5,654 research outputs found
Self-sustained magnetoelectric oscillations in magnetic resonant tunneling structures
The dynamic interplay of transport, electrostatic, and magnetic effects in
the resonant tunneling through ferromagnetic quantum wells is theoretically
investigated. It is shown that the carrier-mediated magnetic order in the
ferromagnetic region not only induces, but also takes part in intrinsic,
robust, and sustainable high-frequency current oscillations over a large window
of nominally steady bias voltages. This phenomenon could spawn a new class of
quantum electronic devices based on ferromagnetic semiconductors.Comment: 5 pages, 4 figure
Resonant Tunneling Magneto Resistance in Coupled Quantum Wells
A three barrier resonant tunneling structure in which the two quantum wells
are formed by a dilute magnetic semiconductor material (ZnMnSe) with a giant
Zeeman splitting of the conduction band is theoretically investigated.
Self-consistent numerical simulations of the structure predict giant
magnetocurrent in the resonant bias regime as well as significant current spin
polarization for a considerable range of applied biases.Comment: 4 pages, 4 figure
Proposal for a ferromagnetic multiwell spin oscillator
The highly nonlinear coupling of transport and magnetic properties in a
multiwell heterostructure, which comprises ferromagnetic quantum wells made of
diluted magnetic semiconductors, is theoretically investigated. The interplay
of resonant tunneling and carrier-mediated ferromagnetism in the magnetic wells
induces very robust, self-sustained current and magnetization oscillations.
Over a large window of steady bias voltages the spin polarization of the
collector current is oscillating between positive and negative values,
realizing a spin oscillator device.Comment: 3 pages, 4 figure
Maximum Entropy Models of Shortest Path and Outbreak Distributions in Networks
Properties of networks are often characterized in terms of features such as
node degree distributions, average path lengths, diameters, or clustering
coefficients. Here, we study shortest path length distributions. On the one
hand, average as well as maximum distances can be determined therefrom; on the
other hand, they are closely related to the dynamics of network spreading
processes. Because of the combinatorial nature of networks, we apply maximum
entropy arguments to derive a general, physically plausible model. In
particular, we establish the generalized Gamma distribution as a continuous
characterization of shortest path length histograms of networks or arbitrary
topology. Experimental evaluations corroborate our theoretical results
Performance Analysis of Unsupervised LTE Device-to-Device (D2D) Communication
Cellular network technology based device-to-device communication attracts
increasing attention for use cases such as the control of autonomous vehicles
on the ground and in the air. LTE provides device-to-device communication
options, however, the configuration options are manifold (leading to 150+
possible combinations) and therefore the ideal combination of parameters is
hard to find. Depending on the use case, either throughput, reliability or
latency constraints may be the primary concern of the service provider. In this
work we analyze the impact of different configuration settings of unsupervised
LTE device-to-device (sidelink) communication on the system performance. Using
a simulative approach we vary the length of the PSCCH period and the number of
PSCCH subframes and determine the impact of different combinations of those
parameters on the resulting latency, reliability and the interarrival times of
the received packets. Furthermore we examine the system limitations by a
scalability analysis. In this context, we propose a modified HARQ process to
mitigate scalability constraints. Our results show that the proposed reduced
HARQ retransmission probability can increase the system performance regarding
latency and interarrival times as well as the packet transmission reliability
for higher channel utilization
Regulation of NGN: Structural Separation, Access Regulation, or No Regulation at All?
Since the introduction of Next Generation Networks (NGNs) by telecommunication network operators, national regulators have begun to adapt their access regulation regimes to the new technological conditions. The regulatory reactions gravitate towards three distinct regulatory trajectories: unregulated competition, access regulation, and structural separation. We first analyze the extent of market power in access Networks in NGNs from a technological perspective. Second, we use case studies to identify patterns between technological and market conditions and regulators' reactions in selected countries. We find that market power in the access network is likely to prevail. Regulatory reactions differ with the extent of infrastructure competition and the regulators position in the trade-off between promoting investment and protecting competitionNext Generation Network, deregulation, access regulation, structural separation.
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