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NRAO and SpaceX have been engaged in coordinated testing efforts since Fall 2021, including conducting experiments on different interference avoidance schemes for the Karl G. Jansky Very Large Array in New Mexico, and the Green Bank Telescope (GBT) inside the National Radio Quiet Zone in West Virginia. The Starlink system is capable of avoiding direct illumination of telescope sites with their adaptive tasking to place downlink beams far away. Nevertheless, even satellites operating in this mode can potentially present strong signals into the telescope’s receiver system if they pass close to the telescope’s main beam at the boresight. For additional protection, Starlink satellites can either momentarily redirect or completely disable their downlink channels while they pass within some minimum angular separation threshold from the telescope’s boresight, methods that are referred to as “telescope boresight avoidance.” In two separate experiments conducted since Fall 2023, NRAO and SpaceX arranged to have the GBT observe a fixed R.A./decl. position in the sky, chosen to have a large number of close-to-boresight Starlink passages. Preliminary analysis from these two experiments illustrates the feasibility of these avoidance methods to significantly reduce, if not eliminate, the negative impact of close-to-boresight satellite passages. Importantly, these experiments demonstrate the value of continuing cooperative efforts between NRAO and SpaceX, and expanding cooperation between the radio astronomy and satellite communities more generally.

 

Silent hypoxemia, or "happy hypoxia", is a puzzling phenomenon in which patients who have contracted COVID-19 exhibit very low oxygen saturation (${\text{SaO}}_2$< 80%) but do not experience discomfort in breathing. The mechanism by which this blunted response to hypoxia occurs is unknown. We have previously shown that a computational model of the respiratory neural network (Diekman et al. in J Neurophysiol 118(4):2194–2215, 2017) can be used to test hypotheses focused on changes in chemosensory inputs to the central pattern generator (CPG). We hypothesize that altered chemosensory function at the level of the carotid bodies and/or thenucleus tractus solitariiare responsible for the blunted response to hypoxia. Here, we use our model to explore this hypothesis by altering the properties of the gain function representing oxygen sensing inputs to the CPG. We then vary other parameters in the model and show that oxygen carrying capacity is the most salient factor for producing silent hypoxemia. We call for clinicians to measure hematocrit as a clinical index of altered physiology in response to COVID-19 infection.

 

Reducing the cost of hydrogen transport is an important priority for the proliferation of clean hydrogen to decarbonize the economy. It is possible to alleviate the hydrogen transportation costs by delivering them via existing natural gas pipeline infrastructure. This strategy, however, necessitates the dilution of hydrogen by blending it with natural gas as hydrogen embrittlement pipeline materials. In this work, we deploy high-temperature polymer electrolyte membrane electrochemical hydrogen pumps (HT-PEM EHPs) to purify hydrogen from dilute hydrogen–natural gas mixtures (5 to 20 vol % hydrogen). Interestingly, we observe that activation overpotentials govern HT-PEM EHP polarization when feeding dilute hydrogen mixtures. Pressurizing the anode to 1.76 barabs enables us to ameliorate interfacial mass transfer resistance and achieve an EHP limiting current density of 1.4 A cm–2 with a 10 vol % of hydrogen in a natural gas feed. The HT-PEM EHP showed a small degradation rate, 44 μV h–1, during a 100 h durability test.