Dark energy degeneracies in the background dynamics

We discuss degeneracies between dark energy and cosmic parameters using a fully non-perturbative and non-parametric approach. This allows us to examine the knock-on bias induced in the reconstructed dark energy equation of state, w(z), if there is a bias in the cosmic curvature or dark matter content. Assuming perfect Hubble, distance and volume measurements, we show that for z > 1, the bias in w(z) is up to two orders of magnitude larger than the corresponding errors in Ω _k or Ω _m .     

Diamond cleavage: importance to high pressure research

The extraordinary properties of diamond make it the number-one choice for anvils in high pressure experiments involving anvil cells. In much of the literature on the properties of diamond the only cleavage mentioned is {111}. However, experience has shown that diamond anvils made with their [001] axis oriented in line with the principal stress axis of the anvil or at a small angle to it often failed with flat faces having {110} orientations; a cleavage plane is reported in some publications. Analysis of the anisotropy of strength and Poisson ratio in diamond has shown that such orientations do, indeed, favor initial failure on {110} cleavage planes. This analysis, in conjunction with stereographic projections of the {111} and {110} cleavage planes, suggests that a 27° tilt of the [001] axis with respect to the linear stress axis by rotation around the [100] or [010] axis should provide significantly greater resistance to failure by cleaving.     

Crystalline polymers in real space

Recent work has resolved uncertainties as to how polymers develop their melt-crystallized textures and brought a unified context to the subject. Spherulites form because of the long molecular length not because of its polydispersity. When a molecule is only partly attached to a growing lamella the unattached portions will occupy adjacent space and exert a short-range repulsive pressure on any neighbouring lamella at a branch point. This is confirmed by monodisperse long n-alkanes forming spherulites only with chainfolded lamellae not when crystallizing as extended chains. An additional textural element, cellulation, is superposed on regular spherulitic growth beyond a certain radius (in linear-low-density polyethylenes) when there is sufficient fractional crystallization of segregated species which lower the local equilibrium melting temperature and thence the isothermal supercooling and growth rate, the last declining continuously to an asymptotic limit. First results show that both the radius to cellulation and the cell width are effectively independent of growth velocity; neither scales with the diffusion length. A possible explanation is proposed for this novel situation which has no precedent in either polymeric or non-polymeric systems.     

Electron microscopy and quantitative polymer morphology

The lamellar nature of semi-crystalline polymers can now be studied systematically using transmission electron microscopy, especially following permanganic etching. In combination with thermal analysis and selective extraction followed by molecular characterisation, this approach allows the distribution of lamellae, thermal stability and molecular constitution to be mapped in real space. Extension of this methodology has allowed the extraction of individual melt-crystallized lamellae from bulk polymer. Their study is adding to understanding of fundamental processes of crystal growth.     

Neuropeptide delivery to the brain: a von Willebrand factor signal peptide to direct neuropeptide secretion

Background  

Multiple neuropeptides, sometimes with opposing functions, can be produced from one precursor gene. To study the roles of the different neuropeptides encoded by one large precursor we developed a method to overexpress minigenes and establish local secretion.     

A Diselenide Turn-On Fluorescent Probe for the Detection of Thioredoxin Reductase

We report the first diselenide-based probe for the selective detection of thioredoxin reductase (TrxR), an enzyme commonly overexpressed in melanomas. The probe design involves conjugation of a seminaphthorhodafluor dye with a diselenide moiety. TrxR reduces the diselenide bond, triggering a fluorescence turn-on response of the probe. Kinetic studies reveal favorable binding of the probe with TrxR with a Michaelis–Menten constant (K_m) of 15.89 μm . Computational docking simulations predict a greater binding affinity to the TrxR active site in comparison to its disulfide analogue. In vitro imaging studies further confirmed the diselenide probe exhibited improved signaling of TrxR activity compared to the disulfide analogue.     

An investigation of permanganic etching of linear low-density polyethylene

Permanganic etching is a technique of removing material selectively to reveal lamellae in crystalline polymers. It is generally found that populations of lamellae with different thicknesses are removed to different depths. In linear poly-ethylene we have previously shown that this discrimination is not an inherent property but a consequence of differential deformation during cutting to expose the surface prior to etching. The work is now extended to linear low-density polyethylene to test whether the changed basis of molecular segregation (with more branched molecules crystallizing later) alters the etching behavior. It is shown that thinner lamellae are etched at a faster rate which is only slightly reduced after removing damage due to cutting. This intrinsic differentiation between crystal thicknesses accompanies faster etching rates than for the linear material. It is inferred that this is due to faster chain scission at fold surfaces which are more penetrable for the linear low-density than for the linear polymer; however, chain scission remains slow compared to stem removal. Fold stems are probably removed as entities rather than incrementally, but it is evident that a fold surface region needs to be etched away before a stem can be removed.     

Changes in the melting behavior with the radial distance in isotactic polypropylene spherulites

The melting of highly tactic i‐polypropylene occurs in two stages even for crystallization at 145 °C, a temperature at which reorganization during scanning is negligible. A comparison of two such polypropylenes, one nucleated and the other not nucleated, together with fractions from the latter, has been made with electron microscopy following permanganic etching, in addition to differential scanning calorimetry. This has allowed the two melting stages to be assigned to two components of the lamellar morphology, with progressive changes in both occurring with increasing radial distance within a spherulite. The highest melting temperature is for dominant radial lamellae far from a spherulite center. The lowest melting regions are the evenly crosshatched spherulite centers and a narrow peripheral band. Lower melting is attributed to the suppression of isothermal lamellar thickening paralleling recent direct demonstrations in polyethylene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2342–2354, 2003     

Stratified Turbulence in the Atmospheric Mesoscales

The first author proposed earlier that the atmospheric energy spectrum in the mesoscale range is controlled by upscale energy transport in stratified and geostrophic turbulence, with the source of the energy probably convective clouds and storms. This hypothesis is reviewed in the light of a variety of theoretical and mechanistic tests, mostly involving numerical simulation. Some conflicting results are noted, with fluid dynamics simulations mostly negative and meteorological simulations positive, including one new set presented here. The rapid increase in larger-scale energy shown in our simulations should, however, be ascribed in part to a different mechanism, involving the rapid growth of the unconstrained outflow and its further spreading by mean shear. Received 23 May 1997 and accepted 21 February 1998     

Neutral transverse momentum spectra in 60 and 200A·GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (p _T) distributions fo inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in 60 and are measured with a lead glass calorimeter in 60 and 200A·Gev¹⁶O+nucleus and and proton+nucleus reactions. Inclusive photon distributions are compared for central and peripheral reactions. The degree of centrality is determined either from the charged particle multiplicity or from the remaining projectile energy in the forward direction. Deviations from a nucleus+nucleus interaction model based upon linear extrapolation from p+p reactions are observed in central¹⁶O+Au data. The variation of theaverage transverse momentum is investigated as function of centrality. The target-mass and energy dependence of π⁰ p _T distributions are presented. For¹⁶O+Au a change of slope in these distributions is observed atp _t ≈0.8 GeV/c compatible with hydrodynamic expansion models.