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- 摘要
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- 实验方案
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Fractional Generalized Inverse Gaussian Process for Population Dynamics of Phase Singularities
摘要： In this paper, a generalized inverse Gaussian (GIG) process is studied in conjunction with the population dynamics of phase singularities (PSs). Special attention is paid to a stochastic analysis of PSs based on combined methods with (i) the theory of information geometry, (ii) the eigenvalue problem related to the double confluent Heun equation, (iii) classification of the statistics (sub-Poisson, Poisson, and super-Poisson), and (iv) fractional generalization to introduce a memory effect. The present theoretical method is applied to describe two-dimensional (2D) spiral wave turbulence in CO oxidation on a Pt surface and in the Aliev–Panfilov model. It is demonstrated that the fractional GIG process with the fractional index μ (μ = 0.5) can capture the profile of the PS number distribution and the scaling law of ω?1.5 in the power spectral density at large frequencies, which have been observed in real experiments and numerical simulations.
关键词： spiral wave turbulence,population dynamics,phase singularities,information geometry,generalized inverse Gaussian process,double confluent Heun equation,fractional generalization
更新于2025-09-23 15:21:21
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exposed to an intense laser pulse
摘要： We investigate the role of the rotational excitation in the coherent and unidirectional B 2Σ+u emission of N2+ at 391 nm called air lasing generated when N2 is irradiated with intense femtosecond near-infrared laser pulses at 800 nm. We simulate the time-dependent population transfer process of N2+, which is assumed to be generated suddenly in an intense ultrashort laser pulse, by including vibrational and rotational degrees of freedom, and reveal that, when the light field intensity is below ≈ 4 × 1014 W cm?2, the population inversion can be achieved in N2+ only between rotationally highly excited levels in the vibrational ground (v' = 0) state of the B 2Σ+u state and those in the vibrational ground (v'' = 0) state of the electronic ground X 2Σ+g state, so that the lasing at 391 nm is realized even when the total population in the v' = 0 state of the electronically excited B 2Σ+u state is not inverted with respect to the total population in the v'' = 0 state of the electronic ground X 2Σ+g state.
关键词： air lasing,N2+,rotational excitation,population inversion,femtosecond laser pulses
更新于2025-09-23 15:21:01
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Impact of Transient Population Grating on the Superradiant Phase Transition in Semiconductor Laser Structures
摘要： We study theoretically and experimentally superradiant dynamics in multiple-section GaAs/AlGaAs laser structures. We develop a model based on the one-dimensional Maxwell curl equations without making use of the slowly-varying envelope approximation and demonstrate that strong transient periodic modulation of both e – h density and refractive index drastically affect the dynamics of emission generation in semiconductor media. We show that the coherent λ/2 transient population and the relative permittivity gratings facilitate e – h self-ordering and the onset of the superradiant phase transition in the e – h system.
关键词： self-organization,superradiance,phase transition,population grating
更新于2025-09-23 15:21:01
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Detecting neural assemblies in calcium imaging data
摘要： Background: Activity in populations of neurons often takes the form of assemblies, where specific groups of neurons tend to activate at the same time. However, in calcium imaging data, reliably identifying these assemblies is a challenging problem, and the relative performance of different assembly-detection algorithms is unknown. Results: To test the performance of several recently proposed assembly-detection algorithms, we first generated large surrogate datasets of calcium imaging data with predefined assembly structures and characterised the ability of the algorithms to recover known assemblies. The algorithms we tested are based on independent component analysis (ICA), principal component analysis (Promax), similarity analysis (CORE), singular value decomposition (SVD), graph theory (SGC), and frequent item set mining (FIM-X). When applied to the simulated data and tested against parameters such as array size, number of assemblies, assembly size and overlap, and signal strength, the SGC and ICA algorithms and a modified form of the Promax algorithm performed well, while PCA-Promax and FIM-X did less well, for instance, showing a strong dependence on the size of the neural array. Notably, we identified additional analyses that can improve their importance. Next, we applied the same algorithms to a dataset of activity in the zebrafish optic tectum evoked by simple visual stimuli, and found that the SGC algorithm recovered assemblies closest to the averaged responses. Conclusions: Our findings suggest that the neural assemblies recovered from calcium imaging data can vary considerably with the choice of algorithm, but that some algorithms reliably perform better than others. This suggests that previous results using these algorithms may need to be reevaluated in this light.
关键词： Population coding,Clustering,Spontaneous activity
更新于2025-09-23 15:21:01
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Design of Electromagnetic Metasurfaces for Directional Scattering in High Temperature Environment
摘要： The focus of this paper was on ?nding wrist sensor-derived features for detecting highly acute fall risk from the sit-to-stand transitions performed in a non-ambulatory environment. Furthermore, the in?uence of the dominant and non-dominant hand on these features was investigated. A cohort of 174 older subjects was monitored for seven consecutive days in their home setting by using inertial sensors attached at the wrist. Based on the reported falls during a one-month follow-up phase, two groups were de?ned. Twenty-one time and frequency domain features were implemented for the quantitative assessment of extracted sit-to-stand transitions. The statistical analysis yielded two features that could convincingly distinguish fallers from non-fallers for the dominant hand, and six for the non-dominant hand. A novel feature, energy of the applied support during standing up, showed statistically good performance independently of on which hand the sensor node was worn, as well as for the dominant and non-dominant hand (p < 0.014, p < 0.027, and p < 0.020, respectively). This paper overcomes limitations of clinical tests and shows a reliable application of wrist-worn bands in terms of assessment of highly acute fall risk. In addition, it reveals the sit-to-stand transition as a potential assessment source for the wrist-worn devices in the elderly population. Early assessment of the risk of falling in a widely accepted and non-stigmatized manner has the ability to bring crucial changes in fall prevention strategies, reducing the number of falls and the fall rate.
关键词： transitions in daily activities,Elderly population,fall risk assessment,inertial sensors
更新于2025-09-23 15:19:57
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Externally controlled Lotka-Volterra dynamics in a linearly polarized polariton fluid
摘要： Spontaneous formation of transverse patterns is ubiquitous in nonlinear dynamical systems of all kinds. An aspect of particular interest is the active control of such patterns. In nonlinear optical systems this can be used for all-optical switching with transistorlike performance, for example, realized with polaritons in a planar quantum-well semiconductor microcavity. Here we focus on a specific configuration which takes advantage of the intricate polarization dependencies in the interacting optically driven polariton system. Besides detailed numerical simulations of the coupled light-field exciton dynamics, in the present paper we focus on the derivation of a simplified population competition model giving detailed insight into the underlying mechanisms from a nonlinear dynamical systems perspective. We show that such a model takes the form of a generalized Lotka-Volterra system for two competing populations explicitly including a source term that enables external control. We present a comprehensive analysis of both the existence and stability of stationary states in the parameter space spanned by spatial anisotropy and external control strength. We also construct phase boundaries in nontrivial regions and characterize emerging bifurcations. The population competition model reproduces all key features of the switching observed in full numerical simulations of the rather complex semiconductor system and at the same time is simple enough for a fully analytical understanding.
关键词： all-optical switching,population competition model,nonlinear optical systems,transverse patterns,Lotka-Volterra system,polaritons,semiconductor microcavity
更新于2025-09-23 15:19:57
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Introduction to Quantum Electronics and Nonlinear Optics || Quantum Amplifiers and Generators
摘要： Under conditions of heat equilibrium, the number of particles with higher energy is always smaller than the number with lower energy. Therefore, n12 > 0, σ > 0, Pabs > 0 and a wave propagating in a medium is damped. Nevertheless, the equilibrium condition can be disturbed by use of an additional energy source (a pumping source). Under definite conditions the number of particles on the upper level becomes greater than in the lower level. As a result, n12 > 0, σ > 0, Pabs < 0 and instead of absorption we may observe electromagnetic wave amplification. Such a state is called population inversion or a state with a negative temperature. A medium with inversion is often called an active medium.
关键词： population inversion,pumping source,electromagnetic wave amplification,quantum amplifiers,active medium
更新于2025-09-23 15:19:57
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Accuracy of Scheimpflug-derived corneal biomechanical and tomographic indices for detecting subclinical and mild keratectasia in a South Asian population
摘要： To test the predictive accuracy of the Belin-Ambrósio deviation index (BAD-D), the stiffness parameter A1 (SPA1), the Corvis biomechanical index (CBI), and the tomographic and biomechanical index (TBI) assessments for distinguishing subclinical and mild keratoconic eyes from normal eyes.
关键词： Scheimpflug-derived corneal biomechanical and tomographic indices,subclinical keratectasia,South Asian population,mild keratectasia
更新于2025-09-23 15:19:57
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Deep SDSS optical spectroscopy of distant halo stars
摘要： Aims. We analyze a sample of tens of thousands of spectra of halo turno? stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population “in situ” out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as ?ux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each observed spectrum best. We used an optimization algorithm and evaluate model ?uxes by means of interpolation in a precomputed grid. In our analysis, we account for the spectrograph’s varying resolution as a function of ?ber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars with log g (cgs units) lower than 2.5. Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g < 2.5, con?rming the systematics identi?ed in the comparison with the SSPP. We ?nd that our metallicity estimates are signi?cantly more precise than the SSPP results. We also ?nd excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turno? stars as ?ux calibrators e?ciently excludes stars with high metallicities, but does not signi?cantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with what is expected from a dual halo system in the Milky Way.
关键词： techniques: spectroscopic,stars: atmospheres,methods: observational,Galaxy: halo,stars: Population II,stars: fundamental parameters
更新于2025-09-23 15:19:57
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An improved weighted multiplicative scatter correction algorithm with the use of variable selection: Application to near-infrared spectra
摘要： Multiplicative light scattering has posed great challenge in near-infrared (NIR) quantitative analysis. When estimating the scattering parameters, uninformative variables for scattering effects may bias the estimation. Weighted least squares (WLS) can be used to avoid the influence of the uninformative variables. In this work, we proposed an improved weighted multiplicative scatter correction algorithm with the use of variable selection (WMSCVS). Baseline is removed first and then variable selection is used to obtain the optimal weights of WLS in estimating multiplicative parameters. The variable selection algorithm, which is designed based on model population analysis (MPA), implements an iterative optimization process. In each iteration, weighted bootstrap sampling (WBS) is used to generate variable subsets and exponentially decreasing function (EDF) is used to control the number of sampled variables. The interpretability and stability of the variable selection results as well as the predictive performance of the corrected spectra were investigated by using two NIR datasets. The experimental results showed that the proposed WMSCVS could give better predictive performance than the state-of-art correction methods.
关键词： Model population analysis,Weighted least squares,Multiplicative scatter correction,Variable selection
更新于2025-09-19 17:15:36