In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
We report measurements of the branching fractions and direct CP asymmetries (ACP ) for B → Kπ, ππ and KK decays (but not π 0 π 0 ) based on the final data sample of 772 × 10 6 BB pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. We set a 90% confidence-level upper limit for K + K − at 2.0 × 10 −7 ; all other decays are observed with branching fractions ranging from 10 −6 to 10 −5 . In the B 0 /B 0 → K ± π ∓ mode, we confirm Belle's previously reported large ACP with a value of −0.069 ± 0.014 ± 0.007 and a significance of 4.4σ. For all other flavor-specific modes, we find ACP values consistent with zero, including ACP (K + π 0 ) = +0.043 ± 0.024 ± 0.007 with 1.8σ significance. The difference of CP asymmetry between.112 ± 0.027 ± 0.007 with 4.0σ significance. We also calculate the ratios of partial widths for the B → Kπ decays. Using our results, we test the validity of the sum rule= 0 and obtain a sum of −0.270 ± 0.132 ± 0.060 with 1.9σ significance.PACS numbers: 11.30. Er, 12.15.Hh, 13.25.Hw, 14.40.Nd Charmless B meson decays to Kπ, ππ and KK final states provide a good test bed to understand B decay mechanisms and to search for physics beyond the Standard Model (SM). Although predictions for the branching fractions under various theoretical approaches suffer from large hadronic uncertainties, direct CP asymmetries and ratios of branching fractions can still provide excellent sensitivity to new physics (NP), since many theoretical and experimental uncertainties cancel out in these quantities. The direct CP asymmetry is defined aswhere f /f denotes a specific final state from a B -3], also known as the ∆A Kπ puzzle, can be explained by an enhanced color-suppressed tree contribution [4] or NP in the electroweak penguin loop [5]. Other variables sensitive to electroweak penguin contributions are the ratios of partial widths, e.g., [3,[6][7][8] of these ratios are consistent with theory expectations [9][10][11][12], albeit with large errors. The experimental uncertainties, therefore, need to be improved to adequately compare data and SM predictions.In this paper, we report measurements of the branching fractions for B → Kπ, ππ, and KK decays, other than B 0 → π 0 π 0 , and of the direct CP asymmetries for the modes with flavor-specific final states [13]. The measurements are based on 772 × 10 6 BB pairs, corresponding to the final Υ(4S) data set collected with the Belle detector [14] at the KEKB e + e − asymmetricenergy collider [15]. Compared to our previous publications [1,6,16] We define our event selection criteria for these measurements as follows. Charged tracks originating from a B decay are required to have a distance of closest approach with respect to the interaction point less than 4.0 cm along the beam direction (z-axis) and less than 0.3 cm in the transverse plane. Charged kaons and pions are identified with information from particle identification detectors, which are combined to form a K-π likeli-is the likelihood of the track being a ka...
Using surface acoustic wave ͑SAW͒ to drive droplets on a piezoelectric chip is a distinctive microfluidic technique developed recently. In the previous research, uniform interdigital transducers ͑IDTs͒ were used to radiate SAW amplitude and move the droplets within the same delay line simultaneously. In this paper, we employ slanted finger interdigital transducers ͑SFITs͒ to replace uniform IDTs. The merit is that we can move individual droplets at will by varying the frequency. This is because SAW amplitude profile actuated by a SFIT is not uniform along the aperture. The position of the maximum amplitude can be changed by adjusting the input frequency. In addition, we apply the coupling-of-modes model to simulate the amplitude profile and the frequency response of SFITs. Since the transmitted SAW intensity is strongly attenuated by the liquid when SAW hits the droplet, we can use the measured frequency response to detect the position of the droplet and verify the validity of the proposed method; we fabricated a SFIT on an Y128X-LiNbO 3 substrate coated with hydrophobic film. The experimental results show good agreement with those predicted by the simulations. We note that the proposed method can further be used to construct a multichannel microfluidic chip.
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