Static Configuration Research Articles

Vibroacoustic Assessment of an Innovative Composite Material for the Roof of a Coupe Car

The objective of this paper is the vibroacoustic evaluation of an innovative material for a sports car roof, aiming at replacing fiberglass composite materials. Such evaluation was carried out using numerical and experimental analysis techniques, with cross-comparison between the corresponding results. The innovative material under analysis is a composite material, with a thermoplastic polypropylene matrix and reinforcement made of cellulose fibers. In order to validate the virtual dynamic modeling of the new material, the inertance on different points of some sheets made of the material under analysis was evaluated by an in-house made experimental activity, performed in the CRF (Fiat Research Center) test room, and cross-compared with corresponding results from a numerical analysis performed with the MSC Nastran software. Then, a realistic model of the car roof of the Alfa Romeo 4C car, made with the new material, was implemented and analyzed from the vibroacoustic point of view. The mere switch to the new material, with no changes in the geometry/structure of the car roof, did not allow preserving the original values of static rigidity, dynamic rigidity, and configuration of modal shapes. For this reason, a geometric/structural optimization of the component was performed. Once the new geometry/structure was defined, a vibroacoustic analysis was carried out, checking for a possible coupling between the fluid cavity modes and the structure car body modes. Finally, the vibroacoustic transfer functions to the driver’s ear node were assessed, considering two different excitation points on the structure. The excellent damping capacity of the proposed material led to an improvement in the vibroacoustic transfer functions and to a reduction in the weight of the pavilion.

Dynamic backup workers for parallel machine learning

The most popular framework for distributed training of machine learning models is the (synchronous) parameter server (PS). This paradigm consists of n workers, which iteratively compute updates of the model parameters, and a stateful PS, which waits and aggregates all updates to generate a new estimate of model parameters and sends it back to the workers for a new iteration. Transient computation slowdowns or transmission delays can intolerably lengthen the time of each iteration. An efficient way to mitigate this problem is to let the PS wait only for the fastest n−b updates, before generating the new parameters. The slowest b workers are called backup workers. The correct choice of the number b of backup workers depends on the cluster configuration and workload, but also (as we show in this paper) on the hyper-parameters of the learning algorithm and the current stage of the training. We propose DBW, an algorithm that dynamically decides the number of backup workers during the training process to maximize the convergence speed at each iteration. Our experiments show that DBW (1) removes the necessity to tune b by preliminary time-consuming experiments, and (2) makes the training up to a factor 3 faster than the optimal static configuration.

Shear-free radiating collapse model via Karmarkar condition in f(R) gravity

In this paper, we have employed the time-dependent Karmarkar condition to the shear-free nonstatic radiative model undergoing dissipative gravitational collapse (GC) with anisotropic radial heat flux distribution in the metric [Formula: see text] formalism. We have obtained the final solutions of the [Formula: see text] field equations under the consideration of three viable models [Formula: see text], [Formula: see text] and [Formula: see text]-[Formula: see text], which are physically realistic at both the early and late-time cosmological epochs. In this relevance, the Karmarkar condition together with boundary condition presents a complete radiating star model which are experienced by the initial static configuration. The matching conditions have been derived between the exterior Vaidya metric and interior line-element across the boundary three surface which permits to study the physical credibility of our radiating star model. Afterwards, we have comprehensively discussed the physical significance of the matter variables and causal thermodynamical profile by graphical representation for our radiating star object. Moreover, we have also studied that the GC proceeds without the appearance of the horizon, i.e. the model is free of horizon.

Modal Analysis of Wake Behind Stationary and Vibrating Cylinders

Abstract The dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) are used to analyze the coherent structures of turbulent flow around vibrating isolated and piggyback cylinders configurations subjected to a uniform flow at a laminar Reynolds number (Re = 200) and a upper transition Reynolds number (Re = 3.6 × 106). Numerical simulations using two-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) approach with the k − ω shear stress transport turbulence model are used to obtain the flow fields snapshots for the analysis. The wake flows behind the cylinders are decomposed into energy optimal modes (POD modes) and dynamical relevant modes (DMD modes). A reduced-order model (ROM) for the flow is built based on the modal analysis. A comparison of POD and DMD is performed to characterize their special features. The present study provides new insights into the flow physics of fluid–structure interaction problem of two coupled cylinders. The characteristic vortex shedding frequencies and their harmonics are identified by DMD modes in all the investigated configurations. It is observed that for single cylinder configurations, the most energetic and the most dynamically important mode is associated with the fundamental shedding frequency. For the stationary piggyback configuration, the gap flow between the cylinders appears to be a dominant flow feature as evidenced by the leading DMD modes. The cylinder vibration increases significantly number of modes necessary to obtain a ROM at the given level of accuracy compared to respective stationary configurations.

Dynamical analysis of screening in scalar-tensor theory

We investigate linear and non-linear dynamics of spherically symmetric perturbations on a static configuration in scalar-tensor theories focusing on the chameleon screening mechanism. We particularly address two questions: how much the perturbations can source the fifth force when the static background is well screened, and whether the resultant fifth force can change the stability and structure of the background configuration. For linear perturbations, we derive a lower bound for the square of the Fourier mode frequency $\omega^2$ using the adiabatic approximation. There may be unstable modes if this lower bound is negative, and we find that the condition of the instability can be changed by the fifth force although this effect is suppressed by the screening parameter. For non-linear perturbations, because we are mainly interested in short wavelength modes for which the fifth force may become stronger, we perform numerical simulations under the planar approximation. For a sufficiently large initial amplitude of the density perturbation, we find that the magnitude of the fifth force can be comparable to that of Newtonian gravity even when the model parameters are chosen so that the static background is well screened. It is also shown that if the screening is effective for the static background, the fluid dynamics is mostly governed by the pressure gradient and is not significantly affected by the fifth force.

In Situ Observations on the Crack Morphology in the Ancient Timber Beams

The conservation of ancient structures is, in the construction panorama, a highly eco-sustainable operation. In fact, it provides for a very limited consumption of resources. This article provides an in-depth analysis of ancient wooden material, an essential element for drawing up correct conservation interventions. Ancient timber beams have a peculiar morphology of failure dependent on many factors, among which are the species of wood, the quality of the material-knots, presence of fissures caused by shrinkage (checks), direction of the grain, and environmental conditions such as temperature and humidity. In addition, it is linked to load conditions and static configuration. This paper presents a case study of failed ancient timber members still in place and describes the type of failure as well as the origin and propagation of the cracks. The objective is to provide a classification of the causes and of the effects and their evolution, useful to practitioners and to those who have to make decisions on the timber structures conservation.

Gravitational collapse of anisotropic stars

We study the gravitational collapse of a spherically symmetric anisotropic relativistic star within Einstein theory of gravity making use of one of our recently developed collapsing stellar models [{\it Astrophys. Space Sci.} {\bf361} 99 (2016)]. The final state of continual gravitational collapse of a massive star under regular initial conditions is analyzed in terms of the formation of black holes. To study the evolution of an anisotropic star undergoing gravitational collapse, it is assumed that the dissipation process happens in the form of radial heat-flux. The interior space-time is described by static metric matched at the boundary with Vaidya metric that describes the exterior to the radiating star. The initial static configuration is described by the relativistic solution obtained by Paul and Deb [{\it Astrophys. Space Sci.} {\bf354} 421 (2014)]. The impact of anisotropy on the dynamical gravitational collapse of a massive star is studied. The relativistic causal heat transport equation of the Maxwell-Cattaneo equation is utilized to show the dependence of anisotropy on the temperature profile of the collapsing system.

Gli «effetti» della tradizione. Trasmutazioni dell’architettura storica nell’opera di Carlo Mollino

“As Daniele Vitale wrote, the elements of historical Alpine tradition seem to be, for Mollino, “pretexts” for an exploration and formal manipulation that seeks its ways and directions. Rural architecture is therefore seen not as the bearer of an “objective rationality”, but as a set of materials that, thanks to the design interpretation, determines unprecedented fields of value. The process that characterizes many of his mountain works rarely follows the linear logic of problem solving but is characterized by a deviation that creates a new value space, a gap that distances it from the outcome considered as a consequential act. Let us think of the device of recovery and distortion of archetypes and conventional configurations of the historical tradition, which become a pretext for reinterpretations that generate new tectonic and formal meanings. Let us consider also their disassembly and reassembly to understand their constructive relationships, static configurations, tectonic logics, which were reused in the creation of his design devices; or the metamorphic and metasemic transmutations of some constructive figures exasperated to the point that, from being part of a whole, they are amplified and hyperbolized until they coincide with the overall architectural configuration. The essay, by retracing some of Carlo Mollino’s numerous projects developed in the Alpine area and some of his main built works, tries to identify some of the conceptual devices employed in his mountain construction site.”

A Moving Target Defense Strategy for Internet of Things Cybersecurity

Internet of Things (IoT) systems are becoming more common and present in our daily lives. The increase of Internet-connected devices has caused attackers to focus their attention more on these devices. Therefore, new and more sophisticated attacks on IoT systems are discovered every day. Currently, to ensure reliability and operability, most IoT systems are designed to operate in a relatively static configuration in a highly heterogeneous environment. However, a system that does not continuously change its configurations, i.e., a static system, gives an advantage to attackers; with enough time and resources, an attacker will eventually find and exploit the vulnerabilities of any static target. This work proposes a Moving Target Defense (MTD) strategy that randomly shuffles the communication protocols through which a node communicates to a gateway in an IoT network. The system’s configuration changes have an associated cost. The objective of the proposed MTD strategy in this work is to balance the increase in system performance overhead, the increase in business impact (system unavailability), and, at the same time, the decrease in the probability of success of a given attack. A framework is proposed to design this strategy; this framework can guide any MTD strategy for IoT systems. The framework’s objective is to find, after several iterations, the MTD strategy parameters that achieve a balance between five different measurable variables of an IoT system.

P. CHEYNE, A. HAMILTON, M. PADDISON (EDS.) PHILOSOPHY OF RHYTHM: AESTHETICS, MUSIC, POETICS. New York: Oxford University Press, 2019 ISBN 978-0-19-934778-0

The review provides an outline of the collective monograph The Philosophy of Rhythm: Aesthetics, Music, Poetics, edited by Peter Cheyne, Andy Hamilton and Max Paddison, published by Oxford University Press, 2019. Concept of rhythm is analysed from different perspectives—philosophical, musicological and psychological. It considers a multidisciplinary approach and also includes both analytic and continental philosophical traditions. Rhythm is viewed as a pulse that is going through various metric structures including particular pieces of music, paintings, examples of poetry and philosophy. Twenty eight authors from the entire world discuss rhythm and specify definitions of rhythm. They try to give answers on crucial questions uniting experienced rhythm in philosophy and arts, thus giving an important contribution to rhythm studies. The book is organised thematically and based on different aspects of rhythm manifestations. The main questions of the research are as follows: How is rhythm experienced? Does rhythm necessarily involve movement? Why rhythm is so deeply rooted in human? How can static configurations be rhythmic? How does a rhythmic structure change from a stable pattern to a flexible texture? All these questions concern two interwoven issues common for the volume in general: immanence of rhythm to arts and human experience of it.

Solvent effect on the 195Pt NMR properties in pyridonate-bridged PtIII dinuclear complex derivatives investigated by ab initio molecular dynamics and localized orbital analysis.

An ab initio molecular dynamics investigation of the solvent effect (water) on the structural parameters, 195Pt NMR spin-spin coupling constants (SSCCs) and chemical shifts of a series of pyridonate-bridged PtIII dinuclear complexes is performed using Kohn-Sham (KS) Car-Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations. The indirect solvent effect (via structural changes) has a dramatic effect on the 1JPtPt SSCCs. The complexes exhibit a strong trans influence in solution, where the Pt-Pt bond lengthens with increasing axial ligand σ-donor strength. In the diaqua complex, where the solvent effect is more pronounced, the SSCCs averaged for CPMD configurations with explicit plus implicit solvation agree much better with the experimental data, while the calculations for static geometry and CPMD unsolvated configurations show large deviations with respect to experiment. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of 1JPtPt and 195Pt chemical shifts. An analysis of 1JPtPt in terms of localized and canonical orbitals shows that the SSCCs are driven by changes in the s-character of the natural atomic orbitals of Pt atoms, which affect the 'Fermi contact' mechanism.

The energy budget of the transition of a neutron star into the third family branch

AbstractTransition of a compact star into the third family for an equation of state (EoS) featuring mass twins is considered. The energy released at a baryon number conserving the transition of static compact stars configurations is computed for two sets of models for comparison. The EoS of choice is the density‐dependent functional DD2 EoS with excluded model corrections for hadronic matter, which suffers a phase transition into deconfined quark matter described by a constant speed of sound approach. The two sets of EoS models feature different compact star mass onsets that maximize the energy and radius difference at the transition while simultaneously fulfilling state‐of‐the‐art constraints from multimessenger astronomy and empirical nuclear data. The maximal energy budget at the transitions was found to fall in the range of 1049 − 1052 ergs.

Scenario-Based Investigation on the Effect of Partial Shading Condition Patterns for Different Static Solar Photovoltaic Array Configurations

This paper presents an in-depth analysis and investigation on the performance of static photovoltaic (PV) array configurations subjected to various partial shading conditions (PSCs). Under PSCs, the electrical characteristics of the PV modules are critically monitored and reasons for their behavioral changes are highlighted. By doing so, this study aims to improve the efficiency of PV systems by minimizing mismatch losses and determining the optimum array configuration which is characterized by the highest maximum power and lowest relative losses under PSCs. Besides, this study complements and carries forward the previous studies through the detailed analysis of each configuration subjected to various practically probable PSCs. Three different PV array sizes ( $5\times4$ , $5\times5$ , and $3\times10$ ) are used to analyze the results and performance under considered shading scenarios. MATLAB/Simulink platform is used to model and simulate the PV array using the single diode (5-parameters) model. In-depth analysis of current flow across cross-ties and bypass diodes activation shows that the diagonal shading pattern leads to lower power loss (PL). Besides, the Total Cross-Tied (TCT) configuration demonstrates superior performance under most of the PSCs compared to other configurations. These results provide valuable information about the performance of PV array which may lead to better estimation and prediction of global maximum power (GMP) generation of a PV system.

Statistical Analysis of Electrical and Non-Electrical Parameters of Photovoltaic Modules in Controlled Tracking Systems

The paper presents statistical analysis of measurement results of electrical parameters for photovoltaic modules installed in stationary and dual-axis configurations. The parameters which were taken into account included: coefficient of variation, skewness and standard deviation. Also a correlation was determined between independent variables such as insolation, sunshine duration, cloudiness, ambient temperature and atmospheric pressure, and the dependent variable in the form of the daily electricity from photovoltaic conversion. In order to determine the repeatability of electricity waveforms occurring between summer months as well as between summer and winter months, the non-parametric U Mann-Whitney test was used. In order to analyse the repeatability of daily peak hours in which the highest value of the hourly electricity production is observed, the non-parametric Kruskal-Wallis test was used. The tested systems were connected to the power grid and operated independently. Test stands consisting of polycrystalline photovoltaic modules, single-phase on-grid inverters, irradiance sensors and a temperature recorder, were located on the building rooftop of the Faculty of Control Robotics and Electrical Engineering of the Poznan University of Technology in Poland (Central Poland, 52°24.4152′N, 16°55.7958′E) at the height of 30 metres above the ground level. A significant increase in the production of electricity using the PV module spatial positioning system was demonstrated in relation to modules based on the year-round modified design.

On Self-configuring IoT with Dual Radios: A Cross-Layer Approach

Growing interest in emerging IoT applications provides a strong drive to release a plethora of communication radios from different standards, which are largely classified into short-range (IEEE 802.15.4) and long-range radios (IEEE 802.15.4g). In this paper, we propose a joint, self-configuring MAC and routing protocol, SEDA-Net, which aims at adaptively choosing the best configuration for communication coordination and data delivery, depending on different deployed topologies and external conditions. SEDA-Net is a combination of SEDA-MAC, SEDA-Routing, and Cross-Opt. SEDA-MAC and SEDA-Routing adaptively determine (i) the best radio configuration for communication coordination under duty-cycling and (ii) each node's next-hop over which radio and Cross-Opt jointly optimizes inter-coupled MAC and routing iteratively. SEDA-Net differs from prior approaches which are designed with static configurations of radios and/or mainly with the goal of throughput maximization for dual Wi-Fi or Wi-Fi/LTE setups. We implement SEDA-Net on Contiki OS and perform extensive simulations and experiments using a testbed in an office building. This testbed consists of 45 nodes equipped with a commercial platform, Firefly, having 2.4 GHz short-range and 920 MHz long-range radios. We demonstrate that energy efficiency quantified by the network lifetime increases by up to 2.1 times, compared to that of existing approaches.

Design and implementation of partition Operating System based on ARINC653 standard

The ARINC series of standards are mainly used to define how to use the computing resources of avionics. The ARINC 653 standard applies to the service interface of the spacecraft’s integrated electronic operating system to the upper-layer application software. It isolates the application software from the underlying processor architecture and meets the requirements of the on-board real-time system with good scalability. This article will follow the ARINC 653 standard, design and implement a partition operating system, providing basic system static configuration capabilities, space partition capabilities, time sharing capabilities, inter-zone communication capabilities, and security monitoring capabilities

Exact hybrid-kinetic equilibria for magnetized plasmas with shearing flows

Context.Magnetized plasmas characterized by shearing flows are present in many natural contexts, such as the Earth’s magnetopause and the solar wind. The collisionless nature of involved plasmas requires a kinetic description. When the width of the shear layer is on the order of ion scales, the hybrid Vlasov-Maxwell approach can be adopted for this purpose.Aims.The aim of this work is to derive explicit forms for stationary configurations of magnetized plasmas with planar shearing flows within the hybrid Vlasov-Maxwell description. Two configurations are considered: the first with a uniform magnetic field obliquely directed with respect to the bulk velocity and the second with a uniform-magnitude variable-direction magnetic field.Methods.We obtained stationary ion distribution functions by combining single-particle constant of motions, which are derived through the study of particle dynamics. Preliminary information about the form of the distribution functions were analytically derived in considering a local approximation for the background electromagnetic field. Then a numerical method was set up to obtain a solution for general profiles.Results.We determined explicit distribution functions that allow us to obtain profiles of density, bulk velocity, temperature, and heat flux. Anisotropy and agyrotropy in the distribution function were also evaluated. The stationarity of the solution during numerical simulations was checked in the uniform oblique magnetic field case.Conclusions.The configurations considered here can be used as models for the Earth’s magnetopause in simulations of the Kelvin-Helmholtz instability.

Numerical analysis of the Cargo Transfer Vessel offloading operation in a Brazilian oil field

In a new concept of offloading operation, the oil from a spread moored FPSO is transferred to a conventional Tanker with an intermediate Cargo Transfer Vessel (CTV) equipped with a DP system. A comprehensive numerical analysis of the CTV offloading operation is here developed considering the sea states in the Libra Field, Brazil. First, the environmental loads on the vessels were estimated. Current and wind forces coefficients were obtained using the CFD software StarCCM+, while wave coefficients were obtained using WAMIT. For the 10-year metocean data, the multi-body static equilibrium configurations of the system – composed of the CTV, Conventional Tanker and Tugboat - were calculated. With those results, it was possible to estimate the downtime considering different offloading sectors and to compare with the DP Shuttle Tanker operation. Finally, a 5-day campaign of real-time simulations was carried out with the presence of DP Operators and captains, to verify critical conditions, considering the human factor. Each vessel was simulated in an individual cabin. For the simulations, the real DP System was integrated with the numerical simulator in a Hardware-in-the-loop configuration, resulting in a more realistic simulation.

Transient dynamics and stability of keyhole at threshold in laser powder bed fusion regime investigated by finite element modeling

A Finite element model is developed with a commercial code to investigate the keyhole dynamics and stability at keyhole threshold, a fusion regime characteristic to laser microwelding or to Laser Powder Bed Fusion. The model includes relevant physics to treat the hydrodynamic problems—surface tension, Marangoni stress, and recoil pressure—as well as a self-consistent ray-tracing algorithm to account for the “beam-trapping” effect. Implemented in both static and scanning laser configurations, the model successfully reproduces some key features that most recent x-ray images have exhibited. The dynamics of the liquid/gas interface is analyzed, in line with the distribution of the absorbed intensity as well as with the increase of the keyhole energy coupling. Based on these results, new elements are provided to discuss our current understanding of the keyhole formation and stability at threshold.

A general way to confined stationary Vlasov-Poisson plasma configurations

We address the existence of stationary solutions of the Vlasov-Poisson system on a domain $\Omega\subset\mathbb{R}^3$ describing a high-temperature plasma which due to the influence of an external magnetic field is spatially confined to a subregion of $\Omega$. In a first part we provide such an existence result for a generalized system of Vlasov-Poisson type and investigate the relation between the strength of the external magnetic field, the sharpness of the confinement and the amount of plasma that is confined measured in terms of the total charges. The key tools here are the method of sub-/supersolutions and the use of first integrals in combination with cutoff functions. In a second part we apply these general results to the usual Vlasov-Poisson equation in three different settings: the infinite and finite cylinder, as well as domains with toroidal symmetry. This way we prove the existence of stationary solutions corresponding to a two-component plasma confined in a Mirror trap, as well as a Tokamak.