339 research outputs found
Symbolic Abstract Heaps for Polymorphic Information-flow Guard Inference (Extended Version)
In the realm of sound object-oriented program analyses for information-flow
control, very few approaches adopt flow-sensitive abstractions of the heap that
enable a precise modeling of implicit flows. To tackle this challenge, we
advance a new symbolic abstraction approach for modeling the heap in Java-like
programs. We use a store-less representation that is parameterized with a
family of relations among references to offer various levels of precision based
on user preferences. This enables us to automatically infer polymorphic
information-flow guards for methods via a co-reachability analysis of a
symbolic finite-state system. We instantiate the heap abstraction with three
different families of relations. We prove the soundness of our approach and
compare the precision and scalability obtained with each instantiated heap
domain by using the IFSpec benchmarks and real-life applications
Exercising Symbolic Discrete Control for Designing Low-power Hardware Circuits: an Application to Clock-gating
We devise a tool-supported framework for achieving power-efficiency of hardware chips from high-level designs described using the popular hardware description language Verilog. We consider digital circuits as hierarchical compositions of sub-circuits, and achieve power-efficiency by switching-off the clock of each sub-circuit according to some clock-gating logic. We encode the computation of the latter as several small symbolic discrete controller synthesis problems, and use the resulting controllers to derive power-efficient versions from original circuit designs. We detail and illustrate our approach using a running example, and validate it experimentally by deriving a low-power version of an actual Reed-Solomon decoder
Logico-numerical Control for Software Components Reconfiguration
International audienceWe target the problem of the safe control of reconfigurations in component-based software systems, where strategies of adaptation to variations in both their environment and internal resource demands need to be enforced. In this context, the computing system involves software components that are subject to control decisions. We approach this problem under the angle of Discrete Event Systems (DES), involving properties on events observed during the execution (e.g., requests of computing tasks, work overload), and a state space representing different configurations such as activity or assemblies of components. We consider in particular the potential of applying novel logico-numerical control techniques to extend the expressivity of control models and objectives, thereby extending the application of DES in component-based software systems. We elaborate methodological guidelines for the application of logico-numerical control based on a case- study, and validate the result experimentally
Nuclear magnetic resonance study of the magnetic-field-induced ordered phase in the NiCl2-4SC(NH2)2 compound
Nuclear magnetic resonance (NMR) study of the high magnetic field (H) part of
the Bose-Einstein condensed (BEC) phase of the quasi-onedimensional (quasi-1D)
antiferromagnetic quantum spin-chain compound NiCl2-4SC(NH2)2 (DTN) was
performed. We precisely determined the phase boundary, Tc(H), down to 40 mK;
the critical boson density, n_c(Tc); and the absolute value of the BEC order
parameter S_perp at very low temperature (T = 0.12 K). All results are
accurately reproduced by numerical quantum Monte Carlo simulations of a
realistic three-dimensional (3D) model Hamiltonian. Approximate analytical
predictions based on the 1D Tomonaga-Luttinger liquid description are found to
be precise for Tc(H), but less so for S_perp(H), which is more sensitive to the
strength of 3D couplings, in particular close to the critical field. A
mean-field treatment, based on the Hartree-Fock-Popov description, is found to
be valid only up to n_c = 4% (T < 0.3 K), while for higher n_c boson
interactions appear to modify the density of states.Comment: Manuscript (6 pages, 3 figures) and the corresponding Supplemental
material (5 pages, 6 figures), altogether 11 pages and 9 figure
Symbolic Limited Lookahead Control for Best-effort Dynamic Computing Resource Management
We put forward a new modeling technique for Dynamic Resource Management (DRM) based on discrete events control for symbolic logico-numerical systems, especially Discrete Controller Synthesis (DCS). The resulting models involve state and input variables defined on an infinite domain (Integers), thereby no exact DCS algorithm exists for safety control. We thus formally define the notion of limited lookahead, and associated best-effort control objectives targeting safety and optimization on a sliding window for a number of steps ahead. We give symbolic algorithms, illustrate our approach on an example model for DRM, and report on performance results based on an implementation in our tool ReaX
Towards Applying Logico-numerical Control to Dynamically Partially Reconfigurable Architectures
International audienceWe investigate the opportunities given by recent developments in the context of Discrete Controller Synthesis algorithms for infinite, logico-numerical systems. To this end, we focus on models employed in previous work for the management of dynamically partially reconfigurable hardware architectures. We extend these models with logico-numerical features to illustrate new modeling possibilities, and carry out some benchmarks to evaluate the feasibility of the approach on such models
Tapping Thermodynamics of the One Dimensional Ising Model
We analyse the steady state regime of a one dimensional Ising model under a
tapping dynamics recently introduced by analogy with the dynamics of
mechanically perturbed granular media. The idea that the steady state regime
may be described by a flat measure over metastable states of fixed energy is
tested by comparing various steady state time averaged quantities in extensive
numerical simulations with the corresponding ensemble averages computed
analytically with this flat measure. The agreement between the two averages is
excellent in all the cases examined, showing that a static approach is capable
of predicting certain measurable properties of the steady state regime.Comment: 11 pages, 5 figure
A Continuized View on Nesterov Acceleration
We introduce the "continuized" Nesterov acceleration, a close variant of Nesterov acceleration whose variables are indexed by a continuous time parameter. The two variables continuously mix following a linear ordinary differential equation and take gradient steps at random times. This continuized variant benefits from the best of the continuous and the discrete frameworks: as a continuous process, one can use differential calculus to analyze convergence and obtain analytical expressions for the parameters; but a discretization of the continuized process can be computed exactly with convergence rates similar to those of Nesterov original acceleration. We show that the discretization has the same structure as Nesterov acceleration, but with random parameters
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