83,951 research outputs found
A comparative study of two 47 Tuc giant stars with different s-process enrichment
Here we aim to understand the origin of 47 Tuc's La-rich star Lee 4710. We
report abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Zn, Y, Zr,
Ba, La, Ce, Pr, Nd, and Eu, and present a detailed abundance analysis of two 47
Tuc stars with similar stellar parameters but different slow neutron-capture
(s-)process enrichment. Star Lee 4710 has the highest known La abundance ratio
in this cluster ([La/Fe] = 1.14), and star Lee 4626 is known to have normal
s-process abundances (e.g., [Ba/Eu]). The nucleosynthetic pattern of
elements with Z56 for star Lee 4710 agrees with the predicted yields
of a asymptotic giant branch (AGB) star. Therefore, Lee 4710 may
have been enriched by mass transfer from a more massive AGB companion, which is
compatible with its location far away from the center of this relatively
metal-rich ([Fe/H]) globular cluster. A further analysis comparing
the abundance pattern of Lee 4710 with data available in the literature reveals
that nine out of the 47 Tuc stars previously studied show strong
s-process enhancements that point towards later enrichment by more massive AGB
stars.Comment: ApJL in press. 6 pages, 4 figure
Open charm tomography of cold nuclear matter
We study the relative contribution of partonic sub-processes to D meson
production and D meson-triggered inclusive di-hadrons to lowest order in
perturbative QCD. While gluon fusion dominates the creation of large angle
DD-bar pairs, charm on light parton scattering determines the yield of single
inclusive D mesons. The distinctly different non-perturbative fragmentation of
c quarks into D mesons versus the fragmentation of quarks and gluons into light
hadrons results in a strong transverse momentum dependence of anticharm content
of the away-side charm-triggered jet. In p+A reactions, we calculate and resum
the coherent nuclear-enhanced power corrections from the final state partonic
scattering in the medium. We find that single and double inclusive open charm
production can be suppressed as much as the yield of neutral pions from
dynamical high-twist shadowing. Effects of energy loss in p+A collisions are
also investigated phenomenologically and may lead to significantly weaker
transverse momentum dependence of the nuclear attenuation.Comment: 24 pages, 21 figure
Radio emission from the massive stars in the Galactic Super Star Cluster Westerlund 1
Current mass-loss rate estimates imply that main sequence winds are not
sufficient to strip away the H-rich envelope to yield Wolf-Rayet (WR) stars.
The rich transitional population of Westerlund 1 (Wd 1) provides an ideal
laboratory to observe mass-loss processes throughout the transitional phase of
stellar evolution. An analysis of deep radio continuum observations of Wd 1 is
presented. We detect 18 cluster members. The radio properties of the sample are
diverse, with thermal, non-thermal and composite thermal/non-thermal sources
present. Mass-loss rates are ~10^{-5} solar mass/year across all spectral
types, insufficient to form WRs during a massive star lifetime, and the stars
must undergo a period of enhanced mass loss. The sgB[e] star W9 may provide an
example, with a mass-loss rate an order of magnitude higher than the other
cluster members, and an extended nebula of density ~3 times the current wind.
This structure is reminiscent of luminous blue variables, and one with evidence
of two eras of high, possibly eruptive, mass loss. Three OB supergiants are
detected, implying unusually dense winds. They also may have composite spectra,
suggesting binarity. Spatially resolved nebulae are associated with three of
the four RSGs and three of the six YHGs in the cluster, which are due to
quiescent mass loss rather than outbursts. For some of the cool star winds, the
ionizing source may be a companion star though the cluster radiation density is
sufficiently high to provide the necessary ionizing radiation. Five WR stars
are detected with composite spectra, interpreted as arising in colliding-wind
binaries.Comment: 15 pages, 6 figures. Accepted for publication in Astronomy and
Astrophysic
Varieties and Cropping Practices for 1951
Choosing the right variety of farm crops is one of the essential steps to get maximum crop yields. The results of research in crop breeding and management none make it possible for farmers to remove many of the hazards in crop production
EffiTest: Efficient Delay Test and Statistical Prediction for Configuring Post-silicon Tunable Buffers
At nanometer manufacturing technology nodes, process variations significantly
affect circuit performance. To combat them, post- silicon clock tuning buffers
can be deployed to balance timing bud- gets of critical paths for each
individual chip after manufacturing. The challenge of this method is that path
delays should be mea- sured for each chip to configure the tuning buffers
properly. Current methods for this delay measurement rely on path-wise
frequency stepping. This strategy, however, requires too much time from ex-
pensive testers. In this paper, we propose an efficient delay test framework
(EffiTest) to solve the post-silicon testing problem by aligning path delays
using the already-existing tuning buffers in the circuit. In addition, we only
test representative paths and the delays of other paths are estimated by
statistical delay prediction. Exper- imental results demonstrate that the
proposed method can reduce the number of frequency stepping iterations by more
than 94% with only a slight yield loss.Comment: ACM/IEEE Design Automation Conference (DAC), June 201
The Hidden Spatial Geometry of Non-Abelian Gauge Theories
The Gauss law constraint in the Hamiltonian form of the gauge theory
of gluons is satisfied by any functional of the gauge invariant tensor variable
. Arguments are given that the tensor is a more appropriate variable. When the Hamiltonian
is expressed in terms of or , the quantity appears.
The gauge field Bianchi and Ricci identities yield a set of partial
differential equations for in terms of . One can show that
is a metric-compatible connection for with torsion, and that the curvature
tensor of is that of an Einstein space. A curious 3-dimensional
spatial geometry thus underlies the gauge-invariant configuration space of the
theory, although the Hamiltonian is not invariant under spatial coordinate
transformations. Spatial derivative terms in the energy density are singular
when . These singularities are the analogue of the centrifugal
barrier of quantum mechanics, and physical wave-functionals are forced to
vanish in a certain manner near . It is argued that such barriers are
an inevitable result of the projection on the gauge-invariant subspace of the
Hilbert space, and that the barriers are a conspicuous way in which non-abelian
gauge theories differ from scalar field theories.Comment: 19 pages, TeX, CTP #223
Basic Treatment of QCD Phase Transition Bubble Nucleation
Starting from the QCD Lagrangian and the surface tension of QCD bubbles we
derive the critical size of bubbles, the nucleation probability and the
nucleation site separation distance. We find the separation of sites is more
than an order of magnitude larger than previous QCD model estimates, which
could lead to observable effects.Comment: 8 pages, one figur
IMPACTS OF LIBERALIZING THE JAPANESE PORK MARKET
The Japanese pork market is protected by a complex set of restrictions, including a variable levy and an import tariff. The combination of these policies distorts the quantity, price, and form of Japanese pork imports. An important issue relevant to the liberalization of the Japanese pork market is the accurate measurement of the price wedge between Japanese and world pork prices. The analysis indicates that the tariff equivalent of the price wedge over the 1986-88 period was 44%. If the tariff equivalent of the price wedge is reduced over a ten-year period, Japanese pork imports are projected to increase by over 39% initially and by over 215% compared to baseline projections by the year 2000. Producer welfare can be maintained by a deficiency payment scheme. A less costly alternative is an industry buffer scheme, which maintains the level of the pork industry for two years and then implements a declining deficiency payment scheme that limits the decrease in production levels to 5% per year.International Relations/Trade,
Radio emission from the massive stars in Westerlund 1
The diverse massive stellar population in the young massive clusterWesterlund 1 (Wd 1) provides an ideal laboratory to observe and constrain mass-loss processes throughout the transitional phase of massive star evolution. A set of high sensitivity radio observations of Wd 1 leads to the detection of 18 cluster members, a sample dominated by cool hypergiants, but with detections among hotter OB supergiants and WR stars. Here the diverse radio properties of the detected sample are briefly described. The mass-loss rates of the detected objects are surprisingly similar across the whole transitional phase of massive star evolution, at ~ 10-5 Mo yr−1. Such a rate is insufficient to strip away the H-rich mantle in a massive star lifetime, unless the stars go through a period of enhanced mass-loss. The radio luminous star W9 provides an example of such an object, with evidence for two eras of mass-loss with rates of ~ 10−4 Mo yr−1
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