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We report a novel vibration control technique of an artificial auditory cochlear epithelium that mimics the function of outer hair cells in the organ of Corti. The proposed piezoelectric and trapezoidal membrane not only has the acoustic/electric conversion and frequency selectivity of the previous device developed mainly by one of the authors and colleagues, but also has a function to control local vibration according to sound stimuli. Vibration control is achieved by applying local electrical stimuli to patterned electrodes on an epithelium made using micro-electro-mechanical system technology. By choosing appropriate phase differences between sound and electrical stimuli, it is shown that it is possible to both amplify and dampen membrane vibration, realizing better control of the response of the artificial cochlea. To be more specific, amplification and damping are achieved when the phase difference between the membrane vibration by sound stimuli and electrical stimuli is zero and π, respectively. We also demonstrate that the developed control system responds automatically to a change in sound frequency. The proposed technique can be applied to mimic the nonlinear response of the outer hair cells in a cochlea, and to realize a high-quality human auditory system.

Particles transport driven by a temperature gradient in a solution is known as thermophoresis or Soret effect. The drift velocity v T of a particle is expressed as v T = −D T ∇T , where D T is a thermophoretic mobility. Therefore, the thermophoretic mobility is a parameter to characterise the nature of thermophoresis, and the systematic measurement of D T for various combinations of particles and solvents is necessary for its potential application. In the present work, we develop the microfluidic system called microgap Soret cell and show its validity by obtaining D T for wide experimental conditions. It is shown that the microgap Soret cell can rapidly and directly obtain the thermophoretic mobility of a particle with the diameter of O(1) mm by maintaining the large temperature gradient in the microfluidic system. Moreover, by using the microgap Soret cell, the temperature dependency of D T is investigated for thermophoresis of polystyrene particles in solutions of sodium hydroxide, polyethylene glycol, and glycerol.

A rhodium-catalyzed addition of sodium tetraarylborates to N-tosyl ketimines is described. Highly efficient asymmetric catalysis has been achieved by employing a chiral diene ligand, constructing chiral amine derivatives possessing α-tetrasubstituted carbon stereocenters with high enantioselectivity.

A temperature gradient in a continuous fluid induces the motion of dispersed micro-and nanoparticles even when the fluid is motionless. This phenomenon is known as thermophoresis, and it is expected to be the basis for techniques to control particle motion. In this study, we use the thermophoresis of microand nanoparticles in a microchannel filled with an aqueous solution to control the particle motion near the inlet of a sudden contraction, which is a narrower channel connecting two wider channels. Microfluidic devices with sudden contractions are widely used to develop various devices with micro-and nanometer dimensions, such as nanopore sensors. A near-infrared laser is used to create a strong temperature gradient of O(10 6) K m −1 and induce thermophoresis of micro-and nanoparticles. Because the heating by the laser irradiation is localized near the inlet of the contraction, this configuration is useful for controlling particle translocation into and through the contraction. We characterize our experimental setup by quantifying flow and temperature fields near the contraction channel using particle image velocimetry and laser-induced fluorescence, respectively. Then, we observe the obstruction of the particle translocation into the contraction channel induced by the laser-induced thermophoresis for various parameters such as channel dimensions, flow speeds, particle sizes, and laser powers. Near the inlet of the contraction channel, the counterbalance of thermophoretic force and flow drag leads to the ringlike pattern formation of the particle distribution. Moreover, we carry out some demonstrations using the proposed system to selectively translocate particles and enhance the sensing performance due to increased particle density. Thanks to the noncontact nature of laser-induced thermophoresis, the integration of our method into existing microfluidic devices is feasible and expected to improve technologies for manipulating particles in fluids.

Optical trapping and manipulation techniques have attracted significant attention in various research fields. Optical forces divided into two terms, such as a scattering force and gradient one, work to push forward and attract objects, respectively. This is a typical property of optical forces. In particular, a tool known as optical tweezers can be created when a laser beam is converged at a focal point, causing strong forces to be generated so as to trap and manipulate small objects. In this study, we propose a novel method to build up assembled structures of polystyrene particles by using optical trapping techniques. Recording trajectories of single particles, the optical forces are quantitatively evaluated using particle tracking velocimetry. Herein, we treat various particle sizes whose diameters range from 1 to 4 μm and expose them to a converged laser beam of 1064 nm wavelength. As a result, both experimental and theoretical results are in good agreement. The behavior of particles is understood in the framework of Ashkin’s ray optics. This finding clarifies optical force fields of microparticles distributed in a slit-like microfluidic channel and will be applicable for effectively forming ordered structures in liquids.

Mechanistic studies for the palladium-catalyzed decarboxylative cyclization reactions of gamma-methylidene-delta-valerolactones 1 with isocyanates 2 are described. The reactions can be effectively catalyzed by palladium triarylphosphine complexes to give piperidones 3 and/or azaspiro[2.4]heptanones 4. Through kinetic studies using NMR spectroscopy, it has been determined that the oxidative addition of lactones 1 to palladium(0) is the turnover-limiting step of the catalytic cycle. By changes in the electronic properties of the triarylphosphine ligands, the product distribution between 3 and 4 can be easily controlled, and an explanation for the origin of this selectivity is provided. The selectivity between 3 and 4 is also influenced by the nature of the nitrogen substituent on isocyanates 2, and more electron-rich substituents tend to give higher selectivity toward azaspiro[2.4]heptanones 4. These studies represent the first systematic investigation into the selectivity between terminal attack and central attack at (pi-allyl)palladium species by nitrogen-based nucleophiles.