A Switching Circulator: S-Band; Stripline; Remanent; 15 kilowatts; I0 microseconds; Temperature-Stable

A stripline, three-port remanence circulator switch has been designed for high-speed switching of time delay in a phased array RADAR at S-band (2.9 GHz). Special attention was devoted to minimizing switching time and energy through design of the magnetic circuit and suppression of eddy currents. Temperature stabilization of insertion phase was accomplished by means of a flux regulating magnetic circuit. Switching performance: time: less than 10 micro-seconds; energy: 450 microjoules. Circulator performance: bandwidth for >26 dB isolation, 8.9 percent; insertion loss, 0.35 dB. Temperature stability of insertion phase: one electrical degree per 10/spl deg/C. Peak RF power: 15 kW. The discussion includes details of the junction design and performance, techniques of eddy current suppression, temperature stabilization, and the method of switching energy measurements.     

The conductivity and Hall effect in CdF<Subscript>2</Subscript>:In and CdF<Subscript>2</Subscript>:Y

Temperature dependences of the static conductivity σ and Hall coefficient R_H in CdF₂ crystals doped with bistable indium and donor yttrium impurities have been measured. It is shown that this material contains different types of free carriers, i.e., electrons and polarons. A comparison of the calculated temperature dependences of σ and R_H with the experimental data also shows that the impurity-band conductivity makes a significant contribution (due to hops of bound polarons or holes) to σ and R_H.     

“Infobahns” in Asia: promises and perils

Experts tout the “infobahn” or “information superhighway” as a necessary catalyst for development in the emerging economic order, in which information is a prime commodity and the market is a global village. Many Asian economies, having experienced a decade or more of high growth, are poised to match or surpass OECD countries in the development of information and communications technologies. The national infobahn efforts being undertaken in a representative sample of Asian countries demonstrate the possibilities for truly global standardization and interconnection of a wide range of services and applications. Paradoxically, standardization and interconnection are preconditions for global multimedia telecommunications services. A typical infobahn architecture includes the physical network, middleware (protocols, APIs and user interfaces), and user applications (for information transfer and/or interchange), all within the legal and policy framework of a regulatory body. Key players usually include the network operators, service developers or providers, content owners, regulators and end users. This report examines the twin issues of the state of the infrastructure (technology) and possible services (applications), or, alternatively, the activities of the leading network operators and service providers. These criteria serve as the basis for comparisons within the region and with two OECD economies in the Asia Pacific region, Japan and Australia     

The MIMO ARQ Channel: Diversity&#8211;Multiplexing&#8211;Delay Tradeoff

In this paper, the fundamental performance tradeoff of the delay-limited multiple-input multiple-output (MIMO) automatic retransmission request (ARQ) channel is explored. In particular, we extend the diversity-multiplexing tradeoff investigated by Zheng and Tse in standard delay-limited MIMO channels with coherent detection to the ARQ scenario. We establish the three-dimensional tradeoff between reliability (i.e., diversity), throughput (i.e., multiplexing gain), and delay (i.e., maximum number of retransmissions). This tradeoff quantifies the ARQ diversity gain obtained by leveraging the retransmission delay to enhance the reliability for a given multiplexing gain. Interestingly, ARQ diversity appears even in long-term static channels where all the retransmissions take place in the same channel state. Furthermore, by relaxing the input power constraint allowing variable power levels in different retransmissions, we show that power control can be used to dramatically increase the diversity advantage. Our analysis reveals some important insights on the benefits of ARQ in slow-fading MIMO channels. In particular, we show that 1) allowing for a sufficiently large retransmission delay results in an almost flat diversity-multiplexing tradeoff, and hence, renders operating at high multiplexing gain more advantageous; 2) MIMO ARQ channels quickly approach the ergodic limit when power control is employed. Finally, we complement our information-theoretic analysis with an incremental redundancy lattice space-time (IR-LAST) coding scheme which is shown, through a random coding argument, to achieve the optimal tradeoff(s). An integral component of the optimal IR-LAST coding scheme is a list decoder, based on the minimum mean-square error (MMSE) lattice decoding principle, for joint error detection and correction. Throughout the paper, our theoretical claims are validated by numerical results     

Holographic optical switching: the “ROSES” demonstrator

The design, assembly, and performance of a prototype 1×8 free-space switch demonstrator using reconfigurable holograms are reported. Central to the switch fabric is a ferroelectric liquid crystal (FLC) on silicon spatial light modulator (SLM) deposited with a 540×1 array of highly reflective and planar mirror strips. The input and output ports of the switch are fabricated as a linear array of silica planar waveguides connected to single-mode fibers, and the holographic beam-steerer operates without the need for adjustment or dynamic alignment. The waveguide array and the single Fourier transform lens for the 2f holographic replay system are housed in an opto-mechanical mount to provide stability. The switch operates at 1.55 μm wavelength and has a designed optical bandwidth of >60 nm. The first measured insertion loss and crosstalk figures are 16.9 dB and -19.1 dB, respectively. Improvements in SLM performance, the use of new addressing schemes and the introduction of better alignment techniques are expected to improve these figures considerably. The preliminary performance of a 3×3 optical crossconnect is also presented to show that this technology is scalable to N×N switching fabrics     

Changeover Improvement: Reinterpreting Shingo's “SMED” Methodology

A rapid changeover capability is widely acknowledged as an essential prerequisite to flexible, responsive small batch manufacturing. Its importance in mass customization is recognized, where minimal losses need to be incurred as manufacture switches between differing products. Retrospective improvement of existing changeover practice is often undertaken, arising from pressure to respond better to customer demands, wherein improvement personnel frequently engage Shigeo Shingo's Single Minute Exchange of Die (SMED) methodology to achieve better performance. Irrespective of the improvement methodology that is employed this paper assesses two fundamental mechanisms by which better changeovers might be achieved. First, improvement can occur by altering when tasks are conducted. Better allocation of tasks to the resources necessary to conduct them is sought, where the tasks themselves remain essentially unchanged. The second mechanism is to seek structural change to existing tasks, thereby intrinsically enabling them to be completed more quickly. These two mechanisms are described in relation to use of the SMED methodology, where it is argued that, by reinterpreting Shingo's work, greater clarity of potential improvement options can be gained     

Optical properties of CdS<Subscript>0.2</Subscript>Se<Subscript>0.8</Subscript>:V

We report here a comparison between two methods for calculating the index of refraction of the CdS_xSe_1−x alloy system and a calculation of the phase-matching angles for second harmonic generation for this system. Analytical expressions for the index and the birefringence of all x values are presented. The low-temperature photoluminescence spectrum has been measured and reveals a native defect at 1.45 eV and a peak at 1.8 eV caused by the vanadium dopant, as well as an exciton peak at 2.24 eV. The transmission spectrum displays three peaks due to the vanadium dopant at 0.979 eV, 1.087 eV, and 1.181 eV. The birefringence has been measured for x = 0.2 from 1 μm to 14 μm and varies from 0.0185 to 0.0125.     

iPTT: peer‐to‐peer push‐to‐talk for VoIP

This paper proposes iPTT, a peer‐to‐peer (P2P) Push‐to‐Talk (PTT) service for Voice over IP (VoIP). In iPTT, a distributed and mobile‐operator independent network architecture is presented to accelerate the deployment of the PTT service. Based on the serverless architecture, we develop two mechanisms, that is, flooding‐based floor control mechanism (FFC) and tree‐based floor control mechanism (TFC), for real‐time talk‐burst determination. The determination algorithms and the corresponding message flows for these two mechanisms are designed to show the feasibility of FFC and TFC. The performance of FFC and TFC is investigated through our analytical and simulation models in terms of the determination latency and the number of floor‐control message exchanges. Copyright © 2008 John Wiley & Sons, Ltd.     

Comment on: “Component relevancy in multistate reliabilitymodels”

The author comments on the paper by A.M. Abouammoh and M.A. Al-Kadi (see ibid., vol.40, p.370-4, 1991) which discusses various notions of component relevancy for multistate systems and suggests a unified form of relevancy. The paper contains many misprints, some wrong examples, and several results that need clarification. The most important are mentioned     

Affine order-statistic filters: “medianization” oflinear FIR filters

This paper introduces a novel, data-adaptive filtering framework: affine order-statistic filters. Affine order-statistic filters operate effectively on a wide range of signal statistics, are sensitive to the dispersion of the observed data, and are therefore particularly useful in the processing of nonstationary signals. These properties result from the introduction of a tunable affinity function that measures the affinity, or closeness, of observation samples in their natural order to their corresponding order statistics. The obtained affinity measures are utilized to control the influence of individual samples in the filtering process. Depending on the spread of the affinity function, which is controlled by a single parameter γ, affine order-statistic filters operate effectively in various environments ranging from Gaussian to impulsive. The class of affine order-statistic filters subsumes the family of weighted order-statistic (WOS) affine filters and the class of FIR affine filters. We focus on a representative of the WOS affine filter class-the median affine filter-whose behavior can be tuned from that of a linear FIR filter to that of a robust median filter by narrowing the affinity function to a process referred to as medianization. The superior performance of affine order-statistic filters is demonstrated in two applications     

High potential of thin (<1 µm) a‐Si: H/µc‐Si:H tandem solar cells

Silicon based thin tandem solar cells were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a 30 × 30 cm² reactor. The layer thicknesses of the amorphous top cells and the microcrystalline bottom cells were significantly reduced compared to standard tandem cells that are optimized for high efficiency (typically with a total absorber layer thickness from 1.5 to 3 µm). The individual absorber layer thicknesses of the top and bottom cells were chosen so that the generated current densities are similar to each other. With such thin cells, having a total absorber layer thickness varying from 0.5 to 1.5 µm, initial efficiencies of 8.6–10.7% were achieved. The effects of thickness variations of both absorber layers on the device properties have been separately investigated. With the help of quantum efficiency (QE) measurements, we could demonstrate that by reducing the bottom cell thickness the top cell current density increased which is addressed to back‐reflected light. Due to a very thin a‐Si:H top cell, the thin tandem cells show a much lower degradation rate under continuous illumination at open circuit conditions compared to standard tandem and a‐Si:H single junction cells. We demonstrate that thin tandem cells of around 550 nm show better stabilized efficiencies than a‐Si:H and µc‐Si:H single junction cells of comparable thickness. The results show the high potential of thin a‐Si/µc‐Si tandem cells for cost‐effective photovoltaics. Copyright © 2010 John Wiley & Sons, Ltd.     

SATS: Structure‐Aware Touch‐Based Scrolling

Non‐linear document navigation refers to the process of repeatedly reading a document at different levels to provide an overview, including selective reading to search for useful information within a document under time constraints. Currently, this function is not supported well by small‐screen tablets. In this study, we propose the concept of structure‐aware touch‐based scrolling (SATS), which allows structural document navigation using region‐dependent touch gestures for non‐sequential navigation within tablets or tablet‐sized e‐book readers. In SATS, the screen is divided into four vertical sections representing the different structural levels of a document, where dragging into the different sections allows navigating from the macro to micro levels. The implementation of a prototype is presented, as well as details of a comparative evaluation using typical non‐sequential navigation tasks performed under time constraints. The results showed that SATS obtained better performance, higher user satisfaction, and a lower usability workload compared with a conventional structural overview interface.     

Study of the photoinduced degradation of tandem photovoltaic converters based on <Emphasis Type="Italic">a</Emphasis>-Si:H/μ<Emphasis Type="Italic">c</Emphasis>-Si:H

The photoinduced degradation of photovoltaic converters based on an a-Si:H/µc-Si:H tandem structure under a standard illuminance of 1000 W/m² is studied. The spectral and current–voltage characteristics of specially fabricated samples with various degrees of crystallinity of the intrinsic layer in the lower (microcrystalline) cascade are measured in the course of the tests.     

CuOx/a‐Si:H heterojunction thin‐film solar cell with an n‐type µc‐Si:H depletion‐assisting layer

We showed that thin n‐type CuO_x films can be deposited by radio‐frequency magnetron reactive sputtering and demonstrated the fabrication of n‐CuO_x/intrinsic hydrogenated amorphous silicon (i‐a‐Si:H) heterojunction solar cells (HSCs) for the first time. A highly n‐doped hydrogenated microcrystalline Si (n‐µc‐Si:H) layer was introduced as a depletion‐assisting layer to further improve the performance of n‐CuO_x/i‐a‐Si:H HSCs. An analysis of the external quantum efficiency and energy‐band diagram showed that the thin depletion‐assisting layer helped establish sufficient depletion and increased the built‐in potential in the n‐CuO_x layer. The fabricated HSC exhibited a high open‐circuit voltage of 0.715 V and an efficiency of 4.79%. Copyright © 2015 John Wiley & Sons, Ltd.