Reducing variability that is due to secondary pigments in the retrieval of chlorophyll a concentration from marine reflectance: a case study in the western equatorial Pacific Ocean

A neural network is developed to retrieve chlorophyll a concentration from marine reflectance by use of the five visible spectral bands of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The network, dedicated to the western equatorial Pacific Ocean, is calibrated with synthetic data that vary in terms of atmospheric content, solar zenith angle, and secondary pigments. Pigment variability is based on in situ data collected in the study region and is introduced through nonlinear modeling of phytoplankton absorption as a function of chlorophyll a, b, and c and photosynthetic and photoprotectant carotenoids. Tests performed on simulated yet realistic data show that chlorophyll a retrievals are substantially improved by use of the neural network instead of classical algorithms, which are sensitive to spectrally uncorrelated effects. The methodology is general, i.e., is applicable to regions other than the western equatorial Pacific Ocean.     

Leveraging countermeasures as a service for VoIP security in the cloud

The emergence of cloud computing is contributing to the integration of multiple services, in particular VoIP services. While the cloud has recently been used for performing security attacks targeting IP telephony, it also provides new opportunities for supporting the security of this service. In that context, we propose a risk management strategy for VoIP cloud based on security countermeasures that may be outsourced as services. We present the architecture of our solution and its components in the context of services implementing the SIP protocol. We describe the mathematical modelling supporting our approach and detail different treatment strategies for the application of countermeasures. Finally, we quantify the benefits and limits of these strategies based on extensive simulation results. When a countermeasure fails, these strategies allow us to maintain the risk level low at an additional cost of up to 7%, or to accept an additional risk of up to 12%. They can also be combined to obtain a trade‐off between cost and performance. Copyright © 2013 John Wiley & Sons, Ltd.     

FIB Aplasia through probabilistic routing and autoforwarding

In this work, we propose Aplasia, an holistic architecture with a radical design. Aiming at simplifying the inner network devices (and so their cost), we tradeoff node architecture- and algorithmic-complexity for an increased (but tunable) communication cost. The main ingredients of our recipe are (i) the use of complete paths directly in the frames header, that allows core devices to perform data-plane switching functions without lookup and (ii) the use of a greedy probabilistic routing algorithm to quickly discover multiple, near optimal, paths in the control plane. We extensively simulate, analyze and implement our proposal to testify its soundness.     

Flame balls in mixing layers

We present a study of flame balls in a two-dimensional mixing layer with one objective being to derive an ignition criterion (for triple-flames) in such a non-homogeneous reactive mixture. The problem is formulated within a thermo-diffusive single-reaction model and leads for large values of the Zeldovich number β$\beta$ to a free boundary problem. The free boundary problem is then solved analytically in the asymptotic limit of large values of the Damköhler number, which represents a non-dimensional measure of the (square of the) mixing layer thickness. The explicit solution, which describes a non-spherical flame ball generalising the classical Zeldovich flame balls (ZFB) to a non-uniform mixture, is shown to exist only if centred at a single location. This location is found to be precisely that of the leading-edge of a triple-flame in the mixing layer, and typically differs from the location of the stoichiometric surface by an amount of order β^-1${\beta }^{-1}$ depending only on a normalised stoichiometric coefficient Δ$\Delta$.     

Expert networks as science-policy interlocutors in the implementation of a monitoring reporting and verification (MRV) system

The Paris Agreement, which entered into effect in 2016, emphasizes a definite timeline for communicating and maintaining successive nationally determined contributions (NDCs) that it plans to achieve in addressing climate change. This calls for the development of a measurement, reporting and verification (MRV) system and a Capacity-building Initiative for Transparency (CBIT). Though such actions are universally accepted by the Parties to the Paris Agreement, earlier studies have shown that there remain technological, social, political and financial constrains which will affect the development and deployment of such a system. In this paper, using a case study on MRV implementation in Bogor City in Indonesia, how the above-mentioned challenges can be overcome is outlined through a technological and policy innovation process where scientists and technologists (collectively referred as expert networks) can join hands with local governments and national policy makers in designing, development and implementation of an MRV system that meets the local, national and global requirements. Through the case study it is further observed that expert networks can act as interactive knowledge generators and policy interlocutors in bridging technology with policy. To be specific, first, a brief history of the international context of MRV and CBIT is outlined. Next, the theoretical underpinning of the study is contextualized within the existing theories related to public policy and international relations. Finally, the case study is outlined and investigated where the engagement of an expert-network and policy makers in the design, development and implementation of an MRV tool is showcased.     

Employing electricity-consumption monitoring systems and integrative time-series analysis models: A case study in Bogor,Indonesia

The Paris Agreement calls for maintaining a global temperature less than 2°C above the pre-industrial level and pursuing efforts to limit the temperature increase even further to 1.5°C. To realize this objective and promote a low-carbon society, and because energy production and use is the largest source of global greenhouse-gas (GHG) emissions, it is important to efficiently manage energy demand and supply systems. This, in turn, requires theoretical and practical research and innovation in smart energy monitoring technologies, the identification of appropriate methods for detailed time-series analysis, and the application of these technologies at urban and national scales. Further, because developing countries contribute increasing shares of domestic energy consumption, it is important to consider the application of such innovations in these areas. Motivated by the mandates set out in global agreements on climate change and low-carbon societies, this paper focuses on the development of a smart energy monitoring system (SEMS) and its deployment in households and public and commercial sectors in Bogor, Indonesia. An electricity demand prediction model is developed for each device using the Auto-Regression eXogenous model. The real-time SEMS data and time-series clustering to explore similarities in electricity consumption patterns between monitored units, such as residential, public, and commercial buildings, in Bogor is, then, used. These clusters are evaluated using peak demand and Ramadan term characteristics. The resulting energy-prediction models can be used for low-carbon planning.     

Robust Finite Volume Schemes for Two-Fluid Plasma Equations

Two-fluid plasma equations are derived by taking moments of Boltzmann equations. Ignoring collisions and viscous terms and assuming local thermodynamic equilibrium we get five moment equations for each species (electrons and ions), known as two-fluid plasma equations. These equations allow different temperatures and velocities for electrons and ions, unlike ideal magnetohydrodynamics equations. In this article, we present robust second order MUSCL schemes for two-fluid plasma equations based on Strang splitting of the flux and source terms. The source is treated both explicitly and implicitly. These schemes are shown to preserve positivity of the pressure and density. In the case of explicit treatment of source term, we derive explicit condition on the time step for it to be positivity preserving. The implicit treatment of the source term is shown to preserve positivity, unconditionally. Numerical experiments are presented to demonstrate the robustness and efficiency of these schemes.     

Channel response to sediment replenishment in a large gravel‐bed river: The case of the Saint‐Sauveur dam in the Buëch River (Southern Alps,France)

The Saint‐Sauveur dam was built in 1992 in the middle section of the Buëch River. Downstream of the dam, a channel incision by several meters was observed. A gravel replenishment operation was planned in order to restore the active channel. An equivalent of two times the mean annual bedload‐transport capacity (43,500 m³) was replenished downstream of the dam in September 2016. The aim of this paper is to quantify morphological change associated with sediment remobilization in order to evaluate the efficiency of the restoration works. The monitoring was based on a combination of (a) change detection using sequential high‐resolution digital elevation models (from airborne LiDAR data), (b) bedload tracing using active ultrahigh‐frequency radio‐frequency identification technology, and (c) complementary field surveys of channel grain‐size distribution and morphology for bedload‐transport computation. Field monitoring allows us to capture a net aggradation along a 2‐km reach after the first post‐replenishment flood. A sediment balance analysis was performed to back‐calculate bedload supply coming from the sluicing operation during the flood. Although the sediment replenishment operation clearly had a positive impact on the morphological conditions of the starved river reach, the effective bedload supply from artificial berms (22,650 m³) was insufficient to initiate substantial channel shifting along the restored reach and a subsequent amplification of the sediment recharge. The combination of high‐resolution topographic resurveys and sediment tracing was successful to evaluate the downstream propagation of sediment replenishment effects.