Although fundamental for astrophysics, the processes that produce massive stars are not well understood. Large distances, high extinction, and short timescales of critical evolutionary phases make observations of these processes challenging. Lacking good observational guidance, theoretical models have remained controversial. This review offers a basic description of the collapse of a massive molecular core and a critical discussion of the three competing concepts of massive star formation: ▪  monolithic collapse in isolated cores ▪  competitive accretion in a protocluster environment ▪  stellar collisions and mergers in very dense systems We also review the observed outflows, multiplicity, and clustering properties of massive stars, the upper initial mass function and the upper mass limit. We conclude that high-mass star formation is not merely a scaled-up version of low-mass star formation with higher accretion rates, but partly a mechanism of its own, primarily owing to the role of stellar mass ...

Toward Understanding Massive Star Formation

This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ($5 \leq \rm \log(Age)\;[yr] \leq 10.3$), masses ($0.1 \leq M/M_{\odot} \leq 300$), and metallicities ($-2.0 \leq \rm [Z/H] \leq 0.5$). The models are self-consistently and continuously evolved from the pre-main sequence to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the pre-main sequence to the end of core helium burning for $-4.0 \leq \rm [Z/H] < -2.0$. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at this http URL

https://iopscience.iop.org/article/10.3847/0004-637X/823/2/102/pdf

Mesa isochrones and stellar tracks (mist). i. solar-scaled models

Knowledge of the progenitors of core-collapse supernovae is a fundamental component in understanding the explosions. The recent progress in finding such stars is reviewed. The minimum initial mass that can produce a supernova (SN) has converged to 8 ± 1 M⊙ from direct detections of red supergiant progenitors of II-P SNe and the most massive white dwarf progenitors, although this value is model dependent. It appears that most type Ibc SNe arise from moderate mass interacting binaries. The highly energetic, broad-lined Ic SNe are likely produced by massive, Wolf-Rayet progenitors. There is some evidence to suggest that the majority of massive stars above ∼20 M⊙ may collapse quietly to black holes and that the explosions remain undetected. The recent discovery of a class of ultrabright type II SNe and the direct detection of some progenitor stars bearing luminous blue variable characteristics suggest some very massive stars do produce highly energetic explosions. The physical mechanism is under debate, and t...

Progenitors of Core-Collapse Supernovae

Within the Local Universe galaxies can be studied in great detail star by star, and here we review the results of quantitative studies in nearby dwarf galaxies. The color-magnitude diagram synthesis method is well established as the most accurate way to determine star-formation histories of galaxies back to the earliest times. This approach received a large boost from the exceptional data sets that wide-field CCD imagers on the ground and the Hubble Space Telescope could provide. Spectroscopic studies using large ground-based telescopes such as VLT, Magellan, Keck, and HET have allowed the determination of abundances and kinematics for significant samples of stars in nearby dwarf galaxies. These studies have shown how the properties of stellar populations can vary spatially and temporally. This leads to important constraints to theories of galaxy formation and evolution. The combination of spectroscopy and imaging and what they have taught us about dwarf galaxy formation and evolution is the aim of this r...

/pdf/star-formation-histories-abundances-and-kinematics-of-dwarf-2huvnw5ldb.pdf

Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group

MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models

OBJECTIVES/GOALS: To determine if decellularized costal cartilage (DCC), which could theoretically be obtained “off the shelf,” would provide similar results to autologous cartilage grafts previously studied in this lab, thereby widening the application of our novel nipple engineering approach to all patients undergoing nipple reconstruction. METHODS/STUDY POPULATION: PLA scaffolds (diameter: 1.0 cm, height: 1.0 cm) were printed using a PRUSA 3D printer and sterilized. Lamb costal cartilage was minced (1 mm3) or zested (<0.2 mm3) and then decellularized. The quality of decellularization was assessed using DNA quantification and histological analysis. DCC was then packed into PLA scaffolds and implanted subcutaneously into immunocompetent Sprague Dawley rats using a CV flap technique. The constructs were explanted and evaluated up to 6 months after implantation. RESULTS/ANTICIPATED RESULTS: All nipple reconstructions showed well-preserved diameter and projection due to persistence of the external scaffolds at 1, 3, and 6 months. Mass and volume of engineered tissue was well-preserved over all timepoints. Compared to implantation values, engineered zested nipples demonstrated a 12% mass increase and a 22% volume increase at 6 months. Minced nipples illustrated a similar mass and volume gain with a 21% increase in mass and a 13% increase in volume at 6 months secondary to infiltration of fibrovascular tissue and growth through scaffold wall pores, respectively. Histologic analysis demonstrated a mild inflammatory infiltrate 1 month after implantation which was replaced by fibrovascular tissue by 3 months that remained stable through 6 months. The processed DCC structure remained unchanged over time. DISCUSSION/SIGNIFICANCE: Using acellular ovine xenograft within bioabsorbable scaffolds, we have engineered neonipples that maintain their volume for at least 6 months. DCC architecture is well-preserved with minimal evidence of immune-mediated degradation. By using DCC, this novel approach to nipple engineering may be applied to any patient requiring reconstruction.

/pdf/270-neonipple-formation-after-implantation-of-acellular-1k5txy64.pdf

270 Neonipple Formation After Implantation Of Acellular Ovine Xenograft

Major histocompatibility complex (MHC)-bound peptides that originate from tumor-specific genetic alterations, known as neoantigens, are an important class of anti-cancer therapeutic targets. Accurately predicting peptide presentation by MHC complexes is a key aspect of discovering therapeutically relevant neoantigens. Technological improvements in mass-spectrometry-based immunopeptidomics and advanced modeling techniques have vastly improved MHC presentation prediction over the past two decades. However, improvement in the sensitivity and specificity of prediction algorithms is needed for clinical applications such as the development of personalized cancer vaccines, the discovery of biomarkers for response to checkpoint blockade and the quantification of autoimmune risk in gene therapies. Toward this end, we generated allele-specific immunopeptidomics data using 25 mono-allelic cell lines and created Systematic HLA Epitope Ranking Pan Algorithm (SHERPA™), a pan-allelic MHC-peptide algorithm for predicting MHC-peptide binding and presentation. In contrast to previously published large-scale mono-allelic data, we used an HLA-null K562 parental cell line and a stable transfection of HLA alleles to better emulate native presentation. Our dataset includes five previously unprofiled alleles that expand MHC binding pocket diversity in the training data and extend allelic coverage in under-profiled populations. To improve generalizability, SHERPA systematically integrates 128 mono-allelic and 384 multi-allelic samples with publicly available immunoproteomics data and binding assay data. Using this dataset, we developed two features that empirically estimate the propensities of genes and specific regions within gene bodies to engender immunopeptides to represent antigen processing. Using a composite model constructed with gradient boosting decision trees, multi-allelic deconvolution and 2.15 million peptides encompassing 167 alleles, we achieved a 1.71 fold improvement of positive predictive value compared to existing tools when evaluated on independent mono-allelic datasets and a 1.24 fold improvement when evaluating on tumor samples. With a high degree of accuracy, SHERPA has the potential to enable precision neoantigen discovery for future clinical applications.

https://biorxiv.org/content/10.1101/2021.04.30.442203v1.full.pdf

Precision neoantigen discovery using large-scale immunopeptidomes and composite modeling of MHC peptide presentation

La presente invention concerne un dispositif fluidique d'analyse d'echantillons. Ledit dispositif fluidique comprend une cuve a circulation possedant des orifices d'entree et de sortie et un canal d'ecoulement reliant lesdits orifices. Ladite cuve a circulation est destinee a accueillir un echantillon a etudier. Ledit dispositif fluidique comporte egalement un logement possedant un espace d'accueil destine a accueillir la cuve a circulation. La taille et la forme dudit dispositif d'accueil sont telles a permettre a la cuve a circulation de flotter par rapport au logement. Le dispositif fluidique comprend egalement un joint couple au logement. Ledit joint comporte des passages d'entree et de sortie et est constitue d'un materiau compressible. Le joint est positionne par rapport a l'espace d'accueil d'une facon telle a ce que les orifices d'entree et de sortie de la cuve a circulation soient, respectivement, a peu pres alignes avec les passages d'entree et de sortie du joint.

Systèmes, procédés et appareils d'imagerie d'un échantillon à des fins d'analyse biologique ou chimique

Assuming that most stars form in clusters (Lada & Lada 2003), one might initially expect to find most massive stars in stellar clusters and to detect most of the UV emission in young compact stellar clusters. However, Meurer et al. (1995) showed that in starburst galaxies only 20% of the UV emission at 2200Å is detected in clusters while 80% is diffuse emission from sources in the inter-cluster medium. This phenomenon is also observed for normal galaxies (Hoopes et al. 2001).

A Missing Link in Galaxy Evolution: The Mysteries of Dissolving Star Clusters

This article describes fabrication of a customizable bioreactor comprised of a perfusion system and coverslip-based tissue culture chamber that allow centimeter-scale vascularized or otherwise canalized tissue constructs to be maintained in weeks long static and/or perfusion culture at exceptionally low cost, with intermittent live imaging and media sampling capabilities. The perfusion system includes a reusable poly-dimethylsiloxane (PDMS) lid generated from a 3D-printed poly-lactic acid (PLA) mold and several lengths of perfusion tubing. The coverslip tissue culture chamber includes PDMS components built with 3D-printed PLA molds, as well as 3D-printed PLA frames and glass coverslips that house perfusable hydrogel constructs. As proof of concept, we fabricated a vascularized hydrogel construct, which was subjected to static and perfusion tissue culture, as well as flow studies using fluorescent beads and widefield fluorescent microscopy. This system can be readily reproduced, promoting the advancement of tissue engineering and regenerative medicine research.

Jason Harris

Papers

270 Neonipple Formation After Implantation Of Acellular Ovine Xenograft

Precision neoantigen discovery using large-scale immunopeptidomes and composite modeling of MHC peptide presentation

Systèmes, procédés et appareils d'imagerie d'un échantillon à des fins d'analyse biologique ou chimique

A Missing Link in Galaxy Evolution: The Mysteries of Dissolving Star Clusters

Perfuse and Reuse: A Low-Cost 3D-Printed Perfusion Bioreactor for Tissue Engineering.