9,382 research outputs found
Landslides in sensitive soils, Tauranga, New Zealand.
In the Tauranga region sensitive soil failures commonly occur after heavy rainfall events, causing considerable infrastructure damage. Several notable landslides include a large failure at Bramley Drive, Omokoroa in 1979, the Ruahihi Canal collapse in 1981, and numerous landslides in May 2005; recently the Bramley Drive scarp was reactivated in 2011. These failures are associated with materials loosely classified as the Pahoia Tephras - a mixture of rhyolitic pyroclastic deposits of approximately 1 Ma.
The common link with extreme rainfall events suggests a pore water pressure control on the initiation of these failures. Recent research on the structure of the soils shows a dominance of halloysite clay minerals packed loosely in arrangements with high porosity (51 â 77 %), but with almost entirely micropores. This leads us to conclude that the permeability is very low, and the materials remain continuously wet. The formation of halloysite is encouraged by a wet environment with no episodes of drying, supporting this assumption.
A high-resolution CPT trace at Bramley Drive indicates induced pore water pressures rising steadily to a peak at approximately 25 m depth; this depth coincides with the base of the landslide scarp. We infer that elevated pore water pressures develop within this single, thick aquifer, triggering failure through reduced effective stresses. The inactive halloysite clay mineral results in low plasticity indices (13 â 44 %) and hence high liquidity indices (1.2 â 2.4) due to the saturated pore space; remoulding following failure is sudden and dramatic and results in large debris runout distances
Research returns redux: a meta-analysis of the returns to agricultural R&D
A total of 294 studies of returns to agricultural R&D (including extension) were compiled and these studies provide 1,858 separate estimates of rates of return. This includes some extreme values, which are implausible. When the highest and lowest 2.5 percent of the rates of return were set aside, the estimated annual rates of return averaged 73 percent overallâ88 percent for research only, 45 percent for research and extension, and 79 percent for extension only. But these averages reveal little meaningful information from a large and diverse body of literature, which provides rate-of-return estimates that are often not directly comparable. The purpose of this study was to go behind the averages, and try to account for the sources of differences, in a meta-analysis of the studies of returns to agricultural R&D. The results conform with the theory and prior beliefs in many ways. Several features of the methods used by research evaluators matter, in particular assumptions about lag lengths and the nature of the research-induced supply shift.Rate of return., Agricultural research.,
Elucidating the role of hyperfine interactions on organic magnetoresistance using deuterated aluminium tris(8-hydroxyquinoline)
Measurements of the effect of a magnetic field on the light output and
current through an organic light emitting diode made with deuterated aluminium
tris(8-hydroxyquinoline) have shown that hyperfine coupling with protons is not
the cause of the intrinsic organic magnetoresistance. We suggest that
interactions with unpaired electrons in the device may be responsible.Comment: Submitte
A meta-analysis of rates of return to agricultural R & D: ex pede Herculem?
IFPRI has long argued that spending on agricultural research constitutes a sound investment in poverty reduction and agricultural and economic growth, through improvements in productivity. This argument is based partly on the reported evidence of high rates of return to agricultural research, typically believed to be in the range of 40â60 percent per year. Yet there continues to be controversy over whether these figures are to be believed, and over what they actually indicate. This study represents the first attempt to take a comprehensive look at all the available evidence on rates of return to investments in agricultural R&D since 1953, and the only attempt to do so in a formal statistical fashion. This report has compiled and documented the literature in ways that make it more accessible and more useful to other researchers and policymakers, as well as others interested in the evidence. The analysis reveals some systematic patterns and some sources of biases that make it easier to interpret the evidence and draw meaningful conclusions. (Excerpted from Summary by Per Pinstrup-Andersen)Development projects Evaluation., Agricultural research, Statistics., Agricultural economics and policies,
Collisional modelling of the AU Microscopii debris disc
The spatially resolved AU Mic debris disc is among the most famous and
best-studied debris discs. We aim at a comprehensive understanding of the dust
production and the dynamics of the disc objects with in depth collisional
modelling including stellar radiative and corpuscular forces. Our models are
compared to a suite of observational data for thermal and scattered light
emission, ranging from the ALMA radial surface brightness profile at 1.3mm to
polarisation measurements in the visible. Most of the data can be reproduced
with a planetesimal belt having an outer edge at around 40au and subsequent
inward transport of dust by stellar winds. A low dynamical excitation of the
planetesimals with eccentricities up to 0.03 is preferred. The radial width of
the planetesimal belt cannot be constrained tightly. Belts that are 5au and
17au wide, as well as a broad 44au-wide belt are consistent with observations.
All models show surface density profiles increasing with distance from the star
as inferred from observations. The best model is achieved by assuming a stellar
mass loss rate that exceeds the solar one by a factor of 50. While the SED and
the shape of the ALMA profile are well reproduced, the models deviate from the
scattered light data more strongly. The observations show a bluer disc colour
and a lower degree of polarisation for projected distances <40au than predicted
by the models. The problem may be mitigated by irregularly-shaped dust grains
which have scattering properties different from the Mie spheres used. From
tests with a handful of selected dust materials, we derive a preference for
mixtures of silicate, carbon, and ice of moderate porosity. We address the
origin of the unresolved central excess emission detected by ALMA and show that
it cannot stem from an additional inner belt alone. Instead, it should derive,
at least partly, from the chromosphere of the central star.Comment: Astronomy and Astrophysics (accepted for publication), 18 pages, 11
figure
Preliminary Results from NEOWISE: An Enhancement to the Wide-field Infrared Survey Explorer for Solar System Science
The Wide-field Infrared Survey Explorer (WISE) has surveyed the entire sky at four infrared wavelengths with greatly improved sensitivity and spatial resolution compared to its predecessors, the Infrared Astronomical Satellite and the Cosmic Background Explorer. NASA's Planetary Science Division has funded an enhancement to the WISE data processing system called "NEOWISE" that allows detection and archiving of moving objects found in the WISE data. NEOWISE has mined the WISE images for a wide array of small bodies in our solar system, including near-Earth objects (NEOs), Main Belt asteroids, comets, Trojans, and Centaurs. By the end of survey operations in 2011 February, NEOWISE identified over 157,000 asteroids, including more than 500 NEOs and ~120 comets. The NEOWISE data set will enable a panoply of new scientific investigations
Young "Dipper" Stars in Upper Sco and Oph Observed by K2
We present ten young (10 Myr) late-K and M dwarf stars observed in
K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or
aperiodic dimming events. Their optical light curves show 10-20 dips in
flux over the 80-day observing campaign with durations of 0.5-2 days and
depths of up to 40%. These stars are all members of the Ophiuchus
(1 Myr) or Upper Scorpius (10 Myr) star-forming regions. To
investigate the nature of these "dippers" we obtained: optical and
near-infrared spectra to determine stellar properties and identify accretion
signatures; adaptive optics imaging to search for close companions that could
cause optical variations and/or influence disk evolution; and
millimeter-wavelength observations to constrain disk dust and gas masses. The
spectra reveal Li I absorption and H emission consistent with stellar
youth (<50 Myr), but also accretion rates spanning those of classical and
weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary
disks extending to within 10 stellar radii in most cases; however, the
sub-mm observations imply disk masses that are an order of magnitude below
those of typical protoplanetary disks. We find a positive correlation between
dip depth and WISE-2 excess, which we interpret as evidence that the dipper
phenomenon is related to occulting structures in the inner disk, although this
is difficult to reconcile with the weakly accreting aperiodic dippers. We
consider three mechanisms to explain the dipper phenomenon: inner disk warps
near the co-rotation radius related to accretion; vortices at the inner disk
edge produced by the Rossby Wave Instability; and clumps of circumstellar
material related to planetesimal formation.Comment: Accepted to ApJ, 19 pages, 10 figure
Monte Carlo Generation of Bohmian Trajectories
We report on a Monte Carlo method that generates one-dimensional trajectories
for Bohm's formulation of quantum mechanics that doesn't involve
differentiation or integration of any equations of motion. At each time,
t=n\delta t (n=1,2,3,...), N particle positions are randomly sampled from the
quantum probability density. Trajectories are built from the sorted N sampled
positions at each time. These trajectories become the exact Bohm solutions in
the limits N->\infty and \delta t -> 0. Higher dimensional problems can be
solved by this method for separable wave functions. Several examples are given,
including the two-slit experiment.Comment: 10 pages, 6 figure
Debris disk size distributions: steady state collisional evolution with P-R drag and other loss processes
We present a new scheme for determining the shape of the size distribution,
and its evolution, for collisional cascades of planetesimals undergoing
destructive collisions and loss processes like Poynting-Robertson drag. The
scheme treats the steady state portion of the cascade by equating mass loss and
gain in each size bin; the smallest particles are expected to reach steady
state on their collision timescale, while larger particles retain their
primordial distribution. For collision-dominated disks, steady state means that
mass loss rates in logarithmic size bins are independent of size. This
prescription reproduces the expected two phase size distribution, with ripples
above the blow-out size, and above the transition to gravity-dominated
planetesimal strength. The scheme also reproduces the expected evolution of
disk mass, and of dust mass, but is computationally much faster than evolving
distributions forward in time. For low-mass disks, P-R drag causes a turnover
at small sizes to a size distribution that is set by the redistribution
function (the mass distribution of fragments produced in collisions). Thus
information about the redistribution function may be recovered by measuring the
size distribution of particles undergoing loss by P-R drag, such as that traced
by particles accreted onto Earth. Although cross-sectional area drops with
1/age^2 in the PR-dominated regime, dust mass falls as 1/age^2.8, underlining
the importance of understanding which particle sizes contribute to an
observation when considering how disk detectability evolves. Other loss
processes are readily incorporated; we also discuss generalised power law loss
rates, dynamical depletion, realistic radiation forces and stellar wind drag.Comment: Accepted for publication by Celestial Mechanics and Dynamical
Astronomy (special issue on EXOPLANETS
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