Routing design of tree‐shaped local public communication networks with high reliability and low cost

This paper discusses reliability problems for local public communication networks such as cable television networks and the subscriber‐loops of telecommunication networks. They have tree‐shapes and expand continuously as new customers join. By introducing a simple model, it is shown that most principal reliability measures and cost measures for such networks can be described through the networks' graphical characteristic quantities. Extensive simulations show that the prior provision of trunk pipes and a suitable choice of the route selecting rule for new customers are effective in constructing a highly reliable network with low cost. This revised version was published online in June 2006 with corrections to the Cover Date.     

High-Speed TDM–WDM Techniques for Long-Haul Submarine Optical Amplifier Systems

Optical amplifier techniques have led to the installation of large-capacity submarine systems and further capacity increases seem likely. This paper reviews the FSA submarine system, which flexibly operates at both 2.5 and 10 Gb/s and offers maximum transmission capacity of 60 Gb/s for commercial use. The system configuration as well as its characteristics and upgradability will be introduced, including measurement results on time-division-multiplexing/wavelength-division-multiplexing (TDM–WDM) transmission at bit rates of 10 and 20 Gb/s using non-return-to-zero or soliton pulses. To further increase transmission capacity, TDM–WDM techniques that permit more than 10 Gb/s signal transmission in each data channel should be developed. Thus, pulse formats, which include non-return-to-zero, return-to-zero, or soliton pulses, and dispersion allocation in transmission fibers are significant issues. We introduce and discuss our recent results from high-speed (10 to 40 Gb/s) TDM–WDM signal transmission experiments with regard to the above aspects.     

Development of 170 GHz/500 kW gyrotron

A development of 170GHz/500kW level gyrotron was carried out as R&D work of ITER. The oscillation mode is TE_31,8. In a short pulse experiment, the maximum power of 750kW was achieved at 85kV/40A. The efficiency was 22%. In the depressed collector operation, 500kW/36%/50ms was obtained. The maximum efficiency of 40% was obtained at P_RF=470kW whereas the power decrease by the electron trapping was observed. Pulse extension was done up to 10s at P_RF=170kW with the depressed collector operation. The power was limited by the temperature increase of the output window.     

Tough and Self‐Recoverable Thin Hydrogel Membranes for Biological Applications

Tough and self‐recoverable hydrogel membranes with micrometer‐scale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spin‐coating method, we successfully fabricated thin (thickness: 5–100 µm), yet tough (work of extension at fracture: 10⁵–10⁷ J m^?3) and 100% self‐recoverable hydrogel membranes with high water content (62–97 wt%) in large size (≈100 cm²). Amphiphilic triblock copolymers, which form physical gels by self‐assembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The inter‐network associations serve as reversible sacrificial bonds that impart toughness and self‐recovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes.     

A modified power control scheme for remedying the effects of traffic nonuniformity in LEO satellite communications systems

It has been shown in our previous studies that the geographical traffic nonuniformity considerably affects the performance of the low earth orbit satellite communications systems. In this paper, a new scheme for improving the throughput characteristics of these systems at nonuniform traffic distribution is proposed. In this method, some parts of the users under the satellite which is flying over the area with high traffic load are assigned to its neighbor satellites with lower transmitting power levels. It is shown that the method equalizes the traffic loads of the satellites to some degree and, hence, can improve the throughput characteristics of the system.     

Electromagnetic wave absorber with wide-band frequencycharacteristics using exponentially tapered ferrite

As a countermeasure of EMI or EMC, various types of electromagnetic wave absorbers are used. A wide-band design method of an electromagnetic wave absorber with using exponentially tapered ferrite, which has very wide-band frequency characteristics, is proposed and discussed. The wide-band electromagnetic wave absorber can be designed under some approximations by the theoretical model using the equivalent material constants (equivalent complex permittivity and permeability) method for the regions varying spatially in the shape of ferrite. Based on the model, wide-band electromagnetic wave absorbers with taper, which have not only excellent reflectivity frequency characteristics but also a bandwidth of 30 MHz to 2150 MHz or 2430 MHz under the tolerance limits of -20 dB reflectivity, were designed     

Experimental studies of bistatic scattering from two-dimensionalconducting random rough surfaces

Despite the recent development of analytical and numerical techniques for problems of scattering from two-dimensional rough surfaces, very few experimental studies were available for verification. The authors present the results of millimeter-wave experiments on scattering from two-dimensional conducting random rough surfaces with Gaussian surface roughness statistics. Machine-fabricated rough surfaces with controlled roughness statistics were examined. Special attention was paid to surfaces with large rms slopes (ranging from 0.35 to 1.00) for which enhanced backscattering is expected to take place. Experimentally, such enhancement was indeed observed in both the copolarized and cross-polarized returns. In addition, it was noticed that at moderate angles of incidence, the scattering profile as a function of observation angle is fairly independent of the incident polarization and operating frequency. This independence justifies the use of the geometric optics approximation embodied in the Kirchhoff formulation for surfaces with large surface radius of curvature. When compared with the experimental data, this analytical technique demonstrates good agreement with the experimental data     

Renewable-Energy paradox in paradise: A case stuty of Hawaii

Hawaii is committed to replacing imported oil with indigenous, renewable energy resources to enhance the economic and environmental security of the state's citizens. A case study of Hawaii's fuel-energy balance by the end of the 21st century which features two scenarios, a ‘Business-as-Usual’ energy system, based on imported fossil fuels, and a ‘Renewable-Energy’ scenario, based on an alternative energy system consisting entirely of indigenous, renewable energy resources, is presented.

In the year 2100, a projected total energy consumption of approximately 335 million gigajoules would be provided from a hypothetical renewable-energy system of approximately 13 gigawatts-electric of installed capacity. This system would feature methanol-from-biomass to meet liquid fuel requirements for surface transportation, industrial, commercial, and residential sectors; hydrogen via electrolysis in liquid form for air transportation and as a gaseous fuel for industrial purposes; and electricity generated from geothermal, ocean thermal, wind, and photovoltaic sources for all power applications.

A comprehensive economic analysis, including capital costs, operating and maintenance costs, air pollution costs for the total fuel cycle of each energy system, and a local multiplier effect factor of 3·75 per dollar, indicates that between the years of 1987 and 2100 the ‘Business-as-Usual’ scenario will have expended approximately $600 billion (1986 US dollars), and the ‘Renewable-Energy’ scenario will have cost approximately $400 billion. By switching from imported fossil fuels to indigenous, renewable energy resources during this time period, Hawaii's citizens could save approximately $200 billion to help preserve paradise.     

Photonic A/D conversion using low-temperature-grown GaAs MSM switches integrated with Si-CMOS

By linking the unique capabilities of photonic devices with the signal processing power of electronics, photonically sampled analog-to-digital (A/D) conversion systems have demonstrated the potential for superior performance over all-electrical A/D conversion systems. We adopt a photonic A/D conversion scheme using low-temperature (LT)-grown GaAs metal-semiconductor-metal (MSM) photoconductive switches integrated with Si-CMOS A/D converters. The large bandwidth of the LT GaAs switches and the low timing jitter and short width of mode-locked laser pulses are combined to accurately sample input frequencies up to several tens of gigahertz. CMOS A/D converters perform back-end digitization, and time-interleaving is used to increase the total sampling rate of the system. In this paper, we outline the development of this system, from optimization of the LT GaAs material, speed and responsivity measurements of the switches, bandwidth and linearity characterization of the first-stage optoelectronic sample-and-hold, to integration of the switches with CMOS chips. As a final proof-of-principle demonstration, a two-channel system was fabricated with LT GaAs MSM switches flip-chip bonded to CMOS A/D converters. When operated at an aggregate sampling rate of 160 megasamples/s, the prototype system exhibits /spl sim/3.5 effective number of bits (ENOB) of resolution for input signals up to 40 GHz.