Search results for "fluctuation"
showing 10 items of 357 documents
Effects of a uniform acceleration on atom–field interactions
2014
We review some quantum electrodynamical effects related to the uniform acceleration of atoms in vacuum. After discussing the energy level shifts of a uniformly accelerated atom in vacuum, we investigate the atom-wall Casimir-Polder force for accelerated atoms, and the van der Waals/Casimir-Polder interaction between two accelerated atoms. The possibility of detecting the Unruh effect through these phenomena is also discussed in detail.
Dynamical mean-field theory versus second-order perturbation theory for the trapped two-dimensional Hubbard antiferromagnet
2011
In recent literature on trapped ultracold atomic gases, calculations for two-dimensional (2D) systems are often done within the dynamical mean-field theory (DMFT) approximation. In this paper, we compare DMFT to a fully 2D, self-consistent second-order perturbation theory for weak interactions in a repulsive Fermi-Hubbard model. We investigate the role of quantum and of spatial fluctuations when the system is in the antiferromagnetic phase, and find that, while quantum fluctuations decrease drastically the order parameter and critical temperatures, spatial fluctuations only play a noticeable role when the system undergoes a phase transition, or at phase boundaries in the trap. We conclude f…
Nanoparticles at fluid interfaces.
2017
Nanoparticles at fluid interfaces are becoming a central topic in colloid science studies. Unlike in the case of colloids in suspensions, the description of the forces determining the physical behavior of colloids at interfaces still represents an outstanding problem in the modern theory of colloidal interactions. These forces regulate the formation of complex two-dimensional structures, which can be exploited in a number of applications of technological interest; optical devices, catalysis, molecular electronics or emulsions stabilization. From a fundamental viewpoint and typical for colloidal systems, nanoparticles and microparticles at interfaces are ideal experimental and theoretical mo…
Enhancement of the Lifetime of Metastable States in Er-Doped Si Nanocrystals by External Colored Noise
2015
The changes in the lifetime of a metastable energy level in Er-doped Si nanocrystals in the presence of an external source of colored noise are analyzed for different values of noise intensity and correlation time. Exciton dynamics is simulated by a set of phenomenological rate equations which take into account all the possible phenomena inherent in the energy states of Si nanocrystals and Er^{3+} ions in the host material of Si oxide. Electronic deexcitation is studied by examining the decay of the initial population of the Er atoms in the first excitation level 4I_{13/2} through fluorescence and cooperative energy transfer upconversion. Our results show that the deexcitation process of th…
Comparative efficiency of green and conventional bonds pre- and during COVID-19: An asymmetric multifractal detrended fluctuation analysis
2021
Abstract Motivated by the lack of research on price efficiency dynamics of green bonds and the impact of the COVID-19 on the pricing of fixed-income securities, this study investigates the comparative efficiency of green and conventional bond markets pre- and during the COVID-19 pandemic applying asymmetric multifractal analysis. Specifically, the multifractal scaling behaviour is examined separately during upward and downward trends in bond markets using the asymmetric multifractal detrended fluctuation analysis (A-MF-DFA) approach. The empirical findings confirm the presence of asymmetric multifractality in the green and traditional bond markets. Not surprisingly, inefficiency in both bon…
Average Structure vs. Real Structure: Molecular Dynamics Studies of Silica
2003
The microscopic structure of a crystal and thermal fluctuations of the atoms constituting the crystal are intimately connected with the macroscopic elastic properties including mechanical stability. In some cases, however, the picture is more complex than that which is drawn in text books on solid state physics. (i) The instantaneous microscopic structure can deviate in a non-Gaussian way from the average structure even when domain disorder and/or crystal defects are absent. Quasi harmonic approximations may then turn out to be meaningless. (ii) The crystal is subject to external pressures that are sufficiently large in order to render the definition of elastic constants non unique. These t…
Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources
2014
We investigate the superconducting lifetime of long current-biased Josephson junctions, in the presence of Gaussian and non-Gaussian noise sources. In particular, we analyze the dynamics of a Josephson junction as a function of the noise signal intensity, for different values of the parameters of the system and external driving currents. We find that the mean lifetime of the superconductive state is characterized by nonmonotonic behavior as a function of noise intensity, driving frequency and junction length. We observe that these nonmonotonic behaviours are connected with the dynamics of the junction phase string during the switching towards the resistive state. An important role is played…
Search for Subsolar Mass Ultracompact Binaries in Advanced LIGO's Second Observing Run
2019
We present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO’s second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between \ud0.2\ud \ud \udM\ud⊙\ud–\ud1.0\ud \ud \udM\ud⊙\ud. We use the null result to constrain the binary merger rate of (\ud0.2\ud \ud \udM\ud⊙\ud, \ud0.2\ud \ud \udM\ud⊙\ud) binaries to be less than \ud3.7\ud×\ud10\ud5\ud \ud \udGpc\ud−\ud3\ud \udyr\ud−\ud1\udand the binary …
Search for Subsolar-Mass Ultracompact Binaries in Advanced LIGO's First Observing Run
2018
We present the first Advanced LIGO and Advanced Virgo search for ultracompact binary systems with component masses between 0.2 $M_\odot$ - 1.0 $M_\odot$ using data taken between September 12, 2015 and January 19, 2016. We find no viable gravitational wave candidates. Our null result constrains the coalescence rate of monochromatic (delta function) distributions of non-spinning (0.2 $M_\odot$, 0.2 $M_\odot$) ultracompact binaries to be less than $1.0 \times 10^6 \text{Gpc}^{-3} \text{yr}^{-1}$ and the coalescence rate of a similar distribution of (1.0 $M_\odot$, 1.0 $M_\odot$) ultracompact binaries to be less than $1.9 \times 10^4 \text{Gpc}^{-3} \text{yr}^{-1}$ (at 90 percent confidence). N…