BRDF reference standards for the infrared

A comparison between various recommended reference standards of diffuse reflectance in the IR is presented. It is shown that at a wavelength of 10.6 μm sulfur is the most Lambertian of the tested samples, although its powdery consistence makes it less suitable for use as a standard. Flame sprayed aluminum, with or without gold coating, also approaches a Lambertian surface and is suitable for use as a standard for BRDF measurements at 10.6 μm. Results for the BRDF of sulfur, gold-coated sandpaper, a commercial diffuse gold surface (by Labsphere) and flame sprayed aluminum are presented.     

Empowerment of Elementary School Teachers to Implement Science Curriculum Reforms

The authors evaluate the Science-Technology-Society (STS) views, attitudes and literacy of Israeli elementary science school teachers in three in-depth, longitudinal inservice programs. The programs were aimed at promoting teacher empowerment for the implementation, on a national scale, of a new STS-oriented elementary science curriculum reform. By using a blend of qualitative and quantitative research methods, the effectiveness of these similar but not identical programs has been determined. It was found that appropriately designed inservice science teacher training courses did induce a shift in the STS views/positions, beliefs/attitudes and literacy of elementary science teachers, and that this shift can be increased by using research-based data, obtained within an ongoing formative education process.     

Cell Identification Codes for Tracking Mobile Users

The minimization of the wireless cost of tracking mobile users is a crucial issue in wireless networks. Some of the previous strategies addressing this issue leave an open gap, by requiring the use of information that is not generally available to the user (for example, the distance traveled by the user). For this reason, both the implementation of some of these strategies and the performance comparison to existing strategies is not clear. In this work we propose to close this gap by the use of Cell Identification Codes (CIC) for tracking mobile users. Each cell periodically broadcasts a short message which identifies the cell and its orientation relatively to other cells in the network. This information is used by the users to efficiently update their location. We propose several cell identification encoding schemes, which are used to implement different tracking strategies, and analyze the amount of information required by each tracking strategy. One of our major results is that there is no need to transmit a code which is unique for each cell. For example, a 3 bits CIC is sufficient to implement a distance-based tracking strategy in a two-dimensional system. In addition, we propose a combination of timer and movement tracking strategy, based on either a one-bit or a two-bit CIC, depending on system topology and user mobility. An important property of our framework is that the overall performance cost, and hence its comparison to existing methods, is evaluated for each tracking strategy. The CIC-based strategies are shown to outperform the geographic-based method currently used in existing networks, and the timer-based method, over a wide range of parameters. Moreover, this superiority increases as the number of users per cell increases.     

Intensity Capping: a simple method to improve cross-correlation PIV results

A common source of error in particle image velocimetry (PIV) is the presence of bright spots within the images. These bright spots are characterized by grayscale intensities much greater than the mean intensity of the image and are typically generated by intense scattering from seed particles. The displacement of bright spots can dominate the cross-correlation calculation within an interrogation window, and may thereby bias the resulting velocity vector. An efficient and easy-to-implement image-enhancement procedure is described to improve PIV results when bright spots are present. The procedure, called Intensity Capping, imposes a user-specified upper limit to the grayscale intensity of the images. The displacement calculation then better represents the displacement of all particles in an interrogation window and the bias due to bright spots is reduced. Four PIV codes and a large set of experimental and simulated images were used to evaluate the performance of Intensity Capping. The results indicate that Intensity Capping can significantly increase the number of valid vectors from experimental image pairs and reduce displacement error in the analysis of simulated images. A comparison with other PIV image-enhancement techniques shows that Intensity Capping offers competitive performance, low computational cost, ease of implementation, and minimal modification to the images.     

Regulating the size and stabilization of lipid raft-like domains and using calcium ions as their probe

We apply a means to probe, stabilize, and control the size of lipid raft-like domains in vitro. In biomembranes the size of lipid rafts is ca. 10-30 nm. In vitro, mixing saturated and unsaturated lipids results in microdomains, which are unstable and coalesce. This inconsistency is puzzling. It has been hypothesized that biological line-active surfactants reduce the line tension between saturated and unsaturated lipids and stabilize small domains in vivo. Using solution X-ray scattering, we studied the structure of binary and ternary lipid mixtures in the presence of calcium ions. Three lipids were used: saturated, unsaturated, and a hybrid (1-saturated-2-unsaturated) lipid that is predominant in the phospholipids of cellular membranes. Only membranes composed of the saturated lipid can adsorb calcium ions, become charged, and therefore considerably swell. The selective calcium affinity was used to show that binary mixtures, containing the saturated lipid, phase separated into large-scale domains. Our data suggests that by introducing the hybrid lipid to a mixture of the saturated and unsaturated lipids, the size of the domains decreased with the concentration of the hybrid lipid, until the three lipids could completely mix. We attribute this behavior to the tendency of the hybrid lipid to act as a line-active cosurfactant that can easily reside at the interface between the saturated and the unsaturated lipids and reduce the line tension between them. These findings are consistent with a recent theory and provide insight into the self-organization of lipid rafts, their stabilization, and size regulation in biomembranes.     

New spectra of strongly minimal theories in finite languages

We describe strongly minimal theories T_n with finite languages such that in the chain of countable models of T_n, only the first n models have recursive presentations. Also, we describe a strongly minimal theory with a finite language such that every non-saturated model has a recursive presentation.     

The dynamic nature of amyloid beta (1-40) aggregation

In this paper, we characterize the dynamic nature of the full amyloid beta (1-40) (Aβ (1-40)) aggregates. We labeled the peptide with either 5-carboxytetramethylrhodamine (TAMRA) or with fluorescein-isothiocyanate (FITC). The labeled peptides were mixed after separate fibrillization, and the dynamic changes in the structure of the fibrils were imaged using confocal microscopy. Fluorescence resonance energy transfer (FRET) measurements showed that the Aβ (1-40) peptides detach from and reattach to the fibrils in a biologically relevant timescale (days). With time, the two peptides mix at the molecular level. This process is concentration dependent and occurs primarily in the external parts of the aggregates with a half time between 4 and 7 days. This study shows that the combination of confocal microscopy and FRET analysis is a facile method for studying dynamic processes in supra-molecular aggregates.     

Electrical body forces and electrical tractions in the nonlinear response of ferroelectric actuators

The influence of the electrical body forces and electrical tractions on the nonlinear response of ferroelectric stack actuators is analytically investigated. While the role of the electrical body forces and tractions in the response of piezoelectric actuators is well documented (and in many cases is not significant), the questions of their effect on ferroelectric active materials is still of interest. To examine this influence, the analytical model for the electro-mechanical behavior of a ferroelectric stack actuator is augmented to account for the electrical body forces along the actuator and the electrical tractions at the material–electrode interfaces. Focusing on the effect of the electrical forces and tractions on the ferroelectric domain switching phenomenon, the model is used for the numerical analysis of a ferroelectric layer and for the comparison with the case that neglects the electrical body forces and traction. The comparison theoretically designates cases in which the effect of the electrical body forces and tractions may be prominent and other cases where the classical approach that neglects these effects can be adopted.     

LU factorizations, q = 0 limits, and p-adic interpretations of some q-hypergeometric orthogonal polynomials

For little q-Jacobi polynomials and q-Hahn polynomials we give particular q-hypergeometric series representations in which the termwise q = 0 limit can be taken. When rewritten in matrix form, these series representations can be viewed as LU factorizations. We develop a general theory of LU factorizations related to complete systems of orthogonal polynomials with discrete orthogonality relations which admit a dual system of orthogonal polynomials. For the q = 0 orthogonal limit functions we discuss interpretations on p-adic spaces. In the little 0-Jacobi case we also discuss product formulas. Dedicated to Dick Askey on the occasion of his seventieth birthday. 2000 Mathematics Subject Classification Primary—33D45, 33D80 Work done at KdV Institute, Amsterdam and supported by NWO, project number 613.006.573.