Table of contents

First measurement of the total proton-proton cross-section at the LHC energy √s = 7 TeV Slippery pre-suffused surfaces Direct measurement of the speed of sound in a complex plasma under microgravity conditions Viscous mechanism for Leidenfrost propulsion on a ratchet

A novel analysis of finite-dimensional Hilbert space is outlined. The approach bypasses the general, inherent, difficulties present in handling angular variables in finite-dimensional problems: the finite-dimensional, d, odd prime, Hilbert space operators are underpinned with a finite geometry which provides intuitive perspectives to the physical operators. The analysis emphasizes a central role for projectors of mutual unbiased bases (MUB) states, extending thereby their use in finite-dimensional quantum-mechanics studies. Interrelations among the Hilbert space operators revealed via their (finite) dual affine plane geometry (DAPG) underpinning are displayed and utilized in formulating the finite-dimensional ubiquitous Radon transformation and its inverse illustrating phase-space-like physics encoded in lines and points of the geometry. The finite geometry required for our study is outlined.

Recently, Verlinde has suggested a novel model of duality between thermodynamics and gravity which leads to an emergent phenomenon for the origin of gravity and general relativity. In this paper, we investigate some features of this model in the presence of noncommutative charged black hole by performing the method of coordinate coherent states representing smeared structures. We derive several quantities, e.g., temperature, energy and entropic force. Our approach clearly exhibits that the entropic force on a smallest fundamental cell of holographic surface with radius r₀ is halted. Accordingly, we can conclude that the black-hole remnants are absolutely inert without gravitational interactions. So, the equivalence principle of general relativity is contravened due to the fact that it is now possible to find a difference between the gravitational and inertial mass. In other words, the gravitational mass in the remnant size does not emit any gravitational field, therefore it is experienced to be zero, contrary to the inertial mass. This phenomenon illustrates a good example for a feasible experimental confirmation to the entropic picture of Newton's Second law in very short distances.

The phenomenon of enhancement of synchronization due to time delay is investigated in an arbitrary delay coupled network with chaotic units. Using the master stability formalism for a delay coupled network, we elaborate that there always exists an extended regime of stable synchronous solutions of the network for appropriate coupling delays. Further, the stable synchronous state is achieved even at smaller values of coupling strength with delay, which can be only attained at much larger coupling strength without delay. This also facilitates the increase in the number of synchronized nodes in the delay coupled network beyond size instability of the same network without delay. Further, the largest transverse Lyapunov exponents in the master stability surface of the network clearly demarcates the stable synchronous solutions from the unstable ones. The generic nature of our results is also corroborated using three paradigmatic models, namely, Rössler and Lorenz systems as well as Hindmarsh-Rose neurons as nodes in the delay coupled network.

Golding and Cox (Phys. Rev. Lett., 96 (2006) 098102) tracked the motion of individual fluorescently labelled mRNA molecules inside live E. coli cells. They found that in the set of 23 trajectories from 3 different experiments, the automatically recognized motion is subdiffusive and published an intriguing microscopy video. Here, we extract the corresponding time series from this video by image segmentation method and present its detailed statistical analysis. We find that this trajectory was not included in the data set already studied and has different statistical properties. It is best fitted by a fractional autoregressive integrated moving average (FARIMA) process with the normal-inverse Gaussian (NIG) noise and the negative memory. In contrast to earlier studies, this shows that the fractional Brownian motion is not the best model for the dynamics documented in this video.

Mean fidelity amplitude and parametric energy-energy correlations are calculated exactly for a regular system, which is subject to a chaotic random perturbation. It turns out that in this particular case on the average both quantities are identical. The result is compared with the susceptibility of chaotic systems against random perturbations. Regular systems are more susceptible to random perturbations than chaotic ones.

It is shown that Fermi acceleration, which is inherent to time-dependent open-horizon two-dimensional billiards, leads to anomalous transport properties. The stochastic oscillations of the scatterers result in superdiffusion of particles with the mean squared displacement growing asymptotically quadratically in time: ⟨q²⟩∼t².

We measure the fluctuations of the position of a Brownian particle confined by an optical trap in an aging gelatin droplet after a fast quench. Its linear response to an external perturbation is also measured. We compute the spontaneous heat flux from the particle to the bath due to the non-equilibrium formation of the gel. We show that the mean heat flux is quantitatively related to the violation of the equilibrium fluctuation-dissipation theorem as a measure of the broken detailed balance during the aging process.

Two significant consequences of quantum fluctuations are entanglement and criticality. Entangled states may not be critical but a critical state shows signatures of universality in entanglement. A surprising result found here is that the entanglement entropy may become arbitrarily large and negative near the dissociation of a bound pair of quantum particles. Although apparently counterintuitive, it is shown to be consistent and essential for the phase transition, by mapping to a classical problem of DNA melting. We associate the entanglement entropy to a sub-extensive part of the entropy of DNA bubbles, which is responsible for melting. The absence of any extensivity requirement in time makes this negative entropy an inevitable consequence of quantum mechanics in continuum. Our results encompass quantum critical points and first-order transitions in general dimensions.

We consider the concept of temperature in a setting beyond the standard thermodynamics prescriptions. Namely, rather than restricting to standard coarse-grained measurements, we consider observers able to master any possible quantum measurement —a scenario that might be relevant at nanoscopic scales. In this setting, we focus on quantum systems of coupled harmonic oscillators and study the question of whether the temperature is an intensive quantity, in the sense that a block of a thermal state can be approximated by an effective thermal state at the same temperature as the whole system. Using the quantum fidelity as figure of merit, we identify instances in which this approximation is not valid, as the block state and the reference thermal state are distinguishable for refined measurements. Actually, there are situations in which this distinguishability even increases with the block size. However, we also show that the two states do become less distinguishable with the block size for coarse-grained measurements —thus recovering the standard picture. We then go further and construct an effective thermal state which provides a good approximation of the block state for any observables and sizes. Finally, we point out the role that entanglement plays in this scenario by showing that, in general, the thermodynamic paradigm of local intensive temperature applies whenever entanglement is not present in the system.

We prove the equivalence between the hard-sphere Bose gas and a system with momentum-dependent zero-range interactions in one spatial dimension, which we call extended hard-sphere Bose gas. The two-body interaction in the latter model has the advantage of being a regular pseudopotential. The most immediate consequence is the existence of its Fourier transform, permitting the formulation of the problem in momentum space, not possible with the original hard-core interaction. In addition, in the extended system, interactions are defined in terms of the scattering length, positive or negative, identified with the hard-sphere diameter only when it is positive. We are then able to obtain, directly in the thermodynamic limit, the ground-state energy of the strongly repulsive Lieb-Liniger gas and, more importantly, the energy of the lowest-lying super Tonks-Girardeau gas state with finite, strongly attractive interactions, in perturbation theory from the novel extended hard-sphere Bose gas.

In this work we present a method, based on the vacuum structure of the potential for a system of two nonlinearly coupled scalar fields in 1+1 space-time dimensions, which yields complete information about the behavior of the topological configurations. This is done by means of an analysis of the orbits and the position of the degenerate vacua of the model on the configuration space.

The properties of impurities immersed in a large Fermi sea are naturally described in terms of dressed quasiparticles: attractive and repulsive polarons, and dressed molecules. Motivated by recent experiments on narrow Feshbach resonances, we analyze here how the quasiparticle properties are affected by a non-zero resonance range. We find two interesting analytic results. For large range, the ground-state energy close to resonance is shown to become perturbative in the inverse range. In the limit of broad resonance instead, we provide a new Tan's relation linking the impurity ground-state energy E_↓ to the number of atoms in its dressing cloud ΔN. As a corollary, at unitarity one finds ΔN=−E_↓/_F, with _F the Fermi energy of the bath.

Recently, a new quantum model —two-dimensional generalization of the Scarf II— was completely solved analytically by the SUSY method for the integer values of a parameter. Now, the same integrable model, but with arbitrary values of a parameter, will be studied by means of supersymmetrical intertwining relations. The Hamiltonian does not allow the conventional separation of variables, but the supercharge operator does, leading to the partial solvability of the model. This approach, which can be called the first variant of SUSY separation, together with the shape invariance of the model, provides the analytical calculation of part of the spectrum and corresponding wave functions (quasi-exact solvability). The model is shown to obey two different variants of shape invariance which can be combined effectively in the construction of energy levels and wave functions.

A particle in a double-well potential is the simplest dynamic system exhibiting non-linear behavior and stochastic resonance. Using Brownian dynamics simulations, we determine non-linear–response functions and quantify the breakdown of linear-response theory in terms of the threshold force amplitude. Based on a factorization approximation for higher-order non-linear–response functions, this threshold force amplitude is self-consistently related to the linear-response function itself.

In this work we investigate the quantum theory of scalar fields propagating in a D-dimensional de Sitter spacetime. The method of dynamic invariants is used to obtain the solution of the time-dependent Schrödinger equation. The quantum behavior of the scalar field in this background is analyzed, and the results generalize previous ones found in the literature. We point that the Bunch-Davies thermal bath depends on the choice of Dand the conformal parameter ξ. This is important in extra-dimension physics, as in the Randall-Sundrum model.

We discuss various continuous and discrete symmetries of the supersymmetric simple harmonic oscillator (SHO) in one (0+1)-dimension of spacetime and show their relevance in the context of mathematics of differential geometry. We show the existence of a novel set of discrete symmetries in the theory which has, hitherto, not been discussed in the literature on theoretical aspects of SHO. We also point out the physical relevance of our present investigation.

An in-line phase-contrast computed tomography algorithm is proposed for the reconstruction of the three-dimensional distribution of the electron density of a weak absorption sample using micro-focus X-ray source. It exploits the natural combination of Feldkamp-Davis-Kress (FDK) cone-beam reconstruction algorithm with a phase retrieval algorithm based on a modified phase-attenuation duality. The effects of the coherence of X-rays and the revolution of the detector are also incorporated into this algorithm. Then an experimental demonstration is given and the results show that the proposed method can reconstruct the electron density of soft tissue effectively.

The development of new techniques for producing random sequences with a high level of security is a challenging topic of research in modern cryptographics. The proposed method is based on the measurement by phase-shifting interferometry of the speckle signals of the interaction between light and structures. We show how the combination of amplitude and phase distributions (maps) under a numerical process can produce random sequences. The produced sequences satisfy all the statistical requirements of randomness and can be used in cryptographic schemes.

Experiments and numerical simulations reveal that in the forward cascade regime, the energy spectrum of two-dimensional turbulence with Ekman friction deviates from Kraichnan's prediction of k⁻³ power spectrum. In this letter we explain this observation using an analytic model based on variable enstrophy flux arising due to Ekman friction. We derive an expression for the enstrophy flux which exhibits a logarithmic dependence in the inertial range for the Ekman-friction–dominated flows. The energy spectrum obtained using this enstrophy flux shows a power law scaling for large Reynolds number and small Ekman friction, but has an exponential behaviour for large Ekman friction and relatively small Reynolds number.

In this letter, we characterize the internal dissipation of coated micro-cantilevers through their mechanical thermal noise. Using a home-made interferometric setup, we achieve a resolution down to in the measurement of their deflection. With the use of the fluctuation dissipation theorem and of the Kramers-Kronig relations, we rebuild the full mechanical response function from the measured noise spectrum, and investigate frequency-dependent dissipation as a function of the air pressure and of the nature of the metallic coatings. Using different thicknesses of gold coatings, we demonstrate that the internal viscoelastic damping is solely due to the dissipation in the bulk of the coating.

The single and multiple scattering regimes of electromagnetic waves in a disordered system with fluctuating permittivity are studied by numerical simulations of Maxwell's equations. For an array of emitters and receivers in front of a medium with randomly varying dielectric constant, we calculate the backscattering matrix from the signal responses at all receiver points j to electromagnetic pulses generated at each emitter point i. We show that the statistical properties of the backscattering matrix are in agreement with the recent experimental results for ultrasonic waves (Aubry A. and Derode A., Phys. Rev. Lett., 102 (2009) 084301) and light (Popoff S. M. et al., Phys. Rev. Lett., 104 (2010) 100601). In the multiple scattering regime the singular value distribution of the backscattering matrix obeys the quarter-circle law.

The existence and stability of defect solitons supported by parity-time (PT) symmetric superlattices with nonlocal nonlinearity are investigated. In the semi-infinite gap, in-phase solitons are found to exist stably for positive or zero defects, but cannot exist in the presence of negative defects with strong nonlocality. In the first gap, out-of-phase solitons are stable for positive or zero defects, whereas in-phase solitons are stable for negative defects. The dependence of soliton stabilities on modulation depth of the PT potentials is studied. It is interesting that solitons can exist stably for positive and zero defects when the PT potentials are above the phase transition points.

We introduce a set of iterative equations that exactly solves the size distribution of components on small arbitrary graphs after the random removal of edges. We also demonstrate how these equations can be used to predict the distribution of the node partitions (i.e., the constrained distribution of the size of each component) in undirected graphs. Besides opening the way to the theoretical prediction of percolation on arbitrary graphs of large but finite size, we show how our results find application in graph theory, epidemiology, percolation and fragmentation theory.

A theoretical investigation of the behavior of atomic friction at low temperatures is performed using a master equation method with a two-mass, two-spring Prandtl-Tomlinson model of an atomic force microscope experiment. A novel approach is taken in which two distinct instability mechanisms are introduced into the model: thermal activation is described by transition state theory with a prefactor associated with the frequency of the tip apex, and athermal instability is introduced by an Arrhenius-like equation with a prefactor associated with the characteristic frequency of the cantilever. Thermal instability causes the often reported decrease of friction with temperature followed by a stable low-friction region at high temperatures. However, the introduction of the athermal term that describes other instability mechanisms extends the predictive capability of the model such that it captures the friction plateau observed at very low temperatures.

The preparation process of a CuZrAl metallic glass is simulated by molecular dynamics. Different temperatures of the initial liquid state and variation of the cooling rate over five decades are considered. Elastic moduli, mass density and frequency of icosahedral clusters follow a power-law scaling with the cooling rate. The ratio of shear to bulk modulus is most sensitive to changes of the cooling rate. Assuming local fluctuations of the cooling rate occurring during the preparation process, regions characterized by comparably low values of shear modulus, mass density and frequency of icosahedral clusters can be proposed as atomistic realizations of flow defects, at which non-crystalline plastic deformation is initiated.

We have investigated the dynamic response of alternating-diameter Ni₈₀Fe₂₀ antidot arrays using broadband ferromagnetic resonance (FMR). We observed a significant modification in both the number of spin wave modes and mode profiles when compared with homogeneous diameter antidot arrays. The FMR response shows a static field amplitude-dependent mode transformation (extinction or emergence) due to a complex non-uniform distribution of the demagnetizing field. Our experimental results have also been modeled using dynamic micromagnetic simulations, and we obtained a good agreement between both results.

The classical hexagonal honeycomb theory for the uniaxial loading case, developed by Gibson and Ashby, considers buckling of the cell walls parallel to one symmetry axis. In general, buckling may also occur in the cell walls inclined with respect to the two symmetry axes. Therefore, in this letter, under the uniaxial loading conditions, we derive the critical stresses of buckling and bending collapses of nanohoneycombs, for which the surface effect is included. Furthermore, the competition between the two failure modes is studied. The present theory could be used to design new nanoporous materials, e.g., scaffolds for the regenerative medicine or energy-absorption materials.

We theoretically analyzed the dispersion relations of director fluctuations along the direction perpendicular to the helical axis in cholesteric liquid crystals, and experimentally verified the validity of the analysis by dynamic light scattering (DLS) measurement. It is found that the dispersion relations are well explained by two independent modes, which we call "splay-bend" and "undulation" modes.

Methods for determining the percolation threshold usually study the behavior of network ensembles and are often restricted to a particular type of probabilistic node/link removal strategy. We propose a network-specific method to determine the connectivity of nodes below the percolation threshold and offer an estimate to the percolation threshold in networks with bidirectional links. Our analysis does not require the assumption that a network belongs to a specific ensemble and can at the same time easily handle arbitrary removal strategies (previously an open problem for undirected networks). In validating our analysis, we find that it predicts the effects of many known complex structures (e.g., degree correlations) and may be used to study both probabilistic and deterministic attacks.

The presence of impurity ions in ferroelectric liquid crystals (FLC) could produce a significant impact on the chirality of the medium with a possible modification in the polarization profile of the system. We theoretically observed these possibilities by considering an in-plane and bulk free energy density for the sample. Based on a suitable chirality transfer formalism, we explained the role of impurity ions in altering the chiral nature of a FLC medium. A continuous transition from modulated phases to uniform phases is also predicted within the framework of this theory. Then, we investigated the possible modification in the polarization profile driven by ionic impurities.

We demonstrate that the temperature-dependent focused ion beam irradiation of (100) Ge surfaces with 20 keV Bi⁺ ions leads to variably ordered hexagonal dot patterns. We show that the average information gain about the spatial order can be significantly increased by image preprocessing transforming the power spectral density into the pair correlation function. Order parameters are derived from the pair correlation function for the comparison of highly ordered patterns.

Recent experiments have shown that fractured GaAs nanowires can heal spontaneously inside a transmission electron microscope. Here we perform molecular-dynamics simulations to investigate the atomic mechanism of this self-healing process. As the distance between two fracture surfaces becomes less than 1.0 nm, a strong surface attraction is generated by the electrostatic interaction, which results in Ga–As re-bonding at the fracture site and restoration of the nanowire. The results suggest that self-healing might be prevalent in ultrathin one-dimensional nanostructures under near vacuum conditions.

Pinning particles at random in supercooled liquids is a promising route to make substantial progress in the glass transition problem. Here we develop a mean-field theory by studying the equilibrium and non-equilibrium dynamics of the spherical p-spin model in the presence of a fraction c of pinned spins. Our study shows the existence of two dynamic critical lines: one corresponding to usual mode coupling transitions and the other one to dynamic spinodal transitions. Quenches in the portion of the c-T phase diagram delimited by those two lines leads to aging. By extending our results to finite dimensional systems we predict non-interrupted aging only for quenches on the ideal glass transition line and two very different types of equilibrium relaxations for quenches below and above it.

The Poisson-Boltzmann equation is often presented via a variational formulation based on the electrostatic potential. However, the functional has the defect of being non-convex. It cannot be used as a local minimization principle while coupled to other dynamic degrees of freedom. We formulate a convex dual functional which is numerically equivalent at its minimum and which is more suited to local optimization.

A theoretical method is proposed to investigate the tensile strength dependence on the impurity concentration in metals using a first-principles method in combination with the classical thermodynamics models. In the present study, helium (He) in an iron (Fe) grain boundary (GB) is taken as an example. The theoretical tensile strength of an FeΣ5(310)/[001] GB with different amounts of He impurity is determined using first-principles computational tensile tests (FPCTT) and the He concentration is derived depending on the solution energy and temperature using thermodynamics models. Thus, the dependence of the tensile strength of an Fe GB on He concentration is established, and a critical He concentration is defined using the amount of the tensile strength reduction compared with that of a clean GB. Such a method is expected to be quite useful in predicting the impurity-induced degradation of the mechanical properties of metals.

Exchange bias (EB) and the training effects (TE) in an antiferromagnetically coupled La_0.7Sr_0.3MnO₃/SrRuO₃ superlattices were studied in the temperature range 1.8–150 K. Strong antiferromagnetic (AFM) interlayer coupling is evidenced from AC-susceptibility measurements. Below 100 K, vertical magnetization shifts are present due to the two remanent states corresponding to the two ferromagnetic (FM) layers at FM and AFM coupling condition. After field cooling (FC), significant decrease in the exchange bias field (H_EB) is observed when cycling the system through several consecutive hysteresis loops. Quantitative analysis for the variation of H_EB vs. number of field cycles (n) indicates an excellent agreement between the theory, based on triggered relaxation phenomena, and our experimental observations. Nevertheless, the crucial fitting parameter K indicates smooth training effect upon repeated field cycling, in accordance with our observation.

The non-coherent rate equation approach to the electrical transport in a serial quantum dot system is presented. The charge density in each quantum dot is obtained using the transfer Hamiltonian formalism for the current expressions. The interactions between the quantum dots and between the quantum dots and the electrodes are introduced by transition rates and capacitive couplings. Within this framework analytical expressions for the current and the charge in each quantum dot are presented. The effects of the local potential are computed within the self-consistent field regime. Despite the simplicity of the model, well-known effects are satisfactorily explained and reproduced. We also show how this approach can be extended into a more general case.

The transversal propagation of the edge states in a two-dimensional quantum spin Hall (QSH) system is classified by the characteristic parameter λ. There are two different types of helical edge states, the normal and special edge states, exhibiting distinct behaviors. The penetration depth of the normal edge state is momentum dependent, and the finite gap for edge bands decays monotonously with sample width, leading to the normal finite size effect. In contrast, the penetration depth maintains a uniform minimal value in the special edge states, and consequently the finite gap decays non-monotonously with sample width, leading to the anomalous finite size effect. To demonstrate their difference explicitly, we compared the real materials in phase diagrams. An intuitive way to search for the special edge states in the two-dimensional QSH system is also proposed.

By invoking the microscopic response method in conjunction with a reasonable set of approximations, we obtain new explicit expressions for the electrical conductivity and temperature coefficient of resistivity (TCR) in amorphous semiconductors, especially a-Si:H and a-Ge:H. The predicted TCR for n-doped a-Si:H and a-Ge:H is in agreement with experiments. The conductivity from the transitions from a localized state to an extended state (LE) is comparable to that from the transitions between two localized states (LL). This resolves a long-standing anomaly, a "kink" in the experimental log₁₀σ-vs.-T⁻¹ curve.

Pure Ti, pure Ni and some Ti-Ni solid-solution alloys have been studied by electron energy loss spectroscopy (EELS) and the d-electron occupancy of both Ti and Ni in the alloys has been calculated in terms of white-line intensity. It is found that after alloying the d-electron occupancy of Ti increases noticeably and the value is larger than 1, and the change of d-electron occupancy of Ni is very small. The change of d-electron occupancy is discussed in terms of charge transfer mechanism, local charge neutrality (LCN) approximation, and hybridization.

By using time-resolved spectroscopy with an alternative σ⁺/σ⁻ laser pulse modulation technique, we are able to measure the fast buildup and decay times of the dynamical nuclear-spin polarization at 5 K for a single InAs quantum dot with positively charged exciton. It is shown that the measured buildup and decay times are 0.27 and 0.5 ms, respectively, in the absence of external magnetic field. By applying an external field of 8 mT in parallel to the sample growth direction, the decay time extends to about 5 ms which is induced by optically pumped electron via the hyperfine interaction between the nuclei and the electron. In addition, it is found that the buildup time is independent of the small external field.

We report on ferromagnetic spin ordering in amorphous Co-doped InGaZnO (Co-IGZO) based on hydrogen mediation. The amorphous structure was maintained after hydrogenation using hot isostatic pressing. Changes in the electrical and optical characteristics were attributed to interactions between hydrogen and each element in Co-IGZO. The ferromagnetism of hydrogenated Co-IGZO, induced in the amorphous phase without long-range ordering, was manifested by spin-spin interactions of the Co–H–Co complex acting as an individual magnetic unit, similar to a single molecular magnet. It is suggested that the electron carriers mediate the correlation between Co–H–Co units.

We report the effect of Sr substitution in an antiferromagnetic insulator LaMnAsO by the measurements of electrical resistivity, Hall coefficient, Seebeck coefficient and magnetization. Upon Sr doping to its limit x∼0.10, the room temperature resistivity drops by five orders of magnitude down to ∼0.01Ω·cm, and the temperature-dependent resistivity shows essentially metallic behavior. Hall and Seebeck measurements confirm consistently that the insulator-to-metal transition is due to hole doping. The room temperature Seebeck coefficient for the metallic samples is as high as ∼240 μ V/K, making the system a possible candidate for thermoelectric applications.

The recently proposed transition voltage (V_t) spectroscopy (TVS) is becoming an increasingly popular tool to analyze electric transport through molecular devices. Very recently, to get additional insight into TVS, the distance (d) dependence V_t(d) in vacuum break junctions has been investigated experimentally. In this letter, we point out inconsistencies of the initial theoretical interpretation, based on approximate Wenzel-Krammers-Brillouin (WKB)-type results within the standard vacuum tunneling barrier model. We demonstrate that even the exact treatment of this model fails to explain the experimental V_t(d)-dependence, but the agreement with experiment is substantially improved by accounting for electron states (or resonances) at electrodes' surface. These findings suggest that surface states may also play a significant role in molecular devices with sharp electrodes and calls for further investigations.

Evidence from NMR of a two-component spin system in cuprate high-T_c superconductors is shown to be paralleled by similar evidence from the electronic entropy so that a two-component quasiparticle fluid is implicated. We propose that this two-component scenario is restricted to the optimal and underdoped regimes and arises from the upper and lower branches of the reconstructed energy-momentum dispersion proposed by Yang, Rice and Zhang (YRZ) to describe the pseudogap. We calculate the spin susceptibility within the YRZ formalism and show that the doping and temperature dependence reproduces the experimental data for the cuprates.

The first heavy fermion superconductor CeCu₂Si₂ is still only partially understood. At high pressures, superconductivity is supposed to be mediated by a different mechanism than at ambient pressure, where spin fluctuations most likely act as pairing glue. We have obtained and analyzed new resistivity data up to 7 GPa on a good quality CeCu₂Si₂ single crystal with an unprecedented high transition temperature. For the first time, we establish quantitatively that CeCu₂Si₂ lies in proximity to a valence transition: the critical end point could be located at 4.5±0.2 GPa and a slightly negative temperature, and the corresponding valence cross-over line has been added to the p-T phase diagram. This outcome is essential for the theoretically predicted critical valence fluctuations scenario, and opens new routes for further investigations in other Ce-based compounds.

The presence of low-symmetry impurities or defect complexes in the zinc-blende direct-gap semiconductors (e.g., interstitials, DX-centers) results in a novel spin-orbit term in the effective Hamiltonian for the conduction band. The new extrinsic spin-orbit interaction is proportional to the matrix element of the defect potential between the conduction and the valence bands. Because this interaction arises already in the first order of the expansion of the effective Hamiltonian in powers of U_ext/E_g≪1 (where U_ext is the pseudopotential of an interstitial atom, and E_g is the band gap), its contribution to the spin relaxation rate may exceed that of the previously studied extrinsic contributions, even for moderate concentrations of impurities.

We consider finite population size effects for Crow-Kimura and Eigen quasispecies models with single-peak fitness landscape. We formulate accurately the iteration procedure for the finite population models, then derive the Hamilton-Jacobi equation (HJE) to describe the dynamic of the probability distribution. The steady-state solution of HJE gives the variance of the mean fitness. Our results are useful for understanding the population sizes of viruses in which the infinite population models can give reliable results for biological evolution problems.

The automatic disambiguation of word senses (i.e., the identification of which of the meanings is used in a given context for a word that has multiple meanings) is essential for such applications as machine translation and information retrieval, and represents a key step for developing the so-called Semantic Web. Humans disambiguate words in a straightforward fashion, but this does not apply to computers. In this paper we address the problem of Word Sense Disambiguation (WSD) by treating texts as complex networks, and show that word senses can be distinguished upon characterizing the local structure around ambiguous words. Our goal was not to obtain the best possible disambiguation system, but we nevertheless found that in half of the cases our approach outperforms traditional shallow methods. We show that the hierarchical connectivity and clustering of words are usually the most relevant features for WSD. The results reported here shed light on the relationship between semantic and structural parameters of complex networks. They also indicate that when combined with traditional techniques the complex network approach may be useful to enhance the discrimination of senses in large texts.

Monte Carlo simulations using an explicit solvent model indicate a new pathway for translocation of a polymer chain through a lipid bilayer. We consider a polymer chain composed of repeat units with a given hydrophobicity and a coarse-grained model of a lipid bilayer in the self-organized liquid state. By varying the degree of hydrophobicity the chain undergoes an adsorption transition with respect to the lipid bilayer. Close to the transition point, at a properly balanced hydrophobicity of the chain, the membrane becomes transparent with respect to the chain. At the same time the solvent permeability of the bilayer is strongly increased in the region close to the adsorbed chain. Our results indicate that the critical point of adsorption of the polymer chain interacting with the fluctuating lipid bilayer could play a key role for the translocation of molecules through biological membranes.

Pair emission by superluminal neutrinos is shown to be causality violating in the 10–50 GeV range covered by the OPERA experiment. Thus, the energy density of a freely propagating superluminal neutrino current is not affected by energy loss due to e⁺e⁻ pair creation, in accordance with the unperturbed energy profile observed by ICARUS. Interaction processes involving sub- and superluminal particles give rise to time inversions in the rest frames of the subluminal constituents, resulting in causality violating predetermination. Therefore, kinematic causality constraints in addition to energy-momentum conservation are necessary to exclude causality violation outside the lightcone. Electron-positron pair production by superluminal muon neutrinos is forbidden in the OPERA energy range, as the kinematic constraints on the neutrino frequencies and wave vectors required by causality and energy-momentum conservation cannot simultaneously be satisfied.