High-precision methods and devices for in situ measurements of thermally induced aberrations in optical elements

An optical system that comprises two devices for remote measurements, a broadband optical interferometer and a scanning Hartmann sensor, is described. The results of simultaneous measurements with both devices and the results of numerical modeling of sample surface heating are presented.     

Thermally induced birefringence in Faraday devices made from terbium gallium garnet-polycrystalline ceramics

We have developed a model that describes thermally induced birefringence in polycrystalline ceramics that are exposed to a magnetic field. Conditions under which traditional compensation techniques (for glass and single crystals) can be effective for ceramics have been found. It is shown that a ceramic is almost equivalent to a [111]-oriented crystal if the ratio of the rod length to the grain size is approximately 300 or more. In particular, residual depolarization (after the compensation techniques are applied) is inversely proportional to this ratio, which is an important consequence of the random nature of thermally induced birefringence in ceramics.     

Transforming engineering knowledge through graph representations: transferring the Willis method to linkages and trusses

The paper introduces an approach for transforming methods and knowledge between different engineering fields through general discrete mathematical models, called graph representations, which carry engineering knowledge of specific systems. The idea is demonstrated by showing the transformation of the known method in planetary gear trains—the Willis method—to two other engineering systems: linkages and trusses. In doing so, two efficient methods were derived: one for analysing compound linkages, such as those containing tetrads, and another for compound trusses. These new methods were derived from two relations characterising graph representations: a representation that is common to two engineering fields and the duality relation between representations. The new approach underlying these transformations is shown to open new ways of conducting engineering research by enabling a systematic derivation of engineering knowledge through knowledge transformations between the graph representations.     

Structure-function relationships in Pt-Cr-H-ZSM-5 alloy catalysts

The activities of 0.5% Pt/H-ZSM-5 and 0.5% Pt/0.75% Cr/H-ZSM-5 catalysts for alkane hydrogenolysis have been compared. The presence of chromium suppresses propane hydrogenolysis by an order of magnitude, but has a much less pronounced effect on ethane hydrogenolysis. Catalyst characterisation by EXAFS and XPS indicates the formation of small alloy particles, typically containing 10 platinum and 3 chromium atoms. The change in catalytic activity is related to electronic structure modification rather than to an ensemble effect.     

The assessment of different models to predict the global solar radiation on a surface tilted to the south

Global and diffuse solar radiation intensities are, in general, measured on horizontal surfaces, whereas stationary solar conversion systems (both flat plate solar collector and PV) are tilted towards the sun in order to maximize the amount of solar radiation incident on the collector surface. Consequently, the solar radiation incident on a tilted surface must be determined by converting the solar radiation intensities measured on a horizontal surface to that incident on the tilted surface of interest. There exist a large number of models designed to perform such a conversion. 11 such models have been tested utilizing data measured in Beer Sheva, Israel. The data consist of hourly global and diffuse solar radiation on a horizontal surface, normal incidence beam and global radiation on a south-oriented surface tilted at 40°. The horizontal diffuse radiation measured using a shadow ring was corrected using four different correction models. This resulted in 44 model permutations. The individual model performance is assessed by an inter-comparison between the calculated and measured solar global radiation on the south-oriented surface tilted at 40° using both graphical and statistical methods. The relative performance of the different models under different sky conditions has been studied. Different grading systems have been applied in an attempt to score the relative performance of the models.     

A method for characterization and inter-comparison of sites with regard to solar energy utilization by statistical analysis of their solar radiation data as performed for three sites in the Israel Negev region

A method for the characterization and inter-comparison of sites with regard to their suitability for utilization of solar energy based upon the statistical analysis of their solar radiation intensities is presented. In this method each monthly data set of the daily global, horizontal beam and diffuse radiation intensities was analyzed and the following parameters were determined: monthly average daily radiation intensity, coefficient of variation, skewness and kurtosis. The values of the skewness and kurtosis have been applied, using generally accepted rules, to describe the distribution curves for each of the radiation intensity data sets. In addition, the same type of statistical analysis was applied to the monthly average daily ratios of the horizontal beam to global radiation, diffuse to global and the clearness index for the three sites. In this investigation, this statistical analysis method has been applied to the global and beam radiation measured at three sites located in the southern, Negev region of Israel, viz., Beer Sheva, Sde Boker and Eilat. The southern region of Israel is characterized by relatively high average daily irradiation intensities for both global and normal incidence radiation. They have been characterized with regard to the distribution of their intensity levels and a site inter-comparison has also been performed. An inter-comparison of the results of these analyses for the three sites has been performed on a monthly basis. The results of this analysis are used both to characterize and compare the composition of the solar radiation at the three sites under investigation. The results of this study will be presented in detail.     

One-shot learners using negative counterexamples and nearest positive examples

As some cognitive research suggests, in the process of learning languages, in addition to overt explicit negative evidence, a child often receives covert explicit evidence in form of corrected or rephrased sentences. In this paper, we suggest one approach to formalization of overt and covert evidence within the framework of one-shot learners via subset and membership queries to a teacher (oracle). We compare and explore general capabilities of our models, as well as complexity advantages of learnability models of one type over models of other types, where complexity is measured in terms of number of queries. In particular, we establish that “correcting” positive examples are sometimes more helpful to a learner than just negative (counter) examples and access to full positive data.     

Quantum Phase Transition in HTSC Thick Films: YBa2Cu3O x , YBa2Cu3O x (5 % Ag-Doped) in a Strong Pulsed Magnetic Field up to 32 T at Low Temperatures (58–100 K), Current Densities and Stress-Effect

We have researched the influence of pulsed magnetic fields up to 32 T on the magneto-resistance of thick films (50 Mk) of YBa₂Cu₃O _x and YBa₂Cu₃O _x (5 % Ag-doped) that were produced from synthesized powders. (Figs. 1–9): concentrate with 6.85–6.9 % O₂ and a tail fraction 6.5–6.6 % O₂. We observed a linear plot at currents of more than 1 mA at 77 K in YBa₂Cu₃O _x (5 % Ag-doped) at B>5 T and in the concentrate YBa₂Cu₃O _x samples with I=1 mA, T=68.2 K. Pulsed magnetic fields up to 32 T, at I=1 mA had practically no influence on the value of the magneto-resistance in the concentrate YBa₂Cu₃O _x specimens at T=57.9 K and up to 17 T for YBa₂Cu₃O _x (5 % Ag) at 77 K (Meissner effect). However, for B>17 T, YBa₂Cu₃O _x (5 % Ag) at 77 K demonstrates a tendency toward lower resistance. In the presence to 10 pulses in a cyclic pulsed magnetic field of 32 T, there is a sharp change of magnetic properties of an HTSC that can lead to nontrivial changes in the transition temperature, due to the strong mechanic stresses, sharp change value structure, and because one of the phases becomes superconducting (Figs. 3A, 3B). The behavior of the magnetoresistance of S-N-S contacts in pulsed magnetic fields is described via the system’s parallel resistance, R _n , and the inductance, L _S-N-S. Analysis of microscopic models of quantum phase transitions was made in a granular superconductor in an attempt to explain the results on the studied HTSC-films and to give a physical interpretation to the deduced parameters of some experiments on the basis of “spin (vortex) glass” (vortex ice).     

Room temperature passive mode-locked laser based on InAs/GaAs quantum-dot superlattice

Passive mode-locking is achieved in two sectional lasers with an active layer based on superlattice formed by ten layers of quantum dots. Tunnel coupling of ten layers changes the structural polarization properties: the ratio between the transverse electric and transverse magnetic polarization absorption coefficients is less by a factor of 1.8 in the entire electroluminescence spectrum range for the superlattice.     

Strong modification of Pt-CO interaction caused by alloying with chromium in Pt-Cr/HZSM-5 catalysts

The catalysts Pt/HZSM-5 and Pt-Cr/HZSM-5 are characterized by FTIR spectroscopy using CO as a probe molecule, and by transmission electron microscopy. The major fraction of the metal phase detected in the micrographs exhibits particles in the range of 1–3 nm uniformly distributed in the zeolite crystals. Nanodiffraction analysis of single particles confirmed the formation of fcc Pt-Cr alloy with lattice constanta = 0.386 nm. The infrared spectra at 300 K exhibit bands assigned to CO linearly bonded to zeolite-hosted metal particles at 2089 cm^–1 for Pt/HZSM-5, and at 2120 and 2092 cm^–1 for Pt-Cr/HZSM-5. The temperature increase to 610 K resulted in a strong shift of the 2089 cm^–1 band for Pt/HZSM-5 by 25 cm^–1 and a slight shift of the corresponding bands for Pt-Cr/HZSM-5 by 6 cm^–1. The differences are referred to different electron backdonation capacities of the CO binding Pt surface atoms of the metal particles. The lower capacity for the Pt-Cr/HZSM-5 sample is due to alloying in the metal particles.