864 research outputs found
2009 Open Access Week: Copyright and Author Rights
No full textA talk about copyright by Danielle M. Conway
Divisibility of the Conway polynomial of links
No full textThe Conway polynomial ∇K = c0 + c1z + c2z2...of a link K is an invariant of links. In this paper we extend a theorem of J. Levine [5] regarding divisibility of the Conway polynomial by monomials of the form zi.
Three different definitions of finite type invariants of links are presented, including a definition of surgery finite type. When the coefficients ci are considered as finite type invariants, the type of these invariants is closely related to the degree of the monomials which can be factored out of ∇K.
With this in mind, we prove an extension of a conjecture by T. Cochran and P. Melvin [2] concerning the divisibility of an alternating sum sum S<L ∇K(Sigma S) of Conway polynomials of an algebraically split link K in various surgered spheres. This result was also proved for a more general case in which the link K is not necessarily algebraically split.
Finally, corollaries relate these theorems to the type of the coefficients ci, considered as finite type invariants
The terraces of the Conway Coast, North Canterbury: Geomorphology, sedimentary facies and sequence stratigraphy
No full textA basin analysis was conducted at the Conway Flat coast (Marlborough Fault Zone, South Island, New Zealand) to investigate the interaction of regional and local structure in a transpressional plate boundary and its control on basin formation. A multi-tiered approach has been employed involving: (i) detailed analysis of sedimentary deposits; (ii) geomorphic mapping of terraces, fault traces and lineaments; (iii) dating of deposits by 14C and OSL and (iv) the integration of data to form a basin-synthesis in a sequence stratigraphy framework.
A complex thrust fault zone (the Hawkswood Thrust Fault Zone), originating at the hinge of the thrust-cored Hawkswood anticline, is interpreted to be a result of west-dipping thrust faults joining at depth with the Hundalee Fault and propagating eastwards. The faults uplift and dissect alluvial fans to form terraces along the Conway Flat coast that provide the necessary relief to form the fan deltas. These terrace/fan surfaces are ~9 km long and ~3 km wide, composite features, with their upper parts representing sub-aerial alluvial fans. These grade into delta plains of Quaternary Gilbert-style fan deltas. Uplift and incision have created excellent 3D views of the underlying Gilbert-style fan delta complexes from topsets to prodelta deposits.
Erosive contacts between the Medina, Rafa, Ngaroma and modern Conway fan delta deposits, coupled with changes in terrace elevations allow an understanding of the development of multiple inset terraces along the Conway Flat coast. These terraces are divided into five stages of evolution based on variations in sedimentary facies and geomorphic mapping: Stage I involves the uplift of the Hawkswood Range and subsequent increased sedimentation rate such that alluvial fans prograded to the sea to form the Medina fan delta Terrace. Stage II began with a period of incision, from lowering sea level or changes in the uplift and sedimentation rate and continued with the deposition of the Dawn and Upham fan deltas. Stage III starts with the incision of the Rafa Terrace and deposition of aggradational terraces in the upper reaches. Stage IV initiated by a period of incision followed by deposition of estuarine facies at ~8ka and Stage V began with a period of incision and continues today with the infilling of the incised valley by the modern fan delta of the Conway River and its continued progradation.
New dates from within the Gilbert-type fan deltas along the Conway Flat coast are presented, using OSL and 14C dating techniques. Faulting at the Conway Flat coast began ~ 94 ka, based on the development of the Medina Terrace fan delta with uplift rates ~1.38~1.42 m/ka. The interplay of tectonics and sea level fluctuations continued as the ~79 ka Rafa Terrace fan deltas were created, with uplift rates calculated at ~1.39 m/ka. Detailed 14C ages from paleoforest (~8.4-~6.4 ka) in the Ngaroma Terrace and from the mouths of smaller streams have established uplift rates during the Holocene ~1-3 m/ka, depending on sea level
The GEOTRACES Intermediate Data Product 2017
No full textThe GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017.
This article is part of a special issue entitled: Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González
Distinct iron isotopic signatures and supply from marine sediment dissolution
No full textIron (Fe) inputs to the surface ocean may stimulate photosynthesis and have an impact on the uptake of carbon dioxide in the ocean on glacial to inter-glacial timescales of climate change1. Global ocean reservoir-flux models2 indicate that 90% of Fe used by marine phytoplankton in the present day surface ocean is supplied from the deep water below, but the sources of dissolved Fe to this deep water are still poorly constrained. Therefore, quantifying and tracking iron supplied to the ocean will provide key information to resolve climate models and sensitivity to the Fe cycle3, 4.Measurable differences in the isotopic composition of Fe between various sources to the ocean have prompted widespread interest in seawater Fe isotope determintions5, 6, 7, which can potentially be used to track Fe inputs and assess the relative importance of different sources of dissolved Fe to the oceanic reservoir. Microbial sediment respiration supports a major flux of dissolved and isotopically light Fe to the global ocean8, 9, 10, by catalysing the reductive dissolution (RD) of Fe oxyhydroxide minerals during organic matter decomposition11. Reduction of Fe oxyhydroxide enriches soluble Fe(II)(aq) in sediment pore water, which diffuses into bottom water when the oxygenated layer of surface sediment is adequately shallow9, 12, most notably from oxygen-deficient continental margins8, 9, 10. Benthic fluxes of Fe are mixed in bottom waters and can be transported to open ocean and surface waters13, 14, where Fe may control the efficacy of the biological carbon pump15, 16.Dissolved Fe(II)(aq) produced by RD initially has ?56Fe values 0.5–2.0‰ lighter than the original substrates17, and at isotopic equilibrium, experiments show ?56Fe(II)(aq) is ?1.05 to ?3.99‰ relative to the common reactive Fe oxides haematite17, goethite18 and ferrihydrite17, 19, 20. Similar light ?56Fe values (?1.82 to ?3.45‰) have been observed in both the pore waters21, 22, 23 and overlying seawater9, 24 of river-dominated and dysoxic margins, and light Fe isotopic compositions are recorded in ocean basin sediments coeval with past episodes of ocean oxygen deficiency, consistent with seawater transport of light Fe from ferruginous shelf sediments to ocean basins25. Thus, benthic fluxes of isotopically light Fe appear to be distinguishable from other sources of Fe to the ocean, such as atmospheric dust dissolution (?56Fe=+0.13±0.18‰)26 and river discharge (?56Fe=+0.14±0.28‰)27.Paradoxically, however, equatorial Pacific seawater originating from the continental margin of New Guinea contains elevated Fe concentrations with heavy Fe isotopic compositions (?56Fe=+0.37±0.15‰)28. These and other seawater isotope measurements have led to the proposition of an additional ‘non-reductive dissolution’ (NRD) mechanism for Fe28, 29, albeit with existing Fe isotope evidence from continental margin sediments indicating otherwise9, 24. These findings coincide with a growing need to evaluate the geographical variability of benthic Fe fluxes to effectively model carbon cycling in the ocean3, 4, where models presently rely on global extrapolations from potentially unrepresentative regions.Here we characterise the pore water isotopic composition and corresponding flux of dissolved Fe from the Cape margin, South Africa—a semi-arid passive margin derived from deeply weathered saprolite soils and surrounded by oxygenated South Atlantic seawater. These sites are distinct from most previous sites of benthic Fe flux investigation, which have focused on active margins next to areas of rapid uplift with oxygen-deficient shelf waters (Fig. 1). This study reveals that the amount of dissolved Fe released from the Cape margin is less than predicted by benthic Fe flux relationships8 widely used to model ocean Fe–CO2 interaction3, 4. We report solid-phase compositional data that suggests that the small pore water Fe flux reflects geological and hydro-climatic influences on reactive Fe substrate delivery to the shelf. Isotopically heavy Fe present in ‘oxidizing’ pore waters of the Cape margin—a zone previously beyond analytical resolution—provides in situ evidence for the role of ‘NRD’ of Fe proposed by Radic et al.28 These discoveries have implications for past and present oceanic Fe cycles and the parameterization of ocean biogeochemical models
An atheoretic evaluation of success in structural adjustment
No full textThe author presents and implements a methodology for assessing the success of structural adjustment based on a"fixed effect"method. He examines data for 75 countries over 11 years. Performance indicators include measures of inflation, economic growth, external balance, and physical investment. He measures government policies in terms of spending, trade regime, financial deepening, and real exchange rate policy. The empirical estimates he obtains suggest that ranking countries by adjusted economic performance yields significantly different results than ranking them by historical performance. Further, countries following a prescription of relatively low government spending, deep financial markets, and outward orientation in trade policy performed significantly better than those that did not. This prescription was correlated significantly with more rapid economic growth, current accounts with lower deficits, expanded investment, and reduced inflation.Environmental Economics&Policies,Economic Theory&Research,Macroeconomic Management,Achieving Shared Growth,Economic Stabilization
Iron colloids dominate sedimentary supply to the ocean interior
No full textDissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a “rusty source”) that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins
Expression of Plasmodium falciparum genes involved in erythrocyte invasion varies among isolates cultured directly from patients.
No full textPlasmodium falciparum merozoites invade erythrocytes using a range of alternative ligands that includes erythrocyte binding antigenic proteins (EBAs) and reticulocyte binding protein homologues (Rh). Variation in the expression of some of these genes among culture-adapted parasite lines correlates with the use of different erythrocyte receptors. Here, expression profiles of four Rh genes and eba175 are analysed in a sample of 42 isolates cultured from malaria patients in Kenya. The profiles cluster into distinct groups, largely because of very strong negative correlations between the levels of expression of particular gene pairs (Rh1 versus Rh2b, eba175 versus Rh2b, and eba175 versus Rh4), previously associated with alternative invasion pathways in culture-adapted parasite lines. High levels of eba175 are seen in isolates in expression profile group I, and may be associated with sialic acid-dependent invasion. Groups II and III are, respectively, characterized by high levels of Rh2b and Rh4, and are more likely to be associated with sialic acid-independent invasion
Sustained inflation in response to price liberalization
No full textThe author demonstrates that sustained inflation is a predictable response to price liberalization in the countries of the former Soviet Union. The author models the phenomenon in a dynamic macroeconomic framework,and demonstrates the immediate price jump followed by sustained inflation that has characterized the transitional economies of the former Soviet Union. The author supports the theoretical derivation with a simulation exercise that demonstrates the scope of sustained inflation for specific parameters.Markets and Market Access,Economic Theory&Research,Environmental Economics&Policies,Banks&Banking Reform,Access to Markets
- …
