Cancellative actions

summary:The following problem is considered: when can the action of a cancellative semigroup $S$ on a set be extended to a simply transitive action of the universal group of $S$ on a larger set

A precedence theorem for semigroups

In a finite semigroup, the least element under a precedence order is an idempotent in the kernel

Commutative orders revisited

This article studies commutative orders, that is, commutative semigroups having a semigroup of quotients. In a commutative order S, the square-cancellable elements S(S) constitute a well-behaved separable subsemigroup. Indeed, S(S) is also an order and has a maximum semigroup of quotients R, which is Clifford.We present a new characterisation of commutative orders in terms of semilattice decompositions of S(S) and families of ideals of S. We investigate the role of tensor products in constructing quotients, and show that all semigroups of quotients of S are homomorphic images of the tensor product R ⊗S(S) S. By introducing the notions of generalised order and semigroup of generalised quotients, we show that if S has a semigroup of generalised quotients, then it has a greatest one. For thiswe determine those semilattice congruences on S(S) that are restrictions of congruences on S

Characteristics of the yearly feeding activity of the Ocellated Lizard (Timon lepidus) based on faeces collected on Oleron Island (French Atlantic coast)

The pattern of the yearly feeding activity of the Ocellated Lizard population on Oleron Island was studied during two one-year periods by collecting the lizards’ faeces along a transect. Collected faeces (753 in 2002, 646 in 2006) allowed understanding in more detail the quantity of the lizards’ food catch over a yearly cycle. Population feeding activity starts in the second 10-day period of March and ends in the third 10-day period of October. The peak of feeding activity was in May in 2002, and in June - July in 2006. This is explained mainly by the length of the day and the average temperature, and to a much lesser extent by the amount of sunshine or rainfall (calculated by multiple linear regression analysis). Findings were that in spite of the extreme geographical position of the Oleron Island population, the pattern of feeding activity varies little from that observed in the Ocellated Lizard populations in the south of France and central Spain. With some conditions, the faeces-collection study method could be used for long-term population monitoringL'activité alimentaire du Lézard ocellé a été étudiée durant 2 années sur l'île d'Oléron, à partir de teces collectees le long d'un transect. La collecte de 753 teces en 2002 et 646 en 2006 permet de suivre avec précision l'importance des prises alimentaires au cours du cycle annuel. L'activité alimentaire débute dans la deuxième décade de mars et s'achève dans la troisième décade d'octobre, avec un pic d'activité en mai en 2002 et en juin-juillet en 2006. Elle est principalement expliquée par la durée du jour et par la température moyenne ; peu par la pluviosité (régression multiple). Le rythme d'activité alimentaire de cette population diffère peu de celui observé dans les populations du sud de la France et du centre de l'Espagne malgré la position géographique extrême de cette population. Moyennant certaines précautions, cette méthode pourrait être utilisée pour un suivi à long terme de la population

Modelling the distribution of the Ocellated Lizard in France : implications for conservation

The Ocellated Lizard, Timon lepidus (Daudin 1802) occupies the Mediterranean regions of southwestern Europe (Portugal, Spain, France, and the extreme northwest of Italy). Over the last decades, a marked decline in its population has been observed, particularly on the northern edge of its distribution. As a result, it is currently considered a threatened species, especially in France and Italy. In France, a national action plan for its conservation has been put in place. In this study, ecological niche modelling (ENM) was carried out over the entire area of France in order to evaluate the species' potential distribution, more accurately define its ecological niche, guide future surveys, and inform land use planning so this species can be better taken into consideration. The modelling used data representing 2,757 observation points spread over the known range of the species, and 34 ecogeographical variables (climate, topography, and vegetation cover) were evaluated. After removing correlated variables, models were fitted with several combinations of variables using eight species distribution model (SDM) algorithms, and then their performance was assessed using three model accuracy metrics. Iterative trials changing the input variables were used to obtain the best model. The optimized model included nine determining variables. The results indicate the presence of this species is linked primarily to three climate variables: precipitation in the driest month, precipitation seasonality, and mean temperature in the driest quarter. The model was checked by a sample dataset that was not used to fit the model, and this validation dataset represented 25% of the overall field observations. Of the known occurrence locations kept aside to check the results, 94% fell within the presence area predicted by the modelled map with a presence probability greater than 0.7, and 90% fell within the area with a presence probability ranging from 0.8 to 1, which represents a very high predictive value. These results indicate that the models closely matched the observed distribution, suggesting a low impact of either geographical factors (barriers to dispersal), historical factors (dispersal process), or ecological factors (e.g., competition, trophic resources). The overlap between the predicted distribution and protected areas for this species reveals that less than 1% of the potential distribution area is protected by strong regulatory measures (e.g., national parks and natural reserves). The knowledge obtained in this study allows us to recommend some guidelines that would favor the conservation of this species.Peer reviewe

A long-term monitoring program of the ocellated lizard (Timon lepidus) population on Oléron Island

The Ocellated Lizard Timon lepidus (Sauria ; Lacertidae) has declined throughout most of its range. Today it is difficult to assess the extent of this decline. The Ocellated Lizard population of Oléron Island (Charente- Maritime, France) is the subject of a long-term monitoring study established in 2007. This study is repeated every 3 years to follow the population evolution. The population is confined to a long-shore dune of 140 ha. The monitoring method consists of 70 plots (50 x 50 m) randomly placed within a study area divided into six distinct zones. Three surveys were conducted in the study area over the spring season (April, May and June). Results were analysed with PRESENCE 3.0 (Beta) and R 2.8.1. The Ocellated Lizard has a highly heterogeneous distribution on Oléron Island. The site-occupancy model allows us to conclude that the probability of detecting the species in the plots increases over the field. In 2010, this probability was 0.78 in April and 0.97 in May and June. The estimated proportion of occupied sites was 0.83 in 2010 and 0.76 in 2007. Colonization and local extinction are the consequences of the evolution of available shelters (colonization if this resource increases and extinction if it disappears) and of the coastal erosion (habitat loss). The relative abundance of Ocellated Lizards on the island (modeling with the N-mixture model) can be principally explained by the presence of permanent shelters (used both during winter and the lizards’ active period), including rabbit and rodent burrows and artificial shelters. Rabbits are essential and their maintaining is crucial for the Ocellated Lizard conservation. The Ocellated Lizard population size was estimated to be 1025 individuals (95 % CI: 695-1355) in 2010. This monitoring survey will be replicated in 2013. Results will help us in evaluating and guiding management and conservation measuresLe Lézard ocellé Timon lepidus subit un déclin marqué sur l'ensemble de son aire de répartition. Il est cependant difficile d'évaluer quantitativement ce déclin sans la mise en place de protocoles de suivi valides. Dans ce but, un suivi à long terme a été initié en 2007 sur l'île d'Oléron. Celui-ci a été répété en 2010. La méthodologie retenue s'appuie sur la technique dite de « site occupancy ». Elle consiste à réaliser trois visites d'une heure au cours du printemps sur 70 placettes de suivi de 2500 m2 réparties sur les 140 hectares de dunes occupés par l'espèce. En 2010, la probabilité de détection de l'espèce sur l'ensemble des placettes a été de 0,78 (0,05) pour la première visite puis de 0,97 (0,02) pour les deux suivantes. Le taux d'occupation des placettes a été de 0,76 (0,05) en 2007 et de 0,83 (0,04) en 2010. Les colonisations et extinctions locales du Lézard ocellé sur certaines placettes sont dues à l'évolution de la ressource en gîtes (terriers de lapins pour l'essentiel) et à l'érosion littorale (perte d'habitats favorables). Les gîtes permanents (terriers de lapins, trous de rongeurs et gîtes artificiels) sont les variables environnementales qui expliquent le mieux les abondances du Lézard ocellé. Le Lapin de garenne joue donc un rôle primordial dans le maintien de la population de lézards. L'estimation des effectifs de la population réalisée par la technique de « site occupancy » donne des valeurs proches pour les deux périodes de suivi: 1018 (compris entre 602 et 1355) en 2007 et 1025 individus en 2010 (compris entre 695 et 1355). Une troisième session du suivi sera réalisée en 2013. La méthodologie mise en place semble bien adaptée aux objectifs poursuivis. Elle devrait permettre de mieux orienter les actions de gestion mises en œuvre depuis plusieurs années sur cette population

Waveguide optical parametric amplifiers in silicon nitride with 2D graphene oxide films

Optical parametric amplification (OPA) represents a powerful solution to achieve broadband amplification in wavelength ranges beyond the scope of conventional gain media, for generating high-power optical pulses, optical microcombs, entangled photon pairs and a wide range of other applications. Here, we demonstrate optical parametric amplifiers based on silicon nitride (Si3N4) waveguides integrated with two-dimensional (2D) layered graphene oxide (GO) films. We achieve precise control over the thickness, length, and position of the GO films using a transfer-free, layer-by-layer coating method combined with accurate window opening in the chip cladding using photolithography. Detailed OPA measurements with a pulsed pump for the fabricated devices with different GO film thicknesses and lengths show a maximum parametric gain of ~24.0 dB, representing a ~12.2 dB improvement relative to the device without GO. We perform a theoretical analysis of the device performance, achieving good agreement with experiment and showing that there is substantial room for further improvement. This work represents the first demonstration of integrating 2D materials on chips to enhance the OPA performance, providing a new way of achieving high performance photonic integrated OPA by incorporating 2D materials.Comment: 38 pages, 8 figures, 80 reference