bluuebunny/crossref_metadata_2025 huggingface dataset:
Continental‐scale measurement of the soil organic carbon pool with climatic, edaphic, and biotic controls
Authors: Wynn Jonathan G. , Bird Michael I. , Vellen Lins , Grand‐Clement Emilie , Carter John , Berry Sandra L.
Published: February 2006

We present data on soil organic carbon (SOC) inventory for 7050 soil cores collected from a wide range of environmental conditions throughout Australia. The data set is stratified over the spatial distribution of trees and grass to account for variability of SOC inventory with vegetation distribution. We model controls on SOC inventory using an index of water availability and mean annual temperature to represent the climatic control on the rate of C input into the SOC pool and decomposition of SOC, in addition to the fraction of soil particles <63 μm in diameter as a measure of textural control on SOC stabilization. SOC inventories in the top 30 cm of soil increase from 35 mg/cm2 in the driest regions to a modeled plateau with respect to a threshold of water availability at 335 mg/cm2, excluding variables controlling SOC decomposition. Above this threshold, decomposition factors begin to control SOC inventory, which we attribute to energetic control on microbial decomposition rates, and relatively weak stabilization of SOC in association with fine particles. When combined, these relationships provide an overall prediction of SOC inventory that accounts for 89–90% of the variance observed in the measured data set. Deviations from this relationship are most likely due to additional factors that also control decomposition rate such as hydrochemical and soil drainage conditions not accounted for by soil texture. Outliers within this data set are explained with respect to these conditions.
Overriding plate thinning in subduction zones: Localized convection induced by slab dehydration
Authors: Arcay D. , Doin M.‐P. , Tric E. , Bousquet R. , de Capitani C.
Published: February 2006

In subduction zones, many observations indicate that the backarc thermal state is particularly hot and that the upper lithosphere is thin, even if no recent extension episode has occurred. This might result from free thermal convection favored by low viscosities in the hydrated mantle wedge. We perform 2‐D numerical experiments of the convective mantle wedge interaction with both the downgoing slab and the overriding plate to test this hypothesis, explore its physical mechanism, and assess its dependencies on some relevant rock properties. Water transfers across the subducting plate and the mantle wedge are explicitly modeled by including in the calculation realistic hydration/dehydration reaction boundaries for a water‐saturated mantle and oceanic crust. The rheology is non‐Newtonian and temperature‐, pressure‐, and water content‐dependent. For low strength reduction associated to water content, the upper plate is locally thinned by an enhanced corner flow. For larger strength reductions, small convection cells rapidly thin the upper plate (in less than 15 Myr) over the area in the overriding lithosphere hydrated by slab‐derived water fluxes. As a result, the thinned region location depends on the subducting plate thermal state, and it increases with high convergence rates and low subduction dip angles. Other simulations are performed to test the sole effect of hydrous rock weakening on the upper plate/mantle convective interaction. They show that the thinning process is not influenced by the corner flow, but develops at the favor of a decoupling level induced by the formation of hydroxylated minerals inside the hydrated lithosphere. The erosion mechanism identified in these simulations allows us to explain the characteristic duration of erosion as a function of the hydrous strength reduction. We find that the presence of amphibole in the upper lithosphere in significant proportions is required down to a temperature of about 980°C, corresponding to an initial depth of ∼70 km, to strongly decrease the strength of the base of the lithosphere and trigger a rapid erosion (<15 Myr).
Evidence for double injections in scatter‐free solar impulsive electron events
Authors: Wang L. , Lin R. P. , Krucker S. , Gosling J. T.
Published: February 2006

We investigate the injection at the Sun for three scatter‐free impulsive electron events (7 August 1999, 28 June and 22 August 2000) observed from ∼0.4 to 300 keV by the WIND 3DP instrument. Taking into account the interplanetary scatter‐free propagation and instrumental effects, we find that the observed time profiles of electron fluxes at all energies fit well to triangular injections at the Sun with equal rise and fall times. We find two distinct injections: that of ∼0.4 to 6–9 keV electrons begins 9.1 ± 4.7 min before the start of the type III radio burst and lasts for 50–300 min, while that of ∼13 to 300 keV electrons starts 7.6 ± 1.3 min after the start of the type III burst and lasts for a factor of 5–10 times shorter. Electrons of the low‐energy injection are likely to be the source of the type III radio bursts, and the delayed high‐energy injection occurs when the associated CME passes altitudes of ∼1–6 R⊙. The observed electron energy spectra fit to double power‐law with a downward break at ∼40–50 keV, but exhibit a smooth power‐law across the transition (∼6–13 keV) between the two injections, suggesting the low‐energy injection may provide the seed electrons for the high‐energy injection.
Unprecedented pressure increase in deep magma reservoir triggered by lava‐dome collapse
Authors: Voight B. , Linde A. T. , Sacks I. S. , Mattioli G. S. , Sparks R. S. J. , Elsworth D. , Hidayat D. , Malin P. E. , Shalev E. , Widiwijayanti C. , Young S. R. , Bass V. , Clarke A. , Dunkley P. , Johnston W. , McWhorter N. , Neuberg J. , Williams P.
Published: February 2006

The collapse of the Soufrière Hills Volcano lava dome on Montserrat in July 2003 is the largest such event worldwide in the historical record. Here we report on borehole dilatometer data recording a remarkable and unprecedented rapid (∼600s) pressurisation of a magma chamber, triggered by this surface collapse. The chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site. By analyzing the strain data and using added constraints from experimental petrology and long‐term edifice deformation from GPS geodesy, we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 MPa and average radius ∼1 km. Pressurisation is attributed to growth of 1–3% of gas bubbles in supersaturated magma, triggered by the dynamics of surface unloading. Recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude.
Antarctic ozone depletion causes an intensification of the Southern Ocean super‐gyre circulation
Authors: Cai W.
Published: February 2006

Recent climate trends over the Southern Hemisphere (SH) summer feature a strengthening of the circumpolar westerly and a weakening of the midlatitude westerly extending from the stratosphere to Earth's surface. Much of the change is attributable to Antarctic ozone depletion. However, the consequential ocean circulation changes are unknown. Here I demonstrate that the observed surface wind changes have forced a southward shift and spin‐up of the super gyre, which links the subtropical South Pacific, Indian and Atlantic Ocean circulation, advecting more warm water southward. The circulation change includes a strengthening of the East Australian Current (EAC) flow passing through the Tasman Sea. The southward shift may be responsible for the observed unusually large warming in the SH midlatitude ocean and may contribute to the reported range extension to the south of many marine species in the South West Pacific.
Effect of nonlinear circularly polarized waves on linear instabilities triggered by an alpha particle beam
Authors: Gomberoff L.
Published: February 2006

It is shown that nonlinear left‐hand polarized waves can either stabilize or destabilize linear right‐hand polarized instabilities triggered by an alpha particle beam in a magnetized electron proton plasma. For differential alpha particle speeds above the threshold for instability the destabilization depends upon the plasma βi = vth.i/vA, where vth.i is the thermal velocity of the i plasma component and vA is the Alfvén velocity. For any given finite‐amplitude wave frequency, there is always a βi value such that above this value the system is destabilized further. For drift alpha particle speeds well above the instability threshold the destabilization can occur for any βi. It is also shown that the presence of the large‐amplitude wave can trigger purely electrostatic ion‐acoustic instabilities. The unstable waves are supported by the proton core.
Interferometric synthetic aperture radar atmospheric correction: GPS topography‐dependent turbulence model
Authors: Li Zhenhong , Fielding Eric J. , Cross Paul , Muller Jan‐Peter
Published: February 2006

Over the last two decades, repeat pass interferometric synthetic aperture radar (InSAR) has been widely used as a geodetic technique for measuring the Earth's surface, including topography and deformation. Like other astronomical and space geodetic techniques, repeat pass InSAR is limited by the variable spatial and temporal distribution of atmospheric water vapor. In this paper, a topography‐dependent turbulence model (GTTM for short) has been developed using GPS data only to produce zenith path delay difference maps for InSAR atmospheric correction. Application of the GTTM model to ERS Tandem data over the Los Angeles Southern California Integrated GPS Network area has shown that use of the GTTM can reduce water vapor effects on interferograms from ∼10 mm down to ∼5 mm, which is of great interest to a wide community of geophysicists. The principal finding of this paper is that interpolation methods should be applied to zenith total delay (ZTD) differences from different times instead of ZTD values themselves for the purpose of InSAR atmospheric correction. This is crucial to reduce (if not completely remove) topographic effects on ZTD values.
Topographic influence on overflow dynamics: Idealized numerical simulations and the Faroe Bank Channel overflow
Authors: Ezer Tal
Published: February 2006

Properties of the North Atlantic Deep Water (NADW) depend on mixing that occurs in the Denmark Strait (DS) and the Faroe Bank Channel (FBC) overflow regions. How the sill's topography in those regions may affect mixing processes and downstream variability is thus investigated using a high‐resolution terrain‐following ocean model. Model results agree with observations that show enhanced mixing and entrainment downstream from the sill; however, mixing seems to occur over a longer distance downstream from the FBC sill and more abruptly downstream from the DS sill. Sensitivity experiments with various FBC sill widths demonstrate that the narrow sill is responsible for the enhanced mixing. The downstream flow variability, eddy propagation, and deep water properties are affected by sill width and background stratification. Similar to the laboratory overflow experiments of Cenedese et al. (2004), three distinct mixing regimes (characterized by the Froude number) are identified in the FBC simulations: a steady subcritical flow regime upstream from the sill, a supercritical wave‐like flow regime downstream from the sill, and an irregular eddy‐dominated regime farther away from the sill. Satellite altimeter data near the FBC show cyclonic anomalies propagating along the northern slope of the channel, resembling the surface eddies associated with the overflow variability in the model. A cross‐channel circulation over the FBC sill, driven by frictional bottom boundary layers, resulted in convergence/divergence zones near the southern/northern slopes and pinching/spreading of isotherms across the channel, similar to the observation‐based mechanism proposed by Johnson and Sanford (1992).
Atmospheric methane sulfonate and non‐sea‐salt sulfate records at the European Project for Ice Coring in Antarctica (EPICA) deep‐drilling site in Dronning Maud Land, Antarctica
Authors: Piel C. , Weller R. , Huke M. , Wagenbach D.
Published: February 2006

During three summer campaigns in January/February 2000, 2001, and 2002 the ionic composition of the aerosol at the European Project for Ice Coring in Antarctica (EPICA) deep‐drilling site at Kohnen Station was measured in daily resolution. In 2000 and 2002 we observed mean (±std) non‐sea‐salt sulfate (nss‐SO42−) concentrations of 353 ± 100 ng m−3 and 320 ± 250 ng m−3, as well as methane sulfonate (MS) concentrations of 59 ± 36 ng m−3 and 74 ± 80 ng m−3, respectively. For the summer campaign in 2001, significantly lower nss‐SO42− and MS levels of 164 ± 150 ng m−3 and 19 ± 12 ng m−3, respectively, were typical. The mean MS/nss‐SO42− ratio ranged from about 0.1 to 0.2. MS and nss‐SO42− concentrations and their variability were roughly comparable to coastal stations at summer. Supported by air mass back trajectory analyses, this finding documented an efficient long‐range transport to Kohnen via the free troposphere. MS/nss‐SO42− ratios exhibited a strong dependence on the MS concentration with systematically higher ratios at higher MS concentrations, a peculiarity which is also evident in a firn core drilled at this site.
Temperature dependence of volatile organic compound evaporative emissions from motor vehicles
Authors: Rubin Juli I. , Kean Andrew J. , Harley Robert A. , Millet Dylan B. , Goldstein Allen H.
Published: February 2006

A chemical mass balance approach is used to determine the relative contributions of evaporative versus tailpipe sources to motor vehicle volatile organic compound (VOC) emissions. Contributions were determined by reconciling time‐resolved ambient VOC concentrations measured downwind of Sacramento, California, in summer 2001 with source speciation profiles. A composite liquid fuel speciation profile was determined from gasoline samples collected at Sacramento area service stations. Vapor‐liquid equilibrium relationships were used to determine the corresponding headspace vapor composition. VOC concentrations measured in a highway tunnel were used to define the composition of running vehicle emissions. The chemical mass balance analysis indicated that headspace vapor contributions ranged from 7 to 29% of total vehicle‐related VOC depending on time of day and day of week, with a mean daytime contribution of 17.0 ± 0.9% (mean ± 95% CI). A positive association between the headspace vapor contribution and ambient air temperature was found for afternoon hours. We estimate a 6.5 ± 2.5% increase in vapor pressure‐driven evaporative emissions and at least a 1.3 ± 0.4% increase in daily total (exhaust plus evaporative) VOC emissions from motor vehicles per degree Celsius increase in maximum temperature.
Dust and the low‐level circulation over the Bodélé Depression, Chad: Observations from BoDEx 2005
Authors: Washington Richard , Todd Martin C. , Engelstaedter Sebastian , Mbainayel Samuel , Mitchell Fiona
Published: February 2006

Dust plays an important role in climate, recognition of which has led to a concentrated research effort in field campaigns, development and analysis of remotely sensed data, and modeling to better understand dust. There have, however, been very few direct surface‐based field measurements from key dust source regions. The Bodélé, Chad, has been shown to be one of the premier sources of dust in the world. This paper reports on the Bodélé Field Experiment (BoDEx 2005) which took place during February and March 2005 and presents the first surface‐based measurements of the circulation over the Bodélé. On the basis of Pilot Balloon and AWS data, we confirm the existence of the Bodélé Low Level Jet (LLJ) and show that winds undergo a strong diurnal cycle such that strongest surface winds typically occur in the midmorning when momentum is mixed downward in turbulence induced by radiative heating. In contrast, the core of the LLJ, near 500 m, peaks during the evening and is weakest during the day. The LLJ was present on all days during BoDEx 2005, but winds at the surface reached speeds necessary for large‐scale dust entrainment on only a few days. The winds strength during the main dust plume event of BoDEx (10–12 March 2005) was in the bottom third of March plume events of the last 4 years. Pathways of dust transport from the Bodélé using a trajectory model show potential advection of dust over the west African coastline within 5 days.
Simulation of vibrational dephasing of I2 in solid Kr using the semiclassical Liouville method
Authors: Riga Jeanne M. , Fredj Erick , Martens Craig C.
Published: February 2006

In this paper, we present simulations of the decay of quantum coherence between vibrational states of I2 in its ground (X) electronic state embedded in a cryogenic Kr matrix. We employ a numerical method based on the semiclassical limit of the quantum Liouville equation, which allows the simulation of the evolution and decay of quantum vibrational coherence using classical trajectories and ensemble averaging. The vibrational level-dependent interaction of the I2(X) oscillator with the rare-gas environment is modeled using a recently developed method for constructing state-dependent many-body potentials for quantum vibrations in a many-body classical environment [J. M. Riga, E. Fredj, and C. C. Martens, J. Chem. Phys. 122, 174107 (2005)]. The vibrational dephasing rates γ0n for coherences prepared between the ground vibrational state ∣0⟩ and excited vibrational state ∣n⟩ are calculated as a function of n and lattice temperature T. Excellent agreement with recent experiments performed by Karavitis et al. [Phys. Chem. Chem. Phys. 7, 791 (2005)] is obtained.
Single-electron tunneling spectroscopy of single C60 in double-barrier tunnel junction
Authors: Li Bin , Zeng Changgan , Zhao Jin , Yang Jinlong , Hou J. G. , Zhu Qingshi
Published: February 2006

The single-electron tunneling (SET) spectroscopy of C60 molecule in a double-barrier tunnel junction is investigated by combining the scanning tunneling spectroscopy experiment and the theoretical simulation using the modified orthodox theory. The interplay between the SET effect and the discrete energy levels of C60 molecule is studied. Three types of SET spectroscopies with different characters are obtained, corresponding to different tunneling processes and consistent with the previous theoretical prediction. Both the charging mode and resonance mode can arouse the current increase in the SET spectroscopy. The resonance mode is realized mainly by two mechanisms, including the resonance when the electron spans the second junction after already spanning the first junction. Some previous confused results have been clarified. Our results show that three types of SET spectroscopies can be together examined to quantitatively determine the frontier orbitals of the nanostructure by identifying the modes of various current increases.
Interaction of an elastic wave with a circular crack in a fluid-saturated porous medium
Authors: Galvin Robert J. , Gurevich Boris
Published: February 2006

We consider interaction of a normally incident time-harmonic longitudinal plane wave with a circular crack imbedded in a porous medium governed by Biot’s equations of dynamic poroelasticity. The problem is formulated in cylindrical coordinates as a system of dual integral equations for the Hankel transform of the wave field, which is then reduced to a single Fredholm integral equation of the second kind. The solution of this equation yields elastic wave dispersion and attenuation in a medium containing a random distribution of aligned cracks. These dissipation effects are caused by wave induced fluid flow between pores and cracks.
Generalized quantum entropy
Authors: Hu Xinhua , Ye Zhongxing
Published: February 2006

The generalized quantum entropies are introduced in this paper. Some important properties such as nonnegativity, continuity, and concavity are proved. But different from the Von Neumann entropy, the subadditivity and additivity fail for the quantum unified (r,s)-entropy in general.
Phosphodiester and N-glycosidic bond cleavage in DNA induced by 4–15 eV electrons
Authors: Zheng Yi , Cloutier Pierre , Hunting Darel J. , Wagner J. Richard , Sanche Léon
Published: February 2006

Thin molecular films of the short single strand of DNA, GCAT, were bombarded under vacuum by electrons with energies between 4 and 15 eV. Ex vacuo analysis by high-pressure liquid chromatography of the samples exposed to the electron beam revealed the formation of a multitude of products. Among these, 12 fragments of GCAT were identified by comparison with reference compounds and their yields were measured as a function of electron energy. For all energies, scission of the backbone gave nonmodified fragments containing a terminal phosphate, with negligible amounts of fragments without the phosphate group. This indicates that phosphodiester bond cleavage by 4–15 eV electrons involves cleavage of the C–O bond rather than the P–O bond. The yield functions exhibit maxima at 6 and 10–12 eV, which are interpreted as due to the formation of transient anions leading to fragmentation. Below 15 eV, these resonances dominate bond dissociation processes. All four nonmodified bases are released from the tetramer, by cleavage of the N-glycosidic bond, which occurs principally via the formation of core-excited resonances located around 6 and 10 eV. The formation of the other nonmodified products leading to cleavage of the phosphodiester bond is suggested to occur principally via two different mechanisms: (1) the formation of a core-excited resonance on the phosphate unit followed by dissociation of the transient anion and (2) dissociation of the CO bond of the phosphate group formed by resonance electron transfer from the bases. In each case, phosphodiester bond cleavage leads chiefly to the formation of stable phosphate anions and sugar radicals with minimal amounts of alkoxyl anions and phosphoryl radicals.
Surface topography and its transition of nematic elastomers due to photoinduced deformation
Authors: Wei Z. Y. , He L. H.
Published: February 2006

Due to the disruption of liquid-crystal order caused by photoisomerization of the rodlike molecules, solids containing light-sensitive molecules such as nematic liquid-crystal elastomers can undergo large reversible shape changes when stimulated by light. In this paper, we study surface deformation of such solids illuminated by light based on a phenomenological model. Numerical computation shows that the deformation topography of the surface depends remarkably on the spot radius of light. The result is expected helpful to practical applications related to the creation of surface patterns, such as guidance of microfluids and manipulation of nanostructures.
Nonequilibrium membrane fluctuations driven by active proteins
Authors: Lin Lawrence C.-L. , Gov Nir , Brown Frank L. H.
Published: February 2006

We extend a model for nonthermal membrane undulations driven by active (adenosine triphosphate-dependent or light-harvesting) membrane proteins [N. Gov, Phys. Rev. Lett. 93, 268104 (2004)]. The present model accounts for the fact that proteins can diffuse laterally across the membrane surface and that individual proteins are expected to exert forces preferentially in one normal direction over the other (due to their orientation within the bilayer). The addition of these effects alters the scaling of fluctuation amplitudes with system size. Additionally, theoretical arguments and dynamic simulations both suggest that, in certain regimes, the probability distribution of fluctuation amplitudes is expected to be non-Gaussian (in contrast to thermal systems).
Sustained spheromak coaxial gun operation in the presence of an n=1 magnetic distortion
Authors: Holcomb C. T. , Jarboe T. R. , Hill D. N. , Woodruff S. , Wood R. D.
Published: February 2006

The Sustained Spheromak Physics Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)] uses a magnetized coaxial gun to form and sustain spheromaks by helicity injection. Internal probes give the magnetic profile within the gun. An analysis of these data show that a number of commonly applied assumptions are not completely correct, and some previously unrecognized processes may be at work. Specifically, the fraction of the available vacuum flux spanning the gun that is stretched out of the gun is variable and not usually 100%. The n=1 mode that is present during sustained discharges has its largest value of δB∕B within the gun, so that instantaneously B within the gun is not axisymmetric. By applying a rigid-rotor model to account for the mode, the instantaneous field and current structure within the gun are determined. The current density is also highly nonaxisymmetric and the local value of λ≡μ0j∣∣∕B is not constant, although the global value λg≡μ0Ig∕ψg closely matches that expected by axisymmetric models. The current distribution near the gun muzzle suggests a cross-field current exists, and this is explained as a line-tying reaction to plasma rotation.
Change in photoluminescence spectra of Eu-doped GaN powders due to the aggregation of nanosized grains into micrometer-sized conglomerations
Authors: Kudrawiec R. , Nyk M. , Podhorodecki A. , Misiewicz J. , Strek W. , Wołcyrz M.
Published: February 2006

In this letter, we report a phenomenon of the aggregation of nanocrystalline grains of GaN:Eu into micrometer-sized conglomerates having optical properties different from those of the initial GaN:Eu grains. The nanocrystalline GaN:Eu powders exhibit no emission related to the GaN band gap and a very broad yellow/red PL band associated with recombination in the GaN host matrix via surface states, in addition to the strong Eu3+-related emission, i.e., the D05→FJ7 transitions with J=1, 2, 3, and 4. For the microcrystalline powders, the yellow/red photoluminescence (PL) band disappears and a strong PL band related to the GaN band gap arises. In addition, the Eu3+-related transitions start to split into individual lines typical of Eu-doped bulk-like GaN crystals. These differences in PL spectra have been correlated with the surface/volume ratio of the GaN grains. It has been concluded that, for very small grains (<50nm), surface states determine the optical properties of GaN:Eu powders. Postgrowth processing, which is able to change the size of the GaN grains, seems to be very useful in order to improve and to control the optical properties of GaN:Eu powders.
Theory of turbulence regulation by oscillatory zonal flows
Authors: Kim Eun-jin
Published: February 2006

The theory of turbulence regulation by oscillatory zonal flows is presented for passive scalar field models. Zonal flows are assumed to have linear spatial variation of the form U=−xΩ(t)ŷ, where Ω(t) has amplitude Ωm and frequency ωz. The flux and fluctuation levels are found to scale as 1∕∣kyUm∣ and τ*∕∣kyUm∣, respectively, for Ωm>ωz. Here, τ*=τη(ωz∕Ωm)2 is the effective decorrelation time, τη=τ*(Ω=0), Um=xΩm, and ky is the typical poloidal wave number of the turbulence. The effect of stochasticity of oscillatory zonal flows on shear decorrelation is discussed. The results complement the theory of turbulence regulation by low-frequency random zonal flows [E. Kim and P. H. Diamond, Phys. Rev. Lett 91, 075001 (2003)].
Analysis of low-pressure dc breakdown in nitrogen between two spherical iron electrodes
Authors: Pejovic Momcilo M. , Nesic Nikola T. , Pejovic Milic M.
Published: February 2006

The influence of afterglow period τ, voltage increase rate k, and electrode gap d on breakdown voltage Ub for a nitrogen-filled tube with spherical electrodes of diameter D⪢d and p=6.5mbar has been investigated. The data for the breakdown voltage were obtained for the case when there is a presence of N(S4) atoms, which release secondary electrons via recombination on the cathode. By fitting the experimental data of breakdown voltage mean values as a function of the voltage increase rate, the static breakdown voltages for afterglow periods of 15 and 100 s were estimated. The electrical field as a function of the electrode gap using breakdown voltage mean values was also determined. It is shown that experimental results of the breakdown voltage mean value as a function of pd in the interval of d from 0.82 to 1.62 mm can be very well described with Paschen’s law, valid for the case of parallel-plate electrodes.
Growth and properties of (104)-oriented ferroelectric Nd-substituted Bi4Ti3O12 films on Si(100) using (111)-oriented SrRuO3∕Pt electrodes
Authors: Lee Sung Kyun , Hesse Dietrich , Gösele Ulrich
Published: February 2006

(104)-oriented Nd-substituted Bi4Ti3O12 (BNT) ferroelectric thin films were grown on (111)-oriented SrRuO3∕Pt electrodes on yttria-stabilized ZrO2 (YSZ)-buffered Si(100) substrates by pulsed laser deposition. X-ray diffraction characterization revealed the epitaxial orienta-tion relationships as follows: BNT(104)‖SrRuO3(111)‖Pt(111)‖YSZ(100)‖Si(100); BNT[010]‖SrRuO3[01¯1]‖Pt[01¯1]‖YSZ⟨001⟩‖Si⟨001⟩. The BNT films exhibited a remanent polarization (2Pr) of 37.8μC∕cm2 and a coercive field (2Ec) of 212kV∕cm, for a maximum applied electric field of 300kV∕cm.
Micron-scale organic thin film transistors with conducting polymer electrodes patterned by polymer inking and stamping
Authors: Li Dawen , Guo L Jay
Published: February 2006

We report organic thin film transistors (OTFTs) with conductive polymer poly (3,4-ethylenedioxythiophene)/poly(4-styrenesulphonate) (PEDOT) electrodes that are fabricated by a simple polymer inking and stamping technique. An OTFT channel length of 2μm has been achieved. This patterning technique is a purely additive process, which does not affect the functionality of the conductive polymers, and is fully compatible for patterning on a flexible substrate. Electrical characteristics of top contact (TC) pentacene TFTs with PEDOT electrodes is superior to those with gold electrodes due to a lower carrier injection barrier. Extracted contact resistance shows that the channel length of TC OTFTs can be further reduced to increase the drain current.
On the relationship between the local tracking procedures and monotonic schemes in quantum optimal control
Authors: Salomon Julien , Turinici Gabriel
Published: February 2006

Numerical simulations of (bilinear) quantum control often rely on either monotonically convergent algorithms or tracking schemes. However, despite their mathematical simplicity, very limited intuitive understanding exists at this time to explain the former type of algorithms. Departing from the usual mathematical formalization, we present in this paper an interpretation of the monotonic algorithms as finite horizon, local in time, tracking schemes. Our purpose is not to present a new class of procedures but rather to introduce the necessary rigorous framework that supports this interpretation. As a by-product we show that at each instant, estimates of the future quality of the current control field are available and used in the optimization. When the target is expressed as reaching a prescribed final state, we also present an intuitive geometrical interpretation as the minimization of the distance between two correlated trajectories: one starting from the given initial state and the other backward in time from the target state. As an illustration, a stochastic monotonic algorithm is introduced. Numerical discretizations of the two procedures are also presented.
van der Waals forces between nanoclusters: Importance of many-body effects
Authors: Kim Hye-Young , Sofo Jorge O. , Velegol Darrell , Cole Milton W. , Lucas Amand A.
Published: February 2006

van der Waals interactions between nanoclusters have been calculated with a self-consistent, coupled dipole method. The method accounts for all many-body (MB) effects. Comparison is made between the exact potential energy, V, and the values obtained with two alternative methods: the sum of two-body interactions and the sum of two-body and three-body interactions. For all cases considered, the three-body term alone does not accurately represent the MB contributions to V. MB contributions are especially large for shape-anisotropic clusters.
Photonic-crystal GaN light-emitting diodes with tailored guided modes distribution
Authors: David Aurélien , Fujii Tetsuo , Sharma Rajat , McGroddy Kelly , Nakamura Shuji , DenBaars Steven P. , Hu Evelyn L. , Weisbuch Claude , Benisty Henri
Published: February 2006

We relate the currently limited efficiency of photonic crystal (PhC)-assisted gallium nitride light-emitting diodes (LEDs) to the existence of unextracted guided modes. To remedy this, we introduce epitaxial structures which modify the distribution of guided modes. LEDs are fabricated according to this concept, and the tailored band structure is determined experimentally. We investigate theoretically the consequences of this improvement, which significantly enhances the potential for efficient light extraction by PhCs.
One quarter million (500×500)pixel arrays of silicon microcavity plasma devices: Luminous efficacy above 6lumens∕watt with Ne/50% Xe mixtures and a green phosphor
Authors: Chen K.-F. , Ostrom N. P. , Park S.-J. , Eden J. G.
Published: February 2006

Arrays comprising 250 000 Si microcavity plasma devices, each with an emitting aperture of 50×50μm2 and tapered sidewalls (inverted pyramid cavity), have been fabricated in 100-mm (4″) diam. wafers and operated in the rare gases and Ar∕N2 mixtures with sinusoidal ac or bipolar dc excitation. Having an overall active area of 25cm2 and a 25% filling factor, these 500×500 arrays exhibit the pixel-to-pixel emission uniformity characteristics of arrays at least a factor of 6 smaller, and yet are efficient in generating vacuum ultraviolet (VUV) radiation. Luminous efficacies above 6lm∕W and luminance values approaching 2000cd∕m2 are measured when a 500×500 array, operating with a Ne/50% Xe gas mixture, illuminates a 20-μm-thick film of a commercial green phosphor (Mn:Zn2SiO4). Despite the nonoptimal transmission geometry of the array-phosphor structure, the efficacy and luminance produced by the VUV-driven phosphor for a Ne/50% Xe mixture and a total pressure of 800Torr are measured to be 7.2±0.6lm∕Watt and 525±75cd∕m2, respectively, for a 20-kHz sinusoidal ac voltage of ∼284V rms. Maximizing the luminous efficacy–luminance product lowers the optimal pressure of Ne/50% Xe mixtures to roughly 1atm. The magnitude of the radiant output generated by these arrays, in addition to the rapid rise in emitting efficiency with increased Xe content in Ne/10%–50% Xe mixtures, suggest that this microplasma array structure will be of value for both microdisplay and biomedical applications.
Mesoscopic electrical conduction in nanocrystalline SrTiO3
Authors: Balaya P. , Jamnik J. , Fleig J. , Maier J.
Published: February 2006

Detailed impedance analysis of dense nanocrystalline SrTiO3 ceramics in comparison to microcrystalline samples gives direct and unambiguous evidence of a space charge overlap as a characteristic size effect. Owing to the significant extension of depletion zones for the holes, the bulk impedance signal disappears at about 100 nm grain boundary spacing. In accordance with the increased homogeneity of this mesoscopic situation the remaining signal is characterized by a frequency dispersion of the circuit parameters that is low compared with the microcrystalline samples. Space charge potentials for various sizes are extracted. The conclusions are corroborated by numerical calculations.
Comparison of valence band x-ray photoelectron spectrum between Al–N-codoped and N-doped ZnO films
Authors: Cong G. W. , Peng W. Q. , Wei H. Y. , Han X. X. , Wu J. J. , Liu X. L. , Zhu Q. S. , Wang Z. G. , Lu J. G. , Ye Z. Z. , Zhu L. P. , Qian H. J. , Su R. , Hong C. H. , Zhong J. , Ibrahim K. , Hu T. D.
Published: February 2006

The valence band structures of Al–N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al–N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al–N increased the relative quantity of Zn–N in ZnO:(Al, N), while N–N decreased that of Zn–N in ZnO:N.
Nonlinear response of a superconducting filter to a wide band excitation
Authors: Salkola M. I.
Published: February 2006

Passive superconducting filters are inherently nonlinear devices that distort information-bearing signals and give rise to spectral broadening. Wide band signals efficiently probe both the causes and effects of filter nonlinearities. In particular, a coherent pulse may evaluate the power spectrum of a distortion signal and the nonlinear transmission coefficient in a single measurement. The nonlinear response depends on the bandwidth of the probing signal and implicitly on the data rate.
Multifunctional characteristics of BaNb0.3Ti0.7O3∕Si p-n junctions
Authors: Huang Yanhong , Zhao Kun , Lu Huibin , Jin Kui-juan , He Meng , Chen Zhenghao , Zhou Yueliang , Yang Guozhen
Published: February 2006

BaNb 0.3 Ti 0.7 O 3 ∕ Si  p-n junction combining the functional properties of oxide and Si electronics was fabricated by laser molecular-beam epitaxy, and the multifunctional properties of rectification, ferroelectricity and photoelectricity were experimentally studied. The good rectifying I-V characteristics, nanosecond ultrafast photoelectric effect, and ferroelectric property due to the interface enhancement were observed experimentally. The mechanisms of ferroelectric behavior and photoelectric process are discussed briefly.
Riemannian geometry of twisted magnetic flux tubes in almost helical plasma flows
Authors: Garcia de Andrade L. C.
Published: February 2006

Riemannian geometry of curves applied recently by Ricca [Fluid Dyn. Res 36, 319 (2005)] in the case of inflectional disequilibrium of twisted magnetic flux tubes is used here to compute the magnetic helicity force-free field case. Here the application of Lorentz force-free to the magnetic flux tube in tokamaks allows one to obtain an equation that generalizes the cylindrical tokamak equation by a term that contains the curvature of the magnetic flux tube. Another example of the use of the magnetic flux tube is done by taking the electron magnetohydrodynamics (MHD) fluid model (EMHD) of plasma physics that allows one to compute the velocity of the fluid in helical and almost helical flows in terms of the Frenet torsion of thin magnetic flux tubes. The cases of straight and curved twisted tubes are examined. Second-order effects on the Frenet torsion arise on the poloidal component of the magnetic field, while curvature effects appear in the toroidal component. The magnetic fields are computed in terms of the penetration depth used in superconductors. The ratio between poloidal and toroidal components of the magnetic field depends on the torsion and curvature of the magnetic flux tube. It is shown that the rotation of the almost helical plasma flow contributes to the twist of the magnetic flux tube through the total Frenet torsion along the tube.
Pyramidal micromirrors for microsystems and atom chips
Authors: Trupke M. , Ramirez-Martinez F. , Curtis E. A. , Ashmore J. P. , Eriksson S. , Hinds E. A. , Moktadir Z. , Gollasch C. , Kraft M. , Vijaya Prakash G. , Baumberg J. J.
Published: February 2006

Concave pyramids are created in the (100) surface of a silicon wafer by anisotropic etching in potassium hydroxide. High quality micromirrors are then formed by sputtering gold onto the smooth silicon (111) faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into micro-optoelectromechanical systems and atom chips. We have shown that structures of this shape can be used to laser-cool and hold atoms in a magneto-optical trap.
In
As
P
∕
In
Ga
As
composite quantum well for separate TE and TM gain
Authors: Prasanth R. , Haverkort J. E. M. , Wolter J. H.
Published: February 2006

Composite InAsP∕InGaAs quantum wells are a promising candidate for realizing polarization-independent semiconductor optical amplifiers at 1.55μm. We investigated the possibility of 8nm tensile-strained InGaAs well surrounded by two compressively-strained InAsP layers, for achieving separate gain for TE and TM polarized light. The InAsP layers provide strain compensation while simultaneously shifting the band gap to 1.55μm. The edge photoluminescence spectra shows that the gain for TE and TM polarized light is in the order of (3:1).
Formation of octahedral FePt nanoparticles by alternate deposition of FePt and MgO
Authors: Shima T. , Takanashi K. , Takahashi Y. K. , Hono K.
Published: February 2006

Two-dimensional assemblies of octahedral-shaped FePt nanoparticles embedded in a MgO matrix were formed by alternate deposition of FePt and MgO layers on MgO (001) single-crystal substrates with a thermal cycling process. Highly ordered L10 structure with the [001] orientation perpendicular to the plane and large coercivity of more than 60kOe were obtained. Cross-sectional transmission electron microscopy observation revealed that the equilibrium crystal shape of L10 ordered FePt particles was octahedral structure due to the anisotropy of the surface energy. The {111} plane shows the minimum surface energy in the L10 structure, which is similar to the case of face-centered-cubic structure.
Efficient light harvesting in multiple-device stacked structure for polymer solar cells
Authors: Shrotriya Vishal , Wu Elbert Hsing-En , Li Gang , Yao Yan , Yang Yang
Published: February 2006

We demonstrate a multiple-device stacked structure of polymer solar cells for efficient light harvesting. Two polymer photovoltaic cells are stacked together and connected in series or in parallel to achieve a tandem structure. In this two-cell structure, a multilayer semitransparent electrode, made of lithium fluoride (LiF)/aluminum (Al)/gold (Au), is used as the top contact in the bottom cell to efficiently transmit the unabsorbed photons to the upper cell. Maximum transparency of up to 80% is achieved for the semitransparent cathode. Upon stacking, the open-circuit voltage and the short-circuit current are almost doubled compared to a single cell.
Dopant source choice for formation of p-type ZnO: Li acceptor
Authors: Zeng Y. J. , Ye Z. Z. , Xu W. Z. , Li D. Y. , Lu J. G. , Zhu L. P. , Zhao B. H.
Published: February 2006

Li-doped, p-type ZnO thin films have been realized via dc reactive magnetron sputtering. An optimized result with a resistivity of 16.4Ωcm, Hall mobility of 2.65cm2∕Vs, and hole concentration of 1.44×1017cm−3 was achieved, and electrically stable over a month. Hall-effect measurements supported by secondary ion mass spectroscopy indicated that the substrate temperature played a key role in optimizing the p-type conduction of Li-doped ZnO thin films. Furthermore, ZnO-based p-n homojunction was fabricated by deposition of a Li-doped p-type ZnO layer on an Al-doped n-type ZnO layer.
Nonlinear theory of beam-wave interaction in the pasotron with a phase-mixed electron beam
Authors: Bliokh Yu. P. , Nusinovich G. S.
Published: February 2006

The nonlinear theory describing the interaction processes in traveling-wave-amplifier (TWT) and backward-wave-oscillator (BWO) configurations of pasotrons is developed. It is shown that space charge forces in electron bunches formed in the process of beam-wave interaction in the pasotron play a role completely different from that in linear-beam devices with a strong magnetic focusing of electron beams. While in the latter devices the space charge forces limit the device efficiency due to saturation of the axial bunching, in the pasotron they do not destroy electron bunches but cause the radial expansion of them, which may increase device efficiency. The role of these forces is compared with the ion focusing and the radial electric field of the wave, and it is shown that, under certain conditions, it may dominate. The efficiency of the pasotron-TWT with a phase-mixed beam well focused at the entrance may exceed 50%. In the pasotron-BWO, the efficiency is lower (up to 26% in the case studied), but it can grow as the equivalent of the Pierce gain parameter increases.
Dedicated fabrication of silicon-based ensembles of dot molecules with a specific and unique number of dots
Authors: Hanke M. , Boeck T. , Gerlitzke A. -K. , Syrowatka F. , Heyroth F.
Published: February 2006

We have performed a two-step liquid phase epitaxy yielding ensembles of SiGe∕Si(001) dot molecules with a specific and unique number of dots. An undersaturation of the initial bismuth solution causes strain-induced pits in the epitaxial Si0.985Ge0.015 layer which are effectively preserved during subsequent Si0.68Ge0.32 dot growth at considerably lower temperatures. Since the latter process happens extremely close to thermodynamic equilibrium, we are able to interrupt it after the formation of ensembles of dimers, trimers or quadruplets, respectively. The crosslike ensemble symmetry is discussed in terms of strain energy distribution as revealed by finite element calculations.
Oriented barium hexaferrite thick films with narrow ferromagnetic resonance linewidth
Authors: Chen Yajie , Sakai Tomokazu , Chen Taiyang , Yoon Soack D. , Geiler Anton L. , Vittoria Carmine , Harris Vincent G.
Published: February 2006

Hexagonal BaFe12O19 ferrite films, having thicknesses ranging from 200–500μm, were prepared by a screen printing process followed by sintering heat treatments. Structural, magnetic, and microwave measurements confirmed that the polycrystalline films were suitable for applications in self-biasing microwave devices in that they exhibited a large remanence (4πMr=3800G), high hysteresis loop squareness (Mr∕Ms=0.96) and low microwave loss. A derivative linewidth ΔH of 310 Oe was measured at 55.6 GHz. This represents the lowest ΔH measured in polycrystalline hexaferrite materials. ΔH can be further improved by reducing porosity and improving the c-axis orientation of grains in polycrystalline ferrite.
Polarization-independent and fast-response phase modulators using double-layered liquid crystal gels
Authors: Ren Hongwen , Lin Yi-Hsin , Wu Shin-Tson
Published: February 2006

A polarization-independent phase modulator using two thin homogeneously stratified but orthogonally oriented liquid crystal (LC) gels is demonstrated. In addition to polarization independence and submillisecond response time, the LC gel possesses a much larger phase change and lower operating voltage than the nanosized polymer-dispersed liquid crystal. For a 16μm transmissive E48 LC gel, the phase shift exceeds 1π at λ=633nm with an electric field strength of ∼11Vrms∕μm. Potential applications of such a phase modulator for laser beam steering, microlens array, and switchable two- and three-dimensional LC displays are foreseeable.
Fabry–Perot effects in THz time-domain spectroscopy of plasmonic band-gap structures
Authors: Lee J. W. , Seo M. A. , Kim D. S. , Jeoung S. C. , Lienau Ch. , Kang J. H. , Park Q.-Han
Published: February 2006

Using terahertz time-domain spectroscopy, we study transmission in one-dimensional arrays of slits fabricated on metal plates by laser machining. The enhanced peaks of zero-order transmission spectra are attributed to the combined effects of Fabry–Perot and surface plasmon resonances. Angle dependence of transmission spectra shows that the strongly surface plasmon-enhanced peaks appear when the Fabry–Perot-type resonance is located nearby in energy. This means that surface waves traveling in the horizontal direction couple with nearest Fabry–Perot resonance to generate enhanced peaks. These results are in excellent agreement with theoretical calculations.