Improving the Gaudry–Schost algorithm for multidimensional discrete logarithms

Designs, Codes and Cryptography - The discrete logarithm problem arises from various areas, including counting the number of points of certain curves and diverse cryptographic schemes. The...     

LWE from non-commutative group rings

Designs, Codes and Cryptography - The Learning-With-Errors (LWE) problem (and its variants including Ring-LWE and Module-LWE), whose security are based on hard ideal lattice problems, has proven to...     

Rational Development of Remote C−H Functionalization of Biphenyl: Experimental and Computational Studies

A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process.     

In Situ Observation of Dynamic Galvanic Replacement Reactions in Twinned Metallic Nanowires by Liquid Cell Transmission Electron Microscopy

Galvanic replacement is a versatile approach to prepare hollow nanostructures with controllable morphology and elemental composition. The primary issue is to identify its fundamental mechanism. In this study, in situ liquid cell transmission electron microscopy was employed to monitor the dynamic reaction process and to explore the mechanism of galvanic replacement. The detailed reaction process was revealed based on in situ experiments in which small Au particles first appeared around Ag nanowires; they coalesced, grew, and adhered to Ag nanowires. After that, small pits grew from the edge of Ag nanowires to form tubular structures, and then extended along the Ag nanowires to obtain hollowed structures. All of our experimental observations from the viewpoint of electron microscopy, combined with DFT calculations, contribute towards an in‐depth understanding of the galvanic replacement reaction process and the design of new materials with hollow structures.     

Size and Shape Effect of Gold Nanoparticles in “Far‐Field” Surface Plasmon Resonance

The “far‐field” surface plasmon resonance (FSPR) of metal nanoparticles, which have built a facile way to emission enhancement of red, green, blue, and white with nice reproducibility, has big potential application in solution‐processed organic light‐emitting diodes (OLEDs). According to the theory of the “far‐field” effect, the reflectivity of the metal surface and the phase shift at the reflection play an important role in enhancing ratio, which strongly relate to the size and shape of nanoparticles. In this work, gold nanospheres with different sizes and nanorods are synthesized in order to determine the size and shape effect of FSPR. The results demonstrate that the one with higher reflectivity in a certain range induces a better emission enhancement in the luminous efficiency and the maximum brightness. The nanoparticles with bigger sizes and shape of rods have higher reflectivity, which is consistent with the simulation based on FSPR effect. The phase shifts of different nanoparticles are optimized by the distance between gold nanoparticles and emitters. The metal NPs with a high reflectivity and the applicable phase shift will have big potential for the emission enhancement in OLEDs.     

BN‐Embedded Tetrabenzopentacene: A Pentacene Derivative with Improved Stability

Considerable efforts have been devoted to achieving stable acene derivatives for electronic applications; however, the instability is still a major issue for such derivatives. To achieve higher stability with minimum structural change, CC units in the acenes were replaced with isoelectronic BN units to produce a novel BN‐embedded tetrabenzopentacene (BNTBP). BNTBP, with a planar structure, is highly stable to air, moisture, light, and heat. Compared with its carbon analogue tetrabenzopentacene (TBP), BN embedment lowered the highest occupied molecular orbital (HOMO) energy level of BNTBP, changed the orbital distribution, and decreased the HOMO orbital coefficients at the central carbon atoms, which stabilize BNTBP molecules upon exposure to oxygen and sunlight. The single‐crystal microribbons of BNTBP exhibited good performance in field‐effect transistors (FETs). The high stability and good mobility of BNTBP indicates that BN incorporation is an effective approach to afford stable large‐sized acenes with desired properties.     

Trimetallic Au@PdPt core-shell nanoparticles with ultrathin PdPt skin as highly stable electrocatalysts for the oxygen reduction reaction in acid solution

To design efficient and low-cost core-shell electrocatalysts with an ultrathin platinum shell, the balance between platinum dosage and durability in acid solution is of great importance. In the present work, trimetallic Au@PdPt core-shell nanoparticles(NPs)with Pd/Pt molar ratios ranging from 0.31:1 to 4.20:1 were synthesized based on the Au catalytic reduction strategy and the subsequent metallic replacement reaction. When the Pd/Pt molar ratio is 1.19:1(designated as Au@Pd_(1.19) Pt_1 NPs), the superior electrochemical activity and stability were achieved for oxygen reduction reaction(ORR) in acid solution. Especially, the specific and mass activities of Au@Pd_(1.19) Pt_1 NPs are 1.31 and 6.09 times higher than those of commercial Pt/C catalyst. In addition, the Au@Pd_(1.19) Pt_1 NPs presented a good durability in acid solution. After 3000 potential cycles between 0.1 and 0.7 V(vs. Ag/AgCl), the oxygen reduction activity is almost unchanged. This study provides a simple strategy to synthesize highperformance trimetallic ORR electrocatalyst for fuel cells.     

Peridynamic modeling and simulation of coupled thermomechanical removal of ice from frozen structures

Meccanica - In this work, a bond-based peridynamic de-icing model has been developed to simulate the thermo-mechanical ice removal process of frozen structures. In the proposed numerical method,...