95,782 research outputs found
Control theoretic models of pointing
This article presents an empirical comparison of four models from manual control theory on their ability to model targeting behaviour by human users using a mouse: McRuer’s Crossover, Costello’s Surge, second-order lag (2OL), and the Bang-bang model. Such dynamic models are generative, estimating not only movement time, but also pointer position, velocity, and acceleration on a moment-to-moment basis. We describe an experimental framework for acquiring pointing actions and automatically fitting the parameters of mathematical models to the empirical data. We present the use of time-series, phase space, and Hooke plot visualisations of the experimental data, to gain insight into human pointing dynamics. We find that the identified control models can generate a range of dynamic behaviours that captures aspects of human pointing behaviour to varying degrees. Conditions with a low index of difficulty (ID) showed poorer fit because their unconstrained nature leads naturally to more behavioural variability. We report on characteristics of human surge behaviour (the initial, ballistic sub-movement) in pointing, as well as differences in a number of controller performance measures, including overshoot, settling time, peak time, and rise time. We describe trade-offs among the models. We conclude that control theory offers a promising complement to Fitts’ law based approaches in HCI, with models providing representations and predictions of human pointing dynamics, which can improve our understanding of pointing and inform design
Macromolecular separation through a porous surface
A new technique for the separation of macromolecules is proposed and
investigated. A thin mesh with pores comparable to the radius of gyration of a
free chain is used to filter chains according to their length. Without a field
it has previously been shown that the permeability decays as a power law with
chain length. However by applying particular configurations of pulsed fields,
it is possible to have a permeability that decays as an exponential. This
faster decay gives much higher resolution of separation. We also propose a
modified screen containing an array of holes with barb-like protrusions running
parallel to the surface. When static friction is present between the
macromolecule and the protrusion, some of the chains get trapped for long
durations of time. By using this and a periodic modulation of an applied
electric field, high resolution can be attained.Comment: 18 pages latex, 6 postscript figures, using psfi
The observational evidence pertinent to possible kick mechanisms in neutron stars
We examine available observations on pulsars for evidence pertaining to
mechanisms proposed to explain the origin of their velocities. We find that
mechanisms predicting a correlation between the rotation axis and the pulsar
velocity are ruled out. Also, that there is no significant correlation between
pulsar magnetic field strengths and velocities. With respect to recent
suggestions postulating asymmetric impulses at birth being solely responsible
for both the spins and velocities of pulsars, single impulses of any duration
and multiple extended duration impulses appear ruled out.Comment: 7 pages. Accepted for publication in Astronomy & Astrophysic
Multiverse Understanding of Cosmological Coincidences
There is a deep cosmological mystery: although dependent on very different
underlying physics, the timescales of structure formation, of galaxy cooling
(both radiatively and against the CMB), and of vacuum domination do not differ
by many orders of magnitude, but are all comparable to the present age of the
universe. By scanning four landscape parameters simultaneously, we show that
this quadruple coincidence is resolved. We assume only that the statistical
distribution of parameter values in the multiverse grows towards certain
catastrophic boundaries we identify, across which there are drastic regime
changes. We find order-of-magnitude predictions for the cosmological constant,
the primordial density contrast, the temperature at matter-radiation equality,
the typical galaxy mass, and the age of the universe, in terms of the fine
structure constant and the electron, proton and Planck masses. Our approach
permits a systematic evaluation of measure proposals; with the causal patch
measure, we find no runaway of the primordial density contrast and the
cosmological constant to large values.Comment: 40 pages, 5 figures; discussion of measures extended, version to
appear in Phys. Rev.
Towards optimization of pulsed sodium laser guide stars
Pulsed sodium laser guide stars (LGS) are useful because they allow for
Rayleigh blanking and fratricide avoidance in multiple-LGS systems.
Bloch-equation simulations of sodium-light interactions show that these may be
able to achieve photon returns nearly equal to, and in some cases greater than,
what is seen from continuous-wave (CW) excitation. In this work, we study the
time-dependent characteristics of sodium fluorescence, and investigate the
optimal format for the new fiber laser LGS that will be part of the upgraded
adaptive optics (AO) system on the Shane telescope at Mt. Hamilton. Results of
this analysis are examined in the context of their general applicability to
other LGS systems and the potential benefits of uplink correction are
considered. Comparisons of simulation predictions with measurements from
existing LGS are also presented and discussed.Comment: 9 pages, 7 figures, accepted by JOSA
Structural reliability analysis of laminated CMC components
For laminated ceramic matrix composite (CMC) materials to realize their full potential in aerospace applications, design methods and protocols are a necessity. The time independent failure response of these materials is focussed on and a reliability analysis is presented associated with the initiation of matrix cracking. A public domain computer algorithm is highlighted that was coupled with the laminate analysis of a finite element code and which serves as a design aid to analyze structural components made from laminated CMC materials. Issues relevant to the effect of the size of the component are discussed, and a parameter estimation procedure is presented. The estimation procedure allows three parameters to be calculated from a failure population that has an underlying Weibull distribution
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