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[en] Synchrotron infrared measurements were conducted on a self-doped LaxMnO3-? (x?0.8) film. From these measurements we determined the conductivity and the temperature dependence of the effective number of carriers. While the metal-insulator transition temperature (TMI) and the magnetic ordering temperature (TC) approximately coincide, the onset of the change in the free carrier density occurs at a significantly lower temperature (?45 K below). This suggests that local distortions exist below TMI and TC which trap the eg conduction electrons. These regions with local distortions constitute an insulating phase which persists for temperatures significantly below TMI and TC.
[en] A dye laser induced resonant fluorescence scattering system has been installed on the Toroidal Cusp Experiment (TCX) at UCLA. This diagnostic has been employed to perform spatially and temporally resolved measurements of the neutral density and ion temperature. The local volume-average effect is used to decrease the fluctuation level in background radiation, thereby enhancing the signal-to-noise ratio. For Balmer alpha fluorescence measurements, the estimation of the neutral hydrogen density is based on either a coronal model or a time-dependent collisional radiative model depending on plasma parameters. By tuning the laser for broadband operation and using a narrow detection resolution, the ion temperature can be measured. The results are compared with other diagnostics
[en] The formation of gold particles containing five radially arranged twin boundaries (called penta-twinned particles) has been investigated by means of high-resolution transmission electron microscopy. The particles were produced by evaporation of gold in helium at low pressure (0.5 kPa). The processes involved in the formation of the particles are deduced from the experimentally observed size distribution, the characteristic particle morphologies and the frequency of different particle structures. The penta-twinned particles are suggested to be formed by the collision and rearrangement of small single crystals in the helium atmosphere. (orig.)
[en] An Organic Rankine Cycle (ORC) with a scroll expander with varying displacement is studied. First, to obtain the isentropic efficiency of the scroll expander modified from an automobile air-condition compressor with a displacement of 66 ml/r, the performance is investigated by experiments on a test rig driven by the compressed air. Second, based on the experimentally obtained isentropic efficiency, thermodynamic and heat transfer models of ORC are established on the basis of sub-models of the main apparatuses. Consequently, energy and exergy efficiencies are analyzed. Based on the simulation, an ORC system is constructed and investigated. Experiments show that for a given heat source temperature of 105 °C, the energy efficiency of the system ranges from 1.7% to 3.2% and the exergy efficiency of the system is 8.6%–16.9%. Additionally, another scroll expander with a displacement of 86 ml/r is utilized to investigate how displacement of the scroll expander influences performance of the ORC system. Finally, experiments also show that the IHX deteriorates the performance of ORC system, which is significantly different from simulation results. - Highlights: • The isentropic efficiency of the scroll expander is investigated by compressed air. • An ORC system with R245fa fluid is designed and simulated. • An ORC system with scroll expanders of different displacements is established. • Reasonable exergy and energy efficiencies of ORC are achieved by experiments. • Experiments show an IHX requires a special design for getting optimal performance
[en] Carotenoid pigments are extensively found in plant tissues with multifunction. The specific carotenoids have been classified in plant photosynthetic centers and most of them are exclusively abundant in colorful fruits and vegetables. Previous results show that lycopene cyclases are fundamental for determining the proportion of carotenoids in fruit, leaves, flowers and roots. A quantitative trait locus (QTL) analysis exhibited that an enzyme is responsible for red versus non-red flesh in watermelon (Citrullus lanatus) and also correlated with the function of lycopene beta-cyclase (lcyb) with flesh colour. The current study was conducted to characterize the two polymorphic genes encoding lcyb enzymes, from two watermelon cultivars (LSW-177and COS) containin the red and pale-yellow flesh, respectively. Results had confirmed the cyclase function of the two lcyb proteins in an Escherichia coli by heterologous complementation. These two lcyb proteins were differential in the amino acids at the 226th and 435th positions and had the effective ability to cyclase lycopene into bicyclic beta-carotene, showing that these amino acid variations did not influence the functionality of lcyb enzymes in E. coli. In addition, the conversion of Ala168 to Glu168 by site-directed mutagenesis which inactivated the enzyme, suggested that this residue was part of the core region for lcyb function in watermelon. The results presented here will help more to clarify the mechanism by which lycopene beta-cyclase performs its function. (author)
[en] The mechanism for creep deformation in dispersion strengthened tungsten alloys was examined. The effects of three dispersoids were investigated: HfC, ZrC, and ThO2. High temperature creep data (up to 2400 K) in these materials were analyzed based on a model that reflects the presence of dispersion carbide particles. The strengthened tungsten creeps in accordance with a dislocation process with the dispersed particles imposing a back stress. Results obtained from this model are in accord with other studies of similar materials systems. Based on this effort, critical controlling parameters were identified. Lifetime predictions were made for conditions appropriate for thermionic emitters using different creep models. It is evident that the proper selection of the model is critical to the accuracy of such predictions
[en] Highlights: • Solid sorption heat pipe (SSHP) with composite NaBr-NH_3 is proposed for continuous heat transfer. • Both vertical and horizontal SSHPs are investigated. • SSHP features non-isothermal heat transfer performance at sorbent and condenser sections. • The highest radial heat flux in vertical and horizontal SSHPs is 22.1 and 12.4 kW/m"2, respectively. • Both SSHPs have axial heat flux higher than 400 kW/m"2. - Abstract: A novel type solid sorption heat pipe (SSHP) is developed for continuous heat transfer. In contrast to conventional heat pipe (HP), SSHP utilizes the composite sorbent-sorbate as working media to replace the wick structure inside HP. Such a technology is expected to alleviate the heat transfer limits of conventional HP. NaBr is chosen as the sorbent, and the expanded natural graphite treated with sulfuric acid serves as the matrix. A certain molar amount of the sorbate (NH_3) is complexed with the composite sorbent. The desorption, condensation and chemisorption processes of NaBr-NH_3 working pairs are investigated for both vertical and horizontal placed SSHP. The results show that the desorption process of NaBr-NH_3 solid-gas reaction can be carried out while the heating temperature reaches up to 60 °C or above. The highest radial heat flux in both vertical and horizontal placed SSHP is around 22.1 and 12.4 kW/m"2, respectively, while the axial heat flux for both SSHPs is not less than 400 kW/m"2. It can be concluded that the SSHP is characterized by the non-isothermal heat transfer performance and verified to be available for continuous heat transfer. The vertical SSHP has a better overall heat transfer performance than horizontal SSHP under the same condition and NaBr-NH_3 working pairs applied in SSHP is suitable for low-grade thermal energy transfer above 60 °C.
[en] A small pumpless ORC (organic rankine cycle) system with different scroll expanders modified from compressors of the automobile air-conditioner is established, and the refrigerant R245fa is chosen as the working fluid. Different hot water temperatures of 80, 85, 90 and 95 °C are employed to drive the pumpless ORC system. Experimental results show that a maximum shaft power of 361.0 W is obtained under the hot water temperature of 95 °C, whereas the average shaft power is 155.8 W. The maximum energy efficiency of 2.3% and the maximum exergy efficiency of 12.8% are obtained at the hot water temperature of 90 °C. Meanwhile a test rig for investigating the mechanical loss of the scroll expander is established. The torque caused by the internal mechanical friction of the expander is about 0.4 N m. Additionally, another scroll expander with a displacement of 86 ml/r is also employed to investigate how scroll expander displacement influences the performance of the pumpless ORC system. Finally, the performance of the pumpless ORC system is compared with that of the conventional ORC system, and experimental results show that the small pumpless ORC system has more advantages for the low-grade heat recovery. - Highlights: • A small pumpless ORC (organic rankine cycle) system is established, and different scroll expanders are tested. • The maximum energy and exergy efficiency are 2.3% and 12.8% respectively. • A maximum shaft power of 361.0 W is obtained under the heat source temperature of 95 °C. • The small pumpless ORC system has characteristics of the high efficiency.
[en] Highlights: • Mg-Zn-Cu-Gd BMGs with 2 mm diameter are fabricated by copper mold casting method. • The σf and Hv of the Mg60Zn5Cu25Gd10 reach up to 754 MPa and 286 Hv, respectively. • The Mg60Zn5Cu25Gd10 alloy exhibits plastic deformation characteristic at micro-level. -- Abstract: The effects of Zn addition on the glass forming ability (GFA) and mechanical properties are investigated in Mg65−xZnxCu25Gd10 (x = 0, 3, 5, 8 at.%) alloys by X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and mechanical property tests. Thermal analysis shows that with the increasing of Zn content from 0 to 8 at.%, the supercooled liquid regions of Mg65−xZnxCu25Gd10 alloys decrease from 68 K to 31 K, indicating the obvious deterioration in their GFA. On the other hand, however, the mechanical property tests demonstrate that the appropriate addition of Zn (5 at.%) in Mg65−xZnxCu25Gd10 alloys greatly improves the mechanical strength, increases their compressive fracture strength and Vickers hardness from 648 MPa and 257 Hv to 754 MPa and 286 Hv, respectively. In addition, the fracture surface morphologies have been characterized by scanning electron microscopy (SEM) and the dominant fracture behaviors of the as-cast alloys have been explained as well
[en] Samples of YBa2Cu3-chiVchiOy with various chi values were made to study the effects of doping element on properties of Y-Ba-Cu-O superconductor. The doped samples show an almost unchanged Tc value. Whereas the volume fraction of superconducting phase decreases with the increase of the value of chi. The sizes of granule in the doped samples are smaller than that of the undoped ones. The doped samples are also denser and harder. Dependence of Jc on T for x=0.6 was also measured at H=510G and in T>50Κ. All of the results made one speculate that the vanadium appears mainly at interface as a kind of impurity. It was considered that improving the connectedness of interface is more important than increasing the fraction of superconducting phase at some conditions for enhancing Jc of oxide superconductors