Fast and Accurate Simulation Technique for Large Irregular Arrays

A fast full-wave simulation technique is presented for the analysis of large irregular planar arrays of identical 3-D metallic antennas. The solution method relies on the Macro Basis Functions (MBF) approach and an interpolatory technique to compute the interactions between MBFs. The Harmonic-polynomial (HARP) model is established for the near-field interactions in a modified system of coordinates. For extremely large arrays made of complex antennas, two approaches assuming a limited radius of influence for mutual coupling are considered: one is based on a sparse-matrix LU decomposition and the other one on a tessellation of the array in the form of overlapping sub-arrays. The computation of all embedded element patterns is sped up with the help of the non-uniform FFT algorithm. Extensive validations are shown for arrays of log-periodic antennas envisaged for the low-frequency SKA (Square Kilometer Array) radio-telescope. The analysis of SKA stations with such a large number of elements has not been treated yet in the literature. Validations include comparison with results obtained with commercial software and with experiments. The proposed method is particularly well suited to array synthesis, in which several orders of magnitude can be saved in terms of computation time.Comment: The paper was submitted to IEEE Transaction on Antennas and Propagation on 01 - Feb.- 2017. The paper is 12 pages with 18 figure

Space-based Aperture Array For Ultra-Long Wavelength Radio Astronomy

The past decade has seen the rise of various radio astronomy arrays, particularly for low-frequency observations below 100MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21cm line emission. However, Earth-based radio astronomy below frequencies of 30MHz is severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths' ionosphere. Various studies in the past were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. We briefly present the achievable science cases, and discuss the system design for selected scenarios, such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.Comment: Submitte

Cartographie des débits d’étiage : application au bassin de la Meurthe

Les campagnes de jaugeages en basses eaux permettent de faire une investigation spatiale des écoulements à l’intérieur des bassins et d’élaborer les profils hydrologiques des différents cours d’eau qui servent à la détermination des zones de rendement homogène. Ces profils sont calés sur les débits fréquentiels caractéristiques des stations hydrométriques. Une carte des rendements hydrologiques pour l’ensemble du bassin est alors réalisée pour chacune des fréquences choisies.Measures of low water conditions facilitate a spatial investigation of flows within river basins and the construction of hydrological profiles of different waterways which can be used to determine zones of homogeneous flows. These profiles are fixed on characteristics flow frequencies of hydrological stations. A map of hydrological outputs for the whole basin is then produced for each of the selected frequencies.Die Messkampagnen bei Niedrigwasser ermöglichen eine räumliche Erforschung der Niderschläge im Inneren der Becken und die Ausarbeitung hydrologischer Profile der verschiedenen Wasserläufe, die zur Bestimmung von Zonen homogener Ergiebigkeit für das ganze Becken und für der ausgewählten Häufigkeiten dargestellt

Cartographie des débits d’étiage : application au bassin de la Meurthe

Les campagnes de jaugeages en basses eaux permettent de faire une investigation spatiale des écoulements à l’intérieur des bassins et d’élaborer les profils hydrologiques des différents cours d’eau qui servent à la détermination des zones de rendement homogène. Ces profils sont calés sur les débits fréquentiels caractéristiques des stations hydrométriques. Une carte des rendements hydrologiques pour l’ensemble du bassin est alors réalisée pour chacune des fréquences choisies.Measures of low water conditions facilitate a spatial investigation of flows within river basins and the construction of hydrological profiles of different waterways which can be used to determine zones of homogeneous flows. These profiles are fixed on characteristics flow frequencies of hydrological stations. A map of hydrological outputs for the whole basin is then produced for each of the selected frequencies.Die Messkampagnen bei Niedrigwasser ermöglichen eine räumliche Erforschung der Niderschläge im Inneren der Becken und die Ausarbeitung hydrologischer Profile der verschiedenen Wasserläufe, die zur Bestimmung von Zonen homogener Ergiebigkeit für das ganze Becken und für der ausgewählten Häufigkeiten dargestellt

Using Embedded Element Patterns to Improve Aperture Array Calibration

Several existing and planned low-frequency (<; 350 MHz) radio astronomical facilities exploit subarrays or stations consisting of receiving elements in an irregular configuration. Calibration of the RF path of each receiving element is crucial for accurate beamforming with these stations. Currently used station calibration methods usually assume that the embedded element patterns (EEPs) of the receiving elements within a station are identical. In this contribution, we show that ignoring the inter-element EEP variations causes systematic errors in the calibration results using the stations of the low-frequency receiving systems of the Square Kilometre Array (SKA) and the Low Frequency Array (LOFAR) as examples. We show that the magnitude of these errors increases with increasing EEP variations. We also discuss the challenges faced by SKA and LOFAR to mitigate these errors by exploiting a priori knowledge of the EEPs

The trophic importance of epiphytic algae in a freshwater macrophyte system (Potamogeton perfoliatus L.): stable isotope and fatty acid analyses

Stable isotope and fatty acid analyses were used to study carbon sources for animals in a submerged plant bed. Epiphytes growing on Potamogeton perfoliatus, sand microflora, and alder leaves were the most important carbon sources. The most abundant macrophyte, P. perfoliatus was unimportant as a food source. Modelling (IsoSource) showed that epiphytes were the most important food source for the most abundant benthic invertebrates, the isopod Asellus aquaticus (annual mean contribution 64%), the amphipod Gammarus pulex (66%), and the gastropod Potamopyrgus antipodarum (83%). The mean annual contributions of sand microflora were, respectively, 21, 19, and 9%; and of alder leaves, 15, 15, and 8% for these three species. The relative importance of carbon sources varied seasonally. The relative contribution of epiphytes was lowest for all three grazer species in July: A. aquaticus 38%, G. pulex 43%, and P. antipodarum 42%. A decline in epiphyte biomass in summer may have caused this switch to less attractive food sources. P. perfoliatus provided habitat and shelter for consumers, but food was mainly supplied indirectly by providing space for attached epiphytes, which are fast-growing and provide a highly nutritious food source

Large-scale plasma metabolome analysis reveals alterations in HDL metabolism in migraine

Objective To identify a plasma metabolomic biomarker signature for migraine. Methods Plasma samples from 8 Dutch cohorts (n = 10,153: 2,800 migraine patients and 7,353 controls) were profiled on a 1H-NMR-based metabolomics platform, to quantify 146 individual metabolites (e.g., lipids, fatty acids, and lipoproteins) and 79 metabolite ratios. Metabolite measures associated with migraine were obtained after single-metabolite logistic regression combined with a random-effects meta-analysis performed in a nonstratified and sex-stratified manner. Next, a global test analysis was performed to identify sets of related metabolites associated with migraine. The Holm procedure was applied to control the family-wise error rate at 5% in single-metabolite and global test analyses. Results Decreases in the level of apolipoprotein A1 (β −0.10; 95% confidence interval [CI] −0.16, −0.05; adjusted p = 0.029) and free cholesterol to total lipid ratio present in small high-density lipoprotein subspecies (HDL) (β −0.10; 95% CI −0.15, −0.05; adjusted p = 0.029) were associated with migraine status. In addition, only in male participants, a decreased level of omega-3 fatty acids (β −0.24; 95% CI −0.36, −0.12; adjusted p = 0.033) was associated with migraine. Global test analysis further supported that HDL traits (but not other lipoproteins) were associated with migr

<i>GRIN2A</i>-related disorders:genotype and functional consequence predict phenotype

Alterations of the N-methyl-d-aspartate receptor (NMDAR) subunit GluN2A, encoded by GRIN2A, have been associated with a spectrum of neurodevelopmental disorders with prominent speech-related features, and epilepsy. We performed a comprehensive assessment of phenotypes with a standardized questionnaire in 92 previously unreported individuals with GRIN2A-related disorders. Applying the criteria of the American College of Medical Genetics and Genomics to all published variants yielded 156 additional cases with pathogenic or likely pathogenic variants in GRIN2A, resulting in a total of 248 individuals. The phenotypic spectrum ranged from normal or near-normal development with mild epilepsy and speech delay/apraxia to severe developmental and epileptic encephalopathy, often within the epilepsy-aphasia spectrum. We found that pathogenic missense variants in transmembrane and linker domains (misTMD+Linker) were associated with severe developmental phenotypes, whereas missense variants within amino terminal or ligand-binding domains (misATD+LBD) and null variants led to less severe developmental phenotypes, which we confirmed in a discovery (P = 10-6) as well as validation cohort (P = 0.0003). Other phenotypes such as MRI abnormalities and epilepsy types were also significantly different between the two groups. Notably, this was paralleled by electrophysiology data, where misTMD+Linker predominantly led to NMDAR gain-of-function, while misATD+LBD exclusively caused NMDAR loss-of-function. With respect to null variants, we show that Grin2a+/- cortical rat neurons also had reduced NMDAR function and there was no evidence of previously postulated compensatory overexpression of GluN2B. We demonstrate that null variants and misATD+LBD of GRIN2A do not only share the same clinical spectrum (i.e. milder phenotypes), but also result in similar electrophysiological consequences (loss-of-function) opposing those of misTMD+Linker (severe phenotypes; predominantly gain-of-function). This new pathomechanistic model may ultimately help in predicting phenotype severity as well as eligibility for potential precision medicine approaches in GRIN2A-related disorders