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71.
K. Böröczky Jr. 《Geometriae Dedicata》1990,34(1):13-18
An E R
2 is r-convex if for every x, y E there exists a closed rectangle R such that x, y R and R E. Several results about r-convexity appeared in [1]. Its authors formulated a conjecture about conditions for a compact, convex set in R
2 to be r-convex. We prove this conjecture in the case of convex domains of constant width. 相似文献
72.
For eachd1 there is a constantc
d>0 such that any finite setXR
d contains a subsetYX, |Y|[1/4d(d+3)]+1 having the following property: ifEY is an ellipsoid, then |E X|c
d |X|.On leave from the Mathematical Institute of the Hungarian Academy of Sciences, 1364 Budapest, P.O. Box 127, Hungary. Supported by a research fellowship from the Science and Engineering Research Council, U.K., and by Hungarian National Foundation for Scientific Research Grant No. 1812. 相似文献
73.
74.
Shkumbatiuk R Bazel YR Andruch V Török M 《Analytical and bioanalytical chemistry》2005,382(6):1431-1437
A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of nitrophenols [picric acid (PA); dinitrophenols (DNP)] in wastewater samples. The method is based on the reaction of nitrophenols with 2-[(E)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3 H-indolium chloride reagent to form the colored ion associates, which are extracted by organic solvents. The molar absorptivity of the ion associates of PA with the investigated reagent ranges from 8.3×104 to 11.3×104 L mol–1 cm–1, depending on the extractant. Because only PA is extracted in an acidic medium with the investigated reagent, but both PA and DNP are extracted in an alkaline medium, it is possible to determine both substances in a mixture. Appropriate reaction conditions have been established. The absorbance of the colored extracts obeys Beers law in the range of 0.04–4.58 mg L–1 PA, 1.0–18.4 mg L–1 2,4-DNP and 1.2–14.7 mg L–1 2,6-DNP, respectively. The limit of detections, calculated from a blank test (n=10; P=0.95), are 0.05 mg L–1 PA, 0.9 mg L–1 (2,4-DNP), and 1.1 mg L–1 (2,6-DNP), respectively. 相似文献
75.
The application of the recently introduced ethylchloroformate derivatization method for the separation and determination of selenomethionine and selenocystein in selenium-enriched yeast and yeast-free tablets by means of a gas chromatography-mass spectrometry (GC-MS) system has been studied. The efficiency of three methods for the extraction of selenomethionine from the tablets were compared. Total selenium content of the same tablets were measured using inductively coupled plasma (ICP)-MS and it was found that in the selenized yeast tablets about 80% of the total selenium is present as selenomethionine. The results were in agreement with the values in the labels and with the literature. The accuracy of the total selenium analysis was controlled by the analysis of a reference material. 相似文献
76.
The present state of a long term program is reviewed. It was started to elaborate a remote controlled automated radiochemical
processing system for the neutron activation analysis of biological materials. The system is based on wet ashing of the sample,
followed by reactive desorption of some volatile components. The distillation residue is passed through a series of columns
filled with selective ion screening materials to remove the matrix activity. The solution is thus “stripped” from the interfering
radioions, and it is processed to single-elements through group separations using ion-exchange chromatographic techniques.
Some special problems concerning this system are treated. (a) General aspects of the construction of a (semi)automated radiochemical
processing system are discussed; (b) Comparison is made between various technical realizations of the same basic concept;
(c) Some problems concerning the “reconstruction” of an already published processing system are outlined. 相似文献
77.
S Çak?r E Co?kunP Naumov E Biçer? Bulut H ?çbudakO Çak?r 《Journal of Molecular Structure》2002,608(1):101-107
Aspartame adduct of copper(II) chloride Cu(Asp)2Cl2·2H2O (Asp=aspartame) is synthesized and characterized by elemental analysis, FT IR, UV/vis, ESR spectroscopies, TG, DTG, DTA measurements and molecular mechanics calculations. Aqueous solution of the green solid absorbs strongly at 774 and 367 nm. According to the FT IR spectra, the aspartame moiety coordinates to the copper(II) ion via its carboxylate ends, whereas the ammonium terminal groups give rise to hydrogen bonding network with the water, the chloride ions or neighboring carboxylate groups. The results suggest tetragonally distorted octahedral environment of the copper ions. 相似文献
78.
James J. Li R. Alan Chrusciel Monica B. Norton David B. Reitz Timothy J. Hagen Sofya Tsymbalov E. Ann Hallinan 《Journal of heterocyclic chemistry》1994,31(6):1689-1696
Lithiation of 8-chlorodibenz[b,f][1,4]oxazepine-10-tert-butylcarbamate ( 1 ) is described. Electrophilic substitution of the resulting N-Boc dibenzoxazepine α- lithioamine 2 with ketones, aldehydes, nitriles, iso-cyanates and imines, followed by an in-situ cyclization, gave fused carbamates 5–26 , fused 2H-imidazol-2-ones 27–29 , fused hydantoins 30–32 , and fused ureas 33–35 , respectively, in 11–66% yield. 相似文献
79.
Irina Odinets Tamás Körtvélyesi Tamás Kégl László Kollár György Keglevich 《Transition Metal Chemistry》2007,32(3):299-303
In the series of 1-(2,4,6-trialkylphenyl-)3-methyl-1H-phospholes (1a–c) that are to a certain extent of aromaticity, only the isopropyl substituted one (1a) entered into reaction with dimeric (pentamethylcyclopentadienyl)rhodium dichloride to afford Rh(III) complex (2a) in a reversible manner. After a careful workup, (2a) could be prepared and characterized whose stereostructure was elucidated by B3LYP/3–21G*, B3LYP/6–31G* and LANL2DZ calculations.
Complex (2a) as a preformed catalyst, as well as the Rh(acac)(CO)2 + 2(1a) in situ catalytic system were useful in the hydroformylation of styrene and gave the branched aldehyde in regioselectivities of 65–96%. 相似文献
80.
Mössbauer study of iron reduction in hematite containing mineral originated from Aswan area in Egypt
E. Kuzmann N. Eissa B. Molnár A. Vértes 《Journal of Radioanalytical and Nuclear Chemistry》1988,127(3):169-176
Mössbauer spectroscopy was used to study iron reduction in mineral originated from Aswan area in Egypt. The Mössbauer spectra of samples heat treated at 1000 °C in hydrogen atmosphere show a gradually reduction process of hematite. The main phase of sample aged for 1 h is magnetite, while alpha-iron as well as some silicates and wustite type oxide can be detected in sample aged for 3 h. Further aging of sample results in dissolution of alloying elements /Si, Al/, being present in the samples. This process starts already in samples aged at 1000 °C for 4 h, but it is more expressive in minerals heat treated at 1200 °C or 1300 °C, when all paramagnetic phases disappeared. 相似文献