Electronic-structure-induced deformations of liquid metal clusters

Ab initio molecular dynamics is used to study deformations of sodium clusters at temperatures $500\cdots 1100$ K. Open-shell Na$_{14}$ cluster has two shape isomers, prolate and oblate, in the liquid state. The deformation is stabilized by opening a gap at the Fermi level. The closed-shell Na$_8$ remains magic also at the liquid state.Comment: REVTex, 11 pages, no figures, figures (2) available upon request (e-mail to hakkinen at jyfl.jyu.fi), submitted to Phys. Rev.

Conductance through analytic constrictions

We study the dependence of the intrinsic conductance of a nanocontact on its shape by using the recursion-transfer-matrix method. Hour-glass, torus, and spherical shapes are defined through analytic potentials, the latter two serving as rough models for ring-like and spherical molecules, respectively. The sensitivity of the conductance to geometric details is analyzed and discussed. Strong resonance effects are found for a spherical contact weakly coupled to electron reservoirs.Comment: 7 pages, 12 figure

Tules-kurssien standardien kehittäminen : Suositukset standardiin

Tutkimuksen tavoitteena oli tuottaa tietoa Kelan Tules-kurssien standardien kehittämistä varten. Kelan kuntoutusryhmän aloitteesta toteutettu tutkimus tukee standardien kehittämistä sekä tutkimusnäytön perusteella, että kuulemalla palveluntuottajia ja palveluja käyttäneitä asiakkaita. Standardien kehittämisen tarkoituksena on, että Kelan järjestämät kuntoutuspalvelut voisivat olla entistä vaikuttavampia. Tutkimus koostui viidestä osatutkimuksesta (kirjallisuuskatsaus, kuntoutujien fokusryhmät, palveluntuottajien haastattelut, GAS-tavoitteiden analyysi ja hyvät kuntoutuskäytännöt -kysely). Osatutkimuksista kootun ja analysoidun tutkimustiedon perusteella koottiin suosituksia sisällöistä, joita standardien kehittämisessä voisi huomioida. Suositukset esiteltiin palveluntuottajien edustajille Kelan kuntoutusryhmän järjestämässä työkokouksessa. Yhdeksässä tutkimustietoon pohjautuvassa suosituksessa kiinnitetään huomiota seuraaviin, nykyisessä standardissakin esiintyvien teemojen sisältöihin: tavoitteen asettelu, mittausten määrä, aloitusjakson rakenne ja resurssit, ryhmät, sisällöt, välityöskentely, työelämäyhteys, asiakkaan osallistaminen ja kuntoutuksen seuranta. Osatutkimuksissa tuotettua tietoa voidaan soveltaa hyvinä kuntoutuskäytäntöinä päivittäisessä työssä kuntoutujien kanssa. Kelan kuntoutusryhmän vastuulla on arvioida, millä tavalla tutkimuksessa esille tuodut suositukset voidaan huomioida, muiden standardin laatimiseen vaikuttavien tekijöiden ohella, tulevissa Tules-kurssien standardeissa. Tutkimus on ensimmäinen Kelan vakiintuneen toiminnan standardien kehittämisen tueksi toteutettu tutkimus. Tutkimuksellisesti eri lähestymistavoilla kerätty tieto on täydentänyt toisiaan ja osoittanut, että standardien kehittämisen tueksi nostetut suositukset saavat vahvistusta useamman näkökulman kautta. Tutkimuksessa käytettyä toimintamallia voi soveltaa muidenkin Kelan vakiintuneen toiminnan standardien kehittämiseen

Common Origin for Surface Reconstruction and the Formation of Chains of Metal Atoms

During the fracture of nanocontacts gold spontaneously forms freely suspended chains of atoms, which is not observed for the iso-electronic noble metals Ag and Cu. Au also differs from Ag and Cu in forming reconstructions at its low-index surfaces. Using mechanically controllable break junctions we show that all the 5d metals that show similar reconstructions (Ir, Pt and Au) also form chains of atoms, while both properties are absent in the 4d neighbor elements (Rh, Pd, Ag), indicating a common origin for these two phenomena. A competition between s and d bonding is proposed as an explanation

Humoral Immune Response to Keyhole Limpet Haemocyanin, the Protein Carrier in Cancer Vaccines

Keyhole limpet haemocyanin (KLH) appears to be a promising protein carrier for tumor antigens in numerous cancer vaccine candidates. The humoral immune response to KLH was characterized at the single-cell level with ELISPOT combined with separations of cell populations according to their expression of homing receptors (HRs). The analysis of HR expressions is expected to reveal the targeting of the immune response in the body. Eight orally primed and four nonprimed volunteers received KLH-vaccine subcutaneously. Circulating KLH-specific plasmablasts were found in all volunteers, 60 KLH-specific plasmablasts/106 PBMC in the nonprimed and 136/106 in the primed group. The proportion of L-selectin+ plasmablasts proved high and integrin α4β7+ low. KLH serving as protein carrier in several vaccines, the homing profile of KLH-specific response may be applicable to the cancer antigen parts in the same vaccines. The present data reflect a systemic homing profile, which appears advantageous for the targeting of immune response to cancer vaccines

Multi-shell gold nanowires under compression

Deformation properties of multi-wall gold nanowires under compressive loading are studied. Nanowires are simulated using a realistic many-body potential. Simulations start from cylindrical fcc(111) structures at T=0 K. After annealing cycles axial compression is applied on multi-shell nanowires for a number of radii and lengths at T=300 K. Several types of deformation are found, such as large buckling distortions and progressive crushing. Compressed nanowires are found to recover their initial lengths and radii even after severe structural deformations. However, in contrast to carbon nanotubes irreversible local atomic rearrangements occur even under small compressions.Comment: 1 gif figure, 5 ps figure

Structure and Magnetism of Neutral and Anionic Palladium Clusters

The properties of neutral and anionic Pd_N clusters were investigated with spin-density-functional calculations. The ground state structures are three-dimensional for N>3 and they are magnetic with a spin-triplet for 2<=N<=7 and a spin nonet for N=13 neutral clusters. Structural- and spin-isomers were determined and an anomalous increase of the magnetic moment with temperature is predicted for a Pd_7 ensemble. Vertical electron detachment and ionization energies were calculated and the former agree well with measured values for anionic Pd_N clusters.Comment: 5 pages, 3 figures, fig. 2 in color, accepted to Phys. Rev. Lett. (2001

Close-Packing of Clusters: Application to Al_100

The lowest energy configurations of close-packed clusters up to N=110 atoms with stacking faults are studied using the Monte Carlo method with Metropolis algorithm. Two types of contact interactions, a pair-potential and a many-atom interaction, are used. Enhanced stability is shown for N=12, 26, 38, 50, 59, 61, 68, 75, 79, 86, 100 and 102, of which only the sizes 38, 75, 79, 86, and 102 are pure FCC clusters, the others having stacking faults. A connection between the model potential and density functional calculations is studied in the case of Al_100. The density functional calculations are consistent with the experimental fact that there exist epitaxially grown FCC clusters starting from relatively small cluster sizes. Calculations also show that several other close-packed motifs existwith comparable total energies.Comment: 9 pages, 7 figure

Temperature dependence of surface reconstructions of Au on Pd(110)

Surface reconstructions of Au film on Pd(110) substrate are studied using a local Einstein approximation to quasiharmonic theory with the Sutton-Chen interatomic potential. Temperature dependent surface free energies for different coverages and surface structures are calculated. Experimentally observed transformations from $(1\times1)$ to $(1 \times 2)$ and $(1 \times 3)$ structures can be explained in the framework of this model. Also conditions for Stranski-Krastanov growth mode are found to comply with experiments. The domain of validity of the model neglecting mixing entropy is analyzed.Comment: 7 pages, REVTeX two-column format, 3 postscript figures available on request from [email protected] To appear in Phys. Rev. Letter

Broken Symmetry in Density-Functional Theory: Analysis and Cure

We present a detailed analysis of the broken-symmetry mean-field solutions using a four-electron rectangular quantum dot as a model system. Comparisons of the density-functional theory predictions with the exact ones show that the symmetry breaking results from the single-configuration wave function used in the mean-field approach. As a general cure we present a scheme that systematically incorporates several configurations into the density-functional theory and restores the symmetry. This cure is easily applicable to any density-functional approach.Comment: 4 pages, 4 figures, submitted to PR