469 research outputs found
Isotopic Insights into Biological Regulation of Zinc in Contaminated Systems
AbstractAquatic organisms use a variety ofbiogeochemical reactions to regulate essential and non-essential trace metals. Many of these mechanisms can lead to isotopic fractionation, thus measurement of metal isotopes may yield insights into the processes by which organisms respond to metal exposure. We illustrate these concepts with two case studies, one involving an intra- and the other an extra-cellular mechanism of Zn sequestration. In the first study, the mayflyNeocloeontrianguliferwas grown in the laboratory, and fed a diet of Zn-doped diatoms at Zn levels exceeding the requirements for normal mayfly life functions. The N. trianguliferlarvae consumed the diatoms and retained their Zn isotopic signature. Upon metamorphosis, the subimago life stage lost Zn mass either in the exuvia or by excretion, and the Zn retainedwas isotopically enriched. Thus, Zn uptake is non-fractionating, but Zn regulation favors the lighter isotope. Thus the Zn remaining in the subimago was isotopically heavier. In the second study, Zn was adsorbed on the cell walls and exopolysaccharide secretions of cyanobacteria, which favored the heavier Zn isotope.Continued adsorption eventually resulted in nucleation and biomineralization of hydrozincite {Zn5(CO3)2(OH)6}. These case studies demonstrate the utility of Zn isotopes to provide insights into how aquatic insects respond to metal exposure
Effects of a nanoscopic filler on the structure and dynamics of a simulated polymer melt and the relationship to ultra-thin films
We perform molecular dynamics simulations of an idealized polymer melt
surrounding a nanoscopic filler particle to probe the effects of a filler on
the local melt structure and dynamics. We show that the glass transition
temperature of the melt can be shifted to either higher or lower
temperatures by appropriately tuning the interactions between polymer and
filler. A gradual change of the polymer dynamics approaching the filler surface
causes the change in the glass transition. We also find that while the bulk
structure of the polymers changes little, the polymers close to the surface
tend to be elongated and flattened, independent of the type of interaction we
study. Consequently, the dynamics appear strongly influenced by the
interactions, while the melt structure is only altered by the geometric
constraints imposed by the presence of the filler. Our findings show a strong
similarity to those obtained for ultra-thin polymer films (thickness nm) suggesting that both ultra-thin films and filled-polymer systems might
be understood in the same context
Measurement schemes for the spin quadratures on an ensemble of atoms
We consider how to measure collective spin states of an atomic ensemble based
on the recent multi-pass approaches for quantum interface between light and
atoms. We find that a scheme with two passages of a light pulse through the
atomic ensemble is efficient to implement the homodyne tomography of the spin
state. Thereby, we propose to utilize optical pulses as a phase-shifter that
rotates the quadrature of the spins. This method substantially simplifies the
geometry of experimental schemes.Comment: 4pages 2 figure
RFID en el servicio bibliotecario de la UTM
The central library of the Technical University of Manabí (UTM), offers the service of electronic equipment loans (laptops and tablets), in which theft has been presented. In the present article the integration of identification technologies through a web application is exposed. To do this, the requirements were raised, systems analysis and identification technologies were analyzed. Based on the study of art, the development methodology, programming languages, tools and technologies applied in the solution were described, the system architecture was designed with visual / audible alarm, the integrating system was developed and implemented and finally functional tests were carried out. As a result, it was evidenced that using bar code and RFID technology in the library service, there is better control of the entry and exit of electronic equipment, preventing any attempt at theft, and the university and general community receive a quality and speedy service.La biblioteca central de la Universidad Técnica de Manabí (Ecuador)brinda el servicio de préstamos de equipos electrónicos (portátiles y tabletas), en el que se han presentado hurtos de los mismos. En este artículo se expone la integración de RFID a través de una aplicación web. Para ello, se realizó el levantamiento de requerimientos, análisis de sistemas y de tecnologías de identificación, tomando como base el estudio del arte se describió la metodología de desarrollo, lenguajes de programación, herramientas y tecnologías aplicadas en la solución, se diseñó la arquitectura del sistema con alarma visual/sonora, se desarrolló e implantó el sistema integrador y, finalmente, se ejecutaron pruebas de funcionamiento. Como resultado se evidenció que al utilizar tecnología de código de barras y RFID en el servicio bibliotecario existe un mejor control de entrada y salida de los equipos electrónicos, previniendo de cualquier intento de hurto; a su vez, la comunidad universitaria y general recibe un servicio de calidad y rapidez
Separability and entanglement in 2x3xN composite quantum systems
The separability and entanglement of quantum mixed states in \Cb^2 \otimes
\Cb^3 \otimes \Cb^N composite quantum systems are investigated. It is shown
that all quantum states with positive partial transposes and rank
are separable.Comment: Latex, 15 page
High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Be star opportunity
Planet formation studies are often focused on solar-type stars, implicitly
considering our Sun as reference point. This approach overlooks, however, that
Herbig Ae/Be stars are in some sense much better targets to study planet
formation processes empirically, with their disks generally being larger,
brighter and simply easier to observe across a large wavelength range. In
addition, massive gas giant planets have been found on wide orbits around early
type stars, triggering the question if these objects did indeed form there and,
if so, by what process. In the following I briefly review what we currently
know about the occurrence rate of planets around intermediate mass stars,
before discussing recent results from Herbig Ae/Be stars in the context of
planet formation. The main emphasis is put on spatially resolved polarized
light images of potentially planet forming disks and how these images - in
combination with other data - can be used to empirically constrain (parts of)
the planet formation process. Of particular interest are two objects, HD100546
and HD169142, where, in addition to intriguing morphological structures in the
disks, direct observational evidence for (very) young planets has been
reported. I conclude with an outlook, what further progress we can expect in
the very near future with the next generation of high-contrast imagers at 8-m
class telescopes and their synergies with ALMA.Comment: Accepted by Astrophysics and Space Science as invited short review in
special issue about Herbig Ae/Be stars; 12 pages incl. 5 figures, 2 tables
and reference
Improved Holographic QCD
We provide a review to holographic models based on Einstein-dilaton gravity
with a potential in 5 dimensions. Such theories, for a judicious choice of
potential are very close to the physics of large-N YM theory both at zero and
finite temperature. The zero temperature glueball spectra as well as their
finite temperature thermodynamic functions compare well with lattice data. The
model can be used to calculate transport coefficients, like bulk viscosity, the
drag force and jet quenching parameters, relevant for the physics of the
Quark-Gluon Plasma.Comment: LatEX, 65 pages, 28 figures, 9 Tables. Based on lectures given at
several Schools. To appear in the proceedinds of the 5th Aegean School
(Milos, Greece
Measurement-based quantum foundations
I show that quantum theory is the only probabilistic framework that permits
arbitrary processes to be emulated by sequences of local measurements. This
supports the view that, contrary to conventional wisdom, measurement should not
be regarded as a complex phenomenon in need of a dynamical explanation but
rather as a primitive -- and perhaps the only primitive -- operation of the
theory.Comment: 8 pages, version to appear in Found. Phy
Low-mass pre--main-sequence stars in the Magellanic Clouds
[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar
stars form in very large numbers. Most attractive places for catching low-mass
star formation in the act are young stellar clusters and associations, still
(half-)embedded in star-forming regions. The low-mass stars in such regions are
still in their pre--main-sequence (PMS) evolutionary phase. The peculiar nature
of these objects and the contamination of their samples by the evolved
populations of the Galactic disk impose demanding observational techniques for
the detection of complete numbers of PMS stars in the Milky Way. The Magellanic
Clouds, the companion galaxies to our own, demonstrate an exceptional star
formation activity. The low extinction and stellar field contamination in
star-forming regions of these galaxies imply a more efficient detection of
low-mass PMS stars than in the Milky Way, but their distance from us make the
application of special detection techniques unfeasible. Nonetheless, imaging
with the Hubble Space Telescope yield the discovery of solar and sub-solar PMS
stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of
such objects are identified as the low-mass stellar content of their
star-forming regions, changing completely our picture of young stellar systems
outside the Milky Way, and extending the extragalactic stellar IMF below the
persisting threshold of a few solar masses. This review presents the recent
developments in the investigation of PMS stars in the Magellanic Clouds, with
special focus on the limitations by single-epoch photometry that can only be
circumvented by the detailed study of the observable behavior of these stars in
the color-magnitude diagram. The achieved characterization of the low-mass PMS
stars in the Magellanic Clouds allowed thus a more comprehensive understanding
of the star formation process in our neighboring galaxies.Comment: Review paper, 26 pages (in LaTeX style for Springer journals), 4
figures. Accepted for publication in Space Science Review
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