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61.
J. Gierak D. Mailly P. Hawkes R. Jede L. Bruchhaus L. Bardotti B. Prével P. Mélinon A. Perez R. Hyndman J.-P. Jamet J. Ferré A. Mougin C. Chappert V. Mathet P. Warin J. Chapman 《Applied Physics A: Materials Science & Processing》2005,80(1):187-194
Controlled and reproducible fabrication of nano-structured materials will be one of the main industrial challenges in the next few years. We have recently proposed exploitation of the nano-structuring potential of a high resolution Focused Ion Beam Tool, to overcome basic limitations of current nano-fabrication techniques. The aim of this article is to present some new routes for material patterning, which benefit from ion-induced local property modifications or damage. In the experiments we describe hereafter an ultra-sharp pencil of 30 keV gallium ions is used to tailor the characteristics of several materials at a scale of a few nanometres. The experimental results are then compared to simulations. First, we simulate the control of collisional defects generated in a thin magnetic layer under FIB irradiation. The results explain the stable magnetic structures we have obtained experimentally. This was achieved with a low surface ion dose (1012 to 1014 ions/cm2). In addition we have explored the promising direction of Bottom-up or self-organization processes using a FIB instrument. We have defined artificial surface defects. These defects created by the impact of an 8-nm FWHM probe were used to pin the diffusion and to organize nanometre-sized gold clusters on a graphite surface. PACS 79.20.Rf; 81.07.-b 相似文献
62.
S.?BlomeierEmail author D.?McGrouther S.?McVitie J. N.?Chapman M. C.?Weber B.?Hillebrands J.?Fassbender 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(2):213-218
Structural investigations of the ion irradiated polycrystalline NiFe/FeMn
exchange bias bilayer system were carried out by means of transmission
electron microscopy. Key structural parameters like average grain size,
lattice constant, and texture, as well as their dependence upon ion
irradiation were determined. This information was extracted from a detailed
analysis of a series of bright field images, dark field images, and
diffraction patterns. Furthermore a previously established model was tested
which ascribes changes in the magnetic properties upon irradiation with 5 keV He+ ions
to the creation of point defects within the antiferromagnetic
layer and to the intermixing between the ferromagnetic and antiferromagnetic
layers. The obtained results indirectly support this model by excluding a
change of the aforementioned structural parameters as a possible source of
the observed modifications of the magnetic properties. 相似文献
63.
Moss RJ Wadsworth KJ Chapman CJ Frost CG 《Chemical communications (Cambridge, England)》2004,(17):1984-1985
The rhodium catalysed addition of potassium trifluoro(organo)borates to dimethyl itaconate generates an intermediate complex which on protonation provides enantioenriched succinic esters. 相似文献
64.
Kuchel PW Durrant CJ Chapman BE Jarrett PS Regan DG 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,145(2):291-301
The alignment of human erythrocytes in aqueous suspensions in the magnetic field B(0) (called the z-direction) of an NMR spectrometer was shown by calculating the diffusion tensor for water in the sample. The diffusion was measured using a pulsed-field-gradient spin-echo NMR method. The extent of diffusion anisotropy for water was exemplified by the values of the apparent diffusion coefficients with erythrocytes of normal shape and volume: for a typical experiment the values for the x-, y-, and z-directions were (6.88 +/- 0.17) x 10(-10), (7.07 +/- 0.17) x 10(-10), and (10.20 +/- 0.17) x 10(-10) m(2) s(-1), respectively. Cells in hypo- and hyperosmotic media were also studied and they too showed the anisotropy of the apparent diffusion coefficients but the extents were different. A new method of data analysis was developed using the Standard Add-On Packages in a Mathematica program. The experimental findings support evidence of erythrocyte alignment that was previously obtained with a high-field-gradient q-space method. 相似文献
65.
6,7Li fast magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is used to study LiMn2O4 and Li3V2(PO4)3. The presence of paramagnetic transition metal centers in these materials has a profound effect on the resulting NMR spectra.
Lithium ion mobility has been studied by two-dimensional (2-D) exchange spectroscopy (EXSY) in Li3V2(PO4)3 but an absence of lithium ion exchange was observed for LiMn2O4. Several differences between the two materials are explored to explain these results. LiMn2O4 experiences a greater donation of electron spin density to the Li nucleus via the Fermi-contact interaction when compared
with Li3V2(PO4)3. This contributes to a greater hyperfine chemical shift and a larger dependence of chemical shift on temperature. The delocalized
electrons in LiMn2O4 cause temperature-independent T
1 relaxation rates and shorter relative T
2 values. The relative rates of ionic conductivity and spin–lattice or spin–spin relaxation in LiMn2O4 and Li3V2(PO4)3 are contrasted to illustrate the constraints on the use of 2-D EXSY to characterize ion dynamics in paramagnetic materials.
Authors' address: Gillian R. Goward, Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University,
1280 Main St. West, Hamilton, ON L8S 4M1, Canada 相似文献
66.
David J. Lowe Andrew V. Chapman Stuart Cook James J. C. Busfield 《Journal of Polymer Science.Polymer Physics》2011,49(22):1621-1627
Small strain Young's moduli of natural rubber (NR)/organoclay nanocomposites were estimated using the Guth–Gold, Halpin–Tsai (HT), and Krieger–Dougherty (KD) models, and compared with experimental measurements of NR vulcanizates containing organo‐montmorillonite (OM) or organo‐sepiolite (OS). To account for the effect on modulus of the NR matrix of the vulcanization‐active modifier in the organoclay, a matrix modulus correction (MMC) term was derived from the vulcanization parameters of the nanocomposites. The KD model gave a better empirical fit with the experimental data than the Guth–Gold model, with both giving good agreement with particle shape factors estimated from transmission electron microscope (TEM) images. The HT model gave the best fit with experiment for both types of nanocomposite, and use of the MMC term meant that the empirical shape factor was sufficiently close to that estimated from TEM images that the model could potentially be used to accurately predict the Young's moduli of NR/OM and NR/OS nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1621–1627, 2011 相似文献
67.
68.
Shozo Kawamura Makoto Suzuki Hossain MD. Zahid Hirofumi Minamoto 《Applied Acoustics》2009,70(11-12):1393-1399
Machine condition monitoring and fault diagnosis of rotating machinery are very important because of the wide use of rotating machinery in industry. Couplings and gears are used in many mechanical systems to connect elements and transmit power. The system is usually modeled as a single-degree-of-freedom system with a piecewise linear spring property, where the mass of main machine is only considered. In the present study, the dynamic behavior of a system with an unsymmetrical nonlinearity and a significant mass of the connecting part was investigated both experimentally and by numerical simulation. In the experiment, a 1/3 sub-harmonic oscillation was observed, but this oscillation was not found in the simulation using a single-degree-of-freedom system, in which the mass of the connecting part was ignored. However, when a two-degrees-of-freedom system was used that considered both the mass of the connecting part and the impact property, the 1/3 sub-harmonic oscillation was observed. Thus it is recognized that an adequate mathematical model for diagnosis in the early stage of abnormality must be selected on the basis of the mass ratio between the connecting part and the main body. 相似文献
69.
70.
Sarah W. Kamau Chapman Paul O. Hassa Sabine Koch-Schneidemann Brigitte von Rechenberg Margarethe Hofmann-Amtenbrink Benedikt Steitz Alke Petri-Fink Heinrich Hofmann Michael O. Hottiger 《Journal of magnetism and magnetic materials》2008
Primary cell lines are more difficult to transfect when compared to immortalized/transformed cell lines, and hence new techniques are required to enhance the transfection efficiency in these cells. We isolated and established primary cultures of synoviocytes, chondrocytes, osteoblasts, melanocytes, macrophages, lung fibroblasts, and embryonic fibroblasts. These cells differed in several properties, and hence were a good representative sample of cells that would be targeted for expression and delivery of therapeutic genes in vivo. The efficiency of gene delivery in all these cells was enhanced using polyethylenimine-coated polyMAG magnetic nanoparticles, and the rates (17–84.2%) surpassed those previously achieved using other methods, especially in cells that are difficult to transfect. The application of permanent and pulsating magnetic fields significantly enhanced the transfection efficiencies in synoviocytes, chondrocytes, osteoblasts, melanocytes and lung fibroblasts, within 5 min of exposure to these magnetic fields. This is an added advantage for future in vivo applications, where rapid gene delivery is required before systemic clearance or filtration of the gene vectors occurs. 相似文献