2,284 research outputs found
Fluctuations and Transients in Quantum-Resonant Evolution
The quantum-resonant evolution of the mean kinetic energy (MKE) of the kicked
particle is studied in detail on different time scales for {\em general}
kicking potentials. It is shown that the asymptotic time behavior of a
wave-packet MKE is typically a linear growth with bounded fluctuations having a
simple number-theoretical origin. For a large class of wave packets, the MKE is
shown to be exactly the superposition of its asymptotic behavior and transient
logarithmic corrections. Both fluctuations and transients can be significant
for not too large times but they may vanish identically under some conditions.
In the case of incoherent mixtures of plane waves, it is shown that the MKE
never exhibits asymptotic fluctuations but transients usually occur.Comment: REVTEX, 12 page
Perbandingan Volatilitas Indeks Harga Saham Gabungan (Ihsg) Sebelum dan Setelah Krisis Subprime Mortgage
Volatilitas merupakan pengukuran statistik fluktuasi dari harga saham selama periode tertentu. Volatilitas suatu harga saham yang tinggi menunjukan karakteristik penawaran dan permintaan saham yang tidak biasa di pasar modal. Volatilitas IHSG mencerminkan tingkat risiko yang dihadapi investor. Krisis subprime mortgage yang terjadi di Amerika Serikat pada tahun 2008 merupakan salah satu kejadian luar biasa yang mengakibatkan volatilitas Indeks Harga Saham Gabungan menjadi tidak stabil. Penelitian ini bertujuan untuk membandingkan volatilitas IHSG sebelum dan setelah krisis subprime mortgage. Populasi menggunakan harga penutupan Indeks Harga Saham Gabungan periode 2005-2011 yaitu sebanyak 36 sebelum krisis dan 36 setelah krisis dengan menggunakan teknik analisis uji t berpasangan. Hasil penelitian menunjukan bahwa terdapat perbandingan antara volatilitas IHSG sebelum krisis lebih rendah daripada volatilitas IHSG setelah krisis subprime mortgage
Kinematics in Kapteyn's Selected Area 76: Orbital Motions Within the Highly Substructured Anticenter Stream
We have measured the mean three-dimensional kinematics of stars in Kapteyn's
Selected Area (SA) 76 (l=209.3, b=26.4 degrees) that were selected to be
Anticenter Stream (ACS) members on the basis of their radial velocities, proper
motions, and location in the color-magnitude diagram. From a total of 31 stars
ascertained to be ACS members primarily from its main sequence turnoff, a mean
ACS radial velocity (derived from spectra obtained with the Hydra multi-object
spectrograph on the WIYN 3.5m telescope) of V_helio = 97.0 +/- 2.8 km/s was
determined, with an intrinsic velocity dispersion sigma_0 = 12.8 \pm 2.1 km/s.
The mean absolute proper motions of these 31 ACS members are mu_alpha cos
(delta) = -1.20 +/- 0.34 mas/yr and mu_delta = -0.78 \pm 0.36 mas/yr. At a
distance to the ACS of 10 \pm 3 kpc, these measured kinematical quantities
produce an orbit that deviates by ~30 degrees from the well-defined swath of
stellar overdensity constituting the Anticenter Stream in the western portion
of the Sloan Digital Sky Survey footprint. We explore possible explanations for
this, and suggest that our data in SA 76 are measuring the motion of a
kinematically cold sub-stream among the ACS debris that was likely a fragment
of the same infalling structure that created the larger ACS system. The ACS is
clearly separated spatially from the majority of claimed Monoceros ring
detections in this region of the sky; however, with the data in hand, we are
unable to either confirm or rule out an association between the ACS and the
poorly-understood Monoceros structure.Comment: Accepted to ApJ. 48 pages, 20 figures, preprint forma
Antiresonance and Localization in Quantum Dynamics
The phenomenon of quantum antiresonance (QAR), i.e., exactly periodic
recurrences in quantum dynamics, is studied in a large class of nonintegrable
systems, the modulated kicked rotors (MKRs). It is shown that asymptotic
exponential localization generally occurs for (a scaled ) in the
infinitesimal vicinity of QAR points . The localization length
is determined from the analytical properties of the kicking potential. This
``QAR-localization" is associated in some cases with an integrable limit of the
corresponding classical systems. The MKR dynamical problem is mapped into
pseudorandom tight-binding models, exhibiting dynamical localization (DL). By
considering exactly-solvable cases, numerical evidence is given that
QAR-localization is an excellent approximation to DL sufficiently close to QAR.
The transition from QAR-localization to DL in a semiclassical regime, as
is varied, is studied. It is shown that this transition takes place via a
gradual reduction of the influence of the analyticity of the potential on the
analyticity of the eigenstates, as the level of chaos is increased.Comment: To appear in Physical Review E. 51 pre-print pages + 9 postscript
figure
Complexity, Tunneling and Geometrical Symmetry
It is demonstrated in the context of the simple one-dimensional example of a
barrier in an infinite well, that highly complex behavior of the time evolution
of a wave function is associated with the almost degeneracy of levels in the
process of tunneling. Degenerate conditions are obtained by shifting the
position of the barrier. The complexity strength depends on the number of
almost degenerate levels which depend on geometrical symmetry. The presence of
complex behavior is studied to establish correlation with spectral degeneracy.Comment: 9 revtex pages, 6 Postscript figures (uuencoded
Unlocking CO Depletion in Protoplanetary Disks II. Primordial C/H Predictions Inside the CO Snowline
CO is thought to be the main reservoir of volatile carbon in protoplanetary
disks, and thus the primary initial source of carbon in the atmospheres of
forming giant planets. However, recent observations of protoplanetary disks
point towards low volatile carbon abundances in many systems, including at
radii interior to the CO snowline. One potential explanation is that gas phase
carbon is chemically reprocessed into less volatile species, which are frozen
on dust grain surfaces as ice. This mechanism has the potential to change the
primordial C/H ratio in the gas. However, current observations primarily probe
the upper layers of the disk. It is not clear if the low volatile carbon
abundances extend to the midplane, where planets form. We have run a grid of
198 chemical models, exploring how the chemical reprocessing of CO depends on
disk mass, dust grain size distribution, temperature, cosmic ray and X-ray
ionization rate, and initial water abundance. Building on our previous work
focusing on the warm molecular layer, here we analyze the results for our grid
of models in the disk midplane at 12 au. We find that either an ISM level
cosmic ray ionization rate or the presence of UV photons due to a low dust
surface density are needed to chemically reduce the midplane CO gas abundance
by at least an order of magnitude within 1 Myr. In the majority of our models
CO does not undergo substantial reprocessing by in situ chemistry and there is
little change in the gas phase C/H and C/O ratios over the lifetime of the
typical disk. However, in the small sub-set of disks where the disk midplane is
subject to a source of ionization or photolysis, the gas phase C/O ratio
increases by up to nearly 9 orders of magnitude due to conversion of CO into
volatile hydrocarbons.Comment: Accepted for publication in ApJ, 15 pages, 10 figures, 3 table
Egorov property in perturbed cat map
We study the time evolution of the quantum-classical correspondence (QCC) for
the well known model of quantised perturbed cat maps on the torus in the very
specific regime of semi-classically small perturbations. The quality of the QCC
is measured by the overlap of classical phase-space density and corresponding
Wigner function of the quantum system called quantum-classical fidelity (QCF).
In the analysed regime the QCF strongly deviates from the known general
behaviour in particular it decays faster then exponential. Here we study and
explain the observed behavior of the QCF and the apparent violation of the QCC
principle.Comment: 12 pages, 7 figure
Cluster Expansion by Transfer Learning from Empirical Potentials
Cluster expansions provide effective representations of the potential energy
landscape of multicomponent crystalline solids. Notwithstanding major advances
in cluster expansion implementations, it remains computationally demanding to
construct these expansions for systems of low dimension or with a large number
of components, such as clusters, interfaces, and multimetallic alloys. We
address these challenges by employing transfer learning to accelerate the
computationally demanding step of generating configurational data from first
principles. The proposed approach exploits Bayesian inference to incorporate
prior knowledge from physics-based or machine-learning empirical potentials,
enabling one to identify the most informative configurations within a dataset.
The efficacy of the method is tested on face-centered cubic Pt:Ni binaries,
yielding a two- to three-fold reduction in the number of first-principles
calculations, while ensuring robust convergence of the energies with low
statistical fluctuations
Multi-Resolution Analysis and Fractional Quantum Hall Effect: an Equivalence Result
In this paper we prove that any multi-resolution analysis of \Lc^2(\R)
produces, for some values of the filling factor, a single-electron wave
function of the lowest Landau level (LLL) which, together with its (magnetic)
translated, gives rise to an orthonormal set in the LLL. We also give the
inverse construction. Moreover, we extend this procedure to the higher Landau
levels and we discuss the analogies and the differences between this procedure
and the one previously proposed by J.-P. Antoine and the author.Comment: Submitted to Journal Mathematical Physisc
Coherent pair production in deformed crystals with a complex base
We investigate the coherent electron-positron pair creation by high-energy
photons in a periodically deformed single crystal with a complex base. The
formula for the corresponding differential cross-section is derived for an
arbitrary deformation field. The conditions are specified under which the
influence of the deformation is considerable. The case is considered in detail
when the photon enters into the crystal at small angles with respect to a
crystallographic axis. The results of the numerical calculations are presented
for single crystal and Moliere parametrization of the
screened atomic potentials in the case of the deformation field generated by
the acoustic wave of type. In dependence of the parameters, the presence of
deformation can either enhance or reduce the pair creation cross-section. This
can be used to control the parameters of the positron sources for storage rings
and colliders.Comment: 10 pages, 4 figures, misprint in the numerical coefficients in figure
captions is correcte
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