| 1. |
- Holland, Linda Z, et al.
(författare)
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The amphioxus genome illuminates vertebrate origins and cephalochordate biology
- 2008
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Ingår i: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051 .- 1549-5469. ; 18:7, s. 1100-1111
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Tidskriftsartikel (refereegranskat)abstract
- Cephalochordates, urochordates, and vertebrates evolved from a common ancestor over 520 million years ago. To improve our understanding of chordate evolution and the origin of vertebrates, we intensively searched for particular genes, gene families, and conserved noncoding elements in the sequenced genome of the cephalochordate Branchiostoma floridae, commonly called amphioxus or lancelets. Special attention was given to homeobox genes, opsin genes, genes involved in neural crest development, nuclear receptor genes, genes encoding components of the endocrine and immune systems, and conserved cis-regulatory enhancers. The amphioxus genome contains a basic set of chordate genes involved in development and cell signaling, including a fifteenth Hox gene. This set includes many genes that were co-opted in vertebrates for new roles in neural crest development and adaptive immunity. However, where amphioxus has a single gene, vertebrates often have two, three, or four paralogs derived from two whole-genome duplication events. In addition, several transcriptional enhancers are conserved between amphioxus and vertebrates--a very wide phylogenetic distance. In contrast, urochordate genomes have lost many genes, including a diversity of homeobox families and genes involved in steroid hormone function. The amphioxus genome also exhibits derived features, including duplications of opsins and genes proposed to function in innate immunity and endocrine systems. Our results indicate that the amphioxus genome is elemental to an understanding of the biology and evolution of nonchordate deuterostomes, invertebrate chordates, and vertebrates.
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| 2. |
- Matsumoto, H., et al.
(författare)
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Plasma/radio wave observations at mercury by the bepicolombo mmo spacecraft
- 2006
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Ingår i: Advances in Geosciences. - : World Scientific Publishing Co.. - 9789812707192 - 9789812569837 ; , s. 83-84
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Bokkapitel (refereegranskat)abstract
- The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft comprises the plasma and radio wave observation system called PlasmaWave Investigation (PWI). The PWI is designed and developed in collaboration between Japanese and European scientists. Since plasma/radio wave receivers were not installed in the former spacecraft, Mariner 10, which observed the planet Mercury, the PWI onboard the MMO spacecraft will provide the first plasma/radio wave data from Mercury orbit. It will give important information for studies of energy exchange processes in the unique magnetosphere of Mercury characterized by the interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM2P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10MHz for the electric field.
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| 3. |
- Retino, A., et al.
(författare)
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Cluster observations of energetic electrons and electromagnetic fields within a reconnecting thin current sheet in the Earth's magnetotail
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:A12
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Tidskriftsartikel (refereegranskat)abstract
- We study the acceleration of energetic electrons during magnetotail reconnection by using Cluster simultaneous measurements of three-dimensional electron distribution functions, electric and magnetic fields, and waves in a thin current sheet. We present observations of two consecutive current sheet crossings where the flux of electrons 35 127 keV peaks within an interval of tailward flows. The first crossing shows the signatures of a tailward moving flux rope. The observed magnetic field and density indicate that the flux rope was very dynamic, and a comparison with numerical simulation suggests a crossing right after coalescence of smaller flux ropes. The second crossing occurs within the ion diffusion region. The flux of electrons is largest within the flux rope where they are mainly directed perpendicular to the magnetic field. At the magnetic separatrices, the fluxes are smaller, but the energy spectra are harder and electrons are mainly field aligned. Reconnection electric fields E-Y similar to 7 mV/m are observed within the diffusion region, whereas in the flux rope, EY are much smaller. Waves around lower hybrid frequency do not show a clear correlation with energetic electrons. We interpret the field-aligned electrons at the separatrices as directly accelerated by the reconnection electric field in the diffusion region, whereas we interpret the perpendicular electrons as trapped within the flux rope and accelerated by a combination of betatron acceleration with nonadiabatic pitch-angle scattering. Our observations indicate that thin current sheets during dynamic reconnection are important for in situ production of energetic electrons and that simultaneous measurements of electrons and electromagnetic fields within thin sheets are crucial to understand the acceleration mechanisms.
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