| 291. |
- Riley, A. H., et al.
(författare)
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Possible Detection of Gamma-Rays from Epsilon Eridani
- 2019
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 878:1
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Tidskriftsartikel (refereegranskat)abstract
- We use the Fermi Large Area Telescope gamma-ray observatory to search for gamma-ray emission from four nearby, debris disk-hosting main-sequence stars: τ Ceti, Eridani, Fomalhaut, and Vega. For three stars (τ Ceti, Fomalhaut, and Vega), we establish upper limits that are consistent with theoretical expectations. For Eridani, we find a possible spatially coincident source with a soft energy spectrum of dN/dE ∼ E -3.6. However, at this stage we are unable to rule out that this emission is due to a more extended feature in the diffuse background. In the interpretation that the emission is due to Eridani, the >100 MeV gamma-ray luminosity is ∼1027 erg s-1 ≃ 3 ×10-7 L o, which is ∼1010 times the gamma-ray luminosity from the disk of the quiet Sun. We find ≲2σ evidence of source variability over a ∼7 yr timescale. In the interpretation that the gamma-ray emission is from Eridani itself, we consider two possible models: (1) cosmic-ray collisions with solid bodies in the debris disk, which extends out ∼60 au from the host star, and (2) emission from the stellar activity. For the former model, assuming a total disk mass consistent with infrared measurements, we find that the size distribution of bodies is steeper than expected for a collisional cascade state. If confirmed as being associated with Eridani, this would be the first indication of gamma-ray emission from the vicinity of a main-sequence star other than the Sun.
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| 292. |
- Rivas, M. J., et al.
(författare)
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Population genomics of parallel evolution in gene expression and gene sequence during ecological adaptation
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Natural selection often produces parallel phenotypic changes in response to a similar adaptive challenge. However, the extent to which parallel gene expression differences and genomic divergence underlie parallel phenotypic traits and whether they are decoupled or not remains largely unexplored. We performed a population genomic study of parallel ecological adaptation among replicate ecotype pairs of the rough periwinkle (Littorina saxatilis) at a regional geographical scale (NW Spain). We show that genomic changes underlying parallel phenotypic divergence followed a complex pattern of both repeatable differences and of differences unique to specific ecotype pairs, in which parallel changes in expression or sequence are restricted to a limited set of genes. Yet, the majority of divergent genes were divergent either for gene expression or coding sequence, but not for both simultaneously. Overall, our findings suggest that divergent selection significantly contributed to the process of parallel molecular differentiation among ecotype pairs, and that changes in expression and gene sequence underlying phenotypic divergence could, at least to a certain extent, be considered decoupled processes. © 2018, The Author(s).
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| 293. |
- Romano, Luigi, 1994, et al.
(författare)
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A Classification Method of Road Transport Missions and Applications Using the Operating Cycle Format
- 2022
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers Inc.. - 2169-3536. ; 10, s. 73087-73121
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Tidskriftsartikel (refereegranskat)abstract
- When dealing with customers, original equipment manufacturers (OEMs) classify vehicular usage by resorting to simplified, often colloquial, descriptions that allow for a rough understanding of the operating conditions and the user's needs. In this way, the information retrieved from the customers is exploited to guide their choices in terms of vehicle design and configuration, based on the characteristics of the transport application, labeled using intuitive metrics. However, a common problem in this context is the absence of any formal connection to lower levels of representation that might effectively be used to assess vehicular energy performance in simulation, or for design optimization using mathematical algorithms. Indeed, both processes require more accurate modeling of the surroundings, including exhaustive information about the local road, weather, and traffic conditions. Therefore, starting with a detailed statistical description of the environment, this paper proposes a method for mathematical classification of transport missions and applications within the theoretical framework of the operating cycle (OC). The approach discussed in the paper combines a collection of statistical models structured hierarchically, called a stochastic operating cycle (sOC), with a bird's-eye view description of the operating environment. The latter postulates the existence of different classes, which are representative of the usage and whose definition is based on simple metrics and thresholds expressed mathematically in terms of statistical measures. Algebraic expressions, called operating classes in the paper, are derived analytically for all the stochastic models presented. This establishes a connection between the two levels of representation, enabling to simulate longitudinal vehicle dynamics in virtual environments generated based on the characteristics of the intended application, using log data collected from vehicles and/or information provided by customers. Additionally, the relationships between the two descriptions are formalized using elementary probability operators, allowing for an intuitive characterization of a transport operation. An example is adduced to illustrate a possible application of the proposed method, using six sOCs parametrized from log data collected during real-world missions. The proposed approach may facilitate the interaction between OEMs, customers, and road operators, allowing for planning of maintenance, and optimization of transport missions, components, and configurations using standard procedures and routines.
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| 294. |
- Romano, Luigi, 1994, et al.
(författare)
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An enhanced stochastic operating cycle description including weather and traffic models
- 2021
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Ingår i: Transportation Research Part D. - : Elsevier Ltd. - 1361-9209 .- 1879-2340. ; 97
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Tidskriftsartikel (refereegranskat)abstract
- The present paper extends the concept of a stochastic operating cycle (sOC) by introducing additional models for weather and traffic. In regard to the weather parameters, dynamic models for air temperature, atmospheric pressure, relative humidity, precipitation, wind speed and direction are included. The traffic models is instead based on a macroscopic approach which describes the density dynamically by means of a simple autoregressive process. The enhanced format is structured in a hierarchical fashion, allowing for ease of implementation and modularity. The novel models are parametrised starting from data available from external databases. The possibility of generating synthetic data using the statistical descriptors introduced in the paper is also discussed. To investigate the impact of the novel parameters over energy efficiency, a sensitivity analysis is conducted with a combinatorial test design. Simulation results show that both seasonality and traffic conditions are responsible for introducing major variations in the CO2 emissions. © 2021 The Author(s)
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| 295. |
- Romano, Luigi, 1994, et al.
(författare)
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Development of the Vastra Gotaland operating cycle for long-haul heavy-duty vehicles
- 2023
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers Inc.. - 2169-3536. ; 11, s. 73268-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a complete operating cycle (OC) description is developed for heavy-duty vehicles traveling long distances in the region of Västra Götaland, Sweden. Variation amongst road transport missions is accounted for using a collection of stochastic models. These are parametrized from log data for all the influential road parameters that may affect the energy performance of heavy trucks, including topography, curvature, speed limits, and stop signs. The statistical properties of the developed OC description are investigated numerically by considering some composite variables, condensing the salient information about the road characteristics, and inspired by two existing classification systems. Two examples are adduced to illustrate the potential of the OC format, which enables ease of classification and detailed simulation of energy efficiency for individual vehicles, with application in vehicle design optimization and selection, production planning, and predictive maintenance. In particular, for the track used in the first example, a Volvo FH13 equipped with a diesel engine, simulation results indicate mean CO2 emissions of around 1700 g km-1, with a standard deviation of 360 g km-1; in the second example, dealing with electrical fleet sizing, the optimal proportion shows a predominance of tractor-semitrailer vehicles (70%) equipping 4 motors and 11 battery packs.
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| 296. |
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| 297. |
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| 298. |
- Saltin, Sara H, et al.
(författare)
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Preference of males for large females causes a partial mating barrier between a large and a small ecotype of Littorina fabalis (W. Turton, 1825)
- 2013
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Ingår i: Journal of Molluscan Studies. - : Oxford University Press (OUP). - 0260-1230 .- 1464-3766. ; 79, s. 128-132
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Tidskriftsartikel (refereegranskat)abstract
- Species occupying different ecological niches may evolve ecotypes that differ in size as a result of divergent selection on this trait. Size differences may affect mate preference and cause deviations from random mating. Several marine snails of the genus Littorina have ecotypes that differ in size and earlier studies have shown strong assortative mating between differently sized ecotypes in at least one of these species, L. saxatilis. Here we studied male mate choice in two ecotypes of the congeneric L. fabalis that differ in size. We found mating to be nonrandom, because males of the large ecotype followed the mucus trails and copulated with females of their own large ecotype more than with females of the smaller ecotype. Males of the smaller ecotype showed no strong preference, but tended to copulate more with females of the large ecotype than with their own females. Further experiments using the small ecotype showed that mate choice was size-based, with a general preference of the males to mate large females. It seems likely that the partial reproductive barrier that we describe somewhat impedes gene flow between the two ecotypes of L. fabalis, a result that corroborates earlier observations of a weak, but significant, gene-flow barrier across zones where the two ecotypes overlap and hybridize.
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| 299. |
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| 300. |
- Stankowski, Sean, et al.
(författare)
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The genetic basis of a recent transition to live-bearing in marine snails
- 2024
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 383:6678, s. 114-119
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Tidskriftsartikel (refereegranskat)abstract
- Key innovations are fundamental to biological diversification, but their genetic basis is poorly understood. A recent transition from egg-laying to live-bearing in marine snails (Littorina spp.) provides the opportunity to study the genetic architecture of an innovation that has evolved repeatedly across animals. Individuals do not cluster by reproductive mode in a genome-wide phylogeny, but local genealogical analysis revealed numerous small genomic regions where all live-bearers carry the same core haplotype. Candidate regions show evidence for live-bearer-specific positive selection and are enriched for genes that are differentially expressed between egg-laying and live-bearing reproductive systems. Ages of selective sweeps suggest that live-bearer-specific alleles accumulated over more than 200,000 generations. Our results suggest that new functions evolve through the recruitment of many alleles rather than in a single evolutionary step.
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