11,092 research outputs found
The Adaptive Priority Queue with Elimination and Combining
Priority queues are fundamental abstract data structures, often used to
manage limited resources in parallel programming. Several proposed parallel
priority queue implementations are based on skiplists, harnessing the potential
for parallelism of the add() operations. In addition, methods such as Flat
Combining have been proposed to reduce contention by batching together multiple
operations to be executed by a single thread. While this technique can decrease
lock-switching overhead and the number of pointer changes required by the
removeMin() operations in the priority queue, it can also create a sequential
bottleneck and limit parallelism, especially for non-conflicting add()
operations.
In this paper, we describe a novel priority queue design, harnessing the
scalability of parallel insertions in conjunction with the efficiency of
batched removals. Moreover, we present a new elimination algorithm suitable for
a priority queue, which further increases concurrency on balanced workloads
with similar numbers of add() and removeMin() operations. We implement and
evaluate our design using a variety of techniques including locking, atomic
operations, hardware transactional memory, as well as employing adaptive
heuristics given the workload.Comment: Accepted at DISC'14 - this is the full version with appendices,
including more algorithm
The HI content of extremely metal-deficient blue compact dwarf galaxies
We have obtained new HI observations with the 100m Green Bank Telescope (GBT)
for a sample of 29 extremely metal-deficient star-forming Blue Compact Dwarf
(BCD) galaxies, selected from the Sloan Digital Sky Survey spectral data base
to be extremely metal-deficient (12+logO/H<7.6). Neutral hydrogen was detected
in 28 galaxies, a 97% detection rate. Combining the HI data with SDSS optical
spectra for the BCD sample and adding complementary galaxy samples from the
literature to extend the metallicity and mass ranges, we have studied how the
HI content of a galaxy varies with various global galaxian properties. There is
a clear trend of increasing gas mass fraction with decreasing metallicity, mass
and luminosity. We obtain the relation M(HI)/L(g)~L(g)^{-0.3}, in agreement
with previous studies based on samples with a smaller luminosity range. The
median gas mass fraction f(gas) for the GBT sample is equal to 0.94 while the
mean gas mass fraction is 0.90+/-0.15, with a lower limit of ~0.65. The HI
depletion time is independent of metallicity, with a large scatter around the
median value of 3.4 Gyr. The ratio of the baryonic mass to the dynamical mass
of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of
~0.2. About 65% of the BCDs in our sample have an effective yield larger than
the true yield, implying that the neutral gas envelope in BCDs is more
metal-deficient by a factor of 1.5-20, as compared to the ionized gas.Comment: 21 pages, 13 figures, accepted for publication in MNRA
K3-fibered Calabi-Yau threefolds I, the twist map
A construction of Calabi-Yaus as quotients of products of lower-dimensional
spaces in the context of weighted hypersurfaces is discussed, including
desingularisation. The construction leads to Calabi-Yaus which have a fiber
structure, in particular one case has K3 surfaces as fibers. These Calabi-Yaus
are of some interest in connection with Type II -heterotic string dualities in
dimension 4. A section at the end of the paper summarises this for the
non-expert mathematician.Comment: 31 pages LaTeX, 11pt, 2 figures. To appear in International Journal
of Mathematics. On the web at
http://personal-homepages.mis.mpg.de/bhunt/preprints.html , #
Benjamin-Ono Kadomtsev-Petviashviliâs models in interfacial electro-hydrodynamics
Three-dimensional nonlinear potential free surface flows in the presence of vertical electric fields are considered. Both the effects of gravity and surface tension are included in the dynamic boundary condition. An asymptotic analysis (based on the assumptions of small depth and small free surface displacements) is presented. It is shown that the problem can be modelled by a Benjamin-Ono Kadomtsev-Petviashvili equation. Furthermore a fifth order Benjamin-Ono Kadomtsev-Petviashvili equation is derived to describe the flows in the particular case of values of the Bond number close to 1/3
From limit cycles to strange attractors
We define a quantitative notion of shear for limit cycles of flows. We prove
that strange attractors and SRB measures emerge when systems exhibiting limit
cycles with sufficient shear are subjected to periodic pulsatile drives. The
strange attractors possess a number of precisely-defined dynamical properties
that together imply chaos that is both sustained in time and physically
observable.Comment: 27 page
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