Southwest Research Institute

The univariate t statistic is well-known to most data analysts. If a random sample of n observations is taken from a normal distribution with mean μ and variance σ 2, the form of the statistic is given by where $\overline x$ is the sample mean and s is the sample standard deviation. This statistic has a Student t-distribution with ( n − 1) degrees of freedom. Squaring the statistic, we obtain

Statistical process control (SPC) includes the use of statistical techniques and tools, such as control charts, to monitor change in a process. These are typically applied separately to each process variable of interest. Statistical process control procedures help provide an answer to the question: “Is the process in control?” When an out-of-control event is identified as a signal in a control chart, procedures often are available for locating the specific process variables that are the cause of the problem.

Magnetic reconnection is a fundamental process that converts magnetic energy into particle energy, with wide applications in space plasmas. A key manifestation of this energy conversion is the acceleration of fast ion outflows. However, ion processes and their associated signatures in energy conversion remains only partially understood in collisionless magnetic reconnection. In this study, we utilize statistical analyses of in‐situ observations and particle‐in‐cell (PIC) simulations to identify a distinct signature in the off‐diagonal component of the ion pressure tensor. This signature displays a bipolar reversal that correlates with ion outflows across the reconnection X‐line. The bipolar signal originates from distorted ion velocity distributions during acceleration. These signals are confirmed by statistical in‐situ evidence for the first time and captured by PIC simulations. PIC simulations further indicate the peak of the off‐diagonal ion pressure is near the magnetic pileup region associated with the ion outflow. Trajectories of ions in the distorted velocity distributions are traced within the PIC simulations. Ions in the distorted distributions undergo partial cyclotron motion around the reconnected magnetic field (Bz) and acceleration by the reconnection electric fields. The observation of bipolar reversal in the off‐diagonal ion pressure term indicate its spatial gradient, which could contribute to supporting ion‐scale reconnection electric fields. These findings provide new insights into the fundamental features of energy conversion in collisionless magnetic reconnection.

NASA’s Cassini mission revealed endogenic activity at the south pole of Saturn’s moon Enceladus. The activity is concentrated along four fractures in Enceladus’ ice shell, which are much warmer than their surroundings and the source of Enceladus’ plumes. This work provides a review of the current state of knowledge of the energy and mass lost by Enceladus through this activity. Specifically, we discuss the composition of the plumes, along with their spatial and temporal variation. The mass flux loss predicted for the three plume constituents (gas, dust and charged particles) is reviewed and a total mass flux of ejected material that subsequently escapes Enceladus is estimated to be $2.1\times 10^{11}$ kg over a Saturn year. Given that Enceladus’ ocean is predicted to be 10¹⁹ kg this loss is sustainable in the very long term (∼1.5 billion Earth years). However, unless a resupply mechanism (such as serpentinization) exists molecular hydrogen is expected to be depleted within ∼1 million Earth years. The difficulty in determining Enceladus’ current heat flow is outlined, along with the advantages and disadvantages of the various techniques used to derive it. We find a robust lower limit for Enceladus’ exogenic production is 7.3 GW. Tidal heating models show endogenic emission of this level is sustainable, and Enceladus may have long-term near-surface heating (a result supported by studies of Enceladus’ geology). Finally, we offer suggestions for future observations, instrumentation, and missions. Enceladus remains a high-priority target for NASA, and as such it is highly likely that we will return to study this enigmatic world. Hopefully these missions will answer some of the questions that remain.

Plain Language Summary The upper atmosphere of Jupiter (overwhelmingly hydrogen) is ionized into a layer of electrons and ions forming the ionosphere. This layer is critical to understanding energy and heat flow through a planet's atmosphere, yet is a turbulent, rapidly changing region. Most spacecraft visit the equatorial regions of Jupiter, but the Juno spacecraft is the first orbiter to be in a polar orbit, visiting the planet's poles as it comes close to the planet roughly every 35 days. When the spacecraft goes behind the planet, a disappearance called an occultation, the radio signals being sent from the spacecraft pass through the ionosphere of Jupiter and undergo a frequency shift due to the electrons along the signal's path. The amount of distortion gives a column density along this pathway, and using a technique called onion peeling the density at each layer can be calculated by subtracting off the amount determined in higher layers. Jupiter is not a sphere but a squished (oblate) oval, which complicates the calculation of local density. The resulting profiles show that the Jovian ionosphere varies dramatically in density and altitude between observations, but tends to have either narrow, dense electron layers below 1,000 km of altitude, or a broad, lower density layer around 2,000 km.

The highly elliptical polar orbit of the Juno mission provides a unique opportunity to simultaneously measure the compression state of Jupiter's magnetosphere and the total power emitted by the planet's ultraviolet aurora, using a single spacecraft. This allows us to study how Jupiter's aurora respond to a compression event. In this paper, we present a case study of an extreme compression event that occurred on December 6–7 2022 when Juno was a distance of 70 RJ from Jupiter. This extreme compression was accompanied by a very large increase in the ultraviolet auroral emissions to 12 TW, a factor of six higher than the baseline level. This event coincided with the predicted arrival of a powerful interplanetary shock, which was expected to cause the largest increase in the solar wind dynamic pressure seen thus far during the Juno mission. The simultaneous occurrence of the interplanetary shock, the extreme compression and the bright ultraviolet aurora suggests that in this case, the auroral brightening was caused by the solar wind shock compressing the magnetosphere.

On the morning of December 8, 2018, two sounding rockets were launched into the northern hemisphere cusp region to investigate the spatial and temporal nature of cusp structures. The two rockets, designated Twin Rockets to Investigate Cusp Electrodynamics 2 (TRICE-2), consisted of a high- and a low-flyer rocket launched two minutes apart. The TRICE-2 mission was a pathfinder for the upcoming Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission and carried almost identical payloads to those proposed for the twin spacecraft of the TRACERS mission. Results from the TRICE-2 mission are summarized, including observed cusp features (low energy ions in the cusp, overlapping cusp ion dispersions and cusp ion signatures) and the connection of the cusp structures to ionospheric convection cells, provided by SuperDARN radar observations, to show the advantages of coordinated space and ground-based observations. A description is provided for how these results – and those of other experiments which made measurements of particles and waves in the cusp and in the dayside magnetosphere – have guided the science objectives of the TRACERS mission.

The Sun’s corona is its tenuous outer atmosphere of hot plasma, which is difficult to observe. Most models of the corona extrapolate its magnetic field from that measured on the photosphere (the Sun’s optical surface) over a full 27-day solar rotational period, providing a time-stationary approximation. We present a model of the corona that evolves continuously in time, by assimilating photospheric magnetic field observations as they become available. This approach reproduces dynamical features that do not appear in time-stationary models. We used the model to predict coronal structure during the total solar eclipse of 8 April 2024 near the maximum of the solar activity cycle. There is better agreement between the model predictions and eclipse observations in coronal regions located above recently assimilated photospheric data.

This work demonstrates a fiber Bragg grating strain sensor system by utilizing the enhanced microwave-photonic Vernier effect, which is generated from two parallel fiber rings inserted with linear chirped fiber Bragg gratings (FR-LCFBGs). The two LCFBGs are configured in forward and backward orientations, enabling the external strain-induced center wavelength shift of the FBG sensor to be converted into frequency shifts in opposite directions within two microwave resonant rings. As a result, the enhanced Vernier effect can be constructed, which greatly improves the strain sensitivity of the system. The experimental results reveal that the sensor based on parallel FR-LCFBGs achieves the strain measurement sensitivity of 102.8 kHz/με with the help of the enhanced Vernier effect, being 175.4 times that in the single FR-LCFBG. Therefore, the proposed device may have potential applications in weak strain measurement.

Organic matter (OM) serves as the primary source of gaseous hydrocarbons in shales. Fundamental understanding of its permeability and gas production characteristics is vital to optimize shale gas exploitation. The focused ion beam scanning electron microscopy (FIB-SEM) imaging can resolve OM macropores with pore radii ranging from tens to hundreds of nanometers, while pore sizes of sub-resolution OM can be characterized using low-temperature gas adsorption. In this work, we focus on multiscale pore structures of OM and contribute to the development of an efficient pore-network-continuum model for simulating nonlinear gas flow in multiscale OM digital rocks, along with its fully coupled implicit numerical implementation. To demonstrate the influence of OM pore structures on its permeability and transient gas production, we select three types of OM featured by their distinct porosities, connectivity of macropores, and pore morphologies. We show that the high-porosity OM with interconnected macropores exhibits markedly different intrinsic permeability, mechanisms of apparent permeability, gas storage, and production behaviors compared to the medium-porosity and low-porosity OM. Moreover, we propose an empirical formula for OM apparent permeability with respect to an effective characterization length used in the calculation of Knudsen number, which will be the key input to the representative elementary volume (REV) size modeling of shale matrix.

Magnetic reconnection is an explosive energy release event. It plays an important role in accelerating particles to high non‐thermal energies. These particles often exhibit energy spectra characterized by a power‐law distribution. However, the partitioning of energy between thermal and non‐thermal components, and between ions and electrons, remains unclear. This study provides estimates of energy partition based on a statistical analysis of magnetic reconnection events in Earth's magnetotail using data from the Magnetospheric Multiscale mission. Ions are up to 10 times more energetic than electrons but have softer spectra. We found for both ions and electrons that, as the average energy of particles (temperature) increases, their energy spectra become softer (steeper) and thus, the fraction of energy carried by the non‐thermal components decreases. These results challenge existing theories of particle acceleration through magnetotail reconnection.

When investigating tenuous densities, in situ mass spectrometry is often limited by the background of the spacecraft. Technological advancements continue to improve overall sensitivity and mass resolution, but background gas not associated with the targeted environment continues to be the limiting factor for future exploration. In space-based applications, background gas is generated through outgassing of the spacecraft and instrument and varies depending on conditions such as illumination, temperature, and particle exposure. This is particularly difficult when studying tenuous atmospheres, such as the exosphere of Mercury for example, where the number density of a species of interest can be less than the number density of outgassing constituents from the spacecraft. To mitigate this problem, either a background suppression system is needed or the outgassing rate and its temporal variation need to be documented and, if possible, corrected for in later data analysis. Strofio is a neutral gas mass spectrometer and one of the scientific instruments on the BepiColombo mission to study the exosphere of Mercury, equipped with a velocity filter for background gas suppression. We simulated the velocity filter under Mercury-like conditions, where the spacecraft travels at 3 km/s relative to the exospheric gas, and we verified its performance in the laboratory. Our results demonstrate that a properly optimized configuration can reduce the contribution from background gas by a factor of 40, significantly improving the in situ detection of neutrals. This highlights the effectiveness of velocity-filtering techniques for studying Mercury’s exosphere and other tenuous planetary atmospheres.

Unconventional shale gas reservoirs are a vital component of oil and gas exploration and development, and hydraulic fracturing is typically required to enhance reservoir permeability. Deep shale reservoirs are characterized by numerous thin layers, complex layer interfaces, and significant property variations between layers, which severely restrict the process of hydraulic fracture propagation. Currently, the propagation patterns of hydraulic fractures under the influence of interlayers and interfaces with varying properties remain unclear. In this study, based on the primary characteristics of deep shale reservoirs in the southern Sichuan Basin, a three-dimensional (3D) fracture propagation model that incorporates the effects of interlayers and interfaces was established using the discrete lattice method. Numerical simulations were conducted to investigate hydraulic fracture propagation under various conditions of interlayer thickness, interface strength, and dilation angle. The study found that interlayers and interfaces hinder the vertical propagation of hydraulic fractures, with shear failure occurring primarily at the interfaces and tensile failure dominating in the surrounding matrix. With the increase in interface tensile strength, friction angle, and cohesion, the hydraulic fracture changes from propagating along the interface to penetrating the interface. When the interface tensile strength is 5 MPa, the friction angle is 35°, and the cohesion is 10 MPa, the hydraulic fracture penetrates the interface significantly, with only a small part propagating along the interface. As the interface dilation angle increases, the ability of hydraulic fractures to penetrate the interface gradually weakens. When the interface dilation angle is greater than 10°, the hydraulic fracture is completely blocked. The research results can provide a theoretical basis for controlling fracture height and hydraulic fracture layer-crossing during on-site fracturing operations, contributing to efficient fracturing and reservoir stimulation.

Metal sulfides with high theoretical capacities have gradually gained attention as preferable anode materials for sodium-ion batteries. Tetragonal Cu3SbS4/rGO was synthesized by solvent thermal and ball milling and evaluated for the first time as lithium/sodium/potassium-ion battery anode material via constant current charge/discharge, rate charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Ex-situ XRD revealed the lithium/sodium/potassium-ion mechanisms of the Cu3SbS4 anode, indicating that its capacity was mainly provided by the alloying reaction and conversion reaction. Due to high electrical conductivity of rGO, the Cu3SbS4/rGO electrode exhibited lower charge transfer resistance and more stable structure during charge/discharge process, reversible capacity and cycle performance of the Cu3SbS4/rGO were significantly improved compared with pristine Cu3SbS4. Therefore, the Cu3SbS4/rGO showed a discharge capacity of 283.9 mAh g⁻¹ after 500 cycles at 1 A g⁻¹ in lithium-ion batteries, a discharge capacity of 243.4 mAh g⁻¹ after 300 cycles at 1 A g⁻¹ in potassium-ion batteries and a discharge capacity of 193.0 mAh g⁻¹ at 9 A g⁻¹ in sodium-ion batteries. The results showed that Sb-based bimetallic sulfide have a certain development prospect as the anodes for lithium/sodium/potassium-ion batteries. Graphical abstract Ex-situ XRD patterns and discharge/charge curves of the electrodes in initial cycle for LIBs/SIBs/PIBs

High-resolution helioseismology observations with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) provide a unique three-dimensional view of the solar interior structure and dynamics, revealing a tremendous complexity of the physical processes inside the Sun. We present an overview of the results of the HMI helioseismology program and discuss their implications for modern theoretical models and simulations of the solar interior.

Exoplanetary systems that contain multiple planets on short-period orbits appear to be prevalent in the current observed exoplanetary population, yet the processes that give rise to such configurations remain poorly understood. A common prior assumption is that planetary accretion commences after the infall of gas and solids to the circumstellar disk ended. However, observational evidence indicates that accretion may begin earlier. We propose that compact systems are surviving remnants of planet accretion that occurred during the final phases of infall. In regions of the disk experiencing ongoing infall, the planetary mass is set by the balance between accretion of infalling solids and the increasingly rapid inward migration driven by the surrounding gas as the planet grows. This balance selects for similarly-sized planets whose mass is a function of infall and disk conditions. We show that infall-produced planets can survive until the gas disk disperses and migration ends, and that across a broad range of conditions, the mass of surviving systems is regulated to a few × 10⁻⁵ to 10⁻⁴ times the host star’s mass. This provides an explanation for the similar mass ratios of known compact systems.

We report the first simultaneous observations of wave activity and pickup ions (PUIs) in the pristine solar wind upstream of Earth's bow shock (i.e., at 1 au) from the Magnetospheric Multiscale (MMS) mission. Low‐frequency electromagnetic waves induced by newborn interstellar PUIs have been confirmed as the dominant energy source that drives turbulence and thermal ion heating in the solar wind beyond 1 au. However, only a few observations of PUI‐generated waves exist near 1 au. Near 1 au, these waves are relatively weak and are best observed in the pristine solar wind, absent of any other wave activity or energized ion populations. In this work, we analyze a ∼3 min interval during which Earth was within the He focusing cone and MMS was in the pristine solar wind. We identify H⁺ and He⁺ PUI ring distributions provided by the Hot Plasma Composition Analyzer and compare their velocity space characteristics, which reveals that these PUIs were likely born from different neutral source populations (e.g., geocornal hydrogen and interstellar helium). We also identify potential signatures of distinct helium and hydrogen wave modes in the magnetic field power spectrum and perform a linear instability analysis which identifies the distinct wave growth rates. The peak growth rates coincide with enhancements in the magnetic power spectrum, suggesting that these waves could be generated by the observed H⁺ and He⁺ PUIs. These observations motivate the need for a systematic study of PUI‐generated waves near 1 au, which can be achieved using MMS data.

The Lucy Thermal Emission Spectrometer (L’TES) instrument acquired hyperspectral thermal infrared (TIR) observations of the Earth's Moon during Lucy's 2022 Earth gravity assist. L’TES covers the spectral range of 100–1,750 cm⁻¹ (100–5.8 μm) at a spectral sampling of 8.64 cm⁻¹ (Christensen et al., 2023, https://doi.org/10.1007/s11214‐023‐01029‐y). The field of view (FOV) is 7.3‐mrad, giving a spatial resolution on the Moon of 1,650 km. Seventeen high‐quality spectra of the warm disk were acquired of Oceanus Procellarum that provide the first well‐calibrated TIR observations of the Moon with high spectral resolution. The lunar surface emissivity was determined by modeling the surface radiance using two different methods that gave nearly identical results. The L’TES spectra have Christiansen feature (CF) maxima at 1,226 cm⁻¹ (8.15 μm), a spectral band depth of ∼0.04, and a downward slope at wavenumbers >1,200 cm⁻¹ that is characteristic of <100 μm particles. Comparison with Diviner 3‐point spectral data (Greenhagen et al., 2010, https://doi.org/10.1126/science.1192196) shows excellent agreement in the CF location and band shape. The L’TES spectra closely match several lunar soil laboratory spectra (Donaldson‐Hanna et al., 2017, https://doi.org/10.1016/j.icarus.2016.05.034), providing excellent ground truth for the L’TES observations, validating the L’TES data processing, and demonstrating that high‐spatial and spectral resolution TIR data would provide a powerful tool for remote compositional mapping. The L’TES nightside observations accurately derived surface temperatures at 110 K, even when the Moon only filled 10% of the FOV, confirming that L’TES will accurately determine the cold Trojan asteroid temperatures.

The decline in malaria deaths has recently stalled owing to several factors, including the widespread resistance of Anopheles vectors to the insecticides used in long-lasting insecticide-treated nets (LLINs)1,2. One way to mitigate insecticide resistance is to directly kill parasites during their mosquito-stage of development by incorporating antiparasitic compounds into LLINs. This strategy can prevent onward parasite transmission even when insecticides lose efficacy3,4. Here, we performed an in vivo screen of compounds against the mosquito stages of Plasmodium falciparum development. Of the 81 compounds tested, which spanned 28 distinct modes of action, 22 were active against early parasite stages in the mosquito midgut lumen, which in turn prevented establishment of infection. Medicinal chemistry was then used to improve antiparasitic activity of the top hits from the screen. We generated several endochin-like quinolones (ELQs) that inhibited the P. falciparum cytochrome bc1 complex (CytB). Two lead compounds that targeted separate sites in CytB (Qo and Qi) showed potent, long-lasting and stable activity when incorporated and/or extruded into bed net-like polyethylene films. ELQ activity was fully preserved in insecticide-resistant mosquitoes, and parasites resistant to these compounds had impaired development at the mosquito stage. These data demonstrate the promise of incorporating ELQ compounds into LLINs to counteract insecticide resistance and to reduce malaria transmission.