Carnot cycle for an oscillator

Carnot established in 1824 that the efficiency of cyclic engines operating between a hot bath at absolute temperature $T_{hot}$ and a bath at a lower temperature $T_{cold}$ cannot exceed $1-T_{cold}/T_{hot}$. We show that linear oscillators alternately in contact with hot and cold baths obey this principle in the quantum as well as in the classical regime. The expression of the work performed is derived from a simple prescription. Reversible and non-reversible cycles are illustrated. The paper begins with historical considerations and is essentially self-contained.Comment: 19 pages, 3 figures, sumitted to European Journal of Physics Changed content: Fluctuations are considere

Mode oscillation and harmonic distortions associated with sinusoidal modulation of semiconductor lasers

This paper investigates mode dynamics, operation characteristics and signal distortions associated with sinusoidal modulation of semiconductor lasers. The study is based on intensive integrations of the multimode rate equation model of semiconductor lasers over wide ranges of the modulation frequency and depth. The rate equations take into account both spectral symmetric and asymmetric suppressions of modal gain. The higher harmonic distortions as well as the half harmonic distortion associated with the period doubling effect are investigated. The study is applied to both cases of single-mode and multimode oscillations of the non-modulated laser. The obtained results showed that the modulated signal has six distinct waveforms depending on the modulation conditions; three types have continuous periodic waveforms and the others have periodic pulsing waveforms. The modulated laser is found to oscillate in a single mode under weak modulation where the modulated signal is continuous, whereas the pulsing signals are associated with multimode oscillation. The higher harmonic distortions of single-mode laser are lower than those of two-mode lasers, and become serious at modulation frequencies around the relaxation oscillation frequency. These distortions are highest when the laser output is pulsating and the pulses are superposed by relaxation oscillations. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012

Automatic full noise characterization of microwave GaAs FETs

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Combining minimum wage and exchange rate policy to release the external constraint on growth

In this article we analyse the combination of a minimum wage and a devaluation/depreciation so as to release the external constraint on growth. The policy maker aims at achieving both balanced trade and higher growth. These may be reached by devaluating the domestic currency, which however supports traditional industries characterized by high price elasticity and low income elasticity of demand. The release of the external constraint in the short term then yields a stronger constraint in the longer term. If traditional industries are unskilled and labour‐intensive, the setting of a minimum wage distorts the specialization towards sectors with high demand growth. Devaluation/depreciation and minimum wage may thus be combined to release both the short term and longer term external constraint. We determine the condition for such a policy to be efficient. This combined policy must come with an educational policy that supports skill upgrading. It is typically tailored to ‘advanced emerging countries’ which aim at changing their specialization without slowing their growth.devaluation, external constraint, growth, minimum wage, F41, F43, J3,

Mesure automatique des paramètres de bruit des MESFET hyperfréquences

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Skill premia and intergenerational education mobility: The French case

International audienceIn the case of France, we analyse the changes in the wage value of each education level and the impact of parents’ education and income upon the education attainment of children, sons and daughters. We find a critical decline in the skill premium of the Baccalauréat (‘bac’) in relation to the lowest educational level, and an increase in the skill premia of higher education degrees in relation to the bac, which is however not large enough to erase the decrease in all the skill premia relative to the lowest education. We also find a significant rise in the impact of family backgrounds upon education from 1993 to 2003, i.e., a decrease in intergenerational education mobility, which primarily derives from higher impact of parental incomes. Finally, the gender wage gap is particularly large for the lowest and the highest education degrees, and intergenerational persistence is greater for sons than for daughters

Picosecond and sub-picosecond pulse generation in semiconductor lasers

Generation of short optical pulses in semiconductor lasers is of practical interest for an increasing number of applications. It is also of fundamental interest because of its tight relation with the field of semiconductor laser dynamics. After an introductory review, we compare the performances of gain-switching, Q-switching and mode-locking techniques. The comparison is illustrated by experimental results as well as by laser modelling, some of which are new. A special emphasis is given on the aspects of phase modulation in the semiconductor laser medium. Finally, we discuss some perspectives for further developments.La génération d'impulsions courtes dans les lasers à semiconducteurs est d'intérêt pratique pour un nombre croissant d'applications. Elle présente aussi un intérêt fondamental de par sa relation étroite avec les études de la dynamique du milieu semiconducteur. Après une revue introductive, nous comparons les performances des techniques de commutation de gain, de commutation de pertes de cavité et de blocage de modes. La comparaison est aussi bien illustrée par des résultats expérimentaux que par des résultats de modélisation. Certains de ces résultats sont nouveaux. Un accent particulier est mis sur les aspects de modulation de phase dans le milieu semiconducteur. Nous discutons finalement quelques persepctives de développements nouveaux

Ultrashort tunable emission from gain- /Q- switched laser diodes with highly-attenuating selective external cavity

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Molecular beam epitaxy growth of 1.3~μm high-reflectivity AlGaAsSb/AlAsSb Bragg mirror

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