1,755 research outputs found
Degradation of di-, tri-, tetra-, and pentachlorophenol mixtures in an aerobic biofilter
Chlorophenols are highly toxic xenobiotic compounds, normally found in the effluents of many industries. Due to the high toxicity of these compounds, it is difficult to treat effluent streams containing high concentrations of chlorophenols. The aim of this work is to demonstrate the capabilities of an aerobic submerged filter previously characterized in the degradation of phenol and chlorophenols in the treatment of highly toxic di-, tri-, tetra- and penta- chlorophenols mixtures (200 - 800 mgL-1 as total phenols concentration). It is shown that the system is capable of treating up to 600 mgL-1 of total chlorophenols with excellent reduction values, and biodegradation rates (BDRs) between 87 - 97%, and 34 - 157 mgL-1 day-1, respectively (total organic carbon, TOC degradations up to80%). In the case of the 800 mgL-1, a strong inhibition due to the high toxicity of the mixture was observed. The system reduced the influent toxicity (EC50 or toxic units) by 48 - 76%, even when the initial toxicities of the mixtures were in the range of 40 - 358 toxic units (classified as very toxic). The kinetics of the phenol and TOC degradation were characterized through a first order kinetic expression. The values of TPho, TOCo, k1 and k2 are reported for the biodegradation of the total phenols and for the TOC, respectively. A system with powerful capabilities in the treatment ofindustrial streams, contaminated aquifers or accidentally contaminated municipal wastewaters containing high quantities of chlorophenols, is described
A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes
NGC 6791 is a well studied open cluster1 that it is so close to us that can
be imaged down to very faint luminosities. The main sequence turn-off age (~8
Gyr) and the age derived from the termination of the white dwarf cooling
sequence (~6 Gyr) are significantly different. One possible explanation is that
as white dwarfs cool, one of the ashes of helium burning, 22Ne, sinks in the
deep interior of these stars. At lower temperatures, white dwarfs are expected
to crystallise and phase separation of the main constituents of the core of a
typical white dwarf, 12C and 16O, is expected to occur. This sequence of events
is expected to introduce significant delays in the cooling times, but has not
hitherto been proven. Here we report that, as theoretically anticipated,
physical separation processes occur in the cores of white dwarfs, solving the
age discrepancy for NGC 6791.Comment: 3 pages, 2 figures, published in Natur
Reporte de 4 casos de inversión de cromosoma 9 en una muestra de 4755 líquidos amnióticos en una población Venezolana
La inversión del cromosoma 9, inv (9), es una reordenación cromosómica relativamente común y generalmente se considera como una variante normal. No obstante, varios estudios han sugerido una posible asociación con Síndrome metabólico, obesidad, galactosemia, diabetes Mellitus y aborto espontáneo recurrente. Este estudio tiene como objetivo describir cuatro casos con la misma inversión cromosómica 9, inv (9) (p12; q12), y compararlo con lo que ha sido expuesto en la literatura. Se realizaron una serie de casos retrospectivos. Se evaluó una gran base de datos de informes de amniocentesis realizados en el centro Policlínica Metropolitana de Caracas entre 2005 y 2016. Como parte del protocolo del centro, todas las muestras de líquido amniótico recuperadas se centrifugaron a 800 rpm. Finalmente, se realizó un análisis de 20 bandas en metafase G para el cariotipo. Se recuperaron todos los cariotipos que informaron inv (9) (p12; q12). De 4755 informes de amniocentesis, se identificaron un total de 4 casos de inv (9) (p12; q12) pericéntrico . Según la literatura, este tipo de reordenamiento se ha asociado a algunas enfermedades metabólicas. Este hallazgo está respaldado por el hecho de que esta región cromosómica contiene el factor 1 promotor de insulina y el factor iniciador para la alfa quinasa 3 del factor de iniciación de traducción eucariótico, ambos implicados en la diabetes transitoria. Existe escasa literatura sobre este tipo de inversión, y se necesitan más estudios para un análisis de correlación adecuado. Los resultados de esta breve serie y los hallazgos de la literatura respaldan la importancia de los primeros estudios de cariotipo para identificar posibles asociaciones
Evolutionary and pulsational properties of white dwarf stars
Abridged. White dwarf stars are the final evolutionary stage of the vast
majority of stars, including our Sun. The study of white dwarfs has potential
applications to different fields of astrophysics. In particular, they can be
used as independent reliable cosmic clocks, and can also provide valuable
information about the fundamental parameters of a wide variety of stellar
populations, like our Galaxy and open and globular clusters. In addition, the
high densities and temperatures characterizing white dwarfs allow to use these
stars as cosmic laboratories for studying physical processes under extreme
conditions that cannot be achieved in terrestrial laboratories. They can be
used to constrain fundamental properties of elementary particles such as axions
and neutrinos, and to study problems related to the variation of fundamental
constants.
In this work, we review the essentials of the physics of white dwarf stars.
Special emphasis is placed on the physical processes that lead to the formation
of white dwarfs as well as on the different energy sources and processes
responsible for chemical abundance changes that occur along their evolution.
Moreover, in the course of their lives, white dwarfs cross different
pulsational instability strips. The existence of these instability strips
provides astronomers with an unique opportunity to peer into their internal
structure that would otherwise remain hidden from observers. We will show that
this allows to measure with unprecedented precision the stellar masses and to
infer their envelope thicknesses, to probe the core chemical stratification,
and to detect rotation rates and magnetic fields. Consequently, in this work,
we also review the pulsational properties of white dwarfs and the most recent
applications of white dwarf asteroseismology.Comment: 85 pages, 28 figures. To be published in The Astronomy and
Astrophysics Revie
Perception of shop floor employees regarding senior management support in lean projects and its relationship with initiatives success
Purpose – Over the years, the lean production philosophy has shown satisfactory results for companies from different sectors in different countries. Aiming to contribute to the knowledge base on the mentioned philosophy, this study aims to verify the perception of shop floor employees regarding senior management support in lean projects and its relationship with initiatives success. Design/methodology/approach – Through a literature review, 18 aspects of a lean journey were identified and divided into four constructs by a panel of specialists. This information was used to compose a questionnaire, and a survey was conducted with 198 shop floor employees of two auto parts companies. Data analysis was done via Structural Equation Modeling. Findings – As a general result, it was possible to prove that when employees perceive more significant support from senior management in lean projects, the greater is the perception of initiatives success. Therefore, it is interesting that the involvement of senior management occurs at all stages of the project. Originality/value – The results described here have practical implications, especially for managers interested in implementing lean projects; they must be aware of the importance of senior management support for the success of previous projects
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