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  • Articles  (36)
  • Springer  (26)
  • Institute of Physics  (10)
  • American Meteorological Society
  • Copernicus
  • 2015-2019  (7)
  • 2000-2004  (4)
  • 1990-1994  (12)
  • 1975-1979  (13)
  • Chemistry and Pharmacology  (18)
  • Mathematics  (16)
  • Architecture, Civil Engineering, Surveying  (2)
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  • Articles  (36)
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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the transient behavior of kidney models (1978)
    Springer
    Bulletin of mathematical biology 40 (1978), S. 211-221 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Non-steady-state equations for kidney models are stated. General conservation relations for these equations are derived. Transient equations for the central core model of the renal medulla are developed. Solution of the equations by Laplace transform methods for time invariant volume flows is discussed. The general theory of solving models with time dependent flows by finite difference methods is developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461436
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  • 2
    Electronic Resource
    Electronic Resource
    Transient behaviour of the single loop solute cycling model of the renal medulla (1978)
    Springer
    Bulletin of mathematical biology 40 (1978), S. 273-300 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Transient solutions are developed for the buildup of a concentration gradient in the single loop solute cycling model of the renal medulla. The “pump” from ascending limb to descending limb is considered in both unsaturated and completely saturated modes of operation. Both analytic solutions and semianalytic solutions obtained from inverting Laplace transforms are considered. The classic representation of concentration buildup by the multiplication process is compared with calculated profiles. The “single effect” is found to vary both in time and space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461602
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  • 3
    Electronic Resource
    Electronic Resource
    Externally driven countercurrent multiplication in a mathematical model of the urinary concentrating mechanism of the renal inner medulla (1994)
    Springer
    Bulletin of mathematical biology 56 (1994), S. 491-514 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Substitution of measured permeabilities into mathematical models of the concentrating mechanism of the renal inner medulla yields less than the known urine osmolalities. To gain a better understanding of the mechanism we analyse a model in which a force of unspecified origin [expressed as fraction, ɛ, of entering descending thin limb (DTL) concentration] drives fluid from DTL to interstitial vascular space (CORE), thus concentrating the solution in DTL. When flow in the DTL reverses at the hairpin bend of the loop of Henle, the high solute permeability of ascending thin limb (ATL) permits solute to diffuse into the CORE thus permitting ɛ to be multiplied many-fold. Behavior of the model is described by two non-linear differential equations. In the limit for infinite salt permeability of ATL the two equations reduce to a single equation that is formally identical with that for the Hargitay and Kuhn multiplier, which assumes fluid transport directly from DTL to ATL (Z. Electrochem. Angew. Phys. Chem. 55, 539, 1951). Solutions of the equations describing the model with parameters taken from perfused thin limbs show that urine osmolalities of the order of 5000 mosm L−1 can be generated by forces of the order of 20 mosm L−1. It seems probable that mammals including desert rodents use some variant of this basic mechanism for inner medullary concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460468
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  • 4
    Electronic Resource
    Electronic Resource
    Spiral hexagonal circle packings in the plane (1994)
    Springer
    Geometriae dedicata 49 (1994), S. 39-70 
    Details
    ISSN: 1572-9168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We discuss an intriguing geometric algorithm which generates infinite spiral patterns of packed circles in the plane. Using Kleinian group and covering theory, we construct a complex parametrization of all such patterns and characterize those whose circles have mutually disjoint interiors. We prove that these ‘coherent’ spirals, along with the regular hexagonal packing, give all possible hexagonal circle packings in the plane. Several examples are illustrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01263534
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  • 5
    Electronic Resource
    Electronic Resource
    An AP-1-like motif in the first intron of human Proα1(I) collagen gene is a critical determinant of its transcriptional activity (1992)
    Springer
    Molecular and cellular biochemistry 116 (1992), S. 119-129 
    Details
    ISSN: 1573-4919
    Keywords: collagen transcription ; intronic Ap-1 ; fos jun trans-acting factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The first intron of the human Proα1(I) collagen gene contains an orientation-dependent enhancer composed of both positive and negative cis-acting elements involved in the transcriptional regulation of this gene. Deletion of a 360 bp Sau 3A intronic fragment spanning nucleotide + 494 to + 854 (S360) resulted in dramatic down-regulation of pCOL-KT (Thompson et al., J Biol Chem 266: 2549–2556, 1991). Using a DNaseI protection assay, we demonstrate a single footprint located at + 590 to + 615 in the S360 fragment; nuclear extracts prepared from mesenchymal and nonmesenchymal cells exhibited similar binding characteristics. A double stranded oligonucleotide representing a consensus Ap-1 binding sequence competed with S360 for binding. In contrast to what occurred in response to S360 deletion which was always accompanied by reduced expression, the deletion of the Ap-1 binding site (+ 598 to + 604) caused either increased or decreased expression of the reporter gene depending on the target cell. Site-directed mutations in the Ap-1-like cis-element of Proα1(I) were also tested in transient expression assays. Consistent with the paradoxical results of Ap-1 deletion, we observed that the functional consequences of mutations in the Ap-1 site also varied in different cells. In A204 cells, one point mutation, which resulted in the loss of protein binding to S360, led to increased CAT activity while another point mutant, which retained binding of the Ap-1 like trans-acting factor(s), showed decreased CAT expression. The effects of these two mutations in the HFL-1 cells were exactly opposite of what was seen for A204 cells. Based on these observations, we postulate that the Ap-1 site plays a critical role in the transcriptional activity of the human Proα1(I) gene. The implications of an apparently dual mode of regulation through a single cis-regulatory element are discussed. (Mol Cell Biochem 118: 119–129, 1992)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299391
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  • 6
    Electronic Resource
    Electronic Resource
    A comparative study of microsomal and cytosolic S6 phosphatase activities in rat liver (1991)
    Springer
    Molecular and cellular biochemistry 107 (1991), S. 103-110 
    Details
    ISSN: 1573-4919
    Keywords: ribosomal protein ; hepatectomy ; cycloheximide ; insulin ; phosphopeptide mapping ; phosphoprotein phosphatases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Spontaneous S6 phosphatase activities dephosphorylating Ser(P)-235 and Ser(P)-236 of the ribosomal protein S6 were measured and compared in microsomes and cytosol of rat liver. The substrate used, small (40S) ribosomal subunits 32P-labelled in vitro by protein kinase A, contained phosphorylated S6 (mainly in the dephosphorylated form) and some minor phosphorylated species. The microsomal and cytosolic S6 phosphatase activities displayed a number of distinct properties. The microsomal activity, representing ca 20% of the S6 phosphatase activity in the post-mitochondrial supernatant, was mainly due to a type-1 phosphatase and dephosphorylated only S6. The remaining post-mitochondrial S6 phosphatase activity, which was fully recovered in the cytosol, and appeared to result from a combination of type-1 (43%) and type 2 (57%) phosphatases, acted on S6 as well as on the minor phosphorylated species. The microsomal activity was 50% inhibited by MgCl2 (l0 mM) and was stimulated at least 4.3 fold by MnCl2 (1 mM), while the cytosolic activity was inhibited only 18% by Mg2+ (10 mM) and was increased 2.2 fold by Mn2+ (1 mM). The microsomal activity was increased 10% (P 〈 0.06) by lower doses of insulin (25 U/Kg) and 14% (P 〈 0.05) by vanadate, but was not significantly (P 〉 0.10) affected by larger doses of insulin (100 U/kg), hepatectomy or cycloheximide. By comparison the cytosolic S6 phosphatase activity was unresponsive to insulin and vanadate, but was decreased 14% and 17% (P 〈 0.05) by hepatectomy and cycloheximide. It is concluded that (i) there. are clear differences between the microsomal and cytosolic S6 phosphatase activities, which may be relevant to their specific functions in the cell, and (ii) the inhibition of cytosolic S6 phosphatase activity by hepatectomy and cycloheximide may contribute to the increase in hepatic S6 phosphorylation induced by these treatments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00225513
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  • 7
    Electronic Resource
    Electronic Resource
    Normal expression of thymidine kinase and O6-methylguanine-DNA methyltransferase in cultured fibroblasts from individuals with hereditary galactokinase deficiency (1991)
    Springer
    Biochemical genetics 29 (1991), S. 135-144 
    Details
    ISSN: 1573-4927
    Keywords: galactokinase ; thymidine kinase ; O6-methylguanine-DNA methyltransferase ; gene regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Expression of the enzymes galactokinase, thymidine kinase, and O6-methylguanine-DNA methyltransferase is occasionally coordinately regulated in human cell lines. We have measured the activities of these three enzymes in extracts of fibroblasts from individuals with hereditary galactokinase deficiency. These cells do not express measurable galactokinase activity. The levels of O6-methylguanine-DNA methyltransferase were in the normal range in cells from three galactokinase-deficient individuals. The activity of thymidine kinase in the affected cells was in the normal range for two of the three individuals. The reduced thymidine kinase activity in the third individual reflected the extremely poor growth of the cells in culture. Immortalization of one galactokinase-deficient cell line resulted in loss of O6-methylguanine-DNA methyltransferase activity, but the galactokinase and thymidine kinase levels remained unchanged. The data indicate that the loss of galactokinase activity in these individuals is the consequence of an alteration of gene expression which does not involve coordinate silencing with the thymidine kinase and methyltransferase loci.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00554207
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  • 8
    Electronic Resource
    Electronic Resource
    Normal expression of thymidine kinase and O6-methylguanine-DNA methyltransferase in cultured fibroblasts from individuals with hereditary galactokinase deficiency (1991)
    Springer
    Biochemical genetics 29 (1991), S. 135-144 
    Details
    ISSN: 1573-4927
    Keywords: galactokinase ; thymidine kinase ; O6-methylguanine-DNA methyltransferase ; gene regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Expression of the enzymes galactokinase, thymidine kinase, and O6-methylguanine-DNA methyltransferase is occasionally coordinately regulated in human cell lines. We have measured the activities of these three enzymes in extracts of fibroblasts from individuals with hereditary galactokinase deficiency. These cells do not express measurable galactokinase activity. The levels of O6-methylguanine-DNA methyltransferase were in the normal range in cells from three galactokinase-deficient individuals. The activity of thymidine kinase in the affected cells was in the normal range for two of the three individuals. The reduced thymidine kinase activity in the third individual reflected the extremely poor growth of the cells in culture. Immortalization of one galactokinase-deficient cell line resulted in loss of O6-methylguanine-DNA methyltransferase activity, but the galactokinase and thymidine kinase levels remained unchanged. The data indicate that the loss of galactokinase activity in these individuals is the consequence of an alteration of gene expression which does not involve coordinate silencing with the thymidine kinase and methyltransferase loci.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401808
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  • 9
    Electronic Resource
    Electronic Resource
    A mathematical model of proximal tubule absorption (1979)
    Springer
    The journal of membrane biology 47 (1979), S. 377-399 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A previous model of the mechanisms of flow through epithelia was modified and extended to include hydrostatic and osmotic pressures in the cells and in the peritubular capillaries. The differential equations for flow and concentration in each region of the proximal tubule were derived. The equations were solved numerically by a finite difference method. The principal conclusions are: (i) Cell NaCl concentration remains essentially isotonic over the pressure variations considered; (ii) channel NaCl concentration varies only a few mosmol from isotonicity, and the hydrostatic and osmotic pressure differences across the cell wall are of the same order of magnitude; (iii) both reabsorbate osmolality and pressure-induced flow are relatively insensitive to the geometry of the system; (iv) a strong equilibrating mechanism exists in the sensitivity of the reabsorbate osmolality to luminal osmolality; this mechanism is far more significant than any other parameter change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869745
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  • 10
    Electronic Resource
    Electronic Resource
    Leaf surface chemicals fromNicotiana affecting germination ofPeronospora tabacina (adam) sporangia (1992)
    Springer
    Journal of chemical ecology 18 (1992), S. 1467-1479 
    Details
    ISSN: 1573-1561
    Keywords: Nicotiana ; Peronospora tabacina ; blue mold ; leaf surface ; chemistry ; diterpenes ; sugar esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A bioassay was used to evaluate the effects of cuticular leaf components, isolated fromN. tabacum, N. glutinosa (accessions 24 and 24a), and 23other Nicotiana species, on germinationof P. tabacina (blue mold). The leaf surface compounds includedα- andβ-4,8,13,-duvatriene-l,3-diols (DVT-diols), (13-E)-labda-13-ene-8α-,15-diol (labdenediol), (12-Z)-labda-12,14-diene-8α-ol (cis-abienol), (13-R)-labda-8,14-diene-13-ol (manool), 2-hydroxymanool, a mixture of (13-R)-labda-14-ene-8α,13-diol (sclareol), and (13-S)-labda-14-ene-8α,13-diol (episclareol), and various glucose and/or sucrose ester isolates. The above in acetone were applied onto leaf disks of the blue moldsusceptibleN. tabacum cv. TI 1406, which was then inoculated with blue mold sporangia. Estimated IC50 values (inhibitory concentration) were 3.0μg/cm2 forα-DVT-diol, 2.9μ/cm2 forβ-DVT-diol, 0.4μg/cm2 for labdenediol and 4.7μg/cm2 for the sclareol mixture. Manool, 2-hydroxymanool, andcis-abienol at application rates up to 30μg/cm2 had little or no effect on sporangium germination. Glucose and/or sucrose ester isolates from the cuticular leaf extracts of 23Nicotiana species and three different fractions fromN. bigelovii were also evaluated for antimicrobial activity at a concentration of 30μg/cm2. Germination was inhibited by 〉20% when exposed to sugar esters isolated fromN. acuminata, N. benthamiana, N. attenuata, N. clevelandii, andN. miersii, and accessions 10 and 12 ofN. bigelovii. These results imply that a number of compounds may influence resistance to blue mold in tobacco.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00993221
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