Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

The synthesis of 11a-carbathromboxane A2

The chemically stable thromboxane analog 11a-carbathromboxane A₂ ($\text{1}$) was synthesized from PGA₂ in 12 steps. 11a-Carba-TXA₂ inhibits PGH₂-induced aggregation of human platelets.     

Dynamics of self-assembled chaining in magnetorheological fluids

The aggregation dynamics of paramagnetic spherical particles embedded in a viscous fluid is investigated via numerical simulations using a fully coupled three-dimensional model. Particles experience simultaneously Brownian motion, dipolar magnetic attraction, and multibody hydrodynamic interactions. When the dipole strength characterizing the ratio of magnetic attraction to random diffusion exceeds a critical value, particles join together forming supraparticle structures. As time evolves, particle/chain and chain/ chain interactions lead to a continuous increase of the cluster size. The mean length of particle chains has a power-law dependence with respect to time, as predicted by the theory of diffusion-limited aggregation. Both the exponent and the characteristic time scale agree very well with the experimental results of Promislow et al.     

Microbial liquefaction of lignite pretreated with dilute acid at elevated temperature and pressure

Two microbial cultures—ML-13 (aCandida sp.) and LSC (a fungal isolate from the University of Arkansas)—have been employed in the direct liquefaction of Louisiana lignite. Lignite samples were pretreated with nitric acid and microbial culture broths at elevated temperatures and pressures. Subsequent treatment with active cultures and culture derivatives resulted in significant solubilization of the lignite. Up to 50% liquefaction of pretreated coal (20% HNO₃ at ambient temperature and pressure) was observed in 4 d with ML-13 cultures, whereas almost 80% liquefaction occurred in a similar time period when exposing pretreated lignite to an autoclaved, cell-free culture broth.     

Modulation of homogeneous turbulence seeded with finite size bubbles or particles

The dynamics of homogeneous, isotropic turbulence seeded with finite sized particles or bubbles is investigated in a series of numerical simulations, using the force-coupling method for the particle phase and low wavenumber forcing of the flow to sustain the turbulence. Results are given on the modulation of the turbulence due to massless bubbles, neutrally buoyant particles and inertial particles of specific density 1.4 at volumetric concentrations of 6%. Buoyancy forces due to gravity are excluded to emphasize finite size and inertial effects for the bubbles or particles and their interactions with the turbulence. Besides observing the classical entrapment of bubbles and the expulsion of inertial particles by vortex structures, we analyze the Lagrangian statistics for the velocity and acceleration of the dispersed phase. The turbulent fluctuations are damped at mid-range wavenumbers by the bubbles or particles while the small-scale kinetic energy is significantly enhanced. Unexpectedly, the modulation of turbulence depends only slightly on the dispersion characteristics (bubble entrapment in vortices or inertial sweeping of the solid particles) but is closely related to the stresslet component (finite size effect) of the flow disturbances. The pivoting wavenumber characterizing the transition from damped to enhanced energy content is shown to vary with the size of the bubbles or particles. The spectrum for the energy transfer by the particle phase is examined and the possibility of representing this, at large scales, through an additional effective viscosity is discussed.     

Role of polyethyleneimine in the purification of recombinant human tumour necrosis factor beta

The chromatographic behaviour of recombinant human tumour necrosis factor beta (rhTNF-β) (pI9.0) during cation-exchange chromatography at pH 7.5 is investigated. Without prior treatment of the Escherichia coli cell extract with polyethyleneimine (PEI), very little rhTNF-β was bound to the column. However, upon addition of 5% PEI (100 μl ml⁻¹) to the cell lysate, rhTNF-β was shown to bind to cation-exchange columns normally. TNF-β was readily precipitated from the clarified cell extract by 20% ammonium sulphate, but only ca. 25% of this precipitate could be re-solubilized for further purification. However, when 5% PEI was included in the solubilization buffer, the balance of the rhTNF-β could be recovered. It is proposed that charge interaction between rhTNF-β and nucleic acids in the cell extract is responsible for both of these anomalous phenomena, and that PEI (a cationic polyelectrolyte) was able to disrupt this interaction by displacing rhTNF-β from the charge complex.     

Interactions of particles and microbubbles with turbulence

Dilute, dispersed two-phase flows arise in many contexts ranging from solid particles or droplets in gas flows to bubbles in liquids. Many of the flows of interest are turbulent, which presents a complex problem to analyze or to determine the dominant physical processes contributing to the observed phenomena. Advances in experimental techniques have made it possible to measure directly turbulent and particle velocity fluctuations in dilute systems. This has provided a counterpart to advances in computational and analytical models and a basis on which to test these models. Three specific areas are considered: the fluctuating forces on an individual particle in an unsteady flow, the response of a solid particle to a turbulent air flow, and the corresponding response of a small bubble in turbulent liquid flows. Results from direct numerical simulations are presented for each of these, including the nonuniform distribution of particles generated by local instantaneous features of the flow. The issue of turbulence modulation at low to moderate void fractions is discussed.     

"Proteomineering" serum biomarkers. A study in scarlet

The performance of sera pre-treatment for biomarker searching via combinatorial peptide ligand libraries (CPLL) has recently been challenged (Proteomics 2010, 10, 1416-1425) and stated to allow discovery of only medium to high-abundance proteins. We have thus investigated four elution protocols, as published in recent reports: (i) in 4?M urea+1% CHAPS; (ii) in 4?M urea+1% CHAPS+5% acetic acid; (iii) in 8?M urea+2% CHAPS+5% acetic acid; (iv) in boiling 4% SDS+25?mM DTT. One milliliter of serum, in all cases, was captured with 50?μL of CPLL beads, which were then eluted with the four eluants described above. In the first three cases, after the first elution, the beads were re-eluted with cocktail (iv), known to offer maximal release of proteins adsorbed by the CPLL ligands. Eluant (i) released only ca. 20% of the species adsorbed, eluant (ii) ca. 60%, eluant (iii) ca. 80%. Thus, the poor performance of the CPLL methodology, as reported in (i) is not due to any fault of the capture technique, but simply to the adoption of a very poor elution protocol. Even those using eluants (ii) and (iii) should know that a substantial fraction of the captured species still remains bound to the beads and is thus not available to biomarker discovery. Once more, eluant (iv) is recognized as the only one able to offer optimal recovery from the CPLL baits.     

Large amplitude oscillatory shear of pseudoplastic and elastoviscoplastic materials

We explore the utility of strain-controlled large amplitude oscillatory shear (LAOS) deformation for identifying and characterizing apparent yield stress responses in elastoviscoplastic materials. Our approach emphasizes the visual representation of the LAOS stress response within the framework of Lissajous curves with strain, strain rate, and stress as the coordinate axes, in conjunction with quantitative analysis of the corresponding limit cycle behavior. This approach enables us to explore how the material properties characterizing the yielding response depend on both strain amplitude and frequency of deformation. Canonical constitutive models (including the purely viscous Carreau model and the elastic Bingham model) are used to illustrate the characteristic features of pseudoplastic and elastoplastic material responses under large amplitude oscillatory shear. A new parameter, the perfect plastic dissipation ratio, is introduced for uniquely identifying plastic behavior. Experimental results are presented for two complex fluids, a pseudoplastic shear-thinning xanthan gum solution and an elastoviscoplastic invert-emulsion drilling fluid. The LAOS test protocols and the associated material measures provide a rheological fingerprint of the yielding behavior of a complex fluid that can be compactly represented within the domain of a Pipkin diagram defined by the amplitude and timescale of deformation.     

Direct observation of adsorbed H2-framework interactions in the Prussian Blue analogue MnII3[CoIII(CN)6]2: the relative importance of accessible coordination sites and van der Waals interactions

Selective recovery of the guest-framework interactions for H(2) adsorbed in a nanoporous Prussian Blue analogue, through differential X-ray and neutron pair distribution function analysis at ca. 77 K, suggests that the H(2) molecule is disordered about a single position at the centre of the pore, ((1/4),(1/4),(1/4)), without binding at accessible Mn(II) sites.