4,115 research outputs found
The ability of fifth grade children to discriminate between fact and opinion statement
Thesis (Ed.M.)--Boston Universit
Spin-charge separation in Aharonov-Bohm rings of interacting electrons
We investigate the properties of strongly correlated electronic models on a
flux-threaded ring connected to semi-infinite free-electron leads. The
interference pattern of such an Aharonov-Bohm ring shows sharp dips at certain
flux values, determined by the filling, which are a consequence of spin-charge
separation in a nanoscopic system.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Spin dynamics and coherent tunnelling in the molecular magnetic rings Fe_6 and Fe_8
We present detailed calculations of low-energy spin dynamics in the ``ferric
wheel'' systems Na:Fe_6 and Cs:Fe_8 in a magnetic field. We compute by exact
diagonalisation the low-energy spectra and matrix elements for total-spin and
N'eel-vector components, and thus the time-dependent correlation functions of
these operators. Comparison of our results with the semiclassical theory of
coherent quantum tunnelling of the N'eel vector demonstrates the validity of a
two-state description for the low-energy dynamics of ferric wheels. We discuss
the implications of our results for mesoscopic quantum coherent phenomena, and
for the experimental techniques to observe them, in molecular magnetic rings.Comment: 10 pages, 8 figures; considerably expanded discussion; to appear in
Eur. Phys. J.
Discrete ordinates-Monte Carlo coupling: A comparison of techniques in NERVA radiation analysis
In the radiation analysis of the NERVA nuclear rocket system, two-dimensional discrete ordinates calculations are sufficient to provide detail in the pressure vessel and reactor assembly. Other parts of the system, however, require three-dimensional Monte Carlo analyses. To use these two methods in a single analysis, a means of coupling was developed whereby the results of a discrete ordinates calculation can be used to produce source data for a Monte Carlo calculation. Several techniques for producing source detail were investigated. Results of calculations on the NERVA system are compared and limitations and advantages of the coupling techniques discussed
Public health training in Europe. Development of European masters degrees in public health.
BACKGROUND: Changing political and economic relations in Europe mean that there are new challenges for public health and public health training. There have been several attempts to develop training at the master's level in public health which is focused on meeting the new needs. These have failed due to being too inflexible to allow participation by schools of public health. METHODS: A project funded by the European Union involving public health trainers has developed a new approach which allows participating schools to retain their national differences and work within local rules and traditions, but which aims to introduce the European dimension into public health training. This paper reports the conclusions of this project. CONCLUSIONS: A network of schools wishing to develop European Master's degrees is being established and other schools offering good quality programmes will be able to join
Discrete port-controlled Hamiltonian dynamics and average passivation
The paper discusses the modeling and control of port-controlled Hamiltonian dynamics in a pure discrete-time domain. The main result stands in a novel differential-difference representation of discrete port-controlled Hamiltonian systems using the discrete gradient. In these terms, a passive output map is exhibited as well as a passivity based damping controller underlying the natural involvement of discrete-time average passivity
Alien Registration- Normand, Arthur A. (Brunswick, Cumberland County)
https://digitalmaine.com/alien_docs/31580/thumbnail.jp
Parametric instability of the helical dynamo
We study the dynamo threshold of a helical flow made of a mean (stationary)
plus a fluctuating part. Two flow geometries are studied, either (i) solid body
or (ii) smooth. Two well-known resonant dynamo conditions, elaborated for
stationary helical flows in the limit of large magnetic Reynolds numbers, are
tested against lower magnetic Reynolds numbers and for fluctuating flows (zero
mean). For a flow made of a mean plus a fluctuating part the dynamo threshold
depends on the frequency and the strength of the fluctuation. The resonant
dynamo conditions applied on the fluctuating (resp. mean) part seems to be a
good diagnostic to predict the existence of a dynamo threshold when the
fluctuation level is high (resp. low).Comment: 37 pages, 8 figure
On possible superconductivity in the doped ladder compound La_(1-x)Sr_xCuO_2.5
LaCuO_2.5 is a system of coupled, two-chain, cuprate ladders which may be
doped systematically by Sr substitution. Motivated by the recent synthesis of
single crystals, we investigate theoretically the possibility of
superconductivity in this compound. We use a model of spin fluctuation-mediated
superconductivity, where the pairing potential is strongly peaked at \pi in the
ladder direction. We solve the coupled gap equations on the bonding and
antibonding ladder bands to find superconducting solutions across the range of
doping, and discuss their relevance to the real material.Comment: RevTex, 4 pages, 7 figure
- …