Long-period Structures Research Articles

Simulation of the Transmission Spectrum of Long-Period Fiber Gratings Structures with a Propagating Acoustic Shock Front.

In this paper, we investigate modification of transmission spectra of long-period fiber grating structures with an acoustic shock front propagating along the fiber. We simulate transmission through inhomogeneous long-period fiber gratings, π-shift and reflective π-shift gratings deformed by an acoustic shock front. Coupled mode equations describing interaction of co-propagating modes in a long-period fiber grating structures with inhomogeneous deformation are used for the simulation. Two types of apodization are considered for the grating modulation amplitude, such as uniform and raised-cosine. We demonstrate how the transmission spectrum is produced by interference between the core and cladding modes coupled at several parts of the gratings having different periods. For the π-shift long-period fiber grating having split spectral notch, the gap between the two dips becomes several times wider in the grating with the acoustic wave front than the gap in the unstrained grating. The behavior of reflective long-period fiber gratings depends on the magnitude of the phase shift near the reflective surface: an additional dip is formed in the 0-shift grating and the short-wavelength dip disappears in the π-shift grating.

In situ synchrotron radiation X-ray diffraction measurements of Fe–Mo alloy hydrides formed under high pressure and high temperature

Conventional hydrides obtained thus far contain at least one type of metal with high hydrogen affinity, which can form metal hydrides near ambient pressure. In contrast, we synthesized metal hydrides comprising only metals with low hydrogenation affinity which are metals that do not form metal hydrides MHx (M stands for metal element, x > 0.5) below 1 GPa. This is because such hydrides are rare and would demonstrate novel properties and functionalities. To provide a guideline for synthesizing such hydrides, we clarified the hydrogenation reaction processes of FexMo1−x alloys at 6 GPa and 750 °C over a wide composition range of 0.41 ≤ x ≤ 0.88, where both Fe and Mo demonstrate low hydrogen affinities. Depending on the alloy composition, the hydrogenation reaction process can be classified into three types. Two kinds of novel hydrides were synthesized herein. First, FexMo1−xH (0.50 ≤ x ≤ 0.74) with metal elements at the vertices of hexagonal close-packed (hcp) lattices, and second, Fe0.88Mo0.12H with a complex crystal structure, which is likely to be a long-period close-packed structure.

Separation of long-period components of ground motion and its impact on seismic response of long-period diagrid structures

The improved modified ensemble empirical mode decomposition (MEEMD) method is used to decompose the long-period ground motion, and the introduction of permutation entropy is used to eliminate the abnormal signal, which can avoid the phenomenon of mode aliasing in the traditional empirical mode decomposition method, so that the components of the long-period ground motion can be accurately separated. Taking the separated and reconstructed ground motions as input action, the influence of long-period components on the seismic response of diagrid structure of high-rise building is studied. The results demonstrate that the MEEMD method can accurately extract long-period ground motion components from long-period ground motion. Long-period ground motion contains abundant short-term energy with low-frequency, which is the main reason for the large seismic response of long-period structure. The seismic response of diagrid structure is closely related to the natural period of the structure and the spectrum characteristics of the ground motion.

Seismic response analysis of loess site under far-field bedrock ground motion of the Wenchuan earthquake.

In this paper, considering the far-field seismic input, an accelerogram recorded in the bedrock at Wuquan Mountain in Lanzhou city during the 2008 Wenchuan Ms8.0 earthquake was selected, and numerical dynamic analyses were conducted. The one-dimensional equivalent linear method was implemented to estimate the ground motion effects in the loess regions. Thereafter, slope topographic effects on ground motion were studied by applying the dynamic finite-element method. The results revealed the relationship between the PGA amplification coefficients and the soil layer thickness, which confirmed that the dynamic response of the sites had obvious nonlinear characteristics. The results also showed that there was an obvious difference in the dynamic magnification factor between the short-period and long-period structures. Moreover, it was found that the amplification coefficient of the observation point at the free surface was greater than the point inside the soil at the same depth, which mainly occurred in the upper slope. Through this study, the quantitative assessment of ground motion effects in loess regions can be approximately estimated, and the amplification mechanism of the far-field ground motion mechanism can be further explained. In addition to the refraction and reflection theory of seismic waves, the resonance phenomenon may help explain the slope topographic effect through spectrum analysis.

Formation Process of Long-Period Stacking-Ordered Structures in Mg97Zn1Y2 Alloy Comprising HCP and Cubic Phases Fabricated by High-Pressure High-Temperature Annealing

As-cast Mg97Zn1Y2 alloy consists of α-Mg matrix and 18R-type long-period stacking-ordered (LPSO) structures. We observed that the alloy undergoes a phase transformation to D03 superlattices and α-Mg matrix due to high-pressure high-temperature (HPHT) annealing at 3 GPa and above 773 K. Further, the alloy recovered after HPHT annealing, consisting of the α-Mg matrix and D03 superlattices, transformed into 18R-type LPSO structures during further annealing at ambient pressure. An fcc structure with a lattice parameter of 1.42 nm, which was twice that of D03, emerged in both the collapse process of the 18R-type LPSO structure under high-pressure, and the formation process of the 18R-type LPSO structure at ambient pressure. This fcc phase was an intermediate structure between 18R-type LPSO and D03. From the electron diffraction results, it is considered that 18R-type LPSO is continuously present with 2H including stacking faults, which almost corresponded with previous studies.

On the texture and superstructure formation in Ti–TiAl3–Al MIL composites

In recent decades, metal-intermetallic laminated (MIL) composites are of great interest to the scientific community. The intermetallic layers in such composites possess a strong crystallographic texture and can form various superstructures. However, these effects are rarely discussed in the literature. By application of synchrotron X-ray diffraction (SXRD) we show, that an intermetallic layer in explosively welded and annealed Ti–Al-based MIL composite consists of two modifications of titanium trialuminide: TiAl3 with a D022 structure and its superstructure Ti8Al24. According to SXRD analysis, the volume fraction of the Ti8Al24 modification increases from Al/intermetallic interface towards Ti/intermetallic interface. This may be caused by the lack of Al for the formation of stoichiometric titanium trialuminide near the interface with Ti, which leads to the formation of a long-period structures having Ti1+xAl3-x stoichiometry. Two types of fiber texture were formed in the titanium trialuminide layer: [001] near the Ti/intermetallic interface and <100> near the Al/intermetallic interface, which is caused by peculiarities of Ti and Al atoms migration. To explain the features of the forming texture, hypothetical mechanisms of Al and Ti diffusion in the intermetallic layer are discussed in this study: a vacancy diffusion, an interstitial diffusion, and a six jump vacancy cycle (6JVC).

Correlation between pulse-like ground motion intensity measures and seismic demands of buildings with three structural systems (moment-resisting frames, structural walls and combination of moment-resisting frames and shear walls)

In this study, the distribution of correlation coefficients between maximum interstory drift ratio (MIDR) of multistorey building structures and ground motion characteristics intensity measures (IMs) is evaluated and compared. For this purpose, a continuum building model is used to estimate the MIDR of multistory building structure including higher mode effects. The MIDRs are computed for building structures with three different lateral resisting systems (structural walls, moment-resisting frames, and their combination) and fundamental periods that ranges from 0.05 to 10s. Nine different ground motion parameters of pulse-like ground motions including PGD, PGA, PGV, Ic, CAV, Ia, SMV, ESD, SMA are selected as ground motion characteristics IMs. The effects of the type of lateral resisting system and the acceleration pulse on the distribution of correlation coefficients are also considered in the study. Based on the assessment results, MIDRs in mid and long-period buildings show a high correlation to PGV, SED and SMV, while a low correlation occurs with respect to PGA and SMA. Also, type of lateral resisting system causes changes in the correlation coefficients and results showed that long-period shear wall structure gives lower coefficients with respect to other structural systems.

Seismic response reduction analysis of large chassis base-isolated structure under long-period ground motions

Long-period structures (e.g. Isolated structures) tend to produce pseudo-resonance with low frequency components of long-period ground motions, resulting in the increase in damage. Stiffness mutation occurs due to the set-back in the upper body of the large chassis structure. In the parts with stiffness mutation, the torsion effect caused by the tower is far greater than that of the chassis itself. In this study, a total of 273 ground motions are collected and then filtered into four types, including the near-field ordinary, near-field pulse, far-field ordinary, and far-field harmonic. An 8-degree (0.2 g) fortified large chassis base-isolated structure is established. Furthermore, ETABS program software is used to conduct nonlinear time history analysis on the isolation and seismic model under bi-directional earthquake ground motions. The comparison results show that the seismic isolation effect of the base-isolated structure under long-period ground motions is worse than that associated with ordinary ground motions when the seismic response reduction rate of the large base floor significantly decreases compared with that of the tower. When the inter-story displacement angle and the displacement of isolation layer of the chassis exceeds the limit of Code for Seismic Design of Buildings (GB 50011-2010), it is recommended to adopt composite seismic isolation technology or add limit devices. Under the condition of long-period ground motions, the base-isolated structure reduces the lateral-torsional coupling effect of the large chassis structure, while the torsion response of large chassis’ top layer increases. Under long-period ground motions with the same acceleration peak, the response of the base-isolated structure increases much more than that of the seismic structure and the consideration of this impact is suggested to be added to the Code.

Seismic Energy Response of SDOF Systems Subjected to Long-Period Ground Motion Records

To provide an important reference for the energy-based seismic design of long-period structures, the elastoplastic dynamic analysis program is employed to study the seismic energy response of single-degree-of-freedom (SDOF) systems under two types of typical long-period ground motions. Then, the influencing relationships of external and internal factors on the energy response spectra under near-fault pulse-like and far-field harmonic ground motions are analyzed one by one. Study results are obtained as follows: within the whole period, all the input energy, hysteretic energy and damping energy spectra of SDOF systems under near-fault pulse-like and far-field harmonic ground motions, are larger than those under common ground motions, even the seismic energy response under far-field harmonic ground motions is larger than that under near-fault pulse-like ground motions. From the aspect of energy concept, the energy response spectra and energy distribution rule of SDOF systems are evaluated based on the intensity and spectral distribution under near-fault pulse-like and far-field harmonic ground motions. If the ratio of hysteretic energy to input energy (RHEIE) is determined, the hysteretic energy which must be dissipated by a structure would be derived by the method of energy-based design. The input energy and hysteretic energy are mainly influenced by damping ratio and ductility coefficient, while the yield stiffness ratio exerts minor effects. It indicates that reasonable structural design parameters would contribute to the hysteretic energy of a structure itself.

Study on Quasi-Static Loading Protocols considering the Action Characteristics of Long-Period Ground Motions

Due to abundant low-frequency components of long-period ground motions (LPGMs), long-period structures are susceptible to severe damage. The corresponding time-history displacement responses have significant “large-displacement” and “long-duration” characteristics. These action characteristics essentially reflect the different loading paths imposed on structures of LPGMs from ordinary ground motions (OGMs). Hence, revealing the influence mechanism of the action characteristics on the seismic performance of structural components is the key to investigating the influence of LPGMs on the whole structure. This paper presents a kind of quasi-static loading protocol considering the action characteristics of LPGMs. Firstly, nonlinear time-history analyses on structural systems subjected to 50 selected representative LPGMs were conducted. Inelastic cycles and corresponding amplitudes of time-history displacement responses under LPGMs were statistically analyzed through the rainflow method. Then, considering two of the most significant factors, structural period and target ductility, a prediction model of cycle number and cycle amplitude was obtained by regression. On this basis, the quasi-static loading protocol considering the action characteristics of LPGMs was developed. Proposed protocols can be directly applied to experimental investigations on the seismic performance for structural components under LPGMs.

Power Analysis of SDOF Structures With Tuned Inerter Dampers Subjected to Earthquake Ground Motions

Abstract Tuned inerter dampers (TID) have been demonstrated as efficient energy dissipation devices for seismic response control. However, its potential capability for energy harvesting remains largely unexplored. Here, we present a theoretical analysis of the power of a structure-TID system subjected to earthquake ground motions. The analytical solutions (ASs) of the average damping power of the system are derived for considering white noise base excitations and the Kanai-Tajimi earthquake model, respectively. Comparisons of the numerical results of a Monte Carlo simulation and the theoretical predictions verify the accuracy of the analytical solutions. Besides, we uncover the influence of the TID parameters on the average damping power and output power of the system. The optimal frequency ratio of the TID for maximizing its output power slightly differs from that for seismic response control, and the former varies with site conditions. In contrast, both the damping power and output power are not sensitive to the damping ratio of the TID. For short-period structures, a small inertance-to-mass ratio (μ) of the TID is beneficial to maximize its output power, while seismic response control requires a large μ. For long-period structures, the damping power and output power are not sensitive to the μ. Generally, a structure-TID system on a soft soil site absorbs more energy from a given earthquake and is capable of harvesting more energy than that on a hard soil site. This study may help develop new strategies for self-powered control and monitoring in civil structures.

Stratum Corneum Function: A Structural Study with Dynamic Synchrotron X-ray Diffraction Experiments.

Studies on the effectiveness of substances such as drugs and cosmetics that act on the skin require structural evidence at the molecular level in the stratum corneum to clarify their interaction with intercellular lipid and soft keratin. For this purpose, when applying the substances to the stratum corneum X-ray diffraction experiment is one of the powerful tools. To detect minute structural changes in a stratum corneum sample, using a "solution cell", dynamic synchrotron X-ray diffraction measurements were performed when applying aqueous solution of the substances to the stratum corneum: (1) It was found that a surfactant, sodium dodecyl sulfate, significantly disrupted the long-period lamellar structure. (2) To study the effects of water, structural modifications of the short-period lamellar structure and the soft keratin in corneocytes were measured as a function of time. At the initial water content of 15 wt%, the spacings of the short-period lamellar structure and the soft keratin increased toward those at the water content of 25 wt%, that is a key water content in the stratum corneum. (3) Nanoparticles composed of assembly of amphiphilic molecules are one of the leading pharmaceutical formulations. When the nanoparticles were applied, a new assembly of amphiphilic molecules originated from the nanoparticle appeared. This phenomenon suggests that the formation of the new assembly at the surface of skin is concerned with the release of the drug from the nanoparticles. (4) When ethanol was applied to the stratum corneum, only the liquid state in the intercellular lipid matrix was dissolved. After the removal of ethanol from this stratum corneum, the ordered hydrocarbon-chain packing structures appeared. From this fact we would propose that the liquid state region is the main pathway for hydrophobic drugs with a small molecular weight in connection with the so-called 500 Da rule. Here, not only the technique but also the background to these studies and the characteristic results obtained from these studies are explained.

Real-Time and Sensitive Immunosensor for Label-Free Detection of Specific Antigen with a Comb of Microchannel Long-Period Fiber Grating.

This study aimed to develop a comb of microchannel and immunosensor based on long-period fiber grating using the process of Lithographie Galvanoformung Abformung-like micro-electromechanical systems (LIGA-like MEMS) for real-time and label-free detection of specific antigen. The coupling between propagating core and cladding modes was conducted from the comb of microchannel long-period fiber grating (CM-LPFG). The CM-LPFG-based immunosensor consisted of a microchannel structure through photoresist stacking processes and was sandwiched with an optical fiber to obtain a long-period structure. Specific immunoglobulin against protein antigen was immobilized onto an optical fiber surface and produced a real-time resonance effect on sensing specific protein antigen from the extracted protein mixtures of the cancer cell lines. The variable transmission loss was -14.07 dB, and the resonant wavelength shift was 11.239 nm. The low limit of detection for total protein concentration was 1.363 ng/μL. Our results revealed that the CM-LPFG-based immnosensor for real-time detection of label-free protein antigen is feasible and sensitive based on the diversification of a transmission loss and achieves specific immunosensing purposes for lab-on-fiber technology.

Study on standard response spectrum parameters of special long-period ground movements

Multiple earthquake damages show that the long-period ground movements have an amplification effect on the dynamic response and seismic damage of long-period structures. To form an improved code design spectrum suitable for long-period ground movements, the standard response spectra consisting of four segments for near-fault pulse-like (NFPL) and far-field harmonic (FFH) ground movements are proposed. Firstly, two types of special long-period ground movements with reliable information are selected for this research. Then, the fundamental period of a single-degree-of-freedom (SDOF) system is extended to 16 s with the damping ratio of 5 %, and the seismic response spectrum and the normalized response spectrum are analyzed. Next, the normalized acceleration spectrum of long-period ground movements is calibrated to the standard response spectrum of regular variation. Finally, the parameters of standard response spectrum about long-period ground movements and the ones of the current code design spectrum are discussed. The results show that the current code design spectrum overestimates the structural seismic response in the short period under NFPL and FFH ground movements, while it underestimates the structural seismic response in the long period. The fundamental period of a SDOF system of china’s current code design spectrum should be extended to consider the influence on long-period structures acted by a long-period earthquake. Further, it accounts for the resonance effect of long-period ground movements which ensures the seismic design safety of long-period structures.

Utilizing a unified structure model in (3 + 1)-dimensional superspace to identify a homologous phase (Ga1−αAlα)2O3(ZnO)min ZnO-based thermoelectric composites

A unified structure model in (3 + 1)-dimensional superspace proved suitable for identification of a homologous phase (Ga1−αAlα)2O3(ZnO)mby the profile fitting of powder X-ray diffraction intensities for thermoelectric composite materials in the pseudoternary system ZnO–Al2O3–Ga2O3. A homologous compound of the phase parameterm≃ 37 was found to coexist with (Al,Ga)-doped ZnO in samples sintered at 1723 K in air. The thermoelectric properties of the composite materials were closely related to the phase fractions. The higher the phase fraction of (Al,Ga)-doped ZnO with the wurtzite structure, the higher the electrical conductivity. On the other hand, the homologous compound with the long-period structure was effective in lowering the thermal conductivity of the materials.

Potential of Mechanically Induced Cascaded Long-Period Grating Structure for Reflectometric Pressure, Strain, and Temperature Sensing

We present the first report on reflectometric optical fiber sensing based on mechanically induced cascaded long-period grating (LPG) structure. This method utilizes in-house designed mechanical casings and a bare fiber. When a fiber is sandwiched between the casings and pressed by tightening screws, an LPG is induced due to a photo-elastic effect. By exploiting Fresnel refection at a fiber end, a cascaded LPG structure can be implemented using a single LPG, enabling reflectometric configuration. When this sensor is subjected to external physical processes, the attenuation bands change clearly, and their shift can be used for non-destructive evaluations. We show experimentally that this sensor can measure loads of up to 10 N without producing any permanent change in the fiber properties, indicating its pressure sensing capability. We also show that this sensor can potentially measure strain and temperature. In our experiments, the strain and temperature sensitivities are 9.4 nm/% and 0.045 nm/°C, respectively.

The Difference in Molecular Orientation and Interphase Structure of SiO2/Shape Memory Polyurethane in Original, Programmed and Recovered States during Shape Memory Process.

In order to further understand the shape memory mechanism of a silicon dioxide/shape memory polyurethane (SiO2/SMPU) composite, the thermodynamic properties and shape memory behaviors of prepared SiO2/SMPU were characterized. Dynamic changes in the molecular orientation and interphase structures of SiO2/SMPU during a shape memory cycle were then discussed according to the small angle X-ray scattering theory, Guinier’s law, Porod approximation, and fractal dimension theorem. In this paper, a dynamic mechanical analyzer (DMA) helped to determine the glass transition start temperature (Tg) by taking the onset point of the sigmoidal change in the storage modulus, while transition temperature (Ttrans) was defined by the peak of tan δ, then the test and the calculated results indicated that the Tg of SiO2/SMPU was 50.4 °C, and the Ttrans of SiO2/SMPU was 72.18 °C. SiO2/SMPU showed good shape memory performance. The programmed SiO2/SMPU showed quite obvious microphase separation and molecular orientation. Large-size sheets and long-period structures were formed in the programmed SiO2/SMPU, which increases the electron density difference. Furthermore, some hard segments had been rearranged, and their gyration radii decreased. In addition, several defects formed at the interfaces of SiO2/SMPU, which caused the generation of space charges, thus leading to local electron density fluctuations. The blurred interphase structure and the intermediate layer formed in the programmed SiO2/SMPU and there was evident crystal damage and chemical bond breakage in the recovered SiO2/SMPU. Finally, the original and recovered SiO2/SMPU samples belong to the surface fractal system, but the programmed sample belongs to the mass fractal and reforms two-phase structures. This study provides an insight into the shape memory mechanism of the SiO2/SMPU composite.

Comparative study of different response spectra based on isolated structures

In order to study the influence of different design response spectra on the internal force of the isolated structure, the response spectra of the “Code for Seismic Design of Buildings” (Abbreviated as SD), the response spectra of “Design Standards for Seismic Isolation of Buildings” (draft for comments)(Abbreviated as ID) and the response spectra based on pseudo acceleration calibration(Abbreviated as PA) are analyzed. Compared with SD response spectra, ID response spectra adopts the (1/T) attenuation mode in the long period, which reduces the value of the earthquake influence coefficient in the long period of the response spectrum. At the same time, there is no overshoot phenomenon in ID response spectra. This paper presents the response spectrum basic on structural elastic displacement. PA response spectra considers the influence of different sites on the long-period structure, and adds the characteristic period corresponding to different sites. The calculation shows that compared with the calculation result of SD response spectra, the floor shear force calculated by ID is reduced, and the reduction ratio is between 31% and 36%. Compared with the floor shear force obtained by using PA response spectra, the reduction ratio is between 19% and 29%.

Analysis of soft and hard nanoparticle alternating multilayers for the development of theory for long-period stacking order structure prepared by Langmuir-Blodgett method

Two types of hard and soft nanoparticles with a size of 5 nm were alternately layered to adjust the multi-particle structure with high regularity, and structural analysis was performed. Specifically, we alternately transferred two kinds of single-particle layers composed of surfactant-modified organo-magnetite and a hydrophobic polymer to a solid substrate using the Langmuir-Blodget (LB) method. The morphology of two-dimensional particle integration in each single particle layer was confirmed by atomic force microscopy observations. The obtained LB multilayers exhibited almost the same periodicity, crystallite size, and lattice distortion, based on X-ray diffraction (XRD) analysis. The alternating multilayers composed of hard and soft particle monolayers were not inferior to single component multilayers in terms of periodicity and regularity. The utilization of this preparation method facilitates effective control of the period of hard and soft layers. It is asserted that the high degree of regularity was attained due to the affinity and miscibility between the organic polymer particle layer and the modified organic chains on the inorganic nanoparticle surface. The most notable result is that in the XRD data, the spacing between inorganic nanoparticles was not enhanced, and the period of the hard-soft particle correlation was confirmed. Therefore, it seems that both layers have the same high degree of regularity.

An improved wave motion input method for application of multi-transmitting boundary

To solve scattering problems with multi-transmitting boundary, we present an improved wave motion input method based on the idea that error caused by the difference between incident wave field used in calculation and waves propagating in finite element grids can be eliminated to suppress drift instability. In this method, a calculation scheme is proposed to obtain the numerical solution of incident wave field, which establishes boundary region models with the multi-transmitting boundary. Numerical experiments demonstrate that this improved wave motion input method not only eliminates drift instability but also effectively improves the calculation accuracy of low-frequency components. Furthermore, the method is easy to implement and, unlike other approaches, does not need artificial parameters. Thus, this method is proposed for use in wave scattering simulation such as seismic response analyses of structures, particularly for long-period structures and those that are sensitive to low frequency.