Showing papers in "Annalen der Physik in 2009"

Conformal transformations and conformal invariance in gravitation

Abstract: Conformal transformations are frequently used tools in order to study relations between various theories of gravity and Einstein relativity. Because of that, in this paper we discuss the rules of conformal transformations for geometric quantities in general relativity. In particular, we discuss the conformal transformations of the matter energy-momentum tensor. We thoroughly discuss the latter and show the subtlety of the conservation law (i.e., the geometrical Bianchi identity) imposed in one of the conformal frames in reference to the other. The subtlety refers to the fact that conformal transformation ``creates'' an extra matter term composed of the conformal factor which enters the conservation law. In an extreme case of the flat original spacetime the matter is ``created'' due to work done by the conformal transformation to bend the spacetime which was originally flat. We also discuss how to construct the conformally invariant gravity which, in the simplest version, is a special case of the Brans-Dicke theory -- the one with the Brans-Dicke parameter $\omega = -3/2$. Conformal transformations are also used to investigate higher-order gravity theories. Motivated by this, we find the conformal transformation rules for the curvature invariants $R^2$, $R_{ab}R^{ab}$, $R_{abcd}R^{abcd}$ and, as a consequence, for the Gauss-Bonnet invariant in a spacetime of an arbitrary dimension. Finally, we present all already obtained rules of the conformal transformations in the fashion of the duality transformation of the superstring theory. In such a case the transitions between conformal frames can just be obtained by a simple change of the sign of the quantity $\om = \ln{\Om}$, where $\Om$ is the conformal factor.

Elementary processes with two quantum transitions

Abstract: The first part of this work considers the coaction of two photons in an elementary process. With the help of Dirac’s dispersion theory, the probability of a process analogous to the Raman effect, namely the simultaneous emission of two photons, is calculated. It appears that a nonzero probability exists that an excited atom divides its excitation energy into two photons, whose energies in sum prove to be the excitation energy but are otherwise arbitrary. When light falls upon the atom with a frequency smaller than the corresponding atomic eigenfrequency, another stimulated double emission occurs during which the atom divides its energy into one incident and one frequency-difference photon. Kramers and Heisenberg have calculated the probability of this last process according to the correspondence principle. Additionally, the reversal of this process is considered, namely, where two photons whose frequencysum equals the excitation frequency of the atom co-act to excite the atom. Furthermore the behavior of an atom toward scattering particles when it simultaneously has the opportunity to spontaneously emit light is examined. Experimentally, Oldenberg finds a broadening of the resonance line of mercury when he lets the excited atoms collide repeatedly with slow particles. He interprets this through the assumption that a positive or negative part of the excitation energy can be transferred as kinetic energy to the colliding particle, and that the frequency-difference photon is emitted. For this process, a formula analogous to the Raman effect and the double-emission, respectively, is derived here. Finally, in connection with Franck’s work, an attempt is made to explain the excitation-intensity’s behavior of spectral lines through collisions with fast electrons via such a double-process. Franck discusses the behavior of the excitation function of a spectral line, i.e., the intensity as a function of the velocity of the incident electrons. This function is zero for small velocities, until the kinetic energy of the electrons becomes equal to the excitation energy of the respective initial state of the line. It then increases strongly, reaches a maximum at a velocity corresponding to just a few volts above this critical voltage, and then decreases again to zero. This part of the curve has repeatedly been calculated with the ordinary collision theory. One obtains a curve which represents the phenomena well, especially the sudden onset of the function at the critical voltage. For large velocities, the theoretical curve yields a monotonic

Improved analytical approximation to arbitrary l-state solutions of the Schrodinger equation for the hyperbolical potential

Abstract: A new approximation scheme to the centrifugal term is proposed to obtain the l = 0 bound-state solutions of the Schrodinger equation for an exponential-type potential in the framework of the hypergeometric method. The corresponding normalized wave functions are also found in terms of the Jacobi polynomials. To show the accuracy of the new proposed approximation scheme, we calculate the energy eigenvalues numerically for arbitrary quantum numbers n and l with two different values of the potential parameter σ0. Our numerical results are of high accuracy like the other numerical results obtained by using program based on a numerical integration procedure for short-range and long-range potentials. The energy bound-state solutions for the s-wave (l = 0) and σ0 = 1 cases are given.

The influence of self‐citation corrections and the fractionalised counting of multi‐authored manuscripts on the Hirsch index

Abstract: The Hirsch index or h-index is widely used to quantify the impact of an individual's scientific research output, determining the highest number h of a scientist's papers that received at least h citations. Fractionalised counting of the publications is an appropriate way to distribute the impact of a paper among all the coauthors of a multi-authored manuscript in an easy way, leading to a simple modification hm of the h-index. On the other hand the exclusion of self-citations allows one to sharpen the index, what is appropriate, because self-citations are usually not reflecting the significance of a publication. I have previously analysed the citation records of 26 physicists discussing the sharpened index hs as well as the modification hm of the original h-index. In the present investigation I combine these two procedures yielding the modified sharpened index hms. For a better comparison, interpolated indices are utilized. The correlations between the indices are rather strong, but nevertheless the positions of some datasets change, in a few cases significantly, depending on whether they are put into order according to the values of h, hm, hs, or hms. This leads to the conclusion that the additional effort in determining the modified sharpened index hms is worth performing in order to obtain a fairer evaluation of the citation records.

The odd couple: Boltzmann, Planck and the application of statistics to physics (1900-1913)

Abstract: In the last forty years a vast scholarship has been dedicated to the reconstruction of Planck's theory of black-body radiation and to the historical meaning of quantization. Since the introduction of quanta took place for combinatorial reasons, Planck's understanding of statistics must have played an important role. In the first part of this paper, I sum up the main theses concerning the status of the quantum and compare the arguments supporting them. In the second part, I investigate Planck's usage of statistical methods and the relation to Boltzmann's analogous procedure. I will argue that this way of attacking the problem is able to give us some interesting insights both on the theses stated by the historians and on the general meaning of Planck's theory.

Indefinite oscillators and black‐hole evaporation

Abstract: We discuss the dynamics of two harmonic oscillators of which one has a negative kinetic term. This model mimics the Hamiltonian in quantum geometrodynamics, which possesses an indefinite kinetic term. We solve for the time evolution in both the uncoupled and coupled case. We use this setting as a toy model for studying some possible aspects of the final stage of black-hole evaporation. We assume that one oscillator mimics the black hole, while the other mimics Hawking radiation. In the uncoupled case, the negative term leads to a squeezing of the quantum state, while in the coupled case, which includes back reaction, we get a strong entangled state between the mimicked black hole and the radiation. We discuss the meaning of this state. We end by analyzing the limits of this model and its relation to more fundamental approaches.

Thermal photon dispersion law and modified black-body spectra

Abstract: Based on the postulate that photon propagation is governed by an SU(2) gauge principle we numerically compute the one-loop dispersion for thermalized photon propagation on the radiatively induced mass shell. Formerly, the dispersion was addressed by assuming p2 = 0. While this approximation turns out to be excellent for temperatures ≤ 2 TCMB the exact result exhibits a much faster (power-like) shrinking of the gap in the black-body spectral intensity with rising temperature. Our previous statements on anomalous large-angle CMB temperature-temperature correlations, obtained in the approximation p2 = 0, remain valid.

The “writing on the cosmic wall”: Is there a straightforward explanation of the cosmic microwave background?

Abstract: The Cosmic Microwave Background (CMB) is taken today as reflecting the thermodynamical state of the universe at these early cosmic times. Based on this assumption and standard cosmological principles meanwhile many fundamental cosmological facts have been deduced from the CMB state which, however, to some surprise reveal that the universe should be dominated by dark energy and dark matter, while for its energy content the usual baryonic matter is nearly negligible. Thus the question which we want to raise in this article is, whether this standard interpretation of the CMB phenomenon is solid and unequivocal enough to support the standard cosmological claims. We shall show, however, that in many details the standard explanation is not straightforward, but allows for important alternatives which seriously should be looked at. Especially arguments for a vanishing cosmic curvature (k = 0) are shown to be weak, and, contrary to the usual claim, the light distance to the recombination horizon is in fact strongly model-biassed. We also show that the CMB dipole which is generally understood as a consequence of a peculiar motion by about 680 km/s with respect to rest system of the CMB can as well, and perhaps even better, be understood as indication of differerent cosmological expansion dynamics seen in an anisotropically expanding universe in different directions of the sky. We also discuss that the power amplitude (i.e. effective Planck temperature) in the dipolar CMB structure depends on wavelength even inverting the dipole maximum orientation in the Wien's branch. In addition unexpected properties of the lowest CMB multipoles could mean that we are at least partly seeing an unquantifyable foreground in the background. Only after its removal the CMB interpretation could at all then, but then on a completely new basis, become a subject of cosmological terms. At the end of this article we shall briefly discuss an alternative explanation of the CMB radiation which helps to better understand the mysterious cosmic photon-to-baryon ratio of about 109.

Thermal dynamics at surfaces

Abstract: The present paper describes what happens at the surface of a crystal as its temperature steadily increases from zero Kelvin close to the bulk melting temperature. We treat thermal motion, such as the diffusion of individual adatoms establishing mass transport, the formation of adatom or vacancy gases coexisting with islands or steps of the condensed phase, surface phonons and the anharmonicity of the surface potential being markedly different from the one in bulk, as well as thermally induced reconstructions, surface roughening, and finally surface melting, which usually well precedes bulk melting. The paper intends to give an overview with references to the original and review literature.

Stripe segregation and magnetic coupling in the nickelate La5/3Sr1/3NiO4

Abstract: We investigate the consequences of the stripe formation in the nickelate La5/3Sr1/3NiO4 for the details of its crystal structure and electronic states. Our data are based on numerical simulations within density functional theory (DFT) and the generalized gradient approximation (GGA). The on-site Coulomb interaction is included in terms of the LDA+U scheme. Structure optimization of preliminary experimental data indicates a strong interaction between the structural and electronic degrees of freedom. In particular, we find a segregation of the diagonal filled stripes induced by a delicate interplay with the magnetic coupling. Beyond the cooperative effect of stripe segregation and spin order, distinct octahedral distortions are essential for the formation of an insulating state.

Optically driven Mott-Hubbard systems out of thermodynamic equilibrium

Abstract: We consider the Hubbard model at half filling, driven by an external, stationary laser field. This stationary, but periodic in time, electromagnetic field couples to the charge current, i.e. it induces an extra contribution to the hopping amplitude in the Hubbard Hamiltonian (photo-induced hopping). We generalize the dynamical mean-field theory (DMFT) for nonequilibrium with periodic-in-time external fields, using a Floquet mode representation and the Keldysh formalism. We calculate the non-equilibrium electron distribution function, the density of states and the optical DC conductivity in the presence of the external laser field for laser frequencies above and below the Mott-Hubbard gap. The results demonstrate that the system exhibits an insulator-metal transition as the frequency of the external field is increased and exceeds the Mott-Hubbard gap. This corresponds to photo-induced excitations into the upper Hubbard band.

A Look at the Abandoned Contributions to Cosmology of Dirac, Sciama and Dicke

Abstract: The separate contributions to cosmology of the above researchers are revisited and a cosmology encompassing their basic ideas is proposed. We study Dirac's article (1938) on the large number hypothesis, Sciama's proposal (1953) of realizing Mach's principle, and Dicke's considerations (1957) on a flat-space representation of general relativity with a variable speed of light (VSL). Dicke's tentative theory can be formulated in a way which is compatible with Sciama's hypothesis on the gravitational constant G. Additionally, such a cosmological model is shown to satisfy Dirac's second ‘large number’ hypothesis on the total number of particles in the universe being proportional to the square of the epoch. In the same context, Dirac's first hypothesis on an epoch-dependent G – contrary to his prediction – does not necessarily produce a visible time dependence of G. While Dicke's proposal reproduces the classical tests of GR in first approximation, the cosmological redshift is described by a shortening of measuring rods rather than an expansion of space. Since the temporal evolution of the horizon R is governed by , the flatness and horizon problems do not arise in the common form.

Effect of electric field on diffusion in disordered materials

Abstract: The effect of electric field on diffusion of charge carriers in disordered materials is studied by Monte Carlo computer simulations and analytical calculations. It is shown how an electric field enhances the diffusion coefficient in the hopping transport mode. The enhancement essentially depends on the temperature and on the energy scale of the disorder potential. It is shown that in one-dimensional hopping the diffusion coefficient depends linearly on the electric field, while for hopping in three dimensions the dependence is quadratic.

Information in asset pricing: a wave function approach

Abstract: This paper introduces a quantum-like wave function as an information wave function. We show how the option pricing partial differential equation can be re-written when we account for such information wave function. We use two stochastic differential equations, one of which relates to Nelson's hypothesis of Universal Brownian motion. We also provide for two examples which further highlight the proposed theory.

Reduction of Quantum Fluctuations by Anisotropy Fields in Heisenberg Ferro- and Antiferromagnets

Abstract: The anisotropic Heisenberg model is influenced by thermal as well as by quantum fluctuations. Thereby, the quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters: It is well-known that both large spin quantum numbers and large anisotropy fields destroy the quantum fluctuations completely and lead to a classical limit that renders the system Ising-like in the easy-axis case. This study aims to elucidate the incipience of these classical trends that is induced by relatively small values for the anisotropy field and spin quantum number. The accompanied incipient suppression of quantum fluctuations is thereby closely related to modern experiments that are currently performed in Hamburg: Corresponding SP-STM measurements, which reveal magnetic structures at the nanoscale, are influenced by non-negligible anisotropy fields and have been modelled by classical Heisenberg systems. This theoretical study reveals the validity of this classical approach by investigating the impact of the anisotropy fields on the quantum properties of the Heisenberg model. In order to illustrate the resulting effects by the anisotropy fields, we determine the critical temperature for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare these quantities with the use of the following theories: Classical Mean Field (CMF), Quantum Mean Field (QMF), Linear Spin Wave Approximation (LSWA) and Random Phase Approximation (RPA). Our findings will be confirmed and quantitatively improved by numerical Quantum Monte Carlo (QMC) simulations. If provided by the respective method, we will investigate the differences between the ferromagnet (FM) and antiferromagnet (AFM). We finally find a consistent picture of the classical trends and elucidate, thereby, the suppression of quantum fluctuations in anisotropic spin systems. We further reveal that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by the introduction of a quantity we want to refer to as anisotropy susceptibility. As an important result, we conclude that even tiny anisotropy fields lead to a strong reduction of quantum fluctuations. In the end, this study enables us to validate the classical modelling of the experiments performed at the University of Hamburg. Das anisotrope Heisenberg-Modell wird sowohl durch thermische als auch durch quantenmechanische Fluktuationen grundlegend beeinflusst. Dabei kann das quantenmechanische Heisenberg-Modell durch die Variation zweier Parameter auf ein System mit rein klassischen Fluktuationen reduziert werden: Es ist bereits langer bekannt, dass sowohl grose Spinquantenzahlen als auch grose Anisotropiefelder die Quantenfluktuationen komplett zerstoren konnen und damit zu einem klassischen Limes fuhren, der fur positive Anisotropiefelder ein Ising-artiges System zurucklasst. Diese Studie untersucht nun das Einsetzen klassischer Tendenzen, die durch vergleichsweise kleine Werte von Anisotropiefeldern und Spinquantenzahlen hervorgerufen werden. Die damit einhergehende und einsetzende Unterdruckung der Quantenfluktuationen steht dabei in direktem Zusammenhang zu aktuellen Experimenten, die mithilfe spinpolarisierter Rastertunnelmikroskopie an der Universitat Hamburg durchgefuhrt werden: Entsprechende spinaufgeloste Messungen, die magnetische Strukturen auf der Nanoskala sichtbar machen, werden durch nicht vernachlassigbare Anisotropiefelder beeinflusst und wurden mithilfe eines klassischen Heisenberg-Modells interpretiert. Die theoretische Untersuchung in der vorliegenden Arbeit uberpruft und bewertet nun den Gultigkeitsbereich dieser klassischen Beschreibung; zu diesem Zweck werden die Auswirkungen der Anisotropiefelder auf die typisch quantenmechanischen Eigenschaften des Heisenbergmodells naher unter die Lupe genommen. Hierzu bestimmen wir die kritischen Temperaturen fur Ferro- und Antiferromagnete und die Untergitter-Magnetisierung in Antiferromagneten. Die resultierende Abhangigkeit von der Dimension, der Spinquantenzahl und dem Anisotropiefeld wird fur einen umfassenden Wertebereich ausge-wertet und dargestellt. Wir vergleichen dabei die Ergebnisse aus folgenden Methoden: Klassisches Mean-Field (CMF), Quanten-Mean-Field (QMF), Lineare Spinwellen-Approximation (LSWA), Random-Phase-Approximation (RPA) und numerische Quanten-Monte-Carlo-Verfahren (QMC). Schlussendlich erhalten wir hieruber konsistente Ansichten uber die einsetzenden klassischen Tendenzen und die damit verbundene Unterdruckung der Quantenfluktuationen. Letztere stellen sich dabei als ausergewohnlich empfindlich auf die Anwesenheit selbst kleinster Anisotropiefelder heraus, was wir durch die Einfuhrung der Anisotropie-Suszeptibilitat explizit quantifizieren konnen. Diese starke Einflussnahme selbst kleinster Anisotropiefelder stellt ein bedeutendes Ergebnis der vorliegenden Arbeit dar. Im Endeffekt ermoglicht diese Studie eine fundierte Bewertung uber die klassische Modellierung der oben erwahnten experimentellen Messungen, die zurzeit in Hamburg durchgefuhrt werden.

The dependence of polymer conductivity on the work function of metallic electrodes

Abstract: It is shown that the occurrence of metallic conductivity in polymers is due to their electrification. In particular, the current density depends on the electron work function of metallic electrodes which are in contact with the polymer.

Effect of Fabry‐Perot resonances in disordered one‐dimensional array of alternating dielectric bi‐layers

Abstract: We study numerically and analytically the role of Fabry-Perot resonances in the transmission through a one-dimensional finite array formed by two alternating dielectric slabs. The disorder consists in varying randomly the width of one type of layers while keeping constant the width of the other type. Our numerical simulations show that localization is strongly inhibited in a wide neighborhood of the Fabry-Perot resonances. Comparison of our numerical results with an analytical expression for the average transmission, derived for weak disorder and finite number of cells, reveals that such expression works well even for medium disorder up to a certain frequency. Our results are valid for photonic and phononic one-dimensional disordered crystals, as well as for semiconductor superlattices.

Organic glasses: cluster structure of the random energy landscape

Abstract: An appropriate model for the random energy landscape in organic glasses is a spatially correlated Gaussian field. We calculated the distribution of the average value of a Gaussian random field in a finite domain. The results of the calculation demonstrate a strong dependence of the width of the distribution on the spatial correlations of the field. Comparison with the simulation results for the distribution of the size of the cluster indicates that the distribution of an average field could serve as a useful tool for the estimation of the asymptotic behavior of the distribution of the size of the clusters for “deep” clusters where value of the field on each site is much greater than the rms disorder. We also demonstrate significant modification of the properties of energetic disorder in organic glasses at the vicinity of the electrode.

Quadrupolar glass as a model for charge carrier transport in nonpolar organic materials

Abstract: Monte Carlo simulation of the charge carrier transport in disordered nonpolar organic materials has been carried out. As a suitable model we considered the model of quadrupolar glass. A general formula for the temperature and field dependence of the mobility was suggested. A comparison with experimental data has been carried out.

Ultra-fast dynamics in solids: non-equilibrium behaviour of magnetism and atomic structure

Abstract: Non-equilibrium physics is of fundamental interest, for example, for extensions of statistical mechanics and thermodynamics. In particular, it is important to understand how conservation laws like energy conservation and angular-momentum conservation in magnetic solids control the time scale of the dynamics. Laser irradiation may cause intense electronic excitations and thus a strong non-equilibrium state. Results are presented for the ultra-fast response of magnetism in ferromagnetic transition metals like Ni, Co, Fe, and Gd and furthermore of the atomic structure in semiconductors like Si, Ge, and InSb. Non-thermal melting is a most spectacular example of ultra-fast bond breaking. Time-resolved magnetooptical experiments yielding sub-picosecond spin dynamics are discussed. The spin dynamics is accompanied by THz light emission. The structural changes in semiconductors, bond changes sp3 s2p2, and phase transitions occur within about 100 fs. The results also shed light on electron-transfer processes, on ionization, and on molecular dissociation dynamics, which may occur during fs and as times. We discuss the application of time-resolved analysis to tunnelling problems and the phase diagram of high-Tc superconductivity.

Low‐frequency line temperatures of the CMB (Cosmic Microwave Background)

Abstract: Based on SU(2) Yang-Mills thermodynamics we interprete Aracde2's and the results of earlier radio-surveys on low-frequency cosmic microwave background (CMB) line temperatures as a phase-boundary effect. We explain the excess at low frequencies by evanescent, nonthermal photon fields of the CMB whose intensity is nulled by that of Planck distributed calibrator photons. The CMB baseline temperature thus is identified with the critical temperature of the deconfining-preconfining transition.

Purely electronic transport and localization in the Bose glass

Abstract: We discuss transport and localization properties on the insulating side of the disorder dominated superconductor-insulator transition, described in terms of the dirty boson model. Analyzing the spectral properties of the interacting bosons in the absence of phonons, we argue that the Bose glass phase admits three distinct regimes. For strongest disorder the boson system is a fully localized, perfect insulator at any temperature. At smaller disorder, only the low temperature phase exhibits perfect insulation while delocalization takes place above a finite temperature. We argue that a third phase must intervene between these perfect insulators and the superconductor. This conducting Bose glass phase is characterized by a mobility edge in the many body spectrum, located at finite energy above the ground state. In this insulating regime purely electronically activated transport occurs, with a conductivity following an Arrhenius law at asymptotically low temperatures, while a tendency to superactivation is predicted at higher T. These predictions are in good agreement with recent transport experiments in highly disordered films of superconducting materials.

Evaluation of the scientific impact, productivity and biological age based upon the h-index in three Latin American countries: the materials science case

Abstract: We discuss the scientific impact of Latin American scientists in the field of materials science. The analysis is based on the h-index as the scientometric index used to quantify the scientific productivity of an individual. In particular, we focus our analysis in Mexico, Chile and Colombia. We compare the level of productivity between all these countries. We also analyzed the h-index as function of the biological age, by using the first year of publication of a given scientists as a reference and discussed the general distribution of its quantification. We do not find a clear relationship between these two quantities. Based in our results we propose some political measures that these countries could implement to improve productivity as well as scientific development in this field. c

Anderson localization of matter waves

Abstract: In 1958, P.W. Anderson predicted the exponential localization1 of electronic wave functions in disordered crystals and the resulting absence of diffusion. It has been realized later that Anderson localization (AL) is ubiquitous in wave physics2 as it originates from the interference between multiple scattering paths, and this has prompted an intense activity. Experimentally, localization has been reported in light waves 3 microwaves4, sound waves5, and electron gases6 but to our knowledge there is no direct observation of exponential spatial localization of matter-waves (electrons or others). We present here the observation of Anderson localization7 of a Bose-Einstein condensate (BEC) released into a one-dimensional waveguide in the presence of a controlled disorder created by laser speckle. We also show that, in our one-dimensional speckle potentials whose noise spectrum has a high spatial frequency cut-off, exponential localization occurs only when the de Broglie wavelengths of the atoms in the expanding BEC are larger than an effective mobility edge corresponding to that cut-off. In the opposite case, we find that the density profiles decay algebraically8.

Approximate analytical solutions of the pseudospin symmetric Dirac equation for exponential-type potentials

Abstract: The solvability of The Dirac equation is studied for the exponential-type potentials with the pseudospin symmetry by using the parametric generalization of the Nikiforov–Uvarov method. The energy eigenvalue equation, and the corresponding Dirac spinors for Morse, Hulthen, and q-deformed Rosen–Morse potentials are obtained within the framework of an approximation to the spin-orbit coupling term, so the solutions are given for any value of the spin-orbit quantum number κ = 0, or κ ≠ 0.

1/f noise and slow relaxations in glasses

Abstract: Recently we have shown that slow relaxations in the electron glass system can be understood in terms of the spectrum of a matrix describing the relaxation of the system close to a metastable state. The model focused on the electron glass system, but its generality was demonstrated on various other examples. Here, we study the noise spectrum in the same framework. We obtain a remarkable relation between the spectrum of relaxation rates λ described by the distribution function P (λ) ∼ 1/λ and the 1/f noise in the fluctuating occupancies of the localized electronic sites. This noise can be observed using local capacitance measurements. We confirm our analytic results using numerics, and also show how the Onsager symmetry is fulfilled in the system.

Gravitoelectromagnetic cavitons in the kinetic regime

Abstract: We consider the interaction of gravitational fields (including “gravitoelectromagnetism”) with interstellar matter dealing with resonant wave-particle and wave-wave interactions on the basis of magnetic-type Maxwell-Vlasov equations. It is found that the behavior of the perturbed GEM fields, the perturbed density and self-generated gravitomagnetic field with very low frequency, can be described by the nonlinear coupling Eqs. (98–100). Numerical results show that they may collapse. In other words, due to self-focusing, a stronger GEM fields magnified up to 103 times, could be produced; they are the GEM cavitons, describing gravity shielding and filament effects. And the self-generated gravitomagnetic field is concurrently focused by the background material to a small space where it may be detected.

Conductance distribution at criticality: one‐dimensional Anderson model with random long‐range hopping

Abstract: We study numerically the conductance distribution function w(T) for the one-dimensional Anderson model with random long-range hopping described by the Power-law Banded Random Matrix model at criticality. We concentrate on the case of two single-channel leads attached to the system. We observe a smooth transition from localized to delocalized behavior in the conductance distribution by increasing b, the effective bandwidth of the model. Also, for b < 1 we show that w(ln T/Ttyp) is scale invariant, where Ttyp = exp 〈 ln T 〉 is the typical value of T. Moreover, we find that for T < Ttyp, w(ln T/Ttyp) shows a universal behavior proportional to (T/Ttyp)-1/2.

Network modules help the identification of key transport routes, signaling pathways in cellular and other networks

Abstract: PACS 89.75.Fb, 89.75.Hc Complex systems are successfully reduced to interacting elements via the network concept. Transport plays a key role in the survival of networks – for example the specialized signaling cascades of cellular networks filter noise and efficiently adapt the network structure to new stimuli. However, our general understanding of transport mechanisms and signaling pathways in complex systems is yet limited. Here we summarize the key network structures involved in transport, list the solutions available to overloaded systems for relaxing their load and outline a possible method for the computational determination of signaling pathways. We highlight that in addition to hubs, bridges and the network skeleton, the overlapping modular structure is also essential in network transport. Path-lenghts in the module-space of the yeast protein-protein interaction network indicated that module-based paths may cross fewer modular boundaries than shortest paths. Moreover, by locating network elements in the space of overlapping network modules and evaluating their distance in this ‘module space’, it may be possible to approximate signaling pathways computationally, which, in turn could serve the identification of signaling pathways of complex systems. Our model may be applicable in a wide range of fields including traffic control or drug design. c

Light transport and correlation length in a random laser

Abstract: A random laser is a strongly disordered, laser-active optical medium. The coherent laser feedback, which has been demonstrated experimentally to be present in these systems beyond doubt, requires the existence of spatially localized photonic quasimodes. However, the origin of these quasimodes has remained controversial. We develop an analytical theory for diffusive random lasers by coupling the transport theory of the disordered medium to the semiclassical laser rate equations, accounting for (coherent) stimulated and (incoherent) spontaneous emission. From the causality of wave propagation in an amplifying, diffusive medium we derive a novel length scale which we identify with the average mode radius of the lasing quasi-modes. We show that truly localized modes do not exist in the system without photon number conservation. However, we find that causality in the amplifying medium implies the existence of a novel, finite intensity correlation length which we identify with the average mode volume of the lasing quasimodes. We show further that the surface of the laser-active medium is crucial in order to stabilize a stationary lasing state. We solve the laser transport theory with appropriate surface boundary conditions to obtain the spatial distributions of the light intensity and of the occupation inversion. The dependence of the intensity correlation length on the pump rate agrees with experimental findings.