Static Case Research Articles

Resource Allocation for OFDM-Based Status Update Systems: A Timeliness Perspective

Increasingly more time-sensitive applications emerge in Internet of things (IoT), requiring fresh status updates. Efficient resource allocation is critical for improving the timeliness of information. This paper investigates how to allocate bandwidth and configure the transmission in an orthogonal frequency division multiplexing (OFDM)-based IoT systems for timely status updating. Specifically, a general resource allocation problem is formulated using age of information (AoI) as the timeliness metric. We first consider a static channel case where we propose a fixed time slot length policy, a fixed blocklength policy, an iterative optimization algorithm, and an approximate optimal policy to address the optimal resource allocation and transmission configuration. Then, we extend the study to quasi-static fading channel cases. In particular, sticking to the transmission rate and spectral efficiency, the four policies designated for static channel case are tailored for the quasi-static fading channel case. We show that the iterative algorithms can improve the timeliness of the system significantly. Besides, the approximate optimal policy achieves an AoI performance competitive with the iterative algorithm, while reduces the computation complexity in both channel cases.

Approaches to Detect Microplastics in Water Using Electrical Impedance Measurements and Support Vector Machines

We propose electrical impedance spectroscopy (EIS) enhanced by machine learning (ML), in particular support vector machines (SVMs), as a noninvasive, in situ method for detecting microplastics in water and as an alternative to slow, expensive laboratory measurements. The primary measurand is the complex-valued electrical impedance of a water-filled measuring cell. We carried out stationary measurements on numerous water samples contaminated with different plastic concentrations in a cylindrical measuring cell and in the frequency range from 20 Hz to 2 MHz. The effects of various influence quantities, such as the concentration of organic material (1.0%, 3.0%, 5.0%) or the salinity of water (0.5%, 1.0%, 3.5%), were also investigated. Measurements at 2 MHz with water flows carrying microplastic particles of different materials and sizes served to investigate the dynamic capabilities of the measurement method. The impedance spectra (stationary measurements) or the measured impedances (dynamic measurements) were then evaluated by specific SVMs. The classification task consisted of distinguishing different plastic materials and particle sizes. In the stationary case, the application of the SVM resulted in assignment accuracies of over 98%. In the dynamic case, the classification accuracies exceeded 91% for the mere classification of particle sizes and 85% for the classification of plastic particles by size and material.

Boson stars and their relatives in semiclassical gravity

We construct boson star configurations in quantum field theory using the semiclassical gravity approximation. Restricting our attention to the static case, we show that the semiclassical Einstein-Klein-Gordon system for a {\it single real quantum} scalar field whose state describes the excitation of $N$ {\it identical particles}, each one corresponding to a given energy level, can be reduced to the Einstein-Klein-Gordon system for $N$ {\it complex classical} scalar fields. Particular consideration is given to the spherically symmetric static scenario, where energy levels are labeled by quantum numbers $n$, $\ell$ and $m$. When all particles are accommodated in the ground state $n=\ell=m=0$, one recovers the standard static boson star solutions, that can be excited if $n\neq 0$. On the other hand, for the case where all particles have fixed radial and total angular momentum numbers $n$ and $\ell$, with $\ell\neq 0$, but are homogeneously distributed with respect to their magnetic number $m$, one obtains the $\ell$-boson stars, whereas when $\ell=m=0$ and $n$ takes multiple values, the multi-state boson star solutions are obtained. Further generalizations of these configurations are presented, including the multi-$\ell$ multi-state boson stars, that constitute the most general solutions to the $N$-particle, static, spherically symmetric, semiclassical real Einstein-Klein-Gordon system, in which the total number of particles is definite. In spite of the fact that the same spacetime configurations also appear in multi-field classical theories, in semiclassical gravity they arise naturally as the quantum fluctuations associated with the state of a single field describing a many-body system. Our results could have potential impact on direct detection experiments in the context of ultralight scalar field/fuzzy dark matter candidates.

Non-linear INAR(1) processes under an alternative geometric thinning operator

We propose a novel class of first-order integer-valued AutoRegressive (INAR(1)) models based on a new operator, the so-called geometric thinning operator, which induces a certain non-linearity to the models. We show that this non-linearity can produce better results in terms of prediction when compared to the linear case commonly considered in the literature. The new models are named non-linear INAR(1) (in short NonLINAR(1)) processes. We explore both stationary and non-stationary versions of the NonLINAR processes. Inference on the model parameters is addressed and the finite-sample behavior of the estimators investigated through Monte Carlo simulations. Two real data sets are analyzed to illustrate the stationary and non-stationary cases and the gain of the non-linearity induced for our method over the existing linear methods. A generalization of the geometric thinning operator and an associated NonLINAR process are also proposed and motivated for dealing with zero-inflated or zero-deflated count time series data.

Effect of boundary conditions on particle spurious movement in Smoothed Particle Hydrodynamics method

SPH method due to its Lagrangian particle nature suffers from non-physical particle motion resulting from its numerical properties. We study these effects associated with solid walls realization.We used stationary test case to investigate behavior of multiple formulations of boundary conditions for solid walls. Multi-layer boundaries with ghost particles are considered (Dynamic Boundary Conditions, Modified Dynamic Boundary Conditions) as well as one-layer boundary conditions based on discretization of boundary terms and usage of boundary integrals. Some aspects of each realization with respect to the stationary case and particle spurious motion are discussed. Moreover we examined the levels of spurious motion caused by different sources as the free surface, straight walls, sharp corners, … The results show that for the boundary conditions good enough the most significant portion of spurious motion arises in place where the water surface connects to the wall and the spurious motion caused by this interaction is several orders of magnitude higher, then artificial motion caused by other sources.

Dynamic Multi-Compartment Vehicle Routing Problem for Smart Waste Collection

The rapid increase in urbanization results in an increase in the volume of municipal solid waste produced every day, causing overflow of the garbage cans and thus distorting the city’s appearance; for this and environmental reasons, smart cities involve the use of modern technologies for intelligent and efficient waste management. Smart bins in urban environments contain sensors that measure the status of containers in real-time and trigger wireless alarms if the container reaches a predetermined threshold, and then communicate the information to the operations center, which then sends vehicles to collect the waste from the selected stations in order to collect a significant waste amount and reduce transportation costs. In this article, we will address the issue of the Dynamic Multi-Compartmental Vehicle Routing Problem (DM-CVRP) for selective and intelligent waste collection. This problem is summarized as a linear mathematical programming model to define optimal dynamic routes to minimize the total cost, which are the transportation costs and the penalty costs caused by exceeding the bin capacity. The hybridized genetic algorithm (GA) is proposed to solve this problem, and the effectiveness of the proposed approach is verified by extensive numerical experiments on instances given by Valorsul, with some modifications to adapt these data to our problem. Then we were able to ensure the effectiveness of our approach based on the results in the static and dynamic cases, which are very encouraging.

The optical appearance of charged four-dimensional Gauss–Bonnet black hole with strings cloud and non-commutative geometry surrounded by various accretions profiles

Thanks for the releasing image of supermassive black holes (BHs) by the event horizon telescope (EHT) at the heart of the M87 galaxy. After the discovery of this mysterious object, scientists paid attention to exploring the BH shadow features under different gravitational backgrounds. In this scenario, we study the light rings and observational properties of BH shadow surrounded by different accretion flow models and then investigate the effect of model parameters on the observational display and space-time structure of BHs in the framework of our considering system. Under the incompatible configuration of the emission profiles, the images of BHs comprise that the observed luminosity is mainly determined by direct emission, while the lensing ring will provide a small contribution of the total observed flux and the photon ring makes a negligible contribution due to its exponential narrowness. More importantly, the observed regions and specific intensities of all emission profiles are changed correspondingly under variations of parameters. For optically thin accreting matters, we analyze the profile and specific intensity of the shadows with static and infalling accretions models, respectively. We find that with an infalling motion the interior region of the shadows will be darker than the static case, due to the Doppler effect of the infalling movement. Finally, it is concluded that these findings support the fact that the change of BH state parameters will change the way of space-time geometry, thus affecting the BH shadow dynamics.

Some recent trends in embeddings of time series and dynamic networks

We give a review of some recent developments in embeddings of time series and dynamic networks. We start out with traditional principal components and then look at extensions to dynamic factor models for time series. Unlike principal components for time series, the literature on time‐varying nonlinear embedding is rather sparse. The most promising approaches in the literature is neural network based, and has recently performed well in forecasting competitions. We also touch on different forms of dynamics in topological data analysis (TDA). The last part of the article deals with embedding of dynamic networks, where we believe there is a gap between available theory and the behavior of most real world networks. We illustrate our review with two simulated examples. Throughout the review, we highlight differences between the static and dynamic case, and point to several open problems in the dynamic case.

Inverse scheme for sound source identification in a vehicle trailer

Tire/road noise is a highly relevant topic for improving the comfort and experience of drivers and residents living in high-traffic areas. With the growing numbers of electric cars, the relevance of tire noise even increases since it is the dominant sound source in the middle-speed range. We investigate acoustic sources relevant to tire/road interactions. In doing so, we apply different sound source localization algorithms to measurement data acquired inside a large measurement trailer equipped with microphone arrays. The methods for sound source identification used are well-known beamforming-based algorithms and inverse schemes based on finite element or boundary element simulations. The latter schemes require the identification of the acoustic properties of the trailer in the stationary case. In this contribution, we present the characterization process and the results of the sound source localization in this stationary case.

Solar Orbiter Data‐Model Comparison in Venus' Induced Magnetotail

AbstractWe investigate the structure of the Venusian magnetotail utilizing magnetic field and electron density measurements that cover a wide range of distances from the planet, from the first two Solar Orbiter Venus flybys. We examine the magnetic field components along the spacecraft trajectory up to 80 Venus radii down the tail. Even though the magnetic field behavior differs considerably between the two cases, we see extended electron density enhancements covering distances greater than ∼20 RV in both flybys. We compare the magnetic field measurements with a global hybrid model of the induced magnetosphere and magnetotail of Venus, to examine to what degree the observations can be understood with the simulation. The model upstream conditions are stationary and the solution encloses a large volume of 83 RV × 60 RV × 60 RV in which we look for spatial magnetic field and plasma variations. We rotate the simulation solution to describe different stationary upstream IMF clock angle cases with a 10° step and find the clock angle for which the agreement between observations and model is maximized along Solar Orbiter's trajectory in 1‐min steps. We find that in both flybys there is better agreement with the observations when we rotate the model for some intervals, while there are parts that cannot be well reproduced by the model irrespective of how we vary the IMF clock angle, suggesting the presence of non‐stationary features in the Venus‐solar wind interaction not accounted for in the hybrid model.

Final-State Structural Behavior of the Long-Span Kömürhan Cable-Stayed Bridge under Torsional and Bending Loadings

Final-state field load testing is an effective method for understanding the real behavior of a bridge before it opens to traffic. The paper presents the procedure and the results of final-state static field tests on the new long span Kömürhan cable-stayed bridge with a single pylon and back span anchorage block under torsional and bending loadings. A total of six static loading cases were conducted to investigate real structural behavior of the bridge having a back span anchorage block and main span deck connected to the pylon with 42 tensioned cables in the deck center. Measured results have been obtained from the surveys and sensors while theoretical results have been calculated from the three-dimensional finite element model of the bridge final-state geometry. The results of final-state static load tests include the main span deck deflections, pylon horizontal displacements, the strains of the main span deck and the pylon, and the cable forces. A good agreement has been achieved between the experimental and theoretical results. Both experimental and theoretical results have shown that the real bridge behavior is in the elastic state under the planned test loads and supplies the design requirements. It is also observed that the results from the torsional and bending load cases positioned in the same sections are close to each other.

Stationary solutions for the fractional Navier–Stokes–Coriolis system in Fourier–Besov spaces

In this work we prove the existence of stationary solutions for the tridimensional fractional Navier–Stokes–Coriolis in critical Fourier–Besov spaces. We first deal with the non-stationary fractional Navier–Stokes–Coriolis and in this framework we get the existence of stationary solutions. Also we state a kind of stability of these non-stationary solutions which applied to the stationary case permits to conclude that, under suitable conditions, non-stationary solutions converge to the stationary ones when the time goes to infinity. Finally we establish a relation between the external force and the Coriolis parameter in order to get a unique solution for the stationary system.

Quasi-static approximation error of electric field analysis for transcranial current stimulation

Objective. Numerical modeling of electric fields induced by transcranial alternating current stimulation (tACS) is currently a part of the standard procedure to predict and understand neural response. Quasi-static approximation (QSA) for electric field calculations is generally applied to reduce the computational cost. Here, we aimed to analyze and quantify the validity of the approximation over a broad frequency range. Approach. We performed electromagnetic modeling studies using an anatomical head model and considered approximations assuming either a purely ohmic medium (i.e. static formulation) or a lossy dielectric medium (QS formulation). The results were compared with the solution of Maxwell’s equations in the cases of harmonic and pulsed signals. Finally, we analyzed the effect of electrode positioning on these errors. Main results. Our findings demonstrate that the QSA is valid and produces a relative error below 1% up to 1.43 MHz. The largest error is introduced in the static case, where the error is over 1% across the entire considered spectrum and as high as 20% in the brain at 10 Hz. We also highlight the special importance of considering the capacitive effect of tissues for pulsed waveforms, which prevents signal distortion induced by the purely ohmic approximation. At the neuron level, the results point a difference of sense electric field as high as 22% at focusing point, impacting pyramidal cells firing times. Significance. QSA remains valid in the frequency range currently used for tACS. However, neglecting permittivity (static formulation) introduces significant error for both harmonic and non-harmonic signals. It points out that reliable low frequency dielectric data are needed for accurate transcranial current stimulation numerical modeling.

Online bin covering with limited migration

Semi-online models where decisions may be revoked in a limited way have been studied extensively in the last years. A well-studied measure of the amount of decisions that can be revoked is the (constant) migration factor. When an object arrives, the decisions for objects of total size at most the migration factor times its size may be revoked. This means that a small object only leads to small changes. We extensively study the bin covering problem with migration in different scenarios. We develop algorithms both for the static case where only insertions are allowed, and for the dynamic case, where items may also depart. We also develop lower bounds for these scenarios both for amortized migration and for worst-case migration showing that our algorithms have nearly optimal migration factor and asymptotic competitive ratio. We therefore resolve the competitiveness of the bin covering problem with migration.

Mode stability results for the Teukolsky equations on Kerr–anti-de Sitter spacetimes

We prove that there are no non-stationary (with respect to the Hawking vectorfield), real mode solutions to the Teukolsky equations on all -dimensional subextremal Kerr–anti-de Sitter spacetimes. We further prove that stationary solutions do not exist if the black hole parameters satisfy the Hawking–Reall bound and . We conclude with the statement of mode stability which preludes boundedness and decay estimates for general solutions which will be proven in a separate paper. Our boundary conditions are the standard ones which follow from fixing the conformal class of the metric at infinity and lead to a coupling of the two Teukolsky equations. The proof relies on combining the Teukolsky–Starobinsky identities with the coupled boundary conditions. In the stationary case the proof exploits elliptic estimates which fail if the Hawking–Reall bound is violated. This is consistent with the superradiant instabilities expected in that regime.

The consistent boundary element method for potential and elasticity: Part I — Formulation and convergence theorem

The collocation boundary element method is outlined for the general three-dimensional, static case of elasticity on the basis of a weighted-residuals statement that leads to the Somigliana’s identity, as already proposed in the literature. However, this is done in a consistent way that sheds light on some conceptual and implementation-oriented aspects that should be – but are missing – in the textbooks on the subject. Arbitrary rigid-body displacements, as for elasticity, are naturally taken into account, and traction force parameters are always in balance independently of problem scale and mesh discretization. For generally curved boundaries, the correct definition of traction force interpolation functions enables the enunciation of a general convergence theorem, the introduction of patch and cut-out tests and, not least, a considerable simplification of the numerical implementations. A rather recreative example of a simple truss element is brought in an Appendix. It enables the demystification of apparently convoluted concepts that might be thought only pertaining to highly elaborated mechanics and mathematics for singularities related to infinity and to ungraspable linear algebra. Simple code schemes based on the outlined concepts are proposed in a companion paper for 2D problems of potential and elasticity, which rely exclusively on Gauss–Legendre quadrature and lead to arbitrarily high computational accuracy of all results of interest independently of a problem’s geometry or topology. Numerical results are shown in another companion paper and convergence features are assessed for 2D potential and elasticity problems with very challenging topology issues and even for subnanometer source-field distances. Summing up, whether a problem we are attempting to simulate consists of smooth fields or not, we are able to reproduce it — maybe with numerical approximations due to a coarse mesh discretization but never introducing unduly singularities.

Distributed job allocation using response threshold for heterogeneous robot team under deadline constraints

SummaryJob allocation among the robots is a significant challenge in a multi‐robot environment. This article proposes a distributed algorithm for job allocation with deadline constraints. It works utilizing the response threshold model inspired by job distribution among insect societies in nature. The team divides the jobs among themselves based on their threshold capacity. The proposed approach focus on maximizing the total jobs completed with the available resources. The static case where the robots never fail is considered first for evaluating the algorithm. Then it is run in a dynamic environment with robot failure to study the effects on job allocation. Two experimental studies are conducted with varying amounts of resources. In static and dynamic cases under experimental study I, the jobs completion percentage increased by an average of 37.6% and 35.8%, respectively, over the existing method. Under experimental study II, the proposed algorithm completed all the jobs with improved resource utilization. The results show that the proposed algorithm achieves better jobs completion. The algorithm is then tested in a real‐world experimental environment using FireBird V mobile robots under static and dynamic cases. The outcomes indicate that the proposed approach is efficient in job allocation in practical circumstances.

The consistent boundary element method for potential and elasticity: Part II — machine-precision numerical evaluations for 2D problems

The collocation boundary element method is outlined in a first companion paper for the general three-dimensional, static case of elasticity. This is done in a consistent way that sheds light on some essential conceptual and implementation-oriented aspects that have been up to now in part overseen and in part mistaken in the technical literature. We show in the present developments that actually only Gauss–Legendre quadratures are needed in a two-dimensional code implementation of potential and elasticity problems, with arbitrarily high – actually only machine-precision limited – computational accuracy of all results of interest independently of a problem’s geometry or topology. In fact, the higher the effect of a quasi-singularity the more accurate a result is achievable with a – for all practical means – restricted number of quadrature points by just having the mathematical aspects properly dealt with beforehand and general preliminary evaluations stored for use as black boxes. The developments are presented for generally curved boundary elements of any high order, with the mathematics related to improper, singular, real or complex quasi-singular integrals adequately outlined, which includes the accurate evaluation of results at internal points that may be arbitrarily close to the boundary. Numerical results are shown in a second companion paper and convergence features are assessed for problems with very challenging topology issues and even for subnanometer source-field distances.

Influence of EMSG on complex systems: Spherically symmetric, static case

Through this study, we intend to present a comprehensive summary of the most recent research on complex systems or complexity factor [Formula: see text] in the background of modified gravity theories (MGT). In this way, we examined [Formula: see text] for the novel MGT named [Formula: see text] gravity under the anisotropic static fluid configuration. [Formula: see text] is defined as one of the structure scalars [Formula: see text] which is trace-free component obtained from the orthogonal splitting of the Riemann tensor. Two mass approaches are used which have immense influence on [Formula: see text]. Furthermore, vanishing complexity condition is used with an eye towards finding the solution of the nonlinear system. Two extra models are explored which ensure one more condition for the purpose of comprehensive results.

The influence of curved surfaces on the propagation of skyrmions in a magnetic racetrack

The purpose of the current study is to analyze the effect of curvature on magnetic skyrmions by micromagnetic simulations. It is divided into two parts: First, we studied the stability of skyrmions on CoPt cylindrical surfaces, analyzing the static conditions for the annihilation of skyrmions as a function of the radius and curvature (positive or negative) of the surface. Unlike planar geometry, the skyrmion can be deformed into an elliptical shape when the surface is curved. In the second part, we analyzed the skyrmion dynamics when a spin-polarized current density is applied to a CoPt racetrack with a geometric defect in the form of a cylindrical surface, intercalated in the racetrack. We studied the conditions for skyrmion annihilation and compared it with the static case on cylindrical surfaces for various values of the radius and width of the geometric defect and also for various intensities of spin-polarized current density. We analyzed the shape of the skyrmion by measuring its radius in two perpendicular directions and its dynamic behavior when going through of the geometric defect, measuring the position and velocities of the skyrmion’s center. Furthermore, we compared the velocity profile obtained in the simulation with the theoretical results obtained by the Thiele’s equation as a function of the radius and width of the geometrical defect, and we showed that skyrmion can be accelerated and its speed can be increased up to 14 times due to an induced force (repulsive and attractive) that arises in the geometric defect region. Our results are in agreement with the results using the Thiele’s equation.