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E-cadherin mediates apical membrane initiation site localisation during de novo polarisation of epithelial cavities
No full textIndividual cells within de novo polarising tubes and cavities must integrate their forming apical domains into a centralised apical membrane initiation site (AMIS). This is necessary to enable organised lumen formation within multi-cellular tissue. Despite the well-documented importance of cell division in localising the AMIS, we have found a division-independent mechanism of AMIS localisation that relies instead on Cadherin-mediated cell–cell adhesion. Our study of de novo polarising mouse embryonic stem cells (mESCs) cultured in 3D suggests that cell–cell adhesion localises apical proteins such as PAR-6 to a centralised AMIS. Unexpectedly, we also found that mESC clusters lacking functional E-cadherin still formed a lumen-like cavity in the absence of AMIS localisation but did so at a later stage of development via a “closure” mechanism, instead of via hollowing. This work suggests that there are two, interrelated mechanisms of apical polarity localisation: cell adhesion and cell division. Alignment of these mechanisms in space allows for redundancy in the system and ensures the development of a coherent epithelial structure within a growing organ
The Long-stable Hard State of XTE J1752-223 and the Disk Truncation Dilemma
No full textThe degree to which the thin accretion disks of black hole X-ray binaries are truncated during hard spectral states remains a contentious open question in black hole astrophysics. During its singular observed outburst in 2009–2010, the black hole X-ray binary XTE J1752−223 spent ∼1 month in a long-stable hard spectral state at a luminosity of ∼0.02–0.1 L_Edd. It was observed with 56 RXTE pointings during this period, with simultaneous Swift-XRT daily coverage during the first 10 days of the RXTE observations. While reflection modeling has been extensively explored in the analysis of these data, there is disagreement surrounding the geometry of the accretion disk and corona implied by the reflection features. We reexamine the combined, high signal-to-noise, simultaneous Swift and RXTE observations, and perform extensive reflection modeling with the latest relxill suite of reflection models, including newer high disk density models. We show that reflection modeling requires that the disk be within ∼5 R_ISCO during the hard spectral state, while weaker constraints from the thermal disk emission imply higher truncation (R_in = 6–80 R_ISCO). We also explore more complex coronal continuum models, allowing for two Comptonization components instead of one, and show that the reflection features still require only a mildly truncated disk. Finally we present a full comparison of our results to previous constraints found from analyses of the same data set
Mapping effective connectivity of human amygdala subdivisions with intracranial stimulation
No full textThe primate amygdala is a complex consisting of over a dozen nuclei that have been implicated in a host of cognitive functions, individual differences, and psychiatric illnesses. These functions are implemented through distinct connectivity profiles, which have been documented in animals but remain largely unknown in humans. Here we present results from 25 neurosurgical patients who had concurrent electrical stimulation of the amygdala with intracranial electroencephalography (electrical stimulation tract-tracing; es-TT), or fMRI (electrical stimulation fMRI; es-fMRI), methods providing strong inferences about effective connectivity of amygdala subdivisions with the rest of the brain. We quantified functional connectivity with medial and lateral amygdala, the temporal order of these connections on the timescale of milliseconds, and also detail second-order effective connectivity among the key nodes. These findings provide a uniquely detailed characterization of human amygdala functional connectivity that will inform functional neuroimaging studies in healthy and clinical populations
Effects of the environment and feedback physics on the initial mass function of stars in the STARFORGE simulations
No full textOne of the key mysteries of star formation is the origin of the stellar initial mass function (IMF). The IMF is observed to be nearly universal in the Milky Way and its satellites, and significant variations are only inferred in extreme environments, such as the cores of massive elliptical galaxies and the Central Molecular Zone. In this work, we present simulations from the STARFORGE project that are the first cloud-scale radiation-magnetohydrodynamic simulations that follow individual stars and include all relevant physical processes. The simulations include detailed gas thermodynamics, as well as stellar feedback in the form of protostellar jets, stellar radiation, winds, and supernovae. In this work, we focus on how stellar radiation, winds, and supernovae impact star-forming clouds. Radiative feedback plays a major role in quenching star formation and disrupting the cloud; however, the IMF peak is predominantly set by protostellar jet physics. We find that the effect of stellar winds is minor, and supernovae ‘occur too late’ to affect the IMF or quench star formation. We also investigate the effects of initial conditions on the IMF. We find that the IMF is insensitive to the initial turbulence, cloud mass, and cloud surface density, even though these parameters significantly shape the star formation history of the cloud, including the final star formation efficiency. Meanwhile, the characteristic stellar mass depends weakly on metallicity and the interstellar radiation field, which essentially set the average gas temperature. Finally, while turbulent driving and the level of magnetization strongly influence the star formation history, they only influence the high-mass slope of the IMF
When Choices Are Mistakes
No full textUsing a laboratory experiment, we identify whether decision-makers consider it a mistake to violate canonical choice axioms. To do this, we incentivize subjects to report axioms they want their decisions to satisfy. Then, subjects make lottery choices which might conflict with their axiom preferences. In instances of conflict, we give subjects the opportunity to re-evaluate their decisions. We find that many individuals want to follow canonical axioms and revise their choices to be consistent with the axioms. In a shorter online experiment, we show correlations of mistakes with response times and measures of cognition
The geometric distribution of Selmer groups of elliptic curves over function fields
No full textFix a positive integer n and a finite field F_q. We study the joint distribution of the rank rk (E), the n-Selmer group Sel_n (E), and the n-torsion in the Tate–Shafarevich group III(E)[n] as E varies over elliptic curves of fixed height d ≥ 2 over F_q (T). We compute this joint distribution in the large q limit. We also show that the "large q, then large height" limit of this distribution agrees with the one predicted by Bhargava–Kane–Lenstra–Poonen–Rains
Meeting With the Goddess: Notes from the First Symposium on Venus Science Enabled by Human Proximity
No full textIn July of 2022, the Keck Institute for Space Studies (KISS) hosted a symposium entitled "Science Enabled by Human Proximity to Venus." Convened to explore the potential science that could be enabled by human mission fly-bys of Venus while en route to Mars, the symposium conversation expanded to encompass the policy and social rationales for a dedicated human mission to Venus, as well as a new concept for a potential human mission to Venus—The Venus Back-Flip.
This symposium summary, compiled by contributions from symposium participants listed at the beginning of this report, is the start of a broader discussion that is likely to become more and more relevant in the coming years as the multiple human space exploration capabilities under development provide potential opportunities to execute a human mission to Venus—whether en route to Mars or as a dedicated mission. This summary will outline some of the relevant options for Venus human fly-by and orbital missions, some of the new or enhanced science investigations that could be achieved in tandem with human fly-by or orbital missions, why integrating Venus into the overall Moon-to-Mars strategy may be valuable, how social and cultural activities might advance human missions to Venus, and why Venus may deserve its own journey of exploration independent of other destinations.
This report is a summary of the discussions, observations, and ideas that were generated at the symposium. The summary is written primarily for three types of audiences: human spaceflight mission and campaign planners, Venus scientists and technical innovators, and individuals interested in the social aspects of organizing to promote the human exploration of Venus.
The symposium revealed that Venus is a desirable human spaceflight destination in its own right. The compelling narrative of exploration combines planetary science at Venus, the search for life in its clouds, and an encounter with our sister planet that may shed light on our future climate
Macromolecular Crowding as an Intracellular Stimulus for Responsive Nanomaterials
No full textStimuli-responsive materials are exploited in biological, materials, and sensing applications. We introduce a new endogenous stimulus, biomacromolecule crowding, which we achieve by leveraging changes in thermoresponsive properties of polymers upon high concentrations of crowding agents. We prepare poly(2-oxazoline) amphiphiles that exhibit lower critical solution temperatures (LCST) in serum above physiological temperature. These amphiphiles stabilize oil-in-water nanoemulsions at temperatures below the LCST but are ineffective surfactants above the LCST, resulting in emulsion fusion. We find that the transformations observed upon heating nanoemulsions above their surfactant’s LCST can instead be induced at physiological temperatures through the addition of polymers and protein, rendering thermoresponsive materials “crowding responsive.” We demonstrate that the cytosol is a stimulus for nanoemulsions, with droplet fusion occurring upon injection into cells of living zebrafish embryos. This report sets the stage for classes of thermoresponsive materials to respond to macromolecule concentration rather than temperature changes
Testing the key role of the stellar mass-halo mass relation in galaxy merger rates and morphologies via DECODE, a novel Discrete statistical sEmi-empiriCal mODEl
No full textThe relative roles of mergers and star formation in regulating galaxy growth are still a matter of intense debate. We here present our DECODE, a new Discrete statistical sEmi-empiriCal mODEl specifically designed to predict rapidly and efficiently, in a full cosmological context, galaxy assembly, and merger histories for any given input stellar mass–halo mass (SMHM) relation. DECODE generates object-by-object dark matter merger trees (hence discrete) from accurate subhalo mass and infall redshift probability functions (hence statistical) for all subhaloes, including those residing within other subhaloes, with virtually no resolution limits on mass or volume. Merger trees are then converted into galaxy assembly histories via an input, redshift-dependent SMHM relation, which is highly sensitive to the significant systematics in the galaxy stellar mass function and on its evolution with cosmic time. DECODE can accurately reproduce the predicted mean galaxy merger rates and assembly histories of hydrodynamic simulations and semi-analytical models, when adopting in input their SMHM relations. In this work, we use DECODE to prove that only SMHM relations implied by stellar mass functions characterized by large abundances of massive galaxies and significant redshift evolution, at least at M_* ≳ 10^(11) M_⊙, can simultaneously reproduce the local abundances of satellite galaxies, the galaxy (major merger) pairs since z ∼ 3, and the growth of Brightest Cluster Galaxies. The same models can also reproduce the local fraction of elliptical galaxies, on the assumption that these are strictly formed by major mergers, but not the full bulge-to-disc ratio distributions, which require additional processes
Ozone Pollution and Its Response to Nitrogen Dioxide Change from a Dense Ground-Based Network in the Yangtze River Delta: Implications for Ozone Abatement in Urban Agglomeration
No full textUnderstanding the response of tropospheric ozone (O₃) to nitrogen dioxide (NO₂) change is important for local O₃ control. The relationship between O₃ and NO₂ at county scale in China has been extensively studied using models, but there is a lack of results from direct measurements. In this study, we used measurements of O₃, NO₂ and meteorological conditions from a dense network in the Yangtze River Delta (YRD), and satellite observed formaldehyde (HCHO) and NO₂ column densities for the analysis of O₃ variabilities and its relationship to NO₂. As a result, severe O₃ pollution occurred mainly in Shanghai city, southern Jiangsu and northern Zhejiang provinces in YRD during April–September. In addition, meteorological conditions could explain 54% the diurnal O₃ variation over YRD. During April–September 2015–2021, O₃ showed a significant positive relationship (r = 0.61 ± 0.10) with NO₂ after removing the impact from meteorological conditions. However, the relationship could be reversed with NO₂ concentration change. Our result suggested that the controllable O₃ related to NO₂ change is up to 100 μg·m⁻³ in megacities over Shanghai and northern Zhejiang province. The O₃ is much more sensitive to the NO₂ reduction in megacities than surrounding areas. Our results evaluate the different impacts of NO₂ changes on O₃ formation, which provides explanation for the simultaneously alleviated O₃ pollution and reduced NO₂ in 2020 in Shanghai and northern Zhejiang, as well as the increased O₃ in most counties before 2019 with reduced NO₂ during October–March. The driving mechanism as revealed from this study for O₃ and NO₂ will be valuable for the O₃ abatement through NO₂ reduction at sub-county scale over YRD in China