High-Dynamic-Range Wireless-Over-Fiber Link Using Feedforward Linearization

We demonstrate the implementation of feedforward linearization at 5 GHz, which is the highest operating frequency yet reported, with 500-MHz linearization bandwidth having at least 24-dB distortion suppression. Simultaneous reduction of 26-dB third-order intermodulation distortion and 7-dB laser-noise reduction is achieved at 5.2 GHz, leading to enhanced spurious-free dynamic range of 107 dB (1 Hz) in a directly modulated uncooled semiconductor laser for applications in wireless-over-fiber (WoF) systems. This paper also provides detailed analysis on feedforward, theoretical distortion reduction, criteria for component selection, and the effect of dispersion. The effectiveness of feedforward in a multichannel system is demonstrated at 5.8 GHz for fixed wireless systems, such as WiMAX. These results suggest that the feedforward-linearization arrangement can make practical multichannel and multioperator WoF systems.     

Atomic force microscopy (AFM) characterisation of the porous silica nanostructure of two centric diatoms

The porous silica nanostructure of two marine, centric diatoms, Coscinodiscus sp. and Thalassiosira eccentrica was investigated by atomic force microscopy (AFM). Important morphological features of the silica frustules of diatoms are described, including: the organisation of porous silica layers, their topography, pore size, shape and density. The outer layer of Coscinodiscus sp., commonly called the cribellum, consists of a characteristic hexagonal array of pores with pore sizes of around 45 nm. This thin membrane covers a second structural layer where two different silica surfaces are identified. The outer part, known as the cribrum consists of hexagonally packed pores of about 200 nm diameter. The inner part, known as the foramen layer, consists of larger and radially distributed holes with a diameter of around 1,150 nm. The second diatom species investigated, T. eccentrica produces a frustule with one silica structural layer featuring two different porous surfaces. The outer surface has large (800 nm diameter) holes (foramen) while the inner surface contains a porous wall with pores comparable in size to the Coscinodiscus sp. cribellum. The inner and outer surfaces of the frustule wall of both diatoms are hence in reverse order. However, the size of the small pores is similar for both species. High-resolution AFM also revealed the granular nanostructure of the diatom biosilica with grain sizes from 20 to 70 nm diameters.     

Perceptual specificity and implicit auditory priming in older and younger adults.

Age differences in perceptual specificity for implicit auditory priming were examined in 3 experiments. All 3 experiments began with a study phase during which participants rated words based on perceptual (shallow encoding) or semantic (deep encoding) attributes. After the study phase, participants were asked to identify filtered versions of repeated and new words (implicit test) and then to make old/new recognition judgments (explicit test). In contrast to earlier findings (D. L. Schacter, B. Church, & D. M. Osowiecki, 1994), older and younger adults were equally sensitive to study-to-test changes in speaking rate (Experiment 1), fundamental frequency (Experiment 2), and voice (Experiment 3). Explicit memory, in contrast, was significantly poorer for older adults but was minimally affected by changes in surface features. Findings from the study are discussed with respect to their implications for establishing the mechanisms mediating perceptual specificity and for their importance in understanding age-related changes in implicit memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Large-area scintillating-fiber time-of-flight/hodoscope detectors for particle astrophysics experiments

A new generation of detectors of ultra-heavy (UH) cosmic rays is being built which require the use of large-area, light-weight detector elements. In this paper, we present the design and operation of a new type of scintillating optical fiber detector, which can serve as both a time-of-flight (TOF) detector and coded hodoscope (i.e. trajectory detector). We demonstrate that this type of detector can make TOF measurements with a time resolution of 48 ps. We also present results of position measurements from a large area TOF/hodoscope that was flown on a high-altitude balloon flight in August, 1995. Finally, we discuss areas of modification and improvements that can be made to these detectors to enable them to be more useful for making UH cosmic ray measurements.     

On the formation of serrated grain boundaries and fan type structures in an advanced polycrystalline nickel-base superalloy

The formation of serrated grain boundaries and fan-type structures in an advanced polycrystalline nickel-base superalloy has been extensively studied and linked to the thermal history. The development of grain boundary serrations has been quantitatively linked to the cooling rate from the solution heat treatment temperature. Slower cooling rates were found to result in more convoluted grain boundaries formed as a result of impingement of growing secondary γ′. Subtle differences were also noted in the γ′ distributions in the vicinities of the grain boundaries, in particular they exhibit differences in size, morphology and chemistry as a function of location within the grain, all of which are reported in the paper. Fan-type structures were found to form in the alloy, irrespective of the cooling rate employed, although their size and volume fraction increased with a decrease in cooling rate. The presence of these structures is shown to impact upon the total length of grain boundary and the degree of serration. The fan-type structures exhibit a typical dendritic morphology and were found to nucleate on minor phases present within the alloy.     

A cubic heat balance integral method for one-dimensional melting of a finite thickness layer

The work in this paper concerns the one-dimensional melting of a finite thickness layer. An asymptotic series solution describes the temperature in the melt regions. In the solid region the thermal boundary layers are approximated by a cubic polynomial. Results are compared with the exact solution for a semi-infinite block, and shown to agree to within less than 1%. The method is then applied to a situation where no analytical solution is available. A finite thickness frozen solid is placed on a warm substrate in a warm environment: initially the base of the solid heats to the melting temperature when a single melted region develops and subsequently a second melting front appears on the top boundary. We also present an example relevant to heating an ice layer from below, which occurs with de-icing systems.     

Factors influencing the measurement of oxygen shortfall of the human cornea: sequencing of test conditions.

PURPOSE: The effects of sequencing of test conditions, in this case contact lens thicknesses, on the measurement of the oxygen shortfall of human corneas were studied. METHODS: Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode on the central, unanesthetized right corneas of 14 human subjects. Measurements were made under the following conditions: (1) the normal open eye; (2) after 5 min of static (without blinking) wear of each of seven rigid gas permeable lenses of seven center thicknesses (0.18, 0.12, 0.16, 0.20, 0.24, 0.28, and 0.32 mm); (3) after 5 min of static wear of a polymethylmethacrylate (PMMA) contact lens. Lens thicknesses were randomly assigned numbers, which were sequenced in seven cycles. Two subjects were assigned to each sequencing cycle, and each subject participated in two identical sessions. RESULTS: The interaction of order x thickness was determined to be insignificant (F=0.99; p=0.5101). The effect of lens order was also insignificant (F=0.76; p=0.6239), indicating that the order of lens placement did not affect the measured corneal oxygen shortfall. Not surprisingly, the analysis indicated a significant effect of lens thickness on corneal oxygen shortfall (F=3.94; p=0.0032). CONCLUSIONS: The sequencing of lenses of various thicknesses on the cornea does not affect the measurement of corneal oxygen shortfall.     

Escherichia coli in urban stormwater: explaining their variability.

The development of a model that predicts the levels of microorganisms in urban stormwater will aid in the assessment of health risks when using stormwater for both recreational uses and as an alternate water resource. However, the development of such a model requires an understanding of the dominant processes that influence the behaviour of microorganisms in urban systems. Using simple and multiple regression analyses this paper determines the dominant processes which affect the inter-event variability of the microbial indicator Escherichia coli (E. coli ) in four urbanised catchments. The results reveal that a number of antecedent climatic conditions, together with rainfall intensity, can significantly explain the inter-event variation in wet weather E. coli levels.     

Prospective memory and the efficacy of a memory strategy in multiple sclerosis.

Prospective memory (PM), which is the ability to remember to carry out actions that are planned for the future, plays an important role in professional and social life as well as in activities of daily living. This study examined PM performance among adults with multiple sclerosis (MS) and evaluated the efficacy of a mnemonic strategy, implementation intentions. Compared to controls, adults with MS were impaired on PM, both in terms of acting when encountering the correct circumstances (prospective component) and in terms of remembering the correct action to perform (retrospective component). The prospective-component deficit was greater for tasks that depended on more resource-demanding cognitive processes and smaller on tasks that could be performed more automatically. Use of implementation intentions improved MS-group performance on the prospective component, particularly on the more resource-demanding tasks, consistent with the explanation that implementation intentions improved performance by allowing the use of more automatic processes to perform these PM tasks. Implications for providing environmental support to encourage the use of mnemonic strategies are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Solids suspension agitation in square tanks

The Zwietering correlation for the just‐suspended speed has been modified to include baffling and geometric effects (impeller‐to‐tank diameter ratio and impeller off‐bottom clearance) for two impeller types (high‐efficiency and pitched‐blade). Baffles are generally not required when using square tanks although they improve solids suspension performance of pitched‐blade turbines. Comparison of square tank solids suspension to that in a fully baffled cylindrical tank has also been made. Very little difference was observed in the power number, but the just‐suspended speed, torque, and power requirements were higher in the square tank.