RESUMEN
The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots.
RESUMEN
The use of organic materials presents a tremendous opportunity to significantly impact the functionality and pervasiveness of large-area electronics. Commercialization of this technology requires reduction in manufacturing costs by exploiting inexpensive low-temperature deposition and patterning techniques, which typically lead to lower device performance. We report a low-cost approach to control the microstructure of solution-cast acene-based organic thin films through modification of interfacial chemistry. Chemically and selectively tailoring the source/drain contact interface is a novel route to initiating the crystallization of soluble organic semiconductors, leading to the growth on opposing contacts of crystalline films that extend into the transistor channel. This selective crystallization enables us to fabricate high-performance organic thin-film transistors and circuits, and to deterministically study the influence of the microstructure on the device characteristics. By connecting device fabrication to molecular design, we demonstrate that rapid film processing under ambient room conditions and high performance are not mutually exclusive.
RESUMEN
The proposed CMOS ultrasound transceiver chip will enable the development of portable high resolution, high-frequency ultrasonic imaging systems. The transceiver chip is designed for close-coupled MEMS transducer arrays which operate with a 3.3-V power supply. In addition, a transmit digital beamforming system architecture is supported in this work. A prototype chip containing 16 receive and transmit channels with preamplifiers, time-gain compensation amplifiers, a multiplexed analog-to-digital converter with 3 kB of on-chip SRAM, and 50-MHz resolution time delayed excitation pulse generators has been fabricated. By utilizing a shared A/D converter architecture, the number of A/D converter and SRAM is cut down to one, unlike typical digital beamforming systems which need 16 A/D converters for 16 receive channels. The chip was fabricated in a 0.35-mum standard CMOS process. The chip size is 10 mm(2), and its average power consumption in receive mode is approximately 270 mW with a 3.3-V power supply. The transceiver chip specifications and designs are described, as well as measured results of each transceiver component and initial pulse-echo experimental results are presented.
RESUMEN
A 19-year-old man, who was a soft contact lens wearer for correction of myopia, presented with right corneal ulceration. The diagnosis of Acanthamoeba polyphaga infection was made by culture and serology. In-vitro sensitivity tests suggested that the organism was sensitive to Neosporin (polymyxin, neomycin and gramicidin) and natamycin. Topical therapy with these agents resulted in complete healing of the corneal ulcer in two months. To our knowledge, our patient is the only case of successful medical treatment of this condition that has achieved a good visual result.