Patterned burst-pulse vocalizations of the northern right whale dolphin, Lissodelphis borealis

Vocalizations from the northern right whale dolphin, Lissodelphis borealis, were recorded during a combined visual and acoustic shipboard survey of cetacean populations off the west coast of the United States. Seven of twenty single-species schools of L. borealis produced click and pulsed vocalizations. No whistles were detected during any of the encounters. Clicks associated with burst-pulse vocalizations were lower in frequency and shorter in duration than clicks associated with echolocation. All burst-pulse sounds were produced in a series containing 6-18 individual burst-pulses. These burst-pulse series were stereotyped and repeated. A total of eight unique burst-pulse series were detected. Variation in the temporal characteristics of like units compared across repeated series was less than variation among all burst-pulses. These stereotyped burst-pulse series may play a similar communicative role as do stereotyped whistles found in other delphinid species.     

Asymptotic behavior and Hamiltonian analysis of anti-de Sitter gravity coupled to scalar fields

We examine anti-de Sitter gravity minimally coupled to a self-interacting scalar field in D ? 4 dimensions when the mass of the scalar field is in the range . Here, l is the AdS radius, and is the Breitenlohner-Freedman mass. We show that even though the scalar field generically has a slow fall-off at infinity which back reacts on the metric so as to modify its standard asymptotic behavior, one can still formulate asymptotic conditions (i) that are anti-de Sitter invariant; and (ii) that allows the construction of well-defined and finite Hamiltonian generators for all elements of the anti-de Sitter algebra. This requires imposing a functional relationship on the coefficients a, b that control the two independent terms in the asymptotic expansion of the scalar field. The anti-de Sitter charges are found to involve a scalar field contribution. Subtleties associated with the self-interactions of the scalar field as well as its gravitational back reaction, not discussed in previous treatments, are explicitly analyzed. In particular, it is shown that the fields develop extra logarithmic branches for specific values of the scalar field mass (in addition to the known logarithmic branch at the B-F bound).     

An Ordered Nanoporous Monolith from an Elastomeric Crosslinked Block Copolymer Precursor

Summary: An ordered nanoporous monolith was prepared from a poly(isoprene‐b‐dimethylsiloxane) (PI‐PDMS) hexagonally packed cylinder precursor. The PDMS cylinders were macroscopically aligned, the PI was crosslinked with dicumyl peroxide, and the PDMS was removed using tetrabutylammonium fluoride. The stability of the pores depended on the modulus of the matrix. At high crosslink density the pores were stable, but they collapsed at a low crosslink density. The nanoporous materials could be swollen in toluene.

A scanning electron micrograph of the end‐on view of crosslinked degraded poly(isoprene‐b‐dimethylsiloxane).     

The Kelvin–Nevanlinna–Royden criterion for p-parabolicity

We generalize the so called Kelvin–Nevanlinna–Royden criterion for the parabolicity of manifolds to the case of p-parabolicity for all . Received July 29, 1998; in final form September 25, 1998     

A novel and efficient alkyl radical trap in aqueous medium

A simple water soluble diselenide derivative 1 shows radical scavenger properties towards alkyl and hydroxyl radicals (k₃ (0°C)=6.8×10⁸ M⁻¹ s⁻¹) in Fenton-type chemistry. The reaction rate between produceded alkyl radicals 2 and the diselenide overwhelms self-termination and halogen transfer reactions.     

Structure prediction of cyclic peptides by molecular dynamics + machine learning

Recent computational methods have made strides in discovering well-structured cyclic peptides that preferentially populate a single conformation. However, many successful cyclic-peptide therapeutics adopt multiple conformations in solution. In fact, the chameleonic properties of some cyclic peptides are likely responsible for their high cell membrane permeability. Thus, we require the ability to predict complete structural ensembles for cyclic peptides, including the majority of cyclic peptides that have broad structural ensembles, to significantly improve our ability to rationally design cyclic-peptide therapeutics. Here, we introduce the idea of using molecular dynamics simulation results to train machine learning models to enable efficient structure prediction for cyclic peptides. Using molecular dynamics simulation results for several hundred cyclic pentapeptides as the training datasets, we developed machine-learning models that can provide molecular dynamics simulation-quality predictions of structural ensembles for all the hundreds of thousands of sequences in the entire sequence space. The prediction for each individual cyclic peptide can be made using less than 1 second of computation time. Even for the most challenging classes of poorly structured cyclic peptides with broad conformational ensembles, our predictions were similar to those one would normally obtain only after running multiple days of explicit-solvent molecular dynamics simulations. The resulting method, termed StrEAMM (Structural Ensembles Achieved by Molecular Dynamics and Machine Learning), is the first technique capable of efficiently predicting complete structural ensembles of cyclic peptides without relying on additional molecular dynamics simulations, constituting a seven-order-of-magnitude improvement in speed while retaining the same accuracy as explicit-solvent simulations.

The StrEAMM method enables predicting the structural ensembles of cyclic peptides that adopt multiple conformations in solution.     

Selective reductions in the sphere of organophosphorus compounds

Recent results on the selective reduction of cyclic vinylphosphine oxides and vinylphosphinates, as well as their refunctionalization by the use of borane, are summarized. The selective reduction of the phosphorus moiety of unsaturated phosphonates, phosphinates, and phosphine oxides is also discussed. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:161–167, 2001