192 research outputs found
Spectral features of Earth-like planets and their detectability at different orbital distances around F, G, and K-type stars
We investigate the spectral appearance of Earth-like exoplanets in the HZ of
different main sequence stars at different orbital distances. We furthermore
discuss for which of these scenarios biomarker absorption bands may be detected
during primary or secondary transit with near-future telescopes and
instruments.We analyze the spectra taking into account different filter
bandpasses of two photometric instruments planned to be mounted to the JWST. We
analyze in which filters and for which scenarios molecular absorption bands are
detectable when using the space-borne JWST or the ground-based telescope E-ELT.
Absorption bands of CO2, H2O, CH4 and O3 are clearly visible in high-resolution
spectra as well as in the filters of photometric instruments. However, only
during primary eclipse bands of CO2, H2O and O3 are detectable for all
scenarios when using photometric instruments and an E-ELT telescope setup. CH4
is only detectable at the outer HZ of the K star since here the atmospheric
modeling results in very high abundances. Since the detectable CO2 and H2O
bands overlap, separate bands need to be observed to prove their existence in
the atmosphere. In order to detect H2O in a separate band, a S/N>7 needs to be
achieved for E-ELT observations, e.g. by co-adding at least 10 transit
observations. Using a spaceborne telescope like the JWST enables the detection
of CO2 at 4.3mu, which is not possible for ground-based observations due to the
Earth's atmospheric absorption. Hence combining observations of spaceborne and
groundbased telescopes might allow to detect the presence of the biomarker
molecule O3 and the related compounds H2O and CO2 in a planetary atmosphere.
Other absorption bands using the JWST can only be detected for much higher
S/Ns, which is not achievable by just co-adding transit observations since this
would be far beyond the planned mission time of JWST.(abridged)Comment: 15 pages, 8 figure
Is a heterozygous missense variant in SGSH the cause of a syndromic form of congenital amastia in an Original Braunvieh calf?
A 5-days-old female purebred Original Braunvieh female calf was referred owing to a congenital absence of teats and cleft palate. Gross pathology revealed the entire absence of the udder including teats, complete palatoschisis affecting both soft and hard palate, hepatomegaly, corneal opacity and an open vulva (Figure S1). Whole genome sequencing (WGS) was performed using genomic DNA obtained from ear tissue from the calf. Reads were mapped to the ARS-UCD1.2 assembly (Rosen et al., 2020), resulting in an average read depth of 14.7×. The WGS data were evaluated as previously described (Jacinto et al., 2021). Variant filtering did not reveal any private homozygous protein-changing variants present in the genome of the affected calf, making a possible recessive inheritance unlikely. Assuming that a spontaneous mutation affecting a protein-coding gene is the cause, filtering for private heterozygous coding variants present in the calf’s genome allowed the identification of six variants with a predicted moderate or high impact (Table S1). These variants were confirmed as true by visual inspection with the integrative genomes viewer software (Robinson et al., 2017). These variants were absent from a total of 5365 controls and a single variant affects SGSH, a putative candidate gene for the observed congenital anomaly. This heterozygous variant at chr19:52427490C>T represents a missense variant in SGSH exon 4 (NM_001102189.2: c.425C>T) (Figure S2). We suspected that the identified variant in SGSH either occurred post-zygotically in the developing embryo or was inherited from a mosaic parent. Unfortunately, no biological samples were available from the parents. The encoded amino acid of SGSH is predicted to be altered at codon 142 (NP_001095659.2: p.Thr142Met) located in the N-sulphoglucosamine sulphohydrolase domain. The substitution of threonine to methionine affects an amino acid that is highly conserved in all species (Figure S2) and has been predicted to be harmful using three different tools (Provean, −4.729; PhD-SNP, 50%; SIFT, 79%)
Statistical Physics of Hard Optimization Problems
Optimization is fundamental in many areas of science, from computer science
and information theory to engineering and statistical physics, as well as to
biology or social sciences. It typically involves a large number of variables
and a cost function depending on these variables. Optimization problems in the
NP-complete class are particularly difficult, it is believed that the number of
operations required to minimize the cost function is in the most difficult
cases exponential in the system size. However, even in an NP-complete problem
the practically arising instances might, in fact, be easy to solve. The
principal question we address in this thesis is: How to recognize if an
NP-complete constraint satisfaction problem is typically hard and what are the
main reasons for this? We adopt approaches from the statistical physics of
disordered systems, in particular the cavity method developed originally to
describe glassy systems. We describe new properties of the space of solutions
in two of the most studied constraint satisfaction problems - random
satisfiability and random graph coloring. We suggest a relation between the
existence of the so-called frozen variables and the algorithmic hardness of a
problem. Based on these insights, we introduce a new class of problems which we
named "locked" constraint satisfaction, where the statistical description is
easily solvable, but from the algorithmic point of view they are even more
challenging than the canonical satisfiability.Comment: PhD thesi
Warming the early Earth - CO2 reconsidered
Despite a fainter Sun, the surface of the early Earth was mostly ice-free.
Proposed solutions to this so-called "faint young Sun problem" have usually
involved higher amounts of greenhouse gases than present in the modern-day
atmosphere. However, geological evidence seemed to indicate that the
atmospheric CO2 concentrations during the Archaean and Proterozoic were far too
low to keep the surface from freezing. With a radiative-convective model
including new, updated thermal absorption coefficients, we found that the
amount of CO2 necessary to obtain 273 K at the surface is reduced up to an
order of magnitude compared to previous studies. For the late Archaean and
early Proterozoic period of the Earth, we calculate that CO2 partial pressures
of only about 2.9 mb are required to keep its surface from freezing which is
compatible with the amount inferred from sediment studies. This conclusion was
not significantly changed when we varied model parameters such as relative
humidity or surface albedo, obtaining CO2 partial pressures for the late
Archaean between 1.5 and 5.5 mb. Thus, the contradiction between sediment data
and model results disappears for the late Archaean and early Proterozoic.Comment: 53 pages, 4 tables, 11 figures, published in Planetary and Space
Scienc
"Beam `a la carte": laser heater shaping for attosecond pulses in a multiplexed x-ray free-electron laser
Electron beam shaping allows the control of the temporal properties of x-ray
free-electron laser pulses from femtosecond to attosecond timescales. Here we
demonstrate the use of a laser heater to shape electron bunches and enable the
generation of attosecond x-ray pulses. We demonstrate that this method can be
applied in a selective way, shaping a targeted subset of bunches while leaving
the remaining bunches unchanged. This experiment enables the delivery of shaped
x-ray pulses to multiple undulator beamlines, with pulse properties tailored to
specialized scientific applications
The LCLS-II Photoinjector Laser Infrastructure
This paper presents a comprehensive technical overview of the Linac Coherent
Light Source II (LCLS-II) photoinjector laser system, its first and foremost
component. The LCLS-II photoinjector laser system serves as an upgrade to the
original LCLS at SLAC National Accelerator Laboratory. This advanced laser
system generates high-quality laser beams to power the LCLS-II, contributing to
the instrument's unprecedented brightness, precision, and flexibility. Our
discussion extends to the various subsystems that comprise the photoinjector,
including the photocathode laser, laser heater, and beam transport systems.
Lastly, we draw attention to the ongoing research and development
infrastructure underway to enhance the functionality and efficiency of the
LCLS-II, and similar X-ray free-electron laser facilities around the world,
thereby contributing to the future of laser technology and its applications.Comment: Submitted to High Power Laser Science and Engineerin
A function-based typology for Earth’s ecosystems
As the United Nations develops a post-2020 global biodiversity framework for the Convention on Biological Diversity, attention is focusing on how new goals and targets for ecosystem conservation might serve its vision of ‘living in harmony with nature’(1,2). Advancing dual imperatives to conserve biodiversity and sustain ecosystem services requires reliable and resilient generalizations and predictions about ecosystem responses to environmental change and management(3). Ecosystems vary in their biota(4), service provision(5) and relative exposure to risks(6), yet there is no globally consistent classification of ecosystems that reflects functional responses to change and management. This hampers progress on developing conservation targets and sustainability goals. Here we present the International Union for Conservation of Nature (IUCN) Global Ecosystem Typology, a conceptually robust, scalable, spatially explicit approach for generalizations and predictions about functions, biota, risks and management remedies across the entire biosphere. The outcome of a major cross-disciplinary collaboration, this novel framework places all of Earth’s ecosystems into a unifying theoretical context to guide the transformation of ecosystem policy and management from global to local scales. This new information infrastructure will support knowledge transfer for ecosystem-specific management and restoration, globally standardized ecosystem risk assessments, natural capital accounting and progress on the post-2020 global biodiversity framework
Experimental Demonstration of Attosecond Pump-Probe Spectroscopy with an X-ray Free-Electron Laser
Pump-probe experiments with sub-femtosecond resolution are the key to
understanding electronic dynamics in quantum systems. Here we demonstrate the
generation and control of sub-femtosecond pulse pairs from a two-colour X-ray
free-electron laser (XFEL). By measuring the delay between the two pulses with
an angular streaking diagnostic, we characterise the group velocity of the XFEL
and demonstrate control of the pulse delay down to 270 as. We demonstrate the
application of this technique to a pump-probe measurement in core-excited
para-aminophenol. These results demonstrate the ability to perform pump-probe
experiments with sub-femtosecond resolution and atomic site specificity.Comment: 55 pages, main manuscript (5 figures) + supplementary materials (25
figures), 30 figures total. Submitted to Nature Photonic
Evaluation of the Neutron Data Standards
With the need for improving existing nuclear data evaluations, (e.g., ENDF/B-VIII.0 and JEFF-3.3 releases) the first step was to evaluate the standards for use in such a library. This new standards evaluation made use of improved experimental data and some developments in the methodology of analysis and evaluation. In addition to the work on the traditional standards, this work produced the extension of some energy ranges and includes new reactions that are called reference cross sections. Since the effort extends beyond the traditional standards, it is called the neutron data standards evaluation. This international effort has produced new evaluations of the following cross section standards: the H(n,n), 6Li(n,t), 10B(n,α), 10B(n,), natC(n,n), Au(n,γ), 235U(n,f) and 238U(n,f). Also in the evaluation process the 238U(n,γ) and 239Pu(n,f) cross sections that are not standards were evaluated. Evaluations were also obtained for data that are not traditional standards: the Maxwellian spectrum averaged cross section for the Au(n,γ) cross section at 30 keV; reference cross sections for prompt γ-ray production in fast neutron-induced reactions; reference cross sections for very high energy fission cross sections; the 252Cf spontaneous fission neutron spectrum and the 235U prompt fission neutron spectrum induced by thermal incident neutrons; and the thermal neutron constants. The data and covariance matrices of the uncertainties were obtained directly from the evaluation procedure
- …