2,174 research outputs found
Kn 26, a New Quadrupolar Planetary Nebula
Once classified as an emission line source, the planetary nebula (PN) nature
of the source Kn 26 has been only recently recognized in digital sky surveys.
To investigate the spectral properties and spatio-kinematical structure of Kn
26, we have obtained high spatial-resolution optical and near-IR narrow-band
images, high-dispersion long-slit echelle spectra, and intermediate-resolution
spectroscopic observations. The new data reveal an hourglass morphology typical
of bipolar PNe. A detailed analysis of its morphology and kinematics discloses
the presence of a second pair of bipolar lobes, making Kn 26 a new member of
the subclass of quadrupolar PNe. The time-lap between the ejection of the two
pairs of bipolar lobes is much smaller than their dynamical ages, implying a
rapid change of the preferential direction of the central engine. The chemical
composition of Kn 26 is particularly unusual among PNe, with a low N/O ratio
(as of type II PNe) and a high helium abundance (as of type I PNe), although
not atypical among symbiotic stars. Such an anomalous chemical composition may
have resulted from the curtail of the time in the Asymptotic Giant Branch by
the evolution of the progenitor star through a common envelope phase.Comment: 9 pages, 5 figures, accepted for publication in A&
Comparing the Overhead of Topological and Concatenated Quantum Error Correction
This work compares the overhead of quantum error correction with concatenated
and topological quantum error-correcting codes. To perform a numerical
analysis, we use the Quantum Resource Estimator Toolbox (QuRE) that we recently
developed. We use QuRE to estimate the number of qubits, quantum gates, and
amount of time needed to factor a 1024-bit number on several candidate quantum
technologies that differ in their clock speed and reliability. We make several
interesting observations. First, topological quantum error correction requires
fewer resources when physical gate error rates are high, white concatenated
codes have smaller overhead for physical gate error rates below approximately
10E-7. Consequently, we show that different error-correcting codes should be
chosen for two of the studied physical quantum technologies - ion traps and
superconducting qubits. Second, we observe that the composition of the
elementary gate types occurring in a typical logical circuit, a fault-tolerant
circuit protected by the surface code, and a fault-tolerant circuit protected
by a concatenated code all differ. This also suggests that choosing the most
appropriate error correction technique depends on the ability of the future
technology to perform specific gates efficiently
Analytical Modeling of Interference Aware Power Control for the Uplink of Heterogeneous Cellular Networks
Inter-cell interference is one of the main limiting factors in current
Heterogeneous Cellular Networks (HCNs). Uplink Fractional Power Control (FPC)
is a well known method that aims to cope with such limiting factor as well as
to save battery live. In order to do that, the path losses associated with
Mobile Terminal (MT) transmissions are partially compensated so that a lower
interference is leaked towards neighboring cells. Classical FPC techniques only
consider a set of parameters that depends on the own MT transmission, like
desired received power at the Base Station (BS) or the path loss between the MT
and its serving BS, among others. Contrary to classical FPC, in this paper we
use stochastic geometry to analyze a power control mechanism that keeps the
interference generated by each MT under a given threshold. We also consider a
maximum transmitted power and a partial compensation of the path loss.
Interestingly, our analysis reveals that such Interference Aware (IA) method
can reduce the average power consumption and increase the average spectral
efficiency. Additionally, the variance of the interference is reduced, thus
improving the performance of Adaptive Modulation and Coding (AMC) since the
interference can be better estimated at the MT.Comment: 13 pages, 1 table and 7 figures. This work has been submitted to the
IEEE for possible publication. Copyright may be transferred without notice,
after which this version may no longer be accessibl
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