19,597 research outputs found
New DNLS Equations for Anharmonic Vibrational Impurities
We examine some new DNLS-like equations that arise when considering
strongly-coupled electron-vibration systems, where the local oscillator
potential is anharmonic. In particular, we focus on a single, rather general
nonlinear vibrational impurity and determine its bound state(s) and its
dynamical selftrapping properties.Comment: 16 pages, 5 figure
Power Switching in Hybrid Coherent Couplers
We report on a theoretical and numerical investigation of the switching of
power in new hybrid models of nonlinear coherent couplers consisting of optical
slab waveguides with various orders of nonlinearity. The first model consists
of two guides with second-order instead of the usual third-order
susceptibilities as typified by the Jensen coupler. This second-order system is
shown to have a power self-trapping transition at a critical power greater than
the third-order susceptibility coupler. Next, we consider a mixed coupler
composed of a second-order guide coupled to a third-order guide and show that,
although it does not display a rigorous self-trapping transition, for a
particular choice of parameters it does show a fairly abrupt trapping of power
at a lower power than in the third-order coupler. By coupling this mixed
nonlinear pair to a third, purely linear guide, the power trapping can be
brought to even lower levels and in this way a satisfactory switching profile
can be achieved at less than one sixth the input power needed in the Jensen
coupler.Comment: Latex source,17 pages, 5 figure
Set-based approach to passenger aircraft family design
Presented is a method for the design of passenger aircraft families. Existing point-based methods found in the literature employ sequential approaches in which a single design solution is selected early and is then iteratively modified until all requirements are satisfied. The challenge with such approaches is that the design is driven toward a solution that, although promising to the optimizer, may be infeasible due to factors not considered by the models. The proposed method generates multiple solutions at the outset. Then, the infeasible solutions are discarded gradually through constraint satisfaction and set intersection. The method has been evaluated through a notional example of a three-member aircraft family design. The conclusion is that point-based design is still seen as preferable for incremental (conventional) designs based on a wealth of validated empirical methods, whereas the proposed approach, although resource-intensive, is seen as more suited to innovative designs
From Disordered Crystal to Glass: Exact Theory
We calculate thermodynamic properties of a disordered model insulator,
starting from the ideal simple-cubic lattice () and increasing the
disorder parameter to . As in earlier Einstein- and Debye-
approximations, there is a phase transition at . For the
low-T heat-capacity whereas for , . The van
Hove singularities disappear at {\em any finite }. For we discover
novel {\em fixed points} in the self-energy and spectral density of this model
glass.Comment: Submitted to Phys. Rev. Lett., 8 pages, 4 figure
Coulomb blockade without potential barriers
We study transport through a strongly correlated quantum dot and show that
Coulomb blockade can appear even in the presence of perfect contacts. This
conclusion arises from numerical calculations of the conductance for a
microscopic model of spinless fermions in an interacting chain connected to
each lead via a completely open channel. The dependence of the conductance on
the gate voltage shows well defined Coulomb blockade peaks which are sharpened
as the interaction strength is increased. Our numerics is based on the
embedding method and the DMRG algorithm. We explain the emergence of Coulomb
blockade with perfect contacts by a reduction of the effective coupling matrix
elements between many-body states corresponding to successive particle numbers
in the interacting region. A perturbative approach, valid in the strong
interaction limit, yields an analytic expression for the interaction-induced
suppression of the conductance in the Coulomb blockade regime.Comment: Fixed problems with eps figure
The role of slip transfer at grain boundaries in the propagation of microstructurally short fatigue cracks in Ni-based superalloys
Crack initiation and propagation under high-cycle fatigue conditions have
been investigated for a polycrystalline Ni-based superalloy by in-situ
synchrotron assisted diffraction and phase contrast tomography. The cracks
nucleated along the longest coherent twin boundaries pre-existing on the
specimen surface, that were well oriented for slip and that presented a large
elastic incompatibility across them. Moreover, the propagation of
microstructurally short cracks was found to be determined by the easy slip
transfer paths across the pre-existing grain boundaries. This information can
only be obtained by characterization techniques like the ones presented here
that provide the full set of 3D microstructural information
- …