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991.
Tina Loth Robert Hennig Christian Kascholke Rudi Hötzel Michael C. Hacker 《Reactive and Functional Polymers》2013,73(11):1480-1492
Macromers with functional groups that allow for chemical derivatization, polymerization reactions or impart specific physico-chemical properties are functional building blocks for polymeric systems used in different biomedical applications. With this motivation, a series of oligomeric macromers was synthesized by free radical polymerization of maleic anhydride (MA) with N-isopropylacrylamide (NiPAAm) and pentaerythritol diacrylate monostearate (PEDAS). This chemical design provides anhydride groups for effective reactivity of the macromers with amines and other nucleophiles, copolymerized NiPAAm for temperature responsiveness and lipophilic stearate domains for increased hydrogel stability. Macromers were synthesized with different MA co-monomer feeds and oligomeric molecules (Mn below 5000 Da) were obtained with MA contents between 7% and 27% as determined by titration. The fraction of chemically intact anhydrides was calculated to range from 75% to 80%. The ability of the macromers to cross-link di- or oligovalent amines as a function of MA content was investigated rheologically. It was also demonstrated that monovalent amines, e.g. aminofluorescein, could be grafted to the macromer chain utilizing only a fraction of the anhydride functionalities. The derivatized macromers could still participate in cross-linking reactions due to the remaining anhydrides. Temperature sensitivity was shown for aqueous solutions of macromers with fully dissociated anhydride groups. The solutions were additionally responsive to changes in calcium ion concentration and pH. Extracts from macromer cross-linked polyether hydrogels showed no toxicity on L929 fibroblasts.The macromers have perspective as biocompatible cross-linkers for hydrogel fabrication from various biomacromolecules with the opportunity to decorate the gels with monoamine molecules that alter the biological or physico-chemical properties. 相似文献
992.
Mohsen Danaie Christian MauerDavid Mitlin Jacques Huot 《International Journal of Hydrogen Energy》2011,36(4):3022-3036
We have tested the hydrogen storage cycling behavior of bulk centimeter-scale magnesium - titanium and magnesium - stainless steel multilayer composites synthesized by accumulative roll-bonding (ARB). Roll-bonding of either titanium or stainless steel with magnesium allows the reversible hydrogen sorption of the resulting composite at 350 °C. Identically roll-bonded pure magnesium can hardly be absorbed at this temperature. In the composites, the kinetics of the first cycle of absorption (also called “activation”) improves with increased number of fold and roll (FR) operations. With increasing FR operations the distribution of the Ti phase is progressively refined, and the shape of the absorption curve no longer remains sigmoidal. Increasing the loading amount of the second phase also accelerates the kinetics. This holds true up to a threshold limit. Microscopy analysis performed on 1-2 wt.% hydrogen absorbed composites demonstrates that MgH2 formed exclusively on various heterogeneous nucleation sites. During activation, MgH2 nucleation occurred at the Mg-hard phase interfaces. During the subsequent absorption cycles, heterogeneous nucleation primarily occurred in the vicinity of “internal” free surfaces such as cracks. 相似文献
993.
994.
995.
Christian Glaßer Katrin Herr Christian Reitwießner Stephen Travers Matthias Waldherr 《Theory of Computing Systems》2010,46(1):80-103
We investigate the complexity of equivalence problems for {∪,∩,−,+,×}-circuits computing sets of natural numbers. These problems were first introduced by Stockmeyer and Meyer (1973). We
continue this line of research and give a systematic characterization of the complexity of equivalence problems over sets
of natural numbers. Our work shows that equivalence problems capture a wide range of complexity classes like NL, C
=
L, P,Π2P, PSPACE, NEXP, and beyond. McKenzie and Wagner (2003) studied related membership problems for circuits over sets of natural numbers. Our results also have consequences for these membership problems: We provide an
improved upper bound for the case of {∪,∩,−,+,×}-circuits. 相似文献
996.
Monica H Carlsen Inger TL Lillegaard Anette Karlsen Rune Blomhoff Christian A Drevon Lene F Andersen 《Nutrition journal》2010,9(1):37
Background
We have developed a food frequency questionnaire (FFQ) for the assessment of habitual diet, with special focus on the intake of fruit, vegetables and other antioxidant-rich foods and beverages. The aim of the present study was to evaluate the relative validity of the intakes of energy, food and nutrients from the FFQ. 相似文献997.
This paper presents two multi-material interpolation schemes as direct generalizations of the well-known SIMP and RAMP material
interpolation schemes originally developed for isotropic mixtures of two isotropic material phases. The new interpolation
schemes provide generally applicable interpolation schemes between an arbitrary number of pre-defined materials with given
(anisotropic) properties. The method relies on a large number of sparse linear constraints to enforce the selection of at
most one material in each design subdomain. Topology and multi-material optimization is formulated within a unified parametrization. 相似文献
998.
We attack the problem of deciding whether a finite collection of finite languages is a code, that is, possesses the unique
decipherability property in the monoid of finite languages. We investigate a few subcases where the theory of rational relations
can be employed to solve the problem. The case of unary languages is one of them and as a consequence, we show how to decide
for two given finite subsets of nonnegative integers, whether they are the nth root of a common set, for some n≥1. We also show that it is decidable whether a finite collection of finite languages is a Parikh code, in the sense that
whenever two products of these sets are commutatively equivalent, so are the sequences defining these products. Finally, we
consider a nonunary special case where all finite sets consist of words containing exactly one occurrence of the specific
letter. 相似文献
999.
Christian Le Carlier de Veslud Michel Cuney Guillaume Lorilleux Jean-Jacques Royer Michel Jébrak 《Computers & Geosciences》2009,35(1):92-107
Unconformity-related uranium deposits are the highest grade, large tonnage uranium resources in the world. In the Athabasca Basin (northern Saskatchewan, Canada), which is the premier host for unconformity-type deposits, the ore deposits are frequently hosted and surrounded by breccias in sandstone. The significance of these breccias and their relation to mineralization are of major importance for the genesis of these high-grade deposits. Therefore, a modeling study, integrating results from structural geology and petrology, was performed with the gOcad 3D modeling software, in order to decipher geometrical and geological relationships between breccias, faults and mineralization zones. Mineralized bodies and the sudoite–dravite breccia bodies display strong spatial correlations. They appear to be controlled by reverse shear zones cross-cutting the unconformity and containing graphite in the basement. Geochemical computations evidenced that volumetric water–rock ratios up to 10,000 could be obtained in these breccia bodies for volume losses of up to 90%. Assuming reasonable values for quartz saturation, hydraulic conductivity and connected porosity, the minimal fluid volume and the time duration necessary to generate the sudoite–dravite breccia bodies were estimated at ca. 2 km3 and ca. 1 Myr, respectively. The comparison of these results with literature data suggests that the formation of sudoite–dravite breccia and mineralization could have been coeval. It may be proposed that within the space created by the quartz dissolution in the breccia body, a mixing between basement and basinal fluids could have induced U deposition and allowed the development of high-grade mineralization. The first-order uranium solubility that this coeval formation would imply is consistent with literature data, which suggests that this conceptual model is reasonable. 相似文献
1000.
Andreas Mattsson Christian Lejon Vclav tengl Snejana Bakardjieva Frantiek Oplutil Per Ola Andersson Lars
sterlund 《Applied catalysis. B, Environmental》2009,92(3-4):401-410
The structure and photocatalytic activity of Zr doped TiO2 nanocrystallites with a varying Zr content between 0 and 15 wt% prepared by an efficient and environmentally benign method has been studied by vibrational spectroscopy, TEM and XRD. It is shown that the presence of Zr4+ ions stabilizes the anatase structure and delays phase transformation to rutile upon annealing as well as retarding grain coarsening. All TiO2 samples up to 13 wt% Zr doping concentration show better or similar photoreactivity compared to P25 (Degussa) for decomposition of adsorbed 2-chloroethyl ethyl sulphide (CEES) and dimethyl methylphosphonate (DMMP) in synthetic air at room temperature. The most efficient sample for photodegradation of both CEES and DMMP is shown to be titania doped with 6.8 wt% Zr. The photodegradation of CEES is faster than DMMP under the same experimental conditions. On the undoped TiO2 sample urea residues are detected spectroscopically. Much less is detected on the Zr doped samples. Mode resolved in situ FTIR surface spectroscopy enables distinction of CEES or DMMP, decomposition products as well as the influence of residues from the particle synthesis. This facilitates extraction of intra-comparable reaction rates. Possible explanations for the improved reactivity of the Zr doped titania are discussed. 相似文献