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581.
582.
Lee JL Gilmore IS Seah MP Fletcher IW 《Journal of the American Society for Mass Spectrometry》2011,22(10):1718-1728
Quantitative chemical characterization of surfaces with topography by secondary ion mass spectrometry (SIMS) remains a significant
challenge due to the lack of systematic and validated measurement methods. In this study, we combine an experimental approach
using a simple model system with computer simulation using SIMION, to understand and quantify the key factors that give rise
to unwanted topographic artefacts in SIMS images of conducting samples with microscale topography. Experimental data are acquired
for gold wires (diameters 33 to 125 μm) mounted onto silicon wafers. Significant loss of ion intensities and shadowing arise
from the distortion of the extraction field, and the chemical analysis over the whole of the sample surface is difficult.
For large primary ion incidence angles of ≥55° to the surface normal, a fraction of the primary ions are scattered from the
target and impact the substrate, emitting secondary ions that may be mistaken as originating from the wire. For conducting
samples, topographic field effects may be reduced by the use of a smaller extraction voltage and an extraction delay. The
effects of an extraction delay on ion intensities, mass resolution and time-of-flight are studied, and its application is
demonstrated on an anisotropically etched silicon sample. The use of a simple sample holder with a V-shaped groove to reduce
topographic field effects for wires is also presented. Using these results, we provide clear guidance to analysts for the
diagnosis and identification of topography effects in SIMS, and present key recommendations to minimize them in practical
analysis. 相似文献
583.
Filopodia are long, fingerlike membrane tubes supported by cytoskeletal filaments. Their shape is determined by the stiffness of the actin filament bundles found inside them and by the interplay between the surface tension and bending rigidity of the membrane. Although one might expect the Euler buckling instability to limit the length of filopodia, we show through simple energetic considerations that this is in general not the case. By further analyzing the statics of filaments inside membrane tubes, and through computer simulations that capture membrane and filament fluctuations, we show under which conditions filopodia of arbitrary lengths are stable. We discuss several in vitro experiments where this kind of stability has already been observed. Furthermore, we predict that the filaments in long, stable filopodia adopt a helical shape. 相似文献
584.
We measure the expansion of an ultracold plasma across the field lines of a uniform magnetic field. We image the ion distribution by extracting the ions with a high-voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (<20 micros), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of the magnetic field (up to 70 G). We observe that the expansion velocity scales as B(-1/2), explained by a nonlinear ambipolar diffusion model with anisotropic diffusion in two different directions. 相似文献
585.
586.
Dr. Inci Barut Dr. Xiulan He Assoc. Prof. Erol Sener Dr. Sanna Sämfors Prof. Andrew G. Ewing Prof. John S. Fletcher 《Angewandte Chemie (International ed. in English)》2023,62(15):e202217993
Aberrant functioning of the proteasome has been associated with crucial pathologic conditions including neurodegeneration. Yet, the complex underlying causes at the cellular level remain unclear and there are conflicting reports of neuroprotective to neurodegenerative effects of proteasomal inhibitors such as lactacystin that are utilised as models for neurodegenerative diseases. The conflicting results may be associated with different dose regimes of lactacystin and hence we have performed a dose dependent study of the effects of lactacystin to identify concurrent changes in the cell membrane lipid profile and the dynamics of exocytosis using a combination of surface sensitive mass spectrometry and single cell amperometry. Significant changes of negatively charged lipids were associated with different lactacystin doses that showed a weak correlation with exocytosis while changes in PE and PE−O lipids showed dose dependent changes correlated with initial pore formation and total release of vesicle content respectively. 相似文献