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Replicate radiocarbon (14C) measurements of organic and inorganic control samples, with known Fraction Modern values in the range Fm = 0–1.5 and mass range 6 μg–2 mg carbon, are used to determine both the mass and radiocarbon content of the blank carbon introduced during sample processing and measurement in our laboratory. These data are used to model, separately for organic and inorganic samples, the blank contribution and subsequently “blank correct” measured unknowns in the mass range 25–100 μg. Data, formulas, and an assessment of the precision and accuracy of the blank correction are presented.
This study investigates the interaction of picosecond laser pulses with sapphire and brass in air using scanning electron microscopy. A picosecond laser system operating at a wavelength of 785 nm, pulse width of 110 ps, and variable repetition rate (1–1000 Hz) was used in this study. The pulse width applied in this work was not widely investigated as it lies in the gap between ultrashort (femtosecond) and long (nanosecond) pulse width lasers. Different surface morphologies were identified using secondary electron and backscattered electron imaging of the ablated material. Thermal ablation effects were more dominant in brass than in sapphire. Exfoliation and fractures of sapphire were observed at high laser fluence. Compared with brass, multiple laser pulses were necessary to initiate ablation in sapphire due to its poor absorption to the incident laser wavelength. Ablation rate of sapphire was lower than that of brass due to the dissipation of a portion of the laser energy due to heating and fracturing of the surface.
We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) μg C with an Fm value of 0.555±0.042 and a δ13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: μ=–0.8‰; ±1σ=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: μ=0.005; ±1σ=0.014; n=36). Lastly, we show there exists no significant intra-sample δ13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12∆E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO δ13C values accurately retain carbon source isotope signals to within 1–2‰.
Triaxial experiments, at confining pressures in the range 0–13.79 MPa, have been performed on glacial ice collected from four icebergs and one glacier. Tests were conducted at strain rates in the range of 5 × 10−5 to 5 × 10−5s−1 and at four temperatures in the range of −1° to −16°C. Depending on test conditions, the ice failed by one of four possible modes ductile deformation, due to extensive non-interacting microcracks; fracture along a shear plane followed by continuous or stick-slip sliding; large-scale brittle fracture; and combined ductile and shear-plane fracture and slip The strength Increased with decreasing temperature, increasing strain rate up to 5 × 10−3s−1 and increasing confining pressure at the lower temperatures. The strength at 5 × 10−2s−1 was lower than at 5 × 10−3s−1 probably because extension and interaction of microcracks is enhanced at the higher rate. For higher confining pressures at −1°C, the strength decreased due to freezing-point depression. The ice from the different sources exhibited different mean uniaxial compressive strengths. The mean number of air bubbles per unit volume correlated with the mean uniaxial compressive strengths and this may be the dominant factor distinguishing the strengths of the various ice types.
Indentation experiments have been performed on fresh-water ice at -9°C using an apparatus which permitted visual observation of the contact zone at the ice/indentor interface by viewing through the specimens. Analysis of the video records and test data indicated that at least 50% of the energy dissipated during the process of indentation was consumed by pressure melting and heat generation through the rapid viscous flow of the liquid. The thickness of the liquid layer was estimated to be 16/μm and the contact pressure in the melting zone was at least 90 MPa. Video records of small-scale impact tests on ice indicated that the same process of pressure melting and extrusion was taking place.
A series of 40 impact tests was conducted an large right-circular cylinders (68.5 cm diameter and 25.7 cm thickness) of iceberg ice collected from an iceberg in Labrador. Temperature profiles were also obtained for the iceberg and the profiles exhibited differences associated with the probe location. Temperatures as low as –15°C were measured at penetration depths of about 8 m. The impact specimens were confined at the perimeter and base by a rigid metallic ring and plate. A spherically terminated impactor, with center-mounted pressure transducer, was dropped on to the flat top surface of specimens from various heights and with various added masses. Impact velocity varied from 1.8 to 3.9 m s−1; impactor mass varied from 155 to 510 kg and the ice-specimen temperature varied from –0.5° to –14.5°C. Peak center pressures averaged from about 25 MPa at the highest temperature to about 41 MPa at the lowest temperature, with the highest recorded pressure being 50 M Pa. Crater volume increased with increasing impact energy, as expected; however, the specific energy of the ejected material was found to decrease as the energy of impact and crater volume increased. A mechanism for this observed behaviour is proposed.
During the four years the Sample Preparation Laboratory (SPL) at the National Ocean Sciences Accelerator Mass Spectrometer (NOSAMS) Facilty has been in operation we have accumulated much data from which we can assess our progress. We evaluate our procedural blanks here and describe modifications in our procedures that have improved our analyses of older samples. In the SPL, we convert three distinct types of samples—seawater, CaCO3 and organic carbon—to CO2 prior to preparing graphite for the accelerator and have distinct procedural blanks for each procedure. Dissolved inorganic carbon (∑CO2) is extracted from acidified seawater samples by sparging with a nitrogen carrier gas. We routinely analyze “line blanks” by processing CO2 from a 14C-dead source through the entire stripping procedure. Our hydrolysis blank, IAEA C-1, is prepared by acidifying in vacuo with 100% H3PO4 at 60° overnight, identical to our sample preparation. We use a dead graphite, NBS-21, or a commercially available carbon powder for our organic combustion blank; organic samples are combusted at 850° for 5 h using CuO to provide the oxidant. Analysis of our water stripping data suggests that one step in the procedure contributes the major portion of the line blank. At present, the contribution from the line blank has no effect on our seawater analyses (fraction modern (fm) between 0.7 and 1.2). Our hydrolysis blanks can have an fm value as low as 0.0006, but are more routinely between 0.0020 and 0.0025. The fm of our best organic combustion blanks is higher than those routinely achieved in other laboratories and we are currently altering our methods to reduce it.
We conducted a study of relative gas composition changes of CO2, CO and CH4 during the formation of graphite targets using different temperatures, catalysts and methods. Reduction with H2 increases the reaction rate without compromising the quality of the AMS target produced. Methane is produced at virtually any temperature, and the amount produced is greater at very low temperatures. The reduction of CO to graphite is very slow when H2 is not included in the reaction.
Numerous natural processes are contingent on microorganisms’ ability to swim through fluids with non-Newtonian rheology. Here, we use the model organism Caenorhabditis elegans and tracking methods to experimentally investigate the dynamics of undulatory swimming in shear-thinning fluids. Theory and simulation have proposed that the cost of swimming, or mechanical power, should be lower in a shear-thinning fluid compared to a Newtonian fluid of the same zero-shear viscosity. We aim to provide an experimental investigation into the cost of swimming in a shear-thinning fluid from (i) an estimate of the mechanical power of the swimmer and (ii) the viscous dissipation rate of the flow field, which should yield equivalent results for a self-propelled low Reynolds number swimmer. We find the cost of swimming in shear-thinning fluids is less than or equal to the cost of swimming in Newtonian fluids of the same zero-shear viscosity; furthermore, the cost of swimming in shear-thinning fluids scales with a fluid’s effective viscosity and can be predicted using fluid rheology and simple swimming kinematics. Our results agree reasonably well with previous theoretical predictions and provide a framework for understanding the cost of swimming in generalized Newtonian fluids.
The swimming behaviour of micro-organisms can be strongly influenced by the rheology of their fluid environment. In this article, we experimentally investigate the effects of shear-thinning (ST) viscosity on the swimming behaviour of an undulatory swimmer, the nematode Caenorhabditis elegans. Tracking methods are used to measure the swimmer’s kinematic data (including propulsion speed) and velocity fields. We find that ST viscosity modifies the velocity fields produced by the swimming nematode but does not modify the nematode’s speed and beating kinematics. Velocimetry data show significant enhancement in local vorticity and circulation and an increase in fluid velocity near the nematode’s tail. These findings are compared with recent theoretical and numerical results.
The Dominion Radio Astrophysical Observatory (DRAO) is carrying out a survey as part of an international collaboration to image the northe, at a common resolution, in emission from all major constituents of the interstellar medium; the neutral atomic gas, the molecular gas, the ionised gas, dust and relativistic plasma. For many of these constituents the angular resolution of the images (1 arcmin) will be more than a factor of 10 better than any previous studies. The aim is to produce a publicly-available database of high resolution, high-dynamic range images of the Galaxy for multi-phase studies of the physical states and processes in the interstellar medium. We will sketch the main scientific motivations as well as describe some preliminary results from the Canadian Galactic Plane Survey/Releve Canadien du Plan Galactique (CGPS/RCPG).
We report room temperature thermopower values and the temperature dependence for several AlPdMn based quasicrystals. In an effort to further understand the complexities of electrical transport in quasicrystalline systems, thermopower data for icosahedral Al71Pd21Mn8-XReX will be presented and discussed. A relation of room temperature thermopower to the curvature of the thermopower is demonstrated. We propose an empirical fit to the thermopower data, utilizing three free variables. The physical significance of the fit parameters is discussed. These results are discussed in brief concerning the relation to the application of quasicrystals for use as thermoelectric materials.
We have grown silicon carbide (SiC) on ultrathin Si (about 300Å) and on thick Si (about 2000Å) on commercial SIMOX (from IBIS Corp and SOITEC, Inc.), and bulk Si. Electron diffraction and Rutherford backscattering spectroscopy (RBS)/channeling studies indicate epitaxial growth of singlecrystal β-SiC even at growth temperatures as low as 1100°C.
We have already demonstrated the fabrication of ultrathin Si, as thin as 140Å on SiO2 by using the low-energy SIMOX (LES) (20 to 30 keV) process to produce films of lower cost and excellent integrity compared to thinned commercial SIMOX. Based on these results, ultrathin Si-on-insulator (SOI) substrates appear to have great potential for device quality SiC films. However, the carbonization and/or growth of SiC on ultrathin Si requires further optimization because the processes for surface cleaning and growth of SiC on bulk Si substrates cannot be applied because of the thinness of the substrate layers. Additional carbonization work at higher temperatures has indicated the possibility of converting the entire Si top layer.
This paper addresses the initial stage of epitaxial growth of SiC on thin (about 300A) and thick (2000Å) Si films. Our results as obtained by Rutherford backscattering spectroscopy (RBS), Auger spectroscopy, and plan-view/cross-sectional TEM, demonstrate epitaxial growth of 3C-SiC structures on ultrathin Si films (even under non-optimized growth conditions). These preliminary results indicate that the crystalline quality of SiC on thin SIMOX is better than that grown on thick SIMOX or bulk Si substrates. Growth of SiC epi on thin Si will pave the way for growth of SiC directly on SiO2 (a compliant substrate) by carbonization of the entire thin Si top layer of SIMOX.
This paper highlights new research on the biomineralization of otoliths and uses a mineralogical approach to understand mechanisms of crystal growth and metal incorporation into otoliths. Petrographic observations of the nucleation of otolith growth in the core for several fish species reveals that sagittal otoliths appear to nucleate around a few or many nucleation sites (primordia) and that these sites vary in size (ranging in diameter from 1 to 20 μm), depending on the species. Spectroscopic data show a large Mn-enrichment in the primordia within the core but the reasons for this enrichment are still unclear (e.g. organic matter or possibly another material other than CaCO3). This study also provides the first multi trace-element data for endolymph fluid and the growing otolith; we found large enrichments (Ca and Sr) and depletions (Na, K, Zn and Rb) of elements in the otolith relative to the endolymph. The last part of this paper examines the effect of crystal structure on the microchemistry ofotoliths. Our investigation helps understand how the chemical characteristics of the metal ions (i.e. ionic radii) and the crystalline structure interact to cause differential trace-metal uptake between the CaCO3 polymorphs, aragonite and vaterite.
Laurence H. Meyer, Distinguished Scholar, Center for Strategic and International Studies in Washington, DC; Senior Advisor and Director, Macroeconomic Advisors,
Brian M. Doyle, Economist in the Division of International Finance, Federal Reserve Board,
Joseph E. Gagnon, Assistant Director in the Division of International Finance, Federal Reserve Board,
Dale W. Henderson, Senior Adviser in the Division of International Finance, Federal Reserve Board; Professor of Economics, Georgetown University
The subject of this chapter is macroeconomic policy coordination among developed countries. The chapter covers both the findings of theoretical models of policy coordination and the historical experience of coordination between policy-makers in different countries. Most importantly, the chapter assesses the extent to which models of policy coordination capture the key features of practical experience. For areas where the models and experience diverge, we attempt to draw some lessons for both modellers and policy-makers.
The past few decades have seen the development of theoretical and empirical models designed to explore the benefits of international macroeconomic policy coordination. The models highlight the fact that macroeconomic policy actions in one country affect economic welfare in other countries; that is, they have externalities for other countries. The key insight of the models is that coordination of policies among countries that takes into account these externalities may lead to higher welfare for all countries. Starting with this key insight, the modelling of international policy coordination has moved in many different directions addressing such issues as the types of problems that coordination is best suited to address, which policies are best suited to address which problems, the means of enforcing international agreements, the roles that uncertainty and information sharing play in the coordination process and the measurement of the gains from policy coordination.
Habitat loss and fragmentation are main causes for Asian elephant population declines. We mapped wildlands - large, unfragmented and undeveloped areas - asking: (1) Where are the largest wildlands that constitute elephant habitats? (2) What proportion of these wildlands is protected? (3) What is their potential for elephant conservation? Our study demonstrates that wildlands constitute only 51% of the Asian elephant range. Myanmar has the largest wildland (∼170,000 km2), followed by Thailand and India. In Principal Components Analysis (PCA), the first two components explained 73% of the variation in fragmentation among ranges. We identified three fragmentation clusters from the PCA. Cluster A contains large ranges with unfragmented wildlands; cluster B includes ranges with well-developed transportation networks and large human populations; and cluster C contains ranges with severely fragmented wildlands. In cluster A, we identified four ranges with elephant populations >1000 animals: ARYO, MYUC, BNMH and BITE. Together with ranges that support >1000 elephants in cluster B, these A ranges have great potential for long-term elephant conservation. We propose that fragmentation clusters and population size can be used to identify different elephant monitoring and management zones.
Disruptive boys in kindergarten, selected from teacher ratings in a large study, were each followed up for four successive years. There was considerable continuity of the boys' fighting, despite a declining prevalence in fighting over the years. High oppositional behavior in one year did not consistently predict fighting in the next year. A history of fighting was associated with being held back in grade. Boys were assigned to fighting evolution status on the basis of their fighting scores over the four years: stable high fighters, desisting high fighters, and variable/initiating high fighters. Stable high fighters, unlike desisting high fighters, scored high on nonaggressive antisocial acts at the end of the four years. For some boys, cessation of fighting was associated with later nonaggressive antisocial behavior. Fighting evolution status was examined further in relationship to anxiety, hyperactivity/inattentiveness, and prosocial behaviors. At age 9, stable high fighters, and to a lesser extent variable/initiating high fighters, were more likely to come from single parent families than desisting high fighters. The results are discussed in the context of the development of conduct problems in children.
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