bluuebunny/crossref_metadata_2025 huggingface dataset:
THE TEMPERATURE DEPENDENCE OF THE SURFACE RELAXATION OF Cu(111) AND Ag(111) — EVIDENCE FOR GIANT ANHARMONIC EFFECTS
Authors: CHAE K. H. , LU H. C. , STATIRIS P. , GUSTAFSSON T.
Published: December 2003

We have used medium energy ion scattering with channeling and blocking to measure the spacing between the two outermost atomic layers on the (111) faces of Cu and Ag as a function of temperature. The Ag (111) surface undergoes a dramatic transformation from being slightly contracted at room temperature to being strongly expanded (+10% of the bulk spacing) around 900°C. Cu (111) shows similar but smaller effects. The change of the surface lattice constant is paralleled by large enhancements of the surface vibration amplitudes. We therefore conclude that our observations are due to large anharmonic effects at the surface. We further discuss our results in terms of a recent microscopic theoretical analysis.
TEMPERATURE DEPENDENCE OF THE STRUCTURE OF Al(110) AND Au(110) SURFACES
Authors: SCHWARZ M. , MAYER C. , VON BLANCKENHAGEN P. , SCHOMMERS W.
Published: December 2003

By temperature-dependent low energy electron diffraction experiments at the Al(110) and the Au(110) surface the roughening transition temperature and the characteristic temperature for the onset of surface melting were determined.
LOW ADATOM MOBILITY ON THE (1 × 2)-MISSING-ROW RECONSTRUCTED Au(110) SURFACE
Authors: GÜNTHER S. , HITZKE A. , BEHM R. J.
Published: December 2003

Adsorption and mobility of Au adatoms on Au (110)-(1×2) were studied by low temperature scanning tunneling microscopy (STM). Up to 0.4-monolayer coverage the troughs of the missing row reconstruction are preferentially filled. By following the mobility of individual adatoms at 125 K and 170 K the adatom hopping barrier inside the troughs in the [Formula: see text] direction is determined to Ed=0.40–0.44 eV, while for diffusion on locally unreconstructed parts of the surface we obtain a lower limit of 0.38 eV. By comparing the cluster size distribution obtained for themally immobile adatoms at 125 K with that from simulations, it is demonstrated that transient mobility plays no significant role in Au / Au (110) self-adsorption. During Au deposition at 190 K domain boundaries ("faulted troughs") are observed to form in the 1× 2 substrate; a tentative mechanism involving exchange diffusion of Au adatoms is proposed.
MISSING-ROW CONTRACTIVE RECONSTRUCTION ON Au(311)
Authors: ERCOLESSI FURIO , TOSATTI ERIO
Published: December 2003

All the low-index surfaces of gold are known to reconstruct, and their vicinals often exhibit magic orientations. The (311) orientation lies in between (100) and (111), and can be regarded as either a (111) or (100) vicinal with a very high step density, or as a flat open surface. In view of rather puzzling reconstructions observed experimentally [(1 × 4), (1 × 5), (1 × 6)], we have undertaken a structural study of Au(311) using the glue model and molecular-dynamics-based simulated annealing. The optical geometry is a (1 × 5) missing-row structure with (111) and reconstructed (100) microfacets, and an alternation of (1 × 2) and (1 × 3) hills. An extra atomic row is present on (1 × 3) hills to optimize packing. The experimentally observed disappearance of the reconstruction between 700 and 750 K is probably associated with an order–disorder transition similar to that of Au(110).
APPLICATION OF A DIRECT ALGEBRAIC METHOD OF CORRELATION FUNCTION CALCULATIONS TO THE THEORY OF ATOMIC ORDERING AT THE SURFACE
Authors: NEBOGATIKOV N. M.
Published: December 2003

The formalism of a direct algebraic method of correlation function calculations in quantum statistical physics is applied to the problem of atomic ordering in binary alloys with the pair interaction between atoms in all coordinational spheres both at the surface and in the bulk.
SURFACE ALLOY FORMATION IN THE Cu–Pd(111) SYSTEM: A KTBIM APPROACH
Authors: GALLIS C. , LEGRAND B. , TRÉGLIA G.
Published: December 2003

We study the kinetics of formation and dissolution of surface alloy obtained by depositing one monolayer of Pd on Cu(111) at room temperature. This is performed within the kinetic tight-binding Ising model. We also present the equilibrium segregation isotherm for Pd c Cu 1-c(111) and show the relation between kinetics (surface alloy) and equilibrium (alloy surface) via the local equilibrium concept.
CLUSTER STRUCTURE OF THE SURFACE OF Al65Cu20Fe15 ALLOY IN THE QUASICRYSTALLINE AND LIQUID STATE
Authors: SHABANOVA I. N. , KHOLZAKOV A. V. , BELASH V. P. , KLIMOVA I. N. , KRAPOSHIN V. S.
Published: December 2003

The atomic structure of an alloy is mainly affected by its electronic structure. The studies of the electronic structure of Al65Cu20Fe15 in both the liquid and quasicrystalline state show that the surface of the sample contains clusters with strong hybridized bonds between atoms which are similar in the liquid and quasicrystalline state. This fact confirms qualitatively the concept of cluster structure of quasicrystals.
NUCLEATION AND GROWTH OF Cu/Ni(100): A VARIABLE TEMPERATURE STM STUDY
Authors: MÜLLER B. , NEDELMANN L. , FISCHER B. , BRUNE H. , KERN K.
Published: December 2003

A detailed study of the nucleation and growth of Cu on Ni(100) as a function of substrate temperature and deposition rate by variable temperature STM is reported. By the quantitative analysis of the saturation island density as a function of temperature and flux for submonolayer coverages, we have deduced the migration barrier (0.35 eV), the dimer bond energy (0.46 eV) as well the sizes of the the critical nuclei. Because the dimer bond energy is large with respect to the migration barrier, a well-defined transition from a critical nucleus of 1 to 3 has been observed, as expected from the adsorption site geometry on square lattices. The large dimer bond energy of Cu on Ni(100) is one of the physical reasons for the recently uncovered strain relief mechanism via internal {111} faceting. The substantially increased island density on mono- and bilayer copper films on Ni(100) with respect to multilayer films might also be attributed to the enhanced lateral bonding.
COMBINED HRLEED AND STM INVESTIGATIONS ON THE INITIAL STAGES OF Cu HETEROEPITAXY Ru(0001)
Authors: AMMER CH. , MEINEL K. , WOLTER H. , BECKMANN A. , NEDDERMEYER H.
Published: December 2003

Recent scanning tunneling microscopy (STM) observations revealed different layer structures in the heteroepitaxial Cu/Ru(0001) system with increasing film thickness attributed to various stages of strain relaxation. High-resolution low-energy electron diffraction (HRLEED) analysis permits one to derive more exactly both lattice periodicities and lattice rotations. Furthermore, the representative character of local STM results can be proved. However, STM measurements are needed to identify and to assign the satellite spots to coexistent different superstructures which are superposed incoherently in the diffraction pattern. Generally, the integral LEED results confirm the crystallographic data obtained by STM in a local scale.
X-RAY SURFACE DIFFRACTION OF METAL DEPOSITS AT METAL/LIQUID INTERFACES PART I: COPPER DEPOSIT ON Au(100)
Authors: CAPPADONIA M. , ROBINSON K. M. , SCHMIDBERGER J. , STIMMING U.
Published: December 2003

In this work the Cu deposition on Au (100) in aqueous perchloric acid has been investigated by in situ X-ray surface diffraction (XRSD). The Cu deposition reaction on gold single crystals exhibits an underpotential deposition (UPD) whereby a fraction of a monolayer is formed. The XRSD measurements show that the Cu UPD layer has a primitive (1×1) structure and that the adsorbed Cu species sit in fourfold hollow sites with a vertical distance between the Cu adlayer and the gold surface of 1.4 Å. The results are discussed in consideration of STM,1 EXAFS2 and XSW3 experiments.
GROWTH INVESTIGATIONS OF ULTRATHIN Ag FILMS ON Pt(111) USING STM AND DYNAMICAL WORK FUNCTION MEASUREMENTS
Authors: GESTERMANN S. , NOHLEN M. , SCHMIDT M. , WANDELT K.
Published: December 2003

The growth of Ag on Pt(111) has been studied with in situ work function change measurements and STM at deposition temperatures of 350 K and 520 K. The strain of the compressively stressed Ag monolayer is relieved in the submonolayer regime by the development of two different reconstructions. One of these reconstructions occurs only at higher coverages (Θ<0.85 ML), partially displacing the other reconstruction which is found on all submonolayer Ag films. For coverages beyond one monolayer the first monolayer Ag becomes pseudomorphic with the Pt(111) substrate. Based on a different work function behavior for a deposition at 350 K and 520 K, respectively, we suggest different mechanisms for the disappearance of these reconstructions during the completion of the first Ag layer and the initial growth of the second layer.
VALENCE-BAND PHOTOEMISSION STUDY OF (Ba, Cs) on W(110)
Authors: PI TUN-WEN , HONG LE-HONG , WU RONG-TZONG , CHENG CHIU-PING
Published: December 2003

We present the first valence-band photoemission study of Ba and Cs on an atomically clean W(110) surface. The cleanness of the tungsten substrate can be justified from both high surface 4f core emission and sharp surface states in the valence-band spectra. Upon Ba (Cs) adsorption, the work function is lowered to 2.02 (1.76) eV, corresponding to one third of a monolayer. Further, the two symmetric high-lying surface states move little in energy but quench rapidly in intensity and diminish at the work-function minimum. On the other hand, the low-lying surface state at 1.41 eV shifts about 215 meV toward higher binding energy and reduces its emission at thicker coverage. The bonding of the Ba d orbital with the W d-like surface states is not found, in contrast to the theoretical calculation and angle-resolved inverse photoemission study of Ba on W(100) . From the coverage-dependent interfacial electronic structure and the parallel behaviors manifest in both Ba on W and Cs on W , the polarized-covalent model for the alkali-metal–substrate interactions is firmly reinforced.
THEORY OF ALKALI-INDUCED RECONSTRUCTION OF THE Cu(100) SURFACE
Authors: QUASSOWSKI S. , HERMANN K.
Published: December 2003

LEED experiments show that Li adsorbed at Cu(100) surfaces at room temperature induces a (2×1) missing row substrate reconstruction while adsorption at lower temperatures, T=180 K , results in an unreconstructed Cu (100)+c(2× 2)-Li overlayer structure. Substrate reconstruction has not been observed for Na or for K adsorption. In order to study the specific reconstruction behavior of the Li adsorbate ab initio DFT calculations have been performed on Cu(100) + Ad, Ad = Li, Na, K, systems at coverages Θ Ad =0.25–0.5 with and without reconstruction. The calculations show that the (2×1)MR-reconstructed surface lies energetically above the ideal (1×1) surface by 0.2 eV per unit cell. However, alkali binding is stronger in the MR geometry as compared to that of the ideal surface where the increase in bond strength becomes smaller in going from Li to Na to K . As a result, the MR-reconstructed and the overlayer adsorbate systems are energetically very close for Cu (100) + Li while for Na and K the overlayer geometry is always favored.
ADSORPTION SITE CHANGE FOR Cs, Rb OR K ADSORPTION ON Ag(111)
Authors: KAUKASOINA P. , LINDROOS M. , LEATHERMAN G. S. , DIEHL R. D.
Published: December 2003

The adsorption geometries for the primitive (3×3), (2×2) and ([Formula: see text] structures of K, Rb and Cs on Ag(111) have been determined using low-energy electron diffraction. In the lower-coverage (3×3) and (2×2) structures, the adatoms occupy fcc hollow sites, while in the [Formula: see text]; structure they occupy the hcp hollow sites. The fcc hollow structures are accompanied by significant substrate rumpling. There is no significant coverage-dependent or site-dependent change in chemisorption bond length. However, there is a large coverage-dependent anisotropy of vibrational amplitude of the adatoms, with the parallel component as much as five times larger than the perpendicular component at low coverages.
COMPLETION OF THE DETERMINATION OF COMPLEX SURFACE STRUCTURES FORMED ON LOW-INDEX PLANES OF COPPER SINGLE CRYSTAL BY Li DEPOSITION: Cu(110)-(4×1)-3Li
Authors: MIZUNO SEIGI , JIANG HONG , TOCHIHARA HIROSHI
Published: December 2003

With increasing Li coverage on Cu(110), (n×1)(4≤n≤8) structures follow the (1×2) missing-row structure at room temperature. We determine the (4×1) structure by a dynamical low-energy electron diffraction (LEED) analysis with symmetrized automated tensor LEED. This completes the solution of the complex surface structures formed on low-index planes of copper single crystal by Li deposition. Every fourth Cu row in the [001] direction is substituted by Li atoms and the remaining Cu rows are covered by Li adatoms. Features of this structure, denoted as Cu (110)-(4×1)-3 Li , are very similar to those of the previously determined Cu (001)-(3×3)-5 Li , Cu (001)-(4×4)-10 Li and Cu (111)-(2×2)-3 Li structures.
(n×n) SURFACE STRUCTURES FORMED COMMONLY ON Cu(001), Ag(001) AND Ni(001) BY ALKALI-METAL ADSORPTION
Authors: JIANG HONG , IMAKI MASAO , MIZUNO SEIGI , TOCHIHARA HIROSHI
Published: December 2003

We have studied structures formed on Ag(001) by Na adsorption at 300 K and on Ni(001) by Li deposition at 370 K by means of low energy electron diffraction (LEED). Structure sequences (2×1)→(3×3)→(4×4)→(4×2)→(2×1) and c (2×2)→(4×4)→(5×5) are found with increasing coverages for Na / Ag (001) and Li / Ni (001), respectively. The (3×3) for Na / Ag (001) is determined by tensor LEED analysis to be identical to the previously determined (3×3) structure formed for Li / Cu (001). We suggest that the (4×4) structures for Na / Ag (001) and Li / Ni (001) are also identical to the previously determined (4×4) for Li / Cu (001), and that the (5×5) for Li / Ni (001) is analogous to the (3×3) and (4×4) structures.
STRUCTURE CHANGES FOR Cu(111)/Li OBSERVED VIA DISCRETE QUANTUM WELL STATES
Authors: CARLSSON A. , CLAESSON D. , KATRICH G. , LINDGREN S.-Å , WALLDÉN L.
Published: December 2003

Via photoemission in the near UV from discrete quantum well states, four different types of atom rearrangements are observed for Cu (111)/ Li . In the monolayer range a gradual energy shift reflects a gradual compression of the Li layer as more atoms are adsorbed. The onset of Li substitution and formation of a (2×2) structure when, at RT, monolayer Li coverage is exceeded is monitored via the appearance of a quantum well state characteristic of the new phase. A small energy shift indicates that, if it is cooled (170 K), the new structure is unstable with respect to Li adsorption. Finally, an energy downshift with increasing coverage observed for a state characteristic of 2 ML Li is ascribed to an increasing area for one-atomic-layer-high islands formed by Li atoms on top of the first full layer.
CHARACTERIZATION OF THE MAGNETIC STRUCTURE OF Cr on Pd(001) BY SPIN-POLARIZED AND ANGLE-RESOLVED PHOTOELECTRON DIFFRACTION
Authors: RENNERT P. , HERGERT W. , MÜCK W. , CHASSÉ A.
Published: December 2003

Recent investigations of the magnetic structure of Cr layers on Pd (001) have shown that two structures appear dependent on the number of Cr layers which have an in-plane antiferromagnetic structure and a layer antiferromagnetic structure, respectively. It is shown that these magnetic structures should be distinguishable experimentally by spin-polarized photoelectron diffraction experiments.

The photoelectron intensity from the Cr 2 p 1/2 core level is calculated for normal incidence of left and right circularly polarized light. It is shown that there is a strong dichroism and spin polarization in the intensities. Dichroism and spin polarization are analyzed with respect to their sources, and thus the contribution of the magnetic scattering is separated. It is an essential contribution for a monolayer Cr on Pd (001).
GROWTH AND ATOMIC STRUCTURE OF ULTRATHIN COBALT LAYERS ON THE Cu(111) FACE CLEAN AND PRECOVERED WITH LEAD
Authors: MRÓZ S. , OTOP H. , JANKOWSKI Z.
Published: December 2003

The growth and atomic structure of ultrathin Co layers deposited on the clean Cu(111) face and precovered with about 0.7 ML of Pb were investigated with the use of Auger electron spectroscopy and directional elastic peak electron spectroscopy (DEPES). Auger spectra for the clean Cu (111) face and covered with 1.5 ML of Co indicate the growth of cobalt bilayer islands sunk at one-monolayer depth in the substrate and covered with one monolayer of copper. The ratio of M2,3VV cobalt and copper Auger peak heights increases with cobalt coverage faster for the Pb -precovered Cu(111) face than for the clean surface. DEPES profiles reveal the threefold symmetry of the cobalt layer up to 4.5 ML. For higher coverages, an arrangement of a sixfold symmetry appears, indicating the presence of fcc(111) cobalt domains rotated 60° with respect to the substrate (i.e. growing after a stacking fault abcbac) separated from the abcabc domains by the bcb layer with the hcp structure.
A bcc–fcc TRANSITION OF A Cu PRECIPITATE IN A bcc Fe–Cu MATRIX
Authors: STOOP PAULINA M. , VAN DER MERWE JAN H. , SHIFLET C. J. , JOHNSON R. A.
Published: December 2003

Three-dimensional, roughly spherical coherent bcc Cu precipitates form in bcc Fe – Cu alloys of low Cu concentration. When the precipitate reaches a critical radius R * of about 60 Å, the precipitate structure changes from coherent bcc to incoherent fcc. Embedded atom method atomic interaction potentials are used to calculate the volume defect energies of Cu precipitate atoms and of Cu – Fe interfacial defect energies. An energetic balance criterion is used to predict a critical radius R somewhat different from R *. Reasons for the discrepancy are discussed.
ADSORBATE-INDUCED GLOBAL AND LOCAL EXPANSIONS AND CONTRACTIONS OF A CLOSE-PACKED TRANSITION METAL SURFACE
Authors: MENZEL DIETRICH
Published: December 2003

For over 20 adsorbate and coadsorbate systems on Ru(0001), the changes of the distance between the first and the second metal layer, d12, are compared. These are taken from geometrical structures which, except for very stable (O, S and Cs) layers, have been determined using a LEED data acquisition system based on a slow scan CCD camera, constructed to minimize the total dose necessary for the accumulation of full IV data without radiation damage. The reproducibility is such that a relative accuracy of d12 of better than 0.02 Å is likely. For the overall (center of mass) changes of d12, we find that in most cases the sign of the change can be correlated with the character of the adsorbate: electronegative adsorbates tend to increase d12, while electropositive or strongly polarizable adsorbates such as noble gases lead to a further contraction beyond that seen for the clean surface (-2.5%). The local changes of d12 are very complex and corroborate the view that even the close-packed surface of a highly refractory metal responds very flexibly to the local electron rearrangement caused by the bonding of adsorbates. Some existing ideas and arguments directed at a conceptual understanding of the observed changes are discussed.
XPS AND XPD ANALYSIS OF NITROGEN ADSORPTION ON THE Ti(0001) SURFACE
Authors: FRICKEL D. P. , KUZNETSOV M. V. , SHALAEVA E. V.
Published: December 2003

X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD) were used to examine the kinetics of nitrogen adsorption on the Ti(0001) surface at temperatures from 220 to 570 K and adsorption exposures from 0 to 1000 L. At the adsorption temperature T=300 K two chemically nonequivalent states of nitrogen were found: NI (1×1 lattice) localized in octapores between the first and second titanium monolayers and NII (presumably [Formula: see text] structure) on the titanium surface. The third nitrogen state, N0 , which is also localized on the surface but has unoccupied octapores in the nearest neighborhood, is observed with a decrease in the adsorption temperature to 220 K. A model of nitrogen interaction with the Ti(0001) surface in vacuum was proposed proceeding from the temperature dependence of the kinetic adsorption curves.
STRUCTURAL DETERMINATION OF THE Si/Cu(110) INTERFACE BY PHOTOELECTRON DIFFRACTION
Authors: ROJAS C. , MARTÍn-GAGO J. A. , ROMÁN E. , PAOLUCCI G. , BRENA B. , COCCO D.
Published: December 2003

Deposition of 0.5 Si monolayer (ML) on a Cu (110) surface at room temperature (RT) leads to the formation of a c(2×2) LEED pattern. In order to find out the surface atomic structure of this ordered phase, X-ray photoelectron diffraction (XPD) azimuthal scans at different photon energies and full hemispherical XPD patterns of the Si 2 p core level have been measured using both synchrotron radiation and a laboratory source. We present an atomic model for the surface structure based on the examination of forward scattering and first order interference XPD features. Refinement of the structural parameters was achieved by performing single scattering cluster (SSC) calculations. In the proposed model Si atoms replace Cu atoms at the surface along the [Formula: see text] atomic rows.
A STUDY OF ADSORBATE VIBRATIONS AT CRYOGENIC TEMPERATURES
Authors: CAMPLIN J. P. , CLOWES S. K. , COOK J. C. , Mccash E. M.
Published: December 2003

Reflection-absorption infrared spectroscopy (RAIRS) has been used to probe adsorbate vibrations in the temperature range below 77 K (the base temperature obtained in most RAIRS experiments), by cooling the metal sample with liquid helium. Spectra can be recorded routinely at any desired temperature from 23 K to the desorption temperature during any experiment using the apparatus which we have constructed.

We report on the adsorption of CO on Pd(100) where CO adopts only bridging sites below 77 K. A significant interaction between the physisorbed and chemisorbed layers is observed using RAIRS.

RAIRS spectra of physisorbed CO 2 on Cu(100) are presented and illustrate the potential of the application of RAIRS to the study of growth and phase formation of molecular crystals.
SURFACE RECONSTRUCTIONS ON GOLD IN CONTACT WITH SOLUTION
Authors: THURGATE S. M. , NAUMOVSKI T. , HALE P. , FINLAYSON K.
Published: December 2003

The low index planes of Au display a number of reconstructions when prepared in vacuum. UHV studies have established that the (100) surface relaxes to a (1×1) surface structure with the adsorption of very small amounts of ad-atoms. This (1×1) surface has been referred to as a metastable surface, and it quickly reverts to the reconstructed surface on heating to mild temperatures (200°C) in vacuum. Early reports indicated that this surface also reverted to a (1×1) if brought into contact with water, though more recent work suggests that this is not necessarily the case. We have just completed construction of a UHV system, equipped with AES, LEED and STM, designed to track changes in surface structure due to reactions in solution. The sample can be brought into contact with a solution without exposure to air, and we have used this to study the effect of exposing the (100) and (110) surfaces of Au to pure H2O . The LEED and STM measurements from these surfaces suggest that they revert to the (1×1), even though the AES indicates that the surface is clean. Whether or not the surface reconstruction is induced by contact with water and not the adsorption of very small amounts of specific ions which are subsequently desorbed, is however, not resolved by these experiments.
ON HARMONIC INVERSION OF CROSS-CORRELATION FUNCTIONS BY THE FILTER DIAGONALIZATION METHOD
Authors: MANDELSHTAM VLADIMIR A.
Published: December 2003

Harmonic inversion of Chebyshev correlation and cross-correlation functions by the filter diagonalization method (FDM) is one of the most efficient ways to accurately compute the complex spectra of low dimensional quantum molecular systems. This explains the growing popularity of the FDM in the past several years. Some of its most attractive features are the predictable convergence properties and the lack of adjusting parameters. These issues however are often misunderstood and mystified. We discuss the questions relevant to the optimal choices for the FDM parameters, such as the window size and the number of basis functions. We also demonstrate that the cross-correlation approach (using multiple initial states) is significantly more effective than the conventional autocorrelation approach (single initial state) for the common case of a non-uniform eigenvalue distribution.
EXACT AND CONSTRAINED KINETIC ENERGY OPERATORS IN POLYSPHERICAL COORDINATES
Authors: GATTI FABIEN , IUNG CHRISTOPHE
Published: December 2003

In this paper the derivation of exact and constrained kinetic energy operators in curvilinear coordinates is presented in a very general context. The polyspherical approach allows us to provide simple and explicit expressions of these operators which are well adapted to the numerical approaches used to solve the Schrödinger equation. These expressions can be exploited to treat a lot of problems such as the calculation of infrared or photoabsorption spectra as well as the study of intramolecular vibrational relaxation of molecules or the study of reactive scattering systems. Special emphasis is placed on concrete applications.
THEORETICAL STUDIES OF $\tilde{A}{}^1
A^{\prime\prime}\to\tilde{X}{}^1 A^\prime$ RESONANCE EMISSION SPECTRA OF HCN/DCN USING SINGLE LANCZOS PROPAGATION METHOD
Authors: XU DINGGUO , GUO HUA , XIE DAIQIAN
Published: December 2003

Using an efficient single Lanczos propagation method, we report the [Formula: see text] resonance emission spectra of HCN and DCN from a number of low-lying vibrational levels of the Ã-state manifold. Our calculations represent the first such undertaking in which a high-quality ab initio based potential energy surface of the excited (Ã1 A″) state and a [Formula: see text] transition dipole surface were used. The results show a significant improvement over previous theoretical work in reproducing experimental stimulated emission pumping spectra of HCN. The improved theory-experiment agreement is attributed to the accurate Ã-state potential energy surface, while the impact of the transition dipole function was found to be relatively minor.
THEORETICAL DETERMINATION OF ROVIBRATIONAL ENERGIES AND ANOMALOUS ISOTOPIC EFFECT OF WEAKLY BOUND CLUSTER HXeOH
Authors: YU HUA-GEN , MUCKERMAN JAMES T.
Published: December 2003

The rovibrational energy levels of HXeOH and its isotopomers have been calculated using a two-layer Lanczos algorithm in Radau-diatom-Jacobi coordinates based on a high level ab initio potential energy surface. The surface is obtained by fitting to 1229 RCCSD(T)/SDB-cc-pVQZ energy points. The equilibrium geometry of HXeOH is determined to have a trans configuration with a nearly collinear HXeO bond angle of 177.32 degrees. The well depth of this minimum is only 0.6123 eV with respect to the OH + Xe + H dissociation limit. The results show that the H–Xe stretching frequency of HXeOH and HXeOD has an anomalous isotopic shift upon 18 O isotope substitution, whereas the D–Xe stretch in DXeOH and DXeOD displays a normal isotopic shift. This trend is consistent with the experimental observations in a Xe solid matrix. The present results predict a lower frequency for the H–Xe stretch than was observed in the solid matrix experiment. Either these results are too low or there is a strong blue shift due to the matrix in the experimental values.
THE EQUILIBRIUM CONSTANTS FOR MOLECULAR HYDROGEN ADSORPTION IN CARBON NANOTUBES BASED ON ITERATIVELY DETERMINED NANO-CONFINED BOUND STATES
Authors: LU TUN , GOLDFIELD EVELYN M. , GRAY STEPHEN K.
Published: December 2003

A model for H 2 inside single-walled carbon nanotubes is outlined. ARPACK (the Arnoldi package), a robust iterative matrix-vector eigenvalue software library, is used to determine the allowed quantum states of H 2 inside various carbon nanotubes. This information is used to construct the equilibrium constants for H 2 adsorption as a function of temperature for a variety of CNTs.
ACCURATE AND HIGHLY EFFICIENT CALCULATION OF THE O(1D)HCl VIBRATIONAL BOUND STATES, USING A COMBINATION OF METHODS
Authors: BIAN WENSHENG , POIRIER BILL
Published: December 2003

Hypochlorous acid, HOCl, is an important intermediate in the O (1D) HCl reactive system. Due in part to a large number of vibrational bound states (over 800), extremely large direct product basis sets (around 300,000) are required to compute the energy levels just below the dissociation threshold. This situation, combined with a very high density of states, results in difficult convergence for iterative methods — e.g. Lanczos requires 50,000 iterations, and filter diagonalization uses 60,000 iterations. In contrast, using new methodologies, we are able to compute the highest-lying bound states with only 271 iterations, although the CPU cost per iteration is substantially greater. Lower lying states are also computed, for a fraction of the CPU cost of the highest energy calculation.
A TWO-GRID TIME-DEPENDENT FORMALISM FOR THE MAXWELL EQUATION
Authors: NEUHAUSER DANIEL , BAER ROI
Published: December 2003

We develop a formalism for efficient iterative solutions of scattering problems involving the Maxwell equations. The methods, borrowed from recent advancements in chemical reaction dynamics, represent the scattering wavefunctions on two grids; one used for the initial wave and is one-dimensional; the other is a small three-dimensional grid padded with absorbing-potentials on which the scattered function is represented. The formalism is automatically suitable for scattering studies of transmission, reflection and scattering components of a wave. The simulations can be done with time-dependent wavepackets or direct iterative solution for the Green's function, but the results are rigorous time-independent (frequency-dependent) scattering amplitudes. Model time-dependent simulations involving up to a 100×100×100 grid for the inner wavefunction were numerically done on a simple PC.
Functional Matrix: A Conceptual Framework for Predicting Multiple Plant Effects on Ecosystem Processes
Authors: Eviner Valerie T. , Chapin III F. Stuart
Published: December 2003

▪ Abstract  Plant species differ in how they influence many aspects of ecosystem structure and function, including soil characteristics, geomorphology, biogeochemistry, regional climate, and the activity and distribution of other organisms. Attempts to generalize plant species effects on ecosystems have focused on single traits or suites of traits that strongly covary (functional groups). However, plant effects on any ecosystem process are mediated by multiple traits, and many of these traits vary independently from one another. Thus, most species have unique combinations of traits that influence ecosystems, and there is no single trait or functional-group classification that can capture the effects of these multiple traits, or can predict the multiple functions performed by different plant species.

We present a new theoretical framework, the functional matrix, which builds upon the functional group and single trait approaches to account for the ecosystem effects of multiple traits that vary independently among species. The functional matrix describes the relationship between ecosystem processes and multiple traits, treating traits as continuous variables, and determining if the effects of these multiple traits are additive or interactive. The power of this approach is that the ecosystem effects of multiple traits are the underlying mechanisms determining species effects, how the effects of an individual species change across seasons and under varying environmental conditions, the nonadditive effects of plant species mixtures, and the effects of species diversity.
The Ecology of Bird Introductions
Authors: Duncan Richard P. , Blackburn Tim M. , Sol Daniel
Published: December 2003

▪ Abstract  A growing number of species have been transported and introduced by humans to new locations and have established self-sustaining wild populations beyond their natural range limits. Many of these species go on to have significant environmental or economic impacts. However, not all species transported and introduced to new locations succeed in establishing wild populations, and of the established species only some become widespread and abundant. What factors underlie this variation in invasion success? Here, we review progress that has been made in identifying factors underpinning invasion success from studies of bird introductions. We review what is known about the introduction, establishment, and spread of introduced bird species, focusing on comparative studies that use historical records to test hypotheses about what factors determine success at different stages in the invasion process. We close with suggestions for future research.
Effects of Introduced Bees on Native Ecosystems
Authors: Goulson Dave
Published: December 2003

▪ Abstract  Bees are generally regarded as beneficial insects for their role in pollination, and in the case of the honeybee Apis mellifera, for production of honey. As a result several bee species have been introduced to countries far beyond their home range, including A. mellifera, bumblebees (Bombus sp.), the alfalfa leafcutter bee Megachile rotundata, and various other solitary species. Possible negative consequences of these introductions include: competition with native pollinators for floral resources; competition for nest sites; co-introduction of natural enemies, particularly pathogens that may infect native organisms; pollination of exotic weeds; and disruption of pollination of native plants. For most exotic bee species little or nothing is known of these possible effects. Research to date has focused mainly on A. mellifera, and has largely been concerned with detecting competition with native flower visitors. Considerable circumstantial evidence has accrued that competition does occur, but no experiment has clearly demonstrated long-term reductions in populations of native organisms. Most researchers agree that this probably reflects the difficulty of carrying out convincing studies of competition between such mobile organisms, rather than a genuine absence of competitive effects. Effects on seed set of exotic weeds are easier to demonstrate. Exotic bees often exhibit marked preferences for visiting flowers of exotic plants. For example, in Australia and New Zealand many weeds from Europe are now visited by European honeybees and bumblebees. Introduced bees are primary pollinators of a number of serious weeds. Negative impacts of exotic bees need to be carefully assessed before further introductions are carried out.
The Effects of Genetic and Geographic Structure on Neutral Variation
Authors: Charlesworth Brian , Charlesworth Deborah , Barton Nicholas H.
Published: December 2003

▪ Abstract  Variation within a species may be structured both geographically and by genetic background. We review the effects of such structuring on neutral variants, using a framework based on the coalescent process. Short-term effects of sex differences and age structure can be averaged out using fast timescale approximations, allowing a simple general treatment of effective population size and migration. We consider the effects of geographic structure on variation within and between local populations, first in general terms, and then for specific migration models. We discuss the close parallels between geographic structure and stable types of genetic structure caused by selection, including balancing selection and background selection. The effects of departures from stability, such as selective sweeps and population bottlenecks, are also described. Methods for distinguishing population history from the effects of ongoing gene flow are discussed. We relate the theoretical results to observed patterns of variation in natural populations.
Performance Comparisons of Co-Occurring Native and Alien Invasive Plants: Implications for Conservation and Restoration
Authors: Daehler Curtis C.
Published: December 2003

▪ Abstract  In the search to identify factors that make some plant species troublesome invaders, many studies have compared various measures of native and alien invasive plant performance. These comparative studies provide insights into the more general question “Do alien invasive plants usually outperform co-occurring native species, and to what degree does the answer depend on growing conditions?” Based on 79 independent native-invasive plant comparisons, the alien invaders were not statistically more likely to have higher growth rates, competitive ability, or fecundity. Rather, the relative performance of invaders and co-occurring natives often depended on growing conditions. In 94% of 55 comparisons involving more than one growing condition, the native's performance was equal or superior to that of the invader, at least for some key performance measures in some growing conditions. Most commonly, these conditions involved reduced resources (nutrients, light, water) and/or specific disturbance regimes. Independently of growing conditions, invaders were more likely to have higher leaf area and lower tissue construction costs (advantageous under high light and nutrient conditions) and greater phenotypic plasticity (particularly advantageous in disturbed environments where conditions are in frequent flux). There appear to be few “super invaders” that have universal performance advantages over co-occurring natives; rather, increased resource availability and altered disturbance regimes associated with human activities often differentially increase the performance of invaders over that of natives.
Analysis of Rates of Morphologic Evolution
Authors: Roopnarine Peter D.
Published: December 2003

▪ Abstract  Rates of morphological evolution exist at several hierarchical levels. The most fundamental rate, termed instantaneous or intrinsic, is a measure of evolutionary change between consecutive generations. Comparisons of these rates between different characters or taxa are best done by measuring change proportionally or logarithmically. The variation of instantaneous rates over geological time, or between taxa, is a reflection of differing intrinsic factors (e.g., mutation rates) or environmental conditions, and may explain rates at higher levels of the hierarchy such as apparent variable rates of evolution and diversification. Such long-term rates, termed here microevolutionary rates, have been measured variously as factors of exponential change over time (the “darwin”), or have been scaled for comparison according to sample standard deviations (the “haldane”). The relationship between these long-term measures and instantaneous rates, however, is not constant, nor measurable, unless evolution is monotonic and directional or static. Those modes produce an inverse relationship between microevolutionary rates and the interval of time over which they are measured. Any introduction of apparent randomness into the morphological evolutionary series of a taxon, however, likewise produces an inverse relationship between rate and timescale. This latter result is largely a mathematical artifact predictable on the basis of the behavior of random walks. Failure to reject a null hypothesis of random walk for an evolutionary series therefore precludes the interpretation of microevolutionary rates as products of real evolutionary processes. Methods developed to use random walk statistics and microevolutionary rates as sources of information about evolutionary mode and instantaneous rates are problematic because they (a) depend on a nonlinear relationship between microevolutionary rates and elapsed time, and (b) are prone to spurious correlation.

Rates of evolution may be measured above the level of species, for example as rates of origination within monophyletic clades. Taxonomic rates of evolution assume genealogical information that is generally not available for the groups under consideration. Likewise, many classic examples of rates of evolution comprise taxa of unknown or dubious genealogical relationship and should not be considered valid unless viewed in phylogenetic frameworks.
The Role of Reinforcement in Speciation: Theory and Data
Authors: Servedio Maria R. , Noor Mohamed A.F.
Published: December 2003

▪ Abstract  To assess the frequency and importance of reinforcement in nature we must begin by looking for its signature in the most likely places. Theoretical studies can pinpoint conditions that favor and inhibit reinforcement, and empirical studies can identify both how often these conditions occur and whether reinforcement results. We examine how well these tools have addressed these questions by searching for gaps and mismatches in theoretical and empirical studies of reinforcement. We concentrate on five areas: (a) a broad assessment of selection against interspecific mating, (b) the mode and genetic basis of nonrandom mating, (c) the geography of speciation, (d) divergent selection on mating cues, (e) and the genetics of reproductive isolation. We conclude that reinforcement has probably not been looked for where it is most likely to occur. We pinpoint however, many further areas of study that may ultimately provide a strong assessment of the importance of reinforcement in speciation.

“The grossest blunder in sexual preference, which we can conceive of an animal making, would be to mate with a species different from its own and with which the hybrids are either infertile or, through the mixture of instincts and other attributes appropriate to different courses of life, at so serious a disadvantage as to leave no descendants.”

          — Fisher, 1930 pp. 130
Flexibility and Specificity in Coral-Algal Symbiosis: Diversity, Ecology, and Biogeography ofSymbiodinium
Authors: Baker Andrew C.
Published: December 2003

Reef corals (and other marine invertebrates and protists) are hosts to a group of exceptionally diverse dinoflagellate symbionts in the genus Symbiodinium. These symbionts are critical components of coral reef ecosystems whose loss during stress-related “bleaching” events can lead to mass mortality of coral hosts and associated collapse of reef ecosystems. Molecular studies have shown these partnerships to be more flexible than previously thought, with different hosts and symbionts showing varying degrees of specificity in their associations. Further studies are beginning to reveal the systematic, ecological, and biogeographic underpinnings of this flexibility. Unusual symbionts normally found only in larval stages, marginal environments, uncommon host taxa, or at latitudinal extremes may prove critical in understanding the long-term resilience of coral reef ecosystems to environmental perturbation. The persistence of bleaching-resistant symbiont types in affected ecosystems, and the possibility of recombination among different partners following bleaching, may lead to significant shifts in symbiont community structure and elevations of future bleaching thresholds. Monitoring symbiont communities worldwide is essential to understanding the long-term response of reefs to global climate change because it will help resolve current controversy over the timescales over which symbiont change might occur. Symbiont diversity should be explicitly incorporated into the design of coral reef Marine Protected Areas (MPAs) where resistance or resilience to bleaching is a consideration.
Effects of Habitat Fragmentation on Biodiversity
Authors: Fahrig Lenore
Published: December 2003

▪ Abstract  The literature on effects of habitat fragmentation on biodiversity is huge. It is also very diverse, with different authors measuring fragmentation in different ways and, as a consequence, drawing different conclusions regarding both the magnitude and direction of its effects. Habitat fragmentation is usually defined as a landscape-scale process involving both habitat loss and the breaking apart of habitat. Results of empirical studies of habitat fragmentation are often difficult to interpret because (a) many researchers measure fragmentation at the patch scale, not the landscape scale and (b) most researchers measure fragmentation in ways that do not distinguish between habitat loss and habitat fragmentation per se, i.e., the breaking apart of habitat after controlling for habitat loss. Empirical studies to date suggest that habitat loss has large, consistently negative effects on biodiversity. Habitat fragmentation per se has much weaker effects on biodiversity that are at least as likely to be positive as negative. Therefore, to correctly interpret the influence of habitat fragmentation on biodiversity, the effects of these two components of fragmentation must be measured independently. More studies of the independent effects of habitat loss and fragmentation per se are needed to determine the factors that lead to positive versus negative effects of fragmentation per se. I suggest that the term “fragmentation” should be reserved for the breaking apart of habitat, independent of habitat loss.
Species-Level Paraphyly and Polyphyly: Frequency, Causes, and Consequences, with Insights from Animal Mitochondrial DNA
Authors: Funk Daniel J. , Omland Kevin E.
Published: December 2003

▪ Abstract  Many uses of gene trees implicitly assume that nominal species are monophyletic in their alleles at the study locus. However, in well-sampled gene trees, certain alleles in one species may appear more closely related to alleles from different species than to other conspecific alleles. Such deviations from species-level monophyly have a variety of causes and may lead to erroneous evolutionary interpretations if undetected. The present paper describes the causes and consequences of these paraphyletic and polyphyletic patterns. It also provides a detailed literature survey of mitochondrial DNA studies on low-level animal phylogeny and phylogeography, results from which reveal the frequency of nonmonophyly and patterns of interpretation and sampling. This survey detected species-level paraphyly or polyphyly in 23% of 2319 assayed species, demonstrating this phenomenon to be statistically supported, taxonomically widespread, and far more common than generally recognized. Our findings call for increased attention to sampling and the interpretation of paraphyletic and polyphyletic gene trees in studies of closely related taxa by systematists and population geneticists alike and thus for a new tradition of “congeneric phylogeography.”
The Ecology and Evolution of Seed Dispersal: A Theoretical Perspective
Authors: Levin Simon A. , Muller-Landau *Helene C. , Nathan *Ran , Chave *Jérôme
Published: December 2003

▪ Abstract  Models of seed dispersal—a key process in plant spatial dynamics—have played a fundamental role in representing dispersal patterns, investigating dispersal processes, elucidating the consequences of dispersal for populations and communities, and explaining dispersal evolution. Mechanistic models of seed dispersal have explained seed dispersion patterns expected under different conditions, and illuminated the circumstances that lead to long-distance dispersal in particular. Phenomenological models have allowed us to describe dispersal pattern and can be incorporated into models of the implications of dispersal. Perhaps most notably, population and community models have shown that not only mean dispersal distances but also the entire distribution of dispersal distances are critical to range expansion rates, recruitment patterns, genetic structure, metapopulation dynamics, and ultimately community diversity at different scales. Here, we review these developments, and provide suggestions for further research.