143,712 research outputs found
Electron yields from spacecraft materials
Photoyields and secondary electron emission (SEE) characteristics were determined under UHV conditions for a group of insulating materials used in spacecraft applications. The SEE studies were carried out with a pulsed primary beam while photoyields were obtained with a chopped photon beam from a Kr resonance source with major emission at 123.6 nm. This provides a photon flux close to that of the Lyman alpha in the space environment. Yields per incident photon are obtained relative to those from a freshly evaporated and air oxidized Al surface. Results are presented for Kapton, FEP Teflon, the borosilicate glass covering of a shuttle tile, and spacesuit outer fabric
Two-component theory of a droplet of electrons in half-filled Landau level
We have investigated low energy excitations of a disk of electrons in
half-filled Landau level using trail wave function and small-size exact
diagonalization approaches. We have constructed a set of many-body basis states
that describe correctly the low energy excitations. In this theory a droplet
consists of two types of composite fermion liquids, and suggests that a droplet
can support an edge magnetoplasmon and low energy droplet excitations. A
possibility of measuring these excitations in a quantum dot is discussed.Comment: Figure1 is available from the authors upon request. Three eps files
are attached to the tex fil
Degenerate states of narrow semiconductor rings in the presence of spin orbit coupling: Role of time-reversal and large gauge transformations
The electron Hamiltonian of narrow semiconductor rings with the Rashba and
Dresselhaus spin orbit terms is invariant under time-reversal operation
followed by a large gauge transformation. We find that all the eigenstates are
doubly degenerate when integer or half-integer quantum fluxes thread the
quantum ring. The wavefunctions of a degenerate pair are related to each other
by the symmetry operation. These results are valid even in the presence of a
disorder potential. When the Zeeman term is present only some of these
degenerate levels anticross
Measurements of Grain Motion in a Dense, Three-Dimensional Granular Fluid
We have used an NMR technique to measure the short-time, three-dimensional
displacement of grains in a system of mustard seeds vibrated vertically at 15g.
The technique averages over a time interval in which the grains move
ballistically, giving a direct measurement of the granular temperature profile.
The dense, lower portion of the sample is well described by a recent
hydrodynamic theory for inelastic hard spheres. Near the free upper surface the
mean free path is longer than the particle diameter and the hydrodynamic
description fails.Comment: 4 pages, 4 figure
Fragmentation or Recombination at High p_T?
All hadronization processes, including fragmentation, are shown to proceed
through recombination. The shower partons in a jet turn out to play an
important role in describing the p_T spectra of hadrons produced in heavy-ion
collisions. Due to the recombination of the shower partons with the soft
thermal partons, the structure of jets produced in AA collisions is not the
same as that of jets produced in pp collisions.Comment: Talk given at Quark Matter 200
Single-input and single-output (SISO) controller reduction based on the -norm
This paper proposes a new method to solve the controller-reduction problem based on the -norm. This method uses a reduced-order closed-loop system to deduce reduced-order controllers. The problem of obtaining the required lower-order closed-loop system was formulated as an -norm optimization, and the conditions were provided for guaranteeing the internal stability and the existence of lower-order controllers from the obtained reduced-order closed-loop system. In addition, the particle swarm optimization and sequence linear programming were adopted to solve the resultant -norm optimization. Two numerical examples demonstrated the effectiveness of the proposed method
- …