Controlling complex policy problems: a multimethodological approach using system dynamics and network controllability

Notwithstanding the usefulness of system dynamics in analyzing complex policy problems, policy design is far from straightforward and in many instances trial-and-error driven. To address this challenge, we propose to combine system dynamics with network controllability, an emerging field in network science, to facilitate the detection of effective leverage points in system dynamics models and thus to support the design of influential policies. We illustrate our approach by analyzing a classic system dynamics model: the World Dynamics model. We show that it is enough to control only 53% of the variables to steer the entire system to an arbitrary final state. We further rank all variables according to their importance in controlling the system and we validate our approach by showing that high ranked variables have a significantly larger impact on the system behavior compared to low ranked variables

Design, development and trials of an airline passenger telephone system

The design, development and trials of a satellite telephone system for airline passengers is described. The requirements for ground and space infrastructure are discussed and the aeronautical system is described. Design criteria for the antennas and avionic boxes are given and system operation and technical flight trial requirements are discussed, together with test methodology and development towards fully commercial trials. Finally, an indication of development requirements to achieve the desired aims of airline users is given

On the Kondo effect in carbon nanotubes at half halfing

In a single state of a quantum dot the Kondo effect arises due to the spin-degeneracy, which is present if the dot is occupied with one electron (N = 1). The eigenstates of a carbon nanotube quantum dot possess an additional orbital degeneracy leading to a four-fold shell pattern. This additional degeneracy increases the possibility for the Kondo effect to appear. We revisit the Kondo problem in metallic carbon nanotubes by linear and non-linear transport measurement in this regime, in which the four-fold pattern is present. We have analyzed the ground state of CNTs, which were grown by chemical vapor deposition, at filling N = 1, N = 2, and N = 3. Of particular interest is the half-filled shell, i.e. N = 2. In this case, the ground state is either a paired electron state or a state for which the singlet and triplet states are effectively degenerate, allowing in the latter case for the appearance of the Kondo effect. We deduce numbers for the effective missmatch d of the levels from perfect degeneracy and the exchange energy J. While d ~ 0.1 - 0.2 (in units of level spacing) is in agreement with previous work, the exchange term is found to be surprisingly small: J < 0.02. In addition we report on the observation of gaps, which in one case is seen at N = 3 and in another is present over an extended sequence of levels.Comment: full paper including figures at: http://www.unibas.ch/phys-meso/Research/Papers/2004/Kondo-4shell-SWNT.pd

Kondo resonance in a nanotube quantum dot coupled to a normal and a superconducting lead

We report on electrical transport measurements through a carbon nanotube quantum dot coupled to a normal and a superconducting lead. The ratio of Kondo temperature and superconducting gap $T_{K}/\Delta$ is identified to govern the transport properties of the system. In the case of $T_{K}<\Delta$ the conductance resonance splits into two resonances at $\pm \Delta$. For the opposite scenario $T_{K}>\Delta$ the conductance resonance persists, however the conductance is not enhanced compared to the normal state due to a relative asymmetry of the lead-dot couplings. Within this limit the data is in agreement with a simple model of a resonant SN-interface.Comment: 4 pages, 2 figures. submitted to the Proc. Rencontres de Moriond on Quantum Information and Decoherence in Nanosystems 200

The development of the image of a selective collegiate public institution and the effects of that image upon admissions : the case of the College of William and Mary in Virginia, 1946-1980

The purpose of this case study was to trace the development of the image of the College of William and Mary in order to test the hypothesis: The image of a selective liberal arts college is not exclusive to the private sector. In tracing the development of the image, the concept of saga, defined by Clark (1968) as an historically based understanding of organizational development was viewed as the theoretical basis for the study. Four factors were found to have a positive impact upon the development of the selective image of the College. (1) The restoration and growth of Colonial Williamsburg which attracts over one million visitors to the area each year. (2) The admission philosophy and policies which projected and fostered a selective image prior to the actual development of selectivity. (3) The administrative philosophy and development of the mission of the institution as espoused by the four presidents who served during the period. (4) The student bodies of the time period studied--their academic credentials, activities and foci during their college careers--both as a group and as individuals.;Statistics were compiled for the period 1946-1980 listing: the number of applicants; the percentage accepted; the percentage of admitted students enrolled; and the high school academic credentials including test scores and ranks-in-class. These were used to demonstrate the degree of selectivity which developed during the period

Permalloy-based carbon nanotube spin-valve

In this Letter we demonstrate that Permalloy (Py), a widely used Ni/Fe alloy, forms contacts to carbon nanotubes (CNTs) that meet the requirements for the injection and detection of spin-polarized currents in carbon-based spintronic devices. We establish the material quality and magnetization properties of Py strips in the shape of suitable electrical contacts and find a sharp magnetization switching tunable by geometry in the anisotropic magnetoresistance (AMR) of a single strip at cryogenic temperatures. In addition, we show that Py contacts couple strongly to CNTs, comparable to Pd contacts, thereby forming CNT quantum dots at low temperatures. These results form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance switchings in the tunneling magnetoresistance, which directly correspond to the magnetization reversals in the individual contacts observed in AMR experiments.Comment: 3 page