139,589 research outputs found
Magnetite pollution nanoparticles in the human brain
No full textBiologically formed nanoparticles of the strongly magnetic mineral, magnetite, were first detected in the human brain over 20 y ago [Kirschvink JL, Kobayashi-Kirschvink A, Woodford BJ (1992) Proc Natl Acad Sci USA 89(16):7683–7687]. Magnetite can have potentially large impacts on the brain due to its unique combination of redox activity, surface charge, and strongly magnetic behavior. We used magnetic analyses and electron microscopy to identify the abundant presence in the brain of magnetite nanoparticles that are consistent with high-temperature formation, suggesting, therefore, an external, not internal, source. Comprising a separate nanoparticle population from the euhedral particles ascribed to endogenous sources, these brain magnetites are often found with other transition metal nanoparticles, and they display rounded crystal morphologies and fused surface textures, reflecting crystallization upon cooling from an initially heated, iron-bearing source material. Such high-temperature magnetite nanospheres are ubiquitous and abundant in airborne particulate matter pollution. They arise as combustion-derived, iron-rich particles, often associated with other transition metal particles, which condense and/or oxidize upon airborne release. Those magnetite pollutant particles which are <200 nm in diameter can enter the brain directly via the olfactory bulb. Their presence proves that externally sourced iron-bearing nanoparticles, rather than their soluble compounds, can be transported directly into the brain, where they may pose hazard to human health
Enrichment of surface-active compounds in coalescing cloud drops
No full text[1] Surfactants often found in tropospheric aerosols, can affect the onset and development of clouds. Due to high dilution during droplet growth, the effects of surfactants on cloud microphysical processes have been mostly neglected. However, while cloud growth by coalescence conserves the combined volume of all cloud droplets, it reduces the combined surface area. This could lead to enrichment of water-insoluble surfactants (WIS) and to reduced surface tension of droplets forming in warm processes. Measurements of individual raindrops reveal the presence of water insoluble surfactants. Our field and laboratory studies as well as simple theoretical arguments suggest that by causing varying and size-dependent surface tension, WIS can affect cloud microphysics. Citation: Taraniuk, I., A. B. Kostinski, and Y. Rudich (2008), Enrichment of surface-active compounds in coalescing cloud drops, Geophys. Res. Lett., 35
Desafíos y riesgos en el uso de monedas virtuales
No full textEl pasado 23 de septiembre de 2022, se realizó el foro virtual “Desafíos y riesgos en el uso de monedas virtuales", En este video se comparte un resumen de las intervenciones de: Denisse Rudich, Directora de los grupos de investigación G20 y G7, especialista en delitos financieros; Jorge Cuéllar, académico del Dartmouth College, investigador sobre asuntos centroamericanos y criptomonedas; Laura Hernández, abogada especialista en tecnologías y seguridad de la información; Rommel Rodríguez, economista investigador de FUNDE y especialista en finanzas públicas
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
Optical and chemical properties of aged biomass burning aerosols
No full textSSCI-VIDE+CARE+DCA:CGOInternational audienceAmong the organic compounds emitted during biomass burning events, methoxyphenols (45%wt. of the particulate matter derived from wood smoke) are present both in the gas and particle phases, and may undergo various transformations during atmospheric ageing induced either by light (photochemistry) or temperature (thermal processes).We report here chemical and optical analyses of syringol (C8H10O3) particles, one of the most abundant methoxyphenol species found in such biomass burning plumes, after both photo- and thermal-ageing. Chemical analyses were performed using a HESI/LC/DAD/MS (orbitrap mass spectrometry). When exposed to UV-light or heated for several hours, syringol became yellowish in both cases while distinct products were identified. The differences in chemistry propagate also to the optical properties of the aerosols as probed by broad band cavity enhanced spectroscopy (BBCES). These results, when considered together, may be of importance considering the possible effects on human health of these detected ageing-products and the contribution to the radiative forcing.This work is supported by the Ministère des Affaires Etrangères et du Développement International (France) and the Ministry of Science (Israel), under the Research Program "Maïmonide-Israel". Two groups collaborate for it: Christian George group (CNRS, FRANCE) for the high resolution MS chemical analyses and Yinon Rudich group (Weizmann Institute, ISRAEL) for the optical properties of aerosols
La 'circunstancia' de 'Herederos y Pretendientes
No full textIn June 2010, the Ortega y Gasset Foundation hosted a Conference about the “Spanish Philosophical Transition” in order to debate the book of Francisco Vázquez, La filosofía española. Herederos y Pretendientes. Una lectura sociológica (1963-1990), recently published. This paper is the author’s response to criticism raised in the Conference and to published reviews received by this book. First, the author summarized the argument of Herederos y pretendientes. Secondly he responds and takes into account the most important objections against the book’s hypothesis and methodology. Finally the author evaluates the favorable judgments received by the book and suggests the limits of the historian’s task.Fundación Ortega y Gasset-Marañó
Author self-citation in orthodontics is associated with author origin and gender.
No full textBACKGROUND
The aims of this bibliometric study were to determine author self-citation trends in high-impact orthodontic literature and to investigate possible association between self-citation and publication characteristics.
METHODS
Six orthodontic journals with the highest impact factor as ranked by 2017 Journal Citation Reports were screened for a full publication year (2018) for original research articles, reviews, and case reports. Eligible articles were scrutinized for article and author characteristics and citation metrics. Univariable and multivariable negative binomial regression was used to examine associations between self-citation incidence and publication characteristics.
RESULTS
Medians for author self-citation rate of the most self-citing authors and self-citations were 3.03% (range 0-50) and 1 (range 0-19), respectively. In the univariable analysis, there was no association between self-citation counts and study type (P = 0.41), article topic (P = 0.61), number of authors (P = 0.62), and rank of authors (P = 0.56). Author origin (P = 0.001), gender (P = 0.001) and journal (P = 0.05) were associated with self-citation counts and in the multivariable analysis only origin and gender remained strong self-citation predictors. Asian authors and females self-cited significantly less often than all other regions and male authors.
CONCLUSIONS
Authors in orthodontics do not self-cite at a frequency that suggests potential citation manipulation. Author origin and gender were the only variables associated with citations counts. More bibliometric research is necessary to draw solid conclusions about author self-citation trends in orthodontic literature
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