15,578 research outputs found
Active Anomaly Detection in Heterogeneous Processes
An active inference problem of detecting anomalies among heterogeneous
processes is considered. At each time, a subset of processes can be probed. The
objective is to design a sequential probing strategy that dynamically
determines which processes to observe at each time and when to terminate the
search so that the expected detection time is minimized under a constraint on
the probability of misclassifying any process. This problem falls into the
general setting of sequential design of experiments pioneered by Chernoff in
1959, in which a randomized strategy, referred to as the Chernoff test, was
proposed and shown to be asymptotically optimal as the error probability
approaches zero. For the problem considered in this paper, a low-complexity
deterministic test is shown to enjoy the same asymptotic optimality while
offering significantly better performance in the finite regime and faster
convergence to the optimal rate function, especially when the number of
processes is large. The computational complexity of the proposed test is also
of a significantly lower order.Comment: This work has been accepted for publication on IEEE Transactions on
Information Theor
HeTM: Transactional Memory for Heterogeneous Systems
Modern heterogeneous computing architectures, which couple multi-core CPUs
with discrete many-core GPUs (or other specialized hardware accelerators),
enable unprecedented peak performance and energy efficiency levels.
Unfortunately, though, developing applications that can take full advantage of
the potential of heterogeneous systems is a notoriously hard task. This work
takes a step towards reducing the complexity of programming heterogeneous
systems by introducing the abstraction of Heterogeneous Transactional Memory
(HeTM). HeTM provides programmers with the illusion of a single memory region,
shared among the CPUs and the (discrete) GPU(s) of a heterogeneous system, with
support for atomic transactions. Besides introducing the abstract semantics and
programming model of HeTM, we present the design and evaluation of a concrete
implementation of the proposed abstraction, which we named Speculative HeTM
(SHeTM). SHeTM makes use of a novel design that leverages on speculative
techniques and aims at hiding the inherently large communication latency
between CPUs and discrete GPUs and at minimizing inter-device synchronization
overhead. SHeTM is based on a modular and extensible design that allows for
easily integrating alternative TM implementations on the CPU's and GPU's sides,
which allows the flexibility to adopt, on either side, the TM implementation
(e.g., in hardware or software) that best fits the applications' workload and
the architectural characteristics of the processing unit. We demonstrate the
efficiency of the SHeTM via an extensive quantitative study based both on
synthetic benchmarks and on a porting of a popular object caching system.Comment: The current work was accepted in the 28th International Conference on
Parallel Architectures and Compilation Techniques (PACT'19
Current challenges for preseismic electromagnetic emissions: shedding light from micro-scale plastic flow, granular packings, phase transitions and self-affinity notion of fracture process
Are there credible electromagnetic (EM) EQ precursors? This a question
debated in the scientific community and there may be legitimate reasons for the
critical views. The negative view concerning the existence of EM precursors is
enhanced by features that accompany their observation which are considered as
paradox ones, namely, these signals: (i) are not observed at the time of EQs
occurrence and during the aftershock period, (ii) are not accompanied by large
precursory strain changes, (iii) are not accompanied by simultaneous geodetic
or seismological precursors and (v) their traceability is considered
problematic. In this work, the detected candidate EM precursors are studied
through a shift in thinking towards the basic science findings relative to
granular packings, micron-scale plastic flow, interface depinning, fracture
size effects, concepts drawn from phase transitions, self-affine notion of
fracture and faulting process, universal features of fracture surfaces, recent
high quality laboratory studies, theoretical models and numerical simulations.
Strict criteria are established for the definition of an emerged EM anomaly as
a preseismic one, while, precursory EM features, which have been considered as
paradoxes, are explained. A three-stage model for EQ generation by means of
preseismic fracture-induced EM emissions is proposed. The claim that the
observed EM precursors may permit a real-time and step-by-step monitoring of
the EQ generation is tested
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