Takahiko Kawai

Precursors in stereo-complex crystals of poly(l-lactic acid)/poly(d-lactic acid) blends under shear flow

To improve the mechanical and the thermal performance of poly(lactic acid) materials, this work focuses on the formation of stereo-complex crystals by blending poly(l-lactic acid) (PLLA) with poly(d-lactic acid) (PDLA). The resulting structure was analyzed using time-resolved in situ X-ray scattering, optical microscopy, differential scanning calorimetry and viscoelastic measurements. The objective of this study is to investigate the effect of shear flow imposed prior to crystallization on higher-order structure formation and acceleration of stereo-complex crystal growth of PLLA and PDLA blends using a wide spatial scale analysis and viscoelastic measurements. Density fluctuations of 100 nm scale were observed prior to nucleation by in situ simultaneous wide- and small-angle X-ray scattering measurements. These density fluctuations grew with time and the intensity increased with increasing shear rate. Furthermore, the results revealed that the PLLA and PDLA chains were only partially interpenetrated; consequently, stereo-complex crystals could grow only in the mixed PLLA/PDLA phase. The correlation length of density fluctuation prior to nucleation was strongly dependent on the mixed phases.

Facility for the development of the multilayer neutron mirror at KUR

The facility for the development of the multilayer mirror as a device for handling slow neutrons is described. The facility consists of a vacuum evaporation system, a neutron reflectometer and a reflectivity calculation program. The properties of the evaporation are discussed. The neutron reflectometer makes use of the time-of-flight method and can measure the reflectivity down to 10−4. In the reflectivity calculation program, we adopt a neutron optical method with a modified optical potential, in which the contrast between layers is reduced, and the potential around the layer boundary is smoothed. It is shown that with a suitable choice of calculation parameters, experimental reflectivity of a supermirror is well reproduced by the calculation.

A resonance neutron-spin flipper for neutron spin echo at pulsed sources

Abstract We have developed a resonance neutron-spin flipper (RSF) with high frequency applicable to pulsed sources. This flipper is necessary for new neutron resonance spin echo spectrometers installed at pulsed neutron sources. The RSF works only for monochromatic neutron beams because of the dependence of its spin–flip probability on neutron velocity. The RSF can, however, be applied to pulsed neutron beam with wide band wavelength by varying the amplitude of the applied oscillating magnetic field since the pulsed neutrons are resolved into monochromatic components according to their velocity. In this paper, we describe the RSF system applicable to pulsed neutron sources, measure the flipping efficiency and discuss the experimental results.

Simulation and mockup tests for developing TRR-II CNS

The Taiwan Research Reactor improvement and the utilization promotion project (TRR-II) with Cold Neutron Source (CNS) was carried out at Institute of Nuclear Energy Research. The CNS with a two-phase thermosiphon loop consists of an annular cylindrical moderator cell, a single moderator transfer tube, and a condenser. The self-regulating characteristics of a two-phase thermosiphon loop are investigated against variations of heat load. The experiments on the thermal-hydraulic characteristics have been performed using a full-scale mockup loop and a Freon-11 was used as a working fluid. Two cases were evaluated by the simulation and experiments. One case is an ORPHEE-type moderator cell in which an inner shell is open at the bottom, the other case is one with an inner cavity with no hole at the bottom but a vapor inlet opening at the uppermost part of the cavity. The flooding limitations, liquid level and void fraction in the moderator cell as a function of the initial Freon-11 inventory and the heat load are also reported.

Cold neutron spin interferometry and its application to modified spin echo methods

Abstract We propose three kinds of modified neutron spin echo methods using cold neutron spin interferometry, which is based on the coherent superposition principle of the neutron spin. Two kinds of the modified methods are based on a novel quantum precession of neutron spin by multilayer spin splitters and another method on time dependent spin interferometry using RF flippers. The performances of the last type are discussed and the firmer two methods are described in other proceedings.

Development of a modified neutron spin echo spectrometer using multilayer spin splitters

Abstract A multilayer spin splitter (MSS) is a device which gives the same effect as a magnetic field to the Larmor-precessing neutron. Since MSS is a single mirror, a neutron spin echo (NSE) can be much smaller (less than 1 m along the neutron beam) when MSSs successfully replace the Larmor precession magnetic field. The aim of our research is to replace the precession magnetic fields in NSE spectrometer by a set of MSSs and realize a very compact neutron spin echo spectrometer. In the present report, we will present the results of the preliminary experiment of the compact NSE spectrometer, and discuss its applicability to the pulsed neutron sources.

Effect of Polymeric Coupling Agent on Mechanical Properties of Kenaf Fiber / Polystyrene Composites

In order to improve the properties and the processability of kenaf fiber (KF) / polystyrene (PS) composites, the newly synthesized polymeric silane coupling agent (CA) was utilized and evaluated. KFs were reacted with CA in the melt system and in the solvent system. The composites reinforced by the modified KF showed enhanced mechanical properties compared with those reinforced by the unmodified KF. The effect was especially remarkable when the KF was modified with CA in the solvent system. As the CA content increases, the surface of KF recovered from the composites showed the higher Si / C ratio indicating the good reaction between KF and CA. The modified composites also showed a remarkable reduction in water uptake rate.

Neutron spin flip chopper with very high S/N ratio for pulsed source

We propose a multiple neutron spin flip chopper system to improve considerably its S/N ratio. Evaluations of a double spin flip chopper system give a high S/N ratio and its experimental results demonstrated good performance. Multiple spin flip chopper systems with high S/N ratio will be applicable to a direct geometry inelastic spectrometer for pulsed source instead of mechanical choppers.

Very cold neutron facility in horizontal arrangement with deuterium cold source

Abstract A very cold neutron guide tube with the characteristic wavelength of 23.5 A was horizontally arranged in combination with the deuterium cold source. The in-pile portion of the guide tube consists of nickel evaporated aluminum mirrors, and the external portion is made of ordinary nickel coated glass mirrors as a curved guide. The VCN output intensity and the energy spectrum are reported. The output is used for ultracold neutron production with a supermirror turbine and VCN interferometer study.

Development of new neutron spin echo spectrometer based on neutron spin interferometry

A multilayer spin splitter (MSS) generates the phase difference between the two neutron spin states, one of which is parallel to the direction of the magnetic field and the other is anti-parallel to it. Since the phase difference is equivalent to the Larmor precession angle, MSS enables us to construct a new type of the neutron spin echo (NSE) spectrometer. The new NSE spectrometer has properties; (1) the size of the spectrometer is small compared with a conventional NSE spectrometer, since the phase shift originates from the neutron flight path difference through the gap layer of the MSS, (2) the neutron spin echo time is proportional to the neutron wavelength. The feasibility of the new NSE spectrometer to the pulsed neutron source and the renewal cold neutron beam line, C3-1-2 at the JRR-3M reactor in the Japan Atomic Energy Research Institute (JAERI ) are reported.