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The physical properties of an ABA triblock copolymer-based thermoplastic elastomer, containing a poly(lauryl methacrylate-co-methacrylic acid) midblock and poly(methyl methacrylate) endblocks, were enhanced through neutralization of the methacrylic acid (MAA) repeat units with NaOH to form ionic interactions in the midblock. Rheological properties of the midblock and mechanical properties of the triblock copolymer were investigated as functions of acid (MAA) and ion content. Midblock relaxation times (τ) increased with increasing acid and ion content, however the activation energy extracted from an Arrhenius analysis appeared constant for all acid and ion contents. Meanwhile, the factors of enhancement of the strain at break and tensile strength (as compared to the baseline polymer without ionic interactions or hydrogen bonding) collapsed onto master curves when plotted as functions of log τ, indicating the mechanical behavior of the triblock copolymer could be tuned through varying the relaxation time of the midblock. The tensile strength increased by as much as a factor of 17 times greater than that of the baseline polymer. More moderate enhancements were observed in the strain at break, with the maximum strain at break occurring at intermediate relaxation times. This suggests that midblock chain dynamics are a governing factor for the mechanical property enhancements, due to the effects of the ionic aggregates and chain mobility on stress dissipation under tensile deformation. 

To facilitate dynamic spectrum sharing, the FCC has designated certified SAS administrators to implement their own spectrum access systems (SASs) that manage the shared spectrum usage in the novel CBRS band. As a premise, different SAS servers must conduct periodic inter-SAS coordination to synchronize service states and avoid allocation conflicts. However, SAS servers may inevitably stop service for regular upgrades, crash down, or even perform maliciously that deviate from the normal routines, posing a fundamental operation security problem — the system shall be robust against these faults to guarantee secure and efficient spectrum sharing service. Unfortunately, the incumbent inter-SAS coordination mechanism, CPAS, is prone to SAS failures and does not support real-time allocation. Recent proposals that rely on blockchain smart contracts or state machine replication mechanisms to realize fault-tolerant inter-SAS coordination require all SASs to follow a unified allocation algorithm. They however face performance bottlenecks and cannot accommodate the current fact that different SASs hold their own proprietary allocation algorithms. In this work, we propose TriSAS—a novel inter-SAS coordination mechanism to facilitate secure, efficient, and dependable spectrum allocation that is fully compatible with the existing SAS infrastructure. TriSAS decomposes the coordination process into two phases including input synchronization and decision finalization. The firstphase ensures participants share a common input set while the second one fulfills a fair and verifiable spectrum allocation selec- tion, which is generated efficiently via SAS proposers’ proprietary allocation algorithms and evaluated by a customized designed allocation evaluation algorithm (AEA), in the face of no more than one-third of malicious participants. We implemented a prototype of TriSAS on the AWS cloud computing platform and evaluated its throughput and latency performance. The results show that TriSAS achieves high transaction throughput and low latency under various practical settings. 

Standard approximations for the exchange–correlation functional in Kohn–Sham density functional theory (KS-DFT) typically lead to unacceptably large errors when applied to strongly correlated electronic systems. Partition-DFT (PDFT) is a formally exact reformulation of KS-DFT in which the ground-state density and energy of a system are obtained through self-consistent calculations on isolated fragments, with a partition energy representing inter-fragment interactions. Here, we show how typical errors of the local density approximation (LDA) in KS-DFT can be largely suppressed through a simple approximation, the multi-fragment overlap approximation (MFOA), for the partition energy in PDFT. Our method is illustrated on simple models of one-dimensional strongly correlated linear hydrogen chains. The MFOA, when used in combination with the LDA for the fragments, improves LDA dissociation curves of hydrogen chains and produces results that are comparable to those of spin-unrestricted LDA, but without breaking the spin symmetry. MFOA also induces a correction to the LDA electron density that partially captures the correct density dimerization in strongly correlated hydrogen chains. Moreover, with an additional correction to the partition energy that is specific to the one-dimensional LDA, the approximation is shown to produce dissociation energies in quantitative agreement with calculations based on the density matrix renormalization group method.