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Cosmic neutrinos are expected to include a significant flux of tau neutrinos due to flavor mixing over astronomical length scales. However, the tau-neutrino content of astrophysical neutrinos is poorly constrained and a significant flux of cosmogenic tau neutrinos awaits discovery. Earth-skimming tau neutrinos undergo charged-current interactions that result in a tau lepton exiting the Earth. The tau lepton decay generates anextensive air shower and geomagnetic radio emission. To target the tau neutrinos, we present a new tau neutrino detector concept that uses phased antenna arrays placed on high elevation mountains. Simulation studies indicate that a modest array size and small number of stations can achieve competitive sensitivity, provided the receivers are at highs enough elevation.

In-ice radio arrays are optimized for detecting the highest energy, cosmogenic neutrinos expected to be produced though cosmic ray interactions with background photons. However, there are two expected populations of high energy neutrinos: the astrophysical flux observed by IceCube (~1 PeV) and the cosmogenic flux (~ 1017 eV or 100 PeV). Typical radio arrays employ a noise-riding trigger, which limits their minimum energy threshold based on the background noise temperature of the ice. Phased radio arrays could lower the energy threshold by combining the signals from several channels before triggering, thereby improving the signal-to-noise at the trigger level. Reducing the energy threshold would allow radio experiments to more efficiently overlap with optical Cherenkov neutrino telescopes as well as for more efficient searches for cosmogenic neutrinos. We discuss the proposed technique and prototypical phased arrays deployed in an anechoic chamber and at Greenland’s Summit Station.

Abstract We present a feasibility study for passive sounding of Uranian icy moons using Uranian Kilometric Radio (UKR) emissions in the 100–900 kHz band. We provide a summary description of the observation geometry, the UKR characteristics, and estimate the sensitivity for an instrument analogous to the Cassini Radio Plasma Wave Science (RPWS) but with a modified receiver digitizer and signal processing chain. We show that the concept has the potential to directly and unambiguously detect cold oceans within Uranian satellites and provide strong constraints on the interior structure in the presence of warm or no oceans. As part of a geophysical payload, the concept could therefore have a key role in the detection of oceans within the Uranian satellites. The main limitation of the concept is coherence losses attributed to the extended source size of the UKR and dependence on the illumination geometry. These factors represent constraints on the tour design of a future Uranus mission in terms of flyby altitudes and encounter timing.

This work describes the instrumental error budget for space‐based measurements of the absolute flux of the sky synchrotron spectrum at frequencies below the ionospheric cutoff (≲ $\lesssim $20 MHz). We focus on an architecture using electrically short dipoles onboard a small satellite. The error budget combines the contributions of the dipole dimensions, plasma noise, stray capacitance, and front‐end amplifier input impedance. We treat the errors using both a Monte Carlo error propagation model and an analytical method. This error budget can be applied to a variety of experiments and used to ultimately improve the sensing capabilities of space‐based electrically short dipole instruments. The impact of individual uncertainty components, particularly stray capacitance, is explored in more detail. Plain Language Summary: This work presents an analysis on the uncertainties from a dipole antenna on a spacecraft that is measuring the Galactic background low frequency radio signal. The focus is on the uncertainties associated with the instruments, such as the dimensions of the dipole antenna. A model was constructed that determines the measurement uncertainty given initial parameters. The results were explored to better understand how the uncertainty in this measurement can be lowered. Key Points: An instrumental error budget was built for space‐based measurements of the absolute flux of the sky synchrotron spectrum below 20 MHzContributions from dipole dimensions, plasma noise, stray capacitance, and the amplifier were combined with a Monte Carlo uncertainty modelThe impact of individual parameters was explored, highlighting the importance of managing stray capacitance and dipole length uncertainties [ABSTRACT FROM AUTHOR]

We present a feasibility study for passive sounding of Uranian icy moons using Uranian Kilometric Radio (UKR) emissions in the 100–900 kHz band. We provide a summary description of the observation geometry, the UKR characteristics, and estimate the sensitivity for an instrument analogous to the Cassini Radio Plasma Wave Science (RPWS) but with a modified receiver digitizer and signal processing chain. We show that the concept has the potential to directly and unambiguously detect cold oceans within Uranian satellites and provide strong constraints on the interior structure in the presence of warm or no oceans. As part of a geophysical payload, the concept could therefore have a key role in the detection of oceans within the Uranian satellites. The main limitation of the concept is coherence losses attributed to the extended source size of the UKR and dependence on the illumination geometry. These factors represent constraints on the tour design of a future Uranus mission in terms of flyby altitudes and encounter timing. Plain Language Summary: The large moons of Uranus are hypothesized to have subsurface oceans beneath their icy crusts. This paper analyzes the possibility to use natural radio emissions originating from Uranian auroras to probe for these oceans. Cold ice is transparent to radio waves allowing reflections from liquid water to be readily observed. Monitoring the radio noise patterns from Uranus and searching for the reflections could constitute a direct way to detect the subsurface oceans. Key Points: Passive Sounding of the Uranian moons is a promising concept and no insurmountable obstacles have been identifiedIn the presence of NH3 rich oceans, the direct detection of the ice‐ocean interface is feasibleThe method works best for the outer moons and low ocean temperatures, making it complementary to magnetic induction measurements [ABSTRACT FROM AUTHOR]

As early T cell precursors transition from multipotentiality to T lineage commitment, they change expression of multiple transcription factors. It is unclear whether individual transcription factors directly control choices between T cell identity and some alternative fate or whether these factors mostly affect proliferation or survival during the normal commitment process. Here, we unraveled the impacts of deleting individual transcription factors at two stages in early T cell development, using synchronized in vitro differentiation systems, single-cell RNA-seq with batch indexing, and controlled gene-disruption strategies. First, using a customized method for single-cell CRISPR disruption, we defined how the early-acting transcription factors Bcl11a, Erg, Spi1 (PU.1), Gata3, and Tcf7 (TCF1) function before commitment. The results revealed a kinetic tug of war within individual cells between T cell factors Tcf7 and Gata3 and progenitor factors Spi1 and Bcl11a, with an unexpected guidance role for Erg. Second, we tested how activation of transcription factor Bcl11b during commitment altered ongoing cellular programs. In knockout cells where Bcl11b expression was prevented, the cells did not undergo developmental arrest, instead following an alternative path as T lineage commitment was blocked. A stepwise, time-dependent regulatory cascade began with immediate-early transcription factor activation and E protein inhibition, finally leading Bcl11b knockout cells toward exit from the T cell pathway. Last, gene regulatory networks of transcription factor cross-regulation were extracted from the single-cell transcriptome results, characterizing the specification network operating before T lineage commitment and revealing its links to both the Bcl11b knockout alternative network and the network consolidating T cell identity during commitment. Knockout commitment: Many transcription factors are involved in the lineage commitment of early T cell precursors, yet how individual transcription factors alter early T cell development is not well defined. Here, Zhou et al. used CRISPR to knockout various transcription factors (Bcl11a, Erg, Spi1, Gata3, Tcf7, and Bcl11b) to determine their individual roles in T cell lineage progression via single-cell transcriptomics. They found that knockout of each of these genes altered the progression of T cells in similar and unique ways, allowing them to identify various gene regulatory networks linked to specific transcription factors. Specifically, they found that Bcl11b was involved in progenitors exiting the T cell pathway. Thus, this work provides a resource and method for studying the dynamics of various transcription factors during T cell lineage commitment. [ABSTRACT FROM AUTHOR]

Recent work has demonstrated a passive radio sounding approach that uses the Sun as a source for echo detection and ranging. As the Sun is a moving source with a position that is known a priori, we evaluate this technique’s capabilities to measure the echo’s phase history, map topography, and perform synthetic aperture radar (SAR) focusing. Here, we present our approach to implementing passive SAR using a compact, temporally incoherent radio-astronomical source as a signal of opportunity. We first evaluate the passive system’s capabilities to obtain an echo from a rough surface by determining the critical signal-to-noise ratio (SNR) for reliably observing the Sun’s echo reflection with our passive instrument. We then demonstrate that our technique can detect the necessary changes in range, phase, and reflectivity of an echo from the Sun. We next present the experimental results of our passive radar testing using the Sun at Dante’s View, Death Valley, to highlight this technique’s ability to perform 2-D imaging. Finally, with synthetic data, we demonstrate that we can use time-domain backprojection to focus a planar white noise signal, perform passive SAR imaging, and improve the measurement’s SNR and azimuth resolution. The results of passive SAR focusing on white noise highlight the potential for the Sun and Jupiter’s radio emissions to perform surface and subsurface imaging for planetary and terrestrial observations. [ABSTRACT FROM AUTHOR]

Ice‐penetrating radar observations are critical for projecting ice‐sheet contribution to sea‐level rise; however, these prognostic models have significant uncertainties due to an incomplete understanding of glacial subsurface processes. Existing radars that can characterize subsurface conditions are too resource‐intensive to simultaneously monitor ice sheets at both the necessary temporal—daily to multiannual—and spatial—tributary to continental—scales. Here, we investigate using an ambient radio source, instead of transmitting a signal, for glaciological monitoring. We demonstrate, for the first time, passive radio sounding using the Sun to accurately measure ice thickness on Store Glacier, Greenland. Passive radar sounding could provide low‐resource time‐series measurements of the cryosphere, enabling us to observe and understand evolving englacial and subglacial conditions across Greenland and Antarctica with unprecedented coverage and resolution. Plain Language Summary: Traditional ice‐penetrating radars transmit a powerful electromagnetic pulse and record the echo's delay time and power to measure ice sheet thickness and subsurface conditions. While active radar sounding is the principle remote sensing technique used to observe the subsurface of Greenland and Antarctica, existing radar systems are resource‐intensive in terms of cost, power, and logistics when simultaneously monitoring ice sheets at both their evolving temporal (daily to multiannual) and spatial (tributary to continental) scales. However, these observations are critical as ice sheet contribution to sea‐level rise presents one of the greatest challenges our society faces in the next century. We address this challenge by developing a novel, low‐resource, passive radar sounding technique that uses ambient radio signals from the Sun to observe the subsurface of ice sheets at these spatiotemporal scales, instead of transmitting its own powerful radio signal for echo detection. We first demonstrate passive radio sounding using the Sun to accurately measure ice thickness on Store Glacier, Greenland. We then evaluate the passive radar's performance and ability to provide valuable glaciological observations, such as melt rates, bed reflectivity changes, and englacial water storage that have traditionally been obtained using active radar systems but never passively. Key Points: We demonstrate a novel "passive" radar sounding approach using the Sun as a radio source to measure ice sheet thickness for the first timeWe evaluate the passive radar's potential to provide continuous records of ice thickness changes, basal conditions, and subsurface processesThis demonstration charts a course for the development of low‐resource, continuous and pervasive monitoring of glacier subsurface conditions [ABSTRACT FROM AUTHOR]

Recent studies have proposed that Jovian decametric radiation (DAM) can be effectively exploited for probing the subsurface of Jupiter’s icy moons by using passive radio sounding. However, these studies were based on the assumption that Jovian noise is white and stationary. Therefore, additional investigations into the temporal stability, predictability, and spectral properties of Jovian noise are required to fully assess the potential of passive radar sounding and improve the acquisitions planning. In this article, we investigate these properties of the Jovian DAM to understand their impact on radar sounding performance. This is done by analyzing the recently available radio spectra acquired by the JUNO Waves instrument. Results are also evaluated for the specific case of the Radar for Icy Moon Exploration (RIME) and the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) that have been selected for European Space Agency (ESA) and NASA missions to Ganymede and Europa. Our results show that the Jovian DAM is not perfectly white, but no severe distortions in the range response should be expected. The results on spatiotemporal occurrence show that Jupiter’s DAM has a variable probability of occurrence, which is rather sporadic for some frequency ranges. The results on RIME and REASON flybys show that the Jovian DAM occurrence probability is relatively low for selected sub-Jovian flybys at Europa. For the RIME Ganymede orbital phase, a large number of high occurrence passive acquisition opportunities are expected. The experimental results also show that a large bandwidth receiver would enhance the chance of recording Jovian noise. [ABSTRACT FROM AUTHOR]

Notch signaling is the dominant intercellular signaling input during the earliest stages of T cell development in the thymus. Although Notch1 is known to be indispensable, we show that it does not mediate all Notch signaling in precommitment stages: Notch2 initially works in parallel to promote early murine T cell development and antagonize other fates. Notch-regulated target genes before and after T lineage commitment change dynamically, and we show that this partially reflects shifts in genome-wide DNA binding by RBPJ, the transcription factor activated by complex formation with the Notch intracellular domain. Although Notch signaling and transcription factor PU.1 can activate some common targets in precommitment T progenitors, Notch signaling and PU.1 activity have functionally antagonistic effects on multiple targets, delineating separation of pro-T cells from alternative PU.1-dependent fates. These results define a distinct mechanism of Notch signal response that distinguishes the initial stages of murine T cell development. [ABSTRACT FROM AUTHOR]

The Antarctic Impulsive Transient Antenna (ANITA) balloon experiment was designed to detect radio signals initiated by high-energy neutrinos and cosmic ray (CR) air showers. These signals are typically discriminated by the polarization and phase inversions of the radio signal. The reflected signal from CRs suffer phase inversion compared to a direct 'tau neutrino' event. In this paper, we study subsurface reflection, which can occur without phase inversion, in the context of the two anomalous up-going events reported by ANITA. It is found that subsurface layers and firn density inversions may plausibly account for the events, while ice fabric layers and wind ablation crusts could also play a role. This hypothesis can be tested with radar surveying of the Antarctic region in the vicinity of the anomalous ANITA events. Future experiments should not use phase inversion as a sole criterion to discriminate between down-going and up-going events, unless the subsurface reflection properties are well understood. [ABSTRACT FROM AUTHOR]

Ice sheet contributions to sea level rise present one of the greatest challenges that our society will face in the next century. However, models predicting sea level rise due to ice melt lack critical information regarding processes at the base of ice sheets. Although radio echo sounders are powerful tools that are currently used to constrain subglacial conditions, existing ice-penetrating radar systems are too resource-intensive in terms of cost, power, and logistics for multiyear deployment at a large scale. To address this, we present passive radio sounding as a low-resource approach for observing ice sheets across a range of spatial and temporal scales. While passive radar has been used for target tracking and military purposes, it has never been used for the sounding of ice sheets. Some recent work has proposed using passive radio sounding of Europa’s icy shell using Jupiter’s decametric radiation. We expand on this idea by evaluating and discussing challenges and opportunities for developing a passive radio sounder using the Sun as an illuminator of opportunity for echo detection. Here, our prototype instrument sits on the side of a cliff and measures the Sun’s direct and reflected path off the ocean surface. We then use an autocorrelation-based method to extract the amplitude and delay of the reflection. This serves as the first in situ demonstration of an autocorrelation-based passive sounder using a compact astronomical white noise signal. [ABSTRACT FROM AUTHOR]

We estimate the sensitivity of a lander-based instrument for the passive radio detection of a subsurface ocean beneath the ice shell of Europa, expected to be between 3 km and 30 km thick, using Jupiter's decametric radiation. A passive technique was previously studied for an orbiter. Using passive detection in a lander platform provides a point measurement with significant improvements due to largely reduced losses from surface roughness effects, longer integration times, and diminished dispersion due to ionospheric effects allowing operation at lower frequencies and a wider band. A passive sounder on-board a lander provides a low resource instrument sensitive to subsurface ocean at Europa up to depths of 6.9 km for high loss ice (16 dB/km two-way attenuation rate) and 69 km for pure ice (1.6 dB/km). [ABSTRACT FROM AUTHOR]

The Antarctic Impulsive Transient Antenna (ANITA) balloon experiment was designed to detect radio signals initiated by high-energy neutrinos and cosmic ray (CR) air showers. These signals are typically discriminated by the polarization and phase inversions of the radio signal. The reflected signal from CRs suffer phase inversion compared to a direct ‘tau neutrino’ event. In this paper, we study subsurface reflection, which can occur without phase inversion, in the context of the two anomalous up-going events reported by ANITA. It is found that subsurface layers and firn density inversions may plausibly account for the events, while ice fabric layers and wind ablation crusts could also play a role. This hypothesis can be tested with radar surveying of the Antarctic region in the vicinity of the anomalous ANITA events. Future experiments should not use phase inversion as a sole criterion to discriminate between down-going and up-going events, unless the subsurface reflection properties are well understood.