408 research outputs found
Study of inducer load and stress Interim report, 15 Feb. 1968 - 15 Oct. 1968
Literature survey, analytic formulations, and test rig designs for cavitating inducers in rocket engine turbopump
Attractive Interaction Between Pulses in a Model for Binary-Mixture Convection
Recent experiments on convection in binary mixtures have shown that the
interaction between localized waves (pulses) can be repulsive as well as {\it
attractive} and depends strongly on the relative {\it orientation} of the
pulses. It is demonstrated that the concentration mode, which is characteristic
of the extended Ginzburg-Landau equations introduced recently, allows a natural
understanding of that result. Within the standard complex Ginzburg-Landau
equation this would not be possible.Comment: 7 pages revtex with 3 postscript figures (uuencoded
Coexisting Pulses in a Model for Binary-Mixture Convection
We address the striking coexistence of localized waves (`pulses') of
different lengths which was observed in recent experiments and full numerical
simulations of binary-mixture convection. Using a set of extended
Ginzburg-Landau equations, we show that this multiplicity finds a natural
explanation in terms of the competition of two distinct, physical localization
mechanisms; one arises from dispersion and the other from a concentration mode.
This competition is absent in the standard Ginzburg-Landau equation. It may
also be relevant in other waves coupled to a large-scale field.Comment: 5 pages revtex with 4 postscript figures (everything uuencoded
Subharmonic bifurcation cascade of pattern oscillations caused by winding number increasing entrainment
Convection structures in binary fluid mixtures are investigated for positive
Soret coupling in the driving regime where solutal and thermal contributions to
the buoyancy forces compete. Bifurcation properties of stable and unstable
stationary square, roll, and crossroll (CR) structures and the oscillatory
competition between rolls and squares are determined numerically as a function
of fluid parameters. A novel type of subharmonic bifurcation cascade (SC) where
the oscillation period grows in integer steps as is found
and elucidated to be an entrainment process.Comment: 7 pages, 4 figure
Bistability of Slow and Fast Traveling Waves in Fluid Mixtures
The appearence of a new type of fast nonlinear traveling wave states in
binary fluid convection with increasing Soret effect is elucidated and the
parameter range of their bistability with the common slower ones is evaluated
numerically. The bifurcation behavior and the significantly different
spatiotemporal properties of the different wave states - e.g. frequency, flow
structure, and concentration distribution - are determined and related to each
other and to a convenient measure of their nonlinearity. This allows to derive
a limit for the applicability of small amplitude expansions. Additionally an
universal scaling behavior of frequencies and mixing properties is found.
PACS: 47.20.-k, 47.10.+g, 47.20.KyComment: 4 pages including 5 Postscript figure
Influence of the Soret effect on convection of binary fluids
Convection in horizontal layers of binary fluids heated from below and in
particular the influence of the Soret effect on the bifurcation properties of
extended stationary and traveling patterns that occur for negative Soret
coupling is investigated theoretically. The fixed points corresponding to these
two convection structures are determined for realistic boundary conditions with
a many mode Galerkin scheme for temperature and concentration and an accurate
one mode truncation of the velocity field. This solution procedure yields the
stable and unstable solutions for all stationary and traveling patterns so that
complete phase diagrams for the different convection types in typical binary
liquid mixtures can easily be computed. Also the transition from weakly to
strongly nonlinear states can be analyzed in detail. An investigation of the
concentration current and of the relevance of its constituents shows the way
for a simplification of the mode representation of temperature and
concentration field as well as for an analytically manageable few mode
description.Comment: 30 pages, 12 figure
Proliferative Activity In Vitro and DNA Repair Indicate that Adult Mouse and Human Sertoli Cells Are Not Terminally Differentiated, Quiescent Cells
Sertoli cells isolated from the adult mouse and human testis resume proliferation in culture. After 20 days of culture in Dulbecco modified Eagle medium/Ham F12 (DMEM/F12) medium containing 5% fetal calf serum, about 36% of the mouse Sertoli cells, identified by their immunohistochemical staining for the Sertoli cell marker vimentin, incorporated bromodeoxyuridine (BrdU). The renewed proliferation was associated with a 70% decrease in expression of the cell cycle inhibitor CDKN1B (P27(kip1)) and a 2-fold increase in the levels of the proliferation inducer ID2. In vivo, the balance between cell cycle inhibitors and inducers probably is such that the cells remain quiescent, whereas in culture the balance is disturbed such that Sertoli cells start to proliferate again. The renewed proliferative activity of Sertoli cells in culture was further confirmed by double staining for BrdU and the Sertoli cell marker clusterin (CLU), showing about 25% of the CLU-positive Sertoli cells to be also positive for BrdU after 13 days of culture. Radiobiologically, Sertoli cells are also different from other quiescent somatic cells in the testis because they express several DNA repair proteins (XRCC1, PARP1, and others). Indeed, a comet assay on irradiated Sertoli cells revealed a 70% reduction in tail length and tail moment at 20 h after irradiation. Hence, Sertoli cells repair DNA damage, whereas other quiescent somatic testicular cells do not. This repair may be accomplished by nonhomologous end joining via XRCC1 and PARP1. In conclusion, cell kinetic and radiobiological data indicate that Sertoli cells more resemble arrested proliferating cells than the classic postmitotic and terminally differentiated somatic cells that they have always been assumed to b
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