Diffusion MRI and MRS of Skeletal Muscle

MR offers powerful tools to measure molecular diffusion in intact tissues under in vivo conditions. This review focuses on the use of diffusion-weighted MR imaging (DW-MRI) and spectroscopy (DW-MRS) to noninvasively study structural and functional aspects of skeletal muscle. It will be shown that DW-MRI allows for a high-resolution reconstruction of the orientation of the muscle fibers, which represents vital input for mathematical models of muscle biomechanics and an improved understanding of contractile dysfunction in muscle disease. DW-MRS can be used to quantitatively measure the translational displacement of endogenous metabolites in intact muscle. DW-MRS is of fundamental interest because it enables one to probe the in situ status of the intracellular space from the diffusion characteristics of the metabolites, while at the same time providing information on the intrinsic diffusion properties of the metabolites themselves. This yields information on cellular architecture and on the intrinsic capacity for diffusional mass transport.     

Group additive kinetic modeling for carbon‐centered radical addition to oxygenates and β‐scission of oxygenates

A consistent set of 32 group additive values is determined for the Arrhenius parameters of carbon‐centered radical addition to oxygenates and the reverse β‐scission of oxygenate compounds, covering a wide temperature range (300–2500 K). These values are derived based on a training set of 66 reactions for which the Arrhenius parameters are calculated using the CBS‐QB3 method in the high‐pressure limit, including corrections for hindered internal rotation. The accuracy of the model is established by comparing model predictions with an ab initio (AI) validation set containing 24 reactions. The mean factor of deviation between the group additively calculated and the AI rate coefficients is 3, for both radical additions and β‐scissions. Therefore, the developed group additive model, constituting an extension of the existing model for carbon‐centered radical additions and β‐scissions of hydrocarbons, can be safely applied for an accurate prediction of kinetics of the corresponding reactions involving oxygenate compounds. © 2015 American Institute of Chemical Engineers AIChE J, 62: 802–814, 2016     

Biosynthetic Origin of the Antibiotic Pseudopyronines A and B in Pseudomonas putida BW11M1

Within the framework of our effort to discover new antibiotics from pseudomonads, pseudopyronines A and B were isolated from the plant‐derived Pseudomonas putida BW11M1. Pseudopyronines are 3,6‐dialkyl‐4‐hydroxy‐2‐pyrones and displayed high in vitro activities against several human pathogens, and in our hands also towards the plant pathogen Pseudomonas savastanoi. Here, the biosynthesis of pseudopyronine B was studied by a combination of feeding experiments with isotopically labeled precursors, genomic sequence analysis, and gene deletion experiments. The studies resulted in the deduction of all acetate units and revealed that the biosynthesis of these α‐pyrones occurs with a single PpyS‐homologous ketosynthase. It fuses, with some substrate flexibility, a 3‐oxo‐fatty acid and a further unbranched saturated fatty acid, both of medium chain‐length and provided by primary metabolism.     

Robust beam compensation for laser-based additive manufacturing

Today’s software for laser-based additive manufacturing compensates for the finite dimensions of the laser spot by insetting the contours of a solid part. However, features having smaller dimensions are removed by this operation, which may significantly alter the structure of thin-walled parts. To avoid potential production errors, this work describes in detail an algorithmic framework that makes beam compensation more reliable by computing laser scan paths for thin features. The geometry of the features can be adjusted by the scan paths by means of five intuitive parameters, which are illustrated with examples. Benchmarks show that the scan path generation comes at a reasonable cost without altering the computational complexity of the overall beam compensation framework. The framework was applied to Selective Laser Melting (SLM) to demonstrate that it can significantly improve the robustness of additive manufacturing. Besides robustness, the framework is expected to allow further improvements to the accuracy of additive manufacturing by enabling a geometry-dependent determination of the laser parameters.     

Quantitative assessment of alkali-reactive aggregate mineral content through XRD using polished sections as a supplementary tool to RILEM AAR-1 (petrographic method)

The mineral content of 5 aggregate samples from 4 different countries, including reactive and non-reactive aggregate types, was assessed quantitatively by X-ray diffraction (XRD) using polished sections. Additionally, electron probe microanalyzer (EPMA) mapping and cathodoluminescence (CL) were used to characterize the opal-CT identified in one of the aggregate samples. Critical review of results from polished sections against traditionally powdered specimen has demonstrated that for fine-grained rocks without preferred orientation the assessment of mineral content by XRD using polished sections may represent an advantage over traditional powder specimens. Comparison of data on mineral content and silica speciation with expansion data from PARTNER project confirmed that the presence of opal-CT plays an important role in the reactivity of one of the studied aggregates. Used as a complementary tool to RILEM AAR-1, the methodology suggested in this paper has the potential to improve the strength of the petrographic method.     

Median Trajectories

We investigate the concept of a median among a set of trajectories. We establish criteria that a “median trajectory” should meet, and present two different methods to construct a median for a set of input trajectories. The first method is very simple, while the second method is more complicated and uses homotopy with respect to sufficiently large faces in the arrangement formed by the trajectories. We give algorithms for both methods, analyze the worst-case running time, and show that under certain assumptions both methods can be implemented efficiently. We empirically compare the output of both methods on randomly generated trajectories, and evaluate whether the two methods yield medians that are according to our intuition. Our results suggest that the second method, using homotopy, performs considerably better.