90,532 research outputs found
On --domains and star operations
Let be a star operation on an integral domain . Let \f(D) be the
set of all nonzero finitely generated fractional ideals of . Call a
--Pr\"ufer (respectively, --Pr\"ufer) domain if
(respectively, ) for all F\in
\f(D). We establish that --Pr\"ufer domains (and --Pr\"ufer
domains) for various star operations span a major portion of the known
generalizations of Pr\"{u}fer domains inside the class of --domains. We also
use Theorem 6.6 of the Larsen and McCarthy book [Multiplicative Theory of
Ideals, Academic Press, New York--London, 1971], which gives several equivalent
conditions for an integral domain to be a Pr\"ufer domain, as a model, and we
show which statements of that theorem on Pr\"ufer domains can be generalized in
a natural way and proved for --Pr\"ufer domains, and which cannot be. We
also show that in a --Pr\"ufer domain, each pair of -invertible
-ideals admits a GCD in the set of -invertible -ideals,
obtaining a remarkable generalization of a property holding for the "classical"
class of Pr\"ufer --multiplication domains. We also link being --Pr\"ufer (or --Pr\"ufer) with the group Inv of -invertible -ideals (under -multiplication) being
lattice-ordered
Comparison of flight data and analysis for hingeless rotor regressive inplane mode stability
Analytical and experimental data obtained during the development of the AH-56A covering stability of the regressive inplane mode, including coupling with other modes such as body and rotor plunge are reported. Data were obtained on two distinctly different control systems; both gyro controlled, but one with feathering moment feedback and the other with direct flapping feedback. A review was made of analytical procedures employed in investigating the stability of this mode and a comparison was made of the analytical and experimental data. The effect of certain parameters including blade droop, sweep, delta 3, alpha 1, vehicle roll inertia, inplane frequency, and rpm and forward speed on the mode were also reviewed. It was shown that the stability of this mode is treatable by analysis and that adequate stability is achievable without recourse to auxiliary inplane damping devices
Phased array antenna beamforming using optical processor
The feasibility of optical processor based beamforming for microwave array antennas is investigated. The primary focus is on systems utilizing the 20/30 GHz communications band and a transmit configuration exclusively to serve this band. A mathematical model is developed for computation of candidate design configurations. The model is capable of determination of the necessary design parameters required for spatial aspects of the microwave 'footprint' (beam) formation. Computed example beams transmitted from geosynchronous orbit are presented to demonstrate network capabilities. The effect of the processor on the output microwave signal to noise quality at the antenna interface is also considered
The implications of precise timekeeping of Doppler gravitational wave observations
Gravitational radiation from galactic and extragalactic astrophysical sources will induce spatial strains in the solar system, strains which can be measured directly by the Doppler radio link to distant spacecraft. Current noise sources in Pioneer and Voyager Doppler data are delineated and a comparison is made with expected signal levels from gravitational wave sources. The main conclusion is that it is possible to detect gravitational radiation with current DSN hydrogen maser systems stable in fractional frequency + or - 2 x 10 to the minus 14th power over 1000 sec. In the future, however, a serious Doppler observational program in gravitational wave astronomy will require frequency systems stable to at least 10 to the minus 16th power, but at the same time the current single frequency S-band uplink transmission will have to be replaced by a dual frequency capability
Antenna beamforming using optical processing
This work concerns itself with the analytical investigation into the feasibility of optical processor based beamforming for microwave array antennas. The primary focus is on systems utilizing the 20 and 30 GHz communications band and a transmit configuration exclusively to serve this band. A mathematical model is developed for computation of candidate design configurations. The model is capable of determination of the necessary design parameters required for both spatial aspects of the microwave footprint (beam) formation as well as transmitted signal quality. Computed example beams transmitted from geosynchronous orbit are presented to demonstrate network capabilities. A comprehensive device/component survey is also conducted in parallel to determine the feasibility of breadboarding a transmit processor. Recommendations are made for the configuration of such a processor and the components which would comprise such a network
A Decidable Confluence Test for Cognitive Models in ACT-R
Computational cognitive modeling investigates human cognition by building
detailed computational models for cognitive processes. Adaptive Control of
Thought - Rational (ACT-R) is a rule-based cognitive architecture that offers a
widely employed framework to build such models. There is a sound and complete
embedding of ACT-R in Constraint Handling Rules (CHR). Therefore analysis
techniques from CHR can be used to reason about computational properties of
ACT-R models. For example, confluence is the property that a program yields the
same result for the same input regardless of the rules that are applied.
In ACT-R models, there are often cognitive processes that should always yield
the same result while others e.g. implement strategies to solve a problem that
could yield different results. In this paper, a decidable confluence criterion
for ACT-R is presented. It allows to identify ACT-R rules that are not
confluent. Thereby, the modeler can check if his model has the desired
behavior.
The sound and complete translation of ACT-R to CHR from prior work is used to
come up with a suitable invariant-based confluence criterion from the CHR
literature. Proper invariants for translated ACT-R models are identified and
proven to be decidable. The presented method coincides with confluence of the
original ACT-R models.Comment: To appear in Stefania Costantini, Enrico Franconi, William Van
Woensel, Roman Kontchakov, Fariba Sadri, and Dumitru Roman: "Proceedings of
RuleML+RR 2017". Springer LNC
Spin-Charge separation in a model of two coupled chains
A model of interacting electrons living on two chains coupled by a transverse
hopping , is solved exactly by bosonization technique. It is shown
that does modify the shape of the Fermi surface also in presence of
interaction, although charge and spin excitations keep different velocities
, . Two different regimes occur: at short distances, , the two chain model is not sensitive to
, while for larger separation inter--chain hopping is
relevant and generates further singularities in the electron Green function
besides those due to spin-charge decoupling. (2 figures not included. Figure
requests: FABRIZIO@ITSSISSA)Comment: 12 pages, LATEX(REVTEX), SISSA 150/92/CM/M
Mapping Low-Density Intergalactic Gas: a Third Helium Lyman-alpha Forest
We present a new HST/STIS spectrum of the z=3.18 quasar PKS 1935-692 and
summarize the spectral features shortwards of 304A in the rest frame likely to
be caused by foreground HeII Lyman-alpha absorption. In accord with previous
results on two other quasars at similar redshifts, we demonstrate a correlation
with the HI Lyman-alpha forest absorption, and show that much of the helium
absorption is caused by a comparable quantity of more diffuse gas with
Omega~0.01, that is not detected in HI. The helium ionization zone around the
quasar is detected as well as a void seen in both HI and HeII. The properties
of the absorption are in broad agreement with those of the other quasars and
with models of the protogalactic gas distribution and ionization at this
redshift.Comment: 17 pages including 5 figures. As accepted for publication in The
Astronomical Journal (minor revisions
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