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At least 865 records · Page 48

Synergistic Retrieval of Temperature and Humidity Profiles from Space-Based and Ground-Based Infrared Sounders Using an Optimal Estimation Method

The atmospheric temperature and humidity profiles of the troposphere are generally measured by radiosondes and satellites, which are essential for analyzing and predicting weather. Nevertheless, the insufficient observation frequencies and low detection accuracy of the boundary layer restricts the description of atmospheric state changes by the temperature and humidity profiles. Therefore, this work focus on retrieving the temperature and humidity profiles using observations of the FengYun-4 (FY-4) Geostationary Interferometric Infrared Sounder (GIIRS) combined with ground-based infrared spectral observations from the Atmospheric Emitted Radiance Interferometer (AERI), which are more accurate than space-based individual retrieval results and have a wider effective retrieval range than ground-based individual retrieval results. Based on the synergistic observations, which are made by matching the space-based and ground-based data with those of different spatial and temporal resolutions, a synergistic retrieval process is proposed to obtain the temperature and humidity profiles at a high frequency under clear-sky conditions based on the optimal estimation method. In this research, using the line-by-line radiative transfer model (LBLRTM) as the forward model for observing simulations, a retrieval experiment was carried out in Qingdao, China, where an AERI is situated. Taking radiosonde data as a reference for comparing the retrieval results of the temperature and humidity profiles of the troposphere, the root-mean-square error (RMSE) of the synergistic retrieval algorithm below 400 hPa is within 2 K for temperature and within 12% for relative humidity. Compared with the GIIRS individual retrieval, the RMSE of temperature and relative humidity for the synergistic method is reduced by 0.13–1.5 K and 2.7–4.4% at 500 hPa, and 0.13–2.1 K and 2.5–7.2% at 900 hPa. Moreover, the forecast index (FI) calculated from the retrieval results shows reasonable consistency with the FIs calculated from the ERA5 reanalysis and from radiosonde data. The synergistic retrieval results have higher temporal resolution than space-based retrieval results and can reflect the changes in the atmospheric state more accurately. Overall, the results demonstrated the promising potential of the synergistic retrieval of temperature and humidity profiles at high accuracy and high temporal resolution under clear-sky conditions from FY-4/GIIRS and AERI.

54 ENVIRONMENTAL SCIENCES↗

VLBI Data Processing on Coronal Radio-sounding Experiments of Mars Express

The ESA’s Mars Express solar corona experiments were performed at two solar conjunctions in the years 2015 and 2017 by a number of radio telescopes in the European VLBI Network. This paper presents the methods to measure the frequency and phase fluctuations of the spacecraft radio signal, and the applications to study the characteristics of the plasma turbulence effects on the signal at a single station and at multiple stations via cross correlation. The power spectra of the frequency fluctuations observed between 4.9 and 76.3 R {sub s} have a power-law shape close to a Kolmogorov spectrum over the frequency interval ν {sub lo} < ν < ν {sub up}, where the nominal value of ν {sub lo} is set to 3 mHz and ν {sub up} is in the range of 0.03–0.15 Hz. The rms of the frequency fluctuations is presented as a function of the heliocentric distance. Furthermore, we analyze the variations of the electron column density fluctuations at solar offsets 4.9 R {sub s} and 9.9 R {sub s} and the cross-correlation products between the VLBI stations. The power density of the differential fluctuations between different stations decreases at ν < 0.01 Hz. Finally, the fast flow speeds of solar wind >700 km s{sup -1} are derived from the cross correlation of frequency fluctuations at ν < 0.01 Hz. The fast flow speeds of solar wind correspond to the high heliolatitude of the coronal region that the radio rays passed. The VLBI observations and analysis methods can be used to study the electron column density fluctuations and the turbulence at multiple spatial points in the inner solar wind by providing multiple lines of sight between the Earth and the spacecraft.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Phenotypic effects of changes in the FTVTxK region of an Arabidopsis secondary wall cellulose synthase compared with results from analogous mutations in other isoforms

Abstract Understanding protein structure and function relationships in cellulose synthase (CesA), including divergent isomers, is an important goal. Here, we report results from mutant complementation assays that tested the ability of sequence variants of AtCesA7, a secondary wall CesA of Arabidopsis thaliana , to rescue the collapsed vessels, short stems, and low cellulose content of the irx3‐1 AtCesA7 null mutant. We tested a catalytic null mutation and seven missense or small domain changes in and near the AtCesA7 FTVTSK motif, which lies near the catalytic domain and may, analogously to bacterial CesA, exist within a substrate “gating loop.” A low‐to‐high gradient of rescue occurred, and even inactive AtCesA7 had a small positive effect on stem cellulose content but not stem elongation. Overall, secondary wall cellulose content and stem length were moderately correlated, but the results were consistent with threshold amounts of cellulose supporting particular developmental processes. Vibrational sum frequency generation microscopy allowed tissue‐specific analysis of cellulose content in stem xylem and interfascicular fibers, revealing subtle differences between selected genotypes that correlated with the extent of rescue of the collapsing xylem phenotype. Similar tests on PpCesA5 from the moss Physcomitrium (formerly Physcomitrella ) patens helped us to synergize the AtCesA7 results with prior results on AtCesA1 and PpCesA5. The cumulative results show that the FTVTxK region is important for the function of an angiosperm secondary wall CesA as well as widely divergent primary wall CesAs, while differences in complementation results between isomers may reflect functional differences that can be explored in further work.

Burris, Jason N.↗

Computational insights into the lattice dynamics of Pu(IV) oxalates

Despite its use in PuO 2 production, the structure of anhydrous Pu(C 2 O 4 ) 2 is still not completely understood. Recently, two candidate structures for Pu(C 2 O 4 ) 2 were proposed via density functional theory (DFT), after which the first experimental optical vibrational spectra were reported. Here, in this study, we calculated the lattice dynamics of the candidate structures using DFT and found that the primary difference between them is the presence of a vibrational mode near 1380 cm -1 in one structure. The frequency and optical activity of this mode agree well with the published experimental results, providing strong support for this calculated structure as that of anhydrous Pu(C 2 O 4 ) 2 .

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

Temporal variabilities of soil carbon dioxide fluxes from cornfield impacted by temperature and precipitation changes through high-frequent measurement and DAYCENT modelling

Soil carbon dioxide (CO 2 ) emissions from the field of corn (Zea mays L.) play an important role in global warming. This study investigated temporal variability of soil CO 2 fluxes (R s ) with soil temperature (T s ) and moisture (θ) and built DAYCENT models for predicting future impacts of climate changes on R s using the measured high-frequency data. R s trend was tested by Mann–Kendall and Sen Estimator. Predicted R s s under different climate scenarios were compared using Parallel-line Analysis. Herein, the findings indicated that daily R s exponentially increased with T s constrained by θ. During the θ of 27–31%, there was a strong exponential relationship between R s and T s , but the relationship was weaker for the θ of 38–41% and 22–26%. Soil environmental index (SEI, T s × θ) significantly impacted R s with linear regression R s 0.5 = 0.4599 + 0.002059 × SEI in 2008, 2009 and 2011. At the diurnal scale, there were different trends in R s s and relationships among R s and T s and θ in different years. Predicted yearly R s s, root R s s and corn yield in 2014–2049 increased with an increase in temperature scenarios, but the R s s significantly increased as temperature rose by 1°C or higher. Predicted yearly R s s, root R s s and yield reduced with precipitation scenario increase, and the root R s s and yield significantly diminished as precipitation increased by 15 and 30%. Predicted yearly R s from cornfields had a significantly increasing trend. Future research is needed to explore methods for mitigating cornfield R s and evaluating sensitivities of different cropland R s s to temperature changes.

54 ENVIRONMENTAL SCIENCES↗

Ice Recrystallization Inhibition Activity of Soy Protein Hydrolysates

Identifying and developing ice recrystallization inhibitors from sustainable food proteins such as soy protein isolate (SPI) can lead to practical applications in both pharmaceutical and food industries. Here, the objective of this study was to investigate the ice recrystallization inhibition (IRI) activity of SPI hydrolysates, and this was achieved by using an IRI activity-guided fractionation approach and relating IRI activity to interfacial molecular activity measured by vibrational sum frequency generation (VSFG). In addition, the impact of molecular weight (MW) and enzyme specificity was analyzed using three different proteases (Alcalase, trypsin, and pancreatin) and varying hydrolysis times. Using preparative chromatography, hydrolysates from each enzyme treatment were fractionated into five different MW fractions (F1–F5), which were then characterized by high-performance liquid chromatography (HPLC). All SPI hydrolysates had IRI activity, resulting in a 57–29% ice crystal diameter reduction when compared to native SPI. The F1 fraction (of 4–14 kDa) was most effective among all tested hydrolysates, while the lower MW peptide fractions lacked activity. One sample (SPI-ALC 20-F1) had a 52% reduction of ice crystal size at a lower concentration of 2% compared to the typical 4% used. SFG showed a difference in H-bonding and hydrophobic interactions of the molecules on the water/air interface, which may be linked to IRI activity. This study demonstrates for the first time the ability of SPI hydrolysates to inhibit ice crystal growth and the potential application of SFG to study molecular interaction at the interface that may help illustrate the mechanism of action.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Probing the electronic structure and spectroscopy of pyrrolyl and imidazolyl radicals using high-resolution photoelectron imaging of cryogenically cooled anions

High-resolution photoelectron imaging and photodetachment spectroscopy of cryogenically cooled pyrrolide and imidazolide anions are used to probe the electronic structure and spectroscopy of pyrrolyl and imidazolyl radicals. The high-resolution data allow the ground state vibronic structures of the two radicals to be completely resolved, yielding accurate electron affinities of 2.1433 ± 0.0008 eV and 2.6046 ± 0.0006 eV for pyrrolyl and imidazolyl radicals, respectively. Fundamental frequencies for eight vibrational modes of pyrrolyl and ten vibrational modes of imidazolyl are measured, including several nonsymmetric Franck–Condon-forbidden modes. Two electronic excited states are also observed for the two radicals, displaying diffuse spectral features in both systems. The observations of nonsymmetric vibrational modes in the ground states and the diffuse excited state features provide strong evidence for vibronic couplings between the ground state and the two close-by excited states. The 2-pyrrolide isomer is also observed as a minor species from the electrospray ionization source and the electron affinity of 2-pyrrolyl is measured to be 1.6690 ± 0.0030 eV along with five vibrational frequencies. Even though the HOMOs of both pyrrolide and imidazolide anions are p orbitals, photodetachment spectroscopy reveals completely different threshold behaviors for the two anions: a d-wave-dominated spectrum for pyrrolide and an s-wave-dominated spectrum for imidazolide. Furthermore, the current study provides a wealth of electronic and spectroscopic information, which is ideal to compare with more accurate vibronic coupling calculations for these two important radicals, as well as interesting information about the photodetachment dynamics of the two anions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

The selective heating effect of microwave irradiation on a binary mixture of water and polyethylene oxide: a molecular dynamics simulation approach

In this study, we investigate the molecular mechanisms of a microwave-driven selective heating process by performing molecular dynamics simulations for three different systems including pure water, pure polyethylene oxide (PEO), and water-PEO mixed systems in the presence of a microwave with two different intensities of electric field such as 0.001 V/Å -1 and 0.01 V/Å -1 at a frequency of 100 GHz. First, from performing molecular dynamics simulations of CO and CO 2 in the presence of the microwave, it is confirmed that the molecular dipole moment is responsible for the rotational motion induced by the oscillating electric field. Second, by analyzing the MD simulations of the pure water system, we discover that the dipole moment of water exhibits a time lag with respect to the microwave. During the heating process, however, the temperature, kinetic, and potential energies increase synchronously with the oscillating electric field of the microwave, showing that the heating of the water system is caused by the molecular reaction of water to the microwave. Comparing the water-PEO mixed system to the pure water and pure PEO systems, the water-PEO mixed system has a higher heating rate than the pure PEO system but a lower heating rate than the pure water system. Therefore, we conclude that heating the water-PEO mixed system is driven by water molecules selectively activated by microwave irradiation. Furthermore, we also calculate the diffusion coefficients of water molecules and PEO chains by describing their mean square displacements, demonstrating that the diffusion coefficients are increased in the presence of microwaves for both water and PEO in pure and mixed systems. Lastly, during the microwave heating process, the structures of the water-PEO mixed system are altered as a function of the intensity of electric field, which is mainly driven by the response of water molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

High precision control of laser energy for laser–matter interaction studies

Precise, highly reproducible control of the laser energy is required for high confidence laser–matter interaction research such as in dynamic compression science and high energy density physics. The energy must be adjustable without affecting the pulse shape (time varying intensity) or beam smoothness. We have developed a convenient two-stage energy tuning method for a nominal 100 J, 351 nm (UV) laser. The energy is adjusted in 10 J (10%) increments by operating the laser at full energy and inserting a beam splitter in the laser output. As the splitter is located after the final frequency tripling optics, the UV pulse shape is unchanged. The energy is varied by substituting a splitter of different reflectivity. For finer 3 J (3%) increments, the infrared pulse is attenuated inside the laser before the final amplifier. This requires modest tuning to preserve the pulse shape. The demonstrated variation in shot-to-shot reproducibility is less than +/–2.5 J (5% of the full energy), irrespective of the laser output energy. These approaches can be adapted to most ~100 J class lasers. We describe these techniques and show two examples where they have elucidated the underlying physics in laser shock compression experiments. One used only the beam splitters to establish the pressure for melting in iron. The other combined both techniques to finely increment the peak stress (~2 GPa steps) in germanium to precisely determine the onset and completion of melting—including the melting kinetics. Furthermore, these unambiguous results would not be possible without the developments described here.

47 OTHER INSTRUMENTATION↗

Magnetron sputter deposition of boron carbide in Ne and Ar plasmas

Conventional magnetron sputter deposition of B 4 C uses Ar as the working gas. In this report we explore the magnetron sputter deposition of B 4 C with a Ne plasma, which is expected to exhibit larger sputtering yields than Ar. We study properties of films deposited with different substrate tilt angles with the magnetron source operated in either direct-current (DC) or radio-frequency (RF) mode in an Ar or Ne plasma. Results show that the B 4 C film properties are determined by a combination of sputtering ballistics and effects of the working gas on the plasma discharge and gas phase scattering of depositing species flux. At constant discharge power, deposition rates for Ar and Ne plasmas are similar, which is attributed to balancing effects of a higher ballistic sputtering yield of Ne and lower ion flux to the target. Both depositing B and C neutral species and bombarding ions have higher energies for the case of Ne plasmas. Films deposited with the RF-driven Ne plasma exhibit a uniform non-columnar structure, lowest oxygen impurity content, and highest mass density and mechanical properties at a cost of Ne incorporation and larger compressive residual stress.

36 MATERIALS SCIENCE↗

An Analytic Benchmark for Neutron Boltzmann Transport with Downscattering—Part I: Flux and Eigenvalue Solutions

Computing in the energy dimension is one of the greatest challenges confronting present-day deterministic neutron transport solvers. Accurately resolving the neutron flux as neutrons downscatter across resonances in the nuclear cross sections currently requires considerable computing power and suffers from approximation errors. Flux uncertainty resulting from the uncertainty of the resonance structure is the single-largest cause of reactivity uncertainty. Any additional reference solution for the critical neutron downscattering problem with resonance phenomena would be a boon to verification and validation of neutronics codes. This paper establishes a benchmark to verify the accuracy of neutron transport criticality solvers along the energy dimension. For the first time, the analytic solution of the flux amplitude is derived in the particular case of an infinite homogeneous medium with isotropic scattering in the center of mass and an arbitrary number of no-threshold, neutral particle reaction resonances (e.g., radiative capture, fission, and resonance scattering). Furthermore, original analytic expressions are established to quantify the discrepancy between the ψ k (E) and ψ α (E) flux amplitudes, respective solutions of the multiplication factor k, or the exponential time-evolution frequency α eigenproblems. The physical study of these relations led to analysis of their first-order relative difference near the criticality condition α=0. Finally, numerical solutions are provided to a benchmark problem constituted of the first resonance of 239 Pu, the 6.67-eV resonance of 238 U, and a scattering isotope with a flat cross section, allowing for the computational verification of the energy resolution of current neutron transport criticality codes. Through these novel results, this analytic benchmark can serve as a reference to verify the energy resolution and sensitivity analysis of neutron transport criticality calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

The Impact of Bias Row Noise to Photometric Accuracy: Case Study Based on a Scientific CMOS Detector

Abstract We tested a new model of CMOS detector manufactured by the Gpixel Inc, for potential space astronomical application. In laboratory, we obtain some bias images under the typical application environment. In these bias images, clear random row noise pattern is observed. The row noise also contains some characteristic spatial frequencies. We quantitatively estimated the impact of this feature to photometric measurements, by making simulated images. We compared different bias noise types under strict parameter control. The result shows the row noise will significantly deteriorate the photometric accuracy. It effectively increases the readout noise by a factor of 2–10. However, if it is properly removed, the image quality and photometric accuracy will be significantly improved.

Astronomy & Astrophysics↗

Dynamical exponent of a quantum critical itinerant ferromagnet: A Monte Carlo study

Here we consider the effect of the coupling between two-dimensional (2D) quantum rotors near an XY ferromagnetic quantum critical point and spins of itinerant fermions. We analyze how this coupling affects the dynamics of rotors and the self-energy of fermions. A common belief is that near a q = 0 ferromagnetic transition, fermions induce an Ω/q Landau damping of rotors (i.e., the dynamical critical exponent is z = 3) and Landau overdamped rotors give rise to non-Fermi liquid fermionic self-energy Σ∝ω 2/3 . This behavior has been confirmed in previous quantum Monte Carlo (QMC) studies. Here we show that for the XY case the behavior is different. We report the results of large-scale quantum Monte Carlo simulations, which show that at small frequencies z = 2 and Σ∝ω 1/2 . We argue that the new behavior is associated with the fact that a fermionic spin is by itself not a conserved quantity due to spin-spin coupling to rotors, and a combination of self-energy and vertex corrections replaces 1/q in the Landau damping by a constant. We discuss the implication of these results to experiments.

36 MATERIALS SCIENCE↗

Competing magnetic fluctuations and orders in a multiorbital model of doped SrCo 2 ⁢As 2

We revisit the intriguing magnetic behavior of the paradigmatic itinerant frustrated magnet Sr⁢Co 2 ⁢As 2 , which shows strong and competing magnetic fluctuations yet does not develop long-range magnetic order. By calculating the static spin susceptibility Χ⁡(q) within a realistic 16-orbital Hubbard-Hund model, we determine the leading instability to be ferromagnetic (FM). We then explore the effect of doping and calculate the critical Hubbard interaction strength U c that is required for the development of magnetic order. We find that U c decreases under electron doping and with increasing Hund's coupling J, but increases rapidly under hole doping. This suggests that magnetic order could possibly emerge under electron doping but not under hole doping, which agrees with experimental findings. We map out the leading magnetic instability as a function of doping and Hund's coupling and find several antiferromagnetic phases in addition to FM. We also quantify the degree of itinerant frustration in the model and resolve the contributions of different orbitals to the magnetic susceptibility. Lastly, we discuss the dynamic spin susceptibility Χ⁡(q,ω) at finite frequencies, where we recover the anisotropy of the peaks at Q π = (π,0) and (0,π) observed by inelastic neutron scattering that is associated with the phenomenon of itinerant magnetic frustration. By comparing results between theory and experiment, we conclude that the essential experimental features of doped SrCo 2 ⁢As 2 are well captured by an itinerant Hubbard-Hund multiorbital model if one considers a small shift of the chemical potential towards hole doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Anisotropic neutron star crust, solar system mountains, and gravitational waves

"Mountains" or non-axisymmetric deformations of rotating neutron stars (NS) efficiently radiate gravitational waves (GW). We consider analogies between NS mountains and surface features of solar system bodies. Both NS and moons such as Europa or Enceladus have thin crusts over deep oceans while Mercury has a thin crust over a large metallic core. Thin sheets may wrinkle in universal ways. Europa has linear features, Enceladus has "Tiger" stripes, and Mercury has lobate scarps. NS may have analogous features. The innermost inner core of the Earth is anisotropic with a shear modulus that depends on direction. If NS crust material is also anisotropic this will produce an ellipticity, when the crust is stressed, that grows with spin frequency. This yields a braking index (log derivative of spin down rate assuming only GW spin down) very different from n=5 and could explain the maximum spin observed for neutron stars and a possible minimum ellipticity of millisecond pulsars.

79 ASTRONOMY AND ASTROPHYSICS↗

Microwave-Free Dynamic Nuclear Polarization via Sudden Thermal Jumps

Dynamic nuclear polarization (DNP) presently stands as the preferred strategy to enhance the sensitivity of nuclear magnetic resonance measurements, but its application relies on the use of high-frequency microwave to manipulate electron spins, an increasingly demanding task as the applied magnetic field grows. Here we investigate the dynamics of a system hosting a polarizing agent formed by two distinct paramagnetic centers near a level anticrossing. We theoretically show that nuclear spins polarize efficiently under a cyclic protocol that combines alternating thermal jumps and radio-frequency pulses connecting hybrid states with opposite nuclear and electronic spin alignment. Central to this process is the difference between the spin-lattice relaxation times of either electron spin species, transiently driving the electronic spin bath out of equilibrium after each thermal jump. Without the need for microwave excitation, this route to enhanced nuclear polarization may prove convenient, particularly if the polarizing agent is designed to feature electronic level anticrossings at high magnetic fields.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Universal Fourier Attack for Time Series

A wide variety of adversarial attacks have been proposed and explored using image and audio data. These attacks are notoriously easy to generate digitally when the attacker can directly manipulate the input to a model, but are much more difficult to implement in the real world. In this paper we present a universal, time invariant attack for general time series data such that the attack has a frequency spectrum primarily composed of the frequencies present in the original data. The universality of the attack makes it fast and easy to implement as no computation is required to add it to an input, while time invariance is useful for real world deployment. Additionally, the frequency constraint ensures the attack can withstand filtering defenses. We demonstrate the effectiveness of the attack on two different classification tasks through both digital and real world experiments, and show that the attack is robust against common transform-and-compare defense pipelines.

97 MATHEMATICS AND COMPUTING↗

Correction for Neutral Pressure-Driven Signal in Radiated Power Measurements on Proto-MPEX

A pinhole camera using four-channel resistive bolometers was designed and implemented on the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) to measure the plasma radiated power. Quantification of the radiated power is required for comprehensive power balance assessments but faces unique challenges on linear plasma devices due to weak absolute signal, compared to typical use in toroidal fusion plasmas, and high neutral pressure changes. Around 1 mTorr, the pressure-driven signal contribution was shown to overwhelm the radiated power signal in Proto-MPEX, found to be ~3 μW . Since the pressure-driven signals could not be predicted from first principle arguments, the signals were corrected using empirical models that take two experimental pressure measurements and the raw bolometer signal to reveal the radiated power signals. Four “gas-only” Proto-MPEX shots were taken, without the radio frequency (rf) plasma discharge, to train, optimize, and validate empirical models. The data included two pressure measurements at different locations along with the bolometer signal. Multiple models were tested; partial least-squares regression with a cross correlation method to account for the time offset in the pressure measurements provided the best combination of accuracy and stability. The model was validated to have a modeling error of 0.0036 V, which was lower than 10% of the expected radiated power signal. The model was tested on a different “gas-only” shot with a complete time-series data. For plasma operation shots, the corrected bolometer measurements were compared with an absolute extreme ultraviolet photodiode measurement and similarities and differences are discussed.

Lee, Seungsup↗