scholarly journals A framework to evaluate IMEX schemes for atmospheric models

2020 ◽  
Author(s):  
Oksana Guba ◽  
Mark A. Taylor ◽  
Andrew M. Bradley ◽  
Peter A. Bosler ◽  
Andrew Steyer
Keyword(s):  
Acoustic Waves ◽  
Normal Modes ◽  
Evaluation Framework ◽  
Acoustic System ◽  
Atmospheric Models ◽  
Imex Methods ◽  
Imex Schemes ◽  
Runge Kutta ◽  
Implicit And Explicit ◽  
New Framework

Abstract. We present a new evaluation framework for implicit and explicit (IMEX) Runge-Kutta timestepping schemes. The new framework uses a linearized nonhydrostatic system of normal modes. We utilize the framework to investigate stability of IMEX methods and their dispersion and dissipation for gravity, Rossby, and acoustic waves. We test the new framework on a variety of IMEX schemes and use it to develop and analyze a set of 2nd order low-storage IMEX Runge-Kutta methods with high CFL. We show that the new framework is more selective than the 2D acoustic system previously used in literature. Schemes that are stable for the 2D acoustic system are not stable for the system of normal modes.

scholarly journals A framework to evaluate IMEX schemes for atmospheric models

2020 ◽  
Vol 13 (12) ◽  
pp. 6467-6480
Author(s):  
Oksana Guba ◽  
Mark A. Taylor ◽  
Andrew M. Bradley ◽  
Peter A. Bosler ◽  
Andrew Steyer
Keyword(s):  
Acoustic Waves ◽  
Normal Modes ◽  
Evaluation Framework ◽  
Acoustic System ◽  
Time Stepping ◽  
Imex Schemes ◽  
Runge Kutta ◽  
The Stability ◽  
Implicit And Explicit ◽  
New Framework

Abstract. We present a new evaluation framework for implicit and explicit (IMEX) Runge–Kutta time-stepping schemes. The new framework uses a linearized nonhydrostatic system of normal modes. We utilize the framework to investigate the stability of IMEX methods and their dispersion and dissipation of gravity, Rossby, and acoustic waves. We test the new framework on a variety of IMEX schemes and use it to develop and analyze a set of second-order low-storage IMEX Runge–Kutta methods with a high Courant–Friedrichs–Lewy (CFL) number. We show that the new framework is more selective than the 2-D acoustic system previously used in the literature. Schemes that are stable for the 2-D acoustic system are not stable for the system of normal modes.

Real-time completion monitoring with acoustic waves

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. E15-E33 ◽  
Author(s):  
Andrey Bakulin ◽  
Alexander Sidorov ◽  
Boris Kashtan ◽  
Mikko Jaaskelainen
Keyword(s):  
Real Time ◽  
Acoustic Waves ◽  
Acoustic System ◽  
Acoustic Signatures ◽  
New Findings ◽  
Sand Control ◽  
Surveillance Method ◽  
4D Seismic ◽  
Permeability Impairment ◽  
Downhole Sensors

Deepwater production is challenged by well underperformance issues that are hard to diagnose early on and expensive to deal with later. Problems are amplified by reliance on a few complex wells with sophisticated sand-control media. New downhole data are required for better understanding and prevention of production impairment. We introduce real-time completion monitoring (RTCM), a new nonintrusive surveillance method that uses acoustic signals sent via the fluid column to identify permeability impairment in sand-screened completions. The signals are carried by tube waves that move borehole fluid back and forth radially across the completion layers. Such tube waves are capable of instant testing of the presence or absence of fluid communication across the completion and are sensitive to changes occurring in sand screens, gravel sand, perforations, and possibly in the reservoir. The part of the completion that has different impairment from its neighbors will carry tube waves with modified signatures (velocity, attenuation) and will produce a reflection from the boundary where impairment changes. We conduct a laboratory experiment with a model of a completed horizontal borehole and focus on effects of sand-screen permeability on transmitted and reflected acoustic signatures. These new findings form the basis of an RTCM method that can be thought of as “miniaturized” 4D seismic and as a “permanent log” in an individual wellbore. We present experiments with a fiber-optic acoustic system that suggest a nonintrusive way to install downhole sensors on the pipe in realistic completions and thus implement real-time surveillance with RTCM.

scholarly journals A General Framework for Implicit and Explicit Debiasing of Distributional Word Vector Spaces

2020 ◽  
Vol 34 (05) ◽  
pp. 8131-8138
Author(s):  
Anne Lauscher ◽  
Goran Glavaš ◽  
Simone Paolo Ponzetto ◽  
Ivan Vulić
Keyword(s):  
General Framework ◽  
Semantic Information ◽  
Evaluation Framework ◽  
Vector Spaces ◽  
Racial Biases ◽  
Definition Of ◽  
Cross Lingual ◽  
Experimental Findings ◽  
Implicit And Explicit ◽  
Embedding Methods

Distributional word vectors have recently been shown to encode many of the human biases, most notably gender and racial biases, and models for attenuating such biases have consequently been proposed. However, existing models and studies (1) operate on under-specified and mutually differing bias definitions, (2) are tailored for a particular bias (e.g., gender bias) and (3) have been evaluated inconsistently and non-rigorously. In this work, we introduce a general framework for debiasing word embeddings. We operationalize the definition of a bias by discerning two types of bias specification: explicit and implicit. We then propose three debiasing models that operate on explicit or implicit bias specifications and that can be composed towards more robust debiasing. Finally, we devise a full-fledged evaluation framework in which we couple existing bias metrics with newly proposed ones. Experimental findings across three embedding methods suggest that the proposed debiasing models are robust and widely applicable: they often completely remove the bias both implicitly and explicitly without degradation of semantic information encoded in any of the input distributional spaces. Moreover, we successfully transfer debiasing models, by means of cross-lingual embedding spaces, and remove or attenuate biases in distributional word vector spaces of languages that lack readily available bias specifications.

EVALUATING PPP PROJECTS USING A LEAN FRAMEWORK

2018 ◽  
Vol 5 (1) ◽  
Author(s):  
Zeina Malaeb ◽  
Farook Hamzeh
Keyword(s):  
Performance Evaluation ◽  
Performance Indicators ◽  
Project Success ◽  
Evaluation Framework ◽  
Risk Allocation ◽  
The Public ◽  
Effective Performance ◽  
Contractual Agreements ◽  
New Framework

A Public Private Partnership (PPP) describes an arrangement between the public and the private sectors for providing a public asset or service. PPPs are characterized by their long-term nature, complex contractual agreements, and distinct risk allocation formulas, all which distinguish them from traditional procurement routes. Performance evaluation is a prerequisite of performance improvement and is vital to the realization of project success, particularly in PPP projects. In fact, the absence of an effective performance evaluation framework in PPPs serves as a trigger for generating below optimum service quality. Although several performance evaluation frameworks exist, they prove more suitable for traditional projects, which highlights the need to account for the unique features of PPPs. This paper first introduces the various perspectives, from the literature, used to classify project success and evaluate performance. The paper then addresses the aforementioned need by introducing a new framework for evaluating project success, using the lean concepts of transformation, flow, and value. Key Performance Indicators (KPIs) are suggested as part of the framework to serve as performance measures on PPP projects. The introduced lean framework is the first of its kind and fills the gap in PPP research by being one of the few performance evaluation tools customized for PPPs.

Gravity waves as a mechanism of coupling oceanic and atmospheric acoustic waveguides to seismic sources

2020 ◽  
Author(s):  
Oleg Godin
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Seismic Waves ◽  
Wind Waves ◽  
Normal Modes ◽  
Internal Gravity Waves ◽  
Body Waves ◽  
Surface Scattering ◽  
Seismic Sources ◽  
T Waves

<p>Direct excitation of acoustic normal modes in horizontally stratified oceanic waveguides is negligible even for shallow earthquakes because of the disparity between velocities of seismic waves and the sound speed in the water column. T-phases, which propagate at the speed of sound in water, are often reported to originate in the open ocean in the vicinity of the epicenter of an underwater earthquake, even in the absence of prominent bathymetric features or significant seafloor roughness. This paper aims to evaluate the contribution of scattering by hydrodynamic waves into generation of abyssal T-waves. Ocean is modeled as a range-independent waveguide with superimposed volume inhomogeneities due to internal gravity waves and surface roughness due to wind waves and sea swell. Guided acoustic waves are excited by volume and surface scattering of ballistic body waves. The surface scattering mechanism is shown to explain key observational features of abyssal T-waves, including their ubiquity, low-frequency cutoff, presence on seafloor sensors, and weak dependence on the earthquake focus depth. On the other hand, volume scattering due to internal gravity waves proves to be ineffective in coupling the seismic sources to T-waves. The theory is extended to explore a possible role that scattering by gravity waves may play in excitation of infrasonic normal modes of tropospheric and stratospheric waveguides by underwater earthquakes. Model predictions are compared to observations [L. G. Evers, D. Brown, K. D. Heaney, J. D. Assink, P. S. M. Smets, and M. Snellen (2014), Geophys. Res. Lett., <strong>41</strong>, 1644–1650] of infrasonic signals generated by the 2004 Macquarie Ridge earthquake.</p>

scholarly journals The Evaluation Framework in the New CAP 2023–2027: A Reflection in the Light of Lessons Learned from Rural Development

2021 ◽  
Vol 13 (10) ◽  
pp. 5528
Author(s):  
Roberto Cagliero ◽  
Francesco Licciardo ◽  
Marzia Legnini
Keyword(s):  
Rural Development ◽  
Monitoring And Evaluation ◽  
Lessons Learned ◽  
Evaluation Framework ◽  
Open Questions ◽  
Development Policies ◽  
Development Programming ◽  
Programming Period ◽  
Future Evaluation ◽  
New Framework

The new Common Agricultural Policy (CAP) proposal includes few improvements compared to previous programming periods which may reinforce future evaluation, but we can also observe elements that may weaken the assessment, with the risk of repeating past failures. The objective of this essay is to analyse the new framework proposed for evaluation in the future CAP and to promote a collective discussion on how to make evaluations more usable, useful and reliable for users and practitioners. The first part of the paper analyses the main elements of evaluation during the different rural development programming cycles. A second part is dedicated to an examination of the current programming period (2014–2020) and the implications of the introduction of the Common Monitoring and Evaluation Framework (CMEF) and the evaluation plan. In a third part, we critically discuss the proposals for the next programming period and we offer some concluding reflections and two main open questions. From the analyses carried out, many elements emerge to encourage discussion on the role that evaluation has played and can play and the critical points to face. The experiences in rural development policies have introduced important changes in theoretical and implementation terms. In particular, they helped to build evaluation capacity and enabled the involvement of the civil society. However, it is also clear that the European Commission (EC) designed path has often led to an increase in rigidity and orthodoxy towards common frameworks compliance.

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