Development and Comparison of Two Types of Cryogen-Free Dilution Refrigerator

Dilution refrigerators are an important tool used in solid state and quantum fluid physics for cooling to temperatures below 0.3 K. Conventional dilution refrigerators consume a lot of liquid helium, which has to be recharged in a helium bath every few days. Cryogen-free dilution refrigerators, however, do not use liquid helium and then automatic operation by electricity can be possible from room temperature to the mK region. In near future, therefore, most conventional dilution refrigerators will be replaced by cryogen-free refrigerators because they are easy to operate, do not require maintenance and do not consume helium. We have developed two types of cryogen-free dilution refrigerator. One is directly cooled by a pulse tube refrigerator in the same cryostat using copper thin wires as a thermal link, and the other is cooled by a separate Gifford McMahon refrigerator using circulating helium gas through a flexible syphon tube. The latter has been developed as a vibration-free cryogen-free dilution refrigerator. These two types of cryogen-free dilution refrigerator are compared considering several key points: base temperature, precooling time, minimum temperature and vibration amplitude.     

A 3.8-ns CMOS 16×16-b multiplier using complementarypass-transistor logic

A 3.8-ns, 257-mW, 16×16-b CMOS multiplier with a supply voltage of 4 V is described. A complementary pass-transistor logic (CPL) is proposed and applied to almost the entire critical path. The CPL consists of complementary inputs/outputs, an nMOS pass-transistor logic network, and CMOS output inverters. The CPL is twice as fast as conventional CMOS due to lower input capacitance and high logic functionality. Its multiplication time is the fastest ever reported, even for bipolar and GaAs ICs, and it can be enhanced further to 2.6 ns with 60 mW at 77 K     

Investigation of the cause of peculiar irradiation behavior of 9Cr-ODS steel in BOR-60 irradiation tests

Four experimental fuel assemblies (EFAs) containing 9Cr-ODS steel cladding fuel pins were previously irradiated in the BOR-60 to demonstrate the in-reactor performance of 9Cr-ODS steel for use as fuel cladding tubes. One of the EFAs achieved the best data, a peak burn-up of 11.9at% and a neutron dose of 51 dpa, without any microstructure instability or any fuel pin rupture. On the other hand, in another EFA (peak burn-up, 10.5at%; peak neutron dose, 44 dpa), peculiar irradiation behaviors, such as microstructure instability and fuel pin rupture, occurred. Investigations of the cause of these peculiar irradiation behaviors were carried out. The detection sensitivity in an ultrasonic inspection test was shown to be low for the metallic Cr and metallic Fe inclusions. The peculiar microstructure change reappeared with high-temperature thermal-aging of the 9Cr-ODS steel containing metallic Cr inclusions. The strength and ductility of the defective part containing metallic Cr inclusions were appreciably lower than those of a standard part without the inclusions. The combined effects of matrix Cr heterogeneity (presence of metallic Cr inclusions) and high-temperature irradiation were concluded to be the main cause of the peculiar microstructure change in 9Cr-ODS steel cladding tubes in the BOR-60 irradiation tests. They contributed to the fuel pin rupture.     

Impurity Scattering Effect on Superfluid Phases of 3He in 97.5% Porous Silica Aerogel

No Heading NMR studies of superfluid ³He in 97.5% aerogel have been performed in a magnetic field of 28.4 mT. A small-angle neutron scattering experiment on the structure of the aerogel shows that the average separation distance of silica strands is 54 nm. The aerogel strands were covered with a few layers of solid ³He whose magnetization shows Curie-Weiss behaviour. On cooling process A-like phase appeared at suppressed superfluid transition temperature T_C^aero and B-like phase appeared at lower temperatures although only the B-like phase was observed up to T_C^aero on warming process above 2.1 MPa. The superfluid transitions in aerogel always occur below the AB phase transition temperature of bulk liquid at all pressures. An isotropic inhomogeneous scattering model(IISM) proposed by Thuneberg et al. explained well the observed suppressed T_C^aero in 97.5% with the radius 59 nm of voids in this model. This radius is similar with the average strand separation distance of 54 nm measured in the structural analysis. This similarity of two lengths shows the connection of the suppression of T_C^aero with the actual average separation distance of the silica strands.PACS numbers: 67.57.Pq, 67.80.Jd     

Investigation on high temperature vapor pressure of UO2 containing simulated fission-product elements

During the hypothetical core disruptive accident (HCDA) of a fast breeder reactor (FBR), the temperature of the fuel would rise above 3000 K. The experimental data concerning the saturated fuel vapor pressure are necessary for the analysis of the HCDA. In this study, the UO₂ containing Cs, Ba, Ag, or Sn was used to simulate the irradiated fuel in the FBR.The saturated vapor pressure of pure UO₂ and UO₂ containing Cs, Ba, Ag, or Sn at 3000 to 5000 K was measured dynamically with a pulse laser and a torsion pendulum. The surface of a specimen on the pendulum was heated to eject vapor by the injection of a giant pulse ruby laser beam. The pressure of the ejected vapor was measured by both the maximum rotation angle of the pendulum and the duration of vapor ejection. The saturated vapor pressure was theoretically calculated by using the ejected vapor pressure. The surface temperature of the specimen was estimated from the irradiated energy density measured with a laser energy meter.The saturated vapor pressure of UO₂ at 3640 to 5880 K measured in this study was near the extrapolated value of Ackermann's low temperature data. The vapor pressure of UO₂ containing Cs, Ba, Ag or Sn was higher than that of UO₂. The saturated vapor pressure of UO₂ and a solid fission products system was calculated by using these experimental data.     

Mechanisms of solidification and subsequent embrittlement of dephosphorization slag used in a subtidal zone as an alternative to sea sand and prevention of solidification by adding dredged soil

In the recent years, steelmaking slag is attracting attention as suitable materials for restoration of estuary ecosystems. However, there is concern about solidification when the material is applied to create seagrass beds. In this study, dephosphorization slag (DePS) was immersed into seawater for 10 months to examine the solidification processes and its mechanisms to control the strength of solidification. The hypothesis in this study is that solidification could be alleviated by adding dredged soil to the DePS. After 5 months of immersion, the shear strength of the DePS increased from 1.8 to 5.0 kN/m²; however, its shear strength decreased significantly to 3 kN/m² after 10 months. Furthermore, after 5 months, reddish color was observed on the surface of the DePS, whereas the color of the surface of the DePS turned black at 7 months under reducing condition with covering by mud. To validate the results, we carried out an additional study, in which the DePS was immersed in seawater, and the solidified DePS was subsequently treated with Na₂S; the increase and decrease of the shear stress of DePS were reproduced. The solidified DePS before and after exposure to reducing conditions was also analyzed using a combination of microanalysis with an electron probe and Mössbauer spectroscopy. These analyses showed that the solidification was caused by the formation of bridges that composed of iron oxyhydroxides, whereas the subsequent embrittlement of the solidified DePS was attributed to changing in the chemical species of iron.     

Auraptene regulates gene expression involved in lipid metabolism through PPARα activation in diabetic obese mice

Scope: Peroxisome proliferator‐activated receptor‐α (PPARα) is a key regulator of circulating lipid level. Thus, various food‐derived compounds that activate PPARα as agonists have been screened and characterized. Methods and results: We investigated the effects of auraptene, a citrus‐derived compound serving as a PPARα agonist in vitro, on abnormalities in lipid and glucose metabolisms. In high‐fat‐diet (HFD)‐fed KK‐Ay diabetic obese mice, auraptene treatment suppressed hyperlipidemia and triglyceride accumulation in the liver and skeletal muscle, and increased the mRNA expression levels of the PPARα target genes involved in fatty acid oxidation in the liver and skeletal muscle. Moreover, the adipocyte size in the auraptene‐treated mice was significantly smaller than that in the control HFD‐fed mice resulting in the improvement of HFD‐induced hyperglycemia and abnormalities in glucose tolerance. Conclusions: These findings indicate that auraptene activates PPARα also in vivo and its treatment may improve abnormalities in lipid and glucose metabolisms, suggesting that auraptene is a valuable food‐derived compound for managing metabolic disorders.     

An iterative approach to system setup problems in flexible manufacturing systems

System setup problems in flexible manufacturing systems deal with short-term planning problems such as part type selection, machine grouping, operation assignment, tooling, fixture and pallet allocation, and routing. In this article, we consider three of the subproblems: part type selection, machine grouping, and loading. We suggest a heuristic approach to solve the subproblems consistently with the objective of maximizing the expected production rate. The proposed procedure includes routines to generate all possible machine grouping alternatives for a given set of machines, to obtain optimal target workloads for each grouping alternative, and to allocate operations and tools to machine groups. These routines are executed iteratively until a good solution to the system setup problem is obtained. Computational experience is reported.     

Improvement of efficiency and temperature control of induction heating vapor source on electron cyclotron resonance ion source

An electron cyclotron resonance ion source (ECRIS) is used to generate multicharged ions for many kinds of the fields. We have developed an evaporator by using induction heating method that can generate pure vapor from solid state materials in ECRIS. We develop the new matching and protecting circuit by which we can precisely control the temperature of the induction heating evaporator. We can control the temperature within ±15?°C around 1400?°C under the operation pressure about 10(-4) Pa. We are able to use this evaporator for experiment of synthesizing process to need pure vapor under enough low pressure, e.g., experiment of generation of endohedral Fe-fullerene at the ECRIS.