Ballistic reflection at a side-gate in a superconductor-semiconductor-superconductor structure

We have fabricated a sub-micron-sized structure consisting of an InAs-based 2DEG, two narrow Nb leads and a gate, where the indirect ballistic transport between the non-oppositely superconducting contacts can be controlled by the voltage applied to the gate. This new kind of tuneable junction can be used for applications and allows several fundamental questions related to the transport mechanism to be studied. First results of experiments carried out in this respect are presented.Comment: 6 pages, 4 eps-figure

Theoretical and Observational Agreement on Mass Dependence of Cluster Life Times

Observations and N-body simulations both support a simple relation for the disruption time of a cluster as a function of its mass of the form: t_dis = t_4 * (M/10^4 Msun)^gamma. The scaling factor t_4 seems to depend strongly on the environment. Predictions and observations show that gamma ~ 0.64 +/- 0.06. Assuming that t_dis ~ M^0.64 is caused by evaporation and shocking implies a relation between the radius and the mass of a cluster of the form: r_h ~ M^0.07, which has been observed in a few galaxies. The suggested relation for the disruption time implies that the lower mass end of the cluster initial mass function will be disrupted faster than the higher mass end, which is needed to evolve a young power law shaped mass function into the log-normal mass function of old (globular) clusters.Comment: 2 pages, to appear in "The Formation and Evolution of Massive Young Star Clusters", 17-21 November 2003, Cancun (Mexico

The Star Cluster Population of M51

We present the age and mass distribution of star clusters in M51. The structural parameters are found by fitting cluster evolution models to the spectral energy distribution consisting of 8 HST-WFPC2 pass bands. There is evidence for a burst of cluster formation at the moment of the second encounter with the companion NGC5195 (50-100 Myr ago) and a hint for an earlier burst (400-500 Myr ago). The cluster IMF has a power law slope of -2.1. The disruption time of clusters is extremely short (< 100 Myr for a 10^4 Msun cluster).Comment: 2 pages, to appear in "The Formation and Evolution of Massive Young Star Clusters", 17-21 November 2003, Cancun (Mexico

Cluster virial expansion for nuclear matter within a quasiparticle statistical approach

Correlations in interacting many-particle systems can lead to the formation of clusters, in particular bound states and resonances. Systematic quantum statistical approaches allow to combine the nuclear statistical equilibrium description (law of mass action) with mean-field concepts. A chemical picture, which treats the clusters as distinct entities, serves as an intuitive concept to treat the low-density limit. Within a generalized Beth-Uhlenbeck approach, the quasiparticle virial expansion is extended to include arbitrary clusters, where special attention must be paid to avoid inconsistencies such as double counting. Correlations are suppressed with increasing density due to Pauli blocking. The contribution of the continuum to the virial coefficients can be reduced by considering clusters explicitly and introducing quasiparticle energies. The cluster-virial expansion for nuclear matter joins known benchmarks at low densities with those near saturation density.Comment: 18 pages, 6 figures, 2 table

The Contamination of Milk.

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Characterization and history of the Helmi streams with Gaia DR2

The halo of the Milky Way has long been hypothesized to harbour significant amounts of merger debris. This view has been supported over more than a decade by wide-field photometric surveys which have revealed the outer halo to be lumpy. The recent release of Gaia DR2 is allowing us to establish that mergers also have been important and possibly built up the majority of the inner halo. In this work we focus on the Helmi streams, a group of streams crossing the Solar vicinity and known for almost two decades. We characterize their properties and relevance for the build-up of the Milky Way's halo. We identify new members of the Helmi streams in an unprecedented dataset with full phase-space information combining Gaia DR2, and the APOGEE DR2, RAVE DR5 and LAMOST DR4 spectroscopic surveys. Based on the orbital properties of the stars, we find new stream members up to a distance of 5 kpc from the Sun, which we characterize using photometry and metallicity information. We also perform N-body experiments to constrain the time of accretion and properties of the progenitor of the streams. We find nearly 600 new members of the Helmi streams. Their HR diagram reveals a broad age range, from approximately 11 to 13 Gyr, while their metallicity distribution goes from $\sim$ 2.3 to $\sim$1.0, and peaks at [Fe/H] $\sim$1.5. These findings confirm that the streams originate in a dwarf galaxy. Furthermore, we find 7 globular clusters to be likely associated, and which follow a well-defined age-metallicity sequence whose properties suggest a relatively massive progenitor object. Our N-body simulations favour a system with a stellar mass of $\sim 10^8\,\mathrm{M}_\odot$ accreted $5 - 8$ Gyr ago. The debris from the Helmi streams is an important donor to the MilkyWay halo, contributing approximately 15\% of its mass in field stars and 10\% of its globular clusters.Comment: 14 pages, 17 figures, submitte

First ALMA Observation of a Solar Plasmoid Ejection from an X-ray Bright Point

Eruptive phenomena such as plasmoid ejections or jets are an important feature of solar activity with the potential for improving our understanding of the dynamics of the solar atmosphere. Such ejections are often thought to be signatures of the outflows expected in regions of fast magnetic reconnection. The 304 A EUV line of Helium, formed at around 10^5 K, is found to be a reliable tracer of such phenomena, but the determination of physical parameters from such observations is not straightforward. We have observed a plasmoid ejection from an X-ray bright point simultaneously at millimeter wavelengths with ALMA, at EUV wavelengths with AIA, in soft X-rays with Hinode/XRT. This paper reports the physical parameters of the plasmoid obtained by combining the radio, EUV and X-ray data. As a result, we conclude that the plasmoid can consist either of (approximately) isothermal 10^5 K plasma that is optically thin at 100 GHz, or else a 10^4 K core with a hot envelope. The analysis demonstrates the value of the additional temperature and density constraints that ALMA provides, and future science observations with ALMA will be able to match the spatial resolution of space-borne and other high-resolution telescopes.Comment: 10 page, 5 figures, accepted for publication in Astrophysical Journal Letter. The movie can be seen at the following link: http://hinode.nao.ac.jp/user/shimojo/data_area/plasmoid/movie5.mp

Constraining star cluster disruption mechanisms

Star clusters are found in all sorts of environments and their formation and evolution is inextricably linked to the star formation process. Their eventual destruction can result from a number of factors at different times, but the process can be investigated as a whole through the study of the cluster age distribution. Observations of populous cluster samples reveal a distribution following a power law of index approximately -1. In this work we use M33 as a test case to examine the age distribution of an archetypal cluster population and show that it is in fact the evolving shape of the mass detection limit that defines this trend. That is to say, any magnitude-limited sample will appear to follow a dN/dt=1/t, while cutting the sample according to mass gives rise to a composite structure, perhaps implying a dependence of the cluster disruption process on mass. In the context of this framework, we examine different models of cluster disruption from both theoretical and observational standpoints.Comment: To appear in the proceedings of IAU Symposium 266: "Star Clusters: Basic Galactic Building Blocks Throughout Time And Space", eds. R. de Grijs and J. Lepin