bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of large‐scale teleconnection patterns on methane sulfonate ice core records in Dronning Maud Land
Authors: Fundel Felix , Fischer H. , Weller R. , Traufetter F. , Oerter H. , Miller H.
Published: February 2006

Records of methane sulfonate (MS−) in ice cores from the high plateau of Dronning Maud Land (DML), Antarctica, drilled in the framework of the European Project for Ice Coring in Antarctica, are investigated for their potential as an environmental and climate archive for the Atlantic sector of the Southern Ocean. Despite postdepositional changes, years of extraordinary MS− concentrations can be clearly detected in the ice core records. We use composite anomaly maps of atmospheric parameters from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis fields for years of extreme MS− concentration to detect atmospheric patterns causing MS− variability. Changing atmospheric transport is shown to be an important, but not exclusive, parameter being conserved in the MS− record in DML. The often hypothesized direct link between high MS− concentrations and El Niño events is not supported for the observed region whereas the Antarctic Dipole (ADP), which is modulated by El Niño–Southern Oscillation conditions, exerts significant influence. A clear 13.9‐year cycle can be found throughout a 2000‐year MS− record that can be related to variations in the ADP. Over the last 300 years a 4.6‐year cycle is revealed in the MS− (and sea‐salt record), which vanishes in the deeper part of the ice core as a consequence of diffusion processes. From the long‐term perspective, periods of high MS− concentrations are connected to, on average, higher sea‐salt aerosol as well, reflecting a seasonally independent influence of transport on both species. A distinctive period of efficient atmospheric transport, probably due to a pronounced ADP, could be found from 1200 to 1600 A.D.
Observations and theories of Polar Mesospheric Summer Echoes at a Bragg wavelength of 16 cm
Authors: La Hoz C. , Havnes O. , Næsheim L. I. , Hysell D. L.
Published: February 2006

We present measurements of Polar Mesospheric Summer Echoes, PMSE, at the very short Bragg wavelength of 16 cm which occur infrequently. The measurements were carried out with the EISCAT 930 MHz UHF radar. Part of the data were taken under the influence of HF heating. A comprehensive comparison of the measurements with the theory of turbulence including enhancement of the Schmidt number is carried out, but other theories are also considered. Estimates of the energy dissipation rates inferred from the signal spectral widths are used to calculate Batchelor scale lengths as a function of the Schmidt number. Hill's multipolar diffusion model is used to calculate the diffusion rates (which depend on the charge number of ice particles of nanometer size radius) leading to estimates of the Schmidt numbers. It is argued that the use of the slow diffusion coefficient in the calculations should give conservative estimates, i.e., lower bounds, of the necessary ice charge numbers to explain the measurements, the condition for enhanced scattering being that the Bragg scale of the radar should be greater than the Batchelor scale. Based on information from other experiments published in the literature, e.g., the charge number of mesospheric ice particles, and theoretical considerations, the main conclusion of this investigation is that none of the most prominent theories can explain satisfactorily the measurements unless charge numbers in excess of 10 electrons for the measured wide spectra and at least in excess of 100s of electrons for the measured narrow spectra are assumed. The HF heating effect on the mesosphere appears to have a similar influence on PMSE at a Bragg wavelength of 16 cm as it has at greater wavelengths, namely a weakening of PMSE during the heater‐on periods and a recovery during the heater off‐periods. This behaviour is as expected given the rapidity and large amount of electron heating that the HF wave produces with the consequent rapid and large enhancement of the electron diffusion rate during heater‐on periods regardless of the electron diffusion model or reference to any particular model of PMSE.
Fine‐scale structure of the extratropical tropopause region
Authors: Birner T.
Published: February 2006

A vertically high resolved climatology of the thermal and wind structure of the extratropical tropopause region is presented. The climatology is based on data from 80 U.S. radiosonde stations covering the period 1998–2002. Time averages for each radiosonde station are computed using the tropopause as a common reference level for all vertical profiles within the mean. A strong inversion at the tropopause in the mean vertical temperature gradient is uncovered; that is, temperature strongly increases with altitude within the lowermost stratosphere. This tropopause inversion layer exists on average throughout the investigated extratropics (about 30°N to 70°N). Accordingly, the static stability parameter shows considerably enhanced values within the lowermost extratropical stratosphere compared to typical extratropical stratospheric values further aloft. Conventional averages are not able to capture the tropopause inversion layer. Mean profiles of the horizontal wind show behavior qualitatively corresponding to thermal wind balance. Winter and summer exhibit distinctly different climate states in the extratropical tropopause region. An approximated potential vorticity is considered and found to be close to well mixed within the troposphere as well as within the tropopause inversion layer. This suggests the view of the tropopause inversion layer as representing a dynamically active atmospheric layer. Some potential implications are discussed.
European hydrocarbon intercomparison experiment AMOHA part 4: Canister sampling of ambient air
Authors: Plass‐Dülmer C. , Schmidbauer N. , Slemr J. , Slemr F. , D'Souza H.
Published: February 2006

The AMOHA (Accurate Measurements of Hydrocarbons in the Atmosphere) project was proposed to evaluate and improve current gas chromatographic methods used across Europe to determine concentrations of nonmethane hydrocarbons (NMHCs) in ambient air. This paper presents results of the final task of AMOHA (4th intercomparison) whose major objective was to test the overall analysis performance of the participating laboratories. The 4th intercomparison, which included both the sampling procedure and storage in stainless steel canisters, was carried out in two phases. In the first phase, canisters used by nine participating laboratories and reference canisters by the Norwegian Institute for Air Research (NILU) were filled at NILU with a compressed air test sample containing hydrocarbons with mixing ratios between 13 pptv (parts per trillion by volume) and 3400 pptv. The canister samples were analyzed immediately by NILU, and then the participants analyzed their own three canisters and one canister from NILU. All analyses considered 28 C2–C8 compounds. The results were based on a gravimetric standard mixture by the National Physical Laboratory (NPL). The hydrocarbon composition in the participants' canisters was generally found to be stable for storage periods of several weeks, except for three canister sets showing substantial deviations from the corresponding reference concentrations by NILU. Discrepancies between the participants' analyses and the reference concentrations were mostly due to analytical uncertainties of the respective laboratory. In the second phase, 11 participating laboratories collected ambient air samples using their own sampling equipment and canisters at the Meteorological Observatory Hohenpeissenberg. The sampling was synchronized with an on‐line NMHC instrument. The air samples were cleaner than during the first phase, with more than 60% of the analyzed compounds below 100 pptv. Generally, the medians of canister analyses were in good agreement with concurrent on‐line measurements, although the concentrations of alkenes and aromatic compounds found by several participants were higher than those measured on‐line. The performance of the participating laboratories differed considerably, and six out of eleven participating laboratories achieved good agreement to the reference values for most compounds.
Use of electron cyclotron resonance x-ray source for nondestructive testing application
Authors: Baskaran R. , Selvakumaran T. S.
Published: February 2006

Electron cyclotron resonance (ECR) technique is being used for generating x rays in the low-energy region (<150keV). Recently, the source is used for the calibration of thermoluminescent dosimetry (TLD) badges. In order to qualify the ECR x-ray source for imaging application, the source should give uniform flux over the area under study. Lead collimation arrangement is made to get uniform flux. The flux profile is measured using a teletector at different distance from the port and uniform field region of 10×10cm2 has been marked at 20cm from the x-ray exit port. A digital-to-analog converter (DAC) circuit pack is used for examining the source performance. The required dose for nondestructive testing examination has been estimated using a hospital x-ray machine and it is found to be 0.05mSv. Our source experimental parameters are tuned and the DAC circuit pack was exposed for nearly 7min to get the required dose value. The ECR x-ray source operating parameters are argon pressure: 10−5Torr, microwave power: 350W, and coil current: 0A. The effective energy of the x-ray spectrum is nearly 40keV. The x-ray images obtained from ECR x-ray source and hospital medical radiography machine are compared. It is found that the image obtained from ECR x-ray source is suitable for NDT application.
Analysis of x-ray spectrum obtained in electron cyclotron resonance x-ray source
Authors: Baskaran R. , Selvakumaran T. S. , Sunil Sunny C.
Published: February 2006

The analysis of the x-ray spectrum obtained in electron cyclotron resonance (ECR) x-ray source is carried out. Assuming single-particle motion, the electron acceleration and its final energy are calculated for TE111 cylindrical cavity field and uniform external dc magnetic field. In the calculation, initial coordinates of 40 000 electrons were uniformly selected over the central plane of the cavity using random number generator. The final energy of each electron when it hits the wall is stored and the electron energy distribution is obtained. Using the general purpose Monte Carlo N-particle transport code version 4A, the geometry of the ECR x-ray source is modeled. The x-ray energy spectrum is calculated for the geometry model and the numerically calculated electron energy distribution. The calculated x-ray spectrum is compared with the experimentally measured x-ray spectrum.
Extraction of single-ion beams from helicon ion source in high plasma density operation mode: Experiment and simulation
Authors: Mordyk S. , Miroshnichenko V. , Nahornyy A. , Nahornyy D. , Shulha D. , Storizhko V. , Voznyy V.
Published: February 2006

Tests of a high plasma density high-brightness helicon ion source for nuclear microscopy applications are underway. Experiments were performed with hydrogen, helium, and argon. Different extraction structures of the helicon rf ion source were investigated with an imposed external magnetic field. We present measurements of the extracted current as a function of the extraction voltage and rf power. The source has been diagnosed by a microwave interferometer. Plasma densities in the vicinity of the emission hole of up to 7.2×1012cm−3 (for argon), 1.6×1012cm−3 (for helium), and 6.0×1011cm−3 (for hydrogen) were obtained for working gas pressure of <5mTorr and rf power <350W (frf=27.12MHz). The ion current density was 80mA∕cm2 with high percentage of protons in the beam (∼80%). In the extraction structure, the cathode channel has a 3mm length and a 0.6mm diameter. The phase set degradation due to aberrations in the extraction structure of the helicon rf ion source was simulated for a fourth-order approximation in series expansion of the electrostatic potential and third-order approximation in series of the magnetic fields, by the matrizant method. The calculations were performed involving experimental data on ion energy spread, average ion energy, and plasma density of the helicon rf ion source with permanent magnets.
Electron cyclotron resonance ion source DECRIS-4 for the U400 cyclotron
Authors: Leporis M. , Bekhterev V. , Bogomolov S. , Efremov A. , Gulbekian G. , Kostyukhov Yu. , Lebedev A. , Loginov V. , Yazvitsky N.
Published: February 2006

The electron cyclotron resonance ion source DECRIS-4 has been designed and constructed at the FLNR to be used as a second injector of heavy multiply charged ions for the U-400 cyclotron. After the modification of the injection side this source can be also used as a “charge breeder” (the “1+→n+” method) for the second phase of the Dubna radioactive ion beams project. The main feature of the ion source design is the creation of the extended resonance zone in a comparatively compact electron cyclotron resonance ion source. For this purpose the axial magnetic field is formed with a flat minimum. In this case the superposition of the axial magnetic field and the radial field of the permanent-magnet hexapole, made from NdFeB, allows one to create a larger resonance volume. For the plasma heating a microwave frequency of 14 GHz is used. In this paper we will present the basic design features of the ion source, including the results of the magnetic-field measurements. Some preliminary results of ion source tests are also reported.
Status of charge breeding with electron cyclotron resonance ion sources (invited)
Authors: Lamy T. , Geller R. , Sortais P. , Thuillier T.
Published: February 2006

Due to the production methods of exotic nuclei, an efficient acceleration of radioactive ion beams needs charge breeding of weakly charged ions. The upgrade of existing isotope separator on-line facilities (TRIUMF-isotope separation and acceleration, CERN-isotope separation on-line detector, etc.) or the development of projects for the acceleration of radioactive ion beams (GANIL-SPIRAL2, MAFF, EURISOL, etc.) requires charge breeders with high efficiency, fast charge breeding time, low background levels, and high intensity acceptance either in continuous or in pulsed mode. The optimization of these parameters is a challenge for the electron cyclotron resonance (ECR) community and is useful to get a better understanding of plasma physics in ECR ion sources (ECRISs). The ECR charge breeding technique has been developed for more than ten years at LPSC (former ISN) Grenoble, typical 1+→n+ efficiencies are in the 3%–10% range depending on the nature of the incoming beam (metallic, alkaline, and gaseous) and remain constant for high intensity injection. Different laboratories have developed programs to study ECR charge breeding, and the progress of these studies will be presented. ECRISs have main advantages to be efficient charge breeders and a few limitations which will be discussed.
Negative halogen ions for fusion applications (invited)
Authors: Grisham L. R. , Kwan J. W. , Hahto S. K. , Hahto S. T. , Leung K. N. , Westenskow G.
Published: February 2006

Over the past quarter century, advances in hydrogen negative-ion sources have extended the usable range of hydrogen-isotope neutral beams to energies suitable for large magnetic confinement fusion devices. Recently negative halogen ions have been proposed as an alternative to positive ions for heavy-ion fusion drivers in inertial confinement fusion, because electron accumulation would be prevented in negative-ion beams, and if desired, the beams could be photodetached to neutrals. This article reports an experiment comparing the current density and beam emittance of Cl+ and Cl− extracted from substantially ion-ion plasmas with that of Ar+ extracted from an ordinary electron-ion plasma, all using the same source, extractor, and emittance scanner. At similar discharge conditions, the Cl− current was typically 85%–90% of the positive chlorine current, with an e−∕Cl− ratio as low as 7 without grid magnets. The Cl− current was as much as 76% of the Ar+ current from a discharge with the same rf drive. The minimum normalized beam emittance and inferred ion temperatures of Cl+, Cl−, and Ar+ were similar, so the current density and optical quality of Cl− appear as suitable for heavy-ion fusion applications as a positive noble gas ion of similar mass. Since F, I, and Br should all behave similarly in an ion source, they should also be suitable as driver beams.
Multipurpose superconducting electron cyclotron resonance ion source, the European roadmap to third-generation electron cyclotron resonance ion sources
Authors: Ciavola G. , Gammino S. , Celona L. , Torrisi L. , Passarello S. , Andó L. , Cavenago M. , Galatà A. , Spaedtke P. , Tinschert K. , Lang R. , Iannucci R. , Leroy R. , Barue C. , Hitz D. , Seyfert P. , Koivisto H. , Suominen P. , Tarvainen O. , Beijers H. , Brandenburg S. , Vanrooyen D. , Hill C. , Kuchler D. , Homeyer H. , Röhrich J. , Schachter L. , Dobrescu S.
Published: February 2006

The major infrastructures of nuclear physics in Europe adopted the technology of electron cyclotron resonance (ECR) ion sources for the production of heavy-ion beams. Most of them use 14GHz electron cyclotron resonance ion sources (ECRISs), except at INFN-LNS, where an 18GHz superconducting ECRIS is in operation. In the past five years it was demonstrated, in the frame of the EU-FP5 RTD project called “Innovative ECRIS,” that further enhancement of the performances requires a higher frequency (28GHz and above) and a higher magnetic field (above 2.2T) for the hexapolar field. Within the EU-FP6 a joint research activity named ISIBHI has been established to build by 2008 two different ion sources, the A-PHOENIX source at LPSC Grenoble, reported in another contribution, and the multipurpose superconducting ECRIS (MS-ECRIS), based on fully superconducting magnets, able to operate in High B mode at a frequency of 28GHz or higher. Such a development represents a significant step compared to existing devices, and an increase of typically a factor of 10 for the intensity is expected (e.g., 1emA for medium charge states of heavy ions, or hundreds of eμA of fully stripped light ions, or even 1eμA of charge states above 50+ for the heaviest species). The challenging issue is the very high level of magnetic field, never achieved by a minimum B trap magnet system; the maximum magnetic field of MS-ECRIS will be higher than 4 or 5T for the axial field and close to 2.7T for the hexapolar field. The detailed description of the MS-ECRIS project and of its major constraints will be given along with the general issues of the developments under way.
Electron-phonon interactions in the monocations of polyacetylenes
Authors: Kato Takashi , Yamabe Tokio
Published: February 2006

Electron-phonon interactions in the monocations of trans-polyacetylenes such as C2H4 (2tpa), C4H6 (2tpa), C6H8 (6tpa), and C8H10 (8tpa) are studied. The C–C stretching Ag modes around 1700cm−1 afford the largest electron-phonon coupling constants in the monocations of polyacetylenes. However, the C–C bending Ag modes around 1200cm−1 afford much smaller electron-phonon coupling constants than the C–C stretching Ag modes around 1700cm−1 in the monocations of polyacetylenes. The total electron-phonon coupling constants for the monocations (lHOMO) are estimated to be 0.357, 0.285, 0.281, and 0.279 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. The lHOMO values for polyacetylenes with C2h geometry hardly change with an increase in molecular size while those for polyacenes with D2h geometry significantly decrease with an increase in molecular size. The lHOMO values for polyacetylenes are larger than those for polyacenes. The calculated results are rationalized in terms of the phase patterns of the molecular orbitals in detail. The electron transfer in the positively charged polyacetylenes is also discussed. Intramolecular electron mobility (σintra,monocation) in the positively charged polyacetylenes is estimated to be smaller than those for the positively charged polyacenes. The reorganization energies for the positively charged polyacetylenes are estimated to be larger than those for the positively charged polyacenes. Thus, the larger overlap integrals between two neighboring molecules are needed for the positively charged polyacetylenes to become good conductor than those for positively charged polyacenes. On the other hand, the conditions under which the electron-electron interactions are attractive are more easily realized in the monocations of polyacetylenes than in the monocations of polyacenes. The quality as conducting materials would not significantly depend on the molecular size in the positively charged polyacetylenes, compared with that in the positively charged polyacenes. Multimode problem is also treated in order to investigate how consideration of multimode problem is closely related to the characteristics of the electron-phonon interactions.
Design and performance of an atmospheric pressure sampling interface for ion-trap/time-of-flight mass spectrometry
Authors: Setz Patrick D. , Schmitz Thomas A. , Zenobi Renato
Published: February 2006

An ion-trap/time-of-flight mass spectrometer in combination with an atmospheric pressure sampling interface was developed in order to simultaneously profit from the ease of sample handling at ambient pressure, from the storage and accumulation capabilities of an ion trap, and from the acquisition speed and sensitivity of a time-of-flight mass spectrometer. The sampling interface is an intermediate-pressure vacuum manifold that serves to enrich sampled analytes by jet separation with respect to the carrier gas (air) and simultaneously maintain vacuum conditions inside the ion-trap/time-of-flight instrument. Neutral analyte molecules are sampled and later ionized either by electron impact or chemical ionization. Ion accumulation is performed with a rf-only quadrupole ion trap with ground potential on the end caps during storage. For mass analysis, the trap’s electrodes serve as a pulsed ion source for the attached linear time-of-flight mass spectrometer. In addition, laser desorbed molecules can also be sampled with this kind of instrument. Successful operation is shown by analyzing volatile substances (aniline, bromobenzene, styrene, and perfluorotributylamine), as well as laser-desorbed organic solids. Figures of merit include a sensitivity of 10 ppm, resolving power of 300 and demonstration of a mass spectrum of laser-desorbed anthracene with a signal-to-noise ratio of 270.
Apparatus for in situ prediction of the thermal conductivity of fiberglass batts using acoustic propagation constant
Authors: Tinianov Brandon D. , Nakagawa Masami , Muñoz David R.
Published: February 2006

This article describes a novel technique for the measurement of the thermal conductivity of low-density (12–18kg∕m3) fiberglass insulation and other related fibrous insulation materials using a noninvasive acoustic apparatus. The experimental method is an extension of earlier acoustic methods based upon the evaluation of the propagation constant from the acoustic pressure transfer function across the test material. To accomplish this, an analytical model is employed that describes the behavior of sound waves at the outlet of a baffled waveguide. The model accounts for the behavior of the mixed impedance interface introduced by the test material. Current results show that the technique is stable for a broad range of absorber thicknesses and densities. Experimental results obtained in the laboratory show excellent correlation between the thermal conductivity and both the real and imaginary components of the propagation constant. Correlation of calculated propagation constant magnitude versus measured thermal conductivity gave an R2 of 0.94 for the bulk density range (12-18kg∕m3) typical for manufactured fiberglass batt materials. As an improvement to earlier acoustic techniques, measurement is now possible in noisy manufacturing environments with a moving test material. Given the promise of such highly correlated measurements in a robust method, the acoustic technique is well suited to continuously measure the thermal conductivity of the material during its production, replacing current expensive off-line methods. Test cycle time is reduced from hours to seconds.
Integrability from an Abelian subgroup of the diffeomorphisms group
Authors: Adam C. , Sánchez-Guillén J. , Wereszczyński A.
Published: February 2006

It has been known for some time that for a large class of nonlinear field theories in Minkowski space with two-dimensional target space the complex eikonal equation defines integrable submodels with infinitely many conservation laws. These conservation laws are related to the area-preserving diffeomorphisms on target space. Here we demonstrate that for all these theories there exists, in fact, a weaker integrability condition which again defines submodels with infinitely many conservation laws. These conservation laws will be related to an Abelian subgroup of the group of area-preserving diffeomorphisms. As this weaker integrability condition is much easier to fulfill, it should be useful in the study of those nonlinear field theories.
Fast singular value decomposition combined maximum entropy method for plasma tomography
Authors: Kim Junghee , Choe W.
Published: February 2006

The maximum entropy method (MEM) is a widely used reconstruction algorithm in plasma physics. Drawbacks of the conventional MEM are its heavy time-consuming process and possible generation of noisy reconstruction results. In this article, a modified maximum entropy algorithm is described which speeds up the calculation and shows better noise handling capability. Similar to the rapid minimum Fisher information method, the modified maximum entropy algorithm uses simple matrix operations instead of treating a fully nonlinear problem. The preprocess for rapid tomographic calculation is based on the vector operations and the singular value decomposition (SVD). The initial guess of the sought-for emissivity is calculated by SVD and this helped reconstruction about ten times faster than the conventional MEM. Therefore, the developed fast MEM can be used for intershot tomographic analyses of fusion plasmas.
Measurement of the sixth overtone band of nitric oxide, and its dipole moment function, using cavity-enhanced frequency modulation spectroscopy
Authors: Bood Joakim , McIlroy Andrew , Osborn David L.
Published: February 2006

We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy) to perform high-resolution spectroscopy of the sixth overtone band of nitric oxide near 797nm. By using novel high-bandwidth balanced detectors, baseline variations caused by residual amplitude modulation were significantly reduced. The ultrahigh sensitivity (2×10−10cm−1 minimum detectable absorption at 1Hz detection bandwidth) of our spectrometer allowed accurate measurements of 15 individual line intensities of P- and R-branch transitions in the Π1∕22-Π1∕22 subband. A vibrational transition moment of 3.09(6)μD±13% and Herman-Wallis coefficients of a=−0.0078(26) and b=0.00125(45) were found by fitting the line intensities. Based on our measured transition moment, and those of other transitions from the literature, a new parametrization for the electric dipole moment function (EDMF) of nitric oxide, valid for 0.91⩽r⩽1.74Å, has been extracted. The residuals of this fit demonstrate that the derived EDMF is the most accurate representation to date of the dipole moment function. The new EDMF will be valuable for accurate intensity prediction of transitions that cannot be easily measured experimentally.
Electrical transport between epitaxial manganites and carbon nanotubes
Authors: Hueso L. E. , Burnell G. , Prieto J. L. , Granja L. , Bell C. , Kang D. J. , Chhowalla M. , Cha S. N. , Jang J. E. , Amaratunga G. A. J. , Mathur N. D.
Published: February 2006

The possibility of performing spintronics at the molecular level may be realized in devices that combine fully spin polarized oxides, such as manganites with carbon nanotubes. However, it is not clear whether electrical transport between such different material systems is viable. Here, we show that the room-temperature conductance of manganite-nanotube-manganite devices is only one-half of the value recorded in similar palladium-nanotube-palladium devices. Interestingly, the former shows a gap in the conductivity below the relatively high temperature of 200 K. Our results suggest the possibility of new spintronics heterostructures that exploit fully spin polarized sources and drains.
Delocalized electron resonance at the alkanethiolate self-assembled monolayer∕Au(111) interface
Authors: Muntwiler M. , Lindstrom C. D. , Zhu X.-Y.
Published: February 2006

We probe the electronic structure of alkanethiolate self-assembled monolayers (SAMs) on Au(111) using two-photon photoemission spectroscopy. We observe a dispersive unoccupied resonance close to the vacuum level with a lifetime shorter than 30 fs. The short lifetime and the insensitivity of the energy level and dispersion to molecular length (and thus layer thickness) suggest that the probability density of the electron wave function is concentrated inside the molecular layer close to the SAM∕Au interface. Such an interfacial resonance results from the image like potential at the SAM∕Au interface.
Ab initio nonadiabatic quantum dynamics of cyclohexadiene/hexatriene ultrafast photoisomerization
Authors: Tamura Hiroyuki , Nanbu Shinkoh , Ishida Toshimasa , Nakamura Hiroki
Published: February 2006

Reaction mechanisms of the ultrafast photoisomerization between cyclohexadiene and hexatriene have been elucidated by the quantum dynamics on the ab initio potential energy surfaces calculated by multireference configuration interaction method. In addition to the quantum wave-packet dynamics along the two-dimensional reaction coordinates, the semiclassical analyses have also been carried out to correctly estimate the nonadiabatic transition probabilities around conical intersections in the full-dimensional space. The reaction time durations of radiationless decays in the wave-packet dynamics are found to be generally consistent with the femtosecond time-resolution experimental observations. The nonadiabatic transition probabilities among the ground (S0), first (S1), and second (S2) excited states have been estimated by using the semiclassical Zhu-Nakamura formula considering the full-dimensional wave-packet density distributions in the vicinity of conical intersections under the harmonic normal mode approximation. The cyclohexadiene (CHD) ring-opening process proceeds descending on the S1(1B1) potential after the photoexcitation. The major part of the wave-packet decays from S1(1B1) to S1(2A1) by the first seam line crossing along the C2-symmetry-breaking directions. The experimentally observed ultrafast S1-S0 decay can be explained by the dynamics through the S1-S0 conical intersection along the direction toward the five-membered ring. The CHD: hexatriene (HT) branching ratio is estimated to be approximately 5:5, which is in accordance with the experiment in solution. This branching ratio is found to be mainly governed by the location of the five-membered ring S1-S0 conical intersection along the ground state potential ridge between CHD and HT.
Solute size effects on the solvation structure and diffusion of ions in liquid methanol under normal and cold conditions
Authors: Chowdhuri Snehasis , Chandra Amalendu
Published: February 2006

We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F−, Cl−, Br−, and I−) ions in liquid methanol at two different temperatures to investigate the effects of ion size on the hydration structure and diffusion of ions in methanol under normal and cold conditions. Simulations are also carried out for some of the larger cations such as I+, (CH3)4N+, and (C2H5)4N+ and also neutral alkali metal atoms in methanol at both temperatures. With the increase of ion size, the diffusion coefficients of both positive and negative ions are found to show anomalous behavior. For cations, it is found that the maximum of the diffusion coefficient versus ion size curve occurs at the rather large cation of (CH3)4N+ unlike in water where the maximum occurs at the relatively smaller ion of Rb+. For halide ions, the anomalous behavior, i.e., the increase of diffusion with ion size, continues up to iodide ion and no maximum is observed. These results are in good agreement with experimental observations. The diffusion coefficients of neutral atoms are found to be greater in methanol than that in water and they decrease monotonically with solute size, whereas the diffusion coefficients of the corresponding ions are found to be smaller in methanol. Accordingly, an ion experiences a smaller Stokes friction and a higher dielectric friction in methanol than in water. These contrasting effects are believed to be responsible for the shift of the maximum of ion diffusion toward a larger ion size when compared with similar anomalous size dependence in liquid water.
Photoelastic modulated imaging ellipsometry by stroboscopic illumination technique
Authors: Han Chien-Yuan , Chao Yu-Faye
Published: February 2006

A novel stroboscopic illumination technique is applied in a photoelastic modulated (PEM) ellipsometry to conquer the slow imaging processing of charge-coupled device camera system and form a fast imaging ellipsometry. The synchronized ultrastable short pulse is used to freeze the intensity variation of the PEM modulated signal. The temporal phase is calibrated with respect to the time reference of PEM. The laser diode is modulated by a programable pulse generator for triggering four short pulses at their specific temporal phase angle. The two-dimensional (2D) ellipsometric parameters can be deduced from those recorded four images. Therefore, the 2D thickness profile of a patterned sample can be measured; a static patterned SiO2 thin film on silicon substrate and the drainage behavior of matching oil on silicon wafer were studied by this imaging ellipsometry.
Laser photoluminescence spectrometer based on charge-coupled device detection for silicon-based photonics
Authors: Zalloum O. H. Y. , Flynn M. , Roschuk T. , Wojcik J. , Irving E. , Mascher P.
Published: February 2006

We describe and characterize a multichannel modular room temperature photoluminescence spectroscopy system. This low cost instrument offers minimization of size and complexity as well as good flexibility and acceptable spectral resolution. The system employs an efficient flexible front end optics and a sensitive spectrometer with a charge-coupled device array detector. The spectrometer has no moving parts and is more robust than a scanning system. The scientific motivation was to enable the photoluminescence study of various silicon photonics structures. Typical applications are presented for SiOx (x<2) films. It is demonstrated that high-quality steady state photoluminescence data with excellent signal to noise enhancement capability can be delivered besides the ability to perform simultaneous multiwavelength measurements in one shot. This instrument is shown to be useful for evaluating semiconductor wafers, including those intended for light emitting structures from silicon-based photonic crystals. The design, construction, calibration, and the unique features of this system are presented, and performance tests of a prototype are discussed.
Control of spontaneous emission in the presence of collisions
Authors: Frishman Einat , Shapiro Moshe
Published: February 2006

We explore the coherent suppression of spontaneous emission processes in the presence of decoherence due to collisions with an external bath.
Defect-mode mirrorless lasing in dye-doped organic/inorganic hybrid one-dimensional photonic crystal
Authors: Yoon Jongseung , Lee Wonmok , Caruge Jean-Michel , Bawendi Moungi , Thomas Edwin L. , Kooi Steven , Prasad Paras N.
Published: February 2006

We have developed a dye-doped organic/inorganic hybrid one-dimensional (1D) photonic crystal containing a dye-doped defect layer for defect-mode photonic band gap lasing. The multilayer laser structure consists of alternating layers of titania nanoparticles and polymethylmethacrylate (PMMA) with an active emission layer of organic dyes in PMMA. Low threshold lasing has been demonstrated at a single defect-mode wavelength of the 1D photonic band gap structure resulting from the inhibited density of states of photons within the stop band and the enhanced rates of spontaneous emission at the localized resonant defect mode.
The structure of the Si9H12 cluster: A coupled cluster and multi-reference perturbation theory study
Authors: Olson Ryan M. , Gordon Mark S.
Published: February 2006

Full geometry optimizations using both singles and doubles coupled cluster theory with perturbative triple excitations, CCSD(T), and second order multi-reference perturbation theory, MRMP2, have been employed to predict the structure of Si9H12, a cluster commonly used in calculations to represent the Si(100) surface. Both levels of theory predict the structure of this cluster to be symmetric (not buckled), and no evidence for a buckled (asymmetric) structure is found at either level of theory.
Monitoring cell-cycle-related viscoelasticity by a quartz crystal microbalance
Authors: Alessandrini A. , Croce M. A. , Tiozzo R. , Facci P.
Published: February 2006

We have monitored viscoelasticity variation of a cell population during the cell cycle by a Quartz Crystal Microbalance (QCM). Balb 3T3 fibroblasts were synchronized in the G0/G1 phase and seeded in a QCM chamber placed in a cell incubator. After cell sedimentation, the frequency signal was characterized by an amplitude modulation attributed to the viscoelasticity variation of the cells proliferating in phase. A control experiment with nonsynchronized cells showed a similar signal trend, but without significant modulation. Interestingly, the system resulted also to perform as a device sensitive to the effect of drugs affecting the cell cycle, such as colchicine.
Structure, optical, and magnetic properties of sputtered manganese and nitrogen-codoped ZnO films
Authors: Gu Zheng-Bin , Lu Ming-Hui , Wang Jing , Wu Di , Zhang Shan-Tao , Meng Xiang-Kang , Zhu Yong-Yuan , Zhu Shi-Ning , Chen Yan-Feng , Pan Xiao-Qing
Published: February 2006

To realize the hole-mediated ferromagnetism, manganese and nitrogen-codoped ZnO (Zn1−xMnxO:N) films were prepared on sapphire (0001) by reactive radio-frequency (rf) magnetron sputtering from Zn0.97Mn0.03O ceramic targets using N2 gas. X-ray photon spectra reveal that the doped Mn ions are mainly in divalent states and the coexistence of O–Zn and N–Zn bonds in the films. According to the absorption spectra, the band gap of Zn0.97Mn0.03O:N films is about 3.15eV, which is slightly lower than that of ZnO films (3.20eV). Compared with Zn0.97Mn0.03O films, ferromagnetic behavior of Zn0.97Mn0.03O:N films were significantly changed with a coercivity of about 70Oe, a saturation magnetization of 0.92μB∕Mn2+ and a remanance over 0.15μB∕Mn2+ at 300K, while at 10K, they increased to be about 110Oe, 1.05μB∕Mn2+ and 0.23μB∕Mn2+, respectively. However, rapid thermal annealing treatment in pure oxygen results in a significant decrease on the magnetic properties of the films.
High-efficiency InGaN-based light-emitting diodes with nanoporous GaN:Mg structure
Authors: Lin Chia-Feng , Zheng Jing-Hui , Yang Zhong-Jie , Dai Jing-Jie , Lin Der-Yuh , Chang Chung-Ying , Lai Zhao-Xu , Hong C. S.
Published: February 2006

In this research nanoporous structures on p-type GaN:Mg and n-type GaN:Si surfaces were fabricated through a photoelectrochemical (PEC) oxidation and an oxide-removing process. The photoluminescence (PL) intensities of GaN and InGaN∕GaN multi-quantum-well (MQW) structures were enhanced by forming this nanoporous structure to increase light extraction efficiency. The PL emission peaks of an MQW active layer have a blueshift phenomenon from 465.5nm (standard) to 456.0nm (nanoporous) measured at 300K which was caused by partially releasing the compressive strain from the top GaN:Mg layers. The internal quantum efficiency could be increased by a partial strain release that induces a lower piezoelectric field in the active layer. The thermal activation energy of a nanoporous structure (85meV) is higher than the standard one (33meV) from a temperature dependent PL measurement. The internal quantum efficiency and light extraction efficiency of an InGaN∕GaN MQW active layer are significantly enhanced by this nanoporous GaN:Mg surface, and this PEC treated nanoporous structure is suitable for high-power lighting applications.
Enhancing light outcoupling of organic light-emitting devices by locating emitters around the second antinode of the reflective metal electrode
Authors: Lin Chun-Liang , Cho Ting-Yi , Chang Chih-Hao , Wu Chung-Chih
Published: February 2006

Due to generally low conductivity and low carrier mobilities of organic materials, organic light-emitting devices (OLEDs) are typically optimized for light outcoupling by locating emitters around the first antinode of the metal electrode. In this letter, by utilizing device structures containing conductive doping, we investigate theoretically and experimentally the influences of the location of emitters relative to the metal electrode on OLED emission, and show that substantial enhancement in light outcoupling (1.2 times) or forward luminance (1.6 times) could be obtained by placing emitters around the second antinode instead of the first antinode. Depending on the detailed condition, the second-antinode device may also give more directed emission as often observed in strong-microcavity devices yet without suffering a color shift with viewing angles.
Vacancy-engineering implants for high boron activation in silicon on insulator
Authors: Smith A. J. , Cowern N. E. B. , Gwilliam R. , Sealy B. J. , Colombeau B. , Collart E. J. H. , Gennaro S. , Giubertoni D. , Bersani M. , Barozzi M.
Published: February 2006

The formation of boron interstitial clusters is a key limiting factor for the fabrication of highly conductive ultrashallow doped regions in future silicon-based device technology. Optimized vacancy engineering strongly reduces boron clustering, enabling low-temperature electrical activation to levels rivalling what can be achieved with conventional preamorphization and solid-phase epitaxial regrowth. An optimized 160keV silicon implant in a 55∕145nm silicon-on-insulator structure enables stable activation of a 500eV boron implant to a concentration ∼5×1020cm−3.
GaSb
-based 2.X μm quantum-well diode lasers with low beam divergence and high output power
Authors: Rattunde M. , Schmitz J. , Kaufel G. , Kelemen M. , Weber J. , Wagner J.
Published: February 2006

We report on GaSb-based 2.Xμm diode lasers with an improved waveguide design, leading to a reduced beam divergence in the fast axis of 44° full width at half maximum (FWHM), compared to 67° FWHM of a conventional broadened waveguide design. 2.3μm ridge-waveguide lasers with the improved epitaxial design showed, besides the narrow beam profile in the fast axis, an excellent slow axis beam quality [M2<1.1 up to 70mW, continuous wave (cw)]. 2.0μm broad-area lasers with the improved waveguide too, exhibit a maximum cw-output power of 1.96W.
Quantifying stoichiometry of mixed-cation-anion III-V semiconductor interfaces at atomic resolution
Authors: Mahalingam K. , Eyink K. G. , Brown G. J. , Dorsey D. L. , Kisielowski C. F. , Thust A.
Published: February 2006

Employing the focal-series reconstruction technique in high-resolution transmission electron microscopy, we obtained true atomic resolution images of interfacial disorder within cation and anion sublattices across interfaces in an InGaSb∕InAs heterostructure. This enabled independent quantitative mapping of changes in the In–Ga and As–Sb contents across interfacial regions ∼0.6nm in width. A comparison of the cation and anion sublattice images revealed that intermixing at the InGaSb-on-InAs interface is confined to the In–Ga sublattice. Also, atomic scale roughness within the As–Sb sublattice of the InAs-on-InGaSb interface was discerned. This approach is general, permitting atomic-scale compositional analysis of heterointerfaces with two species per sublattice.
Efficient optical pulse compression using chalcogenide single-mode fibers
Authors: Fu Libin , Fuerbach Alexander , Littler Ian C. M. , Eggleton Benjamin J.
Published: February 2006

We demonstrate compression of low-power 6ps pulses to 420fs around 1550nm in a compact all-fiber scheme utilizing the strong nonlinearity and positive-normal dispersion of a single-mode As2Se3 fiber, in combination with a tailored chirped fiber Bragg grating. The value and sign of the dispersion, coupled with the high nonlinearity of the chalcogenide, produces a smoothly broadened spectrum with a monotonic chirp via self phase modulation. Measurements of the phase and time evolution of the laser pulses using frequency resolved optical gating are performed showing excellent agreement with theory. We also discuss the limiting influence of two-photon absorption.
Equation of state for fluid helium-3 based on Debye phonon model
Authors: Huang Y. H. , Chen G. B. , Arp V. D.
Published: February 2006

An equation of state for He3 using the Helmholtz potential function has been developed. It is based on the Debye phonon model which goes smoothly to zero in the limit of zero temperature, and reduces to the ideal gas in the limit of zero density and/or very high temperature. The lower temperature limit of the equation 10mK is safely above the superfluid transition at 2.6mK. The upper limit of 60K is approximately the upper limit of available He3 properties measurements. The certain pressure range of validity of the equation is from about 0 to the melting pressure or 15MPa. State properties are determined from the Helmholtz energy by standard thermodynamics.
Effect of charge on the movement of dislocations in SiC
Authors: Eberlein T. A. G. , Jones R. , Blumenau A. T. , Öberg S. , Briddon P. R.
Published: February 2006

SiC bipolar devices show a degradation under forward-biased operation which has been linked with a current induced motion of one of the two glide dislocations having either Si or C core atoms. We have carried out calculations of the core structures and dynamics of partial dislocations in 3C and 2H–SiC. In this work we present results on the effect of charge on the dislocation kinks. The calculations show that silicon kinks have a deep filled band above the valence band and the trapping of holes into this band permits motion at room temperature.
Silicon-based highly-efficient fiber-to-waveguide coupler for high index contrast systems
Authors: Nguyen Victor , Montalbo Trisha , Manolatou Christina , Agarwal Anu , Hong Ching-yin , Yasaitis John , Kimerling L. C. , Michel Jurgen
Published: February 2006

A coupler to efficiently transfer broadband light from a single-mode optical fiber to a single-mode high-index contrast waveguide has been fabricated on a silicon substrate. We utilized a novel coupling scheme, with a vertically asymmetric design consisting of a stepwise parabolic graded index profile combined with a horizontal taper, to simultaneously confine light in both directions. Coupling efficiency has been measured as a function of the device dimensions. The optimal coupling efficiency is achieved for structures whose length equals the focal distance of the graded index and whose input width is close to the mode field diameter of the fiber. The fabricated structure is compact, robust and highly efficient, with an insertion loss of 2.2dB at 1550nm. The coupler exhibits less than 1dB variation in coupling efficiency in the measured spectral range from 1520nmto1620nm. The lowest insertion loss of 1.9dB is measured at 1540nm. The coupler design offers highly efficient coupling for single mode waveguides of core indices up to 2.2.