160 research outputs found
Journey Beyond Full Abstraction: Exploring Robust Property Preservation for Secure Compilation
âGood programming languages provide helpful abstractions for writing secure code, but the security properties of
the source language are generally not preserved when compiling a
program and linking it with adversarial code in a low-level target
language (e.g., a library or a legacy application). Linked target
code that is compromised or malicious may, for instance, read and
write the compiled programâs data and code, jump to arbitrary
memory locations, or smash the stack, blatantly violating any
source-level abstraction. By contrast, a fully abstract compilation
chain protects source-level abstractions all the way down, ensuring that linked adversarial target code cannot observe more about
the compiled program than what some linked source code could
about the source program. However, while research in this area
has so far focused on preserving observational equivalence, as
needed for achieving full abstraction, there is a much larger space
of security properties one can choose to preserve against linked
adversarial code. And the precise class of security properties one
chooses crucially impacts not only the supported security goals
and the strength of the attacker model, but also the kind of
protections a secure compilation chain has to introduce.
We are the first to thoroughly explore a large space of formal
secure compilation criteria based on robust property preservation, i.e., the preservation of properties satisfied against arbitrary
adversarial contexts. We study robustly preserving various classes
of trace properties such as safety, of hyperproperties such as
noninterference, and of relational hyperproperties such as trace
equivalence. This leads to many new secure compilation criteria,
some of which are easier to practically achieve and prove than
full abstraction, and some of which provide strictly stronger
security guarantees. For each of the studied criteria we propose an equivalent âproperty-freeâ characterization that clarifies
which proof techniques apply. For relational properties and
hyperproperties, which relate the behaviors of multiple programs,
our formal definitions of the property classes themselves are
novel. We order our criteria by their relative strength and show
several collapses and separation results. Finally, we adapt existing
proof techniques to show that even the strongest of our secure
compilation criteria, the robust preservation of all relational
hyperproperties, is achievable for a simple translation from a
statically typed to a dynamically typed language
Categorization of species as native or nonnative using DNA sequence signatures without a complete reference library.
New genetic diagnostic approaches have greatly aided efforts to document global biodiversity and improve biosecurity. This is especially true for organismal groups in which species diversity has been underestimated historically due to difficulties associated with sampling, the lack of clear morphological characteristics, and/or limited availability of taxonomic expertise. Among these methods, DNA sequence barcoding (also known as "DNA barcoding") and by extension, meta-barcoding for biological communities, has emerged as one of the most frequently utilized methods for DNA-based species identifications. Unfortunately, the use of DNA barcoding is limited by the availability of complete reference libraries (i.e., a collection of DNA sequences from morphologically identified species), and by the fact that the vast majority of species do not have sequences present in reference databases. Such conditions are critical especially in tropical locations that are simultaneously biodiversity rich and suffer from a lack of exploration and DNA characterization by trained taxonomic specialists. To facilitate efforts to document biodiversity in regions lacking complete reference libraries, we developed a novel statistical approach that categorizes unidentified species as being either likely native or likely nonnative based solely on measures of nucleotide diversity. We demonstrate the utility of this approach by categorizing a large sample of specimens of terrestrial insects and spiders (collected as part of the Moorea BioCode project) using a generalized linear mixed model (GLMM). Using a training data set of known endemic (n = 45) and known introduced species (n = 102), we then estimated the likely native/nonnative status for 4,663 specimens representing an estimated 1,288 species (412 identified species), including both those specimens that were either unidentified or whose endemic/introduced status was uncertain. Using this approach, we were able to increase the number of categorized specimens by a factor of 4.4 (from 794 to 3,497), and the number of categorized species by a factor of 4.8 from (147 to 707) at a rate much greater than chance (77.6% accuracy). The study identifies phylogenetic signatures of both native and nonnative species and suggests several practical applications for this approach including monitoring biodiversity and facilitating biosecurity
Simulating the diversity of shapes of the Lyman- line
The Ly line is a powerful probe of distant galaxies, which contains
information about inflowing/outflowing gas through which Ly photons
scatter. To develop our understanding of this probe, we post-process a zoom-in
radiation-hydrodynamics simulation of a low-mass ()
galaxy to construct 22500 mock spectra in 300 directions from to 4.
Remarkably, we show that one galaxy can reproduce the variety of a large sample
of spectroscopically observed Ly line profiles. While most mock spectra
exhibit double-peak profiles with a dominant red peak, their shapes cover a
large parameter space in terms of peak velocities, peak separation and flux
ratio. This diversity originates from radiative transfer effects at ISM and CGM
scales, and depends on galaxy inclination and evolutionary phase. Red-dominated
lines preferentially arise in face-on directions during post-starburst outflows
and are bright. Conversely, accretion phases usually yield symmetric double
peaks in the edge-on direction and are fainter. While resonant scattering
effects at are responsible for the broadening and
velocity shift of the red peak, the extended CGM acts as a screen and impacts
the observed peak separation. The ability of simulations to reproduce observed
Ly profiles and link their properties with galaxy physical parameters
offers new perspectives to use Ly to constrain the mechanisms that
regulate galaxy formation and evolution. Notably, our study implies that deeper
Ly surveys may unveil a new population of blue-dominated lines tracing
inflowing gas.Comment: Accepted for publication in MNRA
Persistence, prevalence, and polymorphism of sequelae after COVID-19 in unvaccinated, young adults of the Swiss Armed Forces: a longitudinal, cohort study (LoCoMo)
Background: Persistent COVID-19 sequelae could have global, public health ramifications. We therefore aimed to describe sequelae presenting more than 180 days after COVID-19-focussing on several organ systems, general health, and laboratory parameters-in non-hospitalised, unvaccinated, young adults.
Methods: We did a longitudinal cohort study of all army bases in Switzerland. Eligible participants were personnel of the Swiss Armed Forces (SAF) who were aged 18-30 years with a positive or negative RT-PCR test for SARS-CoV-2 during their service between March 1, 2020, and Dec 31, 2020. Exclusion criteria were unwillingness to participate in testing. Females or men with a known reproductive anomaly were excluded from the optional component of male fertility testing. COVID-19 was defined as a positive diagnostic RT-PCR test result for SARS-CoV-2 with concurrent symptoms compatible with COVID-19. Participants were subdivided into four groups: control group (ie, serologically negative), asymptomatic infection group (ie, serologically positive but with no symptoms), non-recent COVID-19 group (>180 days since positive PCR test), and recent COVID-19 group (â€180 days since positive PCR test). Outcomes of interest were part of a comprehensive, intensive test battery that was administered during a single day. The test battery quantified the effect of SARS-CoV-2 infection on cardiovascular, pulmonary, neurological, renal, ophthalmological, male reproductive, psychological, general health, and laboratory parameters. This study was registered with ClinicalTrials.gov, number NCT04942249.
Findings: Between May 20, 2021, and Nov 26, 2021, we enrolled 501 participants. 29 (6%) of 501 were female and 464 (93%) were male, and the median age was 21 years (IQR 21-23). Eight (2%) of 501 had incomplete data and were not included into the study groups. 177 participants had previous COVID-19 that was more than 180 days (mean 340 days) since diagnosis (ie, the non-recent COVID-19 group) compared with 251 serologically negative individuals (ie, the control group). We included 19 participants in the recent COVID-19 group and 46 in the asymptomatic infection group. We found a significant trend towards metabolic disorders in participants of the non-recent COVID-19 group compared with those in the control group: higher BMI (median 24·0 kg/m2 [IQR 22·0-25·8] vs 23·2 kg/m2 [27·1-25·0]; p=0·035), lower aerobic threshold (39% [36-43] vs 41% [37-46]; p=0·012), and higher blood cholesterol (4·2 ΌM [3·7-4·7] vs 3·9 ΌM [3·5-4·5]; p<0·0001) and LDL concentrations (2·4 ΌM [1·9-2·9] vs 2·2 ΌM [1·7-2·7]; p=0·001). The only significant psychosocial difference was found in the results of the Chalder Fatigue scale with the non-recent COVID-19 group reporting higher fatigue scores than the control group (median 12 points [IQR 11-15] vs 11 [9-14]; p=0·027). No significant differences in other psychosocial questionnaire scores, ophthalmological outcomes, and sperm quality or motility were reported between the control group and non-recent COVID-19 group.
Interpretation: Young, previously healthy, individuals largely recover from SARS-CoV-2 infection. However, the constellation of higher BMI, dyslipidaemia, and lower physical endurance 180 days after COVID-19 is suggestive of a higher risk of developing metabolic disorders and possible cardiovascular complications. These findings will guide future investigations and follow-up management
The MUSE Hubble Ultra Deep Field Survey X. Ly Equivalent Widths at
We present rest-frame Ly equivalent widths (EW) of 417 Ly
emitters (LAEs) detected with Multi Unit Spectroscopic Explorer (MUSE) on the
Very Large Telescope (VLT) at in the Hubble Ultra Deep Field.
Based on the deep MUSE spectroscopy and ancillary Hubble Space Telescope (HST)
photometry data, we carefully measured EW values taking into account extended
Ly emission and UV continuum slopes (). Our LAEs reach
unprecedented depths, both in Ly luminosities and UV absolute
magnitudes, from log(/erg s) 41.0 to 43.0 and
from Muv -16 to -21 (0.01-1.0 ). The EW values span the
range of 5 to 240 \AA\ or larger, and their distribution can be well
fitted by an exponential law exp(EW/). Owing to
the high dynamic range in Muv, we find that the scale factor, ,
depends on Muv in the sense that including fainter Muv objects increases
, i.e., the Ando effect. The results indicate that selection
functions affect the EW scale factor. Taking these effects into account, we
find that our values are consistent with those in the literature
within uncertainties at at a given threshold of Muv
and . Interestingly, we find 12 objects with EW \AA\
above uncertainties. Two of these 12 LAEs show signatures of merger
or AGN activity: the weak CIV emission line. For the remaining
10 very large EW LAEs, we find that the EW values can be reproduced by young
stellar ages ( Myr) and low metallicities ( ). Otherwise, at least part of the Ly emission in these LAEs
needs to arise from anisotropic radiative transfer effects, fluorescence by
hidden AGN or quasi-stellar object activity, or gravitational cooling.Comment: 22 pages, 12 figures, 9 tables, accepted for publication in A&A (MUSE
UDF Series Paper X
How to Quench a Dwarf Galaxy: The Impact of Inhomogeneous Reionization on Dwarf Galaxies and Cosmic Filaments
We use the SPHINX suite of high-resolution cosmological radiation
hydrodynamics simulations to study how spatially and temporally inhomogeneous
reionization impacts the baryonic content of dwarf galaxies and cosmic
filaments. The SPHINX simulations simultaneously capture the large-scale
process of reionization, model the escape of ionising radiation from thousands
of galaxies, and resolve haloes well below the atomic cooling threshold. This
makes them an ideal tool for examining how reionization impacts star formation
and the gas content of dwarf galaxies. We compare simulations with and without
stellar radiation to isolate the effects of radiation feedback from that of
supernova, cosmic expansion, and numerical resolution. We find that the gas
content of cosmic filaments can be reduced by more than 80% following
reionization. The gas inflow rates into haloes with
are strongly affected and are reduced by more
than an order of magnitude compared to the simulation without reionization. A
significant increase in gas outflow rates is found for halo masses
. Our simulations show that inflow
suppression (i.e. starvation), rather than photoevaporation, is the dominant
mechanism by which the baryonic content of high-redshift dwarf galaxies is
regulated. At fixed redshift and halo mass, there is a large scatter in the
halo baryon fractions that is entirely dictated by the timing of reionization
in the local region surrounding a halo. Finally, although the gas content of
high-redshift dwarf galaxies is significantly impacted by reionization, we find
that most haloes with can remain self-shielded
and form stars long after reionization, until their local gas reservoir is
depleted, suggesting that local group dwarf galaxies do not necessarily exhibit
star formation histories that peak prior to
Predicting LyC emission of galaxies using their physical and Ly emission properties
The primary difficulty in understanding the sources and processes that
powered cosmic reionization is that it is not possible to directly probe the
ionizing Lyman Continuum (LyC) radiation at that epoch as those photons have
been absorbed by the intervening neutral hydrogen in the IGM on their way to
us. It is therefore imperative to build a model to accurately predict LyC
emission using other properties of galaxies in the reionization era.
In recent years, studies have shown that the LyC emission from galaxies may
be correlated to their Lya emission. Here, we study this correlation by
analyzing thousands of galaxies at high-z in the SPHINX cosmological
simulation. We post-process these galaxies with the Lya radiative transfer code
RASCAS and analyze the Lya - LyC connection.
We find that the Lya and LyC luminosities are strongly correlated with each
other, although with dispersion. There is a positive correlation between Lya
and LyC escape fractions in the brightest Lya emitters (> erg/s),
similar to the recent observational studies. However, when we also include
fainter Lya emitters (LAEs), the correlation disappears, which suggests that
the observed relationship may be driven by selection effects. We also find that
bright LAEs are dominant contributors to reionization ( erg/s
galaxies contribute of LyC emission). Finally, we build predictive
models using multivariate linear regression where we use the physical and the
Lya properties of simulated galaxies to predict their intrinsic and escaping
LyC luminosities with a high degree of accuracy. We find that the most
important galaxy properties to predict the escaping LyC luminosity of a galaxy
are its escaping Lya luminosity, gas mass, gas metallicity, and SFR.
These models can be very useful to predict LyC emissions from galaxies and
can help us identify the sources of reionization.Comment: Accepted to Astronomy and Astrophysics (A&A) Journal. 27 pages, 21
Figure
Interpreting the Si II and C II line spectra from the COS Legacy Spectroscopic SurveY using a virtual galaxy from a high-resolution radiation-hydrodynamic simulation
Observations of low-ionization state (LIS) metal lines provide crucial
insights into the interstellar medium of galaxies, yet, disentangling the
physical processes responsible for the emerging line profiles is difficult.
This work investigates how mock spectra generated using a single galaxy in a
radiation-hydrodynamical simulation can help us interpret observations of a
real galaxy. We create 22,500 C II and Si II spectra from the virtual galaxy at
different times and through multiple lines of sight and compare them with the
45 observations of low-redshift star-forming galaxies from the COS Legacy
Spectroscopic SurveY (CLASSY). We find that the mock profiles provide accurate
replicates to the observations of 38 galaxies with a broad range of stellar
masses ( to ) and metallicities (0.02 to 0.55 ).
Additionally, we highlight that aperture losses explain the weakness of the
fluorescent emission in several CLASSY spectra and must be accounted for when
comparing simulations to observations. Overall, we show that the evolution of a
single simulated galaxy can produce a large diversity of spectra whose
properties are representative of galaxies of comparable or smaller masses.
Building upon these results, we explore the origin of the continuum, residual
flux, and fluorescent emission in the simulation. We find that these different
spectral features all emerge from distinct regions in the galaxy's ISM, and
their characteristics can vary as a function of the viewing angle. While these
outcomes challenge simplified interpretations of down-the-barrel spectra, our
results indicate that high-resolution simulations provide an optimal framework
to interpret these observations.Comment: Accepted for publication in Ap
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The MUSE Extremely Deep Field: The cosmic web in emission at high redshift
We report the discovery of diffuse extended Lyα emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5-4 cMpc. These structures have been observed in overdensities of Lyα emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Lyα emission at high significance with an average surface brightness of 5â
Ăâ
10-20 erg s-1 cm-2 arcsec-2. Remarkably, 70% of the total Lyα luminosity from these filaments comes from beyond the circumgalactic medium of any identified Lyα emitter. Fluorescent Lyα emission powered by the cosmic UV background can only account for less than 34% of this emission at zâ ââ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Lyα emission of a large population of ultra low-luminosity Lyα emitters (< 1040 erg s-1), provided that the faint end of the Lyα luminosity function is steep (αââȘ
â-1.8), it extends down to luminosities lower than 1038â
-â
1037 erg s-1, and the clustering of these Lyα emitters is significant (filling factor < 1/6). If these Lyα emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates < 10-4M yr-1. These observations provide the first detection of the cosmic web in Lyα emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Lyα emitters at high redshift. © R. Bacon et al. 2021
River ecosystem conceptual models and nonâperennial rivers: A critical review
Conceptual models underpin river ecosystem research. However, current models focus on continuously flowing rivers and few explicitly address characteristics such as flow cessation and drying. The applicability of existing conceptual models to nonperennial rivers that cease to flow (intermittent rivers and ephemeral streams, IRES) has not been evaluated. We reviewed 18 models, finding that they collectively describe main drivers of biogeochemical and ecological patterns and processes longitudinally (upstream-downstream), laterally (channel-riparian-floodplain), vertically (surface water-groundwater), and temporally across local and landscape scales. However, perennial rivers are longitudinally continuous while IRES are longitudinally discontinuous. Whereas perennial rivers have bidirectional lateral connections between aquatic and terrestrial ecosystems, in IRES, this connection is unidirectional for much of the time, from terrestrial-to-aquatic only. Vertical connectivity between surface and subsurface water occurs bidirectionally and is temporally consistent in perennial rivers. However, in IRES, this exchange is temporally variable, and can become unidirectional during drying or rewetting phases. Finally, drying adds another dimension of flow variation to be considered across temporal and spatial scales in IRES, much as flooding is considered as a temporally and spatially dynamic process in perennial rivers. Here, we focus on ways in which existing models could be modified to accommodate drying as a fundamental process that can alter these patterns and processes across spatial and temporal dimensions in streams. This perspective is needed to support river science and management in our era of rapid global change, including increasing duration, frequency, and occurrence of drying.info:eu-repo/semantics/publishedVersio
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