High stereographic resolution texture and residual stress evaluation using time-of-flight neutron diffraction.

Neutron diffraction texture measurements provide bulk averaged textures with excellent grain orientation statistics, even for large-grained materials, owing to the probed volume being of the order of 1 cm3. Furthermore, crystallographic parameters and other valuable microstructure information such as phase fraction, coherent crystallite size, root-mean-square microstrain, macroscopic or intergranular strain and stress, etc. can be derived from neutron diffractograms. A procedure for combined high stereographic resolution texture and residual stress evaluation was established on the pulsed-neutron-source-based engineering materials diffractometer TAKUMI at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Center, through division of the neutron detector panel regions. Pole figure evaluation of a limestone standard sample with a well known texture suggested that the precision obtained for texture measurement is comparable to that of the established neutron beamlines utilized for texture measurement, such as the HIPPO diffractometer at the Los Alamos Neutron Science Center (New Mexico, USA) and the D20 angle-dispersive neutron diffractometer at the Institut Laue-Langevin (Grenoble, France). A high-strength martensite-austenite multilayered steel was employed for further verification of the reliability of simultaneous Rietveld analysis of multiphase textures and macro stress tensors. By using a texture-weighted geometric mean micromechanical (BulkPathGEO) model, a macro stress tensor analysis with a plane stress assumption showed a rolling direction-transverse direction (RD-TD) in-plane compressive stress (about -330 MPa) in the martensite layers and an RD-TD in-plane tensile stress (about 320 MPa) in the austenite layers. The phase stress partitioning was ascribed mainly to the additive effect of the volume expansion during martensite transformation and the linear contraction misfit between austenite layers and newly transformed martensite layers during the water quenching process.

Development of a cryogenic load frame for the neutron diffractometer at Takumi in Japan Proton Accelerator Research Complex.

To prepare for projects such as the Large Hadron Collider upgrade, International Thermonuclear Experimental Reactor and Demonstration reactor, it is important to form a clear understanding of stress-strain properties of the materials that make up superconducting magnets. Thus, we have been studying the mechanical properties of superconducting wires using neutron diffraction measurements. To simulate operational conditions such as temperature, stress, and strain, we developed a cryogenic load frame for stress-strain measurements of materials using a neutron diffractometer at Japan Proton Accelerator Research Complex (J-PARC) Takumi beam line. The maximum load that can be applied to a sample using an external driving machine is 50 kN. Using a Gifford-MacMahon cryocooler, samples can be measured down to temperatures below 10 K when loaded. In the present paper, we describe the details of the cryogenic load frame with its test results by using type-304 stainless steel wire.

Accelerated adhesion of grafted skin by laser-induced stress wave-based gene transfer of hepatocyte growth factor.

Gene therapy using wound healing-associated growth factor gene has received much attention as a new strategy for improving the outcome of tissue transplantation. We delivered plasmid DNA coding for human hepatocyte growth factor (hHGF) to rat free skin grafts by the use of laser-induced stress waves (LISWs); autografting was performed with the grafts. Systematic analysis was conducted to evaluate the adhesion properties of the grafted tissue; angiogenesis, cell proliferation, and reepithelialization were assessed by immunohistochemistry, and reperfusion was measured by laser Doppler imaging as a function of time after grafting. Both the level of angiogenesis on day 3 after grafting and the increased ratio of blood flow on day 4 to that on day 3 were significantly higher than those in five control groups: grafting with hHGF gene injection alone, grafting with control plasmid vector injection alone, grafting with LISW application alone, grafting with LISW application after control plasmid vector injection, and normal grafting. Reepithelialization was almost completed on day 7 even at the center of the graft with LISW application after hHGF gene injection, while it was not for the grafts of the five control groups. These findings demonstrate the validity of our LISW-based HGF gene transfection to accelerate the adhesion of grafted skins.

Photoacoustic monitoring of burn healing process in rats.

We performed multiwavelength photoacoustic (PA) measurement for extensive deep dermal burns in rats to monitor the healing process of the wounds. The PA signal peak at 532 nm, an isosbestic point for oxyhemoglobin (HbO(2)) and deoxyhemoglobin (HHb), was found to shift to a shallower region of the injured skin tissue with the elapse of time. The results of histological analysis showed that the shift of the PA signal reflected angiogenesis in the wounds. Until 24 h postburn, PA signal amplitude generally increased at all wavelengths. We speculate that this increase in amplitude is associated with dilation of blood vessels within healthy tissue under the injured tissue layer and increased hematocrit value due to development of edema. From 24 to 48 h postburn, the PA signal showed wavelength-dependent behaviors; signal amplitudes at 532, 556, and 576 nm continued to increase, while amplitude at 600 nm, an HHb absorption-dominant wavelength, decreased. This seems to reflect change from shock phase to hyperdynamic state in the rat; in the hyperdynamic state, cardiac output and oxygen consumption increased considerably. These findings show that multiwavelength PA measurement would be useful for monitoring recovery of perfusion and change in local hemodynamics in the healing process of burns.

In vitro gene transfer to mammalian cells by the use of laser-induced stress waves: effects of stress wave parameters, ambient temperature, and cell type.

Laser-mediated gene transfection has received much attention as a new method for targeted gene therapy because of the high spatial controllability of laser energy. We previously demonstrated both in vivo and in vitro that plasmid DNA can be transfected by applying nanosecond pulsed laser-induced stress waves (LISWs). In the present study, we investigated the dependence of transfection efficiency on the laser irradiation conditions and hence stress wave conditions in vitro. We measured characteristics of LISWs used for gene transfection. For NIH 3T3 cells, transfection efficiency was evaluated as functions of laser fluence and number of pulses. The effect of ambient temperature was also investigated, and it was found that change in ambient temperature in a specific range resulted in drastic change in transfection efficiency for NIH 3T3 cells. Gene transfection of different types of cell lines were also demonstrated, where cellular heating increased transfection efficiency for nonmalignant cells, while heating decreased transfection efficiency for malignant cells.

Structure factors of dispersible units of carbon black filler in rubbers.

We report the structures of dispersible units, a most fundamental but minimal dispersible structural unit of a carbon black (CB) filler that is formed in two kinds of rubber (polyisoprene and styrene-butadiene random copolymer) matrices under a given processing condition. The results obtained from various small-angle scattering techniques showed that the CB aggregates, as observed after the sonification of a CB/toluene solution, were a spherical shape composed of approximately nine primary CB particles fused together. In the rubber matrices, the aggregates clustered into higher order structures defined in this work as the dispersible units, which are the fundamental structural elements (or the "lower cutoff structures") that build up a higher order mass-fractal structure. Furthermore, we found that the morphology of the dispersible units strongly depended on the rubber matrix, although the mass-fractal dimensions remained unchanged.