EPMA and GDOES in Functional-Gradient Hardmetal Systems

 WDS-EPMA and GDOES measurements were applied for the characterization of the in-situ surface modification process of (Ti, W)C-based hardmetals by in-diffusion of carbon and nitrogen leading to complicated microstructures composed by layers and/or gradients. The calibration of the analytical techniques was performed with chemically characterized specimens prepared by diffusional techniques or hot-pressing. In addition, for the GDOES method, certified reference materials (CRMs) have been used. The work was started from a re-investigation of the W-C and Mo-C systems in order to measure homogeneity regions of the various phases prepared by use of diffusion couples. Subsequently, the metal and non-metal contents of various sequences of layers and/or gradients in functional-gradient hardmetals (FGHs) were measured. Both methods were employed as complementary tools to get information about the element-concentration distribution in FGHs so that a better understanding of the influence of process parameters for fabrication of special hardmetals is possible.     

Covariance-Guided Mixture Probabilistic Principal Component Analysis (C-MPPCA)

To extract information from high-dimensional data efficiently, visualization tools based on data projection methods have been developed and shown useful. However, a single two-dimensional visualization is often insufficient for capturing all or most interesting structures in complex high-dimensional datasets. For this reason, Tipping and Bishop developed mixture probabilistic principal component analysis (MPPCA) that separates data into multiple groups and enables a unique projection per group; that is, one probabilistic principal component analysis (PPCA) data visualization per group. Because the group labels are assigned to observations based on their high-dimensional coordinates, MPPCA works well to reveal homoscedastic structures in data that differ spatially. In the presence of heteroscedasticity, however, MPPCA may still mask noteworthy data structures. We propose a new method called covariance-guided MPPCA (C-MPPCA) that groups subsets of observations based on covariance, not locality, and, similar to MPPCA, displays them using PPCA. PPCA projects data in the dimensions with the highest variances, thus grouping by covariance makes sense and enables some data structures to be visible that were masked originally by MPPCA. We demonstrate the performance of C-MPPCA in an extensive simulation study. We also apply C-MPPCA to a real world dataset. Supplementary materials for this article are available online.     

Stereoselective Synthesis of a Tetrameric Fragment of Streptococcus Pneumoniae Type 1 Containing an α-Linked 2-Acetamido-4-amino-2,4,6-trideoxy-D-galactopyranose (SUGp) Unit

Abstract

Block condensation of fully protected donor ethyl 1,2,3,4-tetra-O-benzyl-D-Rib-(5→P→6)-2,3,4-tri-O-benzoyl-l-thio-β-D-Glcp (2), having a (5→6)-phosphotriester union between the ribitol and the glucopyranosyl moieties, with the free 3′-OH group in the acceptor methyl 2-acetamido-4-O-(2-acetamido-4-(benzyloxycarbonyl)amino-2,4,6-trideoxy-α-D-Galp)-3,6-di-O-benzyl-2-deoxy-α-D-Galp (3), under the agency of N-iodosuccinimide and triflic acid, gave the fully protected tetrameric fragment 22. Elimination of the 2-cyanoethyl group from the phosphotriester and subsequent debenzoylation, followed by hydrogenolysis of the benzyl and benzyloxycarbonyl groups provided the target tetramer methyl D-Rib-(5→P→6)-D-Glcp-β(1→3)-Sugp-α(1→4)-α-D-GalpNAc (1).     

Iodonium-Ion Assisted Stereospecific Glycosylation: Synthesis of Oligosaccharides Containing α(1-4)-Linked L-Fucopyranosyl Units

ABSTRACT

The terminal glycosyl acceptor methyl 2,3-di-O-benzyl-α-L-fucopyranoside (6) was extended three times with the non-terminal glycosyl donor ethyl 4-O-acetyl-2,3-di-O-benzyl-1-thio-ß-L-fucopyranoside (13) via iodonium-ion assisted glycosylations and intermittent removal of the C-4 acetyl group in intermediate dimer 16 and trimer 18. The 4-O-acetyl group in trimer 18 and tetramer 20 was highly resistant towards basic hydrolysis. The latter could be nullified by using dichloroacetyl instead of acetyl to protect the C-4-OH in the donor. The exclusive formation of 1,2-cis-linked oligomers could be explained by through-bond interactions exerted by the electron-withdrawing C-4 acyl group in the glycosyl donor.     

Ditopic halogen bonding with bipyrimidines and activated pyrimidines

The potential of pyrimidines to serve as ditopic halogen‐bond acceptors is explored. The halogen‐bonded cocrystals formed from solutions of either 5,5′‐bipyrimidine (C₈H₆N₄) or 1,2‐bis(pyrimidin‐5‐yl)ethyne (C₁₀H₆N₄) and 2 molar equivalents of 1,3‐diiodotetrafluorobenzene (C₆F₄I₂) have a 1:1 composition. Each pyrimidine moiety acts as a single halogen‐bond acceptor and the bipyrimidines act as ditopic halogen‐bond acceptors. In contrast, the activated pyrimidines 2‐ and 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine (C₁₄H₁₃N₃) are ditopic halogen‐bond acceptors, and 1:1 halogen‐bonded cocrystals are formed from 1:1 mixtures of each of the activated pyrimidines and either 1,2‐ or 1,3‐diiodotetrafluorobenzene. A 1:1 cocrystal was also formed between 2‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene, while a 2:1 cocrystal was formed between 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene.     

Synthesis of the C-13 side chain precursors of the 9-dihydrotaxane analogue ABT-271

N-Boc-L-Leucinol was converted to two C-13 side chain precursors of the 9-dihydrotaxane analogue ABT-271. The trans-oxazolidine acid 4 and the cis-Boc-lactam 2b were prepared in 44% and 40% overall yield, respectively, and with excellent (>98%) stereochemical purity.     

More Efficient Parallel Totally Monotone Matrix Searching

We give a parallel algorithm for computing all row minima in a totally monotonen × nmatrix which is simpler and more work efficient than previous polylog-time algorithms. It runs inO(lg n lg lg n) time doingwork on aCRCW PRAM, inO(lg n(lg lg n)²) time doingwork on aCREW PRAM, and intime doingwork on anEREW PRAM. Since finding the row minima of a totally monotone matrix has been shown to be fundamental in the efficient solution of a host of geometric and combinatorial problems, our algorithm leads directly to improved parallel solutions of many algorithms in terms of their work efficiency.