2,275 research outputs found

### Study of the $\Lambda_{b} \to N^\ast \ell^+ \ell^-$ decay in light cone sum rules

The form factors of the $\Lambda_{b} \to N^\ast \ell^+ \ell^-$ decay are
calculated in the framework of the light cone QCD sum rules. In the
calculations the contribution of the negative parity $\Lambda_b^\ast$ baryon is
eliminated by constructing the sum rules for different Lorentz structures.
Furthermore the branching ratio of the semileptonic $\Lambda_b \to N^\ast
\ell^+ \ell^-$ decay is calculated. The numerical study for the branching ratio
of the $\Lambda_{b} \to N^\ast \ell^+ \ell^-$ decay indicates that it is quite
large and could be measurable at future planned experiments to be conducted at
LHCb.Comment: 21 pages, 2 figures, LaTeX formatte

### Analysis of the radiative decays $\Sigma_Q \to \Lambda_Q \gamma$ and $\Xi^\prime_Q \to \Xi_Q \gamma$ in light cone sum rules

The light cone sum rules method is used in studying the radiative decays
$\Sigma_Q \to \Lambda_Q \gamma$ and $\Xi^\prime_Q \to \Xi_Q \gamma$. Firstly,
the sum rules for the form factor $F_2(Q^2=0)$ responsible for these
transitions is constructed. Using this result the decay widths of the
above--mentioned decays are calculated and analyzed. A comparison of our
predictions on the decay widths of considered transitions with the predictions
of the other approaches is presented.Comment: 13 pages, no figures, LaTeX formatte

### Adaptive fair channel allocation for QoS enhancement in IEEE 802.11 wireless LANs

The emerging widespread use of real-time multimedia applications over wireless networks makes the support of quality of service (QoS) a key problem. In this paper, we focus on QoS support mechanisms for IEEE 802.11 wireless ad-hoc networks. First, we review limitations of the upcoming IEEE 802.11e enhanced DCF (EDCF) and other enhanced MAC schemes that have been proposed to support QoS for 802.11 ad-hoc networks. Then, we describe a new scheme called adaptive fair EDCF that extends EDCF, by increasing the contention window during deferring periods when the channel is busy, and by using an adaptive fast backoff mechanism when the channel is idle. Our scheme computes an adaptive backoff threshold for each priority level by taking into account the channel load. The new scheme significantly improves the quality of multimedia applications. Moreover, it increases the overall throughput obtained both in medium and high load cases. Simulution results show that our new scheme outperforms EDCF and other enhanced schemes. Finally, we show that the adaptive fair EDCF scheme achieves a high degree of fairness among applications of the same priority level

- β¦