10,849 research outputs found
A Serendipitous XMM-Newton Observation of the Intermediate Polar WX Pyx
We briefly describe a serendipitous observation of the little-studied
intermediate polar WX Pyx using XMM-Newton. The X-ray spin period is 1557.3
sec, confirming the optical period published in 1996. An orbital period of
approximately 5.54 hr is inferred from the separation of the spin-orbit
sidelobe components. The soft and hard band spin-folded light curves are nearly
sinusoidal in shape. The best-fit spectrum is consistent with a bremsstrahlung
temperature of about 18 keV. An upper limit of approximately 300 eV is assigned
to the presence of Fe line emission. WX Pyx lies near TX and TV Col in the
P_spin-P_orb plane.Comment: 5 pages, 5 figs; accepted A&A 2004 Dec
Periodicities In The X-Ray Intensity Variations of TV Columbae: An Intermediate Polar
We present results from a temporal analysis of the longest and the most
sensitive X-ray observations of TV Columbae--an intermediate polar. The
observations were carried out with the RXTE PCA, ROSAT PSPC, and ASCA. Data
were analyzed using a 1-dimensional CLEAN and Bayesian algorithms. The presence
of a nearly sinusoidal modulation due to the spin of the white dwarf is seen
clearly in all the data, confirming the previous reports based on the EXOSAT
data. An improved period of 1909.7+/-2.5s is derived for the spin from the RXTE
data.The binary period of 5.5hr is detected unambiguously in X-rays for the
first time. Several side-bands due to the interaction of these periods are
observed in the power spectra, thereby suggesting contributions from both the
disk-fed and the stream-fed accretion for TV Col. The accretion disk could
perhaps be precessing as side-bands due to the influence of 4 day period on the
orbital period are seen. The presence of a significant power at certain
side-bands of the spin frequency indicates that the emission poles are
asymmetrically located. The strong power at the orbital side-bands seen in both
the RXTE and ROSAT data gives an indication for an absorption site fixed in the
orbital frame. Both the spin and the binary modulation are found to be
energy-dependent. Increased hardness ratio during a broad dip in the intensity
at binary phase of 0.75--1.0 confirms the presence of a strong attenuation due
to additional absorbers probably from an impact site of the accretion stream
with the disk or magnetosphere. Hardness ratio variations and the energy
dependent modulation depth during the spin modulation can be explained by
partially covered absorbers in the path of X-ray emission region in the
accretion stream.Comment: 34 pages, including 12 figures, Accepted for publication in
Astronomical Journal, scheduled for January 2004 issue (vol. 127
An iterative algorithm for parametrization of shortest length shift registers over finite rings
The construction of shortest feedback shift registers for a finite sequence
S_1,...,S_N is considered over the finite ring Z_{p^r}. A novel algorithm is
presented that yields a parametrization of all shortest feedback shift
registers for the sequence of numbers S_1,...,S_N, thus solving an open problem
in the literature. The algorithm iteratively processes each number, starting
with S_1, and constructs at each step a particular type of minimal Gr\"obner
basis. The construction involves a simple update rule at each step which leads
to computational efficiency. It is shown that the algorithm simultaneously
computes a similar parametrization for the reciprocal sequence S_N,...,S_1.Comment: Submitte
Fly-by-light flight control system technology development plan
The results of a four-month, phased effort to develop a Fly-by-Light Technology Development Plan are documented. The technical shortfalls for each phase were identified and a development plan to bridge the technical gap was developed. The production configuration was defined for a 757-type airplane, but it is suggested that the demonstration flight be conducted on the NASA Transport Systems Research Vehicle. The modifications required and verification and validation issues are delineated in this report. A detailed schedule for the phased introduction of fly-by-light system components has been generated. It is concluded that a fiber-optics program would contribute significantly toward developing the required state of readiness that will make a fly-by-light control system not only cost effective but reliable without mitigating the weight and high-energy radio frequency related benefits
Short-Distance Structure of Nuclei
One of Jefferson Lab's original missions was to further our understanding of
the short-distance structure of nuclei. In particular, to understand what
happens when two or more nucleons within a nucleus have strongly overlapping
wave-functions; a phenomena commonly referred to as short-range correlations.
Herein, we review the results of the (e,e'), (e,e'p) and (e,e'pN) reactions
that have been used at Jefferson Lab to probe this short-distance structure as
well as provide an outlook for future experiments.Comment: 16 pages, 8 figures, for publication in Journal of Physics
On calibrated representations of the degenerate affine periplectic Brauer algebra
We initiate the representation theory of the degenerate affine periplectic Brauer algebra on strands by constructing its finite-dimensional calibrated representations when . We show that any such representation that is indecomposable and does not factor through a representation of the degenerate affine Hecke algebra occurs as an extension of two semisimple representations with one-dimensional composition factors; and furthermore, we classify such representations with regular eigenvalues up to isomorphism
SIRI-OUSLY 2.0: What Artificial Intelligence Reveals About the First Amendment
The First Amendment may protect speech by strong Artificial Intelligence (AI). In this Article, we support this provocative claim by expanding on earlier work, addressing significant concerns and challenges, and suggesting potential paths forward.
This is not a claim about the state of technology. Whether strong AI — as-yet-hypothetical machines that can actually think — will ever come to exist remains far from clear. It is instead a claim that discussing AI speech sheds light on key features of prevailing First Amendment doctrine and theory, including the surprising lack of humanness at its core.
Courts and commentators wrestling with free speech problems increasingly focus not on protecting speakers as speakers but instead on providing value to listeners and constraining the government’s power. These approaches to free speech law support the extension of First Amendment coverage to expression regardless of its nontraditional source or form. First Amendment thinking and practice thus have developed in a manner that permits extensions of coverage in ways that may seem exceedingly odd, counterintuitive, and perhaps even dangerous. This is not a feature of the new technologies, but of free speech law.
The possibility that the First Amendment covers speech by strong AI need not, however, rob the First Amendment of a human focus. Instead, it might encourage greater clarification of and emphasis on expression\u27s value to human listeners — and its potential harms — in First Amendment theory and doctrine. To contemplate — Siri-ously — the relationship between the First Amendment and AI speech invites critical analysis of the contours of current free speech law, as well as sharp thinking about free speech problems posed by the rise of AI
TransverseDiff gravity is to scalar-tensor as unimodular gravity is to General Relativity
Transverse Diffeomorphism (TDiff) theories are well-motivated theories of
gravity from the quantum perspective, which are based upon a gauge symmetry
principle. The main contribution of this work is to firmly establish a
correspondence between TransverseDiff and the better-known scalar-tensor
gravity --- in its more general form ---, a relation which is completely
analogous to that between unimodular gravity and General Relativity. We then
comment on observational aspects of TDiff. In connection with this proof, we
derive a very general rule that determines under what conditions the procedure
of fixing a gauge symmetry can be equivalently applied before the variational
principle leading to the equations of motion, as opposed to the standard
procedure, which takes place afterwards; this rule applies to gauge-fixing
terms without derivatives.Comment: 10 pages; amsart style; v3: version as appeared in JCAP, redaction
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