Towards real‐time optimal VP management for ATM nets

We propose a mathematical model for VP configuration to find an optimal logical network topology of a given ATM‐based B‐ISDN. The model is essentially identical to the model proposed earlier by Kim [13] which finds a virtual path configuration in which an optimal trade‐off is achieved among the relevant gains of ATM technology. Unlike Kim’s model, however, our model explicitly considers the VP’s QoS to enhance the practicality and the bandwidth utilization. A difficulty is to find an efficient solution technique as it involves a large‐scale intractable optimization problem. We propose a heuristic algorithm tailored to the computational structure of the model. A computational experiment shows that the algorithm finds good solutions in dramatically reduced computation time compared to the existing algorithm. This suggests the possibility of a real‐time VP management system in which the optimal VP configuration is implemented on‐line with a dynamic routing (e.g., LLR), to maintain the optimality of the current solutions. This revised version was published online in August 2006 with corrections to the Cover Date.     

A call admission and control scheme for quality‐of‐service (QoS) provisioning in next generation wireless networks

We propose a framework for quality‐of‐service (QoS) provisioning for multimedia services in next generation wireless access networks. This framework aims at providing a differentiated treatment to multimedia traffic flows at the link layer, which can be broadly classified as real‐time (or delay‐sensitive) and non‐real‐time (or delay‐tolerant). Various novel schemes are proposed to support the differential treatment and guarantee QoS. These schemes include bandwidth compaction, channel reservation and degradation, with the help of which a call admission and control algorithm is developed. The performance of the proposed framework is captured through analytical modeling and simulation experiments. Analytically, the average carried traffic and the worst case buffer requirements for real‐time and non‐real‐time calls are estimated. Simulation results show up to 21% improvement in the admission probability of real‐time calls and up to 17% improvement in the admission probability of non‐real‐time calls, when various call control techniques like bandwidth compaction are employed. Using our channel reservation technique, we observe a 12% improvement in the call admission probability compared to another scheme proposed in the literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Performance evaluation of the rate‐based flow control mechanism for ABR service

In this paper we investigate the performances of the EFCI‐based (Explicit Forward Congestion Indication) and ER‐based (Explicit Rate) algorithms for the rate‐based flow control of the ABR (Available Bit Rate) traffic in an ATM network. We consider the case of two switches in tandem. We present several definitions of a bottleneck, and provide conditions that determine whether the first, the second or both queues are bottleneck. We show that it is not necessarily the queue with the slowest transmission rate in which congestion actually occurs. We derive analytic formulas for the maximum queue length. We compare our results to those obtained by approximating a network by a simpler one, containing only the bottleneck switch. We show that the maximum queue lengths under the approximating approach may largely underestimate the ones obtained in the real network. This revised version was published online in June 2006 with corrections to the Cover Date.     

A logarithmic lower bound for time‐spread multiple‐access (TSMA) protocols

Time‐Spread Multiple‐Access (TSMA) protocols are scheduled access protocols for mobile multi‐hop radio networks that guarantee deterministic access to the shared channel regardless of the possibility of radio interference. In scheduled access methods, time is considered to be slotted and time slots are cyclically organized into frames. In general, the shorter the frame, the more efficient the protocol. An Ω(log log n) lower bound is known on the minimum length of the frame of TSMA protocols in networks with n nodes. In this note we improve that lower bound by characterizing the multiple access to the radio channel as a combinatorial problem. The proposed characterization allows us to prove that no TSMA protocols can successfully schedule the transmissions of the nodes of a multi‐hop radio network in frames with less than log n time slots. This revised version was published online in August 2006 with corrections to the Cover Date.     

A deadlock model for a multi‐service medium access protocol employing multi‐slot N‐ary stack algorithm (msSTART)

Many modern multi‐service medium access protocols (MACs) use a collision based capacity request signaling channel as part of a hybrid TDMA frame structure. Multi‐slot Stack Random Access Algorithm (msSTART) is proposed for use in IEEE 802.14 hybrid fiber/coaxial network and will be highly relevant for the S‐MAC development of evolving WATM MAC specifications. This paper studies the performance of msSTART as an example of a Q‐ary tree contention resolution algorithm (CRA) in the wireless environment using the novel Basic Deadlock model. We contrast approximate results for msSTART performance obtained by simulation under extreme inter‐station correlation with analytical results for the more popular p‐persistence CRA used in several testbed WATM implementations. Using three signaling channel schemes designed to provide support for increased system stability, to implement priority in the wireless MAC, and maximise efficiency, we provide comparative results for evaluation of msSTART and p‐persistence ALOHA under what the IEEE 802.14 working group has termed the “disaster scenario”. We find that of the three schemes evaluated the full Contention Mini‐Slot (CMS) sharing scheme employing multiple CMSs per data region extends the protocol's useable load region the furthest. We conclude that Q‐ary tree contention resolution algorithms (in particular msSTART) are best adapted to the wireless environment, providing less case sensitive performance. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the role of metal contacts in solar cells based on titanium dioxide and di-(isothiocyanate)-bis-(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II)

Photoelectric cells based on titanium dioxide and di-(isothiocyanate)-bis-(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II) with titanium and gold electrodes are fabricated. An analysis of the dark and light current-voltage characteristics shows that the electrode material affects the main parameters of the solar cells: the open-circuit voltage, short-circuit current, and efficiency.     

ICANN – EU can't: Internet governance and Europe's role in the formation of the Internet Corporation for Assigned Names and Numbers (ICANN)

This paper analyzes the policy process that led to the formation of the Internet Corporation for Assigned Names and Numbers (ICANN), focusing on the actions of the European Commission. The analysis of the relevant documents shows the difference between the regulatory ideas in the US and the EU. The European Commission would have preferred an institutional framework with a prominent role for public actors, but had to accept the preference of the US Government, which directed the institutionalization of a private regime for the management of Internet addresses and names. Nevertheless, the Commission managed to establish itself as a major player in the emerging field of Internet governance.     

On the Thermoelectric Properties of Zintl Compounds Mg3Bi2−x Pn x (Pn = P and Sb)

A series of Zintl compounds Mg₃Bi_2-x Pn _x (Pn = P and Sb) have been synthesized by the solid-state reaction method. While Sb can be substituted to a level as high as x = 1.0, P can be substituted only up to x = 0.5. The thermoelectric potential of these compounds has been evaluated by measuring resistivity (ρ), Seebeck (α) and Hall coefficients, and thermal conductivity between 80 K and 850 K. The measured resistivity and Seebeck coefficient values are consistent with those expected for small-bandgap semiconductors. Hall measurements suggest that the carriers are p type with concentration (p) increasing from ~10¹⁹ cm^?3 to ~10²⁰ cm^?3 as the Bi content is increased. The Hall mobility decreases with increasing temperature (T) and reaches a more or less similar value (~45 cm²/V s) for all substituted compositions at room temperature. Due to mass defect scattering, the lattice thermal conductivity (κ _L) is decreased to a minimum of ~1.2 W/m K in Mg₃BiSb. The power factor (α ²/ρ) is found to be rather low and falls in the range 0.38 mW/m K² to 0.66 mW/m K². As expected, at a high temperature of 825 K, the total thermal conductivity (κ) of Mg₃BiSb reaches an impressive value of ~1.0 W/m K. The highest dimensionless figure of merit (ZT) is realized for Mg₃BiSb and is ~0.4 at 825 K.     

On the Current Dependence of the Injection Efficiency and the Relative Contribution of the Escape Rate and Internal Optical Loss to Saturation of the Power–Current Characteristics of High-Power Pulsed Lasers (λ = 1.06 μm)

Semiconductors - The results of numerical simulation of the current dependence of the efficiency of injection into the active area of a laser based on separate-confinement double heterostructures...     

Molecular Engineering for Shortening the Pt···Pt Distances in Pt(II) Dinuclear Complexes and Enhancing the Efficiencies of these Complexes for Application in Deep-Red and Near-IR OLEDs

Deep-red (DR)-to-near-infrared (NIR) phosphorescent organic light-emitting diodes (OLEDs) have potentials for application in various fields ranging from phototherapy to sensing. Accordingly, herein, phenylpyridazine-based bidentate ligands are synthesized and subsequently utilized for the preparation of dinuclear Pt(II) complexes ( 1 – 6 ). The molecular structures of 1 – 3 is investigated by single-crystal X-ray diffraction, and the results suggest that these complexes have substantially shortened Pt···Pt distances (2.906–2.911 Å). Complexes 1 – 6 exhibit intense emissions in the NIR region (700–726 nm), high photoluminescence quantum yield (PLQY) (0.11–0.18), and short phosphorescence decay lifetimes (τ = 0.64–0.95 µs) in a CH₂Cl₂ solution. To examine the effect of N-substitution on the dinuclear Pt complexes, the phenylpyrimidine-based Pt(II) emitters 7 and 8 are prepared and discovered to have Pt···Pt distances of 2.933 Å. 7 and 8 demonstrate strong emissions in the 628–650 nm range with high PLQY of 0.52–0.65. Theoretical studies indicate that the functional groups or atoms in the ligands play crucial roles in the formation of emitters with significantly shortened Pt···Pt distances. 3 and 7 are employed as non-doped emitters to fabricate NIR OLEDs, and the resulting OLEDs exhibit electroluminescence peaks at 754 and 692 nm with maximum external quantum efficiencies of 3.0 and 4.4%, respectively.     

On the spectra of electrons and holes in an open spherical nanoheterostructure (through the example of GaAs/AlxGa1−x As/GaAs)

The spectra of the quasi-stationary electron and hole states in an open spherical nanoheterostructure are calculated in the effective mass approximation using the S-matrix theory. Numerical calculation is performed through the example of the GaAs/Al_xGa_1?x As/GaAs system. A complete system of electron and hole wave functions is obtained for nanoheterostructures consisting of an arbitrary number of layers. Quasiparticle lifetimes as a function of the GaAs/Al_xGa_1?x As/GaAs nanosystem geometrical parameters and Al content x are calculated.     

Independent operation time of photodetectors of the (3—5)-μm spectral band based on InSb and CdHgTe heteroepitaxial structures

The time of independent operation t _ind of indium antimonide photoresistors and photodiodes and photoresistors based on Cd _х Hg_1–х Te (х ~ 0.3) heterostructures deeply cooled with a Joule–Thomson throttling system is investigated. The largest independent operation time (taut ≥ 28 s) was obtained for Cd _х Hg_1–х Te (х ~ 0.3) photoresistors. Time t _ind of the photoresistors and photodiodes is found to be related to the temperature of transition of the semiconductor materials from the impurity region to the intrinsic region. The possibility of increasing time t _ind of the photodetectors by optimizing the requirements for the characteristics of InSb and Cd _х Hg_1–х Te is discussed.     

Ethylthio-substituted sandwich phthalocyaninato europium (III) semiconductors for sensing NO2 and NH3: Effect of the extended π-conjugate systems on tuning the conductivity and sensing behavior

By using the π-conjugated phthalocyanine macrocycle as the versatile building block, a series of five sandwich-type ethylthio substituted phthalocyaninato europium complexes, namely double-decker Eu[Pc(SC₂H₅)₈]₂ (Pc-1), triple-decker Eu₂[Pc(SC₂H₅)₈]₃ (Pc-2), and their corresponding dimers, [Pc(SC₂H₅)₈]₂Eu₂[BiPc(SC₂H₅)₁₂] (Pc-1@Pc-1), [Pc(SC₂H₅)₈]₃Eu₃[BiPc(SC₂H₅)₁₂] (Pc-1@Pc-2) and [Pc(SC₂H₅)₈]₄Eu₄[BiPc(SC₂H₅)₁₂] (Pc-2@Pc-2), are synthesized and prepared into the solution-processed films by a simple quasi-Langmuir-Shäfer (QLS) method. Combination between the extending π-conjugated system in the longitudinal and transverse directions of Pc macrocycles and/or radical nature of Pc-1 unit among different semiconducting molecules result in unusually small energy gaps (0.345–0.91 eV). Consequently, all of the semiconductors exhibit excellent conductivities. Among these materials, the conductivity for the radical species Pc-1@Pc-1, Pc-1@Pc-2 and Pc-1 is about 3–4 times larger than that for the non-radical compounds Pc-2@Pc-2 and Pc-2. Moreover, the QLS films of five semiconductors take excellent linear responses for both oxidizing NO₂ (100–300 ppb) and reducing NH₃ (4–8.6 ppm). Respectively, the sensitivity (in % ppm⁻¹) gets increased in the order of Pc-1 < Pc-2 < Pc-1@Pc-1 < Pc-1@Pc-2 < Pc-2@Pc-2 for NO₂, and Pc-1@Pc-2 < Pc-1 < Pc-1@Pc-1 < Pc-2@Pc-2 < Pc-2 for NH₃. Depending on the highly extended π-conjugated systems, Pc-2@Pc-2 and Pc-2 films achieve the highest sensitivity of 208.2% ppm⁻¹ and 0.97% ppm⁻¹ to NO₂ and NH₃, respectively. In addition, with a less than 2 min response time within a limit of detection at 10 ppb for NO₂ and 0.48 ppm for NH₃, good reproducibility and selectivity have been revealed for the Pc-2@Pc-2 and Pc-2 films among the best gas sensors obtained so far for all the solution-processed films based on organic semiconductors in dry air at room temperature. More importantly, it is firstly demonstrated that the high NO₂ sensing is resulted from low Oxd₁, and high NH₃ sensing is resulted from high Red₁ among the sandwich Pc-based semiconductors.     

On the preparation and photoelectric properties of Tl1–x In1–x Sn x Se2 (x = 0.1–0.25) alloys

The technological conditions for growing single crystals of Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.     

Simplified procedure for decoding nonsystematic reed-solomon codes over gf(2m) using euclid?s algorithm and the fast fourier transform

Gao?s algorithm similar to Shiozaki?s algorithm for decoding nonsystematic Reed-Solomon (RS) codes which is a subclass of the redundant residue polynomial codes is considered here. This algorithm computes the message polynomial directly without explicitly finding the error-locator polynomial and errorevaluator polynomial. In this letter, a simplified decoding algorithm to correct both errors and erasures is used in conjunction with Gao?s algorithm for efficiently decoding RS codes. In addition, we show that the extended Gao algorithm similar to the Shiozaki-Truong-Cheung-Reed algorithm significantly reduces the decoding complexity.