2,654 research outputs found
Towards an explanation for the 30 Dor (LMC) Honeycomb nebula - the impact of recent observations and spectral analysis
The unique Honeycomb nebula, most likely a peculiar supernova remnant, lies
in 30 Doradus in the Large Magellanic Cloud. Due to its proximity to SN1987A,
it has been serendipitously and intentionally observed at many wavelengths.
Here, an optical spectral analysis of forbidden line ratios is performed in
order to compare the Honeycomb high-speed gas with supernova remnants in the
Galaxy and the LMC, with galactic Wolf-Rayet nebulae and with the optical line
emission from the interaction zone of the SS433 microquasar and W50 supernova
remnant system. An empirical spatiokinematic model of the images and spectra
for the Honeycomb reveals that its striking appearance is most likely due to a
fortuitous viewing angle. The Honeycomb nebula is more extended in soft X-ray
emission and could in fact be a small part of the edge of a giant LMC shell
revealed for the first time in this short wavelength domain. It is also
suggested that a previously unnoticed region of optical emission may in fact be
an extension of the Honeycomb around the edge of this giant shell. A secondary
supernova explosion in the edge of a giant shell is considered for the creation
of the Honeycomb nebula. A microquasar origin of the Honeycomb nebula as
opposed to a simple supernova origin is also evaluated.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Life Cycle Assessment Applied to Green Building Certification in South Korea
AbstractThe purpose of this study is to apply life cycle assessment (LCA) methodology for green building certification in South Korea. The method of environmental assessment in the field of building materials was examined using United States’ LEED, and the United Kingdom's BREEAM building certification systems. Life cycle data and assessment methods were established on major categories of materials thorough theoretical consideration on life cycle assessment.Building materials, assembly methods, and building use considerations were used to develop an assessment model to evaluate the environmental performance of a building. Numeric values for use in the developed model were established for concrete, rebar, gypsum board, steel, cement brick, glass, and insulation materials to potentially reduce greenhouse gas (GHG) emissions by 95% or more. An assessment method and LCA database were established. The model will be used to show that the choice of building materials can affect the GHG emissions during the construction phase of a building
Frustrated H-Induced Instability of Mo(110)
Using helium atom scattering Hulpke and L"udecke recently observed a giant
phonon anomaly for the hydrogen covered W(110) and Mo(110) surfaces. An
explanation which is able to account for this and other experiments is still
lacking. Below we present density-functional theory calculations of the atomic
and electronic structure of the clean and hydrogen-covered Mo(110) surfaces.
For the full adsorbate monolayer the calculations provide evidence for a strong
Fermi surface nesting instability. This explains the observed anomalies and
resolves the apparent inconsistencies of different experiments.Comment: 4 pages, 2 figures, submitted to PR
Broadband 180 degree universal rotation pulses for NMR spectroscopy designed by optimal control
Broadband inversion pulses that rotate all magnetization components 180
degrees about a given fixed axis are necessary for refocusing and mixing in
high-resolution NMR spectroscopy. The relative merits of various methodologies
for generating pulses suitable for broadband refocusing are considered. The de
novo design of 180 degree universal rotation pulses using optimal control can
provide improved performance compared to schemes which construct refocusing
pulses as composites of existing pulses. The advantages of broadband universal
rotation by optimized pulses (BURBOP) are most evident for pulse design that
includes tolerance to RF inhomogeneity or miscalibration. We present new
modifications of the optimal control algorithm that incorporate symmetry
principles and relax conservative limits on peak RF pulse amplitude for short
time periods that pose no threat to the probe. We apply them to generate a set
of pulses suitable for widespread use in Carbon-13 spectroscopy on the majority
of available probes
Excess AGN Activity in the z=2.30 Protocluster in HS 1700+64
We present the results of spectroscopic, narrow-band and X-ray observations
of a z=2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of
BX/MD galaxies, which are selected to be at z~2.2-2.7 by their rest-frame
ultraviolet colours, we find that there are 5 protocluster AGN which have been
identified by characteristic emission-lines in their optical/near-IR spectra;
this represents an enhancement over the field significant at ~98.5 per cent
confidence. Using a ~200 ks Chandra/ACIS-I observation of this field we detect
a total of 161 X-ray point sources to a Poissonian false-probability limit of
4x10^{-6} and identify 8 of these with BX/MD galaxies. Two of these are
spectroscopically confirmed protocluster members and are also classified as
emission-line AGN. When compared to a similarly selected field sample the
analysis indicates this is also evidence for an enhancement of X-ray selected
BX/MD AGN over the field, significant at ~99 per cent confidence. Deep Lya
narrow-band imaging reveals that a total of 4/123 Lya emitters (LAEs) are found
to be associated with X-ray sources, with two of these confirmed protocluster
members and one highly likely member. We do not find a significant enhancement
of AGN activity in this LAE sample over that of the field (result significant
at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD
and LAE samples are found to be 6.9_{-4.4}^{+9.2} and 2.9_{-1.6}^{+2.9} per
cent, respectively, for protocluster AGN with L_{2-10 keV}>4.6x10^{43} erg
s^{-1} at z=2.30. These findings are similar to results from the z=3.09
protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both
suggest AGN activity is favoured in dense environments at z>2.Comment: 8 pages, 2 figures. Accepted for publication in MNRAS
Constraining warm dark matter with cosmic shear power spectra
We investigate potential constraints from cosmic shear on the dark matter
particle mass, assuming all dark matter is made up of light thermal relic
particles. Given the theoretical uncertainties involved in making cosmological
predictions in such warm dark matter scenarios we use analytical fits to linear
warm dark matter power spectra and compare (i) the halo model using a mass
function evaluated from these linear power spectra and (ii) an analytical fit
to the non-linear evolution of the linear power spectra. We optimistically
ignore the competing effect of baryons for this work. We find approach (ii) to
be conservative compared to approach (i). We evaluate cosmological constraints
using these methods, marginalising over four other cosmological parameters.
Using the more conservative method we find that a Euclid-like weak lensing
survey together with constraints from the Planck cosmic microwave background
mission primary anisotropies could achieve a lower limit on the particle mass
of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for
publication in JCA
Quantum feedback control of a superconducting qubit: Persistent Rabi oscillations
The act of measurement bridges the quantum and classical worlds by projecting
a superposition of possible states into a single, albeit probabilistic,
outcome. The time-scale of this "instantaneous" process can be stretched using
weak measurements so that it takes the form of a gradual random walk towards a
final state. Remarkably, the interim measurement record is sufficient to
continuously track and steer the quantum state using feedback. We monitor the
dynamics of a resonantly driven quantum two-level system -- a superconducting
quantum bit --using a near-noiseless parametric amplifier. The high-fidelity
measurement output is used to actively stabilize the phase of Rabi
oscillations, enabling them to persist indefinitely. This new functionality
shows promise for fighting decoherence and defines a path for continuous
quantum error correction.Comment: Manuscript: 5 Pages and 3 figures ; Supplementary Information: 9
pages and 3 figure
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