Fluorescent quantum dots have been used in biological applications as desirable fluorescent labels instead of traditional fluorophores. Incorporation into microspheres enhances many features of quantum dots that make ...
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Fluorescent quantum dots have been used in biological applications as desirable fluorescent labels instead of traditional fluorophores. Incorporation into microspheres enhances many features of quantum dots that make them ideal for biological detection, such as photostability, multi-target, and improved brightness. Quantum dot-tagged microbeads are emerging as a new class of fluorescent labels and are expected to open new opportunities in nanotechnology and biology. In this review, we describe different approaches for the synthesis of quantum dot-tagged microbeads, surface modification methods that make microbeads suitable for bioconjugation, and the biological applications of the quantum dot-tagged fluorescent microbeads with their desired features in recent research. We also discuss the limitations of some kinds of quantum dot-tagged microbeads and the developments that will enhance their abilities in biological applications.
In this paper, we consider cooperation in the low power (low SNR) regime for the multiple access channel with the assumption that the transmitters have no channel state information. A relevant performance measure to c...
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In this paper, we consider cooperation in the low power (low SNR) regime for the multiple access channel with the assumption that the transmitters have no channel state information. A relevant performance measure to consider is therefore the outage capacity. We develop cooperation methods based on multiplexed coding in conjunction with rateless codes and find the achievable rates and in particular the minimum energy per bit required to achieve a certain outage probability. We consider two modes of operation: full duplex [code-division multiple access (CDMA)], where nodes can transmit and receive simultaneously on the same frequency band, and half duplex [frequency-division multiple access (FDMA)], where the nodes transmit and listen on different frequency bands. We show that, perhaps surprisingly, there is little loss in performance when using FDMA. Furthermore, our results show that multiplexed rateless codes come within 0.1 dB of the outer bound on capacity. We also develop practical rateless coding methods for FDMA using multiplexed Raptor codes which operate within 0.52 and 1.1 dB of the theoretical limit for the two-and four-user case, respectively.
We consider the design of cooperation coding schemes for a two-user multiaccess;channel (MAC). In particular, we consider two block Markov coding schemes, namely, the multiplexed coding and the superposition coding. A...
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We consider the design of cooperation coding schemes for a two-user multiaccess;channel (MAC). In particular, we consider two block Markov coding schemes, namely, the multiplexed coding and the superposition coding. Although the fully multiplexed (IMP) coding outperforms the superposition coding in theory, it is difficult to implement with practical error-correction codes. We, therefore, introduce a partially multiplexed (PMP) coding scheme for code rate R < 0.5, and propose a simplified superposition coding scheme. The outage analysis shows that these cooperation schemes provide significant gains over the noncooperative MAC in the low-power regime when the bandwidth W --> infinity. We then propose a PMP code design using irregular repeat accumulate (IRA) codes. The design method can be extended to build the low-rate PMP codes using irregular repeat zigzag Hadamard (IRZH) codes, a new class of capacity achieving low-rate codes. Simulation results demonstrate that the block Markov multiplexed coding using PMP-IRA codes outperforms the practical superposition coding by 2 dB at 10(-2) FER, and it provides a 10-dB;gain over the noncooperative MAC. The multiplex coding using PMP-IRZH codes offers 1-dB gain over the superposition coding, and a 9.5-dB gain over noncooperative MAC at 10(-2) FER. Moreover, the PMP-IRZH coding performs only 0.5 dB away from the outage capacity of multiplexed coding in the low-power regime.
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