162 research outputs found
Noise-Resistant Spectral Features for Retrieving Foliar Chemical Parameters
Foliar chemical constituents are important indicators for understanding vegetation growing status and ecosystem functionality. Provided the noncontact and nondestructive traits, the hyperspectral analysis is a superior and efficient method for deriving these parameters. In practice, thespectral noise issue significantly impacts the performance of the hyperspectral retrieving system. To systematically investigate this issue, by introducing varying levels of noise to spectral signals, an assessment on noiseresistant capability of spectral features and models for retrieving concentrations of chlorophyll, carotenoids, and leaf water content was conducted. Given the continuous waveletanalysis (CWA) showed superior performance in extracting critical information associating plants biophysical and biochemical status in recent years, both wavelet features (WFs) and some conventional features (CFs) were chosen for the test. Two datasets including a leaf optical properties experiment dataset (n = 330), and a corn leaf spectral experiment dataset (n = 213) were used for analysis and modeling. The results suggested that the WFs had stronger correlations with all leaf chemical parameters than the CFs. According to an evaluation by decay rate of retrieving error that indicates noise-resistant capability, both WFs and CFs exhibited strong resistance to spectral noise. Particularly for WFs, the noise-resistant capability is relevant to the scale of the features. Based on the identified spectral features, both univariate and multivariate retrieving models were established and achieved satisfactory accuracies. Synthesizing the retrieving accuracy, noise resistivity, and model’s complexity, the optimal univariate WF-models were recommended in practice for retrieving leaf chemical parameters
Spectral analysis of winter wheat leaves for detection and differentiation of diseases and insects
Yellow rust (Puccinia striiformis f. sp. Tritici), powdery mildew (Blumeria graminis) and wheat aphid (Sitobion avenae F.) infestation are three serious conditions that have a severe impact on yield and grain quality of winter wheat worldwide. Discrimination among these three stressors is of practical importance, given that specific procedures (i.e. adoption of fungicide and insecticide) are needed to treat different diseases and insects. This study examines the potential of hyperspectral sensor systems in discriminating these three stressors at leaf level. Reflectance spectra of leaves infected with yellow rust, powdery mildew and aphids were measured at the early grain filling stage. Normalization was performed prior to spectral analysis on all three groups of samples for removing differences in the spectral baseline among different cultivars. To obtain appropriate bands and spectral features (SFs) for stressor discrimination and damage intensity estimation, a correlation analysis and an independent t-test were used jointly. Based on the most efficient bands/SFs, models for discriminating stressors and estimating stressor intensity were established by Fisher’s linear discriminant analysis (FLDA) and partial least square regression (PLSR), respectively. The results showed that the performance of the discrimination model was satisfactory in general, with an overall accuracy of 0.75. However, the discrimination model produced varied classification accuracies among different types of diseases and insects. The regression model produced reasonable estimates of stress intensity, with an R2 of 0.73 and a RMSE of 0.148. This study illustrates the potential use of hyperspectral information in discriminating yellow rust, powdery mildew and wheat aphid infestation in winter wheat. In practice, it is important to extend the discriminative analysis from leaf level to canopy level
Assessment of Isoprene as a Possible Biosignature Gas in Exoplanets with Anoxic Atmospheres
Research for possible biosignature gases on habitable exoplanet atmosphere is
accelerating. We add isoprene, C5H8, to the roster of biosignature gases. We
found that formation of isoprene geochemical formation is highly
thermodynamically disfavored and has no known abiotic false positives. The
isoprene production rate on Earth rivals that of methane (~ 500 Tg yr-1). On
Earth, isoprene is rapidly destroyed by oxygen-containing radicals, but its
production is ubiquitous to a diverse array of evolutionarily distant
organisms, from bacteria to plants and animals-few, if any at all, volatile
secondary metabolite has a larger evolutionary reach. While non-photochemical
sinks of isoprene may exist, the destruction of isoprene in an anoxic
atmosphere is mainly driven by photochemistry. Motivated by the concept that
isoprene might accumulate in anoxic environments, we model the photochemistry
and spectroscopic detection of isoprene in habitable temperature, rocky
exoplanet anoxic atmospheres with a variety of atmosphere compositions under
different host star UV fluxes. Limited by an assumed 10 ppm instrument noise
floor, habitable atmosphere characterization using JWST is only achievable with
transit signal similar or larger than that for a super-Earth sized exoplanet
transiting an M dwarf star with an H2-dominated atmosphere. Unfortunately,
isoprene cannot accumulate to detectable abundance without entering a run-away
phase, which occurs at a very high production rate, ~ 100 times Earth's
production rate. In this run-away scenario isoprene will accumulate to > 100
ppm and its spectral features are detectable with ~ 20 JWST transits. One
caveat is that some spectral features are hard to be distinguished from that of
methane. Despite these challenges, isoprene is worth adding to the menu of
potential biosignature gases.Comment: 62 pages, 24 figure
Local control of a single nitrogen-vacancy center by nanoscale engineered magnetic domain wall motions
Effective control and readout of qubits form the technical foundation of
next-generation, transformative quantum information sciences and technologies.
The nitrogen-vacancy (NV) center, an intrinsic three-level spin system, is
naturally relevant in this context due to its excellent quantum coherence, high
fidelity of operations, and remarkable functionality over a broad range of
experimental conditions. It is an active contender for the development and
implementation of cutting-edge quantum technologies. Here, we report magnetic
domain wall motion driven local control and measurements of NV spin properties.
By engineering the local magnetic field environment of an NV center via
nanoscale reconfigurable domain wall motions, we show that NV
photoluminescence, spin level energies, and coherence time can be reliably
controlled and correlated to the magneto-transport response of a magnetic
device. Our results highlight the electrically tunable dipole interaction
between NV centers and nanoscale magnetic structures, providing an attractive
platform to realize interactive information transfer between spin qubits and
non-volatile magnetic memory in hybrid quantum spintronic systems.Comment: 13 pages, 5 figure
Photochemical runaway in exoplanet atmospheres: implications for biosignatures
About 2.5 billion years ago, microbes learned to harness plentiful solar energy to reduce CO2 with H2O, extracting energy and producing O2 as waste. O2 production from this metabolic process was so vigorous that it saturated its photochemical sinks, permitting it to reach "runaway" conditions and rapidly accumulate in the atmosphere despite its reactivity. Here we argue that O2 may not be unique: diverse gases produced by life may experience a "runaway" effect similar to O2. This runaway occurs because the ability of an atmosphere to photochemically cleanse itself of trace gases is generally finite. If produced at rates exceeding this finite limit, even reactive gases can rapidly accumulate to high concentrations and become potentially detectable. Planets orbiting smaller, cooler stars, such as the M dwarfs that are the prime targets for the James Webb Space Telescope (JWST), are especially favorable for runaway, due to their lower UV emission compared to higher-mass stars. As an illustrative case study, we show that on a habitable exoplanet with an H2–N2 atmosphere and net surface production of NH3 orbiting an M dwarf (the "Cold Haber World" scenario), the reactive biogenic gas NH3 can enter runaway, whereupon an increase in the surface production flux of one order of magnitude can increase NH3 concentrations by three orders of magnitude and render it detectable by JWST in just two transits. Our work on this and other gases suggests that diverse signs of life on exoplanets may be readily detectable at biochemically plausible production rates
Revealing intrinsic domains and fluctuations of moir\'e magnetism by a wide-field quantum microscope
Moir\'e magnetism featured by stacking engineered atomic registry and lattice
interactions has recently emerged as an appealing quantum state of matter at
the forefront condensed matter physics research. Nanoscale imaging of moir\'e
magnets is highly desirable and serves as a prerequisite to investigate a broad
range of intriguing physics underlying the interplay between topology,
electronic correlations, and unconventional nanomagnetism. Here we report spin
defect-based wide-field imaging of magnetic domains and spin fluctuations in
twisted double trilayer (tDT) chromium triiodide CrI3. We explicitly show that
intrinsic moir\'e domains of opposite magnetizations appear over arrays of
moir\'e supercells in low-twist-angle tDT CrI3. In contrast, spin fluctuations
measured in tDT CrI3 manifest little spatial variations on the same mesoscopic
length scale due to the dominant driving force of intralayer exchange
interaction. Our results enrich the current understanding of exotic magnetic
phases sustained by moir\'e magnetism and highlight the opportunities provided
by quantum spin sensors in probing microscopic spin related phenomena on
two-dimensional flatland
JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b
Clouds are prevalent in many of the exoplanet atmospheres that have been
observed to date. For transiting exoplanets, we know if clouds are present
because they mute spectral features and cause wavelength-dependent scattering.
While the exact composition of these clouds is largely unknown, this
information is vital to understanding the chemistry and energy budget of
planetary atmospheres. In this work, we observe one transit of the hot Jupiter
WASP-17b with JWST's MIRI LRS and generate a transmission spectrum from 5-12
m. These wavelengths allow us to probe absorption due to the
vibrational modes of various predicted cloud species. Our transmission spectrum
shows additional opacity centered at 8.6 m, and detailed atmospheric
modeling and retrievals identify this feature as SiO(s) (quartz) clouds.
The SiO(s) clouds model is preferred at 3.5-4.2 versus a cloud-free
model and at 2.6 versus a generic aerosol prescription. We find the
SiO(s) clouds are comprised of small m particles,
which extend to high altitudes in the atmosphere. The atmosphere also shows a
depletion of HO, a finding consistent with the formation of
high-temperature aerosols from oxygen-rich species. This work is part of a
series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we
will use Guaranteed Time Observations to perform Deep Reconnaissance of
Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).Comment: 19 pages, 7 figures, accepted for publication in ApJ
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