[en] From a theoretical study of published QSO spectra, it is concluded that the Lyman-alpha forest lines and the most prevalent metal-line systems (those optically thin at the Lyman limit) arise in very different absorber populations. It is found for these systems that the observed increase with redshift of the C IV 1548, 1550A doublet ratio can be explained as being due to slowly changing metagalactic ionization conditions; there is no need to invoke any cosmic chemical evolution. No correlation is found between equivalent widths of Ly-alpha and C IV lines having the same absorption redshift, and consequently it is suggested that these C IV absorption-line systems arise in clouds strongly ionized by OB stars, presumably in young galaxies. The possibility that the clouds, which are known to exhibit clustering on a velocity scale of few hundred km/s, are protoglobular clusters is explored in some detail. 85 refs

[en] Graphical abstract: Comparison of the experiment results with predictions of the revised Rock ‘n’ Roll model by Biasi et al. indicate that the model accurately predicts the resuspension of graphite dust in a HTR depressurization accident. - Highlights: • Results of aerodynamic verification tests agreed well with the theory. • Higher initial pressures result in higher resuspension fractions. • Revised Rock ‘n’ Roll model by Biasi et al. showed good agreement with the experimental results. - Abstract: Graphite dust has a significant effect on the safety of high temperature gas-cooled reactors. The present study experimentally analyzes the resuspension of graphite dust in a depressurization accident. A series of aerodynamic verification tests in an experimental system with gas flow at the sound speed at the orifice agree well with theoretical results. The results showed that the friction velocity decreases with time during the depressurization while the resuspension fraction increases when augmenting the initial pressure. The experiment results show good agreement with the predictions of the revised Rock ‘n’ Roll model by Biasi et al., indicating that this model accurately predicts the resuspension of graphite dust in a HTR depressurization accident

[en] Nuclear steam generator (SG) is a highly complex nonlinear time-changed system. The inverse dynamics effects, which are caused by shrink and swell under transient, startup and lower power operation, make the water level difficult to control. Methods of SG water level control are analyzed. The shortcoming of conventional PI(D) control for SG level is pointed out. It emphatically expounds the fuzzy logic control and the neural network control to nuclear steam generator level. Finally, the author brings forward his opinion upon the advance tendency of SG water level control. (authors)

[en] Highlights: • The theoretical capacity of non-aqueous lithium-air batteries is predicted. • Key battery design parameters are defined and considered. • The theoretical battery capacity is about 10% of the lithium capacity. • The battery mass and volume changes after discharge are also studied. - Abstract: In attempt to realistically assess the high-capacity feature of emerging lithium-air batteries, a model is developed for predicting the theoretical capacity of non-aqueous lithium-air batteries. Unlike previous models that were formulated by assuming that the active materials and electrolyte are perfectly balanced according to the electrochemical reaction, the present model takes account of the fraction of the reaction products (Li₂O₂ and Li₂O), the utilization of the onboard lithium metal, the utilization of the void volume of the porous cathode, and the onboard excess electrolyte. Results show that the gravimetric capacity increases from 1033 to 1334 mA h/g when the reaction product varies from pure Li₂O₂ to pure Li₂O. It is further demonstrated that the capacity declines drastically from 1080 to 307 mA h/g when the case of full utilization of the onboard lithium is altered to that only 10% of the metal is utilized. Similarly, the capacity declines from 1080 to 144 mA h/g when the case of full occupation of the cathode void volume by the reaction products is varied to that only 10% of the void volume is occupied. In general, the theoretical gravimetric capacity of typical non-aqueous lithium-air batteries falls in the range of 380–450 mA h/g, which is about 10–12% of the gravimetric capacity calculated based on the energy density of the lithium metal. The present model also facilitates the study of the effects of different parameters on the mass and volume change of non-aqueous lithium-air batteries

[en] The inclusion complex of β-cyclodextrin (β-CD) and dialkyl pentasulfide (DPS), in which DPS was incorporated into β-CD cavities, was prepared by a co-precipitation method. The tribological properties of the complex used as lubricant additive in PEG 600 aqueous solution were investigated by a four-ball tester. The complex exhibited better tribological properties than β-CD under different loads, and also showed better anti-friction performance than DPS in the latter half of the test duration. The tribological action mechanism of the complex on a steel surface was studied according to the X-ray photoelectron spectroscopy (XPS) analyses. The β-CD molecules of the complexes were decomposed into various molecular fragments and the DPS molecules were released under the friction condition. It revealed that thiolate and ferrous sulfide (FeS) films formed by DPS played a major role, and iron alkoxide and carbon deposition films formed by the friction fragments of β-CD mainly exhibited anti-friction property on FeS-to-FeS interface. The interactions among different films led to the formation of a mixed boundary lubrication film.

[en] In order to overcome shortcomings of the traditional PID controller for nuclear steam generator water level, the paper designs a fuzzy control system for steam generator water level using fuzzy reasoning and digital signal processor (DSP) technology. By summing up the experience of skilled operators, it gave a set of fuzzy control rules, and determined some important control parameters. Considering the real-time control, and system stability, it also designed a fuzzy control system using DSP. Simulation results show that the system has good performance. (authors)

[en] Moyamoya disease (MMD) is a chronic progressive cerebrovascular occlusive disease, and its ischemic symptoms, such as cerebral infarction and hemorrhage due to the angiorrhexis of the abnormal venous blood network of the skull base. The former may occur during childhood, whereas the latter may occur in adulthood. The continuous development of nuclear medical imaging technology has provided new methods and abundant information for determining the affected area, scope, and degree of the disease and for studying the cerebral blood flow reserves of patients. Thus, the technology is essential to the clinical treatment of MMD and evaluation of the efficacy of MMD treatment. The current paper reviews the progress in MMD research by nuclear medical imaging technology. (authors)

[en] The charge-compensation mechanism and host stability of a cathode play the central role in determining its reversible capacity. Here, first-principle calculations are presented to study the charge compensation and its effect on the stability of orthosilicates, Li_2−xTMSiO₄ (TM = Fe, Mn), as the promising high-capacity cathode materials for Li-ion batteries. The charge compensation in Li_2−xTMSiO₄ upon delithiation is found to be achieved first by a combined reversible TM and oxygen redox process, originating from the dynamic response of their electronic structures to the Li ions (or electrons) removal and the associated charge transfer from the O to Fe ions, and then by the irreversible formation of O vacancy (V_O) that destroys the host stability of these materials. Whether the formation of V_O in these materials upon delithiation would occur is demonstrated to be essentially determined by the energy level of their highest occupied electronic states and can be understood by the defect charge transition mechanism which provides a quantitative way to estimate to what extent the oxygen redox could be reversibly used in a cathode that being important for the future design of high-capacity cathode materials.

[en] Highlights: • Conducting solar rays via two mirrors into the sunray trap as a receiver tube with minimum energy losses. • Increasing the sunrays path length inside the receiver tube by consecutive reflections and subsequently decreasing the required nanoparticles. • The presented DASC has 7% and 3% more efficiency than the conventional DASC with and without evacuated glass cover respectively. • As the prominent finding, the highly-efficient DASC (i.e., 81%) can be achieved using the lower percentage of nanoparticle (i.e., $\alpha =0.07$). In this work, adapted from the concept of cavity, a new model of receiver tube presented and used in one direct-absorption solar collector (DASC) equipped with two linear parabolic reflectors (LPR). Using both the insulated wall and the cavity-like receiver tube minimize the energy loss in this new-presented receiver tube. Its other advantage is the increase of sun-rays path length created by the sequential reflections of rays in the receiver tube which leads to the attenuation of nanoparticle agglomeration. Therefore, the effect of mentioned two advantages of receiver tube as well as the effect of nanoparticles is analyzed separately. The new presented receiver tube with the absorbent walls is utilized in surface-base solar collector (SBSC) to survey the effect of using the nanoparticle. Also, to investigate the effect of using new-presented absorber tube in SBSC, the obtained results are compared with the conventional type of SBSC. For these purposes, after the sun-rays tracing conducted by a mathematical method, the numerical simulation is carried out by COMSOL software to investigate some effective parameters. Accordingly, using nanoparticle in the new-presented DASC enhances the efficiency by 5% than SBSC. Also, using the new presented cavity-like receiver tube in SBSC augments the efficiency up to 2% rather than conventional LS-2 collector. Finally, as the prominent finding of the current work, the highly-efficient DASC (i.e., 81%) can be achieved using the lower percentage of nanoparticle (i.e., $\alpha =0.07$).

[en] A series of single phase Y_1_−_xEr_xFeO_3 (0≤x≤1) orthoferrite samples were synthesized by sol-gel method and their magnetic properties were studied in detail. The prepared samples were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC). The obviously weak ferromagnetic property, which caused by Dzialoshinski Moriya (DM) antisymmetric exchange mechanism, was observed in YFeO_3 for the magnetization jump at H=0 Oe. The magnetization of YFeO_3 was evidently changed by doping Er"3"+. The increase of the Er"3"+ content in Y_1_−_xEr_xFeO_3 greatly enhanced the paramagnetic component and gradually decreased the ferromagnetic component. - Highlights: • We synthesized a series of single phase Y_1_−_xEr_xFeO_3 orthoferrite powder by sol–gel method. • We studied magnetic properties of Y_1_−_xEr_xFeO_3 (0≤x≤1) in detail. • The magnetization of YFeO_3 was evidently changed by doping Er"3"+.