Critical Behaviour of the 3d Gross-Neveu and Higgs-Yukawa Models

We measure the critical exponents of the three dimensional Gross-Neveu model with two four-component fermions. The exponents are inferred from the scaling behaviour of observables on different lattice sizes. We also calculate the exponents, through a second order epsilon-expansion around 4d, for the three dimensional Higgs-Yukawa model, which is expected to be in the same universality class and we find that the exponents agree. We conclude that the equivalence of the two models remains valid in 3d at fixed small N_f values.Comment: 14 Latex pages 8 PSfigures included at the end,BI-TP-93/31,AZPH-TH/93-19,SPhT 93/0

Identifying spatial patterns of Mediterranean landscapes from geostatistic analysis of remotely-sensed data

The basic tool of geostatistics, the semi-variograms, has been used for quantifying spatial structures of soil and vegetation, as depicted by multi-resolution remotely-sensed images. Experimental semi-variograms of two contrasting Mediterranean landscapes were analysed by reference to simple theoretical models (spherical, exponential, allometric). A more general approach based on the superposition of spherical models of similar sills and varying ranges of influences is proposed for the interpretation of complex spatial patterns of natural vegetated landscapes. (Résumé d'auteur

Testing an area-weighted model for albedo or surface temperature of mixed pixels in mediterranean woodlands

International audienceWe have tested the following assumption for a spatially complex area of natural vegetation in Southern France. The spectral response of a mixed pixel is a linear combination of the individual responses of its components. The test has been done with HCMM data: each pixel (500m spatial resolution) has been characterized by its components defined as physiognomical vegetation units. Results from the analysis of multitemporal HCMM data indicate that the assumption is verified for albedos and surface temperatures

Calculation of power spectra for processes with cyclostationnary characteristics

Modulated transmission is most often achieved by the application of a periodic function . This paper gives the minimum hypotheses allowing a simple and general calculation of the spectrum of the stationarized signal .Les transmissions codées se font, la plupart du temps, à l'aide de processus pilotés par une horloge périodique. On donne les hypothèses minimales permettant d'obtenir un calcul simple et général du spectre de puissance du processus stationnarisé

The sampling formula and A. L. Cauchy

The works of A . L . Cauchy appear in many referencies about band-limited function periodic sampling . The usual Shannon formul a is generally associated with the famous paper of A . L. Cauchy untitled "Mémoire sur diverses formules d'analyse", published in 1841 in the "comptes rendus de l'Académie des Sciences" . This paper shows that the sampling formula may come from anothe r reference by A . L. Cauchy. Moreover, other interpolation formulas (even in the non-periodic case) can be derived from a thir d paper on complex integral calculus .A. L. Cauchy apparaît dans beaucoup de bibliographies concernant l'échantillonnage périodique des fonctions ou des processus à spectre borné. On y associe la formule de Shannon à un article de Cauchy intitulé Mémoire sur diverses formules d'analyse paru en 1841 dans les Comptes rendus de l'Académie des Sciences. Ce qui suit tend à démontrer que c'est dans un autre article de Cauchy que l'on trouve le matériel à l'origine de la formule d'échantillonnage habituelle. On montrera qu'un troisième de ses articles, concernant le calcul des résidus, permet d'envisager d'autres formules d'interpolation, y compris à prises d'échantillons non périodiques

Bioévaluation de la pollution des sédiments de la Seine (région parisienne) par l'emploi d'un bioessai basé sur la croissance à court terme de la micro-algue Selenastrum capricornutum Printz

La bioévaluation de l'état de santé des fonds meubles dépend des conditions expérimentales du traitement des échantillons de sédiment conduisant à l'obtention de la phase aqueuse sur laquelle sont effectuées les analyses chimiques et toxicologiques.Au cours de cette étude préliminaire nous avons considéré l'action de ces principales conditions ; nous constatons que l'effet inhibiteur d'un sédiment vis-à-vis de la croissance à court terme de la micro-algue Selenastrum capricornutum Printz n'est pas aisément levé, que ce soit par lessivages successifs du sédiment, par filtration plus fine de l'eau extraite à partir de ce dernier ou par autoclavage préalable de ce même sédiment, il peut l'être par contre après biodégradation.Cette étude expérimentale a permis de comparer entre eux les pouvoirs inhibiteurs des fonds meubles de la Seine (région parisienne).On note qu'il n'y a pas de corrélation entre les teneurs en métaux lourds souvent importantes des eaux issues des sédiments (Pb 70, Cu 100, Cr 150, Cd 9, Ni 280, Zn 400 µg.L-1) et le développement des algues : les polluants métalliques sont masqués par le pouvoir chélateur de ces biotopes riches en substances organiques.Une conclusion à cette étude préliminaire est que l'analyse chimique des sédiments, utilisée seule, n'a qu'un intérêt limité : les données les plus fiables correspondent à celles fournies par les bioessais.A bioevaluation of the state of health of soft bottoms depends on the experimental conditions in which samples of sediment are treated to obtain the water phase to be subjected to chemical and toxicological analyses.In the course of this preliminary study we have considered the action of these principal conditions. We have noted that the inhibiting effect of a sediment on the short-term growth of a microalga Selenastrum capricornutum is not easy to eliminate, whether by a series of washes of the sediment, by a finer filtration of the water extracted from this sediment or by e previous autoclavage of this sediment.This study quickly revealed which sediments in the River Seine (Paris area) inhibited most the test micro-alga Selenastrum capricornutum (Chlorophyceae); the cause of these inhibitions was then sought.There is no correlation between the often high content of heavy metals in the sediment water (Pb 70, Cu 100, Cr 150, Cd 9, Ni 280, Zn 400 µg.L-1) and the development of the algae; the metal pollutants are probably masked by the chelating capacity of these biotopes rich in organic substances. The experimental conditions under which the sediment samples are treated to obtain the water phase used for the chemical and toxicological analyses are also important.One conclusion drawn is that a chemical analysis alone of the sediments is of limited interest. The most reliable data from the ecological point of view are those provided by the bio-assays

Study of the Eutectoid Transformation in Nodular Cast Irons in Relation to Solidification Microsegregation

Eutectoid transformation in cast irons may proceed in the stable or the metastable systems giving ferrite and graphite for the former and pearlite for the latter. The present work demonstrates that composition profiles across ferrite/pearlite boundaries are smooth and similar to those issued from the solidification step. No trace of long-range diffusion of substitutional solutes due to austenite decomposition could be observed. In turn, this ascertains that both stable and metastable transformations proceed with the product matrix—either ferrite opearlite—inheriting the parent austenite content in substitutional solutes. This result sustains a physical model for eutectoid transformation based on the so-called local para-equilibrium which is commonly used for describing solid-state transformation in steels

spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models

The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site complete graph extended with on-site repulsion is obtained from the underlying spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic ground state is realized for 1 and N+1 electrons only. We identify the large density of states to be responsible for the suppression of the ferromagnetic state and argue that a similar situation is encountered in the Kagome, pyrochlore, and other lattices with flat bands in their one-particle density of states.Comment: 7 pages, 1 figur