38,042 research outputs found
Predictive protocol of flocks with small-world connection pattern
By introducing a predictive mechanism with small-world connections, we
propose a new motion protocol for self-driven flocks. The small-world
connections are implemented by randomly adding long-range interactions from the
leader to a few distant agents, namely pseudo-leaders. The leader can directly
affect the pseudo-leaders, thereby influencing all the other agents through
them efficiently. Moreover, these pseudo-leaders are able to predict the
leader's motion several steps ahead and use this information in decision making
towards coherent flocking with more stable formation. It is shown that drastic
improvement can be achieved in terms of both the consensus performance and the
communication cost. From the industrial engineering point of view, the current
protocol allows for a significant improvement in the cohesion and rigidity of
the formation at a fairly low cost of adding a few long-range links embedded
with predictive capabilities. Significantly, this work uncovers an important
feature of flocks that predictive capability and long-range links can
compensate for the insufficiency of each other. These conclusions are valid for
both the attractive/repulsive swarm model and the Vicsek model.Comment: 10 pages, 12 figure
On the thermal conduction in tangled magnetic fields in clusters of galaxies
Thermal conduction in tangled magnetic fields is reduced because heat
conducting electrons must travel along the field lines longer distances between
hot and cold regions of space than if there were no fields. We consider the
case when the tangled magnetic field has a weak homogeneous component. We
examine two simple models for temperature in clusters of galaxies: a
time-independent model and a time-dependent one. We find that the actual value
of the effective thermal conductivity in tangled magnetic fields depends on how
it is defined for a particular astrophysical problem. Our final conclusion is
that the heat conduction never totally suppressed but is usually important in
the central regions of galaxy clusters, and therefore, it should not be
neglected.Comment: 16 pages, 4 figure
Note about a second "evidence" for a WIMP annual modulation
This note, with its five questions, is intended to contribute to a
clarification about a claimed "evidence" by the DAMA group of an annual
modulation of the counting rate of a Dark Matter NaI(Tl) detector as due to a
neutralino (SUSY-LSP) Dark Matter candidate.Comment: LaTex, 3 pages, 2 figure
Maximum likelihood based estimation of frequency and phase offset in DCT OFDM systems under non-circular transmissions: algorithms, analysis and comparisons
Recently, the advantages of the discrete cosine transform (DCT) based orthogonal frequency-division multiplexing (OFDM) have come to the light. We thus consider DCT- OFDM with non-circular transmission (our results cover circular transmission as well) and present two blind joint maximum- likelihood frequency offset and phase offset estimators. Both our theoretical analysis and numerical comparisons reveal new advantages of DCT-OFDM over the traditional discrete Fourier transform (DFT) based OFDM. These advantages, as well as those already uncovered in the early works on DCT-OFDM, support the belief that DCT-OFDM is a promising multi-carrier modulation scheme
Ultrasensitive mechanical detection of magnetic moment using a commercial disk drive write head
Sensitive detection of weak magnetic moments is an essential capability in
many areas of nanoscale science and technology, including nanomagnetism,
quantum readout of spins, and nanoscale magnetic resonance imaging. Here, we
show that the write head of a commercial hard drive may enable significant
advances in nanoscale spin detection. By approaching a sharp diamond tip to
within 5 nm from the pole and measuring the induced diamagnetic moment with a
nanomechanical force transducer, we demonstrate a spin sensitivity of 0.032
Bohr magnetons per root Hz, equivalent to 21 proton magnetic moments. The high
sensitivity is enabled in part by the pole's strong magnetic gradient of up to
28 million Tesla per meter and in part by the absence of non-contact friction
due to the extremely flat writer surface. In addition, we demonstrate
quantitative imaging of the pole field with about 10 nm spatial resolution. We
foresee diverse applications for write heads in experimental condensed matter
physics, especially in spintronics, ultrafast spin manipulation, and mesoscopic
physics.Comment: 21 pages, 6 figure
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