Extension of the Frozen Sonic Flow Method to mixtures of polyatomic gases

A contemporary issue of crucial importance for further developments in the field of thermal protection systems and related arc-jet-based testing activities calls for improvements in existing abilities to measure the centerline total enthalpy. Starting from the original assumptions of Vincenti and Kruger (1965) and through the elaboration of a mathematical framework relying on a specific modelling hierarchy of balance equations for the moles of different species involved, we show that the extension of the Frozen Sonic Flow Method (FSFM) to the case of polyatomic molecules can be made well posed. Dedicated experiments have been conducted using a re-entry simulation facility and varying the mass-averaged enthalpy in the range between 5 and 30 [MJ/kg]. In particular, three different gas mixtures have been considered (using Nitrogen as hot feeding gas and adding cold Oxygen, Carbon Dioxide and Methane, respectively). The enthalpy ratios calculated by the FSFM, found to depend on the gas mixture, have been compared with the values determined using two alternate techniques, namely, 1) the Heating Rate Method and 2) the Calorimetric Probe Method. Given the extremely complex experimental conditions considered (high-enthalpy, low density, supersonic reactive flows), the agreement between the theoretical and experimental results can be considered very satisfactory

High velocity infrared thermography and numerical trajectories of solid particles in compressible gas flow

The use of High Velocity Infrared Thermography as a valuable alternative to other existing techniques for the visualization and tracking of solid particles transported by a gas jet has been assessed by considering different situations in terms of problem characteristic numbers (jet Reynolds and Mach numbers and Particle Stokes and gravitational Froude numbers). Particles paths have also been calculated by means of a hybrid Eulerian-Lagrangian technique under the intent to cross-validate the two (experimental and numerical) approaches. The results indicate that such a strategy is robust and sufficiently flexible to be used in relatively wide regions of the space of parameters. Experiments have clearly demonstrated that thermography can properly capture particle dynamics with a level of detail comparable to that provided by simulations. Computations have proved to be valuable on their own by allowing the explorations of regions of the parameters space otherwise out of reach. Different tests have been conducted considering both isolated particles and "swarms". We show that the observed dynamics are induced by the delicate interplay of different effects, including inertial, gravitational and eventually "lift" contributions produced by a non-perfect horizontal orientation of the jet or other uncertainties (such as those due to a non mono-sized set of particles). (C) 2018 Elsevier B.V. All rights reserved

Impact of assumptions concerning containment failure on the risk from nuclear power plants

We describe the containment failure mode and release category assumptions used in the seismic risk study of the Zion nuclear power plant, which was performed by the Seismic Safety Margins Research Program (SSMRP). We then, for the dominant accident sequences, reassign containment failure modes and release categories based upon current thinking. We recalculate the seismic risk from the Zion facility using the new assumptions. Lastly, we discuss the impact of the new assumptions on the results and the relevance of the assumptions to value/impact analyses. 5 references, 5 tables

On the highly unsteady dynamics of multiple thermal buoyant jets in cross flows

Thermal plumes of small scale generated by spatially separated heat sources can form, like atoms in a chemical compound, complex structures of different kind and with distinct behaviors. The situation becomes even more complex if plumes can interact with imposed vertical shear (a horizontal wind). In this analysis a ‘minimal framework’ based on the application of a filtering process to the governing balance equations for mass, momentum and energy (falling under the general heading of ‘Large Eddy Simulation’ approach), is used together with Direct Numerical Simulation to inquiry about the relative importance of buoyancy and vertical shear effects in determining the patterning scenario when highly unsteady dynamics are established (turbulent flow). Emerging patterns range from the flow dominated by a static rising jet produced by the aggregation of plumes, which are pushed by horizontal leftwards and rightwards winds towards the center of the physical domain, to convective systems with disconnected thermal pillars of smaller scale, which travel in the same direction of the prevailing wind. The classical sheltering effect, which for flows that are steady ‘in mean’ simply consists of an increased deflection of the leading buoyant jet with respect to the trailing ones, is taken over by a variety of new phenomena, including (but not limited to) fast plume removal-rebirth mechanisms (with local increase in the velocity frequency and shrinkage in the related amplitude), ‘bubble’ formation-rupture and local departure of the frequency spectrum from the Kolmogorov similarity law

Microstructural modification of Sn–Bi and Sn–Bi–Al immiscible alloys by shearing

Sn–20 wt-%Bi and immiscible Sn–20 wt-%Bi–1 wt-%Al alloys were used to understand the effect of high-intensity shearing on microstructural refinement. Novel ACME (Axial Centrifugal Metal Expeller) shearing device, based on axial compressor and rotor–stator mechanism to generate high shear rate and intense turbulence, was used to condition the melts prior to solidification. Microstructure in the Sn–Bi alloy deviated from dendritic grains with coarse eutectic pockets under conventional solidification to compact grains with well-dispersed eutectic under semisolid-state shearing. Decreasing the shearing temperature and increasing shearing time increased the globularity of grains. Following shearing, remnant liquid solidified into fine grain structure. In the immiscible Sn–Bi–Al alloy, shearing produced uniform dispersion of refined Al-rich particles in Sn-rich matrix as opposed to severe segregation under conventional solidification. The primary effect of shearing appears to originate from the thermo-solutal homogenisation of the melt and its effect on interface stability during solidification

Scientific investigation plan for NNWSI WBS element 1.2.2.5.L: NNWSI waste package performance assessment: Revision 1

Waste package performance assessment contains three broad categories of activities. These activities are: (1) development of a hydrothermal flow and transport model to test concepts to be used in establishing boundary conditions for performance calculations, and to interface EBS release calculations with total system performance calculations; (2) development of a waste package systems model to provide integrated deterministic assessments of performance and analyses of waste package designs; and (3) development of an uncertainty methodology for combination with the system model to perform probabilistic reliability and performance analysis waste package designs. The first category contains activities that aid in determining the scope of a separate, simplified set of hydrologic calculations needed to characterize the waste package environment for performance assessment calculations. The last two activity categories are directly concerned with waste package performance calculations. A rationale for each activity under these groups is presented. All of the activities of performance assessment are either code development or analyses of waste package problems

The JEREMI-project on thermocapillary convection in liquid bridges. Part B : Overview on impact of co-axial gas flow

Pure surface-tension-driven flow is a unique type of flow that can be controlled through external manipulation of thermal and/or mechanical boundary conditions at the free liquid surface where the entire driving force for the convection is generated. This unique feature has been exploited in recent studies for the active control of the flow instability. The use of forced coaxial gas streams has been proposed as a way to stabilize the Marangoni convection in liquid bridges in the planned space experiment JEREMI (Japanese and European Research Experiment on Marangoni Instabilities). It is aimed at understanding the mechanism of the instability and the role of the surface heat transfer and surface shear stresses. This overview presents corresponding preparatory experimental and numerical studies

High rate of colistin resistance among patients with carbapenem-resistant Klebsiella pneumoniae infection accounts for an excess of mortality

AbstractCarbapenem-resistant Klebsiella pneumoniae (CR-KP) is becoming a common cause of healthcare-associated infection in Italy, with high morbidity and mortality. Prevalent CR-KP clones and resistance mechanisms vary between regions and over time. Therapeutic approaches and their impact on mortality have to be investigated. We performed a prospective study of patients with CR-KP isolation, hospitalized in nine hospitals of Rome, Italy, from December 2010 to May 2011, to describe the molecular epidemiology, antibiotic treatment and risk factors for mortality. Overall, 97 patients (60% male, median age 69 years) were enrolled. Strains producing blaKPC-3 were identified in 89 patients, blaVIM in three patients and blaCTX-M-15 plus porin defects in the remaining five patients. Inter-hospital spread of two major clones, ST512 and ST258, was found. Overall, 36.1% and 20.4% of strains were also resistant to colistin and tigecycline, respectively. Infection was diagnosed in 91 patients who received appropriate antibiotic treatment, combination therapy and removal of the infectious source in 73.6%, 59.3% and 28.5% of cases, respectively. Overall, 23 different antibiotic regimens were prescribed. In-hospital mortality was 25.8%. Multivariate analysis adjusted for appropriate treatment, combination therapy and infectious-source removal, showed that Charlson comorbidity score, intensive-care unit onset of infection, bacteraemia and infection due to a colistin-resistant CR-KP strain were independent risk factors for mortality. The spread of clones producing K. pneumoniae carbapenemases, mainly ST258, is currently the major cause of CR-KP infection in central Italy. We observed a high rate of resistance to colistin that is independently associated with worse outcome

Adipose Tissue, Bile Acids, and Gut Microbiome Species Associated With Gallstones After Bariatric Surgery

Several risk factors are associated with gallstone disease after bariatric surgery, but the underlying pathophysiological mechanisms of gallstone formation are unclear. We hypothesize that gallstone formation after bariatric surgery is induced by different pathways compared with gallstone formation in the general population, since postoperative formation occurs rapidly in patients who did not develop gallstones in preceding years. To identify both pathophysiological and potentially protective mechanisms against postoperative gallstone formation, we compared the preoperative fasting metabolome, fecal microbiome, and liver and adipose tissue transcriptome obtained before or during bariatric surgery of obese patients with and without postoperative gallstones. In total, 88 patients were selected from the BARIA longitudinal cohort study. Within this group, 32 patients had postoperative gallstones within 2 years. Gut microbiota metagenomic analyses showed group differences in abundance of 41 bacterial species, particularly abundance of Lactobacillaceae and Enterobacteriaceae in patients without gallstones. Subcutaneous adipose tissue transcriptomic analyses revealed four genes that were suppressed in gallstone patients compared with patients without gallstones. These baseline gene expression and gut microbiota composition differences might relate to protective mechanisms against gallstone formation after bariatric surgery. Moreover, baseline fasting blood samples of patients with postoperative gallstones showed increased levels of several bile acids. Overall, we revealed different genes and bacteria associated with gallstones than those previously reported in the general population, supporting the hypothesis that gallstone formation after bariatric surgery follows a different trajectory. Further research is necessary to confirm the involvement of the bile acids, adipose tissue activity, and microbial species observed here