1,765 research outputs found

    Bostonia. Volume 12

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    Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

    Use of Clumped-Isotope Thermometry To Constrain the Crystallization Temperature of Diagenetic Calcite

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    We describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped-isotope thermometry, a paleothermometer based on the ^(13)C–^(18)O-bond enrichment in carbonates. Application of this thermometer to calcified gastropod shells and calcite cements in an early Eocene limestone from the Colorado Plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123°C. The early Eocene host sediments were never deeply buried, but they experienced a significant thermal pulse associated with the emplacement of a late Miocene basalt flow. The combination of independent constraints on thermal history with clumped-isotope thermometry, petrographic (including cathodoluminescence) observations, and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources. The petrography and calcite δ^(18)O values, taken alone, suggest that the aragonite-to-calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample. However, addition of clumped-isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94–123°C in a highly rock-buffered microenvironment (i.e., with the isotopic composition of fluid buffered by coexisting carbonate), millions of years after lithification of the matrix and formation of initial low-temperature (14–19°C) calcite cements within shell body cavities. Clumped-isotope temperatures in excess of reasonable Earth-surface conditions recorded by later-formed cements demand that cement growth occurred in association with the lava emplacement. Our results illustrate the potential for clumped-isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable-isotopic and petrographic data alone, and demonstrate how petrographic characterization of clumped-isotope thermometry samples can benefit paleoclimate studies

    RNA-Seq identifies SPGs as a ventral skeletal patterning cue in sea urchins

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    The sea urchin larval skeleton offers a simple model for formation of developmental patterns. The calcium carbonate skeleton is secreted by primary mesenchyme cells (PMCs) in response to largely unknown patterning cues expressed by the ectoderm. To discover novel ectodermal cues, we performed an unbiased RNA-Seq-based screen and functionally tested candidates; we thereby identified several novel skeletal patterning cues. Among these, we show that SLC26a2/7 is a ventrally expressed sulfate transporter that promotes a ventral accumulation of sulfated proteoglycans, which is required for ventral PMC positioning and skeletal patterning. We show that the effects of SLC perturbation are mimicked by manipulation of either external sulfate levels or proteoglycan sulfation. These results identify novel skeletal patterning genes and demonstrate that ventral proteoglycan sulfation serves as a positional cue for sea urchin skeletal patterning

    Swings and roundabouts: the vagaries of democratic consolidation and ‘electoral rituals’ in Sierra Leone

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    YesThe history of the electoral process in Sierra Leone is at the same time tortuous and substantial. From relatively open competitive multi-party politics in the 1960s, which led to the first turnover of power at the ballot box, through the de facto and de jure one-party era, which nonetheless had elements of electoral competition, and finally to contemporary post-conflict times, which has seen three elections and a second electoral turnover in 2007, one can discern evolving patterns. Evidence from the latest local and national elections in 2012 suggests that there is some democratic consolidation, at least in an electoral sense. However, one might also see simultaneous steps forward and backward – What you gain on the swings, you may lose on the roundabouts. This is particularly so in terms of institutional capacities, fraud and violence, and one would need to enquire of the precise ingredients – in terms of political culture or in other words the attitudes and motivations of electors and the elected – of this evolving Sierra Leonean, rather than specifically liberal type, of democracy. Equally, the development of ‘electoral rituals’, whether peculiar to Sierra Leone or not and whether deemed consolidatory or not, has something to say as part of an investigation into the electoral element of democratic consolidation.1 The literature on elections in Africa most often depicts a number of broad features, such as patronage, ethno-regionalism, fraud and violence, and it is the intention of this article to locate contemporary Sierra Leone, as precisely as possible, within the various strands of this discourse

    The Third wave in globalization theory

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    This essay examines a proposition made in the literature that there are three waves in globalization theory—the globalist, skeptical, and postskeptical or transformational waves—and argues that this division requires a new look. The essay is a critique of the third of these waves and its relationship with the second wave. Contributors to the third wave not only defend the idea of globalization from criticism by the skeptics but also try to construct a more complex and qualified theory of globalization than provided by first-wave accounts. The argument made here is that third-wave authors come to conclusions that try to defend globalization yet include qualifications that in practice reaffirm skeptical claims. This feature of the literature has been overlooked in debates and the aim of this essay is to revisit the literature and identify as well as discuss this problem. Such a presentation has political implications. Third wavers propose globalist cosmopolitan democracy when the substance of their arguments does more in practice to bolster the skeptical view of politics based on inequality and conflict, nation-states and regional blocs, and alliances of common interest or ideology rather than cosmopolitan global structures
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