bluuebunny/crossref_metadata_2025 huggingface dataset:
Total basin discharge for the Amazon and Mississippi River basins from GRACE and a land‐atmosphere water balance
Authors: Syed T. H. , Famiglietti J. S. , Chen J. , Rodell M. , Seneviratne S. I. , Viterbo P. , Wilson C. R.
Published: December 2005

Freshwater discharge along continental margins is a key Earth system variable that is not well monitored globally. Here we propose a method for estimating monthly river basin outflows based on the use of new GRACE satellite estimates of terrestrial water storage changes in a coupled land‐atmosphere water balance. Using GRACE land water storage changes (which include changes in groundwater storage) in the water balance method results in more holistic estimates of basin discharge, which we call total basin discharge, that include not only streamflow, but the net of surface, groundwater and tidal inflows and outflows. The method was tested on the Amazon and Mississippi river basins, and could ultimately be applied to the major drainage regions and river basins of the globe. Estimated Amazon total basin discharge was well correlated with observed streamflow, but with a phase lag and underestimation of low flows. Estimated total basin discharge in the Mississippi river basin had a greater annual amplitude than observed streamflow, but showed good temporal covariance. Results for both basins highlight important differences between estimated total basin discharge and observed streamflow, at least part of which can be attributed to groundwater storage changes. Atmospheric moisture data and methods of GRACE data processing also contributed to the differences.
Coupled geophysical constraints on heat flow and fluid flux at a salt diapir
Authors: Hornbach Matthew J. , Ruppel Carolyn , Saffer Demian M. , Van Dover Cindy Lee , Holbrook W. Steven
Published: December 2005

Within a largely steady‐state low‐flux passive margin, a seafloor seep at the Blake Ridge Diapir transiently releases methane gas and sulfide‐laden fluids. Until now, fluid flux estimates on the diapir have been too small to reconcile with seafloor gas emission and the survival of a chemosynthetic community at the seep. Analysis of heat flow and high‐resolution seismic data collected across the diapir confirms fluid flux through a sub‐vertical chimney with apparent fluid velocities between 20 to 400 m ky−1, ∼100 times larger than previous estimates derived from pore water geochemical data. Away from the chimneys, observations indicate that conductive thermal processes and low fluid fluxes dominate in the hydrate reservoir and that dissolution of the salt diapir does not control the thickness of the hydrate stability zone. The results suggest that, despite limited fluid flux in the larger area, focused flux can be significant enough to sustain a seafloor chemosynthetic community at the diapir.
Radial variations in the Io plasma torus during the Cassini era
Authors: Delamere P. A. , Bagenal F. , Steffl A.
Published: December 2005

A radial scan through the midnight sector of the Io plasma torus was made by the Cassini Ultraviolet Imaging Spectrograph on 14 January 2001, shortly after closest approach to Jupiter. From these data, Steffl et al. (2004a) derived electron temperature, plasma composition (ion mixing ratios), and electron column density as a function of radius from L = 6 to 9 as well as the total luminosity. We have advanced our homogeneous model of torus physical chemistry (Delamere and Bagenal, 2003) to include latitudinal and radial variations in a manner similar to the two‐dimensional model by Schreier et al. (1998). The model variables include: (1) neutral source rate, (2) radial transport coefficient, (3) the hot electron fraction, (4) hot electron temperature, and (5) the neutral O/S ratio. The radial variation of parameters 1–4 are described by simple power laws, making a total of nine parameters. We have explored the sensitivity of the model results to variations in these parameters and compared the best fit with previous Voyager era models (Schreier et al., 1998), Galileo data (Crary et al., 1998), and Cassini observations (Steffl et al., 2004a). We find that radial variations during the Cassini era are consistent with a neutral source rate of 700–1200 kg/s, an integrated transport time from L = 6 to 9 of 100–200 days, and that the core electron temperature is largely determined by a spatially and temporally varying superthermal electron population.
Criteria for and statistics of electron diffusion regions associated with subsolar magnetic field reconnection
Authors: Mozer F. S.
Published: December 2005

The definition of “electron diffusion regions” and criteria for identifying them in magnetic field reconnection events are given. By employing these criteria and further constraints on the measured parallel electric field, 117 electron diffusion regions have been found in searching through 3 years of Polar satellite subsolar data. They exist in filamentary currents in which parallel electric fields and depressed plasma densities are found and where the electron beta is generally less than 1. The average parallel electric field in these events is about 30% of the average 38 mV/m perpendicular field. The size of these regions is the order of the electron skin depth or less. These electron diffusion regions are topological boundaries in the electron and magnetic field line flows because the components of E × B/B2 on their opposite sides are frequently different. These regions are found throughout the magnetopause but mainly at the magnetospheric separatrix. The divergence of the pressure tensor in the Generalized Ohm's Law may be the leading term that balances the parallel electric field if the observed large plasma density variations (and hence electron pressure variations) were spatial and not temporal. The picture resulting from this data is of a magnetopause that is highly structured and filamentary and very different from a linear, laminar, symmetric structure sometimes considered in theories or simulations. However, it is emphasized that events such as those described have been found in fewer than 20% of the magnetopauses examined, so the conventional picture may be more prevalent.
Ground and satellite observations of substorm onset arcs
Authors: Shiokawa K. , Yago K. , Yumoto K. , Baishev D. G. , Solovyev S. I. , Rich F. J. , Mende S. B.
Published: December 2005

Auroral features and associated particles and fields are investigated for a sequence of substorm onsets observed at ∼1900 MLT on 24 October 2000. During a 30‐min interval at 1020–1050 UT, we identified three Pi 2 wave packets with positive H enhancements at midlatitudes and associated auroral brightenings in auroral images obtained by a ground all‐sky camera and the IMAGE FUV imager. The DMSP F15 satellite crossed brightening arcs during the third Pi 2 pulsation in the field‐of‐view of the ground camera at Tixie (66.0° MLAT), Russia. The crossing was 1–2 hours duskside of the main onset local time. The brightening arcs were located in the region 1 upward field‐aligned current system. The most equatorward arc, which brightened just after the second Pi 2 pulsation, was at the equatorward boundary of the region 1 current and in the sunward convection region. The arcs corresponded to inverted‐V accelerated electrons with energies of ∼10 keV. On the basis of these simultaneous ground‐satellite measurements, we discuss substorm onset models of reconnection/flow braking and near‐Earth plasma sheet instabilities.
Electron temperature enhancement effects on plasma irregularities associated with charged dust in the Earth's mesosphere
Authors: Chen C. , Scales W. A.
Published: December 2005

Recently, experimental observations have shown that Polar Mesospheric Summer Echoes (PMSE) may be modulated by radio wave heating the irregularity source region with a ground‐based ionospheric heating facility. It is clear from these past investigations that the temporal behavior of PMSE during ionospheric heating shows promise as a diagnostic for the associated dust layer. To investigate the temporal behavior of plasma irregularities thought to produce PMSE, this work describes a new model that incorporates both finite diffusion time effects as well as dust charging. The hybrid model utilizes fluid ions described by continuity and momentum equations, electrons whose behavior is determined from quasi‐neutrality, and charged dust described by the standard Particle‐In‐Cell (PIC) method. The model has been used to investigate the temporal behavior of charged dust associated electron irregularities during electron temperature enhancement associated with radio wave heating. The model predicts that the temporal behavior of the irregularities depends on the ratio of the electron‐ion ambipolar diffusion time to the dust particle charging time τdif/τchg. The results indicate that typically for τdif/τchg ≪ 1, an enhancement in electron irregularity amplitude occurs for a period after turn‐off of the radio wave heating. The work also predicts that for τdif/τchg ≫ 1, an enhancement in electron irregularity amplitude occurs for a time period after the turn‐on of the radio wave heating. Owing to the dependence of τdif on irregularity scale size, these results have important implications for observations of PMSE modification at different radar frequencies. Therefore new possibilities may exist for diagnosing the dust layer with radio wave heating which are discussed.
Water vapor distributions measured with the Michelson Interferometer for Passive Atmospheric Sounding on board Envisat (MIPAS/Envisat)
Authors: Milz M. , von Clarmann T. , Fischer H. , Glatthor N. , Grabowski U. , Höpfner M. , Kellmann S. , Kiefer M. , Linden A. , Mengistu Tsidu G. , Steck T. , Stiller G. P. , Funke B. , López‐Puertas M. , Koukouli M. E.
Published: December 2005

We present water vapor profiles obtained from infrared limb emission measurements recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European Environmental Satellite (Envisat). These retrievals are based on constrained nonlinear least squares fitting. The retrievals are very sensitive to the radiative signals of thin transparent clouds and measurements showing any signature of cloud contamination have been rigorously excluded. The vertical resolution of the retrieved water vapor profiles is 4.5 to 6.5 km up to an altitude of approximately 42 km. The resulting total error of the retrieved water vapor profiles, including measurement noise, systematic and random parameter uncertainties like interfering species or preretrieved temperature or spectroscopic data, is in the range of 6 to 9% in the stratosphere. Towards the tropopause, the error increases up to 30% due to the exponential gradient of the tropospheric water vapor profile, where small line of sight uncertainties lead to strong absolute variations in the water vapor profile below the hygropause. Averaged water vapor distributions obtained from measurements taken during 11 days in June, July, and August 2003 show the expected distributions with low water vapor volume mixing ratios (VMRs) above the tropopause, comparatively dry air inside the tropical stratospheric updraft region and indications for strong dehydration above the Antarctic continent inside the polar vortex. Additionally, in the transition from tropics to subtropics, a latitude band was observed where, in higher altitudes, large water vapor VMRs were measured compared to adjacent tropical and midlatitudinal regions. Especially over the Arabic peninsula, a moist region at 18 km altitude was observed, which was probably related to the South Asian monsoon circulation.
Downward transport of upper atmospheric NOx into the polar stratosphere and lower mesosphere during the Antarctic 2003 and Arctic 2002/2003 winters
Authors: Funke B. , López‐Puertas M. , Gil‐López S. , von Clarmann T. , Stiller G. P. , Fischer H. , Kellmann S.
Published: December 2005

Pronounced upper stratospheric and mesospheric NOx enhancements were measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) in the Southern Hemisphere (SH) polar vortex from May to August 2003, reaching average abundances of 60 ppbv at 50–60 km in July. Peak mixing ratios of around 200 ppbv were measured in the polar night, representing the highest values ever recorded in the SH. The observed NOx enhancements are attributed to production by electron precipitation in the upper mesosphere and lower thermosphere and subsequent descent with the meridional circulation. Using measured CH4 and CO distributions as dynamic tracers, the downward transport of NOx‐rich air masses into the lower and middle stratosphere has been investigated. Upper atmospheric air with average NOx abundances of 15 ppbv reached the 800–1000 K potential temperature region (around 30 km) by the end of July, where it remained until the final warming in late October. The NOx descent was confined to the polar vortex, although significant mixing of tropical and NOx‐rich vortex air masses began already in August above 40 km. The amount of upper atmospheric NOy measured inside of the SH vortex in late spring was 1.1 Gigamoles (GM) which is in good agreement with previous estimates from HALOE data. The global coverage of MIPAS data further allows to quantify the upper atmospheric NOx dispersed into the stratosphere during August‐September, estimated in 1.3 GM. The net deposition of NOx into the stratosphere during the 2003 Antarctic winter (2.4 GM) makes up 9% of the N2O oxidation source in the SH, twice as much as estimated in previous studies. NOx and tracer distributions observed on several days during the NH winter 2002/2003 have been analyzed for comparison. We found that high planetary wave activity, resulting in the major midwinter warming had led to a rather inefficient NOx downward transport with negligible deposition of NOx into the lower and middle stratosphere.
Physics‐based forecasts of equatorial radio scintillation for the Communication and Navigation Outage Forecasting System (C/NOFS)
Authors: Retterer John M.
Published: December 2005

The plans for producing long‐term (6–24 hour) forecasts of equatorial plasma structure and radio scintillation for the Communication and Navigation Outage Forecasting System (C/NOFS) program are described. We discuss the calculations and computer models required to represent the physics of the phenomena pertinent to the C/NOFS mission. We describe the means by which the models will be integrated into a system that ingests satellite data and provides forecast maps. The plans for validation of the calculations are outlined briefly, with a few sample results.
Simultaneous observations of convective ionospheric storms: ROCSAT‐1 and ground‐based imagers
Authors: Makela J. J. , Kelley M. C. , Su S.‐Y.
Published: December 2005

The irregularities that occur in the postsunset equatorial ionosphere are one of the most spectacular effects of space weather. They occur over many decades of scale sizes and can cause scintillation of signals transmitted on a wide range of frequencies used by satellite communication and navigation systems, rendering such systems inoperable for a period of time. In the near future, a new era will begin with the launch of the Communication/Navigation Outage Forecast System (C/NOFS). The centerpiece of this program will be a new low‐inclination satellite that will make in situ measurements of electric fields, neutral winds, and electron densities. This program will also encompass state‐of‐the‐art modeling and corollary ground‐based instruments. In order to show the utility of such corollary measurements, we present two examples using data collected by a ground‐based imaging system on Haleakala Volcano on Maui, Hawaii, and the first Republic of China Satellite (ROCSAT‐1). We find that the images are useful for putting the one‐dimensional satellite data into a broader two‐dimensional context. We also investigate how the velocities in both directions perpendicular to the magnetic field estimated from the images compare to those measured in situ by the satellite. Finally, we suggest that these images will be crucial in providing the link between one‐dimensional ground‐based measurements, such as GPS scintillation measurements, and the in situ measurements provided by the satellite. With the launch of the C/NOFS satellite, comparisons of this type will become routine, allowing for new insight into the development and decay of the irregularities.
Extrinsic origin of giant permittivity in hexagonal BaTiO3 single crystals: Contributions of interfacial layer and depletion layer
Authors: Yu Jianding , Ishikawa Takehiko , Arai Yasutomo , Yoda Shinichi , Itoh Mitsuru , Saita Yutaka
Published: December 2005

Three dielectric relaxations in hexagonal (h)-BaTiO3 single crystals exhibiting giant permittivity were detected in a frequency range of 100Hz–3GHz and analyzed by an equivalent circuit with three parallel RC elements. A best-fit result indicated that the three dielectric relaxations were the responses of bulk crystal with a capacitance of 1pF, an interfacial layer with a capacitance of 1.4nF, and a depletion layer with a capacitance of 1nF. We confirmed that a giant permittivity exceeding 105 could be achieved by the interfacial layer in the h-BaTiO3 crystal. In addition, a Schottky barrier height at the contacting interface between Cu electrodes and the h-BaTiO3 surface was estimated as 1.56eV from the voltage dependence of capacitance.
Vibrational predissociation spectroscopy of the (H2O)6–21− clusters in the OH stretching region: Evolution of the excess electron-binding signature into the intermediate cluster size regime
Authors: Hammer Nathan I. , Roscioli Joseph R. , Bopp Joseph C. , Headrick Jeffrey M. , Johnson Mark A.
Published: December 2005

We report vibrational predissociation spectra of the (H2O)n− cluster ions in the OH stretching region to determine whether the spectral signature of the electron-binding motif identified in the smaller clusters [Hammer et al. Science 306, 675 (2004)] continues to be important in the intermediate size regime (n=7−21). This signature consists of a redshifted doublet that dominates the OH stretching region, and has been traced primarily to the excitation of a single water molecule residing in a double H-bond acceptor (AA) binding site, oriented with both of its H atoms pointing toward the excess electron cloud. Strong absorption near the characteristic AA doublet is found to persist in the spectra of the larger clusters, but the pattern evolves into a broadened triplet around n=11. A single free OH feature associated with dangling hydrogen atoms on the cluster surface is observed to emerge for n⩾15, in sharp contrast to the multiplet pattern of unbonded OH stretches displayed by the H+∙(H2O)n clusters throughout the n=2−29 range. We also explore the vibration-electronic coupling associated with normal-mode displacements of the AA molecule that most strongly interact with the excess electron. Specifically, electronic structure calculations on the hexamer anion indicate that displacement along the −OH2 symmetric stretching mode dramatically distorts the excess electron cloud, thus accounting for the anomalously large oscillator strength of the AA water stretching vibrations. We also discuss these vibronic interactions in the context of a possible relaxation mechanism for the excited electronic states involving the excess electron.
Theory of transport in nanofluidic channels with moderately thin electrical double layers: Effect of the wall potential modulation on solutions of symmetric and asymmetric electrolytes
Authors: Petsev Dimiter N.
Published: December 2005

Electrokinetic phenomena play an important role for the transport in submicrometer-size channels since the electric double layers formed at the walls can occupy a substantial part of the channel volume. This presents a theoretical difficulty and specific problems are usually treated numerically or not comprehensively. In our work we present a theoretical model that allows one to obtain analytical expressions for the transport of fluid (electro-osmotic flow), ions (electric current), and dissolved charged molecules (analytes). The model is based on the weak double layer approximation and has a wide range of validity. An important feature of this theoretical approach is that it is applicable not only to symmetric but also to asymmetric 2:1 and 1:2 electrolytes which exhibit very interesting properties in nanoscale channels. The possibility of affecting the wall electrokinetic ζ potential by applying a transverse voltage bias is analyzed. This transverse bias is used in an attempt to control the transport in the channel and such devices are often called “fluidic field-effect transistors.” Our model quantifies the effect of the voltage bias on the ζ potential of the channel wall and therefore can be used for prediction of transport and optimization of separations in such fluidic devices.
Determination of the space-charge field amplitude in polymeric photorefractive polymers
Authors: Hwang Ui-Jung , Choi Chil-Sung , Vuong Nguyen Quoc , Kim Nakjoong
Published: December 2005

The space-charge field built in a polymeric photorefractive polymer was calculated by a simple method based on the oriented gas model. When anisotropic chromophores in a photorefractive polymer were exposed to an external field, they oriented preferentially to exhibit a birefringence. Then, under illumination of two coherent beams and an external field, they reoriented to form a photorefractive grating. During the formation of the grating, the chromophores were reoriented by the space-charge field as well as by the external applied field. The birefringence induced in the material by an external electric field was determined by measuring the transmittance of the sample which is placed between crossed polarizers, where birefringence depicts the orientation of the chromophores. By measuring the diffraction efficiency with a modified degenerate four-wave mixing setup, the index amplitude of the grating was determined. Finally, the space-charge field was determined by comparing the diffraction efficiency with the birefringence with respect to the applied electric field. In our study, the space-charge field was about 20% of the external applied field, which coincided with previous results obtained from our laboratory.
Activated sampling in complex materials at finite temperature: The properly obeying probability activation-relaxation technique
Authors: Vocks Henk , Chubynsky M. V. , Barkema G. T. , Mousseau Normand
Published: December 2005

While the dynamics of many complex systems is dominated by activated events, there are very few simulation methods that take advantage of this fact. Most of these procedures are restricted to relatively simple systems or, as with the activation-relaxation technique (ART), sample the conformation space efficiently at the cost of a correct thermodynamical description. We present here an extension of ART, the properly obeying probability ART (POP-ART), that obeys detailed balance and samples correctly the thermodynamic ensemble. Testing POP-ART on two model systems, a vacancy and an interstitial in crystalline silicon, we show that this method recovers the proper thermodynamical weights associated with the various accessible states and is significantly faster than molecular dynamics in the simulations of a vacancy below 700 K.
Quasiphase matched harmonic generation in a two-dimensional octagonal photonic superlattice
Authors: Ma Boqin , Wang Ting , Sheng Yan , Ni Peigen , Wang Yiquan , Cheng Bingying , Zhang Daozhong
Published: December 2005

We have fabricated LiNbO3 nonlinear photonic crystals with a two-dimensional octagonal quasilattice. The effective collinear quasiphase matched second-harmonic orange and green lights, with conversion efficiencies of ∼38% and 23%, were realized. The noncollinear harmonic processes at multiple wavelengths were also observed with the conversion efficiency of around 5%. All the-same results can be obtained when the crystal is rotated by the integral multiples of π∕4.
Exploring the free-energy landscape of a short peptide using an average force
Authors: Chipot Christophe , Hénin Jérôme
Published: December 2005

The reversible folding of deca-alanine is chosen as a test case for characterizing a method that uses an adaptive biasing force (ABF) to escape from the minima and overcome the barriers of the free-energy landscape. This approach relies on the continuous estimation of a biasing force that yields a Hamiltonian in which no average force is exerted along the ordering parameter ξ. Optimizing the parameters that control how the ABF is applied, the method is shown to be extremely effective when a nonequivocal ordering parameter can be defined to explore the folding pathway of the peptide. Starting from a β-turn motif and restraining ξ to a region of the conformational space that extends from the α-helical state to an ensemble of extended structures, the ABF scheme is successful in folding the peptide chain into a compact α helix. Sampling of this conformation is, however, marginal when the range of ξ values embraces arrangements of greater compactness, hence demonstrating the inherent limitations of free-energy methods when ambiguous ordering parameters are utilized.
Switch-on overshoot transient decay mechanism in polycrystalline silicon thin-film transistors
Authors: Papaioannou G. J. , Exarchos M. , Kouvatsos D. N. , Voutsas A. T.
Published: December 2005

The present work investigates the switch-on transient decay in polycrystalline thin-film transistors. The decay is found to follow the stretched exponential relaxation model independently of the polycrystalline film properties and the device bias conditions or operating temperature. The temperature dependence of the stretched exponential relaxation allows for the determination of the decay time and, furthermore, the process activation energy.
Electron propagator theory study of N-∕O-methylglycine conformers
Authors: Tian Shan Xi
Published: December 2005

The low-lying conformers of N-∕O-methylglycine are studied by ab initio calculations at the B3LYP, MP3, and MP4(SDQ) levels of theory with the aug-cc-pVDZ basis set. The conformers having the intramolecular hydrogen bonds N–H⋯OC or O–H⋯N are more stable than the others. Vertical ionization energies for the valence molecular orbitals of each conformer predicted with the electron propagator theory in the partial third-order quasiparticle approximation are in good agreement with the experimental data available in the literatures. The relative energies of the conformers and comparison between the simulated and the experimental photoelectron spectra demonstrate that there are at least three and two conformers of N- and O-methylglycine, respectively, in the gas-phase experiments. The intramolecular hydrogen bonding O–H⋯N effects on the molecular electronic structures are discussed for the glycine methyl derivatives, on the basis of the ab initio electronic structure calculations, natural orbital bond, and atoms-in-molecules analyses. The intramolecular hydrogen bonding O–H⋯N interactions hardly affect the electronic structures of the O-NH2–CH2–C(O)–O–CH3 and α-methylated NH2–CH2–C(CH3)OOH conformers, while the similar intramolecular interactions lead to the significantly lower-energy levels of the highest occupied molecular orbitals for the N-(CH3–NH–CH2–COOH) and β-methylated (NH2–CH2–CH2–COOH) conformers.
Theoretical prediction of the coordination number, local composition, and pressure-volume-temperature properties of square-well and square-shoulder fluids
Authors: Hu Jiawen , Duan Zhenhao
Published: December 2005

By assuming a Boltzmann distribution for the molecular equilibrium between local and bulk environments, a general model is derived for the prediction of coordination numbers and local compositions of square-well and square-shoulder fluids. The model has no empirical parameter fitted from the data of square-well and square-shoulder fluids, but is valid from the low-density limit to the high-density limit. The applicable width of well or shoulder covers the commonly used range varying from 1.0 to 2.0. The model can accurately predict the coordination numbers of pure square-well and square-shoulder fluids, so the equation of state derived from it is superior to other equations of state based on the existing coordination number models. The model also accurately predicts the local compositions of mixtures in wide ranges of density and size ratio (1.0–8.0), as well as the configuration energy of lattice gases and highly nonideal lattice mixtures. It is remarkable that the model correctly predicts temperature-dependent coordination numbers and local compositions for both equal- and unequal-sized mixtures at close packing, which cannot be predicted by the existing coordination number models. Our derivation demonstrates that the energy parameters in local composition models should represent the potential difference of a molecule between the local and bulk environments, not the pair-interaction potential, and depend on the system conditions and different kinds of pair-interaction parameters. This result is very useful for the development of local composition and activity coefficient models and the mixing rules of equations of state.
Carrier transport in PbS nanocrystal conducting polymer composites
Authors: Watt Andrew , Eichmann Troy , Rubinsztein-Dunlop Halina , Meredith Paul
Published: December 2005

In this letter we report the carrier mobilities in an inorganic nanocrystal: conducting polymer composite. The composite material in question (lead sulphide nanocrystals in the conducting polymer poly [2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) was made using a single-pot, surfactant-free synthesis. Mobilties were measured using time of flight techniques. We have found that the inclusion of PbS nanocrystals in MEH-PPV both balances and markedly increases the hole and electron mobilities—the hole mobility is increased by a factor of ∼105 and the electron mobility increased by ∼107 under an applied bias of 5kVcm−1. These results explain why dramatic improvements in electrical conductivity and photovoltaic performance are seen in devices fabricated from these composites.
Kinetic model for binary homogeneous nucleation in the H2O–H2SO4 system: Comparison with experiments and classical theory of nucleation
Authors: Sorokin A. , Vancassel X. , Mirabel P.
Published: December 2005

A kinetic model to predict nucleation rates in the sulfuric acid-water system is presented. It allows calculating steady-state nucleation rates and the corresponding time lag, using a direct solution of a system of kinetic equations that describe the populations of sub- and near-critical clusters. This kinetic model takes into account cluster-cluster collisions and decay of clusters into smaller clusters. The model results are compared with some predictions obtained with the classical nucleation theory (CNT) and also with available measurement data obtained in smog chambers or flow tubes. It is shown that in the case of slow nucleation processes, the kinetic model and the CNT as used by Shugard et al. [J. Chem. Phys. 75, 5298 (1974)] give the same results. However, in the case of intensive nucleation, a large part of the nucleation flux is due to cluster-cluster collisions and the CNT underestimates the nucleation rates.
Manganese pentacarbonyl bromide as candidate for a molecular qubit system operated in the infrared regime
Authors: Korff B. M. R. , Troppmann U. , Kompa K. L. , de Vivie-Riedle R.
Published: December 2005

Our concept for a quantum computational system is based on qubits encoded in vibrational normal modes of polyatomic molecules. The quantum gates are implemented by shaped femtosecond laser pulses. We adopt this concept to the new species manganese pentacarbonyl bromide [MnBr(CO)5] and show that it is a promising candidate in the mid-infrared (IR) frequency range to connect theory and experiment. As direct reference for the ab initio calculations we evaluated experimentally the absorption bands of MnBr(CO)5 in the mid-IR as well as the related transition dipole moments. The two-dimensional potential-energy surface spanned by the two strongest IR active modes and the dipole vector surfaces are calculated with density-functional theory. The vibrational eigenstates representing the qubit system are determined. Laser pulses are optimized by multitarget optimal control theory to form a set of global quantum gates: NOT, CNOT, Π, and Hadamard. For all of them simply structured pulses with low pulse energies around 1μJ could be obtained. Exemplarily for the CNOT gate we investigated the possible transfer to experimental shaping, based on the mask function for pulse shaping in the frequency regime as well as decomposition into a train of subpulses.
Low-temperature (∼250°C) route to lateral growth of ZnO nanowires
Authors: Xu Congkang , Rho Keehan , Chun Junghwan , Kim Dong-Eon
Published: December 2005

Zinc oxide nanowires were obtained through a vapor transport route at temperatures as low as around 250°C. The diameters of the nanowires are ∼40nm and their lengths reach up to a few microns. The high-resolution transmission electron microscopy showed that ZnO nanowires are of hexagonal wurtzite structures with the [112¯0] growth direction. Raman spectrum reveals that the ZnO nanowires are of high-quality crystal and have an oxygen deficiency. The energy dispersive x-ray spectroscopy result verifies that the nanowires contain a small amount of Bi besides Zn and O. The investigation of the growth mechanism suggests that BiI3 plays a key role on the fabrication of ZnO nanowires around 250°C.
High carrier mobility in low band gap polymer-based field-effect transistors
Authors: Chen Miaoxiang , Crispin Xavier , Perzon Erik , Andersson Mats R. , Pullerits Tönu , Andersson Mattias , Inganäs Olle , Berggren Magnus
Published: December 2005

A conjugated polymer with a low band gap of 1.21 eV, i.e., absorbing infrared light, is demonstrated as active material in field-effect transistors (FETs). The material consists of alternating fluorene units and low band gap segments with electron donor-acceptor-donor units composed of two electron-donating thiophene rings attached on both sides of a thiadiazolo-quinoxaline electron-acceptor group. The polymer is solution-processable and air-stable; the resulting FETs exhibit typical p-channel characteristics and field-effect mobility of 0.03cm2V−1s−1.
Determination of the local structure of luminescent sites in ZnS nanowires using x-ray excited optical luminescence
Authors: Rosenberg R. A. , Shenoy G. K. , Heigl F. , Lee S.-T. , Kim P.-S. G. , Zhou X.-T. , Sham T. K.
Published: December 2005

We have monitored the optical luminescence from ZnS nanowires as a function of x-ray energy at the Zn L edge (1022 eV). The x-ray absorption spectrum obtained using the 338 nm, band edge emission as a signal resembles that of the wurtzite form of ZnS, while that obtained using the 430 and 520 nm defect emissions, resembles that of the sphalerite phase. Wurtzite is the dominant phase of the wire, while sphalerite is only found at the end of the wire adjacent to the gold particle used for nucleation and in small, highly localized regions of the wire. Therefore, the present results support the idea that the defect luminescence centers are caused by Au ions (520 nm) and vacancies (430 nm), which are located in regions of sphalerite and show how x-ray excited optical luminescence may be used to probe the local environment of such centers.
Photoluminescence of Si nanocrystal memory devices obtained by ion beam synthesis
Authors: Carrada Marzia , Wellner Anja , Paillard Vincent , Bonafos Caroline , Coffin Hubert , Claverie Alain
Published: December 2005

In this letter, we propose an original method to investigate Si nanocrystal-based nonvolatile memory devices, taking benefit of the photoluminescence (PL) spectroscopy and the specific optoelectronic properties of Si nanocrystals (Si-NCs). Ordered two-dimensional-arrays of Si-NCs were synthesized by ultralow-energy ion implantation in 7-nm-thick SiO2 and subsequent annealing. The Si-NCs population characteristics (size and density) were adjusted by different oxidizing annealing. This allowed, at the same time, the progressive healing of the oxide matrix. The analysis of the spectra revealed the presence of two PL bands, one due to quantum confinement effects in Si-NCs, and the other one attributed to silicon-rich oxide. Therefore, the evolution in energy and intensity of the PL bands was correlated to the oxidizing conditions, thus to the change of the Si-NCs size and density, and to the formation of stoichiometric SiO2. These results are of great interest as being the first step in using PL spectroscopy as a nondestructive method to assess or monitor the electrical performances of the future memory devices, before any step of contact fabrication.
Molecular-dynamics study of anomalous volumetric behavior of water-benzene mixtures in the vicinity of the critical region
Authors: Ikawa Shun-ichi
Published: December 2005

Molecular-dynamics simulations of water-benzene mixtures at 573 K and pressures in the 85–140 bars range have been performed to examine local structure and dynamics of the mixtures, which exhibit anomalously large volume expansion on mixing as recently found by in situ near-infrared measurements. Fractional charges for a simple-point-charge-type potential of water were adjusted so as to reproduce liquid densities and the gas-to-liquid transition pressure of neat water at 573 K. A Lennard-Jones-type potential for benzene was used and the Lorentz-Berthelot combination rule was applied to the water-benzene interaction. Simulations with a N-P-T ensemble of 800-molecule system have been performed and the results reproduce well the anomalous volumetric behavior of the mixtures with the mole fraction of benzene in the 0.3–0.8 range. Pair distribution functions, coordination numbers, and self-diffusion coefficients for the mixtures are calculated, and it is suggested that the local structure around water molecules undergoes drastic change by dissolution of benzene in the vicinity of the critical region, but that around benzene molecules seems to be understood as that of ordinary liquid mixtures.
A hybrid model for molecular-dynamics simulations of semiflexible main-chain liquid-crystalline polymer melts
Authors: Yung K. L. , He Lan , Xu Yan , Shen Y. W.
Published: December 2005

This Note proposes a new hybrid model that combines the Gay-Berne/Lennard-Jones (GB/LJ) and bead-spring models to simulate semiflexible main-chain liquid-crystalline polymers (LCPs) for improving simulation efficiency without compromising accuracy. In the new model, one bead and two nonlinear springs are used to describe the flexible spacers between two adjacent rigid units described by ellipsoidal particles. The model is found to be able to describe, with accuracy, detailed structural properties of semiflexible main-chain LCPs, such as the odd-even effects of their thermodynamic properties, where the bead-spring model cannot depict. In our experiments, the speed of simulation for the hybrid model was shown to be up to ten times faster than that for the GB/LJ model when the number of molecular chains exceeded 150.
Moisture-induced capacitance-voltage instabilities in mesoporous silica thin films
Authors: Singh A. P. , Victor P. , Ganesan P. G. , Nalamasu O. , Ramanath G.
Published: December 2005

Thin films of mesoporous silica (MPS) are attractive for low-permittivity interlayer isolation in integrated circuit wiring. Here, we report the mechanisms of moisture-induced capacitance-voltage (C-V) instabilities in MPS films. Upon annealing Al∕MPS∕Si(001)∕Al capacitors between 80 to 200 °C, the flat-band voltage first increases, reaches a maximum, and then decreases. Concurrently, the initially observed deep depletion behavior is replaced by strong inversion. Subsequent air exposure restores the preanneal C-V characteristics. Kinetics analyses reveal two thermally activated processes: Proton generation through fissure of silanol bonds (activation energy Ea1=0.42±0.04eV) and proton-induced depassivation of dangling bond traps (Ea2=0.54±0.05eV) at the MPS∕Si interface. We present an empirical model correlating these processes with the C-V characteristics. Our findings will be important considerations in designing processes for integrating MPS films into microdevices.
Surface passivation of III-V compound semiconductors using atomic-layer-deposition-grown Al2O3
Authors: Huang M. L. , Chang Y. C. , Chang C. H. , Lee Y. J. , Chang P. , Kwo J. , Wu T. B. , Hong M.
Published: December 2005

Al 2 O 3 was deposited on In0.15Ga0.85As∕GaAs using atomic-layer deposition (ALD). Without any surface preparation or postthermal treatment, excellent electrical properties of Al2O3∕InGaAs∕GaAs heterostructures were obtained, in terms of low electrical leakage current density (10−8 to 10−9A∕cm2) and low interfacial density of states (Dit) in the range of 1012cm−2eV−1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy (HRXPS) and high-resolution transmission electron microscopy (HRTEM). The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar+ sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al2O3∕InGaAs heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.
Simulation of phonon-assisted band-to-band tunneling in carbon nanotube field-effect transistors
Authors: Koswatta Siyuranga O. , Lundstrom Mark S. , Anantram M. P. , Nikonov Dmitri E.
Published: December 2005

Electronic transport in a carbon nanotube metal-oxide-semiconductor field effect transistor (MOSFET) is simulated using the nonequilibrium Green’s functions method with the account of electron-phonon scattering. For MOSFETs, ambipolar conduction is explained via phonon-assisted band-to-band (Landau–Zener) tunneling. In comparison to the ballistic case, we show that the phonon scattering shifts the onset of ambipolar conduction to more positive gate voltage (thereby increasing the off current). It is found that the subthreshold swing in ambipolar conduction can be made as steep as 40mV∕decade despite the effect of phonon scattering.
Ultrafast dynamics of femtosecond laser-induced periodic surface pattern formation on metals
Authors: Wang Jincheng , Guo Chunlei
Published: December 2005

In this paper, we perform a comparison study of periodic structures on the surfaces of three different noble metals, Cu, Ag, and Au, following femtosecond laser radiation. Under identical experimental conditions, laser-induced surface patterns show distinctly different level of morphological clearness on the three different metals. Simple calculations based on metal melting fail to explain the pattern differences. We show that our observation result from the competition of two ultrafast processes, electron-phonon energy coupling and hot electron diffusion, following femtosecond laser heating of metals.
The short pulse hierarchy
Authors: Brunelli J. C.
Published: December 2005

We study a new hierarchy of equations containing the short pulse equation, which describes the evolution of very short pulses in nonlinear media, and the elastic beam equation, which describes nonlinear transverse oscillations of elastic beams under tension. We show that the hierarchy of equations is integrable. We obtain the two compatible Hamiltonian structures. We construct an infinite series of both local and nonlocal conserved charges. A Lax description is presented for both systems. For the elastic beam equations we also obtain a nonstandard Lax representation.
On Chern-Simons theory with an inhomogeneous gauge group and BF theory knot invariants
Authors: Naot Gad
Published: December 2005

We study the Chern-Simons topological quantum field theory with an inhomogeneous gauge group, a non-semi-simple group obtained from a semisimple one by taking its semidirect product with its Lie algebra. We find that the standard knot observable (i.e., trace of the holonomy along the knot) essentially vanishes, and yet, the non-semi-simplicity of the gauge group allows us to consider a class of unorthodox observables which breaks gauge invariance at one point and leads to a nontrivial theory on long knots in R3. We have two main morals. (1) In the non-semi-simple case there is more to observe in Chern-Simons theory. There might be other interesting non-semi-simple gauge groups to study in this context beyond our example. (2) In the case of an inhomogeneous gauge group, we find that Chern-Simons theory with the unorthodox observable is actually the same as three-dimensional BF theory with the Cattaneo-Cotta-Ramusino-Martellini knot observable. This leads to a simplification of their results and enables us to generalize and solve a problem they posed regarding the relation between BF theory and the Alexander-Conway polynomial. We prove that the most general knot invariant coming from pure BF topological quantum field theory is in the algebra generated by the coefficients of the Alexander-Conway polynomial.
Nonstandard connections in k-cosympletic field theory
Authors: Muñoz-Lecanda Miguel-C. , Salgado Modesto , Vilariño Silvia
Published: December 2005

In the jet-bundle description of time-dependent mechanics there are some elements, such as the Lagrangian energy and the construction of the Hamiltonian formalism, which require the prior choice of a connection. This situation is analyzed by Echeverría-Enríquez et al. [J. Phys. A 28, 5553–5567 (1995)]. The aim of this paper is to extend the results in that paper to first order field theory, using the k-cosymplectic formalism described by de León and co-workers [J. Math. Phys. 39, 876–893 (1998); 42, 2092–2104 (2001)]. If the trivial configuration bundle of a Lagrangian system is endowed with one connection, different from the trivial one given by the product structure, we study the consequences on the geometric elements of the theory, the dynamical equations and the variational principles.
Representations of the q-deformed algebras Uq(so3) and Uq(so5) and q-orthogonal polynomials
Authors: Rozenblyum Alexander
Published: December 2005

Orthogonal polynomials related to irreducible representations of the classical type of the q-deformed algebras Uq(so3) and Uq(so5) are investigated. The main method consists in the diagonalization of corresponding infinitesimal operators (generators) of representations. For the algebra Uq(so3) this method leads to q-analogs of Krawtchouk polynomials. The properties of these polynomials are considered, the q-difference equation, the recurrence and explicit formulas. For the algebra Uq(so5), the diagonalization process of generators of representations leads to the connection with some class of orthogonal polynomials in two discrete variables. These variables are the so-called q-numbers [n], where [n]=(qn−q−n)∕(q−q−1). The introduced polynomials can be considered as two-dimensional q-analogs of Krawtchouk polynomials. The q-difference equation of the Sturm-Liouville type for these polynomials is constructed. The corresponding eigenvalues are investigated including the explicit formulas for their multiplicities. The structure of polynomial solutions is described.
p-type behavior in In–N codoped ZnO thin films
Authors: Chen L. L. , Lu J. G. , Ye Z. Z. , Lin Y. M. , Zhao B. H. , Ye Y. M. , Li J. S. , Zhu L. P.
Published: December 2005

p -type ZnO thin films have been realized by the In–N codoping method. Secondary ion mass spectroscopy revealed that the nitrogen incorporation was enhanced by the presence of indium in ZnO. The as-grown In–N codoped ZnO film shows acceptable p-type behavior at room temperature with high film quality. A conversion from p-type conduction to n type in a range of temperature was confirmed by Hall effect measurement. The lowest reliable room-temperature resistivity was found to be 3.12Ωcm with a carrier concentration of 2.04×1018cm−3 and a Hall mobility of 0.979cm2V−1S−1. The p-type behavior is stable.