33,057 research outputs found
Project management techniques for highly integrated programs
The management and control of a representative, highly integrated high-technology project, in the X-29A aircraft flight test project is addressed. The X-29A research aircraft required the development and integration of eight distinct technologies in one aircraft. The project management system developed for the X-29A flight test program focuses on the dynamic interactions and the the intercommunication among components of the system. The insights gained from the new conceptual framework permitted subordination of departments to more functional units of decisionmaking, information processing, and communication networks. These processes were used to develop a project management system for the X-29A around the information flows that minimized the effects inherent in sampled-data systems and exploited the closed-loop multivariable nature of highly integrated projects
Transit Time and Charge Correlations of Single Photoelectron Events in R7081 PMTs
During the calibration phase of the photomultiplier tubes (PMT) for the
Double Chooz experiment the PMT response to light with single photoelectron
(SPE) intensity was analysed. With our setup we were able to measure the
combined transit time and charge response of the PMT and therefore we could
deconstruct and analyse all physical effects having an influence on the PMT
signal. Based on this analysis charge and time correlated probability density
functions were developed to include the PMT response in a Monte Carlo
simulation.Comment: minor changes by referee reques
Transit Time and Charge Correlations of Single Photoelectron Events in R7081 PMTs
During the calibration phase of the photomultiplier tubes (PMT) for the
Double Chooz experiment the PMT response to light with single photoelectron
(SPE) intensity was analysed. With our setup we were able to measure the
combined transit time and charge response of the PMT and therefore we could
deconstruct and analyse all physical effects having an influence on the PMT
signal. Based on this analysis charge and time correlated probability density
functions were developed to include the PMT response in a Monte Carlo
simulation.Comment: minor changes by referee reques
Nonsequential Double Recombination in Intense Laser Fields
A second plateau in the harmonic spectra of laser-driven two-electron atoms
is observed both in the numerical solution of a low-dimensional model helium
atom and using an extended strong field approximation. It is shown that the
harmonics well beyond the usual cut-off are due to the simultaneous
recombination of the two electrons, which were emitted during different,
previous half-cycles. The new cut-off is explained in terms of classical
trajectories. Classical predictions and the time-frequency analysis of the ab
initio quantum results are in excellent agreement. The mechanism corresponds to
the inverse single photon double ionization process in the presence of a (low
frequency) laser field.Comment: 4 pages, RevTeX, v2 with an extended strong field approximation
treatment of the process; instead, v1 describes an attosecond control scheme
to enhance the proces
A laser technique for characterizing the geometry of plant canopies
The interception of solar power by the canopy is investigated as a function of solar zenith angle (time), component of the canopy, and depth into the canopy. The projected foliage area, cumulative leaf area, and view factors within the canopy are examined as a function of the same parameters. Two systems are proposed that are capable of describing the geometrical aspects of a vegetative canopy and of operation in an automatic mode. Either system would provide sufficient data to yield a numerical map of the foliage area in the canopy. Both systems would involve the collection of large data sets in a short time period using minimal manpower
Metamagnetism and Lifshitz Transitions in Models for Heavy Fermions
We investigate metamagnetic transitions in models for heavy fermions by
considering the doped Kondo lattice model in two dimensions. Results are
obtained within the framework of dynamical mean field and dynamical cluster
approximations. Universal magnetization curves for different temperatures and
Kondo couplings develop upon scaling with the lattice coherence temperature.
Furthermore, the coupling of the local moments to the magnetic field is varied
to take into account the different Land\'e factors of localized and itinerant
electrons. The competition between the lattice coherence scale and the Zeeman
energy scale allows for two interpretations of the metamagnetism in heavy
fermions: Kondo breakdown or Lifshitz transitions. By tracking the
single-particle residue through the transition, we can uniquely conclude in
favor of the Lifshitz transition scenario. In this scenario, a quasiparticle
band drops below the Fermi energy which leads to a change in topology of the
Fermi surface.Comment: 8 pages, 7 figure
Extreme vortex pinning in the non-centrosymmetric superconductor CePtSi
We report on the vortex dynamics of a single crystal of the
non-centrosymmetric heavy-fermion superconductor CePtSi. Decays of the
remnant magnetization display a clean logarithmic time dependence with rates
that follow the temperature dependence expected from the Kim-Anderson theory.
The creep rates are lower than observed in any other centrosymmetric
superconductor and are not caused by high critical currents. On the contrary,
the critical current in CePtSi is considerably lower than in other
superconductors with strong vortex pinning indicating that an alternative
impediment on the flux line motion might be at work in this superconductor.Comment: 4 pages, 5 figure
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