3,434 research outputs found
Surprisingly Little O VI Emission Arises in the Local Bubble
This paper reports the first study of the O VI resonance line emission (1032,
1038 Angstroms) originating in the Local Bubble (or Local Hot Bubble)
surrounding the solar neighborhood. In spite of the fact that O VI absorption
within the Local Bubble has been observed, no resonance line emission was
detected during our 230 ksec Far Ultraviolet Spectroscopic Explorer observation
toward a ``shadowing'' filament in the southern Galactic hemisphere. As a
result, tight 2 sigma upper limits are set on the intensities in the 1032 and
1038 Angstrom emission lines: 500 and 530 photons cm^{-2} s^{-1} sr^{-1},
respectively. These values place strict constraints on models and simulations.
They suggest that the O VI-bearing plasma and the X-ray emissive plasma reside
in distinct regions of the Local Bubble and are not mixed in a single plasma,
whether in equilibrium with T ~ 10^6 K or highly overionized with T ~ 4 to 6 x
10^4 K. If the line of sight intersects multiple cool clouds within the Local
Bubble, then the results also suggest that hot/cool transition zones differ
from those in current simulations. With these intensity upper limits, we
establish limits on the electron density, thermal pressure, pathlength, and
cooling timescale of the O VI-bearing plasma in the Local Bubble. Furthermore,
the intensity of O VI resonance line doublet photons originating in the
Galactic thick disk and halo is determined (3500 to 4300 photons cm^{-2} s^{-1}
sr^{-1}), and the electron density, thermal pressure, pathlength, and cooling
timescale of its O VI-bearing plasma are calculated. The pressure in the
Galactic halo's O VI-bearing plasma (3100 to 3800 K cm^{-3}) agrees with model
predictions for the total pressure in the thick disk/lower halo. We also report
the results of searches for other emission lines.Comment: accepted by ApJ, scheduled for May 2003, replacement astro-ph
submission corrects typos and grammatical errors in original versio
Analog and digital simulations of multiplex system performance
Analog and digital simulations of multiplex system performanc
HYDROLOGIC EVALUATION OF RESIDENTIAL RAIN GARDENS USING A STORMWATER RUNOFF SIMULATOR
Engineered bioretention cells with underdrains have shown water quality and hydrologic benefits for abating urban stormwater problems. Less is known about the hydrologic performance of residential rain gardens that rely on in situ soil infiltration as the primary mechanism of volume control. Eleven residential rain gardens in Lincoln, Nebraska, were evaluated using a variable-rate stormwater runoff simulator. A volume-based water quality volume (WQV) design storm of 3.0 cm was applied to each rain garden as an SCS Type II runoff hydrograph until the system began overflowing to test the rain gardens for surface and subsurface storage capacity, drawdown rate, ponding depth, and overflow characteristics. Every rain garden tested drained in 30 h or less, with six gardens draining in less than 1 h. Rain garden surface storage capacity was poor, retaining on average only 16% of the WQV. On average, the rain gardens studied could store and infiltrate only 40% of the WQV, with only two gardens able to store and infiltrate greater than 90% of the WQV. On average, 59% of the runoff was captured as subsurface storage. Results of this study indicate that these 2- to 4-year-old rain gardens are limited not by drain times and rates, which often met or exceeded common design recommendations, but rather by inadequate surface storage characteristics. Extrapolating measured surface storage volumes to hypothetical systems with evenly graded depths of 15.2 cm, a minimum local depth recommendation, resulted in only one garden with enough storage to contain the WQV. On average, the extrapolated storage held only 65% of the WQV. It was shown that subsurface storage can make up for a lack of surface storage; the systems studied herein had an average of 2.7 times more subsurface storage than surface storage as a percentage of inflow volume before overflow began
FUSE Detection of Galactic OVI Emission in the Halo above the Perseus Arm
Background observations obtained with the Far Ultraviolet Spectroscopic
Explorer (FUSE) toward l=95.4, b=36.1 show OVI 1032,1038 in emission. This
sight line probes a region of stronger-than-average soft X-ray emission in the
direction of high-velocity cloud Complex C above a part of the disk where
Halpha filaments rise into the halo. The OVI intensities, 1600+/-300
ph/s/cm^2/sr (1032A) and 800+/-300 ph/s/cm^2/sr (1038A), are the lowest
detected in emission in the Milky Way to date. A second sight line nearby
(l=99.3, b=43.3) also shows OVI 1032 emission, but with too low a
signal-to-noise ratio to obtain reliable measurements. The measured
intensities, velocities, and FWHMs of the OVI doublet and the CII* line at
1037A are consistent with a model in which the observed emission is produced in
the Galactic halo by hot gas ejected by supernovae in the Perseus arm. An
association of the observed gas with Complex C appears unlikely.Comment: accepted for publication in ApJL, 11 pages including 3 figure
Gene editing restores dystrophin expression in a canine model of Duchenne muscular dystrophy
Mutations in the gene encoding dystrophin, a protein that maintains muscle integrity and function, cause Duchenne muscular dystrophy (DMD). The deltaE50-MD dog model of DMD harbors a mutation corresponding to a mutational âhotspotâ in the human DMD gene. We used adeno-associated viruses to deliver CRISPR gene editing components to four dogs and examined dystrophin protein expression 6 weeks after intramuscular delivery (n = 2) or 8 weeks after systemic delivery (n = 2). After systemic delivery in skeletal muscle, dystrophin was restored to levels ranging from 3 to 90% of normal, depending on muscle type. In cardiac muscle, dystrophin levels in the dog receiving the highest dose reached 92% of normal. The treated dogs also showed improved muscle histology. These large-animal data support the concept that, with further development, gene editing approaches may prove clinically useful for the treatment of DMD
Nuclear spin relaxation rates in two-leg spin ladders
Using the transfer-matrix DMRG method, we study the nuclear spin relaxation
rate 1/T_1 in the two-leg s=1/2 ladder as function of the inter-chain
(J_{\perp}) and intra-chain (J_{|}) couplings. In particular, we separate the
q_y=0 and \pi contributions and show that the later contribute significantly to
the copper relaxation rate ^{63}(1/T_1) in the experimentally relevant coupling
and temperature range. We compare our results to both theoretical predictions
and experimental measures on ladder materials.Comment: Few modifications from the previous version 4 pages, 5 figures,
accepted for publication in PR
Variability in H9N2 haemagglutinin receptor-binding preference and the pH of fusion
H9N2 avian influenza viruses are primarily a disease of poultry; however, they occasionally infect humans and are considered a potential pandemic threat. Little work has been performed to assess the intrinsic biochemical properties related to zoonotic potential of H9N2 viruses. The objective of this study, therefore, was to investigate H9N2 haemagglutinins (HAs) using two well-known correlates for human adaption: receptor-binding avidity and pH of fusion. Receptor binding was characterized using bio-layer interferometry to measure virus binding to human and avian-like receptor analogues and the pH of fusion was assayed by syncytium formation in virus-infected cells at different pHs. We characterized contemporary H9N2 viruses of the zoonotic G1 lineage, as well as representative viruses of the zoonotic BJ94 lineage. We found that most contemporary H9N2 viruses show a preference for sulphated avian-like receptor analogues. However, the âEasternâ G1 H9N2 viruses displayed a consistent preference in binding to a human-like receptor analogue. We demonstrate that the presence of leucine at position 226 of the HA receptor-binding site correlated poorly with the ability to bind a human-like sialic acid receptor. H9N2 HAs also display variability in their pH of fusion, ranging between pH 5.4 and 5.85 which is similar to that of the first wave of human H1N1pdm09 viruses but lower than the pH of fusion seen in zoonotic H5N1 and H7N9 viruses. Our results suggest possible molecular mechanisms that may underlie the relatively high prevalence of human zoonotic infection by particular H9N2 virus lineages
Non-Abelian bosonization of the frustrated antiferromagnetic spin-1/2 chain
We study the spin-1/2 chain with nearest neighbor () and
next-nearest neighbor () interactions in the regime , which is equivalent to two chains with a `zig-zag' interaction. In
the continuum limit, this system is described in term of two coupled level-1
WZW field theories. We illustrate its equivalence with four off-critical Ising
models (Majorana fermions). This description is used to investigate the opening
of a gap as a function of and the associated spontaneous breakdown
of parity. We calculate the dynamic spin structure factor near the wavevectors
accessible to the continuum limit. We comment on the nonzero string order
parameter and show the presence of a hidden
symmetry via a nonlocal transformation on the microscopic Hamiltonian. For a
ferromagnetic interchain coupling, the model is conjectured to be critical,
with different velocities for the spin singlet and spin triplet excitations.Comment: 20 pages, RevTeX, 1 postscript figure. Minor corrections added,
resulting in different velocity renormalizations; no qualitative change in
conclusion
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