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991.
The role of order within a porous separation matrix on the separation efficiency of DNA was studied systematically. DNA separation was based on a ratchet mechanism. Monodisperse colloidal suspensions of nanoparticles were used to fabricate highly ordered separation media with a hexagonal close-packed structure. Doping with a second particle size yielded structures with different degrees of disorder, depending upon the volume fraction of each particle size. Radial distribution functions and orientational order parameters were calculated from electron micrographs to characterize the scale of disorder. The peak separation distance, band broadening, and separation resolution of DNA molecules was quantified for each structure. DNA separation parameters using pulsed fields and the ratchet effect showed a strong dependence on order within the porous nanoparticle array. Ordered structures gave large separation distances, smaller band broadening and better resolution than highly disordered, nearly random, porous structures. The effect dominated these three parameters when compared to the effect of pore size. However, the effect of order on separation performance was not monotonic. A small, but statistically significant improvement was seen in structures with short range order compared to those with long range order. 相似文献
992.
G. Moldovan M. J. Roe I. Harrison M. Kappers C. J. Humphreys P. D. Brown 《哲学杂志》2013,93(16):2315-2327
The effects of a KOH treatment on the properties of n-type GaN surfaces and associated Au/n-GaN contacts have been investigated by X-ray photoelectron spectroscopy, atomic force microscopy, reflection high-energy-electron diffraction, current–voltage and electron-beam-induced current characterization. Ga-polar surfaces grown by molecular beam epitaxy and metal–organic chemical vapour deposition were compared. A decrease in electron barrier height and an increase in non-radiative recombination properties of Au/n-GaN contacts were found with KOH treatment, correlated with an increase of surface Ga vacancies, an increase in surface N–H2 content and a decrease in surface C contamination. A 0.3-eV shift in the Ga3d peak position towards the valence band and a reduction in the dislocation contrast were observed for the case of molecular-beam-epitaxy-grown GaN only, demonstrating that surface Ga vacancies and threading dislocations play only a limited role in defining the resultant metal/GaN contact properties. Accordingly, the surface atomic content and the resulting surface states, following KOH treatment, should be taken into consideration when appraising the electrical properties of n-GaN surfaces and the performance of associated metallic contacts. 相似文献
993.
The crystal lamella is well established as a basic structural unit of most semicrystalline polymers. It is also accepted that the chain axis is generally not parallel to the normal to the large flat lamella surfaces, but inclined at some angle θ to it. Due to the random orientation of lamellae in bulk polymers where spherulitic growth predominates, no direct method exists for determining θ. However, the angle has been determined by acid etching bulk samples and then using electron microscopy techniques on fragments. An alternative approach is utilized in this work. The etched fragments, after suitable washing procedures, were sedimented to form an oriented mat. An x-ray diffraction technique was employed in which the regions of high pole density for several crystallographic planes were determined. From these results, the inclination angle was determined to be 40.4°, with a standard deviation of 1.5°. This study represents the first time that an x-ray pole figure technique has been used to determine chain inclination in isotherm-ally crystallized PE. 相似文献
994.
Abstract The recent interest in gas discharge ion sources for analytical mass spectrometry illustrates the often cyclic nature of scientific progress. The ion source capabilities of a gas discharge were discovered by Goldstein [1] in 1886 and such discharges were used by the pioneer mass spectroscopists (Thomson, Aston, and Bainbridge) as a convenient source of ions. The simplicity of design (see Fig. 1) and the high output ion currents were decisive factors in such applications. Alternative ion sources then replaced the gas discharge, to the point where the production of ions by gaseous discharge was suggested, correctly, to be of “more historical than contemporary interest” [2]. Nevertheless, new requirements and developments, as described in this paper, have once again drawn attention to the plasma ion source as having possible specialized and valuable analytical applications. 相似文献
995.
J. Runt I. R. Harrison W. D. Varnell J. I. Wang 《Journal of Macromolecular Science: Physics》2013,52(2):197-212
Chain lengths have been calculated from the peak positions of the longitudinal acoustic modes (LAM) of polyethylene single crystals grown at several different temperatures. The data are consistent with other experimental results when the crystalline elastic modulus is taken to be 3.6 × 1012 dyn/cm2. However, this is true only if the vibrations of the crystalline chain segments are unaffected by the presence of folds and cilia on the crystal surface. The LAMs of several crystal preparations were also deconvoluted with the first-order LAM of C94H190 in order to remove instrumental broadening. The band shapes of the deconvoluted spectra are consistent with the idea that the LAM of polyethylene crystals is composed of two contributions: One due to chain stems in 110 sectors and a second due to chains in 200 sectors. 相似文献
996.
Albert Koulman Geoffrey A. Lane Scott J. Harrison Dietrich A. Volmer 《Analytical and bioanalytical chemistry》2009,394(3):663-670
The current developments in metabolomics and metabolic profiling technologies have led to the discovery of several new metabolic
biomarkers. Finding metabolites present in significantly different levels between sample sets, however, does not necessarily
make these metabolites useful biomarkers. The route to valid and applicable biomarkers (biomarker qualification) is long and
demands a significant amount of work. In this overview, we critically discuss the current state-of-the-art of metabolic biomarker
discovery, with highlights and shortcomings, and suggest a pathway to clinical usefulness.
相似文献
Dietrich A. VolmerEmail: |
997.
W. W. Harrison 《Analytical and bioanalytical chemistry》1986,324(8):886-886
998.
999.
The nanosecond optical Kerr constants of a series of alkanoic acids from formic acid to nonanoic acid have been measured at the two inducing wavelengths of 532 and 1064 nm. Results indicate that the values are of similar magnitude to a previous study of the 1-alkyne series and exhibit a similar behaviour of relatively invariant values amongst the higher members of the series. This effect is attributed to the dominant contribution of the carbonyl group to the observed optical Kerr constant. 相似文献
1000.