The interplay between hydrogen bonding, hydrophobic interaction and the molecular geometry of amino acid side-chains is crucial to the development of nanostructures of short peptide amphiphiles. An important step towards developing their practical use is to understand how different amino acid side-chains tune hydrophobic interaction and hydrogen bonding and how this process leads to the control of the size and shape of the nanostructures. In this study, we have designed and synthesized three sets of short amphiphilic peptides (I(3)K, LI(2)K and L(3)K; L(3)K, L(4)K and L(5)K; I(3)K, I(4)K and I(5)K) and investigated how I and L affected their self-assembly in aqueous solution. The results have demonstrated a strong tendency of I groups to promote the growth of β-sheet hydrogen bonding and the subsequent formation of nanofibrillar shapes. All I(m)K (m = 3-5) peptides assembled into nanofibers with consistent β-sheet conformation, whereas the nanofiber diameters decreased as m increased due to geometrical constraint in peptide chain packing. In contrast, L groups had a weak tendency to promote β-sheet structuring and their hydrophobicity became dominant and resulted in globular micelles in L(3)K assembly. However, increase in the number of hydrophobic sequences to L(5)K induced β-sheet conformation due to the cooperative hydrophobic effect and the consequent formation of long nanofibers. The assembly of L(4)K was, therefore, intermediate between L(3)K and L(5)K, similar to the case of LI(2)K within the set of L(3)K, LI(2)K and I(3)K, with a steady transition from the dominance of hydrophobic interaction to hydrogen bonding. Thus, changes in hydrophobic length and swapping of L and I can alter the size and shape of the self-assembled nanostructures from these simple peptide amphiphiles.

In performance-based seismic design, bridges are expected to satisfy specific performance objectives under several levels of seismic hazard. In this paper, a multi-level SMA/lead rubber bearing (ML-SLRB) isolation system was proposed to ensure both isolation efficiency and capability to limit excessive bearing displacements under different levels of earthquake excitations. The ML-SLRBs also offer advantages such as the ability to provide re-centering forces and good fatigue and corrosion-resistant. The ML-SLRB isolation system consists of three groups of SMA cables, each is designed to be activated at a certain seismic hazard level, and a conventional lead rubber bearing. First, the design and working mechanism of this new isolation system were described in detail. Then, a design procedure was proposed for seismic isolation of bridge structures with ML-SLRBs. Next, the hysteretic response of ML-SLRBs was simulated in a general-purpose structural engineering software. A four-span continuous box-girder bridge was designed and modeled with different isolation systems including ML-SLRBs. Nonlinear dynamic analyses of the isolated bridges were conducted under both far-fault and near-fault earthquakes. Results show that compared to isolations systems that do not adapt their stiffness according to increasing seismic demand, e.g. the isolators with a bilinear force-displacement response, the proposed isolation system exhibits high isolation efficiency at small or moderate earthquakes, while effectively limits the bridge displacements to avoid pounding and girder unseating under extreme earthquakes.

No abstract

No abstract

No abstract