An official website of the United States government
Ultraviolet and visible integrated photonics enable applications in quantum information, sensing, and spectroscopy, among others. Few materials support low-loss photonics into the UV, and the relatively low refractive index of known depositable materials limits the achievable functionality. Here, we present a high-index integrated photonics platform based on HfO2and Al2O3composites deposited via atomic layer deposition (ALD) with low loss in the visible and near UV. We show that Al2O3incorporation dramatically decreases bulk loss compared to pure HfO2, consistent with inhibited crystallization due to the admixture of Al2O3. Composites exhibit refractive indexnfollowing the average of that of HfO2and Al2O3, weighted by the HfO2fractional compositionx. Atλ = 375 nm, composites withx = 0.67 exhibitn = 2.01, preserving most of HfO2’s significantly higher index, and 3.8(7) dB/cm material loss. We further present fully etched and cladded waveguides, grating couplers, and ring resonators, realizing a single-mode waveguide loss of 0.25(2) dB/cm inferred from resonators of 2.6 million intrinsic quality factor atλ = 729 nm, 2.6(2) dB/cm atλ = 405 nm, and 7.7(6) dB/cm atλ = 375 nm. We measure the composite’s thermo-optic coefficient (TOC) to be 2.44(3) × 10−5RIU/°C nearλ = 397 nm. This work establishes (HfO2)x(Al2O3)1−xcomposites as a platform amenable to integration for low-loss, high-index photonics spanning the UV to NIR.
more »
« less
This content will become publicly available on May 23, 2026
Poorly quantified trends in ammonium nitrate remain critical to understand future urban aerosol control strategies
Despite decades of progress in reducing nitrogen oxide (NOx) emissions, ammonium nitrate (AN) remains the primary inorganic component of particulate matter (PM) in Los Angeles (LA). Using aerosol mass spectrometry over multiple years in LA illustrates the controlling dynamics of AN and their evolution over the past decades. These data suggest that much of the nitric acid (HNO3) production required to produce AN in LA occurs during the nighttime via heterogeneous hydrolysis of N2O5. Further, we show that US Environmental Protection Agency–codified techniques for measuring total PM2.5fail to quantify the AN component, while low-cost optical sensors demonstrate good agreement. While previous studies suggest that declining NOxhas reduced AN, we show that HNO3formation is still substantial and leads to the formation of many tens of micrograms per cubic meter of AN aerosol. Continued focus on reductions in NOxwill help meet the PM2.5standards in the LA basin and many other regions.
more »
« less
- Award ID(s):
- 2131914
- PAR ID:
- 10629755
- Publisher / Repository:
- American Association for the Advancement of Science (AAAS)
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 11
- Issue:
- 21
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) deployed the NSF/NCAR C‐130 aircraft in summer 2018 across the western U.S. to sample wildfire smoke during its first days of atmospheric evolution. We present a summary of a subset of reactive oxidized nitrogen species (NOy) in plumes sampled in a pseudo‐Lagrangian fashion. Emissions of nitrogen oxides (NOx = NO + NO2) and nitrous acid (HONO) are rapidly converted to more oxidized forms. Within 4 h, ∼86% of the ΣNOyis in the form of peroxy acyl nitrates (PANs) (∼37%), particulate nitrate (pNO3) (∼27%), and gas‐phase organic nitrates (Org N(g)) (∼23%). The averagee‐folding time and distance for NOxare ∼90 min and ∼40 km, respectively. Nearly no enhancements in nitric acid (HNO3) were observed in plumes sampled in a pseudo‐Lagrangian fashion, implying HNO3‐limited ammonium nitrate (NH4NO3) formation, with one notable exception that we highlight as a case study. We also summarize the observed partitioning of NOyin all the smoke samples intercepted during WE‐CAN. In smoke samples intercepted above 3 km above sea level (ASL), the contributions of PANs andpNO3to ΣNOyincrease with altitude. WE‐CAN also sampled smoke from multiple fires mixed with anthropogenic emissions over the California Central Valley. We distinguish samples where anthropogenic NOxemissions appear to lead to an increase in NOxabundances by a factor of four and contribute to additional PAN formation.more » « less
-
We present a novel symbolic reasoning engine for SQL which can efficiently generate an inputIfornqueriesP1, ⋯,Pn, such that their outputs onIsatisfy a given property (expressed in SMT). This is useful in different contexts, such as disproving equivalence of two SQL queries and disambiguating a set of queries. Our first idea is to reason about an under-approximation of eachPi— that is, a subset ofPi’s input-output behaviors. While it makes our approach both semantics-aware and lightweight, this idea alone is incomplete (as a fixed under-approximation might miss some behaviors of interest). Therefore, our second idea is to perform search over an expressive family of under-approximations (which collectively cover all program behaviors of interest), thereby making our approach complete. We have implemented these ideas in a tool, Polygon, and evaluated it on over 30,000 benchmarks across two tasks (namely, SQL equivalence refutation and query disambiguation). Our evaluation results show that Polygon significantly outperforms all prior techniques.more » « less
-
Abstract Ammonia (NH3) from animal feeding operations (AFOs) is an important source of reactive nitrogen in the US, but despite its ramifications for air quality and ecosystem health, its near‐source evolution remains understudied. To this end, Phase I of the Transport and Transformation of Ammonia (TRANS2Am) field campaign was conducted in the northeastern Colorado Front Range in summer 2021 and characterized atmospheric composition downwind of AFOs during 10 research flights. Airborne measurements of NH3, nitric acid (HNO3), and a suite of water‐soluble aerosol species collected onboard the University of Wyoming King Air research aircraft present an opportunity to investigate the sensitivity of particulate matter (PM) formation to AFO emissions. We couple the observations with thermodynamic modeling to predict the seasonality of ammonium nitrate (NH4NO3) formation. We find that during TRANS2Am northeastern Colorado is consistently in the NH3‐rich and HNO3‐limited NH4NO3formation regime. Further investigation using the Extended Aerosol Inorganics Model reveals that summertime temperatures (mean: 23°C) of northeastern Colorado, especially near the surface, inhibit NH4NO3formation despite high NH3concentrations (max: ≤114 ppbv). Finally, we model spring/autumn and winter conditions to explore the seasonality of NH4NO3formation and find that cooler temperatures could support substantially more NH4NO3formation. Whereas NH4NO3only exceeds 1 μg m−3∼10% of the time in summer, modeled NH4NO3would exceed 1 μg m−361% (88%) of the time in spring/autumn (winter), with a 10°C (20°C) temperature decrease relative to the campaign.more » « less
-
Constraints on the thickness, transitional boundaries, and composition of Earth's crust are pivotal in studying its formation and evolution. We use data from 132 seismic installations throughout the northeastern US to explore how tectonic events, such as orogenesis and rifting, have altered the crust of the northeastern US and southeastern Canada, and to distinguish between Laurentia and the Appalachian terranes. We include data from seismic installations from the NEST and SEISConn experiments, spanning the Laurentia–Appalachian boundary, and present estimates of crustal thickness,Vp/Vs, and thickness of the transition between crustal and mantle rocks using Ps receiver functions. We find some first-order differences between Laurentia and Appalachian terranes, with Laurentia exhibiting thicker crust (c.39 v.c.33 km) and a broader crust–mantle transition thickness (c.3 v. <1.5 km). AverageVp/Vsvalues are similar between Laurentia (c.1.77) and Appalachian terranes (c.1.74); however, we identify anomalousVp/Vsin a few regions, including highVp/Vsaround the Adirondack Mountains and lowVp/Vsin southern New England. The southern New England region is also anomalous in terms of its systematically thinner crust and sharper crust–mantle transition, which may be a consequence of the formation and collapse of the Acadian altiplano during the mid-to-late Paleozoic.more » « less
