Evaluation of the Growth of Dislocations Density in Fatigue Loading Process via Electrical Resistivity Measurements

The paper focuses on quantitative evaluation of the microstructural changes - growth of the dislocation density - in stainless steel specimens subjected to fatigue loading. We propose to use electrical resistivity measurements for this goal. Change in electrical resistance of the specimens has been monitored in dependence on the number of fatigue cycles and the relative growth of the dislocation density was calculated from these data and known values of the specific resistivity of dislocations for iron. We also estimated the growth of dislocation density using analysis of Scanning Electron Microscopy (SEM) images of etched specimens. This estimate however appears to be unreasonably low, so that SEM may be used for qualitative analysis only.     

Magnetotransport Properties and Electronic Structure of Ni 8 1 Fe 1 9 /W 9 0 Ti 1 0 Multilayers

The magnetotransport properties of Ni₈₁Fe₁₉/W₉₀Ti₁₀ multilayers are investigated. The effect of the thicknesses of magnetic (Ni₈₁Fe₁₉) and nonmagnetic (WTi) layers on the magnetoresistance (MR) is theoretically discussed in the framework of the Johnson–Camley semiclassical approach based on the Boltzmann transport equation. A comparison between the calculated and measured MR ratios is obtained. The observed MR ratio oscillates for WTi layer thickness with an average period of 10 Å. A weak MR(t_NiFe) ratio for a fixed t_WTi is obtained, and it presents a maximum peak of the MR with a value of 0.8 % located at t_NiFe = 50 Å. In addition, electronic and magnetic properties of multilayers are investigated by self-consistent ab initio calculations based on the Korringa–Kohn–Rostocker (KKR) approximation. Spin polarized within the framework of the coherent potential approximation (CPA) is considered for calculations.     

Synthesis and characterization of polysiloxanes with pendant bicyclic fragments

Transparent poly vinyl alcohol (PVA) based coatings with antimicrobial activity against a wide range of microorganisms have been prepared. The films have been prepared by spincoating a mixture of PVA, ammonium dichromate and metal (zinc or silver) precursor from water solutions, and then rendered insoluble by crosslinking under UV illumination. Antimicrobial activity has been tested against different bacteria and fungi, such as Bacillus atrophaeus, Bacillus megaterium, Staphylococcus aureus, Enterococcus faecium, Pseudomonas aeruginosa, Salmonella enterica, Escherichia coli, Neurospora crassa, and Saccharomyces cerevisiae. It was found that combining the zinc and silver precursors resulted in films which had excellent antimicrobial activity and at the same time exhibited superior environmental stability compared to films containing prepared with single metal precursor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

La1−xSrxFe0.7Ni0.3O3−δ as both cathode and anode materials for Solid Oxide Fuel Cells

La_1?xSr_xFe_0.7Ni_0.3O_3?δ (x = 0, 0.1 and 0.2, LSFNx) are investigated as both cathode and anode materials for Solid Oxide Fuel Cells (SOFCs). The structure, microstructure and electrochemical properties of these materials are studied under oxidizing and reducing atmospheres. In air, the electrodes exhibit polarization resistance of 0.1 Ωcm² at 800 °C under open circuit voltage. In a H₂ atmosphere, Ni nanoparticles are exsolved on the surface, leading to a polarization resistance as low as 0.06 Ωcm². A cell with a 350 μm thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_3?δ electrolyte and LSFN electrodes generates a power output of 540 mWcm^?2 at 800 °C. Moreover, stable values of power density are obtained after successive oxidation/reduction cycles, confirming the reversibility of the electrodes.     

Enhancement of heat transfer from hot water by co-flowing it with mercury in a mini-channel

The present study is a numerical investigation on the flow and heat transfer in a mini-channel where both hot liquid water and mercury co-flow together in a direct contact manner. Results show that the presence of a high thermal conductivity liquid metal such as mercury enables the hot water to lose much more of its initial thermal energy content, than when only water alone flows in the channel. However, too unjustified excessive mercury co-flowing with the hot water can lead to adverse effects in regards to the heat loss from the hot water. The reason behind the enhanced heat transfer between the two liquids is due to the initiation of high temperature gradients sites inside the channel, especially in the region of the interface between the two liquids, in addition to the high thermal conductivity of mercury, as compared to water thermal conductivity. These two effects lead to effective conduction cooling in the transverse direction over the whole length of the channel. These aspects are quantified in this study.     

Synthesis of thermoreactive polysiloxanes with cyclic fragments in the side chain

The synthesis of polysiloxanes with pendant unsaturated cyclic fragments have been successfully performed by hydrosilylation reactions of polymethylhydrosiloxane with 4‐vinyl‐1‐cyclohexene in the presence of platinum hydrochloric acid (0.1 M solution in THF), Karstedt's catalyst (Pt₂[(VinSiMe₂)₂O]₃) and platinum on the charcoal (5%). Reactions were carried out at various temperatures with different ratios of initial compounds. It was shown, that not all active ≡Si? H groups take part in the hydrosilylation reaction. Some kinetic parameters of reactions were studied. The synthesized oligomers were characterized by FTIR, ¹H, ¹³C, H,H‐COSY, and C,H‐correlation NMR spectroscopy. Calculations using the quantum‐chemical semi empirical AM1 method for modeling reactions between methyldimethoxysilane [Me(MeO)₂SiH] and 4‐vinyl‐1‐cyclohexene were performed to evaluate possible reaction paths. Synthesized oligomers were characterized by gel‐permeation chromatography, differential scanning calorimetric, thermogravimetric, and wide‐angle X‐ray analyses. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Accelerant‐promoted free radical polymerization of methacrylates by stabilized nitroxide unimolecular initiators: synthesis and characterization

BACKGROUND: This investigation evaluates the effectiveness of initiator adducts for living and controlled polymerization of methacrylates, crosslinking of dimethacrylates and thermal stabilities of the resulting polymers. Adducts of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy with benzoyl peroxide and with azobisisobutyronitrile were prepared and evaluated as stabilized unimolecular initiators for the free radical polymerization of methacrylate monomers using sulfuric acid as catalyst. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Successful polymerization was achieved at 70 and 130 °C with reaction times ranging from 45 min to 120 h. The dispersity (D) of poly(methyl methacrylate) (PMMA) was 1.09–1.28. The livingness and extent of control over polymerization were confirmed with plots of M_n evolution as a function of monomer conversion and of the first‐order kinetics. The glass transition temperature (T_g) for PMMA was 123–128 °C. The degradation temperature (T_d) for PMMA was 350–410 °C. T_d for poly(TEGMA) was 250–310 °C and for poly(EBPADMA) was 320–390 °C. CONCLUSION: The initiators are suitable for free radical living and controlled polymerization of methacrylates and dimethacrylates under mild thermal and acid‐catalyzed conditions, yielding medium to high molecular weight polymers with low dispersity, high crosslinking and good thermal stability. Copyright © 2008 Society of Chemical Industry     

Local transverse arch repair for type A aortic dissection

BACKGROUND: The management of retrograde dissections originating from the transverse arch is controversial. Although replacing the ascending aorta is clearly beneficial, the appropriate approach to the management of the arch tear is not as apparent and ranges from no intervention to total arch replacement. METHODS: Three patients presented with acute (n = 2) or subacute (n = 1) aortic dissection, with tears involving the transverse arch. All underwent local transaortic pledgeted suture repair of the arch tears during hypothermic circulatory arrest, as well as graft replacement of the ascending aorta. RESULTS: Circulatory arrest times ranged from 12 to 15 minutes (transaortic arch repairs alone) to 48 minutes (transaortic arch repair and open distal graft anastomosis). Postoperatively all patients awoke within 12 hours and subsequently did well neurologically. CONCLUSIONS: In the face of a type A dissection with an entry in the transverse arch, local transaortic repair with concomitant ascending aortic replacement represents a viable middle ground between no arch intervention and lengthy arch replacement. Huge entry tears or aneurysmal arch enlargement would preclude such an approach.