21,273 research outputs found
Improving Lexical Choice in Neural Machine Translation
We explore two solutions to the problem of mistranslating rare words in
neural machine translation. First, we argue that the standard output layer,
which computes the inner product of a vector representing the context with all
possible output word embeddings, rewards frequent words disproportionately, and
we propose to fix the norms of both vectors to a constant value. Second, we
integrate a simple lexical module which is jointly trained with the rest of the
model. We evaluate our approaches on eight language pairs with data sizes
ranging from 100k to 8M words, and achieve improvements of up to +4.3 BLEU,
surpassing phrase-based translation in nearly all settings.Comment: Accepted at NAACL HLT 201
High temperature refractory member with radiation emissive overcoat
A radiation type heat dissipator for use in a plasma engine is formed of a refractory metal layer upon which there is deposited a radiation emissive coating made of a high emissivity material such as zirconium diboride. The radiation emissive coating has a surface emissivity coefficient substantially greater than the emissivity coefficient of the refractory metal and thereby enhances the optical radiating efficiency of the heat dissipator
An approximation scheme for quasi-stationary distributions of killed diffusions
In this paper we study the asymptotic behavior of the normalized weighted
empirical occupation measures of a diffusion process on a compact manifold
which is killed at a smooth rate and then regenerated at a random location,
distributed according to the weighted empirical occupation measure. We show
that the weighted occupation measures almost surely comprise an asymptotic
pseudo-trajectory for a certain deterministic measure-valued semiflow, after
suitably rescaling the time, and that with probability one they converge to the
quasi-stationary distribution of the killed diffusion. These results provide
theoretical justification for a scalable quasi-stationary Monte Carlo method
for sampling from Bayesian posterior distributions.Comment: v2: revised version, 29 pages, 1 figur
The NASA Electric Propulsion Program
The NASA OAST Propulsion, Power, and Energy Division supports an electric propulsion program aimed at providing benefits to a broad class of missions. Concepts which have the potential to enable or significantly benefit space exploration and exploitation are identified and advanced toward application in the near and far term. This paper summarizes recent program progress in mission/system analysis; in electrothermal, electrostatic, and electromagnetic propulsion technologies; and in propulsion/spacecraft integration
Energy-Efficient Transmission Scheduling with Strict Underflow Constraints
We consider a single source transmitting data to one or more receivers/users
over a shared wireless channel. Due to random fading, the wireless channel
conditions vary with time and from user to user. Each user has a buffer to
store received packets before they are drained. At each time step, the source
determines how much power to use for transmission to each user. The source's
objective is to allocate power in a manner that minimizes an expected cost
measure, while satisfying strict buffer underflow constraints and a total power
constraint in each slot. The expected cost measure is composed of costs
associated with power consumption from transmission and packet holding costs.
The primary application motivating this problem is wireless media streaming.
For this application, the buffer underflow constraints prevent the user buffers
from emptying, so as to maintain playout quality. In the case of a single user
with linear power-rate curves, we show that a modified base-stock policy is
optimal under the finite horizon, infinite horizon discounted, and infinite
horizon average expected cost criteria. For a single user with piecewise-linear
convex power-rate curves, we show that a finite generalized base-stock policy
is optimal under all three expected cost criteria. We also present the
sequences of critical numbers that complete the characterization of the optimal
control laws in each of these cases when some additional technical conditions
are satisfied. We then analyze the structure of the optimal policy for the case
of two users. We conclude with a discussion of methods to identify
implementable near-optimal policies for the most general case of M users.Comment: 109 pages, 11 pdf figures, template.tex is main file. We have
significantly revised the paper from version 1. Additions include the case of
a single receiver with piecewise-linear convex power-rate curves, the case of
two receivers, and the infinite horizon average expected cost proble
A catalogue of integrated H-alpha fluxes for 1,258 Galactic planetary nebulae
We present a catalogue of new integrated H-alpha fluxes for 1258 Galactic
planetary nebulae (PNe), with the majority, totalling 1234, measured from the
Southern H-Alpha Sky Survey Atlas (SHASSA) and/or the Virginia Tech
Spectral-line Survey (VTSS). Aperture photometry on the continuum-subtracted
digital images was performed to extract H-alpha + [NII] fluxes in the case of
SHASSA, and H-alpha fluxes from VTSS. The [NII] contribution was then
deconvolved from the SHASSA flux using spectrophotometric data taken from the
literature or derived by us. Comparison with previous work shows that the flux
scale presented here has no significant zero-point error. Our catalogue is the
largest compilation of homogeneously derived PN fluxes in any waveband yet
measured, and will be an important legacy and fresh benchmark for the
community. Amongst its many applications, it can be used to determine
statistical distances for these PNe, determine new absolute magnitudes for
delineating the faint end of the PN luminosity function, provide baseline data
for photoionization and hydrodynamical modelling, and allow better estimates of
Zanstra temperatures for PN central stars with accurate optical photometry. We
also provide total H-alpha fluxes for another 75 objects which were formerly
classified as PNe, as well as independent reddening determinations for ~270
PNe, derived from a comparison of our H-alpha data with the best literature
H-beta fluxes. In an appendix, we list corrected H-alpha fluxes for 49 PNe
taken from the literature, including 24 PNe not detected on SHASSA or VTSS,
re-calibrated to a common zero-point.Comment: 49 pages, 7 figures, 10 tables, to appear in MNRAS. This version
includes full-length tables 1 and
- …