Energy-selective neutron imaging for materials science

Common neutron imaging techniques study the attenuation of a neutron beam penetrating a sample of interest. The recorded radiograph shows a contrast depending on traversed material and its thickness. Tomography allows separating both and obtaining 3D spatial information about the material distribution, solving problems in numerous fields ranging from virtually separating fossils from surrounding rock to water management in fuel cells. It is nowadays routinely performed at PSI¿s neutron imaging facilities. Energy-selective neutron imaging studies the wavelength-dependency of the cross-section by using a beam of reduced wavelength bandwidth instead of averaging out the cross-section over the incident beam spectrum. The range of observed contrasts/image information is than extended and can largely be understood in the context of the Bragg law. Different types of monochromator (mechanical neutron velocity selector, double crystal monochromator, filter materials) are characterized for use in neutron imaging. In polycrystalline samples, sharp Bragg edges are observed as coherent elastic scattering at the (hkl) plane can occur for all wavelengths up to 2dhkl, after which a sharp increase in transmission intensity is observed. Much like diffraction peaks, they contain information on e.g. crystal phase or projected strain. The absence of coherent elastic scattering past the last Bragg edge (Bragg cut-off) allows for quantification. In samples with few grains or even single crystals, all orientations w.r.t. the beam are no longer present and rather than Bragg edges, the cross section now exhibits distinct peaks, the ensemble of which holds information on the crystallite¿s phase, orientation and shape. A spatial variation in contrast appears across the sample, between those grains fulfilling the Bragg condition ¿ scattering and decreasing the transmitted beam intensity ¿ and those that do not. After initial qualitative assessments, recent advances on the quantitative grain orientation mapping are made based on time-of-flight measurements of high energy resolution recorded at the ISIS pulsed neutron source. But where do these scattered neutrons go to? A new set-up was developed to permit simultaneous transmission and diffractive neutron imaging. Capturing the neutrons diffracted by a grain also yields a projection of that grain, with the position on the detector indicative of the orientation. These projections can in turn be used for algebraic reconstruction, which yields a grain volume as well. After feasibility studies on an iron single crystal cube the recent push towards polycrystalline samples will is illustrated with a neutron diffraction contrast tomography (nDCT) of a coarse-grained aluminium strain sample

Structural Characterization of Iron Meteorites through Neutron Tomography

In this communication, we demonstrate the use of neutron tomography for the structural characterization of iron meteorites. These materials prevalently consist of metallic iron with variable nickel content. Their study and classification is traditionally based on chemical and structural analysis. The latter requires cutting, polishing and chemical etching of large slabs of the sample in order to determine the average width of the largest kamacite lamellae. Although this approach is useful to infer the genetical history of these meteorites, it is not applicable to small or precious samples. On the base of different attenuation coefficient of cold neutrons for nickel and iron, neutron tomography allows the reconstruction of the Ni-rich (taenite) and Ni-poor (kamacite) metallic phases. Therefore, the measure of the average width of the largest kamacite lamellae could be determined in a non-destructive way. Furthermore, the size, shape, and spatial correlation between kamacite and taenite crystals were obtained more efficiently and accurately than via metallographic investigation

Salt crystallization dynamics in building rocks: a 4D study using laboratory X-ray micro-CT

We employ laboratory X-ray micro-computed tomography (μCT) during climate-controlled salt weathering experiments to acquire data on the kinetics of drying and salt precipitation and the distribution of crystals within the pore space of Mšené sandstone. For that purpose, a custom-designed setup was built at the UGCT’s scanners of the Ghent University Centre for X-ray Tomography (UGCT) that allows to acquire 4D scans while drying. Samples were initially capillary saturated with a saturated NaCl-solution and subsequently dried at 20% RH and at 50% RH, at room temperature. These RH-values are representative for winter and summer conditions for the salt NaCl, which is not temperature sensitive. Different salt precipitation dynamics result in different drying kinetics at the two RH’s. These crystallization and transport dynamics can be directly linked as revealed by the 4D X-ray μCT datasets

Stereotypering, ideologie en overtuiging in digitale games: De rol van geobserveerd realisme en morele betrokkenheid

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Clinical presentation, causes and outcome of febrile episodes in a prospective cohort of HIV-infected patients

BACKGROUND: Fever was frequently caused by opportunistic conditions in HIV-patients in the early years of the epidemic. Little is known about diagnostic spectrum and outcome of febrile episodes in patients with good access to antiretroviral therapy. METHODS: We prospectively studied clinical presentation, diagnosis and outcome of febrile episodes in a contemporary cohort of HIV-patients with good access to antiretroviral therapy. Fever was defined as temperature 38.3 °C or higher, measured by a health care provider. RESULTS: We found 220 febrile episodes in 146 patients. In 25.9% of episodes the patient had a CD4 less than 200/mm³ and in 78.6% the patient was on antiretroviral therapy. There were multiple episodes in 44 patients. A diagnosis was established in 91.8%. Infection accounted for 82.3%, mainly respiratory tract infections, viral syndromes and abdominal infections. Malignancy, drug reactions and inflammatory conditions accounted together for less than 12% of episodes. Fifteen percent were attributed to opportunistic conditions. Episodes in patients with CD4 less than 200 were less likely to be caused by infection, but more likely to be caused by malignancy, drug reactions and opportunistic conditions. In 6.4% the patient died within six months after the onset of fever. Risk factors for death at six months in multivariable analysis were higher age and lower CD4. CONCLUSIONS: HIV-patients with access to antiretroviral therapy present with fever mostly due to conditions common in the general population. HIV-patients with low CD4 remain at risk for fever due to opportunistic conditions and death.peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=infd20status: publishe

Opposing expectations and suboptimal use of a local antibiotic hospital guideline: a qualitative study

Objectives The aim of this study was to determine the opinions and problems concerning the use of a local antibiotic hospital guideline in a 1900-bed tertiary-care, university teaching hospital. Methods A qualitative study using focus group discussions explored the usability and applicability of local antibiotic guidelines together with possible supportive measures. The sample included 22 physicians, deliberately divided between internal medicine (59.1%) and surgery (40.9%), and levels of experience (59.1% residents; 40.9% supervisors). Focus groups were conducted within one specific subgroup. Analysis was carried out using a framework analysis approach. Results General acceptance of local guidelines was high but clear differences were present between subgroups with different desires and requirements from guideline contents. Opposing views were present towards supportive measures, especially multidisciplinary collaboration. Guideline distribution and accessibility appeared to be confusing, resulting in delayed application. An important supplementary barrier was the need to collect the guideline personally. Supervisors in their role as opinion leaders were mentioned as highly influential towards residents' practice. Conclusions Locally developed hospital guidelines experience the same barriers as other guidelines. Within one hospital, prescribers have to be seen as a number of different target groups instead of a homogeneous population. For an optimal effect, interventions will have to consider these differences. Also, in order to improve local guideline use and antibiotic consumption, supervisors have to be aware of how their role as opinion leaders can influence residents. Lastly, active guideline distribution and promotion remains critical to ensure efficient guideline use. Future research should focus on how to adapt interventions to these different target groups.status: publishe

Consumption Patterns and In Vitro Resistance of Streptococcus pneumoniae to Fluoroquinolones▿

This article analyzes patterns of consumption of fluoroquinolones and documents the in vitro resistances of Streptococcus pneumoniae isolates to fluoroquinolones in the ambulatory care setting in Belgium over time. The volume of fluoroquinolone consumption has fallen consistently since 2003. Fluoroquinolones were used primarily for their registered indications (i.e., urinary tract infections and lower respiratory tract infections). The MIC distributions of moxifloxacin and levofloxacin in S. pneumoniae isolates remained stable during 2004 to 2009, and the level of resistance to moxifloxacin and levofloxacin was low (≤1%)

Outcome of patients requiring valve surgery during active infective endocarditis

BACKGROUND: The optimal timing of cardiac operations in patients with infective endocarditis continues to be debated. This observational study analyzed the profile and outcome of patients with active infective endocarditis undergoing operations. METHODS: Between June 2000 and June 2006, 95 surgically treated patients with definite infective endocarditis by the modified Duke criteria were included. RESULTS: Fifty-eight patients were operated on within the first 7 days after diagnosis of infective endocarditis and 37 at more than 7 days after diagnosis up to immediately after completion of antibiotic treatment. Staphylococci predominated and were significantly associated with embolism, abscess, and septic shock. The most frequent indication for operation was severe regurgitation with heart failure. The 6-month mortality was 15%. Early operation showed a trend towards increased mortality vs late operation. In univariable analysis, factors associated with 6-month mortality included staphylococci and septic shock. Multivariable analysis revealed that septic shock predicted 6-month mortality. Despite early operation in patients experiencing septic shock, 57% died. No patients without heart failure died after undergoing (early or late) procedures for severe regurgitation. CONCLUSIONS: The prognosis in surgically treated patients was determined by the occurrence of septic shock. The outcome in patients who underwent late operations was favorable compared with the early group. This difference was probably not due to the timing of the surgical intervention but to the severity of infective endocarditis. In patients with severe regurgitation without heart failure, early operation may offer benefit in length of hospitalization and prevention of development of new heart failure.status: publishe