294 research outputs found
Similarities and dissimilarities between pattern VEPs and motion VEPs
The contrast response functions (CRF) of pattern-appearance and motion-onset VEPs for periodic stimuli (gratings) were compared. The CRF for pattern-appearance is accelerative for the P100 component and compressive for the N200 component. Contrary to these results, the CRF for motion-onset shows an almost negligible slope for both components within the contrast range tested (0.5–64%). To better isolate the neural contributions to these different VEP components, we studied the effects of prior adaptation to stationary and moving gratings. Adaptation to stationary gratings has no effect on both VEP components for motion-onset and the P100 component for pattern-appearance, but did reduce the amplitude of the N200 for pattern-appearance. Adaptation to slow (1 deg/s) and fast (4 deg/s) gratings left the P100 amplitudes unaltered, while it significantly reduced the N200 amplitudes for both pattern-appearance and motion-onset. These results suggest that the N200 component of the motion-onset VEP is generated by motion-dependent neurons, whereas the same component for pattern-appearance arises from contrast-dependent neurons. The observed differences between P100 and N200 components appear to reflect the activity of both transient and sustained neural mechanism
Relationship between motion VEP and perceived velocity of gratings: effects of stimulus speed and motion adaptation
The N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable speed (0.25–13.5°/s), constant spatial frequency (2 cpd), contrast (4%), and direction (horizontally rightward) was studied before and after adaptation to a stationary or drifting grating (1 or 4°/s). Psychophysical measurements were made simultaneously of the perceived speed. In the unadapted condition the slope of the N200 amplitude versus speed function is positive, but lower for high compared to low speeds. The N200 amplitude increases slightly after stationary adaptation. An increase in perceived speed is also evident after stationary adaptation. This increase is more pronounced for low compared to high speeds. Motion adaptation reduces N200 amplitudes over the entire speed range, whereas perceived speeds change from under-estimation to over-estimation when the speed exceeds 1.8°/s after 1°/s adaptation and 4.5°/s after 4°/s adaptation. The simultaneous evaluation of motion VEP and psychophysical results supports the view that the neurons generating the N200 component are also involved in speed perception. The data suggest the existence of a limited number (three or more) speed channels
Muskuläre Biomechanik in der Sprunggelenkprothetik
Zusammenfassung: Das Ziel dieser orthopädisch-biomechanischen Studie war die Evaluation der Muskelfunktion von Patienten, bei welchen infolge unilateraler, schwerer Arthrose am oberen Sprunggelenk (OSG) eine Prothese eingesetzt wurde. Bei 10Patienten wurde vor und 1Jahr nach Implantation einer OSG-Prothese eine orthopädische und biomechanische Untersuchung durchgeführt. Dabei wurden der Schmerzscore, der "American Orthopaedic Foot and Ankle Society"- (AOFAS-)Ankle-Score, der Bewegungsumfang (ROM) des Sprunggelenks und der Unterschied zwischen dem Umfang des Unterschenkels des betroffenen und des kontralateralen gesunden Beins gemessen. Die biomechanische Beurteilung bestand aus einer simultanen Messung des maximal willkürlichen, isometrischen Drehmoments bei Plantarflexion und Dorsalextension des OSG sowie aus einem Oberflächenelektromyogramm (EMG; mittlere Frequenz und Intensität) von 4 Unterschenkelmuskeln: Tibialis anterior (TA), Gastrocnemius medialis (GM), Soleus (SO) und Peroneus longus (PL). Im Vergleich zur präoperativen Evaluation verbesserten sich der Schmerzscore von 6,7 auf 0,8Punkte, der AOFAS-Ankle-Score von 35,6 auf 92,3Punkte und der ROM nach Implantation der OSG-Prothese signifikant. Die mittlere Differenz des Unterschenkelumfangs zwischen den beiden Beinen nahm von 2,2cm auf 1,4cm ab. Dies war jedoch nicht signifikant. Das mittlere Drehmoment des betroffenen Sprunggelenks bei Dorsalextension stieg von 17,0 auf 25,8Nm und bei Plantarflexion von 15,7 auf 24,6Nm signifikant an. Bei der 1-Jahres-Nachkontrolle war die mittlere EMG-Frequenz in allen atrophischen Muskeln tiefer als bei den gesunden Muskeln der kontralateralen Seite. Ein Unterschied der mittleren EMG-Intensität zur kontralateralen gesunden Seite konnte nicht verifiziert werden. Daraus kann gefolgert werden, dass Patienten mit symptomatischer OSG-Arthrose mit einer Prothese eine bessere Funktion erlangen; 1Jahr nach der Operation entspricht dies jedoch nicht dem Ausmaß derjenigen des kontralateralen gesunden Bein
Motion VEPs with simultaneous measurement of perceived velocity
The dependency of the N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable speed (0.25 – 13.5 deg/s, corresponding to 0.5 – 27 Hz) and constant contrast (4%) was studied. Additional measurements were made with parafoveally presented gratings of constant speed (2 deg/s, corresponding to 4 Hz) and a variable contrast (0.5 – 64%) before and after adaptation to a stationary or drifting grating. In this latter experiment, simultaneous psychophysical measurements were made of the perceived speed. The amplitude of the N200 wave increased with increasing stimulus speed within the slow speed range up to 1.5 deg/s (corresponding to 3 Hz). Adaptation to a stationary grating had no significant effect on the relationship between the N200 amplitude and stimulus contrast. Contrary to this, adaptation to a slowly drifting grating (1 deg/s, corresponding to 2 Hz) or to a rapidly drifting grating (4 deg/s, corresponding to 8 Hz) reduced the N200 amplitude significantly. Adaptation to a stationary grating slightly reduced the perceived speed of subsequently viewed gratings. Adaptation to a slowly drifting grating increased the perceived speed of the subsequently viewed gratings, whereas adaptation to a rapidly drifting grating decreased the perceived speed. The findings can be best explained by a two-channel model of speed perception. While the motion VEP reflects the sum of both channel activities, the psychophysical measures point to the antagonistic encoding of low and high velocities
Gauge-ball spectrum of the four-dimensional pure U(1) gauge theory
We investigate the continuum limit of the gauge-ball spectrum in the
four-dimensional pure U(1) lattice gauge theory. In the confinement phase we
identify various states scaling with the correlation length exponent . The square root of the string tension also scales with this
exponent, which agrees with the non-Gaussian fixed point exponent recently
found in the finite size studies of this theory. Possible scenarios for
constructing a non-Gaussian continuum theory with the observed gauge-ball
spectrum are discussed. The state, however, scales with a Gaussian
value . This suggests the existence of a second, Gaussian
continuum limit in the confinement phase and also the presence of a light or
possibly massless scalar in the non-Gaussian continuum theory. In the Coulomb
phase we find evidence for a few gauge-balls, being resonances in multi-photon
channels; they seem to approach the continuum limit with as yet unknown
critical exponents. The maximal value of the renormalized coupling in this
phase is determined and its universality confirmed.Comment: 46 pages, 12 figure
Drosophila TRPN( = NOMPC) Channel Localizes to the Distal End of Mechanosensory Cilia
BACKGROUND: A TRPN channel protein is essential for sensory transduction in insect mechanosensory neurons and in vertebrate hair cells. The Drosophila TRPN homolog, NOMPC, is required to generate mechanoreceptor potentials and currents in tactile bristles. NOMPC is also required, together with a TRPV channel, for transduction by chordotonal neurons of the fly's antennal ear, but the TRPN or TRPV channels have distinct roles in transduction and in regulating active antennal mechanics. The evidence suggests that NOMPC is a primary mechanotransducer channel, but its subcellular location-key for understanding its exact role in transduction-has not yet been established. METHODOLOGY/PRINCIPAL FINDINGS: Here, by immunostaining, we locate NOMPC at the tips of mechanosensory cilia in both external and chordotonal sensory neurons, as predicted for a mechanotransducer channel. In chordotonal neurons, the TRPN and TRPV channels are respectively segregated into distal and proximal ciliary zones. This zonal separation is demarcated by and requires the ciliary dilation, an intraciliary assembly of intraflagellar transport (IFT) proteins. CONCLUSIONS: Our results provide a strong evidence for NOMPC as a primary transduction channel in Drosophila mechansensory organs. The data also reveals a structural basis for the model of auditory chordotonal transduction in which the TRPN and TRPV channels play sequential roles in generating and amplifying the receptor potential, but have opposing roles in regulating active ciliary motility
Effective Field Theories
Effective field theories encode the predictions of a quantum field theory at
low energy. The effective theory has a fairly low ultraviolet cutoff. As a
result, loop corrections are small, at least if the effective action contains a
term which is quadratic in the fields, and physical predictions can be read
straight from the effective Lagrangean.
Methods will be discussed how to compute an effective low energy action from
a given fundamental action, either analytically or numerically, or by a
combination of both methods. Basically,the idea is to integrate out the high
frequency components of fields. This requires the choice of a "blockspin",i.e.
the specification of a low frequency field as a function of the fundamental
fields. These blockspins will be the fields of the effective field theory. The
blockspin need not be a field of the same type as one of the fundamental
fields, and it may be composite. Special features of blockspins in nonabelian
gauge theories will be discussed in some detail.
In analytical work and in multigrid updating schemes one needs interpolation
kernels \A from coarse to fine grid in addition to the averaging kernels
which determines the blockspin. A neural net strategy for finding optimal
kernels is presented.
Numerical methods are applicable to obtain actions of effective theories on
lattices of finite volume. The constraint effective potential) is of particular
interest. In a Higgs model it yields the free energy, considered as a function
of a gauge covariant magnetization. Its shape determines the phase structure of
the theory. Its loop expansion with and without gauge fields can be used to
determine finite size corrections to numerical data.Comment: 45 pages, 9 figs., preprint DESY 92-070 (figs. 3-9 added in ps
format
Design principles of hair-like structures as biological machines
Hair-like structures are prevalent throughout biology and frequently act to sense or alter interactions with an organism's environment. The overall shape of a hair is simple: a long, filamentous object that protrudes from the surface of an organism. This basic design, however, can confer a wide range of functions, owing largely to the flexibility and large surface area that it usually possesses. From this simple structural basis, small changes in geometry, such as diameter, curvature and inter-hair spacing, can have considerable effects on mechanical properties, allowing functions such as mechanosensing, attachment, movement and protection. Here, we explore how passive features of hair-like structures, both individually and within arrays, enable diverse functions across biology. Understanding the relationships between form and function can provide biologists with an appreciation for the constraints and possibilities on hair-like structures. Additionally, such structures have already been used in biomimetic engineering with applications in sensing, water capture and adhesion. By examining hairs as a functional mechanical unit, geometry and arrangement can be rationally designed to generate new engineering devices and ideas
Series Expansions for three-dimensional QED
Strong-coupling series expansions are calculated for the Hamiltonian version
of compact lattice electrodynamics in (2+1) dimensions, with 4-component
fermions. Series are calculated for the ground-state energy per site, the
chiral condensate, and the masses of `glueball' and positronium states.
Comparisons are made with results obtained by other techniques.Comment: 13 figure
A Novel Mutation in the Upstream Open Reading Frame of the CDKN1B Gene Causes a MEN4 Phenotype
PubMed ID: 23555276This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
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