Indeterminacy problems and the interpretation of factor analysis results

Abstract  This paper reviews indeterminacy problems for the factor analysis model and their consequences for the interpretation of the results. Two types of indeterminacy are discerned: indeterminacy of the parameters in the model (the number of factors, the specific variances and the factorloadings) and the indeterminacy of the factors, given the parameters in the model. It is argued that parameter indeterminacy is partly to be overcome, provided that a strong underlying theory for the subject matter under research is present. Factor indeterminacy remains a major stumbling‐block for the interpretation of results. The Guttman criterion is advocated as a measure of factor indeterminacy. Copyrigh

Under Pressure: A Laboratory Investigation into the Effects of Mechanical Loading on Charred Organic Matter in Archaeological Sites

The present publication investigates what happens to archaeological sites when they are built over. Focus is put on the degradation of charred organic materials by static loading. It is assumed that materials lose archaeological value if their fragments become too small to be recovered, or too distorted to be classified at species level. Several charred ecofacts of a few millimetres in size (wood fragments, hazelnut shells, and seeds) have been selected and subjected to individual particle strength tests. Assemblages of these particles have also been compressed one-dimensionally and scanned at several stages of testing using laboratory based X-ray microtomography. Microscopic damage by splitting or crushing is found to be limited at the macroscopic yield stress. It initiated at stresses less than 80 kPa for the weakest assemblages, and in all cases at stresses below 320 kPa. (80 kPa represents the load of a 6 m high sand embankment on soft soil that has half-settled underneath the groundwater table, while 320 kPa corresponds to stresses applied beneath the pile foundation level of high-rise buildings.) Sand seeded with charred particles has also been tested to illustrate the beneficial effect of embedment of charred particles in sand during static one dimensional loading

Quantum dots-labeled polymeric scaffolds for in vivo tracking of degradation and tissue formation

The inevitable gap between in vitro and in vivo degradation rate of biomaterials has been a challenging factor in the optimal designing of scaffold's degradation to be balanced with new tissue formation. To enable non-/minimum-invasive tracking of in vivo scaffold degradation, chemical modifications have been applied to label polymers with fluorescent dyes. However, the previous approaches may have limited expandability due to complicated synthesis processes. Here, we introduce a simple and efficient method to fluorescence labeling of polymeric scaffolds via blending with near-infrared (NIR) quantum dots (QDs), semiconductor nanocrystals with superior optical properties. QDs-labeled, 3D-printed PCL scaffolds showed promising efficiency and reliability in quantitative measurement of degradation using a custom-built fiber-optic imaging modality. Furthermore, QDs-PCL scaffolds showed neither cytotoxicity nor secondary labeling of adjacent cells. QDs-PCL scaffolds also supported the engineering of fibrous, cartilaginous, and osteogenic tissues from mesenchymal stem/progenitor cells (MSCs). In addition, QDs-PCL enabled a distinction between newly forming tissue and the remaining mass of scaffolds through multi-channel imaging. Thus, our findings suggest a simple and efficient QDs-labeling of PCL scaffolds and minimally invasive imaging modality that shows significant potential to enable in vivo tracking of scaffold degradation as well as new tissue formation

A generalized 3DLS-DEM scheme for grain breakage

We introduce a new generalized 3DLS-DEM (3D Level Set Discrete Element Method) scheme that incorporates grain breakage, taking an important step towards realistic modeling at the micro-scale with DEM. For the first time, simulating thousands of real 3D grains that are able to break, which was possible due to the algorithm used for grain breakage. The presented scheme is not only capable of efficiently simulating grains with real shapes but also preserving mass and grains morphology with high fidelity when breakage occurs. Hence, with this approach, further works within the original 3DLS-DEM scheme could take into account other physical phenomena at the grain-scale such as electrostatic induced cohesion, heat transfer, or the presence of a fluid, etc. On the other hand, the breakage process modified grain size and roundness distributions, which, in turn, might change the strength and critical state of the sample. Withal, the overall process seems to suggest that grain breakage may be a sufficient condition to exacerbate the prevalence of shear banding within the sample. Finally, our model is able to perform breakage on several real 3D grains of a sample consisting of thousands of grains in a generalized 3DLS-DEM scheme