2,727 research outputs found
Virtual Hand Illusion Induced by Visuomotor Correlations
Background: Our body schema gives the subjective impression of being highly stable. However, a number of easily-evoked illusions illustrate its remarkable malleability. In the rubber-hand illusion, illusory ownership of a rubber-hand is evoked by synchronous visual and tactile stimulation on a visible rubber arm and on the hidden real arm. Ownership is concurrent with a proprioceptive illusion of displacement of the arm position towards the fake arm. We have previously shown that this illusion of ownership plus the proprioceptive displacement also occurs towards a virtual 3D projection of an arm when the appropriate synchronous visuotactile stimulation is provided. Our objective here was to explore whether these illusions (ownership and proprioceptive displacement) can be induced by only synchronous visuomotor stimulation, in the absence of tactile stimulation.Methodology/Principal Findings: To achieve this we used a data-glove that uses sensors transmitting the positions of fingers to a virtually projected hand in the synchronous but not in the asynchronous condition. The illusion of ownership was measured by means of questionnaires. Questions related to ownership gave significantly larger values for the synchronous than for the asynchronous condition. Proprioceptive displacement provided an objective measure of the illusion and had a median value of 3.5 cm difference between the synchronous and asynchronous conditions. In addition, the correlation between the feeling of ownership of the virtual arm and the size of the drift was significant.Conclusions/Significance: We conclude that synchrony between visual and proprioceptive information along with motor activity is able to induce an illusion of ownership over a virtual arm. This has implications regarding the brain mechanisms underlying body ownership as well as the use of virtual bodies in therapies and rehabilitation
EAGLE ISS - A modular twin-channel integral-field near-IR spectrograph
The ISS (Integral-field Spectrograph System) has been designed as part of the
EAGLE Phase A Instrument Study for the E-ELT. It consists of two input channels
of 1.65x1.65 arcsec field-of-view, each reconfigured spatially by an
image-slicing integral-field unit to feed a single near-IR spectrograph using
cryogenic volume-phase-holographic (VPH) gratings to disperse the image
spectrally. A 4k x 4k array detector array records the dispersed images. The
optical design employs anamorphic magnification, image slicing, VPH gratings
scanned with a novel cryo-mechanism and a three-lens camera. The mechanical
implementation features IFU optics in Zerodur, a modular bench structure and a
number of high-precision cryo-mechanisms.Comment: 12 pages, to be published in Proc SPIE 7735: Ground-based & Airborne
Instrumentation for Astronomy II
Hysteresis and Avalanches in the Random Anisotropy Ising Model
The behaviour of the Random Anisotropy Ising model at T=0 under local
relaxation dynamics is studied. The model includes a dominant ferromagnetic
interaction and assumes an infinite anisotropy at each site along local
anisotropy axes which are randomly aligned. Two different random distributions
of anisotropy axes have been studied. Both are characterized by a parameter
that allows control of the degree of disorder in the system. By using numerical
simulations we analyze the hysteresis loop properties and characterize the
statistical distribution of avalanches occuring during the metastable evolution
of the system driven by an external field. A disorder-induced critical point is
found in which the hysteresis loop changes from displaying a typical
ferromagnetic magnetization jump to a rather smooth loop exhibiting only tiny
avalanches. The critical point is characterized by a set of critical exponents,
which are consistent with the universal values proposed from the study of other
simpler models.Comment: 40 pages, 21 figures, Accepted for publication in Phys. Rev.
Spanning avalanches in the three-dimensional Gaussian Random Field Ising Model with metastable dynamics: field dependence and geometrical properties
Spanning avalanches in the 3D Gaussian Random Field Ising Model (3D-GRFIM)
with metastable dynamics at T=0 have been studied. Statistical analysis of the
field values for which avalanches occur has enabled a Finite-Size Scaling (FSS)
study of the avalanche density to be performed. Furthermore, direct measurement
of the geometrical properties of the avalanches has confirmed an earlier
hypothesis that several kinds of spanning avalanches with two different fractal
dimensions coexist at the critical point. We finally compare the phase diagram
of the 3D-GRFIM with metastable dynamics with the same model in equilibrium at
T=0.Comment: 16 pages, 17 figure
Vacancy-assisted domain-growth in asymmetric binary alloys: a Monte Carlo study
A Monte Carlo simulation study of the vacancy-assisted domain-growth in
asymmetric binary alloys is presented. The system is modeled using a
three-state ABV Hamiltonian which includes an asymmetry term, not considered in
previous works. Our simulated system is a stoichiometric two-dimensional binary
alloy with a single vacancy which evolves according to the vacancy-atom
exchange mechanism. We obtain that, compared to the symmetric case, the
ordering process slows down dramatically. Concerning the asymptotic behavior it
is algebraic and characterized by the Allen-Cahn growth exponent x=1/2. The
late stages of the evolution are preceded by a transient regime strongly
affected by both the temperature and the degree of asymmetry of the alloy. The
results are discussed and compared to those obtained for the symmetric case.Comment: 21 pages, 9 figures, accepted for publication in Phys. Rev.
Management of Acute Spinal Fractures in Ankylosing Spondylitis
Ankylosing Spondylitis (AS) is a multifactorial
and polygenic rheumatic condition without a well-understood pathophysiology (Braun and Sieper (2007)). It results in
chronic pain, deformity, and fracture of the axial
skeleton. AS alters the biomechanical properties
of the spine through a chronic inflammatory
process, yielding a brittle, minimally compliant
spinal column. Consequently, this patient
population is highly susceptible to unstable spine
fractures and associated neurologic devastation
even with minimal trauma. Delay in diagnosis is
not uncommon, resulting in inappropriate
immobilization and treatment. Clinicians must
maintain a high index of suspicion for fracture
when evaluating this group to avoid morbidity and
mortality. Advanced imaging studies in the form of
multidetector CT and/or MRI should be employed to
confirm the diagnosis. Initial immobilization in
the patient's preinjury alignment is
mandatory to prevent iatrogenic neurologic injury.
Both nonoperative and operative treatments can be
employed depending on the patient's age,
comorbidities, and fracture stability. Operative
techniques must be individually tailored for this
patient population. A multidisciplinary team
approach is best with preoperative nutritional
assessment and pulmonary evaluation
Crackling Noise, Power Spectra and Disorder Induced Critical Scaling
Crackling noise is observed in many disordered non-equilibrium systems in
response to slowly changing external conditions. Examples range from Barkhausen
noise in magnets to acoustic emission in martensites to earthquakes. Using the
non-equilibrium random field Ising model, we derive universal scaling
predictions for the dependence of the associated power spectra on the disorder
and field sweep rate, near an underlying disorder-induced non-equilibrium
critical point. Our theory applies to certain systems in which the crackling
noise results from avalanche-like response to a (slowly) increasing external
driving force, and is characterized by a broad power law scaling regime of the
power spectra. We compute the critical exponents and discuss the relevance of
the results to experiments.Comment: 27 Latex Pages, 14 eps figure
Agency and responsibility over virtual movements controlled through different paradigms of brain−computer interface
Agency is the attribution of an action to the self and is a prerequisite for experiencing responsibility over its consequences. Here we investigated agency and responsibility by studying the control of movements of an embodied avatar, via brain computer interface (BCI) technology, in immersive virtual reality. After induction of virtual body ownership by visuomotor correlations, healthy participants performed a motor task with their virtual body. We compared the passive observation of the subject's ‘own’ virtual arm performing the task with (1) the control of the movement through activation of sensorimotor areas (motor imagery) and (2) the control of the movement through activation of visual areas (steady‐state visually evoked potentials). The latter two conditions were carried out using a brain–computer interface (BCI) and both shared the intention and the resulting action. We found that BCI‐control of movements engenders the sense of agency, which is strongest for sensorimotor areas activation. Furthermore, increased activity of sensorimotor areas, as measured using EEG, correlates with levels of agency and responsibility. We discuss the implications of these results for the neural basis of agency
Magnetic hysteresis in the Cu-Al-Mn intermetallic alloy: experiments and modeling
We study isothermal magnetization processes in the Cu-Al-Mn intermetallic
alloy. Hysteresis is observed at temperatures below the spin-freezing of the
system. The characteristics of the hysteresis cycles as a function of
temperature and Mn content (magnetic element) are obtained. At low temperature
(5 K) a change from smooth to sharp cycles is observed with increasing Mn
content, which is related to the decrease of configurational disorder. We also
study a zero-temperature site-diluted Ising model, suitable for the description
of this Cu-Al-Mn system. The model reproduces the main features of the
hysteresis loops observed experimentally. It exhibits a disorder-induced
critical line separating a disordered phase from an incipient ferromagnetic
ground-state. The comparison between the model and the experiments allows to
conclude that the observed change in the experimental hysteresis loops can be
understood within the framework of the theory of disorder-induced criticality
in fluctuationless first-order phase transitions.Comment: 30 pages, 15 eps figures, 2 tables. To appear Phys. Rev. B 59 (June
1999
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