Search

Liquefaction damage from earthquakes frequently indicates effects of sand aging on liquefaction resistance: Liquefaction damage in natural or aged reclaimed ground has been much less than that in young reclaimed ground. However, the mechanisms underlying aging effects remain unclear. Cementation and stress history of sand strongly influence aging effects: Cementation raises liquefaction resistance, whereas liquefaction history sometimes reduces liquefaction resistance. Small cyclic shear strain, from which the induced density change is almost negligible, was adopted as representing the stress history. To evaluate liquefaction resistance, initial shear modulus, and deformation characteristics of sand, we prepared specimens by adding cement and by applying a small cyclic shear strain. In cementitious sand, liquefaction resistance increased when cement contents exceeded 0.3% by mass. The initial shear modulus apparently increased at the same degree of cement addition as that which increased the liquefaction resistance. For sand with a small cyclic shear strain, the liquefaction resistance increased when the applied cyclic axial strain exceeded 0.01%. Application of small cyclic shear strain only slightly increased the initial shear modulus, but the linear elastic region tended to expand to greater shear strain. Shear properties of sand with small cyclic shear strain resembled those found for sand that had been consolidated for a long time. [ABSTRACT FROM AUTHOR]

Cohesive soils in nature are created under anisotropic stress and have various stress histories. Embankments generate greater vertical loads underground. Moreover, associated excavation activities can exacerbate the extensional stress state. This study investigated the effects of induced anisotropy on the shear modulus in saturated and unsaturated cohesive soils. A triaxial testing apparatus, equipped with local small strain (LSS) measurement devices and bender elements (BEs), was used to measure the small strain shear modulus. Two series of tests were conducted: (1) LSS and BE tests used specimens normally consolidated under a constant mean effective stress of p' = 300 kPa or net mean stress p net = 300 kPa with different stress ratios to investigate the effects of anisotropic consolidation. The values of the applied stress ratios, represented as K = σ ' h / σ ' v for the saturated soil and K net = (σ h – u a)/(σ v – u a) for the unsaturated soil, were 0.35, 0.43, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, and 3.5. (2) BE tests used specimens consolidated under various mean effective stresses in the order of p' = 50, 100, 200, 300, 400, 500, and 600 kPa, and swollen in reverse order under K of 0.35, 0.43, 0.6, and 1.0, to elucidate p' and the effects of the overconsolidation ratio (OCR). The results demonstrated that K -consolidation under constant p' produces large differences in initial shear modulus G 0 in saturated cohesive soil, but K net produces only slight differences in unsaturated cohesive soil because of the influence of strong matric suction. Finally, G 0 was normalized successfully considering the effects of void ratio e , K , and OCR. [ABSTRACT FROM AUTHOR]

Grounds subjected to cyclic loading, either continuous or fragmentary, widely exist in natural deposits and at reclaimed sites, e.g., induced by traffic loads, earthquakes, and wave-induced loading environments. Assessing the ground deformation under cyclic loading conditions is necessary for proper design and maintenance planning for traffic services. Accordingly, a testing program, in which vertical, horizontal, and shear stresses are automatically controlled, were newly developed in this study to reproduce the actual cyclic traffic load conditions using a hollow-cylindrical torsional shear apparatus. Estimations based on the results obtained from cyclic triaxial stress conditions were seen to underestimate the ground settlement compared to actual stresses, with combined vertical, horizontal, and shear stresses. Two kinds of vertical strain arose after a certain number of cycles: incremental collapse, in which unstable deformation (failure) is caused, and plastic creep, in which deformation continues to accumulate with the dampened rate (per cycle). The number of cycles of combined vertical, horizontal, and shear stresses necessary to reach a certain vertical strain increased linearly on a logarithmic scale when the magnitude of loading decreased. Moreover, the relationship between vertical strain and excess pore water pressure presented the same trend independent of the magnitude of loading. Practical uses of the obtained results were proposed and discussed. [ABSTRACT FROM AUTHOR]

This paper presents the effects of inherent anisotropy on the shear strength and shear modulus of both saturated and unsaturated sands. Several triaxial compression tests were performed using Toyoura sand with different contents of mica: 0%, 1%, 2.5%, 5%, and 10%. Specimens with various deposition angles α were prepared using the air pluviation (AP) and dry vibration (DV) methods. The shear strength properties were measured by conventional triaxial tests, whereas the small strain stiffness was measured by both local small strain (LSS) tests and bender element (BE) tests. The orientation of the sand particles was assessed based on two-dimensional optical microscopic measurements and mathematical estimation. The results showed that an increase in the mica content brought about a decrease in the degree of anisotropy of the shear strength because of mica particle breakage. However, the degree of anisotropy of the shear modulus became higher with a 0%–10% increase in the mica content. The shear modulus of the unsaturated sand had a slightly higher degree of anisotropy than that of the saturated sand. In addition, the degree of anisotropy of the shear modulus was assessed based on the average orientation angle θ of the sand particles. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The strain rate during shearing has been shown in experimental studies to strongly affect the mechanical behaviour of soil. For saturated soil, sufficient knowledge has been obtained to achieve equilibrium conditions for the pore water pressure. Nevertheless, little is known about unsaturated soil. Therefore, this study used a hollow cylindrical torsional shear apparatus to investigate the rate dependence on the deformation and strength properties of unsaturated soil. First, unsaturated specimens were anisotropically consolidated with different directions of major principal stress to assess the rate dependence of the anisotropic behaviour. Then, the shear stress was removed to produce an isotropic stress state. Shearing was applied using the specimens to evaluate the strain rate effects on the mechanical properties of unsaturated cohesive soil. The results indicate that the secant shear modulus increased with the strain rate in both constant suction (CS) and constant water content (CW) conditions. The shear strength did not change with the strain rate under a CW condition, but it decreased with the strain rate under a CS condition. [ABSTRACT FROM AUTHOR]

Liquefaction resistance is known to increase concomitantly with the increase in time after construction or sedimentation. Nevertheless, the mechanisms of its aging effect on liquefaction have not been completely elucidated. To clarify the mechanisms of aging in sandy soils, the liquefaction resistance (CRR), initial and secant shear moduli (G 0 and G sec), and laboratory penetration resistance of long-term consolidated sand specimens were examined using cyclic undrained triaxial tests, local small strain (LSS) tests equipped with bender elements (BEs), and penetration index tests, respectively. Based on the existing reports, the CRR was inferred from G 0 , G sec , and the laboratory penetration resistance. In the case of Toyoura sand of D r = 40%, the CRR increased by about 14% with a 360-day consolidated specimen in the cyclic undrained triaxial tests. However, increases in the CRR evaluated from G 0 and the laboratory penetration resistance were nothing and only 2%, respectively. G sec started to degrade at greater shear strain in the long-term consolidated specimens. An increase in the CRR, evaluated from the G sec of 0.01% shear strain, had a much better agreement with that obtained from the cyclic undrained triaxial tests. [ABSTRACT FROM AUTHOR]

Magnetic properties and internal stresses of AlN(20 nm)/[CoPt(2 nm)/AlN(20 nm)] 5 multilayer structure deposited at different substrate temperatures by dc magnetron sputtering have been studied. It is found that with increasing the substrate temperature from room temperature to 400 °C, in-plane magnetic anisotropy field of the film becomes smaller, and the out-of-plane magnetization becomes stronger. Especially when the film is deposited at substrate temperature of 400 °C, the out-of-plane magnetization becomes as strong as the in-plane magnetization. On the other hand, the total in-plane residual stress of the film changes gradually from compressive to tensile. The compressive intrinsic stress is generated during deposition process and decreases with increasing the substrate temperature. After annealing at high temperatures, the films show strong perpendicular magnetic anisotropy. With increasing the annealing temperature, the in-plane thermal stress also increases and becomes dominant, which is considered to result in the perpendicular magnetic anisotropy of the films. [ABSTRACT FROM AUTHOR]

We designed the single-flux-quantum (SFQ) circuits that were fabricating using the NEC 2.5 kA/cm2 standard process that has four Nb layers. Before designing circuits with two ground planes, we estimated sheet inductances of the base and counter planes using simple rectangular-shape inductors. Estimated sheet inductance of the base plane was 0.75 of the original value for the circuits with only under-ground plane. For the counter plane, sheet inductance was estimated to be 0.55 of the original value. We designed a 2-branch D-FF gate and fabricated SFQ circuits including the 2-branch D-FF using the NEC standard process. Parasitic inductances of the counter layer in the 2-branch D-FF were effectively minimized using two ground planes and frequency dependences of the lower bias margin were improved. [ABSTRACT FROM AUTHOR]

Double relaxation oscillation SQUID (DROS) combined with an on-chip superconducting digital flux locked-loop (FLL) circuit has been proposed. In this study, we described superconducting digital FLL circuit which consists of an 8-bit up/down counter and an 8-bit R-2R ladder D/A converter. The circuit was designed using 4-Junction Logic (4JL)-gates which are driven by a two phase power supply. In the up/down counter, we employed binary carry lookahead (B CL) circuits for high-speed operation. Logic simulations for the BCL 8-bit up/down counter showed correct operation up to 4 GHz, assuming a 2.5 kA/cm² Nb/Al-AlOx/Nb junction technology. From simulation results high slew rate of 107 Φ0/s and dynamic range of 2.5 Φ0 can be expected. [ABSTRACT FROM AUTHOR]

Photosensitive polyimide insulation layers have been Introduced to fabricate superconducting integrated circuits. It is shown to simplify the fabrication process, because the photosensitive polyimide insulation layer can be patterned by conventional photolithography process, resulting in the etching process unnecessary in the present new fabrication process. Three kinds of contact hole (junction top electrode contact, junction base electrode contact, and resistor contact) are simultaneously formed in the photolithography process of the polyimide. A minimum contact hole size is designed to be 1.5 μm square for a 3 μm × 3 μm squared junction. Superconducting current density of 2.4 × 106 A/cm² of the contact hole was measured. Palladium resistors were successfully made with through hole contacts of the photosensitive polyimide insulation layer. We demonstrated superconducting integrated circuits using this new fabrication process including the minimum 3 μm × 3 μm squared Nb/Al - AlOx/Nb Josephson tunnel junction. The circuit operation is also demonstrated in the fabricated superconducting integrated circuits with the photosensitive polyimide insulation layers. [ABSTRACT FROM AUTHOR]

A superconducting tunnel junction (STJ) is very attractive for use in high-energy-resolution photon detectors because of its small energy gap. To detect a single photon, the Josephson current of the STJ has had to be suppressed by an external magnetic field. We demonstrated an on-chip coil-integrated STJ photon detector, which excludes the external magnetic field, allowing a small device size. A normal-distribution function shape was adopted for the superconducting electrodes, which makes the magnetic field supplied to the STJ small. We devise a new superconducting photon detector by combining the above techniques. A new Josephson switching gate is also integrated on the same detector chip in order to drive an on-chip integrated coil by a persistent superconducting current. This behavior was confirmed experimentally using the technology of the fabrication process of the Nb/AI-AIOx/Nb Josephson tunnel junction. [ABSTRACT FROM AUTHOR]

In recent years, linear motors are gaining wide popularity in the field of office and factory automation. Therefore, small and high thrust linear motors are needed. This paper deals with a proposal of a new interior permanent magnet type linear pulse motor and it's characteristics. The thrust density of the interior permanent magnet linear pulse motor is larger compared to the other type linear pulse motors. [ABSTRACT FROM AUTHOR]

Studies the properties of NbTiN superconducting thin films prepared by reactive DC magnetron sputtering. Sputtering conditions for NbTiN films; Superconducting characteristics of NbTiN films; X-ray diffraction patterns for NbTiN thin films.

Studies normal-distribution-shaped Josephson tunnel junctions for superconducting tunnel junction photon detector applications. Suppression of the sidelobes of the Josephson current; Magnetic field dependence of the Josephson current of the Josephson junctions.

We have fabricated Nb-based superconducting tunnel junctions (STJs) with Al trapping layers using the photosensitive polyimide insulation layer for X-ray detector. It is possible to simplify the fabrication process of the STJs, because the photosensitive polyimide is used as the insulation layer instead of conventional inorganic insulation films without an etching process in a vacuum chamber. The polyimide insulation layer expects to be stable for thermal cycling between 03 K and room temperature. The preliminary experiments of 5.9 keV radiation shows the energy resolution of 86 eV. [ABSTRACT FROM AUTHOR]

We have developed a Phononmediated radiation detector using Nb-based superconducting tunnel junctions (STJs). The STJs are fabricated on a substrate as an absorber of the radiation, and a substantial amount of emergent phonons with an energy above the energy gap are detected. The performance of the detector depends on the collection efficiency of the phonon. A selection of an appropriate substrate is required for optimizing the detector performance. We fabricated Nb-bass STJs on a Al2O3 and a LiNbO3 substrates, and compared the pulse heights of substrate phonon events due to X-ray irradiation to the substrates. We found that the maximum pulse height of the phonon events for the LiNbO3 substrate was about twice of that for the Al2 O3 substrate, so that these spectra which was obtained from two STJs showed different shapes, especially the peak due to phonon events. [ABSTRACT FROM AUTHOR]

We have successfully fabricated Nb-based superconducting tunnel junctions (STJs) with β-Ta trapping layers. In an Nb/ β-Ta stacked structure, β-Ta film showed the thickness dependence of critical temperature T[sub c] in current-voltage (I-V) characteristics due to the proximity effect from Nb films. We fabricated Nb-based STJs with Β-Ta trapping layers for X-ray detector working at 0.4 K. We obtained an energy resolution of 52 eV for 5.9 kev X-ray irradiation at 0.4 K. We expect a high energy resolution by optimizing the thickness of Β-Ta trapping layers and improving the fabrication process. [ABSTRACT FROM AUTHOR]

Switching functions using a parallel connection of conventional-type and πtype junctions have been investigated. Both junctions consist of Nb/Au/YBa[sub 2]Cu[sub 3]O[sub 7]-δ Josephson junctions on YBa[sub 2]Cu[sub 3]O[sub 7]-δ edges, whose faces are (110) and (100). The modulation patterns of critical currents in low magnetic fields indicate that the d-wave component is dominant: the (100) junctions exhibit the conventional type, but the (110) junctions the π type. Superconducting current path is alternated between the conventional junction and the π junction by applied magnetic fields using these anisotropic magnetic field dependences of the critical current. [ABSTRACT FROM AUTHOR]

Demonstrates the anisotropic Josephson effect in all (103)-oriented junctions consisting of YBa[sub 2]Cu[sub 3]O[sub 7-delta]/PrBa[sub 2]Cu[sub 3]O[sub 7-delta']/YBa[sub 2]Cu[sub 3]O[sub 7-delta] films. Characteristics of the junction; Use of the junction isolation technology; Exhibition of anisotropic Fraunhofer interference patterns.

We have investigated the magnetic field dependence of the Josephson tunnel junctions whose shape is defined with a normal-distribution function. It was revealed that the normal-distribution-shaped Josephson tunnel junctions show an exponential decay and no side lobes of the Josephson current as the external magnetic field is increased. This behavior was confirmed experimentally by using the Nb/AlO[sub x]/Nb tunnel junctions with a Josephson critical current density of J[sub c]=50 A/cm[sup 2], and an area of 10 000 μm[sup 2] corresponding to the "small" junction region. Normal-distribution junctions should have a potential for wide applications to photon detection since the external magnetic field to suppress the Josephson current can be lowered to less than one tenth that of other junctions reported. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]