bluuebunny/crossref_metadata_2025 huggingface dataset:
Latitudinal and vertical distribution of bromine monoxide in the lower stratosphere from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography limb scattering measurements
Authors: Sioris C. E. , Kovalenko L. J. , McLinden C. A. , Salawitch R. J. , Van Roozendael M. , Goutail F. , Dorf M. , Pfeilsticker K. , Chance K. , von Savigny C. , Liu X. , Kurosu T. P. , Pommereau J.‐P. , Bösch H. , Frerick J.
Published: July 2006

Vertical profiles of stratospheric bromine monoxide (BrO) in the 15–30 km range are retrieved from SCIAMACHY limb scatter data over the globe. First validation comparisons with the balloon‐borne SAOZ‐BrO and LPMA/DOAS instruments indicate retrieval biases of ∼20% or less. Propagated spectral fitting uncertainties lead to a precision approaching ∼25% on a 2 km grid at 25 km. This worsens at higher altitudes because of reduced signal and at lower altitudes because of the reduced penetrability of the atmosphere. In terms of volume mixing ratio (VMR), the single profile precision increases from ∼4 pptv at 17 km to ∼8 pptv at 27 km. Repeatability, an alternative indicator of precision, is 2–3 pptv for SCIAMACHY retrievals and independent of altitude. The BrO stratospheric number density peak generally lies 5 ± 2 km above the tropopause. In the tropics, the stratospheric BrO VMR generally increases with increasing altitude. The observed stratospheric BrO global distribution is generally consistent with previous balloon measurements but does not agree well with results of a model that uses Bry inferred only from the observed breakdown of long‐lived bromoalkanes (i.e., methyl bromide and halons). We find best agreement with the observed vertical and latitudinal distribution of BrO for model results that include an 8.4 ± 2 pptv contribution to stratospheric Bry, most of which is expected from the breakdown of VSL (very short lived) bromocarbons, in addition to the ∼16 pptv contribution from longer‐lived sources. This suggests that stratospheric Bry exceeds 20 pptv. Profiles of Bry profiles derived from the balloon measurements of BrO also suggest Bry is in excess of 20 pptv, but the uncertainty and variability of these results do not allow us to definitively rule out this concentration. We find typical BrO VMRs of ∼4 pptv at 15 km in the tropical tropopause layer, suggesting that a significant portion of the bromine from VSL bromoalkane sources may be carried across the tropopause in the form of inorganic decomposition products. We discuss a variety of VSL bromocarbons species that may be contributing to the elevated concentrations of stratospheric BrO.
Upper level atmospheric stationary waves in the twentieth century climate of the Intergovernmental Panel on Climate Change simulations
Authors: Boyle J. S.
Published: July 2006

The upper level stationary waves are defined as the deviations from longitudinal symmetry of the 250 hPa climatological monthly mean stream function. The climatological averaging period is over the years 1980 to 2000. The coupled model simulations are those of the climate of the 20th Century experiment (20C3M) prescribed by IPCC. The model results are compared to the NCEP/NCAR and ERA40 Reanalyses. The comparison shows the following. (1) The amplitude of the modeled waves in the Northern Hemisphere is generally weaker than observed; that is, modeled flow is too zonal. In the Southern Hemisphere, there are phase as well as amplitude discrepancies but no clear biases. (2) The correlation of the waves in the reanalyses and models in the Northern Hemisphere in winter averages about 0.9, but decreases sharply outside of winter. (3) For many models the correlation of the waves in the reanalyses and models outside of the wintertime Northern Hemisphere is poor, sometimes being less than 0.7. The most prominent systematic error, occurring across all models, is the underestimate of the trough/ridge in the Northern Hemisphere winter over the north Atlantic sector, 60°W–0°W. (4) The models having the coarsest horizontal resolution consistently underperform compared to the others. For models of horizontal resolution finer than approximately 2.5°, the relation to horizontal resolution and fidelity of the simulation is somewhat less clear. (5) The interannual variability of the waves is consistently underestimated by almost all the models throughout the year and over the Northern Hemisphere. The differences between the models and the reanalyses are surprisingly large, given the large scale of the features diagnosed and the fairly long averaging period. Comparison to AMIP2 integrations indicates that differences in the ocean simulation in the coupled models are likely not an overwhelming influence on the agreement with reanalyses.
Diurnal effects in limb scatter observations
Authors: McLinden Chris A. , Haley Craig S. , Sioris Christopher E.
Published: July 2006

Instruments that measure UV/visible scattered light from the Earth's limb are emerging as an important class of sensors capable of providing high‐quality profiles of aerosols and trace gases from the upper troposphere to the mesosphere. Critical to the inversion of limb scatter observations is the forward radiative transfer model. A fast and accurate radiative transfer model, VECTOR (Vector Orders‐of‐scattering Radiative transfer model), is presented that is able to account for the diurnal variation of species such as NO2 and BrO along the observing line of sight and the incoming solar beam. VECTOR has been used to quantify for the first time diurnal effect errors in NO2 and BrO with application to OSIRIS (Optical Spectrograph and Infra‐Red Imager System) and SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography), two limb viewing satellite instruments. For a solar zenith angle near 90° at the tangent point, errors can exceed 50% for NO2 and 100% for BrO in the lower stratosphere, with the largest errors generally occurring when viewing across, and at large angles to, the terminator. These results applied to OSIRIS NO2 and SCIAMACHY BrO reveal that diurnal effect errors are generally small (<10%). Yet 1 out of every 6 OSIRIS NO2 profiles experiences large (10–35%) errors and 1 out of every 11 SCIAMACHY BrO profiles experiences large (10–100%, or larger) errors in the lower stratosphere.
Consistency of global MODIS aerosol optical depths over ocean on Terra and Aqua CERES SSF data sets
Authors: Ignatov Alexander , Minnis Patrick , Miller Walter F. , Wielicki Bruce A. , Remer Lorraine
Published: July 2006

Aerosol retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua platforms are available from the Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) data sets. Over ocean, two aerosol products are reported side by side. The primary M product is generated by subsetting and remapping the multispectral (from 0.47 to 2.1 μm) MOD04/MYD04 oceanic aerosol data onto CERES footprints. M*D04 processing uses cloud screening and aerosol algorithms developed by the MODIS science team. The secondary AVHRR‐like A product is generated in only two MODIS bands. The A processing uses the CERES cloud‐screening algorithm and NOAA/NESDIS glint identification and single‐channel aerosol retrieval algorithms. The M and A products have been documented elsewhere and preliminarily compared using 2 weeks of global Terra CERES SSF edition 1A data, in which the M product was based on MOD04 collection 3. In this study, the comparisons between the M and A aerosol optical depths (AOD) in MODIS band 1 (0.64 μm), τ1M and τ1A, are reexamined using 9 days of global CERES SSF Terra edition 2A and Aqua edition 1B data from 13 to 21 October 2002 and extended to include cross‐platform comparisons. The M and A products on the new CERES SSF release are generated using the same aerosol algorithms as before but with different preprocessing and sampling procedures, thus lending themselves to a simple sensitivity check to nonaerosol factors. Both τ1M and τ1A generally compare well across platforms. However, the M product shows larger differences, which increase with ambient cloud amount and toward the solar side of the orbit. The cross‐platform, cross‐product, and cross‐release comparisons conducted in this study confirm an earlier observation that the major area for improvement in the current aerosol processing lies in a more formalized and standardized sampling (most importantly, cloud screening), whereas optimization of the aerosol algorithm is deemed to be an important yet less critical element.
Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California
Authors: McLaughlin Karen , Kendall Carol , Silva Steven R. , Young Megan , Paytan Adina
Published: July 2006

A seasonal analysis assesing variations in the oxygen isotopic composition of dissolved inorganic phosphate (DIP) was conducted in the San Francisco Bay estuarine system, California. Isotopic fractionation of oxygen in DIP (exchange of oxygen between phosphate and environmental water) at surface water temperatures occurs only as a result of enzyme‐mediated, biological reactions. Accordingly, if phospate demand is low relative to input and phosphate is not heavily cycled in the ecosystem, the oxygen isotopic composition of DIP (δ18Op) will reflect the isotopic composition of the source of phosphate to the system. Such is the case for the North San Francisco Bay, an anthropogenically impacted estuary with high surface water phosphate concentrations. Variability in the δ18Op in the bay is primarily controlled by mixing of water masses with different δ18Op signatures. The δ18Op values range from 11.4‰ at the Sacramento River to 20.1‰ at the Golden Gate. Deviations from the two‐component mixing model for the North Bay reflect additional, local sources of phosphate to the estuary that vary seasonally. Most notably, deviations from the mixing model occur at the confluence of a major river into the bay during periods of high river discharge and near wastewater treatment outlets. These data suggest that δ18Op can be an effective tool for identifying P point sources and understanding phosphate dynamics in estuarine systems.
Hyperspectral cathodoluminescence imaging of modern and fossil carbonate shells
Authors: England Jennifer , Cusack Maggie , Paterson Niall W. , Edwards Paul , Lee Martin R. , Martin Robert
Published: July 2006

Optical cathodoluminescence (CL) is commonly used to identify diagenetically altered carbonate fossils, yet such an interpretation is problematic as present‐day carbonate shells may also luminesce. Hyperspectral CL imaging combines CL microscopy and CL spectroscopy to quantitatively analyze luminescence emission. Cold optical CL and hyperspectral CL imaging were carried out on four modern biominerals, a Rhynchonelliform brachiopod, a Craniid brachiopod, a bivalve, and the eggshell of the domestic fowl. A fossil Craniid brachiopod was analyzed to compare luminescence emission with that from the modern Craniid brachiopod. The beam conditions used for optical CL vary between studies, which hinders the direct comparison of CL analyses. This study assesses the effect of beam current and beam diameter on the intensity of luminescence emission. By characterizing the effect of beam conditions on different CaCO3 biominerals, comparisons can be made between CL studies. Hyperspectral CL imaging can be carried out in combination with WDS element analysis. By comparing hyperspectral CL images with element maps the causes of luminescence can to some extent be determined. The intensity of luminescence emitted from the modern biominerals differs under the same beam conditions. All four modern shells emit blue luminescence. In N. anomala, there is a correlation between Mn2+ concentration and luminescence intensity in the 620‐ to 630‐nm wavelength band, which is apparent in the inner region of the shell. The fossil Craniid also emits blue luminescence, and texture within the shell wall is apparent; however, the luminescence emission between 620 and 630 nm that is evident in N. anomala is absent.
Improving the accuracy of the magnetic field integral equation with the linear‐linear basis functions
Authors: Ergül Özgür , Gürel Levent
Published: July 2006

Basis functions with linear variations are investigated in terms of the accuracy of the magnetic field integral equation (MFIE) and the combined‐field integral equation (CFIE), on the basis of recent reports indicating the inaccuracy of the MFIE. Electromagnetic scattering problems involving conducting targets with arbitrary geometries, closed surfaces, and planar triangulations are considered. Specifically, two functions with linear variations along the triangulation edges in both tangential and normal directions (linear normal and linear tangential (LN‐LT) type) are defined. They are compared to the previously employed divergence‐conforming Rao‐Wilton‐Glisson (RWG) and curl‐conforming × RWG functions. Examples are presented to demonstrate the significant improvement in the accuracy of the MFIE and the CFIE gained by replacing the commonly used RWG functions with the LN‐LT type functions.
A study of the shape of topside electron density profile derived from incoherent scatter radar measurements over Arecibo and Millstone Hill
Authors: Luan Xiaoli , Liu Libo , Wan Weixing , Lei Jiuhou , Zhang Shun‐Rong , Holt John M. , Sulzer Michael P.
Published: July 2006

The shape of the topside electron density (Ne) profile is studied using incoherent scatter radar (ISR) measurements. On the basis of more than 90,000 and 84,000 Ne profiles measured over Arecibo (18.4°N, 66.7°W, dip 49.7°) and Millstone Hill (42.6°N, 71.5°W, dip 71.6°), respectively, shape factors have been derived by fitting the ISR observed profile using a Chapman‐type layer with a height‐independent scale height. The results reveal that the shape factor shows a general departure from the typically used values of 0.5 (Chapman α layer) except during the night and also undergoes appreciable variation with local time, season, solar activity, and latitude. Over Arecibo, the averaged shape factor is characterized by a daytime maximum of ∼0.55–0.75, a nearly constant nighttime value close to 0.5, and a marked morning decline; over Millstone Hill, the shape factor shows pronounced seasonal variations, and the diurnal variation in summer is opposite to that in other seasons. Over both stations, the shape factor exhibits a high correlation with the F2 layer peak electron density (NmF2), and it has strong solar cycle dependence during the late morning hours. It indicates that the temperature structure of the topside ionosphere can explain much of the variation of the shape factor when the plasma density is low, especially during nighttime. During daytime hours, the topside shape factor is thought to be associated with ion‐neutral drag during periods of large plasma density.
Trans‐Hudson Orogen of North America and Himalaya‐Karakoram‐Tibetan Orogen of Asia: Structural and thermal characteristics of the lower and upper plates
Authors: St‐Onge Marc R. , Searle Michael P. , Wodicka Natasha
Published: July 2006

The Trans‐Hudson Orogen (THO) of North America and the Himalaya‐Karakoram‐Tibetan Orogen (HKTO) of Asia preserve a Paleoproterozoic and Cenozoic record, respectively, of continent‐continent collision that is notably similar in scale, duration and character. In THO, the tectonothermal evolution of the lower plate involves (1) early thin‐skinned thrusting and Barrovian metamorphism, (2) out‐of‐sequence thrusting and high‐T metamorphism, and (3) fluid‐localized reequilibration, anatexis, and leucogranite formation. The crustal evolution of the Indian lower plate in HKTO involves (1) early subduction of continental crust to ultrahigh pressure (UHP) eclogite depths, (2) regional Barrovian metamorphism, and (3) widespread high‐T metamorphism, anatexis, and leucogranite formation. The shallow depths of the high‐T metamorphism in HKTO are consistent with early to mid‐Miocene ductile flow of an Indian lower plate midcrustal channel, from beneath the southern Tibetan Plateau to the Greater Himalaya. Melt weakening of the lower plate in THO is not observed at a similar scale probably due to the paucity of pelitic lithologies. Tectonothermal events in the upper plate of both orogens include precollisional accretion of crustal blocks, emplacement of Andean‐type plutonic suites, and high‐T metamorphism. Syncollisional to postcollisional events include emplacement of garnet‐biotite‐muscovite leucogranites, anatectic granites, and sporadic metamorphism (up to 90 Myr following the onset of collision in THO). Comparing the type and duration of tectonothermal events for THO and HKTO supports the notion of tectonic uniformitarianism for at least the later half of dated Earth history and highlights the complementary nature of the rock record in an older “exhumed” orogen compared to one undergoing present‐day orogenesis.
Relationships between Pacific and Atlantic ocean sea surface temperatures and U.S. streamflow variability
Authors: Tootle Glenn A. , Piechota Thomas C.
Published: July 2006

An evaluation of Pacific and Atlantic Ocean sea surface temperatures (SSTs) and continental U.S. streamflow was performed to identify coupled regions of SST and continental U.S. streamflow variability. Both SSTs and streamflow displayed temporal variability when applying the singular value decomposition (SVD) statistical method. Initially, an extended temporal evaluation was performed using the entire period of record (i.e., all years from 1951 to 2002). This was followed by an interdecadal‐temporal evaluation for the Pacific (Atlantic) Ocean based on the phase of the Pacific Decadal Oscillation (PDO) (Atlantic Multidecadal Oscillation (AMO)). Finally, an extended temporal evaluation was performed using detrended SST and streamflow data. A lead time approach was assessed in which the previous year's spring‐summer season Pacific Ocean (Atlantic Ocean) SSTs were evaluated with the current water year continental U.S. streamflow. During the cold phase of the PDO, Pacific Ocean SSTs influenced streamflow regions (southeast, northwest, southwest, and northeast United States) most often associated with El Niño–Southern Oscillation (ENSO), while during the warm phase of the PDO, Pacific Ocean SSTs influenced non‐ENSO streamflow regions (Upper Colorado River basin and middle Atlantic United States). ENSO and the PDO were identified by the Pacific Ocean SST SVD first temporal expansion series as climatic influences for the PDO cold phase, PDO warm phase, and the all years analysis. Additionally, the phase of the AMO resulted in continental U.S. streamflow variability when evaluating Atlantic Ocean SSTs. During the cold phase of the AMO, Atlantic Ocean SSTs influenced middle Atlantic and central U.S. streamflow, while during the warm phase of the AMO, Atlantic Ocean SSTs influenced upper Mississippi River basin, peninsular Florida, and northwest U.S. streamflow. The AMO signal was identified in the Atlantic Ocean SST SVD first temporal expansion series. Applying SVD, first temporal expansions series were developed for Pacific and Atlantic Ocean SSTs and continental U.S. streamflow. The first temporal expansion series of SSTs and streamflow were strongly correlated, which could result in improved streamflow predictability.
Dynamic averaging of rainfall‐runoff model simulations from complementary model parameterizations
Authors: Oudin Ludovic , Andréassian Vazken , Mathevet Thibault , Perrin Charles , Michel Claude
Published: July 2006

In this paper, we analyze how our evaluation of the capacity of a rainfall‐runoff model to represent low or high flows depends on the objective function used during the calibration process. We present a method to combine models to produce a more satisfactory streamflow simulation, on the basis of two different parameterizations of the same model. Where we previously had to choose between a more efficient simulation for either high flows or low flows (but inevitably less efficient in the other range), we show that a balanced simulation can be obtained by using a seasonal index to weigh the two simulations, providing good efficiency in both low and high flows.
Sea ice is a mushy layer
Authors: Feltham D. L. , Untersteiner N. , Wettlaufer J. S. , Worster M. G.
Published: July 2006

Sea ice is a two‐phase, two‐component, reactive porous medium: an example of what is known in other contexts as a mushy layer. The fundamental conservation laws underlying the mathematical description of mushy layers provide a robust foundation for the prediction of sea‐ice evolution. Here we show that the general equations describing mushy layers reduce to the model of Maykut and Untersteiner (1971) under the same approximations employed therein.
Laurent series expansion of a class of massive scalar one-loop integrals up to O(ε2) in terms of multiple polylogarithms
Authors: Körner J. G. , Merebashvili Z. , Rogal M.
Published: July 2006

In a recent paper we have presented results for a set of massive scalar one-loop master integrals needed in the NNLO parton model description of the hadroproduction of heavy flavors. The one-loop integrals were evaluated in n=4−2ε dimension and the results were presented in terms of a Laurent series expansion up to O(ε2). We found that some of the ε2 coefficients contain a new class of functions which we termed the L functions. The L functions are defined in terms of one-dimensional integrals involving products of logarithm and dilogarithm functions. In this paper we derive a complete set of algebraic relations that allow one to convert the L functions of our previous approach to a sum of classical and multiple polylogarithms. Using these results we are now able to present the ε2 coefficients of the one-loop master integrals in terms of classical and multiple polylogarithms.
Scalar gauge theory on a cylinder
Authors: Bingol Elif , Tevfik Kaynak Burak , Turgut O. Teoman
Published: July 2006

In this work, we study the complex bosonic matter coupled to the SU(Nc) gauge fields on a cylinder, which has a circular space part. We extend the ideas used for fermions on a cylinder in [S. G. Rajeev and Guruswamy, Mod. Phys. Lett. A 7, 3783 (1992)] to this case. Here, the normal ordering rule for bosonic bilinears is found. In the large-Nc limit, we can reformulate the whole problem in terms of a set of basic mesonic operators. The full equations of motion satisfied by these mesonic variables are too complicated. An approximation method, which is a kind of linearization, is suggested for this problem.
Phase coexistence in polydisperse multi-Yukawa hard-sphere fluid: High temperature approximation
Authors: Kalyuzhnyi Yu. V. , Hlushak S. P.
Published: July 2006

High temperature approximation (HTA) is used to describe the phase behavior of polydisperse multi-Yukawa hard-sphere fluid mixtures. It is demonstrated that in the frames of the HTA the model belongs to the class of “truncatable free energy models,” i.e., the models with thermodynamical properties (Helmholtz free energy, chemical potential, and pressure) defined by the finite number of generalized moments. Using this property we were able to calculate the complete phase diagram (i.e., cloud and shadow curves as well as binodals) and size distribution functions of the coexisting phases of several different models of polydisperse fluids. In particular, we consider polydisperse one-Yukawa hard-sphere mixture with factorizable Yukawa coefficients and polydisperse Lennard-Jones (LJ) mixture with interaction energy parameter and/or size polydispersity. To validate the accuracy of the HTA we compare theoretical results with previously published results of more advanced mean spherical approximation (MSA) for the one-Yukawa model and with the Monte Carlo (MC) computer simulation results of [Wilding et al. J. Chem. Phys. 121, 6887 (2004); Phys. Rev. Lett. 95, 155701 (2005)] for the LJ model. We find that overall predictions of the HTA are in reasonable agreement with predictions of the MSA and MC, with the accuracy range from semiquantitative (for the phase diagram) to quantitative (for the size distribution functions).
H(D)-atom yields in the quenching of Xe(6s[3∕2]1) by methane, ethane, ethene, ethyne, and their deuterated isotopologues
Authors: Umemoto Hironobu
Published: July 2006

The yields for the production of H(D) atoms in the reactions of Xe(6s[3∕2]1) with simple hydrocarbons and their deuterated variants were determined. Xe(6s[3∕2]1) was produced by two-photon laser excitation of Xe(6p[1∕2]0) followed by concomitant amplified spontaneous emission. H(D) atoms are detected using a vacuum-ultraviolet laser-induced fluorescence (LIF) technique. The H(D)-atom yields were evaluated from the LIF intensities and the overall rate constants for the quenching, which were determined from the temporal profile measurements of the resonance fluorescence from Xe(6s[3∕2]1). H∕D isotope effects were observed not only in the overall rate constants but also in the H(D)-atom yields. The yields for CH4, C2H4, and C2H2 were determined to be 0.89, 1.43, 1.03, respectively, while those for CD4, C2D4, and C2D2 were found to be smaller; 0.63, 0.86, and 0.79, respectively. The H∕D yield ratio for CH2D2 was 1.76. The presence of the isotope effects both in the rate constants and the yields suggests that electronic-to-electronic energy transfer processes and abstractive processes are competing.
Scanning and transmission electron microscope images of a suspended single-walled carbon nanotube
Authors: Kasumov Yu. A. , Khodos I. I. , Kociak M. , Kasumov A. Yu.
Published: July 2006

For the first time we perform simultaneous observations of individual single-walled carbon nanotubes using scanning electron microscope (SEM) and transmission electron microscope modes of a transmission electron microscope equipped with a scanning attachment operating at 100kV. We show that in the SEM mode both individual single-walled carbon nanotubes situated on thin Si3N4 membranes and portions of these tubes projecting far beyond the membranes can be observed. The contrast and width of the nanotube images depend on their diameter and density on a substrate. Possible mechanisms of the observed nanotube contrast are discussed.
High temperature (NaBi)0.48◻0.04Bi2Nb2O9-based piezoelectric ceramics
Authors: Gai Zhi-Gang , Wang Jin-Feng , Zhao Ming-Lei , Wang Chun-Ming , Zang Guo-Zhong , Ming Bao-Quan , Qi Peng , Zhang Shujun , Shrout Thomas R.
Published: July 2006

The effect of (LiCe) substitution for A site on the properties of (NaBi)0.48◻0.04Bi2Nb2O9 (NB◻N)-based ceramics was investigated. The coercive fields (EC) of NB◻N)-based ceramics were significantly decreased from 61.0to32.5kV∕cm and the Curie temperature (TC) gradually decreases from 820to803°C with increasing the (LiCe) modification. The piezoelectric coefficient d33, planar coupling factor kp, and mechanical quality factor Q of (NaBi)0.38(LiCe)0.05◻0.14Bi2Nb2O9 ceramic were found to be 27pC∕N, 11.2%, and 2600, respectively, together with the high TC (∼809°C) and stable piezoelectric properties, demonstrating that the (LiCe) modified NB◻N-based material a promising candidate for high temperature applications.
Compression induced chiral symmetry breaking of monolayers comprised of banana-shaped achiral molecules at an air-water interface: Williams-Bragg approach
Authors: Yamamoto Tetsuya , Manaka Takaaki , Taguchi Dai , Iwamoto Mitsumasa
Published: July 2006

Chirality of monolayers comprised of banana-shaped achiral molecules at an air-water interface was investigated theoretically, and a forming mechanism of chiral structure as an assembly of achiral molecules was argued. A model of such monolayers was constructed taking into account the short-range repulsive interaction between constituent banana-shaped achiral molecules, and the free energy density functional of the model was derived as a generalization of Williams-Bragg approach. It was predicted that chiral symmetry breaking occurs by monolayer compression, where two-dimensional characteristics of monolayers at an interface plays an important role in the formation of chiral structure by banana-shaped achiral molecules.
Linear arrays of ceramic microcavity plasma devices (127–180μm diameter) driven by buried coplanar electrodes: Shaping the intracavity electric field and emission profile
Authors: Park S.-J. , Spinka T. M. , Eden J. G.
Published: July 2006

Shaping the electric field within a microcavity plasma device can be accomplished by the introduction of curvature into the dielectric-plasma interface when the microcavity is inserted between coplanar electrodes. To that end, linear arrays of cylindrical microcavity plasma devices with diameters of 127 or 180μm have been fabricated in low temperature cofired ceramic(εr=40) and operated in the rare gases at pressures in the 400–800Torr range. Comprising 72 microcavities, each linear array is powered by two buried Ag electrodes lying parallel to the array and driven by either a sinusoidal ac or bipolar pulsed dc waveform. Examination of Ne microplasmas with an optical telescope reveals the existence of pressure-dependent structure on the spatially resolved emission profiles. Strongest emission is observed from two negative glows on opposite sides of the microcavity. Confined to regions of low electric field strength and a weak gradient, the negative glows generate maximum intensity 25–35μm from the wall of a 180μm diameter microcavity. A central peak appears along the longitudinal axis of symmetry of the microcavity for pNe≳700Torr, reflecting the formation of a positive column. Operating voltages as low as 190V rms have been measured for excitation of a linear array of 180μm diameter devices operating at a Ne pressure of 400–700Torr and driven by a 20kHz voltage waveform.
Magnetic anisotropy of Ga1−xMnxAs thin films on GaAs (311)A probed by ferromagnetic resonance
Authors: Bihler C. , Huebl H. , Brandt M. S. , Goennenwein S. T. B. , Reinwald M. , Wurstbauer U. , Döppe M. , Weiss D. , Wegscheider W.
Published: July 2006

We have studied the magnetic anisotropy of Ga1−xMnxAs thin films grown by low-temperature molecular beam epitaxy on GaAs (311)A substrates by means of ferromagnetic resonance spectroscopy. The angular dependence of the ferromagnetic resonance fields observed can be explained by two main contributions to the magnetic anisotropy: a cubic magnetic anisotropy field oriented along the crystallographic ⟨001⟩ axes caused by the symmetry of the GaAs host lattice, and an effective uniaxial magnetic anisotropy field along [311] presumably caused by the homoepitaxial growth of the layer. Additional smaller magnetic anisotropy contributions are discussed. Consequently, the dominating magnetic anisotropy of Ga1−xMnxAs on GaAs (311)A substrate appears to have the same origin as on GaAs (100) substrate.
Current spin-polarization in an inhomogeneous semiconductor
Authors: Villegas-Lelovsky L.
Published: July 2006

We investigate the spin-resolved transient dynamics of spin-polarized carriers injected via a ferromagnetic scanning-tunneling-microscope tip into nonuniformly n-doped bulk semiconductor externally driven by a current source. We propagate the injected spin packets by considering a spin hydrodynamic approach based on balance equations directly derived from a spin-dependent Boltzmann equation. We determine the spin polarization profiles for carrier and current densities. While the carrier spin polarization shows a drastic suppression in the interface the current spin polarization exhibits an enhancement.
Time series analysis of ionization waves in dc neon glow discharge
Authors: Hassouba M. A. , Al-Naggar H. I. , Al-Naggar N. M. , Wilke C.
Published: July 2006

The dynamics of dc neon glow discharge is examined by calculating a Lyapunov exponent spectrum (LES) and correlation dimension (Dcorr) from experimental time series. The embedding theory is used to reconstruct an attractor with the delay coordinate method. The analysis refers to periodic, chaotic, and quasi-periodic attractors. The results obtained are confirmed by a comparison with other methods of time series analysis such as the Fourier power spectrum and autocorrelation function. The main object of the present work is the positive column of a dc neon glow discharge. The positive column is an excellent model for the study of a non-linearity plasma system because it is nonisothermal plasma far from equilibrium.
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x-ray absorption and magnetic circular dichroism in ferromagnetic Ga1−xMnxP
Authors: Stone P. R. , Scarpulla M. A. , Farshchi R. , Sharp I. D. , Haller E. E. , Dubon O. D. , Yu K. M. , Beeman J. W. , Arenholz E. , Denlinger J. D. , Ohldag H.
Published: July 2006

We have measured the x-ray absorption and x-ray magnetic circular dichroism (XMCD) at the MnL3,2 edges in ferromagnetic Ga1−xMnxP films for 0.018⩽x⩽0.042. Large XMCD asymmetries at the L3 edge indicate significant spin polarization of the density of states at the Fermi energy. The temperature dependence of the XMCD and moment per Mn of 2.67±0.45μB calculated using sum rules are consistent with magnetometry values. The spectral shapes of the x-ray absorption and XMCD are nearly identical with those for Ga1−xMnxAs indicating that the hybridization of Mn d states and anion p states is similar in the two materials.
Possible method to determine the two-dimensional to three-dimensional crossover of gold clusters by examining their vibrational modes
Authors: Fa Wei , Dong Jinming
Published: July 2006

The structural and vibrational properties of AuN (N⩽16) have been studied by the relativistic all-electron density-functional calculations, in which a particular attention is paid to characterize the two-dimensional (2D) to three-dimensional (3D) crossover by their vibrational modes. There exist distinctly different vibrational spectra for the 2D and 3D AuN, which could be used as a fingerprint signal to identify their structures. More interestingly, it is found that each isomer of AuN has its characteristic radial breathing mode, whose frequency shows a remarkable jump at the 2D-3D transition point, thus offering a realizable and powerful experimental tool to determine the 2D-3D crossover size of AuN.
Switching effect in spin field-effect transistors
Authors: Jiang K. M. , Zheng Z. M. , Wang Baigeng , Xing D. Y.
Published: July 2006

We study how the conductance of a spin field-effect transistor (SFET) is manipulated by spin-orbit coupling strength, interfacial barrier height, and spin polarization in source and drain. It is shown that the conductance of the SFET exhibits an excellent switching characteristic for high potential barriers. By tuning the split-gate voltage one can vary the Dresselhaus [Phys. Rev. 100, 580 (1955)] spin-orbit coupling strength so as to switch the SFET on or off. On the other hand, in the SFET with almost Ohmic-contact interfaces there is pronounced conductance modulation mainly due to the Rashba [Sov. Phys. Solid State 2, 1190 (1960)] and Dresselhaus spin precession.
Electron and metastable state interactions in two-step ionization waves
Authors: Siefert Nicholas S. , Sands Brian L. , Ganguly Biswa N.
Published: July 2006

We demonstrate the use of a microwave hairpin resonator to measure the time-dependent, phase-resolved electron number density in ionization waves. Under our argon glow discharge conditions, the instability was caused by two-step ionization; and the wave frequency depended on the volume quenching rate of the metastable states. We measured the 1s5 metastable state density using diode laser absorption. The peak electron number density lagged behind the peak metastable state density by 60°. This phase shift reveals the nonlocal nature of the electron kinetics due to two-step ionization.
Accurate programmable electrocardiogram generator using a dynamical model implemented on a microcontroller
Authors: Chien Chang Jia-Ren , Tai Cheng-Chi
Published: July 2006

This article reports on the design and development of a complete, programmable electrocardiogram (ECG) generator, which can be used for the testing, calibration and maintenance of electrocardiograph equipment. A modified mathematical model, developed from the three coupled ordinary differential equations of McSharry et al. [IEEE Trans. Biomed. Eng. 50, 289, (2003)], was used to locate precisely the positions of the onset, termination, angle, and duration of individual components in an ECG. Generator facilities are provided so the user can adjust the signal amplitude, heart rate, QRS-complex slopes, and P- and T-wave settings. The heart rate can be adjusted in increments of 1BPM (beats per minute), from 20to176BPM, while the amplitude of the ECG signal can be set from 0.1to400mV with a 0.1mV resolution. Experimental results show that the proposed concept and the resulting system are feasible.
Optimizing spectral phase interferometry for direct electric-field reconstruction
Authors: Stibenz Gero , Steinmeyer Günter
Published: July 2006

Spectral phase interferometry for direct electric-field reconstruction has become a standard technique for the measurement and characterization of extremely short laser pulses. Here we describe an improved setup that employs a planar geometry, uses an interferometrically stable pulse-splitting scheme, and is suitable for broadband pulse characterization up to one optical octave bandwidth and beyond. We devote particular attention to optimization of parameters for the few-cycle regime, resulting in an instrument with an order-of-magnitude sensitivity improvement and a higher spectral resolution than in previous work.
Fast lifetime measurements of infrared emitters using a low-jitter superconducting single-photon detector
Authors: Stevens Martin J. , Hadfield Robert H. , Schwall Robert E. , Nam Sae Woo , Mirin Richard P. , Gupta James A.
Published: July 2006

We use a superconducting single-photon detector with less than 40Hz dark count rate to measure spontaneous emission lifetimes of quantum wells emitting light at wavelengths of 935 and 1245nm. The timing jitter of the measurement system—which includes the detector and all other electronic and optical components—is 68±3ps. We demonstrate how the infrared sensitivity and Gaussian temporal response function of this superconducting detector present clear advantages over conventional detector technologies.
Compact bakable in-line valve for ultrahigh vacuum
Authors: Pravica L. , Cvejanović D. , Williams J. F. , Napier S. A. , Samarin S. N. , Sergeant A. D.
Published: July 2006

The design and performance of a thin bakable in-line valve are described. The valve is designed for use in electron scattering experiments for efficient and minimal spatial separation of ultrahigh vacuum from a region containing metal vapors, base pressure of 8×10−8Torr, or atmosphere. The simple compact design permits experiments with metal vapors and spin polarized electrons to be conducted with high efficiency and over months, without loss of emission from GaAs crystal or need for frequent bakeout of ultrahigh vacuum chamber.
Metallic behavior of copper sulfide nanowires grown within Na-4 mica
Authors: Mukherjee Pijush Kanti , Bose Anindita , Chakravorty Dipankar
Published: July 2006

Copper sulfide nanowires of diameter of ∼1.2nm were grown within the crystal channels of Na-4 mica. These consist of both CuS and Cu2S strands. Electrical conduction over the temperature range of 130–300K was characterized by very low activation energies in the range of 0.008–0.004eV. The nanocomposites exhibit giant dielectric permittivity of ∼1617 which has been explained on the basis of one-dimensional metallic nanowires as predicted by the Gorkov-Eliashberg [Sov. Phys. JETP 21, 940 (1965)] and Rice-Bernasconi [Phys. Rev. Lett. 29, 113 (1972)] models.
Magneto-optic characteristics of BiTbGaIG film/TbYbBiIG bulk crystal composite structure in 1550nm band
Authors: Xu Z. C.
Published: July 2006

Using Tb0.85Yb1.62Bi0.53Fe5O12 (TbYbBiIG) instead of the conventional nonmagnetic Gd3Ga5O12, Tb2.43Bi0.57Ga0.1Fe4.9O12 (TbBiGaIG) films were grown on the TbYbBiIG substrate. Excellent magneto-optical characteristics were obtained in the TbBiGaIG∕TbYbBiIG composite structure: 4πMs=0.48×106A∕m, θf=−1117.2deg∕cm at λ=1550nm (Faraday rotation wavelength coefficient) FWC=0.049%∕nm in the wavelength range of 1550–1620nm at 25°C, and Faraday rotation temperature coefficient FTC=−5.48×10−5deg∕K at λ=1550nm. The TbYbBiIG with low FWC and FTC could be obtained due to the compensation effect. The TbBiGaIG layer with a compensation temperature centered in the operating temperature range creates a step function in Faraday rotation, and subsequently reduces the net change of Faraday rotation caused by the temperature dependence of TbYbBiIG substrate.
Size-induced strain and stiffness of nanocrystals
Authors: Ouyang G. , Li X. L. , Tan X. , Yang G. W.
Published: July 2006

An analytical model has been developed for the size-induced strain and stiffness of a nanocrystal from the perspective of thermodynamics and continuum medium mechanics. A core-shell structure with surface skin shell of an atomic diameter has been considered for the nanocrystal structure. Contribution from chemical and structural effects to the surface energy has also been considered. It has been found that the elastic modulus increases with the inverse of crystal size and the vibration frequency is higher than that of the bulk. The theoretical predictions are consistent with experimental observations.
Mobility comparison between front and back channels in ultrathin silicon-on-insulator metal-oxide-semiconductor field-effect transistors by the front-gate split capacitance-voltage method
Authors: Ohata Akiko , Cristoloveanu Sorin , Cassé Mikael
Published: July 2006

The mobilities of the front and back channels in ultrathin silicon-on-insulator metal-oxide-semiconductor field-effect transistors with a thin (2nm) gate oxide were compared. From front-gate split capacitance-voltage measurements, it was confirmed that the effective mobility of the front channel is lower than that of the back channel. A detailed analysis shows that this lowering strongly depends on the electron density, suggesting the presence of additional Coulomb scattering centers at the front channel.
Optical and dielectric properties of ZnO tetrapod structures at terahertz frequencies
Authors: Han Jiaguang , Zhu Zhiyuan , Ray Sanith , Azad Abul K. , Zhang Weili , He Mingxia , Li Shihong , Zhao Yiping
Published: July 2006

The low-frequency optical and dielectric properties of ZnO tetrapod structures prepared by thermophysical method were studied by terahertz time-domain spectroscopy. The power absorption, refractive index, and the complex dielectric function were measured in the frequency range from 0.2to3.5THz. Based on a simple effective medium theory, the low-frequency dielectric properties of ZnO tetrapods were found to be associated with the transverse optical E1 phonon mode, which is consistent with that observed in bulk single-crystal ZnO.
Fast response film-compensated liquid crystal on silicon display
Authors: Yu X. J. , Kwok H. S.
Published: July 2006

We have designed and constructed a fast response liquid crystal on silicon display. The stable alignment of this liquid crystal cell at zero-bias voltage is in the bend deformation. The measured total response time is 0.8ms for the worst case and averages 0.3ms for all gray levels. The optical reflectivity has been optimized to nearly 85% by using a compensation film. The white light contrast ratio is >500 at 6V. This fast mode can be used in field sequential color systems.
Vertical quantum wire realized with double cleaved-edge overgrowth
Authors: Roth S. F. , Krenner H. J. , Schuh D. , Bichler M. , Grayson M.
Published: July 2006

A quantum wire is fabricated on (001) GaAs at the intersection of two overgrown cleaves. The wire is contacted at each end to n+-GaAs layers via two-dimensional (2D) leads. A side gate controls the density of the wire revealing conductance quantization. The step height is strongly reduced from 2e2∕h due to the 2D lead series resistance. We characterize the 2D density and mobility for both cleave facets with four-point measurements. The density on the first facet is modulated by the substrate potential, depleting a 2μm wide strip that defines the wire length. Microphotoluminescence shows an extra peak consistent with one-dimensional electron states at the corner.
Photoreflectance-probed excited states in InAs∕InGaAlAs quantum dashes grown on InP substrate
Authors: Rudno-Rudziński W. , Kudrawiec R. , Podemski P. , Sęk G. , Misiewicz J. , Somers A. , Schwertberger R. , Reithmaier J. P. , Forchel A.
Published: July 2006

Photoreflectance (PR) measurements have been performed on InAs∕In0.53Ga0.23Al0.24As quantum dashes (QDashes) molecular-beam epitaxy grown on InP substrate. The PR features related to all relevant parts of the structure have been detected, including the ground and excited state optical transitions in QDashes. QDash ground state transition shifts from 1.5 to almost 2μm with the increase in the thickness of InAs layer, corresponding to the increase in the average size of the dashes. Excited state transitions have been clearly observed at the energy of about 150meV above the ground state transition energy.
Study of void formation due to electromigration in flip-chip solder joints using Kelvin bump probes
Authors: Chang Y. W. , Liang S. W. , Chen Chih
Published: July 2006

Kelvin bump probes were fabricated in flip-chip solder joints, and they were employed to monitor the void formation during electromigration. We found that voids started to form at approximately 5% of the failure time under 0.8A at 150°C, and the bump resistance increased only 0.02mΩ in the initial stage of void formation. Three-dimensional simulation was performed to examine the increase in bump resistance at different stages of void formation, and it fitted the experimental results quite well. This technique provides a systematic way for investigating the void formation during electromigration.
Photoluminescence and optical gain due to exciton-electron scattering in a high quality GaN thin film
Authors: Nakayama M. , Tanaka H. , Ando M. , Uemura T.
Published: July 2006

We have investigated photoluminescence (PL) properties of a high quality GaN thin film grown by metal organic vapor phase epitaxy under intense excitation conditions in a high temperature regime from 120K to room temperature. It is found that a PL band peculiar to intense excitation conditions appears with a threshold-like behavior. The energy spacing between the PL band at the threshold excitation power and the A exciton is proportional to temperature. The extrapolation of the linear dependence results in zero value of the energy spacing at absolute zero temperature. These PL profiles are specific to an emission process originating from exciton-electron scattering. Furthermore, we have demonstrated that the exciton-electron scattering process produces optical gain at room temperature from measurements of PL with a variable stripe-length method.
Simultaneous control of numerical enhancement of N atoms and decrease in heat flux into reaction chamber using Ar–N2 pulse-modulated induction thermal plasmas
Authors: Tanaka Yasunori , Muroya Takafumi , Hayashi Kouhei , Uesugi Yoshihiko
Published: July 2006

A numerical enhancement of nitrogen atoms and a simultaneous decrease in heat flux flowing into the reaction chamber were found using a high-power Ar–N2 pulse-modulated induction thermal plasma. Optical emission spectroscopy was carried out to estimate the relative number of excited nitrogen atoms flowing into the reaction chamber. The relative heat flux into the reaction chamber was evaluated from surface temperature measurement of a metal specimen installed at the downstream portion of the plasma torch. Results showed that decreasing the shimmer current level, which means the modulation degree of the coil current, increases the number of excited nitrogen atoms, while the heat flux can be reduced compared to a conventional steady state induction thermal plasma.