Transparent conducting silver nanowire networks

We present a transparent conducting electrode composed of a periodic two-dimensional network of silver nanowires. Networks of Ag nanowires are made with wire diameters of 45-110 nm and a pitch of 500, 700, and 1000 nm. Anomalous optical transmission is observed, with an averaged transmission up to 91% for the best transmitting network and sheet resistances as low as 6.5 Ω/sq for the best conducting network. Our most dilute networks show lower sheet resistance and higher optical transmittance than an 80 nm thick layer of ITO sputtered on glass. By comparing measurements and simulations, we identify four distinct physical phenomena that govern the transmission of light through the networks: all related to the excitation of localized surface plasmons and surface plasmon polaritons on the wires. The insights given in this paper provide the key guidelines for designing high-transmittance and low-resistance nanowire electrodes for optoelectronic devices, including thin-film solar cells. For the latter, we discuss the general design principles to use the nanowire electrodes also as a light trapping scheme.     

Nanostructured porous silicon films for terahertz optics

A simple technique is reported to create 31 and 45 μm thick, graded-index Si films in the form of nanospirals on a Si substrate using a dynamic, oblique angle deposition technique. We show that the success in producing such a thick, nanostructured film without delamination from the Si substrate is primarily due to the nano-porous nature of the film which effectively eliminates the stress generated during growth. Effective refractive indices of 1.9 and 2.1 were extracted from the terahertz time-domain reflectivity data, which correspond to 57% and 51% porosity for the 31 and 45 μm thick films, respectively. The gradient of porosity through the film was modeled to describe quantitatively the terahertz reflectance data in the 0.2-2.0 THz regime.     

Nonuniform and Unsteady Solute Transport in Furrow Irrigation. I: Model Development

A cross-section-averaged advection-dispersion equation (ADE) model was developed to simulate the transport of fertilizer in furrow irrigation. The advection and dispersion processes were solved separately at each time step by implementing a method of characteristics with cubic-spline interpolation and a time-weighted finite-difference scheme, respectively. The upstream boundary condition was a prescribed concentration. Downstream, a zero-flux boundary condition during advance and a concentration gradient following completion of advance were prescribed. Local pseudosteady state was assumed in order to apply Fischer’s longitudinal dispersion equation under nonuniform and unsteady furrow flow conditions. Statistical parameters were used to evaluate the ADE model performance.     

Diagnosing Transformers Getting to the Heart of the Matter

From drying your hair in the morning to using your computer at work to watching a DVD on your big screen TV at night, transformers are involved in the many things we do every day. As the name implies, transformers transform electricity from one voltage to another. In the early days of electricity, it was costly to move electricity from Point A to Point B. As a result, people who wanted electricity had to live very close to a power plant. At the 1893 World’s Fair, George Westinghouse and Nikola Tesla introduced alternating current, or AC power, to the world. Up until this time, Thomas Edison’s direct current, or DC power, was the only form of electricity in the United States. Among the many positive attributes of AC power, engineers discovered that if the power could be converted (or transformed) to use higher voltage and lower current, then it would be cost-effective to transport the electricity over longer distances from a power plant to a home or business. This discovery and the invention of the transformer led to the power distribution system as we know it today. Transformers are the backbone of our electrical transmission and distribution system. Of these, high- and medium-voltage transformers are the most complex and the most expensive pieces of equipment in this system. Consequently, it is important that transformers be properly constructed and maintained to ensure a long service life.     

A quadratic approximation for structural topology optimization

In topology optimization, it is customary to use reciprocal‐like approximations, which result in monotonically decreasing approximate objective functions. In this paper, we demonstrate that efficient quadratic approximations for topology optimization can also be derived, if the approximate Hessian terms are chosen with care. To demonstrate this, we construct a dual SAO algorithm for topology optimization based on a strictly convex, diagonal quadratic approximation to the objective function. Although the approximation is purely quadratic, it does contain essential elements of reciprocal‐like approximations: for self‐adjoint problems, our approximation is identical to the quadratic or second‐order Taylor series approximation to the exponential approximation. We present both a single‐point and a two‐point variant of the new quadratic approximation. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and psychometric evaluation of the Yale–Brown Obsessive-Compulsive Scale—Second Edition.

The Yale–Brown Obsessive-Compulsive Scale (Y-BOCS; Goodman, Price, Rasmussen, Mazure, Delgado, et al., 1989) is acknowledged as the gold standard measure of obsessive-compulsive disorder (OCD) symptom severity. A number of areas where the Y-BOCS may benefit from revision have emerged in past psychometric studies of the Severity Scale and Symptom Checklist. Therefore, we created the Yale–Brown Obsessive-Compulsive Scale—Second Edition (Y-BOCS–II) by revising the Severity Scale item content and scoring framework, integrating avoidance into the scoring of Severity Scale items, and modifying the Symptom Checklist content and format. One hundred thirty treatment-seeking adults with OCD completed a battery of measures assessing OCD symptom severity and typology and depressive and anxious symptomology. Interrater and test–retest reliability were assessed on a subsample of participants. The Y-BOCS–II showed strong internal consistency for the Symptom Checklist (Kuder–Richardson-20 = .91) and Severity Scale (α = .89). Test–retest and interrater reliabilities were both high (intraclass correlations > .85). Confirmatory factor analyses did not show adequate fit with previous models of the Y-BOCS. Exploratory factor analysis revealed a two-factor solution generally consistent with the Obsession and Compulsion Severity subscales. Construct validity was supported by strong correlations with clinician-rated measures of OCD symptom severity and moderate correlations with measures of worry and depressive symptoms. Taken together, the Y-BOCS–II has excellent psychometric properties in assessing the presence and severity of obsessive-compulsive symptoms. Although the Y-BOCS remains a reliable and valid measure, the Y-BOCS–II may provide an alternative method of assessing symptom presence and severity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Terminal Distribution

Could the late 20th-century rejection of Modernist planning, and along with it the notion of a ‘universal subject’, mean that urban designers and architects might have lost sight of who they are designing cities for? Albert Pope sets out on a search to define the contemporary ‘who’ and finds some answers in Michel Foucault's notion of the historically grounded subject. Copyright © 2008 John Wiley & Sons, Ltd.