5,586 research outputs found
Data conversion and interoperability for FCA
This paper proposes a tool that converts non-FCA format data files into an FCA format, thereby making a wide range of public data sets and data produced by non-FCA tools interoperable with FCA tools. This will also offer the power of FCA to a wider community of data analysts. A repository of converted data is also proposed, as a consistent resource of public data for analysis and for the testing, evaluation and comparison of FCA tools and algorithms.</p
Programmable synthesis of organic cages with reduced symmetry
Integrating symmetry-reducing methods into self-assembly methodology is desirable to efficiently realise the full potential of molecular cages as hosts and catalysts. Although techniques have been explored for metal organic (coordination) cages, rational strategies to develop low symmetry organic cages remain limited. In this article, we describe rules to program the shape and symmetry of organic cage cavities by designing edge pieces that bias the orientation of the amide linkages. We apply the rules to synthesise cages with well-defined cavities, supported by evidence from crystallography, spectroscopy and modelling. Access to low-symmetry, self-assembled organic cages such as those presented, will widen the current bottleneck preventing study of organic enzyme mimics, and provide synthetic tools for novel functional material design
Thermal Protection System with Staggered Joints
The thermal protection system disclosed herein is suitable for use with a spacecraft such as a reentry module or vehicle, where the spacecraft has a convex surface to be protected. An embodiment of the thermal protection system includes a plurality of heat resistant panels, each having an outer surface configured for exposure to atmosphere, an inner surface opposite the outer surface and configured for attachment to the convex surface of the spacecraft, and a joint edge defined between the outer surface and the inner surface. The joint edges of adjacent ones of the heat resistant panels are configured to mate with each other to form staggered joints that run between the peak of the convex surface and the base section of the convex surface
Resolved gas cavities in transitional disks inferred from CO isotopologues with ALMA
Transitional disks around young stars are promising candidates to look for
recently formed, embedded planets. Planet-disk interaction models predict that
planets clear a gap in the gas while trapping dust at larger radii. Other
physical mechanisms could be responsible for cavities as well. Previous
observations have revealed that gas is still present inside these cavities, but
the spatial distribution of this gas remains uncertain. We present high spatial
resolution observations with the Atacama Large Millimeter/submillimeter Array
(ALMA) of 13CO and C18O lines of four well-studied transitional disks. The
observations are used to set constraints on the gas surface density,
specifically cavity size and density drop inside the cavity. The
physical-chemical model DALI is used to analyze the gas images of SR21,
HD135344B, DoAr44 and IRS48. The main parameters of interest are the size,
depth and shape of the gas cavity. CO isotope-selective photodissociation is
included to properly constrain the surface density in the outer disk from C18O
emission. The gas cavities are up to 3 times smaller than those of the dust in
all four disks. Model fits indicate that the surface density inside the gas
cavities decreases by a factor of 100-10000 compared with the surface density
profile derived from the outer disk. A comparison with an analytical model of
gap depths by planet-disk interaction shows that the disk viscosities are
likely low, with a<1E-3 for planet masses <10 MJup. The resolved measurements
of the gas and dust in transition disk cavities support the predictions of
models that describe how planet-disk interactions sculpt gas disk structures
and influence the evolution of dust grains. These observed structures strongly
suggest the presence of giant planetary companions in transition disk cavities,
although at smaller orbital radii than is typically indicated from the dust
cavity radii alone.Comment: Accepted by A&A; version after language-editin
Enzyme-like Acyl Transfer Catalysis in a Bifunctional Organic Cage
Amide-based organic cage cavities are, in principle, ideal enzyme active site mimics. Yet, cage-promoted organocatalysis has remained elusive, in large part due to synthetic accessibility of robust and functional scaffolds. Herein, we report the acyl transfer catalysis properties of robust, hexaamide cages in organic solvent. Cage structural variation reveals that esterification catalysis with an acyl anhydride acyl carrier occurs only in bifunctional cages featuring internal pyridine motifs and two crucial antipodal carboxylic acid groups. H NMR data and X-ray crystallography show that the acyl carrier is rapidly activated inside the cavity as a covalent mixed-anhydride intermediate with an internal hydrogen bond. Michaelis-Menten (saturation) kinetics suggest weak binding ( = 0.16 M) of the alcohol pronucleophile close to the internal anhydride. Finally, activation and delivery of the alcohol to the internal anhydride by the second carboxylic acid group forms ester product and releases the cage catalyst. Eyring analysis indicates a strong enthalpic stabilization of the transition state (5.5 kcal/mol) corresponding to a rate acceleration of 10 over background acylation, and an ordered, associative rate-determining attack by the alcohol, supported by DFT calculations. We conclude that internal bifunctional organocatalysis specific to the cage structural design is responsible for the enhancement over the background reaction. These results pave the way for organic-phase enzyme mimicry in self-assembled cavities with the potential for cavity elaboration to enact selective acylations
Evaluation of ranks of real space and particle entanglement spectra for large systems
We devise a way to calculate the dimensions of symmetry sectors appearing in
the Particle Entanglement Spectrum (PES) and Real Space Entanglement Spectrum
(RSES) of multi-particle systems from their real space wave functions. We first
note that these ranks in the entanglement spectra equal the dimensions of
spaces of wave functions with a number of particles fixed. This also yields
equality of the multiplicities in the PES and the RSES. Our technique allows
numerical calculations for much larger systems than were previously feasible.
For somewhat smaller systems, we can find approximate entanglement energies as
well as multiplicities. We illustrate the method with results on the RSES and
PES multiplicities for integer quantum Hall states, Laughlin and Jain composite
fermion states and for the Moore-Read state at filling , for system
sizes up to 70 particles.Comment: 5 pages, 2 figures; minor changes; New version includes the Real
Space ES of Jain states; accepted for publication in Phys.Rev.Let
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