Electron-matter interaction probed with time-resolved cathodoluminescence

Ultrafast electron microscopy is a powerful technique to study material dynamics at the nanoscale. In particular, cathodoluminescence (CL) microscopy, which relies on the analysis of the light emitted by a material when excited with a high-energy electron, allows us to study optical properties with nanometer spatial resolution. In this thesis we investigate the dynamics of high-energy (1-30 keV) electron interaction with matter using pump-probe cathodoluminescence microscopy (PP-CL). PP-CL is a novel technique that relies on the synchronized excitation of a sample with electron and light pulses, in a timescale only limited by the electron pulse duration (≤ ps). In the first part of the thesis, we present the design, implementation and characterization of the PP-CL setup, which is based on a modified scanning electron microscope. We discuss the photogeneration of electron pulses upon excitation of the electron cathode with fs laser pulses and we revise the differences between excitation of matter with light and electrons. In contrast to previous works, our PP-CL setup enables the use of the electron as a pump and the light as a probe, thus allowing us to directly track the changes induced by the electron on the sample. In the second part of the thesis, we exploit this capability of our PP-CL setup, together with second-order autocorrelation measurements of the CL emission, to study the dynamics of electron-matter interaction in diamond nitrogen-vacancy centers and InGaN/GaN quantum wells. Overall, this thesis provides new insights into the dynamics of electron-matter interaction through the development of PP-CL, thus bringing new capabilities to electron microscopes

Semiempirical Modeling of Reset Transitions in Unipolar Resistive-Switching based Memristors

We have measured the transition process from the high to low resistivity states, i.e., the reset process of resistive switching based memristors based on Ni/HfO2/Si-n+ structures, and have also developed an analytical model for their electrical characteristics. When the characteristic curves are plotted in the current-voltage (I-V) domain a high variability is observed. In spite of that, when the same curves are plotted in the charge-flux domain (Q-phi), they can be described by a simple model containing only three parameters: the charge (Qrst) and the flux (rst) at the reset point, and an exponent, n, relating the charge and the flux before the reset transition. The three parameters can be easily extracted from the Q-phi plots. There is a strong correlation between these three parameters, the origin of which is still under study

Contribuição para a caracterização da recolha comercial de macrofungos comestíveis no distrito de Bragança, Portugal

Com este trabalho pretendeu-se caracterizar a actividade de recolha de cogumelos comestíveis no distrito de Bragança relativamente a espécies e quantidades, habitats, formas de recolha e transporte e valor comercial. Apurou-se que as recolhas incidem principalmente sobre Amanita caesarea, Boletus pinicola, B. edulis, B. aereus, Lactarius deliciosus, Tricholoma equestre, T. georgii, e T. portentosum. As quantidades recolhidas são geralmente inferiores a 5 kg/colector/dia observando-se no global um maior peso das recolhas superiores a 5 kg/colector/dia. As espécies são recolhidas em ecossistemas florestais de e em sistemas agro-florestais. A recolha de cogumelos não constitui a actividade principal dos colectores

Grey-Box Model: An ensemble approach for addressing semi-supervised classification problems

In this paper, we propose a novel and interpretable grey-box ensemble using a selflabeled approach for semi-supervised classification problems. The prospective greybox ensembles a more interpretable whitebox model with a black-box technique. This scheme could guide the comparatively data expensive white-box component with the results from the more accurate black-box part. We evaluate the proposal in an inductive learning setting showing good performance in partially labeled datasets

Planothidum audax sp. nov. (Bacillariophyta, Achnanthidiaceae), a new diatom from temporary streams in southern Portugal

emporary streams represent ca. half of the river network at the worldwide level, and in regions such as southern Europe their dominance of the landscape is evident (Larned et al. 2010, McDonough et al. 2011, Barbosa et al. 2020). Currently, these streams are receiving increased attention due to their importance as high diversity spots for algae, arthropods, plants, etc., and due to the ecosystem services they provide (Acuña et al. 2014, Datry et al. 2018b). Because of their geographical position and the land use changes in their watersheds (increased urbanization, agriculture, etc.), climate change, contamination and habitat fragmentation constitute forces threatening their integrity and ecological characteristics (Datry et al. 2018a, Bonada et al. 2020)

SMYD3 tandem repeats polymorphism is not associated with the occurrence and metastasis of hepatocellular carcinoma in a Chinese population

A variable number of tandem repeats (VNTR) polymorphism in regulatory region of SMYD3 coding for histone methyltransferase has been shown to be associated with colorectal cancer, hepatocellular carcinoma (HCC), and breast cancer in Japanese population. Aim of the study is to investigate the potential association between the functional SMYD3 tandem repeats polymorphism and HCC in Chinese population. Material and Methods: The case-control study included 200 HCC patients and 261 healthy controls. The VNTR polymorphism in the promoter of SMDY3 was genotyped by PCR and direct-sequencing analysis. Odds ratio and 95% confidence interval were used to estimate the association between the polymorphisms and risk of HCC. Results: The allele frequencies for SMYD3 2 and 3 repeats were 15.71% and 84.29% among controls; and 12.75%, and 87.25% among cases (P = 0.22). The odds ratio for 3/3 versus 2/2 and 2/3 genotypes was 1.30 (P = 0.18). The frequencies of 3 alleles were not increased with HCC stage increased (trend test, P = 0.45). Conclusion: SMYD3 polymorphism is not associated with the occurrence and metastasis of HCC in Chinese population.Известно, что полиморфизм тандемных повторов (VNTR) в регуляторном участке гена SMYD3,кодирующем метилтрансферазу гистонов, ассоциирован с развитием рака прямой кишки, карциномы печени (HCC) и рака молочной железы и является популяционно-зависимой характеристикой. Цель работы состояла в исследовании возможной связи междуVNTR Геном SMYD3 и развитием HCC у населения Китая. Материалы и методы: исследование типа “случай-контроль” проводили с участием 200 пациентов с HCC и 261 здорового донора. Полиморфизм VNTR в промоторной области гена SMDY3генотипировали методами PCR. Для оценки связи между полиморфизмом и риском развитияHCC использовали отношение шансов (OR) и 95% доверительные интервалы. Результаты: частота аллелей для повторов SMYD3 2 и 3 составила 15,71 и 84,29% в контрольной группе и 12,75 и 87,25% — в группе больных (P = 0,22). OR Генотипов 3/3 versus 2/2 и 2/3 составило 1,30 (P = 0.18). Частота 3 аллелей не возрастала при повышении стадии заболевания (P = 0,45). Выводы: полиморфизм гена SMYD3 не ассоциирован с развитием и метастазированием HCC у населения Китая

Electrochemical characterization of bioactive hydroxyxanthones by cyclic voltammetry

The present study reports the electrochemical behavior of several phenolic and catecholic-substituted 2,3-diarylxanthones on a glassy carbon electrode, challenged by cyclic voltammetry at different pH values (4.0, 7.4, and 11.0). Higher pH values required lower anodic and cathodic peak voltages. The oxidation of catecholic groups occurred at lower peak potentials in a reversible and pH dependent manner. Anodic peak potentials appeared at higher pH values and were attributed to the electrochemically irreversible oxidation of the phenolic groups. The number and position of hydroxyl substituents were the determinants for the electrochemical behavior and found to correlate with the scavenging activity for reactive oxygen (ROS) and nitrogen species (RNS). A xanthone with two catechol units presented the lowest anodic potential voltage (Epa = 0.15 V) and proved to be the most effective ROS and RNS scavenger.Faculdade de Farmácia da Universidade do Porto, Universidade de Aveiro, Fundação para a Ciência e a Tecnologia (Portugal) and FEDER for funding the Organic Chemistry Research Unit (project PEst-C/QUI/UI0062/2011) and also to the Portuguese National NMR Network (RNRMN)

Prosopis, Retama monosperma. Phragmites y Arundo donax en cosechas sucesivas a uno y dos años de crecimiento, para la elaboración de pasta celulósica y papel

Se evalúa la aptitud de ciertas especies regeneradoras de terrenos degradados: Prosopis (variedades: alba y juliflora),Retama monosperma, Phragmites y Arundo donax, para la fabricación de pastas celulósicas y hojas de papel, mediante un proceso de pasteo organosolv alcalino. Se caracterizan y comparan las materias primas, pastas celulósicas y hojas de papel, para cosechas de un año (más rebrotes de un año de edad, después de haberlas cortado al año) y dos años de crecimiento. Las especies Retama monosperma, Phragmites y Arundodonax muestran potencialidad para su aprovechamientoindustrial, en cosechas de corta rotación, para la obtenciónde pastas celulósicas y papel. Los números kappa de las pastas de 2º año están entre 10,3 y 12,6, con números de tracción entre 13,7 y 20,9 kNm·kg–1 en las pastas sin refinar. Sin embargo la explotación industrial de las dos variedades de Prosopis precisaría su adecuación a tiempos de explotación más largos, que los estudiados en este trabajo

Electrical Characterization Of Epitaxial Layers Of In0.71ga 0.29as0.63p0.37

We have performed measurements of carrier concentration and Hall mobility, between 4.2 K and room temperature, in InGaAsP (energy gap of 0.96 eV) epitaxial layers grown on semi-insulating InP. It is shown that for this kind of material in the range of concentration studied (2.0×101 6-1.6×1018 cm-3), alloy scattering has to be taken into account as a mechanism limiting the mobility even at low temperatures. Also, in the entire range of temperature and concentration studied, Fermi-Dirac statistics are better suited than Boltzmann statistics for theoretical calculations of Fermi energy, because even for concentrations as low as 2.0×1016 cm -3, the material is degenerated at low temperatures. Following these assumptions, we have calculated the alloy scattering potential as being between 0.52 and 0.62 eV.641235238IEEE AESS,IEEE Instrumentation and Measurement Societ

Sex differences in steroid levels and steroidogenesis in the nervous system : Physiopathological role

The nervous system, in addition to be a target for steroid hormones, is the source of a variety of neuroactive steroids, which are synthesized and metabolized by neurons and glial cells. Recent evidence indicates that the expression of neurosteroidogenic proteins and enzymes and the levels of neuroactive steroids are different in the nervous system of males and females. We here summarized the state of the art of neuroactive steroids, particularly taking in consideration sex differences occurring in the synthesis and levels of these molecules. In addition, we discuss the consequences of sex differences in neurosteroidogenesis for the function of the nervous system under healthy and pathological conditions and the implications of neuroactive steroids and neurosteroidogenesis for the development of sex-specific therapeutic interventions