76,276 research outputs found
The coexistence of superconductivity and ferromagnetism in nano-scale metallic grains
A nano-scale metallic grain in which the single-particle dynamics are chaotic
is described by the so-called universal Hamiltonian. This Hamiltonian includes
a superconducting pairing term and a ferromagnetic exchange term that compete
with each other: pairing correlations favor minimal ground-state spin, while
the exchange interaction favors maximal spin polarization. Of particular
interest is the fluctuation-dominated regime where the bulk pairing gap is
comparable to or smaller than the single-particle mean level spacing and the
Bardeen-Cooper-Schrieffer theory of superconductivity breaks down.
Superconductivity and ferromagnetism can coexist in this regime. We identify
signatures of the competition between superconductivity and ferromagnetism in a
number of quantities: ground-state spin, conductance fluctuations when the
grain is weakly coupled to external leads and the thermodynamic properties of
the grain, such as heat capacity and spin susceptibility.Comment: 13 pages, 13 figures, Proceedings of the Conference on the Frontiers
of Quantum and Mesoscopic Thermodynamics (FQMT11
A Low Cost and Labor Efficient Method for Rearing Black Cutworms (Lepidoptera: Noctuidae)
The black cutworm, Agrotis ipsilon (Hufnagel), has been and continues to be the subject of many biological and control studies in the north-central states. Interest in this insect can often be traced to its status as a major, but sporadic pest of field com in the region
Charge transfer statistics of a molecular quantum dot with strong electron-phonon interaction
We analyze the nonequilibrium transport properties of a quantum dot with a
harmonic degree of freedom (Holstein phonon) coupled to metallic leads, and
derive its full counting statistics (FCS). Using the Lang-Firsov (polaron)
transformation, we construct a diagrammatic scheme to calculate the cumulant
generating function. The electron-phonon interaction is taken into account
exactly, and the employed approximation represents a summation of a diagram
subset with respect to the tunneling amplitude. By comparison to Monte Carlo
data the formalism is shown to capture the basic properties of the strong
coupling regime
Reduced basis method for computational lithography
A bottleneck for computational lithography and optical metrology are long
computational times for near field simulations. For design, optimization, and
inverse scatterometry usually the same basic layout has to be simulated
multiple times for different values of geometrical parameters. The reduced
basis method allows to split up the solution process of a parameterized model
into an expensive offline and a cheap online part. After constructing the
reduced basis offline, the reduced model can be solved online very fast in the
order of seconds or below. Error estimators assure the reliability of the
reduced basis solution and are used for self adaptive construction of the
reduced system. We explain the idea of reduced basis and use the finite element
solver JCMsuite constructing the reduced basis system. We present a 3D
optimization application from optical proximity correction (OPC).Comment: BACUS Photomask Technology 200
Numerical analysis of nanostructures for enhanced light extraction from OLEDs
Nanostructures, like periodic arrays of scatters or low-index gratings, are
used to improve the light outcoupling from organic light-emitting diodes
(OLED). In order to optimize geometrical and material properties of such
structures, simulations of the outcoupling process are very helpful. The finite
element method is best suited for an accurate discretization of the geometry
and the singular-like field profile within the structured layer and the
emitting layer. However, a finite element simulation of the overall OLED stack
is often beyond available computer resources. The main focus of this paper is
the simulation of a single dipole source embedded into a twofold infinitely
periodic OLED structure. To overcome the numerical burden we apply the Floquet
transform, so that the computational domain reduces to the unit cell. The
relevant outcoupling data are then gained by inverse Flouqet transforming. This
step requires a careful numerical treatment as reported in this paper
Navigation systems for approach and landing of VTOL aircraft
The formulation and implementation of navigation systems used for research investigations in the V/STOLAND avionics system are described. The navigation systems prove position and velocity in a cartestian reference frame aligned with the runway. They use filtering techniques to combine the raw position data from navaids (e.g., TACAN, MLS) with data from onboard inertial sensors. The filtering techniques which use both complementary and Kalman filters, are described. The software for the navigation systems is also described
Dynamical critical exponent of the Jaynes-Cummings-Hubbard model
An array of high-Q electromagnetic resonators coupled to qubits gives rise to
the Jaynes-Cummings-Hubbard model describing a superfluid to Mott insulator
transition of lattice polaritons. From mean-field and strong coupling
expansions, the critical properties of the model are expected to be identical
to the scalar Bose-Hubbard model. A recent Monte Carlo study of the superfluid
density on the square lattice suggested that this does not hold for the
fixed-density transition through the Mott lobe tip. Instead, mean-field
behavior with a dynamical critical exponent z=2 was found. We perform
large-scale quantum Monte Carlo simulations to investigate the critical
behavior of the superfluid density and the compressibility. We find z=1 at the
tip of the insulating lobe. Hence the transition falls in the 3D XY
universality class, analogous to the Bose-Hubbard model.Comment: 4 pages, 4 figures. To appear as a Rapid Communication in Phys. Rev.
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