Small-angle neutron-scattering study of concentrated nonionic-amphiphile solutions

The structure of aqueous solutions of two polyoxyethylene non-ionic amphiphiles, C₁₀E₅ and C₈E₄, is studied by small-angle neutron-scattering along isothermal paths crossing the isotropic single-phase region from 0% to 100% amphiphile volume fractions. The scattered intensityI(k) shows a peak at a valuek _m , which grows monotonically as the amphiphile volume fraction increases. The interpretation of the scattering data lead to the following conclusion: as increases the micellar structure becomes less and less sharp, but some orientational correlations between neighboring amphiphile molecules are preserved even in the pure amphiphile phase.     

Enantioselective synthesis of 2-arylpiperidines from chiral lactams. A concise synthesis of (-)-anabasine

Cyclodehydration of achiral or racemic aryl-delta-oxoacids with (R)-phenylglycinol stereoselectively affords chiral non-racemic bicyclic lactams, from which the enantiodivergent synthesis of (R)- and (S)-2-phenylpiperidine, the diastereodivergent synthesis of cis- and trans-3-ethyl-2-phenylpiperidine, and the enantioselective synthesis of the piperidine alkaloid (-)-anabasine is reported.     

On identifiability for chemical systems from measurable variables

The dynamics of the composition of chemical species in reacting systems can be characterized by a set of autonomous differential equations derived from mass conservation principles and some elementary hypothesis related to chemical reactivity. These sets of ordinary differential equations (ODEs) are basically non-linear, their complexity grows as much increases the number of substances present in the reacting media and can be characterized by a set of phenomenological constants (kinetic rate constants) which contains all the relevant information about the physical system. The determination of these kinetic constants is critical for the design or control of chemical systems from a technological point of view but the non-linear nature of the ODEs implies that there are hidden correlations between the parameters which maybe can be revealed with a identifiability analysis.     

On the Decay of Turbulence in the 20-Liter Explosion Sphere

The transient flow field in the standard 20-liter explosion sphere was investigated by means of laser Doppler anemometry. Velocities were measured at various locations within the flow field, and this information was used to quantify the transient behavior of the root-mean-square of the velocity fluctuations and to investigate the spatial homogeneity and the directional isotropy of the turbulence. The investigation involved the transient flow fields generated by the three most widely used dust dispersion systems, namely, the Perforated Dispersion Ring, the Rebound Nozzle, and the Dahoe Nozzle. With all three dispersion dust devices, the decay of turbulence could be correlated by a decay law of the form

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.