Hasil untuk "Materials of engineering and construction. Mechanics of materials"

Jianan Wang

This paper proposes a new hypothesis that breaks through the framework of traditional archaeological chronology and engineering to explain the mystery of megalithic structures that exist widely around the world and whose technical features exceed current understanding.The core of this hypothesis is: 1) The Earth civilization has periodicity with the period of the Sun's movement around the Milky Way as the period, and at least two periods have already existed; 2) The continuous expansion of the universe leads to the continuous expansion of atoms and the continuous reduction of material strength. Based on this, a coupling model of "atomic characteristic scale - material strength - individual human physique and physiological function - engineering technology limit" was established, and the quantitative relationship between the maximum weight of a single stone in a megaliite building and its construction year, as well as the qualitative relationship between the splicing accuracy and the construction year, were derived. Analysis using this model indicates that the construction dates of ultra-precise megalithic structures such as Pumapengu, the Pyramids of Giza, and Balbek may be much older than traditional dating results, or they might be the products of the previous or even earlier civilization cycle.

Andreas Hausoel, Simone Di Cataldo, Motoharu Kitatani et al.

Abstract Following the successful prediction of the superconducting phase diagram for infinite-layer nickelates, here we calculate the superconducting T c vs. the number of layers n for finite-layer nickelates using the dynamical vertex approximation. To this end, we start with density functional theory, and include local correlations non-perturbatively by dynamical mean-field theory for n = 2–7. For all n, the Ni $${d}_{{x}^{2}-{y}^{2}}$$ d x 2 − y 2 orbital crosses the Fermi level, but for n > 4 there are additional (π, π) pockets or tubes that slightly enhance the layer-averaged hole doping of the $${d}_{{x}^{2}-{y}^{2}}$$ d x 2 − y 2 orbitals beyond the leading 1/n contribution stemming from the valence electron count. We finally calculate T c for the single-orbital $${d}_{{x}^{2}-{y}^{2}}$$ d x 2 − y 2 Hubbard model by dynamical vertex approximation.

Tomohiro Nozawa, Renke Liu, Hideyuki Sawada

In this paper, we propose a novel tactile display that can present vibration patterns and thermal stimuli simultaneously. The vibration actuator employs a shape memory alloy (SMA) wire to generate micro-vibration with a frequency control of up to 300 Hz. The micro-vibration is conducted to a tactile pin for amplifying the vibration, to be sufficiently recognized by a user. A thermal stimulation unit, on the other hand, consists of four Peltier elements with heatsinks for heat radiation. Four vibration actuators and a thermal unit are arranged in a flat plane with a size of 20 mm × 20 mm, on which a user places the tip of an index finger to feel the presented vibratory stimuli under different temperature conditions. We conducted an experiment by employing nine subjects to evaluate the performance of the proposed tactile display and also to investigate the effects of temperature on recognizing tactile sensation. The results demonstrated that the proposed device was feasible for the quantitative diagnosis of tactile sensation. In addition, we verified that the sensitivity of tactile sensation decreased with colder stimuli.

Abhishek Shiva Kumar, Mikhail Maslov, Mikhail Lemeshko et al.

In standard quantum electrodynamics (QED), the so-called non-minimal (Pauli) coupling is suppressed for elementary particles and has no physical implications. Here, we show that the Pauli term naturally appears in a known family of Dirac materials -- the lead-halide perovskites, suggesting a novel playground for the study of analogue QED effects. We outline measurable manifestations of the Pauli term in the phenomena pertaining to (i) relativistic corrections to bound states (ii) the Klein paradox, and (iii) spin effects in scattering. In particular, we demonstrate that (a) the binding energy of an electron in the vicinity of a positively charged defect is noticeably decreased due to the polarizability of lead ions and the appearance of a Darwin-like term, (b) strong spin-orbit coupling due to the Pauli term affects the exciton states, and (c) scattering of an electron off an energy barrier with broken mirror symmetry produces spin polarization in the outgoing current. Our study adds to understanding of quantum phenomena in lead-halide perovskites, and paves the way for tabletop simulations of analogue Dirac-Pauli equations.

Lorenzo Sciandra, Roberto Esposito, Andrea Cesare Grosso et al.

This article explores the integration of deep learning models into combinatorial optimization pipelines, specifically targeting NP-hard problems. Traditional exact algorithms for such problems often rely on heuristic criteria to guide the exploration of feasible solutions. In this work, we propose using neural networks to learn informative heuristics, most notably, an optimality score that estimates a solution's proximity to the optimum. This score is used to evaluate nodes within a branch-and-bound framework, enabling a more efficient traversal of the solution space. Focusing on the Traveling Salesman Problem, we introduce Concorde, a state-of-the-art solver, and present a hybrid approach called Graph Convolutional Branch and Bound, which augments it with a graph convolutional neural network trained with a novel unsupervised training strategy that facilitates generalization to graphs of varying sizes without requiring labeled data. Empirical results demonstrate the effectiveness of the proposed method, showing a significant reduction in the number of explored branch-and-bound nodes and overall computational time. Some of the results concerning the use of the 1-tree relaxation are in the supplementary materials.

Jing Zhou, Donghui Li, Liang Wang et al.

Abstract Realizing bicontinuous fibrillar charge transport networks in the photoactive layer has been considered a promising method to achieve high‐efficiency organic solar cells (OSCs); however, this has been rarely achieved due to the interference of molecular organization of donor and acceptor components during solution casting. In this contribution, the fibrillization of polymer donor PM6 and small molecular nonfullerene acceptor L8‐BO is realized with the assistance of conjugated polymer D18‐Cl. Atomic force microscopy and photo‐induced force microscopy reveal that PM6 and D18‐Cl co‐assemble into long and slender fibrils within wide blending ratios due to their high compatibility; in contrast, the fibrillization of L8‐BO can be encouraged with the incorporation of 1% D18‐Cl. By utilizing a pseudo‐bulk heterojunction (p‐BHJ) active layer fabricated by layer‐by‐layer deposition, the optimized PM6+20% D18‐Cl/L8‐BO+1% D18‐Cl OSCs obtain bicontinuous fibril networks, leading to enhanced exciton dissociation and charge transport processes and superior power conversion efficiency of 19.2% (certified 18.91%) compared to 18.8% of the PM6:D18‐Cl:L8‐BO ternary BHJ OSCs.

Popescu Ileana Nicoleta, Poinescu Aurora Anca, Ungureanu Dan Nicolae et al.

In this brief review, porous and non-porous biomaterials used as scaffolds in regenerative medicine and tissue engineering and new innovative techniques to obtain biomaterials were discussed. Various methods have been presented to obtain advanced materials used as scaffolds, such as (i) 3D printed biomineral composites obtained with bacteria-loaded ink (bactoInk), (ii) the use of vegetable waste, such as rice husks, parsley, spinach or cocoa in the development of bioplastics, (iii) the use of natural biological materials of animal origin (such as bovine bones, corals, snail shells or eggshells) from waste, or (iv) the creation of new biomaterials that can reduce or combat the infection of scaffolds after implantation.

Hendrik Holz, Benoit Merle

We introduce a new nanoindentation method to continuously measure the hardness while sweeping through orders of magnitudes of strain rates within a single experiment. While nanoindentation already allows the determination of the strain rate sensitivity of materials by means of strain rate jump tests, these are typically limited to few discrete strain rates. With the new method, the strain rate sensitivity can be measured continuously as a function of the strain rate. Applications to fused silica, Zn-22 %Al superplastic alloy, single crystalline aluminum, various nanocrystalline metals and a palladium-based metallic glass are shown. Besides some discrepancy with the reference measurements, the new method seems only affected by the presence of a strong nanoindentation size effect. Provided this indentation size effect is not excessively large and can be corrected for accurately, the method proves robust, with no suggestion that the direction of the strain rate sweep affects the evaluation of the strain rate sensitivity.

Abedulgader Baktheer, Henrik Becks

Monika Dubey, Shikha Wadhwa, Ashish Mathur et al.

Materials and innovation in earth-abundant materials are vital in addressing societal challenges such as air purification, alternate energy, wastewater remediation, and better living. In this fast growing world, several important technological materials can be applied to this goal. Metal Oxide based materials are exiting due to their tunable band gap leading to a variety of properties that address climate change. This review presents the updated account of mesoporous ceria (MC), which is one of the important and vastly researched mesoporous metal oxide, their synthesis, and applications. Ceria has been one of the most studied materials due to its unique crystal structure, high oxygen storage capacity (OSC), and redox properties. MC has more active sites at the surface, larger pore size distributions, and high oxygen storage capability than bulk ceria. The effect of the synthesis method of MC has a pronounced impact on its properties like surface area, pore size, and catalytic activity. MC is non-toxic, eco-friendly, compatible with biological and chemical processes, sustainable, and stable in acidic and basic mediums. It provides enhanced performance for various industrial applications, and the structure-activity relationship plays an important role in its catalytic activity. MC is able to supply and withdraw oxygen, and provides high level of synergetic interaction with other metals and metal oxides. The presence of cerium-based oxides generally allows for obtaining a strong metal-support interaction, thereby helping the dispersion of active metal phases, selectivity, and durability of the catalysts. Moreover, it introduces different functionalities such as redox and acid-base, which provides solutions to a wide range of problems in catalysis. Additionally, oxygen vacancies in the lattice structure allow for alternating between CeO2 and CeO2−x during redox reactions. This review discusses: (1) the methods of synthesis for ceria nanoparticles, including the recent green synthesis methods; (2) their characteristics, merits, and limitations; and (3) catalytic applications.

Yuriy Abrashkevich, Mykola Prystaylo, Andriy Polishchuk

Собівартість абразивної різки в основному визначається зносостійкості абразивного круга, що складається з абразивного зерна, наповнювача, фенольного сполучного і склосітки. У зв'язку з тим, що в процесі різання в результаті підсумовування теплових імпульсів від ріжучих зерен, які перебувають на ріжучій кромці круга, виділяють значну кількість тепла, в зоні різання досягаються великі значення температури. Тим часом добре відомо, що фенольна сполучна володіє низькою теплостійкістю, вона руйнується при температурі 520-570 °К, тому характер теплових процесів, що протікають при абразивному різанні, визначає і температуру в крузі і, відповідно, швидкість його зносу. В ідеалі, звичайно, швидкість теплового руйнування зв'язки повинна корелювати зі швидкістю механічного руйнування абразивних зерен з тим, щоб різання здійснювалося лише гострими, неспрацьовану зернами, при цьому усуватися з ріжучої кромки повинні лише тупі зерна. Оскільки швидкість стирання абразивних зерен різна для різних оброблюваних матеріалів, то й характеристики зв'язуючих повинні бути в залежності від виду оброблюваного матеріалу, тобто необхідно створювати абразивні круги для різки різних матеріалів. На практиці ж випускаються абразивні круги без особливого урахування особливостей розрізає мого матеріалу, що в значній мірі пояснюється неясністю характеру теплових процесів в абразивних армованих кругах і технологічними складнощами, пов'язаними зі зміною теплофізичних властивостей кругів.

Christopher Igwe Idumah

Recently, hydrogels (HYD) have garnered tremendous interest because of their potential uses in sensors, flexible energy storing gadgets, human@machine-interfacial systems, soft electronics and actuating machines. As a result of their inherent exhibition of hydrophilicity, metallically inclined conductivity, elevated aspect ratio, architectural disposition along with tune-able attributes, when 2-D transitionally inclined metallic carbides/nitrides or M−X are embedded within HYD systems, they give enchanting and wide settings for the fabrication of M−X oriented soft materials with tunable applicability and multifunctional properties. M−X@HYD bionanoarchitectures exceptional properties are propelled by intricate gel architectures along with gelation strategies, requiring versatile studies and engineering at the nanoscale. Nevertheless, M−X embedment within HYD can notably increment M−X stability, which regularly is an inhibiting parameter for varying M−X oriented uses. Nevertheless, through simplified modifications, M−X@HYD derivatives like aerogels, are liable to be garnered, thereby broadening their horizon. Therefore, this elucidation presents recently emerging trends in M−X@HYD architectures, multifunctional applications and enhancement of the performance of M−X−oriented gadgets. Herein, the prevailing architectures of varying M−X@HYD constructions as well as inherent gelation mechanisms along with their interlinkage propelling forces are elucidated. Their unique properties and multifunctional applications (electromagnetic interference shielding, biomedicals, energy storage/harvesting, sensing and catalysis), emanating from embedment of M−X within HYD are comprehensively and elaborately elucidated in this review paper.

WANG Yanlong, MA Xinyu, WANG Qingxiang

In order to obtain titanium alloys with better mechanical properties, Ti-Ta-Mo alloys with different element contents were obtained by spark plasma sintering with the addition of β -phase stable elements Ta and Mo to Ti. The effects of sintering temperature and the content of Ta and Mo elements on the microstructure and mechanical properties of the alloy were systematically studied. The results show that the microstructure of Ti-Ta-Mo alloy is mainly composed of α-Ti phase and β-Ti phase. With the increase of sintering temperature, the β phase in the alloy increases gradually. With the increase of Ta and Mo contents, the content of β phase in the alloy increases and the grain size decreases. When the sintering temperature is 1 250 ℃ and the Ta and Mo content (mass fraction) is 16%, the hardness and density of the alloy are higher. The compressive strength and yield strength of Ti-Ta-Mo alloy increase with the increase of sintering temperature and β -phase stable elements, while the elastic modulus shows an opposite trend.

J. Abuthakir, R. Subramanian, K. Somasundara Vinoth et al.

In the present investigation Ni particles were added in varying weight fractions (0.5, 1.0 and 1.5%) to AA6061 alloy during stir casting. To prepare Al-Ni intermetallic reinforced Aluminium Metal Matrix Composites (Al MMCs), as-cast samples were subjected to T6 treatment (Solutionization at 550°C followed by ageing at 2,4,6,8 and 10 hours). Base alloy was also subjected to T6 treatment for comparison purpose. Hardness of the samples were obtained using Vickers hardness test. Samples in the peak aged (T6) condition were subjected to metallographic examination. Influence of Ni particles on the hardness and grain refinement was investigated. X-ray Diffraction analysis of the Ni added samples revealed the presence of Al-Ni intermetallic phase formation in the peak aged (T6) Condition. Scanning Electron Microscope – Energy Dispersive X-Ray Spectroscopy analysis of composites in the peak aged (T6) condition were carried out to study the formation of the Al-Ni intermetallic phase. Effect of Al-Ni intermetallic phase on wear and friction behavior of the composite samples were studied and compared with that of the base alloy in the peak aged (T6) condition.

Tomoki Sasada, Kento Yasuda, Yuto Hosaka et al.

We investigate the mechanical properties of a layered material with interlayer friction. We propose a model that contains lateral elasticity and interlayer friction to obtain the response function both in the Fourier and real spaces. By investigating how the internal deformation is laterally induced due to the applied surface displacement, we find that it is transmitted into the material with an apparent phase difference. We also obtain the effective complex modulus of the layered material and show that it exhibits an intermediate power-law behavior in the low-frequency regime. Our result can be used to estimate the internal deformation of layered materials that exist on various different scales.

Yusheng Hou, Feng Xue, Liang Qiu et al.

Two-dimensional van der Waals Janus materials and their heterostructures offer fertile platforms for designing fascinating functionalities. Here, by means of systematic first-principles studies on van der Waals Janus monolayer Cr-based dichalcogenide halides CrYX (Y=S, Se, Te; X=Cl, Br, I), we find that CrSX (X=Cl, Br, I) are the very desirable high TC ferromagnetic semiconductors with an out-of-plane magnetization. Excitingly, by the benefit of the large magnetic moments on ligand S2- anions, the sought-after large-gap quantum anomalous Hall effect and sizable valley splitting can be achieved through the magnetic proximity effect in van der Waals heterostructures CrSBr/Bi2Se3/CrSBr and MoTe2/CrSBr, respectively. Additionally, we show that large Dzyaloshinskii-Moriya interactions give rise to skyrmion states in CrTeX (X=Cl, Br, I) under external magnetic fields. Our work reveals that two-dimensional Janus magnet Cr-based dichalcogenide halides have appealing multifunctionalities in the applications of topological electronic and valleytronic devices.

Adam Alfieri, Surendra B. Anantharaman, Huiqin Zhang et al.

Quantum information science and engineering (QISE) which entails use of quantum mechanical states for information processing, communications, and sensing and the area of nanoscience and nanotechnology have dominated condensed matter physics and materials science research in the 21st century. Solid state devices for QISE have, to this point, predominantly been designed with bulk materials as their constituents. In this review, we consider how nanomaterials (i.e. materials with intrinsic quantum confinement) may offer inherent advantages over conventional materials for QISE. We identify the materials challenges for specific types of qubits, and we identify how emerging nanomaterials may overcome these challenges. Challenges for and progress towards nanomaterials based quantum devices are identified. We aim to help close the gap between the nanotechnology and quantum information communities and inspire research that will lead to next generation quantum devices for scalable and practical quantum applications.

Abbas Mukhtar Adnan, Xue Luo, Chaofeng Lü et al.

Nripat Singh, Mukesh Sharma, Dibyendu Mondal et al.

Large-scale production of graphene sheets by liquid-phase exfoliation of graphite is a challenging task from a sustainability point of view. Certain bio-derived solvents were found to exfoliate graphite to produce single-layered graphene sheets but the high cost of the solvent is always a deterring factor towards upscaling of the process. Herein, Kappaphycus alvarezii, a cultivable red seaweed is demonstrated as a sustainable resource for producing a bio solvent for exfoliation and to produce graphene sheets from graphite. A solvent system consisting of levulinic acid, acetic acid, and γ-valerolactone was prepared from the polysaccharide obtained from the seaweed biomass through acid hydrolysis under pressure and the mixture was found to exfoliate graphite to produce few-layered pristine graphene nanosheets. The process is scalable and cost-effective and the seaweed biomass-derived solvent mixture can be recovered and reused in the subsequent cycles of exfoliation for large-scale production of graphene nanosheets.

Zijun Qin, Zi Wang, Yunqiang Wang et al.

Predicting the phase precipitation of multicomponent alloys, especially the Ni-base superalloys, is a difficult task. In this work, we introduced a dependable and efficient way to establish the relationship between composition and detrimental phases in Ni-base superalloys, by integrating high throughput experiments and machine learning algorithms. 8371 sets of data about composition and phase information were obtained rapidly, and analyzed by machine learning to establish a high-confidence phase prediction model. Compared with the traditional methods, the proposed approach has remarkable advantage in acquiring and analyzing the experimental data, which can also be applied to other multicomponent alloys. IMPACT STATEMENT By integrating the high throughput experiments and machine learning algorithms, it is hopeful to facilitate the design of new Ni-base superalloys, and even other multicomponent alloys.