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Reprogramming of trunk neural crest to a cranial crest-like identity alters their transcriptome and developmental potential
No full textNeural crest cells along the body axis of avian embryos differ in their developmental potential, such that the cranial neural crest forms cartilage and bone whereas the trunk neural crest is unable to do so. Previous studies have identified a cranial crest-specific subcircuit that can imbue the trunk neural crest with the ability to form cartilage after grafting to the head. Here, we examine transcriptional and cell fate changes that accompany this reprogramming. First, we examined whether reprogrammed trunk neural crest maintain the ability to form cartilage in their endogenous environment in the absence of cues from the head. The results show that some reprogrammed cells contribute to normal trunk neural crest derivatives, whereas others migrate ectopically to the forming vertebrae and express cartilage markers, thus mimicking heterotypically transplanted cranial crest cells. We find that reprogrammed trunk neural crest upregulated more than 3000 genes in common with cranial neural crest, including numerous transcriptional regulators. In contrast, many trunk neural crest genes are downregulated. Together, our findings show that reprogramming trunk neural crest with cranial crest subcircuit genes alters their gene regulatory program and developmental potential to be more cranial crest-like
Dominant Two-Dimensional Electron–Phonon Interactions in the Bulk Dirac Semimetal Na₃Bi
No full textBulk Dirac semimetals (DSMs) exhibit unconventional transport properties and phase transitions due to their peculiar low-energy band structure, yet the electronic interactions governing nonequilibrium phenomena in DSMs are not fully understood. Here we show that electron–phonon (e–ph) interactions in a prototypical bulk DSM, Na3Bi, are predominantly two-dimensional (2D). Our first-principles calculations reveal a 2D optical phonon with strong e–ph interactions associated with in-plane vibrations of Na atoms. We show that this 2D mode governs e–ph scattering and charge transport in Na₃Bi and induces a dynamical phase transition to a Weyl semimetal. Our work advances the quantitative analysis of electron interactions in Na3Bi and reveals a dominant low-dimensional interaction in a bulk Dirac semimetal
TOI-2525 b and c: A Pair of Massive Warm Giant Planets with Strong Transit Timing Variations Revealed by TESS
No full textThe K-type star TOI-2525 has an estimated mass of M = 0.849^(+0.024)_(-0.033) M_⊙ and radius of R = 0.785^(+0.007)_(-0.007) R_⊙ observed by the TESS mission in 22 sectors (within sectors 1 and 39). The TESS light curves yield significant transit events of two companions, which show strong transit timing variations (TTVs) with a semiamplitude of ∼6 hr. We performed TTV dynamical and photodynamical light-curve analysis of the TESS data combined with radial velocity measurements from FEROS and PFS, and we confirmed the planetary nature of these companions. The TOI-2525 system consists of a transiting pair of planets comparable to Neptune and Jupiter with estimated dynamical masses of m_b = 0.088^(+0.005)_(-0.004) and m_c = 0.709^(+0.034)_(-0.033) M_(Jup), radii of r_b = 0.88^(+0.02)_(-0.02) and r_c = 0.98^(+0.02)_(-0.02) R_(Jup), and orbital periods of P_b = 23.288^(+0.001)_(-0.002) and P_c = 49.260^(+0.001)_(-0.001) days for the inner and outer planet, respectively. The period ratio is close to the 2:1 period commensurability, but the dynamical simulations of the system suggest that it is outside the mean-motion resonance (MMR) dynamical configuration. Object TOI-2525 b is among the lowest-density Neptune-mass planets known to date, with an estimated median density of ρ_b = 0.174^(+0.016)_(-0.015) g cm⁻³. The TOI-2525 system is very similar to the other K dwarf systems discovered by TESS, TOI-2202 and TOI-216, which are composed of almost identical K dwarf primaries and two warm giant planets near the 2:1 MMR
Success of the small mass-ratio approximation during the final orbits of binary black hole simulations
No full textRecent studies have shown the surprising effectiveness of the small mass-ratio approximation (SMR) in modeling the relativistic two-body problem even at comparable masses. Up to now this effectiveness has been demonstrated only during inspiral, before the binary transitions into plunge and merger. Here we examine the binding energy of nonspinning binary black hole simulations with mass ratios from
20
∶
1
to equal mass. We show for the first time that the binaries undergo a transition to plunge as predicted by analytic theory, and estimate the size of the transition region, which is
∼
10
gravitational wave cycles for equal mass binaries. By including transition, the SMR expansion of the binding energy is accurate until the last cycle of gravitational wave emission. This is true even for comparable mass binaries such as those observed by current gravitational wave detectors, where the transition often makes up much of the observed signal. Our work provides further evidence that the SMR approximation can be directly applied to current gravitational wave observations
Jupiter’s interior from Juno: Equation-of-state uncertainties and dilute core extent
No full textContext. The Juno mission has provided measurements of Jupiter’s gravity field with an outstanding level of accuracy, leading to better constraints on the interior of the planet. Improving our knowledge of the internal structure of Jupiter is key to understanding its formation and evolution but is also important in the framework of exoplanet exploration.
Aims. In this study, we investigated the differences between the state-of-the-art equations of state and their impact on the properties of interior models. Accounting for uncertainty on the hydrogen and helium equation of state, we assessed the span of the interior features of Jupiter.
Methods. We carried out an extensive exploration of the parameter space and studied a wide range of interior models using Markov chain Monte Carlo simulations. To consider the uncertainty on the equation of state, we allowed for modifications of the equation of state in our calculations.
Results. Our models harbour a dilute core and indicate that Jupiter’s internal entropy is higher than what is usually assumed from the Galileo probe measurements. We obtain solutions with extended dilute cores, but contrary to other recent interior models of Jupiter, we also obtain models with small dilute cores. The dilute cores in such solutions extend to ~20% of Jupiter’s mass, leading to better agreement with formation–evolution models.
Conclusions. We conclude that the equations of state used in Jupiter models have a crucial effect on the inferred structure and composition. Further explorations of the behaviour of hydrogen–helium mixtures at the pressure and temperature conditions in Jupiter will help to constrain the interior of the planet, and therefore its origin
Behaviour and the Origin of Organisms
No full textIt is common in origins of life research to view the first stages of life as the passive result of particular environmental conditions. This paper considers the alternative possibility: that the antecedents of life were already actively regulating their environment to maintain the conditions necessary for their own persistence. In support of this proposal, we describe ‘viability-based behaviour’: a way that simple entities can adaptively regulate their environment in response to their health, and in so doing, increase the likelihood of their survival. Drawing on empirical investigations of simple self-preserving abiological systems, we argue that these viability-based behaviours are simple enough to precede neo-Darwinian evolution. We also explain how their operation can reduce the demanding requirements that mainstream theories place upon the environment(s) in which life emerged
Recovering density disturbance spectra from FLDI. Part 2: comparisons with previous methods
No full textAn exact analytical method for recovering density disturbance spectra in multi-frequency, multi-dimensional fields from focused laser differential interferometry (FLDI) measurements, developed in Part 1 [Appl. Opt. 62, 3042 (2023) [CrossRef https://opg.optica.org/ao/fulltext.cfm?uri=ao-62-12-3042&id=529079] ], is compared with previous methods for quantitative interpretation of FLDI. It is shown that previous exact analytical solutions can be recovered as special cases of the more general present method. It is also found that despite outwards dissimilarity, a previous approximate method that is becoming widely used can be related to the general model. It is demonstrated that the previous approach—while a suitable approximation for spatially restricted disturbance fields such as conical boundary layers it was originally applied to—does not work well in general applications. While corrections can be made, informed by results from the exact method, doing so offers no computational or analytical advantages
Soliton pulse pairs at multiple colors in normal dispersion microresonators
No full textSoliton microcombs are helping to advance the miniaturization of a range of comb systems. These combs mode lock through the formation of short temporal pulses in anomalous dispersion resonators. Here, a new microcomb is demonstrated that mode locks through the formation of pulse pairs in normal-dispersion coupled-ring resonators. Unlike conventional microcombs, pulses in this system cannot exist alone, and instead must phase lock in pairs to form a bright soliton comb. Also, the pulses can form at recurring spectral windows and the pulses in each pair feature different optical spectra. This pairwise mode-locking modality extends to higher dimensions and we demonstrate 3-ring systems in which 3 pulses mode lock through alternating pairwise pulse coupling. The results are demonstrated using the new CMOS-foundry platform that has not previously produced bright solitons on account of its inherent normal dispersion. The ability to generate multi-color pulse pairs over multiple rings is an important new feature for microcombs. It can extend the concept of all-optical soliton buffers and memories to multiple storage rings that multiplex pulses with respect to soliton color and that are spatially addressable. The results also suggest a new platform for the study of quantum combs and topological photonics
Low Complexity, Low Probability Patterns and Consequences for Algorithmic Probability Applications
No full textDeveloping new ways to estimate probabilities can be valuable for science, statistics, engineering, and other fields. By considering the information content of different output patterns, recent work invoking algorithmic information theory inspired arguments has shown that a priori probability predictions based on pattern complexities can be made in a broad class of input-output maps. These algorithmic probability predictions do not depend on a detailed knowledge of how output patterns were produced, or historical statistical data. Although quantitatively fairly accurate, a main weakness of these predictions is that they are given as an upper bound on the probability of a pattern, but many low complexity, low probability patterns occur, for which the upper bound has little predictive value. Here, we study this low complexity, low probability phenomenon by looking at example maps, namely a finite state transducer, natural time series data, RNA molecule structures, and polynomial curves. Some mechanisms causing low complexity, low probability behaviour are identified, and we argue this behaviour should be assumed as a default in the real-world algorithmic probability studies. Additionally, we examine some applications of algorithmic probability and discuss some implications of low complexity, low probability patterns for several research areas including simplicity in physics and biology, a priori probability predictions, Solomonoff induction and Occam’s razor, machine learning, and password guessing
Paragenesis of an Ediacaran carbonate-platform phosphorite: Constraints from optical petrography and texture-specific clumped isotope paleothermometry
No full textThe Salitre Formation is comprised of several hundred meters of primarily carbonate rocks, representing sedimentation in an intracratonic foreland basin during the Ediacaran Period (c. 600–550 Ma). The lowermost member of the Salitre Formation contains sedimentary phosphorite deposits, in which the dominant phosphate-bearing phase is cryptocrystalline carbonate-rich fluorapatite (CFA) cement. These CFA cements occur exclusively associated with digitate stromatolite buildups, decimeters to meters in vertical and lateral scale, which interfinger with cross-stratified grainstone. Notably, there are also non-phosphatic stromatolite buildups in close proximity to the phosphatic, in the same depositional facies. This implies that the mechanisms that control the distribution of phosphate cement development versus carbonate cement development are not driven by the location of depositional facies within the architecture of the Salitre paleobasin. Other models which could explain the distribution and style of phosphate mineralization there include: (1) differential diagenesis involving diagenetic fluids which infiltrate one lithofacies more pervasively than another to effect the replacement of primary cement mineralogies according to microtextural differences, and (2) differences in primary porewater chemistries over minute spatial scales which result in the formation of different primary cement phases. In this study, we present paired petrographic thin sections and novel measurements of ∆₄₇, δ¹³C_(mineral), and δ¹⁸O_(mineral). We provide a paragenetic framework for phosphatic and non-phosphatic lithofacies of the Salitre Formation which constrains the thermal and chemical alteration history of CFA, calcite, and dolomite cements. Structural carbonate in the CFA and calcite cements co-occurring in partially phosphatic digitate stromatolite buildups and adjacent carbonate grainstone generally yield similar δ¹³C_(mineral) values (0–5 ‰ VPDB), δ¹⁸O_(mineral) values (−5–0 ‰ VPDB), as well as similar ∆47 temperatures (90–115 °C) and calculated δ¹⁸O_(water) (10–19 ‰ VSMOW), supporting a scenario in which CFA and calcite formed and then both recrystallized in equilibrium with the same diagenetic fluids under low water–rock ratio conditions at depth. Dolomite cements yielded similar δ¹⁸O(mineral) values to CFA and calcite, and similar to slightly higher temperatures (85–150 °C) — supporting a scenario in which dolomite cements were recrystallized in equilibrium with a different, and isotopically lighter, generation of fluids. Given the general absence of pervasive, fabric-destructive replacement is scarce, these geochemical data do not support later stage, differential diagenesis as a mechanism for controlling the distribution of phosphatic versus non-phosphatic cements. Rather, primary differences in porewater biogeochemistry seem the likeliest explanation. This is important, as it implies that the ecology of the Ediacaran seafloor controlled the style and quality of mineralization observed today, and that the presence of CFA cements in these rocks represents a unique taphonomic window for select microbial communities