DRED‐MP: Queue management with multiple levels of drop precedence

There is current interest in differentiated service architectures where packets with different priorities can share the same queue. In the case of congestion, packets marked with higher drop probability are preferentially dropped in order to make buffer room for packets marked with lower drop probability. Active queue management (AQM) based on randomized packet dropping has become a key component of this packet forwarding model. This paper extends our previously developed AQM algorithm called DRED with multiple packet drop precedence to allow for priority treatment of traffic in a network. The main advantage of using the DRED algorithm is the lower parameter configuration complexity it offers and the ease of configuration for a wide range of network conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Self‐consistent electrical parameter extraction from bias dependent spectral response measurements of III‐V multi‐junction solar cells

Spectral response of multi‐junction solar cell is complicated because of the interplay between external measurement conditions such as bias light intensity, monochromatic light intensity, bias voltage, and intrinsic electrical properties of series interconnected subcells. In this paper, we report an experimental study on the bias voltage‐dependent spectral response (SR) for multi‐junction solar cell. A self‐consistent iteration loop was developed from a nonlinear least square Powell hybrid algorithm that was used for curve fitting the experimental SR versus bias voltage data of each subcell. We demonstrated for the first time that this approach enabled us to derive the electrical parameters such as dark saturation currents (J₀), shunt resistance (R_sh), series resistance (R_s), and spectra response (J_photo) for each subcell of a Ga_0.99In_0.01As/Ge dual junction solar cell with stable convergence. The accuracies of the fitting results were confirmed by the agreement between the J–V curves calculated on the basis of these parameters and the experimental J–V curve of multi‐junction solar cell measured under AM1.5 and 1 sun condition. Copyright © 2013 John Wiley & Sons, Ltd.     

Profiles of Work Function Shifts and Collective Charge Transfer in Submonolayer Metal–Organic Films

Vacuum level shifts Δ(d) at metal–organic (m–O) interfaces indicate the formation of surface dipoles for film thickness d ≤ d_ML up to a monolayer (ML). Shifts or profiles Δ(θ) of submonolayer films are nonlinear in the coverage θ = d/d_ML ≤ 1, which points to cooperative interactions between adsorbed molecules. Adsorption with weak nonspecific bonding is modeled as charge transfer (CT) between molecules M and localized surface states S of the metal. The dipole μ₀ of ions S^?M⁺ or S⁺M^? gives upper bounds for the vacuum level shift ? ₀ and dipole–dipole repulsion V₀ at θ = 1. Partial CT ρ(θ) < 1 is found self consistently and accounts for published profiles Δ(θ) of representative planar and nonplanar molecules with d_ML～ 4 and ～10 Å. Initial adsorption at θ ～ 0 has considerable ionic character, ρ(0) ～ 1/2, that decreases to ρ(1) ～ 1/10 at θ = 1. Planar molecules with small μ₀ and V₀ have slightly nonlinear profiles while molecules with large μ₀ and V₀ have highly nonlinear Δ(θ). Collective CT is a phenomenological model for m–O interfaces with nonspecific bonding. The CT model is contrasted to fixed dipoles on the surface, to calculations of Δ(1) and to simulations of sub‐ML films.     

Sensitive and Ultrabroadband Phototransistor Based on Two‐Dimensional Bi2O2Se Nanosheets

Bi₂O₂Se, a high‐mobility and air‐stable 2D material, has attracted substantial attention for application in integrated logic electronics and optoelectronics. However, achieving an overall high performance over a wide spectral range for Bi₂O₂Se‐based devices remains a challenge. A broadband phototransistor with high photoresponsivity (R) is reported that comprises high‐quality large‐area ( ≈ 180 µm) Bi₂O₂Se nanosheets synthesized via a modified chemical vapor deposition method with a face‐down configuration. The device covers the ultraviolet (UV), visible (Vis), and near‐infrared (NIR) wavelength ranges (360–1800 nm) at room temperature, exhibiting a maximum R of 108 696 A W^?1 at 360 nm. Upon illumination at 405 nm, the external quantum efficiency, R, and detectivity (D*) of the device reach up to 1.5 × 10⁷%, 50055 A W^?1, and 8.2 × 10¹² Jones, respectively, which is attributable to a combination of the photogating, photovoltaic, and photothermal effects. The devices reach a ?3 dB bandwidth of 5.4 kHz, accounting for a fast rise time (τ_rise) of 32 µs. The high sensitivity, fast response time, and environmental stability achieved simultaneously in these 2D Bi₂O₂Se phototransistors are promising for high‐quality UV and IR imaging applications.     

Effect of carbon containing SiNx antireflection coating on the screen‐printed contact and low illumination performance of silicon solar cell

Screen‐printed metal contact formation through a carbon containing antireflection coating was investigated for silicon solar cells by fabricating conventional carbon‐free SiN_x and carbon‐rich SiC_xN_y film. An appreciable difference was found in the average shunt resistance (R_sh), which was about an order of magnitude higher for SiC_xN_y‐coated solar cells relative to the counterpart SiN_x‐coated solar cells. Series resistance (R_s) and fill factor (FF) were comparable for both antireflection coatings but the starting efficiency of SiC_xN_y‐coated cell was ~0·2% lower because of slightly inferior surface passivation. However, SiC_xN_y‐coated solar cells showed less degradation under lower illumination (<1000 W/m²) compared with the SiN_x‐coated cells due to reduced FF degradation under low illumination. Theoretical calculations in this paper support that this is a direct result of high R_sh. Detailed photovoltaic system and cost modeling is performed to quantify the enhanced energy production and the reduced levelized cost of electricity due to higher shunt resistance of the SiC_xN_y‐coated cells. It is shown that R_sh value below 30 Ω (7000 Ω cm² for 239 cm² cell) can lead to appreciable loss in energy production in regions of low solar insolation. Copyright © 2011 John Wiley & Sons, Ltd.     

Time division inter‐satellite link topology generation problem: Modeling and solution

In this paper, we study the time‐division inter‐satellite link topology generation (TDILTG) problem for the well‐known Chinese BeiDou Global Navigation Satellite System. The TDILTG problem consists in generating a time‐division topology of the inter‐satellite link network for the navigation satellite system to spread systematic data to all satellites via a few source satellites with the purpose of minimizing the time required to spread the data. We propose a mathematical model to formulate the TDILTG problem and study its 2 lower bounds through a thorough analysis of the problem characteristics. We also present a deterministic constructive (DC) algorithm to solve this problem approximately but very quickly, with a time complexity of O(n³), where n is the number of satellites. Extensive experimental studies on a wide range of randomly generated instances show that the proposed DC algorithm is able to obtain the optimal solutions for most tested instances in less than 1 second. Meanwhile, we also validate that the DC algorithm performs well when the problem scale is large. Furthermore, we provide insights of the effects of different instance parameters on the final results.     

Porous Cu(I) Triazolate Framework and Derived Hybrid Membrane with Exceptionally High Sensing Efficiency for Gaseous Oxygen

Phosphorescent complexes of precious metal ions are widely studied as optical sensing materials for molecular oxygen. Combining the advantages of luminescent complexes and porous matrixes, porous coordination polymers show great potential for oxygen‐sensing, although their sensitivity, requirement of precious metal, and device fabrication remain challenging issues. In this work, the photoluminescence and oxygen‐sensing properties of the porous Cu(I) triazolate framework [Cu(detz)] (MAF‐2, Hdetz = 3,5‐diethyl‐1,2,4‐trizole) is studied in detail, which shows high chemical stability in moisture and water, very long phosphorescent lifetime (116 μs) and large Stokes shift (14 562 cm^?1), as well as considerable oxygen permeability (1.7 × 10^?11 mol cm^?1 s^?1 bar^?1) at ambient conditions, giving rise to exceptionally high luminescence quenching efficiency of 99.7% at 1 bar O₂ (I ₀/I ₁₀₀ = 356) with a perfectly linear Stern‐Volmer plot (K _SV = 356 bar^?1, R ² = 0.9998), fast response and good reversibility. Further, a counter‐diffusion crystal‐growth method was developed to fabricate MAF‐2 thin films protected by silicone rubbers as the first example of soft membrane oxygen sensor based on coordination polymer or metal‐organic framework, which exhibited extraordinary oxygen‐sensing performance (limit of detection = 0.047 mbar) and outstanding mechanical property, as well as outstanding chemical stability even in an acidic atmosphere.     

Channel estimation algorithms for cooperative spectrum sensing in amplify‐and‐forward cooperative system

In amplify‐and‐forward (AF)‐based cooperative spectrum sensing system, the bit‐error‐rate (BER) performance and detection probability will decrease because of the existence of channel estimation error. In this paper, the influence of channel estimation error on system performance is firstly deduced, and then, linear minimum mean‐square error (LMMSE) channel estimation algorithm with filtering delay time‐domain windowing (LMMSE‐filtering‐DTW) technique and modified singular value decomposition‐based LMMSE algorithm are proposed to improve the channel estimation performance for code division multiple access system and orthogonal frequency division multiplexing system in AF cooperative scenario, respectively. Simulation results verify the effectiveness of the two proposed channel estimation algorithms in cooperative spectrum sensing, and when E_b/ N₀ is bigger than 20 dB, given the required false alarm probability smaller than 15%, the difference of detection probability between the channel obtained using the proposed channel estimation algorithms and the ideal channel is less than 2.5%, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficiency Enhancement in Organic Photovoltaic Cells: Consequences of Optimizing Series Resistance

Here, means to enhance power conversion efficiency (PCE or η) in bulk‐heterojunction (BHJ) organic photovoltaic (OPV) cells by optimizing the series resistance (R_s)—also known as the cell internal resistance—are studied. It is shown that current state‐of‐the‐art BHJ OPVs are approaching the limit for which efficiency can be improved via R_s reduction alone. This evaluation addresses OPVs based on a poly(3‐hexylthiophene):6,6‐phenyl C₆₁‐butyric acid methyl ester (P3HT:PCBM) active layer, as well as future high‐efficiency OPVs (η > 10%). A diode‐based modeling approach is used to assess changes in R_s. Given that typical published P3HT:PCBM test cells have relatively small areas (～0.1 cm²), the analysis is extended to consider efficiency losses for larger area cells and shows that the transparent anode conductivity is then the dominant materials parameter affecting R_s efficiency losses. A model is developed that uses cell sizes and anode conductivities to predict current–voltage response as a function of resistive losses. The results show that the losses due to R_s remain minimal until relatively large cell areas (>0.1 cm²) are employed. Finally, R_s effects on a projected high‐efficiency OPV scenario are assessed, based on the goal of cell efficiencies >10%. Here, R_s optimization effects remain modest; however, there are now more pronounced losses due to cell size, and it is shown how these losses can be mitigated by using higher conductivity anodes.     

Adaptive Variable Structure Control for Uncertain Switched Delay Systems

This paper investigates the robust H _∞ control problem for a class of uncertain switched delay systems with parameter uncertainties, unknown nonlinear perturbations, and external disturbance. Based on the multiple Lyapunov functions method, a sufficient condition for the solvability of the robust H _∞ control problem is derived by employing a hysteresis switching law and variable structure controllers. When the upper bounds of the nonlinear perturbations are unknown, an adaptive variable structure control strategy is developed. The use of the adaptive technique is to adapt the unknown upper bounds of the nonlinear disturbances so that the objective of asymptotic stabilization with an H _∞-norm bound is achieved under the hysteresis switching law. A numerical example illustrates the effectiveness of the proposed design methods.     

Non-linear analysis of an S-I-S Josephson junction

The simplest model of an S-I-S Josephson junction is analysed by simulation in order to understand its switching behaviour. This model is assumed to have a parallel quasi-particle tunnelling current component, which is non.linear and ideal in the BCS sense. Fundamental properties, such as I _min and V _min, which specify hysteretic behaviour, as well as rise and fall times for switching, are calculated as functions of parameters β_c = 2ΠI _m0 R _n ² C/Φ₀ and γ = R _L R _n. How an AC Josephson current spoils the stability of a non-zero voltage state is discussed for the first time.     

Adaptive fuzzy sliding mode active queue management algorithms

Active queue management (AQM) is aimed at achieving the tradeoff between link utilization and queuing delay to enhance TCP congestion control and is expected to perform well for a wider-range of network conditions. Static AQM schemes despite their simplicity, often suffer from long response time due to conservative parameter setting to ensure stability. Adaptive parameter settings, which might solve this problem, remain difficult from implementation point of view. In this paper, we propose an adaptive fuzzy sliding mode (AFSM) AQM algorithm to achieve fast response and yet good robustness. The AFSM algorithm uses the queue length and its differential as the input of AQM and adjusts fuzzy rules by the measurement of packet loss ratio dynamically. The stability analysis under heterogeneous round trip times provides guidelines for parameter settings in AFSM and guarantees that the stability of AFSM is independent of the active TCP flows. This merit as well as other performances is examined under various network environments. Compared to some typical AQMs, the AFSM algorithm trades off the throughput with queuing delay better and achieves a higher per-flow throughput. Finally, AFSM can be executed at a scale of seconds with the least fuzzy rules.     

Performance of optimum and suboptimum OFDM‐CPM receivers over multipath fading channels

A class of orthogonal frequency division multiplexing‐continuous phase modulation (OFDM‐CPM) signals is introduced in which binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. Canonical optimum and suboptimum multiple‐symbol‐observation OFDM‐CPM receivers are derived. Multipath channel with AWGN is assumed. The receivers are analyzed for bit error rate (BER) performance in terms of high‐ and low‐SNR bounds. These bounds are illustrated as a function of parameter h, time delay and attenuation level. It is shown that OFDM‐CPM systems, with h=0.5,0.25 and an observation interval length of two symbols, can outperform conventional OFDM‐PSK system for a two‐ray multipath model. Copyright © 2005 John Wiley & Sons, Ltd.     

Ultrahigh Stability 3D TI Bi2Se3/MoO3 Thin Film Heterojunction Infrared Photodetector at Optical Communication Waveband

Infrared (IR) detection at 1300–1650 nm (optical communication waveband) is of great significance due to its wide range of applications in commerce and military. Three dimensional (3D) topological insulator (TI) Bi₂Se₃ is considered a promising candidate toward high‐performance IR applications. Nevertheless, the IR devices based on Bi₂Se₃ thin films are rarely reported. Here, a 3D TI Bi₂Se₃/MoO₃ thin film heterojunction photodetector is shown that possesses ultrahigh responsivity (R_i), external quantum efficiency (EQE), and detectivity (D*) in the broadband spectrum (405–1550 nm). The highest on–off ratio of the optimized device can reach up to 5.32 × 10⁴. R_i, D*, and the EQE can reach 1.6 × 10⁴ A W^?1, 5.79 × 10¹¹ cm² Hz^1/2 W^?1, and 4.9 × 10⁴% (@ 405 nm), respectively. Surprisingly, the R_i can achieve 2.61 × 10³ A W^?1 at an optical communication wavelength (@ 1310 nm) with a fast response time (63 µs), which is two orders of magnitude faster than that of other TIs‐based devices. In addition, the device demonstrates brilliant long‐term (>100 days) environmental stability under environmental conditions without any protective measures. Excellent device photoelectric properties illustrate that the 3D TI/inorganic heterojunction is an appropriate way for manufacturing high‐performance photodetectors in the optical communication, military, and imaging fields.     

A compensated PID active queue management controller using an improved queue dynamic model

Beside the major objective of providing congestion control, achieving predictable queuing delay, maximizing link utilization, and robustness are the main objectives of an active queue management (AQM) controller. This paper proposes an improved queue dynamic model while incorporating the packet drop probability as well. By applying the improved model, a new compensated PID AQM controller is developed for Transmission Control Protocol/Internet Protocol (TCP/IP) networks. The non‐minimum phase characteristic caused by Padé approximation of the network delay restricts the direct application of control methods because of the unstable internal dynamics. In this paper, a parameter‐varying dynamic compensator, which operates on tracking error and internal dynamics, is proposed to not only capture the unstable internal dynamics but also reduce the effect of uncertainties by unresponsive flows. The proposed dynamic compensator is then used to design a PID AQM controller whose gains are obtained directly from the state‐space representation of the system with no further gain tuning requirements. The packet‐level simulations using network simulator (ns2) show the outperformance of the developed controller for both queuing delay stability and resource utilization. The improved underlying model leads also to the faster response of the controller. Copyright © 2013 John Wiley & Sons, Ltd.     

3D Graphene Films Enable Simultaneously High Sensitivity and Large Stretchability for Strain Sensors

Integration of 2D membranes into 3D macroscopic structures is essential to overcome the intrinsically low stretchability of graphene for the applications in flexible and wearable electronics. Herein, the synthesis of 3D graphene films (3D‐GFs) using chemical vapor deposition (CVD) is reported, in which a porous copper foil (PCF) is chosen as a template in the atmospheric‐pressure CVD preparation. When the 3D‐GF prepared at 1000 °C (noted as 3D‐GF‐1000) is transferred onto a polydimethylsiloxane (PDMS) membrane, the obtained 3D‐GF‐1000/PDMS hybrid film shows an electrical conductivity of 11.6 S cm^?1 with good flexibility, indicated by small relative resistance changes (ΔR/R₀) of 2.67 and 0.36 under a tensile strain of 50% and a bending radius of 1.6 mm, respectively. When the CVD temperature is reduced to 900 °C (generating a sample noted as 3D‐GF‐900), the 3D‐GF‐900/PDMS hybrid film exhibits an excellent strain‐sensing performance with a workable strain range of up to 187% and simultaneously a gauge factor of up to ≈1500. The 3D‐GF‐900/PDMS also shows a remarkable durability in resistance in repeated 5000 stretching‐releasing cycles. Kinetics studies show that the response of ΔR/R₀ upon strain is related to the graphitization and conductivity of 3D‐GF which are sensitive to the CVD preparation temperature.     

Narrowband M-ary DPSK-DPD with L-diversity maximum ratio combining in Rician fading channels

In this paper the bit error probability (BEP) of narrowband M-ary differential phase shift keying with differential phase detection (MDPSK-DPD) and maximum ratio combining (MRC) in Rician fading channels is computed. Two systems shall be investigated. In the first system the transmitted pulse is a Nyquist pulse with bandwidth B = R(1 + β), where R is the symbol rate and 0 ≤ β ≤ 1 is the roll-off and the receiver is matched to the transmitter. In the second system the shaping pulse is a rectangle of duration T = 1/R modified by narrowband Butterworth filters in the transmitter and receiver. The fading channel is both time selective with Doppler frequency shifts of f_DT = 0, 0·01, 0·02 and frequency selective with time delays of t_d/T = 0, 0·1, 0·2. The number of diversity channels is L = 1, 2, 3 and the Rician factor is K = 0, 1, 6 dB, 10, ∞, thus the whole range between Rayleigh and Gaussian channels is covered. © 1997 John Wiley & Sons, Ltd.     

FQL‐RED: an adaptive scalable schema for active queue management

In a potentially congested network, random early detection (RED) active queue management (AQM) proved effective in improving throughput and average queuing delay. The main disadvantage of RED is its sensitive parameters that are impossible to estimate perfectly and adjust manually because of the dynamic nature of the network. For this reason, RED performs differently during different phases of a scenario and there is no guarantee that it will have optimal performance. Giving adaptability to RED has been the subject of broad research studies ever since RED was proposed. After a substantial study of AQM schemes and presenting a novel categorization for so‐called modern approaches utilizing artificial intelligence tools to improve AQM, this paper proposes an algorithm enhancing RED as an add‐on patch that makes minimal changes to the original RED. Being built on the basis of AQM schemes like ARED and Fuzzy‐RED, this algorithm inherits adaptability and is able to adjust RED inaccurate parameters regarding network traffic status, trying to optimize throughput and average queuing delay in a scenario. This algorithm is a Q‐learning method enhanced with a fuzzy inference system to provide RED with self‐adaptation and improved performance as a result. Given the name of FQL‐RED, this algorithm outperformed RED, ARED, and Fuzzy‐RED, as the OPNET simulations show. Copyright © 2010 John Wiley & Sons, Ltd.     

Robust H ∞ Output Tracking Control for a Class of Nonlinear Systems with Time-Varying Delays

This paper addresses the H _∞ output tracking problem for a class of nonlinear systems subjected to model uncertainties and with interval time-varying delay. The stability of the nonlinear time-delay system is analyzed with a novel delay-interval-dependent Lyapunov–Krasovskii functional. Compared to state-of-the-art criteria for linear and nonlinear time-delay systems, less conservative stability conditions are derived with the introduction of new delay-interval-dependent terms and the exploitation of the delay subintervals size. The proposed analysis considers that the delay derivative is either upper and lower bounded, bounded above only, or unbounded, i.e., no restrictions are cast upon the derivative. Numerical examples are provided to enlighten the importance and advantages of the present criterion which outperforms previous criteria in time-delay systems literature. Also, an additional example is provided to highlight the effectiveness of the proposed H _∞ output tracking control design technique for complex nonlinear systems with time-varying delay.     

New Organic Nonlinear Optical Polyene Crystals and Their Unusual Phase Transitions

A series of new nonlinear optical chromophores based on configurationally locked polyenes (CLPs) with chiral pyrrolidine donors are synthesized. All CLP derivatives exhibit high thermal stability with decomposition temperatures T_d at least > 270 °C. Acentric single crystals of enantiopure D ‐ and L ‐prolinol‐based chromophores with a monoclinic space group P2₁ exhibit a macroscopic second‐order nonlinearity that is twice as large than that of analogous dimethylamino‐based crystal. This is attributed to a strong hydrogen‐bonded polar polymer‐like chain built by these molecules, which is aligned along the polar crystallographic b‐axis. Five α‐phase CLP crystals with different donors grown from solution exhibit a reversible or irreversible thermally induced structural phase transition to a β‐phase. These phase transitions are unusual, changing the crystal symmetry from higher to lower at increasing temperatures, for example, from centrosymmetric to non‐centrosymmetric, enhancing their macroscopic second‐order nonlinear optical properties.