Many-Beam Solution to the Phase Problem in Crystallography

Solving crystal structures from electron diffraction patterns rather than X-ray diffraction data is hampered by multiple scattering of the fast electrons within even very thin samples and the difficulty of obtaining diffraction data at a resolution high enough for applying direct phasing methods. This letter presents a method by which the effect of multiple scattering is being used for solving the phase problem, allowing the retrieval of electron structure factors from diffraction patterns recorded with varying angle of incidence without any assumption about the scattering potential itself. In particular, the resolution in the diffraction data does not need to be sufficient to resolve atoms, making this method particularly interesting for electron crystallography of 2-dimensional protein crystals and other beam-sensitive complex structures.Comment: 4 pages, 3 figure

Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

Star clusters, particularly those objects in the disk-bulge-halo interface are as of yet poorly charted, albeit carrying important information about the formation and the structure of the Milky Way. Here, we present a detailed chemical abundance study of the recently discovered object Gaia 1. Photometry has previously suggested it as an intermediate-age, moderately metal-rich system, although the exact values for its age and metallicity remained ambiguous in the literature. We measured detailed chemical abundances of 14 elements in four red giant members, from high-resolution (R=25000) spectra that firmly establish Gaia 1 as an object associated with the thick disk. The resulting mean Fe abundance is $-0.62\pm$0.03(stat.)$\pm$0.10(sys.) dex, which is more metal-poor than indicated by previous spectroscopy from the literature, but it is fully in line with values from isochrone fitting. We find that Gaia 1 is moderately enhanced in the $\alpha$-elements, which allowed us to consolidate its membership with the thick disk via chemical tagging. The cluster's Fe-peak and neutron-capture elements are similar to those found across the metal-rich disks, where the latter indicate some level of $s$-process activity. No significant spread in iron nor in other heavy elements was detected, whereas we find evidence of light-element variations in Na, Mg, and Al. Nonetheless, the traditional Na-O and Mg-Al (anti-)correlations, typically seen in old globular clusters, are not seen in our data. This confirms that Gaia 1 is rather a massive and luminous open cluster than a low-mass globular cluster. Finally, orbital computations of the target stars bolster our chemical findings of Gaia 1's present-day membership with the thick disk, even though it remains unclear, which mechanisms put it in that place.Comment: 11 pages, 11 figures, accepted for publication in Astronomy & Astrophysics. Some figure sizes reduce

Analysis And Performance Of A Picosecond Dye Laser Amplifier Chain

Design considerations are discussed for a simple, easy to use and relatively efficient high gain dye laser amplifier chain for CW mode-locked dye lasers. The amplifier boosts the output of a synchronously mode-locked dye laser to obtain ≈005 mj, ≤ 1 psec pulses over a ≈ 400 Å bandwidth. These pulses are suitable for efficient Raman Shifting, frequency mixing and continuum generation to vastly extend the spectral range of the system. Our amplifier is pumped by a frequency doubled Nd:YAG oscillator only, which longitudinally pumps three identical brewster cells with the same flowing dye solution in each. Contrary to popular belief, high small signal gains (≥ 105) are easily attained in a single stage with longitudinal pumping, with better beam homogeneity and easier alignment than transverse pumping. Gain saturation measurements are presented which agree well with calculations. Factors which relax the pump timing sensitivity are examined. The importance of gain saturation for both efficient amplification and for amplitude stability is also discussed. The need for isolated amplifier stages is stressed and optimal amplifier cell areas for a given stage are calculated

Searching for the QCD Critical Point Using Particle Ratio Fluctuations and Higher Moments of Multiplicity Distributions

Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results from new measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations are presented. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations from Au+Au collisions to lower energies. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies $\sqrt{s_{NN}}$ = 7.7, 11.5, 39, 62.4, and 200 GeV. New results are compared to previous measurements and to theoretical predictions from several models. The measured dynamical $K/\pi$ fluctuations are found to be independent of collision energy, while dynamical $p/\pi$ and $K/p$ fluctuations have a negative value that increases toward zero at top RHIC energy. Fluctuations of the higher moments of conserved quantities (net-proton and net-charge) distributions, which are predicted to be sensitive to the presence of a critical point, are also presented.Comment: 4 pages, 2 figures, Proceedings of the 21st International Conference On Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), Annecy, France, May 23 - May 28, 201

Fast and Simple Relational Processing of Uncertain Data

This paper introduces U-relations, a succinct and purely relational representation system for uncertain databases. U-relations support attribute-level uncertainty using vertical partitioning. If we consider positive relational algebra extended by an operation for computing possible answers, a query on the logical level can be translated into, and evaluated as, a single relational algebra query on the U-relation representation. The translation scheme essentially preserves the size of the query in terms of number of operations and, in particular, number of joins. Standard techniques employed in off-the-shelf relational database management systems are effective for optimizing and processing queries on U-relations. In our experiments we show that query evaluation on U-relations scales to large amounts of data with high degrees of uncertainty.Comment: 12 pages, 14 figure

Development of New Venture Support Networks and the Role of "Promoters"

New Venture Support Networks (NVSN) are a political instrument for the purpose of contributing to regional economic development by fostering more and qualitatively better start-ups. NVSN bundle together different available sources of information and consultation for potential entrepreneurs, including e.g. authorities, universities, financial institutions, trade associations and private consultants. Achieving effective cooperation between such a wide range of institutions is not a simple task. The initial situation is often characterised by conflicts between the varying individual interests of the participants and the politically defined goal of fostering more and better start-ups. Moreover, since the network has been established by a political initiative for a pre-determined funding period, the actor relations within it are “artificial” (as opposed to naturally developed). Thus, the actors lack common experiences, social bonds, values and other common motivators contributing to trust-based cooperative relationships. Such relationships are a crucial factor in turning the “artificial” network into a “real” one, which continues to exist also after the political funding period is over. Our hypothesis is that certain key actors are a critical success factor in developing NVSN into “real” networks. Following the “promoter model” – an expansion of champion models that has established itself in the German innovation management literature – we suggest that there are administrative, organisational and know-how related barriers that are detrimental to the development of NVSN. The overcoming of these barriers requires a combination of different organisational resources, which the promoter model discusses in terms of three different ideal types: promoter by power, promoter by know-how, and relationship promoter. One person can act in one or more of these roles simultaneously and the roles can appear in different combinations, known as promoter structures. The specific research objectives of the proposed paper are to identify a) the types of barriers faced in the different developmental stages of NVSN and b) the roles the key actors play and the resources they use in coping with them. Our sample consists of key actors in five regional NVSN in Germany, which were established in 1998 as part of the governmental initiative “EXIST – Entrepreneurs from Universities”. The author team is also involved in one of these networks. Using a grounded theory based qualitative approach, we intend to map the development process of these NVSN with respect to the above research objectives. The contribution of the study is two-fold: 1) It presents the first application of the promoter model in the context of NVSN and produces tentative results that can be used as a basis for further research. 2) It offers practical implications to NVSN by analysing how their effectiveness and continuity could be improved by an effective use of promoter structures.