432 research outputs found
High Resolution Polar Kerr Effect Measurements of Sr2RuO4: Evidence for Broken Time Reversal Symmetry in the Superconducting State
Polar Kerr effect in the spin-triplet superconductor Sr2RuO4 was measured
with high precision using a Sagnac interferometer with a zero-area Sagnac loop.
We observed non-zero Kerr rotations as big as 65 nanorad appearing below Tc in
large domains. Our results imply a broken time reversal symmetry state in the
superconducting state of Sr2RuO4, similar to He3-A
Adaptive thermal compensation of test masses in advanced LIGO
As the first generation of laser interferometric gravitational wave detectors
near operation, research and development has begun on increasing the
instrument's sensitivity while utilizing the existing infrastructure. In the
Laser Interferometer Gravitational Wave Observatory (LIGO), significant
improvements are being planned for installation in ~2007, increasing strain
sensitivity through improved suspensions and test mass substrates, active
seismic isolation, and higher input laser power. Even with the highest quality
optics available today, however, finite absorption of laser power within
transmissive optics, coupled with the tremendous amount of optical power
circulating in various parts of the interferometer, result in critical
wavefront deformations which would cripple the performance of the instrument.
Discussed is a method of active wavefront correction via direct thermal
actuation on optical elements of the interferometer. A simple nichrome heating
element suspended off the face of an affected optic will, through radiative
heating, remove the gross axisymmetric part of the original thermal distortion.
A scanning heating laser will then be used to remove any remaining
non-axisymmetric wavefront distortion, generated by inhomogeneities in the
substrate's absorption, thermal conductivity, etc. A proof-of-principle
experiment has been constructed at MIT, selected data of which are presented.Comment: 11 pages, 7 figures, submitted to Classical and Quantum Gravit
Spectral absorption of biomass burning aerosol determined from retrieved single scattering albedo during ARCTAS
Actinic flux, as well as aerosol chemical and optical properties, were measured aboard the NASA DC-8 aircraft during the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) mission in Spring and Summer 2008. These measurements were used in a radiative transfer code to retrieve spectral (350-550 nm) aerosol single scattering albedo (SSA) for biomass burning plumes encountered on 17 April and 29 June. Retrieved SSA values were subsequently used to calculate the absorption Angstrom exponent (AAE) over the 350-500 nm range. Both plumes exhibited enhanced spectral absorption with AAE values that exceeded 1 (6.78 ± 0.38 for 17 April and 3.34 ± 0.11 for 29 June). This enhanced absorption was primarily due to organic aerosol (OA) which contributed significantly to total absorption at all wavelengths for both 17 April (57.7%) and 29 June (56.2%). OA contributions to absorption were greater at UV wavelengths than at visible wavelengths for both cases. Differences in AAE values between the two cases were attributed to differences in plume age and thus to differences in the ratio of OA and black carbon (BC) concentrations. However, notable differences between AAE values calculated for the OA (AAEOA) for 17 April (11.15 ± 0.59) and 29 June (4.94 ± 0.19) suggested differences in the plume AAE values might also be due to differences in organic aerosol composition. The 17 April OA was much more oxidized than the 29 June OA as denoted by a higher oxidation state value for 17 April (+0.16 vs. -0.32). Differences in the AAEOA, as well as the overall AAE, were thus also possibly due to oxidation of biomass burning primary organic aerosol in the 17 April plume that resulted in the formation of OA with a greater spectral-dependence of absorption. © Author(s) 2012. CC Attribution 3.0 License
Observational evidence for the convective transport of dust over the central United States
Bulk aerosol composition and aerosol size distributions measured aboard the DC-8 aircraft during the Deep Convective Clouds and Chemistry Experiment mission in May/June 2012 were used to investigate the transport of mineral dust through nine storms encountered over Colorado and Oklahoma. Measurements made at low altitudes (\u3c5 km mean sea level (MSL)) in the storm inflow region were compared to those made in cirrus anvils (altitude \u3e 9 km MSL). Storm mean outflow Ca2+ mass concentrations and total coarse (1 µm \u3c diameter \u3c 5 µm) aerosol volume (Vc) were comparable to mean inflow values as demonstrated by average outflow/inflow ratios greater than 0.5. A positive relationship between Ca2+, Vc, ice water content, and large (diameter \u3e 50 µm) ice particle number concentrations was not evident; thus, the influence of ice shatter on these measurements was assumed small. Mean inflow aerosol number concentrations calculated over a diameter range (0.5 µm \u3c diameter \u3c 5.0 µm) relevant for proxy ice nuclei (NPIN) were ~15–300 times higher than ice particle concentrations for all storms. Ratios of predicted interstitial NPIN (calculated as the difference between inflow NPIN and ice particle concentrations) and inflow NPIN were consistent with those calculated for Ca2+ and Vc and indicated that on average less than 10% of the ingested NPIN were activated as ice nuclei during anvil formation. Deep convection may therefore represent an efficient transport mechanism for dust to the upper troposphere where these particles can function as ice nuclei cirrus forming in situ
Spectral aerosol extinction (SpEx): a new instrument for in situ ambient aerosol extinction measurements across the UV/visible wavelength range
We introduce a new instrument for the measurement of in situ ambient aerosol extinction over the 300– 700 nm wavelength range, the spectral aerosol extinction (SpEx) instrument. This measurement capability is envisioned to complement existing in situ instrumentation, allowing for simultaneous measurement of the evolution of aerosol optical, chemical, and physical characteristics in the ambient environment. In this work, a detailed description of the instrument is provided along with characterization tests performed in the laboratory. Measured spectra of NO2 and polystyrene latex spheres (PSLs) agreed well with theoretical calculations. Good agreement was also found with simultaneous aerosol extinction measurements at 450, 530, and 630 nm using CAPS PMex instruments in a series of 22 tests including nonabsorbing compounds, dusts, soot, and black and brown carbon analogs. SpEx measurements are expected to help identify the presence of ambient brown carbon due to its 300 nm lower wavelength limit compared to measurements limited to longer UV and visible wavelengths. Extinction spectra obtained with SpEx contain more information than can be conveyed by a simple power law fit (typically represented by Ångström exponents). Planned future improvements aim to lower detection limits and ruggedize the instrument for mobile operation
Characterization of Spatial Coherence of Synchrotron Radiation with Non-Redundant Arrays of Apertures
We present a method to characterize the spatial coherence of soft X-ray
radiation from a single diffraction pattern. The technique is based on
scattering from non-redundant arrays (NRA) of slits and records the degree of
spatial coherence at several relative separations from one to 15 microns,
simultaneously. Using NRAs we measured the transverse coherence of the X-ray
beam at the XUV X-ray beamline P04 of the PETRA III synchrotron storage ring as
a function of different beam parameters. To verify the results obtained with
the NRAs additional Young's double pinhole experiments were conducted and show
good agreement.Comment: 15 pages, 6 figures, 2 tables, 42 reference
Signaling Signatures and Functional Properties of Anti-Human CD28 Superagonistic Antibodies
Superagonistic CD28 antibodies (CD28SAs) activate T lymphocytes without concomitant perturbation of the TCR/CD3-complex. In rodents these reagents induce the preferential expansion of regulatory T cells and can be used for the treatment of autoimmune diseases. Unexpectedly, the humanized CD28 superagonist TGN1412 caused severe and life threatening adverse effects during a recently conducted phase I clinical trail. The underlying molecular mechanisms are as yet unclear. We show that TGN1412 as well as the commercially available CD28 superagonist ANC28.1 induce a delayed but extremely sustained calcium response in human naïve and memory CD4+ T cells but not in cynomolgus T lymphocytes. The sustained Ca++-signal was associated with the activation of multiple intracellular signaling pathways and together these events culminated in the rapid de novo synthesis of high amounts of pro-inflammatory cytokines, most notably IFN-γ and TNF-α. Importantly, sustained transmembranous calcium flux, activation of Src-kinases as well as activation of PI3K were found to be absolutely required for CD28SA-mediated production of IFN-γ and IL-2. Collectively, our data suggest a molecular basis for the severe side effects caused by TGN1412 and impinge upon the relevance of non-human primates as preclinical models for reagents that are supposed to modify the function of human T cells
Aerosol optical and microphysical retrievals from a hybrid multiwavelength lidar data set - DISCOVER-AQ 2011
© Author(s) 2014. This open access work is distributed under the Creative Commons Attribution 3.0 License (https://creativecommons.org/licenses/by/3.0/).Retrievals of aerosol microphysical properties (effective radius, volume and surface-area concentrations) and aerosol optical properties (complex index of refraction and single-scattering albedo) were obtained from a hybrid multiwavelength lidar data set for the first time. In July 2011, in the Baltimore-Washington DC region, synergistic profiling of optical and microphysical properties of aerosols with both airborne (in situ and remote sensing) and ground-based remote sensing systems was performed during the first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar data set combines ground-based elastic backscatter lidar measurements at 355 nm with airborne High-Spectral-Resolution Lidar (HSRL) measurements at 532 nm and elastic backscatter lidar measurements at 1064 nm that were obtained less than 5 km apart from each other. This was the first study in which optical and microphysical retrievals from lidar were obtained during the day and directly compared to AERONET and in situ measurements for 11 cases. Good agreement was observed between lidar and AERONET retrievals. Larger discrepancies were observed between lidar retrievals and in situ measurements obtained by the aircraft and aerosol hygroscopic effects are believed to be the main factor in such discrepancies.Peer reviewe
Reductions in aircraft particulate emissions due to the use of Fischer–Tropsch fuels
The use of alternative fuels for aviation is likely to increase due to
concerns over fuel security, price stability, and the sustainability of fuel
sources. Concurrent reductions in particulate emissions from these
alternative fuels are expected because of changes in fuel composition
including reduced sulfur and aromatic content. The NASA Alternative Aviation
Fuel Experiment (AAFEX) was conducted in January–February 2009 to
investigate the effects of synthetic fuels on gas-phase and particulate
emissions. Standard petroleum JP-8 fuel, pure synthetic fuels produced from
natural gas and coal feedstocks using the Fischer–Tropsch (FT) process, and
50% blends of both fuels were tested in the CFM-56 engines on a DC-8
aircraft. To examine plume chemistry and particle evolution with time,
samples were drawn from inlet probes positioned 1, 30, and 145 m downstream
of the aircraft engines. No significant alteration to engine performance was
measured when burning the alternative fuels. However, leaks in the aircraft
fuel system were detected when operated with the pure FT fuels as a result
of the absence of aromatic compounds in the fuel.
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Dramatic reductions in soot emissions were measured for both the pure FT
fuels (reductions in mass of 86% averaged over all powers) and blended
fuels (66%) relative to the JP-8 baseline with the largest reductions at
idle conditions. At 7% power, this corresponds to a reduction from 7.6 mg kg<sup>−1</sup>
for JP-8 to 1.2 mg kg<sup>−1</sup> for the natural gas FT fuel. At full
power, soot emissions were reduced from 103 to 24 mg kg<sup>−1</sup>
(JP-8 and natural gas FT, respectively). The alternative fuels also produced
smaller soot (e.g., at 85% power, volume mean diameters were reduced from
78 nm for JP-8 to 51 nm for the natural gas FT fuel), which may reduce their
ability to act as cloud condensation nuclei (CCN). The reductions in
particulate emissions are expected for all alternative fuels with similar
reductions in fuel sulfur and aromatic content regardless of the feedstock.
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As the plume cools downwind of the engine, nucleation-mode aerosols form.
For the pure FT fuels, reductions (94% averaged over all powers) in
downwind particle number emissions were similar to those measured at the
exhaust plane (84%). However, the blended fuels had less of a reduction
(reductions of 30–44%) than initially measured (64%). The likely
explanation is that the reduced soot emissions in the blended fuel exhaust
plume results in promotion of new particle formation microphysics, rather
than coating on pre-existing soot particles, which is dominant in the JP-8
exhaust plume. Downwind particle volume emissions were reduced for both the
pure (79 and 86% reductions) and blended FT fuels (36 and 46%) due to
the large reductions in soot emissions. In addition, the alternative fuels
had reduced particulate sulfate production (near zero for FT fuels) due to
decreased fuel sulfur content.
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To study the formation of volatile aerosols (defined as any aerosol formed as
the plume ages) in more detail, tests were performed at varying ambient
temperatures (−4 to 20 °C). At idle, particle number and volume
emissions were reduced linearly with increasing ambient temperature, with
best fit slopes corresponding to −8 × 10<sup>14</sup> particles
(kg fuel)<sup>−1</sup> °C<sup>−1</sup> for particle number emissions and
−10 mm<sup>3</sup> (kg fuel)<sup>−1</sup> °C<sup>−1</sup> for particle volume
emissions. The temperature dependency of aerosol formation can have large
effects on local air quality surrounding airports in cold regions.
Aircraft-produced aerosols in these regions will be much larger than levels
expected based solely on measurements made directly at the engine exit plane.
The majority (90% at idle) of the volatile aerosol mass formed as
nucleation-mode aerosols, with a smaller fraction as a soot coating.
Conversion efficiencies of up to 2.8% were measured for the partitioning
of gas-phase precursors (unburned hydrocarbons and SO<sub>2</sub>) to form volatile
aerosols. Highest conversion efficiencies were measured at 45% power
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