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991.
992.
Maria G. Babashkina Elmira R. Shakirova Dr. Damir A. Safin Felix D. Sokolov Axel Klein Łukasz Szyrwiel Maria Kubiak Henryk Kozlowski Dmitriy B. Krivolapov 《无机化学与普通化学杂志》2010,636(15):2626-2632
Reaction of O,O′‐diisopropylthiophosphoric acid isothiocyanate (iPrO)2P(S)NCS with 1,10‐diaza‐18‐crown‐6, 1,7‐diaza‐18‐crown‐6, or 1,7‐diaza‐15‐crown‐5 leads to the N‐thiophosphorylated bis‐thioureas N,N′‐bis[C(S)NHP(S)(OiPr)2]‐1,10‐diaza‐18‐crown‐6 ( H2LI ), N,N′‐bis[C(S)NHP(S)(OiPr)2]‐1,7‐diaza‐18‐crown‐6 ( H2LII ) and N,N′‐bis[C(S)NHP(S)(OiPr)2]‐1,7‐diaza‐15‐crown‐5 ( H2LIII ). Reaction of the potassium salts of H2LI–III with a mixture of CuI and 2,2′‐bipyridine ( bpy ) or 1,10‐phenanthroline ( phen ) in aqueous EtOH/CH2Cl2 leads to the dinuclear complexes [Cu2(bpy)2LI–III] and [Cu2(phen)2LI–III] . The structures of these compounds were investigated by 1H, 31P{1H} NMR spectroscopy, and elemental analysis. The crystal structures of H2LI and [Cu2(phen)2LI] were determined by single‐crystal X‐ray diffraction. Extraction capacities of the obtained compounds in comparison to the related compounds 1,10‐diaza‐18‐crown‐6, N,N′‐bis[C(=CMe2)CH2P(O)(OiPr)2]‐1,10‐diaza‐18‐crown‐6, N,N′‐bis[C(S)NHP(O)(OiPr)2]‐1,10‐diaza‐18‐crown‐6 towards the picrate salts LiPic, NaPic, KPic. and NH4Pic were also studied. 相似文献
993.
Eghbali E Colombani O Drechsler M Müller AH Hoffmann H 《Langmuir : the ACS journal of surfaces and colloids》2006,22(10):4766-4776
The surface activity and the rheological properties of aqueous solutions of the amphiphilic block copolymer poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA-b-PAA) were studied as a function of the degree of neutralization, alpha, of the poly(acrylic acid) block. Although the block copolymer spontaneously forms spherical micelles having a stretched PAA corona and a collapsed PnBA core in water for alpha > 0.1, the solutions do not exhibit any surface activity at this degree of neutralization. Cryo-TEM micrographs show that the radii of the hydrophobic core of the largest micelles are as long as the length of the hydrophobic chain. The micelles, however, have a broad size distribution, and on average, as shown by SANS, the micelles are only about half as long. At concentrations as low as 1 wt %, the solutions exhibit highly viscoelastic behavior and have a yield stress value depending on alpha. The globular micelles are highly ordered in the bulk phase, and the viscoelastic properties are a result of the dense packing of the micelles. The addition of salt or cationic surfactants dramatically decreases the viscosity of the solution. The observed properties seem to be due to electrostatic interactions between the PAA chains of the micelles. 相似文献
994.
The methodology for obtaining two- and three-dimensional magnetic resonance images by using azimuthally symmetric dipolar magnetic fields from ferromagnetic spheres is described. We utilize the symmetric property of a geometric sphere in the presence of a large externally applied magnetic field to demonstrate that a complete two- or three-dimensional structured rendering of a sample can be obtained without the motion of the sample relative to the sphere. Sequential positioning of the integrated sample-sphere system in an external magnetic field at various angular orientations provides all the required imaging slices for successful computerized tomographic image reconstruction. The elimination of the requirement to scan the sample relative to the ferromagnetic tip in this imaging protocol is a potentially valuable simplification compared to previous scanning probe magnetic resonance imaging proposals. 相似文献
995.
Eimear Byrne Marcus Greferath Axel Kohnert Vitaly Skachek 《Designs, Codes and Cryptography》2010,57(2):169-179
We give further results on the question of code optimality for linear codes over finite Frobenius rings for the homogeneous
weight. This article improves on the existing Plotkin bound derived in an earlier paper (Greferath and O’Sullivan, Discr Math
289:11–24, 2004) and suggests a version of a Singleton bound. We also present some families of codes meeting these new bounds. 相似文献
996.
A graph G is close to regular or more precisely a (d, d + k)-graph, if the degree of each vertex of G is between d and d + k. Let d ≥ 2 be an integer, and let G be a connected bipartite (d, d+k)-graph with partite sets X and Y such that |X|- |Y|+1. If G is of order n without an almost perfect matching, then we show in this paper that·n ≥ 6d +7 when k = 1,·n ≥ 4d+ 5 when k = 2,·n ≥ 4d+3 when k≥3.Examples will demonstrate that the given bounds on the order of G are the best possible. 相似文献
997.
Gianmarco Aversano John Camilo Parra-Alvarez Benjamin J. Isaac Sean T. Smith Axel Coussement Olivier Gicquel Alessandro Parente 《Proceedings of the Combustion Institute》2019,37(4):4461-4469
For stationary power sources such as utility boilers, it is useful to dispose of parametric models able to describe their behavior in a wide range of operating conditions, to predict some Quantities of Interest (QOIs) that need to be consistent with experimental observations. The development of predictive simulation tools for large scale systems cannot rely on full-order models, as the latter would lead to prohibitive costs when coupled to sampling techniques in the model parameter space. An alternative approach consists of using a Surrogate Model (SM). As the number of QOIs is often high and many SMs need to be trained, Principal Component Analysis (PCA) can be used to encode the set of QOIs in a much smaller set of scalars, called PCA scores. A SM is then built for each PCA score rather than for each QOI. The advantage of reducing the number of variables is twofold: computational costs are reduced (less SMs need to be trained) and information is preserved (correlation among the original variables).The strategy is applied to a CFD model simulating the Alstom 15 MWth oxy-pilot Boiler Simulation Facility (BSF). In practice, experiments cannot provide full coverage of the pulverized-coal utility boiler due to both practicality and costs. Values of the model’s parameters which guarantee consistency with the experimental data of this test facility for 121 QOIs are found, by training a SM based on the combination of Kriging and PCA, using only 5 latent variables. 相似文献
998.
The International System of Units’ (SI) base unit of the quantity “amount of substance” is the mole (symbol: mol). After the revision of the SI to be implemented in 2019, when all SI units will be based solely on constants, the mole will be defined through a fixed value of the Avogadro constant NA. One mole contains exactly 6.02214076 × 1023 elementary entities, meaning the mole will no longer be linked to the kilogram. Currently, the mole is defined via the mass of exactly 0.012 kg of the 12C isotope which links it to the kilogram prototype. The history, changes, and implications of the revised definition of the mole are discussed here from the chemist's point of view. The ability to count entities such as atoms or molecules (precisely enough to enable a revision of the SI and preserve consistency of previous and future measurements) is crucial. This is achieved with the realization (Mise en Pratique) based on the X‐ray‐crystal density (XRCD) method (counting the atoms in a silicon sphere). The determination of NA, focusing on the measurement of the molar mass of silicon highly enriched in the 28Si isotope, with the lowest uncertainty so far, is presented. 相似文献
999.
1000.
Enhancements in full‐field PIXE imaging—Large area elemental mapping with increased lateral resolution devoid of optics artefacts
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Josef Buchriegler Nico Klingner Daniel Hanf Frans Munnik Stanisław H. Nowak Oliver Scharf René Ziegenrücker Axel D. Renno Johannes von Borany 《X射线光谱测定》2018,47(4):327-338
The combination of a pn‐junction charge‐coupled device‐based pixel detector with a poly‐capillary X‐ray optics was installed and examined at the Helmholtz‐Zentrum Dresden‐Rossendorf. The set‐up is intended for particle‐induced X‐ray emission imaging to survey the trace elemental composition of flat/polished geological samples. In the standard configuration, a straight X‐ray optics (20 μm capillary diameter) is used to guide the emitted photons from the sample towards the detector with nearly 70 000 pixels. Their dimensions of 48 × 48 μm2 are the main limitation of the lateral resolution. This limitation can be bypassed by applying a dedicated subpixel algorithm to recalculate the footprint of the photon's electron cloud in the detector. The lateral resolution is then mainly determined by the capillary's diameter. Nevertheless, images are still superimposed by the X‐ray optics pattern. The optics' capillaries are grouped in hexagonal bundles resulting in a reduced transmission of X‐rays in the boundary regions. This influence can be largely suppressed by combining a series of short measurements at slightly shifted positions using a precision stage and correcting the image data for this shifting. The use of a subpixel grid for the image reconstruction allows a further increase of the spatial resolution. This approach of image‐stacking and multiframe super‐resolution in combination with the subpixel correction algorithm is presented and illustrated with experimental data. Additionally, a flat‐field correction is shown to remove the remaining imaging inhomogeneity caused by non‐uniform X‐ray transmission. The described techniques can be used for all X‐ray spectrometry methods using an X‐ray camera to obtain high‐quality elemental images. 相似文献