Relations between environmental black carbon sorption and geochemical sorbent characteristics

Pyrogenic carbon particles in sediments (soot and charcoal, collectively termed "black carbon" or BC) appear to be efficient sorbents of many hydrophobic organic compounds, so they may play an important role in the fate and toxicity of these substances. To properly model toxicant sorption behavior, it is important to (i) quantify the magnitude of the role of BC in sorption and (ii) elucidate which geochemical BC characteristics determine the strength of environmental BC sorption. Sorption isotherms of d10-phenanthrene (d10-PHE) were determined over a wide concentration range (0.0003-20 microg/L), for five sediments with widely varying characteristics. From the sorption isotherms, we determined Freundlich coefficients of environmental BC sorption, K(F,BCenv. These varied from 10(4.7) to 10(5.5). From the data, it could be deduced that BC was responsible for 49-85% of the total d10-PHE sorption at a concentration of 1 ng/L. At higher concentrations, the importance of BC for the sorption process diminished to <20% at 1 microg/L and 0-1% at 1 mg/L. There were no significant relationships between BC sorption strength and the tested geochemical BC characteristics [the fraction of small (<38 microm) BC particles, the BC resistance to high-temperature oxidation, the fraction of biomass-derived BC, the native polycyclic aromatic hydrocarbon and total organic carbon contents]. Because of the limited variation in BC sorption strength with widely varying BC characteristics, the presented BC sorption coefficients may putatively be used as generic starting points for environmental modeling purposes.     

A discrete spectral analysis for determining quasi-linear viscoelastic properties of biological materials

The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress–relaxation data by imposing a simple form upon a material''s temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model''s ‘box’-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material''s relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material''s temporal relaxation spectrum from stress–relaxation data in an unbiased way. Our ‘discrete QLV’ (DQLV) approach identifies ranges of time constants over which the Fung QLV model''s typical box spectrum provides an accurate representation of a particular material''s temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress–relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit.     

Sticky-free and overhang-free DNA languages

An essential step of any DNA computation is encoding the input data on single or double DNA strands. Due to the biochemical properties of DNA, complementary single strands can bind to one another forming double-stranded DNA. Consequently, data-encoding DNA strands can sometimes interact in undesirable ways when used in computations. It is crucial thus to analyze properties that guard against such phenomena and study sets of sequences that ensure that no unwanted bindings occur during any computation. This paper formalizes and investigates properties of DNA languages that guarantee their robusteness during computations. After defining and investigating several types of DNA languages possessing good encoding properties, such as sticky-free and overhang-free languages, we give algorithms for deciding whether regular DNA languages are invariant under bio-operations. We also give a method for constructing DNA languages that, in addition to being invariant and sticky-free, possess error-detecting properties. Finally, we present the results of running tests that check whether several known gene languages (the set of genes of a given organism) as well as the input DNA languages used in Adlemans DNA computing experiment, have the defined properties.Received: 6 February 2003, Published online: 2 September 2003Research partially supported by Grants R2824A01 and R220259 of the Natural Sciences and Engineering Research Council of Canada.     

Use of rosemary extract in preventing oxidation during deep-fat frying of potato chips

The effect of using a rosemary extract on the stability of oil used for frying potato chips has been evaluated. Sliced potatoes were fried intermittently in soybean oil containing a natural extract from rosemary. The conditions used for frying were 185°C for 90 s. Two separate experiments, with and without replenishment of oil, were carried out. Oil samples were taken each day, not only from the frying pans but also by extraction with hexane from the chips. Changes in the induction period of the oil samples (Rancimat method) were determined. The induction period decreased as frying progressed. The reduction in the induction period was higher in the oil free of rosemary extract, and the chips were much darker in color. The oil containing the extract showed greater antioxidant activity, and reduced darkening and rancidity of the oil. Potato chips fried in the oil with added rosemary extract were more acceptable than chips fried in oil containing no extract until the last frying. The free radical scavenging activity of rosemary extract in comparison to other natural antioxidants was also determined by the reduction of O₂ ^.- in a hypoxanthine/xanthine oxidase system.     

Comparative Analysis of Synthetic Natural Gas versus Hydrogen Production from Bagasse

A rigorous and comparative evaluation of two biomass‐to‐gases (BtG) conversion routes was performed and, according to this outcome, it is suggested which of the options evaluated is most desirable. These options, the hydrogen and synthetic natural gas (SNG) production, were designed in Aspen Plus process simulation software. Sugar cane bagasse was considered as feedstock. Mass and energy balance data were extracted from the simulations, and consequently thermodynamic (exergy analysis), economic (financial and uncertainty analysis), and environmental (CO₂ emissions) evaluations were carried out. Exergy and environmental analysis favor the SNG production while the hydrogen route provides higher profits.     

A comparative techno‐economic assessment of three bio‐oil upgrading routes for aviation biofuel production

The aviation industry continues to grow, and consequently, more fuel is needed. With the intention of decarbonising the aviation sector, sustainable routes that have the potential to mitigate emissions, such as biomass fast pyrolysis, can positively contribute to this direction. Within this context, the present study performs a comparative techno‐economic evaluation of aviation biofuel manufacture via the main bio‐oil upgrading pathways, namely, hydroprocessing (HP), gasification followed by Fischer‐Tropsch synthesis (G+FT), and zeolite cracking (ZC). The research constitutes the first endeavour to investigate and compare the feasibility of producing biojet fuel via pyrolysis‐based routes. The presented work provides an inclusive evaluation that comprises process modelling and financial assessment. Based on the simulations, overall energy efficiencies of 48.8%, 45.73%, and 45.38% and jet fuel energy efficiencies of 23.70%, 21.45%, and 20.53% were calculated, while the implementation of a discounted cash flow analysis estimated minimum jet fuel selling prices (MJSPs) of 1.98, 2.32, and 2.21 $/L for the HP, the G+FT, and the ZC, respectively. Sensitivity analysis revealed that the processes are capital and feedstock intensive while an increase to the bio‐oil yield will favour the economic performance of the examined biorefineries. An increase of the plant size from 100 (base case) to 150 dry tonnes per hour of feedstock will decrease the selling prices by approximately 25% for all cases. Monte Carlo simulations exhibited that without establishing and/or maintaining appropriate policy schemes, there is no pragmatic prospect for the examined biorefineries to beat the competition against the prevailing oil infrastructures.     

Practical Product Path Guiding Using Linearly Transformed Cosines

Path tracing is now the standard method used to generate realistic imagery in many domains, e.g., film, special effects, architecture etc. Path guiding has recently emerged as a powerful strategy to counter the notoriously long computation times required to render such images. We present a practical path guiding algorithm that performs product sampling, i.e., samples proportional to the product of the bidirectional scattering distribution function (BSDF) and incoming radiance. We use a spatial-directional subdivision to represent incoming radiance, and introduce the use of Linearly Transformed Cosines (LTCs) to represent the BSDF during path guiding, thus enabling efficient product sampling. Despite the computational efficiency of LTCs, several optimizations are needed to make our method cost effective. In particular, we show how we can use vectorization, precomputation, as well as strategies to optimize multiple importance sampling and Russian roulette to improve performance. We evaluate our method on several scenes, demonstrating consistent improvement in efficiency compared to previous work, especially in scenes with significant glossy inter-reflection.     

A Pipeline Technique for Dynamic Data Transfer on a Multiprocessor Grid

This paper describes a pipeline technique which is used to redistribute data on a multiprocessor grid during runtime. The main purposes of the algorithm are to minimize the data transfer time, prevent congestion on the ports of the receiving processors, and minimize the number of idle processors. One of the key ideas for this algorithm is the creation of processor classes, firstly introduced by Desprez et al. [IEEE Transactions on Parallel and Distributed Systems 9(2):102 (1998).] Based on the idea of classes, we create the pipeline tasks used to organize the redistribution of data. Our experimental results show that this pipeline technique can significantly reduce the amount of time required to complete a dynamic data transfer task.