7,687 research outputs found
On Toroidal Horizons in Binary Black Hole Inspirals
We examine the structure of the event horizon for numerical simulations of
two black holes that begin in a quasicircular orbit, inspiral, and finally
merge. We find that the spatial cross section of the merged event horizon has
spherical topology (to the limit of our resolution), despite the expectation
that generic binary black hole mergers in the absence of symmetries should
result in an event horizon that briefly has a toroidal cross section. Using
insight gained from our numerical simulations, we investigate how the choice of
time slicing affects both the spatial cross section of the event horizon and
the locus of points at which generators of the event horizon cross. To ensure
the robustness of our conclusions, our results are checked at multiple
numerical resolutions. 3D visualization data for these resolutions are
available for public access online. We find that the structure of the horizon
generators in our simulations is consistent with expectations, and the lack of
toroidal horizons in our simulations is due to our choice of time slicing.Comment: Submitted to Phys. Rev.
Symmetry-Breaking and Symmetry-Restoring Dynamics of a Mixture of Bose-Einstein Condensates in a Double Well
We study the coherent nonlinear tunneling dynamics of a binary mixture of
Bose-Einstein condensates in a double-well potential. We demonstrate the
existence of a new type of mode associated with the "swapping" of the two
species in the two wells of the potential. In contrast to the symmetry breaking
macroscopic quantum self-trapping (MQST) solutions, the swapping modes
correspond to the tunneling dynamics that preserves the symmetry of the double
well potential. As a consequence of two distinct types of broken symmetry MQST
phases where the two species localize in the different potential welils or
coexist in the same well, the corresponding symmetry restoring swapping modes
result in dynamics where the the two species either avoid or chase each other.
In view of the possibility to control the interaction between the species, the
binary mixture offers a very robust system to observe these novel effects as
well as the phenomena of Josephson oscillations and pi-mode
Magellan/M2FS Spectroscopy of Galaxy Clusters: Stellar Population Model and Application to Abell 267
We report the results of a pilot program to use the Magellan/M2FS
spectrograph to survey the galactic populations and internal kinematics of
galaxy clusters. For this initial study, we present spectroscopic measurements
for quiescent galaxies observed along the line of sight to the galaxy
cluster Abell 267 (). We develop a Bayesian method for modeling the
integrated light from each galaxy as a simple stellar population, with free
parameters that specify redshift () and characteristic age,
metallicity (), alpha-abundance (), and
internal velocity dispersion () for individual galaxies.
Parameter estimates derived from our 1.5-hour observation of A267 have median
random errors of ,
, $\sigma_{\mathrm{[Fe/H]}}=0.11\
\mathrm{dex}\sigma_{[\alpha/\mathrm{Fe}]}=0.07\ \mathrm{dex}\sigma_{\sigma_\mathrm{int}}=20\ \mathrm{km\ s^{-1}}$. In a companion paper,
we use these results to model the structure and internal kinematics of A267.Comment: 16 pages, 11 figures, accepted for publication in The Astronomical
Journa
CRT-129 Outcomes in Chronic Kidney Disease Patients Treated for Coronary Arterial Disease Utilizing the Orbital Atherectomy System: An ORBIT II Sub-Analysis
Shaper Nations: Stategies for a Changing World
Shaper Nations provides illuminating perspectives on the national strategies of eight emerging and established countries that are shaping global politics at the beginning of the twenty-first century. The volume’s authors offer a unique viewpoint: they live and work primarily in the country about which they write, bringing an insider’s feel for national debates and politics.
The conventional wisdom on national strategy suggests that these states have clear central authority, coherently connect means to ends, and focus on their geopolitical environment. These essays suggest a different conclusion. In seven key countries―Brazil, China, Germany, India, Israel, Russia, and Turkey―strategy is dominated by nonstate threats, domestic politics, the distorting effect of history and national identity, economic development concerns, and the sheer difficulty, in the face of many powerful internal and external constraints, of pursuing an effective national strategy.
The shapers represent a new trend in the international arena with important consequences. Among them is a more uncertain world in which countries concentrate on their own development rather than on shared problems that might divert precious resources, and attend more to regional than to global order. In responding to these shaper states, the United States must understand the sources of their national strategies in determining its own role on the global stage.https://scholarship.richmond.edu/bookshelf/1274/thumbnail.jp
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