On the Observation of Phase Transitions in Collisions of Elementary Matter

We investigate the excitation function of directed flow, which can provide a clear signature of the creation of the QGP and demonstrate that the minimum of the directed flow does not correspond to the softest point of the EoS for isentropic expansion. A novel technique measuring the compactness is introduced to determine the QGP transition in relativistic-heavy ion collisions: The QGP transition will lead to higher compression and therefore to higher compactness of the source in coordinate space. This effect can be observed by pion interferometry. We propose to measure the compactness of the source in the appropriate principal axis frame of the compactness tensor in coordinate space.Comment: LaTeX, 8 pages, 6 figures, Conference proceedings to CRIS 2000, 3rd Catania Relativistic Ion Studie

New Physics at the International Facility for Antiproton and Ion Research (FAIR) Next to GSI

The project of the international Facility for Antiproton and Ion Research (FAIR), co-located to the GSI facility in Darmstadt, has been officially started on November 7, 2007. The current plans of the facility and the planned research program will be described. An investment of about 1 billion euro will permit new physics programs in the areas of low and medium energy antiproton research, heavy ion physics complementary to LHC, as well as in nuclear structure and astrophysics. The facility will comprise about a dozen accelerators and storage rings, which will enable simultaneous operations of up to four different beams.Comment: 7 pages, 1 figure. Invited Talk presented at the "Fourth International Conference on Fission and Properties of Neutron-Rich nuclei", held at Sanibel Island, Florida, November 11-17, 200

A machine learning study to identify spinodal clumping in high energy nuclear collisions

The coordinate and momentum space configurations of the net baryon number in heavy ion collisions that undergo spinodal decomposition, due to a first-order phase transition, are investigated using state-of-the-art machine-learning methods. Coordinate space clumping, which appears in the spinodal decomposition, leaves strong characteristic imprints on the spatial net density distribution in nearly every event which can be detected by modern machine learning techniques. On the other hand, the corresponding features in the momentum distributions cannot clearly be detected, by the same machine learning methods, in individual events. Only a small subset of events can be systematically differ- entiated if only the momentum space information is available. This is due to the strong similarity of the two event classes, with and without spinodal decomposition. In such sce- narios, conventional event-averaged observables like the baryon number cumulants signal a spinodal non-equilibrium phase transition. Indeed the third-order cumulant, the skewness, does exhibit a peak at the beam energy (Elab = 3–4 A GeV), where the transient hot and dense system created in the heavy ion collision reaches the first-order phase transition

Modelling the many-body dynamics of heavy ion collisions: Present status and future perspective

Basic problems of the semiclassical microscopic modelling of strongly interactingsystems are discussed within the framework of Quantum Molecular Dynamics (QMD). This model allows to study the influence of several types of nucleonic interactions on a large variety of observables and phenomena occurring in heavy ion collisions at relativistic energies.It is shown that the same predictions can be obtained with several -- numerically completely different and independently written -- programs as far as the same model parameters are employed and the same basic approximations are made. Many observables are robust against variations of the details of the model assumptions used. Some of the physical results, however, depend also on rather technical parameters like the preparation of the initial configuration in phase space. This crucial problem is connected with the description of the ground state of single nuclei,which differs among the various approaches. An outlook to an improved molecular dynamics scheme for heavy ion collisions is given.Comment: 39 pages, 12 figure

Changes in the Sea-Ice Brine Community During the Spring-Summer Transition, McMurdo Sound, Antarctica .2. Phagotrophic Protists

The land-fast sea-ice brine contains a diverse phagotrophic protist assemblage consisting of \u3c 5 mum heterotrophic flagellates, Cryothecomonas spp., heterotrophic dinoflagellates, and heterotrophic and mixotrophic ciliates. Fine-scale horizontal spatial variability is a feature of this assemblage; samples taken within 1 m of each other can be dominated by different heterotrophic protists. Many of the larger heterotrophic protists found in the brine are also found in the water column. The photosynthetic ciliate Mesodinium rubrum is also common. In mid to late austral spring, the heterotrophic assemblage accounts for ca 10% of the total protist biomass in the brine and is dominated by Cryothecomonas spp. This flagellate can reach densities of over 106 cells l-1 of brine. In the early austral summer, ciliates (primarily Strombidium spp., Mesodinium rubrum and Didinium spp.) and heterotrophic dinoflagellates (primarily a small Gymnodinium sp. and Polykrikos sp.) increase in abundance in the brine. Ciliate densities of ≥ 3 x 103 l-1 and heterotrophic dinoflagellate densities of 104 cells l-1 are common in the brine during early summer. By the end of January (just prior to ice decay and break-out), heterotrophic flagellates and ciliates can account for 50 % of the protist biomass

Seasonal Dynamics of Mesodinium rubrum in Chesapeake Bay

The photosynthetic ciliate Mesodinium rubrum is a common member of coastal phytoplankton communities that is well adapted to low-light, turbid ecosystems. It supports the growth of, or competes with, harmful dinoflagellate species for cryptophyte prey, as well as being a trophic link to copepods and larval fish. We have compiled data from various sources (n = 1063), on the abundance and distribution of M. rubrum in Chesapeake Bay and its tributaries. Because M. rubrum relies on obtaining organelles from cryptophyte algae to maintain rapid growth, we also enumerated cryptophyte algae in the portion of these samples that we collected (n =386). Mesodinium rubrum occurred in oligohaline to polyhaline regions of Chesapeake Bay and throughout the year. Blooms (\u3e100 cells mL-1) primarily occurred during spring, followed by autumn. When compared across all seasons, M. rubrum abundance was positively correlated to temperature and cryptophytes, and negatively correlated with salinity. However, more focused analyses revealed that M. rubrum abundance during spring was associated with surface layer warming and decreased salinity, while early autumn assemblages were associated with surface cooling. These results imply that there are distinct seasonal niches for M. rubrum blooms. Blooms were more common in tributaries than in the main stem Bay and tended to be restricted to salinities under 10 PSU. Despite the rarity of red water events, M. rubrum is a ubiquitous mixotroph in Chesapeake Bay and at times likely exerts a strong influence on cryptophyte algal abundance and hence planktonic food web structure

Ecophysiological traits of mixotrophic Strombidium spp

This is a pre-copyedited, author-produced version of an article accepted for publication in Journal of Plankton Research following peer review. The version of record Maselli, M., Altenburger, A., Stoecker, D. K. & Hansen, P. J. (2020). Ecophysiological traits of mixotrophic Strombidium spp. Journal of Plankton Research, 42(5), 485-496 is available online at: https://doi.org/10.1093/plankt/fbaa041.Ciliates represent an important trophic link between nanoplankton and mesoplankton. Many species acquire functional chloroplasts from photosynthetic prey, being thus mixotrophs. Little is known about which algae they exploit, and of the relevance of inorganic carbon assimilation to their metabolism. To get insights into these aspects, laboratory cultures of three mixotrophic Strombidium spp. were established and 35 photosynthetic algal species were tested as prey. The relative contributions of ingestion and photosynthesis to total carbon uptake were determined, and responses to prey starvation were studied. Ciliate growth was supported by algal species in the 2–12 μm size range, with cryptophytes and chlorophytes being the best prey types. Inorganic carbon incorporation was only quantitatively important when prey concentration was low (3–100 μgCL−1), when it led to increased gross growth efficiencies. Chla specific inorganic carbon uptake rates were reduced by 60–90% compared to that of the photosynthetic prey. Inorganic carbon uptake alone could not sustain survival of cultures and ciliate populations declined by 25–30% during 5 days of starvation. The results suggest that mixotrophy in Strombidium spp. may substantially bolster the efficiency of trophic transfer when biomass of small primary producers is low