16,603 research outputs found
Energy and momentum of cylindrical gravitational waves. II
Recently Nathan Rosen and the present author obtained the energy and momentum
densities of cylindrical gravitational waves in Einstein's prescription and
found them to be finite and reasonable. In the present paper we calculate the
same in prescriptions of Tolman as well as Landau and Lifshitz and discuss the
results.Comment: 8 pages, LaTex, To appear in Pramana- J. Physic
Contributions of temporal encodings of voicing, voicelessness, fundamental frequency, and amplitude variation to audiovisual and auditory speech perception
Auditory and audio-visual speech perception was investigated using auditory signals of invariant spectral envelope that temporally encoded the presence of voiced and voiceless excitation, variations in amplitude envelope and F-0. In experiment 1, the contribution of the timing of voicing was compared in consonant identification to the additional effects of variations in F-0 and the amplitude of voiced speech. In audio-visual conditions only, amplitude variation slightly increased accuracy globally and for manner features. F-0 variation slightly increased overall accuracy and manner perception in auditory and audio-visual conditions. Experiment 2 examined consonant information derived from the presence and amplitude variation of voiceless speech in addition to that from voicing, F-0, and voiced speech amplitude. Binary indication of voiceless excitation improved accuracy overall and for voicing and manner. The amplitude variation of voiceless speech produced only a small increment in place of articulation scores. A final experiment examined audio-visual sentence perception using encodings of voiceless excitation and amplitude variation added to a signal representing voicing and F-0. There was a contribution of amplitude variation to sentence perception, but not of voiceless excitation. The timing of voiced and voiceless excitation appears to be the major temporal cues to consonant identity. (C) 1999 Acoustical Society of America. [S0001-4966(99)01410-1]
Inverse problems in the modeling of vibrations of flexible beams
The formulation and solution of inverse problems for the estimation of parameters which describe damping and other dynamic properties in distributed models for the vibration of flexible structures is considered. Motivated by a slewing beam experiment, the identification of a nonlinear velocity dependent term which models air drag damping in the Euler-Bernoulli equation is investigated. Galerkin techniques are used to generate finite dimensional approximations. Convergence estimates and numerical results are given. The modeling of, and related inverse problems for the dynamics of a high pressure hose line feeding a gas thruster actuator at the tip of a cantilevered beam are then considered. Approximation and convergence are discussed and numerical results involving experimental data are presented
On a generalized quantum SWAP gate
The SWAP gate plays a central role in network designs for qubit quantum computation. However, there has been a view to generalize qubit quantum computing to higher dimensional quantum systems. In this paper we construct a generalized SWAP gate using only instances of the generalized controlled-NOT gate to cyclically permute the states of d qudits for d prime
The (im)possibilities of dialogue across feminism and childhood scholarship and activism
The relations between those positioned as women and as children, and the political and intellectual consequences of how we conceptualise these connections, has received only scant attention. In this article we describe a symposium and on-going project which aim to bring together community-based and academic scholars to debate the intersections and perceived antagonisms between various forms of feminism and the politics of childhood. We trace how these intersections have been debated in the literature and outline the potential benefits and pitfalls of encouraging further connections between these fields. Drawing on our symposium experience, we also outline the challenges involved in bringing together academic and community-based scholars and activists, and consider the implications for similar future endeavours
Getting Jobs, Keeping Jobs, and Earning a Living Wage: Can Welfare Reform Work?
Most discussions of welfare and work have focused on how demographic characteristics, schooling, training, and work experience limit welfare mothers’ employment and wages, but they have largely ignored factors such as inappropriate workplace behaviors, expectations of discrimination and harassment, depression, alcoholism, and domestic violence, all of which may affect welfare mothers and make employment difficult. In this paper we review the prevalence of these individual-level barriers and argue that they, in combination with an economy which does not pay low-skill workers well, are likely to impede employment and self-sufficiency for a large proportion of welfare mothers. At the end of the review, we summarize the current state of knowledge about barriers to the employment of welfare recipients and suggest several ways in which welfare-to-work programs might address these barriers.
Simultaneous X-ray and Optical Observations of EX Hydrae
The intermediate polar, EX Hydrae, was the object of a large simultaneous
multiwavelength observational campaign during 2000 May - June. Here we present
the Rossi X-ray Timing Explorer photometry and optical photometry and
spectroscopy from ground-based observatories obtained as part of this campaign.
Balmer line radial velocities and Doppler maps provide evidence for an extended
bulge along the outer edge of the accretion disk and some form of
extended/overflowing material originating from the hot spot. In addition, the
optical binary eclipse possesses an extended egress shoulder, an indication
that an additional source (other than the white dwarf) is coming out of
eclipse. We also compare the X-ray and optical results with the results
obtained from the EUV and UV observations from the multiwavelength data set.Comment: to appear in the Astronomical Journal, April 200
ORFEUS II and IUE Spectroscopy of EX Hydrae
Using ORFEUS-SPAS II FUV spectra, IUE UV spectra, and archival EUVE deep
survey photometry, we present a detailed picture of the behavior of the
magnetic cataclysmic variable EX Hydrae. Like HUT spectra of this source, the
FUV and UV spectra reveal broad emission lines of He II, C II-IV, N III and V,
O VI, Si III-IV, and Al III superposed on a continuum which is blue in the UV
and nearly flat in the FUV. Like ORFEUS spectra of AM Her, the O VI doublet is
resolved into broad and narrow emission components. Consistent with its
behavior in the optical, the FUV and UV continuum flux densities, the FUV and
UV broad emission line fluxes, and the radial velocity of the O VI broad
emission component all vary on the spin phase of the white dwarf, with the
maximum of the FUV and UV continuum and broad emission line flux light curves
coincident with maximum blueshift of the broad O VI emission component. On the
binary phase, the broad dip in the EUV light curve is accompanied by strong
eclipses of the UV emission lines and by variations in both the flux and radial
velocity of the O VI narrow emission component. The available data are
consistent with the accretion funnel being the source of the FUV and UV
continuum and the O VI broad emission component, and the white dwarf being the
source of the O VI narrow emission component.Comment: 21 pages, 10 Postscript figures; LaTeX format, uses aaspp4.sty;
table2.tex included separately because it must be printed sideways - see
instructions in the file; accepted on 1999 Feb 20 for publication in The
Astrophysical Journa
An EUV Study of the Intermediate Polar EX Hydrae
On 2000 May 5, we began a large multi-wavelength campaign to study the
intermediate polar, EX Hydrae. The simultaneous observations from six
satellites and four telescopes were centered around a one million second
observation with EUVE. Although EX Hydrae has been studied previously with
EUVE, our higher signal-to-noise observations present new results and challenge
the current IP models. Previously unseen dips in the light curve are
reminiscent of the stream dips seen in polar light curves. Also of interest is
the temporal extent of the bulge dip; approximately 0.5 in phase, implying that
the bulge extends over half of the accretion disk. We propose that the magnetic
field in EX Hydrae is strong enough (a few MG) to begin pulling material
directly from the outer edge of the disk, thereby forming a large accretion
curtain which would produce a very broad bulge dip. This would also result in
magnetically controlled accretion streams originating from the outer edge of
the disk. We also present a period analysis of the photometric data which shows
numerous beat frequencies with strong power and also intermittent and wandering
frequencies, an indication that physical conditions within EX Hya changed over
the course of the observation. Iron spectral line ratios give a temperature of
log T=6.5-6.9 K for all spin phases and a poorly constrained density of
n_e=10^10-10^11 cm^-3 for the emitting plasma. This paper is the first in a
series detailing our results from this multi-wavelength observational campaign.Comment: 27 pages, 7 figures, accepted for publication in Ap
X-ray and UV observations of V751 Cyg in an optical high state
Aims: The VY Scl system (anti-dwarf nova) V751 Cyg is examined following a
claim of a super-soft spectrum in the optical low state. Methods: A
serendipitous XMM-Newton X-ray observation and, 21 months later, Swift X-ray
and UV observations, have provided the best such data on this source so far.
These optical high-state datasets are used to study the flux and spectral
variability of V751 Cyg. Results: Both the XMM-Newton and Swift data show
evidence for modulation of the X-rays for the first time at the known 3.467 hr
orbital period of V751 Cyg. In two Swift observations, taken ten days apart,
the mean X-ray flux remained unchanged, while the UV source brightened by half
a magnitude. The X-ray spectrum was not super-soft during the optical high
state, but rather due to multi-temperature optically thin emission, with
significant (10^{21-22} cm^-2) absorption, which was higher in the observation
by Swift than that of XMM-Newton. The X-ray flux is harder at orbital minimum,
suggesting that the modulation is related to absorption, perhaps linked to the
azimuthally asymmetric wind absorption seen previously in H-alpha.Comment: 6 pages, 9 figures, accepted for publication in A&
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