bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent scatterer selection using maximum likelihood estimation
Authors: Shanker Piyush , Zebker Howard
Published: November 2007

We present here a new InSAR persistent scatterer selection method using maximum likelihood estimation to identify persistent scattering pixels, which results in a denser network of reliable phase measurements than do existing methods. We analyze the phase of each pixel in a series of interferograms and estimate the relative strength of any slowly fluctuating component of the radar echo from a dominant scatterer to the background scattering within a pixel. We find a fairly dense network of scatterers with stable phase characteristics in areas where conventional InSAR fails due to decorrelation. We examined data over two vegetated regions in the San Francisco Bay Area. The average phases of these pixels clearly show the slip along the Hayward fault, and set upper bounds on any slip along the Bay Area segment of the San Andreas fault.
Kinematic GPS solutions for aircraft trajectories: Identifying and minimizing systematic height errors associated with atmospheric propagation delays
Authors: Shan Shan , Bevis Michael , Kendrick Eric , Mader Gerald L. , Raleigh David , Hudnut Kenneth , Sartori Michael , Phillips David
Published: November 2007

When kinematic GPS processing software is used to estimate the trajectory of an aircraft, unless the delays imposed on the GPS signals by the atmosphere are either estimated or calibrated via external observations, then vertical height errors of decimeters can occur. This problem is clearly manifested when the aircraft is positioned against multiple base stations in areas of pronounced topography because the aircraft height solutions obtained using different base stations will tend to be mutually offset, or biased, in proportion to the elevation differences between the base stations. When performing kinematic surveys in areas with significant topography it should be standard procedure to use multiple base stations, and to separate them vertically to the maximum extent possible, since it will then be much easier to detect mis‐modeling of the atmosphere.
Recovery of atmospheric flow statistics in a general circulation model without nonlinear eddy‐eddy interactions
Authors: O'Gorman Paul A. , Schneider Tapio
Published: November 2007

The closure problem of turbulence arises because nonlinear interactions among turbulent fluctuations (eddies) lead to an infinite hierarchy of moment equations for flow statistics. Here we demonstrate with an idealized general circulation model (GCM) that many atmospheric flow statistics can already be recovered if the hierarchy of moment equations is truncated at second order, corresponding to the elimination of nonlinear eddy‐eddy interactions. Some, but not all, features of the general circulation remain the same. The atmospheric eddy kinetic energy spectrum retains a −3 power‐law range even though this is usually explained in terms of an enstrophy cascade mediated by nonlinear eddy‐eddy interactions. Our results suggest that it may be possible to construct fast general circulation models that solve for atmospheric flow statistics directly rather than via simulation of individual eddies and their interactions.
Radiation belt electron precipitation into the atmosphere: Recovery from a geomagnetic storm
Authors: Rodger Craig J. , Clilverd Mark A. , Thomson Neil R. , Gamble Rory J. , Seppälä Annika , Turunen Esa , Meredith Nigel P. , Parrot Michel , Sauvaud Jean‐André , Berthelier Jean‐Jacques
Published: November 2007

Large geomagnetic storms are associated with electron population changes in the outer radiation belt and the slot region, often leading to significant increases in the relativistic electron population. The increased population decays in part through the loss, that is, precipitation from the bounce loss cone, of highly energized electrons into the middle and upper atmosphere (30–90 km). However, direct satellite observations of energetic electrons in the bounce loss cone are very rare due to its small angular width. In this study we have analyzed ground‐based subionospheric radio wave observations of electrons from the bounce loss cone at L = 3.2 during and after a geomagnetic disturbance which occurred in September 2005. Relativistic electron precipitation into the atmosphere leads to large changes in observed subionospheric amplitudes. Satellite‐observed energy spectra from the CRRES and DEMETER spacecraft were used as an input to an ionospheric chemistry and subionospheric propagation model, describing the ionospheric ionization modifications caused by precipitating electrons. We find that the peak precipitated fluxes of >150 keV electrons into the atmosphere were 3500 ± 300 el cm−2 s−1 at midday and 185 ± 15 el cm−2 s−1 at midnight. For 6 d following the storm onset the midday precipitated fluxes are approximately 20 times larger than observed at midnight, consistent with observed day/night patterns of plasmaspheric hiss intensities. The variation in DEMETER observed wave power at L = 3.2 in the plasmaspheric hiss frequency band shows similar time variation to that seen in the precipitating particles. Consequently, plasmaspheric hiss with frequencies below ∼500 Hz appears to be the principal loss mechanism for energetic electrons in the inner zone of the outer radiation belts during the nonstorm time periods of this study, although off‐equatorial chorus waves could contribute when the plasmapause is L < 3.0.
Case for a new process, not mechanism, for cusp irregularity production
Authors: Carlson Herbert C. , Pedersen Todd , Basu Santimay , Keskinen Mike , Moen Jøran
Published: November 2007

Two plasma instability mechanisms are currently thought to dominate formation of plasma irregularities in the F region high‐latitude and polar ionosphere: the gradient‐drift driven instability and velocity‐shear driven instability. The former mechanism is accepted as accounting for structuring plasma in polar cap patches and the latter for structuring plasma in polar cap Sun‐aligned arcs. Recent work has established a dominant patch formation process, involving magnetic reconnection driving strong plasma shears repeatedly observed in the cusp. Proceeding from this, we present the case for a needed new plasma structuring process (not new mechanism), whereby shear‐driven instabilities first rapidly structure the entering plasma, after which gradient drift instabilities build on these large “seed” irregularities. Correct modeling of cusp and early polar cap patch structuring will not be accomplished without allowing for this compound process. This compound process also explains previously unexplained characteristics of cusp and early polar cap patch irregularities.
Crustal structure of the basin and ridge system west of New Caledonia (southwest Pacific) from wide‐angle and reflection seismic data
Authors: Klingelhoefer F. , Lafoy Y. , Collot J. , Cosquer E. , Géli L. , Nouzé H. , Vially R.
Published: November 2007

During the Zoneco 11 marine geophysical survey (September 2004), two deep reflection seismic profiles recorded by ocean bottom seismometers were acquired in the offshore domain west of New Caledonia. The northern profile crosses the New Caledonia Basin, the Fairway Ridge, the Fairway Basin, and the Lord Howe Rise. The southern profile crosses the Norfolk Rise south of New Caledonia, the New Caledonia Basin, the Fairway Ridge and Basin, and ends at the foot of Lord Howe Rise. On the northern profile the Lord Howe Rise has a crustal thickness of 23 km and exhibits seismic velocities and velocity gradients characteristic of continental crust. The crust thins to 12–15 km in the neighboring Fairway Basin, which is interpreted to be of thinned continental origin based on the seismic velocities. The crustal thickness of the Fairway Rise is 22 km, and it is also interpreted to be of continental origin. The New Caledonian Basin is underlain by crust of 10 km thickness, which shows unusally high velocities (between 7.0 and 7.4) uncharacteristic for either thinned continental or oceanic crust. On the southern profile the Norfolk Rise is also found to be of continental nature. Here, the New Caledonia Basin shows velocities, crustal thickness, and basement roughness characteristic of typical oceanic crust. The crust in the Fairway Basin shows higher velocities than on the northern profile, which could be caused by volcanic intrusions into the crust during extension. A deep reflector in the upper mantle was imaged underneath the New Caledonian Basin on the northern profile.
Decadal variations of global energy and ocean heat budget and meridional energy transports inferred from recent global data sets
Authors: Zhang Yuanchong , Rossow William B. , Stackhouse Paul , Romanou Anastasia , Wielicki Bruce A.
Published: November 2007

We use the most recent global, decades‐long data sets, consisting of two satellite‐derived top‐of‐atmosphere (TOA) and surface radiative flux data sets from the International Satellite Cloud Climatology Project Flux product (ISCCP‐FD) and the Global Energy and Water Cycle Experiment Surface Radiation Budget project (GEWEX‐SRB), three ocean surface turbulent flux data sets from Goddard Satellite‐based Surface Turbulent Fluxes (GSSTF), Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data (HOAPS) and Woods Hole Oceanographic Institution Objectively Analyzed air‐sea Fluxes (WHOI) and one ocean heat content (or energy storage rate) data set from Willis et al. to investigate what can be learned about how decadal‐scale variations of the global energy budget at TOA are partitioned between the atmosphere and ocean and their mean meridional heat transports. Although the mean differences among the TOA radiative flux data sets are large enough that direct measurements of planetary energy imbalances are still unreliable, comparison of the interannual anomalies of the ocean heat content with the two (satellite‐derived) planetary energy imbalances converted to accumulated ocean heat content (or equivalently comparison of the anomalies of ocean heat content converted to ocean heat storage rate with the planetary energy imbalances) show excellent quantitative agreement. These data sets essentially show a heating of the upper ocean since the 1990s but different “trends” at the beginning of this century that need further investigation. The comparison of interannual anomalies of total ocean surface energy fluxes converted to accumulated ocean heat content do not show such good agreement, the former generally indicating a cooling over the past decade. The fact that the anomalies in surface net radiative heating are slightly too large suggests that the latent heat flux anomalies are also too large (causing an overall cooling). The interannual anomalies of the mean meridional heat transport by the atmosphere‐ocean system inferred from the two TOA radiative flux data sets all show similar patterns of weakened poleward transport associated with El Niño events. Each event is different in character. The most interesting difference suggested by the latitudinal patterns is that some heat transport anomalies appear in the atmosphere and some in the ocean, but the current quality of the surface turbulent energy flux data sets precludes confirmation. Although not completely successful, we believe that this analysis indicates that these products are somewhat better than might have been expected and that the goal of further work should now be to reduce their uncertainties enough to diagnose the variations of the coupling of the atmosphere and ocean heat exchanges and transports over decadal timescales.
Preface to special section on East Asian Studies of Tropospheric Aerosols: An International Regional Experiment (EAST‐AIRE)
Authors: Li Zhanqing , Chen H. , Cribb M. , Dickerson R. , Holben B. , Li C. , Lu D. , Luo Y. , Maring H. , Shi G. , Tsay S.‐C. , Wang P. , Wang Y. , Xia X. , Zheng Y. , Yuan T. , Zhao F.
Published: November 2007

Papers published in this special section report findings from the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST‐AIRE). They are concerned with (1) the temporal and spatial distributions of aerosol loading and precursor gases, (2) aerosol single scattering albedo (SSA), (3) aerosol direct radiative effects, (4) validation of satellite products, (5) transport mechanisms, and (6) the effects of air pollution on ecosystems. Aerosol loading is heaviest in mideastern China with a mean aerosol optical depth (AOD) of 0.5 and increasing to 0.7 around major cities that reduced daily mean surface solar radiation by ∼30–40 W m−2, but barely changed solar reflection at the top of the atmosphere. Aerosol loading, particle size and composition vary considerably with location and season. The MODIS AOD data from Collection 5 (C5) agree much better with ground data than earlier releases, but considerable discrepancies still exist because of treatments of aerosol SSA and surface albedo. Four methods are proposed/adopted to derive the SSA by means of remote sensing and in situ observation, which varies drastically with time and space. The nationwide means of AOD, Ångström exponent, and SSA (0.5 μm) in China are 0.69 ± 0.17, 1.06 ± 0.26, and 0.89 ± 0.04, respectively. Measurements of trace gases reveal substantial uncertainties in emission inventories. An analysis of aircraft measurements revealed that dry convection is an important mechanism uplifting pollutants over northern China. Model simulations of nitrogen deposition and impact of ozone pollution on net primary productivity indicate an increasing threat of air pollution on the ecosystem.
Magnetofossil spike during the Paleocene‐Eocene thermal maximum: Ferromagnetic resonance, rock magnetic, and electron microscopy evidence from Ancora, New Jersey, United States
Authors: Kopp Robert E. , Raub Timothy D. , Schumann Dirk , Vali Hojatollah , Smirnov Alexei V. , Kirschvink Joseph L.
Published: November 2007

Previous workers identified a magnetically anomalous clay layer deposited on the northern United States Atlantic Coastal Plain during the Paleocene‐Eocene thermal maximum (PETM). The finding inspired the highly controversial hypothesis that a cometary impact triggered the PETM. Here we present ferromagnetic resonance (FMR), isothermal and anhysteretic remanent magnetization, first‐order reversal curve, and transmission electron microscopy analyses of late Paleocene and early Eocene sediments in drill core from Ancora, New Jersey. A novel paleogeographic analysis applying a recent paleomagnetic pole from the Faeroe Islands indicates that New Jersey during the initial Eocene had a ∼6°–9° lower paleolatitude (∼27.3° for Ancora) and a more zonal shoreline trace than in conventional reconstructions. Our investigations of the PETM clay from Ancora reveal abundant magnetite nanoparticles bearing signature traits of crystals produced by magnetotactic bacteria. This result, the first identification of ancient biogenic magnetite using FMR, argues that the anomalous magnetic properties of the PETM sediments are not produced by an impact. They instead reflect environmental changes along the eastern margin of North America during the PETM that led to enhanced production and/or preservation of magnetofossils.
Surface breakthrough of a basement fault by repeated seismic slip episodes: The Ostler Fault, South Island, New Zealand
Authors: Ghisetti Francesca C. , Gorman Andrew R. , Sibson Richard H.
Published: November 2007

The Ostler Fault is one of the major active reverse faults in the piedmont of the Southern Alps, SE of the Alpine Fault. We present a new geological and morphotectonic map of the southern Ostler Fault, integrated with two seismic reflection profiles across the active central segments of the fault. Segmented, subparallel scarps define a N‐S belt (∼40 km long and 2−3 km wide) of pure reverse faults, which upthrow and back‐tilt a panel of Plio‐Pleistocene terrestrial units (2.4−1.0 Ma) plus the overlying glacial outwash (<200 ka). Uplift gradients, the chronology of newly faulted markers, and tectonically controlled diversion of paleodrainages, all indicate progressive S to N breakthrough of the surface trace of the Ostler Fault in the last 2.4 Ma. The new seismic data define a main fault segment dipping 50°−60°W to depths of ∼1.5 km, with a vertical throw of 800 m, and a shortening of ∼30%. The fault geometry and kinematics and the subsurface data favor the interpretation that the Ostler Fault propagated updip across the Plio‐Quaternary terrestrial sequence as the emerging, high‐angle splay of an inherited Late Cretaceous−Paleocene normal fault, that underwent repeated cycles of compressional reactivation in the last 2.4 Ma.
Saccharomyces cerevisiae Rad16 mediates ultraviolet‐dependent histone H3 acetylation required for efficient global genome nucleotide‐excision repair
Authors: Teng Yumin , Liu Hairong , Gill Hefin W , Yu Yachuan , Waters Raymond , Reed Simon H
Published: November 2007

In yeast, global genome nucleotide‐excision repair (GG‐NER) requires a protein complex containing Rad7 and Rad16. Rad16 is a member of the switch/sucrose nonfermentable superfamily, and it is presumed that chromatin remodelling is its primary function during repair. We show that RAD16 is required for ultraviolet‐dependent hyperacetylation of histone H3 (Lys 9 and Lys 14) at the MFA2 promoter and throughout the genome. The yeast repressor complex Ssn6–Tup1 represses many genes including MFA2. TUP1 deletion results in constitutive hyperacetylation of histone H3, nucleosome disruption and derepression of gene transcription in Tup1‐regulated genes. GG‐NER in the MFA2 promoter proceeds more rapidly in tup1Δ α‐cells compared with wild type, even when transcription is inhibited. We show that elevated histone H3 acetylation levels in the MFA2 promoter in tup1Δ α‐cells result in Rad7‐ and Rad16‐independent GG‐NER, and that Rad16 mediates the ultraviolet‐induced acetylation of histone H3, necessary for efficient GG‐NER.
Exponential decay of correlations for randomly chosen hyperbolic toral automorphisms
Authors: Ayyer Arvind , Stenlund Mikko
Published: November 2007

We consider pairs of toral automorphisms (A,B) satisfying an invariant cone property. At each iteration, A acts with probability p∊(0,1) and B with probability 1−p. We prove exponential decay of correlations for a class of Hölder continuous observables.
Blueshift and intramolecular tunneling of NH3 umbrella mode in Hen4 clusters
Authors: Viel Alexandra , Whaley K. Birgitta , Wheatley Richard J.
Published: November 2007

We present diffusion Monte Carlo calculations of the ground and first excited vibrational states of NH3Hen4 for n⩽40. We use the potential energy surface developed by one of us [M. P. Hodges and R. J. Wheatley, J. Chem. Phys. 114, 8836 (2001)], which includes the umbrella mode coordinate of NH3. Using quantum Monte Carlo calculations of excited states, we show that this potential is able to reproduce qualitatively the experimentally observed effects of the helium environment, namely, a blueshift of the umbrella mode frequency and a reduction of the tunneling splittings in ground and first excited vibrational states of the molecule. These basic features are found to result regardless of whether dynamical approximations or exact calculations are employed.
Quadrupolar nuclear magnetic resonance spectroscopy in solids using frequency-swept echoing pulses
Authors: Bhattacharyya Rangeet , Frydman Lucio
Published: November 2007

The acquisition of ideal powder line shapes remains a recurring challenge in solid-state wideline nuclear magnetic resonance (NMR). Certain species, particularly quadrupolar spins in sites associated with large electric field gradients, are difficult to excite uniformly and with good efficiencies. This paper discusses some of the opportunities that arise upon departing from standard spin-echo excitation approaches and switching to echo sequences that use low-power, frequency-swept radio frequency (rf) pulses instead. The reduced powers demanded by such swept rf fields allow one to excite spins in different crystallites efficiently and with orientation-independent pulse angles, while the large bandwidths of interest that are needed by the measurement can be covered, thanks to the use of broadband frequency sweeps. The fact that the spins’ evolution and ensuing dephasing starts at the beginning of such rf manipulation calls for the use of spin-echo sequences; a number of alternatives capable of providing the desired line shapes both in the frequency and in the time domains are introduced and experimentally demonstrated. Sensitivity- and lineshape-wise these experiments are competitive vis-à-vis current implementations of wideline quadrupolar NMR based on hard rf pulses; additional opportunities that may derive from these ideas are also briefly discussed.
Confinement effects on the glass transition of hydrogen bonded liquids
Authors: Zheng Wei , Simon Sindee L.
Published: November 2007

The glass transition behavior of glycerol and propylene glycol confined in nanoporous glass is investigated using differential scanning calorimetry. Both silanized and unsilanized porous glasses are used to confine the liquids with nominal pore sizes ranging from 2.5to7.5nm, and the glass transition temperature (Tg) and the limiting fictive temperature (Tf′) sare measured on cooling and heating, respectively. The effect of pore fullness is also examined. We find that differences in Tg, ΔCp, and the enthalpy overshoot behavior observed on heating are significant between partially and completely filled pores for the case of the unsilanized controlled pore glasses (CPGs) but that the effect of pore fullness is insignificant for the silanized CPGs. In general, the behavior in the silanized CPGs is similar to the behavior in the completely filled unsilanized pores. For glycerol, this includes a small depression in Tf′ on the order of 5K at 2.5nm. For propylene glycol, similar behavior is found except that an additional glass transition is observed in both silanized and unsilanized systems approximately 30K higher than the bulk and a slightly smaller depression on the order of 3K at 2.5nm is observed in the completely filled unsilanized pores and in partially and completely filled silanized pores. The results are compared to those in the literature, and the confinement effects are discussed.
Quantization of the dipole moment and of the end charges in push-pull polymers
Authors: Kudin Konstantin N. , Car Roberto , Resta Raffaele
Published: November 2007

A theorem for end-charge quantization in quasi-one-dimensional stereoregular chains is formulated and proved. It is a direct analog of the well-known theorem for surface charges in physics. The theorem states the following: (1) Regardless of the end groups, in stereoregular oligomers with a centrosymmetric bulk, the end charges can only be a multiple of 1∕2 and the longitudinal dipole moment per monomer p can only be a multiple of 1∕2 times the unit length a in the limit of long chains. (2) In oligomers with a noncentrosymmetric bulk, the end charges can assume any value set by the nature of the bulk. Nonetheless, by modifying the end groups, one can only change the end charge by an integer and the dipole moment p by an integer multiple of the unit length a. (3) When the entire bulk part of the system is modified, the end charges may change in an arbitrary way; however, if upon such a modification the system remains centrosymmetric, the end charges can only change by multiples of 1∕2 as a direct consequence of (1). The above statements imply that—in all cases—the end charges are uniquely determined, modulo an integer, by a property of the bulk alone. The theorem’s origin is a robust topological phenomenon related to the Berry phase. The effects of the quantization are first demonstrated in toy LiF chains and then in a series of trans-polyacetylene oligomers with neutral and charge-transfer end groups.
A Reynolds stress closure description of separation control with vortex generators in a plane asymmetric diffuser
Authors: Törnblom Olle , Johansson Arne V.
Published: November 2007

A way to model the effects of streamwise vortices in a turbulent flow with one homogeneous direction is presented. The Reynolds averaged Navier-Stokes equations are solved with a differential Reynolds stress turbulence model. Assuming that the vortices can be approximated with the Lamb-Oseen model, wall-normal Reynolds stress distributions are calculated, corresponding to the spanwise variances of the estimated velocity distribution downstream of the vortex generators. The Reynolds stress contributions that are due to the vortex generators are added to the Reynolds stresses from the turbulence model so as to mimic the increased mixing due to the vortex generators. Volume forces are applied also in the mean momentum equations to account for the drag of the vortex generators. The model is tested and compared with experimental data from a plane asymmetric diffuser flow which is separating without vortex generators. The results indicate that the model is able to mimic the major features of vortex generator flow control and that the flow case in question is susceptible to separation control. The model results show that the pressure recovery of the diffuser could be increased by almost 10% by applying vortex generators and that, if keeping the shape of the vortex generators fixed, their optimal position is close to the diffuser inlet. Computations also indicated that the time to re-establish the separation zone when the control suddenly is turned off is substantially longer than the time it takes to remove the separation after the control is turned on again. Some work on adapting a differential Reynolds stress turbulence model was necessary in order to make it capable of realistic predictions of the asymmetric diffuser flow in which the vortex generator model is tested. However, the main focus of the article is on the modelling of vortex generator effects.
Formation of ferromagnetic interface between β-FeSi2 and Si(111) substrate
Authors: Hattori Azusa N. , Hattori Ken , Kodama Kenji , Hosoito Nobuyoshi , Daimon Hiroshi
Published: November 2007

Epitaxial β-FeSi2 thin films were grown on Si(111)7×7 clean surfaces by solid phase epitaxy in ultrahigh vacuum: iron deposition at low temperature and subsequent annealing. We found that a ferromagnetic interface layer of iron-rich silicides forms between a β-FeSi2 surface layer and a Si(111) substrate spontaneously from transmission electron microscopy observations and magnetization measurements.
New eigenvalue based approach to synchronization in asymmetrically coupled networks
Authors: Li Zhi , Lee Ju-Jang
Published: November 2007

Locally and globally exponential stability of synchronization in asymmetrically nonlinear coupled networks and linear coupled networks are investigated in this paper, respectively. Some new synchronization stability criteria based on eigenvalues are derived. In these criteria, both a term that is the second largest eigenvalue of a symmetrical matrix and a term that is the largest value of the sum of the column of the asymmetrical coupling matrix play a key role. Comparing with existing results, the advantage of our synchronization stability results is that they can be analytically applied to the asymmetrically coupled networks and can overcome the complexity of calculating eigenvalues of the coupling asymmetric matrix. Therefore, these conditions are very convenient to use. Moreover, a necessary condition of globally exponential synchronization stability criterion is also given by the elements of the coupling asymmetric matrix, which can conveniently be used in judging the synchronization stability condition without calculating the eigenvalues of the coupling matrix.
High-temperature phase transitions in CsH2PO4 under ambient and high-pressure conditions: A synchrotron x-ray diffraction study
Authors: Botez Cristian E. , Hermosillo Juan D. , Zhang Jianzhong , Qian Jiang , Zhao Yusheng , Majzlan Juraj , Chianelli Russell R. , Pantea Cristian
Published: November 2007

To clarify the microscopic origin of the temperature-induced three-order-of-magnitude jump in the proton conductivity of CsH2PO4 (superprotonic behavior), we have investigated its crystal structure modifications within the 25–300°C temperature range under both ambient- and high-pressure conditions using synchrotron x-ray diffraction. Our high-pressure data show no indication of the thermal decomposition/polymerization at the crystal surface recently proposed as the origin of the enhanced proton conductivity [Phys. Rev. B 69, 054104 (2004)]. Instead, we found direct evidence that the superprotonic behavior of the title material is associated with a polymorphic structural transition to a high-temperature cubic phase. Our results are in excellent agreement with previous high-pressure ac impedance measurements.
One dimensional and two dimensional photonic crystal GaInSb∕AlGaAsSb microlasers
Authors: Mueller M. , Bauer A. , Lehnhardt T. , Rössner K. , Hümmer M. , Forchel A.
Published: November 2007

The authors present microlasers on the GaInSb∕AlGaAsSb material system. These microlasers are equipped with one dimensional or two dimensional photonic crystals (PhCs) acting as highly reflecting microscaled mirrors. Hence, microlasers with cavity lengths as short as 100μm could be realized, exhibiting output powers per facet of up to 6mW and side mode suppression ratios of 20dB in continuous wave operation.
Kinetic Monte Carlo simulation of vapor-liquid-solid nanostructure growth
Authors: White Richard , Welland Mark E.
Published: November 2007

The vapor-liquid-solid growth of nanostructures is simulated using a two-dimensional kinetic Monte Carlo model. The model considers the deposition of reactants from the vapor, solute diffusion in the solution droplet, and the nucleation and growth of the precipitated solid phase. The extrusion of the solid from the solution into the vapor is also modeled. A morphological transition from one-dimensional to two-dimensional growth is observed in response to changes in reactant vapor pressure and to changes in the solute diffusivity at the liquid-vapor interface. The morphology is determined by the dominant growth direction of the solid and is dependent on the speed at which deposited solute species can be diffused from the surface. Such a fundamental change in morphology has been observed experimentally in the growth of silicon carbide nanostructures and insight into the cause of this transition is achieved.
Parallel electric fields in nonlinear magnetosonic waves
Authors: Takahashi Seiichi , Ohsawa Yukiharu
Published: November 2007

The electric field parallel to the magnetic field, E‖, in nonlinear magnetosonic waves is studied theoretically and numerically. In the calculation of E‖ based on the conventional reductive perturbation method, the terms related to the magnetic pressure cancel, and E‖ is proportional to the electron temperature Te. With a modified perturbation scheme assuming that the wave amplitude is in the range (me∕mi)1∕2<ϵ<1, an expression for E‖ is obtained that is proportional to the magnetic pressure in a cold plasma. Its integral along the magnetic field, F=−∫E‖ds, is proportional to ϵ2mivA2. One-dimensional, fully kinetic, electromagnetic particle simulations verify the theoretical predictions for small-amplitude waves. Further, they demonstrate that eF becomes of the order of ϵ(mivA2+ΓeTe) in large-amplitude [ϵ∼O(1)] oblique shock waves. These theory and simulations indicate that E‖ in magnetosonic waves can be strong in a strong magnetic field.
Influence of the electrode work function on the energy level alignment at organic-organic interfaces
Authors: Braun Slawomir , de Jong Michel P. , Osikowicz Wojciech , Salaneck William R.
Published: November 2007

The energy level alignment at interfaces, in stacks comprising of (4,4′-N,N′-dicarbazolyl-biphenyl) (CBP), (4,4,4″-tris[3-methyl-phenyl(phenyl)amino]-triphenylamine) (m-MTDATA), and a conductive substrate, has been studied. We show that the alignment of energy levels depends on the equilibration of the chemical potential throughout the layer stack, while any electronic coupling between the individual layers is of lesser importance. This behavior is expected to occur for a broad class of weakly interacting interfaces and can have profound consequences for the design of organic electronic devices.
Effect of interparticle distance and interfacial area on the properties of insulator-conductor composites
Authors: Deepa K. S. , Sebastian M. T. , James J.
Published: November 2007

The influence of conducting phase characteristics on dielectric properties of insulator-conductor composites was demonstrated by studying composites of polytetrafluoroethylene and different volume fractions of La0.5Sr0.5CoO3−y (LSCO). LSCO was prepared as coarse grained powder by solid state reaction and as fine powder by citrate gel method. The composites with fine powder of LSCO showed a rapid increase in dielectric constant and conductivity at 30%, while the corresponding value for coarse powder was 50%. The percolative behavior was found when the interparticle distance reduced to ∼250nm in both cases. The permittivity and conductivity of the composites were found to increase with the interfacial area.
Properties of omnidirectional gap and defect mode of one-dimensional photonic crystal containing indefinite metamaterials with a hyperbolic dispersion
Authors: Xiang Yuanjiang , Dai Xiaoyu , Wen Shuangchun , Fan Dianyuan
Published: November 2007

The structure of one-dimensional photonic crystal (1DPC) containing indefinite metamaterials with a hyperbolic dispersion relation is proposed to realize the omnidirectional gap for the design of omnidirectional reflectors and filters. It is demonstrated that this 1DPC can result in a similar zero average index (zero-n¯) gap usually appearing in the 1DPC containing isotropic left-handed materials. The properties of zero-n¯ gap and defect modes of this photonic crystal are studied in detail. The edge of this zero-n¯ gap is insensitive to incident angle and polarization of light in contrast to the Bragg gap. When a defect layer is introduced into the 1DPC, a defect mode appears inside the omnidirectional gap. The spectral position of defect mode is found to be weakly dependent on the incident angle of light and nearly invariant to the scale length of photonic crystal.
Application of gamma distribution in electromigration for submicron interconnects
Authors: Ming Tan Cher , Raghavan Nagarajan , Roy Arijit
Published: November 2007

Traditionally, the lognormal distribution has been used to analyze electromigration (EM) failure data for both Al- and Cu-based interconnect technologies. However, from a statistical perspective, the lognormal distribution is found to be inappropriate for submicron interconnects because their resistance degradation profiles are no longer “gradual” as compared to the wider interconnects. In such cases, the gamma distribution is found to be a good choice to represent such failures which are initially “gradual” and later “catastrophic” in nature. The invalidity of the lognormal model for submicron interconnects is assessed and a statistical proof in favor of the gamma statistics is presented. Experimental EM test data for submicron Cu interconnects are analyzed and it is found that the data fitting is generally more accurate for submicron interconnects when the gamma distribution is used. The use of a gamma distribution also changes the field operation lifetime estimates obtained through reliability extrapolation.
Ultrathin n+∕p junction in preamorphized silicon by phosphorus and carbon coimplantation engineering: Influence of C location
Authors: Cagnat N. , Mathiot D. , Laviron C.
Published: November 2007

This paper reports the influence of carbon coimplantation on the redistribution of phosphorus implanted in preamorphized Si. A strong influence of the carbon location, with respect to the P profile, is evidenced. With the help of specific simulations, a model is proposed to explain this dependence. It is shown that, in optimized conditions, it is possible to achieve P profiles suitable for the thin junctions required for future device generations.
Self-adjointness for Dirac operators via Hardy-Dirac inequalities
Authors: Esteban Maria J. , Loss M.
Published: November 2007

Distinguished self-adjoint extensions of Dirac operators are constructed for a class of singular potentials including Coulombic ones up to (and including) the critical case, −∣x∣−1. The method uses Hardy-Dirac inequalities and quadratic form techniques.
Thermal stability of CdZnO∕ZnO multi-quantum-wells
Authors: Thompson A. V. , Boutwell C. , Mares J. W. , Schoenfeld W. V. , Osinsky A. , Hertog B. , Xie J. Q. , Pearton S. J. , Norton D. P.
Published: November 2007

The thermal stability of CdZnO∕ZnO multi-quantum-well (MQW) structures was studied using rapid thermal annealing in nitrogen from 300to750°C. Photoluminescence (PL) emission from the MQWs was studied while varying the annealing temperature and time. For 15min annealings, the PL center wavelength showed a 7nm reduction for temperatures up to 650°C. Above 650°C, the wavelength changed rapidly, with a 50nm reduction at 750°C. Annealing at 700°C for up to 20min produced a systematic reduction in PL wavelength up to 39nm. The data suggest that CdZnO∕ZnO MQWs are relatively stable for nitrogen annealing below 650°C for times up to 15min.
Using ring-shaped and magnetically coated tungsten wire as the probe of spin-polarized scanning tunneling microscopy
Authors: Wu Chii-Bin , Hsu Pin-Jui , Yen Hong-Yu , Lin Minn-Tsong
Published: November 2007

We report a method of magnetic probe fabrication using ring-shaped and iron-coated tungsten wire for spin-polarized scanning tunneling microscopy. Magneto-optic Kerr effect measurement on the probe front end shows that by controlling the saturating field direction, we can fix the probe magnetization in the specific in-plane direction. The ring is applied to the scanning tunneling microscopy and spectroscopy experiment on 6.8 ML Mn∕Fe(001), and spin contrast in the in-plane direction is demonstrated.
Molecular dynamics simulation of pore growth in lipid bilayer membranes in the presence of edge-active agents
Authors: Moldovan Dorel , Pinisetty Dinesh , Devireddy Ram V.
Published: November 2007

Using molecular dynamics simulations, we investigated the mechanism of entropy-driven pore formation in a phospholipid bilayer in the presence of a line tension lowering agent. Even in the absence of an external stress, our simulations show that it is possible to observe with atomistic detail and on nanosecond time scale the nucleation and growth of hydrophilic pores. We rationalize the nucleation process in terms of a simplified free energy model that includes the entropy of the pore shape. By estimating the line tensions within the lipid bilayers with and without edge-active agents, our simulations corroborate the pore growth model.
Ultralow thermal conductivity of nanoparticle packed bed
Authors: Hu X. Jack , Prasher Ravi , Lofgreen Kelly
Published: November 2007

We show that thermal conductivity of packed bed of alumina nanoparticles can be as low as 0.035W∕mK which is only 35% higher than the thermal conductivity of air and is smaller than the recently reported lowest thermal conductivity of solids using disordered layered WeS2. These findings show a promising approach for making low-cost and ultralow thermal conductivity thermal insulation materials with high density and good sustainability at high pressures.
Spin-filtering multiferroic-semiconductor heterojunctions
Authors: Sai Na , Lee Jaekwang , Fennie Craig J. , Demkov Alexander A.
Published: November 2007

We report on the structural and electronic properties of the interface between the multiferroic oxide YMnO3 and semiconductor GaN studied with the Hubbard-corrected local-spin-density approximation to density-functional theory. We find that the band offsets at the interface between antiferromagnetically ordered YMnO3 and GaN are different for spin-up and spin-down states. This behavior is due to the spin splitting of the valence band induced by the interface. The energy barrier depends on the relative orientation of the electric polarization with respect to the polarization direction of the GaN substrate suggesting an opportunity to create magnetic tunnel junctions in this material system.
Microstructure and magnetic properties of (001) oriented FePt∕B4C composite films
Authors: Yang F. J. , Wang Hao , Wang H. B. , Cao X. , Yang C. P. , Li Q. , Zhou M. J. , Chong Y. M. , Zhang W. J.
Published: November 2007

FePt ∕ B 4 C multilayer composite films have been prepared by magnetron sputtering and subsequent annealing in vacuum. It was found that the B4C layers effectively serve as spacers to separate the FePt layers, enhancing (001) orientation of FePt alloy. Our results show that highly (001) oriented [Fe45Pt55(8 nm)∕B4C (4 nm)]3 film with satisfactory perpendicular coercivity (4.75 kOe) has significant potential as a perpendicular recording medium.
Crystalline structures, surface morphology, and ferroelectric response in ultrathin film of vinylidene fluoride and trifluoroethylene copolymer
Authors: Tsutsumi Naoto , Otsuji Masayuki
Published: November 2007

This paper presents crystalline structures, surface morphology, and improved ferroelectric response in ultrathin film of 70 mol % vinylidene fluoride and 30 mol % trifluoroethylene copolymer with 22 nm thickness. Remanent polarization (Pr) of 45 mC∕m2 was obtained at maximum applied voltage of 11 V (500 MV/m) for the ultrathin film annealed at 142 °C. This Pr value is twice as high than that previously reported. We ascribed higher Pr to both smoothness of sample surface and no significant reduction of crystallinity and crystallite size when film thickness is down to 22 nm. Thermal annealing at the temperature above 135 °C induced the growth of flat-on lamella crystals with smoothed uniform surface morphology, and further thermal annealing at temperature of 142 °C led the realignment of crystal c axis in flat-on lamella parallel to the substrate.
Spectrally narrowed emissions occurring near an interface between a single crystal thiophene/phenylene co-oligomer and a glass substrate
Authors: Yamao Takeshi , Yamamoto Kazunori , Taniguchi Yuki , Hotta Shu
Published: November 2007

Polarized emission microspectroscopy has been investigated on a single crystal of a thiophene/phenylene co-oligomer. We measured polarized emissions occurring from the thin cloven facets of the crystal mounted on a glass substrate. The polarized UV light from a mercury lamp was used for the excitation. The spectrally narrowed emissions have been observed with an unusually low excitation intensity (∼90mW∕cm2) at the parts of the substrate very close to the interface between the crystal and the substrate.
High-Q GaN nanowire resonators and oscillators
Authors: Tanner S. M. , Gray J. M. , Rogers C. T. , Bertness K. A. , Sanford N. A.
Published: November 2007

We report high mechanical quality factors Q for GaN nanowire cantilevers grown by molecular beam epitaxy. Nanowires with 30–500nm diameters and 5–20μm lengths having resonance frequencies from 400kHzto2.8MHz were measured. Q near room temperature and 10−4Pa ranged from 2700 to above 60 000 with most above 10 000. Positive feedback to a piezoelectric stack caused spontaneous nanowire oscillations with Q exceeding 106. Spontaneous oscillations also occurred with direct e-beam excitation of unintentionally doped nanowires. Doped nanowires showed no oscillations, consistent with oscillation arising via direct actuation of piezoelectric GaN.
Growth mode mapping and structural properties of controlled perovskite BaTiO3∕SrTiO3 heterostructure
Authors: Li Jin Long , Hao J. H. , Ying Zhang , Li Yanrong
Published: November 2007

Perovskite heteroepitaxy was investigated under various conditions using laser molecular beam epitaxy. Well-controlled BaTiO3∕SrTiO3 heterostructure was studied with in situ reflective high energy electron diffraction and ex situ atomic force microscopy, x-ray diffraction, and transmission electron microscopy. The growth mode map of BaTiO3 thin films was obtained as a function of substrate temperature under 600°C for various laser repetition rates. The effective activation energy of surface migration was determined to be 0.33eV. A mechanism of surface migration in BaTiO3 heteroepitaxy was described for a basic understanding of atomic-scale controlled preparation of ferroelectric heterostructures at low temperature.
Temperature-dependent Raman study of Ce0.75Nd0.25O2−δ nanocrystals
Authors: Dohčević-Mitrović Z. D. , Radović M. , Šćepanović M. , Grujić-Brojčin M. , Popović Z. V. , Matović B. , Bošković S.
Published: November 2007

Raman spectra of Nd doped ceria nanocrystals were measured by gradual heating and cooling over the temperature range of 293–1073K and analyzed using the phonon confinement model that incorporates inhomogeneous strain and anharmonic effects. We have demonstrated that in nanograins, four-phonon anharmonic processes are more dominant at higher temperatures than size effects. After the heat treatment, Nd doped ceria nanocrystals remain of nanometric range (∼20nm) while the concentration of oxygen vacancies is still high in ceria lattice, making this material convenient for solid oxide fuel cells application.
Gas-discharge plasma sources for nonlocal plasma technology
Authors: Demidov V. I. , DeJoseph C. A. , Simonov V. Ya.
Published: November 2007

Nonlocal plasma technology is based on the effect of self-trapping of fast electrons in the plasma volume [V. I. Demidov, C. A. DeJoseph, Jr., and A. A. Kudryavtsev, Phys. Rev. Lett. 95, 215002 (2006)]. This effect can be achieved by changing the ratio of fast electron flux to ion flux incident on the plasma boundaries. This in turn leads to a significant change in plasma properties and therefore can be useful for technological applications. A gas-discharge device which demonstrates control of the plasma properties by this method is described.
Testing the simulation capability of APSIM-ORYZA under different levels of nitrogen fertiliser and transplanting time regimes in Korea
Authors: Zhang Xike , Lee Jae-Hong , Abawi Yahya , Kim Young-ho , McClymont David , Kim Hee-Dong
Published: November 2007

APSIM-ORYZA is a new functionality developed in the APSIM framework to simulate rice production while addressing management issues such as fertilisation and transplanting, which are particularly important in Korean agriculture. To validate the model for Korean rice varieties and field conditions, the measured yields and flowering times from three field experiments conducted by the Gyeonggi Agricultural Research and Extension Services (GARES) in Korea were compared against the simulated outputs for different management practices and rice varieties. Simulated yields of early-, mid- and mid-to-late-maturing varieties of rice grown in a continuous rice cropping system from 1997 to 2004 showed close agreement with the measured data. Similar results were also found for yields simulated under seven levels of nitrogen application. When different transplanting times were modelled, simulated flowering times ranged from within 3 days of the measured values for the early-maturing varieties, to up to 9 days after the measured dates for the mid- and especially mid-to-late-maturing varieties. This was associated with highly variable simulated yields which correlated poorly with the measured data. This suggests the need to accurately calibrate the photoperiod sensitivity parameters of the model for the photoperiod-sensitive rice varieties in Korea.
Susceptibility of Japanese pears to low concentrations of ethylene during storage
Authors: Szczerbanik M. J. , Scott K. J. , Paton J. E. , Best D. J.
Published: November 2007

The ‘Nijisseiki’ cultivar of Japanese pears (Pyrus pyrifolia) is also known as nashi in Australia. Nashi were exposed to levels of <0.005, 0.01, 0.1 and 1.0 µL/L of ethylene in air during 26 weeks storage at 0°C. Levels of ethylene as low as 0.01 µL/L increased chlorophyll loss and visual green colour. Increasing ethylene levels also increased softening and internal browning, although flesh spot decay was reduced in the presence of ethylene. While it would be worthwhile to remove ethylene during long-term storage of ‘Nijisseiki’ in air, another alternative, adding 2% carbon dioxide to the atmosphere, is suggested as a possible low cost means to overcome the ripening effect of ethylene.