The effect of skewness and kurtosis on the Kenward-Roger approximation when group distributions differ

This study examined the independent effect of skewness and kurtosis on the robustness of the linear mixed model (LMM), with the Kenward-Roger (KR) procedure, when group distributions are different, sample sizes are small, and sphericity cannot be assumed. Methods: A Monte Carlo simulation study considering a split-plot design involving three groups and four repeated measures was performed. Results: The results showed that when group distributions are different, the effect of skewness on KR robustness is greater than that of kurtosis for the corresponding values. Furthermore, the pairings of skewness and kurtosis with group size were found to be relevant variables when applying this procedure. Conclusions: With sample sizes of 45 and 60, KR is a suitable option for analyzing data when the distributions are: (a) mesokurtic and not highly or extremely skewed, and (b) symmetric with different degrees of kurtosis. With total sample sizes of 30, it is adequate when group sizes are equal and the distributions are: (a) mesokurtic and slightly or moderately skewed, and sphericity is assumed; and (b) symmetric with a moderate or high/extreme violation of kurtosis. Alternative analyses should be considered when the distributions are highly or extremely skewed and samples sizes are small.

Protocol de conservació ex situ del Centre Ictiològic del Parc Natural del Delta de l'Ebre

En aquest Treball de Fi de Grau es pretén establir un protocol per a la conservació ex situ de les espècies que hi ha en el Centre Ictiològic del Parc Natural del Delta de l’Ebre. Les espècies que es troben en el CI són espècies vulnerables o en perill: espinós, samaruc, fartet, rabosa, llopet de riu i tritó palmat. Els objectius d’aquest protocol són: que el CI tingui un protocol propi, aprendre com funciona tot el centre, totes les espècies, com alimentar-les, com manipular-les i com tractar-les durant tot el seu cicle de vida. Un altre objectiu és el de veure si a finals d’any s’obté una alta població de cada espècie, quines són reintroduïdes, les patologies sorgides i els valors dels paràmetres químics de les basses naturals exteriors. El protocol s’elabora a partir de les pràctiques realitzades durant l’estiu del 2013 i els coneixements adquirits, la bibliografia i les dades del CI. Gràcies a això s’ha elaborat el treball. S’ha tractat la conservació ex situ; la problemàtica que sofreixen les espècies; cadascuna d’aquestes espècies; com funciona el CI a nivell de centre i a nivell de personal; les tasques que hi ha diàriament, setmanalment i ocasionalment segons les necessitats de l’estoc; el maneig sanitari; les patologies i com tractar-les; i l’anàlisi genètic. Els resultats obtinguts d’aquest protocol són els resultats numèrics obtinguts de l’any 2013 que són: 1. El gran nombre de cries nascudes de samaruc i fartet, menys de raboseta de riu, poques d’espinós i tritó palmat, i menys de llopet que tot just comença ara en el CI. 2. El total d’uns 5700 individus reitnroduits (samaruc, raboseta de riu i espinós de Girona). 3. La patologia més sorgida és el punt blanc. 4. I els paràmetres químics (amoni, nitrits, nitrats i fòsfor) no són molt elevats. La conclusió final i més important a la que arribo en fer el protocol és la gran importància que té el CI per a conservar aquestes espècies que no es saben apreciar fins que comencen a desparèixer. La existència del CI és més aviat una mesura correctora de tots els impactes que han sofert els habitatges de les espècies tractades i de la introducció d’espècies exòtiques que són una amenaça per les autòctones.

Ancient DNA of the extinct Lava shearwater (Puffinus olsoni) from the Canary Islands reveals incipient differentiation within the P. puffinus complex

The loss of species during the Holocene was, dramatically more important on islands than on continents. Seabirds from islands are very vulnerable to human-induced alterations such as habitat destruction, hunting and exotic predators. For example, in the genus Puffinus (family Procellariidae) the extinction of at least five species has been recorded during the Holocene, two of them coming from the Canary Islands.

A Eterna Busca do Indivisível: do Átomo Filosófico aos Quarks e Léptons

The fascinating search of the inner boundaries of the Universe, has been entangled, since the birth of greek philosophy 25 centuries ago, with the main epistemological changes in the History of Science. This paper does not intend to present a systematic description of the discovery of the elementary particles. By stressing the main achievements of the knowledge of matter's structure and their dependence on symmetry arguments, it is argued that even considering profound differences in each historical period, there is a paradgima of atom shared by Chemistry and Particle Physics. This text could help High School Teachers of Chemistry and Physics, as well as motivate them, in the challenge of explaining to their pupils how the idea of atom evolved.

Defeitos superficiais em 2H-WS2 observados por microscopia de tunelamento

Scanning tunnelling microscopy (STM) was used to characterise the basal surface of fresh cleaved crystals of 2H-WS2. Although no impurity or stacking faults could be detected by X-ray diffraction, STM images obtained with negative bias voltage showed two kinds of defects. These defects were attributed to an iodine derivative used as transport agent. In a flat surface free of defects, an image with atomic resolution was achieved with sulphur distances and angles as expected for hexagonal symmetry of 2H-WS2.

The ESRg matrix for strong field d5 systems

This review has tried to collect and correlate all the various equations for the g matrix of strong field d5 systems obtained from different basis sets using full electron and hole formalism calculations. It has corrected mistakes found in the literature and shown how the failure to properly take in symmetry boundary conditions has produced a variety of apparently inconsistent equations in the literature. The review has reexamined the problem of spin-orbit interaction with excited t4e states and finds that the earlier reports that it is zero in octahedral symmetry is not correct. It has shown how redefining what x, y, and z are in the principal coordinate system simplifies, compared to previous methods, the analysis of experimental g values with the equations.

Studies of Eu- and Yb-induced Reconstructions on the Si(100) Surface

This thesis presents experimental studies of rare earth (RE) metal induced structures on Si(100) surfaces. Two divalent RE metal adsorbates, Eu and Yb, are investigated on nominally flat Si(100) and on vicinal, stepped Si(100) substrates. Several experimental methods have been applied, including scanning tunneling microscopy/spectroscopy (STM/STS), low energy electron diffraction (LEED), synchrotron radiation photoelectron spectroscopy (SR-PES), Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS), and work function change measurements (Δφ). Two stages can be distinguished in the initial growth of the RE/Si interface: the formation of a two-dimensional (2D) adsorbed layer at submonolayer coverage and the growth of a three-dimensional (3D) silicide phase at higher coverage. The 2D phase is studied for both adsorbates in order to discover whether they produce common reconstructions or reconstructions common to the other RE metals. For studies of the 3D phase Yb is chosen due to its ability to crystallize in a hexagonal AlB2 type lattice, which is the structure of RE silicide nanowires, therefore allowing for the possibility of the growth of one-dimensional (1D) wires. It is found that despite their similar electronic configuration, Eu and Yb do not form similar 2D reconstructions on Si(100). Instead, a wealth of 2D structures is observed and atomic models are proposed for the 2×3-type reconstructions. In addition, adsorbate induced modifications on surface morphology and orientational symmetry are observed. The formation of the Yb silicide phase follows the Stranski-Krastanov growth mode. Nanowires with the hexagonal lattice are observed on the flat Si(100) substrate, and moreover, an unexpectedly large variety of growth directions are revealed. On the vicinal substrate the growth of the silicide phase as 3D islands and wires depends drastically on the growth conditions. The conditions under which wires with high aspect ratio and single orientation parallel to the step edges can be formed are demonstrated.

Fragmentation of massive dense cores down to <~ 1000 AU: relation between fragmentation and density structure

In order to shed light on the main physical processes controlling fragmentation of massive dense cores, we present a uniform study of the density structure of 19 massive dense cores, selected to be at similar evolutionary stages, for which their relative fragmentation level was assessed in a previous work. We inferred the density structure of the 19 cores through a simultaneous fit of the radial intensity profiles at 450 and 850 μm (or 1.2 mm in two cases) and the spectral energy distribution, assuming spherical symmetry and that the density and temperature of the cores decrease with radius following power-laws. Even though the estimated fragmentation level is strictly speaking a lower limit, its relative value is significant and several trends could be explored with our data. We find a weak (inverse) trend of fragmentation level and density power-law index, with steeper density profiles tending to show lower fragmentation, and vice versa. In addition, we find a trend of fragmentation increasing with density within a given radius, which arises from a combination of flat density profile and high central density and is consistent with Jeans fragmentation. We considered the effects of rotational-to-gravitational energy ratio, non-thermal velocity dispersion, and turbulence mode on the density structure of the cores, and found that compressive turbulence seems to yield higher central densities. Finally, a possible explanation for the origin of cores with concentrated density profiles, which are the cores showing no fragmentation, could be related with a strong magnetic field, consistent with the outcome of radiation magnetohydrodynamic simulations.

Síntese, caracterização e propriedades espectroscópicas de criptatos de lantanídeo do tipo [LnÌ(bipy)2py(CO2Et) 2(3+)]

This work reports on the synthesis, characterization (infrared and hidrogen nmr spectra) and photophysical properties (luminescence spectra and emission quantum yield) of the lanthanide cryptates [LnÌ(bipy)2py(CO2Et) 2]3+ with Ln = Eu3+, Tb3+ or Gd3+, which can be applied as efficient Light-Conversion-Molecular-Devices. From emission spectra of [EuÌ(bipy)2py(CO2Et) 2]3+ it was possible to assign C3 symmetry to the metal ion. The spectroscopic studies show a higher emission quantum yield (q=25%) for [TbÌ(bipy)2py(CO2Et) 2]3+ in aqueous solution, whereas the europium cryptate presents q=14%. This is justified by a more efficient energy transfer between triplet and emission levels of terbium (T->5D4).