On Embeddings of Tori in Euclidean Spaces

Using the relation between the set of embeddings of tori into Euclidean spaces modulo ambient isotopies and the homotopy groups of Stiefel manifolds, we prove new results on embeddings of tori into Euclidean spaces.     

Access to Metastable Gel States Using Seeded Self‐Assembly of Low‐Molecular‐Weight Gelators

Here we report on how metastable supramolecular gels can be formed through seeded self‐assembly of multicomponent gelators. Hydrazone‐based gelators decorated with non‐ionic and anionic groups are formed in situ from hydrazide and aldehyde building blocks, and lead through multiple self‐sorting processes to the formation of heterogeneous gels approaching thermodynamic equilibrium. Interestingly, the addition of seeds composing of oligomers of gelators bypasses the self‐sorting processes and accelerates the self‐assembly along a kinetically favored pathway, resulting in homogeneous gels of which the network morphologies and gel stiffness are markedly different from the thermodynamically more stable gel products. Importantly, over time, these metastable homogeneous gel networks are capable of converting into the thermodynamically more stable state. This seeding‐driven formation of out‐of‐equilibrium supramolecular structures is expected to serve as a simple approach towards functional materials with pathway‐dependent properties.     

Real-time optodynamic monitoring of pulsed laser decoating rate

This paper deals with a laser-cleaning process for removing a layer of paint. The effects of each individual laser pulse were monitored by a three-probe system. Ultrasonic signals from the rear surface of the substrate were obtained using an arm compensated Michelson interferometer, the optoacoustic waves in the surrounding air were detected using a laser beam deflection probe and the shape of the growing crater was measured using a laser anamorph profilometer. Two different cleaning lasers were used: an Excimer and a Nd:YAG laser. Typical parameters of the optodynamic signals versus the laser-pulse number are presented. A linear correlation between the quantity of ablated material and the integral of the ultrasonic signals was found together with an exponential relationship between the time-of-flight of the optoacoustic signals and the decoating rate.     

Multifunctionalization of synthetic polymer systems through self-assembly

A straightforward methodology towards the replacement of covalent strategies for the synthesis of multifunctional synthetic materials with a self-assembling strategy that employs multiple noncovalent recognition units to attach multiple functional molecules to a polymeric scaffold is outlined. Design requirements, advantages, and potential applications, as well as the possibility of rapid optimization of materials during the manufacturing process as a result of the parallel character of self-assembly, are presented. While still in its infancy, this novel methodology may overcome several shortcomings of current covalent multifunctionalization strategies and may yield highly complex materials that are extremely difficult or impossible to fabricate with current methods.     

Monochromatic paths in random tournaments

We prove that, with high probability, any 2‐edge‐coloring of a random tournament on n vertices contains a monochromatic path of length . This resolves a conjecture of Ben‐Eliezer, Krivelevich, and Sudakov and implies a nearly tight upper bound on the oriented size Ramsey number of a directed path.     

3-Color bipartite Ramsey number of cycles and paths

The -color bipartite Ramsey number of a bipartite graph is the least integer for which every -edge-colored complete bipartite graph contains a monochromatic copy of . The study of bipartite Ramsey numbers was initiated, over 40 years ago, by Faudree and Schelp and, independently, by Gyárfás and Lehel, who determined the 2-color Ramsey number of paths. In this paper we determine asymptotically the 3-color bipartite Ramsey number of paths and (even) cycles.     

Structure-based computational database screening, in vitro assay, and NMR assessment of compounds that target TAR RNA

There has been little prior effort to discover new drugs on the basis of a unique RNA structure. Binding of the viral transactivator Tat to the 5' bulge of the transactivation response (TAR) element is necessary for HIV-1 replication, so TAR RNA is a superb target. A computational approach was developed to screen a large chemical library for binding to a three-dimensional RNA structure. Scoring function development, flexible ligand docking, and limited target flexibility were essential. From the ranked list of compounds predicted to bind TAR, 43 were assayed for inhibition of the Tat-TAR interaction via electrophoretic mobility shift assays. Eleven compounds (between 0.1 and 1 microM) inhibited the Tat-TAR interaction, and some inhibited Tat transactivation in cells. NMR spectra verified specific binding to the 5' bulge and no interaction with other regions of TAR.     

Sensitivity enhancement using chemically reactive gas cluster ion beams in secondary ion mass spectrometry (SIMS)

We report for the first time on significant molecular secondary ion yield increases by modifying the chemistry of a water cluster primary ion beam. This was demonstrated using 70-keV ion beams of 0.15 eV/amu. For the neutral drug Bezafibrate, secondary ion yield enhancements ×5–10 were observed when replacing the Ar carrier gas in a water gas cluster ion beam (GCIB) source with a mixture containing 12% CO₂ and 2% O₂ in Ar. For the cationic drug Ranitidine, the ion yield enhancements using the CO₂-containing carrier gas were up to ×20–50 in positive mode and ×2–4 in negative mode. The extent of molecular fragmentation was very similar from both cluster beams. We conclude that additional chemically reactive species are present in the impact zone using the (H₂O/CO₂)_n projectile, which promote the formation of secondary ions of both polarity through projectile impact-induced chemical reactions. This methodology can be applied to further extend the capabilities of high-resolution 3-dimensional mass spectral imaging using reactive GCIB-SIMS.