Search results for "Station"

An MO study of neutral C8 high-symmetry clusters

1997

Abstract Highly symmetric octacarbon clusters, i.e. a cube (O h ), a twisted cube (T d ), a tricyclic cage (C 3v ) and a planar (D 4h ) structure, were fully optimized at the HF, B3LYP and MP2(Full) levels of theory. These stationary points were shown to be local minima on the potential energy surface by frequency calculations. The stability of these clusters compared to the cyclic planar (C 4h ) ground state was found to be strongly dependent on the level of theory. MP2(Full) calculations suggest that cubic C 8 is a local minimum, its energy being 273 kJ/mol higher than the ground state. Structural parameters and fundamental vibrations are presented.

CPMAS 13C NMR Characterization of Leaves and Litters from the Reafforestated Area of Mustigarufi in Sicily (Italy)

2010

Reafforestation is generally based on the planting of exotic fast growing tree species suitable for adapting to even harsh environments. Once the introduced plants ameliorate soil conditions, they can be progressively replaced by au- tochthonous plant species. Reafforestation is applied worldwide. However, only few studies on the effect of reafforesta- tion on lands from Mediterranean regions are available. This paper reports the characterization by cross polarization 13C NMR spectroscopy of fresh leaves and superficial litters from a reafforestated area in central Sicily (Italy). NMR assign- ment is attempted. A differentiation among the molecular systems within leaves and litters is also …

A Validation Methodology for a Combined Heating Cooling and Power (CHCP) Pilot Plant

2004

A great number of variables significantly influence the energetic, environmental and economic results of CHP (Combined Heating and Power) and CHCP (Combined Heating Cooling and Power) plants operation, and as a consequence their project activity is rather complex. In order to select the best layout and properly size the machines, detailed data on hourly electric, thermal, and cooling demand are necessary, so that a series of plant life cycle simulations may have to be carried out. Unfortunately, such detailed data are rarely available, because energy consumptions data for existing buildings are usually derived from aggregated monthly or bimonthly gas and electricity bills. Even more difficu…

Modelo empírico para la determinación de clorofila-a en aguas continentales a partir de los futuros Sentinel-2 y 3. Validación con imágenes HICO

2014

[EN] Chlorophyll-a concentration is one of the main indicators of inland waters quality. Using CHRIS/PROBA images and in situ data obtained in four lakes in Colombia and Spain, we obtained empirical models for the estimation of chlorophyll-a concentration, which can be directly applied to future images of MSI Sentinel-2 and OLCI Sentinel-3 sensors. The models, based on spectral band indices, were validated with data from the hyperspectral sensor HICO, onboard of the International Space Station.

Stationary phase modulation in liquid chromatography through the serial coupling of columns: A review

2016

Liquid chromatography with single columns often does not succeed in the analysis of complex samples, in terms of resolution and analysis time. A relatively simple solution to enhance chromatographic resolution is the modulation of the stationary phase through the serial coupling of columns. This can be implemented with any type of column using compatible elution conditions and conventional instruments. This review describes the key features of column coupling and published procedures, where two or more columns were coupled in series to solve separation problems. In all reports, the authors could not resolve their samples with single columns, whereas significant enhancement in chromatographi…

Optimization of experimental conditions for the identification of pesticide mixtures on six GLC columns

1994

Study of polychlorinated biphenyls in street dust by supercritical fluid extraction-gas chromatography/mass spectrometry

1996

Street dust samples have been collected from highways, urban streets, a gasoline station, a pedestrian tunnel, and railway stations in some German cities. Nine polychlorinated biphenyls (PCBs from tri- to heptachlorobiphenyls) were quantitatively extracted by supercritical fluid extraction with CO2 at 200 bar and 40°C and analyzed by gas chromatography/mass spectrometry. The highest PCB loads (sum of the nine studied PCBs) of ca. 1 to 4 μg/g have been found in the samples from motorway A60 near Mainz, while in almost all other samples PCBs could be detected at only ca. 0.1 to 1 μg/g. At three sampling sites, a winter maximum of the PCB concentrations has been found.

Chromatographic Efficiency in Micellar Liquid Chromatography: Should it Be Still a Topic of Concern?

2013

Micellar liquid chromatography (MLC) was first proposed as an attractive alternative to avoid the use of organic solvents. It was soon apparent that pure micellar solutions yield poor efficiencies. This problem was remediated by the addition of a small amount of an organic solvent. However, the general opinion of the poor peak shape has prevailed as a handicap for MLC, in spite of the fact that the hybrid mode often offers similar or even improved efficiencies (for basic compounds) relative to that attained in the hydro-organic mode. Only the efficiencies for apolar non-ionizable compounds are still clearly inferior. This work describes the type of interactions and polarity changes with org…

Gas-liquid chromatographic analyses

1984

A mixture of all nine chlorinated 4-hydroxybenzaldehydes and the parent homologue was separated on a non-polar SE-30 capillary column using various isothermal and temperature-programmed operating conditions. The relative retention data for the compounds are given and the retention indices together with the retention index increments for each position of chlorine substitution are examined. The retention order 3-Cl<parent<2,5-di-Cl<2,3-di-Cl<3,5-di-Cl<2-Cl<2,3,5-tri-Cl<2,3,6-tri-Cl<2,6-di-Cl<tetra-Cl isomer obtained indicates that the effect of the position of substitution on the retention behaviour is greater than that of the number of chlorine atoms. The retention is maximal with 2-Cl and 2…

Study of Chromatographic Properties of Catecholamines and their Acidic Metabolites Using Novel Molecularly Imprinted Polymers as Stationary Phases

2021

Quantitative analysis of catecholamines and their acidic metabolites can provide vital information for diagnosis and treatment of various diseases (such as adrenal tumors). However, complicated purification protocols are usually required to isolate the analytes. Molecularly imprinted polymers (MIPs) have attracted considerable attention as a method of selectively separating desired compounds from their matrix. Therefore, we propose a synthetic procedure for new molecularly imprinted sorbents that possess selective binding sites for both catecholamines and their acidic metabolites. The new polymer utilizes non-covalent and semi-covalent imprinting methods. The binding properties of MIPs were…