Probabilistic enhancement of approximate indexing in metric spaces

Some approximate indexing schemes have been recently proposed in metric spaces which sort the objects in the database according to pseudo-scores. It is known that (1) some of them provide a very good trade-off between response time and accuracy, and (2) probability-based pseudo-scores can provide an optimal trade-off in range queries if the probabilities are correctly estimated. Based on these facts, we propose a probabilistic enhancement scheme which can be applied to any pseudo-score based scheme. Our scheme computes probability-based pseudo-scores using pseudo-scores obtained from a pseudo-score based scheme. In order to estimate the probability-based pseudo-scores, we use the object-specific parameters in logistic regression and learn the parameters using MAP (Maximum a Posteriori) estimation and the empirical Bayes method. We also propose a technique which speeds up learning the parameters using pseudo-scores. We applied our scheme to the two state-of-the-art schemes: the standard pivot-based scheme and the permutation-based scheme, and evaluated them using various kinds of datasets from the Metric Space Library. The results showed that our scheme outperformed the conventional schemes, with regard to both the number of distance computations and the CPU time, in all the datasets.     

Direct Measurements of Terahertz Meta-atoms with Near-Field Emission of Terahertz Waves

We present the direct measurements of terahertz meta-atoms, an elementary unit of metamaterials, by using locally generated terahertz waves in the near-field region. In contrast to a conventional far-field terahertz spectroscopy or imaging, our technique features the localized emission of coherent terahertz pulses on a sub-wavelength scale, which has a potential for visualizing details of dynamics of each meta-atom. The obtained data show the near-field coupling among the meta-atoms and the impact of the electric field distribution from the excited meta-atom to neighbor meta-atoms. The observable LC resonance response is enhanced with an increase of numbers of meta-atoms. Furthermore, our approach also has a potential for visualizing the individual mode of meta-atom at different terahertz irradiation spots. These data can help us to understand the important role of the meta-atom in metamaterials and develop the novel terahertz components and devices such as active terahertz metamaterial and compact, high-sensitive bio-sensor devices.     

Synthesis of alternating polyamide esters by melt and solution polycondensations of N,N′-Di(6-hydroxycaproyl) diamines and N-6-hydroxycaproyl aminoalcohol with terephthalic and adipic dimethyl esters and dichlorides

Alternating polyamide esters of structures A and B were obtained by melt polymerization of dimethyl adipate and terephthalate or by solution polymerization of adipoyl and terephthaloyl chlorides, with N,N′-di(6-hydroxycaproyl)diamines and an N-6-hydroxycaproyl aminoalcohol: where R₁ is selected from dimethylene, hexamethylene, and p-phenylene radicals, and R₂ is selected from tetramethylene or p-phenyl radical. Polyamide esters of structure A′ were also prepared: Average values of melting points of the resulting polyamide esters were dependent on the starting diacid derivatives, amide diols, and methods of polymerizations as follows: where CPZ, CHD, CED, and CPPD are N,N′-di(6-hydroxycaproy1)-, each in this order: piperazine, hexamethylenediamine, ethylenediamine, and p-phenylenediamine. ECA is N-(2-hydroxyethyl)6-hydroxycaproamide. For a given polyamide ester obtained from the same starting materials and by the same method of polymerization, the melting points increased with inherent viscosities. Polyamide esters of high molecular weight were obtained from CHD with both adipic and terepbthalic derivatives both by melt and solution polymerizations. Polymerizations of the other amide diols gave lower molecular weights. Solution polymerization gave colorless or light-colored polymers, while melt polymerization gave deeper-colored polymers.