Non-equilibrium ionization by a periodic electron beam II. Synthetic Si IV and O IV transition region spectra

Transition region (TR) spectra typically show the Si IV 1402.8 A line to be enhanced by a factor of 5 or more compared to the neighboring O IV 1401.2 A, contrary to predictions of ionization equilibrium models and the Maxwellian distribution of particle energies. Non-equilibrium effects in TR spectra are therefore expected. To investigate the combination of non-equilibrium ionization and high-energy particles, we apply the model of the periodic electron beam, represented by a kappa-distribution that recurs at periods of several seconds, to plasma at chromospheric temperatures of 10^4 K. This simple model can approximate a burst of energy release involving accelerated particles. Instantaneous time-dependent charge states of silicon and oxygen were calculated and used to synthesize the instantaneous and period-averaged spectra of Si IV and O IV. The electron beam drives the plasma out of equilibrium. At electron densities of N_e = 10^10 cm^-3, the plasma is out of ionization equilibrium at all times in all cases we considered, while for a higher density of N_e = 10^11 cm^-3, ionization equilibrium can be reached toward the end of each period, depending on the conditions. In turn, the character of the period-averaged synthetic spectra also depends on the properties of the beam. While the case of kappa = 2 results in spectra with strong or even dominant O IV, higher values of kappa can approximate a range of observed TR spectra. Spectra similar to typically observed spectra, with the Si IV 1402.8 A line about a factor 5 higher than O IV 1401.2 A, are obtained for kappa = 3. An even higher value of kappa = 5 results in spectra that are exclusively dominated by Si IV, with negligible O IV emission. This is a possible interpretation of the TR spectra of UV bursts, although an interpretation that requires a density that is 1-3 orders of magnitude lower than for equilibrium estimates.Comment: Astronomy & Astrophysics, accepte

Synthetic IRIS spectra of the solar transition region: Effect of high-energy tails

The solar transition region satisfies the conditions for presence of non-Maxwellian electron energy distributions with high-energy tails at energies corresponding to the ionization potentials of many ions emitting in the EUV and UV portions of the spectrum. We calculate the synthetic Si IV, O IV, and S IV spectra in the far ultra-violet (FUV) channel of the Interface Region Imaging Spectrograph (IRIS). Ionization, recombination, and excitation rates are obtained by integration of the cross-sections or their approximations over the model electron distributions considering particle propagation from the hotter corona. The ionization rates are significantly affected by the presence of high-energy tails. This leads to the peaks of the relative abundance of individual ions to be broadened with pronounced low-temperature shoulders. As a result, the contribution functions of individual lines observable by IRIS also exhibit low-temperature shoulders, or their peaks are shifted to temperatures an order of magnitude lower than for the Maxwellian distribution. The integrated emergent spectra can show enhancements of Si IV compared toO IV by more than a factor of two. The high-energy particles can have significant impact on the emergent spectra and their presence needs to be considered even in situations without strong local acceleration

Framework for successfully implementing an inaugural GRI reporting process

ProjectThis thesis is a corporate project analyzing the Global Reporting Initiative (GRI) reporting process. Its main objective is to propose a practical framework to guide organizations that plan to engage in first-time voluntary sustainability reporting using GRI’s Sustainability Reporting Guidelines. The thesis provides insight into the exact tasks involved in each stage of the GRI reporting process, as well as the specific resources and capabilities that are necessary in order for organizations to succeed in reporting, regardless of size, location, sector, or organization type. Two international case companies, one in the Service sector and the other in the Forest and Paper Products sector became objects of study and specific recommendations were provided to each one. As a conclusion, the thesis presents general recommendations that are thought to be universal for any first-time GRI reporter, assisting organizations to successfully implement an inaugural GRI reporting process.Esta tese é um projeto empresarial que analisa o processo de reporte da Global Reporting Initiative (GRI). O seu principal objectivo é a definição de um guia prático para apoiar as empresas que pretendem iniciar voluntariamente a publicação de relatórios de sustentabilidade segundo as directrizes da GRI. Esta tese descreve as actividades concretas a executar em cada etapa do processo de reporte da GRI, assim como os recursos e competências que as organizações necessitam para serem bem-sucedidas no reporte, independentemente da sua dimensão, localização, sector, ou tipo de organização. Duas empresas multinacionais foram objecto de estudo, uma do sector de serviços e outra do sector florestal, tendo sido elaboradas recomendações específicas para cada uma. Como conclusão, a tese apresenta recomendações gerais, aplicáveis a qualquer organização que elabore o GRI pela primeira vez, para apoiar a sua implementação com sucesso