5,344 research outputs found
Efficient and Reasonable Object-Oriented Concurrency
Making threaded programs safe and easy to reason about is one of the chief
difficulties in modern programming. This work provides an efficient execution
model for SCOOP, a concurrency approach that provides not only data race
freedom but also pre/postcondition reasoning guarantees between threads. The
extensions we propose influence both the underlying semantics to increase the
amount of concurrent execution that is possible, exclude certain classes of
deadlocks, and enable greater performance. These extensions are used as the
basis an efficient runtime and optimization pass that improve performance 15x
over a baseline implementation. This new implementation of SCOOP is also 2x
faster than other well-known safe concurrent languages. The measurements are
based on both coordination-intensive and data-manipulation-intensive benchmarks
designed to offer a mixture of workloads.Comment: Proceedings of the 10th Joint Meeting of the European Software
Engineering Conference and the ACM SIGSOFT Symposium on the Foundations of
Software Engineering (ESEC/FSE '15). ACM, 201
Handling Parallelism in a Concurrency Model
Programming models for concurrency are optimized for dealing with
nondeterminism, for example to handle asynchronously arriving events. To shield
the developer from data race errors effectively, such models may prevent shared
access to data altogether. However, this restriction also makes them unsuitable
for applications that require data parallelism. We present a library-based
approach for permitting parallel access to arrays while preserving the safety
guarantees of the original model. When applied to SCOOP, an object-oriented
concurrency model, the approach exhibits a negligible performance overhead
compared to ordinary threaded implementations of two parallel benchmark
programs.Comment: MUSEPAT 201
GIS-based multicriteria analysis as decision support in flood risk management
In this report we develop a GIS-based multicriteria flood risk assessment and mapping approach. This approach has the ability a) to consider also flood risks which are not measured in monetary terms, b) to show the spatial distribution of these multiple risks and c) to deal with uncertainties in criteria values and to show their influence on the overall assessment. It can furthermore be used to show the spatial distribution of the effects of risk reduction measures. The approach is tested for a pilot study at the River Mulde in Saxony, Germany. Therefore, a GISdataset of economic as well as social and environmental risk criteria is built up. Two multicriteria decision rules, a disjunctive approach and an additive weighting approach are used to come to an overall assessment and mapping of flood risk in the area. Both the risk calculation and mapping of single criteria as well as the multicriteria analysis are supported by a software tool (FloodCalc) which was developed for this task. --
Dzyaloshinskii-Moryia interaction at an antiferromagnetic interface: first-principles study of FeIr bilayers on Rh(001)
We study the magnetic interactions in atomic layers of Fe and 5d
transition-metals such as Os, Ir, and Pt on the (001) surface of Rh using
first-principles calculations based on density functional theory. For both
stackings of the 5d-Fe bilayer on Rh(001) we observe a transition from an
antiferromagnetic to a ferromagnetic nearest-neighbor exchange interaction upon
5d band filling. In the sandwich structure 5d/Fe/Rh(001) the nearest neighbor
exchange is significantly reduced. For FeIr bilayers on Rh(001) we consider
spin spiral states in order to determine exchange constants beyond nearest
neighbors. By including spin-orbit coupling we obtain the Dzyaloshinskii-Moriya
interaction (DMI). The magnetic interactions in Fe/Ir/Rh(001) are similar to
those of Fe/Ir(001) for which an atomic scale spin lattice has been predicted.
However, small deviations between both systems remain due to the different
lattice constants and the Rh vs. Ir surface layers. This leads to slightly
different exchange constants and DMI and the easy magnetization direction
switches from out-of-plane for Fe/Ir(001) to in-plane for Fe/Ir/Rh(001).
Therefore a fine tuning of magnetic interactions is possible by using single 5d
transition-metal layers which may allow to tailor antiferromagnetic skyrmions
in this type of ultrathin films. In the sandwich structure Ir/Fe/Rh(001) we
find a strong exchange frustration due to strong hybridization of the Fe layer
with both Ir and Rh which drastically reduces the nearest-neighbor exchange.
The energy contribution from the DMI becomes extremely large and DMI beyond
nearest neighbors cannot be neglected. We attribute the large DMI to the low
coordination of the Ir layer at the surface. We demonstrate that higher- order
exchange interactions are significant in both systems which may be crucial for
the magnetic ground state
Pointer Race Freedom
We propose a novel notion of pointer race for concurrent programs
manipulating a shared heap. A pointer race is an access to a memory address
which was freed, and it is out of the accessor's control whether or not the
cell has been re-allocated. We establish two results. (1) Under the assumption
of pointer race freedom, it is sound to verify a program running under explicit
memory management as if it was running with garbage collection. (2) Even the
requirement of pointer race freedom itself can be verified under the
garbage-collected semantics. We then prove analogues of the theorems for a
stronger notion of pointer race needed to cope with performance-critical code
purposely using racy comparisons and even racy dereferences of pointers. As a
practical contribution, we apply our results to optimize a thread-modular
analysis under explicit memory management. Our experiments confirm a speed-up
of up to two orders of magnitude
Model-based testing for space-time interaction using point processes: An application to psychiatric hospital admissions in an urban area
Spatio-temporal interaction is inherent to cases of infectious diseases and
occurrences of earthquakes, whereas the spread of other events, such as cancer
or crime, is less evident. Statistical significance tests of space-time
clustering usually assess the correlation between the spatial and temporal
(transformed) distances of the events. Although appealing through simplicity,
these classical tests do not adjust for the underlying population nor can they
account for a distance decay of interaction. We propose to use the framework of
an endemic-epidemic point process model to jointly estimate a background event
rate explained by seasonal and areal characteristics, as well as a superposed
epidemic component representing the hypothesis of interest. We illustrate this
new model-based test for space-time interaction by analysing psychiatric
inpatient admissions in Zurich, Switzerland (2007-2012). Several socio-economic
factors were found to be associated with the admission rate, but there was no
evidence of general clustering of the cases.Comment: 21 pages including 4 figures and 5 tables; methods are implemented in
the R package surveillance (https://CRAN.R-project.org/package=surveillance
On the clinical potential of ion computed tomography with different detector systems and ion species
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