Dynamic stability of weakly damped oscillators with elastic impacts and wear

The dynamics of non-linear oscillators comprising of a single-degree-of-freedom system and beams with elastic two-sided amplitude constraints subject to harmonic loads is analyzed. The beams are clamped at one end, and constrained against unilateral contact sites near the other end. The structures are modelled by a Bernoulli-type beam supported by springs using the finite element method. Rayleigh damping is assumed. Symmetric and elastic double-impact motions, both harmonic and sub-harmonic, are studied by way of a Poincaré mapping that relates the states at subsequent impacts. Stability and bifurcation analyses are performed for these motions, and domains of instability are delineated. Impact work rate, which is the rate of energy dissipation to the impacting surfaces, is evaluated and discussed. In addition, an experiment conducted by Moon and Shaw on the vibration of a cantilevered beam with one-sided amplitude constraining stop is modelled. Bifurcation observed in the experiment could be captured.     

Membrane ion-exchange chromatography for process-scale antibody purification

Microemulsion electrokinetic chromatography (MEEKC) was evaluated as a screening tool for the indirect measurement of octanol–water partition coefficients (log P_o/w) of pesticide compounds. Over 80 pesticide compounds representing a variety of structural characteristics were studied, and good correlation of log P_o/w with the logarithm of the retention factor was found. The microemulsion system studied allowed the separation of compounds in the log P_o/w range of −1 to 7. In addition, a smaller set of simple organic molecules that vary in structural features was evaluated and compared to the pesticide log P_o/w calibration. The pesticide and simple organic molecule log P_o/w calibration lines were statistically similar. This suggests that a universal set of standard compounds may be employed for the log P_o/w calibration to provide measurements for a variety of compounds with good accuracy.     

Evolutionary rate variation and RNA secondary structure prediction

Predicting RNA secondary structure using evolutionary history can be carried out by using an alignment of related RNA sequences with conserved structure. Accurately determining evolutionary substitution rates for base pairs and single stranded nucleotides is a concern for methods based on this type of approach. Determining these rates can be hard to do reliably without a large and accurate initial alignment, which ideally also has structural annotation. Hence, one must often apply rates extracted from other RNA families with trusted alignments and structures. Here, we investigate this problem by applying rates derived from tRNA and rRNA to the prediction of the much more rapidly evolving 5'-region of HIV-1. We find that the HIV-1 prediction is in agreement with experimental data, even though the relative evolutionary rate between A and G is significantly increased, both in stem and loop regions. In addition we obtained an alignment of the 5' HIV-1 region that is more consistent with the structure than that currently in the database. We added randomized noise to the original values of the rates to investigate the stability of predictions to rate matrix deviations. We find that changes within a fairly large range still produce reliable predictions and conclude that using rates from a limited set of RNA sequences is valid over a broader range of sequences.     

Phase separation and structural properties of semidilute aqueous mixtures of ethyl(hydroxyethyl)cellulose and an ionic surfactant

Turbidity and small-angle neutron scattering (SANS) measurements have been carried out over an extended temperature range (10-60 °C) on thermoreversible gelling and non-gelling semidilute aqueous systems of ethyl(hydroxyethyl)cellulose (EHEC) in the presence of various amounts of sodium dodecyl sulfate (SDS). EHEC dissolved in D₂O exhibits a lower consolute solution temperature with an abrupt change of the turbidity upon heating the sample. The turbidity transformation is shifted toward higher temperatures (the cloud point temperature rises) and it becomes gradually gentler as the level of surfactant addition increases. Precision turbidity measurements demonstrate the existence of hysteresis effects when heating and cooling scans are conducted. This effect is reduced with SDS addition and disappears at a sufficiently high SDS concentration where most aggregates are disrupted. It is shown from temperature quench turbidity experiments that it takes a very long time for the temperature-induced complexes to disintegrate. The scattered intensity results from SANS at low values of the scattering vector (q) disclose that elevated temperature and low SDS concentration promote the formation of large-scale associations, and at higher levels of surfactant addition the tendency to form aggregates is suppressed. At high surfactant concentrations (8 and 16 mm), an interaction peak appears in the spectrum at intermediate values of q. For the EHEC sample with 8 mm SDS, the peak disappears at higher temperatures because of enhanced hydrophobicity of the polymer. The analysis of the SANS data for the gelling sample (EHEC with 4 mm SDS) reveals that the inhomogeneity of the gel becomes more pronounced in the post-gel region.     

Reaction of dicobalt octacarbonyl with acetylene and carbon monoxide at low temperature and pressure: Formation of cyclic enone products

Dicobalt octacarbonyl is shown to react with acetylene and carbon monoxide under mild conditions in dimethoxyethane or benzene to produce, in low yields, bicyclo[3.3.0]octa-3,7-diene-2,6-dione, benzoquinone, and the cyclopentadienone-derived products 3a,4,7,7a-tetrahydro-2,7-methanoindene-1,10-dione, 1-indanone, tetracyclo[5.5.2.0^2,60^8,12]tetradeca-4,10,13-triene-3,9-dione, and tetracyclo[5.5.2.0^2,60^8,12]tetradeca-4,9,13-triene-3,11-dione. Possible mechanisms for the formation of these products are discussed.     

Merging and splitting in cooperative games: some (im)possibility results

Allocation rules for cooperative games can be manipulated by coalitions merging into single players, or, conversely, players splitting into a number of smaller units. This paper collects some (im)possibility results on merging- and splitting-proofness of (core) allocation rules for cooperative games with side-payments.