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Abstract

Effect of illumination distribution in the circle of confusion on the measurement of the photoelectric coupling coefficient of the second-generation photodetector devices is studied. A theoretical study is carried out using mathematical modeling for illumination patterns of different structure and several ratios of photodetector pitch to the effective size of the photosensitive area. A formula is derived for calculation of the photoelectric coupling coefficient for a known distribution of photodetector sensitivity. The main conditions that affect the reliability of the results on the simulated measurement process are presented.

Abstract

Distributions of dark currents, lifetimes of minority carrier, and microdefects revealed by selective etching are compared. The main reason for increased dark currents and decreased photosensitivity in silicon photodiodes fabricated on n-type silicon using the Czochralski method are the generation–recombination processes on fine oxide precipitates.

Abstract

The results of the development of a recursive algorithm for temporal noise reduction with an adaptive threshold for thermal imaging systems are presented. This algorithm is designed to reduce the level of temporal noise based on the results of analyzing a sequence of images obtained using a thermal imaging channel. A mathematical model of the algorithm is provided, as well as the required amount of computing resources needed for its hardware implementation in field programmable gate arrays (FPGAs). Several characteristics of the thermal imaging system with the developed algorithm were measured and conclusions were made about the positive influence of the algorithm on its noise equivalent temperature difference (NETD).

Abstract

The resonant scattering spectra by the main magnetic mode of a subwavelength linear structure consisting of two dielectric flat thin rings located along the wave vector and excited by the displacement currents of the incident plane electromagnetic wave of the microwave range are investigated experimentally and using computer modeling. As distinct from a single ring, splitting of the resonant frequency is observed in the scattering spectra of the magnetic field in the far wave zone, near wave zone, and near the centers of the rings. The measured spectra coincide with the spectra resulting from computer calculations at all measurement points.

Abstract

For the task of Earth remote sensing (ERS) in the short-wave infrared (IR) range of the spectrum, the most promising are matrix and multi-row photodetector modules of the short-wave infrared (IR) range of the spectrum based on heteroepitaxial structures of materials of the ternary solution of cadmium-mercury-tellurium (HgCdTe) and the ternary solution of indium-gallium-arsenide (InGaAs), sensitive in the spectral range from 1 to 2.5 μm. Possible architectures of photosensitive elements that provide reduced dark currents and noise are analyzed. Ways of improvement are considered and dark currents and parameters of n-on-p-type heterostructures based on HgCdTe in a wide temperature range, as well as the parameters of p+-B–n-N+-type barrier structures based on InGaAs are investigated.

Abstract

An overview of various sensor designs for recording the parameters of microparticles in the accelerator path is provided, which are used to simulate the impact of micrometeoroids and space debris particles on structural elements of a spacecraft. A model of a cylindrical induction sensor (a Faraday cup) and a possible modification of its design for measuring the microparticle distribution in the accelerator path are considered in more detail.

Abstract

The parameters of photodetectors based on photosensitive barrier structures and photodiodes with absorbing layers of InAs1–xSbx and In1–xGaxSb ternary solutions of the mid-wave infrared spectrum range are studied. Temperature dependences of lifetime and dark current in InAs1–xSbx and In1–xGaxSb layers have been calculated. The signal-to-noise ratio in the operating temperature range was determined. Parameter modeling has shown that for photodetectors based on InAs0.8Sb0.2 with a cutoff wavelength λ0.5 ∼ 4.8 µm the detectability at T = 100 K will be D* ≈ 1012 cm W–1 Hz1/2; for photodiodes based on In0.7Ga0.3Sb with cutoff wavelength λ0.5 ∼ 5.2 µm the detectability at T = 100 K will be D* ≈ 1011 cm W–1 Hz1/2, which is suitable for high temperature applications.

Abstract

A new deselection method has been developed for detecting defects in infrared photomodules (IR PMs) with time delay and accumulation mode (TDM). The developed method is used to detect and deselect defective photosensitive elements (PSEs), which most reduce the signal-to-noise ratio (SNR) in IR PM channels. This method increases the SNR of IR PM channels, which improves the ability of IR PMs to detect low-power infrared optical signals. This result is ensured by the fact that the detection of defective PSEs is achieved by processing the signals and noise of all PSEs using the detection criterion of PSEs that most reduce the SNR of the IR PM channels. This method is a general rule for detecting defective PSEs, since the criterion analyzes the influence of all PSEs on the SNR of IR PM channels, including the noisiest elements.

Abstract

The electric field on the surface of a metal electrode immersed in plasma with an electron temperature of Te ∼ 10 eV and plasma density ne from 1010 to 1013 cm−3 has been calculated under negative electric potential Ψ0 of the electrode and large values of parameter |eΨ0|/Te  \( \gg \)  1. The obtained asymptotic formula for the field strength at |eΨ0|/Te  \( \gg \)   1 differs significantly from the classical formulas for calculating the electric field and the Debye length of field screening near the electrode surface in plasma, which are valid under condition |eΨ0|/Te  \( \ll \)  1. It has been shown that, at |eΨ0|/Te  \( \gg \)  1, near the electrode in a plasma, a modified Debye layer can exceed the classical Debye length by two orders of magnitude. To calculate the electric field on the electrode surface in plasma, a generalized formula has been proposed in the explicit form, which is valid in a wide range of parameter 0 < |eΨ0|/Te < 104 at negative electrode potentials of up to 10 kV.

Abstract

The electrostatic reflection method is formulated and proven for a point charge located near a plane-layered medium consisting of two films on a dielectric half-space. The method is generalized to the case of an arbitrary system of charges and is used to solve mathematically similar problems of electrostatics and the stationary thermal conductivity of plane-layered media. The problem of finding the electrostatic potential distributions around a conducting sphere located near a plane-layered structure consisting of two dielectric films on a dielectric half-space is solved. Solutions to similar problems of finding the temperature distribution of uniformly heated bodies located near a heat-conducting plane-layered structure of two heat-conducting films on a heat-conducting half-space are discussed.

Abstract

Global ionospheric total electron content (TEC) map prediction is important for improving the accuracy of global navigation satellite systems. There are two main issues with the current TEC prediction: (1) The deep learning models used for TEC prediction are mainly designed using a stacked structure. When stacking multiple layers, the input data will undergo continuous multi-layer convolution operations, leading to the loss of fine-grained features and the degradation of model performance; (2) The model optimization methods for TEC prediction are relatively outdated, mainly using manual optimization or grid search methods. To address these two issues, an automatic framework for global TEC map prediction and optimization is proposed, named as CGAOA-STRA-BiConvLSTM. It includes a global TEC map prediction model, STRA-BiConvLSTM, which can simultaneously extract both coarse-grained and fine-grained spatiotemporal features. It also contains an optimization algorithm, CGAOA, to optimize the model. We first experimentally verified the effectiveness of CGAOA. Then, the effectiveness of STRA-BiConvLSTM was verified through ablation experiments. Finally, we conducted comparative experiments from multiple perspectives between our framework and 5 mainstream methods: C1PG, C2PG, ConvLSTM, ConvGRU, and ED-ConvLSTM. The results show that in all cases, the proposed CGAOA-STRA-BiConvLSTM outperforms the comparative models.

Nature Geoscience, Published online: 20 January 2025; doi:10.1038/s41561-024-01634-8

The Martian dichotomy boundary receded hundreds of kilometres in the Mawrth Vallis region and left behind mounds that record changing aqueous conditions during the Noachian (4.1–3.7 Ga), according to a geomorphological and spectroscopic study.

SummaryForward modeling is crucial for seismic data processing, which is the core of reverse time migration and full-waveform inversion. Numerical simulation based on conventional elastic wave equations in stationary solids neglects the fluidity of fluids (e.g., seawater), making it difficult to simulate the propagation of seismic waves in moving fluids accurately. To solve the problem, we start with classical equations of fluid mechanics and derive a new set of elastic wave equations that can be used to simultaneously model wave propagation both in moving fluids and stationary solids. For high-precision numerical simulations, a staggered-grid finite-difference scheme is used to solve the proposed equations. Numerical tests on a homogeneous uniformly moving model demonstrate that the dynamic and kinematic characteristics (e.g., wavelength, amplitude) of elastic waves in moving fluids are quite different from those in stationary medium. Forward modeling for a two-layer model that has a flowing water layer and a stationary rock layer is used to study the reflection and transmission patterns of elastic waves in the solid-fluid interface. With the help of the superposition principle of vectors and Snell's law, the transmission angles can be easily calculated. A further test for a more complex stratified model indicates that the energy and travel time differences of reflected waves are expected to be evidence for the identification of moving fluids. Numerical experiments on the Marmousi II model demonstrate that the relative wavefield error is positively correlated with the maximum moving velocity and the wavelet dominant frequency.

SummaryDispersion curves of surface waves are widely used for the inversion of subsurface structures. To extract dispersion curves, many methods have been developed. Among them, multichannel analysis of surface waves such as slant stack and frequency-Bessel transform can extract not only the fundamental mode but also overtones. Inversion with overtones is proven to be more stable and has better resolution at greater depths. However, with a limited number of array receivers, artifacts and misfits due to array-layout effects arise in the dispersion spectra and impede the identification of dispersion curves. We evaluate the array-layout effects in the frequency-Bessel transform and calculate the array response functions which can help to mitigate artifacts and calibrate dispersion curves. We apply this technique to synthetic simulated, active source and ambient noise data. The artifacts caused by array-layout effects can be mitigated, which helps the identification of dispersion curves. We further calculate the Pearson correlation coefficient between the array response function and the dispersion spectrum section. It is used to calibrate the biases produced by the array-layout effects if we select dispersion curves by maximum values. The confidence intervals of the dispersion curves are then determined based on the correlation coefficients. It is helpful for the design of array layouts according to the investigation depths of interest.

SummaryPowerful infrasound (acoustic waves <20 Hz) can be produced by explosive volcanic eruptions. The long-range propagation capability, over hundreds to thousands of kilometers, of atmospheric infrasound motivates the development of regional or even global scale volcano-infrasound monitoring systems. Infrasound propagation paths are subject to spatiotemporal atmospheric dynamics, which lead to deviations in the direction-of-arrival (back-azimuth) observed at sensor arrays and contribute to source location uncertainty. Here we further investigate the utility of empirical climatologies combined with 3-dimensional ray-tracing for providing first-order estimates of infrasound propagation paths and back-azimuth deviation corrections. The intended application is in scenarios requiring rapid or precomputed infrasound propagation calculations, such as for a volcano-infrasound monitoring system. Empirical climatologies are global observationally based function fitting models of the atmosphere, representing robust predictors of the bulk diurnal to seasonal atmospheric variability. Infrasound propagation characteristics have previously been shown to have strong seasonal and diurnal components. At the International Monitoring System (IMS) infrasound station IS22, New Caledonia, quasi-continuous multi-year infrasound array detections show oscillating azimuthal variations for arrivals from volcanoes in Vanuatu, including Yasur (∼400 km range), Ambrym (∼670 km range), and Lopevi (∼650 km range). We perform 3-dimensional ray-tracing to model infrasound propagation from the Ambrym and Yasur volcano locations to IS22 every six hours (00:00, 06:00, 12:00, and 18:00 UTC) for every day of 2004 and 2019 for Ambrym and Yasur, respectively and evaluate the results as compared to the multi-year observations. We assess a variety of models and parameterizations, including both empirical climatologies and hybrid descriptions; range-independent and range dependent atmospheric discretizations; and unperturbed and perturbed range-independent empirical climatologies. The hybrid atmospheric descriptions are composed of ERA 5 reanalysis descriptions from the European Centre for Medium-Range Weather Forecasts (ECMWF) below ∼80 km altitude combined with empirical climatologies above. We propose and employ simple parametric perturbations to the empirical climatologies, which are designed to enhance the stratospheric duct and compensate for missing gravity wave perturbations not included in the climatologies, and thereby better match observations. We build year-long back-azimuth deviation interpolations from the simulations and compare them with three different multi-year array detection datasets from IS22 covering from 2003 up to 2022. Through a systematic comparison, we find that the range-independent empirical climatologies can capture bulk azimuth deviation variability and could thus be useful for rapid infrasound propagation calculation scenarios, particularly during favorable sustained propagation ducting conditions. We show that the hybrid models better describe infrasound propagation during periods of weak stratospheric ducting and during transient atmospheric changes such as stratospheric wind reversals. Overall, our results support the notion that climatologies, if perturbed to compensate for missing gravity wave structure, can improve rapid low-latency and precomputed infrasound source discrimination and location procedures.

Abstract

The Rashid-1 lunar rover represented the first attempt by the United Arab Emirates to explore the surface of the Moon. The mission of Rashid-1 was supposed to begin only a few hours following the planned landing by the iSpace Hakuto-R M1 lunar lander inside the Atlas crater of the Moon. Unfortunately, the lander was unable to successfully complete the landing maneuver and it crashed on the surface of the Moon destroying both itself and its payloads in the process. In this paper, we present the characterization of the optical image acquisition systems onboard the Rashid-1 rover which consisted of two wide-field ( \(82^{\circ } \times 82^{\circ }\) ) identical cameras aptly named CAM-1 and CAM-2 and mounted on the front and back of the rover respectively. Additionally, a third high resolution optical imager (CAM-M) with a spatial resolution of approximately 27 μm/pixel was placed on the front of the rover and was tasked with obtaining what would have been, at that time, the highest resolution in-situ images ever taken of the lunar regolith. We discuss the basic calibration processes such as the thermal, radiometric, color, distortion and perspective corrections of the three optical systems. We also provide an overview of both the onboard as well as the ground processing steps that were set up to receive and examine the images the rover would have sent from the lunar surface.

Abstract

Metasomatism refers to the process during which a pre-existing rock undergoes compositional and mineralogical transformations associated with chemical reactions triggered by the reaction of fluids which invade the protolith. It changes chemical compositions of minerals, promotes their dissolution and precipitation of new minerals. In this paper, we review metasomatic alteration of type 3 ordinary (H, L, LL) and carbonaceous (CV, CO, CK) chondrites, including (i) secondary mineralization, (ii) physicochemical conditions, (iii) chronology (53Mn-53Cr, 26Al-26Mg, 129I-129Xe) of metasomatic alteration, (iv) records of metasomatic alteration in H, O, N, C, S, and Cl isotopic systematics, (v) effects of metasomatic alteration on O- and Al-Mg-isotope systematics of primary minerals in chondrules and refractory inclusions, and (vi) sources of water ices in metasomatically altered CV, CO, and ordinary chondrites, and outline future studies.

In this paper, we augment airborne gravity anomaly data from Antarctica, expanding the coverage area by 10.4% based on the existing data set. These data are combined with a gravity field model to establish a m...

Carbon dioxide in the atmosphere is increasing at rates that are incompatible with staying below 1.5 degrees Celsius (2.7 degrees Fahrenheit) of global warming, a Met Office study warns.

Abstract

Latest harmonic developments of the Earth tide-generating potential (TGP), e.g., HW95 (Hartmann and Wenzel in Geoph Res Lett 22:3553, 1995), RATGP95 (Roosbeek in Geophys J Int 126:197, 1996), KSM03 (Kudryavtsev in J Geodesy 77:829, 2004), include a number of terms caused by the joint effect of the Earth’s polar flattening (that can be numerically described by the \({J}_{2}\) geopotential coefficient) and the Moon/the Sun gravitational attraction. In the present study, we additionally consider the effect of the Earth’s equatorial flattening due to the Earth’s triaxiality. Explicit analytical expressions for the relevant part of the TGP are derived. New terms of the TGP development due to the Earth’s triaxial figure are found. Amplitudes of nineteen of them exceed the threshold level of 10–8 m2s−2 used by the modern tidal potential catalogs. Three of the new terms have the frequency sign opposite to that of the Earth rotation. It is not the case for any previously known term of the Earth TGP development. Every term has a new feature that an integer multiplier of the mean local lunar time used in its argument is not equal to the order of the spherical harmonic associated with the term. It necessitates a relevant modification of the standard HW95 format for representing the Earth TGP. The new terms are suggested for including in the current and future tidal potential catalogs.