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111.
A greater ductility of cellulosic materials is important if they are to be used in increasingly advanced applications. This study explores the potential for using chemical core-shell structuring on the nanofibril level to alter the mechanical properties of cellulose fibres and sheets made thereof. The structuring was achieved by a selective oxidation of the cellulose C2–C3 bonds with sodium periodate, followed by a reduction of the aldehydes formed with sodium borohydride, i.e. locally transforming cellulose to dialcohol cellulose. The resulting fibres were morphologically characterised and the sheets made of these modified fibres were mechanically tested. These analyses showed a minor decrease in the degree of polymerisation, a significantly reduced cellulose crystal width and a greater ductility. At 27 % conversion of the available C2–C3 bonds, sheets could be strained 11 %, having a stress at break of about 90 MPa, and consequently a remarkable tensile energy absorption at rupture of about 9 kJ/kg, i.e. 3–4 times higher than a strong conventional paper. Zero-span tensile measurements indicated that the treatment increased the ductility not only of sheets but also of individual fibres. This suggests that the amorphous and molecularly more mobile dialcohol cellulose is located as a shell surrounding the crystalline core of the cellulose fibrils, and that, at deformations beyond the yield point, this facilitates plastic deformation both within and between individual fibres. 相似文献
112.
A high-order immersed boundary method is devised for the compressible Navier-Stokes equations by employing high-order summation-by-parts difference operators. The immersed boundaries are treated as sharp interfaces by enforcing the solid wall boundary conditions via flow variables at ghost points. Two different interpolation schemes are tested to compute values at the ghost points and a hybrid treatment is used. The first method provides the bilinearly interpolated flow variables at the image points of the corresponding ghost points and the second method applies the boundary condition at the immersed boundary by using the weighted least squares method with high-order polynomials. The approach is verified and validated for compressible flow past a circular cylinder at moderate Reynolds numbers. The tonal sound generated by vortex shedding from a circular cylinder is also investigated. In order to demonstrate the capability of the solver to handle complex geometries in practical cases, flow in a cross-section of a human upper airway is simulated. 相似文献
113.
Ab initio calculatios have been made for a series of simple alkanes and the atomic charges have been estimated in two ways, using the Mulliken population analysis and also using an analysis due to Karlström where the charges are fitted to describe the electrical moments derived from the SCF wave function. Also the orbital energies were calculated. The results were used to interpret experimental data of the carbon core electron binding energies. It is found that the Karlström technique is best suited to describe the XPS data. 相似文献
114.
Martin Adiels Thomas Larsson Pauline Sutton Marja‐Riitta Taskinen Jan Borén Barbara A. Fielding 《Rapid communications in mass spectrometry : RCM》2010,24(5):586-592
Stable isotope kinetic studies play an important role in the study of very‐low density lipoprotein (VLDL) metabolism, including basic and clinical research. Today, [1,1,2,3,3‐2H5]glycerol is the most cost‐effective alternative to measure glycerol and triglyceride kinetics. Recycling of glycerol from glycolysis and gluconeogenesis may lead to incompletely labelled tracer molecules. Many existing methods for the measurement of glycerol isotopic enrichment involve the production of glycerol derivatives that result in fragmentation of the glycerol molecule after ionization. It would be favourable to measure the intact tracer molecule since incompletely labelled tracer molecules may be measured as fully labelled. The number of methods available to measure the intact tracer in biological samples is limited. The aim of this project was to develop a gas chromatography/mass spectrometry (GC/MS) method for glycerol enrichment that measures the intact glycerol backbone and is suitable for electron ionization (EI), which is widely available. A previously published method for N‐methyl‐N‐[tert‐butyldimethylsilyl]trifluoroacetamide (MTBSTFA) derivatization was significantly improved; we produced a stable derivative and increased recovery 27‐fold in standards. We used the optimized MTBSTFA method in VLDL‐triglyceride and found that further modification was required to take matrix effects into account. We now have a robust method to measure glycerol isotopic enrichment by GC/EI‐MS that can be used to rule out the known problem of tracer recycling in studies of VLDL kinetics. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
115.
A. Jurgilaitis R. Nüske H. Enquist H. Navirian P. Sondhauss J. Larsson 《Applied Physics A: Materials Science & Processing》2010,100(1):105-112
In this paper, we present the investigation and characterization of the laser-induced surface structure on an asymmetrically
cut InSb crystal. We describe diffraction from the ripple surface and present a theoretical model that can be used to simulate
X-ray energy scans. The asymmetrically cut InSb sample was irradiated with short-pulse radiation centred at 800 nm, with fluences
ranging from 10 to 80 mJ/cm2. The irradiated sample surface profile was investigated using optical and atomic force microscopy. We have investigated how
laser-induced ripples influence the possibility of studying repetitive melting of solids using X-ray diffraction. The main
effects arise from variations in local asymmetry angles, which reduce the attenuation length and increase the X-ray diffraction
efficiency. 相似文献
116.
A. V. Ivanov V. A. Konfederatov A. V. Gerasimenko A. -C. Larsson 《Russian Journal of Coordination Chemistry》2009,35(11):857-863
The crystalline polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S2P(O-iso-C3H7)2}]
n
(I) was obtained and examined by solid-state 13C and 31P CP/MAS NMR spectroscopy. Diagrams of the χ2 statistic were constructed from the complete 31P MAS NMR spectra and used to calculate the 31P chemical shift anisotropy (δaniso = (δ
zz
− δiso)) and the asymmetry parameter (η = (δ
yy
− δ
xx
)/(δ
zz
− δiso)). The 31P chemical shift tensor has a nearly axial symmetry (η = 0.22, δ
zz
< δ
yy
≈ δ
xx
). The MAS NMR spectral patterns correspond to the negative sign of δaniso (δ
zz
< δ
yy
< δ
xx
), which indicates bridging or chelating-bridging coordination of the dithiophosphate ligands (Dtph). X-ray diffraction analysis
revealed a polymeric structure of compound I. The polymer chain consists of alternating mononuclear [Tl{S2P(O-iso-C3H7)2}] molecules with opposite spatial orientations. The Dtph ligands are coordinated in a mixed, chelating-μ3-bridging fashion. The shape of the 31P NMR signal was interpreted in terms of the 31P-203,205Tl coupling pattern proposed from crystallographic data. 相似文献
117.
Kristensen EM Larsson R Sánchez J Rensmo H Gelius U Siegbahn H 《Colloids and surfaces. B, Biointerfaces》2006,49(1):1-7
The durability and functionality of a heparin coating on artificial heart valve leaflets were evaluated with X-ray photoelectron spectroscopy (XPS) and by the coatings' capacity to bind antithrombin. Current methods for accelerated life-time testing are based on exposing leaflets to water solutions. In this paper a method is explored, in which heart valve leaflets were exposed to a continuous high shear rate (4 L/min) of human citrated plasma. It was found that the heparin coating was stable and wear resistant enough to still be present after 3 weeks and to have about the same antithrombin uptake as coatings not exposed to circulating plasma. It was, however, partly destroyed by the test as found using XPS. We suggest that heparin chains from the upper layer of heparin have been torn off from the carrier chain, in combination with loss of heparin conjugate and plasma deposition in patches. This study showed that XPS provides additional information to biological measurements such as antithrombin uptake. XPS is therefore a valuable technique not only to characterize biomaterials but also to evaluate the effect of a performance test. 相似文献
118.
A non-alcoholic coulometric reagent based on N-methylformamide (NMF) was shown to eliminate the severe interference effect caused by the alcohol component of the conventional Karl Fischer (KF) reagent on the battery electrolyte lithium bis(oxalato)borate (LiBOB). For sample amounts up to 240 μg of water, the stoichiometry of the KF reaction deviated only slightly from the ideal 1:1 ratio for the best reagent composition. Both solid and dissolved (in acetonitrile, tetrahydrofuran (THF), and ethylene carbonate/ethyl methyl carbonate) LiBOB were titrated successfully using a Metrohm 756 KF Coulometer with a diaphragm cell. The detection limit was estimated to be 0.5-1 μg of water using 100 ml of reagent in this system. 相似文献
119.
We consider a semilinear parabolic PDE driven by additive noise. The equation is discretized in space by a standard piecewise linear finite element method. We show that the orthogonal expansion of the finite-dimensional Wiener process, that appears in the discretized problem, can be truncated severely without losing the asymptotic order of the method, provided that the kernel of the covariance operator of the Wiener process is smooth enough. For example, if the covariance operator is given by the Gauss kernel, then the number of terms to be kept is the quasi-logarithm of the number of terms in the original expansion. Then one can reduce the size of the corresponding linear algebra problem enormously and hence reduce the computational complexity, which is a key issue when stochastic problems are simulated. 相似文献
120.
Maria Daneva Torbjörn Larsson Michael Patriksson Clas Rydergren 《Computational Optimization and Applications》2010,46(3):451-466
The feasible direction method of Frank and Wolfe has been claimed to be efficient for solving the stochastic transportation
problem. While this is true for very moderate accuracy requirements, substantially more efficient algorithms are otherwise
diagonalized Newton and conjugate Frank–Wolfe algorithms, which we describe and evaluate. Like the Frank–Wolfe algorithm,
these two algorithms take advantage of the structure of the stochastic transportation problem. We also introduce a Frank–Wolfe
type algorithm with multi-dimensional search; this search procedure exploits the Cartesian product structure of the problem.
Numerical results for two classic test problem sets are given. The three new methods that are considered are shown to be superior
to the Frank–Wolfe method, and also to an earlier suggested heuristic acceleration of the Frank–Wolfe method. 相似文献