Dynamic analysis of crack arrest properties in compact arrest tests

The transverse wedge-loaded compact crack arrest test is a widely used small scale test to evaluate the crack arrest toughness of nuclear pressure vessel steels. Crack arrest toughness is determined wholly on the basis of static analysis in this test method.The present study tried to clarify the dynamic features of this test. Crack extension and the opening displacement behavior were measured using a sensitive time scale. The crack attained a high velocity after initiation, then decelerated to a low velocity prior to arrest. The opening displacement remained constant during the crack propagation and began to increase several tens of microseconds after crack arrest.Numerical analysis of the dynamic stress intensity factor was also performed by a finite element code ADINA. Crack propagation was simulated by the elimination of truss elements which connected crack surfaces. Discussion is directed to the comparison between the conventional static approach and the present dynamic analysis.     

Quantitative Determination of phosphatidylcholine by an HPLC-RI system

The following describes the quantitative determining method for phosphatidylcholine (PC) using the HPLC-RI system which we have developed. It uses Lichromsorb, Si 60 (10 μm), 4.6 mm × 250 mm as the column and a mobile phase consisting of n-hexane/isopropanol/water =1:4:1. In this report, we compared data from selected high-purity (60–100 wt%) samples using the HPLC-RI, HPLC-UV and conventional TLC-P methods. Under the conditions we described, the HPLC-UV method was somewhat affected by fatty acid compositions. As a result, there were some inconsistencies in the measured values. However, the HPLC-RI method we propose was applicable to PC from both egg yolk and soybeans. In addition, the HPLC-RI method produced data which correlated well with data from the TLC-P method, and this data was highly accurate and exhibited satisfac-tory reproductibility.     

Preparation of high-modulus and high-strength nylon-6 fibre by the zone-annealing method

In order to produce ultra-high strength fibre, a new method which was developed in our laboratory, called the zone-annealing method', has been applied to nylon-6. In spite of very simple apparatus and easy procedure, the dynamic modulus of the zone-annealed fibre was 10.8 × 10¹⁰ dyne cm^?2, which corresponds to 2.2–4.0 times that of the high-tenacity fibre available commercially. To elucidate the effectiveness of the zone-annealing process, the relationship between mechanical properties and superstructure of the fibre obtained has been investigated. It was found that the structure of the amorphous regions, especially the orientation of amorphous chains, played an important role in improving the mechanical properties. The principle and the characteristics of this method are also described in this paper.     

A genetic algorithm based molecular modeling technique for RNA stem-loop structures

A new modeling technique for arriving at the three dimensional (3-D) structure of an RNA stem-loop has been developed based on a conformational search by a genetic algorithm and the following refinement by energy minimization. The genetic algorithm simultaneously optimizes a population of conformations in the predefined conformational space and generates 3-D models of RNA. The fitness function to be optimized by the algorithm has been defined to reflect the satisfaction of known conformational constraints. In addition to a term for distance constraints, the fitness function contains a term to constrain each local conformation near to a prepared template conformation. The technique has been applied to the two loops of tRNA, the anticodon loop and the T-loop, and has found good models with small root mean square deviations from the crystal structure. Slightly different models have also been found for the anticodon loop. The analysis of a collection of alternative models obtained has revealed statistical features of local variations at each base position.     

Pseudo-dynamic buckling experiments on thin cylindrical shells under biaxial seismic loads

A buckling design research program has been carried out to establish seismic design guidelines for a fast breeder reactor. In doing so, the buckling strength of the cylindrical part of the reactor vessel of a fast breeder reactor under horizontal and vertical seismic loads has been clarified. The effects of axial loads on the horizontal seismic responses in pre- and post-buckling states of thin cylindrical shells are investigated. Pseudo-dynamic buckling experiments are performed to study the dynamic buckling characteristics of thin cylindrical structures when subjected to seismic loads. The buckling tests use model cylinders made of an aluminum plate and a biaxial loading test apparatus. The axial seismic loads reduce the lateral load-carrying capacity of the shells in the pre- and post-buckling regions so that they amplify the horizontal response displacement. An amplification factor that accounts for the effects of the vertical loads is presented and its validity is verified experimentally.     

Crystallite size determination and identification of lamellar surfaces of microparacrystallites for uniaxially and doubly oriented polyethylene films

Low density polyethylene (PE) films stretched 4 x at 20° C and annealed at 100° C show the well-known SAXS four-point diagrams with a tilting angle of lamellae of 35°. The 7.5 nm thick lamellae consist of rod-like microparacrystallites (mPCs) of 25 nm x 7.2 nm lateral sizes; the long axes of the mPCs are turned around the c-axis by 31° from the b-axis. The mPCs of each lamella stack together laterally like monolayers of cigars. After rolling the molten film at room temperature and then annealing at 100° C, a doubly oriented film arises, each half of it, anterior or posterior, producing a monoclinic two-point diagram. These are superimposed in SAXS. The mPCs are oriented in the plane stress field so that their b-axis is orthorgonal to the stretching direction and parallel to the film surface; their long axes however are again turned as before, but now by 26°. Furthermore their a-axis is tilted around the b-axis by 8° and the lamellar basal surface tilted against the b-axis in the opposite direction by 40°. The line profiles of the SAXS reflections give evidence that statistical irregularities of the lamellar surfaces are correlated in the 8° tilted direction or along the chain axis with the neighbouring surfaces by means of ultrafibrillar properties of the lamellar bundles, e.g. ribbon-like microfibrillar details of the lamellae. These can be described quantitatively by applying the theory of paracrystals on the superlattice generated by the centres of the mPCs. The lamellar surfaces are approximately parallel to the {523} and {311} netplanes of mPCs for the uniaxially and doubly oriented films, respectively. The conventional theory of mesophases can never describe structures which combine lamellar and fibrillar properties.Dedicated to P. P. Ewald on the occasion of his 90th birthday.     

New insulated-gate inverted structure AlGaAs/GaAs/n-AlGaAs HEMT ring oscillator

Inverted-structure high electron mobility transistors with insulated-gate structure, i.e. AlGaAs/GaAs/n-AlGaAs, have been successfully applied to E/D-type DCFL ring oscillators. High transconductance of 280 mS/mm was obtained at 77 K in an enhancement-mode FET with 0.8 ?m gate length. Gate leakage current was small enough even at a gate voltage of +1.4 V both at 300 K and 77 K, and a high logic swing of more than 1 V was achieved using a DCFL inverter. A 21-stage ring oscillator showed a minimum gate delay as small as 18.0 ps with power dissipation of 520 ?W/gate at 77 K.     

A magnetic flowmeter with conducting pipe wall for expanded field of applications

The internal pipe wall of magnetic flowmeters should be non-conductive to prevent generated electromotive force from short-circuiting. Usually the inside of metallic pipe is lined with insulating material. The lining limits applicable temperature range of measured fluid and also its reliability. A new structure is proposed, in which the insulating liner is eliminated. A potential distribution is formed on the pipe wall by applying voltage proportional to fluid flowrate. The potential distribution is kept almost identical to the flow-induced potential in the fluid so that no current flows across the boundary between fluid and wall. Therefore the output signal is exactly the same as that of conventional magnetic flowmeters.     

Thermal conductivity and cycle characteristic of metal hydride sheet formed using aramid pulp and carbon fiber

This paper describes the thermal and hydrogenation properties of a metal hydride (MH) sheet consisting of MH powder, aramid pulp, and carbon fiber. MH sheets were prepared by the wet paper method in which an agglutinated slurry of raw materials was dispersed onto a stainless steel mesh in water and then the sheet was dehydrated and dried. The cyclic characteristics and thermal conductivities of the MH sheets were experimentally investigated. The effects of changing the carbon fiber ratio and the measurement direction on the effective thermal conductivity were measured by the steady heat flow method. The thermal conductivity increased to 3.20 W/m·K with increasing carbon fiber ratio only in the planar direction. The decreases in mass due to removing MH powder and/or carbon fiber from sheet were less than 1 mass% after around 100 hydrogen absorption/desorption cycles. Moreover, the MH sheet was effective at decreasing the stress on the reactor vessel due to the expansion of MH during hydrogen absorption/desorption.