8,238 research outputs found
Quantum dynamics of the avian compass
The ability of migratory birds to orient relative to the Earth's magnetic
field is believed to involve a coherent superposition of two spin states of a
radical electron pair. However, the mechanism by which this coherence can be
maintained in the face of strong interactions with the cellular environment has
remained unclear. This Letter addresses the problem of decoherence between two
electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei.
Dynamics of the radical pair density matrix are derived and shown to yield a
simple mechanism for sensing magnetic field orientation. Rates of dephasing and
decoherence are calculated ab initio and found to yield millisecond coherence
times, consistent with behavioral experiments
Exploring the Design Space of Robot Appearance and Behavior in an Attention-Seeking Living Room Scenario for a Robot Companion
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Semiconductor technology program: Progress briefs
Measurement technology for semiconductor materials, process control, and devices, is discussed. Silicon and silicon based devices are emphasized. Highlighted activities include semiinsulating GaAs characterization, an automatic scanning spectroscopic ellipsometer, linewidth measurement and coherence, bandgap narrowing effects in silicon, the evaluation of electrical linewidth uniformity, and arsenicomplanted profiles in silicon
Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions
We report a neutron spin-echo study of the critical dynamics in the
antiferromagnets MnF and RbMnF with three-dimensional (3D) and
two-dimensional (2D) spin systems, respectively, in zero external field. Both
compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy
resulting from dipolar spin-spin interactions, which leads to a crossover in
the critical dynamics close to the N\'eel temperature, . By taking
advantage of the energy resolution of the spin-echo
spectrometer, we have determined the dynamical critical exponents for both
longitudinal and transverse fluctuations. In MnF, both the characteristic
temperature for crossover from 3D Heisenberg to 3D Ising behavior and the
exponents in both regimes are consistent with predictions from the
dynamical scaling theory. The amplitude ratio of longitudinal and transverse
fluctuations also agrees with predictions. In RbMnF, the critical
dynamics crosses over from the expected 2D Heisenberg behavior for
to a scaling regime with exponent , which has not been predicted
by theory and may indicate the influence of long-range dipolar interactions
An empirical framework for human-robot proxemics
The work described in this paper was conducted within the EU Integrated Projects COGNIRON ("The Cognitive Robot Companion") and LIREC (LIving with Robots and intEractive Companions) and was funded by the European Commission under contract numbers FP6- 002020 and FP7-215554.An empirical framework for Human-Robot (HR) proxemics is proposed which shows how the measurement and control of interpersonal distances between a human and a robot can be potentially used by the robot to interpret, predict and manipulate proxemic behaviour for Human-Robot Interactions (HRIs). The proxemic framework provides for incorporation of inter-factor effects, and can be extended to incorporate new factors, updated values and results. The framework is critically discussed and future work proposed
The measurement of the material parameters of viscoelastic fluids using a rotating sphere and a rheogoniometer
Close encounters : spatial distances between people and a robot of mechanistic appearance
Peer reviewe
A Discrimination Report Card
We develop an Empirical Bayes grading scheme that balances the
informativeness of the assigned grades against the expected frequency of
ranking errors. Applying the method to a massive correspondence experiment, we
grade the racial biases of 97 U.S. employers. A four-grade ranking limits the
chances that a randomly selected pair of firms is mis-ranked to 5% while
explaining nearly half of the variation in firms' racial contact gaps. The
grades are presented alongside measures of uncertainty about each firm's
contact gap in an accessible rubric that is easily adapted to other settings
where ranks and levels are of simultaneous interest
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