A combined FEG-SEM and TEM study of silicon nanodot assembly

Nanodots forming dense assembly on a substrate are difficult to characterize in terms of size, density, morphology and cristallinity. The present study shows how valuable information can be obtained by a combination of electron microscopy techniques. A silicon nanodots deposit has been studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to estimate essentially the dot size and density, quantities emphasized because of their high interest for application. High resolution SEM indicates a density of 1.6 × 1012 dots/cm2 for a 5 nm to 10 nm dot size. TEM imaging using a phase retrieval treatment of a focus series gives a higher dot density (2 × 1012 dots/cm2) for a 5 nm dot size. High Resolution Transmission Electron Microscopy (HRTEM) indicates that the dots are crystalline which is confirmed by electron diffraction. According to HRTEM and electron diffraction, the dot size is about 3 nm which is significantly smaller than the SEM and TEM results. These differences are not contradictory but attributed to the fact that each technique is probing a different phenomenon. A core-shell structure for the dot is proposed which reconcile all the results. All along the study, Fourier transforms have been widely used under many aspects

Clustering of galaxies: evolution, segregation, and baryon acoustic oscillations

In this thesis, we tackle several open problems in the study of large-scale structure through the clustering of galaxies. To this end, we analyse data from some of the latest surveys, and we also develop new statistical techniques needed for this analysis in specific cases. In the first part, we focus on small and intermediate scales, where the relation between galaxy properties and their clustering (known as segregation) is important. The work in this part is driven by the exploitation of data from the ongoing Advanced Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey, which is perfectly suited to study the evolution of segregation trough cosmic time. We developed a method for the recovery of the real-space clustering from photometric surveys with the characteristics of ALHAMBRA. This method is based on the use of the projected correlation function, and is adapted to data with typical photometric redshift errors Dz < 0.015 (1+z). We tested the method using N-body simulations, and then applied it to the calculation of the correlation function for several samples drawn from the ALHAMBRA survey. We divided our sample in three redshift bins, and selected several galaxy samples in each of them based on B-band luminosity. In the range of scales studied, the correlation function for all samples was well fitted by a power law. We observed as well the effects of evolution, and of luminosity segregation. We also reviewed the basic tools available in the framework of the statistics of marked point processes to study galaxy segregation. We illustrated their application using a galaxy sample drawn from the 2dFGRS, characterised by a spectral classification parameter. We introduced the mark connection function, showing that it gives valuable information when analysing different galaxy populations defined by some set of galaxy characteristics. In the second part, we focus on the study of a large scale feature of the galaxy distribution, the baryon acoustic oscillations (BAO). We measured the two-point correlation function for several samples drawn from the largest surveys to date, 2dFGRS and SDSS. We obtained a peak corresponding to BAO at the expected scale in all cases, which shows the reliability of the detection of this feature. Finally, we developed a new method for the analysis of the BAO phenomenon. This method makes use of the possibilities of wavelets methods to look for the actual structures in configuration space which are responsible for the BAO. It is also based on the use of two complementary mass tracers, and we illustrated it using a catalogue formed by `Main' and Luminous Red Galaxy samples from SDSS. In this way, we showed how we were able not only to detect BAO in the samples, but also to localise regions giving lower or higher BAO signal. This kind of information is completely lost when using the traditional two-point statistics methods.Peer Reviewe

Developing communication and thinking skills in English as a Foreign Language Education undergraduate students: a proposal for a syllabus model

It is our aim to share a proposal for a new syllabus model and learner-centered methodology for English as a Foreign Language students in the Degree in Teaching in Primary Education at the Universidad de Zaragoza (Spain), presenting the theoretical tenets and analyzing samples of resources and materials that have been designed. In a context of great diversity of levels and learning profiles in the abovementioned educational setting, it is no longer valid to conceive this part of teacher training only in terms of language proficiency, but rather it is necessary to equip students with learning to learn tools and metacognitive strategies as well as materials and resources purposefully designed bearing in mind their context, professional interests and linguistic needs. As a result, throughout the three 6 ECTS courses in the Degree (English in Primary Education I, II and III, for ist, 2nd and 4th year students respectively) we seek to implement active methodologies and make use of a variety of resources following Communicative Language Teaching and Task-based Instruction principles, such as the following: (i) Deep Learning (Clark, 2009a, 2009b) and Scaffolded, Visible Thinking (Ritchhart, Church, and Morrison, 2011); (ii) Cooperative Learning (Kagan and Kagan, 1994); (iii) ICTs and EdTech; (iv) reflective learning, promoting self-assessment and peer-assessment, and (v) Project Based Learning (BIE, 2003). Overall, the teaching proposal designed has enabled us to partially respond to heterogeneity in our large classes and make our students'' learning of a language relevant and meaningful

Relativistic semiclassical approach in strong-field nonlinear photoionization

Nonlinear relativistic ionization phenomena induced by a strong laser radiation with elliptically polarization are considered. The starting point is the classical relativistic action for a free electron moving in the electromagnetic field created by a strong laser beam. The application of the relativistic action to the classical barrier-suppression ionization is briefly discussed. Further the relativistic version of the Landau-Dykhne formula is employed to consider the semiclassical sub-barrier ionization. Simple analytical expressions have been found for: (i) the rates of the strong-field nonlinear ionization including relativistic initial and final state effects; (ii) the most probable value of the components of the photoelectron final state momentum; (iii) the most probable direction of photoelectron emission and (iv) the distribution of the photoelectron momentum near its maximum value.Comment: 13 pages, 3 figures, to be published in Phys. Rev.

Measuring galaxy segregation using the mark connection function

(abridged) The clustering properties of galaxies belonging to different luminosity ranges or having different morphological types are different. These characteristics or `marks' permit to understand the galaxy catalogs that carry all this information as realizations of marked point processes. Many attempts have been presented to quantify the dependence of the clustering of galaxies on their inner properties. The present paper summarizes methods on spatial marked statistics used in cosmology to disentangle luminosity, colour or morphological segregation and introduces a new one in this context, the mark connection function. The methods used here are the partial correlation functions, including the cross-correlation function, the normalised mark correlation function, the mark variogram and the mark connection function. All these methods are applied to a volume-limited sample drawn from the 2dFGRS, using the spectral type as the mark. We show the virtues of each method to provide information about the clustering properties of each population, the dependence of the clustering on the marks, the similarity of the marks as a function of the pair distances, and the way to characterise the spatial correlation between the marks. We demonstrate by means of these statistics that passive galaxies exhibit stronger spatial correlation than active galaxies at small scales (r <20 Mpc/h). The mark connection function, introduced here, is particularly useful for understanding the spatial correlation between the marks.Comment: 6 pages, 5 figures, accepted for publication in Astronomy and Astrophysic