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21.
Supershell structure in alkali metal nanowires 总被引:1,自引:0,他引:1
Nanowires are formed by indenting and subsequently retracting two pieces of sodium metal. Their cross section gradually reduces upon retraction and the diameters can be obtained from the conductance. In previous work we have demonstrated that when one constructs a histogram of diameters from large numbers of indentation-retraction cycles such histograms show a periodic pattern of stable nanowire diameters due to shell structure in the conductance modes. Here, we report the observation of a modulation of this periodic pattern, in agreement with predictions of a supershell structure. 相似文献
22.
Dung T. Tran Ian P. Jones Jon A. Preece Roy L. Johnston Coenraad R. van den Brom 《Journal of nanoparticle research》2011,13(9):4229-4237
Dodecanethiol-capped Cu–Au nanoparticles, synthesized via a successive two-phase (water/toluene) and galvanic-exchange procedure,
were characterized using transmission electron microscopy (TEM). The size range of the particles is around 1–7 nm. Electron-induced
morphological evolution was observed under high resolution (HR) TEM. Cuboctahedral morphology was found to be thermodynamically
stable. Electron-induced aggregation of two particles was also observed. Chemical ordering of cuboctahedral particles was
studied by atomic-resolution high angle annular dark field (HAADF) imaging in scanning TEM (STEM) mode and energy dispersive
X-ray (EDX) element mapping using a silicon drift detector (SDD). The particles were found to be Cu–Au mixed, and to be stable
in air. Surface plasmon resonance (SPR), which is dependent on local structure and morphology, was investigated by electron
energy loss spectroscopy (EELS). 相似文献
23.
M. Derrick K. K. Gan P. Kooijman J. S. Loos B. Musgrave L. E. Price J. Repond K. Sugano M. Valdata-Nappi D. Blockus B. Brabson J. -M. Brom C. Jung H. Ogren D. R. Rust C. Akerlof J. Chapman D. Errede M. T. Ken D. I. Meyer D. Nitz R. Thun R. Tschirhart S. Abachi P. Baringer B. G. Bylsma R. DeBonte D. Koltick F. J. Loeffler E. H. Low R. L. McIlwain D. H. Miller C. R. Ng L. K. Rangan E. I. Shibata B. Cork 《Zeitschrift fur Physik C Particles and Fields》1987,35(3):323-328
The charged particle multiplicity distributions for two-jet events ine + e ? annihilation at 29 GeV have been measured using the High Resolution Spectrometer at PEP. A Poisson distribution describes the data for both the complete event and for the single jets. In addition, no correlation is observed between the multiplicities in the two jets of an event. For fixed values of the prong number of the complete event, the multiplicity sharing between the two jets is in good agreement with a binomial distribution. The rapidity gap distribution is exponential with a slope equal to the mean rapidity density. These observations, which are consistent with a picture of independent emission of single particles, are contrasted to the results from soft hadronic collisions and conclusions are drawn about the nature of clusters. 相似文献
24.
Anthony JM Garrett 《Contemporary Physics》2013,54(2):163-165
The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed. 相似文献
25.
J. Albino O. de Aguiar H. B. Brom L. J. de Jongh G. Schmid 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):457-459
We present EPR measurements on the polynuclear metal-cluster compound Pd561Phen36O200 for temperatures ranging from 300 K to 8 K. No temperature dependence was found in either the resonance field or the line-width. The signal intensity shows a Curie-like behavior. The effect of the ligand on this behavior is discussed. We also discuss the possibility that quantum size effects govern the observed temperature dependence of the line-width and resonance field. 相似文献
26.
M. P. J. van Staveren H. B. Brom L. J. de Jongh G. Schmid 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):451-452
In this paper we present measurements of nuclear relaxation times of31P in the polynuclear cluster compounds Au55(PPh3)12Cl6 and Ru55(P(t-Bu)3)12Cl20. Above 15 K the data can be described as a Korringa process, while below 15 K the relaxation time appears to be thermally activated. 相似文献
27.
Bakharev ON Bono D Brom HB Schnepf A Schnöckel H de Jongh LJ 《Physical review letters》2006,96(11):117002
Compelling evidence for band-type conductivity and even bulk superconductivity below Tc approximately 8 K has been found in (69,71)Ga NMR experiments in crystalline ordered, giant Ga84 cluster compounds. This material appears to represent the first realization of a theoretical model proposed by Friedel in 1992 for superconductivity in ordered arrays of weakly coupled, identical metal nanoparticles. 相似文献
28.
Cletus A D'Souza Vikramjit Chopra Richard Varhol Yuan-Yun Xie Slavita Bohacec Yongjun Zhao Lisa LC Lee Mikhail Bilenky Elodie Portales-Casamar An He Wyeth W Wasserman Daniel Goldowitz Marco A Marra Robert A Holt Elizabeth M Simpson Steven JM Jones 《BMC neuroscience》2008,9(1):1-14
Background
We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.Results
Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.Conclusion
Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex. 相似文献29.
本文报导了采用氩离子激光器来泵浦Pr3+:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转. 相似文献
30.
We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of AT. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included. 相似文献