Strong methane point sources contribute a disproportionate fraction of total emissions across multiple basins in the United States

Understanding, prioritizing, and mitigating methane (CH₄) emissions requires quantifying CH₄ budgets from facility scales to regional scales with the ability to differentiate between source sectors. We deployed a tiered observing system for multiple basins in the United States (San Joaquin Valley, Uinta, Denver-Julesburg, Permian, Marcellus). We quantify strong point source emissions (>10 kg CH₄ h⁻¹) using airborne imaging spectrometers, attribute them to sectors, and assess their intermittency with multiple revisits. We compare these point source emissions to total basin CH₄ fluxes derived from inversion of Sentinel-5p satellite CH₄ observations. Across basins, point sources make up on average 40% of the regional flux. We sampled some basins several times across multiple months and years and find a distinct bimodal structure to emission timescales: the total point source budget is split nearly in half by short-lasting and long-lasting emission events. With the increasing airborne and satellite observing capabilities planned for the near future, tiered observing systems will more fully quantify and attribute CH₄ emissions from facility to regional scales, which is needed to effectively and efficiently reduce methane emissions.

Due to its short atmospheric lifetime and strong contribution to global radiative forcing, methane (CH₄) has been a focus for near-term climate mitigation efforts (1). Robust, unbiased accounting systems are requisite to prioritizing and validating CH₄ mitigation, ideally from multiple independent data streams. Atmospheric observations of CH₄ can be key for mitigation, as observed CH₄ concentrations are used to quantify emission rates and attribute emissions to sources. Findings from many independent research efforts have shown that CH₄ emissions across multiple sectors follow heavy-tailed distributions (2–5), meaning that a small fraction of emission sources emits at disproportionately higher rates than the full population of emitters. CH₄ sources can be intermittent or persistent in duration, which may be associated with short-lasting process-driven releases or long-lasting emissions due to abnormal or otherwise avoidable operating conditions such as malfunctions or leaks (5). Isolating populations of large emitters at varying levels of intermittency while quantifying their contribution to regional budgets creates a clear direction for mitigation focus. This tiered observing system strategy can be deployed in data-rich regions where multiple independent layers of observations are jointly leveraged to quantify and isolate emissions, and then drive action.Advances in CH₄ remote sensing have enabled quantification of emissions from global to facility scales. Generally, these observing systems operate by measuring solar backscattered radiance in shortwave infrared regions where CH₄ is a known absorber. Global mapping satellite missions have been used to identify CH₄ hotspots and infer global- to regional-scale CH₄ emission fluxes (6–8). In particular, the TROPOspheric Monitoring Instrument [TROPOMI (9)] onboard the Sentinel-5p satellite has proven capable of quantifying fluxes at basin scales (10, 11). Due to the kilometer-scale resolution of measurements from these global mapping missions, further attribution to particular facilities or even emission sectors is often not feasible. Less precise, target-mode satellites [e.g., PRISMA (12), GHGSat (13)] have proven capable of quantifying very large emissions at an ∼30-m scale, allowing for direct emission attribution to facilities or even subfacility-level infrastructure. However, the current generation of CH₄ plume imaging satellites lack the spatial and temporal coverage to provide quantification completeness across multiple basins. For global mapping, high–spatial resolution multispectral satellites such as Sentinel-2 and Landsat are capable of CH₄ detection (14, 15), but only for large emission sources (e.g., 2+ t h⁻¹) over very bright surfaces.Airborne imaging spectrometers with shortwave infrared sensitivities and sufficient instrument signal-to-noise ratios can also quantify column CH₄ concentrations. These remote sensing platforms are capable of resolving CH₄ concentrations at high spatial resolution (∼3 to 5 m) depending on flight altitude, and can quantify point source emissions as low as 5 to 10 kg h⁻¹ (16, 17). These instruments are sensitive to concentrated point-source emissions, and less sensitive to diffuse emissions spread over large areas (e.g., wetlands). Given the heavy-tailed nature of anthropogenic emissions, point-source detections above an imaging spectrometer’s detection limit may constitute a sizable fraction of the total regional CH₄ flux, but independent measurements are needed to provide that context. Therefore, in this study, we flew a combination of the Global Airborne Observatory (GAO) and next-generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) over multiple CH₄ emitting regions between 2019 and 2021, including the southern San Joaquin Valley (SJV), the Permian, the Denver-Julesburg (DJ), the Unita, and the southwestern Pennsylvania portion of the Marcellus. We generally mapped each basin at least three times during each campaign to quantify persistence of emission sources. For the Permian, DJ, and SJV, we surveyed each region again after several months to assess trends and identify long-lasting emission sources. We also performed simultaneous regional CH₄ flux inversions based on TROPOMI CH₄ retrievals to quantify the total CH₄ flux for each survey and compared against the quantified airborne point source budgets. With this tiered approach, we are able to quantify the contribution of unique point sources by sector on the regional budget, therefore highlighting specific points of action for mitigation.     

In Situ Nano-Indentation of a Gold Sub-Micrometric Particle Imaged by Multi-Wavelength Bragg Coherent X-ray Diffraction

The microstructure of a sub-micrometric gold crystal during nanoindentation is visualized by in situ multi-wavelength Bragg coherent X-ray diffraction imaging. The gold crystal is indented using a custom-built atomic force microscope. A band of deformation attributed to a shear band oriented along the (221) lattice plane is nucleated at the lower left corner of the crystal and propagates towards the crystal center with increasing applied mechanical load. After complete unloading, an almost strain-free and defect-free crystal is left behind, demonstrating a pseudo-elastic behavior that can only be studied by in situ imaging while it is invisible to ex situ examinations. The recovery is probably associated with reversible dislocations nucleation/annihilation at the side surface of the particle and at the particle-substrate interface, a behavior that has been predicted by atomistic simulations. The full recovery of the particle upon unloading sheds new light on extraordinary mechanical properties of metal nanoparticles obtained by solid-state dewetting.     

Multiscale Femoral Neck Imaging and Multimodal Trabeculae Quality Characterization in an Osteoporotic Bone Sample

Although multiple structural, mechanical, and molecular factors are definitely involved in osteoporosis, the assessment of subregional bone mineral density remains the most commonly used diagnostic index. In this study, we characterized bone quality in the femoral neck of one osteoporotic patients as compared to an age-matched control subject, and so used a multiscale and multimodal approach including X-ray computed microtomography at different spatial resolutions (pixel size: 51.0, 4.95 and 0.9 µm), microindentation and Fourier transform infrared spectroscopy. Our results showed abnormalities in the osteocytes lacunae volume (358.08 ± 165.00 for the osteoporotic sample vs. 287.10 ± 160.00 for the control), whereas a statistical difference was found neither for shape nor for density. The osteoporotic femoral head and great trochanter reported reduced elastic modulus (Es) and hardness (H) compared to the control reference (−48% (p < 0.0001) and −34% (p < 0.0001), respectively for Es and H in the femoral head and −29% (p < 0.01) and −22% (p < 0.05), respectively for Es and H in the great trochanter), whereas the corresponding values in the femoral neck were in the same range. The spectral analysis could distinguish neither subregional differences in the osteoporotic sample nor between the osteoporotic and healthy samples. Although, infrared spectroscopic measurements were comparable among subregions, and so regardless of the bone osteoporotic status, the trabecular mechanical properties were comparable only in the femoral neck. These results illustrate that bone remodeling in osteoporosis is a non-uniform process with different rates in different bone anatomical regions, hence showing the interest of a clear analysis of the bone microarchitecture in the case of patients’ osteoporotic evaluation.     

Intramuscular [18F]F-FDG Administration for Successful PET Imaging of Golden Hamsters in a Maximum Containment Laboratory Setting

Positron emission tomography (PET) is becoming an important tool for the investigation of emerging infectious diseases in animal models. Usually, PET imaging is performed after intravenous (IV) radiotracer administration. However, IV injections are difficult to perform in some small animals, such as golden hamsters. This challenge is particularly evident in longitudinal imaging studies, and even more so in maximum containment settings used to study high-consequence pathogens. We propose the use of intramuscular (IM) administration of 2-deoxy-2[¹⁸F]fluoro-D-glucose ([¹⁸F]F-FDG) for PET imaging of hamsters in a biosafety level 4 (BSL-4) laboratory setting. After [¹⁸F]F-FDG administration via IM or IV (through surgically implanted vascular access ports), eight hamsters underwent static or dynamic PET scans. Time–activity curves (TACs) and standardized uptake values (SUVs) in major regions of interest (ROIs) were used to compare the two injection routes. Immediately after injection, TACs differed between the two routes. At 60 min post-injection, [¹⁸F]F-FDG activity for both routes reached a plateau in most ROIs except the brain, with higher accumulation in the liver, lungs, brain, and nasal cavities observed in the IM group. IM delivery of [¹⁸F]F-FDG is an easy, safe, and reliable alternative for longitudinal PET imaging of hamsters in a BSL-4 laboratory setting.     

Influence of intensive lipid‐lowering on CT derived fractional flow reserve in patients with stable chest pain: Rationale and design of the FLOWPROMOTE study

IntroductionCoronary CT angiography (CTA) derived fractional flow reserve (FFR_CT) shows high diagnostic performance when compared to invasively measured FFR. Presence and extent of low attenuation plaque density have been shown to be associated with abnormal physiology by measured FFR. Moreover, it is well established that statin therapy reduces the rate of plaque progression and results in morphology alterations underlying atherosclerosis. However, the interplay between lipid lowering treatment, plaque regression, and the coronary physiology has not previously been investigated.AimTo test whether lipid lowering therapy is associated with significant improvement in FFR_CT, and whether there is a dose–response relationship between lipid lowering intensity, plaque regression, and coronary flow recovery.MethodsInvestigator driven, prospective, multicenter, randomized study of patients with stable angina, coronary stenosis ≥50% determined by clinically indicated first‐line CTA, and FFR_CT ≤ 0.80 in whom coronary revascularization was deferred. Patients are randomized to standard (atorvastatin 40 mg daily) or intensive (rosuvastatin 40 mg + ezetimibe 10 mg daily) lipid lowering therapy for 18 months. Coronary CTA scans with blinded coronary plaque and FFR_CT analyses will be repeated after 9 and 18 months. The primary endpoint is the 18‐month difference in FFR_CT using (1) the FFR_CT value 2 cm distal to stenosis and (2) the lowest distal value in the vessel of interest. A total of 104 patients will be included in the study.ConclusionThe results of this study will provide novel insights into the interplay between lipid lowering, and the pathophysiology in coronary artery disease.     

Association Between Ischemic Stroke and Left Atrial Appendage Morphology in Patients With Atrial Fibrillation and Low CHA2DS2-VASc Scores

BackgroundPatients with atrial fibrillation are at risk for ischemic stroke, even with low CHA₂DS₂-VASc scores. The left atrial appendage is a known site of thrombus formation in individuals with atrial fibrillation.MethodsWe conducted a prospective study, enrolling patients with nonvalvular atrial fibrillation and CHA₂DS₂-VASc scores of 0 or 1. Patients were divided into groups based on left atrial appendage morphology (determined by computed tomography): the “chicken wing” group and the non–chicken wing group. We followed patients for more than 1 year to observe the incidence of stroke.ResultsOf 509 patients with a mean (SD) age of 48.9 (11.6) years; 332 (65.2%) were men. The chicken wing group had fewer left atrial appendage lobes, a lower left atrial appendage depth, and a smaller left atrial appendage orifice area (all P < .001). During the follow-up period, 5 of the 133 patients (3.8%) in the chicken wing group and 56 of the 376 patients (14.9%) in the non–chicken wing group experienced ischemic stroke (P < .001). The following findings were significantly associated with the incidence of stroke: left atrial appendage depth (hazard ratio [HR], 1.98; 95% CI, 1.67-3.12; P = .03), left atrial appendage orifice area (HR, 2.16; 95% CI, 1.59–3.13; P < .001), and non–chicken wing left atrial appendage morphology (HR, 1.16; 95% CI, 1.10–1.23; P < .001).ConclusionFor patients with atrial fibrillation and a low CHA₂DS₂-VASc score, the non–chicken wing left atrial appendage morphology type is independently associated with ischemic stroke.     

Differences in the thalamocortical tract of the ascending reticular activating system in disorders of consciousness after hypoxic-ischemic brain injury: A pilot study

This study purposed to investigate differences in the thalamocortical tract of the ascending reticular activating system between vegetative state (VS) and minimally conscious state (MCS) patients with hypoxic-ischemic brain injury (HI-BI). Fourteen patients with disorders of consciousness following HI-BI (VS group: 7 patients, MCS group: 7 patients) and 12 normal subjects were recruited. The 5 parts of reconstructed thalamocortical tract were prefrontal cortex (PFC), premotor cortex, primary motor cortex (M1), primary somatosensory cortex (S1), and posterior parietal cortex (PPC). The fractional anisotropy (FA) value and tract volume (TV) in each part of the thalamocortical tract were estimated. The FA values and TV of all parts of the thalamocortical tract in the VS group and the FA values of all parts and TV of PFC, premotor cortex, and PPC parts in the MCS group were lower than the control group (P < .05). In addition, the FA values of PFC and PPC parts were significantly lower in the VS group than the MCS group (P < .05). The results of our pilot study indicate that PFC and PPC parts of the thalamocortical tract are important areas to assess for differentiation of VS and MCS after HI-BI.