Browsing by Subject "Statistical mechanics"
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Open Access Active matter alters the growth dynamics of coffee rings(OSA, 2018) Callegari, Agnese; Andaç, Tuğba; Weigmann, Pascal; Velu, Sabareesh K. P.; Pinçe, Erçağ; Volpe, G.; Volpe, GiovanniWe show that bacterial mobility starts playing a major role in determining the growth dynamics of the edge of drying droplets, as the droplet evaporation rate slows down.Item Open Access An alternative method to measure the likelihood of a financial crisis in an emerging market(Elsevier BV, 2007) Özlale, Ü.; Özcan, K. M.This paper utilizes an early warning system in order to measure the likelihood of a financial crisis in an emerging market economy. We introduce a methodology, where we can both obtain a likelihood series and analyze the time-varying effects of several macroeconomic variables on this likelihood. Since the issue is analyzed in a non-linear state space framework, the extended Kalman filter emerges as the optimal estimation algorithm. Taking the Turkish economy as our laboratory, the results indicate that both the derived likelihood measure and the estimated time-varying parameters are meaningful and can successfully explain the path that the Turkish economy had followed between 2000 and 2006. The estimated parameters also suggest that overvalued domestic currency, current account deficit and the increase in the default risk increase the likelihood of having an economic crisis in the economy. Overall, the findings in this paper suggest that the estimation methodology introduced in this paper can also be applied to other emerging market economies as well. © 2007 Elsevier B.V. All rights reserved.Item Open Access Bell solitons in ultra-cold atomic Fermi gas(2013) Khan, A.; Panigrahi P.K.We demonstrate the existence of supersonic bell solitons in the Bardeen-Cooper-Schrieffer-Bose-Einstein condensate crossover regime. Starting from the extended Thomas-Fermi density functional theory of superfluid order parameter, a density transformation is used to map the hydrodynamic mean field equation to a Lienard-type equation. As a result, bell solitons are obtained as exact solutions, which is further verified by the numerical solution of the dynamical equation. The stability of the soliton is established and its behaviour in the entire crossover domain is obtained. It is found that, akin to the case of vortices, bell solitons yield highest contrast in the BEC regime. © 2013 IOP Publishing Ltd.Item Open Access Effects of adopting inflation targeting regimes on inflation variability(Elsevier BV, 2007) Berument, Hakan; Yuksel, E.This paper investigates whether inflation-targeting programs have altered the pattern of inflation and its variability for five developed countries and four emerging economies implementing inflation-targeting programs. A GARCH specification is used to model inflation variability, which accounts for public perception of the future levels of inflation variability-conditional variance. We could not find lower conditional inflation expectations except for Australia, Chile and Sweden under various specifications. Moreover, the conditional variance decreases only for Chile and the UK. Therefore, the empirical support for the lower inflation and its variability for the inflation targeting regimes is limited. © 2006 Elsevier B.V. All rights reserved.Item Open Access Intraday dynamics of stock market returns and volatility(Elsevier BV, 2006) Selçuk, F.; Gençay, R.This paper provides new empirical evidence for intraday scaling behavior of stock market returns utilizing a 5 min stock market index (the Dow Jones Industrial Average) from the New York Stock Exchange. It is shown that the return series has a multifractal nature during the day. In addition, we show that after a financial "earthquake", aftershocks in the market follow a power law, analogous to Omori's law. Our findings indicate that the moments of the return distribution scale nonlinearly across time scales and accordingly, volatility scaling is nonlinear under such a data generating mechanism. © 2006 Elsevier B.V. All rights reserved.Item Open Access Ionic current inversion in pressure-driven polymer translocation through nanopores(American Physical Society, 2015) Buyukdagli, S.; Blossey, R.; Ala-Nissila, T.We predict streaming current inversion with multivalent counterions in hydrodynamically driven polymer translocation events from a correlation-corrected charge transport theory including charge fluctuations around mean-field electrostatics. In the presence of multivalent counterions, electrostatic many-body effects result in the reversal of the DNA charge. The attraction of anions to the charge-inverted DNA molecule reverses the sign of the ionic current through the pore. Our theory allows for a comprehensive understanding of the complex features of the resulting streaming currents. The underlying mechanism is an efficient way to detect DNA charge reversal in pressure-driven translocation experiments with multivalent cations. © 2015 American Physical Society.Item Open Access Quantum correlations among superradiant bose-einstein condensate atoms(M A I K Nauka - Interperiodica, 2010) Taşgin, M. E.; Öztop, B.; Oktel, M. Ö.; Müstecapliog̃lu, Ö. E.Quantum correlations among atoms in superradiant Bose-Einstein condensates are discussed. It is shown that atoms in the superradiant atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein-Podolsky-Rosen (EPR)-type quantum correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided.Item Open Access Quantum Dynamics of Long-Range Interacting Systems Using the Positive-P and Gauge-P Representations(American Physical Society, 2017) Wüster, S.; Corney, J. F.; Rost, J. M.; Deuar, P.We provide the necessary framework for carrying out stochastic positive-P and gauge-P simulations of bosonic systems with long-range interactions. In these approaches, the quantum evolution is sampled by trajectories in phase space, allowing calculation of correlations without truncation of the Hilbert space or other approximations to the quantum state. The main drawback is that the simulation time is limited by noise arising from interactions. We show that the long-range character of these interactions does not further increase the limitations of these methods, in contrast to the situation for alternatives such as the density matrix renormalization group. Furthermore, stochastic gauge techniques can also successfully extend simulation times in the long-range-interaction case, by making using of parameters that affect the noise properties of trajectories, without affecting physical observables. We derive essential results that significantly aid the use of these methods: estimates of the available simulation time, optimized stochastic gauges, a general form of the characteristic stochastic variance, and adaptations for very large systems. Testing the performance of particular drift and diffusion gauges for nonlocal interactions, we find that, for small to medium systems, drift gauges are beneficial, whereas for sufficiently large systems, it is optimal to use only a diffusion gauge. The methods are illustrated with direct numerical simulations of interaction quenches in extended Bose-Hubbard lattice systems and the excitation of Rydberg states in a Bose-Einstein condensate, also without the need for the typical frozen gas approximation. We demonstrate that gauges can indeed lengthen the useful simulation time.Item Open Access Quantum entanglement via superradiance of a Bose-Einstein condensate(Institute of Physics Publishing, 2010) Taşgın, M. E.; Oktel, M. Ö.; You, L.; Müstecaploǧlu, Ö. E.We adopt the coherence and built-in swap mechanism in sequential superradiance as a tool for obtaining continuous-variable (electric/magnetic fields) quantum entanglement of two counter-propagating pulses emitted from the two end-fire modes. In the first-sequence, end-fire modes are entangled with the side modes. In the second sequence, this entanglement is swapped to in between the two opposite end-fire modes. Additionally, we also examine the photon number correlations. No quantum correlations is observed in this variable.Item Open Access Stepwise Positional-Orientational Order and the Multicritical-Multistructural Global Phase Diagram of the s=3/2 Ising Model From Renormalization-Group Theory(American Physical Society, 2016) Yunus, Ç.; Renklioǧlu, B.; Keskin, M.; Berker, A. N.The spin-32 Ising model, with nearest-neighbor interactions only, is the prototypical system with two different ordering species, with concentrations regulated by a chemical potential. Its global phase diagram, obtained in d=3 by renormalization-group theory in the Migdal-Kadanoff approximation or equivalently as an exact solution of a d=3 hierarchical lattice, with flows subtended by 40 different fixed points, presents a very rich structure containing eight different ordered and disordered phases, with more than 14 different types of phase diagrams in temperature and chemical potential. It exhibits phases with orientational and/or positional order. It also exhibits quintuple phase transition reentrances. Universality of critical exponents is conserved across different renormalization-group flow basins via redundant fixed points. One of the phase diagrams contains a plastic crystal sequence, with positional and orientational ordering encountered consecutively as temperature is lowered. The global phase diagram also contains double critical points, first-order and critical lines between two ordered phases, critical end points, usual and unusual (inverted) bicritical points, tricritical points, multiple tetracritical points, and zero-temperature criticality and bicriticality. The four-state Potts permutation-symmetric subspace is contained in this model.Item Open Access Temperature-dependent optoelectronic properties of quasi-2D colloidal cadmium selenide nanoplatelets(Royal Society of Chemistry, 2017) Bose, S.; Shendre, S.; Song, Z.; Sharma, V. K.; Zhang, D. H.; Dang C.; Fan, W.; Demir, Hilmi VolkanColloidal cadmium selenide (CdSe) nanoplatelets (NPLs) are a recently developed class of efficient luminescent nanomaterials suitable for optoelectronic device applications. A change in temperature greatly affects their electronic bandstructure and luminescence properties. It is important to understand how and why the characteristics of NPLs are influenced, particularly at elevated temperatures, where both reversible and irreversible quenching processes come into the picture. Here we present a study of the effect of elevated temperatures on the characteristics of colloidal CdSe NPLs. We used an effective-mass envelope function theory based 8-band k·p model and density-matrix theory considering exciton-phonon interaction. We observed the photoluminescence (PL) spectra at various temperatures for their photon emission energy, PL linewidth and intensity by considering the exciton-phonon interaction with both acoustic and optical phonons using Bose-Einstein statistical factors. With a rise in temperature we observed a fall in the transition energy (emission redshift), matrix element, Fermi factor and quasi Fermi separation, with a reduction in intraband state gaps and increased interband coupling. Also, there was a fall in the PL intensity, along with spectral broadening due to an intraband scattering effect. The predicted transition energy values and simulated PL spectra at varying temperatures exhibit appreciable consistency with the experimental results. Our findings have important implications for the application of NPLs in optoelectronic devices, such as NPL lasers and LEDs, operating much above room temperature.Item Open Access Trapped interacting Bose gas in nonextensive statistical mechanics(The American Physical Society, 2002) Tanatar, BilalWe study the Bose-Einstein condensation (BEC) phenomenon in an interacting trapped Bose gas using the semiclassical two-fluid model and nonextensive statistical mechanics. The effects of nonextensivity characterized by a parameter are explored by calculating the temperature dependent thermodynamic properties, fraction of condensed particles, and density distributions of condensed and thermal components of the system. It is found that nonextensivity in the underlying statistical mechanics may have large effects on the BEC transition temperature.