Deformation classification of real non-singular cubic threefolds with a marked line

We prove that the space of pairs $(X,l)$ formed by a real non-singular cubic hypersurface $X\subset P^4$ with a real line $l\subset X$ has 18 connected components and give for them several quite explicit interpretations. The first one relates these components to the orbits of the monodromy action on the set of connected components of the Fano surface $F_\mathbb{R}(X)$ formed by real lines on $X$. For another interpretation we associate with each of the 18 components a well defined real deformation class of real non-singular plane quintic curves and show that this deformation class together with the real deformation class of $X$ characterizes completely the component

Optically active quantum dots in bottom-up nanowires

This thesis is dedicated to the discovery and progressive study of quantum emitters embedded in the shell of coaxial gallium arsenide/ aluminum gallium arsenide nanowires. The bottom-up core/shell nanowires were grown in a molecular beam epitaxy machine. During the shell growth, diffusion-driven phenomena lead to segregation effects. Gallium-rich regions are formed at the nanoscopic scale. The observation has been made that the reduced dimensionality of these regions provides true tridimensional confinement for the carriers. The recombination spectra of the electrons with the holes in what was coined shell quantum dots (shell-QDs) thus appear as sets of narrow, intense peaks. The formation of shell quantum dots is taking place on a large range of growth temperatures and nominal alloy fractions, giving freedom to engineer the growth process. The shell thickness plays an important role in the quantum dot density and total ensemble spectrum. In addition, the adjunction of an aluminum arsenide predeposition layer increasing the local curvature has been seen to foster the quantum dots formation. Single emitter spectroscopy reveals the few-particles electronic structure of quantum dots, with systematic signatures for the different degrees of occupation of the quantum dot. The shape anisotropy of the quantum dots leads to observable spin-spin interactions, which lift the degeneracy of the exciton level (one hole and one electron). Generally undesirable, this effect allows here to find that the orientation of the quantum dots in the nanowire is not hard-wired to the growth direction or to the nanowire long axis. This observation is confirmed by magneto-photoluminescence experiments. The energetic splitting and shift of the spin sublevels when an external magnetic field is applied also confirms the small size of the quantum dots. It is found that for GaAs in the strong confinement regime, the Landé coefficients of the electron and hole take opposite signs and are dependent on the angle at which the field is applied. These effects allow to tune the exciton composite Landé coefficient and could be used to reduce the splitting between the exciton spin sublevels or create optically degenerate coupled systems. Finally, the sub-nanosecond dynamics happening in the quantum dots are probed with time-correlated photon counting. It is shown that the carriers in the shell are quickly captured by the quantum dots. In addition, it is proposed that the electron population is reduced due to diffusion-assisted mechanisms or through electron-donor recombination

Quasar variability: an astrostatistical challenge

Variable behavior on all time scales seems to be ubiquitous phenomenon in almost all classes of active galactic nuclei. This work deals with two topics. One being detection of microvariability (intra-night variability) in the sources which are obscured and were believed to be non variable - type 2 quasars. The detection of a variable behavior in obscured sources is challenging as the detection is hampered by the low contrast between the presumably variable nucleus and the host galaxy. The second part deals with comparing of the variable behavior with larger amplitudes amongst two types of unobscured quasars: core dominated radio loud quasars (CRLQ) and radio quiet quasars (RQQ). Microvariability studies of obscured quasars are the focus of chapters 2 and 3. We have explored the possibility to search for short, small amplitude variations, with statistical tests, namely the F-test and one-way analysis of variance, ANOVA. The data for our sample were obtained during two observing runs, one using the 1.5 m telescope at San Pedro M\'artir observatory in Mexico and another one with Nordic Optical Telescope (NOT) at Observatorio Roque de los Muchachos, La Palma. Both samples were observed in optical wavelengths. The fourth chapter is dedicated to a study independent on the previous two chapters, which studies data set obtained during a year long campaign carried out at San Pedro M\'artir observatory. The data set contains observations of a paired set of unobscured CRLQ and RQQ. The observations were obtained in a weekly cadence, in optical wavelengths, thus focusing on a low frequency observations. We used Bartels test to search for variability in this case. As a result, we report detection of microvariability phenomenon in a subset of targets observed during the microvariability campaigns described in chapters 2 and 3. It is a result previously unaccounted for in obscured type 2 quasars. We explore possible explanations such as structure in the obscuring medium. In the second part of the thesis, we focused no comparing whether it is more likely that CRLQ are variable than RQQ. We have conducted this study on a set of targets which was studied previously. The previous study focused on a similar comparison on high frequencies. We have confirmed the results of the previous study using low frequency observations and report no statistically significant difference between RQQ and CRLQ. We have demonstrated feasibility of different statistical tests in variability studies

Hands-on Science: brightening our future

Light, either sunlight or coming from the moon or the stars, emitted by the fireflies or the bulbs in our room or coming out of our TV screen, is not only one of the first main vehicles of contact with the world around us but also adds beauty and fascination to our lives. Blessing all of us, it is definitely one of the corner stones of the structure of our modern world and crucial to its development. The book herein aims to contribute to an effective implementation of a sound widespread scientific literacy and effective Science Education in our schools and at all levels of society