Failure of a geomembrane lined embankment dam – Case study

The right wing embankment of the headrace channel of a hydropower plant, failed adjacent to the concrete intake structure. The failure also caused damages of the penstocks and flooding of the powerhouse.     

Low temperature aqueous precipitation of needle-like nanophase hydroxyapatite

The use of tissue engineered biodegradable porous scaffolds has become an important focus of the biomedical research field. The precursor materials used to form these structures play a vital role in their overall performance thus making the study and synthesis of these selected materials imperative. The authors present a comparison and characterisation of hydroxyapatite (HA), a popular calcium phosphate (CaP) biomaterial, synthesised by an aqueous precipitation (AP) method. The influence of various reaction conditions on the phase, crystallinity, particle size as well as morphology, molecular structure, potential in-vivo bioactivity and cell viability were assessed by XRD, SEM and TEM, FTIR, a simulated body fluid (SBF) test and a live/dead assay using MC3T3 osteoblast precursor cells, respectively. Naturally carbonated nanoparticles of HA with typically needle-like morphology were synthesised by the reported AP method. Initial pH was found to influence the crystallisation process and determine the CaP phase formed as well as the resultant particle and crystallite sizes. A marked change in particle morphology was also observed above pH 9. The use of toluene as a replacement solvent for water up to 60 % was found to reduce the crystallinity of as-synthesised HA. This has marked influence on the effect of ethanolamine (5 wt%), which was found to improve HA crystallinity. SEM and EDS were used to confirm the growth of carbonated apatite on the surface of HA pellets immersed in SBF for up to 28 days. Cell culture results revealed viable cells on all samples where pH was controlled and maintained at 10–11 during precipitation, including those that used ethanolamine and toluene in preparation. When the initial alkali pH was not maintained non-viable cells were observed on HA substrates.     

Mycobacterium behavior in wastewater treatment plant, a bacterial model distinct from Escherichia coli and Enterococci

Mycobacteria are waterborne emerging pathogens causing infections in human. Mycobacteria have been previously isolated from wastewater and sludge, but their densities were not estimated due to cultural biases. In order to evaluate the impact of wastewater treatment processes on mycobacteria removal, we used a real time PCR method. First we compared six DNA extraction methods and second we used the more efficient DNA extraction procedure (i.e., enzymatic lysis combined with hexadecyltrimethylammonium bromide-NaCl procedure) in order to quantify Mycobacterium. With the aim to identify parameters that could serve as indicator of mycobacterial behavior, mycobacterial densities were measured in parallel to those of Escherichia coli and enterococci, and to concentrations of chemical parameters usually monitored in wastewater. Mycobacterium reached 5.5 × 10? ± 3.9 × 10? copies/L in the influent, but was not detected in the effluent after decantation and biofiltration. Most mycobacteria (98.6 ± 2.7%, i.e. 2.4 ± 0.7 log??) were removed by the physical-chemical decantation, and the remaining mycobacteria were removed by biofiltration. In contrast, enterococci and E. coli were lightly removed by decantation step and mainly removed by biofiltration. Our results showed that Mycobacterium corresponds to a hydrophobic behavior linked to insoluble compound removal, whereas enterococci and E. coli refer to hydrophilic behaviors linked to soluble compound removals.     

Role of incubation conditions and protein fraction on the antimicrobial activity of egg white against Salmonella Enteritidis and Escherichia coli

The mechanism of egg white antimicrobial activity involves specific molecules and environmental factors. However, it is difficult to compare the data from the literature because of the use of various bacterial strains and incubation conditions. The aim of our study was to determine the effect of temperature, pH, inoculum size, and egg white protein concentration on egg white antimicrobial activity and to investigate the putative interactions among these factors by conducting a complete factorial design analysis. The behavior of Salmonella Enteritidis and Escherichia coli was studied after precultivation in tryptic soy broth and Luria-Bertani broth, respectively, using three different egg white protein concentrations (0, 10, and 100%), five temperatures (37, 40, 42, 45, and 48°C), two pHs (7.8 and 9.3), and six inoculum levels (3 to 8 log CFU/ml). The essential role of temperature was identified. An inverse relationship was observed between bacterial growth and an increase in temperature. The role of egg white proteins was clearly demonstrated. In the absence of egg white proteins, bacterial growth occurred under most incubation conditions, whereas the presence of 10 and 100% protein produced bacteriostatic or bactericidal effects. The interaction between temperature and protein concentration was significant. At the highest tested temperatures, proteins were less involved in the bactericidal effect. Bacterial destruction was higher at pH 9.3 than at pH 7.8. Under our experimental conditions, Salmonella Enteritidis was more resistant to inactivation by egg white than was E. coli.     

Tandem mass spectrometry for the direct assay of lysosomal enzymes in dried blood spots: application to screening newborns for mucopolysaccharidosis II (Hunter Syndrome)

We have developed a tandem mass spectrometry based assay of iduronate-2-sulfatase (IdS) activity for the neonatal detection of mucopolysaccharidosis II (MPS-II, Hunter Syndrome). The assay uses a newly designed synthetic substrate (IdS-S) consisting of α-L-iduronate-2-sulfate, which is glycosidically conjugated to a coumarin and a linker containing a tert-butyloxycarbamido group. A short synthesis of the substrate has been developed that has the potential of being scaled to multigram quantities. Sulfate hydrolysis of IdS-S by IdS found within a 3 mm dried blood spot specifically produces a nonsulfated product (IdS-P) which is detected by electrospray tandem mass spectrometry and quantified using a deuterium-labeled internal standard, both carried out in positive ion mode. Analysis of DBS from 75 random human newborns showed IdS activities in the range of 4.8-16.2 (mean 9.1) μmol/(h L of blood), which were clearly distinguished from the activities measured for 14 MPS-II patients at 0.17-0.52 (mean 0.29) μmol/(h L of blood). The assay shows low blank activity, 0.15 ± 0.03 μmol/(h L of blood). The within-assay coefficient of variation (CV) was 3.1% while the interassay CV was 15%.     

Spectroscopic null ellipsometer using a variable retarder

We describe a polarizer-compensator-sample-analyzer (PCSA) null ellipsometer in which a variable retarder is used as the compensator and either the polarizer or the analyzer is held at a fixed azimuthal angle. Ellipsometric angles ψ and Δ are determined directly from the azimuth of the rotating component and the compensator delay, respectively. A Soleil-Babinet compensator with quartz plates is used as the variable delay element and the delay at any wavelength is calculated from the independently measured delay at 632.8 nm and a knowledge of the dispersion of quartz. The thicknesses of thin silicon dioxide films on a silicon wafer were determined both spectroscopically and at a single wavelength and show excellent agreement with those determined using a traditional single wavelength PCSA null ellipsometer.     

Retention of aroma compounds in food matrices of similar rheological behaviour and different compositions

Two matrices with a similar rheological behaviour but with a different composition have been developed: one containing carbohydrates (d-glucose, pectin and starch) and in the second one, called complex matrix, a lipid (triolein) was added. The release of six aroma compounds is quantified by using the measurements of partition coefficients at thermodynamic equilibrium. The role of lipid (triolein) on the retention of all the aroma compounds was pointed out. The effect of carbohydrates was more complex: in comparison with water, ethyl hexanoate and trans-2-hexenal were more retained whereas diacetyl, 2-pentanone and cis-3-hexenol were “repulsed” from the matrix. The kinetic study of the release from these matrices had shown a decrease of the initial rate of release by reference with water. From carbohydrates matrix, the decrease of the release for three compounds (ethyl acetate, ethyl hexanoate, 2-pentanone) seemed to arise from the variation of diffusion and/or retention by carbohydrates. For the three other aroma compounds (diacetyl, cis-3-hexenol and trans-2-hexenal) no variation of the initial rate was registered. The comparison of the release rates from carbohydrate and complex matrices indicated the role of lipids and the comparison of the release rates from water and complex matrix showed the combined effects of texture and lipids. The decrease of initial release rate was more important in presence of lipids than in presence of carbohydrates. The most important decrease was observed with the most hydrophobic compound.     

Study of the Transit-Time Limitations of the Impulse Response in Mid-Wave Infrared HgCdTe Avalanche Photodiodes

The impulse response in frontside-illuminated mid-wave infrared HgCdTe electron avalanche photodiodes (APDs) has been measured with localized photoexcitation at varying positions in the depletion layer. Gain measurements have shown an exponential gain, with a maximum value of M = 5000 for the diffusion current at a reverse bias of V _b = 12 V. When the light was injected in the depletion layer, the gain was reduced as the injection approached the N+ edge of the junction. The impulse response was limited by the diode series resistance–capacitance product, RC, due to the large capacitance of the diode metallization. Hence, the fall time is given by the RC constant, estimated as RC = 270 ps, and the rise time is due to the charging of the diode capacitance via the transit and multiplication of carriers in the depletion layer. The latter varies between t _10–90 = 20 ps (at intermediate gains M < 500) and t _10–90 = 70 ps (at M = 3500). The corresponding RC-limited bandwidth is BW = 600 MHz, which yields a new absolute record in gain–bandwidth product of GBW = 2.1 THz. The increase in rise time at high gains indicates the existence of a limit in the transit-time-limited gain–bandwidth product, GBW = 19 THz. The impulse response was modeled using a one-dimensional deterministic model, which allowed a quantitative analysis of the data in terms of the average velocity of electrons and holes. The fitting of the data yielded a saturation of the electron and hole velocity of v _e = 2.3 × 10⁷ cm/s and v _h = 1.0 × 10⁷ cm/s at electric fields E > 1.5 kV/cm. The increase in rise time at high bias is consistent with the results of Monte Carlo simulations and can be partly explained by a reduction of the electron saturation velocity due to frequent impact ionization. Finally, the model was used to predict the bandwidth in diodes with shorter RC = 5 ps, giving BW = 16 GHz and BW = 21 GHz for x _j = 4 μm and x _j = 2 μm, respectively, for a gain of M = 100.     

Modeling of a continuous rotary reactor for carbon nanotube synthesis by catalytic chemical vapor deposition

The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric, hydrodynamic, physical and physicochemical factors governing the process were analyzed in order to establish the reactor equations. While the study of the hydrodynamic factor suggests a co‐current plug‐flow approximation, the physical factor mainly deals with the phenomena of transport and the transfer of mass, which can be neglected. Concerning the physicochemical factor, the modeling is based on knowledge of the expression of the initial reaction rate, and takes into account catalytic deactivation as a function of time, according to a sigmoid decreasing law. The reactor modeling allows obtaining the evolution of partial pressure, carbon nanotube production and catalytic deactivation along the reactor for given initial operating conditions. The comparison between experimental and calculated production highlights a very good fit of data. © 2009 American Institute of Chemical Engineers AIChE J, 2009