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排序方式: 共有216条查询结果,搜索用时 125 毫秒
51.
George H. Major Vincent Fernandez Neal Fairley Matthew R. Linford 《Surface and interface analysis : SIA》2022,54(3):262-269
The Gaussian–Lorentzian sum (GLS) and product (GLP) functions remain important in X-ray photoelectron spectroscopy (XPS) peak fitting. Here, we present a detailed view of these functions, comparing them with each other and with the Voigt function (the “LA(m)” function). First, we show the GLS, GLP, and LA(m) functions as a function of their mixing parameters, m, which reveals differences between them. We then illustrate the use of these functions to fit a series of spectra acquired at different pass energies (resolutions). Next, we show the underlying Gaussian and Lorentzian components of a series of GLS and GLP functions as a function of m, which confirms that the GLS is a simple linear combination of Gaussian and Lorentzian functions. However, one of the two functions used to make the GLP can be very wide, that is, at its extremes, one of these functions has infinite width. We then discuss a plot of the areas of the GLS, GLP, and LA(m) functions as a function of m, which reveals the expected, linear increase in area of the GLS, but nonlinear changes in the areas of the other two functions. Finally, to better understand them, we fit these functions to each other. These results indicate that the GLS and GLP better match the LA(m) function at lower and higher values of the mixing parameter, respectively. 相似文献
52.
53.
Combined QM/MM simulations have been carried out to investigate the origin of the carbon acidity enhancement in the alanine racemization reaction catalyzed by alanine racemase (AlaR). The present studies show that enhancement of carbon acidity of alpha-amino acids by cofactor pyridoxal 5'-phosphate, PLP, with an unusual, unprotonated pyridine is due to solvation effects, in contrast to the intrinsic electron-withdrawing stabilization by the pyridinium ion to form a quinonoid intermediate. Alanine racemase further lowers the alpha-proton acidity and provides an overall 14-17 kcal/mol transition state stabilization. Our computational results are consistent with the hypothesis that the use of the unusual form of PLP cofactor in AlaR is to raise the free energy of the intermediate, thereby increasing the reprotonation rate and enhancing the enzyme selectivity for racemization. 相似文献
54.
Combined quantum mechanical/molecular mechanical simulations have been carried out to investigate the origin of the carbon acidity enhancement in the alanine racemization reaction catalyzed by alanine racemase (AlaR). The present study shows that the enhancement of carbon acidity of alpha-amino acids by the cofactor pyridoxal 5'-phosphate (PLP) with an unusual, unprotonated pyridine is mainly due to solvation effects, in contrast to the intrinsic electron-withdrawing stabilization by the pyridinium ion to form a quinonoid intermediate. Alanine racemase further lowers the alpha-proton acidity and provides an overall 14-17 kcal/mol transition-state stabilization. The second key finding of this study is that the mechanism of racemization of an alanine zwitterion in water is altered from an essentially concerted process to a stepwise reaction by formation of an external aldimine adduct with the PLP cofactor. Finally, we have used a centroid path integral method to determine the intrinsic kinetic isotope effects for the two proton abstraction reactions, which are somewhat greater than the experimental estimates. 相似文献
55.
Péter Major 《Probability Theory and Related Fields》2006,134(3):489-537
Let a sequence of iid. random variables ξ
1, . . . ,ξ
n
be given on a space
with distribution μ together with a nice class
of functions f(x
1, . . . ,x
k
) of k variables on the product space
For all f ∈
we consider the random integral J
n,k
(f) of the function f with respect to the k-fold product of the normalized signed measure
where μ
n
denotes the empirical measure defined by the random variables ξ
1, . . . ,ξ
n
and investigate the probabilities
for all x>0. We show that for nice classes of functions, for instance if
is a Vapnik–Červonenkis class, an almost as good bound can be given for these probabilities as in the case when only the
random integral of one function is considered. A similar result holds for degenerate U-statistics, too.
Supported by the OTKA foundation Nr. 037886 相似文献
56.
Dugdale SB Watts RJ Laverock J Major Z Alam MA Samsel-Czekała M Kontrym-Sznajd G Sakurai Y Itou M Fort D 《Physical review letters》2006,96(4):046406
The Fermi surface topology of the shape-memory alloy Ni0.62Al0.38 has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of approximately 0.18[1,1,0](2pi/a), which corresponds to the wave vector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these phenomena are driven by the enhanced electron-lattice coupling due to the Fermi surface nesting. 相似文献
57.
58.
Katarzyna Kasperkiewicz Roman Major Anna Sypien Marcin Kot Marcin Dyner ukasz Major Adam Byrski Magdalena Kopernik Juergen M. Lackner 《Molecules (Basel, Switzerland)》2021,26(11)
The goal of the work was to develop materials dedicated to spine surgery that minimized the potential for infection originating from the transfer of bacteria during long surgeries. The bacteria form biofilms, causing implant loosening, pain and finally, a risk of paralysis for patients. Our strategy focused both on improvement of antibacterial properties against bacteria adhesion and on wear and corrosion resistance of tools for spine surgery. Further, a ~35% decrease in implant and tool dimensions was expected by introducing ultrahigh-strength titanium alloys for less-invasive surgeries. The tested materials, in the form of thin, multi-layered coatings, showed nanocrystalline microstructures. Performed direct-cytotoxicity studies (including lactate dehydrogenase activity measurement) showed that there was a low probability of adverse effects on surrounding SAOS-2 (Homo sapiens bone osteosarcoma) cells. The microbiological studies (e.g., ISO 22196 contact tests) showed that implanting Ag nanoparticles into Ti/TixN coatings inhibited the growth of E. coli and S. aureus cells and reduced their adhesion to the material surface. These findings suggest that Ag-nanoparticles present in implant coatings may potentially minimize infection risk and lower inherent stress. 相似文献
59.
M. Hampele A. Kratzer K. Maier J. Major K. -H. Münch Th. Pfiz 《Hyperfine Interactions》1994,87(1):1043-1047
A new analog integrating detection technique for time resolvedSR measurements at high intensity pulsed muon beams has been developed. Data acquisition is realized by digitizing the integrated anode signal for each burst by means of a fast transient recorder. Details of setup and performance are described. 相似文献
60.
Nonlinear Dynamics - Port Knocking is a method for authenticating clients through a closed stance firewall, and authorising their requested actions, enabling severs to offer services to... 相似文献