A vibrational CASSCF study of stretch-bend interactions and their influence on infrared intensities in the water molecule

Summary An extension of the multiconfigurational SCF approach for the resolution of the vibrational problem is presented; it follows the philosophy of the CASSCF method developed in Quantum Chemistry. The new method allows a more complete treatment of anharmonic mode couplings, converges much faster and gives a clearer physical insight of vibrational interactions. This is exemplified by the calculation of infrared transition moments in the H₂O and D₂O isotopomers of the water molecule. It is shown how this property varies with the quality of the wave function when vibrational resonances occur. A detailed analysis by means of this new VCASSCF method demonstrates the crucial importance of excited bending oscillators in the intensity of some pure stretching transitions.Boursier F.R.I.A.     

Potential,value, and coalition formation

In this paper, a simple probabilistic model of coalition formation provides a unified interpretation for several extensions of the Shapley value. Weighted Shapley values, semivalues, weak (weighted or not) semivalues, and the Shapley value itself appear as variations of this model. Moreover, some notions that have been introduced in the search of alternatives to Shapley’s seminal characterization, as ‘balanced contributions’ and the ‘potential’ are reinterpreted from this point of view. Natural relationships of these conditions with some mentioned families of ‘values’ are shown. These reinterpretations strongly suggest that these conditions are more naturally interpreted in terms of coalition formation than in terms of the classical notion of ‘value.’      

Voting to select projects in participatory budgeting

In participatory budgeting, citizens are invited to vote on different projects. This paper sets out to study the voting stage of participatory budgeting from theoretical and practical perspectives. At theoretical level, the potential objectives of voting procedures are examined. From the practical point of view it should be easy to select projects, even when the number of projects is large. This paper proposes three algorithms which are theoretically justified and can be easily applied. Participatory budgeting in the town of Portugalete (Spain) provides a test for them. The results obtained with 2018 voting data suggest that the algorithm that includes the costs of the projects at the selection stage performs better than the others. KEYWORDS: decision processes; participatory budgeting; collective decision-making; cost-benefit analysis.     

Zone–edge optical transitions in GaAs/AlAs lateral superlattices grown on vicinal surfaces by molecular beam epitaxy

We report on new features in the photoluminescence excitation (PLE) spectra and PLE linear polarization spectra of GaAs/AlAs lateral superlattices grown by molecular beam epitaxy (MBE). These lines appear systematically as the tilt angle of the lateral superlattice is varied. They are identified as zone–edge excitonic transitions by comparison between experimental data and detailed numerical calculations of optical transitions including valence-band mixing and tilt effects.     

Optimal posting price of limit orders: learning by trading

We model a trader interacting with a continuous market as an iterative algorithm that adjusts limit prices at a given rhythm and propose a procedure to minimize trading costs. We prove the $a.s.$ convergence of the algorithm under assumptions on the cost function and give some practical criteria on model parameters to ensure that the conditions to use the algorithm are met (notably, using the co-monotony principle). We illustrate our results with numerical experiments on both simulated and market data.     

From the vanadates to 3d-metal oxides negative electrodes

With respect to lithium batteries, vanadate-based electrodes display large electrochemical capacities that rapidly decay during the cycling. A full study of the 3d-metal(M)-based vanadates performed using in situ DRX, XAS and TEM has enabled to pinpoint the important role of the 3d-metal cations, and has motivated the study of simple metal oxides MO, (M=Co, Ni, Cu, Fe) in rechargeable Li cells. We found that these materials could reversibly react with a large amount of lithium leading to capacities as high as 800 mAh/g. The reactivity mechanism totally differs from the well established one based on Li insertion-deinsertion or Li alloying reactions but mainly involves the formation of highly reactive metallic nanoparticles that favor Li₂O formation-decomposition. Besides, we gave experimental evidence of an electrochemically driven polymerization-dissolution process at low potential, which is highly reversible, and emphasized the importance of the role of the electrolyte on such a process. Finally, the universality of this mechanism to account for the large Li reactivity at low voltage in many 3d-metal (Co, Ni, Fe, Cu, Mn)-based oxides is discusséd together with the urgent issues to be solved for such oxide anodes to stand as serious alternative candidates for today’s carbon anodes in Li-ion cells. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.