BWR core-wide stability analysis with respect to dominant feedback mechanisms and characteristic poles

BWR core-wide stability is studied from the viewpoint of linear dynamic stability treated via poles of a closed-loop transfer function. The quantitative study is performed using a BWR noise model describing neutronic and thermal-hydraulic core dynamics. Transfer functions of neutron power to reactivity and core inlet flow are derived in explicit forms and their poles are evaluated both numerically and analytically. It is shown that the characteristic poles may be classed into three groups relating to neutronic process, fuel heat transfer and core void dynamics. In particular, the poles for the void dynamics take complex values and hence give rise to core-wide damped oscillation of neutron power. Furthermore, the study of characteristic poles serves for the stability analysis of the Ringhals-1 benchmark test data. It is shown and clarified that two stability indexes, decay ratio and resonance frequency, have clear dependence on reactor power and core inlet flow.     

Molecularly imprinted fluorescent-shift receptors prepared with 2-(trifluoromethyl)acrylic acid

Methacrylic acid (MAA) and 2-(trifluoromethyl)acrylic acid (TFMAA) were used to prepare molecularly imprinted polymers exhibiting diastereoselectivity for cinchona alkaloids. Fluorescent spectra of the cinchona alkaloid exhibit a characteristic shift through binding to these polymer particles, originating most likely from the highly acidic residues in the imprinted polymers acting as a proton donator. Our results show that TFMAA based imprinted polymers can be used as polymer reagents for quantitating the cinchona alkaloid bound to the polymers without bound/free separation.     

Atrazine-selective polymers prepared by molecular imprinting of trialkylmelamines as dummy template species of atrazine

Synthetic polymer receptors selective for atrazine have been prepared by molecular imprinting using trialkylmelamines as template molecules in place of atrazine. Trialkylmelamines were shown to be useful as templates for introducing affinity for atrazine into ethylene glycol dimethacrylate-methacrylic acid copolymers. The polymers showed the selective binding capacity for triazine herbicides including atrazine, whereas agrochemicals in other categories were not adsorbed to the imprinted polymers. The group selectivity demonstrated was comparable with that of the original atrazine imprinted polymers. Use of the nonagrochemical template molecules as a substitution to atrazine has made it possible to synthesize herbicide-receptor polymers free from troubles caused by analyte contaminants, which are desired for analytical applications.     

The application of the atomic force microscope to studies of medically important protozoan parasites

Both living and fixed specimens of the medically-important parasitic protozoa, Trypanosoma cruzi, Toxoplasma gondii, Giardia lamblia, Entamoeba histolytica, and Acanthamoeba spp. were studied by atomic force microscopy (AFM). The preparation of fixed specimens was similar to methods used for either scanning or transmission electron microscopy. AFM scanning was performed using both contact and tapping modes. A classical fixation procedure utilizing glutaraldehyde followed by ethanol dehydration was not suitable for all parasite species. AFM images could not be obtained from fixed samples of T. cruzi, T. gondii or E. histolytica. However, excellent topographic images could be obtained from specimens of G. lamblia and Acanthamoeba under identical conditions. Critical point drying permitted AFM imaging of both trypomastigote and epimastigote stages of T. cruzi. Phase imaging of T. cruzi elucidated unique surface details at a level of resolution not visible using any other imaging modalities. AFM elasticity map imaging of T. cruzi-infected and T. gondii-infected cells demonstrated that both parasites were markedly firmer than the surrounding host cell cytoplasm. The parasitophorous vacuole surrounding replicating T. gondii tachyzoites was also visualized by elasticity map imaging. These data suggest that although much remains to be learned about preparing parasitic protozoa for AFM imaging, the technique has the potential of providing unique and important insights into these disease causing organisms.     

A 56-nm CMOS 99-mm2 8-Gb Multi-Level NAND Flash Memory With 10-MB/s Program Throughput

A single 3.3-V only, 8-Gb NAND flash memory with the smallest chip to date, 98.8 mm², has been successfully developed. This is the world's first integrated semiconductor chip fabricated with 56-nm CMOS technologies. The effective cell size including the select transistors is 0.0075 mum² per bit, which is the smallest ever reported. To decrease the chip size, a very efficient floor plan with one-sided row decoder, one-sided page buffer, and one-sided pad is introduced. As a result, an excellent 70% cell area efficiency is realized. The program throughput is drastically improved to twice as large as previously reported and comparable to binary memories. The best ever 10-MB/s programming is realized by increasing the page size from 4kB to 8kB. In addition, noise cancellation circuits and the dual VDD-line scheme realize both a small die size and a fast programming. An external page copy achieves a fast 93-ms block copy, efficiently using a 1-MB block size     

Improvement of thickness uniformity and crystallinity of AlN films prepared by off-axis sputtering

We improved both the thickness uniformity and crystallinity of Aluminum nitride (AlN) films deposited by off-axis sputtering. The results in thickness uniformity and X-ray rocking curve full-width at half-maximum (FWHM) of AlN (0 0 0 2) are achieved to be ±0.2% and 1.4°, respectively on a 100 mm Si (1 0 0) substrate. The residual stress can be controlled from tensile to compressive by varying sputtering parameters such as gas pressure, RF power and DC bias voltage applied to a substrate without degradation in the crystallinity and thickness uniformity.     

A unifying framework for detecting outliers and change points from time series

We are concerned with the issue of detecting outliers and change points from time series. In the area of data mining, there have been increased interest in these issues since outlier detection is related to fraud detection, rare event discovery, etc., while change-point detection is related to event/trend change detection, activity monitoring, etc. Although, in most previous work, outlier detection and change point detection have not been related explicitly, this paper presents a unifying framework for dealing with both of them. In this framework, a probabilistic model of time series is incrementally learned using an online discounting learning algorithm, which can track a drifting data source adaptively by forgetting out-of-date statistics gradually. A score for any given data is calculated in terms of its deviation from the learned model, with a higher score indicating a high possibility of being an outlier. By taking an average of the scores over a window of a fixed length and sliding the window, we may obtain a new time series consisting of moving-averaged scores. Change point detection is then reduced to the issue of detecting outliers in that time series. We compare the performance of our framework with those of conventional methods to demonstrate its validity through simulation and experimental applications to incidents detection in network security.     

Postcolumn concentration in liquid chromatography. On-line eluent evaporation and analyte postconcentration in ion chromatography

On-line sample concentration by evaporation through a narrow-bore membrane tube is described. The device can be deployed just prior to the detector or the sample may be concentrated prior to injection. As solution flows through a solvent-permeable membrane tube, (heated) drying gas (nitrogen/air) flows outside it to remove the solvent. The removal rate increases with increasing sample residence time, drying gas flow rate, and temperature. Various membranes and three concentrator designs (a rectangular maze, a serpentine and a filament-filled helix, the last performing the best) were fabricated and tested for post- and preseparation applications in suppressed anion chromatography. An order of magnitude concentration factors are readily obtained. The present system involves active mass transport radially outward through the walls of a tube. This is a system in which many of the traditional paradigms of flow through a tubular conduit no longer hold true. Because the flow rate continuously varies along the tube, residence time does not scale linearly with residence volume or conduit length. The effects of such mass transport on the parabolic velocity profile of laminar flow remain unknown.     

Development and design of DC‐GIS

In order to realize a reliable, compact, and economical converter station for HVDC transmission, applications of gas insulated switchgear (GIS) for dc transmission lines are considered. The characteristics of dc gas insulation differ from those of ac. The behavior of metallic particles left in the enclosure is one of the largest differences. The accumulation of electrical charges on solid insulators is another essential factor in designing a DC‐GIS. Also, degradation of metal oxide arrester blocks under dc stress must be deliberated. Based on the fundamental studies, we developed the components of ± 500‐kV DC‐GIS. Electrical and mechanical performances of these components have been tested and proven to be satisfactory. Finally these components have been assembled into a full DC‐GIS and subjected to a long‐term voltage endurance test. In this paper, the design philosophy of ± 500‐kV DC‐GIS, details of the components, and the test results are described. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 51–61, 1999