1,243 research outputs found
A4_5 Solar Propelled Rocket
In this paper we discuss whether it would be feasible to replace the current Soyuz rocketās Earth launch phase, with the radiation pressure from reflected solar radiation. We find that the mirror would need an area 2.05 Ć 105 km^2 in an ideal situation. This is deemed too large to be practical
A4_2 Flipping Vehicles
Vehicles sometimes roll over when driving. We investigated whether this was due only to excessive speeding or if other factors were at play. By creating a model comparing bend radius, velocity and angle to the vehicle's centre of mass, we concluded that in most cases other factors relating to the road surface would be involved
Phylogenetic relationships of the Wolbachia of nematodes and arthropods
Wolbachia are well known as bacterial symbionts of arthropods, where they are reproductive parasites, but have also been described from nematode hosts, where the symbiotic interaction has features of mutualism. The majority of arthropod Wolbachia belong to clades A and B, while nematode Wolbachia mostly belong to clades C and D, but these relationships have been based on analysis of a small number of genes. To investigate the evolution and relationships of Wolbachia symbionts we have sequenced over 70 kb of the genome of wOvo, a Wolbachia from the human-parasitic nematode Onchocerca volvulus, and compared the genes identified to orthologues in other sequenced Wolbachia genomes. In comparisons of conserved local synteny, we find that wBm, from the nematode Brugia malayi, and wMel, from Drosophila melanogaster, are more similar to each other than either is to wOvo. Phylogenetic analysis of the protein-coding and ribosomal RNA genes on the sequenced fragments supports reciprocal monophyly of nematode and arthropod Wolbachia. The nematode Wolbachia did not arise from within the A clade of arthropod Wolbachia, and the root of the Wolbachia clade lies between the nematode and arthropod symbionts. Using the wOvo sequence, we identified a lateral transfer event whereby segments of the Wolbachia genome were inserted into the Onchocerca nuclear genome. This event predated the separation of the human parasite O. volvulus from its cattle-parasitic sister species, O. ochengi. The long association between filarial nematodes and Wolbachia symbionts may permit more frequent genetic exchange between their genomes
Adiantum capillus-veneris (Maidenhair Fern) along the Vale of Glamorgan Coastline, South Wales, UK: a comparison of surveys over 30 years
Adiantum capillus-veneris (Maidenhair Fern),
occurs on all continents except the Antarctic,
and is considered stable worldwide (Lansdown
& Bilz, 2013). In the UK the vascular plants
red data list reports the status of A. capillusveneris
as of āleast concernā (Cheffings et al.,
2005). Native populations occur mainly in
crevices or on tufa deposits, limited to a few
scattered coastal localities (Stewart et al.,
1994). Wales is home to about 25% of the
UKās native population (Dines, 2008) mainly
concentrated along the Vale of Glamorgan
Coastline and to a lesser extent in Pembrokeshire
and Carmarthenshire. The earliest record
(Llwyd, 1698), at Jacksons Bay, Barry Island
suggest populations have been persistent for at
least 300 years. Historical records for A. capillus-
veneris can also be found for Porthkerry;
1838, Dunraven Bay; 1849, Aberthaw; 1862
and Font-y-Gary, 1927 and A. capillus-veneris
is still present at all of the aforementioned sites.
A. capillus-venerisās natural habitat in South
Wales is primarily restricted to active post
glacial tufaceous cliff face seepages which are
frequently, but not entirely, associated with the
Jurassic Lias bedrock that defines the Vale of
Glamorgan āHeritage Coastā. The interbedded
nature of the Jurassic Lias rocks, with
relatively impermeable, thinly interbedded
limestones and calcareous mudstones (Wilson
et al., 1990), favours the slow diffuse seepage
of groundwater across large areas of cliff face
supporting the formation of tufa. Tufa forms
when groundwater, supersaturated with
calcium carbonate dissolved from the bedrock
aquifer, re-deposits the material on contact
with the atmosphere.
Three surveys across the Vale of Glamorgan
coastline have been undertaken, the first by
Peter S. Jones (1983-4) then Kate Pryor 1996
(reported in Pryor, 2001) and again in 2015 by
the authors. Molecular studies of several
populations along the coast (Pryor, 2001 &
Pryor et al., 2001) provide insight into the
genetics of satellite populations, however
further discussion of this is outside of the
scope of this note. The aim of this survey was
to collate and compare the locations of populations
recorded over the last 30 years. It is
hoped that this will serve as a useful baseline
for repeat surveys in the future
Streams Going Notts: The tidal debris finder comparison project
While various codes exist to systematically and robustly find haloes and
subhaloes in cosmological simulations (Knebe et al., 2011, Onions et al.,
2012), this is the first work to introduce and rigorously test codes that find
tidal debris (streams and other unbound substructure) in fully cosmological
simulations of structure formation. We use one tracking and three non-tracking
codes to identify substructure (bound and unbound) in a Milky Way type
simulation from the Aquarius suite (Springel et al., 2008) and post-process
their output with a common pipeline to determine the properties of these
substructures in a uniform way. By using output from a fully cosmological
simulation, we also take a step beyond previous studies of tidal debris that
have used simple toy models. We find that both tracking and non-tracking codes
agree well on the identification of subhaloes and more importantly, the {\em
unbound tidal features} associated with them. The distributions of basic
properties of the total substructure distribution (mass, velocity dispersion,
position) are recovered with a scatter of . Using the tracking code as
our reference, we show that the non-tracking codes identify complex tidal
debris with purities of . Analysing the results of the substructure
finders, we find that the general distribution of {\em substructures} differ
significantly from the distribution of bound {\em subhaloes}. Most importantly,
both bound and unbound {\em substructures} together constitute of the
host halo mass, which is a factor of higher than the fraction in
self-bound {\em subhaloes}. However, this result is restricted by the remaining
challenge to cleanly define when an unbound structure has become part of the
host halo. Nevertheless, the more general substructure distribution provides a
more complete picture of a halo's accretion history.Comment: 19 pages, 12 figures, accepted for publication in MNRA
Geodynamic setting and origin of the Oman/UAE ophiolite
The ~500km-long mid-Cretaceous Semail nappe of the Sultanate of Oman and UAE (henceforth referred to as the Oman ophiolite) is the largest and best-preserved ophiolite complex known. It is of particular importance because it is generally believed to have an internal structure and composition closely comparable to that of crust formed at the present-day East Pacific Rise (EPR), making it our only known on-land analogue for ocean lithosphere formed at a fast spreading rate. On the basis of this assumption Oman has long played a pivotal role in guiding our conceptual understanding of fast-spreading ridge processes, as modern fast-spread ocean crust is largely inaccessible
Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction
Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form the uppermost part of the outer-arc high at Site 782. All four groups can be explained by remelting above a subduction zone of oceanic mantle lithosphere that has been depleted by its previous episode of partial melting at an ocean ridge. We estimate that the average boninite source had lost 10-15 wt% of melt at the ridge before undergoing further melting (5-10%) shortly after subduction started. The composition of the harzburgite (<2% clinopyroxene, Fo content of about 92%) indicates that it underwent a total of about 25% melting with respect to a fertile MORB mantle. The low concentration of Nb in the boninite indicates that the oceanic lithosphere prior to subduction was not enriched by any asthenospheric (OIB) component.
The subduction component is characterized by (1) high Zr and Hf contents relative to Sm, Ti, Y, and middle-heavy REE, (2) light REE-enrichment, (3) low contents of Nb and Ta relative to Th, Rb, or La, (4) high contents of Na and Al, and (5) Pb isotopes on the Northern Hemisphere Reference Line. This component is unlike any subduction component from active arc volcanoes in the Izu-Mariana region or elsewhere. Modeling suggests that these characteristics fit a trondhjemitic melt from slab fusion in amphibolite facies. The resulting metasomatized mantle may have contained about 0.15 wt% water. The overall melting regime is constrained by experimental data to shallow depths and high temperatures (1250Ā°C and 1.5 kb for an average boninite) of boninite segregation. We thus envisage that boninites were generated by decompression melting of a diapir of metasomatized residual MORB mantle leaving the harzburgites as the uppermost, most depleted residue from this second stage of melting. Thermal constraints require that both subducted lithosphere and overlying oceanic lithosphere of the mantle wedge be very young at the time of boninite genesis. This conclusion is consistent with models in which an active transform fault offsetting two ridge axes is placed under compression or transpression following the Eocene plate reorganization in the Pacific. Comparison between Leg 125 boninites and boninites and related rocks elsewhere in the Western Pacific highlights large regional differences in petrogenesis in terms of mantle mineralogy, degree of partial melting, composition of subduction components, and the nature of pre-subduction lithosphere. It is likely that, on a regional scale, the initiation of subduction involved subducted crust and lithospheric mantle wedge of a range of ages and compositions, as might be expected in this type of tectonic setting
Galaxies going MAD: The Galaxy-Finder Comparison Project
With the ever increasing size and complexity of fully self-consistent
simulations of galaxy formation within the framework of the cosmic web, the
demands upon object finders for these simulations has simultaneously grown. To
this extent we initiated the Halo Finder Comparison Project that gathered
together all the experts in the field and has so far led to two comparison
papers, one for dark matter field haloes (Knebe et al. 2011), and one for dark
matter subhaloes (Onions et al. 2012). However, as state-of-the-art simulation
codes are perfectly capable of not only following the formation and evolution
of dark matter but also account for baryonic physics (e.g. hydrodynamics, star
formation, feedback) object finders should also be capable of taking these
additional processes into consideration. Here we report on a comparison of
codes as applied to the Constrained Local UniversE Simulation (CLUES) of the
formation of the Local Group which incorporates much of the physics relevant
for galaxy formation. We compare both the properties of the three main galaxies
in the simulation (representing the MW, M31, and M33) as well as their
satellite populations for a variety of halo finders ranging from phase-space to
velocity-space to spherical overdensity based codes, including also a mere
baryonic object finder. We obtain agreement amongst codes comparable to (if not
better than) our previous comparisons, at least for the total, dark, and
stellar components of the objects. However, the diffuse gas content of the
haloes shows great disparity, especially for low-mass satellite galaxies. This
is primarily due to differences in the treatment of the thermal energy during
the unbinding procedure. We acknowledge that the handling of gas in halo
finders is something that needs to be dealt with carefully, and the precise
treatment may depend sensitively upon the scientific problem being studied.Comment: 14 interesting pages, 17 beautiful figures, and 2 informative tables
accepted for publication in MNRAS (matches published version
How to create new subduction zones: A global perspective
The association of deep-sea trenchesāsteeply angled, planar zones where earthquakes occur deep into Earthās interiorāand chains, or arcs, of active, explosive volcanoes had been recognized for 90 years prior to the development of plate tectonic theory in the 1960s. Oceanic lithosphere is created at mid-ocean ridge spreading centers and recycled into the mantle at subduction zones, where down-going lithospheric plates dynamically sustain the deep-sea trenches. Study of subduction zone initiation is a challenge because evidence of the processes involved is typically destroyed or buried by later tectonic and crust-forming events. In 2014 and 2017, the International Ocean Discovery Program (IODP) specifically targeted these processes with three back-to-back expeditions to the archetypal Izu-Bonin-Mariana (IBM) intra-oceanic arcs and one expedition to the Tonga-Kermadec (TK) system. Both subduction systems were initiated ~52 million years ago, coincident with a proposed major change of Pacific plate motion. These expeditions explored the tectonism preceding and accompanying subduction initiation and the characteristics of the earliest crust-forming magmatism. Lack of compressive uplift in the overriding plate combined with voluminous basaltic seafloor magmatism in an extensional environment indicates a large component of spontaneous subduction initiation was involved for the IBM. Conversely, a complex range of far-field uplift and depression accompanied the birth of the TK system, indicative of a more distal forcing of subduction initiation. Future scientific ocean drilling is needed to target the three-dimensional aspects of these processes at new converging margins
How to Create New Subduction Zones: A Global Perspective
The association of deep-sea trenchesāsteeply angled, planar zones where earthquakes occur deep into Earthās interiorāand chains, or arcs, of active, explosive volcanoes had been recognized for 90 years prior to the development of plate tectonic theory in the 1960s. Oceanic lithosphere is created at mid-ocean ridge spreading centers and recycled into the mantle at subduction zones, where down-going lithospheric plates dynamically sustain the deep-sea trenches. Study of subduction zone initiation is a challenge because evidence of the processes involved is typically destroyed or buried by later tectonic and crust-forming events. In 2014 and 2017, the International Ocean Discovery Program (IODP) specifically targeted these processes with three back-to-back expeditions to the archetypal Izu-Bonin-Mariana (IBM) intra-oceanic arcs and one expedition to the Tonga-Kermadec (TK) system. Both subduction systems were initiated ~52 million years ago, coincident with a proposed major change of Pacific plate motion. These expeditions explored the tectonism preceding and accompanying subduction initiation and the characteristics of the earliest crust-forming magmatism. Lack of compressive uplift in the overriding plate combined with voluminous basaltic seafloor magmatism in an extensional environment indicates a large component of spontaneous subduction initiation was involved for the IBM. Conversely, a complex range of far-field uplift and depression accompanied the birth of the TK system, indicative of a more distal forcing of subduction initiation. Future scientific ocean drilling is needed to target the three-dimensional aspects of these processes at new converging margins
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