629 research outputs found
Bistability in sine-Gordon: the ideal switch
The sine-Gordon equation, used as the representative nonlinear wave equation,
presents a bistable behavior resulting from nonlinearity and generating
hysteresis properties. We show that the process can be understood in a
comprehensive analytical formulation and that it is a generic property of
nonlinear systems possessing a natural band gap. The approach allows to
discover that sine-Gordon can work as an it ideal switch by reaching a
transmissive regime with vanishing driving amplitude.Comment: Phys. Rev. E, (to be published, May 2005
Experimental realization of a relativistic fluxon ratchet
We report the observation of the ratchet effect for a relativistic flux
quantum trapped in an annular Josephson junction embedded in an inhomogeneous
magnetic field. In such a solid state system mechanical quantities are
proportional to electrical quantities, so that the ratchet effect represents
the realization of a relativistic-flux-quantum-based diode. Mean static voltage
response, equivalent to directed fluxon motion, is experimentally demonstrated
in such a diode for deterministic current forcing both in the overdamped and in
the underdamped dynamical regime. In the underdamped regime, the recently
predicted phenomenon of current reversal is also recovered in our fluxon
ratchet.Comment: 4 pages, 6 figures. To appear in PHYSICA
Coupling of Josephson flux-flow oscillators to an external RC load
We investigate by numerical simulations the behavior of the power dissipated
in a resistive load capacitively coupled to a Josephson flux flow oscillator
and compare the results to those obtained for a d.c. coupled purely resistive
load. Assuming realistic values for the parameters R and C, both in the high-
and in the low-Tc case the power is large enough to allow the operation of such
a device in applications.Comment: uuencoded, gzipped tar archive containing 11 pages of REVTeX text + 4
PostScript figures. To appear in Supercond. Sci. Techno
New Antenna Deployment, Pointing and Supporting Mechanism
On ITALSAT Flight 2, the Italian telecommunications satellite, the two L-Ka antennas (Tx and Rx) use two large deployable reflectors (2000-mm diameter), whose deployment and fine pointing functions are accomplished by means of an innovative mechanism concept. The Antenna Deployment & Pointing Mechanism and Supporting Structure (ADPMSS) is based on a new configuration solution, where the reflector and mechanisms are conceived as an integrated, self-contained assembly. This approach is different from the traditional configuration solution. Typically, a rigid arm is used to deploy and then support the reflector in the operating position, and an Antenna Pointing Mechanism (APM) is normally interposed between the reflector and the arm for steering operation. The main characteristics of the ADPMSS are: combined implementation of deployment, pointing, and reflector support; optimum integration of active components and interface matching with the satellite platform; structural link distribution to avoid hyperstatic connections; very light weight and; high performance in terms of deployment torque margin and pointing range/accuracy. After having successfully been subjected to all component-level qualification and system-level acceptance tests, two flight ADPMSS mechanisms (one for each antenna) are now integrated on ITALSAT F2 and are ready for launch. This paper deals with the design concept, development, and testing program performed to qualify the ADPMSS mechanism
A Human-centric AI-driven Framework for Exploring Large and Complex Datasets
Human-Centered Artificial Intelligence (HCAI) is a new frontier of research at the intersection between HCI and AI. It fosters an innovative vision of human-centred intelligent systems, which are systems that take advantage of computer features, such as powerful algorithms, big data management, advanced sensors and that are useful and usable for people, providing high levels of automation and enabling high levels of human control. This position paper presents our ongoing research aiming to extend the HCAI framework for better supporting designers in creating AI-based systems
Observation of progressive motion of ac-driven solitons
We report the first experimental observation of phase-locked motion of a
topological soliton at a nonzero average velocity in a periodically modulated
lossy medium, under the action of an ac force with no dc component [the effect
was predicted by G. Filatrella, B.A. Malomed, and R.D. Parmentier, Phys. Lett.
A 198, 43 (1995)]. The velocity is related by a resonant condition to the
driving frequency. The observation is made in terms of the current-voltage,
I(V), characteristics for a fluxon trapped in an annular Josephson junction
placed into dc magnetic field. Large zero-crossing constant-voltage steps,
exactly corresponding to the resonantly locked soliton motion at different
orders of the resonance, are found on the experimental I(V) curves. A measured
dependence of the size of the steps vs. the external magnetic field is in good
agreement with predictions of an analytical model based on the balance equation
for the fluxon's energy. The effect has a potential application as a
low-frequency voltage standard. The work was supported by a grant from the
German-Israeli Foundation.Comment: Physical Review B, in press (Rapid Communication
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