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This article analyzes the forced and free vibrations of bi-directional functionally graded (BDFG) porous nanobeams under moving loads by considering the thickness effect based on the nonlocal strain gradient theory (NSGT). It is assumed that the material properties of the system are graded across the transverse and axial directions according to power and exponential laws, respectively. Various porosity models, including even, uneven, and asymmetric porosity distribution patterns, are considered to model the porosity effects. The dynamic equation of the system is derived by implementing the physical neutral surface concept. Analytical and numerical approaches are adopted to acquire the vibration response of the system. Mathematical closed-form expressions are provided for various dynamic phenomena, such as two types of cancelation, two types of resonance, maximum resonance, cancelation disappearance, and resonance disappearance. In addition, for the first time in this article, it is demonstrated that BDFG porous nanobeams under moving loads are prone to experience the double cancelation phenomenon. Several comparison studies with published data are conducted to validate the results. Also, comprehensive parametric studies are carried out to elucidate the impacts of system parameters such as thickness power index, axial gradient parameter, scale parameter ratio, axial force, porosity coefficient, and porosity distribution pattern on the dynamic magnification factor, critical load speed, and maximum free-response. The outcomes established that by considering the thickness effect, the stiffening behavior of the system is amplified depending on the slenderness ratio. Also, it is concluded that, among the considered porous models, the critical load speed for the system with an even porosity distribution is more dependent on the thickness power index. [ABSTRACT FROM AUTHOR]

The dynamics and its phenomena can be interpreted as a physical, objective, and independent measure, but it is ultimately the individual who observes, declares, and predicts it in a subjective approach. Recognizing the existence of these two worlds (objective and subjective) and under the premise that every system is dynamic, this communication highlights the absence of a focus on dynamics in management and especially in entrepreneurship, whose main characteristic is to refer to an individual in action who seeks to develop a project, in a dynamic interaction both external and internal. Under these conditions, the questions arise: Which method do we have to use to help the entrepreneur to develop his project considering the dynamic that surrounds him? This method could help the researcher to generate theories that be useful to the former? To answer them, we base ourselves on the phenomena derived from dynamic systems and on a constructivist epistemological position, to highlight the importance of qualitative method to help the entrepreneur to build both his project and his reality and at the same time for the researcher to develop theories that have the character of actionable. [ABSTRACT FROM AUTHOR]

Sessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarisation optical (video)microscopy (POM). During heating/cooling cycles, at first, the droplets change their shape from spherical to extended ellipsoidal. Then, they start to move rapidly along the surface electric field, i.e. along the crystal's polar axis (c-axis). During this motion, several droplets merge into running streams (tendrils) extending towards the edges of the top surface area. Finally, practically all liquid crystalline material is transported from the top surface to the side surfaces of the crystal. At stabilised temperatures, laser illumination of the assembly causes dynamic processes that are localised to the illuminated area. Also, in this case, the LC droplets merge into several tendril-like formations that are preferentially oriented along the c-axis of the crystal. The pattern of tendrils fluctuates with time, but it persists as long as the illumination is present. In this case, the LC material is transported between the central and the edge regions of the illuminated area. [ABSTRACT FROM AUTHOR]

We studied the dynamic magnetic properties such as dynamic phase transitions, dynamic compensation temperatures, and dynamic phase diagrams in the spin-7/2 multilayer Ising system under an oscillating external magnetic field The system was simulated in the mean-field approximation using a Glauber type stochastic dynamic. The mean sublattice magnetizations' time variations were examined to determine the system's dynamic phases. The thermal behavior of dynamic sublattice magnetizations was investigated to determine the type of dynamic phase transitions (first- or second-order) and to obtain the dynamic compensation temperatures. P − , Q − , R − , S − , and L − type compensating behaviors were seen in various types of magnetization curves. The phase diagrams are calculated in J − T , T − h , and d − T planes, for different values of the Hamiltonian parameters. The p, i, f1/2, f7/2, af7/2, and af1/2 fundamental phases, as well as the i + p, i + f1/2, af1/2 + p, af7/2 + p and i + af1/2 mixed phases. The system illustrated one, two, or three dynamic critical points (•) and E, TP, Z, and B special points. [ABSTRACT FROM AUTHOR]

Ni0.80-xCu0.20ZnxFe2O4 (step size 0.05) with titular compiled chemical of various spinel ferrites have been synthesized through auto-combustion and characterized through X-ray diffraction for structural analysis which showed 43 to 46 nm distributed cubic spinel. The effect of Zn2+ substitutions to dilute the NiCuZn ferrites has been studied with electrical modulus analysis and impedance measurements within the frequency range from 20 to 5 MHz. Besides semicircular arc tendency, two-layer leaky capacitor model is indicated by the complex impedance spectroscopy at lower- and higher-frequency ranges. Non-Debye type relaxation has been revealed clearly in the electric modulus spectra. Non-Debye type dielectric nature is found in the dielectric spectrum and checked by the Non-modified Debye equation. The AC conductivity spectrum is found in increasing order and justified by theoretical Jonscher Power Law. The Cole–Cole plots confirm the single semicircles for grain boundary contribution at the lower-frequency zone, which is further justified by the theoretical model. The role of Zn in modifying nanostructure and impedance spectra of these ferrites has been explained. [ABSTRACT FROM AUTHOR]

Insects use dynamic articulation and actuation of their abdomen and other appendages to augment aerodynamic flight control. These dynamic phenomena in flight serve many purposes, including maintaining balance, enhancing stability, and extending maneuverability. The behaviors have been observed and measured by biologists but have not been well modeled in a flight dynamics framework. Biological appendages are generally comparatively large, actuated in rotation, and serve multiple biological functions. Technological moving masses for flight control have tended to be compact, translational, internally mounted and dedicated to the task. Many flight characteristics of biological flyers far exceed any technological flyers on the same scale. Mathematical tools that support modern control techniques to explore and manage these actuator functions may unlock new opportunities to achieve agility. The compact tensor model of multibody aircraft flight dynamics developed here allows unified dynamic and aerodynamic simulation and control of bioinspired aircraft with wings and any number of idealized appendage masses. The demonstrated aircraft model was a dragonfly-like fixed-wing aircraft. The control effect of the moving abdomen was comparable to the control surfaces, with lateral abdominal motion substituting for an aerodynamic rudder to achieve coordinated turns. Vertical fuselage motion achieved the same effect as an elevator, and included potentially useful transient torque reactions both up and down. The best performance was achieved when both moving masses and control surfaces were employed in the control solution. An aircraft with fuselage actuation combined with conventional control surfaces could be managed with a modern optimal controller designed using the multibody flight dynamics model presented here. [ABSTRACT FROM AUTHOR]

Insects use dynamic articulation and actuation of their abdomen and other appendages to augment aerodynamic flight control. These dynamic phenomena in flight serve many purposes, including maintaining balance, enhancing stability, and extending maneuverability. The behaviors have been observed and measured by biologists but have not been well modeled in a flight dynamics framework. Biological appendages are generally comparatively large, actuated in rotation, and serve multiple biological functions. Technological moving masses for flight control have tended to be compact, translational, internally mounted and dedicated to the task. Many flight characteristics of biological flyers far exceed any technological flyers on the same scale. Mathematical tools that support modern control techniques to explore and manage these actuator functions may unlock new opportunities to achieve agility. The compact tensor model of multibody aircraft flight dynamics developed here allows unified dynamic and aerodynamic simulation and control of bioinspired aircraft with wings and any number of idealized appendage masses. The demonstrated aircraft model was a dragonfly-like fixed-wing aircraft. The control effect of the moving abdomen was comparable to the control surfaces, with lateral abdominal motion substituting for an aerodynamic rudder to achieve coordinated turns. Vertical fuselage motion achieved the same effect as an elevator, and included potentially useful transient torque reactions both up and down. The best performance was achieved when both moving masses and control surfaces were employed in the control solution. An aircraft with fuselage actuation combined with conventional control surfaces could be managed with a modern optimal controller designed using the multibody flight dynamics model presented here.

The development of the automotive industry is conditioned by the application of production technologies, which directly depend on production volumes. Today's development of car production is possible only in conjunction with the volume of production, ensuring both the parameters of assembly and production quality. Their constant monitoring is related to the application of the verification tools and technologies used. Such is the length measurement process that needs to be precise in the automotive industry. The paper analyzes the precision length measurement system and its dynamic characteristics. The research is applied to solve the problems of dynamic processes of a precision length measuring system, and the obtained results can be used in the development of precision systems for other purposes. The obtained results describe the vibrations of the length measuring system housing and the measuring head, which show the weak points of the system at the respective frequencies. The paper analyzes the precision length measurement system and its dynamic characteristics. The obtained results describe the vibrations of the length measuring system housing and the measuring head, which show the weak points of the system at the respective frequencies. [ABSTRACT FROM AUTHOR]

Sensor networks (SN) are increasingly used for the observation and monitoring of spatiotemporal phenomena and their dynamics such as pollution, noise and forest fires. In multisensory systems, a sensor node may be equipped with different sensing units to observe and detect several spatiotemporal phenomena at the same time. Simultaneous detection of different phenomena can be used to infer their spatial interactions over space and time. For this purpose, decentralized spatial computing approaches have shown their potential for effective reasoning on spatial phenomena within a sensor network. However, in most cases, spatial extents of continuous dynamic phenomena are uncertain, and their relations and interactions cannot be inferred by the existing approaches at the sensor node level. To address this limitation, in this paper, we propose and develop a decentralized fuzzy rule-based spatial reasoning approach to depict the spatial relations that hold between two evolving spatial phenomena with fuzzy boundaries. The proposed method benefits from a more adapted fuzzy-crisp representation of dynamic phenomena observed by SN where each vague phenomenon is composed of five distinguished zones including the kernel, conjecture and exterior zone and their boundaries. For each detected phenomenon, a sensor node will report one of these zones based on its location. Aggregation of the information reported from the sensor nodes allows reasoning on spatial relations between the observed phenomena and their evolution. Such spatial information provides users with more valuable near real-time information on the state of different phenomena that can be used for informed decision-making.

Dynamic Mode Decomposition (DMD) is a technique that enables investigation of unsteady and dynamic phenomena by decomposing data into coherent modes with corresponding growth rates and oscillatory frequencies. Because the method identifies structures unbiased by energy, it is particularly well suited to exploring dynamic processes having phenomena that span disparate temporal and spatial scales. In turbulent combustion, DMD has been previously applied to the analysis of narrowband phenomena such as combustion instabilities utilising both experimental and computational data. In this work, DMD is used as a tool to analyse broadband turbulent combustion phenomena from a three-dimensional direct numerical simulation of a low Mach number spatially-evolving turbulent planar premixed hydrogen/air jet flame. The focus of this investigation is on defining the metric of convergence of the DMD modes for broadband phenomena when both the temporal resolution and number of data snapshots can be varied independently. The residual is identified as an effective, even if imperfect, metric for judging convergence of the DMD modes. Other metrics - specifically, the convergence of the mode eigenvalues and the decay of the amplitudes of the modes - fail to capture convergence of the modes independently but do complete the information needed to evaluate the quality of the DMD analysis. [ABSTRACT FROM AUTHOR]

Substituting a valve plate-based commutation unit with a hydrostatic-load-free commutation bushing controllable with a signal of negligible power, that could be applied in constant and variable displacement pumps introduced a different approach to the design of commutation units in multi-piston axial hydraulic pumps. Conducted research showed that valve plate-based commutator is responsible for over 50% energy loss. The new idea assumed a stationary cylinder block and the replacement of the valve plate with a camdriven commutation unit that would be totally unloaded hydrostatically. That eliminated main source of mechanical losses as well as a flow resistance loss. Additionally, the dead volume was significantly reduced, which helped to reduce the pump noise level and resulted in a great decrease in power needed to control the pump displacement. That allowed to eliminate a servomechanism and the direct control of the pump displacement with a low power element. However, the new design presented a challenge in the form of pressure peaks occurring in the working chamber, which were difficult to eliminate. This article presents attempts to solve problems connected with those dynamic phenomena. [ABSTRACT FROM AUTHOR]

Monitoring highly dynamic environments is a difficult task when the changes within the systems require high speed monitoring systems. An active sensing system has to solve the problem of overlapped responses coming from different parts of the surveyed environment. Thus, the need of a new representation space which separates the overlapped responses, is mandatory. This paper describes two new concepts for high speed active sensing systems. On the emitter side, we propose a phase-space-based waveform design that presents a unique shape in the phase space, which can be easily converted into a real signal. We call it phase space lobe. The instantaneous frequency (IF) law of the emitted signal is found inside the time series. The main advantage of this new concept is its capability to generate several distinct signals, non-orthogonal in the time/frequency domain but orthogonal within the representation space, namely the phase diagram. On the receiver side, the IF law information is estimated in the phase diagram representation domain by quantifying the recurrent states of the system. This waveform design technique gives the possibility to develop the high speed sensing methods, adapted for monitoring complex dynamic phenomena In our paper, as an applicative context, we consider the problem of estimating the time of flight in an dynamic acoustic environment. In this context, we show through experimental trials that our approach provides three times more accurate estimation of time of flight than spectrogram based technique. This very good accuracy comes from the capability of our approach to generate separable IF law components as well as from the quantification in phase diagram, both of them being the key element of our approach for high speed sensing.

There exists a sort of dynamic geographic phenomenon in the real world that has a property which is maintained from production through development to death. Using traditional storage units, e.g., point, line, and polygon, researchers face great challenges in exploring the spatial evolution of dynamic phenomena during their lifespan. Thus, this paper proposes a process-oriented two-tier graph model named PoTGM to store the dynamic geographic phenomena. The core ideas of PoTGM are as follows. 1) A dynamic geographic phenomenon is abstracted into a process with a property that is maintained from production through development to death. A process consists of evolution sequences which include instantaneous states. 2) PoTGM integrates a process graph and a sequence graph using a node⁻edge structure, in which there are four types of nodes, i.e., a process node, a sequence node, a state node, and a linked node, as well as two types of edges, i.e., an including edge and an evolution edge. 3) A node stores an object, i.e., a process object, a sequence object, or a state object, and an edge stores a relationship, i.e., an including or evolution relationship between two objects. Experiments on simulated datasets are used to demonstrate an at least one order of magnitude advantage of PoTGM in relation to relationship querying and to compare it with the Oracle spatial database. The applications on the sea surface temperature remote sensing products in the Pacific Ocean show that PoTGM can effectively explore marine objects as well as spatial evolution, and these behaviors may provide new references for global change research.

In this work, the coopetitive relationships among dynamic ferrite transformation, reverse ferrite transformation, and austenite recrystallization were investigated by using dynamic dilatometry, optical metallography, and electron backscattering diffraction in an aluminum-containing low-carbon steel subjected to hot compressions in the two-phase region. The microscopic mechanism of concurrent dynamic softening was studied based on the analysis of transformation crystallography. Moreover, this analysis method was used to discover the occurrence of reverse-transformation-induced recrystallization. In this microscopic mechanism, new austenite grains formed by reverse transformation can act as seeds for recrystallization. These paths for microstructural control in steels are not common, but they can be enabled by critical thermo-mechanical treatments combined with proper alloy design. [ABSTRACT FROM AUTHOR]

We demonstrate a strong dependence of twinning stress (TS) on twin boundary (TB) velocity in Ni 50 Mn 28 Ga 22 5M martensite. Different types of TBs exhibit substantially different dynamic properties under magnetic field actuation. For type 1 interface, the dynamic TS drastically increases from its quasi-static value of ~ 0.6 to ~ 3.2 MPa, limiting the TB velocity to 3–4 m/s at saturation magnetic driving force. Type 2 TBs show a gradual increase of the TS from ~ 0.1 MPa to ~ 2 MPa, reaching velocities of ~ 35–39 m/s. Our findings bring to the fore type 2 interfaces for applications demanding high actuation speeds and frequencies. [ABSTRACT FROM AUTHOR]

The use of high strength Al-Zn-Mg-Cu alloys in automotive components is restricted by their low formability. Warm forming in the under-aged state improves formability, but induces a strain-dependent microstructure evolution due to dynamic precipitation. We present a new methodology to quantitatively evaluate the dynamic precipitation strain dependence which is applicable to strain rates relevant to forming. The plastic strain is varied using a tapered tensile sample and the precipitation state is measured in terms of size and volume fraction using spatially resolved small-angle X-ray scattering, showing its evolution during straining is dependent on the imposed strain level and rate. [ABSTRACT FROM AUTHOR]

Glass is a liquid-like disordered material but behaves mechanically like a solid. Ubiquitous in nature and important in technology, the vitreous state manifests its presence from window glass, polymers, to optical fiber, and almost all kinds of materials have ability to form glass. Significant progress has been made in understanding the nature of the phenomenon, yet the issue remains a major scientific challenge. Here we propose one concise, explicit thermodynamic expression in both temperature and pressure for the configurational entropy of the Adam-Gibbs theory, and show its excellent universal description of experimental data. The formulation generalizes the most important equations in the field such as the VFT equation, judiciously unifies for the first time the two key thermodynamic variables in one form, has non-divergence which resolves the long-standing Kauzmann paradox, tentatively provides a sound foundation addressing the mutual effects of temperature and pressure, and predicts the glass transition as a second-order phase transition. This approach should thus offer an organizing principle to rationalize the vast body of dynamic properties and advance researches on the thermodynamics including the glass transition of glass-forming substances. [ABSTRACT FROM AUTHOR]

The microscopic origin of the remarkable optoelectronic properties of one of the most studied contemporary materials remains unclear. Here, we identify the existence of magnetic interactions between intermolecular proton orbitals in CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3. In particular, a unique sharp drop and a pronounced step-up discontinuity in the magnetic susceptibility at the tetragonal-to-cubic phase transitions are identified in CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 , respectively. The magnetic interactions in the orthorhombic and tetragonal phases are dependent on thermal history and lattice orientation while nearly independent of the applied external magnetic field. In CH 3 NH 3 PbBr 3 , the CH 3 and NH 3 + components reorient in an uncorrelated fashion resulting the cubic phase to also exhibit magnetic anisotropy. Our findings provide a potential link connecting the highly light-absorbing CH 3 NH 3 + and the exceptional properties of the charge carriers of the inorganic framework in hybrid perovskite solar cells. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] We report time- and angle-resolved photoemission spectroscopy on SnSe which currently attracts great interest due to its extremely high thermoelectric performance. Laser-assisted photoemission signals are observed within ± 20 fs of the pump pulse arrival. Around 30–50 fs after the photoexcitation, the conduction band minima are not populated by the photoexcited electrons while the valence bands are considerably broadened. In going from 90 fs to 550 fs after the photoexcitation, the photoexcited carriers are decayed into the multiple conduction band minima. The observed conduction bands are consistent with the band structure calculations. The multiple conduction minima suggest possibility of high and anisotropic thermoelectric performance of n -type SnSe single crystal if it is realized. [ABSTRACT FROM AUTHOR]

In this work we show how dynamic speckle information can be extracted directly from digital holograms. This allows improving the analysis and characterization of dynamic phenomena by combining dynamic speckle with digital holographic interferometry measurements. We have studied the drying process of paint coatings, which is a typical study case in the field of dynamic speckle characterization, since the speckle activity (SA) of drying coatings is known to decay smoothly as a function of time. We recorded both holograms and speckle images during the process. In this way, we could compare the evolution of global SA calculated from speckle images by a standard method with the evolution of speckle correlation extracted directly from the holograms. The results obtained from both methods have shown to be in good agreement. [ABSTRACT FROM AUTHOR]

We report a direct observation of fast Type II twin boundary motion under a pulsed magnetic field excitation in Ni–Mn–Ga 5 M martensite, utilizing high-speed camera technique. Our results demonstrate saturation velocities up to ~ 39 m/s measured along [100] direction for individual boundaries moving at RT, showing an order of magnitude larger values as compared to the earlier studies. Actuation response times of ~ 1 μs were observed using laser vibrometry technique. The reported results show a minor role of magneto-static forces and emphasize the role of inertia and internal friction in twin boundary dynamics at the measured speeds. [ABSTRACT FROM AUTHOR]

We measured the temperature rise of the high-frequency magnetic-field-induced martensite reorientation in Ni–Mn–Ga Ferromagnetic Shape Memory Alloy and observed the morphology of the associated twin boundaries. It was found that this temperature rise is mainly caused by low-friction Type II twin boundary motion, even though high-friction Type I twin boundary motion is dominant in quasi-static stress-induced martensite reorientation. A simple formula considering the frictional twin boundary motion and heat transfer is derived to describe this temperature rise. [ABSTRACT FROM AUTHOR]

The dynamics of plane front growth during directional solidification is investigated in a well-characterized system of succinonitrile–acetone, and the results show significant deviations from the predictions of existing models. This discrepancy is shown to arise from the assumption of solidification from one end in the theories that ignore the presence of an initial solute boundary layer generally present in experiments. A numerical model that relaxes this assumption is presented that gives excellent agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: It is shown that assumed anelastic relaxation-time spectra can be recovered reliably from simulated loss–modulus curves that include noise by nonlinear least-squares fitting. The same method is used to obtain spectra for published experimental data on a metallic glass. The results provide a comprehensive kinetic picture of the atomically quantized hierarchy of shear transformation zones (STZs). We resolve a window of STZs consisting of 25–33atoms, and a simultaneous fit yields the Arrhenius behavior for each size. The corresponding activation energies are 1.75–2.31eV. The high activation energy that is often observed above T g is shown to be an artifact of the temperature dependence of the high-frequency shear modulus. The hierarchy of STZ sizes is consistent with both α and β relaxations, suggesting that they originate from the same microscopic mechanism. [Copyright &y& Elsevier]

Abstract: This Viewpoint highlights recent advances in oxygen evolution reaction (OER) catalysis using well-defined/characterized systems and outlines a path for possible further improvements. First, we review our results on ultra-thin film catalysts and compare them to other systems, emphasizing methods that provide accurate intrinsic catalyst activities. We then discuss reports that catalysts with the highest OER activities (in base) often undergo structural and chemical changes during the OER. These findings have implications on how OER catalysts are studied and designed. We suggest opportunities to control molecular-scale interactions in hydrous layered hydroxide/oxyhydroxide catalysts as well as the control of three-dimensional nano- and microstructures using templating approaches. [Copyright &y& Elsevier]

Abstract: We investigate the effect of grain boundary inclination with respect to the loading direction on void nucleation at a boundary, using plate impact experiments on polycrystalline copper. Examination of damaged specimens reveals that boundaries perpendicular to the loading direction are an order of magnitude more susceptible to failure than those parallel to the loading direction. We investigate the mechanisms and reasons behind this experimental observation through molecular dynamics (MD) simulations, as a function of loading direction, in a copper bicrystal. Two extremes of loading directions are considered, either parallel or perpendicular to the grain boundary plane, spanning the range that grain boundaries within a polycrystalline sample will ordinarily experience under uniaxial strain conditions. Using MD simulations, we demonstrate that, during shock compression, the ability of a boundary to undergo plastic deformation is altered measurably by changing the loading direction with respect to the boundary plane. This change in the plastic response of the GB affects the development of stress concentrations believed to be responsible for void nucleation. MD simulations show that boundaries perpendicular to the loading direction do not undergo as much plastic deformation, by dislocation emission, as those parallel to the loading direction. The lack of plastic deformation at the GB, in the perpendicular loading case, can decrease the stress required for void nucleation. The MD results are consistent with experimental observations, and support the contention that plastic response of a grain boundary under shock compression can be a contributing, or even dominating, factor in determining the stress for void nucleation. [Copyright &y& Elsevier]

A novel temperature-dependent electrochemical system has been designed for in-operando time-resolved X-ray diffraction (XRD) study with laboratory X-ray sources. Meanwhile, a dedicated in-situ XRD battery cell has been designed for the in-situ XRD characterization of standard coin cell batteries. Thanks to a shaped Be window, the detection-angle of this in-operando system covers a wide range from 4° to 160° XRD patterns can be collected over the wide temperature range, -30 °C to 100 °C. To test the device, LiMn 2 O 4 and LiFePO 4 electrode materials are measured and in-operando XRD data are collected in electrochemical processes at low and high temperatures. This in-operando system enables original in-operando investigations on the electrode structural evolution of batteries vs. temperature, allowing a deeper understanding of the structural evolution of electrode materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Recent interest in lightweight metallic hollow sphere foams for aerospace applications requires a better physical understanding of dynamic properties of single spheres. Finite element modelling supported by high rate experiments was developed to investigate the underlying deformation and failure mechanisms of electrodeposited nickel thin-walled hollow spheres. Parametric simulation was performed to further explore the effect of sphere geometry (wall thickness to diameter ratio) and loading rate. It was found that decreasing the ratio of wall thickness to diameter tends to transit the side wall failure mode from bending to buckling. For a thin-walled sphere (the thickness to diameter ratio less than a critical value), the macroscopic dynamic behaviour is primarily dominated by the two deformation and failure mechanisms: (1) buckling failures of wall materials and (2) self-contacts of wall surfaces and wall-anvil contacts. At higher impact velocity (greater than a critical velocity), inertia effect due to dynamic localisation of wall crushing arises and significantly influences the deformation/failure mode of the sphere, resulting in an increased initial crushing strength and asymmetric deformation. Finally, the behaviour of hollow spheres was correlated to explore the power law behaviour of bulk foams with respect to the relative density; it was found that metallic thin-walled hollow sphere foams can be better approximated as open-cell rather than closed-cell foams. [Copyright &y& Elsevier]

Abstract: The thermal barrier coatings (TBCs) used on the hot section components of many aero-turbines face a variety of compromising conditions while in service. One condition of particular concern on high-pressure turbine (HPT) blades is foreign object damage (FOD) wherein hard foreign particles, often found in the gas path of operating aero-turbines, are struck by the leading edge of the HPT blades. Even single impacts of this kind can cause complete spallation of the local TBC, removing thermal protection on one of the hottest component surfaces in the entire engine. We present here the first experimental FOD study we know of where the impacting particle size, geometry, and velocity, as well as TBC temperature, are well known at each impact site. We then quantitatively compare the experimental impact crater profiles with numerical simulations of equivalent impact scenarios, finding excellent agreement and thereby validating the numerical modeling techniques and parameters. Finally, we present a numerical parameter study of particle and TBC material properties using the validated model. [Copyright &y& Elsevier]

Abstract: Using high-resolution extensometry, the recurrent occurrence of deformation bands is observed both before and after the onset of macroscopic stress serrations during tensile deformation of a FeMnC steel at a constant crosshead velocity. The serrations are due to intense deformation bands but the overall spatiotemporal pattern reveals progressive emerging and not a well-defined onset of these strain localizations, thus questioning the conventional approach to the determination of the critical strain for the onset of plastic instability in such steels, based on the observation of the macroscopic stress serrations. The analysis of the local strain-rate maps uncovers distinct scales of plastic processes. This conjecture is confirmed by Fourier analysis of the macroscopically smooth portions of tensile curves displaying small-scale multiple-frequency stress oscillations. [Copyright &y& Elsevier]

Abstract: The jerky flow of dilute alloys, or the Portevin–Le Chatelier effect, has a burst-like intermittent character at different fluctuation size levels. Multifractal analysis is applied to both the macroscopic stress serrations and the acoustic emission accompanying the plastic deformation. Multifractal scaling is found for both kinds of time series. The scaling range of the stress serrations is limited from below by their characteristic frequency. Unexpectedly, the scaling range for acoustic bursts not only covers this range but spreads to much shorter time scales with the same scaling exponent. This result testifies that the deformation processes revealed by the acoustic emission at a mesoscopic scale have a similar nature during both stress serrations and smooth plastic flow. The implications on the crossovers in the dynamics of jerky flow are discussed. [Copyright &y& Elsevier]

Abstract: Four different mesoporous silica (MS) samples were synthesized for assessment as candidate rapid-response desiccant materials. Their behaviour was compared with that of conventional desiccants. The aim was to enable tuning of hygrothermal functional behaviour by correlating this with microstructural composition. Pore geometry was characterized and validated using small-angle X-ray diffraction, Brunauer–Emmett–Teller analysis, Barrett–Joyner–Halenda analysis and high-resolution transmission electron microscopy. The volume and mean diameter of the mesopore network are directly related, and when increased cause a proportional decrease in macropore volume and bulk porosity, suggesting that the pore wall thickness decreases at larger mesopore volumes. Thermophysical properties were characterized using modified transient plane source and differential scanning calorimetry. Vapour storage and sorption/desorption response rates were characterized using modified dynamic vapour sorption (DVS) techniques. The DVS response time, t emc, has a positive logarithmic relationship with both mesopore diameter and mesopore volume, whilst vapour permeance appears to be inversely related. All MS samples had a significantly higher vapour storage capacity and quicker DVS response rate than the conventional desiccants, including silica gel, zeolite, molecular sieve and bentonite. [Copyright &y& Elsevier]

Using a work-hardened aluminum alloy that exhibits dynamic strain aging, oscillations in strain rate transitioning into intermittent local plastic activity are observed through an extended elastoplastic transition, before onset of the Portevin–Le Chatelier effect. Fourier analysis confirms this intermittency spans multiple scales. Wavelet analysis provides a method of quantifying transitions in the deformation behavior in both the time and frequency domains, and reveals a period doubling transition in both the local strain rate and global load signals. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the dynamic performances of partially bonded or unbonded metallic hollow sphere structure (MHSS). Under the condition that the densities of MHSS are the same, three morphologies, that is, simple cubic (SC), body-centered cubic (BCC) and face-centered cubic (FCC) are investigated to see the topological effect of lattice structure on the dynamic performance of MHS agglomerates. [Copyright &y& Elsevier]

Abstract: Inelastic light scattering is used to study lattice dynamics of strontium titanate (STO) ceramics with several heterovalent dopants (La3+, Gd3+, Y3+), which substitute Sr2+ ions. An extraordinary shift of the antiferrodistortive transition temperature (T a) is ascertained when just a small percentage of any of the dopants is used. T a is dependent on the tolerance factor (t). In this work, it is clearly shown that, regardless of the dopant used, a common linear dependence of T a vs. t is obtained if strontium vacancies are taken into account. A vacancy size of ∼1.547Å was estimated, which is ∼7% larger than the Sr2+ radius. The vacancy size obtained can directly explain the increase in lattice parameter with increasing Bi3+ content in Bi-doped STO, as opposed to the dopants referred to above. Furthermore, the introduction of La3+, Gd3+ or Y3+ ions at the Sr site causes a considerable stiffening of the transverse optic TO1 mode at low temperatures, thereby decreasing the phonon contribution to the dielectric permittivity. Thus, no traces of a ferroelectric phase are found for any of the dopants used in this work. [Copyright &y& Elsevier]

Abstract: This paper presents a multi-physical dynamic fuel cell stack model. This model covers three major physical domains: electrical, fluidic and thermal. The dynamic model in each domain is presented. The fuel cell stack model is obtained by stacking method from a generalized single cell model, thus the spatial effect through the stack can be modelled and observed. The stack model is validated temporally and spatially against a Ballard NEXA 1.2kW 47 cells fuel cell stack. Then, the dynamic behaviour in each physical domain is analysed. It can be approximated by a first order system, thus the expressions of time constants in different domain are obtained. Finally, the fuel cell stack spatial non-homogeneity is analysed. From the results, a fuel cell stack model reduction method is proposed in order to reduce the computation time during simulations. The reduced fuel cell stack model is validated against the full model. [ABSTRACT FROM AUTHOR]

Abstract: The grain boundary kinetics of a SrTiO3 bicrystal with a misorientation relationship of 36.8°/[100] (Σ5) is examined at elevated temperatures by in situ high-resolution transmission electron microscopy. At 973K, the grain boundary migrates by the propagation of atomic steps with a height of half a unit cell (∼0.2nm), but at 1173K, it becomes rough and advances without the requirement of steps. All the temperatures examined are below the thermal roughening transition temperature of the grain boundary. These results give a clear indication of grain boundary kinetic roughening. We suggest that our present results may lead to the development of a unifying framework for previously suggested grain boundary migration mechanisms. [Copyright &y& Elsevier]

We are surrounded by collective phenomena, with examples existing on many levels of granularity. Despite our frequent experiences of such phenomena they seem to have been largely ignored within the field of ontology. In this paper, existing ontologies are examined to determine the extent to which they can adequately represent collective phenomena, and are found wanting in a number of important respects. An adequate representation of collective phenomena must do justice to the often subtle relationship that exists between a collective viewed as a whole and its constitution as a plurality of individual participants. An important prerequisite for this is to determine the range of variation that exists within the broad class of collectives. Numerous examples of collective phenomena have been studied to extract appropriate classification criteria. The results from this study are used to produce a new typology of collectives which is intended to establish a basis for the adequate treatment of collectives within an ontology. To illustrate the classification system we show how it can be used to highlight the significant distinctions between a suitably diverse range of examples. The paper concludes with a set of further research questions that have been raised during the development of the taxonomy. [ABSTRACT FROM AUTHOR]

Abstract: Atomistic simulations are used to investigate how the nanoindentation mechanism influences dislocation nucleation under molecular dynamic behavior on the aluminum (001) surface. The characteristics of molecular dynamics in terms of various nucleation criteria are explored, including various molecular models, a multi-step load/unload cycle, deformation mechanism of atoms, tilt angle of the indenter, and slip vectors. Simulation results show that both the plastic energy and the adhesive force increase with increasing nanoindentation depths. The maximum forces for all indentation depths decrease with increasing multi-step load/unload cycle time. Dislocation nucleation, gliding, and interaction occur along Shockley partials on (111) slip planes. The indentation force applied along the normal direction, a tilt angle of 0°, is smaller than the force component that acts on the surface atoms. The corresponding slip vector of the atoms in the (111) plane has low-energy sessile stair-rod dislocations in the pyramid of intrinsic stacking faults. [Copyright &y& Elsevier]

At approximately 13GPa, body-centered cubic alpha-iron undergoes a fully reversible, pressure-induced phase transition into hexagonal close-packed epsilon-iron. Microstructural evidence of this phase transition has been identified in the fully reverted alpha-iron as a large number of {332} twins found primarily as secondary twins within {112} primary twins. The {332} twins were produced during high-pressure shock-loading of 1018 steel at a peak pressure above the alpha-epsilon phase transition pressure. The twins were identified using electron backscattered diffraction and transmission electron microscopy. [Copyright &y& Elsevier]

Micron-size titanium powder was deposited on a steel substrate by a warm spraying process, in which particles were accelerated and simultaneously heated by a supersonic gas flow. The gas temperature was controlled to soften the metal below its melting point before impacting onto the substrate. The particles were deposited with very high efficiency and bonded well to the substrate due to the thermal softening. Remarkably, fully nanocrystalline particles were formed by dynamic recrystallization without any pretreatment of the powder. [Copyright &y& Elsevier]

Abstract: The evolution of orientation distributions of γ and γ′ phases in crept Ni-base single crystal superalloys have been investigated by theoretical calculations with elastic–plastic models and by experiments. As creep deformation proceeds, the crystallographic orientation distributions for both phases are broadened as a result of the waving of the raft structure, which occurs to reduce the total mechanical energy. The broadening of the orientation distribution occurs in such a way that the 001 pole broadens isotropically while the h k 0 poles broaden preferentially along the 〈001〉 directions. Since the extent of the broadening increases almost linearly with the number of creep deformation, the measurement of the broadening by X-ray diffraction can be utilized in non-destructive methods to predict the lifetime of Ni-base superalloys. [Copyright &y& Elsevier]

The anisotropic effects on the microstructure and mechanical response of rolled magnesium alloy Mg–3Al–1Zn in the H24 condition have been quantified. Strong strain rate dependences on the compressive yield, hardening rate and ductility were observed in the normal direction, while the rolling and transverse directions exhibited no strain rate dependence on the yield strength, but did show a marked increase in hardening at a characteristic strain level. The microstructural characteristics associated with the different mechanical property tests were also determined. [Copyright &y& Elsevier]