3,802 research outputs found

    Lattice sites of ion-implanted Li in diamond

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    Published in: Appl. Phys. Lett. 66 (1995) 2733-2735 citations recorded in [Science Citation Index] Abstract: Radioactive Li ions were implanted into natural IIa diamonds at temperatures between 100 K and 900 K. Emission channelling patterns of a-particles emitted in the nuclear decay of 8Li (t1/2 = 838 ms) were measured and, from a comparison with calculated emission channelling and blocking effects from Monte Carlo simulations, the lattice sites taken up by the Li ions were quantitatively determined. A fraction of 40(5)% of the implanted Li ions were found to be located on tetrahedral interstitial lattice sites, and 17(5)% on substitutional sites. The fractions of implanted Li on the two lattice sites showed no change with temperature, indicating that Li diffusion does not take place within the time window of our measurements.

    Diluted manganese on the bond-centered site in germanium

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    The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes

    Biologische Kontrolle von Eulenraupen im Kohl mittels Baculoviren

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    Baculoviren sind als hoch selektive biologische Kontrollagenzien fĂŒr Kohleulenraupen (Mamestra brassicae) seit lĂ€ngerem bekannt und ihre gute Wirksamkeit wurde schon in verschiedenen GewĂ€chshaus- und Freilandversuchen nachgewiesen. Um die Kontrollsituation von Kohleulenraupen im ökologischen GemĂŒseanbau insbesondere bei niedrigen Temperaturen zu verbessern, wurden die eulenpathogenen Mamestra brassicae Nukelopolyhedrovirus (MbMNPV) und Mamestra configurata Nukleopolyhedrovirus (MacoNPV-A) als mögliche Kontrollagentien geprĂŒft. Es konnte gezeigt werden, dass auch MacoNPV-A fĂŒr M.brassicae pathogen ist. In vergleichenden Bioassays bei 24°C zeigten MbMNPV und MacoNPV-A keinen signifikanten Unterschied hinsichtlich ihrer biologischen AktivitĂ€t gegenĂŒber M.brassicae. In weiteren Bioassays wurden die konzentrationsabhĂ€ngige MortalitĂ€t von M.brassicae im 2. Larvenstadium sowie die gefressene BlattflĂ€che bei 24, 20, 16 und 12°C bestimmt. Im Vergleich zu 24 und 20°C waren die mittleren Letalkonzentrationen bei 16 und 12°C 100 bzw. 1000fach höher. FĂŒr eine mittlere Reduktion der konsumierten BlattflĂ€che waren hingegen bei Temperaturen unter 20°C 10 bis 100fach höhere Konzentrationen notwendig. Durch die Neuformulierung von MbMNPV (Probis GmbH, Wiernsheim) konnte eine Wirkungssteigerung im Vergleich zu der nicht formulierten Virussuspension im Bioassay erzielt werden. In einem Freilandtest mit kĂŒnstlicher Infestation in Kohlrabi konnte eine weitere Steigerung des Wirkungsgrades durch die Kombination mit dem Bacillus thuringiensis PrĂ€parat XenTariÂź im Vergleich zur Einzelapplikation der beiden PrĂ€parate erreicht werden. Eine breite Freilandtestung der Baculoviren-PrĂ€paraten gegen Kohlraupen bei kĂŒhler Witterung als EinzelprĂ€parat und in Kombination mit Bacillus thuringiensis PrĂ€paraten sowie neuester Applikationstechnik fĂŒr Ober- und Unterblattbehandlung wird empfohlen

    The right pick Structural basis of snRNA selection by Gemin5

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    Macromolecular complexes, rather than individual biopolymers, perform many cellular activities. Faithful assembly of these complexes in vivo is therefore a vital challenge of all cells, and its failure can have fatal consequences. To form functional complexes, cells use elaborate measures to select the “right” components and combine them into working entities. How assembly is achieved at the molecular level is unclear in many cases. Three groups (Jin and colleagues, pp. 2391–2403; Xu and colleagues, pp. 2376–2390; and Tang and colleagues in Cell Research) have now provided insights into how an assembly factor specifically recognizes substrate RNA molecules and enables their usage for assembly of Sm-class uridine-rich small nuclear RNA–protein complexes

    Conditional regularity of solutions of the three dimensional Navier-Stokes equations and implications for intermittency

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    Two unusual time-integral conditional regularity results are presented for the three-dimensional Navier-Stokes equations. The ideas are based on L2mL^{2m}-norms of the vorticity, denoted by Ωm(t)\Omega_{m}(t), and particularly on Dm=ΩmαmD_{m} = \Omega_{m}^{\alpha_{m}}, where αm=2m/(4m−3)\alpha_{m} = 2m/(4m-3) for m≄1m\geq 1. The first result, more appropriate for the unforced case, can be stated simply : if there exists an 1≀m<∞1\leq m < \infty for which the integral condition is satisfied (Zm=Dm+1/DmZ_{m}=D_{m+1}/D_{m}) ∫0tln⁥(1+Zmc4,m)dτ≄0 \int_{0}^{t}\ln (\frac{1 + Z_{m}}{c_{4,m}}) d\tau \geq 0 then no singularity can occur on [0,t][0, t]. The constant c4,m↘2c_{4,m} \searrow 2 for large mm. Secondly, for the forced case, by imposing a critical \textit{lower} bound on ∫0tDmdτ\int_{0}^{t}D_{m} d\tau, no singularity can occur in Dm(t)D_{m}(t) for \textit{large} initial data. Movement across this critical lower bound shows how solutions can behave intermittently, in analogy with a relaxation oscillator. Potential singularities that drive ∫0tDmdτ\int_{0}^{t}D_{m} d\tau over this critical value can be ruled out whereas other types cannot.Comment: A frequency was missing in the definition of D_{m} in (I5) v3. 11 pages, 1 figur

    Direct evidence for stability of tetrahedral interstitial Er in Si up to 900∘^{\circ}C

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    Conversion electron emission channeling from the isotope 167m^{167m}Er (2.28 s), which is the decay product of radioactive 167^{167}Tm (9.25 d), offers a means of monitoring the lattice sites of Er in single crystals. We have used this method to determine the lattice location of 167m^{167m}Er in Si directly following room temperature implantation of 167^{167}Tm, after subsequent annealing steps, and also in situ during annealing up to 900°C. Following the recovery of implantation damage around 600°C, about 90% of Er occupies near-tetrahedral interstitial sites in both FZ and CZ Si. While in FZ Si 167m^{167m}Er was found to be stable on these sites even at 900°C, the tetrahedral Er fraction in CZ Si decreased considerably after annealing for 10 min at 800°C and above

    Direct evidence for As as a Zn-Site impurity in ZnO

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