X-ray magnetic circular dichroism measurements using an X-ray phase retarder on the BM25 A-SpLine beamline at the ESRF.

Circularly polarized X-rays produced by a diamond X-ray phase retarder of thickness 0.5 mm in the Laue transmission configuration have been used for recording X-ray magnetic circular dichroism (XMCD) on the bending-magnet beamline BM25A (SpLine) at the ESRF. Field reversal and helicity reversal techniques have been used to carry out the measurements. The performance of the experimental set-up has been demonstrated by recording XMCD in the energy range from 7 to 11 keV.

Origin of the X-ray magnetic circular dichroism at the L-edges of the rare-earths in RxR(1-x)'Al2 systems.

An X-ray magnetic circular dichroism (XMCD) study performed at the rare-earth L(2,3)-edges in the R(x)R(1-x)'Al(2) compounds is presented. It is shown that both R and R' atoms contribute to the XMCD recorded at the L-edges of the selected rare-earth, either R or R'. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R') magnetic moments, but it is related to the molecular field acting on the rare-earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L-edge of the rare-earths in multi-component systems, allowing a full understanding of the exact nature of these signals.

Addition of a macrolide to a beta-lactam-based empirical antibiotic regimen is associated with lower in-hospital mortality for patients with bacteremic pneumococcal pneumonia.

To assess the association between inclusion of a macrolide in a beta-lactam-based empirical antibiotic regimen and mortality among patients with bacteremic pneumococcal pneumonia, 10 years of data from a database were analyzed. The total available set of putative prognostic factors was subjected to stepwise logistic regression, with in-hospital death as the dependent variable. Of the 409 patients analyzed, 238 (58%) received a beta-lactam plus a macrolide and 171 (42%) received a beta-lactam without a macrolide. Multivariate analysis revealed 4 variables to be independently associated with death: shock (P<.0001), age of >or=65 years (P=.02), infections with pathogens that have resistance to both penicillin and erythromycin (P=.04), and no inclusion of a macrolide in the initial antibiotic regimen (P=.03). For patients with bacteremic pneumococcal pneumonia, not adding a macrolide to a beta-lactam-based initial antibiotic regimen is an independent predictor of in-hospital mortality. However, only a randomized study can definitively determine whether this association is due to a real effect of macrolides.

Temperature dependence of the Ho L2-edge XMCD spectra of Ho6Fe23.

An X-ray magnetic circular dichroism (XMCD) study performed at the Ho L2,3-edges in Ho6Fe23 as a function of temperature is presented. It is demonstrated that the anomalous temperature dependence of the Ho L2-edge XMCD signal is due to the magnetic contribution of Fe atoms. By contrast, the Ho L3-edge XMCD directly reflects the temperature dependence of the Ho magnetic moment. By combining the XMCD at both Ho L2- and L3-edges, the possibility of determining the temperature dependence of the Fe magnetic moment is demonstrated. Then, both microHo(T) and microFe(T) have been determined by tuning only the absorption L-edges of Ho. This result opens new possibilities of applying XMCD at these absorption edges to obtain quantitative element-specific magnetic information that is not directly obtained by other experimental tools.

Disentanglement of magnetic contributions in multi-component systems by using X-ray magnetic circular dichroism at a single absorption edge.

X-ray magnetic circular dichroism (XMCD) has become in recent years an outstanding tool for studying magnetism. Its element specificity, inherent to core-level spectroscopy, combined with the application of magneto-optical sum rules allows quantitative magnetic measurements at the atomic level. These capabilities are now incorporated as a standard tool for studying the localized magnetism in many systems. However, the application of XMCD to the study of the conduction-band magnetism is not so straightforward. Here, it is shown that the atomic selectivity is not lost when XMCD probes the delocalized states. On the contrary, it provides a direct way of disentangling the magnetic contributions to the conduction band coming from the different elements in the material. This is demonstrated by monitoring the temperature dependence of the XMCD spectra recorded at the rare-earth L(2)-edge in the case of RT(2) (R = rare-earth, T = 3d transition metal) materials. These results open the possibility of performing element-specific magnetometry by using a single X-ray absorption edge.

Microbial airway colonization is associated with noninvasive ventilation failure in exacerbation of chronic obstructive pulmonary disease.

OBJECTIVE: Abnormal airway colonization in patients with chronic obstructive pulmonary disease (COPD) needing invasive mechanical ventilation (IMV) is considered a first step in the acquisition of nosocomial pneumonia. Noninvasive ventilation (NIV) could potentially avoid this, but airway colonization has not been studied in patients who undergo NIV. We hypothesized that patients undergoing NIV would have lower rates of colonization than patients undergoing IMV. The aim of the study was to assess the microbial airway colonization in patients with exacerbated COPD needing NIV and IMV. DESIGN: A 2-yr prospective cohort study. SETTING: Respiratory intensive and intermediate care unit. PATIENTS: Eighty-six patients with exacerbated COPD undergoing NIV on admission (64 successes and 22 failures, according to subsequent intubation), and 51 patients undergoing IMV on admission. INTERVENTIONS: Quantitative culture specimens of sputum or tracheal aspirate were collected on admission and at follow-up (day 3) during NIV or IMV, respectively. Clinical assessment, including severity scores, and arterial blood gas measurements were also determined. MEASUREMENTS AND MAIN RESULTS: Compared with the NIV-success group, colonization by potentially pathogenic microorganisms was greater in the NIV-failure group on admission (13 [59%] vs. 14 [22%]; p < .001) and at follow-up while patients still underwent NIV (14 [93%] vs. 7 [14%]; p < .001), and it was even higher than during IMV at follow-up (20 [50%]; p = .027). Colonization by nonfermenting Gram-negative bacilli, mainly Pseudomonas aeruginosa, was significantly associated with NIV failure on admission (OR, 5.6; p = .016) and at follow-up (OR, 23.5; p < .001). Moreover, colonization by these microorganisms at follow-up (OR, 8.8; p = .008) and inadequate antimicrobial treatment (OR 11.3; p = .001) were associated with increased hospital mortality. CONCLUSIONS: Airway colonization by nonfermenting Gram-negative bacilli is strongly associated with NIV failure. Because it occurs before intubation, this would be a marker rather than just a consequence of NIV failure necessitating intubation. The efficacy of decreasing airway colonization in preventing NIV failure needs to be assessed.