Role Of Fluctuations Research Articles

Mechanism for turbulence proliferation in subcritical flows

The subcritical transition to turbulence, as occurs in pipe flow, is believed to generically be a phase transition in the directed percolation universality class. At its heart is a balance between the decay rate and proliferation rate of localized turbulent structures, called puffs in pipe flow. Here, we propose the first-ever dynamical mechanism for puff proliferation—the process by which a puff splits into two. In the first stage of our mechanism, a puff expands into a slug. In the second stage, a laminar gap is formed within the turbulent core. The notion of a split-edge state, mediating the transition from a single puff to a two-puff state, is introduced and its form is predicted. The role of fluctuations in the two stages of the transition, and how splits could be suppressed with increasing Reynolds number, are discussed. Using numerical simulations, the mechanism is validated within the stochastic Barkley model. Concrete predictions to test the proposed mechanism in pipe and other wall-bounded flows, and implications for the universality of the directed percolation picture, are discussed.

Fluctuations and phases in baryonic matter

The phase structure of baryonic matter is investigated with focus on the role of fluctuations beyond the mean-field approximation. The prototype test case studied is the chiral nucleon-meson model, with added comments on the chiral quark-meson model. Applications to nuclear matter include the liquid-gas phase transition. Extensions to high baryon densities are performed for both nuclear and neutron matter. The role of vacuum fluctuations is systematically explored. It is pointed out that such fluctuations tend to stabilize the hadronic phase characterized by spontaneously broken chiral symmetry, shifting the chiral restoration transition to very high densities. This stabilization effect is shown to be further enhanced by additional dynamical fluctuations treated with functional renormalisation group methods.

Galactic factories of cosmic-ray electrons and positrons

We present a novel calculation of the spectrum of electrons and positrons from random sources, supernova remnants and pulsars, distributed within the spiral arms of the Galaxy. The pulsar emissivity in terms of electron-positron pairs is considered as time dependent, following the magnetic dipole spin-down luminosity, and the temporal evolution of the potential drop is accounted for. Moreover each pulsar, with the magnetic field and initial spin period selected at random from the observed distribution, is considered as a source of pairs only after it leaves the parent supernova due to its birth kick velocity (also selected at random from the observed distribution). We show that (i) the spectrum of electrons is characterized by a feature at $\gtrsim 50$ GeV that proves that their transport is dominated by radiative losses. The flux reduction at $E\gtrsim 1$ TeV is explained as a result of lepton transport from sources in the spiral arms. (ii) The spectrum of positrons is very well described by the contribution of pulsars and the rising positron fraction originates naturally. The implications of pulsars as positron sources in terms of positron fraction at very high energies are also discussed. (iii) The role of fluctuations in the high-energy regime is thoroughly discussed and used to draw conclusions on the possibility to single out the contribution of local sources to the lepton spectrum with current and upcoming experiments.

Role of fluctuations in epidemic resurgence after a lockdown

Most popular statistical models in epidemic evolution focus on the dynamics of average relevant quantities and overlooks the role of small fluctuations on the model parameters. Models for Covid-19 are no exception. In this paper we show that the role of time-correlated fluctuations, far from being negligible, can in fact determine the spreading of an epidemic and, most importantly, the resurgence of the exponential diffusion in the presence of time-limited episodes in promiscuity behaviours. The results found in this work are not only relevant and specific for the Covid-19 epidemic but are more general and can be applied to other epidemics.

Infection process near criticality: influence of the initial condition

We investigate how the initial number of infected individuals affects the behavior of the critical susceptible-infected-recovered process. We analyze the outbreak size distribution, duration of the outbreaks, and the role of fluctuations.

Test for asymmetry on the ex-pump price of premium gasoline in Ghana, Kenya, and Colombia

Once again, the World has been faced with an oil price shock as a result of the SARS-CoV-2 coronavirus pandemic. This has resurrected an old debate of whether retail fuel prices adjust significantly to either increases or decreases in international crude oil prices. With many countries moving towards the deregulation of their petroleum sub-sector, the impact of the US dollar exchange rate on retail fuel prices cannot be overlooked. This study investigates the rate at which positive and negative changes in international Brent crude oil prices and the US dollar exchange rate affected the increases or decreases in the ex-pump price of premium gasoline between February 2012 and December 2019. Using a non-linear auto-regressive distributed lag model, the exchange rate was found to play a significant role in fluctuations in the retail price of premium gasoline in Ghana and Colombia in the long run, howev-er, the rate of adjustment between the negative and positive changes was not significant, dispelling the perception of price asymmetry. There was no significant relationship between the ex-pump price of premium gasoline and the international Brent crude oil price in Ghana and Kenya in the long run. This study recommends that the aforementioned countries prioritise the creation of ex-change rate buffers to prevent exchange rate shocks that may affect retail fuel prices.

Локальные и интегральные свойства квазиодномерного сверхпроводника в режиме квантовых флуктуаций параметра порядка

Utilization of superconducting materials for the new generation of nanoelectronic devices seems extremely tempting from the point of view of the absence of Joule heating. However, in small systems, the role of fluctuations can be very significant. In this work, the transport properties of thin superconducting titanium nanostructures were studied experimentally and theoretically. It has been shown that quantum fluctuations of the order parameter have a dif-ferent impact on integral and local characteristics of a quasi-one-dimensional superconductor. In sufficiently thin nanowires, a finite electrical resistance can be observed at the lowest tem-peratures, while the tunneling current-voltage characteristics exhibit only slightly broadened gap singularity and a finite Josephson current. The observation is of fundamental importance for understanding the phenomenon of mesoscopic superconductivity and should be taken into account when designing nanometer scale cryoelectronic devices.

Periodic fluctuations of marine oxygen content during the latest Permian

Widespread oceanic anoxia has been implicated as a killing mechanism during the end-Permian mass extinction (EPME). A high-resolution investigation of pyrite framboids and bioturbation structures in the Shangsi section of South China has revealed repeated and frequent fluctuations of coupled anoxic/euxinic to dysoxic/oxic episodes in the latest Permian, immediately preceding the EPME. Anoxic bottom waters and interstitial water conditions are documented by the smallest pyrite framboids (3–5 μm) and the absence of bioturbation, and dysoxic bottom waters and anoxic interstitial waters are inferred from larger pyrite framboids (6–10 μm) and the occurrence of Zoophycos. In comparison, oxic conditions for both bottom waters and interstitial waters are revealed by a high bioturbation index (BI = 4) and the occurrence of mid-tier Thalassinoides. Fluctuating pyrite framboid sizes and bioturbation structures suggest that bottom and interstitial oxygen levels were neither fully, nor persistently, anoxic/euxinic before the EPME, and instead recorded frequent periodic fluctuations between anoxic/euxinic and dysoxic/oxic conditions. The paleoceanic redox variation appears to correlate with the 405-ka eccentricity cycles in the anhysteretic remanent magnetization (ARM) series, suggesting that fluctuations might have been controlled by Milankovitch cycles. The role of fluctuations between anoxic/euxinic and dysoxic/oxic episodes in the latest Permian to the EPME is unclear, but it seems plausible that they represent a prelude to the highly stressed conditions that are characteristic of the EPME.

Influence of the Effective Intensity of Laser-Pulse Radiation on the Rate of Multiphoton Processes

The influence of uncertainty in intensity of radiation of individual laser pulses on probabilities of multiphoton ionization/photodetachment is analyzed quantitatively. Both multiphoton (using an example of an F− anion) and tunnel regimes are studied. It is demonstrated that intensity fluctuations substantially change probabilities of the discussed processes. As to the tunnel regime, the role of fluctuations is negligibly small not only in the region of saturation but also far from it in this case.

Role of fluctuations in the yielding transition of two-dimensional glasses

We numerically study yielding in two-dimensional glasses which are generated with a very wide range of stabilities by swap Monte-Carlo simulations and then slowly deformed at zero temperature. We provide strong numerical evidence that stable glasses yield via a nonequilibrium discontinuous transition in the thermodynamic limit. A critical point separates this brittle yielding from the ductile one observed in less stable glasses. We find that two-dimensional glasses yield similarly to their three-dimensional counterparts but display larger sample-to-sample disorder-induced fluctuations, stronger finite-size effects, and rougher spatial wandering of the observed shear bands. These findings strongly constrain effective theories of yielding.

The role of fluctuations in determining cellular network thermodynamics.

The steady state distributions of phenotypic responses within an isogenic population of cells result from both deterministic and stochastic characteristics of biochemical networks. A biochemical network can be characterized by a multidimensional potential landscape based on the distribution of responses and a diffusion matrix of the correlated dynamic fluctuations between N-numbers of intracellular network variables. In this work, we develop a thermodynamic description of biological networks at the level of microscopic interactions between network variables. The Boltzmann H-function defines the rate of free energy dissipation of a network system and provides a framework for determining the heat associated with the nonequilibrium steady state and its network components. The magnitudes of the landscape gradients and the dynamic correlated fluctuations of network variables are experimentally accessible. We describe the use of Fokker-Planck dynamics to calculate housekeeping heat from the experimental data by a method that we refer to as Thermo-FP. The method provides insight into the composition of the network and the relative thermodynamic contributions from network components. We surmise that these thermodynamic quantities allow determination of the relative importance of network components to overall network control. We conjecture that there is an upper limit to the rate of dissipative heat produced by a biological system that is associated with system size or modularity, and we show that the dissipative heat has a lower bound.

Combining LE4PD Normal Modes and Markov State Modeling to Elucidate the Fluctuation Dynamics of Ubiquitin

Local fluctuations are important for protein binding and molecular recognition because they provide conformational states that can be trapped through a conformational selection mechanism of binding. Thus, an accurate characterization of local fluctuations can be important for modeling the mechanisms leading to the biological activity of a protein. In this presentation we quantify the fluctuation dynamics of the regulatory protein ubiquitin and propose a novel theoretical approach to modelling its fluctuations. A coarse-grained, diffusive, mode-dependent description of the protein's fluctuation dynamics is accomplished using the Langevin Equation for Protein Dynamics (LE4PD); this equation decomposes the dynamics of a protein, modeled through a molecular dynamics (MD) simulation, into dynamical pathways that explore mode-dependent free energy surfaces. Using as input to the theory a one-microsecond, atomistic MD simulation, we calculate the time scales of the slow, high-amplitude fluctuations by modeling the kinetics of barrier crossing in the two-dimensional free-energy surfaces using a Markov state model (MSM) approach. We find that the LE4PD predicts slow fluctuations in three biologically significant binding regions in ubiquitin: the C-terminal tail, the Lys11 loop, and the 50 s loop. The combination of the LE4PD modes with the MSM analysis can provide useful information on the role of fluctuations in the process of molecular recognition regulating the biological activity of ubiquitin, with the LE4PD modes describing the location and magnitude of high-amplitude conformational changes and the MSM giving the associated timescales.

Kinetics analysis of ubiquitin local fluctuations with Markov state modeling of the LE4PD normal modes.

Local fluctuations are important for protein binding and molecular recognition because they provide conformational states that can be trapped through a selection mechanism of binding. Thus, an accurate characterization of local fluctuations may be important for modeling the kinetic mechanism that leads to the biological activity of a protein. In this paper, we study the fluctuation dynamics of the regulatory protein ubiquitin and propose a novel theoretical approach to model its fluctuations. A coarse-grained, diffusive, mode-dependent description of fluctuations is accomplished using the Langevin Equation for Protein Dynamics (LE4PD). This equation decomposes the dynamics of a protein, simulated by molecular dynamics, into dynamical pathways that explore mode-dependent free energy surfaces. We calculate the time scales of the slow, high-amplitude fluctuations by modeling the kinetics of barrier crossing in the two-dimensional free energy surfaces using Markov state modeling. We find that the LE4PD predicts slow fluctuations in three important binding regions in ubiquitin: the C-terminal tail, the Lys11 loop, and the 50 s loop. These results suggest that the LE4PD can provide useful information on the role of fluctuations in the process of molecular recognition regulating the biological activity of ubiquitin.

Bulk Superconductivity and Role of Fluctuations in the Iron-Based Superconductor FeSe at High Pressures.

The iron-based superconductor FeSe offers a unique possibility to study the interplay of superconductivity with purely nematic as well magnetic-nematic order by pressure (p) tuning. By measuring specific heat under p up to 2.36GPa, we study the multiple phases in FeSe using a thermodynamic probe. We conclude that superconductivity is bulk across the entire p range and competes with magnetism. In addition, whenever magnetism is present, fluctuations exist over a wide temperature range above both the bulk superconducting and the magnetic transitions. Whereas the magnetic fluctuations are likely temporal, the superconducting fluctuations may be either temporal or spatial. These observations highlight similarities between FeSe and underdoped cuprate superconductors.

(307) The Role of Fluctuations in Pain Acceptance, Coping, and Catastrophizing in the Daily Lives of People with Chronic Pain and Spinal Cord Injury

The experience of chronic pain can be influenced by choice of coping skills, the presence of catastrophizing, and the degree of acceptance of chronic pain. Neither the independent contributions of coping, catastrophizing, and acceptance of the pain experience nor the relative variability of these factors on a day-to-day basis are well understood. Thus, this study aimed to examine the role of daily changes in pain acceptance, coping, and catastrophizing in the daily lives of people with chronic pain and spinal cord injury (SCI). We collected seven days of end-of-day diary assessments of pain acceptance, pain coping, and pain catastrophizing, and five additional criterion variables of interest – pain interference, social participation, depressive symptoms, and positive affect and well-being in 124 individuals. In multilevel random effects modeling (controlling for age, gender, mobility, and pain intensity), pain acceptance, coping, and catastrophizing were each independently associated with some, but not all, of the daily criterion variables. Both acceptance and catastrophizing demonstrated similarly robust and consistent associations with outcomes, whereas pain coping demonstrated weaker and less consistent relationships with outcomes. Days of higher than usual catastrophizing were related to same-day lower positive affect and well-being and higher pain interference and depressed mood. Days of high pain acceptance were associated with higher same-day social participation and lower pain interference and depressed mood. Interestingly, when people reported higher than usual pain coping, they also reported higher same-day depressed mood. The findings suggest that psychosocial interventions targeting both pain catastrophizing and pain acceptance may be beneficial in terms of pain, mood, and social outcomes for those with chronic pain. Individuals may engage in more behavioral coping strategies to manage pain when experiencing negative mood. Further research examining the complex dynamics of adaptive and maladaptive responses to pain in daily life is warranted.

Role of fluctuations in a thermal phase transition in a nucleus probed via the giant dipole resonance

We present an experimental investigation of thermal phase transition in atomic nuclei by measuring the $\ensuremath{\gamma}$ rays from the decay of the giant dipole resonance in $^{169}\mathrm{Tm}$ populated by using the reaction $^{4}\mathrm{He}+^{165}\mathrm{Ho}$. The systematic measurement confirms the prolate shape, similar to the ground-state value, till temperature $T=1.23$ MeV. Moreover, the present data, together with the previous experimental studies, point towards the persistence of prolate shape with deformation similar to that of the ground state till $T=1.5$ MeV. In addition, the emergence and evolution of thermal fluctuations observed directly in the experiment suggest that the sharp phase transition from prolate to near spherical at $T\ensuremath{\approx}1.7$ MeV will not be evident experimentally due to statistical fluctuations owing to the finite size of the nucleus.

Correlated response to selection for litter size environmental variability in rabbits’ resilience

Resilience is the ability of an animal to return soon to its initial productivity after facing diverse environmental challenges. This trait is directly related to animal welfare and it plays a key role in fluctuations of livestock productivity. A divergent selection experiment for environmental variance of litter size has been performed successfully in rabbits over ten generations. The objective of this study was to analyse resilience indicators of stress and disease in the divergent lines of this experiment. The high line showed a lower survival rate at birth than the low line (−4.1%). After correcting by litter size, the difference was −3.2%. Involuntary culling rate was higher in the high than in the low line (+12.4%). Before vaccination against viral haemorrhagic disease or myxomatosis, concentration of lymphocytes, C-reactive protein (CRP), complement C3, serum bilirubin, triglycerides and cholesterol were higher in the high line than in the low line (difference between lines +4.5%, +5.6 µg/ml, +4.6 mg/ml, +7.9 mmol/l, +0.3 mmol/l and +0.4 mmol/l). Immunological and biochemical responses to the two vaccines were similar. After vaccination, the percentage of lymphocytes and CRP concentration were higher in the low line than in the high one (difference between lines +4.0% and +13.1 µg/ml). The low line also showed a higher increment in bilirubin and triglycerides than the high line (+14.2 v. +8.7 mmol/l for bilirubin and +0.11 v. +0.01 mmol/l for triglycerides); these results would agree with the protective role of bilirubin and triglycerides against the larger inflammatory response found in this line. In relation to stress, the high line had higher basal concentration of cortisol than the low line (+0.2ng/ml); the difference between lines increased more than threefold after the injection of ACTH 1 to 24, the increase being greater in the high line (+0.9 ng/ml) than in the low line (+0.4 ng/ml). Selection for divergent environmental variability of litter size leads to dams with different culling rate for reproductive causes and different kits’ neonatal survival. These associations suggest that the observed fitness differences are related to differences in the inflammatory response and the corticotrope response to stress, which are two important components of physiological adaptation to environmental aggressions.

Ion Dynamics and the Shock Profile of a Low‐Mach Number Shock

AbstractThe directly measured magnetic field fluctuates even at low‐Mach number shocks. Separation of the essential shock profile from features superimposed onto it is one of the basic problems of shock physics. The essential structure is one which affects the ion motion and is shaped by the produced ion distributions: the macroscopic fields which are built self‐consistently and together with the ion dynamics. The advanced test particle analysis is used to derive the magnetic profile which is consistent with the collisionless ion motion in the macroscopic fields of the shock front. The downstream side of the derived profile is in good agreement with the observed profile of a low‐Mach number interplanetary shock. The analysis allows us to improve the determination of the Mach number and provides an approximate value of the cross‐shock potential, which is not measured. It is shown that α‐particles cause nonperiodicity of the downstream magnetic oscillations. The performed hybrid simulations support the conclusion that the macroscopic fields of the shock play the main role in the formation of downstream ion distributions. The role of fluctuations is to enhance smoothing of the distributions and speed up relaxation to gyrotropy. The measured ion distributions well agree with the theoretically predicted onset of the anisotropy at the shock crossing and its persistence well into the downstream region.

A comparison of dynamic mean field theory and grand canonical molecular dynamics for the dynamics of pore filling and capillary condensation of fluids in mesopores.

We use results from grand canonical molecular dynamics (GCMD) to test the predictions from dynamic mean field theory (DMFT) for the pore filling and capillary condensation mechanisms of a fluid confined in slit shaped mesopores. The theory predicts that capillary condensation occurs by a nucleation process in which a liquid bridge forms between the two walls, and the pore is filled via the growth of this bridge. For longer pores, multiple bridging is seen. These mechanisms are confirmed by the molecular dynamics simulations. The primary difference between the theory and simulations lies in the role of fluctuations. DMFT predicts a single nucleation time and location, while in GCMD (and in nature) a distribution of nucleation times and locations is seen.

The role of fluctuations in artificial intelligence from Zadeh’s fuzzy sets point of view

Abstract It has been analyzed a decision-making in fuzzy environment. Here the system under control is the control-related system in the human or machine brain. Fluctuations of neuron electrical signals as fuzzy environment are represented the white noise. In this case the stochastic integral is being defined not only by Ito, Stratonovich, Klimantovich but spectrum of definitions. This spectrum can be considered as set of alternatives at a decision-making process.