Correlation Between Structural and Optical Properties of Composite Polymer/Fullerene Films for Organic Solar Cells

We investigate thin poly(3‐hexylthiophene‐2,5‐diyl)/[6,6]‐phenyl C₆₁ butyric acid methyl ester (P3HT/PCBM) films, which are widely used as active layers in plastic solar cells. Their structural properties are studied by grazing‐incidence X‐ray diffraction (XRD). The size and the orientation of crystalline P3HT nanodomains within the films are determined. PCBM crystallites are not detected in thin films by XRD. Upon annealing, the P3HT crystallinity increases, leading to an increase in the optical absorption and spectral photocurrent in the low‐photon‐energy region. As a consequence, the efficiency of P3HT/PCBM solar cells is significantly increased. A direct relation between efficiency and P3HT crystallinity is demonstrated.     

Notes on waves with negative phase velocity

Negative refraction is a wave phenomenon beyond geometrical optics - it depends on the way waves behave when their phase velocity reaches a zero. Various forms of linear wave processes in media can be concisely described in one wave equation that is inspired by the interpretation of a medium as an effective space-time geometry. Depending on the conformal factor of the effective metric, the waves may show positive or negative refraction. For electromagnetic waves in two-dimensional dielectrics the conformal factor corresponds to the impedance.     

A comparison between three simple crystallographic principles of precipitate morphology

The connection between the optimum shape and orientation relationship of precipitates in a solid is examined. Three simple criteria for precipitate morphology are compared and illustrated schematically: the principle that precipitate dimensions tend to be inverse to the magnitude of the transformation strain; the postulate that precipitates are bounded by unrotated planes (eigenplanes); and the proposal that interfaces are parallel to the planes of three independent dislocation loop arrays necessary to accommodate the transformation strain completely. These principles are illustrated for different orientation relationships, and it is shown that special features are displayed by invariant-line precipitates. The implications of these criteria for experimental studies of precipitate morphologies are discussed and their predictions compared with results from a recent study of lath-shaped precipitates in Cu-Cr alloys. This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Research in object-oriented manufacturing simulations:an assessment of the state of the art

Object-oriented programming (OOP) has been revolutionizing software development and maintenance. When applied to simulation of manufacturing systems, OOP also provides an opportunity for developing new ways of thinking and modeling. In this paper, we identify existing large-scale, persistent OOP-based research efforts focusing on manufacturing system simulation, and present an integrating framework for discussing the associated modeling abstractions, implementation strategies, common themes, and distinctive features. The goal is to identify the fundamental research and application issues, assess the current state of the art, and identify key research needs.     

Efficient immune responses in mice lacking N-region diversity

Mice with a null mutation in the terminal deoxynucleotidyl transferase (TdT) gene harbor immunoglobulin and T cell receptor repertoires essentially devoid of N-region diversity. Consequently, the CDR3 loops important for antigen recognition are shorter and considerably less diverse than those of wild-type controls. We find surprisingly normal immune responses in TdT0 mice, as regards both efficiency and specificity. This provokes a reconsideration of the assumption that N-region diversity is required for an effective T and B cell repertoire.     

Mobile robot localization: integrating measurements from atime-of-flight laser

This paper presents an algorithm for environment mapping by integrating scans from a time-of-flight laser and odometer readings from a mobile robot. The range weighted Hough transform (RWHT) is used as a robust method to extract lines from the range data. The resulting peaks in the RWHT are used as feature coordinates when these lines/walls are used as landmarks during navigation. The associations between observations over the time sequence are made in a systematic way using a decision directed classifier. Natural geometrical landmarks are described in the robot frame together with a covariance matrix representing the spatial uncertainty. The map is thus built up incrementally as the robot moves. If the map is given in advance, the robot can find its location and navigate relative to this a priori given map. Experimental results are presented for a mobile robot with a scanning range measuring laser having 2-cm resolution. The algorithm was also used for an autonomous plastering robot on a construction site. The sensor fusion algorithm makes few erroneous associations     

Repetitively pulsed Nd-glass slab lasers

The possibility of obtaining high laser output energies at a 1.32-μm wavelength using thin LiNdLa phosphate glass slabs with a high Nd³⁺ concentration is discussed. In the experiments, 3×14×125-mm slabs were prepared from LiNdLa phosphate glass with a Nd-concentration of 1.2×10²¹ cm^-3. The facets of the slabs were not antireflection-coated. They were tested in a silver-coated quartz tube reflector of 25-mm diameter and pumped by 450-μs pulses from a flash lamp with a 120-mm arc length. In this construction the light, which passes through the slab, returns to it after reflection from the tube surface. Most of the radiation falls on the wider side of the slab at large angles of incidence, thus maximizing its path inside the slab. The quartz reflector was water cooled. The 150-mm laser resonator was formed by two flat mirrors. At 1.32-μm lasing wavelength an output mirror of r=95% reflectivity was used with less than 10% reflectivity at 1.32 μm