1,903 research outputs found
A system to geometrically rectify and map airborne scanner imagery and to estimate ground area
A system of computer programs were developed which performs geometric rectification and line-by-line mapping of airborne multispectral scanner data to ground coordinates and estimates ground area. The system requires aircraft attitude and positional information furnished by ancillary aircraft equipment, as well as ground control points. The geometric correction and mapping procedure locates the scan lines, or the pixels on each line, in terms of map grid coordinates. The area estimation procedure gives ground area for each pixel or for a predesignated parcel specified in map grid coordinates. The results of exercising the system with simulated data showed the uncorrected video and corrected imagery and produced area estimates accurate to better than 99.7%
Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature
We investigate the transport properties of double-gated bilayer graphene
nanoribbons at room temperature. The devices were fabricated using conventional
CMOS-compatible processes. By analyzing the dependence of the resistance at the
charge neutrality point as a function of the electric field applied
perpendicular to the graphene surface, we show that a band gap in the density
of states opens, reaching an effective value of ~sim50 meV. This demonstrates
the potential of bilayer graphene as FET channel material in a conventional
CMOS environment.Comment: 3 pages, 3 figure
Extended Wertheim theory predicts the anomalous chain length distributions of divalent patchy particles under extreme confinement
Colloidal patchy particles with divalent attractive interaction can
self-assemble into linear polymer chains. Their equilibrium properties in 2D
and 3D are well described by Wertheim's thermodynamic perturbation theory which
predicts a well-defined exponentially decaying equilibrium chain length
distribution. In experimental realizations, due to gravity, particles sediment
to the bottom of the suspension forming a monolayer of particles with a
gravitational height smaller than the particle diameter. In accordance with
experiments, an anomalously high monomer concentration is observed in
simulations which is not well understood. To account for this observation, we
interpret the polymerization as taking place in a highly confined quasi-2D
plane and extend the Wertheim thermodynamic perturbation theory by defining
addition reactions constants as functions of the chain length. We derive the
theory, test it on simple square well potentials, and apply it to the
experimental case of synthetic colloidal patchy particles immersed in a binary
liquid mixture that are described by an accurate effective critical Casimir
patchy particle potential. The important interaction parameters entering the
theory are explicitly computed using the integral method in combination with
Monte Carlo sampling. Without any adjustable parameter, the predictions of the
chain length distribution are in excellent agreement with explicit simulations
of self-assembling particles. We discuss generality of the approach, and its
application range.Comment: The following article has been submitted to The Journal of Chemical
Physic
Population Characteristics of Co-Managed White Bass and Hybrid Striped Bass in Lake McConaughy, Nebraska
White Bass (Morone chrysops) and Hybrid Striped Bass (M. saxatillis × M. chrysops) populations often coexist in the same waterbody and are known to achieve different lengths, have differing reproductive success, and provide different opportunities for anglers. However, comparative population dynamics from systems where Moronids are managed with the same regulation is often lacking. This study aimed to assess the recruitment, mortality, and growth of these species from seasonal samples collected at Lake McConaughy in 2015 and fall 2016. White Bass demonstrated highly variable recruitment in Lake McConaughy despite stocking efforts (mean recruitment variability index = 0.157). Hybrid Striped Bass year class strength was also variable, but RVI was not calculated as the number of missing year classes exceed the number of present year classes. Total annual mortality estimates for Hybrid Striped Bass (39.7%) and White Bass (41.4%) were consistent with values reported in other populations, but both species were observed to achieve uncommon longevity. Both species exhibited sexual size dimorphism, and growth was moderate and consistent with average values presented for North American populations. This study provides insight into the population dynamics of two species with trophy potential managed by the same regulation in Lake McConaughy. Differences in growth patterns indicate the current regulation affects each species differently, and managers may be able to utilize this to inform decisions about management of coexisting Moronid populations
Incentivizing High Quality Crowdwork
We study the causal effects of financial incentives on the quality of
crowdwork. We focus on performance-based payments (PBPs), bonus payments
awarded to workers for producing high quality work. We design and run
randomized behavioral experiments on the popular crowdsourcing platform Amazon
Mechanical Turk with the goal of understanding when, where, and why PBPs help,
identifying properties of the payment, payment structure, and the task itself
that make them most effective. We provide examples of tasks for which PBPs do
improve quality. For such tasks, the effectiveness of PBPs is not too sensitive
to the threshold for quality required to receive the bonus, while the magnitude
of the bonus must be large enough to make the reward salient. We also present
examples of tasks for which PBPs do not improve quality. Our results suggest
that for PBPs to improve quality, the task must be effort-responsive: the task
must allow workers to produce higher quality work by exerting more effort. We
also give a simple method to determine if a task is effort-responsive a priori.
Furthermore, our experiments suggest that all payments on Mechanical Turk are,
to some degree, implicitly performance-based in that workers believe their work
may be rejected if their performance is sufficiently poor. Finally, we propose
a new model of worker behavior that extends the standard principal-agent model
from economics to include a worker's subjective beliefs about his likelihood of
being paid, and show that the predictions of this model are in line with our
experimental findings. This model may be useful as a foundation for theoretical
studies of incentives in crowdsourcing markets.Comment: This is a preprint of an Article accepted for publication in WWW
\c{opyright} 2015 International World Wide Web Conference Committe
Shear-induced anisotropic decay of correlations in hard-sphere colloidal glasses
Spatial correlations of microscopic fluctuations are investigated via
real-space experiments and computer simulations of colloidal glasses under
steady shear. It is shown that while the distribution of one-particle
fluctuations is always isotropic regardless of the relative importance of shear
as compared to thermal fluctuations, their spatial correlations show a marked
sensitivity to the competition between shear-induced and thermally activated
relaxation. Correlations are isotropic in the thermally dominated regime, but
develop strong anisotropy as shear dominates the dynamics of microscopic
fluctuations. We discuss the relevance of this observation for a better
understanding of flow heterogeneity in sheared amorphous solids.Comment: 6 pages, 4 figure
Inhibitory control in mind and brain 2.0: blocked-input models of saccadic countermanding.
The interactive race model of saccadic countermanding assumes that response inhibition results from an interaction between a go unit, identified with gaze-shifting neurons, and a stop unit, identified with gaze-holding neurons, in which activation of the stop unit inhibits the growth of activation in the go unit to prevent it from reaching threshold. The interactive race model accounts for behavioral data and predicts physiological data in monkeys performing the stop-signal task. We propose an alternative model that assumes that response inhibition results from blocking the input to the go unit. We show that the blocked-input model accounts for behavioral data as accurately as the original interactive race model and predicts aspects of the physiological data more accurately. We extend the models to address the steady-state fixation period before the go stimulus is presented and find that the blocked-input model fits better than the interactive race model. We consider a model in which fixation activity is boosted when a stop signal occurs and find that it fits as well as the blocked input model but predicts very high steady-state fixation activity after the response is inhibited. We discuss the alternative linking propositions that connect computational models to neural mechanisms, the lessons to be learned from model mimicry, and generalization from countermanding saccades to countermanding other kinds of responses
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