bluuebunny/crossref_metadata_2025 huggingface dataset:
Interrelations of mud volcanism, fluid venting, and thrust‐anticline folding: Examples from the external northern Apennines (Emilia‐Romagna, Italy)
Authors: Bonini Marco
Published: August 2007

The present work aims to provide an example of connection between fluid seepage and fault/fracture zones associated with compressional thrust folds. Surface fluid seepage along the Pede‐Apennine margin consists of mud volcanism and methane‐rich emissions showing an intimate link with thrust‐related folds. Dominant gaseous or CH4‐bearing fluid emissions characterize thrust fold settings in which fluid escape from the main reservoir and source rock (i.e., the Marnoso Arenacea flysch) is not impeded by a seal layer. Conversely, remarkable mud volcanism is closely linked to the presence of the impermeable Ligurian units sealing the Marnoso Arenacea reservoir. Structural analyses focused on selected thrust folds exhibiting clear relations between surface seepage and brittle elements associated with the fold. Various scenarios potentially explaining mud volcanism and venting over the crestal region of the thrust‐related folds are discussed with respect to fluid pressure state and the development of second‐order fault and fracture sets that are observed to control surface fluid expulsion. It is proposed that mud volcanism can be potentially triggered by first‐order fault failure cycles during which the overpressured fluid is released during faulting events. Past anomalous eruptions associated with strong earthquakes seem to support this hypothesis. The relatively quiescent but continuous activity of the current Pede‐Apennine mud volcanoes could instead reflect a short‐lived leakage of overpressured fluids along permeable fractures/faults. Expansion of methane contained in the rising mud may assist this process fundamentally.
Alkaline rocks and carbonatites of northwestern Russia and northern Norway: Linked Wilson cycle records extending over two billion years
Authors: Burke Kevin , Roberts David , Ashwal Lewis D.
Published: August 2007

Tectonic analysis reveals a previously unidentified link between alkaline rocks and carbonatites (ARCs) forming the Kola Alkaline and Carbonatite Province (KACP) in Arctic Russia, and ARCs of the Seiland Igneous Province (SIP), in the northern Caledonides of Finnmark, Norway. We here conclude that the rocks of the two provinces have been derived by decompression melting of deformed alkaline rocks and carbonatites (DARCs) under rifts and within the underlying lithospheric mantle preserved within the Paleoproterozoic Lapland‐Kola Suture Zone (LKSZ) and its extension beneath the allochthons of the Norwegian Caledonides. The LKSZ projects under the Caledonide allochthons to the postulated site of eruption of the ARCs of the SIP in an intra‐continental rift at a place where an ocean was soon to open. We suggest that the SIP ARCs formed in this intra‐continental rift by decompression melting involving DARCs that had lain in the underlying lithospheric mantle within the along‐strike extension of the LKSZ for more than one billion years. Thrusting and metamorphism during the Scandian collision between Laurentia and Baltica transformed the SIP ARCs into DARCs that occupy the immediate footwall to the suture zone between Laurentia and Baltica. At the collision, the SIP rocks were carried south‐southeastwards from their then location on the outermost continental margin of Baltica to their current location in the highest level of a sandstone‐dominated nappe complex. The ARCs and DARCs of Kola and Finnmark provide independent evidence of the operation of two complete Wilson cycles of the opening and the closing of oceans in the region.
Evaluation of sediment transport formulae and detachment parameters in eroding rills using PSEM_2D and the Water Erosion Prediction Project (WEPP) database
Authors: Nord Guillaume , Esteves Michel
Published: August 2007

The numerical model PSEM_2D is applied to reproduce the rill experiments described by Elliot et al. (1989) for five different textured soils. PSEM_2D is a two‐dimensional water flow and erosion model incorporating the first‐order detachment‐transport coupling model. The infiltration parameters and the friction factor are calibrated to reproduce both the flow discharges and the flow velocities measured by Elliot et al. (1989). Values of the determined friction factors are higher for the cohesive soils compared to the noncohesive soils. Four sediment transport capacity formulae for rills are tested: the Yalin, the Low, the unit stream power (Govers USP), and the effective stream power (Govers ESP) equations. These equations do not require any calibration. The erosion parameters for the first‐order detachment‐transport coupling model come from the Water Erosion Prediction Project (WEPP) database. They were calibrated by Elliot et al. (1989) using observed data and the rill component of WEPP. The Govers USP formula gives the best results for the cohesive soils. Nevertheless, none of the equations performs well for the noncohesive soils. The study also focuses on the results obtained for the Barnes_ND, the Bonifay, and the Collamer soils to explore the implication of the detachment‐transport coupling model on the spatial erosion patterns along the rills. A detachment‐limiting regime is produced over the whole rill for the Barnes_ND soil, a transport‐limiting regime is reached over a very short flow distance for the Bonifay soil, and a detachment‐limiting regime in the upper part along with a transport‐limiting regime in the lower part of the rills is experienced for the Collamer soil.
Detectability of day‐to‐day variability in the evaporative flux ratio: A field examination in the Loess Plateau of China
Authors: Liu Yuanbo , Hiyama Tetsuya
Published: August 2007

The ratio of latent heat flux to available energy, termed the evaporative fraction (EF), and the ratio of latent heat flux to downward shortwave radiation (ES), are two useful evaporative flux ratios (EFR) for estimating daily evaporation. Both EF and ES remain relatively constant during daytime, but their value varies from day to day. It is yet unclear if long‐term change signals are detectable given the uncertainty associated with the diurnal variations. Using EF and ES data obtained during the major rainy seasons on a tableland of the Loess Plateau of China, we showed that day‐to‐day variability in the EF or ES was detectable given diurnal variation. The EF and ES showed slight increasing trends from midmorning to afternoon, but the ES was superior to the EF for satellite‐based monitoring of long‐term evaporation trends.
An empirical estimate of the Southern Ocean air‐sea CO2 flux
Authors: McNeil Ben I. , Metzl Nicolas , Key Robert M. , Matear Richard J. , Corbiere Antoine
Published: August 2007

Despite improvements in our understanding of the Southern Ocean air‐sea flux of CO2, discrepancies still exist between a variety of differing ocean/atmosphere methodologies. Here we employ an independent method to estimate the Southern Ocean air‐sea flux of CO2 that exploits all available surface ocean measurements for dissolved inorganic carbon (DIC) and total alkalinity (ALK) beyond 1986. The DIC concentrations were normalized to the year 1995 using coinciding CFC measurements in order to account for the anthropogenic CO2 signal. We show that independent of season, surface‐normalized DIC and ALK can be empirically predicted to within ∼8 μmol/kg using standard hydrographic properties. The predictive equations were used in conjunction with World Ocean Atlas (2001) climatologies to give a first estimate of the annual cycle of DIC and ALK in the surface Southern Ocean. These seasonal distributions will be very useful in both validating biogeochemistry in general circulation models and for use in situ biological studies within the Southern Ocean. Using optimal CO2 dissociation constants, we then estimate an annual cycle of pCO2 and associated net air‐sea CO2 flux. Including the effects of sea ice, we estimate a Southern Ocean (>50°S) CO2 sink of 0.4 ± 0.25 Pg C/yr. Our analysis also indicates a substantial CO2 sink of 1.1 ± 0.6 Pg C/yr within the sub‐Antarctic zone (40°S–50°S), associated with strong cooling and high winds. Our results imply the Southern Ocean CO2 flux south of 50°S to be very similar to those found by Takahashi et al. (2002), but on the higher end of a range of atmospheric/oceanic CO2 inversion methodologies. This paper estimates for the first time basic seasonal carbon cycle parameters within the circumpolar Southern Ocean, which have up to now been extremely difficult to measure and sparse. The application of such an empirical technique using more widely available hydrographic parameters in the Southern Ocean provides an important independent estimate to not only CO2 uptake, but also for other future biogeochemical studies. Refining and testing these empirical methods with new carbon measurements will be important to further reduce uncertainties and extend our understanding of Southern Ocean CO2 dynamics.
How ENSO impacts precipitation in southwest central Asia
Authors: Mariotti Annarita
Published: August 2007

A linkage between ENSO and the hydroclimatic variability of the southwest central Asia region (SWCA) is established through observational analysis of precipitation, moisture flux and sea level pressure data, with further support from an atmospheric model of intermediate complexity. Enhanced precipitation in SWCA during warm ENSO events results from an anomalous southwesterly moisture flux coming from the Arabian Sea and tropical Africa, which is generated along the northwestern flank of the high pressure anomaly over the Indian and western Pacific Oceans, part of the canonical ENSO sea‐saw pressure anomalies. The ENSO impact on SWCA precipitation is found to be greatest in the transition seasons of autumn and spring, but the dynamical impact on pressure and circulation persists throughout the year. This connection was particularly strong in recent decades. Model sensitivity experiments further show that this is driven primarily by tropical Pacific SST anomalies and associated large‐scale sea‐level pressure changes, while the Indian Ocean SST has opposite effects.
Evidence for interhemispheric stratosphere‐mesosphere coupling derived from noctilucent cloud properties
Authors: Karlsson B. , Körnich H. , Gumbel J.
Published: August 2007

We investigate the link between the cold summer mesopause region and the dynamics in the stratosphere. In particular, we use Odin observations of noctilucent cloud (NLC) properties as a proxy for the state of the summer mesosphere and ECMWF winter stratospheric temperatures as a proxy for the residual circulation in the stratosphere. Large areas of strong anticorrelation between winter stratospheric temperature and summer mesospheric NLC indicate that there is an interhemispheric connection. Time‐lagged cross correlation shows that the wave activity flux at 100 hPa leads the NLC response by several weeks. The presented findings are consistent with recent model studies where the modulation of the mesospheric gravity wave drag by the stratospheric planetary waves yields an interhemispheric stratosphere‐mesosphere coupling.
Review of aerosol mass scattering efficiencies from ground‐based measurements since 1990
Authors: Hand J. L. , Malm W. C.
Published: August 2007

We performed a survey of ground‐based estimates of aerosol mass scattering efficiencies (αsp, m2 g−1) for various aerosol species and size modes from peer‐reviewed literature published since 1990. Accurate estimates of αsp are important in aerosol modules of global circulation and chemical transport models to compute radiative forcing effects of aerosols and in chemical extinction budgets used for visibility regulatory purposes. The variety of techniques used to compute αsp can be categorized into four basic methods. We separate reported αsp on the basis of the methods used to derive them and normalize estimates of αsp to a common dry relative humidity (RH, RH ≈ 0%) and mass composition basis, removing some of the variability inherent in αsp reported under different monitoring conditions. The values of αsp reviewed here represent common aerosol species and correspond to data from a variety of time periods and global locations. For the 60 studies reviewed, the average (and one standard deviation) αsp (at visible wavelengths) for fine mode dry ammonium sulfate and dry ammonium nitrate are 2.5 ± 0.6 m2 g−1 and 2.7 ± 0.5 m2 g−1, respectively. The fine mode particulate organic matter αsp is 3.9 ± 1.5 m2 g−1. The fine mode dust αsp is 3.3 ± 0.6 m2 g−1and the fine mode dry sea salt αsp is 4.5 ± 0.9 m2 g−1. Coarse mode αsp estimates are also reported. The range of αsp may reflect differences in aerosol morphology, age, physicochemical properties and mixing state; however, this survey suggests that the type of method used to derive αsp can contribute considerably to the variability observed.
Inverting ionospheric radio occultation measurements using maximum entropy
Authors: Hysell D. L.
Published: August 2007

Practical aspects of the inversion of ionospheric radio occultation data using the Abel transform and its inverse are discussed. The linear inverse transform exhibits poor error propagation characteristics, producing significant artifacts preferentially at low altitudes where they might easily be mistaken for intermediate or sporadic layers in the ionosphere. Tikhonov regularization, which can be viewed as fixed linear filtering, reduces the artifacts at the expense of discarding fine structure in the profiles. Improved results are obtained using maximum entropy and Bayesian statistics. The maximum entropy algorithm can be viewed as a nonlinear adaptive filter which suppresses artifacts while preserving fine structure to the degree the data can support. Other advantages of and avenues for improving the basic maximum entropy algorithm are discussed.
Variation in susceptibility of grapevine pruning wound to infection by Eutypa lata in south‐western France
Authors: Chapuis L. , Richard L. , Dubos B.
Published: August 2007

Grapevine cultivars Cabernet Sauvignon (susceptible to Eutypa dieback), and Merlot (tolerant), were pruned three times during the dormant season (mid‐December, mid‐January and mid‐February) and wounds on the 1‐year‐old canes were inoculated weekly with ascospores of Eutypa lata after pruning. No differences in susceptibility to infection were observed between cultivars, although in the vineyard they differed in symptom expression. Infection by E. lata varied with pruning date and the age of the pruning wound, and was higher and of longer duration with early pruning (December). At low temperature, infection of the pruning wounds by E. lata was increased, whereas the growth of other microorganisms was reduced. Moderate temperatures encouraged the growth of other microorganisms, notably Rhodotorula sp. This natural colonizer of grapevine pruning wounds was able to reduce the infection capacity of E. lata. It was more effective when inoculation with E. lata was carried out with low numbers of ascospores and when it was delayed until 14 days after application of the wound colonizer, infection being reduced by 95–100%.
Evolution of Phytophthora infestans populations in the two most important potato production areas of France during 1992–96
Authors: Lebreton L. , Laurent C. , Andrivon D.
Published: August 2007

Phytophthora infestans isolates, collected in the two most important potato production regions of France (Brittany during 1992–96 and northern France during 1994–96), were analysed for mating type, Gpi and Pep allozyme genotypes, mitochondrial DNA haplotypes, response to metalaxyl and virulence patterns in order to determine the structure of populations. ‘New’ populations, similar to those observed in northern Europe and characterized by the presence of both mating types, Gpi 90/100 Pep 83/100, Gpi 90/100 Pep 100/100, Gpi 100/100 Pep 100/100 and Gpi 100/100 Pep 83/100 allozyme genotypes, Ia and IIa mitochondrial haplotypes and common races 1.3.4.7, 1.4.10.11, 1.3.4.7.11 and 1.3.4.7.10.11 were present in both areas. A new allozyme genotype (Gpi 90/90 Pep 83/100), never previously detected in Europe, was discovered in Brittany in 1992, but disappeared in later years. Despite the appearance of the A2 mating type in Brittany in 1996 and in northern France since 1995, both populations were highly homogeneous and probably consisted of a few related clones. No evidence for sexual recombination was obtained. Although Brittany, isolated from other potato production areas, and northern France, situated close to north European production areas where the A2 mating type was discovered some years ago, are two contrasted regions, no geographic substructuring was apparent between the two regions. However, variations in genotypic frequencies and in race composition were observed from one year to the next at a single site, as well as between several local sites during the same year. The role of possible evolutionary mechanisms implicated in these evolutions, especially founder effects, is discussed.
Local fields for asymptotic matching in multidimensional mode conversion
Authors: Tracy E. R. , Kaufman A. N. , Jaun A.
Published: August 2007

The problem of resonant mode conversion in multiple spatial dimensions is considered. Using phase space methods, a complete theory is developed for constructing matched asymptotic expansions that fit incoming and outgoing WKB solutions. These results provide, for the first time, a complete and practical method for including multidimensional conversion in ray tracing algorithms. The paper provides a self-contained description of the following topics: (1) how to use eikonal (also known as ray tracing or WKB) methods to solve vector wave equations and how to detect conversion regions while following rays; (2) once conversion is detected, how to fit to a generic saddle structure in ray phase space associated with the most common type of conversion; (3) given the saddle structure, how to carry out a local projection of the full vector wave equation onto a local two-component normal form that governs the two resonantly interacting waves. This determines both the uncoupled dispersion functions and the coupling constant, which in turn determine the uncoupled WKB solutions; (4) given the normal form of the local two-component wave equation, how to find the particular solution that matches the amplitude, phase, and polarization of the incoming ray, to the amplitude, phase, and polarization of the two outgoing rays: the transmitted and converted rays.
Collisionless magnetohydrodynamics with gyrokinetic effects
Authors: Passot T. , Sulem P. L.
Published: August 2007

Anisotropic magnetohydrodynamics equations, which also capture the dynamics of quasi-transverse small scales obeying the gyrokinetic ordering, are derived using fourth-rank moment closures, based on a refined description of linear Landau damping and finite Larmor radius (FLR) corrections. This “FLR-Landau fluid model” reproduces the dispersion relation of low-frequency waves, up to scales that, in the case of quasi-transverse kinetic Alfvén waves, can be much smaller than the ion gyroradius. The mirror instability, which requires temperature anisotropy, is also captured, together with its quenching at small scales. This model that accurately reproduces the collisionless dissipation of low-frequency modes, should provide an efficient tool to simulate mesoscale turbulence in a magnetized collisionless plasma.
Oxygen vacancy formation energy in Pd-doped ceria: A DFT+U study
Authors: Yang Zongxian , Luo Gaixia , Lu Zhansheng , Hermansson Kersti
Published: August 2007

Using the DFT+U method, i.e., first principles density functional theory calculations with the inclusion of on-site Coulomb interaction, the effects of Pd doping on the O vacancy formation energy (Evac) in CeO2 has been studied. We find that Evac is lowered from 3.0eV in undoped ceria to 0.6eV in the Pd-doped compound. Much of this decrease can be attributed to emerging Pd-induced gap states above the valence band and below the empty Ce 4f states. These localized defect states involve the Pd ion and its nearest neighbors, which are also the main acceptors of the extra electrons left on reduction. The effect of the Pd dopant on the geometric structure is very modest for CeO2 but considerable for CeO2−x.
A drift model of interchange instability
Authors: Benilov E. S. , Power O. A.
Published: August 2007

A set of asymptotic equations is derived, describing the dynamics of the flute mode in a magnetized plasma with cold ions, under a “local” approximation (i.e., near a particular point). The asymptotic set is then used to calculate the growth rate of interchange instability in the slab model. It is shown that, unlike the magnetohydrodynamic ordering, the drift one allows instability to occur for either sign of the pressure gradient (i.e., for both “bad” and “good” curvature of the magnetic field). It is also demonstrated that finite beta gives rise to an extra instability that does not exist in the small-beta limit.
Formation of tripolar vortices in toroidal ion-temperature-gradient driven modes in the presence of dust contamination
Authors: Mirza Arshad M. , Qamar Anisa , Khan M. Yaqub , Ayub M.
Published: August 2007

A system of nonlinear equations that governs the dynamics of toroidal-ion-temperature-gradient (TITG) driven modes in the presence of dust contamination is presented. In the linear limit, a local dispersion relation is derived and analyzed for a flat density profile case. In the nonlinear case, and by taking some specific profiles of equilibrium density, ion temperature, magnetic field, and sheared plasma flows, the stationary solutions of the nonlinear system can be represented in the form of a tripolar vortex solution. Numerical results obtained in the present study show that the inclusion of dust modifies the nonlinear vortical structures, and the amplitude of the normalized potential is found to be increased in the presence of negatively charged dust grains. The results of our present investigation would be useful to understand some linear as well as nonlinear properties of TITG modes in a dust-contaminated tokamak plasma.
A study of the ionic conduction of mica surface by admittance spectroscopy
Authors: Dolci D. , Aloisi G. , Lanzi L. , Carlà M.
Published: August 2007

The ionic conduction on the surface of humid mica has been analyzed by admittance spectroscopy as a function of relative humidity for different surface treatments. Measurements at low frequency indicate that water adsorption proceeds first in the form of a strongly adsorbed uniform thin layer, then with the formation of highly inhomogeneous thick aggregates.
Experimental investigation of mu negative of Bragg gap in one-dimensional composite right/left-handed transmission line
Authors: Li Haiyang , Zhang Yewen , Zhang Liwei , He Li , Li Hongqiang , Chen Hong
Published: August 2007

An experimental demonstration of mu negative of the Bragg gap in a one-dimensional composite right/left-handed transmission line (CRLH-TL) is presented. In this structure, a band gap which is independent of the scale length and is insensitive to disorder may be mu negative (MNG) or epsilon negative, depending on the value of loading lumped-element components. Another band gap, which is induced by Bragg scattering, depends on the scale length and is sensitive to disorder of the structure of transmission line. As far as CRLH-TL is concerned, it is shown that the Bragg gap can be considered as a single negative gap, furthermore, it is always a MNG gap no matter what the gap between left-handed passband and right-handed passband is a mu-negative gap or an epsilon-negative gap.
Interactions between glide dislocations and parallel interfacial dislocations in nanoscale strained layers
Authors: Akasheh F. , Zbib H. M. , Hirth J. P. , Hoagland R. G. , Misra A.
Published: August 2007

Plastic deformation in nanoscale multilayered structures is thought to proceed by the successive propagation of single dislocation loops at the interfaces. Based on this view, we simulate the effect of predeposited interfacial dislocation on the stress (channeling stress) needed to propagate a new loop parallel to existing loops. Single interfacial dislocations as well as finite parallel arrays are considered in the computation. When the gliding dislocation and the predeposited interfacial array have collinear Burgers vectors, the channeling stress increases monotonically as the density of dislocations in the array increases. In the case when their Burgers vectors are inclined at 60°, a regime of perfect plasticity is observed which can be traced back to an instability in the flow stress arising from the interaction between the glide dislocation and a single interfacial dislocation dipole. This interaction leads to a tendency for dislocations of alternating Burgers vectors to propagate during deformation leading to nonuniform arrays. Inclusion of these parallel interactions in the analysis improves the strength predictions as compared with the measured strength of a Cu-Ni multilayered system in the regime where isolated glide dislocation motion controls flow, but does not help to explain the observed strength saturation when the individual layer thickness is in the few nanometer range.
Solution of the master equation for Wigner’s quasiprobability distribution in phase space for the Brownian motion of a particle in a double well potential
Authors: Coffey William T. , Kalmykov Yuri P. , Titov Serguey V.
Published: August 2007

Quantum effects in the Brownian motion of a particle in the symmetric double well potential V(x)=ax2∕2+bx4∕4 are treated using the semiclassical master equation for the time evolution of the Wigner distribution function W(x,p,t) in phase space (x,p). The equilibrium position autocorrelation function, dynamic susceptibility, and escape rate are evaluated via matrix continued fractions in the manner customarily used for the classical Fokker-Planck equation. The escape rate so yielded has a quantum correction depending strongly on the barrier height and is compared with that given analytically by the quantum mechanical reaction rate solution of the Kramers turnover problem. The matrix continued fraction solution substantially agrees with the analytic solution. Moreover, the low-frequency part of the spectrum associated with noise assisted Kramers transitions across the potential barrier may be accurately described by a single Lorentzian with characteristic frequency given by the quantum mechanical reaction rate.
Spectroscopic characterization of femtosecond laser filament in argon gas
Authors: Liu W. , Bernhardt J. , Théberge F. , Chin S. L. , Châteauneuf M. , Dubois J.
Published: August 2007

We report a spectroscopic approach to measure the plasma density and electron temperature inside a filament created by an intense femtosecond laser pulse in atmospheric pressure argon gas. The technique relies on the proportionality between the Stark broadened argon fluorescence line width due to electron impact and the plasma density, while the electron temperature is determined from the well known Boltzmann plot. The obtained maximum plasma density is about 5.5×1016 cm−3, and the electron temperature is about 5800 K. Our method provides a promising and convenient way to characterize the filament for further understanding the fundamental physics and potential applications of filamentation.
Vacuum-ultraviolet spectroscopy measurement of poly(methylphenylsilylene) photosensitivity
Authors: Chandra H. , Potter B. G. , Jamison G. M. , Thomes W. J.
Published: August 2007

Photoinduced optical absorption changes in the vacuum-ultraviolet (VUV) spectral range have been measured in poly(methylphenylsilylene) thin films under varied excitation photon energies and local atmospheric environments. Spectral changes in resonances associated with both the linear chain Si–Si backbone and the side groups of the hybrid structure are consistent with the photodisruption of backbone topology. These effects are more pronounced under a higher energy photon exposure (5.10eV) resonant with the fundamental π-π* transition of the phenyl moiety. An aerobic environment also favors more dramatic bleaching of VUV absorption in these materials. Finally, the present study enables a Kramers-Kronig analysis of absorption change from the visible to the VUV. These results do not adequately describe the photoinduced refractive index changes measured at 632.8nm via ellipsometry, indicating the presence of other contributions to the index modifications observed.
Strain distributions and electronic subband energies of self-assembled CdTe quantum wires grown on ZnTe buffer layers
Authors: Woo J. T. , Song S. H. , Lee I. , Kim T. W. , Yoo K. H. , Lee H. S. , Park H. L.
Published: August 2007

The structural properties and the shape of self-assembled CdTe/ZnTe quantum wires (QWRs) grown by using molecular beam epitaxy and atomic layer epitaxy were determined by using atomic force microscopy (AFM) measurements, and the interband transitions in the CdTe/ZnTe QWRs were investigated by using temperature-dependent photoluminescence (PL) measurements. The shape of the CdTe/ZnTe QWRs on the basis of the AFM image was modeled to be a half-ellipsoidal cylinder approximately. The temperature-dependent PL spectra showed that the PL peaks corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band (E1-HH1) shifted to lower energy with increasing temperature. Strain distributions and electronic subband energies at several temperatures were numerically calculated by using a finite-difference method (FDM) with and without taking into account shape-based strain and nonparabolicity effects. The excitonic peak corresponding to (E1-HH1) interband transitions, as determined from the PL spectra, was in reasonable agreement with that corresponding to the (E1-HH1) transitions obtained, as determined from the FDM calculations taking into account shape-based strain and nonparabolicity effects. The present results help improve understanding of the electronic structures of CdTe/ZnTe QWRs.
Elastic stability and the onset of plastic flow in accelerated solid plates
Authors: Terrones Guillermo
Published: August 2007

For accelerated incompressible, ideal elastoplastic plates of finite thickness with a preformed sinusoidal perturbation at the interface, we investigate the stability behavior encompassing neutral and most-unstable modes, stable oscillatory modes, and the onset of plastic flow. We show that the largest perturbation wavelength that can maximize the growth rate corresponds to a finite thickness plate. For elastically stable configurations, stress gradients that arise as a result of the interfacial disturbance can lead to the formation of counter-rotating particle displacement trajectories that tessellate the extent of the plate. By computing the spatiotemporal evolution of the stress tensor, we are able to construct the boundaries that demarcate the transition from elastically stable oscillatory modes to the onset of plastic flow based on the von Mises yield criterion. Earlier estimates of these boundaries for thick plates differ qualitatively and quantitatively from the present results, in which the common simplifying assumptions of thin-plate theory were not invoked. We show that multimodal solutions are necessary to accurately represent the actual oscillatory behavior of the stress tensor, which in general is not time periodic, that thin-plate bimodal solutions are unable to capture.
Structure and thermodynamics of a two-dimensional Coulomb fluid in the strong association regime
Authors: Lomba E. , Weis J. J. , Lado F.
Published: August 2007

The behavior of a two-dimensional neutral Coulomb fluid in the strong association regime (low density, high ionic charge) is explored by means of computer simulation and the hypernetted chain integral equation. The theory reproduces reasonably well the structure and thermodynamics of the system but presents a no-solution region at temperatures well above the computer simulation estimates of the metal-insulator transition. In contrast with hypernetted chain predictions for the three-dimensional Coulomb fluid, here the breakdown of the solution is not accompanied by divergences in any physical quantity.
Landau model of the RII-RI-RV rotator phases in mixtures of alkanes
Authors: Mukherjee Prabir K.
Published: August 2007

A phenomenological approach to the description of the rotator phases and transitions among them in mixtures of normal alkanes is proposed. The mixture exhibits crystal and three different rotator phases RII, RI, and RV. The two phase regions are formed where the crystal+rotator and rotator+rotator phases coexist. The reason of these two phase regions is discussed by means of the Landau formalism. The influence of the concentration on these transitions and the transition temperatures are discussed by varying the coupling between the concentration variable and the order parameters. The theoretical predictions are found to be in good qualitative agreement with the experimental results.
Effects of chirality and diameter on the transport properties of semiconducting carbon nanotubes
Authors: Kauser M. Z. , Ruden P. P.
Published: August 2007

The effects of chirality and diameter on the electron transport properties of semiconducting, single wall, carbon nanotubes are explored by the Ensemble Monte Carlo method and an iterative solution of the Boltzmann’s transport equation. The results show that the effect of chirality is significant for small diameter tubes and becomes negligible at large diameters. The two zigzag carbon nanotube groups (+1 and −1) set upper and lower bounds for important low- and high-field transport parameters. This trend can be attributed to the band structure, especially to the effective mass of the lowest subband. The effect of diameter on the transport properties is stronger than those of chirality and group.
Delayed failure of the shock compressed inhomogeneous brittle material
Authors: Chen Dengping , He Hongliang , Jing Fuqian
Published: August 2007

Inhomogeneous brittle material contains numerous preexisting microcracks and under the shock wave compression they could be activated and grow due to the shear stress effect. This failure property has been studied in this work by using amphibolized olivine websterite (AOW) rock as a representative candidate for the inhomogeneous brittle materials. At stresses much below the Hugoniot elastic limit, the AOW rock specimens have been shock compressed with the impact from a thick copper plate, and the velocity histories at the rear surface of the specimens have been measured. A delayed failure zone has been detected. It expands into the stressed material with a velocity comparable to the shock wave front, and follows the propagation of the shock wave with a time delay that decreases with the increase of shock stress. The time delay is 1.2 μs at shock stress of 0.9±0.2 GPa and 0.5 μs at 3.7±0.2 GPa. A physical explanation considering the in situ activation and growth of the preexisting microcracks by the local shear stress under shock compression is proposed for these observations. The results provide a further understanding for the dynamic fracture of inhomogeneous brittle materials under the shock wave loadings.
The influence of magnetic dilution in the Zn1−xMnxGa2Se4 series with 0.5<x⩽1
Authors: Morón M. C. , Hull S.
Published: August 2007

The Zn1−xMnxGa2Se4 system with 0.5<x<1, which represents a magnetic dilution of the tetragonal MnGa2Se4, retains the defective chalcopyrite structure of the parent compound. Neutron powder diffraction experiments and temperature dependent magnetic susceptibility measurements show that such dilution has a significant influence on the magnetic properties of the system. The distance between the closest magnetic atoms decreases from a to a∕2Å (where a is the lattice parameter and a≈5.6Å), making the Curie-Weiss temperature greater than the expected value. The magnetic dilution also decreases the internal distortion, so that the structure becomes closer to that of the ideal zinc-blende arrangement. Although MnGa2Se4 behaves as an antiferromagnet below TC=6.4±0.1K, the magnetic properties of Zn1−xMnxGa2Se4 with 0.5<x<1 suggest a glassy type behavior at low temperatures. This magnetic behavior is found to be compatible with the distribution of the Mn ions within the lattice and can be tuned by tailoring the concentration of magnetic ions. Surprisingly, the magnetically undiluted system corresponding to the Zn1−xMnxGa2Se4 0.5<x<1 series is not MnGa2Se4, a magnetic lattice with a body centered cubic symmetry, but a structure possessing a greater number of sites available to the magnetic ions.
Ultralow drift in organic thin-film transistor chemical sensors by pulsed gating
Authors: Yang Richard D. , Park Jeongwon , Colesniuc Corneliu N. , Schuller Ivan K. , Trogler William C. , Kummel Andrew C.
Published: August 2007

A pulsed gating method has been developed to enhance the baseline stability of organic thin-film transistor (OTFT) chemical sensors. Trap states in the organic films are the major source of the OTFTs baseline drift under static gate bias, which is identified as the bias stress effect (BSE). BSE typically reduces the baseline current by 60% over 20h in phthalocyanine based OTFT sensors. The baseline drift has been reduced below 1% over 20h in the absence of the analyte using the pulsed gating method. With pulsed gating, the baseline drift on exposure to 15 methanol pulses is less than 0.09%∕h, and the response to this analyte is fully recoverable. Similar ultralow drift results were obtained for methanol sensing on three different phthalocyanine OTFTs. Combining the pulsed gating with low duty cycle analyte pulses, this method is also applicable to obtain ultralow drift (0.04%∕h) even for low vapor pressure analytes such as organophosphonate nerve agent simulants.
Quantifying cation grain boundary diffusion
Authors: Nychka J. A. , Clarke D. R. , Dryden J. R.
Published: August 2007

Evolution in the shape of grooves formed at grain boundaries at the air/aluminum oxide interface is analyzed for the case in which there is both diffusion along the oxide surface and oxidation-induced mass flow along grain boundaries of the already-formed oxide. The shape evolution is compared with atomic force microscope measurements of the groove profiles produced when thermally grown alumina on FeCrAl alloys is polished flat and reoxidized. A method of quantifying the grain boundary flux, based upon the shape of the surface profile, is presented.
Further remarks on super-resolving pupils
Authors: Mugnai D. , Ranfagni A.
Published: August 2007

A way to overcome the usual diffraction limit of an optical instrument was proposed in 1952 by Toraldo di Francia. This theoretical prediction was recently confirmed by recent microwave experiments. Further microwave investigations, using the same kinds of devices, provide the possibility of obtaining a significant concentration of the intensity also along the axial axis.
Landau-Ginzburg to Calabi-Yau dictionary for D-branes
Authors: Aspinwall Paul S.
Published: August 2007

Based on the work by Orlov (e-print arXiv:math.AG∕0503632), we give a precise recipe for mapping between B-type D-branes in a Landau-Ginzburg orbifold model (or Gepner model) and the corresponding large radius Calabi-Yau manifold. The D-branes in Landau-Ginzburg theories correspond to matrix factorizations and the D-branes on the Calabi-Yau manifolds are objects in the derived category. We give several examples including branes on quotient singularities associated with weighted projective spaces. We are able to confirm several conjectures and statements in the literature.
Anisotropic nonlinear response of silicon in the near-infrared region
Authors: Zhang J. , Lin Q. , Piredda G. , Boyd R. W. , Agrawal G. P. , Fauchet P. M.
Published: August 2007

The authors characterize experimentally the anisotropy of two-photon absorption and the Kerr nonlinearity in silicon over a broad spectral region in the near infrared using the z-scan technique. The results show that both of these parameters decrease by about 12% along the [0 1 0] direction compared with the [011¯] direction, and this change occurs for wavelengths in the range of 1.2–2.4μm.
High performance thyratron driver with low jitter
Authors: Verma Rishi , Lee P. , Springham S. V. , Tan T. L. , Rawat R. S.
Published: August 2007

We report the design and development of insulated gate bipolar junction transistor based high performance driver for operating thyratrons in grounded grid mode. With careful design, the driver meets the specification of trigger output pulse rise time less than 30ns, jitter less than ±1ns, and time delay less than 160ns. It produces a −600V pulse of 500ns duration (full width at half maximum) at repetition rate ranging from 1Hzto1.14kHz. The developed module also facilitates heating and biasing units along with protection circuitry in one complete package.
Negative refractivity assisted optical power limiting
Authors: Baev Alexander , Furlani Edward P. , Samoc Marek , Prasad Paras N.
Published: August 2007

We propose an approach for achieving optical power limiting (OPL) using planar multilayered media. The approach involves the use of multiple bilayer structures that consist of a negative index (NIM) layer followed by a nonlinear two-photon absorbing (TPA) layer. The NIM layers refocus light in the TPA layers to increase intensity and nonlinear absorption. We perform parametric two-dimensional finite difference time domain simulations and compute the power transmittance of the media as a function of the incident light intensity, the number of layers, the layer thickness, and the material properties. Our analysis demonstrates proof-of-concept and indicates that the TPA-based OPL can be enhanced and optimized using NIM focusing.
Simple analytical expression for electron temperature in an alternating current plasma display discharge
Authors: Muraoka K. , Suzuki K. , Azumi M. , Yamagata Y. , Yagi M.
Published: August 2007

A simple analytical expression was derived for electron temperature Te in discharge conditions typical for an alternating current plasma display panel discharge, in which the least possible number of parameters was introduced so as to provide good physical insight into the mechanisms of determining Te under various discharge conditions. From this derivation, an explicit dependence of Te on discharge parameters (gas composition and pressure, and the strength of the electric field E) has been derived. It was tested for a discharge condition studied in our previous article on the discharge-radiation dynamics, yielding reasonable values for a cathode fall and a positive column. Also, the values of Te obtained experimentally using laser Thomson scattering in a positive column are well predicted from this analysis.
Microstructural evolution and atomic transport by thermomigration in eutectic tin-lead flip chip solder joints
Authors: Yang Dan , Wu B. Y. , Chan Y. C. , Tu K. N.
Published: August 2007

The thermomigration behavior of eutectic tin-lead flip chip solder joints at an ambient temperature of 150 °C was investigated in terms of microstructural evolution, atomic transport, and numerical simulation. Pb accumulation and phase separation were observed in solder joints near a melting temperature after 50 h, which was supported by energy dispersive x-ray and element mapping analysis. It is believed that Pb atoms migrated from the chip side (the hot side) to the substrate side (the cold side) under a temperature gradient. Thermal electrical finite element simulation for the real flip chip test structure showed the existence of a temperature difference between the substrate side and the chip side. In addition, a temperature gradient above 1000 °C∕cm across the adjacent unpowered solder joints was predicted. This was also verified by temperature measurements with thermocouples. The atomic flux of Pb due to thermomigration was calculated here, which was agreeable with the values originally reported. Also, the driving force of thermomigration was estimated to be 10−17 N, even approaching the same order with that of electromigration under a current density of 104 A∕cm2.
Temperature-dependent behavior of Ni/4H-nSiC Schottky contacts
Authors: Aydın Mehmet Enver , Yıldırım Nezir , Türüt Abdulmecit
Published: August 2007

The current-voltage (I-V) characteristics of Ni/4H-nSiC Schottky diodes have been measured in the temperature range of 180–300 K with a temperature step of 20 K. An experimental barrier height (BH) Φap value of about 1.32 eV was obtained for the Ni/4H-nSiC Schottky diode at the 300 K. A decrease in the experimental BH Φap and an increase in the ideality factor n with a decrease in temperature have been explained on the basis of a thermionic emission mechanism with Gaussian distribution of the barrier heights due to the BH inhomogeneities at the metal-semiconductor interface. Φ¯b and A* as 1.71 eV, and 156.3 A/cm2 K2, respectively, have been calculated from a modified ln(I0/T2)−q2σs2/2k2T2 vs 1/T plot using the temperature-dependent experimental I-V characteristics of the Ni/4H-nSiC contact. The Richardson constant value of 156.3 A/cm2 K2 is in close agreement with 146 A/cm2 K2 known for 4H-nSiC.
Rotatable anisotropy in epitaxial exchange-biased materials revealed by Brillouin light scattering
Authors: Blachowicz T.
Published: August 2007

Rotatable anisotropy in exchange-biased CoO∕Co epitaxial films deposited on oriented single crystalline MgO(100) and MgO(110) substrates has been discussed. It has been shown that the rotatable anisotropy, usually observed in ferromagnetic resonance experiments in polycrystalline exchange-biased materials, can also be seen by Brillouin light scattering. Appropriate analysis on the basis of the second derivative of the free energy density for nonbiased and biased systems, i.e., in temperatures below and above the Néel temperature of CoO, has been performed. A quantitative measure of the rotatable anisotropy was proposed. It has been shown that the rotatable effect, being independent from in-plane orientations, can be tailored by different types of anisotropy fields expressed in terms of effective anisotropy constants.
Enhanced 1.5μm emission and simultaneously suppressed green upconversion emission in Er:LiNbO3 crystals heavily codoped with MgO
Authors: Sun Liang , Li Ai-Hua , Guo Feng-Yun , Lü Qiang , Xu Yu-Heng , Zhao Lian-Cheng
Published: August 2007

Enhanced 1.5μm emission and simultaneously suppressed green upconversion emission was observed for Er(1.0mol%):LiNbO3 crystals codoped with 8mol% MgO. The heavy MgO codoping results in the lengthening of the 1.5μm emission by 11.7%. Time-resolved spectroscopy study shows that the decay trace of the green upconversion emission of the Er∕Mg codoped crystal is obviously nonexponential. These spectroscopic characteristics are associated with the lower concentration of the cluster sites of Er3+ ion, the higher nonradiative energy transfer upconversion probability, and the lower OH− content in the crystal.
Controlled interface profile in Sm–Co∕Fe exchange-spring magnets
Authors: Choi Y. , Jiang J. S. , Pearson J. E. , Bader S. D. , Kavich J. J. , Freeland J. W. , Liu J. P.
Published: August 2007

In exchange-spring magnets with temperature-induced interfacial intermixing, differences in the extent of diffusion of constituent elements typically lead to local compositional changes. The authors demonstrate that adding an artificially created intermixed layer in Sm–Co∕Fe exchange-spring permanent magnets enhances the exchange coupling effectiveness without modifying the local composition of the Sm–Co layer. Element- and depth-resolved magnetization measurements verify that the diffusion extent of Sm and Co is similar across the interface.