650 research outputs found
The distance to the LMC cluster NGC 1866 and the surrounding field
We use the Main Sequence stars in the LMC cluster NGC 1866 and of Red Clump
stars in the local field to obtain two independent estimates of the LMC
distance. We apply an empirical Main Sequence-fitting technique based on a
large sample of subdwarfs with accurate {\sl Hipparcos} parallaxes in order to
estimate the cluster distance modulus, and the multicolor Red Clump method to
derive distance and reddening of the LMC field. We find that the Main
Sequence-fitting and the Red Clump distance moduli are in significant
disagreement; NGC 1866 distance is equal to 0.08 (consistent with a previous estimate using the same data
and theoretical Main Sequence isochrones), while the field stars provide 0.07. This difference reflects the more general
dichotomy in the LMC distance estimates found in the literature. Various
possible causes for this disagreement are explored, with particular attention
paid to the still uncertain metallicity of the cluster and the star formation
history of the field stars.Comment: 5 pages, incl. 1 figure, uses emulateapj.sty, ApJ accepte
Openspritzer: an open hardware pressure ejection system for reliably delivering picolitre volumes
The ability to reliably and precisely deliver picolitre volumes is an important component of biological research. Here we describe a high-performance, low-cost, open hardware pressure ejection system (Openspritzer), which can be constructed from off the shelf components. The device is capable of delivering minute doses of reagents to a wide range of biological and chemical systems. In this work, we characterise the performance of the device and compare it to a popular commercial system using twophoton fluorescence microscopy. We found that Openspritzer provides the same level of control over
delivered reagent dose as the commercial system. Next, we demonstrate the utility of Openspritzer in a series of standard neurobiological applications. First, we used Openspritzer to deliver precise amounts of reagents to hippocampal neurons to elicit time- and dose-precise responses on neuronal voltage. Second, we used Openspritzer to deliver infectious viral and bacterial agents to living tissue. This included viral transfection of hippocampal interneurons with channelrhodopsin for the optogenetic manipulation of hippocampal circuitry with light. We anticipate that due to its high performance and
low cost Openspritzer will be of interest to a broad range of researchers working in the life and physical
sciences
On the accuracy of ERS-1 orbit predictions
Since the launch of ERS-1, the D-PAF (German Processing and Archiving Facility) provides regularly orbit predictions for the worldwide SLR (Satellite Laser Ranging) tracking network. The weekly distributed orbital elements are so called tuned IRV's and tuned SAO-elements. The tuning procedure, designed to improve the accuracy of the recovery of the orbit at the stations, is discussed based on numerical results. This shows that tuning of elements is essential for ERS-1 with the currently applied tracking procedures. The orbital elements are updated by daily distributed time bias functions. The generation of the time bias function is explained. Problems and numerical results are presented. The time bias function increases the prediction accuracy considerably. Finally, the quality assessment of ERS-1 orbit predictions is described. The accuracy is compiled for about 250 days since launch. The average accuracy lies in the range of 50-100 ms and has considerably improved
Laser ranging network performance and routine orbit determination at D-PAF
ERS-1 is now about 8 months in orbit and has been tracked by the global laser network from the very beginning of the mission. The German processing and archiving facility for ERS-1 (D-PAF) is coordinating and supporting the network and performing the different routine orbit determination tasks. This paper presents details about the global network status, the communication to D-PAF and the tracking data and orbit processing system at D-PAF. The quality of the preliminary and precise orbits are shown and some problem areas are identified
New optical and near-infrared Surface Brightness Fluctuations models. A primary distance indicator ranging from Globular Clusters to distant galaxies?
We present new theoretical models for Surface Brightness Fluctuations (SBF)
both for optical and near-infrared bands in standard ground-based and Hubble
Space Telescope filter systems. Simple Stellar Population simulations are
adopted. Models cover the age and metallicity ranges from to and
from to 0.04 respectively. Effects due to the variation of the
Initial Mass Function and the stellar color-temperature relations are explored.
Particular attention is devoted to very bright stars in the color-magnitude
diagram and to investigate the effects of mass loss along the Red Giant Branch
(RGB) and the Asymptotic Giant Branch (AGB). It is found that and bands
SBF amplitudes are powerful diagnostics for the morphology of the Horizontal
Branch and the Post-AGB stars population. We point out that a careful treatment
of mass loss process along the RGB and AGB is fundamental in determining
reliable SBF evaluations. The SBF measurements are used to give robust
constraints on the evolution of AGB stars, suggesting that mass loss activity
on AGB stars should be twice more efficient than on the RGB stars. Our models
are able to reproduce the absolute SBF magnitudes of the Galactic Globular
Clusters and of galaxies, and their integrated colors. New calibrations of
absolute SBF magnitude in , , , and photometric filters are
provided, which appear reliable enough to directly gauge distances bypassing
other distance indicators. The SBF technique is also used as stellar population
tracer to derive age and metallicity of a selected sample of galaxies of known
distances. Finally, {\it SBF color} versus {\it integrated color} diagrams are
proposed as particularly useful in removing the well known {\it age-metallicity
degeneracy} affecting our knowledge of remote stellar systems.Comment: AJ accepted, 46 pages, 21 figures, 10 tables, uses aastex.cl
Alternative mechanism for bacteriophage adsorption to the motile bacterium Caulobacter crescentus
2D and 3D cryo-electron microscopy, together with adsorption kinetics assays of ÏCb13 and ÏCbK phage-infected Caulobacter crescentus, provides insight into the mechanisms of infection. ÏCb13 and ÏCbK actively interact with the flagellum and subsequently attach to receptors on the cell pole. We present evidence that the first interaction of the phage with the bacterial flagellum takes place through a filament on the phage head. This contact with the flagellum facilitates concentration of phage particles around the receptor (i.e., the pilus portals) on the bacterial cell surface, thereby increasing the likelihood of infection. Phage head filaments have not been well characterized and their function is described here. Phage head filaments may systematically underlie the initial interactions of phages with their hosts in other systems and possibly represent a widespread mechanism of efficient phage propagation
An optical/NIR survey of globular clusters in early-type galaxies III. On the colour bimodality of GC systems
The interpretation that bimodal colour distributions of globular clusters
(GCs) reflect bimodal metallicity distributions has been challenged.
Non-linearities in the colour to metallicity conversions caused by the
horizontal branch (HB) stars may be responsible for transforming a unimodal
metallicity distribution into a bimodal (optical) colour distribution. We study
optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0
galaxies. We test whether the bimodal feature, generally present in optical
colour distributions, remains in the optical/NIR ones. The latter colour
combination is a better metallicity proxy than the former. We use KMM and GMM
tests to quantify the probability that different colour distributions are
better described by a bimodal, as opposed to a unimodal distribution. We find
that double-peaked colour distributions are more commonly seen in optical than
in optical/NIR colours. For some of the galaxies where the optical (g-z)
distribution is clearly bimodal, the (g-K) and (z-K) distributions are better
described by a unimodal distribution. The two most cluster-rich galaxies in our
sample, NGC4486 and NGC4649, show some interesting differences. The (g-K)
distribution of NGC4649 is better described by a bimodal distribution, while
this is true for the (g-K) distribution of NGC4486 GCs only if restricted to a
brighter sub-sample with small K-band errors (< 0.05 mag). Formally, the K-band
photometric errors cannot be responsible for blurring bimodal metallicity
distributions to unimodal (g-K) colour distributions. However, simulations
including the extra scatter in the colour-colour diagrams (not fully accounted
for in the photometric errors) show that such scatter may contribute to the
disappearance of bimodality in (g-K) for the full NGC4486 sample. For the less
cluster-rich galaxies results are inconclusive due to poorer statistics.
[Abridged]Comment: A&A accepted, 15 pages, 10 figures, 4 table
Age-related differences in patterns of criminal activity among a large sample of polydrug injectors in Australia
Background: The relationship between age and criminal activity among drug-using populations is poorly understood. Methods: Data from 10 years of repeat cross-sectional surveys of sentinel samples of regular people who inject drugs (PWID) across Australia (n=5844) were used to explore the relationship between age and past-month drug dealing, property crime and violent crime, and past-year arrest. Descriptive statistics were used to explore the prevalence and frequency of each outcome. The relationship between age and each outcome was measured using multivariable Poisson regression with robust error variance. Results: After adjusting for confounding factors, each 5-year increase in age was associated with significant reductions in drug dealing (adjusted incidence rate ratio [AIRR]: 0.90, 95% confidence interval [CI]: 0.87â0.94), property crime (AIRR: 0.85, 95% CI: 0.82â0.89) and violent crime (AIRR: 0.77, 95% CI: 0.70â0.85). Older participants were also significantly less likely to report being arrested in the past 12 months (AIRR: 0.91, 95% CI: 0.88â0.93). Conclusions: Younger PWID are more heavily involved in criminal activity compared with their older counterparts. This study highlights the need for early intervention programmes to prevent offending behaviour becoming entrenched, as well as continued efforts to redirect young PWID away from the criminal justice system and into treatment and education programmes
Open Government Data: A Focus on Key Economic and Organizational Drivers
Grounding the analysis on multidisciplinary literature on the topic, the existing EU legislation and relevant examples, this working paper aims at highlighting some key economic and organizational aspects of the "Open Government Data" paradigm and its drivers and implications within and outside Public Administrations. The discussion intends to adopt an "Internet Science" perspective, taking into account as enabling factors the digital environment itself, as well as specific models and tools. More "traditional" and mature markets grounded on Public Sector Information are also considered, in order to indirectly detect the main differences with respect to the aforementioned paradig
The politicisation of evaluation: constructing and contesting EU policy performance
Although systematic policy evaluation has been conducted for decades and has been growing strongly within the European Union (EU) institutions and in the member states, it remains largely underexplored in political science literatures. Extant work in political science and public policy typically focuses on elements such as agenda setting, policy shaping, decision making, or implementation rather than evaluation. Although individual pieces of research on evaluation in the EU have started to emerge, most often regarding policy âeffectivenessâ (one criterion among many in evaluation), a more structured approach is currently missing. This special issue aims to address this gap in political science by focusing on four key focal points: evaluation institutions (including rules and cultures), evaluation actors and interests (including competencies, power, roles and tasks), evaluation design (including research methods and theories, and their impact on policy design and legislation), and finally, evaluation purpose and use (including the relationships between discourse and scientific evidence, political attitudes and strategic use). The special issue considers how each of these elements contributes to an evolving governance system in the EU, where evaluation is playing an increasingly important role in decision making
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