Ultrasonic scanner for radial and flat panels

An ultrasonic scanning mechanism is described that scans panels of honeycomb construction or with welded seams. It incorporates a device which by simple adjustment is adapted to scan either a flat panel or a radial panel. The supporting structure takes the form of a pair of spaced rails. An immersion tank is positioned between the rails and below their level. A work holder is mounted in the tank and is adapted to hold the flat or radial panel. A traveling bridge is movable along the rails and a carriage is mounted on the bridge

Axisymmetric constraints on cross-equatorial Hadley cell extent

We consider the relevance of known constraints from each of Hide's theorem, the angular momentum conserving (AMC) model, and the equal-area model on the extent of cross-equatorial Hadley cells. These theories respectively posit that a Hadley circulation must span: all latitudes where the radiative convective equilibrium (RCE) absolute angular momentum ($M_\mathrm{rce}$) satisfies $M_\mathrm{rce}>\Omega a^2$ or $M_\mathrm{rce}<0$ or where the RCE absolute vorticity ($\eta_\mathrm{rce}$) satisfies $f\eta_\mathrm{rce}<0$; all latitudes where the RCE zonal wind exceeds the AMC zonal wind; and over a range such that depth-averaged potential temperature is continuous and that energy is conserved. The AMC model requires knowledge of the ascent latitude $\varphi_\mathrm{a}$, which need not equal the RCE forcing maximum latitude $\varphi_\mathrm{m}$. Whatever the value of $\varphi_\mathrm{a}$, we demonstrate that an AMC cell must extend at least as far into the winter hemisphere as the summer hemisphere. The equal-area model predicts $\varphi_\mathrm{a}$, always placing it poleward of $\varphi_\mathrm{m}$. As $\varphi_\mathrm{m}$ is moved poleward (at a given thermal Rossby number), the equal-area predicted Hadley circulation becomes implausibly large, while both $\varphi_\mathrm{m}$ and $\varphi_\mathrm{a}$ become increasingly displaced poleward of the minimal cell extent based on Hide's theorem (i.e. of supercritical forcing). In an idealized dry general circulation model, cross-equatorial Hadley cells are generated, some spanning nearly pole-to-pole. All homogenize angular momentum imperfectly, are roughly symmetric in extent about the equator, and appear in extent controlled by the span of supercritical forcing.Comment: 18 pages, 9 figures, publishe

Robust Responses of the Sahelian Hydrological Cycle to Global Warming

How the globally uniform component of sea surface temperature (SST) warming influences rainfall in the African Sahel remains insufficiently studied, despite mean SST warming being among the most robustly simulated and theoretically grounded features of anthropogenic climate change. A prior study using the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) AM2.1 atmospheric general circulation model (AGCM) demonstrated that uniform SST warming strengthens the prevailing northerly advection of dry Saharan air into the Sahel. The present study uses uniform SST warming simulations performed with 7 GFDL and 10 CMIP5 AGCMs to assess the robustness of this drying mechanism across models and uses observations to assess the physical credibility of the severe drying response in AM2.1. In all 17 AGCMs, mean SST warming enhances the free-tropospheric meridional moisture gradient spanning the Sahel and with it the Saharan dry-air advection. Energetically, this is partially balanced by anomalous subsidence, yielding decreased precipitation in 14 of the 17 models. Anomalous subsidence and precipitation are tightly linked across the GFDL models but not the CMIP5 models, precluding the use of this relationship as the start of a causal chain ending in an emergent observational constraint. For AM2.1, cloud–rainfall covariances generate radiative feedbacks on drying through the subsidence mechanism and through surface hydrology that are excessive compared to observations at the interannual time scale. These feedbacks also act in the equilibrium response to uniform warming, calling into question the Sahel’s severe drying response to warming in all coupled models using AM2.1

Recent ν\nus from IceCube

IceCube is a 1 km$^3$ neutrino detector now being built at the South Pole. Its 4800 optical modules will detect Cherenkov radiation from charged particles produced in neutrino interactions. IceCube will search for neutrinos of astrophysical origin, with energies from 100 GeV up to $10^{19}$ eV. It will be able to separate $\nu_e$, $\nu_\mu$ and $\nu_\tau$. In addition to detecting astrophysical neutrinos, IceCube will also search for neutrinos from WIMP annihilation in the Sun and the Earth, look for low-energy (10 MeV) neutrinos from supernovae, and search for a host of exotic signatures. With the associated IceTop surface air shower array, it will study cosmic-ray air showers. IceCube construction is now 50% complete. After presenting preliminary results from the partial detector, I will discuss IceCube's future plans.Comment: Invited talk presented at Neutrino 2008; 7 page

Uncovering New Mechanisms of Cdc34 and Cullin-Ring Activity

Ubiquitylation is a cellular regulatory system found in all eukaryotic cells, which has managed to find a role in most pathways imaginable. The system works fundamentally through the ligation of a small protein known as ubiquitin onto a substrate. Depending on the context of the ubiquitin ligation, the substrate can be directed towards a number of cellular fates, the best-studied being degradation of the substrate. While originally thought of as a signal for cellular disposal units to degrade aberrant proteins, we now know that ubiquitin plays a highly nuanced role in cellular epistasis, controlling everything from the cell cycle to the immune response. Of the many enzymes involved in transferring ubiquitin molecules to and from targeted substrates, the cullin-RING ubiquitin ligases (CRLs) stand out for their particular breadth. Hundreds of CRLs exist in human cells owing to their modular structure, which in turn allows them to regulate an even greater number of substrates. They have also been targets of a number of different drug therapies, due to their involvement in the cell cycle and cancer. However, there are many vital gaps in how they function. Particularly, CRLs function with a number ubiquitylating enzymes, referred to here as CRL partners. The first discovered of these, Cdc34, has been prominently studied for decades, but particular aspects of its molecular mechanism for transferring ubiquitin to substrates were not yet known. Further complexity was added when other CRL partners were discovered to also function in addition to Cdc34. Promising models suggested that these CRL partners could complement the activity of Cdc34 to maximize CRL turnover of substrate, but relatively little work had been done to study this system under the consideration of physiological conditions and concentrations. Therefore, the central aims of the studies within the planned dissertation are three-fold. First, by designing and refining current assays to set a guideline by which to measure complex, multi-component reactions. Second, by uncovering the molecular mechanism of Cdc34’s catalytic activity, so that it can be understood in the context of full CRL activity. Lastly, by determining how CRLs and their partners operate in the context of a living cell. For these efforts, we discovered a new molecular mechanism of Cdc34 activity, a new understanding of how CRL partners are balanced and used in the context of physiological CRL ubiquitylation pathways, and the unexpected complementary role of a little-studied CRL partner

Axisymmetric Hadley Cell Theory with a Fixed Tropopause Temperature Rather than Height

Axisymmetric Hadley cell theory has traditionally assumed that the tropopause height (H_t) is uniform and unchanged from its radiative–convective equilibrium (RCE) value by the cells’ emergence. Recent studies suggest that the tropopause temperature (T_t), not height, is nearly invariant in RCE, which would require appreciable meridional variations in H_t. Here, we derive modified expressions of axisymmetric theory by assuming a fixed T_t and compare the results to their fixed-H_t counterparts. If T_t and the depth-averaged lapse rate are meridionally uniform, then at each latitude H_t varies linearly with the local surface temperature, altering the diagnosed gradient-balanced zonal wind at the tropopause appreciably (up to tens of meters per second) but the minimal Hadley cell extent predicted by Hide’s theorem only weakly (≲1°) under standard annual-mean and solsticial forcings. A uniform T_t alters the thermal field required to generate an angular-momentum-conserving Hadley circulation, but these changes and the resulting changes to the equal-area model solutions for the cell edges again are modest (<10%). In numerical simulations of latitude-by-latitude RCE under annual-mean forcing using a single-column model, assuming a uniform T_t is reasonably accurate up to the midlatitudes, and the Hide’s theorem metrics are again qualitatively insensitive to the tropopause definition. However imperfectly axisymmetric theory portrays the Hadley cells in Earth’s macroturbulent atmosphere, evidently its treatment of the tropopause is not an important error source