Off-site toxic consequence assessment: A simplified modeling procedure and case study

An assessment of off-site exposure from spills/releases of toxic chemicals can be conducted by compiling site-specific operational, geographic, demographic, and meteorological data and by using screening-level public-domain modeling tools (e.g., RMP*Comp, ALOHA and DEGADIS). In general, the analysis is confined to the following: event-based simulations (allow for the use of known, constant, atmospheric conditions), known receptor distances (on the order of miles or less), short time scale for the distances considered (order of 10's of minutes or less), gently sloping rough terrain, dense and neutrally buoyant gas dispersion, known chemical inventory and infrastructure (used to define source-term), and known toxic endpoint (defines significance). While screening-level models are relatively simple to use, care must be taken to ensure that the results are meaningful. This approach allows one to assess risk from catastrophic release (e.g., via terrorism), or plausible release scenarios (related to standard operating procedures and industry standards). In addition, given receptor distance and toxic endpoint, the model can be used to predict the critical spill volume to realize significant off-site risk. This information can then be used to assess site storage and operation parameters and to determine the most economical and effective risk reduction measures to be applied.     

Numerical simulation of the motion of red blood cells and vesicles in microfluidic flows

We study the mathematical modeling and numerical simulation of the motion of red blood cells (RBC) and vesicles subject to an external incompressible flow in a microchannel. RBC and vesicles are viscoelastic bodies consisting of a deformable elastic membrane enclosing an incompressible fluid. We provide an extension of the finite element immersed boundary method by Boffi and Gastaldi (Comput Struct 81:491–501, 2003), Boffi et al. (Math Mod Meth Appl Sci 17:1479–1505, 2007), Boffi et al. (Comput Struct 85:775–783, 2007) based on a model for the membrane that additionally accounts for bending energy and also consider inflow/outflow conditions for the external fluid flow. The stability analysis requires both the approximation of the membrane by cubic splines (instead of linear splines without bending energy) and an upper bound on the inflow velocity. In the fully discrete case, the resulting CFL-type condition on the time step size is also more restrictive. We perform numerical simulations for various scenarios including the tank treading motion of vesicles in microchannels, the behavior of ‘healthy’ and ‘sick’ RBC which differ by their stiffness, and the motion of RBC through thin capillaries. The simulation results are in very good agreement with experimentally available data.     

An efficient, repetitive nanosecond pulsed power generator with ten synchronized spark gap switches

This paper describes an efficient, repetitive nanosecond pulsed power generator using a Transmission-Line-Transformer (TLT) based multiple-switch technology. Within this setup, a 10-stage TLT and ten high-pressure spark-gap switches are adopted. At the input side, ten spark-gap switches are interconnected in series via the TLT, so that all the spark-gap switches can be synchronized automatically. At the output side, all the stages of the TLT are connected in parallel, thus a low output impedance (5 ?) is obtained, and a large output current is realized by adding the currents through all the switches. Experimental results show that 10 spark-gap switches can be synchronized within about 10 ns. The system has been successfully demonstrated at repetition rates up to 300 pps (Pulses Per Second). Pulses with a rise-time of about 11 ns, a pulse width of about 55 ns, an energy of 9-24 J per pulse, a peak power of 300-810 MW, a peak voltage of 40-77 kV, and a peak current of 6-11 kA have been achieved with an energy conversion efficiency of 93-98%.     

Maximum delay computation for interdomain path selection

One important problem when deploying interdomain path selection is advertising metrics that hold for a long period of time. In this paper we propose a method to aid interdomain path selection mechanisms in that sense. We present a means of computing a bound on the end‐to‐end delay of traversing a domain considering that the traffic varies within a given uncertainty set. This provides a robust and a verifiable quality of service value for traversing the autonomous system (AS), without revealing confidential information. Consequently, the bound can be safely conceived as a metric to be announced by each AS in the process of interdomain path selection. We show how the maximum delay value is obtained for an interdomain bandwidth demand and we propose an exact method and a numerical approximation method for computing it, neither of which rely on a complex monitoring infrastructure. Simulations with real data that illustrate the problem and validate our results are also presented. Copyright © 2011 John Wiley & Sons, Ltd.     

Biomarker versus environmental factors: seasonal variations and modelling multixenobiotic defence (MXD) transport activity in transplanted zebra mussels

The occurrence of biomarker temporal variations linked to environmental factors makes it difficult to distinguish the specific effect of pollution. The present work aims to investigate the seasonal variations of the transport activity of the multixenobiotic defence (MXD), which is used as a biological tool for the monitoring of pollution in aquatic ecosystems. The MXD transport activity was monitored monthly from August 2001 to October 2002 in zebra mussels (Dreissena polymorpha) transplanted to three sites in the Moselle River. The 'efflux method' was used to evaluate functional activity of MXD by assessing rhodamine B efflux with or without an inhibitor (verapamil). Environmental parameters were provided by a French regulatory agency (Water Agency) that monitors river water quality. The results of a principal components analysis describe the seasonal cycle of water characteristics and demonstrate that MXD activity is subjected to significant temporal variations. These data were described with a generalised linear model that enables it to link MXD variability to the seasonal variations of environmental parameters such as temperature or levels of organic contamination. This work proposes a modelling approach and highlights that the occurrence of seasonal variations in MXD response has to be taken into account in the interpretation of in situ monitoring studies.     

Cationic photopolymerization of epoxides containing carbon black nanoparticles

The active centers responsible for cationic photopolymerizations are essentially non-terminating, and continue to propagate after the illumination is ceased. In this contribution, the mobility of the long-lived cationic active centers is investigated for the cure of epoxides containing carbon black nanoparticles. Concentration profiles for the cationic active centers produced during illumination were coupled with an analysis of the active center reactive diffusion during the post-illumination period, revealing that migration of the active centers leads to cure beyond the illuminated depth. A kinetic analysis yielded predicted cure times for coatings of varying thickness and carbon black loading, showing good agreement with experimental results obtained for photopolymerizations of cycloaliphatic diepoxide coatings containing a monodisperse carbon black with mean hydrodynamic radius of 29.2 nm. These results indicate that the long lifetimes and reactive diffusion of cationic active centers may be used for effective curing of coatings containing carbon black nanoparticles. This comprehensive approach could be applied to other opaque nanocomposite systems.     

Studies toward new anti-cancer strategies based on alpha-mannosidase inhibition

Changes in the glycosylation pattern of cellular glycoproteins constitute a hallmark in human cancer and influence tumor progression, suggesting that inhibitors of selected glycosidases may control cancer progression. Following the studies on swainsonine, a natural inhibitor of Golgi alpha-mannosidase II, which highlighted the inhibition of cellular mannosidases as a potential innovative approach for the treatment of cancer, several dihydroxylated pyrrolidines and analogues were developed as new potent inhibitors of alpha-mannosidases II able to induce antiproliferative effects in human cancer cells.     

Alternative choices for voltage-tunable dielectrics

Abstract

Barium strontium titanate (BST) has been exhaustively studied as a voltage tunable dielectric to the apparent exclusion of other materials. Since undoped BST shows dielectric losses which are higher than desirable, it is reasonable to seek alternative materials with characteristically lower losses. In this paper alternative dielectrics are introduced and compared with BST for their use in frequency-agile applications. Data are presented (capacitance and loss tangent as a function of field) for lead magnesium niobate and cadmium niobate materials which suggest that these dielectrics can be used to provide satisfactory levels of voltage tunability whilst at the same time exhibiting lower dielectric losses than BST.