Geometry and material effects in Casimir physics - Scattering theory

We give a comprehensive presentation of methods for calculating the Casimir force to arbitrary accuracy, for any number of objects, arbitrary shapes, susceptibility functions, and separations. The technique is applicable to objects immersed in media other than vacuum, to nonzero temperatures, and to spatial arrangements in which one object is enclosed in another. Our method combines each object's classical electromagnetic scattering amplitude with universal translation matrices, which convert between the bases used to calculate scattering for each object, but are otherwise independent of the details of the individual objects. This approach, which combines methods of statistical physics and scattering theory, is well suited to analyze many diverse phenomena. We illustrate its power and versatility by a number of examples, which show how the interplay of geometry and material properties helps to understand and control Casimir forces. We also examine whether electrodynamic Casimir forces can lead to stable levitation. Neglecting permeabilities, we prove that any equilibrium position of objects subject to such forces is unstable if the permittivities of all objects are higher or lower than that of the enveloping medium; the former being the generic case for ordinary materials in vacuum.Comment: 44 pages, 11 figures, to appear in upcoming Lecture Notes in Physics volume in Casimir physic

Chaetopterid tubes from vent and seep sites: Implications for fossil record and evolutionary history of vent and seep annelids

Vestimentiferan tube worms living at deep-sea hydrothermal vents and cold seeps have been considered as a clade with a long and continuing evolutionary history in these ecosystems. Whereas the fossil record appears to support this view, molecular age estimates do not. The two main features that are used to identify vestimentiferan tubes in the fossil record are longitudinal ridges on the tube's surface and a tube wall constructed of multiple layers. It is shown here that chaetopterid tubes from modern vents and seeps—as well as a number of fossil tubes from shallow-water environments—also show these two features. This calls for a more cautious interpretation of tubular fossils from ancient vent and seep deposits. We suggest that: current estimates for a relatively young evolutionary age based on molecular clock methods may be more reliable than the inferences of ancient “vestimentiferans” based on putative fossils of these worms; not all of these putative fossils actually belong to this group; and that tubes from fossil seeps should be investigated for chitinous remains to substantiate claims of their potential siboglinid affinities

Anatomical distinctions of the Mesozoic lingulide brachiopods

The long held view that Lingula represents an extremely bradytelic lineage is questioned. Examination of Mesozoic lingulides has shown that they significantly differ from their Recent relatives Lingula and Glottidia in having longer lophophoral cavities, shorter ventral canals, better developed posterior adductor muscles, and less acute umbones. Morphological characters of the shell interior are needed to identify members of the Lingulidae, not solely external shell characteristics. The apparent evolutionary tendency towards a reduction of the volume of the lophophoral cavity contradics the traditional view that the ‘living fossil’ Lingula has survived without significant morphological change since the Paleozoic. Actually the today living lingulide genera probably arose in the early Cenozoic. A new inarticulate brachiopod genus, Lingularia is introduced, with three new species. Middle Triassic L. siberica, Middle Jurassic L. similis, and Cretaceous L. smirnovae.Badania dobrze zachowanych okazów mezozoicznych lingul wskazały, że te różnią się zasadniczo od współczesnych rodzajów Ligula i Glottidia objętością jamy lofoforalnej, długością kanałów wentralnego płaszcza, wykształceniem nieparzystego mięśnia tylnego adduktora oraz, dodatkowo, morfologią części dziobowych muszli. Zaznaczająca się tendencja ewolucyjna w kierunku redukcji objętości jamy lofoforalnej przeczy ogólnie przyjętemu poglądowi, że Lingula to „żyjąca skamieniałość”, która przeżyła, od wczesnego paleozoiku do dzisiaj, prawie bez zmian morfologicznych. W pracy wyodrębniono nowy rodzaj Lingularia z 3-ma nowymi gatunkami: L. sibirica (trias), L. similis (jura), L. smirnovae (kreda).La traditionnelle opinion que Lingula représente une lingée très ancienne est remise en question. L’étude de lingules mésozoïques démontre que celles-ci diffèrent significativement des genres actuels Lingula et Glottidia par une cavité lophophorale plus volumineuse, des canaux ventraux du manteau plus courts, un développement plus important du muscle adducteur postérieur, les régions umbonales. Les caractères morphologiques internes s’avèrent indispensables pour pouvoir identifier les genres et espèces des Lingulidae, les caractères externes de la coquille étant insuffisants. La tendance évolutive d’une réduction de la cavité lophophorale s’oppose à l’opinion traditionnellement véhiculée que le genre fossile-vivant Lingula a survécu sans modification morphologique significative depuis le début du Paléozoïque: en fait, l’origine des lingules actuelles date probablement du début du Cénozoïque. Un nouveau genre de brachiopode inarticulé, Lingularia, est décrit avec trois nouvelle espèces, L. siberica (Trias Moyen), L. similis (Jurassique Moyen) et L. smirnovae (Crétacé)

Phoronida from the Eastern Mediterranean and Black Sea [Phoronida de la mer Méditerranée orientale et de la Mer Noire]

Faunistic analysis of benthic materials collected in various habitats at different depths in the eastern Mediterranean and the Black Sea revealed two phoronid species, Phoronis muelleri and P. psammophila, which were also known in many localities in the western Mediterranean. The Black Sea material comprised only Phoronis psammophila whereas the Aegean Sea and Levant Sea materials contained both P. psammophila and P. muelleri. The diagnosis and the ecological and reproductive features of these species as well as their associated polychaete fauna are provided. Our present knowledge of the biodiversity and geographic distribution of the three phoronid species occuring in the studied area, the third being P. australis, is developed including unpublished data