Turbulence Closure with a Topography-parameter-free Single Equation Model

A new topography-parameter-free turbulence closure, based on a transport equation for the pseudo eddy viscosity, is described. The model is tested against experimental data of several flow cases across the Mach number range and compared to Menter's single equation model and to the Spalart-Allmaras model. The main conclusion is that the new closure outperforms the other two models in both low and high speed flows.     

The Examination Where the Student Asks the Question

The Examination where the Student Asks the Questions (ESAQ) is an innovative, system-oriented teaching/evaluation strategy ideated, developed and successfully implemented by the author, initially within the teaching of freshman chemistry (general and organic) in a four-year college. It constitutes a reflective, multidimensional response to the urgent need for effective teaching and evaluation strategies which will foster question asking, and higher order cognitive skills (HOCS). Such strategies are, ideally, relevant, challenging, and compatible with the new goals of science teaching and student performance evaluation. The core element of the ESAQ is a prearranged oral examination in which the course professor is examined by students, using home-prepared, written questions. Our experience suggests that the ESAQ can be creatively adopted and successfully implemented in different contexts of science teaching worldwide and would benefit both educators and students. The increase in the HOCS capacity of students is attainable.     

Cyclic reservation schemes for efficient operation of multiple-queue single-server systems

We study two new cyclic reservation schemes for the efficient operation of systems consisting of a single server and multiple queues. The schemes are the Globally Gated regime and the Cyclic-Reservation Multiple-Access (CRMA). Both procedures possess mechanisms for prioritizing the queues and lend themselves to a closed-form analysis. The combination of these two properties allows for effective and efficient operation of the systems, for which we provide a thorough delay analysis and derive simple rules for optimal operation.     

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.