How effective and efficient are multiobjective evolutionary algorithms at hydrologic model calibration?

International audienceThis study provides a comprehensive assessment of state-of-the-art evolutionary multiobjective optimization (EMO) tools' relative effectiveness in calibrating hydrologic models. The relative computational efficiency, accuracy, and ease-of-use of the following EMO algorithms are tested: Epsilon Dominance Nondominated Sorted Genetic Algorithm-II (?-NSGAII), the Multiobjective Shuffled Complex Evolution Metropolis algorithm (MOSCEM-UA), and the Strength Pareto Evolutionary Algorithm 2 (SPEA2). This study uses three test cases to compare the algorithms' performances: (1) a standardized test function suite from the computer science literature, (2) a benchmark hydrologic calibration test case for the Leaf River near Collins, Mississippi, and (3) a computationally intensive integrated surface-subsurface model application in the Shale Hills watershed in Pennsylvania. One challenge and contribution of this work is the development of a methodology for comprehensively comparing EMO algorithms that have different search operators and randomization techniques. Overall, SPEA2 attained competitive to superior results for most of the problems tested in this study. The primary strengths of the SPEA2 algorithm lie in its search reliability and its diversity preservation operator. The biggest challenge in maximizing the performance of SPEA2 lies in specifying an effective archive size without a priori knowledge of the Pareto set. In practice, this would require significant trial-and-error analysis, which is problematic for more complex, computationally intensive calibration applications. ?-NSGAII appears to be superior to MOSCEM-UA and competitive with SPEA2 for hydrologic model calibration. ?-NSGAII's primary strength lies in its ease-of-use due to its dynamic population sizing and archiving which lead to rapid convergence to very high quality solutions with minimal user input. MOSCEM-UA is best suited for hydrologic model calibration applications that have small parameter sets and small model evaluation times. In general, it would be expected that MOSCEM-UA's performance would be met or exceeded by either SPEA2 or ?-NSGAII

Spin wave emission by spin-orbit torque antennas

We study the generation of propagating spin waves in Ta/CoFeB waveguides by spin-orbit torque antennas and compare them to conventional inductive antennas. The spin-orbit torque was generated by a transverse microwave current across the magnetic waveguide. The detected spin wave signals for an in-plane magnetization across the waveguide (Damon-Eshbach configuration) exhibited the expected phase rotation and amplitude decay upon propagation when the current spreading was taken into account. Wavevectors up to about 6 rad/$\mu$m could be excited by the spin-orbit torque antennas despite the current spreading, presumably due to the non-uniformity of the microwave current. The relative magnitude of generated anti-damping spin-Hall and Oersted fields was calculated within an analytic model and it was found that they contribute approximately equally to the total effective field generated by the spin-orbit torque antenna. Due to the ellipticity of the precession in the ultrathin waveguide and the different orientation of the anti-damping spin-Hall and Oersted fields, the torque was however still dominated by the Oersted field. The prospects for obtaining a pure spin-orbit torque response are discussed, as are the energy efficiency and the scaling properties of spin-orbit torque antennas.Comment: 20 pages, 5 figure

Magnetic dephasing in mesoscopic spin glasses

We have measured Universal Conductance Fluctuations in the metallic spin glass Ag:Mn as a function of temperature and magnetic field. From this measurement, we can access the phase coherence time of the electrons in the spin glass. We show that this phase coherence time increases with both the inverse of the temperature and the magnetic field. From this we deduce that decoherence mechanisms are still active even deep in the spin glass phase

Operational experience with a CID camera system

In future high intensity, high energy accelerators particle losses must be minimized as activation of the vacuum chambers or other components makes maintenance and upgrade work time consuming and costly. It is imperative to have a clear understanding of the mechanisms that can lead to halo formation, and to have the possibility to test available theoretical models with an adequate experimental setup. Measurements based on optical transition radiation (OTR) provide an interesting opportunity for analyzing the transverse beam profile due to the fast time response and very good linearity of the signal with respect to the beam intensity. On the other hand, the dynamic range of typical acquisition systems as they are used in the CLIC test facility (CTF3) is typically limited and must be improved before these systems can be applied to halo measurements. One possibility for high dynamic range measurements is an innovative camera system based on charge injection device (CID) technology. With possible future measurements in CTF3 in mind, comparative measurements performed with this innovative camera system, a standard CCD camera and a step-by-step measurement technique based on a small photomultiplier are summarized with emphasi

A transmission problem across a fractal self-similar interface

We consider a transmission problem in which the interior domain has infinitely ramified structures. Transmission between the interior and exterior domains occurs only at the fractal component of the interface between the interior and exterior domains. We also consider the sequence of the transmission problems in which the interior domain is obtained by stopping the self-similar construction after a finite number of steps; the transmission condition is then posed on a prefractal approximation of the fractal interface. We prove the convergence in the sense of Mosco of the energy forms associated with these problems to the energy form of the limit problem. In particular, this implies the convergence of the solutions of the approximated problems to the solution of the problem with fractal interface. The proof relies in particular on an extension property. Emphasis is put on the geometry of the ramified domain. The convergence result is obtained when the fractal interface has no self-contact, and in a particular geometry with self-contacts, for which an extension result is proved

EFFECTS OF ZOLEDRONATE ON TWO- AND THREE-DIMENSIONAL OSTEOBLAST CULTURES

Oral Communication presented at the ";;Forum des Jeunes Chercheurs";;, Brest (France) 2011

Development of an ENVISAT altimetry processor providing sea level continuity between open ocean and Arctic leads

Over the Arctic regions, current conventional altimetry products suffer from a lack of coverage or from degraded performance due to the inadequacy of the standard process- ing applied in the ground segments. This paper presents a set of dedicated algorithms able to process consistently returns from open ocean and from sea ice leads in the Arctic Ocean (detection of water surfaces and derivation of water levels using returns from these surfaces). This processing extends the area over which a precise sea level can be com- puted. In the frame of the ESA Sea Level Climate Change Initiative (CCI, http://cci.esa.int), we have first developed a new surface identification method combining two complementary solutions, one using a multiple criteria approach (in particular the backscattering coefficient and the peakiness coefficient of the waveforms) and one based on a supervised neural net- work approach. Then, a new physical model has been developed (modified from the Brown model to include anisotropy in the scattering from calm protected water surfaces) and has been implemented in a Maximum Likelihood Estimation retracker. This allows us to process both sea-ice lead waveforms (characterized by their peaky shapes) and ocean waveforms (more diffuse returns), guaranteeing, by construction, continuity between open ocean and ice-covered regions. This new processing has been used to produce maps of Arctic sea level anomaly from 18Hz ENVISAT/RA-2 dat

Local impacts of climate change on winter wheat in Great Britain

Under future CMIP5 climate change scenarios for 2050, an increase in wheat yield of about 10% is predicted in Great Britain (GB) as a result of the combined effect of CO2 fertilization and a shift in phenology. Compared to the present day, crops escape increases in the climate impacts of drought and heat stresses on grain yield by developing before these stresses can occur. In the future, yield losses from water stress over a growing season will remain about the same across Great Britain with losses reaching around 20% of potential yield, while losses from drought around flowering will decrease and account for about 9% of water limited yield. Yield losses from heat stress around flowering will remain negligible in the future. These conclusions are drawn from a modelling study based on the response of the Sirius wheat simulation model to local-scale 2050-climate scenarios derived from 19 Global Climate Models from the CMIP5 ensemble at 25 locations representing current or potential wheat-growing areas in GB. However, depending on susceptibility to water stress, substantial interannual yield variation between locations is predicted, in some cases suggesting low wheat yield stability. For this reason, local-scale studies should be performed to evaluate uncertainties in yield prediction related to future weather patterns