3,075 research outputs found
High-Q-factor Al [subscript 2]O[subscript 3] micro-trench cavities integrated with silicon nitride waveguides on silicon
We report on the design and performance of high-Q integrated optical micro-trench cavities on silicon. The microcavities are co-integrated with silicon nitride bus waveguides and fabricated using wafer-scale silicon-photonics-compatible processing steps. The amorphous aluminum oxide resonator material is deposited via sputtering in a single straightforward post-processing step. We examine the theoretical and experimental optical properties of the aluminum oxide micro-trench cavities for different bend radii, film thicknesses and near-infrared wavelengths and demonstrate experimental Q factors of > 10[superscript 6]. We propose that this high-Q micro-trench cavity design can be applied to incorporate a wide variety of novel microcavity materials, including rare-earth-doped films for microlasers, into wafer-scale silicon photonics platforms
The Fire and Smoke Model Evaluation Experiment—A Plan for Integrated, Large Fire–Atmosphere Field Campaigns
The Fire and Smoke Model Evaluation Experiment (FASMEE) is designed to collect integrated observations from large wildland fires and provide evaluation datasets for new models and operational systems. Wildland fire, smoke dispersion, and atmospheric chemistry models have become more sophisticated, and next-generation operational models will require evaluation datasets that are coordinated and comprehensive for their evaluation and advancement. Integrated measurements are required, including ground-based observations of fuels and fire behavior, estimates of fire-emitted heat and emissions fluxes, and observations of near-source micrometeorology, plume properties, smoke dispersion, and atmospheric chemistry. To address these requirements the FASMEE campaign design includes a study plan to guide the suite of required measurements in forested sites representative of many prescribed burning programs in the southeastern United States and increasingly common high-intensity fires in the western United States. Here we provide an overview of the proposed experiment and recommendations for key measurements. The FASMEE study provides a template for additional large-scale experimental campaigns to advance fire science and operational fire and smoke models
Changes in PM2.5 Peat Combustion Source Profiles with Atmospheric Aging in an Oxidation Flow Reactor
Smoke from laboratory chamber burning of peat fuels from Russia, Siberia, the USA (Alaska and Florida), and Malaysia representing boreal, temperate, subtropical, and tropical regions was sampled before and after passing through a potential-aerosol-mass oxidation flow reactor (PAM-OFR) to simulate intermediately aged (∼2 d) and well-aged (∼7 d) source profiles. Species abundances in PM2.5 between aged and fresh profiles varied by several orders of magnitude with two distinguishable clusters, centered around 0.1 % for reactive and ionic species and centered around 10 % for carbon. Organic carbon (OC) accounted for 58 %–85 % of PM2.5 mass in fresh profiles with low elemental carbon (EC) abundances (0.67 %–4.4 %). OC abundances decreased by 20 %–33 % for well-aged profiles, with reductions of 3 %–14 % for the volatile OC fractions (e.g., OC1 and OC2, thermally evolved at 140 and 280 ∘C). Ratios of organic matter (OM) to OC abundances increased by 12 %–19 % from intermediately aged to well-aged smoke. Ratios of ammonia (NH3) to PM2.5 decreased after intermediate aging. Well-aged NH+4 and NO−3 abundances increased to 7 %–8 % of PM2.5 mass, associated with decreases in NH3, low-temperature OC, and levoglucosan abundances for Siberia, Alaska, and Everglades (Florida) peats. Elevated levoglucosan was found for Russian peats, accounting for 35 %–39 % and 20 %–25 % of PM2.5 mass for fresh and aged profiles, respectively. The water-soluble organic carbon (WSOC) fractions of PM2.5 were over 2-fold higher in fresh Russian peat (37.0±2.7 %) than in Malaysian (14.6±0.9 %) peat. While Russian peat OC emissions were largely water-soluble, Malaysian peat emissions were mostly water-insoluble, with WSOC ∕ OC ratios of 0.59–0.71 and 0.18–0.40, respectively. This study shows significant differences between fresh and aged peat combustion profiles among the four biomes that can be used to establish speciated emission inventories for atmospheric modeling and receptor model source apportionment. A sufficient aging time (∼7 d) is needed to allow gas-to-particle partitioning of semi-volatilized species, gas-phase oxidation, and particle volatilization to achieve representative source profiles for regional-scale source apportionment
Effects of intersegmental transfers on target location by proteins
We study a model for a protein searching for a target, using facilitated
diffusion, on a DNA molecule confined in a finite volume. The model includes
three distinct pathways for facilitated diffusion: (a) sliding - in which the
protein diffuses along the contour of the DNA (b) jumping - where the protein
travels between two sites along the DNA by three-dimensional diffusion, and
finally (c) intersegmental transfer - which allows the protein to move from one
site to another by transiently binding both at the same time. The typical
search time is calculated using scaling arguments which are verified
numerically. Our results suggest that the inclusion of intersegmental transfer
(i) decreases the search time considerably (ii) makes the search time much more
robust to variations in the parameters of the model and (iii) that the optimal
search time occurs in a regime very different than that found for models which
ignore intersegmental transfers. The behavior we find is rich and shows
surprising dependencies, for example, on the DNA length.Comment: 40 pages, 14 figure
SAMI-HI: the connection between global asymmetry in the ionised and neutral atomic hydrogen gas in galaxies
Observations of the neutral atomic hydrogen (HI) gas in galaxies are
predominantly spatially unresolved, in the form of a global HI spectral line.
There has been substantial work on quantifying asymmetry in global HI spectra
(`global HI asymmetry'), but due to being spatially unresolved, it remains
unknown what physical regions of galaxies the asymmetry traces, and whether the
other gas phases are affected. Using optical integral field spectrograph (IFS)
observations from the Sydney AAO Multi-object IFS (SAMI) survey for which
global HI spectra are also available (SAMI-HI), we study the connection between
asymmetry in galaxies' ionised and neutral gas reservoirs to test if and how
they can help us better understand the origin of global HI asymmetry. We
reconstruct the global H spectral line from the IFS observations and
find that, while some global H asymmetries can arise from disturbed
ionised gas kinematics, the majority of asymmetric cases are driven by the
distribution of H-emitting gas. When compared to the HI, we find no
evidence for a relationship between the global H and HI asymmetry.
Further, a visual inspection reveals that cases where galaxies have
qualitatively similar H and HI spectral profiles can be spurious, with
the similarity originating from an irregular 2D H flux distribution.
Our results highlight that comparisons between global H and HI
asymmetry are not straightforward, and that many global HI asymmetries trace
disturbances that do not significantly impact the central regions of galaxies.Comment: 11 pages, 6 figures, 1 appendix, accepted for publication in MNRA
CMOS-compatible 75 mW erbium-doped distributed feedback laser
On-chip, high-power, erbium-doped distributed feedback lasers are demonstrated in a CMOS-compatible fabrication flow. The laser cavities consist of silicon nitride waveguide and grating features, defined by wafer-scale immersion lithography and an erbium-doped aluminum oxide layer deposited as the final step in the fabrication process. The large mode size lasers demonstrate single-mode continuous wave operation with a maximum output power of 75 mW without any thermal damage. The laser output power does not saturate at high pump intensities and is, therefore, capable of delivering even higher on-chip signals if a stronger pump is utilized. The amplitude noise of the laser is investigated and the laser is shown to be stable and free from self-pulsing when the pump power is sufficiently above threshold. Efficient, low noise, narrow band and stable on-chip lasers are essential for a variety of important applications, ranging from integrated analog photonics and microwave generation to coherent communications and light detection and ranging (LiDAR). Recently, two methods have shown the greatest promise for delivering high performance, integrated silicon-compatible lasers; namely, hybrid integration of silicon-on-oxide (SOI) waveguides with III-V semiconductor gain media [1-3], and erbium/ ytterbium-doped glasses on silico
VERTICO VI: Cold-gas asymmetries in Virgo cluster galaxies
We analyze cold-gas distributions in Virgo cluster galaxies using resolved
CO(2-1) (tracing molecular hydrogen, H2) and HI observations from the Virgo
Environment Traced In CO (VERTICO) and the VLA Imaging of Virgo in Atomic Gas
(VIVA) surveys. From a theoretical perspective, it is expected that
environmental processes in clusters will have a stronger influence on diffuse
atomic gas compared to the relatively dense molecular gas component, and that
these environmental perturbations can compress the cold interstellar medium in
cluster galaxies leading to elevated star formation. In this work we
observationally test these predictions for star-forming satellite galaxies
within the Virgo cluster. We divide our Virgo galaxy sample into HI-normal,
HI-tailed, and HI-truncated classes and show, unsurprisingly, that the
HI-tailed galaxies have the largest quantitative HI asymmetries. We also
compare to a control sample of non-cluster galaxies and find that Virgo
galaxies, on average, have HI asymmetries that are 40 +/- 10 per cent larger
than the control. There is less separation between control, HI-normal,
HI-tailed, and HI-truncated galaxies in terms of H2 asymmetries, and on
average, Virgo galaxies have H2 asymmetries that are only marginally (20 +/- 10
per cent) larger than the control sample. We find a weak correlation between HI
and H2 asymmetries over our entire sample, but a stronger correlation for those
specific galaxies being strongly impacted by environmental perturbations.
Finally, we divide the discs of the HI-tailed Virgo galaxies into a leading
half and trailing half according to the observed tail direction. We find
evidence for excess molecular gas mass on the leading halves of the disc. This
excess molecular gas on the leading half is accompanied by an excess in star
formation rate such that the depletion time is, on average, unchanged.Comment: 15 pages, 8 figures, 1 table, accepted for publication in A&
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