Categorical scaling of time: Implications for clock-counter models.

Pigeons partitioned time into three intervals. Responses to one key could be reinforced after a short time, to a second key after an intermediate time, and to a third key after a long time. The values of the short, intermediate, and long times and the proportion of trials ending with reinforcement were varied. Absolute and relative response rates on each key were an orderly function of time and showed approximately proportional changes with changes in the interval values, consistent with Weber's law, Gibbon's (1977) scalar expectancy theory, and Killeen and Fetterman's (1988) behavioral theory of timing (BeT). Standard deviations of the times at which subjects switched between successive keys increased more slowly within a condition than across conditions, as predicted by BeT. Increases and decreases in reinforcement probability produced both transient and longer lasting changes in timing behavior, once again, in accord with predictions of BeT. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photo-bleaching induced electro-optic polymer modulators with dual driving electrodes operating at 1.55 /spl mu/m wavelength

Electro-optic (EO) polymeric Mach-Zehnder (MZ) modulators with photo-bleaching (PB) induced waveguides and dual driving electrodes operating at 1.55 /spl mu/m wavelength have been demonstrated. The half-wave voltage of the integrated polymeric modulator was 4.5 V in a push-pull configuration with a 1.5 cm interaction length. The extinction ratio was greater than 20 dB, and the fibre-to-fibre insertion loss was 8 dB for the TM polarisation. The achieved fibre-to-fibre insertion loss and driving voltage are the best, to the authors knowledge, in the reported PB induced MZ EO polymeric modulators.     

Metal-defined polymeric variable optical attenuator

A variable optical attenuator (VOA) based on a metal-defined polymeric optical waveguide has been demonstrated for the first time. The metal film stressor deposited on top of the upper cladding layer not only produces the refractive index change within the core layer, but also acts as a thin-film heater allowing thermal tuning of the optical power within a metal-defined optical waveguide. Fabricated devices exhibit greater than 25 dB of optical attenuation with an applied electrical current of /spl sim/40 mA at 1550-nm wavelength. The switching speed of the VOA exhibits 800 /spl mu/s of rising and 720 /spl mu/s of falling time.     

AP1000 core design with 50% MOX loading

The European uility requirements (EUR) document states that the next generation European passive plant (EPP) reactor core design shall be optimized for UO₂ fuel assemblies, with provisions made to allow for up to 50% mixed-oxide (MOX) fuel assemblies. The use of MOX in the core design will have significant impacts on key physics parameters and safety analysis assumptions. Furthermore, the MOX fuel rod design must also consider fuel performance criterion important to maintaining the integrity of the fuel rod over its intended lifetime. The purpose of this paper is to demonstrate that the AP1000 is capable of complying with the EUR requirement for MOX utilization without significant changes to the design of the plant. The analyses documented within will compare a 100% UO₂ core design and a mixed MOX/UO₂ core design, discussing relevant results related to reactivity management, power margin and fuel rod performance.     

Fabrication and characterization of high-speedpolyurethane-disperse red 19 integrated electrooptic modulators foranalog system applications

The fabrication and characterization of polymeric electrooptic modulators, made of a thermally crosslinkable polyurethane with Disperse Red 19 side chains, are summarized in this paper. Straight channel and Mach-Zehnder modulators have been fabricated, packaged and tested for the fiber-optic analog transmission system applications. Device performances including halfwave voltage, insertion loss, on-off ratio, and modulation frequency responses were measured. Long-term halfwave voltage stability, dc-bias voltage stability, and optical power handling capability at 1.3-μm wavelength were investigated. A carrier-to-noise ratio of 53 dB and 80-channel television transmission have been demonstrated using the packaged polymer modulators     

Application of high Tc superconductors asfrequency selective surfaces: experiment and theory

The use of YBa₂Cu₃O_7-x and Tl₂CaBa₂Cu₂O₈ high-temperature superconducting thin films to fabricate frequency selective surfaces (FSS) at millimeter-wave frequencies (75-110 GHz) is discussed. An analytical/numerical model was applied, using a Floquet expansion and the method of moments, to analyze bandstop superconducting frequency selective surfaces. Experimental results were compared with the model, and showed agreement with resonant frequency prediction with an accuracy of better than 1%. The use of the superconducting frequency selective surfaces as quasi-optical millimeter-wave bandpass filters was also demonstrated     

40-GHz polymer electrooptic phase modulators

A broad-band high-frequency traveling wave electrooptic phase modulator made from stable nonlinear optical polymers has been tested. Using a 1.319-μm light source, single-mode operation was achieved with high-input optical power, resulting in improved modulation depths and signal-to-noise ratios. The high-frequency optical modulation was observed up to 40 GHz using external microwave mixers. Direct optical-heterodyne detection of electrooptic phase modulation has also been demonstrated with high sensitivity at 40 GHz. The devices were tested with 10⁵ W/cm² power density for 21 hours, and have showed no observable decay in nonlinearity     

Discrimination of temporal relations by pigeons.

In 4 experiments, pigeons were tested on a duration comparison task involving the successive presentation of two visual stimuli that varied in duration from trial to trial. Following presentation of the durations, 2 choice keys were lit, and reinforcement for choices was based on the temporal relation between durations of the pair. In Exp 1, the range of durations was varied over conditions. Responding changed as an orderly function of the ratio of the 2 durations. There was a decrease in discrimination accuracy as average duration increased over conditions. In Exp 2, Ss were transferred from a task involving spatially differentiated choices to one involving hue-differentiated choices. Performance was similar to that of Exp 1. In Exp 3, Ss were exposed to a single duration range that included many durations from the 4 ranges of Exp 1. Discrimination accuracy was comparable on 3 problem duration categories within this range and declined slightly for problems in the 4th and longest category. Manipulation of absolute reinforcement rate in Exp 4 resulted in no change in discrimination accuracy, suggesting that the decline in accuracy over conditions of Exp 1 could not be attributed to decreases in reinforcement rate that accompanied lengthier durations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heterodyne radiometry measurements of the 557 GHz H2O rotational line

A high-resolution heterodyne radiometer that utilizes a crossed-guide harmonic mixer pumped by a 300 GHz carcinotron as a local oscillator has been developed for submillimeter wavelengths. Previous investigations of the radiation transfer properties of spectral lines in supersonic gas flow have been extended to longer wavelengths using the tunability of this system. With less than 2 mW of fundamental local oscillator power, traces of the 557 GHz ortho-H2O rotational transition (1_{10} leftarrow 1_{01}), Doppler-broadened to only a few MHz, were observed in absorption against a continuum background.