A minimal model for studying properties of the mode-coupling type instability in friction induced oscillations

A minimal two degree of freedom model is used to clarify from an intuitive perspective the physical mechanisms underlying the mode-coupling instability of self-excited friction induced oscillations. It is shown that simultaneous out-of-phase oscillations of friction force and displacement tangential to the friction force may lead to energy transfer from the frictional system to vibrational energy. Also it is shown that the friction force acts like a cross-coupling force linking motion normal to the contact surface to motion parallel to it and that a necessary condition for the onset of instability is that these friction-induced cross-coupling forces balance the corresponding structural cross-coupling forces of the system. Finally the origin and the role of phase shifts between oscillations normal and parallel to the contact surface is clarified with respect to the mode-coupling instability. It may be expected that the intuitive picture gained will be of considerable help for practical design purposes.     

Interpolation of nonlinear positive or order preserving operators on Banach lattices

Positivity - We study the relationship between exact interpolation spaces for positive, linear operators, for order preserving, Lipschitz continuous operators, and for positive...     

Protein dielectrophoresis: Key dielectric parameters and evolving theory

Globular proteins exhibit dielectrophoresis (DEP) responses in experiments where the applied field gradient factor ∇E² appears far too small, according to standard DEP theory, to overcome dispersive forces associated with the thermal energy kT of disorder. To address this a DEP force equation is proposed that replaces a previous empirical relationship between the macroscopic and microscopic forms of the Clausius–Mossotti factor. This equation relates the DEP response of a protein directly to the dielectric increment δε⁺ and decrement δε⁻ that characterize its β-dispersion at radio frequencies, and also indirectly to its intrinsic dipole moment by way of providing a measure of the protein's effective volume. A parameter Γ_pw, taken as a measure of cross-correlated dipole interactions between the protein and its water molecules of hydration, is included in this equation. For 9 of the 12 proteins, for which an evaluation can presently be made, Γ_pw has a value of ≈4600 ± 120. These conclusions follow an analysis of the failure of macroscopic dielectric mixture (effective medium) theories to predict the dielectric properties of solvated proteins. The implication of a polarizability greatly exceeding the intrinsic value for a protein might reflect the formation of relaxor ferroelectric nanodomains in its hydration shell.     

Cucurbituril‐mediated immobilization of fluorescent proteins on supramolecular biomaterials

The reversible introduction of functionality at material surfaces is of interest for the development of functional biomaterials. In particular, the use of supramolecular immobilization strategies facilitates mild reaction and processing conditions, as compared to other covalent analogues. Here, the engineering of multicomponent supramolecular materials, beyond the use of a single supramolecular entity is proposed. Cucurbit[8]uril (Q8) mediated host–guest chemistry is combined with hydrogen bonding supramolecular 2‐ureido‐4‐pyrimidinone (UPy)‐based materials. The modular incorporation of a UPy‐additive that presents one guest to incorporate into the Q8 host allows for selective supramolecular functionalization at the water–polymer material interface. Supramolecular ternary complex formation at the material surface was studied by X‐ray photoelectron spectroscopy, which as a result of large overlap in atomic composition of the different components showed minor changes is surface composition upon complex formation. Surface MALDI‐ToF MS measurements revealed useful insights in the formation of complexes. Protein immobilization was monitored using both fluorescence spectroscopy and quartz crystal microbalance with dissipation monitoring, which successfully demonstrated ternary complex formation. Although proteins could selectively be immobilized onto the surfaces, control of the system's stability remains a challenge as a result of the dynamicity of the host–guest assembly. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3607–3616