Consolidation of Al2O3/Al Nanocomposite Powder by Cold Spray

While the improvement in mechanical properties of nanocomposites makes them attractive materials for structural applications, their processing still presents significant challenges. In this article, cold spray was used to consolidate milled Al and Al₂O₃/Al nanocomposite powders as well as the initial unmilled and unreinforced Al powder. The microstructure and nanohardness of the feedstock powders as well as those of the resulting coatings were compared. The results show that the large increase in hardness of the Al powder after mechanical milling is preserved after cold spraying. Good quality coating with low porosity is obtained from milled Al. However, the addition of Al₂O₃ to the Al powder during milling decreases the powder and coating nanohardness. This lower hardness is attributed to non-optimized milling parameters leading to cracked particles with insufficient Al₂O₃ embedding in Al. The coating produced from the milled Al₂O₃/Al mixture also showed lower particle cohesion and higher amount of porosity.     

Measurement of the Interaction Between Recombinant I-domain from Integrin alpha 2 beta 1 and a Triple Helical Collagen Peptide with the GFOGER Binding Motif Using Molecular Force Spectroscopy

The role of the collagen-platelet interaction is of crucial importance to the haemostatic response during both injury and pathogenesis of the blood vessel wall. Of particular interest is the high affinity interaction of the platelet transmembrane receptor, alpha 2 beta 1, responsible for firm attachment of platelets to collagen at and around injury sites. We employ single molecule force spectroscopy (SMFS) using the atomic force microscope (AFM) to study the interaction of the I-domain from integrin alpha 2 beta 1 with a synthetic collagen related triple-helical peptide containing the high-affinity integrin-binding GFOGER motif, and a control peptide lacking this sequence, referred to as GPP. By utilising synthetic peptides in this manner we are able to study at the molecular level subtleties that would otherwise be lost when considering cell-to-collagen matrix interactions using ensemble techniques. We demonstrate for the first time the complexity of this interaction as illustrated by the complex multi-peaked force spectra and confirm specificity using control blocking experiments. In addition we observe specific interaction of the GPP peptide sequence with the I-domain. We propose a model to explain these observations.     

Fluorinated Pseudopeptide Analogues of the Neuropeptide 26RFa: Synthesis,Biological, and Structural Studies

A series of four fluorinated dipeptide analogues each containing a fluoro‐olefin moiety as peptide bond surrogate has been designed and synthesized. These motifs have been successfully introduced into the bioactive C‐terminal heptapeptide of the neuropeptide 26RFa by conventional SPPS. We then evaluated the ability of the generated pseudopeptides to increase [Ca²⁺]_i in GPR103‐transfected cells. For these fluorinated analogues, greater stability in human serum was observed. Their conformations were also investigated, leading to the valuable identification of differences depending on the position of the fluoro‐olefin moiety in the sequence.     

New thermosets obtained from bisphenol A diglycidyl ether and hydroxyl‐ended hyperbranched polymers partially blocked with benzoyl and trimethylsilyl groups

New epoxy thermosets with improved flexibility were prepared by chemical modification of bisphenol A diglycidyl ether (DGEBA) with hyperbranched polymers (HBPs). Hydroxyl‐ended hyperbranched polyesters were modified by blocking part of the hydroxyl groups with trimethylsilyl or benzoyl groups. The curing of mixtures of DGEBA with various proportions of two modified HBPs using ytterbium triflate as cationic initiator was investigated using differential scanning calorimetry and thermomechanical analysis. The characterization of these materials was performed using several thermal analysis techniques and their morphology was investigated using electron microscopy. High proportions of HBPs reduced the glass transition temperature and the relaxed storage modulus but barely affected gelation. The overall curing shrinkage was controlled by the content of hydroxyl groups and by the changes of HBP molecular interactions during curing. The results indicated that the relative proportion and type of terminal groups play a role in the evolution of the curing and the properties of the thermosets. Hydroxyl groups promoted the covalent incorporation of the HBP to the network via hydroxyl‐induced chain‐transfer reactions, whereas benzoyl groups promoted phase separation. Formulations containing HBP blocked with benzoyl groups showed two phases connected through covalent linkages between the HBP‐rich phase and the epoxy matrix. Copyright © 2010 Society of Chemical Industry     

Preemptive open shop scheduling with multiprocessors: polynomial cases and applications

This paper addresses a multiprocessor generalization of the preemptive open-shop scheduling problem. The set of processors is partitioned into two groups and the operations of the jobs may require either single processors in either group or simultaneously all processors from the same group. We consider two variants depending on whether preemptions are allowed at any fractional time points or only at integer time points. We reduce the former problem to solving a linear program in strongly polynomial time, while a restricted version of the second problem is solved by rounding techniques. Applications to course scheduling and hypergraph edge coloring are also discussed.     

Beschleunigter Sinkprozess fester Partikel bei laminarer und turbulenter Umströmung

Separation of particles is often designed based on the terminal settling velocity as separation parameter. Until now, the particle state of motion is described by solving the force balance equation numerically, which is highly complex. In this work, algebraic equations are presented, which describe the temporal changes of the setting velocity and the displacement at sinking in laminar and turbulent flows around the particle. These equations solely depend upon particle size, density and shape and are independent of the initial velocity. Using the characteristic values, the time period where a sufficient convergence to the terminal sinking velocity is reached, can be clearly identified.     

Characterization of MgAl2O4 Precursor Powders Prepared by Aqueous Route

MgAl₂O₄ spinel precursors have been prepared by two different aqueous synthesis routes: spray drying and citrate complexing. The spinel precursors exhibit different morphology and crystallization behavior. ²⁷Al high-resolution magic-angle spinning (MAS), multiple quantum MAS, and ²⁷Al-{¹H} rational echo double resonance (REDOR) nuclear magnetic resonance experiments, show that the spinel precursors have different aluminum local structures. ²⁷Al-{¹H} REDOR experiments detect Al_IV- and Al_V-bearing proton-free domains, possibly stabilized by residual carbonates, characteristic of the complexed precursor.     

Fenofibrate protects lipoproteins from lipid peroxidation: Synergistic interaction with α-tocopherol

One of the earliest steps of atherosclerotic plaque formation is an increase of circulating apolipoprotein B-containing lipoproteins which, after infiltrating the subendothelial space, undergo oxidative modification. Fenofibrate is an effective cholesterol- and triglyceride-lowering agent which has been shown to be beneficial in the treatment of atherosclerosis. Vitamin E, or α-tocopherol, is a powerful antioxidant which has been shown in a variety of studies to prevent lipoprotein peroxidation. The purpose of the present study was to investigate the effect of fenofibrate treatment, either alone or in combination with α-tocopherol, in reducing the susceptibility of lipoproteins to oxidative modification. Rats fed a normal diet were treated for up to 27 d with fenofibrate, either alone or in combination with equimolar doses of α-tocopherol. Combined VLDL (very low density lipoproteins) and LDL (low density lipoproteins) isolated after fenofibrate treatment were more resistant to coppermediated oxidation, as assessed by conjugated diene formation. Lag time was prolonged up to 3.2-fold, while the maximal rate of diene production was significantly decreased by up to 2.2-fold. Treatment of rats with α-tocopherol alone at the selected dose had no significant effect on lag time, while the propagation rate was slightly decreased. Coadministration of fenofibrate with α-tocopherol prolonged the lag phase to a greater extent than fenofibrate alone, showing a synergistic interaction between the two compounds. Finally, the combination of fenofibrate and α-tocopherol was significantly more effective in modifying lipoprotein oxidation parameters than what was observed with α-tocopherol and bezafibrate or gemfibrozil. Thus, in addition to its well-established effects on lipoprotein concentrations and atherogenic parameters, fenofibrate reduces the susceptibility of VLDL and LDL to oxidative modification and exerts its action synergistically with α-tocopherol.