Chemical Engineering

An analyticai procedure involving Sequential chemical extractions has been developed for the partitioning of Particulate trace metals (Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn) into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual. Experimental results obtained on replicate samples of fluvial bottom sediments demonstrate that the relative standard deviation of the Sequential extraction procedure is generally better than A10 %. The accuracy, evaluated by comparing total trace metal concentrations with the sum of the five individual fractions, proved to be satisfactory. Complementary measurements were performed on the individual leachates, and on the residual sediments foilowing each extraction, to evaluate the selectivity of the various reagents toward specific geochemical phases. An application of the proposed method lo river sediments is described, and the resulting trace metal speciation is discussed.

Anti-DPPH radical effect as well as anti-peroxide activity of o-hydroxyl, o-methoxy, and alkyl ester derivatives of p-hydroxybenzoic acid in a bulk fish oil system and its O/W emulsion were investigated. Electronic phenomena, intra-and/or intermolecular hydrogen bonds, interfacial properties, and chemical reaction of the solvent molecules with phenolic compounds were considered to be mainly involved in the antiradical activities observed. Antioxidant activity of the phenolic acids derivatives as a function of these factors was variously affected by the environmental conditions which may occur in practice.

The CASTEP code for first principles electronic structure calculations will be described. A brief, nontechnical overview will be given and some of the features and capabilities highlighted. Some features which are unique to CASTEP will be described and near-future development plans outlined.

Highly Enantioselective Organocatalytic Addition of Unmodified Aldehydes to N-Boc Protected Imines: One-Pot Asymmetric Synthesis of β-Amino Acids. -With L-proline as the catalyst, β-amino aldehyde derivatives are obtained in up to 99% e.e. The reaction is highly diastereoselective (>19:1) and the desired isomers (III) are separated via SiO2 chromatography. -(VESELY, J.; RIOS, R.; IBRAHEM, I.; CORDOVA*, A.; Tetrahedron Lett. 48 (2007) 3, 421-425; Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -Mais 16-185

This study examines the evidence for the effectiveness of active learning. It defines the common forms of active learning most relevant for engineering faculty and critically examines the core element of each method. It is found that there is broad but uneven support for the core elements of active, collaborative, cooperative and problem-based learning.

Concern about environmental protection has increased over the years from a global viewpoint. To date, the prevalence of adsorption separation in the environmental chemistry remains an aesthetic attention and consideration abroad the nations, owning to its low initial cost, simplicity of design, ease of operation, insensitivity to toxic substances and complete removal of pollutants even from dilute solutions. With the renaissance of isotherms modeling, there has been a steadily growing interest in this research field. Confirming the assertion, this paper presents a state of art review of adsorption isotherms modeling, its fundamental characteristics and mathematical derivations. Moreover, the key advance of the error functions, its utilization principles together with the comparisons of linearized and non-linearized isotherm models have been highlighted and discussed. Conclusively, the expanding of the nonlinear isotherms represents a potentially viable and powerful tool, leading to the superior improvement in the area of adsorption science.

We present a statistical model to estimate the accuracy of peptide assignments to tandem mass (MS/MS) spectra made by database search applications such as SEQUEST. Employing the expectation maximization algorithm, the analysis learns to distinguish correct from incorrect database search results, computing probabilities that peptide assignments to spectra are correct based upon database search scores and the number of tryptic termini of peptides. Using SEQUEST search results for spectra generated from a sample of known protein components, we demonstrate that the computed probabilities are accurate and have high power to discriminate between correctly and incorrectly assigned peptides. This analysis makes it possible to filter large volumes of MS/MS database search results with predictable false identification error rates and can serve as a common standard by which the results of different research groups are compared.

A statistical model is presented for computing probabilities that proteins are present in a sample on the basis of peptides assigned to tandem mass (MS/MS) spectra acquired from a proteolytic digest of the sample. Peptides that correspond to more than a single protein in the sequence database are apportioned among all corresponding proteins, and a minimal protein list sufficient to account for the observed peptide assignments is derived using the expectation-maximization algorithm. Using peptide assignments to spectra generated from a sample of 18 purified proteins, as well as complex H. influenzae and Halobacterium samples, the model is shown to produce probabilities that are accurate and have high power to discriminate correct from incorrect protein identifications. This method allows filtering of large-scale proteomics data sets with predictable sensitivity and false positive identification error rates. Fast, consistent, and transparent, it provides a standard for publishing largescale protein identification data sets in the literature and for comparing the results obtained from different experiments.

To obtain a semi-theoretical equation for the excess Gibbs energy of a liquid mixture, Guggenheim's quasi-chemical analysis is generalized through introduction of the local area fraction as the primary concentration variable. The resulting universal quasi-chemical (UNIQUAC) equation uses only two adjustable parameters per binary. Extension to multicomponent systems requires no ternary (or higher) parameters.The UNIQUAC equation gives good representation of both vapor-liquid and liquid-liquid equilibria for binary and multicomponent mixtures containing a variety of nonelectrolyte components such as hydrocarbons, ketones, esters, amines, alcohols, nitriles, etc., and water. When well-defined simplifying assumptions are introduced into the generalized quasi-chemical treatment, the UNIQUAC equation reduces to any one of several well-known equations for the excess Gibbs energy, including the Wilson, Margules, van Laar, and NRTL equations.The effects of molecular size and shape are introduced through structural parameters obtained from pure-component data and through use of Staverman's combinatorial entropy as a boundary condition for athermal mixtures. The UNIQUAC equation, therefore, is applicable also to polymer solutions.

New, hydrophobic ionic liquids with low melting points (<-30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also described. The molten salts were characterized by NMR and elemental analysis. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1, 2, 3, and 4(5)-positions on these properties was scrutinized. Viscosities as low as 35 cP (for 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide). The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications.

Metabolite profiling in biomarker discovery, enzyme substrate assignment, drug activity/specificity determination, and basic metabolic research requires new data preprocessing approaches to correlate specific metabolites to their biological origin. Here we introduce an LC/MS-based data analysis approach, XCMS, which incorporates novel nonlinear retention time alignment, matched filtration, peak detection, and peak matching. Without using internal standards, the method dynamically identifies hundreds of endogenous metabolites for use as standards, calculating a nonlinear retention time correction profile for each sample. Following retention time correction, the relative metabolite ion intensities are directly compared to identify changes in specific endogenous metabolites, such as potential biomarkers. The software is demonstrated using data sets from a previously reported enzyme knockout study and a large-scale study of plasma samples. XCMS is freely available under an open-source license at http:// metlin.scripps.edu/download/.

Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.

Automobile manufacturers and fuel cell developers have produced PEMFCs for many years, but recent significant technological advances have left two major remaining challenges to widespread fuel cell use: cost and lifetime, which are interrelated. For example, adding more catalyst to a fuel cell increases catalyst lifetime but increases fuel cell cost. Similarly, increasing a fuel cell membrane's thickness increases its lifetime but also increases its cost by Rod Borup is a Team Leader in the fuel cell program at Los Alamos National Lab in Los Alamos, New Mexico. He received his B.S.E. in Chemical Engineering from the University of Iowa in 1988 and his Ph.D. from the University of Washington in 1993. He has worked on fuel cell technology since 1994, working in the areas of hydrogen production and PEM fuel cell stack components. He has been awarded 12 U.S. patents, authored over 40 papers related to fuel cell technology, and presented over 50 oral papers at national meetings. His current main research area is related to water transport in PEM fuel cells and PEM fuel cell durability. Recently, he was awarded the 2005 DOE Hydrogen Program R&D Award for the most significant R&D contribution of the year for his team's work in fuel cell durability and was the Principal Investigator for the 2004 Fuel Cell Seminar (San Antonio, TX, USA) Best Poster Award.

Oxide nanofluids were produced and their thermal conductivities were measured by a transient hot-wire method. The experimental results show that these nanofluids, containing a small amount of nanoparticles, have substantially higher thermal conductivities than the same liquids without nanoparticles. Comparisons between experiments and the Hamilton and Crosser model show that the model can predict the thermal conductivity of nanofluids containing large agglomerated Al 2 0 3 particles. However, the model appears to be inadequate for nanofluids containing CuO particles. This suggests that not only particle shape but size is considered to be dominant in enhancing the thermal conductivity of nanofluids.

Being a motion on a discontinuity set of a dynamic system, sliding mode is used to keep accurately a given constraint and features theoretically-infinite-frequency switching. Standard sliding modes provide for finite-time convergence, precise keeping of the constraint and robustness with respect to internal and external disturbances. Yet the relative degree of the constraint has to be 1 and a dangerous chattering effect is possible. Higher-order sliding modes preserve or generalize the main properties of the standard sliding mode and remove the above restrictions. r-Sliding mode realization provides for up to the rth order of sliding precision with respect to the sampling interval compared with the first order of the standard sliding mode. Such controllers require higher-order real-time derivatives of the outputs to be available. The lacking information is achieved by means of proposed arbitrary-order robust exact differentiators with finite-time convergence. These differentiators feature optimal asymptotics with respect to input noises and can be used for numerical differentiation as well. The resulting controllers provide for the full output-feedback real-time control of any output variable of an uncertain dynamic system, if its relative degree is known and constant. The theoretical results are confirmed by computer simulation.

The aim of the methods described is to calculate the properties of turbulent reactive flow fields. At each point in the flow field, a complete statistical description of the state of the fluid is provided by the velocity-composition joint pdf. This is the joint probability density function (pdf) of the three components of velocity and of the composition variables (species mass fractions and enthalpy). The principal method described is to solve a modelled transport equation for the velocity-composition joint pdf. For a variable-density flow with arbitrarily complex and nonlinear reactions, it is remarkable that in this equation the effects of convection, reaction, body forces and the mean pressure gradient appear exactly and so do not have to be modelled. Even though the joint pdf is a function of many independent variables, its transport equation can be solved by a Monte Carlo method for the inhomogeneous flows of practical interest. A second method that is described briefly is to solve a modelled transport equation for the composition joint pdf.The objective of the paper is to provide a comprehensive and understandable of the theoretical foundations of the pdf approach.

Novel gold catalysts were prepared by coprecipitation from an aqueous solution of HAuCl 4 and the nitrates of various transition metals. Calcination of the coprecipitates in air at 400 °C produced ultrafine gold particles smaller than 10 nm which were uniformly dispersed on the ...

We use multifractal detrended fluctuation analysis (MF-DFA), to See query 1 study sunspot number fluctuations. The result of the MF-DFA shows that there are three crossover timescales in the fluctuation function. We discuss how the existence of the crossover timescales is related to a sinusoidal trend. Using Fourier detrended fluctuation analysis, the sinusoidal trend is eliminated. The Hurst exponent of the time series without the sinusoidal trend is $0.12\pm 0.01$. Also we find that these fluctuations have multifractal nature. Comparing the MF-DFA results for the remaining data set to those for shuffled and surrogate series, we conclude that its multifractal nature is almost entirely due to long range correlations.

In this final part, we discuss fault diagnosis methods that are based on historic process knowledge. We also compare and evaluate the various methodologies reviewed in this series in terms of the set of desirable characteristics we proposed in Part I. This comparative study reveals the relative strengths and weaknesses of the different approaches. One realizes that no single method has all the desirable features one would like a diagnostic system to possess. It is our view that some of these methods can complement one another resulting in better diagnostic systems. Integrating these complementary features is one way to develop hybrid systems that could overcome the limitations of individual solution strategies. The important role of fault diagnosis in the broader context of process operations is also outlined. We also discuss the technical challenges in research and development that need to be addressed for the successful design and implementation of practical intelligent supervisory control systems for the process industries. #

Research and development activities directed toward commercial production of cellulosic ethanol have created the opportunity to dramatically increase the transformation of lignin to value-added products. Here, we highlight recent advances in this lignin valorization effort. Discovery of genetic variants in native populations of bioenergy crops and direct manipulation of biosynthesis pathways have produced lignin feedstocks with favorable properties for recovery and downstream conversion. Advances in analytical chemistry and computational modeling detail the structure of the modified lignin and direct bioengineering strategies for future targeted properties. Refinement of biomass pretreatment technologies has further facilitated lignin recovery, and this coupled with genetic engineering will enable new uses for this biopolymer, including low-cost carbon fibers, engineered plastics and thermoplastic elastomers, polymeric foams, fungible fuels, and commodity chemicals.

We describe a modification of two-dimensional (2-D) polyacrylamide gel electrophoresis that requires only a single gel to reproducibly detect differences between two protein samples. This was accomplished by fluorescently tagging the two samples with two different dyes, running them on the same 2-D gel, post-run fluorescence imaging of the gel into two images, and superimposing the images. The amine reactive dyes were designed to insure that proteins common to both samples have the same relative mobility regardless of the dye used to tag them. Thus, this technique, called difference gel electrophoresis (DIGE), circumvents the need to compare severa1 2-D gels. DIGE is reproducible, sensitive, and can detect an exogenous difference between two Drosophila embryo extracts at nanogram levels. Moreover, an inducible protein from E. coli was detected after 15 min of induction and identified using DIGE preparatively. Nonstandard abbreviationa: DIGE, difference gel electrophoresis; IPTG, isopropylthiogalacto pyranoside Keywords: Two-dimensional polyacrylamide gel electrophoresis / Fluorescence imaging 2 Materials and methods 2.1 Synthesis of the dyes Cy3 and Cy5 were synthesized using a modification of the previously described protocol [7]: (i) Indole deriva-* A list of known 2-D gel databases is available at :he following URL: http://www-lmmb.ncifcrf.gov/EP/EPemail. html

Most of the particle number emitted by engines is in the nanoparticle range, D (50 nm, while most of the mass is in the accumulation mode, 50 nm(D (1000 nm, range. Nanoparticles are typically hydrocarbons or sulfate and form by nucleation during dilution and cooling of the exhaust, while accumulation mode particles are mainly carbonaceous soot agglomerates formed directly by combustion. Emission standards on diesel engines have led to dramatic reductions in particle mass emitted. However, a new HEI study shows that some low-emission diesel engines emit much higher concentrations of nanoparticles than older designs and other low-emission designs. Many recent studies suggest that at similar mass concentrations; nanometer size particles are more dangerous than micron size particles. This has raised questions about whether nanoparticle (number based) emission standards should be imposed. Unlike mass, number is not conserved. It may change dramatically by nucleation and coagulation during dilution and sampling, making it very difficult to design a standard. Furthermore, if nanoparticles are a problem, spark ignition engines may also have to be controlled.

The original protocol of two-dimensional electrophoresis with immobilized pH gradient (IPG-Dalt; Görg et al., Electrophoresis 1988, 9, 531±546) is updated. Merits and limits of different methods for sample solubilization, sample application (by cup-loading or ingel rehydration) with respect to the pH interval used for IPG-isoelectric focusing are critically discussed. Guidelines for running conditions of analytical and micropreparative IPG-Dalt, using wide IPGs up to pH 12 for overview patterns, or narrow IPGs for zoom-in gels for optimum resolution and detection of minor components, are stated. Results with extended separation distances as well as automated procedures are demonstrated, and a comparison between protein detection by silver staining and fluorescent dyes is given. A brief trouble shooting guide is also included.

The quantitative experimental uncertainty in the structure of fully hydrated, biologically relevant, fluid (L K ) phase lipid bilayers has been too large to provide a firm base for applications or for comparison with simulations. Many structural methods are reviewed including modern liquid crystallography of lipid bilayers that deals with the fully developed undulation fluctuations that occur in the L K phase. These fluctuations degrade the higher order diffraction data in a way that, if unrecognized, leads to erroneous conclusions regarding bilayer structure. Diffraction measurements at high instrumental resolution provide a measure of these fluctuations. In addition to providing better structural determination, this opens a new window on interactions between bilayers, so the experimental determination of interbilayer interaction parameters is reviewed briefly. We introduce a new structural correction based on fluctuations that has not been included in any previous studies. Updated measurements, such as for the area compressibility modulus, are used to provide adjustments to many of the literature values of structural quantities. Since the gel (L L P) phase is valuable as a stepping stone for obtaining fluid phase results, a brief review is given of the lower temperature phases. The uncertainty in structural results for lipid bilayers is being reduced and best current values are provided for bilayers of five lipids. ß

Biodiesel is an alternative diesel fuel that is produced from vegetable oils and animal fats. It consists of the monoalkyl esters formed by a catalyzed reaction of the triglycerides in the oil or fat with a simple monohydric alcohol. The reaction conditions generally involve a trade-off between reaction time and temperature as reaction completeness is the most critical fuel quality parameter. Much of the process complexity originates from contaminants in the feedstock, such as water and free fatty acids, or impurities in the final product, such as methanol, free glycerol, and soap. Processes have been developed to produce biodiesel from high free fatty acid feedstocks, such as recycled restaurant grease, animal fats, and soapstock. D

Information is stored in neural circuits through long-lasting changes in synaptic strengths 1,2. Most studies of information storage have focused on mechanisms such as long-term potentiation and depression (LTP and LTD), in which synaptic strengths change in a synapse-specific manner 3,4. In contrast, little attention has been paid to mechanisms that regulate the total synaptic

In contrary to other 1D momentum-conserving lattices such as the Fermi-Pasta-Ulam β (FPU-β) lattice, the 1D coupled rotator lattice is a notable exception which conserves total momentum while exhibits normal heat conduction behavior. The temperature behavior of the thermal conductivities of 1D coupled rotator lattice had been studied in previous works trying to reveal the underlying physical mechanism for normal heat conduction. However, two different temperature behaviors of thermal conductivities have been claimed for the same coupled rotator lattice. These different temperature behaviors also intrigue the debate whether there is a phase transition of thermal conductivities as the function of temperature. In this work, we will revisit the temperature dependent thermal conductivities for the 1D coupled rotator lattice. We find that the temperature dependence follows a power law behavior which is different with the previously found temperature behaviors. Our results also support the claim that there is no phase transition for 1D coupled rotator lattice. We also give some discussion about the similarity of diffusion behaviors between the 1D coupled rotator lattice and the single kicked rotator also called the Chirikov standard map.

Modern analytical tools should enable highly specific identification and characterization of inorganic and organic matter with minimal effort for sample preparation. Raman spectroscopy is one such highly specific method that enables identification of molecules through their specific molecular fingerprint information. Unfortunately the sensitivity of Raman spectroscopy is quite low, meaning that it cannot be used for the analysis of samples with low analyte concentration. One possible solution to this problem is the use of metal nanostructures or particles to enhance the intrinsically weak Raman effect. This method is known as surface enhanced Raman spectroscopy (SERS) and it combines the specificity of Raman with high sensitivity which enables analysis of samples with minimal analyte concentration. However, to develop SERS further and to convert it in a standard analytical tool several problems have to be solved. A major issue for routine application of SERS is the production of reproducible SERS substrates, which have predictable and reliable enhancement factors, because the enhancement of the Raman effect is highly dependent on the structure of the SERS substrates.

The TiO 2 /UV photocatalytic degradation of methylene blue (MB) has been investigated in aqueous heterogeneous suspensions. In addition to a prompt removal of the color, TiO 2 /UV-based photocatalysis was simultaneously able to oxidize the dye, with an almost complete mineralization of carbon and of nitrogen and sulfur heteroatoms into CO 2 , NH 4 + , NO 3 − and SO 4 2− , respectively. A detailed degradation pathway has been determined by a careful identification of intermediate products, in particular aromatics, whose successive hydroxylations lead to the aromatic ring opening. These results suggest that TiO 2 /UV photocatalysis may be envisaged as a method for treatment of diluted waste waters in textile industries.

Interest in meat fatty acid composition stems mainly from the need to find ways to produce healthier meat, i.e. with a higher ratio of polyunsaturated (PUFA) to saturated fatty acids and a more favourable balance between n-6 and n-3 PUFA. In pigs, the drive has been to increase n-3 PUFA in meat and this can be achieved by feeding sources such as linseed in the diet. Only when concentrations of a-linolenic acid (18:3) approach 3% of neutral lipids or phospholipids are there any adverse effects on meat quality, defined in terms of shelf life (lipid and myoglobin oxidation) and flavour. Ruminant meats are a relatively good source of n-3 PUFA due to the presence of 18:3 in grass. Further increases can be achieved with animals fed grain-based diets by including whole linseed or linseed oil, especially if this is ''protected'' from rumen biohydrogenation. Long-chain (C20-C22) n-3 PUFA are synthesised from 18:3 in the animal although docosahexaenoic acid (DHA, 22:6) is not increased when diets are supplemented with 18:3. DHA can be increased by feeding sources such as fish oil although too-high levels cause adverse flavour and colour changes. Grass-fed beef and lamb have naturally high levels of 18:3 and long chain n-3 PUFA. These impact on flavour to produce a 'grass fed' taste in which other components of grass are also involved. Grazing also provides antioxidants including vitamin E which maintain PUFA levels in meat and prevent quality deterioration during processing and display. In pork, beef and lamb the melting point of lipid and the firmness/hardness of carcass fat is closely related to the concentration of stearic acid (18:0).

Simplified reaction mechanisms for the oxidation of hydrocarbon fuels have been examined using a numerical laminar flame model. The types of mechanisms studied include one and two global reaction steps as well as quasi-global mechanisms. Reaction rate parameters were varied in order to provide the best agreement between computed and experimentally observed flame speeds in selected mixtures of fuel and air. The influences of the various reaction rate parameters on the laminar flame properties have been identified, and a simple procedure to determine the best values for the reaction rate parameters is demonstrated. Fuels studied include II-paraffins from methane to II-decane, some methyl-substituted II-paraffins, acetylene, and representative olefin, alcohol and aromatic hydrocarbons. Results show that the often-employed choice of simultaneous first order fuel and oxidizer dependence for global rate expressions cannot yield the correct dependence of flame speed on equivalence ratio or pressure and cannot correctly predict the rich flammability limit. However, the best choice of rate parameters suitably reproduces rich and lean flammability limits as well as the dependence of the flame speed on pressure and equivalence ratio for all of the fuels examined. Two-step and quasi-global approaches also yield information on flame temperature and burned gas composition. However, none of the simplified mechanisms studied accurately describes the chemical structure of the flame itself.

Over the past decade, the formation and growth of nanometer-size atmospheric aerosol particles have been observed at a number of sites around the world. Measurements of particle formation have been performed on di erent platforms (ground, ships, aircraft) and over di erent time periods (campaign or continuous-type measurements). The development during the 1990s of new instruments to measure nanoparticle size distributions and several gases that participate in nucleation have enabled these new discoveries. Measurements during nucleation episodes of evolving size distributions down to 3 nm can be used to calculate the apparent source rate of 3-nm particles and the particle growth rate. We have collected existing data from the literature and data banks (campaigns and continuous measurements), representing more than 100 individual investigations. We conclude that the formation rate of 3-nm particles is often in the range 0.01-10 cm −3 s −1 in the boundary layer. However, in urban areas formation rates are often higher than this (up to 100 cm −3 s −1 ), and rates as high as 10 4 -10 5 cm −3 s −1 have been observed in coastal areas and industrial plumes. Typical particle growth rates are in the range 1-20 nm h −1 in mid-latitudes depending on the temperature and the availability of condensable vapours. Over polar areas the growth rate can be as low as 0:1 nm h −1 . Because nucleation can lead to a signiÿcant increase in the number concentration of cloud condensation nuclei, global climate models will require reliable models for nucleation. ?

A com parison of kinetic models describing the sorption of pollutants has been reviewed. The rate m odels evaluated include the Elovich equation, the pseudo-® rst order equation and the pseudo-second order equation. Results show that chemisorption processes could be rate limiting in the sorption step. The pseudo-second order equation m ay be applied for chem isorption processes with a high degree of correlation in several literature cases where a pseudo-® rst order rate mechanism has been arbitrarily assumed.

This paper reviews the factors affecting the fatty acid composition of adipose tissue and muscle in pigs, sheep and cattle and shows that a major factor is the total amount of fat. The effects of fatty acid composition on meat quality are also reviewed. Pigs have high levels of polyunsaturated fatty acids (PUFA), including the long chain (C20-22) PUFA in adipose tissue and muscle. The full range of PUFA are also found in sheep adipose tissue and muscle whereas cattle 'conserve' long chain PUFA in muscle phospholipid. Linoleic acid (18:2n À 6) is a major ingredient of feeds for all species. Its incorporation into adipose tissue and muscle in relation to the amount in the diet is greater than for other fatty acids. It is deposited in muscle phospholipid at a high level where it and its long chain products eg aracidonic acid (20:4n À 6) compete well for insertion into phospholipid molecules. Its proportion in pig adipose tissue declines as fat deposition proceeds and is an index of fatness. The same inverse relationships are not seen in ruminant adipose tissue but in all species the proportion of 18:2n À 6 declines in muscle as fat deposition increases. The main reason is that phospholipid, where 18:2n À 6 is located, declines as a proportion of muscle lipid and the proportion of neutral lipid, with its higher content of saturated and monounsaturated fatty acids, increases. Oleic acid (18:1cis À 9), formed from stearic acid (18:0) by the enzyme stearoyl Co-A desaturase, is a major component of neutral lipid and in ruminants the same enzyme forms conjugated linoleic acid (CLA), an important nutrient in human nutrition. Like 18:2n À 6, a-linolenic acid (18:3n À 3) is an essential fatty acid and is important to ruminants since it is the major fatty acid in grass. However it does not compete well for insertion into phospholipid compared with 18:2n À 6 and its incorporation into adipose tissue and muscle is less efficient. Greater biohydrogenation of 18:3n À 3 and a long rumen transit time for forage diets also limits the amount available for tissue uptake compared with 18:2n À 6 from concentrate diets. A positive feature of grass feeding is that levels of the nutritionally important long chain n À 3 PUFA are increased ie EPA (20:5n À 3) and DHA (22:6n À 3). Future research should focus on increasing n À 3 PUFA proportions in lean carcasses and the use of biodiverse pastures and conservation processes which retain the benefits of fresh leafy grass offer opportunities to achieve this. The varying fatty acid compositions of adipose tissue and muscle have profound effects on meat quality. Fatty acid composition determines the firmness/oiliness of adipose tissue and the oxidative stability of muscle, which in turn affects flavour and muscle colour. Vitamin E is an essential nutrient, which stabilises PUFA and has a central role in meat quality, particularly in ruminants.