465,046 research outputs found

    Figure of merit for direct-detection optical channels

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    The capacity and sensitivity of a direct-detection optical channel are calculated and compared to those of a white Gaussian noise channel. Unlike Gaussian channels in which the receiver performance can be characterized using the noise temperature, the performance of the direct-detection channel depends on both signal and background noise, as well as the ratio of peak to average signal power. Because of the signal-power dependence of the optical channel, actual performance of the channel can be evaluated only by considering both transmit and receive ends of the systems. Given the background noise power and the modulation bandwidth, however, the theoretically optimum receiver sensitivity can be calculated. This optimum receiver sensitivity can be used to define the equivalent receiver noise temperature and calculate the corresponding G/T product. It should be pointed out, however, that the receiver sensitivity is a function of signal power, and care must be taken to avoid deriving erroneous projections of the direct-detection channel performance

    Study of the Wealth Inequality in the Minority Game

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    To demonstrate the usefulness of physical approaches for the study of realistic economic systems, we investigate the inequality of players' wealth in one of the most extensively studied econophysical models, namely, the minority game (MG). We gauge the wealth inequality of players in the MG by a well-known measure in economics known as the modified Gini index. From our numerical results, we conclude that the wealth inequality in the MG is very severe near the point of maximum cooperation among players, where the diversity of the strategy space is approximately equal to the number of strategies at play. In other words, the optimal cooperation between players comes hand in hand with severe wealth inequality. We also show that our numerical results in the asymmetric phase of the MG can be reproduced semi-analytically using a replica method.Comment: 9 pages in revtex 4 style with 3 figures; minor revision with a change of title; to appear in PR

    Effective amplifier noise for an optical receiver based on linear mode avalanche photodiodes

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    The rms noise charge induced by the amplifier for an optical receiver based on the linear-mode avalanche photodiode (APD) was analyzed. It is shown that for an amplifier with a 1-pF capacitor and a noise temperature of 100 K, the rms noise charge due to the amplifier is about 300. Since the noise charge must be small compared to the signal gain, APD gains on the order of 1000 will be required to operate the receiver in the linear mode

    Non-universal pairing symmetry and pseudogap phenomena in hole- and electron-doped cuprate superconductors

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    Experimental studies of the pairing state of cuprate superconductors reveal asymmetric behaviors of the hole-doped (p-type) and electron-doped (n-type) cuprates. The pairing symmetry, pseudogap phenomenon, low-energy spin excitations and the spatial homogeneity of the superconducting order parameter appear to be non-universal among the cuprates, which may be attributed to competing orders. We propose that the non-universal pseudogap and nano-scale variations in the quasiparticle spectra may be the result of a charge nematic (CN) phase stabilized by disorder in highly two-dimensional (2D) p-type cuprates. The CN phase is accompanied by gapped spin excitations and competes with superconductivity (SC). In contrast, gapless spin excitations may be responsible for the absence of pseudogap and the presence of excess sub-gap spectral weight in the momentum-independent quasiparticle spectra of n-type cuprates. The physical implications and further verifications for these conjectures are discussed

    Phase locked loop synchronization for direct detection optical PPM communication systems

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    Receiver timing synchronization of an optical pulse position modulation (PPM) communication system can be achieved using a phase locked loop (PLL) if the photodetector output is properly processed. The synchronization performance is shown to improve with increasing signal power and decreasing loop bandwidth. Bit error rate (BER) of the PLL synchronized PPM system is analyzed and compared to that for the perfectly synchronized system. It is shown that the increase in signal power needed to compensate for the imperfect synchronization is small (less than 0.1 dB) for loop bandwidths less than 0.1% of the slot frequency

    Rotten Bananas, Hip Hop Heads, and the American Individual: Teaching Eddie Huang’s Memoir Fresh Off the Boat and Its Tropes of Literacy

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    This essay focuses on Fresh Off the Boat as an eminently teachable coming-of-age story, provides critical contexts and directions for teaching this ideologically suggestive text, and sets forth the interpretive argument that the structures and themes of the memoir are fundamentally shaped by the literacy narrative at its core. As such, the text enters into conversation with other literacy narratives that have become so foundational in the teaching of multiethnic literature in the U.S. Moreover, Huang’s tropes of literacy draw from enduring, mythified Americanist discourses that are suggestive of a masculine individualism that, while not unique, is recognizable, instructive, and even problematic as an illustration of a powerful discourse of self-formation. In an effort to speak not only to specialists in U.S. multiethnic literature but also to nonspecialists/generalists, this discussion offers a tripartite approach to teaching this memoir: opening the unit with a sustained, critical, and creative discussion of genre(s), including traditional and popular forms; then inviting students to hone their critical thinking skills through careful rhetorical and ideological analyses of the text’s representations of race, identity, assimilation, and resistance; and ultimately setting forth a focused, conceptual argument about Fresh Off the Boat as a “literacy narrative” while placing the text within a broader U.S. literary history and discourse about the American individual
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