The cosmic coincidence in Brans-Dicke cosmologies

Among the suggested solutions to the cosmological constant problem, we find the idea of a dynamic vacuum, with an energy density decaying with the universe expansion. We investigate the possibility of a variation in the gravitational constant as well, induced, at the cosmological scale, by the vacuum decay. We consider an effective Brans-Dicke theory in the spatially flat FLRW spacetime, finding late time solutions characterized by a constant ratio between the matter and vacuum energy densities. By using the observed limits for the universe age, we fix the only free parameter of our solutions, obtaining a relative matter density in the range 0.25-0.4. In particular, for Ht = 1 we obtain a relative matter density equals to 1/3. This constitutes a possible explanation for another problem related to the cosmological term, the cosmic coincidence problem.Comment: This essay received an "honorable mention" in the 2005 Essay Competition of the Gravity Research Foundatio

Performance comparison of clustered and replicated information retrieval systems

The amount of information available over the Internet is increasing daily as well as the importance and magnitude of Web search engines. Systems based on a single centralised index present several problems (such as lack of scalability), which lead to the use of distributed information retrieval systems to effectively search for and locate the required information. A distributed retrieval system can be clustered and/or replicated. In this paper, using simulations, we present a detailed performance analysis, both in terms of throughput and response time, of a clustered system compared to a replicated system. In addition, we consider the effect of changes in the query topics over time. We show that the performance obtained for a clustered system does not improve the performance obtained by the best replicated system. Indeed, the main advantage of a clustered system is the reduction of network traffic. However, the use of a switched network eliminates the bottleneck in the network, markedly improving the performance of the replicated systems. Moreover, we illustrate the negative performance effect of the changes over time in the query topics when a distributed clustered system is used. On the contrary, the performance of a distributed replicated system is query independent

From de Sitter to de Sitter: A non-singular inflationary universe driven by vacuum

A semi-classical analysis of vacuum energy in the expanding spacetime suggests that the cosmological term decays with time, with a concomitant matter production. For early times we find, in Planck units, $\Lambda \approx H^4$, where H is the Hubble parameter. The corresponding cosmological solution has no initial singularity, existing since an infinite past. During an infinitely long period we have a quasi-de Sitter, inflationary universe, with $H \approx 1$. However, at a given time, the expansion undertakes a phase transition, with H and $\Lambda$ decreasing to nearly zero in a few Planck times, producing a huge amount of radiation. On the other hand, the late-time scenario is similar to the standard model, with the radiation phase followed by a dust era, which tends asymptotically to a de Sitter universe, with vacuum dominating again.Comment: This essay received an "honorable mention" in the 2006 Essay Competition of the Gravity Research Foundatio

Bursts in discontinuous Aeolian saltation

Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number $\theta_c$. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold

A flying start? Long term consequences of maternal time investments in children during their first year of life

We study the impact of increasing the time that the mother spends with her child in the first year of her life. In particular, we examine a reform that increased paid and unpaid maternity leave entitlements in Norway. In response to this reform, maternal leave increased on average by 4 months and family income was unaffected. We find that this increase in maternal time with the child led to a 2.7 percentage points decline in high school dropout rates, going up to 5.2 percentage points for those whose mothers have less than 10 years of education. This effect is especially large for children of mothers who, in the absence of the reform, would take very low levels of unpaid leave. Finally, there is a weak impact on college attendance. The results also suggest that much of the impact of early time with the child is at low levels of maternal education.

A Flying Start? Long Term Consequences of Maternal Time Investments in Children During Their First Year of Life

We study the impact on children of increasing the time that the mother spends with her child in the first year by exploiting a reform that increased paid and unpaid maternity leave in Norway. The reform increased maternal leave on average by 4 months and family income was unaffected. The increased time with the child led to a 2.7 percentage points decline in high school dropout. For mothers with low education we find a 5.2 percentage points decline. The effect is also especially large for children of mothers who, prior to the reform, would take very low levels of unpaid leave.adult outcomes, time with mother, maternity leave

A Flying Start? Maternity Leave Benefits and Long Run Outcomes of Children

We study the impact on children of increasing maternity leave benefits using a reform that increased paid and unpaid maternity leave in Norway in July 1977. Mothers giving birth before this date were eligible only for 12 weeks of unpaid leave, while those giving birth after were entitled to 4 months of paid leave and 12 months of unpaid leave. This increased time with the child led to a 2.7 percentage points decline in high school dropout and a 5% increase in wages at age 30. For mothers with low education we find a 5.2 percentage points decline in high school dropout and an 8% increase in wages at age 30. The effect is especially large for children of those mothers who, prior to the reform, would take very low levels of unpaid leave.maternity leave, children's outcomes

Economic evaluation for the Bolivia-Brazil pipeline

http://deepblue.lib.umich.edu/bitstream/2027.42/96887/1/MBA_Carneiro_Henrique_Fall_1996Final.pd

Sustainability Assessment of indicators for integrated water resources management

The scientific community strongly recommends the adoption of indicators for the evaluation and monitoring of progress towards sustainable development. Furthermore, international organizations consider that indicators are powerful decision-making tools. Nevertheless, the quality and reliability of the indicators depends on the application of adequate and appropriate criteria to assess them. The general objective of this study was to evaluate how indicators related to water use and management perform against a set of sustainability criteria. Our research identified 170 indicators related to water use and management. These indicators were assessed by an international panel of experts that evaluated whether they fulfil the four sustainability criteria: social, economic, environmental, and institutional. We employed an evaluation matrix that classified all indicators according to the DPSIR (Driving Forces, Pressures, States, Impacts and Responses) framework. A pilot study served to test and approve the research methodology before carrying out the full implementation. The findings of the study show that 24 indicators comply with the majority of the sustainability criteria; 59 indicators are bi-dimensional (meaning that they comply with two sustainability criteria); 86 are one-dimensional indicators (fulfilling just one of the four sustainability criteria) and one indicator do not fulfil any of the sustainability criteria.Postprint (author's final draft