Search results for "electromagnetic [radiation]"
showing 10 items of 873 documents
Theoretical electronic spectra of 2-aminopurine in vapor and in water
2006
The accurate quantum chemical CASSCF and CASPT2 methods combined with a Monte Carlo procedure to mimic solvation effects have been used in the calculation of the spectroscopic properties of two tautomers of 2-aminopurine (2AP). Absorption and emission spectra have been simulated both in vacuum and in aqueous environment. State and transition energies and properties have been obtained with high accuracy, leading to the assignment of the most important spectroscopic features. The lowest-lying 1 (,*) ( 1 La) state has been determined as responsible for the first band in the absorption spectrum and also for the strong fluorescence observed for the system in water. The combined approach used in …
Reactor model for fast reactions in the micro-bubble column and validation
2007
A simple reactor model for predicting conversions in a micro-bubble column is described. It assumes fast reactions so that the gaseous component is readily consumed at the gas-liquid interface. Then, gas-liquid mass transfer becomes determining. As input parameters for the model, the hydrodynamics, specific interfacial area, and mass transport need to be described. Two fast model reactions, the catalytic oxidation of butyraldehyde and the absorption of CO2 in aqueous NaOH, show the applicability of the model but also its limits. The model was used for predicting reaction performance in dependence of operating conditions, in particular to get maximum conversion with the antagonistic paramete…
Determination of the number densities of argon metastables in argon-hydrogen plasma by absorption and self-absorption methods
2006
The number densities of Ar 3s23p54s levels have been measured by means of two methods: a self-absorption method with a mirror behind the discharge vessel and an absorption method with a high-frequency electrodeless discharge lamp. Concentrations ranging from 6 × 107–4 × 109 cm−3 were obtained for the Ar 3s23p54s levels, depending on the argon content (10–100% Ar) in Ar/H2 microwave plasma. The populations of various sublevels of measured resonant and metastable states coincide within the experimental errors. It was observed that values from measurements of both methods are in good agreement.
Observation of Poincaré-Andronov-Hopf Bifurcation in Cyclotron Maser Emission from a Magnetic Plasma Trap.
2018
We report the first experimental evidence of a controlled transition from the generation of periodic bursts of electromagnetic radiation into the continuous-wave regime of a cyclotron maser formed in magnetically confined nonequilibrium plasma. The kinetic cyclotron instability of the extraordinary wave of weakly inhomogeneous magnetized plasma is driven by the anisotropic electron population resulting from electron cyclotron plasma heating in a MHD-stable minimum-$B$ open magnetic trap.
Effects of radiation in accretion regions of classical T Tauri stars
2019
Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns, in which optically thin and thick plasma components coexist. Thus an accurate description of these impacts requires to account for the effects of absorption and emission of radiation. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock downfalling material. We investigate if a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. We developed a radiation hydrodynamics model describing an accretion column impacting onto the su…
Analysis of the aerosol radiative forcing over a Mediterranean urban coastal site
2014
Abstract The aerosol radiative forcing for the period 2003–2011 has been analyzed in Burjassot, Spain, an urban coastal site on the western Mediterranean, using measurements of global solar irradiance and aerosol properties, as well as simulated data. The aerosol radiative forcing was calculated at 5 minute intervals, and then integrated over 24 h to obtain daily mean values for 200 complete days under cloud-free skies. The monthly mean values of the aerosol radiative forcing showed a clear variation during the year, associated to the annual variability of the aerosol optical depth at 500 nm, ranging from − 6 to − 29 Wm− 2 at the surface, and from − 1.5 to − 3.9 Wm− 2 at the top of the atmo…
Atmospheric water vapour content retrieval from visible and thermal data in the framework of the DAISEX campaigns
2005
In this paper three methods are presented that retrieve the atmospheric water vapour from DAIS (digital airborne imaging spectrometer) data in the framework of the DAISEX (DAIS Experiment) campaigns carried out by ESA (European Space Agency). The three methodologies analysed in the paper are: (i) the ratio technique, in which the water vapour is obtained from visible and near‐infrared bands; (ii) the split‐window technique; and (iii) the split‐window covariance‐variance ratio technique, in which the water vapour content is retrieved from thermal infrared bands. A comparison between the atmospheric water vapour content extracted from the DAIS images using these techniques and that obtained f…
The novel HALO mini-DOAS instrument: inferring trace gas concentrations from airborne UV/visible limb spectroscopy under all skies using the scaling …
2017
Abstract. We report on a novel six-channel optical spectrometer (further on called mini-DOAS instrument) for airborne nadir and limb measurements of atmospheric trace gases, liquid and solid water, and spectral radiances in the UV/vis and NIR spectral ranges. The spectrometer was developed for measurements from aboard the German High-Altitude and Long-Range (HALO) research aircraft during dedicated research missions. Here we report on the relevant instrumental details and the novel scaling method used to infer the mixing ratios of UV/vis absorbing trace gases from their absorption measured in limb geometry. The uncertainties of the scaling method are assessed in more detail than before for …
Multiyear in-situ measurements of atmospheric aerosol absorption properties at an urban coastal site in western Mediterranean
2016
Abstract In-situ aerosol absorption properties measured in Valencia (Spain) for four years, from February 2011 to February 2015, have been analysed. Spectral absorption properties have been obtained using a seven-wavelength Aethalometer AE-31 which covers the range from UV (370 nm) to IR (950 nm). In order to obtain the absorption coefficients, compensation parameters have been calculated for the Aethalometer considering seasonal and spectral differences. For this multiyear measurement period, seasonal site-specific calibration parameters have been obtained. Furthermore, estimations of the absorption Angstrom Exponent (α abs ) have been calculated using the seven Aethalometer wavelengths. T…
Electron microscopy of particles collected at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: particle chemistry, shape, mixing state …
2011
A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. The aerosol at Praia is a superposition of mineral dust, sea-salt, sulphates and soot. Particles smaller than 500 nm are mainly mineral dust, mineral dust–sulphate mixtures, sulphates and soot–sulphate mixtures. Particles larger then 2.5 μm consist of mineral dust, sea-salt and few mineral dust–sulphate mixtures. A transition range exists in between. The major internal mixtures are mineral dust–sulphate and soot–sulphate. Mineral dust–sea-salt mixtures occur occasionally, mineral dust–soot mixtures were not observed. The aspect ratio was 1.3–1.4 for dry p…