CROSS - a Program for Determination of Coefficients of Subgrade Reaction

Soil Mechanics and Foundation Engineering -     

Bioaccumulation potential of polycyclic aromatic hydrocarbons in Daphnia pulex

The bioaccumulation potentials by aquatic biota from aqueous solution were determined for seven polycyclic aromatic hydrocarbons (PAH). The PAH were tested usingDaphnia pulex and consisted of the following compounds: naphthalene, anthracene, phenanthrene, pyrene, 9-methylanthracene, benz(a)anthracene and perylene. Bioaccumulation kinetics were described as a first order approach to equilibrium in a two-compartment model (water and Daphnia), using a two-stage technique to estimate uptake and elimination rates, while accounting for decreasing aqueous concentrations. Estimates of equilibrium concentration factors were obtained by two methods: (1) evaluating the kinetic model as t tends to infinity and (2) direct measurement of concentration factor at t =24 h.Estimations of equilibrium concentration factors obtained by the two methods were in good agreement, and increased dramatically with increasing molecular weight within the series of compounds. The calculated n-octanol-water partition coefficient was shown to be a good predictor of bioaccumulation potential of PAH in Daphnia. PAH were concentrated from a high of about 10,000-fold for benz(a)anthracene to a low of about 100-fold for naphthalene.     

Evaluation of the fern Azolla for growth, nitrogen and phosphorus removal from wastewater

Water fern (Azolla filiculoides Lam.) has been assessed for nitrogen and phosphorus removal in outdoor experiments comparing sewage water (S) from an experimental aquaculture plant, well water (W) and mineral growth medium Hoagland (H). The experiments were undertaken during the spring and the summer. The yield of fern biomass and nitrogenase activity was higher in H than in W and S waters. The enzyme activity had a decreasing trend with significant differences (p < 0.05) in the three waters. Peroxidase (POD) activity in April decreased with significative differences in W and S waters (p < 0.05). The electrical conductivity and the concentrations of NO3- in the three waters decreased significantly (p < 0.05). The highest removal of nitrate from the media was obtained in July. In S water, NO2- concentration decreased, while it increased in W water. PO(4)3- concentration was very low in W and S waters and decreased in H medium. The results obtained confirm the ability of the fern to grow in sewage water.     

A Power-Supply Unit for Pulsed Lasers without a Storage Capacitor

A power-supply unit for pulsed lasers that are pumped by low- and medium-power flashlamps with long pump pulses that does not require a capacitive storage unit is described. The pump-pulse duration is limited by the radiation and thermal stability of the active elements and pump lamps. A functional diagram of the power-supply unit and a circuit diagram of its power system are presented. The basic parameters and elements of this unit, as well as the results of using a laser with the described power supply in experiments, are presented.     

Producing Polydicyclopentadiene from Lower-Grade Dicyclopentadiene

Russian Engineering Research - Polymer samples based on polydicyclopentadiene produced from Russian dicyclopentadiene are investigated by thermogravimetric analysis and differential scanning...     

Thermal Properties of (Zr,TM)B2 Solid Solutions with TM = Hf,Nb, W,Ti, and Y

The thermal properties were investigated for hot‐pressed zirconium diboride—transition‐metal boride solid solutions. The transition‐metal additives included hafnium, niobium, tungsten, titanium, and yttrium. The nominal additions were equivalent to 3 at.% of each metal with respect to zirconium. Powders were hot‐pressed to nearly full density at 2150°C using 0.5 wt% carbon as a sintering aid. Thermal diffusivity was measured using the laser flash method. Thermal conductivity was calculated from the thermal diffusivity results using temperature‐dependent values for density and heat capacity. At 25°C, the thermal conductivity ranged from 88 to 34 W·(m·K)^?1 for specimens with various additives. Electrical resistivity measurements and the Wiedemann–Franz law were used to calculate the electron contribution of the thermal conductivity and revealed that thermal conductivity was dominated by the electron contribution. The decrease in thermal conductivity correlated with a decrease in unit cell volume, indicating that lattice strain may affect both phonon and electron transport in ZrB₂.     

Carbon nanotubes/amorphous carbon composites as high-power negative electrodes in lithium ion capacitors

A nitrogen-rich carbon nanotubes/amorphous carbon (CNT/C) composite was prepared by carbonising a CNT/polyaniline (PANI) composite, and characterised. Scanning electron microscopy and X-ray photoelectron spectroscopy confirmed that the composite retained a mesoporous CNT structure as its backbone, whilst the nitrogen-rich PANI-derived carbon formed a thin amorphous coating on the CNT surface. Electrochemical characterisation of the CNT/C composite indicated that it had nearly double the reversible Li⁺ intercalation capacity (390 vs. 219 mAh g^?1) and 39 % less irreversible capacity (622 vs. 1,015 mAh g^?1) than the pristine CNT. The CNT/C composite showed exceptionally high rate capability with a de-intercalation capacity of 81 mAh g^?1 at a very high charge/discharge rate of 60 C (time taken for charge or discharge is 1 min) (1 C = 1 h charge or discharge), whereas the pristine CNT delivered 53 mAh g^?1 at this C-rate. By comparison, the rate capabilities of conventional graphite (N3 and SLP30) were very poor above 5 C (~17 mAh g^?1 at 5 C). Both the pristine CNT and CNT/C composite showed an excellent cyclability at 1 C charge/discharge over 600 cycles. The CNT/C composite maintained a fairly stable capacity of ~200 mAh g^?1 after 600 cycles, whilst the commercial graphite showed a steady and significant decrease in de-intercalation capacity; reaching <70 mAh g^?1 after 600 cycles.     

Pt nanoparticles synthesized with new surfactants: improvement in C1–C3 alcohol oxidation catalytic activity

Platinum electrocatalysts were prepared using PtCl₄ as a starting material and 1-decylamine, N,N-dimethyldecylamine, 1-dodecylamine, N,N-dimethyldodecylamine, 1-hexadecylamine, and 1-octadecylamine as surfactants. These surfactants were used for the first time in this synthesis to determine whether the primary and/or tertiary structure and/or chain length of the surfactants, affects the size and/or activity of the catalysts in C₁–C₃ alcohol electro-oxidation reactions. Electrochemical measurements (cyclic voltammetry and chronoamperometry) indicated that the highest electrocatalytic performance was observed for the Pt nanocatalysts that were stabilized by N,N-dimethyldecylamine, and this has a tertiary amine structure with a short chain length (R = C₁₀H₂₁). The high performance may be due to the high electrochemical surface area, Pt(0)/Pt(IV) ratio, %Pt utility, and roughness factor (R _f). X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy were used to determine the parameters that affect the catalytic activities.     

Improved electro-assisted removal of phosphates and nitrates using mesoporous carbon aerogels with controlled porosity

Three-activated carbon aerogels were synthesized by CO₂ activation of the materials prepared by the polycondensation of resorcinol and formaldehyde mixtures followed by supercritical drying. The obtained carbon aerogels were characterized and used as electrode materials for the electrosorption of sodium phosphate and nitrate. X-ray diffraction and Raman spectroscopy showed the dependence of the structural ordering of the aerogels with the resorcinol/catalyst ratio and the extent of activation. The electrosorption capacitance evaluated by cyclic voltammetry revealed large values for the activated samples containing a large contribution of mesopores, regardless the electrolyte salt. Due to an adequate combination of chemical and porous features, the desalting capacity of the activated carbon aerogel electrodes exceeded that of the as-prepared materials. The evaluation of the kinetic properties by chronocoulometric relaxation and impedance spectroscopy showed a decrease of time constant and resistances for highly mesoporous activated samples. A high deionization capacity and fast electrode discharge was detected for the deionization of sodium nitrate on the highly mesoporous activated aerogel. Data also showed the efficient electrosorption of ionic species on consecutive charge/discharge cycles, confirming the stability of the aerogel electrodes at the high applied potentials.