Optical frequency tripling with improved suppression and sideband selection

Journal Article, Impact factor:3.749A novel optical dispersion tolerant millimetre-wave radio-over-fibre system using optical frequency tripling technique with enhanced and selectable sideband suppression is demonstrated. The implementation utilises cascaded optical modulators to achieve either an optical single sideband (OSSB) or double sideband-suppressed carrier (DSB-SC) signal with high sideband suppression. Our analysis and simulation results indicate that the achievable suppression ratio of this configuration is only limited by other system factors such as optical noise and drifting of the operational conditions. The OSSB transmission system performance is assessed experimentally by the transport of 4 WiMax channels modulating a 10 GHz optical upconverted RF carrier as well as for optical frequency doubling and tripling. The 10 GHz and tripled carrier at 30 GHz are dispersion tolerant resulting both in an average relative constellation error (RCE) of -28.7 dB after 40 km of fibre. (C)2011 Optical Society of AmericaFundação para a Ciência e Tecnologi

Keck IR Spectroscopy of WZ Sge: Detection of Molecular Emission from the Accretion Disk

Time-resolved IR spectroscopy of WZ Sge was obtained using NIRSPEC on Keck II. We detect CO and H$_{\rm 2}$ emission from the accretion disk placing WZ Sge into a rarefied class of astronomical objects including YSOs and high luminosity early-type stars. During the eclipse phase, the molecular emission greatly weakens but no firm evidence for the secondary star is seen allowing new limits on its luminosity to be determined. The detection of molecular emission provides physical properties within the outer disk of T=3000K and N$_H$$>10^{10}$ cm$^{-3}$. Such a cool, dense region, not associated with areas of H I and He I emission, provides the first observational confirmation of predictions made by accretion disk models.Comment: 10 pages, 3 figures. Accepted for publication in ApJ Letter

V3885 Sagittarius: a Comparison with a Range of Standard Model Accretion Disks

A $\widetilde{\chi}^2$ analysis of standard model accretion disk synthetic spectrum fits to combined $FUSE$ and STIS spectra of V3885 Sagittarius, on an absolute flux basis, selects a model that accurately represents the observed SED. Calculation of the synthetic spectrum requires the following system parameters. The cataclysmic variable secondary star period-mass relation calibrated by Knigge in 2007 sets the secondary component mass. A mean white dwarf (WD) mass from the same study, that is consistent with an observationally-determined mass ratio, sets the adopted WD mass of $0.7M_{\odot}$, and the WD radius follows from standard theoretical models. The adopted inclination, i=65{\arcdeg}, is a literature consensus, and is subsequently supported by $\widetilde{\chi}^2$ analysis. The mass transfer rate is the remaining parameter to set the accretion disk $T_{\rm eff}$ profile, and the $Hipparcos$ parallax constrains that parameter to $\dot{M}=5.0{\pm}2.0{\times}10^{-9} M_{\odot} {\rm yr}^{-1}$ by a comparison with observed spectra. The fit to the observed spectra adopts the contribution of a $57,000{\pm}5000$K WD. The model thus provides realistic constraints on $\dot{M}$ and $T_{\rm eff}$ for a large $\dot{M}$ system above the period gap.Comment: 41 pages, 7 figures, 9 tables. Astrophysical Journal (accepted

GALEX and Optical Light Curves of EF Eridanus During a Low State: the Puzzling Source of UV Light

Low state optical photometry of EF Eri during an extended low accretion state combined with GALEX near and far UV time-resolved photometry reveals a source of UV flux that is much larger than the underlying 9500K white dwarf, and that is highly modulated on the orbital period. The near UV and optical light curves can be modeled with a 20,000K spot but no spot model can explain both the large amplitude FUV variations and the SED. The limitations of limb darkening, cyclotron and magnetic white dwarf models in explaining the observations are discussed.Comment: 10 pages, 4 figures to be published in ApJ Letter

Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Nova-like BB Doradus

We present an analysis of the Far Ultraviolet Spectroscopic Explorer ({\it{FUSE}}) spectra of the little-known southern nova-like BB Doradus. The spectrum was obtained as part of our Cycle 8 {\it FUSE} survey of high declination nova-like stars. The FUSE spectrum of BB Dor, observed in a high state, is modeled with an accretion disk with a very low inclination (possibly lower than 10deg). Assuming an average WD mass of 0.8 solar leads to a mass accretion rate of 1.E-9 Solar mass/year and a distance of the order of 650 pc, consistent with the extremely low galactic reddening in its direction. The spectrum presents some broad and deep silicon and sulfur absorption lines, indicating that these elements are over-abundant by 3 and 20 times solar, respectively

Associate inverse subsemigroups of regular semigroups

By an associate inverse subsemigroup of a regular semigroup S we mean a subsemigroup T of S containing a least associate of each x ∈ S, in relation to the natural partial order ≤S. We describe the structure of a regular semigroup with an associate inverse subsemigroup, satisfying two natural conditions. As a articular application, we obtain the structure of regular semigroups with an associate subgroup with medial identity element.Fundação para a Ciência e a Tecnologia (FCT

Videotaping Children\u27s Testimony: An Empirical View

Increases in the number of reported incidents of child abuse and sexual molestation have resulted in more and younger children becoming courtroom participants. Some courts refuse to consider the special needs of the child in this adversarial environment. Relying on questionable precedent, these courts hold that the defendant\u27s right to directly confront the child, as well as strict compliance with evidentiary rules, overrides that child\u27s interest in freedom from embarrassment or psychological trauma. This Note focuses on pressures felt by the testifying child and the ways in which these pressures affect her testimony; it then proposes using videotaped testimony as a means of overcoming such pressures. Part I reviews the psychological research undertaken in conjunction with this Note and concludes that, as compared to a courtroom setting, the quality and reliability of children\u27s testimony is significantly enhanced in a smaller, more intimate videotape environment. Based in part on such findings, this Note argues that using videotape technology to capture and portray in court the child witness\u27 testimony serves both to lessen emotional trauma to the child and to maintain a fair trial for the defendant. Part I concludes by calling for regular use of videotapes to present children\u27s testimony. Part II focuses on the defendant\u27s sixth amendment right to confrontation as developed by the United States Supreme Court, other federal appellate courts, and state courts. An analysis of these decisions reveals that the right to face one\u27s accuser is far from absolute: the confrontation clause is peppered with exceptions based on policies which embrace the use of videotaped testimony in child sexual abuse cases. This Note concludes that when properly introduced, a child\u27s videotaped testimony will not infringe on the defendant\u27s right to confrontation