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241.
Dennis J. Garity Dusan Repovs Matjaz Zeljko 《Proceedings of the American Mathematical Society》2006,134(8):2447-2456
We prove that there exist uncountably many inequivalent rigid wild Cantor sets in with simply connected complement. Previous constructions of wild Cantor sets in with simply connected complement, in particular the Bing- Whitehead Cantor sets, had strong homogeneity properties. This suggested it might not be possible to construct such sets that were rigid. The examples in this paper are constructed using a generalization of a construction of Skora together with a careful analysis of the local genus of points in the Cantor sets.
242.
We present intermodal interference of modes LP0j in silica optical fiber with liquid core. An appropriate detection method is proposed for observation of intermodal interference of LP0j modes. Measured spectral dependencies reveal a clear local minimum, where position is a function of optical fiber parameters. We focused on investigation of dependence of that minimum position on length of optical fiber with liquid core. From measured spectral dependencies the evident blue shift of local minimum is observed as length of optical fiber increases. Character of spectral characteristics correspond with intermodal interference of modes LP0j and is demonstrated by numerical calculations. Presented intermodal interference in combination with liquid-filled core of optical fiber can be attractive for sensing applications. 相似文献
243.
Summary The extremely high mol. mass (EHMM) polystyrene (PS) samples prepared by emulsion polymerization with an initiator forming heterogeneous phase were characterized by gel permeation chromatography (GPC). A bicomponent eluent methyl ethyl ketone (MEK) and methanol (McOH) in a ratio slightly different from the composition of theta solvent for PS was applied in GPC measurements. The GPC apparatus was calibrated with a series of PS reference materials. The course of calibration curves in the EHMM region was mathematically or graphically simulated by the third and second degree polynomial respectively. Correction of GPC data for the broadening effect was made mathematically by solving the Tung integral equation by the iterative method ofChang andHuang. The
values of the EHMM PS samples varied between 1.07 × 107 and (>4 × 107). The values of
were higher than 1.5. Besides distribution analysis by GPC also light scattering (LS) was used for measurement of
of EHMM PS samples and a sample was partially characterized also by the method of sedimentation in ultracentrifuge (UC).
With 4 figures 2 tables
Dedicated to Prof. Dr. G. Rehage on the occasion of his 60th birthday. 相似文献
Zusammenfassung Polystyrol-Proben mit extrem hohen Molekulargewichten (EHMM-PS) wurden durch Emulsions-Polymerisation mit einem eine heterogene Phase bildenden Initiator hergestellt. Sie wurden mittels GPC charakterisiert unter Verwendung einer MEK-MeOH-Mischung, deren Zusammensetzung etwas vom -Lösungsmittel abweicht. Die Eichung erfolgte mit mehreren Referenz-Polystyrolen. Der Verlauf der Kalibrierungs-Kurven im EHMM-PS-Bereich wurde mathematisch oder graphisch unter Zugrundelegung eines Polynoms 2. und 3. Grades simuliert. Die GPC-Daten wurden unter Berücksichtigung des Verbreiterungs-Effektes unter Verwendung von in der Literatur angegebenen Gleichungen korrigiert.M w von EHMM-PS wurde von 1,07 · 107 bis > 4 · 107 variiert;M w /M n war > 1,5. Ferner wurdeM w mittels Lichtstreuung und für eine Probe durch Sedimentations-Messungen bestimmt.
With 4 figures 2 tables
Dedicated to Prof. Dr. G. Rehage on the occasion of his 60th birthday. 相似文献
244.
T. Bleha T. Spychaj R. Vondra D. Berek 《Journal of Polymer Science.Polymer Physics》1983,21(10):1903-1912
The dependence of the elution volume Ve on the concentration of injected polymer c in gel chromatography is presented for several systems including poly(styrene) and poly(methyl methacrylate) in a number of pure solvents with SiO2-based gels. The linear dependence of Ve on c and Kav on c (where Kav is the distribution coefficient) is confirmed in the region of very low concentration. The slopes k of the straight lines increase with increasing relative molecular masses M of the polymer injected and with increasing thermodynamic nonideality of the system (as expressed by the second virial coefficient A2). The significance of the slope of the GPC calibration curve for meaningful comparison of the concentration effects in various chromatographic systems is pointed out. A recently found correlation between k and (A2M)γ is confirmed with a γ value of about 0.8. A possible theoretical explanation for the deviation of γ from unity is discussed. Finally, the influence of both the polymer concentration and the thermodynamic quality of the eluent on the resolution index of the chromatographic system is evaluated with the conclusion that thermodynamically poor solvents should be preferred for preparative GPC separations with very high loads. 相似文献
245.
This work is, according to our knowledge, the first experimental matrix isolation study of a molecular system with a very short and strong intramolecular OH...O hydrogen bond. It also includes a satisfying interpretation of its entire infrared spectrum. The interpretation relies on the calculation at the DFT/B3LYP/6-31G(d,p) level of the harmonic spectrum and of the anharmonic relaxed potential energy for the stretching motion of the hydrogen-bonded proton, used with our recently modified quantum-mechanics-based normal-coordinate analysis. An important observation about the anharmonic spectrum obtained from this procedure is that the OH stretch coordinate contributes to several normal modes, mixing extensively with other in-plane internal coordinates, in particular OH-bending and C=O-stretching. The two intense normal modes with the largest contributions from the OH-stretching coordinate to the potential energy distribution and to the intensity are located near 1700 and 1500 cm(-1). A calculated anharmonic spectrum obtained from this procedure agrees with the experimental spectrum (frequencies and intensity distribution), within the limits of the estimated uncertainties for the calculation and experiment, allowing the interpretation of the latter. The agreement for the frequencies is about 1-3%. The anharmonic spectrum calculated using the anharmonic keyword in Gaussian 03w is not in satisfactory agreement with experiment insofar as the OH-stretching mode is concerned. 相似文献
246.
Capillary zone electrophoresis in wide bore capillary tubes with fiber-coupled diode array detection
Strasík S Danková M Molnárová M Olvecká E Kaniansky D 《Journal of chromatography. A》2003,990(1-2):23-33
This feasibility study deals with the use of a wide bore (320 μm I.D.) capillary tube for the detection and identification of capillary zone electrophoresis (CZE) analytes by optical fiber-coupled diode array detection. A 250-μm mean effective pathlength of the detection cell with an inherently enhanced photon flux through the cell were significant contributors in reaching 0.2–1 μmol/l concentration detectabilities of the CZE analytes by this combination. Experiments with model analytes (p-sulfanilic, sorbic and naphthalene-2-sulfonic acids, tryptophan and asulam) revealed that spectral confirmations of their identities were still possible when their concentrations in the loaded samples (200 nl) were 1–5 μmol/l. Here, chemometry procedures (target transformation factor analysis, fixed size moving window-target transformation factor analysis, fixed size moving window-evolving factor analysis and orthogonal projection approach) employed in the data processing effectively contributed to reliable confirmation of the identities of the analytes also in critical situations (e.g. peak overlaps). The CZE separations were carried out in tandem-coupled columns of identical I.D. This made it possible to use, in the first column of the tandem, carrier electrolyte solutions that provide the desired separative effects, while in the second (detection) column the compositions of the carrier electrolyte solutions employed could reflect favorable conditions for obtaining spectral data. Mixtures containing model constituents at significantly differing concentrations and Maillard’s reaction products spiked with tryptophan enantiomers were employed in experiments aimed at assessing practical applicabilities and limits of the present approach to the analysis of samples characterized by complex ionic matrices. 相似文献
247.
Analytical potentialities of capillary zone electrophoresis in the separation system with tandem-coupled columns to the spectral identification and determination of orotic acid (OA) in urine by diode array detection (DAD), coupled to the separation system via optical fibers, were investigated. A very significant “in-column” clean-up of OA from urine matrix was reached in the separation stage of the tandem by combining a low pH (2.8) with complexing effects of electroneutral agents [- and β-cyclodextrins, poly(vinylpyrrolidone) and 3-(N,N-dimethyldodecylammonio)propanesulfonate]. Due to this, its DAD spectral data could be acquired in the detection stage of the tandem with almost no disturbances by matrix co-migrants. The concentration limits of detection obtained under such working conditions for a 200-nl sample load of OA and 320 μm I.D. capillary tubes were 3.5 μmol/l (218 nm) and 0.4 μmol/l (280 nm). Using chemometry procedures (target transformation factor analysis, fixed size moving window-evolving factor analysis, orthogonal projection approach and fixed size moving window–target transformation factor analysis) in processing of the acquired spectral data, the presence of OA in the loaded urine matrix could be confirmed with confidence when its concentration was 10 μmol/l or slightly less. 相似文献
248.
Masár M Danková M Olvecká E Stachurová A Kaniansky D Stanislawski B 《Journal of chromatography. A》2004,1026(1-2):31-39
This work deals with the determination of free sulfite in wine by zone electrophoresis (ZE) with on-line isotachophoresis (ITP) sample pretreatment on a column-coupling (CC) chip with conductivity detection. A rapid pre-column conversion of sulfite to hydroxymethanesulfonate (HMS), to minimize oxidation losses of the analyte, was included into the developed analytical procedure, while ITP and ZE were responsible for specific analytical tasks in the separations performed on the CC chip. ITP, for example, eliminated the sample matrix from the separation compartment and, at the same time, provided a selective concentration of HMS before its transfer to the ZE stage of the separation. On the other hand, ZE served as a final separation (destacking) method and it was used under the separating conditions favoring a sensitive conductivity detection of HMS. In this way, ITP and ZE cooperatively contributed to a 900 microg/l concentration detectability for sulfite as attained for a 60 nl load of wine (a 15-fold wine dilution and the use of a 0.9 microl sample injection channel of the chip) and, consequently, to the determination of free sulfite when this was present in wine at the concentrations as low as 3 mg/l. The separations were carried out in a closed separation compartment of the chip with suppressed hydrodynamic and electroosmotic flows. Such transport conditions, minimizing fluctuations of the migration velocities of the separated constituents, made a frame for precise migration and quantitation data as achieved for HMS in both the model and wine samples. Ninety percent recoveries, as typically obtained for free sulfite in wine samples, indicate promising potentialities of the present method as far as the accuracies of the provided analytical results are concerned. 相似文献
249.
Liquid chromatography under limiting conditions of desorption (LC LCD) is a method which allows molar mass independent elution of various synthetic polymers. A narrow, slowly moving zone of small molecules, which promotes full adsorption of one kind of polymer species within column (an adsorli) acts as an impermeable barrier for the fast moving macromolecules. The latter accumulate on the barrier edge and elute nearly in total volume of liquid within column. At the same time, transport of less adsorptive macromolecules is not hampered so that these are eluted in the size exclusion (SEC) mode. As result, polymers differing in their polarity and adsorptivity can be easily separated without molar mass interference. Three methods of barrier creation are discussed and compared. It is shown that a fraction of sample may elute unretained if the adsorli sample solvent is used as a barrier in connection with a narrow-pore column packing. One part of excluded macromolecules likely breaks-out from the adsorli zone and this results in partial loss of sample and distortion of the LC LCD peaks. This problem can be avoided if the adsorli zone is injected immediately before sample solution. Applicability of the LC LCD method for polymer separation has been demonstrated with a model mixture of poly(methyl methacrylate) (adsorbing polymer) and polystyrene (non adsorbing polymer) using bare silica gel as a column packing with a combination of tetrahydrofuran (a desorption promoting liquid -a desorli) and toluene (adsorli). It has been shown that the LC LCD procedure with tandem injection allows simple and fast discrimination of polymer blend components with good repeatability and high sample recovery. For quantitative determination of molar masses of both LC LCD and SEC eluted polymers, an additional size exclusion chromatographic column can be applied either in a conventional way or in combination with a multi-angle light scattering detector. A single eluent is used in the latter column, which separates the mixed mobile phase, system peaks and the desorli zone from the polymer peaks so that measurements are free from disturbances caused by the changing eluent composition. The resulting LC LCD x SEC procedure has been successfully applied to poly(methyl methacrylate) samples. 相似文献
250.
A. Bdzki M. I. Prusinska D. Berek 《Journal of polymer science. Part A, Polymer chemistry》1978,16(1):107-114
The polydispersity of diallyl phthalate prepolymers was determined by gel-permeation chromatography (GPC). The measurements were carried out in tetrahydrofuran and chloroform on Mexel 2000, Poragel, and Styragel polystyrene gels. The influence of the polymerization conditions, initiator, and type of transfer agent on the molecular weight distribution of the prepolymers is shown. Other correlations of interest, such as molecular weight distribution of Dapon 35 and Dapon 201, are also presented. 相似文献