11,820 research outputs found
What accounts for the changes in U.S. fiscal policy transmission?
Using vector autoregressions on U.S. time series for 1957-1979 and 1983-2004, we find government spending shocks to have stronger effects on output, consumption, and wages in the earlier sample. We try to account for this observation within a DSGE model featuring price rigidities and limited asset market participation. Specifically, we estimate the structural parameters of the model for both samples by matching impulse responses. Model-based counterfactual experiments suggest that increased asset market participation accounts for some of the changes in fiscal transmission. However, the key quantitative factor appears to be the more active monetary policy of the Volcker-Greenspan period. JEL Classification: E21, E62, E63Asset Market Participation, DSGE, Fiscal Policy, government spending, Minimum Distance Estimation, monetary policy, Vector autoregression
The VLQ Calorimeter of H1 at HERA: A Highly Compact Device for Measurements of Electrons and Photons under Very Small Scattering Angles
In 1998, the detector H1 at HERA has been equipped with a small backward
spectrometer, the Very Low Q^2 (VLQ) spectrometer comprising a silicon tracker,
a tungsten - scintillator sandwich calorimeter, and a Time-of-Flight system.
The spectrometer was designed to measure electrons scattered under very low
angles, equivalent to very low squared four - momentum transfers Q^2, and high
energy photons with good energy and spatial resolution. The VLQ was in
operation during the 1999 and 2000 run periods. This paper describes the design
and construction of the VLQ calorimeter, a compact device with a fourfold
projective energy read-out, and its performance during test runs and in the
experiment.Comment: 32 pages, 25 figures, 2 tables (To be submitted to Nucl. Instrum.
Meth. A
Faraday Rotation Spectroscopy of Quantum-Dot Quantum Wells
Time-resolved Faraday rotation studies of CdS/CdSe/CdS quantum-dot quantum
wells have recently shown that the Faraday rotation angle exhibits several
well-defined resonances as a function of probe energy close to the absorption
edge. Here, we calculate the Faraday rotation angle from the eigenstates of the
quantum-dot quantum well obtained with k.p theory. We show that the large
number of narrow resonances with comparable spectral weight observed in
experiment is not reproduced by the level scheme of a quantum-dot quantum well
with perfect spherical symmetry. A simple model for broken spherical symmetry
yields results in better qualitative agreement with experiment.Comment: 9 pages, 4 figure
A quasi-periodic oscillation in the blazar J1359+4011
The OVRO 40-m telescope has been monitoring the 15 GHz radio flux density of
over 1200 blazars since 2008. The 15 GHz light curve of the flat spectrum radio
quasar J1359+4011 shows a strong and persistent quasi-periodic oscillation. The
time-scale of the oscillation varies between 120 and 150 days over a
year time span. We interpret this as the active galactic nucleus mass-scaled
analog of low-frequency quasi-periodic oscillations from Galactic microquasars,
or as evidence of modulation of the accretion flow by thermal instabilites in
the "inner" accretion disc.Comment: 4 pages, 2 figures, 1 table. Accepted for publication in MNRAS
Letter
First principles study of local electronic and magnetic properties in pure and electron-doped NdCuO
The local electronic structure of Nd2CuO4 is determined from ab-initio
cluster calculations in the framework of density functional theory.
Spin-polarized calculations with different multiplicities enable a detailed
study of the charge and spin density distributions, using clusters that
comprise up to 13 copper atoms in the CuO2plane. Electron doping is simulated
by two different approaches and the resulting changes in the local charge
distribution are studied in detail and compared to the corresponding changes in
hole doped La2CuO4. The electric field gradient (EFG) at the copper nucleus is
investigated in detail and good agreement is found with experimental values. In
particular the drastic reduction of the main component of the EFG in the
electron-doped material with respect to LaCuO4 is explained by a reduction of
the occupancy of the 3d3z^2-r^2 atomic orbital. Furthermore, the chemical
shieldings at the copper nucleus are determined and are compared to results
obtained from NMR measurements. The magnetic hyperfine coupling constants are
determined from the spin density distribution
Exact bosonization for an interacting Fermi gas in arbitrary dimensions
We present an exact mapping of models of interacting fermions onto boson
models. The bosons correspond to collective excitations in the initial
fermionic models. This bosonization is applicable in any dimension and for any
interaction between fermions. We show schematically how the mapping can be used
for Monte Carlo calculations and argue that it should be free from the sign
problem. Introducing superfields we derive a field theory that may serve as a
new way of analytical study.Comment: Basic equations are derived more carefully and in a simpler wa
Characterisation of the PSI whole body counter by radiographic imaging
A joint project between the Paul Scherrer Institut (PSI) and the Institute of Radiation Physics was initiated to characterise the PSI whole body counter in detail through measurements and Monte Carlo simulation. Accurate knowledge of the detector geometry is essential for reliable simulations of human body phantoms filled with known activity concentrations. Unfortunately, the technical drawings provided by the manufacturer are often not detailed enough and sometimes the specifications do not agree with the actual set-up. Therefore, the exact detector geometry and the position of the detector crystal inside the housing were determined through radiographic images. X-rays were used to analyse the structure of the detector, and 60Co radiography was employed to measure the core of the germanium crystal. Moreover, the precise axial alignment of the detector within its housing was determined through a series of radiographic images with different incident angles. The hence obtained information enables us to optimise the Monte Carlo geometry model and to perform much more accurate and reliable simulation
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