532 research outputs found
Time transfer by IRIG-B time code via dedicated telephone link
Measurements were made of the stability of time transfer by the IRIG-B code over a dedicated telephone link on a microwave system. The short and long term Allan Variance was measured on both types of microwave system, one of which is synchronized, the other having free local oscillators. The results promise a time transfer accuracy of 10 microns. The paper also describes a prototype slave clock designed to detect interference in the IRIG-B code to ensure local time is kept during such interference
Polarization of Broad Absorption Line QSOs I. A Spectropolarimetric Atlas
We present a spectropolarimetric survey of 36 broad absorption line
quasi-stellar objects (BAL QSOs). The continuum, absorption trough, and
emission line polarization of BAL QSOs yield clues about their structure. We
confirm that BAL QSOs are in general more highly polarized than non-BAL QSOs,
consistent with a more equatorial viewing direction for the former than the
latter. We have identified two new highly-polarized QSOs in our sample
(1232+1325 and 1333+2840). The polarization rises weakly to the blue in most
objects, perhaps due to scattering and absorption by dust particles. We find
that a polarization increase in the BAL troughs is a general property of
polarized BAL QSOs, indicating an excess of scattered light relative to direct
light, and consistent with the unification of BAL QSOs and non-BAL QSOs. We
have also discovered evidence of resonantly scattered photons in the red wing
of the C IV broad emission lines of a few objects. In most cases, the broad
emission lines have lower polarization and a different position angle than the
continuum. The polarization characteristics of low-ionization BAL QSOs are
similar to those of high-ionization BAL QSOs, suggesting a similar BAL wind
geometry.Comment: 39 pages, 6 figures (20 .gif files), accepted for publication in The
Astrophysical Journal Supplement
Digital technology and copyright law
Thesis (S.B.)--Massachusetts Institute of Technology, Program in Science, Technology, and Society, 2002.Includes bibliographical references (p. 88-108).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Intellectual Property is an ideology of the late Twentieth Century which reserves property-like rights in information, so that creators may extract its economic value. Current American copyright law draws mainly from this concept; it has been constructed through history by negotiation between various established economic interests. Information Freedom is a competing ideology which has been successful in the software community. It emphasizes the dangers of over-propertization and the benefits of freely accessible resources, especially non-depletable information resources. Compromise must be reached in a practical (non-ideological) fashion in order to achieve the social goals of: production of creative content (encouraged by fair but not excessive compensation for creators); promotion of scientific, political, technical, artistic, cultural, and economic progress by removing obstacles to accessing content and taking advantage of innovations which change the status quo; protection of creative freedom; and ensuring quality and diversity in the content which is created. Civil disobedience as a means to achieve these goals may be counterproductive if it results in tighter technological restrictions on content availability or stricter legal mechanisms; legal reforms proposed by Lawrence Lessig and Jessica Litman are unlikely to be enacted. Internet-based technologies have strong potential to increase exposure to diversity, decrease costs, and improve the subjective experience for music consumers. Cheaper film-making equipment may have similar positive effects for motion pictures to a lesser degree. Internet bandwidth and other practical limitations suggest that immediate changes in video distribution and consumption patterns are more likely to be driven by the availability of Digital Video Recorders, or perhaps competing Video On Demand services. Different economic models which fund content creation may be appropriate for different applications, and may in some cases further social goals better than strong propertization. Alternative models include voluntary contributions (either from creators or consumers); indirect benefit by establishing reputation, selling related services, cross-promotion, or selling advertising; and public funding. The history of telecommunication, including the telegraph, radio, television, and the Internet, provides evidence that important uses for new technology may not be initially obvious, that the maturation of digital information technology and related economic models is just beginning.by Christopher D. Beland.S.B
A "superstorm": When moral panic and new risk discourses converge in the media
This is an Author's Accepted Manuscript of an article published in Health, Risk and Society, 15(6), 681-698, 2013, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/13698575.2013.851180.There has been a proliferation of risk discourses in recent decades but studies of these have been polarised, drawing either on moral panic or new risk frameworks to analyse journalistic discourses. This article opens the theoretical possibility that the two may co-exist and converge in the same scare. I do this by bringing together more recent developments in moral panic thesis, with new risk theory and the concept of media logic. I then apply this theoretical approach to an empirical analysis of how and with what consequences moral panic and new risk type discourses converged in the editorials of four newspaper campaigns against GM food policy in Britain in the late 1990s. The article analyses 112 editorials published between January 1998 and December 2000, supplemented with news stories where these were needed for contextual clarity. This analysis shows that not only did this novel food generate intense media and public reactions; these developed in the absence of the type of concrete details journalists usually look for in risk stories. Media logic is important in understanding how journalists were able to engage and hence how a major scare could be constructed around convergent moral panic and new risk type discourses. The result was a media âsuperstormâ of sustained coverage in which both types of discourse converged in highly emotive mutually reinforcing ways that resonated in a highly sensitised context. The consequence was acute anxiety, social volatility and the potential for the disruption of policy and social change
Evidence for a companion to BM Gem, a silicate carbon star
Balmer and Paschen continuum emission as well as Balmer series lines of P
Cygni-type profile from H_gamma through H_23 are revealed in the violet spectra
of BM Gem, a carbon star associated with an oxygen-rich circumstellar shell
(`silicate carbon star') observed with the high dispersion spectrograph (HDS)
on the Subaru telescope. The blue-shifted absorption in the Balmer lines
indicates the presence of an outflow, the line of sight velocity of which is at
least 400 km s^-1, which is the highest outflow velocity observed to date in a
carbon star. We argue that the observed unusual features in BM Gem are strong
evidence for the presence of a companion, which should form an accretion disk
that gives rise to both an ionized gas region and a high velocity, variable
outflow. The estimated luminosity of ~0.2 (0.03-0.6) L_sun for the ionized gas
can be maintained by a mass accretion rate to a dwarf companion of ~10^-8 M_sun
yr^-1, while ~10^-10 M_sun yr^-1 is sufficient for accretion to a white dwarf
companion. These accretion rates are feasible for some detached binary
configurations on the basis of the Bond-Hoyle type accretion process. We
concluded that the carbon star BM Gem is in a detached binary system with a
companion of low mass and low luminosity. However, we are unable to determine
whether this companion object is a dwarf or a white dwarf. The upper limits for
binary separation are 210 AU and 930 AU for a dwarf and a white dwarf,
respectively. We also note that the observed features of BM Gem mimic those of
Mira (omi Cet), which may suggest actual similarities in their binary
configurations and circumstellar structures.Comment: 11 pages, 2 figures, 1 table, accepted for publication in Ap
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs
We describe the design and performance of the near-infrared (1.51--1.70
micron), fiber-fed, multi-object (300 fibers), high resolution (R =
lambda/delta lambda ~ 22,500) spectrograph built for the Apache Point
Observatory Galactic Evolution Experiment (APOGEE). APOGEE is a survey of ~
10^5 red giant stars that systematically sampled all Milky Way populations
(bulge, disk, and halo) to study the Galaxy's chemical and kinematical history.
It was part of the Sloan Digital Sky Survey III (SDSS-III) from 2011 -- 2014
using the 2.5 m Sloan Foundation Telescope at Apache Point Observatory, New
Mexico. The APOGEE-2 survey is now using the spectrograph as part of SDSS-IV,
as well as a second spectrograph, a close copy of the first, operating at the
2.5 m du Pont Telescope at Las Campanas Observatory in Chile. Although several
fiber-fed, multi-object, high resolution spectrographs have been built for
visual wavelength spectroscopy, the APOGEE spectrograph is one of the first
such instruments built for observations in the near-infrared. The instrument's
successful development was enabled by several key innovations, including a
"gang connector" to allow simultaneous connections of 300 fibers; hermetically
sealed feedthroughs to allow fibers to pass through the cryostat wall
continuously; the first cryogenically deployed mosaic volume phase holographic
grating; and a large refractive camera that includes mono-crystalline silicon
and fused silica elements with diameters as large as ~ 400 mm. This paper
contains a comprehensive description of all aspects of the instrument including
the fiber system, optics and opto-mechanics, detector arrays, mechanics and
cryogenics, instrument control, calibration system, optical performance and
stability, lessons learned, and design changes for the second instrument.Comment: 81 pages, 67 figures, PASP, accepte
On the progenitor of SN 2005gl and the nature of Type IIn supernovae
We present a study of the type IIn supernova (SN) 2005gl, in the relatively
nearby (d~66 Mpc) galaxy NGC 266. Photometry and spectroscopy of the SN
indicate it is a typical member of its class. Pre-explosion Hubble Space
Telescope (HST) imaging of the location of the SN, along with a precise
localization of this event using the Laser-Guide-Star assisted Adaptive Optics
(LGS-AO) system at Keck Observatory, are combined to identify a luminous
(M_V=-10.3) point source as the possible progenitor of SN 2005gl. If the source
is indeed a single star, it was likely a member of the class of luminous blue
variable stars (LBVs). This finding leads us to consider the possible general
association of SNe IIn with LBV progenitors. We find this is indeed supported
by observations of other SNe, and the known properties of LBV stars. For
example, we argue that should the prototypical Galactic LBV eta Carina explode
in a phase similar to its current state, it will likely produce a type IIn SN.
We discuss our findings in the context of current ideas about the evolution of
massive stars, and review the census of SNe with identified progenitors. We
introduce the concept of the progenitor-SN map as a convenient means to discuss
the present status and future prospects of direct searches for SN progenitors.
We conclude that this field has matured considerably in recent years, and the
transition from anecdotal information about rare single events to robust
associations of progenitor classes with specific SN types has already begun.Comment: Submitted to ApJ. Comments welcom
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