The formation of the eccentric-orbit millisecond pulsar J1903+0327 and the origin of single millisecond pulsars

The millisecond pulsar J1903+0327 is accompanied by an ordinary G-dwarf star in an unusually wide ($P_{\rm orb} \simeq 95.2$\,days) and eccentric ($e \simeq 0.44$) orbit. The standard model for producing MSPs fails to explain the orbital characteristics of this extraordinary binary, and alternative binary models are unable to explain the observables. We present a triple-star model for producing MSPs in relatively wide eccentric binaries with a normal (main-sequence) stellar companion. We start from a stable triple system consisting of a Low-Mass X-ray Binary (LMXB) with an orbital period of at least 1 day, accompanied by a G-dwarf in a wide and possibly eccentric orbit. Variations in the initial conditions naturally provide a satisfactory explanation for the unexplained triple component in the eclipsing soft X-ray transient 4U~2129+47 or the cataclysmic variable EC 19314-5915. The best explanation for J1903, however, results from the expansion of the orbit of the LMXB, driven by the mass transfer from the evolving donor star to its neutron star companion, which causes the triple eventually to becomes dynamically unstable. Using numerical computations we show that, depending on the precise system configuration at the moment the triple becomes dynamically unstable, the ejection of each of the three components is possible. If the donor star of the LMXB is ejected, a system resembling J1903, will result. If the neutron star is ejected, a single MSP results. This model therefore also provides a straightforward mechanism for forming single MSP in the Galactic disk. We conclude that the Galaxy contains some 30--300 binaries with characteristics similar to J1903, and about an order of magnitude fewer single millisecond pulsars produced with the proposed triple scenario.Comment: ApJ accepted for publicatio

Manipulating Replisome Dynamics to Enhance Lambda Red-Mediated Multiplex Genome Engineering

Disrupting the interaction between primase and helicase in Escherichia coli increases Okazaki fragment (OF) length due to less frequent primer synthesis. We exploited this feature to increase the amount of ssDNA at the lagging strand of the replication fork that is available for λ Red-mediated Multiplex Automatable Genome Engineering (MAGE). Supporting this concept, we demonstrate that MAGE enhancements correlate with OF length. Compared with a standard recombineering strain (EcNR2), the strain with the longest OFs displays on average 62% more alleles converted per clone, 239% more clones with 5 or more allele conversions and 38% fewer clones with 0 allele conversions in 1 cycle of co-selection MAGE (CoS-MAGE) with 10 synthetic oligonucleotides. Additionally, we demonstrate that both synthetic oligonucleotides and accessible ssDNA targets on the lagging strand of the replication fork are limiting factors for MAGE. Given this new insight, we generated a strain with reduced oligonucleotide degradation and increased genomic ssDNA availability, which displayed 111% more alleles converted per clone, 527% more clones with 5 or more allele conversions and 71% fewer clones with 0 allele conversions in 1 cycle of 10-plex CoS-MAGE. These improvements will facilitate ambitious genome engineering projects by minimizing dependence on time-consuming clonal isolation and screening

Affordable In-Space Transportation

Current and proposed launch systems will provide access to low-Earth orbit (LEO), and destinations beyond LEO, but the cost of delivering payloads will preclude the use of these services by many users. To develop and encourage revolutionary commercial utilization of geosynchronous orbit (GEO) and to provide an affordable means to continue NASA space science and exploration missions, the transportation costs to in-space destinations must be reduced. The principal objective of this study was to conceptually define three to four promising approaches to in-space transportation for delivery of satellites and other payloads, 3,000- to 10,000-lb class, to GEO destinations. This study established a methodology for evaluating in-space transportation systems based on life-cycle cost. The reusable concepts seemed to fare better in the evaluation than expendable, since a major driver in the life-cycle cost was the stage production cost

DIFFICULTÉS DE LA PARTICIPATION EN RECHERCHE- ACTION : retour d'expériences de modélisation d'accompagnement en appui à l'aménagement du territoire au Sénégal et à la Réunion

International audienceComment aider les institutions et acteurs locaux à investir davantage les processus d'affectation des terres pour aménager leur territoire ? La décentralisation de l'aménagement du territoire engagée à la Réunion et au Sénégal est inachevée. Malgré l'arsenal législatif, les populations locales semblent peu impliquées dans les décisions les concernant en raison notamment de la difficulté à appréhender la complexité des systèmes d'interactions entre dynamiques sociales et environnementales. Le projet Domino vise à accompagner les processus de décision en proposant aux acteurs de construire et d'explorer des scenarii prospectifs d'affectation des terres. Cette expérience de modélisation participative repose sur une dynamique partenariale complexe sur chaque terrain, source de difficultés. Conscients des dérives potentielles, nous discutons la nécessité de construire une démarche qualité de notre recherche-action. Mots clés : montage de partenariat, démarche qualité, modèle, changement social, ComMod, interdisciplinarité, décentralisation, foncier, Sénégal, Réunio

On the incidence of weak magnetic fields in DA white dwarfs

Context: About 10% of white dwarfs have magnetic fields with strength in the range between about 10^5 and 3x10^8 G. It is not known whether the remaining white dwarfs are not magnetic, or if they have a magnetic field too weak to be detected with the techniques adopted in the large surveys. Aims. We describe the results of the first survey specifically devised to clarify the detection frequency of kG-level magnetic fields in cool DA white dwarfs. Methods: Using the FORS1 instrument of the ESO VLT, we have obtained Balmer line circular spectropolarimetric measurements of a small sample of cool (DA6 - DA8) white dwarfs. Using FORS and UVES archive data, we have also revised numerous white dwarf field measurements previously published in the literature. Results: We have discovered an apparently constant longitudinal magnetic field of \sim9.5 kG in the DA6 white dwarf WD2105-820. This star is the first weak-field white dwarf that has been observed sufficiently to roughly determine the characteristics of its field. The available data are consistent with a simple dipolar morphology with magnetic axis nearly parallel to the rotation axis, and a polar strength of \simeq 56 kG. Our re-evaluation of the FORS archive data for white dwarfs indicates that longitudinal magnetic fields weaker than 10 kG had previously been correctly identified in at least three white dwarfs. Conclusions: We find that the probability of detecting a field of kG strength in a DA white dwarf is of the order of 10% for each of the cool and hot DA stars. If there is a lower cutoff to field strength in white dwarfs, or a field below which all white dwarfs are magnetic, the current precision of measurements is not yet sufficient to reveal it.Comment: Accepted for publication in Astronomy & Astrophysic

The Mid-Infrared Instrument for the James Webb Space Telescope, V: Predicted Performance of the MIRI Coronagraphs

The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with four coronagraphs that provide high contrast imaging capabilities for studying faint point sources and extended emission that would otherwise be overwhelmed by a bright point-source in its vicinity. Such bright sources might include stars that are orbited by exoplanets and circumstellar material, mass-loss envelopes around post-main-sequence stars, the near-nuclear environments in active galaxies, and the host galaxies of distant quasars. This paper describes the coronagraphic observing modes of MIRI, as well as performance estimates based on measurements of the MIRI flight model during cryo-vacuum testing. A brief outline of coronagraphic operations is also provided. Finally, simulated MIRI coronagraphic observations of a few astronomical targets are presented for illustration

Histone deacetylase 1 and 2 drive differentiation and fusion of progenitor cells in human placental trophoblasts

Cell fusion occurs when several cells combine to form a multinuclear aggregate (syncytium). In human placenta, a syncytialized trophoblast (syncytiotrophoblast) layer forms the primary interface between maternal and fetal tissue, facilitates nutrient and gas exchange, and produces hormones vital for pregnancy. Syncytiotrophoblast development occurs by differentiation of underlying progenitor cells called cytotrophoblasts, which then fuse into the syncytiotrophoblast layer. Differentiation is associated with chromatin remodeling and specific changes in gene expression mediated, at least in part, by histone acetylation. However, the epigenetic regulation of human cytotrophoblast differentiation and fusion is poorly understood. In this study, we found that human syncytiotrophoblast development was associated with deacetylation of multiple core histone residues. Chromatin immunoprecipitation sequencing revealed chromosomal regions that exhibit dynamic alterations in histone H3 acetylation during differentiation. These include regions containing genes classically associated with cytotrophoblast differentiation (TEAD4, TP63, OVOL1, CGB), as well as near genes with novel regulatory roles in trophoblast development and function, such as LHX4 and SYDE1. Prevention of histone deacetylation using both pharmacological and genetic approaches inhibited trophoblast fusion, supporting a critical role of this process for trophoblast differentiation. Finally, we identified the histone deacetylases (HDACs) HDAC1 and HDAC2 as the critical mediators driving cytotrophoblast differentiation. Collectively, these findings provide novel insights into the epigenetic mechanisms underlying trophoblast fusion during human placental development

A Unified, Scalable Framework for Neural Population Decoding

Our ability to use deep learning approaches to decipher neural activity would likely benefit from greater scale, in terms of both model size and datasets. However, the integration of many neural recordings into one unified model is challenging, as each recording contains the activity of different neurons from different individual animals. In this paper, we introduce a training framework and architecture designed to model the population dynamics of neural activity across diverse, large-scale neural recordings. Our method first tokenizes individual spikes within the dataset to build an efficient representation of neural events that captures the fine temporal structure of neural activity. We then employ cross-attention and a PerceiverIO backbone to further construct a latent tokenization of neural population activities. Utilizing this architecture and training framework, we construct a large-scale multi-session model trained on large datasets from seven nonhuman primates, spanning over 158 different sessions of recording from over 27,373 neural units and over 100 hours of recordings. In a number of different tasks, we demonstrate that our pretrained model can be rapidly adapted to new, unseen sessions with unspecified neuron correspondence, enabling few-shot performance with minimal labels. This work presents a powerful new approach for building deep learning tools to analyze neural data and stakes out a clear path to training at scale.Comment: Accepted at NeurIPS 202

Using Online Digital Tools and Video to Support International Problem-Based Learning

The goal of this study is to examine how to facilitate cross-cultural groups in problem-based learning (PBL) using online digital tools and videos. The PBL consisted of two video-based cases used to trigger student-learning issues about giving bad news to HIV-positive patients. Mixed groups of medical students from Canada and Hong Kong worked with facilitators from each country along with an expert facilitator. The study used AdobeConnect to support the international model through synchronous video interaction and shared applications. This study examines strategies and challenges in facilitating PBL across distance and cultures. Discourse was analyzed using both an inductive and deductive approach where the later used the Community of Inquiry coding scheme. The international context provides a way to facilitate multiple perspectives about how to communicate bad news to patients from different cultural backgrounds. In addition, we present the results of an exploratory analysis of pre and post tests using a standardized patient that demonstrate that the students’ pattern of communication showed qualitative change. Several conjectures were developed for future research