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  • 1
    ISSN: 1432-0878
    Schlagwort(e): Central canal ; Cerebrospinal fluid ; Circulation ; Horseradish peroxidase ; Ependyma ; Rat (Sprague Dawley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The circulation of the cerebrospinal fluid along the central canal and its access to the parenchyma of the spinal cord of the rat have been analyzed by injection of horseradish peroxidase (HRP) into the lateral ventricle. Peroxidase was found throughout the central canal 13 min after injection, suggesting a rapid circulation of cerebrospinal fluid along the central canal of the rat spinal cord. It was cleared from the central canal within 2 h, in contrast with the situation in the brain tissue, where it remained in the periventricular areas for 4 h. In the central canal, HRP bound to Reissner's fiber and the luminal surface of the ependymal cells; it penetrated through the intercellular space of the ependymal lining, reached the subependymal neuropil, the basement membrane of local capillaries, and appeared in the lumen of endothelial pinocytotic vesicles. Furthermore, it accumulated in the labyrinths of the basement membrane contacting the basolateral aspect of the ependymal cells. In ependymocytes, HRP was found in single pinocytotic vesicles. The blood vessels supplying the spinal cord were classified into two types. Type-A vessels penetrated the spinal cord laterally and dorsally and displayed the tracer along their external wall as far as the gray matter. Type-B vessels intruded into the spinal cord from the medial ventral sulcus and occupied the anterior commissure of the gray matter, approaching the central canal. They represented the only vessels marked by HRP along their course through the gray matter. HRP spread from the wall of type-B vessels, labeling the labyrinths, the intercellular space of the ependymal lining, and the lumen of the central canal. This suggests a communication between the central canal and the outer cerebrospinal fluid space, at the level of the medial ventral sulcus, via the intercellular spaces, the perivascular basement membrane and its labyrinthine extensions.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1432-0878
    Schlagwort(e): Key words Subcommissural organ ; Reissner’s fiber ; ELISA ; Glycoproteins ; Cerebrospinal fluid ; Monoclonal antibodies ; Bovine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The subcommissural organ (SCO) is an ependymal brain gland that releases glycoproteins into the ventricular cerebrospinal fluid where they condense to form the Reissner’s fiber (RF). We have developed a highly sensitive and specific two-antibody sandwich enzyme-linked immunosorbent assay (ELISA) for the quantification of the bovine SCO secretory material. The assay was based on the use of the IgG fraction of a polyclonal antiserum against the bovine RF as capture antibody and a pool of three peroxidase-labeled monoclonal antibodies that recognize non-overlapping epitopes of the RF glycoproteins as detection antibody. The detection limit was 1 ng/ml and the working range extended from 1 to 4000 ng/ml. The calibration curve, generated with RF glycoproteins, showed two linear segments: one of low sensitivity, ranging from 1 to 125 ng/ml, and the other of high sensitivity between 125 and 4000 ng/ml. This assay was highly reproducible (mean intra- and interassay coefficient of variation 2.2% and 5.3%, respectively) and its detectability and sensitivity were higher than those of ELISAs using exclusively either polyclonal or monoclonal antibodies against RF glycoproteins. The assay succeeded in detecting and measuring secretory material in crude extracts of bovine SCO, culture medium supernatant of SCO explants and incubation medium of bovine RF; however, soluble secretory material was not detected in bovine cerebrospinal fluid.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 2361-2384 
    ISSN: 0887-6266
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Accurate dynamic mechanical measurements have been performed on semicrystalline isotactic polypropylene over wide ranges of temperature and frequency. A mechanical model has been used to analyze experimental results in order to separate the behavior of amorphous and crystalline phases. The two main α and β relaxation processes have been analyzed. The β relaxation, related to the glass-rubber transition of the amorphous fraction, has been studied with the help of a physical model. The behavior is similar to that of a wholly amorphous polymer, with two characteristics: a high rubbery plateau, indicating a crosslinking effect by the crystalline phase, and a strong effect of interfaces in shear strain. Experimental data suggest the α relaxation originates within the crystalline phase and that it can be attributed to diffusion of defects. The amorphous phase plays an important role in this process, because it has to adapt itself by cooperative movements to respect the compatibility of deformations of the two phases. The formalism developed here rationalizes experimental results obtained with samples having different thermal histories.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1559-1572 
    ISSN: 0887-6266
    Schlagwort(e): core-shell ; N-methylol acrylamide ; N-methylol methacrylamide ; N-isobutoxy methyl acrylamide ; butyl acrylate ; polystyrene seed ; latex ; emulsion polymerization ; structured particles ; particle morphology ; functional monomers ; latex films ; phase arrangement ; mechanical properties ; film forming ; scanning electron microscopy ; annealing ; percolation ; coalescence ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polystyrene (PS) (1)/Poly (n-butyl acrylate (BA)/amide type functional monomer) (2) structured latex particles were prepared through emulsion polymerization varying the hydrophilicity of the functional monomer employed. The second-stage polymerization kinetics, the size and morphology of latex particles, and the location of the functional groups in the final latexes were studied, in order to relate them to the thermomechanical properties of films cast from these latexes. It has been shown that, as expected, increasing the hydrophobicity leads to a better homogeneity in the copolymer formed during the second-stage polymerization, while the more hydrophilic functional monomer partly homopolymerizes in a separate phase. However, the functionalization by all the monomers used in this work, prevents the PS seed particles to form a continuous skeleton (percolated network). Further heat treatments at 140°C do not lead to the formation of a continuous PS phase as for pure BA/pure PS two-stage particles. In addition, some thermally induced crosslinking effects are discussed in relation with the functional monomer location within the particles. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 1847-1858 
    ISSN: 0887-6266
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The dynamic mechanical behavior of 10 and 20% poly(vinyl methyl ether)-polystyrene blends has been studied in the frequency range 10-5 Hz to 5 Hz and temperature range 100-450 K. Isochronal plots of modulus G′ and loss factor, tan φ, show the presence of one relaxation process at temperatures below the transition zone. A second relaxation process at intermediate temperatures but below Tg may be inferred from the breadth of the G″ frequency curves in the transition zone of both blends. This process, at 280 〈 T 〈 300 K, is independent of PVME concentration and seems to be associated with the local modes of motions of PS chains. The rheological behavior of the blends shows them to be compatible up to 20% PVME. Their G′ and G″ data cannot be shifted along a frequency axis to produce a satisfactory master curve. The departure from thermorheological simplicity is much more clearly observed in the tan φ than in the modulus-frequency plots. This departure is due to the change in the segmental correlation effects, or length, with temperature near Tg. A molecular model of the growth of microshear domains with hierarchically constrained molecular motions, given elsewhere, quantitatively agrees with the dynamic mechanical behavior.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 569-586 
    ISSN: 0887-6266
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: By using an automated low-frequency apparatus, dynamic mechanical experiments are performed on bulk-crystallized high-density polyethylene in the temperature range of the α relaxation. In order to characterize the key morphological features governing the presence of multiple α relaxations, we have developed a simple model from calorimetric data to assess the crystallite size distribution of samples with different thermal histories. The morphological characterizations are completed by wide-angle x-ray diffraction measurements. Isochronal spectrometry and frequency scans performed under isothermal conditions both exhibit two α relaxations designated α1 and α2, with increasing temperature (or increasing frequency). These two relaxations are frequency dependent but they are not thermorheologically simple processes. Some analogy is found between tan φ versus temperature or frequency and the biomodal lamellar size distribution curves determined from calorimetric data. Moreover, both the temperature of α2 peak and the most probable lamellar thickness of the larger lamellae depend on the thermal history of the sample: with increasing thickness of the larger lamellae, the α2 peak temperature is shifted toward higher temperature. In contrast, both the temperature of the a peak and the most probable lamellar thickness of the thinner lamellae seem to be independent of thermal history: the thinner lamellae should be formed on cooling from the remaining uncrystallized fraction. From thege findings, it is proposed that the α, and α2 relaxations have the same origins and that they could arise from defect diffusion within the thinner and thicker crystallites, respectively, with some influence of the amorphous matter in the interfacial regions.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 1235-1251 
    ISSN: 0887-6266
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The dynamic mechanical behavior of monodisperse atactic polystyrene (mol. wt. 98,000) has been measured in the frequency range, 10-5 to 10 Hz and temperature range 359-374K. The time-temperature superposition of the entire data in the frequency range of overlap seems less satisfactory in both the real and imaginary components of the complex shear modulus, G′ and G″, respectively. The lack of adequate superposition becomes pronounced in the tan φ (G″/G′) plots. The tan φ plots provide a more discerning criteria for the superposition than the G′ or G″ spectra.An analysis based on an earlier model for anelastic deformation shows that of the several changes that may occur in the dynamic mechanical behavior on heating of polystyrene, the predominant ones are both an increase in the size of the microshear domains and the correlations of movement of segments near entanglements. These decrease the contribution to the modulus on heating near Tg so that the time-temperature superposition is vitiated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 2691-2705 
    ISSN: 0887-6266
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The shear modulus and loss of ca. 30% crystalline nylon-12 have been measured over the temperature range 100-440 K and frequency range 10-4-1 Hz. The effect of water and physical aging of the amorphous regions on the relaxation spectra have been investigated. Absorbed water decreases both the temperature and height of the γ-relaxation peak, induces a β-relaxation peak, and decreases the temperature of the α-relaxation peak. These results are interpreted in terms of the hydrogen-bonding effect of water on nylon-12 monomer and polymer. The G″ spectrum of the polymer has a half-width of ca. 6 decades of frequency, and neither the G″, nor G″, nor the tan φ spectra can be superposed by shifting along the frequency axis. The large half-width is attributed to the random distribution of crystalline regions in the polymer. The results are further discussed in terms of hydrogen-bonding, with or without H2O, and compared with the properties of other nylons.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 1439-1453 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) (80/20 w/w) polymer blend was studied by mechanical spectroscopy. Two relaxations can be distinguished: in the glassy state, a very large secondary relaxation in the range of 100 K to 325 K which results from the combination of secondary relaxations of PVC and PMMA; and only one main relaxation at 364 K associated to the glass rubber transition. The relaxation spectrum in the range of the β relaxation has been described by a relaxation time distribution function based upon a Gaussian function and a series-parallel model. The α relaxation was studied by means of a theoretical approach for the nonelastic deformation of polymers. We found that the miscibility of this blend appears to be a function of the observation scale: the PVC/PMMA blend is heterogeneous at the scale of molecular movements involved for the β relaxation process but homogeneous at the scale of the chain segments responsible for the α relaxation dynamics. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 1214-1218 
    ISSN: 1040-0397
    Schlagwort(e): Ephedrine ; N-Nitrosoephedrine ; Differential pulse polarography ; Nitrosation ; Urine ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The nitrosation of ephedrine and the electrochemical reduction of N-nitrosoephedrine were investigated by differential pulse polarography and have been optimized in order to attain the optimum analytical signal. Reduction of the N-nitrosoephedrine was carried out in one irreversible, diffusion-controlled step using potassium chloride-hydrochloric acid. In 0.1 M hydrochloric acid the N-nitrosoephedrine shows a well-defined reduction peak at -0.77 V (vs. Ag/AgCl/ 3 M KCl). An indirect differential-pulse polarographic method is described for the determination of ephedrine at levels higher than 2.5 μg per mL of urine. An extraction procedure with C18 cartridge and a fast and easy nitrosation reaction with sodium nitrite in 0.2 M phthalate potassium hydrogen is also described. Determination of 5 μg/mL of N-nitrosoephedrine in urine samples of 4 mL was possible using the standard addition method, with a relative error of -4.0% and relative standard deviations no higher than 2.1%.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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