74 research outputs found
Teaching engineering design through Lego Mindstorms
This paper examines a particular methodology of teaching engineering design to undergraduate engineering
students, which relies on Lego® Mindstormsâ¢. A number of important issues are addressed,
including the timing of the design module within the programme, prior knowledge required and
assessment components. The module, which has been running for three years, was found to have
many positive attributes, not only in relation to the core design activity, but also in generating good
team-building and engaging students with the degree programme
Flow-Driven Cloud Formation and Fragmentation: Results From Eulerian and Lagrangian Simulations
The fragmentation of shocked flows in a thermally bistable medium provides a
natural mechanism to form turbulent cold clouds as precursors to molecular
clouds. Yet because of the large density and temperature differences and the
range of dynamical scales involved, following this process with numerical
simulations is challenging. We compare two-dimensional simulations of
flow-driven cloud formation without self-gravity, using the Lagrangian Smoothed
Particle Hydrodynamics (SPH) code VINE and the Eulerian grid code Proteus.
Results are qualitatively similar for both methods, yet the variable spatial
resolution of the SPH method leads to smaller fragments and thinner filaments,
rendering the overall morphologies different. Thermal and hydro-dynamical
instabilities lead to rapid cooling and fragmentation into cold clumps with
temperatures below 300K. For clumps more massive than 1 Msun/pc, the clump mass
function has an average slope of -0.8. The internal velocity dispersion of the
clumps is nearly an order of magnitude smaller than their relative motion,
rendering it subsonic with respect to the internal sound speed of the clumps,
but supersonic as seen by an external observer. For the SPH simulations most of
the cold gas resides at temperatures below 100K, while the grid-based models
show an additional, substantial component between 100 and 300K. Independently
of the numerical method our models confirm that converging flows of warm
neutral gas fragment rapidly and form high-density, low-temperature clumps as
possible seeds for star formation.Comment: 9 pages, 8 figures, MNRAS accepte
Temporal and spatial variability of dissolved organic and inorganic phosphorus, and metrics of phosphorus bioavailability in an upwelling-dominated coastal system
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 110 (2005): C10S13, doi:10.1029/2004JC002837.High-frequency temporal and spatial shifts in the various dissolved P pools (total, inorganic, and organic) are linked to upwelling/relaxation events and to phytoplankton bloom dynamics in the upwelling-dominated Oregon coastal system. The presence and regulation of alkaline phosphatase activity (APA) is apparent in the bulk phytoplankton population and in studies of cell-specific APA using Enzyme Labeled Fluorescence (ELF®). Spatial and temporal variability are also evident in phytoplankton community composition and in APA. The spatial pattern of dissolved phosphorus and APA variability can be explained by bottom-controlled patterns of upwelling, and flushing times of different regions within the study area. The presence of APA in eukaryotic taxa indicates that dissolved organic phosphorus (DOP) may contribute to phytoplankton P nutrition in this system, highlighting the need for a more complete understanding of P cycling and bioavailability in the coastal ocean.KCR acknowledges WHOI for
rapid-response funding that made possible participation on this first
COAST cruise, and NSF-OCE grant 0119134 for support of subsequent
work on these and other COAST samples
Conformally Flat Smoothed Particle Hydrodynamics: Application to Neutron Star Mergers
We present a new 3D SPH code which solves the general relativistic field +
hydrodynamics equations in the conformally flat approximation. Several test
cases are considered to test different aspects of the code. We finally apply
then the code to the coalescence of a neutron star binary system. The neutron
stars are modeled by a polytropic equation of state (EoS) with adiabatic
indices , and . We calculate the
gravitational wave signals, luminosities and frequency spectra by employing the
quadrupole approximation for emission and back reaction in the slow motion
limit. In addition, we consider the amount of ejected mass.Comment: 23 pages, 12 figures. Accepted for publication in Phys. Rev. D. v3:
Final Versio
Magnetic field amplification and X-ray emission in galaxy minor mergers
We investigate the magnetic field evolution in a series of galaxy minor
mergers using the N-body/smoothed particle hydrodynamics (SPH) code
\textsc{Gadget}. The simulations include the effects of radiative cooling, star
formation and supernova feedback. Magnetohydrodynamics (MHD) is implemented
using the SPH method. We present 32 simulations of binary mergers of disc
galaxies with mass ratios of 2:1 up to 100:1, whereby we have additionally
varied the initial magnetic field strengths, disc orientations and resolutions.
We investigate the amplification of a given initial magnetic field within the
galaxies and an ambient intergalactic medium (IGM) during the interaction. We
find that the magnetic field strengths of merger remnants with mass ratios up
to 10:1 saturate at a common value of several G. For higher mass ratios,
the field strength saturates at lower values. The saturation values correspond
to the equipartition value of magnetic and turbulent energy density. The
initial magnetization, disc orientation and numerical resolution show only
minor effects on the saturation value of the magnetic field. We demonstrate
that a higher impact energy of the progenitor galaxies leads to a more
efficient magnetic field amplification. The magnetic and turbulent energy
densities are higher for larger companion galaxies, consistent with the higher
impact energy supplied to the system. We present a detailed study of the
evolution of the temperature and the bolometric X-ray luminosity within the
merging systems. Thereby we find that magnetic fields cause a more efficient
increase of the IGM temperature and the corresponding IGM X-ray luminosity
after the first encounter. However, the presence of magnetic fields does not
enhance the total X-ray luminosity. Generally, the final value of the X-ray
luminosity is even clearly lower for higher initial magnetic fields.Comment: 20 pages, 12 figures. Submitted to MNRA
Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis
BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London
Formation versus destruction: the evolution of the star cluster population in galaxy mergers
(Abridged) Interacting galaxies are well-known for their high star formation
rates and rich star cluster populations, but the rapidly changing tidal field
can also efficiently destroy clusters. We use numerical simulations of merging
disc galaxies to investigate which mechanism dominates. The simulations include
a model for the formation and dynamical disruption of the entire star cluster
population. We find that the dynamical heating of clusters by tidal shocks is
about an order of magnitude higher in interacting galaxies than in isolated
galaxies. This is driven by the increased gas density, and is sufficient to
destroy star clusters at a higher rate than new clusters are formed: the total
number of clusters in the merger remnant is 2-50% of the amount in the
progenitor discs, with low-mass clusters being disrupted preferentially. By
adopting observationally motivated selection criteria, we find that the
observed surplus of star clusters in nearby merging galaxies is caused by the
bias to detect young, massive clusters. We provide a general expression for the
survival fraction of clusters, which increases with the gas depletion
time-scale. Due to the preferential disruption of low-mass clusters, the mass
distribution of the surviving star clusters in a merger remnant develops a peak
at a mass of about 10^3 Msun, which evolves to higher masses at a rate of
0.3-0.4 dex per Gyr. The peak mass initially depends weakly on the
galactocentric radius, but this correlation disappears as the system ages. We
discuss the similarities between the cluster populations of the simulated
merger remnants and (young) globular cluster systems. Our results suggest that
the combination of cluster formation and destruction should be widespread in
the dense star-forming environments at high redshifts, which could provide a
natural origin to present-day globular cluster systems.Comment: 15 pages, 9 figures, 2 tables; Accepted for publication in MNRAS. A
movie of the full time sequence in Figure 1 can be found at
http://www.mpa-garching.mpg.de/~diederik/1m11clusters.htm
Dissolved organic phosphorus uptake by marine phytoplankton is enhanced by the presence of dissolved organic nitrogen
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