The sidewall-localized mode in a resonant precessing cylinder

ArticleWe investigate, via direct numerical simulation using a finite-element method, the precessionally driven flow of a homogeneous fluid confined in a fluid-filled circular cylinder that rotates rapidly about its symmetry axis and precesses about a different axis that is fixed in space. Our numerical simulation, after validating with the asymptotic analytical solution for a weakly precessing cylinder and with the constructed exact solution for the strongly nonlinear problem, focuses on the strongly precessing flow at asymptotically small Ekman numbers. An unusual form of the resonant precessing flow is found when the precessing rate is sufficiently large and the corresponding nonlinearity is sufficiently strong. The nonlinear precessing flow is marked by a sidewall-localized non-axisymmetric traveling wave and a wall-localized axisymmetric shear together with an overwhelmingly dominant interior rigid-body rotation whose direction and magnitude substantially reduce the angular momentum of the rotating fluid system.K.Z. is supported by grants from UK Science and Technology Facilities Council and Natural Environment Research Council. X.L. is supported by National Natural Science Foundation of China/11133004 and Chinese Academy of Sciences under Grant Nos. KZZD-EW-01-3 and XDB09000000

Study on flow and temperature drop behavior of six-stream tundish with less-flow casting

In this paper, numerical simulation method was used to study the influence of closing different nozzles on the flow state and temperature distribution of molten steel in the six-stream tundish, which provides a theoretical basis for ensuring the temperature uniformity of molten steel in the tundish and the subsequent stable continuous casting production during the less-flow casting. The results show that: (a) In the case of closing one nozzle, when the No. 3 nozzle is closed, the overall temperature is relatively uniform. (b) In the case of closing two nozzles, when the No. 2 and No. 3 nozzles are closed, the overall temperature is more uniform

Study on cleanliness of interstitial-free (IF) steel continuous casting slab

By means of metallographic observation, scanning electron microscopy and electron probe micro analysis, the quantity, particle size, distribution, morphology and composition of inclusions in the slab were discussed in detail. Which can provide a reference for the process optimization of IF steel and the production of pure steel slabs. The results show that the content of C, N and O in the IF steel continuous casting slab produced by this plant is controlled at about 20 ppm, and the content of P and S is lower and the steel is relatively pure. Most of the inclusions are below 2 μm. Most of the inclusions are pure Al2O3, a small part contains a small amount of microscopic MnS

Equatorial Zonal Jets and Jupiter’s Gravity

ArticleThe depth of penetration of Jupiter’s zonal winds into the planet’s interior is unknown. A possible way to determine the depth is to measure the effects of the winds on the planet’s high-order zonal gravitational coefficients, a task to be undertaken by the Juno spacecraft. It is shown here that the equatorial winds alone largely determine these coefficients which are nearly independent of the depth of the non-equatorial winds.X.L. is supported by NSFC/11133004 and CAS under grant numbers KZZD-EW-01-3 and XDB09000000, K.Z. is supported by UK NERC and STFC grants and G.S. is supported by the National Science Foundation under grant NSF AST-0909206. The parallel computation is supported by the Shanghai Supercomputer Center

The shape, internal structure and gravity of the fast spinner β Pictoris b

ArticleA young extrasolar gas giant planet, β Pictoris b, recently discovered in the β Pictoris system, spins substantially faster than the giant gas planets Jupiter and Saturn. Based on the newly measured parameters – the rotation period of the planet, its mass and radius – together with an assumption that the gas planet β Pictoris b is in hydrostatic equilibrium and made of a fully compressible barotropic gas with a polytropic index of unity, we are able to compute, via a hybrid inverse method, its non-spherical shape, internal density/pressure distribution and gravitational zonal coefficients up to degree 8. Since the mass Mβ for the planet β Pictoris b is highly uncertain, various models with different values of Mβ are studied in this Letter, providing the upper and lower bounds for its shape parameter as well as its gravitational zonal coefficients. If Mβ is assumed to be 6MJ with MJ being Jupiter's mass, we show that the shape of the planet β Pictoris b is approximately described by an oblate spheroid whose eccentricity at the one-bar surface is E β =0.36928 Eβ=0.36928 with the gravitational coefficient (J2)β = +15 375.972 × 10−6. It follows that our results open the possibility of constraining or inferring the mass Mβ of the planet β Pictoris b if its shape can be measured or constrained. By assuming that the planet β Pictoris b will shrink to the size of Jupiter in the process of cooling down and, hence, rotate much faster, we also calculate the future shape and internal structure of the planet β Pictoris b.XL is supported by NSFC/11133004 and CAS under grant numbers KZZD-EW-01-3 and XDB09000000, KZ is supported by UK NERC and STFC grants and GS is supported by the National Science Foundation under grant NSF AST-0909206. The parallel computation is supported by the Shanghai Supercomputer Center

The influence of structural defects on intra-granular critical currents of bulk MgB2

Bulk MgB2 samples were prepared under different synthesis conditions and analyzed by scanning and transmission electron microscopy. The critical current densities were determined from the magnetization versus magnetic field curves of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow cooling process, the oxygen dissolved in bulk MgB2 at high synthesis temperatures can segregate and form nanometer-sized coherent precipitates of Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these precipitates act as effective flux pinning centers and therefore significantly improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied Superconductivit

Static QˉQ\bar Q Q Potentials and the Magnetic Component of QCD Plasma near TcT_c

Static quark-anti-quark potential encodes important information on the chromodynamical interaction between color charges, and recent lattice results show its very nontrivial behavior near the deconfinement temperature $T_c$. In this paper we study such potential in the framework of the ``magnetic scenario'' for the near Tc QCD plasma, and particularly focus on the linear part (as quantified by its slope, the tension) in the potential as well as the strong splitting between the free energy and internal energy. By using an analytic ``ellipsoidal bag'' model, we will quantitatively relate the free energy tension to the magnetic condensate density and relate the internal energy tension to the thermal monopole density. By converting the lattice results for static potential into density for thermal monopoles we find the density to be very large around Tc and indicate at quantum coherence, in good agreement with direct lattice calculation of such density. A few important consequences for heavy ion collisions phenomenology will also be discussed.Comment: 10 pages, 6 figure

Coded aperture compressive temporal imaging.

We use mechanical translation of a coded aperture for code division multiple access compression of video. We discuss the compressed video's temporal resolution and present experimental results for reconstructions of > 10 frames of temporal data per coded snapshot