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Nanocelluloses: a new family of nature-based materials 总被引:2,自引:0,他引:2
Klemm D Kramer F Moritz S Lindström T Ankerfors M Gray D Dorris A 《Angewandte Chemie (International ed. in English)》2011,50(24):5438-5466
Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants. 相似文献
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For pairing based cryptography we need elliptic curves defined over finite fields
whose group order is divisible by some prime
with
where k is relatively small. In Barreto et al. and Dupont et al. [Proceedings of the Third Workshop on Security in Communication Networks (SCN 2002), LNCS, 2576, 2003; Building curves with arbitrary small Mov degree over finite fields, Preprint, 2002], algorithms for the construction of ordinary elliptic curves over prime fields
with arbitrary embedding degree k are given. Unfortunately, p is of size
.We give a method to generate ordinary elliptic curves over prime fields with p significantly less than
which also works for arbitrary k. For a fixed embedding degree k, the new algorithm yields curves with
where
or
depending on k. For special values of k even better results are obtained.We present several examples. In particular, we found some curves where
is a prime of small Hamming weight resp. with a small addition chain.AMS classification: 14H52, 14G50 相似文献
25.
Laser-induced breakdown spectroscopy has been used for quantitative measurement of trace elements, e.g. sulfur and chlorine,
in concrete. Chloride and sulfate ions have a large effect on the durability of concrete structures, and quantitative measurement
is important for condition assessment and quality assurance. Concrete is a highly heterogeneous material in composition and
grain-size distribution, i.e. the spatial distribution of elements. Calibration plots were determined by use of laboratory-made
reference samples consisting of pressings of cement powder, hydrated cement, cement mortar, and concrete, in which the heterogeneity
of the material is increasing because of the aggregates. Coarse aggregate and cement paste are distinguishable by the intensity
of the Ca spectral lines. More advanced evaluation is necessary to account for the effect of the fine aggregate. The three
series of reference samples enable systematic study of the effects of heterogeneity on spectral intensity, signal fluctuation,
uncertainty, and limits of detection. Spatially resolved measurements and many spectra enable statistical evaluation of the
data. The heterogeneity has an effect on measurement of the sulfur and chlorine content, because both occur mainly in the
cement matrix. Critical chloride concentrations are approximately 0.04% (m/m). The chlorine spectral line at 837.6 nm is evaluated. The natural sulfur content of concrete is approximately 0.1% (m/m). The spectral line at 921.3 nm is evaluated. One future application may be simultaneous determination of the amount of damaging
trace elements and the cement content of the concrete. 相似文献
26.
Mareike Frensemeier Christof Koplin Raimund Jaeger Friederike Kramer Dieter Klemm 《Macromolecular Symposia》2010,294(2):38-44
The mechanical characteristics of bacterially synthesized nano-cellulose (BNC) were studied with uniaxial compression and tensile tests. Compressive loads result in a release of water and the deformation of the water-saturated network corresponds approximately to the volume of released water. The BNC hydrogel exhibits a mainly viscous response under compression. The strain response under tensile loads has an elastic and a viscous component. This can be described with a Maxwell model, where the viscosity is strain rate-dependent. When the aqueous phase of the BNC hydrogel is stabilized with an additional alginate hydrogel matrix, the system exhibits an elastic response under compressive loads. The analysis of the ‘alginated’ BNC network with the Maxwell model shows that the alginate matrix increases the viscosity of the composite system. The results of the mechanical tests show that the water absorbed in the BNC hydrogel strongly influences its mechanical behavior. 相似文献
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Ursula M Kotyrba Kevin Pr?pper Eike-F Sachs Anastasiya Myanovska Tobias Joppe Friederike Lissy George M Sheldrick Konrad Koszinowski Ulf Diederichsen 《ChemistryOpen》2014,3(4):152-160
The DNA bisintercalator triostin A is structurally based on a disulfide-bridged depsipeptide scaffold that provides preorganization of two quinoxaline units in 10.5 Å distance. Triostin A analogues are synthesized with nucleobase recognition units replacing the quinoxalines and containing two additional recognition units in between. Thus, four nucleobase recognition units are organized on a rigid template, well suited for DNA double strand interactions. The new tetra-nucleobase binders are synthesized as aza-TANDEM derivatives lacking the N-methylation of triostin A and based on a cyclopeptide backbone. Synthesis of two tetra-nucleobase aza-TANDEM derivatives is established, DNA interaction analyzed by microscale thermophoresis, cytotoxic activity studied and a nucleobase sequence dependent self-aggregation investigated by mass spectrometry. 相似文献