The top 500 results for "G M W Kroesen" are:

The performance of the electromagnetic calorimeter of the ALICE experiment during operation in 2010–2018 at the Large Hadron Collider is presented. After a short introduction into the design, readout, and trigger capabilities of the detector, the procedures for data taking, reconstruction, and validation are explained. The methods used for the calibration and various derived corrections are presented in detail. Subsequently, the capabilities of the calorimeter to reconstruct and measure photons, light mesons, electrons and jets are discussed. The performance of the calorimeter is illustrated mainly with data obtained with test beams at the Proton Synchrotron and Super Proton Synchrotron or in proton-proton collisions at √s = 13 TeV, and compared to simulations.

The knowledge of the material budget with a high precision is fundamental for measurements of direct photon production using the photon conversion method due to its direct impact on the total systematic uncertainty. Moreover, it influences many aspects of the charged-particle reconstruction performance. In this article, two procedures to determine data-driven corrections to the material-budget description in ALICE simulation software are developed. One is based on the precise knowledge of the gas composition in the Time Projection Chamber. The other is based on the robustness of the ratio between the produced number of photons and charged particles, to a large extent due to the approximate isospin symmetry in the number of produced neutral and charged pions. Both methods are applied to ALICE data allowing for a reduction of the overall material budget systematic uncertainty from 4.5% down to 2.5%. Using these methods, a locally correct material budget is also achieved. The two proposed methods are generic and can be applied to any experiment in a similar fashion.

Luminosity determination within the ALICE experiment is based on the measurement, in van der Meer scans, of the cross sections for visible processes involving one or more detectors (visible cross sections). In 2015 and 2018, the Large Hadron Collider provided Pb–Pb collisions at a centre-of-mass energy per nucleon pair of √s_NN = 5.02 TeV. Two visible cross sections, associated with particle detection in the Zero Degree Calorimeter (ZDC) and in the V0 detector, were measured in a van der Meer scan. This article describes the experimental set-up and the analysis procedure, and presents the measurement results. The analysis involves a comprehensive study of beam-related effects and an improved fitting procedure, compared to previous ALICE studies, for the extraction of the visible cross section. The resulting uncertainty of both the ZDC-based and the V0-based luminosity measurement for the full sample is 2.5%. The inelastic cross section for hadronic interactions in Pb–Pb collisions at √s_NN = 5.02 TeV, obtained by efficiency correction of the V0-based visible cross section, was measured to be 7.67 ± 0.25 b, in agreement with predictions using the Glauber model.

The Advanced Oxidation Process pulsed corona discharges have been utilized for the degradation of phenol in aqueous solution. The pulsed positive corona discharges are struck in the ambient gas phase over the solution. Experiments have been performed using both an air and argon atmosphere. Phenol conversion and the production of major oxidation products in the solution have been determined, using ion-exclusion chromatography with UV absorbance and conductivity detectors in series. The corona pulse energy has been measured from voltage and current waveforms using capacitive current correction. Oxidation products are polyhydroxybenzenes and carboxylic acids. Even though phenol conversion efficiencies by pulsed positive corona discharges in air and argon are similar, the degradation pathways are different.

The growth of particles in a radiofrequency (RF) (13.56 MHz) plasma at pressures from 25 to 200 mTorr in mixtures of CF₄, CF₂Cl₂ and argon has been studied experimentally. A planar configuration was used, with a silicon wafer on the powered electrode. The electron density has been measured with microwave resonance spectroscopy using a cylindrical cavity surrounding the plasma. The same geometry has been used to measure the density of various species of negative ions by detecting the extra electrons created by laser-induced photo detachment. It appears that the negative ion density is much larger in the case of CF₂Cl₂ than in the case of CF₄. There seems to be hardly any dependence of the negative ion concentration on the CF₂Cl₂/Ar partial pressure ratio in the range where powder growth occurs. However, the attachment rate to chlorine is found to be much higher than to fluorine. Furthermore the gas phase discharge chemistry has been studied using infrared absorption spectroscopy. Both a tunable diode laser system, and a Fourier transform spectrometer have been applied. The CF₂ concentration appears to decrease strongly when powder growth occurs. The SiF₄ concentration then has a maximum. The results indicate that the presence of chlorine in the plasma feed gas is essential. In CF₄ no particle formation is detected. The wafer surface is blackened during powder formation. SEM inspection indicates that this is caused by micromasking. Considering all the information, we arrive at the conclusion that particle growth is initiated by micromasking at the Si surface combined with a highly directional etching process. Due to residual isotropic etching the particles are released from the surface and enter the plasma, where they start coalescing and growing under the influence of CF₂ polymerization.

In situ Fourier transform infrared spectroscopy has been used to study particulate formation in a CCl₂F₂/Ar RF discharge. Strong absorption bands at 1000-1100 cm^-1 have been found and attributed to C-F and Si-F absorption. Furthermore continuous extinction due to Rayleigh and Mie scattering has been observed. The relative intensities of C-F, Si-F and scattering signals vary with plasma conditions. There are several experimental indications that the clusters are formed on the surface and ejected into the plasma. An SEM study of the substrate surface has allowed us to establish the mechanism for the particulate production in this discharge.

Infrared absorption spectroscopy has been used to measure the absolute densities of neutral particles in various fluorocarbon RF plasmas. The densities of CF₂ radicals have been measured using a tunable diode laser. Moreover, broadband absorption spectra obtained using a Fourier transform spectrometer have been used to determine the densities of stable reaction products and to assess the degree of dissociation in the plasma. The results indicate that the rotational temperatures of all species involved are slightly above room temperature. The density of CF₂ at high gas pressures increases close to the electrodes, indicating production near or on the electrodes and loss in the gas phase. The dissociation degree in plasmas of gases with a high C/F ratio can be as high as 90%. From an analysis of the flow dependence of the degree of dissociation the total dissociation rate coefficients of CF₄, CF₂Cl₂, CF₃Cl and C₂F₄Cl₂ have been calculated.

LIF spectroscopy has been introduced for the in situ diagnostic of phenol degradation in the aqueous solution under pulsed-corona discharges. The applicability of LIF to the measurements of phenol concentration up to 1×10^-5 mol l^-1 was confirmed. The temporal variation of the absolute concentration of phenol was measured in an aqueous solution exposed by pulsed-corona discharges. This exhibited two characteristic decay times.

The phenol degradation processes by pulsed corona discharges are investigated under three kinds of discharge atmosphere (air, argon and oxygen). The temporal variations of the concentrations of phenol and the intermediate products are monitored by LIF spectroscopy. The species of the intermediate products are identified by spectral analysis. It is clarified that the oxidative gaseous reagents produced from O₂ and those from H₂O degrade phenol to intermediate products with comparable degradation rates. The degradation via the reagents from H₂O gives rise to the formation of molecules exhibiting fluorescence at 400-500 nm, in addition to dihydroxybenzene (DHB), while the degradation via the reagents from O₂ produces only DHB. The reagents from O₂ play an important role in the conversion of phenol to DHB.

Axial segregation in metal-halide lamps is caused by a complex interaction between convection and diffusion and is not yet fully understood. By enhancing convection, by placing the lamp in a centrifuge, the effect of convection on axial segregation was studied. The centrifuge caused the lamp to be accelerated between 1g and 10g. Optical emission spectroscopy was performed on a metal-halide lamp while placed in the centrifuge. Several transitions of atomic and ionic Dy, and atomic Hg were measured at different lateral positions from which we obtained atomic and ionic Dy and atomic Hg intensity profiles. Atomic lateral profiles of Dy at different axial positions in the lamp were used for the calculation of Fischer's axial segregation parameter. The theoretical model of the Fischer curve, which shows the axial segregation parameter as a function of convection, was verified along the full range by measuring lamps of different fillings and geometry. Moreover, the radial temperature profile of the arc for the different accelerations was determined.