Parameter Region Research Articles

Network mechanisms underlying the regional diversity of variance and time scales of the brain's spontaneous activity fluctuations.

The brain's activity fluctuations have different temporal scales across the brain regions, with associative regions displaying slower timescales than sensory areas. This so-called hierarchy of timescales has been shown to correlate with both structural brain connectivity and intrinsic regional properties. Here, using publicly available human resting-state fMRI and dMRI data it was found that, while more structurally connected brain regions presented activity fluctuations with longer timescales, their activity fluctuations presented lower variance. The opposite relationships between the structural connectivity and the variance and temporal scales of resting-state fluctuations, respectively, were not trivially explained by simple network propagation principles. To understand these structure-function relationships, two commonly used whole-brain models were studied, namely the Hopf and Wilson-Cowan models. These models use the brain's connectome to coupled local nodes (representing brain regions) displaying noise-driven oscillations. The models show that the variance and temporal scales of activity fluctuations can oppositely relate to connectivity within specific model's parameter regions, even when all nodes have the same intrinsic dynamics -but also when intrinsic dynamics are constrained by the myelinization-related macroscopic gradient. These results show that, setting aside intrinsic regional differences, connectivity and network state are sufficient to explain the regional differences in fluctuations' scales. State-dependence supports the vision that structure-function relationships can serve as biomarkers of altered brain states. Finally, the results indicate that the hierarchies of timescales and variances reflect a balance between stability and responsivity, with greater and faster responsiveness at the network periphery, while the network core ensures overall system robustness.Significance Statement Brain regions exhibit activity fluctuations at different temporal scales, with associative areas displaying slower timescales than sensory areas. This hierarchical organization is shaped by both large-scale connectivity and local properties. The present study demonstrates that the variance of fluctuations is also hierarchically organized but, in contrast to timescales, it decreases as a function of structural connectivity. Whole-brain models show that the hierarchies of timescales and variances jointly emerge within specific parameter regions, indicating a state-dependence that could serve as a biomarker for brain states and disorders. Furthermore, these hierarchies link to the responsivity of different network parts, with greater and faster responsiveness at the network periphery and more stable dynamics at the core, achieving a balance between stability and responsiveness.

Free wave propagation in pretensioned 2D textile metamaterials

Abstract A parametric lattice model is formulated to describe the dispersion properties of harmonic elastic waves propagating in two-dimensional textile metamaterials. Within a weak nonlinear regime, the free undamped motion of the textile metamaterial, starting from a spatially periodic prestressed configuration, is governed by nonlinear differential difference equations, where nonlinearities arise from the elastic contact between plain woven yarns. Within the linear field, the linear dispersion properties characterizing the regime of small oscillation amplitudes are obtained, by applying the Bloch's theorem. Parametric analyses are carried out to study the influence of the mechanical parameters on wavefrequencies, waveforms and group velocities. As major outcome, the dispersion spectrum is found to possess two distinct passbands, covering the low- and the high-frequency ranges, respectively, while a complete mid-frequency bandgap exists for large parameter regions. Within the nonlinear field, the nonlinear wavefrequencies and the multi-harmonic non-resonant response in the time domain are described, by means of perturbation techniques. As interesting finding, the free wave are shown to propagate with a systematic softening behavior. The wave polarization exalts the nonlinear effects in the high-frequency passband.

Normal Form Formulae of Turing–Turing Bifurcation for Partial Functional Differential Equations With Nonlinear Diffusion

ABSTRACTFor most systems, the appearance of Turing bifurcation means that it is possible to excite Turing–Turing bifurcation, thus inducing superimposed spatial patterns, multistable spatial patterns co‐existing, and others.It is undoubtedly of interest to qualitatively analyze the structures and stability of these spatially heterogeneous solutions generated by Turing–Turing bifurcation. Therefore, in this paper, with the aid of the center manifold theory and the normal form method, for general partial functional differential equations with nonlinear diffusion, the third‐order normal form is firstly derived. It is locally topologically equivalent to the primitive partial functional differential equations at the Turing–Turing bifurcation point. And then the explicit formulae for the coefficients in the normal form associated with three different spatial modes are presented. As an application, a predator–prey model with predator–taxis is considered. It is theoretically revealed that the system admits the coexistence of a pair of stable steady states with a single characteristic wavelength and the coexistence of four stable steady states with different single characteristic wavelengths. Further, the parameter regions in which these phenomena will arise are quantitatively given. It is illustrated that the self‐diffusion of prey and predator–taxis complement each other to promote the formation for the spatially homogeneous distributions of populations.

Restricting sterile neutrinos by neutrinoless double beta decay

The bounds on parameters of the eV and higher scale Majorana sterile neutrinos from the 0νββ decay have been refined and updated. We present a simple and compact analytic expression for the bound in the Δm412−sin22θ14 plane, which includes all relevant parameters. Dependencies of the bound on unknown CP phases and the type of mass spectrum of light neutrinos (mass ordering and level of degeneracy) are studied in detail. We have computed the bounds using the latest and most stringent data from KamLAND-Zen. The projected constraints from future experiments are estimated. The obtained bounds are confronted with positive indications of the presence of sterile neutrinos as well as with the other existing bounds. The 0νββ decay results exclude the regions of parameters implied by BEST and Neutrino-4, and the regions indicated by LSND and MiniBooNE are in conflict with 0νββ decay results combined with νμ-disappearance bounds. Published by the American Physical Society 2025

Searching for heavy neutral leptons coupled to axion-like particles at the LHC far detectors and SHiP

In hidden-sector models, axion-like particles (ALPs) can couple to heavy neutral leptons (HNLs), leading to rich phenomenologies. We study ALPs produced from D- and B-meson decays via quark-flavor-violating couplings, and decaying exclusively into a pair of HNLs which mix with active neutrinos. The ALP can be either short- or long-lived, depending on the masses of the ALP and the HNL, as well as the corresponding coupling strength. Such GeV-scale HNLs are necessarily long-lived given the current bounds on their mixing parameters. We assess the sensitivities of the LHC far detectors and SHiP, to the long-lived HNLs in such theoretical scenarios. We find that for currently allowed values of the ALP couplings, most of these experiments can probe the active-sterile-neutrino mixing parameters multiple orders of magnitude beyond the present bounds, covering large parameter region targeted with the type-I seesaw mechanism. In addition, our results show that compared to the case of a promptly decaying ALP, assuming an ALP of longer lifetimes weakens the sensitivities of the considered experiments to the long-lived HNLs.

Constraining Dark Matter Models with a Light Mediator from CDEX-10 Experiment at China Jinping Underground Laboratory

Abstract We search for nuclear recoil signals of dark matter models with a light mediator using data taken
from a p-type point-contact germanium detector of the CDEX-10 experiment at the China Jinping
Underground Laboratory. The 90% confidence level upper limits on the DM-nucleon interaction
cross section from 205.4 kg-day exposure data are derived, excluding new parameter space in 2∼3
GeV DM mass when the mediator mass is comparable to or lighter than the typical momentum
transfer. We further interpret our results to constrain a specific self-interacting dark matter model
with a light mediator coupling to the photon through kinetic mixing, and set experimental limits
on the model parameter region favored by astrophysical observations.

Neutrinoless double beta decay from scalar leptoquarks: interplay with neutrino mass and flavor physics

We perform a comprehensive analysis of neutrinoless double beta (0νββ) decay and its interplay with low-energy flavor observables in a radiative neutrino mass model with scalar leptoquarks S1(3¯, 1, 1/3) and R~2321/6. We carve out the parameter region consistent with constraints from neutrino mass and mixing, collider searches, as well as measurements of several flavor observables, such as muon and electron anomalous magnetic moments, charged lepton flavor violation and rare (semi)leptonic kaon and B-meson decays, including the recent anomalies in RD∗ and B→Kνν¯ observables. We perform a global analysis to all the existing constraints and show the (anti)correlations between all relevant Yukawa couplings satisfying these restrictions. We find that the most stringent constraint on the parameter space comes from μ → e conversion in nuclei and K+→π+νν¯ decay. We also point out a tension between the muon and electron (g – 2) anomalies in this context. Taking benchmark values from the combined allowed regions, we study the implications for 0νββ decay including both the canonical light neutrino and the leptoquark contributions. We find that for normal ordering of neutrino masses, the leptoquark contribution removes the cancellation region that occurs for the canonical case. The effective mass in presence of leptoquarks can lie in the desert region between the standard normal and inverted ordering cases, and this can be probed in future ton-scale experiments like LEGEND-1000 and nEXO.

Enhancing Hydrological Modeling of Ungauged Watersheds through Machine Learning and Physical Similarity-based Regionalization of Calibration Parameters

Enhancing Hydrological Modeling of Ungauged Watersheds through Machine Learning and Physical Similarity-based Regionalization of Calibration Parameters

NUMERICAL STUDY OF TRANSITION TO THERMOACOUSTIC INSTABILITY IN A RIJKE TUBE: IMPACT OF ENERGY INPUT AND TRIGGERING PARAMETERS

In the present study, a horizontal Rijke tube is used to investigate the thermoacoustic instability. Twodimensional, unsteady Reynolds-averaged numerical simulations are performed on the Rijke tube. To trigger the instability, an oscillating pressure signal with a small time scale is applied at the inlet of the Rijke tube. The effects of amplitude (1-30 Pa), frequency (100-250 Hz), and impulse time (10-20 ms) of the triggering pressure on the thermoacoustic instability are investigated. The heater is used as a heating source to investigate the impact of heater temperature on thermoacoustic instability. The results demonstrate that the temperature variation (800-5000 K) leads to concurrent variation in both amplitude (0-6500 Pa) and frequency (177-186 Hz) of oscillation. At heater temperature of 2000 K, beating-type instability is observed, with the main and beating cycle frequency of 183.64 Hz and 0.33 Hz, respectively. In a Rijke tube viable to thermoacoustic instability, the amplitude and frequency of limit cycle pressure waves do not depend on the triggering pressure. An increase in the amplitude of triggering pressure amplifies the amplitude of nonlinear oscillations and decreases the time taken to attain limit cycle oscillation. The present study successfully identifies the tipping surface separating the stable and unstable region of triggering parameters in a Rijke tube.

Resonant or asymmetric: the status of sub-GeV dark matter

Sub-GeV dark matter (DM) particles produced via thermal freeze-out evade many of the strong constraints on heavier DM candidates but at the same time face a multitude of new constraints from laboratory experiments, astrophysical observations and cosmological data. In this work we combine all of these constraints in order to perform frequentist and Bayesian global analyses of fermionic and scalar sub-GeV DM coupled to a dark photon with kinetic mixing. For fermionic DM, we find viable parameter regions close to the dark photon resonance, which expand significantly when including a particle-antiparticle asymmetry. For scalar DM, the velocity-dependent annihilation cross section evades the strongest constraints even in the symmetric case. Using Bayesian model comparison, we show that both asymmetric fermionic DM and symmetric scalar DM are preferred over symmetric fermionic DM due to the reduced fine-tuning penalty. Finally, we explore the discovery prospects of near-future experiments both in the full parameter space and for specific benchmark points.We find that the most commonly used benchmark scenarios are already in tension with existing constraints and propose a new benchmark point that can be targeted with future searches.

Constraints on axion-like particles from the gamma-ray observation of the Galactic Center

High energy photons originating from the Galactic Center (GC) region have the potential to undergo significant photon-axion-like particle (ALP) oscillation effects, primarily induced by the presence of intense magnetic fields in this region. Observations conducted by imaging atmospheric Cherenkov telescopes have detected very high energy gamma-rays originating from a point source known as HESS J1745-290, situated in close proximity to the GC. This source is conjectured to be associated with the supermassive black hole Sagittarius A*. The GC region contains diverse structures, including molecular clouds and non-thermal filaments, which collectively contribute to the intricate magnetic field configurations in this region. By utilizing a magnetic field model specific in the GC region, we explore the phenomenon of photon-ALP oscillations in the gamma-ray spectrum of HESS J1745-290. Our analysis does not reveal any discernible signature of photon-ALP oscillations, yielding significant constraints that serve as a complement to gamma-ray observations of extragalactic sources across a broad parameter region. The uncertainties arising from the outer Galactic magnetic field models have minor impacts on our results, except for ALP masses around 10-7 eV, as the dominant influence originates from the intense magnetic field strength in the inner GC region.

Revealing formation mechanism of end of process depression in laser powder bed fusion by multi-physics meso-scale simulation

ABSTRACT Unintended end-of-process depression (EOPD) commonly occurs in laser powder bed fusion (LPBF), leading to poor surface quality and lower fatigue strength, especially for many implants. In this study, a high-fidelity multi-physics meso-scale simulation model is developed to uncover the forming mechanism of this defect. A defect-process map of the EOPD phenomenon is obtained using this simulation model. It is found that the EOPD formation mechanisms are different under distinct regions of process parameters. At low scanning speeds in keyhole mode, the long-lasting recoil pressure and the large temperature gradient easily induce EOPD. While at high scanning speeds in keyhole mode, the shallow molten pool morphology and the large solidification rate allow the keyhole to evolve into an EOPD quickly. Nevertheless, in the conduction mode, the Marangoni effects along with a faster solidification rate induce EOPD. Finally, a ‘step’ variable power strategy is proposed to optimise the EOPD defects for the case with high volumetric energy density at low scanning speeds. This work provides a profound understanding and valuable insights into the quality control of LPBF fabrication.

Multistability and organization of chaos and quasiperiodicity in a memristor-based Shimizu-Morioka oscillator under two-frequency excitation

In this paper we investigate the organization of chaos and quasiperiodicity in a parameter plane of a continuous-time three-dimensional nonautonomous dynamical system. More specifically, we investigate a memristor-based Shimizu-Morioka oscillator, where the external excitation is represented by the sum of two different sinusoidal functions with angular frequencies ω1 and ω2. Through a scan carried out in the (ω1, ω2) parameter plane, with the dynamical behavior of each point in the phase-space being characterized by the Lyapunov exponents spectrum, we show that this system presents chaos and quasiperiodicity regions, without presenting, however, periodicity regions. Parameter regions for which the multistability phenomenon was detected, also are observed. Basins of attraction of coexisting chaotic and quasiperiodic attractors, as well as the attractors themselves, are reported.

On the motion of a dynamically symmetric satellite in one case of multiple parametric resonance

The paper studies the motions of a dynamically symmetric satellite (rigid body) relative to the center of mass in the central Newtonian gravitational field on a weakly elliptical orbit in the neighborhood of its stationary rotation (cylindrical precession). We consider the values of the parameters for which, in the limiting case of a circular orbit, one of the frequencies of small linear oscillations is equal to unity and the other is equal to zero, and the rank of the coefficient matrix of the linearized equations of the perturbed motion is equal to two, as well as a small neighborhood of this resonant point in the three-dimensional space of parameters. The resonant periodic motions of the satellite, analytical in fractional powers of a small parameter (the eccentricity of the orbit of the satellite's center of mass), are constructed. A rigorous nonlinear analysis of their stability is carried out. The methods of KAM theory are used to describe two- and three-frequency conditionally periodic motions of a satellite, with frequencies of different orders in a small parameter. A number of general theoretical issues concerning the considered multiple parametric resonance in Hamiltonian systems with two degrees of freedom that are close to autonomous and periodic in time are discussed. Several qualitatively different variants of parametric resonance regions are constructed. It is shown that in the general case the nature of nonlinear resonant oscillations of the system is determined by the first approximation system in a small parameter.

Incorporating Spatial Information for Regionalization of Environmental Parameters in Machine Learning Models

AbstractMachine learning models have gained popularity for environmental variable predictions due to their capacity to capture complex relationships and automate learning. However, incorporating spatial information as covariates into these models remains a challenge, as they may struggle to recognize spatial structures or autocorrelation without explicit training. In this study, we address this challenge by integrating spatial information into a random forest model, enhancing nitrate concentration predictions in groundwater. Using a dataset from 1,550 well locations in Baden-Wuerttemberg, Germany, spanning 2016 through 2019, we consider various environmental covariates including climate data, topography, land cover, soil properties, and hydrology. To incorporate spatial information, we employ eight techniques leveraging spatial coordinates (geographic coordinates, polynomial geographic coordinates, oblique geographic coordinates) or distances (Wendland transformed coordinates, Euclidean distance fields, Euclidean distance matrix, principal component analysis, eigenvector spatial filtering). Results are compared with a baseline model and a univariate ordinary kriging benchmark, evaluated through leave-one-out cross validation, various error metrics, and Moran’s I of residuals. Our findings highlight that integrating spatial information significantly enhances random forest model accuracy in predicting groundwater nitrate concentrations. Distance-based methods, like the Euclidean distance matrix, outperform coordinate-based approaches, albeit with higher computational requirements. Employing a dimension-reduced matrix strikes a balance between performance and accuracy. This study advances groundwater management and demonstrates the effectiveness of machine learning models in environmental studies.

Search for QCD axion dark matter with transmon qubits and quantum circuit

We propose a direct axion dark matter (DM) search using superconducting transmon quantum bits (qubits) as quantum sensors. With an external magnetic field applied, axion DM generates an oscillating electric field, which causes the excitation of the qubit. Such an excitation can be regarded as a signal of the axion DM. We provide a theoretical consideration of the excitation process of the qubits, taking into account the effects of the shielding cavity surrounding the qubits, and estimate the signal rate for the axion DM detection. We also discuss the enhancement of the DM signal by using cavity resonance and entangled quantum sensors realized by a quantum circuit. Combining these two effects, we can reach the parameter region suggested by QCD axion models. Published by the American Physical Society 2024

The axion is going dark

In this work we explore the effect of a non-Abelian dark sector gauge group that couples to the axion field. In particular, we analyze effects that arise if the dark sector gauge group mixes topologically with the Standard Model. This is achieved by gauging a subgroup of the global center 1-form symmetries which embeds non-trivially in both the visible as well as the dark sector gauge groups. Leaving the local dynamics unchanged, this effect modifies the quantization conditions for the topological couplings of the axion, which enter the estimate of a lower bound on the axion-photon coupling. In the presence of a dark sector this lower bound can be reduced significantly, which might open up interesting new parameter regions for axion physics. We further determine the allowed exotic matter representations in the presence of topological mixing with a dark sector, explore the generalized categorical symmetries of such axion theories, and comment on other model-independent phenomenological consequences.

Proving the absence of large one-loop corrections to the power spectrum of curvature perturbations in transient ultra-slow-roll inflation within the path-integral approach

We revisit one-loop corrections to the power spectrum of curvature perturbations ζ in an inflationary scenario containing a transient ultra-slow-roll (USR) period. In ref. [1], it was argued that one-loop corrections to the power spectrum of ζ can be larger than the tree-level one within the parameter region generating the seeds of primordial black holes during the USR epoch, which implies the breakdown of perturbation theory. We prove that this is not the case by using a master formula for one-loop corrections to the power spectrum obtained in ref. [2]. We derive the same formula within the path-integral formalism, which is simpler than the original derivation in [2]. To show the smallness of one-loop corrections, the consistency relations and the effective constancy of tree-level mode functions of ζ for super-Hubble modes play essential roles, with which the master formula gives a simple expression for one-loop corrections. For concreteness, we provide a reduced set of interactions including the leading-order one, while establishing the consistency relations in a self-consistent manner. We also show how the consistency relations of various operators hold explicitly, which plays a key role in proving the absence of large one-loop corrections.

Interval Estimation for the Two-Parameter Exponential Distribution Based on Upper Record Value Data Using Bayesian Approaches

Using upper record value data, we provide a credible interval estimate for the scale parameter of a two-parameter exponential distribution based on Bayesian methods. Additionally, we propose two Bayesian credible confidence regions for both parameters. In addition to interval estimations for the parameters, we propose a Bayesian prediction interval for a future upper record value. A simulation study is conducted to compare the performance of the proposed Bayesian credible interval, regions and prediction intervals with existing non-Bayesian approaches, focusing on coverage probabilities. The simulation results show that the Bayesian approaches achieve higher coverage probabilities than existing methods. Finally, we use an engineering example to demonstrate all the proposed Bayesian credible estimations for the exponential distribution based on upper record value data.

Influence of the homotopy stability perturbation on physical variations of non-local opto-electronic semiconductor materials

In the current work, we investigate a novel technique specialized in stability perturbation theory to analyze the primary variations such as thermal, carrier, elastic, and mechanical waves in photothermal theory. The interface of the non-local semiconductor material is utilized to study the stability analysis. The problem is established using a 1D opto-electronic-thermoelastic deformation in the context of the photo-thermoelasticity (PTE) framework. The Laplace transform method is used to convert the system from the time domain into the frequency domain, and the boundary conditions for the thermal, elastic, and plasma waves are applied to the interface of the medium. The homotopy perturbation method was used as an innovative approach to analyze the stability of the non-local silicon’s primary physical fields. The numerical inversion method is applied, yielding many graphs focusing on important numerical factors such as non-local effects, thermo-energy, and thermo-electric coupling parameters. Investigating dual solutions between stable and unstable regions for critical parameters like thermo-electric and thermo-energy coupling factors demonstrates that the homotopy perturbation technique can effectively analyze the stability analysis. The comparison between silicon and germanium is illustrated graphically. Utilizing the homotopy perturbation technique, we can effectively examine the stability of the primary physical variations with the effect of some values for eigenvalues approaches.Graphical abstract