Initial Stages Of Decomposition Research Articles

Domain formation and growth in spinodal decomposition of a binary fluid by molecular dynamics simulations

The two initial stages of spinodal decomposition of a symmetric binary Lennard-Jones fluid have been simulated by molecular dynamics simulations, using a hydrodynamics-conserving thermostat. By analyzing the growth of the average domain size R(t) with time, a satisfactory agreement is found with the R(t) proportional t1/3 Lifshitz-Slyozov growth law for the early diffusion-driven stage of domain formation in a quenched homogeneous mixture. In the subsequent stage of viscous-dominated growth, the mean domain size appears to follow the linear growth law predicted by Siggia.

Decomposition of Juncus seeds in a valley mire (Faroe Islands) over a 900 year period

The influence of past depositional environments on the chemistry of sub-fossil Juncus seed coats (testa) from the top 1 m (corresponding to ca. 900 years of peat accumulation) of a peat bog in the Faroe Islands was examined. The chemistry of the testa of fresh Juncus seeds were characterised using thermally assisted pyrolysis and methylation (THM) in the presence of tetramethyl ammonium hydroxide (TMAH) and ‘type’ compounds were identified, representative of the major chemical groups in the testa (cellulose-related sugars, lignin-related phenolics, fatty acids). The abundance of the ‘type’ compounds in the products from sub-fossil testae (the internal tissues of the seeds do not survive beyond the very early stages of decomposition) was then quantified at contiguous 1 cm depth intervals. Major losses of C 18 unsaturated fatty acid methyl esters and sugars were associated with the fresh to sub-fossil transition at ca. 7 cm depth. The preservation of the phenolic ferulic acid in the seed testa appears to be favoured by the input of small basaltic particles from the nearby stream channel. The mechanism by which inwash of inorganic material may be responsible for the improved chemical preservation of the Juncus seed testa is, however, unclear. The sugars were easily metabolised by microorganisms under aerobic conditions of low water table and preserved under anoxic conditions with high water table, suggesting that a drier mire surface may result in the more efficient depletion of polysaccharides and cellulose during the initial stage of decomposition in the acrotelm.

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

Fast-growing bacteria and fungi are expected to cause the initial stage of decomposition of woody fragments in and on soils, i.e. the respiration of sugars, organic acids, pectin and easily accessible cellulose and hemi-cellulose. However, little is known about the factors regulating initial wood decomposition. We examined the effect of wood fragment size, vertical position, nitrogen addition and soil origin on initial wood decay and on the relative importance of fungi and bacteria therein. Two fractions of birch wood were used in microcosm experiments, namely wood blocks (dimensions: 3 × 0.5 × 0.5 cm) and sawdust (dimensions: 0.5–2 mm). The woody fragments were enclosed in nylon bags and placed on top of- or buried in an abandoned arable soil and in a heathland soil. After 15, 25 and 40 weeks of incubation, fungal biomass was quantified (as ergosterol and chitin content) and bacterial numbers were determined. The results indicated that initial wood decay was mostly caused by fungi; bacteria were only contributing in sawdust in/on abandoned arable soil. Larger fragment size, burial of fragments and nitrogen addition positively influenced fungal biomass and activity. Fungal biomass and decay activities were much lower in woody fragments incubated in/on heathland soil than in those incubated in/on abandoned arable soil, indicating that soil origin is also an important factor determining initial wood decay.

Insect herbivores and their frass affect Quercus rubra leaf quality and initial stages of subsequent litter decomposition

Defoliation‐induced changes in plant foliage are ubiquitous, though factors mediating induction and the extent of their influence on ecosystem processes such as leaf litter decomposition are poorly understood. Soil nitrogen (N) availability, which can be affected by insect herbivore frass (feces), influences phytochemical induction. We conducted experiments to test the hypotheses that insect frass deposition would (1) reduce phytochemical induction following herbivory and (2) increase the decomposition and nutrient release of the subsequent leaf litter. During the 2002 growing season, 80 Quercus rubra saplings were subjected to a factorial experiment with herbivore and frass manipulations. Leaf samples were collected throughout the growing season to measure the effects of frass deposition on phytochemical induction. In live foliage, herbivore damage increased tannin concentrations early, reduced foliar N concentrations throughout the growing season, and lowered lignin concentrations in the late season. Frass deposition apparently reduced leaf lignin concentrations, but otherwise did not influence leaf chemistry. Following natural senescence, litter samples from the treatment groups were decomposed in replicated litterbags for 18 months at the Coweeta Hydrologic Laboratory, NC. In the dead litter samples, initial tannin concentrations were lower in the herbivore damage group and higher in the frass addition group relative to their respective controls. Tannin and N release rates in the first nine months of decomposition were also affected by both damage and frass. However, decomposition rates did not differ among treatment groups. Thus, nutrient dynamics important for some ecosystem processes may be independent from the physical loss of litter mass. Overall, while lingering effects of damage and even frass deposition can therefore carry over and affect ecosystem processes during decomposition, their effects appear short lived relative to abiotic forces that tend to homogenize the decomposition process.

Microbial characteristics during the initial stages of litter decomposition in forest and adjacent cropland soil

To evaluate the functional microbial changes during initial decomposition stages of one model litter type in two ecosystems with lower and higher human impact, straw was buried in nylon bags for 52 days in soil under beech forest and cropland. In the two adjacent soils, microbial biomass in the litter estimated by fumigation-extraction (FE) decreased continuously after day 10 and the substrate-induced respiration (SIR) peaked at day 17. As a result, the SIR-to-FE-ratio referring to the metabolic responsive biomass increased until day 17 and decreased afterwards. This ratio indicated that metabolic responsive biomass became rapidly active and later dormant or inactive, which was most apparent in the forest soil. The basal respiration increased continuously until day 32 and then it decreased. In the first 2 weeks, bacteria estimated with the inhibition technique dominated the microbial biomass on the decomposing litter in the forest soil and fungi dominated the microbial biomass in the cropland soil. Correspondingly, high abundance of nematodes repressed the bacterial biomass in the forest soil and the fungal biomass in the two soils. We conclude that shifts in microbial physiology were similar during oat straw decomposition in the two ecosystems but microbial biomass components changed in a functionally significant manner at the initial decomposition stages of litter.

INTERRELATIONSHIPS AMONG SHRUB ENCROACHMENT, LAND MANAGEMENT, AND LITTER DECOMPOSITION IN A SEMIDESERT GRASSLAND

Encroachment of woody plants into grasslands, and subsequent brush management, are among the most prominent changes to occur in arid and semiarid systems over the past century. Despite the resulting widespread changes in landcover, substantial uncertainty about the biogeochemical impacts of woody proliferation and brush management exists. We explored the role of shrub encroachment and brush management on leaf litter decomposition in a semidesert grassland where velvet mesquite (Prosopis velutina) abundance has increased over the past 100 years. This change in physiognomy may affect decomposition directly, through altered litter quality or quantity, and indirectly through altered canopy structure. To assess the direct and indirect impacts of shrubs on decomposition, we quantified changes in mass, nitrogen, and carbon in litterbags deployed under mesquite canopies and in intercanopy zones. Litterbags contained foliage from mesquite and Lehmann lovegrass (Eragrostis lehmanniana), a widespread, nonnative grass in southern Arizona. To explore short- and long-term influences of brush management on the initial stages of decomposition, litterbags were deployed at sites where mesquite canopies were removed three weeks, 45 years, or 70 years prior to study initiation. Mesquite litter decomposed more rapidly than lovegrass, but negative indirect influences of mesquite canopies counteracted positive direct effects. Decomposition was positively correlated with soil infiltration into litterbags, which varied with microsite placement, and was lowest under canopies. Low under-canopy decomposition was ostensibly due to decreased soil movement associated with high under-canopy herbaceous biomass. Decomposition rates where canopies were removed three weeks prior to study initiation were comparable to those beneath intact canopies, suggesting that decomposition was driven by mesquite legacy effects on herbaceous cover-soil movement linkages. Decomposition rates where shrubs were removed 45 and 70 years prior to study initiation were comparable to intercanopy rates, suggesting that legacy effects persist less than 45 years. Accurate decomposition modeling has proved challenging in arid and semiarid systems but is critical to understanding biogeochemical responses to woody encroachment and brush management. Predicting brush-management effects on decomposition will require information on shrub-grass interactions and herbaceous biomass influences on soil movement at decadal timescales. Inclusion of microsite factors controlling soil accumulation on litter would improve the predictive capability of decomposition models.

Yeasts in peatlands: A review of richness and roles in peat decomposition

The richness and ecological roles of yeasts in peatlands are largely unknown. This paper presents a review of the literature on yeasts in peatlands and also provides new data with species isolated from peatlands in Saskatchewan, Canada, and West Siberia, Russia. To date, 75 yeast taxa have been reported from peatlands, including 46 identified species and 29 isolates identified only to genus or not at all. This represents 5%-10% of known yeasts and about 10% of all peatland fungi. Cryptococcus, Candida, Pichia ,a ndRhodotorula are the most prevalent genera, accounting for 58% of known peatland yeast species. We obtained 34 isolates from western Canadian and West Siberian bog and fen peat, including 12 identified species and eight unidentified taxa. Identified taxa comprised mostly species of Candida, Cryptococcus ,a ndRhodotorula. Unidentified taxa were described based on physiology and morphology. Globally, more species have been reported from bogs than fens (41 vs. 13 taxa), and the species composition differs between the two peatland classes. The effect of depth within the acrotelm on yeast abundance and species composition varies among peatlands. Physiological profiling of the yeasts from our study showed that they can use (poly)saccharides (primarily D-glucose, maltotriose, n-acetyl glucosamine, trehalose, and sucrose), organic acids (primarily D-gluconic acid, fumaric acid, malic acid, and succinic acid), sugar alcohols (primarily D-arabitol, D-mannitol, and D-sorbitol), glycosides (primarily arbutin and salicin), and amino acids (primarily L-glutamic acid) as carbon and nitrogen sources. Based on these profiles, yeasts likely access simple polymers that leach from senesced and/or dead plant materials in peatlands and probably play important roles during the initial stages of organic matter decomposition.

The Long-term Stability of Sodium Percarbonate in Presence of Zeolite as Measured by Heat Flow Calorimetry

Abstract Heat flow calorimetry has been evaluated as an alternative technique to conventional stability testing of sodium percarbonate [15630-89-4] (SPC) based on analysis of the hydrogen peroxide content. Stability tests were performed with different SPC samples as well as under various experimental conditions. In general, stable samples exhibiting high concentration of hydrogen peroxide were accompanied by low heat flow values. It was found that the results obtained by heat flow calorimetry and conventional stability testing were in agreement. It was also demonstrated that the long-term stability could be predicted from heat flow data obtained during the initial stage of decomposition. Furthermore, different manufacturing and experimental conditions were manifested as a change of the heat flow curve. The results indicate that the rate of heat production is closely associated with the stability of sodium percarbonate, i. e. the rate of decomposition of sodium percarbonate. In presence of zeolite the stability of sodium percarbonate was reduced, particularly under humid conditions.

Decomposição de agulhas de Pinus pinaster e de folhas de Eucalyptus globulus em regiões do interior e do litoral de Portugal

Decomposition of needle litter of Pinus pinaster (PP) and leaf litter of Eucalyptus globulus (EG) was assessed using the litterbag methodology. Decomposition rate of these residues and release dynamics of nutrients with more relevance to the sustainability of forest systems were measured. The study was carried out in the litoral of Central Portugal (Furadouro,Obidos), using both PP and EG, in inland of North Portugal (Vila Pouca de Aguiar), using PP, and in an intermediate climate condition (Pegoes, Rio Maior), using EG. Decomposition rate of PP was lower than that observed for EG, differences being more pronounced in the initial stage of decomposition (first six months), when weight loss of the former was about one half of that observed for the latter. During the initial phase of decomposition of both PP and EG there was a remarkable release of P, K and Mg. N was rapidly released from EG with highest decomposition rate, and immobilized in PP with lowest decomposition rate. The pattern of Ca dynamics was dependent on species, with a general tendency of releasing from EG and, in contrast to be retained in PP. Green leaves corresponding to harvest residues decomposed and released nutrients faster than senescent leaves of EG.

Thermal Decomposition and Oxidation Ageing Behaviour of Polypropylene/Halloysite Nanotube Nanocomposites

The thermal decomposition and oxidation ageing behaviour of polypropylene (PP) and PP/halloysite nanotube (HNT) nanocomposites were studied. The kinetics of thermal decomposition were calculated by integral models. The thermal oxidation ageing was investigated by Fourier transform infrared spectroscopy (FTIR). The PP nanocomposites showed a higher activation energy of thermal decomposition than neat PP. Their surface treatment and lower HNT loading led to a higher activation energy of decomposition. Their improved thermal stability in nitrogen was attributed to entrapment of decomposition products at initial decomposition stage and to barrier effects. Nanocomposites made by using silane-modified HNT (m-HNT) and also those with lower quantities of (unsilanated) HNT showed improved resistance to thermo-oxidative ageing. The rate of thermo-oxidative ageing was correlated with the number of acidic sites and the volume of entrapped oxygen in the lumen of the HNT and in cavities.

Investigation of new aspects in the initial stages of decomposition of Cu2at.%Co with the tomographic atom probe and the field ion microscope

AbstractThe initial stages of nucleation and precipitation of the Co‐rich phase in a supersaturated Cu2at.%Co alloy were studied with the field ion microscope (FIM) and the tomographic atom probe (TAP). The specimens of nominal composition Cu2at.%Co were homogenised at 1173 K and aged for different times at different temperatures from 703 to 853 K to follow the decomposition path at these reaction temperatures. In this paper, results on the time evolution of the decomposition are presented. New aspects in the decomposition of CuCo were found, which are discussed. At the initial stages of the nucleation, fluctuations were observed, which could be quantitatively characterised.Decomposition was found to take different paths at different annealing temperatures. At 853 K individual precipitates grew, whereas during coarsening the elastic soft [100] directions were preferred.At 763 K, cigar‐shaped precipitates formed along the [100] directions as a metastable state, which degraded into individual spherical precipitates for longer aging times. The initial stages of decomposition were also characterised for 703 K by using the cluster search algorithm. Copyright © 2007 John Wiley & Sons, Ltd.

Initial stage of spinodal decomposition in a rigid-rod system

The initial stage of spinodal decomposition is investigated for a rigid-rod system. Spinodal decomposition proceeds through either of two mechanisms: (1) The randomly aligned rods rotate toward a common director with no inherent length scale. (2) The rods diffuse axially and segregate into regions of common alignment with a selected length scale [script-l]. Previous studies on spinodal decomposition yielded radically different conclusions about which mechanism is dominant. A computational method is employed to analyze the growth rate and properties of the dominant fluctuation mode through an eigenvalue analysis of the linearized Doi diffusion equation in Fourier space. The linearized operator is discretized in Fourier mode and orientation space (k,theta,phi) space, and the maximum eigenvalue and corresponding eigenvector of the operator are calculated. Our analysis generalizes the results of previous studies and shows that the conflicts seen in those studies are due to differences in the diffusivities for rotational motion, motion perpendicular to the rod axis, and motion along the rod axis. For a given system density, a plot of the dominant perturbation wave number k(max) as a function of the diffusivity ratios shows two separate regions corresponding to mechanisms (1) and (2). High rotational diffusivity corresponds to mechanism (1), whereas high axial diffusivity corresponds to mechanism (2). The transition between the two mechanisms depends on the ratio of diffusivities and on system density. Also, the dominant wave number increases with increasing density indicating that a deeper quench into the spinodal regime leads to a smaller characteristic length scale.

Relation of biogenic amines to microbial and sensory changes of precooked chicken meat stored aerobically and under modified atmosphere packaging at 4 °C

The formation of biogenic amines and their correlation to microflora and sensory characteristics of a precooked chicken meat product stored aerobically and under modified atmosphere packaging (MAP) (30% CO2, 70% N2) was studied. Putrescine was the main amine formed both in aerobically and MA-packaged chicken samples. For the rest of the biogenic amines, including tyramine, histamine, and cadaverine, a stepwise increase was recorded throughout the 23-day storage period under the above packaging conditions. Spermidine was found in higher amounts, as compared to spermine in both aerobically and MA-packaged chicken samples at 4 °C. Formation of these amines in precooked chicken stored either aerobically or under a 30% CO2, 70% N2 atmosphere followed an inconsistent trend during the entire storage period at 4 °C. Agmatine, β-phenyl-ethylamine, and tryptamine were not detected in precooked chicken. Of the bacterial groups monitored, lactic acid bacteria (LAB) became the dominant bacteria after day 8 of storage under MAP while LAB were the dominant population of natural microflora of precooked chicken stored both aerobically or under MAP, reaching 7.5 and 8.0 log cfu/g, respectively, on day 23 of refrigerated storage. Enterobacteriaceae populations in chicken meat were below the detection limit (<1 log cfu/g) by pour plating throughout the 23-day storage period, irrespective of packaging conditions. Based on sensory data, after ca. 8 days for the precooked chicken meat stored aerobically and after 12 days under MAP (time to reach initial decomposition stage, score of 2) the putrescine and tyramine content of chicken samples were ca. 14–19 and 1.4 mg/kg, values that may be proposed as the limit for spoilage initiation of precooked chicken meat (respective TVC for both aerobically and MA-packaged chicken meat were ca. 6.5 log cfu/g).

Interparticle interference and elastic interphase deformations upon X-ray scattering by precipitates statistically distributed in a crystal: III. Analysis of results of applied investigations

Based on theoretical data [1, 2], results of X-ray diffraction investigations of the initial stages of decomposition of Fe-25Ni-25Al and NaCl-AgCl solid solutions have been analyzed critically. It has been established that the interpretation of diffuse effects in diffraction patterns of the Fe-Ni-Al alloy in terms of the three-phase model is wrong; numerous errors and inaccuracies have been revealed in the representation and explanation of diffuse scattering in works devoted to the NaCl-AgCl alloys. A new interpretation of effects of diffuse scattering is given and a quantitative estimation is given to the structural parameters of alloys and elastic interphase stresses. It is shown that diffraction triplets consisting of relatively wide maxima caused by scattering by the matrix and precipitates and of a peaked maximum caused by scattering by both phases can be formed in the fundamental reflections of alloys with precipitates isomorphic to the matrix. Kinetic and structural factors that determine the formation of high magnetic properties, including the high coercive force and magnetic saturation, in the Fe-Ni-Al alloy are discussed. The necessity of a further reconsideration of the results of investigations that rest upon the three-phase model of solid-solution decomposition when interpreting diffuse scattering is noted.

Diaminofurazan (DAF): Thermolysis and evaluation as ballistic modifier in double base propellant

Diaminofurazan (DAF) is used as a precursor in the synthesis of many high performance insensitive high explosives. This paper reports the thermal studies on DAF and its evaluation as a ballistic modifier in double base propellant formulations. Differential scanning calorimetry (DSC) and differential thermal analysis (DTA) revealed that DAF shows two-stage decomposition, whereas the kinetics of initial stage of thermal decomposition of DAF evaluated from TG data gave activation energy ( E a) of 67 kJ mol −1. The evolution of gases containing species such as CN, NH, OH and oxides of nitrogen during thermal decomposition of DAF was also revealed by hyphenated TG–FTIR data. Evaluation of DAF as a ballistic modifier in RDX incorporated double base propellant formulations indicated that it brings down the pressure index to 0.20 compared to 0.70 for a control composition in the pressure range 6.9–8.8 MPa when used in combination with basic lead salicylate (BLS). It was observed that DAF does not have adverse effect on vulnerability and chemical stability of the propellant formulation.

Chemical composition controls residue decomposition in soils differing in initial pH

Laboratory incubation studies were conducted to determine the dynamics of low-molecular-weight aliphatic carboxylic acids and their anions (LACAs) and respiration in three soils incorporated with five types of plant residues differing in chemical composition. Concentrations of total and individual LACAs in soils decreased sharply with initial 3 days after addition of plant residues, and varied with types of plant residue and soil. Irrespective of soil types, the amount of total extractable LACAs was highest in the soils treated with chickpea, followed by lucerne and high-N wheat straw, and lowest with low-N wheat straw. Lancelin soil [initial pH(CaCl 2) 5.06] contained higher concentration of extractable LACAs compared with Bodallin (pH 4.54) and Wodjil soil (pH 3.87). Soil respiration rate was rapidly increased by the addition of plant residues, and reached the peak by Day 3. Respiration rate was the greatest in Lancelin soil and the smallest in Wodjil soil. The amounts of CO 2 respired over 7 days were equivalent to 6–25% of the added C for Wodjil soil, 6–39% for Bodallin soil and 6–47% for Lancelin soil, depending on type of plant residue. Those amounts over 105 days increased further. Irrespective of plant residue and soil type, the cumulative respiration correlated positively with concentrations of N, excess cations and soluble C in plant residues and initial soil pH, and negatively with C:N of plant residues. The results suggest that chemical composition of plant residues plays an important role at the initial stage of residue decomposition.

Studies on diaminoglyoxime (DAG): Thermolysis and evaluation as ballistic modifier in double base propellant

This paper reports thermolysis of diaminoglyoxime (DAG) and its evaluation as a ballistic modifier in double base propellant formulations. Differential scanning calorimetry (DSC) and simultaneous thermal analysis (DTA–thermogravimetric (TG)) revealed that DAG decomposes in two stages. Kinetics of initial stage of thermal decomposition of DAG evaluated from TG data gave activation energy ( E a) of 153 kJ mol −1. The high-temperature Fourier transform Infrared (FTIR) spectra of DAG suggested preferential cleavage of N O and C NH 2 during decomposition. Mass spectral data also suggest possibility of similar process. The hyphenated TG–FTIR data also revealed the evolution of gases containing species, such as CN, NH, OH and oxides of nitrogen during thermal decomposition. Evaluation of DAG as a ballistic modifier in RDX incorporated double base propellant formulations indicated that it brings down the pressure index to 0.17 compared to 0.79 for a control composition in the pressure range 6.9–8.8 MPa when used in combination with basic lead salycilate (BLS). The study suggests that combination of DAG and BLS need to be optimized to achieve more remarkable effects than BLS alone. It was observed that DAG does not have adverse effect on vulnerability and chemical stability of the propellant formulation.

Kinetics of decomposition of poly(vinyl chloride)/low-migration polyesterurethane plasticizer blend - a thermogravimetric study

Kinetics of decomposition of poly(vinyl chloride) (PVC), plasticized either by di(2-ethylhexyl)phthalate (DEHP) or medium molecular weight polyesterurethane (PESTUR) or by both plasticizers, was studied by isoconversionalmethods on the basis of thermogravimetric data under dynamic heating conditions. It has been found that the initial decomposition temperature is higher for PVC plasticized with PESTUR in comparison with PVC plasticized with DEHP or with PESTUR/DEHP, and thermal degradation shows features of multistep complex process. Application of polymeric plasticizer leads to the increase in values and a smoothing effect in the course of energy of activation and pre-exponential factor at initial stage of decomposition indicating thus the hindered migration of medium molecular weight compound from PVC matrix (in comparison with PVC containing monomeric DEHP) due to steric hindrances as well as due to specific interactions between C=O and Cl groups along the macrochains.

Does coarsening begin during the initial stages of spinodal decomposition?

The initial stages of spinodal decomposition were studied by subjecting a critical blend of model polyolefins to a pressure quench and monitoring the evolution by time-resolved small angle neutron scattering. Contrary to the predictions of the widely accepted Cahn-Hilliard-Cook theory, we demonstrate that coarsening of the phase-separated structure begins immediately after the quench and occurs throughout the initial stages of spinodal decomposition.

On the initial stage of spinodal decomposition

A consistent theory describing the initial stage of spinodal decomposition of a two-component system is proposed. It is shown that the structure factor S(q, t) has two maxima as a function of wavenumber at this stage. The main maximum point q+ varies with time, first moving from qsaddle to qm (given by expressions (22) and (12), respectively) and then back after the turning point in time given by (26) is passed. The other maximum point is localized at q ≈ 0, and the corresponding peak amplitude is virtually independent of time. The characteristics of the main maximum are sensitive to the existence of the “zero” peak. Available experimental observations support the predictions of the theory.