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Kick-starting ancient warming
No full textRapid global warming marked the boundary between the Palaeocene and Eocene periods 55.6 million years ago,
but how the temperature rise was initiated remains elusive. A catastrophic release of greenhouse gases from the
Kilda basin could have served as a trigger
Developmental modularity and the marsupial-placental dichotomy
No full textThe contrasting evolutionary histories of marsupial and placental mammals have often been attributed to their different reproductive strategies. The speciose placentals develop mainly in utero and have radiated into diverse niches, whereas marsupials are born in a highly altricial state with immediate functional requirements and are limited in taxonomic, ecological, and morphological diversity. These differences have been tied to heterochrony, and it has been hypothesized that coordinated shifts in developmental timing occur among functionally- or developmentally related structures, such as forelimbs in marsupials. We use new ossification sequence data for 11 marsupial and 14 placental species to assess the integration of first ossification timing among skeletal elements. Although cranial elements fail to demonstrate significant coordination, marsupials and placentals differ markedly in postcranial integration. Marsupials display independent anterior and posterior developmental modules, whereas placentals show significant integration of the entire appendicular skeleton. This developmental integration of the placental postcranium is consistent with a recent study of phenotypic modularity in limbs of placental mammals, showing a potential correspondence between integration of developmental timing and of shape. The observed differences in postcranial integration between marsupials and placentals may reflect the disparate evolutionary histories of these two mammalian clades. J. Exp. Zool. (Mol. Dev. Evol.) 312B:186-195, 2009. � 2009 Wiley-Liss, Inc
Magnetic phases of bismuth ferrite
No full textWe have recently shown that BiFeO3 has at least four different magnetic phases, contrary to the conventional wisdom. Below room temperature it undergoes spin reorientation transitions at T2=200 K and T1=140 K analogous to those in orthoferrites; and above room temperature it undergoes a structural transition near 185°C first reported by Polomska et al. This may help explain the apparent linear magnetoelectric effect at 20°C reported by D. Lebeugle et al. [Phys. Rev. Lett. 100, 227602 (2008)] which is nominally forbidden due to the long wavelength cycloidal spin structure assumed. We also find evidence of an unusual acentric spin glass below ca. 200 K, related not to TN but to T1 and T2
FORCinel: An improved algorithm for calculating first-order reversal curve distributions using locally weighted regression smoothing
No full textFigure 8. Smoothing effects on LOESS smoothed FORC distributions for a natural sample of pure hematite. In Figure 8a, optimum smoothing range is shown in green. Figures 8b, 8c, and 8d correspond to smoothing factors 2, 6, and 10, respectively. Undersmoothing produces a distribution that is dominated by noise (Figure 8b). Oversmoothing produces a distribution that obscures the presence of noninteracting grains along Hu = 0 (Figure 8d). Using the optimization routine described in Figure 5, the ideal FORC distribution is SF = 6
Carbon isotopic constraints on CO2 degassing in cold-water Geysers, Green River, Utah
No full textCold-water geysers at Green River, in east central Utah are sourced by natural springs situated along the Little Grand Wash and Salt Wash faults zones, as well as abandoned oil and water wells. The intermittent geysers are driven by degassing of CO2 from CO2-rich waters sourced from the Jurassic Navajo sandstone. Here we discuss use of analyses of water and gases to estimate the depth at which the ascending waters become CO2 saturated. This is a potentially important control in the unlikely event of rapid CO2 escape from CO2 reservoirs. In Green River, it is also important for calculation of the kinetics of fluid-mineral reactions in the Navajo sandstone as an analogue for predicting the fate of CO2 in carbon storage reservoirs
Size effects on thin film ferroelectrics: Experiments on isolated single crystal sheets
No full textThin lamellae were cut from bulk single crystal BaTiO3 using a focused ion beam microscope. They were then removed and transferred onto single crystal MgO substrates, so that their functional properties could be measured independent of the original host bulk ferroelectric. The temperature dependence of the capacitance of these isolated single crystal films was found to be strongly bulklike, demonstrating a sharp Curie anomaly, as well as Curie–Weiss behavior. In addition, the sudden change in the remanent polarization as a function of temperature at TC was characteristic of a first order phase change. The work represents a dramatic improvement on that previously published by Saad et al. [J. Phys.: Condens. Matter 16, L451 (2004)], as critical shortcomings in the original specimen geometry, involving potential signal contributions from bulk BaTiO3, have now been obviated. That the functional properties of single crystal thin film lamellae are comparable to bulk, and not like those of conventionally deposited heterogeneous thin film systems, has therefore been confirme
Impact of lower plate structure on upper plate deformation at the NW Sumatran convergent margin from seafloor morphology
No full textWe present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysis of the combined dataset accurately highlights those portions of the seafloor shaped by active tectonic, depositional and/or erosional processes. The greatest slope gradients are located in the frontal 30 km of the forearc, at the toe of the accretionary wedge. This suggests that long-term deformation rates are highest here and that probably only minor amounts of slip are accommodated by other thrust faults further landward. Obvious N-S oriented lineaments observed on the incoming oceanic plate are aligned sub-parallel to the fracture zones associated with the Wharton fossil spreading center. Active strike-slip motion is suggested by recent deformation with up to 20-30 m of vertical offset. The intersection of these N-S elongated bathymetric scarps with the accretionary wedge partly controls the geometry of thrust anticlines and the location of erosional features (e.g. slide scars, canyons) at the wedge toe. Our interpretation suggests that these N-S lineaments have a significant impact on the oceanic plate, the toe of the wedge and further landward in the wedge. Finally, the bathymetric data indicate that folding at the front of the accretionary wedge occurs primarily along landward-vergent (seaward-dipping) thrusts, an unusual style in accretionary wedges worldwide. The N-S elongated lineaments locally act as boundaries between zones with predominant seaward versus landward vergence
Global warming's proof in the puddingstone
No full textThe Earth heated up 55 million years ago - and that gives us important clues on how to deal with climate change no
A new large basal tetanuran (Dinosauria: Theropoda) from the Wessex Formation (Barremian) of the Isle of Wight, England.
No full textThe Wessex Formation of the Isle of Wight, southern
England, has yielded one of the most diverse Early Cretaceous dinosaur assemblages in the world. While isolated theropod remains have been known from the Wessex Formation since the 1860s (Fox in Anon., 1866), it is only recently that associated specimens, and remains representing large-bodied taxa, have been described in the literature. Foremost among these is the allosauroid Neovenator salerii, which is represented by approximately
70% of the skeleton, making it the most complete large
theropod known from Europe (Hutt et al., 1996; Naish et al.,
2001; Brusatte et al., in press). Other large-bodied theropods from the Wessex Formation include the spinosauroid Baryonyx,which is represented by isolated teeth and vertebrae (Martill and Hutt, 1996; Hutt and Newbery, 2004; Naish and Martill, 2007), and the basal tyrannosauroid Eotyrannus lengi, which is known
from an associated specimen and referred material that indicates some individuals obtained large size (Hutt et al., 2001; Naish, 2006). Other Wessex Formation theropod remains pertain to mostly small-bodied coelurosaurs, and include the enigmatic taxa Aristosuchus pusillus, Calamosaurus foxi, Ornithodesmus cluniculus, and Thecocoelurus daviesi (Naish et al., 2001), as well
as isolated teeth that have been interpreted as belonging to
dromaeosaurids (Sweetman, 2004). Two large-bodied theropod
taxa, Becklespinax altispinax and Valdoraptor oweni, are known from the Hastings Beds Group, of somewhat older age than the Wessex Formation (Berriasian-Valanginian; Naish and
Martill, 2007).
Here we report remains collected by Keith Simmonds of
Brighstone from Chilton Chine, Brighstone Bay, Isle of Wight
in 1986, that represent an additional large-bodied Wessex Formation theropod (MIWG 6350). Although briefly listed as Theropoda indet. in a table of specimens published by Hutt (2001), MIWG 6350 has not yet been described in the literature. While this material is highly incomplete, it can be compared with contemporaneous theropods from the Wessex Formation and other Lower Cretaceous units worldwide. It is significant in indicating
the presence of a hitherto unrecognized large-bodied theropod from the Wessex Formation. This demonstrates that at least three large-bodied predators were present in theropod faunas of the Barremian of the United Kingdom
Experiments on standing bubbles in a vertical pipe
No full textWe present a series of laboratory experiments in which a steady stream of air is supplied through a small hole in the wall of a vertical pipe of rectangular cross-section down which there is a steady flux of water. For a range of liquid flow rates, the air forms a steady standing bubble whose nose is attached to the point of air supply. The steady bubble sheds a flux of much smaller air bubbles at its base, located downstream of the air injection point. The minimum liquid speed for which steady standing bubbles develop occurs at a particular Froude number of the liquid flow, Frd = U/ = 0.38, where U is the upstream speed, g the acceleration due to gravity and d the width of the cell. These trapped bubbles are distinct from the freely rising Taylor bubble, in that the Froude number at the nose is variable. Also, on a length scale greater than that influenced by surface tension, we find that the bubble nose asymptotes to a cusp-like shape, with an angle that decreases with Frd. We show that numerical solutions of the potential flow equations replicate the bubble shape and angle of the cusp, which appear independent of the gas flux. We also find that there is a minimum gas flux for which these standing bubbles develop. As the gas flux decreases below this threshold, the standing bubbles become unstable and, instead, a much shorter oscillating bubble develops. This produces a wake which has similarities with that formed downstream of a cylinder in a confined channel, but which also carries bubbles downstream. We also find that with sufficiently small gas flux, no bubble develops. For liquid flow rates smaller than the critical value, Frd < 0.38, we find that the bubbles become unstable and detach from the injection point and rise up the tube