5,449 research outputs found
Forecasting the money multiplier: implications for money stock control and economic activity
Forecasting ; Money supply
A multiwavlength study of PSR B0628-28: The first overluminous rotation-powered pulsar?
The ROSAT source RX J0630.8-2834 was suggested by positional coincidence to
be the X-ray counterpart of the old field pulsar PSR B0628-28. This
association, however, was regarded to be unlikely based on the computed
energetics of the putative X-ray counterpart. In this paper we report on
multiwavelength observations of PSR B0628-28 made with the ESO/NTT observatory
in La Silla, the Jodrell Bank radio observatory and XMM-Newton. Although the
optical observations do not detect any counterpart of RX J0630.8-2834 down to a
limiting magnitude of V=26.1 mag and B=26.3 mag, XMM-Newton observations
finally confirmed it to be the pulsar's X-ray counterpart by detecting X-ray
pulses with the radio pulsar's spin-period. The X-ray pulse profile is
characterized by a single broad peak with a second smaller peak leading the
main pulse component by ~144 degree. The fraction of pulsed photons is (38 +-
7)% with no strong energy dependence in the XMM-Newton bandpass. The pulsar's
X-ray spectrum is well described by a single component power law with photon
index 2.63^{+0.23}_{-0.15}, indicating that the pulsar's X radiation is
dominated by non-thermal emission processes. A low level contribution of
thermal emission from residual cooling or from heated polar caps, cannot be
excluded. The pulsar's spin-down to X-ray energy conversion efficiency is
obtained to be ~16% for the radio dispersion measure inferred pulsar distance.
If confirmed, PSR B0628-28 would be the first X-ray overluminous
rotation-powered pulsar identified among all ~1400 radio pulsars known today.Comment: Accepted for publication in ApJ. Find a paper copy with higher
resolution images at
ftp://ftp.xray.mpe.mpg.de/people/web/astro-ph-0505488_rev2.pd
The chemistry of La on the Si(001) surface
This paper reports state-of-the-art electronic structure calculations of La
adsorption on the Si(001) surface. We predict La chains in the low coverage
limit, which condense in a stable phase at a coverage of 1/5 monolayer. At 1/3
monolayer we predict a chemically rather inert, stable phase. La changes its
oxidation state from La(3+) at lower coverages to La(2+) at coverages beyond
1/3 monolayer. In the latter oxidation state, one electron resides in a state
with a considerable contribution from La-d and f states.Comment: 10 pages, 13 figures, 3 table
Chen-Ruan cohomology of ADE singularities
We study Ruan's \textit{cohomological crepant resolution conjecture} for
orbifolds with transversal ADE singularities. In the -case we compute both
the Chen-Ruan cohomology ring and the quantum corrected
cohomology ring . The former is achieved in general, the
later up to some additional, technical assumptions. We construct an explicit
isomorphism between and in the -case,
verifying Ruan's conjecture. In the -case, the family
is not defined for . This implies that
the conjecture should be slightly modified. We propose a new conjecture in the
-case which we prove in the -case by constructing an explicit
isomorphism.Comment: This is a short version of my Ph.D. Thesis math.AG/0510528. Version
2: chapters 2,3,4 and 5 has been rewritten using the language of groupoids; a
link with the classical McKay correpondence is given. International Journal
of Mathematics (to appear
Comparing Multi-State Kalman Filter and ARIMA forecasts: an application to the money multiplier
This paper derives one-month ahead forecasts of the money (M I) multiplier using the Multi-State Kalman Filter and Box-Jenkins ARIMA methods. A comparison of the forecasts far the period 1980-82 reveals that the Multi-State Kalman Filter procedure was generally superior to the ARIMA procedure In terms of most summary statistics. The superiority is traced to the turbulent period of 1980-81. This paper also compares aggregate and component forecasts of the multiplier. The aggregate Multi-State Kalman Filter was the most accurate in predicting the one-month ahead money multiplier.
Noise enhanced performance of ratchet cellular automata
We present the first experimental realization of a ratchet cellular automaton
(RCA) which has been recently suggested as an alternative approach for
performing logical operations with interacting (quasi) particles. Our study was
performed with interacting colloidal particles which serve as a model system
for other dissipative systems i.e. magnetic vortices on a superconductor or
ions in dissipative optical arrays. We demonstrate that noise can enhance the
efficiency of information transport in RCA and consequently enables their
optimal operation at finite temperatures.Comment: accepted for publication at Phys. Rew. Let
A Pulsational Model for the Orthogonal Polarization Modes in Radio Pulsars
In an earlier paper, we introduced a model for pulsars in which non-radial
oscillations of high spherical degree (\el) aligned to the magnetic axis of a
spinning neutron star were able to reproduce subpulses like those observed in
single-pulse measurements of pulsar intensity. The model did not address
polarization, which is an integral part of pulsar emission. Observations show
that many pulsars emit radio waves that appear to be the superposition of two
linearly polarized emission modes with orthogonal polarization angles. In this
paper, we extend our model to incorporate linear polarization. As before, we
propose that pulsational displacements of stellar material modulate the pulsar
emission, but now we apply this modulation to a linearly-polarized mode of
emission, as might be produced by curvature radiation. We further introduce a
second polarization mode, orthogonal to the first, that is modulated by
pulsational velocities. We combine these modes in superposition to model the
observed Stokes parameters in radio pulsars.Comment: 19 pages, 4 figures accepted Ap
Dynamics of precipitation pattern formation at geothermal hot springs
We formulate and model the dynamics of spatial patterns arising during the
precipitation of calcium carbonate from a supersaturated shallow water flow.
The model describes the formation of travertine deposits at geothermal hot
springs and rimstone dams of calcite in caves. We find explicit solutions for
travertine domes at low flow rates, identify the linear instabilities which
generate dam and pond formation on sloped substrates, and present simulations
of statistical landscape evolution
High Resolution Spectroscopy of the Pulsating White Dwarf G29-38
We present the analysis of time-resolved, high resolution spectra of the cool
white dwarf pulsator, G29-38. From measuring the Doppler shifts of the H-alpha
core, we detect velocity changes as large as 16.5 km/s and conclude that they
are due to the horizontal motions associated with the g-mode pulsations on the
star. We detect seven pulsation modes from the velocity time-series and
identify the same modes in the flux variations. We discuss the properties of
these modes and use the advantage of having both velocity and flux measurements
of the pulsations to test the convective driving theory proposed for DAV stars.
Our data show limited agreement with the expected relationships between the
amplitude and phases of the velocity and flux modes. Unexpectedly, the velocity
curve shows evidence for harmonic distortion, in the form of a peak in the
Fourier transform whose frequency is the exact sum of the two largest
frequencies. Combination frequencies are a characteristic feature of the
Fourier transforms of light curves of G29-38, but before now have not been
detected in the velocities, nor does published theory predict that they should
exist. We compare our velocity combination frequency to combination frequencies
found in the analysis of light curves of G29-38, and discuss what might account
for the existence of velocity combinations with the properties we observe.
We also use our high-resolution spectra to determine if either rotation or
pulsation can explain the truncated shape observed for the DAV star's line
core. We are able to eliminate both mechanisms: the average spectrum does not
fit the rotationally broadened model and the time-series of spectra provides
proof that the pulsations do not significantly truncate the line.Comment: 24 pages, 9 figures, Accepted for publication in ApJ (June
Nonclassical effects in a driven atoms/cavity system in the presence of arbitrary driving field and dephasing
We investigate the photon statistics of light transmitted from a driven
optical cavity containing one or two atoms interacting with a single mode of
the cavity field. We treat arbitrary driving fields with emphasis on departure
from previous weak field results. In addition effects of dephasing due to
atomic transit through the cavity mode are included using two different models.
We find that both models show the nonclassical correlations are quite sensitive
to dephasing. The effect of multiple atoms on the system dynamics is
investigated by placing two atoms in the cavity mode at different positions,
therefore having different coupling strengths.Comment: 8 pages, 10 figures, minor typographical errors corrected, submitted
to Phys Rev
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