Excess concentration,electron and hole currents in an epitaxial emitter

Algorithms for calculating the emitter hole and electron currents in the case of an n⁺n^? epitaxial emitter have been published by Yu [2] and Rofail et al. [3]. Both algorithms are restricted to a small ratio of hole to electron current whereas Yu's algorithm is further restricted by the assumption of a constant electric field in the epilayer.In the present paper an algorithm is presented in which both restrictions have been removed and which is valid from low through high injection. The assumption of quasineutrality in the epilayer, which is used in the present algorithm, is veryfied using Adlers criterium [4]. Calculation results are presented for a structure treated by Poorter [1] and a comparison is made with his results.     

Enteric virus infection risk from intrusion of sewage into a drinking water distribution network

Contaminants from the soil surrounding drinking water distribution systems are thought to not enter the drinking water when sufficient internal pressure is maintained. Pressure transients may cause short intervals of negative pressure, and the soil near drinking water pipes often contains fecal material due to the proximity of sewage lines, so that a pressure event may cause intrusion of pathogens. This paper presents a risk model for predicting intrusion and dilution of viruses and their transport to consumers. Random entry and dilution of virus was simulated by embedding the hydraulic model into a Monte Carlo simulation. Special attention was given to adjusting for the coincidence of virus presence and use of tap water, as independently occurring short-term events within the longer interval that the virus is predicted to travel in any branch of the distribution system. The probability that a consumer drinks water contaminated with virus is small, but when this happens the virus concentration tends to be high and the risk of infection may be considerable. The spatial distribution of infection risk is highly heterogeneous. The presence of a chlorine residual reduces the infection risk.     

Automated Folding of Origami Lattices: From Nanopatterned Sheets to Stiff Meta-Biomaterials

Folding nanopatterned flat sheets into complex 3D structures enables the fabrication of meta-biomaterials that combine a rationally designed 3D architecture with nanoscale surface features. Self-folding is an attractive approach for realizing such materials. However, self-folded lattices are generally too compliant as there is an inherent competition between ease-of-folding requirements and final load-bearing characteristics. Inspired by sheet metal forming, an alternative route is proposed for the fabrication of origamilattices. This ‘automated-folding’ approach allows for the introduction of sharp folds into thick metal sheets, thereby enhancing their stiffness. The first time realization of automatically folded origami lattices with bone-mimicking mechanical properties is demonstrated. The proposed approach is highly scalable given that the unit cells making up the meta-biomaterial can be arbitrarily large in number and small in dimensions. To demonstrate the scalability and versatility of the proposed approach, it is fabricated origamilattices with > 100 unit cells, lattices with unit cells as small as 1.25 mm, and auxetic lattices. The nanopatterned the surface of the sheets prior to folding. Protected by a thin coating layer, these nanoscale features remained intact during the folding process. It is found that the nanopatterned folded specimens exhibits significantly increased mineralization as compared to their non-patterned counterparts.     

Base current and dominant time constant of an n+n−pn+ transistor operating in the upward mode

An attempt will be made to put together all information on I²L base current available from literature. The aim is to get explicit relations for all base current components at low, medium and high injection. This requires knowledge of excess concentration patterns and stored excess charge as well as of the associated time constants. As a final result the upward current amplification β_u and the upward time constant τ_u are obtained. In the latter no depletion charges have been taken along and a quasi-static condition is assumed. Lateral base current effects have not been taken into account.     

Short- and long-term variations of norovirus concentrations in the Meuse river during a 2-year study period

Faecally impacted surface waters used for drinking water production may encompass risk for norovirus infections. To be able to assess a possible health risk, noroviruses should be quantified and fluctuations identified. In 2001, norovirus concentrations in the river Meuse displayed a seasonal distribution with high peaks during wintertime as determined by RT-PCR on serially diluted RNA. An intensified day-by-day sampling scheme in the winter of 2002/2003 revealed that the winter peak consisted of several peaks of varying duration and magnitude, possibly due to contamination events in the catchment. The highest estimated concentration was 1700 PCR-detectable units per litre (95% CI 250-8000), which if coinciding with failing treatment could lead to significant numbers in drinking water. Adaptive dynamic filtering was shown to adequately predict subsequent sample concentrations. If valid, such analyses could prove to be useful as early warning systems in risk management of water sources.     

Mixed plaques: statistical evidence how plaque assays may underestimate virus concentrations

Even at very low concentrations human pathogenic viruses may result in infection and possibly subsequent disease. Ideally, viruses are quantified by use of cell culture assays to determine their infectivity. Plaque assays are common tools for enumeration of viruses in inocula and this process is straightforward when a plaque results from the offspring of a single infectious virus particle. In the course of a study on the usefulness of sewage monitoring for surveillance of polio-virus transmission, sewage samples containing a mixture of two live polio vaccine strains (type 1 and type 3) were analyzed. The total poliovirus concentration in plaque forming units (pfu) was estimated by means of a monolayer plaque assay on L20B cells. Subsequent typing of virus directly by neutralisation of virus from excised plaques revealed the occurrence of plaques containing both type 1 and type 3 virus. This means that there must be plaques that originate from more than one initial infectious virus particle. As a consequence, the estimated virus concentration is incorrect. We present statistical methods that utilize these mixed plaque counts to estimate the concentrations of either virus type in our sewage samples. We can also calculate a correction factor for the error in virus concentration, which would result from equating a pfu to a single infectious particle. Since many quantitative methods in microbiology are based on colony counts, we conclude that such counts should be interpreted with caution, especially when data are used in quantitative microbial risk assessment to estimate the public health impact.