Molecular Dynamics Study of Self-Diffusion in Zr

We employed a recently developed semi-empirical Zr potential to determine the diffusivities in the hcp and bcc Zr via molecular dynamics simulation. The point defect concentration was determined directly from MD simulation rather than from theoretical methods using T=0 calculations. We found that the diffusion proceeds via the interstitial mechanism in the hcp Zr and both the vacancy and interstitial mechanisms give contribution in diffusivity in the bcc Zr. The agreement with the experimental data is excellent for the hcp Zr and for the bcc Zr it is rather good at high temperatures but there is a considerable disagreement at low temperatures

Effect of Thermal Exposure on Structure of the Ultrafine-GrainedZr-1Nb Alloy

Effect of annealing at temperature range of 573–823 K on stability of the ultrafine-grained structure of the Zr-1wt.%Nb alloy was studied by methods of transmission electron microscopy. Growth kinetics of grain–subgrain structure elements of alloy was investigated

Effect of nonequilibrium hydrogen release in the ultrafine-grained Zr-1Nb alloy under the electron beam exposure

The evolution of structural and phase state and hydrogen release from the ultrafine-grained hydrogenated zirconium Zr-1Nb alloy during vacuum annealing and electron beams exposure were studied. The use of electron beam irradiation for hydrogen degassing is shown to decrease the temperature of active hydrogen release by 100-200 K and/or reduce the time required for hydrogen degassing from the alloy to concentrations corresponding to technical standards

Ground-state spin of 59^{59}Mn

Beta decay of $^{59}$Mn has been studied at PSB-ISOLDE, CERN. The intense and pure Mn beam was produced using the Resonance Ionization Laser Ion Source (RILIS). Based on the measured $\beta$-decay rates the ground-state spin and parity are proposed to be $J^{\pi}$ = 5/2$^{-}$. This result is consistent with the systematic trend of the odd-A Mn nuclei and extends the systematics one step further towards the neutron drip line

Atomic spectroscopy studies of short-lived isotopes and nuclear isomer separation with the ISOLDE RILIS

The Resonance Ionization Laser Ion Source (RILIS) at the ISOLDE on-line isotope separator is based on the selective excitation of atomic transitions by tunable laser radiation. Ion beams of isotopes of 20 elements have been produced using the RILIS setup. Together with the mass separator and a particle detection system it represents a tool for high-sensitive laser spectroscopy of short-lived isotopes. By applying narrow-bandwidth lasers for the RILIS one can study isotope shifts (IS) and hyperfine structure (HFS) of atomic optical transitions. Such measurements are capable of providing data on nuclear charge radii, spins and magnetic moments of exotic nuclides far from stability. Although the Doppler broadening of the optical absorption lines limits the resolution of the technique, the accuracy of the HFS measurements examined in experiments with stable Tl isotopes approaches a value of 100 MHz. Due to the hyperfine splitting of atomic lines the RILIS gives an opportunity to separate nuclear isomers. Isomer selectivity of the RILIS has been used in studies of short-lived Ag, Cu and Pb isotopes

Neuraminidase Inhibitor Susceptibility Testing in Human Influenza Viruses: A Laboratory Surveillance Perspective

Neuraminidase inhibitors (NAIs) are vital in managing seasonal and pandemic influenza infections. NAI susceptibilities of virus isolates (n = 5540) collected during the 2008–2009 influenza season were assessed in the chemiluminescent neuraminidase inhibition (NI) assay. Box-and-whisker plot analyses of log-transformed IC50s were performed for each virus type/subtype and NAI to identify outliers which were characterized based on a statistical cutoff of IC50 >3 interquartile ranges (IQR) from the 75th percentile. Among 1533 seasonal H1N1 viruses tested, 1431 (93.3%) were outliers for oseltamivir; they all harbored the H275Y mutation in the neuraminidase (NA) and were reported as oseltamivir-resistant. Only 15 (0.7%) of pandemic 2009 H1N1 viruses tested (n = 2259) were resistant to oseltamivir. All influenza A(H3N2) (n = 834) and B (n = 914) viruses were sensitive to oseltamivir, except for one A(H3N2) and one B virus, with D151V and D197E (D198E in N2 numbering) mutations in the NA, respectively. All viruses tested were sensitive to zanamivir, except for six seasonal A(H1N1) and several A(H3N2) outliers (n = 22) which exhibited cell culture induced mutations at residue D151 of the NA. A subset of viruses (n = 1058) tested for peramivir were sensitive to the drug, with exception of H275Y variants that exhibited reduced susceptibility to this NAI. This study summarizes baseline susceptibility patterns of seasonal and pandemic influenza viruses, and seeks to contribute towards criteria for defining NAI resistance

FIELD ELECTRON EMISSION FROM A NICKEL-CARBON NANOCOMPOSITE

The field-emission properties of nanocomposite films comprised of 10 -20 nm-sized nickel particles immersed in a carbon matrix were investigated. The films were deposited onto silicon substrates by means of a metal-organic chemical vapor deposition (MOCVD) method. The composite's structure was controlled via deposition process parameters. Experiments demonstrated that the composite films can efficiently emit electrons, yielding current densities of up to 1.5 mA/cm 2 in electric fields below 5 V/µm. Yet, good emission properties were only shown in films with low effective thickness, when nickel grains did not form a solid layer, but left a part of the substrate area exposed to the action of the electric field. This phenomenon can be naturally explained in terms of the two-barrier emission model

Computational Modeling and Experimental Characterization of Martensitic Transformations in Nicoal for Self-Sensing Materials

Fundamental changes to aero-vehicle management require the utilization of automated health monitoring of vehicle structural components. A novel method is the use of self-sensing materials, which contain embedded sensory particles (SP). SPs are micron-sized pieces of shape-memory alloy that undergo transformation when the local strain reaches a prescribed threshold. The transformation is a result of a spontaneous rearrangement of the atoms in the crystal lattice under intensified stress near damaged locations, generating acoustic waves of a specific spectrum that can be detected by a suitably placed sensor. The sensitivity of the method depends on the strength of the emitted signal and its propagation through the material. To study the transition behavior of the sensory particle inside a metal matrix under load, a simulation approach based on a coupled atomistic-continuum model is used. The simulation results indicate a strong dependence of the particle's pseudoelastic response on its crystallographic orientation with respect to the loading direction and suggest possible ways of optimizing particle sensitivity. The technology of embedded sensory particles will serve as the key element in an autonomous structural health monitoring system that will constantly monitor for damage initiation in service, which will enable quick detection of unforeseen damage initiation in real-time and during onground inspections

First on-line β\beta-NMR on oriented nuclei: magnetic dipole moments of the νp1/2−1;1/2−\nu{p}^{-1}_{1/2}; 1/2^- ground state in 67^{67}Ni and πp3/2+1;3/2−\pi{p}^{+1}_{3/2}; 3/2^- ground state in 69^{69}Cu

The first fully on-line use of the angular distribution of $\beta$ - emission in detection of NMR of nuclei oriented at low temperatures is reported. The magnetic moments of the single valence particle, intermediate mass, isotopes $^{67}$Ni($\nu{p}^{-1}_{1/2}$; 1/2$^{-}$) and $^{69}$Cu($\pi{p}^{+1}_{ 3/2}$; 3/2$^{-}$) are measured to be +0.601(5)$\mu_{N}$ and +2.84(1)$\mu_{N}$ respectively, revealing only a small deviation from the neutron $p_{1/2}$ single-particle value in the former and a large deviation from the proton $p_{3/2}$ single-particle value in the latter. Quantitative interpretation is given in terms of core polarization and meson-exchange currents