Propagation of nonstationary curved and stretched premixed flames with multistep reaction mechanisms

The propagation speed of a thin premixed flame disturbed by an unsteady fluid flow of a larger scale is considered. The flame may also have a general shape but the reaction zone is assumed to be thin compared to the flame thickness. Unlike in preceding publications, the presented asymptotic analysis is performed for a general multistep reaction mechanism and, at the same time, the flame front is curved by the fluid flow. The resulting equations define the propagation speed of disturbed flames in terms of the properties of undisturbed planar flames and the flame stretch. Special attention is paid to the near-equidiffusion limit. In this case, the flame propagation speed is shown to depend on the effective Zeldovich number Z(f) , and the flame stretch. Unlike the conventional Zeldovich number, the effective Zeldovich number is not necessarily linked directly to the activation energies of the reactions. Several examples of determining the effective Zeldovich number for reduced combustion mechanisms are given while, for realistic reactions, the effective Zeldovich number is determined from experiments. Another feature of the present approach is represented by the relatively simple asymptotic technique based on the adaptive generalized curvilinear system of coordinates attached to the flame (i.e., intrinsic disturbed flame equations [IDFE]).

Combined chemical separation of Lu, Hf, Sm, Nd, and REEs from a single rock digest: Precise and accurate isotope Determinations of Lu-Hf and Sm-Nd using multicollector-ICPMS

A combined procedure for separating Lu, Hf, Sm, Nd, and rare earth elements (REEs) from a single sample digest is presented. The procedure consists of the following five steps: (1) sample dissolution via sodium peroxide sintering; (2) separation of the high field strength elements from the REEs and other matrix elements by a HF-free anion-exchange column procedure; (3) purification of Hf on a cation-exchange resin; (4) separation of REEs from other matrix elements by cation exchange; (5) Lu, Sm, and Nd separation from the other REEs by reversed-phase ion chromatography. Analytical reproducibilities of Sm-Nd and Lu-Hf isotope systematics are demonstrated for standard solutions and international rock reference materials. Results show overall good reproducibilities for Sm-Nd systematics independent of the rock type analyzed. For the Lu-Hf systematics, the reproducibility of the parent/daughter ratio is much better for JB-1 (basalt) than for two analyzed felsic crustal rocks (DR-N and an Archaean granitoid). It is demonstrated that this poorer reproducibility of the Lu/Hf ratio is truly caused by sample heterogeneity; thus, results are geologically reasonable.

A cassette ligation strategy with thioether replacement of three Gly-Gly peptide bonds: Total chemical synthesis of the 101 residue protein early pregnancy factor [psi(CH2S)(28-29,56-57,76-77)]

The 101 residue protein early pregnancy factor (EPF), also known as human chaperonin 10, was synthesized from four functionalized, but unprotected, peptide segments by a sequential thioether ligation strategy. The approach exploits the differential reactivity of a peptide-NHCH2CH2SH thiolate with XCH2CO-peptides, where X = Cl or I/Br. Initial model studies with short functionalized (but unprotected) peptides showed a significantly faster reaction of a peptide-NHCH2CH2SH thiolate with a BrCH2CO-peptide than with a CICH2CO-peptide, where thiolate displacement of the halide leads to chemoselective formation of a thioether surrogate for the Gly-Gly peptide bond. This rate difference was used as the basis of a novel sequential ligation approach to the synthesis of large polypeptide chains. Thus, ligation of a model bifunctional N-alpha-chloroacetyl, C-terminal thiolated peptide with a second N-alpha-bromoacetyl peptide demonstrated chemoselective bromide displacement by the thiol group. Further investigations showed that the relatively unreactive N-alpha-chloroacetyl peptides could be activated by halide exchange using saturated KI solutions to yield the highly reactive No-iodoacetyl peptides. These findings were used to formulate a sequential thioether ligation strategy for the synthesis of EPF, a 101 amino acid protein containing three Gly-Gly sites approximately equidistantly spaced within the peptide chain. Four peptide segments or cassettes comprising the EPF protein sequence (BrAc-[EPF 78-101] 12, ClAc-[EPF 58-75]-[NHCH2CH2SH] 13, ClAc-[EPF 30-55]-[NHCH2CH2SH] 14, and Ac-[EPF 1-27]-[NHCH2CH2SH] 15) of EPF were synthesized in high yield and purity using Boc SPPS chemistry. In the stepwise sequential ligation strategy, reaction of peptides 12 and 13 was followed by conversion of the N-terminal chloroacetyl functional group to an iodoacetyl, thus activating the product peptide for further ligation with peptide 14. The process of ligation followed by iodoacetyl activation was repeated to yield an analogue of EPF (EPF psi(CH2S)(28-29,56-57,76-77)) 19 in 19% overall yield.

Mixed gas equilibrium adsorption on zeolites and energetic heterogeneity of adsorption volume

A model for binary mixture adsorption accounting for energetic heterogeneity and intermolecular interactions is proposed in this paper. The model is based on statistical thermodynamics, and it is able to describe molecular rearrangement of a mixture in a nonuniform adsorption field inside a cavity. The Helmholtz free energy obtained in the framework of this approach has upper and lower limits, which define a permissible range in which all possible solutions will be found. One limit corresponds to a completely chaotic distribution of molecules within a cavity, while the other corresponds to a maximum ordered molecular structure. Comparison of the nearly ideal O-2-N-2-zeolite NaX system at ambient temperature with the system Of O-2-N-2-zeolite CaX at 144 K has shown that a decrease of temperature leads to a molecular rearrangement in the cavity volume, which results from the difference in the fluid-solid interactions. The model is able to describe this behavior and therefore allows predicting mixture adsorption more accurately compared to those assuming energetic uniformity of the adsorption volume. Another feature of the model is its ability to correctly describe the negative deviations from Raoult's law exhibited by the O-2-N-2-CaX system at 144 K. Analysis of the highly nonideal CO2-C2H6-zeolite NaX system has shown that the spatial molecular rearrangement in separate cavities is induced by not only the ion-quadrupole interaction of the CO2 molecule but also the significant difference in molecular size and the difference between the intermolecular interactions of molecules of the same species and those of molecules of different species. This leads to the highly ordered structure of this system.

The influence of key chemical constituents in activated sludge on surface and flocculating properties

This paper examines the influence of the chemical constituents of activated sludge and extracted extracellular polymeric substances (EPS) on the surface properties, hydrophobicity, surface charge (SC) and flocculating ability (FA) of activated sludge floes. Activated sludge samples from 7 different full-scale wastewater treatment plants were examined. Protein and humic substances were found to be the dominant polymeric compounds in the activated sludges and the extracted EPS, and they significantly affected the FA and surface properties, hydrophobicity and SC, of the sludge floes. The polymeric compounds proteins, humic substances and carbohydrates in the sludge floes and the extracted EPS contributed to the negative SC, but correlated negatively to the hydrophobicity of sludge floes. The quantity of protein and carbohydrate within the sludge and the extracted EPS was correlated positively to the FA of the sludge floes, while increased amounts of humic substances resulted in lower FA. In contrast, increased amounts of total extracted EPS had a negative correlation to FA. The results reveal that the quality and quantity of the polymeric compounds within the sludge floes is more informative, with respect to understanding the mechanisms involved in flocculation, than if only the extracted EPS are considered. This is an important finding as it indicates that extracting EPS may be insufficient to characterise the EPS. This is due to the low extraction efficiency and difficulties involved in the separation of EPS from other organic compounds. Correlations were observed between the surface properties and FA of the sludge floes., This confirms that the surface properties of the, sludge flocs play an important role in the bioflocculation process but that also other interactions like polymer entanglement are important. (C) 2002 Elsevier Science Ltd. All rights reserved.

Chemical characterisation of deep profile Ferrosols under sugarcane in wet tropical northern Queensland

The chemical properties of deep profile samples ( up to 12 m) of Ferrosols from northern Queensland were investigated to provide an understanding of the accumulation of nitrate ( NO3) within these soil profiles. The influence of other cations and anions present in the soil solution or on the exchange and the charge chemistry of the profiles were examined with respect to the NO3 accumulations. The major ions in the soil solution were Na, NO3, and chloride ( Cl). Distinct regions of anion accumulation were observed; SO4 accumulated in the upper profile of all cores, whereas NO3 and Cl accumulations were restricted to the lower profile of cores with appreciable AEC (> 1 cmol(c)/kg). Gaines-Thomas selectivity coefficients were used to indicate exchange preference for cations and anions, and are as follows: Al > Ca similar to Mg > K > Na and sulfate (SO4) > Cl similar to NO3. The selectivity of SO4 increased and the extractable SO4 decreased in the lower profile of all cores. This has important implications for the adsorption of NO3 and Cl. The NO3 and Cl accumulations were shown to correspond to a region of low SO4 occupancy of the exchange sites in the lower profile. Along with the high SO4 selectivity, this suggests that SO4 may control the positioning of the NO3 accumulations. It was concluded that the NO3 accumulations were relatively stable under current management practices, although the reduction in NO3 inputs would likely see the gradual replacement of NO3 with Cl as a result of their comparable selectivity for exchange sites.

Phase equilibria and surface tension of pure fluids using a molecular layer structure theory (MLST) model

This paper presents a new model based on thermodynamic and molecular interaction between molecules to describe the vapour-liquid phase equilibria and surface tension of pure component. The model assumes that the bulk fluid can be characterised as set of parallel layers. Because of this molecular structure, we coin the model as the molecular layer structure theory (MLST). Each layer has two energetic components. One is the interaction energy of one molecule of that layer with all surrounding layers. The other component is the intra-layer Helmholtz free energy, which accounts for the internal energy and the entropy of that layer. The equilibrium between two separating phases is derived from the minimum of the grand potential, and the surface tension is calculated as the excess of the Helmholtz energy of the system. We test this model with a number of components, argon, krypton, ethane, n-butane, iso-butane, ethylene and sulphur hexafluoride, and the results are very satisfactory. (C) 2002 Elsevier Science B.V. All rights reserved.

A technique to assess small-scale heterogeneity of chemical properties in soil aggregates

A new method is presented which allows the separation of the soil aggregate exterior from the aggregate core. The method employs a combination of aggregate freezing with rapid separation of aggregate exteriors using ultrasonic energy. The factors influencing the thickness of the removed aggregate surface layer include water content of the aggregate prior to freezing, temperature difference between that of the frozen aggregate and that of the liquid it is submerged in during sonification, sonification time and energy, and the type of the immersion liquid. The success of the method and the thickness of the removed aggregate surface were examined using barium ( Ba2+) as a tracer. Barium ( as BaCl2) is rapidly absorbed by soil and is present at only very low levels in natural soils. Surface layers of 0.2 - 0.4 cm thickness were successfully removed from aggregates of 1 - 4 cm diameter. Two examples are given from soils in northern NSW to demonstrate the occurrence of small- scale heterogeneity in soil chemical properties. Compared with the surface fraction, a 4 - 7% higher calcium concentration was found in the core fraction of a clay loam soil ( Dermosol). Conversely, on a cracking clay soil ( Vertosol), atrazine concentration was around 15 times greater in the aggregate surface fractions compared with core fractions. Compared with the traditional estimation of soil chemical properties on homogenised bulk soil samples, it is suggested that separate analysis of aggregate surface and core fractions could provide useful additional information on the relationships between soil properties and environmental responses.

Effect of pore-network connectivity on multicomponent adsorption of large molecules

The effect of pore-network connectivity on binary liquid-phase adsorption equilibria using the ideal adsorbed solution theory (LAST) was studied. The liquid-phase binary adsorption experiments used ethyl propionate, ethyl butyrate, and ethyl isovalerate as the adsorbates and commercial activated carbons Filtrasorb-400 and Norit ROW 0.8 as adsorbents. As the single-component isotherm, a modified Dubinin-Radushkevich equation was used. A comparison with experimental data shows that incorporating the connectivity of the pore network and considering percolation processes associated with different molecular sizes of the adsorptives in the mixture, as well as their different corresponding accessibility, can improve the prediction of binary adsorption equilibria using the LAST Selectivity of adsorption for the larger molecule in binary systems increases with an increase in the pore-network coordination number, as well with an increase in the mean pore width and in the spread of the pore-size distribution.