108 research outputs found
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Source Signatures of Fine Particulate Matter from Petroleum Refining and Fuel Use
Combustion experiments were carried out on four different residual fuel oils in a 732 kW boiler. Particulate matter (PM) emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 microns in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the <2.5 micron fraction (PM{sub 2.5}) in fact consists of carbonaceous cenospheres and vesicular particles that range up to 10 microns in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As Kedges, and at the Pb L-edge. Deconvolution of the x-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM{sub 2.5} samples than in the >2.5 micron samples (PM{sub 2.5+}). Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agree fairly well with that of NiSO4, while most of the V spectra closely resemble that of vanadyl sulfate (VO{center_dot}SO{sub 4}{center_dot}xH{sub 2}O). The other metals investigated (Fe, Cu, Zn, and Pb) were also present predominantly as sulfates. Arsenic is present as an arsenate (As{sup +5}). X-ray diffraction patterns of the PM{sub 2.5} fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the LOI ranging from 64 to 87 % for the PM{sub 2.5} fraction and from 88 to 97% for the PM{sub 2.5+} fraction. {sup 13}C nuclear magnetic resonance (NMR) analysis indicates that the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined
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In Situ Electrostatic Separation of Ambient PM2.5 into Source-Specific Fractions During Collection in a FRM Sampler
Coal combustion is generally viewed as a major source of PM2.5 emissions into the atmosphere. For some time, toxicologists have been asking for an exposure environment enriched with the coal combustion source specific PM{sub 2.5} to conduct meaningful exposure studies to better understand the mechanisms of the adverse health effects of coal combustion specific PM2.5 in the ambient environment. There are several unique characteristics of primary PM generated from coal combustion. In this research project, an attempt has been made to exploit some of the unique properties of PM generated from coal fired power plants to preferentially separate them out from the rest of the primary and secondary PM in the ambient environment. An existing FRM sampler used for monitoring amount of PM{sub 2.5} in the ambient air is modified to incorporate an electrostatic field. A DC corona charging device is also installed at the ambient air inlet to impart positive or negative charge to the PM. Visual Basic software has been written to simulate the lateral movement of PM as it passes through the electrostatic separator under varying operating conditions. The PM samples collected on polycarbonate filters under varying operating conditions were extensively observed for clustering and/or separation of PM in the direction parallel to the electric field. No systematic PM separation was observed under any of the operating conditions. A solution to overcome this kind of turbulence caused remixing has been offered. However, due to major programmatic changes in the DOE UCR program, there are no venues available to further pursue this research
From Bipolar to Elliptical: Simulating the Morphological Evolution of Planetary Nebulae
The majority of Proto-planetary nebulae (PPN) are observed to have bipolar
morphologies. The majority of mature PN are observed to have elliptical shapes.
In this paper we address the evolution of PPN/PN morphologies attempting to
understand if a transition from strongly bipolar to elliptical shape can be
driven by changes in the parameters of the mass loss process. To this end we
present 2.5D hydrodynamical simulations of mass loss at the end stages of
stellar evolution for intermediate mass stars. We track changes in wind
velocity, mass loss rate and mass loss geometry. In particular we focus on the
transition from mass loss dominated by a short duration jet flow (driven during
the PPN phase) to mass loss driven by a spherical fast wind (produced by the
central star of the PN). We address how such changes in outflow characteristics
can change the nebula from a bipolar to an elliptical morphology. Our results
show that including a period of jet formation in the temporal sequence of PPN
to PN produces realistic nebular synthetic emission geometries. More
importantly such a sequence provides insight, in principle, into the apparent
difference in morphology statistics characterizing PPN and PN systems. In
particular we find that while jet driven PPN can be expected to be dominated by
bipolar morphologies, systems that begin with a jet but are followed by a
spherical fast wind will evolve into elliptical nebulae. Furthermore, we find
that spherical nebulae are highly unlikely to ever derive from either bipolar
PPN or elliptical PN.Comment: Accepted for publication in the MNRAS, 15 pages, 7 figure
The coronal line regions of planetary nebulae NGC6302 and NGC6537: 3-13um grating and echelle spectroscopy
We report on advances in the study of the cores of NGC6302 and NGC6537 using
infrared grating and echelle spectroscopy. In NGC6302, emission lines from
species spanning a large range of ionization potential, and in particular
[SiIX]3.934um, are interpreted using photoionization models (including CLOUDY),
which allow us to reestimate the central star's temperature to be about
250000K. All of the detected lines are consistent with this value, except for
[AlV] and [AlVI]. Aluminium is found to be depleted to one hundredth of the
solar abundance, which provides further evidence for some dust being mixed with
the highly ionized gas (with photons harder than 154eV). A similar depletion
pattern is observed in NGC6537. Echelle spectroscopy of IR coronal ions in
NGC6302 reveals a stratified structure in ionization potential, which confirms
photoionization to be the dominant ionization mechanism. The lines are narrow
(< 22km/s FWHM), with no evidence of the broad wings found in optical lines
from species with similar ionization potentials, such as [NeV]3426A. We note
the absence of a hot bubble, or a wind blown bipolar cavity filled with a hot
plasma, at least on 1'' and 10km/s scales. We also provide accurate new
wavelengths for several of the infrared coronal lines observed with the
echelle.Comment: Accepted for publication in MNRA
Disulfide-activated protein kinase G I alpha regulates cardiac diastolic relaxation and fine-tunes the Frank-Starling response
British Heart Foundation, European Research Council (ERC Advanced award), Medical Research Council and the Department of Health via the NIHR cBRC award to Guyâs & St Thomasâ NHS Foundation Trust.
Part supported by the NIHR University College London Hospitals Biomedical Research Centre
Long-range chemical sensitivity in the sulfur K-edge X-ray absorption spectra of substituted thiophenes
© 2014 American Chemical Society. Thiophenes are the simplest aromatic sulfur-containing compounds and are stable and widespread in fossil fuels. Regulation of sulfur levels in fuels and emissions has become and continues to be ever more stringent as part of governments' efforts to address negative environmental impacts of sulfur dioxide. In turn, more effective removal methods are continually being sought. In a chemical sense, thiophenes are somewhat obdurate and hence their removal from fossil fuels poses problems for the industrial chemist. Sulfur K-edge X-ray absorption spectroscopy provides key information on thiophenic components in fuels. Here we present a systematic study of the spectroscopic sensitivity to chemical modifications of the thiophene system. We conclude that while the utility of sulfur K-edge X-ray absorption spectra in understanding the chemical composition of sulfur-containing fossil fuels has already been demonstrated, care must be exercised in interpreting these spectra because the assumption of an invariant spectrum for thiophenic forms may not always be valid
A sensorimotor control framework for understanding emotional communication and regulation
JHGW and CFH are supported by the Northwood Trust. TEVR was supported by a National Health and Medical Research Council (NHMRC) Early Career Fellowship (1088785). RP and MW were supported by the the Australian Research Council (ARC) Centre of Excellence for Cognition and its Disorders (CE110001021)Peer reviewedPublisher PD
Suppressing quantum errors by scaling a surface code logical qubit
Practical quantum computing will require error rates that are well below what
is achievable with physical qubits. Quantum error correction offers a path to
algorithmically-relevant error rates by encoding logical qubits within many
physical qubits, where increasing the number of physical qubits enhances
protection against physical errors. However, introducing more qubits also
increases the number of error sources, so the density of errors must be
sufficiently low in order for logical performance to improve with increasing
code size. Here, we report the measurement of logical qubit performance scaling
across multiple code sizes, and demonstrate that our system of superconducting
qubits has sufficient performance to overcome the additional errors from
increasing qubit number. We find our distance-5 surface code logical qubit
modestly outperforms an ensemble of distance-3 logical qubits on average, both
in terms of logical error probability over 25 cycles and logical error per
cycle ( compared to ). To investigate
damaging, low-probability error sources, we run a distance-25 repetition code
and observe a logical error per round floor set by a single
high-energy event ( when excluding this event). We are able
to accurately model our experiment, and from this model we can extract error
budgets that highlight the biggest challenges for future systems. These results
mark the first experimental demonstration where quantum error correction begins
to improve performance with increasing qubit number, illuminating the path to
reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references,
Fig. S12, Table I
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