356 research outputs found
Electronic properties of alkali-metal loaded zeolites -- a "supercrystal" Mott insulator
First-principles band calculations are performed for the first time for an
open-structured zeolite (LTA) with guest atoms (potassium) introduced in their
cages. A surprisingly simple band structure emerges, which indicates that this
system may be regarded as a "supercrystal", where each cluster of guest atoms
with diameter 10\AA acts as a "superatom" with well-defined - and
-like orbitals, which in turn form the bands around the Fermi energy. The
calculated Coulomb and exchange energies for these states turn out to be in the
strongly-correlated regime. With the dynamical mean-field theory we show the
system should be on the Mott-insulator side, and, on a magnetic phase diagram
for degenerate-orbital systems, around the ferromagnetic regime, in accord with
experimental results. We envisage this class of systems can provide a new
avenue for materials design.Comment: 4 pages, 4 figure
On the distortion of twin building lattices
We show that twin building lattices are undistorted in their ambient group;
equivalently, the orbit map of the lattice to the product of the associated
twin buildings is a quasi-isometric embedding. As a consequence, we provide an
estimate of the quasi-flat rank of these lattices, which implies that there are
infinitely many quasi-isometry classes of finitely presented simple groups. In
an appendix, we describe how non-distortion of lattices is related to the
integrability of the structural cocycle
LiFtEr: Language to Encode Induction Heuristics for Isabelle/HOL
Proof assistants, such as Isabelle/HOL, offer tools to facilitate inductive
theorem proving. Isabelle experts know how to use these tools effectively;
however, there is a little tool support for transferring this expert knowledge
to a wider user audience. To address this problem, we present our
domain-specific language, LiFtEr. LiFtEr allows experienced Isabelle users to
encode their induction heuristics in a style independent of any problem domain.
LiFtEr's interpreter mechanically checks if a given application of induction
tool matches the heuristics, thus automating the knowledge transfer loop.Comment: This is the pre-print of our paper of the same title accepted at
APLAS2019 (https://doi.org/10.1007/978-3-030-34175-6_14). We updated the
draft after fixing the errata found by Kenji Miyamot
Revealing the chemical characteristics of Arctic low-level cloud residuals – in situ observations from a mountain site
The role aerosol chemical composition plays in Arctic
low-level cloud formation is still poorly understood. In this study we
address this issue by combining in situ observations of the chemical
characteristics of cloud residuals (dried liquid cloud droplets or ice
crystals) and aerosol particles from the Zeppelin Observatory in
Ny-Ålesund, Svalbard (approx. 480 m a.s.l.). These measurements were
part of the 1-year-long Ny-Ålesund Aerosol and Cloud Experiment
2019–2020 (NASCENT). To obtain the chemical composition of cloud residuals
at molecular level, we deployed a Filter Inlet for Gases and AEROsols
coupled to a Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) with
iodide as the reagent ion behind a ground-based counterflow virtual impactor
(GCVI). The station was enshrouded in clouds roughly 15 % of the time
during NASCENT, out of which we analyzed 14 cloud events between December
2019 and December 2020. During the entire year, the composition of the cloud
residuals shows contributions from oxygenated organic compounds, including
organonitrates, and traces of the biomass burning tracer levoglucosan. In
summer, methanesulfonic acid (MSA), an oxidation product of dimethyl sulfide
(DMS), shows large contributions to the sampled mass, indicating marine
natural sources of cloud condensation nuclei (CCN) and ice nucleating
particle (INP) mass during the sunlit part of the year. In addition, we
also find contributions of the inorganic acids nitric acid and sulfuric acid,
with outstanding high absolute signals of sulfuric acid in one cloud
residual sample in spring and one in late summer (21 May and 12 September 2020), probably caused by high anthropogenic sulfur emissions near the
Barents Sea and Kara Sea. During one particular cloud event, on 18 May 2020,
the air mass origin did not change before, during, or after the
cloud. We therefore chose it as a case study to investigate cloud impact on
aerosol physicochemical properties. We show that the overall chemical
composition of the organic aerosol particles was similar before, during, and
after the cloud, indicating that the particles had already undergone one or
several cycles of cloud processing before being measured as residuals at the
Zeppelin Observatory and/or that, on the timescales of the observed cloud event, cloud
processing of the organic fraction can be neglected. Meanwhile, there were on
average fewer particles but relatively more in the accumulation mode after
the cloud. Comparing the signals of sulfur-containing compounds of cloud
residuals with aerosols during cloud-free conditions, we find that sulfuric
acid had a higher relative contribution to the cloud residuals than to
aerosols during cloud-free conditions, but we did not observe an increase in
particulate MSA due to the cloud. Overall, the chemical composition,
especially of the organic fraction of the Arctic cloud residuals, reflected
the overall composition of the general aerosol population well. Our results
thus suggest that most aerosols can serve as seeds for low-level clouds in
the Arctic.</p
Arctic observations of hydroperoxymethyl thioformate (HPMTF) – seasonal behavior and relationship to other oxidation products of dimethyl sulfide at the Zeppelin Observatory, Svalbard
Dimethyl sulfide (DMS), a gas produced by phytoplankton, is the largest
source of atmospheric sulfur over marine areas. DMS undergoes oxidation in
the atmosphere to form a range of oxidation products, out of which sulfuric
acid (SA) is well known for participating in the formation and growth of
atmospheric aerosol particles, and the same is also presumed for
methanesulfonic acid (MSA). Recently, a new oxidation product of DMS,
hydroperoxymethyl thioformate (HPMTF), was discovered and later also measured
in the atmosphere. Little is still known about the fate of this compound and
its potential to partition into the particle phase. In this study, we present
a full year (2020) of concurrent gas- and particle-phase observations of
HPMTF, MSA, SA and other DMS oxidation products at the Zeppelin Observatory
(Ny-Ålesund, Svalbard) located in the Arctic. This is the first time
HPMTF has been measured in Svalbard and attempted to be observed in
atmospheric particles. The results show that gas-phase HPMTF concentrations
largely follow the same pattern as MSA during the sunlit months
(April–September), indicating production of HPMTF around Svalbard. However,
HPMTF was not observed in significant amounts in the particle phase, despite
high gas-phase levels. Particulate MSA and SA were observed during the
sunlit months, although the highest median levels of particulate SA were
measured in February, coinciding with the highest gaseous SA levels with
assumed anthropogenic origin. We further show that gas- and particle-phase
MSA and SA are coupled in May–July, whereas HPMTF lies outside of this
correlation due to the low particulate concentrations. These results provide
more information about the relationship between HPMTF and other DMS
oxidation products, in a part of the world where these have not been explored
yet, and about HPMTF's ability to contribute to particle growth and cloud
formation.</p
The dependency pair framework: Combining techniques for automated termination proofs
Abstract. The dependency pair approach is one of the most powerful techniques for automated termination proofs of term rewrite systems. Up to now, it was regarded as one of several possible methods to prove termination. In this paper, we show that dependency pairs can instead be used as a general concept to integrate arbitrary techniques for termination analysis. In this way, the benefits of different techniques can be combined and their modularity and power are increased significantly. We refer to this new concept as the “dependency pair framework ” to distinguish it from the old “dependency pair approach”. Moreover, this framework facilitates the development of new methods for termination analysis. To demonstrate this, we present several new techniques within the dependency pair framework which simplify termination problems considerably. We implemented the dependency pair framework in our termination prover AProVE and evaluated it on large collections of examples.
A gain-of-function TBX20 mutation causes congenital atrial septal defects, patent foramen ovale and cardiac valve defects
BACKGROUND: Ostium secundum atrial septal defects (ASDII) account for approximately 10% of all congenital heart defects (CHD) and mutations in cardiac transcription factors, including TBX20, were identified as an underlying cause for ASDII. However, very little is known about disease penetrance in families and functional consequences of inherited TBX20 mutations. METHODS: The coding region of TBX20 was directly sequenced in 170 ASDII patients. Functional consequences of one novel mutation were investigated by surface plasmon resonance, CD spectropolarymetry, fluorescence spectrophotometry, luciferase assay and chromatin immunoprecipitation. RESULTS: We found a novel mutation in a highly conserved residue in the T-box DNA-binding domain (I121M) segregating with CHD in a three generation kindred. Four mutation carriers revealed cardiac phenotypes in terms of cribriform ASDII, large patent foramen ovale or cardiac valve defects. Interestingly, tertiary hydrophobic interactions within the mutant TBX20 T-box were significantly altered leading to a more dynamic structure of the protein. Moreover, Tbx20-I121M resulted in a significantly enhanced transcriptional activity, which was further increased in the presence of co-transcription factors GATA4/5 and NKX2-5. Occupancy of DNA binding sites on target genes was also increased. CONCLUSIONS: We suggest that TBX20-I121M adopts a more fluid tertiary structure leading to enhanced interactions with cofactors and more stable transcriptional complexes on target DNA sequences. Our data, combined with that of others, suggest that human ASDII may be related to loss- as well as gain-of-function TBX20 mutations
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