47,853 research outputs found
Qualitative Properties of alpha-Weighted Scheduling Policies
We consider a switched network, a fairly general constrained queueing network
model that has been used successfully to model the detailed packet-level
dynamics in communication networks, such as input-queued switches and wireless
networks. The main operational issue in this model is that of deciding which
queues to serve, subject to certain constraints. In this paper, we study
qualitative performance properties of the well known -weighted
scheduling policies. The stability, in the sense of positive recurrence, of
these policies has been well understood. We establish exponential upper bounds
on the tail of the steady-state distribution of the backlog. Along the way, we
prove finiteness of the expected steady-state backlog when , a
property that was known only for . Finally, we analyze the
excursions of the maximum backlog over a finite time horizon for . As a consequence, for , we establish the full state space
collapse property.Comment: 13 page
Optical spectroscopy study on single crystalline LaFeAsO
Millimeter-sized single crystals of LaFeAsO were grown from NaAs flux and the
in-plane optical properties were studied over a wide frequency range. A sizable
electronic correlation effect was indicated from the analysis of the
free-carrier spectral weight. With decreasing temperature from 300 K, we
observed a continuous suppression of the spectral weight near 0.6 eV. But a
spin-density-wave gap formation at lower energy scale was seen only in the
broken-symmetry state. We elaborate that both the itinerancy and local spin
interactions of Fe\emph{3d} electrons are present for the FeAs-based systems;
however, the establishment of the long-range magnetic order at low temperature
has a dominantly itinerant origin.Comment: 4 figures, 5 page
Frequency pulling and mixing of relaxation oscillations in superconducting nanowires
Many superconducting technologies such as rapid single flux quantum computing
(RSFQ) and superconducting quantum interference devices (SQUIDs) rely on the
modulation of nonlinear dynamics in Josephson junctions for functionality. More
recently, however, superconducting devices have been developed based on the
switching and thermal heating of nanowires for use in fields such as single
photon detection and digital logic. In this paper, we use resistive shunting to
control the nonlinear heating of a superconducting nanowire and compare the
resulting dynamics to those observed in Josephson junctions. We show that
interaction of the hotspot growth with the external shunt produces high
frequency relaxation oscillations with similar behavior as observed in
Josephson junctions due to their rapid time constants and ability to be
modulated by a weak periodic signal. In particular, we use a microwave drive to
pull and mix the oscillation frequency, resulting in phase locked features that
resemble the AC Josephson effect. New nanowire devices based on these
conclusions have promising applications in fields such as parametric
amplification and frequency multiplexing
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