792 research outputs found
Analysis procedures and subjective flight results of a simulator validation and cue fidelity experiment
A joint experiment to investigate simulator validation and cue fidelity was conducted by the Dryden Flight Research Facility of NASA Ames Research Center (Ames-Dryden) and NASA Langley Research Center. The primary objective was to validate the use of a closed-loop pilot-vehicle mathematical model as an analytical tool for optimizing the tradeoff between simulator fidelity requirements and simulator cost. The validation process includes comparing model predictions with simulation and flight test results to evaluate various hypotheses for differences in motion and visual cues and information transfer. A group of five pilots flew air-to-air tracking maneuvers in the Langley differential maneuvering simulator and visual motion simulator and in an F-14 aircraft at Ames-Dryden. The simulators used motion and visual cueing devices including a g-seat, a helmet loader, wide field-of-view horizon, and a motion base platform
Phase transitions in three-dimensional topological lattice models with surface anyons
We study the phase diagrams of a family of 3D "Walker-Wang" type lattice
models, which are not topologically ordered but have deconfined anyonic
excitations confined to their surfaces. We add a perturbation (analogous to
that which drives the confining transition in Z_p lattice gauge theories) to
the Walker-Wang Hamiltonians, driving a transition in which all or some of the
variables associated with the loop gas or string-net ground states of these
models become confined. We show that in many cases the location and nature of
the phase transitions involved is exactly that of a generalized Z_p lattice
gauge theory, and use this to deduce the basic structure of the phase diagram.
We further show that the relationship between the phases on opposite sides of
the transition is fundamentally different than in conventional gauge theories:
in the Walker-Wang case, the number of species of excitations that are
deconfined in the bulk can increase across a transition that confines only some
of the species of loops or string-nets. The analogue of the confining
transition in the Walker-Wang models can therefore lead to bulk deconfinement
and topological order
Classical spin liquids in stacked triangular lattice Ising antiferromagnets
We study Ising antiferromagnets that have nearest-neighbour interactions on
multilayer triangular lattices with frustrated ( and ) stacking, and
make comparisons with the unfrustrated () stacking. If interlayer
couplings are much weaker than in-plane ones, the paramagnetic phase of models
with frustrated stackings has a classical spin-liquid regime at low
temperature, in which correlations are strong both within and between planes,
but there is no long-range order. We investigate this regime using Monte Carlo
simulations and by mapping the spin models to coupled height models, which are
treated using renormalisation group methods and an analysis of the effects of
vortex excitations. The classical spin-liquid regime is parametrically wide at
small interlayer coupling in models with frustrated stackings. By contrast, for
the unfrustrated stacking there is no extended regime in which interlayer
correlations are strong without three-dimensional order.Comment: 25 pages, 21 figures; version to appear in Physical Review B,
includes minor correction
Deuteron and proton NMR study of D₂, p-dichlorobenzene and 1,3,5-trichlorobenzene in bimesogenic liquid crystals with two nematic phases
The solutes dideuterium, 1,3,5-trichlorobenzene and p-dichlorobenzene (pdcb) are co-dissolved in a 61/39 wt% mixture of CBC9CB/5CB, a bimesogenic liquid crystal with two nematic phases. NMR spectra are collected for each solute. The local electric field gradient (FZZ) is obtained from the dideuterium spectrum. A double Maier-Saupe potential (MSMS) is used to rationalize the order parameters of pdcb. The liquid-crystal fields G₁ and G₂ are taken to be due to size and shape interactions and interactions between the solute molecular quadrupole and the mean FZZ of the medium. The FZZ’s obtained from D₂ and G₂ (from pdcb) are compared and discussed
A Protocol for Citizen Science Monitoring of Recently-Planted Urban Trees
In this article, we present a protocol for citizen science monitoring of planted urban trees. Informed by social-ecological systems, urban forestry, and tree physiology research, the Planted Tree Re-Inventory Protocol is designed to allow minimally-trained volunteers or citizen scientists to collect data about the factors that influence urban tree survival and growth. We consider characteristics of the tree, the biophysical environment, institutions and management, and the community as factors that influence urban forest outcomes. Here, we reflect on tree planting organizations and their desire and capacity for monitoring. Then we define citizen science and review its use in urban forestry to date. Next we discuss the measurement of urban tree outcomes (survival and growth), and summarize the literature on factors influencing tree success and urban forest outcomes. Finally we present an overview of the main categories of variables included the Protocol. The entire Protocol is available on the Bloomington Urban Forestry Research Group website (http://www.indiana.edu/~cipec/research/bufrg_protocol) and as an Appendix to this paper
Effect of Patterned Slip on Micro and Nanofluidic Flows
We consider the flow of a Newtonian fluid in a nano or microchannel with
walls that have patterned variations in slip length. We formulate a set of
equations to describe the effects on an incompressible Newtonian flow of small
variations in slip, and solve these equations for slow flows. We test these
equations using molecular dynamics simulations of flow between two walls which
have patterned variations in wettability. Good qualitative agreement and a
reasonable degree of quantitative agreement is found between the theory and the
molecular dynamics simulations. The results of both analyses show that
patterned wettability can be used to induce complex variations in flow. Finally
we discuss the implications of our results for the design of microfluidic
mixers using slip.Comment: 13 pages, 12 figures, final version for publicatio
NMR study of a bimesogenic liquid crystal with two nematic phases
Recent interest in bimesogenic liquid crystals showing two nematic phases has led us to investigate the nematic mean-field interactions in these nematic phases by using rigid solutes as probes. The nematic potential that is modelled by two independent Maier-Saupe terms is successful in fitting the observed dipolar couplings (order parameters) of para-, meta- and ortho-dichlorobenzene solutes in both the nematic phases of 39 wt% of 4-n-pentyl-4′-cyanobiphenyl (5CB) in α,ω-bis(4-4′-cyanobiphenyl)nonane (CB_C9_CB) to better than the 5% level. The derived liquid-crystal potential parameters G₁ and G₂ for each solute in the N and Ntb phases will be discussed. The most interesting observation is that G1 (associated with size and shape interactions) is almost constant in the Ntb phase, whereas G₂ (associated with longer-range electrostatic interactions) has large variation, even changing sign
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