38,411 research outputs found

    Iterative test suites refinement for elastic computing systems

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    Elastic computing systems can dynamically scale to continuously and cost-effectively provide their required Quality of Service in face of time-varying workloads, and they are usually implemented in the cloud. Despite their wide-spread adoption by industry, a formal definition of elasticity and suitable procedures for its assessment and verification are still missing. Both academia and industry are trying to adapt established testing procedures for functional and non-functional properties, with limited effectiveness with respect to elasticity. In this paper we propose a new methodology to automatically generate test-suites for testing the elastic properties of systems. Elasticity, plasticity, and oscillations are first formalized through a convenient behavioral abstraction of the elastic system and then used to drive an iterative test suite refinement process. The outcomes of our approach are a test suite tailored to the violation of elasticity properties and a human-readable abstraction of the system behavior to further support diagnosis and fix

    Laboratory observations of permeability enhancement by fluid pressure oscillation of in situ fractured rock

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    We report on laboratory experiments designed to investigate the influence of pore pressure oscillations on the effective permeability of fractured rock. Berea sandstone samples were fractured in situ under triaxial stresses of tens of megapascals, and deionized water was forced through the incipient fracture under conditions of steady and oscillating pore pressure. We find that short-term pore pressure oscillations induce long-term transient increases in effective permeability of the fractured samples. The magnitude of the effective permeability enhancements scales with the amplitude of pore pressure oscillations, and changes persist well after the stress perturbation. The maximum value of effective permeability enhancement is 5 × 10^(−16) m^2 with a background permeability of 1 × 10^(−15) m^2; that is, the maximum enhanced permeability is 1.5 × 10^(−15) m^2. We evaluate poroelastic effects and show that hydraulic storage release does not explain our observations. Effective permeability recovery following dynamic oscillations occurs as the inverse square root of time. The recovery indicates that a reversible mechanism, such as clogging/unclogging of fractures, as opposed to an irreversible one, like microfracturing, is responsible for the transient effective permeability increase. Our work suggests the feasibility of dynamically controlling the effective permeability of fractured systems. The result has consequences for models of earthquake triggering and permeability enhancement in fault zones due to dynamic shaking from near and distant earthquakes

    Simulation of Single Reed Instruments Oscillations Based on Modal Decomposition of Bore and Reed Dynamics

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    This paper investigates the sound production in a system made of a bore coupled with a reed valve. Extending previous work (Debut, 2004), the input impedance of the bore is projected on the modes of the air column. The acoustic pressure is therefore calculated as the sum of modal components. The airrrflow blown into the bore is modulated by reed motion, assuming the reed to be a single degree of freedom oscillator. Calculation of self-sustained oscillations controlled by time-varying mouth pressure and player's embouchure parameter is performed using ODE solvers. Results emphasize the par ticipation of the whole set of components in the mode locking process. Another impor tant feature is the mutual innnfluence of reed and bore resonance during growing blowing pressure transients, oscillation threshold being altered by the reed natural frequency and the reed damping. Steady-state oscillations are also investigated and compared with results given by harmonic balance method and by digital sound synthesis

    Autonomous Driving Platform Performance Analysis

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    Through data analysis of various plots and figures it will be possible to determine the best control parameters to get the best performance out of the autonomous driving platform. This data, presented in this thesis, will show quantitatively what the best control strategies are through comparison of different versions of the platform

    Combining different validation techniques for continuous software improvement - Implications in the development of TRNSYS 16

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    Validation using published, high quality test suites can serve to identify different problems in simulation software: modeling and coding errors, missing features, frequent sources of user confusion. This paper discusses the application of different published validation procedures during the development of a new TRNSYS version: BESTEST/ASHRAE 140 (Building envelope), HVAC BESTEST (mechanical systems) and IEA ECBCS Annex 21 / SHC Task 12 empirical validation (performance of a test cell with a very simple mechanical system). It is shown that each validation suite has allowed to identify different types of problems. Those validation tools were also used to diagnose and fix some of the identified problems, and to assess the influence of code modifications. The paper also discusses some limitations of the selected validation tools

    Characterizing mixed mode oscillations shaped by noise and bifurcation structure

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    Many neuronal systems and models display a certain class of mixed mode oscillations (MMOs) consisting of periods of small amplitude oscillations interspersed with spikes. Various models with different underlying mechanisms have been proposed to generate this type of behavior. Stochastic versions of these models can produce similarly looking time series, often with noise-driven mechanisms different from those of the deterministic models. We present a suite of measures which, when applied to the time series, serves to distinguish models and classify routes to producing MMOs, such as noise-induced oscillations or delay bifurcation. By focusing on the subthreshold oscillations, we analyze the interspike interval density, trends in the amplitude and a coherence measure. We develop these measures on a biophysical model for stellate cells and a phenomenological FitzHugh-Nagumo-type model and apply them on related models. The analysis highlights the influence of model parameters and reset and return mechanisms in the context of a novel approach using noise level to distinguish model types and MMO mechanisms. Ultimately, we indicate how the suite of measures can be applied to experimental time series to reveal the underlying dynamical structure, while exploiting either the intrinsic noise of the system or tunable extrinsic noise.Comment: 22 page

    Circumbinary Chaos: Using Pluto's Newest Moon to Constrain the Masses of Nix & Hydra

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    The Pluto system provides a unique local laboratory for the study of binaries with multiple low mass companions. In this paper, we study the orbital stability of P4, the most recently discovered moon in the Pluto system. This newfound companion orbits near the plane of the Pluto-Charon binary, roughly halfway between the two minor moons Nix and Hydra. We use a suite of few body integrations to constrain the masses of Nix and Hydra, and the orbital parameters of P4. For the system to remain stable over the age of the Solar System, the masses of Nix and Hydra likely do not exceed 5e16 kg and 9e16 kg, respectively. These upper limits assume a fixed mass ratio between Nix and Hydra at the value implied by their median optical brightness. Our study finds that stability is more sensitive to their total mass and that a downward revision of Charon's eccentricity (from our adopted value of 0.0035) is unlikely to significantly affect our conclusions. Our upper limits are an order of magnitude below existing astrometric limits on the masses of Nix and Hydra. For a density at least that of ice, the albedos of Nix and Hydra would exceed 0.3. This constraint implies they are icy, as predicted by giant impact models. Even with these low masses, P4 only remains stable if its eccentricity e < 0.02. The 5:1 commensurability with Charon is particularly unstable, Combining stability constraints with the observed mean motion places the preferred orbit for P4 just exterior to the 5:1 resonance. These predictions will be tested when the New Horizons satellite visits Pluto. Based on the results for the Pluto-Charon system, we expect that circumbinary, multi-planet systems will be more widely spaced than their singleton counterparts. Further, circumbinary exoplanets close to the three-body stability boundary, such as those found by Kepler, are less likely to have other companions nearby.Comment: 12 pages, 7 figure

    Neutrino Signals of Core-Collapse Supernovae in Underground Detectors

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    For a suite of fourteen core-collapse models during the dynamical first second after bounce, we calculate the detailed neutrino "light" curves expected in the underground neutrino observatories Super-Kamiokande, DUNE, JUNO, and IceCube. These results are given as a function of neutrino-oscillation modality (normal or inverted hierarchy) and progenitor mass (specifically, post-bounce accretion history), and illuminate the differences between the light curves for 1D (spherical) models that don't explode with the corresponding 2D (axisymmetric) models that do. We are able to identify clear signatures of explosion (or non-explosion), the post-bounce accretion phase, and the accretion of the silicon/oxygen interface. In addition, we are able to estimate the supernova detection ranges for various physical diagnostics and the distances out to which various temporal features embedded in the light curves might be discerned. We find that the progenitor mass density profile and supernova dynamics during the dynamical explosion stage should be identifiable for a supernova throughout most of the galaxy in all the facilities studied and that detection by any one of them, but in particular more than one in concert, will speak volumes about the internal dynamics of supernovae.Comment: Accepted to Monthly Notices of the Royal Astronomical Societ
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