Mott Transition and Magnetism in Rare Earth Nickelates and its Fingerprint on the X-ray Scattering

The metal-insulator transition (MIT) remains among the most thoroughly studied phenomena in solid state physics, but the complexity of the phenomena, which usually involves cooperation of many degrees of freedom including orbitals, fluctuating local moments, magnetism, and the crystal structure, have resisted predictive ab-initio treatment. Here we develop ab-initio theoretical method for correlated electron materials, based on Dynamical Mean Field Theory, which can predict the change of the crystal structure across the MIT at finite temperature. This allows us to study the coupling between electronic, magnetic and orbital degrees of freedom with the crystal structure across the MIT in rare-earth nickelates. We predict the free energy profile of the competing states, and the theoretical magnetic ground state configuration, which is in agreement with neutron scattering data, but is different from the magnetic models proposed before. The resonant elastic X-ray response at the K-edge, which was argued to be a direct probe of the charge order, is theoretically modelled within the Dynamical Mean Field Theory, including the core-hole interaction. We show that the line-shape of the measured resonant elastic X-ray response can be explained with the "site-selective" Mott scenario without real charge order on Ni sites.Comment: Acknowledgments updated, citations adde

The Chandra Deep Group Survey -- cool core evolution in groups and clusters of galaxies

We report the results of a study which assembles deep observations with the ACIS-I instrument on the Chandra Observatory to study the evolution in the core properties of a sample of galaxy groups and clusters out to redshifts $z\approx 1.3$. A search for extended objects within these fields yields a total of 62 systems for which redshifts are available, and we added a further 24 non-X-ray-selected clusters, to investigate the impact of selection effects and improve our statistics at high redshift. Six different estimators of cool core strength are applied to these data: the entropy (K) and cooling time ($t_{cool}$) within the cluster core, the cooling time as a fraction of the age of the Universe ($t_{cool}/t_{Uni}$), and three estimators based on the cuspiness of the X-ray surface brightness profile. A variety of statistical tests are used to quantify evolutionary trends in these cool core indicators. In agreement with some previous studies, we find that there is significant evolution in $t_{cool}/t_{Uni}$, but little evolution in $t_{cool}$, suggesting that gas is accumulating within the core, but that the cooling time deep in the core is controlled by AGN feedback. We show that this result extends down to the group regime and appears to be robust against a variety of selection biases (detection bias, archival biases and biases due to the presence of central X-ray AGN) which we consider.Comment: Accepted by MNRAS, 24 pages, 11 figure

Tracking amino acid’s uptake into the protozoan Acanthamoeba castellanii by stable-isotope labelling and Raman spectral imaging

The capacity of pathogens to acquire nutrients from their host cells is one of the most fundamental aspects of infection biology. Hence, measuring the patterns of nutrients’ uptake by pathogens is essential for understanding the interactions of pathogens with eukaryotic host cells. In this study, we optimized a technique that allows fast and non-destructive measurement of the amino acid Phenylalanine (Phe) acquired by the trophozoite stage of the protozoan Acanthamoeba castellanii (A. castellanii) as they engage with individual human retinal pigment epithelial cells (ARPE-19). ARPE-19 host cells were pre-saturated with Deuterated Phe (L-Phe(D8)) to replace the native substrate Phe (L-Phe). The uptake of L-Phe(D8) by A. castellanii trophozoites was measured by Raman microspectroscopy. This approach allowed us to characterize the uptake patterns of this essential amino acid into A. castellanii trophozoites at a single cell level. At 24 hours post infection (PI) A. castellanii trophozoites are capable of salvaging L-Phe(D8) from host cells. The uptake pattern was time-dependent during the first 24 hours of infection and complete substitution with L-Phe(D8) in all parasites was detected at 48 hours PI. On the other hand, isolated A. castellanii trachyzoites (grown without host cells) did not show significant uptake for L-Phe(D8) from the media; only achieved an uptake ratio of 16-18% of L-Phe(D8) from the culture medium after 24 hours. These findings demonstrate the potential of combining Raman microspectroscopy and stable isotope labelling approaches to elucidate the role of metabolism in mediating A. castellanii interaction with host cells

Role of orbital selectivity on crystal structures and electronic states in BiMnO3_3 and LaMnO3_3 perovskites

Correlated oxides, such as BiMnO$_3$ and LaMnO$_3$, show complex interplay of electronic correlations and crystal structure exhibiting multiple first order phase transitions, some without a clear order parameter. The quantitative theoretical description of this temperature dependent electronic-structural interplay in the vicinity of a Mott transition is still a challenge. Here we address this issue by simultaneously considering both structural and electronic degrees of freedom, within a self-consistent density functional theory with embedded dynamical mean field theory. Our results show the existence of novel electronic states characterized by coexistence of insulating, semi-metallic and metallic orbitals. This state is in agreement with resonant X-ray scattering. We also show that electronic entropy plays a decisive role in both electronic and structural phase transitions. By self-consistent determination of both, the electronic state and the corresponding crystal structure, we show that the temperature evolution of these phases can be quantitatively explained from first principles, thus demonstrating the predictive power of the theoretical method for both the structural and the electronic properties.Comment: 10 pages, 5 figure

Evolution of X-ray properties of galaxy groups

This thesis presents the results from the Chandra Deep Group Survey, a survey dedicated to find high redshift groups of galaxies in deepest observations available in the Chandra archive. The catalogue compiled from this survey contains 26 groups and 36 clusters with available redshifts, with largest redshift being 1.3. This sample has been used to investigate the evolution of the thermal state of the gas at the centre of groups and compare this evolution to that of clusters. Different parameters have been used to quantify the strength of cool cores and it has been showed that groups and clusters have similar evolution of their cool core properties. Both classes of systems have a wide spread in the cool core strength at low redshifts, which then narrows at high redshifts showing a lack of strong cool core systems

Predictive Factors of Anxiety, Depression, and Health-Related Quality of Life in Community-Dwelling and Institutionalized Elderly during the COVID-19 Pandemic

The COVID-19 health emergency and restrictive measures have increased psychological problems, particularly anxiety and depression, in the general population. However, little is known about mental health conditions and the possible risk and protective factors of specific population groups, such as institutionalized vs. community-dwelling elderly. We investigated the abovementioned aspects in a sample of 65–89-year-old people during the third wave of COVID-19 in Italy. We employed a sociodemographic survey and four questionnaires on health-related quality of life (SF-36), loneliness (UCLA), spirituality (FACIT-Sp), and anxiety/depression (HADS). Our findings suggest that the physical, psychological, and spiritual well-being of the elderly had not been seriously impaired by the events related to the pandemic, although most of the participants reported a worsening of their social life and a moderate/high fear of COVID-19. In regression analyses, these two latter aspects turned out to be predictors of higher anxiety, while spiritual well-being and the possibility to get out of the house/institution emerged as protective factors against anxiety and for preserving quality of life, respectively. Our findings help refine the picture of the condition of the elderly in the aftermath of the pandemic, giving some hints about how to continue supporting their well-being and quality of life

Monitoring the mineralisation of bone nodules in vitro by space- and time-resolved Raman micro-spectroscopy.

Raman microscopy was used as a label-free method to study the mineralisation of bone nodules formed by mesenchymal stem cells cultured in osteogenic medium in vitro. Monitoring individual bone nodules over 28 days revealed temporal and spatial changes in the crystalline phase of the hydroxyapatite components of the nodules