10,653 research outputs found
Multiplication theory for dynamically biased avalanche photodiodes: new limits for gain bandwidth product
Novel theory is developed for the avalanche multiplication process in avalanche photodiodes (APDs) under time-varying reverse-biasing conditions. Integral equations are derived characterizing the statistics of the multiplication factor and the impulse-response function of APDs, as well as their breakdown probability, all under the assumption that the electric field driving the avalanche process is time varying and spatially nonuniform. Numerical calculations generated by the model predict that by using a bit-synchronous sinusoidal biasing scheme to operate the APD in an optical receiver, the pulse-integrated gain-bandwidth product can be improved by a factor of 5 compared to the same APD operating under the conventional static biasing. The bit-synchronized periodic modulation of the electric field in the multiplication region serves to (1) produce large avalanche multiplication factors with suppressed avalanche durations for photons arriving in the early phase of each optical pulse; and (2) generate low avalanche gains and very short avalanche durations for photons arriving in the latter part of each optical pulse. These two factors can work together to reduce intersymbol interference in optical receivers without sacrificing sensitivity
Clumping and quantum order: Quantum gravitational dynamics of NUT charge
Gravitational instantons with NUT charge are magnetic monopoles upon
dimensional reduction. We determine whether NUT charge can proliferate via the
Polyakov mechanism and partially screen gravitational interactions. In
semiclassical Einstein gravity, Taub-NUT instantons experience a universal
attractive force in the path integral that prevents proliferation. This
attraction further leads to semiclassical clumping instabilities, similar to
the known instabilities of hot flat space and the Kaluza-Klein vacuum. Beyond
pure Einstein gravity, NUT proliferation depends on the following question: is
the mass of a gravitational instanton in the theory always greater than its NUT
charge? Using spinorial methods we show that the answer to this question is
`yes' if all matter fields obey a natural Euclidean energy condition.
Therefore, the attractive force between instantons in the path integral wins
out and gravity is dynamically protected against screening. Semiclassical
gravity with a compactified circle can be self-consistently quantum ordered, at
the cost of suffering from clumping instabilities
Joint User Scheduling and Power optimization in Full-Duplex Cells with Successive Interference Cancellation
This paper considers a cellular system with a full-duplex base station and
half-duplex users. The base station can activate one user in uplink or downlink
(half-duplex mode), or two different users one in each direction simultaneously
(full-duplex mode). Simultaneous transmissions in uplink and downlink causes
self-interference at the base station and uplink-to-downlink interference at
the downlink user. Although uplink-to-downlink interference is typically
treated as noise, it is shown that successive interference decoding and
cancellation (SIC mode) can lead to significant improvement in network utility,
especially when user distribution is concentrated around a few hotspots. The
proposed temporal fair user scheduling algorithm and corresponding power
optimization utilizes full-duplex and SIC modes as well as half-duplex
transmissions based on their impact on network utility. Simulation results
reveal that the proposed strategy can achieve up to 95% average cell throughput
improvement in typical indoor scenarios with respect to a conventional network
in which the base station is half-duplex.Comment: To be appeared in IEEE Asilomar Conference on Signals, Systems, and
Computers, 201
Direct CP violation in decays as a probe for new physics
In this paper we investigate CP violation in charged decays of meson.
Particularly, we study the direct CP asymmetry of the Cabibbo favored
non-leptonic and the doubly Cabibbo-suppressed
decay mode within standard model, two Higgs doublet
model with generic Yukawa structure and left right symmetric models. In the
standard model, we first derive the contributions from box and di-penguin
diagrams contributing to their amplitudes which are relevant to the generation
of the weak phases essential for non-vanishing direct CP violation. Then, we
show that these phases are so tiny leading to a direct CP asymmetry of order
in both decay modes. Regarding the two Higgs doublet model with
generic Yukawa structure and after taking into account all constraints on the
parameter space of the model, we show that the enhanced direct CP asymmetries
can be 6 and 7 orders of magnitudes larger than the standard model prediction
for and
respectively. Finally, within left right symmetric models, we find that sizable
direct CP asymmetry of can be obtained for the decay
mode after respecting all relevant
constraints.Comment: 20 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1710.0041
- β¦