Study of the residual surface resistance of niobium films at 1.5 GHz

Potential contributions to the residual surface resistance of niobium films exposed to 1.5 GHz microwaves are reviewed and studied. These include the oxidation of the film surface, the formation of hydride precipitates, the contamination by noble gas atoms and the presence of macroscopic film defects such as those resulting from the roughness of the substrate. Particular attention is given to the dependence of the residual resistance on the amplitude of the microwave. Results similar to those obtained for bulk niobium provide strong evidence against the conjecture that the small size of the film grains should be a fundamental limitation to the production of films having a low residual resistance

Fluxon induced resistance and field emission

The surface resistance of superconducting niobium films induced by the presence of trapped magnetic flux, presumably in the form of a pinned fluxon lattice, is shown to be modified by the presence of a field emitting impurity or defect. The modification takes the form of an additional surface resistance proportional to the density of the fluxon lattice and increasing linearly with the amplitude of the microwave above a threshold significantly lower than the field emission threshold. Such an effect, precursor of electron emission, is observed here for the first time in a study using radiofrequency cavities operated at their fundamental 1.5 GHz frequency. The measured properties of the additional surface resistance severely constrain possible explanations of the observed effect

High-Q, high gradient niobium-coated cavities at CERN

Superconducting cavities made by sputter-deposition of a thin niobium film onto copper have proven over the years to be a viable alternative to bulk niobium, the best example being the very successful operation of LEP at 200 GeV. It will be shown that this technology, investigated at 1.5 GHz by a dedicated R&D effort at CERN, can be developed to unprecedented performance, proving that no fundamental limitation prevents high quality factors to be maintained over a broad range of accelerating field

Study of the Residual Resistance of Superconducting Niobium Films at 1.5 GHz

A study of the main potential contributions to the residual surface resistance of niobium-coated cavities is reviewed. They are the formation of hydride precipitates, the contamination by discharge gas atoms and the presence of macroscopic defects in the film, induced by defects in the substrate. It will be shown that residual resistances as low as those obtained for bulk niobium can be achieved, together with a very small dependence on the amplitude of the RF field

Superconducting niobium cavities, a case for the film technology

Evidence is presented for niobium film cavities performing as well as niobium bulk cavities, at variance with a widespread belief that their much smaller grain size should be a fundamental limitation preventing high quality factors to be maintained over a wide range of accelerating fields. By comparing the relative merits of the bulk and film technologies, a strong case is presented in favour of the latter

Probiotic yogurt in the elderly with intestinal bacterial overgrowth: endotoxaemia and innate immune functions

A study was conducted in healthy elderly living independently in senior housing to assess the impact of a probiotic yoghurt supplement on small intestinal bacterial overgrowth. Twenty-three participants with positive and thirteen participants with negative hydrogen breath test were studied before and after a period of 4 weeks of probiotic yoghurt administration. Intestinal permeability, plasma endotoxin levels, phagocytic activity of leucocytes, cytokine production by monocytes and free radical response of neutrophils were determined. Intestinal permeability was similar for the two groups and was unaffected by probiotic treatment. Both plasma endotoxin levels and the basal phagocytic activity of leucocytes decreased after yoghurt intake in the two groups. Exposure of monocytes and neutrophils ex vivo led to an increased cytokine response and free radical response, respectively. The normalisation of the various cytokine responses was more apparent in the group with positive breath test. In addition, the plasma levels of lipoplysaccharide binding protein and soluble CD14, lipoplysaccharide pattern recognition receptors and surrogate markers of lipoplysaccharide permeability were diminished by the end of the study. In conclusion, probiotic administration in the elderly normalises the response to endotoxin, and modulates activation markers in blood phagocytes, and therefore may help reduce low-grade chronic inflammatio

Use of Xpert MTB/RIF in Decentralized Public Health Settings and Its Effect on Pulmonary TB and DR-TB Case Finding in India

Background Xpert MTB/RIF, the first automated molecular test for tuberculosis, is transforming the diagnostic landscape in high-burden settings. This study assessed the impact of up-front Xpert MTB/RIF testing on detection of pulmonary tuberculosis (PTB) and rifampicin-resistant PTB (DR-TB) cases in India. Methods This demonstration study was implemented in 18 sub-district level TB programme units (TUs) in India in diverse geographic and demographic settings covering a population of 8.8 million. A baseline phase in 14 TUs captured programmatic baseline data, and an intervention phase in 18 TUs had Xpert MTB/RIF offered to all presumptive TB patients. We estimated changes in detection of TB and DR-TB, the former using binomial regression models to adjust for clustering and covariates. Results In the 14 study TUs, which participated in both phases, 10,675 and 70,556 presumptive TB patients were enrolled in the baseline and intervention phase, respectively, and 1,532 (14.4%) and 14,299 (20.3%) bacteriologically confirmed PTB cases were detected. The implementation of Xpert MTB/RIF was associated with increases in both notification rates of bacteriologically confirmed TB cases (adjusted incidence rate ratio [aIRR] 1.39; CI 1.18-1.64), and proportion of bacteriological confirmed TB cases among presumptive TB cases (adjusted risk ratio (aRR) 1.33; CI 1.6-1.52). Compared with the baseline strategy of selective drug-susceptibility testing only for PTB cases at high risk of drug-resistant TB, Xpert MTB/RIF implementation increased rifampicin resistant TB case detection by over fivefold. Among, 2765 rifampicin resistance cases detected, 1055 were retested with conventional drug susceptibility testing (DST). Positive predictive value (PPV) of rifampicin resistance detected by Xpert MTB/RIF was 94.7% (CI 91.3-98.1), in comparison to conventional DST. Conclusion Introduction of Xpert MTB/RIF as initial diagnostic test for TB in public health facilities significantly increased case-notification rates of all bacteriologically confirmed TB by 39% and rifampicin-resistant TB case notification by fivefold