5,161 research outputs found
It takes two to tango:if you want students to harness culturally diverse syndicate groups for their learning, assure high interdependence and students value cultural differences
On how cultural diversity is a double edged sword that can undermine students’ learning in work groups, but also has the potential to enrich students’ learning experiences
Checkpointing algorithms and fault prediction
This paper deals with the impact of fault prediction techniques on
checkpointing strategies. We extend the classical first-order analysis of Young
and Daly in the presence of a fault prediction system, characterized by its
recall and its precision. In this framework, we provide an optimal algorithm to
decide when to take predictions into account, and we derive the optimal value
of the checkpointing period. These results allow to analytically assess the key
parameters that impact the performance of fault predictors at very large scale.Comment: Supported in part by ANR Rescue. Published in Journal of Parallel and
Distributed Computing. arXiv admin note: text overlap with arXiv:1207.693
Reclaiming the energy of a schedule: models and algorithms
We consider a task graph to be executed on a set of processors. We assume
that the mapping is given, say by an ordered list of tasks to execute on each
processor, and we aim at optimizing the energy consumption while enforcing a
prescribed bound on the execution time. While it is not possible to change the
allocation of a task, it is possible to change its speed. Rather than using a
local approach such as backfilling, we consider the problem as a whole and
study the impact of several speed variation models on its complexity. For
continuous speeds, we give a closed-form formula for trees and series-parallel
graphs, and we cast the problem into a geometric programming problem for
general directed acyclic graphs. We show that the classical dynamic voltage and
frequency scaling (DVFS) model with discrete modes leads to a NP-complete
problem, even if the modes are regularly distributed (an important particular
case in practice, which we analyze as the incremental model). On the contrary,
the VDD-hopping model leads to a polynomial solution. Finally, we provide an
approximation algorithm for the incremental model, which we extend for the
general DVFS model.Comment: A two-page extended abstract of this work appeared as a short
presentation in SPAA'2011, while the long version has been accepted for
publication in "Concurrency and Computation: Practice and Experience
Analysis and Diversion of Duqu's Driver
The propagation techniques and the payload of Duqu have been closely studied
over the past year and it has been said that Duqu shared functionalities with
Stuxnet. We focused on the driver used by Duqu during the infection, our
contribution consists in reverse-engineering the driver: we rebuilt its source
code and analyzed the mechanisms it uses to execute the payload while avoiding
detection. Then we diverted the driver into a defensive version capable of
detecting injections in Windows binaries, thus preventing further attacks. We
specifically show how Duqu's modified driver would have detected Duqu.Comment: Malware 2013 - 8th International Conference on Malicious and Unwanted
Software (2013
Polarizers, optical bridges and Sagnac interferometers for nanoradian polarization rotation measurements
The ability to measure nanoradian polarization rotations, , in the
photon shot noise limit is investigated for partially crossed polarizers (PCP),
a static Sagnac interferometer and an optical bridge, each of which can in
principal be used in this limit with near equivalent figures-of-merit (FOM). In
practice a bridge to PCP/Sagnac source noise rejection ratio of
enables the bridge to operate in the photon shot noise limit even at high light
intensities. The superior performance of the bridge is illustrated via the
measurement of a 3 nrad rotation arising from an axial magnetic field of 0.9 nT
applied to a terbium gallium garnet. While the Sagnac is functionally
equivalent to the PCP in terms of the FOM, unlike the PCP it is able to
discriminate between rotations with different time () and parity ()
symmetries. The Sagnac geometry implemented here is similar to that used
elsewhere to detect non-reciprocal () rotations like those due
to the Faraday effect. Using a Jones matrix approach, novel Sagnac geometries
uniquely sensitive to non-reciprocal (e.g. magneto-electric or
magneto-chiral) rotations, as well as to reciprocal rotations (e.g. due to
linear birefringence, , or to chirality, ) are proposed.Comment: 12 pages, 7 figure
Co-Scheduling Algorithms for High-Throughput Workload Execution
This paper investigates co-scheduling algorithms for processing a set of
parallel applications. Instead of executing each application one by one, using
a maximum degree of parallelism for each of them, we aim at scheduling several
applications concurrently. We partition the original application set into a
series of packs, which are executed one by one. A pack comprises several
applications, each of them with an assigned number of processors, with the
constraint that the total number of processors assigned within a pack does not
exceed the maximum number of available processors. The objective is to
determine a partition into packs, and an assignment of processors to
applications, that minimize the sum of the execution times of the packs. We
thoroughly study the complexity of this optimization problem, and propose
several heuristics that exhibit very good performance on a variety of
workloads, whose application execution times model profiles of parallel
scientific codes. We show that co-scheduling leads to to faster workload
completion time and to faster response times on average (hence increasing
system throughput and saving energy), for significant benefits over traditional
scheduling from both the user and system perspectives
Views of pi : definition and computation
We study several formal proofs and algorithms related to the number pi in the context of Coq's standard library. In particular, we clarify the relation between roots of the cosine function and the limit of the alternated series whose terms are the inverse of odd natural numbers (known as Leibnitz' formula).We give a formal description of the arctangent function and its expansion as a power series. We then study other possible descriptions of pi, first as the surface of the unit disk, second as the limit of perimeters of regular polygons with an increasing number of sides.In a third section, we concentrate on techniques to effectively compute approximations of pi in the proof assistant by relying on rational numbers and decimal representations
A split analysis of nasal harmony in Mbyá
This paper proposes an optimality theoretic analysis of nasal harmony in Mbyá Guaraní. I propose that nasal harmony in Mbyá is best understood as the product of two distinct phenomena: (i) nasal harmony between adjacent syllable nuclei and (ii) nasal coarticulation from a vowel to an adjacent consonant edge. The proposed analysis, which is laid out in optimality theory (OT), is inspired by the work of Piggott and van der Hulst (1997)
Quasi-interpretations a way to control resources
International audienceThis paper presents in a reasoned way our works on resource analysis by quasi- interpretations. The controlled resources are typically the runtime, the runspace or the size of a result in a program execution. Quasi-interpretations allow analyzing system complexity. A quasi-interpretation is a numerical assignment, which provides an upper bound on computed func- tions and which is compatible with the program operational semantics. Quasi- interpretation method offers several advantages: (i) It provides hints in order to optimize an execution, (ii) it gives resource certificates, and (iii) finding quasi- interpretations is decidable for a broad class which is relevant for feasible com- putations. By combining the quasi-interpretation method with termination tools (here term orderings), we obtained several characterizations of complexity classes starting from Ptime and Pspace
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