Large amplitude oscillatory shear rheology of three different shear-thickening particle dispersions

We present a large amplitude oscillatory shear rheology (LAOS) investigation of three different shear-thickening particle dispersions - fumed silica in polyethylene oxide (FLOC), fumed silica in polypropylene glycol (HydroC), and cornstarch in water (JAM). These systems shear-thicken by three different mechanisms - shear-induced formation of particle clusters flocculated by polymer bridging, hydrocluster formation, and jamming. The viscoelastic non-linearities of the three fluids were studied as a function of strain and strain-rate space through the use of Lissajous-Bowditch curves and local nonlinear viscoelastic moduli of an oscillatory shear cycle. The nonlinear behaviors of the three fluids were compared and contrasted to understand the nonlinear shear-thickening mechanism of each. Both HydroC and JAM dispersions were found to exhibit strong strain stiffening of the elastic moduli and strain thickening of the loss moduli behavior associated with possible hydrocluster formation and particle jamming. However, the FLOC dispersion, in contrast, showed strong strain softening and strain thinning behavior at large strain amplitudes associated with yielding of the microstructure. The expected thickening of the loss modulus of FLOC in LAOS with increasing strain was not observed even though viscosity of FLOC was found to shear-thicken in steady-shear measurements. This disagreement is likely due to very large strain amplitudes required for shear-thickening to occur by shear-induced polymer bridging mechanism. The hypothesis was confirmed through stress growth experiments. Conversely, the HydroC and JAM dispersions required relatively small applied strains for shear-thickening to occur by hydrocluster and jamming mechanism. The comparison of local intra-cycle nonlinearity through Lissajous-Bowditch plots and nonlinear viscoelastic parameters indicated that the elastic nonlinearities of all three systems are primarily driven by a strong dependence on the magnitude of the applied strain-rates within an oscillatory cycle rather than the amplitude of the applied strain. A close inspection of the LAOS data reveals strong differences in the viscoelastic nonlinearities of these three different shear-thickening dispersions which can be used to create a nonlinear rheological fingerprint for each and offers valuable new insights into the nonlinear dynamics associated with each of the shear-thickening mechanisms.     

Mitochondrial BNIP3 upregulation precedes endonuclease G translocation in hippocampal neuronal death following oxygen-glucose deprivation

Background  

Caspase-independent apoptotic pathways are suggested as a mechanism for the delayed neuronal death following ischemic insult. However, the underlying signalling mechanisms are largely unknown. Recent studies imply the involvement of several mitochondrial proteins, including endonuclease G (EndoG) and Bcl-2/adenovirus E1B 19 kDa-interacting protein (BNIP3), in the pathway of non-neuronal cells.     

Optimization of the operational bandwidth in air-core photonic bandgap fibers for IR transmission

We determine the optimal inner glass ring thickness in infrared air-core photonic bandgap fibers (PBGFs) with 19-cell and 7-cell cores. For PBGFs with a 19-cell core, we find that an inner ring thickness of , where Λ is pitch, yields the widest operational bandwidth, which is nearly 6%. The operational bandwidth increases as the refractive index decreases from 2.8 to 2.0. For PBGFs with a 7-cell core, one needs to draw fiber with a ring thickness of less than to achieve a comparable operational bandwidth.     

An L2 model for selfadjoint elliptic differential operators with constant coefficients on bounded domains

The selfadjoint realization of a second order elliptic differential expression with Dirichlet boundary conditions is shown to be unitarily equivalent to the maximal multiplication operator with the independent variable in an explicit L² model space. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The proton‐transfer compounds of strychnine with achiral salicylic acids: strychninium 3,5‐dinitro­salicylate and the strychninium 5‐nitro­salicylate bis­(5‐nitro­salicylic acid) adduct

In the crystal structures of the proton‐transfer compounds of strychnine with 3,5‐dinitro­salicylic acid, namely strychninium 3,5‐dinitro­salicylate, C₂₁H₂₃N₂O₂⁺·C₇H₃N₂O₇⁻, (I), and 5‐nitro­salicylic acid, namely strychninium–5‐nitro­salicylate–5‐nitro­salicylic acid (1/1/2), C₂₁H₂₃N₂O₂⁺·C₇H₄NO₅⁻·2C₇H₅NO₅, (II), protonation of one of the N atoms of the strychnine mol­ecule occurs and this group is subsequently involved in inter­molecular hydrogen‐bonding inter­actions. In (I), this is four‐centred, the primary being with an adjacent strychninium carbonyl O‐atom acceptor in a side‐to‐side inter­action giving linear chains. Other inter­actions are with the phenolate and nitro O‐atom acceptors of the anionic species, resulting in a one‐dimensional polymer structure. In (II), the N⁺—H inter­action is three‐centred, the hydrogen bonding involving carboxyl O‐atom acceptors of the anion and both acid adduct species, giving unique discrete hetero‐tetramer units. The structure of (II) also features π‐bonding inter­actions between the two acid adduct mol­ecules.     

黄钾铁矾的生物合成与鉴定

利用氧化亚铁硫杆菌的生物催化氧化作用,在FeSO4—K2SO4—H2O体系中和常温常压条件下合成赭黄色的黄钾铁矾。借助SEM,XRD,FTIR,ICP—AES等方法对它的化学组成和结构进行了分析与表征。结果表明,Thiobacillus ferrooxidans休止细胞可在2天内将FeSO4-K2SO4-H2O体系中的Fe^2 全部氧化为Fe^3 ,Fe^3 在高浓度硫酸根、K^ 存在和酸性条件下水解生成赭黄色高铁沉淀,经鉴定为黄钾铁矾,其晶体粒径均匀,分散性好,且没有无定形的羟基硫酸高铁副产物。     

Enantiomerically enriched atropisomeric N,N′-diaryl ureas by oxidative kinetic resolution of their 2-sulfanyl derivatives

Atropisomeric N-methyl-N,N′-diaryl ureas may be obtained in enantiomerically enriched form by oxidative kinetic resolution of their sulfide derivatives. The atropisomeric sulfides may be obtained in up to 97:3 er and display high stability to racemisation (half-lives at 25 °C of up to 500 years). Unlike related fully alkylated ureas, the product sulfoxides exhibit relatively weak thermodynamic conformational selectivity.     

Sample temperatures during outdoor and laboratory weathering exposures

Effective exposure temperatures (T_eff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The T_eff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel T_eff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (E_a) of 21 kJ/mol (5 kcal/mol). T_eff was only weakly dependent on E_a over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have T_eff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample T_eff if the annual black panel T_eff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor T_eff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year.     

Novel spiro and fused heterocycles from the allylation of indigo

The allylation of indigo results in the one-step synthesis of two unique complex heterocyclic systems: a spiroindoline-pyridoindolone arising from the addition of three allyl moieties and a fused pyridoindolo-azepinoindolone generated from the addition and subsequent cyclisation of two allyl moieties. The structures of these novel heterocycles are assigned unambiguously using extensive NMR experiments and by X-ray crystallographic analysis. The distribution of the products is influenced by the use of thermal versus microwave heating.