Search results for "Processes"
showing 10 items of 3831 documents
Soil microbial biomass and activity under different agricultural management systems in a semiarid Mediterranean agroecosystem
2010
Abstract A field experiment was carried out in a semiarid agricultural Mediterranean area located at the “El Teularet” experimental field in the Enguera Sierra (Valencia, southeast Spain) to assess the influence of different agricultural management systems on indicators of soil biological quality and activity (microbial biomass C, basal respiration, C mineralization coefficients, metabolic quotient (qCO2), respiratory quotient (RQ: moles CO2 evolved/moles O2 consumed), soluble C and dehydrogenase, urease, protease-BAA, phosphatase and β-glucosidase activities), one year after treatment establishment. The management practices assayed were as follows: application of the herbicides paraquat, g…
Alkane dehydrogenation on defective BN quasi-molecular nanoflakes: DFT studies
2020
Lower alkanes are feedstocks readily available but relatively inert. The con- version of low cost alkanes to industrially relevant alkenes is usually carried out on metal-based heterogeneous catalysts. Considering both the cost and the potential harmfulness of the metal involved in the dehydrogenation cat- alysts (typically, platinum or chromium), the study of metal-free processes represents an important challenge for the industrial chemistry in order to address more sustainable protocols and different routes either to activate or transform alkanes. Framed in this context, it was investigated, using a den- sity functional theory approach, the potential dehydrogenation activity of de- fectiv…
Influence of HCl pretreatment and organo-mineral complexes on laser diffraction measurement of loess–paleosol-sequences
2016
Abstract The influence of different sample pretreatment methods on grain size distributions in particle size analysis has been subject to controversial discussions. Standard sample preparation typically comprises the disaggregation of aggregated and agglomerated particles into single primary particles, i.e., the organic binding material is oxidized by hydrogen peroxide (H2O2) and the contained carbonates are dissolved by hydrochloric acid (HCl). The aim of this study is to evaluate the effects of HCl treatment on grain size analyses of Late Pleistocene and Holocene loess–paleosol-sequences investigated by a Beckman Coulter LS 13320 laser particle analyzer. For this purpose, samples from two…
Soil water repellency assessment in olive groves in Southern and Eastern Spain
2016
Soil water repellency (SWR) has been reported under different soils, land uses and regions of the world, particularly in forest land and after wildfires, yet the understanding of this variable in agricultural lands is still rather limited. This study presents the characterization from field-based measurements of SWR in four contrasted olive groves (Olea europaea L.) in Spain in terms of different environmental conditions and management: abandoned and commercial farms under permanent cover crop, conventional tillage and herbicide use. The main objectives were [1] to evaluate the potential occurrence, intensity and persistence of soil water repellency in different types of olive groves and [2…
Responses to salt stress in the halophyte Plantago crassifolia (Plantaginaceae)
2004
Abstract General responses to salt stress have been investigated in the halophyte Plantago crassifolia. Seed germination was strongly inhibited by NaCl, although seed viability and germination capacity were not affected by salt pre-treatments. A concentration-dependent inhibition of plant growth was observed in the presence of NaCl, which was accompanied by the accumulation of Na+ ions in the leaves, as determined by cation exchange HPLC. A 20-fold increase of proline content in leaves was observed when plants were treated with 500 m m NaCl, suggesting a protective role against high salinity stress for this amino acid, whose possible mechanism of action is discussed.
Studying the role of protein dynamics in an SN2 enzyme reaction using free-energy surfaces and solvent coordinates
2013
Conformational changes are known to be able to drive an enzyme through its catalytic cycle, allowing, for example, substrate binding or product release. However, the influence of protein motions on the chemical step is a controversial issue. One proposal is that the simple equilibrium fluctuations incorporated into transition-state theory are insufficient to account for the catalytic effect of enzymes and that protein motions should be treated dynamically. Here, we propose the use of free-energy surfaces, obtained as a function of both a chemical coordinate and an environmental coordinate, as an efficient way to elucidate the role of protein structure and motions during the reaction. We sho…
Synthesis and photophysical properties of hyperbranhced polyfluorenes containing 2,4,6-tris(tiophen-2-yl)-1,3,5-triazine as the core
2011
A series of new hyperbranched polymers containing a 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine core unit and polyfluorene chain arms have been synthesized via Suzuki coupling, and characterized by NMR, IR and GPC. All the polymers exhibit good thermal stability with a high decomposition temperature. By changing the 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine/fluorene ratio the UV-vis absorption and emission spectra can be partially tuned. It has been found that the polymers containing a low ratio of 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine units (P1-P3) have an absorption maximum around 385 nm, localized in the polyfluorene chain, and a shoulder around 425 nm ascribable to a charge transfer stat…
Effects of soil compaction, rain exposure and their interaction on soil carbon dioxide emission
2012
Soils release more carbon, primarily as carbon dioxide (CO2), per annum than current global anthropogenic emissions. Soils emit CO2 through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO2 emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO2 emission, however, none exami…
Determination of volatile fatty acids in the hot springs of Vulcano, Aeolian Islands, Italy
1998
Abstract Samples of relatively acid hydrothermal fluids were collected in the spring of 1996 from seeps, springs, and wells on the Island of Vulcano in the southern Tyrrhenian Sea and analyzed for volatile fatty acids 1 using liquid chromatography. Concentrations of VFAs in the seeps were in the range 65–140 ppb formic, 133–184 ppb acetic, and
Influence of soil properties on the aggregation of some Mediterranean soils and the use of aggregate size and stability as land degradation indicators
2001
Abstract Soil aggregation in relation to other soil properties was studied along a climatological transect in the Southeast of Spain. Three sites were selected along this transect ranging from semiarid to subhumid climatological conditions. The aggregate size distribution, the macro and microaggregate stability of the superficial soil horizon and their relations with other soil properties were analysed. Large aggregates (>10, 10–5, 5–2 mm) were present in highest proportions in the most arid of the studied areas. These large aggregates were associated with high values of water-stable microaggregates; however, they did not improve soil structure and are related to high bulk densities and low…