Quartz oscillators: deriving oscillation condition by symbolic calculus

International audienceThis paper presents the method used to derive the oscillation condition by using symbolic calculus. The program is based on the full nonlinear Barkhausen criterion method. The behaviour of an oscillator is described by a complex polynomial called the characteristic polynomial. This polynomial enables us to calculate the steady state features of the oscillation as well as the differential equation for transient analysis in the time domain. The literal determination of this characteristic polynomial involves lengthy algebraic calculations and cannot be done by hand as soon as the electronic oscillator circuit involves too many components. We recently developed a formal calculus program allowing to automatically obtain all necessary equations for oscillation analysis. We propose new methods to calculate them in an optimal form

Automatic formal derivation of the oscillation condition

International audienceThe behavior of a quartz crystal oscillator can be described by a nonlinear characteristic polynomial whose coefficients are function of the circuit parameters. Solving the polynomial in the frequency domain leads to the steady state oscillation amplitude and frequency. In the time domain, it gives the oscillator signal transient. Deriving the characteristic polynomial from the circuit description involves lengthy and tedious algebraic calculations if they are performed by hand. They may be now performed by using the symbolic manipulation capabilities of commercially available softwares. However, symbolic analysis using brute force method inevitably leads to an explosion of terms in equations. The paper will present a fully automatic method for generating the coding of an oscillator characteristic polynomial directly from the SPICE description netlist. The code thus generated is eventually compiled and takes place in an oscillator library. Then it is linked with the numerical main program that solves the polynomials. Solutions to overcome problems related to automatic symbolic calculations are presented and discussed. It is shown that the method used leads to concise and efficient code

Am and pm noise analysis in quartz crystal oscillators: symbolic calculus approach

International audienceIncreasing performance of quartz crystal oscillators as well as predictability requirements when developing the devices need accurate analysis of noise sources. Our work is devoted to understand how an oscillator reacts to additive noise of an element in the electronic circuit. Up to now, oscillator designers often refer to the well-known Leeson's model to explain the shape of phase noise spectral density. This physical model only allows one to obtain the global phase noise spectrum. By considering each noise source individually, we can obtain the comparative contribution of the sources. Then AM and PM noise source spectra can be related to the circuit architecture. The influence of an individual noise source can be obtained from the differential equation describing the oscillator behavior. Nevertheless, setup of the differential equation from the inspection of the circuit involves lengthy and tedious algebraic calculations almost impossible to achieve by hand. By using symbolic calculation capability of formal calculus programs, it is possible to automatically derive the differential equation of the oscillator including noise sources from a SPICE netlist description of the circuit. The resulting expressions can be edited under the form of high level language code (Fortran, C, ...) which is eventually compiled and linked with the numerical programs calculating the noise spectra. This paper presents the method to construct the differential equations in a fully automatic way regardless of the studied oscillator circuit

Managing small-scale fisheries confronted with socio-economic changes in New Caledonia (South Pacific)

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Functional Redundancy Patterns Reveal Non-Random Assembly Rules in a Species-Rich Marine Assemblage

The relationship between species and the functional diversity of assemblages is fundamental in ecology because it contains key information on functional redundancy, and functionally redundant ecosystems are thought to be more resilient, resistant and stable. However, this relationship is poorly understood and undocumented for species-rich coastal marine ecosystems. Here, we used underwater visual censuses to examine the patterns of functional redundancy for one of the most diverse vertebrate assemblages, the coral reef fishes of New Caledonia, South Pacific. First, we found that the relationship between functional and species diversity displayed a non-asymptotic power-shaped curve, implying that rare functions and species mainly occur in highly diverse assemblages. Second, we showed that the distribution of species amongst possible functions was significantly different from a random distribution up to a threshold of ∼90 species/transect. Redundancy patterns for each function further revealed that some functions displayed fast rates of increase in redundancy at low species diversity, whereas others were only becoming redundant past a certain threshold. This suggested non-random assembly rules and the existence of some primordial functions that would need to be fulfilled in priority so that coral reef fish assemblages can gain a basic ecological structure. Last, we found little effect of habitat on the shape of the functional-species diversity relationship and on the redundancy of functions, although habitat is known to largely determine assemblage characteristics such as species composition, biomass, and abundance. Our study shows that low functional redundancy is characteristic of this highly diverse fish assemblage, and, therefore, that even species-rich ecosystems such as coral reefs may be vulnerable to the removal of a few keystone species

Caractérisation du comportement anisotrope en fatigue d’un acier forgé

Dans cette étude, différentes méthodes expérimentales sont employées pour déterminer le comportement anisotrope monotone et en fatigue d’un acier 25MnCrSiVB6 laminé: le METASCO MC. Ce matériau de microstructure bainitique a la particularité de posséder des inclusions allongées dans le sens du laminage. Des résultats d’essais de traction monotone et de résilience sont présentés. Concernant la caractérisation du comportement en fatigue, des résultats issus d’essais d’auto-échauffement et de fatigue classiques sont comparés et discutés

Microgéométrie et tenue en fatigue d'un acier bainitique à haute limite d'élasticité usiné par fraisage de finition à l'outil hémisphérique

La tenue en fatigue des pièces usinées est fortement influencée par l'intégrité de surface et donc les conditions de coupe. Différents essais de fatigue ont été réalisés et montrent une corrélation entre les aspects mécaniques, géométriques de l'intégrité de surface et la limite d'endurance. Une approche probabiliste à 2 échelles, basée sur la distribution de tailles d'entaille, est proposée pour prendre en compte l'influence de la microgéométrie sur la tenue en fatigue. Les résultats montrent une bonne corrélation entre la distribution de défauts obtenue par le modèle et celle mesurée

Managing Small-Scale Fisheries Confronted With Socio-Economic Changes in New Caledonia (South Pacific)

On the rural Northwest coast of New Caledonia, the settlement of a world class mining complex has initiated rapid socio-economic changes, linked with a considerable demographic increase (+ 65% between 2007 and 2015) and plentiful job opportunities. In 2007 and 2009, studies on fisheries and commercialization of reef finfish and invertebrates were conducted to assess how these changes could impact resource-use patterns. Results showed that 1) economic, 2) social and 3) ecological changes were expected. 1) The increase in demand (+70%) may strengthen the market for marine products through the increase in local commercial fishing or external supply that would diversify and lessen local fishing pressure. 2) The lagoon uses were strongly linked to the social background of fishers. Subsistence and recreational fishing practises were part of ways of life in this rural area and may be modified by the ongoing local economic boom. 3) The overall fishing pressure (0.26 t/km²/year) was low. However, its spatial distribution showed that some areas were close to overfishing. Results suggested that the expected rise in commercial and recreational fishing could lead to unsustainable exploitation levels in these zones. Given the scope of potential changes, public authorities have to manage changing lagoon uses to balance the indirect effects of economic development on the local natural and social landscape. They will have to choose options that would support the development of local fisheries, representing about 500,000 ¬ of sales a year, or maintain the present social organization and ecological status of reefs.Keywords: Fish and Aquaculture Sectors Development, Small Scale Fisheries, Fisheries Economic

Imaging and multi-omics datasets converge to define different neural progenitor origins for ATRT-SHH subgroups

Atypical teratoid rhabdoid tumors (ATRT) are divided into MYC, TYR and SHH subgroups, suggesting diverse lineages of origin. Here, we investigate the imaging of human ATRT at diagnosis and the precise anatomic origin of brain tumors in the Rosa26-Cre$^{ERT2}$::Smarcb1$^{flox/flox}$ model. This cross-species analysis points to an extra-cerebral origin for MYC tumors. Additionally, we clearly distinguish SHH ATRT emerging from the cerebellar anterior lobe (CAL) from those emerging from the basal ganglia (BG) and intra-ventricular (IV) regions. Molecular characteristics point to the midbrain-hindbrain boundary as the origin of CAL SHH ATRT, and to the ganglionic eminence as the origin of BG/IV SHH ATRT. Single-cell RNA sequencing on SHH ATRT supports these hypotheses. Trajectory analyses suggest that SMARCB1 loss induces a de-differentiation process mediated by repressors of the neuronal program such as REST, ID and the NOTCH pathway