33 research outputs found
Characterization of free standing InAs quantum membranes by standing wave hard x-ray photoemission spectroscopy
Free-standing nanoribbons of InAs quantum membranes (QMs) transferred onto a
(Si/Mo) multilayer mirror substrate are characterized by hard x-ray
photoemission spectroscopy (HXPS), and by standing-wave HXPS (SW-HXPS).
Information on the chemical composition and on the chemical states of the
elements within the nanoribbons was obtained by HXPS and on the quantitative
depth profiles by SW-HXPS. By comparing the experimental SW-HXPS rocking curves
to x-ray optical calculations, the chemical depth profile of the InAs(QM) and
its interfaces were quantitatively derived with angstrom precision. We
determined that: i) the exposure to air induced the formation of an InAsO
layer on top of the stoichiometric InAs(QM); ii) the top interface between the
air-side InAsO and the InAs(QM) is not sharp, indicating that
interdiffusion occurs between these two layers; iii) the bottom interface
between the InAs(QM) and the native oxide SiO on top of the (Si/Mo)
substrate is abrupt. In addition, the valence band offset (VBO) between the
InAs(QM) and the SiO/(Si/Mo) substrate was determined by HXPS. The value of
eV is in good agreement with literature results obtained
by electrical characterization, giving a clear indication of the formation of a
well-defined and abrupt InAs/SiO heterojunction. We have demonstrated that
HXPS and SW-HXPS are non-destructive, powerful methods for characterizing
interfaces and for providing chemical depth profiles of nanostructures, quantum
membranes, and 2D layered materials.Comment: three figure
Bulk Electronic Structure of Lanthanum Hexaboride (LaB6) by Hard X-ray Angle-Resolved Photoelectron Spectroscopy
In the last decade rare-earth hexaborides have been investigated for their
fundamental importance in condensed matter physics, and for their applications
in advanced technological fields. Among these compounds, LaB has a special
place, being a traditional d-band metal without additional f- bands. In this
paper we investigate the bulk electronic structure of LaB using hard x-ray
photoemission spectroscopy, measuring both core-level and angle-resolved
valence-band spectra. By comparing La 3d core level spectra to cluster model
calculations, we identify well-screened peak residing at a lower binding energy
compared to the main poorly-screened peak; the relative intensity between these
peaks depends on how strong the hybridization is between La and B atoms. We
show that the recoil effect, negligible in the soft x-ray regime, becomes
prominent at higher kinetic energies for lighter elements, such as boron, but
is still negligible for heavy elements, such as lanthanum. In addition, we
report the bulk-like band structure of LaB determined by hard x-ray
angle-resolved photoemission spectroscopy (HARPES). We interpret HARPES
experimental results by the free-electron final-state calculations and by the
more precise one-step photoemission theory including matrix element and phonon
excitation effects. In addition, we consider the nature and the magnitude of
phonon excitations in HARPES experimental data measured at different
temperatures and excitation energies. We demonstrate that one step theory of
photoemission and HARPES experiments provide, at present, the only approach
capable of probing true bulk-like electronic band structure of rare-earth
hexaborides and strongly correlated materials.Comment: Total 26 pages, Total 11 figure
Diastolic delta best predicts paravalvular regurgitation after transcatheter aortic valve replacement as assessed by cardiac magnetic resonance: the APPOSE trial
Aims: Paravalvular regurgitation (PVR) is a common complication after transcatheter aortic valve replacement (TAVR) that poses an increased risk of rehospitalization for heart failure and mortality. The aim of this study was to assess the accuracy of haemodynamic indices to predict relevant PVR. Methods and results: In this prospective single-centre clinical trial, four haemodynamic indices of PVR measured during TAVR were assessed for their correlation with gold standard cardiac magnetic resonance (CMR)-derived regurgitant fraction (CMR-RF) at 1 month follow-up: diastolic delta (DD), heart rate-adjusted diastolic delta (HR-DD), aortic regurgitation index (ARI), and aortic regurgitation index ratio (ARI ratio). These haemodynamic indices were analysed for their ability to predict relevant PVR (defined as CMR-RF > 20%) using receiver operating characteristic (ROC) curves with corresponding area under the ROC curves (AUCs). A total of 77 patients were included and had CMR performed 41 ± 14 days after TAVR. Mean CMR-RF was 12.4 ± 9.3%. Fifteen (19.5%) patients had CMR-RF > 20%. DD had the best correlation with CMR-RF and the highest AUC to predict relevant PVR (0.82; 95% CI, 0.72-0.92), followed by HR-DD (AUC 0.78; 95% CI, 0.67-0.89), ARI (AUC 0.78; 95% CI, 0.66-0.89), and ARI ratio (AUC 0.65; 95% CI, 0.49-0.81). The optimal cut-off value for DD was 32 mmHg, with sensitivity of 69% and specificity of 77% in predicting relevant PVR. Conclusion: DD measured during TAVR best predicts relevant PVR. Correction for heart rate (HR-DD) or systolic blood pressure (ARI, ARI ratio) did not improve this predictive value
Multiple coronary artery fistulae or Thebesian veins?
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Novel X-ray image noise reduction technology reduces patient radiation dose while maintaining image quality in coronary angiography
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152546.pdf (publisher's version ) (Open Access)AIMS: The consequences of high radiation dose for patient and staff demand constant improvements in X-ray dose reduction technology. This study assessed non-inferiority of image quality and quantified patient dose reduction in interventional cardiology for an anatomy-specific optimised cine acquisition chain combined with advanced real-time image noise reduction algorithms referred to as 'study cine', compared with conventional angiography. METHODS: Fifty patients underwent two coronary angiographic acquisitions: one with advanced image processing and optimised exposure system settings to enable dose reduction (study cine) and one with standard image processing and exposure settings (reference cine). The image sets of 39 patients (18 females, 21 males) were rated by six experienced independent reviewers, blinded to the patient and image characteristics. The image pairs were randomly presented. Overall 85 % of the study cine images were rated as better or equal quality compared with the reference cine (95 % CI 0.81-0.90). The median dose area product per frame decreased from 55 to 26 mGy.cm(2)/frame (53 % reduction, p < 0.001). CONCLUSION: This study demonstrates that the novel X-ray imaging technology provides non-inferior image quality compared with conventional angiographic systems for interventional cardiology with a 53 % patient dose reduction
Concomitant coronary artery revascularization and right pneumonectomy without cardiopulmonary bypass
Combined coronary artery bypass grafting (CABG) and pneumonectomy has a high morbidity and mortality rate, especially when the right lung has to be removed. A patient is described who underwent a CABG operation through a midline sternotomy without the use of cardiopulmonary bypass (CPB), and a right pneumonectomy through a right lateral thoracotomy in one operative session. To our knowledge, this is the first case in which this operative strategy was employed. CABG operations without the use of CPB might put concomitant lung surgery in a new perspective
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An Efficient Algorithm for Automatic Structure Optimization in X-ray Standing-Wave Experiments
X-ray standing-wave photoemission experiments involving multilayered samples are emerging as unique probes of the buried interfaces that are ubiquitous in current device and materials research. Such data require for their analysis a structure optimization process comparing experiment to theory that is not straightforward. In this work, we present a new computer program for optimizing the analysis of standing-wave data, called SWOPT, that automates this trial-and-error optimization process. The program includes an algorithm that has been developed for computationally expensive problems: so-called black-box simulation optimizations. It also includes a more efficient version of the Yang X-ray Optics Program (YXRO) [Yang, S.-H., Gray, A.X., Kaiser, A.M., Mun, B.S., Sell, B.C., Kortright, J.B., Fadley, C.S., J. Appl. Phys. 113, 1 (2013)] which is about an order of magnitude faster than the original version. Human interaction is not required during optimization. We tested our optimization algorithm on real and hypothetical problems and show that it finds better solutions significantly faster than a random search approach. The total optimization time ranges, depending on the sample structure, from minutes to a few hours on a modern computer, and can be up to 100x faster than a corresponding manual optimization. These speeds make the SWOPT program a valuable tool for real-time analyses of data during synchrotron experiments