Differential impact of two major polychaete guilds on microbial communities in marine sediments: a microcosm study

Even though sediment macrofauna are widespread in the global seafloor, the influence of these fauna on microbial communities that drive sediment biogeochemical cycles remains poorly understood. According to recent field investigations, macrofaunal activities control bacterial and archaeal community structure in surface sediments, but the inferred mechanisms have not been experimentally verified. Here we use laboratory microcosms to investigate how activities of two major polychaete guilds, the lugworms, represented by Abarenicola pacifica, and the clamworms, represented by Nereis vexillosa, influence microbial communities in coastal sediments. A. pacifica treatments show >tenfold increases in microbial cell-specific consumption rates of oxygen and nitrate, largely due to the strong ventilation activity of A. pacifica. While ventilation resulted in clearly elevated percentages of nitrifying archaea (Nitrosopumilus spp.) in surface sediments, it only minorly affected bacterial community composition. By comparison, reworking – mainly by deposit-feeding of A. pacifica – had a more pronounced impact on microorganismal communities, significantly driving down abundances of Bacteria and Archaea. Within the Bacteria, lineages that have been linked to the degradation of microalgal biomass (e.g., Flavobacteriaceae and Rhodobacteraceae), were especially affected, consistent with the previously reported selective feeding of A. pacifica on microalgal detritus. In contrast, N. vexillosa, which is not a deposit feeder, did not significantly influence microbial abundances or microbial community structure. This species also only had a relatively minor impact on rates of oxygen and nitrogen cycling, presumably because porewater exchanges during burrow ventilation by this species were mainly restricted to sediments immediately surrounding the burrows. Collectively our analyses demonstrate that macrofauna with distinct bioturbation modes differ greatly in their impacts on microbial community structure and microbial metabolism in marine sediments

Thermal barrier coatings on polymer materials

Polyimide matrix composite (PIMC) has been widely used to replace metallic parts due to its low density and high strength. It is considered as an effective approach to improve thermal oxidation resistance, operation temperature and lifetime of PIMC by depositing a protection coating. The objective of the research was to fabricate a series of thermal barrier coatings (TBCs) on PIMC by a combined sol-gel/sealing treatment process and air plasma spraying (APS). By optimizing the experimental parameters, thermal shock resistance, thermal oxidation resistance and thermal ablation resistance of PIMC could be improved significantly. The ZrO2 sol was prepared by sol-gel process and the effects of the different organic additions on phase structure, crystallite size and crystal growth behavior of the ZrO2 nanocrystallite were investigated. The addition of HAc and DMF were beneficial to decrease the crystallite size and alter the activation energy for crystal growth, further inducing the crystallization of ZrO2 nanocrystallite at low temperature (300ºC) and the stability of tetragonal ZrO2 at 600ºC. Based on the optimized parameters of the sol preparation, the ZrO2/phosphates duplex coating was fabricated on PIMC via a combined sol-gel and sealing treatment process. The sealing mechanism of the phosphates in the duplex coating was primarily attributed to the adhesive binding of the phosphates and the chemical bonding between the sealant and the coating. It was demonstrated that the duplex coating exhibited excellent thermal shock resistance and no apparent delamination or spallation occurred. Relatively, the duplex coating with the thickness of 150 μm provided excellent thermal oxidation and thermal ablation resistance for the polymer substrate. However, the presence of cracks and delamination in the coatings provided the channels for oxygen diffusion, causing the final failure of the protection coating. Figure 4 – TBCs on CFPI The Zn/YSZ and Al/YSZ coating systems were successfully deposited on PIMC by APS. Metals with comparatively low melting point as the bond coats (Cu, Al, Zn) were beneficial to increase thermal shock resistance of the coating systems. In comparison with the Al/YSZ coating system, the Zn/YSZ coating exhibited the better thermal shock resistance, which was ascribable to the lower residual stress in the Zn layer after deposition and the lower thermal stress induced during thermal shock test. For these coatings, the increase in surface toughness of the substrate as well as the decrease in thickness of metal layer favored the improvement of thermal shock resistance of the coatings. With the temperature increases, thermal shock lifetime of the coatings decreased disastrously. However, the difference was that the slight increase of the thickness of YSZ layer favored the increase in thermal shock resistance of the Al/YSZ coatings, while for the Zn/YSZ coating systems the increase in the thickness of YSZ layer made thermal shock resistance weaken. Owing to the protection of Zn/YSZ and Al/YSZ coating systems, the time for 5 wt% weight loss of the sample was prolonged from 16 h to 50 h when oxidation at 400ºC; as the oxidation temperature increased to 450ºC, the time for 5wt% weight loss was extended from 5 h to 13 h. By depositing different coatings, the anti-ablation property of PIMC was significantly improved. During property testing, the formation of cracks and delamination in the coating and the occurrence of the spallation led to the failure of the coating systems, which was mainly due to the residual stress during the deposition process, thermal stress induced by the mismatch in thermal expansion coefficient and further oxidation of the substrate. Please click Additional Files below to see the full abstract

Correlation between porosity, amorphous phase and CMAS corrosion behaviour of LaMgAl11O19 thermal barrier coatings

Calcium-magnesium-alumino-silicate (CMAS) attack is one of the significant failure mechanisms of thermal barrier coatings (TBCs), which can facilitate TBC’s degradation at elevated temperatures. To clarify the correlation between the porosity, CMAS corrosion behaviour, lanthanum magnesium hexaluminate (LaMgAl11O19, LMA) TBCs were prepared by atmospheric plasma spraying (APS) and then heat-treated at 1173K and 1523K, respectively. For comparison, LMA tablets were prepared by mechanical and cold isostatic pressing. CMAS attack at 1523K was carried out both for LMA tablets and LMA coatings. Their microstructure, phase composition, and crystallization behavior after CMAS attack were investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction as well as differential scanning calorimetry (DSC). The results indicated that CMAS attack was arrested for LMA tablets due to the formation of a dense crystalline layer induced by the chemical interactions between LMA and CMAS glass, while the as-sprayed LMA coatings were completely penetrated by molten CMAS due to the presence of amorphous phase and connected pores. Although the isothermal heat-treatment promoted a crystallization of LMA coatings, much vertical cracks formed during heat-treatment. The heat-treated LMA coatings suffered a severer CMAS attack than the as-sprayed one, since the vertical cracks inevitably provided efficient infiltration paths for molten CMAS

Carbohydrate compositional trends throughout Holocene sediments of an alpine lake (Lake Cadagno)

Carbohydrates are a ubiquitous constituent of organisms and contribute significantly to sedimentary organic carbon pools. Yet, the factors that control the degradation and long-term preservation of sedimentary carbohydrates are not well understood. Here, we investigate carbohydrate pool sizes and chemical compositions in high-altitude, meromictic Lake Cadagno (Switzerland) over a 13,500-year-old sedimentary succession that has recorded past changes from oxic to anoxic conditions and consists mostly of intercalations of lacustrine sediments and terrestrial-derived sediments. Analyses of the organic matter chemical composition by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) show that carbohydrates are selectively preserved over other organic matter constituents over time. The carbohydrate pyrolysis products levosugars (potentially cellulose-derived) and (alkyl)furans and furanones (potentially pectin-derived) dominate both lacustrine and terrestrially derived sediment layers, suggesting aquatic and terrestrial-derived sources of these compounds. Carbohydrate monomer analyses indicate galactose and glucose as dominant monomers and show no clear differences between aquatic and terrestrial organic matter. No clear impacts of past changes in redox conditions on carbohydrate compositions were observed. Our study shows that carbohydrates are a major contributor to sedimentary organic carbon burial in Lake Cadagno and indicates the effective preservation of both aquatic and terrestrial derived carbohydrates over millennia in lake sediments

Employment Protection and Domestic Violence: Addressing Abuse in the Labor Grievance Process

The effects of domestic violence are not limited to the home environment. Its effects are felt in employment when abused employees are absent from work and when violent incidents erupt in the workplace. For example, a bruised employee might be too injured and embarrassed to attend work, or an estranged spouse might stalk and harass a victim on the job. Another issue arises in that employers often discipline victims of domestic violence for absenteeism and incidents of violence that occur in the workplace. Discipline of union members is governed by collective bargaining agreements and subject to the labor grievance process. These grievances often end in arbitration, where the union represents the battered employee. Because of this occurrence, employers, unions, and arbitrators must be educated about domestic violence to ensure victims of abuse receive adequate job protection

Interactions between temperature and energy supply drive microbial communities in hydrothermal sediment

Temperature and bioavailable energy control the distribution of life on Earth, and interact with each other due to the dependency of biological energy requirements on temperature. Here we analyze how temperature-energy interactions structure sediment microbial communities in two hydrothermally active areas of Guaymas Basin. Sites from one area experience advective input of thermogenically produced electron donors by seepage from deeper layers, whereas sites from the other area are diffusion-dominated and electron donor-depleted. In both locations, Archaea dominate at temperatures >45 °C and Bacteria at temperatures <10 °C. Yet, at the phylum level and below, there are clear differences. Hot seep sites have high proportions of typical hydrothermal vent and hot spring taxa. By contrast, high-temperature sites without seepage harbor mainly novel taxa belonging to phyla that are widespread in cold subseafloor sediment. Our results suggest that in hydrothermal sediments temperature determines domain-level dominance, whereas temperature-energy interactions structure microbial communities at the phylum-level and below

On the formation of hydrothermal vents and cold seeps in the Guaymas Basin, Gulf of California

Magmatic sill intrusions into organic-rich sediments cause the release of thermogenic CH4 and CO2. Pore fluids from the Guaymas Basin (Gulf of California), a sedimentary basin with recent magmatic activity, were investigated to constrain the link between sill intrusions and fluid seepage as well as the timing of sill-induced hydrothermal activity. Sampling sites were close to a hydrothermal vent field at the northern rift axis and at cold seeps located up to 30km away from the rift. Pore fluids close to the active hydrothermal vent field showed a slight imprint by hydrothermal fluids and indicated a shallow circulation system transporting seawater to the hydrothermal catchment area. Geochemical data of pore fluids at cold seeps showed a mainly ambient diagenetic fluid composition without any imprint related to high temperature processes at greater depth. Seep communities at the seafloor were mainly sustained by microbial methane, which rose along pathways formed earlier by hydrothermal activity, driving the anaerobic oxidation of methane (AOM) and the formation of authigenic carbonates. Overall, our data from the cold seep sites suggest that at present, sill-induced hydrothermalism is not active away from the ridge axis, and the vigorous venting of hydrothermal fluids is restricted to the ridge axis. Using the sediment thickness above extinct conduits and carbonate dating, we calculated that deep fluid and thermogenic gas flow ceased 28 to 7kyr ago. These findings imply a short lifetime of hydrothermal systems, limiting the time of unhindered carbon release as suggested in previous modeling studies. Consequently, activation and deactivation mechanisms of these systems need to be better constrained for the use in climate modeling approaches

A versatile nodal energy consumption monitoring method for wireless sensor network testbed

Energy efficiency is a critical criterion in wireless sensor networks (WSN). Given the energy consumption of a node, or even the whole network, is precisely measured. Great improvement can be expected in the WSN system optimization. In this paper, we propose a versatile nodal energy consumption monitoring schema, which precisely measures the energy consumption of each node at any moment. In addition, our schema can be integrated with existing testbed technologies to measure the energy consumption of the overall network. Results show that our method can fulfill various challenges in energy consumption measurement in wireless sensor network. We believe the design and implementation of this monitoring schema is an important move towards accurate and flexible energy efficiency analysis. © 2011 IEEE