2,229 research outputs found
Chromatic dispersion compensation using full-field maximum-likelihood sequence estimation
We investigate full-field detection-based maximum-likelihood sequence estimation (MLSE) for chromatic dispersion compensation in 10 Gbit/s OOK optical communication systems. Important design criteria are identified to optimize the system performance. It is confirmed that approximately 50% improvement in transmission reach can be achieved compared to conventional direct-detection MLSE at both 4 and 16 states. It is also shown that full-field MLSE is more robust to the noise and the associated noise amplifications in full-field reconstruction, and consequently exhibits better tolerance to nonoptimized system parameters than full-field feedforward equalizer. Experiments over 124 km spans of field-installed single-mode fiber without optical dispersion compensation using full-field MLSE verify the theoretically predicted performance benefits
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An apparatus to measure frictional, inelastic, and viscous behavior in ice at temperate and planetary conditions
In this paper, we describe a cryogenic, servo-controlled biaxial friction apparatus designed to measure the deformational behaviors of ice. The apparatus is specifically designed to accurately achieve and measure the low differential stresses applicable to deforming ice on earth and on icy satellites. We can apply loads in the range ∼2–1800 kPa and velocities up to 4 mm/s, with resolution of 39 Pa and 0.7 μm, respectively. Precise temperature control, measurement, and insulation allow testing at constant temperature (from −2 to −30 °C) for prolonged periods of time. The apparatus is tested with various plastics as well as with polycrystalline ice samples and the results are consistent with previously published values. Critical components of the instrument are described along with examples of data collection schemes and preliminary results. The flexibility of the design allows for both glaciological and planetary applications over a range of deformational behaviors including friction, anelastic, and viscous
Mitigation of pattern sensitivity in full-field electronic dispersion compensation
We investigate the pattern-dependent decoding failures in full-field electronic dispersion compensation (EDC) by offline processing of experimental signals, and find that the performance of such an EDC receiver may be degraded by an isolated "1" bit surrounded by long strings of consecutive "0s". By reducing the probability of occurrence of this kind of isolated "1" and using a novel adaptive threshold decoding method, we greatly improve the compensation performance to achieve 10-Gb/s on-off keyed signal transmission over 496-km field-installed single-mode fiber without optical dispersion compensation
On the 3D structure of the mass, metallicity, and SFR space for SF galaxies
We demonstrate that the space formed by the star-formation rate (SFR),
gas-phase metallicity (Z), and stellar mass (M), can be reduced to a plane, as
first proposed by Lara-Lopez et al. We study three different approaches to find
the best representation of this 3D space, using a principal component analysis,
a regression fit, and binning of the data. The PCA shows that this 3D space can
be adequately represented in only 2 dimensions, i.e., a plane. We find that the
plane that minimises the chi^2 for all variables, and hence provides the best
representation of the data, corresponds to a regression fit to the stellar mass
as a function of SFR and , M=f(Z,SFR). We find that the distribution
resulting from the median values in bins for our data gives the highest chi^2.
We also show that the empirical calibrations to the oxygen abundance used to
derive the Fundamental Metallicity Relation (Nagao et al.) have important
limitations, which contribute to the apparent inconsistencies. The main problem
is that these empirical calibrations do not consider the ionization degree of
the gas. Furthermore, the use of the N2 index to estimate oxygen abundances
cannot be applied for ~8.8 because of the saturation of the [NII]6584 line in
the high-metallicity regime. Finally we provide an update of the Fundamental
Plane derived by Lara-Lopez et al.Comment: ApJ, accepted. 15 pages, 13 figure
Translation calibration of inverse-kappa goniometers in macromolecular crystallography
A rapid, easy-to-perform translation calibration procedure has been developed for use with the EMBL/ESRF mini-κ goniometer head and for other inverse-kappa goniometers designed for macromolecular crystallography. Regular calibration ensures the precision of experiments that rely on many degrees of freedom in crystal reorientation
SEGUE-2 Limits on Metal-Rich Old-Population Hypervelocity Stars In the Galactic Halo
We present new limits on the ejection of metal-rich old-population
hypervelocity stars from the Galactic center (GC) as probed by the SEGUE-2
survey. Our limits are a factor of 3-10 more stringent than previously
reported, depending on stellar type. Compared to the known population of B-star
ejectees, there can be no more than 30 times more metal-rich old-population F/G
stars ejected from the GC. Because B stars comprise a tiny fraction of a normal
stellar population, this places significant limits on a combination of the GC
mass function and the ejection mechanism for hypervelocity stars. In the
presence of a normal GC mass function, our results require an ejection
mechanism that is about 5.5 times more efficient at ejecting B-stars compared
to low-mass F/G stars.Comment: 18 pages including 5 figures; Submitted to Ap
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