In the past decades, many efforts have focused on analyzing typical-case hardness in optimization and inference problems. Some recent work has pointed out that polynomial algorithms exist, running with a time that grows more than linearly with the system size, which can do better than linear algorithms, finding solutions to random problems in a wider range of parameters. However, a theory for polynomial and superlinear algorithms is in general lacking. Here, we examine the performance of the simulated annealing algorithm, a standard, versatile, and robust choice for solving optimization and inference problems, in the prototypical random K-SAT problem. For the first time, we show that the algorithmic thresholds depend on the time scaling of the algorithm with the size of the system. Indeed, one can identify not just one but different thresholds for linear, quadratic, and cubic regimes (and so on). This observation opens new directions in studying the typical case hardness in optimization problems.
The electrocaloric effect and energy-storage performance of the (Bi0.5Na0.5)0.92Ba0.08TiO3 (BNT-8BT) ceramic composition were explored from 250 to 450 K. Anomalous behavior was observed in both the recovered energy density (JR) as well as the adiabatic temperature change (Delta TIEC), obtained from the P-E dependence, which extend in a broad temperature range around the previously reported depolarization temperature (Td = 416 K) for this composition. Maximum values of 360 mJ/cm3 and 37 %, were obtained at 410 K for JR and eta, respectively. A strong discrepancy between the values obtained from direct measurements (Delta TDEC) and indirect estimation (Delta TIEC) of the electrocaloric effect was observed, which originates from the irreversibility feature of the fieldinduced phase transition. Delta TDEC is positive in the entire studied temperature range and monotonously increases with the increasing electric field. However, Delta TIEC yields negative values for several temperatures, and changes non-monotonously with the applied field. Furthermore, a significant anomaly in the pyroelectric coefficient is observed around the depolarization temperature, showing a high pyroelectric coefficient value (p approximate to 0.01 mu C/cm2 & sdot;K) at room temperature. The obtained results confirm the multifunctional characteristic of the studied ceramic composition and reveal this material as an environmentally friendly lead-free candidate for using in strategic applications based on energy-storage and electrocaloric devices, where the physical properties can be tailored for the operating temperature range close to the depolarization temperature.
This contribution reports the preparation and structural study of the titled series of zinc octacyanometallates. This series of coordination polymers crystallizes in a monoclinic unit cell with the P21/c space group (No. 14). Its crystal structure was solved and refined from powder XRD patterns recorded within the 80-300 K temperature range. The solid framework is formed from dodecahedral building blocks, [M(CN)8]4-, linked by Zn2+ atoms with tetrahedral coordination to the N end of the CN ligands, resulting in coordination polymers with an open microporous framework. This series of solids exhibits negative thermal expansion in that temperature range, attributed to the activation of transverse vibrational modes in the CN ligand. Related to repulsive interactions between C atoms in the building block, the M-C interatomic distance is substantially increased relative to that observed in other transition metal cyanides. Such a feature affects the structural and bonding properties, as well as the stability on heating, of the titled series of coordination polymers.
In epistatic fitness landscapes, the fitness effect of a mutation depends on the genetic background and may even switch between deleterious and beneficial depending on the presence of another mutation. Epistatic interactions may cause both mutations to change the sign of each other's fitness effects (reciprocal sign epistasis) or only one mutation to do so (simple sign epistasis). Both these forms of epistasis influence evolutionary trajectories. While reciprocal sign epistasis has been associated with multi-peaked landscapes and their ruggedness, the role and relative frequency of simple sign epistasis in fitness landscapes have not been systematically investigated. Here, we prove that the presence of simple sign epistasis is associated with evolutionary detours, i.e., indirect, longer fitness-increasing paths to fitness peaks that include back-mutations. We also show that in experimentally resolved, weakly epistatic landscapes, simple sign epistasis occurs much more frequently than reciprocal sign epistasis. This result is consistent with the theoretical predictions we derive for most landscape models, with the exception of the block model and of landscapes dominated by pairwise allelic incompatibilities, such as RNA stability landscapes. Our results suggest that detours represent a general feature of evolutionary trajectories in weakly epistatic landscapes.
Nanostructured CuO samples were irradiated with He+ ions at doses of 3.13 x 10(13)-3.38 x 10(16) particles/cm(2) to probe defect dynamics and lattice recovery. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, positron annihilation lifetime spectroscopy (PALS), and Doppler broadening spectroscopy (DBS) revealed that short irradiation promotes lattice recovery, while prolonged exposure induces a competition between recovery, Cu vacancy (V-Cu) formation, and complex vacancy cluster (V-Cu(-)-V-O(+)) evolution. Elevated positron lifetimes (tau(2)) highlight defective, isolated nanorod surfaces, with a defective surface region averaging (rho) over bar approximate to 1.5 nm. These results demonstrate the dual role of irradiation in defect creation and lattice healing, offering insights into CuO stability under radiation environments.
