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1
Frascella, A., et C. Guido. « Structured lattices and ground categories ofL-sets ». International Journal of Mathematics and Mathematical Sciences 2005, no 17 (2005) : 2783–803. http://dx.doi.org/10.1155/ijmms.2005.2783.
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Complete lattices are considered with suitable families of lattice morphisms that provide a structure(L,Φ), useful to characterize ground categories ofL-sets by means of powerset operators associated to morphisms of these categories. The construction of ground categories and powerset operators presented here extends and unifies most approaches previously considered, allowing the use of noncrisp objects and, with some restriction, the change of base. A sufficiently large category ofL-sets that includes all possible ground categories on a structured lattice(L,Φ)is provided and studied, and its usefulness is justified. Many explanatory examples have been given and connection with the categories considered by J. A. Goguen and by S. E. Rodabaugh are stated.
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Bathla, Pranjal, et John Kennedy. « 3D Printed Structured Porous Treatments for Flow Control around a Circular Cylinder ». Fluids 5, no 3 (14 août 2020) : 136. http://dx.doi.org/10.3390/fluids5030136.
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The use of porous coatings is one of the passive flow control methods used to reduce turbulence, noise and vibrations generated due to fluid flow. Porous coatings for flow stabilization have potential for a light-weight, cost-effective, and customizable solution. The design and performance of a structured porous coating depend on multiple control parameters like lattice size, strut thickness, lattice structure/geometry, etc. This study investigated the suitability of MSLA 3D printers to manufacture porous coatings based on unit cell designs to optimize porous lattices for flow control behind a cylinder. The Reynolds number used was 6.1×104–1.5×105 and the flow measurements were taken using a hotwire probe. Different experiment sets were conducted for single cylinder with varying control parameters to achieve best performing lattice designs. It was found that lattice structures with higher porosity produced lower turbulence intensity in the wake of the cylinder. However, for constant porosity lattice structures, there was negligible difference in turbulence and mean wake velocity levels. Coating thickness did not have a linear relationship with turbulence reduction, suggesting an optimal thickness value. For constant porosity coatings, cell count in coating thickness did not influence the turbulence or mean wake velocity. Partial coating designs like helical and spaced coatings had comparable performance to that of a full coating. MSLA printers were found capable of manufacturing thin and complex porous lattices.
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HORE, VICTORIA R. A., JOHN B. TROY et STEPHEN J. EGLEN. « Parasol cell mosaics are unlikely to drive the formation of structured orientation maps in primary visual cortex ». Visual Neuroscience 29, no 6 (30 octobre 2012) : 283–99. http://dx.doi.org/10.1017/s0952523812000338.
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AbstractThe receptive fields of on- and off-center parasol cell mosaics independently tile the retina to ensure efficient sampling of visual space. A recent theoretical model represented the on- and off-center mosaics by noisy hexagonal lattices of slightly different density. When the two lattices are overlaid, long-range Moiré interference patterns are generated. These Moiré interference patterns have been suggested to drive the formation of highly structured orientation maps in visual cortex. Here, we show that noisy hexagonal lattices do not capture the spatial statistics of parasol cell mosaics. An alternative model based upon local exclusion zones, termed as the pairwise interaction point process (PIPP) model, generates patterns that are statistically indistinguishable from parasol cell mosaics. A key difference between the PIPP model and the hexagonal lattice model is that the PIPP model does not generate Moiré interference patterns, and hence stimulated orientation maps do not show any hexagonal structure. Finally, we estimate the spatial extent of spatial correlations in parasol cell mosaics to be only 200–350 μm, far less than that required to generate Moiré interference. We conclude that parasol cell mosaics are too disordered to drive the formation of highly structured orientation maps in visual cortex.
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Budinski, Ljubomir, Julius Fabian et Matija Stipić. « Lattice Boltzmann method for groundwater flow in non-orthogonal structured lattices ». Computers & ; Mathematics with Applications 70, no 10 (novembre 2015) : 2601–15. http://dx.doi.org/10.1016/j.camwa.2015.09.027.
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Kumar, K. Raj, et Giuseppe Caire. « Space–Time Codes From Structured Lattices ». IEEE Transactions on Information Theory 55, no 2 (février 2009) : 547–56. http://dx.doi.org/10.1109/tit.2008.2009595.
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Dziobiak, Wieslaw, Jaroslav Ježek et Ralph McKenzie. « Avoidable structures, II : Finite distributive lattices and nicely structured ordered sets ». Algebra universalis 60, no 3 (16 mars 2009) : 259–91. http://dx.doi.org/10.1007/s00012-009-2098-0.
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Boley, J. William, Wim M. van Rees, Charles Lissandrello, Mark N. Horenstein, Ryan L. Truby, Arda Kotikian, Jennifer A. Lewis et L. Mahadevan. « Shape-shifting structured lattices via multimaterial 4D printing ». Proceedings of the National Academy of Sciences 116, no 42 (2 octobre 2019) : 20856–62. http://dx.doi.org/10.1073/pnas.1908806116.
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Shape-morphing structured materials have the ability to transform a range of applications. However, their design and fabrication remain challenging due to the difficulty of controlling the underlying metric tensor in space and time. Here, we exploit a combination of multiple materials, geometry, and 4-dimensional (4D) printing to create structured heterogeneous lattices that overcome this problem. Our printable inks are composed of elastomeric matrices with tunable cross-link density and anisotropic filler that enable precise control of their elastic modulus (E) and coefficient of thermal expansion (α). The inks are printed in the form of lattices with curved bilayer ribs whose geometry is individually programmed to achieve local control over the metric tensor. For independent control of extrinsic curvature, we created multiplexed bilayer ribs composed of 4 materials, which enables us to encode a wide range of 3-dimensional (3D) shape changes in response to temperature. As exemplars, we designed and printed planar lattices that morph into frequency-shifting antennae and a human face, demonstrating functionality and geometric complexity, respectively. Our inverse geometric design and multimaterial 4D printing method can be readily extended to other stimuli-responsive materials and different 2-dimensional (2D) and 3D cell designs to create scalable, reversible, shape-shifting structures with unprecedented complexity.
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Anoop, V. S., et S. Asharaf. « Extracting Conceptual Relationships and Inducing Concept Lattices from Unstructured Text ». Journal of Intelligent Systems 28, no 4 (25 septembre 2019) : 669–81. http://dx.doi.org/10.1515/jisys-2017-0225.
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Abstract Concept and relationship extraction from unstructured text data plays a key role in meaning aware computing paradigms, which make computers intelligent by helping them learn, interpret, and synthesis information. These concepts and relationships leverage knowledge in the form of ontological structures, which is the backbone of semantic web. This paper proposes a framework that extracts concepts and relationships from unstructured text data and then learns lattices that connect concepts and relationships. The proposed framework uses an off-the-shelf tool for identifying common concepts from a plain text corpus and then implements machine learning algorithms for classifying common relations that connect those concepts. Formal concept analysis is then used for generating concept lattices, which is a proven and principled method of creating formal ontologies that aid machines to learn things. A rigorous and structured experimental evaluation of the proposed method on real-world datasets has been conducted. The results show that the newly proposed framework outperforms state-of-the-art approaches in concept extraction and lattice generation.
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Khoromskaia, Venera, et Boris N. Khoromskij. « Block Circulant and Toeplitz Structures in the Linearized Hartree–Fock Equation on Finite Lattices : Tensor Approach ». Computational Methods in Applied Mathematics 17, no 3 (1 juillet 2017) : 431–55. http://dx.doi.org/10.1515/cmam-2017-0004.
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AbstractThis paper introduces and analyzes the new grid-based tensor approach to approximate solutions of the elliptic eigenvalue problem for the 3D lattice-structured systems. We consider the linearized Hartree–Fock equation over a spatial{L_{1}\times L_{2}\times L_{3}}lattice for both periodic and non-periodic problem setting, discretized in the localized Gaussian-type orbitals basis. In the periodic case, the Galerkin system matrix obeys a three-level block-circulant structure that allows the FFT-based diagonalization, while for the finite extended systems in a box (Dirichlet boundary conditions) we arrive at the perturbed block-Toeplitz representation providing fast matrix-vector multiplication and low storage size. The proposed grid-based tensor techniques manifest the twofold benefits: (a) the entries of the Fock matrix are computed by 1D operations using low-rank tensors represented on a 3D grid, (b) in the periodic case the low-rank tensor structure in the diagonal blocks of the Fock matrix in the Fourier space reduces the conventional 3D FFT to the product of 1D FFTs. Lattice type systems in a box with Dirichlet boundary conditions are treated numerically by our previous tensor solver for single molecules, which makes possible calculations on rather large{L_{1}\times L_{2}\times L_{3}}lattices due to reduced numerical cost for 3D problems. The numerical simulations for both box-type and periodic{L\times 1\times 1}lattice chain in a 3D rectangular “tube” withLup to several hundred confirm the theoretical complexity bounds for the block-structured eigenvalue solvers in the limit of largeL.
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STRACCIA, UMBERTO. « DESCRIPTION LOGICS OVER LATTICES ». International Journal of Uncertainty, Fuzziness and Knowledge-Based Systems 14, no 01 (février 2006) : 1–16. http://dx.doi.org/10.1142/s0218488506003807.
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It is generally accepted that knowledge based systems would be smarter if they could manage uncertainty and/or imprecision. In this paper we extend Description Logics, well-known logics for managing structured knowledge, allowing to express that a sentence is not just true or false, but true to some degree, which is taken from a certainty lattice.
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Ryvkin, Michael, Viacheslav Slesarenko, Andrej Cherkaev et Stephan Rudykh. « Fault-tolerant elastic–plastic lattice material ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 378, no 2162 (25 novembre 2019) : 20190107. http://dx.doi.org/10.1098/rsta.2019.0107.
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The paper describes a fault-tolerant design of a special two-dimensional beam lattice. The morphology of such lattices was suggested in the theoretical papers (Cherkaev and Ryvkin 2019 Arch. Appl. Mech. 89 , 485–501; Cherkaev and Ryvkin 2019 Arch. Appl. Mech. 89 , 503–519), where its superior properties were found numerically. The proposed design consists of beam elements with two different thicknesses; the lattice is macro-isotropic and stretch dominated. Here, we experimentally verify the fault-tolerant properties of these lattices. The specimens were three-dimensional-printed from the VeroWhite elastoplastic material. The lattice is subjected to uniaxial tensile loading. Due to its morphology, the failed beams are evenly distributed in the lattice at the initial stage of damage; at this stage, the material remains intact, preserves its bearing ability, and supports relatively high strains before the final failure. At the initial phase of damage, the thinner beams buckle; then another group of separated thin beams plastically yield and rupture. The fatal macro-crack propagates after the distributed damage reaches a critical level. This initial distributed damage stage allows for a better energy absorption rate before the catastrophic failure of the structure. The experimental results are supported by simulations which confirm that the proposed fault-tolerant material possesses excellent energy absorption properties thanks to the distributed damage stage phenomenon. This article is part of the theme issue ‘Modelling of dynamic phenomena and localization in structured media (part 2)’.
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Koo, Zahyun, Yongwoo Lee, Joon-Woo Lee, Jong-Seon No et Young-Sik Kim. « Improved Reduction Between SIS Problems Over Structured Lattices ». IEEE Access 9 (2021) : 157083–92. http://dx.doi.org/10.1109/access.2021.3128139.
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Frascella, A., et C. Guido. « Structured lattices and topological categories of L-sets ». Fuzzy Sets and Systems 161, no 3 (février 2010) : 444–52. http://dx.doi.org/10.1016/j.fss.2009.09.009.
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Zhu, Xuanmin, Yuanchun Deng, Dezheng Zhang, Runping Gao, Qun Wei et Zijiang Luo. « Spatial search by continuous-time quantum walk on truncated simplex lattices ». Laser Physics Letters 20, no 3 (2 février 2023) : 035205. http://dx.doi.org/10.1088/1612-202x/acb594.
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Abstract Quantum search via continuous-time quantum walk on truncated simplex lattices is an important example of the quantum search on the structured database. In this letter, when the search target is a set of the marked vertices, the run time of the quantum search and the critical jumping rates are derived. Quantum search with the partial information of the location of the marked vertex is also discussed. Furthermore, with the edge weights suitably adjusted, the three-stage search process can be optimized into a two-stage quantum search algorithm on the second-order truncated simplex lattice.
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Wang, Junying, Zhiwei Shi, Xifeng Ji, Yajing Zhang, Huagang Li, Yaohua Deng et Kang Xie. « Topological Edge States on Different Domain Walls of Two Opposed Helical Waveguide Arrays ». Photonics 10, no 11 (31 octobre 2023) : 1220. http://dx.doi.org/10.3390/photonics10111220.
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Floquet topological insulators (FTIs) have richer topological properties than static systems. In this work, we designed different domain wall (DW) structures consisting of a Floquet photonic lattice with opposite helical directions. We investigated the existence and types of edge states in three shared coupling structures and the impact of these shared coupling structures on edge states. When two opposite helical lattices share a straight waveguide array coupling, the edge states are localized on the straight waveguide. When two opposite helical lattices share a clockwise (or anticlockwise) helical waveguide array coupling, the DWs consist of zigzag and bearded edges, but the positions of the zigzag and bearded edges of the shared clockwise waveguide array are different from those of the shared anticlockwise waveguide array. The slope and transmission rate of the edge states both vary with the degree of coupling between the shared waveguides. The characteristics of these edge states, such as transmission speed and band gap width, are also affected by the incidence angle, modulation phase factor, and helical radii, and the methods for controlling the edge states in different shared coupling structures are provided. This will help deepen our understanding of how topological structures influence the electronic and photonic properties of materials. This could also lead to combining topology with metasurface-based structured light, which would highlight many novel properties with great application potential for various fields, such as imaging, metrology, communication, quantum information processing, and light–matter interaction.
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Reboud, Julien, Rab Wilson, Yi Zhang, Mohd H. Ismail, Yannyk Bourquin et Jonathan M. Cooper. « Nebulisation on a disposable array structured with phononic lattices ». Lab on a Chip 12, no 7 (2012) : 1268. http://dx.doi.org/10.1039/c2lc20705b.
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Wallbanks, Matthew, Muhammad Farhan Khan, Mahdi Bodaghi, Andrew Triantaphyllou et Ahmad Serjouei. « On the design workflow of auxetic metamaterials for structural applications ». Smart Materials and Structures 31, no 2 (21 décembre 2021) : 023002. http://dx.doi.org/10.1088/1361-665x/ac3f78.
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Abstract Auxetic metamaterials exhibit an unexpected behaviour of a negative Poisson’s ratio (NPR), meaning they expand transversely when stretched longitudinally. This behaviour is generated predominantly due to the way individual elements of an auxetic lattice are structured. These structures are gaining interest in a wide variety of applications such as energy absorption, sensors, smart filters, vibration isolation and medical etc. Their potential could be further exploited by the use of additive manufacturing. Currently there is a lack of guidance on how to design these structures. This paper highlights state-of-the-art in auxetic metamaterials and its commonly used unit-cell types. It further explores the design approaches used in the literature on creating auxetic lattices for different applications and proposes, for the first time, a workflow comprising design, simulation and testing of auxetic structures. This workflow provides guidance on the design process for using auxetic metamaterials in structural applications.
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Abdukadirov, Sagdulla A., Mark V. Ayzenberg-Stepanenko et Gregory G. Osharovich. « Resonant waves and localization phenomena in lattices ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 377, no 2156 (2 septembre 2019) : 20190110. http://dx.doi.org/10.1098/rsta.2019.0110.
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Transient wave processes in mass-spring lattices excited by point oscillating sources are studied. Dispersion properties of uniform periodic three-dimensional (3D) square-cell and two-dimensional (2D) hexagonal-cell lattices including revealed star-shaped localization phenomena are analysed. The resonant-like waves and localization-like patterns in non-uniform lattices possessing predetermined and randomly distributed defects are numerically examined in order to identify the sensitivity of star-shape forms to different types of defects. This article is part of the theme issue ‘Modelling of dynamic phenomena and localization in structured media (part 1)’.
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Kandiy, S. О. « Security analysis of promising key encapsulation mechanisms in the core-SVP model ». Radiotekhnika, no 212 (28 mars 2023) : 66–84. http://dx.doi.org/10.30837/rt.2023.1.212.06.
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The study of key encapsulation mechanisms on structured lattices is one of the important directions in modern post-quantum cryptography, as many mechanisms are either already standardized (DSTU 8961:2019 "Skelya") or are promising candidates for standardization (CRYSTALS-Kyber). Estimating the complexity of lattice reduction for cryptographic schemes is an old problem. Asymptotic estimates differ greatly from experimental values, therefore, a number of heuristic methods were developed to solve practical problems. The coreSVP model is a standard means of assessing the security of cryptographic schemes on lattices. The purpose of the work is to analyze the encapsulation mechanisms of DSTU 8961:2019 "Skelya" and CRYSTALS-Kyber keys in the coreSVP model. The analysis was performed using two popular heuristics – GSA (Geometric Series Assumption) and the Chen-Nguyen simulator. The analysis showed that the Chen-Nguyen simulator gives slightly lower estimates than the GSA heuristic. As a result of the analysis, it was found that 8961:2019 The “Skelya” and CRYSTALS-Kyber in the coreSVP model for classical computers have slightly lower than declared security values, but for quantum computers the key encapsulation mechanisms provide the declared security levels. Note that during the analysis, the accuracy of the GSA heuristics and the Chen-Nguyen simulator were analyzed separately. Examples of parameters for which heuristics do not give sufficiently accurate results are given. The performed analysis does not take into account the algebraic structure of lattices used in 8961:2019 "Skelya" and CRYSTALS-Kyber. The inclusion of an algebraic structure in the analysis is a further direction of work. The use of simulators is a promising direction, however, more accurate simulators that take into account the structuring of LWE and NTRU arrays are needed.
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Santos, José I., David J. Poza, José M. Galán et Adolfo López-Paredes. « Evolution of Equity Norms in Small-World Networks ». Discrete Dynamics in Nature and Society 2012 (2012) : 1–18. http://dx.doi.org/10.1155/2012/482481.
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The topology of interactions has been proved very influential in the results of models based on learning and evolutionary game theory. This paper is aimed at investigating the effect of structures ranging from regular ring lattices to random networks, including small-world networks, in a model focused on property distribution norms. The model considers a fixed and finite population of agents who play the Nash bargaining game repeatedly. Our results show that regular networks promote the emergence of the equity norm, while less-structured networks make possible the appearance of fractious regimes. Additionally, our analysis reveals that the speed of adoption can also be affected by the network structure.
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Xiong, Kezhao, Zonghua Liu, Chunhua Zeng et Baowen Li. « Thermal-siphon phenomenon and thermal/electric conduction in complex networks ». National Science Review 7, no 2 (2 septembre 2019) : 270–77. http://dx.doi.org/10.1093/nsr/nwz128.
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Abstract In past decades, a lot of studies have been carried out on complex networks and heat conduction in regular lattices. However, very little attention has been paid to the heat conduction in complex networks. In this work, we study (both thermal and electric) energy transport in physical networks rewired from 2D regular lattices. It is found that the network can be transferred from a good conductor to a poor conductor, depending on the rewired network structure and coupling scheme. Two interesting phenomena were discovered: (i) the thermal-siphon effect—namely the heat flux can go from a low-temperature node to a higher-temperature node and (ii) there exits an optimal network structure that displays small thermal conductance and large electrical conductance. These discoveries reveal that network-structured materials have great potential in applications in thermal-energy management and thermal-electric-energy conversion.
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Tang, Liqin, Daohong Song, Shiqi Xia, Shiqiang Xia, Jina Ma, Wenchao Yan, Yi Hu, Jingjun Xu, Daniel Leykam et Zhigang Chen. « Photonic flat-band lattices and unconventional light localization ». Nanophotonics 9, no 5 (1 avril 2020) : 1161–76. http://dx.doi.org/10.1515/nanoph-2020-0043.
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AbstractFlat-band systems have attracted considerable interest in different branches of physics in the past decades, providing a flexible platform for studying fundamental phenomena associated with completely dispersionless bands within the whole Brillouin zone. Engineered flat-band structures have now been realized in a variety of systems, in particular, in the field of photonics. Flat-band localization, as an important phenomenon in solid-state physics, is fundamentally interesting in the exploration of exotic ground-state properties of many-body systems. However, direct observation of some flat-band phenomena is highly nontrivial in conventional condensed-matter systems because of intrinsic limitations. In this article, we briefly review recent developments on flat-band localization and the associated phenomena in various photonic lattices, including compact localized states, unconventional line states, and noncontractible loop states. We show that the photonic lattices offer a convenient platform for probing the underlying physics of flat-band systems, which may provide inspiration for exploring the fundamentals and applications of flat-band physics in other structured media from metamaterials to nanophotonic materials.
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Santoliquido, Oscar, Francesco Camerota, Marco Pelanconi, Davide Ferri, Martin Elsener, Panayotis Dimopoulos Eggenschwiler et Alberto Ortona. « Structured Alumina Substrates for Environmental Catalysis Produced by Stereolithography ». Applied Sciences 11, no 17 (6 septembre 2021) : 8239. http://dx.doi.org/10.3390/app11178239.
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Modern catalysts for internal combustion engine applications are traditionally constituted by honeycomb substrates on which a coating of the catalytically active phase is applied. Due to the laminar flow of the gases passing through their straight channels, these structures present low heat and mass transfer, thus leading to relatively large catalyst sizes to compensate for the low catalytic activity per unit of volume. Better conversion efficiency can be achieved if three-dimensional periodic structures are employed, because of the resulting gases’ tortuous paths. Furthermore, the increased catalytic activity implies a reduction in the overall catalyst volume, which can translate to a decreased usage of precious metals as active phase. By exploiting the ceramic Stereolithography technique (i.e., SLA) it is nowadays possible to accurately 3D print complex alumina-based lattices to be used as ceramic substrates for catalysis. In this work, closed-walls lattices consisting of a rotated cubic cell of 2 mm dimensions were designed, 3D printed via SLA and finally washcoated with V2O5-WO3-TiO2. The samples were tested for the selective catalytic reduction of NO by NH3 in a heated quartz glass reactor and the performance of the innovative 3D-printed substrate was compared with the catalytic efficiency of the conventional cordierite honeycombs.
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Kitamura, Takayuki, Yoshitaka Umeno et Akihiro Kushima. « Ideal Strength of Nano-Components ». Materials Science Forum 482 (avril 2005) : 25–32. http://dx.doi.org/10.4028/www.scientific.net/msf.482.25.
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The ideal (theoretical) strength was originally defined as the stress or strain at which perfect crystal lattice became mechanically unstable with respect to arbitrary homogeneous infinitesimal deformation. This has been intensely investigated because the ultimate strength without defects is a fundamental mechanical characteristic of materials. In the analyses, the instability criteria have been studied on the basis of elastic constants. Recent developments in computational technology make it possible to analyze the ideal strength on the basis of quantum mechanics. On the other hand, it is well known that the mechanical strength of components is dependent not only on (1) material (atom species), but also on (2) loading condition and (3) structure. Because most studies on the strength in terms of atomic mechanics have focused on the factor (1) (materials), analysis has mainly been conducted on simple crystal consisting of perfect lattices (e.g. fcc and bcc) under simple loading conditions (e.g. tension), though some have explored the properties of bulk materials with defects (e.g. vacancy and grain boundary). Small atomic components (nano-structured components) such as nano-films, nano-wires (tubes) and nano-dots (clusters) possess their own beautiful, defect-free structures, namely ideal structure. Thus, they show characteristic high strength. Moreover, utilizing the structure at the nanometer or micron level is a key technology in the development of electronic devices and elements of micro (nano) electro-mechanical systems (MEMS/NEMS). Therefore, it is important to understand the mechanical properties not only for the sake of scientific interest, but also for engineering usefulness such as design of fabrication/assembly processes and reliability in service. In the other words, the effects of structure (factor (3); e.g. film/wire/dot) have to be understood as the basic properties of atomic components. Thus, the definition of ideal strength should be expanded to include the strength at instability of components with ideal structures under various external loads (factor (2)), which provides fundamental knowledge of nano-structured materials. In this paper, we review works on the strength of ideal nano-structured components in terms of factor (3), mainly under tension.
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Colquitt, D. J., I. S. Jones, N. V. Movchan, A. B. Movchan, M. Brun et R. C. McPhedran. « Making waves round a structured cloak : lattices, negative refraction and fringes ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 469, no 2157 (8 septembre 2013) : 20130218. http://dx.doi.org/10.1098/rspa.2013.0218.
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Using the framework of transformation optics, this paper presents a detailed analysis of a non-singular square cloak for acoustic, out-of-plane shear elastic and electromagnetic waves. Analysis of wave propagation through the cloak is presented and accompanied by numerical illustrations. The efficacy of the regularized cloak is demonstrated and an objective numerical measure of the quality of the cloaking effect is provided. It is demonstrated that the cloaking effect persists over a wide range of frequencies. As a demonstration of the effectiveness of the regularized cloak, a Young's double slit experiment is presented. The stability of the interference pattern is examined when a cloaked and uncloaked obstacle are successively placed in front of one of the apertures. This novel link with a well-known quantum mechanical experiment provides an additional method through which the quality of cloaks may be examined. In the second half of the paper, it is shown that an approximate cloak may be constructed using a discrete lattice structure. The efficiency of the approximate lattice cloak is analysed and a series of illustrative simulations presented. It is demonstrated that effective cloaking may be obtained by using a relatively simple lattice structure, particularly, in the low-frequency regime.
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Zhang, Cilong, et Qiaofeng Tan. « Super-oscillatory lattices structured illumination microscopy beyond two-fold resolution enhancement ». Optics and Lasers in Engineering 173 (février 2024) : 107912. http://dx.doi.org/10.1016/j.optlaseng.2023.107912.
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Badini, Silvia, Stefano Regondi, Carmen Lammi, Carlotta Bollati, Giordana Donvito et Raffaele Pugliese. « Computational Mechanics of Form-Fitting 3D-Printed Lattice-Based Wrist-Hand Orthosis for Motor Neuron Disease ». Biomedicines 11, no 7 (22 juin 2023) : 1787. http://dx.doi.org/10.3390/biomedicines11071787.
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Motor neuron disease (MND) patients often experience hand-wrist muscle atrophy resulting in severe social consequences and hampering their daily activities. Although hand-wrist orthosis is commonly used to assist weakened muscles, its effectiveness is limited due to the rapid progression of the disease and the need for customization to suit individual patient requirements. To address these challenges, this study investigates the application of three-dimensional (3D) printing technology to design and fabricate two lattice structures inspired by silkworm cocoons, using poly-ε-caprolactone as feedstock material. Finite element method (FEM) analysis is employed to study the mechanical behavior, enabling control over the geometric configuration incorporated into the hand-wrist orthosis. Through tensile displacement and three-point bending simulations, the stress distribution is examined for both lattice geometries. Geometry-1 demonstrates anisotropic behavior, while geometry-2 exhibits no strict directional dependence due to its symmetry and uniform node positioning. Moreover, the biocompatibility of lattices with human skin fibroblasts is investigated, confirming excellent biocompatibility. Lastly, the study involves semi-structured interviews with MND patients to gather feedback and develop prototypes of form-fitting 3D-printed lattice-based hand-wrist orthosis. By utilizing 3D printing technology, this study aims to provide customized orthosis that can effectively support weakened muscles and reposition the hand for individuals with MND.
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Gorbenko, Yu I., et Ye V. Ostrianska. « Evaluation and comparison of lattice-based digital signature of the "Digital Signature Schemes" PQC NIST competition ». Radiotekhnika, no 217 (14 juin 2024) : 69–78. http://dx.doi.org/10.30837/rt.2024.2.217.06.
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Over the past decade, post-quantum cryptography has reached a tipping point; institutional bodies and stakeholders have initiated standardization and deployment, and various projects have achieved a reasonably high level of progress and even deployment and implementation. In July 2022, at the end of Round 3 of the NIST's PQC competition, 3 candidates were proposed for the NIST standardization for post-quantum digital signatures scheme: one signature scheme based on MLWE (Crystals-Dilithium), one signature based on NTRU (Falcon), and one signature based on hash (Sphincs+). Although the performance profiles and “black-box” security of these schemes are well understood, resistance to side-channel attacks remains a weak point for all of them. After that, the NIST announced that the PQC standardization process is continuing with a fourth round, with the following KEMs still under consideration: BIKE, Classic McEliece, HQC, and SIKE. However, there are no candidates of digital signature schemes left for consideration. As such, the NIST has issued a call for additional digital signature proposals to be considered in the PQC standardization process. Acceptance of documents ended on June 1, 2023. As a result, 40 candidates were selected for the role of DS standard, namely: 6 DS algorithms based on codes, one DS algorithm based on isogenies, 7 DS algorithms based on lattice operations, 7 candidates for the role of DS algorithm based on the MPC method -in-the-Head and 10 algorithms based on multivariate transformations, 4 DS schemes were selected based on symmetric cryptographic transformations, and 5 more candidates based on other types of cryptographic transformations. The NIST is primarily interested in additional general purpose signature schemes that are not based on structured lattices. For certain applications, such as certificate transparency, the NIST may also be interested in signature schemes that have short signatures and fast verification. The NIST is open to receiving additional materials based on structured lattices, but intends to diversify post-quantum signature standards. Therefore, any structured array-based signature proposal would need to significantly outperform CRYSTALS-Dilithium and FALCON in relevant applications and/or provide significant additional security properties to be considered for standardization. Thus, the purpose of this paper is to analyze, evaluate, and compare digital signature algorithms based on lattice cryptography, an additional PQC NIST competition, and compare them with already standardized lattice-based DS mechanisms, such as CRYSTALS-Dilithium and FALCON.
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González-Tudela, A., et J. I. Cirac. « Non-Markovian Quantum Optics with Three-Dimensional State-Dependent Optical Lattices ». Quantum 2 (1 octobre 2018) : 97. http://dx.doi.org/10.22331/q-2018-10-01-97.
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Quantum emitters coupled to structured photonic reservoirs experience unconventional individual and collective dynamics emerging from the interplay between dimensionality and non-trivial photon energy dispersions. In this work, we systematically study several paradigmatic three dimensional structured baths with qualitative differences in their bath spectral density. We discover non-Markovian individual and collective effects absent in simplified descriptions, such as perfect subradiant states or long-range anisotropic interactions. Furthermore, we show how to implement these models using only cold atoms in state-dependent optical lattices and show how this unconventional dynamics can be observed with these systems.
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Mondal, Rakesh, Himanshu Ratnawat, Sarvesh Kumar, Anil Kumar et Preetam Singh. « Ni stabilized rock-salt structured CoO ; Co1−xNixO : tuning of eg electrons to develop a novel OER catalyst ». RSC Advances 10, no 30 (2020) : 17845–53. http://dx.doi.org/10.1039/d0ra03050c.
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Tsakiris, Antonios, Christos Salpistis et Athanassios Mihailidis. « Design Right Once for Additive Manufacturing ». MATEC Web of Conferences 188 (2018) : 03020. http://dx.doi.org/10.1051/matecconf/201818803020.
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Additive Manufacturing (AM) has been widely considered a key factor for innovative design. However, the utilization of AM has not been as high as expected, although the technology offers key innovative design capabilities, weight reduction, parts count and assembly consolidation as well as material saving. This low utilization is attributed to the lack of AM understanding, mature CAE/CAM software tools addressing AM specific issues such as design support structure generation and removal, residual stresses, surface quality. In most cases, Design for AM (DfAM) is a crucial requisite for a “Design Right Once” approach. Such an approach is shown in the current study using three parts as example: an arthropod’s leg, a gearshift drum and an electric motor mounting frame. The implementation of geometrical conformal lattice structures and lattices with variable density are discussed. A structured design approach is presented and design dilemmas are solved in terms of a DfAM approach. Primary design optimizations are evaluated. Weight reduction is considered throughout the design and free form surfaces are being used. “Freedom to Design” principle is also portrayed and assembly parts consolidation occurs as a natural process of DfAM in comparison with previous design practices. It is concluded that, even from the primary design phase the design engineer can reveal his creativity because of the absence of constraints set by the traditional manufacturing technologies.
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Hýsek, Štěpán, Miroslav Frydrych, Miroslav Herclík, Petr Louda, Ludmila Fridrichová, Su Le Van et Hiep Le Chi. « Fire-Resistant Sandwich-Structured Composite Material Based on Alternative Materials and Its Physical and Mechanical Properties ». Materials 12, no 9 (2 mai 2019) : 1432. http://dx.doi.org/10.3390/ma12091432.
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The development of composite materials from alternative raw materials, and the design of their properties for the intended purpose is an integral part of the rational management of raw materials and waste recycling. The submitted paper comprehensively assesses the physical and mechanical properties of sandwich composite material made from particles of winter rapeseed stalks, geopolymer and reinforcing basalt lattices. The developed composite panel is designed for use as a filler in constructions (building or building joinery). The observed properties were: bending characteristics, internal bonding, thermal conductivity coefficient and combustion characteristics. The results showed that the density of the particleboard has a significant effect on the resulting mechanical properties of the entire sandwich panel. On the contrary, the density of the second layer of the sandwich panel, geopolymer, did not have the same influence on its mechanical properties as the density of the particleboard. The basalt fibre reinforcement lattice positively affected the mechanical properties of sandwich composites only if it was sufficiently embedded in the structure of the particle board. All of the manufactured sandwich composites resisted flame for more than 13 min and the fire resistance was positively affected by the density of the geopolymer layer.
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Hou, Mengjie, Jinxing Liu et Ai Kah Soh. « Modeling lattice metamaterials with deformable joints as an elastic micropolar continuum ». AIP Advances 12, no 6 (1 juin 2022) : 065116. http://dx.doi.org/10.1063/5.0093094.
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Planar lattice metamaterials, such as periodic beam networks, are often considered as the micropolar continuum, where each material point has two translational degrees of freedom and one rotational degree of freedom. The joints through which bars are linked to one another are generally approximated as rigid. This study focuses on lattices with complex-structured deformable joints. The deformation field in each joint is obtained by conducting structural analyses. Once the “stiffness matrix” of the joint-centered unit cell is obtained by the finite element method, it can be used as the input for the standard procedure of calculating micropolar elastic moduli that are based on the equivalence of strain energy. As a result, effective moduli can be expressed in a semi-analytical form, meaning that only the cell structural stiffness is given numerically. The present model is validated by comparison to the FEM simulations. Particularly, the auxetic and anisotropic properties are discussed for various lattice metamaterials with deformable joints. We then take the obtained effective moduli as inputs to the in-house micropolar FEM code and obtain results agreeing well with the FEM structural simulations.
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Mager, Tom, Carlo Fiorina, Mathieu Hursin et Andreas Pautz. « Investigation and Validation of Unstructured Mesh Methodologies for Modeling Experimental Reactors ». Energies 15, no 4 (18 février 2022) : 1512. http://dx.doi.org/10.3390/en15041512.
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This paper summarizes a methodology developed at École Polytechnique Fédérale de Lausanne for the neutronic modeling of the CROCUS experimental reactor and proposes solutions to the challenges one may face while modeling a research reactor with a complex geometry. Indeed, the double-lattice configuration of CROCUS makes it difficult to use codes for neutron diffusion and transport relying on a structured mesh description. For this reason, and based on the available in-house competences, we decided to make use of the neutronic capabilities of the GeN-Foam multiphysics solver, which takes advantage of general finite volume methodologies on unstructured meshes to provide sufficient flexibility for the study of unconventional reactor designs. In this work, GeN-Foam is used to build a first SP3 model of CROCUS based on an unstructured mesh to have an explicit modeling of the double lattice and the water gap between the two lattices. Form functions are then used to reconstruct the intra-pin fission rates for validation against measured distributions. We also discuss the limitations of the SP3 approximation of neutron transport in regions with steep neutron flux gradients and the planned future developments.
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de-Camino-Beck, T., et M. A. Lewis. « Invasion with stage-structured coupled map lattices : Application to the spread of scentless chamomile ». Ecological Modelling 220, no 23 (décembre 2009) : 3394–403. http://dx.doi.org/10.1016/j.ecolmodel.2009.09.003.
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Rosu, Radu Alexandru, Peer Schütt, Jan Quenzel et Sven Behnke. « LatticeNet : fast spatio-temporal point cloud segmentation using permutohedral lattices ». Autonomous Robots 46, no 1 (19 octobre 2021) : 45–60. http://dx.doi.org/10.1007/s10514-021-09998-1.
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AbstractDeep convolutional neural networks have shown outstanding performance in the task of semantically segmenting images. Applying the same methods on 3D data still poses challenges due to the heavy memory requirements and the lack of structured data. Here, we propose LatticeNet, a novel approach for 3D semantic segmentation, which takes raw point clouds as input. A PointNet describes the local geometry which we embed into a sparse permutohedral lattice. The lattice allows for fast convolutions while keeping a low memory footprint. Further, we introduce DeformSlice, a novel learned data-dependent interpolation for projecting lattice features back onto the point cloud. We present results of 3D segmentation on multiple datasets where our method achieves state-of-the-art performance. We also extend and evaluate our network for instance and dynamic object segmentation.
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Perc, Matjaž, Jesús Gómez-Gardeñes, Attila Szolnoki, Luis M. Floría et Yamir Moreno. « Evolutionary dynamics of group interactions on structured populations : a review ». Journal of The Royal Society Interface 10, no 80 (6 mars 2013) : 20120997. http://dx.doi.org/10.1098/rsif.2012.0997.
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Interactions among living organisms, from bacteria colonies to human societies, are inherently more complex than interactions among particles and non-living matter. Group interactions are a particularly important and widespread class, representative of which is the public goods game. In addition, methods of statistical physics have proved valuable for studying pattern formation, equilibrium selection and self-organization in evolutionary games. Here, we review recent advances in the study of evolutionary dynamics of group interactions on top of structured populations, including lattices, complex networks and coevolutionary models. We also compare these results with those obtained on well-mixed populations. The review particularly highlights that the study of the dynamics of group interactions, like several other important equilibrium and non-equilibrium dynamical processes in biological, economical and social sciences, benefits from the synergy between statistical physics, network science and evolutionary game theory.
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Razmjooei, Nasrin, et Robert Magnusson. « Band Dynamics of Multimode Resonant Nanophotonic Lattices with Adjustable Liquid Interfaces ». Nanomaterials 13, no 16 (16 août 2023) : 2350. http://dx.doi.org/10.3390/nano13162350.
Texte intégralRésumé :
Subwavelength resonant lattices offer a wide range of fascinating spectral phenomena under broadside illumination. The resonance mechanism relies on the generation of lateral Bloch modes that are phase matched to evanescent diffraction orders. The spectral properties and the total number of resonance states are governed by the structure of leaky modes and the mode count. This study investigates the effect of interface modifications on the band dynamics and bound-state transitions in guided-mode resonant lattices. We provide photonic lattices comprising rectangular Si3N4 rods with a liquid film with an adjustable boundary. The band structures and band flips are examined through numerical simulations using the rigorous coupled-wave analysis (RCWA) method and analyzing the zero-order spectral reflectance as a function of the incident angle. The band structures and band flips are examined through numerical simulations, and the influences of the refractive index and the thickness of the oil layer on the band dynamics are investigated. The results reveal distinct resonance linewidths corresponding to different refractive indices of the oil layer. Furthermore, the effect of the oil thickness on the band dynamics is explored, demonstrating precise control over the number of propagating modes within the lattice structure. Theoretical simulations and experimental results are presented for a subwavelength silicon-nitride lattice combined with a liquid film featuring an adjustable boundary. The presence of a relatively thick liquid waveguiding region enables the emergence of additional modes, including the first four transverse-electric (TE) leaky modes, which produce observable resonance signatures. Through experimental manipulation of the basic lattice’s duty cycle, the four bands undergo quantifiable band transitions and closures. The experimental results obtained within the 1400–1600 nm spectral range exhibit reasonable agreement with the numerical analysis. These findings underscore the significant role played by the interface in shaping the band dynamics of the lattice structure, providing valuable insights into the design and optimization of photonic lattices with adjustable interfaces.
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Dong, Wei, Yang Li, Kehao Xin, Dezheng Yin, Longlong Song et Tong Gao. « A method of designing plate structure consisting of lattices and stiffeners based on topology optimization ». Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 39, no 6 (décembre 2021) : 1233–39. http://dx.doi.org/10.1051/jnwpu/20213961233.
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In order to satisfy the lightweight design requirements of the equipment mounting plate in the hypersonic vehicle instrument cabin and improve its static/dynamic performance, a novel structure consisting of both lattices and stiffeners are studied and topology optimization method is proposed in this paper. This structure combines the advantages of lattice structures and conventional stiffened structures. First, the lattice structure is regarded as a kind of virtual material, and its equivalent mechanical properties are calculated by the homogenization method. Then, a marerial interpolation model of the virtual and solid materials are established. A topology optimization problem to minimize the mean compliance under the mass constraint is proposed to realize the layout optimization design of stiffened structure with lattices. Taking an equipment mounting plate as an example, the optimization design of the traditional stiffened structure and the novel stiffened structure with lattices is completed, respectively. Numerical analysis indicates that the lattice stiffened plate structure provides advantageous mechanical performation in the condition of the same weight. The maximum deformation under inertial force is reduced by 11.17% and the peak displacement response under harmonic excitation is reduced by 73.81% by using the stiffened structure with lattices.
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Abusabir, Ahmed, Muhammad A. Khan, Muhammad Asif et Kamran A. Khan. « Effect of Architected Structural Members on the Viscoelastic Response of 3D Printed Simple Cubic Lattice Structures ». Polymers 14, no 3 (5 février 2022) : 618. http://dx.doi.org/10.3390/polym14030618.
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Three-dimensional printed polymeric lattice structures have recently gained interests in several engineering applications owing to their excellent properties such as low-density, energy absorption, strength-to-weight ratio, and damping performance. Three-dimensional (3D) lattice structure properties are governed by the topology of the microstructure and the base material that can be tailored to meet the application requirement. In this study, the effect of architected structural member geometry and base material on the viscoelastic response of 3D printed lattice structure has been investigated. The simple cubic lattice structures based on plate-, truss-, and shell-type structural members were used to describe the topology of the cellular solid. The proposed lattice structures were fabricated with two materials, i.e., PLA and ABS using the material extrusion (MEX) process. The quasi-static compression response of lattice structures was investigated, and mechanical properties were obtained. Then, the creep, relaxation and cyclic viscoelastic response of the lattice structure were characterized. Both material and topologies were observed to affect the mechanical properties and time-dependent behavior of lattice structure. Plate-based lattices were found to possess highest stiffness, while the highest viscoelastic behavior belongs to shell-based lattices. Among the studied lattice structures, we found that the plate-lattice is the best candidate to use as a creep-resistant LS and shell-based lattice is ideal for damping applications under quasi-static loading conditions. The proposed analysis approach is a step forward toward understanding the viscoelastic tolerance design of lattice structures.
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Taylor, William R. « Exploring Protein Fold Space ». Biomolecules 10, no 2 (27 janvier 2020) : 193. http://dx.doi.org/10.3390/biom10020193.
Texte intégralRésumé :
The model of protein folding proposed by Ptitsyn and colleagues involves the accretion of secondary structures around a nucleus. As developed by Efimov, this model also provides a useful way to view the relationships among structures. Although somewhat eclipsed by later databases based on the pairwise comparison of structures, Efimov’s approach provides a guide for the more automatic comparison of proteins based on an encoding of their topology as a string. Being restricted to layers of secondary structures based on beta sheets, this too has limitations which are partly overcome by moving to a more generalised secondary structure lattice that can encompass both open and closed (barrel) sheets as well as helical packing of the type encoded by Murzin and Finkelstein on small polyhedra. Regular (crystalline) lattices, such as close-packed hexagonals, were found to be too limited so pseudo-latticses were investigated including those found in quasicrystals and the Bernal tetrahedron-based lattice that he used to represent liquid water. The Bernal lattice was considered best and used to generate model protein structures. These were much more numerous than those seen in Nature, posing the open question of why this might be.
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Li, Kun. « Existence of traveling wave solutions in a stage structured cooperative system on higher-dimensional lattices ». Rocky Mountain Journal of Mathematics 49, no 5 (septembre 2019) : 1617–31. http://dx.doi.org/10.1216/rmj-2019-49-5-1617.
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Liang, Wenqi, Zhaoman Liu, Xuyang Zhao, Yafang Yang et Zhichuang Liang. « Flexible and Compact MLWE-Based KEM ». Mathematics 12, no 11 (6 juin 2024) : 1769. http://dx.doi.org/10.3390/math12111769.
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In order to resist the security risks caused by quantum computing, post-quantum cryptography (PQC) has been a research focus. Constructing a key encapsulation mechanism (KEM) based on lattices is one of the promising PQC routines. The algebraically structured learning with errors (LWE) problem over power-of-two cyclotomics has been one of the most widely used hardness assumptions for lattice-based cryptographic schemes. However, power-of-two cyclotomic rings may be exploited in the inflexibility of selecting parameters. Recently, trinomial cyclotomic rings of the form Zq[x]/(xn−xn/2+1), where n=2k3l, k≥1,l≥0, have received widespread attention due to their flexible parameter selection. In this paper, we propose Tyber, a variant scheme of the NIST-standardized KEM candidate Kyber over trinomial cyclotomic rings. We provide three parameter sets, aiming at the quantum security of 128, 192, and 256 bits (actually achieving 129, 197, and 276 bits) with matching and negligible error probabilities. When compared to Kyber, our Tyber exhibits stronger quantum security, by 22, 31, and 44 bits, than Kyber for three security levels.
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Shatabda, Swakkhar, M. A. Hakim Newton, Mahmood A. Rashid, Duc Nghia Pham et Abdul Sattar. « How Good Are Simplified Models for Protein Structure Prediction ? » Advances in Bioinformatics 2014 (29 avril 2014) : 1–9. http://dx.doi.org/10.1155/2014/867179.
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Protein structure prediction (PSP) has been one of the most challenging problems in computational biology for several decades. The challenge is largely due to the complexity of the all-atomic details and the unknown nature of the energy function. Researchers have therefore used simplified energy models that consider interaction potentials only between the amino acid monomers in contact on discrete lattices. The restricted nature of the lattices and the energy models poses a twofold concern regarding the assessment of the models. Can a native or a very close structure be obtained when structures are mapped to lattices? Can the contact based energy models on discrete lattices guide the search towards the native structures? In this paper, we use the protein chain lattice fitting (PCLF) problem to address the first concern; we developed a constraint-based local search algorithm for the PCLF problem for cubic and face-centered cubic lattices and found very close lattice fits for the native structures. For the second concern, we use a number of techniques to sample the conformation space and find correlations between energy functions and root mean square deviation (RMSD) distance of the lattice-based structures with the native structures. Our analysis reveals weakness of several contact based energy models used that are popular in PSP.
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Nadia Drisi, Brahim Es-sebbar, Ezzinbi Khalil et Samir Fatajou. « On the asymptotic behavior of a size-structured model arising in population dynamics ». Malaya Journal of Matematik 11, S (1 octobre 2023) : 92–114. http://dx.doi.org/10.26637/mjm11s/007.
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We study the asymptotic behavior of a semilinear size-structured population model withdelay when the nonlinearity is small in some sense. The novelty in this work is that theoperator governing the linear part of the equation does not generate a compact semigroupunlike in the results present in literature. In such a case the spectrum does not consist whollyof eigenvalues but also has a non-trivial component called Browder’s essential spectrum. Toovercome the lack of compactness, we give a localization of Browder’s essential spectrum of theoperator governing the linear part and we use the Perron-Frobenius spectral analysis adaptedto semigroups of positive operators in Banach lattices to investigate the long time behavior ofthe system.Keywords: Perron-Frobenius, positive operators, structured population models, Browder’sessential spectrum, asymptotic behavior, semigroups of operatorsAMS Subject Classifications: 35B40, 35R10, 47D06.
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Lyudmila, Solonenko, Repyakh Sergei et Uzlov Kostiantyn. « Sand-sodium-silicate mixtures grains composition optimization for structuring by steam-microwave solidification method ». Theory and practice of metallurgy 1,2021, no 1,2021(126) (22 février 2021) : 28–38. http://dx.doi.org/10.34185/tpm.1.2021.05.
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Abstract. Mixture sizes of sand-sodium-silicate conglomerates and sodium silicate solute content in them influences on the basic physical and technological indicators of molding and core mixtures structured in steam-microwave environment have been investigated. Sand-sodium-silicate mixture structured by steam-microwave environment (steam-microwave solidification method – SMS-process) composition has been optimized. Standard and generally accepted methods and techniques of molding mixtures investigation have beenused in this study. For mixtures manufacturing have been used: quartz sand brand 1K2O202; sodium silicate solute with silicate modulus of 2.8…3.0 and specific gravity of 1.42…1.44 g/cm3. Quartz sand cladding has been implemented with 0.5 and 2.5% sodium silicate solute (by weight, over 100% sand). Sand-sodium-silicate conglomerates have been scattered in sieves and conglomerates with sizes less than 0.315mm and with sizes from 0.315 to 0.63mm have been used for research. Mixture composition has been optimized according to results of simplex planning and experimental data by simplex triangles constructing and superimposing their formatted images on each other with darkened fields between isolines that do not meet of each parameters required level. To plot simplex lattices, model with simplex lattice plan of incomplete cube in Scheffe’s triple system has been used. For the first time, influence of mixture sand-sodium-silicate conglomerates sizes and sodium-silicate-solute content in them on basic indicators of mold and rod mixtures structured in steam-microwave environment has been established, and their composition has been optimized. Data obtained will be useful in molds and rods structured by SMS-process manufacturing. They will have predictable indicators of properties that correspond to their allowable level. Optimal composition of sand-sodium-silicate mixture, structured by SMS-process, is mixture of quartz sand, part of which passed through sieve with cell of 0.315 mm and have sodium silicate solute content (МSiO2=2.8…3.0, 2=1.42…1.44 g/сm3) in amount of 1.5% (by weight, over 100% quartz sand). Keywords.Sand, silicon silicate solute, steam-microwave solidification, optimization, conglomerates, strength, gas permeability, crushability, density, beam deflection, knockout energy.
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Liu, Tinghao, et Guangbo Hao. « Design of Deployable Structures by Using Bistable Compliant Mechanisms ». Micromachines 13, no 5 (19 avril 2022) : 651. http://dx.doi.org/10.3390/mi13050651.
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A deployable structure can significantly change its geometric shape by switching lattice configurations. Using compliant mechanisms as the lattice units can prevent wear and friction among multi-part mechanisms. This work presents two distinctive deployable structures based on a programmable compliant bistable lattice. Several novel parameters are introduced into the bistable mechanism to better control the behaviour of bistable mechanisms. By adjusting the defined geometry parameters, the programmable bistable lattices can be optimized for specific targets such as a larger deformation range or higher stability. The first structure is designed to perform 1D deployable movement. This structure consists of multi-series-connected bistable lattices. In order to explore the 3D bistable characteristic, a cylindrical deployable mechanism is designed based on the curved double tensural bistable lattice. The investigation of bistable lattices mainly involves four types of bistable mechanisms. These bistable mechanisms are obtained by dividing the long segment of traditional compliant bistable mechanisms into two equal parts and setting a series of angle data to them, respectively. The experiment and FEA simulation results confirm the feasibility of the compliant deployable structures.
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Koca, Nazife O., Mehmet Koca et Ramazan Koc. « Twelvefold symmetric quasicrystallography from the latticesF4,B6andE6 ». Acta Crystallographica Section A Foundations and Advances 70, no 6 (26 septembre 2014) : 605–15. http://dx.doi.org/10.1107/s2053273314015812.
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One possible way to obtain the quasicrystallographic structure is the projection of the higher-dimensional lattice into two- or three-dimensional subspaces. Here a general technique applicable to any higher-dimensional lattice is introduced. The Coxeter number and the integers of the Coxeter exponents of a Coxeter–Weyl group play a crucial role in determining the plane onto which the lattice is to be projected. The quasicrystal structures display the dihedral symmetry of order twice that of the Coxeter number. The eigenvectors and the corresponding eigenvalues of the Cartan matrix are used to determine the set of orthonormal vectors inn-dimensional Euclidean space which lead to suitable choices for the projection subspaces. The maximal dihedral subgroup of the Coxeter–Weyl group is identified to determine the symmetry of the quasicrystal structure. Examples are given for 12-fold symmetric quasicrystal structures obtained by projecting the higher-dimensional lattices determined by the affine Coxeter–Weyl groupsWa(F4),Wa(B6) andWa(E6). These groups share the same Coxeter numberh= 12 with different Coxeter exponents. The dihedral subgroupD12of the Coxeter groups can be obtained by defining two generatorsR1andR2as the products of generators of the Coxeter–Weyl groups. The reflection generatorsR1andR2operate in the Coxeter planes where the Coxeter elementR1R2of the Coxeter–Weyl group represents the rotation of order 12. The canonical (strip, equivalently, cut-and-project technique) projections of the lattices determine the nature of the quasicrystallographic structures with 12-fold symmetry as well as the crystallographic structures with fourfold and sixfold symmetry. It is noted that the quasicrystal structures obtained from the latticesWa(F4) andWa(B6) are compatible with some experimental results.
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Li, He, Lingjie Li, Haozhang Zhong, Hanxuan Mo et Mengyuan Gu. « Hierarchical lattice : Design strategy and topology characterization ». Advances in Mechanical Engineering 15, no 6 (juin 2023) : 168781322311796. http://dx.doi.org/10.1177/16878132231179623.
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The structure-material integrated design is an art-of-state concept and be enabled by additive manufacturing. The lattice material is classified into structure as well as material because mechanical properties are determined by its topology. However, the lack of a flexible design strategy hinders the lattice achieve the structure-material integrated material candidate. This work suggests the strut-nested based strategies to effectively conduct the hierarchical lattice design. The strut in the larger-scale lattice can be replaced by the smaller-scale lattice structure through the rotation, stretching, and translation operations combining the local and global numbering, thereby complete the multi-scale lattice design. The design skills are well elucidated with custom-developed algorithm; a serious of complex lattices achieve multi-scale design. The influence of hierarchical structures in lattices on a significant parameter, strut length-to-diameter, is identified. Our work offers the alternative strategy to realize the hierarchical lattice design.
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Zhu, Lei, Xiaoyang Wang, Liao Sun, Quandong Hu et Nan Li. « Optimisation of Selective Laser Melted Ti6Al4V Functionally Graded Lattice Structures Accounting for Structural Safety ». Materials 15, no 24 (19 décembre 2022) : 9072. http://dx.doi.org/10.3390/ma15249072.
Texte intégralRésumé :
This paper presents a new framework for lightweight optimisation of functionally graded lattice structures (FGLSs) with a particular focus on enhancing and guaranteeing structural safety through three main contributions. Firstly, a design strategy of adding fillets to the joints of body-centred cubic (BCC) type lattice cells was proposed to improve the effective yield stress of the lattices. Secondly, effective properties of lattice metamaterials were experimentally characterised by conducting quasi-static uniaxial compression tests on selective laser melted specimens of both Ti6Al4V BCC and filleted BCC (BCC-F) lattices with different relative densities. Thirdly, a yield stress constraint for optimising FGLSs was developed based on surrogate models quantifying the relationships between the relative density and the effective properties of BCC and BCC-F lattices developed using experimental results assisted by numerical homogenisation. This framework was tested with two case studies. Results showed that structural safety with respect to avoiding yield failure of the optimised FGLSs can be ensured and the introduction of fillets can effectively improve the strength-to-weight ratio of the optimised FGLSs composed of BCC type lattices. The BCC-F FGLS achieved 14.5% improvement in weight reduction compared with BCC FGLS for the Messerschmitt-Bölkow-Blohm beam optimisation case study.