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  • 1995-1999  (130)
  • 1965-1969  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Relaxation times in transient electric birefringence and electric-field light scattering of flexible polymer chains (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7631-7639 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study in the present paper the response of a flexible macromolecular chain to the application or removal of an electric field. The polymer is mainly modeled as a Gaussian chain, and the case of freely jointed chains is also treated. We consider the dynamics of the chains, after the inception and subsequent cessation of an electric field. In particular, we calculate two properties. One of them is the time-dependent chain expansion, as measured by the components of the gyration tensor, that can be determined by transient electric-field light scattering. The other property is the transient electric birefringence, related to the reorientation of the chain segments. In this way, the dynamics of two different properties can be compared. The transient properties are analyzed in terms of a series of relaxation times. We propose the use of a mean relaxation time as a convenient representation of the rate of the dynamic process, and show that it can be deduced from simulation or experiments with more accuracy than the longest relaxation time. Our computational procedure is based on Brownian dynamics simulation. For Gaussian chains without hydrodynamic interaction, the results are compared with the predictions from the Rouse theory. We evaluate the influence of the strength of the force or field. Simulations are also carried out including hydrodynamic interactions, so that the importance of this effect can be assessed. We propose some combination of relaxation times with other macromolecular properties that take universal numerical values. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470282
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  • 2
    Electronic Resource
    Electronic Resource
    Microscopic analysis of the influence of strain and band-gap offsets on noise characteristics in Si1−xGex/Si heterojunctions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5012-5020 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study under forward-bias conditions of the physical origin of high frequency noise in p+(Si)-n (Si1−xGex) heterojunctions using ensemble Monte Carlo simulation is reported. Based on the internal magnitudes, we determine how the strained SiGe layer induces different features in the perpendicular transport of a heterojunction as compared with that of a silicon p+n homojunction. The main part of this study focuses on a comparative microscopic analysis of current fluctuations in homojunction and heterojunctions over a wide range of frequencies. A method based on considering a spatial analysis of noise to isolate the contributions of both types of carrier on the Si and Si1−xGex epilayers of the devices is described. The role of electrons and holes in the different regions of the devices and the combined effects of the band discontinuities and strain on noise characteristics in Si1−xGex/Si bipolar heterojunctions is discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368748
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  • 3
    Electronic Resource
    Electronic Resource
    Impedance spectroscopy study with H-doped ammonium uranylphosphate self supported membranes (1995)
    Springer
    Journal of applied electrochemistry 25 (1995), S. 68-72 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Equivalent circuit and electrical parameters for H-doped NH4UO2 PO4.3H2O self supported membranes have been determined by impedance spectroscopy. The measurements were carried out with a dry membrane, at different temperatures, and a wet membrane in contact with different electrolyte solutions. Resistance values for the dry membrane decrease with temperature increase, which agrees with the weak protonic character of the H-doped ammonium uranylphosphate. On the other hand, differences in the electrical parameters, depending on the electrolyte considered were also obtained and are attributed to different conduction mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00251267
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  • 4
    Electronic Resource
    Electronic Resource
    On the interaction of metal extractant reagents. Investigation of the aggregation ofdi(2,4,4-trimethylpentyl)phosphinic acid anddi(n-octyl)phosphinic acid in toluene by vapour-pressure osmometry (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 401-409 
    Details
    ISSN: 1434-4475
    Keywords: Aggregation ; di(2,4,4-Trimethylpentyl)phosphinic acid ; di(n-Octyl)phosphinic acid ; Vapour-pressure osmometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Aggregationsgleichgewichte von in Toluol gelösterdi-(2,4,4-Trimethylphentyl)-phosphinsäure (HDTMPP) unddi-(n-Octyl)-phosphinsäure (HDOP) wurden mittels Dampfdruckosmometrie (VPO) bei verschiedenen Temperaturen untersucht. Die experimentellen Daten wurden sowohl graphisch als auch numerisch ausgewertet; es wurden sowohl die mittlere Aggregationszahlñ als auch die Aggregationskonstante bestimmt. Die Resultate lassen vermuten, daß Dimere gebildet werden und die Dimerisationskonstante mit der Temperatur abnimmt. Mit Hilfe dervan't Hoffschen Gleichung wurden die Enthalpien der Aggregation vondi-(2,4,4-Trimethylpentyl)-phosphinsäure unddi-(n-Octyl)-phosphinsäure in Toluol abgeschätzt.
    Notes: Summary The aggregation equilibria ofdi(2,4,4-trimethylpentyl)phosphinic acid (HDTMPP) anddi(n-octyl)phosphinic acid (HDOP) dissolved in toluene have been investigated by vapour-pressure osmometry (VPO) at different temperatures. The experimental data have been treated both graphically and numerically, and the average aggregation numberñ as well as the aggregation constant have been determined. The results suggest that dimers are formed and that the dimerization constant decreases with temperature. Finally, the enthalpies for the aggregation ofdi(2,4,4-trimethylpentyl)phosphinic acid anddi(n-octyl)phosphinic acid in toluene have been estimated using thevan't Hoff equation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00813202
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  • 5
    Electronic Resource
    Electronic Resource
    Monitoring of organophosphorus insecticides in the guadalete river (Southern Spain) (1995)
    Springer
    Bulletin of environmental contamination and toxicology 55 (1995), S. 431-438 
    Details
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206683
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  • 6
    Electronic Resource
    Electronic Resource
    Radioactive (Chromium-51) Heinz Bodies (1966)
    [s.l.] : Nature Publishing Group
    Nature 210 (1966), S. 1064-1066 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A prime difficulty in investigating Heinz bodies has been the absence of methods for quantitative evaluation. Most research workers simply estimated the number and size of granules observed under the light microscope4'5. Beutler et al.6, in their study of Heinz body formation during exposure of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2101064a0
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  • 7
    Electronic Resource
    Electronic Resource
    The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Ålesund and comparison with model calculations (1999)
    Springer
    Annales geophysicae 17 (1999), S. 941-956 
    Details
    ISSN: 0992-7689
    Keywords: Atmospheric composition and structure (troposphere - composition and chemistry; instruments and techniques)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract During the Arctic Tropospheric Ozone Chemistry (ARCTOC) campaigns at Ny-Ålesund, Spitsbergen, the role of halogens in the depletion of boundary layer ozone was investigated. In spring 1995 and 1996 up to 30 ppt bromine monoxide were found whenever ozone decreased from normal levels of about 40 ppb. Those main trace gases and others were specifically followed in the UV-VIS spectral region by differential optical absorption spectroscopy (DOAS) along light paths running between 20 and 475 m a.s.l. The daily variation of peroxy radicals closely followed the ozone photolysis rate J(O3(O1D)) in the absence of ozone depletion most of the time. However, during low ozone events this close correlation was no longer found because the measurement of radicals by chemical amplification (CA) turned out to be sensitive to peroxy radicals and ClOx. Large CA signals at night can sometimes definitely be assigned to ClOx and reached up to 2 ppt. Total bromine and iodine were both stripped quantitatively from air by active charcoal traps and measured after neutron activation of the samples. Total bromine increased from background levels of about 15 ppt to a maximum of 90 ppt during an event of complete ozone depletion. For the spring season a strong source of bromine is identified in the pack ice region according to back trajectories. Though biogenic emission sources cannot be completely ruled out, a primary activation of halogenides by various oxidants seems to initiate an efficient autocatalytic process, mainly driven by ozone and light, on ice and perhaps on aerosols. Halogenides residing on pack ice surfaces are continuously oxidised by hypohalogenous acids releasing bromine and chlorine into the air. During transport and especially above open water this air mixes with upper layer pristine air. As large quantities of bromine, often in the form of BrO, have been observed at polar sunrise also around Antarctica, its release seems to be a natural phenomenon. The source strength of bromine from halogen activation on the pack ice, as based on the measured inorganic bromine levels, averages about 1012 Br-atoms m−2 s−1 during sunlit periods in Arctic spring. The total source strength of inorganic bromine from sunlit polar regions may therefore amount to 30 kt y−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0941-4
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of Clodronate on Calcidiol Serum Levels in Women with Breast Cancer (1997)
    Springer
    Calcified tissue international 61 (1997), S. 148 -150 
    Details
    ISSN: 1432-0827
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900313
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Polyethylene on Osteocalcin, Alkaline Phosphatase and Procollagen Secretion by Human Osteoblastic Cells (1998)
    Springer
    Calcified tissue international 62 (1998), S. 453-456 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Polyethylene — Osteocalcin — Alkaline phosphatase — Procollagen — Osteoblast.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. We have studied the direct effects of polyethylene particles on osteoblastic function in primary human bone cell cultures. The cells were obtained from trabecular bone fragments of patients undergoing knee reconstructive surgery. When the cells reached confluency, they were subcultured into two flasks, one untreated (control culture) and the other treated with polyethylene particles, and incubated until confluency. Osteoblastic function was evaluated by assaying osteocalcin, alkaline phosphatase, and C-terminal procollagen type I, with and without 1,25(OH)2D stimulation, in the cell-conditioned medium. We found that addition of polyethylene to these osteoblastic cell cultures induced higher levels of secreted osteocalcin after 1,25(OH)2D stimulation. Alkaline phosphatase levels increased whereas C-terminal procollagen type I levels decreased in the cell conditioned medium after polyethylene was added to the cultures. Treatment of the control cultures with 1,25(OH)2D stimulated alkaline phosphatase levels and decreased C-terminal procollagen type I. However, these osteoblastic markers in 1,25(OH)2D-treated cells did not change in cultures with polyethylene. This study demonstrates that polyethylene particles have a direct effect on osteoblastic markers in human bone cells in culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900459
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of Skeletal Site of Origin and Donor Age on Osteoblastic Cell Growth and Differentiation (1999)
    Springer
    Calcified tissue international 64 (1999), S. 280-286 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Human osteoblastic cells — Skeletal site — Aging.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Bone loss with aging may be due, at least in part, to inadequate bone formation. Moreover, the process of bone aging is known to follow a different pattern throughout the skeleton. In this study, we examined the cell proliferation rate (area under the cell growth curve, AUC) and the secretion of C-terminal type I procollagen (PICP), alkaline phosphatase (ALP), and osteocalcin (OC) in primary cultures of osteoblastic cells from human trabecular bone. Osteoblastic cells were obtained for 168 donors (100 women and 68 men). Ninety-eight bone samples were obtained from subjects undergoing knee arthroplastia, 52 aged 50–70 years (64 ± 5) and 46 over age 70 (73 ± 2). Another 70 bone samples were obtained from subjects undergoing hip arthroplastia; 51 were 50–70 years old (64 ± 4) and 19 were over 70 (75 ± 5). Osteoblastic cells from the older donors had a lower proliferation rate and OC secretion than those from younger subjects. However, ALP secretion was higher in the former subjects, whereas PICP secretion was unchanged. Osteoblastic cells from hip had a lower proliferation rate than those from knee. PICP secretion was also lower and ALP secretion was higher in the former cells. In age-matched cell cultures, osteoblastic cells from the knee had higher proliferation rate and PICP secretion than osteoblastic cells from the hip. However, ALP secretion was lower in knee osteoblastic cells than those from hip only in the younger group. With aging, ALP secretion was found to increase in knee osteoblactic cells, whereas OC secretion decreased in osteoblastic cell cultures from the hip. Our findings suggest that bone loss with aging may be accounted for, at least in part, by a decreased osteoblastic cell proliferation and an increased osteoblastic maturation. In addition, our data indicate that these changes with aging do not occur similarly at different skeletal sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900619
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