31,244 research outputs found
Ending Child Marriage in a Generation: What Research is Needed?
In recent years, the obstacles that child marriage poses to development and to the achievement of the Millennium Development Goals have been widely recognized. Varied responses to the problem have been devised. The number of programs testing different approaches to ending child marriage has grown, and many have been evaluated. We are starting to get a sense of what works and the general areas in which investing in research could make a difference.The purpose of this paper is to identify gaps in the research on child marriage in which additional investment could catalyze change. Much remains to understand about child marriage and how to influence it. By mapping out current knowledge of child marriage and the programs designed to address it, and by highlighting questions to which we do not yet know the answers, the paper is intended to generate discussion in the field and clarify what we need to know to bring an end to this deeply harmful practice.The paper also moves us closer to the development of a shared theory of change for this field: given that many organizations are now working in this area, how can their programs and related research be understood -- aligned -- in such a way that their work feeds into a single theory of change?The research gaps on their own should not drive investments in child marriage. A worthy research mandate must also be driven by programmatic and advocacy needs. The recommended areas for research are not meant to provide a definitive menu, but rather to describe the general contours of what we know and what we need to understand better
Performance evaluation of a class of systematic, rate (M-1)/M, convolutional codes
The implementation and performance evaluation are described for a class of rate (M-1)/M, systematic, convolutional codes being decoded with a simple majority logic decoder. The encoding logic appends one parity bit for each PCM telemetry word. It is shown that over the critical range of received PCM telemetry signal-to-noise ratios, this coding procedure produces a net coding gain of from 1.5 to 2.5 db relative to an equal power transmission of uncoded PCM telemetry. Being a low-redundancy systematic code, it is possible to process this data without convolutional decoding with a small rate loss penalty of about 0.5 db
Dwarf Galaxies with Optical Signatures of Active Massive Black Holes
We present a sample of 151 dwarf galaxies (10^8.5 < M_stellar < 10^9.5 Msun)
that exhibit optical spectroscopic signatures of accreting massive black holes
(BHs), increasing the number of known active galaxies in this stellar mass
range by more than an order of magnitude. Utilizing data from the Sloan Digital
Sky Survey Data Release 8 and stellar masses from the NASA-Sloan Atlas, we have
systematically searched for active BHs in ~25,000 emission-line galaxies with
stellar masses comparable to the Magellanic Clouds and redshifts z<0.055. Using
the narrow-line [OIII]/H-beta versus [NII]/H-alpha diagnostic diagram, we find
photoionization signatures of BH accretion in 136 galaxies, a small fraction of
which also exhibit broad H-alpha emission. For these broad-line AGN candidates,
we estimate BH masses using standard virial techniques and find a range of 10^5
< M_BH < 10^6 Msun and a median of M_BH ~ 2 x 10^5 Msun. We also detect broad
H-alpha in 15 galaxies that have narrow-line ratios consistent with
star-forming galaxies. Follow-up observations are required to determine if
these are true type 1 AGN or if the broad H-alpha is from stellar processes.
The median absolute magnitude of the host galaxies in our active sample is Mg =
-18.1 mag, which is ~1-2 magnitudes fainter than previous samples of AGN hosts
with low-mass BHs. This work constrains the smallest galaxies that can form a
massive BH, with implications for BH feedback in low-mass galaxies and the
origin of the first supermassive BH seeds.Comment: 26 pages, 15 figures, 6 tables. Accepted for publication in The
Astrophysical Journa
Active Galaxies and the Study of Black Hole Demographics
We discuss the critical importance of black hole mass indicators based on
scaling relations in active galaxies. We highlight outstanding uncertainties in
these methods and potential paths to substantial progress in the next decade.Comment: 4 pages, 1 figure, Invited review to appear in PAS
Offset Active Galactic Nuclei as Tracers of Galaxy Mergers and Supermassive Black Hole Growth
Offset active galactic nuclei (AGNs) are AGNs that are in ongoing galaxy
mergers, which produce kinematic offsets in the AGNs relative to their host
galaxies. Offset AGNs are also close relatives of dual AGNs. We conduct a
systematic search for offset AGNs in the Sloan Digital Sky Survey, by selecting
AGN emission lines that exhibit statistically significant line-of-sight
velocity offsets relative to systemic. From a parent sample of 18314 Type 2
AGNs at z<0.21, we identify 351 offset AGN candidates with velocity offsets of
50 km/s < |v| < 410 km/s. When we account for projection effects in the
observed velocities, we estimate that 4% - 8% of AGNs are offset AGNs. We
designed our selection criteria to bypass velocity offsets produced by rotating
gas disks, AGN outflows, and gravitational recoil of supermassive black holes,
but follow-up observations are still required to confirm our candidates as
offset AGNs. We find that the fraction of AGNs that are offset candidates
increases with AGN bolometric luminosity, from 0.7% to 6% over the luminosity
range 43 < log(L_bol) [erg/s] < 46. If these candidates are shown to be bona
fide offset AGNs, then this would be direct observational evidence that galaxy
mergers preferentially trigger high-luminosity AGNs. Finally, we find that the
fraction of AGNs that are offset AGN candidates increases from 1.9% at z=0.1 to
32% at z=0.7, in step with the growth in the galaxy merger fraction over the
same redshift range.Comment: 14 pages, 14 figures, accepted for publication in Ap
Satellite altimeters after Skylab and GEOS-C - should they utilize a single transmitter or an array of pulsed amplifiers?
An attempt was made to determine if future satellite altimeters, operating at K-band, should use a single transmitter or an array of pulsed amplifiers. The two systems were compared as a function of reliability, power, service life, system requirements, and weight. Preliminary results indicate the modular system to be superior in service life and reliability although it requires more power and is substantially heavier than the single system. No concrete conclusions were reached as to which system should be used
The Riemann mapping theorem from Riemann's viewpoint
This article presents a clear proof of the Riemann Mapping Theorem via
Riemann's method, uncompromised by any appeals to topological intuition.Comment: 14 pages, 2 figure
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