An analysis of stress wave propagation in slender bars using a discrete particle approach

In this paper, a discrete particle approach is developed for the quantitative analysis of stress wave propagation in metal bars. Though linear forces are emphasized, nonlinear forces are also considered. Cylindrical, tapered, homogeneous, and nonhomogeneous bars are studied. Computer results show most favourable agreement with available theoretical and experimental results.     

Molecular models for the structure of solvent in an interphase

In view of the difficulties encountered in the discussion of interfacial solvent structure in terms of simple dipolar molecules in a small number of orientations, an attempt is made here to investigate more realistic models for this region. A new technique of searching for minimum energy configurations is developed. The results confirm that even with a more realistic point charge model of the water molecule the dipole tends to be oriented in the plane of a two-dimensional array.     

Theoretical analysis of vertical colloidal deposition

We have modeled the dynamics of a relatively new deposition technique, vertical colloidal deposition (VCD), for preparing nanoparticle thin films. In this process, the substrate is placed vertically in a nanoparticle suspension and is gradually exposed by evaporation or other slow solvent removal. During the film's formation, we observe that the colloidal particles are deposited only at the solid-liquid-gas interface. In contrast with the horizontal geometry, treated elsewhere, where the meniscus is pinned, we observe qualitatively different deposition behaviors. In particular, uniform films rather than rings or lines are produced. Thus, we are led to model a diffusion-driven rather than a convection-driven film growth kinetics, and we are able to predict, consistent with our experimental observations, that the film's areal density is inversely proportional to the descent speed of the suspension surface. Additionally, we find that for submonolayer films, the areal density is proportional to the square of the suspension concentration, converting to a linear dependence once monolayer coverage is attained.     

Transition-metal-mediated cascade reactions: the water-accelerated carboalumination-Claisen rearrangement-carbonyl addition reaction

[Chemical reaction: See text] A three-step cascade reaction involving a water-accelerated catalytic carboalumination, a Claisen rearrangement, and a nucleophilic carbonyl addition converts terminal alkynes and allyl vinyl ethers into allylic alcohols containing up to three contiguous asymmetric carbon centers. Stoichiometric quantities of water as an additive increase the rate of the [3,3] sigmatropic rearrangement as well as the diastereoselectivity of the carbonyl addition process. Reaction products contain 1,6-diene functionalities that are readily cyclized to substituted cyclopentenes. An extension of this methodology to a sequence involving a [1,3] sigmatropic shift was feasible with a cyclopropylmethyl vinyl ether substrate.     

Facile synthesis of N-substituted-4-cyano-4-phenylpiperidines via phase-transfer catalysis

Phenylacetonitrile can be condensed with N-substituted-bis(2-chloroethyl)amines in aqueous sodium hydroxide solution to produce N-substituted-4-cyano-4-phenylpiperidines. Hexadecyltributylphosphonium bromide is an effective catalyst for this phase-transfer reaction.