56 research outputs found
Low-Prandtl-number B\'enard-Marangoni convection in a vertical magnetic field
The effect of a homogeneous magnetic field on surface-tension-driven
B\'{e}nard convection is studied by means of direct numerical simulations. The
flow is computed in a rectangular domain with periodic horizontal boundary
conditions and the free-slip condition on the bottom wall using a
pseudospectral Fourier-Chebyshev discretization. Deformations of the free
surface are neglected. Two- and three-dimensional flows are computed for either
vanishing or small Prandtl number, which are typical of liquid metals. The main
focus of the paper is on a qualitative comparison of the flow states with the
non-magnetic case, and on the effects associated with the possible
near-cancellation of the nonlinear and pressure terms in the momentum equations
for two-dimensional rolls. In the three-dimensional case, the transition from a
stationary hexagonal pattern at the onset of convection to three-dimensional
time-dependent convection is explored by a series of simulations at zero
Prandtl number.Comment: 26 pages, 9 figure
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Phylogenomic analysis of a 55.1 kb 19-gene dataset resolves a monophyletic Fusarium that includes the Fusarium solani Species Complex
Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-userÂżs needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option availabl
Larval case architecture and implications of host-plant associations for North American Coleophora (Lepidoptera; Coleophoridae)
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FOUR NEW FEATHER MITE SPECIES OF THE FAMILY PTERONYSSIDAE(ASTIGMATA: ANALGOIDEA) FROM LAUGHING-THRUSHES (PASSERIFORMES: TIMALIIDAE) IN CHINA
Four new species of the feather mite family Pteronyssidae are described from passerines of the family Timaliidae in China (Guangxi and Guizhou Provinces): Mouchetia stachyris sp. n. from Stachyris ruficeps Blyth, Pteroherpus garrulacis sp. n. from Garrulax maesi (Oustalet), Timalinyssus curvilobus sp. n. from Garrulax sannio Swinhoe, and T. grallator sp. n. from Alcippe chrysotis (Blyth). New data on distribution and host associations are provided for six more species of pteronyssids found in the area surveyed. Four species, M. indochinensis Mironov, 1990, P. pycnonoti Mironov, 1992, P. krivolutskii Mironov, 1992 and Pteronyssoides (Pteronyssoides) faini Mironov et Wauthy, 2005, are found in China for the first time; for the two latter species and for Pteronyssoides (Holonyssoides) desmiphorus (Gaud, 1952) and Timalinyssus longitarsus Wang et Wang, 2008 new avian hosts are recorded
Feeding behaviour and phylogeny: Observations on early derivative Acari
Based on laboratory observations of three species of Allothyrus (Parasitiformes: Holothyrida: Allothyridae) from south east Queensland and gut content analysis of 62 individuals representing 11 species of Allothyrus from eastern Australia, we determined that Australian Allothyridae are scavengers that ingest fluids only. Living arthropods, nematodes, snails and annelids were ignored, but dead arthropods were readily fed upon and were sufficient to maintain adults and nymphs for many months. The adults were sluggish, timid animals that relied on armour, thanatosis and probably on noxious chemicals for protection: the juveniles produced secretions from idiosomal glands. In contrast, most early derivative Mesostigmata that we tested (Sejina, species of Sejus and Uropodella; Uropodina, Polyaspi, sp. and Cercomegistina, an undescribed Asternoseiidae) were aggressive predators of small invertebrates and ingested fluids only; however, two species of Asternolaelaps (Sejina) had solid fungal and animal material in their guts. Similarly, the early derivative acariform (Palaeosomata, species of Stomacarus and Loftacarus) and opilioacariform mites (an undescribed Opilioacarida from Australia) that we examined all ingested particulate foods, including fungal and animal material. These observations are consistent with the hypothesis that the earliest mites were scavengers and opportunistic that ingested solid foods and that fluid feeding is a derived condition linking the three orders of Parasitiformes (Holothyrida, Ixodida and Mesostigmata)
Predatory mites in tropical Australia: Local species richness and complementarity
Although little supporting data is available, mites (Acari) are often considered to be one of the 'hyperdiverse' taxa in tropical ecosystems. To test this assumption, we sampled single guilds of predatory mites (Hydracarina and Mesostigmata) in three different habitats (fresh water, rotting fungi, and forest foliage) across a range of sites in monsoonal, wet-tropical, and subtropical Australia. Most species (61%) were collected at a single site; as a result, all seven collector's curves rose steeply with little indication of reaching asymptotes. Regional faunas ranged from 87-94 percent distinct and of the 247 species identified, 114 (46%) were previously unknown in Australia and appear to be new. Even within taxonomically well-studied groups, such as the Hydracarina and Phytoseiidae, we found many new species (32% and 60%, respectively). Our results suggest that the diversity of tropical mites is very high and comparable to that of many insect taxa. We propose a simple model to explain our results, i.e. that in the tropics, high levels of complementarity between sites amplify local mite species richness. We tested this model by additional sampling, comparing within-site to between-site complementarity, and contrasting temperate with tropical foliar Mesostigmata. As predicted by the model, collecting at new sites continued to accumulate new species, complementarity was significantly greater between-sites than within-sites (72 vs. 25%), and temperate collections were more homogeneous and less diverse than tropical collections
Like A Glove: Do The Dimensions Of Male Adanal Suckers And Tritonymphal Female Docking Papillae Correlate In The Proctophyllodidae (Astigmata: Analgoidea)?
Byers, K.A., Proctor, H.C. (2014): Like A Glove: Do The Dimensions Of Male Adanal Suckers And Tritonymphal Female Docking Papillae Correlate In The Proctophyllodidae (Astigmata: Analgoidea)? Acarologia 54 (1): 3-14, DOI: 10.1051/acarologia/20142110, URL: http://dx.doi.org/10.1051/acarologia/2014211
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