7,811 research outputs found
An optimal control approach to pilot/vehicle analysis and Neal-Smith criteria
The approach of Neal and Smith was merged with the advances in pilot modeling by means of optimal control techniques. While confirming the findings of Neal and Smith, a methodology that explicitly includes the pilot's objective in attitude tracking was developed. More importantly, the method yields the required system bandwidth along with a better pilot model directly applicable to closed-loop analysis of systems in any order
Coherence-Preserving Quantum Bits
Real quantum systems couple to their environment and lose their intrinsic
quantum nature through the process known as decoherence. Here we present a
method for minimizing decoherence by making it energetically unfavorable. We
present a Hamiltonian made up solely of two-body interactions between four
two-level systems (qubits) which has a two-fold degenerate ground state. This
degenerate ground state has the property that any decoherence process acting on
an individual physical qubit must supply energy from the bath to the system.
Quantum information can be encoded into the degeneracy of the ground state and
such coherence-preserving qubits will then be robust to local decoherence at
low bath temperatures. We show how this quantum information can be universally
manipulated and indicate how this approach may be applied to a quantum dot
quantum computer.Comment: 5 pages, 1 figur
Recurrence rates for SIDS - the importance of risk stratification
Objective:
To investigate the importance of stratification by risk factors in computing the probability of a second SIDS in a family.
Design: Simulation Study
Background:
The fact that a baby dies suddenly and unexpectedly means that there is a raised probability that the baby’s family have risk factors associated with Sudden Infant Death Syndrome (SIDS). Thus one cannot consider the risk of a subsequent death to be that of the general population. The Confidential Enquiry into Stillbirths and Deaths in Infancy (CESDI)6 identified three major social risk factors: smoking, age1, and unemployed/unwaged as major risk factors. It gave estimates of risk for families with different numbers of these risk factors. We investigate whether it is reasonable to assume that, conditional on these risk factors, the risk of a second event is independent of the risk of the first and as a consequence one can square the risks to get the risk of two SIDS in a family. We have used CESDI data to estimate the probability of a second SID in a family under different plausible scenarios of the prevalence of the risk factors. We have applied the model to make predictions in the Care of Next Infant (CONI) study7.
Results:
The model gave plausible predictions. The CONI study observed 18 second SIDS. Our model predicted 14 (95% prediction interval 7 to 21).
Conclusion:
When considering the risk of a subsequent SIDS in a family one should always take into account the known risk factors. If all risks have been identified, then conditional on these risks, the risk of two events is the product of the individual risks However for a given family we cannot quantify the magnitude of the increased risk because of other possible risk factors not accounted for in the model
A tutorial task and tertiary courseware model for collaborative learning communities
RAED provides a computerised infrastructure to support the development and administration of Vicarious Learning in collaborative learning communities spread across multiple universities and workplaces. The system is based on the OASIS middleware for Role-based Access Control. This paper describes the origins of the model and the approach to implementation and outlines some of its benefits to collaborative teachers and learners
Weak Gravitational Flexion
Flexion is the significant third-order weak gravitational lensing effect
responsible for the weakly skewed and arc-like appearance of lensed galaxies.
Here we demonstrate how flexion measurements can be used to measure galaxy halo
density profiles and large-scale structure on non-linear scales, via
galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation
functions. We describe the origin of gravitational flexion, and discuss its
four components, two of which are first described here. We also introduce an
efficient complex formalism for all orders of lensing distortion. We proceed to
examine the flexion predictions for galaxy-galaxy lensing, examining isothermal
sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric
and elliptical cases. We show that in combination with shear we can precisely
measure galaxy masses and NFW halo concentrations. We also show how flexion
measurements can be used to reconstruct mass maps in 2-D projection on the sky,
and in 3-D in combination with redshift data. Finally, we examine the
predictions for cosmic flexion, including convergence-flexion
cross-correlations, and find that the signal is an effective probe of structure
on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA
A double-helix neutron detector using micron-size B-10 powder
A double-helix electrode configuration is combined with a B powder
coating technique to build large-area (9 in 36 in) neutron detectors.
The neutron detection efficiency for each of the four prototypes is comparable
to a single 2-bar He drift tube of the same length (36 in). One unit has
been operational continuously for 18 months and the change of efficiency is
less than 1%. An analytic model for pulse heigh spectra is described and the
predicted mean film thickness agrees with the experiment to within 30%. Further
detector optimization is possible through film texture, power size, moderator
box and gas. The estimated production cost per unit is less than 3k US\$ and
the technology is thus suitable for deployment in large numbers
ANALYSIS OF TRENDS AND FORECASTS IN COFFEE PRICES AND CONSUMER CONSUMPTION IN THE NORTHEAST AND UNITED STATES
Demand and Price Analysis, Food Consumption/Nutrition/Food Safety,
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