Subjecting metallic glasses repeatedly to liquid nitrogen temperature has become a popular method to homogeneously rejuvenate the material. Here we reveal the atomic-scale structural dynamics using ...in-situ x-ray photon correlation spectroscopy (XPCS) during and after cryogenic cycling of a Zr-based metallic glass in two structural states (plate and ribbon). Heterogeneous structural dynamics is observed at 300 K that changes to monotonic aging at 78 K. It is found that cryogenic cycling homogenizes the relaxation time distribution. This effect is much more pronounced in the ribbon, which is the only structural state that rejuvenates upon cycling. We furthermore reveal how fast atomic-scale dynamics is correlated with long-time structural relaxation times irrespective of the structural state, and that the ribbon exhibits unexpected additional fast atomic-scale relaxation in comparison to the plate material. A structural picture emerges that points towards heterogeneities in the fictive temperature as a requirement for cryogenic energy storage.
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In the last few decades, there has been a surge of research in the area of non-contact measurement techniques. Photogrammetry has received considerable attention due to its ability to achieve ...full-field measurement and its robustness to work in testing environments and on testing articles in which using other measurement techniques may not be practical. More recently, researchers have used this technique to study transient phenomena and to perform measurements on vibrating structures. The current paper reviews the most current trends in the photogrammetry technique (point tracking, digital image correlation, and target-less approaches) and compares the applications of photogrammetry to other measurement techniques used in structural dynamics (e.g. laser Doppler vibrometry and interferometry techniques). The paper does not present the theoretical background of the optical techniques, but instead presents the general principles of each approach and highlights the novel structural dynamic measurement concepts and applications that are enhanced by utilizing optical techniques.
•Photogrammetry measures displacements to monitor dynamics of structures.•The paper reviews the most current trends in photogrammetry.•The paper compares the applications of photogrammetry to conventional approaches.•Photogrammetry effectively measures high-displacement and low-frequency vibrations.•Photogrammetry can be applied to measure dynamics of rotating structures.
We perform extensive simulations and systematic statistical analyses on the structural dynamics of a model of amorphous silicon. The simulations follow the dynamics introduced by Wooten, Winer and ...Weaire: the energy is obtained with the Keating potential, and the dynamics consists of bond transpositions proposed at random locations and accepted with the Metropolis acceptance ratio. The structural quantities we track are the variations in time of the lateral lengths (Lx, Ly, Lz) of the cuboid simulation cell. We transform these quantities into the volume V and two aspect ratios B1 and B2. Our analysis reveals that at short times, the mean squared displacement (MSD) for all of them exhibits normal diffusion. At longer times, they cross over to anomalous diffusion (AD), with a temperature-dependent anomalous exponent α<1. We analyze our findings in the light of two standard models in statistical physics that feature anomalous dynamics, viz., continuous time random walker (CTRW) and fractional Brownian motion (fBm). We obtain the distribution of waiting times, and find that the data are consistent with a stretched-exponential decay. We also show that the three quantities, V, B1 and B2 exhibit negative velocity autocorrelation functions. These observations together suggest that the dynamics of the material belong to the fBm class.
The COVID-19 pandemic unveils unforeseen and unprecedented fragilities in supply chains (SC). A primary stressor of SCs and their subsequent shocks derives from disruption propagation (i.e., the ...ripple effect) through related networks. In this paper, we conceptualize current state and future research directions on the ripple effect for pandemic context. We scrutinize the existing OR (Operational Research) studies published in international journals dealing with disruption propagation and structural dynamics in SCs. Our study pursues two major contributions in relation to two research questions. First, we collate state-of-the-art research on disruption propagation in SCs and identify a methodical taxonomy along with theories displaying their value and applications for coping with the impacts of pandemics on SCs. Second, we reveal and systemize managerial insights from theory used for operating (adapting) amid a pandemic and during times of recovery, along with becoming more resistant to future pandemics. Streamlining the literature allowed us to reveal several new research tensions and novel categorizations and classifications. The outcomes of our study show that methodical contributions and the resulting managerial insights can be categorized into three levels, i.e., network, process, and control. Our analysis reveals that adaptation capabilities play the most crucial role in managing the SCs under pandemic disruptions. Our findings depict how the existing OR methods can help coping with the ripple effect at five pandemic stages (i.e., Anticipation; Early Detection; Containment; Control and Mitigation; and Elimination) following the WHO classification. The outcomes and findings of our study can be used by industry and researchers alike to progress the decision-support systems guiding SCs amid the COVID-19 pandemic and toward recovery. Suggestions for future research directions are offered and discussed.
In structural engineering, model updating is often used for non-destructive damage assessment: by calibrating stiffness parameters of finite element models based on experimentally obtained (modal) ...data, structural damage can be identified, quantified and located. However, the model updating problem is an inverse problem prone to ill-posedness and ill-conditioning. This means the problem is extremely sensitive to small errors, which may potentially detract from the method׳s robustness and reliability. As many errors or uncertainties are present in model updating, both regarding the measurements as well as the employed numerical model, it is important to take these uncertainties suitably into account. This paper aims to provide an overview of the available approaches to this end, where two methods are treated in detail: a non-probabilistic fuzzy approach and a probabilistic Bayesian approach. These methods are both elaborated for the specific case of vibration-based finite element model updating for damage assessment purposes.
•Accounting for uncertainty is important in vibration-based FE model updating.•A wide range of methods is available for uncertainty quantification in inverse problems.•Bayesian model updating and fuzzy model updating are addressed in detail.•The most suitable approach is dependent on the end goal of the uncertainty assessment.•All discussions focus on structural health monitoring and damage assessment applications.
Polymer nanocomposite (PNC) films based on the blend matrix of poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) (50/50 wt%) incorporated with zinc oxide (ZnO) nanoparticles (i.e., ...(PVA–PVP)–x wt% ZnO; x = 0, 1, 3 and 5) were prepared by solution-cast method. The behaviour of polymer-polymer and polymer-nanoparticle interactions in the PNC films was ascertained by employing X-ray diffraction, energy dispersive X-ray, and Fourier transform infra-red spectroscopies. Scanning electron microscopy and atomic force microscopy were performed for the morphological characterization, whereas the thermal and optical properties of the PNC films were investigated by using differential scanning calorimetry and ultraviolet–visible spectroscopy, respectively. The dielectric and electrical behaviour of these PNC materials were determined by employing the dielectric relaxation spectroscopy over the frequency range from 20 Hz to 1 MHz. The influence of ZnO concentration on the degree of PVA crystalline phase and the crystallite size, surface morphology and roughness of the films, the glass phase transition and melting phase transition temperatures, direct and indirect optical energy band gap, refractive index, complex permittivity, electrical conductivity, activation energy and the structural dynamics of these PNC materials were explored. The investigated properties of the PNC films were credited to an innovation and engineering of novel high performance flexible nanodielectrics in the area of advanced functional materials for their promising applications especially in the next generation optoelectronic, gas sensor and microelectronic devices.
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•Multifunctional (PVA–PVP)–x wt% ZnO films were prepared by solution-cast method.•Polymer-polymer and polymer-nanofiller interactions vary with ZnO concentration.•Optical band gap decrease with the increase of ZnO contents in the PNC films.•Only 1 wt% ZnO dispersion enhances permittivity and thermal stability of PNC film.•Uses as nanodielectric, sensor and base matrix for electrolyte were established.
•Summarized collective experience of vision-based dynamic response measurement and SHM.•Reviewed basics and principles of vision-based sensor system.•Discussed the measurement error sources and ...mitigation methods.•Presented outlook of future directions of vision-based sensors for SHM.
To address the limitations of current sensor systems for field applications, the research community has been actively exploring new technologies that can advance the state-of-the-practice in structural health monitoring (SHM). Thanks to the rapid advances in computer vision, the camera-based noncontact vision sensor has emerged as a promising alternative to conventional contact sensors for structural dynamic response measurement and health monitoring. Significant advantages of the vision sensor include its low cost, ease of setup and operation, and flexibility to extract displacements of any points on the structure from a single video measurement. This review paper is intended to summarize the collective experience that the research community has gained from the recent development and validation of the vision-based sensors for structural dynamic response measurement and SHM. General principles of the vision sensor systems are firstly presented by reviewing different template matching techniques for tracking targets, coordinate conversion methods for determining calibration factors to convert image pixel displacements to physical displacements, measurements by tracking artificial targets vs. natural targets, measurements in real time vs. by post-processing, etc. Then the paper reviews laboratory and filed experimentations carried out to evaluate the performance of the vision sensors, followed by a discussion on measurement error sources and mitigation methods. Finally, applications of the measured displacement data for SHM are reviewed, including examples of structural modal property identification, structural model updating, damage detection, and cable force estimation.
NMR spectroscopy sheds light on receptor activation: Molecular switches are conserved motifs of G protein‐coupled receptors that undergo structural changes during activation. Tryptophan residues are ...often part of these molecular switches and thus provide insights in the activation mechanism of the molecule. In their Research Article on page 23854, D. Huster and co‐workers use NMR spectroscopy to monitor structural alterations of the neuropeptide Y1 receptor with atomic resolution observable by changes in the chemical shifts of six native tryptophan residues.
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