Search results for "FREQUENCY"
showing 10 items of 2158 documents
Impact of Converter-Interfaced Generation to the Frequency Response of the European Power System
2019
The increase of converter-interfaced generation (CIG) typically related to renewable energy sources is progressively causing a significant change of power systems operation. The curtailment of synchronous generation with the consequent reduction of the overall kinetic energy is one of the related issues, currently under investigation in academia and industry. The work considers the problem of overall inertia reduction from a large-scale point of view, analyzing the impact of different CIG integration levels to the frequency response of the power system of Continental Europe. The kinetic energy is evaluated for each country of the synchronous area, and the system is modified substituting con…
Impact of the high share of converter-interfaced generation on electromechanical oscillations in Continental Europe power system
2020
This study investigates the effects of converter-interfaced generation integration on the dynamic response of the power system of Continental Europe. The system is analysed with a large-scale dynamic model of the entire synchronous area, considering different instantaneous integration percentages of converter-interfaced generation across the system. The study focuses on the reduction of the overall available kinetic energy and the impact on frequency dynamics and system oscillations. The dynamic model of the system originally provided by ENTSO-E is further developed according to a specific methodology, replacing a determined amount of synchronous generation and introducing a corresponding a…
Review of studies of polymorphic blood systems in the Aymara indigenous population from Bolivia, Peru, and Chile.
1995
A review was made of all studies available from the literature referring to polymorphic blood systems of South American Aymara Indians. 33 original papers published up to 1990 covering a period of 45 years were summarized. Aymara samples were considered from a total of 55 localities in Bolivia, Peru, and Chile. Gene frequencies were tabulated for 21 polymorphic genetic systems comprising blood groups (AB0, MNSs, P, Rh, Lu, K, Le, Fy, Jk, Di), erythrocyte enzyme groups (AcP, 6PGD, PGM1, AK, ADA, EsD), and plasma protein groups (Hp, Tf, Gc, Gm, Km). Weighted average and range over all Aymara samples were computed for each blood system and compared with corresponding mean value and range in So…
Influences of geographic differentiation in the forewing warning signal of the wood tiger moth in Alaska
2014
Aposematic organisms have warning signals advertising their unpalatability to predators, and because signal efficiency is better in higher densities, positive frequency-dependent selection is expected to select against less common signals. The wood tiger moth (Parasemia plantaginis) occurs across the Holarctic and its conspicuous hindwings serve as warning signals to predators. It also has conspicuous black and white forewing patterns that could act as warning signals, or help to hide the moth by preventing predators from seeing the outline of the moth’s body (a strategy known as disruptive coloration). In Alaska, the predominant forewing pattern changes distinctly between the regions aroun…
Large Hardy-Weinberg equilibrium deviations in the Daphnia longispina of Lake El Tobar
1995
The population structure of Daphnia longispina in Lake El Tobar, Spain was studied by measuring variation at the aldehyde oxidase (AO), phosphoglucose isomerase (PGI) and phosphoglucose mutase (PGM) loci in each of 1337 individuals from four collections. In 9 of the 12 comparisons between observed allele frequencies and those expected by Hardy-Weinberg equilibrium there was an excess of heterozygotes. We found 27 of the potential number of 54 composite electromorphs (‘clones’) based on the three allozymes. Clone diversities were rather high in all collections. Three clones reached frequencies of over 25% and different clones were dominant in each of the four collections. Strong temporal var…
Genetic database development for the characterisation of Sicilian sheep population
2019
The most representative sheep in Sicily are Belicina, Comisana, Pinzirita, Barbarescaand the crossbred derived sheep from all this species. In this study, the allelic frequencies of the Sicilian sheep population were investigated. It currently represents the best way to determine the genetic identity and/or family even with limited amounts of sample or when the DNA is degraded. The aim of the study was to provide a reference data bank and to evaluate a microsatellite panel for pedigree analysis as suggested by the International Society for Animal Genetics (ISAG). There are various studies on European sheep, but few datasets were developed on the population of Sicilian sheep. The reference d…
Population structure of a parasitic plant and its perennial host
2002
Characterization of host and parasite population genetic structure and estimation of gene flow among populations are essential for the understanding of parasite local adaptation and coevolutionary interactions between hosts and parasites. We examined two aspects of population structure in a parasitic plant, the greater dodder (Cuscuta europaea) and its host plant, the stinging nettle (Urtica dioica), using allozyme data from 12 host and eight parasite populations. First, we examined whether hosts exposed to parasitism in the past contain higher levels of genetic variation. Second, we examined whether host and parasite populations differ in terms of population structure and if their populati…
Genetic differentiation and structure of Hippocrepis valentina (Leguminosae) populations
2000
We present an analysis of isozyme variability in natural populations of the plant species Hippocrepis valentina (Leguminosae), which is endemic to the eastern Mediterranean coast of Spain and currently has endangered species status. Our results, obtained by starch-gel electrophoresis of 15 loci, show normal levels of variability for species with similar biology. The comparison with the patterns of genetic variability of two closely related species, H. balearica and H. grosii, confirms the taxonomic status of H. valentina as a proper species, independent of H. balearica, as previously suggested. The analysis of population subdivision shows that substantial variation among populations is pres…
HLA antigens in ulcerative colitis: a study in the Sicilian population
2008
HLA antigens were investigated in 41 Sicilian patients with ulcerative colitis and in 151 healthy controls. Frequencies of HLA-B5 and DR2 were increased in the group of patients with ulcerative colitis whereas the DR3 antigen frequency was decreased. However the corrected p values were not significant. Thus, present results indicate that in ulcerative colitis HLA linked genetic factors play a marginal role, if any.