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"Lin, Yu-Shen"
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Instabilities of Thin Films on a Compliant Substrate: Direct Numerical Simulations from Surface Wrinkling to Global Buckling
For structures consisting of a thin film bonded to a compliant substrate, wrinkling of the thin film is commonly observed as a result of mechanical instability. Although this surface undulation may be an undesirable feature, the development of new functional devices has begun to take advantage of wrinkled surfaces. The wrinkled structure also serves to improve mechanical resilience of flexible devices by suppressing crack formation upon stretching and bending. If the substrate has a reduced thickness, buckling of the entire structure may also occur. It is important to develop numerical design tools for predicting both wrinkle and buckle formations. In this paper we report a comprehensive finite element-based study utilizing embedded imperfections to directly simulate instabilities. The technique overcomes current computational challenges. The temporal evolution of the wrinkling features including wavelength and amplitude, as well as the critical strains to trigger the surface undulation and overall structural buckling, can all be predicted in a straightforward manner. The effects of model dimensions, substrate thickness, boundary condition, and composite film layers are systematically analyzed. In addition to the separate wrinkling and buckling instabilities developed under their respective geometric conditions, we illustrate that concurrent wrinkling and buckling can actually occur and be directly simulated. The correlation between specimen geometry and instability modes, as well as how the deformation increment size can influence the simulation result, are also discussed.
Journal Article
Establishing the effects of mesoporous silica nanoparticle properties on in vivo disposition using imaging-based pharmacokinetics
The progress of nanoparticle (NP)-based drug delivery has been hindered by an inability to establish structure-activity relationships in vivo. Here, using stable, monosized, radiolabeled, mesoporous silica nanoparticles (MSNs), we apply an integrated SPECT/CT imaging and mathematical modeling approach to understand the combined effects of MSN size, surface chemistry and routes of administration on biodistribution and clearance kinetics in healthy rats. We show that increased particle size from ~32- to ~142-nm results in a monotonic decrease in systemic bioavailability, irrespective of route of administration, with corresponding accumulation in liver and spleen. Cationic MSNs with surface exposed amines (PEI) have reduced circulation, compared to MSNs of identical size and charge but with shielded amines (QA), due to rapid sequestration into liver and spleen. However, QA show greater total excretion than PEI and their size-matched neutral counterparts (TMS). Overall, we provide important predictive functional correlations to support the rational design of nanomedicines.
Nanoparticle applications are limited by insufficient understanding of physiochemical properties on in vivo disposition. Here, the authors explore the influence of size, surface chemistry and administration on the biodisposition of mesoporous silica nanoparticles using image-based pharmacokinetics.
Journal Article
A Potential Reason for a More CP El Nino‐Like SSTA Performance in CMIP6 Simulations
A systematic bias of the extremely westward zonal current (EWZC) was revealed over the equatorial Pacific in Coupled Model Intercomparison Project 6 (CMIP6) models. It tends to weaken the modeled interannual variability of equatorial zonal current anomaly (ZCA) with its maximum variability concentrated in the western Pacific. A mixed‐layer heat budget analysis demonstrates that the simulation of mean circulation effect is slightly affected by the zonal current bias. However, the zonal advective feedback is closely linked to the biased equatorial ZCA variability and is overestimated (underestimated) in the Niño‐4 (Niño‐3) region. The magnitude of zonal advective feedback is even greater than that of thermocline feedback and becomes the most dominant process contributing to the growth of mixed‐layer temperature anomaly tendency in the Niño‐4 region. Such a bias is essential for a more central‐Pacific El Niño‐like performance in CMIP6 models. Plain Language Summary El Niño is a significant climate variability characterized by a strong seasonal‐locking pattern in the tropical Pacific. It can be roughly classified into eastern‐Pacific and central‐Pacific El Niño, where the maximum warm sea surface anomaly (SSTA) takes place in the equatorial eastern and central Pacific, respectively. Previous studies have utilized a series of coupled models to investigate the dynamics of El Niño diversity. Here, we discovered a serious error in the state‐of‐the‐art CMIP6 models in reproducing equatorial Pacific zonal flows. Through a mixed‐layer heat budget analysis, the overestimated zonal advective feedback was revealed to be predominantly attributed to the zonal current bias, leading to an excessive warm El Niño SSTA toward the maritime continent. A higher proportion of central‐Pacific El Niño pattern was captured when contrasting the two types of El Niño in CMIP6 simulations. Key Points A systematic bias of extremely westward zonal current anomaly field was revealed over the equatorial Pacific in CMIP6 models The bias in the equatorial Pacific zonal current field deeply influences the simulation of zonal advective feedback Excessive zonal advective feedback is one of the key factors to result in a more central‐Pacific El Niño‐like pattern in CMIP6 models
Journal Article
Effects of Equatorial Ocean Current Bias on Simulated El Niño Pattern in CMIP6 Models
This study utilized the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to examine the simulations of equatorial ocean currents and explore their substantial influences on the systematic bias of westward‐extended sea surface temperature anomalies (SSTA) pattern during El Niño. The results show that models simulate an excessive westward ocean current field over the equatorial central Pacific in the mean state. It tends to suppress the equatorial eastward ocean current anomalies with their maximum centering over the equatorial western Pacific in the El Niño developing phase. As a consequence, an overestimated zonal advective feedback toward the maritime continent exists, subsequently inducing the biased westward extension of SSTA pattern. Our results show that the mean‐state performance of equatorial ocean currents plays a key role on simulations of El Niño evolution in CMIP6 models. Plain Language Summary El Niño is the warm phase of El Niño–Southern Oscillation, known as a coupled air–sea phenomenon with considerable interannual variability in the tropics. In recent decades, many climate models have been developed to help us better understand the potential dynamics of El Niño. This study emphasizes the role of dynamical processes related to ocean currents in affecting the behavior of El Niño patterns in a series of the latest released CMIP6 climate models. We find that models have a relatively large bias in simulating the equatorial ocean currents in the Pacific. With an extremely strong equatorial zonal current in mean‐state field, the maximum of zonal current anomalies tends to shift toward the equatorial western Pacific and enhances the corresponding oceanic feedback mechanism, which substantially contributes to the overestimated sea surface temperature anomalies during El Niño evolution. Key Points The Coupled Model Intercomparison Project Phase 6 (CMIP6) models simulate an excessive westward ocean current field over the equatorial central Pacific in the mean state Overestimated zonal advective feedback in the warm pool region is the dominant factor for the westward extension of El Niño pattern Mean‐state performance of equatorial ocean current field plays a key role on the simulations of El Niño evolution in CMIP6 models
Journal Article
Shear Band Formation in Thin-Film Multilayer Columns Under Compressive Loading: A Mechanistic Study
Micro-pillar compression is a popular experimental technique used for characterizing the mechanical behavior of nano- and micro-laminates. The compressive stress–strain response of the column-shaped thin-film composite can be measured, and the deformation and damage features can be revealed by post-test cross-section microscopy. The development of plastic instability in the form of localized strain concentration (shear bands), leading to eventual failure, is frequently observed. In the present study, a computational approach is used to illustrate the commonality of shear band formation from a continuum standpoint. Systematic finite element analyses are conducted, showing that the strain field tends to become localized once plastic yielding commences. Distinct shear offsets of the layered structure can be revealed from the numerical model, which is similar to those observed in experiments. The actual appearance of shear bands depends on the materials’ constitutive behavior and precise geometries. Post-yield strain hardening reduces the propensity of shear band formation, while strain softening enhances it. Imperfections such as the undulated layer geometry, as well as the frictional characteristics between the specimen and test apparatus, can also influence the shear band morphology and overall stress–strain response.
Journal Article
Direct numerical simulations of three-dimensional surface instability patterns in thin film-compliant substrate structures
A comprehensive numerical study of three-dimensional surface instability patterns is presented. The formation of wrinkles is a consequence of deformation instability when a thin film, bonded to a compliant substrate, is subject to in-plane compressive loading. We apply a recently developed computational approach to directly simulate complex surface wrinkling from pre-instability to post-instability in a straightforward manner, covering the entire biaxial loading spectrum from pure uniaxial to pure equi-biaxial compression. The simulations use embedded imperfections with perturbed material properties at the film-substrate interface. This approach not only triggers the first bifurcation mode but also activates subsequent post-buckling states, thus capable of predicting the temporal evolution of wrinkle patterns in one simulation run. The state of biaxiality is found to influence the surface pattern significantly, and each bifurcation mode can be traced back to certain abrupt changes in the overall load–displacement response. Our systematic study reveals how the loading condition dictates the formation of various instability modes including one-dimensional (1D) sinusoidal wrinkles, herringbone, labyrinth, and checkerboard.
Journal Article
Potential Processes of Two‐Phase AMOC Recovery After the Younger Dryas in the TraCE‐21K‐II Simulation
A two‐phase recovery of the Atlantic Meridional Overturning Circulation (AMOC) is revealed following the abrupt cessation of freshwater forcing (FWF) input at the end of the Younger Dryas in the TraCE‐21K‐II simulation. This staged AMOC reactivation is attributed to changes in sea surface salinity (SSS) pattern in the North Atlantic Ocean. The first recovery phase is mainly due to the termination of FWF; however, the increasing SSS through hemispheric‐scale northward transport of salty water is partially suppressed by melting water from high‐latitude regions, resulting in a subsequent oscillation in the AMOC strength. The second recovery phase is primarily linked to the sea ice retreat in the Greenland–Iceland–Norwegian Seas, which reinitiates the SSS transport through the Norwegian Current. Exploring such model characteristics in simulating the surface oceanic processes may improve our understanding of the AMOC's response to FWF.
Journal Article
Plasticity-mediated deformation instabilities in thin film-compliant substrate systems: direct three-dimensional simulations
Surface wrinkles driven by mechanical instability commonly form in thin-film structures attached to a compliant substrate. In this study, a recently developed computational approach is employed to simulate the formation and transformation of wrinkles involving plastic yielding of the thin film. The three-dimensional (3D) finite element models contain an embedded imperfection at the film-substrate interface, serving to trigger the bifurcation modes. Successful application of this technique to allow for film plasticity is demonstrated, including the evolution of 3D surface patterns and their correlation with the overall load–displacement response. The simulations reveal that plastic yielding transforms the surface instability patterns into more localized forms. Under uniaxial loading, the sinusoidal elastic wrinkles undergo the wrinkle-to-fold transition. With equi-biaxial loading, the initial square-checkerboard array turns into continuous tall ridges along the 45° directions. In both loading modes, the plasticity-induced instability patterns are only partially relieved upon unloading, leaving permanent features on the surface.
Journal Article
Prefabricated platinum nanomaterial matrix for MALDI-MS imaging of oligosaccharides and lipids in plant tissues
Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) can visualize the spatial distribution characteristics of molecules in tissues in situ, in which the matrix plays a key role. In this paper, we propose a platinum nanomaterial pre-coated matrix, which can be prepared in bulk by sputtering platinum nanoparticles onto slides using an ion sputterer and then used for MALDI-MS analysis by placing tissue sections on the matrix. We used this matrix for MALDI-MS imaging analysis of corn kernels and germinated wheat sections, and the results show that triacylglycerides were mainly distributed in the embryo of corn kernels and germinated wheat, and sugars were mainly distributed in the endosperm, with the highest content of disaccharides.It provides a simple and reliable experimental condition for analyzing the distribution of oligosaccharide and lipid components in plant tissues.
Journal Article