Particle image velocimetry measurements of the separated flow behind a rearward facing step

Particle image velocimetry (PIV) was used to measure mean flow and turbulence characteristics in the separated flow behind a rearward facing step. The confidence limits characterising estimates of mean velocity and turbulence intensity obtained by PIV are discussed. The relevance of background turbulence levels and sample size in determining these limits is considered.     

Combing DNAzyme with single-walled carbon nanotubes for detection of Pb(II) in water

A sensitive and simple assay for the detection of Pb(2+) in aqueous solutions is reported. It takes advantage of the high affinity between single-stranded DNA (ssDNA) and single-walled carbon nanotubes (SWCNT) as well as the capability of SWCNT in fluorescence quenching. Lead(II) catalyzes the cleavage of a fluorescently labeled DNA substrate by a DNAzyme, which releases the single-stranded product to be adsorbed onto a SWCNT. The decrease in fluorescence is proportional to the Pb(2+) concentration. Concentrations as low as 1 nM Pb(2+) in water could be detected and the detection range spans over 5 orders of magnitude. The unique combination of Pb-specific DNAzyme with SWCNT produces a universal, facile and cost-effective sensing platform for lead ions. The concept can be applied to the design of detection assays for other metal ions or small molecules.     

Nuclear corrections in neutrino-nucleus deep inelastic scattering and their compatibility with global nuclear parton-distribution-function analyses

We perform a global χ2 analysis of nuclear parton distribution functions using data from charged current neutrino-nucleus (νA) deep-inelastic scattering (DIS), charged-lepton-nucleus (?(±)A) DIS, and the Drell-Yan (DY) process. We show that the nuclear corrections in νA DIS are not compatible with the predictions derived from ?(±)A DIS and DY data. We quantify this result using a hypothesis-testing criterion based on the χ2 distribution which we apply to the total χ2 as well as to the χ2 of the individual data sets. We find that it is not possible to accommodate the data from νA and ?(±)A DIS by an acceptable combined fit. Our result has strong implications for the extraction of both nuclear and proton parton distribution functions using combined neutrino and charged-lepton data sets.     

The angular distribution of the 12C(γ,pn) reaction for Eγ=120−150 MeV

The angular distribution of nucleons emitted in the ¹²C(γ,pn) reaction has been measured using tagged photons at the Mainz microtron MAMI. The variation of the reaction strength with the polar angles of the two emitted nucleons is reported for E_γ=120−150 MeV. The proton angular distribution peaks at more backward angles than the ²H(γ,p) differential cross section indicating a departure from the simple quasi-deuteron model of 2N photo-emission. The distribution shape is in reasonable agreement with microscopic theoretical models which include both π- and ρ-exchange. Received: 3 September 1997 / Revised version: 17 December 1997     

Book reviews

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Book reviews

     

Effect of nanosizing on lattice and magnon modes of hematite

Broadening of Raman lines and a decrease of frequencies relative to the bulk material are observed for the lattice modes of nanoparticles of the hematite phase of Fe₂O₃. The magnon mode frequency is observed to shift up with reduced particle size in contrast to the lattice modes. The effects are suggested to be a result of phonon confinement and represent the first observation of phonon confinement effects on magnon modes. The Fe₂O₃ nanoparticles are produced by laser decomposition of Fe₃O₄ nanoparticles. X-ray diffraction and Raman frequency shifts indicate the Fe₂O₃ nanoparticles are smaller than the parent Fe₃O₄ nanoparticles.     

5-regular 3-polytopal graphs with edges of only two types and shortness exponents less than one

It is shown that, if q 29 and q 0 (mod 3), the infinite class of 5-regular 3-polytopal graphs whose edges are incident with either two triangles or a triangle and a q-gon contains nonhamiltonian members and even has shortness exponent less than one.     

Simulation of flourine migration in NiF2

The point defect and transport properties of nickel fluoride have been predicted using atomistic simulation. Results suggest that the dominant intrinsic defect reaction is anion Frenkel, however, formation energies are sufficiently high to suggest that intrinsic defect concentrations are low. Migration activation energies are consistent with flourine, as the most highly mobile species, being transported in the ab plane via the formation of a split interstitial configuration. Transport of both flourine and nickel will be considerably anisotropic.