40 research outputs found
Is Rust Used Safely by Software Developers?
Rust, an emerging programming language with explosive growth, provides a
robust type system that enables programmers to write memory-safe and data-race
free code. To allow access to a machine's hardware and to support low-level
performance optimizations, a second language, Unsafe Rust, is embedded in Rust.
It contains support for operations that are difficult to statically check, such
as C-style pointers for access to arbitrary memory locations and mutable global
variables. When a program uses these features, the compiler is unable to
statically guarantee the safety properties Rust promotes. In this work, we
perform a large-scale empirical study to explore how software developers are
using Unsafe Rust in real-world Rust libraries and applications. Our results
indicate that software engineers use the keyword unsafe in less than 30% of
Rust libraries, but more than half cannot be entirely statically checked by the
Rust compiler because of Unsafe Rust hidden somewhere in a library's call
chain. We conclude that although the use of the keyword unsafe is limited, the
propagation of unsafeness offers a challenge to the claim of Rust as a
memory-safe language. Furthermore, we recommend changes to the Rust compiler
and to the central Rust repository's interface to help Rust software developers
be aware of when their Rust code is unsafe
Low-Mass Seyfert 2 Galaxies in the Sloan Digital Sky Survey
(Abridged) We describe a sample of low-mass Seyfert 2 galaxies selected from
the Sloan Digital Sky Survey, having a median absolute magnitude of M_g = -19.0
mag. These galaxies are Type 2 counterparts to the Seyfert 1 galaxies with
intermediate-mass black holes identified by Greene & Ho (2004). Spectra
obtained with the Echellette Spectrograph and Imager at the Keck Observatory
are used to determine the central stellar velocity dispersions and to examine
the emission-line properties. Overall, the stellar velocity dispersions are low
(40-90 km/s), and we find 12 objects having sigma < 60 km/s, a range where very
few Seyfert 2 galaxies were previously known. The sample follows the
correlation between stellar velocity dispersion and FWHM([OIII]) seen in more
massive Seyfert galaxies, indicating that the narrow-line FWHM values are
largely determined by virial motion of gas in the central regions of the host
galaxies. Using estimates of the black hole masses and AGN bolometric
luminosities, we find that these galaxies are typically radiating at a high
fraction of their Eddington rate, with a median L_bol/L_Edd = 0.4. We identify
one galaxy, SDSS J110912.40+612346.7, as a Type 2 analog of the nearby dwarf
Seyfert 1 galaxy NGC 4395, with a nearly identical narrow-line spectrum and a
dwarf spiral host of only M_g = -16.8 mag. Forthcoming observations of this
sample, including X-ray and mid-infrared spectroscopy, can provide new tests of
the obscuring torus model for active galaxies at low luminosities.Comment: 34 pages, 16 figures. Some figures bitmapped to reduce size. To
appear in A
Pahs, Ionized Gas, and Molecular Hydrogen in Brightest Cluster Galaxies of Cool Core Clusters of Galaxies
We present measurements of 5-25 {\mu}m emission features of brightest cluster
galaxies (BCGs) with strong optical emission lines in a sample of 9 cool-core
clusters of galaxies observed with the Infrared Spectrograph on board the
Spitzer Space Telescope. These systems provide a view of dusty molecular gas
and star formation, surrounded by dense, X-ray emitting intracluster gas. Past
work has shown that BCGs in cool-core clusters may host powerful radio sources,
luminous optical emission line systems, and excess UV, while BCGs in other
clusters never show this activity. In this sample, we detect polycyclic
aromatic hydrocarbons (PAHs), extremely luminous, rotationally-excited
molecular hydrogen line emission, forbidden line emission from ionized gas ([Ne
II] and [Ne III]), and infrared continuum emission from warm dust and cool
stars. We show here that these BCGs exhibit more luminous forbidden neon and H2
rotational line emission than star-forming galaxies with similar total infrared
luminosities, as well as somewhat higher ratios of 70 {\mu}m / 24 {\mu}m
luminosities. Our analysis suggests that while star formation processes
dominate the heating of the dust and PAHs, a heating process consistent with
suprathermal electron heating from the hot gas, distinct from star formation,
is heating the molecular gas and contributing to the heating of the ionized gas
in the galaxies. The survival of PAHs and dust suggests that dusty gas is
somehow shielded from significant interaction with the X-ray gas.Comment: 27 preprint pages, 18 figures, accepted by Astrophysical Journa
Ubiquitous outflows in DEEP2 spectra of star-forming galaxies at z=1.4
Galactic winds are a prime suspect for the metal enrichment of the
intergalactic medium and may have a strong influence on the chemical evolution
of galaxies and the nature of QSO absorption line systems. We use a sample of
1406 galaxy spectra at z~1.4 from the DEEP2 redshift survey to show that
blueshifted Mg II 2796, 2803 A absorption is ubiquitous in starforming galaxies
at this epoch. This is the first detection of frequent outflowing galactic
winds at z~1. The presence and depth of absorption are independent of AGN
spectral signatures or galaxy morphology; major mergers are not a prerequisite
for driving a galactic wind from massive galaxies. Outflows are found in
coadded spectra of galaxies spanning a range of 30x in stellar mass and 10x in
star formation rate (SFR), calibrated from K-band and from MIPS IR fluxes. The
outflows have column densities of order N_H ~ 10^20 cm^-2 and characteristic
velocities of ~ 300-500 km/sec, with absorption seen out to 1000 km/sec in the
most massive, highest SFR galaxies. The velocities suggest that the outflowing
gas can escape into the IGM and that massive galaxies can produce
cosmologically and chemically significant outflows. Both the Mg II equivalent
width and the outflow velocity are larger for galaxies of higher stellar mass
and SFR, with V_wind ~ SFR^0.3, similar to the scaling in low redshift
IR-luminous galaxies. The high frequency of outflows in the star-forming galaxy
population at z~1 indicates that galactic winds occur in the progenitors of
massive spirals as well as those of ellipticals. The increase of outflow
velocity with mass and SFR constrains theoretical models of galaxy evolution
that include feedback from galactic winds, and may favor momentum-driven models
for the wind physics.Comment: Accepted by ApJ. 25 pages, 17 figures. Revised to add discussions of
intervening absorbers and AGN-driven outflows; conclusions unchange
The First Luminous Quasars and Their Host Galaxies
The discovery of luminous quasars at redshifts up to 7.5 demonstrates the
existence of several billion M_sun supermassive black holes (SMBHs) less than a
billion years after the Big Bang. They are accompanied by intense star
formation in their host galaxies, pinpointing sites of massive galaxy assembly
in the early universe, while their absorption spectra reveal an increasing
neutral intergalactic medium (IGM) at the epoch of reionization. Extrapolating
from the rapid evolution of the quasar density at z=5-7, we expect that there
is only one luminous quasar powered by a billion M_sun SMBH in the entire
observable universe at z~9. In the next decade, new wide-field, deep
near-infrared (NIR) sky surveys will push the redshift frontier to the first
luminous quasars at z~9-10; the combination with new deep X-ray surveys will
probe fainter quasar populations that trace earlier phases of SMBH growth. The
identification of these record-breaking quasars, and the measurements of their
BH masses and accretion properties require sensitive spectroscopic observations
with next generation of ground-based and space telescopes at NIR wavelengths.
High-resolution integral-field spectroscopy at NIR, and observations at
millimeter and radio wavelengths, will together provide a panchromatic view of
the quasar host galaxies and their galactic environment at cosmic dawn,
connecting SMBH growth with the rise of the earliest massive galaxies.
Systematic surveys and multiwavelength follow-up observations of the earliest
luminous quasars will strongly constrain the seeding and growth of the first
SMBHs in the universe, and provide the best lines of sight to study the history
of reionization.Comment: 7 pages, 3 figures, Science white paper submitted to the Astro2020
Decadal Surve
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance
INTRODUCTION
Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic.
RATIONALE
We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs).
RESULTS
Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants.
CONCLUSION
Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
Fair Play and Fascism: The Development of British Olympic Team Uniforms 1908-1948
This essay looks at how British sporting ideals were embodied and given material form in the outfitting and presentation of British Olympic teams in the opening ceremonies of the modern games held up to and including those of London in 1948. An exploration of the formative development of Olympic ceremonial attire from the late nineteenth century provides a conceptual framework for examining how such clothing functioned as a conduit through which wider ideals of British nationhood were discursively produced in the twentieth century. To what extent did a historical model of British Olympic amateurism and its embodiment in the development of British Olympic team uniforms together operate as a counter to the aggressive body culture of fascist ideology in the 1930s