2,777 research outputs found
Effects of hybrid maturity and growth stage on yield and composition of forage and grain sorghums when harvested as silage
Thirteen sorghum hybrids chosen to represent a range of sorghum types
were evaluated in two separate trials. Each was harvested at three stages of grain
development: milk to early-dough, late-dough, and hard-grain.
Among the forage sorghums, there was a 26-day range in days to half bloom
from early to late maturing varieties. Harvest date did not affect crude protein
content. However, whole-plant DM yield was significantly lower at the last
harvest for the three latest maturing varieties. Grain yield increased over time in
the early and intermediate hybrids. Lodging increased significantly over time for
all varieties except DeKalb FS-25E.
Among the grain sorghums, there was only a 4-day range in days to half
bloom and very little difference in plant height. The forage sorghum was later
maturing and taller. Whole-plant DM yields for the grain sorghums were highest at
late-dough. Grain yields and grain to forage ratios generally increased with
maturity, except when there were losses due to birds. Grain sorghums started to
lodge by the hard-grain stage
A Precision Angle Sensor using an Optical Lever inside a Sagnac Interferometer
We built an ultra low noise angle sensor by combining a folded optical lever
and a Sagnac interferometer. The instrument has a measured noise floor of 1.3
prad / Hz^(1/2) at 2.4 kHz. We achieve this record angle sensitivity using a
proof-of-concept apparatus with a conservative N=11 bounces in the optical
lever. This technique could be extended to reach sub-picoradian / Hz^(1/2)
sensitivities with an optimized design.Comment: 3 pages, 4 figure
Electric-Field Tuning of Spin-Dependent Exciton-Exciton Interactions in Coupled Quantum Wells
We have shown experimentally that an electric field decreases the energy
separation between the two components of a dense spin-polarized exciton gas in
a coupled double quantum well, from a maximum splitting of meV to
zero, at a field of 35 kV/cm. This decrease, due to the field-induced
deformation of the exciton wavefunction, is explained by an existing
calculation of the change in the spin-dependent exciton-exciton interaction
with the electron-hole separation. However, a new theory that considers the
modification of screening with that separation is needed to account for the
observed dependence on excitation power of the individual energies of the two
exciton components.Comment: 5 pages, 4 eps figures, RevTeX, Physical Review Letters (in press
Allocation in Practice
How do we allocate scarcere sources? How do we fairly allocate costs? These
are two pressing challenges facing society today. I discuss two recent projects
at NICTA concerning resource and cost allocation. In the first, we have been
working with FoodBank Local, a social startup working in collaboration with
food bank charities around the world to optimise the logistics of collecting
and distributing donated food. Before we can distribute this food, we must
decide how to allocate it to different charities and food kitchens. This gives
rise to a fair division problem with several new dimensions, rarely considered
in the literature. In the second, we have been looking at cost allocation
within the distribution network of a large multinational company. This also has
several new dimensions rarely considered in the literature.Comment: To appear in Proc. of 37th edition of the German Conference on
Artificial Intelligence (KI 2014), Springer LNC
Investigating Sources of Variability and Error in Simulations of Carbon Dioxide in an Urban Region
Greenhouse gas (GHG) emissions estimation methods that use atmospheric trace gas observations, including inverse modeling techniques, perform better when carbon dioxide (CO2) fluxes are more accurately transported and dispersed in the atmosphere by a numerical model. In urban areas, transport and dispersion is particularly difficult to simulate using current mesoscale meteorological models due, in part, to added complexity from surface heterogeneity and fine spatial/temporal scales. It is generally assumed that the errors in GHG estimation methods in urban areas are dominated by errors in transport and dispersion. Other significant errors include, but are not limited to, those from assumed emissions magnitude and spatial distribution. To assess the predictability of simulated trace gas mole fractions in urban observing systems using a numerical weather prediction model, we employ an Eulerian model that combines traditional meteorological variables with multiple passive tracers of atmospheric CO2 from anthropogenic inventories and a biospheric model. The predictability of the Eulerian model is assessed by comparing simulated atmospheric CO2 mole fractions to observations from four in situ tower sites (three urban and one rural) in the Washington DC/Baltimore, MD area for February 2016. Four different gridded fossil fuel emissions inventories along with a biospheric flux model are used to create an ensemble of simulated atmospheric CO2 observations within the model. These ensembles help to evaluate whether the modeled observations are impacted more by the underlying emissions or transport. The spread of modeled observations using the four emission fields indicates the model's ability to distinguish between the different inventories under various meteorological conditions. Overall, the Eulerian model performs well; simulated and observed average CO2 mole fractions agree within 1% when averaged at the three urban sites across the month. However, there can be differences greater than 10% at any given hour, which are attributed to complex meteorological conditions rather than differences in the inventories themselves. On average, the mean absolute error of the simulated compared to actual observations is generally twice as large as the standard deviation of the modeled mole fractions across the four emission inventories. This result supports the assumption, in urban domains, that the predicted mole fraction error relative to observations is dominated by errors in model meteorology rather than errors in the underlying fluxes in winter months. As such, minimizing errors associated with atmospheric transport and dispersion may help improve the performance of GHG estimation models more so than improving flux priors in the winter months. We also find that the errors associated with atmospheric transport in urban domains are not restricted to certain times of day. This suggests that atmospheric inversions should use CO2 observations that have been filtered using meteorological observations rather than assuming that meteorological modeling is most accurate at certain times of day (such as using only mid-afternoon observations)
The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules
An on-going Arecibo line search between 1.1 and 10 GHz of the prototypical
starburst/megamaser galaxy, Arp 220, has revealed a spectrum rich in molecular
transitions. These include the ``pre-biotic'' molecules: methanimine
(CHNH) in emission, three direct l-type absorption lines of
HCN, and an absorption feature likely to be from either OH or formic
acid (HCOOH). In addition, we report the detection of two, possibly three,
transitions of 4-cm excited OH not previously detected in Arp~220
which are seen in absorption, and a possible absorption feature from the
6.668-GHz line of methanol. This marks the first distant extragalactic
detection of methanimine, a pre-biotic molecule. Also, if confirmed, the
possible methanol absorption line presented here would represent the first
extragalactic detection of methanol at a distance further than 10 Mpc. In
addition, the strong, previously undetected, cm-wave HCN direct
l-type lines will aid the study of dense molecular gas and active star-forming
regions in this starburst galaxy.Comment: 25 pages, 10 figures. Accepted for publication in A
Drawing Trees with Perfect Angular Resolution and Polynomial Area
We study methods for drawing trees with perfect angular resolution, i.e.,
with angles at each node v equal to 2{\pi}/d(v). We show:
1. Any unordered tree has a crossing-free straight-line drawing with perfect
angular resolution and polynomial area.
2. There are ordered trees that require exponential area for any
crossing-free straight-line drawing having perfect angular resolution.
3. Any ordered tree has a crossing-free Lombardi-style drawing (where each
edge is represented by a circular arc) with perfect angular resolution and
polynomial area. Thus, our results explore what is achievable with
straight-line drawings and what more is achievable with Lombardi-style
drawings, with respect to drawings of trees with perfect angular resolution.Comment: 30 pages, 17 figure
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