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  • 1995-1999  (130)
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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.470282
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368748
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  • 3
    Digitale Medien
    Digitale Medien
    Somatic embryogenesis from stem and leaf explants of Quercus robur L. (1999)
    Springer
    Plant cell reports 18 (1999), S. 538-543 
    Details
    ISSN: 1432-203X
    Schlagwort(e): Key words Oak ; Quercus robur ; Secondary embryogenesis ; Somatic embryo induction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Internodal and leaf segments from pedunculate oak (Quercus robur L.) seedlings were used as explant source to induce somatic embryogenesis. Auxin treatment influenced embryogenic response, which only occurred in explants initially cultured on media containing 4 mg/l naphthaleneacetic acid (NAA) and different benzyladenine (BA) concentrations. After 6 weeks of culture on induction medium, the explants were transferred to medium supplemented with 0.1 mg/l BA and 0.1 mg/l NAA, and 4 weeks later, they were subcultured in a growth-regulator-free medium, in which somatic embryos arose through indirect regeneration on the surface of a nodular callus. Somatic embryos were induced in explants of two out of four seedling provenances. The induction frequency ranged from 16% in leaf explants to 4% in internodal explants. Somatic embryos developed two cotyledons, which were translucent or opaque-white in appearance, but anomalous morphologies were also observed. Different embryogenic lines were established and maintained by repetitive embryogenesis in multiplication medium containing 0.1 mg/l BA plus 0.05 mg/l NAA. These results indicate that tissues from explants other than Q. robur zygotic embryos are able to produce embryogenic cultures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002990050618
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Aggregation ; di(2,4,4-Trimethylpentyl)phosphinic acid ; di(n-Octyl)phosphinic acid ; Vapour-pressure osmometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: 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.
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00813202
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Key words: Polyethylene — Osteocalcin — Alkaline phosphatase — Procollagen — Osteoblast.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002239900459
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  • 6
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Key words: Human osteoblastic cells — Skeletal site — Aging.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002239900619
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  • 7
    Digitale Medien
    Digitale Medien
    Lack of Relationship Between BsmI Vitamin D Receptor Polymorphism and Primary Hyperparathyroidism in a Spanish Female Population (1999)
    Springer
    Calcified tissue international 65 (1999), S. 214-216 
    Details
    ISSN: 1432-0827
    Schlagwort(e): Key words: Hyperparathyroidism — VDR polymorphism — Parathyroid adenoma.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract. The role of vitamin D receptor (VDR) gene polymorphisms in the pathogenesis of hyperparathyroidism is uncertain. Controversial results have been reported. The aim of this study was to explore the relevance of BsmI VDR gene polymorphism in patients with primary hyperparathyroidism (PHPT) due to adenomas. For this purpose, 36 postmenopausal patients with PHPT, mean age 64 years, were compared with a normal age-matched female population (n = 81). BsmI polymorphism distribution in PHPT group was as follows: Bb 50% (18/36); BB 22% (8/36); bb 28% (10/36). In the control group, the distribution was Bb 49% (40/81); BB 16% (13/81); bb 35% (28/81). No statistical differences were found between the two groups. In the PHPT group, no statistical associations were found between different allelic distribution and age, creatinine, hematocrit, phosphorus, alkaline phosphatase (ALP), total calcium, serum parathyroid hormone (PTH), or gland weight. By contrast, levels of serum calcium and iPTH values positively correlated with the PT weight (r = 0.421 and 0.599, respectively, P= 0.0001). Our data suggest that at least in this group, BsmI VDR gene polymorphism appears to be of minor relevance in clinical presentation and possibly, tumorigenesis in PHPT due to adenomas.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002239900685
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  • 8
    Digitale Medien
    Digitale Medien
    Further insights on chromosomal pairing of autopolyploids: a triploid and tetraploids of rye (1995)
    Springer
    Chromosoma 104 (1995), S. 298-307 
    Details
    ISSN: 1432-0886
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Chromosomal pairing of one triploid and three tetraploid plants of rye, Secale cereale, was analyzed by electron microscopy in surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I cells. Prophase I is characterized by: (i) the weak alignment showed by the three or four unsynapsed or partially homologous synapsed axes; (ii) the low number ber of pairing partner switches (PPSs) displayed by both trivalents and quadrivalents; and (iii) the existence of complex multivalents in which up to 13 chromosomes in the triploid and 22 chromosomes in the tetraploids were involved. However, only few heterologous chromosomal associations were maintained at metaphase I. The results obtained are discussed under the assumptions of the random end pairing model with some modifications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00352261
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002239900313
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  • 10
    Digitale Medien
    Digitale Medien
    Trends of prescribing patterns for the secondary prevention of myocardial infarction over a 13-year period (1998)
    Springer
    European journal of clinical pharmacology 54 (1998), S. 203-208 
    Details
    ISSN: 1432-1041
    Schlagwort(e): Key words Myocardial infarction ; Drug utilization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Medizin
    Notizen: Abstract Objective: The efficacy of β-adrenergic blocking agents and acetylsalicylic acid in the secondary prevention of myocardial infarction has been well recognized since the beginning of the 1980s. In a previous paper, however, we reported a lower than expected use of these drugs during the period 1982–1988. In 1989 the results of this survey were presented and discussed with the prescribing physicians. In the present paper we describe the prescription patterns for the same indication and in the same centre over the following 6 years (1989–1994). We also describe the use of angiotensin-converting enzyme (ACE) inhibitors, for which efficacy in certain subgroups has been recently shown. Methods: Random samples of patients discharged from our hospital between 1989 and 1994 with a diagnosis of acute myocardial infarction with Q-wave were studied. Information about diagnoses, other clinical variables and treatments prescribed at discharge was obtained from the hospital discharge forms. The results were compared with those obtained in the previous study. Results: We studied 514 patients (80% men) with a median age of 59 years (range 31–89). The proportions of patients prescribed β-adrenergic blocking agents and acetylsalicylic acid increased from 34% and 28%, respectively, in 1986–1988, to 62% and 75% in 1989–1991. In 1994 they had reached a steady state (63% and 71%). In addition, a continued decrease in the use of calcium channel blockers was noted, from 36% in 1986–1988 to 17% in 1994. The increase in the prescription of β-adrenergic blocking agents was especially remarkable in the subgroups for which a larger underuse was recorded in the previous study, such as the elderly. The proportion of patients prescribed an ACE inhibitor increased from 14% in 1989–1991 to 23% in 1994. In a multivariate analysis the prescription of ACE inhibitors was associated with female gender, hypertension during admission, heart failure during admission, and previous myocardial infarction. A substantial increase in the prescription of β-adrenergic blocking agents and acetylsalicylic acid and a decrease in the prescription of calcium channel blockers was recorded between 1982 and 1994. The prescription rate of β-adrenergic blocking agents has increased substantially in certain subgroups where underuse had been previously recorded. Most of the changes occurred in 1989–1991, and reached a steady state in 1994. In 1994 an increase in the prescription of ACE inhibitors was also recorded.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002280050446
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