Defect modes for (200), GGTGG,tight fold re-entry in polyethylene single crystals

Lattice dynamical calculations on trans-planar polyethylene chains containing conformational defects of the type GGTGG have been carried out. The purpose of the work is to predict the points in the vibrational infra-red and/or Raman spectrum at which a tight, (200) type, fold should show absorptions and/or scattering. Calculations are verified for the cyclic hydrocarbon C₃₄H₆₈ which contains two GGTGG defects. The usefulness and limitations of the vibrational spectrum as evidence for the existence of (200) tight folds are discussed. Two infra-red bands near 1342 cm^?1 and a third near 700 cm^?1 may indicate GGTGG defects in single crystals. Raman spectra seem insensitive to such defects.     

Software project development cost estimation

This paper reports the results of an empirical investigation of the relationships between effort expended, time scales, and project size for software project development. The observed relationships were compared with those predicted by Lawrence Putnam's Rayleigh curve model and Barry Boehm's COCOMO model. The results suggested that although the form of the basic empirical relationships were consistent with the cost models, the COCOMO model was a poor estimator of cost for the current data set and the data did not follow the Rayleigh curve suggested by Putnam. However, the results did suggest that it was possible to develop cost models tailored to a particular environment and to improve the precision of the models as they are used during the development cycle by including additional information such as the known effort for the early development phases. The paper finishes by discussing some of the problems involved in developing useful cost models.     

Electrical properties of ferromagnetic Gd3−xS4 near its Curie temperature

Nonstoichiometric $\text{Gd}{}_{\mathrm{<mtext>3?</mtext><mtext>x</mtext>}}\text{S}{}_4\text{(0 <}\text{x}\text{<}\text{1}\text{3}\text{)}$, which exhibits a metallic behavior, was obtained by heating an insulating Gd₂S₃ at various temperatures under a vacuum. Electrical and magnetic properties of the samples obtained have been investigated from 4.2 K to 300 K. A maximum in resistivity was observed in the curve of resistivity vs. temperature. The temperature T_P, at which the maximum emerged, was very close to the Curie temperature T_C for the sample. An increase in resistivity at T_P, Δ_?, is proportional to ?_P exp ($\text{E}\text{k}{}_{\mathrm{B}}\text{T}{}_{\mathrm{P}}$), where ?_P is the resistivity obtained by the extrapolation from the linear portion to T_P in the ? vs. T curve. Using the relationship obtained, a model based on the formation of magnetic polaron was proposed for this system.     

Internal carbon deposition resulting from a redistribution of gaseous species under combined diffusion and steam reforming reactions in a catalyst pellet

In steam reforming of hydrocarbons, the diverse relative rates of diffusion of the individual gaseous species within the catalyst can cause a redistribution of the composition with progress of the gas mixture into the pellet.Consequently, the changes of partial pressure can give rise to conditions favourable to the formation of carbon within the internal pore structure, even though it is not predicted on thermodynamic grounds at the pellet surface. Using the dusty gas model for diffusion in the transition regime coupled with two steam reforming reactions, this situation is examined for isothermal steady-state operation. By applying thermodynamic tests for carbon prediction within the pellet the conditions promoting an internal fouling problem are outlined.     

Design of a system for solar energy storage via water electrolysis

This article elaborates on the design and economic evaluation of a system that provides electricity for an average one-family dwelling by utilizing solar energy. Solar energy is converted by photovoltaic arrays to electricity which is then used for the electrolysis of water. The hydrogen produced is stored in the form of hydride and can be used either for direct burning, to meet the thermal energy requirements, or in a fuel cell to supply the electric energy needed. Particular emphasis was given to designing a control system that could guarantee a smooth intermittent operation of the electrolytic unit and the utilization of the maximum output of the photovoltaic cells. The system selected can operate with minimum attendance and very little maintenance. However, the cost of the electricity produced is at present prohibitive, being as high as $3.30 k Wh^?1.     

Global and selectivity analysis of periodically operated chemical reactors square-wave and sine-wave control of feed concentration in an isothermal CSTR with Van de Vusse kinetics

An isothermal, homogeneous CSTR with a Van de Vusse kinetics under forced square-wave and sine-wave controls of feed concentration is examined. Analytic or semi-analytic expressions for the time behavior of species concentrations are derived. For both square-wave and sine-wave control modes, the reacting system approaches a unique limit cycle. The time average selectivity of the products favors the side product under both control modes, when compared to steady state mode.     

MBi2Ge2O8 molten glasses: A new host environment for the growth of garnets,spinels, and related phases

The molar volumes of MO/Bi₂O₃/2 GeO₂ glasses ($\text{M= Zn, Cd, Ca, Sr, Pb, \& Ba}$) vary directly with cation volume and inversely with cation field strength. Small needles of ZnBi₂Ge₂O₈ (up to 0.75 mm) & SrBi₂Ge₂O₈ (up to 0.20 mm) can form during slow cooling of the parent melts. Al₂O₃ (or Ga₂O₃) additions expand these glasses by introducing AlO₄ Tetrahedra. Precipitation of spinel-like arrays from such molten polyhedral jumbles requires more Al₂O₃ (or Ga₂O₃) with larger cations for solubility reasons. This is confirmed by the nuclei concentrations.     

A grid middleware for distributed Java computing with MPI binding and process migration supports

“Grid” computing has emerged as an important new research field. With years of efforts, grid researchers have successfully developed grid technologies including security solutions,resource management protocols, information query protocols, and data management services. How-ever, as the ultimate goal of grid computing is to design an infrastructure which supports dynarnic,cross-organizational resource sharing, there is a need of solutions for efficient and transparent task re-scheduling in the grid. In this research, a new grid middleware is proposed, called G-JavaMPI. This middleware adds the parallel computing capability of Java to the grid with the support of a Grid-enabled message passing interface (MPI) for inter-process communication between Java processes executed at dif-ferent grid points. A special feature of the proposed G-JavaMPI is the support of Java process migration with post-migration message redirection. With these supports, it is possible to migrate executing Java process from site to site for continuous computation, if some site is scheduled to be turned down for system reconfiguration. Moreover, the proposed G-JavaMPI middleware is very portable since it requires no modification of underlying OS, Java virtual machine, and MPI package. Preliminary performance tests have been conducted. The proposed mechanisms have shown good migration efficiency in a simulated grid environment.     

移动机器人地图创建中的不确定传感信息处理

该文研究移动机器人自主创建地图中的不确定传感信息处理问题,基于灰色系统理论 提出了一种新的对传感信息进行解释和融合的方法用于声纳信息的处理,并以此建立环境的栅 格地图.声纳的传感信息存在较大的不确定性,这里引入灰数的概念来表示和处理这种不确定 性,对于机器人在不同位置的测量结果,根据灰色系统理论对信息的理解方式设计融合方法,得 到一个对环境的整体表示.通过仿真环境和真实机器人平台上进行的创建地图实验,表明这种 方法具有良好的鲁棒性和准确度.