63 research outputs found
Two evolutional paths of an axisymmetric gravitational instability in the dust layer of a protoplanetary disk
Nonlinear numerical simulations are performed to investigate the density
evolution in the dust layer of a protoplanetary disk due to the gravitational
instability and dust settling toward the midplane. We assume the region where
the radial pressure gradient at equilibrium is negligible so that the
shear-induced instability is avoided, and also restrict to an axisymmetric
perturbation as a first step of nonlinear numerical simulations of the
gravitational instability. We find that there are two different evolutional
paths of the gravitational instability depending on the nondimensional gas
friction time, which is defined as the product of the gas friction time and the
Keplerian angular velocity. If the nondimensional gas friction time is equal to
0.01, the gravitational instability grows faster than dust settling. On the
other hand, if the nondimensional gas friction time is equal to 0.1, dust
aggregates settle sufficiently before the gravitational instability grows. In
the latter case, an approximate analytical calculation reveals that dust
settling is faster than the growth of the gravitational instability regardless
of the dust density at the midplane. Thus, the dust layer becomes extremely
thin and may reach a few tenth of the material density of the dust before the
gravitational instability grows.Comment: 4 pages, 3 figure
Activin B is produced early in antral follicular development and suppresses thecal androgen production
Little is known about the role of activin B during folliculogenesis. This study investigated the expression levels of activin/inhibin subunits (ÎČA, ÎČB, and α), steroid enzyme, and gonadotrophin receptors in theca (TC) and granulosa cells (GC) by QPCR and activin A and B and inhibin A protein levels in follicular fluid (FF) of developing sheep follicles during estrus and anestrus. The effect of activin B on androgen production from primary TC cultures in vitro was also assessed. During folliculogenesis, in anestrus and estrus, FF activin B concentrations and thecal and GC activin ÎČB mRNA levels decreased as follicle diameter increased from 1â3 to >6âmm regardless of estrogenic status. Estrogenic preovulatory follicles had reduced concentrations of FF activins B and A, and TC and GCs expressed higher levels of activin ÎČA mRNA at 3â4âmm, and TCs more inhibin α mRNA at >4âmm stages of development compared with nonestrogenic follicles. Activin B decreased androstenedione production from primary TCs in vitro, an effect blocked by inhibin A. Thus, sheep follicles 1â3âmm in diameter contained high FF levels of activin B, which decreased as the follicle size increased, and, like activin A, suppressed thecal androgen production in vitro, an effect blocked by inhibin. Furthermore, the theca of large estrogenic follicles expressed high levels of inhibin α and activin ÎČA mRNA suggesting local thecal derived inhibin A production. This would inhibit the negative effects of thecal activins B and A ensuring maximum androgen production for enhanced estradiol production by the preovulatory follicle(s)
Plasma physics and control studies planned in JT-60SA for ITER and DEMO operations and risk mitigation
| openaire: EC/H2020/633053/EU//EUROfusionA large superconducting machine, JT-60SA has been constructed to provide major contributions to the ITER program and DEMO design. For the success of the ITER project and fusion reactor, understanding and development of plasma controllability in ITER and DEMO relevant higher beta regimes are essential. JT-60SA has focused the program on the plasma controllability for scenario development and risk mitigation in ITER as well as on investigating DEMO relevant regimes. This paper summarizes the high research priorities and strategy for the JT-60SA project. Recent works on simulation studies to prepare the plasma physics and control experiments are presented, such as plasma breakdown and equilibrium controls, hybrid and steady-state scenario development, and risk mitigation techniques. Contributions of JT-60SA to ITER and DEMO have been clarified through those studies.Peer reviewe
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