58,338 research outputs found
Robust active heave compensated winch-driven overhead crane system for load transfer in marine operation
Active heave compensation (AHC) is important for load transfer in marine operation using the overhead crane system (OCS). The control of marine OCS aims to continuously regulate the displacement of the cart and the payload sway angle, whilst at the same time, maintaining the gap between the payload and the vessel main deck at a desirable and safe distance. As the marine OHC system is to be operated in a continuously changing environment, with plenty inevitable disturbances and undesirable loads, a robust controller, i.e., active force control (AFC) is thus greatly needed to promote accuracy and robustness features into the controllability of OCS in rough working environment. This paper highlights a novel method for controlling the payload in an OCS based on the combination of both AFC and AHC. Results from the simulation study clearly indicate that the performance of OCS can be greatly improved by the proposed robust AFC controller, as compared with the classical PID controller scheme
Attacking quantum key distribution with single-photon two-qubit quantum logic
The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual
attack on Bennett-Brassard 1984 quantum key distribution (BB84 QKD) by means of
a single controlled-NOT (CNOT) gate. This paper describes a complete physical
simulation of the FPB-probe attack on polarization-based BB84 QKD using a
deterministic CNOT constructed from single-photon two-qubit quantum logic.
Adding polarization-preserving quantum nondemolition measurements of photon
number to this configuration converts the physical simulation into a true
deterministic realization of the FPB attack.Comment: 8 pages, 9 figures; references added, 1 new figure, appendix
expanded; accepted for publication in Phys. Rev.
Self-Organization of Balanced Nodes in Random Networks with Transportation Bandwidths
We apply statistical physics to study the task of resource allocation in
random networks with limited bandwidths along the transportation links. The
mean-field approach is applicable when the connectivity is sufficiently high.
It allows us to derive the resource shortage of a node as a well-defined
function of its capacity. For networks with uniformly high connectivity, an
efficient profile of the allocated resources is obtained, which exhibits
features similar to the Maxwell construction. These results have good
agreements with simulations, where nodes self-organize to balance their
shortages, forming extensive clusters of nodes interconnected by unsaturated
links. The deviations from the mean-field analyses show that nodes are likely
to be rich in the locality of gifted neighbors. In scale-free networks, hubs
make sacrifice for enhanced balancing of nodes with low connectivity.Comment: 7 pages, 8 figure
Spin-Seebeck effect in a strongly interacting Fermi gas
We study the spin-Seebeck effect in a strongly interacting, two-component
Fermi gas and propose an experiment to measure this effect by relatively
displacing spin up and spin down atomic clouds in a trap using spin-dependent
temperature gradients. We compute the spin-Seebeck coefficient and related
spin-heat transport coefficients as functions of temperature and interaction
strength. We find that when the inter-spin scattering length becomes larger
than the Fermi wavelength, the spin-Seebeck coefficient changes sign as a
function of temperature, and hence so does the direction of the
spin-separation. We compute this zero-crossing temperature as a function of
interaction strength and in particular in the unitary limit for the inter-spin
scattering
- …