Tracer Distribution Research Articles

129I and 236U distribution in the subpolar North Atlantic unravels water mass provenance in AR7W and A25 lines

The subpolar North Atlantic (SPNA) is crucial in the global ocean circulation system and one of the few regions where deep convection occurs. The intermediate and deep waters formed in the SPNA have long been investigated, yet their sources and pathways are not fully understood. In this study, we employ a combination of two radionuclide tracers, namely, 129I and 236U, to understand water mass provenance and mixing in the SPNA. The concentrations measured between Portugal and Greenland and across the Labrador Sea in 2020/2021 agreed with previously observed tracer distributions. The highest tracer concentrations were measured in the East Greenland Current (EGC), Denmark Strait Overflow Water (DSOW), and, to a lesser extent, in the eastward-flowing Labrador Sea Water (LSW). In contrast, waters of southern origin such as the North East Antarctic Bottom Water and North East Atlantic Central Water (ENACW) carried comparably smaller amounts of 129I. By using a binary mixing model, we estimated that the EGC contains about 29%–32% of the Polar Surface Water outflowing the Fram Strait. DSOW was mainly derived from 20% to 35% Return Atlantic Water and mixed with LSW. The Iceland Scotland Overflow Water (ISOW) evolved into North East Atlantic Deep Water in the Irminger and Labrador seas primarily by mixing with LSW and, to a lesser extent, with DSOW. The 129I and 236U binary mixing approach was less conclusive for LSW, reaching the current limitation of the model. This study suggests potential benefits and limitations of using 129I and 236U to investigate the mixing and provenance of water masses in the SPNA.

Metastatic Prostate Carcinoma to the Ankle Seen on Bone Scintigraphy and Extended Field-of-View PSMA PET/CT.

We describe a rare case of metastatic prostate carcinoma to the heel. Bone scintigraphy revealed high uptake simulating fractures. Standard PSMA PET/CT was negative. As PSA elevated, extended field-of-view PET/CT revealed ankle uptake with virtually identical spatial distribution and intensity of both tracers. Histopathology confirmed ankle metastases of prostate carcinoma, which retrospectively was the inaugural manifestation of the metastatic skeletal disease. This case highlights the need to consider peripheral limb bone metastases in patients with biochemical recurrence. In case of focal symptoms or unexplained bone scan findings, the PSMA acquisition coverage should be extended to include the respective body part.

Bacteria-targeted imaging using vancomycin-based positron emission tomography tracers can distinguish infection from sterile inflammation.

Bacterial infections pose major challenges in medicine. To guide effective infection treatment, faster and more accurate diagnostic modalities are needed. Bacteria-targeted molecular imaging can meet these needs. The present study was aimed at the in vivo evaluation of two 18F-vancomycin-based PET tracers, for detection of deep-seated Gram-positive bacterial infections. These tracers were bench-marked against the current standard of care, [18F]FDG. The potential of [18F]BODIPY-FL-vancomycin and [18F]PQ-VE1-vancomycin ([4+2]photocycloadduct of 9,10-phenanthrenequinone-vancomycin and [18F]fluorinated vinyl ether) to distinguish bacterial infections from sterile inflammation was evaluated in a murine myositis model. Tracer specificity was assessed by infecting mice either with the Gram-positive bacterium Staphylococcus aureus (n = 12) or the Gram-negative bacterium Escherichia coli (n = 12). The contralateral leg was injected with Cytodex beads to induce sterile inflammation, or with phosphate-buffered saline for control. In parallel, mice were imaged with [18F]FDG (n = 12). Dynamic positron emission tomography (PET) measurements, biodistribution analyses, and immunohistopathology were performed to determine tracer distribution and bacterial burden. Both 18F-vancomycin-PET tracers accumulated at sites of infection, but not at sites of sterile inflammation, in contrast to [18F]FDG. The tracers exhibited distinct biodistribution profiles, with [18F]BODIPY-FL-vancomycin being cleared more rapidly. Both 18F-vancomycin-PET tracers displayed significant target to non-target ratios of 2.95 for [18F]BODIPY-FL-vancomycin and 1.48 for [18F]PQ-VE1-vancomycin. Vancomycin-based PET is a potentially attractive approach to distinguish Gram-positive bacterial infections from sterile inflammation.

An In Vitro Platform for Pharmacokinetic Quantification and Optimization of Cerebrospinal Fluid Filtration and Drug Circulation

Abstract Modification of cerebrospinal fluid (CSF) transport dynamics is an expanding method for treating central nervous system injury and diseases. One application of this route is to modify the distribution of solutes in the CSF; however, few tools currently exist for this purpose. The present study describes the use of a subject-specific in vitro CSF phantom to perform a parametric evaluation of the Neurapheresis™ CSF Management System (NP) for both CSF filtration and intrathecal drug circulation. An in vitro CSF phantom was constructed which included realistic anatomy for the complete subarachnoid space (SAS). This platform was configured to test multiple parametric modifications of a dual-lumen catheter and filtration system. Calibrated mapping of tracer distribution and area under the curve (AUC) measurements were used to compare filtration and intrathecal-circulation schemes using the NP device versus the clinical standards of care. The NP device showed potential advantages over lumbar drain (LD) for clearance of simulated subarachnoid hemorrhage (SAH), especially in the spinal canal. Use of the NP device in combination with simulated intracerebroventricular (ICV) drug infusion resulted in an increased extent and uniformity of tracer spread compared to ICV alone. NP improved clearance of simulated subarachnoid hemorrhage compared to LD and increased uniformity of tracer concentration via simulated ICV, providing support for NP use in these scenarios. The in vitro CSF phantom system presented here quantitatively described the effects of parametric boundary modification on solute distribution in the intrathecal space.

Apostle–auriga: effects of stellar feedback subgrid models on the evolution of angular momentum in disc galaxies

ABSTRACT Utilizing the apostle–auriga simulations, which start from the same zoom-in initial conditions of Local Group-like systems, but run with different galaxy formation subgrid models and hydrodynamic solvers, we study the impact of stellar feedback models on the evolution of angular momentum in disc galaxies. At $z = 0$, auriga disc galaxies tend to exhibit higher specific angular momenta compared to their cross-matched apostle counterparts. By tracing the evolution history of the Lagrangian mass tracers of the in-situ star particles in the $z = 0$ galaxies, we find that the specific angular momentum distributions of the gas tracers from the two simulations at the halo accretion time are relatively similar. The present-day angular momentum difference is mainly driven by the physical processes occurring inside dark matter haloes, especially galactic fountains. Due to the different subgrid implementations of stellar feedback processes, auriga galaxies contain a high fraction of gas that has gone through recycled fountain (${\sim } 65$ per cent) which could acquire angular momentum through mixing with the high angular momentum circumgalactic medium (CGM). In apostle, however, the fraction of gas that has undergone the recycled fountain process is significantly lower (down to ${\sim } 20$ per cent for Milky Way-sized galaxies) and the angular momentum acquisition from the CGM is marginal. As a result, the present-day auriga galaxies overall have higher specific angular momenta.

Enhanced Diffusion and Non-Gaussian Displacements of Colloids in Quasi-2D Suspensions of Motile Bacteria

In the real world, active agents interact with surrounding passive objects, thus introducing additional degrees of complexity. The relative contributions of far-field hydrodynamic and near-field contact interactions to the anomalous diffusion of passive particles in suspensions of active swimmers remain a subject of ongoing debate. We constructed a quasi-two-dimensional microswimmer–colloid mixed system by taking advantage of Serratia marcescens’ tendency to become trapped at the air–water interface to investigate the origins of the enhanced diffusion and non-Gaussianity of the displacement distributions of passive colloidal tracers. Our findings reveal that the diffusion behavior of colloidal particles exhibits a strong dependence on bacterial density. At moderate densities, the collective dynamics of bacteria dominate the diffusion of tracer particles. In dilute bacterial suspensions, although there are multiple dynamic types present, near-field contact interactions such as collisions play a major role in the enhancement of colloidal transport and the emergence of non-Gaussian displacement distributions characterized by heavy exponential tails in short times. Despite the distinct types of microorganisms and their diverse self-propulsion mechanisms, a generality in the diffusion behavior of passive colloids and their underlying dynamics is observed.

CHARACTERIZATION OF FINE CARBONACEOUS AEROSOLS FROM THE EASTERN MEDITERRANEAN: CONTRIBUTIONS OF FOSSIL AND NON-FOSSIL CARBON SOURCES

ABSTRACT In order to better characterise carbonaceous components in atmospheric aerosols and to assess the contributions of fossil carbon (FC) and non-fossil carbon (NFC) sources and their seasonality in the Eastern Mediterranean, we collected fine (PM1.3) aerosols at a remote marine background site, the Finokalia Research Station, Crete, Greece, over a period of one-year. PM1.3 samples were analysed for elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC), and stable carbon isotope ratio (δ13CTC) and radiocarbon content (14CTC) (pMC) of total carbon (TC). All the parameters, i.e., PM1.3, δ13CTC and 14CTC showed a clear temporal pattern with higher values in summer and lower values in autumn. The 14CTC ranged from 54.7 to 99.1 pMC with an average of 74.5 pMC during the entire year. The FC content in TC (FCTC) was found to be slightly lower in winter and almost stable in other seasons, whereas the NFC contents (NFCTC) showed a clear seasonality with the highest level in summer followed by spring and the lowest level in winter. Based on these results together with the seasonal distributions of organic tracers, we found that biomass burning (BB) and soil dust are two major sources of the fine aerosols in winter. Although biogenic emissions of VOCs followed by subsequent secondary oxidation processes are significant in summer followed by spring and autumn, pollen is a significant contributor to TC in spring. This study showed that emissions from fossil fuel combustion are significant (25.5%) but minor compared to NFC sources in the eastern Mediterranean.

Horizontal and vertical dispersion in a wind-driven oceanic gyre model

This study addresses the horizontal and vertical dispersion of passive tracers in idealized wind-driven subtropical gyres. Synthetic particles within a closed basin are numerically advected to analyze their dispersion under different theoretical velocity fields. Horizontal dispersion simulations incorporate the classic wind-driven Stommel circulation along with (i) surface Ekman drift associated with the Stommel wind field and (ii) inertial effects due to particle size and buoyancy. Results reveal that the Ekman drift inhibits particle dispersion across the entire domain leading to tracer concentration in a quasi-stable distribution skewed toward the western side of the basin. Similar behavior is observed with inertial particles. The equilibrium state is quantified for different diffusivity values, particle sizes, and buoyancies. For vertical dispersion, simulations incorporate the three-dimensional Ekman velocity, which includes a negative vertical component, while ignoring inertial effects. Initially, surface particles accumulate around the gyre center while slowly sinking, but they disperse across the basin once they surpass the Ekman layer and are free from surface effects. Tracers sink more on the western side of the basin, regardless of horizontal diffusivity. On average, ignoring inertial effects, particles sink less with higher diffusivity and more with lower diffusivity, suggesting a potential for high horizontal distribution of sunken tracers in the ocean.

The Rapid Response of Southern Ocean Biological Productivity to Changes in Background Small Scale Turbulence

AbstractBackground subsurface vertical mixing rates in the Southern Ocean (SO) are known to vary by an order of magnitude temporally and spatially, due to variability in their generating mechanisms, which include winds and shear instabilities at the surface, and the interaction of tides and lee waves with rough bottom topography. There is great uncertainty in the parameterization of this mixing in coarse resolution Earth System Models (ESM), and in the impact that this has on SO biological productivity on sub decadal timescales. Using a data assimilating biogeochemical ocean model we show that SO phytoplankton productivity is highly sensitive to differences in background diapycnal mixing over short timescales. Changes in the background vertical mixing rates alter key biogeochemical and physical conditions. The greatest changes to the distribution of physical and biogeochemical tracers occur in regions with very strong tracer vertical gradients. A combination of reduced nutrient limitation and reduced light limitation causes a strong increase in SO phytoplankton productivity with higher background mixing. This leads to increased summer carbon export but reduced wintertime export over the mixed layer depth, which could alter the strength of the SO biological carbon pump and atmospheric concentrations on centennial to millennial timescales. This study demonstrates the importance of accurately representing diapycnal mixing in ESM to predict SO biogeochemical dynamics and their broader climatic implications.

Design, Synthesis, and Preclinical Evaluation of a High-Affinity 18F-Labeled Radioligand for Myocardial Growth Hormone Secretagogue Receptor Before and After Myocardial Infarction.

The peptide hormone ghrelin is produced in cardiomyocytes and acts through the myocardial growth hormone secretagogue receptor (GHSR) to promote cardiomyocyte survival. Administration of ghrelin may have therapeutic effects on post-myocardial infarction (MI) outcomes. Therefore, there is a need to develop molecular imaging probes that can track the dynamics of GHSR in health and disease to better predict the effectiveness of ghrelin-based therapeutics. We designed a high-affinity GHSR ligand labeled with 18F for imaging by PET and characterized its invivo properties in a canine model of MI. Methods: We rationally designed and radiolabeled with 18F a quinazolinone derivative ([18F]LCE470) with subnanomolar binding affinity to GHSR. We determined the sensitivity and invivo and ex vivo specificity of [18F]LCE470 in a canine model of surgically induced MI using PET/MRI, which allowed for anatomic localization of tracer uptake and simultaneous determination of global cardiac function. Uptake of [18F]LCE470 was determined by time-activity curve and SUV analysis in 3 regions of the left ventricle-area of infarct, territory served by the left circumflex coronary artery, and remote myocardium-over a period of 1.5 y. Changes in cardiac perfusion were tracked by [13N]NH3 PET. Results: The receptor binding affinity of LCE470 was measured at 0.33 nM, the highest known receptor binding affinity for a radiolabeled GHSR ligand. In vivo blocking studies in healthy hounds and ex vivo blocking studies in myocardial tissue showed the specificity of [18F]LCE470, and sensitivity was demonstrated by a positive correlation between tracer uptake and GHSR abundance. Post-MI changes in [18F]LCE470 uptake occurred independently of perfusion tracer distributions and changes in global cardiac function. We found that the regional distribution of [18F]LCE470 within the left ventricle diverged significantly within 1 d after MI and remained that way throughout the 1.5-y duration of the study. Conclusion: [18F]LCE470 is a high-affinity PET tracer that can detect changes in the regional distribution of myocardial GHSR after MI. In vivo PET molecular imaging of the global dynamics of GHSR may lead to improved GHSR-based therapeutics in the treatment of post-MI remodeling.

Trough‐Scale Slope Countercurrent Over the East China Sea Continental Slope Driven by Upwelling Divergence

AbstractObservations have revealed the existence of persistent slope countercurrents (SCCs) that flow southwestward beneath the Kuroshio Current at several locations over the East China Sea (ECS) continental slope. It was not clear whether these flows are localized circulation features or segments of a trough‐scale circulation system in the Okinawa Trough (OT). We demonstrate that there indeed exists a potentially continuous trough‐scale SCC along the ECS slope that is associated with an OT‐wide cyclonic circulation using high‐resolution model simulations and physical interpretations. The detailed features of the deep OT circulation are illustrated by the trajectories of the Lagrangian drifters and the time‐varying distributions of passive tracers. The SCC in the ECS is characterized by its weak yet persistent nature, typically located in narrow sloping regions at the isopycnal layer of 26.6–27.3 kg m−3. It exhibits a characteristic speed of approximately O‐(1) cm s−1. Analyses and experiments suggest that the divergence of upwelling in the SCC layer (26.6–27.3 σθ surface) gives rise to lateral potential vorticity transport, ultimately driving the deep cyclonic circulation. Furthermore, the SCC also displays a substantial connection with the onshore intrusion of the Kuroshio Current, particularly to the northeast of Taiwan Island. The SCC may potentially play a crucial role in the transport of heat and nutrients, as well as in regulating sediment distributions within the deep OT. This mechanism offers fresh insights into explaining the presence of undercurrents in semi‐enclosed marginal seas.

The Development and Evaluation of a Novel Highly Selective PET Radiotracer for Targeting BET BD1.

Background/Objectives: Small molecules that interfere with the interaction between acetylated protein tails and the tandem bromodomains of BET (bromodomain and extra-terminal) family proteins are pivotal in modulating immune/inflammatory and neoplastic diseases. This study aimed to develop a novel PET imaging tracer, [11C]GSK023, that targets the N-terminal bromodomain (BD1) of BET family proteins with high selectivity and potency, thereby enriching the chemical probe toolbox for epigenetic imaging. Methods: [11C]GSK023, a radio-chemical probe, was designed and synthesized to specifically target the BET BD1. In vivo PET imaging evaluations were conducted on rodents, focusing on the tracer's distribution and binding specificity in various tissues. Blocking studies were performed to confirm the probe's selectivity and specificity. Results: The evaluations revealed that [11C]GSK023 demonstrated good uptake in peripheral organs with limited brain penetration. Further blocking studies confirmed the probe's high binding specificity and selectivity for the BET BD1 protein, underscoring its potential utility in epigenetic imaging. Conclusions: The findings suggest that [11C]GSK023 is a promising PET probe for imaging the BET BD1 protein, offering the potential to deepen our understanding of the roles of BET bro-modomains in disease and their application in clinical settings to monitor disease progression and therapeutic responses.

Using Shortened Spin‐Ups to Speed Up Ocean Biogeochemical Model Optimization

AbstractThe performance of global ocean biogeochemical models can be quantified as the misfit between modeled tracer distributions and observations, which is sought to be minimized during parameter optimization. These models are computationally expensive due to the long spin‐up time required to reach equilibrium, and therefore optimization is often laborious. To reduce the required computational time, we investigate whether optimization of a biogeochemical model with shorter spin‐ups provides the same optimized parameters as one with a full‐length, equilibrated spin‐up over several millennia. We use the global ocean biogeochemical model MOPS with a range of lengths of model spin‐up and calibrate the model against synthetic observations derived from previous model runs using a derivative‐free optimization algorithm (DFO‐LS). When initiating the biogeochemical model with tracer distributions that differ from the synthetic observations used for calibration, a minimum spin‐up length of 2,000 years was required for successful optimization due to certain parameters which influence the transport of matter from the surface to the deeper ocean, where timescales are longer. However, preliminary results indicate that successful optimization may occur with an even shorter spin‐up by a judicious choice of initial condition, here the synthetic observations used for calibration, suggesting a fruitful avenue for future research.

Tracer transport in fractured porous media: Distribution of tracer concentration within the rock matrix and the implementation of time domain random walk algorithm

In this work, a new Time Domain Random Walk (TDRW) algorithm is proposed to estimate the tracer distribution profile within the rock matrix. The development of the new algorithm stems from the statistical properties of the analytical solution to a single fracture-matrix system, in which the particle position at a certain time is calculated and recorded. With the position of each particle determined, the resulting distribution will then provide an estimate of the tracer distribution profile directly. In addition, the newly developed algorithm can readily be extended to a case of more complicated fracture-matrix system, in which an arbitrary injection boundary condition may also be used. To verify the accuracy and applicability of the new algorithm, three benchmark simulations are made, in which the results of different approaches are found to be identical. Nevertheless, the new algorithm has a higher computational efficiency, due to its lower calculation demand.

A Framework for Constraining Ocean Mixing Rates and Overturning Circulation from Age Tracers

Abstract The age of seawater refers to the amount of time that has elapsed since that water encountered the surface. This age measures the ventilation rate of the ocean, and the spatial distribution of age can be influenced by multiple processes, such as overturning circulation, ocean mixing, and air–sea exchange. In this work, we aim to gain new quantitative insights about how the ocean’s age tracer distribution reflects the strength of the meridional overturning circulation and diapycnal diffusivity. We propose an integral constraint that relates the age tracer flow across an isopycnal surface to the geometry of the surface. With the integral constraint, a relationship between the globally averaged effective diapycnal diffusivity and the meridional overturning strength at an arbitrary density level can be inferred from the age tracer concentration near that level. The theory is tested in a set of idealized single-basin simulations. A key insight from this study is that the age difference between regions of upwelling and downwelling, rather than any single absolute age value, is the best indicator of overturning strength. The framework has also been adapted to estimate the strength of abyssal overturning circulation in the modern North Pacific, and we demonstrate that the age field provides an estimate of the circulation strength consistent with previous studies. This framework could potentially constrain ocean circulation and mixing rates from age-like realistic tracers (e.g., radiocarbon) in both past and present climates. Significance Statement The age of seawater—the local mean time since local water from different pathways was last at the surface—is a valuable indicator of ocean circulation and the transport time scale of heat and carbon. We introduce a novel constraint that relates total age flow across a density surface to its geometry, which provides new insights into constraining ocean circulation and mixing rates from age-like realistic tracers (e.g., radiocarbon).

StepBrain: A 3-Dimensionally Printed Multicompartmental Anthropomorphic Brain Phantom to Simulate PET Activity Distributions.

An innovative multicompartmental anatomic brain phantom (StepBrain) is described to simulate the invivo tracer uptake of gray matter, white matter, and striatum, overcoming the limitations of currently available phantoms. Methods: StepBrain was created by exploiting the potential of fused deposition modeling 3-dimensional printing to replicate the real anatomy of the brain compartments, as modeled through ad hoc processing of healthy-volunteer MR images. Results: A realistic simulation of 18F-FDG PET brain studies, using target activity to obtain the real concentration ratios, was obtained, and the results of postprocessing with partial-volume effect correction tools developed for human PET studies confirmed the accuracy of these methods in recovering the target activity concentrations. Conclusion: StepBrain compartments (gray matter, white matter, and striatum) can be simultaneously filled, achieving different concentration ratios and allowing the simulation of different (e.g., amyloid, tau, or 6-fluoro-l-dopa) tracer distributions, with a potentially valuable role for multicenter PET harmonization studies.

Estimation of Effective Fracture Aperture in Glacial Tills by Analysis of Dye Tracer Penetration.

This study advances a methodology to estimate effective apertures of fractures in glacial tills based on dye tracer infiltration tests and numerical simulations. The approach uses the visible penetration depth of the dye tracer along fracture flow paths as primary information to calculate effective fracture apertures. Further data used in the calculation are the dye tracer input concentration and retardation, the duration of the tracer injection, and the hydraulic gradient applied to control the infiltrating water fluxes. The method does not require measurement of hydraulic conductivity for the fractured till and enables direct observation of flow and transport patterns within the fractures (e.g., uniform flow and dye tracer distribution, channeling due to aperture variability, and presence of biogenic macropores in fractures). The approach was successfully verified by using the estimated effective fracture aperture values in Large Undisturbed Columns (LUCs) to consistently simulate both the observed LUC effluent breakthrough of a conservative bromide tracer and the water fluxes with the hydraulic gradient applied in the experiments. Sensitivity analyses revealed that estimation of small effective fracture apertures (<10 μm) required accurate determination of the dye tracer retardation factor. By contrast, in the case of larger effective apertures (>20 μm), the sensitivity of the estimated effective fracture aperture to variations in the porous material and solute transport parameters was low compared to the dominant sensitivity to the water flow through the fractures (cubic relation between flow and aperture). The proposed approach may be extended beyond laboratory applications and assist in characterizing field-scale fracture networks.

An electron backscatter diffraction study of monazite: Linking the time-deformation path

Monazite, (Ce,REE)PO4, is a common accessory mineral used to quantify the timing and duration of tectono-metamorphic processes in (poly)metamorphosed orogenic terranes. As monazite frequently yields a spread of dates, there can be ambiguity linking age domains to specific metamorphic reactions and/or deformation events. This study aims to: (1) discern the effect of deformation on the monazite crystal structure; (2) understand how dynamic recrystallisation and dissolution-precipitation mechanisms are recorded by microtexture and/or the distribution and concentration of elements and isotopes within the monazite; and (3) assess the usefulness of microtextural imaging for the interpretation of complex petrochronological datasets.Monazites are analysed from several different geological settings including, the Himalaya (India), Western Gneiss Region (Norway), Snake Range (Nevada, USA), and Madagascar. Here, combined laser-ablation split stream isotopic (U-Th/Pb) and trace element analysis and Electron Backscatter Diffraction (EBSD) are used to investigate links between monazite (re)crystallisation/precipitation mechanisms, microtextures, age and trace-element distribution in individual grains. The studied monazite display a variety of microtexture including (001)[100] and (120)[120] (deformation) twins, micron-scale lattice rotation, and sub-grain boundaries.Observed monazite microtextures are interpreted to have formed during ductile deformation. Microtextures typically coincide with geochemically distinct, younger monazite, suggesting that crystallographic defects focus coupled dissolution-precipitation mechanisms during deformation and metamorphism. Crystallographic defects (including twins and sub-grains) are interpreted to be significant pathways for fluid, enabling coupled dissolution-precipitation of chemically distinct monazite during ductile deformation and metamorphism. This study highlights the power of combining traditional petrochronology approaches with microtextural imaging to better link monazite ages to specific deformation events.

In-flight characterization of a compact airborne quantum cascade laser absorption spectrometer

Abstract. Here, we report on the development of a new quantum cascade laser infrared absorption spectroscopy (QLAS) instrument, the Airborne Tropospheric Tracer In-situ Laser Absorption spectrometer (ATTILA), for atmospheric trace-gas measurements on board of the German High-Altitude Long-range Observatory (HALO) aircraft. Its small and light design makes it suitable for airborne measurements up to approximately 150 hPa of ambient pressure (13–14 km). The dual laser instrument can measure several trace gases simultaneously in two 36.4 m path astigmatic Herriott cells with a data acquisition frequency of 1 Hz. We describe the measurement method and the data acquisition of ATTILA and its in-flight performance by focusing on potential sources of influences on the signal, which we investigated with a dedicated test flight during which the instrument sampled from a constant source. We show that linear critical influences associated with challenging movement patterns can be corrected afterwards, while nonlinear limitations can be minimized by appropriate calibration frequencies and integrated time intervals. During the recent aircraft campaign CAFE Brazil (Chemistry of the Atmosphere Field Experiment in Brazil) from December 2022 to January 2023, carbon monoxide (CO) measurements from ATTILA show a good agreement of a R2 of 0.89 with simultaneous CO measurements from an established IR spectrometer for airborne measurements, the TRacer In Situ TDLAS (tunable diode laser absorption spectroscopy) for Atmospheric Research (TRISTAR), at a 10 s time resolution. First dynamical characteristics and tracer distributions of CO and methane (CH4) over the Amazon rainforest can be identified with ATTILA measurements with a total measurement uncertainty of 10.1 % and 17.5 % for calibration gas mixing ratios of 153 and 1990 ppbv and a data accuracy of 0.3 % and 5.5 % for a data acquisition frequency of 1 Hz for CO and CH4, respectively.

Enhanced transport of brain interstitial solutes mediated by stimulation of sensorimotor area in rats.

Solute transport in the brain is essential for maintaining cerebral homeostasis. Recent studies have shown that neuronal activity enhances the transport of cerebrospinal fluid solutes, but its impact on interstitial solute transport has not been established. In this study, we investigated whether neuronal activity affects the transport of interstitial solutes. Fluorescent Texas Red ovalbumin was injected intracortically into the unilateral sensorimotor area of the Sprague-Dawley rats. Regional neuronal activity around the injection site was elicited by transdermal electrical stimulation of a corresponding forelimb for 90 min ( n = 6). The control group of rats ( n = 6) did not receive any electrical stimulation. Subsequently, the spatial distributions of the tracer over the cortical surface and from the brain sections were imaged and compared between two groups. The ovalbumin fluorescence from the cervical lymph nodes was also compared between the groups to evaluate the effect of neuronal activity on solute clearance from the brain. Tracer distribution over the brain surface/sections revealed a significantly higher uptake of ovalbumin in the hemisphere ipsilateral to the injection among the stimulated animals compared to the unstimulated group. This difference, however, was not seen in the hemisphere contralateral to injection. A trace amount of ovalbumin in the lymph nodes was equivalent between the groups, which indicated a considerable time needed for interstitial solutes to be drained from the brain. The results suggest that neuronal activity enhances interstitial solute transport, calling for further examination of ultimate routes and mechanisms for brain solute clearance.