3,570 research outputs found
A Study of the Dark Core in A520 with Hubble Space Telescope: The Mystery Deepens
We present a Hubble Space Telescope/Wide Field Planetary Camera 2
weak-lensing study of A520, where a previous analysis of ground-based data
suggested the presence of a dark mass concentration. We map the complex mass
structure in much greater detail leveraging more than a factor of three
increase in the number density of source galaxies available for lensing
analysis. The "dark core" that is coincident with the X-ray gas peak, but not
with any stellar luminosity peak is now detected with more than 10 sigma
significance. The ~1.5 Mpc filamentary structure elongated in the NE-SW
direction is also clearly visible. Taken at face value, the comparison among
the centroids of dark matter, intracluster medium, and galaxy luminosity is at
odds with what has been observed in other merging clusters with a similar
geometric configuration. To date, the most remarkable counter-example might be
the Bullet Cluster, which shows a distinct bow-shock feature as in A520, but no
significant weak-lensing mass concentration around the X-ray gas. With the most
up-to-date data, we consider several possible explanations that might lead to
the detection of this peculiar feature in A520. However, we conclude that none
of these scenarios can be singled out yet as the definite explanation for this
puzzle.Comment: Published in ApJ. Figures are slightly degraded to meet the size
limi
Dynamic Pricing in the Presence of Antidumping Policy: Theory and Evidence
Antidumping (AD) duties are calculated as the difference between the foreign firm's product price in the export market and some definition of 'normal' or 'fair' value, often the foreign firm's product price in its own market. Additionally, AD laws allow for recalculation of these AD duties over time in what are known as administrative reviews. This paper examines for the first time the resulting dynamic pricing problem of a foreign firm that faces such an AD trade protection policy in its export market. When AD duties are certain for any dumping that occurs, we obtain the surprising result that dumping and AD duties should increase over time toward a stationary equilibrium value. Adding uncertainties prevalent in AD enforcement into our analysis changes these conclusions substantially and leads to more realistic testable implications. Firms with ex ante expectations that the probability of AD enforcement is low, or with expectations that the probability of a termination/VER (instead of AD duties) is high, will decrease their dumping and AD duties over time in the administrative review process once they face AD duties. Using detailed data from U.S. AD investigations filed from 1980-1995, we find evidence consistent with these hypotheses stemming from our analysis with uncertain AD enforcement and provide empirical evidence consistent with James Anderson's domino dumping hypothesis.
Two-Photon Pathway to Ultracold Ground State Molecules of NaK
We report on high-resolution spectroscopy of ultracold fermionic
\nak~Feshbach molecules, and identify a two-photon pathway to the rovibrational
singlet ground state via a resonantly mixed \Bcres intermediate state.
Photoassociation in a Na-K atomic mixture and one-photon
spectroscopy on \nak~Feshbach molecules reveal about 20 vibrational levels of
the electronically excited \ctrip state. Two of these levels are found to be
strongly perturbed by nearby \Bsing states via spin-orbit coupling, resulting
in additional lines of dominant singlet character in the perturbed complex
{}, or of
resonantly mixed character in {}. The dominantly singlet level is used to locate
the absolute rovibrational singlet ground state via Autler-Townes spectroscopy. We demonstrate coherent
two-photon coupling via dark state spectroscopy between the predominantly
triplet Feshbach molecular state and the singlet ground state. Its binding
energy is measured to be 5212.0447(1) \cm, a thousand-fold improvement in
accuracy compared to previous determinations. In their absolute singlet ground
state, \nak~molecules are chemically stable under binary collisions and possess
a large electric dipole moment of Debye. Our work thus paves the way
towards the creation of strongly dipolar Fermi gases of NaK molecules.Comment: 23 pages, 8 figure
Ultracold Dipolar Gas of Fermionic NaK Molecules in their Absolute Ground State
We report on the creation of an ultracold dipolar gas of fermionic
NaK molecules in their absolute rovibrational and hyperfine
ground state. Starting from weakly bound Feshbach molecules, we demonstrate
hyperfine resolved two-photon transfer into the singlet ground state, coherently bridging a binding energy
difference of 0.65 eV via stimulated rapid adiabatic passage. The
spin-polarized, nearly quantum degenerate molecular gas displays a lifetime
longer than 2.5 s, highlighting NaK's stability against two-body chemical
reactions. A homogeneous electric field is applied to induce a dipole moment of
up to 0.8 Debye. With these advances, the exploration of many-body physics with
strongly dipolar Fermi gases of NaK molecules is in experimental
reach.Comment: 5 pages, 5 figure
Criteria for formation of metallic glasses: The role of atomic size ratio
We consider metallic alloys of Cu*, Cu, and Cu** in which the atoms differ only in their atomic radii and examine how the size ratio affects the local orders in the alloy systems. These studies use molecular dynamics simulations in which the atomic interactions are modeled with a Sutton–Chen many-body potential. Considering rapid cooling of these binary and ternary alloys from the melt, we find three regimes defined by the magnitude of atomic size ratio lambda (lambda<=1.0): with (i) large size ratios of 0.95<lambda<=1.0, crystallization occurs; (ii) with moderate size ratios of 0.60<=lambda<=0.95, a glass phase forms; and (iii) with small size ratios of lambda<0.60, the alloy phase separates into pure phases and crystallize. From analyzing the structures of these binary and ternary alloys, we find that the liquid phase is characterized by local structures in which bonded atoms have local fivefold symmetry, which becomes more prominent as the glass phase forms. For phases that crystallize this local fivefold symmetry disappears as the long-range order of the crystalline phase dominates. The fivefold symmetry in the glass phase is mainly due to the icosahedral cluster formation. Energetically, the formation of icosahedral cluster is favored at the atomic size ratio of lambda~0.85, which is close to the lambda at which our analyses shows the maximum in the fivefold symmetry and the number of icosahedral clusters. As lambda decreases further, the phase separation is observed. The fivefold symmetry character and the number of icosahedral cluster shows the local minimum at this onset of the phase separation
MC: Multi-wavelength and dynamical analysis of the merging galaxy cluster ZwCl 0008.8+5215: An older and less massive Bullet Cluster
We analyze a rich dataset including Subaru/SuprimeCam, HST/ACS and WFC3,
Keck/DEIMOS, Chandra/ACIS-I, and JVLA/C and D array for the merging galaxy
cluster ZwCl 0008.8+5215. With a joint Subaru/HST weak gravitational lensing
analysis, we identify two dominant subclusters and estimate the masses to be
M
and 1.2 M. We estimate the
projected separation between the two subclusters to be
924 kpc. We perform a clustering analysis on
confirmed cluster member galaxies and estimate the line of sight velocity
difference between the two subclusters to be 92164 km s. We
further motivate, discuss, and analyze the merger scenario through an analysis
of the 42 ks of Chandra/ACIS-I and JVLA/C and D polarization data. The X-ray
surface brightness profile reveals a remnant core reminiscent of the Bullet
Cluster. The X-ray luminosity in the 0.5-7.0 keV band is
1.70.110 erg s and the X-ray
temperature is 4.900.13 keV. The radio relics are polarized up to 40.
We implement a Monte Carlo dynamical analysis and estimate the merger velocity
at pericenter to be 1800 km s. ZwCl
0008.8+5215 is a low-mass version of the Bullet Cluster and therefore may prove
useful in testing alternative models of dark matter. We do not find significant
offsets between dark matter and galaxies, as the uncertainties are large with
the current lensing data. Furthermore, in the east, the BCG is offset from
other luminous cluster galaxies, which poses a puzzle for defining dark matter
-- galaxy offsets.Comment: 22 pages, 19 figures, accepted for publication in the Astrophysical
Journal on March 13, 201
Coherent Microwave Control of Ultracold NaK Molecules
We demonstrate coherent microwave control of rotational and hyperfine states
of trapped, ultracold, and chemically stable NaK molecules.
Starting with all molecules in the absolute rovibrational and hyperfine ground
state, we study rotational transitions in combined magnetic and electric fields
and explain the rich hyperfine structure. Following the transfer of the entire
molecular ensemble into a single hyperfine level of the first rotationally
excited state, , we observe collisional lifetimes of more than , comparable to those in the rovibrational ground state, . Long-lived
ensembles and full quantum state control are prerequisites for the use of
ultracold molecules in quantum simulation, precision measurements and quantum
information processing.Comment: 5 pages, 4 figure
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
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