Study of Surface Acoustic Wave propagation using Synchrotron Radiation X-Ray Topography

X-ray topography is an accurate and sensitive method to image the strain fields existing in crystals, particularly those created by bulk or surface acoustic waves (BAW or SAW). The time structure of the synchrotron radiation allows to image progressive waves having a frequency multiple of that of the synchrotron. The main purpose of this study is the understanding of the exact nature of the information obtained about SAW by means of X-Ray topography. To this end we will consider experimental and computed images obtained for SAW propagating on ST-cut quartz and YZ-LNB. Most experiments were made using wide X-ray beams. Depending on the diffraction conditions, the so-called "translation" topographs seem often as being good maps of the displacement existing near the surface of the SAW device. These images may be considered as the result of a process of spatial integration of section topographs, more simply related to the X-ray diffraction process and to the displacement gradients of the acoustic field. These section topographs, corresponding to an extremely thin X-ray beam, contain, in fact, more information about the SAW. Quite intricate section topographs of low amplitude SAW propagating on YZ lithium niobate and ST-cut quartz were experimentally obtained using the Bragg diffraction geometry (reflection). Simulations of these section topographs gave information about the displacement gradients existing near the surface (most intense contrast) and about the depth dependence of this gradient (weak contrasts). In the summation process, leading to the "translation" topographs, only the intense contrasts (representing the largest strains) contribute significantly while the weaker ones are blurred into a grey level. Thus, the main contrast in translation topographs arise mainly from the gradients of the component of the displacement along the diffraction vector, at (or very near) the surface. These derivatives are proportional to the displacement so that these topographs represent essentially, with a different phase, the corresponding displacement. When the amplitude of the SAW becomes large enough, a kinematical diffraction process explains that the most intense contrast generated near the surface is enlarged proportionally to the local amplitude. This allows a simple method to measure the transverse amplitude variations of the surface modes. The two other elastic components of the SAW are imaged using the Laue diffraction geometry (transmission) with appropriate diffraction vectors. The corresponding section topographs obtained with ST-cut quartz are also complex and again, simulated images were used to understand the contrasts observed. Similarly the summation process, leading to the translation images, is dominated by the largest displacement gradient and so leads to a representation of the lateral displacements existing near the surface. Small velocity (phase) variations most probably induced by the dislocations present in the synthetic quartz crystal, were observed in the sections images

Strain state in single quantum well GaAs/1ML-InAs/GaAs(100) analysed by high-resolution X-ray diffraction

dépôt d'une copie effectué avec l'aimable autorisation de EDP SciencesThe epitaxy-induced tetragonal strain in one monolayer of InAs buried in a GaAs(100) crystal is determined by measuring weak oscillations in X-ray reflectivity profiles. It is shown that the reflectivity of such heterostructure consists of a sinusoidal modulation of the usual rocking curve of a thick crystal. The oscillation period provides the distance of the buried layer from the crystal surface and the maximum positions in oscillations give the displacement induced by the buried layer. The vertical spacing between the In and As atom planes is found to be 1.64 ± 0.02 Å, which is consistent with an elastic behaviour

Geometrical structure of an iron epilayer on Si (111) : an X-ray standing wave analysis

dépôt d'une copie effectué avec l'aimable autorisation de EDP SciencesThe structure of an iron film, deposited at low temperature (50 °C) upon a silicon (111) substrate, has been determined by means of X-ray Standing Wave experiments performed at LURE (Orsay, France). Experimental results are coherent with the model of an abrupt interface between the adsorbate and the surface : the first site of adsorption terminates the bulk silicon and a body-centred iron layer epitaxially grows on the substrate with a preferential growth orientation

A Harmonized Nitrous Oxide (N2O) Ocean Observation Network for the 21st Century

Nitrous oxide (N2O) is an important atmospheric trace gas involved in tropospheric warming and stratospheric ozone depletion. Estimates of the global ocean contribution to N2O emissions average 21% (range: 10 to 53%). Ongoing environmental changes such as warming, deoxygenation and acidification are affecting oceanic N2O cycling and emissions to the atmosphere. International activities over the last decades aimed at improving estimates of global N2O emissions, including (i) the MarinE MethanE and NiTrous Oxide database (MEMENTO) for archiving of quality-controlled data, and (ii) a recent large-scale inter-laboratory comparison by Working Group 143 of the Scientific Committee on Ocean Research (SCOR). To reduce uncertainties in oceanic N2O emission estimates and to characterize the spatial and temporal variability in N2O distributions in a changing ocean, we propose the establishment of a harmonized N2O Observation Network (N2O-ON) combining discrete and continuous data from various platforms. The network will integrate observations obtained by calibrated techniques, using time series measurements at fixed stations and repeated hydrographic sections on voluntary observing ships and research vessels. In addition to exploiting existing oceanographic infrastructure, we propose the establishment of central calibration facilities in selected international laboratories to improve accuracy, and ensure standardization and comparability of N2O measurements. Final data products will include a harmonized global N2O concentration and emission fields for use in model validation and projections of future oceanic N2O emissions, to inform the global research community and policy makers

Non-Standard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Mgr M. Andrieu, Les Ordines Romani du haut moyen-âge. II. Les textes (Ordines I - XIII) (Spicil. sacrum lovan. fasc. 23), 1948

Capelle Bernard. Mgr M. Andrieu, Les Ordines Romani du haut moyen-âge. II. Les textes (Ordines I - XIII) (Spicil. sacrum lovan. fasc. 23), 1948. In: Revue des Sciences Religieuses, tome 24, fascicule 3-4, 1950. pp. 390-391

R. Metz, La consécration des vierges dans l'Église romaine. Etude d'histoire de la liturgie, 1954

Capelle Bernard. R. Metz, La consécration des vierges dans l'Église romaine. Etude d'histoire de la liturgie, 1954. In: Revue des Sciences Religieuses, tome 29, fascicule 3, 1955. pp. 296-299

Mgr M. Andrieu, Les Ordines Romani du haut moyen-âge. II. Les textes (Ordines I - XIII) (Spicil. sacrum lovan. fasc. 23), 1948

Capelle Bernard. Mgr M. Andrieu, Les Ordines Romani du haut moyen-âge. II. Les textes (Ordines I - XIII) (Spicil. sacrum lovan. fasc. 23), 1948. In: Revue des Sciences Religieuses, tome 24, fascicule 3-4, 1950. pp. 390-391