25 research outputs found
Holographic modeling of nuclear matter and neutron stars
I review holographic models for (dense and cold) nuclear matter, neutron
stars, and their mergers. I start by a brief general discussion on current
knowledge of cold QCD matter and neutron stars, and go on discussing various
approaches to model cold nuclear and quark matter by using gauge/gravity
duality, pointing out their strengths and weaknesses. Then I concentrate on
recent results for a complex bottom-up holographic framework (V-QCD), which
also takes input from lattice QCD results, effective field theory, and
perturbative QCD. Dense nuclear matter is modeled in V-QCD through a
homogeneous non-Abelian bulk gauge field. Feasible "hybrid" equations of state
for cold nuclear (and quark) matter can be constructed by using traditional
methods (e.g., effective field theory) at low densities and the holographic
V-QCD model at higher densities. I discuss the constraints from this approach
to the properties of the nuclear to quark matter transition as well as to
properties of neutron stars. Using such hybrid equations of state as an input
for numerical simulations of neutron star mergers, I also derive predictions
for the spectrum of produced gravitational waves.Comment: Review article submitted to Eur.Phys.J.C. 56 pages, 24 figures, 2
table
Compound codes based on irregular graphs and their iterative decoding.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004.Low-density parity-check (LDPC) codes form a Shannon limit approaching class of linear block codes. With iterative decoding based on their Tanner graphs, they can achieve outstanding performance. Since their rediscovery in late 1990's, the design,
construction, and decoding of LDPC codes as well as their generalization have become one of the focal research points. This thesis takes a few more steps in these directions. The first significant contribution of this thesis is the introduction of a new class of codes
called Generalized Irregular Low-Density (GILD) parity-check codes, which are adapted from the previously known class of Generalized Low-Density (GLD) codes. GILD codes are generalization of irregular LDPC codes, and are shown to outperform GLD codes. In addition, GILD codes have a significant advantage over GLD codes in terms of encoding and decoding complexity. They are also able to match and even beat LDPC codes for small block lengths. The second significant contribution of this thesis is the proposition of several decoding algorithms. Two new decoding algolithms for LDPC codes are introduced. In principle and complexity these algorithms can be grouped with bit flipping algorithms. Two soft-input soft-output (SISO) decoding algorithms for linear block codes are also proposed. The first algorithm is based on Maximum a Posteriori Probability (MAP) decoding of low-weight subtrellis centered around a generated candidate codeword. The second algorithm modifies and utilizes the improved Kaneko's decoding algorithm for soft-input hard-output decoding. These hard outputs are converted to soft-decisions using
reliability calculations. Simulation results indicate that the proposed algorithms provide a significant improvement in error performance over Chase-based algorithm and achieve practically optimal performance with a significant reduction in decoding complexity.
An analytical expression for the union bound on the bit error probability of linear codes on the Gilbert-Elliott (GE) channel model is also derived. This analytical result is shown to be accurate in establishing the decoder performance in the range where
obtaining sufficient data from simulation is impractical
The Telecommunications and Data Acquisition Report
Developments in space communications, radio navigation, radio science, ground-base radio astronomy, reports on the Deep Space Network (DSN) and its Ground Communications Facility (GCF), and applications of radio interferometry at microwave frequencies are discussed
Space programs summary no. 37-32, volume IV FOR the period February 1, 1965 to March 31, 1965. Supporting research and advanced development
Space exploration research on systems analyses, guidance and control, engineering development, propulsion systems, telecommunications, and space science
Understanding Quantum Technologies 2022
Understanding Quantum Technologies 2022 is a creative-commons ebook that
provides a unique 360 degrees overview of quantum technologies from science and
technology to geopolitical and societal issues. It covers quantum physics
history, quantum physics 101, gate-based quantum computing, quantum computing
engineering (including quantum error corrections and quantum computing
energetics), quantum computing hardware (all qubit types, including quantum
annealing and quantum simulation paradigms, history, science, research,
implementation and vendors), quantum enabling technologies (cryogenics, control
electronics, photonics, components fabs, raw materials), quantum computing
algorithms, software development tools and use cases, unconventional computing
(potential alternatives to quantum and classical computing), quantum
telecommunications and cryptography, quantum sensing, quantum technologies
around the world, quantum technologies societal impact and even quantum fake
sciences. The main audience are computer science engineers, developers and IT
specialists as well as quantum scientists and students who want to acquire a
global view of how quantum technologies work, and particularly quantum
computing. This version is an extensive update to the 2021 edition published in
October 2021.Comment: 1132 pages, 920 figures, Letter forma