It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (T g ) of polyurethane. Accompanying the decrease of T g , the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between T g and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 • C, which is the melting temperature of this SMP.

We study two coupled Su-Schrieffer-Heeger (SSH) chains system, which is shown to contain rich quantum phases associated with topological invariants protected by symmetries. In the weak coupling region, the system supports two non-trivial topological insulating phases, characterized by winding number N = ±1, and two types of edge states. The boundary between the two topological phases arises from two band closing points, which exhibit topological characteristics in onedimensional k space. By mapping Bloch states on a vector field in k space, the band degenerate points correspond to a pair of kinks of the field, with opposite topological charges. Two topological nodal points move and merge as the inter-chain coupling strength varies. This topological invariant is protected by the translational and inversion symmetries, rather than the antiunitary operation. Furthermore, we find that when a pair of nodal points is created, a second order quantum phase transition (QPT) occurs, associating with a gap closing and spontaneously symmetry breaking. This simple model demonstrates several central concepts in the field of quantum materials and provides a theoretical connection between them.

We systematically study a Kitaev chain with imbalanced pair creation and annihilation, which is introduced by non-Hermitian pairing terms. Exact phase diagram shows that the topological phase is still robust under the influence of the conditional imbalance. The gapped phases are characterized by a topological invariant, the extended Zak phase, which is defined by the biorthonormal inner product. Such phases are destroyed at the points where the coalescence of groundstates occur, associating with the time-reversal symmetry breaking. We find that the Majorana edge modes also exist for the open chain within unbroken time-reversal symmetric region, demonstrating the bulk-edge correspondence in such a non-Hermitian system.

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Simulating the measured size dependence of both the E 4f level shift and the melting-point suppression of Au nanosolids reveals that (i) the E 4f core-level energy of an isolated Au atom is estimated to be −81.50 eV and the E 4f binding energy is −2.87 eV and (ii) the melting point of the Au monatomic chain (MC) is around 320 K, about 1/4.2 times the bulk value (1337.33 K). These intriguing changes are attributed to the effect of atomic coordination imperfection. An analytical solution has been derived showing that the maximal strain of a metallic bond in a MC under tensile stress varies inapparently with the mechanical stress but apparently with temperature in the form of exp[A/(T m − 4.2T)], where A is a constant and T m is the bulk melting point. Matching calculations to all the insofar-measured breaking limits (at 4 K, it is around 0.23 nm, and in the vicinity of room temperature, it is 0.29−0.48 nm) indicates that the measured divergent values originate from thermal and mechanical fluctuation near the melting point of the MC.