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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Although the sex-determining gene Sry has been identified in mammals, no comparable genes have been found in non-mammalian vertebrates. Here, we used recombinant breakpoint analysis to restrict the sex-determining region in medaka fish (Oryzias latipes) to a 530-kilobase (kb) stretch of the Y ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1516-1522 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new set of equations appropriate for the study of the turbulence, due to the ion temperature gradient in the slab in the fluid description, is proposed. This model is similar to many existing models including the one used in the work of Hamaguchi and Horton (HH) [S. Hamaguchi and W. Horton, Phys. Fluids B 2, 1834 (1990)]. The main difference is that in this model the ion diamagnetic drift contributes to the kinetic energy in the energy balance relation. It is achieved through more complete analysis for the polarization drift due to the finite-Larmor-radius effects. The linear growth rate in the model is found to be smaller and the numerical results show that the heat transport is smaller by an order of magnitude when compared to HH.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1833-1851 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ion temperature gradient driven mode or ηi-mode turbulence is reinvestigated based on two-component compressible fluid equations with the polarization drift velocity and adiabatic electrons. The scaling of the anomalous ion heat conductivity with magnetic shear s=Ln/Ls and the excess of ηi over the critical value ηi,c for marginal stability is found to vary as χi=g(ρs/Ln)(cTi/eB) (ηi−ηi,c)exp(−αs), where g(approximately-equal-to)1 and α(approximately-equal-to)5.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 3040-3046 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anomalous heat transport arising from the ion temperature gradient driven mode or ηi-mode turbulence is extended to the range of the weak density gradient limit (ηi=Ln/LT→∞), which is appropriate for H-mode dishcarges. It is shown that the anomalous ion heat conductivity χi with Ln→∞ scales as χi=g(ρs/LT) (cTi/eB) exp(−βσ) with σ=(Te/Ti) (LT/Ls), β(approximately-equal-to)4, and g(approximately-equal-to)1. This χi scaling is the natural extension for high ηi of the scaling of χi for K=(Ti/Te) (1+ηi)(approximately-less-than)4 obtained [Phys. Fluids B 2, 1833 (1990)] from analytical and numerical studies.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1416-1430 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anomalous transport caused by fluctuations of resistive pressure-driven modes is discussed within the framework of magnetohydrodynamics (MHD). The nonlinear-reduced equations describing fluctuations localized near a particular magnetic field line are derived for tokamak and reversed-field-pinch (RFP) plasmas, taking into account nonzero viscosity and heat conductivity. For an ideally stable but resistively slightly unstable plasma, the anomalous transport is caused particularly by convective motions. The convection is studied as bifurcation from the linearly unstable equilibrium and the expression of the anomalous transport in a tokamak plasma is obtained as a function of the mean pressure gradient near the critical point. In order to evaluate the effects of the convection on the anomalous transport under various conditions, the reduced equations are also solved numerically. It is found that Nusselt number, that is, the ratio of the total heat conductivity including the anomalous heat transport to the classical collisional heat conductivity, is significantly large under some conditions. This partially accounts for the large heat losses in controlled thermonuclear fusion devices.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1184-1189 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: With the use of the general formulation developed in an earlier paper, the nonlinear evolution of the resistive fast interchange mode near the marginally stable state is obtained analytically. The nonlinear amplitude equation of the mode is shown to be of the Landau type. It is also shown that there is a stable equilibrium bifurcating from the initial equilibrium. Comparing this analytical result to numerical simulations, it is confirmed that the saturation level and the saturation time are well estimated by this Landau type of nonlinear amplitude equation.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 227 (1982), S. 139-151 
    ISSN: 1432-0878
    Keywords: Migration ; Primordial germ cell ; Teleost ; Oryzias latipes ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The primordial germ cells (PGCs) of Oryzias latipes in migration to the gonadal anlage have been investigated by light and electron microscopy. The ultrastructure of the PGCs, which occur in the subendodermal space on the syncytial periblast, differ conspicuously from that of the surrounding endodermal cells. After the PGCs move to the cavity between lateral plate and ectoderm, they are taken into the somatomesodermal layer and transferred to the dorsal mesentery where they form gonadal anlage with mesodermal cells. During their translocation to the dorsal mesentery through the somatic mesoderm, apparently without formation of pseudopods, the PGCs are completely surrounded by mesodermal cells. Since these conditions seem unfavorable to the active translocation of the PGCs to the dorsal mesentery, it is more likely that the PGCs are transferred passively by the morphogenic activity of the lateral-plate mesoderm. Counts of the number of the PGCs revealed that they are mitotically dormant during the migratory period. After the completion of the migration, they regain their proliferative activity. The PGCs in the female proliferate more actively than those in the male, which provides the first morphological indication of sex differentiation in this species of fish.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 240 (1985), S. 669-673 
    ISSN: 1432-0878
    Keywords: Germinal dense bodies ; Primordial germ cells ; Oryzias latipes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In many organisms, the germinal dense bodies (GDBs) are known to be organelles unique to the cells of germ-line. In the present study, GDBs in primordial germ cells (PGCs) of the teleost, Oryzias latipes, were examined by electron microscopy. An obvious change was noticed in the morphology of GDBs. In PGCs situated in the endoderm, GDBs consisted of a loosely woven strand-like structure, whereas, GDBs in PGCs in the gonadal anlage, which were amorphous bodies of various sizes and shapes, were composed of electron-dense fine fibrils. The changes in the morphology of GDBs proceeded gradually according to the progress of the stages in migration of the PGCs. GDBs of intermediate morphology were found. The change in the morphology of the GDBs began at the stage of movement of the PGCs from endoderm to mesoderm. It is suggested that the differentiation of PGCs proceeds during their migratory stages under the influence of surrounding somatic cells.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 248 (1987), S. 375-380 
    ISSN: 1432-0878
    Keywords: Germinal dense bodies ; Prespermatogonia ; Spermatogonia ; Oryzias latipes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The germinal dense body (GDB) in the teleost, Oryzias latipes, an organelle unique to the cells of germ line, is regarded as a counterpart of nuage material in amphibians and mammals. In the study described herein, GDBs in male germ line cells were examined by electron microscopy. GDBs existed continuously in the cytoplasm of primordial germ cells (PGCs), prespermatogonia, type-A spermatogonia and early type-B spermatogonia. But they became rudimentary in late type-B spermatogonia and early spermatocytes, and no longer occurred in spermatids. Differences in the morphology of GDBs of PGCs and male germ cells were also noted. In PGCs of indifferent gonads, about 50% of GDBs were amorphous bodies of fine electron-dense fibrils, whereas in spermatogonia amorphous bodies decreased in number and GDBs of strand-like structure were more frequent. The change in the morphology of GDBs began when the sex differentiation of gonads became evident, and proceeded gradually in prespermatogonia. No obvious differences in morphology of GDBs were noted between prespermatogonia in the fry at later stages of development and spermatogonia in adult fish.
    Type of Medium: Electronic Resource
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