The flower-visiting social wasps (Hymenoptera, Vespidae, Polistinae) in two areas of Rio Grande do Sul State, southern Brazil

The flower-visiting social wasps (Hymenoptera, Vespidae, Polistinae) in two areas of Rio Grande do Sul State, southern Brazil. The structure of flower-visiting social wasps' assemblages in the CPCN Pró-Mata of São Francisco de Paula and in the Green Belt of Santa Cruz do Sul, Rio Grande do Sul, are characterized. A total of 879 polistine wasps were collected, of which 475 (11 spp.) in the CPCN and 404 (21 spp.) in the Green Belt, from September 1997 to April 2001 and from September 2001 to April 2004, respectively. Foraging social wasps were observed on flowers of 36 species of angiosperms (20 families) in the Green Belt, and on flowers of 54 species of angiosperms (21 families) in the CPCN. Asteraceae was the most visited plant family on both studied localities. A list of pant species visited by the polistines is provided.

New enigmatic Andean bee species of Protandrena (Hymenoptera, Andrenidae, Panurginae)

Panurgine bees are diverse and abundant in temperate areas of the Americas but poorly represented to nearly absent in the tropics. We describe and illustrate five distinctive new species of the genus Protandrena that occur at high altitudes (2000-3400 m) in the Andes, from Venezuela to Ecuador. The species are also described to make the names available in forthcoming papers on their biology. These Andean species resemble some members of the subgenus Heterosarus but differ from it, as well as from any other subgenera of Protandrena, primarily in characters of the male genitalia and hidden sterna. The South American Protandrena s. l. are morphologically highly diverse and a complete study of the group is needed before supraspecific names are proposed for unusual species. Thus, to avoid further nomenclatural changes, we decided not to place these species in a new subgenus or any of the available subgenera. We also provide notes on the biology for some of the species.

Polinização de Vochysia lucida C. Presl (Vochysiaceae) em uma área de restinga na Bahia

As espécies de Vochysia são neotropicais e apresentam flores que podem ser visitadas por abelhas, beija-flores e borboletas. Este estudo teve como objetivo a análise das interações entre as flores de Vochysia lucida e seus visitantes florais, em uma área de restinga no Estado da Bahia, Brasil. V. lucida é uma espécie arbórea e apresenta inflorescências do tipo racemo, com cerca de 100 a 170 flores. As flores são zigomorfas, amarelas e foram consideradas melitófilas. O néctar floral é produzido e estocado em esporão, localizado no cálice. O pico de floração de V. lucida ocorreu em novembro e dezembro. Durante o estudo as flores abriam às 6:00 h, quando o estigma já estava receptivo. Na abertura da flor a antera já não estava mais presente e os grãos de pólen estavam depositados na parede do estilete, ocorrendo apresentação secundária de pólen. As pétalas caíam no final da tarde, por volta das 17:00 h. Os beija-flores embora freqüentes nas flores de V. lucida foram considerados visitantes oportunistas. Entre os visitantes florais registrados, as abelhas de grande porte foram consideradas os polinizadores mais eficientes, especialmente Xylocopa frontalis, por ter morfologia e comportamento adequados para contatar as estruturas reprodutivas da flor, durante as coletas de néctar, e por sua elevada freqüência de visita.

Comportamento de abelhas visitantes florais de Lecythis lurida (Lecythidaceae) no norte do estado do Rio de Janeiro

Este estudo descreve e analisa o comportamento dos visitantes florais de L. lurida em fragmentos de mata de tabuleiro. Esta espécie monóica floresceu de outubro a janeiro. As flores abriram-se entre 5h30 e 10h00 e a antese floral não ultrapassou um dia. Durante amostragens padronizadas foram coletadas 172 abelhas visitantes florais, pertencentes a 10 gêneros e 18 espécies. As maiores freqüências foram de Epicharis flava (42,3%), Xylocopa frontalis (16,3%) e Eufriesea surinamensis (11,6%), com atividade principalmente de 7h00 às 11h00. Abelhas Centridini, Euglossina e Xylocopini buscam néctar nas flores e foram considerados polinizadores efetivos. Megachile coleta pólen e também é potencial polinizador. Oxaea flavescens atuou como pilhador de néctar, perfurando o capuz da flor. Experimentos de polinização indicaram ausência de autopolinização espontânea e baixa taxa de frutificação (0,48%) sob condições naturais. Como observado para outras espécies zigomórficas de Lecythidaceae, a complexa morfologia floral restringe os visitantes a abelhas de grande porte ou abelhas robustas que conseguem entrar pelo capuz floral. Entretanto, Centridini foi principal grupo de polinizadores de L.lurida, o que difere dos polinizadores indicados em outros trabalhos sobre Lecythis e outros gêneros de Lecythidaceae na região amazônica.

Nest distribution and nesting habits of Xylocopa ordinaria Smith (Hymenoptera, Apidae) in a restinga area in the northern Rio de Janeiro State, Brazil

This paper aims to study the distribution of natural nests of Xylocopa ordinaria and characterize its nesting habits in the restinga of Grussai/Iquipari (RJ), supporting future studies on the pollinators management in the northern Rio de Janeiro state. The data obtained from Aug/2003 to Dec/2004, in an area of 11.6ha, were related to the nest distribution, substrate identification and dimensions, emergence, sex ratio, nest structure (n= 23 nests) and pollen content analysis of provisioning masses and feces. X. ordinaria nests were abundant and presented a clustered distribution. These bees do not present taxonomical affinity for nesting substrates, but preferences for wood availability and characteristics, being Pera glabrata the main substrate. X. ordinaria is a multivoltine species that tolerates co-specifics in their nests. These bees were generalist on their nectar and pollen consumption, but presented floral constancy while provisioning brood cells. These behaviors, activity along the year, flights throughout the day, and legitimate visits to flowers indicate the importance of X. ordinaria on the pollination of plants in the restinga.

Gall inducing arthropods from a seasonally dry tropical forest in Serra do Cipó, Brazil

Highly diverse forms of galling arthropods can be identified in much of southeastern Brazil's vegetation. Three fragments of a Seasonally Dry Tropical Forest (SDTF) located in the southern range of the Espinhaço Mountains were selected for study in the first survey of galling organisms in such tropical vegetation. Investigators found 92 distinct gall morphotypes on several organs of 51 host plant species of 19 families. Cecidomyiidae (Diptera) was the most prolific gall-inducing species, responsible for the largest proportion of galls (77%) observed. Leaves were the most frequently galled plant organ (63%), while the most common gall morphotype was of a spherical shape (30%). The two plant species, Baccharis dracunculifolia (Asteraceae) and Celtis brasiliensis (Cannabaceae), presented the highest number of gall morphtypes, displaying an average of 5 gall morphotypes each. This is the first study of gall-inducing arthropods and their host plant species ever undertaken in a Brazilian SDTF ecosystem. Given the intense human pressure on SDTFs, the high richness of galling arthropods, and implied floral host diversity found in this study indicates the need for an increased effort to catalogue the corresponding flora and fauna, observe their intricate associations and further understand the implications of such rich diversity in these stressed and vulnerable ecosystems.

Visitantes florais do maracujá-amarelo (Passiflora edulis f. flavicarpa Deg. Passifloraceae) em áreas de cultivo com diferentes proximidades a fragmentos florestais na região Norte Fluminense, RJ

Este trabalho teve como objetivos estudar a biologia floral e identificar os principais polinizadores do maracujá-amarelo em áreas de cultivo com diferentes proximidades a fragmentos florestais no norte do estado do Rio de Janeiro. A floração do maracujá-amarelo teve duração de nove meses, no período de setembro a maio. As flores iniciavam a antese às 12:00 h e abriam-se ao longo do dia até às 16:30 h. O processo de curvatura dos estiletes ocorreu ao longo da antese e 72,4% das flores curvaram seus estiletes. A produção de néctar deu-se continuamente, atingindo 18μl/flor/hora e a concentração de solutos totais variou entre 38 e 42%. Xylocopa frontalis e Xylocopa ordinaria foram os principais polinizadores do maracujá-amarelo pela freqüência de visitas, comportamento intrafloral e porte corporal. Estas espécies de abelhas, além de Apis mellifera, estiveram presentes em todas as áreas de cultivo. A maior riqueza de visitantes polinizadores do maracujá-amarelo foi observada em áreas de cultivo próximas a fragmentos florestais, fato relacionado à presença de certos grupos de abelhas nativas, como Centridini e Euglossina (Apidae) que dependem de áreas florestais para nidificação e alimentação. A proximidade a fragmentos florestais também é importante para o fornecimento de recursos alimentares e de nidificação ao longo do ano para a manutenção de populações de Xylocopa.

Giffen goods and market making

This paper shows that information effects per se are not responsible forthe Giffen goods anomaly affecting competitive traders demands in multi-asset, noisy rational expectations equilibrium models. The role thatinformation plays in traders strategies also matters. In a market withrisk averse, uninformed traders, informed agents havea dual motive for trading: speculation and market making. Whilespeculation entails using prices to assess the effect of private signalerror terms, market making requires employing them to disentangle noisetraders effects in traders aggregate orders. In a correlated environment,this complicates a trader s signal-extraction problem and maygenerate upward-sloping demand curves. Assuming either (i) that competitive,risk neutral market makers price the assets, or that (ii) the risktolerance coefficient of uninformed traders grows without bound, removesthe market making component from informed traders demands, rendering themwell behaved in prices.

Pólen coletado por Scaptotrigona depilis (Moure) (Hymenoptera, Meliponini), na região de Dourados, Mato Grosso do Sul, Brasil

Foram identificados os pólens coletados por operárias de Scaptotrigona depilis (Moure, 1942), na Região de Dourados-Ms, durante o período de setembro de 2006 a agosto de 2007. Ao todo foram coletados 42 tipos polínicos, sendo mais representativa em número de espécies, as famílias Myrtaceae (Eucalyptus spp.) e Mimosaceae. Os picos de valores de amplitude de nicho trófico (H') em Setembro (2,32), Novembro (2,29) e Outubro (2,02) mostraram que essa abelha pode ser generalista, dependendo da disponibilidade e características das fontes florais. Os valores de equitatividade (J'), também indicam maior uniformidade de uso das fontes florais durante esses meses de máxima amplitude de nicho. Os fatores ambientais (temperatura, umidade relativa e pluviosidade) não mostraram relação direta com a equitatividade e amplitude do nicho trófico. Estas variáveis parecem estar mais relacionadas com os ciclos diários ou sazonais de produção de pólen e néctar.

Diplostigmaty in plants: a novel mechanism that provides reproductive assurance.

Differentiation of female sexual organs in flowering plants is rare and contrasts with the wide range of male reproductive strategies. An unusual example involves diplostigmaty, the possession of spatially and temporally distinct stigmas in Sebaea (Gentianaceae). Here, the single pistil within a flower has an apical stigma, as occurs in most flowering plants, but also a secondary stigma that occurs midway down the style, which is physically discrete and receptive several days after the apical stigma. We examined the function of diplostigmaty in Sebaea aurea, an insect-pollinated species of the Western Cape of South Africa. Floral manipulations and measurements of fertility and mating patterns provided evidence that basal stigmas function to enable autonomous delayed self-pollination, without limiting opportunities for outcrossing and thus avoiding the costs of seed discounting. We suggest that delayed selfing serves as a mechanism of reproductive assurance in populations with low plant density. The possession of dimorphic stigma function provides a novel example of a flexible mixed-mating strategy in plants that is responsive to changing demographic conditions.

Seasonal flight and resource collection patterns of colonies of the stingless bee Melipona bicolor schencki Gribodo (Apidae, Meliponini) in an Araucaria forest area in southern Brazil

Melipona bicolor schencki occurs in southern Brazil and at high elevations in southeastern Brazil. It has potential for use in meliponiculture but this stingless bee species is vulnerable to extinction and we have little knowledge about its ecology. In order to gather essential information for species conservation and management, we made a study of seasonal flight activities in its natural environment. We sampled bees entering the nests with pollen, nectar/water and resin/mud, in five colonies during each season. In parallel, we analyzed the influence of hour of the day and meteorological factors on flight activity. Flights were most intense during spring and summer, with daily mean estimates of 2,100 and 2,333 flights respectively, while in fall and winter the daily flight estimate was reduced to 612 and 1,104 flights, respectively. Nectar and water were the most frequently-collected resources, followed by pollen and building materials. This preference occurred in all seasons, but with variations in intensity. During spring, daily flight activity lasted over 14 hours; this period was reduced in the other seasons, reaching eight hours in winter. Meteorological factors were associated with 40.2% of the variation in flight and resource collection activity. Apparently, other factors that we did not measure, such as colony needs and availability of floral resources, also strongly influence the intensity of resource collection.

First record of the behavior of latex drainage by Trigona spinipes (Fabricius) (Hymenoptera, Apidae) in laticiferous flowers

This paper describes the behavior of the bee Trigona spinipes, to avoid the latex, when piercing the base of the tubular corolla of the flowers of Mandevilla guanabarica in order to steal the nectar.

Autosomal Recessive Posterior Microphthalmos/Nanophthalmos is Caused by Loss-of-function Mutations in LOC646960, a Novel Gene Encoding a Trypsin-like Serine Protease

Purpose: Posterior microphthalmos (MCOP)/nanophthalmos (NNO) is a developmental anomaly characterized by extreme hyperopia due to short axial length. The population of the Faroe Islands shows a high prevalence of an autosomal recessive form (arMCOP). The gene mutated in arMCOP is not yet known.Methods: Genetic mapping by linkage analysis using microsatellite and single nucleotide polymorphisms, mutation analysis by PCR and sequencing, molecular modellingResults: Having refined the position of the disease locus (MCOP6) in an interval of 250 kb in chromosome 2q37.1 in Faroese families, we detected 3 mutations in a novel gene, LOC646960: Patients of 10 different Faroese families were either homozygous (n=22) for c.926G>C (p.Trp309Ser) or compound heterozygous (n=6) for c.926G>C and c.526C>G (p.Arg176Gly), whereas a homozygous 1 bp duplication (c.1066dupC) was identified in patients with arNNO from a Tunisian family. In two unrelated patients with MCOP, no LOC646960 mutation was found. LOC646960 is expressed in the human adult retina and RPE. The expression of the mouse homologue in the eye can be first detected at E17 and is highest in adults. The predicted protein is a 603 amino acid long secreted trypsin-like serine peptidase. c.1066dupC should result in a functional null allele. Molecular modelling of the p.Trp309Ser mutant suggests that both affinity and reactivity of the enzyme towards in vivo substrates are substantially reduced.Conclusions: Postnatal growth of the eye is important for proper development of the refractive components (emmetropization), and is mainly due to elongation of the posterior segment from 10-11 mm at birth to 15-16 mm at the age of 13 years. Optical defocus leads to changes in axial length by moving the retina towards the image plane. arMCOP may theoretically be explained, in line with the expression pattern of LOC646960, by a postnatal growth retardation of the posterior segment.

Méthodologie intégrée de microgravimétrie en milieu urbain : test d'application au génie civil sur le métro M2 de Lausanne

RESUME Dès le printemps 2004, la construction d'une 2ème ligne de métro est entreprise dans la ville de Lausanne en Suisse. En reliant Ouchy, au bord du lac Léman (alt. 373 m) à Epalinges (alt. 711 m), le nouveau métro "M2" traversera dès 2008 l'agglomération lausannoise du Sud au Nord sur une distance de 6 km. Depuis l'avant-projet, en 1999, une grande quantité de données géologiques a été récolté et de nombreux forages exécutés sur le site. Ceci nous a donné une occasion unique d'entreprendre une étude de microgravimétrique urbaine de détail. Le mode de creusement du tunnel dépend fortement des matériaux à excaver et il est classiquement du domaine du géologue, avec ses connaissances de la géologie régionale et de la stratigraphie des forages, de fournir à l'ingénieur un modèle géologique. Ce modèle indiquera dans ce cas l'épaisseur des terrains meubles qui recouvrent le soubassement rocheux. La représentativité spatiale d'une information très localisée, comme celle d'un forage, est d'autant plus compliquée que le détail recherché est petit. C'est à ce moment là que la prospection géophysique, plus spécialement gravimétrique, peut apporter des informations complémentaires déterminantes pour régionaliser les données ponctuelles des forages. La microgravimétrie en milieu urbain implique de corriger avec soin les perturbations gravifiques sur la mesure de la pesanteur dues aux effets de la topographie, des bâtiments et des caves afin d'isoler l'effet gravifique dû exclusivement à l'épaisseur du remplissage des terrains meubles. Tenant compte de l'intensité des corrections topographiques en milieu urbain, nous avons donné une grande importance aux sous-sols, leurs effets gravifiques pouvant atteindre l'ordre du dixième de mGal. Nous avons donc intégré ces corrections celle de topographie et traité les effets des bâtiments de manière indépendante. Nous avons inclus dans le modèle numérique de terrain (MNT) la chaussée et les sous-sols afin de construire un modèle numérique de terrain urbain. Nous utiliserons un nouvel acronyme « MNTU »pour décrire ce modèle. Nous proposons d'établir des cartes de corrections topographiques préalables, basées sur les données à disposition fournies par le cadastre en faisant des hypothèses sur la profondeur des sous-sols et la hauteur des bâtiments. Les deux zones de test choisies sont caractéristiques des différents types d'urbanisation présente à Lausanne et se révèlent par conséquent très intéressantes pour élaborer une méthodologie globale de la microgravimétrie urbaine. Le but était d'évaluer l'épaisseur du remplissage morainique sur un fond rocheux molassique se situant à une profondeur variable de quelques mètres à une trentaine de mètres et d'en établir une coupe dans l'axe du futur tracé du métro. Les résultats des modélisations se sont révélés très convaincants en détectant des zones qui diffèrent sensiblement du modèle géologique d'avant projet. Nous avons également démontré que l'application de cette méthode géophysique, non destructive, est à même de limiter le nombre de sondages mécaniques lors de l'avant-projet et du projet définitif, ce qui peut limiter à la fois les coûts et le dérangement engendré par ces travaux de surface. L'adaptabilité de la technique gravimétrique permet d'intervenir dans toutes les différentes phases d'un projet de génie civil comme celui de la construction d'un métro en souterrain. KURZFASSUNG Seit dem Frühling 2004 ist in der Stadt Lausanne (Schweiz) die neue U-Bahn "M2" in Konstruktion. Diese soll auf 6 km Länge die Lausanner Agglomeration von Süd nach Nord durchqueren. Die dem Projekt zu Grunde liegende technische Planung sieht vor, daß die Bahnlinie hauptsächlich in der Molasse angesiedelt sein wird. Seit dem Vorentwurf (1999) ist eine große Anzahl geologischer Angaben gesammelt worden. Daraus ergab sich die einmalige Gelegenheit, die Informationen aus den damit verbundenen zahlreichen Bohrungen zu einer detaillierten mikrogravimetrischen Studie der Stadt Lausanne zu erweitern und zu vervollständigen. Das Ziel bestand darin, die Mächtigkeit der die Molasseüberdeckenden Moräneablagerung abzuschätzen, um eine entsprechendes geologisches Profile entlang der künftigen Bahnlinie zu erstellen. Weiterhin sollte gezeigt werden, daß die Anwendung dieser nicht-invasiven geophysikalischen Methode es ermöglicht, die Anzahl der benötigten Bohrungen sowohl in der Pilotphase wie auch im endgültigen Projekt zu reduzieren, was zu wesentlichen finanziellen Einsparungen in der Ausführung des Werkes beitragen würde. Die beiden in dieser Studie bearbeiteten Testzonen befinden sich im Nordteil und im Stadtzentrum von Lausanne und sind durch eine unterschiedliche Urbanisierung charakterisiert. Das anstehende Gestein liegt in verschiedenen Tiefen: von einigen Metern bis zu etwa dreißig Metern. Diese Zonen weisen alle Schwierigkeiten einer urbanen Bebauung mit hoher Verkehrsdichte auf und waren daher massgebend bei der Ausarbeitung einer globalen mikrogravimetrischen Methodologie für die Stadt Lausanne. Die so entwickelte Technik ermöglicht, die störenden Auswirkungen der Topographie, der Gebäude, der Keller und der Öffentlichen Infrastrukturen sorgfältig zu korrigieren, um so die ausschließlich auf die Mächtigkeit des Lockergesteins zurückzuführenden Effekte zu isolieren. In Bezug auf die Intensität der Auswirkungen der topographischen Korrekturen im Stadtgebiet wurde den Untergeschossen eine besonders grosse Bedeutung zugemessen da die entsprechenden Schwerkrafteffekte eine Grösse von rund einem Zehntel mGal erreichen können. Wir schlagen deshalb vor, vorläufige Karten der topographischen Korrekturen zu erstellen. Diese Korrekturen basieren auf den uns vom Katasterplan gelieferten Daten und einigen Hypothesen bezüglich der Tiefe der Untergeschosse und der Höhe der Gebäude. Die Verfügbarkeit einer derartigen Karte vor der eigentlichen gravimetrischen Messkampagne würde uns erlauben, die Position der Meßstationen besser zu wählen. Wir sahen zudem, daß ein entsprechenden a priori Filter benutzt werden kann, wenn die Form und die Intensität der Anomalie offensichtlich dem entsprechenden Gebäude zugeordnet werden können. Diese Strategie muß jedoch mit Vorsicht angewandt werden, denn falls weitere Anomalien dazukommen, können bedeutende Verschiebungen durch Übèrlagerungen der Schwerewirkung verschiedener Strukturen entstehen. Die Ergebnisse der Modellierung haben sich als sehr überzeugend erwiesen, da sie im Voraus unbekannte sensible Zonen korrekt identifiziert haben. Die Anwendbarkeit der in dieser Arbeit entwickelten gravimetrischen Technik ermöglicht es, während allen Phasen eines Grossbauprojekts, wie zum Beispiel bei der Konstruktion einer unterirdischen U-Bahn, einzugreifen. ABSTRACT Since Spring of 2004 a new metro line has been under construction in the city of Lausanne in Switzerland. The new line, the M2, will be 6 km long and will traverse the city from south to north. The civil engineering project determined that the line would be located primarily in the Molasse. Since the preparatory project in 1999, a great quantity of geological data has been collected, and the many drillings made on the site have proved to be a unique opportunity to undertake a study of urban microgravimetry. The goal was to evaluate the thickness of the morainic filling over the molassic bedrock, and to establish a section along the axis of the future line. It then had to be shown that the application of this nondestructive geophysical method could reduce the number of mechanical surveys required both for a preparatory and a definitive project, which would lead to real savings in the realization of a civil engineering project. The two test zones chosen, one in the northern part of the city and one in the city centre, are characterised by various types of urbanisation. Bedrock is at a depth varying from a few metres to about thirty metres. These zones well exemplify the various difficulties encountered in an urban environment and are therefore very interesting for the development of an overall methodology of urban microgravimetry. Microgravimetry in an urban environment requires careful corrections for gravific disturbances due to the effects of topography, buildings, cellars, and the infrastructure of distribution networks, in order to isolate the gravific effect due exclusively to the thickness of loose soil filling. Bearing in mind the intensity of the topographic corrections in an urban environment, we gave particular importance to basements. Their gravific effects can reach the order of one tenth of one meal, and can influence above all the precision of the Bouguer anomaly. We propose to establish preliminary topographic correction charts based on data provided to us by the land register, by making assumptions on the depths of basements and the heights of buildings. Availability of this chart previous to a gravimetry campaign would enable us to choose optimum measuring sites. We have also seen that an a priori filter can be used when the form and the intensity of the anomaly correspond visually to the corresponding building. This strategy must be used with caution because if other anomalies are to be associated, important shifts can be generated by the superposition of the effects of different structures. The results of the model have proved to be very convincing in detecting previously unknown sensitive zones. The adaptability of the gravimetry technique allows for application in all phases of a civil engineering project such as the construction of an underground metro line. RIASSUNTO Dalla primavera 2004 una nuova linea metropolitana é in costruzione nella città di Losanna in Svizzera. La nuova metropolitana "M2" traverserà per la lunghezza di 6 km il centro urbano di Losanna da sud a nord. II progetto d'ingegneria civile prevedeva un tracciato situato essenzialmente nel fondo roccioso arenaceo terziario (molassa). Dalla redazione del progetto preliminare, avvenuta nel 1999, una grande quantità di dati geologici sono stati raccolti e sono stati eseguiti numerosi sondaggi. Questo sì é presentato come un'occasione unica per mettere a punto uno studio microgravimetrico in ambiente urbano con lo scopo di valutare lo spessore dei terreni sciolti di origine glaciale che ricoprono il fondo roccioso di molassa e di mettere in evidenza come l'applicazione di questo metodo geofisico non distruttivo possa limitare il numero di sondaggi meccanici nella fase di progetto preliminare ed esecutivo con conseguente reale risparmio economico nella realizzazione di una tale opera. Le due zone di test sono situate una nella zona nord e la seconda nel centro storico di Losanna e sono caratterizzate da stili architettonici differenti. II fondo roccioso é situato ad una profondità variabile da qualche metro ad una trentina. Queste due zone sembrano ben rappresentare tutte le difficoltà di un ambiente urbano e ben si prestano per elaborare una metodologia globale per la microgravimetria in ambiente urbano. L'applicazione di questa tecnica nell'ambiente suddetto implica la correzione attenta delle perturbazioni sulla misura dell'accelerazione gravitazionale, causate dalla topografia, gli edifici, le cantine e le infrastrutture dei sottoservizi, per ben isolare il segnale esclusivamente causato dallo spessore dei terreni sciolti. Tenuto conto, dell'intensità delle correzioni topografiche, abbiamo dato grande importanza alle cantine, poiché il loro effetto sulle misure può raggiungere il decimo di mGal. Proponiamo quindi di redigere una carta delle correzioni topografiche preliminare all'acquisizione, facendo delle ipotesi sulla profondità delle cantine e sull'altezza degli edifici, sulla base delle planimetrie catastali. L'analisi di questa carta permetterà di scegliere le posizioni più adatte per le stazioni gravimetriche. Abbiamo anche osservato che un filtro a priori, qualora la forma e l'intensità dell'anomalia fosse facilmente riconducibile in maniera visuale ad un edificio, possa essere efficace. Tuttavia questa strategia deve essere utilizzata con precauzione, poiché può introdurre uno scarto, qualora più anomalie, dovute a differenti strutture, si sovrappongano. I risultati delle modellizzazioni si sono rivelati convincenti, evidenziando zone sensibili non conosciute preventivamente. L'adattabilità della tecnica gravimetrica ha mostrato di poter intervenire in differenti fasi di un progetto di ingegneria civile, quale è quella di un'opera in sotterraneo.

Portable alphas from pension mispricing

We introduce a new dynamic trading strategy based on the systematic misspricing of U.S. companies sponsoring Defined Benefit pension plans. This portfolio produces an average return of 1.51% monthly between 1989 and 2004, with a Sharpe Ratio of 0.26. The returns of the strategy are not explained by those of primary assets. These returns are not related to those of benchmarks in the alternative investments industry either. Hence, we are in the presence of a "pure alpha" strategy that can be ported into a large variety of portfolios to significantly enhance their performance.