7,451 research outputs found
Anthropomorphic teleoperation: Controlling remote manipulators with the DataGlove
A two phase effort was conducted to assess the capabilities and limitations of the DataGlove, a lightweight glove input device that can output signals in real-time based on hand shape, orientation, and movement. The first phase was a period for system integration, checkout, and familiarization in a virtual environment. The second phase was a formal experiment using the DataGlove as input device to control the protoflight manipulator arm (PFMA) - a large telerobotic arm with an 8-ft reach. The first phase was used to explore and understand how the DataGlove functions in a virtual environment, build a virtual PFMA, and consider and select a reasonable teleoperation control methodology. Twelve volunteers (six males and six females) participated in a 2 x 3 (x 2) full-factorial formal experiment using the DataGlove to control the PFMA in a simple retraction, slewing, and insertion task. Two within-subjects variables, time delay (0, 1, and 2 seconds) and PFMA wrist flexibility (rigid/flexible), were manipulated. Gender served as a blocking variable. A main effect of time delay was found for slewing and total task times. Correlations among questionnaire responses, and between questionnaire responses and session mean scores and gender were computed. The experimental data were also compared with data collected in another study that used a six degree-of-freedom handcontroller to control the PFMA in the same task. It was concluded that the DataGlove is a legitimate teleoperations input device that provides a natural, intuitive user interface. From an operational point of view, it compares favorably with other 'standard' telerobotic input devices and should be considered in future trades in teleoperation systems' designs
Theory of a general class of dissipative processes
General theory of dissipative periodic processes for systems defined by partial, functional, or neutral differential equation
Hot phonon decay in supported and suspended exfoliated graphene
Near infrared pump-probe spectroscopy has been used to measure the ultrafast
dynamics of photoexcited charge carriers in monolayer and multilayer graphene.
We observe two decay processes occurring on 100 fs and 2 ps timescales. The
first is attributed to the rapid electron-phonon thermalisation in the system.
The second timescale is found to be due to the slow decay of hot phonons. Using
a simple theoretical model we calculate the hot phonon decay rate and show that
it is significantly faster in monolayer flakes than in multilayer ones. In
contrast to recent claims, we show that this enhanced decay rate is not due to
the coupling to substrate phonons, since we have also seen the same effect in
suspended flakes. Possible intrinsic decay mechanisms that could cause such an
effect are discussed.Comment: 4 pages, 3 figure
Strong nonlinear optical response of graphene flakes measured by four-wave mixing
We present the first experimental investigation of nonlinear optical
properties of graphene flakes. We find that at near infrared frequencies a
graphene monolayer exhibits a remarkably high third-order optical nonlinearity
which is practically independent of the wavelengths of incident light. The
nonlinear optical response can be utilized for imaging purposes, with image
contrasts of graphene which are orders of magnitude higher than those obtained
using linear microscopy.Comment: 4 pages, 5 figure
Spatial incoherence of solar granulation: a global analysis using BiSON 2B data
A poor understanding of the impact of convective turbulence in the outer
layers of the Sun and Sun-like stars challenges the advance towards an improved
understanding of their internal structure and dynamics. Assessing and
calibrating these effects is therefore of great importance. Here we study the
spatial coherence of granulation noise and oscillation modes in the Sun, with
the aim of exploiting any incoherence to beat-down observed granulation noise,
hence improving the detection of low-frequency p-modes. Using data from the
BiSON 2B instrument, we assess the coherence between different atmospheric
heights and between different surface regions. We find that granulation noise
from the different atmospheric heights probed is largely incoherent; frequency
regions dominated by oscillations are almost fully coherent. We find a
randomised phase difference for the granulation noise, and a near zero
difference for the evanescent oscillations. A reduction of the incoherent
granulation noise is shown by application of the cross-spectrum.Comment: 8 pages, 7 figures, MNRAS in pres
Variable-delay feedback control of unstable steady states in retarded time-delayed systems
We study the stability of unstable steady states in scalar retarded
time-delayed systems subjected to a variable-delay feedback control. The
important aspect of such a control problem is that time-delayed systems are
already infinite-dimensional before the delayed feedback control is turned on.
When the frequency of the modulation is large compared to the system's
dynamics, the analytic approach consists of relating the stability properties
of the resulting variable-delay system with those of an analogous distributed
delay system. Otherwise, the stability domains are obtained by a numerical
integration of the linearized variable-delay system. The analysis shows that
the control domains are significantly larger than those in the usual
time-delayed feedback control, and that the complexity of the domain structure
depends on the form and the frequency of the delay modulation.Comment: 13 pages, 8 figures, RevTeX, accepted for publication in Physical
Review
Can distributed delays perfectly stabilize dynamical networks?
Signal transmission delays tend to destabilize dynamical networks leading to
oscillation, but their dispersion contributes oppositely toward stabilization.
We analyze an integro-differential equation that describes the collective
dynamics of a neural network with distributed signal delays. With the gamma
distributed delays less dispersed than exponential distribution, the system
exhibits reentrant phenomena, in which the stability is once lost but then
recovered as the mean delay is increased. With delays dispersed more highly
than exponential, the system never destabilizes.Comment: 4pages 5figure
The clustering and bias of radio-selected AGN and star-forming galaxies in the COSMOS field
Dark matter haloes in which galaxies reside are likely to have a significant
impact on their evolution. We investigate the link between dark matter haloes
and their constituent galaxies by measuring the angular two-point correlation
function of radio sources, using recently released 3 GHz imaging over $\sim 2 \
\mathrm{deg}^2z<1b = 1.5
^{+0.1}_{-0.2}z=0.62b = 2.1\pm 0.2b =
2.9 \pm 0.3b = 1.8^{+0.4}_{-0.5}z \sim 0.7M_{h} \sim 3-4
\times 10^{13}h^{-1}_{\odot}M_{h} \sim 1-2 \times
10^{13}h^{-1}_{\odot}z \ge 1z<1$.Comment: 20 pages, 10 figures, 1 table, accepted by MNRA
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