Hybrid Generators-based AC Microgrid Performance Assessment in Island Mode

Achieving an accurate steady-state averaged active power sharing between parallel inverters in islanded AC microgrids could be realized by a traditional droop control. For identical inverters having the same droop gains, it is assumed that the transient average power responses will be similar, and no circulating current will flow between the units. However, different line impedances could influence the instantaneous power significantly and thus circulating power flows among the inverters particularly during sudden disturbances such as load changes. This power, if absorbed by an inverter, will lead the DC link voltage to rise abruptly and trip the inverter, thus, degrading the performance of the whole microgrid. The problem becomes worse when hybrid generators are serving as unidirectional power source. This paper assesses the performance of hybrid generators within an islanded microgrid against the mismatch in line impedances. Two schemes to stabilize the microgrid are proposed. In addition, a participation factor analysis is developed to select the most effective controller scheme to bound the DC link voltage and minimize the circulating power. Simulation and experimental results are presented to verify the analysis and the capability of the proposed controller

Pinwheel stabilization by ocular dominance segregation

We present an analytical approach for studying the coupled development of ocular dominance and orientation preference columns. Using this approach we demonstrate that ocular dominance segregation can induce the stabilization and even the production of pinwheels by their crystallization in two types of periodic lattices. Pinwheel crystallization depends on the overall dominance of one eye over the other, a condition that is fulfilled during early cortical development. Increasing the strength of inter-map coupling induces a transition from pinwheel-free stripe solutions to intermediate and high pinwheel density states.Comment: 10 pages, 4 figure

Adrenal lesions found incidentally: how to improve clinical and cost-effectiveness

Introduction Adrenal incidentalomas are lesions that are incidentally identified while scanning for other conditions. While most are benign and hormonally non-functional, around 20% are malignant and/or hormonally active, requiring prompt intervention. Malignant lesions can be aggressive and life-threatening, while hormonally active tumours cause various endocrine disorders, with significant morbidity and mortality. Despite this, management of patients with adrenal incidentalomas is variable, with no robust evidence base. This project aimed to establish more effective and timely management of these patients. Methods We developed a web-based, electronic Adrenal Incidentaloma Management System (eAIMS), which incorporated the evidence-based and National Health Service–aligned 2016 European guidelines. The system captures key clinical, biochemical and radiological information necessary for adrenal incidentaloma patient management and generates a pre-populated outcome letter, saving clinical and administrative time while ensuring timely management plans with enhanced safety. Furthermore, we developed a prioritisation strategy, with members of the multidisciplinary team, which prioritised high-risk individuals for detailed discussion and management. Patient focus groups informed process-mapping and multidisciplinary team process re-design and patient information leaflet development. The project was partnered by University Hospital of South Manchester to maximise generalisability. Results Implementation of eAIMS, along with improvements in the prioritisation strategy, resulted in a 49% reduction in staff hands-on time, as well as a 78% reduction in the time from adrenal incidentaloma identification to multidisciplinary team decision. A health economic analysis identified a 28% reduction in costs. Conclusions The system’s in-built data validation and the automatic generation of the multidisciplinary team outcome letter improved patient safety through a reduction in transcription errors. We are currently developing the next stage of the programme to proactively identify all new adrenal incidentaloma cases

Abundant dust found in intergalactic space

Galactic dust constitutes approximately half of the elements more massive than helium produced in stellar nucleosynthesis. Notwithstanding the formation of dust grains in the dense, cool atmospheres of late-type stars, there still remain huge uncertainties concerning the origin and fate of galactic stardust. In this paper, we identify the intergalactic medium (i.e. the region between gravitationally-bound galaxies) as a major sink for galactic dust. We discover a systematic shift in the colour of background galaxies viewed through the intergalactic medium of the nearby M81 group. This reddening coincides with atomic, neutral gas previously detected between the group members. The dust-to-HI mass ratio is high (1/20) compared to that of the solar neighborhood (1/120) suggesting that the dust originates from the centre of one or more of the galaxies in the group. Indeed, M82, which is known to be ejecting dust and gas in a starburst-driven superwind, is cited as the probable main source.Comment: 5 pages, 3 figures, 1 table. ApJ Letters in pres

Microbiotic soil crusts in the Sahel of Western Niger and their influence on Soil POROSITY and water dynamics

International audienceMicrobiotic soil crusts are common features of the surface of fallow land in Western Niger. We investigated the interaction between these microbial covers and the porosity and water dynamics of soils at the surface of a Sahelian landscape. The soil pore system was examined by microscopic observations and mercury porosimetry. The soil water retention capacity was measured using a Richard pressure membrane apparatus. Runoff measurements were performed in situ at a one m2 scale under natural rainfall. Samples with dense cyanobacterial cover had microbially-originated pores ranging from 0.04 and 50 μm in size. These samples also showed higher total soil porosity and retained two to four times more water than samples with thin microbial cover. These properties are closely related to the hydrophobic nature of cyanobacterial components. Final runoff values obtained on densely covered surfaces were significantly higher compared to those measured on surfaces with thin microbial cover due to the geometry of the microbially-originated pore system and its functioning

A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves

We present an exhaustive, quantitative comparison of all of the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior of Milky Way extinction curves. The R_V dependent CCM relationship and the sample of extinction curves used to derive this relationship is used to describe the general behavior of Milky Way extinction curves. The ultraviolet portion of the SMC and LMC extinction curves are derived from archival IUE data, except for one new SMC extinction curve which was measured using HST/STIS observations. The optical extinction curves are derived from new (for the SMC) and literature UBVRI photometry (for the LMC). The near-infrared extinction curves are calculated mainly from 2MASS photometry supplemented with DENIS and new JHK photometry. For each extinction curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust column as the extinction curve. We compare the properties of the SMC and LMC extinction curves with the CCM relationship three different ways: each curve by itself, the behavior of extinction at different wavelengths with R_V, and behavior of the extinction curve FM fit parameters with R_V. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship, but majority of the LMC and all of the SMC curves do not follow the CCM relationship. For the first time, we find that the CCM relationship seems to form a bound on the properties of all of the LMC and SMC extinction curves. This result strengthens the picture of dust extinction curves exhibit a continuum of properties between those found in the Milky Way and the SMC Bar. (abridged)Comment: 18 pages, 10 figures, ApJ in pres

A Reduced Nonlinear Model for the Simulation of Two Phase Flow in a Horizontal Pipe.

In the last 10 years many 3D numerical schemes have been developed for the study the flow of a mixture of liquid and gas in a pipeline (Frank, Numerical simulation of slug flow regime for an air-water two-phase flow in horizontal pipes. In: The 11th international topical meeting on nuclear reactor thermal-hydraulics (NURETH-11), Avignon, 2005; Vallée et al., Nucl Eng Des 238(3):637–646, 2008; Höhne, Experiments and numerical simulations of horizontal two-phase flow regimes. In: Proceeding of the seventh international conference on CFD in the minerals and process industries, Melbourne, 2009; Bartosiewicz et al., Nucl Eng Des 240(9):2375–2381, 2010) but although they offer a very good accuracy, they are rarely fit for modelling a long pipe, due to the high computational costs. Then one is usually led to consider 1D models, see e.g. the works of Issa and his group (Issa and Kempf, Int J Multiphase Flow 29(1):69–95, 2003). Such models offer much faster simulations than 3D schemes, on the other hand they almost completely miss the dynamics in the transversal direction. Here we present a model able of representing the full 3D dynamics, but with the computational cost typical of 1D simulation. The main feature of our model consists in describing the dynamical variables in the direction transversal to the pipe by means of a family of functions depending on a set of parameters. The model is then solved by a standard finite volume scheme

Características morfogênicas e estruturais do capim-massai sob diferentes estratégias de desfolhação.

Gramíneas forrageiras apresentam grande plasticidade quando impostas a diferentes estratégias de desfolhação e o entendimento dessas mudanças na estrutura do dossel é de grande importância para a adoção de estratégias de colheita mais eficientes. No presente trabalho teve-se por objetivo avaliar as características morfogênicas e estruturais do Panicum maximum Jacq. cv Massai sob diferentes intensidades e freqüências de corte

Fluxo de tecidos do capim-milênio sob regime de cortes.

O estudo da dinâmica do fluxo de tecidos via morfogênese é uma importante ferramenta para a determinação de práticas de manejo mais eficientes no controle de utilização de forrageiras. Por esta razão foi conduzido em experimento com o objetivo de avaliar as características morfogênicas e estruturais do Panicum maximum Jacq. cv Milênio sob diferentes intensidades e freqüências de corte