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We present an overview of a small-scale tracer migration experiment that was carried out in July 2018 at the Nevada National Security Site. This experiment involved the injection of .sup.133Xe into the bottom of a shallow borehole with multiple sampling intervals. Sampling was then conducted in the injection borehole and in a second borehole located 17 m from the injection site. A simple system for measurement of the .sup.133Xe activity in whole air was utilized onsite. Though many samples were well below MDC, cross-hole tracer transport was observed. Along with experimental results, additional insights gained from numerical modeling are presented.

The aim of present study was to determine the efficiency of commercially available PEG-based resins for separation of .sup.99mTc from irradiated .sup.100Mo target. Stable and radioactive tracer studies demonstrated that these PEG-based resins have extreme selectivity toward ReO.sub.4.sup.- (.sup.99mTcO.sub.4.sup.-) over MoO.sub.4.sup.2- ions. Moreover, PEG-based resins still have 95% adsorption efficiency even after 600 kGy [gamma]-irradiation, suggesting the excellent irradiation stability. The adsorption rate of ReO.sub.4.sup.- and .sup.99mTcO.sub.4.sup.- rapidly increased to 90% in 10 s. Subsequently, three-column chromatographic processing based on these superior resins for isolating .sup.99mTc was developed and examined. The separation investigation of .sup.99mTc medical radioisotope produced by .sup.100Mo(p, 2n).sup.99mTc reaction was successfully performed. The recovery yield and the radionuclidic purity of .sup.99mTc was about 90% and 99.9%, respectively. Moreover, the separation of .sup.99mTc from a low specific activity .sup.99Mo was also investigated. We are excited about the potential of this procedure with these accessible commercial availability PEG-based resins to address .sup.99mTc separation problems and increase access to medical nuclide .sup.99mTc for the general community.

PM.sub.2.5, generated via both direct emission and secondary formation, can have varying environmental impacts due to different physical and chemical properties of its components. However, traditional methods to quantify different PM.sub.2.5 components are often based on online or offline observations and numerical models, which are generally high economic cost- or labor-intensive. In this study, we develop a new method, named Multi-Tracer Estimation Algorithm (MTEA), to identify the primary and secondary components from routine observation of PM.sub.2.5 . By comparing with long-term and short-term measurements of aerosol chemical components in China and the United States, it is proven that MTEA can successfully capture the magnitude and variation of the primary PM.sub.2.5 (PPM) and secondary PM.sub.2.5 (SPM). Applying MTEA to the China National Air Quality Network, we find that (1) SPM accounted for 63.5 % of the PM.sub.2.5 in cities in southern China on average during 2014-2018, while the proportion dropped to 57.1 % in the north of China, and at the same time the secondary proportion in regional background regions was â¼ 19 % higher than that in populous regions; (2) the summertime secondary PM.sub.2.5 proportion presented a slight but consistent increasing trend (from 58.5 % to 59.2 %) in most populous cities, mainly because of the recent increase in O.sub.3 pollution in China; (3) the secondary PM.sub.2.5 proportion in Beijing significantly increased by 34 % during the COVID-19 lockdown, which might be the main reason for the observed unexpected PM pollution in this special period; and finally, (4) SPM and O.sub.3 showed similar positive correlations in the Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD) regions, but the correlations between total PM.sub.2.5 and O.sub.3 in these two regions, as determined from PPM levels, were quite different. In general, MTEA is a promising tool for efficiently estimating PPM and SPM, and has huge potential for future PM mitigation.

Nitrogen dioxide (NO.sub.2) is a precursor of ozone (O.sub.3) and fine particulate matter (PM.sub.2.5) - two pollutants that are above regulatory guidelines in many cities. Bringing urban areas into compliance of these regulatory standards motivates an understanding of the distribution and sources of NO.sub.2 through observations and simulations. The TRACER-AQ campaign, conducted in Houston, Texas, in September 2021, provided a unique opportunity to compare observed NO.sub.2 columns from ground-, airborne-, and satellite-based spectrometers. In this study, we investigate how these observational datasets compare and simulate column NO.sub.2 using WRF-CAMx with fine resolution (444 x 444 m.sup.2) comparable to the airborne column measurements. We compare WRF-simulated meteorology to ground-level monitors and find good agreement. We find that observations from the GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) instrument were strongly correlated (r.sup.2 = 0.79) to observations from Pandora spectrometers with a slight high bias (normalized mean bias (NMB) = 3.4 %). Remote sensing observations from the TROPOspheric Monitoring Instrument (TROPOMI) were generally well correlated with Pandora observations (r.sup.2 = 0.73) with a negative bias (NMB = -22.8 %). We intercompare different versions of TROPOMI data and find similar correlations across three versions but slightly different biases (from -22.8 % in v2.4.0 to -18.2 % in the NASA MINDS product). Compared with Pandora observations, the WRF-CAMx simulation had reduced correlation (r.sup.2 = 0.34) and a low bias (-21.2 %) over the entire study region. We find particularly poor agreement between simulated NO.sub.2 columns and GCAS-observed NO.sub.2 columns in downtown Houston, an area of high population and roadway densities. These findings point to a potential underestimate of NO.sub.x emissions (NO.sub.x = NO + NO.sub.2) from sources associated with the urban core of Houston, such as mobile sources, in the WRF-CAMx simulation driven by the Texas state inventory, and further investigation is recommended.

Here, we describe the case of a 43-year-old male patient with a metastatic parathyroid carcinoma who underwent dual-tracer whole-body positron emission tomography/computed tomography (PET/CT) with [[sup.18]F]fluorocholine and fluorodeoxyglucose ([[sup.18]F]FDG) for staging. [[sup.18]F]FDG PET/CT detected multiple cervical and mediastinal lymph nodal lesions with increased tracer uptake, whereas [[sup.18]F]fluorocholine PET/CT detected increased tracer uptake on cervical and mediastinal lymph nodal lesions and bone and lung lesions with a better evaluation of metastatic spread. Due to these imaging findings, the patient underwent systemic treatment with chemotherapy. This case demonstrates the added value of dual-tracer PET/CT in this rare metastatic tumor.

Neurons build vast gap junction-coupled networks (GJ-nets) that are permeable to ions or small molecules, enabling lateral signaling. Herein, we investigate (1) the effect of blinding diseases on GJ-nets in mouse retinas and (2) the impact of electrical stimulation on GJ permeability. GJ permeability was traced in the acute retinal explants of blind retinal degeneration 1 (rd1) mice using the GJ tracer neurobiotin. The tracer was introduced via the edge cut method into the GJ-net, and its spread was visualized in histological preparations (fluorescent tagged) using microscopy. Sustained stimulation was applied to modulate GJ permeability using a single large electrode. Our findings are: (1) The blind rd1 retinas displayed extensive intercellular coupling via open GJs. Three GJ-nets were identified: horizontal, amacrine, and ganglion cell networks. (2) Sustained stimulation significantly diminished the tracer spread through the GJs in all the cell layers, as occurs with pharmaceutical inhibition with carbenoxolone. We concluded that the GJ-nets of rd1 retinas remain coupled and functional after blinding disease and that their permeability is regulatable by sustained stimulation. These findings are essential for understanding molecular signaling in diseases over coupled networks and therapeutic approaches using electrical implants, such as eliciting visual sensations or suppressing cortical seizures.

[This retracts the article DOI: 10.1155/2022/6387030.].[This retracts the article DOI: 10.1155/2022/6387030.].