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11.
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
12.
Julia Lindberg Peter Saetre Seiji Nishino Emmanuel Mignot Elena Jazin 《BMC neuroscience》2007,8(1):34
Background
Narcolepsy causes dramatic behavioral alterations in both humans and dogs, with excessive sleepiness and cataplexy triggered by emotional stimuli. Deficiencies in the hypocretin system are well established as the origin of the condition; both from studies in humans who lack the hypocretin ligand (HCRT) and in dogs with a mutation in hypocretin receptor 2 (HCRTR2). However, little is known about molecular alterations downstream of the hypocretin signals. 相似文献13.
J. P. Mignot A. Isalgué X. Obradors J. C. Joubert J. Tejada 《Hyperfine Interactions》1986,28(1-4):565-568
The temperature dependence of the hyperfine fields corresponding to ferric ions in the different sublattices of BaLiFe17O27 W-type hexagonal ferrite has been measured. A mean field analysis of these sublattice magnetizations has been done and a set of nearest neighbour isotropic exchange interactions has been obtained. The relative strenght of these fitted exchange values is in accordance with superexchange theory 相似文献
14.
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
15.
V. N. Lazukov P. A. Alekseev E. S. Klement’ev E. V. Nefedova I. P. Sadikov J. -M. Mignot N. B. Kol’chugina O. D. Chistyakov 《Journal of Experimental and Theoretical Physics》1998,86(5):943-952
To examine the effect of hybridization of 4f electrons with conduction electrons on the crystal field potential using neutron spectroscopy, we studied the effects of
the crystal electric field (CEF) in intermetallic compounds of the type ReNi, in which chemical substitution is followed by
a transition of the cerium ions from an intermediate valence state to the Kondo state. Measurements were performed both on
cerium ions in the compounds Ce1−x
LaxNi (x=0.5, 0.8), where they have a whole-number population of the 4f shell, and on the paramagnetic impurity ion Nd in the series of compounds Re1−x
NdxNi (Re=Ce, La, Y), in which the cerium ions are found either in an intermediate valence state or in the Kondo state. From
the neutron inelastic magnetic scattering spectra on Nd ions, we have reconstructed the crystal field parameters in ReNi compounds
and calculated the CEF level diagram of Ce ions in these compounds as functions of the interion distances Re-Ni. The results
of our calculations are in good agreement with the experimentally determined splitting diagram of the ground-state multiplet
of the Ce ions. We have determined that as the degree of hybridization with the conduction electrons grows the CEF potential
varies considerably and the effective splitting of the 4f shell of the cerium ions increases. The estimated energy scale of the splitting of the ground-state multiplet of the Ce3+ ions in the ReNi CEF (ΔCEF∼15 meV) turns out to be commensurate with the Kondo temperature (T
K
;140 K for CeNi. Analysis indicates that the CEF potential has a substantial effect on the formation of the valence-unstable
ground state of the f shell in this compound.
Zh. éksp. Teor. Fiz. 113, 1731–1747 (May 1998) 相似文献
16.
Sans résumé
Mémoire présenté par J. L. Lions 相似文献
17.
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18.
A. V. Rybina P. A. Alekseev K. S. Nemkovski E. V. Nefeodova J. -M. Mignot Yu. B. Paderno N. Yu. Shitsevalova R. I. Bewley 《Crystallography Reports》2007,52(5):770-773
The density of phonon states for the YbB12 Kondo insulator is calculated from the inelastic neutron scattering spectra of this compound. It is established that thermal vibrations of rare-earth atoms predominantly occur in the low-energy range. These atoms are most weakly bound in the crystal structure of the YbB12 Kondo insulator. The high-energy part of the vibrational spectrum is determined by thermal vibrations of the boron atoms forming a rigidly connected structure of the compound. It is revealed that the temperature dependence of the intensity of the phonon peak attributed to thermal vibrations of the ytterbium atoms exhibits an anomalous behavior. This circumstance suggests that the magnetoelastic coupling occurring in the structure of the YbB12 Kondo insulator is relatively strong and can contribute to the magnetic excitation spectrum of this compound. 相似文献
19.
Alekseev PA Mignot JM Nemkovski KS Rybina AV Lazukov VN Ivanov AS Iga F Takabatake T 《J Phys Condens Matter》2012,24(20):205601
Peculiarities in the lattice dynamics of the Kondo insulator Y bB(12) have been studied by inelastic neutron scattering. Selected phonon modes were traced above and below the temperature region (T ~ 50 K) where the gap opens in the electron density of states. The intensities of some low-energy modes exhibit an anomalous temperature dependence for q vectors close to the Brillouin zone boundary, suggesting a renormalization of the phonon eigenvectors. This effect is thought to arise from a coupling with magnetic excitations of the same symmetry, which exist at nearby energies. It is argued that this magnetovibrational coupling may in turn play a role in the steep temperature crossover existing in Y bB(12) between the low-temperature (Kondo insulator) and high-temperature (incoherent spin-fluctuation) regimes, which is rapidly suppressed by lighter Zr substitution. 相似文献
20.
G. Litsardakis D. Samaras A. Collomb J. P. Mignot 《Applied Physics A: Materials Science & Processing》1988,47(4):327-331
The Mn cation distribution in the seven sublattices of theW-type structure has been determined from high temperature neutron diffraction data of a SrMn2Fe16O27 powder sample. The Mn2+ ions enter the tetrahedral sites of blockS with a preference for site 4e. Mn3+ ions in small amounts are found in the octahedral sites, substituting for Fe3+, while 0.3 Fe2+ has been found in site 6g. The sample has the formula SrMn2.4Fe15.6O27. The crystal structure has been described in the non-centrosymmetric Pˉ62c space group, instead of the usual P63/mmc one. The magnetic structure, obtained from low temperature (4.2 K) data, is collinear, with the spins parallel to thec axis, according to the Gorter model. The magnetic moments of the sites give an experimental magnetization valueM
s=28.4(1.5) μB/f.u., in good agreement with magnetic measurements and the theoretical value. 相似文献