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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 3 (1988), S. 325-341 
    ISSN: 1573-1634
    Keywords: Natural convection ; heat transfer ; boundaries ; modes ; critical ; Nusselt ; power integral method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The ‘power integral method’ of calculating heat transfer across a convecting porous layer is extended to flux and porous boundaries. Convection starts at lower Rayleigh numbers for constant flux than for isothermal impervious boundaries and the flux is much greater. At higher Rayleigh numbers, as more of the higher modes contribute to the flux, the type of boundary has less influence on the heat transfer across the layer. For constant flux boundaries, simplified equations are developed to determine critical values for the second and higher modes and these values can be related simply to those for isothermal impervious boundaries.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 3 (1988), S. 437-453 
    ISSN: 1573-1634
    Keywords: Natural convection ; heat transfer ; flow ; critical ; Nusselt ; power integral method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Temperature decay in sealed rockbeds has been recorded. The rockbeds lost energy through the top surface and the results indicated that different natural convective flows occurred in beds of fixed depth and rock size but different lateral dimensions. However, the different flows had no effect on the mean power density dissipated through the top of the beds. A simple numerical conduction model based on the ‘power integral method’ was used to calculate the temperature decay. The experimental results suggested that an insulated porous lower boundary was appropriate for the model and this gave the best agreement with the experiments.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 215-229 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Results of the kinetics of adhesion of granulocytes as well as fresh and glutaraldehyde-fixed erythrocytes, suspended in Hanks Balanced Salt Solution (HBSS; pH 7.2, ionic strength of 0.15) to various polymeric substrates are presented. Cell adhesion increases rapidly initially and reaches a plateau value after approximately 30 minutes. There is no evidence for a lag-time in the onset of cell adhesion, suggesting that electrostatic double-layer forces are negligible under these experimental conditions. For the experiments in which the cells are suspended in HBSS, which has a surface tension larger than that of the cells, the level of cell adhesion increases with decreasing surface tension of the polymeric substrates. An additional experiment with fresh human granulocytes suspended in HBSS containing 10% dimethyl sulfoxide was also performed. The surface tension of the resulting liquid medium is below that of the cells and the pattern of adhesion is reversed, in agreement with the predictions of a thermodynamic model for cell adhesion. The slightly different behavior of siliconized glass as a substrate is discussed in terms of „screening“.
    Additional Material: 8 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 287-302 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Porous coated Ti-6Al-4V alloy implant systems provide a biocompatible interface between implant and bone, resulting in firm fixation and potential long-term retention via bony ingrowth. In order to achieve an acceptable porous coating structure, the sintering protocol for Ti-6Al-4V alloy systems often requires that the material be heat treated above the beta transus. This transforms the as-received equiaxed microstructure, recommended for surgical implants, to a lamellar alpha-beta distribution, which has been shown to have the worst fatigue properties of the most common structures attainable in Ti-6Al-4V alloy. However, post-sintering heat treatments may be used to improve these properties by producing microstructures more resistant to crack initiation and propagation. This study investigated the influence of microstructural variations on the fatigue properties of porous coated Ti-6Al-4V alloy material. Nonporous coated and porous coated Ti-6Al-4V alloy fatigue specimens were subjected to a standard sintering heat treatment to produce a lamellar microstructure. In addition, two post-sintering heat treatments were used to produce coarse and fine acicular microstructures. Rotating beam (reversed bending) fatigue testing was performed and the endurance limits determined for the noncoated and porous coated microstructures. The values determined were 668 MPa (noncoated asreceived equiaxed), 394 MPa (noncoated lamellar), 488 MPa (non-coated coarse acicular), 494 MPa (noncoated fine acicular), 140 MPa (porous coated lamellar), 161 MPa (porous coated coarse acicular), and 162 MPa (porous coated fine acicular). The noncoated coarse and fine acicular specimens displayed an approximate 25% increase over the noncoated lamellar specimens. The porous coated coarse and fine acicular specimens showed an approximate 15% improvement over the porous coated lamellar specimens.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 339-351 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In order to investigate the interactions of cellular elements and protein on constantly deforming (fatiguing) blood contact surfaces, a series of ex vivo canine arteriovenous shunt experiments were conducted. While fresh blood was flowing through Silastic tubing shunts, portions of the tubing were stretched 20 to 60% at a frequency of 20 to 90 cycles per minute for 10 to 90 min. The surfaces of the tubing that were stretched were compared with control tubing surfaces taken from the arterial side of the test segment using scanning electron microscopy and interference phase contrast microscopy.Approximately the same number of platelets were deposited on the stretched as on the unstretched portions of the tubing in the ten minute experiments. On the control portions of the tubing, the platelets were deposited singly and uniformly in what appeared to be a fairly inactivated state. On the stretched tubing, more pseudopod extension and aggregation was observed. In these preliminary experiments, no differences were noted as a function of frequency of stretch. As the blood contact time and the percent stretch were increased, only nonuniform, scattered aggregations of platelets, and platelets mingled with fibrin were seen. Significant numbers of spread white blood cells were observed on many of the segments of Silastic tubing stretched 20% for as short a time as 15 min. Granulocytes have occasionally been reported on less hemocompatible biomaterials after exposure to canine blood. This helps to confirm that substrate stretching of 20-60% had an adverse effect on the blood compatibility of the Siliastic tubing.
    Additional Material: 12 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 383-404 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Adhesion of cells to substrates strongly influences many of their functions and therefore plays an important role in a variety of processes, including phagocytosis, hemostasis, and the response of tissue to implanted materials. In previous studies, the influence of substrate hydrophilicity on cell adhesion has not been separated from effects due to major differences in other properties of the substrate, such as charge, rigidity, and the specific chemical composition of the materials. In addition, very few careful studies of the force required for cell detachment from various substrates have been performed. In this study, 3T3 cell detachment from a chemically homologous series of copolymers based on hydroxyethylmethacrylate (HEMA) and ethylmethacrylate (EMA) was measured with a spinning-disc apparatus. The spinning-disc technique allowed measurements of cell detachment over a wide range of applied shear stress on each sample. Cell detachment did not occur until a critical value of shear stress was exceeded. The critical shear stress of detachment decreased linearly with increasing HEMA content, from 18 dynes/cm2 on poly-EMA to 0 on the polymers containing 83% or more HEMA. “Plating efficiency,” calculated as the fraction of cells initially applied which remained after dip rinsing the surfaces, did not vary significantly among most of the copolymers. Dip rinsing, however, exposes the cells to only one, relatively low shear stress (estimated to be somewhat less than 3 dynes/cm2). The existence of a critical shear stress for 3T3 cell detachment suggests that cell adhesion to surfaces cannot be fully understood with single shear stress methods because cells may attach with a wide range of strengths which are either all above or all below the applied shear stress. The influence of surface hydrophilicity on cell adhesion and the variety of forces which may contribute to this phenomenon are discussed.
    Additional Material: 7 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 359-382 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The initial adsorption rate of delipidized Human Serum Albumin (HSA) is increased by addition of C-18 alkyl chains to a poly-urethane. The presence of alkyl chains does not appear to influence the total amount of HSA adsorbed after one hour exposure to a 5.0 mg/mL HSA solution. Neither does the desorption following one hour of adsorption appear to be influenced by the presence of alkyl chains. A study of the effects of solution concentration and temperature showed that the initial adsorption rates on both polymers are proportional to the protein concentration raised to the 0.36 power, and that alkylation of the polymer increases the activation energy of the initial adsorption rate above the 14 kJ/mol observed for the underivatized polyurethane. A new technique is presented to quantify the mass of adsorbed protein using Fourier transform infrared spectroscopy and attenuated total reflection optics. This technique uses the absorbance of bulk protein as an internal calibration reference, and appears to be as accurate and perhaps more precise than radiolabeling techniques.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 441-442 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 459-473 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The effects of grooved epoxy substrata on epithelial (E) cell behavior were studied in vitro and in vivo. V-shaped grooves, 10 μm deep, were produced in silicon wafers by micromachining, a process which was developed for the fabrication of microelectronic components. The grooved substrata were replicated in epoxy resin. More E cells attached to grooved surfaces than to adjacent smooth surfaces. Clusters of E cells were markedly oriented by the grooved surfaces in comparison to the adjacent smooth surfaces where the orientation was random. Grooved and smooth epoxy implants were placed percutaneously in the parietal area of rats. One week after implantation E cells were found to adhere tightly to the implant surfaces. In the grooved portion of the implant E cells interdigitated into the grooves and had rounded nuclei. Histomorphometric measurements indicated that there was a shorter length of epithelial attachment and a longer length of connective tissue attachment in the grooved, compared to the smooth, portion of implants. After 10 days the epithelial attachment had migrated down the length of the protruding smooth portion of the implant and was located on the base of the implant. However, epithelium remained attached to the grooved portion of the implant. These observations indicate that grooved surfaces have the potential to impede epithelial downgrowth on percutaneous devices.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 589-591 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
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