Type Boundary Research Articles

Extending the admissible control-loop delays for the inverted pendulum by fractional-order proportional-derivative controller

Stabilization of the inverted pendulum by fractional-order proportional-derivative (PD) feedback with two delays is investigated. This feedback law is obtained as a combination of PD feedback with two delays and fractional-order PD feedback with a single delay. Different types of stabilizability boundaries and the corresponding geometric and multiplicity conditions are determined using the D-subdivision method. The stabilizable region is depicted in the plane of the delay parameters for given fractional derivative orders. Several special cases and the concept of delay detuning are also discussed. It is shown that the admissible delay can be slightly increased compared to the integer-order PD feedback by introducing a fractional-order feedback term.

Effect of hydrogen-vacancy cluster on the tensile strength of alpha-titanium twin boundaries: A first-principles investigation

This study investigated the formation of hydrogen-vacancy cluster at twin boundaries (TBs) in alpha-titanium and their impact on TB strength. Using first-principles calculations, it is found that a single vacancy (VA) on the {10−12} TB plane can trap up to five hydrogen atoms, while the single VA on the {10−11} TB plane can accommodate up to eight hydrogen atoms. The presence of VA weakens TBs by reducing the number of Ti-Ti bonds near the TBs. However, in the {10−12} TB with VAH5, the enhancement effect of Ti-H-Ti bonds dominates over the weakening effect of electron transfer, resulting in a slight increase in tensile strength compared to {10−12} TB with VA. On the other hand, in the {10−11} TB with VAH8, the weakening effect of electron transfer dominates, leading to a further reduction in tensile strength relative to {10−11} TB with VA. Therefore, the effect of hydrogen-vacancy cluster on the strength of twin boundaries is sensitive to the type of twin boundary. These findings provide valuable insights into the role of hydrogen in the embrittlement of alpha-titanium.

De Sitter space, extremal surfaces, and time entanglement

We refine previous investigations on de Sitter space and extremal surfaces anchored at the future boundary $I^+$. Since such surfaces do not return, they require extra data or boundary conditions in the past (interior). In entirely Lorentzian de Sitter spacetime, this leads to future-past timelike surfaces stretching between $I^\pm$. Apart from an overall $-i$ factor (relative to spacelike surfaces in $AdS$) their areas are real and positive. With a no-boundary type boundary condition, the top half of these timelike surfaces joins with a spacelike part on the hemisphere giving a complex-valued area. Motivated by these, we describe two aspects of "time-entanglement" in simple toy models in quantum mechanics. One is based on a future-past thermofield double type state entangling timelike separated states, which leads to entirely positive structures. Another is based on the time evolution operator and reduced transition amplitudes, which leads to complex-valued entropy.

A coupled domain–boundary type meshless method for phase-field modelling of dendritic solidification with the fluid flow

PurposeThis study aims to simulate the dendritic growth in Stokes flow by iteratively coupling a domain and boundary type meshless method.Design/methodology/approachA preconditioned phase-field model for dendritic solidification of a pure supercooled melt is solved by the strong-form space-time adaptive approach based on dynamic quadtree domain decomposition. The domain-type space discretisation relies on monomial augmented polyharmonic splines interpolation. The forward Euler scheme is used for time evolution. The boundary-type meshless method solves the Stokes flow around the dendrite based on the collocation of the moving and fixed flow boundaries with the regularised Stokes flow fundamental solution. Both approaches are iteratively coupled at the moving solid–liquid interface. The solution procedure ensures computationally efficient and accurate calculations. The novel approach is numerically implemented for a 2D case.FindingsThe solution procedure reflects the advantages of both meshless methods. Domain one is not sensitive to the dendrite orientation and boundary one reduces the dimensionality of the flow field solution. The procedure results agree well with the reference results obtained by the classical numerical methods. Directions for selecting the appropriate free parameters which yield the highest accuracy and computational efficiency are presented.Originality/valueA combination of boundary- and domain-type meshless methods is used to simulate dendritic solidification with the influence of fluid flow efficiently.

Determining the Efficiency of Small-Scale Propellers via Slipstream Monitoring

A large part of small-sized UAVs that are used for surface scanning, video- and photography, or other similar applications are of the multirotor type. These small aircraft perform mainly in hovering or nearly hovering flight mode, and the endurance of these vehicles depends greatly on the efficiency of their motors and the aerodynamic efficiency of their thrust-generating systems, including propellers, ducted fans, etc. Propellers may therefore work in different regimes: in a regime where the propeller performs work to move the vehicle through the air, and the static or hovering regime, in which standing air is accelerated. In both cases, the concept of efficiency can be used to describe the propeller’s performance. There have been several previous studies on static and advancing propellers’ performances. In these studies, when determining the efficiency of a static propeller, the thrust and power coefficients are most commonly compared to evaluate the propeller’s performance. Sometimes, the inducted velocities are calculated via the momentum theory. As small-scale propellers work on very low Reynolds (Re) numbers below 500,000, the flow type transition and boundary layer separation make it very hard to predict the actual efficiency of the propellers in static mode. Therefore, the aim of this paper is to introduce a method to determine the static efficiency of small-scale propellers directly and empirically via a comparison between the output and input power, wherein the output power is determined via the measured thrust and mean induced velocity. The used method combines thrust, torque, and angular velocity measurements with slipstream monitoring. The performed tests showed a decrease in efficiency, with the Re number rising in spite of the rising values of the thrust coefficient. This study led to two main conclusions: thrust and power coefficients are not always the key parameters to determine the efficiency of a propeller; the role of the Re number in the propeller’s efficiency is not yet clear and requires further investigation. The presence of Re number effects has been proven in numerous works, but the impact of those effects seems to not be as trivial as the claim that the lower the Re number, the weaker the propeller’s performance.

Atomistically informed phase field study of austenite grain growth

Atomistically-informed phase field simulations have been performed to investigate the effect of five common alloying elements (Nb, Ti, Mo, V, Mn) on austenite grain growth. The anisotropic simulations based on the segregation energy profiles of the solutes to four different grain boundary (GB) types from density functional theory calculations suggest a secondary role of solute drag anisotropy on grain growth. Hence, the solute trends are determined to be the same for all investigated GBs, and as a result, the Σ5(310)[001] GB can be considered as a representative GB for solute trend predictions. The decrease in grain growth rates due to solute additions is quantitatively described using a solute trend parameter. The following hierarchy of the solute’s effectiveness to retard austenite grain growth has been determined based on the results of the presented model calculations in agreement with the experimental observations: Nb>Ti>Mo>V≈Mn. The limitations and the strengths of the proposed approach are discussed in detail, and a potential application of this approach to steel design is suggested.

Effect of bainitic or martensitic microstructure of a pressure vessel steel on grain boundary segregation induced by step cooling simulating thermal aging

During operating lifetime of a nuclear power plant, the pressure boundary components, usually in 16MND5 (SA508 Cl. 3) steel, are subjected to thermal aging that may induce phosphorus intergranular segregation. This is known to decrease brittle fracture stress and induce intergranular fracture, which causes reversible temper embrittlement. Large components such as the reactor pressure vessel presents microstructure heterogeneity due to forging and welding. Tempered martensite can locally be found in the nominally bainitic steel. The question of microstructure susceptibility to reversible temper embrittlement has been raised in literature suggesting that tempered martensite has higher sensibility to phosphorus intergranular segregation than tempered bainite. In this paper, a comparative study of intergranular segregation in tempered bainitic and martensitic 16MND5 steel after thermal aging is conducted using energy dispersive X-ray spectroscopy on transmission electron microscope. Focus ion beam is used to precisely prepare lamellae at prior austenite grain boundaries on step cooled bainitic and martensitic samples. Different types of grain boundaries are identified using precession assisted crystal orientation mapping and then the local chemical composition is analyzed. Phosphorus, nickel, manganese and molybdenum were observed at all types of grain boundaries in both microstructures. The segregation levels are higher in prior austenitic grain boundaries than in other types of boundaries for both microstructures. Taking into account the segregation amount in different types of boundaries, the phosphorus bulk depletion is shown negligible. The results show similar segregation levels in the two studied microstructures, indicating that the susceptibility to thermally induced grain boundary segregation between the tempered bainite and tempered martensite is the same.

Development and Validation of Empirical Formulations for Predicting the Frequency of Historic Masonry Towers

ABSTRACT In the present work, a large database comprising a set of features related to geometry, type of boundary condition, type of material and experimental value of the first natural frequency for 184 historic masonry towers is collected. The database is then used to develop empirical formulas for the estimation of the fundamental frequency related to the first bending mode. The data are divided into a training set and a validation set for a correct assessment of the empirical equations, generated through power regression and artificial neural network. Different combinations of features are exploited as independent variables to investigate their influence on the dynamic behaviour of masonry towers. To improve the accuracy of the prediction, distinct models are generated for specific clusters with likely homogeneous behaviour, according to the boundary conditions (isolated or bounded) and type of materials (brick, stone or mixed masonry).

The Synergistic Effects of Boron and Impression Creep Testing during Paced Controlling of Temperature for P91 Steels

This article induces the quadruple knowledge on effects of 100 ppm (P91B) and 22 ppm (P91) boron in as‐received 9Cr steels in normalized and tempered conditions (NT) and impression crept conditions (ICC). Herein, impression creep testing is improved through paced temperature to fast evaluate creep performance. P91B performs the utmost by advancing activation energy and 30% better creep life, leading to same targeted creep life to 574 °C than P91 at 550 °C. Further, it incisively discusses variations in microstructure, precipitate size, geometrically necessary dislocations (GNDs), pseudo‐rocking curve, grain size (GS), several types of grain boundaries (GBs), effective GB energy, and elastic stiffness. Novel phenomenological mechanisms like GB hardening/softening; antithetical mechanisms; boron‐dependent mosaicity; grain refinement/fragmentation/coarsening/homogenization; interaction among various types of GBs, triggering re/degeneration of dislocations and Σ boundaries as Σ reactions; super‐continuous and geometric dynamic recrystallizations; enhanced creep immunity of like‐oriented GBs than unlike oriented GBs; primary/secondary recrystallization; specialness; boron/NT/ICC‐dependent stiffness; high stiffness is dependent on low GNDs and big GS, and vice versa are observed. The synergistic effects of [100 ppm boron in NT/ICC] and ICC in manifestation of 22/100 ppm boron are ascertained. However, dependency [proportionally and antithetically] and independency of GB character on creep‐microstructural reciprocity discourse and converse into the mathematical relationship.

Twin density and twin thickness evolution in sputtered Al–Mg alloys

Twinned Al–Mg alloys have been reported. However, the role of Mg solute in facilitating the formation of growth twins remains unclear. By using a precession-assisted crystal orientation mapping technique (PACOM) coupled with transmission electron microscopy (known as ASTAR), we examined the evolution of twin boundaries in Al, Al–1Mg, and Al–2.2Mg (at. %) films. The twinned grain fraction elevates with increasing film thickness until it reaches a peak when the film thickness is 120–160 nm. The Al–Mg alloys exhibited greater twinned grain fractions than pure Al. To investigate the fluctuation of twinned grain fraction, two types of twin boundaries were classified including intergranular and intragranular twins. The initial increase in twin density is attributed to the impingement of twinned grains during island coalescence and the twinned grains are more likely to survive during the grain growth process. Whereas the decrease in twinned grain fraction in thicker films is related to the removal of intragranular twins, and a lack of formation mechanisms of new twins.

Morphological focus and its agreement features in Kakabe

The paper explores the morphological expression of focus on the example of Focus Particle (FP) in Kakabe. The analysis addresses questions that are rarely if ever investigated with respect to morphological focus: i) how FP is related to the boundaries of a focus constituent, in particular, VP and IP focus; ii) how givenness affects the position of FP; iii) FP with respect to types of CP and CP boundaries. I demonstrate that, even though FP resembles prosodic focus in some respects, its distribution cannot be fitted into a prosodic account of focus, contra Büring 2010 and Féry 2013. More specifically, I propose that Kakabe has a Focus operator located lower than CP. Similarly to Cable’s (2006, 2010) Q-operator that can be involved a bi-partite agreement relationship, Foc operator agrees at a time with C0 above it and with the DP below it. I demonstrate how the pattern of FP distribution follows, in particular, from the conditions on Agree (Chomsky 2000, 2001), such as locality, superiority and activity conditions.

Innovation on technological “islands”: domain contrast, boundary spanning, knowledge depth and breadth

Abstract Prior literature has long examined innovation as a recombination process within or across the boundaries of technological domains. However, limited attention is paid to boundaries per se. Building upon recent development of categorical contrast, this study distinguishes domains with crisp boundaries from those with fuzzy boundaries and examines their effects on innovation outputs. Analyzing a large sample of US patents, we find that spanning crisp boundaries is more likely to generate impactful inventions but at the same time leads to significantly higher recombinant uncertainty. We continue to explore what types of inventors are better able to span such types of domain boundaries. Focusing specifically on the role of inventors’ knowledge expertise, we find that while both knowledge depth and breadth enhance the impact of technologies that span crisp boundaries, knowledge breadth is also found to escalate the associated uncertainty. Our emphasis on the contrast of technological domains contributes to the literature on recombinative innovation and boundary spanning.

Influence of type of drainage boundary on coefficient of horizontal consolidation

Vertical drains are used widely to accelerate the consolidation of soft clay deposits when preloading is used as a ground improvement technique. One of the essential input parameters required in Barron's theory is the coefficient of horizontal consolidation, ch. The values of ch can be determined by the radial consolidation test, using either a central sand drain or a porous plastic peripheral drain. This paper presents the laboratory tests carried out to understand the reason for the difference in values of ch determined from inward and outward radial flow consolidations tests. A 150 mm wide instrumented consolidation cell was used to carry out the inward or outward radial consolidation tests. The total stress measurements during consolidation showed non-uniform stress distribution in clay with higher effective stress values close to the drainage boundary. This stiffening of the clay close to the drain retards the consolidation rate resulting in reduced values of ch. As a result, the ch values determined by radially outward consolidation tests with a larger drainage boundary area are lower to those obtained by inward radial flow tests. The pore water pressure measurements showed significantly higher undissipated pore water pressure away from the drainage boundary for the outward flow tests.

Molecular Dynamics Study on the Effects of Substrate Grain Boundaries on the Adsorption State of Graphene: Implications for Nanoscale Lubrication

Graphene on polycrystalline surfaces, such as stainless steel, exhibits frictional strengthening properties during nanofriction. The adsorption state of graphene is directly related to the nanofriction behavior, and graphene’s adsorption state is affected by substrate grain boundaries. However, the mechanism of the influence of the substrate grain boundaries on the adsorption state of graphene is not clear. Herein, the adsorption states of graphene on different stainless-steel grain boundary surfaces are analyzed, and the mechanism of the substrate grain boundaries regulating the surface graphene bulge is revealed. The notion that graphene bulges are related to the type of substrate grain boundaries has been confirmed. Moreover, we demonstrate that the difference in the crystal surfaces on both sides of the grain boundaries and the gradient of adsorption energy are the key factors regulating the graphene bulge. Graphene bulging can only be caused by the existence of crystal surface differences in the grain boundary structure; therefore, the tilt grain boundaries are unable to cause graphene bulging. In addition, the adsorption energy distribution within the grain boundary will also influence graphene bulging if there is a grain surface difference in the grain boundary structure. When the direction of the adsorption energy gradient is perpendicular to the grain boundary, such a grain boundary structure favors the appearance of graphene bulges. In contrast, graphene bulging is suppressed when the direction of the adsorption energy gradient is parallel to the grain boundary. It provides a theoretical basis for explaining graphene’s nanofriction on polycrystalline substrates such as stainless steel. It is important for the use of graphene for the nano-lubrication of stainless-steel components in microelectromechanical systems.

Improvements of the Brownian walkers method towards the modeling of conduction-radiation coupling

This work directly follows the one presented in a previous article of V. Gonneau, D. Rochais and F. Enguehard (2022) [1]. This contribution describes new results and improvements to existing methods for the modeling of transient thermal conduction within a heterogeneous medium by the movement of Brownian walkers. The material structure is voxelized, and each walker transports an elementary enthalpy during its displacement within the structure. This enthalpy transport associated with the displacement of the walkers represents the conductive flow and makes it possible to simulate transient conduction with a quantitative stochastic approach.This article presents a new method for accounting for Dirichlet type boundary conditions that is quite efficient and that allows to relax quite substantially a constraint of maximum value of the time step of the Brownian walker simulations that had previously been pointed out in [1]. Other boundary condition treatments are also upgraded, in terms of speed (for Neumann type conditions) or generalization (for Robin type conditions). Then, a first non-linear conduction-radiation coupling model in an optically thick and gray semi-transparent medium is solved by Brownian walkers through two approaches: the first one based on a global conductivity function of temperature and allowing to confirm the validity of a stochastic transmission criterion at the interface of two constituents within a heterogeneous medium, and the second one based on the radiative volume power field. This second approach is preceded by the description and the validation of a procedure for the management of a volume power field using Brownian walkers. This procedure introduces the notion of negative Brownian walkers, which prove necessary for representing negative local values of the volume power field as is frequently the case with the radiative volume power.

The mutual benefits of comparing energy system models and integrated assessment models

Background: The transition to a carbon neutral society such as that envisaged in the European Union Green Deal requires careful and comprehensive planning. Integrated assessment models (IAMs) and energy system models (ESMs) are both commonly used for policy advice and in the process of policy design. In Europe, a vast landscape of these models has emerged and both kinds of models have been part of numerous model comparison and model linking exercises. However, IAMs and ESMs have rarely been compared or linked with one another. Methods: This study conducts an explorative comparison and identifies possible flows of information between 11 of the integrated assessment and energy system models in the European Climate and Energy Modelling Forum. The study identifies and compares regional aggregations and commonly reported variables We define harmonised regions and a subset of shared result variables that enable the comparison of results across the models. Results: The results highlight similarities and differences on final electricity demand, electricity supply and hydrogen across three levels of aggregation. However, the differences between the regional aggregation of the models limit detailed analysis. Conclusions: This first-of-its-kind comparison and analysis of modelling results across model type boundaries provides modellers and policymakers with a better understanding of how to interpret both IAM and ESM results. It also highlights the need for community standards for region definitions and information about reported variables to facilitate future comparisons of this kind.

Alkali Sulfates with Aphthitalite-Like Structures from Fumaroles of the Tolbachik Volcano, Kamchatka, Russia. IV. Aphthitalite–Palmierite Regular Intergrowths: Crystallography, Chemistry, and Genesis

Abstract The first discovery of regular intergrowths of aphthitalite K3Na(SO4)2 and palmierite K2Pb(SO4)2 are reported. Crystals of aphthitalite, intergrown with lamellae of palmierite (up to 15 μm thick), along with grains of arcanite, occur in encrustations recovered from the active Arsenatnaya fumarole (Tolbachik volcano, Kamchatka, Russia). These were studied using a combination of scanning electron microscopy, electron probe microanalysis, powder X-ray diffraction, and electron backscatter diffraction techniques. Three types of grain boundaries involving intergrowths of aphthitalite and palmierite were observed: (1) those with a misorientation angle of 60° relative to [001] (twinning), (2) those parallel to the (001) plane, and (3) those with a misorientation angle of 60° relative to [001]. The twinned aphthitalite domains are related by a two-fold rotation about [001] (Dauphiné twin law). The heating of aphthitalite crystals containing palmierite lamellae at 400, 600, and 750 °C shows a nearly complete redistribution and gradual dissolution of palmierite in the aphthitalite matrix. The character of solid-state transformations in the K2SO4–Na2SO4–PbSO4 system during cooling is controlled by the structural similarity of aphthitalite-type sulfates and palmierite, which contain topologically identical 2[M(SO4)2] (M = Na, Pb) layers.

Noncoercive problems for elastic bodies with thin elastic inclusions

The paper concerns boundary value problems for an elastic body with a thin elastic inclusion for a noncoercive case. The inclusion is assumed to be delaminated thus forming a crack between the inclusion and the surrounding elastic body. To provide a mutual nonpenetration between crack faces, we consider inequality type boundary conditions with unknown set of a contact. In the paper, a solution existence of the equilibrium problems is proved for the cases when one or two given points of the inclusion are fixed as well as and for the case without these restrictions.

Optimizing Thermomechanical Processing of Bimetallic Laminates.

Thermomechanical processing combining plastic deformation and heat treatment is a favorable way to enhance the performance and lifetime of bimetallic laminates, especially those consisting of metals, which tend to form intermetallic layers on the interfaces when produced using methods involving increased temperatures. The presented work focuses on optimizing the conditions of thermomechanical treatment for an Al + Cu bimetallic laminate of innovative design involving a shear-strain-based deformation procedure (rotary swaging) and post-process heat treatment in order to acquire microstructures providing advantageous characteristics during the transfer of direct and alternate electric currents. The specific electric resistivity, as well as microhardness, was particularly affected by the structural features, e.g., grain size, the types of grain boundaries, and grain orientations, which were closely related to the applied thermomechanical procedure. The microhardness increased considerably after swaging (up to 116 HV02 for the Cu components), but it decreased after the subsequent heat treatment at 350 °C. Nevertheless, the heat-treated laminates still featured increased mechanical properties. The measured electric characteristics for DC transfer were the most favorable for the heat-treated 15 mm bimetallic laminate featuring the lowest measured specific electric resistivity of 22.70 × 10-9 Ωm, while the 10 mm bimetallic laminates exhibited advantageous behavior during AC transfer due to a very low power loss coefficient of 1.001.

Analytical and numerical solution for multiple shape memory effect of smart corrugated-core sandwich panels with different patterns

Shape memory polymers (SMPS) are a class of smart materials used in various industries due to their unique properties. On the other hand, sandwich structures have attracted the attention of many researchers and industries due to their low weight and high strength. Therefore, this study it is aimed to present a semi-analytical solution to describe the behavior of a sandwich plate made of temperature-sensitive SMPs with a corrugated structure, based on the Reissner-Mindlin plate theory together with the viscoelastic theory. The solution is implemented for both dual shape memory (shape and force recovery) and triple shape memory scenarios. Three types of structure, including rectangular, triangular and trapezoidal, have been studied. In addition, in order to examine the impact of the support type, simply supported and clamped boundary conditions have also been investigated for three different geometries. Also, this work examines the impact of thermal stress caused by expansion. In addition to the semi-analytical solution, finite element modeling has also been carried out in all problems. Comparing the results in different geometries and supports shows the proposed semi-analytical solution's ability to predict the material's behavior with great accuracy. Moreover, by examining different cores and supports, one may observe a significant difference in the amount and distribution of the force and deformation, which are key to the design. Therefore, the semi-analytical solution can be considered reliable and accurate for various problems. In addition, compared to the finite element solution, the analytical solution enjoys a much higher speed; thus, it can be used for optimization and design problems that require a huge number of simulations.