Dispersion Integral Research Articles

STEWART PLATFORM MULTIDIMENSIONAL TRACKING CONTROL SYSTEM SYNTHESIS

Context. Creating guaranteed competitive motion control systems for complex multidimensional moving objects, including unstable ones, that operate under random controlled and uncontrolled disturbing factors, with minimal design costs, is one of the main requirements for achieving success in this class devices market. Additionally, to meet modern demands for the accuracy of motion control processes along a specified or programmed trajectory, it is essential to synthesize an optimal control system based on experimental data obtained under conditions closely approximating the real operating mode of the test object. Objective. The research presented in this article aims to synthesize an optimal tracking control system for the Stewart platform’s working surface motion, taking into account its multidimensional dynamic model. Method. The article employs a method of a multidimensional tracking control system structural transformation into an equivalent stabilization system for the motion of a multidimensional control object. It also utilizes an algorithm for synthesizing optimal stabilization systems for dynamic objects, whether stable or not, under stationary random external disturbances. The justified algorithm for synthesizing optimal stochastic stabilization systems is constructed using operations such as addition and multiplication of polynomial and fractional-rational matrices, Wiener factorization, Wiener separation of fractional-rational matrices, and the calculation of dispersion integrals. Results. As a result of the conducted research, the problem of defining the concept of analytical design for a Stewart platform’s optimal motion control system has been formalized. The results include the derived transformation equations from the tracking control system to the equivalent stabilization system of the Stewart platform’s working surface motion. Furthermore, the structure and parameters of the main controller transfer function matrix for of this control system have been determined. Conclusions. The justified use of the analytical design concept for the Stewart platform’s working surface optimal motion control system formalizes and significantly simplifies the solution to the problem of synthesizing complex dynamic systems, applying the developed technology presented in [1]. The obtained structure and parameters of the Stewart platform’s working surface motion control system main controller, which is divided into three components W1, W2, and W3, improve the tracking quality of the program signal vector, account for the cross-connections within the Stewart platform, and increase the accuracy of executing the specified trajectory by increasing the degrees of freedom in choosing the controller structure

Investigation of DG units influence on 66 kV sub-transmission system network considering region load growth: a case study

Abstract Voltage breakdown in sub-transmission networks resulting from an increase in load demand can be addressed by incorporating distributed generation (DG) units such as hydro, wind, photovoltaic, and geothermal in some buses. This approach can lower power losses and the price of the primary generated energy while increasing network dependability and efficiency. Feasibility of dispersed generation integration & its effect on sub-transmission system operation were investigated using Ben Walied 66 kV sub-transmission network in Libya as a state. This study presents modified particle swarm optimization (MOPSO) technique to select the best option with dispersed generation units under various operating conditions. The Ben Walied 66 kV sub-transmission network has been subject of effects research on both normal operation and load growth scenarios. The goal of this study was to find best way to adjust penetration level of the three DGs in response to changes in the network loading. Three DG units have been refitted to study the effects on test networks for sub-transmission, which consist of 30 and 51 buses. A comparison analysis shows that while the ideal locations of DG units remain constant with load expansion, the optimal solution for the penetration level percentage of three DG units was boosted by new optimal sizes. Research has been done on how the power factor of distributed generators (DGs) affects the practical performance of 66 kV networks in steady-state conditions. The integration of DG units in regulating these losses and voltage variations is demonstrated by the results, which indicate that the ideal solution for DG unit’s power factor was at a value of 0.87 lagging.

Final-state interactions in the CP asymmetry of D meson two-body decays

Urgent theoretical progress is needed in order to provide an estimate in the Standard Model of the recent measurement by LHCb of direct CP violation in charm-meson two-body decays. Rescattering effects must be taken into account for a meaningful theoretical description of the amplitudes involved in such category of observables, as signaled by the presence of large strong phases. We discuss the computation of the latter effects based on a two-channel coupled dispersion relation, which exploits isospin-zero phase shifts and inelasticity parameterizations of data coming from the rescattering processes [Formula: see text], [Formula: see text], and [Formula: see text]. The determination of the subtraction constants of the dispersive integrals relies on the leading contributions to the transition amplitudes from the [Formula: see text] counting, where [Formula: see text] is the number of QCD colors. Furthermore, we use the measured values of the branching ratios to help in selecting the non-perturbative inputs in the isospin limit, from which we predict values for the CP asymmetries. We find that the predicted level of CP violation is much below the experimental value.

Field-assisted sintering of high-entropy alloy-reinforced aluminium matrix composites: phase identification and microstructural properties

This study investigates the design, phase identification, and microstructural properties of high-entropy alloy (HEA)-reinforced aluminium (Al) matrix composites. Thermophysical expressions for HEAs were employed during the design phase of the HEA; both theoretical frameworks and experimental analyses were used to anticipate stable phases while a field-assisted sintering technique was employed to consolidate the samples. Calculation of phase diagram (CALPHAD) predictions for the phases present in the HEA align with valence electron concentration (VEC) calculations as both predicted the presence of BCC and FCC phases. The microhardness results reveal a substantial increase in the hardness value of the composites as compared to the pure Al, such that as low as 5 wt% HEA addition resulted in over a 100% improvement, while the densification of the composites was found to decrease with an increase in the wt% of HEA. SEM micrographs and XRD analyses show fair dispersion, bonding, and phase integration in the HEA-reinforced composites.

Preparation and characterization of high-performance water-based graphene dispersions for conductive coating on textiles

Studies on e-textile applications have gained momentum with advanced material technologies. Graphene derivatives have become the focus of e-textile advanced studies due to their high conductivity potential. The chemical selection while preparing graphene dispersions to functionalize textiles affects the dispersion quality and integration into the fabric. In this study, water-based green graphene dispersions were prepared using sodium dodecyl benzene sulfonate (SDBS) as a surfactant and polyvinyl alcohol (PVA) as a binder due to its high solubility in water. The stability of graphene nanoplatelets (GNP), GNP/SDBS and GNP/SDBS/PVA dispersions were examined with the naked eye at certain time intervals. UV–vis spectroscopy results indicated that SDBS provided better dispersion and stability of graphene. The XPS results showed a strong interaction between GNP and SDBS, while the binding of PVA and SDBS in the dispersion was supported by FTIR results. Overall, the dispersion quality of water-based graphene dispersion was enhanced using PVA and SDBS for e-textile application. The electrical conductivity and tensile strength of the graphene-coated fabrics increased up to ∼1.6 (MΩ/☐) and 388%, respectively, in compared to the intact fabric.

STEWART PLATFORM DYNAMICS MODEL IDENTIFICATION

Context. At the present stage, with the current demands for the accuracy of motion control processes for a moving object on a specified or programmable trajectory, it is necessary to synthesize the optimal structure and parameters of the stabilization system (controller) of the object, taking into account both real controlled and uncontrolled stochastic disturbing factors. Also, in the process of synthesizing the optimal controller structure, it is necessary to assess and consider multidimensional dynamic models, including those of the object itself, its basic components, controlled and uncontrolled disturbing factors that affect the object in its actual motion.
 Objective. The aim of the research, the results of which are presented in this article, is to obtain and assess the accuracy of the Stewart platform dynamic model using a justified algorithm for the multidimensional moving object dynamics identification.
 Method. The article employs a frequency-domain identification method for multidimensional stochastic stabilization systems of moving objects with arbitrary dynamics. The proposed algorithm for multidimensional moving object dynamics model identification is constructed using operations of polynomial and fractional-rational matrices addition, multiplication, Wiener factorization, Wiener separation, and determination of dispersion integrals.
 Results. As a result of the conducted research, the problem of identifying the dynamic model of a multidimensional moving object is formalized, illustrated by the example of a test stand based on the Stewart platform. The outcomes encompass the identification of the dynamic model of the Stewart platform, its transfer function, and the transfer function of the shaping filter. The verification of the identification results confirms the sufficient accuracy of the obtained models.
 Conclusions. The justified identification algorithm allows determining the order and parameters of the linearized system of ordinary differential equations for a multidimensional object and the matrix of spectral densities of disturbances acting on it under operating conditions approximating the real functioning mode of the object prototype. The analysis of the identification results of the dynamic models of the Stewart platform indicates that the primary influence on the displacement of the center of mass of the moving platform is the variation in control inputs. However, neglecting the impact of disturbances reduces the accuracy of platform positioning. Therefore, for the synthesis of the control system, methods should be applied that enable determining the structure and parameters of a multidimensional controller, considering such influences.

Region-based flexibility quantification in distribution systems: An analytical approach considering spatio-temporal coupling

Operational flexibility is to depict the ability of a power system in guaranteeing a secure and high-performance system operation, which is essential for distribution systems (DSs) with high renewable energy generation (REG) penetration. However, due to the dispersed integration of energy storage systems and uncertain REGs, the available regulation capability exhibits spatio-temporal coupling. It poses a challenge to quantify flexibility considering multiple locations and time periods. This paper proposes a novel analytical region-based method to characterize the flexibility considering spatio-temporal coupling, where the total dispatch budget and carbon emission constraints are considered to guarantee economic and environmental benefits. Leveraging the basic feasible solution theory, we derive an analytical formulation of the flexibility region, expressed as a set of linear inequalities. Note that no inner or outer approximation techniques are employed in the deduction procedure. The effectiveness and scalability of the proposed method are validated on test systems. Case studies demonstrate that the proposed method enables precise quantification and visualization of operational flexibility for DSs. The derived flexibility region is a closed polyhedron in a high-dimensional space, signifying the maximum ranges of uncertainties that can be accommodated.

Fractional analytic QCD beyond leading order in the timelike region

In this paper we show that, as in the spacelike case, the inverse logarithmic expansion is applicable for all values of the argument of the analytic coupling constant. We present two different approaches, one of which is based primarily on trigonometric functions, and the latter is based on dispersion integrals. The results obtained up to the 5th order of perturbation theory, have a compact form and their acquiring is much easier than the methods that have been used before. As an example, we apply our results to study the Higgs boson decay into a bb pair.

Optoelectronic oscillator controlled by photodiode-based optoelectronic chromatic dispersion and FBG integration

High Optoelectronic Chromatic Dispersion in Ge PN-type photodetectors affects the output of the Optoelectronic Oscillator. This is utilized to achieve high sensitivity wavelength monitoring and strain sensing. The sensitivity is enhanced for higher oscillating mode numbers and lower cavity lengths.

Fractional analytic QCD beyond leading order

Fractional analytic QCD is constructed beyond leading order using the standard inverse logarithmic expansion. It is shown that, contrary to the usual QCD coupling constant, for which this expansion can be used only for large values of its argument, in the case of analytic QCD, the inverse logarithmic expansion is applicable for all values of the argument of the analytic coupling constant. We present four different views, two of which are based primarily on Polylogarithms and generalized Euler ζ-functions, and the other two are based on dispersion integrals. The results obtained up to the 5th order of perturbation theory, have a compact form and do not contain complex special functions that were used to solve this problem earlier. As an example, we apply our results to study the polarized Bjorken sum rule, which is currently measured very accurately.

CEO Compensation Complexity and Firm Performance

How does the complexity in CEO compensation affect firm performance? With unknown consequences, the complexity of executive compensation contracts is rising. In this study, we explore how the complexity of executive compensation relates to ?rm performance. We conceptualize and operationalize the objective constituents of complex compensation contracts and find negative outcomes on both accounting- and marked-based measures of firm performance for CEOs. Based on these findings, we furthermore offer and explore theoretical explanations for the relationship, namely multitasking and cognitive limitations. We link these findings to the top management team (TMT) and suggest that compensation complexity is an important extension for the TMT pay dispersion and behavioral integration literature. We discuss these findings and close with potential research opportunities in the nascent research field of compensation complexity.

Four-fermion operators at dimension 6: Dispersion relations and UV completions

A major task in phenomenology today is constraining the parameter space of Standard Model effective field theory and constructing models of fundamental physics from which the Standard Model derives. To this effect, we report an exhaustive list of sum rules for 4-fermion operators of dimension 6, connecting low-energy Wilson coefficients to cross sections in the UV. Unlike their dimension-8 counterparts which are amenable to a positivity bound, the discussion here is more involved due to the weaker convergence and indefinite signs of the dispersion integrals. We illustrate this by providing examples with weakly coupled UV completions leading to opposite signs of the Wilson coefficients for both convergent and nonconvergent dispersion integrals. We further decompose dispersion integrals under weak isospin and color groups, which lead to a tighter relation between IR measurements and UV models. These sum rules can become an effective tool for constructing consistent UV completions for Standard Model effective field theory following the prospective measurement of these Wilson coefficients.

An N/D study of the S 11 channel πN scattering amplitude * *Support in part by National Nature Science Foundations of China (11975028, 10925522), the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) (196253076 -TRR 110)

Extensive dynamical calculations are conducted in the study of channel low energy scatterings, based on various phenomenological model inputs of left cuts at the tree level. The subtleties of the singular behavior of the partial wave amplitude, at the origin of the complex plane, are analysed in detail. Furthermore, it is found that the dispersion representation for the phase shift, , must be modified in the case of scatterings. An additional contribution from the dispersion integral exists, which approximately cancels the contribution of the two virtual poles located near the end points of the segment cut, induced by channel nucleon exchanges. With limited reliance on the details of the dynamical inputs, the subthreshold resonance survives.

Group velocity dispersion in terahertz frequency combs within a generalized Maxwell-Bloch framework

As many molecules have their rotovibrational resonance frequencies in the mid-infrared or terahertz regime, efficient generation of corresponding frequency combs may lead to large progress in gas spectroscopy and sensing. Quantum cascade lasers (QCLs) are among the most promising candidates for a compact and cheap radiation source in this frequency range. This contribution presents a full-wave numerical solution of the Maxwell-Liouville-von Neumann equations, thus avoiding the limited applicability of the rotating wave approximation to moderate field strengths and spectral bandwidths. We include losses and chromatic dispersion of the optically active material in the QCL. The semiclassical approach uses the finite-difference time-domain (FDTD) method to derive update equations for the electric field, starting from the one-dimensional Maxwell equations. There, the optical full-wave propagation is coupled to the electronic quantum system via a polarization term that arises from the evolution of the density matrix. Furthermore, dispersion effects are considered through a classical polarization term and losses are introduced by a finite material conductivity. This work mainly focuses on the integration of group velocity dispersion (GVD) due to the bulk material and, if applicable, the waveguide geometry into the update equations. It is known to be one of the main degradation mechanisms of terahertz frequency combs, but has not yet been added to the existing full-wave solver. The implementation is carried out as Lorentz model and is applied to an experimentally investigated QCL frequency comb setup from the literature. The reported results are in good agreement with the experimental data. Especially, they confirm the need for dispersion compensation for the generation of terahertz frequency combs in QCLs.

Contributions of environmental and maternal transmission to the assembly of leaf fungal endophyte communities

Leaf fungal endophytes (LFEs) contribute to plant growth and responses to stress. Fungi colonize leaves through maternal transmission, e.g. via the seed, and through environmental transmission, e.g. via aerial dispersal. The relative importance of these two pathways in assembly and function of the LFE community is poorly understood. We used amplicon sequencing to track switchgrass ( Panicum virgatum ) LFEs in a greenhouse and field experiment as communities assembled from seed endophytes and rain fungi (integration of wet and dry aerial dispersal) in germinating seeds, seedlings, and adult plants. Rain fungi varied temporally and hosted a greater portion of switchgrass LFE richness (greater than 65%) than were found in seed endophytes (greater than 25%). Exposure of germinating seeds to rain inoculum increased dissimilarity between LFE communities and seed endophytes, increasing the abundance of rain-derived taxa, but did not change diversity. In the field, seedling LFE composition changed more over time, with a decline in seed-derived taxa and an increase in richness, in response to environmental transmission than LFEs of adult plants. We show that environmental transmission is an important driver of LFE assembly, and likely plant growth, but its influence depends on both the conditions at the time of colonization and plant life stage.

Surface Plasmonic Sensors: Sensing Mechanism and Recent Applications.

Surface plasmonic sensors have been widely used in biology, chemistry, and environment monitoring. These sensors exhibit extraordinary sensitivity based on surface plasmon resonance (SPR) or localized surface plasmon resonance (LSPR) effects, and they have found commercial applications. In this review, we present recent progress in the field of surface plasmonic sensors, mainly in the configurations of planar metastructures and optical-fiber waveguides. In the metastructure platform, the optical sensors based on LSPR, hyperbolic dispersion, Fano resonance, and two-dimensional (2D) materials integration are introduced. The optical-fiber sensors integrated with LSPR/SPR structures and 2D materials are summarized. We also introduce the recent advances in quantum plasmonic sensing beyond the classical shot noise limit. The challenges and opportunities in this field are discussed.

Analysis of the contribution to PM10 concentrations of the largest coal-fired power plant of Italy in four different sites

A source apportionment study was performed on PM10 samples collected in four sites nearby the largest Italian coal-fired power plant (SE Italy). A multi-model approach, based on integration of receptor (Positive Matrix Factorization - PMF, Chemical Mass Balance - CMB) and dispersion (CALPUFF) models, estimated the contribution of the power plant to primary PM10 and to secondary ammonium sulphate. Maximum PM10 daily concentrations were observed at all sites during winter period, with exceedances of the daily legislation threshold mainly due to biomass burning and road traffic. Chemical analysis explained about 55% of PM10 in the Brindisi area, 62% in the Lecce area. Eight PM sources were identified: crustal and power plant, resuspended dust, traffic, secondary ammonium sulphate, secondary nitrate, marine, biomass burning and harbour – industrial, with a reasonable comparability between receptor models outputs. Combining the information from receptor and dispersion models, the average contribution of the power plant to primary PM10 was 2% (±1%) of PM10 for Lecce site and 3% (±1%) as average of the three sites of Brindisi province. The contribution to secondary ammonium sulphate was ranging between 1.3% (±0.3%) of PM10 and 1.7% (±0.4%). These results were compared with those obtained using the same approach in the area close to Torrevaldaliga Nord (TVN) coal-fired power plant. Results indicate a lower primary contribution to PM10 of the TVN station, likely associated to lower PM emissions at the stack of TVN station and different heights of release, comparable contributions to secondary ammonium sulphate founded.

Dielectric Metalens: Properties and Three-Dimensional Imaging Applications

Recently, optical dielectric metasurfaces, ultrathin optical skins with densely arranged dielectric nanoantennas, have arisen as next-generation technologies with merits for miniaturization and functional improvement of conventional optical components. In particular, dielectric metalenses capable of optical focusing and imaging have attracted enormous attention from academic and industrial communities of optics. They can offer cutting-edge lensing functions owing to arbitrary wavefront encoding, polarization tunability, high efficiency, large diffraction angle, strong dispersion, and novel ultracompact integration methods. Based on the properties, dielectric metalenses have been applied to numerous three-dimensional imaging applications including wearable augmented or virtual reality displays with depth information, and optical sensing of three-dimensional position of object and various light properties. In this paper, we introduce the properties of optical dielectric metalenses, and review the working principles and recent advances in three-dimensional imaging applications based on them. The authors envision that the dielectric metalens and metasurface technologies could make breakthroughs for a wide range of compact optical systems for three-dimensional display and sensing.

Towards more integration of physiology, dispersal and land-use change to understand the responses of species to climate change.

The accelerating biodiversity crisis, for which climate change has become an important driver, urges the scientific community for answers to the question of whether and how species are capable of responding successfully to rapidly changing climatic conditions. For a better understanding and more realistic predictions of species' and biodiversity responses, the consideration of extrinsic (i.e. environment-related) and intrinsic (i.e. organism-related) factors is important, among which four appear to be particularly crucial: climate change and land-use change, as extrinsic factors, as well as physiology and dispersal capacity, as intrinsic factors. Here, I argue that these four factors should be considered in an integrative way, but that the scientific community has not yet been very successful in doing so. A quantitative literature review revealed a generally low level of integration within global change biology, with a pronounced gap especially between the field of physiology and other (sub)disciplines. After a discussion of potential reasons for this unfortunate lack of integration, some of which may relate to key deficits e.g. in the reward and incentive systems of academia, I suggest a few ideas that might help to overcome some of the barriers between separated research communities. Furthermore, I list several examples for promising research along the integration frontier, after which I outline some research questions that could become relevant if one is to push the boundary of integration among disciplines, of data and methods, and across scales even further - for a better understanding and more reliable predictions of species and biodiversity in a world of global change.

Hadronic vacuum-polarization contribution to various QED observables

Due to precision tests of quantum electrodynamics (QED), determination of accurate values of fundamental constants, and constraints on new physics, it is important in a consistent way to evaluate a number of QED observables such as the Lamb shift in hydrogen-like atomic systems. Even in a pure leptonic case, those QED variables are in fact not pure QED ones since hadronic effects are involved through intermediate states while accounting for higher-order effects. One of them is hadronic vacuum polarization (hVP). Complex evaluations often involve a number of QED quantities, for which treatment of hVP is not consistent. The highest accuracy for a calculation of the hVP term is required for the anomalous magnetic moment of a muon. However, a standard data-driven treatment of hVP, based on a dispersion integration of experimental data on electron-positron annihilation to hadrons and some other phenomena, leads to a contradiction with the experimental value of a_mu . This experimental value can be considered as an indirect determination of the hVP contribution to a_mu and the scatter of theory and experiment allows one to obtain a conservative estimation of the related hVP contribution. In this paper, we derive exact and approximate relations between the leading-order (LO) hVP contributions to various observables. Using those relations, we obtain for them a consistent set of the results, based on the scatter of a_mu values. While calculating the LO hVP term, we have to remember that next-to-LO (NLO) hVP corrections are often comparable with the uncertainty of the LO term. Special attention is payed to hVP contribution to simple atoms. In particular, we discuss the NLO contribution to the Lamb shift in ordinary and muonic hydrogen and other two-body atoms for Zle 10. We also consider the NLO contribution of the muonic vacuum polarization to the Lamb shift in hydrogen-like atoms. With the a_mu puzzle unresolved, one may still require present-days values of the hVP contributions to various observable for comparison to experiment etc. the presence of contradicting values and a lack of consistency means an additional uncertainty for a_mu and for key contributions to it, including the LO hVP one. We present here an estimation of such a propagated uncertainty in hVP contributions to different QED observables and recommend a consistent set of the related LO hVP contributions.Graphic