Composition methods for four-port couplers in photonic integrated circuitry

Planar photonic integrated circuits based on four-port couplers offer enhanced sophistication and functionality. Each four-port coupler is characterized by sixteen signal coupling coefficients governed by ten energy constraints. The ability to generate the constrained sixteen coupling coefficients is needed in the analysis of the four-port coupler. However, the energy constraint equations are nonlinear and cumbersome to solve directly. We introduce two techniques to reduce these signal coupling coefficients to a set of six free parameters. Hence we can characterize all possible couplers in terms of their sixteen constrained coupling coefficients, or either of two sets of six free parameters. This reduction in parameters has significant ramifications for the design, specification, and empirical characterization of these useful building blocks.     

Chemical stability and human plasma pharmacokinetics of reduced folates

The vast majority of signalling pathways in mammalian cells are mediated by heterotrimeric (alpha betagamma) G proteins. Reviewed here is regulation of signal transduction by the betagamma complex at different protein interfaces: subunit-subunit, receptor-G protein and G protein-effector. The role of diverse beta and gamma subunit types in achieving specificity in signalling and potentially unidentified functions for these subunits also are discussed.     

Whole-farm nitrogen balance on western dairy farms

Environmental legislation has made it necessary for livestock producers to be able to quantify and adjust the N balance on their farms. Whole-farm N balance and efficiencies were computed for 41 commercial dairies in Utah and Idaho using the University of Maryland Nutrient Balancer. The average N balance, or unaccounted for N, was 81 tonnes per year for the average herd size of 466 cows with 35.8% of the inputs accounted for in the outputs. The major inputs for farms that grew crops (n = 23, herd size = 284 total cows) were imported feed (57.4% of all inputs) and nitrogen fixation (30% of inputs). The major outputs were animal products (primarily milk and some meat, 80% of outputs). For farms that grew no crops (n = 18, herd size = 700 total cows), 98% of the inputs were from imported feed. Of the outputs, 57% of the N was in animal products and 42.9% in manure and compost. Whole-farm balance per product for those farms that grew crops was most affected by herd N utilization efficiency (kg feed N per kg product N), crop N utilization efficiency, and availability of manure N applied to crops, while manure N storage efficiency was of lesser importance. For farms that grew no crops, whole-farm N balance per product was most affected by herd N utilization efficiency and manure N storage efficiency. Maximizing conversion of feed N to product N was the best way to reduce whole-farm N balance.     

Understanding Web home page perception

A home page is the gateway to an organization's Web site. To design effective Web home pages, it is necessary to understand the fundamental drivers of user's perception of Web pages. Not only do designers have to understand potential users' frame of mind, they also have at their choosing a stupefying array of attributes – including numerous font types, audio, video, and graphics – all of which can be arranged on a page in different ways, compounding the complexity of the design task. A theoretical model capable of explaining user reactions at a molar level should be invaluable to Web designers as a complement to prevalent intuitive and heuristic approaches. Such a model transcends piecemeal page attributes to focus on overall Web page perceptions of users. Reasoning that people perceive the cyberspace of Web pages in ways similar to their perception of physical places, we use Kaplan and Kaplan's informational model of place perception from the field of environmental psychology to predict that only two dimensions: understanding of information on a Web page, and the involvement potential of a Web page, should adequately capture Web page perception at a molar level. We empirically verify the existence of these dimensions and develop valid scales for measuring them. Using a home page as a stimulus in a lab experiment, we find that understanding and involvement together account for a significant amount of the variance in the attitude toward the Web page and in the intention to browse the underlying Web site. We show that the informational model is a parsimonious and powerful theoretical framework to measure users' perceptions of Web home pages and it could potentially serve as a guide to Web page design and testing efforts.     

Analysis and design of active optical filter structures with two-port couplers

A signal processing approach to modeling, analyzing, and synthesizing a particular integrated photonic architecture of optical filters with tunable gains is presented. This particular architecture has two-port couplers and current-controlled semiconductor optical amplifiers (SOAs) fabricated on the same substrate. The device architecture forms a new lattice filter structure. Layer-peeling-type algorithms are developed for the analysis and synthesis of the device. The role of the adjustable gains in a lossless or lossy device is considered, and a novel stability algorithm for the filter structure is presented.     

An investigation of different instructional methods on number-concept understanding and arithmetic learning.

Made a 3-yr investigation of 3 different methods of teaching arithmetic to 1st-3rd grade children. The methods were: traditional, cuisenaire, and sets and numbers. No reliable differences in arithmetic achievement could be detected between Ss taught by the different methods. Also, no differences in number concept understanding were found, when assessed by a Piagetian-type of standardized test. Consistent differences between classes taught by the same method were found, but were attributed tentatively to differences in teaching ability. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative processes in personal and group judgments: Resolving the discrepancy.

The judgment mechanisms underlying personal- and group-level ratings of discrimination and privilege were investigated in high- and low-status groups. A consistent personal–group discrepancy is found for discrimination and privilege but is not due to personal differentiation from the group. Instead, personal and group ratings are based on different comparison standards and levels of self (personal vs. social identity); personal motives influence personal ratings, and social motivations influence group ratings. This analysis is supported by contrasting the traditional discrepancy score with a direct comparison measure (Study 2) and by showing the sensitivity of group ratings (but not personal ratings) to group audience and degree of group identification (Studies 3 and 4). Studying the different meanings communicated with personal and group ratings provides more insight into the dimensions of deprivation than do analyses of discrepancy scores. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of Combustion Aerosol Produced by a Mini-CAST and Treated in a Catalytic Stripper

We characterized the properties of combustion aerosol produced at different operating conditions of a mini-CAST burner that was treated in a Catalytic Stripper (CS) operating at 300°C. The goal was to establish a methodology for the production of soot particles resembling those emitted from internal combustion engines. Thermo-optical analysis of samples collected on Quartz filters revealed that the particles contained semi-volatile material that survived the CS. The amount of semi-volatile species strongly depended on the operating conditions ranging from less than 10% to as high as 30% of the particle mass. The mini-CAST operating conditions were also found to have a strong effect on the effective particle density (ρ_e ). The ρ_e , for example, ranged from as low as 0.3 to 1.05 g/cm³ for mondisperse 80 nm particles, although the mass-mobility exponent remained relatively constant (2.1–2.25). These differences are indicative of differences in the primary particle diameter, which was estimated to range between 8.5 and 34 nm depending on the operating conditions. The different types of particles produced were also found to exhibit different affinities for butanol but also different light absorption per mass of elemental carbon which can, therefore, lead to inconsistencies in aerosol instrumentation calibrations (e.g., condensation and optical particle counters, photoacoustic sensors). The work highlights the importance of establishing a detailed and well-defined method in using the mini-CAST-CS approach for instrument calibration in ways mimicking various engine combustion sources.

Copyright 2013 American Association for Aerosol Research     

Microscopic Removal Function and the Relationship Between Slurry Particle Size Distribution and Workpiece Roughness During Pad Polishing

Various ceria and colloidal silica polishing slurries were used to polish fused silica glass workpieces on a polyurethane pad. Characterization of the slurries' particle size distribution (PSD) (using both ensemble light scattering and single particle counting techniques) and of the polished workpiece surface (using atomic force microscopy) was performed. The results show the final workpiece surface roughness is quantitatively correlated with the logarithmic slope of the distribution function for the largest particles at the exponential tail end of the PSD. Using the measured PSD, fraction of pad area making contact, and mechanical properties of the workpiece, slurry, and pad as input parameters, an Ensemble Hertzian Gap (EHG) polishing model was formulated to estimate each particle's penetration, load, and contact zone. The model is based on multiple Hertzian contact of slurry particles at the workpiece–pad interface in which the effective interface gap is determined through an elastic load balance. Separately, ceria particle static contact and single pass sliding experiments were performed showing ~1‐nm depth removal per pass (i.e., a plastic type removal). Also, nanoindentation measurements on fused silica were made to estimate the critical load at which plastic type removal starts to occur (P_crit~5 × 10^?5 N). Next the EHG model was extended to create simulated polished surfaces using the Monte Carlo method where each particle (with the calculated characteristics described above) slides and removes material from the silica surface in random directions. The polishing simulation utilized a constant depth removal mechanism (i.e., not scaling with particle size) of the elastic deformation zone cross section between the particle and silica surface, which was either 0.04 nm (for chemical removal) at low loads (<P_crit) or 1.0 nm (for plastic removal) at intermediate loads (>P_crit). The simulated surfaces quantitatively compare well with the measured rms roughness, power spectra, surface texture, absolute thickness material removal rate, and load dependence of removal rate.