Experiments on metal clusters of a definite size

Positively and negatively charged metal clusters ions generated by sputtering are investigated by a variety of experimental techniques. Gas-phase experiments include photofragmentation measurements, which reveal information about the ionization energies of silver and aluminum clusters, and gas-phase nickel carbonyl formation, from which the structures of nickel clusters are determined. In addition, the size dependence of the catalytic activity of deposited silver clusters in the development of photographic films are presented.     

Experiments on small (H2)N clusters

The nucleation process of small hydrogen clusters has been studied in detail with space, time, and number size resolution on the basis of supersonic expansions of the gas through a cryogenic nozzle operating in the thermal range 24 < T <110 K. The diagnostic of the jet medium is based on high sensitivity (few photons/sec) Raman spectroscopy with very high spatial resolution ( $\approx 2~\mu$ m), enabling for quantitative measurements with time resolution in the domain of nanoseconds. Temperatures down to 0.1 K have been attained in the jet at a collisional rate low enough to avoid sudden freezing of the gas. Clusters between two and eight molecular units are observed size-resolved. Features of the ortho-ortho and ortho-para hydrogen dimers, and the role of three-body collisions for nascent dimers and trimers are reported.     

Experiments on four-nucleon reactions

The status of experimental evidence on four-nucleon reactions in the range from very low to medium energies (50 MeV) is reviewed. The recent progress of microscopic theories as well as computer capabilities, the renewed interest in astrophysical and the new fusion-energy aspects of the four-nucleon reactions, the emphasis on improved measurements of polarization observables especially at very low energies and on new types of studies such as break-up reactions with polarized projectiles prompt such a survey. The aim is to stimulate interest in the four-nucleon system. It is expected that the four-nucleon system will undergo a development similar to the three-nucleon system as a special testing ground for nuclear forces.     

Comments on small superconducting clusters

The feasibility of an experimental study of small superconducting clusters (SC) is analyzed. Critical sizes for SC are calculated. Oscillations of the energy gap and the diamagnetic susceptibility of SC are considered.     

Directed paths on percolation clusters

We consider a variant of the problem of directed polymers on a disordered lattice, in which the disorder is geometrical in nature. In particular, we allow a finite probability for each bond to be absent from the lattice. We show, through the use of numerical and scaling arguments on both Euclidean and hierarchical lattices, that the model has two distinct scaling behaviors, depending upon whether the concentration of bonds on the lattice is at or above the directed percolation threshold. We are particularly interested in the exponents and, defined by ft and xt , describing the free-energy and transverse fluctuations, respectively. Above the percolation threshold, the scaling behavior is governed by the standard random energy exponents (=1/3 and =2/3 in 1+1 dimensions). At the percolation threshold, we predict (and verify numerically in 1+1 dimensions) the exponents=1/2 and =v/v, where v and v are the directed percolation exponents. In addition, we predict the absence of a free phase in any dimension at the percolation threshold.     

Experiments on positronium negative ions

This paper is a review of new developments in the experimental field of the efficient emission of the positronium negative ion, a bound state of one positron and two electrons, from alkali-metal coated surfaces. Following the prediction of its existence by Wheeler in 1946, this ion has been one of the most attractive subjects for theorists to investigate in the field of positron physics, resulting in a large number of studies. Though the first observation of the ions, formed using a carbon thin film, was made in 1981 by Mills, there have been few experimental works since, limited by the low-production efficiency achievable for nearly 30 years. In 2008, a dramatic effect on the ion emission from tungsten surfaces was discovered upon coating it with Cs. This has opened the door to a new era of experimental investigations of this ion. This paper reports the investigations performed so far. Advances discussed include efficient formation of the ion, its photodetachment and the production of an energy-tunable positronium beam based on the technique of the photodetachment.     

有效衔接基础性实验与设计性实验的探究

引导学生利用现有仪器和原理,将常规基础性实验"惠斯登单臂电桥测电阻"改进为"利用单臂电桥非平衡性测电阻"的设计探索性实验,强化对学生创新精神和研究能力的培养,为开展后面更高层次的设计性实验奠定基础,从而形成基础性实验与设计性实验合理过渡、有序衔接的实验教学体系。     

Experiments on underwater acoustic tomography

Three full-scale experiments on acoustic tomography of the ocean that were carried out under the supervision and with the participation of L.M. Brekhovskikh by researchers from the Shirshov Institute of Oceanology, Russian Academy of Sciences, are described. An attempt is made to combine and generalize the results of three sets of publications devoted to the Norway Sea (1990), THETIS-II (1994), and ACOUS (1998–1999) experiments.     

数字平面全息光栅实验研究

通过数字全息实验平台,制作平面全息光栅,利用高精度CMOS相机记录两束平行光的干涉,改变两平行光束的夹角和光斑相对方向,观测干涉条纹的疏密变化和方向变化,加深学生对光的干涉的理解,训练学生基本光路的搭建与调整。     

基于LED的色度学实验研究

作为环保、节能、可智能控制的新型光源,发光二极管（LED）广泛应用于人们的现代生活、生产中,更有望替代传统的照明光源。以三基色LED为光源,制作了三路独立可调恒流电源,通过调节三基色光的不同配比实现加法混色,研究设计了加法混色的色度学实验,既可以直接观察混色后的实验现象,又能通过测量光谱数据得到色度参数。LED光源环保...     

Theoretical study of small Mo clusters and molecular nitrogen adsorption on Mo clusters

This paper studies the small molybdenum clusters of Mo_n (n=2--8) and their adsorption of N₂ molecule by using the density functional theory (DFT) with the generalized gradient approximation. The optimized structures of Mo_n clusters show the onset of a structural transition from a close-packed structure towards a body-centred cubic structure occurred at n=7. An analysis of adsorption energies suggests that the Mo₂ is of high inertness and Mo₆ cluster is of high activity against the adsorption of N₂. Calculated results indicate that the N₂ molecule prefers end-on mode by forming a linear or quasi-linear structure Mo--N--N, and the adsorption of nitrogen on molybdenum clusters is molecular adsorption with slightly elongated N--N bond. The electron density of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the partial density of states of representative cluster are also used to characterize the adsorption properties of N₂ on the sized Mo_n clusters.     

CO adsorption on neutral iridium clusters

The adsorption of carbon monoxide on neutral iridium clusters in the size range of n = 3 to 21 atoms is investigated with infrared multiple photon dissociation spectroscopy. For each cluster size only a single ν(CO) band is present with frequencies in the range between 1962 cm^-1 (n = 8) and 1985 cm^-1 (n = 18) which can be attributed to an atop binding geometry. This behaviour is compared to the CO binding geometries on clusters of other group 9 and 10 transition metals as well as to that on extended surfaces. The preference of Ir for atop binding is rationalised by relativistic effects on the electronic structure of the later 5d metals.     

X-ray photoemission studies on InSb clusters

The changes in core-level electronic structure of In_1−xSb_x nano-clusters have been studied using X-ray photoelectron spectroscopy. Though, clusters with mean composition InSb show shallow and deep core-level binding energies similar to those of bulk InSb, the Sb and In rich versions show a negative BE shift for the excess element and a positive shift for the minority element. The observed BE shifts have been explained considering a core and surface shell model for the structure of the clusters and possible surface atom core-level shifts.     

A comment on clusters free-energy models

We discuss the concept of the clusters free-energy in nucleation phenomena, and we analyse and compare recent explicit expressions for this quantity.     

甲烷团簇与氘团簇的团簇源特性比较

利用瑞利散射法测量了特定喷嘴产生的甲烷团簇及氘团簇的大小随背压的变化曲线。将团簇大小的实验值与Hagena理论进行了比较,当背压超过3MPa时,两种团簇的实验值都明显高于理论值。实验发现,特定喷嘴在相同的背压下,常温(298K)甲烷团簇尺寸小于低温(80K)氘团簇尺寸,而甲烷团簇中氢原子数至少是氘团簇中氘原子数的1.98倍。     

金属材料激光打孔试验研究

本文通过对激光打孔的有关参数进行统计分析表明,焦距的调整距离、材料厚度及介质压力等参数对成孔形状有明显影响。如何综合考虑来选择这些参数,是激光打孔有待解决的问题。本文作者通过试验来说明对不同材料激光打孔时,其最佳焦距调整值与空气介质和氧气介质的压力大小及材料的厚度之间的关系。试验结果表明,在所有不同的介质压力下,最佳焦距调整值仅随材料厚度的增加而减少。     

Experiments on partially coherent multiple-beam interference

The intensity distribution in the interference pattern of a multiple-slit aperture illuminated with the partially coherent light is examined experimentally. The experimental results showing excellent agreement with the theoretical predictions indicate both a gradual loss in the contrast of interference fringes and a broadening of the principal maximum fringes with decreasing spatial coherence of the illumination.