We report the controllable coiling of colloidal gold nanowires induced by the contraction of their polymer shells. The mechanical energy stored in this process can be released upon removal or swelling of the polymer shells.

No abstract

Flexible electronic devices are developing rapidly, especially in medical applications. This paper reports an arrayed flexible piezoelectric micromachined ultrasonic transducer (FPMUT) with a sandwich structure for adjuvant treatment of bone injury. To make the device conformable and stretchable for attaching to the skin surface, the flexible substrate of polydimethylsiloxane (PDMS) was combined with the flexible metal line interconnection between the bulk lead zirconate titanate (PZT) arrays. Simulations and experiments were carried out to verify the resonant frequency and tensile property of the reported FPMUT device. The device had a resonant frequency of 321.15 KHz and a maximum sound pressure level (SPL) of 180.19 dB at the distance of 5 cm in water. In addition, detailed experiments were carried out to test its acoustic performance with different pork tissues, and the results indicated good ultrasound penetration. These findings confirm that the FPMUT shows unique advantages for adjuvant treatment of bone injury.

No abstract

No abstract

Amides are among the most fundamental functional groups and essential structural units, widely used in chemistry, biochemistry and material science. Amide synthesis and transformations is a topic of continuous interest in organic chemistry. However, direct catalytic asymmetric activation of amide C-N bonds still remains a long-standing challenge due to high stability of amide linkages. Herein, we describe an organocatalytic asymmetric amide C-N bonds cleavage of N-sulfonyl biaryl lactams under mild conditions, developing a general and practical method for atroposelective construction of axially chiral biaryl amino acids. A structurally diverse set of axially chiral biaryl amino acids are obtained in high yields with excellent enantioselectivities. Moreover, a variety of axially chiral unsymmetrical biaryl organocatalysts are efficiently constructed from the resulting axially chiral biaryl amino acids by our present strategy, and show competitive outcomes in asymmetric reactions.

Nanopowders of nickel‐doped β‐silicon carbide (β‐SiC) with improved dielectric properties (compared with pure β‐SiC) were successfully produced using the mechanically activated self‐propagating high‐temperature synthesis method in an argon (Ar) atmosphere. The molar substitution of nickel (Ni) for silicon (Si) was 1%, 3%, and 5%. Powders of poly(tetrafluoroethylene) and ammonium chloride (NH4Cl) were used to promote the combustion reaction. The experimental results indicated an active role of Ni in the mechanism of combustion synthesis of SiC powders, which was reflected in the increase in combustion temperature and the velocity of propagation of the combustion wave, the microstructure of the produced nanopowders with a grain size of 100 nm for 5% Ni, and an improvement in the dielectric properties, specifically the increase in real (ɛ′) and imaginary parts (ɛ″) of the complex permittivity, in the frequency range of 8.2–12.4 GHz, compared with pure SiC. The X‐ray analysis of the produced powders suggests that Ni is accommodated in the lattice of SiC, which shrinks with increasing amounts of Ni.

The design and fabrication of efficient inexpensive electrocatalysts are critical for electrochemical energy conversion technologies. Control and understanding of electronic configuration at the active sites are of fundamental importance to achieve this goal. Herein, highly porous Ni 1−x Cu x O (p-Ni 1−x Cu x O) nanowire (NW) arrays grown on carbon fiber paper (CFP) were synthesized, characterized, and utilized as high-performance catalytic anode for catalyzing the ammonia-borane (AB) electrooxidation reaction (ABOR). This electrocatalyst shows exceptional electrocatalytic properties including an extremely low onset potential (−0.316 V vs the reversible hydrogen electrode (RHE)), a high Faradaic efficiency (>98%), and long-term durability toward the ABOR, far outperforming the noble metalbased catalysts. Reaction free energies computed as a function of electrode potential by density-functional theory indicate that doping of Cu for Ni 1−x Cu x O is favorable for energetically decreasing the energy barriers in the multistep reaction pathways. The modulation of the electronic structure of bimetallic Ni 1−x Cu x O catalysts underlies the catalytic mechanism by the electronic coupling effect between Ni and Cu.