X-shaped Structure Research Articles

Comparison of the Chemical Compositions between the Bright and Faint Red Clumps for the Metal-poor and Metal-rich Populations in the Milky Way Bulge

We examined the double red clump (RC) observed in the Galactic bulge, interpreted as a difference in distance (“X-shaped bulge scenario”) or in chemical composition (“multiple population scenario”). To verify chemical differences between the RC groups, we performed low-resolution spectroscopy for RC and red giant branch (RGB) stars using Gemini-South/GMOS in three fields of the bulge and collected diverse data from the literature. We divided our sample stars not only into bright RC (bRC) and faint RC (fRC) groups, but also into bluer ([Fe/H] < −0.1) and redder ([Fe/H] > −0.1) groups following recent u-band photometric studies. For the metal-poor stars, no statistically significant difference in the CN index was detected between the bright and faint RC groups for all observed fields. However, we found, from crossmatching with high-resolution spectroscopic data, a sign of Na enhancement in the “metal-poor and bright” RC group compared to the “metal-poor and faint” group at (l, b) = (−1°, −8.°5). When the contributions of the RGB stars on the RC regimes are taken into account, the Na abundance difference between genuine RCs would correspond to Δ[Na/Fe] ≃ 0.23 dex, similar to a globular cluster (GC) with multiple populations. In contrast, the metal-rich stars do not show chemical differences between the bright and faint RC groups. This implies that the double RC observed in the metal-poor component of the bulge might be linked to the multiple populations originating from GC-like subsystems, whereas that of the metal-rich component would have been produced by the X-shaped structure. Our results support previous studies suggesting the composite nature of the Milky Way bulge.

Arylimidazole-terminated phenylene ethynylene molecules as organic luminescent materials

Three phenylene ethynylene derivatives substituted by arylimidazole groups (benzo[d]imidazole, phenanthro[9,10-d]imidazole and pyreno[4,5-d]imidazole) at both ends were successfully synthesized and characterized for organic electroluminescence devices. The photophysical, electrochemical, and thermal stability of the compounds were systematically investigated to reveal their structure-property relationships. All compounds presented a X-shaped structure, and exhibited excellent thermal stability and intense emission in solution and solid states. Furthermore, the solution-processed doped devices using the blend of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) with the phenylene ethynylene derivatives as emitting layers emitted deep-blue emission with maximum external quantum efficiency (EQEmax) of 0.63 % for the benzo[d]imidazole-terminated derivative and blue emission with EQEmax of 1.93 % and 1.45 % for the phenanthro[9,10-d]imidazole- and pyreno[4,5-d]imidazole-terminated derivatives, respectively, suggesting that these compounds have a great potential as the organic emitters for deep-blue and blue devices.

A concave X-shaped structure supported by variable pitch springs for low-frequency vibration isolation

Based on the known X-shaped structure, a concave X-shaped structure (CXSS) featuring custom-designed variable pitch springs (VPS) is proposed. This design aims to enhance the displacement range of the quasi-zero stiffness (QZS) system and improve its performance in isolating low-frequency vibrations. The CXSS is obtained by merging two semi-X-shaped structures. The negative stiffness property of the concave structure can be improved by utilizing the motion limitations of the mechanical structure. Of particular concern is the VPS, it can provide nonlinear restoring force and variable stiffness by self-adjusting the effective number of coils. This special spring is suitable to neutralize the negative stiffness of the concave structure, enabling a wider range of QZS properties than linear springs and magnets. The average error between the practical and theoretical restoring force of the VPS is less than 10 %. Based on a special compression coefficient, the objective-load design method (OLDM) is proposed to obtain the stiffness conditions implementing QZS properties against rated mass. The stiffness obtained by the OLDM is considerably accurate. Under this condition, the vibration transmissibility is about 0.45 at 3.5 Hz and 0.1 at 14 Hz, which is lower than that of the unmatched load and stiffness coefficients. Compared with the X-shaped structure, the proposed structure has better low-frequency vibration isolation performance with a natural frequency of about 2 Hz. The vibration transmissibility is about 0.2 at 5 Hz and is about 0.1 at 10 Hz. Pulse excitations with an amplitude of 16 g can be attenuated to about 0.51 g through the CXSS compensated by VPS. It is convenient and efficient to implement QZS properties using the VPS to compensate negative stiffness.

Design of Tri-Band Bandpass Filter Using Modified X-Shaped Structure for IoT-Based Wireless Applications

Design of Tri-Band Bandpass Filter Using Modified X-Shaped Structure for IoT-Based Wireless Applications

Modelling and simulation of a novel secretary bird-inspired vibration isolator

Abstract In this article, a novel secretary bird-inspired vibration isolator (SBIVI) is presented and investigated. The vibration isolator consists of an X-shaped stiffness adjustment mechanism and a lever arm structure that mimics the leg and wing of the secretary bird respectively. The biodynamics of the secretary bird is briefly introduced. The structure mapping from the body of the secretary bird to the scheme of the proposed SBIVI is analyzed. For the purpose of confirming the isolation performance of the SBIVI, the theoretical dynamics model is built while the virtual prototype simulation is carried out. By adjusting the values of the inertial mass and spring stiffness, the SBIVI can be easily installed with optimal operating conditions. From the simulation results, it is concluded that the vibration suppression ability of the SBIVI surpasses the traditional X-shaped structure within the interest of the frequency bandwidth.

Revolutionizing tire engineering: Finite element analysis and design of an X-shaped spoke structure for non-pneumatic military tires

In this study, we developed a non-pneumatic tire (NPT) specifically designed for military vehicles, such as the Humvee. Our aim was to enhance performance on challenging terrains crucial for mission success. We selected a novel X-shaped polygonal structure for the spoke design owing its exceptional load-carrying capacity and durability. The equivalent modulus, which is the key factor in spoke design, was analytically derived and formulated. This calculated modulus served as a benchmark for achieving the desired vertical stiffness of the NPT. We manufactured a prototype NPT and evaluated its mechanical properties by using a polyurethane (PU) spoke structure. Multiple finite element models of the novel NPT, considering different parameters such as the number of spoke sections, thickness, and modulus of elasticity, were developed while maintaining a consistent equivalent modulus value. Dynamic finite element analysis was then performed to assess the rolling performance of the NPT. We found that the maximum dynamic stress at the spoke was 2.387 MPa, which is 0.398 times the allowable yield strength of the PU spoke. This finding confirms the durability of the novel NPT under dynamic usage in military vehicles, with promising implications for overcoming challenging terrains.

Edge-enhanced minimum-margin graph attention network for short text classification

With the rapid advancement of the internet, there has been a dramatic increase in short-text data. Due to the brevity of short texts, sparse features, and limited contextual information, short-text classification has become a challenging task in natural language processing. However, current methods primarily capture semantic information from locally-sequenced words in short text, which ignores the intricate feature relationships that pervade both the intra-text and inter-text. Therefore, this paper proposes a novel Edge-Enhanced Minimum-Margin Graph Attention Network (EMGAN) for short text classification to address this issue. Specifically, we construct a Heterogeneous Information Graph (HIG) to represent complex relationships among short text features. HIG mainly considers the relationship between document features and three attribute features, such as entities, topics, and keywords, and can represent short text features from multiple dimensions and levels. Then, to enhance the connectivity and expressiveness of the HIG for more effective propagation of feature information within it, we present a novel X-shaped structure edge-enhancement method. It enriches their relationships by reconstructing the edge structures. Furthermore, we design a Minimum Margin Graph Attention Network (MMGAN) for short text classification. Specifically, this method aims to explore the minimum margin between high-order neighbors and central nodes at the minimum cost, efficiently extracting and aggregating feature information. Extensive experimental results demonstrate that our proposed EMGAN model outperforms existing methods on five datasets, validating its effectiveness in short-text classification. Our code is submitted at https://github.com/w123yy/EMGAN.

Enhanced circular dichroism of an X-shaped nanostructure by asymmetric surface plasmon interference

A plasmonic chiral structure, which is a nanostructure composed of noble metals that lacks planar symmetry, demonstrates significant potential for various applications in bio-sensing, optical forces, switching and controlling the photoluminescence, and detecting chiral light. Understanding its fundamental property of circular dichroism (CD) is critical for these applications. Although the surface plasmon resonance (SPR) mode at a specific moment can explain the CD properties of chiral structures, to gain a better understanding of chirality, the mode shape of the SPR on a nanostructure must be analyzed throughout an entire period. Our study proposes an X-shaped nanostructure to investigate the temporal evolution of plasmon resonance in chiral structures. The simulation results demonstrated that our structure exhibited a significant temporal evolution in plasmonic oscillations, providing new insights into the nature of chirality. In addition, we provided a comprehensive theoretical explanation of CD using the Born–Kuhn model. Furthermore, we discovered that the CD in the X-shaped structure was intensified by the asymmetric interference between the structure and underlying gold film substrate.

The vibration isolation proprieties of an X-shaped structure with enhanced high-static and low-dynamic stiffness via torsional magnetic negative stiffness mechanism

The vibration isolation proprieties of an X-shaped structure with enhanced high-static and low-dynamic stiffness via torsional magnetic negative stiffness mechanism

Chiastic thinking: A cognitive process closely related to Janusian thinking

This article aims to explore a way of thinking based on chiastic structure (X-shaped structure), chiastic thinking. Characterized by its juxtaposition of opposite structure, chiastic thinking has an intriguing connection to Janusian thinking. This is because Janusian thinking is deemed a creative process wherein two opposite concepts or images are conceived simultaneously. At the beginning of the article, conceptual combination and Janusian thinking are presented, along with empirical research data to support the effectiveness of Janusian thinking. The paper then shifts to a discussion of chiastic thinking, which occupies a unique place in human culture and civilization but does not receive due attention. In the last part of this article, the examples of chiastic thinking in literature, science, and art are provided. Across diverse disciplines, the combination of opposites manifests in various ways, often adopting different technical terms that give rise to different theories. These terms and theories may share fundamental commonalities but differ in certain aspects. The main purpose of this review article is to examine the close relation between Chiastic and Janusian thinking. Hopefully, this review article can rekindle the academic interest in these two thinking processes and give them new meaning.

Bifurcation and dynamic analysis of quasi-zero stiffness isolator with asymmetric stiffness and mismatched load based on X-shaped negative stiffness structure

Bifurcation and dynamic analysis of quasi-zero stiffness isolator with asymmetric stiffness and mismatched load based on X-shaped negative stiffness structure

Flexible thermoelectrics in crossed graphene/hBN composites

Nanostructures exhibit unusual properties due to the dominance of quantum mechanical effects. In addition, the geometry of a nanostructure can have a strong influence on its physical properties. Using the tight-binding and force-constant approaches with the help of the non-equilibrium Green’s function method, the transport and thermoelectric properties of cross-shaped (X-shaped) composite heterostructures are studied in two cases: Mixed graphene and h-BN (HETX-CBN) and all graphene (HETX-C) cross-shaped structures. Our numerical results show that an X-shaped structure helps to manipulate its electronic and phononic properties. The transport energy gap can be tuned in the range of ~ 0.8 eV by changing one arm width. Due to the drastic decrease in the electronic conductance of HETX-CBN and the dominance of the phononic thermal conductance, the ZT performance is degraded despite the high Seebeck coefficient value (in the order of meV). However, HETX-C has better ZT performance due to better electronic conductance and lower phononic/electronic thermal ratio, it can enhance the ZT ~ 2.5 times compared to that of zigzag graphene nanoribbon. The thermoelectric properties of the system can be tuned by controlling the size of the arms of the device and the type of its atoms.

The X-shaped structure with nonlinear positive stiffness compensation for low-frequency vibration isolation

X-shaped structure with quasi-zero stiffness (QZS) properties are suitable for low-frequency vibration isolation because of its simple structure. The effective working range of classic X-shaped structure (CXS) is narrow for the existence of negative stiffness region, and using positive stiffness compensation to overcome this deficiency is a common way. This paper proposes a novel nonlinear positive stiffness compensation method (NPSC) to improve the load capacity and QZS range of CXS. Different from the previous studies that utilize linear or hardening stiffness compensation, the NPSC exhibits the characteristics of softening stiffness first and then hardening stiffness and is provided by torsion springs simply. The static properties of X-shaped structure with NPSC are investigated. The result indicates the NPSC possesses dual significant advantages. Firstly, the X-shaped structure with NPSC can achieve larger load capacity and wider QZS range than that with linear or hardening stiffness compensation in optimal parameter region. Secondly, the X-shaped structure with NPSC can conveniently overlap the equilibrium position with QZS point to obtain ultra-low frequency vibration isolation effect compared to that with linear stiffness compensation. The motion equation of the proposed system is derived, and the dynamic response is solved through harmonic balance method (HBM). The influence of different parameters on displacement transmissibility is investigated and the result is verified by numerical simulation. The transmissibility comparison between the proposed model and the CXS with linear compensation shows that the proposed model possesses better vibration isolation performance. Besides, the static compression test and dynamic sweep frequency experiment are implemented, and the experiment results verify the validity of proposed model. The proposed NPSC is an important inspiration for the stiffness compensation research of X-shaped structures.

Negative biaxial retarder made from reactive molecules with X-shaped core structure

Although biaxial retarder films have merits of optical applications, limited numbers of the biaxial retarder have been developed using reactive mesogen (RM) materials. New X-shaped RM (XRM) molecules were synthesized and optical retarder films were fabricated using mixtures of a rodlike RM and the XRM. The in-plane retardation, the out-of-plane retardation and the NZ coefficient of the retarder films were investigated. The retarder films represented negative biaxial property or z-plate property depending on the chemical structure and the concentration of XRM.

Mechanism of tRNA recognition by heterotetrameric glycyl-tRNA synthetase from lactic acid bacteria.

Glycyl-tRNA synthetases (GlyRSs) have different oligomeric structures depending on the organisms. While a dimeric α2 GlyRS species is present in archaea, eukaryotes and some eubacteria, a heterotetrameric α2β2 GlyRS species is found in most eubacteria. Here, we present the crystal structure of heterotetrameric α2β2 GlyRS, consisting of the full-length α and β subunits, from Lactobacillus plantarum (LpGlyRS), gram-positive lactic bacteria. The α2β2LpGlyRS adopts the same X-shaped structure as the recently reported Escherichia coli α2β2 GlyRS. A tRNA docking model onto LpGlyRS suggests that the α and β subunits of LpGlyRS together recognize the L-shaped tRNA structure. The α and β subunits of LpGlyRS together interact with the 3'-end and the acceptor region of tRNAGly, and the C-terminal domain of the β subunit interacts with the anticodon region of tRNAGly. The biochemical analysis using tRNA variants showed that in addition to the previously defined determinants G1C72 and C2G71 base pairs, C35, C36 and U73 in eubacterial tRNAGly, the identification of bases at positions 4 and 69 in tRNAGly is required for efficient glycylation by LpGlyRS. In this case, the combination of a purine base at Position 4 and a pyrimidine base at Position 69 in tRNAGly is preferred.

Dynamic characteristics analysis of bilayer bio-inspired X-shaped vibration isolation structure

Based on the vibration isolation properties of the coupled toe-leg structure of the biped bird, a bilayer bio-inspired X-shaped vibration isolation structure (BBXVI) considering the coordination function between skeleton type and muscle/tendon is proposed in this research. The mapping relationships of equivalent restoring force–displacement and equivalent stiffness–displacement with various parameters are analyzed by statics, the parameter condition and the modulation of nonlinear behavior of the BBXVI to achieve quasi-zero stiffness (QZS) are investigated. Based on establishing dynamic model of the bilayer X-shaped structure, the effects of initial angle, rod-length ratio and rod length on dynamic characteristics and vibration transmissibility of the BBXVI subjected to displacement excitation are studied by incremental harmonic balance method (IHBM). The study found that the BBXVI presents excellent low frequency vibration isolation performance. With increasing α1, the QZS characteristic, vibration isolation bandwidth and response amplitude of the BBXVI increase first and then decrease. The larger rod-length ratio and longer rod length can increase the vibration isolation bandwidth and improve the vibration isolation performance. In addition, longer rod length could make the equivalent stiffness of the BBXVI gradually evolve from hardening spring to softening spring properties, and the vibration transmission property of the vibration isolation system is changed.

Vibration isolation performance analysis of a bilateral supported bio-inspired anti-vibration control system

To achieve better anti-vibration performance in a low frequency region and expand the range of vibration isolation, a bilateral supported bio-inspired anti-vibration (BBAV) structure composed of purely linear elements is proposed, inspired by the motion form of bird legs and the nonlinear extension and compression of muscles and tendons. The kinematic relations and nonlinear dynamic model considering vertical and rotational vibrations are established. The loading capacity and equivalent stiffness are investigated with key parameters. The amplitude-frequency characteristics and force transmissibility are used to evaluate the stability and anti-vibration performance with the effects of the excitation amplitude, rod length, installation angle, and spring stiffness. The results show that the loading requirements and resonant characteristics of the BBAV structure are adjustable, and superior vibration isolation performance can be achieved readily by tuning the parameters. The X-shaped vibration structure is sensitive to the spring stiffness, which exhibits a wider vibration isolation bandwidth with smaller spring stiffness. Besides, depending on the parameters, the nonlinear behavior of the BBAV system can be interconverted between the softening type and the hardening type. The theoretical analysis in this study demonstrates the advantages and effectiveness of the vibration isolation structure.

Fabrication of an X-shaped micro-copper structure containing a merging joint based on localized electrochemical deposition

Local electrochemical deposition (LECD) has proved to be an efficient and economical method for fabricating three-dimensional micron structures. Realizing complex structures that join up when deposited using LECD has been complex; therefore, the fabrication of an X-shaped joining structure was investigated in this study. A horizontal trace model was proposed, and the effects of the number of deposition layers and the horizontal sweep width on the merging joint were studied. The horizontal trace model could complete the merging joint. Multiple deposition layers and a large horizontal sweep width could stabilize and better connect the X-shaped structure containing merging joints. The merging mechanism of the X-shaped structure was also investigated using COMSOL. The stable deposition of the joining structure enables the LECD method to have a broader range of applications in micro-nano manufacturing.

The binding mode of orphan glycyl-tRNA synthetase with tRNA supports the synthetase classification and reveals large domain movements.

As a class of essential enzymes in protein translation, aminoacyl-transfer RNA (tRNA) synthetases (aaRSs) are organized into two classes of 10 enzymes each, based on two conserved active site architectures. The (αβ)2 glycyl-tRNA synthetase (GlyRS) in many bacteria is an orphan aaRS whose sequence and unprecedented X-shaped structure are distinct from those of all other aaRSs, including many other bacterial and all eukaryotic GlyRSs. Here, we report a cocrystal structure to elucidate how the orphan GlyRS kingdom specifically recognizes its substrate tRNA. This structure is sharply different from those of other aaRS-tRNA complexes but conforms to the clash-free, cross-class aaRS-tRNA docking found with conventional structures and reinforces the class-reconstruction paradigm. In addition, noteworthy, the X shape of orphan GlyRS is condensed with the largest known spatial rearrangement needed by aaRSs to capture tRNAs, which suggests potential nonactive site targets for aaRS-directed antibiotics, instead of less differentiated hard-to-drug active site locations.

High-Gain Circularly Polarized Antenna Array for Full Incident Angle Coverage in RF Energy Harvesting

In this paper, a high-gain circularly polarized (CP) hexagonal antenna array is proposed for RF energy-harvesting applications. The hexagonal antenna array is intended to operate at the frequency of 5.8 GHz. It is composed of 6 multilayer substrate CP antennas excited by an X-shaped aperture-coupling feed structure. A frequency selective surface (FSS) was added to further improve the gain, resulting in a maximum gain of 12.7 dBi per element. The main advantage of the proposed hexagonal antenna array is the ability to cover 360 degrees in the azimuth plane with a high gain in all directions without the use of any additional circuitry, allowing the effective absorption of ambient RF energy. A prototype was fabricated and measured, and a good agreement with the simulation results is achieved. In addition, a rectifier is used to convert RF energy absorbed by the antenna into DC energy at the frequency of 5.8 GHz. The measured RF-to-DC conversion efficiency of 44.5% and a DC output voltage of 423 mV at -10 dBm are observed. The performance of the rectenna array with one and six rectifiers has been demonstrated. With the use of a DC combiner, the total RF to DC efficiency of the array is 67.75%, with a DC output voltage of 1.115 V from -10 dBm has been recorded. Due to the immunity to misalignment of the CP antenna, the proposed rectenna array is very suitable for wireless power transfer (WPT).