On the Locality of the No Hair Conjecture and the Measure of the Universe

We reanalize the recently proposed proof by Jensen and Stein-Schabes [1] of the No Hair Theorem for inhomogeneous spacetimes, putting a special emphasis on the asymptotic behaviour of the shear and curvature. We conclude that the theorem only holds locally and estimate the minimum size a region should be in order for it to inflate. We discuss in some detail the assumptions used in the theorem. In the last section we speculate about the possible measure of the set of spacetimes that would undergo inflation.     

Influence of the size,geometry and temporal response of the finite piezoelectric sensor on the photoacoustic signal: the case of the point-like source

Most photoacoustic (PA) work assumes a point-like detection of generated pressure waves; this assumption results in important differences between predicted and experimental signals, as shown in this paper. We used the geometry of a real sensor in the theoretical signal generation through the discretization of the sensing surface, considering each element as a point-like sensor. We modeled the interaction between the wavefront and the real sensor, starting from a well-known PA pressure relation for a point-like source and punctual detection. We obtained the electrical response of the real sensor experimentally and modeled it as a summation of Gaussian functions. The impulse response was convolved with the total PA pressure to obtain the theoretical PA signal. We analyzed the dependence of the source-sensor distance on the discretization size. Then the predicted signal and experimental data were compared for two different frequency response transducers. We found differences in shape and temporal width of simulated PA signals for point-like-source/punctual-detection model and for point-like-source/finite-sensor model.     

Analysis of the effects of the global financial crisis on the Turkish economy, using hierarchical methods

We have analyzed the topology of 50 important Turkish companies for the period 2006-2010 using the concept of hierarchical methods (the minimal spanning tree (MST) and hierarchical tree (HT)). We investigated the statistical reliability of links between companies in the MST by using the bootstrap technique. We also used the average linkage cluster analysis (ALCA) technique to observe the cluster structures much better. The MST and HT are known as useful tools to perceive and detect global structure, taxonomy, and hierarchy in financial data. We obtained four clusters of companies according to their proximity. We also observed that the Banks and Holdings cluster always forms in the centre of the MSTs for the periods 2006-2007, 2008, and 2009-2010. The clusters match nicely with their common production activities or their strong interrelationship. The effects of the Automobile sector increased after the global financial crisis due to the temporary incentives provided by the Turkish government. We find that Turkish companies were not very affected by the global financial crisis.     

Simulations of the Hubbard model

We discuss results of simulations of the Hubbard model of interacting electrons on a lattice. We start with a brief discussion of methodology and point out some of the outstanding problems. We then discuss results of simulations of the model in three, two, and one dimension, particularly in connection with its magnetic and superconducting properties. We conclude with a brief discussion of future directions.     

Inhomogeneous Cosmologies, the Copernican Principle and the Cosmic Microwave Background: More on the EGS Theorem

We discuss inhomogeneous cosmological models which satisfy the Copernican principle. We construct some inhomogeneous cosmological models starting from the ansatz that the all the observers in the models view an isotropic cosmic microwave background. We discuss multi-fluid models, and illustrate how more general inhomogeneous models may be derived, both in General Relativity and in scalar-tensor theories of gravity. Thus we illustrate that the cosmologicalprinciple, the assumption that the Universe we live in is spatially homogeneous, does not necessarily follow from the Copernican principle and the high isotropy of the cosmic microwave background. We also present some new conformally flat two-fluid solutions of Einstein's field equations.     

Calculations of the propagator within the tomographic-probability framework

We show that the ambiguity in choosing the tomographic propagator for an evolving linear quantum system is related to the homogeneity properties of the system symplectic tomogram. We study in detail an example of the driven harmonic oscillator. We prove that two formally different propagators of the quantum kinetic equation for the oscillator are identical on the domain of homogeneous tomographic probability distributions.     

Influence of temperature gradient at the reflectors on the bit-error rate in periscope laser communication systems in the presence of platform vibrations

We propose a reflector back-fixing method for substantially improving the pointing accuracy in comparison with the around-fixing method. We use the developed model for analyzing the bit-error rate (BER) in the presence of the satellite??s platform vibration. We consider the relationship between the BER and temperature gradient at elliptical reflectors, in view of the two fixing methods mentioned above. We also analyze the effect of beam wavelength and truncation ratio on the BER. We find that the back-fixing of the reflectors can reduce substantially the BER, thus, providing stabler performance of periscope laser-communication systems.     

On the Mathematical Basis of the Dirac Formulation of Quantum Mechanics

We discuss various attempts to implement mathematically the Dirac formulation of Quantum Mechanics. A first attempt used Hilbert space. This formalization realizes the Dirac formalism if and only if the spectra of the observables under consideration is purely discrete. Therefore, generalized spectral decompositions are needed. These spectral decompositions can be constructed in the framework of rigged Hilbert spaces. We construct generalized spectral decompositions for self-adjoint operators using their spectral measures. We review the previous work by Marlow (in Hilbert spaces), Antoine, Roberts, and Melsheimer and complete it. We show that these generalized spectral decompositions fit well in the framework of a theory constructed by Kato and Kuroda and that all the results can be reproduced in this framework.     

On the nucleation of hadronic domains in the quark-hadron transition

We present numerical results on bubble profiles, nucleation rates and time evolution for a weakly first-order quark-hadron phase transition in different expansion scenarios. We confirm the standard picture of a cosmological first-order phase transition, in which the phase transition is entirely dominated by nucleation. We also show that, even for expansion rates much lower than those expected in heavy-ion collisions nucleation is very unlikely, indicating that the main phase conversion mechanism is spinodal decomposition.     

The thermodynamics of electrons and the thermoelectric transport in epitaxial graphene on the size-quantized films

We investigated the thermodynamic parameters (chemical potential, heat capacity and thermodynamic potential) and a thermoelectric transport in an epitaxial graphene on the size-quantized metal and semiconductor films within the framework of simple analytical model. We considered limiting cases of high and low temperatures. We showed that the chemical potential of epitaxial graphene is smaller than the chemical potential of isolated graphene at the same carrier concentration. Conversely, the heat capacity of the epitaxial graphene is greater than the heat capacity of the isolated graphene. We investigated a conductivity and thermopower of the epitaxial graphene. We showed that in such system there are the kinks of conductivity and peaks of thermoelectric power. These peaks are several times greater than those of isolated graphene. We compared our system with cases of 2D and 3D substrates.     

Conditions and features of the lasing in traps for the bose condensation of dipolar excitons

We study the conditions and features of the polariton mode lasing in traps for the Bose condensation of dipolar excitons. We discuss the spectral linewidth of lasing modes and the effects of spatial and spectral inhomogeneity of the exciton distribution. We study in detail the possibility of the polariton mode lasing in the vicinity of the Bose condensation threshold. We analyze the impact of the inhomogeneous broadening of the exciton line on the stability of stationary lasing. We also propose additional experiments aimed at obtaining more information on the polariton mode lasing in semiconductor structures for the Bose condensation of excitons.     

Non-stationary effects in the coupled quantum dots influenced by the electron-phonon interaction

We analyzed time evolution of the localized charge in the system of two interacting single level quantum dots coupled with the continuous spectrum states in the presence of electron-phonon interaction. We demonstrated that electron-phonon interaction leads to an increase in localized charge relaxation rate. We also found that several time scales with different relaxation rates appear in the system in the case of non-resonant tunneling between the dots. We revealed the formation of oscillations in the filling numbers time evolution caused by the emission and adsorption processes of phonons.     

On the branching structure of the tree of states in spin glasses

We review some known results on the nature of the tree of states in spin glasses and we present new results on its topology. We pay particular attention to the so-called continuum limit in which the levels are labeled by a continuous variablex. We also study the dependence on the levelx of the type of branching (bifurcation, trifurcation,...). We show that the statistics of the tree is universal in the continuum limit, i.e., it does not depend on the details of the algorithm used to generate the tree.     

On the logarithmic solutions of the WDVV equations

We consider restrictions and subsystems in the ∨-systems corresponding to the logarithmic solutions of the WDVV equations. We present certain solutions through restrictions of the Coxeter systems.     

On the origin of the anomalous sign reversal in the Hall effect in Nb thin films

We re-visit the anomalous sign reversal problem in the Hall effect of the sputtered Nb thin films. We find that the anomalous sign reversal in the Hall effect is extremely sensitive to a small tilting of the magnetic field and to the magnitude of the applied current. Large anomalous variations are also observed in the symmetric part of the transverse resistance R_xy. We suggest that the surface current loops on superconducting grains at the edges of the superconducting thin films may be responsible for the Hall sign reversal and the accompanying anomalous effects in the symmetric part of R_xy.     

Chiral corrections to the masses of the doubly heavy baryons

We study the masses of the doubly bottom baryons and the charmed-bottom baryons up to ${ \mathcal O }\left({p}^{3}\right)$ in heavy baryon chiral perturbation theory. We determine the unknown low energy constants in the quark model and lattice QCD. We show the numerical results for the masses of the doubly bottom baryons and the charmed-bottom baryons up to ${ \mathcal O }\left({p}^{3}\right)$.     

On the interbasis expansion for the Kaluza-Klein monopole system

We study the interbasis expansion of the wave-functions of the Kaluza-Klein monopole system in the parabolic coordinate system with respect to the spherical coordinate system, and vice versa. We show that the coefficients of the expansion are proportional to Clebsch-Gordan coefficients. We analyse the discrete and continuous spectrum as well, briefly discuss the feature that the (reduced) Kaluza-Klein monopole system is separable in three coordinate systems, and the fact that there are five functionally independent integrals of motion, respectively observables, a property which characterizes this system as super-integrable.     

The quantum effects of the spin and the Bohm potential in the oblique propagation of magnetosonic waves

We study the quantum corrections to the oblique propagation of the magnetosonic waves in a warm quantum magnetoplasma composed by mobile ions and electrons. We use a fluid formalism to include quantum corrections due to the Bohm potential and to the spin magnetization energy of electrons. The effects of both quantum corrections are shown in the dispersion relation for perpendicular, parallel and oblique propagation. We find that the quantum contributions to the low frequency depend on the type in the oblique propagation with respect to the background magnetic field. The relevance in astrophysical scenarios is exemplified.     

Nonlinear optical studies of the transient coherence in the Quantum Hall system

We review recent investigations of the femtosecond nonlinear optical response of the two-dimensional electron gas (2DEG) in a strong magnetic field. We probe the Quantum Hall (QH) regime for filling factors ν∼1. Our focus is on the transient coherence induced via optical excitation and on its time evolution during early femtosecond timescales. We simultaneously study the interband and intraband coherence in this system by using a nonlinear spectroscopic technique, transient three-pulse four wave mixing optical spectroscopy, and a many-body theory. We observe striking differences in the temporal and spectral profile of the nonlinear optical signal between a modulation doped quantum well system (with the 2DEG) and a similar undoped quantum well (without a 2DEG). We attribute these qualitative differences to Coulomb correlations between the photoexcited electron-hole pairs and the 2DEG. We show, in particular, that intraband many-particle coherences assisted by the inter-Landau-level magnetoplasmon excitations of the 2DEG dominate the femtosecond nonlinear optical response. The most striking effect of these exciton-magnetoplasmon coherences is a large off-resonant four-wave-mixing signal in the case of very low photoexcited carrier densities, not observed in the undoped system, with strong temporal oscillations and unusually symmetric temporal profile.     

On the validity of the Fokker-Planck equation for the Heisenberg magnet

We assume an explicit stochastic dynamics for the microscopic variables in the Heisenberg magnet based on experimental data. We obtain additional terms to the Fokker-Planck Equation and also explicit expressions for the numerical coefficients in the Master Equation, near T_c.