Adaptable-radius, time-orbiting magnetic ring trap for Bose-Einstein condensates

We theoretically investigate an adjustable-radius magnetic storage ring for laser-cooled and Bose-condensed atoms. Additionally, we discuss a novel time-dependent variant of this and other ring traps. Time-orbiting ring traps provide a high optical access method for spin-flip loss prevention near a storage ring's circular magnetic field zero. Our scalable storage ring will allow one to probe the fundamental limits of condensate Sagnac interferometry.Comment: 5 pages, 3 figures. accepted in J Phys

Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study

A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface

Terrestrial exposure of a fresh Martian meteorite causes rapid changes in hydrogen isotopes and water concentrations

Determining the hydrogen isotopic compositions and H2O contents of meteorites and their components is important for addressing key cosmochemical questions about the abundance and source(s) of water in planetary bodies. However, deconvolving the effects of terrestrial contamination from the indigenous hydrogen isotopic compositions of these extraterrestrial materials is not trivial, because chondrites and some achondrites show only small deviations from terrestrial values such that even minor contamination can mask the indigenous values. Here we assess the effects of terrestrial weathering and contamination on the hydrogen isotope ratios and H2O contents of meteoritic minerals through monitored terrestrial weathering of Tissint, a recent Martian fall. Our findings reveal the rapidity with which this weathering affects nominally anhydrous phases in extraterrestrial materials, which illustrates the necessity of sampling the interiors of even relatively fresh meteorite falls and underlines the importance of sample return missions

Aniline incorporated silica nanobubbles

We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution, precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and voltammetric properties of the system were studied in order to understand the interaction of aniline with the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the silica shell

Parameter identification problems in the modelling of cell motility

We present a novel parameter identification algorithm for the estimation of parameters in models of cell motility using imaging data of migrating cells. Two alternative formulations of the objective functional that measures the difference between the computed and observed data are proposed and the parameter identification problem is formulated as a minimisation problem of nonlinear least squares type. A Levenberg–Marquardt based optimisation method is applied to the solution of the minimisation problem and the details of the implementation are discussed. A number of numerical experiments are presented which illustrate the robustness of the algorithm to parameter identification in the presence of large deformations and noisy data and parameter identification in three dimensional models of cell motility. An application to experimental data is also presented in which we seek to identify parameters in a model for the monopolar growth of fission yeast cells using experimental imaging data. Our numerical tests allow us to compare the method with the two different formulations of the objective functional and we conclude that the results with both objective functionals seem to agree

Effect of Ta 2 O 5 , Nb 2 O 5 , and HfO 2 Alloying on the Transformability of Y 2 O 3 -Stabilized Tetragonal ZrO 2

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65528/1/j.1151-2916.1990.tb05100.x.pd

Revealing Correlation of Valence State with Nanoporous Structure in Cobalt Catalyst Nanoparticles by in Situ Environmental TEM

Simultaneously probing the electronic structure and morphology of materials at the nanometer or atomic scale while a chemical reaction proceeds is significant for understanding the underlying reaction mechanisms and optimizing a materials design. This is especially important in the study of nanoparticle catalysts, yet such experiments have rarely been achieved. Utilizing an environmental transmission electron microscope (ETEM) equipped with a differentially pumped gas cell, we are able to conduct nanoscopic imaging and electron energy loss spectroscopy (EELS) in situ for cobalt catalysts under reaction conditions. Analysis revealed quantitative correlation of the cobalt valence states to the particles' nanoporous structures. The in situ experiments were performed on nanoporous cobalt particles coated with silica while a 15 mTorr hydrogen environment was maintained at various temperatures (300-600\degreeC). When the nanoporous particles were reduced, the valence state changed from cobalt oxide to metallic cobalt and concurrent structural coarsening was observed. In situ mapping of the valence state and the corresponding nanoporous structures allows quantitatively analysis necessary for understanding and improving the mass activity and lifetime of cobalt-based catalysts, i.e., for Fischer-Tropsch synthesis that converts carbon monoxide and hydrogen into fuels, and uncovering the catalyst optimization mechanisms.Comment: ACS Nano, accepte

Sintering and compensation effect of donor and acceptor codoped 3 mol% Y 2 O 3 -ZrO 2

Addition of 0.15–0.5 mol% acceptor oxide, Al 2 O 3 , to 3 mol% Y 2 O 3 -ZrO 2 results in enhanced densification at 1350°C. The enhancement is accounted for by a liquid phase sintering mechanism. While the addition of donor oxide, Ta 2 O 5 , of 0.15–2.5 mol% at 1300–1600°C results in the decrease of final density and in the destabilization of the tetragonal (t) phase of the 3 mol% Y 2 O 3 -t-ZrO 2 (TZP). X-ray diffractometry (XRD) reveals that the Ta 2 O 5 -added 3 mol% Y 2 O 3 -ZrO 2 contains monoclinic (m) ZrO 2 phase and a second Ta 2 Zr 6 O 17 phase. The decrease is attributed to the increase of m-ZrO 2 content in these samples. Complete phase transformation from t-ZrO 2 to m-ZrO 2 observed in samples added with 2.5 mol% Ta 2 O 5 is interpreted by the compensation effect based on donor and acceptor codoping defect chemistry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44737/1/10853_2004_Article_BF00356138.pd

Sintering and compensation effect of donor- and acceptor-codoped 3mol% Y 2 O 3 -ZrO 2

Addition of ∼0.15–0.5 mol% acceptor oxide, Al 2 O 3 , to 3 mol% Y 2 O 3 -ZrO 2 results in enhanced densification at 1350 °C. The enhancement is accounted for by a liquid phase sintering mechanism. The addition of donor oxide, Ta 2 O 5 , of 0.15–2.5 mol % at 1300–1600 °C results in the destabilization of tetragonal (t-) phase and the decrease of final density in 3 mol% Y 2 O 3 -TZP (tetragonal ZrO 2 polycrystals). X-ray diffractometry (XRD) reveals that the Ta 2 O 5 -added 3 mol% Y 2 O 3 -ZrO 2 contains monoclinic (m-) ZrO 2 and a second phase of Ta 2 Zr 6 O 17 . The decreasing in final density is attributed to the increase of m-ZrO 2 content. Complete destabilization of t-ZrO 2 to m-ZrO 2 in samples added with 2.5 mol% Ta 2 O 5 is interpreted by the compensation effect based on donor- and acceptor-codoping defect chemistry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44714/1/10853_2005_Article_BF01166021.pd