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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 42 (1980), S. 173-180 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Zadeh's transfer function method for linear time-variable systems is used to apply frequency-domain analysis to a periodically time-varying elastance model of the left ventricle. Left ventricular pressure computed from the system function of the time-varying elastance and the phasors of aortic flow shows a typical waveform of the measured ventricular pressure.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 41 (1979), S. 217-227 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A performance criterion and weighting factors for the optimal cardiac assistance are investigated by applying Tellegen's network theorem and tolerance analysis on animal experimental data for left ventricular (LV) bypass on the failing heart. Two major factors with respect to cardiac assistance (total power delivered to the peripheral circulatory system, and changes in temporal pattern of ventricular contraction) are represented by two performance criteria,J 1 andJ 2 whereJ 1 relates to the sum of LV and pump power, andJ 2 relates to the “peakedness” factor of LV power. The total performance index (J) is determined as the weighted sum ofJ 1 andJ 2;J=w 1J1+w2J2. The weighting factors,w 1 andw 2, are computed as inverses of the tolerance in the performance contours with respect to improvement of stroke work per minute from pre- to post-bypass condition.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 35 (1995), S. 641-648 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The low temperature relaxation of epoxy resin modified with siloxane oligomers was investigated by using thermally stimulated current (TSC) and relaxation map analysis (RMA). The β-relaxation of epoxy resin and the glass transition temperature of siloxane oligomer were folded and shifted to higher temperature as the concentration of trifluoropropyl (TFP) in siloxane oligomer increased. In the systems containing over 50% of TFP a new relaxation peak due to the dipole orientation was observed at around-45°C. As the concentration of TFP increased the compensation temperature (Tc) and the degree-of-disorder (DOD) were increased while the compensation time, τc was decreased.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 6 (1978), S. 352-366 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Sinusoidal variations of expired oxygen fraction (FEO2) and arterial blood oxygen saturation (S aO2) were measured in three paralyzed and anesthetized goats after producing sinusoidal changes in inspired oxygen fraction (FIO2) under controlled ventilation. These frequency-domain data were used to evaluate the quantitative dynamic relations among FIO2, FEO2, oxygen uptake at the lung $$\dot VO_2 $$ and S aO2 using the material balance equation at the lung and the Fourier transform of this equation. The overall transfer function between FIO2 and FEO2 was T(s)=0.07/(s+0.075) with a time constant of 13.3 sec, and $$\dot VO_2 $$ and S aO2(s) were related by a transfer function, G 1(s)=0.03/(s+0.008), with a time constant of 125 sec. The magnitude of the fundamental component of S aO2(s), |S aO2(jw)|, was related to |FEO2(jw)| by a constant, K=0.607, as S aO2 remained near the linear portion of the O2-hemoglobin dissociation curve in moderate hypoxia. Based upon the present frequency-domain analysis, the slow time response of S aO2 to the transient change of O2 concentration of the atmosphere is related to the homeostatic mechanism of the change of oxygen stores in the blood due to circulatory responses. The fast time response in FEO2 to the change of FIO2 is produced by the tachometer feedback function of the oxygen stored in the functional residual capacity of the lung. The present analysis and experimental observation provide a new method of investigating oxygen uptake using frequency-domain analysis.
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  • 5
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Water absorption and desorption of the diglycidyl ether of bisphenol A (DGEBA)/4,4′-diaminodiphenyl sulfone (DDS) resin systems, cured isothermally at three different temperatures (160, 180 and 220°C), were monitored at 80°C, as a function of soaking and drying times. New near infra-red spectroscopic (NIR) technique as well as the conventional gravimetric method were used. The data from two different techniques were reasonably identical showing that the new NIR technique is valid. The resin systems cured at higher temperature absorbed more water. The degree of structural packing of the network systems has been estimated from the observations in water absorption characteristics.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 24 (1986), S. 169-173 
    ISSN: 1741-0444
    Keywords: Correlation ; Visual evoked potential ; Visual pathway ; Weighting matrix
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Visual evoked potentials (VEPs) were measured using 19 electrodes attached to the scalps of five normal human subjects during stimulations of the full-field and hemifield chequerboard pattern reversal. These signals were analysed by a new method based on the time locus of the potential distribution centre, where this locus was computed from the spatial potential distribution using the weighting matrix and maximum mean cross-correlation criteria. The results showed that the loci of normal subjects are similar, with an average correlation of 0·87. The loci produced in the left hemifield stimulation were different from the loci produced during the right hemifield stimulation, with a correlation of −0·66. Experimental results from four cats showed significant changes of the time loci after surgical division of the visual path-ways.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0959-8103
    Keywords: acrylonitrile ; copolymer ; methylacrylate ; hydration ; melting ; solid-state transition ; double melting transition ; double crystallization ; dipole-dipole interaction ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of chemical composition of copolymers of acrylonitrile (AN) and methylacrylate (MA) on the hydration and thermal transition behaviour was investigated. An increase of the MA content considerably depressed both Tm and Tc of the hydrated polymers. A double melting and crystallization transition behaviour was observed when the hydrated polymer was reheated after cooling from the molten state. The separation between primary and secondary peaks was more notable in the second heating scan than in the first heating scan. A novel solid-state transition was observed in the dried acrylic polymers which had experienced hydration and melting in the wet state, followed by drying in the open state at 200°C.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1065-1073 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The microstructure and fracture properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resins modified with phenolic hydroxyl-terminated polysulfone (PSF) and cured with diaminodiphenyl sulfone (DDS) hardener have been investigated as a function of the molecular weight and concentration of PSF. The microstructure changed from a typical particulate structure to a phase-inverted structure as the molecular weight and/or the concentration of the modifier increased. The fracture toughness, measured by compact tension tests, increased with the microstructural changes toward the phase-inverted structure. The microstructural changes observed have been interpreted in terms of variation in the reaction mechanisms as determined by near-infrared spectroscopy. The level of minor reactions such as etherification and homopolymerization reactions increased with increasing molecular weight and/or concentration of the modifier, in line with the tendencies observed in microstructure and fracture toughness. In the system containing 20 wt% of Mn 10,000 PSF, about 30% of the epoxy groups were consumed by etherification and homopolymerization reactions, whereas none of these reactions occurred in the unmodified system. The increase in minor reactions in the modified systems may be to be due to the restricted molecular mobility, resulting from the increase of system viscosity caused by the modification. This increase in viscosity also reduced the rate of phase separation. The degree of heterogeneity in the epoxy network must increase with the increasing side reactions. The formation of the heterogeneous epoxy network and the slowdown of phase separation will prevent a uniform precipitation of the modifier and finally result in a heterogeneous partially phase-inverted structure or the completely phase-inverted structure, depending on the amount of modifier incorporated over the critical concentration. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1511-1518 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have studied an epoxy resin formulation consisting of the diglycidyl ether of bisphenol-A (DGEBA), modified with phenolic hydroxyl-terminated polysulfone (PSF) and cured with an aromatic amine curing agent, diaminodiphenyl sulfone (DDS). A range of microstructures and fracture properties have been obtained by controlling the formulation cure conditions (cure temperature and cure cycle in an isothermal mode). The chemical conversion of the cured resins has been monitored by near-infrared spectroscopy (NIR). Although only a single material formulation was used, three distinct types of microstructure were identified by scanning electron microscope (SEM) observations on samples prepared at different cure temperatures. Surprisingly, the thermal and fracture properties of the cured samples did not vary noticeably, in spite of the significant microstructure variations. The consistency of these fracture toughness results with cure temperature changes was an unexpected result in the light of our earlier observations of a strong dependence of fracture toughness on cure temperature in neat resin systems. The difference in behavior between neat and modified resins reveals that the fracture toughness of the latter is dependent on a combination of the microstructure and the matrix resin properties. This hypothesis was also supported by an observation of high fracture thoughness in a sample cured in a two-step process, which we believe is due to the optimum microstructure and matrix resin properties, being achieved separately during precure and postcure, respectively. The increase in fracture toughness values caused by the modification (ΔGIC) was calculated from the fracture toughness values of neat and modified resins, prepared under the same cure conditions, using a proposed theoretical equation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 1303-1312 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The glass transition temperature (Tg), water- and solvent-absorption characteristics, fracture toughness, and tensile properties of a diglycidyl ether of bisphenol-A (DGEBA) -based epoxy resin (Epikote 8283) cured with an aromatic amine curing agent, 4,4' -diaminodiphenyl sulfone (DDS), were studied as a function of cure temperature and cure cycle (one-step or two-step cure). The glass transition temperature (which depends on the extent of cure) shows a linear increase with increasing cure temperature and levels off toward the cure temperature of 200°C. Water and solvent uptake tended to increase with increasing cure temperature and, hence, with cross-linking level. Fracture toughness, tensile strength, strain to break, and tensile fracture energy also increased significantly with increasing final cure temperature regardless of cure cycle. In contrast, the small strain properties such as modulus, yield stress, and yield strain were not influenced greatly by cure temperature and cure cycle. From these results, we infer that the large strain properties of the resin are not inversely proportional to the cross-link density of the network as reported in many publications, 1 but, rather, that they are dependent on other structural parameters such as free volume and the flexibility of the cross-linked chains. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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