12 resultados para stability study
em Digital Commons at Florida International University
Resumo:
The International Coffee Agreements (ICA) involved the majority of nations producing and consuming coffee and provided relative economic stability to the coffee sectors of the exporting Third World countries. This study focuses on the serious impact of the 1989 collapse of the ICA on the domestic coffee sectors of Colombia and Côte d'Ivoire. In particular, the dissertation examines the role of the Colombian and Ivoirian coffee parastatals, the Federacion Nacional de Cafeteros de Colombia and the Caisse de Stabilisation et Soutien des Prix des Produits Agricoles, during the crisis and their transformation by it. ^ The theoretical framework employed in this study is borrowed from the literature on state-society relations. The methodology includes: in-depth analysis of the historical roles of the parastatal agencies in coffee production, state-society relations and economic development in Colombia and Côte d'Ivoire; interviews with parastatal administrators, producers and other knowledgeable informants in both countries; and a comprehensive review of newspaper articles and official statements of coffee policy published in Colombia and Côte d'Ivoire. prior to, during, and after the crisis. ^ The Colombian and Ivoirian coffee sectors and their producers faced serious economic and social problems following the drop in coffee prices. The coffee parastatals in Colombia and Côte d'lvoire first lost some of their responsibilities following the world coffee crisis. The Caisse was in the end eliminated while FEDECAFE struggled to remain in existence. Along the way, both entities faced protests from disgruntled coffee producers, who organized politically for the first time in their nations' histories. I argue that the outcome for the parastatals depended in part on the conditions of their formation, particularly the level of societal involvement in their creation. I also posit that the country's dependence on foreign aid played a key role in the fate of the parastatals. ^ This dissertation concludes that developments in the Colombian and Ivoirian coffee sectors have significantly contributed to the creation of the difficult political and economic conditions of both countries today. ^
Resumo:
The current study examined the role of three important components in the use of structured employment interviewing in performance prediction: construct bandwidth, observed communication skill, and the stability/dynamicity of performance criteria over time. A matched sample of 242 hospitality managers was derived from a field data set provided by a large hospitality management organization. Interview data and two years of performance appraisal data were provided. Bandwidth analysis demonstrated only minimal differences in prediction between matched predictor-criterion pairs compared with predictor to overall aggregate ratings (unmatched). The communication skill analysis revealed that this interviewer rated observation significantly predicted a number of the individual performance dimensions as well as overall performance over time. Of the five interview items, the strongest overall predictor of performance was interviewer rated communication skill. The stability/dynamicity analyses demonstrated the performance criteria to be generally stable over the two year period examined, which provides support for the long held notion that performance criteria is stabile over time. However, there were two exceptions. The interview dimension customer service orientation had shifting relationships over time with four of the criteria over the two year period. The performance criteria employee development also demonstrated some instability in its relationships with predictors. Thus, some evidence of dynamicity in performance criteria was revealed. Interestingly, both of the most noteworthy findings in the study involved items that were rated differently than the others in the study. The rated interview item communication skill and the rated performance criteria client satisfaction were ratings that involved a more direct level of observation. Additional analyses also revealed evidence of a general factor of performance. These two themes are more fully covered in the discussion.
Resumo:
Mn+1AXn compounds, the ternary layered nanolaminates have gathered momentum in the last decade since its advent because of their unusual but exciting properties. These technologically important compounds combine some of the best properties of metals and ceramics. Like ceramics they are refractory, oxidation resistant, elastically stiff and relatively light. They also exhibit metallic properties like excellent machinability, thermal and electrical conductivity. This dissertation concentrates on the synthesis of germanium-based 211 Mn+1AXn compounds. The main objective of the research was to synthesize predominantly single phase samples of Cr2GeC, V2GeC and Ti2GeC. Another goal was to study the effect of solid substitutions on the M-site of Mn+1AXn compounds with Ge as an A-element. This study is in itself the first to demonstrate the synthesis of (Cr0.5V0.5)2GeC a novel Mn+1AXn compound. Scanning electron microscopy coupled with energy dispersive spectroscopy, x-ray diffraction and electron probe microanalysis were employed to confirm the presence of predominantly single phase samples of M2GeC compounds where M = Ti, V, Cr and (Cr 0.5V0.5). A large part of the dissertation also focuses on the effect of the compressibility on the Ge-based 211 Mn+1AXn compounds with the aid of diamond anvil cell and high energy synchrotron radiation. This study also concentrates on the stability of these compounds at high temperature and thereby determines its suitability as high temperature structural materials. In order to better understand the effect of substitutions on A-site of 211 Mn+1 AXn compounds under high pressure and high temperature, a comparison is made with previously reported 211 Mn+1AXn compounds with Al, Ga and S as A-site elements.
Resumo:
Structural vibration control is of great importance. Current active and passive vibration control strategies usually employ individual elements to fulfill this task, such as viscoelastic patches for providing damping, transducers for picking up signals and actuators for inputting actuating forces. The goal of this dissertation work is to design, manufacture, investigate and apply a new type of multifunctional composite material for structural vibration control. This new composite, which is based on multi-walled carbon nanotube (MWCNT) film, is potentially to function as free layer damping treatment and strain sensor simultaneously. That is, the new material integrates the transducer and the damping patch into one element. The multifunctional composite was prepared by sandwiching the MWCNT film between two adhesive layers. Static sensing test indicated that the MWCNT film sensor resistance changes almost linearly with the applied load. Sensor sensitivity factors were comparable to those of the foil strain gauges. Dynamic test indicated that the MWCNT film sensor can outperform the foil strain gage in high frequency ranges. Temperature test indicated the MWCNT sensor had good temperature stability over the range of 237 K-363 K. The Young’s modulus and shear modulus of the MWCNT film composite were acquired by nanoindentation test and direct shear test, respectively. A free vibration damping test indicated that the MWCNT composite sensor can also provide good damping without adding excessive weight to the base structure. A new model for sandwich structural vibration control was then proposed. In this new configuration, a cantilever beam covered with MWCNT composite on top and one layer of shape memory alloy (SMA) on the bottom was used to illustrate this concept. The MWCNT composite simultaneously serves as free layer damping and strain sensor, and the SMA acts as actuator. Simple on-off controller was designed for controlling the temperature of the SMA so as to control the SMA recovery stress as input and the system stiffness. Both free and forced vibrations were analyzed. Simulation work showed that this new configuration for sandwich structural vibration control was successful especially for low frequency system.
Resumo:
This dissertation was an analysis of the root and proximate causes of the September 2002 civil war in Côte d’Ivoire. The central question of this study was: Why did Côte d’Ivoire, which was relatively stable under President Houphouët-Boigny, suddenly begin to experience political violence in the 1990s and an explosion in 2002? Côte d’Ivoire was an interesting case because it was stable for a long period of time, apparently making it an infertile ground for conflict. It was also interesting for comparative purposes because of the fact that several states in West Africa (for instance, Benin, Togo, and Ghana) have experienced military coups but not have civil wars. Finally, this case was an opportunity to revisit the debate on the causes of civil wars in the African context. Chapter one has outlined the entire dissertation project and contextualized the analysis that follows in the subsequent chapters. Chapter two has reviewed the literature on civil wars in general, identified the different types of civil wars, and the type the Ivoiran war is. Chapter three has examined the domestic and international political economy as a source of the civil violence in Côte d’Ivoire. Chapter four has examined the role of ethnicity and region as identities of the war, while chapter five has analyzed the role of the foreign relations in the civil war, as well as the regional political context. Chapter six has distinguished between the root and proximate causes of the Ivoirian civil war, made judgments about the relative weight of the various causes, and the extent to which the weight of the causes can be measured. The study found that the “Ivoirité” was the most important trigger of the civil war in Côte d’Ivoire. The overall conclusion of my dissertation was that the September 2002 crisis in that country was a political crisis which occured in the context of a political reform. It first started with succession problems in 1993 followed by the controversial elections in 1995 and 2000. Later, this electoral politics spread beyond electoral issues, namely citizenship matters.
Resumo:
The purpose of this study is to validate the Study Behavior Inventory-High School, an instrument designed to measure study behaviors of high school students and to determine the stability of its scores across populations and across grades. Numerous studies have shown the relationship between the level of students' use of appropriate study behaviors and their levels of academic achievement and this is particularly relevant at a time of increasing demands for school and teacher accountability for their students' academic achievement. ^ The instrument was administered to 3,336 students in grades 9 through 12 in four high schools in diverse parts of the United States. Factor analysis yielded a four factor structure for the instrument and evidence for its construct validity was obtained using convergent and discriminant methods. The four factors include academic self-perception and feelings of low self-efficacy, academic preparation behaviors, time management, and the social nature of taking tests and studying. Internal consistency reliability for the scores on each of the four factors was calculated and found to range between .68 and .87. Finally, confirmatory factor analysis indicated acceptable levels of fit between the factor structure obtained in this study and an earlier one obtained during a pilot study using 800 participants. ^ The SBI-HS appears to be a valid and reliable instrument for the measure of study behaviors in high school students. ^
Resumo:
Hydrogen has been considered as a potentially efficient and environmentally friendly alternative energy solution. However, one of the most important scientific and technical challenges that the "hydrogen economy" faces is the development of safe and economically viable on-board hydrogen storage for fuel cell applications, especially to the transportation sector. Ammonia borane (BH3NH 3), a solid state hydrogen storage material, possesses exceptionally high hydrogen content (19.6 wt%).However, a fairly high temperature is required to release all the hydrogen atoms, along with the emission of toxic borazine. Recently research interests are focusing on the improvement of H2 discharge from ammonia borane (AB) including lowering the dehydrogenation temperature and enhancing hydrogen release rate using different techniques. Till now the detailed information about the bonding characteristics of AB is not sufficient to understand details about its phases and structures. ^ Elemental substitution of ammonia borane produces metal amidoboranes. Introduction of metal atoms to the ammonia borane structure may alter the bonding characteristics. Lithium amidoborane is synthesized by ball milling of ammonia borane and lithium hydride. High pressure study of molecular crystal provides unique insight into the intermolecular bonding forces and phase stability. During this dissertation, Raman spectroscopic study of lithium amidoborane has been carried out at high pressure in a diamond anvil cell. It has been identified that there is no dihydrogen bond in the lithium amidoborane structure, whereas dihydrogen bond is the characteristic bond of the parent compound ammonia borane. It has also been identified that the B-H bond becomes weaker, whereas B-N and N-H bonds become stronger than those in the parent compound ammonia borane. At high pressure up to 15 GPa, Raman spectroscopic study indicates two phase transformations of lithium amidoborane, whereas synchrotron X-ray diffraction data indicates only one phase transformation of this material. ^ Pressure and temperature has a significant effect on the structural stability of ammonia borane. This dissertation explored the phase transformation behavior of ammonia borane at high pressure and low temperature using in situ Raman spectroscopy. The P-T phase boundary between the tetragonal (I4mm) and orthorhombic (Pmn21) phases of ammonia borane has been determined. The transition has a positive Clapeyron slope which indicates the transition is of exothermic in nature. Influence of nanoconfinemment on the I4mm to Pmn2 1 phase transition of ammonia borane was also investigated. Mesoporus silica scaffolds SBA-15 with pore size of ~8 nm and MCM-41 with pore size of 2.1-2.7 nm, were used to nanoconfine ammonia borane. During cooling down, the I4mm to Pmn21 phase transition was not observed in MCM-41 nanoconfined ammonia borane, whereas the SBA-15 nanocondfined ammonia borane shows the phase transition at ~195 K. Four new phases of ammonia borane were also identified at high pressure up to 15 GPa and low temperature down to 90 K.^
Resumo:
Long-span bridges are flexible and therefore are sensitive to wind induced effects. One way to improve the stability of long span bridges against flutter is to use cross-sections that involve twin side-by-side decks. However, this can amplify responses due to vortex induced oscillations. Wind tunnel testing is a well-established practice to evaluate the stability of bridges against wind loads. In order to study the response of the prototype in laboratory, dynamic similarity requirements should be satisfied. One of the parameters that is normally violated in wind tunnel testing is Reynolds number. In this dissertation, the effects of Reynolds number on the aerodynamics of a double deck bridge were evaluated by measuring fluctuating forces on a motionless sectional model of a bridge at different wind speeds representing different Reynolds regimes. Also, the efficacy of vortex mitigation devices was evaluated at different Reynolds number regimes. One other parameter that is frequently ignored in wind tunnel studies is the correct simulation of turbulence characteristics. Due to the difficulties in simulating flow with large turbulence length scale on a sectional model, wind tunnel tests are often performed in smooth flow as a conservative approach. The validity of simplifying assumptions in calculation of buffeting loads, as the direct impact of turbulence, needs to be verified for twin deck bridges. The effects of turbulence characteristics were investigated by testing sectional models of a twin deck bridge under two different turbulent flow conditions. Not only the flow properties play an important role on the aerodynamic response of the bridge, but also the geometry of the cross section shape is expected to have significant effects. In this dissertation, the effects of deck details, such as width of the gap between the twin decks, and traffic barriers on the aerodynamic characteristics of a twin deck bridge were investigated, particularly on the vortex shedding forces with the aim of clarifying how these shape details can alter the wind induced responses. Finally, a summary of the issues that are involved in designing a dynamic test rig for high Reynolds number tests is given, using the studied cross section as an example.
Petrologic and geochemical study of crustal xenoliths from Calbuco Volcano, Chile (latitude 41°20ʹS)
Resumo:
Twenty Four samples of xenoliths and country rocks from the 1961 lava flow of Calbuco volcano have been studied. Fourteen samples have been analyzed for major elements and P, Ni, Ba, Cr, V, Zr, Sc, Y, and Sr. Five of these samples were further analyzed for Sm, Nd, Sr, and Pb isotope ratios. Seventeen samples were studied under the microscope and three samples were analyzed by microprobe for their pyroxene compositions. Based on petrographic studies xenoliths were divided into three groups. Fine grained xenoliths (groups I and II) probably formed from metamorphosed MORB-like basalts, whereas coarse grained xenoliths (group III) were apparently derived from cumulate minerals that crystallized from the Calbuco magma. The fine grained xenoliths were probably entrained in magma at intermediate levels of the crust, near the stability limit of amphibole to form pyroxene and plagioclase. In the coarse grained xenoliths amphibole that formed at depth dehydrated as the xenoliths were brought to the surface. The country rocks are apparently unrelated to the xenoliths.
Resumo:
This dissertation was an analysis of the root and proximate causes of the September 2002 civil war in Côte d’Ivoire. The central question of this study was: Why did Côte d’Ivoire, which was relatively stable under President Houphouët-Boigny, suddenly begin to experience political violence in the 1990s and an explosion in 2002? Côte d’Ivoire was an interesting case because it was stable for a long period of time, apparently making it an infertile ground for conflict. It was also interesting for comparative purposes because of the fact that several states in West Africa (for instance, Benin, Togo, and Ghana) have experienced military coups but not have civil wars. Finally, this case was an opportunity to revisit the debate on the causes of civil wars in the African context. Chapter one has outlined the entire dissertation project and contextualized the analysis that follows in the subsequent chapters. Chapter two has reviewed the literature on civil wars in general, identified the different types of civil wars, and the type the Ivoiran war is. Chapter three has examined the domestic and international political economy as a source of the civil violence in Côte d’Ivoire. Chapter four has examined the role of ethnicity and region as identities of the war, while chapter five has analyzed the role of the foreign relations in the civil war, as well as the regional political context. Chapter six has distinguished between the root and proximate causes of the Ivoirian civil war, made judgments about the relative weight of the various causes, and the extent to which the weight of the causes can be measured. The study found that the “Ivoirité” was the most important trigger of the civil war in Côte d’Ivoire. The overall conclusion of my dissertation was that the September 2002 crisis in that country was a political crisis which occured in the context of a political reform. It first started with succession problems in 1993 followed by the controversial elections in 1995 and 2000. Later, this electoral politics spread beyond electoral issues, namely citizenship matters.
Resumo:
The International Coffee Agreements (ICA) involved the majority of nations producing and consuming coffee and provided relative economic stability to the coffee sectors of the exporting Third World countries. This study focuses on the serious impact of the 1989 collapse of the ICA on the domestic coffee sectors of Colombia and Cote d'Ivoire. In particular, the dissertation examines the role of the Colombian and Ivoirian coffee parastatals, the Federacion Nacional de Cafeteros de Colombia and the Caisse de Stabilisation et Soutien des Prix des Produits Agricoles, during the crisis and their transformation by it. The theoretical framework employed in this study is borrowed from the literature on state-society relations. The methodology includes: in-depth analysis of the historical roles of the parastatal agencies in coffee production, state-society relations and economic development in Colombia and Côte d'Ivoire; interviews with parastatal administrators, producers and other knowledgeable informants in both countries; and a comprehensive review of newspaper articles and official statements of coffee policy published in Colombia and Côte d'Ivoire prior to, during, and after the crisis. The Colombian and Ivoirian coffee sectors and their producers faced serious economic and social problems following the drop in coffee prices. The coffee parastatals in Colombia and Côte d'Ivoire first lost some of their responsibilities following the world coffee crisis. The Caisse was in the end eliminated while FEDECAFE struggled to remain in existence. Along the way, both entities faced protests from disgruntled coffee producers, who organized politically for the first time in their nations' histories. I argue that the outcome for the parastatals depended in part on the conditions of their formation, particularly the level of societal involvement in their creation. I also posit that the country's dependence on foreign aid played a key role in the fate of the parastatals. This dissertation concludes that developments in the Colombian and Ivoirian coffee sectors have significantly contributed to the creation of the difficult political and economic conditions of both countries today.
Resumo:
Hydrogen has been considered as a potentially efficient and environmentally friendly alternative energy solution. However, one of the most important scientific and technical challenges that the “hydrogen economy” faces is the development of safe and economically viable on-board hydrogen storage for fuel cell applications, especially to the transportation sector. Ammonia borane (BH3NH3), a solid state hydrogen storage material, possesses exceptionally high hydrogen content (19.6 wt%).However, a fairly high temperature is required to release all the hydrogen atoms, along with the emission of toxic borazine. Recently research interests are focusing on the improvement of H2 discharge from ammonia borane (AB) including lowering the dehydrogenation temperature and enhancing hydrogen release rate using different techniques. Till now the detailed information about the bonding characteristics of AB is not sufficient to understand details about its phases and structures. Elemental substitution of ammonia borane produces metal amidoboranes. Introduction of metal atoms to the ammonia borane structure may alter the bonding characteristics. Lithium amidoborane is synthesized by ball milling of ammonia borane and lithium hydride. High pressure study of molecular crystal provides unique insight into the intermolecular bonding forces and phase stability. During this dissertation, Raman spectroscopic study of lithium amidoborane has been carried out at high pressure in a diamond anvil cell. It has been identified that there is no dihydrogen bond in the lithium amidoborane structure, whereas dihydrogen bond is the characteristic bond of the parent compound ammonia borane. It has also been identified that the B-H bond becomes weaker, whereas B-N and N-H bonds become stronger than those in the parent compound ammonia borane. At high pressure up to 15 GPa, Raman spectroscopic study indicates two phase transformations of lithium amidoborane, whereas synchrotron X-ray diffraction data indicates only one phase transformation of this material. Pressure and temperature has a significant effect on the structural stability of ammonia borane. This dissertation explored the phase transformation behavior of ammonia borane at high pressure and low temperature using in situ Raman spectroscopy. The P-T phase boundary between the tetragonal (I4mm) and orthorhombic (Pmn21) phases of ammonia borane has been determined. The transition has a positive Clapeyron slope which indicates the transition is of exothermic in nature. Influence of nanoconfinemment on the I4mm to Pmn21 phase transition of ammonia borane was also investigated. Mesoporus silica scaffolds SBA-15 with pore size of ~8 nm and MCM-41 with pore size of 2.1-2.7 nm, were used to nanoconfine ammonia borane. During cooling down, the I4mm to Pmn21 phase transition was not observed in MCM-41 nanoconfined ammonia borane, whereas the SBA-15 nanocondfined ammonia borane shows the phase transition at ~195 K. Four new phases of ammonia borane were also identified at high pressure up to 15 GPa and low temperature down to 90 K.