2,324 research outputs found
Multidimensional Range Queries on Modern Hardware
Range queries over multidimensional data are an important part of database
workloads in many applications. Their execution may be accelerated by using
multidimensional index structures (MDIS), such as kd-trees or R-trees. As for
most index structures, the usefulness of this approach depends on the
selectivity of the queries, and common wisdom told that a simple scan beats
MDIS for queries accessing more than 15%-20% of a dataset. However, this wisdom
is largely based on evaluations that are almost two decades old, performed on
data being held on disks, applying IO-optimized data structures, and using
single-core systems. The question is whether this rule of thumb still holds
when multidimensional range queries (MDRQ) are performed on modern
architectures with large main memories holding all data, multi-core CPUs and
data-parallel instruction sets. In this paper, we study the question whether
and how much modern hardware influences the performance ratio between index
structures and scans for MDRQ. To this end, we conservatively adapted three
popular MDIS, namely the R*-tree, the kd-tree, and the VA-file, to exploit
features of modern servers and compared their performance to different flavors
of parallel scans using multiple (synthetic and real-world) analytical
workloads over multiple (synthetic and real-world) datasets of varying size,
dimensionality, and skew. We find that all approaches benefit considerably from
using main memory and parallelization, yet to varying degrees. Our evaluation
indicates that, on current machines, scanning should be favored over parallel
versions of classical MDIS even for very selective queries
Exotic Higgs boson decay modes as a harbinger of flavor symmetry
Discrete symmetries employed to explain flavor mixing and mass hierarchies
can be associated with an enlarged scalar sector which might lead to exotic
Higgs decay modes. In this paper, we explore such a possibility in a scenario
with flavor symmetry which requires three scalar SU(2) doublets. The
spectrum is fixed by minimizing the scalar potential, and we observe that the
symmetry of the model leads to tantalizing Higgs decay modes potentially
observable at the CERN Large Hadron Collider (LHC).Comment: v2: 7 pages, 5 eps figures, to appear as a Rapid Communication in
Physical Review D (Title expanded in journal
A common origin of fermion mixing and geometrical CP violation, and its test through Higgs physics at the LHC
We construct for the first time a flavor model, based on the smallest
discrete symmetry Delta(27) that implements spontaneous CP violation with a
complex phase of geometric origin, which can actually reproduce all quark
masses and mixing data. We show that its scalar sector has exotic properties
that can be tested at the LHC.Comment: v3: accepted by PR
Menschenwürde
Muss ein Mensch Selbstachtung haben, um Empfänger der Menschenwürde zu sein? Spielt Menschenwürde auch in der Wirtschaft und im Rechtssystem eine Rolle? Und wie lässt sich „Menschenwürde“ überhaupt definieren? Im Dossier findet man die philosophischen Hintergründe zum Thema „Menschenwürde“
- …