Conditional stability of unstable viscous shock waves in compressible gas dynamics and MHD

Extending our previous work in the strictly parabolic case, we show that a linearly unstable Lax-type viscous shock solution of a general quasilinear hyperbolic--parabolic system of conservation laws possesses a translation-invariant center stable manifold within which it is nonlinearly orbitally stable with respect to small $L^1\cap H^3$ perturbations, converging time-asymptotically to a translate of the unperturbed wave. That is, for a shock with $p$ unstable eigenvalues, we establish conditional stability on a codimension-$p$ manifold of initial data, with sharp rates of decay in all $L^p$. For $p=0$, we recover the result of unconditional stability obtained by Mascia and Zumbrun. The main new difficulty in the hyperbolic--parabolic case is to construct an invariant manifold in the absence of parabolic smoothing.Comment: 32p

A multilevel study of social networks and collective reactions to organizational change

The purpose of this study is to examine the micro-level dynamics underlying macro-level associations between organizational change and its outcomes, focusing in particular on the role of networks in shaping individual reactions to change. Drawing upon multilevel research on situational and individual antecedents of change, we first argue that the magnitude of change at the unit level has a nonlinear effect on change recipients' tendency to resist change, which in turn influences their adaptive behaviors. We argue, further, that the attitudinal and structural composition of the professional networks in which change recipients are embedded account for differences in their adaptive behaviors. Finally, we argue that individual adaptivity coalesces at the collective, that is, unit level, and predicts the attainment of desired change goals. We find general support for our arguments in a longitudinal study using multi-source data on 170 physicians in 29 units of a large hospital that experienced a major restructuring intervention. Results confirm that multilevel mechanisms involving individuals and their social context fundamentally undergird macro-level outcomes of change. We discuss the theoretical and practical implications of bringing a network perspective to bear on issues of individual and collective reactions to organizational change

Vorticity dynamics past an inclined elliptical cylinder at different re numbers: from periodic to chaotic solutions

Vortex methods offer an alternative way for the numerical simulation of problems regarding incompressible flows. In the present paper, a Vortex Particle Method (VPM) is combined with a Boundary Element Method for the study of viscous incompressible planar flow around solid bodies. The method is based on the viscous splitting approach of Chorin [3] for the Navier-Stokes equations in vorticity-velocity formulation and consists of an advection step followed by a diffusion step. The evaluation of the advection velocity exploits the Helmholtz- Hodge Decomposition (HHD), while the no–slip condition is enforced by an indirect boundary integral equation. In order to deal with the problem of disordered spacial distribution of particles, caused by the advection along the Lagrangian trajectories [1], in the present method the particles are redistributed on a Regular Point distribution (RPD) during the diffusive step. The RPDs close to the solid bodies are generated through a packing algorithm developed by [4], thanks to which the use of a mesh generator is avoided. The developed Vortex Particle Method has been called Diffused Vortex Hydrodynamics (DVH) and it is implemented within a completely meshless framework, hence, neither advection nor diffusion requires topological connection of the computational nodes. The DVH has been extensively validated in the past years (see e.g. [8]) and is used in the present article to study the vorticity evolution past an inclined elliptical cylinder while increasing the Reynolds number from 200 up to 10,000 in a 2D framework. The flow evolution is characterized by a periodic behaviour for the lower Reynolds numbers which is gradually lost to give its the place to a chaotic behaviour

How Much Can We Trust Major Element Quantification in Bioapatite Investigation?

Bioapatite is probably the key factor in the unreplicated success of vertebrates. Chemical data on bioapatite composition can be achieved on a solid sample by using different analytical tools such as spectroscopic and spectrometric methods. As analytical outputs can be affected by the physical-chemical characteristics of the sample matrix, an internal standard is usually required to correct and validate the results. Bioapatite lattice can accommodate iso- and heterovalent substitutions during life or diagenesis varying its chemical composition through (geological) time. If on the one hand, this makes bioapatite a unique archive of physical and chemical information for both the living cycle and the events occurring after death, on the other, it excludes the identification of a sole internal standard. Here, we propose a method to measure major element concentration with specific care for P, Ca, Mg, Na, K, Si, Al, and Fe, which are the main substituent atoms in bioapatite, through homemade matrix-matched external calibration standards for laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). We tested the method on living and fossil shark teeth, critically comparing the results obtained using other analytical techniques and certified external standards. We demonstrated that matrix-matched calibration in LA-ICPMS is mandatory for obtaining a reliable chemical characterization even if factors such as matrix aggregation variability, diverse presence of volatile compounds, the fossilization footprint, and the instrumental variability can represent further variability parameters

CARBOTRAF: A decision Support system for reducing pollutant emissions by adaptive traffic management

Traffic congestion with frequent “stop & go” situations causes substantial pollutant emissions. Black carbon (BC) is a good indicator of combustion-related air pollution and results in negative health effects. Both BC and CO2 emissions are also known to contribute significantly to global warming. Current traffic control systems are designed to improve traffic flow and reduce congestion. The CARBOTRAF system combines real-time monitoring of traffic and air pollution with simulation models for emission and local air quality prediction in order to deliver on-line recommendations for alternative adaptive traffic management. The aim of introducing a CARBOTRAF system is to reduce BC and CO2 emissions and improve air quality by optimizing the traffic flows. The system is implemented and evaluated in two pilot cities, Graz and Glasgow. Model simulations link traffic states to emission and air quality levels. A chain of models combines micro-scale traffic simulations, traffic volumes, emission models and air quality simulations. This process is completed for several ITS scenarios and a range of traffic boundary conditions. The real-time DSS system uses all these model simulations to select optimal traffic and air quality scenarios. Traffic and BC concentrations are simultaneously monitored. In this paper the effects of ITS measures on air quality are analysed with a focus on BC

Pro/con clinical debate: Tracheostomy is ideal for withdrawal of mechanical ventilation in severe neurological impairment

Most clinical trials on the topic of extubation have involved patients outside the neurological intensive care unit. As a result, in this area clinicians are left with little evidence on which to base their decision making. Although tracheostomies are increasingly common procedures, they are not without complications and costs, and hence a decision to perform them should not be taken lightly. In this issue of Critical Care two groups debate the merits of tracheostomy before extubation in a patient with neurological impairment. What becomes very clear is the need for more high quality data for this common clinical problem

Existence and stability of viscoelastic shock profiles

We investigate existence and stability of viscoelastic shock profiles for a class of planar models including the incompressible shear case studied by Antman and Malek-Madani. We establish that the resulting equations fall into the class of symmetrizable hyperbolic--parabolic systems, hence spectral stability implies linearized and nonlinear stability with sharp rates of decay. The new contributions are treatment of the compressible case, formulation of a rigorous nonlinear stability theory, including verification of stability of small-amplitude Lax shocks, and the systematic incorporation in our investigations of numerical Evans function computations determining stability of large-amplitude and or nonclassical type shock profiles.Comment: 43 pages, 12 figure

Delayed open conversion after endovascular abdominal aortic aneurysm: Device-specific surgical approach

none7Objectives: Despite several advances in endoluminal salvage for failed endovascular abdominal aortic repair (EVAR), in our experience an increasing number of cases necessitate delayed open conversion (dOC). Methods: EVAR patients requiring delayed (>30 days) conversion were prospectively collected in a computerized database including demographics, details of aortoiliac anatomy, procedural and clinical success, and postoperative complications. Results: Between 2005 and 2011, 54 patients were treated for aortic stent-graft explantation. Indications included 34 type I and III endoleaks, 13 type II endoleaks with aneurysm growth, 4 cases of material failures, and 3 stent-graft infections. All fit-for-surgery patients with type I/III endoleak underwent directly dOC. Different surgical approaches were used depending on the type of stent-graft. Overall 30-day mortality was 1.9%. Overall morbidity was 31% mainly due to acute renal failure (13 cases). Mean hospitalization was 6 days (range, 5-27 days). Overall survival at mean follow-up of 19 months was 78%. Conclusions: In recent years, the use of EVAR has increased dramatically, including in young patients regardless of their fitness for open repair. dOC after endovascular abdominal aortic aneurysm seems to be a lifesaving procedure with satisfactory initial and mid-term results. © 2013 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.Marone, E.M.; Mascia, D.; Coppi, D.; Tshomba, Y.; Bertoglio, L.; Kahlberg, A.; Chiesa, R.Marone, ENRICO MARIA; Mascia, D.; Coppi, D.; Tshomba, Y.; Bertoglio, L.; Kahlberg, A.; Chiesa, R