Dependence of SWNT Growth Mechanism on Temperature and Catalyst Particle Size: Bulk versus Surface Diffusion

MD simulations reveal that many aspects of SWNT nucleation and growth from solid and liquid metal particles are similar. In both cases graphitic islands lift off the cluster surface to form caps that grow into SWNTs. However, in contrast to liquid particles, where C atoms primarily diffuse into the bulk of the cluster before adding to the growing SWNT, incorporation of C into SWNTs on solid particles occurs predominantly via surface diffusion

DOAS for flue gas monitoring—II. Deviations from the Beer-Lambert law for the UV/visible absorption spectra of NO, NO2, SO2 and NH3

Deviations from the Beer-Lambert law were studied for the differential absorption cross-sections for NO, SO2, NO2 and NH3. This was performed by simple calculations, computer simulations of spectra and by recordings of spectra for the above mentioned species at various total columns. The linearity studies for the DOAS instrument displayed large variations for the molecules studied and for different wavelength bands. In a calculation it was shown that the optical depth deviated from a linear concentration dependence by a term which was directly proportional to the statistical variance of the true absorption cross sections and proportional to the square of the total column, under the assumption of a boxcar instrument lineshape. Species exhibiting little variance or fine structure in their spectra, for instance NO2, displayed a larger linear region compared with molecules exhibiting a rich structure, i.e., NO. The former species was linear to a total column of 3150 mg/m2, which correspond to a maximum optical depth of 0.7, while the latter was linear to only 6 mg/m2, corresponding to a maximum optical depth of 0.024, in the resolution range studied. The linear regions for the other species studied were 90 mg/m2 for SO2 at 230 nm, 180 mg/m2 for SO2 at 300 nm and 36 mg/m2 for NH3. The main effect of the nonlinearity was to cause a reduction in the peak height of the absorption. It was shown that the nonlinearity effect is independent on the spectral resolution when a large number of absorption lines are covered by the bandpass of the instrument. It was also shown that the largest change in linearity occurs when the resolution is similar in magnitude to the absorption linewidth. The nonlinear behavior for NO varied less than 2% in the temperature range 300–1000 K and the spectral resolution range 0.25–1 nm. The nonlinearity effect caused quantitative rather than qualitative changes of the spectral features and typical relative errors can be as high as 35% in a flue gas

DOAS for flue gas monitoring—III. In-situ monitoring of sulfur dioxide, nitrogen monoxide and ammonia

A methodology is described for the in-situ detection of NO, NH3 and SO2 in flue gases by DOAS (Differential Optical Absorption Spectroscopy). In order to perform accurate measurements of the concentration it is necessary to compensate for the temperature dependence of the absorption cross-sections as well as for potential deviations from the Beer-Lambert law (nonlinearity effects). From the experimental data in two previous papers, empirical equations were derived for the compensation of the nonlinearity and temperature effects. These were used to compensate obtained concentration values of NO and SO2 retrieved from DOAS spectra that were recorded in a flue gas at 413 K. The measurements of SO2 showed that in a concentration interval of 500–1600 ppm at 413 K, the resulting systematic discrepancies between the DOAS and a conventional reference system decreased from 40 to only 2% when compensating the DOAS data. The maximum random difference was approximately 15%. In the same manner the systematic difference for NO decreased from 23 to 1%, with a maximum random error of 5%, for concentrations between 60 and 160 ppm. The measurements of NH3 demonstrated the versatility of the DOAS technique for time resolved in-situ measurements (<20 sec), and also the feasibility of the technique for measuring several species simultaneously. The measurement methodology developed for NH3 was more complicated than for NO and SO2 and required a larger amount of laboratory calibrations. In the spectral evaluation procedure of NH3 hot bands were utilized for flue gas temperatures above 450 K

Pulse length dependence of photoelectron circular dichroism

We investigate photoelectron circular dichroism (PECD) with coherent light sources whose pulse durations range from femtoseconds to nanoseconds. To that end, we employed an optical parametric amplifier, an ultraviolet optical pulse shaper, and a nanosecond dye laser, all centered around a wavelength of 380 nm. A multiphoton ionization experiment on the gas-phase chiral prototype fenchone found that PECD measured via the 3s intermediate resonance is about 15% and robust over five orders of magnitude of the pulse duration. PECD remains robust despite ongoing molecular dynamics such as rotation, vibration, and internal conversion. We used the Lindblad equation to model the molecular dynamics. Under the assumption of a cascading internal conversion, from the 3p to the 3s and further to the ground state, we estimated the lifetimes of the internal conversion processes in the 100 fs regime

Distribution and composition of mesopelagic macroplankton and micronekton in the North-east Atlantic

acceptedVersio

Audiences’ Communicative Agency in a Datafied Age: Interpretative, Relational and Increasingly Prospective

This article develops a conceptualization of audience agency in the face of datafication. We consider how people, as audiences and users of media and technologies, face transforming communicative conditions, and how these conditions challenge the power potentials of audiences in processes of communication—that is, their communicative agency. To develop our conceptualization, we unpack the concept of audiences’ communicative agency by examining its foundations in communication scholarship, in reception theory and sociology, arguing that agency is understood as interpretative and relational, and applied to make important normative assessments. We further draw on emerging scholarship on encounters with data in the everyday to discuss how audience agency is now challenged by datafication, arguing that communicative agency is increasingly prospective in a datafied age. Thereby, we provide a theoretical conceptualization for further analysis of audiences in transforming communicative conditions.publishedVersio

Valuation of small and multiple health risks: A critical analysis of SP data applied to food and water safety

This study elicits individual risk preferences in the context of an infectious disease using choice experiments. A main objective is to examine scope sensitivity using a novel approach. Our results suggest that the value of a mortality risk reduction (VSL) is highly sensitive to the survey design. Our result cast doubt on the standard scope sensitivity tests in choice experiments, but also on the validity and reliability of VSL estimates based on stated-preference studies in general. This is important due to the large empirical literature on non-market evaluation and the elicited values’ central role in policy making

DOAS for flue gas monitoring—II. Deviations from the Beer-Lambert law for the UV/visible absorption spectra of NO, NO2, SO2 and NH3

Deviations from the Beer-Lambert law were studied for the differential absorption cross-sections for NO, SO2, NO2 and NH3. This was performed by simple calculations, computer simulations of spectra and by recordings of spectra for the above mentioned species at various total columns. The linearity studies for the DOAS instrument displayed large variations for the molecules studied and for different wavelength bands. In a calculation it was shown that the optical depth deviated from a linear concentration dependence by a term which was directly proportional to the statistical variance of the true absorption cross sections and proportional to the square of the total column, under the assumption of a boxcar instrument lineshape. Species exhibiting little variance or fine structure in their spectra, for instance NO2, displayed a larger linear region compared with molecules exhibiting a rich structure, i.e., NO. The former species was linear to a total column of 3150 mg/m2, which correspond to a maximum optical depth of 0.7, while the latter was linear to only 6 mg/m2, corresponding to a maximum optical depth of 0.024, in the resolution range studied. The linear regions for the other species studied were 90 mg/m2 for SO2 at 230 nm, 180 mg/m2 for SO2 at 300 nm and 36 mg/m2 for NH3. The main effect of the nonlinearity was to cause a reduction in the peak height of the absorption. It was shown that the nonlinearity effect is independent on the spectral resolution when a large number of absorption lines are covered by the bandpass of the instrument. It was also shown that the largest change in linearity occurs when the resolution is similar in magnitude to the absorption linewidth. The nonlinear behavior for NO varied less than 2% in the temperature range 300–1000 K and the spectral resolution range 0.25–1 nm. The nonlinearity effect caused quantitative rather than qualitative changes of the spectral features and typical relative errors can be as high as 35% in a flue gas