1,255 research outputs found
Classification of All Poisson-Lie Structures on an Infinite-Dimensional Jet Group
A local classification of all Poisson-Lie structures on an
infinite-dimensional group of formal power series is given. All
Lie bialgebra structures on the Lie algebra {\Cal G}_{\infty} of
are also classified.Comment: 11 pages, AmSTeX fil
A quantitative theory of current-induced step bunching on Si(111)
We use a one-dimensional step model to study quantitatively the growth of
step bunches on Si(111) surfaces induced by a direct heating current.
Parameters in the model are fixed from experimental measurements near 900 deg C
under the assumption that there is local mass transport through surface
diffusion and that step motion is limited by the attachment rate of adatoms to
step edges. The direct heating current is treated as an external driving force
acting on each adatom. Numerical calculations show both qualitative and
quantitative agreement with experiment. A force in the step down direction will
destabilize the uniform step train towards step bunching. The average size of
the step bunches grows with electromigration time as t^beta, with beta = 0.5,
in agreement with experiment and with an analytical treatment of the steady
states. The model is extended to include the effect of direct hopping of
adatoms between different terraces. Monte-Carlo simulations of a solid-on-solid
model, using physically motivated assumptions about the dynamics of surface
diffusion and attachment at step edges, are carried out to study two
dimensional features that are left out of the present step model and to test
its validity. These simulations give much better agreement with experiment than
previous work. We find a new step bending instability when the driving force is
along the step edge direction. This instability causes the formation of step
bunches and antisteps that is similar to that observed in experiment.Comment: 11 pages, 7 figure
Electromigration-Induced Propagation of Nonlinear Surface Waves
Due to the effects of surface electromigration, waves can propagate over the
free surface of a current-carrying metallic or semiconducting film of thickness
h_0. In this paper, waves of finite amplitude, and slow modulations of these
waves, are studied. Periodic wave trains of finite amplitude are found, as well
as their dispersion relation. If the film material is isotropic, a wave train
with wavelength lambda is unstable if lambda/h_0 < 3.9027..., and is otherwise
marginally stable. The equation of motion for slow modulations of a finite
amplitude, periodic wave train is shown to be the nonlinear Schrodinger
equation. As a result, envelope solitons can travel over the film's surface.Comment: 13 pages, 2 figures. To appear in Phys. Rev.
Quasiparticle RPA with finite rank approximation for Skyrme interactions
A finite rank separable approximation for the particle-hole RPA calculations
with Skyrme interactions is extended to take into account the pairing. As an
illustration of the method energies and transition probabilities for the
quadrupole and octupole excitations in some O, Ar, Sn and Pb isotopes are
calculated. The values obtained within our approach are very close to those
that were calculated within QRPA with the full Skyrme interaction. They are in
reasonable agreement with experimental data.Comment: 20 pages, 1 figure, submitted to Phys.Rev.
Separabelized Skyrme Interactions and Quasiparticle RPA
A finite rank separable approximation for the quasiparticle RPA with Skyrme
interactions is applied to study the low lying quadrupole and octupole states
in some S isotopes and giant resonances in some spherical nuclei. It is shown
that characteristics calculated within the suggested approach are in a good
agreement with available experimental data.Comment: 12 pages, 2 figures, proceedings of the Seventh School-Seminar on
Heavy Ion Physics, Dubna, Russia, May 27-June 1, 2002; to appear in Physics
of Atomic Nucle
Evaluation of Advanced Adhesives for Aerospace Structures
Polymer adhesives are finding increased use in panel joining applications in aircraft and aerospace structures where the applied stresses permit their use and where a uniform stress distribution is needed. One such adhesive, Hysol EA-9394 (TM), was compared to three other formulations in this study. The new formulations were Hysol EA-9396, Hysol EA-9396 filled with nickel nanofibers and mixed by machine (Jamesbury Blender), and Hysol EA-9396 filled with nickel nanofibers and hand mixed in the laboratory. The comparison consisted of measuring shear lap strengths of aluminum test pieces bonded together with the candidate adhesives. The mechanical tests were supplemented by a Weibull analysis of the strength data and by a visual inspection of the failure mode (adhesive/cohesive). The lap shear strengths (fracture stress values) of all three Hysol EA-9396 adhesives were greater than that of the baseline Hysol EA-9394 polymer
Long Term Safety Area Tracking (LT-SAT) with online failure detection and recovery for robotic minimally invasive surgery.
Despite the benefits introduced by robotic systems in abdominal Minimally Invasive Surgery (MIS), major complications can still affect the outcome of the procedure, such as intra-operative bleeding. One of the causes is attributed to accidental damages to arteries or veins by the surgical tools, and some of the possible risk factors are related to the lack of sub-surface visibilty. Assistive tools guiding the surgical gestures to prevent these kind of injuries would represent a relevant step towards safer clinical procedures. However, it is still challenging to develop computer vision systems able to fulfill the main requirements: (i) long term robustness, (ii) adaptation to environment/object variation and (iii) real time processing. The purpose of this paper is to develop computer vision algorithms to robustly track soft tissue areas (Safety Area, SA), defined intra-operatively by the surgeon based on the real-time endoscopic images, or registered from a pre-operative surgical plan. We propose a framework to combine an optical flow algorithm with a tracking-by-detection approach in order to be robust against failures caused by: (i) partial occlusion, (ii) total occlusion, (iii) SA out of the field of view, (iv) deformation, (v) illumination changes, (vi) abrupt camera motion, (vii), blur and (viii) smoke. A Bayesian inference-based approach is used to detect the failure of the tracker, based on online context information. A Model Update Strategy (MUpS) is also proposed to improve the SA re-detection after failures, taking into account the changes of appearance of the SA model due to contact with instruments or image noise. The performance of the algorithm was assessed on two datasets, representing ex-vivo organs and in-vivo surgical scenarios. Results show that the proposed framework, enhanced with MUpS, is capable of maintain high tracking performance for extended periods of time ( ≃ 4 min - containing the aforementioned events) with high precision (0.7) and recall (0.8) values, and with a recovery time after a failure between 1 and 8 frames in the worst case
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