Composition Of POM Research Articles

Source, composition and molecular diversity of dissolved and particulate organic matter varied with riparian land use in tropical coastal headstreams

Source, composition and molecular diversity determine the reactivity and stabilization of organic matter (OM, dissolved [DOM]/particulate [POM]), affecting its behavior and fate. Here, multiple spectral and mass spectrometry techniques were applied to examine how riparian land-use shaped the source, composition and molecular diversity of POM and DOM (HDOM) in adjacent headstreams. Compared to HDOM with abundant lignins, microbially-transformed heteroatoms and carboxyl-rich alicyclic acids (CRAMs), POM exhibited higher allochthonous characteristics and more bioactive components, but lower molecular weight and diversity in different land-use-dominated streams. Compared to wetland-dominated headstreams, both POM and HDOM exhibited more terrestrial origin and condensed aromatics/tannins molecules for agriculture-impacted headstreams and bio-labile lipids, proteins and carbohydrates for forest-impacted headstreams. Structural equation mode (SEM) showed that soil-derived DOM (SDOM) showed the most prominent influence on the source, composition and molecular diversity of POM and the source of HDOM. The molecular composition and diversity of HDOM were mainly influenced by soil properties/SDOM and aquatic microorganisms, respectively. Redundancy analysis (RDA) revealed that autochthonous, bio-labile compositions of POM in forest and wetland streams were positively related to aquatic Bacteroidetes/Cyanobacteria, and carbohydrates/biogenic index of SDOM, while that of HDOM were positively linked with aquatic Bacteroidetes/Cyanobacteria, and SDOM molecular diversity. Terrestrial and aromatic POM in agricultural headstreams were associated with aquatic total nitrogen/Actinobacteria, and humification degree, aromatic/phenolic substances of SDOM, while that of HDOM were mainly regulated by aquatic nitrate/total nitrogen/Actinobacteria, and aromatic/carboxylic-containing moieties of SDOM. Noteworthily, the molecular diversity of agricultural OM increased along the soil-stream continuum due to the input of soil condensed aromatics and tannins. The opposite trend was observed in forest and wetland streams due to the input of bioactive carbohydrates and the microbial-degradation in-stream. These results are helpful to predict the behavior and fate of OM and determine effective management strategies in tropical coastal regions undergoing intense anthropogenic alterations.

Effects of glass fiber reinforcing and thermal post‐treatment on the mechanical properties and crystallization behaviors of polyoxymethylene

AbstractPolyoxymethylene (POM)‐based composites reinforced with pristine short glass fiber (SGF) and surface modified SGF with silane coupling agent (SGF550) were prepared by a twin‐screw extruder, and then injection molded via various processing, including natural air‐cooling, water‐cooling, and oven heat‐treating. The mechanical properties, micro‐structures of tensile fracture surfaces and crystallization behaviors were investigated. The results indicated that the above properties were tightly related to the interfacial bonding ability. POM composites reinforced with SGF550 can significantly improve the tensile strength by 33%–43% and the elongation at break by 50% and 66%, comparing with POM/SGF. Further considering the thermal post‐treatments, prompt water‐cooling can induce insufficient crystallization and form tough amorphous regions beneficial to lock firmly with SGF550, thus enhancing the mechanical properties. This work commits to propose an idea to improve performance by means of screening different processing techniques, and provide a route to tailor some nature of thermoplastics to meet practical application. Based on the lightweight trend, these reinforced composites can be made parts with high load‐bearing requirements, instead of the original metals, such as silent gear, automobile, and machinery instruments.

Study of CeO2@ TiO2/ POM and CoFe2O4@ SiO2 / POM Composites as Highly Efficient Eco-friendly Anti-Corrosion Coating for 316 Stainless Steel

Study of CeO2@ TiO2/ POM and CoFe2O4@ SiO2 / POM Composites as Highly Efficient Eco-friendly Anti-Corrosion Coating for 316 Stainless Steel

Chemical composition of labile carbon fractions in Hungarian forest soils: Insight into biogeochemical coupling between DOM and POM

Understanding how the chemical composition of dissolved and particulate organic matter (DOM and POM) is affected by environment factors is critical because these labile pools of carbon are involved in an array of biological, chemical and physical processes. In this study, the chemical composition of DOM and POM was measured in 13 forest soils using UV–Vis spectroscopy, fluorescence spectroscopy with parallel factor analysis (PARAFAC modelling) and FT-IR spectroscopy.There were significant differences between the soils for the SUVA indexes, PARAFAC components and relative intensities of different IR bands. Redundancy analysis (RDA) revealed that soil parameters had a strong influence on the chemical composition of DOM and POM with high constrained variability (77.9 and 77.1 %, respectively). The pH of the soils proved to be an important controlling factor for both DOM and POM, regulating the concentration of the C3 PARAFAC component (low-molecular-weight compounds associated with biological activity) and the aromatic compounds of POM (aromaticity, rA1630 and rA1515). The silt content was the other main regulating factor controlling the chemical characteristics of the labile pool, having a strong negative correlation with the specific UV absorbance (SUVA) values of DOM due to the preferential adsorption of hydrophobic moieties. RDA analysis also revealed that there is a strong correlation between the chemical composition of POM and DOM: the relative amount of aromatic compounds (rA1515, rA1630 for aromatic rings and rA1270 for phenolic compounds) in the POM fraction was closely correlated with the SUVA values of the DOM. This clearly indicates a strong biogeochemical link between the two labile organic carbon fractions; the high molecular weight compounds of the DOM fraction may be derived from lignin-like structures of the POM fraction.

Stable isotopes reveal that fungal residues contribute more to mineral-associated organic matter pools than plant residues

We still lack crucial knowledge about the contribution of plant vs. microbial residues to specific SOM pools, particularly the relative contribution of arbuscular (AM), ectomycorrhizal (ECM), and saprotrophic (SAP) fungi.We investigated sources of particulate and mineral-associated organic matter (POM and MAOM) around trees with distinct mycorrhizal types, Liriodendron tulipifera (AM-association) and Quercus alba (ECM-association), in a temperate deciduous forest in Indiana, USA. Combining 13C and 15N natural abundance analyses with measurements of microbial residues using amino sugars, the isotope signatures of large, medium and small-sized POM and MAOM fractions were compared with those of leaves, roots and biomass of mycorrhizal and saprotrophic fungi. A Bayesian inference isotope mixing model calculated sources of C and N to SOM fractions.While the isotope composition of POM resembled that of plants, MAOM was close to fungal values. This was confirmed by mixing model calculations and microbial residue analysis, which additionally and independent from tree partner suggested saprobic fungi contributing with 4–53% to POM and 23–42% to MAOM, as opposed to ECM contributions.Our results suggest fungal, not plant residues, as the source of the most putatively stable OM pool; thus, altering fungal communities may enhance efforts to increase long-term soil C storage.

The Content and Composition of Organic Matter in Soils of the Subpolar Urals

Soil organic matter at high latitudes is an important and sensitive indicator of climate change. This article describes the main morphological features, chemical properties, and composition of organic matter in the main types of soils along the altitudinal gradient of the Subpolar Urals. Soils formed in the mountain tundra zone (gleyic humus-illuvial podbur/Skeletiс Stagnic Entic Podzol (Turbic)), in the mountain subalpine zone (gray-humus soil/Skeletiс Umbrisol), in the mountain taiga zone (iron-illuvial podzol/Skeletiс Albic Podzol), and in the mountain tundra zone with permafrost (permafrost-affected gleyic humus-illuvial podbur/Skeletiс Folic Cryosol (Humic)) were studied. The method of densimetric fractionation was applied to study soil organic matter; it enabled us to distinguish its three fractions, differing in carbon participation in the biological turnover: free particulate organic matter (fPOM 1.6). The latter fraction dominated in the upper mineral soil horizons and comprised 89–93% of the total organic carbon. The content of light fractions was significantly lower (0.6–4.7%). However, the content of organic carbon and nitrogen in the studied soils directly correlated with the contents of light fractions fPOM<1.6 (r = 0.40 and r = 0.79, p < 0.05) and oPOM<1.6 (r = 0.68 and r = 0.83, p < 0.05). Aliphatic fragments dominated in the composition of POM; their content varied from 74.5 to 80.5% for fPOM<1.6 and from 77.9 to 84.2% for oPOM<1.6. In addition, it was found that the organic matter of the oPOM<1.6 fraction was characterized by a higher decomposition rate (0.4–2.4) and hydrophobicity (34.7–66.5%).

Flame retardant effect and mechanism of benzoxazine as synergist in intumescent flame‐retardant polyoxymethylene

Benzoxazine monomers of traditional bisphenol‐A benzoxazine (BA‐a) and bisphenol‐A benzoxazine containing trialkoxysilane (BA‐a‐Si) were synthesized and incorporated into polyoxymethylene/ammonium polyphosphate/melamine (POM/APP/ME) to improve the fire retardancy of POM. The flame retardation, thermal, and mechanical properties of POM composites were evaluated by cone calorimeter, limiting oxygen index (LOI), and the Underwriters Laboratories‐94 (UL‐94) vertical burning tests, as well as thermogravimetric analysis and mechanical tests. Addition of BA‐a‐Si (2 wt%) into POM could simultaneously improve its flame retardancy (UL‐94 vertical burning rating to V‐0 rating and LOI value reached 52.1%) and notched impact strength (increased by 33.3% and 100.0% compared with that of POM/APP/ME and POM/APP/ME/BA‐a composites). Notably, compared with POM/APP/ME composite, the smoke productions of both the composites with benzoxazines were significantly suppressed. In contrast, the peak heat release rate and total heat release of composite with 2 wt% BA‐a‐Si were 33.3% and 32.9% lower than those of composite with 2 wt% BA‐a, which were closely related to the formation of high quality and quantity of charred residue. In summary, benzoxazine, especially siloxane‐containing benzoxazine, plays an effective role in flame retarding POM acting as charring agent and synergistic flame retardant.

River discharge effects on the contribution of small-sized phytoplankton to the total biochemical composition of POM in the Gwangyang Bay, Korea

It is hypothesized that the proportion of small phytoplankton increases if the water temperature increases. However, limited information on the biochemical compositions of small phytoplankton and their ecological contributions is currently available for estuary and coastal environments. In the present study, our goal is to determine the roles of small phytoplankton under different environmental conditions, which influence higher trophic consumers. Water samples were obtained in the Gwangyang Bay, Korea from 2012 to 2014. The contribution of small phytoplankton to the total chlorophyll-a (chl-a) concentration increased from the first period (October 2012–April 2013) to the following period (August 2013–April 2014), which was mainly due to lower nutrient inputs available to phytoplankton because of decreasing river input. Based on biochemical compositions (carbohydrates, proteins, and lipids), the overall contributions of small phytoplankton to the total food material (FM) and caloric content were significantly higher than the chl-a contribution of small phytoplankton. This result indicates that the small phytoplankton assimilated more FM and energy per unit of chl-a concentration compared to those of the large phytoplankton. These findings reveal that the potential impacts of river inputs on phytoplankton cell size and the photosynthetic biochemical composition of this primary food source should be considered in coastal management plans for anthropogenic influences, such as dam constructions.

Composition and vertical flux of particulate organic matter to the oxygen minimum zone of the central Baltic Sea: impact of a sporadic North Sea inflow

Abstract. Particle sinking is a major form of transport for photosynthetically fixed carbon to below the euphotic zone via the biological carbon pump (BCP). Oxygen (O2) depletion may improve the efficiency of the BCP. However, the mechanisms by which O2 deficiency can enhance particulate organic matter (POM) vertical fluxes are not well understood. Here, we investigate the composition and vertical fluxes of POM in two deep basins of the Baltic Sea (GB: Gotland Basin and LD: Landsort Deep). The two basins showed different O2 regimes resulting from the intrusion of oxygen-rich water from the North Sea that ventilated the water column below 140 m in GB, but not in LD, during the time of sampling. In June 2015, we deployed surface-tethered drifting sediment traps in oxic surface waters (GB: 40 and 60 m; LD: 40 and 55 m), within the oxygen minimum zone (OMZ; GB: 110 m and LD: 110 and 180 m) and at recently oxygenated waters by the North Sea inflow in GB (180 m). The primary objective of this study was to test the hypothesis that the different O2 conditions in the water column of GB and LD affected the composition and vertical flux of sinking particles and caused differences in export efficiency between those two basins. The composition and vertical flux of sinking particles were different in GB and LD. In GB, particulate organic carbon (POC) flux was 18 % lower in the shallowest trap (40 m) than in the deepest sediment trap (at 180 m). Particulate nitrogen (PN) and Coomassie stainable particle (CSP) fluxes decreased with depth, while particulate organic phosphorus (POP), biogenic silicate (BSi), chlorophyll a (Chl a) and transparent exopolymeric particle (TEP) fluxes peaked within the core of the OMZ (110 m); this coincided with the presence of manganese oxide-like (MnOx-like) particles aggregated with organic matter. In LD, vertical fluxes of POC, PN and CSPs decreased by 28 %, 42 % and 56 %, respectively, from the surface to deep waters. POP, BSi and TEP fluxes did not decrease continuously with depth, but they were higher at 110 m. Although we observe a higher vertical flux of POP, BSi and TEPs coinciding with abundant MnOx-like particles at 110 m in both basins, the peak in the vertical flux of POM and MnOx-like particles was much higher in GB than in LD. Sinking particles were remarkably enriched in BSi, indicating that diatoms were preferentially included in sinking aggregates and/or there was an inclusion of lithogenic Si (scavenged into sinking particles) in our analysis. During this study, the POC transfer efficiency (POC flux at 180 m over 40 m) was higher in GB (115 %) than in LD (69 %), suggesting that under anoxic conditions a smaller portion of the POC exported below the euphotic zone was transferred to 180 m than under reoxygenated conditions present in GB. In addition, the vertical fluxes of MnOx-like particles were 2 orders of magnitude higher in GB than LD. Our results suggest that POM aggregates with MnOx-like particles formed after the inflow of oxygen-rich water into GB, and the formation of those MnOx–OM-rich particles may alter the composition and vertical flux of POM, potentially contributing to a higher transfer efficiency of POC in GB. This idea is consistent with observations of fresher and less degraded organic matter in deep waters of GB than LD.

Trophic cues promote secondary migrations of bivalve recruits in a highly dynamic temperate intertidal system

AbstractPost‐settlement dispersal is a key process in the recruitment of bivalves. To assess the role of such secondary migrations and to identify potential associated triggers, we conducted an in situ sampling survey during the summer recruitment period on the bivalve assemblages of a coarse‐sediment temperate tidal habitat in the Chausey archipelago (Normandy, France). The dynamics of drifters were studied using three types of settler traps (for example, bedload, pelagic, and sinking transports), and we monitored both the abiotic (hydrological and hydrodynamic conditions) and the trophic (nano‐ and pico‐sized particulate organic matter [POM]; fatty acid composition of POM and sediment organic matter [SOM]) environmental parameters. Such an approach allows the discrimination of passive migration (due to sediment erosion by tidal currents and waves) from active migration (related to recruit behavior). Secondary migrations were observed in 25 bivalve taxa, and these mainly involved decreasing abundances of Mytilidae, Nuculidae, Semelidae, Mactridae, and Lucinidae individuals on the study site, highlighting the crucial role of these processes in highly dynamic coastal benthic assemblages. Surprisingly, the intense post‐settlement dispersal observed at the end of the recruitment season was not synchronized with periods of high hydrodynamic stress but to a change in the structure of phytoplanktonic assemblages, particularly the nanoeukaryotic component. Such a response by bivalve recruits to a trophic pelagic cue—triggering secondary migrations—could result from an increased demand for energy required for active migratory behavior.

Molecular fingerprinting of particulate organic matter as a new tool for its source apportionment: changes along a headwater drainage in coarse, medium and fine particles as a function of rainfalls

Abstract. Tracking the sources of particulate organic matter (POM) exported from catchments is important to understand the transfer of energy from soils to oceans. The suitability of investigating the molecular composition of POM by thermally assisted hydrolysis and methylation using tetramethylammonium hydroxide directly coupled to gas chromatography and mass spectrometry is presented. The results of this molecular-fingerprint approach were compared with previously published elemental (% C, % N) and isotopic data (δ13C, δ15N) acquired in a nested headwater catchment in the Piedmont region, eastern United States of America (12 and 79 ha). The concordance between these results highlights the effectiveness of this molecular tool as a valuable method for source fingerprinting of POM. It emphasizes litter as the main source of exported POM at the upstream location (80±14 %), with an increasing proportion of streambed (SBed) sediment remobilization downstream (42 ± 29 %), specifically during events characterized by high rainfall amounts. At the upstream location, the source of POM seems to be controlled by the maximum and median hourly rainfall intensity. An added value of this method is to directly investigate chemical biomarkers and to mine their distributions in terms of biogeochemical functioning of an ecosystem. In this catchment, the distribution of plant-derived biomarkers characterizing lignin, cutin and suberin inputs were similar in SBed and litter, while the proportion of microbial markers was 4 times higher in SBed than in litter. These results indicate that SBed OM was largely from plant litter that has been processed by the aquatic microbial community.

Isotopic composition of nitrate and particulate organic matter in a pristine dam reservoir of western India: implications for biogeochemical processes

Abstract. Isotopic composition of nitrate (δ15N and δ18O) and particulate organic matter (POM; δ15N and δ13C) were measured in the Tillari Reservoir, located at the foothills of the Western Ghats, Maharashtra, western India. The reservoir, which is stratified during spring–summer and autumn seasons but gets vertically mixed during the southwest monsoon (SWM) and winter, is characterized by diverse redox nitrogen transformations in space and time. The δ15N and δ18O values of nitrate were low (δ15N = 2–10 ‰, δ18O = 5–8 ‰) during normoxic conditions but increased gradually (the highest at δ15N = 27 ‰, δ18O = 29 ‰) when anoxic conditions facilitated denitrification in the hypolimnion during spring–early summer. Once nitrate was fully utilized and sulfidic conditions set in, NH4+ became the dominant inorganic N species, with δ15N ranging from 1.3 to 2.6 ‰. Low δ15N (∼ −5 ‰) and δ13C (−37 to −32 ‰) of POM co-occurring with high NH4+ and CH4 in sulfidic bottom waters were probably the consequence of microbial chemosynthesis. Assimilation of nitrate in the epilimnion was the major controlling process on the N isotopic composition of POM (δ15N = 2–6 ‰). Episodic low δ15N values of POM (−2 to 0 ‰) during early summer, coinciding with the absence of nitrate, might arise from N fixation, although further work is required to confirm the hypothesis. δ13C POM in the photic zone ranged between −29 and −27 ‰ for most parts of the year. The periods of mixing were characterized by uniform δ15N–NO3− and δ18O–NO3− at all depths. Higher POM (particulate organic carbon, POC, as well as particulate organic nitrogen, PON) contents and C ∕ N values with lower δ13C POM during the SWM point to allochthonous inputs. Overall, this study, the first of its kind in the Indian subcontinent, provides an insight into biogeochemistry of Indian reservoirs, using stable carbon and nitrogen isotopes as a tool, where the monsoons play an important role in controlling vertical mixing and dynamics of carbon and nutrients.

TPU Inclusion Complex Modified POM: Fabrication of High Performance POM Composites with Both Excellent Stiffness–Toughness Balance and Thermostability

The inclusion complex of thermoplastic polyurethane (TPU) and β-cyclodextrins (β-CD) with high TPU contents has been synthesized. The channel structure with large amount of uncovered TPU was confirmed by wide-angle X-ray diffraction (WAXD). High performance poly(oxymethylene) (POM) alloys were fabricated by simply melt mixing neat POM with the synthesized TPU inclusion complex (IC-TPU). The effects of the incorporation of IC-TPU on the structure and properties of POM have been investigated. Scanning electron microscope (SEM) results showed that IC-TPU was dispersed uniformly in POM matrix and there was robust interface between IC-TPU and POM matrix. Tensile test results indicated significant improvement in both strength and ductility of the IC-TPU modified POM as compared with neat POM. Moreover, the incorporation of IC-TPU resulted in the drastically enhanced thermal stability of POM. The initial degradation temperature increased as high as 40 °C with the addition of a small amount of IC-TPU. The investi...

Major Sources of Organic Matter in a Complex Coral Reef Lagoon: Identification from Isotopic Signatures (δ13C and δ15N).

A wide investigation was conducted into the main organic matter (OM) sources supporting coral reef trophic networks in the lagoon of New Caledonia. Sampling included different reef locations (fringing, intermediate and barrier reef), different associated ecosystems (mangroves and seagrass beds) and rivers. In total, 30 taxa of macrophytes, plus pools of particulate and sedimentary OM (POM and SOM) were sampled. Isotopic signatures (C and N) of each OM sources was characterized and the composition of OM pools assessed. In addition, spatial and seasonal variations of reef OM sources were examined. Mangroves isotopic signatures were the most C-depleted (-30.17 ± 0.41 ‰) and seagrass signatures were the most C-enriched (-4.36 ± 0.72 ‰). Trichodesmium spp. had the most N-depleted signatures (-0.14 ± 0.03 ‰) whereas mangroves had the most N-enriched signatures (6.47 ± 0.41 ‰). The composition of POM and SOM varied along a coast-to-barrier reef gradient. River POM and marine POM contributed equally to coastal POM, whereas marine POM represented 90% of the POM on barrier reefs, compared to 10% river POM. The relative importance of river POM, marine POM and mangroves to the SOM pool decreased from fringing to barrier reefs. Conversely, the relative importance of seagrass, Trichodesmium spp. and macroalgae increased along this gradient. Overall, spatial fluctuations in POM and SOM were much greater than in primary producers. Seasonal fluctuations were low for all OM sources. Our results demonstrated that a large variety of OM sources sustain coral reefs, varying in their origin, composition and role and suggest that δ13C was a more useful fingerprint than δ15N in this endeavour. This study also suggested substantial OM exchanges and trophic connections between coral reefs and surrounding ecosystems. Finally, the importance of accounting for environmental characteristics at small temporal and spatial scales before drawing general patterns is highlighted.

New Aluminum Foam/Polyformaldehyde Interpenetrating Phase Composites Prepared by Injection Molding

A new type of interpenetrating phase composite was formed by filling 70%-porous open-cell aluminum foam with polyformaldehyde through injection molding process. The results showed that both mechanical properties and tribological behavior of composites were improved. The interphase behaviour of aluminum foam/polyformaldehyde composites was examined by scanning electron microscopy(SEM).The worn surfaces of composites were also examined and discussed. It could be indicated that injection molding and Al foam surface preprocessing including both alkaline wash and KH550 treatment for Al foam/ POM composites was available. The new composite could be used where moderate strength and wear properties are needed.

Elemental and isotopic characterization of dissolved and particulate organic matter in a unique California upwelling system: Importance of size and composition in the export of labile material

We report the interseasonal variation in bulk elemental and stable isotopic (δ13C, δ15N) composition of dissolved and particulate organic matter (DOM, POM) during a high‐resolution time series (2007–2009) on the Big Sur coast. In addition to interseasonal variations, we explore the relationships between physical size and reactivity (i.e., composition) of exportable organic matter (OM) pools, and characterize the elemental and isotopic composition of size‐fractionated POM and DOM pools within this potentially high‐nutrient, low‐chlorophyll (HNLC) California upwelling region. Average POM concentrations were low (&lt; 5.2 µmol C L−1 and &lt; 0.7 µmol N L−1), and all OM pools had low C : N ratios (DOM average = 15.0 and POM &lt; 7.8)—indicating that this upwelling center may represent an important source of N‐rich material to offshore environments. Seasonal “excess” dissolved organic carbon (DOC) production was significant (~ 30–80 µmol L−1 DOC); however, dissolved organic nitrogen (DON) production and cycling was largely decoupled from both DOC and physical processes. Overall, our results are consistent with this region representing an “HNLC upwelling system.” The distinct bulk elemental and isotopic OM composition and seasonality vs. that of high‐productivity upwelling regions highlights the need to better understand the biogeochemical diversity of upwelling systems. Finally, we observed a quantifiable size–composition relationship across both POM and DOM size classes, perhaps representing a powerful new tool for modeling N vs. C fluxes in ocean biogeochemical cycles.

Influence of nano-SiO2 and carbon fibers on the mechanical properties of POM composites

Polyoxymethylene/carbon fiber(POM/CF)composites containing nano-SiO2 were prepared, and their mechanical properties were investigated. At a content of 1-5 vol.%, the nano-SiO2 exerted an obvious reinforcing effect on POM, leading to an increase in the elastic modulus and stiffness of the composites.

Effect of nanofiller aspect ratio on the stress relaxation and creep response of toughened pom composites

Ternary composites composed of polyoxymethylene (POM), polyurethane (PU), and sodium fluorohectorite (FH) or sodium bentonite (BN) were produced by the melt compounding masterbatch (MB) technique. The related MB was produced by mixing the PU latex with water-swellable FH or BN. The dispersion of the nanofillers in the composites was studied by X-ray diffraction techniques. The crystallization of the POM-based systems was inspected by polarized optical microscopy (PLM). The stress relaxation and creep properties of the composites were determined in short-time stress relaxation and creep tests (creep at various temperatures), respectively. The POM/PU/FH composites produced by the MB technique outperformed the POM/PU blend and the POM/PU/BN system in respect to most of the stress relaxation and creep characteristics. This fact was attributed to the higher aspect ratio of FH compared with that of BN. The master curves (creep compliance vs. time) constructed by employing the time-temperature superposition principle showed that the Findley power law was fully applicable to the experimental results obtained.

Tribological Performance of POM, PTFE and PSU Composites Used in Electrical Engineering Applications

In this experimental study, the tribological performance of polysulfone, poly-tetra-fluoro-ethylene, poly-oxy-methylene composites sliding against a poly-phenylene-sulfide polymer composite was studied. Tribological experiments were run under dry ambient conditions and at sliding speeds of 0.5–1.5 m/s under nominal load values of 20–40 N. Results for tested materials showed for the range of applied load and sliding speed values of this investigation that the friction coefficient and the wear rate are much more sensitive to the change in sliding speed rather than to the change in applied load values. The wear mechanism is mainly an adhesive process, but includes some abrasive process as well.

Autochthonous and allochthonous plant contributions to coastal benthic detritus deposits: a dual-stable isotope study in a volcanic lake

The high numbers of primary producers represent multiple sources of organic matter accumulating onto lake bottoms. The difficulty of distinguishing the relative contribution to the mixture presents considerable challenges to the analysis of these organic deposits. In this study, dual-stable isotope analysis and IsoSource model were used to identify allochthonous and autochthonous components of detritus deposits (Particulate Organic Matter: POM) at two different bottom slope sites of a volcanic lake (lake Bracciano). Experiments were carried out to calibrate IsoSource on constructed plant mixtures and assess changes in isotope ratios during plant decomposition. IsoSource satisfactorily discriminated the constructed mixture sources with a few exceptions. Changes in isotopic enrichment during decomposition were low, and thus did not represent a confounding variable in the isotopic analysis. By contrast, chemical and geological differences of the study sites were associated with differences in plant δ13C and δ15N values (more than 2‰ within single plant species). At both sites, the isotopic signals of POM fell between polygons delineated by source end members with an evident shift of δ13C toward allochthonous sources. POM amount and diversity were greater at the flatter bottom site, where allochthonous contributions were larger than at the other site. In particular, IsoSource ranked species contributions as follows: A. glutinosa > P. australis > A. donax > S. alba > P. nigra > the benthic macroalga Chara sp. at the first site, and A. glutinosa > P. nigra > the aquatic macrophyte C. demersum at the latter. The composition of littoral POM was determined by allochthonous sources in proportion to their relative abundances (as percent land cover) with differences between sites due to bottom slope.