Vacuum ultraviolet ͑VUV͒ laser photoionization is combined with time-of-flight ͑TOF͒ mass spectrometry to determine the photofragments produced from the laser photodissociation of allene and propyne in a molecular beam. Detection of C 3 H 3 ϩ confirms that atomic hydrogen elimination is the primary process for both of these molecules. A hydrogen molecule elimination channel and a low mass carbon fragmentation channel of allene to produce C 3 H 2 ϩH 2 and CH 2 ϩC 2 H 2 , respectively, have also been identified. Different ratios of various dissociation channels from these two molecules suggest that the dissociation mechanisms of these two isomers are different. Dissociation must occur before complete isomerization. These results are discussed in terms of recent theoretical calculations on the ground and excited states of these molecules. Secondary photodissociation of the products has been observed, even though the laser energies that have been used are less than 8 mJ/cm 2 and the photolysis laser is not focused. Therefore, the present results show how important it is to determine product distributions as a function of the laser energy.

Cognitive radio networks (CRNs) have emerged as a critical technique to solve spectrum shortage problem and enhance the utilization of licensed channels. To prevent from interfering with the co-locate incumbent networks, before data transmission, nodes in CRNs should rendezvous on an available channel (i.e., idle licensed channel) for establishing a link or exchanging control information. However, implementing rendezvous is challenging because the availability of channels is time-varying and position-varying. For reducing rendezvous failure and increasing throughput, a node pair in CRN should be able to rendezvous on every licensed channels (i.e., maximizing rendezvous diversity) and rendezvous on an available channel as soon as possible (i.e., minimizing maximum conditional time to rendezvous (MCTTR)). Besides, in order to take full advantage of the frequency diversity of multi-channel medium access, rendezvous should be spread out in time and channel (i.e., minimizing channel loading). In this paper, we proposed two rendezvous channel hopping algorithms, T-CH and D-CH, which can be used without time synchronization and role preassignment (each node has a pre-assigned role as either a sender or a receiver). D-CH requires that SUs in CRNs should have unique ID (identifier), while T-CH does not. Both of our T-CH and D-CH have maximum rendezvous diversity and minimum channel loading, and outperform in terms of MCTTR.

A novel microcomputer-based ultrasonic distance measurement system is presented. This study proposes an efficient algorithm which combines both the amplitude modulation (AM) and the phase modulation (PM) of the pulse-echo technique. The proposed system can reduce error caused by inertia delay and amplitude attenuation effect when using the AM and PM envelope square wave form (APESW). The APESW ultrasonic driving wave form causes a phase inversion phenomenon in the relative wave form of the receiver. The phase inversion phenomenon sufficiently identifies the "measurement pulse" in the received wave forms, which can be used for accurate time-of-flight (TOF) measurement. In addition, combining a countertechnique to compute the phase shifts of the last cycle for TOF, the presented system can obtain distance resolution of 0.1% of the wavelength corresponding to the 40 kHz frequency of the ultrasonic wave. The standard uncertainty of the proposed distance measurement system is found to be 0.2 mm at a range of 50-500 mm. The APESW signal generator and phase detector of this measuring system are designed on a complex programmable logic device, which is used to govern the TOF measurement and send the data to a personal computer for distance calibration and examination. The main advantages of this APESW system are high resolution, low cost, narrow bandwidth requirement, and ease of implementation.

Software defined networks (SDN) provide flexibility for developing new network protocols and policies in real networks. The SDN controller translates network policies into specific rules in the flow tables (which are usually implemented using ternary content addressable memory (TCAM)) of each network switch. However, due to the limitation of TCAM (e.g., high power consumption and high heat generation), flow tables cannot scale beyond a few hundred entries. Hence, switches usually reactively cache rules (i.e., installing rules on demand). However, reactively caching rules causes packet delay and large buffers, when cache misses happen. To improve the performance, in this paper, we propose a rule partition and allocation algorithm to distribute rules across network switches. Our algorithm not only is applicable to small TCAM switch scenario, but also guarantees semantically-invariant (i.e., the global action of the network is unchanged).

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