dimensional particle-in-cell model. It is found that the anisotropic non-Maxwellian EDF makes the electron temperature threshold for the appearance of a spatial oscillation wall sheath much lower than the Maxwellian EDF does. Furthermore, even though the sheath potential drop in the anisotropic non-Maxwellian case is found much smaller than those in Maxwellian cases, the plasma-wall interaction becomes much weaker since the anisotropic non-Maxwellian EDF is depleted at high energies.

An analytical model is developed for the effective thermal conductivity of the composites with graphene nanoplates (GNPs) within the framework of differential-effective-medium (DEM) theory. Results of the present model are compared to an effective-medium-approximation (EMA) based model and available experimental results. Predictions on the effective thermal conductivity of GNP/PA-6 and GNP/epoxy composites are in good agreement with the experimental data. Moreover, the present model can well describe the large thermal conductivity enhancement in GNP composites and, in particular, the nonlinear dependence of effective thermal conductivity on the volume fractions of GNPs, which is superior to the EMA model.

In studies of complex heterogeneous networks, particularly of the Internet, significant attention was paid to analyzing network failures caused by hardware faults or overload, where the network reaction was modeled as rerouting of traffic away from failed or congested elements. Here we model another type of the network reaction to congestion —a sharp reduction of the input traffic rate through congested routes which occurs on much shorter time scales. We consider the onset of congestion in the Internet where local mismatch between demand and capacity results in traffic losses and show that it can be described as a phase transition characterized by strong non-Gaussian loss fluctuations at a mesoscopic time scale. The fluctuations, caused by noise in input traffic, are exacerbated by the heterogeneous nature of the network manifested in a scale-free load distribution. They result in the network strongly overreacting to the first signs of congestion by significantly reducing input traffic along the communication paths where congestion is utterly negligible.

Glass formers exhibit, upon an oscillatory excitation, a response function whose imaginary and real parts are known as the loss and storage moduli, respectively. The loss modulus typically peaks at a frequency known as the α frequency which is associated with the main relaxation mechanism of the super-cooled liquid. In addition, the loss modulus is decorated by a smaller peak, shoulder or wing which is referred to as the β-peak. The physical origin of this secondary peak had been debated for decades, with proposed mechanisms ranging from highly localized relaxations to entirely cooperative ones. Using numerical simulations we bring an end to the debate, exposing a clear and unique cooperative mechanism for the said β-peak which is distinct from that of the α-peak.

We present comprehensive results from Monte Carlo (MC) simulations of ordering dynamics in d = 2 nematic liquid crystals. We compare our MC results with an analytic form obtained for the correlation function of the liquid crystal order parameter. The numerical and analytical results are in excellent agreement. The domain growth law is consistent with L(t) ∼ (t/ln t)^1/2.

Molecular-dynamics simulations based on many-body interatomic potentials are conducted to investigate the clusters of discrete breathers in graphene under in-plane homogeneous strain. It is found that the discrete breather clusters can easily be excited when the gap in the phonon density of states is introduced by the homogeneous strain. Clusters of up to four discrete breathers were studied. We demonstrate that such clusters are robust with respect to small perturbations and can have the lifetime of order of 10³ oscillation periods. Partial energy exchange between discrete breathers in the clusters was observed under certain conditions. The possible role of discrete breather clusters in formation of lattice defects is discussed.

We obtain the Paris law of fatigue crack propagation in a fuse network model where the accumulated damage in each resistor increases with time as a power law of the local current amplitude. When a resistor reaches its fatigue threshold, it burns irreversibly. Over time, this drives cracks to grow until the system is fractured into two parts. We study the relation between the macroscopic exponent of the crack-growth rate —entering the phenomenological Paris law— and the microscopic damage accumulation exponent, γ, under the influence of disorder. The way the jumps of the growing crack, Δa, and the waiting time between successive breaks, Δt, depend on the type of material, via γ, are also investigated. We find that the averages of these quantities, $\left \langle \Delta a\right \rangle$ and $\left \langle \Delta t\right \rangle /\left \langle t_r\right \rangle$, scale as power laws of the crack length a, $\left \langle \Delta a\right \rangle \propto a^{\alpha }$ and $\left \langle \Delta t\right \rangle /\left \langle t_r\right \rangle \propto a^{-\beta }$, where $\left \langle t_r\right \rangle$ is the average rupture time. Strikingly, our results show, for small values of γ, a decrease in the exponent of the Paris law in comparison with the homogeneous case, leading to an increase in the lifetime of breaking materials. For the particular case of γ = 0, when fatigue is exclusively ruled by disorder, an analytical treatment confirms the results obtained by simulation.

We derive and study the anisotropic Ginzburg-Landau and Lawrence-Doniach models describing a layered superfluid ultracold Fermi gas in optical lattices. We compute from the microscopic model the Josephson couplings entering the Lawrence-Doniach model across the crossover BCS-BEC passing from the 3D isotropic case to the quasi-2D one, showing that a model with only nearest-neighbor Josephson couplings is not adequate at the unitary limit (since the pairs have a diameter larger than the interlayer distance). We also show that the effective anisotropy of the system is strongly reduced at the unitary limit. Finally, we obtain a relation between the interlayer Josephson couplings and the Ginzburg-Landau masses: we find that using only couplings between adjacent planes is correct in the BEC side, while at the unitary limit one has to use also next-nearest-neighboring couplings.

We use first-principles calculations to extract two essential microscopic parameters, the charge-transfer energy and the inter-cell oxygen-oxygen hopping, which correlate with the maximum superconducting transition temperature T_c,max across the cuprates. We explore the superconducting state in the three-band model of the copper-oxygen planes using cluster Dynamical Mean-Field Theory. We find that the variation in the charge-transfer energy largely accounts for the empirical trend in T_c,max, resolving a long-standing contradiction with theoretical calculations.

Based on a phenomenological model with s_± or s-wave pairing symmetry, the mixed-state effect on quasiparticle interference in iron-based superconductors is investigated by solving large-scale Bogoliubov-de Gennes equations based on the Chebyshev polynomial expansion. Taking into account the presence of magnetic field, our result for the s_± pairing is in qualitative agreement with recent scanning tunneling microscopy experiment while for the s-wave pairing, the result is in apparent contradiction with experimental observations, thus excluding the s-wave pairing. Furthermore, we treat the effect of vortices rigorously instead of approximating the vortices as magnetic impurities, thus our results are robust and should be more capable of explaining the experimental data.

The electronic and structural properties of fluorinated monovacancies in graphene are studied using density functional theory. Our calculations show that an odd number of F atoms adsorbed on a monovacancy gives rise to a p-type metallic state with a local magnetic moment of 1 μ_B. In contrast, an even number of F atoms leads to a non-magnetic semiconducting state. We explain the behaviour in terms of local structure properties.

We model the quasiparticle interference (QPI) pattern in the recently discovered (K,Tl)Fe_xSe₂ superconductors. We show in the superconducting state that, due to the absence of hole pockets at the Brillouin zone center, the quasiparticle scattering occurs around the momentum transfer q = (0,0) and (±π,±π) between electron pockets located at the zone boundary. More importantly, although both d_x²−y²-wave and s-wave pairing symmetry lead to nodeless quasiparticle excitations, distinct QPI features are predicted between both types of pairing symmetry. The so-called Z-map of the QPI exhibits strongest scattering with q = (±π,±π) for the d_x²−y²-wave pairing symmetry, which is absent in the case of an isotropic s-wave pairing symmetry. The significant contrast in the QPI pattern between the d_x²−y²-wave and the isotropic s-wave pairing symmetry can be used to probe the pairing symmetry within the Fourier-transform STM technique.

It has been recently shown that the competition between unscreened Coulomb and Fröhlich electron-phonon interactions can be described in terms of a short-range spin exchange J_p and an effective on-site interaction $\tilde {U}$ in the framework of the polaronic t-J_p-$\tilde {U}$ model. This model, that provides an explanation for high-temperature superconductivity in terms of Bose-Einstein condensation (BEC) of small and light bipolarons, is now studied as a charged Bose-Fermi mixture. Within this approximation, we show that a gap between bipolaron and unpaired polaron bands results in a strong suppression of low-temperature spin susceptibility, specific heat and tunnelling conductance, signalling the presence of a pseudogap regime in the normal state without any assumptions on pre-existing orders or broken symmetries in the normal state of the model.

This work aims to optimize the overall performance of a model oscillator, as an energy harvester of Lévy-like mesoscopic fluctuations through piezoelectric conversion. As a further step in the description of a realistic harvesting device we consider a monostable Woods-Saxon oscillator, which can interpolate between square well and harmonic-like behaviors. We study the interplay between the potential shape and the noise's spectrum and statistics. The dependence of the power output on the parameters determining those features indicates the directions in which the former can be increased.

Living systems are typically characterized by irreversible processes. A condition equivalent to the reversibility is the detailed balance, whose absence is an obstacle for analytically solving ecological models. We revisit a promising model with an elegant field-theoretic analytic solution and show that the theoretical analysis is invalid because of an implicit assumption of detailed balance. A signature of the difficulties is evident in the inconsistencies appearing in the many-point correlation functions and in the analytical formula for the species area relationship.

We analyze the condensation phase transitions in out-of-equilibrium complex networks in a unifying framework which includes the nonlinear model and the fitness model as its appropriate limits. We show a novel phase structure which depends on both the fitness parameter and the nonlinear exponent. The occurrence of the condensation phase transitions in the dynamical evolution of the network is demonstrated by using Bianconi-Barabási method. We find that the nonlinear and the fitness preferential-attachment mechanisms play important roles in the formation of an interesting phase structure.

The influence of polarization on the two-dimensional structure of heterogeneous dumbbells is studied by Monte Carlo simulation. The dumbbell consists of two fused hard spheres whose centers are embedded with point dipoles $\vec \mu _a$ and $\vec \mu _b$, respectively. The axis of the dumbbell can rotate freely in the x-y plane but $\vec \mu _a$ and $\vec \mu _b$ are always along the x-axis which is the polarization direction. When the dipolar strength μ_a is much larger than μ_b, the dumbbells are perpendicular to the polarization direction and form zigzag chains; when μ_a and μ_b are comparable, the dumbbells will form end-to-end chains if $\vec \mu _a$ and $\vec \mu _b$ are parallel, or side-by-side chains if $\vec \mu _a$ and $\vec \mu _b$ are antiparallel. All the chains are along the polarization direction and the detailed information about them is given through extracting the radial and angular distributions from the simulation results. Finally, we calculate the energies of four kinds of ideal chains to explain structural transition. Our simulation results can explain the very recent experiment by Nagao D. et al. (Langmuir, 28 (2012) 6546) which studied the assembly of dumbbells with inducible dipoles, where magnitude of the dipoles was frequency-dependent and by changing frequency, different assemblies could be obtained.

The distribution of returns in financial time series exhibits heavy tails. It has been found that gaps between the orders in the order book lead to large price shifts and thereby to these heavy tails. We set up an agent-based model to study this issue and, in particular, how the gaps in the order book emerge. The trading mechanism in our model is based on a double-auction order book. In situations where the order book is densely occupied with limit orders we do not observe fat-tailed distributions. As soon as less liquidity is available, a gap structure forms which leads to return distributions with heavy tails. We show that return distributions with heavy tails are an order-book effect if the available liquidity is constrained. This is largely independent of specific trading strategies.

We probe the diffusive motion of particles in slowly sheared three-dimensional granular suspensions. For sufficiently large strains, the particle dynamics exhibits diffusive Gaussian statistics, with the diffusivity proportional to the local strain rate —consistent with a local, quasi-static picture. Surprisingly, the diffusivity is also inversely proportional to the depth of the particles below the granular surface —at their free surface, the diffusivity thus appears to diverge and is ill defined. We find that the crossover to Gaussian displacement statistics is governed by the same depth dependence, evidencing a non-trivial strain scale in three-dimensional granular flows.

We propose a special solution of Einstein equations in the general Vaidya form representing a dynamical black hole having horizon cross-sections with toroidal topology. The concrete model enables us to study for the first time dynamical horizons with toroidal topology, its area law, and the question of matter flux inside the horizon, without using a cut-and-paste technology to construct the solution.

By analyzing in natural time the Southern California Earthquake Catalog (SCEC) during the period 1979–2003, the probability distribution of the order parameter of seismicity is studied. Remarkable changes in the feature of this distribution are identified well before the occurrence of the three major mainshocks reported by SCEC: Landers in 1992, Northridge in 1994 and Hector Mine in 1999. In addition, just before the occurrence of these mainshocks, i.e., for 100 successive events of magnitude M ⩾ 2.0 before each of them, their scaled order parameter probability distributions almost collapse onto a single curve and share over two orders of magnitude a characteristic "exponential tail" reflecting non-Gaussian fluctuations.

We investigate the physical processes that generate the ocean tides, whose understanding has important influence on the marine activities. We analyze historical sea-level oscillations, continuously recorded from six stations in the North Atlantic Ocean spanning a time period of eighty years from 1926. In this paper, an Independent-Component-Analysis–based approach is adopted to obtain a clear identification of the main tidal constituents in term of waveform in time domain from the simultaneously recorded signals. This technique separates at most six nonlinear tidal components which are weakly superimposed. The fundamental objective is to extract information on the degree of complexity of the involved dynamics and on the very long-term tidal constituents. This is particularly significant to understand the response of the ocean to the tidal forcing. We put the emphasis on the near-bidecadal time scale and its influence on the short-periods tides. In details the Moon 18.6 y nodal cycle modulation acts in the ocean in quite an analogous manner to the fortnightly modulation in many shallow seas. Our results give new insights into the evidence for an 18.6 y effect in the climate/ocean variation whose physical mechanism details remain murky.

The stability of any self-gravitating cluster of matter is affected by the repulsive effect of the so-called dark energy. Using a simple method we estimate the limit of existence of Newtonian clusters formed by pure fermion or boson populations in their ground state. These clusters simulate lumps of dark matter. As the length scale of the clusters is limited by the effect of dark energy, this implies a lower bound for their mass. From these bounds for the clusters one can infer constraints for the mass of the underlying constituent dark matter particle. The computations are carried out comparing two characteristic length scales which provide an order of magnitude for this problem. The repulsive effect of dark energy is implemented by using an up-to-date value of the cosmological constant. For both fermions and bosons, the condition of existence is expressed in a similar way and a significant common mass scale is identified.