The in vitro degradation behavior of poly-l-lactide (PLLA), PLLA/aragonite pearl powder and PLLA/vaterite pearl powder scaffolds was investigated. The scaffolds were soaked in phosphate buffer ...solution (PBS) up to 200days. Scanning electron microscopy (SEM), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were used to observe any degradation of the scaffolds. Degradation behaviors such as changes in pH, porosity, bulk density, water absorption, weight loss and mechanical properties were discussed. The results show that a gradual increase of the pH in composite scaffolds can decrease the rate of hydrolysis of PLLA. PLLA/vaterite and PLLA/aragonite scaffolds have a similar degradation behavior but a slower rate of degradation than PLLA.
•PLLA/pearl powder scaffolds release more Ca2+ than pearl powders in PBS.•Increase of pH in PLLA/pearl powder scaffolds declines the hydrolysis rate of PLLA.•PLLA/vaterite and PLLA/aragonite scaffolds show similar degradation behaviors.
The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin‐up and spin‐down neutrons. For polarized neutron reflectometry, this must be included in the ...reference potential energy of the Schrödinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin‐flip scattering) and so this additional potential is constant throughout the scattering region. When there is non‐collinear magnetization in the sample, however, there will be significant scattering from one spin state into the other, and the reference potentials will differ between the incoming and outgoing wavefunctions, changing the angle and intensities of the scattering. The theory of the scattering and recommended experimental practices for this type of measurement are presented, as well as an example measurement.
A procedure is described for polarized neutron reflectometry when the Zeeman corrections are significant, which occurs when both the magnetic anisotropy and the applied magnetic field are significant. Calculations and a recommended procedure for an example system are provided.
This study aims to determine an acquisitional and computational workflow that yields the highest quality spatio-spectral reconstructions in four-dimensional neutron tomography studies. The properties ...of neutrons enable unique image contrast modes, but accessing these modes requires defining the energy of the neutron beam, resulting in long acquisition times. We seek sparse angular tomography approaches to collect of order 100 tomograms at different neutron wavelengths using the minimum number of input projection images. In these computational image workflows, we identified and evaluated the main factors affecting the quality of the tomographic reconstruction such as the projection number, the reconstruction method, and the post-processing method and we report relationships between 3D reconstruction quality metrics and acquisition time. Based on these relationships, the performance of seeded simultaneous iterative reconstruction-based techniques (SIRT and SIRT with total variation regularization) yielded improved image quality and more accurate estimates of the reconstructed attenuation values compared to other methods, which included convolutional neural networks. The methods were then applied to a dose-reduced monochromatic dataset and characterized via signal-to-noise ratio (SNR) and single-voxel resolution.
Rietveld refinement of X‐ray and neutron diffraction patterns is routinely used to solve crystal and magnetic structures of organic and inorganic materials over many length scales. Despite its ...success over the past few decades, conventional Rietveld analysis suffers from tedious iterative methodologies, and the unfortunate consequence of many least‐squares algorithms discovering local minima that are not the most accurate solutions. Bayesian methods which allow the explicit encoding of a priori knowledge pose an attractive alternative to this approach by enhancing the ability to determine the correlations between parameters and to provide a more robust method for model selection. Global approaches also avoid the divergences and local minima often encountered by practitioners of the traditional Rietveld technique. The goal of this work is to demonstrate the effectiveness of an automated Bayesian algorithm for Rietveld refinement of neutron diffraction patterns in the solution of crystallographic and magnetic structures. A new software package, BLAND (Bayesian library for analyzing neutron diffraction data), based on the Markov–Chain Monte Carlo minimization routine, is presented. The benefits of such an approach are demonstrated through several examples and compared with traditional refinement techniques.
The implementation of Bayesian data analysis techniques for refinement of diffraction patterns is presented. The effectiveness of the method is shown through example refinements of a variety of neutron diffraction patterns from real materials.
In multilayer systems with exchange-coupled layers such as exchange-spring magnets, interfacial pinning can give rise to spiral domain walls and other complex magnetic structures that are sensitive ...to temperature, relative layer thicknesses, etc. Though these spin structures develop in subsurface layers, the depth-dependent magnetic profile can be fully characterized using polarized neutron reflectivity (PNR). In order to obtain the profile of the vector magnetization as well as the chemical composition, these data are typically analyzed using software in which the sample is described by a series of flat layers. This approach is cumbersome for continuously varying depth profiles, such as magnetic spirals, since the magnetic layers must be artificially subdivided to mimic the smooth changes in the vector magnetization. Thus, we have developed a flexible PNR fitting program in which users can specify a formula for the model (e.g., flat, power law, or piecewise polynomials). The program can easily be extended to handle simultaneous fitting of multiple data sets from measurements made with different techniques (such as PNR and X-rays) with constraints between the models.
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