bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐time resolution dayside convection monitoring by incoherent scatter radar and a sample application
Authors: Zou S. , Lyons L. R. , McCready M. A. , Heinselman C. J.
Published: January 2008

Convection and its changes, driven by the solar wind, are related to geomagnetic disturbances such as substorms, dynamic pressure disturbances and convection bays. Furthermore, convection is theoretically related to the evolution of the Harang electric field reversal (or “discontinuity”), which has been related observationally and theoretically to these disturbances. Interplanetary measurements generally used for studying and making associations of convection with disturbances are acceptable for statistical studies, but spatial structure and propagation timing errors due to the highly variable orientation of interplanetary structures create significant ambiguity for case studies and have prevented definitive understanding. Moreover, small but geoeffective structure in the solar wind may be missed by even multispacecraft observations. Direct observation of dayside convection with high time resolution offers a potential solution to this problem. In this paper, we demonstrate that Sondrestrom incoherent scatter radar (ISR) observations have the ability to accurately monitor the dayside convection with ∼2.5 min temporal resolution. The observations clearly show the dayside convection responses to IMF Bz, By and solar wind dynamic pressure variations and thus shed new light on how the magnetosphere and ionosphere respond to different external driving. Then, we illustrate an application of this technique by showing how it can be applied to study substorm triggering. We plan to use this technique in the future to study the relationships between convection, other geomagnetic disturbances, and the Harang reversal, as well as to evaluate the preceding convection strength and duration and the convection changes that lead to substorm onset.
A Shock Fitting Procedure Based on Monte Carlo Calculations: Application to Slow Shocks
Authors: Lin C. C. , Feng H. Q. , Chao J. K. , Lee L. C. , Lyu L. H. , Wu D. J.
Published: January 2008

Recent derived procedure of fitting the Rankine‐Hugoniot shock jump relations for fast MHD shocks (Lin et al., 2006) is here applied to slow‐mode shocks. The present paper is a continuation of Lin et al. (2006). We modify the method to be applicable to slow shocks. We have tested the new method via a simulated slow shock. The result shows that the method can find a best fit solution that is close to the “true answer” as long as the systematic errors in the synthetic data are not too large. We also apply the method to one interplanetary slow shock and two slow shocks observed in the magnetotail. The results have been compared to the previous studies. The new method of shock fitting is demonstrated successfully for identifying slow shocks.
Electron circulation in Saturn's magnetosphere
Authors: Rymer A. M. , Mauk B. H. , Hill T. W. , Paranicas C. , Mitchell D. G. , Coates A. J. , Young D. T.
Published: January 2008

We present a model wherein electrons produced in Saturn's inner magnetosphere circulate through a combination of outward and inward motions driven by the centrifugal interchange instability and azimuthal motion through gradient and curvature drifts. Cool (<100 eV) electrons produced inside L ∼ 12 move slowly outward. To balance outflowing flux, inward transport occurs in small scale injection events. Electrons in these inwardly moving flux tubes are heated adiabatically to energies greater than 100 eV and their pitch angle distributions evolve from isotropic to “pancake” (peaked at 90°). We show that this evolution is observed, and that the pitch angle distributions observed inside a plasma injection are consistent with loss free inward adiabatic transport from L ∼ 11. As the flux tube moves inward the warm electrons undergo energy dependent gradient and curvature drifts out of the inwardly moving flux tube and find themselves superposed on cold, locally produced, plasma. At this point they turn around and are transported along with the cold plasma back toward the outer magnetosphere. With reasonable assumptions about scattering and loss this motion can naturally lead to the “butterfly” electron pitch angle distributions (with local minima at both 90° and 0/180°) that are observed in the warm electron plasma component. We note that we cannot reproduce the butterfly distributions using loss free outward adiabatic transport alone. This is to be expected because there exist pitch angle dependent losses in the form of Saturn's neutral gas cloud and E‐ring.
Gravity Waves in the Thermosphere Simulated by a General Circulation Model
Authors: Miyoshi Yasunobu , Fujiwara Hitoshi
Published: January 2008

By using a general circulation model that contains the region from the ground surface to the upper thermosphere, characteristics of gravity waves in the mesosphere and thermosphere are examined. At 100 km height, the dominant periods of gravity waves for zonal wave number 20 (zonal wavelength λx ≈ 2000 km), 40(λx ≈ 1000 km) and 80 (λx ≈ 500 km) are 6 h, 3 h and 1.5–2 h, respectively. For the individual zonal wave numbers, the corresponding dominant period becomes shorter at higher altitudes due to dissipation processes in the thermosphere, such as molecular viscosity and ion drag force. This means that gravity waves with larger horizontal phase velocity (larger vertical wavelength) can penetrate into the lower thermosphere. The vertical energy flux due to gravity waves indicates that upward propagation from the lower atmosphere to the thermosphere is dominant. Fluctuations of the horizontal wind associated with gravity waves and its relation to the ionospheric variation are discussed. Short‐period gravity waves into the thermosphere induce day‐to‐day variations of the zonal wind in the upper thermosphere. This result suggests that day‐to‐day variability of the zonal wind caused by gravity waves is expected to contribute to the ionospheric variability.
On the role of defects and surface chemistry for surface-assisted laser desorption ionization from silicon
Authors: Alimpiev S. , Grechnikov A. , Sunner J. , Karavanskii V. , Simanovsky Ya. , Zhabin S. , Nikiforov S.
Published: January 2008

The generation of ions from silicon substrates in surface-assisted laser desorption ionization (SALDI) has been studied using silicon substrates prepared and etched by a variety of different methods. The different substrates were compared with respect to their ability to generate peptide mass spectra using standard liquid sample deposition. The desorption/ionization processes were studied using gas-phase analyte deposition. Mass spectra were obtained from compounds with gas-phase basicities above 850kJ∕mol and with molecular weights up to 370Da. UV, VIS, and IR lasers were used for desorption. Ionization efficiencies were measured as a function of laser fluence and accumulated laser irradiance dose. Solvent vapors were added to the ion source and shown to result in fundamental laser-induced chemical and physical changes to the substrate surfaces. It is demonstrated that both the chemical properties of the substrate surface and the presence of a highly disordered structure with a high concentration of “dangling bonds” or deep gap states are required for efficient ion generation. In particular, amorphous silicon is shown to be an excellent SALDI substrate with ionization efficiencies as high as 1%, while hydrogen-passivated amorphous silicon is SALDI inactive. Based on the results, a novel model for SALDI ion generation is proposed with the following reaction steps: (1) the adsorption of neutral analyte molecules on the SALDI surface with formation of a hydrogen bond to surface Si–OH groups, (2) the electronic excitation of the substrate to form free electron/hole pairs (their relaxation results in trapped positive charges in near-surface deep gap states, causing an increase in the acidity of the Si–OH groups and proton transfer to the analyte molecules), and (3) the thermally activated dissociation of the analyte ions from the surface via a “loose” transition state.
Density matrix renormalization group calculations on relative energies of transition metal complexes and clusters
Authors: Marti Konrad H. , Ondík Irina Malkin , Moritz Gerrit , Reiher Markus
Published: January 2008

The accurate first-principles calculation of relative energies of transition metal complexes and clusters is still one of the great challenges for quantum chemistry. Dense lying electronic states and near degeneracies make accurate predictions difficult, and multireference methods with large active spaces are required. Often density functional theory calculations are employed for feasibility reasons, but their actual accuracy for a given system is usually difficult to assess (also because accurate ab initio reference data are lacking). In this work we study the performance of the density matrix renormalization group algorithm for the prediction of relative energies of transition metal complexes and clusters of different spin and molecular structure. In particular, the focus is on the relative energetical order of electronic states of different spin for mononuclear complexes and on the relative energy of different isomers of dinuclear oxo-bridged copper clusters.
First principles and classical molecular dynamics simulations of solvated benzene
Authors: Allesch Markus , Lightstone Felice C. , Schwegler Eric , Galli Giulia
Published: January 2008

We have performed extensive ab initio and classical molecular dynamics (MD) simulations of benzene in water in order to examine the unique solvation structures that are formed. Qualitative differences between classical and ab initio MD simulations are found and the importance of various technical simulation parameters is examined. Our comparison indicates that nonpolarizable classical models are not capable of describing the solute-water interface correctly if local interactions become energetically comparable to water hydrogen bonds. In addition, a comparison is made between a rigid water model and fully flexible water within ab initio MD simulations which shows that both models agree qualitatively for this challenging system.
On the dynamics of the H++D2(v=,j=)→HD+D+ reaction: A comparison between theory and experiment
Authors: Carmona-Novillo Estela , González-Lezana Tomás , Roncero Octavio , Honvault Pascal , Launay Jean-Michel , Bulut Niyazi , Javier Aoiz F. , Bañares Luis , Trottier Alexandre , Wrede Eckart
Published: January 2008

The H++D2(v=0,j=0)→HD+D+ reaction has been theoretically investigated by means of a time independent exact quantum mechanical approach, a quantum wave packet calculation within an adiabatic centrifugal sudden approximation, a statistical quantum model, and a quasiclassical trajectory calculation. Besides reaction probabilities as a function of collision energy at different values of the total angular momentum, J, special emphasis has been made at two specific collision energies, 0.1 and 0.524eV. The occurrence of distinctive dynamical behavior at these two energies is analyzed in some detail. An extensive comparison with previous experimental measurements on the Rydberg H atom with D2 molecules has been carried out at the higher collision energy. In particular, the present theoretical results have been employed to perform simulations of the experimental kinetic energy spectra.
Microwave spectrum of the H2DO+ ion: Inversion-rotation transitions and inversion splitting
Authors: Furuya Takashi , Saito Shuji , Araki Mitsunori
Published: January 2008

Inversion-rotation spectral lines of the monodeuterated hydronium ion, H2DO+, have been observed by a source-modulation spectrometer in the millimeter- to submillimeter-wave region. The ion was generated by a hollow-cathode discharge in a gas mixture of H2O and D2O. Nine inversion-rotation lines were measured precisely for the lowest pair of inversion doublets in the frequency region from 210to720GHz. The measured lines were analyzed to derive rotational constants in the inversion-doublet states and inversion splitting. The inversion splitting in the ground state was determined to be 1215866(410)MHz, that is, 40.5569(137)cm−1, where the numbers in parentheses give probable uncertainties estimated from the Jacobian matrix of the assumed centrifugal distortion constants of the inversion-doublet states. The determined inversion splitting is off by −0.58cm−1 from the predicted value of 41.14cm−1 by Rayamäki et al. using high-order coupled cluster ab initio calculations [J. Chem. Phys. 118, 10929 (2003)], and by 0.039cm−1 from the observed value of 40.518(10)cm−1 by Dong and Nesbitt using high-resolution jet-cooled infrared spectroscopy [J. Chem. Phys. 125, 144311 (2006)] beyond the quoted uncertainty. The most astronomically important transition 000−-10+ for the ortho species was measured at 673257.024(31)MHz, which could be used as a radioastronomical probe investigating interstellar chemistry of deuterium fractionation in space.
Quantum dynamics of an excited alkali atom in a noble gas cluster: Lithium attached to a helium cluster
Authors: Pacheco Alexander B. , Thorndyke Brian , Reyes Andrés , Micha David A.
Published: January 2008

An alkali atom–noble gas cluster system is considered as a model for solvation effects in optical spectra, within a quantum-classical description based on the density operator of a many-atom system and its partial Wigner transform. This leads to an eikonal-time-dependent molecular orbital treatment suitable for a time-dependent description of the coupling of light emission and atom dynamics in terms of the time-dependent electric dipole of the whole system. As an application, we consider an optically excited lithium atom as the dopant in a helium cluster at 0.5K. We describe the motions of the excited Li atom interacting with a cluster of He atoms and calculate the time-dependent electric dipole of the Li–He99 system during the dynamics. The electronic Hamiltonian is taken as a sum of three-body Li–He diatomic potentials including electronic polarization and repulsion, with l-dependent atomic pseudopotentials for Li and He, while we use a modified pair potential for He–He. The calculations involve the coupling of 12 quantum states with 300 classical degrees of freedom. We present results for the dynamics and spectra of a Li atom interacting with a model cluster surface of He atoms and also interacting with a droplet of He. We have found that the Li atom is attracted or repulsed from the He surface, depending on the orientation of its 2p orbitals. The spectra and dynamics of Li inside and at the surface of a cluster are found to be strongly dependent on its electronic states, its velocity direction, and whether light is present during emission or not.
Compact cantilever force probe for plasma pressure measurements
Authors: Nedzelskiy I. S. , Silva C. , Fernandes H. , Duarte P. , Varandas C. A. F.
Published: January 2008

A simple, compact cantilever force probe (CFP) has been developed for plasma pressure measurements. It is based on the pull-in phenomenon well known in microelectromechanical-system electrostatic actuators. The probe consists of a thin (25μm) titanium foil cantilever (38mm of length and 14mm of width) and a fixed electrode separated by a 0.75mm gap. The probe is shielded by brass box and enclosed into boron nitride housing with a 9mm diameter window for exposing part of cantilever surface to the plasma. When the voltage is applied between the cantilever and the electrode, an attractive electrostatic force is counterbalanced by cantilever restoring spring force. At some threshold (pull-in) voltage the system becomes unstable and the cantilever abruptly pulls toward the fixed electrode until breakdown occurs between them. The threshold voltage is sensitive to an additional externally applied force, while a simple detection of breakdown occurrence can be used to measure that threshold voltage value. The sensitivity to externally applied forces obtained during calibration is 0.28V∕μN (17.8V∕Pa for pressure). However, the resolution of the measurements is ±0.014mN (±0.22Pa) due to the statistical scattering in measured pull-in voltages. The diagnostic temporal resolution is ∼10ms, being determined by the dynamics of pull-in process. The probe has been tested in the tokamak ISTTOK edge plasma, and a plasma force of ∼0.07mN (plasma pressure ∼1.1Pa) has been obtained near the leading edge of the limiter. This value is in a reasonable agreement with the estimations using local plasma parameters measured by electrical probes. The use of the described CFP is limited by a heat flux of Q∼106W∕m2 due to uncontrollable rise of the cantilever temperature (ΔT∼20°C) during CFP response time.
Migration of Ag in low-temperature Ag2S from first principles
Authors: Wang Zhongchang , Gu Tingkun , Kadohira Takuya , Tada Tomofumi , Watanabe Satoshi
Published: January 2008

Using the density-functional theory combined with the nudged elastic band method, we have calculated migration pathways and estimated the activation energy barriers for the diffusion of Ag ions in low-temperature Ag2S. The activation energy barriers for four essential migrations for an Ag ion, namely, from a tetrahedral (T) site to an adjacent T vacancy (VT), from an octahedral (O) site to an adjacent O vacancy (VO), from T to VO, and from O to VT, are estimated as 0.461, 0.668, 0.212, and 0.318eV, respectively, which are comparable to experimental values. This means that diffusions of Ag ions between nonequivalent sites are preferable to those between equivalent sites, and that direct T-VT and O-VO diffusions are less likely to occur than indirect T-VO-T and O-VT-O diffusions. These diffusion behaviors between nonequivalent sites have also been supported by ab initio molecular dynamics simulations, in which the diffusion pathways are directly observed.
Thermodynamic and structural properties of mixed colloids represented by a hard-core two-Yukawa mixture model fluid: Monte Carlo simulations and an analytical theory
Authors: Yu Yang-Xin , Jin Lin
Published: January 2008

The interaction between colloidal particles is well represented by a hard-core two-Yukawa potential. In order to assess the accuracy of theoretical predictions for the thermodynamic and structural properties of mixed colloids, standard Monte Carlo simulations are carried out for the hard-core two-Yukawa mixtures. In the simulations, one range parameter in the two-Yukawa potential is taken as 1.8 or 2.8647, and another is taken as 4, 8, or 13.5485. Both attractive and repulsive dominant cases of the potential outside the hard core are considered. The effects of temperature, density, composition, size and energy parameter ratios on internal energy, compressibility factor, and radial distribution function are investigated extensively. Theoretical calculations are performed in the framework of analytical solution for the Ornstein-Zernike equation with the first-order mean spherical approximation (FMSA). Our analysis shows that the FMSA is very accurate for the prediction of the compressibility factor of the hard-core two-Yukawa mixtures at all conditions studied. The FMSA generally predicts accurate internal energy, but overestimates the internal energy of the systems at lower temperatures. Furthermore, we found that a simplified exponential version of the FMSA predicts fairly good radial distribution function at contact for the mixed two-Yukawa fluids. The comparison of the theoretical compressibility factor with that from the Monte Carlo simulations suggests that the FMSA can be used to investigate the fluid-fluid equilibria of hard-core two-Yukawa mixtures.
Scanning tunneling microscopy studies of pulse deposition of dinuclear organometallic molecules on Au(111)
Authors: Guo Song , Alex Kandel S.
Published: January 2008

Ultrahigh-vacuum scanning tunneling microscopy (STM) was used to study trans-[Cl(dppe)2Ru(CC)6Ru(dppe)2Cl] [abbreviated as Ru2, diphenylphosphinoethane (dppe)] on Au(111). This large organometallic molecule was pulse deposited onto the Au(111) surface under ultrahigh-vacuum (UHV) conditions. UHV STM studies on the prepared sample were carried out at room temperature and 77K in order to probe molecular adsorption and to characterize the surface produced by the pulse deposition process. Isolated Ru2 molecules were successfully imaged by STM at room temperature; however, STM images were degraded by mobile toluene solvent molecules that remain on the surface after the deposition. Cooling the sample to 77K allows the solvent molecules to be observed directly using STM, and under these conditions, toluene forms organized striped domains with regular domain boundaries and a lattice characterized by 5.3 and 2.7Å intermolecular distances. When methylene chloride is used as the solvent, it forms analogous domains on the surface at 77K. Mild annealing under vacuum causes most toluene molecules to desorb from the surface; however, this annealing process may lead to thermal degradation of Ru2 molecules. Although pulse deposition is an effective way to deposit molecules on surfaces, the presence of solvent on the surface after pulse deposition is unavoidable without thermal annealing, and this annealing may cause undesired chemical changes in the adsorbates under study. Preparation of samples using pulse deposition must take into account the characteristics of sample molecules, solvent, and surfaces.
Kinetic phase diagrams of GaN-based polariton lasers
Authors: Solnyshkov D. , Ouerdane H. , Malpuech G.
Published: January 2008

The simulations of polariton relaxation and Bose condensation in GaN microcavities (both bulk and with quantum wells) are performed by solving semiclassical Boltzmann equations. A complete set of kinetic phase diagrams for the most important parameters is calculated. We show that such cavities can operate as low-threshold polariton lasers at room temperature. The lasing threshold of cavity with quantum wells is found to be about ten times smaller than that of a bulk cavity.
Void growth modeling upon electromigration stressing in narrow copper lines
Authors: Tio Castro D. , Hoofman R. J. O. M. , Michelon J. , Gravesteijn D. J. , Bruynseraede C.
Published: January 2008

A simple three-dimensional void growth model is presented that can be used to simulate the resistance behavior in narrow copper lines upon thermo-electrical stressing. The output of the model is compared with experimental results obtained from electromigration tests carried out on single damascene copper lines encapsulated by a physical vapor deposition tantalum nitride–tantalum barrier. The electromigration resistance profiles are found to depend on different line and barrier parameters. The simulations yield a better understanding of the physical phenomena responsible for changes in the resistance profiles. The effect of a void cutting a copper line is seen as an asymptotic increase or “jump” in the measured resistance profile. At that moment, the barrier shunts the current and the void does not necessarily induce a catastrophic failure. Therefore, more voids can be formed in the line upon electromigration (EM) stress; every void spanning the line initiates a “jump” in the resistance profile. The described model approximates the experimental results with sufficient accuracy. The model can be used to predict the height of the jumps, setting adequate failure criteria beforehand for the EM experiments. The simplicity and sufficient accuracy of this model allow for easy prediction and interpretation of the EM resistance traces.
Transient of scanning electron microscopic images for a buried microstructure in insulators
Authors: Zhang Hai-Bo , Li Dao-Yu , Li Wei-Qin
Published: January 2008

We clarify the transient process and its mechanism of scanning electron microscope (SEM) images of a trench microstructure buried in insulators. First, interface charges of primary electrons trapped on the trench are derived from the charging model of a capacitor considering the electron beam induced current, and the surface potential is therefore assumed. The SEM signal current is then determined from its simplified relation with the surface potential. Calculated profiles of the secondary electron (SE) signal current and their time-evolution behaviors can well fit the transient of the experimental SEM images. Results show that the variation of the surface potential due to the transient interface charges and the effect of SE redistribution result in transients of the SEM imaging signal and the image width of the buried trench.
Analysis of crystallographic evolution in (Na,K)NbO3-based lead-free piezoceramics by x-ray diffraction
Authors: Wang Ke , Li Jing-Feng
Published: January 2008

The crystallographic structure of (Na,K)NbO3-based compounds and phase transitional behavior in (1−x)(K0.5Na0.5)NbO3–xLiNbO3 (x=0, 3, 6, and 8mol%) ceramics were accurately determined using high resolution x-ray diffraction (XRD). The phase transition between orthorhombic and tetragonal was distinctly characterized focusing on the XRD peak changes in {222} and {400} diffraction planes, by which lattice parameters of the perovskite type subcell, a, b, and c as well as angle β can be calculated. The discontinuous change in angle β at x=6mol% is located at the phase transitional region, where enhanced piezoelectric constant d33=215pC∕N was obtained. The present study provides a precise as well as simple method to investigate crystallographic structures in (Na,K)NbO3-based ceramics.
Micromachined optical well structure for thermo-optic switching
Authors: Zhu W. M. , Zhong T. , Liu A. Q. , Zhang X. M. , Yu M.
Published: January 2008

This letter demonstrates the thermo-optic switching function using an adjustable optical well structure, which is constructed by a thin air gap sandwiched between two micromachined hemicylindrical prisms. The device is etched on a silicon-on-insulator wafer within a footprint of 400×400μm2. In experiment, it measures an extinction ratio of 30.2dB and a switching time of 2.2μs. Compared with the other demonstrated switches that have optical barrier structures, this device is unique in the working principle and optical design, and shows various merits such as high extinction ratio, fast speed, low power consumption, and small size.
Magnetism of thin polycrystalline nickel nanowires
Authors: Tian F. , Chen J. , Zhu J. , Wei D.
Published: January 2008

The magnetism of one-dimensional (1D) nanowires is still unclear. The absence of experimental results on magnetic structures and microstructure of nanowires hampers their applications. In this paper, the magnetism of nanowires is studied by comparing the microstructures and simulating the M-H loops of two kinds of electrodeposited nickel nanowires of identical shape. In contrast to the existing views, it was found that the size distributions and interactions of grains within nanowires are the origin of the difference in magnetism. The magnetism of nanowires is affected deeply by the grains in nanowires.
Effect of laser parameters on electron injection into laser wakefields in plasma with a counterpropagating additional laser pulse
Authors: Wang W.-M. , Sheng Z.-M.
Published: January 2008

The interaction of a pump laser pulse with a counterpropagating additional laser pulse and resulting electron injection into the wakefield of the pump pulse in rarefied plasmas is analyzed. The impact of laser parameters on the injected electron number is discussed. When the injection pulse is moderately intense, the injected electron number increases with the injection pulse duration until it reaches some critical value beyond which the injected electron number is saturated. The critical pulse duration is estimated analytically and confirmed by particle-in-cell simulations. When the injection pulse intensity is decreased, the pump pulse intensity should be increased for the injection to occur. In this case, the injection pulse can only slightly affect the wakefield of the pump pulse. The injected electron number can increase with growing injection pulse duration continuously up to some limit that the wakefield can support.
Neutrino induced charge in a superdense two-electron Fermi plasma
Authors: Rios L. A. , Shukla P. K.
Published: January 2008

Using plasma physics methods, the effective neutrino charge in a superdense two-electron Fermi plasma is determined. The Fermi plasma has distinct groups of hot and cold electrons. Accounting for the quantum statistical pressure for the hot electron component and the quantum force associated with the quantum Bohm potential, the neutrino induced charge produced by the neutrino driving force is estimated. The influence of the quantum-mechanical effects on the neutrino effective electric charge has been investigated.
A dual wavelength distributed-feedback fiber laser
Authors: Groothoff Nathaniel , Martelli Cicero , Canning John
Published: January 2008

An approach to accessing air holes in a structured optical fiber with a distributed-feedback (DFB) laser based on higher order mode lasing is proposed and demonstrated. A narrow linewidth DFB fiber laser is fabricated in rare-earth-doped structured optical fiber. A higher order mode is shown to lase. Dual laser operation in both fundamental and higher order modes is also achieved. Numerical simulation of the mode profiles within the fiber using the adjustable boundary conditions-Fourier decomposition method supports the experimental results. Laser performance for each mode is characterized including imaging the emission of pump and lasing mode intensity profiles.
Characterization of long-range surface plasmon-polariton in stripe waveguides using scanning near-field optical microscopy
Authors: Salakhutdinov Ildar , Thakur Jagdish S. , Leosson Kristjan
Published: January 2008

Propagation characteristics of long-range surface plasmon-polariton (LRSPP) guiding along thin gold stripes embedded in polymer cover layers are investigated by scanning near-field optical microscopy (SNOM). It is shown that the characterization of samples with cover layers up to 10 μm is feasible in the optical communication wavelength range. We found that the spatial dimension of the optical signal is directly related to the geometrical dimension of the guiding layer, and the light collected by the SNOM is scattered light from the surface and not the evanescent field. We also discuss the limitations of the SNOM technique for the characterization of LRSPP modes.
Low temperature dependence of elastic parameters and internal frictions for glassy alloy Cu45Zr45Al5Ag5
Authors: Fukuhara M. , Kawashima A. , Zhang W. , Inoue A. , Yin F.
Published: January 2008

Using ultrasonics, acoustic characteristics of a glassy alloy Cu45Zr45Al5Ag5 are examined in order to understand its low-temperature elasticity. Longitudinal and transverse wave velocities, eight kinds of elastic parameters, and dilational and shear internal frictions were simultaneously measured as a function of temperature between 77 and 373 K in Cu45Zr45Al5Ag5 alloy, using an ultrasonic pulse method. The inflection at around 328 K for the anisotropy factor, the four elastic moduli, the Poisson ratio, the Debye temperature, and the 295 K peak of dilational friction show one topological change (pseudo-transition) associated with electron-phonon coupling, accompanied by accumulation of strain. A monotonic decrease from 77 K in Young and shear moduli and the Debye temperature as well as a pronounced increase from 150 K in shear friction indicates thermal relaxation of squeezed free-volume, accompanied by an increase in atomic distance and uniaxial volume-preserving deformation.
Terahertz emission mechanisms in InAsxP1−x
Authors: Lockhart Patric , Dutta P. S. , Han Pengyu , Zhang X.-C.
Published: January 2008

The terahertz emission mechanisms from the surface of bulk InAsxP1−x crystals have been examined. The dominant terahertz emission mechanism from InAsxP1−x for low-fluence optical excitation is the photo-Dember effect for As compositions of 78% and greater while the surface field effect is dominant for As compositions of 50% and lower for the measured transport properties. The observed terahertz emission magnitude from the photo-Dember effect increased with As composition due to decreasing absorption depth. The observed terahertz emission magnitude from the surface field effect decreased with increasing As composition and was lower than modeled values due to the lower high-field mobility in the depletion region in those samples.
Complex magnetic susceptibility setup for spectroscopy in the extremely low-frequency range
Authors: Kuipers B. W. M. , Bakelaar I. A. , Klokkenburg M. , Erné B. H.
Published: January 2008

A sensitive balanced differential transformer was built to measure complex initial parallel magnetic susceptibility spectra in the 0.01–1000Hz range. The alternating magnetic field can be chosen sufficiently weak that the magnetic structure of the samples is only slightly perturbed and the low frequencies make it possible to study the rotational dynamics of large magnetic colloidal particles or aggregates dispersed in a liquid. The distinguishing features of the setup are the novel multilayered cylindrical coils with a large sample volume and a large number of secondary turns (55 000) to measure induced voltages with a good signal-to-noise ratio, the use of a dual channel function generator to provide an ac current to the primary coils and an amplitude- and phase-adjusted compensation voltage to the dual phase differential lock-in amplifier, and the measurement of several vector quantities at each frequency. We present the electrical impedance characteristics of the coils, and we demonstrate the performance of the setup by measurement on magnetic colloidal dispersions covering a wide range of characteristic relaxation frequencies and magnetic susceptibilities, from χ≈−10−5 for pure water to χ>1 for concentrated ferrofluids.
A nanogap measuring method beyond optical diffraction limit
Authors: Wu Pao-Tung , Wu Meng-Chyi , Wu Chien-Ming
Published: January 2008

In this article, we report an optical method for the nanogap measurements beyond optical diffraction limit of a half of wavelength. This method is derived from Fresnel’s equations of the traditional Kretschmann-Raether configuration based on surface plasmon resonance. Numerical simulation shows that a decrease of air gap width to be smaller than a half of wavelength of incident light will reveal a larger resonance angle shift. The resonance angle monotonically shifts from 45° to 50° by reducing the air gap width around from 300to100nm. The measured smallest air gap width is about 126nm by fitting the simulated curves to the experimental data. This gap measurement method provides a simple and real-time measurement system beyond the physical diffraction limit of a half of wavelength.
Nonrelativistic electron bunch train for coherently enhanced terahertz radiation sources
Authors: Li Yuelin , Kim Kwang-Je
Published: January 2008

We propose to generate a train of prebunched electron beams for producing coherently enhanced Smith-Purcell radiation [S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953)] in the terahertz wavelength range. In this scheme, a train of picosecond laser pulses is produced to drive a photoemission gun to generate a train of 50keV electron pulses. The parameters are chosen so that the space-charge effect does not destroy the pulse time structure. Smith-Purcell radiation from the electron pulse train is enhanced due both to the short length of the individual electron bunch and to the repetitive structure of the beam. Example systems producing coherent terahertz power at about 1mW are described.
Atomic structure of binary Cu64.5Zr35.5 bulk metallic glass
Authors: Wang X. D. , Yin S. , Cao Q. P. , Jiang J. Z. , Franz H. , Jin Z. H.
Published: January 2008

Atomic structures of bulk glass-forming Cu64.5Zr35.5 and the eutectic composition Cu61.8Zr38.2 metallic glasses (MGs) have been studied by a combination of state-of-the-art experimental techniques and computational methods. Three-dimensional atomic configuration of the Cu64.5Zr35.5 MG is established. It is found that icosahedronlike clusters are dominant in both MGs. However, icosahedronlike clusters centered by Cu atoms are slightly denser packing and less distorted in Cu64.5Zr35.5, which can enhance the glass forming ability (GFA) by suppressing atomic movements and increasing the structural incompatibility with competing crystalline phases. The atomic arrangements from short to medium-range order are envisaged and compared between both MGs.
Adiabatic light transfer via dressed states in optical waveguide arrays
Authors: Della Valle G. , Ornigotti M. , Toney Fernandez T. , Laporta P. , Longhi S. , Coppa A. , Foglietti V.
Published: January 2008

We report on the experimental demonstration of adiabatic light transfer between the outer waveguides in a finite array of evanescently coupled optical waveguides with negligible excitation of all the intermediate waveguides. Such a counterintuitive light transfer scheme is an optical analogue of stimulated Raman adiabatic passage via an auxiliary dressed state proposed in atomic physics for multilevel systems.
Visual phenomena of surface plasmon polaritons at the dielectric-plasma interface
Authors: Xu Xu , Liu Feng , Zhou Qianhong , Liang Bo , Liang Yizi , Liang Rongqing
Published: January 2008

Some interesting experiment phenomena of light patterns that appear in microwave plasma have been investigated. The wavelength of surface plasmon polaritons (SPPs) at the dielectric-plasma interface as the functions of incident wave frequency and plasma density has been calculated. The comparison of the experiment results with the calculating results has been carried out. By experimentally and theoretically analyzing, the phenomena are considered to be caused by the surface wave of SPPs at the interface between Pyrex wall and plasma.
Schottky-like behavior of progressive breakdown of polycrystalline- silicon/silicon oxynitride gate dielectric stack
Authors: Lo V. L. , Pey K. L. , Tung C. H.
Published: January 2008

The postbreakdown (BD) I-V characteristics of a relatively stable percolation path within ultrathin silicon oxynitride have been found to exhibit Schottky-like behavior. The ideality factors in the range of 1.3–1.7 indicate that a Schottky-like barrier could exist in controlling the conduction mechanism in the later stage of progressive BD (PBD). The extracted effective barrier heights associated with the percolation path provides possible insights into the nature of the percolation path. We found that there are two possible mechanisms governing the post-BD I-V characteristics in the later stage of PBD: (1) a material property change in the vicinity of the percolation path and (2) the percolation path dilation.
Complete and robust bandgap switching in double-inverse-opal photonic crystals
Authors: Aryal Durga P. , Tsakmakidis Kosmas L. , Jamois Cécile , Hess Ortwin
Published: January 2008

The authors theoretically demonstrate a practical scheme for robust and complete photonic bandgap switching using a three-dimensional double-inverse-opal photonic crystal. The investigated structure consists of a close-packed face-centered-cubic arrangement of spherical air pores, interconnected via air channels and embedded in a high-index (tin disulfide) backbone. We show that by placing lower-index movable dielectric scatterers (titania) inside the air pores, a complete photonic bandgap opens for certain positions of the scatterers, which altogether closes for other positions. Our analysis reveals that this switching scheme is robust to geometric imperfections and allows for sizeable bandgap switching.
Magnetically responsive elastic microspheres
Authors: Peng Suili , Zhang Mengying , Niu Xize , Wen Weijia , Sheng Ping , Liu Zhengyou , Shi Jing
Published: January 2008

We report the design, fabrication, and characterization of magnetically responsive elastic microspheres consisting of polydimethylsioxane (PDMS) and magnetic nano-/microparticles. The microspheres can have either core-shell or solid structure, fabricated by using a microfluidic technique. The mechanical characteristics are determined with a modified electronic balance, and the results show that the microspheres exhibit magnetostrictive effect. Such microspheres can in addition behave as a smart material controllable through an external magnetic field. Owing to the transparency, biocompatibility and nontoxicity of PDMS, the magnetically responsive elastic microspheres may have potential applications in drug delivery, biosensing, bioseparation, and medical diagnosis.
Next-generation high-T c superconducting wires debut in the power grid
Authors: Matthews Jermey N. A.
Published: January 2008

Electric power companies are demonstrating the capacity of new flexible wire to deliver more current in less space and to limit power surges.
Dynamic Rearrangement of Nucleoporins during Fungal “Open” Mitosis
Authors: Theisen Ulrike , Straube Anne , Steinberg Gero
Published: January 2008

Mitosis in animals starts with the disassembly of the nuclear pore complexes and the breakdown of the nuclear envelope. In contrast to many fungi, the corn smut fungus Ustilago maydis also removes the nuclear envelope. Here, we report on the dynamic behavior of the nucleoporins Nup214, Pom152, Nup133, and Nup107 in this “open” fungal mitosis. In prophase, the nuclear pore complexes disassembled and Nup214 and Pom152 dispersed in the cytoplasm and in the endoplasmic reticulum, respectively. Nup107 and Nup133 initially spread throughout the cytoplasm, but in metaphase and early anaphase occurred on the chromosomes. In anaphase, the Nup107-subcomplex redistributed to the edge of the chromosome masses, where the new envelope was reconstituted. Subsequently, Nup214 and Pom152 are recruited to the nuclear pores and protein import starts. Recruitment of nucleoporins and protein import reached a steady state in G2 phase. Formation of the nuclear envelope and assembly of nuclear pores occurred in the absence of microtubules or F-actin, but not if both were disrupted. Thus, the basic principles of nuclear pore complex dynamics seem to be conserved in organisms displaying open mitosis.
Degradation of histone mRNA requires oligouridylation followed by decapping and simultaneous degradation of the mRNA both 5′ to 3′ and 3′ to 5′
Authors: Mullen Thomas E. , Marzluff William F.
Published: January 2008

Histone mRNAs are rapidly degraded at the end of S phase or when DNA replication is inhibited. Histone mRNAs end in a conserved stem–loop rather than a poly(A) tail. Degradation of histone mRNAs requires the stem–loop sequence, which binds the stem–loop-binding protein (SLBP), active translation of the histone mRNA, and the location of the stem–loop close to the termination codon. We report that the initial step in histone mRNA degradation is the addition of uridines to the 3′ end of the histone mRNA, both after inhibition of DNA replication and at the end of S phase. Lsm1 is required for histone mRNA degradation and is present in a complex containing SLBP on the 3′ end of histone mRNA after inhibition of DNA replication. We cloned degradation intermediates that had been partially degraded from both the 5′ and the 3′ ends. RNAi experiments demonstrate that both the exosome and 5′-to-3′ decay pathway components are required for degradation, and individual histone mRNAs are then degraded simultaneously 5′ to 3′ and 3′ to 5′.
Transcription factories are nuclear subcompartments that remain in the absence of transcription
Authors: Mitchell Jennifer A. , Fraser Peter
Published: January 2008

Nascent transcription occurs at nuclear foci of concentrated, hyperphosphorylated RNA polymerase II (RNAPII). We investigate RNAPII localization, distal gene coassociation, and Hbb locus conformation during inhibition of transcription. Our results show distal active genes remain associated with RNAPII foci and each other in the absence of elongation. When initiation is inhibited, active genes dissociate from RNAPII foci and each other, suggesting initiation is necessary to tether distal active genes to shared foci. In the absence of transcription RNAPII foci remain, indicating they are not simple accumulations of RNAPII on transcribed genes but exist as independent nuclear subcompartments.
Learning and generalization on asynchrony and order tasks at sound offset: Implications for underlying neural circuitry
Authors: Mossbridge Julia A. , Scissors Beth N. , Wright Beverly A.
Published: January 2008

Normal auditory perception relies on accurate judgments about the temporal relationships between sounds. Previously, we used a perceptual-learning paradigm to investigate the neural substrates of two such relative-timing judgments made at sound onset: detecting stimulus asynchrony and discriminating stimulus order. Here, we conducted parallel experiments at sound offset. Human adults practiced ∼1 h/d for 6–8 d on either asynchrony detection or order discrimination at sound offset with tones at 0.25 and 4.0 kHz. As at sound onset, learning on order-offset discrimination did not generalize to the other task (asynchrony), an untrained temporal position (onset), or untrained frequency pairs, indicating that this training affected a quite specialized neural circuit. In contrast, learning on asynchrony-offset detection generalized to the other task (order) and temporal position (onset), though not to untrained frequency pairs, implying that the training on this condition influenced a less specialized, or more interdependent, circuit. Finally, the learning patterns induced by single-session exposure to asynchrony and order tasks differed depending on whether these tasks were performed primarily at sound onset or offset, suggesting that this exposure modified circuitry specialized to separately process relative-timing tasks at these two temporal positions. Overall, it appears that the neural processes underlying relative-timing judgments are malleable, and that the nature of the affected circuitry depends on the duration of exposure (multihour or single-session) and the parameters of the judgment(s) made during that exposure.
Geological tours of the southwestern United States
Authors: FORD TREVOR D.
Published: January 2008

In the recent re–run of Alistair Cooke's TV series ‘America’, one of the most intriguing programmes was that on the pioneers trekking westwards from the Mississippi to California. Their journey took only four months. Today's tourist can fly the same distance in a little over two hours. The pioneers saw the geological marvels close at hand but few knew enough to appreciate them. The airborne tourist may know enough but can't see them. How does one overcome this problem? By an educational tour with a leader who knows the country.
Limestone landscapes of South China
Authors: SWEETING MARJORIE M.
Published: January 2008

More than 14% of China is covered by limestone, giving rise to the world's most spectacular karst landscapes comprising pinnacles, cones and towers.
Collecting fossil fishes in cowboy country
Authors: MARTILL DAVID M.
Published: January 2008

The Eocene Green River Formation fishes of southwestern Wyoming are among the best preserved and best known fossil fishes yet discovered. Collecting them is hard work and a very technical and time‐consuming process, but is made worthwhile by the fantastic setting in which the fossils occur. This is an account of a collecting trip under the leadership ofDr Lance Grande to expand the already spectacular collection of Green River fishes in the Field Museum of Natural History, Chicago.
The geology of the Morecambe gas field
Authors: LEVISON ALAN
Published: January 2008

The subsurface of the Irish Sea contains one of the United Kingdom's most important gas fields, the Morecambe Field, owned by British Gas. Approximately 10% of the UK's daily consumption of natural gas will be supplied by this giant accumulation trapped within fluvial deposits of the Lower Triassic Sherwood Sandstone Formation.
Carboniferous trilobites: the beginning of the end
Authors: OWENS R. M.
Published: January 2008

It is commonly assumed that by Carboniferous times trilobites were all but extinct, represented by only a handful of species belonging to the genera Phillipsia or Griffithides and found occasionally at a few localities. In fact, there is afar greater abundance and diversity of forms than is usually realized, and in parts of the Carboniferous System trilobites can be as stratigraphically important as many other fossil groups.