Estudo para um sistema de CVD para obtenção de placas auto sustentadas de silício para aplicações fotovoltaicas

Tese de mestrado em Engenharia Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2008O desenvolvimento do mercado das energias renováveis levou a um aumento significativo da procura de tecnologia fotovoltaica. A investigação na área de fornecimento de substratos de silício cristalino para produção de células fotovoltaicas, está direccionada para a procura de soluçoes que substituam o recurso que domina actualmente o mercado, as wafers obtidas por corte de lingotes que representam cerca de um terço do preço final de uma célula fotovoltaica. Nesta perspectiva, foi desenvolvido no Laboratório de Aplicações Fotovoltaicas e Semicondutores da Universidade de Lisboa um processo de crescimento de silício multicristalino directamente na forma de uma fita, o processo SDS Ribbons. Este processo baseia-se na deposição de silício por CVD, a baixas temperatura e a pressão ambiente, a partir de silano, sobre um substrato de pó de silício de elevada pureza. Após a deposição, o filme de silício nanoporoso é recristalizado através da técnica de zona fundida flutuante (ZMR), que garante a elevada qualidade cristalina e pureza das fitas de silício multicristalino. Apesar da elevada qualidade das células fotovoltaicas produzidas a partir das fitas de silício do reactor SDS de 1ª geração, verificou-se uma reduzida taxa de sucessos na fase de recristalizacao, devido ao colapso da zona fundida. Pensa-se que na base destes resultados esteja a heterogeneidade da porosidade e a espessura do filme depositado. Por esta razão deu-se início ao projecto de um reactor SDS de 2º geração, que visa não só resolver os problemas do primeiro, como também implementar novas ideias que tornarão o processo mais eficiente do ponto de vista da rentabilização do silano e permitirão a sua integração num processo em cadeia. Os estudos apresentados neste documento consistem em duas partes distintas: A primeira e direccionada ao reactor SDS de 1ª geração, em que se explora a distribuição da radiação na amostra e o comportamento dinâmico do gás no interior do reactor, e nomeadamente da convecção natural, de modo a correlaciona-los com os perfis de deposição dos filmes depositados por CVD. Para este estudos foram explorados dois softwares comerciais de análise numérica, o FloWorks no âmbito de dinâmica de fluidos e modos de trocas de calor, e o ZEMAX para simulações de ray-tracing. A segunda é dedicada ao desenvolvimento do reactor de 2ª geração. Com recurso ao software Floworks, exploram-se factores do foro geométrico e termofísico que proporcionam a formação de células de convecção dentro da cavidade do reactor CVD, de modo a permitir a circulação controlada do gás junto as zonas de deposição, com o objectivo de a rentabilizar. Este estudo culminou numa proposta para um novo reactor de CVD. Efectuou-se também um estudo analítico para um sistema óptico concentrador para este reactor CVD.The development of the renewable energies market lead to a significant increase in the demand of photovoltaic technology. The research in the area of crystalline silicon feedstock for photovoltaic cells production, is focused on the research of solutions to replace the dominant path in nowadays market - the wafers obtained by the cut of ingots which represents about a third of the final price of a photovoltaic cell. In this framework, the Laboratório de Aplicações Fotovoltaicas e Semicondutores da Universidade de Lisboa, is developing a new process for the growth of multicrystalline silicon ribbons, the SDS Ribbons process. This process is based on the silicon deposition by CVD at low temperatures and atmospheric pressure, from silane, on top of a high purity silicon powder substrate. After the deposition, the nano-porous silicon film is recrystallized by the zone melting recrystallization (ZMR) technique, which guarantees the high crystalline quality and purity of the multicrystalline silicon ribbons. Despite the high quality of solar cells produced from the first generation SDS reactor, a reduced rate of successes in the recrystallization step was obtained, due to the collapse of the molten zone during the ZMR step. This problem seems to be related to the porosity and thickness heterogeneity of the deposited film. For this reason a new design for a second generation SDS reactor was started, with the purpose to solve the first reactor problems and to implement new ideas which will make the process more efficient from the point of view of silane conversion and to allow its integration into a continuous mode process. The studies presented in this document are divide in two distinct parts: The first one is related to the first generation reactor, where both the radiation distribution in the sample and the dynamic behavior of the gas in the interior of the reactor are analysed, in order to correlate them with the deposition profiles of the deposited films by CVD. For these studies two numerical analysis commercial softwares where explored; the FloWorks module for fluids dynamic and heat exchange modes, and the ZEMAX ray tracing simulation. The second one is dedicated to the development of the second generation reactor. Using the software FloWorks, geometric and thermophysics factors were explored to analyze the convection cells formation inside the CVD reactor cavity, to allow a controlled circulation of the gas nearby the deposition zones, with the purpose of enhancing the deposition rate. This study culminated in a proposal for a new CVD reactor. An analytical study for a concentrator optical system for this new reactor is also presented

Structuring the problem of an inclusive and sustainable energy transition – A pilot study

The purpose of the article is to contribute to structuring the problem of how to advance a sustainable energy transition and achieve carbon neutrality goals while ensuring a democratic and inclusive process, by drawing on a pilot case – i.e., the energy transition in Portugal. By building on approaches and concepts from the Sustainability Transitions research field, the article explores perceptions, values, and concerns regarding distributed and centralized energy models; inclusivity and energy democracy; energy systems’ sustainability concerns and the speed of the transition. The study draws on the hypothesis that stakeholders across the state, market, community and third sector spheres, while equally supporting decarbonization, have different perceptions, values, and concerns regarding the social, environmental, and technological dynamics of the energy transition that need to be better understood for accelerating the transition. The multi-method approach included interviews, a survey (N = 110) and a stakeholder workshop, to unpack the key values and preferences around energy system technologies, sustainability and inclusionary aspects, the role of centralized and distributed energy systems and new investments, namely in green hydrogen and lithium mining. The results indicate there is a significant convergence on the fact that decarbonization is a priority that needs to be supported by inclusive and democratic processes. Decentralization, energy communities and solar energy are extremely valued, and transparency and information sharing are crucial expectations for new lithium mining projects, large-scale solar and green hydrogen investments. These findings outline some avenues for future research, where participation and transparency become anchors for a sustainable and inclusive transition.info:eu-repo/semantics/publishedVersio

An interventional nationwide surveillance program lowers postoperative infection rates in elective colorectal surgery: a cohort study (2008–2019)

Colorectal surgery; Postoperative infection; Cohort studiesCirugía colorrectal; Infección postoperatoria; Estudios de cohortesCirurgia colorectal; Infecció postoperatòria; Estudis de cohortsBackground: Colorectal surgery is associated with the highest rate of surgical site infection (SSI). This study analyses the effectiveness of an interventional surveillance program on SSI rates after elective colorectal surgery. Material and methods: Cohort study showing temporal trends of SSI rates and Standardized Infection Ratio (SIR) in elective colorectal surgery over a 12-year period. Prospectively collected data of a national SSI surveillance program was analysed and the effect of specific interventions was evaluated. Patient and procedure characteristics, as well as SIR and SSI rates were stratified by risk categories and type of SSI analysed using stepwise multivariate logistic regression models. Results: In a cohort of 42,330 operations, overall cumulative SSI incidence was 16.31%, and organ-space SSI (O/S-SSI) was 8.59%. There was a 61.63% relative decrease in SSI rates (rho = -0.95804). The intervention which achieved the greatest SSI reduction was a bundle of 6 measures. SSI in pre-bundle period was 19.73% vs. 11.10% in post-bundle period (OR 1.969; IC 95% 1.860-2.085; p < 0.0001). O/S-SSI were 9.08% vs. 6.06%, respectively (OR 1.547; IC 95% 1.433-1.670; p < 0.0001). Median length of stay was 7 days, with a significant decrease over the studied period (rho = -0.98414). Mortality of the series was 1.08%, ranging from 0.35% to 2.0%, but a highly significant decrease was observed (rho = -0.67133). Conclusions: Detailed analysis of risk factors and postoperative infection in colorectal surgery allows strategies for reducing SSI incidence to be designed. An interventional surveillance program has been effective in decreasing SIR and SSI rates

Understanding the expectations of nursing students following the first clinical internship: A qualitative study

"This study aimed to describe how nursing students' expectations are achieved in their first clinical internship, as part of a longitudinal qualitative study conducted in a public nursing school in Barcelona, Spain. Data in the current phase were collected in 2019 from students (n = 15) after completing an internship for the first time, recruited with purposive sampling until data saturation was reached in semi-structured interviews, and thematic analysis was performed on the interview content. Positive factors that had a powerful influence on students included the accessibility at the internship location and the experience with the clinical instructor, when these provided assessment and integration of the student in the health team. Practical learning is mediated by chance in terms of the center, service, teacher, and clinical instructor assigned. It is crucial to establish consensual measures among all the actors involved to facilitate the efficacy of teaching and learning.

Tratamiento ambulatorio de la diverticulitis aguda no complicada : impacto sobre los costes sanitarios

OBJETIVOS: Se ha demostrado previamente que el tratamiento ambulatorio de la diverticulitis aguda no complicada es seguro, eficaz y aplicable en la mayoría de los pacientes que toleran la dieta oral y que tienen un adecuado apoyo familiar. El objetivo de este estudio es cuantificar el impacto que el tratamiento ambulatorio tiene en la reducción de costes sanitarios. MATERIAL Y MÉTODOS: Estudio comparativo retrospectivo realizado sobre una base de datos mantenida de forma prospectiva. Periodo de estudio: enero del 2005 hasta junio del 2011. Grupo de estudio: pacientes diagnosticados de diverticulitis aguda no complicada tratados con antibióticos vía oral de forma ambulatoria (7-10 días). Grupo control: pacientes diagnosticados de diverticulitis aguda no complicada que cumplían criterios de tratamiento ambulatorio pero que fueron ingresados con tratamiento antibiótico endovenoso (7-10 días). El diagnóstico se confirmó mediante TC abdominal. Se han analizado las características de los pacientes y los motivos del ingreso así como el resultado del tratamiento. El análisis de costes se ha realizado mediante el sistema "full costing", sumación de todos los costes variables (costes directos) más el conjunto de costes generales repartidos por actividad (costes indirectos) y que incluye los gastos en urgencias, unidad de hospitalización, laboratorio, radiología y farmacia. Se ha añadido el coste del tratamiento ambulatorio tanto en el grupo de estudio (tratamiento completo) como en el grupo control, cuando completaron el tratamiento una vez dados de alta. Se ha realizado el análisis comparativo según intención de tratamiento. RESULTADOS: Se incluyeron 136 pacientes, 90 en el grupo de estudio y 46 en el grupo control. No hubo diferencias en la edad, sexo, número de episodios anteriores, fiebre o leucocitosis entre los dos grupos. Los motivos de tratamiento hospitalario más frecuentes fueron: ingreso en la fase inicial del protocolo, decisión del médico de guardia o negativa del paciente al tratamiento ambulatorio. Cinco de los 90 pacientes del grupo de estudio precisaron ingreso por persistencia del dolor o vómitos mientras que 2 de los pacientes del grupo control reingresaron por recurrencia de la sintomatología (5,5% vs. 4,3%; p=0,7). Ninguno de estos pacientes precisó cirugía urgente. El coste global por episodio fue de 882±462 euros en el grupo de estudio frente a 2376±830 euros en el grupo control (p=0,0001). CONCLUSION El tratamiento ambulatorio de la diverticulitis agua no sólo es seguro y eficaz sino que también reduce más de un 50% los costes sanitarios. Palabras clave: Diverticulitis aguda. Tratamiento ambulatorio. Impacto sobre coste sanitarioOBJECTIUS: S'ha demostrat prèviament que el tractament ambulatori de la diverticulitis aguda no complicada és segur, eficaç i aplicable en la majoria dels pacients que toleren la dieta oral i que tenen un bon suport familiar. L'objectiu d'aquest estudi és quantificar l'impacte que el tractament ambulatori té en la reducció dels costos sanitaris. MATERIAL I MÈTODES: Estudi comparatiu retrospectiu realitzat sobre una base de dades mantinguda de forma prospectiva. Període d'estudi: del gener del 2005 fins al juny del 2011. Grup d'estudi: pacients diagnosticats de diverticulitis aguda no complicada tractats amb antibiòtics via oral ambulatòriament ( 7-10 dies ). Grup control: pacients diagnosticats de diverticulitis aguda no complicada que acomplien criteris de tractament ambulatori però van ser ingressats amb tractament antibiòtic endovenós ( 7-10dies ). El diagnòstic es va confirmar mitjançant TC abdominal. S'han analitzat les característiques dels pacients , els motius d'ingrés i el resultat del tractament. L'anàlisi de costos s'ha realitzat mitjançant el sistema "full costing", suma de tots els costos variables (directes) més el conjunt de costos generals repartits per activitats (indirectes), inclusos els costos a urgències, sala d'hospitalització, laboratori, radiologia i farmàcia. S'ha afegit el cost del tractament ambulatori tant en el grup d'estudi ( tractament complet ) com en el grup control, quan van completar el tractament un cop donats d'alta. S'ha realitzat l'anàlisi comparatiu per intenció de tractar. RESULTATS: Es van incloure 136 pacients, 90 en el grup d'estudi i 46 en el grup control. No existien diferències d'edat, sexe, nombre d'episodis anteriors, febre o leucocitosis entre els dos grups. Els motius de tractament hospitalari més freqüents foren: ingrés a la fase inicial del protocol, decisió del metge de guàrdia o negativa del pacient a rebre tractament ambulatori. 5 dels 90 pacients del grup estudi van precisar ingrés hospitalari per persistència del dolor o vòmits mentre que 2 dels pacients del grup control van reingressar per recurrència de la simptomatologia ( 5,5% vs. 4,3%; p=0,7). Cap d'aquests pacients va ser operat d'urgències. El cost global per episodi va ser de 882±462 euros en el grup d'estudi, en front els 2376±830 euros en el grup control ( p=0,0001). CONCLUSIÓ: El tractament ambulatori de la diverticulitis aguda no només és segur i efectiu sinó que també redueix en més d'un 50% els costos sanitaris

Temporal dynamics of soil fungal communities after partial and total clear-cutting in a managed Pinus sylvestris stand

Forest management aimed to maximize timber production might impact soil fungi, especially those symbiotically associated to tree roots. In this study, we analyse the temporal dynamics of soil fungi along five sampling years after tree removal in a managed Pinus sylvestris stand in northern Spain, where timber production is combined with regular mushroom harvesting. Two management methods were tested: total and partial clear-cutting leaving retention trees for seedling regeneration. Undisturbed, uncut plots were also included in the experiment as a control treatment. The whole fungal community (phylotypes and ecological guilds) were analysed by high-throughput Illumina MiSeq sequencing of fungal ITS1 amplicons. We hypothesized that (1) ectomycorrhizal fungal communities will decrease after both clear-cutting treatments with a concurrent increase in the abundance of saprotrophs, (2) the abundance and diversity of the ectomycorrhizal guild will be more preserved in partially clear-cut than in total clear-cut plots, and (3) the overall fungal diversity will decrease in the cut plots leading to major losses of ectomycorrhizal species. Our results show that soil fungal composition changed across the five years after clear-cutting by decreasing ectomycorrhizal fungi and increasing saprotrophs. However, these changes did not significantly affect fungal diversity and there were taxa-specific responses to tree harvest treatments. Boletus edulis, the most abundant ectomycorrhizal species fruiting in the study area and a valuable local non-forest resource, was negatively affected by either clear-cutting treatments. Soil fungal community composition in partially clear-cut areas was not different from that of total clear-cut areas. Our results indicate a strong effect of tree harvest on the relative abundance of ectomycorrhizal fungi along the first years after clear-cutting. However, levels of fungal diversity were comparable to the undisturbed forest, thus suggesting a potential further recovery of ectomycorrhizal fungi through the colonization of the regenerated seedlings.info:eu-repo/semantics/acceptedVersio

Mortality risk estimation in acute calculous cholecystitis : beyond the Tokyo Guidelines

Acute calculous cholecystitis (ACC) is the second most frequent surgical condition in emergency departments. The recommended treatment is the early laparoscopic cholecystectomy; however, the Tokyo Guidelines (TG) advocate for different initial treatments in some subgroups of patients without a strong evidence that all patients will benefit from them. There is no clear consensus in the literature about who is the unfit patient for surgical treatment. The primary aim of the study is to identify the risk factors for mortality in ACC and compare them with Tokyo Guidelines (TG) classification. Retrospective unicentric cohort study of patients emergently admitted with and ACC during 1 January 2011 to 31 December 2016. The study comprised 963 patients. Primary outcome was the mortality after the diagnosis. A propensity score method was used to avoid confounding factors comparing surgical treatment and non-surgical treatment. The overall mortality was 3.6%. Mortality was associated with older age (68 IQR 27 vs. 83 IQR 5.5; P = 0.001) and higher Charlson Comorbidity Index (3.5 5.3 vs. 02; P = 0.001). A logistic regression model isolated four mortality risk factors (ACME): chronic obstructive pulmonary disease (OR 4.66 95% CI 1.7-12.8 P = 0.001), dementia (OR 4.12; 95% CI 1.34-12.7, P = 0.001), age 80 years (OR 1.12: 95% CI 1.02-1.21, P = 0.001) and the need of preoperative vasoactive amines (OR 9.9: 95% CI 3.5-28.3, P = 0.001) which predicted the mortality in a 92% of the patients. The receiver operating characteristic curve yielded an area of 88% significantly higher that 68% (P = 0.003) from the TG classification. When comparing subgroups selected using propensity score matching with the same morbidity and severity of ACC, mortality was higher in the non-surgical treatment group. (26.2% vs. 10.5%). Mortality was higher in ACC patients treated with non-surgical treatment. ACME identifies high-risk patients. The validation to ACME with a prospective multicenter study population could allow us to create a new alternative guideline to TG for treating ACC. Retrospectively registered and recorded in Clinical Trials

Lack of thinning effects over inter-annual changes in soil fungal community and diversity in a Mediterranean pine forest

Predicted changes in global climate might negatively affect the soil microbiome and associated ecosystem processes in Mediterranean forests. Forest treatments, such as forest thinning, have been suggested to mitigate climate change impacts on vegetation by reducing competition between trees, thus increasing water availability. Studies addressing the combined effects of climate and forest thinning on belowground fungal communities are still scarce, being fundamental to elaborate adaptive strategies to global warming. The aim of this study was to evaluate the tree density reduction effects on soil fungal communities and their response to inter-annual changes in weather conditions. The temporal dynamics of soil fungal communities in relation to these two drivers (i.e., forest management and weather conditions) were studied from 2009 until 2014 in a set of 12 pairs of thinned and un-thinned plots dominated by Pinus pinaster Ait. Thinning (from 30% up to 70% reduction in stand basal area) was conducted in 2009 and soil fungal community composition was studied during 4 years. Here, we used autumn precipitation and temperature to describe the impact of inter-annual weather changes. We used Pacific Biosciences sequencing of fungal ITS2 amplicons to study fungal communities in soil samples. Forest thinning did not significantly affect fungal community composition nor fungal species richness and diversity, indicating that the soil fungal community is resistant to forest thinning regardless of its intensity. However, fungal species composition changed progressively across years, both at the species level and with regards to functional guilds. These changes in community composition were partly driven by inter-annual variation in precipitation and temperature, with free-living fungi increasing in abundance under wetter conditions, and symbiotic fungi being more prominent under drier and colder conditions. The results indicate that mycorrhizal communities in Mediterranean forest ecosystems can resist forest thinning, if enough trees and functional roots from thinned trees are retained.info:eu-repo/semantics/acceptedVersio

Incidence of peripheral arterial disease in the ARTPER population cohort after 5 years of follow-up

To know the epidemiology (prevalence, incidence, progression and morbidity and mortality associated) of peripheral artery disease in general population and the factors associated with this progression is essential to know the evolution of atherosclerosis and develop preventive strategies. The aim of the study was to determine the incidence of PAD after 5 years of follow-up population-based cohort ARTPER, and the evolution of Ankle brachial Index (ABI) in this period. Peripheral artery disease incidence analysis after 5 years of follow-up of 3786 subjects > 50 years old. Peripheral artery disease incident when the second cross section Ankle brachial Index was <0.9 in any of the lower limbs, with normal baseline (0.9 to 1.4). Between 2012 and 2013 2762 individuals (77 % participation) were re-examined. Finally analyzed 2256 subjects (after excluding pathological Ankle brachial Index) followed for 4.9 years (range 3.8 to 5.8 years), totalling 11,106 person-years. Peripheral artery disease 95 new cases were detected, representing an incidence of 4.3 % at 5 years and 8.6 per 1000 person-years (95 % CI 6.9 to 10.5) being higher in men (10.2, 95 % CI 7.4 to 13.5) than in women (7.5, 95 % CI 5.5 to 9.9). Linear correlation between the baseline Ankle brachial Index and the second cross section was low (r = 0.23). The incidence of peripheral artery disease in ARTPER cohort was 8.6 cases per 1000 person-years, being higher in men, especially <65 years. The correlation between two measures Ankle brachial Index after 5 years of follow-up was low. One might consider whether Ankle brachial Index repeated measures could improve the correlation

Caminar més d'una hora al dia redueix a la meitat el risc de patir arteriopatia perifèrica

L'arteriopatia perifèrica és el conjunt de signes i símptomes que es manifesten quan es produeix una disminució del flux sanguini a una extremitat, i és un potent predictor d'episodis cardiovasculars i cerebrovasculars. Un estudi realitzat amb 3.207 persones majors de 49 anys de 28 centres de l'àrea metropolitana de Barcelona i el Barcelonès Nord ha demostrat que caminar una hora al dia redueix a la meitat el risc de patir aquesta malaltia i que l'activitat física en pacients ja malalts s'associa a un menor empitjorament.La arteriopatía periférica es el conjunto de signos y síntomas que se manifiestan cuando se produce una disminución del flujo sanguíneo en una extremidad, y es un potente predictor de episodios cardiovasculares y cerebrovasculares. Un estudio realizado con 3.207 personas mayores de 49 años de 28 centros del área metropolitana de Barcelona y el Barcelonés Norte ha demostrado que caminar una hora al día reduce a la mitad el riesgo de padecer esta enfermedad y que la actividad física en pacientes ya enfermos se asocia a un menor empeoramiento