Selective X-ray generation by heavy ions (Part 2) measurement of the concentration distribution of ion-implanted antimony in silicon by the use of selective heavy ion X-ray excitation

This investigation demonstrates how the total, concentration distribution of antimony, previously implanted into silicon at 100 keV, may be elucidated without recourse to the usual radioactive isotope techniques. It uses the fact that 100 keV Kr⁺ ions can preferentially excite characteristic X-rays from antimony, even in the presence of a huge excess of silicon. The resultant high sensitivity for the detection of antimony in silicon is accompanied by the fact that the X-rays arise predominantly from less than one hundred Angstroms below the surface of the specimen. Thus bombardment by 100 keV Kr⁺ íons is used ín conjunction with an anodic stripping technique (which removes 169±20 Å at a time) to obtain the antimony distribution profile in silicon. Consideration is also given to the possibility of obtaining the implanted antimony range distribution by using 100 keV Kr⁺ ions to detect the antimony and simultaneously remove silicon by sputtering.     

Magnetic nanocomposite spinel and FeCo core-shell and mesoporous systems

The fabrication of condensed silica and mesoporous silica coated spinel CoFe₂O₄ and FeCo alloy magnetic nanocomposites are reported. The encapsulation of well-defined 5 nm thick uniform silica layer on CoFe₂O₄ magnetic nanoparticles was performed. The formation of mesopores in the shell was a consequence of removal of organic group of the precursor through annealing. The NiO nanoparticles were loaded into the mesoporous silica. The mesoporous silica shells leads to a larger coercivity than that of pure CoFe₂O₄ magnetic nanoparticles due to the decrease of interparticle interactions and magneto-elastic anisotropy. In addition, the FeCo nanoparticles were coated by condensed and mesoporous silica. The condensed silica can protect the reactive FeCo alloy from oxidation up to 300 °C. However, saturation magnetization of FeCo nanoparticles coated by silica after 400 °C annealing is dramatically decreased due to the oxidation of the FeCo core. The mesoporous silica coated magnetic nanostructure loaded with NiO as a final product could be used in the field of biomedical applications.     

Chronic administration of R-flurbiprofen attenuates learning impairments in transgenic amyloid precursor protein mice

Background  

Long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with a reduced incidence of Alzheimer's disease (AD). We and others have shown that certain NSAIDs reduce secretion of Aβ42 in cell culture and animal models, and that the effect of NSAIDs on Aβ42 is independent of the inhibition of cyclooxygenase by these compounds. Since Aβ42 is hypothesized to be the initiating pathologic molecule in AD, the ability of these compounds to lower Aβ42 selectively may be associated with their protective effect. We have previously identified R-flurbiprofen (tarenflurbil) as a selective Aβ42 lowering agent with greatly reduced cyclooxygenase activity that shows promise for testing this hypothesis. In this study we report the effect of chronic R-flurbiprofen treatment on cognition and Aβ loads in Tg2576 APP mice.     

Broue's Conjecture for the Hall-Janko Group and its Double Cover

Broué's abelian defect conjecture suggests a deep linkbetween the module categories of a block of a group algebraand its Brauer correspondent, viz. that they should be derivedequivalent. We are able to verify Broué's conjecturefor the Hall–Janko group, even its double cover 2.J₂,as well as for U₃(4) and Sp₄(4). In fact we verify Rickard'srefinement to Broué's conjecture and show that the derivedequivalence can be chosen to be a splendid equivalence for theseexamples. 2000 Mathematical Subject Classification: 20C20, 20C34.     

The effects of temperature upon NiO formation and oxygen removal on Ni(110)

Oxygen chemisorption and NiO nucleation and growth on Ni(110) have been studied with low energy electron diffraction and Auger electron spectroscopy. Changes in the Auger peak energies and shapes were shown to occur only upon NiO formation. The effects of step-changes in temperature upon NiO nucleation and growth were studied and it was shown that temperature steps or annealing during the chemisorption regime did not significantly affect either chemisorption or NiO formation. During NiO growth, temperature steps to a higher temperature caused reduced growth rates, while steps to lower temperature caused increased growth rates. The reaction rate constant from the island growth model was calculated and shown to agree with literature data. The values obtained from temperature step measurements agreed within a factor of two with those obtained for reactions without temperature steps. Therefore, no systematic temperature effect upon the NiO nuclei density was observed for Ni(110). The activation energy for growth of NiO was found to be 5.5 kcal/mole. Dissolution of oxygen into bulk nickel was also studied and it was shown that bulk diffusion of oxygen in nickel was not rate controlling. Rather, surface phase transitions were observed which allowed incorporation of oxygen over the temperature range of 150°C to greater than 800°C, depending on the quantity of oxygen already incorporated.     

Energy loss of atoms at metal surfaces due to electron-hole pair excitations: first-principles theory of "chemicurrents"

A method is presented for calculating electron-hole pair excitation due to an incident atom or molecule interacting with a metal surface. Energy loss is described using an ab initio approach that obtains a position-dependent friction coefficient for an adsorbate moving near a metal surface from a total energy pseudopotential calculation. A semiclassical forced oscillator model is constructed to describe excitation of the electron gas due to the incident molecule. This approach is applied to H and D atoms incident on a Cu(111) surface, and we obtain theoretical estimates of the "chemicurrents" measured by Nienhaus et al. [Phys. Rev. Lett. 82, 446 (1999)] for these atoms incident on the surface of a Schottky diode.     

Morphology and scaling of impact craters in granular media

We present the results of experiments on impact craters formed by dropping a steel ball vertically into a container of small glass beads. As the energy of impact increases, we observe a progression of crater morphologies analogous to that seen in craters on the moon. We find that both the diameter and the depth of the craters are proportional to the 1/4 power of the energy. The ratio of crater diameter to rim-to-floor depth is constant for low-energy impacts, but increases at higher energy, similar to what is observed for lunar craters.