Cosmic String in Scalar-Tensor Gravity

The gravitational properties of a local cosmic string in the framework of scalar-tensor gravity are examined. We find the metric in the weak-field approximation and we show that, contrary to the General Relativity case, the cosmic string in scalar-tensor gravitation exerces a force on non-relativistic, neutral test particle. This force is proportional to the derivative of the conformal factor $A^{2}(\phi)$ and it is always attractive. Moreover, this force could have played an important role at the Early Universe, although nowadays it can be neglegible. It is also shown that the angular separation $\delta\varphi$ remains unaltered for scalar-tensor cosmic strings.Comment: 15 pages, LATEX, no figure

The use of linear programming to evaluate the impact of credit for investments in small goat farms.

Abstract: The PRONAF is a governmental program that subsidies the credit for investment to smallholder farming and improves the social development in Brazil. This research was carried out to evaluate the effect of increasing the values of credit for investment used for the PRONAF farmers in semi-arid areas, and their impact in the income and labor in smallholder farming production system. Economic data of dairy and meat goat systems of PRONAF farmers in ?Rio Grande do Norte?, Brazil was used. The limit of the model was the credit for investment, maximum number of animals in the system and the labor time. The current values of credit for investment (US$ 2,850.00) were increased by 25%, 50% and 100% and its impact analyzed in the farm income when considering milk and meat production. The maximum number of animals in the system was estimated by multiplying the carry capacity (1.5 heads/ha/year) plus the average pasture areas of PRONAF farms (35 ha). The maximum labor time, available for farm work, was 12 hours/day. This mathematical model was solved using linear programming with LINDO® software. When the credit for investment was expanded in 25 and 50%, the income of the system increased, respectively, to 22 and 41%. It happened because the values of credit allowed increasing the number of dairy goats in the system. However, this income was not enough to use and pay more than 5 hours/day in dairy goat system activities. When raising the credit for investment up to 100% it could increase the income of the system around 81%. It happened because the number of dairy goats grew up to 83% and the dairy production had better results than meat production. The system with more dairy goats produces enough income as to pay the farmer labor (7 hours/day) and during the other five hours could develop other activities. Therefore, the results of the analysis indicated that an increase in the credit for investment in small goat farms in semi-arid areas in Brazil could be addressed towards the dairy goat production, enhancing the income of families and employment opportunities.Edição de proceedings 9th International Goat Conference; 23th Conference ofthe Asociación Mexicana de Producción Caprinaat Queretaro, Mexico, in September 2008. XXIII Conference ofthe Asociación Mexicana de Producción Caprin

Study of the impact of breeding seasons in the dynamics of dairy goat herds.

Abstract: The competitiveness in the animal production field has forced the smaller activities to be more efficient when compared to big business of the agro-industries. The dairy goat production is one of those market niches that need a better understand of its sector. For those reasons it has been proposed that by changing the number of reproduction seasons would increase income of the producers. The objectives of this study were to evaluate the impact of 1 or 2 annual reproductive cycles on production and economical health of dairy goats and to identify differences of production costs and revenues associated with changes in the herd dynamics as predicted by a mathematical model. A previously developed goat model using the System Dynamics approach to study long-term changes in the dynamics of the herd was used in these simulations. The model simulations used feeds, labor, and fixed costs as inputs and the outputs were revenues from milk production sales and sales of animals from all categories of the herd. The simulation time unit was ?month? and a long-term horizon of 10 years was considered for these simulations. The model was set up to simulate a freestall facility of a herd in equilibrium with 100 does in lactation. All parameters considered in this model assumed average values reported in production systems in the Southeast region of Brazil. The simulations results indicated that improvements of 10% in the fertility rate would increase the number animals in the herd up to 185% and 35% for one and two breeding season, respectively. Establishing a milk price as US$0.68 the break even for one and two breeding seasons was respectively US$0.62, and US$0.50, giving the systems with two breeding a capacity to support reductions on milk price up to 26% against 9% with one breeding season. When comparing the models with 1 or 2 breeding seasons was found that models with 2 breeding seasons was considerably more profitable and had a higher turnover than the model with 1 breeding season. The results indicate that the use of a second (artificial) breeding season might be an important management strategy to improve the efficiency of the dairy goat production systems. [Estudio del impacto de la estación reproductiva sobre la dinâmica de los rebaños lecheros]

A dairy goat model to study the impacts on herd dynamics.

The understanding of a dairy goat production system is crucial to establish a more competitive activity. Therefore, a simulation model was built to evaluate the dynamics of dairy goat herd under different scenarios of production. A System Dynamics approach was used to identify management policies that affect the behavior of the herd. All parameters considered in this model assumed average values reported in production systems in the Southeast region of Brazil. To simulate a herd in dynamic equilibrium, the culling and retention rates were used. Thereafter, simulations were performed based on changes in reproductive and mortality rates. All the simulations were planned to take the variation in herd development based on simple management strategies over 10 years of simulation. The dynamic equilibrium of 50 lactating does was obtained when fixed culling and retention rates of 20 and 70%, respectively, were assigned to the does after 36 months of simulation. A sensitivity analysis was made and indicated that an increase of 20% in the reproduction rates increased the number of animals in the herd in 56%. A decrease in the reproduction rate of 20% reduced the number of animals in 43%. A third simulation indicated that increasing mortality rate from 4 to 10% of the female kids decreased the number of lactating does by 36%. These results indicated that small changes in reproduction and mortality rates can considerably affect the dynamics of the herd, even though the herd may not be immediately affected because of the intrinsic delays in the system. This result is extremely important to justify the need of activity planning to consider the gap between a measurement taken and the consequences, preparing the producers to potential delays in the system. The use of mathematical models is important to understand the relationships between variables and the dynamic of the system and to assist in applying best management strategies to enhance productivity of dairy goats. [Modelo de cabras lecheras para evaluar el impacto de las estrategias de manejo en la dinámica del rebaño]

Caprinocultura e ovinocultura: crescimento promissor x desorganização preocupante.

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O associativismo como ferramenta para a inclusão de agricultores familiares produtores de caprinos e ovinos no Território de Aracatiaçu (CE).

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Sistema de produção agrossilvipastorial para a região de caatinga - SAF: avaliação dos impactos econômicos, sociais e ambientais.

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Sistema Agrossilvipastoril caprinos e ovinos: reunião técnica.

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