Hardware simulation of diesel generator and microgrid stability

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis. Also includes: Reference manual for microgrid hardware simulation system / by Jared P. Monnin and Michael M. Zieve. (c2012. (71 p. : ill.). Includes bibliographical references (p. 71)).Includes bibliographical references (p. 27).Over the last few years, people have begun to depend less on large power plants with extensive distribution systems, and more on local distributed generation sources. A microgrid, a local collection of distributed generators, has the potential to offer a more flexible and customizable power generation system, while significantly improving its effect on the environment. In order to properly deploy and scale microgrids to meet diverse energy needs, there must be more study on their stability. This paper details the process and design of the modeling of a diesel generator. With the constructed diesel generator as a component of the microgrid project, the voltage and power stability of the modeled microgrid can be tested under various load conditions and faulted islanded conditions to help design the future of the electrical grid.by Michael M. Zieve.M.Eng

Influence of detector collimation on SNR in four different MDCT scanners using a reconstructed slice thickness of 5mm

The purpose of this paper is to compare the influence of detector collimation on the signal-to-noise ratio (SNR) for a 5.0mm reconstructed slice thickness for four multi-detector row CT (MDCT) units. SNRs were measured on Catphan test phantom images from four MDCT units: a GE LightSpeed QX/I, a Marconi MX 8000, a Toshiba Aquilion and a Siemens Volume Zoom. Five-millimetre-thick reconstructed slices were obtained from acquisitions performed using detector collimations of 2.0-2.5mm and 5.0mm, 120kV, a 360° tube rotation time of 0.5s, a wide range of mA and pitch values in the range of 0.75-0.85 and 1.25-1.5. For each set of acquisition parameters, a Wiener spectrum was also calculated. Statistical differences in SNR for the different acquisition parameters were evaluated using a Student's t-test (P<0.05). The influence of detector collimation on the SNR for a 5.0-mm reconstructed slice thickness is different for different MDCT scanners. At pitch values lower than unity, the use of a small detector collimation to produce 5.0-mm thick slices is beneficial for one unit and detrimental for another. At pitch values higher than unity, using a small detector collimation is beneficial for two units. One manufacturer uses different reconstruction filters when switching from a 2.5- to a 5.0-mm detector collimation. For a comparable reconstructed slice thickness, using a smaller detector collimation does not always reduce image noise. Thus, the impact of the detector collimation on image noise should be determined by standard deviation calculations, and also by assessing the power spectra of the nois

Water chemistry and soil radon survey at the Poas volcano (Costa Rica)

Radon-in-soil monitoring at the Poas volcano (Costa Rica) has been performed together with water chemistry from the hot crater lake since 1981 and 1983 respectively. The results are discussed as a function of the eruptive evolution of the volcano over a 13 years period (1981-1994). It is shown that no definitely clear precursory radon signals have been recorded. On the contrary, ionic species concentrations are likely to be considered good precursors, together with the temperature variations of the crater lake water

Rapid interhemispheric climate links via the Australasian monsoon during the last deglaciation

Recent studies have proposed that millennial-scale reorganization of the ocean-atmosphere circulation drives increased upwelling in the Southern Ocean, leading to rising atmospheric carbon dioxide levels and ice age terminations. Southward migration of the global monsoon is thought to link the hemispheres during deglaciation, but vital evidence from the southern sector of the vast Australasian monsoon system is yet to emerge. Here we present a 230thorium-dated stalagmite oxygen isotope record of millennial-scale changes in Australian–Indonesian monsoon rainfall over the last 31,000 years. The record shows that abrupt southward shifts of the Australian–Indonesian monsoon were synchronous with North Atlantic cold intervals 17,600–11,500 years ago. The most prominent southward shift occurred in lock-step with Heinrich Stadial 1 (17,600–14,600 years ago), and rising atmospheric carbon dioxide. Our findings show that millennial-scale climate change was transmitted rapidly across Australasia and lend support to the idea that the 3,000-year-long Heinrich 1 interval could have been critical in driving the last deglaciation

Parallel Evolution in the Integration of a Co-obligate Aphid Symbiosis

Dependence on multiple nutrient- provisioning symbionts has evolved numerous times in insects. Monnin et al. provide evidence from the symbionts of aphids that these dependencies evolve in a predictable manner. The repeated losses of the same metabolic pathways bind the symbionts into co-dependence, and integration follows in a stepwise manner

Climate change challenges for central banks and financial regulators

The academic and policy debate regarding the role of central banks and financial regulators in addressing climate-related financial risks has rapidly expanded in recent years. This Perspective presents the key controversies and discusses potential research and policy avenues for the future. Developing a comprehensive analytical framework to assess the potential impact of climate change and the low-carbon transition on financial stability seems to be the first crucial challenge. These enhanced risk measures could then be incorporated in setting financial regulations and implementing the policies of central banks

Nutritional Asymmetries Are Related to Division of Labor in a Queenless Ant

Eusocial species exhibit pronounced division of labor, most notably between reproductive and non-reproductive castes, but also within non-reproductive castes via morphological specialization and temporal polyethism. For species with distinct worker and queen castes, age-related differences in behavior among workers (e.g. within-nest tasks versus foraging) appear to result from physiological changes such as decreased lipid content. However, we know little about how labor is divided among individuals in species that lack a distinct queen caste. In this study, we investigated how fat storage varied among individuals in a species of ant (Dinoponera australis) that lacks a distinct queen caste and in which all individuals are morphologically similar and capable of reproduction (totipotent at birth). We distinguish between two hypotheses, 1) all individuals are physiologically similar, consistent with the possibility that any non-reproductive may eventually become reproductive, and 2) non-reproductive individuals vary in stored fat, similar to highly eusocial species, where depletion is associated with foraging and non-reproductives have lower lipid stores than reproducing individuals. Our data support the latter hypothesis. Location in the nest, the probability of foraging, and foraging effort, were all associated with decreased fat storage

Convergent evolution of a labile nutritional symbiosis in ants

Ants are among the most successful organisms on Earth. It has been suggested that forming symbioses with nutrient-supplementing microbes may have contributed to their success, by allowing ants to invade otherwise inaccessible niches. However, it is unclear whether ants have evolved symbioses repeatedly to overcome the same nutrient limitations. Here, we address this question by comparing the independently evolved symbioses in Camponotus, Plagiolepis, Formica and Cardiocondyla ants. Our analysis reveals the only metabolic function consistently retained in all of the symbiont genomes is the capacity to synthesise tyrosine. We also show that in certain multi-queen lineages that have co-diversified with their symbiont for millions of years, only a fraction of queens carry the symbiont, suggesting ants differ in their colony-level reliance on symbiont-derived resources. Our results imply that symbioses can arise to solve common problems, but hosts may differ in their dependence on symbionts, highlighting the evolutionary forces influencing the persistence of long-term endosymbiotic mutualisms.Peer reviewe

Systematic radon survey over active volcanoes

In-soil radon-222 monitoring has been conducted on active volcanoes, in particular on the Arenal, Irazu and Poas volcanoes in Costa Rica and on the Piton de la Fournaise volcano, La Réunion island. Automatic electronic probes buried in soil at one meter depth were used to study the short- and long-term fluctuations of radon related to the external parameters and/or related with the volcanic activity. Three radon stations are in operation on each Costa Rican volcano and a network of 24 stations (with 3 teletransmitted) is operated on the Piton de la Fournaise. Data obtained since 1993 on Costa Rica volcanoes are presented and radon anomalies recorded before the December 8, 1994 eruption of the Irazu volcano are discussed. The Piton de la Fournaise volcano is inactive since mid 1992. We could intensively study the influence of the external parameters on the radon behavior and individuate the type of perturbations induced on short-term measurements. One seismic crisis occurred on November 27, 1996. Radon anomalies appear on most of 50% of the stations 36 hours before the occurrence of the crisis