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1.
Clapp M.A. Etienne-Cummings R. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(4):769-783
Presented is a mixed-signal full-custom VLSI chip designed to receive sonar return signals from an ultrasonic microphone array, and extract input bearing angles of the incoming signals. Processing utilizes simple low-power analog spatiotemporal bandpass filters to extract wavefront velocity across the array, which translates to input bearing angle. Processing uses phase information of array signals, not onset or offset of ultrasonic burst. With such synchronous processing, multiple angle readings from different returns of the same ultrasonic transmit burst are possible. Compatible microphone arrays are compact in size-test array has a total baseline of 26.5 mm. In a test with ultrasonic beacon 65 cm from a microphone array, angular precision of 1/spl deg/ was demonstrated in most instances in the range -60/spl deg/ to 60/spl deg/. Applications include sonar localization of remote objects, sonar imaging, and improved interference rejection between objects within the field of view of the sensor microphones. The chip was fabricated on a standard 3M2P CMOS process with a 0.5-/spl mu/m feature size. 相似文献
2.
3.
Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors 总被引:7,自引:0,他引:7
Clapp AR Medintz IL Mauro JM Fisher BR Bawendi MG Mattoussi H 《Journal of the American Chemical Society》2004,126(1):301-310
We used luminescent CdSe-ZnS core-shell quantum dots (QDs) as energy donors in fluorescent resonance energy transfer (FRET) assays. Engineered maltose binding protein (MBP) appended with an oligohistidine tail and labeled with an acceptor dye (Cy3) was immobilized on the nanocrystals via a noncovalent self-assembly scheme. This configuration allowed accurate control of the donor-acceptor separation distance to a range smaller than 100 A and provided a good model system to explore FRET phenomena in QD-protein-dye conjugates. This QD-MBP conjugate presents two advantages: (1) it permits one to tune the degree of spectral overlap between donor and acceptor and (2) provides a unique configuration where a single donor can interact with several acceptors simultaneously. The FRET signal was measured for these complexes as a function of both degree of spectral overlap and fraction of dye-labeled proteins in the QD conjugate. Data showed that substantial acceptor signals were measured upon conjugate formation, indicating efficient nonradiative exciton transfer between QD donors and dye-labeled protein acceptors. FRET efficiency can be controlled either by tuning the QD photoemission or by adjusting the number of dye-labeled proteins immobilized on the QD center. Results showed a clear dependence of the efficiency on the spectral overlap between the QD donor and dye acceptor. Apparent donor-acceptor distances were determined from efficiency measurements and corresponding F?rster distances, and these results agreed with QD bioconjugate dimensions extracted from structural data and core size variations among QD populations. 相似文献
4.
F?rster resonance energy transfer (FRET), which involves the nonradiative transfer of excitation energy from an excited donor fluorophore to a proximal ground-state acceptor fluorophore, is a well-characterized photophysical tool. It is very sensitive to nanometer-scale changes in donor-acceptor separation distance and their relative dipole orientations. It has found a wide range of applications in analytical chemistry, protein conformation studies, and biological assays. Luminescent semiconductor nanocrystals (quantum dots, QDs) are inorganic fluorophores with unique optical and spectroscopic properties that could enhance FRET as an analytical tool, due to broad excitation spectra and tunable narrow and symmetric photoemission. Recently, there have been several FRET investigations using luminescent QDs that focused on addressing basic fundamental questions, as well as developing targeted applications with potential use in biology, including sensor design and protein conformation studies. Herein, we provide a critical review of those developments. We discuss some of the basic aspects of FRET applied to QDs as both donors and acceptors, and highlight some of the advantages offered (and limitations encountered) by QDs as energy donors and acceptors compared to conventional dyes. We also review the recent developments made in using QD bioreceptor conjugates to design FRET-based assays. 相似文献
5.
Clapp AR Medintz IL Fisher BR Anderson GP Mattoussi H 《Journal of the American Chemical Society》2005,127(4):1242-1250
We assessed the ability of luminescent quantum dots (QDs) to function as energy acceptors in fluorescence resonance energy transfer (FRET) assays, with organic dyes serving as donors. Either AlexaFluor 488 or Cy3 dye was attached to maltose binding protein (MBP) and used with various QD acceptors. Steady-state and time-resolved fluorescence measurements showed no apparent FRET from dye to QD. We attribute these observations to the dominance of a fast radiative decay rate of the donor excitation relative to a slow FRET decay rate. This is due to the long exciton lifetime of the acceptor compared to that of the dye, combined with substantial QD direct excitation. 相似文献
6.
Background
Taste buds are the sensory organs of taste perception. Three types of taste cells have been described. Type I cells have voltage-gated outward currents, but lack voltage-gated inward currents. These cells have been presumed to play only a support role in the taste bud. Type II cells have voltage-gated Na+ and K+ current, and the receptors and transduction machinery for bitter, sweet, and umami taste stimuli. Type III cells have voltage-gated Na+, K+, and Ca2+ currents, and make prominent synapses with afferent nerve fibers. Na+ salt transduction in part involves amiloride-sensitive epithelial sodium channels (ENaCs). In rodents, these channels are located in taste cells of fungiform papillae on the anterior part of the tongue innervated by the chorda tympani nerve. However, the taste cell type that expresses ENaCs is not known. This study used whole cell recordings of single fungiform taste cells of transgenic mice expressing GFP in Type II taste cells to identify the taste cells responding to amiloride. We also used immunocytochemistry to further define and compare cell types in fungiform and circumvallate taste buds of these mice. 相似文献7.
8.
We construct positive and sign changing multipeak solutions to the pure critical exponent problem in a bounded domain with a shrinking hole, having a peak which concentrates at some point inside the shrinking hole (i.e. outside the domain) and one or more peaks which concentrate at interior points of the domain. These are, to our knowledge, the first multipeak solutions in a domain with a single small hole. 相似文献
9.
J. Beals N. Bamiedakis A. Wonfor R. V. Penty I. H. White J. V. DeGroot K. Hueston T. V. Clapp M. Glick 《Applied Physics A: Materials Science & Processing》2009,95(4):983-988
An optical backplane based on a meshed polymer waveguide architecture enabling high-speed board-to-board optical interconnection
is presented. This planar array of multimode polymer waveguides can provide passive strictly non-blocking links between server
line cards fitted with optical transmitter and receiver arrays. This architecture offers a scalable and low-cost solution
to the bandwidth limitations faced by electrical backplanes and is suitable for PCB integration. The reported backplane demonstrator
uses a matrix of 100 waveguides each capable of 10 Gb/s operation to interconnect 10 cards for a total capacity of a terabit
per second aggregate data rate in multicast mode. Characterisation of the backplane demonstrator reveals low link losses of
2 to 8 dB for a multimode fibre input and crosstalk values below −35 dB. Error free data transmission at 10 Gb/s is achieved
with a power penalty of only 0.2 dB at a bit-error-rate of 10−9. Additionally, lossless operation of a Gigabit Ethernet link over the backplane is achieved even when using the worst-case
highest loss links. 相似文献
10.