22,389 research outputs found
Real Estate Asset Allocations and International Real Estate Markets
In this paper we examine the institutional real estate ownership patterns of life insurance companies for 10 countries over the period 1986-96. The countries included are ustralia, Austria, Belgium, France, Italy, the Netherlands, Spain, Sweden, the United Kingdom, and the United States. We find that most institutional investors worldwide have shifted out of real estate assets and into stocks and bonds over the last decade. We then investigate whether this behavior is the result of changing investor perceptions or a shift in stock market apitalization. To test this hypothesis, the paper derives measures of ex ante real estate returns following previous empirical work in finance. The results indicate that only a small proportion of what is driving institutional investors' real estate portfolio decisions is actually explained by changing investor perceptions and lagged unexpected excess returns.Institutions, International Investment, Portfolio Diversification
Decomposing Productivity Growth in the U.S. Computer Industry
In this paper, we examine the sources of the productivity growth in the U.S. computer industry from 1978 to 1999. We estimate a joint production model of output quantity and quality that distinguishes two types of technological changes: process and product innovations. Based on the estimation results, we decompose total factor productivity (TFP) growth rate into the contributions of process and product innovations and scale economies. The results show that product innovation associated with better quality accounts for about 30 percent of the TFP growth in the computer industry. Furthermore, we find that the TFP acceleration in the computer industry in the late 1990s is mainly derived from a rapid increase in product innovation.COMPUTER, PRODUCTIVITY; PROCESS AND PRODUCT INNOVATIONS; HEDONIC PRICE
Model Predictions for Neutrino Oscillation Parameters
We have surveyed leptonic and grand unified models of neutrino masses and
mixings in the literature which are still viable and give numerical predictions
for the reactor angle, . The results are of considerable interest
in anticipation of the next generation reactor experiments and the possible
future need for neutrino factories. Of the 63 models considered which were
published or posted on the Archive before June 2006, half predict values of
\sin^2 2\theta_{13} \gsim 0.015, which should yield positive signals for
disappearance in the reactor experiments planned for the near
future. Depending upon the outcome of those experiments, half of the models can
be eliminated on the basis of the presence or absence of such an observed
disappearance signal.Comment: 23 pages including 3 figures; published versio
Minimal Models for Axion and Neutrino
The PQ mechanism resolving the strong CP problem and the seesaw mechanism
explaining the smallness of neutrino masses may be related in a way that the PQ
symmetry breaking scale and the seesaw scale arise from a common origin.
Depending on how the PQ symmetry and the seesaw mechanism are realized, one has
different predictions on the color and electromagnetic anomalies which could be
tested in the future axion dark matter search experiments. Motivated by this,
we construct various PQ seesaw models which are minimally extended from the
(non-) supersymmetric Standard Model and thus set up different benchmark points
on the axion-photon-photon coupling in comparison with the standard KSVZ and
DFSZ models.Comment: 12 pages and 2 figures, references added, matched with the published
version in PL
Substantial gain enhancement for optical parametric amplification and oscillation in two-dimensional χ(2) nonlinear photonic crystals
We have analyzed optical parametric interaction in a 2D NPC. While in general the nonlinear coefficient is small compared to a 1D NPC, we show that at numerous orientations a multitude of reciprocal vectors contribute additively to enhance the gain in optical parametric amplification and oscillation in a 2D patterned crystal. In particular, we have derived the effective nonlinear coefficients for common-signal amplification and common-idler amplification for a tetragonal inverted domain pattern. We show that in the specific case of signal amplification with QPM by both G10 and G11, symmetry of the crystal results in coupled interaction with the corresponding signal amplification by G10 and G1,-1. As a consequence, this coupled utilization of all three reciprocal vectors leads to a substantial increase in parametric gain. Using PPLN we demonstrate numerically that a gain that comes close to that of a 1D QPM crystal could be realized in a 2D NPC with an inverted tetragonal domain pattern. This special mechanism produces two pairs of identical signal and idler beams propagating in mirror-imaged forward directions. In conjunction with this gain enhancement and multiple beams output we predict that there is a large pulling effect on the output wavelength due to dynamic signal build-up in the intrinsic noncollinear geometry of a 2D NPC OPO
Potential Vorticity Mixing in a Tangled Magnetic Field
A theory of potential vorticity (PV) mixing in a disordered (tangled)
magnetic field is presented. The analysis is in the context of -plane
MHD, with a special focus on the physics of momentum transport in the stably
stratified, quasi-2D solar tachocline. A physical picture of mean PV evolution
by vorticity advection and tilting of magnetic fields is proposed. In the case
of weak-field perturbations, quasi-linear theory predicts that the Reynolds and
magnetic stresses balance as turbulence Alfv\'enizes for a larger mean magnetic
field. Jet formation is explored quantitatively in the mean field-resistivity
parameter space. However, since even a modest mean magnetic field leads to
large magnetic perturbations for large magnetic Reynolds number, the physically
relevant case is that of a strong but disordered field. We show that numerical
calculations indicate that the Reynolds stress is modified well before
Alfv\'enization -- i.e. before fluid and magnetic energies balance. To
understand these trends, a double-average model of PV mixing in a stochastic
magnetic field is developed. Calculations indicate that mean-square fields
strongly modify Reynolds stress phase coherence and also induce a magnetic drag
on zonal flows. The physics of transport reduction by tangled fields is
elucidated and linked to the related quench of turbulent resistivity. We
propose a physical picture of the system as a resisto-elastic medium threaded
by a tangled magnetic network. Applications of the theory to momentum transport
in the tachocline and other systems are discussed in detail.Comment: 17 pages, 10 figures, 2 table
Fan-extensions in fragile matroids
If S is a set of matroids, then the matroid M is S-fragile if, for every
element e in E(M), either M\e or M/e has no minor isomorphic to a member of S.
Excluded-minor characterizations often depend, implicitly or explicitly, on
understanding classes of fragile matroids. In certain cases, when F is a
minor-closed class of S-fragile matroids, and N is in F, the only members of F
that contain N as a minor are obtained from N by increasing the length of fans.
We prove that if this is the case, then we can certify it with a finite
case-analysis. The analysis involves examining matroids that are at most two
elements larger than N.Comment: Small revisions and correction
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