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PubMed2001

Isomer spectroscopy in (216)(90)Th(126) and the magicity of (218)(92)U(126).

Excited states in (216)Th were investigated via prompt and delayed gamma decays and the recoil-decay tagging method. The decay schemes of the I(pi) = (8+), t(1/2) = 128(8) micros, the I(pi) = (11-), t(1/2) = 615(55) ns, and the I(pi) = (14+), t(1/2) > or = 130 ns isomers were established. The configuration pi h(9/2)f(7/2) is assigned to the I(pi) = (8+) isomer, which implies that the h(9/2) and f(7/2) states are nearly degenerate. This is ascribed to increased binding of the f(7/2) orbital by its coupling to a low-lying I(pi) = (3-) state at E(x) = 1687 keV. The role of octupole and pairing correlations for a Z = 92 shell closure prediction is discussed on the basis of shell model calculations.

Journal Article↗
PubMed2002

(68)(28)Ni(40): Magicity versus superfluidity.

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)-->2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy. The B(E2) value for (68)Ni(40) is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the B(E2) values and indicates the erosion of the N = 40 harmonic-oscillator subshell by neutron-pair scattering.

Journal Article↗
PubMed2003

"Magic" heteroepitaxial growth on vicinal surfaces.

The step period (Lambda) of vicinal surfaces can be used as a new parameter for the control of metallic heteroepitaxial growth. This is evidenced here in the case of Ag/Cu(211). The deposition of 1 monolayer (ML) exhibits a c(2 x 10) superstructure leading to the formation of [111] steps in the Ag adlayer in contrast with the original [100] steps for the Cu substrate. This wetting layer can be viewed as a (133) Ag plane and it will be the starting point for the epitaxial growth. The deposition of 4 ML shows that the thin Ag film results homogeneous and no twins or stacking faults are detected. Moreover, the film grows along the [133] axis which is the orientation that minimizes the misfit between Cu(211) and the Ag film. Thus, the use of a regular stepped substrate allows one to select the crystallographic orientation of the growth and seems to be a way to avoid the creation of stacking faults.

Journal Article↗
PubMed2005

Melting of sodium clusters: where do the magic numbers come from?

Melting temperatures of Na clusters show size-dependent fluctuations that have resisted interpretation so far. Here we discuss that these temperatures, in fact, cannot be expected to exhibit an easily understandable behavior. The energy and entropy differences between the liquid and the solid clusters turn out to be much more relevant parameters. They exhibit pronounced maxima that correlate well with geometrical shell closings, demonstrating the importance of geometric structure for the melting process. Icosahedral symmetry dominates, a conclusion corroborated by new photoelectron spectra measured on cold cluster anions. In the vicinity of the geometrical shell closings the measured entropy change upon melting is in good agreement with a simple combinatorial model.

Journal Article↗
PubMed2005

Magic number 7+/-2 in networks of threshold dynamics.

Information processing by random feed-forward networks consisting of units with a sigmoidal input-output response is studied by focusing on the dependence of its outputs on the number of parallel paths M. It is found that the system leads to a combination of on-off outputs when M less or similar to 7, while for M greater or similar to 7, chaotic dynamics arises, resulting in a continuous distribution of outputs. This universality of the critical number M approximately 7 is explained by a combinatorial explosion, i.e., the dominance of factorial over exponential increase. The relevance of the result to biological problems is briefly discussed.

Animals↗
PubMed2005

Magic doping fractions for high-temperature superconductors.

We report hole-doping dependence of the in-plane resistivity rho(ab) in a cuprate superconductor La(2-x)Sr(x)CuO4, carefully examined using a series of high-quality single crystals. Our detailed measurements find a tendency towards charge ordering at particular rational hole-doping fractions of 1/16, 3/32, 1/8, and 3/16. This observation appears to suggest a specific form of charge order and is most consistent with the recent theoretical prediction of the checkerboard-type ordering of the Cooper pairs at rational doping fractions x = (2m+1)/2n, with integers m and n.

Journal Article↗
PubMed2005

Mapping the magic numbers in binary Lennard-Jones clusters.

Using a global optimization approach that directly searches for the composition of greatest stability, we have been able to find the particularly stable structures for binary Lennard-Jones clusters with up to 100 atoms for a range of Lennard-Jones parameters. In particular, we have shown that just having atoms of different sizes leads to a remarkable stabilization of polytetrahedral structures, including both polyicosahedral clusters and at larger sizes structures with disclination lines.

Journal Article↗
PubMed2006

Magic structures and quantum conductance of silver nanowires.

We investigate the pathway of thinning process for transient [110] nanowires (NWs) of Ag. The result is in good agreement with experimental observations. An unambiguous identification of the structure of a NW requires at least two views along different directions. In the cases where two views of different NW structures are practically the same for very thin NWs which pose experimental difficulty due to small signal-to-noise ratio, our theoretical analysis helps distinguish these structures. On the basis of conductance (G) calculations vis-á-vis the structure of transient NWs, the puzzling experimental observation of fractionally quantized G values is explained by considering the existence of mixed structures for thin wires.

Journal Article↗
PubMed2006

"Magic melters" have geometrical origin.

Recent experimental reports bring out extreme size sensitivity in the heat capacities of gallium and aluminum clusters. In the present work we report results of our extensive ab initio molecular dynamical simulations on Ga30 and Ga31, the pair which has shown rather dramatic size sensitivity. We trace the origin of this size sensitive heat capacities to the relative order in their respective ground state geometries. Such an effect of nature of the ground state on the characteristics of heat capacity is also seen in case of small gallium and sodium clusters, indicating that the observed size sensitivity is a generic feature of small clusters.

Journal Article↗
PubMed2006

Discovery of 109Xe and 105Te: superallowed alpha decay near doubly magic 100Sn.

Two new alpha emitters 109Xe and 105Te were identified through the observation of the 109Xe --> 105Te --> 101Sn alpha-decay chain. The 109Xe nuclei were produced in the fusion-evaporation reaction 54Fe(58Ni,3n)109Xe and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at Ealpha = 4062 +/- 7 keV and Ealpha = 3918 +/- 9 keV were interpreted as the l = 2 and l = 0 transitions from the 7/2+ ground state in 109Xe (T1/2 = 13 +/- 2 ms) to the 5/2+ ground state and a 7/2+ excited state, located at 150 +/- 13 keV in 105Te. The observation of the subsequent decay of 105Te marks the discovery of the lightest known alpha-decaying nucleus. The measured transition energy Ealpha = 4703 +/- 5 keV and half-life T1/2 = 620 +/- 70 ns were used to determine the reduced alpha-decay width delta2. The ratio delta105Te(2)/delta213Po(2) of approximately 3 indicates a superallowed character of the alpha emission from 105Te.

Journal Article↗
PubMed1999

Dissociation and the self in the magical pre-Oedipal field.

This paper explores the clinical relevance of Jung's idea of the Self in pre-Oedipal and pre-individuation psychology. Incorporating data from neurobiology and recent theories of memory and narrative reconstruction, a post-modern conception of the Self is proposed akin to what Jung called a 'dream of totality'. Such a conception of the Self is distinguished from a reified structure or a deified imago, and is considered to be that aspect of psychological functioning consonant with emerging meanings, and the birth of new psychological ground. Links are made back to Flournoy, William James, and depth psychology's early interest in teleology, the occult, and the creative capacities of the psyche. Updating this mystery tradition, clinical material illustrates how narratives of the Self are present in such pre-Oedipal dynamics as dissociation and projective identification. These dynamics are understood not only as primitive defences but as reconstitutive symbolic metaphors and mythopoetic expressions of an emergent rather than a superordinate Self.

Dissociative Disorders↗
PubMed1997

Magic--'A'.

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