Search results for "carbon"
showing 10 items of 6057 documents
t-Curves for n-Hexane
1992
The adsorption and desorption isotherms of n-hexane on powdered alumina and silica have been studied at 25°C over a wide range of relative pressures. Two t-curves for pore structure analysis are proposed, one for alumina (C = 12) and the second for silica (3 ≤ C ≤ 9). The statistical thickness t of the adsorbed n-hexane layer has been drawn as a function of the relative pressure assuming a maximal thickness of 0.55 nm and a mean thickness of 0.42 nm for the monolayer. The results are discussed in relation to previous published data.
Determination of indoor air quality of a phytosanitary plant.
2011
A new methodology has been developed to determine volatile organic compounds (VOCs) and pesticides in ambient air using membrane based devices as passive samplers. Pesticides were determined by gas chromatography with mass spectrometry detection (GC-MS) after their microwave-assisted extraction (MAE) from the passive sampler and the required clean-up. On the other hand, VOCs were also caught with the same samplers and directly determined by head space (HS) coupled to GC-MS. The use of samplers filled with florisil and activated carbon allows us to catch with a simple device both, VOCs and pesticides, with a high vapor pressure. Results obtained in the deployment of samplers in different sit…
Determination of polycyclic aromatic hydrocarbons in atmospheric particulate matter of Valencia city
1991
Polycyclic aromatic hydrocarbons (PAHs) were determined in atmospheric particulate matter in 11 sites of the Valencia area and at several times during the year. Sample analysis was carried out by ultrasonic acetonitrile extraction followed by reverse phase HPLC separation and fluorescence detection. The maximum concentration of total PAH developed in winter and spring. Mean values per sampling site varied from 0.193 to 1.668 μg/m3 of filtered air. Environmental noise and temperature were determined at those same 11 sites and correlated with PAH levels.
Complex Metabolic Activation Pathways of Polycyclic Aromatic Hydrocarbons: 3-Hydroxy-trans-7,8-Dihydroxy-7,8-Dihydrobenzo[a]Pyrene as a Proximate Mut…
1988
3-Hydroxybenzo[a]pyrene (3-OH-BP) is a major metabolite of benzo[a]pyrene (BP) in various systems. Metabolites of 3-OH-BP, formed by liver enzymes, bind to DNA1,2 and are mutagenic3,4. However, the active species have not yet been identified. Administration of 3-OH-BP to rats results in the excretion of sulfate and glucuronic acid conjugates of 3-hydroxy-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (3-OH-BP-7,8-diol) (Fig. 1) as major metabolites in the bile5. The hydroxyl groups of this triol are structurally superimposable to those of 9-hydroxy-trans-1,2-dihydroxy-1,2-dihydrochrysene (9-hydroxychrysene-1,2-diol, Fig. 1), which is a metabolite of chrysene6,7 and a potent promutagen8,9. 9-…
Effects of compost input and tillage intensity on soil microbial biomass and activity under Mediterranean conditions
2010
Organic amendment and tillage reduction are two common practices to contrast soil organic matter decline, thus promoting sustainable cropping and carbon sequestration. In a horticultural land use system under Mediterranean climate, we evaluated the 9-year effects of two compost inputs (15 and 30 t ha−1 y−1, low and high input, respectively) and two tillage intensities (intensive and reduced) on soil macronutrients concentration, microbial biomass and activity. Total organic C, total N and POlsen were smaller in plots amended at low input, whilst intensive tillage decreased them at both compost inputs. These decreases in intensively tilled plots was ascribed to the disruption of soil aggrega…
Effect of Processing Conditions on the Degradation and on the Recycling of Polycarbonate
2003
Polycarbonate, like other polycondensation polymers, can be easily recycled without significant loss of properties only with careful drying. Indeed, the presence of humidity strongly decreases the molecular weight of the polymer by hydrolytic chain scission. In this paper, the degradation and the recycling of an extrusion grade polycarbonate sample has been investigated considering mainly the effect of the humidity. Some degradation is observed also for the material reprocessed in dry conditions and due to the thermomechanical stress acting on the melt. The chain scission is strongly reduced if the processing is carried out under nitrogen flow. In these conditions less degradation effects …
Effective conductivity in association with model structure and spatial inhomogeneity of polymer/carbon black composites
1996
The relationship between effective conductivity and cell structure of polyethylene/carbon composites as well as between effective conductivity and spatial distribution of carbon black are discussed. Following Yoshida's model both structures can, in a way, be said to be intermediate between the well known Maxwell-Garnett (MG) and Bruggeman (BR) limiting structures. Using TEM photographs on composites with various carbon blacks we have observed that the larger is Garncarek's inhomogeneity measure H of two-dimensional (2D) representative distribution of the carbon black, the smaller is the effective conductivity of the composite.
Electropolymerization of N-methylanthranilic acid and spectroelectrochemical characterization of the formed film
2009
Abstract The electropolymerization of N-methylanthranilic acid (NMAA) is reported in this paper. The monomer is substituted both at ortho- and N-position and, to the best of our knowledge, it has not been previously electropolymerized. Electropolymerization of NMAA was done on glassy carbon and optically transparent (indium) tin oxide electrodes. The obtained films, which are probably of an oligomeric nature (oligoNMMA), were characterized with cyclic voltammetry (CV), in situ UV–vis and Raman spectroscopy, ex situ FTIR spectroscopy and scanning electron microscopy (SEM). Our results show that NMAA can be electropolymerized as thin films in 1.0 M HClO4, but the oxidation and reduction peak …
Long-term cropping systems and tillage management effects on soil organic carbon stocks and steady state level of C sequestration rates in a semiarid…
2010
A calcareous and clayey xeric Chromic Haploxerept of a long-term experimental site in Sicily (Italy) was sampled (0–15 cm depth) under different land use management and cropping systems (CSs) to study their effect on soil aggregate stability and organic carbon (SOC). The experimental site had three tillage managements (no till [NT], dual-layer [DL] and conventional tillage [CT]) and two CSs (durum wheat monocropping [W] and durum wheat/faba bean rotation [WB]). The annually sequestered SOC with W was 2·75-times higher than with WB. SOC concentrations were also higher. Both NT and CT management systems were the most effective in SOC sequestration whereas with DL system no C was sequestered. …
ChemInform Abstract: Enantioselective Addition of Nitromethane to α-Keto Esters Catalyzed by Copper(II)-Iminopyridine Complexes.
2008
The copper complex of a chiral iminopyridine easily prepared from (R)-(−)-fenchone and picolylamine catalyzes the enantioselective Henry (nitroaldol) reaction between nitromethane and α-keto esters. Good yields and modest to good enantioselectivities are obtained for a wide range of α-keto esters, bearing aromatic, alkyl or alkenyl groups attached to the ketone carbonyl group.