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Bennu regolith mobilized by TAGSAM: Expectations for the OSIRIS-REx sample collection event and application to understanding naturally ejected particles
The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission will collect material from the asteroid Bennu and return it to Earth. The sample collection method uses pressurized nitrogen gas to mobilize regolith. It is likely that the gas will mobilize more, potentially much more, material than is captured by the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) for return. The amount, velocities, and fate of this mobilized material have important implications for our understanding of Bennu's physical properties and processes, such as impact cratering, regolith mobility, and the recently observed natural ejection of particles. The nature of the TAGSAM-ejected material is also significant for mission operations. We conducted numerical simulations and ground-based tests to estimate the amount and speeds of material mobilized by the sampling event. The estimated ejected masses range from 12 kg to >165 kg; given that Bennu appears to be a nearly strengthless rubble pile, the higher end of the mass range is more likely. Maximum ejection speeds for 1-cm-diameter particles could reach 10 m/s; smaller particles will be ejected at faster speeds. Minimum ejection speeds will be determined by the as yet unknown cohesive strength of Bennu's regolith. Material ejected more slowly than 10 cm/s will reaccrete on Bennu; material ejected between 10 and 30 cm/s may or may not reaccrete; and material ejected faster than 30 cm/s will escape. Some of the ejected material is predicted to remain in transient orbits around Bennu. The lifetimes of these orbits span from days to several weeks, the maximum duration of our integrations. Reaccreted material should be concentrated in a region near the sample site, although re-impacts will occur globally. Gas from TAGSAM will mobilize material beyond the contact perimeter; because of interactions between cohesion and microgravity, there is a preferred particle size of mobility, predicted to be tens of centimeters, depending on the TAG latitude. Observing Bennu during and after the sampling event will make it possible to test these predictions and understand how the asteroid responds to disruption and particle mobility across the surface
Phospholipase C-β4 Is Essential for the Progression of the Normal Sleep Sequence and Ultradian Body Temperature Rhythms in Mice
BACKGROUND: THE SLEEP SEQUENCE: i) non-REM sleep, ii) REM sleep, and iii) wakefulness, is stable and widely preserved in mammals, but the underlying mechanisms are unknown. It has been shown that this sequence is disrupted by sudden REM sleep onset during active wakefulness (i.e., narcolepsy) in orexin-deficient mutant animals. Phospholipase C (PLC) mediates the signaling of numerous metabotropic receptors, including orexin receptors. Among the several PLC subtypes, the beta4 subtype is uniquely localized in the geniculate nucleus of thalamus which is hypothesized to have a critical role in the transition and maintenance of sleep stages. In fact, we have reported irregular theta wave frequency during REM sleep in PLC-beta4-deficient mutant (PLC-beta4-/-) mice. Daily behavioral phenotypes and metabotropic receptors involved have not been analyzed in detail in PLC-beta4-/- mice, however. METHODOLOGY/PRINCIPAL FINDINGS: Therefore, we analyzed 24-h sleep electroencephalogram in PLC-beta4-/- mice. PLC-beta4-/- mice exhibited normal non-REM sleep both during the day and nighttime. PLC-beta4-/- mice, however, exhibited increased REM sleep during the night, their active period. Also, their sleep was fragmented with unusual wake-to-REM sleep transitions, both during the day and nighttime. In addition, PLC-beta4-/- mice reduced ultradian body temperature rhythms and elevated body temperatures during the daytime, but had normal homeothermal response to acute shifts in ambient temperatures (22 degrees C-4 degrees C). Within the most likely brain areas to produce these behavioral phenotypes, we found that, not orexin, but group-1 metabotropic glutamate receptor (mGluR)-mediated Ca(2+) mobilization was significantly reduced in the dorsal lateral geniculate nucleus (LGNd) of PLC-beta4-/- mice. Voltage clamp recordings revealed that group-1 mGluR-mediated currents in LGNd relay neurons (inward in wild-type mice) were outward in PLC-beta4-/- mice. CONCLUSIONS/SIGNIFICANCE: These lines of evidence indicate that impaired LGNd relay, possibly mediated via group-1 mGluR, may underlie irregular sleep sequences and ultradian body temperature rhythms in PLC-beta4-/- mice
The Neuronal Transition Probability (NTP) Model for the Dynamic Progression of Non-REM Sleep EEG: The Role of the Suprachiasmatic Nucleus
Little attention has gone into linking to its neuronal substrates the dynamic structure of non-rapid-eye-movement (NREM) sleep, defined as the pattern of time-course power in all frequency bands across an entire episode. Using the spectral power time-courses in the sleep electroencephalogram (EEG), we showed in the typical first episode, several moves towards-and-away from deep sleep, each having an identical pattern linking the major frequency bands beta, sigma and delta. The neuronal transition probability model (NTP) – in fitting the data well – successfully explained the pattern as resulting from stochastic transitions of the firing-rates of the thalamically-projecting brainstem-activating neurons, alternating between two steady dynamic-states (towards-and-away from deep sleep) each initiated by a so-far unidentified flip-flop. The aims here are to identify this flip-flop and to demonstrate that the model fits well all NREM episodes, not just the first. Using published data on suprachiasmatic nucleus (SCN) activity we show that the SCN has the information required to provide a threshold-triggered flip-flop for timing the towards-and-away alternations, information provided by sleep-relevant feedback to the SCN. NTP then determines the pattern of spectral power within each dynamic-state. NTP was fitted to individual NREM episodes 1–4, using data from 30 healthy subjects aged 20–30 years, and the quality of fit for each NREM measured. We show that the model fits well all NREM episodes and the best-fit probability-set is found to be effectively the same in fitting all subject data. The significant model-data agreement, the constant probability parameter and the proposed role of the SCN add considerable strength to the model. With it we link for the first time findings at cellular level and detailed time-course data at EEG level, to give a coherent picture of NREM dynamics over the entire night and over hierarchic brain levels all the way from the SCN to the EEG
The essential oil from Lippia alba induces biochemical stress in the silver catfish (Rhamdia quelen) after transportation
Circuit-based interrogation of sleep control.
Sleep is a fundamental biological process observed widely in the animal kingdom, but the neural circuits generating sleep remain poorly understood. Understanding the brain mechanisms controlling sleep requires the identification of key neurons in the control circuits and mapping of their synaptic connections. Technical innovations over the past decade have greatly facilitated dissection of the sleep circuits. This has set the stage for understanding how a variety of environmental and physiological factors influence sleep. The ability to initiate and terminate sleep on command will also help us to elucidate its functions within and beyond the brain