bluuebunny/crossref_metadata_2025 huggingface dataset:
Reassessment of the molecular mechanisms for H2 thermal desorption pathways from Si(1−x)Gex(001)-(2×1) surfaces
Authors: Li Qiang , Tok E. S. , Zhang J. , Chuan Kang H.
Published: January 2007

One of the aims of temperature-programmed desorption experiments is to facilitate identification of molecular pathways for desorption. The authors provide a rigorous assessment of the difficulty of doing this for H2∕Si(1−x)Gex(100)-(2×1). An extensive series of density functional calculations using both cluster and slab methods is performed. The resulting desorption barriers are used to compute thermal desorption spectra. A mean-field approximation is used to treat the populations of the various adsites present on the surface. The authors find a number of significant results. First, slab and cluster calculations do not appear to predict consistent differences in desorption barriers between intradimer and interdimer channels. Second, they find that a germanium atom affects the desorption barrier significantly only if it is present at the adsite. A germanium atom adjacent to an adsite or in the second layer influences the desorption barrier negligibly. Both cluster and slab calculations consistently predict a decrease of approximately 0.3–0.4eV per germanium atom at the adsite. Third, current analysis of thermal desorption spectra in the literature, although yielding good fits to experimental data, is not rigorous. The authors’ calculated spectra can be fitted rather well by assuming, as in current analysis of experimental data, three independent second-order channels, even though the underlying molecular pathways used to calculate the spectra are considerably different. Fourth, the authors’ results highlight the importance of treating the rearrangement of hydrogen and germanium atoms at the surface during the thermal desorption process. This is generally not taken into account in kinetics modeling of desorption spectra.
Differential scattering cross-sections for CNA2Π+Ar
Authors: Alagappan Azhagammai , Ballingall Iain , Costen Matthew L. , McKendrick Kenneth G.
Published: January 2007

We present the first results from a novel experimental approach to the measurement of state-to-state differential scattering cross-sections for inelastic scattering of electronically excited CNA2Π with Ar. Photodissociation of ICN with linearly polarized 266nm radiation generates CNX2Σ+ (υ″=0,J″) with a near mono-energetic speed distribution and large anisotropy. Saturated optical pumping of the nascent CNX2Σ+ transfers this speed distribution without distortion to selected rotational quantum states of the A2Π (υ′=4) level. The products of rotational energy transfer within the A2Π (υ′=4) level into the J′=0.5, F2, f, state are probed using frequency modulated stimulated emission spectroscopy on the A–X (4,2) band with a single frequency external cavity tunable diode laser. Doppler profiles of transitions from individual rotational, spin-orbit and lambda doublet specific levels are acquired for different geometrical arrangements of photolysis polarization and probe propagation directions. The resulting Doppler profiles, which for this J′=0.5 state cannot display a rotational angular momentum alignment, are combined to yield composite Doppler profiles depending on speed and translational anisotropy, which are analyzed to determine fully state-to-state resolved differential scattering cross-sections.
Perception of Motion Transparency in 5-Month-Old Infants
Authors: Kanazawa So , Shirai Nobu , Otsuka Yumiko , Yamaguchi Masami K
Published: January 2007

We investigated the perceptual development of motion transparency in 3- to 5-month-old infants. In two experiments we tested a total of 55 infants and examined their preferential looking behaviour. In experiment 1, we presented transparent motion as a target, and uniform motion as a non-target consisting of random-dot motions. We measured the time during which infants looked at the target and non-target stimuli. In experiment 2, we used paired-dot motions (Qian et al, 1994 Journal of Neuroscience14 7357 – 7366) as non-targets and also measured target looking time. We calculated the ratio of the target looking time to the total target and no-target looking time. In both experiments we controlled the dot size, speed, the horizontal travel distance of the dots, and the motion pattern of the dots. The results demonstrated that 5-month-old infants showed a statistically significant preference for motion transparency in almost all stimulus conditions, whereas the preference in 3- and 4-month-old infants depended on stimulus conditions. These results suggest that the sensitivity to motion transparency was robust in 5-month-olds, but not in 3- and 4-month-olds.
Additivity of Retinal and Pursuit Velocity in the Perceptions of Depth and Rigidity from Object-Produced Motion Parallax
Authors: Mitsudo Hiroyuki , Ono Hiroshi
Published: January 2007

Two psychophysical experiments were conducted to investigate the mechanism that generates stable depth structure from retinal motion combined with extraretinal signals from pursuit eye movements. Stimuli consisted of random dots that moved horizontally in one direction (ie stimuli had common motion on the retina), but at different speeds between adjacent rows. The stimuli were presented with different speeds of pursuit eye movements whose direction was opposite to that of the common retinal motion. Experiment 1 showed that the rows moving faster on the retina appeared closer when viewed without eye movements; however, they appeared farther when pursuit speed exceeded the speed of common retinal motion. The ‘transition’ speed of the pursuit eye movement was slightly, but consistently, larger than the speed of common retinal motion. Experiment 2 showed that parallax thresholds for perceiving relative motion between adjacent rows were minimum at the transition speed found in experiment 1. These results suggest that the visual system calculates head-centric velocity, by adding retinal velocity and pursuit velocity, to obtain a stable depth structure.
High Spin States in39K from the36Ar(α,pγ)39K Reaction
Authors: G Alenius  , S E Arnell  , O Stankiewicz
Published: January 2007

The decay properties of high-spin states in39K have been investigated by means of the36Ar(α,pγ)39K reaction atEα=10-14 MeV. From measurements of the yield function and the angular distribution of the γ-transitions it can be concluded that the following states have been excited: 2 814 keV, 7/2-, 3 597 keV, 9/2-, 3 943 keV, 11/2-, 4 126 keV, 5/2(-), 4 521 keV, 9/2(-)(11/2-), 5 717 keV, 13/2 and 6 474 keV, (15/2). Multipole mixing ratios and transition strengths are given for some transitions. Comparisons are made with a recent shell-model calculation and with calculations involving collective features.
On Positive Parity Levels of High Angular Momentum in69,71,73Ge
Authors: K Forssten  , A Hasselgren  , Ph Monseu  , A Nilsson  , Z P Sawa
Published: January 2007

Results of an attempt to establish in69,71,73Ge the low-lying states of the presumed 1g9/2⊗ core configuration are reported. The excited states in these nuclei were formed in the66,68,70Zn(α,n) compound reactions mainly at 14.2 MeV incident energy. Properties of the states were assigned from investigations of the prompt γ-ray transitions. Measuring γ-γ coincidences, yield functions, angular distributions (and in a few cases also linear polarization) of γ-rays, evidences were found for states in

69Ge: 1 350.4 keV 11/2+, 1 407.0 keV 13/2+, 2 017.9 keV 11/2+or 13/2+, 2 119.2 keV 9/2+, 11/2+or 13/2+, 3 075.5 keV 13/2+or 15/2+, (and tentatively: 2 474.8 keV 11/2+or 13/2+, and 2 754.6 keV 13/2+or 15/2+).

71Ge: 589.7 keV 7/2+, 1 037.8 keV (7/2 or 9/2), 1 172.6 keV 13/2+, 1 192.3 keV 11/2+, 1 205.2 keV (5/2+), 1 477.0 keV 11/2+, 1 559.3 keV, 1 566 keV, 1 959.7 keV 11/2+or 13/2+, 2 299.2 keV 17/2+, 2 314.2 keV 15/2+(and tentatively 1 697.8 keV).

73Ge: 659.0 keV 9/2+, 825.8 keV 13/2+, 868.1 keV 11/2+, 1 610.3 keV 9/2+or 13/2+, 1 871.6 keV 17/2+.
Multireaction Spallation Detectors for Measuring Fluxes and Energy Spectra of High Energy Hadrons
Authors: J T Routti
Published: January 2007

A method is described for measuring fluxes and energy spectra of high energy hadron cascade particles in the energy range of tens to hundreds of MeV. A multitude of spallation reactions induced in copper foils are identified and quantitatively measured by the use of high resolution Ge(Li) gamma spectroscopy and computerized analysis. Calculated spallation cross sections are used to estimate hadron fluxes above different threshold energies and to determine the energy spectra of these particles. Results obtained with high energy proton accelerators are presented and compared with hadron cascade calculations.
On the Possibilities in Calculations of Stripping Form Factors
Authors: J Bang  , V E Bunakov  , F A Gareev  , R M Jamalejev  , H Schulz
Published: January 2007

Approximate equations for stripping form factors are derived in perturbation theory. The expansion into a set of Sturmian functions is suggested for the form factors, thus partly justifying the well-depth prescription procedure. Numerical calculations are carried out. The asymptotic behaviour of the form factors is discussed.
Analysis of 4d-4f Transitions in Fe II
Authors: Sveneric Johansson  , Ulf Litzén
Published: January 2007

The Fe II-spectrum emitted from a pulsed hollow cathode has been investigated in the region 4 800-11 500 Å. As a first result of the analysis 481 lines have been identified as belonging to the 3d
6(5
D)4d-3d
6 (5
D)4f transition array. The term structure shows good agreement with predictions by R. D. Cowan.
Analysis of Elastic and Inelastic Scattering of 185 MeV Protons with Parametrized Reflection Coefficients
Authors: A Ingemarsson
Published: January 2007

The differential cross section and the polarization of 185 MeV protons in the elastic scattering from12C,40Ca,90Zr and208Pb and in the inelastic scattering from the lowest octupole levels of the same nuclei have been calculated. The calculations are based on a parametrization of the elastic scattering reflection coefficients and the Austern-Blair theory for one-phonon excitations in the adiabatic approximation.
Optical Model Analysis of Proton and Deuteron Scattering and DWBA Calculations on (p,d)-Reactions at 185 MeV
Authors: A Ingemarsson  , G Tibell
Published: January 2007

Distorted-wave Born approximation (DWBA) calculations have been performed for (p,d)-reactions in12C and28Si induced by 185 MeV protons and the results have been compared with experimental data on differential cross sections and vector polarizations. In order to obtain a consistent set of parameters for the potential generating the distorted waves, a reanalysis has been made of experimental data from proton and deuteron elastic scattering. The effect on the results of the spin-orbit terms in the optical potentials has been studied, and it seems clear that at these intermediate energies the spin-orbit potentials are quite important e.g., in the extraction of spectroscopic factors.
Hyperfine Structure Analysis in the 6p7s Configuration of Singly Ionized Bi
Authors: Lennarth Holmgren  , Arne Rosén
Published: January 2007

In this paper we perform a relativistic analysis of the magnetic dipole and electric quadrupole hyperfine interaction in the 6p7sconfiguration of the singly ionized Bi spectrum. Explicit expressions for the magnetic dipole and electric quadrupole interaction constants for a generalnsn'lconfiguration are presented, including the effects of intermediate coupling. Hyperfine integrals calculated with the Optimized Hartree-Fock-Slater (OHFS) and the Hartree-Fock (HF) wavefunctions have been used for the evaluation of the magnetic dipole interaction constants and the quadrupole moment. As our final results we obtain the average value for the quadrupole moment from our calculations (Sternheimer uncorrected) asQ= -0.40 b, which we compare with previous calculations of the quadrupole moment from hfs constants in the ground configuration of Bi.
Photoelectron Spectrum and Rydberg Transitions of CO
Authors: L Åsbrink  , C Fridh  , E Lindholm  , K Codling
Published: January 2007

A He II (304 Å) photoelectron spectrum of CO is presented and a new interpretation of the Rydberg series going to the higher excited states of CO+is discussed. This work supports earlier assignments of these excited states.
Studies of Time Resolved Spectra from Pulsed GaAs-Lasers
Authors: O Steinvall
Published: January 2007

This paper reports measurements of time resolved spectra from pulsed GaAs injection lasers of single heterojunction type. A detailed study of the wavelength shift of the broad emission spectrum as well as individual axial modes is given. The transient temperature rise of the junction during the current pulse is calculated and the wavelength shift caused by this rise is compared with the observed shifts.
The Enhancement of the Interaction between Transverse and Longitudinal Waves by Turbulent Plasmon Condensation
Authors: K Kamilov  , F Kh Khakimov  , L Stenflo  , V N Tsytovich
Published: January 2007

It is shown that three-wave interaction processes can be enhanced and change sign in the presence of strong Langmuir turbulence, which is treated as a nonlinear stage of modulational instability of plasmon condensation. In particular we point out the possibility of enhanced emissions at the double plasma frequency (ωt ≈ 2ωp). We demonstrate that depression occurs when the intensity of the transverse wave is less than a certain threshold value but that the wave is enhanced when it is larger than this value.
Where Do Diffractive Nucleons Go?
Authors: K Kajantie  , P V Ruuskanen  , S Sohlo
Published: January 2007

Nucleon and pion-nucleon distributions from the diffractive component in pp collisions are analysed. Diffractive events are assumed to come from a mechanism pp → N*p, in which a proton is diffractively excited to a nova N*. The decay properties of N* are determined by assuming that a Pomeron-proton collision behaves as a proton-proton collision. Correlations within the diffractive component are computed and seen to be numerically small. Even interference with the pionization component does not reproduce the observed pattern of pion (in the plateau)-proton (in the fragmentation region) correlations. This may imply the existence of long-range correlations within the pionization component.
Lifetime Measurements in Ne VII and Ne VIII
Authors: L Barrette  , R Drouin
Published: January 2007

Mean lives have been measured for 19 excited levels of Ne VII and Ne VIII in the region 60-130 Å using the beam-foil technique. The results range between 3 to 50 picoseconds and are compared with theory and other experimental results where available.
Theoretical Transition Probabilities between the np3(n+1)s → np4Configurations of SeI and TeI
Authors: S Garpman  , L Holmgren  , A Rosén
Published: January 2007

A theoretical calculation was performed on the transition probabilities between thenp3(n+1)sandnp4configurations of SeI and TeI. The relativistic effects were included using the effective-operator formalism. The radial integrals were evaluated using relativistic self-consistent-field wave functions and lifetimes predicted for thep3sconfiguration. In order to investigate the importance of relativity on the transition probabilities, an analysis was also carried out within the non-relativistic formalism. The breakdown ofLScoupling was taken into account and a comparison was made between the results obtained using the dipole length and the dipole velocity formula for the transition operator.
On the Evolution and Saturation of the World Population
Authors: J Weiland  , H Wilhelmsson
Published: January 2007

The result of solving a simple non-linear rate equation is compared with empirical data on the world population. An astonishingly good agreement is obtained assuming constant coefficients of the equation. Deviation from the present trend of evolution necessitates some kind of saturation mechanism corresponding to certain time dependent features of the coefficients in our equation. Different models for saturation have been investigated.
Correlation Contribution to the Surface Energy of Metals
Authors: M Jonson  , G Srinivasan
Published: January 2007

We have derived a formal expression for the free energy of an electron gas confined in a slab geometry (within the Random Phase Approximation). The result is expressed in terms of the bulk and surface dielectric functions. The structure of the perturbation theory (in e
2) of the surface energy terms is carried out in the high density limit. The correlation part of the surface energy has been numerically evaluated in an approximate scheme. The result is found to be a factor of five larger than the Lang and Kohn correlation energy.
Motion in Fluosilicates Studied with Nuclear Magnetic Resonance
Authors: Svein M Skjæveland  , Ivar Svare
Published: January 2007

Motional narrowing of H1and F19NMR lines in the fluosilicates of Mn, Fe, Co, Ni, Cu and Zn has been studied. Narrowing due to SiF62-complex reorientation occurs at about 225 K, 180 K, 200 K, 150 K, 120 K and 150 K, respectively, and rapid Me(H2O)62+reorientation occurs at 225 K, 220 K, 340 K, 375 K, 350 K and 340 K respectively. This variation is correlated with the variation in density of these nearly isomorphic crystals. At nitrogen temperatures the lattices are static and no effect of any Jahn-Teller motion in CuSiF6·6H2O could be seen.
Evidence for a Core-excited Isomeric 31/2-State in209Po
Authors: I Bergström  , J Blomqvist  , C J Herrlander  , K Wikström  , B Fant
Published: January 2007

Using alpha particles from the Stockholm 225-cm cyclotron, gamma rays from the208Pb(α, 3n) reaction have been studied. Excitation functions, angular distributions, prompt and delayed gamma rays and gamma-gamma coincidences were measured. The results give strong evidence for a 31/2-isomeric state in20984Po125with a half-life of 118 ± 3 ns, which is interpreted as being mainly due to the core-excited πh9/2πi13/2νg9/2(ν-2)0+ configuration.
Evidence for Two-Nucleon Polarization in the π(h9/2i13/2)11- ν(j-2)0+Level in208Po
Authors: K Wikström  , I Bergström  , J Blomqvist  , C J Herrlander  , B Fant  , V Rahkonen
Published: January 2007

From in-beam gamma-ray spectroscopy measurements on the208Pb(α, 4n)208Po reaction using the Stockholm 225-cm cyclotron, we have concluded that there is an 11-, 8 ns isomeric state in208Po, which lies 1 175 keV above the π(h9/22)8+ state and that this isomeric state should have the configuration π(h9/2i13/2)11- ν(j-2)0+. Calculations based on the use of empirical two-particle interactions give a position of the 11-level which deviates by about + 100 keV from the experimentally found position. It is suggested that this deviation is mainly due to the difference in the polarization of the206Pb-and208Pb-cores by the two alignedh9/2andi13/2protons.
The Decay of the T = 3/2 Level at 8.66 MeV in 23Na
Authors: J E Christiansson  , J Dubois  , L Jarneborn  , H Odelius  , H Roth
Published: January 2007

The 22Ne(d,nγ)23Na reaction has been used to study the γ-ray deexcitation of 1/2+ levels in 23Na. New branches were found for the T = 3/2 level at 8.66 MeV. The experimental ΔT = 1, γ-ray transition strengths for this level cannot be explained by simple shell model theory but agree very well with those predicted by the collective model using Nilsson wavefunctions.
The Spectrum of CuO: Rotational Analysis of Some Blue and Red Bands
Authors: O Appelblad  , A Lagerqvist
Published: January 2007

The emission spectrum of CuO has been photographed at high resolution in the region from 4 000 Å to 6 500 Å. In the red region also the pure isotopic molecule63CuO has been studied. Different light sources have been used. A blue band system, a2Πi-X2Πitransition, as well as a red band system, a2Σ+-X2Πitransition, has been rotationally analyzed. Tables of the molecular constants of all the known states of CuO are given.
Rotational Analysis of the Spectra of SbH and SbD
Authors: P Bollmark  , B Lindgren
Published: January 2007

TheA3Πi-X3Σ-transitions have been studied in SbH and SbD. The spectra were obtained after flash photolysis of stibine and deuterostibine. The ground state is separated into two sub-states and is described in terms of Hund's coupling case (c). The splitting between theX0+andX1 sub-states is 660 cm-1. The upper state3Πiis predissociated and only the3Π0+substate show rotational structure (but a few levels in3Π2of SbD). A second upper stateB0+and a third upper stateC0+, only observed in SbD, causes perturbations to the3Π0+sub-state. Molecular constants have been derived where possible.
Rotational Analysis of the A-X and B-X Band Systems of CaH
Authors: L-E Berg  , L Klynning
Published: January 2007

The absorption spectrum of CaH in the region 6 130-7 125 Å has been generated using a King furnace. The spectrum was recorded photographically in a 10.685 m concave grating spectrograph. Ten bands belonging to theA2Π-X2Σ andB2Σ-X2Σ systems have been rotationally analyzed. Perturbations between the two excited states have been observed. Computer methods have been used to calculate term values and to evaluate molecular constants.
Molecular Orbitals for Excited States
Authors: Sten Lunell  , Peter Lindner
Published: January 2007

The use of Mulliken's "ionic Hamiltonian" to obtain excited state orbitals is investigated. When compared with the ordinary virtual orbital method it is found to give improved charge distributions for the excited orbitals, but seems to be of less value for improving excitation energies in a minimal-basis calculation. As examples, INDO calculations have been carried out on the ethylene, formaldehyde, and pyridine molecules.
Correlation of Properties of Materials to Debye and Melting Temperatures
Authors: G Grimvall  , S Sjödin
Published: January 2007

Many solid state properties are correlated to simple parameters like the atomic mass, the interatomic distance and some measure of the strength of the interatomic interaction, e.g. the melting temperatureTmor some Debye temperature θD. Such empirical relations are investigated for elastic properties, melting temperature, thermal expansion, vacancy formation energy, grain boundary and surface energy, cohesive energy, heat of fusion, activation energies for bulk, grain boundary, surface and dislocation pipe diffusion, viscosity, activation energy for creep, recrystallization temperature and other properties. When experimental data are available, both elements and diatomic compounds (alkali halides, oxides, carbides, III-V semiconductors) are considered. The correlations toTm, θD(T= 0) and a high temperature effective θDare compared. It is found that for all practical purposesTmgives the best correlation. For diatomic compounds, the average mass is not uniquely defined and various averages are discussed. The purpose of the paper is not only to present empirical relations but also to give a short account of the possibilities to calculate the considered parameters using solid state theory in its most advanced present state.
The Search for New Elements: the Projects of Today in a Larger Perspective
Authors: Glenn T Seaborg
Published: January 2007

The search for new elements is based on the irradiation of heavy element targets with heavy ions followed by identification through physical or chemical methods. Success seems assured for the production and identification of short-lived elements immediately beyond the heaviest presently known. Predictions indicate that still heavier elements, the superheavy elements as part of an "island of stability", would have sufficient stability to allow their identification; however, there is no equal assurance that nuclear reactions suitable for their synthesis can be found.

The chemical properties of a wide range of such prospective new elements have been predicted, in many cases in rather extensive detail. Special considerations related to their high atomic numbers suggest interesting differences between the chemical properties of these heavy elements and their lighter homologs.

Chemical separation schemes for the identification of superheavy elements have been devised and applied to heavy targets irradiated with heavy ions. While there may be some positive indications of such identification in experiments performed at Dubna, experiments at Berkeley have given negative results.

In the Berkeley experiments the yields of a broad range of isotopes of the known elements in the separated chemical fractions have been determined. The resulting distribution of products formed in the irradiation of uranium with krypton ions suggest some interesting new reaction mechanisms.
Some Current Themes in Nuclear Research
Authors: A Bohr  , B R Mottelson
Published: January 2007

The topics covered include: (a) Elementary modes of excitation with special emphasis on the isoscalar highfrequency quadrupole vibrations. (b) Conditions for shell structure in both spherical and deformed potentials. (c) Modifications in nuclear structure produced by large angular momentum, including a discussion of stability conditions as well as of the spectrum of quantum states in the yrast region for very large angular momentum.
Macroscopic Aspects of Heavy lon Reactions
Authors: S G Thompson  , L G Moretto  , R C Jared  , R P Babinet  , J Galin  , M M Fowler  , R C Gatti  , J B Hunter
Published: January 2007

Heavy ion beams of 40Ar (288 MeV) and 84Kr (∼ 600 MeV) from Hilac acceleration and 14N (100, 160, 250, MeV) and 20Ne (250 MeV) from the 88" cyclotron have been used to bombard natural silver targets. Formation cross sections, angular distributions and kinetic energy distributions for reaction products in the range Z = 6-20 have been measured using gas ΔE-E telescopes. Kinetic energy distributions generally agree well with coulomb repulsion energies for binary division. Angular distributions are discussed in terms of relaxation time for the mass asymmetry mode compared to rotational periods.
The Single-Particle Mechanism behind the Asymmetric Distortions
Authors: S E Larsson  , P Möller  , S G Nilsson
Published: January 2007

The relation between nuclear shell structure and nuclear shapes is brought out in diverse mass regions. Thus certain nuclear orbitals, shown to be responsible for the development of mass-asymmetric distortions, are here followed in more detail for large and realistic shape changes. The same holds for axial asymmetries. The study is applied to actinide and superheavy nuclei as as well as very light ones, among the latter 24Mg, which is shown to exhibit a deep octupole-shape second minimum.
Many-Body Theory and Observed Single Particle Levels
Authors: H S Köhler
Published: January 2007

It is emphasized that the single-particle levels calculated from a shell model potential are physically meaningful only if the shell model potential is calculated in a selfconsistent Hartree-Fock manner. Rearrangement corrections to the single-particle levels calculated in this fashion are small for atoms. For nuclei there is experimental evidence that these corrections are quite large. One of these corrections is the 1h-2h1p coupling that shifts single-particle levels close to the Fermi surface up and gives a decay (Auger decay) width to the deeper states.
On the Stability of Super-heavy Nuclei: Some Recent Results of Self-consistent Calculations
Authors: M Beiner  , H Flocard  , M Veneroni  , P Quentin
Published: January 2007

Self-consistent calculations of super-heavy elements are presented. The Skyrme effective interaction SIII has been used. This force gives an overall good fit of a wide range of nuclear properties, in particular for closed shell nuclei. The quality of these results puts reasonable limits on the reliability of extrapolation to unknown nuclei.QαandQβvalues are calculated and corresponding lifetimes are estimated. For the nucleus298114, the fission barrier has been obtained by a constrained self-consistent calculation.
Nuclear Collisions with Friction
Authors: C F Tsang
Published: January 2007

A theory of nuclear collisions where a frictional force is introduced explicitly from the beginning is worked out based on a macroscopic and leptodermous idealization. A solution of the problem is made by freezing all degrees of freedom but four: the distance between centres and the two angles measuring the spins of the nuclei. The conditions for capture as a function of energy and angular momentum is discussed in detail. Results on the kinetic energy and angular distributions of collision products are also obtained.
Potential-Energy Surfaces for Heavy-Ion Collisions
Authors: J R Nix  , A J Sierk
Published: January 2007

We calculate the nuclear potential energy of deformation for the collision of two heavy nuclei by means of a macroscopic-microscopic method. The nuclear macroscopic energy is calculated in terms of a double volume integral of a Yukawa function, and the microscopic shell and pairing corrections are calculated by use of Strutinsky's method from the single-particle levels of a realistic diffuse-surface single-particle potential. The time evolution of the system after the point of first contact is determined by solving the classical equations of motion for incompressible, irrotational hydrodynamical flow. The effect of nuclear viscosity on the fusion path is to slow down the formation of the neck and to inhibit the excitation of collective shape vibrations. For nuclear systems in which the fission saddle point lies well outside the contact point it is possible to interpret experimental fusion cross sections at relatively low bombarding energies in terms of a one-dimensional interaction barrier, as is customarily done. For heavier nuclear systems and higher bombarding energies, where the larger Coulomb and centrifugal forces tend to deform the fusing nuclei and lead to immediate fission, only those dynamical paths that pass inside the fission saddle point contribute significantly to fusion.
Classical Treatment of Heavy-Ion Collisions
Authors: Daniel Sperber
Published: January 2007

Heavy ion reactions high above the Coulomb barrier are analysed by using a classical model with dissipative forces. It is shown, in agreement with experiment, that the reaction can be divided into three parts: (1) quasielastic scattering, associated with high-angular momenta, (2) deep inelastic scattering, with intermediate angular momenta, and (3) complete fusion associated with the lowest angular momenta. Good agreement between theory and experiment is obtained for the cross section for complete fusion and for the cross section for deep inelastic scattering.
The Role of Inertial Parameters in Nuclear Fission
Authors: Z Szymanski
Published: January 2007

The properties of the nuclear tensor of inertia are discussed in connection with the fission process. In particular, the relations between the nuclear inertial parameters and the characteristics of the nuclear intrinsic motion are considered.
Rapid Nuclear Reactions in Supernovae and Cosmic Rays
Authors: E R Hilf  , W Hillebrandt  , K Takahashi  , M F E1 Eid  , T Kodama
Published: January 2007

A synopis of the transmutations of matter in a supernova to the final stages of neutron-star matter, r-nuclei, p-nuclei and cosmic rays if given. In particular discussed are (1) the freezing-out of nuclear reactions during cooling, (2) the consequences of an improved β-decay and β-delayed neutron emission systematics for the calculations of the r-process element abundances and of its application to the estimation of the nucleosynthesis-age of the galaxy, (3) the production mechanism of the high-energy light-element cosmic rays, which we propose to originate from the neutron star's surface.
Possible Paths for Synthesis of Superheavy Elements in Nature
Authors: W M Howard
Published: January 2007

We discuss the possibility of producing superheavy elements in the astrophysical r-process. Thus, we consider a detailed calculation of fission-barrier heights and neutron separation energies for heavy neutron-rich nuclei. The dependence of the neutron-induced fission cutoff of the r-process on the uncertainty in the nuclear models is discussed in some detail.
Stability of Elements in the r-Process Region
Authors: R Bengtsson  , R Boleu  , S E Larsson  , J Randrup
Published: January 2007

The fission barriers of the nuclei in the r-process region have been calculated with inclusion of axial asymmetry and reflection asymmetry. Neutron separation energies and spontaneous-fission half-lives have been calculated and the possibilities of producing superheavy elements by means of neutron-capture processes are discussed.
The Importance of Delayed Fission in the Production of very Heavy and Superheavy Elements
Authors: C-O Wene  , S A E Johansson
Published: January 2007

Recent advances in the calculation of fission barriers and in the experimental determination of beta strength functions make it possible to derive reliable estimates of the effect of beta-delayed fission in the decay of very heavy nuclides far from the line of beta-stability. The model presented here is used to calculate the amount of delayed fission during the decay back of nuclides produced in the astrophysical decay r-process. An interesting feature of these calculations is that they reproduce the reversal of the odd-even effect found for the yield of beta-stable nuclides obtained in the thermonuclear explosions. The preliminary results from the r-process calculations indicate that the effect of delayed fission has to be considered when the yield of very heavy beta stable nuclides from this process is estimated.
Disappearance of Shell Effects at High Excitation. Self-consistent Calculations at Finite Temperatures
Authors: M Brack  , Ph Quentin
Published: January 2007

Self-consistent calculations of highly excited nuclei are presented. The changes in the average nuclear field as a function of temperature are discussed; they are found to be negligible in the calculation of the entropy versus excitation energy at a fixed deformation. The disappearance of shell effects at temperatures T ≃ 2-3 MeV in heavy nuclei is demonstrated both by calculations of deformation energy curves at different temperatures and by considering the asymptotic behaviour of the entropy. Finally, the validity of some simplifying approximations is discussed.
The Change of the Vacuum in Superheavy Quasi-Molecules
Authors: Berndt Müller  , Walter Greiner
Published: January 2007

In collisions of very heavy ions (Z
1 + Z
2 > 172) molecular electronic orbitals are formed. Generalized Hartree-Fock equations for this case are derived from field theoretic principles. It is shown that the lowest ground state (i.e. the vacuum) becomes charged for Z > Z
cr and R < R
cr. If the K-shell is vacant, positron production sets in. The energy distribution of the positrons and the cross-section for this process are calculated.
Recent Experimental Results from Spectroscopy of Superheavy Quasiatoms
Authors: P Armbruster  , G Kraft  , P Mokler  , B Fricke  , H J Steïn
Published: January 2007

The concept of a "Superheavy Quasiatom" is discussed. Radiative transition times are compared with the lifetime of the intermediate system, cross sections are calculated within a two-collision model and induced transitions and their anisotropic emission are discussed. Recent experimental and theoretical results are presented from collision systems obtained with I-beams bombarding various heavy targets, giving combined Z-values between 120 and 145. Results include the energy dependence of the peak structure interpreted as M X-rays from superheavy quasiatoms and the anisotropy of X-ray emission referred to the beam direction. The data are discussed within the models available. These cannot explain the strong emission of anisotropic radiation in the X-ray energy range of quasiatomic M X-ray at small bombarding energies.
Banquet address, Noble Symposium on Superheavy Elements, Ronneby, June 14, 1974
Authors: P G Hansen
Published: January 2007

Without abstract; see full text
Molecular basis for specificity in the druggable kinome: sequence-based analysis
Authors: Chen Jianping , Zhang Xi , Fernández Ariel
Published: January 2007

Motivation: Rational design of kinase inhibitors remains a challenge partly because there is no clear delineation of the molecular features that direct the pharmacological impact towards clinically relevant targets. Standard factors governing ligand affinity, such as potential for intermolecular hydrophobic interactions or for intermolecular hydrogen bonding do not provide good markers to assess cross reactivity. Thus, a core question in the informatics of drug design is what type of molecular similarity among targets promotes promiscuity and what type of molecular difference governs specificity. This work answers the question for a sizable screened sample of the human pharmacokinome including targets with unreported structure.

Results: We show that drug design aimed at promoting pairwise interactions between ligand and kinase target actually fosters promiscuity because of the high conservation of the partner groups on or around the ATP-binding site of the kinase. Alternatively, we focus on a structural marker that may be reliably determined from sequence and measures dehydration propensities mostly localized on the loopy regions of kinases. Based on this marker, we construct a sequence-based kinase classifier that enables the accurate prediction of pharmacological differences. Our indicator is a microenvironmental descriptor that quantifies the propensity for water exclusion around preformed polar pairs. The results suggest that targeting polar dehydration patterns heralds a new generation of drugs that enable a tighter control of specificity than designs aimed at promoting ligand–kinase pairwise interactions.

Availability: The predictor of polar hot spots for dehydration propensity, or solvent-accessible hydrogen bonds in soluble proteins, named YAPView, may be freely downloaded from the University of Chicago website http://protlib.uchicago.edu/dloads.html

Contact:  arifer@rice.edu, ariel@uchicago.edu

Supplementary information: Supplementary data are available at Bioinformatics online.
Epidermal stem cells arise from the hair follicle after wounding
Authors: Levy Vered , Lindon Catherine , Zheng Ying , Harfe Brian D. , Morgan Bruce A.
Published: January 2007

During normal development, the epidermis and hair follicle are distinct lineage compartments maintained by independent stem cell populations. Both epidermal and follicular keratinocytes are recruited to participate in epidermal repair in response to injury. However, it is generally thought that follicular cells contribute to the wound epidermis only transiently and are ultimately replaced by the progeny of stem cells derived from the original epidermal compartment prior to wounding. Here we use inducible and constitutive cre recombinase expressed from the Sonic hedgehog locus (Shh) for in vivo lineage tracing. This analysis confirms that follicular cells participate in the initial resurfacing of the wound but also reveals that their progeny persist in wound epidermis for months after the wound is healed. It further demonstrates that Shh is not induced in keratinocytes during the wound healing process. We conclude that follicular cells can undergo reprogramming to become long‐term repopulating epidermal progenitors following wounding.—Levy, V., Lindon, C., Zheng, Y., Harfe, B. D., Morgan, B. A. Epidermal stem cells arise from the hair follicle after wounding. FASEB J. 21, 1358–1366 (2007)
A murine model of hyperdopaminergic state displays altered respiratory control
Authors: Vincent Sandra G. , Waddell Andrea E. , Caron Marc G. , Walker Julia K. L. , Fisher John T.
Published: January 2007

The dopamine transporter (DAT) protein plays an important role in the termination of dopamine signaling. We addressed the hypothesis that loss of DAT function would result in a distinctive cardiorespiratory phenotype due to the significant role of dopamine in the control of breathing, especially with respect to chemical control, metabolism, and thermoregulation. The DAT knockout mouse (DAT”/‐) displays a state of functional hyperdopaminergia characterized by marked novelty driven hyperactivity. Certain behavioral and drug responses in these mice are reminiscent of endophenotypes of individuals with attention deficit hyperactivity disorders (ADHD). We performed experiments on conscious, unrestrained DAT‐/‐ mice (KO) and littermate DAT+/+ wild‐type (WT) controls. Ventilation was measured by the barometric technique during normoxia, hypoxia, or hypercapnia. We measured core body temperature and CO2 production as an index of metabolism. DAT‐/‐ mice displayed a significantly lower respiratory frequency than WT mice, reflecting a prolonged inspiratory time. DAT−/− mice exhibited a reduced ventilatory response to hypoxia characterized by an attenuation of both the respiratory frequency and tidal volume responses. Both groups showed similar metabolic responses to hypoxia. Circadian measurements of body temperature were significantly lower in DAT−/− mice than WT mice during inactive periods. We conclude that loss of the DAT protein in this murine model of altered dopaminergic neurotransmission results in a significant respiratory and thermal phenotype that has possible implications for understanding of conditions associated with altered dopamine regulation.—Vincent, S. G., Waddell, A. E., Caron, M. G., Walker, J. K. L., Fisher, J. T. A murine model of hyperdopaminergic state displays altered respiratory control. FASEB J. 21, 1463–1471 (2007)
Late Holocene extinction of Puerto Rican native land mammals
Authors: Turvey S.T , Oliver J.R , Narganes Storde Y.M , Rye P
Published: January 2007

West Indian land mammals have suffered the most severe extinctions of any Holocene mammal faunas. However, ‘last-occurrence’ dates based on radiometric or robust stratigraphic data remain unavailable for most West Indian species, making it impossible to identify factors responsible for these extinctions. Here, we present new radiometric dates from archaeological and palaeontological sites on Puerto Rico, the only Greater Antillean island to have lost all native land mammals. Although it has been suggested that these species died out earlier than other West Indian mammals, we demonstrate that Puerto Rican mammal last-occurrence dates are in close agreement with those from other Antillean islands, as several species in fact persisted for millennia following Amerindian arrival. Echimyid rodents and nesophontid ‘island-shrews’ were still present on Puerto Rico approximately 1000 years BP, and probably became extinct following European arrival. The large (13 kg) heptaxodontid rodent
Elasmodontomys obliquus
also appears to have survived for over 2000 years after Amerindian colonization, suggesting that at least some large West Indian mammals became extinct in protracted pre-European ‘sitzkrieg’-style events rather than ‘blitzkrieg’-style overkill.
No evidence that polymorphisms of brain regulator genes
Microcephalin
and
ASPM
are associated with general mental ability, head circumference or altruism
Authors: Rushton J. Philippe , Vernon Philip A , Bons Trudy Ann
Published: January 2007

We test the hypothesis that polymorphisms of the brain regulator genes
MCPH1
and
ASPM
contribute to variations in human brain size and its correlates. We measured general mental ability, head circumference and social intelligence in 644 Canadian adults (496 Caucasians, 36 Orientals, 84 Mixed Race/Other and 28 Blacks; 257 men and 387 women). The gene polymorphisms were assessed from buccal DNA; mental ability by Wonderlic Personnel Test and Multidimensional Aptitude Battery; head circumference by stretchless tape; and social intelligence by prosocial attitude questionnaires. Although all measures were construct valid and the allele frequencies showed expected population differences, no relationship was found between the genes and any of the criteria. Among Caucasian 18–25 year olds, for example, the two mental ability tests correlated with each other (
r
=0.78,
N
=476,
p
<0.001), with head circumference (
r
=0.17,
N
=182,
p
<0.05) and with prosocial attitudes (
r
=0.23,
N
=182,
p
<0.001).
Mitochondrial DNA recombination in a free-ranging Australian lizard
Authors: Ujvari Beata , Dowton Mark , Madsen Thomas
Published: January 2007

Mitochondrial DNA (mtDNA) is the traditional workhorse for reconstructing evolutionary events. The frequent use of mtDNA in such analyses derives from the apparent simplicity of its inheritance: maternal and lacking bi-parental recombination. However, in hybrid zones, the reproductive barriers are often not completely developed, resulting in the breakdown of male mitochondrial elimination mechanisms, leading to leakage of paternal mitochondria and transient heteroplasmy, resulting in an increased possibility of recombination. Despite the widespread occurrence of heteroplasmy and the presence of the molecular machinery necessary for recombination, we know of no documented example of recombination of mtDNA in any terrestrial wild vertebrate population. By sequencing the entire mitochondrial genome (16 761 bp), we present evidence for mitochondrial recombination in the hybrid zone of two mitochondrial haplotypes in the Australian frillneck lizard (Chlamydosaurus kingii).
Precopulatory stabbing, hypodermic injections and unilateral copulations in a hermaphroditic sea slug
Authors: Anthes Nils , Michiels Nico K
Published: January 2007

Reciprocity constitutes the prevalent mating mechanism among simultaneous hermaphrodites. Yet, when copulations in the female role confer fitness costs through male manipulation, it becomes advantageous sometimes to mate unilaterally in the male role only. In the sea slug
Siphopteron quadrispinosum
, acting males stab their partner with a bipartite penis, which not only hypodermically injects prostate fluids, but also apparently mechanically enforces unilateral male matings. Despite a pronounced male mating drive in both partners, unilaterality ensued when one slug stabbed more rapidly than its partner. The acting male may thus avoid the costs inflicted by traumatic injections and penial spines. While future studies need to elucidate the net fitness consequences of stabbing, our behavioural evidence is in line with the hypothesis that mating in
S. quadrispinosum
represents conflicting rather than complementary mating interests between mates.
The smaller your mouth, the longer your snout: predicting the snout length ofSyngnathus acus,Centriscus scutatusand other pipette feeders
Authors: de Lussanet Marc H.E , Muller M
Published: January 2007

Like most ray-finned fishes (Actinopterygii), pipefishes (Syngnathoidei) feed by suction. Most pipefishes reach their prey by a rapid dorso-rotation of the head. In the present study, we analysed the feeding kinematics of the razor fish,Centriscus scutatus, and of the greater pipefish,Syngnathus acusin detail. We found capture times of as little as 4–6 ms forC. scutatusand 6–8 ms forS. acus. We then hypothesized that the long snout of pipefishes is optimal for such fast feeding. To test this, we implemented in a mathematical model the following considerations. To reach the prey as fast as possible, a low moment of inertia increases the head's angular speed, whereas a long snout decreases the angle over which the head must be turned. The model accurately predicted the snout lengths of a number of pipefishes. We found that the optimal snout length, with which a prey will be reached fastest, is inversely related to its cross-section. In spite of the small cross-section, the development of a long snout can be an evolutionary advantage because this reduces the time to approach the prey.