40 research outputs found

    XPS–SIMS Surface Characterization of Aluminovanadate Oxide Catalyst Precursors Co-Precipitated at Different pH: Effect of Calcination

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    X-ray photoelectron spectroscopy and time-offlight secondary ion mass spectrometry were employed in a comparative study of the surface physical and chemical state of aluminovanadate oxide catalyst precursors (V-Al- O), which were precipitated in the range of pH from 5.5 to 10, after drying and calcination. Core-level photoelectron spectra, X-ray induced Auger and valence band spectra of the samples were measured so as to quantitatively evaluate the surface concentrations of the catalyst components. The binding energy shifts of the respective O 1s, V 2p and Al 2p lines were determined as a function of pH and analyzed in terms of the initial state effect related to the atomic charge and Madelung potential. The surface of the catalysts was composed of aluminum hydroxide/oxyhydroxide and of dispersed vanadium oxide species. Increasing pH was found to result in a monotonic variation of the elemental surface composition, modification of the valence band, progressive hydroxylation of the surface and increasing dispersion of vanadium oxide species. Increasing pH was also accompanied by an increase in the abundance of V4? species, specific surface area and reducibility. Calcination in air at 500 °C gave rise to surface segregation of vanadium, changes in the valence band and partial dehydroxylation. The structural transformations in vanadium oxide species and aluminium hydroxide support and their interaction were accompanied by an increasing abundance of V-O-Al bonds. The net result of the restructuring was a decrease in the specific surface area and reducibility of the calcined catalysts. The enhancement of the catalytic activity in propane oxidative dehydrogenation demonstrated by V-Al-O samples with increasing precipitation pH and after calcination was in good correlation with a growing population of the V4? states and increasing nucleophilicity of oxygen sites. © Springer Science+Business Media, LLC 2012.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    Effect of surgical delay on outcome in hip fracture patients: a retrospective multivariate analysis of 192 patients

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    Previous studies have not demonstrated consistent results on the effect of surgical delay on outcome. This study investigated the association between the delay to surgery and the development of postoperative complications, length of hospital stay (LOS) and one-year mortality. Patients that underwent surgery for a hip fracture in a two-year period were included in a retrospective study. Uni- and multivariate regression analysis was performed in 192 hip fracture patients. There was a trend towards fewer postoperative complications (P = 0.064; multivariate regression, MR) and shorter LOS (P = 0.088; MR) in patients with a delay of less than one day to surgery. No association between surgical delay and one-year mortality was found in the population as a whole (P = 0.632; univariate regression, UR). Delay to surgery beyond one day was associated with an increased risk of infectious complications (P = 0.004; MR). In ASA I and II class patients, operation beyond one day from admission was associated with an increased risk of one-year mortality (P = 0.03; MR) and more postoperative infectious complications (P = 0.02; MR). The trends towards fewer complications and shorter LOS suggest that early surgery (within one day from admission) is beneficial for hip fracture patients who are able to undergo an operation

    Analysis of surgical intervention populations using generic surgical process models.

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    International audiencePURPOSE: According to differences in patient characteristics, surgical performance, or used surgical technological resources, surgical interventions have high variability. No methods for the generation and comparison of statistical 'mean' surgical procedures are available. The convenience of these models is to provide increased evidence for clinical, technical, and administrative decision-making. METHODS: Based on several measurements of patient individual surgical treatments, we present a method of how to calculate a statistical 'mean' intervention model, called generic Surgical Process Model (gSPM), from a number of interventions. In a proof-of-concept study, we show how statistical 'mean' procedure courses can be computed and how differences between several of these models can be quantified. Patient individual surgical treatments of 102 cataract interventions from eye surgery were allocated to an ambulatory or inpatient sample, and the gSPMs for each of the samples were computed. Both treatment strategies are exemplary compared for the interventional phase Capsulorhexis. RESULTS: Statistical differences between the gSPMs of ambulatory and inpatient procedures of performance times for surgical activities and activity sequences were identified. Furthermore, the work flow that corresponds to the general recommended clinical treatment was recovered out of the individual Surgical Process Models. CONCLUSION: The computation of gSPMs is a new approach in medical engineering and medical informatics. It supports increased evidence, e.g. for the application of alternative surgical strategies, investments for surgical technology, optimization protocols, or surgical education. Furthermore, this may be applicable in more technical research fields, as well, such as the development of surgical workflow management systems for the operating room of the future
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