83 research outputs found
Thermodynamics of Fateev's models in the Presence of External Fields
We study the Thermodynamic Bethe Ansatz equations for a one-parameter quantum
field theory recently introduced by V.A.Fateev. The presence of chemical
potentials produces a kink condensate that modifies the excitation spectrum.
For some combinations of the chemical potentials an additional gapless mode
appears. Various energy scales emerge in the problem. An effective field
theory, describing the low energy excitations, is also introduced.Comment: To appear in Nucl.Phys.
Exactly solvable model for isospin S=3/2 fermionic atoms on an optical lattice
We propose an exact solution of a model describing a low energy behavior of
cold isospin S=3/2 fermionic atoms on a one-dimensional optical lattice.
Depending on the band filling the effective field theory has a form of a
deformed Gross-Neveu model with either (half filling)
or symmetry.Comment: 4 pages, no figures, replaced with the final version to appear in PR
On the mass spectrum of the two-dimensional O(3) sigma model with theta term
Form Factor Perturbation Theory is applied to study the spectrum of the O(3)
non--linear sigma model with the topological term in the vicinity of . Its effective action near this value is given by the non--integrable
double Sine--Gordon model. Using previous results by Affleck and the explicit
expressions of the Form Factors of the exponential operators , we show that the spectrum consists of a stable triplet
of massive particles for all values of and a singlet state of higher
mass. The singlet is a stable particle only in an interval of values of
close to whereas it becomes a resonance below a critical value
.Comment: 4 pages REVTEX4, 2 figures reference added,corrected typo
Exactly Solvable Ginzburg-Landau theories of Superconducting Order Parameters coupled to Elastic Modes
We consider two families of exactly solvable models describing thermal
fluctuations in two-dimensional superconductors coupled to phonons living in an
insulating layer, and study the stability of the superconducting state with
respect to vortices. The two families are characterized by one or two
superconducting planes. The results suggest that the effective critical
temperature increases with the thickness of the insulating layer. Also the
presence of the additional superconducting layer has the same effect.Comment: Submitted to Physical Review
On the relationship between sigma models and spin chains
We consider the two-dimensional non-linear sigma model with
topological term using a lattice regularization introduced by Shankar and Read
[Nucl.Phys. B336 (1990), 457], that is suitable for studying the strong
coupling regime. When this lattice model is quantized, the coefficient
of the topological term is quantized as , with integer or
half-integer. We study in detail the relationship between the low energy
behaviour of this theory and the one-dimensional spin- Heisenberg model. We
generalize the analysis to sigma models with other symmetries.Comment: To appear in Int. J. MOd. Phys.
Grip control and motor coordination with implanted and surface electrodes while grasping with an osseointegrated prosthetic hand
Background: Replacement of a lost limb by an artificial substitute is not yet ideal. Resolution and coordination of motor control approximating that of a biological limb could dramatically improve the functionality of prosthetic devices, and thus reduce the gap towards a suitable limb replacement. Methods: In this study, we investigated the control resolution and coordination exhibited by subjects with transhumeral amputation who were implanted with epimysial electrodes and an osseointegrated interface that provides bidirectional communication in addition to skeletal attachment (e-OPRA Implant System). We assessed control resolution and coordination in the context of routine and delicate grasping using the Pick and Lift and the Virtual Eggs Tests. Performance when utilizing implanted electrodes was compared with the standard-of-care technology for myoelectric prostheses, namely surface electrodes. Results: Results showed that implanted electrodes provide superior controllability over the prosthetic terminal device compared to conventional surface electrodes. Significant improvements were found in the control of the grip force and its reliability during object transfer. However, these improvements failed to increase motor coordination, and surprisingly decreased the temporal correlation between grip and load forces observed with surface electrodes. We found that despite being more functional and reliable, prosthetic control via implanted electrodes still depended highly on visual feedback. Conclusions: Our findings indicate that incidental sensory feedback (visual, auditory, and osseoperceptive in this case) is insufficient for restoring natural grasp behavior in amputees, and support the idea that supplemental tactile sensory feedback is needed to learn and maintain the motor tasks internal model, which could ultimately restore natural grasp behavior in subjects using prosthetic hands
Paperclip at
We study the ``paperclip'' model of boundary interaction with the topological
angle equal to . We propose exact expression for the disk
partition function in terms of solutions of certain ordinary differential
equation. Large distance asymptotic form of the partition function which
follows from this proposal makes it possible to identify the infrared fixed
point of the paperclip boundary flow at .Comment: 22 pages, 4 figure
- …