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[en] Based on a data sample of an integrated luminosity of 57.4 fb-1 at the Υ(4S) resonance taken with the BABAR detector using the SLAC PEP-II asymmetric-energy B-Factory, hadronic decays of B meson with the final states D(*) and three pions are studied. The study is performed by fully reconstructing the exclusive decays of B → D(*) a1(1260) and the non-resonant modes B → D(*) ρ0π and B → D(*) πππ. The current status of the study is presented and a dominant B → D(*) a1(1260) decay is shown
[en] The Aharonov-Bohm-like mesoscopic transport through a toroidal carbon nanotube (TCN) system coupled to two metallic electrodes has been investigated. The TCN is applied with a static magnetic flux, and the Zeeman effect also affects the transport properties. The novel oscillation structures are obtained in the zero-bias conductance, differential conductance and tunneling current, which are strongly associated with the structures of TCNs. The aperiodic and resonant behaviors are observed due to the Zeeman effect and finite size of TCNs. The conductance increases with the size of TCN. The tunneling current through metallic armchair TCN possesses rich oscillation structure compared with that of semiconducting zigzag TCN, and the conductance G>2e2/h is exhibited due to the interference effect. The I-V characteristics are calculated to exhibit nonlinear and stair-like behaviors. The stairs in the I-V characteristics for the zigzag TCN are associated with the resonant peaks of differential conductance versus source-drain bias
[en] A new approach to isochron dating is described using different sizes of quartz and K-feldspar grains. The technique can be applied to sites with time-dependent external dose rates. It is assumed that any underestimation of the equivalent dose (De) using K-fledspar is by a factor F, which is independent of grain size (90-350 μm) for a given sample. Calibration of the beta source for different grain sizes is discussed, and then the sample ages are calculated using the differences between quartz and K-feldspar De from grains of similar size. Two aeolian sediment samples from north-eastern China are used to illustrate the application of the new method. It is confirmed that the observed values of De derived using K-feldspar underestimate the expected doses (based on the quartz De) but, nevertheless, these K-feldspar De values correlate linearly with the calculated internal dose rate contribution, supporting the assumption that the underestimation factor F is independent of grain size. The isochron ages are also compared with the results obtained using quartz De and the measured external dose rates. (author)
[en] Pore formation is an important concern in laser welding of automotive aluminum alloys. This paper investigates the influence of the laser beam defocusing on pore formation during continuous wave Nd:YAG laser welding of aluminum automotive alloys 5182 and 5754. It was found that the instability of the keyhole during welding was a dominant cause of pore formation while hydrogen rejection played an insignificant role. The defocusing of the laser beam greatly affected the stability of the keyhole. Finally, the mechanism of the collapse of the keyhole and pore formation is proposed. (Author) 45 refs
[en] In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in which flow regime transition occurs.
[en] The PIUS reactor is a pressurized water reactor with passive safety features. It is based on a concept developed and verified at ABB Atom during the last 10 yr. The basic design of PIUS features core degradation protection by connecting the core to a large pool of highly borated water to form a natural circulation loop. During normal operations, the hydraulic balance is maintained between the primary coolant loop and the reactor pool by controlling the main coolant pumps. During inadvertent conditions, when the hydraulic balance cannot be maintained, the borated pool water will enter the primary coolant loop to shut down the reactor, and a natural circulation path will be established to provide long-term cooling for the core
[en] Mechanical properties of steels depend on the phase constitutions of the final microstructures which can be related to the processing parameters. Therefore, accurate quantification of different phases is necessary to investigate the relationships between processing parameters, final microstructures and mechanical properties. Point counting on micrographs observed by optical or scanning electron microscopy is widely used as a phase quantification method, and different phases are discriminated according to their morphological characteristics. However, it is difficult to differentiate some of the phase constituents with similar morphology. Differently, for EBSD based phase quantification methods, besides morphological characteristics, other parameters derived from the orientation information can also be used for discrimination. In this research, a phase quantification method based on EBSD data in the unit of grains was proposed to identify and quantify the complex phase constitutions of a microalloyed steel subjected to accelerated coolings. Characteristics of polygonal ferrite/quasi-polygonal ferrite, acicular ferrite and bainitic ferrite on grain averaged misorientation angles, aspect ratios, high angle grain boundary fractions and grain sizes were analysed and used to develop the identification criteria for each phase. Comparing the results obtained by this EBSD based method and point counting, it was found that this EBSD based method can provide accurate and reliable phase quantification results for microstructures with relatively slow cooling rates. - Highlights: •A phase quantification method based on EBSD data in the unit of grains was proposed. •The critical grain area above which GAM angles are valid parameters was obtained. •Grain size and grain boundary misorientation were used to identify acicular ferrite. •High cooling rates deteriorate the accuracy of this EBSD based method.
[en] The deviation of magnetization (M) relaxation from logarithmic time dependence is due to both the low pinning potential influenced by the driving energy formed by the gradient of flux lines and the large thermal activation. Considering the structural relaxation of the vortex state under the action of the driving force and thermal activation, the dependence of M on time t can be obtained as M=A+Bt-β, where A, B, and β keep constant at a given field and temperature
[en] Piezoelectric and ferroelectric films are very promising materials for microelectronic applications. In this paper, some important issues for these materials and applications are reviewed, and recent progresses on integrated ferroelectrics have been given. The physical and chemical preparation methods of the silicon-based piezoelectric and ferroelectric films, such as Sol-Gel, sputtering, metal organic chemical vapor deposition, have been described and compared. To realize a microelectronic device, the integrated circuits compatible ferroelectric/piezoelectric etching method is very important. The wet-chemical etching methods and dry-etching methods, such as reactive ion etching, have been introduced. There are many important applications for the silicon-based piezoelectric and ferroelectric films. One is the micro-sensors or micro-actuators or micro-electro-mechanical-system. Another is the memory devices. Some typical devices using piezoelectric and ferroelectric films have been introduced