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  • Analytical Chemistry and Spectroscopy  (9)
  • Polymer and Materials Science  (3)
  • Magnetic resonance imaging  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    Baseline and follow-up MRI of the internal auditory canal after suboccipital resection of acoustic schwannoma: appearances and clinical correlations (1995)
    Springer
    Neuroradiology 37 (1995), S. 317-320 
    Details
    ISSN: 1432-1920
    Schlagwort(e): Internal auditory canal ; Acoustic schwannoma ; Magnetic resonance imaging
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Prospective baseline MRI was obtained on 31 patients who had “total” removal of acoustic schwannoma 6 months to 9 years previously. Follow-up MRI was performed after 1–2 years on patients with questionable abnormalities. We found four patterns (1) internal auditory canals (IAC) with nonenhancing soft-tissue strands, possibly scars or distorted residual nerves (8); (2) IAC with marginal enhancement-reactive dura mater (16); (3) IAC with contrast-enhancing globular tissues suggesting residual or recurrent tumour (5); (4) high-signal intensity in the IAC before contrast medium administration, probably related to graft with fat/fascia/muscle (2). Prospective 1-to 2-year follow-up studies were available in 8, 5, and 1 patients in groups 2, 3, and 4 respectively. In group 2, dural enhancement remained unchanged in 5 patients and decreased in 3. In group 3 follow-up showed 1 tumor recurrence (surgically confirmed) and 4 stable abnormalities. In group 4, follow-up in 1 of the 2 patients was stable. In groups 1 and 2, the MRI features correlate well with complete tumor removal. Whether follow-up in these groups is indicated needs to be determined. In group 3 residual or recurrent tumor cannot be excluded. In group 4, grafts may prevent adequate visualization of the IAC.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00588345
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  • 2
    Digitale Medien
    Digitale Medien
    Baseline and follow-up MRI of the internal auditory canal after suboccipital resection of acoustic schwannoma: appearances and clinical correlations (1995)
    Springer
    Neuroradiology 37 (1995), S. 317-320 
    Details
    ISSN: 1432-1920
    Schlagwort(e): Key words Internal auditory canal ; Acoustic schwannoma ; Magnetic resonance imaging
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Prospective baseline MRI was obtained on 31 patients who had “total” removal of acoustic schwannoma 6 months to 9 years previously. Follow-up MRI was performed after 1–2 years on patients with questionable abnormalities. We found four patterns (1) internal auditory canals (IAC) with nonenhancing soft-tissue strands, possibly scars or distorted residual nerves (8); (2) IAC with marginal enhancement-reactive dura mater (16); (3) IAC with contrast-enhancing globular tissues suggesting residual or recurrent tumour (5); (4) high-signal intensity in the IAC before contrast medium administration, probably related to graft with fat/fascia/muscle (2). Prospective 1- to 2-year follow-up studies were available in 8, 5, and 1 patients in groups 2, 3, and 4 respectively. In group 2, dural enhancement remained unchanged in 5 patients and decreased in 3. In group 3 follow-up showed 1 tumor recurrence (surgically confirmed) and 4 stable abnormalities. In group 4, follow-up in 1 of the 2 patients was stable. In groups 1 and 2, the MRI features correlate well with complete tumor removal. Whether follow-up in these groups is indicated needs to be determined. In group 3 residual or recurrent tumor cannot be excluded. In group 4, grafts may prevent adequate visualization of the IAC.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00588345
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  • 3
    Digitale Medien
    Digitale Medien
    Ionization dynamics within the high pressure electron capture mass spectrometer; the unusual spectra of derivatized polycyclic aromatic amines and perchlorinated unsaturated hydrocarbons (1987)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 14 (1987), S. 401-415 
    Details
    ISSN: 0887-6134
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A kinetic model for chemical events occurring within the high pressure electron capture mass spectrometer (HPECMS) ion source is developed which includes four different pathways by which unconventional negative ions can be produced. These routes to unusual ions include reactions of gas phase free radicals, surface-assisted reactions, ion-electron and ion-ion recombination reactions, and ion-wall neutralization. The model developed here provides a diagnostic tool useful for the elucidation of unusual HPEC spectra. Such spectra for two environmentally important classes of compounds are explained by use of the model. These compound classes include the trifluoroacetic derivatives of polycyclic aromatic amines, which have been shown to be present in materials derived from liquified coal, and the derivatives of hexachlorocyclopentadiene, which are used as pesticides. It is shown in this study that several processes, in addition to electron capture, can be operative in the typical HPECMS ion source, and that these processes can be used advantageously for the generation of informative and sensitive mass spectral signals.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bms.1200140808
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  • 4
    Digitale Medien
    Digitale Medien
    The mass spectra of 4-aminophenanthrene and its trifluoroacetic anhydride and perflnoropropionic anhydride derivatives (1990)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1990), S. 613-618 
    Details
    ISSN: 1052-9306
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Several aminophenanthrenes have been examined with electron impact mass spectrometry. The trifluoroacetic anhydride (TFAA) and perfluoropropionic anhydride (PFPA) derivatives of 4-aminophenanthrene have been studied with electron impact as well as both positive and negative ion chemical ionization mass spectrometry utilizing methane as a reagent gas. The resulting mass spectra indicate a loss of water from the derivatives and a mechanism is proposed to account for this loss. The spectra also indicate unique fragmentation patterns associated with the position of the substituent, particularly the four position which is in the region of the molecule termed the bay region. Another interesting aspect is the spectral differences observed for the TFAA and PFPA derivatives of 4-aminophenanthrene. The positive ion chemical ionization mass spectrum of the TFAA derivative indicates an ion [M + H — H2O]+; however, the mass spectrum of the PFPA derivative of 4-aminophenanthrene indicates no water loss from the [M + H]+ ion. The negative ion chemical ionization mass spectra of the two derivatives are also very different. The mass spectrum of the TFAA derivative shows an [M — 18]- ion and the PFPA derivative shows successive losses of HF with no apparent loss of water.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bms.1200191007
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  • 5
    Digitale Medien
    Digitale Medien
    Study of the reaction of diazomethane with dansylated amino acid derivatives by gas chromatography/mass spectrometry (1990)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1990), S. 520-522 
    Details
    ISSN: 1052-9306
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Since the methylation of acids with diazomethane is widely used in trace analysis, it is extremely important for those using this technique to be alert to the analysis of compounds containing other functional groups which might become methylated with high concentrations of diazomethane. We have shown that by adding an excess of diazomethane to dansylated amino acids, not only is the methyl ester formed, but the products can be further methylated. The only remaining acidic hydrogen in the molecule is the hydrogen attached to the sulfonamide nitrogen, and the mass spectrometry results indicate that the methyl ester is formed first, and the N-methylated derivative is formed with excess diazomethane.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bms.1200190810
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  • 6
    Digitale Medien
    Digitale Medien
    Effect of impurities on emulsion polymerization: Case II kinetics (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 35 (1988), S. 2009-2021 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effects of water-soluble and monomer-soluble impurities on the kinetics of emulsion polymerization of monomers following Case II kinetics (e.g., styrene) are investigated. Experimental studies reveal that impurities can have an appreciable effect on both polymer particle nucleation and growth. These effects are shown to be well predicted by a mathematical model.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1988.070350803
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  • 7
    Digitale Medien
    Digitale Medien
    Improved model for the intensity of low-energy tailing in Si(Li) x-ray spectra (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 20 (1991), S. 191-197 
    Details
    ISSN: 0049-8246
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Accurate tail-to-peak intensity ratios are extracted from the spectra produced in a Si(Li) detector by x-rays of energies 2-10 keV. The widely used model of a surface layer of incomplete charge collection fails to explain the energy dependence of these data. The model is augmented to include loss of photoelectrons travelling back into the ICC layer from an interaction in the active silicon region; this gives excellent agreement with experiment. It is shown that the detection efficiency in the region of low x-ray energy may be deduced from the tail-to-peak ratios, together with measurement of the thicknesses of the beryllium window and the metal contact; a potential source of error in measuring the latter by the popular fluorescence technique is demonstrated.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/xrs.1300200408
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  • 8
    Digitale Medien
    Digitale Medien
    Lorentzian contributions to x-ray lineshapes in Si(Li) spectroscopy (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 21 (1992), S. 223-227 
    Details
    ISSN: 0049-8246
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: If the lineshape response of a Si(Li) detector is measured using monoenergetic x-rays provided by a monochromator, it must be convoluted by a Lorentzian of appropriate width in order to represent the lineshape encountered in directly measured x-ray spectra. It is shown that the Lorentzian component is responsible for a significant fraction of low-energy peak tailing, a phenomenon usually attributed to detector imperfections.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/xrs.1300210506
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  • 9
    Digitale Medien
    Digitale Medien
    Semi-empirical schemes for x-ray attenuation coefficients in the context of PIXE (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 18 (1989), S. 235-242 
    Details
    ISSN: 0049-8246
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Various semi-empirical schemes for generating x-ray attenuation coefficients, μ/ρ, devised primarily for use in electron probe microanalysis, are considered for application in the PIXE analysis of thick specimens where the relevant x-ray energy region is 1-40 keV. Using selected high-accuracy experimental data, it is shown that current theoretical values of μ/ρ agree better with the data than do the various schemes. The errors transmitted into PIXE analysis by use of the theoretical values are estimated, and a new parameterization of these values suitable for microcomputer use is justified and tested.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/xrs.1300180511
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  • 10
    Digitale Medien
    Digitale Medien
    Electron-stimulated desorption total cross-section determination for digermane on Si(100) (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 105-108 
    Details
    ISSN: 0142-2421
    Schlagwort(e): ESD ; Si(100) ; electron-stimulated desorption ; silicon ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: We have studied digermane-covered Si(100) using electron-stimulated desorption (ESD). Estimates are presented for the total H(a) ESD removal cross-section for digermane-exposed Si(100) substrates at 85 K using electrons incident at 150 eV energy. It is found that electron-enhanced deposition of Ge occurs only when physisorbed digermane is present. Auger electron spectroscopy provided the means for determining the relative amounts of germanium adsorbed on the Si(100) surface following digermane exposures, electron irradiation and surface reconstruction. It is found that two coverage regimes are important: initial dosing of digermane on Si(100) at 85 K results in overlayers consisting of both physisorbed digermane and chemisorbed GeHx(a) (x=1, 2 or 3) species; and short anneals to 200 K following exposure of the Si(100) surface at 85 K lead to the presence of only chemisorbed GeHx(a). The two coverage regimes exhibit different ESD behavior. Two kinetic energy distribution (KED) peaks are seen when physisorbed digermane is present, and only one when it is absent. The ESD signal decay curves obtained from the two surfaces are also different: the presence of physisorbed digermane results in a two-component exponential signal decay; the absence of the physisorbed species results in a single-exponential decay. The total H removal cross-section from the physisorbed digermane overlayer was determined to be σ∽1.4×10-15 cm2, while that from Si(100) with only adsorbed GeHx present was found to be σ∽2.6×10-16 cm2. Our results suggest that adsorbed GeHx(a) species remain intact on the surface even when the Si(100) substrate is annealed to 200 K, indicating that hydrogen migration from surface GeHx(a) to Si surface sites does not occur at 200 K. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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