12,987 research outputs found
The Bipartisan Bayh Amendment: Republican Contributions to the Twenty-Fifth Amendment
It is appropriate that Senator Birch Bayh has been widely recognized as the author and person most responsible for the Twenty-Fifth Amendment. His work was indispensable, and he was helped by other Democrats and nonpartisan actors including the American Bar Association and John D. Feerick, among others. Yet the Amendment was also the product of bipartisan cooperation. Important provisions were based on work done during the administration of President Dwight D. Eisenhower, and Eisenhower and his Attorney General, Herbert Brownell, played important roles in supporting Bayhâs proposal as did other Republicans in and out of Congress. Republicans like Representative Richard Poff pushed ideas and provisions that found their way into the Amendment, helped create important legislative history, and contributed in the legislative process. Bayhâs legislative contribution included the inclusive manner in which he operated, and many Republicans deserve credit for participating constructively in a process they could not direct. In describing the bipartisan character of the Bayh Amendment, this Article seeks to fill a void in scholarly writing since no prior work has this focus. It also uses the Twenty-Fifth Amendment as a case study of the sort of bipartisan effort on which any constitutional amendment depends. And it suggests that the dispositions that produced the Twenty-Fifth Amendmentâin particular, communal problem solving based on a recognition of the need for interested parties to build from areas of agreementâwould contribute to addressing other social problems
Single and multiple recurrence along non-polynomial sequences
We establish new recurrence and multiple recurrence results for a rather
large family of non-polynomial functions which includes tempered
functions defined in [11], as well as functions from a Hardy field with the
property that for some , and . Among
other things, we show that for any , any invertible
probability measure preserving system , any
with , and any , the sets of returns and possess somewhat unexpected properties of
largeness; in particular, they are thick, i.e., contain arbitrarily long
intervals.Comment: 51 page
Disjointness for measurably distal group actions and applications
We generalize Berg's notion of quasi-disjointness to actions of countable
groups and prove that every measurably distal system is quasi-disjoint from
every measure preserving system. As a corollary we obtain easy to check
necessary and sufficient conditions for two systems to be disjoint, provided
one of them is measurably distal. We also obtain a Wiener--Wintner type theorem
for countable amenable groups with distal weights and applications to weighted
multiple ergodic averages and multiple recurrence.Comment: 28 page
Common Patterns in the Evolution between the Luminous Neutron Star Low-Mass X-ray Binary Subclasses
The X-ray transient XTE J1701-462 was the first source observed to evolve
through all known subclasses of low-magnetic-field neutron star low-mass X-ray
binaries (NS-LMXBs), as a result of large changes in its mass accretion rate.
To investigate to what extent similar evolution is seen in other NS-LMXBs we
have performed a detailed study of the color-color and hardness-intensity
diagrams (CDs and HIDs) of Cyg X-2, Cir X-1, and GX 13+1 -- three luminous
X-ray binaries, containing weakly magnetized neutron stars, known to exhibit
strong secular changes in their CD/HID tracks. Using the full set of Rossi
X-ray Timing Explorer Proportional Counter Array data collected for the sources
over the 16 year duration of the mission, we show that Cyg X-2 and Cir X-1
display CD/HID evolution with close similarities to XTE J1701-462. Although GX
13+1 shows behavior that is in some ways unique, it also exhibits similarities
to XTE J1701-462, and we conclude that its overall CD/HID properties strongly
indicate that it should be classified as a Z source, rather than as an atoll
source. We conjecture that the secular evolution of Cyg X-2, Cir X-1, and GX
13+1 -- illustrated by sequences of CD/HID tracks we construct -- arises from
changes in the mass accretion rate. Our results strengthen previous suggestions
that within single sources Cyg-like Z source behavior takes place at higher
luminosities and mass accretion rates than Sco-like Z behavior, and lend
support to the notion that the mass accretion rate is the primary physical
parameter distinguishing the various NS-LMXB subclasses.Comment: 20 pages, 14 figures, 5 tables -- matches published version in Ap
On the geometric nature of low-frequency quasi-periodic oscillations in neutron-star low-mass X-ray binaries
We report on a detailed analysis of the so-called ~1 Hz quasi-periodic
oscillation (QPO) in the eclipsing and dipping neutron-star low-mass X-ray
binary EXO 0748-676. This type of QPO has previously been shown to have a
geometric origin. Our study focuses on the evolution of the QPO as the source
moves through the color-color diagram, in which it traces out an
atoll-source-like track. The QPO frequency increases from ~0.4 Hz in the hard
state to ~25 Hz as the source approaches the soft state. Combining power
spectra based on QPO frequency reveals additional features that strongly
resemble those seen in non-dipping/eclipsing atoll sources. We show that the
low-frequency QPOs in atoll sources and the ~1 Hz QPO in EXO 0748-676 follow
similar relations with respect to the noise components in their power spectra.
We conclude that the frequencies of both types of QPOs are likely set by (the
same) precession of a misaligned inner accretion disk. For high-inclination
systems, like EXO 0748-676, this results in modulations of the neutron-star
emission due to obscuration or scattering, while for lower-inclination systems
the modulations likely arise from relativistic Doppler boosting and
light-bending effects.Comment: Updated to published version (ApJ, 812, 80
Modular Invariant Gaugino Condensation in the Presence of an Anomalous U(1)
Starting from the previously constructed effective supergravity theory below
the scale of U(1) breaking in orbifold compactifications of the weakly coupled
heterotic string, we study the effective theory below the scale of
supersymmetry breaking by gaugino and matter condensation in a hidden sector.
Issues we address include vacuum stability, soft supersymmetry-breaking masses
in the observable sector, and the masses of the various moduli fields,
including those associated with flat directions at the U(1)-breaking scale, and
of their fermionic superpartners. The consistent treatment of U(1) breaking
together with condensation yields qualitatively new results.Comment: 73 pages, full postscript also available from
http://phyweb.lbl.gov/theorygroup/papers/53960.p
Sparse Approximation Via Iterative Thresholding
The well-known shrinkage technique is still relevant for contemporary signal processing problems over redundant dictionaries. We present theoretical and empirical analyses for two iterative algorithms for sparse approximation that use shrinkage. The GENERAL IT algorithm amounts to a Landweber iteration with nonlinear shrinkage at each iteration step. The BLOCK IT algorithm arises in morphological components analysis. A sufficient condition for which General IT exactly recovers a sparse signal is presented, in which the cumulative coherence function naturally arises. This analysis extends previous results concerning the Orthogonal Matching Pursuit (OMP) and Basis Pursuit (BP) algorithms to IT algorithms
Molecular emission near metal interfaces: the polaritonic regime
The strong coupling of a dense layer of molecular excitons with
surface-plasmon modes in a metal gives rise to polaritons (hybrid light-matter
states) called plexcitons. Surface plasmons cannot directly emit into (or be
excited by) free-space photons due to the fact that energy and momentum
conservation cannot be simultaneously satisfied in photoluminescence. Most
plexcitons are also formally non-emissive, even though they can radiate via
molecules upon localization due to disorder and decoherence. However, a
fraction of them are bright even in the presence of such deleterious processes.
In this letter, we theoretically discuss the superradiant emission properties
of these bright plexcitons, which belong to the upper energy branch and reveal
huge photoluminescence enhancements compared to bare excitons. Our study
generalizes the well-known problem of molecular emission next to a metal
interface to collective molecular states and provides new design principles for
the control of photophysical properties of molecular aggregates using
polaritonic strategies.Comment: Replaced previous version, noticing that van Hove anomalies are only
observed in the direct and reflected contributions of photoluminescence, but
they cancel out when added up in the total photoluminescence. The correct
phenomenology is that enhancements of photoluminescence are still huge (not
infinite) and are near (not exactly at) the critical poin
Number squeezed and fragmented states of strongly interacting bosons in a double well
We present a systematic study of the phenomena of number squeezing and
fragmentation for a repulsive Bose-Einstein condensate (BEC) in a three
dimensional double well potential over a range of interaction strengths and
barrier heights, including geometries that exhibit appreciable overlap in the
one-body wavefunctions localized in the left and right wells. We compute the
properties of the condensate with numerically exact, full dimensional path
integral ground state (PIGS) Quantum Monte Carlo simulations and compare with
results obtained from using two- and eight-mode truncated basis models. The
truncated basis models are found to agree with the numerically exact PIGS
simulations for weak interactions, but fail to correctly predict the amount of
number squeezing and fragmentation exhibited by the PIGS simulations for strong
interactions. We find that both number squeezing and fragmentation of the BEC
show non-monotonic behavior at large values of interaction strength a. The
number squeezing shows a universal scaling with the product of number of
particles and interaction strength (Na) but no such universal behavior is found
for fragmentation. Detailed analysis shows that the introduction of repulsive
interactions not only suppresses number fluctuations to enhance number
squeezing, but can also enhance delocalization across wells and tunneling
between wells, each of which may suppress number squeezing. This results in a
dynamical competition whose resolution shows a complex dependence on all three
physical parameters defining the system: interaction strength, number of
particles, and barrier height.Comment: 33 pages, 21 figures. Submitted for publication in Physical Review
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