Dislodgement of a Wiktor stent during intracoronary ultrasound examination

We report a case of stent dislodgement complicating adjuvant intracoronary ultrasound (ICUS) imaging that required emergency coronary bypass grafting. This probably very rare complication gains importance since ICUS is increasingly used to confirm adequate stent expansion and full coverage of the lesion.     

Development of a database of pipe fracture experiments

Over the last 35 years, researchers worldwide have conducted hundreds—if not thousands—of pipe fracture experiments. In the early years, researchers focused their attention on studying the failure pressure and crack propagation behavior of axially cracked pipe loaded by internal pressure. The earliest work was sponsored by the oil and gas industry and, as such, involved relatively thin-walled, low toughness carbon steel pipes. This work was eventually followed up by efforts in the USA and Germany on nuclear piping with axial cracks. In recent years, attention has turned to understanding the behavior of circumferentially cracked nuclear piping subjected to both pressure and bending loads. The loading histories for these experiments range from the relatively simple case of quasi-static, monotonic displacement control to the more complex cases of dynamic cyclic loading, and pipe system experiments. In this paper, two of the leaders in this research, i.e. Battelle in the USA and MPA Stuttgart in Germany, have collaborated to develop a database of pipe fracture experiments. The database includes data from other organizations as well as the data from Battelle and MPA. In addition, as part of this paper, an example of how the database was used to assess the failure pressure of axially cracked pipe is given.     

The effects of submergence on structural response in confined pools

In this paper the response of single and multi degree of submerged systems is investigated. The complete equations of motions including fluid coupling terms are developed for submerged bodies where the surrounding fluid is both moving in phase and out of phase with the support motion. The analysis considers both structural and fluid damping.Also included is an analysis of two degrees of freedom fluid coupling for submerged bodies completely enclosed within another body. In this case limiting conditions of the inner body hydrodynamic mass are examined, along with the frequency response characteristics of these systems.The paper developes a simplified forcing function approach for in phase fluid support motion systems. This method is applicable for both modal-spectral and time history dynamic analyses of any linear structure.The results of the analysis are expanded for structures with non-linear support configurations, i.e., (sliding or rocking bases) to again define a simplified analytical approach accounting for in phase fluid support motion.     

Graded-base Si/Si1-xGex/Si heterojunctionbipolar transistors grown by rapid thermal chemical vapor depositionwith near-ideal electrical characteristics

Graded-base and uniform-base Si/Si_1-xGe_x/Si heterojunction bipolar transistors with near-ideal base and collector currents have been fabricated by rapid thermal chemical vapor deposition. The temperature dependences of the collector currents are shown to obey a simple analytical model of an effective Gummel number. The model can be applied to devices which have arbitrary base profiles. The base currents are independent of base composition, and current gains in excess of 11000 have been observed at 133 K     

Measurements and trend analysis of O2, CO2 and delta13C of CO2 from the high altitude research station Junfgraujoch, Switzerland--a comparison with the observations from the remote site Puy de Dôme, France

Atmospheric O2 and CO2 flask measurements from the high altitude research station Jungfraujoch, Switzerland, and from the observatory at Puy de D?me, France, are presented. Additionally, the Jungfraujoch delta13C record of CO2 is discussed. The observations on flask samples collected at the Jungfraujoch station show, since 2003, an enhancement of the oxygen trend which amounts to about 45 per meg/year with a corresponding CO2 increase of around 2.4 ppm/year. This enhancement is comparable with that observed at the Puy de D?me station where oxygen, since mid 2002, has decreased with a rate of about 50 per meg/year whilst the CO2 increase was of around 1.7 ppm/year but exhibiting a higher variability. Several processes influence deltaO2/N2. However, these processes are marked with different oxidation ratios (O2:CO2) that can be used to distinguish them. The apparent slopes calculated from correlation plots between de-trended CO2 and deltaO2/N2 records as well as between corresponding trends are significantly larger than the observe ratios depending on processes within the ocean, it is to our understanding the only possibility to explain our observations. The stability of the deltaO2/N2 scale is critical in this regard, therefore, it is addressed here and we found no significant scale drift which would influence our trend calculations. In our view more important are criterions on the data selection before trend analysis.     

Selection of an appropriate time integration scheme for the discrete element method (DEM)

With increasing computer power simulation methods addressing discrete problems in a broad range of scientific fields become more and more available. The discrete element method is one of these discontinuous approaches used for modeling granular assemblies. Within this method the dynamics of a system of particles is modeled by tracking the motion of individual particles and their interaction with their adjacencies over time. For the interaction of particles, force models need to be specified. The resulting equations of motion are of coupled ordinary differential configuration, which are usually solved by explicit numerical schemes. In large-scale systems like avalanches, planetary rings, hoppers or chemical reactors vast numbers of particles need to be addressed. Therefore, integration schemes need to be accurate on the one hand, but also numerically efficient on the other hand. This numerical efficiency is characterized by the method's demand for memory and CPU-time. In this paper a number of mostly explicit numerical integration schemes are reviewed and applied to the benchmark problem of a particle impacting a fixed wall as investigated experimentally by Gorham and Kharaz [Gorham, D. A., & Kharaz, A. H. (2000). The measurement of particle rebound characteristics. Powder Technology, 112(3), 193–202]. The accurate modeling which includes the correct integration of the equations of motion is essential. In discrete simulation methods the accuracy of properties on the single particle level directly influence the global properties of the granular assembly like velocity distributions, porosities or flow rates, whereas their correct knowledge is often of key interest in engineering applications. The impact experiment is modeled with simple force displacement approaches which allow an analytical solution of the problem. Aspects discussed are the dependency of the step size on the accuracy of certain collision properties and the related computing time. The effect of a fixed time step is analyzed. Guidelines for the efficient selection of an integration scheme considering the additional computational cost by contact detection and force calculation are presented.     

Influence of Sediment Structure on Erosional Strength and Density of Kaolinite Sediment Beds

The role of sediment pore-water chemistry and the resulting particle structure in determining the erosional stability of settled cohesive sediment beds in rivers, lakes, and estuaries is examined. Kaolinite sediment is used as the surrogate sediment in this experimental investigation with the beds settled from concentrated suspensions. The bed stability with respect to erosion or resuspension is measured in a laboratory flume as a function of sediment pore-water chemistry. The chemical properties varied are sediment pH, ionic strength, and natural organic matter. The remolded bed sample is prepared from a sediment suspension having controlled chemical properties that is allowed to settle into the flume bed where its erosional strength and density are determined with depth in the sample. Different structures of settled beds are observed with changes in chemical parameters. Under low pH and low organic content conditions, the initial suspension before settling is flocculated. The resulting settled beds show strong stratification with respect to erosional strength but weak stratification of bulk density with depth. On the other hand, under high pH or high organic content conditions at low ionic strength, the initial suspension is dispersed. The resulting settled beds have lower erosional strength and weak stratification of erosional strength with depth but strong stratification of bulk density with depth. This research shows that the relationship between erosional strength and bulk density of a settled bed depends strongly on the structure of the sediment particle associations as determined by pore-water chemistry.     

Microstructural studies on nanocrystalline oxide dispersion strengthened austenitic (Fe–18Cr–8Ni–2W–0.25Y<Subscript>2</Subscript>O<Subscript>3</Subscript>) alloy synthesized by high energy ball milling and vacuum hot pressing

In the present work, nanostructured (Fe–18Cr–8Ni–2W) austenitic base and oxide dispersion strengthened (ODS) alloy powders were produced through mechanical alloying and these nano powders were consolidated by vacuum hot pressing. The results showed that initially bcc solid solution formed in both the alloys and this transformed to fcc with continued milling. The bcc solid solution formation and the subsequent transformation to fcc were significantly faster in the ODS alloys when compared to the base alloy. In the ODS alloy, a grain size of ~25 nm is achieved within 5 h of milling. Study of variation of microhardness of mechanically alloyed powder particles with grain size showed linear Hall–Petch kind of behavior. Following vacuum hot pressing of mechanically alloyed powders, nearly fully dense (>99% of theoretical density) compacts were obtained with a grain size of ~80 nm. The bulk hardness of base and ODS alloys are ~530 and ~900 HV, respectively. These are significantly higher than the values reported in the literature so far. The enhanced strength the ODS alloy is due to increased dislocation density and presence of fine dispersoids along with the nanocrystalline grains.     

A theoretical approach to the deposition and clearance of fibers with variable size in the human respiratory tract

In the study presented here, a mathematical approach for the deposition and clearance of rigid and chemically stable fibers in the human respiratory tract (HRT) is described in detail. For the simulation of fiber transport and deposition in lung airways an advanced concept of the aerodynamic diameter is applied to a stochastic lung model with individual particle trajectories computed according to a random walk algorithm. Interception of fibrous material at airway bifurcations is considered by implementation of correction factors obtained from previously published numerical approaches to fiber deposition in short bronchial sequences. Fiber clearance is simulated on the basis of a multicompartment model, within which separate clearance scenarios are assumed for the alveolar, bronchiolar, and bronchial lung region and evacuation of fibrous material commonly takes place via the airway and extrathoracic path to the gastrointestinal tract (GIT) or via the transepithelial path to the lymph nodes and blood vessels.Deposition of fibrous particles in the HRT is controlled by the fiber aspect ratio β in as much as particles with diameters <0.1 μm deposit less effectively with increasing β, while larger particles exhibit a positive correlation between their deposition efficiencies and β. A change from sitting to light-work breathing conditions causes only insignificant modifications of total fiber deposition in the HRT, whereas alveolar and, above all, tubular deposition of fibrous particles with a diameter ≥0.1 μm are affected remarkably. For these particles enhancement of the inhalative flow rate results in an increase of the extrathoracic and bronchial deposition fractions. Concerning the clearance of fibers from the HRT, 24-h retention is noticeably influenced by β and, not less important, by the preferential deposition sites of the simulated particles. The significance of β with respect to particle size may be regarded as similar to that determined for the deposition scenarios, while breathing conditions do not have a valuable effect on clearance.