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  • 1
    Electronic Resource
    Electronic Resource
    Meson spectrum in Regge phenomenology (2004)
    Springer
    The European physical journal 37 (2004), S. 323-333 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Under the assumption that both light and heavy quarkonia populate approximately linear Regge trajectories with the requirements of additivity of intercepts and inverse slopes, the masses of different meson multiplets are estimated. The predictions derived from the quasi-linear Regge trajectories are in reasonable agreement with those given by many other references.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjc/s2004-02002-5
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  • 2
    Electronic Resource
    Electronic Resource
    Global convergence of the method of shortest residuals (1999)
    Springer
    Numerische Mathematik 83 (1999), S. 581-598 
    Details
    ISSN: 0945-3245
    Keywords: Mathematics Subject Classification (1991):65k, 90c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary. The method of shortest residuals (SR) was presented by Hestenes and studied by Pytlak. If the function is quadratic, and if the line search is exact, then the SR method reduces to the linear conjugate gradient method. In this paper, we put forward the formulation of the SR method when the line search is inexact. We prove that, if stepsizes satisfy the strong Wolfe conditions, both the Fletcher-Reeves and Polak-Ribière-Polyak versions of the SR method converge globally. When the Wolfe conditions are used, the two versions are also convergent provided that the stepsizes are uniformly bounded; if the stepsizes are not bounded, an example is constructed to show that they need not converge. Numerical results show that the SR method is a promising alternative of the standard nonlinear conjugate gradient method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002119900080
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  • 3
    Electronic Resource
    Electronic Resource
    Transmission of male cytoplasm during fertilization in Nicotiana tabacum (1994)
    Springer
    Sexual plant reproduction 7 (1994), S. 313-323 
    Details
    ISSN: 1432-2145
    Keywords: Cytoplasmic inheritance Double fertilization ; Embryo sac Mitochondrial transmission ; Tobacco ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Serially sectioned embryo sacs of Nicotiana tabacum were examined during fertilization events using transmission electron microscopy. After pollen tube discharge, the outer membrane of the sperm pair is removed, the two sperm cells are deposited in the degenerate synergid and the sperm cells migrate to the chalazal edge of the synergid where gametic fusion occurs. During fertilization, the male cytoplasm, including heritable organelles, is transmitted into the female reproductive cells as shown by: (1) the cytoplasmic confluence of one sperm and the central cell during cellular fusion, (2) the occurrence of sperm mitochondria (distinguished by ultrastructural differences) in the zygote cytoplasm and adjacent to the sperm nucleus, (3) the presence of darkly stained aggregates which are found exclusively in mature sperm cells within the cytoplasm of both female cells soon after cell fusion, and (4) the absence of any large enucleated cytoplasmic bodies containing recognizable organelles outside the zygote or endosperm cells. The infrequent occurrence of plastids in the sperm and the transmission of sperm cytoplasm into the egg during double fertilization provide the cytological basis for occasional biparental plastid inheritance as reported previously in tobacco. Although sperm mitochondria are transmitted into the egg/zygote, their inheritance has not been detected genetically. In one abnormal embryo sac, a pair of sperm cells was released into the cytoplasm of the presumptive zygote. Although pollen tube discharge usually removes the inner pollen-tube plasma membrane containing the two sperm cells, this did not occur in this case. When sperm cells are deposited in a degenerating synergid or outside of a cell, this outer membrane is removed, as it apparently is for fertilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230510
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  • 4
    Electronic Resource
    Electronic Resource
    Male reproductive cell development in Nicotiana tabacum: male germ unit associations and quantitative cytology during sperm maturation (1994)
    Springer
    Sexual plant reproduction 7 (1994), S. 324-332 
    Details
    ISSN: 1432-2145
    Keywords: Generative cell ; Male germ unit Nicotiana tabacum ; Pollen tube ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Generative and sperm cells were examined at four stages of development from generative cell formation to sperm cell maturation using serial transmission electron microscopy. The generative cell and vegetative nucleus are associated in a male germ unit association during pollen maturation and tube elongation, except for generative cell mitosis. At late stages of prophase, this association loosens; the generative cell separates from the vegetative nucleus at metaphase. Slender, unbranched, or occasionally branched projections may be found at one or both ends of the generative cell, or they may be single, blunt, and short. Slender projections are rare during anaphase and telophase. The vegetative nucleus moves back into apposition with one sperm cell at the end of mitosis. During the re-establishment of the association, the vegetative nucleus first touches the end of the leading sperm cell and then moves next to the middle of the sperm nucleus. As the sperm cells enter interphase, a conventional association is re-established between one cell and the vegetative nucleus through one or more long and slender cytoplasmic extensions; these associations are maintained throughout later passage in the pollen tube. During maturation, a significant increase occurs in the surface area of the sperm cells (particularly in the sperm cell in association with the vegetative nucleus), and a lesser increase in nuclear volume and surface area. Other sperm cell parameters, including those of heritable organelles, remain unchanged during sperm cell maturation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230511
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  • 5
    Electronic Resource
    Electronic Resource
    Nucleotide sequence of a ripening-related cDNA from avocado fruit (1990)
    Springer
    Plant molecular biology 15 (1990), S. 165-167 
    Details
    ISSN: 1573-5028
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00017736
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  • 6
    Electronic Resource
    Electronic Resource
    Populations of plastids and mitochondria during male reproductive cell maturation in Nicotiana tabacum L.: A cytological basis for occasional biparental inheritance (1994)
    Springer
    Planta 193 (1994), S. 115-122 
    Details
    ISSN: 1432-2048
    Keywords: Autophagy ; Cytoplasmic inheritance ; Generative cell ; Nicotiana (reproductive cells) ; Plastid diminution ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dynamics of plastid and mitochondrial populations in male reproductive cells of tobacco (Nicotiana tabacum L.) were examined during development using serial ultrathin sections and transmission electron microscopy to reconstruct 58 generative cells and 31 sperm cells at selected stages of maturation from generative cell formation through gametic fusion. The first haploid mitosis resulted in incomplete exclusion of plastids providing an average of 2.81 plastids and 82.7 mitochondria for each newly formed generative cell. During generative-cell maturation, plastid content decreased to an average of 0.48 plastids/generative cell at anthesis owing to autophagy of organelles. Plastids were present in low frequency within generative and sperm cells in the pollen tube and appeared to be transmitted, according to observations immediately prior to fertilization. This forms a cytological basis for genetic reports of occasional biparental plastid inheritance. In contrast, mitochondria were transmitted in larger numbers, and approximately 80 mitochondria per generative cell or sperm cell pair were retained throughout development. This provides a potentially stable source for the transmission of male mitochondrial DNA, if present at fertilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191614
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  • 7
    Electronic Resource
    Electronic Resource
    Role of the melanocortin-4 receptor in metabolic rate and food intake in mice (2000)
    Springer
    Transgenic research 9 (2000), S. 145-154 
    Details
    ISSN: 1573-9368
    Keywords: food intake ; melanocortin-4 receptor ; metabolic rate ; MT-II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We evaluated the role of the melanocortin-4 receptor (MC-4R) in the control of metabolic rate and food intake in mice. Intraperitoneal administration of the non-selective MC-R agonist melanotan II (MT-II; a cyclic heptapeptide) increases metabolic rate in wildtype mice, while MC-4R knockout mice are insensitive to the effects of MT-II on metabolic rate. MC-4R knockout mice are also insensitive to the effects of MT-II on reducing food intake. We conclude that MC-4R can mediate control of both metabolic rate and food intake in mice. We infer that a role for MC-3R in mediating the acute effects of MT-II on basal metabolic rate and food intake in wildtype mice seems limited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008983615045
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  • 8
    Electronic Resource
    Electronic Resource
    Ultrastructure of sperm cells and the male germ unit in pollen tubes ofNicotiana tabacum (1989)
    Springer
    Protoplasma 152 (1989), S. 29-36 
    Details
    ISSN: 1615-6102
    Keywords: Male germ unit ; Nicotiana tabacum ; Pollen tube ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The structure of sperm cells and their association with the vegetative nucleus in pollen tubes ofNicotiana tabacum grown in styles were observed with the electron microscope, demonstrating the existence of a male germ unit. The two sperm cells are arranged in tandem and are closely associated with the vegetative nucleus, which always takes the lead. The leading sperm cell (SC 1) has a long and narrow cytoplasmic projection which lies within the enclaves of the much lobed vegetative nucleus, thus forming a physical association. The trailing sperm cell (SC 2) and the SC 1 are not only joined by a common transverse cell wall but also are surrounded by a periplasm bounded by the plasma membrane of the sperm cells and that of the vegetative cell, thus forming a structural connection. The sperm cells are elongated, with cytoplasmic projections at the anterior end of the SC 1 and at both ends of the SC 2. The cytoplasm of both sperm cells includes mitochondria, endoplasmic reticulum, dictyosomes, ribosomes, small vacuoles and axially oriented microtubules. No plastids were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01354237
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  • 9
    Electronic Resource
    Electronic Resource
    Preliminary observations on the formation of the male germ unit in pollen tubes ofCyphomandra betacea sendt. (1988)
    Springer
    Protoplasma 147 (1988), S. 55-63 
    Details
    ISSN: 1615-6102
    Keywords: Generative cell ; Sperm cell ; Treetomato ; Ultrastructure ; Vegetative nucleus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The structure of the generative cell and its association with the vegetative nucleus in the pollen tube ofCyphomandra betacea Sendt. were observed with the electron microscope. The generative cell, bounded by its own plasma membrane and the inner plasma membrane of the vegetative cell, possesses the cytoplasmic extension which lies within the embayments of a vegetative nucleus. The generative cell contains the normal complement of organelles and, especially, microtubules which cluster into several groups adjacent to the plasma membrane, oriented along the longitudinal axis of the cell. In the pollen tube reaching the lower end of the style aftersemivivo pollination, both of the sperm cells are elongated and polyribosomes and microtubules are the outstanding feature in the cytoplasm. The two sperm cells are connected by a common transverse cell wall, while cytoplasmic channels exist in both the periplasm of the two sperm cells and the transverse wall. The leading sperm cell (Svn) is closely associated with the vegetative nucleus. Thus the present study demonstrates the existence of the male germ unit in the pollen tube ofC. betacea. The possible cytoplasmic continuity between the sperm cells and between the gametes and vegetative cell is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403877
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  • 10
    Electronic Resource
    Electronic Resource
    Isolation and characterization from porcine serum of a soluble sulfotransferase responsible for 6-O-sulfation of the galactose residue in 2′-fucosyllactose: Implications in the synthesis of the ligand for L-selectin (1999)
    Springer
    Glycoconjugate journal 16 (1999), S. 357-363 
    Details
    ISSN: 1573-4986
    Keywords: L-selectin ; sialyl Lewisx ; sulfation ; sulfotransferase ; inflammation ; 2′-FL, 2′-fucosyllactose ; PAPS, adenosine 3′-phosphate 5′-phosphosulphate ; PLP, pyridoxal 5′ phosphate ; DTT, dithiothreitol ; SDS, sodium dodecyl sulphate ; PAGE, polyacrylamide gel electrophoresis ; HP-TLC, high performance-thin layer chromatography ; Galactose-6-O sulfotransferase, Gal-6-O-Stase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A soluble sulfotransferase from porcine serum which catalyzes the transfer of sulfate from adenosine 3′-phosphate 5′-phosphosulphate (PAPS) to 2′-fucosyllactose (2′-FL) was purified 36,333-fold using a combination of conventional and affinity chromatographic steps. The purified enzyme preparation after non-denaturing discontinuous-PAGE exhibited a molecular mass of about 80 kDa by reducing SDS-PAGE. However, when a partially purified enzyme preparation was subjected to gel filtration on Sephacryl S-300, the enzyme activity eluted in the void volume, which indicated that the native enzyme existed as an oligomer. The purified enzyme showed Km values of 9.15 µM for PAPS and 15.38 mM for 2′-FL at the optimum pH value of 7.4. The substrate specificity of the purified enzyme was evaluated with various sugars that are structurally similar to sialyl Lewisx (sLex). Results indicated that 3′-sialyllactose and lactose were efficient acceptors of sulfation, whereas 6′-sialyllactose and 6′-sialyllactosamine were poor substrates for this sulfotransferase. Further, the reaction product analysis revealed that the sulfate substitution, when using 2′-FL as the substrate, was at the C-6 position of the galactose residue. Coincidentally, a similar enzyme activity was also found in porcine lymphoid tissues such as, lymph nodes (peripheral and mesenteric) and spleen. Collectively, these findings suggest that this enzyme might be involved in the synthesis of the ligand for L-selectin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007052228230
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