Pressure induces major changes in the nature of Americium's 5f electrons

Americium occupies a pivotal position in the actinide series with regard to the behavior of 5f electrons. High-pressure techniques together with synchrotron radiation have been used to determine the structural behavior up to 100 GPa. We have resolved earlier controversial findings regarding americium and find that our experimental results are in discord with recent theoretical predictions. We have two new findings: (1) that there exists a critical, new structural link between americium under pressure and its near neighbor, plutonium; and (2) that the 5f electron delocalization in americium occurs in two rather than one step.     

Facile synthesis of SnO2–ZnO core–shell nanowires for enhanced ethanol-sensing performance

The design of core–shell heteronanostructures is powerful tool to control both the gas selectivity and the sensitivity due to their hybrid properties. In this work, the SnO₂–ZnO core–shell nanowires (NWs) were fabricated via two-step process comprising the thermal evaporation of the single crystalline SnO₂ NWs core and the spray-coating of the grainy polycrystalline ZnO shell for enhanced ethanol sensing performance. The as-obtained products were investigated by X-ray diffraction, scanning electron microscopy, and photoluminescence. The ethanol gas-sensing properties of pristine SnO₂ and ZnO–SnO₂ core–shell NW sensors were studied and compared. The gas response to 500 ppm ethanol of the core–shell NW sensor increased to 33.84, which was 12.5-fold higher than that of the pristine SnO₂ NW sensor. The selectivity of the core–shell NW sensor also improved. The response to 100 ppm ethanol was about 14.1, whereas the response to 100 ppm liquefied petroleum gas, NH₃, H₂, and CO was smaller, and ranged from 2.5 to 5.3. This indicates that the core–shell heterostructures have great potential for use as gas sensing materials.     

聚变实验堆真空室壳体成型残余应力分析

为了了解聚变实验堆真空室壳体表面残余应力的分布以及退火工艺对残余应力的影响,通过模拟分析和实验检测两种方式对不锈钢316LN冷压曲面和热压曲面残余应力进行研究,获得退火前后曲面表面残余应力的大小,得到冷压曲面和热压曲面残余应力的分布以及退火工艺对残余应力分布的影响。研究结果为分析成型工艺提供数据支撑,对中国聚变工程实验堆真空室的研究与制造具有重要意义。     

Reactivity of the Cu2O(1 0 0) surface: Insights from first principles calculations

We present a summary of results of systematic first principles calculations of the electronic and geometric structures of the Cu₂O(1 0 0) surface and the process of CO oxidation on this surface (energetics and pathways of adsorption, diffusion and reactions of CO and O₂ on the surface). The (p, T) phase diagram of the Cu₂O(1 0 0) in equilibrium of with gas phase O₂ built using the ab initio thermodynamics approach suggests that the O-terminated surface is preferred over the Cu-terminated one within the entire ranges of pressures and temperatures in which the compound exists. Metastable Cu-terminated Cu₂O(1 0 0) is found to undergo a surface reconstruction in agreement with experiment. We find CO to oxidize spontaneously on the O-terminated Cu₂O(1 0 0) surface by consuming surface O atoms. Our calculations also show that the surface O-vacancies left in the course of the CO oxidation can be easily filled with dissociative adsorption of the gas phase O₂ molecules, which are usually present in reaction environment.     

Improvement of the PLD process assisted by RF plasma for AlN growth

The pulsed-laser-deposition (PLD) method is particularly well suited for the growth of oxide thin films, but in the case of other compounds, such as nitrides, PLD presents some limitations which are mainly due to the low reactivity of nitrogen in comparison with oxygen. A possible way to overcome this problem is to increase the reactivity of the constituent species, via plasma assisted-pulsed-laser deposition. A plasma is coupled to the ablation chamber, in order to increase the density of reactive atomic species, which can be further incorporated in the growing film. This approach is described in this paper as well as the nature, energy, and concentration of the atomic and molecular species in the plasma as determined by various plasma diagnostics. These results are correlated to the growth of thin films in the particular case of the aluminum nitride compound. The composition and structure of the films are studied as a function of the growth conditions, and the positive effects of the additional discharge are evidenced on the film purity and properties. The fundamental problem with the PLD technique, especially with metallic targets, is the production of unwanted droplets that significantly worsen the properties of the films. To eliminate these droplets, a thin film has been grown with an experimental setup using two targets and crossed laser beams which gave positive results. PACS 81.15.Fg; 52.80.Pi; 77.84.Bw     

Detection

This review on second- and third-generation multidetectors devoted to heavy-ion collisions aims to cover the last twenty years. The presented list of devices is not exhaustive but regroups most of the techniques used during this period for nuclear reactions at intermediate energy (≃ 10A MeV to 1A GeV), both for charged-particle and neutron detection. The main part will be devoted to 4π multidetectors, projectile decay fragmentation, high-resolution magnetic spectrometers, auxiliary detectors and neutron detection. The last part will present the progress in electronics and detection in view of the construction of future-generation detectors.     

Synthesis and characterization of hollow ��-Fe2O3 sub-micron spheres prepared by sol�Cgel

In this work we report the preparation of magnetic hematite hollow sub-micron spheres (??-Fe₂O₃) by colloidal suspensions of ferric nitrate nine-hydrate (Fe(NO₃)₃·9H₂O) particles in citric acid solution by following the sol?Cgel method. After the gel formation, the samples were annealed at different temperatures in an oxidizing atmosphere. Annealing at 180°C resulted in an amorphous phase, without iron oxide formation. Annealing at 250°C resulted in coexisting phases of hematite, maghemite and magnetite, whereas at 400°C, only hematite and maghemite were found. Pure hematite hollow sub-micron spheres with porous shells were formed after annealing at 600°C. The characterization was performed by X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM).     

Relaxation of photoexcited Na$_\mathsf{3}$F

This paper describes the spectroscopy of Na₃F both in the frequency and time domains. The photoionization efficiency curve shows two thresholds, associated to two isomers. The excited electronic states of the C_2v isomer have been probed by photodepletion spectroscopy, and the results are used to analyze a time-resolved study of photoexcited Na₃F, probed by photoionization. The pump-probe signal clearly shows damped oscillations, the period of which is fitted to fs, close to twice the previously measured bending mode of Na₂F [1], while the relaxation time is fs.Received: 31 October 2003, Published online: 6 January 2004PACS: 36.40.Qv Stability and fragmentation of clusters - 33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)     

Hopf bifurcation control via a dynamic state-feedback control

To relocate two Hopf bifurcation points, simultaneously, to any desired locations in n-dimensional nonlinear systems, a novel dynamic state-feedback control law is proposed. Analytical schemes to determine the control gains according to the conditions for the emergence of Hopf bifurcation are derived. To verify the effectiveness of the proposed control law, numerical examples are provided.