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581.
Niko Guskos Grzegorz Zolnierkiewicz Janusz Typek Aleksander Guskos Pawel Berczynski Dimitri Petridis 《Central European Journal of Physics》2012,10(1):166-171
Solids containing an extended network of free radicals have been prepared and studied by magnetic resonance techniques in
the 4–290 K temperature range. One solid contained additionally a small amount of magnetic γ-Fe2O3 in the form of nanoparticle agglomerates. The solid without agglomerates displayed only a narrow, single resonance line centered
at g
eff
= 2.0043. The magnetic resonance measurements of the solid with γ-Fe2O3 agglomerates gave a spectrum composed of two lines attributed to two different magnetic centers: a narrow line due to free
radicals and a broad line arising from magnetic iron oxide agglomerates. In the high temperature range the integrated intensities
of both lines decreased with decreasing temperature. The resonance field of the broad line shifted to lower magnetic fields
upon lowering the temperature with the gradient ΔH
r
/ΔT = 2.3 G/K, while the narrow line shifted towards higher magnetic fields. The linewidth of the broader line increased with
decreasing temperature while for the narrow lines in both samples this change was small. The magnetic iron oxide clusters
produce a magnetic field which acts on the free radicals network and its strength depends essentially on the concentration
of clusters. The reorientation process in the free radicals network is more intense in the sample without magnetic clusters. 相似文献
582.
The procedure of derivation of a new dynamical equation governing the vorticity mode that is generated by sound, is discussed in detail. It includes instantaneous quantities and does not require averaging over sound period. The resulting equation applies to both periodic and aperiodic sound as the origin of the vorticity mode. Under certain conditions, the direction of streamlines of the vorticity mode may be inverted as compared with that in a fluid with standard attenuation. This reflects an anomalous absorption of sound, when transfer of momentum of the vorticity mode into momentum of sound occurs. The theory is illustrated by a representative example of the generation of vorticity in a vibrationally relaxing gas in the field of periodic weakly diffracting acoustic beam. 相似文献
583.
Urban PL Jefimovs K Amantonico A Fagerer SR Schmid T Mädler S Puigmarti-Luis J Goedecke N Zenobi R 《Lab on a chip》2010,10(23):3206-3209
Functional high-density micro-arrays for mass spectrometry enable rapid picolitre-volume aliquoting and ultrasensitive analysis of microscale samples, for example, single cells. 相似文献
584.
A radially viewed inductively coupled argon plasma was used for optical emission spectrometry of volatile species formed by
reaction with NaBH4 (hydride generation). The volatile hydrides were either introduced into the plasma alone or at the same time as a sample
aerosol generated by pneumatic nebulization with a commercially available Concomitant Metals Analyzer. The effects of the
forward power, the presence of pre-reducing agents [(NH2)2SC, KI, KBr and hot HCl], the occurrence of easily ionized elements (Ca, K, Mg and Na) in the analyte solutions on the excitation
temperature (as measured via Ar atomic lines) and the electron number density were investigated for both of the sample introduction
modes applied. The detection limits and the signal-to-background intensity ratios for As, Bi, Sb, Se and Sn lines were also
evalutated and were observed to deteriorate with increasing power. When simultaneous hydride generation and pneumatic nebulization
was employed under optimized experimental conditions, detection limits of 3.5, 2.9, 4.3, 1.5 and 2.1 μg L−1 for As, Bi, Sb, Se and Sn, respectively, were obtained, and the intensities of the analytical lines for elements that do
not form volatile hydrides were found to be 40% (Cd), 30% (Ni), 20% (Co, Cr, Fe, Mn and Zn) and 10% (Cu, Mg, V) greater than
those obtained when only pneumatic nebulization was used. 相似文献
585.
Nataly Carolina Rosero-Navarro Pawel Figiel Roman Jedrzejewski Anna Biedunkiewicz Yolanda Castro Mario Aparicio Sergio Antonio Pellice Alicia Durán 《Journal of Sol-Gel Science and Technology》2010,54(3):301-311
The aim of this work was to study the effect of the incorporation of cerium nitrate in a silica-methacrylate sol–gel hybrid
matrix reinforced with silica nanoparticles. Sols, coatings and powders have been studied, focusing specially in the determination
of the redox ratio Ce3+/Ce4+ and films structure. Sols have been characterised using viscosity measurements and FT-IR spectroscopy, and powders and coatings
obtained with different Ce contents through UV–Vis and FT-IR spectroscopy, TGA, TEM, AFM and FE-SEM. The goal was to reach
the best compromise between maximum cerium concentration and coating stability to better understand the mechanisms acting
in active anti-corrosive processes. 相似文献
586.
Czerwinska M Sikora A Szajerski P Zielonka J Adamus J Marcinek A Piech K Bednarek P Bally T 《The Journal of organic chemistry》2006,71(14):5312-5319
One-electron reduction significantly enhances the ability of anthralin, 1, to act as a hydrogen atom donor. On annealing of an MTHF glass in which the radical anion of anthralin, 1*-, is generated radiolytically, this species decays mainly by loss of H* to give the anthralyl anion, 2- . On the other hand, radicals formed on radiolysis of matrices that are suitable for the generation of radical anions or cations are capable to abstract H* from anthralin to give the anthralyl radical, 2* . Both 2- and 2* are obtained simultaneously by mesolytic cleavage of the radical anion of the anthralin dimer. Contrary to general assumptions, the anthralyl radical is found to be much more reactive toward oxygen than the anion. All intermediates are characterized spectroscopically and by reference to quantum chemical calculations. Attempts to generate the radical cation of anthralin by X-irradiation of an Ar matrix containing anthralin led also to significant formation of its radical anion, i.e., anthralin acts apparently as an efficient electron trap in such experiments. 相似文献
587.
Two mechanisms of the Scholl reaction were investigated in the series 1, 2, ..., n-oligophenylbenzenes (n = 2, 3, 4, 6) at the B3LYP/6-31G(d) level of theory. A mechanism involving generation of a radical cation followed by C-C bond formation and dehydrogenation is unlikely on the basis of unfavorable energies of activation. A mechanism involving generation of an arenium cation followed by C-C bond formation and dehydrogenation is energetically feasible. An explanation for the facile polycondensation of hexaphenylbenzene to hexa-peri-hexabenzocoronene, where six new aryl-aryl bonds are formed, is provided. Kinetic simulations based on the calculated activation energies of the arenium cation mechanism predict that intermediates will not accumulate; this is supported by mass balance experiments. Reaction optimization studies suggest that PhI(O2CCF3)2/BF3.OEt2 or MoCl5 are superior to FeCl3 or AlCl3/CuCl2. This is a full account of our work reported partially as a communication previously (Rempala, P.; Kroulík, J.; King, B. T. J. Am. Chem. Soc. 2004, 126, 15002-15003). 相似文献
588.
We provide an explicit formula for the Fefferman-Graham ambient metric of an n-dimensional conformal pp-wave in those cases where it exists. In even dimensions we calculate the obstruction explicitly. Furthermore, we describe
all 4-dimensional pp-waves that are Bach-flat, and give a large class of Bach-flat examples which are conformally Cotton-flat, but not conformally
Einstein. Finally, as an application, we use the obtained ambient metric to show that even-dimensional pp-waves have vanishing critical Q-curvature. 相似文献
589.
Density functional theory and quantum mechanics/molecular mechanics computations predict cob(I)alamin (Co(+)Cbx), a universal B(12) intermediate state, to be a pentacoordinated square pyramidal complex, which is different from the most widely accepted viewpoint of its tetracoordinated square planar geometry. The square pyramidality of Co(+)Cbx is inspired by the fact that a Co(+) ion, which has a dominant d(8) electronic configuration, forms a distinctive Co(+)--H interaction because of the availability of appropriately oriented filled d orbitals. This uniquely H-bonded Co(+)Cbx may have catalytic relevance in the context of thermodynamically uphill Co(2+)/Co(+) reduction that constitutes an essential component in a large variety of methyltransferases. 相似文献
590.
Pawel Mrozowski Andrzej Chydzinski 《Methodology and Computing in Applied Probability》2018,20(1):97-115
We present an analysis of the queueing system in which arriving jobs are dropped with probability depending on the queue size. The arrivals are assumed to be autocorrelated and they are modeled by the Markov-modulated Poisson process. Both transient and stationary distributions of the queue size, as well as the system loss ratio and throughput are obtained. The analytical results are accompanied with numerical examples based on the autocorrelated traffic recorded in an IP computer network. 相似文献