Adaptive arrays for communication systems: An overview of research at the Ohio State University

Adaptive array research at The Ohio State University is presented in a summary form. The main objective of the research was to assess the capabilities of adaptive arrays for communication systems in real environments. Consequently the theoretical work was often corroborated by experimental implementation and testing of proposed techniques. Specifically, three systems in which adaptive arrays were successfully incorporated are described, a single channel spread spectrum communication system, a TDMA satellite communication system, and a remote sensor communication system. Numerous other adaptive array studies are briefly summarized.     

The fabrication and performance of long lengths of silica core fiber

Three hundred kilometers of single-mode fiber exhibiting median optical losses of 0.19 dB/km at 1.57 μm have been fabricated from preforms made by a high-rate Modified Chemical Vapor Deposition (MCVD) process. A new fiber design [1] was utilized which minimizes Rayleigh scattering loss by reducing the amount of dopants in the core. Milestone systems experiments incorporating this fiber have already demonstrated 420-Mbit transmission through 203 km [2], 2-Gbit transmission through 130 km [3], 1.37 Tbit km/s using 10 wavelength division multiplexed lasers [4], 4-Gbit through 102 km using a novel electronic multiplexer/demultiplexer [5], and 4 Gbit through 117 km using a Ti:LiNbO3external modulator [6]. Additionally, very low induced losses from hydrogen and radiation are reported.     

Partial oxidation of CH4 and C2H6 over noble metalcoated monoliths

The direct partial oxidation of hydrocarbons offers promising alternatives to chemical synthesis. By replacing endothermic processes such as steam reforming and steam cracking, fast and exothermic oxidation reactions should require much smaller and simpler reactors. However, direct oxidation reactions are much more difficult to manage because of potential heat release in total oxidation and hazardous because of the possibility of homogeneous reactions which are nonselective and can produce flames and explosions. We describe experiments in which monolith catalysts are used for partial oxidation of CH₄ and C₂H₆ to produce synthesis gas or alkenes by direct oxidation at or above atmospheric pressure in pure O₂ in nearly adiabatic reactors operating at 1000°C with very high flowrates (space velocities of 10⁶h⁻¹ and residence times of 10⁻³ s). With methane oxidation we obtain over 90% selectivities to synthesis gas (a 2:1 H₂:CO mixture) with> 90% conversion of the methane and complete conversion of O₂ on Rh coated ceramic monoliths with contact times of 10⁻³ s. With Pt catalysts under the same conditions, the H₂ selectivity drops to 70%; while with Pd, the catalyst rapidly forms carbon. This process appears to be primarily a surface reaction in which CH4 pyrolyzes on the hot Rh surface and the H atoms dimerize and the carbon is oxidized to CO. A model has been constructed which accurately predicts the conversions and selectivities and the variations between Rh and Pt. With higher alkanes, synthesis gas is produced on Rh with comparable selectivities and conversions on metal-coated monoliths. However, with Pt we observe up to 70% selectivity to alkenes with 80% conversion of alkanes at adiabatic temperatures near 1000°C with approximately 5 ms contact times. These results can be explained as occurring by predominantly surface reactions in which the alkane adsorbs to form the alkyl by H abstraction with adsorbed O atoms. Then the adsorbed alkyls undergo primarily β-elimination reactions on Pt to produce alkenes. These products are therefore far from thermodynamic equilibrium at these very short contact times, even though the temperatures are very high. The use of very short contact times and high temperatures promises to provide new routes to production of partial oxidation products with very small adiabatic reactors and thus opens up new types of reactions and reactors for chemical synthesis.     

Formation and reactivity of oxides and basic salts. II. Radio-isotope studies of some calcareous materials

Rates of calcium exchange between solid and solution in the ageing of hydrated lime and of calcium carbonate samples have been determined using calcium-45 radio-isotope. After a comparatively rapid calcium uptake of about 1 molecular layer at the hydrated lime surface, the exchange rate diminishes as the ions need to diffuse more deeply into the hydrated lime structure. Results for calcium carbonate samples of widely different specific surfaces are compatible with very slow ageing in water. Rates of gypsum precipitation from radioactive calcium chloride and nitrate solutions have been compared in neutral and acidic media and in the presence of albumen. Lower gypsum saturation ratios are established ultimately in neutral rather than acidic media, particularly in solutions containing no salts other than gypsum. Solid hydrated lime reacts rapidly with dilute sulphuric acid, aluminium and magnesium sulpnates, magnesium chloride or sea-water, releasing calcium ions into solution. The radioactivities of the solutions decrease subsequently as gypsum separates out or calcium ions are adsorbed by the finely-divided magnesium hydroxide precipitated. At higher magnesium salt concentrations, the calcium-45 radioactivity does not initially increase so sharply. This is ascribed to basic salt formation preventing all of the lime from going quickly into solution.     

The environmental impact of cadmium: an overview

The author examines the problem of disturbed‐disruptive children and first presents an ecological view of disturbance. This is followed by a section dealing with the diagnosis of excitor behaviour and then management of the problem from a short‐term and long‐term point of view. The role of the teacher is examined in this context.     

Studies of Diesel Engine Particle Emissions During Transient Operations Using an Engine Exhaust Particle Sizer

Diesel engine particle emissions during transient operations, including emissions during FTP transient cycles and during active regenerations of a NOx adsorber, were studied using a fast Engine Exhaust Particle Sizer (EEPS). For both fuels tested, a No. 2 certification diesel and a low sulfur diesel (BP-15), high particle concentrations and emission rates were mainly associated with heavy engine acceleration, high speed, and high torque during transient cycles. Averaged over the FTP transient cycle, the particle number concentration during tests with the certification fuel was 1.2e8/cm³, about four times the particle number concentration observed during tests using the BP-15 fuel. The effect of each engine parameter on particle emissions was studied. During tests using BP-15, the particle number emission rate was mainly controlled by the engine speed and torque, whereas for Certification fuel, the engine acceleration also had a strong effect on number emission rates. The effects of active regenerations of a diesel NOx adsorber on particle emissions were also characterized for two catalyst regeneration strategies: Delayed Extended Main (DEM) and Post 80 injection (Post80). Particle volume concentrations observed during DEM regenerations were much higher than those during Post80 regenerations, and the minimum air to fuel ratio achieved during the regenerations had little effect on particle emission for both strategies. This study provides valuable information for developing strategies that minimize the particle formation during active regenerations of NOx adsorbers.     

塔里木盆地塔河油田奥陶系油气藏储集层特征

塔里木盆地塔河油田已经发现的储量中,88%储藏在奥陶系碳酸盐岩储集层中,其储集空间是相互不连接的与连接的网状溶岩内的孔隙.奥陶系储集层内不同位置的油、气、水特征明显,油田内没有统一的油/水界面,更增加了油气藏的复杂性.经过酸化压裂处理后,获得高产及商业油流的井可达总井数的75.9%.酸化压裂是塔河油田改善储集层内连通性、改造非生产井、提高产量的重要手段,也是其它具有类似储集层油田开发的基本方法.     

Effects of split attention revisited: A new display technology for troubleshooting tasks

Knowledge acquisition processes benefit from presentations that depict related information – like diagrams and formulas – in an integrated way. In contrast, disconnecting interrelated information impairs learning. However, not every task is suitable for an integrated presentation. In the current study, 80 naïve college students were presented with a troubleshooting task preventing an integrated presentation format. We compared performance in a split screen setup depicting two images side-by side with performance in a vexing-image setup. The latter enables the presentation of two images such that participants are able to switch between them without moving the visual focus. Compared to the split screen condition in which participants have to shift their visual focus frequently, troubleshooting performance of correctly identified malfunctioning mechanical devices was higher in the vexing image mode. Thus, not the separation of external representations but re-orientation processes after switching the visual focus seems to be responsible for split attention effects.