8,050 research outputs found
Insights and Puzzles from Branes: 4d SUSY Yang-Mills from 6d Models
5-branes of nontrivial topology are associated in the
Diaconescu-Hanany-Witten-Witten (DHWW) approach with the Seiberg-Witten (SW)
theory of low-energy effective actions. There are two different "pictures",
related to the IIA and IIB phases of M-theory. They differ by the choice of
theory on the 5-brane world volume. In the IIB picture it is just the 6d
SUSY Yang-Mills, while in the IIA picture it is a theory of SUSY self-dual
2-form. These two pictures appear capable to describe the (non-abelian) Lax
operator and (abelian) low-energy effective action respectively. Thus IIB-IIA
duality is related to the duality between Hitchin and Whitham integrable
structures.Comment: LaTeX, 12pp, 4 figs in ps-format requiring psfig.te
Molecular Motors Interacting with Their Own Tracks
Dynamics of molecular motors that move along linear lattices and interact
with them via reversible destruction of specific lattice bonds is investigated
theoretically by analyzing exactly solvable discrete-state ``burnt-bridge''
models. Molecular motors are viewed as diffusing particles that can
asymmetrically break or rebuild periodically distributed weak links when
passing over them. Our explicit calculations of dynamic properties show that
coupling the transport of the unbiased molecular motor with the bridge-burning
mechanism leads to a directed motion that lowers fluctuations and produces a
dynamic transition in the limit of low concentration of weak links. Interaction
between the backward biased molecular motor and the bridge-burning mechanism
yields a complex dynamic behavior. For the reversible dissociation the backward
motion of the molecular motor is slowed down. There is a change in the
direction of the molecular motor's motion for some range of parameters. The
molecular motor also experiences non-monotonic fluctuations due to the action
of two opposing mechanisms: the reduced activity after the burned sites and
locking of large fluctuations. Large spatial fluctuations are observed when two
mechanisms are comparable. The properties of the molecular motor are different
for the irreversible burning of bridges where the velocity and fluctuations are
suppressed for some concentration range, and the dynamic transition is also
observed. Dynamics of the system is discussed in terms of the effective driving
forces and transitions between different diffusional regimes
Microdisk Resonators with Two Point Scatterers
Optical microdisk resonators exhibit modes with extremely high Q-factors. Their low lasing thresholds make circular microresonators good candidates for the realization of miniature laser sources. They have, however, the serious drawback that their light emission is isotropic, which is inconvenient for many applications. In our previous work, we showed that the presence of a point scatterer inside the disk can lead to highly directional modes in various frequency ranges while preserving the high Q-factors. In the present paper we generalize this idea to two point scatterers. The motivation for this work is that the strength of a point scatterer is difficult to control in experiments, and the presence of a second scatterer leads to a higher dimensional parameter space which permits to compensate this deficiency. Similar to the case of a single scatterer in a circular disk, the problem of finding the resonance modes in the presence of two scatterers is to a large extent analytically tractable.
Phase behaviour of block copolymer melts with arbitrary architecture
The Leibler theory [L. Leibler, Macromolecules, v.13, 1602 (1980)] for
microphase separation in AB block copolymer melts is generalized for systems
with arbitrary topology of molecules. A diagrammatic technique for calculation
of the monomeric correlation functions is developed. The free energies of
various mesophases are calculated within the second-harmonic approximation.
Model highly-branched tree-like structures are considered as an example and
their phase diagrams are obtained. The topology of molecules is found to
influence the spinodal temperature and asymmetry of the phase diagrams, but not
the types of phases and their order. We suggest that all model AB
block-copolymer systems will exhibit the typical phase behaviour.Comment: Submitted to J. Chem. Phys., see also
http://rugmd4.chem.rug.nl/~morozov/research.htm
New matrix model solutions to the Kac-Schwarz problem
We examine the Kac-Schwarz problem of specification of point in Grassmannian
in the restricted case of gap-one first-order differential Kac-Schwarz
operators. While the pair of constraints satisfying always
leads to Kontsevich type models, in the case of the
corresponding KP -functions are represented as more sophisticated matrix
integrals.Comment: 19 pages, latex, no figures, contribution to the proceedings of the
29th International Symposium Ahrenshoop on the Theory of Elementary
Particles, Buckow, German
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