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  • 11
    Electronic Resource
    Electronic Resource
    The influence of sintering process and atmosphere on the non-ohmic properties of SnO2 based varistor (1999)
    Springer
    Journal of materials science 10 (1999), S. 321-327 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The non-ohmic properties of the 98.95% SnO2 + 1.0%,CoO + 0.05%,Nb2O5 (all in mole%) system, as well as the influence of sintering temperature and atmosphere on these properties, were characterized in this study. The maximum non-linear coefficient (α = 32) was obtained for a sintering temperature of 1300°C in an oxygen atmosphere and this maximum is associated with the presence of O in SnO2 grain boundaries, as interface defects. Experimental results also indicate thermionic-type conduction mechanisms, which are associated with the potential barrier of Schottky or Poole–Frenkel types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008933004042
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  • 12
    Electronic Resource
    Electronic Resource
    Progression of retinopathy and alteration of the blood-retinal barrier in patients with type 2 diabetes: a 7-year prospective follow-up study (1998)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 236 (1998), S. 264-268 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  · Background: The study was carried out to evaluate the correlation between blood-retinal barrier (BRB) permeability and the progression of diabetic retinopathy (DR), defined by development of “need for photocoagulation”, over a 7-year period by means of vitreous fluorometry (VF). · Methods: Forty type 2 diabetic patients with minimal or no retinopathy, aged 40–65 years (mean 53.9 + 7.3 years), were followed up prospectively for 7 years. Investigations including standard ophthalmological examination, fundus photography, fluorescein angiography and VF were performed at entry and 1, 4, 5 and 7 years later. Only one eye per patient was included in the study. Need for photocoagulation was based on Early Treatment Diabetic Retinopathy Study protocols and decided by the attending ophthalmologist. · Results: After 7 years of follow-up a total of 22 of the 40 eyes had received photocoagulation. The eyes that needed photocoagulation were those that had higher VF values at the entry of the study and showed higher rates of deterioration (initial values 5.1 + 1.9 vs 2.8 + 1.5×10–6 min–1, P〈0.001; annual increase in leakage for the first year, 1.5 + 0.8 vs 0.5 + 1.0×10–6 min–1 , P〈0.001,). The eyes that did not need photocoagulation during the 7 years of follow-up showed stable VF readings (-0.1 + 1.2×10–6 min– 1, difference between initial values and 7 years later). · Conclusions: Abnormally high VF values and their rapid increase over time are good indicators of progression and worsening of the retinopathy in diabetes type 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004170050075
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  • 13
    Electronic Resource
    Electronic Resource
    Microstructural development of ZnO varistor during reactive liquid phase sintering (1996)
    Springer
    Journal of materials science 31 (1996), S. 5391-5398 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The microstructural evolution, grain growth and densification for the varistor systems ZnO-Bi2O3 (ZB), ZnO-Bi2O3-Sb2O3 (ZBS), ZnO-Bi2O3-Sb2O3-MnO-Cr2O3-CoO (ZBSCCM) were studied using constant heating rate sintering, scanning electron microscopy (SEM) andin situ phase formation measurement by high temperature X-ray diffraction (HT-XRD). The results showed that the densifying process is controlled by the formation and decomposition of the Zn2Bi3Sb3O14 pyrochlore (PY) phase for the ZBS and ZBSCCM systems. The addition of transition metals (ZBSCCM system) alters the formation and decomposition reaction temperatures of the pyrochlore phase and the morphology of the Zn7Sb2O12 spinel phase. Thus, the spinel grains act as inclusions and decrease the ZnO grain growth rate. Spinel grain growth kinetics in the ZBSCCM system showed ann value of 2.6, and SEM and HT-XRD results indicate two grain growth mechanisms based on coalescence and Ostwald ripening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159308
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  • 14
    Electronic Resource
    Electronic Resource
    Preparation and properties of ferroelectric BaTiO3 thin films produced by the polymeric precursor method (2000)
    Springer
    Journal of materials science 19 (2000), S. 1457-1459 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011027624446
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  • 15
    Electronic Resource
    Electronic Resource
    A new interpretation for the degradation phenomenon of ZnO varistors (1992)
    Springer
    Journal of materials science 27 (1992), S. 5325-5329 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The electrical degradation phenomena of zinc oxide-based varistors were studied using a high-energy current pulse and a.c. polarization at different temperatures. Activation energy measurements during the degradation process showed that these phenomena are associated with diffusion and that the diffusion-controlling species are slower than Zn., For degradation promoted by current pulses of 8×20 μs, the Schottky potential barrier deformation was measured. A decrease in height and width of the potential barrier due to the reduction of surface states density,N s, without a significant change in donor density,N d, was observed. To explain these results, a modification of the unstable components model is proposed for the potential barrier in which the degradation is due to oxi-reduction reactions between atomic defects. These reactions promote the elimination of zinc vacancies and/or adsorbed oxygen on the grain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02403838
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  • 16
    Electronic Resource
    Electronic Resource
    A new interpretation for the degradation phenomenon of ZnO varistors (1992)
    Springer
    Journal of materials science 27 (1992), S. 5325-5329 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The electrical degradation phenomena of zinc oxide-based varistors were studied using a high-energy current pulse and a.c. polarization at different temperatures. Activation energy measurements during the degradation process showed that these phenomena are associated with diffusion and that the diffusion-controlling species are slower than Zn., For degradation promoted by current pulses of 8×20 μs, the Schottky potential barrier deformation was measured. A decrease in height and width of the potential barrier due to the reduction of surface states density,N s, without a significant change in donor density,N d, was observed. To explain these results, a modification of the unstable components model is proposed for the potential barrier in which the degradation is due to oxi-reduction reactions between atomic defects. These reactions promote the elimination of zinc vacancies and/or adsorbed oxygen on the grain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553413
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  • 17
    Electronic Resource
    Electronic Resource
    Spectrophotometric analysis of sodium fluorescein aqueous solutions. Determination of molar absorption coefficient (1991)
    Springer
    International ophthalmology 15 (1991), S. 321-326 
    Details
    ISSN: 1573-2630
    Keywords: absorption spectrum ; calibration ; fluorometry ; infrared spectrum ; sodium fluorescein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The usefulness of sodium fluorescein (SF) and related physical parameters were analysed. Two factors that may affect the molar absorption coefficient (ɛ) of this compound were the presence of impurities and the pH of the solution. As discrepant values can be found in the literature for that coefficient, a purification technique was used and SF quantification was performed according to sodium concentration determined by atomic absorption spectrophotometry. The molar absorption coefficient of the SF solution in phosphate buffer pH 7.4 was determined. To study the influence of pH on ɛ determination, absorption spectra at pH 1, 3, 5, and 10 were also analysed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00128951
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  • 18
    Electronic Resource
    Electronic Resource
    Morphological and/or functional imagiology diagnosis of epiphora (1993)
    Springer
    Documenta ophthalmologica 83 (1993), S. 337-348 
    Details
    ISSN: 1573-2622
    Keywords: Conventional subtraction macrodacryocystopraphy (CSMD) ; Digital subtraction macrodacryocystography (DSMD) ; Epiphora ; Lacrimal ducts (LD) ; Sequential dacryoscyntygraphy (SD)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Several tests and examinations are necessary for an accurate diagnosis of disorders of the lacrimal drainage system. The AA studied 100 patients with epiphora, divided in two groups. Forty patients, first group (I), aged between 4 and 78 years old (mean age 47.8 ± 9.6 years), were examined using the classical tests for the study of epiphora, sequential dacryoscintigraphy (SD) and conventional subtraction macrodacryocystrography (CSMD). In the second group (II), 60 patients (aged 45.5 ± 8.7 years) were studied using the classical tests and by digital subtraction macrodacryocystography (DSMD). The results showed that when functional epiphora is present, there is no difference between a simple clinical approach and sequential dacryoscintigraphy. However, when information is needed regarding choice of surgical approach, DSMD appears to give the best results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204336
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  • 19
    Electronic Resource
    Electronic Resource
    Effect of cyclospasmol on early diabetic retinopathy (1987)
    Springer
    International ophthalmology 10 (1987), S. 3-9 
    Details
    ISSN: 1573-2630
    Keywords: cyclospasmol ; cyclandelate ; diabetic retinopathy ; quantitative vitreous fluorophotometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A randomized, double-blind, placebo controlled study to investigate the long-term effect of CyclospasmolR (cyclandelate) on the abnormal permeability of the blood-retinal barrier was performed in 26 patients with insulin-dependent diabetes mellitus for at least 1 year and minimal retinopathy. Cyclospasmol 400 mg or placebo capsules were taken 4 times daily for 12 months by equal numbers in both groups. Each patient underwent a routine ophthalmoscopic examination, retinal fluorescein angiography and quantitative vitreous fluorophotometry to assess the permeability of the blood-retinal barrier just before the trial and following 6 and 12 months of therapy. Laboratory tests for determining blood and urine glucose levels and blood HbA1-levels were also carried out at these assessments. Statistically significant changes in diabetic control, in HbA1-levels or in the frequency of retinal microaneurysms could not be shown in either treatment group during the trial, nor were there any significant differences in these parameters between the two groups. Analysis of fluorophotometric data on fluorescein penetration into the left posterior vitreous demonstrated significant reductions in this parameter during the trial compared to the pretreatment level in Cyclospasmol treated diabetics. These changes in the pretreatment level after 6 and 12 months also differed significantly between the two groups. However, this statistically significant beneficial reduction in fluorescein penetration into the left posterior vitreous did not occur in the right eye in the Cyclospasmol group. In placebo treated patients a consistently deleterious trend for this parameter was observed for both eyes during the one year study. The consistently beneficial trend in the right eye following Cyclospasmol and the consistently deleterious trend in both eyes following placebo with regard to the abnormal permeability of the blood-retinal barrier of diabetics with minimal retinopathy could probably be explained by the small number of patients in both groups. No side-effects were reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202775
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  • 20
    Electronic Resource
    Electronic Resource
    Effect of calcium dobesilate on the blood-retinal barrier in early diabetic retinopathy (1990)
    Springer
    International ophthalmology 14 (1990), S. 81-88 
    Details
    ISSN: 1573-2630
    Keywords: calcium dobesilate ; diabetic retinopathy ; blood-retinal barrier ; vitreous fluorophotometry ; penetration ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of calcium dobesilate on the alteration of the blood-retinal barrier was studied in 41 adult-onset, non-insulin dependent diabetic patients with minimal or no retinopathy, randomly assigned to receive either oral calcium dobesilate (1000 mg twice daily) or a placebo for 12 months. The posterior vitreous value and the penetration ratio, determined by vitreous fluorophotometry, reflected stabilisation of blood-retinal barrier permeability in the calcium dobesilate patients and deterioration of blood retinal barrier in those given placebo. During the relatively short period of the study, one year, no significant change in microaneurysm and capillary closure gradings was observed. No side effects were associated with calcium dobesilate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154206
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