Prandtl-Blasius temperature and velocity boundary layer profiles in turbulent Rayleigh-B\'{e}nard convection

The shape of velocity and temperature profiles near the horizontal conducting plates in turbulent Rayleigh-B\'{e}nard convection are studied numerically and experimentally over the Rayleigh number range $10^8\lesssim Ra\lesssim3\times10^{11}$ and the Prandtl number range $0.7\lesssim Pr\lesssim5.4$. The results show that both the temperature and velocity profiles well agree with the classical Prandtl-Blasius laminar boundary-layer profiles, if they are re-sampled in the respective dynamical reference frames that fluctuate with the instantaneous thermal and velocity boundary-layer thicknesses.Comment: 10 pages, 6 figure

Horizontal Structures of Velocity and Temperature Boundary Layers in 2D Numerical Turbulent Rayleigh-B\'{e}nard Convection

We investigate the structures of the near-plate velocity and temperature profiles at different horizontal positions along the conducting bottom (and top) plate of a Rayleigh-B\'{e}nard convection cell, using two-dimensional (2D) numerical data obtained at the Rayleigh number Ra=10^8 and the Prandtl number Pr=4.4 of an Oberbeck-Boussinesq flow with constant material parameters. The results show that most of the time, and for both velocity and temperature, the instantaneous profiles scaled by the dynamical frame method [Q. Zhou and K.-Q. Xia, Phys. Rev. Lett. 104, 104301 (2010) agree well with the classical Prandtl-Blasius laminar boundary layer (BL) profiles. Therefore, when averaging in the dynamical reference frames, which fluctuate with the respective instantaneous kinematic and thermal BL thicknesses, the obtained mean velocity and temperature profiles are also of Prandtl-Blasius type for nearly all horizontal positions. We further show that in certain situations the traditional definitions based on the time-averaged profiles can lead to unphysical BL thicknesses, while the dynamical method also in such cases can provide a well-defined BL thickness for both the kinematic and the thermal BLs.Comment: 16 pages, 16 figure

Flow reversals in thermally driven turbulence

We analyze the reversals of the large scale flow in Rayleigh-B\'enard convection both through particle image velocimetry flow visualization and direct numerical simulations (DNS) of the underlying Boussinesq equations in a (quasi) two-dimensional, rectangular geometry of aspect ratio 1. For medium Prandtl number there is a diagonal large scale convection roll and two smaller secondary rolls in the two remaining corners diagonally opposing each other. These corner flow rolls play a crucial role for the large scale wind reversal: They grow in kinetic energy and thus also in size thanks to plume detachments from the boundary layers up to the time that they take over the main, large scale diagonal flow, thus leading to reversal. Based on this mechanism we identify a typical time scale for the reversals. We map out the Rayleigh number vs Prandtl number phase space and find that the occurrence of reversals very sensitively depends on these parameters.Comment: 4 pages, 4 figure

Thermal boundary layer profiles in turbulent Rayleigh-B\'enard convection in a cylindrical sample

We numerically investigate the structures of the near-plate temperature profiles close to the bottom and top plates of turbulent Rayleigh-B\'{e}nard flow in a cylindrical sample at Rayleigh numbers Ra=10^8 to Ra=2\times10^{12} and Prandtl numbers Pr=6.4 and Pr=0.7 with the dynamical frame method [Q. Zhou and K.-Q. Xia, Phys. Rev. Lett. 104, 104301 (2010)] thus extending previous results for quasi-2-dimensional systems to 3D systems for the first time. The dynamical frame method shows that the measured temperature profiles in the spatially and temporally local frame are much closer to the temperature profile of a laminar, zero-pressure gradient boundary layer according to Pohlhausen than in the fixed reference frame. The deviation between the measured profiles in the dynamical reference frame and the laminar profiles increases with decreasing Pr, where the thermal BL is more exposed to the bulk fluctuations due to the thinner kinetic BL, and increasing Ra, where more plumes are passing the measurement location.Comment: 5 pages, 2 figure

COLLABORATIVE BOOK REVIEW: Baker, D. P. (2014). The Schooled Society: The Educational Transformation of Global Culture

For many years the discussion of education as a global and social institution has been prevalent in Comparative and International Education. In his book, The Schooled Society, David P. Baker offers up a unique perspective on a much-discussed theoretical framework in which to view education as an institution. Through this work, Baker uses a multidisciplinary approach to explain the influence that mass education has on societies and informs the readers of new educational paradoxes that are being discussed in the field. Not only is The Schooled Society an explanation of educational influence on society, but it also provides reason for further research to be done to explain the existing paradoxes found in modern society and education. The following book review, informed by the wide span of each contributing reviewer’s previous educational and professional experiences, provides a variety of reactions to The Schooled Society and is intended to provide the reader with a holistic examination of the book. The primary review, authored by Calley Stevens Taylor and Amanda Blain Pritt, presents an introductory review and critique of the book’s structure, premise, evidence, and conclusions as well as general statements about the book’s contents. Following the primary review, Maria Spinosa Ebert, Angel Oi Yee Cheng, and Xia Zhao respond to the primary review and offer their own reactions to The Schooled Society

Interleukin-33 Primes Mast Cells for Activation by IgG Immune Complexes

Mast cells (MCs) are heterogeneous cells whose phenotype is modulated by signals received from the local microenvironment. Recent studies have identified the mesenchymal-derived cytokine IL-33 as a potent direct activator of MCs, as well as regulator of their effector phenotype, and have implicated this activity in the ability of mast cells to contribute to murine experimental arthritis. We explored the hypothesis that IL-33 enables participation of synovial MCs in murine K/BxN arthritis by promoting their activation by IgG immune complexes. Compared to wild-type (WT) control mice, transgenic animals lacking the IL-33 receptor ST2 exhibited impaired MC-dependent immune complex-induced vascular permeability (flare) and attenuated K/BxN arthritis. Whereas participation of MCs in this model is mediated by the activating IgG receptor FcγRIII, we pre-incubated bone marrow-derived MCs with IL-33 and found not only direct induction of cytokine release but also a marked increase in FcγRIII-driven production of critical arthritogenic mediators including IL-1β and CXCL2. This “priming” effect was associated with mRNA accumulation rather than altered expression of Fcγ receptors, could be mimicked by co-culture of WT but not ST2−/− MCs with synovial fibroblasts, and was blocked by antibodies against IL-33. In turn, WT but not ST2−/− MCs augmented fibroblast expression of IL-33, forming a positive feedback circuit. Together, these findings confirm a novel role for IL-33 as an amplifier of IgG immune complex-mediated inflammation and identify a potential MC-fibroblast amplification loop dependent on IL-33 and ST2

Structural Properties of Eu-Doped GaN Investigated by Raman Spectroscopy

Rare-earth (RE) impurities doped GaN are highly promising candidates for light emitting device applications due to their efficient electroluminescence properties at room temperature. Among those, Eu doped GaN has been identified as an excellent material for the red spectral region due to its strong emission at 620 nm. As a transition internal to the Eu doping atom (4f-4f), light emission originates in a much smaller complex than the more flexibly controllable quantum structures of wells, wires, and dots. This is thought to make the center less susceptible to structural defects and in particular radiation damage in the lattice host. Nevertheless, the lattice host is crucial for providing the excitation in from of free electrons and holes. In this respect, the actual lattice site Eu occupies in the host lattice, i.e. in GaN, is important. A large fraction of Eu atoms are typically inactive which must be attributed to their lattice site and local environment. GaN films implanted with Eu to concentrations of {approx}10{sup 18} cm{sup -3} were subjected to a highly directed beam of 500 keV He{sup +} at a dose of 5 x 10{sup 14} cm{sup -2}. By means of a shadow mask, irradiated and unexposed regions lie very close to each other on the same sample. We used optical and structural analysis to identify the exerted radiation damage. At the full radiation dose, photoluminescence intensity has decayed to {approx}0.01 of its initial value. From the dose dependence of the radiation decay we previously concluded, that this decay is in part due to the destruction of radiative Eu sites [J.W. Tringe, unpublished (2006)]. Along the transition from virgin to irradiated material we analyze the accumulated damage in terms of surface morphology (atomic force microscopy), crystallinity (x-ray diffraction), and phonon dispersion using micro-Raman spectroscopy. In addition to the well-studied E{sub 2}(high) mode, two new vibrational modes at 659 cm{sup -1} and 201 cm{sup -1} were observed in the Eu implanted and annealed sample, prior to He{sup +} irradiation. These modes are either remnants of the implantation damage or related to the Eu impurity. As such they can be indicative of the actual lattice site the Eu atom resides on. After irradiation, broad Raman modes at 300 cm-1 are being observed. This band indicates disorder activated Raman scattering (DARS) due to the radiation damage. An additional narrow mode appears at 672 cm{sup -1}, which can possibly be due to a nitrogen vacancy related vibrational mode. The continuous transition from irradiated to un-irradiated sample allows the direct evolution of radiation damage and its coordinated effects in structural, optical and vibrational properties. By its systematic correlation we anticipate to be able to elucidate the Eu lattice interaction and the processes of radiation damage

Palaeoenvironmental and diagenetic reconstruction of a closed-lacustrine carbonate system - the challenging marginal setting of the Miocene Ries Crater Lake (Germany)

Chemostratigraphic studies on lacustrine sedimentary sequences provide essential insights on past cyclic climatic events, on their repetition and prediction through time. Diagenetic overprint of primary features often hinders the use of such studies for palaeoenvironmental reconstruction. Here the potential of integrated geochemical and petrographic methods is evaluated to record freshwater to saline oscillations within the ancient marginal lacustrine carbonates of the Miocene Ries Crater Lake (Germany). This area is critical because it represents the transition from shoreline to proximal domains of a hydrologically closed system, affected by recurrent emergent events, representing the boundaries of successive sedimentary cycles. Chemostratigraphy targets shifts related to subaerial exposure and/or climatic fluctuations. Methods combine facies changes with δ13C–δ18O chemostratigraphy from matrix carbonates across five closely spaced, temporally equivalent stratigraphic sections. Isotope composition of ostracod shells, gastropods and cements is provided for comparison. Cathodoluminescence and back‐scatter electron microscopy were performed to discriminate primary (syn‐)depositional, from secondary diagenetic features. Meteoric diagenesis is expressed by substantial early dissolution and dark blue luminescent sparry cements carrying negative δ13C and δ18O. Sedimentary cycles are not correlated by isotope chemostratigraphy. Both matrix δ13C and δ18O range from ca −7·5 to +4·0‰ and show clear positive covariance (R = 0·97) whose nature differs from that of previous basin‐oriented studies on the lake: negative values are here unconnected to original freshwater lacustrine conditions but reflect extensive meteoric diagenesis, while positive values probably represent primary saline lake water chemistry. Noisy geochemical curves relate to heterogeneities in (primary) porosity, resulting in selective carbonate diagenesis. This study exemplifies that ancient lacustrine carbonates, despite extensive meteoric weathering, are able to retain key information for both palaeoenvironmental reconstruction and the understanding of diagenetic processes in relation to those primary conditions. Also, it emphasizes the limitation of chemostratigraphy in fossil carbonates, and specifically in settings that are sensitive for the preservation of primary environmental signals, such as lake margins prone to meteoric diagenesis