High performance,low complexity cooperative caching for wireless sensor networks

During the last decade, Wireless Sensor Networks have emerged and matured at such point that they currently support several applications such as environment control, intelligent buildings, target tracking in battlefields. The vast majority of these applications require an optimization to the communication among the sensors so as to serve data in short latency and with minimal energy consumption. Cooperative data caching has been proposed as an effective and efficient technique to achieve these goals concurrently. The essence of these protocols is the selection of the sensor nodes which will take special roles in running the caching and request forwarding decisions. This article introduces two new metrics to aid in the selection of such nodes. Based on these metrics, we propose two new cooperative caching protocols, PCICC and scaPCICC, which are compared against the state-of-the-art competing protocol, namely NICoCa. The proposed solutions are evaluated extensively in an advanced simulation environment and the results confirm that the proposed caching mechanisms prevail over its competitor. The evaluation attests also that the best policy is always scaPCICC, achieving the shortest latency and the least number of transmitted messages.     

Time‐of‐Flight Studies of Electron‐Collection Kinetics in Polymer:Fullerene Bulk‐Heterojunction Solar Cells

The charge‐collection dynamics in poly(3‐hexylthiophene:[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (P3HT:PCBM) bulk heterojunctions are studied in thick (>1 μm) devices using time‐of‐flight measurements and external quantum‐efficiency measurements. The devices show Schottky‐diode behavior with a large field‐free region in the device. Consequently, electron transport occurs by diffusion in the bulk of the active layer. At high applied biases where the depletion region spans the entire active layer, normal time‐of‐flight transients are observed from which the electron mobility can be determined. Here, the electron mobility follows Poole–Frenkel behavior as a function of field. At lower applied biases, where the depletion region only spans a small portion of the active layer, due to a high density of dark holes, the recombination kinetics follow a first‐order rate law with a rate constant about two orders of magnitude lower than that predicted by Langevin recombination.     

Carbon-nanofiber-based nanocomposite membrane as a highly stable solid-state junction for reference electrodes

There is currently a need for a reliable solid-state reference electrode, especially in applications such as autonomous sensing or long-term environmental monitoring. We present here for the first time a novel solid-state nanofiber junction reference electrode (NFJRE) incorporating a junction consisting of poly(methyl methacrylate) and carbon graphene stacked nanofibers. The NFJRE operates by using the membrane polymer junction, which has a very high glass transition temperature (T(g)) and small diffusion coefficient, to control the diffusion of ions, and the carbon nanofibers lower the junction resistance and act as ion-to-electron transducers. The fabrication of the NFJRE is detailed, and its behavior is characterized in terms of its impedance, stability, and behavior in comparison with traditional reference electrodes. The NFJRE showed a response of <5-13 mV toward a variety of electrolyte solutions from 10(-5) to 10(-2) M, <10 mV over a pH range of 2-12, and excellent behavior when used with voltammetric methods.     

Understanding Local and Macroscopic Electron Mobilities in the Fullerene Network of Conjugated Polymer‐based Solar Cells: Time‐Resolved Microwave Conductivity and Theory

The efficiency of bulk heterojunction (BHJ) organic photovoltaics is sensitive to the morphology of the fullerene network that transports electrons through the device. This sensitivity makes it difficult to distinguish the contrasting roles of local electron mobility (how easily electrons can transfer between neighboring fullerene molecules) and macroscopic electron mobility (how well‐connected is the fullerene network on device length scales) in solar cell performance. In this work, a combination of density functional theory (DFT) calculations, flash‐photolysis time‐resolved microwave conductivity (TRMC) experiments, and space‐charge‐limit current (SCLC) mobility estimates are used to examine the roles of local and macroscopic electron mobility in conjugated polymer/fullerene BHJ photovoltaics. The local mobility of different pentaaryl fullerene derivatives (so‐called ‘shuttlecock’ molecules) is similar, so that differences in solar cell efficiency and SCLC mobilities result directly from the different propensities of these molecules to self‐assemble on macroscopic length scales. These experiments and calculations also demonstrate that the local mobility of phenyl‐C₆₀ butyl methyl ester (PCBM) is an order of magnitude higher than that of other fullerene derivatives, explaining why PCBM has been the acceptor of choice for conjugated polymer BHJ devices even though it does not form an optimal macroscopic network. The DFT calculations indicate that PCBM's superior local mobility comes from the near‐spherical nature of its molecular orbitals, which allow strong electronic coupling between adjacent molecules. In combination, DFT and TRMC techniques provide a tool for screening new fullerene derivatives for good local mobility when designing new molecules that can improve on the macroscopic electron mobility offered by PCBM.     

Multi-parameter performance analysis for decentralized cognitive radio networks

In this paper, we investigate the impact of primary user activity, secondary user activity, interface switching, channel fading and finite-length queuing on the performance of decentralized cognitive radio networks. The individual processes of these service-disruptive effects are modeled as Markov chains based on cross-layer information locally available at the network nodes. A queuing analysis is conducted and various performance measures are derived regarding the packet loss, throughput, spectral efficiency, and packet delay distribution. Numerical results demonstrate the impact of various system parameters on the system performance, providing insights for cross-layer design and autonomous decision making in decentralized cognitive radio networks.     

Application of the Extended Langmuir Model for the Determination of Lyophobicity of 1-Propanol in Acetonitrile

Surface tensions (σ) of binary liquid mixtures of acetonitrile (ACN) with 1-propanol (PrOH) were measured over the entire composition range at eight different temperatures, 278.15 K, 283.15 K, 288.15 K, 293.15 K, 298.15 K, 303.15 K, 308.15 K, and 313.15 K. The lyophobicities (β) of the surfactant PrOH relative to that of ACN as well as the surface mole fractions () of PrOH at various temperatures were derived using the extended Langmuir model (Langmuir 17, 4261, 2001). The β values indicate the greater affinity of PrOH for the surface, and this trend slightly increases with rising temperature. The determined values indicate that the surface concentration of PrOH is always higher than its bulk concentration and consequently confirm that the surface is enriched with PrOH.     

Evaluation of registration methods on thoracic CT: the EMPIRE10 challenge

EMPIRE10 (Evaluation of Methods for Pulmonary Image REgistration 2010) is a public platform for fair and meaningful comparison of registration algorithms which are applied to a database of intrapatient thoracic CT image pairs. Evaluation of nonrigid registration techniques is a nontrivial task. This is compounded by the fact that researchers typically test only on their own data, which varies widely. For this reason, reliable assessment and comparison of different registration algorithms has been virtually impossible in the past. In this work we present the results of the launch phase of EMPIRE10, which comprised the comprehensive evaluation and comparison of 20 individual algorithms from leading academic and industrial research groups. All algorithms are applied to the same set of 30 thoracic CT pairs. Algorithm settings and parameters are chosen by researchers expert in the configuration of their own method and the evaluation is independent, using the same criteria for all participants. All results are published on the EMPIRE10 website (http://empire10.isi.uu.nl). The challenge remains ongoing and open to new participants. Full results from 24 algorithms have been published at the time of writing. This paper details the organization of the challenge, the data and evaluation methods and the outcome of the initial launch with 20 algorithms. The gain in knowledge and future work are discussed.     

Studies on parametric sensitivity and safe operation criteria of batch processes

Heat accumulation in batch reactors may eventually lead to a temperature runaway. Critical values of process parameters were used to investigate process safety. Parameter sensitivity is discussed for a wide range of operating conditions. Two criteria for safe operation are presented, based on critical values of process parameters.     

A Convergence-Free Predistortion Technique for Adaptive Linearisation of RF Power Amplifiers

Adaptive digital baseband predistortion is a well-known linearisation technique for removing intermodulation products that radio frequency power amplifiers (PAs) introduce. This paper proposes a new baseband predistortion method that is based on a non-iterative, fast adaptation algorithm without convergence restrictions. The response of the PA in a batch of training magnitude stimuli is used for the computation of the predistortion gain. The latter is directly extracted in rectangular form without prior transformations and AM/AM and AM/PM non-linearities sequential estimation. The influence of the gain table size and the imperfections of the modulator and demodulator in the method's performance are examined. Experimental measurements of an in-house prototype show a linearity improvement of about 25 dB.