42,713 research outputs found
Thermal Effects on Photon-Induced Quantum Transport
We theoretically investigate laser induced quantum transport in a two-level
quantum dot attached to electric contacts. Our approach, based on
nonequilibrium Green function technique, allows to include thermal effects on
the photon-induced quantum transport and excitonic coherent dynamics. By
solving a set of coupled integrodifferential equations, involving correlation
and propagator functions, we obtain the photocurrent and the dot occupations as
a function of time. The characteristic coherent Rabi oscillations are found in
both occupations and photocurrent, with two distinct sources of decoherence:
incoherent tunneling and thermal fluctuations. In particular, for increasing
temperature the dot becomes more thermally occupied which shrinks the amplitude
of the Rabi oscillations, due to Pauli blockade. Finally, due to the interplay
between photon and thermal induced electron populations, the photocurrent can
switch sign as time evolves and its stationary value can be maximized by
tunning the laser intensity.Comment: 5 pages, 4 figure
Impact of Power Allocation and Antenna Directivity in the Capacity of a Multiuser Cognitive Ad Hoc Network
This paper studies the benefits that power control and antenna directivity can bring to the capacity of a multiuser cognitive radio network. The main objective is to optimize the secondary network sum rate under the capacity constraint of the primary network. Exploiting location awareness, antenna directivity, and the power control capability, the cognitive radio ad hoc network can broaden its coverage and improve capacity. Computer simulations show that by employing the proposed method the system performance is significantly enhanced compared to conventional fixed power allocation
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