5,986 research outputs found
Simultaneous localization and map-building using active vision
An active approach to sensing can provide the focused measurement capability over a wide field of view which allows correctly formulated Simultaneous Localization and Map-Building (SLAM) to be implemented with vision, permitting repeatable long-term localization using only naturally occurring, automatically-detected features. In this paper, we present the first example of a general system for autonomous localization using active vision, enabled here by a high-performance stereo head, addressing such issues as uncertainty-based measurement selection, automatic map-maintenance, and goal-directed steering. We present varied real-time experiments in a complex environment.Published versio
The control of a nuclear reactor using helium- 3 gas control elements
Control system for water moderated reactor using helium-3 ga
TESTING FOR AGGREGATION AND SIMULTANEOUS BIAS IN U.S. SOYBEAN EXPORT EQUATIONS
Most previous estimates of elasticities of export demand for U.S. soybeans have emanated from single import equations subject to aggregation and simultaneous equation bias. This analysis tests U.S. soybean export data for aggregation and simultaneous equation bias and divides the aggregated data into six market equations to reduce these biases. Elasticity estimates from the six equations are compared with elasticity estimates from single equation OLS and 2SLS estimations using the same aggregate data. Results suggest that distortions from unjustified 2SLS estimation may exceed those from aggregation bias.International Relations/Trade,
Advanced-power-reactor design concepts and performance characteristics
Five reactor cooling concepts which allow continued reactor operation following a single rupture of the coolant system are presented for application with the APR. These concepts incorporate convective cooling, double containment, or heat pipes to ensure operation after a coolant line rupture. Based on an evaluation of several control system concepts, a molybdenum clad, beryllium oxide sliding reflector located outside the pressure vessel is recommended
Towards More Accurate Molecular Dynamics Calculation of Thermal Conductivity. Case Study: GaN Bulk Crystals
Significant differences exist among literature for thermal conductivity of
various systems computed using molecular dynamics simulation. In some cases,
unphysical results, for example, negative thermal conductivity, have been
found. Using GaN as an example case and the direct non-equilibrium method,
extensive molecular dynamics simulations and Monte Carlo analysis of the
results have been carried out to quantify the uncertainty level of the
molecular dynamics methods and to identify the conditions that can yield
sufficiently accurate calculations of thermal conductivity. We found that the
errors of the calculations are mainly due to the statistical thermal
fluctuations. Extrapolating results to the limit of an infinite-size system
tend to magnify the errors and occasionally lead to unphysical results. The
error in bulk estimates can be reduced by performing longer time averages using
properly selected systems over a range of sample lengths. If the errors in the
conductivity estimates associated with each of the sample lengths are kept
below a certain threshold, the likelihood of obtaining unphysical bulk values
becomes insignificant. Using a Monte-Carlo approach developed here, we have
determined the probability distributions for the bulk thermal conductivities
obtained using the direct method. We also have observed a nonlinear effect that
can become a source of significant errors. For the extremely accurate results
presented here, we predict a [0001] GaN thermal conductivity of 185 at 300 K, 102 at 500 K, and 74
at 800 K. Using the insights obtained in the work, we have achieved a
corresponding error level (standard deviation) for the bulk (infinite sample
length) GaN thermal conductivity of less than 10 , 5 , and 15 at 300 K, 500 K, and 800 K respectively
Female teat size is a reliable indicator of annual breeding success in European badgers: Genetic validation
Assessing which females have bred successfully is a central requirement in many ecological field studies,
providing an estimate of the effective female population size. Researchers have applied teat measurements
previously to assess whether females, in a variety of mammalian species, have bred; however, this
technique has not been validated genetically. Furthermore, several analytical techniques are available to
classify individuals, but their misclassification rates have not been compared. We used 22 microsatellite
loci to assign maternity, with 95% confidence, within a high-density population of European badgers Meles
meles, as plural and subterranean breeding means that maternity cannot be inferred from behavioural
observations. The teat lengths and diameters of 136 females, measured May–July 1994–2005, from social
groups in which all offspring were assigned a mother, were reliable indicators of recent breeding success.
A Generalised Linear Mixed Model (GLMM) classified both breeding and non-breeding females with
lower error rates than discriminant analyses and crude teat-size criteria. The GLMM model logit probability
=
−20 + 1.8 month + 1.6 mean teat length + 1.0 mean teat diameter can be applied quickly in the field
to assess the probability with which a female badger should be assigned maternity. This is a low-cost
measure which, after validation, could be used in other badger or mammalian populations to assess the
breeding success of females. This may be a particularly useful welfare tool for veterinary practitioners,
especially during badger culls
Glassy behaviour in a simple topological model
In this article we study a simple, purely topological, cellular model which
is allowed to evolve through a Glauber-Kawasaki process. We find a
non-thermodynamic transition to a glassy phase in which the energy (defined as
the square of the local cell topological charge) fails to reach the equilibrium
value below a characteristic temperature which is dependent on the cooling
rate. We investigate a correlation function which exhibits aging behaviour, and
follows a master curve in the stationary regime when time is rescaled by a
factor of the relaxation time t_r. This master curve can be fitted by a von
Schweidler law in the late beta-relaxation regime. The relaxation times can be
well-fitted at all temperatures by an offset Arrhenius law. A power law can be
fitted to an intermediate temperature regime; the exponent of the power law and
the von Schweidler law roughly agree with the relationship predicted by
Mode-coupling Theory. By defining a suitable response function, we find that
the fluctuation-dissipation ratio is held until sometime later than the
appearance of the plateaux; non-monotonicity of the response is observed after
this ratio is broken, a feature which has been observed in other models with
dynamics involving activated processes.Comment: 11 pages LaTeX; minor textual corrcetions, minor corrections to figs
4 & 7
Quantifying micro-niche behaviour in sediments: Precise and accurate measurements of DGT gels by laser ablation high resolution laser ablation ICPMS
(±)-trans-3-Oxo-1,2,3,4,4a,9,10,10a-octahydrophenanthrene-10a-carboxylic acid: catemeric hydrogen bonding in a δ-keto acid
The title compound, C15H16O3, aggregates as hydrogen-bonded catemers progressing from each carboxyl to the ketone of a screw-related neighbor [O⋯O = 2.6675 (14) Å and O—H⋯O = 170°]. Two parallel centrosymmetrically related single-strand hydrogen-bonding helices proceed through the cell in the b-axis direction. The packing includes three intermolecular C—H⋯O=C close contacts, involving both the ketone and the carboxyl group. The structure is isomorphous with that of the previously described Δ4 α,β-unsaturated ketone
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