2,929 research outputs found
Displacement energy of unit disk cotangent bundles
We give an upper bound of a Hamiltonian displacement energy of a unit disk
cotangent bundle in a cotangent bundle , when the base manifold
is an open Riemannian manifold. Our main result is that the displacement
energy is not greater than , where is the inner radius of ,
and is a dimensional constant. As an immediate application, we study
symplectic embedding problems of unit disk cotangent bundles. Moreover,
combined with results in symplectic geometry, our main result shows the
existence of short periodic billiard trajectories and short geodesic loops.Comment: Title slightly changed. Close to the version published online in Math
Zei
Coupling of Josephson flux-flow oscillators to an external RC load
We investigate by numerical simulations the behavior of the power dissipated
in a resistive load capacitively coupled to a Josephson flux flow oscillator
and compare the results to those obtained for a d.c. coupled purely resistive
load. Assuming realistic values for the parameters R and C, both in the high-
and in the low-Tc case the power is large enough to allow the operation of such
a device in applications.Comment: uuencoded, gzipped tar archive containing 11 pages of REVTeX text + 4
PostScript figures. To appear in Supercond. Sci. Techno
Precision Measurements of d(d,p)t and d(d,n)^3He Total Cross Sections at Big-Bang Nucleosynthesis Energies
Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have
determined the baryon density of the Universe with a precision of
about 4%. With tightly constrained, comparisons of Big Bang
Nucleosynthesis (BBN) abundance predictions to primordial abundance
observations can be made and used to test BBN models and/or to further
constrain abundances of isotopes with weak observational limits. To push the
limits and improve constraints on BBN models, uncertainties in key nuclear
reaction rates must be minimized. To this end, we made new precise measurements
of the d(d,p)t and d(d,n)^3He total cross sections at lab energies from 110 keV
to 650 keV.
A complete fit was performed in energy and angle to both angular distribution
and normalization data for both reactions simultaneously. By including
parameters for experimental variables in the fit, error correlations between
detectors, reactions, and reaction energies were accurately tabulated by
computational methods. With uncertainties around 2% +/- 1% scale error, these
new measurements significantly improve on the existing data set. At relevant
temperatures, using the data of the present work, both reaction rates are found
to be about 7% higher than those in the widely used Nuclear Astrophysics
Compilation of Reaction Rates (NACRE). These data will thus lead not only to
reduced uncertainties, but also to modifications in the BBN abundance
predictions.Comment: 15 pages, 11 figures, minor editorial change
Analytic Study for the String Theory Landscapes via Matrix Models
We demonstrate a first-principle analysis of the string theory landscapes in
the framework of non-critical string/matrix models. In particular, we discuss
non-perturbative instability, decay rate and the true vacuum of perturbative
string theories. As a simple example, we argue that the perturbative string
vacuum of pure gravity is stable; but that of Yang-Lee edge singularity is
inescapably a false vacuum. Surprisingly, most of perturbative minimal string
vacua are unstable, and their true vacuum mostly does not suffer from
non-perturbative ambiguity. Importantly, we observe that the instability of
these tachyon-less closed string theories is caused by ghost D-instantons (or
ghost ZZ-branes), the existence of which is determined only by non-perturbative
completion of string theory.Comment: v1: 5 pages, 2 figures; v2: references and footnote added; v3: 7
pages, 4 figures, organization changed, explanations expanded, references
added, reconstruction program from arbitrary spectral curves shown explicitl
Theory of BiSrCaCuO Cross-Whisker Josephson Junctions
Takano {\it et al.} [Phys. Rev. B {\bf 65}, 140513 (2002) and unpublished]
made Josephson junctions from single crystal whiskers of
BiSrCaCuO crossed an angle about the
axis.
From the mesa structures that formed at the cross-whisker interface, they
inferred a critical current density . Like the single crystal
results of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)], we show
that the whisker data are unlikely to result from a predominantly d-wave order
parameter. However, unlike the single crystals, these results, if correct,
require the whisker c-axis transport to be coherent.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Resonance phenomena in the annular array of underdamped Josephson junctions
Appearance and origin of resonance phenomena have been studied in the annular
system of underdamped Josephson junctions. If no fluxon is trapped in the
system, dynamics is governed by the motion of fluxon-antifluxon pairs, while if
trapped fluxons are present, they can move solely but also simultaneously with
the pairs. Locking between the rotating excitations (fluxons and antifluxons)
and the Josephson frequency leads to the appearance of zero field steps in the
current-voltage characteristics, which can further exhibit branching due to
resonance between the rotating excitations and plasma oscillations in their
tale. The number of zero field steps and their branching are strongly
determined by the total number of excitations present in the system. High
resolution analysis further reveals not only some interesting properties of
zero field steps, but also shows that the current-voltage characteristics is
determined not only by the number, but also by the type of excitations, i.e.,
whether the dynamics is governed only by the motion of fluxon-antifluxon pairs
or the trapped fluxons, or they move simultaneously in the system
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