An analogy between vortical and thermal fields subject to the large pressure gradient

Local thermal disturbances generated by a small confined mechanical forcing on the curved surface are under consideration within the framework of the interacting boundary layer in the limit of large Reynolds number. The variations of the self-induced pressure and temperature are found to be explicitly related, and an analytic solution of a linear perturbation analysis is presented. The heat flux associated with the self-induced pressure may attain values comparable with the heat flux existing in the oncoming boundary layer. The analogy between the normal-to-wall vorticity and spanwise derivative of temperature is rigorously derived to supersede locally the well-known analogy by Reynolds. Heavily increased thermal loads can cause severe damage to the engine in operation.     

Structure and Reactivity of the Distonic and Aromatic Radical Cations of Tryptophan

In this work, we regiospecifically generate and compare the gas-phase properties of two isomeric forms of tryptophan radical cations—a distonic indolyl N-radical (H₃N⁺ - TrpN^?) and a canonical aromatic π (Trp^?+) radical cation. The distonic radical cation was generated by nitrosylating the indole nitrogen of tryptophan in solution followed by collision-induced dissociation (CID) of the resulting protonated N-nitroso tryptophan. The π-radical cation was produced via CID of the ternary [Cu^II(terpy)(Trp)] ^?2+ complex. CID spectra of the two isomeric species were found to be very different, suggesting no interconversion between the isomers. In gas-phase ion-molecule reactions, the distonic radical cation was unreactive towards n-propylsulfide, whereas the π radical cation reacted by hydrogen atom abstraction. DFT calculations revealed that the distonic indolyl radical cation is about 82 kJ/mol higher in energy than the π radical cation of tryptophan. The low reactivity of the distonic nitrogen radical cation was explained by spin delocalization of the radical over the aromatic ring and the remote, localized charge (at the amino nitrogen). The lack of interconversion between the isomers under both trapping and CID conditions was explained by the high rearrangement barrier of ca.137 kJ/mol. Finally, the two isomers were characterized by infrared multiple-photon dissociation (IRMPD) spectroscopy in the ~1000–1800 cm^–1 region. It was found that some of the main experimental IR features overlap between the two species, making their distinction by IRMPD spectroscopy in this region problematic. In addition, DFT theoretical calculations showed that the IR spectra are strongly conformation-dependent.      

Two kinds of nanoscale dynamic heterogeneity in single‐phase polymer blends and their common origin

Differential scanning calorimetry (DSC) and laser‐interferometric creep rate spectroscopy (CRS) were used for kinetic and discrete analysis of segmental motion within (and close to) glass transition range in polystyrene ‐ poly(α‐methyl styrene) (PS/PMS) and polystyrene ‐ poly(vinyl methyl ether) (PS/PVME) miscible blends. Two kinds of segmental dynamics heterogeneity were found. Separate ‘unfreezing’ of PS and PMS segmental motions was observed that manifested itself in two T_gs and simultaneous large drop in the Tg s, as well as glass transition activation energy, motional event scale and cooperativity degree values, down to the β‐relaxation parameters. The wide activation energy dispersion within a single broad glass transition in PS/PVME blends was found, and this relaxation region was subdivided, by CRS, into several predicted kinds of segmental motion. Both results are treated in the framework of the concept of common segmental nature of α‐ and β‐relaxations in flexible chain polymers.