2,811 research outputs found
Parallel TREE code for two-component ultracold plasma analysis
The TREE method has been widely used for long-range interaction {\it N}-body
problems. We have developed a parallel TREE code for two-component classical
plasmas with open boundary conditions and highly non-uniform charge
distributions. The program efficiently handles millions of particles evolved
over long relaxation times requiring millions of time steps. Appropriate domain
decomposition and dynamic data management were employed, and large-scale
parallel processing was achieved using an intermediate level of granularity of
domain decomposition and ghost TREE communication. Even though the
computational load is not fully distributed in fine grains, high parallel
efficiency was achieved for ultracold plasma systems of charged particles. As
an application, we performed simulations of an ultracold neutral plasma with a
half million particles and a half million time steps. For the long temporal
trajectories of relaxation between heavy ions and light electrons, large
configurations of ultracold plasmas can now be investigated, which was not
possible in past studies
Driving down the Detection Limit in Microstructured Fiber-Based Chemical Dip Sensors
We present improvements to fluorescence sensing in soft-glass microstructured optical fibers that result in significantly improved sensitivity relative to previously published results. Concentrations of CdSe quantum dots down to 10 pM levels have been demonstrated. We show that the primary limitation to the sensitivity of these systems is the intrinsic fluorescence of the glass itself
A 1D microphysical cloud model for Earth, and Earth-like exoplanets. Liquid water and water ice clouds in the convective troposphere
One significant difference between the atmospheres of stars and exoplanets is
the presence of condensed particles (clouds or hazes) in the atmosphere of the
latter.
The main goal of this paper is to develop a self-consistent microphysical
cloud model for 1D atmospheric codes, which can reproduce some observed
properties of Earth, such as the average albedo, surface temperature, and
global energy budget. The cloud model is designed to be computationally
efficient, simple to implement, and applicable for a wide range of atmospheric
parameters for planets in the habitable zone.
We use a 1D, cloud-free, radiative-convective, and photochemical equilibrium
code originally developed by Kasting, Pavlov, Segura, and collaborators as
basis for our cloudy atmosphere model. The cloud model is based on models used
by the meteorology community for Earth's clouds. The free parameters of the
model are the relative humidity and number density of condensation nuclei, and
the precipitation efficiency. In a 1D model, the cloud coverage cannot be
self-consistently determined, thus we treat it as a free parameter.
We apply this model to Earth (aerosol number density 100 cm^-3, relative
humidity 77 %, liquid cloud fraction 40 %, and ice cloud fraction 25 %) and
find that a precipitation efficiency of 0.8 is needed to reproduce the albedo,
average surface temperature and global energy budget of Earth. We perform
simulations to determine how the albedo and the climate of a planet is
influenced by the free parameters of the cloud model. We find that the
planetary climate is most sensitive to changes in the liquid water cloud
fraction and precipitation efficiency.
The advantage of our cloud model is that the cloud height and the droplet
sizes are self-consistently calculated, both of which influence the climate and
albedo of exoplanets.Comment: To appear in Icaru
Surface Irrigation Systems
In surface irrigation, water is conveyed to the point of infiltration directly on
the soil surface. Thus, the soil surface may be considered as the conveyance
channel boundary. Surface irrigation channels vary widely in shape, size, and
hydraulic characteristics
Nanopods: A New Bacterial Structure and Mechanism for Deployment of Outer Membrane Vesicles
Background:
Bacterial outer membrane vesicles (OMV) are packets of periplasmic material that, via the proteins and other molecules they contain, project metabolic function into the environment. While OMV production is widespread in proteobacteria, they have been extensively studied only in pathogens, which inhabit fully hydrated environments. However, many (arguably most) bacterial habitats, such as soil, are only partially hydrated. In the latter, water is characteristically distributed as films on soil particles that are, on average thinner, than are typical OMV (ca. ≤10 nm water film vs. 20 to >200 nm OMV;).
Methodology/Principal Findings:
We have identified a new bacterial surface structure, termed a "nanopod", that is a conduit for projecting OMV significant distances (e.g., ≥6 µm) from the cell. Electron cryotomography was used to determine nanopod three-dimensional structure, which revealed chains of vesicles within an undulating, tubular element. By using immunoelectron microscopy, proteomics, heterologous expression and mutagenesis, the tubes were determined to be an assembly of a surface layer protein (NpdA), and the interior structures identified as OMV. Specific metabolic function(s) for nanopods produced by Delftia sp. Cs1-4 are not yet known. However, a connection with phenanthrene degradation is a possibility since nanopod formation was induced by growth on phenanthrene. Orthologs of NpdA were identified in three other genera of the Comamonadaceae family, and all were experimentally verified to form nanopods.
Conclusions/Significance:
Nanopods are new bacterial organelles, and establish a new paradigm in the mechanisms by which bacteria effect long-distance interactions with their environment. Specifically, they create a pathway through which cells can effectively deploy OMV, and the biological activity these transmit, in a diffusion-independent manner. Nanopods would thus allow environmental bacteria to expand their metabolic sphere of influence in a manner previously unknown for these organisms
Strategies for prompt searches for GRB afterglows: the discovery of the GRB 001011 optical/near-infrared counterpart using colour-colour selection
We report the discovery of the optical and near-infrared counterparts to GRB
001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously
imaged in the near-infrared by the 3.58-m New Technology Telescope and in the
optical by the 1.54-m Danish Telescope ~8 hr after the gamma-ray event. Here we
implement the colour-colour discrimination technique proposed by Rhoads (2001)
and extend it using near-IR data as well. We present the results provided by an
automatic colour-colour discrimination pipe-line developed to discern the
different populations of objects present in the GRB 001011 error box. Our
software revealed three candidates based on single-epoch images. Second-epoch
observations carried out ~3.2 days after the burst revealed that the most
likely candidate had faded, thus identifying it with the counterpart to the
GRB. In deep R-band images obtained 7 months after the burst a faint
(R=25.38+/-0.25) elongated object, presumably the host galaxy of GRB 001011,
was detected at the position of the afterglow. The GRB 001011 afterglow is the
first discovered with the assistance of colour-colour diagram techniques. We
discuss the advantages of using this method and its application to error boxes
determined by future missions.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 16
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Quartz crystallite size and moganite content as indicators of the mineralogical maturity of the carboniferous chert: the case of cherts from Eastern Asturias (Spain)
Chert samples from different coastal and inland outcrops in the Eastern Asturias (Spain) were mineralogically investigated for the first time for archaeological purposes. X-ray diffraction, X-ray fluorescence, transmission electron microscopy, infrared and Raman spectroscopy and total organic carbon techniques were used. The low content of moganite, since its detection by X-ray diffraction is practically imperceptible, and the crystallite size (over 1000 Å) of the quartz in these cherts would be indicative of its maturity and could potentially be used for dating chert-tools recovered from archaeological sites. Also, this information can constitute essential data to differentiate the cherts and compare them with those used in archaeological tools. However, neither composition nor crystallite size would allow distinguishing between coastal and inland chert outcrops belonging to the same geological formations.This research was funded by the Spanish State Plan for R+D, grant number HAR2017–82557-
Corporate Social Responsibility and Multiple Agency Theory: A case study of internal stakeholder engagement
[Abstract]: Employee engagement via Corporate Social Responsibility (CSR) involves conflicts of
interests among firms, employees and political institutions. We studied the international transfer
of employees in an airline company as a case study of a CSR strategy based on human resource
management. From a double approach of Multiple Agency Theory and Resource-Based
perspective we found that, by increasing worker mobility costs, the European Union hindered
the firm´s CSR strategy of employee engagement. This contrasts with the stated aim of the
European Union to promote worker mobility
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