Contribution Of Fluctuations Research Articles

Anomalous hardening of two-component disordered crystals

The nature of increasing the strength of disordered two-component solid solutions in comparison with materials consisting of atoms of one component is studied. For this purpose, the contribution of extreme fluctuations in the distribution of solution atoms, which create obstacles for the movement of dislocation kinks, is calculated. It is shown that a slow - power - decrease in the probability of large delays on such obstacles leads to anomalous kinetics of kinks. It is accompanied by a slowdown in the movement of dislocations. This may be the reason for the hardening of the material.

Wideband ratiometric measurement of tonic and phasic dopamine release in the striatum.

Reward learning, cognition, and motivation are supported by changes in neurotransmitter levels across multiple timescales. Current measurement technologies for various neuromodulators (such as dopamine and serotonin) do not bridge timescales of fluctuations, limiting the ability to define the behavioral significance, regulation, and relationship between fast (phasic) and slow (tonic) dynamics. To help resolve longstanding debates about the behavioral significance of dopamine across timescales, we developed a novel quantification strategy, augmenting extensively used carbon-fiber Fast Scan Cyclic Voltammetry (FSCV). We iteratively engineered the FSCV scan sequence to rapidly modify electrode sensitivity within a sampling window and applied ratiometric analysis for wideband dopamine measurement. This allowed us to selectively eliminate artifacts unrelated to electrochemical detection (i.e., baseline drift), overcoming previous limitations that precluded wideband dopamine detection from milliseconds to hours. We extensively characterize this approach in vitro , validate performance in vivo with simultaneous microdialysis, and deploy this technique to measure wideband dopamine changes across striatal regions under pharmacological, optogenetic, and behavioral manipulations. We demonstrate that our approach can extend to additional analytes, including serotonin and pH, providing a robust platform to assess the contributions of multi-timescale neuromodulator fluctuations to cognition, learning, and motivation.

Lifelong longitudinal assessment of the contribution of multi-fractal fluctuations to heart rate and heart rate variability in aging mice: role of the sinoatrial node and autonomic nervous system.

Aging is a major risk factor for sinoatrial node (SAN) dysfunction, which can impair heart rate (HR) control and heart rate variability (HRV). HR and HRV are determined by intrinsic SAN function and its regulation by the autonomic nervous system (ANS). The purpose of this study wasto use multi-scale multi-fractal detrended fluctuation analysis (MSMFDFA; a complexity-based approach to analyze multi-fractal dynamics) to longitudinally assess changes in multi-fractal HRV properties and SAN function in ECG time series recorded repeatedly across the full adult lifespan in mice. ECGs were recorded in anesthetized mice in baseline conditions and after autonomic nervous system blockade every three months beginning at 6months of age until the end of life. MSMFDFA was used to assess HRV and SAN function every three months between 6 and 27months of age. Intrinsic HR (i.e. HR during ANS blockade) remained relatively stable until 15months of age, and then progressively declined until study endpoint at 27months of age. MSMFDFA revealed sudden and rapid changes in multi-fractal properties of the ECG RR interval time series in aging mice. In particular, multi-fractal spectrum width (MFSW, a measure of multi-fractality) was relatively stable between 6months and 15months of age and then progressively increased at 27months of age. These changes in MFSW were evident in baseline conditions and during ANS blockade. Thus,intrinsic SAN function declines progressively during aging and is manifested by age-associated changes in multi-fractal HRV across the lifespan in mice, which can be accurately quantified by MSMFDFA.

Evolution of superconductivity in twisted graphene multilayers

The group of moiré graphene superconductors keeps growing, and by now it contains twisted graphene multilayers as well as untwisted stacks. We analyze here the contribution of long-range charge fluctuations in the superconductivity of twisted double bilayers and helical trilayers, and compare the results to twisted bilayer graphene. A diagrammatic approach which depends on a few, well-known parameters is used. We find that the critical temperature and the order parameter differ significantly between twisted double bilayers and helical trilayers on one hand, and twisted bilayer graphene on the other. This trend, consistent with experiments, can be associated with the role played by moiré Umklapp processes in the different systems.

Impact of H[formula omitted]-enrichment on the response of a partially premixed CH[formula omitted]–air flame to velocity and equivalence ratio fluctuations

The dynamics of hydrogen-enriched partially premixed methane–air flames are investigated, focusing on the frequency response to velocity and equivalence ratio fluctuations. Large-eddy simulations (LES) with conjugate heat transfer are performed on the partially premixed PRECCINSTA combustor for various methane–hydrogen mixtures, maintaining a constant thermal power and global equivalence ratio of 10 kW and 0.8, respectively. To reduce the computational cost of the LES, a three-step global mechanism is calibrated for each hydrogen-enriched partially premixed flame. The accuracy of the LES is assessed against experimental data, showing a good agreement with the mean velocity field and shape of the swirl-stabilized flame. The multiple-input–single-output structure for the flame transfer function is applied to separate the individual contributions of velocity and equivalence ratio fluctuations to the overall heat release rate oscillation in the partially premixed flames. System identification with broadband forcing is used to compute the various flame transfer functions. Hydrogen enrichment significantly influences the flame response to equivalence ratio fluctuations, explained by the respective impact on the response of the heat of reaction, the flame speed, and the flame surface area to equivalence ratio fluctuations. The interaction between velocity and equivalence ratio fluctuations is further characterized by the mixing transfer function, which describes the equivalence ratio fluctuations reaching the flame. The higher mass diffusivity of hydrogen results in lower equivalence ratio fluctuations reaching the flame as the frequency increases, attenuating the pronounced effect of hydrogen on the flame sensitivity to equivalence ratio fluctuations. This study contributes to the understanding of the impact of hydrogen enrichment on the thermoacoustic response of partially premixed flames.

Poissonian Cellular Potts Models Reveal Nonequilibrium Kinetics of Cell Sorting

Cellular Potts models are broadly applied across developmental biology and cancer research. We overcome limitations of the traditional approach, which reinterprets a modified Metropolis sampling as dynamics, by introducing a physical timescale through Poissonian kinetics and by applying principles of stochastic thermodynamics to separate thermal and relaxation effects from athermal noise and nonconservative forces. Our method accurately describes cell-sorting dynamics in mouse-embryo development and identifies the distinct contributions of nonequilibrium processes, e.g., cell growth and active fluctuations. Published by the American Physical Society 2024

A novel battery abnormality diagnosis method using multi-scale normalized coefficient of variation in real-world vehicles

Accurate and efficient diagnosis of battery voltage abnormality is crucial for the safe operation of electric vehicles. This paper proposes an innovative battery voltage abnormality diagnosis method based on a normalized coefficient of variation in real-world electric vehicles. Vehicle and laboratory data are collected and analyzed, with joint preprocessing to improve data quality, and battery voltages are log-transformed to improve the contribution of anomalous voltage fluctuations. The normalized coefficient of variation is proposed to detect the fluctuation inconsistency of cell voltage, and the risk coefficient rule is formulated by Z-score and normalization. Furthermore, the validity and robustness are verified by laboratory and real-world battery faults. The results demonstrate that the optimal slide step and calculation window for real-world under-voltage fault are 10 and 40, and those for laboratory lithium plating and real-world thermal runaway are both 10 and 50, respectively. More importantly, this study introduces a battery abnormality diagnosis strategy based on the vehicle T-box, anticipated to be widely implemented to ensure the safety of real-vehicle operations. This method not only enhances the accuracy and efficiency of detecting electric vehicle battery abnormalities, but also offers a practical solution to prevent battery related faults.

Mid‐Air Collisions Control the Wavelength of Aeolian Sand Ripples

AbstractThe wavelength of aeolian sand ripples increases with wind velocity, but the cause for this increase remained unclear until now. Using numerical simulations, we find that the relationship between the wind strength and the initial wavelength disappears without mid‐air collisions, which means that mid‐air collisions crucially contribute to the initial wavelength of ripples. As wind strength increases, the average hop length of non‐colliding particles decreases. Affected by the bed surface topography and the non‐uniform mid‐air colliding probability along the wavy surface, non‐colliding particles cause a surface modulated erosion/deposition flux. The first order contribution of the flux fluctuation destabilizes the original bed surface and has a wind‐dependent phase shift with respect to the surface profile. This phase shift leads to an initial wavelength that increases with wind velocity. Based on these findings we derive the scaling law for the initial wavelength of aeolian sand ripples, which agrees well with experimental results. A weak non‐linear relationship between ripple wavelength and wind velocity has been found, especially for large wind strengths.

Quantum criticality features in the Co,Fe doped MnSi

An universal line revealing an independence of spin fluctuation contributions to the heat capacity on impurity content and its nature is discovered in the helical phase of Mn(Co,Fe)Si. This situation declares an invariance of the heat capacity of spin subsystem under doping, which probably arises as a result of relative stiffness of the helical spin structure in respect to the impurity spins. On the other hand the situation drastically changes at the helical fluctuation region when no long range spin order exists. At low temperatures the spin fluctuation contributions to the heat capacity for a whole set of compositions of Mn(Co,Fe)Si are described by a single power expression with an exponent less then unity, which implies divergence of the ratio Cp/T at T→0. The current data are revealing that a singular quantum critical point does not exist in the system under study. In its place, one can see some sort of a quantum critical cloud covering a significant range of dopant concentrations.

Particle Image Velocimetry Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade

Abstract Particle image velocimetry (PIV) measurements in the blade-to-blade (B2B) plane and cascade outlet plane (COP) of a high-speed low-pressure turbine (LPT) cascade were performed at engine-representative outlet Mach number (0.70–0.95), and Reynolds number (70–120 k) under steady flow conditions. The freestream turbulence characteristics were imposed by means of a passive turbulence grid. The PIV results on the B2B plane were compared against five-hole probe (5HP) and Reynolds-averaged Navier–Stokes (RANS) computations to assess the validity of measurement and simulation techniques in the engine-relevant LPT cascade flows. The PIV captured the wake depth and width measured by the 5HP whereas the RANS displayed an overprediction of the wake Mach number deficit. The 5HP was found to impose sinewave fluctuations of the measured flow angle downstream, around three times higher than PIV. Additionally, PIV estimated turbulence intensity (TI) in the cascade, showing TI decay along a streamline. At the highest Mach number, a peak TI occurred past a shock wave. Measurements of the outlet flow field highlighted a high TI in the secondary flow region whereas high degree of anisotropy (DA) was registered in the boundary of the secondary flow and freestream regions. The contribution of the streamwise fluctuation component was found to be less than the crosswise and radial components in the freestream region. Increasing the cascade outlet Mach number, the contribution of streamwise fluctuation to the DA was observed to decrease.

Fluctuations, bias, variance and ensemble of learners: exact asymptotics for convex losses in high-dimension *

From the sampling of data to the initialisation of parameters, randomness is ubiquitous in modern Machine Learning practice. Understanding the statistical fluctuations engendered by the different sources of randomness in prediction is therefore key to understanding robust generalisation. In this manuscript we develop a quantitative and rigorous theory for the study of fluctuations in an ensemble of generalised linear models trained on different, but correlated, features in high-dimensions. In particular, we provide a complete description of the asymptotic joint distribution of the empirical risk minimiser for generic convex loss and regularisation in the high-dimensional limit. Our result encompasses a rich set of classification and regression tasks, such as the lazy regime of overparametrised neural networks, or equivalently the random features approximation of kernels. While allowing to study directly the mitigating effect of ensembling (or bagging) on the bias-variance decomposition of the test error, our analysis also helps disentangle the contribution of statistical fluctuations, and the singular role played by the interpolation threshold that are at the roots of the ‘double-descent’ phenomenon.

Analog model for Euclidean wormholes effects

Using results of statistical field theory for systems with an anisotropic disorder, we present an analog model for Euclidean wormholes and topological fluctuation effects in a Riemannian space [Formula: see text]. The contribution of wormholes and topological fluctuations to the Euclidean gravitational functional integral is modeled by quenched randomness defined in the [Formula: see text] manifold. We obtain a disorder-averaged free energy by taking the average over all the realizations of the random fields. In the scenario of topology fluctuation, there appears a superposition of infinite branes that contribute to the physical quantities. All topology fluctuations can be understood as two distinct kinds of Euclidean wormholes: wormholes confined to one brane, and wormholes connecting different branes.

Interaction potential of two nonidentical ground-state atoms

We study the interaction potential of two nonidentical ground-state atoms coupled to a scalar field in a vacuum by separately calculating the contributions of vacuum fluctuations and those of the radiation reaction of the atoms. Both cases of atoms in a free space and in parallel or vertical alignment to a reflecting boundary are considered. For the former case, we find that the leading-order interaction potential in the region λ A ≪ L ≪ λ B exhibits the same separation-dependence as that in the region L ≪ λ A ≪ λ B , where L, λ A and λ B are respectively the interatomic separation and the transition wavelengths of two atoms with λ A ≪ λ B . For the latter case, we find that boundary-induced modifications are very remarkable when L ≫ z, with z characterizing the separation between the two-atom system and the boundary. Particularly, when L further satisfies L ≫ λ A and L ≫ λ B , the interaction potential in the parallel- and the vertical-alignment cases respectively scales as z 4 L −7 and z 2 L −5, the L-dependence of which is one order higher than those of two atoms in regions where L ≫ z and meanwhile L ≪ λ A or/and L ≪ λ B . Our results suggest that retardation for the interaction potential of two nonidentical atoms with remarkably distinctive transition frequencies happens only when the interatomic separation is much greater than the transition wavelengths of both atoms.

Nature of striation in 21 cm channel Maps: velocity caustics

ABSTRACT The alignment of striated intensity structures in thin neutral hydrogen (H i) spectroscopic channels with Galactic magnetic fields has been observed. However, the origin and nature of these striations are still debatable. Some studies suggest that the striations result solely from real cold-density filaments without considering the role of turbulent velocity fields in shaping the channel’s intensity distribution. To determine the relative contribution of density and velocity in forming the striations in channel maps, we analyse synthetic observations of channel maps obtained from realistic magnetized multiphase H i simulations with thermal broadening included. We vary the thickness of the channel maps and apply the Velocity Decomposition Algorithm to separate the velocity and density contributions. In parallel, we analyse GALFA-H i observations and compare the results. Our analysis shows that the thin channels are dominated by velocity contribution, and velocity caustics mainly generate the H i striations. We show that velocity caustics can cause a correlation between unsharp-masked H i structures and far-infrared emission. We demonstrate that the linear H i fibers revealed by the Rolling Hough Transform (RHT) in thin velocity channels originate from velocity caustics. As the thickness of channel maps increases, the relative contribution of density fluctuations in channel maps increases and more RHT-detected fibers tend to be perpendicular to the magnetic field. Conversely, the alignment with the magnetic field is the most prominent in thin channels. We conclude that similar to the velocity channel gradients (VChGs) approach, RHT traces magnetic fields through the analysis of velocity caustics in thin channel maps.

The \(120^{0}\) ordered phase of the spin-1 \(J_{1} - J_{2}\) antiferromagnetic Heisenbeberg model on a triangular lattice

We study the effect of quantum and thermal fluctuations on the excitation energy spectrum and sublattice magnetization of the 1200 ordered phase of the spin-1 antiferromagnetic Heisenberg model on a triangular lattice with nearest J1 and next-nearest-neighbor J2 exchange interactions. The auxiliary fermionic representation of the spin operators within a functional integral formalism with an imaginary Lagrange multiplier is employed to retain an exact constraint of single particle occupancy. Representing the classical ground state by Luttinger-Tisza ordering vector Q one may consider the fluctuation contributions to the free energy of the system in the entire range of the coupling parameters. We derived the magnon spectrum in one-loop approximation and the magnetization taking into account thermal fluctuations. The obtained results are compared with the result of the linear spin-wave approximation and experimental findings on compound NiGa2S4.

Evaluation of the Feynman Propagator by Means of the Quantum Hamilton-Jacobi Equation

It is shown that the complex phase of the Feynman propagator is a solution of the quantum Hamilton–Jacobi equation, namely, it is the quantum Hamilton's principal function (or quantum action). Therefore, the Feynman propagator can be computed either by means of the path integration, or by the way of the Hamilton–Jacobi equation. This is analogous to what happens in classical mechanics, where the Hamilton's principal function can be computed either by integrating the Lagrangian along the extremal paths, or as a solution of partial differential equation, namely the classical Hamilton–Jacobi equation. If the path is decomposed in the classical one and quantum fluctuations, the contribution of these quantum fluctuations satisfies a non-linear partial differential equation, whose coefficients depend on the classical action. When the contribution of the quantum fluctuations depend only on the time, it can be computed by means of a simple integration. The final results for the propagators in this case are equal to the Van Vleck–Pauli–Morette expressions, even though the two derivations are quite different.Quanta 2023; 12: 22–26.

Measurements of the unsteady lift force on a 5:1 rectangular cylinder based on active-passive hybrid wind tunnel tests

Active-passive hybrid wind tunnel test method was conducted to investigate the unsteady lift force on a 5:1 rectangular cylinder. Active and passive control wind tunnels are adopted to generate streamwise and grid-generated turbulences. Thus, a hybrid theoretical framework was proposed to obtain the u- and w-related aerodynamic admittances (u- and w-AAF) and investigate the effects of streamwise and vertical fluctuating winds on the unsteady behaviour of the lift force on a 5:1 rectangular cylinder at AoAs. The findings revealed that vertical wind fluctuations in the low-frequency domain dominated the lift force at low frequencies. In contrast, the streamwise component of turbulence substantially affects the energy distribution of the lift force in the high-frequency region. Notably, the contribution of streamwise wind fluctuations to unsteady lift becomes more pronounced as the AoA increases within a given range. When the AoA is further increased, the impact returns predominantly to the vertical wind fluctuations.

Weak itinerant magnetic behaviour in Al substituted Ni 92 Cr 8 alloys

In the present work we report low temperature magnetic properties of Ni92−xAlxCr8 alloys. It is found that the Curie temperature and spontaneous magnetization (MSP) get suppressed around xC ≈ 7. From the analysis of the temperature and field dependent magnetization data we have obtained high value of Rhodes–Wohlfarth ratio, which indicates the weak itinerant ferromagnetic behavior for samples below xC. This is further supported by analysing the temperature variation of MSP in the framework of spin fluctuations, SCR theory. Furthermore, the Ginzburg-Landau formalism-based on spin fluctuation theory revealed that the contribution of spin fluctuations at low temperature increases as we approach xC.

General framework for interatomic interaction energy of two ground-state atoms in a thermal bath

We give a general derivation of the fourth-order DDC formalism (a formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji) for calculating the interaction energy between two ground-state multilevel atoms which are coupled to electromagnetic fields in a thermal bath at temperature $T$. Both the contributions of the thermal field fluctuations and the radiation reaction of atoms are separately identified. As an application of the formalism, we revisit the interaction energy of two static ground-state two-level atoms in a free space and discover new behaviors such as the $\ensuremath{\sim}T{L}^{\ensuremath{-}2}$ behavior of the van der Waals interaction energy in the region where ${\ensuremath{\lambda}}^{3/4}{T}^{\ensuremath{-}1/4}\ensuremath{\ll}L\ensuremath{\ll}\ensuremath{\lambda}$, with $\ensuremath{\lambda}$ the transition wavelength of the atoms and $L$ the interatomic separation, and an oscillatory behavior of the Casimir-Polder interaction energy as $L$ varies which is superimposed on the monotonic $\ensuremath{\sim}T{L}^{\ensuremath{-}6}$ dependence when $L\ensuremath{\gg}\ensuremath{\lambda}\ensuremath{\gg}{T}^{\ensuremath{-}1}$.

Quantum vacuum fluctuations in inorganic compound CdSe

In the present work, we study the quantum vacuum fluctuations at finite temperature in the propagation of light in nonlinear optical media. We present nonlinear materials, that have the second-order electrical susceptibility tensor, and the fluctuating effective refractive index caused by fluctuating vacuum electric fields. Likewise, we study the fluctuations of the vacuum, which led to the contributions of thermal and mixed fluctuations being associated with a faithful test function to perform the calculations, in contrast to the Lorentzian distribution. We show the contribution of thermal and mixed fluctuations to time-of-flight fluctuations compared to the contributions of vacuum fluctuations. The result reveals a numerical estimate performed on cadmium selenide (CdSe) suggesting that the effects of fluctuations can cause uncertainty in time of flight due to quantum vacuum fluctuations in terms of thermal and mixed fluctuations.