Transcritical phenomena of autoignited fuel droplet at high pressures under microgravity

An experimental study has been performed under microgravity to obtain the detailed information needed for the deep understanding of the combustion phenomena of single fuel droplets which autoignite in supercritical gaseous environment. The microgravity environments both in a capsule of a drop shaft and during the parabolic flight of an aircraft were utilized for the experiments. An octadecanol droplet suspended at the tip of a fine quartz fiber in the cold section of the high-pressure combustion chamber was transferred quickly to be subjected to a hot gaseous medium in an electric furnace, this followed by autoignition and combustion of the fuel droplet in supercritical gaseous environment. High-pressure gaseous mixture of oxygen and nitrogen was used as the ambient gas. Temporal variation of temperature of the fuel droplet in supercritical gaseous environment was examined using an embedded fine thermocouple. Sequential backlighted images of the autoignited fuel droplet or the lump of fuel were acquired in supercritical gaseous environment with reduced oxygen concentration. The observed pressure dependence of the ignition delay and that of the burning time of the droplet with the embedded thermocouple were consistent with the previous results. Simultaneous imaging with thermometry showed that the appearance of the fuel changed remarkably at measured fuel temperatures around the critical temperature of the pure fuel. The interface temperature of the fuel rose well beyond the critical temperature of the pure fuel in supercritical gaseous environment. The fuel was gasified long before the end of combustion in supercritical gaseous environment. The proportion of the gasification time to the burning time decreased monotonically with increasing the ambient pressure.     

AC loss properties of elliptic superconducting wires exposed to a transverse magnetic field with an arbitrary angle

Analytical expressions of alternating current (AC) losses are derived in a superconducting wire with an infinite length and elliptic cross-section for limiting cases in which the amplitude of an external transverse magnetic field is much smaller or larger than the full penetration field. Since it is assumed that the superconducting wire is subject to Bean’s critical state model, in which the critical current density is independent of the magnitude of the local magnetic field, the AC losses under consideration are completely hysteretic. The expressions obtained explicitly include the effects of the aspect ratio of the wire cross-section and the external-field angle with respect to the broadest face. An approximated curve of the AC loss, which becomes equal to the analytical results under the limiting conditions mentioned above, is also proposed for a wide range of external-field amplitudes. In order to validate the proposed curve, the AC losses in the elliptic wires are numerically calculated by means of the minimization of magnetic energy. It is concluded that the discrepancy between the approximated curves and the numerical results of the AC losses is less than 40%.     

Multichannel biosensing platform of surface-immobilized gold nanospheres for linear and nonlinear optical imaging

What we believe to be a new label-free multichannel biosensing platform is proposed. It is composed of surface-immobilized gold nanospheres (SIGNs) above a gold surface with a nanogap supported by a merocyanine self-assembled monolayer. The circular SIGN spots with a diameter of 120 microm were arrayed for multichannel biosensing on a glass slide. Two kinds of sensing methods were examined: One is a reflectivity measurement of a blue ray and the other is a second-harmonic generation measurement. It was found that the SIGN system can be used as a promising platform for multichannel biosensing in both sensing methods.     

Effects of operating conditions on durability of polymer electrolyte membrane fuel cell Pt cathode catalyst layer

In this study, we investigated the effects of humidity and oxygen reduction on the degradation of the catalyst of a polymer electrolyte membrane fuel cell (PEMFC) in a voltage cycling test. To elucidate the effect of humidity on the voltage cycling corrosion of a carbon-supported Pt catalyst with 3 nm Pt particles, voltage cycling tests based on 10,000 cycles were conducted using 100% relative humidity (RH) hydrogen as anode gas and nitrogen of varying humidities as cathode gas. The degradation rate of an electrochemical surface area (ECSA) was almost 50% under 189% RH nitrogen atmosphere and the Pt average particle diameter after 10,000 cycles under these conditions was about 2.3 times that of a particle of fresh catalyst because of the agglomeration of Pt particles.The oxygen reduction reaction (ORR) that facilitated Pt catalyst agglomeration when oxygen was employed as the cathode gas also demonstrated that Pt agglomeration was prominent in higher concentrations of oxygen. The ECSA degradation figure in 100% RH oxygen was similar to that in 189% RH nitrogen. It was concluded that liquid water, which was dropped under a supersaturated condition or generated by ORR, accelerated Pt agglomeration. In this paper, we suggest that the Pt agglomeration degradation occurs in a flooding area in a cell plane.     

AC Loss Evaluation of MgB2 Superconducting Windings Located in a Stator Core Slot with a Finite-Element Method

AC losses in stator windings of fully superconducting motors with an MgB₂ wire are numerically evaluated by means of a finite-element method using edge elements for a self-magnetic field. The physical properties of the MgB₂ wire for numerical calculations are obtained from the corresponding experiments with an existing wire. It is assumed that the voltage?Ccurrent characteristics of the MgB₂ wire are given by Bean??s critical-state model, in which the critical current density is independent of the local magnetic field. The influences of core slot size and turn number of windings on the AC losses are discussed quantitatively toward the optimum design of the stator winding with the MgB₂ wire.     

A design method of optical bandpass filters

A design method of optical bandpass filters which are composed of several resonators consisting of dielectric layers is discussed. The relation between the loaded Q of a resonator and the thickness of each layer is calculated by treating equivalently each layer as a segment of transmission line and represented on a chart. It becomes possible to design an arbitrary value of loaded Q by using the chart. Thus, an optical bandpass filter of required bandwidth and rejection characteristic can be designed by finding out the optimum thickness of each layer of the resonator which is the component of the filter     

An extrusion method of tube with spiral inner fins by utilizing generation of spiral outer fins/grooves

This paper presents a new extrusion method for fabrication of a tube with spiral inner fins. The spiral fins are formed by utilizing the generation of spiral outer fins or grooves, which drive the metal to circumferentially move with twist deformation. The effect of the outer fins/grooves is examined for realizing the circumferential metal flow. The position of the mandrel has an ability to flexibly control the spiral angle. This method would drastically enhance the productivity and reduce the manufacturing cost, as the tube would be manufactured directly from a billet through only one process.     

Tracking modularity in citation networks

Citation network analysis is an effective tool to analyze the structure of scientific research. Clustering is often used to visualize scientific domain and to detect emerging research front there. While we often set arbitrarily clustering threshold, there is few guide to set appropriate threshold. This study analyzed basic process how clustering of citation network proceeds by tracking size and modularity change during clustering. We found that there are three stages in clustering of citation networks and it is universal across our case studies. In the first stage, core clusters in the domain are formed. In the second stage, peripheral clusters are formed, while core clusters continue to grow. In the third stage, core clusters grow again. We found the minimum corpus size around one hundred assuring the clustering. When the corpus size is less than one hundred, clustered network structure tends to be more random. In addition even for the corpus whose size is larger than it, the clustering quality for some clusters formed in the later stage is low. These results give a fundamental guidance to the user of citation network analysis.