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Heidrun Pionteck Werner Berger Bernd Morgenstern Dietrich Fengel 《Cellulose (London, England)》1996,3(1):127-139
The influence of different solvents on the morphology of cellulose during the dissolution process was studied. Spruce sulfite pulp, cotton linters and hydrolysed cotton linters were treated for a short time with lithium chloride: N,N-dimethylacetamide (LiCl:DMAc) and an alkaline solution of iron sodium tartrate (EWNN), respectively. The changes occurring at the fibre surfaces and within the cell walls were observed by scanning as well as by transmission electron microscopy. The cellulose fibres show significant differences in the dissolution behaviour when comparing the reaction of the two solvents. Using LiCl:DMAc, the cotton linters fibres become lamellar separated and within the spruce sulfite pulp fibres solvent channels appear in the first step with the fibrils becoming separated. In contrast, EWNN has a swelling effect on the surface of the cellulose fibres. Both solvent systems predominantly affect the ends of the fibres and places where the wall structure has been damaged. 相似文献
44.
J. Swakon P. Olko D. Adamczyk T. Cywicka-Jakiel J. Dabrowska B. Dulny L. Grzanka T. Horwacik T. Kajdrowicz B. Michalec T. Nowak M. Ptaszkiewicz U. Sowa L. Stolarczyk M.P.R. Waligorski 《Radiation measurements》2010,45(10):1469-1471
In the Henryk Niewodniczański Institute of Nuclear Physics of the Polish Academy of Science in Krakow (IFJ PAN), Poland, in cooperation with the Department of Ophthalmology and Ophthalmic Oncology of the Collegium Medicum, Jagiellonian University and the Centre of Oncology of the Maria Sk?odowska-Curie Memorial Institute Krakow Branch, is running the project of designing and operating a proton ocular radiotherapy facility in which the 60 MeV proton beam accelerated in the AIC-144 isochronous cyclotron of IFJ PAN is applied. The facility will be able to satisfy national needs of ocular melanoma therapy in Poland (about 100 cases per year). 相似文献
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van Pinxteren MS Montero L Jäsch S Paschke H Popp P 《Analytical and bioanalytical chemistry》2009,393(2):767-775
A new approach for headspace sorptive extraction is presented and demonstrated for the determination of 12 chlorobenzenes
in water samples. It consists of a silicone tube (15-mm length) arranged around a stainless steel rod. This device is fixed
on a septum cap and exposed to the headspace of 50 mL of a salt-saturated water sample. After extraction (60-min optimized
extraction time), thermodesorption is carried out by direct insertion of the silicone tube into the thermodesorption-gas chromatography-mass
spectrometry system. Desorption of the analytes is performed at 250 °C for 5 min with a gas flow of 50 mL/min. Repeatability
(relative standard deviation 5–10%), extraction yields (9–46%), enrichment factors (129–657), and detection limits (0.002–0.012 μg/L)
were determined and four real water samples were analyzed with the headspace tube extraction. The results were verified by
standard addition. A comparison of headspace tube extraction with other headspace enrichment techniques underlined the high
extraction capacity of the proposed method. A big advantage of tube extraction is the low cost of the silicone material. The
tubes can be discarded after single use, avoiding carryover problems and cross-contamination.
Figure Scheme of the HS-tube extraction and thermodesorption system 相似文献
48.
The existence of a Picard-Vessiot extension for a homogeneous linear differential equation has been established when the differential field over which the equation is defined has an algebraically closed field of constants. In this paper, we prove the existence of a Picard-Vessiot extension for a homogeneous linear differential equation defined over a real differential field K with real closed field of constants. We give an adequate definition of the differential Galois group of a Picard-Vessiot extension of a real differential field with real closed field of constants and we prove a Galois correspondence theorem for such a Picard-Vessiot extension. 相似文献
49.
Let νp denote a totally positive integer of an algebraic number field K such that νp is a least quadratic non-residue modulo a prime ideal p of K, least in the sense that N(νp) is minimal. Then the following result is shown: For x ≥ 2 and ε > 0, 相似文献
50.
Two new chelating sorbents for metal ions were prepared by the impregnation of chemically modified silicas LiChroprep RP-8
and RP-18 with ion pairs composed of the cation of Aliquat 336 and the anion of Calcon. The sorbents were compared with an
analogous sorbent with a plain silica carrier containing the same ion pairs. A hypothesis for binding this ion pair by the
surfaces of the applied carriers was presented. A higher stability of the two sorbents in comparison with that of the plain
silica chelating sorbent was demonstrated. The sorbents obtained were applied for chromatographic separations of some chosen
mixtures of some metal ions and for additional purification of aqueous solutions of alkali metals from trace amounts of heavy
metals. The multiple use of the sorbents based on RP-8 and RP-18 in sorption–desorption processes of metal ions without deterioration
of their sorption capacities was demonstrated.
Received March 8, 2000. Revision March 5, 2001. 相似文献