Boundary-layer Flows Past an Hemispherical Roughness Element: DNS, Global Stability and Sensitivity Analysis

We investigate the full three-dimensional instability mechanism arising in the wake of an hemispherical roughness element immersed in a laminar Blasius boundary layer. The inherent three-dimensional flow pattern beyond the critical Reynolds number is characterized by coherent vortical structures called hairpin vortices. Direct numerical simulation is used to analyze the formation and the shedding of hairpin packets inside the shear layer. The first bifurcation characteristics are investigated by global stability tools. We show the spatial structure of the linear direct and adjoint global eigenmodes of the linearized Navier-Stokes operator and use structural sensitivity analysis to locate the region where the instability mechanism acts. Results show that the “wavemaker” driving the self-sustained instability is located in the region immediately past the roughness element, in the shear layer separating the outer flow from the wake region

Lying and Shirking Under Oath

This study explores whether an oath to honesty can reduce both shirking and lying among crowd-sourced internet workers. Using a classic coin-flip experiment, we first show that a substantial majority of Mechanical Turk workers both shirk and lie when reporting the number of heads flipped. We then demonstrate lying can be reduced by first asking each worker to swear voluntarily on his or her honor to tell the truth in subsequent economic decisions. The oath, however, did not reduce shirking as measured by time- at-coin-flip-task, although it did increase the time they spent answering a demographic survey. Conditional on response, MTurk shirkers and liars were less likely to agree to an ex post honesty oath. Our results suggest oaths may help elicit more truthful behavior in on-line crowd-sourced environments

Sorção, degradação e lixiviação dos herbicidas tebuthiuron e diuron em colunas de Solo.

Leaching potentials of three acidic herbicides were assessed for three different Brazilian soils, by means of the multi-layered AFi model. Values of AFi were also calculated for each herbicide using a modified model (AFi*), where sorption coefficient (Kd) values are pH-dependent. The pH-dependent Kd values estimated for all three herbicides were always higher than pH-independent Kd values calculated using average Koc data. The pHdependent Kd values for the three herbicides evidenced a large variation from layer to layer following changes in OC and pH for the different soil depths. When OC decreases, Kd tends to decrease; on the other hand, lowering pH tends to increase Kd. For all three soils, OC and pH exhibit an overall decrease with depth. Despite differences between the pH-independent Kd and the pH-dependent Kd values, the AFi values for 2,4-D, calculated by the original multilayered-soil model and by the modified model (AFi*), were similarly low for all three soils, mostly due to the short half-life of 2,4-D. The pH-dependent AFi values for flumetsulam were always much lower than values calculated by the original multi-layered model. Therefore, the pH-independent model appears to overestimate leaching potential of flumetsulam. The AFi values for sulfentrazone calculated by the original and the modified models were similarly high for all three soils, despite the differences in Kd values. The long half-life of sulfentrazone mostly contributed to the similar high values of AFi for the three different soils. Overall AFi values showed large differences for sulfentrazone when calculated by the original and by the modified model (AFi*), owing to its high AF value for each layer. Thus, the original AFi model would seem to markedly overestimate the leaching potential for sulfentrazone, as well as for flumetsulam for these soil conditions

Monitoramento do risco ambiental de agrotóxicos: princípios e recomendações.

Uso de Agrotóxicos no Brasil. Princípios do Monitoramento de Risco Ambiental. Exposição Ambiental aos Agrotóxicos. Efeitos Ambientais dos Agrotóxicos. Plano de Monitoramento do Risco Ambiental. Procedimentos de Amostragem. Indicadores de Risco Ambiental. Recomendações Técnicas para Monitoramento do Risco Ambiental.bitstream/CNPMA/5810/1/documentos_42.pd

Movimento do herbicida tebutiuron em dois solos representativos das áreas de recarga do Aqüífero Guarani.

O movimento do herbicida tebutiuron foi analisado em um Latossolo Vermelho Distrófico psamítico (LVdq) e um Neossolo Quartzarênico Órtico típico (RQo), representativos das áreas de recarga do aqüífero Guarani no Brasil, tendo como fatores influenciadores, a condutividade hidráulica (K), o teor de carbono orgânico (CO) e o teor de argila (TAr). O presente estudo foi realizado em colunas de solos indeformados, com aplicação do produto comercial contendo o herbicida em discussão. Esses parâmetros evidenciam certa influência na movimentação vertical do herbicida tebutiuron, particularmente no RQo, uma vez que esse herbicida é quimicamente neutro. Observou-se, por exemplo, uma diferença significativa entre os valores K dos dois solos, sendo superior no RQo. Além de uma relação inversa entre teores de CO e de TAr e os valores de K dos dois solos, indicando serem aqueles parâmetros inibidores do deslocamento do tebutiuron no perfil do solo. Os resultados aqui obtidos neste trabalho visam subsidiar estudos de avaliação de risco ambiental, sobretudo água subterrânea, a partir de áreas de recarga de aqüíferos naturalmente frágeis, com ênfase para o aqüífero Guarani