Relaxation dynamics induced in glasses by the absorption of hard X-ray photons

X-ray photon correlation is used to probe the slow dynamics of the glass-former B2O3 across the glass transition. In the undercooled liquid phase the decay times of the measured correlation functions are consistent with visible light scattering results and independent of the incoming flux; in the glass they are instead temperature independent and show a definite dependence on the X-ray flux. This dependence can be exploited to obtain information on the volume occupied by the atoms that move in the glass following an absorption event. The length scale derived in this way, of the order of the nanometer, is consistent with that reported for the dynamical heterogeneities, suggesting the existence of a new scheme to get access to this fundamental quantity

Screening in YBCO at large wave vectors

We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7-{\delta}. The response of the low-lying Ba 5p and Y 4p core electrons is shown to interact strongly with the Cu 3d and O 2p excitations, with important consequences on screening. The agreement between IXS and TDDFT results is excellent, apart from a new type of excitations, mainly related to loosely bound Ba electrons and significantly affected by correlations. This points to correlation mechanisms not fully described by TDDFT that might have a role in giving rise to antiscreening.Comment: 6 pages, 3 figure

Study on the reflectivity properties of spherically bent analyser crystals

Corrigendum (J. Synchrotron Rad. - 2017 : 24, 545-546). DOI: 10.1107/S1600577516019287.Peer reviewe

Characterization of the breccia deposits in downtown L’Aquila (Central Italy) through multichannel analysis of surface waves

On April 6th 2009 an Mw 6.3 earthquake hit the historical city of L’Aquila (Central Italy) causing about 300 causalities, more than 39000 homeless and strong damage in the city and in the surrounding villages. L’Aquila downtown suffered Mercalli-Cancani-Sieberg (MCS; Sieberg 1930) intensity > VIII. Heavy damage and collapses were concentrated in the unreinforced masonry buildings including historical churches. Starting from June 2009, the Italian Civil Defense Department promoted a microzoning study of the epicentral area, aimed at identifying, at a detailed scale, areas were local seismic amplification could occur due to the characteristics of surface geology. L’Aquila is founded on a terrace that slopes down moving in the southwest direction, and raises about 50 meters above the Aterno river bed. The terrace is formed by alluvial Quaternary breccias consisting of limestone clasts in a marly matrix. In the northern part of the city the terrace is in contact with outcropping limestone, while moving toward south, breccias are over imposed to lacustrine sediments formed mainly of silty and sandy layers and minor gravel beds. As found by boreholes, the thickness of the breccias formation ranges from tenths of meters at north to just few meters at south. The uppermost weathered part of breccias outcrops at south and is indicated as “limi rossi”. The presence of breccias and “limi rossi” in the northern and southern part of the city respectively, is well identified by collected geotechnical data. Shear wave velocity (Vs) are quite high in the northern sector and can reach values of about 1000 m/s, whereas in the southernmost part the Vs of “limi rossi” drops down to 300-400 m/s. The microzoning studies at L’Aquila evidenced the presence of low-frequency (about 0.6 Hz) amplification diffused in the historical center with high amplification factors in the southern area of the city were “limi rossi” outcrops. We here present the results of multichannel surface waves analysis (MASW) based on active and passive sources. Active methods consist of 1D linear arrays of 4.5 Hz-vertical geophones using a minigun as source. Passive methods consist of 2D arrays of seismic three-component sensors. In order to investigate the low-frequency amplification, the geometry of 2D arrays was accordingly designed, using 16 seismic stations with maximum aperture of 1 km that recorded many hours of ambient seismic noise. We deployed three 2D arrays, one in the northern part and two in the southern part of the city. The 1D linear array was dedicated to characterize the shallower part of “limi rossi”. With the aim to derive the shear wave velocity profiles, the apparent phase velocity estimated through arrays technique has been inverted through a neighborhood algorithm

Characterization of the breccia deposits in downtown L’Aquila (Central Italy) through multichannel analysis of surface waves

On April 6th 2009 an Mw 6.3 earthquake hit the historical city of L’Aquila (Central Italy) causing about 300 causalities, more than 39000 homeless and strong damage in the city and in the surrounding villages. L’Aquila downtown suffered Mercalli-Cancani-Sieberg (MCS; Sieberg 1930) intensity > VIII. Heavy damage and collapses were concentrated in the unreinforced masonry buildings including historical churches. Starting from June 2009, the Italian Civil Defense Department promoted a microzoning study of the epicentral area, aimed at identifying, at a detailed scale, areas were local seismic amplification could occur due to the characteristics of surface geology. L’Aquila is founded on a terrace that slopes down moving in the southwest direction, and raises about 50 meters above the Aterno river bed. The terrace is formed by alluvial Quaternary breccias consisting of limestone clasts in a marly matrix. In the northern part of the city the terrace is in contact with outcropping limestone, while moving toward south, breccias are over imposed to lacustrine sediments formed mainly of silty and sandy layers and minor gravel beds. As found by boreholes, the thickness of the breccias formation ranges from tenths of meters at north to just few meters at south. The uppermost weathered part of breccias outcrops at south and is indicated as “limi rossi”. The presence of breccias and “limi rossi” in the northern and southern part of the city respectively, is well identified by collected geotechnical data. Shear wave velocity (Vs) are quite high in the northern sector and can reach values of about 1000 m/s, whereas in the southernmost part the Vs of “limi rossi” drops down to 300-400 m/s. The microzoning studies at L’Aquila evidenced the presence of low-frequency (about 0.6 Hz) amplification diffused in the historical center with high amplification factors in the southern area of the city were “limi rossi” outcrops. We here present the results of multichannel surface waves analysis (MASW) based on active and passive sources. Active methods consist of 1D linear arrays of 4.5 Hz-vertical geophones using a minigun as source. Passive methods consist of 2D arrays of seismic three-component sensors. In order to investigate the low-frequency amplification, the geometry of 2D arrays was accordingly designed, using 16 seismic stations with maximum aperture of 1 km that recorded many hours of ambient seismic noise. We deployed three 2D arrays, one in the northern part and two in the southern part of the city. The 1D linear array was dedicated to characterize the shallower part of “limi rossi”. With the aim to derive the shear wave velocity profiles, the apparent phase velocity estimated through arrays technique has been inverted through a neighborhood algorithm

A computationally efficient method to solve the Takagi-Taupin equations for a large deformed crystal

We present a treatise on solving the Takagi-Taupin equations in the case of a strain field with an additional, spatially slowly varying component (owing to e.g. heat expansion or angular compression). We show that the presence of such a component in a typical case merely shifts the reflectivity curve as a function of wavelength or incidence angle, while having a negligible effect on its shape. On the basis of the derived result, we develop a computationally efficient method to calculate the reflectivity curve of a large deformed crystal. The validity of the method is demonstrated by compared computed reflectivity curves with experimental ones for bent silicon wafers. An excellent agreement is observed.Peer reviewe