A new cure rate model with flexible competing causes with applications to melanoma and transplantation data
In this article, we introduce a long-term survival model in which the number of competing causes of the event of interest follows the zero-modified geometric (ZMG) distribution. Such distribution accommodates equidispersion, underdispersion, and overdispersion and captures deflation or inflation of zeros in the number of lesions or initiated cells after the treatment. The ZMG distribution is also an appropriate alternative for modeling clustered samples when the number of competing causes of the event of interest consists of two subpopulations, one containing only zeros (cure proportion), while in the other (noncure proportion) the number of competing causes of the event of interest follows a geometric distribution. The advantage of this assumption is that we can measure the cure proportion in the initiated cells. Furthermore, the proposed model can yield greater or lower cure proportion than that of the geometric distribution when modeling the number of competing causes. In this article, we present some statistical properties of the proposed model and use the maximum likelihood method to estimate the model parameters. We also conduct a Monte Carlo simulation study to evaluate the performance of the estimators. We present and discuss two applications using real-world medical data to assess the practical usefulness of the proposed model.
Declining fisheries and increasing prices: The economic cost of tropical rivers impoundment
This work tests the null hypothesis that the coefficients of the total landings, landed values, mean catches and price per kg of migratory and resident species are constant over time following the installation of two large run- of-the-river hydroelectric dams in a large tropical river. To identify shifts in catches and economic returns due to river impoundment, we inspected daily landing data (25-year time series) and wholesale prices (19-year time series) for the Madeira River, the largest tributary of the Amazon River. Our results show that the period of decreasing catches and increasing prices observed for fisheries in the Madeira River matched the timings of the construction of the two dams. According to the results, both dams quickly changed catches and fish supply to market, which were immediately echoed in the price per kg of exploited fish species. Following the dam con- struction, prices rose for both fish that became scarce and fish that became abundant. Though catches declined 58% in 25 years, the price increased 49% over the same period, representing a high economic cost for the local population. Further, there was a clear decline in the catches of some species (e.g., the dourada and the curimatã), but increased catches of others (e.g., the sardine and the tucunaré). Moreover, some fluctuation patterns across years showed natural oscillations, or changes, in local habitats and even fishing efforts.
Seasonal variation in net ecosystem co2 exchange of a Brazilian seasonally dry tropical forest
Forest ecosystems sequester large amounts of atmospheric CO2, and the contribution from seasonally dry tropical forests is not negligible. Thus, the objective of this study was to quantify and evaluate the seasonal and annual patterns of CO2 exchanges in the Caatinga biome, as well as to evaluate the ecosystem condition as carbon sink or source during years. In addition, we analyzed the climatic factors that control the seasonal variability of gross primary production (GPP), ecosystem respiration (Reco) and net ecosystem CO2 exchange (NEE). Results showed that the dynamics of the components of the CO2 fluxes varied depending on the magnitude and distribution of rainfall and, as a consequence, on the variability of the vegetation state. Annual cumulative NEE was significantly higher (p < 0.01) in 2014 (−169.0 g C m−2) when compared to 2015 (−145.0 g C m−2) and annual NEP/GPP ratio was 0.41 in 2014 and 0.43 in 2015. Global radiation, air and soil temperature were the main factors associated with the diurnal variability of carbon fluxes. Even during the dry season, the NEE was at equilibrium and the Caatinga acted as an atmospheric carbon sink during the years 2014 and 2015.
Environmental and biophysical controls of evapotranspiration from Seasonally Dry Tropical Forests (Caatinga) in the Brazilian Semiarid
Seasonally dry tropical forests are among the most important biomes regarding regional and global hydrological and carbon fluxes. Thus, the objective of this study was to evaluate the seasonal and interannual variability of evapotranspiration (ET) and its biophysical control and characteristics (surface conductance—Gs; decoupling coefficient—Ω; ratio between actual evapotranspiration and equilibrium evapotranspiration—ET/ETeq) in a preserved Caatinga Biome environment during two dry years in the Northeast Brazil region. A study on this subject with this level of detail in this biome is unprecedent. Measurements were carried out using an eddy covariance system during the period from 1st January 2014 to 31st December 2015. The lowest ET values were observed in the dry season of both experiment years (0.3 and 0.2 mm day−1) as a consequence of poor water availability, which favored partial stomatal closure and reduced Gs values (0.22 and 0.13 mm s−1). The opposite occurred in the wet season, when ET (2.6 and 1.7 mm day−1) and Gs (3.74 and 2.13 mm s−1) means reached higher values. Regarding annual values, differences between total annual rainfall in both years is the most probable cause for the differences observed in annual ET values. In 2014, annual ET was of 473.3 mm while in 2015 it was 283.4 mm, which incurred in an overall decrease in Gs, Ω and ET/ETeq values. Leaf senescence and extremely low Gs values during the dry season suggest that the trees of the Caatinga Biome are more resilient regarding the use of water and are avoiding water stress caused under low water availability.
Closure and partitioning of the energy balance in a preserved area of a Brazilian seasonally dry tropical forest
The energy balance closure obtained through the eddy covariance method is a problem which persists, despite advances in the development and improvement of instruments and recent efforts in the description of corrections and in the characterization of measuring uncertainties. In most places the sum of sensible and latent heat fluxes (H and λE) is less than available energy, i.e. the difference between net radiation (Rn) and soil heat flux (G). This study analyzed the annual and seasonal behavior of the energy partitioning and energy balance closure in the Caatinga Biome, which is a seasonally dry tropical forest located in the semiarid lands of Brazil, using the eddy covariance method. Results showed high seasonal variability in the energy partitioning. During the dry season, approximately 70% of Rn was converted into H and less than 5% of it was converted into latent heat flux (λE). During the wet season, the Rn portion converted into H and λE was similar ˜ 40%. In annual terms, the Rn portion converted into H and λE was of the order of 50% and 20% respectively. The degree of the energy balance closure varied depending on the method used. When the closure was calculated using orthogonal regressions, the slope varied from 0.87 to 0.90 in 2014 and from 0.92 to 1.00 in 2015. However, when the closure was calculated by the energy balance ratio method, values varied from 0.70 to 0.79 in 2014 and from 0.73 to 0.82 in 2015. The closure was better in 2015 if compared to 2014 possibly due to the more intense turbulence observed in 2015 because friction velocity was higher than in 2014. The better closure in 2015 may also be associated with large eddies, which were more frequent in 2014 as evidenced by the correction coefficients for vertical wind velocity and water vapor and vertical wind velocity and sonic temperature. The energy balance closure was also analyzed considering atmospheric instability conditions and the best results were found under very unstable conditions, while the least expressive results were found under stable conditions. Under these conditions negative values of the energy balance ratio were also observed during dry and transition seasons, indicating that fluxes were reversed during these periods.