abstract: The mineralogy of the deep mantle is one of the key factors for the chemical evolution of the Earth. The constituent minerals of the mantle rock control the physical properties of the mantle, which have significant impacts on the large-scale processes occurring in the Earth's interior. In my PhD research, I adopted experimental approaches to investigate the mineralogy and the physical properties of the Earth's materials in the deep mantle by using the diamond anvil cells (DACs) combined with in-situ X-ray diffraction techniques. First, I found that Ca-bearing bridgmanite can be stable in the deeper part of the Earth's lower mantle where temperature is sufficiently high. The dissolution of calcium into bridgmanite can change the physical properties of the mantle, such as compressibility and viscosity. This study suggests a new mineralogical model for the lower mantle, which is composed of the two layers depending on whether calcium dissolves in bridgmanite or forms CaSiO3 perovskite as a separate phase. Second, I investigated the mineralogy and density of the subducting materials in the Archean at the P-T conditions near 670 km-depth. The experiments suggest that the major phases of Archean volcanic crust is majoritic garnet and ringwoodite in the P-T conditions of the deep transition zone, which become bridgmanite with increasing pressure. The density model showed that Archean volcanic crust would have been denser than the surrounding mantle, promoting sinking into the lower mantle regardless of the style of the transportation in the Archean. Lastly, I further investigated the mineralogies and densities of the ancient volcanic crusts for the Archean and Proterozoic at the P-T conditions of the lower mantle. The experiments suggest that the mineralogy of the ancient volcanic crusts is composed mostly of bridgmanite, which is systemically denser than the surrounding lower mantle. This implies that the ancient volcanic crusts would have accumulated at the base of the mantle because of their large density and thickness. Therefore, the distinctive chemistry of the ancient volcanic crusts from the surrounding mantle would have given a rise to the chemical heterogeneities in the region for billions of years. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

Layered lithium transition metal oxides represent a major type of cathode materials that are widely used in commercial lithium-ion batteries. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and are not yet fully understood. In this thesis, the cycling-induced chemical and structural evolution of LiNi1/3Mn1/3Co1/3O2 (NMC) and high-energy Li1.2Ni0.13Mn0.54Co0.13O2 (HENMC) cathodes are investigated in details using state-of-the-art electron microscopy techniques combined with other bulk measurements to uncover the mechanisms at the source of cell deterioration. / Thesis / Doctor of Philosophy (PhD)

Water is a major component of living organisms, which can be 70-85% of the weight of cells. For this reason, water is a main target of ionizing radiations and plays a central role in radiobiology. Heavy ions, electrons and photons interact with water molecules; mainly by ionization and excitation. Neutrons interact with water molecules by elastic interactions, which generate recoil ions that will create ionizations and excitations in water molecules. These fast events (~10[superscript -12] s) lead to the formation of Reactive Oxygen Species (ROS). The ROS, in particular the hydroxyl radical (¨OH), interact with neighbour molecules such as proteins, lipids and nucleic acids by chemical interaction. Microbeams can irradiate selectively either the external membrane, the cytoplasm and the cell nucleus. These studies have shown that cell survival is greatly reduced when the nucleus is irradiated, but that this is not the case when cytoplasm or cell membrane is irradiated. Thus, DNA is a very sensitive site to ionizing radiation and ROS. For this reason, DNA has long been considered the most important molecule to explain radiobiological effects such as cell death. However, this concept has been challenged recently by new experimental results that have shown that cells which have not been directly in contact with radiation are also affected. This is called the bystander effect. Further studies have shown that a group of cells and their environment reacts collectively to radiation. A hypothesis put forward to explain this radiobiological phenomenon is that a irradiated cell will secrete signalling molecules that will affect non-irradiated cells. The implicated phenomenon and molecules are poorly understood at this moment. The purpose of this work is to improve our comprehension of the phenomenon in the microsecond that follows the irradiation. To these ends, a new Monte-Carlo simulation program of water radiolysis by photons has been generated. For photons of energy <2 MeV, they interact with water mainly by Compton and photoelectric effects, which create energetic electrons in water. The created electrons are then followed by our existing programs to simulate the radiolysis of water by photons. Similarly, a new code has been built to simulate the neutrons interaction with water. This code simulates the elastic collisions of a neutron with water molecules and calculates the number and energy of recoil protons and oxygen ions. The main part of this Ph.D. work was the generation of a non-homogeneous Monte-Carlo Step-By-Step (SBS) simulation code of non-homogeneous radiation chemistry. This new program has been used successfully to simulate radiolysis of water by ions of various LET, pH, ion types ([superscript 1]H[superscript +], [superscript 4]He[superscript 2+], [superscript 12]C[superscript 6+]) and temperature. The program has also been used to simulate the dose-rate effect and the Fricke and Ceric dosimeters. More complex systems (glycine, polymer gels and HCN) have also been simulated.

Tracing the element enrichment in the Universe requires to understand the element production in stellar models which is not well understood, in particular at low metallicity. In this thesis a variety of nucleosynthesis processes in stellar models across initial masses and metallicities is investigated and their relevance for chemical evolution explored. Stellar nucleosynthesis is investigated in asymptotic giant branch (AGB) models and massive star models with initial masses between 1 M⊙ and 25 M⊙ for metal fractions of Z = 0.02, 0.01, 0.006, 0.001, 0.0001. A yield grid with elements from H to Bi is calculated. It serves as an input for chemical evolution simulations. AGB models are computed towards the end of the AGB phase and massive star models are calculated until core collapse followed by explosive core-collapse nucleosynthesis. The simulations include convective boundary mixing in all AGB star models and feature efficient hot-bottom burning and hot dredge-up in AGB models as well the predictions of both heavy elements and CNO species under hot-bottom burning conditions. H-ingestion events in the low-mass low-Z AGB model with initial mass of 1M⊙ at Z = 0.0001 result in the production of large amounts of heavy elements. In super-AGB models H ingestion could potentially lead to the intermediate neutron-capture process. To model the chemical enrichment and feedback of simple stellar populations in hydrodynamic simulations and semi-analytic models of galaxy formation the SYGMA module is created and its functionality is verified through a comparison with a widely adopted code. A comparison of ejecta of simple stellar populations based on yields of this work with a commonly adopted yield set shows up to a factor of 3.5 and 4.8 less C and N enrichment from AGB stars at low metallicity which is attributed to complete stellar models, the modeling of the AGB stage and hot-bottom burning in super- AGB stars. Analysis of two different core-collapse supernova fallback prescriptions show that the total amount of Fe enrichment by massive stars differs by up to two at Z = 0.02. Insights into the chemical evolution at very low metallicity as motivated by the observations of extremely metal poor stars require to understand the H-ingestion events common in stellar models of low metallicity. The occurrence of H ingestion events in super-AGB stars is investigated and identified as a possible site for the production of heavy elements through the intermediate neutron capture process. The peculiar abundance of some C-Enhanced Metal Poor stars are explained with simple models of the intermediate neutron capture process. Initial efforts to model this heavy element production in 3D hydrodynamic simulations are presented. For the first time the nucleosynthesis of interacting convective O and C shells in massive star models is investigated in detail. 1D calculations based on input from 3D hydrodynamic simulations of the O shell show that such interactions can boost the production of odd-Z elements P, Cl, K and Sc if large entrainment rates associated with O-C shell merger are assumed. Such shell merger lead in stellar evolution models to overproduction factors beyond 1 dex and p-process overproduction factors above 1 dex for 130,132Ba and heavier isotopes. Chemical evolution models are able to reproduce the Galactic abundance trends of these odd-Z elements if O-C shell merger occur in more than 50% of all massive stars. / Graduate

O presente trabalho propõe uma abordagem abrangente para descrever a evolução da região central da Via Láctea, compreendendo-se aí o bojo, a barra e as interfaces dos mesmos com o limite interno do disco e com a região central do halo. Pretende-se investigar as propriedades químicas e cinemáticas destas estruturas, que são interconectadas, com o objetivo de separá-las e aplicar os resultados daí obtidos a um modelo de formação e evolução do bojo e da região interna do disco que descreva simultaneamente distintos aspectos da evolução da região central da Galáxia. Na primeira parte do trabalho, uma amostra de nebulosas planetárias (NPs) localizadas no disco interno e no bojo da Galáxia é utilizada para encontrar a distância galactocêntrica que melhor separa estas duas populações, do ponto de vista das abundâncias. Foram utilizadas escalas de distâncias estatísticas para o estudo da distribuição das abundâncias na interface bojo-disco. A aplicação do teste Kolmogorov-Smirnov mostrou que, em média, a população interna não segue o gradiente radial de abundâncias do disco na direção do centro galáctico. Baseado neste estudo, propõe-se uma distância galactocêntrica de 1.5 kpc para definir a interface bojo-disco. Na segunda parte do trabalho, foram realizadas observações espectrofotométricas de 21 NPs localizadas na direção do centro da Galáxia com o telescópio SOAR. Estes objetos estão localizados bem próximos ao plano galáctico na direção central da Via Láctea, onde não existem dados de NPs na literatura. Os resultados mostram que as NPs localizadas nesta região apresentam baixas abundâncias de oxigênio comparadas com as NPs do disco interno e de outras regiões do bojo. Os resultados indicam que o bojo apresenta uma complexa composição de populações estelares. Por um lado, a presença de nebulosas com baixas abundâncias mostra que o bojo pode ter se formado a partir de um disco galáctico antigo através de uma evolução secular. Por outro lado, existem alguns objetos do bojo para os quais as abundâncias coincidem com o limite do gradiente radial do disco nesta região. Esta é uma evidência para um bojo composto por duas ou mais populações: uma originada do disco fino, e outra originada do disco espesso. Na última parte do trabalho propõe-se a inclusão de fluxos radiais de gás em um modelo de evolução química para simular os efeitos de uma barra localizada no centro da Galáxia nas distribuições de abundâncias, densidade de gás e taxa de formação estelar (SFR). Os resultados das simulações indicam que os modelos com fluxos de gás apresentam uma SFR mais alta no bojo e que os perfis da SFR e da densidade de gás na região central são melhor reproduzidos após a inclusão dos fluxos radiais no modelo. As simulações indicam ainda que o gradiente de abundâncias do disco é mais plano para o caso da inclusão da barra. Estes resultados indicam que a barra e os fluxos de gás exercem um importante papel na formação de estrelas no centro das galáxias espirais barradas. / This project proposes a comprehensive approach to describe the evolution of the central region of the Galaxy, comprising the bulge, the bar and their interfaces with the inner disk and the central region of the halo. We intend to investigate the chemical and kinematic properties of these structures, which are interconnected, aiming to separate them and apply these results to a model for the formation and evolution of the bulge and inner disk, capable to describe simultaneously distinct aspects of the evolution of the central region of the Galaxy. First, a sample of planetary nebulae (PNe) located in the inner-disk and bulge of the Galaxy is used in order to find the galactocentric distance that better separates these two populations, from the point of view of abundances. Statistical distance scales were used to study the distribution of abundances across the disk-bulge interface. A Kolmogorov-Smirnov test was used to find the distance in which the chemical properties of these regions better separates. The results of the statistical analysis indicate that, on the average, the inner population has lower abundances than the outer. Additionally, for the $\\alpha$-elements abundances, the inner population does not follow the disk radial gradient towards the galactic centre. Based on our results, we suggest a bulge-disk interface at 1.5 kpc, marking the transition between the bulge and inner-disk of the Galaxy, as defined by the intermediate mass population. Second, we present spectrophotometric observations for a sample of 21 PNe located towards the galactic centre of the Galaxy. The abundances are derived based on observations in the optical domain made at the SOAR telescope. Their location is interesting since there are no observations of PNe in this region. The data show lower oxygen abundances compared to those from PNe located in the inner disk and other bulge regions. The results show that the bulge has a complex composition of stellar populations. The presence of PNe with low abundances indicates that the bulge might be formed from an old galactic disk through secular evolution. On the other hand, other objects from our sample have abundances compared to those from inner disk PNe. This is evidence that two or more populations might compose the bulge: one originated from the thin disk, and the other from the thick disk. Last, we propose a chemical evolution model that includes radial gas flows. This is done in order to mimic the effects of the galactic bar on the chemical abundances distributions and the gas density profiles and the star formation rate (SFR). The results of the models with radial flows point to a high SFR in the bulge and, additionally, the SFR and gas density profiles in the inner Galaxy are better reproduced after the inclusion of radial gas flows in the model. After including a specific velocity pattern for the bar, the results show a flattening of the radial abundance gradient. Our results indicate that radial gas flows may play an important role in the star formation near the centre of barred spiral galaxies.

<p>Chemical evolution addresses the problem of the formation of the chemical elements and their evolution throughout the history of the universe. This thesis discusses in particular the chemical evolution in the young universe and what we may learn from the observations of the oldest stars. The present day production of carbon in the Galaxy is also discussed. Interstellar media of young, metal-poor, star-forming systems are expected to show large chemical abundance inhomogeneities due to local supernova explosions. These inhomogeneities are reflected in the surface abundances of the population of longlived, low-mass stars. A stochastic model of the chemical evolution in such systems is presented and used to study the metallicity distribution and the scatter in chemical abundance ratios. The model takes into account mixing of the enriched material by turbulent motions and cloud collisions in the interstellar medium as well as infall of pristine matter. The predicted metallicity distribution shows, in accordance with observations of extreme Pop II strars in the Galactic halo, a distinct cut-off at [Fe/H]~-4. However, the fraction of stars below [Fe/H]=-4 agrees with observatrion only if a population of metal-free stars (Pop III) was never able to form. The predicted scatter in abundance ratios is demonstrated to be crucially dependent on the as yet uncertain supernova yields and the relatively small star-to-star scatter is tentatively explained by the averaging of a large number of contributing supernovae and by the selection effects favouring contributions from supernovae in a certain mass range for the most metal-poor stars. Furthermore, stars enriched by one single supernova are predicted to be found in very narrow sequences in the abundance ratio diagrams (so called A/A diagrams). Verification of the existence of such features, called single supernova sequences, is observationally challenging. Abundance analysis of carbon was performed in a large sample of solar-type stars in the Galactic disk using the forbidden [C I] line at 8727 Å. A comparison between the relation of [C/O] with metallicity for the Galactic stars and that of dwarf irregular galaxies suggests that large amounts of carbon are produced today by massive, so called Wolf-Rayet stars. Low-mass stars are less important. This was also demonstrated by modelling the chemical evolution of carbon.</p>

<p>The information about the chemical compositions of stars is encoded in their spectra. Accurate determinations of these compositions are crucial for our understanding of stellar nucleosynthesis and Galactic chemical evolution. The determination of elemental abundances in stars requires models for the stellar atmospheres and the processes of line formation. Nearly all spectroscopic analyses of late-type stars carried out today are based on one-dimensional (1D), hydrostatic model atmospheres and on the assumption of local thermodynamic equilibrium (LTE). This approach can lead to large systematic errors in the predicted stellar atmospheric structures and line-strengths, and, hence, in the derived stellar abundances. In this thesis, examples of departures from LTE and from hydrostatic equilibrium are explored. The effects of background line opacities (line-blocking) due to atomic lines on the statistical equilibrium of Fe are investigated in late-type stars. Accounting for this line opacity is important at solar metallicity, where line-blocking significantly reduces the rates of radiatively induced ionizations of Fe. On the contrary, the effects of line-blocking in metal-poor stars are insignificant. In metal-poor stars, the dominant uncertainty in the statistical equilibrium of Fe is the treatment of inelastic H+Fe collisions. Substantial departures of Fe abundances from LTE are found at low metallicities: about 0.3 dex with efficient H+Fe collisions and about 0.5 dex without. The impact of three-dimensional (3D) hydrodynamical model atmospheres on line formation in red giant stars is also investigated. Inhomogeneities and correlated velocity fields in 3D models and differences between the mean 3D stratifications and corresponding 1D model atmospheres can significantly affect the predicted line strengths and derived abundances, in particular at very low metallicities. In LTE, the differences between 3D and 1D abundances of C, N, and O derived from CH, NH, and OH weak low-excitation lines are in the range -0.5 dex to -1.0 dex at [Fe/H]=-3. Large negative corrections (about -0.8 dex) are also found in LTE for weak low-excitation neutral Fe lines. We also investigate the impact of 3D hydrodynamical model stellar atmospheres on the determination of elemental abundances in the carbon-rich, hyper iron-poor stars HE 0107-5240 and HE 1327-2326. The lower temperatures of the line-forming regions of the 3D models compared with 1D models cause changes in the predicted spectral line strengths. In particular we find the 3D abundances of C, N, and O to be lower by about -0.8 dex (or more) than estimated from a 1D analysis. The 3D abundance of Fe is decreased but only by -0.2 dex. Departures from LTE for Fe might actually be very large for these stars and dominate over the effects due to granulation.</p>

Chemical evolution addresses the problem of the formation of the chemical elements and their evolution throughout the history of the universe. This thesis discusses in particular the chemical evolution in the young universe and what we may learn from the observations of the oldest stars. The present day production of carbon in the Galaxy is also discussed. Interstellar media of young, metal-poor, star-forming systems are expected to show large chemical abundance inhomogeneities due to local supernova explosions. These inhomogeneities are reflected in the surface abundances of the population of longlived, low-mass stars. A stochastic model of the chemical evolution in such systems is presented and used to study the metallicity distribution and the scatter in chemical abundance ratios. The model takes into account mixing of the enriched material by turbulent motions and cloud collisions in the interstellar medium as well as infall of pristine matter. The predicted metallicity distribution shows, in accordance with observations of extreme Pop II strars in the Galactic halo, a distinct cut-off at [Fe/H]~-4. However, the fraction of stars below [Fe/H]=-4 agrees with observatrion only if a population of metal-free stars (Pop III) was never able to form. The predicted scatter in abundance ratios is demonstrated to be crucially dependent on the as yet uncertain supernova yields and the relatively small star-to-star scatter is tentatively explained by the averaging of a large number of contributing supernovae and by the selection effects favouring contributions from supernovae in a certain mass range for the most metal-poor stars. Furthermore, stars enriched by one single supernova are predicted to be found in very narrow sequences in the abundance ratio diagrams (so called A/A diagrams). Verification of the existence of such features, called single supernova sequences, is observationally challenging. Abundance analysis of carbon was performed in a large sample of solar-type stars in the Galactic disk using the forbidden [C I] line at 8727 Å. A comparison between the relation of [C/O] with metallicity for the Galactic stars and that of dwarf irregular galaxies suggests that large amounts of carbon are produced today by massive, so called Wolf-Rayet stars. Low-mass stars are less important. This was also demonstrated by modelling the chemical evolution of carbon.

The information about the chemical compositions of stars is encoded in their spectra. Accurate determinations of these compositions are crucial for our understanding of stellar nucleosynthesis and Galactic chemical evolution. The determination of elemental abundances in stars requires models for the stellar atmospheres and the processes of line formation. Nearly all spectroscopic analyses of late-type stars carried out today are based on one-dimensional (1D), hydrostatic model atmospheres and on the assumption of local thermodynamic equilibrium (LTE). This approach can lead to large systematic errors in the predicted stellar atmospheric structures and line-strengths, and, hence, in the derived stellar abundances. In this thesis, examples of departures from LTE and from hydrostatic equilibrium are explored. The effects of background line opacities (line-blocking) due to atomic lines on the statistical equilibrium of Fe are investigated in late-type stars. Accounting for this line opacity is important at solar metallicity, where line-blocking significantly reduces the rates of radiatively induced ionizations of Fe. On the contrary, the effects of line-blocking in metal-poor stars are insignificant. In metal-poor stars, the dominant uncertainty in the statistical equilibrium of Fe is the treatment of inelastic H+Fe collisions. Substantial departures of Fe abundances from LTE are found at low metallicities: about 0.3 dex with efficient H+Fe collisions and about 0.5 dex without. The impact of three-dimensional (3D) hydrodynamical model atmospheres on line formation in red giant stars is also investigated. Inhomogeneities and correlated velocity fields in 3D models and differences between the mean 3D stratifications and corresponding 1D model atmospheres can significantly affect the predicted line strengths and derived abundances, in particular at very low metallicities. In LTE, the differences between 3D and 1D abundances of C, N, and O derived from CH, NH, and OH weak low-excitation lines are in the range -0.5 dex to -1.0 dex at [Fe/H]=-3. Large negative corrections (about -0.8 dex) are also found in LTE for weak low-excitation neutral Fe lines. We also investigate the impact of 3D hydrodynamical model stellar atmospheres on the determination of elemental abundances in the carbon-rich, hyper iron-poor stars HE 0107-5240 and HE 1327-2326. The lower temperatures of the line-forming regions of the 3D models compared with 1D models cause changes in the predicted spectral line strengths. In particular we find the 3D abundances of C, N, and O to be lower by about -0.8 dex (or more) than estimated from a 1D analysis. The 3D abundance of Fe is decreased but only by -0.2 dex. Departures from LTE for Fe might actually be very large for these stars and dominate over the effects due to granulation.

O presente trabalho propõe uma abordagem abrangente para descrever a evolução da região central da Via Láctea, compreendendo-se aí o bojo, a barra e as interfaces dos mesmos com o limite interno do disco e com a região central do halo. Pretende-se investigar as propriedades químicas e cinemáticas destas estruturas, que são interconectadas, com o objetivo de separá-las e aplicar os resultados daí obtidos a um modelo de formação e evolução do bojo e da região interna do disco que descreva simultaneamente distintos aspectos da evolução da região central da Galáxia. Na primeira parte do trabalho, uma amostra de nebulosas planetárias (NPs) localizadas no disco interno e no bojo da Galáxia é utilizada para encontrar a distância galactocêntrica que melhor separa estas duas populações, do ponto de vista das abundâncias. Foram utilizadas escalas de distâncias estatísticas para o estudo da distribuição das abundâncias na interface bojo-disco. A aplicação do teste Kolmogorov-Smirnov mostrou que, em média, a população interna não segue o gradiente radial de abundâncias do disco na direção do centro galáctico. Baseado neste estudo, propõe-se uma distância galactocêntrica de 1.5 kpc para definir a interface bojo-disco. Na segunda parte do trabalho, foram realizadas observações espectrofotométricas de 21 NPs localizadas na direção do centro da Galáxia com o telescópio SOAR. Estes objetos estão localizados bem próximos ao plano galáctico na direção central da Via Láctea, onde não existem dados de NPs na literatura. Os resultados mostram que as NPs localizadas nesta região apresentam baixas abundâncias de oxigênio comparadas com as NPs do disco interno e de outras regiões do bojo. Os resultados indicam que o bojo apresenta uma complexa composição de populações estelares. Por um lado, a presença de nebulosas com baixas abundâncias mostra que o bojo pode ter se formado a partir de um disco galáctico antigo através de uma evolução secular. Por outro lado, existem alguns objetos do bojo para os quais as abundâncias coincidem com o limite do gradiente radial do disco nesta região. Esta é uma evidência para um bojo composto por duas ou mais populações: uma originada do disco fino, e outra originada do disco espesso. Na última parte do trabalho propõe-se a inclusão de fluxos radiais de gás em um modelo de evolução química para simular os efeitos de uma barra localizada no centro da Galáxia nas distribuições de abundâncias, densidade de gás e taxa de formação estelar (SFR). Os resultados das simulações indicam que os modelos com fluxos de gás apresentam uma SFR mais alta no bojo e que os perfis da SFR e da densidade de gás na região central são melhor reproduzidos após a inclusão dos fluxos radiais no modelo. As simulações indicam ainda que o gradiente de abundâncias do disco é mais plano para o caso da inclusão da barra. Estes resultados indicam que a barra e os fluxos de gás exercem um importante papel na formação de estrelas no centro das galáxias espirais barradas. / This project proposes a comprehensive approach to describe the evolution of the central region of the Galaxy, comprising the bulge, the bar and their interfaces with the inner disk and the central region of the halo. We intend to investigate the chemical and kinematic properties of these structures, which are interconnected, aiming to separate them and apply these results to a model for the formation and evolution of the bulge and inner disk, capable to describe simultaneously distinct aspects of the evolution of the central region of the Galaxy. First, a sample of planetary nebulae (PNe) located in the inner-disk and bulge of the Galaxy is used in order to find the galactocentric distance that better separates these two populations, from the point of view of abundances. Statistical distance scales were used to study the distribution of abundances across the disk-bulge interface. A Kolmogorov-Smirnov test was used to find the distance in which the chemical properties of these regions better separates. The results of the statistical analysis indicate that, on the average, the inner population has lower abundances than the outer. Additionally, for the $\\alpha$-elements abundances, the inner population does not follow the disk radial gradient towards the galactic centre. Based on our results, we suggest a bulge-disk interface at 1.5 kpc, marking the transition between the bulge and inner-disk of the Galaxy, as defined by the intermediate mass population. Second, we present spectrophotometric observations for a sample of 21 PNe located towards the galactic centre of the Galaxy. The abundances are derived based on observations in the optical domain made at the SOAR telescope. Their location is interesting since there are no observations of PNe in this region. The data show lower oxygen abundances compared to those from PNe located in the inner disk and other bulge regions. The results show that the bulge has a complex composition of stellar populations. The presence of PNe with low abundances indicates that the bulge might be formed from an old galactic disk through secular evolution. On the other hand, other objects from our sample have abundances compared to those from inner disk PNe. This is evidence that two or more populations might compose the bulge: one originated from the thin disk, and the other from the thick disk. Last, we propose a chemical evolution model that includes radial gas flows. This is done in order to mimic the effects of the galactic bar on the chemical abundances distributions and the gas density profiles and the star formation rate (SFR). The results of the models with radial flows point to a high SFR in the bulge and, additionally, the SFR and gas density profiles in the inner Galaxy are better reproduced after the inclusion of radial gas flows in the model. After including a specific velocity pattern for the bar, the results show a flattening of the radial abundance gradient. Our results indicate that radial gas flows may play an important role in the star formation near the centre of barred spiral galaxies.