Magnetostatics of synthetic ferrimagnet elements

We calculate the magnetostatic energy of synthetic ferrimagnet (SyF) elements, consisting of two thin ferromagnetic layers coupled antiferromagnetically through RKKY coupling. We calculate exact formulas as well as approximate yet accurate ones, which can be used to easily derive energy barriers and anisotropy fields of SyF. These can be used to evaluate coercivity, thermal stability and other useful quantities

Affine Solitons: A Relation Between Tau Functions, Dressing and B\"acklund Transformations

We reconsider the construction of solitons by dressing transformations in the sine-Gordon model. We show that the $N$-soliton solutions are in the orbit of the vacuum, and we identify the elements in the dressing group which allow us to built the $N$-soliton solutions from the vacuum solution. The dressed $\tau$-functions can be computed in two different ways~: either using adjoint actions in the affine Lie algebra $\hat {sl_2}$, and this gives the relation with the B\"acklund transformations, or using the level one representations of the affine Lie algebra $\widehat{sl_2}$, and this directly gives the formulae for the $\tau$-functions in terms of vertex operators.Comment: 33 pages. SPhT-92-055; LPTHE-92-1

Consensus theories: an oriented survey

This article surveys seven directions of consensus theories: Arrowian results, federation consensus rules, metric consensus rules, tournament solutions, restricted domains, abstract consensus theories, algorithmic and complexity issues. This survey is oriented in the sense that it is mainly – but not exclusively – concentrated on the most significant results obtained, sometimes with other searchers, by a team of French searchers who are or were full or associate members of the Centre d'Analyse et de Mathématique Sociale (CAMS).Consensus theories ; Arrowian results ; aggregation rules ; metric consensus rules ; median ; tournament solutions ; restricted domains ; lower valuations ; median semilattice ; complexity

Analysis of explicit and implicit discrete-time equivalent-control based sliding mode controllers

Different time-discretization methods for equivalent-control based sliding mode control (ECB-SMC) are presented. A new discrete-time sliding mode control scheme is proposed for linear time-invariant (LTI) systems. It is error-free in the discretization of the equivalent part of the control input. Results from simulations using the various discretized SMC schemes are shown, with and without perturbations. They illustrate the different behaviours that can be observed. Stability results for the proposed scheme are derived

Career Concerns and the Acquisition of Firm-Specific Skills

This paper studies compensation schemes that can motivate a worker to acquire nonverifiable firm-specific skills, when the acquisition process is also one of learning about managerial talent. At the beginning of the employment relationship, the worker encounters opportunities to enhance her specific human capital. Greater skills may increase the chances of being promoted; but as more opportunities are taken, more is learned about the worker's talent, and someone displaying low talent is sure not to be promoted. In this context we show that first-best firm-specific skills collection can be implemented with a scheme that combines discretionary promotions, an appropriate wage schedule and subsidies of training at the margin. ZUSAMMENFASSUNG - (Karrierepläne und der Erwerb von unternehmensspezifischen Fähigkeiten) In diesem Beitrag werden Entlohnungssysteme untersucht, die einen Beschäftigten dazu motivieren können nichtverifizierbare unternehmensspezifische Fähigkeiten zu erwerben, wenn es sich darum handelt, in diesem Prozeß auch Managementfähigkeiten zu erlernen. Zu Beginn der Beschäftigung sieht sich der Beschäftigte Möglichkeiten gegenübergestellt, sein spezifisches Humankapital zu vergrößern. Bessere Fähigkeiten können die Wahrscheinlichkeit für eine Beförderung erhöhen. Je mehr Gelegenheiten er wahrnimmt, desto besser wird auch das Talent des Beschäftigten erkannt. Bei geringem Talent wird auch deutlich, daß keine Beförderung ansteht. In diesem Zusammenhang wird gezeigt, daß der erstbeste unternehmensspezifische Fähigkeitserwerb mit einem Entlohnungsschema umgesetzt werden kann, das Beförderungen mit Ermessensspielraum bei einem angemessenem Gehalt und ein Fortbildungsförderungssystem "am Rand" verbindet.personnel management; human capital formation; occupational choice; labor productivity

Periodic optimal control for biomass productivity maximization in a photobioreactor using natural light

We address the question of optimization of the microalgal biomass long term productivity in the framework of production in photobioreactors under the influence of day/night cycles. For that, we propose a simple bioreactor model accounting for light attenuation in the reactor due to biomass density and obtain the control law that optimizes productivity over a single day through the application of Pontryagin's maximum principle, with the dilution rate being the main control. An important constraint on the obtained solution is that the biomass in the reactor should be at the same level at the beginning and at the end of the day so that the same control can be applied everyday and optimizes some form of long term productivity. Several scenarios are possible depending on the microalgae's strain parameters and the maximal admissible value of the dilution rate: bang-bang or bang-singular-bang control or, if the growth rate of the algae is very strong in the presence of light, constant maximal dilution. A bifurcation diagram is presented to illustrate for which values of the parameters these different behaviors occur. Finally, a simple sub-optimal bang-bang strategy is proposed that numerically achieves productivity levels that almost match those of the optimal strategy

Cross-border metropolitan integration in Europe (Luxembourg, Basel and Geneva)

This article questions the integration processes in three small cross-border metropolitan areas: Luxembourg, Basel and Geneva. By referring to an original analysis framework, it evaluates the nature and intensity of the functional and institutional integration and highlights the elements that structure the cooperation between the actors. The analysis shows that there is not necessarily a reciprocal link between the size of the functional area and the extent of the cooperation. Whilst no metropolitan-sized project is on the agenda in Luxembourg, the example of Basel and Geneva shows that the presence of a national border offers an opportunity to invent original forms of governance, increase the autonomy of the local authorities by different types of cooperation which transcend the institutional and territorial divides, and enable the international character of the metropolitan centre to be valued for what it is. In a context of global competition, these features represent an undeniable benefit.Metropolitan regions ; Governance ; Border studies ; Integration ; Europe

Synthetic aperture radar demonstration kit for signal processing education

A Synthetic Aperture Radar scale model has been developed to improve signal processing teaching. Based on low frequency ultrasound transmission, it is a low cost demonstration kit. The overall software is directly running on Matlab® and allows easy and realtime modifications. This educational tool can be used to illuminate a scene using different waveforms, and then see the effects on the formed image. It can also be used in a more advanced way to test different signal processing in order to improve image focusing or to reduce computation burden