| 1. |
- Govindaraju, Indira, et al.
(författare)
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Microscopic and spectroscopic characterization of rice and corn starch
- 2020
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Ingår i: Microscopy research and technique (Print). - : John Wiley & Sons. - 1059-910X .- 1097-0029. ; 83:5, s. 490-498
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Tidskriftsartikel (refereegranskat)abstract
- Starch granules from rice and corn were isolated, and their molecular mechanism on interaction with alpha-amylase was characterized through biochemical test, microscopic imaging, and spectroscopic measurements. The micro-scale structure of starch granules were observed under an optical microscope and their average size was in the range 1-100 mu m. The surface topological structures of starch with micro-holes due to the effect of alpha- amylase were also visualized under scanning electron microscope. The crystallinity was confirmed by X-ray diffraction patterns as well as second-harmonic generation microscopy. The change in chemical bonds before and after hydrolysis of the starch granules by alpha- amylase was determined by Fourier transform infrared spectroscopy. Combination of microscopy and spectroscopy techniques relates structural and chemical features that explain starch enzymatic hydrolysis which will provide a valid basis for future studies in food science and insights into the energy transformation dynamics.
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| 2. |
- Habibi, Maryam, et al.
(författare)
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Corrosion resistance and surface microstructure of Mg 3 N 2 / SS thin films by plasma focus instrument
- 2022
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 85:8, s. 2880-2893
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing a plasma focus (PF) instrument, magnesium nitride (Mg3 N2 ) thin films were synthesized on stainless steel substrates. Twenty five optimum focus shots at 8 cm distance from the anode tip were used to deposit the films at different angular positions regarded to the anode axis. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analyses were performed to assess the surface morphology and structural characteristics of Mg3 N2 films. Based on AFM images, these films were studied to understand the effect of angular position variation on their surfaces through morphological and fractal parameters. By increasing the angle, we verify that the grain size decreased from 130(0) nm to 75(5) nm and also the mean quadratic surface roughness of the films reduced in its average values from (28.97 ± 3.24) nm to (23.10 ± 1.34) nm. Power spectrum density analysis indicated that films become more self-affine at larger angles. Furthermore, the corrosion behavior of the films was investigated through a potentiodynamic polarization test in H2 SO4 solution. It was found that the ion energy and flux, varying with the angular positions from the anode tip, directly affected the nanostructured roughness and surface morphology of the samples. The electrochemical studies of films show that the uncoated sample presented the lowest corrosion resistance. The highest corrosion resistance was obtained for the sample deposited with 25 optimum shots and at 0° angular position reaching a reduction in the corrosion current density of almost 800 times compared to the pure stainless steel-304 substrate.
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| 3. |
- Palisaitis, Justinas
(författare)
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Use of cleaved wedge geometry for plan-view transmission electron microscopy sample preparation
- 2021
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Ingår i: Microscopy research and technique (Print). - : Wiley-Blackwell. - 1059-910X .- 1097-0029. ; 84:12, s. 3182-3190
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Tidskriftsartikel (refereegranskat)abstract
- A fast, convenient, and easy to perform method for preparing plan-view transmission electron microscopy (TEM) specimens of brittle materials is proposed. The method is ideal for thin films/coatings and based on obtaining wedge-shape geometries of the samples via conventional cutting and cleaving followed by gentle focused ion beam (FIB) milling to electron transparency. It enables multiple parallel windows for depth sectioning of the samples and facilitates FIB lift-out procedure. The method has been successfully applied for preparing high-quality plan-view TEM samples for a range of films deposited on Si, SiC, and Al2O3 which significantly enhances throughput and reduces time at the FIB. The method further offers high success rate even for the novice, stable handling and reproducibility, which greatly widens the application of advanced plan-view TEM studies in material science.
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| 4. |
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| 5. |
- Tanner, Hugh, et al.
(författare)
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Labelling strategies for correlative light electron microscopy
- 2023
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Ingår i: Microscopy research and technique (Print). - : John Wiley & Sons. - 1059-910X .- 1097-0029. ; 86:8, s. 901-910
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Forskningsöversikt (refereegranskat)abstract
- Imaging is one of the key technologies underpinning discoveries in biomedical research. Each imaging technique however usually only provides a specific type of information. For instance, live-cell imaging using fluorescent tags can show us the dynamics of a system. On the other hand, electron microscopy (EM) gives us better resolution combined with the structural reference space. By applying a combination of light and electron microscopy modalities to a single sample one can exploit the advantages of both techniques in correlative light electron microscopy (CLEM). Although CLEM approaches can generate additional insights into the sample that cannot be gained by either technique in isolation, the visualization of the object of interest via markers or probes is still one of the bottlenecks in a Correlative Microscopy workflow. Whereas fluorescence is not directly visible in a standard electron microscope, gold particles, as the most common choice of probe for EM can also only be visualized using specialized light microscopes. In this review we will discuss some of the latest developments of probes for CLEM and some strategies how to choose a probe, discussing pros and cons of specific probes, and ensuring that they function as a dual modality marker.
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| 6. |
- Thore, Carl-Johan, 1981-, et al.
(författare)
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Game formulations for structural optimization under uncertainty
- 2020
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Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 121:1, s. 165-185
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Tidskriftsartikel (refereegranskat)abstract
- We consider structural optimization (SO) under uncertainty formulated as a mathematical game between two players -- a "designer" and "nature". The first player wants to design a structure that performs optimally, whereas the second player tries to find the worst possible conditions to impose on the structure. Several solution concepts exist for such games, including Stackelberg and Nash equilibria and Pareto optima. Pareto optimality is shown not to be a useful solution concept. Stackelberg and Nash games are, however, both of potential interest, but these concepts are hardly ever discussed in the literature on SO under uncertainty. Based on concrete examples of topology optimization of trusses and finite element-discretized continua under worst-case load uncertainty, we therefore analyze and compare the two solution concepts. In all examples, Stackelberg equilibria exist and can be found numerically, but for some cases we demonstrate nonexistence of Nash equilibria. This motivates a view of the Stackelberg solution concept as the correct one. However, we also demonstrate that existing Nash equilibria can be found using a simple so-called decomposition algorithm, which could be of interest for other instances of SO under uncertainty, where it is difficult to find a numerically efficient Stackelberg formulation.
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| 7. |
- Araujo-Cabarcas, Juan Carlos, 1981-, et al.
(författare)
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Shape optimization for the strong directional scattering of dielectric nanorods
- 2021
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Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 122:8, s. 3683-3704
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Tidskriftsartikel (refereegranskat)abstract
- In this project, we consider the shape optimization of a dielectric scatterer aiming at efficient directional routing of light. In the studied setting, light interacts with a penetrable scatterer with dimension comparable to the wavelength of an incoming planar wave. The design objective is to maximize the scattering efficiency inside a target angle window. For this, a Helmholtz problem with a piecewise constant refractive index medium models the wave propagation, and an accurate Dirichlet-to-Neumann map models an exterior domain. The strategy consists of using a high-order finite element (FE) discretization combined with gradient-based numerical optimization. The latter consists of a quasi-Newton (BFGS) with backtracking line search. A discrete adjoint method is used to compute the sensitivities with respect to the design variables. Particularly, for the FE representation of the curved shape, we use a bilinear transfinite interpolation formula, which admits explicit differentiation with respect to the design variables. We exploit this fact and show in detail how sensitivities are obtained in the discrete setting. We test our strategy for a variety of target angles, different wave frequencies, and refractive indexes. In all cases, we efficiently reach designs featuring high scattering efficiencies that satisfy the required criteria.
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| 8. |
- Auth, Kim Louisa, 1995, et al.
(författare)
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Modeling of environmentally assisted intergranular crack propagation in polycrystals
- 2023
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 124:23, s. 5183-5199
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline nickel-based superalloys experience accelerated intergranular crack growth when exposed to dwell times in oxygen-rich environments and a combination of high temperature and tensile mechanical loading. Increasing crack growth rates are observed for increasing amounts of environmental oxygen in a certain oxygen concentration range, while below and above that range crack growth rates remain approximately constant. A fully coupled chemo-mechanical modeling framework accounting for the degradation of grain boundaries by oxygen has been presented by the authors. In this work, we expand the framework by a moving boundary condition to capture a realistic oxygen flux in grain boundary cracks for both edge cracks connected to the environment and interior cracks. In numerical simulation results, the behavior of the moving boundary condition is shown for intergranular crack propagation through a polycrystal subjected to cyclic loading. Finally, the capabilities of the modeling framework to qualitatively predict the dependence of the average crack growth rate on the environmental oxygen content, load level, and dwell time are evaluated and it is shown that predictions qualitatively agree with experimental observations for intergranular fracture.
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| 9. |
- Ekre, Fredrik, 1992, et al.
(författare)
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A posteriori error estimation for numerical model reduction in computational homogenization of porous media
- 2020
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 121:23, s. 5350-5380
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Tidskriftsartikel (refereegranskat)abstract
- Numerical model reduction is adopted for solving the microscale problem that arizes from computational homogenization of a model problem of porous media with displacement and pressure as unknown fields. A reduced basis is obtained for the pressure field using (i) spectral decomposition (SD) and (ii) proper orthogonal decomposition (POD). This strategy has been used in previous work—the main contribution of this article is the extension with an a posteriori estimator for assessing the error in (i) energy norm and in (ii) a given quantity of interest. The error estimator builds on previous work by the authors; the novelty presented in this article is the generalization of the estimator to a coupled problem, and, more importantly, to accommodate the estimator for a POD basis rather than the SD basis. Guaranteed, fully computable and low-cost bounds are derived and the performance of the error estimates is demonstrated via numerical results.
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| 10. |
- Friemann, J., et al.
(författare)
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A micromechanics-based recurrent neural networks model for path-dependent cyclic deformation of short fiber composites
- 2023
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 124:10, s. 2292-2314
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Tidskriftsartikel (refereegranskat)abstract
- The macroscopic response of short fiber reinforced composites (SFRCs) is dependent on an extensive range of microstructural parameters. Thus, micromechanical modeling of these materials is challenging and in some cases, computationally expensive. This is particularly important when path-dependent plastic behavior is needed to be predicted. A solution to this challenge is to enhance micromechanical solutions with machine learning techniques such as artificial neural networks. In this work, a recurrent deep neural network model is trained to predict the path-dependent elasto-plastic stress response of SFRCs, given the microstructural parameters and the strain path. Micromechanical mean-field simulations are conducted to create a database for training the validating the model. The model gives very accurate predictions in a computationally efficient manner when compared with independent micromechanical simulations.
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