Lawns are a common ecosystem type in human-dominated landscapes which can have negative impacts on water quality due to fertilizer applications, but also host a range of ecosystem services. While ...many studies have addressed water and nitrogen (N) dynamics in lawns, few have considered how topography interacts with human behaviors to control these dynamics. Our overarching objective was to determine if mesoscale topography (hillslopes within lawns) interacts with human behavior (fertilizer use) influencing patterns of N mobilization and removal in lawns. To that end, we measured several hydrobiogeochemical characteristics associated with N dynamics along topographic gradients in fertilized and unfertilized residential and institutional lawns. We found topographic gradients affect the hydrobiogeochemistry of lawns, with significant effects of landscape position (top versus toe slope versus bottomland swales), but with direction and strength of the effect often varying among different lawn types (exurban versus suburban front yards versus suburban backyards versus institutional). Fertilizer application did not affect the hydrobiogeochemical properties of lawns. Rather, results from this study suggest lawns in suburban front yards were at greatest risk of N mobilization due to a complex suite of characteristics including proximity to impervious surfaces, swales with low saturated infiltration rates, and potential vulnerability to N deposition from vehicles. This study highlights the need to consider landscape controls of water and N fluxes and how they interact with human behaviors to better understand how these landscapes function. These results contribute to the emerging understanding of the structure, function and environmental impacts of lawns.
Millions of hectares of cropland have slopes of less than 2%, which can result in an enormous amount of pollutants transported with clay–silt sized particles via interrill erosion. However, few ...studies have attempted to understand the detachment-transport mechanism of particles with different wetting processes as determined by the surface soil cover of a field. The goal of this study was to determine the effects of different wetting rates on the runoff rate, temporal sediment particle size distribution (PSD), and sediment delivery rate produced via interrill erosion in low slopes under two contrasting tillage systems. Selected sites were under continuous corn rotations on Maury silt loam (Typic Paleudalf) or corn/soybean on Calloway silt (Aquic Fragiudult), both under either moldboard plow (MT) or no-till (NT) soil management. A nozzle-type rain simulator was used to deliver 87.5mmh−1 for 1h on a plot of 1m2. High kinetic energy wetting (HKE) was evaluated on a bare soil surface. Low kinetic energy wetting (LKE) was accomplished by covering the bare soil surface with layers of plastic mesh. Soil texture and aggregate stability were more important than overland flow in modifying the temporal PSD. Transport capacity appears to be diminished due to soil cover, making all predictions based on settling velocity ineffective. Comparison between HKE and LKE showed that soils can produce different temporal PSD in the sediment without changes in total soil loss. HKE increases both the total and temporal sediment delivery rate (Di) values. Observed differences in Di were consequences not of particle size but of the number of particles released.
► Temporal PSD depends on soil texture and aggregate stability. ► Wetting produces different PSDs without any differences in total soil loss. ► Temporal PSD can invalidate soil loss comparison before reaches steady state. ► How different wetting energy modifies Di in the same soil was discussed.
Gamma Ray Glow Observations at 20‐km Altitude Østgaard, N.; Christian, H. J.; Grove, J. E. ...
Journal of geophysical research. Atmospheres,
16 July 2019, Letnik:
124, Številka:
13
Journal Article
Recenzirano
Odprti dostop
In the spring of 2017 an ER‐2 aircraft campaign was undertaken over continental United States to observe energetic radiation from thunderstorms and lightning. The payload consisted of a suite of ...instruments designed to detect optical signals, electric fields, and gamma rays from lightning. Starting from Georgia, USA, 16 flights were performed, for a total of about 70 flight hours at a cruise altitude of 20 km. Of these, 45 flight hours were over thunderstorm regions. An analysis of two gamma ray glow events that were observed over Colorado at 21:47 UT on 8 May 2017 is presented. We explore the charge structure of the cloud system, as well as possible mechanisms that can produce the gamma ray glows. The thundercloud system we passed during the gamma ray glow observation had strong convection in the core of the cloud system. Electric field measurements combined with radar and radio measurements suggest an inverted charge structure, with an upper negative charge layer and a lower positive charge layer. Based on modeling results, we were not able to unambiguously determine the production mechanism. Possible mechanisms are either an enhancement of cosmic background locally (above or below 20 km) by an electric field below the local threshold or an enhancement of the cosmic background inside the cloud but then with normal polarity and an electric field well above the Relativistic Runaway Electron Avalanche threshold.
Key Points
Gamma ray glows were observed for the first time at 20‐km altitude above thunderclouds
The thunderclouds below the aircraft had an anomalous charge structure
Possible production mechanisms for gamma ray glow are tested by Monte Carlo modeling
We demonstrate a compact fully tunable narrowband fourth-order pole-zero optical filter that is fabricated in a silicon complementary-metal-oxide-semiconductor foundry. The filter is implemented ...using silicon on oxide channel waveguides and consists of a Mach-Zehnder interferometer with two ring resonator all-pass filters (APFs) on each arm. The filter architecture is based on the sum and difference of the APFs responses. The ring resonators introduce a nonlinear phase response in each arm that allows carving narrow frequency bands out of a broad spectrum. In this paper, we demonstrate a 3-dB filter bandwidth of 1.0 GHz with a stopband rejection of better than 25 dB. The filter free spectral range is 16.5 GHz. Thermooptic phase shifters are used to tune the filter. As silicon has a large thermooptic coefficient compared to silica, the demonstrated filter requires a low tuning power of less than 300 mW. In addition, this filter is compact with dimensions 25 times smaller than the same filter would be if it were made using standard silica on silicon waveguides with a 0.8% step index contrast
We announce the discovery of 1-100 GeV gamma-ray emission from the archetypal TeV pulsar wind nebula (PWN) HESS J1825--137 using 20 months of survey data from the Fermi-Large Area Telescope (LAT). ...The gamma-ray emission detected by the LAT is significantly spatially extended, with a best-fit rms extension of Delta *s = 056 ? 007 for an assumed Gaussian model. The 1-100 GeV LAT spectrum of this source is well described by a power law with a spectral index of 1.38 ? 0.12 ? 0.16 and an integral flux above 1 GeV of (6.50 ? 0.21 ? 3.90) X 10--9 cm--2 s--1. The first errors represent the statistical errors on the fit parameters, while the second ones are the systematic uncertainties. Detailed morphological and spectral analyses bring new constraints on the energetics and magnetic field of the PWN system. The spatial extent and hard spectrum of the GeV emission are consistent with the picture of an inverse Compton origin of the GeV-TeV emission in a cooling-limited nebula powered by the pulsar PSR J1826--1334.
•Research suggests residents seek to ‘fit in’ via establishing particular aesthetics.•This explanation does not meaningfully grapple with back yards, which are more hidden.•Lawns and nitrogen cycling ...processes were not different between front and back yards.•Yards however had more species of vegetation in back yards than front yards.•Social norms may be reducing biodiversity.
We hypothesize that lower public visibility of residential backyards reduces households’ desire for social conformity, which alters residential land management and produces differences in ecological composition and function between front and backyards. Using lawn vegetation plots (7 cities) and soil cores (6 cities), we examine plant species richness and evenness and nitrogen cycling of lawns in Boston, Baltimore, Miami, Minneapolis-St. Paul, Phoenix, Los Angeles (LA), and Salt Lake City (SLC). Seven soil nitrogen measures were compared because different irrigation and fertilization practices may vary between front and backyards, which may alter nitrogen cycling in soils. In addition to lawn-only measurements, we collected and analyzed plant species richness for entire yards—cultivated (intentionally planted) and spontaneous (self-regenerating)—for front and backyards in just two cities: LA and SLC. Lawn plant species and soils were not different between front and backyards in our multi-city comparisons. However, entire-yard plant analyses in LA and SLC revealed that frontyards had significantly fewer species than backyards for both cultivated and spontaneous species. These results suggest that there is a need for a more rich and social-ecologically nuanced understanding of potential residential, household behaviors and their ecological consequences.
Abstract
We present a maximum-likelihood (ML) algorithm that is fast enough to detect
γ
-ray transients in real time on low-performance processors often used for space applications. We validate the ...routine with simulations and find that, relative to algorithms based on excess counts, the ML method is nearly twice as sensitive, allowing detection of 240%–280% more short
γ
-ray bursts. We characterize a reference implementation of the code, estimating its computational complexity and benchmarking it on a range of processors. We exercise the reference implementation on archival data from the Fermi Gamma-ray Burst Monitor (GBM), verifying the sensitivity improvements. In particular, we show that the ML algorithm would have detected GRB 170817A even if it had been nearly 4 times fainter. We present an ad hoc but effective scheme for discriminating transients associated with background variations. We show that the onboard localizations generated by ML are accurate, but that refined off-line localizations require a detector response matrix with about 10 times finer resolution than is the current practice. Increasing the resolution of the GBM response matrix could substantially reduce the few-degree systematic uncertainty observed in the localizations of bright bursts.
Residential yards across the US look remarkably similar despite marked variation in climate and soil, yet the drivers of this homogenization are unknown. Telephone surveys of fertilizer and ...irrigation use and satisfaction with the natural environment, and measurements of inherent water and nitrogen availability in six US cities (Boston, Baltimore, Miami, Minneapolis-St. Paul, Phoenix, Los Angeles) showed that the percentage of people using irrigation at least once in a year was relatively invariant with little difference between the wettest (Miami, 85%) and driest (Phoenix, 89%) cities. The percentage of people using fertilizer at least once in a year also ranged narrowly (52%-71%), while soil nitrogen supply varied by 10x. Residents expressed similar levels of satisfaction with the natural environment in their neighborhoods. The nature and extent of this satisfaction must be understood if environmental managers hope to effect change in the establishment and maintenance of residential ecosystems.
Context
As urban areas increase in extent globally, domestic yards play an increasingly important role as potential contributors to ecosystem services and well-being. These benefits largely depend on ...the plant species richness and composition of yards.
Objectives
We aim to determine the factors that drive plant species richness and phylogenetic composition of cultivated and spontaneous flora in urban yards at the continental scale, and how these potential drivers interact.
Methods
We analyzed plant species richness and phylogenetic composition of cultivated and spontaneous flora of 117 private yards from six major metropolitan areas in the US. Yard plant species richness and phylogenetic composition were expressed as a function of biophysical and socioeconomic variables and yard characteristics using linear mixed-effects models and spatially explicit structural equation modeling.
Results
Extreme temperatures largely determined yard species richness and phylogenetic composition at the continental scale. Precipitation positively predicted spontaneous richness but negatively predicted cultivated richness. Only the phylogenetic composition of the spontaneous flora was associated with precipitation. The effect of lower temperatures and precipitation on all yard diversity parameters was partly mediated by yard area. Among various socioeconomic variables, only education level showed a significant effect on cultivated phylogenetic composition.
Conclusions
Our results support the hypothesis that irrigation compensates for precipitation in driving cultivated yard plant diversity at the continental scale. Socioeconomic variables among middle and upper class families have no apparent influence on yard diversity. These findings inform the adaptation of US urban vegetation in cities in the face of global change.
Objective
To examine levels of 3 neurotrophic factors (NTFs): Brain derived neurotrophic factor (BDNF), Neurotrophin‐4 (NT‐4), and transforming growth factor‐β (TGF‐β) in dried blood spot samples of ...neonates diagnosed with autism spectrum disorders (ASD) later in life and frequency‐matched controls.
Method
Biologic samples were retrieved from the Danish Newborn Screening Biobank. NTFs for 414 ASD cases and 820 controls were measured using Luminex technology. Associations were analyzed with continuous measures (Tobit regression) as well as dichotomized at the lower and upper 10th percentiles cutoff points derived from the controls' distributions (logistic regression).
Results
ASD cases were more likely to have BDNF levels falling in the lower 10th percentile (odds ratios OR, 1.53 95% confidence intervals (CI), 1.04–2.24, P‐value = 0.03). Similar pattern was seen for TGF‐β in females with ASD (OR, 2.36 95% CI, 1.05–5.33, P‐value = 0.04). For NT‐4, however, ASD cases diagnosed with ICD‐10 only were less likely to have levels in upper 10th percentile compared with controls (OR, 0.22 95% CI, 0.05–0.98, P‐value = 0.05).
Conclusion
Results cautiously indicate decreased NTFs levels during neonatal period in ASD. This may contribute to the pathophysiology of ASD through impairments of neuroplasticity. Further research is required to confirm our results and to examine the potential therapeutic effects of NTFs in ASD.
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