Microstructure evolution during sintering: discrete element method approach

We present a new numerical model describing the transformation of a powder of crystalline particles into a dense poly-crystalline material. It is based on the key phenomena of sintering: shrinkage and grain coarsening driven by the minimization of the free energy. Representing each grain by a truncated sphere, the model takes into account the complex and changing shape of grains for determining the thermodynamic driving forces and associated kinetic coefficients. We validate the model by comparing the temporal evolution of a system of four particles with that obtained from a mesh-based method. We performed simulations on polydisperse packings of up to 16,000 particles. Using material and process parameters from the literature, the model accurately reproduces experimental data on the evolution of the grain size distribution for alumina.     

23Na chemical shift imaging in the living rat brain using a chemical shift agent,Tm[DOTP]5–

Objective

It is well known that the use of shift reagents (SRs) in nuclear magnetic resonance (NMR) studies is substantially limited by an intact blood–brain barrier (BBB). The current study aims to develop a method enabling chemical shift imaging in the living rat brain under physiological conditions using an SR, Tm[DOTP]⁵⁻.

Materials and methods

Hyperosmotic mannitol bolus injection followed by 60 min infusion of a Tm[DOTP]⁵⁻ containing solution was administered via a catheter inserted into an internal carotid artery. We monitored the homeostasis of physiological parameters, and we measured the thulium content in brain tissue post mortem using total reflection fluorescence spectroscopy (T-XRF). The alterations of the ²³Na resonance spectrum were followed in a 9.4T small animal scanner.

Results

Based on the T-XRF measurements, the thulium concentration was estimated at 2.3 ± 1.8 mM in the brain interstitial space. Spectroscopic imaging showed a split of the ²³Na resonance peak which became visible 20 min after starting the infusion. Chemical shift imaging revealed a significant decrease of the initial intensity level to 0.915 ± 0.058 at the end of infusion.

Conclusion

Our novel protocol showed bulk accumulation of Tm[DOTP]⁵⁻ thus enabling separation of the extra-/intracellular ²³Na signal components in the living rat brain while maintaining physiological homeostasis.

     

Zinc Modulates Glutamine Metabolism in T Cells

Scope

Zinc and glutamine are well known to be essential for the function and polarization of immune cells. T_H17 cells are more frequently induced during zinc deficiency and cover their energy requirement mainly through glutaminolysis. A dysregulation of T_H17 cells can contribute to the development of autoimmune diseases. Both inhibition of glutaminolysis and zinc supplementation suppress experimental autoimmune encephalomyelitis in mice. Therefore, the aim of this study is to investigate whether zinc modulates glutaminolysis in T cells.

Methods and results

CD3/CD28 stimulation and mixed lymphocytes culture are used as in vitro models for T cell activation. Then, the glutaminolysis is investigated on mRNA, protein, and functional level. Zinc deficiency and glutaminase (GLS) inhibition decrease immune responses in vitro. Furthermore, extracellular zinc and glutamine levels both modulate glutaminolysis by changing the expression of glutamine transporters and key enzymes. Intriguingly, zinc directly interferes with the activity of GLS both in a cell free system and in the cytosol.

Conclusion

Besides T cell subset differentiation, zinc also impacts on the cellular metabolism by inhibiting glutaminolysis. This suggests that zinc deficiency can contribute to the development of autoimmune diseases whereas zinc supplementation can support their therapy.     

Kritische Einschätzung zum Stand des PVC-Recycling

A Critical Estimation of the PVC Recycling The aim of this paper is to give a view of the latest developments in the recycling of Poly(vinylchloride) (PVC), one of the most important plastics of our time. After a short survey concerning the technical importance of PVC and its outstanding properties, the volume of wast disposal expected in the future is considered in chapter 2. In chapter 3 a short review about the controversial environmental discussion concerning PVC is given. In chapter 4 the synthesis of the monomer vinylchloride and the processing of PVC are illustrated including trends in developing new systems for stabilization and to replace Cadmium stabilizators. After a short survey to the general possibilities for plastic recycling in chapter 5 the following chapters deal with the special processes for PVC recycling. Chapter 6 involves the chemical recycling that means the recovery of chlorine in form of HCl, whereas the material-recycling is represented in chapter 7, including the recycling of windows, tubes, coverings and sealing foils.     

Structure and properties of cerium phosphate and silicophosphate glasses

We report on the fabrication, properties, and structure of cerium pyrophosphate glasses and partially substituted cerium silicophosphates. In those glasses, cerium occurs predominantly as Ce(III). A combination of dynamic nuclear magnetic resonance and electrical impedance spectroscopy is used to overcome the problem of assessing cerium speciation. While optical spectroscopy is unable to quantify the ratio of Ce(III)/Ce(IV) due to spectral overlap, proxy observations of the effect of silica-for-cerium substitution on optical extinction and the shape and width of the UV band gap corroborate vibrational spectroscopic data of the structural roles of cerium and silica. While silica bonding to phosphate units appears to stabilize Ce(IV), it also impedes the polaron transport, leading to higher polaron activation energy and lower electronic conductivity. On the other hand, Ce(III) is stabilized by coordinating to P = O.     

The Influence of Zinc and Citrate on T Cell Activation and Differentiation in Mixed Lymphocyte Cultures

Scope

Zinc is important for a balanced immune system, but the mechanisms are not yet fully elucidated. One possibility is an interaction of zinc with the tricarboxylic acid cycle (TCA), in which zinc inhibits the mitochondrial aconitase leading to an increase in intracellular citrate concentration as described for prostate cells. Therefore, the immune modulatory effects of zinc and citrate and their interaction in mixed lymphocyte cultures (MLC) are studied.

Methods and results

After allogeneic (MLC) or superantigen stimulation, the interferon-γ (IFNγ) production is quantified by ELISA and T cell subpopulations are determined by Western Blot. Intracellular concentrations of citrate and zinc are measured. Zinc and citrate reduce the IFNγ expression and the pro-inflammatory T helper cells (Th) 1 and Th17 in MLC. While zinc increases regulatory T cells, citrate reduces them. After superantigen stimulation IFNγ production is decreased only by citrate but increased by zinc. Zinc does not affect citrate concentration, while citrate impairs zinc uptake. Thus, zinc and citrate independently regulate IFNy expression.

Conclusion

These results may explain the immunosuppressive effect of blood products anticoagulated by citrate. In addition, high citrate consumption may lead to immunosuppressive effects, so upper limits for citrate should be established.     

Spektroskopische Untersuchungen an Naphtho[1,2-d]thiazolen. II. Bandenanalyse der Absorptions- und Fluoreszenzspektren von 2-Aryl-naphtho[1,2-d]thiazolen

Spectroscopic Investigations on Naphtho[1.2-d]thiazoles. II. Deconvolution of Absorption and Fluorescence Spectra of 2-Aryl-naphtho[1.2-d]thiazoles Fluorescence measurements were carried out of organic fluorescent compounds of the type of 2-aryl-naphtho[1.2-d]thiazoles ( 1a–k ) substituted in the aryl group by different electronic donor and acceptor substituents. 2-Phenyl-naphtho[1.2-d]thiazole was used in the series of these compounds as the reference system for optical properties. A scheme of vibronic terms in ground and excited states resulting from the spectra of emission, ultraviolet absorption and excitation is given.     

Second-harmonic generation and structural rearrangements in multicomponent antimonite glasses by electrothermal poling

Electrothermal poling is shown here to effectively induce second-order nonlinear effects in heavy-metal oxide antimonite glasses. In M₂O–PbO–WO₃–Sb₂O₃ (M = Li, Na, K) glasses, the poling-induced second-harmonic generation intensity is five times larger than in silica (Infrasil) for M = Na, twice as large as in silica for M = Li, and smaller than in silica for M = K. X-ray photoelectron spectroscopy suggests that antimony ions exist predominantly in the trivalent oxidation state in the studied glass samples. Raman and infrared spectroscopy confirm that the glass network is comprised of SbO₃, WO₄, WO₆, and PbO₄ units—with some SiO₄ moieties due to leaching from the silica crucible. The WO₄ units appear to exist in two distinct sites, as evidenced by comparison of the vibrational spectra of alkali–tungsten–antimonite glasses with those of previously reported crystalline tungstate phases. The alkali type influences the equilibrium between tetrahedral tungstate anions, [WO₄]²⁻, and the isomeric partially polymerized octahedral tungstate units, [WØ₄O₂]²⁻ (Ø denotes a bridging oxygen). Raman spectroscopy line scans were used to track near-surface structural changes on the anode side of poled glasses. They reveal that the tungstate equilibrium is also affected by poling. At the anode side, the population of partially polymerized [WØ₄O₂]²⁻ species increases at the expense of anionic [WO₄]²⁻ species. This yields a net increase in the average bond length of the network forming constituents, which is commensurate with poling-induced structural changes observed in other systems experimentally and computationally.     

Neue Hybridinsuline mit synthetisch sequenzveränderten B-Ketten

New Hybrid Insulins with Synthetically Sequence-Modified B-chains The shortened and modified insulin-B-chain sequences B 4–30 (Ala 4) 1 , B 4–27 (Ala 4, Ala 27) 2 , B 1–27 (Ala 9, Ala 10, Ala 27) 3 , B 4–27 (Ala4, Ala 9, Ala 10, Ala 27) 4 and B 4–27(Ala 4, Val 6, Ala 9, Ala 10, Ala 27) 5 (¹) were synthesized in protected form, converted by deprotection and oxidative sulfitolysis into the S-sulfonates and combined with native insulin-A-chain-S-sulfonate to the corresponding hybrid insulins 6–10 . The biological activities indicate that distinct simplifications of the sequence in the region of the B-chain are tolerated relatively well.