425 research outputs found
Curves on torus layers and coding for continuous alphabet sources
In this paper we consider the problem of transmitting a continuous alphabet
discrete-time source over an AWGN channel. The design of good curves for this
purpose relies on geometrical properties of spherical codes and projections of
-dimensional lattices. We propose a constructive scheme based on a set of
curves on the surface of a 2N-dimensional sphere and present comparisons with
some previous works.Comment: 5 pages, 4 figures. Accepted for presentation at 2012 IEEE
International Symposium on Information Theory (ISIT). 2th version: typos
corrected. 3rd version: some typos corrected, a footnote added in Section III
B, a comment added in the beggining of Section V and Theorem I adde
Characterization of 30 Ge enriched Broad Energy Ge detectors for GERDA Phase II
The GERmanium Detector Array (GERDA) is a low background experiment located
at the Laboratori Nazionali del Gran Sasso in Italy, which searches for
neutrinoless double beta decay of Ge into Se+2e. GERDA has
been conceived in two phases. Phase II, which started in December 2015,
features several novelties including 30 new Ge detectors. These were
manufactured according to the Broad Energy Germanium (BEGe) detector design
that has a better background discrimination capability and energy resolution
compared to formerly widely-used types. Prior to their installation, the new
BEGe detectors were mounted in vacuum cryostats and characterized in detail in
the HADES underground laboratory in Belgium. This paper describes the
properties and the overall performance of these detectors during operation in
vacuum. The characterization campaign provided not only direct input for GERDA
Phase II data collection and analyses, but also allowed to study detector
phenomena, detector correlations as well as to test the strength of pulse shape
simulation codes.Comment: 29 pages, 18 figure
Accurate numerical simulations of inspiralling binary neutron stars and their comparison with effective-one-body analytical models
Binary neutron-star systems represent one of the most promising sources of
gravitational waves. In order to be able to extract important information,
notably about the equation of state of matter at nuclear density, it is
necessary to have in hands an accurate analytical model of the expected
waveforms. Following our recent work, we here analyze more in detail two
general-relativistic simulations spanning about 20 gravitational-wave cycles of
the inspiral of equal-mass binary neutron stars with different compactnesses,
and compare them with a tidal extension of the effective-one-body (EOB)
analytical model. The latter tidally extended EOB model is analytically
complete up to the 1.5 post-Newtonian level, and contains an analytically
undetermined parameter representing a higher-order amplification of tidal
effects. We find that, by calibrating this single parameter, the EOB model can
reproduce, within the numerical error, the two numerical waveforms essentially
up to the merger. By contrast, analytical models (either EOB, or Taylor-T4)
that do not incorporate such a higher-order amplification of tidal effects,
build a dephasing with respect to the numerical waveforms of several radians.Comment: 25 pages, 17 figs. Matched published versio
Generalized Dicke model and gauge-invariant master equations for two atoms in ultrastrongly-coupled cavity quantum electrodynamics
We study a generalization of the well-known Dicke model, using two dissimilar
atoms in the regime of ultrastrongly coupled cavity quantum electrodynamics.
Our theory uses gauge invariant master equations, which yields consistent
results in either of the standard multipolar and Coulomb gauges, including
system-bath interactions for open cavity systems. We first show how a second
atom can be treated as a sensor atom to measure the output spectrum from a
single atom in the ultrastrong-coupling regime, and compare results with the
quantum regression theorem, explaining when they can be different. We then
focus on the case where the second atom is also ultrastrongly coupled to the
cavity, but with different parameters from those of the first atom, which
introduces complex coupling effects and additional resonances and spectral
features. In particular, we show multiple resonances in the cavity spectra that
are visible off-resonance, which cannot be seen when the second atom is
on-resonance with the rest of the system. We also observe clear anti-crossing
features particularly pronounced for when the second atom tunes through
resonance.Comment: Revised Pape
Recommended from our members
Design of Energy-Efficient Equalization and Data Encoding/Decoding Techniques for Wireline Communication Systems
Ever increasing global internet data traffic has driven up the demand for cutting-edge high-speed wireline communication systems including SerDes PHY for various interfaces, interconnects, data centers servers and switches in optical systems. Operating wireline communications at higher data rates leads to signals suffering from greater channel loss and exponential increase in power consumption, mainly caused by a heavier amount of required equalization.
In this dissertation, two distinct methodologies for designing SerDes transceivers are presented: 1) a pulse width modulated (PWM) time-domain feed forward equalizer (FFE) and linearity improvement technique for higher-order pulse amplitude modulation (PAM) including PAM-8, and 2) an inter-symbol interference (ISI)-resilient data encoding and decoding technique with Dicode encoding and error correction logic for low-bandwidth wireline channels, as an alternative strategy for communicating in an energy-efficient way on bandwidth-limited wireline channels without using conventional equalizers or filters.
The first topic is a PAM-8 wireline transceiver with receiver-side pulse-width-modulated (PWM) or time-domain based feed forward equalization (FFE) technique. The receiver converts voltage-modulated signals or PAM signals to PWM signals and processes them using inverter based delay elements having rail to rail voltage swing. Time-to-voltage and voltage-to-time converters are designed to have non-linearity with opposite signs with the aim of achieving higher front-end linearity on the receiver. The proposed PAM-8 transceiver can operate from 12.0 Gb/s to 39.6 Gb/s and compensates 14 dB loss at 6.6 GHz with an efficiency of 8.66 pJ/bit in 65 nm CMOS.
The second topic is an alternative strategy for communicating on bandwidth-limited wireline channels without using conventional equalizers or filters (FFE, DFE, and CTLE): Inter-symbol interference (ISI) resilient Dicode encoding and error correction for low-bandwidth wireline channels. The key observation is that Dicode-encoded data have no consecutive 1s or -1s. With this known information, the error correction logic at the receiver can correct multi-bit errors due to ISI. Implemented in 65 nm CMOS, the proposed digital encoding and decoding approach can achieve BER less than 10−12 while communicating on a channel with an insertion loss of 24.2 dB and 21.4 dB with 2.56 pJ/bit and 2.66 pJ/bit efficiency while operating at 13.6 Gb/s and 16 Gb/s, respectively
Three Dimensional Simulations of Vertical Magnetic Flux in the Immediate Vicinity of Black Holes
This article reports on three-dimensional (3-D) MHD simulations of
non-rotating and rapidly rotating black holes and the adjacent black hole
accretion disk magnetospheres. A particular emphasis is placed on the vertical
magnetic flux that is advected inward from large radii and threads the
equatorial plane near the event horizon. In both cases of non-rotating and
rotating black holes, the existence of a significant vertical magnetic field in
this region is like a switch that creates powerful jets. There are many
similarities in the vertical flux dynamics in these two cases in spite of the
tremendous enhancement of azimuthal twisting of the field lines and enhancement
of the jet power because of an "ergospheric disk" in the Kerr metric. A 3-D
approach is essential because two-dimensional axisymmetric flows are incapable
of revealing the nature of vertical flux near a black hole. Poloidal field
lines from the ergospheric accretion region have been visualized in 3-D and
much of the article is devoted to a formal classification of the different
manifestations of vertical flux in the Kerr case.Comment: To appear in ApJ. The referenced movies can be found in the
electronic on-line journal or http://85.20.11.14/punsly/PHI/movies
- …