| 1. |
- Abelev, B., et al.
(författare)
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Technical Design Report for the Upgrade of the ALICE Inner Tracking System
- 2014
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
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Tidskriftsartikel (refereegranskat)abstract
- LICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. A key element of the ALICE upgrade is the construction of a new, ultra-light, high-resolution Inner Tracking System (ITS) based on monolithic CMOS pixel detectors. The primary focus of the ITS upgrade is on improving the performance for detection of heavy-flavour hadrons, and of thermal photons and low-mass di-electrons emitted by the QGP. With respect to the current detector, the new Inner Tracking System will significantly enhance the determination of the distance of closest approach to the primary vertex, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a 50 μm thick CMOS pixel sensor with a pixel pitch of about 30×30 μm2. This document, submitted to the LHCC (LHC experiments Committee) in September 2013, presents the design goals, a summary of the R&D activities, with focus on the technical implementation of the main detector components, and the projected detector and physics performance.
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| 2. |
- Adamo, A., et al.
(författare)
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Revealing a ring-like cluster complex in a tidal tail of the starburst galaxy NGC 2146
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 426:2, s. 1185-1194
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a ring-like cluster complex in the starburst galaxy NGC?2146. The Ruby Ring, so named due to its appearance, shows a clear ring-like distribution of star clusters around a central object. It is located in one of the tidal streams that surround the galaxy. NGC?2146 is part of the Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/F336W data have added critical information to the available archival Hubble Space Telescope imaging set of NGC?2146, allowing us to determine ages, masses and extinctions of the clusters in the Ruby Ring. These properties have then been used to investigate the formation of this extraordinary system. We find evidence of a spatial and temporal correlation between the central cluster and the clusters in the ring. The latter are about 4?Myr younger than the central cluster, which has an age of 7?Myr. This result is supported by the Ha emission which is strongly coincident with the ring, and weaker at the position of the central cluster. From the derived total Ha luminosity of the system, we constrain the star formation rate density to be quite high (SSFR = 0.47?M??yr-1?kpc-2). The Ruby Ring is the product of an intense and localized burst of star formation, similar to the extended cluster complexes observed in M?51 and the Antennae, but more impressive because it is quite isolated. The central cluster contains only 5 per cent of the total stellar mass in the clusters that are determined within the complex. The ring-like morphology, the age spread and the mass ratio support a triggering formation scenario for this complex. We discuss the formation of the Ruby Ring in a collect and collapse framework. The predictions made by this model agree quite well with the estimated bubble radius and expansion velocity produced by the feedback from the central cluster, making the Ruby Ring an interesting case of triggered star formation.
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| 3. |
- Konstantopoulos, I. S., et al.
(författare)
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THE SNAPSHOT HUBBLE U-BAND CLUSTER SURVEY (SHUCS). I. SURVEY DESCRIPTION AND FIRST APPLICATION TO THE MIXED STAR CLUSTER POPULATION OF NGC 4041
- 2013
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 145:5, s. 137-
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Tidskriftsartikel (refereegranskat)abstract
- We present the Snapshot Hubble U-band Cluster Survey (SHUCS), a project aimed at characterizing the star cluster populations of 10 nearby galaxies (d < 23 Mpc, half within approximate to 12 Mpc) through new F336W (U-band equivalent) imaging from Wide Field Camera 3, and archival BVI-equivalent data with the Hubble Space Telescope. Completing the UBVI baseline reduces the age-extinction degeneracy of optical colors, thus enabling the measurement of reliable ages and masses for the thousands of clusters covered by our survey. The sample consists chiefly of face-on spiral galaxies at low inclination, in various degrees of isolation (isolated, in group, merging), and includes two active galactic nucleus hosts. This first paper outlines the survey itself, the observational datasets, the analysis methods, and presents a proof-of-concept study of the large-scale properties and star cluster population of NGC 4041, a massive SAbc galaxy at a distance of approximate to 23 Mpc, and part of a small grouping of six giant members. We resolve two structural components with distinct stellar populations, a morphology more akin to merging and interacting systems. We also find strong evidence of a truncated, Schechter-type mass function, and a similarly segmented luminosity function. These results indicate that binning must erase much of the substructure present in the mass and luminosity functions, and might account for the conflicting reports on the intrinsic shape of these functions in the literature. We also note a tidal feature in the outskirts of the galaxy in Galaxy Evolution Explorer UV imaging, and follow it up with a comprehensive multi-wavelength study of NGC 4041 and its parent group. We deduce a minor merger as a likely cause of its segmented structure and the observed pattern of a radially decreasing star formation rate. We propose that combining the study of star cluster populations with broadband metrics is not only advantageous, but often easily achievable thorough archival datasets.
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| 4. |
- Wiedensohler, A., et al.
(författare)
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Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions
- 2012
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 5:3, s. 657-685
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Tidskriftsartikel (refereegranskat)abstract
- Mobility particle size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide range of applications in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards and guidelines with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. Technical standards were developed for a minimum requirement of mobility size spectrometry to perform long-term atmospheric aerosol measurements. Technical recommendations include continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyzer. We compared commercial and custom-made inversion routines to calculate the particle number size distributions from the measured electrical mobility distribution. All inversion routines are comparable within few per cent uncertainty for a given set of raw data. Furthermore, this work summarizes the results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research) and ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) to determine present uncertainties especially of custom-built mobility particle size spectrometers. Under controlled laboratory conditions, the particle number size distributions from 20 to 200 nm determined by mobility particle size spectrometers of different design are within an uncertainty range of around +/- 10% after correcting internal particle losses, while below and above this size range the discrepancies increased. For particles larger than 200 nm, the uncertainty range increased to 30%, which could not be explained. The network reference mobility spectrometers with identical design agreed within +/- 4% in the peak particle number concentration when all settings were done carefully. The consistency of these reference instruments to the total particle number concentration was demonstrated to be less than 5%. Additionally, a new data structure for particle number size distributions was introduced to store and disseminate the data at EMEP (European Monitoring and Evaluation Program). This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.
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| 5. |
- Eierhoff, T., et al.
(författare)
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A lipid zipper triggers bacterial invasion
- 2014
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424. ; 111:35, s. 12895-12900
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Tidskriftsartikel (refereegranskat)abstract
- Glycosphingolipids are important structural constituents of cellular membranes. They are involved in the formation of nanodomains ("lipid rafts"), which serve as important signaling platforms. Invasive bacterial pathogens exploit these signaling domains to trigger actin polymerization for the bending of the plasma membrane and the engulfment of the bacterium-a key process in bacterial uptake. However, it is unknown whether glycosphingolipids directly take part in the membrane invagination process. Here, we demonstrate that a "lipid zipper," which is formed by the interaction between the bacterial surface lectin LecA and its cellular receptor, the glycosphingolipid Gb3, triggers plasma membrane bending during host cell invasion of the bacterium Pseudomonas aeruginosa. In vitro experiments with Gb3-containing giant unilamellar vesicles revealed that LecA/Gb3-mediated lipid zippering was sufficient to achieve complete membrane engulfment of the bacterium. In addition, theoretical modeling elucidated that the adhesion energy of the LecA-Gb3 interaction is adequate to drive the engulfment process. In cellulo experiments demonstrated that inhibition of the LecA/Gb3 lipid zipper by either lecA knockout, Gb3 depletion, or application of soluble sugars that interfere with LecA binding to Gb3 significantly lowered P. aeruginosa uptake by host cells. Of note, membrane engulfment of P. aeruginosa occurred independently of actin polymerization, thus corroborating that lipid zippering alone is sufficient for this crucial first step of bacterial host-cell entry. Our study sheds new light on the impact of glycosphingolipids in the cellular invasion of bacterial pathogens and provides a mechanistic explication of the initial uptake processes.
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| 6. |
- Bastian, N., et al.
(författare)
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Evidence for environmentally dependent cluster disruption in M83
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925. ; 417:1, s. l6-L10
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Tidskriftsartikel (refereegranskat)abstract
- Using multiwavelength imaging from the Wide Field Camera 3 on the Hubble Space Telescope we study the stellar cluster populations of two adjacent fields in the nearby face-on spiral galaxy, M83. The observations cover the galactic centre and reach out to similar to 6 kpc, thereby spanning a large range of environmental conditions, ideal for testing empirical laws of cluster disruption. The clusters are selected by visual inspection to be centrally concentrated, symmetric and resolved on the images. We find that a large fraction of objects detected by automated algorithms (e. g. SEXTRACTOR or DAOFIND) are not clusters, but rather are associations. These are likely to disperse into the field on time-scales of tens of Myr due to their lower stellar densities and not due to gas expulsion (i.e. they were never gravitationally bound). We split the sample into two discrete fields (inner and outer regions of the galaxy) and search for evidence of environmentally dependent cluster disruption. Colour-colour diagrams of the clusters, when compared to simple stellar population models, already indicate that a much larger fraction of the clusters in the outer field are older by tens of Myr than in the inner field. This impression is quantified by estimating each cluster's properties (age, mass and extinction) and comparing the age/mass distributions between the two fields. Our results are inconsistent with 'universal' age and mass distributions of clusters, and instead show that the ambient environment strongly affects the observed populations.
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| 7. |
- Bastian, N., et al.
(författare)
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Stellar clusters in M83 : formation, evolution, disruption and the influence of the environment
- 2012
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 419:3, s. 2606-2622
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Tidskriftsartikel (refereegranskat)abstract
- We study the stellar cluster population in two adjacent fields in the nearby, face-on spiral galaxy M83 using multiwavelength Wide Field Camera 3/Hubble Space Telescope imaging. After automatic detection procedures, the clusters are selected through visual inspection to be centrally concentrated, symmetric, and resolved on the images, which allows us to differentiate between clusters and likely unbound associations. We compare our sample with previous studies and show that the differences between the catalogues are largely due to the inclusion of a large numbers of diffuse associations within previous catalogues as well as the inclusion of the central starburst region, where the completeness limit is significantly worse than in the surrounding regions. We derive the size distribution of the clusters, which is well described by a lognormal distribution with a peak at ˜2.5 pc, and find evidence for an expansion in the half-light radius of clusters with age. The luminosity function of the clusters is well approximated by a power law with an index of -2 over most of the observed range; however, a steepening is seen at MV=-9.3 and -8.8 in the inner and outer fields, respectively. Additionally, we show that the cluster population is inconsistent with a pure power-law mass distribution, but instead exhibits a truncation at the high-mass end. If described as a Schechter function, the characteristic mass is 1.6 × 105 and 0.5 × 105 M&sun; for the inner and outer fields, respectively, in agreement with previous estimates of other cluster populations in spiral galaxies. Comparing the predictions of the mass-independent disruption (MID) and mass-dependent disruption (MDD) scenarios with the observed distributions, we find that both models can accurately fit the data. However, for the MID case, the fraction of clusters destroyed (or mass lost) per decade in age is dependent on the environment; hence, the age and mass distributions of clusters are not universal. In the MDD case, the disruption time-scale scales with galactocentric distance (being longer in the outer regions of the galaxy) in agreement with analytic and numerical predictions. Finally, we discuss the implications of our results on other extragalactic surveys, focusing on the fraction of stars that form in clusters and the need (or lack thereof) for infant mortality.
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| 8. |
- Ryon, J. E., et al.
(författare)
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THE SNAPSHOT HUBBLE U-BAND CLUSTER SURVEY (SHUCS). II. THE STAR CLUSTER POPULATION OF NGC 2997
- 2014
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 148:2, s. 33-
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Tidskriftsartikel (refereegranskat)abstract
- We study the star cluster population of NGC 2997, a giant spiral galaxy located at 9.5 Mpc and targeted by the Snapshot Hubble U-band Cluster Survey (SHUCS). Combining our U-band imaging from SHUCS with archival BVI imaging from the Hubble Space Telescope, we select a high confidence sample of clusters in the circumnuclear ring and disk through a combination of automatic detection procedures and visual inspection. The cluster luminosity functions in all four filters can be approximated by power laws with indices of -1.7 to -2.3. Some deviations from pure power-law shape are observed, hinting at the presence of a high-mass truncation in the cluster mass function. However, upon inspection of the cluster mass function, we find it is consistent with a pure power law of index -2.2 +/- 0.2 despite a slight bend at similar to 2.5 x 10(4) M-circle dot. No statistically significant truncation is observed. From the cluster age distributions, we find a low rate of disruption(zeta similar to -0.1) in both the disk and circumnuclear ring. Finally, we estimate the cluster formation efficiency (Gamma) over the last 100 Myr in each region, finding 7% +/- 2% for the disk, 12% +/- 4% for the circumnuclear ring, and 10% +/- 3% for the entire UBVI footprint. This study highlights the need for wide-field UBVI coverage of galaxies to study cluster populations in detail, though a small sample of clusters can provide significant insight into the characteristics of the population.
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| 9. |
- Aurand, Bastian, et al.
(författare)
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Enhanced radiation pressure-assisted acceleration by temporally tuned counter-propagating pulses
- 2014
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 83-86
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Tidskriftsartikel (refereegranskat)abstract
- Within the last decade, laser-ion acceleration has become a field of broad interest. The possibility to generate short proton- or heavy ion bunches with an energy of a few tens of MeV by table-top laser systems could open new opportunities for medical or technical applications. Nevertheless, today's laser-acceleration schemes lead mainly to a temperature-like energy distribution of the accelerated ions, a big disadvantage compared to mono-energetic beams from conventional accelerators. Recent results 111 of laser-ion acceleration using radiation-pressure appear promising to overcome this drawback. In this paper, we demonstrate the influence of a second counter-propagating laser pulse interacting with a nm-thick target, creating a well defined pre-plasma. (C) 2013 Elsevier B.V. All rights reserved.
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| 10. |
- Aurand, Bastian, et al.
(författare)
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Radiation pressure-assisted acceleration of ions using multi-component foils in high-intensity laser-matter interactions
- 2013
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results on the acceleration of protons and carbon ions from ultra-thin polymer foils at intensities of up to 6x10(19)Wcm(-2) are presented revealing quasi-monoenergetic spectral characteristics for different ion species at the same time. For carbon ions and protons, a linear correlation between the cutoff energy and the peak energy is observed when the laser intensity is increased. Particle-in-cell simulations supporting the experimental results imply an ion acceleration mechanism driven by the radiation pressure as predicted for multi-component foils at these intensities.
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