A digital holography technique for generating beams with arbitrary polarization and shape

A method for generating beams with arbitrary polarization and shape is proposed. Our design requires the use of a Mach-Zehnder set-up combined with translucent liquid crystal displays in each arm of the interferometer; in this way, independent manipulation of each transverse beam components is possible. The target of this communication is to develop a numerical procedure for calculating the holograms required for dynamically encode any amplitude value and polarization state in each point of the wavefront. Several examples demonstrating the capabilities of the method are provided.

Absence of flash-lag when judging global shape from local positions

When a flash is presented aligned with a moving stimulus, the former is perceived to lag behind the latter (the flash-lag effect). We study whether this mislocalization occurs when a positional judgment is not required, but a veridical spatial relationship between moving and flashed stimuli is needed to perceive a global shape. To do this, we used Glass patterns that are formed by pairs of correlated dots. One dot of each pair was presented moving and, at a given moment, the other dot of each pair was flashed in order to build the Glass pattern. If a flash-lag effect occurs between each pair of dots, we expect the best perception of the global shape to occur when the flashed dots are presented before the moving dots arrive at the position that physically builds the Glass pattern. Contrary to this, we found that the best detection of Glass patterns occurred for the situation of physical alignment. This result is not consistent with a low-level contribution to the flash-lag effect.

Simulation-based evaluation of susceptibility distortion correction methods in diffusion MRI for connectivity analysis

Connectivity analysis on diffusion MRI data of the whole- brain suffers from distortions caused by the standard echo- planar imaging acquisition strategies. These images show characteristic geometrical deformations and signal destruction that are an important drawback limiting the success of tractography algorithms. Several retrospective correction techniques are readily available. In this work, we use a digital phantom designed for the evaluation of connectivity pipelines. We subject the phantom to a âeurooetheoretically correctâeuro and plausible deformation that resembles the artifact under investigation. We correct data back, with three standard methodologies (namely fieldmap-based, reversed encoding-based, and registration- based). Finally, we rank the methods based on their geometrical accuracy, the dropout compensation, and their impact on the resulting connectivity matrices.

On the physical realizability of highly focused electromagnetic field distributions

A method to evaluate the physical realizability of an arbitrary three-dimensional vectorial field distribution in the focal area is proposed. A parameter that measures the similarity between the designed (target) field and the physically achievable beam is provided. This analysis is carried out within the framework of the closest electromagnetic field to a given vectorial function, and the procedure is applied to two illustrative cases.

Design of highly focused fields that remain unpolarized on axis

Research on the properties of highly focused fields mainly involved fully polarized light, whereas partially polarized waves received less attention. The aim of this Letter is to provide an appropriate framework, for designing some features of the focused field, when dealing with incoming partially polarized beams. In particular, in this Letter, we describe how to get an unpolarized field on the axis of a high numerical aperture objective lens. Some numerical results that corroborate theoretical predictions are provided.

Paleontological research on late Triassic radiolarians from Oman and Sicily

Les radiolaires sont des unicellulaires planctoniques qui peuplent nos océans depuis plus de 500 millions d'années. Ces microorganismes développent un squelette en silice ayant des géométries extrêmement diversifiées et sophistiqués qui varient rapidement à l'échelle géologique et permettent de construire des échelles biochronologiques basées sur les différents assemblages qui se succèdent dans le temps. On retrouve ces organismes à l'état fossile dans les roches ma¬rines siliceuse desquelles on peut les extraire avec de l'acide. Des échantillons provenant du sultanat d'Oman et de Sicile ont été étudiés afin de mieux com¬prendre les relations de parenté entre les groupes et de comparer les faunes avec celles du même âge venant de Colombie britannique, du Japon et de Turquie, qui sont représentatives de divers domaines océaniques de l'époque. Certains radiolaires possèdent un anneau autour de leur coque centrale sphérique et ont ainsi été baptisés Saturnalides. Il y a 215 millions d'années, au Norien moyen, ce groupe se diversifie soudainement et donne naissance à une multitude d'espèces qui évoluent rapidement ce qui a permis d'établir des subdivisions temporelles supplémentaires et d'affiner les zonations exis¬tantes. L'étude détaillée de formes intermédiaires entre les espèces a permis d'établir de nouveaux liens de parenté et de considérer le genre Praehexasaturnalis comme l'ancêtre probable de nom¬breuses formes dans le Norien moyen et supérieur. Grâce à l'étude comparative des espèces de Saturnalidae allant du Mésozoïque au Cénozoïque, un certain type d'asymétrie de l'anneau a pu être identifiée comme étant propre à cette famille et plus précisément liée à la disposition de la coque la plus interne (microsphère). Deux nouveaux genres, Blechschmidtia et Tjerkium, s'inscrivent dans une lignée parallèle au Saturnalidae. Cette lignée met en évidence la formation au cours du temps d'un anneau à partir de la fusion de deux épines opposées. -- Late Triassic marine deposits of the Tethyan realm have been investigated in the Sultanate of Oman and in Sicily in order to contribute to the knowledge of radiolarian taxonomy and bio- stratigraphy of this key period preceding the Triassic-Jurassic boundary. In the middle Norian, the saturnalid radiolarians display intense diversification. This blooming of fast evolving spe¬cies has been used to establish a new zonation based on evolutionary successions that refine the existing zonal schemes. One new genus and 16 new species are described. The chronologic distribution of 172 species belonging to 72 genera is established from five sections in the Umar and Al Aridh units of the Hawasina Basin. Many Late Triassic saturnalid species are interpreted to originate from the genus Praehexasaturnalis Kozur & Mostler, which shows strong morpho¬logical diversification patterns. Detailed comparative studies of different types of asymmetric ring morphologies of Mesozoic to Cainozoic saturnalid species permitted to relate the origin of the asymmetry to the disposition of the initial skeletal structure and to gain new insight on the internal and external geometrical transformations of this group trough time and how the emergence of new families is induced by environmental stress. RÉSUMÉ Les formations marines du Trias supérieur du domaine téthysien ont été étudiées dans le Sultanat d'Oman et en Sicile afin de contribuer à la connaissance et au développement de la taxonomie et de la biostratigraphie des radiolaires de cette période clé qui précède la crise de la limite Trias-Jurassique. Au Norien moyen, les radiolaires Saturnalides montrent une intense diversi¬fication. Ce véritable "bloom" d'espèces qui évoluent rapidement a été utilisé pour l'établisse¬ment d'une nouvelle zonation basée sur les successions évolutives de ce groupe qui permettent d'affiner les subdivisions biochronologiques existantes. Un nouveau genre et seize nouvelles espèces sont décrits. La distribution stratigraphique de 172 espèces appartenant à 72 genres est établie pour 5 sections dans les unités d'Umar et d'Al Aridh du bassin de Hawasina. Un essai d'établissement d'une phylogénèse des Saturnalidae du Trias supérieur mène à proposer que le genre Praehexasaturnalis Kozur & Mostler est l'ancêtre de beaucoup d'espèces de Saturnalidae du Trias supérieur. L'étude comparative détaillée des différents types d'asymétrie de l'anneau chez les Saturnali¬dae du Mésozoïque au Cénozoïque a permis de lier l'origine de ce phénomène à la disposition de la structure initiale de leur squelette et par ce fait d'avoir une meilleure compréhension des transformations géométriques internes et externes subies par ce groupe au cours du temps et de concevoir comment l'émergence de nouvelles familles est induite lors de périodes de stress environnemental.

Experimental implementation of tightly focused beams with unpolarized transversal component at any plane

The aim of this paper is to provide a formal framework for designing highly focused fields with specific transversal features when the incoming beam is partially polarized. More specifically, we develop a field with a transversal component that remains unpolarized in the focal area. Moreover, its longitudinal component exhibits non-zero values on axis. Special attention is paid to the design of the input beam and the development of the experiment. The implementation of such fields is possible by using an interferometric setup combined with the use of digital holography techniques. Experimental results are compared with those obtained numerically.

Isomerismo cis-trans: de Werner aos nossos dias

In coordination chemistry the study of geometrical isomerization and reactivity of specific isomers is a topic of major importance. The preparation of specific isomers often requires considerable complexity, and it is important to acquire a sense of what is involved in studying isomerism in laboratory. If it is difficult sometimes to prepare pure isomers, it is not easier to understand the mechanisms of isomerization reactions since studies on this subject have shown conflicting results and diferent interpretations on the same system have been reported in the literature. Although cis-trans isomerism in octahedral metal complexes is a common occurrence, there are relatively few studies reporting how these isomerizations occur. This paper gives an overview on cis-trans isomerization processes and identification of these species.

Imaging polarimetry of the fogbow: polarization characteristics of white rainbows measured in the high Arctic

The knowledge on the optics of fogbows is scarce, and their polarization characteristics have never been measured to our knowledge. To fill this gap we measured the polarization features of 16 fogbows during the Beringia 2005 Arctic polar research expedition by imaging polarimetry in the red, green and blue spectral ranges. We present here the first polarization patterns of the fogbow. In the patterns of the degree of linear polarization p, fogbows and their supernumerary bows are best visible in the red spectral range due to the least dilution of fogbow light by light scattered in air. In the patterns of the angle of polarization α fogbows are practically not discernible because their α-pattern is the same as that of the sky: the direction of polarization is perpendicular to the plane of scattering and is parallel to the arc of the bow, independently of the wavelength. Fogbows and their supernumeraries were best seen in the patterns of the polarized radiance. In these patterns the angular distance δ between the peaks of the primary and the first supernumerary and the angular width σ of the primary bow were determined along different radii from the center of the bow. δ ranged between 6.08° and 13.41° , while σ changed from 5.25° to 19.47° . Certain fogbows were relatively homogeneous, meaning small variations of δ and σ along their bows. Other fogbows were heterogeneous, possessing quite variable δ- and σ-values along their bows. This variability could be a consequence of the characteristics of the high Arctic with open waters within the ice shield resulting in the spatiotemporal change of the droplet size within the fog

Jean-Paul Marat (1743-1793), cientista e tradutor de Newton

Although Jean Paul Marat (1743-1793) is known as a political activist and as a founder of the controversial journal L'Ami du Peuple during the French Revolution, an important period of his life was spent as a medical practionner, and as a scientist. In 1765 he went to England, where he remained for eleven years mostly dedicated to medical practice and publications on that subject and on political and moral questions. Returning to France in 1776 he iniciated his researches on fire, electricity and light, that lasted practically until the French Revolution. In 1787 he published a translation of Newton's Opticks. In this article we describe in some detail his medical and scientific practice giving particular emphasis to his experiments on optics and to his theory about colors which strongly departs from newtonian theory, fully accepted by the French scientific community of the time.

Determinação da estrutura molecular do ciclooctano por métodos ab initio e difração de elétrons na fase gasosa

The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase and ab initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions.

OLED-teknologia silmänäytössä ja linssiokulaarin korvaaminen muoviprismalla

Tämä diplomityö esittelee monikäyttöisen kamerajärjestelmän, mikä on pääsääntöisesti tarkoitettu valovahvistimen perään integroitavaksi. Tarkoituksena on parantaa sotilaan pimeätoimintakykyä ja urbaanissa ympäristössä operointia. Järjestelmän yhtenä moduulina on silmänäyttö, joka perustuu itse-emittoivaan orgaaniseen LED-näyttöelementtiin ja perinteiseen okulaarioptiikkaan. Työssä tutustutaan näyttöelementin teknologiaan, sen mahdollisiin rajoituksiin sekä selvitetään optisilla mittauksilla, voitaisiinko konventionaalinen linssiokulaari korvata muovisella prismaokulaarilla. Tämä mahdollistaisi pienemmän ja kevyemmän silmänäytön kehittämisen, mikä parantaisi kamerajärjestelmän käytettävyyttä ja kilpailukykyä.

Radiaalikompressorin juoksupyörän virtauskanavan suunnittelu

Diplomityössä on tutkittu radiaalikompressorin juoksupyörän virtauskanavan suunnittelua ja esitelty yleisesti käytetyt suunnittelumenetelmät. Virtauskanavan muodon vaikutukset virtauskenttään on esitetty. Työssä on kehitetty uusi tietokoneohjelma juoksupyörän kolmiulotteisen geometrian luomiseen, yksiulotteisesta suunnittelusta saatujen päämittojen pohjalta. Ohjelmalla luotua juoksupyörän geometriaa voidaan käyttää virtaus- ja lujuusanalyyseissä. Ohjelmaan on myös liitetty kaksiulotteinen kokoonpuristuvan viskoosittoman virtauksen ratkaisija.

On the effects of welding parameters on weld quality of plasma arc keyhole welding of structural steels

The possibility and the usefulness of applying plasma keyhole welding to structural steels with different compositions and material thicknesses, and in various welding positions has been examinated. Single pass butt welding with I groove in flat, horizontal vertical and vertical positions and root welding with V , Y and U grooves of thick plate material in flat position have been studied and the welds with high quality has been obtained. The technological conditions for successful welding are presented. The single and interactive effects of welding parameters on weld quality, especially on surface weld defects, geometrical form errors, internal defects and mechanical properties (strength, ductility, impact toughness, hardness and bendability) of weld joint, are presented. Welding parameter combinations providing the best quality welds are also presented.

Los domos graníticos de la Cuenca del Ridaura (Girona)

Se describen los domos graníticos de la cuenca del río Ridaura. Sus caraterísticas geométricas se relacionan estrechamente con la disposición de las fracturas. Su génesis deriva de una fase subsuperficial, bajo un manto de alteración, presumiblemente desarrollada durante el Plioceno, y una fase de exhumación torrencial, que comprende desde el Plioceno terminal hasta la actualidad