X-shaped Structure Research Articles

Bio-inspired anti-vibration with nonlinear inertia coupling

Abstract This paper presents a unique human body inspired passive vibration isolation system with a special coupled nonlinear inertia design. This human body inspired anti-vibration structure with nonlinear inertia consists of a compact X-shaped structure with a horizontally-installed spring system to simulate the functions of legs and muscles, and a compact rotational unit to mimic the arms swinging (or upper body movement) and/or muscle extension-flexion motion during human walking. It is particularly focused on the beneficial nonlinear effect incurred by the rotational unit, including a nonlinear equivalent mass and a very special nonlinear inertia incurred conservative force. It is shown that, the nonlinear properties (in equivalent stiffness, damping and mass simultaneously) can obviously improve the vibration isolation at low frequencies and/or in a broadband frequency range, and increase the stability of the mass center of the overall isolation system during vibration, irrespective of the loading and excitation conditions. The muscle function and swinging arms of human body are for the first time employed with an innovative and simple mechanical design for vibration control and successfully validated by experimental prototypes for their excellent beneficial nonlinear features. This paper presents a unique simple passive and adjustable anti-vibration solution of great potential in extensive engineering applications.

Synthesis of a Double-Helical Naphthotetraindole Core via an Intramolecular Dehydrogenative Homocoupling Reaction

A novel naphthotetraindole (NTI) core was synthesized in two steps via the McMurry reaction and a [Cu]/[Ag]-promoted intramolecular dehydrogenative homocoupling reaction. NTI shows a unique X-shaped double-helical structure as determined by single-crystal X-ray diffraction analysis. The hole-transport mobility of the bare NTI core was measured to be 2.3 × 10-5 cm2 V-1 s-1, which is comparable with the commonly used Spiro-OMeTAD.

Synthesis, characterization and comparative studies of nonlinear optical chromophores with rod-like, Y-shaped and X-shaped configurations

A series of highly polarizable nonlinear optical (NLO) chromophores ZJ1-4 with three different configurations, including rod-like, Y-shaped and X-shaped configurations, have been synthesized with facile routes and systematically studied. The resulted chromophores exhibited excellent thermal stabilities. The relationship between molecular configuration and NLO activity was analyzed from the theoretical calculation and experiment. The molecular dipole moment of chromophore ZJ4 was enhanced by X-shaped structure with two acceptors. Meanwhile, the tendency of forming anti-parallel interactions could be inhibited by disk-like molecular configuration with larger steric hindrance. ZJ4 exhibits the largest EO activity of 103 pm/V, and both of molecular and material NLO properties are improved for the chromophore ZJ4 with the X-shaped configuration compared with corresponding benchmark chromophore ZJ1 with rod-like molecular structure.

Development of small robot using piezoelectric benders

In this paper, a piezoelectric small robot was proposed and experimented. The piezoelectric bender of the actuator was composed of trapezoid ceramics which were attached on both surfaces of the elastic body. And an X-shaped structure was composed of four piezoelectric ceramic benders. When AC voltages which have different duty ratio were applied to the four benders, the motion of straight line according to a stick slip of the bender tips was obtained. A FEA simulation was used to analyze the motion of straight line. The output characteristics of the prototype actuator which was fabricated based on the analysis data were measured.

RETRACTED ARTICLE: IoT-based 3D convolution for video salient object detection

The video salient object detection (SOD) is the first step for the devices in the Internet of Things (IoT) to understand the environment around them. The video SOD needs the objects’ motion information in contiguous video frames as well as spatial contrast information from a single video frame. A large number of IoT devices’ computing power is not sufficient to support the existing SOD methods’ expensive computational complexity in emotion estimation, because they might have low hardware configurations (e.g., surveillance camera, and smartphone). In order to model the objects’ motion information efficiently for SOD, we propose an end-to-end video SOD algorithm with an efficient representation of the objects’ motion information. This algorithm contains two major parts: a 3D convolution-based X-shape structure that directly represents the motion information in successive video frames efficiently, and 2D densely connected convolutional neural networks (DenseNet) with pyramid structure to extract the rich spatial contrast information in a single video frame. Our method not only can maintain a small number of parameters as the 2D convolutional neural network but also represents spatiotemporal information uniformly that enables it can be trained end-to-end. We evaluate our proposed method on four benchmark datasets. The results show that our method achieves state-of-the-art performance compared with the other five methods.

LiTFSI/TBP-free hole transport materials with nonlinear π-conjugation for efficient inverted perovskite solar cells

We have synthesized two non-linear molecules with Y-shaped (XSln847) and X-shaped (XSln1453) structures via a facile synthetic route. Comparable to an X-shaped structure, the Y-shaped structural backbone of XSln847 enables a tight molecular stacking arrangement through multiple intermolecular short contacts, which affords a nest-layer in molecules. As a result, the pristine, Y-shaped XSln847 gives higher hole-mobility and more effective photoluminescence quenching than does XSln1453. Additionally, a decreased charge recombination occurs in the XSln847-fabricated inverted perovskite solar cells. As a consequence, the device based on XSln847 affords a higher power conversion efficiency of 15.02% than does that of XSln1453 (12.65%) under standard global AM 1.5 illumination. The efficiency is further improved to 17.16% when using XSln847 doping with 2, 3, 5, 6-tetrafluoro- 7, 7, 8, 8-tetracyanoquinodimethane, which is much higher than that of the widely-used PEDOT:PSS (11.95%) when measured under the same condition. These results demonstrate that the molecular engineering of hole transport materials with non-linear structure is a promising strategy for designing efficient molecules for inverted perovskite solar cells.

Three-dimensional magnetic reconnection in a collapsing coronal loop system

Context. Magnetic reconnection is believed to be the primary mechanism by which non-potential energy stored in coronal magnetic fields is rapidly released during solar eruptive events. Unfortunately, owing to the small spatial scales on which reconnection is thought to occur, it is not directly observable in the solar corona. However, larger scale processes, such as associated inflow and outflow, and signatures of accelerated particles have been put forward as evidence of reconnection. Aims. Using a combination of observations we explore the origin of a persistent Type I radio source that accompanies a coronal X-shaped structure during its passage across the disk. Of particular interest is the time range around a partial collapse of the structure that is associated with inflow, outflow, and signatures of particle acceleration. Methods. Imaging radio observations from the Nançay Radioheliograph were used to localise the radio source. Solar Dynamics Observatory (SDO) AIA extreme ultraviolet (EUV) observations from the same time period were analysed, looking for evidence of inflows and outflows. Further mpole magnetic reconstructions using SDO HMI observations allowed the magnetic connectivity associated with the radio source to be determined. Results. The Type I radio source was well aligned with a magnetic separator identified in the extrapolations. During the partial collapse, gradual (1 km s−1) and fast (5 km s−1) inflow phases and fast (30 km s−1) and rapid (80–100 km s−1) outflow phases were observed, resulting in an estimated reconnection rate of ∼0.06. The radio source brightening and dimming was found to be co-temporal with increased soft X-ray emission observed in both Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Geostationary Operational Environmental Satellite (GOES). Conclusions. We interpret the brightening and dimming of the radio emission as evidence for accelerated electrons in the reconnection region responding to a gradual fall and rapid rise in electric drift velocity, in response to the inflowing and outflowing field lines. These results present a comprehensive example of 3D null-point reconnection.

Numerical Tests Research on Mechanical Parameters of Rockmass considering Structural Plane Combination Characteristics

It is essential to determine rockmass mechanical parameters in stability assessment. The structural z is the main factor in this regard, and we know little about the relationship between mechanical parameters and multiple structure planes. In this paper, we have conducted a series of numerical tests to obtain mechanical parameters for a dam foundation in Southwest China. The biaxial numerical test was performed based on the discrete element method. This numerical test considers the spacing, types, dip angles, and size effect. We established a relationship of mechanical parameters between small size lab samples and large size field samples. We forecasted the strength parameters for a spillway slope in Southwest China. The dip angle has a significant effect on the slope strength and stability. In this case, the rockmass fracture stress-dip angle curve forms a U-shaped distribution. The X-shaped double structure plane demonstrates severe strength weakening relative to a single structure plane. As structure plane spacing reaches a certain level, its influence on rockmass strength diminishes. The elementary volume of the rockmass for dam foundation analysis is about 4 m × 4 m × 4 m.

Assembling the Milky Way Bulge from Globular Clusters: Evidence from the Double Red Clump

Abstract Two red clumps (RCs) observed in the color–magnitude diagram of the Milky Way bulge are widely accepted as evidence for an X-shaped structure that originated from the bar instability. A drastically different interpretation has been suggested, however, based on the He-enhanced multiple stellar population phenomenon as is observed in globular clusters (GCs). Because these two scenarios imply very different pictures of the formation of the bulge and elliptical galaxies, understanding the origin of the double RC is of crucial importance. Here we report our discovery that the stars in the two RCs show a significant (>5.3σ) difference in CN-band strength, in stark contrast to that expected in the X-shaped bulge scenario. The difference in CN abundance and the population ratio between the two RCs are comparable to those observed in GCs between the first- and later-generation stars. Because CN-strong stars trace a population with enhanced N, Na, and He abundances that originated in GCs, this is direct evidence that the double RC is due to the multiple population phenomenon, and that a significant population of stars in the Milky Way bulge were assembled from disrupted proto-GCs. Our result also calls for the major revision of the 3D structure of the Milky Way bulge, given that the current view is based on the previous interpretation of the double RC phenomenon.

Nonlinear stiffness and dynamical response characteristics of an asymmetric X-shaped structure

Abstract Nonlinearity is more and more shown to be very beneficial to various engineering practice, including vibration control, vibration energy harvesting and structural health monitoring, etc. An X-shaped structure has been investigated recently for its special and beneficial nonlinear stiffness and damping characteristics in passive vibration isolation and suppression. In this study, a novel n-layer vertically-asymmetric X-shaped structure is systematically studied for its generic modelling, nonlinear stiffness/damping features and dynamic response in vibration isolation. It is shown that, (a) micro-gravity environment can reduce the linear natural frequency and it can improve the vibration isolation performance in the vertical direction (good for micro-gravity environment vibration control), and an optimal assembly angle α1 and rod-length ratio s1 can be designed to achieve the minimum natural frequency when the gravity acceleration is not equal to zero for the best vibration isolation performance; (b) the asymmetric structure can produce lower natural frequency than that of symmetric counterparts (i.e. s1 = 1/s2 = 1) by properly adjusting rod-length ratio s1 (or s2), and the developed generic model can be used freely to study the structure response under different asymmetric settings; (c) the transmissibility of the asymmetric X-shaped structure can be tuned to have much lower transmissibility than that of the symmetric counterpart, which is very beneficial for vibration isolation; (d) the structure in the horizontal direction demonstrates very special dynamic response characteristics which can well explain a linear damper in the horizontal direction much better for vibration energy absorption for a much wider frequency range compared with the vertical direction. It should be noticed that instead of direct modeling of the vibration system in vertically direction, the dynamical equation is established with an intermediate variable, due to vertical asymmetry of the structure. The results provide new understanding on the X-shaped structures including its modelling, gravity effect, asymmetric ratio and nonlinear response in both vertical and horizontal directions, which can help practical applications of this class of structures.

Improving low-frequency piezoelectric energy harvesting performance with novel X-structured harvesters

Vibration energy harvesting systems via an X-structure coupled with piezoelectric patches of special arrangements are investigated in this study. Two piezoelectric harvesters are specially installed on the X-shaped structure to explore potential benefits that the X-shaped structure could provide, and each piezoelectric pad has two layers composed of a polyvinyl chloride base patch and a micro-fibre composite patch. The theoretical analysis and experiment results indicate that the energy harvesting performance of the proposed novel arrangements of the piezoelectric harvesters can be enhanced especially in low-frequency range (below 10 Hz), compared with conventional cantilevered piezoelectric harvesters. More and higher energy harvesting peaks can be created and the effective harvesting frequency band can be obviously enlarged by expanding it to low-frequency range with the proposed methods. The X-structure-based generators can enable piezoelectric materials to harvest power from low-frequency vibration sources due to its advantages in designable equivalent nonlinear stiffness, which can be easily tuned by adjusting the key structural parameters. The design and results would provide an innovative solution and insight for smart piezoelectric materials to improve the energy harvesting efficiency in the low-frequency range including small-scale ocean wave power harvesting, human motion power and animal kinetic power harvesting, etc.

Superior nonlinear passive damping characteristics of the bio-inspired limb-like or X-shaped structure

Abstract Natural biological systems can always demonstrate amazing properties or performance subject to external excitation. The nonlinear damping characteristics of a passive bio-inspired limb-like structure (LLS) or X-shaped structure is studied in this paper with theoretical modelling and experimental validation. It is revealed that, (1) the linear horizontally-placed damper and joint friction can both produce equivalent nonlinear damping in the vertical direction; (2) the equivalent damping characteristic is shown to be a nonlinear function of the vibration displacement and varies at different frequency; (3) the equivalent damping can be beneficially varying with vibration displacement and frequencies, i.e., automatically high at around resonance frequency (for large-displacement vibration) but low at other frequencies (for low-displacement vibration), showing an ideal passive and nonlinear damping property; (4) the structural rod length, asymmetric rod length ratio, layer number, and assembly angle can all affect the equivalent nonlinear damping and thus can be used to tune the damping characteristic to the ideal case conveniently in practice. The results of this study demonstrate an innovative and passive solution for designing desired nonlinear damping characteristics in various engineering practices by employing the LLS.

Design of a Conceptual Bumper Energy Absorber Coupling Pedestrian Safety and Low-Speed Impact Requirements

The car front bumper system needs to meet the requirements of both pedestrian safety and low-speed impact which are somewhat contradicting. This study aims to design a new kind of modular self-adaptive energy absorber of the front bumper system which can balance the two performances. The X-shaped energy-absorbing structure was proposed which can enhance the energy absorption capacity during impact by changing its deformation mode based on the amount of external collision energy. Then, finite element simulations with a realistic vehicle bumper system are performed to demonstrate its crashworthiness in comparison with the traditional foam energy absorber, which presents a significant improvement of the two performances. Furthermore, the structural parameters of the X-shaped energy-absorbing structure including thickness (t u), side arc radius (R), and clamping boost beam thickness (t b) are analyzed using a full factorial method, and a multiobjective optimization is implemented regarding evaluation indexes of both pedestrian safety and low-speed impact. The optimal parameters are then verified, and the feasibility of the optimal results is confirmed. In conclusion, the new X-shaped energy absorber can meet both pedestrian safety and low-speed impact requirements well by altering the main deformation modes according to different impact energy levels.

A 6-DOF passive vibration isolator based on Stewart structure with X-shaped legs

By employing the nonlinear stiffness and damping characteristics of a bio-inspired X-shaped structure (XSS) with passive springs and the Stewart platform with six degrees of freedom, a passive 6-DOF vibration isolation platform is designed and experimentally studied for its vibration isolation performance. A three-layer asymmetrical XSS is adopted as legs to construct a passive Stewart platform. Because of the specially designed XSS, the stiffness and damping properties of the system can be adjusted by changing structural parameters and thus it is designable to achieve an excellent performance including excellent stability and high-static-low-dynamic-stiffness isolation effect in all six directions with satisfactory loading capacity in the vertical direction, without any active control. Analytical and extensive experimental analysis of static stiffness and vibration response of the system revealed that (a) the aXSS Stewart platform has very beneficial high static nonlinear stiffness which can provide sufficient loading capacity; (b) the platform can achieve very low dynamic stiffness in each direction without losing loading capacity; (c) both static and dynamic stiffness is adjustable and designable with structure parameters and very easy to implement in a pure passive manner.

Measuring the X-shaped structures in edge-on galaxies

We present a detailed photometric study of a sample of 22 edge-on galaxies with clearly visible X-shaped structures. We propose a novel method to derive geometrical parameters of these features, along with the parameters of their host galaxies based on the multi-component photometric decomposition of galactic images. To include the X-shaped structure into our photometric model, we use the IMFIT package, in which we implement a new component describing the X-shaped structure. This method is applied for a sample of galaxies with available SDSS and Spitzer IRAC 3.6 $\mu$m observations. In order to explain our results, we perform realistic $N$-body simulations of a Milky Way-type galaxy and compare the observed and the model X-shaped structures. Our main conclusions are as follows: (1) galaxies with strong X-shaped structures reside in approximately the same local environments as field galaxies; (2) the characteristic size of the X-shaped structures is about 2/3 of the bar size; (3) there is a correlation between the X-shaped structure size and its observed flatness: the larger structures are more flattened; (4) our $N$-body simulations qualitatively confirm the observational results and support the bar-driven scenario for the X-shaped structure formation.

X-shaped inferior extensor retinaculum and its doubtful use in the Bröstrom-Gould procedure.

The inferior extensor retinaculum (IER) is an aponeurotic structure located in the anterior aspect of the ankle. According to the literature, it can be used to reinforce a repair of the anterior talofibular ligament in ankle instability. Despite its usual description as an Y-shaped structure, it is still unclear which part of the retinaculum is used for this purpose, or if it is instead the crural fascia that is being used. The purpose of this study is to define the anatomical characteristics of the IER to better understand its role in the Broström-Gould procedure. Twenty-one ankles were dissected. The morphology of the IER and its relationship with neighbouring structures were recorded. Seventeen (81%) of the IER in this study had an X-shaped morphology, with the presence of an additional oblique superolateral band. This band, by far the thinnest of the retinaculum, is supposed to be used to reinforce the repair of the anterior talofibular ligament. The intermediate dorsal cutaneous nerve (lateral branch of the superficial peroneal nerve) was found to cross the retinaculum in all cases. The IER is most commonly seen as an X-shaped structure, but the fact that the oblique superolateral band is a thin band of tissue probably indicates that it may not add significant strength to ankle stability. Furthermore, the close relationship of the retinaculum with the superficial peroneal nerve is another factor to consider before deciding to perform a Broström-Gould procedure. These anatomical findings advise against the use of the Gould augmentation.

On the claimed X-shaped structure in the Milky Way bulge

AbstractA number of recent studies have claimed that the double red clump observed in the Milky Way bulge is a consequence of an X-shaped structure. In particular, Ness & Lang (2016) report a direct detection of a faint X-shaped structure in the bulge from the residual map of the Wide-Field Infrared Survey Explorer (WISE) image. Here we show, however, that their result is seriously affected by a bulge model subtracted from the original image. When a boxy bulge model is subtracted, instead of a simple exponential bulge model as has been done by Ness & Lang, we find that most of the X-shaped structure in the residuals disappears. Furthermore, even if real, the stellar density in the claimed X-shaped structure is way too low to be observed as a strong double red clump (dRC) at l = 0°.

The double red clump of the Milky Way bulge has nothing to do with an X-shaped structure!

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New Insight on the Origin of the Double Red Clump in the Milky Way Bulge

Abstract The double red clump (RC) observed in the Milky Way bulge is widely interpreted as evidence for an X-shaped structure. We have recently suggested, however, an alternative interpretation based on the multiple population phenomenon, where the bright RC is from helium-enhanced second-generation stars (G2), while the faint RC is representing first-generation stars (G1) with normal helium abundance. Here, our RC models are constructed in a large parameter space to see the effects of metallicity, age, and helium abundance on the double RC feature. Our models show that the luminosity of RC stars is mainly affected by helium abundance, while the RC color is primarily affected by metallicity. The effect of age is relatively small, unless it is older than 12 Gyr or much younger than 6 Gyr. The observed double RC feature can therefore be reproduced in a relatively large parameter space, once ΔY between G2 and G1 is assumed to be greater than ∼0.10. We further show that the longitude dependence of the double RC feature at , which was pointed out by Gonzalez et al. as a potential problem of our model, is well explained in our scenario by a classical bulge embedded in a tilted bar.

Nonlinear passive damping of the X-shaped structure

Nonlinear damping can demonstrate excellent performance in vibration control. It is known that the ideal nonlinear damping could be performed as that the damping effect is as high as possible around resonance frequencies but as low as possible at other frequencies. However, how to realize such a nonlinear damping in real engineering practice with a convenient and passive manner would be an open problem in the literature. To this aim, this study investigates the nonlinear damping effect of an X-shaped structure which is inspired from biological limb skeleton systems. It is shown that, (a) the equivalent damping characteristic of the X-shaped structure is a nonlinear function of the vibration displacement and varies at different frequency; (b) the equivalent damping is adjustable with several structural parameters, and can be very high at around resonance frequencies but very low at other frequencies, showing an ideal passive and nonlinear damping property; (c) the linear horizontally-placed damper and joint friction can both produce the desired equivalent nonlinear damping in the vertical direction. The results of this study demonstrate an innovative and passive solution for designing desired nonlinear damping characteristics in various engineering practices by employing the X-shaped structure.