10,767 research outputs found
The Pliocene closure fo the Central American Seaway : reconstructing surface-, intermediate- and deep-water connections
Timing of Gateway Closure
The shoaling of the Isthmus of Panama and the associated reorganisation of deep-ocean circulation have been controversially reported as contributing to both a warming and a cooling of global climate. A resulting increase in moisture supply to the northern hemisphere, through the initiation or strengthening of the Gulf Stream, may have been an important precondition for Northern Hemisphere Glaciation. A robust timeframe for the closure of this major ocean gateway is essential for understanding its direct and indirect effects on global climate.
Method
We use radiogenic isotopes of Nd and Pb to reconstruct the history of shallow, intermediate and deep water connections between the Caribbean Sea and the eastern Equatorial Pacific Ocean from 5.0 to 2.0 million years ago. Surface water exchange is characterised using the Nd isotope composition of planktonic foraminiferal calcite. The Nd and Pb isotope compositions of early diagenetic ferromanganese coatings of the same sediment samples are employed to reconstruct intermediate and deep water exchange.
Results and Conclusion
Our results indicate that Caribbean Intermediate Water continued to diverge from a relatively constant Pacific deepwater Nd composition from 5.0 to 2.0 Ma. Comparison with published stable isotope and Mg/Ca records from the same ODP Sites 999, 1000 and 1241 suggest that Caribbean Intermediate Water composition continued to change even after a decrease in surface water exchange with the Pacific (4.5 Ma onwards [1]). A more rapid restriction of mixing between the Pacific and Caribbean at intermediate depths from 4 to 3.5 Ma clearly preceeded the major increase in ice-rafted-debris north of Iceland [2].
[1] Groeneveld et al. (2008) G3 9, Q01P23.
[2] Jansen et al. (2000) Paleoceanography 15, 709-721
Stabilizability and percolation in the infinite volume sandpile model
We study the sandpile model in infinite volume on . In
particular, we are interested in the question whether or not initial
configurations, chosen according to a stationary measure , are
-almost surely stabilizable. We prove that stabilizability does not depend
on the particular procedure of stabilization we adopt. In and a
product measure with density (the known critical value for
stabilizability in ) with a positive density of empty sites, we prove that
is not stabilizable. Furthermore, we study, for values of such
that is stabilizable, percolation of toppled sites. We find that for
small enough, there is a subcritical regime where the distribution of
a cluster of toppled sites has an exponential tail, as is the case in the
subcritical regime for ordinary percolation.Comment: Published in at http://dx.doi.org/10.1214/08-AOP415 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Intertemporal Equilibria with Knightian Uncertainty
We study a dynamic and infinite-dimensional model with Knightian uncertainty modeled by incomplete multiple prior preferences. In interior efficient allocations, agents share a common risk-adjusted prior and use the same subjective interest rate. Interior efficient allocations and equilibria coincide with those of economies with subjective expected utility and priors from the agents' multiple prior sets. We show that the set of equilibria with inertia contains the equilibria of the economy with variational preferences anchored at the initial endowments. A case study in an economy without aggregate uncertainty shows that risk is fully insured, while uncertainty can remain fully uninsured. Pessimistic agents with Gilboa-Schmeidler's max-min preferences would fully insure risk and uncertainty.Knightian Uncertainty, Ambiguity, Incomplete Preferences, General Equilibrium Theory, No Trade
Recent Research and Publications
Bibliography of publications in Hmong Studie
Factorization and Resummation for Massive Quark Effects in Exclusive Drell-Yan
Exclusive differential spectra in color-singlet processes at hadron colliders
are benchmark observables that have been studied to high precision in theory
and experiment. We present an effective-theory framework utilizing
soft-collinear effective theory to incorporate massive (bottom) quark effects
into resummed differential distributions, accounting for both heavy-quark
initiated primary contributions to the hard scattering process as well as
secondary effects from gluons splitting into heavy-quark pairs. To be specific,
we focus on the Drell-Yan process and consider the vector-boson transverse
momentum, , and beam thrust, , as examples of exclusive
observables. The theoretical description depends on the hierarchy between the
hard, mass, and the (or ) scales, ranging from the decoupling
limit to the massless limit . The phenomenologically
relevant intermediate regime requires in particular quark-mass
dependent beam and soft functions. We calculate all ingredients for the
description of primary and secondary mass effects required at NNLL
resummation order (combining NNLL evolution with NNLO boundary conditions) for
and in all relevant hierarchies. For the distribution
the rapidity divergences are different from the massless case and we discuss
features of the resulting rapidity evolution. Our results will allow for a
detailed investigation of quark-mass effects in the ratio of and boson
spectra at small , which is important for the precision measurement of the
-boson mass at the LHC.Comment: 42 pages + appendices, 21 figures; v2: journal versio
The Diary of Anne Frank
The famous Diary of Anne Frank was performed at John Carroll University beginning March 30, 2001.https://collected.jcu.edu/plays/1124/thumbnail.jp
Investigation of the Coupling Paths of a Galvanically Isolated AC/AC Converter
A galvanically isolated three-phase AC/AC converter with a high-frequency AC-link has been analyzed from an EMC point of view. This is a special configuration because of a large number of switches, a high frequency transformer, and a fourwire output. The essential coupling paths are identified.\ud
Corresponding suppression remedies are given. The results, before and after measures, have been presented to demonstrate the improvement in EMC.\ud
Keywords: AC/AC converter; electromagnetic interference; galvanically isolated\u
Reliability approach in spacecraft structures
This paper presents an application of the probabilistic approach with reliability assessment on a spacecraft structure. The adopted strategy uses meta-modeling with first and second order polynomial functions. This method aims at minimizing computational time while giving relevant results. The first part focuses on computational tools employed in the strategy development. The second part presents a spacecraft application. The purpose is to highlight benefits of the probabilistic approach compared with the current deterministic one. From examples of reliability assessment we show some advantages which could be found in industrial applications
GONG p-mode parameters through two solar cycles
We investigate the parameters of global solar p-mode oscillations, namely
damping width , amplitude , mean squared velocity , energy , and energy supply rate ,
derived from two solar cycles' worth (1996 - 2018) of Global Oscillation
Network Group (GONG) time series for harmonic degrees . We correct
for the effect of fill factor, apparent solar radius, and spurious jumps in the
mode amplitudes. We find that the amplitude of the activity related changes of
and depends on both frequency and harmonic degree of the modes,
with the largest variations of for modes with and with a min-to-max variation of
and of for modes with and with a min-to-max variation of
. The level of correlation between the solar radio flux
and mode parameters also depends on mode frequency and harmonic
degree. As a function of mode frequency, the mode amplitudes are found to
follow an asymmetric Voigt profile with
. From the mode parameters, we
calculate physical mode quantities and average them over specific mode
frequency ranges. This way, we find that the mean squared velocities and energies of p modes are anti-correlated with the level of
activity, varying by and , respectively, and that
the mode energy supply rates show no significant correlation with activity.
With this study we expand previously published results on the temporal
variation of solar p-mode parameters. Our results will be helpful to future
studies of the excitation and damping of p modes, i.e., the interplay between
convection, magnetic field, and resonant acoustic oscillations.Comment: Accepted for publication in Solar Physics. 33 pages, 16 figures, 5
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