Parameter Constraints Research Articles

Stability analysis of axial geometry with anisotropic background in f(R,T) gravity

In this paper, we highlight the variables preserving stability of a very restricted class of anisotropic axial symmetrical compact geometry in the scenario of [Formula: see text] gravity, where [Formula: see text] stands for energy–momentum tensor’s trace and [Formula: see text] is invariant Ricci curvature. In the framework of [Formula: see text] gravity, we set up field equations as well as non-conservation equations. We use a perturbation technique for all variables involved in non-conservation equations, field equations, extra curvature terms of modified gravity as well as for considered gravity model (i.e. [Formula: see text]) to evaluate the collapse equation. We establish certain significant constraints for the stiffness parameter [Formula: see text] in Newtonian [Formula: see text] and post-Newtonian [Formula: see text] approximation to study the dynamical instability of a stellar compact configuration. In order to preserve the stability of an anisotropic self-gravitating axially symmetric configuration, we place certain restrictions on physical quantities. To examine the stable and unstable behavior of considered geometry via graphical approaches, we include schematic diagrams at the [Formula: see text] and [Formula: see text] eras.

A general correlation between ductile fracture toughness and unified constraint parameter for different materials

In structural integrity assessment based on the two-parameter approach with considering constraint, it is an important step to establish a correlation between fracture toughness and constraint parameter for a specific material. But it is difficult and costly. In this work, based on a large number of ductile fracture toughness JC data measured from specimens with different geometries and crack sizes for different materials and finite element calculation of a newly developed unified constraint parameter Ad* for each specimen, a general correlation equation between JC and Ad* has been established. This correlation equation may be applied to predict constraint-dependent fracture toughness for different materials and structures, and its prediction capability has been validated by a great quantity of experimental fracture toughness data of various specimen geometries and materials (including welded joints). This correlation equation has a wide application range and may provide a simple and convenient engineering method to estimate constraint-dependent ductile fracture toughness.

Evolving stochastic configure network: A more compact model with interpretability

Stochastic Configure Networks (SCNs) are an incremental variant of randomly weighted neural networks of which one of the key highlights lies in the constraints while adding hidden layer nodes. Recent studies show two weaknesses of SCNs. One is the redundancy of added hidden layer nodes while the other is the lack of interpretability to the designed constraints. Motivated by overcoming these weaknesses, this paper proposes a new model named Evolving SCN to increase the interpretability of the design for constraints from the viewpoint of evolution by a sampling mechanism and to promote the model compactness by optimizing random weights within the space of constraint parameters. Surprisingly, although an evolving method is used in our model, the effectiveness and efficiency are significantly improved with respect to running time and prediction accuracy in comparison with the existing versions of SCNs. This work makes a first attempt to enhance the interpretability of incrementally adding nodes and simultaneously reduce the redundancy of hidden nodes in SCNs, which brings some new insights to understand the model compactness from the view of Occam's razor and further to the nature of incremental learning.

Research on Demand-Based Scheduling Scheme of Urban Low-Altitude Logistics UAVs

Aiming at the problem of the scheduling scheme of urban low-altitude logistics unmanned aerial vehicles (UAVs), this paper establishes a demand-based UAV scheduling scheme model using an improved simulated annealing algorithm, taking minimizing the cost of distribution as the objective function and considering restrictions such as UAV performance constraints, airspace constraints, and distribution constraints, among others. For verification, actual express data and airspace constraints in Shanghai are taken as examples. Two urban air traffic networks are constructed using road and building data. The analysis results show that the planning scheme of this model is superior to other forecasting models in terms of delivery cost and delivery time. In addition, this model can flexibly calculate the optimal scheduling scheme under the constraints of multiple parameters, according to the requirements of delivery volume, delivery distance, UAV performance, etc.

Optical Solitons for the Concatenation Model with Differential Group Delay: Undetermined Coefficients

In the current study, the concatenation model of birefringent fibers is explored for the first time, and we present optical soliton solutions to the model. The integration algorithm used to achieve this retrieval is the method of undetermined coefficients, which yields a wide range of soliton solutions. The parameter constraints arise naturally during the derivation of the soliton solutions, which are essential for such solitons to exist.

Gap Solitons in Fiber Bragg Gratings Having Polynomial Law of Nonlinear Refractive Index and Cubic–Quartic Dispersive Reflectivity by Lie Symmetry

The current paper recovers cubic–quartic optical solitons in fiber Bragg gratings having polynomial law of nonlinear refractive index structures. Lie symmetry analysis is carried out, starting with the basic analysis. Then, it is followed through with improved Kudryashov and generalized Arnous schemes. The parameter constraints are also identified for the existence of such solitons. Numerical surface plots support the adopted applied analysis.

Assessing theoretical uncertainties for cosmological constraints from weak lensing surveys

ABSTRACT Weak gravitational lensing is a powerful probe, which is used to constrain the standard cosmological model and its extensions. With the enhanced statistical precision of current and upcoming surveys, high-accuracy predictions for weak lensing statistics are needed to limit the impact of theoretical uncertainties on cosmological parameter constraints. For this purpose, we present a comparison of the theoretical predictions for the non-linear matter and weak lensing power spectra, based on the widely used fitting functions ($\texttt {mead}$ and $\texttt {rev-halofit}$ ), emulators ($\texttt {EuclidEmulator}$ , $\texttt {EuclidEmulator2}$ , $\texttt {BaccoEmulator}$ , and $\texttt {CosmicEmulator}$ ), and N-body simulations (pkdgrav3). We consider the forecasted constraints on the $\Lambda \texttt {CDM}$ and $\texttt {wCDM}$ models from weak lensing for stage III and stage IV surveys. We study the relative bias on the constraints and their dependence on the assumed prescriptions. Assuming a $\Lambda \texttt {CDM}$ cosmology, we find that the relative agreement on the S8 parameter is between 0.2 and 0.3σ for a stage III-like survey between the above predictors. For a stage IV-like survey the agreement becomes 1.4–3.0σ. In the $\texttt {wCDM}$ scenario, we find broader S8 constraints, and agreements of 0.18–0.26σ and 0.7–1.7σ for stage III and stage IV surveys, respectively. The accuracies of the above predictors therefore appear adequate for stage III surveys, whereas the fitting functions would need improvements for future stage IV surveys. Furthermore, we find that, of the fitting functions, $\texttt {mead}$ provides the best agreement with the emulators. We discuss the implication of these findings for the preparation of future weak lensing surveys, and the relative impact of theoretical uncertainties to other systematics.

Guess the cheese flavour by the size of its holes: a cosmological test using the abundance of popcorn voids

ABSTRACT We present a new definition of cosmic void and a publicly available code with the algorithm that implements it. Underdense regions are defined as free-form objects, called popcorn voids, made from the union of spheres of maximum volume with a given joint integrated underdensity contrast. The method is inspired by the excursion-set theory and consequently no rescaling processing is needed, the removal of overlapping voids and objects with sizes below the shot noise threshold is inherent in the algorithm. The abundance of popcorn voids in the matter field can be fitted using the excursion-set theory provided the relationship between the linear density contrast of the barrier and the threshold used in void identification is modified relative to the spherical evolution model. We also analysed the abundance of voids in biased tracer samples in redshift space. We show how the void abundance can be used to measure the geometric distortions due to the assumed fiducial cosmology, in a test similar to an Alcock–Paczyński test. Using the formalism derived from previous works, we show how to correct the abundance of popcorn voids for redshift-space distortion effects. Using this treatment, in combination with the excursion-set theory, we demonstrate the feasibility of void abundance measurements as cosmological probes. We obtain unbiased estimates of the target parameters, albeit with large degeneracies in the parameter space. Therefore, we conclude that the proposed test in combination with other cosmological probes has potential to improve current cosmological parameter constraints.

Reconstruction schemes of load and constraint for global vibration evaluation of pipeline structures

In this paper, inversion schemes for reconstruction of load and constraint of pipeline structure of a liquid rocket engine for global vibration evaluation of pipelines have been proposed and validated. The method involved modeling for forward simulation of random vibration and a multistep inversion scheme to reconstruct the unknown load and constraint parameters. In parallel, a piping structure vibration experimental system was also established to acquire the measured vibration signals for experimental validation of the numerical method. From both the numerical and experimental results, it was verified that a fine finite element model of a pipeline structure can be established based on the reconstructed load and constraint parameters which enabled a global vibration evaluation of the pipeline structure based on limited vibration information.

Dynamic evolution of the relationship quality among participants in integrated project delivery: based on supply chain theory

PurposeThe core of the successful implementation of the integrated project delivery (IPD) mode is to establish a high-quality relationship of cooperation, trust and sharing among participants. This paper proposes recommendations to improve the relationship quality of participants from the owner's perspective. The results provide the theoretical basis and practical guidance for the popularization and application of the IPD mode.Design/methodology/approachThis paper analyzes the dynamic relationship among participants in IPD mode based on supply chain theory and similarity theory. A tripartite game model of the owner, designer and the contractor is constructed to obtain the evolutionary equilibrium strategies under different parameter constraints. Then, numerical simulations under various scenarios are conducted to explore the dynamic evolution and the influencing factors of the relationship quality among the participant in the IPD mode.FindingsThe results show that (1) the relationship quality under certain conditions gradually improves as the project progresses until stable and high-quality cooperation is formed and (2) the owner's positive supervision cost, the distribution coefficient of incentive and punishment of participants and the scale of incentive pool are important factors influencing the relationship quality.Originality/valueThis study incorporates the following three innovations. First, analyzing the relationship quality among the participants of IPD mode based on supply chain theory. Second, the evolutionary game theory is applied to the relationship quality analysis. Third, conclusion innovation. The authors conclude that the relationship quality may progress, decrease or cycle with the progress of the project and targeted recommendations are presented based on the results.

A Passive-Constrained Observer and Controller Applied to an In-Wheel Synchronous Machine Implemented on a Fixed-Point DSP

In this paper, we describe a passivity-based control (PBC) approach for in-wheel permanent magnet synchronous machines that expands on the conventional passivity-based controller. We derive the controller and observer parameter constraints in order to maintain the passivity of the interconnected system and thus improve the control system’s robustness to varying loads and plant parameters. The advantages of the proposed PBC technique are demonstrated in contrast with conventional PBC. The control technique is implemented on an electronic development board equipped with a fixed-point digital signal processor and coupled to a gallium nitride voltage source inverter and 350 W electric machine. Test bench results and numerical simulations in Matlab-Simulink demonstrate the control performance and behaviour under varying loads and parameters.

Transport phenomena in Darcy-Forchheimer flow over a rotating disk with magnetic field and multiple slip effects: modified Buongiorno nanofluid model

The current study focuses on investigating the significance of magnetic field and multiple slip constraints on the water-based graphene Darcy-Forchheimer nanofluid flow over a rotating disk. For a realistic approach, the modified Buongiorno nanofluid model that incorporates the combination of effective thermophysical properties, thermophoretic diffusion, and Brownian diffusion has been utilized. Engineering quantities like moment coefficient and pumping efficiency of the disk are also elucidated. The transmutation of the mathematically modeled nonlinear equations into a system of first-order ODEs are achieved through Von Kármán’s similarity transformations and are then resolved using the shooting technique along with the Runge–Kutta-Fehlberg algorithm. The highest heat transfer rate is experienced for smaller values of magnetic field parameter, Forchheimer number, porosity parameter, and thermal slip constraint. An increment rate of 88.14355% in the azimuthal drag coefficient and a decrement rate of 39.849732% in the radial drag coefficient are noted when the values of hydrodynamic slip constraint are augmented. Further, per unit increase in the volume fraction of graphene nanoparticles descends the moment coefficient and the entrainment velocity by 456.25501% and 12.48875%, respectively. The tidings of this numerical simulation have applications in spin coating, centrifugal filtration, medical equipment, gas turbine rotors, and thermal power generating systems.

On fractional semidiscrete Dirac operators of Lévy–Leblond type

AbstractIn this paper, we introduce a wide class of space‐fractional and time‐fractional semidiscrete Dirac operators of Lévy–Leblond type on the semidiscrete space‐time lattice (), resembling to fractional semidiscrete counterparts of the so‐called parabolic Dirac operators. The methods adopted here are fairly operational, relying mostly on the algebraic manipulations involving Clifford algebras, discrete Fourier analysis techniques as well as standard properties of the analytic fractional semidiscrete semigroup , carrying the parameter constraints and . The results obtained involve the study of Cauchy problems on .

Quasar UV/X-ray relation luminosity distances are shorter than reverberation-measured radius–luminosity relation luminosity distances

ABSTRACT We use measurements of 59/58 quasars (QSOs), over a redshift range 0.0041 ≤ z ≤ 1.686, to do a comparative study of the radius–luminosity (R − L) and X-ray−UV luminosity (LX − LUV) relations and the implication of these relations for cosmological parameter estimation. By simultaneously determining R − L or LX − LUV relation parameters and cosmological parameters in six different cosmological models, we find that both R − L and LX − LUV relations are standardizable but provide only weak cosmological parameter constraints, with LX − LUV relation data favouring larger current non-relativistic matter density parameter Ωm0 values than R − L relation data and most other available data. We derive LX − LUV and R − L luminosity distances for each of the sources in the six cosmological models and find that LX − LUV relation luminosity distances are shorter than R − L relation luminosity distances as well as standard flat ΛCDM model luminosity distances. This explains why LX − LUV relation QSO data favour larger Ωm0 values than do R − L relation QSO data or most other cosmological measurements. While our sample size is small and only spans a small z range, these results indicate that more work is needed to determine whether the LX − LUV relation can be used as a cosmological probe.

Quiescent Optical Solitons for the Concatenation Model with Nonlinear Chromatic Dispersion

This paper recovers quiescent optical solitons that are self-sustaining, localized wave packets that maintain their shape and amplitude over long distances due to a balance between nonlinearity and dispersion. When a soliton is in a state of quiescence, it means that it is stationary in both space and time. Quiescent optical solitons are typically observed in optical fibers, where nonlinearity and dispersion can lead to the formation of solitons. The concatenation model is considered to understand the behavior of optical pulses propagating through nonlinear media. Here, we consider the familiar nonlinear Schrödinger equation, the Lakshmanan–Porsezian–Daniel equation, and the Sasa–Satsuma equation. The current paper also addresses the model with nonlinear chromatic dispersion, a phenomenon that occurs in optical fibers and other dispersive media, where the chromatic dispersion of the material is modified by nonlinear effects. In the presence of nonlinearities, such as self-phase modulation and cross-phase modulation, the chromatic dispersion coefficient becomes a function of the optical intensity, resulting in nonlinear chromatic dispersion. A full spectrum of stationary optical solitons, along with straddled stationary solitons, are obtained. There are four integration schemes that made this retrieval possible. The numerical simulations are also included for these solitons. The parameter constraints also indicate the existence criteria for these quiescent solitons.

A Hierarchical Compliance-Based Contextual Policy Search for Robotic Manipulation Tasks With Multiple Objectives

Contextual policy search methods have demonstrated the potential to acquire robotic skill generalization on trajectory-shaping-based tasks. However, it is still challenging for robotic contact-rich manipulation tasks because contact force regulation, reference trajectory adaptation, and task generalization must be fulfilled simultaneously. To this end, a hierarchical compliance-based contextual policy search (HC-CPS) approach is proposed to learn the robotic compliant skills for force, motion, and task adaptation. Specifically, the parameterized impedance-conditioned action space is proposed for reinforcement learning lower-level policy to obtain the compliance for reference motion regulation and contact force control, while a linear Gaussian contextual policy is formulated as the higher-level policy to optimize the context-conditioned impedance parameters for task generalization; therefore, a family of contact-rich manipulation tasks with multiple objectives is achieved. Moreover, data efficiency is further improved by two aspects: first, a variation encoder-decoder model is proposed to estimate the underlying constraints of impedance parameters over the actions, leading to the mitigated extrapolation error for lower-level policy off-policy learning; second, a composite forward model is proposed to generate artificial trajectories and reduce the reward bias for higher-level contextual policy learning. The HC-CPS approach is validated by three simulated manipulation tasks and the real-world dual peg-in-hole assembly tasks with two kinds of objectives, and the results demonstrate the effectiveness of HC-CPS.

A roadmap to cosmological parameter analysis with third-order shear statistics

Context. Third-order weak lensing statistics are a promising tool for cosmological analyses since they extract cosmological information in the non-Gaussianity of the cosmic large-scale structure. However, such analyses require precise and accurate models for the covariance of the statistics. Aims. In this second paper of a series on third-order weak lensing statistics, we derive and validate an analytic model for the covariance of the third-order aperture statistics 〈Map3〉. Methods. We derive the covariance model from a real-space estimator for 〈Map3〉, including the Gaussian and non-Gaussian parts. We validate the model by comparing it to estimates from simulated Gaussian random fields (GRFs) and two sets of N-body simulations. Finally, we perform mock cosmological analyses with the model covariance and the simulation estimate to compare the resulting parameter constraints. Results. We find good agreement between the analytic model and the simulations, both for the GRFs and the N-body simulations. The figure of merit in the S8 − Ωm plane from our covariance model is within 3% of the one obtained from the simulated covariances. We also show that our model, which is based on an estimator using convergence maps, can be used to obtain upper and lower bounds for the covariance of an estimator based on three-point shear correlation functions. This second estimator is required to measure 〈Map3〉 in realistic survey data. In our derivation, we find that the covariance of 〈Map3〉 cannot be obtained from the bispectrum covariance and that it includes several ‘finite-field terms’ that do not scale with the inverse survey area. Conclusions. Our covariance model is sufficiently accurate for analysing stage III surveys. Covariances for statistics in Fourier space cannot always be straightforwardly converted into covariance for real-space statistics.

Rational and semi-rational solution to the (3+1)-dimensional Kadomtsev-Petviashvili-Boussinesq-like equation

In the paper, we take the (3+1)-dimensional KP-Boussinesq-like equation as an instance and utilize long wave limit approach to generate rational solution and semi-rational solution from the N-order soliton solution. For N = 2, 3, with specific parametric constraints, we have constructed rational solutions which can be presented as first order line rogue wave and single breather from two-soliton solution, and semi-rational solution is classified as first order kink-shaped rogue wave and a hybrid of breather and one soliton from three-soliton solution. For N = 4, the rational solution includes second order line rogue wave, double breather, interaction between two breathers and a hybrid of breather and line rogue wave. The semi-rational solution contains second order kink-shaped rogue wave and interaction between breather, soliton and line rogue wave. In addition, we give mathematical expressions for higher N-order rational solution.

Simulation and sensitivity analysis for cloud and precipitation measurements via spaceborne millimeter-wave radar

Abstract. This study presents a simulation framework for cloud and precipitation measurements via spaceborne millimeter-wave radar composed of eight submodules. To demonstrate the influence of the assumed physical parameters and to improve the microphysical modeling of the hydrometeors, we first conducted a sensitivity analysis. The results indicated that the radar reflectivity was highly sensitive to the particle size distribution (PSD) parameter of the median volume diameter and particle density parameter, which can cause reflectivity variations of several to more than 10 dB. The variation in the prefactor of the mass–power relations that related to the riming degree may result in an uncertainty of approximately 30 %–45 %. The particle shape and orientation also had a significant impact on the radar reflectivity. The spherical assumption may result in an average overestimation of the reflectivity by approximately 4 %–14 %, dependent on the particle type, shape, and orientation. Typical weather cases were simulated using improved physical modeling, accounting for the particle shapes, typical PSD parameters corresponding to the cloud precipitation types, mass–power relations for snow and graupel, and melting modeling. We present and validate the simulation results for a cold-front stratiform cloud and a deep convective process with observations from a W-band cloud profiling radar (CPR) on the CloudSat satellite. The simulated bright band features, echo structure, and intensity showed a good agreement with the CloudSat observations; the average relative error of radar reflectivity in the vertical profile was within 20 %. Our results quantify the uncertainty in the millimeter-wave radar echo simulation that may be caused by the physical model parameters and provide a scientific basis for optimal forward modeling. They also provide suggestions for prior physical parameter constraints for the retrieval of the microphysical properties of clouds and precipitation.

A Non-Uniform Interrupted-Sampling Repeater Jamming Method for Intra-Pulse Frequency Agile Radar

The existing research proposes an intra-pulse frequency agile radar waveform with “active” anti-jamming characteristics. It uses the discontinuity and periodicity of the interrupted-sampling repeater jamming and combines the anti-jamming algorithm to effectively suppress interrupted-sampling repeater jamming. In order to improve the jamming effectiveness of the interferer for the intra-pulse frequency agile waveform, this paper proposes to jam the intra-pulse frequency agile radar by using a non-uniform interrupted-sampling and forwarding method under parameter constraints. The proposed method first obtains the sub-pulse width of the intra-pulse frequency agile radar waveform by parameter estimation of the intercepted intra-pulse frequency agile radar signal through time–frequency ridge extraction and wavelet transform. Then, we construct non-uniform interrupted-sampling repeater jamming based on sub-pulse width constraint interference parameters. Theoretical analysis and results show that the non-uniform interrupted-sampling forwarding under parameter constraints makes it challenging to suppress interference in multiple domains, such as the time–frequency and pulse compression domain for intra-pulse frequency agile radar, which significantly improves the jamming capability of the jammer for intra-pulse frequency agile radar.