24,395 research outputs found
Data mining and accelerated electronic structure theory as a tool in the search for new functional materials
Data mining is a recognized predictive tool in a variety of areas ranging
from bioinformatics and drug design to crystal structure prediction. In the
present study, an electronic structure implementation has been combined with
structural data from the Inorganic Crystal Structure Database to generate
results for highly accelerated electronic structure calculations of about
22,000 inorganic compounds. It is shown how data mining algorithms employed on
the database can identify new functional materials with desired materials
properties, resulting in a prediction of 136 novel materials with potential for
use as detector materials for ionizing radiation. The methodology behind the
automatized ab-initio approach is presented, results are tabulated and a
version of the complete database is made available at the internet web site
http://gurka.fysik.uu.se/ESP/ (Ref.1).Comment: Project homepage: http://gurka.fysik.uu.se/ESP
Selective nonresonant excitation of vibrational modes in suspended graphene via vibron-plasmon interaction
We theoretically study a doped graphene ribbon suspended over a trench and
subject to an ac-electrical field polarized perpendicularly to the graphene
plane. In such a system, the external ac-field is coupled to the relatively
slow mechanical vibrations via plasmonic oscillations in the isolated graphene
sheet. We show that the electrical field generates an effective pumping of the
mechanical modes. It is demonstrated that in the case of underdamped plasma
oscillation, a peculiar kind of geometrical resonance of the mechanical and
plasma oscillations appear. Namely the efficiency of pumping significantly
increases when the wave number of the mechanical mode is in close agreement
with the wave number of the plasma waves. The intensity of the pumping
increases with the wave number of the mode. This phenomenon allows selective
actuation of different mechanical modes although the driving field is
homogeneous
Pseudo-digital quantum bits
Quantum computers are analog devices; thus they are highly susceptible to
accumulative errors arising from classical control electronics. Fast
operation--as necessitated by decoherence--makes gating errors very likely. In
most current designs for scalable quantum computers it is not possible to
satisfy both the requirements of low decoherence errors and low gating errors.
Here we introduce a hardware-based technique for pseudo-digital gate operation.
We perform self-consistent simulations of semiconductor quantum dots, finding
that pseudo-digital techniques reduce operational error rates by more than two
orders of magnitude, thus facilitating fast operation.Comment: 4 pages, 3 figure
Estimation of phase noise in oscillators with colored noise sources
In this letter we study the design of algorithms for estimation of phase
noise (PN) with colored noise sources. A soft-input maximum a posteriori PN
estimator and a modified soft-input extended Kalman smoother are proposed. The
performance of the proposed algorithms are compared against those studied in
the literature, in terms of mean square error of PN estimation, and symbol
error rate of the considered communication system. The comparisons show that
considerable performance gains can be achieved by designing estimators that
employ correct knowledge of the PN statistics
Capacity of SIMO and MISO Phase-Noise Channels with Common/Separate Oscillators
In multiple antenna systems, phase noise due to instabilities of the
radio-frequency (RF) oscillators, acts differently depending on whether the RF
circuitries connected to each antenna are driven by separate (independent)
local oscillators (SLO) or by a common local oscillator (CLO). In this paper,
we investigate the high-SNR capacity of single-input multiple-output (SIMO) and
multiple-output single-input (MISO) phase-noise channels for both the CLO and
the SLO configurations.
Our results show that the first-order term in the high-SNR capacity expansion
is the same for all scenarios (SIMO/MISO and SLO/CLO), and equal to , where stands for the SNR. On the contrary, the second-order
term, which we refer to as phase-noise number, turns out to be
scenario-dependent. For the SIMO case, the SLO configuration provides a
diversity gain, resulting in a larger phase-noise number than for the CLO
configuration. For the case of Wiener phase noise, a diversity gain of at least
can be achieved, where is the number of receive antennas. For
the MISO, the CLO configuration yields a higher phase-noise number than the SLO
configuration. This is because with the CLO configuration one can obtain a
coherent-combining gain through maximum ratio transmission (a.k.a. conjugate
beamforming). This gain is unattainable with the SLO configuration.Comment: IEEE Transactions on Communication
Receiver Algorithm based on Differential Signaling for SIMO Phase Noise Channels with Common and Separate Oscillator Configurations
In this paper, a receiver algorithm consisting of differential transmission
and a two-stage detection for a single-input multiple-output (SIMO) phase-noise
channels is studied. Specifically, the phases of the QAM modulated data symbols
are manipulated before transmission in order to make them more immune to the
random rotational effects of phase noise. At the receiver, a two-stage detector
is implemented, which first detects the amplitude of the transmitted symbols
from a nonlinear combination of the received signal amplitudes. Then in the
second stage, the detector performs phase detection. The studied signaling
method does not require transmission of any known symbols that act as pilots.
Furthermore, no phase noise estimator (or a tracker) is needed at the receiver
to compensate the effect of phase noise. This considerably reduces the
complexity of the receiver structure. Moreover, it is observed that the studied
algorithm can be used for the setups where a common local oscillator or
separate independent oscillators drive the radio-frequency circuitries
connected to each antenna. Due to the differential encoding/decoding of the
phase, weighted averaging can be employed at a multi-antenna receiver, allowing
for phase noise suppression to leverage the large number of antennas. Hence, we
observe that the performance improves by increasing the number of antennas,
especially in the separate oscillator case. Further increasing the number of
receive antennas results in a performance error floor, which is a function of
the quality of the oscillator at the transmitter.Comment: IEEE GLOBECOM 201
Effect of Synchronizing Coordinated Base Stations on Phase Noise Estimation
In this paper, we study the problem of oscillator phase noise (PN) estimation
in coordinated multi-point (CoMP) transmission systems. Specifically, we
investigate the effect of phase synchronization between coordinated base
stations (BSs) on PN estimation at the user receiver (downlink channel). In
this respect, the Bayesian Cram\'er-Rao bound for PN estimation is derived
which is a function of the level of phase synchronization between the
coordinated BSs. Results show that quality of BS synchronization has a
significant effect on the PN estimation
- …