Gain equalization of EDFA cascades

Investigates the impact of wavelength-dependent erbium-doped fiber amplifier (EDFA) gain spectrum on multichannel direct-detection lightwave transmission systems employing multiple amplifiers. An analysis is presented which quantifies the constraints imposed by received power imbalance, signal-to-noise ratio (SNR), and receiver sensitivity on an EDFA cascade. Expressions are derived which relate the system constraints to the EDFA gain imbalance, bit rate, number of channels, and receiver dynamic range. Results demonstrate that when four-wave mixing (FWM) is compensated in an 11-channel system, received power imbalance can impose a significant constraint on transmission distance when the EDFA gain imbalance is greater than 1 dB or when bit rate is less than 1.8 Gb/s. In addition, performance of the preemphasis gain equalization technique is studied for multichannel systems employing APD or p-i-n/FET direct-detection optical receivers. Simple expressions are derived which can be used to quantify the increase in transmission distance obtained when employing preemphasis equalization. Results indicate that equalization of the received power spectrum can provide a two- to four-fold increase in the transmission distance when using APD receivers, compared to a one- to two-fold improvement with p-i-n/FET receivers. Analytic results are compared with results obtained by proven simulation methods and found to be in good agreement     

Teleost telencephalon and learning: an interpretive review of data and hypotheses

Immunization is the most important single public health measure available to control many important infectious diseases. The childhood schedule of immunization consists of five injections of TA/CDT, five doses of Sabin vaccine, one injection of measles vaccine, and one injection of rubella vaccine. Even if TA/CDT and Sabin are given at the same time, this still means seven decisions to be made by the mother to take her child for immunization. Unless there is an effective health education programme, combined with cheap convenient effective immunization facilities, the herd immunity might drop to a level at which epidemics could occur. This article deals with the deterrents to immunization and suggests means of overcoming them.     

Developments in Coarse-Grain Modeling of Transient Heat-Flow in Buildings

The note reports on recent developments to the coarse-grain method (CGM) of modeling transient heat flow in buildings. CGM was originally developed as an alternative to conventional fine-grain modeling techniques [such as the finite-difference method (FDM) and finite-element method (FEM)] to increase simulation speed to a degree that facilitates three-dimensional modeling, and to ease the tasks of model development and experimentation. Earlier work has shown that CGM can provide reasonably accurate simulations at a processing speed several orders of magnitude faster than FDM or FEM. This note describes and demonstrates refinements to the CGM approach that increase its modeling accuracy to a level comparable to FEM, while doubling its processing speed. These refinements are: (1) the use of a hybrid linear regression model with an artificial neural network (ANN) to represent each coarse-grain modeling element (the hybridization of the ANN effectively halves its complexity); and (2) a linear calibration of the ANN-based coarse-grain modeling elements to account for an observed positive bias in their predictions. The improved approach is demonstrated for a two-dimensional model of a bay in a research building located at the University of Florida. The note concludes with some suggestions for continuing research.     

Behaviour of Double Glazing in Corner Fires

The results of fifteen experiments in which a double glazing assembly was exposed to enclosure fires of increasing severity are presented. The glazing assembly was exposed to the typical two zone or one zone fire enclosure environment with consistency and repeatability within each set of three experiments conducted at each severity level, evident from the enclosure gas temperature profiles. The results presented include; enclosure local gas temperatures, local exposed glass surface temperatures, local shaded glass temperatures, total incident fluxes, convective and radiative fluxes, incident flux distributions at time of first cracking and inner and outer pane behaviours. A simple lumped model approach is developed to predict the response of the glazing to thermal insult. Total loss of glazing integrity is related graphically to the time of first crack.     

Modeling construction processes using artificial neural networks

The paper evaluates a neural network approach to modeling the dynamics of construction processes that exhibit both discrete and stochastic behavior, providing an alternative to the more conventional method of discrete-event simulation. The incentive for developing the technique is its potential for (i) facilitating model development in situations where there is limited theory describing the dependence between component processes; and (ii) rapid execution of a simulation through parallel processing. The alternative ways in which neural networks can be used to model construction processes are reviewed and their relative merits are identified. The most promising approach, a recursive method of dynamic modeling, is examined in a series of experiments. These involve the application of the technique to two classes of earthmoving system, the first comprising a push-dozer and a fleet of scrapers, and the second a loader and fleet of haul trucks. The viability of the neural network approach is demonstrated in terms of its ability to model the discrete and stochastic behavior of these classes of construction processes. The paper concludes with an indication of some areas for further development of the technique.     

确保三峡工程2001年安全度汛

2001年是三峡工程建设攻坚克难的一年,施工任务十分艰巨.厂坝项目和永久船闸项目是今年施工的重点.确保二期围堰和其它工程安全度汛是完成今年施工计划,实现三峡工程2003年发电、通航目标的一件大事.三峡总公司对此高度重视,三峡工程施工区度汛领导小组对度汛标准、防汛重点及主要措施以及重点部位的防汛预备方案进行了统一布署和安排,确保2001年安全度汛.     

Harnessing Split-Inteins as a Tool for the Selective Modification of Surface Receptors in Live Cells

Biochemical studies of integral membrane proteins are often hampered by low purification yields and technical limitations such as aggregation causing in vitro manipulations to be challenging. The ability of controlling proteins in live cells bypasses these limitations while broadening the scope of accessible questions owing to the proteins being in their native environment. Here we take advantage of the intein biorthogonality to mammalian systems, site specificity, fast kinetics, and auto-processing nature as an attractive option for modifying surface proteins. Using EGFR as a model, we demonstrate that the split-intein pair Ava^N/Npu^C can be used to efficiently and specifically modify target membrane proteins with a synthetic adduct for downstream live cell application.     

Space photovoltaics

The key elements of spacecraft photovoltaic cell and array design are identified and the historical development of space photovoltaics is discussed. Important parameters are listed for earth orbiting, near-earth, near-sun and outer planetary missions. The earth-orbiting missions are described within the context of low earth orbit, mid-altitude earth orbit and geosynchronous earth orbit. Requirements governed by the choice of mission, such as total power, insolation, temperature, radiation environment and stowed volume, are discussed with respect to the solar cell parameters important to that mission (conversion efficiency, weight, tolerance to the space radiation environment, cost and availability). Array parameters (dollars per watt, watts per kilogram, watts per square meter) are discussed for three types of arrays (rigid, lightweight flexible and concentrator). Progress in cell efficiencies is noted with a record GaInP/GaAs cell efficiency of 26·9%. Recent advances in thin-film cells (copper–indium diselenide and amorphous silicon) are discussed. Manufacturing capability and progress in multiple bandgap cells is noted. Space photovoltaics can look forward to an exciting next 10 years as the demand for a variety of satellites continues to grow. © 1998 John Wiley & Sons, Ltd. This paper was produced under the auspices of the US Government and it is therefore not subject to copyright in the USA     

Heteroepitaxial Inp solar cells for space applications

This review summarizes the current status of research aimed at development of heteroepitaxial InP solar cells. Details are presented for single junction and multijunction cells. We conclude with recommendations for future research.