Search Results (44)

The defects in zinc oxide crystals are of crucial importance for their usability in many applications and are not yet fully understood. Here, we demonstrate that dioxygen species are present as defects in the grown ZnO, resulting in a bending of the atom layers that lie perpendicular to the c-axis. In the Raman spectra, these defects cause the appearance of bands different from the known bands of perfect ZnO crystals allowed by symmetry. These additional Raman bands, which have been frequently reported for ZnO in the past, can thus be fully explained by the presence of dioxygen species, and the widespread assumption of second-order modes for the assignments of these bands is not necessary. Furthermore, the Raman spectrum belonging to perfect zinc oxide in the ideal wurtzite structure is presented, obtained from small domains in ZnO(0001) crystals exposed to pressures up to 2 GPa. The dependence of the O-O stretching modes on the applied pressure proves the presence of dioxygen species in ZnO, which is also confirmed by phonon calculations of structure models with embedded dioxygen species. The surface quality of the ZnO crystals studied is also reflected in the Raman spectra and is included in the analysis. Full article

The automotive industry is a key pillar of many national economies, and automotive body manufacturing is among the most complex production processes. In the automotive body manufacturing process, quality control and safety assurance are of paramount importance, directly influencing the overall safety performance, structural reliability, and comfort of vehicles. Therefore, it is crucial to analyze the primary factors that influence quality and safety during the car body manufacturing process. The study first focuses on four key processes of car body manufacturing—stamping, welding, painting, and assembly—using the man, machine, material, method, environment (4M1E) framework to analyze the factors affecting quality and safety. Subsequently, a quality and safety early-warning indicator system is established for the automotive body manufacturing process, followed by a comprehensive analysis of the constructed system. To address the issue of subjectivity in traditional technique for order of preference by similarity to an ideal solution (TOPSIS) evaluation methods, this paper employs the coefficient of variation method for objective analysis of criterion-level indicators, the trapezoidal fuzzy number method for subjective analysis of criterion-level indicators, and establishes a model for optimizing target weight that balances subjective and objective approaches. Furthermore, a relative entropy-based method is applied to comprehensively evaluate criterion-level indicators. This approach reduces the information loss associated with separate weighting schemes and overcomes a known limitation of traditional TOPSIS—its inability to distinguish alternatives that lie equidistant from ideal solutions. Finally, an evaluation model for quality and safety influencing factors in body manufacturing is developed and validated through a case study, demonstrating its feasibility. The results show that the proposed model can effectively identify the key quality and safety influencing factors in the automobile body manufacturing process, guarantee quality control and safety assurance in the body manufacturing process, and thus ensure that the automobile production process meets the quality and safety requirements. Full article

This paper employs the similarity method to derive self-similar solutions for a model of a spherical shock wave. The discussion involves the propagation of a spherical shock wave within an ideal gas experiencing self-gravitating effects, utilizing the equation of motion and shock conditions. The expressions of infinitesimal generators within the Lie group of transformations contain arbitrary constants, leading to the identification of four potential solution cases. Among these, we focus on two cases, one following a power-law and the other an exponential law. The outcomes discussed are contingent on the variation of flow variables behind the shock, visually represented through graphical illustrations. Full article

This paper extends the notions of n-derivations and n-automorphisms from Lie algebras to nest algebras via exponential mappings. We establish necessary and sufficient conditions for triangularity, and examine the preservation of the radical, center, and ideals under these higher-order algebraic transformations. The induced group structures of n-automorphisms are explicitly characterized, including inner and non-abelian components. Several concrete examples demonstrate the applicability and depth of the theoretical findings. Full article

Let S be a 2-torsion free semiprime ring and U be a noncentral square-closed Lie ideal of $S.$ An additive mapping ℏ on S is defined as a homoderivation if $\hslash \left(ab\right)=\hslash \left(a\right)\hslash \left(b\right)+\hslash \left(a\right)b+a\hslash \left(a\right)$ for all $a,b\in S.$ In the present paper, we shall prove that ℏ is a commuting map on U if any one of the following holds: (i)$\hslash \left({\tilde{a}}_1{\tilde{a}}_2\right)+{\tilde{a}}_1{\tilde{a}}_2\in Z,$(ii)$\hslash \left({\tilde{a}}_1{\tilde{a}}_2\right)-{\tilde{a}}_1{\tilde{a}}_2\in Z,$(iii)$\hslash \left({\tilde{a}}_1\circ {\tilde{a}}_2\right)=0,$(iv)$\hslash \left({\tilde{a}}_1\circ {\tilde{a}}_2\right)=\left[{\tilde{a}}_1,{\tilde{a}}_2\right],$(v)$\hslash \left(\left[{\tilde{a}}_1,{\tilde{a}}_2\right]\right)=0,$(vi)$\hslash \left(\left[{\tilde{a}}_1,{\tilde{a}}_2\right]\right)=$ $({\tilde{a}}_1\circ {\tilde{a}}_2),$(vii)${\tilde{a}}_1\hslash \left({\tilde{a}}_2\right)\pm {\tilde{a}}_1{\tilde{a}}_2\in Z,$(viii)${\tilde{a}}_1\hslash \left({\tilde{a}}_2\right)\pm {\tilde{a}}_2{\tilde{a}}_1=0,$(ix)${\tilde{a}}_1\hslash \left({\tilde{a}}_2\right)\pm {\tilde{a}}_1\circ {\tilde{a}}_2=0,$(x)$[\hslash \left({\tilde{a}}_1\right),{\tilde{a}}_2]\pm {\tilde{a}}_1{\tilde{a}}_2=0,$(xi)$[\hslash \left({\tilde{a}}_1\right),{\tilde{a}}_2]\pm {\tilde{a}}_2{\tilde{a}}_1=0,$ for all ${\tilde{a}}_1,{\tilde{a}}_2\in U,$ where ℏ is a homoderivation on $S.$ Full article

Organic field-effect transistors (OFETs) are an ideal platform for intrinsically stretchable sensors due to their diverse mechanisms and unique electrical signal amplification characteristics. The remarkable advantages of intrinsically stretchable sensors lie in their molecular tunability, lightweight design, mechanical robustness, solution processability, and low Young’s modulus, which enable them to seamlessly conform to three-dimensional curved surfaces while maintaining electrical performance under significant deformations. Intrinsically stretchable sensors have been widely applied in smart wearables, electronic skin, biological detection, and environmental protection. In this review, we summarize the recent progress in intrinsically stretchable sensors based on OFETs, including advancements in functional layer materials, sensing mechanisms, and applications such as gas sensors, strain sensors, stress sensors, proximity sensors, and temperature sensors. The conclusions and future outlook discuss the challenges and future outlook for stretchable OFET-based sensors. Full article

For the first time, density functional theory (DFT) calculations have been employed for the measurement of the structural, mechanical, optical, and electrical properties of a bismuth-layered structure ferroelectrics (BLSFs) family member possessing an orthorhombic structure with Cmc2₁ space group. Based on the exchange–correlation approximation, our calculations show that Pb₂Bi₄Ti₅O₁₈ possesses an indirect band gap, while the materials X₂Bi₄Ti₅O₁₈ (X = Ba, Ca, and Sr) demonstrate direct band gap, where the estimated density functional fundamental band gap values lie between 1.84 to 2.33 eV, which are ideal for photovoltaic applications. The optical performance of these materials has been investigated by tuning the band gaps. The materials demonstrated outstanding optical characteristics, such as high absorption coefficients and low reflection. They exhibited impressive absorption coefficient (α = 10⁵ cm⁻¹) throughout a broad energy range, especially in the visible spectrum (10⁵ cm⁻¹ region). The findings show that the compounds demonstrate lower reflectivity in the visible and UV regions, making them suitable for single-junction photovoltaic cells and optoelectronic applications. The Voigt–Reuss–Hill averaging technique has been employed to derive elastic parameters like bulk modulus (B), Young’s modulus, shear modulus (G), the Pugh ratio (B/G) and the Frantesvich ratio (G/B) at 0.1 GPa. The mechanical stability of the compounds was analyzed using the Born stability criteria. Pugh’s ratio and Frantesvich’s ratio show that all the compounds are ductile, making them ideal for flexible optical applications. Full article

Proper documentation is fundamental to providing structural health monitoring, damage identification and failure assessment for Cultural Heritage (CH). Three-dimensional models from photogrammetric and laser scanning surveys usually provide 3D point clouds that can be converted into meshes. The point clouds usually contain noise data due to different causes: non-cooperative material or surfaces, bad lighting, complex geometry and low accuracy of the instruments utilized. Point cloud denoising has become one of the hot topics of 3D geometric data processing, removing these noise data to recover the ground-truth point cloud and adding smoothing to the ideal surface. These cleaned point clouds can be converted in volumes with different algorithms, suitable for different uses, mainly for structural analysis. This paper aimed to analyse the geometric accuracy of algorithms available for the conversion of 3D point clouds into volumetric models that can be used for structural analyses through the FEA process. The process is evaluated, highlighting problems and difficulties that lie in poor reconstruction results of volumes from denoised point clouds due to the geometric complexity of the objects. Full article

The aim of this work is to investigate the properties and classification of an interesting class of 4-dimensional 3-Hom-Lie algebras with a nilpotent twisting map $\alpha$ and eight structure constants as parameters. Derived series and central descending series are studied for all algebras in this class and are used to divide it into five non-isomorphic subclasses. The levels of solvability and nilpotency of the 3-Hom-Lie algebras in these five classes are obtained. Building upon that, all algebras of this class are classified up to Hom-algebra isomorphism. Necessary and sufficient conditions for multiplicativity of general $(n+1)$-dimensional n-Hom-Lie algebras, as well as for algebras in the considered class, are obtained in terms of the structure constants and the twisting map. Furthermore, for some algebras in this class, it is determined whether the terms of the derived and central descending series are weak subalgebras, Hom-subalgebras, weak ideals, or Hom-ideals. Full article

Solar sails are propellantless propulsion systems that extract momentum from solar radiation pressure. They consist of a large ultrathin membrane, typically aluminized, that reflects incident photons from the Sun to generate thrust for space navigation. The purpose of this study is to investigate the optimal performance of a solar sail-based spacecraft in performing two-dimensional heliocentric transfers to inertial points on the ecliptic that lie within an assigned annular region centered in the Sun. Similar to ESA’s Comet Interceptor mission, this type of transfer concept could prove useful for intercepting a potential celestial body, such as a long-period comet, that is passing close to Earth’s orbit. Specifically, it is assumed that the solar sail transfer occurs entirely in the ecliptic plane and, in analogy with recent studies, the flyby points explored are between $0.85\mathrm{au}$ and $1.35\mathrm{au}$ from the Sun. The heliocentric dynamics of the solar sail is described using the classical two-body model, assuming the spacecraft starts from Earth orbit (assumed circular), and an ideal force model to express the sail thrust vector. Finally, no constraint is imposed on the arrival velocity at flyby. Numerical simulation results show that solar sails are an attractive option to realize these specific heliocentric transfers. Full article

Let $n\ge 2$ be a fixed integer and $\mathcal{A}$ be a $C^{\ast }$-algebra. A permuting n-linear map $\mathcal{G}:{\mathcal{A}}^n\to \mathcal{A}$ is known to be symmetric generalized n-derivation if there exists a symmetric n-derivation $\mathfrak{D}:{\mathcal{A}}^n\to \mathcal{A}$ such that $\mathcal{G}\left({\varsigma }_1,{\varsigma }_2,\dots ,{\varsigma }_i{\varsigma }_i^{\prime },\dots ,{\varsigma }_n\right)=\mathcal{G}\left({\varsigma }_1,{\varsigma }_2,\dots ,{\varsigma }_i,\dots ,{\varsigma }_n\right){\varsigma }_i^{\prime }+{\varsigma }_i\mathfrak{D}({\varsigma }_1,{\varsigma }_2,\dots ,{\varsigma }_i^{\prime },\dots ,{\varsigma }_n)$ holds ∀${\varsigma }_i,{\varsigma }_i^{\prime }\in \mathcal{A}$. In this paper, we investigate the structure of $C^{\ast }$-algebras involving generalized linear n-derivations. Moreover, we describe the forms of traces of linear n-derivations satisfying certain functional identity. Full article

It is a common view that Popper’s defense of the open society has been a defense of Western, liberal democracies. This seems to imply that by fostering democratic institutions we are ipso facto fostering open societies. I criticize this view by arguing that in-built incentives in democratic mechanisms move us away from (or hamper) the open society. Democracy promotes voters’ ignorance, indulges voters’ irrationality, and allows voters to externalize costs. This is contrary to well-informed, rational decisions and personal responsibility that lie at the fundamentals of the open society. I suggest that it has been free-market capitalism, or free-market societies, which has moved us closer to the ideal of the open society and which best realizes open society’s values. Full article

In China, private-owned cooperatives are becoming increasingly involved in agricultural production. In order to find the key characteristics of smallholders’ social networks after the appearance of cooperatives and better organize different farmland operators, this study completed a field survey of 114 smallholders who adopted farmland trusteeship service of a private-owned cooperative in China and applied the social network analysis to reveal the following results. (1) Compared to the theoretical ideal value, smallholders’ social networks showed low network density, efficiency, and little relevancy. (2) In the social network of mechanical-sharing, neighbor, kinship, and labor-sharing relationships, some isolated nodes existed, but no isolated nodes are found in the synthetic network. (3) The mechanical-sharing relationship among smallholders was stronger than the other relationships. (4) Machinery owners, farmers whose plots are on the geometric center and experienced older farmers showed higher centralities in the network, but village cadres did not. (5) The centralities and QAP correlation coefficients among different networks inside the cooperative were lower than that inside a single village. As a result, this paper confirmed that the ability of cooperatives to organize farmers’ social networks is not ideal. Farmers’ trust of farmland to a cross-village cooperatives does not help them to form a larger social network than their villages. In the future, the answer to the question of “who will farm the land” will still lie with the professional farmers and highly autonomous cooperatives. Full article

In the present work, we extend to Lie modules of Banach space nest algebras a well-known characterisation of Lie ideals of (Hilbert space) nest algebras. Let $\mathcal{A}$ be a Banach space nest algebra and $\mathcal{L}$ be a weakly closed Lie $\mathcal{A}$-module. We show that there exist a weakly closed $\mathcal{A}$-bimodule $\mathcal{K}$, a weakly closed subalgebra ${\mathcal{D}}_{\mathcal{K}}$ of $\mathcal{A}$, and a largest weakly closed $\mathcal{A}$-bimodule $\mathcal{J} \mathrm{contained} \mathrm{in} \mathcal{L}$$,\mathrm{such} \mathrm{that} \mathcal{J}\subseteq \mathcal{L}\subseteq \mathcal{K}+{\mathcal{D}}_{\mathcal{K}}$, $\mathrm{with} [\mathcal{K},\mathcal{A}]\subseteq \mathcal{L}$. The first inclusion holds in general, whilst the second is shown to be valid in a class of nest algebras. Full article

Leibniz algebras are generalizations of Lie algebras. Similar to Lie algebras, inner derivations play a crucial role in characterizing complete Leibniz algebras. In this work, we demonstrate that the algebra of inner derivations of a Leibniz algebra can be decomposed into the sum of the algebra of left multiplications and a certain ideal. Furthermore, we show that the quotient of the algebra of derivations of the Leibniz algebra by this ideal yields a complete Lie algebra. Our results independently establish that any derivation of a semisimple Leibniz algebra can be expressed as a combination of three derivations. Additionally, we compare the properties of the algebra of inner derivations of Leibniz algebras with the algebra of central derivations. Full article