4,307 research outputs found
Precise characterization of nanometer-scale systems using interferometric scattering microscopy and Bayesian analysis
Interferometric scattering microscopy (iSCAT) can image the dynamics of
nanometer-scale systems. The typical approach to analyzing interferometric
images involves intensive processing, which discards data and limits the
precision of measurements. We demonstrate an alternative approach: modeling the
interferometric point spread function (iPSF) and fitting this model to data
within a Bayesian framework. This approach yields best-fit parameters,
including the particle's three-dimensional position and polarizability, as well
as uncertainties and correlations between these parameters. Building on recent
work, we develop a model that is parameterized for rapid fitting. The model is
designed to work with Hamiltonian Monte Carlo techniques that leverage
automatic differentiation. We validate this approach by fitting the model to
interferometric images of colloidal nanoparticles. We apply the method to track
a diffusing particle in three dimensions, to directly infer the diffusion
coefficient of a nanoparticle without calculating a mean-square displacement,
and to quantify the ejection of DNA from an individual lambda phage virus,
demonstrating that the approach can be used to infer both static and dynamic
properties of nanoscale systems
Self-Dual N=8 Supergravity as Closed N=2(4) Strings
As open N=2 or 4 strings describe self-dual N=4 super Yang-Mills in 2+2
dimensions, the corresponding closed (heterotic) strings describe self-dual
ungauged (gauged) N=8 supergravity. These theories are conveniently formulated
in a chiral superspace with general supercoordinate and local OSp(8|2) gauge
invariances. The super-light-cone and covariant-component actions are analyzed.
Because only half the Lorentz group is gauged, the gravity field equation is
just the vanishing of the torsion.Comment: 17 pg., (uuencoded dvi file; revision: forgot 1 stupid term in the
last equation) ITP-SB-92-3
Close Packing of Atoms, Geometric Frustration and the Formation of Heterogeneous States in Crystals
To describe structural peculiarities in inhomogeneous media caused by the
tendency to the close packing of atoms a formalism based on the using of the
Riemann geometry methods (which were successfully applied lately to the
description of structures of quasicrystals and glasses) is developed. Basing on
this formalism we find in particular the criterion of stability of precipitates
of the Frank-Kasper phases in metallic systems. The nature of the ''rhenium
effect'' in W-Re alloys is discussed.Comment: 14 pages, RevTex, 2 PostScript figure
Gauge theories of spacetime symmetries
Gauge theories of conformal spacetime symmetries are presented which merge
features of Yang-Mills theory and general relativity in a new way. The models
are local but nonpolynomial in the gauge fields, with a nonpolynomial structure
that can be elegantly written in terms of a metric (or vielbein) composed of
the gauge fields. General relativity itself emerges from the construction as a
gauge theory of spacetime translations. The role of the models within a general
classification of consistent interactions of gauge fields is discussed as well.Comment: 8 pages, revtex; v2: minor improvements of text and formulas; v3:
typo in formula after eq. (35) correcte
Thermal Effects on the Low Energy N=2 SUSY Yang-Mills Theory
Using the low energy effective action of the N=2 supersymmetric SU(2)
Yang-Mills theory we calculate the free energy at finite temperature, both in
the semiclassical region and in the dual monopole/dyon theory. In all regions
the free energy depends on both the temperature T and the appropriate moduli
parameter, and is thus minimized only for specific values of the moduli
parameter, in contrast to the T=0 case where the energy vanishes all over the
moduli space. Within the validity of perturbation theory, we find that the
finite temperature Yang-Mills theory is stable only at definite points in the
moduli space, i.e. for a specific value of the monopole/dyon mass or when the
scalar field expectation value goes to infinity.Comment: 24 pages, Latex, uses axodra
Eleven-dimensional massless superparticles and matrix theory spin-orbit couplings revisited
The classical probe dynamics of the eleven-dimensional massless
superparticles in the background geometry produced by N source M-momenta is
investigated in the framework of N-sector DLCQ supergravity. We expand the
probe action up to the two fermion terms and find that the fermionic
contributions are the spin-orbit couplings, which precisely agree with the
matrix theory calculations. We comment on the lack of non-perturbative
corrections in the one-loop matrix quantum mechanics effective action and its
compatibility with the supergravity analysis.Comment: 11 pages, Latex, no figure
Six-dimensional Supergravity and Projective Superfields
We propose a superspace formulation of N=(1,0) conformal supergravity in six
dimensions. The corresponding superspace constraints are invariant under
super-Weyl transformations generated by a real scalar parameter. The known
variant Weyl super-multiplet is recovered by coupling the geometry to a
super-3-form tensor multiplet. Isotwistor variables are introduced and used to
define projective superfields. We formulate a locally supersymmetric and
super-Weyl invariant action principle in projective superspace. Some families
of dynamical supergravity-matter systems are presented.Comment: 39 pages; v3: some modifications in section 2; equations (2.3),
(2.14b), (2.16) and (2.17) correcte
Off-shell supergravity-matter couplings in three dimensions
We develop the superspace geometry of N-extended conformal supergravity in
three space-time dimensions. General off-shell supergravity-matter couplings
are constructed in the cases N=1,2,3,4.Comment: 73 pages; V5: typos in eqs. (3.4b), (3.17) and (4.24) correcte
Non-singular screw dislocations as the Coulomb gas with smoothed out coupling and the renormalization of the shear modulus
A field theory is developed for a thermodynamical description of array of
parallel non-singular screw dislocations in elastic cylinder. The partition
function of the system is considered in the functional integral form.
Self-energy of the dislocation cores is chosen in the form suggested by the
gauge-translational model of non-singular screw dislocation. It is shown that
the system of the dislocations is equivalent to the two-dimensional Coulomb
gas. The coupling potential is prevented from a short-distance divergency since
the core energies are taken into account. Two-point correlation functions of
the stress components are obtained. Renormalization of the shear modulus caused
by the presence of the dislocations is studied in the approximation of
non-interacting dislocation dipoles. It is demonstrated that the finite size of
the dislocation cores results in a modification of the renormalization law.Comment: 20 pages, LaTe
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