175 research outputs found
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Wintertime Transport of Reactive Trace Gases From East Asia Into the Deep Tropics
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Reflecting optics in the diverticular eye of a deep-sea barreleye fish (Rhynchohyalus natalensis)
We describe the bi-directed eyes of a mesopelagic teleost fish, Rhynchohyalus natalensis, that possesses an extensive lateral diverticulum to each tubular eye. Each diverticulum contains a mirror that focuses light from the ventro-lateral visual field. This species can thereby visualize both downwelling sunlight and bioluminescence over a wide field of view. Modelling shows that the mirror is very likely to be capable of producing a bright, well focused image. After Dolichopteryx longipes, this is only the second description of an eye in a vertebrate having both reflective and refractive optics. Although superficially similar, the optics of the diverticular eyes of these two species of fish differ in some important respects. Firstly, the reflective crystals in the D. longipes mirror are derived from a tapetum within the retinal pigment epithelium, whereas in R. natalensis they develop from the choroidal argentea. Secondly, in D. longipes the angle of the reflective crystals varies depending on their position within the mirror, forming a Fresnel-type reflector, but in R. natalensis the crystals are orientated almost parallel to the mirror's surface and image formation is dependent on the gross morphology of the diverticular mirror. Two remarkably different developmental solutions have thus evolved in these two closely related species of opisthoproctid teleosts to extend the restricted visual field of a tubular eye and provide a well-focused image with reflective optics
Cloud impacts on photochemistry: Building a climatology of photolysis rates from the Atmospheric Tomography mission
Abstract. Measurements from actinic flux spectroradiometers on board the
NASA DC-8 during the Atmospheric Tomography (ATom) mission provide an
extensive set of statistics on how clouds alter photolysis rates (J values)
throughout the remote Pacific and Atlantic Ocean basins. J values control
tropospheric ozone and methane abundances, and thus clouds have been included
for more than three decades in tropospheric chemistry modeling. ATom made
four profiling circumnavigations of the troposphere capturing each of the
seasons during 2016â2018. This work examines J values from the Pacific
Ocean flights of the first deployment, but publishes the complete Atom-1 data
set (29Â July to 23Â August 2016). We compare the observed J values (every 3âs along flight track) with those calculated by nine global
chemistryâclimate/transport models (globally gridded, hourly, for a
mid-August day). To compare these disparate data sets, we build a
commensurate statistical picture of the impact of clouds on J values using
the ratio of J-cloudy (standard, sometimes cloudy conditions) to J-clear
(artificially cleared of clouds). The range of modeled cloud effects is
inconsistently large but they fall into two distinct classes: (1)Â models with
large cloud effects showing mostly enhanced J values aloft and or
diminished at the surface and (2)Â models with small effects having nearly
clear-sky J values much of the time. The ATom-1 measurements generally
favor large cloud effects but are not precise or robust enough to point out
the best cloud-modeling approach. The models here have resolutions of 50â200âkm
and thus reduce the occurrence of clear sky when averaging over grid
cells. In situ measurements also average scattered sunlight over a mixed
cloud field, but only out to scales of tens of kilometers. A primary uncertainty
remains in the role of clouds in chemistry, in particular, how models average
over cloud fields, and how such averages can simulate measurements.
NERC ACSIS LTSM projec
Plastisol Foaming Process. Decomposition of the Foaming Agent, Polymer Behavior in the Corresponding Temperature Range and Resulting Foam Properties
The decomposition of azodicarbonamide, used as foaming agent in PVC - plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min-1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g -1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol-1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse
Does Selective Migration Explain the Hispanic Paradox?: A Comparative Analysis of Mexicans in the U.S. and Mexico
Latino immigrants, particularly Mexican, have some health advantages over U.S.-born Mexicans and Whites. Because of their lower socioeconomic status, this phenomenon has been called the epidemiologic âHispanic Paradox.â While cultural theories have dominated explanations for the Paradox, the role of selective migration has been inadequately addressed. This study is among the few to combine Mexican and U.S. data to examine health selectivity in activity limitation, self-rated health, and chronic conditions among Mexican immigrants, ages 18 and over. Drawing on theories of selective migration, this study tested the âhealthy migrantâ and âsalmon-biasâ hypotheses by comparing the health of Mexican immigrants in the U.S. to non-migrants in Mexico, and to return migrants in Mexico. Results suggest that there are both healthy migrant and salmon-bias effects in activity limitation, but not other health aspects. In fact, consistent with prior research, immigrants are negatively selected on self-rated health. Future research should consider the complexities of migrantsâ health profiles and examine selection mechanisms alongside other factors such as acculturation
Digital Atlasing and Standardization in the Mouse Brain
Computer Systems, Imagery and Medi
Justice and Corporate Governance: New Insights from Rawlsian Social Contract and Senâs Capabilities Approach
By considering what we identify as a problem inherent in the ânature of the firmââthe risk of abuse of authorityâwe propound the conception of a social contract theory of the firm which is truly Rawlsian in its inspiration. Hence, we link the social contract theory of the firm (justice at firmâs level) with the general theory of justice (justice at societyâs level). Through this path, we enter the debate about whether firms can be part of Rawlsian theory of justice showing that corporate governance principles enter the âbasic structure.â Finally, we concur with Senâs aim to broaden the realm of social justice beyond what he calls the âtranscendental institutional perfectionismâ of Rawlsâ theory. We maintain the contractarian approach to justice but introduce Senâs capability concept as an element of the constitutional and post-constitutional contract model of institutions with special reference to corporate governance. Accordingly, rights over primary goods and capabilities are (constitutionally) granted by the basic institutions of society, but many capabilities have to be turned into the functionings of many stakeholders through the operation of firms understood as post-constitutional institutional domains. The constitutional contract on the distribution of primary goods and capabilities should then shape the principles of corporate governance so that at post-constitutional level anyone may achieve her/his functionings in the corporate domain by exercising such capabilities. In the absence of such a condition, post-constitutional contracts would distort the process that descends from constitutional rights and capabilities toward social outcomes
Variability and Action Mechanism of a Family of Anticomplement Proteins in Ixodes ricinus
Background: Ticks are blood feeding arachnids that characteristically take a long blood meal. They must therefore counteract host defence mechanisms such as hemostasis, inflammation and the immune response. This is achieved by expressing batteries of salivary proteins coded by multigene families. Methodology/Principal Findings: We report the in-depth analysis of a tick multigene family and describe five new anticomplement proteins in ixodes ricinus. Compared to previously described Ixodes anticomplement proteins, these segregated into a new phylogenetic group or subfamily. These proteins have a novel action mechanism as they specifically bind to properdin, leading to the inhibition of C3 convertase and the alternative complement pathway. An excess of non-synonymous over synonymous changes indicated that coding sequences had undergone diversifying selection. Diversification was not associated with structural, biochemical o, functional diversity, adaptation to host species or stage specificity but rather to differences in antigenicity. Conclusion/Significance: Anticomplement proteins from I. ricinus are the first inhibitors that specifically target a positive regulator of complement, properdin. They may provide new tools for the investigation of role of properdin in physiological and pathophysiological mechanisms. They may also be useful in disorders affecting the alternative complement pathway, Looking for and detecting the different selection pressures involved will help in understanding the evolution of multigene families and hematophagy in arthropods. © 2008 Couveur et al.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe
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
Mean-field transport theory for the two-flavour NJL model
By making decomposition of the Wigner function simultaneously in both the
spinor and the isospin spaces we derive a set of kinetic equations for the
quark distribution functions and the spin densities. A detailed analysis of the
consequences imposed by the chiral invariance on the form of the transport
equations is presented.Comment: Revtex, 25 pages, no figure
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