Well-type phoswich counter for low-flux X-ray/γ-ray detection

Phoswich counters that can detect low-flux hard-X-ray/γ-ray from localized sources are described. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The first model counter was built by using a new scintillator, gadolinium silicate (GSO), in the decision part and CsI(Tl) in the shielding part. A detector system consisting of 64 such phoswich counters (total area ~740 cm²) was flown onboard a balloon, setting a limit to the ⁵⁷Co line flux from SN 1987A, at ~10^-4 cm^-2 s The sensitivity for continuum flux was around a few ×10 ^-6 cm^-2 s^-1 keV^-1 between 100 and 200 keV. In the second model, CsI(Tl) was replaced by bismuth germanate (BGO), and radioactive contaminations in GSO were reduced. Improvements are planned to reach a sensitivity (3σ) around 5×10^-7 cm^-1 s^-1 keV^-1 for the continuum     

APPLICATION OF GASndashLIQUID TWO-PHASE CROSS-FLOW FILTRATION TO PILOT-SCALE METHANE FERMENTATION

ABSTRACT

As part of a national project, “Aqua-Renaissance '90,” by the MITI, a pilot-scale evaluation of membrane-enhanced anaerobic fermentation, has progressed for the wastewater from a pulp and paper mill. A novel membrane filtration system was newly proposed with the aim of saving energy. That is, a gas-liquid two-phase cross-flow filtration which was generated with liquid circulation by an air-lift pump effect, was combined in the anaerobic bioreactor. It was confirmed that the membrane filtration not only offered very stable and large permeate flux, but enhanced the processing efficiency by retaining the microorganisms in the bioreactor. Furthermore, the power consumption per unit permeate volume in the membrane system of 1.78 kWh/m³ was achieved. which was a very highperformance result from the viewpoint of saving energy, as compared with 3ndash;5 kWh/m³ of conventional liquid single-phase cross-flow filtration.     

Envelope analysis of nonlinear electronic circuits based on harmonic balance method

We propose here a Spice‐oriented envelope analysis based on the HB (harmonic balance) method, where Fourier coefficients are assumed to be slowly varying. The Fourier expansions of nonlinear devices are executed by MATLAB in the symbolic forms. In this time, the nonlinearities need to be approximated by the polynomial functions. The determining equation of the HB method is formulated as Sine–Cosine circuit in the form of schematic diagram using ABMs (analog behavior models) of Spice. Each sub‐circuit corresponding to the higher harmonic component is almost the same circuit topology as the original one and has dynamic elements such as capacitors and inductors. The Sine–Cosine circuit can be solved by the transient analysis of Spice. Thus, our method is rather a symbolic approach in the meaning that the HB determining equation is given by the schematic diagram of Spice. Our method can be easily applied to the analysis of middle order of nonlinear communication circuits such as mixers and amplitude modulators and to the analysis of interesting phenomena in the nonlinear oscillations. After many simulation experiments, the results show that our envelope analysis is about 50 times faster than the direct transient analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

Improvement of electrical characteristics of local BOX MOSFETs by heavily doped structures and elucidation of the related mechanism

We proposed heavily doped silicon between insulators (HDSBI) MOSFETs to improve electrical characteristics of local BOX MOSFETs by using simple structures that combine local BOX regions with additional doped regions. HDSBI MOSFETs have heavily doped regions between local BOX regions, in which acceptors or traps are introduced. Simulated electrical characteristics demonstrated that they can suppress the SCEs and the kink effect, as well as the self-heating effect (SHE), which is suppressed by conventional local BOX MOSFETs. We elucidated how the additional doped regions in HDSBI MOSFETs suppress the SCEs and the kink effect. We concluded that HDSBI MOSFETs are suitable for applications, such as multi-purpose system-on-chip on which both short-channel logic circuits and high drive current circuits are integrated.     

Relationship between Mutagenicity of Heterocyclic Aromatic Amines and Stability of Their DNA Adducts: A Study by Semi-empirical Molecular Orbital Method

Quantitative structure-mutagenicity correlations were investigated for heterocyclic aromatic amines (HCAs) by use of a DNA model with three-base pairs. DNA adducts of thirteen HCAs were optimized by the PM3 method and energy decrease, ΔE, of each HCA due to formation of a DNA adduct was obtained as the stability of the adduct. The calculations for the HCA-DNA adducts revealed the interaction between HCA's methyl group and DNA's phosphate, which plays an important role in the stabilization of the adducts. The ΔE values plotted against the logarithm of HCA's mutagenicity, M, provided an almost straight line with the regression coefficient (R) of ?0.89 (R ²= 0.79). This good correlation suggests that binding reaction between HCA's nitrenium ion and DNA is an important rate-determining step in the metabolic transformation of HCAs.     

Stabilization of free and immobilized enzymes using hyperthermophilic chaperonin

Chaperonins suppress the denaturation of proteins and promote protein folding in vivo. Because hyperthermophilic chaperonins are expected to be used as a stabilizer for proteins, the effects of a group II chaperonin from a hyperthermophilic archaeum, Thermococcus strain KS-1 (T. KS-1 cpn), on the stabilization of mesophilic and thermophilic free enzymes and an enzyme co-immobilized with T. KS-1 cpn were studied. T. KS-1 cpn prevented the thermal inactivation of yeast alcohol dehydrogenase (ADH), jack bean urease, and Thermus flavus malate dehydrogenase (MDH) at high temperatures. T. KS-1 cpn also improved the long-term stability of ADH at lower temperatures. Moreover, the residual ADH activity of ADH co-entrapped with T. KS-1 cpn was improved and maintained at a higher level than that of the entrapped ADH without chaperonin. T. KS-1 cpn is useful for the stabilization of free and immobilized enzymes and applicable to various fields of biotechnology.     

A 45-nm Bulk CMOS Embedded SRAM With Improved Immunity Against Process and Temperature Variations

The variation tolerant assist circuits of an SRAM against process and temperature are proposed. Passive resistances are introduced to the read assist circuit with replica memory transistors to lower the wordline voltage accurately reflecting the process and temperature variations. For the sake of not only enlarging the write margin but also reducing power consumption and speed overhead, the divided dynamic power-line scheme based on a charge sharing is adopted. Test chips of 512-Kb SRAM macros and isolated memory cell TEGs are fabricated using 45-nm bulk CMOS technology. Two types of 6-T SRAM cells, whose sizes were 0.245 mum² and 0.327 mum² were designed and evaluated. From the measurement results, we achieved over 100-mV improvement for static noise margin, and 35 mV for write margin for both SRAM cells at 1.0-V worst condition by using assist circuitry. It enables the wordline level to keep higher voltage at the slowest condition than the typical process condition, which results in 83% improvement of the cell current compared with the conventional assist circuit. Furthermore, the minimum operating voltage in the worst case condition was improved by 170 mV, confirming a high immunity against process and temperature variations with less than 10% area overhead.     

Evaluation of a 2k CCD camera with an epitaxially grown CsI scintillator for recording energy-filtered electron cryo-micrographs

Zero-loss imaging of frozen-hydrated specimens requires a detector with high sensitivity, a low noise level and high spatial resolution, because more electrons are scattered inelastically than elastically by cryo-specimens and the number of electrons detected is approximately 1/4 of incident electrons after energy filtering. Cameras using charge-coupled devices (CCDs) are good candidates due to their high sensitivity. They have been used mainly to record electron diffraction patterns for electron crystallography due to their limited spatial resolution but recently used for acquiring direct images due to their convenience. The spatial resolution has been limited by the characteristics of a phosphor that is necessary to convert high-energy electrons to photons and the coupling. We adopted a CsI scintillator with good modulation transfer function (MTF), which was epitaxially grown from each of optical fibres. The stripes of carbon graphite with 3.4 A spacing and 1.4 A stripes of gold thin crystals could be recorded with a magnification of 240,000x and 560,000x at 200 kV, respectively. A computed Fourier transform of an image of a frozen-hydrated crystal of catalase containing about 1000 units showed diffraction spots at spatial frequencies of 1/9.6 A(-1) up to 1/8 A(-1) without background subtraction, when the image was recorded at 140,000x. These results show that the resolution of the developed camera was good enough to record images. Our used test method for MTF determination may be useful for others.