1,006 research outputs found
Engineering Aggregation Operators for Relational In-Memory Database Systems
In this thesis we study the design and implementation of Aggregation operators in the context of relational in-memory database systems. In particular, we identify and address the following challenges: cache-efficiency, CPU-friendliness, parallelism within and across processors, robust handling of skewed data, adaptive processing, processing with constrained memory, and integration with modern database architectures. Our resulting algorithm outperforms the state-of-the-art by up to 3.7x
Inflating a Rubber Balloon
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.A spherical balloon has a non-monotonic pressure-radius characteristic. This fact leads to interesting stability properties when two balloons of different radii are interconnected, see [1, 2, 3]. Here, however, we investigate what happens when a single balloon is inflated, say, by mouth. We simulate that process and show how the maximum of the pressure-radius characteristic is overcome by the pressure in the lungs and how the downward sloping part of the characteristic is ‘bridged’ while the lung pressure relaxes
Ordering in granular rod monolayers driven far from thermodynamic equilibrium
The orientational order in vertically agitated granular rod monolayers is
investigated experimentally and compared quantitatively with equilibrium Monte
Carlo simulations and density functional theory. At sufficiently high number
density, short rods form a tetratic state and long rods form a uniaxial nematic
state. The length-to-width ratio at which the order changes from tetratic to
uniaxial is around in both experiments and simulations. This agreement
illustrates the universal aspects of the ordering of rod-shaped particles
across equilibrium and nonequilibrium systems. Moreover, the assembly of
granular rods into ordered states is found to be independent of the agitation
frequency and strength, suggesting that the detailed nature of energy injection
into such a nonequilibrium system does not play a crucial role.Comment: 8 pages, 7 figure
Rumble: Data Independence for Large Messy Data Sets
This paper introduces Rumble, an engine that executes JSONiq queries on
large, heterogeneous and nested collections of JSON objects, leveraging the
parallel capabilities of Spark so as to provide a high degree of data
independence. The design is based on two key insights: (i) how to map JSONiq
expressions to Spark transformations on RDDs and (ii) how to map JSONiq FLWOR
clauses to Spark SQL on DataFrames. We have developed a working implementation
of these mappings showing that JSONiq can efficiently run on Spark to query
billions of objects into, at least, the TB range. The JSONiq code is concise in
comparison to Spark's host languages while seamlessly supporting the nested,
heterogeneous data sets that Spark SQL does not. The ability to process this
kind of input, commonly found, is paramount for data cleaning and curation. The
experimental analysis indicates that there is no excessive performance loss,
occasionally even a gain, over Spark SQL for structured data, and a performance
gain over PySpark. This demonstrates that a language such as JSONiq is a simple
and viable approach to large-scale querying of denormalized, heterogeneous,
arborescent data sets, in the same way as SQL can be leveraged for structured
data sets. The results also illustrate that Codd's concept of data independence
makes as much sense for heterogeneous, nested data sets as it does on highly
structured tables.Comment: Preprint, 9 page
The First Bridged, Bifunctional Cyclopentadienyl-Imidazolylidene Ligand and Complexes with Titanium and Zirconium
Starting from imidazole, 1-[2-(cyclopenta-2,4-dienyl)ethyl]-3-methylimidazolium iodide (3) was obtained as a mixture of isomers by a simple three-step synthesis. The reaction of 3 with Ti(NEt2)4 or Zr(NEt2)4 by double deprotonation of the imidazolium salt led to the isomerically pure cationic complexes [{η5-C5H4-(CH2)2-NHC}M(NEt2)2]+I− (NHC = N-heterocyclic carbene) 4a (M = Ti) and 4b (M = Zr), respectively, in which a cyclopentadienyl and a methylimidazol-2-ylidene unit are linked by an ethylidene-1,2 bridge to form a novel chelating ligand system. In the case of the reaction of 3 with Zr(NEt2)4 the neutral compound [{η5-C5H4-(CH2)2-NHC}Zr(NEt2)I2] (5) is formed as an additional product. According to the X-ray structure analyses, the titanium atom of 4a is tetracoordinated while no coordinative interaction exists with the iodide anion; on the other hand, in 5 the zirconium centre is pentacoordinated.DFG, 272017, GRK 352: Synthetische, mechanistische und reaktionstechnische Aspekte von Metallkatalysatore
Wavelength-converted light sources in fluorescence-based methods in medical technology
This contribution proposes phosphors as excitation for fluorescence analysis and evaluates their potential in this application area. Aim of this research is to provide a method which allows to quantify how well a phosphor fits as excitation in a given optical system with spectral filters for fluorescence analysis. The approach consists of a mathematical calculation of crosstalk which is first applied to abstract and subsequentially defined phosphor emission spectra. The resulting crosstalk is used as measure indicating the fit of a phosphor spectrum. Result of this contribution is a detailed description of the applied method as well as an example exercise on a given optical system which gives an impression of possibilities phosphors offer in this application. The presented method is applicable to any (new) phosphor or even LED spectra. Especially evaluations on the example optical system allow conclusions which help to design future optical systems
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