Effect of grain size on the mechanisms of plastic deformation in wrought Mg–Zn–Zr alloy revealed by acoustic emission measurements

The present study has clarified the roles of dislocation slip and twinning as the deformation mechanisms in magnesium alloys, as well as the effect of grain size on their relative contributions. The details of these mechanisms were studied by monitoring acoustic emission (AE) in conjunction with a novel signal categorization technique in Mg alloy ZK60. Through the analysis of AE time series the sequences of predominant deformation mechanisms in coarse grained (～70 μm) and fine grained (～2 μm) specimens of the alloy were identified with a high degree of confidence. It was found that dislocation slip and twinning occur during tensile loading simultaneously for both microstructural states of the material, while a change from one predominant mechanism to the other occurs in the course of loading. Specifically, in the fine grained material plastic deformation is initially carried by dislocation slip, but deformation twinning takes over as the lead mechanism early on. In the coarse grained variant this sequence is reversed. The implications of the changing roles of the mechanisms of plastic deformation for the overall mechanical performance of ZK60 in the two contrasting microstructural states are discussed.     

A key intermediate in the platinum-mediated hydrodesulfurization of dibenzothiophene

The thiaplatinacycles, [PtL2(C,S–C₁₂ H₈S)] and [PtL₂(C,S–C₁₃H10S)] (L = PEt₃, PMe₃; L₂=Ph₂PCH₂ CH2PPh₂), obtained from oxidative insertion of [Pt⁰Ln] into dibenzothiophene and 4-methyldibenzothiophene are hydrodesulfurized by reaction with hydrogen (toluene, 20 atm, 100°C) to biphenyl and 3-methylbiphenyl, respectively; addition of acidic alumina improves the reaction. These observations link the model systems and the latest generation of commercial second-stage HDS catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Zinc Induced Aβ16 Aggregation Modeled by Molecular Dynamics

It is widely accepted that the addition of zinc leads to the formation of neurotoxic nonfibrillar aggregates of beta-amyloid peptides Aβ₄₀ and Aβ₄₂ and at the same time destabilizes amyloid fibrils. However, the mechanism of the effect of zinc on beta-amyloid is not fully understood. In this study, a fast zinc-induced aggregation of Aβ₁₆ (as compared to a system without zinc) via the formation of Aβ₁₆ dimers with one zinc ion coordinated in the metal-binding site ₁₁EVHH₁₄, followed by their polymerization, has been studied by molecular dynamics. The best aggregation was shown by the system composed of Aβ₁₆ dimers bound by one zinc ion, with no additional zinc in solution. The presence of Aβ₁₆ dimers was a major condition, sufficient for fast aggregation into larger complexes. It has been shown that the addition of zinc to a system with already formed dimers does not substantially affect the characteristics and rate of aggregation. At the same time, an excessive concentration of zinc at the early stages of the formation of conglomerates can negatively affect aggregation, since in systems where zinc ions occupied the ₁₁EVHH₁₄ coordination center and the His6 residue of every Aβ₁₆ monomer, the aggregation proceeded more slowly and the resulting complexes were not as large as in the zinc-free Aβ system. Thus, this study has shown that the formation of Aβ₁₆ dimers bound through zinc ions at the ₁₁EVHH₁₄ sites of the peptides plays an important role in the formation of neurotoxic non-fibrillar aggregates of beta-amyloid peptide Aβ₁₆. The best energetically favorable structure has been obtained for the complex of two Aβ₁₆ dimers with two zinc ions.     

高分辨率X射线衍射光学元件

评述了BESSY研制的用于X射线聚焦的各种衍射光学元件。基于布拉格-菲涅耳光学元件,设计了高效高分辨率X射线聚焦和色散光学元件。描述了对长焦距布拉格-菲涅耳透镜与可变曲率半径反射镜组合所做的实验研究。用一块反射菲涅耳波带板作聚焦和色散光学元件进行了短脉冲X射线吸收谱(XAS)的测量。     

Canrenone Restores Vasorelaxation Impaired by Marinobufagenin in Human Preeclampsia

Previous studies implicated cardiotonic steroids, including Na/K-ATPase inhibitor marinobufagenin (MBG), in the pathogenesis of preeclampsia (PE). Recently, we demonstrated that (i) MBG induces fibrosis in rat tissues via a mechanism involving Fli1, a negative regulator of collagen-1 synthesis, and (ii) MBG sensitive Na/K-ATPase inhibition is reversed by mineralocorticoid antagonists. We hypothesized that in human PE elevated MBG level is associated with the development of fibrosis of the umbilical arteries and that this fibrosis can be attenuated by canrenone. Fifteen patients with PE (mean BP = 118 ± 4 mmHg; 34 ± 2 years; 38 ± 0.3 weeks gest. age) and twelve gestational age-matched normal pregnant subjects (mean BP = 92 ± 2 mmHg; 34 ± 1 years; 39 ± 0.2 weeks gest. age) were enrolled in the study. PE was associated with a higher plasma MBG level, with a four-fold decrease in Fli1 level and a three-fold increase in collagen-1 level in the PE umbilical arteries vs. those from the normal subjects (p < 0.01). Isolated rings of umbilical arteries from the subjects with PE exhibited impaired responses to the relaxant effect of sodium nitroprusside vs. control vessels (EC₅₀ = 141 nmol/L vs. EC₅₀ = 0.9 nmol/L; p < 0.001). The effects of PE on Fli1 and collagen-1 were blocked by the in vitro treatment of umbilical arteries by 10 μmol/L canrenone. Similar results were obtained for umbilical arteries pretreated with MBG. These data demonstrate that elevated MBG level is implicated in the development of the fibrosis of umbilical arteries in PE, and that this could be blocked by mineralocorticoid antagonists.     

Silver Cluster Interactions with Tyrosine: Towards Amino Acid Detection

Tyrosine (Tyr) is involved in the synthesis of neurotransmitters, catecholamines, thyroid hormones, etc. Multiple pathologies are associated with impaired Tyr metabolism. Silver nanoclusters (Ag NCs) can be applied for colorimetric, fluorescent, and surface-enhanced Raman spectroscopy (SERS) detection of Tyr. However, one should understand the theoretical basics of interactions between Tyr and Ag NCs. Thereby, we calculated the binding energy (E_b) between Tyr and Ag_n^q (n = 1–8; q = 0–2) NCs using the density functional theory (DFT) to find the most stable complexes. Since Ag NCs are synthesized on Tyr in an aqueous solution at pH 12.5, we studied Tyr⁻¹, semiquinone (SemiQ⁻¹), and Tyr⁻². Ag₃²⁺ and Ag₅⁺ had the highest E_b. The absorption spectrum of Tyr⁻² significantly red-shifts with the attachment of Ag₃²⁺, which is prospective for colorimetric Tyr detection. Ag₃²⁺ interacts with all functional groups of SemiQ⁻¹ (phenolate, amino group, and carboxylate), which makes detection of Tyr possible due to band emergence at 1324 cm⁻¹ in the vibrational spectrum. The ground state charge transfer between Ag and carboxylate determines the band emergence at 1661 cm⁻¹ in the Raman spectrum of the SemiQ⁻¹–Ag₃²⁺ complex. Thus, the prospects of Tyr detection using silver nanoclusters were demonstrated.     

The boundary layer interaction with shock wave and expansion fan

IntrotcttonThe hypersonic bounce layer develOPment and itsstrUctUre under the influence of distUrbing factorsPresent one of the most complicated problems of fluidmechanics. Such captors affechng the boundal layer arethe adverse andlor favoUrable Pressure gradient,roughness, gas mjechon, cooling, etc. A speCific case ofthis Problem is the study of the flow with successiveimpact of pressure gradients on the bounce layer.Though these factors are intensely stUdied, the queshonof their joint e…     

Antenna Selection for MIMO–OFDM WLAN Systems

This paper discusses the packet error rate (PER) performance of multiple-input multiple-output (MIMO) wireless systems. We focus our discussion on communication systems based on the IEEE 802.11a/g standard. In particular, we study the performance of spatial multiplexing systems with joint encoding at the transmitter and linear detection at the receiver. We show that spatial multiplexing systems based on minimum mean square error (MMSE) or zero forcing (ZF) demultiplexing benefit greatly from antenna subset selection. These results agree with recent analytical results showing the equivalence in diversity order between a full system (all receive antennas) and a system with antenna selection.     

Folding of chains with random and edited sequences: similarities and differences

We have investigated the process of protein folding by Monte-Carlosimulation of folding occurring in a simple 3D lattice modelof a protein globule. We have found the range of ‘optimal’temperatures where the native fold is achieved by the Monte-Carloprocess much faster than that by exhaustive sorting of all thechain folds. The ‘optimal’ temperatures are essentiallythe same for different random and lsquo;edited’ sequences(for the latter, the native fold energy is separated by a considerablegap from the energies of other low-energy folds; for randomsequences, this gap is negligible). At the ‘optimal’temperatures, the ‘edited’ chains attain their nativefold faster than the random ones. However, the essence is thatthe native folds of ‘edited’ chains are thermodynamicallystable at temperatures optimal for fast folding, while the nativefolds of random chains are unstable at the temperatures optimalfor fast folding; also, at low temperatures where the nativefolds of random chains are stable, folding kinetics is veryslow. Consequently, stable native folds are formed slowly byrandom sequences and rapidly by the ‘edited’ ones