The transition of flight from manned to unmanned systems has led to new research and applications of technology within the field that, until recently, were previously thought to be unfeasible. The industry has become interested in alternative control surfaces and uses for smart materials. A Macro Fiber Composite (MFC), a smart material, takes advantage of the piezoelectric effect and provides an attractive alternative actuator to servos in the Small Unmanned Aerial Systems (SUAS) regime of flight. This research looks to take MFC actuated control surfaces one step further by pulling inspiration from and avian flight. A dual mode control surface, created by applying two sets of two MFCs to patch of carbon fiber, can mimic the tip feathers of a bird. This actuator was modeled both using Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD). Real-world static testing on a feather confirmed preliminary FEA results, and wind tunnel tests simulating assumed cruise conditions confirmed the feather would not exhibit any adverse structural behaviors, such as flutter or aeroelastic divergence. From its modeled performance on a wing using CFD, the MFC feather proved to be a success. It was able to produce a wing that, when compared to a traditional rectangular wing, yielded 73% less induced drag and generated proverse yaw. However, the MFC feathers alone, in the configuration tested, did not produce enough roll authority to feasibly control an aircraft. / Master of Science / The transition of flight from manned to unmanned systems has led to new research and applications of technology within the field that, until recently, were previously thought to be unfeasible. The industry has become interested in alternative control surfaces and uses for smart materials. A Macro Fiber Composite (MFC), a smart material, takes advantage of a specific material property and provides an attractive alternative actuator to servos in the Small Unmanned Aerial Systems (SUAS) regime of flight. This research looks to take MFC actuated control surfaces one step further by pulling inspiration from and avian flight. A dual mode control surface, created by applying two sets of two MFCs to patch of carbon fiber, can mimic the tip feathers of a bird. This actuator was modeled both using Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD). Real-world static testing on a feather confirmed preliminary FEA results, and wind tunnel tests simulating assumed cruise conditions confirmed the feather would not exhibit any adverse structural behaviors, such as flutter or aeroelastic divergence. From its modeled performance on a wing using CFD, the MFC feather proved to be a success. It was able to produce a wing that, when compared to a traditional rectangular wing, yielded 73% less induced drag and generated proverse yaw. However, the MFC feathers alone, in the configuration tested, did not produce enough roll authority to feasibly control an aircraft.

yes / In this work, the interfacial bond performance of recycled aggregate concrete filled stainless steel tube (RAC-FSST) members was investigated through the repeated push-out tests. Three coarse recycled aggregate (CRA) replacements (0, 50% and 100%) and two cross-sectional dimensions were considered in the experimental program. The failure pattern, bond stress-slip response and strain development of stainless steel tube were obtained, and the bond mechanisms under different loading stages were analyzed. Test results showed that the ultimate bond stress increases with the increasing CRA content and decreasing cross-sectional dimensions. Compared with CFST members having carbon steel, RAC-FSST members present lower bond stress. The macro-interlocking effect is obvious in the later loading stage, resulting in a significant increase in the post-peak bond slip curves. Finally, the ultimate bond strength and idealized bond stress-slip models for the RAC-FSST members were suggested on the basis of the test results.

The response of global soil respiration (Rs) to climate change determines how long the land can continue acting as a carbon sink in the future. This dissertation research identifies how temporal and spatial variation in environmental factors affects global scale Rs modeling and predictions of future Rs under global warming. Chapter 1 describes the recommend time range for measuring Rs across differing climates, biomes, and seasons and found that the best time for measuring the daily mean Rs is 10:00 am in almost all climates and biomes. Chapter 2 describes commonly used surrogates in Rs modeling and shows that air temperature and soil temperature are highly correlated and that they explain similar amounts of Rs variation; however, average monthly precipitation between 1961 and 2014, rather than monthly precipitation for a specific year, is a better predictor in global Rs modeling. Chapter 3 quantifies the uncertainty generated by four different assumptions of global Rs models. Results demonstrate that the time-scale of the data, among other sources, creates a substantial difference in global estimates, where the estimate of global annual Rs based on monthly Rs data (70.85 to 80.99 Pg C yr-1) is substantially lower than the current benchmark for land models (98 Pg C yr-1). Chapter 4 simulates future global Rs rates based on two temperature scenarios and demonstrates that temperature sensitivity of Rs will decline in warm climates where the level of global warming will reach 3°C by 2100 relative to current air temperature; however, these regional decelerations will be offset by large Rs accelerations in the boreal and polar regions. Chapter 5 compares CO2 fluxes from turfgrass and wooded areas of five parks in Blacksburg, VA and tests the ability of the Denitrification-Decomposition model to estimate soil temperature, moisture and CO2 flux across the seasons. Cumulatively, this work provides new insights into the current and future spatial and temporal heterogeneity of Rs and its relationship with environmental factors, as well as key insights in upscaling methodology that will help to constrain global Rs estimates and predict how global Rs will respond to global warming in the future. / Ph. D. / CO₂ flux emitted from global soil is the second largest carbon exchange between the land and atmosphere. Accurately estimating global soil CO₂ flux and how it responds to climate change is critical to predict terrestrial carbon stocks. The objectives of this dissertation are to evaluate how time-scale affects our ability to estimate global soil CO₂ flux. In Chapter 1, we show that the best time period for measuring daily mean soil CO₂ flux is at around 10:00 am in almost all climate regions and vegetation types. The previously recommended time range (09:00 am and 12:00 pm) reasonably captures the daily mean soil CO₂ flux. The results from Chapter 2 indicate that air temperature is a good proxy for soil temperature in modeling global soil CO₂ flux. However, monthly precipitation is a uniformly poor proxy for soil water content; instead, average monthly precipitation is a better predictor for global soil CO₂ flux modeling. Chapter 3 demonstrates that the time-scale used in parameterizing models strongly affects the prediction of global CO₂ flux. When using monthly time-scale soil CO₂ flux and air temperature data, soil CO₂ flux increases as air temperature increases at air temperatures below 27 ℃, but soil CO₂ flux begins to decrease when air temperature is over 27 ℃. However, when using annual time-scale data, this response to temperature is masked, soil CO₂ flux increases as air temperature increases in all temperature conditions. As a result, the estimate of global annual soil CO₂ flux, based on monthly soil respiration data (70.85 to 80.99 Pg C yr⁻¹ ), is lower than the estimate based on the annual soil respiration data (98 Pg C yr⁻¹ ). Chapter 4 shows that if the level of global warming maintains its current rate (3ºC by the year 2100), then the annual soil CO₂ flux will either decrease or remains the same in arid, winter-dry temperate and tropical climate regions. However, these regional decelerations were offset by large soil CO₂ flux accelerations in the boreal and polar regions. Chapter 5 shows a significant difference in CO₂ flux among the five selected parks in Blacksburg, VA. The Denitrification-Decomposition model, despite having been developed for agriculture and undeveloped lands, closely estimates soil temperature, moisture and CO₂ flux across the seasons and therefore can be used to estimate and understand CO₂ fluxes from urban ecosystems in future studies. This study highlights that the relationship between soil CO₂ fluxes and environmental factors such as air temperature and precipitation differs from region to region. The study also demonstrates that daily and monthly time-scale soil CO₂ fluxes and environmental data help constrain global soil CO₂ flux estimates and help to predict how global soil CO₂ fluxes will respond to global warming in the future.

Structural health monitoring (SHM) is the process of using measurements of a structure's response to known excitations and trying to determine if damage has occurred to the structure. This also fits the description of non-destructive evaluation (NDE). The main difference is that NDE takes place while the structure is out of service and SHM is intended to take place while the structure is in service. As such, SHM provides the opportunity to provide early warning against structural failure. This thesis intends to advance the state of the art in SHM by examining two approaches to SHM: vibration based and impedance based, and to associate these with the NDE method of stress intensity factors. By examining these methods the goal is to try and answer some of the important questions in SHM process. The first is to experimentally validate a crack model and to see how small of a crack can be detected by vibration methods. The second is to use the concept of stress intensity factor to perform an SHM type of measurement to determine the remaining life of a structure once the impedance method has determined that damage has occurred. The measurement system considered consists of using several different piezoceramic materials as self-sensing actuators and sensors. The structures are a simple beam and a more complex lug element used in aircraft applications. The approach suggested here is to use the impedance and vibration methods to detect crack initiation and then to use the proposed stress intensity method to measure the stress intensity factor of the structure under consideration. / Master of Science

Human trafficking within and across nations is a pervasive, insidious global criminal enterprise that endangers human rights and impedes social justice. Sex and labor are two fundamental types of human trafficking, but media and policies prioritize the former. Social work calls for empowering marginalized groups, and labor trafficking survivors—who are more likely women and immigrants of color—certainly fall into this category. Since 2003, every U.S. state has criminalized human trafficking, yet the issue persists. Most human trafficking analyses focus on federal or international, not state, policies. Thus, this critical analysis aimed to explore how human trafficking is conceptualized at the state level so that policies can be equitable. The research questions of this qualitative multiple-case study were: How do state policymakers conceptualize the problem of human trafficking, and how does this conceptualization differ among states? For answers, this dissertation applied content analysis to a purposive sample of legislative speeches about old and new state human trafficking laws. This dissertation adopted an intersectional lens to uncover what types of survivors (i.e., demographics, labor or sex trafficking survivors) policymakers emphasize when publicly justifying their stances. This study found that, on the whole, state human trafficking policymaking does not consider survivors’ intersectionality, primarily focuses on sex trafficking and prostitution, employs a prosecution-heavy frame, and highlights children and girls as prototypical survivors—minimizing the experiences of women, trans, and immigrant survivors of color. These findings lend empirical support to the observation that U.S. policies prioritize the prototypical young female survivor and sex over labor trafficking. The study carries implications for survivors, policymakers, and social workers, including helping equivocate sex and labor trafficking and ensure that policymaking better reflects the experiences of marginalized groups.

La crise financière actuelle, en raison de sa similarité avec celle du Japon des années 1990, a poussé les autorités monétaires des plus grandes banques centrales à adopter l’assouplissement quantitatif. Seul le Japon, ayant connu une expérience d’assouplissement quantitatif récente mais depuis suffisamment d’années pour être étudiée, peut fournir des éléments de solution à cette crise.Cette thèse applique les techniques économétriques les plus appropriées et récentesà l’analyse de l’assouplissement quantitatif, appliqué par la Banque du Japon entre 2001 et 2006. En trois chapitres sont traitées les questions de savoir s’il était efficace ; sous quelles conditions ? Par quels canaux ?L’efficacité de cette stratégie de politique monétaire à stimuler l’activité et à stopperla spirale déflationniste a été montrée. Cette expérience met en avant le rôle important que la politique monétaire peut jouer pour sortir de la crise, même quand le taux directeur atteint zéro. Le canal des anticipations comme le canal de rééquilibrage des portefeuilles ont tous deux joué un rôle important dans la transmission de ces effets. Les principaux enseignements que l’on peut tirer de l’expérience japonaise sont, d’abord de remédier radicalement et immédiatement aux fragilités du secteur financier, deuxièmement, de mener une politique monétaire particulièrement agressive. Enfin, d’attendre le temps nécessaire pour que les fruits de cette politique viennent. L’expérience japonaise suggère que la Fed et la banque d’Angleterre doivent reporter leur sortie de cette stratégie, sortie qui doit être menée dansle cadre d’un programme et selon des objectifs numériques clairs. / The current financial crisis has now led most major central banks to rely on quantitative easing. The unique Japanese experience of quantitative easing is the only experience which enables us to judge this therapy’s effectiveness and the timing of the exit strategy. Is quantitative easing effective ? Under which conditions ? Through which canal ?This thesis, consisting of three essays, applies appropriate and recent econometrictechniques to examine the quantitative easing in Japan between 2001 and 2006. We show, for the first time, that quantitative easing was able not only to prevent further recession and deflation but also to provide considerable stimulation to both output and prices. Moreover, both expectation and portfolio-rebalancing channels play a crucial role in transmitting monetary policy effects. This experience shows that the monetary policy is still potent even when short-term interest rates reach a zero lower bound. The Japanese experience suggests that efforts to clean up the bank’s balance sheets significantly improved the effectiveness of quantitative easing. However, this effect, although considerable, was short-lived ; it became insignificant after one year. The short duration of this effect confirms the wisdom of the Fed’s decision to maintain quantitative easing longer, so that being short-lived, the positive effects could be exploited. In the light of the Japanese experience, we argue that, in addition to their fast reaction and the huge amount of CABs employed, which may have helped relieve short-term liquidity pressures in the financial system, the Fed was better off postponing its exit from quantitative easing.

Sur la base de constats globaux concernant l’importance d’appliquer des modes de gestion durable des zones forestières et le manque d’investigation concernant l’histoire passée des feux en Europe centrale, il a été entrepris de reconstruire l’histoire des événements de feux et de la dynamique forestière pour des sites d’étude en Allemagne. L’ensemble des données obtenues et analysées ont été utilisées pour l’évaluation du niveau de naturalité des sites étudiés, cette notion étant essentielle pour la mise en place d’une gestion durable, et/ou pour des projets de conservation et / ou de restauration des systèmes perturbés. Concernant les dynamiques des écosystèmes en Europe centrale, il a été souvent mis en évidence que l’homme joue un rôle essentiel depuis des millénaires. Par conséquent, l’approche historique des événements de feux et de la dynamique forestière à été réalisée sur de longues échelles temporelles. Neuf sites d’étude ont été sélectionnés incluant une large gamme de systèmes forestiers d’Europe centrale. Les sites d’études sont répartis dans deux zones générales d’étude : le nord de l’Allemagne (Schleswig-Holstein), qui comprend quatre sites d’étude, et le centre de l’Allemagne (le Harz), qui comprend cinq sites d’étude. Quatre disciplines ont été principalement utilisées. Pour définir l’état actuel des sites d’études ceux-ci ont été caractérisés, utilisant divers indicateurs dendrométriques concernant la structure et la composition des parcelles analysées. Pour obtenir des informations à propos de la dynamique forestière des peuplements forestiers en place des analyses dendroécologiques ont été utilisées. Pour analyser la dynamique forestière sur une longue échelle temporelle, à une échelle spatiale comparable, des analyses pédoanthracologiques ont été menées, combinées à des analyses de sols. De plus, des analyses anthracologiques de séquences de tourbes ont été réalisées, fournissant, combinées avec les données pedoanthracologiques, des enseignements à propos de l’histoire des incendies. L’état actuel et la dynamique forestière récente des sites étudiés indiquent divers niveaux de complexité des peuplements forestiers, correspondant souvent à divers niveaux postulés d’impact anthropique. Il a été obtenu huit chronologies moyennes, standardisées en haute et moyenne fréquences, âgées au maximum de 1744 et au minimum de 1923 ans. A partir de ces chronologies des changements dans les conditions de croissance de peuplements forestiers ont été mises en évidence. Basées sur un ensemble de 71 charbons de bois datés par radiocarbone, il a été mis en évidence, à l’échelle locale et globale, deux principales phases présentant plus d’événements de feux datés, une durant le Pléistocène supérieur/Holocène inférieur, une autre durant l’Holocène supérieur. Pour les deux phases identifiées des forçages climatique et anthropogénique ont été respectivement postulés comme déterminisme des occurrences de feux. Finalement, les différentes données collectées ont été utilisées de façon combinée pour reconstruire l’histoire des feux et des forêts des sites étudiés, afin de contribuer à l’évaluation de leur niveau de naturalité. / Considering two global observations in Central Europe of, firstly, the need for, and development of, sustainable and biological conservation practices for forest and/or woodland areas and, secondly, the lack of long-term fire history, an attempt has been made to reconstruct the fire and the forest history at several investigation sites in Germany. The overall data set gathered and analyzed has been used for on-site naturalness assessment. This latter notion is crucial for forest system conservation/restoration planning, considering the past human impact on forest dynamics. Also, in view of this past human impact on forest systems, which is well-documented for Central Europe, as occurring on a multi-millennium scale, an historical perspective perceptive that combined a long and short temporal scale of investigation was used.Nine investigation sites were selected, in order to include various and representative types of Central European forest. Therefore, the investigation sites were located in two main investigation areas. One is in Northern Germany (Schleswig-Holstein) and includes four investigation sites. The other is in Central Germany (Harz Mountains) and includes five investigation sites. Four main approaches were used. To assess the current state of the investigated site, forest stand characterization was undertaken (i.e. based on various forest attributes that concern stand structure and composition). Tree ring series were analyzed to provide insights about short-term forest tree population dynamics. Then, charcoal records from soil (combined with soil analysis) and peat sequences were qualitatively and quantitatively analyzed. These last two approaches also provide information about the past fire history. Forest current and short-term dynamics illustrated various levels of stand complexity, often corresponding to various levels of human impact that had been postulated. Eight mean site tree-ring chronologies, standardized in high and mid-frequency signal, spanning at a maximum of up to AD 1744 and at a minimum of up to AD 1923, were obtained. The insight, about the identification of events of growing changes and the correlated temporal and, if possible, spatial patterns, was discussed. Charcoal analysis provided a long-term insight about fire history. Based on 71 charcoal radiocarbon dates, it was shown on a macro-scale that there were two phases that had a greater frequency of fire - one during the transition from the late Pleistocene to the early Holocene, and one during the mid- and late Holocene. A strong human control during the most recent fire phase has been postulated. This is supported by on-site soil and peat charcoal record analysis, allowing one to point out the event of environmental changes (disturbances), at local scales. In the end, the on-site data from the various indicators were combined to assess the fire and forest history and the naturalness level of the investigated sites, based on past insights, thereby contributing to a better understanding of the present and helping to anticipate the future.

Le chapitre 1 introduit les modèles et donne les principaux résultats obtenus. Dans le chapitre 2, on présente des simulations numériques d'un modèle macroscopique en deux dimensions. La méthode de discrétisation par éléments finis utilisée est décrite. Pour le cas test de l'écoulement autour d'un cylindre, les phénomènes en jeu dans les fluides vieillissants sont observés. Le chapitre 3 concerne l'étude mathématique de la version unidimensionnelle du système d'équations aux dérivées partielles utilisé pour les simulations. On montre que le problème est bien posé et on examine le comportement en temps long de la solution. Dans le dernier chapitre, des équations macroscopiques sont dérivées à partir d'une équation mésoscopique. L'analyse mathématique de cette équation mésoscopique est également menée / This thesis is devoted to the modelling, the mathematical analysis and the simulation of non-Newtonian fluids. Some fluids in an intermediate liquid-solid phase are particularly considered: aging fluids. Modelling scales are macroscopic and mesoscopic. In Chapter 1, we introduce the models and give the main results obtained. In Chapter 2, we present numerical simulations of a macroscopic two-dimensional model. The finite element method used for discretization is described. For the flow past a cylinder test-case, phenomena at play in aging fluids are observed. The Chapter 3 contains a mathematical analysis of the one-dimensional version of the system of partial differential equations used for the simulations. We show well-posedness and investigate the longtime behaviour of the solution. In the last chapter, macroscopic equations are derived from a mesoscopic equation. The mathematical analysis of this mesoscopic equation is also carried out

Les fluctuations électriques des composants sont une limitation à la miniaturisation des circuits. Malgré des procédés de fabrications en continuelle évolution, les variations des caractéristiques électriques dues au désappariement entre deux dispositifs limitent les performances des circuits. Concernant les applications à faible consommation, ces fluctuations locales peuvent devenir très critiques. Dans le contexte du développement d’une technologie CMOS 90nm avec mémoire Flash embarquée pour des applications basse consommation, l’appariement de transistors MOS est étudié. Une analyse de l’impact du dopage de grille des transistors NMOS est menée. L’étude se focalise sur l’appariement en tension des paires différentielles polarisées dans la zone de fonctionnement sous le seuil. Il est démontré que cet appariement peut être dégradé à cause de l’effet « hump », c'est-à-dire la présence de transistors parasites en bord d’active. Un macro-modèle permettant aux concepteurs de modéliser cet effet est présenté. Il est étudié au niveau composant, au niveau circuit et en température. Enfin, une étude de la dégradation de l’appariement des transistors MOS sous stress porteurs chauds est réalisée, validant un modèle de dégradation. Des transistors octogonaux sont proposés pour supprimer l’effet « hump » et donnent d’excellents résultats en termes d’appariement ainsi qu’en fiabilité. / Electrical fluctuations of devices limit chip miniaturization. Despite manufacturing processes in continuous evolution, circuit performances are limited by electrical characteristics variations due to mismatch between two devices. Concerning low power applications, local fluctuations can become very critical. In the context of development of a 90nm CMOS technology with Embedded Flash memory for low power applications, MOS transistors matching is studied. A study of NMOS transistors gate doping impact is conducted. Study focuses on voltage matching of differential pairs biased under threshold. It is demonstrated that this matching can be degraded due to « hump » effect, meaning presence of parasitic devices on active edge. A macro-model allowing designers to model this effect is presented. It is studied at device level, circuit level and for different temperatures. Finally, a degradation study of MOS transistors mismatch under Hot Carriers Injection stress is performed, validating a degradation model. Octagonal devices are proposed to suppress « hump » effect and give good results in terms of matching as well as reliability.

A influência das variáveis associadas ao laser como a fluência, o comprimento de onda, e a duração do pulso, assim como as relacionadas às propriedades das amostras, como a distribuição do tamanho das partículas e as características químicas da matriz, foram avaliadas visando à determinação quantitativa de macro- (P, K, Ca, Mg) e micronutrientes (Cu, Fe, Mn, Zn, B) em pastilhas de materiais vegetais por espectrometria de emissão óptica com plasma induzido por laser (LIBS). Os efeitos da distribuição do tamanho das partículas e da fluência do laser foram investigados a partir da análise de amostras peneiradas (150-20 µm) empregando-se um sistema LIBS, em regime temporal de nanossegundos (ns-LIBS), montado com um laser de Nd:YAG a 1064 nm (pulsos de 5 ns e 360 mJ)e um espectrômetro com óptica Echelle e detector ICCD. Observou-se um aumento na sensibilidade e na precisão das medições com a diminuição do tamanho das partículas usadas no preparo das pastilhas, e uma diminuição dos efeitos de matriz causados por diferenças no tamanho das partículas, quando pastilhas preparadas com partículas < 75 µm foram analisadas com pulsos de 50 J cm-2. Verificou-se uma melhora significativa na exatidão das medições de Mg, Fe, Mn e Zn feitas em um conjunto de pastilhas de folhas de cana-de-açúcar (partículas < 75 µm) empregando-se esta fluência. Em uma segunda etapa, observou-se que variações no comprimento de onda do laser de Nd:YAG (1064, 532, 355 e 266 nm) não influenciaram de maneira significativa a precisão e exatidão das medições em pastilhas de folhas de cana-de-açúcar, obtendo-se correlações lineares entre as intensidades dos sinais de emissão e as correspondentes frações de massa dos analitos. Variações no comprimento de onda do laser de Nd:YAG não afetaram a análise de um conjunto heterogêneo de amostras, composto por pastilhas de folhas de plantas de diferentes espécies, como soja, cana-de-açúcar, milho, citros, café, por exemplo, por ns-LIBS. No entanto, diferentemente do observado para o conjunto de pastilhas de folhas de cana-de-açúcar, observou-se, uma baixa correlação (r cal < 0,90) entre as frações de massa de Ca, Mg, P, Cu, Fe, Mn e Zn determinadas por ns-LIBS e os valores de referência, o que demonstra a baixa robustez de ns-LIBS frente às variações na composição química das matrizes. Posteriormente, analisou-se este conjunto heterogêneo de amostras com sistema LIBS, em regime temporal de femtossegundos (fs-LIBS), montado com laser de Ti:Safira (pulsos de 60 fs e 1,65 mJ) e espectrômetro com óptica Czerny-Turner e ICCD. Demonstrou-se que o uso de pulsos em regime de fs proporcionou calibrações e validação menos dependentes da composição química das matrizes. As frações de massa de Ca, Mg, P, Fe e Mn previstas por fs-LIBS foram estatisticamente concordantes com os valores de referência, independentemente do modelo de calibração usado. Além disso, o uso de calibração multivariada melhorou a capacidade preditiva de ns-LIBS, assemelhando-se à de fs-LIBS. Concluiu-se que o emprego de fs-LIBS foi a estratégia mais robusta e que ofereceu maior flexibilidade à variabilidade matricial / The influence of laser properties, such as fluence, wavelength and pulse duration, as well as sample characteristics, such as particle size distribution and chemical matrix composition, was evaluated aiming at the quantitative determination of macro- (P, K, Ca, Mg) and micronutrients (Cu, Fe, Mn, Zn, B) in pellets of plant materials by laser-induced breakdown spectroscopy (LIBS). Firstly, the effects of particle size distribution and laser fluence on the analysis of pellets (test samples) prepared with sieved samples (from 150 to 20 µm apertures) were investigated. Experiments were carried out with a nanosecond LIBS (ns-LIBS) system by using a Q-switched Nd:YAG laser at 1064 nm (5 ns; 360 mJ) and a spectrometer with Echelle optics and intensified charge-coupled device (ICCD) detector. Results indicated that smaller particles yielded to sensitivities\' enhancement and attained better measurements\' precision. Moreover, matrix effects were reduced by analyzing pellets prepared from < 75 ?m sieved fractions and pulses of 50 J cm-2. In addition, there was a significant improvement on accuracy of Mg, Fe, Mn and Zn measurements in a set of test samples of sugarcane leaves by using this fluence. In a second experiment, variations in the Nd:YAG laser wavelength (1064, 532, 355 and 266 nm) did not affect the analysis of test samples of sugarcane leaves, and provided linear correlations between emission signal intensities and corresponding analytes mass fractions. In addition, variations within Nd:YAG laser wavelength did not affect the analysis of a heterogeneous sample set composed by pellets of leaves from different crops, such as soy, sugarcane, maize, citrus and coffee by ns-LIBS. However, in contrast to previous findings, the univariate calibration models for ns-LIBS presented lower linearity (r cal < 0.90) for Ca, Mg, P, Cu, Fe, Mn and Zn, no matter the laser wavelength used for the analysis. These circumstances reflect the low robustness of ns-LIBS to variations within matrix chemical composition among test samples. Afterwards, test samples from different crops were analyzed by a femtosecond LIBS (fs-LIBS) by using a Ti:Sapphire laser, including a mode-locked oscillator and an ultrafast amplifier (60 fs; 1.65 mJ per pulse), and a spectrometer with Czerny-Turner optics and ICCD. Findings indicated that the pulse duration was a decisive variable for providing accurate quantification of nutrients in different plant species, which present substantial differences in terms of matrix chemical composition. Close agreement between Ca, Mg, P, Fe and Mn mass fractions predicted by fs-LIBS and those determined by ICP OES was evidenced, whatever the modeling approach used. Contrarily, for ns-LIBS analysis of test samples from different crops, only the use of multivariate partial least squares (PLS) regression appears capable for resolving the non-linear transformations of the emission intensities according to the physical mechanisms governing this temporal regime of ablation. Thus, when using multivariate modeling, the figures-of merit reflecting the predictive capabilities of ns-LIBS resemble to those achieved by fs-LIBS. Either way, fs-LIBS is a more robust approach that better offers larger flexibility to the matrix variability