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 present the development of the first ultrafast transmission electron microscope (UTEM) driven by localized photoemission from a field emitter cathode. We describe the implementation of the ...instrument, the photoemitter concept and the quantitative electron beam parameters achieved. Establishing a new source for ultrafast TEM, the Göttingen UTEM employs nano-localized linear photoemission from a Schottky emitter, which enables operation with freely tunable temporal structure, from continuous wave to femtosecond pulsed mode. Using this emission mechanism, we achieve record pulse properties in ultrafast electron microscopy of 9Å focused beam diameter, 200fs pulse duration and 0.6eV energy width. We illustrate the possibility to conduct ultrafast imaging, diffraction, holography and spectroscopy with this instrument and also discuss opportunities to harness quantum coherent interactions between intense laser fields and free-electron beams.
•First implementation of an ultrafast TEM employing a nanoscale photocathode.•Localized single photon-photoemission from nanoscopic field emitter yields low emittance ultrashort electron pulses.•Electron pulses focused down to ~9Å, with a duration of 200fs and an energy width of 0.6eV are demonstrated.•Quantitative characterization of ultrafast electron gun emittance and brightness.•A range of applications of high coherence ultrashort electron pulses is shown.
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.
Flexible metal–organic frameworks (MOFs) hold great promise as smart materials for specific applications such as gas separation. These materials undergo interesting structural changes in response to ...guest molecules, which is often associated with unique adsorption behavior not possible for rigid MOFs. Understanding the dynamic behavior of flexible MOFs is crucial yet challenging as it involves weak host–guest interactions and subtle structural transformation not only at the atomic/molecular level but also in a nonsteady state. We report here an in-depth study on the adsorbate- and temperature-dependent adsorption in a flexible MOF by crystallizing atomic gases into its pores. Mn(ina)2 shows an interesting temperature-dependent response toward noble gases. Its nonmonotonic, temperature-dependent adsorption profile results in an uptake maximum at a temperature threshold, a phenomenon that is unusual. Full characterization of Xe-loaded MOF structures is performed by in situ single-crystal and synchrotron X-ray diffraction, IR spectroscopy, and molecular modeling. The X-ray diffraction analysis offers a detailed explanation into the dynamic structural transformation and provides a convincing rationalization of the unique adsorption behavior at the molecular scale. The guest and temperature dependence of the structural breathing gives rise to an intriguing reverse of Xe/Kr adsorption selectivity as a function of temperature. The presented work may provide further understanding of the adsorption behavior of noble gases in flexible MOF structures.
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.
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