22,103 research outputs found
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Simulating the Martian Chemical Enivronment
We report on new analogue materials to simulate Martian rocks and soils, especially under realistic redox conditions
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The Physio-Chemical Properties for the Interior of Enceladus
We have reviewed the current physical and chemical conditions of the Enceladus sub-surface environment, including the composition, temperature, pH and pressure. Here we have defined some of these parameters and, through the aid of modelling, will define and refine the remaining parameters needed for our experimental work. Simulations of the chemical reactions occurring within Enceladus can then be carried
out to advance our understanding of the internal environment of Enceladus and help evaluate its potential habitability. Once a better understanding of the chemical reactions occurring at the rock-water interface has been carried out, then potential analogues on Earth can be evaluated and known microbial life can be tested to see if it could survive the conditions of Enceladus
Orbit targeting specialist function: Level C formulation requirements
A definition of the level C requirements for onboard maneuver targeting software is provided. Included are revisions of the level C software requirements delineated in JSC IN 78-FM-27, Proximity Operations Software; Level C Requirements, dated May 1978. The software supports the terminal phase midcourse (TPM) maneuver, braking and close-in operations as well as supporting computation of the rendezvous corrective combination maneuver (NCC), and the terminal phase initiation (TPI). Specific formulation is contained here for the orbit targeting specialist function including the processing logic, linkage, and data base definitions for all modules. The crew interface with the software is through the keyboard and the ORBIT-TGT display
A possible dearth of hot gas in galaxy groups at intermediate redshift
We examine the X-ray luminosity of galaxy groups in the CNOC2 survey, at
redshifts 0.1 < z < 0.6. Previous work examining the gravitational lensing
signal of the CNOC2 groups has shown that they are likely to be genuine,
gravitationally bound objects. Of the 21 groups in the field of view of the
EPIC-PN camera on XMM-Newton, not one was visible in over 100 ksec of
observation, even though three of the them have velocity dispersions high
enough that they would easily be visible if their luminosities scaled with
their velocity dispersions in the same way as nearby groups' luminosities
scale. We consider the possibility that this is due to the reported velocity
dispersions being erroneously high, and conclude that this is unlikely. We
therefore find tentative evidence that groups at intermediate redshift are
underluminous relative to their local cousins.Comment: 16 pages, 5 figures, reference added in section 1, typos corrected,
published in Ap
Subthreshold characteristics of pentacene field-effect transistors influenced by grain boundaries.
Grain boundaries in polycrystalline pentacene films significantly affect the electrical characteristics of pentacene field-effect transistors (FETs). Upon reversal of the gate voltage sweep direction, pentacene FETs exhibited hysteretic behaviours in the subthreshold region, which was more pronounced for the FET having smaller pentacene grains. No shift in the flat-band voltage of the metal-insulator-semiconductor capacitor elucidates that the observed hysteresis was mainly caused by the influence of localized trap states existing at pentacene grain boundaries. From the results of continuous on/off switching operation of the pentacene FETs, hole depletion during the off period is found to be limited by pentacene grain boundaries. It is suggested that the polycrystalline nature of a pentacene film plays an important role on the dynamic characteristics of pentacene FETs
Key dating features for timber-framed dwellings in Surrey
This article is made available through the Brunel Open Access Publishing Fund. Copyright @ The Vernacular Architecture Group 2013. MORE OpenChoice articles are open access and distributed under the terms of the Creative Commons Attribution License 3.0.The main component of the Surrey Dendrochronology Project is the accurate dating of 177 ‘dwellings’, nearly all by tree-ring analysis. The dates are used to establish date ranges for 52 ‘key features’, which cover many aspects of timber-framing from building type to details of carpentry. It is shown that changes of method and fashion were in many cases surprisingly rapid, almost abrupt in historical terms. Previous dating criteria for timber-framed dwellings in the county have been refined and new criteria introduced. Clusters of change from the 1440s and the 1540s are shown and some possible historical links suggested.The Heritage Lottery Fund, the Domestic Buildings Research Group (Surrey), the Surrey Archaeological Society and the historical societies of Charlwood, Farnham and Nutfield
Slip energy barriers in aluminum and implications for ductile versus brittle behavior
We conisder the brittle versus ductile behavior of aluminum in the framework
of the Peierls-model analysis of dislocation emission from a crack tip. To this
end, we perform first-principles quantum mechanical calculations for the
unstable stacking energy of aluminum along the Shockley partial
slip route. Our calculations are based on density functional theory and the
local density approximation and include full atomic and volume relaxation. We
find that in aluminum J/m. Within the Peierls-model
analysis, this value would predict a brittle solid which poses an interesting
problem since aluminum is typically considered ductile. The resolution may be
given by one of three possibilites: (a) Aluminum is indeed brittle at zero
temperature, and becomes ductile at a finite temperature due to motion of
pre-existing dislocations which relax the stress concentration at the crack
tip. (b) Dislocation emission at the crack tip is itself a thermally activated
process. (c) Aluminum is actually ductile at all temperatures and the
theoretical model employed needs to be significantly improved in order to
resolve the apparent contradiction.Comment: 4 figures (not included; send requests to [email protected]
A Widespread, Clumpy Starburst in the Isolated Ongoing Dwarf Galaxy Merger dm1647+21
Interactions between pairs of isolated dwarf galaxies provide a critical
window into low-mass hierarchical, gas-dominated galaxy assembly and the
buildup of stellar mass in low-metallicity systems. We present the first
VLT/MUSE optical IFU observations of the interacting dwarf pair dm1647+21,
selected from the TiNy Titans survey. The H emission is widespread and
corresponds to a total unobscured star formation rate (SFR) of 0.44 M
yr, 2.7 times higher than the SFR inferred from SDSS data. The implied
specific SFR (sSFR) for the system is elevated by more than an order of
magnitude above non-interacting dwarfs in the same mass range. This increase is
dominated by the lower-mass galaxy, which has a sSFR enhancement of 50.
Examining the spatially-resolved maps of classic optical line diagnostics, we
find the ISM excitation can be fully explained by star formation. The velocity
field of the ionized gas is not consistent with simple rotation. Dynamical
simulations indicate that the irregular velocity field and the stellar
structure is consistent with the identification of this system as an ongoing
interaction between two dwarf galaxies. The widespread, clumpy enhancements in
star formation in this system point to important differences in the effect of
mergers on dwarf galaxies, compared to massive galaxies: rather than the
funneling of gas to the nucleus and giving rise to a nuclear starburst,
starbursts in low-mass galaxy mergers may be triggered by large-scale ISM
compression, and thus be more distributed.Comment: Accepted for publication in ApJ. 11 pages, 5 figures, 1 table.
Figures slightly degraded to meet arXiv size restrictions. For more
information about TiNy Titans see https://lavinia.as.arizona.edu/~tinytitans
Polarization Observations with the Cosmic Background Imager
We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13 element interferometer which operates in the 26-36 GHz band from Llano de Chajnantour in northern Chile. The array consists of 90-cm Cassegrain antennas mounted on a steerable platform which can be rotated about the optical axis to facilitate polarization observations. The CBI employs single mode circularly polarized receivers which sample multipoles from ℓ~400
to ℓ~4250. The instrumental polarization of the CBI was calibrated with 3C279, a bright polarized point source
which was monitored with the VLA
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