37,192 research outputs found
Signal-to-noise ratio estimation in digital computer simulation of lowpass and bandpass systems with applications to analog and digital communications, volume 3
Techniques are developed to estimate power gain, delay, signal-to-noise ratio, and mean square error in digital computer simulations of lowpass and bandpass systems. The techniques are applied to analog and digital communications. The signal-to-noise ratio estimates are shown to be maximum likelihood estimates in additive white Gaussian noise. The methods are seen to be especially useful for digital communication systems where the mapping from the signal-to-noise ratio to the error probability can be obtained. Simulation results show the techniques developed to be accurate and quite versatile in evaluating the performance of many systems through digital computer simulation
Higher homotopy operations and cohomology
We explain how higher homotopy operations, defined topologically, may be
identified under mild assumptions with (the last of) the Dwyer-Kan-Smith
cohomological obstructions to rectifying homotopy-commutative diagrams.Comment: 28 page
On the analysis of mixed-index time fractional differential equation systems
In this paper we study the class of mixed-index time fractional differential
equations in which different components of the problem have different time
fractional derivatives on the left hand side. We prove a theorem on the
solution of the linear system of equations, which collapses to the well-known
Mittag-Leffler solution in the case the indices are the same, and also
generalises the solution of the so-called linear sequential class of time
fractional problems. We also investigate the asymptotic stability properties of
this class of problems using Laplace transforms and show how Laplace transforms
can be used to write solutions as linear combinations of generalised
Mittag-Leffler functions in some cases. Finally we illustrate our results with
some numerical simulations.Comment: 21 pages, 6 figures (some are made up of sub-figures - there are 15
figures or sub-figures
Analog tree-organized multiplexer
An analog tree-organized multiplexer (ATOM) which is intended for use in the telemetry system of an interplanetary spacecraft is designed. The ATOM will be fabricated by a monolithic, dielectric isolation process, and will contain silicon junction field effect transistors (JFET) as the active elements. The effect of the radiation environment on the performance of the ATOM is analyzed. The result indicates that the expected radiation environment will cause only minor changes in the preradiation characteristics of ATOM. The JFET in the ATOM is designed to meet the electrical requirements when fabricated by either the double poly-dielectric isolation process or the raised dielectric isolation process. The effect of the heat treatment required for the dielectric isolation process on the diffusion profile of the JFET is described. The layout of the ATOM circuit for fabrication by either the double poly or raised dielectric isolation process is also given
Scalable iterative methods for sampling from massive Gaussian random vectors
Sampling from Gaussian Markov random fields (GMRFs), that is multivariate
Gaussian ran- dom vectors that are parameterised by the inverse of their
covariance matrix, is a fundamental problem in computational statistics. In
this paper, we show how we can exploit arbitrarily accu- rate approximations to
a GMRF to speed up Krylov subspace sampling methods. We also show that these
methods can be used when computing the normalising constant of a large
multivariate Gaussian distribution, which is needed for both any
likelihood-based inference method. The method we derive is also applicable to
other structured Gaussian random vectors and, in particu- lar, we show that
when the precision matrix is a perturbation of a (block) circulant matrix, it
is still possible to derive O(n log n) sampling schemes.Comment: 17 Pages, 4 Figure
Electronic Structure of Pyrochlore Iridates: From Topological Dirac Metal to Mott Insulator
In 5d transition metal oxides such as the iridates, novel properties arise
from the interplay of electron correlations and spin-orbit interactions. We
investigate the electronic structure of the pyrochlore iridates, (such as
YIrO) using density functional theory, LDA+U method, and
effective low energy models. A remarkably rich phase diagram emerges on tuning
the correlation strength U. The Ir magnetic moment are always found to be
non-collinearly ordered. However, the ground state changes from a magnetic
metal at weak U, to a Mott insulator at large U. Most interestingly, the
intermediate U regime is found to be a Dirac semi-metal, with vanishing density
of states at the Fermi energy. It also exhibits topological properties -
manifested by special surface states in the form of Fermi arcs, that connect
the bulk Dirac points. This Dirac phase, a three dimensional analog of
graphene, is proposed as the ground state of YIrO and related
compounds. A narrow window of magnetic `axion' insulator, with axion parameter
, may also be present at intermediate U. An applied magnetic field
induces ferromagnetic order and a metallic ground state.Comment: 7pages + 2pages appendices. 7 figures; see also viewpoint article by
L. Balents, "Weyl Electrons Kiss", at Physics 4, 36 (2011
Hawking Radiation via Tunneling from Hot NUT-Kerr-Newman-Kasuya Spacetime
We study the Hawking thermal spectrum in dragging coordinate system and the
tunneling radiation characteristics of hot NUT-Kerr-Newman-Kasuya spacetime.
The tunneling rates at the event and cosmological horizon are found to be
related to the change of Bekenstein-Hawking entropy. The radiation spectrum is
not pure thermal and thus there is a correction to the Hawking thermal
spectrum.Comment: To appear in Class. Quant. Gra
Feasibility study of an Integrated Program for Aerospace vehicle Design (IPAD). Volume 2: The design process
The extent to which IPAD is to support the design process is identified. Case studies of representative aerospace products were developed as models to characterize the design process and to provide design requirements for the IPAD computing system
Audit of Lone Star Gas Invoices and Billing Procedures, Task #3
Lone Star Gas Company uses standard methods to convert measured gas volumes to standard
volumes by assuming constant gas CO2 content (2.8%), N2 content (0.79%) and gas specific gravity
value (0.647). In 1995, the gravity value measured varied from 0.601 to 0.627, which is lower than the
assumed value. Hence, Lone Star Gas Company overcharged TAMU Power Plant by 0.17% to 0.39%
depending on the actual specific gravity values (see the chart below). The impact of assuming constant
CO2 and N2 levels on the bills is negligible.
After a joint meeting with ESL and TAMU Physical Plant personnel, Lone Star Gas Company
agreed to update the gas specific gravity value every four months in the future and to reconcile gas bills
back to 1994 with measured specific gravity values. This reconciliation will result in a credit to Texas
A&M University of approximately $20,000 for 1995. Results of the reconciliation for other years will
depend on the measured specific gravity values.At the request of the TAMU Power Plant, the ESL staff audited the 1995 Lone Star Gas
Company invoices. Gas consumption is measured and the measured volume is converted to standard
volume (at T=60 °F, P= 14.65 psia) to determine the energy content and cost. This audit was performed to
determine if the bills from Lone Star Gas Company had correctly converted the measured volumes to
standard volumes, and had charged the proper amounts
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