187,751 research outputs found
Nanomechanical single-photon routing
The merger between integrated photonics and quantum optics promises new
opportunities within photonic quantum technology with the very significant
progress on excellent photon-emitter interfaces and advanced optical circuits.
A key missing functionality is rapid circuitry reconfigurability that
ultimately does not introduce loss or emitter decoherence, and operating at a
speed matching the photon generation and quantum memory storage time of the
on-chip quantum emitter. This ambitious goal requires entirely new active
quantum-photonic devices by extending the traditional approaches to
reconfigurability. Here, by merging nano-optomechanics and deterministic
photon-emitter interfaces we demonstrate on-chip single-photon routing with low
loss, small device footprint, and an intrinsic time response approaching the
spin coherence time of solid-state quantum emitters. The device is an essential
building block for constructing advanced quantum photonic architectures
on-chip, towards, e.g., coherent multi-photon sources, deterministic
photon-photon quantum gates, quantum repeater nodes, or scalable quantum
networks.Comment: 7 pages, 3 figures, supplementary informatio
Delay-Energy lower bound on Two-Way Relay Wireless Network Coding
Network coding is a novel solution that significantly improve the throughput
and energy consumed of wireless networks by mixing traffic flows through
algebraic operations. In conventional network coding scheme, a packet has to
wait for packets from other sources to be coded before transmitting. The
wait-and-code scheme will naturally result in packet loss rate in a finite
buffer. We will propose Enhanced Network Coding (ENC), an extension to ONC in
continuous time domain.
In ENC, the relay transmits both coded and uncoded packets to reduce delay.
In exchange, more energy is consumed in transmitting uncoded packets. ENC is a
practical algorithm to achieve minimal average delay and zero packet-loss rate
under given energy constraint. The system model for ENC on a general renewal
process queuing is presented. In particular, we will show that there exists a
fundamental trade-off between average delay and energy. We will also present
the analytic result of lower bound for this trade-off curve, which can be
achieved by ENC
An Optimal Medium Access Control with Partial Observations for Sensor Networks
We consider medium access control (MAC) in multihop sensor networks, where only partial information about the shared medium is available to the transmitter. We model our setting as a queuing problem in which the service rate of a queue is a function of a partially observed Markov chain representing the available bandwidth, and in which the arrivals are controlled based on the partial observations so as to keep the system in a desirable mildly unstable regime. The optimal controller for this problem satisfies a separation property: we first compute a probability measure on the state space of the chain, namely the information state, then use this measure as the new state on which the control decisions are based. We give a formal description of the system considered and of its dynamics, we formalize and solve an optimal control problem, and we show numerical simulations to illustrate with concrete examples properties of the optimal control law. We show how the ergodic behavior of our queuing model is characterized by an invariant measure over all possible information states, and we construct that measure. Our results can be specifically applied for designing efficient and stable algorithms for medium access control in multiple-accessed systems, in particular for sensor networks
Throughput Scaling of Wireless Networks With Random Connections
This work studies the throughput scaling laws of ad hoc wireless networks in
the limit of a large number of nodes. A random connections model is assumed in
which the channel connections between the nodes are drawn independently from a
common distribution. Transmitting nodes are subject to an on-off strategy, and
receiving nodes employ conventional single-user decoding. The following results
are proven:
1) For a class of connection models with finite mean and variance, the
throughput scaling is upper-bounded by for single-hop schemes, and
for two-hop (and multihop) schemes.
2) The throughput scaling is achievable for a specific
connection model by a two-hop opportunistic relaying scheme, which employs
full, but only local channel state information (CSI) at the receivers, and
partial CSI at the transmitters.
3) By relaxing the constraints of finite mean and variance of the connection
model, linear throughput scaling is achievable with Pareto-type
fading models.Comment: 13 pages, 4 figures, To appear in IEEE Transactions on Information
Theor
Magnetic noise reduction of in-wheel permanent magnet synchronous motors for light-duty electric vehicles
This paper presents study of a multi-slice subdomain model (MS-SDM) for persistent low-frequency sound, in a wheel hub-mounted permanent magnet synchronous motor (WHM-PMSM) with a fractional-slot non-overlapping concentrated winding for a light-duty, fully electric vehicle applications. While this type of winding provides numerous potential benefits, it has also the largest magnetomotive force (MMF) distortion factor, which leads to the electro-vibro-acoustics production, unless additional machine design considerations are carried out. To minimize the magnetic noise level radiated by the PMSM, a skewing technique is targeted with consideration of the natural frequencies under a variable-speed-range analysis. To ensure the impact of the minimization technique used, magnetic force harmonics, along with acoustic sonograms, is computed by MS-SDM and verified by 3D finite element analysis. On the basis of the studied models, we derived and experimentally verified the optimized model with 5 dBA reduction in A-weighted sound power level by due to the choice of skew angle. In addition, we investigated whether or not the skewing slice number can be of importance on the vibro-acoustic objectives in the studied WHM-PMSM.Postprint (published version
Jet formation and interference in a thin QCD medium
In heavy-ion collisions, an abundant production of high-energy QCD jets
allows to study how these multiparticle sprays are modified as they pass
through the quark-gluon plasma. In order to shed new light on this process, we
compute the inclusive two-gluon rate off a hard quark propagating through a
color deconfined medium at first order in medium opacity. We explicitly impose
an energy ordering of the two emitted gluons, such that the "hard" gluon can be
thought of as belonging to the jet substructure while the other is a "soft"
emission (which can be collinear or medium-induced). Our analysis focusses on
two specific limits that clarify the modification of the additional angle- and
formation time-ordering of splittings. In one limit, the formation time of the
"hard" gluon is short compared to the "soft" gluon formation time, leading to a
probabilistic formula for production of and subsequent radiation off a
quark-gluon antenna. In the other limit, the ordering of formation is reverted,
which automatically leads to the fact that the jet substructure is resolved by
the medium. We observe in this case a characteristic delay: the jet radiates as
one color current (quark) up to the formation of the "hard" gluon, at which
point we observe the onset of radiation of the new color current (gluon). Our
computation supports a picture in which the in-medium jet dynamics are
described as a collection of subsequent antennas which are resolved by the
medium according to their transverse extent.Comment: 33 page
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