bluuebunny/crossref_metadata_2025 huggingface dataset:
Quaternary paleoceanography of the central Arctic based on Integrated Ocean Drilling Program Arctic Coring Expedition 302 foraminiferal assemblages
Authors: Cronin Thomas M. , Smith Shannon A. , Eynaud Frédérique , O'Regan Matthew , King John
Published: March 2008

The Integrated Ocean Drilling Program (IODP) Arctic Coring Expedition (ACEX) Hole 4C from the Lomonosov Ridge in the central Arctic Ocean recovered a continuous 18 m record of Quaternary foraminifera yielding evidence for seasonally ice‐free interglacials during the Matuyama, progressive development of large glacials during the mid‐Pleistocene transition (MPT) ∼1.2–0.9 Ma, and the onset of high‐amplitude 100‐ka orbital cycles ∼500 ka. Foraminiferal preservation in sediments from the Arctic is influenced by primary (sea ice, organic input, and other environmental conditions) and secondary factors (syndepositional, long‐term pore water dissolution). Taking these into account, the ACEX 4C record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages (MIS) 13–37, and although less precise dating is available for older sediments, these trends appear to continue through the Matuyama. The MPT is characterized by nearly barren intervals during major glacials (MIS 12, 16, and 22–24) and faunal turnover (MIS 12–24). Abundant calcareous planktonic (mainlyNeogloboquadrina pachydermasin.) and benthic foraminifers occur mainly in interglacial intervals during the Brunhes and very rarely in the Matuyama. A distinct faunal transition from calcareous to agglutinated foraminifers 200–300 ka in ACEX 4C is comparable to that found in Arctic sediments from the Lomonosov, Alpha, and Northwind ridges and the Morris Jesup Rise. Down‐core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100‐ka cycles, pore water dissolution, or both.
Paleogene record of elemental concentrations in sediments from the Arctic Ocean obtained by XRF analyses
Authors: Spofforth David J. A. , Pälike Heiko , Green Darryl
Published: March 2008

We present a high‐resolution X‐ray fluorescence (XRF) core scanner record for the expanded middle Eocene section from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. The division of the middle Eocene into two units (subunit 1/6 and unit 2) is seen in the cyclical behavior of the elements as well as the changing interelemental correlations and their relationship to physical property measurements of bulk sediment. Al, Ti, and K strongly correlate throughout the record, while the behavior of Fe, Mn, and Si is more complex. Utilizing sediment geochemistry calibration to ground truth the XRF data, we suggest the middle Eocene Arctic Ocean was predominately euxinic, although periodic oxygenation of bottom waters must have occurred during unit 2 (49.7–45.4 Ma). Initially, the sediments are rich in biogenic silica (unit 2), but there is a pronounced shift to terrigenous dominated sediment accumulation in subunit 1/6. We report changes in the elemental concentrations of these elements and investigate the relationship between Fe content and pyrite. Additionally, we explore the potential change in paleoenvironmental conditions across the unit boundary.
A method for automatic scaling of F1 critical frequencies from ionograms
Authors: Pezzopane Michael , Scotto Carlo
Published: March 2008

This work describes a method that has been developed to automatically assess whether the F1 layer is present or not on an ionogram trace, and, if present, to scale the F1 critical frequency foF1. The ionograms in which the information related to the F1 trace is insufficient are identified and considered separately. In order to test the performance of this method and the conditions in relation to which it could be improved, a data set of ionograms recorded from September 2005 to June 2006 by the AIS‐INGV ionosonde installed at Rome was used. The values obtained automatically by Autoscala, with the addition of this new F1 layer routine, were compared with those obtained by the standard manual method.
The double Renner effect in the X̃A″2 and ÃA′2 electronic states of HO2
Authors: Melnikov Vladlen V. , Odaka Tina Erica , Jensen Per , Hirano Tsuneo
Published: March 2008

A theoretical investigation of the X̃A″2 and ÃA′2 electronic states of the HO2 radical is reported. Both electronic states have nonlinear equilibrium geometries and they correlate with a Π2 state at linear geometries so that they exhibit the Renner effect. In highly excited bending states, there is tunneling between two equivalent minima (with geometries where the H nucleus is bound to one, or the other, of the two O nuclei), and the two linear geometries H–O–O and O–O–H become accessible to the molecule. Thus, HO2 affords an example of the so-called double Renner effect. Three-dimensional potential energy surfaces for the X̃A″2 and ÃA′2 electronic states of HO2 have been calculated ab initio and the global potential energy surfaces for the states have been constructed. These surfaces have been used, in conjunction with the computer program DR [Odaka et al., J. Mol. Structure 795, 14 (2006); Odaka et al., J. Chem. Phys. 126, 094301 (2007)], for calculating HO2 rovibronic energies in the “double-Renner”-degenerate electronic states X̃A″2 and ÃA′2. The results of the ab initio calculations, the rovibronic energies obtained, and analyses of the wavefunctions for selected states are presented.
State of the art theoretical study and comparison to experiment for the phenol⋯argon complex
Authors: Černý Jiří , Tong Xin , Hobza Pavel , Müller-Dethlefs Klaus
Published: March 2008

The phenol⋯argon complex was studied by means of various high level ab initio quantum mechanics methods and high resolution threshold ionization spectroscopy. The structure and stabilization energy of different conformers were determined. Stabilization energy of van der Waals bonded and H-bonded PhOH⋯Ar complex determined at CCSD(T) complete basis set (CBS) level for CP-RI-MP2/cc-pVTZ/Ar aug-cc-pVTZ geometries amount to 434 and 285cm−1. The CCSD(T)/CBS were constructed either as a sum of MP2/CBS interaction energy and CCSD(T) correction term [difference between CCSD(T) and MP2 correlation energies determined with medium basis set] or directly from CCSD(T)/aug-cc-pVDZ and aug-cc-pVTZ energies. Both schemes provide very similar values. Harmonic vibrational analysis revealed that the H-bonded structure does not represent energy minimum but first order transition structure. The respective imaginary vibrational mode (16cm−1) connects two possible argon locations—above and below the phenol aromatic ring. Including the ΔZPVE, we obtained stabilization enthalpy at 0K of 389cm−1. This value is marginally higher (25–35cm−1, 0.07–0.10kcal∕mol) than the experimental value. The determination of ΔZPVE constitutes the most significant error and possible improvements should come from more accurate evaluation of the (nonharmonic) vibrational frequencies.
Electron-electron cusp condition and asymptotic behavior for the Pauli potential in pair density functional theory
Authors: Nagy Á. , Amovilli C.
Published: March 2008

In the ground state, the pair density n can be determined by solving a single auxiliary equation of a two-particle problem. Electron-electron cusp condition and asymptotic behavior for the Pauli potential of the effective potential of the two-particle equation are presented.
Permittivity study of multiferroic AlN∕NiFe∕AlN multilayer films
Authors: Hung D. S. , Yao Y. D. , Wei D. H. , Wu K. T. , Hsu J. C. , Ding T. , Chen Y. C.
Published: March 2008

NiFe inserted layer with different thicknesses on the dielectric properties of multiferroic AlN∕NiFe∕AlN multilayer films fabricated on the B270 glass substrates by the reactive sputtering technique was studied. The variation of dielectric constant for multilayer films is dependent on the thickness of the NiFe inserted layer observed from 40Hzto30MHz. In this work, single AlN layer exhibits dielectric constant value of around 6.5. However, we find that the dielectric constant of the AlN∕NiFe∕AlN multilayer films is raised up to 60 for even with a 1nm thick NiFe inserted layer. Additionally, this work also indicates that the dielectric tunability of AlN∕NiFe∕AlN films is dependent on the external magnetic field. These results conclude some magnetoelectric properties of AlN films those in relation to the NiFe ferromagnetic inserted layer. Possible mechanisms for the enhanced dielectric constant in the AlN∕NiFe∕AlN films have been discussed in the paper.
A new method of magnetic shielding: Combination of flux repulsion and backing up magnetic pathways
Authors: Sasada Ichiro , Nakashima Yoshihiro
Published: March 2008

The guiding principle of the magnetic shield is to redirect magnetic fluxes so that they do not enter an area of interest. There are two ways to do this: the one way is to provide magnetic fluxes with good pathways and the other way is to use repulsive forces acting on the magnetic flux. In this paper, a new method of magnetic shielding combining the above two is proposed. A circulating current and a thin magnetic plate working as a back yoke are the key components. Repulsive forces that act on the magnetic fluxes originating from a noise source are present only on one side of a thin back yoke. By enclosing an area to be shielded with several of those, one can make a magnetic shield in which thin magnetic plates are not necessarily connected. Several numerical examples as well as experimental results are given to demonstrate this idea.
Statistical mechanical theory for steady state systems. VIII. General theory for a Brownian particle driven by a time- and space-varying force
Authors: Attard Phil , Gray–Weale Angus
Published: March 2008

A Brownian particle subject to a time- and space-varying force is studied with the second entropy theory for nonequilibrium statistical mechanics. A fluctuation expression is obtained for the second entropy of the path, and this is maximized to obtain the most likely path of the particle. Two approaches are used, one based on the velocity correlation function and one based on the position correlation function. The approaches are a perturbation about the free particle result and are exact for weak external forces. They provide a particularly simple way of including memory effects in time-varying driven diffusion. The theories are tested against computer simulation data for a Brownian particle trapped in an oscillating parabolic well. They accurately predict the phase lag and amplitude as a function of drive frequency, and they account quantitatively for the memory effects that are important at high frequencies and that are missing in the simplest Langevin equation.
Size dependence of C and S states in circular and square Permalloy dots
Authors: Lai Mei-Feng , Liao Chun-Neng
Published: March 2008

From the micromagnetic simulation, it is found that the size-dependent stably existing regions of quasiuniform∕flower state, C, S, and vortex states are different in thin circular and square Permalloy dots. In very small dot’s size, the quasiuniform∕flower state is the most stable state both in circular and square Permalloy dots. For larger size, C, S, and vortex states may exist. The vortex state can stably exist from small diameter to large one both in square dot and circular dot. In circular dot, only one of the C and S states can exist for one given diameter and in some diameter range, none of the quasiuniform∕flower, C and S states can exist. Only the vortex state can be stable in this range. In square dot, C and S states can simultaneously exist, which are very different from the case in the circular dot.
Sound velocity dispersion in room temperature ionic liquids studied using the transient grating method
Authors: Fukuda M. , Terazima M. , Kimura Y.
Published: March 2008

Sound velocity is determined by the transient grating method in a range from 106to1010Hz in three room temperature ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium hexafluorophosphate, and N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide. In all room temperature ionic liquids studied, the sound velocity increased with increasing frequency. The cause of this change is posited to be structural relaxation in the room temperature ionic liquids. Frequency dependence of the sound velocity is not reproduced by a simple Debye relaxation model. The sound velocity dispersion relation in 1-butyl-3-methylimidazolium hexafluorophosphate matches a Cole–Davidson function with parameters determined by a dielectric relaxation [C. Daguenet et al., J. Phys. Chem. B 110, 12682 (2006)], indicating that structural and reorientational relaxations are strongly coupled. Conversely, the sound velocity dispersions of the other two ionic liquids measured do not match those measured for dielectric relaxation, implying that structural relaxation is much faster than the reorientational relaxation. This difference is discussed in relation to the motilities of anions and cations.
Allovalency revisited: An analysis of multisite phosphorylation and substrate rebinding
Authors: Locasale Jason W.
Published: March 2008

The utilization of multiple phosphorylation sites in regulating a biological response is ubiquitous in cell signaling. If each site contributes an additional, equivalent binding site, then one consequence of an increase in the number of phosphorylations may be to increase the probability that, upon dissociation, a ligand immediately rebinds to its receptor. How such effects may influence cell signaling systems is not well understood. Here, a self-consistent integral equation formalism for ligand rebinding, in conjunction with Monte Carlo simulations, is employed to further investigate the effects of multiple, equivalent binding sites on shaping biological responses. Multiple regimes that characterize qualitatively different physics due to the differential prevalence of rebinding effects are predicted. Calculations suggest that when ligand rebinding contributes significantly to the dose response, a purely allovalent model can influence the binding curves nonlinearly. The model also predicts that ligand rebinding in itself appears insufficient to generate a highly cooperative biological response.
General nonlocality in quantum fields
Authors: Wang Hai-Jun
Published: March 2008

The natural recognition of quantum nonlocality follows from the fact that a quantum wave is spatially extended. The waves of fermions display nonlocality in low energy limit of quantum fields. In this ab initio paper, we propose a complex-geometry model that reveals the effect of nonlocality on the interaction between material particles of spin 12. To make nonlocal properties appropriately involved in a quantum theory, the special unitary group SU(n) and spinor representation D(1∕2,1∕2) of Lorentz group are generalized by making complex spaces—which are spanned by wave functions of quantum particles—curved. The curved spaces are described by the geometry used in general relativity by replacing the real space with complex space and additionally imposing the analytic condition on the space. The field equations for fermions and for bosons are, respectively, associated with geodesic motion equations and with local curvature of the considered space. The equation for fermions can restore almost all the terms of quadratic form of Dirac equation. According to the field equation, it is found that for the U(1) field (generalized quantum electrodynamics), when the electromagnetic fields E⃗ and B⃗ satisfy E⃗2−B⃗2≠0, the bosons will gain masses. In this model, a physical region is empirically defined, which can be characterized by a determinant occurring in boson field equation. Applying the field equation to U(3) field (generalized quantum chromodynamics), the quark-confining property can be understood by carrying out the boundary of physical region. It is also found out that under the conventional form of interaction vertex, γμAμ, only when the color group SU(3) is generalized to U(3) is it possible to understand the strongly bound states of quarks.
The three-dimensional nonadiabatic dynamics calculation of DH2+ and HD2+ systems by using the trajectory surface hopping method based on the Zhu–Nakamura theory
Authors: Li Bin , Han Ke-Li
Published: March 2008

A theoretical investigation on the nonadiabatic processes of the full three-dimensional D++H2 and H++D2 reaction systems has been performed by using trajectory surface hopping (TSH) method based on the Zhu–Nakamura (ZN) theory. This ZN-TSH method refers to not only classically allowed hops but also classically forbidden hops. The potential energy surface constructed by Kamisaka et al. is employed in the calculation. A new iterative method is proposed to yield the two-dimensional seam surface from the topography of the adiabatic potential surfaces, in which the inconvenience of directly solving the first-order partial differential equation is avoided. The cross sections of these two systems are calculated for three competing channels of the reactive charge transfer, the nonreactive charge transfer, and the reactive noncharge transfer, for ground rovibrational state of H2 or D2. Also, this study provides reaction probabilities of these three processes for the total angular momentum J=0 and ground initial vibrational state of H2 or D2. The calculated results from ZN-TSH method are in good agreement with the exact quantum calculations and the experimental measurements.
Onset of diffusive behavior in confined transport systems
Authors: Jepps Owen G. , Bianca Carlo , Rondoni Lamberto
Published: March 2008

We investigate the onset of diffusive behavior in polygonal channels for disks of finite size, modeling simple microporous membranes. It is well established that the point-particle case displays anomalous transport, because of slow correlation decay in the absence of defocusing collisions. We investigate which features of point-particle transport survive in the case of finite-sized particles (which undergo defocusing collisions). A similar question was investigated by Lansel, Porter, and Bunimovich [Chaos 16, 013129 (2006)], who found that certain integrals of motion and multiple ergodic components, characteristic of the point-particle case, remain in “mushroom”-like systems with few finite-sized particles. We quantify the time scales over which the transport of disks shows features typical of the point particles, or is driven toward diffusive behavior. In particular, we find that interparticle collisions drive the system toward diffusive behavior more strongly than defocusing boundary collisions. We illustrate how, and at what stage, typical thermodynamic behavior (consistent with kinetic theory) is observed, as particle numbers grow and mean free paths diminish. These results have both applied (e.g., nanotechnological) and theoretical interest.
Protein association with circular DNA: Rate enhancement by nonspecific binding
Authors: Alsallaq Ramzi , Zhou Huan-Xiang
Published: March 2008

An analytical solution for the nonspecific-binding-facilitated diffusion-controlled rate of association of a protein with a specific site on a circular DNA is derived. Nonspecific binding is modeled by a short-range attractive surface potential. The protein undergoes diffusion in the bulk solution and in the surface layer. The association rate for a circular DNA is compared to the counterpart for a linear DNA, in which the ends of the surface layer are treated as reflecting. As expected, when the DNA length is long, the shape of the DNA does not affect the association rate. For a shorter length, the association rate for the linear DNA is modestly higher than the circular counterpart. The higher rate of the linear DNA is possibly due to its more open shape, which affords it a higher ability to draw the protein from the bulk to its surface. The analytical solution is verified by Brownian dynamics simulations.
Effects of nondenumerable fixed points in finite dynamical systems
Authors: Chakraborty Sagar , Bhattacharjee J. K.
Published: March 2008

The motion of a spinning soccer ball brings forth the possible existence of a whole class of finite dynamical systems where there may be a nondenumerably infinite number of fixed points. They defy the very traditional meaning of the fixed point that a point on the fixed point in the phase space should remain there forever, for, a fixed point can evolve as well! Under such considerations one can argue that a free-kicked soccer ball should be nonchaotic.
Phase synchronization in an array of driven Josephson junctions
Authors: N. Chitra R. , Kuriakose V. C.
Published: March 2008

We consider an array of N Josephson junctions connected in parallel and explore the condition for chaotic synchronization. It is found that the outer junctions can be synchronized while they remain uncorrelated to the inner ones when an external biasing is applied. The stability of the solution is found out for the outer junctions in the synchronization manifold. Symmetry considerations lead to a situation wherein the inner junctions can synchronize for certain values of the parameter. In the presence of a phase difference between the applied fields, all the junctions exhibit phase synchronization. It is also found that chaotic motion changes to periodic in the presence of phase differences.
Size dependence of martensite transformation temperature in ferromagnetic shape memory alloy FePd
Authors: Seki Kenta , Kura Hiroaki , Sato Tetsuya , Taniyama Tomoyasu
Published: March 2008

Martensite transformation temperature of ferromagnetic shape memory alloy FePd was studied in the shape of nanoparticle and the polycrystalline samples with grain size in micrometers based on the x-ray diffraction and magnetic measurement as a function of sample size. Both the forward transformation start temperature Ms and reverse transformation finish temperature Af of polycrystalline sample monotonically decreased with decreasing grain size and were not observed in the nanoparticles. The size dependence of transformation temperature is explained based on the change in transformation mode, i.e., the decrease in sample size induces the change from the multivariant mode to single variant mode in which the strain energy is large. In the small sample, the strain energy becomes large, and thus the large driving force is required for the transformation. As a result, the large amount of undercooling occurs, which leads to the lowering of Ms. The measurement of heat capacity indicates that the strain energy is elastically stored without dispersion in the transformation process even in the small size because the volume change of FePd at the transformation is very small. The large elastic strain energy works as the driving force to reverse transformation, and then the lowering of Af is induced. Therefore, the lowering of transformation temperature in FePd is characterized by the lowering of thermodynamic equilibrium temperature.
Transparent nonlinear optical crystallized glass fibers with highly oriented Ba2TiGe2O8 crystals
Authors: Hane Yosuke , Komatsu Takayuki , Benino Yasuhiko , Fujiwara Takumi
Published: March 2008

Glass fibers with a diameter of 100–200μm are drawn by just pulling up melts of 30BaO–15TiO2–55GeO2 glass, and transparent crystallized glass fibers consisting of nonlinear optical Ba2TiGe2O8 crystals are fabricated by crystallization of glass fibers. It is clarified from linearly polarized micro-Raman scattering spectra that fibers show the surface crystallization and Ba2TiGe2O8 crystals grow from the surface to the interior, giving c-axis orientations. It is found that holes are formed frequently in the center of fully crystallized glass fibers, and transparent hollow crystallized glass fibers are fabricated through careful heat treatments, e.g., fibers with ϕ=200μm show hollows (capillary-type holes) with ϕ=40μm. By adding a small amount of Sb2O3 in glass fiber preparations, transparent crystallized glass fibers with no holes are developed and second harmonic generations (SHGs) are clearly observed from such fibers. The present study proposes that transparent crystallized glass fibers showing strong SHGs would have a potential for fiber-type light control optical devices.
X-ray luminescence of LaF3:Tb3+ and LaF3:Ce3+,Tb3+ water-soluble nanoparticles
Authors: Liu Yuanfang , Chen Wei , Wang Shaopeng , Joly Alan G. , Westcott Sarah , Woo Boon Kuan
Published: March 2008

We report x-ray luminescence from LaF3:Ce3+,Tb3+ and LaF3:Tb3+ water-soluble nanoparticles. The x-ray luminescence is dominated by emission from Tb3+ ions, similar to photoluminescence spectra of the nanoparticle aqueous solutions and spectra from nanoparticle powders precipitated from the aqueous samples. Coating the nanoparticles with an insulating inorganic LaF3 or organic H2N–(CH2)10–COOH layer can enhance the x-ray luminescence from the aqueous nanoparticles. This enhancement is most likely due to the decreased energy loss due to the particle-solvent interactions.
Reconstruction of eye movements during blinks
Authors: Baptista M. S. , Bohn C. , Kliegl R. , Engbert R. , Kurths J.
Published: March 2008

In eye movement research in reading, the amount of data plays a crucial role for the validation of results. A methodological problem for the analysis of the eye movement in reading are blinks, when readers close their eyes. Blinking rate increases with increasing reading time, resulting in high data losses, especially for older adults or reading impaired subjects. We present a method, based on the symbolic sequence dynamics of the eye movements, that reconstructs the horizontal position of the eyes while the reader blinks. The method makes use of an observed fact that the movements of the eyes before closing or after opening contain information about the eyes movements during blinks. Test results indicate that our reconstruction method is superior to methods that use simpler interpolation approaches. In addition, analyses of the reconstructed data show no significant deviation from the usual behavior observed in readers.
Nanoinsulators and nanoconnectors for optical nanocircuits
Authors: Silveirinha Mário G. , Alù Andrea , Li Jingjing , Engheta Nader
Published: March 2008

Following our recent idea of using plasmonic and nonplasmonic nanoparticles as nanoinductors and nanocapacitors in the infrared and optical domains [N. Engheta et al., Phys. Rev. Letts. 95, 095504 (2005)], in this work we analyze in detail some complex circuit configurations involving series and parallel combinations of these lumped nanocircuit elements at optical frequencies. Using numerical simulations, it is demonstrated that, after a proper design, the behavior of these nanoelements may closely mimic that of their lower-frequency [i.e., radio frequency (rf) and microwave] counterparts, even in relatively complex configurations. In addition, we analyze here in detail the concepts of nanoinsulators and nanoconnectors in the optical domain, demonstrating how these components may be crucial in minimizing the coupling between adjacent optical nanocircuit elements and in properly connecting different branches of the nanocircuit. The unit nanomodules for lumped nanoelements are introduced as building blocks for more complex nanocircuits at optical frequencies. Numerical simulations of some complex circuit scenarios considering the frequency response of these nanocircuits are presented and discussed in detail, showing how practical applications of such optical nanocircuit concepts may indeed be feasible within the current limits of nanotechnology.
Incorporation of Ge on GaN(0001)
Authors: Qi Y. , King S. T. , Cheung S. H. , Weinert M. , Li L.
Published: March 2008

We investigate Ge incorporation into the Ga-rich GaN(0001) pseudo-1×1 surface using scanning tunneling microscopy and first-principles calculations. We find that the Ge induces a structural change by forming covalent bonds with the Ga. The liberated Ga atoms, together with additional Ge atoms, reside on the T4 sites, forming a 2×2 structure. Different domains of hcp and fcc stacking are formed to relieve the strain caused by the size mismatch between Ga and Ge.
First-principles calculations of magnetic circular dichroism spectra
Authors: Ganyushin Dmitry , Neese Frank
Published: March 2008

An elaborate approach for the prediction of magnetic circular dichroism (MCD) spectra in the framework of highly correlated multiconfigurational ab initio methods is presented. The MCD transitions are computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. These states are obtained from the diagonalization of the SOC and SSC operators along with the spin and orbital Zeeman operators in the basis of a preselected number of roots of the spin-free Hamiltonian. Therefore, zero-field splittings due to the SOC and SSC interactions along with the magnetic field splittings are explicitly accounted for in the ground as well as the excited states. This makes it possible to calculate simultaneously all MCD A, B, and C terms even beyond the linear response limit. The SOC is computed using a multicenter mean-field approximation to the Breit–Pauli Hamiltonian. Two-electron SSC terms are included in the treatment without further approximations. The MCD transition intensities are subjected to numerical orientational averaging in order to treat the most commonly encountered case of randomly oriented molecules. The simulated MCD spectra for the OH, NH, and CH radicals as well as for [Fe(CN)6]3− are in good agreement with the experimental spectra. In the former case, the significant effects of the inert gas matrices in which the experimental spectra were obtained were modeled in a phenomenological way.
Adsorption dynamics of water on Pt{110}−(1×2)
Authors: Laffir Fathima R. , Fiorin Vittorio , King David A.
Published: March 2008

The dynamics of H2O adsorption on Pt{110}−(1×2) is studied using supersonic molecular beam and temperature programed desorption techniques. The sticking probabilities are measured using the King and Wells method at a surface temperature of 165K. The absolute initial sticking probability s0 of H2O is 0.54±0.03 for an incident kinetic energy of 27kJ∕mol. However, an unusual molecular beam flux dependence on s0 is also found. At low water coverage (θ<1), the sticking probability is independent of coverage due either to diffusion in an extrinsic precursor state formed above bilayer islands or to incorporation into the islands. We define θ=1 as the water coverage when the dissociative sticking probability of D2 on a surface predosed with water has dropped to zero. The slow falling H2O sticking probability at θ>1 results from compression of the bilayer and the formation of multilayers. Temperature programed desorption of water shows fractional order kinetics consistent with hydrogen-bonded islands on the surface. A remarkable dependence of the initial sticking probability on the translational (1–27kJ∕mol) and internal energies of water is observed: s0 is found to be essentially a step function of translational energy, increasing fivefold at a threshold energy of 5kJ∕mol. The threshold migrates to higher energies with increasing nozzle temperature (300–700K). We conclude that both rotational state and rotational alignment of the water molecules in the seeded supersonic expansion are implicated in dictating the adsorption process.
High temperature superconductor micro-superconducting-quantum-interference-device magnetometer for magnetization measurement of a microscale magnet
Authors: Takeda Keiji , Mori Hatsumi , Yamaguchi Akira , Ishimoto Hidehiko , Nakamura Takayoshi , Kuriki Shinya , Hozumi Toshiya , Ohkoshi Shin-ichi
Published: March 2008

We have developed a high temperature superconductor (HTS) micrometer-sized dc superconducting quantum interference device (SQUID) magnetometer for high field and high temperature operation. It was fabricated from YBa2Cu3O7−δ of 92nm in thickness with photolithography techniques to have a hole of 4×9μm2 and 2μm wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the modulation patterns of critical current Ic were observed for three different field directions. They were successfully used to measure the magnetic properties of a molecular ferrimagnetic microcrystal (23×17×13μm3), [Mn2(H2O)2(CH3COO)][W(CN)8]⋅2H2O. The magnetization curve was obtained in magnetic field up to 0.12T between 30 and 70K. This is the first to measure the anisotropy of hysteresis curve in the field above 0.1T with an accuracy of 10−12JT−1 (10−9emu) with a HTS micro-SQUID magnetometer.
Nonempirical statistical theory for molecular evaporation from nonrigid clusters
Authors: Fujii Mikiya , Takatsuka Kazuo
Published: March 2008

We propose a nonempirical statistical theory to give the reaction rate and the kinetic energy distribution of fragments for molecular evaporation from highly nonrigid atomic and van der Waals clusters. To quantify the theory, an efficient and accurate method to evaluate the absolute value of classical density of states (the Thomas–Fermi density in phase space) and the flux at the so-called dividing surface is critically important, and we have devised such an efficient method. The theory and associated methods are verified by numerical comparison with the corresponding molecular dynamics simulation through the study of Ar2 evaporation from Ar8 cluster, in which evaporation is strongly coupled with structural isomerization dynamics. It turns out that the nonempirical statistical theory gives quite an accurate reaction rate. We also study the kinetic energy release (KER) arising from these evaporations and its Boltzmann-like distribution both for atomic and diatomic evaporations. This provides a general relation between the KER and temperature of the fragments.
Modeling, design, and characterization of multisegment cantilevers for resonant mass detection
Authors: Lobontiu Nicolae , Lupea Iulian , Ilic Rob , Craighead Harold G.
Published: March 2008

The work presents the analytic modeling, design, and the experimental and numerical characterization of multisegment cantilevers’ bending and torsion resonant responses with the aim of evaluating the amount and position of matter which deposits on these elastic structures. The cantilevers may comprise any number of geometrically different segments that are serially connected, and actual results are presented for the two-segment, circularly notched configuration. The generic analytical model, which formulates the bending and torsion resonant frequencies of both the original cantilever and the one with the attached mass, is derived by means of Rayleigh’s quotient approach. Relationships are formulated between nondimensional parameters characterizing the geometry, resonant frequencies, and deposited mass amount and position for both bending and torsion. The sensitivity of the frequency shift to the landing parameters and mass amount are also studied. Analytical model, finite element, and experimental testing data corresponding to the bending and torsion resonant responses of macro- and nano-two-segment, circularly notched cantilever specimens are in agreement. The analytical model of the circularly notched cantilever is further employed to investigate the relationships between the cantilever geometry parameters, the deposited mass amount, and its landing position to the change in the bending and torsion resonant frequency.
Acoustic wave propagation in one-dimensional phononic crystals containing Helmholtz resonators
Authors: Wang Zhi Guo , Lee Sam Hyeon , Kim Chul Koo , Park Choon Mahn , Nahm Kyun , Nikitov S. A.
Published: March 2008

One-dimensional acoustic waveguide containing subwavelength-sized Helmholtz resonators is known to exhibit novel physical phenomena. However, no systematic theoretical study on this system has been carried out so far except on a few limited cases. We present a thorough theoretical calculation on the acoustic wave propagation in phononic crystals containing Helmholtz resonators without any geometrical size restrictions. The band structures, transmission spectra, and defect states are studied for diverse geometries using the interface response theory. It is shown that the acoustic band structure of the model is fundamentally different from the conventional acoustic–elastic cases and richer due to the coexistence of the resonant and the Bragg gaps. It is also shown that the presence of a defect resonator in the system can give rise to a localized mode inside the resonance gaps. The results clearly show that the presence of the Helmholtz resonators singly or periodically can play a prominent role in designing any acoustic band gap materials.
Charging of dielectrics under focused ion beam irradiation
Authors: Yogev S. , Levin J. , Molotskii M. , Schwarzman A. , Avayu O. , Rosenwaks Y.
Published: March 2008

We present a detailed experimental and theoretical study of the charging of silicon nitride and silicon oxide thin films following focused ion beam irradiation. The samples were irradiated using 30keV Ga+ ions at different ion doses and their consequent work function changes were measured by Kelvin probe force microcopy. The surface potential of both samples increased following the ion irradiation up to a critical ion dose, and then moderately decreased. The dependence of the sample surface potential on the irradiated ion dose is analyzed by taking into account all the main factors affecting charging in dielectric thin films: electron-hole generation by the incident fast ions, secondary ion-electron emission, sputtering of surface atoms, electron-hole recombination, electron recombination with the incident stopped ions, hole leakage current to the Si substrate, and various charge trapping processes. It was found that the much larger surface potential induced in Si3N4 in comparison to SiO2 is associated with the different resistance to the Ga+ ion bombardment. Under equal ion irradiation dose, a larger concentration of shallow traps is created in SiO2 than in Si3N4. This leads to an increased hole capture in shallow traps versus deep traps, and a consequent decrease in the surface potential.
Phonons in ferroelectric Bi2WO6: Raman and infrared spectra and lattice dynamics
Authors: Maczka Mirosław , Hanuza Jerzy , Paraguassu Waldeci , Gomes Souza Filho Antonio , Tarso Cavalcante Freire Paulo , Mendes Filho Josue
Published: March 2008

Bi 2 W O 6 ferroelectric single crystal was investigated by micro-Raman scattering and infrared spectroscopies. Symmetry of modes was established and the mode assignment was proposed.
Self-assembled thulium silicide nanostructures on silicon(001) studied by scanning tunneling microscopy and transmission electron microscopy
Authors: Zhang J. , Crimp M. A. , Cui Y. , Nogami J.
Published: March 2008

Since the formation of epitaxial silicide nanowires by deposition of rare earth (RE) metals on Si(001) was first discovered, intense interest has been focused on their growth mechanism. Unlike many of the other nanowire forming RE metals, which have several different polymorphic silicides at about the same stoichiometry, thulium forms three bulk silicides, Tm5Si3, TmSi, and Tm3Si5, with very different compositions and crystal structures. Due to their lattice mismatch anisotropy with the substrate when grown on the Si(001) surface, the latter two phases have the potential for nanowire formation. Scanning tunneling microscopy shows the formation of both nanowires and larger square islands. Cross-sectional high resolution transmission electron microscopy reveals both orthorhombic TmSi and hexagonal Tm3Si5, forming nanostructures either as connected neighboring structures or as overlapping structures. The coexistence of layers of both silicides in many nanostructures suggests a new mechanism for strain relief at the interface with the substrate.
Specific heat of CdS/CdSe/CdS quantum-dot quantum wells
Authors: Chen I-Chuen , Weng Chih-Li , Tsai Yan-Chr
Published: March 2008

The vibrational modes of acoustic phonons and their corresponding eigenfrequencies in CdS/CdSe/CdS quantum-dot quantum wells (QDQWs) are obtained by taking on the continuum model. The energy spectra of the phonons in nanocrystals from the analytic solutions are checked by the finite-element method. Based on the spectrum of acoustic phonons and the Debye model, the temperature dependences of the specific heat contributed from lattice phonons are calculated to investigate the size-dependent effects. The lattice softening is also demonstrated and the results qualitatively agree with the experimental observations for fine particles and quantum dots. We found that the phonon density of states of a QDQW plays an important role in the calculation of specific heat, and the modification of the effective sound velocity in the nanocrystal is also suggested.
Effect of strain on the electron effective mobility in biaxially strained silicon inversion layers: An experimental and theoretical analysis via atomic force microscopy measurements and Kubo-Greenwood mobility calculations
Authors: Bonno Olivier , Barraud Sylvain , Mariolle Denis , Andrieu François
Published: March 2008

Recently, in order to explain the long-channel electron effective mobility at a high sheet carrier density in strained silicon channel transistors, it has been suggested by [M. V. Fischetti, F. Gamiz, and W. Hansch, J. Appl. Phys. 92, 7230 (2002)] that biaxial tensile strain should smooth the Si/SiO2 interface. To address this topic, the roughness properties of biaxial strained silicon-on-insulator (s-SOI) films are investigated by means of atomic force microscopy. Through in-depth statistical analysis of the digitalized surface profiles, the roughness parameters are extracted for unstrained and strained SOI films, with 0.8% biaxial tensile strain. Especially, it is found that strain significantly reduces the roughness amplitude. Then, mobility calculations in SOI and s-SOI inversion layers are performed in the framework of the Kubo-Greenwood formalism. The model accounts for the main scattering mechanisms that are dominant in the high electron density range, namely phonon and surface roughness. Special attention has been paid to the modeling of the latter by accounting for all the contributions of the potential which arise from the deformed rough interface, and by using a multisubband wavelength-dependent screening model. This model is then applied to study the influence of the surface morphology on the mobility in s-SOI inversion layers. In this context, the mobility gain between s-SOI and unstrained SOI layers is found to agree significantly better with experimental data if the strain-induced decrease of the roughness amplitude is taken into account.
Thermoelectric properties of p-type half-Heusler alloys Zr1−xTixCoSnySb1−y (0.0<x<0.5; y=0.15 and 0.3)
Authors: Ponnambalam V. , Alboni Paola N. , Edwards J. , Tritt Terry M. , Culp Slade R. , Poon S. Joseph
Published: March 2008

Half-Heusler alloys Zr1−xTixCoSnySb1−y (0.0<x<0.5; y=0.15 and 0.3) are investigated for their possible use as high temperature thermoelectric materials. In these p-type materials, the Zr site is primarily substituted with Ti to reduce thermal conductivity (κ), while the Sn content is varied to optimize thermoelectric properties. For these compositions, these alloys exhibit moderate resistivity (ρ) in the mΩcm range and high positive thermopower (α), on the order of hundreds of μV∕K. Measured Hall coefficients suggest that holes are dominant charge carriers. Calculated carrier mobilities are rather low in the range of 0.8–1.5cm2∕Vs. Thermal conductivity (κ) values as low as ∼8.5–4.5Wm−1K−1 are also measured. The calculated thermoelectric figure of merit ZT=α2T∕ρκ is as high as 0.2 at T=1000K, implying that these alloys could be potential p-type thermoelectric materials for energy conversion at high temperatures.
Epitaxially grown n-ZnO∕MgO∕TiN∕n+-Si(111) heterostructured light-emitting diode
Authors: Sun X. W. , Zhao J. L. , Tan S. T. , Tan L. H. , Tung C. H. , Lo G. Q. , Kwong D. L. , Zhang Y. W. , Li X. M. , Teo K. L.
Published: March 2008

Epitaxial n-ZnO∕MgO∕TiN∕n+-Si heterostructured light-emitting diodes have been fabricated. The epitaxial growth of MgO∕TiN on Si(111) was established by pulsed laser deposition, which was further employed as a buffer layer for epitaxial growth of ZnO layer by metal-organic chemical-vapor deposition. Good epitaxial quality was found using high-resolution x-ray diffraction and transmission electron microscopy. A strong wide electroluminescence band, ranging from 350to850nm and centered at ∼530nm, was observed from the diode when a positive voltage was applied on Si substrate. The diode exhibited a linear light-output-current characteristic with an injection current up to 192mA.
A soft x-ray beamline capable of canceling the performance impairment due to power absorbed on its optical elements
Authors: Reininger Ruben , Kriesel Ken , Hulbert S. L. , Sánchez-Hanke Cecilia , Arena D. A.
Published: March 2008

We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>104) and spot size (4×4μm2) at the sample position despite being exposed to more than 2.15kW of undulator radiation and a maximum power density on the optics of more than 0.9W∕mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator’s central cone, which contains the usable photons but is considerably smaller than the angular power distribution.
Bianchi type-I cosmological model for perfect fluid distribution in Lyra geometry
Authors: Bali Raj , Chandnani Naresh Kumar
Published: March 2008

In this paper, we have investigated Bianchi type-I cosmological model with time dependent gauge function β for perfect fluid distribution within the framework of Lyra geometry. To get the deterministic model of the universe, we have assumed that eigenvalue (σ11) of shear tensor (σij) is proportional to the expansion (θ). This leads to A=(BC)n, where A,B,C are metric potentials. The physical and geometrical aspects of the model and singularities in the model are also discussed.
Highly efficient bilayer green phosphorescent organic light emitting devices
Authors: Jeon Woo Sik , Park Tae Jin , Park Jung Joo , Kim Sun Young , Jang Jin , Kwon Jang Hyuk , Pode Ramchandra
Published: March 2008

We present a highly efficient green phosphorescent device comprising only of two organic layers. A host material bis[2-(2-hydroxyphenyl)-pyridine]beryllium having a good electron transporting and energy transfer characteristics, and a wide band gap hole transport material N,N′-di(4-(N,N′-diphenyl-amino)phenyl)-N,N′-diphenylbenzidine lead to the fabrication of a simplified high efficiency device. The driving voltage value of 3.3V to reach a luminance of 1000cd∕m2 is reported. The maximum current- and power-efficiency values of 38.30cd∕A and 46.60lm∕W are demonstrated in this device. Results reveal a practical way to fabricate highly efficient truly bilayer organic devices for trouble-free manufacturing processes.
Photoluminescence and Raman spectral study of C incorporation in strained Si1−x−yGexCy epilayers on Si(100)
Authors: Rowell N. L. , Lockwood D. J. , Baribeau J.-M.
Published: March 2008

Photoluminescence (PL) and Raman spectroscopy have been used to study the incorporation of C in strained Si1−x−yGexCy epilayers lattice matched to Si(001). The samples were characterized by both secondary ion mass spectrometry and Auger emission spectroscopy to obtain the total C concentration and x-ray diffraction data were used to obtain the substitutional C concentration. The difference between the total and substitutional C concentrations, i.e., the nonsubstitutional carbon fraction, was found to be directly correlated with specific spectral lines in both the room temperature Raman and low temperature PL spectra. These variations are discussed and related to C related defects in the epilayers.