Power-Based Droop Control in DC Microgrids Enabling Seamless Disconnection From Upstream Grids

This paper proposes a local power-based droop controller for distributed energy resource converters in dc microgrids that are connected to upstream grids by grid-interface converters. During normal operation, the grid-interface converter imposes the microgrid bus voltage, and the proposed controller allows power flow regulation at distributed energy resource converters\u2019 output. On the other hand, during abnormal operation of the grid-interface converter (e.g., due to faults in the upstream grid), the proposed controller allows bus voltage regulation by droop control. Notably, the controller can autonomously convert from power flow control to droop control, without any need of bus voltage variation detection schemes or communication with other microgrid components, which enables seamless transitions between these two modes of operation. Considering distributed energy resource converters employing the power-based droop control, the operation modes of a single converter and of the whole microgrid are defined and investigated herein. The controller design is also introduced. Furthermore, the power sharing performance of this control approach is analyzed and compared with that of classical droop control. The experimental results from a laboratory-scale dc microgrid prototype are reported to show the final performances of the proposed power-based droop control

Association of nail biting and psychiatric disorders in children and their parents in a psychiatrically referred sample of children

<p>Abstract</p> <p>Background</p> <p>Nail biting (NB) is a very common unwanted behavior. The majority of children are motivated to stop NB and have already tried to stop it, but are generally unsuccessful in doing so. It is a difficult behavior to modify or treat. The objective of this study was to investigate the prevalence of co-morbid psychiatric disorders in a clinical sample of children with NB who present at a child and adolescent mental healthcare outpatient clinic and the prevalence of psychiatric disorders in their parents.</p> <p>Method</p> <p>A consecutive sample of 450 referred children was examined for NB and 63 (14%) were found to have NB. The children and adolescents with nail biting and their parents were interviewed according to DSM-IV diagnostic criteria. They were also asked about lip biting, head banging, skin biting, and hair pulling behaviors.</p> <p>Results</p> <p>Nail biting is common amongst children and adolescents referred to a child and adolescent mental health clinic. The most common co-morbid psychiatric disorders in these children were attention deficit hyperactivity disorder (74.6%), oppositional defiant disorder (36%), separation anxiety disorder (20.6%), enuresis (15.6%), tic disorder (12.7%) and obsessive compulsive disorder (11.1%). The rates of major depressive disorder, mental retardation, and pervasive developmental disorder were 6.7%, 9.5%, 3.2%, respectively. There was no association between the age of onset of nail biting and the co-morbid psychiatric disorder. Severity and frequency of NB were not associated with any co-morbid psychiatric disorder. About 56.8% of the mothers and 45.9% of the fathers were suffering from at least one psychiatric disorder. The most common psychiatric disorder found in these parents was major depression.</p> <p>Conclusion</p> <p>Nail biting presents in a significant proportion of referrals to a mental healthcare clinic setting. Nail biting should be routinely looked for and asked for in the child and adolescent mental healthcare setting because it is common in a clinical population, easily visible in consultation and relatively unintrusive to ask about. If present, its detection can then be followed by looking for other more subtle stereotypic or self-mutilating behaviors.</p

Precision requirements for space-based XCO2 data

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): D10314, doi:10.1029/2006JD007659.Precision requirements are determined for space-based column-averaged CO2 dry air mole fraction (XCO2) data. These requirements result from an assessment of spatial and temporal gradients in XCO2, the relationship between XCO2 precision and surface CO2 flux uncertainties inferred from inversions of the XCO2 data, and the effects of XCO2 biases on the fidelity of CO2 flux inversions. Observational system simulation experiments and synthesis inversion modeling demonstrate that the Orbiting Carbon Observatory mission design and sampling strategy provide the means to achieve these XCO2 data precision requirements.This work was supported by the Orbiting Carbon Observatory (OCO) project through NASA’s Earth System Science Pathfinder (ESSP) program. SCO and JTR were supported by a NASA IDS grant (NAG5-9462) to JTR

Zoonotic hepatitis E: animal reservoirs and emerging risks

Hepatitis E virus (HEV) is responsible for enterically-transmitted acute hepatitis in humans with two distinct epidemiological patterns. In endemic regions, large waterborne epidemics with thousands of people affected have been observed, and, in contrast, in non-endemic regions, sporadic cases have been described. Although contaminated water has been well documented as the source of infection in endemic regions, the modes of transmission in non-endemic regions are much less known. HEV is a single-strand, positive-sense RNA virus which is classified in the Hepeviridae family with at least four known main genotypes (1–4) of mammalian HEV and one avian HEV. HEV is unique among the known hepatitis viruses, in which it has an animal reservoir. In contrast to humans, swine and other mammalian animal species infected by HEV generally remain asymptomatic, whereas chickens infected by avian HEV may develop a disease known as Hepatitis-Splenomegaly syndrome. HEV genotypes 1 and 2 are found exclusively in humans while genotypes 3 and 4 are found both in humans and other mammals. Several lines of evidence indicate that, in some cases involving HEV genotypes 3 and 4, animal to human transmissions occur. Furthermore, individuals with direct contact with animals are at higher risk of HEV infection. Cross-species infections with HEV genotypes 3 and 4 have been demonstrated experimentally. However, not all sources of human infections have been identified thus far and in many cases, the origin of HEV infection in humans remains unknown

Identification of Candidate Genes for Dyslexia Susceptibility on Chromosome 18

Background: Six independent studies have identified linkage to chromosome 18 for developmental dyslexia or general reading ability. Until now, no candidate genes have been identified to explain this linkage. Here, we set out to identify the gene(s) conferring susceptibility by a two stage strategy of linkage and association analysis. Methodology/Principal Findings: Linkage analysis: 264 UK families and 155 US families each containing at least one child diagnosed with dyslexia were genotyped with a dense set of microsatellite markers on chromosome 18. Association analysis: Using a discovery sample of 187 UK families, nearly 3000 SNPs were genotyped across the chromosome 18 dyslexia susceptibility candidate region. Following association analysis, the top ranking SNPs were then genotyped in the remaining samples. The linkage analysis revealed a broad signal that spans approximately 40 Mb from 18p11.2 to 18q12.2. Following the association analysis and subsequent replication attempts, we observed consistent association with the same SNPs in three genes; melanocortin 5 receptor (MC5R), dymeclin (DYM) and neural precursor cell expressed, developmentally down-regulated 4-like (NEDD4L). Conclusions: Along with already published biological evidence, MC5R, DYM and NEDD4L make attractive candidates for dyslexia susceptibility genes. However, further replication and functional studies are still required.Publisher PDFPeer reviewe

Summertime photochemistry of the troposphere at high northern latitudes

The budgets of O, NO (NO+NO), reactive nitrogen (NO), and acetic acid in the 0–6 km column over western Alaska in summer are examined by photochemical modeling of aircraft and ground‐based measurements from the Arctic Boundary Layer Expedition (ABLE 3A). It is found that concentrations of O in the region are regulated mainly by input from the stratosphere, and losses of comparable magnitude from photochemistry and deposition. The concentrations of NO (10–50 ppt) are sufficiently high to slow down O photochemical loss appreciably relative to a NO‐free atmosphere; if no NO were present, the lifetime of O in the 0–6 km column would decrease from 46 to 26 days because of faster photochemical loss. The small amounts of NO present in the Arctic troposphere have thus a major impact on the regional O budget. Decomposition of peroxyacetyl nitrate (PAN) can account for most of the NO below 4‐km altitude, but for only 20% at 6‐km altitude. Decomposition of other organic nitrates might supply the missing source of NO. The lifetime of NO, in the ABLE 3A flight region is estimated at 29 days, implying that organic nitrate precursors of NO could be supplied from distant sources including fossil fuel combustion at northern mid‐latitudes. Biomass fire plumes sampled during ABLE 3A were only marginally enriched in O; this observation is attributed in part to low NO emissions in the fires, and in part to rapid conversion of NO to PAN promoted by low atmospheric temperatures. It appears that fires make little contribution to the regional O budget. Only 30% of the acetic acid concentrations measured during ABLE 3A can be accounted for by reactions of CHCO with HO and CHO. There remains a major unidentified source of acetic acid in the atmosphere.Engineering and Applied Science