152 research outputs found
Phase-field simulations of solidification in binary and ternary systems using a finite element method
We present adaptive finite element simulations of dendritic and eutectic
solidification in binary and ternary alloys. The computations are based on a
recently formulated phase-field model that is especially appropriate for
modelling non-isothermal solidification in multicomponent multiphase systems.
In this approach, a set of governing equations for the phase-field variables,
for the concentrations of the alloy components and for the temperature has to
be solved numerically, ensuring local entropy production and the conservation
of mass and inner energy. To efficiently perform numerical simulations, we
developed a numerical scheme to solve the governing equations using a finite
element method on an adaptive non-uniform mesh with highest resolution in the
regions of the phase boundaries. Simulation results of the solidification in
ternary NiCuCr alloys are presented investigating the
influence of the alloy composition on the growth morphology and on the growth
velocity. A morphology diagram is obtained that shows a transition from a
dendritic to a globular structure with increasing Cr concentrations.
Furthermore, we comment on 2D and 3D simulations of binary eutectic phase
transformations. Regular oscillatory growth structures are observed combined
with a topological change of the matrix phase in 3D. An outlook for the
application of our methods to describe AlCu eutectics is given.Comment: 5 pages, 3 figures, To appear in the proceedings of 14th
"International Conference on Crystal Growth", ICCG-14, 9-13 August 2004
Grenoble Franc
Processing information during regressions:An application of the reverse boundary-change paradigm
Although 10â15% of eye-movements during reading are regressions, we still know little about the information that is processed during regressive episodes. Here, we report an eye-movement study that uses what we call the reverse boundary change technique to examine the processing of lexical-semantic information during regressions, and to establish the role of this information during recovery from processing difficulty. In the critical condition of the experiment, an initially implausible sentence (e.g., There was an old house that John had ridden when he was a boy) was rendered plausible by changing a context word (house) to a lexical neighbor (horse) using a gaze-contingent display change, at the point where the reader's gaze crossed an invisible boundary further on in the sentence. Due to the initial implausibility of the sentence, readers often launched regressions from the later part of the sentence. However, despite this initial processing difficulty, reading was facilitated, relative to a condition where the display change did not occur (i.e., the word house remained on screen throughout the trial). This result implies that the relevant lexical semantic information was processed during the regression, and was used to aid recovery from the initial processing difficulty
Producing Adulthood: Adolescent Employment, Fertility, and the Life Course
Adolescent employment is typically framed as having either positive or negative effects. Yet cutting edge research yields apparently contradictory results; work lowers delinquency but also increases school dropout. Both opportunity cost and life course development theories could explain these results. This study investigates effects of employment on fertility among adolescent women, which pits life course development against opportunity cost theory. Using 2006 and 2007 American Community Surveys, individual instrumental variable and state-level difference-in-difference models (following the same cohort over time) control for self-selection and find a positive effect of employment on adolescent fertility. National Vital Statistics birth data confirm state-level results. Results for fertility (and some evidence for other early transitions) indicate that youth employment speeds the transition to adulthood, supporting life course theory. Findings suggest adolescent employment should be reconceived as promoting adult rather than positive or negative behavior
Growth of the C4 dicot Flaveria bidentis: photosynthetic acclimation to low light through shifts in leaf anatomy and biochemistry
In C4 plants, acclimation to growth at low irradiance by means of anatomical and biochemical changes to leaf tissue is considered to be limited by the need for a close interaction and coordination between bundle sheath and mesophyll cells. Here differences in relative growth rate (RGR), gas exchange, carbon isotope discrimination, photosynthetic enzyme activity, and leaf anatomy in the C4 dicot Flaveria bidentis grown at a low (LI; 150âÎŒmol quanta m2 sâ1) and medium (MI; 500âÎŒmol quanta m2 sâ1) irradiance and with a 12âh photoperiod over 36âd were examined. RGRs measured using a 3D non-destructive imaging technique were consistently higher in MI plants. Rates of CO2 assimilation per leaf area measured at 1500âÎŒmmol quanta m2 sâ1 were higher for MI than LI plants but did not differ on a mass basis. LI plants had lower Rubisco and phosphoenolpyruvate carboxylase activities and chlorophyll content on a leaf area basis. Bundle sheath leakiness of CO2 (Ï) calculated from real-time carbon isotope discrimination was similar for MI and LI plants at high irradiance. Ï increased at lower irradiances, but more so in MI plants, reflecting acclimation to low growth irradiance. Leaf thickness and vein density were greater in MI plants, and mesophyll surface area exposed to intercellular airspace (Sm) and bundle sheath surface area per unit leaf area (Sb) measured from leaf cross-sections were also both significantly greater in MI compared with LI leaves. Both mesophyll and bundle sheath conductance to CO2 diffusion were greater in MI compared with LI plants. Despite being a C4 species, F. bidentis is very plastic with respect to growth irradiance
The twilight of the Liberal Social Contract? On the Reception of Rawlsian Political Liberalism
This chapter discusses the Rawlsian project of public reason, or public justification-based 'political' liberalism, and its reception. After a brief philosophical rather than philological reconstruction of the project, the chapter revolves around a distinction between idealist and realist responses to it. Focusing on political liberalismâs critical reception illuminates an overarching question: was Rawlsâs revival of a contractualist approach to liberal legitimacy a fruitful move for liberalism and/or the social contract tradition? The last section contains a largely negative answer to that question. Nonetheless the chapter's conclusion shows that the research programme of political liberalism provided and continues to provide illuminating insights into the limitations of liberal contractualism, especially under conditions of persistent and radical diversity. The programme is, however, less receptive to challenges to do with the relative decline of the power of modern states
Global Atmospheric Budget of Acetone: Air-Sea Exchange and the Contribution to Hydroxyl Radicals
Acetone is one of the most abundant oxygenated volatile organic compounds (VOCs) in the atmosphere. The oceans impose a strong control on atmospheric acetone, yet the oceanic fluxes of acetone remain poorly constrained. In this work, the global budget of acetone is evaluated using two global models: CAMâchem and GEOSâChem. CAMâchem uses an online airâsea exchange framework to calculate the bidirectional oceanic acetone fluxes, which is coupled to a dataâoriented machineâlearning approach. The machineâlearning algorithm is trained using a global suite of seawater acetone measurements. GEOSâChem uses a fixed surface seawater concentration of acetone to calculate the oceanic fluxes. Both model simulations are compared to airborne observations from a recent globalâscale, multiseasonal campaign, the NASA Atmospheric Tomography Mission (ATom). We find that both CAMâchem and GEOSâChem capture the measured acetone vertical distributions in the remote atmosphere reasonably well. The combined observational and modeling analysis suggests that (i) the ocean strongly regulates the atmospheric budget of acetone. The tropical and subtropical oceans are mostly a net source of acetone, while the highâlatitude oceans are a net sink. (ii) CMIP6 anthropogenic emission inventory may underestimate acetone and/or its precursors in the Northern Hemisphere. (iii) The MEGAN biogenic emissions model may overestimate acetone and/or its precursors, and/or the biogenic oxidation mechanisms may overestimate the acetone yields. (iv) The models consistently overestimate acetone in the upper troposphereâlower stratosphere over the Southern Ocean in austral winter. (v) Acetone contributes up to 30â40% of hydroxyl radical production in the tropical upper troposphere/lower stratosphere
Global Atmospheric Budget of Acetone: AirâSea Exchange and the Contribution to Hydroxyl Radicals
Acetone is one of the most abundant oxygenated volatile organic compounds (VOCs) in the atmosphere. The oceans impose a strong control on atmospheric acetone, yet the oceanic fluxes of acetone remain poorly constrained. In this work, the global budget of acetone is evaluated using two global models: CAMâchem and GEOSâChem. CAMâchem uses an online airâsea exchange framework to calculate the bidirectional oceanic acetone fluxes, which is coupled to a dataâoriented machineâlearning approach. The machineâlearning algorithm is trained using a global suite of seawater acetone measurements. GEOSâChem uses a fixed surface seawater concentration of acetone to calculate the oceanic fluxes. Both model simulations are compared to airborne observations from a recent globalâscale, multiseasonal campaign, the NASA Atmospheric Tomography Mission (ATom). We find that both CAMâchem and GEOSâChem capture the measured acetone vertical distributions in the remote atmosphere reasonably well. The combined observational and modeling analysis suggests that (i) the ocean strongly regulates the atmospheric budget of acetone. The tropical and subtropical oceans are mostly a net source of acetone, while the highâlatitude oceans are a net sink. (ii) CMIP6 anthropogenic emission inventory may underestimate acetone and/or its precursors in the Northern Hemisphere. (iii) The MEGAN biogenic emissions model may overestimate acetone and/or its precursors, and/or the biogenic oxidation mechanisms may overestimate the acetone yields. (iv) The models consistently overestimate acetone in the upper troposphereâlower stratosphere over the Southern Ocean in austral winter. (v) Acetone contributes up to 30â40% of hydroxyl radical production in the tropical upper troposphere/lower stratosphere
Bringing KASH under the SUN: the many faces of nucleo-cytoskeletal connections
The nucleus is the most prominent cellular organelle, and its sharp boundaries suggest the compartmentalization of the nucleoplasm from the cytoplasm. However, the recent identification of evolutionarily conserved linkers of the nucleoskeleton to the cytoskeleton (LINC) complexes, a family of macromolecular assemblies that span the double membrane of the nuclear envelope, reveals tight physical connections between the two compartments. Here, we review the structure and evolutionary conservation of SUN and KASH domainâcontaining proteins, whose interaction within the perinuclear space forms the ânuts and boltsâ of LINC complexes. Moreover, we discuss the function of these complexes in nuclear, centrosomal, and chromosome dynamics, and their connection to human disease
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