X-shaped Structure Research Articles

In-situ adjustable nonlinear passive stiffness using X-shaped mechanisms

A desired structural or material stiffness is critical in many engineering systems for structural stability, vibration control, energy saving and manipulation efficiency. However, passive low-cost high-efficiency in-situ adjustable stiffness systems have not yet been well explored, due to uncertain and unexpected nonlinear behavior within materials and structures, difficulty or limitations in manufacturing or implementation, and various demanding requirements. To address these challenges, we present an efficient stiffness-manipulation method using a flexible and compact X-shaped structure (or mechanism). The resulting nonlinear stiffness systems can be conveniently realized and are capable for achieving various desired stiffness (positive, negative, zero or quasi-zero, multi-stable-equilibria). The inherent nonlinearity of such nonlinear stiffness systems is completely controllable and predictable with simple and reliable mathematical modelling, compared to many other metal materials or foldable mechanisms/structures. Due to the advantages of linkage mechanisms, the X-shaped structure (or mechanism) approach offers superior in-situ adjustability which can be easily achieved via various and simple pre-extension/distance/length/height adjustable mechanisms in practical mechanical designs. The stiffness-manipulation methods demonstrated in this study have also advantages including simplicity and efficiency in manufacturing and assembly, high-quality nonlinearity control and in-situ adjustability, and low-cost part production, without stability issues, manufacturing difficulty and strict material restriction, leading to revolutionary or upgrading technologies to existing engineering systems. Theoretical analysis and experimental validation (or case studies) demonstrate the advantages, effectiveness, and great potential of this new approach for exploiting nonlinearities in various engineering applications.

The structure of the Milky Way based on unWISE 3.4 μm integrated photometry

ABSTRACT We present a detailed analysis of the Galaxy structure using an unWISE wide-field image at $3.4\,\mu$m. We perform a 3D photometric decomposition of the Milky Way taking into account (i) the projection of the Galaxy on the celestial sphere and (ii) that the observer is located within the Galaxy at the solar radius. We consider a large set of photometric models starting with a pure disc model and ending with a complex model that consists of thin and thick discs plus a boxy-peanut-shaped bulge. In our final model, we incorporate many observed features of the Milky Way, such as the disc flaring and warping, several overdensities in the plane, and the dust extinction. The model of the bulge with the corresponding X-shape structure is obtained from N-body simulations of a Milky Way-like galaxy. This allows us to retrieve the parameters of the aforementioned stellar components, estimate their contribution to the total Galaxy luminosity, and constrain the position angle of the bar. The mass of the thick disc in our models is estimated to be 0.4–1.3 of that for the thin disc. The results of our decomposition can be directly compared to those obtained for external galaxies via multicomponent photometric decomposition.

X-shaped structure of bacterial heterotetrameric tRNA synthetase suggests cryptic prokaryote functions and a rationale for synthetase classifications.

AaRSs (aminoacyl-tRNA synthetases) group into two ten-member classes throughout evolution, with unique active site architectures defining each class. Most are monomers or homodimers but, for no apparent reason, many bacterial GlyRSs are heterotetramers consisting of two catalytic α-subunits and two tRNA-binding β-subunits. The heterotetrameric GlyRS from Escherichia coli (EcGlyRS) was historically tested whether its α- and β-polypeptides, which are encoded by a single mRNA with a gap of three in-frame codons, are replaceable by a single chain. Here, an unprecedented X-shaped structure of EcGlyRS shows wide separation of the abutting chain termini seen in the coding sequences, suggesting strong pressure to avoid a single polypeptide format. The structure of the five-domain β-subunit is unique across all aaRSs in current databases, and structural analyses suggest these domains play different functions on α-subunit binding, ATP coordination and tRNA recognition. Moreover, the X-shaped architecture of EcGlyRS largely fits with a model for how two classes of tRNA synthetases arose, according to whether enzymes from opposite classes can simultaneously co-dock onto separate faces of the same tRNA acceptor stem. While heterotetrameric GlyRS remains the last structurally uncharacterized member of aaRSs, our study contributes to a better understanding of this ancient and essential enzyme family.

An innovative X-shaped vibration isolation mount with tunable quasi-zero-stiffness property

Passive vibration isolation is always preferable in many engineering practices. To this aim, an innovative, compact, and passive vibration isolation mount is studied in this paper. The novel mount is adjustable to different payloads due to a special oblique and tunable stiffness mechanism, and of high vibration isolation performance with a wider quasi-zero-stiffness range due to the deliberate employment of negative stiffness of the X-shaped structure. The X-shaped structure has been well studied recently due to its excellent nonlinear stiffness and damping properties. In this study, by using of the negative stiffness property within the X-shaped structure, the X-shaped mount (X-mount) can have an obviously larger vibration displacement range which maintains the quasi-zero-stiffness property. A special oblique spring is thus introduced such that the overall equivalent stiffness can be much easily adjusted. Systematic parametric study is conducted to reveal the critical design parameters and their relationship with vibration isolation performance. A prototype and experimental validations are implemented to validate the theoretical results. It is believed that the X-mount would provide an innovative technical upgrade to many existing vibration isolation mounts in various engineering practices and it could also be the first prototyped mount which can offer adjustable quasi-zero stiffness conveniently.

Parsec-scale properties of eight Fanaroff–Riley type 0 radio galaxies

ABSTRACT We report the high-resolution radio observations of eight Fanaroff–Riley type 0 radio galaxies (FR 0s), selected from the published FR 0 sample. These observations were carried out with the Very Long Baseline Array (VLBA) and European VLBI Network (EVN) at frequencies of 5 and 8 GHz with a highest resolution of ∼0.6 milliarcsec. All eight sources show compact structures on projected physical sizes of 0.3–10 parsec. Six sources show a two-sided structure and two sources show a one-sided jet structure. J1025+1022 shows an X-shaped jet structure, which could result from a reorientation of the jet axis due to a restart of the central engine or a projection of a highly curved inner jet. However, more studies are needed to examine these scenarios. Proper motions for 22 jet components of the eight sources are determined to be between $-0.08\, c$ and $0.51\, c$. Although most of the sources exhibit flat spectra, other observed characteristics, such as low-amplitude flux density variations, low jet proper motion speeds and symmetric two-sided jet structures, tend to support the fact that the parsec-scale FR 0 jets are mildly relativistic with lower bulk Lorentz factors and larger viewing angles.

Study on dynamic characteristics of bio-inspired vibration isolation platform

Inspired by the body movement of the kangaroo, a multi-degree-of-freedom vibration isolation platform containing three units, that is, a protected object, a nonlinear energy sink, and an X-shaped structure, has been modeled, and the differential equations of the system have been given in the form of uniform relative coordinates. Furthermore, the displacement transmissibility analysis and numerical calculation are supported by the method of harmonic balance and Runge–Kutta algorithm, which shows that (a) there are nonlinear behaviors and resonant phenomenon in the time–frequency response and (b) quasi-periodic motion may be a predictor of periodic steady-state response or strong resonance, and the displacement evolution before quasi-periodic motion may be used to distinguish the two phenomena. In addition, based on the numerical method, the system energy changes in a selected frequency are discussed. Finally, the correctness of the theoretical analysis is verified by simulation data in Adams. Taken together, these results demonstrate that the dynamic characteristics are adjustable and designable of structural parameters in a specific frequency band and can provide a useful way to reduce the amplitude of resonant peaks and improve the vibration isolation performance for practical engineering applications.

A nonlinear X-shaped structure based tuned mass damper with multi-variable optimization (X-absorber)

Installing a tuned mass damper (TMD) is a promising vibration control method in many engineering applications which can suppress excessive vibration of a primary structure by transferring and dissipating vibration energy from the primary structure to the TMD. To overcome some limitations and drawbacks of traditional tuned mass dampers in practice, a bio-inspired X-shaped structure/mechanism is utilized to design a novel tunable and nonlinear TMD (X-absorber) in this study. To this aim, multi-variable optimization analysis, tunable stiffness and damping properties, nonlinear influence and vibration suppression performance of the new X-absorber are systematically investigated. The X-absorber can provide beneficial nonlinear damping and tunable quasi-zero stiffness which can significantly improve system parametric robustness, widen vibration suppression bandwidth with a widened anti-resonance, effectively suppress resonant peaks of very low frequencies, and eliminate potential instabilities (e.g., bifurcation, jump) inherently existing in Duffing systems, compared with traditional absorbers. The effectiveness and robustness of the X-absorber with different excitations compared with a traditional spring-mass absorber are verified in experiments. The X-absorber presents a new insight into the design of nonlinear passive absorbers of high performance, and a more flexible and reliable solution to many engineering problems.

A novel three-TMH Na+/H+ antiporter and the functional role of its oligomerization

Na+/H+antiportersare a category of ubiquitous transmembrane proteins with various important physiological roles in almost all living organisms ranging from bacteria to humans. However, the knowledge of novel Na+/H+antiporters remains to be broadened, and the functional roles ofoligomerization in theseantiportershave not yet been thoroughly understood. Here, we reported functional analysis of an unknown transmembrane protein composed of 103 amino acid residues. This protein was found to function as a Na+(Li+, K+)/H+ antiporter. To the best of our knowledge, this antiporter is the minimal one of known Na+/H+antiporters and thus designated as NhaM to represent the minimal Na+/H+antiporter. NhaM and its homologs have not yet been classified into any protein family. Based on phylogenetic analysis and protein alignment, we propose NhaM and its homologs to constitute a novel transporter family designated as NhaM family. More importantly, we found that NhaM is assembled with parallel protomers into a homo-oligomer and oligomerization is vital for the function of this antiporter. This implies that NhaM may adopt and require an oligomer structure for its normal function to create a similar X-shaped structure to that of the NhaA fold. Taken together, current findings not only present the proposal of a novel transporter family but also positively contribute to the functional roles of oligomerization in Na+/H+antiporters.

Analysis and design of a novel and compact X-structured vibration isolation mount (X-Mount) with wider quasi-zero-stiffness range

Passive vibration isolation is always preferable in most engineering practices. To this aim, a novel, compact and passive vibration isolation mount is studied in this paper, which is designed by using the X-shaped structure with a much smaller size. The novel mount is adjustable to different payloads due to a special oblique and tunable spring mechanism, and of high vibration isolation performance with a wider quasi-zero-stiffness range due to the deliberate employment of negative stiffness of the X-shaped structure. The X-shaped structure has been well studied recently due to its excellent nonlinear stiffness and damping properties. In this study, it is for the first time to explore the utilization of the negative stiffness property within the X-shaped structure such that the resulting design, the X-structured mount (X-mount), can have an obviously larger vibration displacement range which maintains the quasi-zero-stiffness property. A special oblique spring is thus introduced such that the overall equivalent stiffness of the X-mount can be much easily adjusted according to different payloads. Systematic parametric study is conducted to reveal the critical design parameters and their relationship with vibration isolation performance. A prototype and experimental validations are implemented to validate the theoretical results. It is believed that the X-mount would provide an innovative technical upgrade to many existing vibration isolation mounts in various engineering practices and it could also be the first prototyped mount which can offer adjustable quasi-zero stiffness and adjustable loading capacity conveniently.

CHANG-ES

Context.Radio continuum observations of edge-on spiral galaxies reveal the appearance of radio halos as well as the large-scale structure of their magnetic fields. Furthermore, with multiple frequency observations, it is possible to deduce the transport mechanisms of the cosmic ray electrons (CREs).Aims.In order to gain a better understanding of the influence of cosmic rays (CRs) and magnetic fields in the disk-halo interface of edge-on spiral galaxies, we investigate the radio continuum halo, the magnetic field, and the transport processes of the CRs of the edge-on spiral galaxy NGC 4217 using CHANG-ES radio data at two frequencies, 6 GHz (C-band) and 1.5 GHz (L-band), and supplemental LOFAR data of this galaxy at 150 MHz. With additional X-rayChandradata, we study the connection of radio features to the diffuse hot gas around NGC 4217.Methods.We investigate the total intensity (StokesI) data in detail and determine the integrated spectral behavior. The radio scale heights of all three radio frequencies for NGC 4217 were extracted via exponential fits to the intensity profiles. From these, individual absolute flux densities of the disk and the halo were also calculated. Furthermore, we present magnetic field orientations from the polarization data using rotation measure synthesis (RM-synthesis), showing the large-scale ordered magnetic field of NGC 4217. After a separation of thermal and nonthermal emission, we calculated the resolved magnetic field strength via the revised equipartition formula. Additionally, we modeled the transport processes of CREs into the halo with the 1D modelSPINNAKER.Results.NGC 4217 shows a large-scale X-shaped magnetic field structure, covering a major part of the galaxy with a mean total magnetic field strength in the disk of 9μG. From the analysis of the rotation measure map atC-band, we found that the direction of the disk magnetic field is pointing inward. A helical outflow structure is furthermore present in the northwestern part of the galaxy, which is extended nearly 7 kpc into the halo. More polarized emission is observed on the approaching side of the galaxy, indicating that Faraday depolarization has to be considered atC-band. With a simplified galaxy disk model, we are able to explain the finding of higher polarized intensity on the approaching side. We generalize the model to predict that roughly 75% of edge-on spiral galaxies will show higher polarized intensity on the approaching side. Many loop and shell structures are found throughout the galaxy in total intensity atC-band. One structure, a symmetric off-center (to southwest of the disk) superbubble-like structure is prominent in total and polarized intensity, as well as in Hαand optical dust filaments. This is at a location where a second peak of total intensity (to the southwest of the disk) is observed, making this superbubble-like structure a possible result of a concentrated star formation region in the disk. The X-ray diffuse emission shows similarities to the polarized diffuse emission of NGC 4217. The flux density extension of the radio continuum halo increases toward lower frequencies. While the total flux density of the disk and halo are comparable atC-band, the contribution of the disk flux density decreases toward LOFAR to 18% of the total flux density. Dumbbell-shaped structures are present atC-band and at the LOFAR frequency. Total intensity profiles at the two CHANG-ES bands and the LOFAR frequency show a clear two-component behavior and were fit best with a two-component exponential fit. The halo scale heights are 1.10 ± 0.04 kpc, 1.43 ± 0.09 kpc, and 1.55 ± 0.04 kpc inC-band,L-band, and 150 MHz, respectively. The frequency dependence of these scale heights betweenC-band andL-band suggests advection to be the main transport process. The 1D CRE transport modeling shows that advection appears to be more important than diffusion.

CHANG-ES

Context. The magnetic field in spiral galaxies is known to have a large-scale spiral structure along the galactic disk and is observed as X-shaped in the halo of some galaxies. While the disk field can be well explained by dynamo action, the three-dimensional structure of the halo field and its physical nature are still unclear. Aims. As first steps towards understanding the halo fields, we want to clarify whether or not the observed X-shaped field is a wide-spread pattern in the halos of spiral galaxies. We also aim to investigate whether these halo fields are simply turbulent fields ordered by compression or shear (anisotropic turbulent fields), or have a large-scale regular structure. Methods. Analysis of the Faraday rotation in the halo is used as a tool to distinguish anisotropic turbulent fields from large-scale magnetic fields. However, this has been challenging until recently because of the faint halo emission in linear polarization. Our sensitive VLA broadband observations in C-band and L-band of 35 spiral galaxies seen edge-on (called CHANG-ES) allowed us to perform rotation measure synthesis (RM synthesis) in their halos and to analyze the results. We further accomplished a stacking of the observed polarization maps of 28 CHANG-ES galaxies in C-band. Results. Though the stacked edge-on galaxies were of different Hubble type, and had differing star formation activity and interaction activity, the stacked image clearly reveals an X-shaped structure of the apparent magnetic field. We detected a large-scale (coherent) halo field in all 16 galaxies that have extended polarized emission in their halos. We detected large-scale field reversals in all of their halos. In six galaxies, these are along lines that are approximately perpendicular to the galactic midplane (vertical RMTL) with about 2 kpc separation. Only in NGC 3044 and possibly in NGC 3448 did we observe vertical giant magnetic ropes (GMR) similar to those detected recently in NGC 4631. Conclusions. The observed X-shaped structure of the halo field seems to be an underlying feature of spiral galaxies. It can be regarded as the two-dimensional projection of the regular magnetic field which we found to have scales of typically 1 kpc or larger observed over several kiloparsecs. The ordered magnetic field extends far out in the halo and beyond. We detected large-scale magnetic field reversals in the halo that may indicate that GMR are more or less tightly wound. With these discoveries, we hope to stimulate model simulations for the halo magnetic field that should also explain the determined asymmetry of the polarized intensity (PI).

Simulating the Fermi Bubbles as Forward Shocks Driven by AGN Jets

Abstract The Fermi bubbles are two giant bubbles in gamma-rays lying above and below the Galactic Center (GC). Despite numerous studies on the bubbles, their origin and emission mechanism remain elusive. Here we use a suite of hydrodynamic simulations to study the scenario where the cosmic rays (CRs) in the bubbles are mainly accelerated at the forward shocks driven by a pair of opposing jets from Sgr A*. We find that an active galactic nucleus (AGN) jet event that happened 5–6 Myr ago can naturally reproduce the bilobular morphology of the bubbles, and the postshock gas temperature in the bubbles is heated to ∼0.4 keV, consistent with recent X-ray observations. The forward shocks compress the hot halo gas, and at low latitudes, the compressed gas shows an X-shaped structure, naturally explaining the biconical X-ray structure in the ROSAT 1.5 keV map in both morphology and X-ray surface brightness. CR acceleration is most efficient in the head regions of the bubbles during the first 2 Myr. The opposing jets release a total energy of ∼1055 erg with an Eddington ratio of ∼10−3, which falls well in the range of the hot accretion flow mode for black holes. Our simulations further show that the forward shocks driven by spherical winds at the GC typically produce bubbles with much wider bases than observed and could not reproduce the biconical X-ray structure at low latitudes. This suggests that starburst or AGN winds are unlikely the origin of the bubbles in the shock scenario.

Formation of Two Homologous Transequatorial Loops

The formation mechanism of two homologous transequatorial loops (TLs) of July 7–8, 1999 (SOL1999-07-07) is studied. The TLs connected active region AR 8614 from the northern hemisphere to AR 8626 in the southern hemisphere. The first TL appeared as a distinct structure at 12:49 UT on July 7, the second TL appeared at 06:21 UT, on July 8. Important results are obtained in this analysis: (i) The configuration of the two TLs is similar in X-rays. (ii) The sizes of the two active regions related to the TLs increased before and during the formation of the two TLs, this induced the expansion of their coronal loops. (iii) Both TLs formed globally on a time scale shorter than 110 min (time resolution of observations). (iv) An X-shaped coronal structure was observed. This observational evidence suggests that the two TLs formed by the same physical mechanism, magnetic reconnection, between the two expanding magnetic configurations of the two ARs.

Hybrid Passive/Active Vibration Control of a Loosely Connected Spacecraft System

In this paper, a hybrid passive/active vibration (HPAV) controller of a loosely connected spacecraft consisting of a servicing satellite, a target and an X-shape structure isolator is first proposed to suppress vibrations of the system when subjected to the impulsive external excitations during the on-orbit missions. The passive dynamic response of the combined system can be adjusted appropriately to achieve the desired vibration isolation performance by tuning the structural parameters of the bio-inspired X-shape structure. Moreover, the adaptive control design through dynamic scaling technique is selected as the active component to maintain high vibration isolation performance in the presence of parameter uncertainties such as mass of the satellite platform, the damping and rotation friction coefficients of the X-shape structure. Compared with the pure passive system and the traditional spring-mass-damper (SMD) isolator, the HPAV strategy witnesses lower transmissibility, smaller vibration amplitude and higher convergence rate when subjected to the post-capture impact. Numerical simulations demonstrate the feasibility and validity of the proposed hybrid control scheme in suppressing vibrations of the free-floating spacecraft.

Vibration suppression for post-capture spacecraft via a novel bio-inspired Stewart isolation system

In the process of on-orbit capture mission, some undesirable vibrations arising from the relative motions between the servicing spacecraft and the target are inevitable, which can make the post-capture combined spacecraft unstable or even tumbling. Therefore, suppressing post-capture vibrations is critical to mission success. In this work, a novel bio-inspired X-shape structure-based Stewart isolation platform (XSSIP) system is first proposed to install between the satellite platform and the capture mechanism. It can suppress the post-capture vibrations of a free-floating spacecraft subjected to the impulsive or periodic external forces. Beneficial nonlinear stiffness and nonlinear damping characteristics with the existence of X-shape structure can be acquired, which is helpful to achieve much better vibration isolation performance in multiple directions. Different from the traditional ground vibration isolation system, the dynamic equations of the 6-DOF under-constrained system in the weightless environment of space are established by Lagrange's principle. Influences on vibration isolation performance of the XSSIP system incurred by different structural parameters are systematically studied under either periodic or impulsive excitations. In addition, ADAMS simulation is conducted to verify the accuracy and feasibility of the theoretical model. Compared with the traditional spring-mass-damper (SMD)-based Stewart isolation platform system, the XSSIP system possesses an obvious advantage and offers a highly efficient passive way for suppressing post-capture vibrations of the floating spacecraft.

Counter-rotation and High-velocity Outflow in the Parsec-scale Molecular Torus of NGC 1068

Abstract We present 1.4 pc resolution observations of 256 GHz nuclear radio continuum and HCN (J = 3 → 2) in the molecular torus of NGC 1068. The integrated radio continuum emission has a flat spectrum consistent with free–free emission and resolves into an X-shaped structure resembling an edge-brightened bicone. HCN is detected in absorption against the continuum, and the absorption spectrum shows a pronounced blue wing that suggests a high-velocity molecular outflow with speeds reaching 450 km s−1. Analysis of the off-nucleus emission line kinematics and morphology reveals two nested, rotating disk components. The inner disk, inside r ∼ 1.2 pc, has kinematics that are consistent with the nearly edge-on, geometrically thin H2O megamaser disk in Keplerian rotation around a central mass of 1.66 × 107 M ⊙. The outer disk, which extends to ∼7 pc radius, counter-rotates relative to the inner disk. The rotation curve of the outer disk is consistent with rotation around the same central mass as the megamaser disk but in the opposite sense. The morphology of the molecular gas is asymmetric around the nuclear continuum source. We speculate that the outer disk formed from more recently introduced molecular gas falling out of the host galaxy or from a captured dwarf satellite galaxy. In NGC 1068, we find direct evidence that the molecular torus consists of counter-rotating and misaligned disks on parsec scales.

Novel tunable broadband piezoelectric harvesters for ultralow-frequency bridge vibration energy harvesting

With a nonlinear X-shaped structure connected with piezoelectric harvesters through two types of special mounting configurations (horizontal and vertical cases), novel coupled vibration energy harvesting systems are purposely constructed and investigated for exploiting nonlinearity and structural coupling effect in vibration energy harvesting. Different from concentrating on a beam harvester itself in the literature (i.e. the beneficial nonlinearity comes from the beam itself), this study focuses on exploring the nonlinear benefits that the X-shaped structure could provide, together with structural coupling effect. The novelty lies in that the coupled X-structured harvesting systems have both the advantages of the existing simple cantilevered beam harvester (harvesting power only at around the natural frequency of the beam) and the spring-mass system supported beam harvester (harvesting energy only at around the natural frequency of the supporting spring-mass system). With the proposed X-structures, the effective operation bandwidth of traditional cantilever based harvesters can be greatly enlarged and also be extended to an ultralow frequency range. This is a very special feature of the proposed X-structure based harvesting systems compared with conventionally designed cantilevered harvesters or the spring-mass supported cantilevered harvesters. The proposed devices can be regarded as advantageous versions of the cantilever-based configurations for ultralow frequency range. In addition, the X-structured harvesters can achieve very tunable harvesting bandwidth (i.e. tuning the harvesting frequency of the first peak) by adjusting several structural parameters. The experiment tests demonstrate that the proposed harvesting devices hold potentials for traffic-induced bridge vibration energy harvesting, which can be used for powering the sensors for bridge health monitoring.

3D observation of chromosome scaffold structure using a 360° electron tomography sample holder

The chromosome scaffold is considered to be a key structure of the mitotic chromosome. It plays a vital role in chromosome condensation, shaping the X-shaped structure of the mitotic chromosome, and also provides flexibility for chromosome movement during cell division. However, it remains to be elucidated how the chromosome scaffold organizes the mitotic chromosome and how it supports shaping the structure of the chromosome during metaphase. Here we present a new technique that enables the observation of the chromosome scaffold structure in metaphase chromosomes from any direction, by transferring an isolated chromosome to a 360° rotational holder for electron tomography (ET). The chromosome was stained with immunogold-labeled condensin complex, one of the major chromosome scaffold proteins and then observed in three dimensions using ET. Using the locations of gold nanoparticles to visualize the underlying structure, the tomograms we obtained reveal the patterns of chromosome scaffold organization, which appears to consist of a helical structure that serves to organize chromatin loops into the metaphase chromosome.

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.