34,359 research outputs found
Booms and busts: consumption, house prices and expectations
Over much of the past 25 years, the cycles of house price and consumption growth have been closely
synchronised. Three main hypotheses for this co-movement have been proposed in the literature.
First, that an increase in house prices raises householdsâ wealth, particularly for those in a position to
trade down the housing ladder, which increases their desired level of expenditure. Second, that
house price growth increases the collateral available to homeowners, reducing credit constraints and
thereby facilitating higher consumption. And third, that house prices and consumption have tended
to be influenced by common factors. This paper finds that the relationship between house prices and
consumption is stronger for younger than older households, which appears to contradict the wealth
channel. These findings therefore suggest that common causality has been the most important factor
behind the link between house price and consumption
SP mountain data analysis
An analysis of synthetic aperture radar data of SP Mountain was undertaken to demonstrate the use of digital image processing techniques to aid in geologic interpretation of SAR data. These data were collected with the ERIM X- and L-band airborne SAR using like- and cross-polarizations. The resulting signal films were used to produce computer compatible tapes, from which four-channel imagery was generated. Slant range-to-ground range and range-azimuth-scale corrections were made in order to facilitate image registration; intensity corrections were also made. Manual interpretation of the imagery showed that L-band represented the geology of the area better than X-band. Several differences between the various images were also noted. Further digital analysis of the corrected data was done for enhancement purposes. This analysis included application of an MSS differencing routine and development of a routine for removal of relief displacement. It was found that accurate registration of the SAR channels is critical to the effectiveness of the differencing routine. Use of the relief displacement algorithm on the SP Mountain data demonstrated the feasibility of the technique
Development techniques for generic software
In developing the first version of a generic implementation of X.25, Levels 2 and 3, three development techniques are examined: table driven finite state machine implementation, an integrated testing environment, and top down design. A finite state machine (FSM) is a powerful tool for both specifying and implementing protocols. This technique was used in the X.25 specification. A table driven implementation of the FSM was chosen to facilitate changes and simplify coding. The effect that this technique have on program size, speed of execution, coding time, and debugging time are investigated
Metamaterials for light rays: ray optics without wave-optical analog in the ray-optics limit
Volumes of sub-wavelength electromagnetic elements can act like homogeneous
materials: metamaterials. In analogy, sheets of optical elements such as prisms
can act ray-optically like homogeneous sheet materials. In this sense, such
sheets can be considered to be metamaterials for light rays (METATOYs).
METATOYs realize new and unusual transformations of the directions of
transmitted light rays. We study here, in the ray-optics and scalar-wave
limits, the wave-optical analog of such transformations, and we show that such
an analog does not always exist. Perhaps, this is the reason why many of the
ray-optical possibilities offered by METATOYs have never before been
considered.Comment: 10 pages, 3 figures, references update
Dust Grain Orbital Behavior Around Ceres
Many asteroids show indications they have undergone impacts with meteoroid
particles having radii between 0.01 m and 1 m. During such impacts, small dust
grains will be ejected at the impact site. The possibility of these dust grains
(with radii greater than 2.2x10-6 m) forming a halo around a spherical asteroid
(such as Ceres) is investigated using standard numerical integration
techniques. The orbital elements, positions, and velocities are determined for
particles with varying radii taking into account both the influence of gravity,
radiation pressure, and the interplanetary magnetic field (for charged
particles). Under the influence of these forces it is found that dust grains
(under the appropriate conditions) can be injected into orbits with lifetimes
in excess of one year. The lifetime of the orbits is shown to be highly
dependent on the location of the ejection point as well as the angle between
the surface normal and the ejection path. It is also shown that only particles
ejected within 10 degrees relative to the surface tangential survive more than
a few hours and that the longest-lived particles originate along a line
perpendicular to the Ceres-Sun line.Comment: 8 pages, Presented at COSPAR '0
Power Spectrum Correlations Induced by Non-Linear Clustering
Gravitational clustering is an intrinsically non-linear process that
generates significant non-Gaussian signatures in the density field. We consider
how these affect power spectrum determinations from galaxy and weak-lensing
surveys. Non-Gaussian effects not only increase the individual error bars
compared to the Gaussian case but, most importantly, lead to non-trivial
cross-correlations between different band-powers. We calculate the
power-spectrum covariance matrix in non-linear perturbation theory (weakly
non-linear regime), in the hierarchical model (strongly non-linear regime), and
from numerical simulations in real and redshift space. We discuss the impact of
these results on parameter estimation from power spectrum measurements and
their dependence on the size of the survey and the choice of band-powers. We
show that the non-Gaussian terms in the covariance matrix become dominant for
scales smaller than the non-linear scale, depending somewhat on power
normalization. Furthermore, we find that cross-correlations mostly deteriorate
the determination of the amplitude of a rescaled power spectrum, whereas its
shape is less affected. In weak lensing surveys the projection tends to reduce
the importance of non-Gaussian effects. Even so, for background galaxies at
redshift z=1, the non-Gaussian contribution rises significantly around l=1000,
and could become comparable to the Gaussian terms depending upon the power
spectrum normalization and cosmology. The projection has another interesting
effect: the ratio between non-Gaussian and Gaussian contributions saturates and
can even decrease at small enough angular scales if the power spectrum of the
3D field falls faster than 1/k^2.Comment: 34 pages, 15 figures. Revised version, includes a clearer explanation
of why the hierarchical ansatz does not provide a good model of the
covariance matrix in the non-linear regime, and new constraints on the
amplitudes Ra and Rb for general 4-pt function configurations in the
non-linear regim
Electrometry using the quantum Hall effect in a bilayer 2D electron system
We discuss the development of a sensitive electrometer that utilizes a
two-dimensional electron gas (2DEG) in the quantum Hall regime. As a
demonstration, we measure the evolution of the Landau levels in a second,
nearby 2DEG as the applied perpendicular magnetic field is changed, and extract
an effective mass for electrons in GaAs that agrees within experimental error
with previous measurements.Comment: 3.5 pages, 3 figures, submitted to APL
Origin of the hysteresis in bilayer 2D systems in the quantum Hall regime
The hysteresis observed in the magnetoresistance of bilayer 2D systems in the
quantum Hall regime is generally attributed to the long time constant for
charge transfer between the 2D systems due to the very low conductivity of the
quantum Hall bulk states. We report electrometry measurements of a bilayer 2D
system that demonstrate that the hysteresis is instead due to non-equilibrium
induced current. This finding is consistent with magnetometry and electrometry
measurements of single 2D systems, and has important ramifications for
understanding hysteresis in bilayer 2D systems.Comment: 4 pages, 3 figs. Accepted for publication in PR
Ballistic transport in induced one-dimensional hole systems
We have fabricated and studied a ballistic one-dimensional p-type quantum
wire using an undoped AlGaAs/GaAs heterostructure. The absence of modulation
doping eliminates remote ionized impurity scattering and allows high mobilities
to be achieved over a wide range of hole densities, and in particular, at very
low densities where carrier-carrier interactions are strongest. The device
exhibits clear quantized conductance plateaus with highly stable gate
characteristics. These devices provide opportunities for studying spin-orbit
coupling and interaction effects in mesoscopic hole systems in the strong
interaction regime where rs > 10.Comment: 6 pages, 4 figures (accepted to Applied Physics Letters
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