Hydrodynamical simulations are increasingly able to accurately model physical systems on stellar, galactic, and cosmological scales; however, the utility of these simulations is often limited by our ...ability to directly compare them with the data sets produced by observers: spectra, photometry, etc. To address this problem, we have created trident, a Python-based open-source tool for post-processing hydrodynamical simulations to produce synthetic absorption spectra and related data. trident can (i) create absorption-line spectra for any trajectory through a simulated data set mimicking both background quasar and down-the-barrel configurations; (ii) reproduce the spectral characteristics of common instruments like the Cosmic Origins Spectrograph; (iii) operate across the ultraviolet, optical, and infrared using customizable absorption-line lists; (iv) trace simulated physical structures directly to spectral features; (v) approximate the presence of ion species absent from the simulation outputs; (vi) generate column density maps for any ion; and (vii) provide support for all major astrophysical hydrodynamical codes. trident was originally developed to aid in the interpretation of observations of the circumgalactic medium and intergalactic medium, but it remains a general tool applicable in other contexts.
We present a simulation of the formation of the earliest Population II stars, starting from cosmological initial conditions and ending when metals created in the first supernovae are incorporated ...into a collapsing gas cloud. This occurs after a supernova blast-wave collides with a nearby mini-halo, inducing further turbulence that efficiently mixes metals into the dense gas in the centre of the halo. The gas that first collapses has been enriched to a metallicity of Z ∼ 2 × 10−5 Z⊙. Due to the extremely low metallicity, collapse proceeds similarly to metal-free gas until dust cooling becomes efficient at high densities, causing the cloud to fragment into a large number of low-mass objects. This external enrichment mechanism provides a plausible origin for the most metal-poor stars observed, such as SMSS J031300.36-670839.3, that appear to have formed out of gas enriched by a single supernova. This mechanism operates on shorter time-scales than the time for low-mass mini-haloes (M ≤ 5 × 105 M⊙) to recover their gas after experiencing a supernova. As such, metal-enriched stars will likely form first via this channel if the conditions are right for it to occur. We identify a number of other externally enriched haloes that may form stars in this manner. These haloes have metallicities as high as 0.01 Z⊙, suggesting that some members of the first generation of metal-enriched stars may be hiding in plain sight in current stellar surveys.
History, law, bioethics, and geocultural influences all have impacted the modern application of informed consent. It is a complex, multilayered process to communicate information and obtain voluntary ...patient permission before a health care intervention. Lack of provider education about genetic disorders, complexities of advanced genomic technologies, limited time during patient encounters, and low health literacy within a population all represent challenges to effective communication. There is no consensus on how informed consent in reproductive genetics is optimally obtained. Expanded carrier screening (ECS) is purposed to simultaneously test for a large list of diseases in a pan‐ethnic manner. The increased use of ECS is driven by advances in genomic technologies, decreased cost, an improved understanding of single gene disorders, and in support of reproductive autonomy. Academic organizations recommend pretest counseling when patients consider ECS, yet best practice is not established. Ongoing research is needed to determine how optimally implement informed consent given the increased complexity of ECS.
Key points
What is already known about this topic?
The increasing use of expanded carrier screening (ECS) raises unique challenges relative to the informed consent process. Best practice is not established and is influenced by historical, cultural, and legal precedents. Practical implementation is limited by provider knowledge and time for discussion as well as the complexity of genomic medicine. Limited data exist with respect to patient preferences or how various communication processes impact decision‐making.
What does this study add?
This article provides a unique perspective on informed consent and ECS beginning with a review of medical history and legal precedent and their influence on the current application of informed consent. This commentary then pivots to provide contextual analysis of ECS, genetic counseling, and genomic education that render informed consent challenging in modern obstetric practice. Finally, the article highlights future challenges of the implementation and research initiatives.
We present simulations from the new "Figuring Out Gas & Galaxies in Enzo" (FOGGIE) project. In contrast to most extant simulations of galaxy formation, which concentrate computational resources on ...galactic disks and spheroids with fluid and particle elements of fixed mass, the FOGGIE simulations focus on extreme spatial and mass resolution in the circumgalactic medium (CGM) surrounding galaxies. Using the Enzo code and a new refinement scheme, FOGGIE reaches spatial resolutions of 381 comoving h−1 pc and resolves extremely low masses ( 1-100 ) out to 100 comoving h−1 kpc from the central halo. At these resolutions, cloud and filament-like structures giving rise to simulated absorption are smaller, and better resolved, than the same structures simulated with standard density-dependent refinement. Most of the simulated absorption arises in identifiable and well-resolved structures with masses 104 , well below the mass resolution of typical zoom simulations. However, integrated quantities such as mass surface density and ionic covering fractions change at only the 30% level as resolution is varied. These relatively small changes in projected quantities-even when the sizes and distribution of absorbing clouds change dramatically-indicate that commonly used observables provide only weak constraints on the physical structure of the underlying gas. Comparing the simulated absorption features to the KODIAQ (Keck Observatory Database of Ionized Absorption toward Quasars) survey of z ∼ 2-3.5 Lyman limit systems, we show that high-resolution FOGGIE runs better resolve the internal kinematic structure of detected absorption and better match the observed distribution of absorber properties. These results indicate that circumgalactic medium resolution is key in properly testing simulations of galaxy evolution with circumgalactic observations.
Stoma formation is a commonly performed procedure in colorectal surgery as a part of operations performed for malignant‐ and inflammatory bowel disease. Stoma formation is a simple, but not trivial, ...undertaking. When performed badly, it can leave the patients with a legacy of complications such as leakage, prolapse, parastomal hernia and retraction. Various studies have reported a complication rate of 21–70%. We performed a literature search using the Medline, Ovid and Google scholar database for all the articles published between January 1980 and December 2008. The search terms used were colostomy, ileostomy, stoma, parastomal hernia, stenosis, prolapse, necrosis and complications. The following article summarizes the common complications associated with stomas.
Traditional cosmological hydrodynamics simulations fail to spatially resolve the circumgalactic medium (CGM), the reservoir of tenuous gas surrounding a galaxy and extending to its virial radius. We ...introduce the technique of Enhanced Halo Resolution (EHR), enabling more realistic physical modeling of the simulated CGM by consistently forcing gas refinement to smaller scales throughout the virial halo of a simulated galaxy. We investigate the effects of EHR in the tempest simulations, a suite of enzo-based cosmological zoom simulations following the evolution of an L* galaxy, resolving spatial scales of 500 comoving pc out to 100 comoving kpc in galactocentric radius. Among its many effects, EHR (1) changes the thermal balance of the CGM, increasing its cool gas content and decreasing its warm/hot gas content; (2) preserves cool gas structures for longer periods; and (3) enables these cool clouds to exist at progressively smaller size scales. Observationally, this results in a boost in "low ions" like H i and a drop in "high ions" like O vi throughout the CGM. These effects of EHR do not converge in the tempest simulations, but extrapolating these trends suggests that the CGM is actually a mist consisting of ubiquitous, small, long-lived, cool clouds suspended in a medium at the halo virial temperature. We find that EHR produces the above effects by (1) better sampling the distribution of CGM phases, enabling runaway cooling in the dense, cool tail of the phase distribution; and (2) preventing cool gas clouds from artificially mixing with the ambient hot halo and evaporating.
Although galaxies, groups, and clusters contain ~10% of the baryons, many more reside in the photoionized and shocked-heated intergalactic medium (IGM) and in the circumgalactic medium (CGM). We ...update the baryon census in the (H I) Lyalpha forest and warm-hot IGM (WHIM) at 10 super(5-6) K traced by O VI lambda1032, 1038 absorption. From Enzo cosmological simulations of heating, cooling, and metal transport, we improve the H I and O VI baryon surveys using spatially averaged corrections for metallicity (Z/Z sub(middot in circle)) and ionization fractions (f sub(H I), f sub(O VI)). Statistically, the O VI correction product correlates with column density, (Z/Z sub(middot in circle))f sub(O VI) approximately (0.015)(N sub(O VI)/10 super(14) cm super(-2)) super(0.70), with an N sub(O VI)-weighted mean of 0.01, which doubles previous estimates of WHIM baryon content. We also update the Lyalpha forest contribution to baryon density out to z = 0.4, correcting for the (1 + z) super(3) increase in absorber density, the (1 + z) super(4.4) rise in photoionizing background, and cosmological proper length dl/dz. We find substantial baryon fractions in the photoionized Lyalpha forest (28% + or - 11%) and WHIM traced by O VI and broad-Lyalpha absorbers (25% + or - 8%). The collapsed phase (galaxies, groups, clusters, CGM) contains 18% + or - 4%, leaving an apparent baryon shortfall of 29% + or - 13%. Our simulations suggest that ~15% reside in hotter WHIM (T > or =, slanted 10 super(6) K). Additional baryons could be detected in weaker Lyalpha and O VI absorbers. Further progress requires higher-precision baryon surveys of weak absorbers, down to minimum column densities N sub(H I) > or =, slanted 10 super(12.0) cm super(-2), N sub(O VI) > or =, slanted 10 super(12.5) cm super(-2), N sub(O VII) > or =, slanted 10 super(14.5) cm super(-2), using high signal-to-noise data from high-resolution UV and X-ray spectrographs.
We present the grackle chemistry and cooling library for astrophysical simulations and models. grackle provides a treatment of non-equilibrium primordial chemistry and cooling for H, D and He ...species, including H2 formation on dust grains; tabulated primordial and metal cooling; multiple ultraviolet background models; and support for radiation transfer and arbitrary heat sources. The library has an easily implementable interface for simulation codes written in c, c++ and fortran as well as a python interface with added convenience functions for semi-analytical models. As an open-source project, grackle provides a community resource for accessing and disseminating astrochemical data and numerical methods. We present the full details of the core functionality, the simulation and python interfaces, testing infrastructure, performance and range of applicability. grackle is a fully open-source project and new contributions are welcome.
Radiative cooling is central to a wide range of astrophysical problems. Despite its importance, cooling rates are generally computed using very restrictive assumptions, such as collisional ionization ...equilibrium and solar relative abundances. We simultaneously relax both assumptions and investigate the effects of photoionization of heavy elements by the metagalactic ultraviolet (UV)/X-ray background and of variations in relative abundances on the cooling rates of optically thin gas in ionization equilibrium. We find that photoionization by the metagalactic background radiation reduces the net cooling rates by up to an order of magnitude for gas densities and temperatures typical of the shock-heated intergalactic medium and proto-galaxies (104 K ≲T≲ 106 K, ρ/〈ρ〉≲ 100). In addition, photoionization changes the relative contributions of different elements to the cooling rates. We conclude that photoionization by both the ionizing background and heavy elements needs to be taken into account in order for the cooling rates to be correct to an order of magnitude. Moreover, if the rates need to be known to better than a factor of a few, then departures of the relative abundances from solar need to be taken into account. We propose a method to compute cooling rates on an element-by-element basis by interpolating pre-computed tables that take photoionization into account. We provide such tables for a popular model of the evolving UV/X-ray background radiation, computed using the photoionization package cloudy.
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