bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic microstructure in Saturn's rings A and B
Authors: Thomson Fraser S. , Marouf Essam A. , Tyler G. Leonard , French Richard G. , Rappoport Nicole J.
Published: December 2007

Diffraction of coherent radio waves transmitted by the Cassini spacecraft at 0.94‐ and 3.6‐cm wavelengths indicates the presence of fine‐scale structure in Saturn's rings A and B, characterized by a periodic radial variation in optical depth. Interpretation of the observed spectral signature in terms of a simple diffraction grating model yields estimates of the structural period λgr ≈ 100–250 meters and orientation ϕgr ≈ 0. In particular, two regions in Ring A of radial extent 123.05–123.4 × 103 km and 123.6–124.6 × 103 km yield average estimates of gr = 163 ± 6 meters and gr = 217 ± 8 meters, respectively. Three regions in Ring B of radial extent 92.1–92.6 × 103, 99.0–104.5 × 103 km, and 110.0–115.0 × 103 yield average estimates of gr = 115−15+20, 146 ± 14, and 250−75+150 meters, respectively. In all regions, the structure appears to be azimuthally symmetric with −3° ≤ ϕgr ≤ 3°.
Saturnian magnetospheric dynamics: Elucidation of a camshaft model
Authors: Southwood D. J. , Kivelson M. G.
Published: December 2007

Periodic modulation of magnetospheric phenomena at Earth and Jupiter results principally from the tilt of the dipole axis relative to the rotation axis. Saturn's nearly aligned dipole moment is tilted by less than 0.5° from the spin axis, yet the power of radio‐frequency emissions, the orientation of the magnetic field, and many properties of the magnetospheric plasma vary periodically at the approximate rate of Saturn's rotation. Here we examine properties of the periodic magnetic signal detected in the magnetospheric regions inside ∼12–15 RS. We show that it is associated with a rotating nonaxisymmetric system of field‐aligned currents flowing on magnetic shells bounding the region where the signals are seen. Magnetohydrodynamic ideas suggest that these currents would drive rotating plasma flow patterns in the northern and southern ionospheres, with the flows oppositely directed in the two hemispheres. On magnetic shells beyond the sheets of field‐aligned current, the magnetic perturbations generate an effective rotating equatorial dipole moment that when added to the planetary dipole moment, produces a dipole moment tilted relative to the spin axis at an angle of order 12–15°. The overt source of the north–south asymmetric ionospheric circulation could link to different ionospheric conductances that result from nonuniform solar illumination. Other possible sources are discussed but, although we can elucidate much, the origin of the cam signal (as well as other phenomena such as the Saturn kilometric radio emission with close to the same period) remains enigmatic.
Three‐dimensional multifluid simulation of the plasma interaction at Titan
Authors: Snowden D. , Winglee R. , Bertucci C. , Dougherty M.
Published: December 2007

Using a three‐dimensional multifluid simulation, we demonstrate the importance of ion gyroradius and heavy ion effects when characterizing Titan's plasma interaction with the Kronian magnetosphere. Ion gyroradius and heavy ion effects drastically change the mass loading and magnetic field draping at Titan. We find that the large ion gyroradius of picked up ionospheric species results in an extension of the ionosphere and therefore the mass loading and magnetic pileup region on the anti‐Saturn side of Titan. Also, the additional thermal pressure provided by heavy ion cyclotron motion near Titan causes boundary layer currents to form at higher altitudes. The Saturn‐facing side of Titan's ionosphere experiences both magnetic shielding from the incident plasma at lower altitudes and additional heating due to the acceleration of heavy ions in the ionosphere. Finally, we find that well‐confined heavy ion beams form on the anti‐Saturn side of Titan's magnetosphere and extend more than three Titan radii from Titan's main ion tail. The location of this ion beam is dependent on the Kronian field orientation, and we find that during the TA, TB, and T3 encounters, the bulk of the ion beam was located below Titan's equatorial plane. We also find that for a single set of incident conditions, good agreement with Cassini magnetometer data from the TA, TB, and T3 encounters is obtained with the ion loss rate similar to that measured by Cassini during the TA encounter.
Characterization of waves in the vicinity of an interplanetary directional discontinuity
Authors: Tjulin A. , Lucek E. A. , Dandouras I.
Published: December 2007

Directional discontinuities are frequently encountered in the solar wind. This study utilizes the possibility of simultaneous four‐point measurements that the Cluster satellites provide for an investigation of the waves near one such interplanetary discontinuity event. In particular, the k‐filtering technique has for the first time been applied for the wave characterization in terms of frequency, wave vector, wave power, and polarization at different distances from a discontinuity. The advantages of the k‐filtering method are that these parameters can be transformed into the plasma frame of reference to allow comparison with theory and that it is possible to detect more than one wave mode at each frequency in the spacecraft frame of reference. The discontinuity event in this study was chosen because its wave activity had unusually high power and because it also contains signatures of large‐scale magnetic reconnection, such as a reconnection exhaust. Two wave modes are found: one which has the features of a shear Alfvén wave with propagation direction ordered by the background magnetic field direction and one which behaves like a compressional Alfvén wave and is ordered by the discontinuity normal. Both wave modes become weaker farther away from the discontinuity, but the compressional Alfvén mode is more suppressed. The shear mode dominates for long wavelengths at all distances from the discontinuity. The wave field is also found to be asymmetric on the two sides of the event.
Calculated densities of H3O+(H2O)n,NO2− (H2O)n, CO3− (H2O)n and electron in the nighttime ionosphere of Mars: Impact of solar wind electron and galactic cosmic rays
Authors: Haider S. A. , Singh V. , Choksi V. R. , Maguire W. C. , Verigin M. I.
Published: December 2007

We have calculated the densities of positive ions and negative ions in the ionosphere of Mars at solar zenith angle 106° between height interval 0 km and 220 km. This model couples ion‐neutral, electron neutral, dissociation of positive and negative ions, electron detachment, ion‐ion, ion‐electron recombination processes through 117 chemical reactions. Of the 34 ions considered in the model, the chemistry of 17 major ions (O2+, NO+, CO2+, H3O+H2O, H3O+(H2O)2, H3O+(H2O)3, H3O+(H2O)4, O2+CO2, H3O+, CO4−, CO3−, CO3−H2O, CO3− (H2O)2, NO2−H2O, NO2− (H2O)2, NO3−H2O, and NO3− (H2O)2) are discussed in this paper. At altitude below 70 km, the electron density is mainly controlled by hydrated hydronium ions and water clusters of NO2− and CO3−. The ions O2+ and NO+ dominate above this altitude. This calculation suggests that the ionosphere of Mars contains F and D peaks at altitude ∼130 km and ∼30 km due to precipitation of solar wind electron and galactic cosmic rays respectively. F peak is mainly produced by O2+ after heavy loss of CO2+ with atomic oxygen. D peak occurs due to high efficiency of electron attachment to Ox molecules, which entails that concentration of negative ions is higher than that of electron below 30 km. These results are compared with radio measurements made by Mars 4 and Mars 5 in the nighttime ionosphere.
Polarization measurements of Saturn Electrostatic Discharges with Cassini/RPWS below a frequency of 2 MHz
Authors: Fischer G. , Gurnett D. A. , Lecacheux A. , Macher W. , Kurth W. S.
Published: December 2007

Early in 2006 the RPWS (Radio and Plasma Wave Science) instrument and the ISS (Imaging Science Subsystem) onboard the Cassini spacecraft detected a lightning storm on Saturn that lasted for about one month. The RPWS measured the so‐called SEDs (Saturn Electrostatic Discharges), which are high frequency radio signals produced by lightning discharges. The ISS imaged a remarkable cloud system associated with these SEDs at a latitude of 35° South. Below the frequency of 1825 kHz the RPWS was in a mode capable of measuring the polarization of the SEDs. A surprising result was gained; SEDs appeared to be highly polarized (80%) and were exclusively right‐handed polarized with a high degree of circular polarization. We will present an explanation for this diagnosis involving magneto‐ionic modes and their differential absorption in the magnetoplasma of Saturn's ionosphere.
Optical estimation of auroral ion upflow: Theory
Authors: Zettergren M. , Semeter J. , Blelly P.‐L. , Diaz M.
Published: December 2007

This work presents a systematic analysis of optical emissions related to auroral ion upflow. Optical intensities and field‐aligned ion transport are computed for a set of monoenergetic incident electron beams using a combined fluid‐kinetic model. The kinetic portion models the energetic particle transport with a multiple stream approach and provides ionization, excitation, and heating rates to an eight‐moment fluid model of the ionosphere, which then calculates the resulting ion upflow. The analysis is used to develop a technique for estimating upward ion flux from photometric measurements at five discrete wavelengths: 427.8 nm, 557.7 nm, 630.0 nm, 732 nm, and 844.6 nm. The procedure involves (1) estimating the incident particle spectrum by inversion of multiwavelength optical measurements in the magnetic zenith, (2) applying this incident spectrum to the fluid‐kinetic model to estimate the upflow response. The robustness of the procedure is demonstrated by inverting brightnesses computed for a known electron spectrum and then comparing upflow directly calculated from the known spectrum to the upflow calculated from the estimated spectrum. The inversion is found to provide a reliable estimate of the precipitating electron spectrum and ion upflow, even in the presence of realistic uncertainties in brightness. The technique represents a new tool for studying mass coupling between the magnetosphere and ionosphere. Potential applications range from upflow event studies to estimating the total amount of plasma entering the transition region during a substorm surge via fusion of optical data from multiple sensors.
Modeling long duration meteor trails
Authors: Dyrud Lars P. , Kudeki Erhan , Oppenheim Meers
Published: December 2007

We constructed a model of the plasma evolution of meteor trails in order to simulate high‐power‐large‐aperture radar observations. This model follows meteor evolution from ablation and ionization to head echo formation and through non‐specular trail reflections. Meteor plasma field aligned irregularities (FAI) result in radar reflections called non‐specular meteor trails. We have updated our model to include the polarizing effects of winds and background electric fields on meteor trail instability. This model incorporates existing meteor physics together with knowledge we gained from the simulations, such as instability physics and anomalous diffusion. Comparing results from this model with large radar observations of head echoes and non‐specular trails shows that we can reproduce many of the observed features, such as the detailed altitude profile and duration of head echoes and non‐specular trails. Specifically when external electric fields are included in our model, the same model predicts both short duration (order of 1 s) and long duration meteor trails (several minutes) depending upon the characteristics of the meteoroid and atmosphere. The addition of a background E‐field or wind also reproduces a commonly observed non‐specular trail feature we call an “extended tail” where the delay time between head echo and non‐specular reflection at the lower altitude portion of the trail increases as the meteor gets lower in the atmosphere. We also demonstrate a dependence on trail duration with the electron density of the background ionosphere.
Characterizing earthquake recurrence parameters for offshore faults in the low‐strain, compressional Kapiti‐Manawatu Fault System, New Zealand
Authors: Nodder Scott D. , Lamarche Geoffroy , Proust Jean‐Noël , Stirling Mark
Published: December 2007

Seafloor fault scarps and near‐surface deformation of late Quaternary seismic reflectors occur along the eastern margin of the Wanganui Basin, 200 km behind the active Hikurangi subduction front, southern North Island, New Zealand. The offshore scarps are associated with the low‐strain, compressional Kapiti‐Manawatu Fault System (KMFS), which comprises high‐angle (>60°) reactivated reverse and normal faults oriented NE‐SW, highly oblique to the coast. Seafloor scarps range from <10 to 50 km in length with vertical seafloor offsets of 2 to 30 m. The longest structure is the Mascarin Fault, with maximum late Quaternary vertical slip rates of 3 mm a−1(where a is years). Other faults in the KMFS have typical rates of <1 mm a−1, comparable to long‐term estimates. Three zones of recent deformation are identified: faults in the north and south of the KMFS are characterized by high scarps (>10 m high) and moderate to long fault seafloor rupture lengths, and those in central parts of the fault system are characterized by low scarps (<5 m high), variable slip rates, and short to moderate fault lengths. Empirical equations indicate that KMFS faults may generate earthquakes with moment magnitudes (Mw) of 5.7–7.5 (mean 6.9 ± 0.3, ±1 standard deviation, for sources with Mw≥ 6.5). Estimated recurrence intervals that are generally >10,000 a, suggest that the seismic hazard of the Kapiti‐Manawatu region is relatively low. Incorporation of these new geological data, however, is likely to increase slightly the expected seismic hazard in southern North Island. The method of determining the earthquake recurrence parameters of offshore faults has potentially wider applications elsewhere.
Three‐dimensional gravity and magnetic modeling of crustal indentation and wedging in the western Pyrenees‐Cantabrian Mountains
Authors: Pedreira D. , Pulgar J. A. , Gallart J. , Torné M.
Published: December 2007

The complex crustal structure of the boundary zone between the Iberian and European plates, from the western Pyrenees to the Cantabrian Mountains, is probed by three‐dimensional (3‐D) gravity and magnetic modeling constrained by deep seismic profiles. The 3‐D modeling results support the presence of a continuous Iberian crustal root and suggest that the geometry of the orogenic belt that formed in latest Cretaceous‐Tertiary times along the northern margin of Iberia was conditioned by oblique structures separating areas characterized by different tectonic styles. In the western Pyrenees and the Basque‐Cantabrian basin (a thick Mesozoic basin presently incorporated to the Pyrenean‐Cantabrian belt), the relatively narrow thinning of the crust inherited from the Mesozoic rifting stage conditioned a structural style in which portions of the southward indenting European lower crust are interpreted to be back thrusted toward the north and uplifted to shallow depths, promoting the appearance of significant potential field anomalies. In the Basque‐Cantabrian basin, the strongest aeromagnetic anomaly of the whole Iberian Mainland is superimposed on the eastern part of a well‐defined positive gravity anomaly, similar in amplitude and wavelength to those located along the North Pyrenean Zone. These observations suggest that the eastern part of the dense, lower crustal causative body is strongly magnetized and may correspond to a gabbroic cumulate originated in the axis of the ancient Mesozoic rift. To the west, Tertiary compression affected the North Iberian (Cantabrian) passive continental margin, whose geometry and inherited structures conditioned the formation of a double crustal delamination and the uplift of the Cantabrian Mountains.
Water mass characteristics in the equatorial North Atlantic: A section nominally along 6.5°N, July 2000
Authors: Sarafanov Artem , Sokov Alexey , Demidov Alexander
Published: December 2007

In July 2000, a transatlantic conductivity‐temperature‐depth/hydrographic section was occupied on board the Russian R/V Akademik Ioffe in the northern equatorial region from 9°26′N, 17°22′W to 3°48′N, 47°16′W near the World Ocean Circulation Experiment (WOCE) A06 line. The water mass characteristics and the main features of cross‐sectional circulation are reported on the basis of the potential temperature, salinity, potential density, and silicate distributions along the section. A scheme of the upper ocean circulation dominated by the near‐surface eastward North Equatorial Countercurrent, most intense at 5.5°–6°N, and the subsurface cyclonic flow of the North Equatorial Undercurrent, is presented. The boundary flows along the Brazilian slope are revealed at the Upper and Lower North Atlantic Deep Water (NADW) levels, while the main pathways of intermediate waters and the Middle NADW are offshore. The northward recirculation of NADW is observed in both the western and eastern basins; in particular, a reversal of the Deep Western Boundary Current at the Middle NADW level is detected. The warming of the intermediate, deep, and near‐bottom waters in the interior eastern basin is revealed from comparison of the section temperature data with those obtained at the WOCE A06 line in 1993. The substantial 1993–2000 temperature increase (+0.02°C–0.1°C) at the intermediate and upper deep levels suggests that the previously reported long‐term warming above 2500–3000 m in the equatorial and subtropical North Atlantic between the late 1950s and early 1990s continued in the interior eastern equatorial basin during the last decade of the 20th century.
Effect of wind variability on topographic waves: Lake Kinneret case
Authors: Shilo Elad , Ashkenazy Yosef , Rimmer Alon , Assouline Shmuel , Katsafados Petros , Mahrer Yitzhaq
Published: December 2007

We studied the winter wind driven circulation in Lake Kinneret (northern Israel) using state of the art atmospheric (Regional Atmosphere Modeling System (RAMS)) and oceanic (Regional Ocean Modeling System (ROMS)) general circulation models. During winter the lake is completely mixed and mainly forced by the passage of synoptic weather systems. The lake's dynamic response was identified using various wind regimes. The response of the lake to a uniform wind stress resulted in the formation of a double‐gyre circulation pattern. After removal of the wind stress, the double‐gyre pattern slowly rotated cyclonically (with a time period of several days) around the lake perimeter, consistent with the pattern of the lowest‐mode basin‐scale topographic (vorticity) wave. The use of RAMS‐simulated wind fields resulted in a less symmetric structure of the double‐gyre pattern due to the presence of a curl in the wind field. Using various wind regimes to force the lake indicated that the presence of a positive or negative curl in the wind field might result in a shift in the topographic wave frequency to a higher or lower value, respectively. This result may be easily applied to motions on the geophysical scale. The currents predicted by RAMS‐ROMS agree well with measured data near the center of the lake. Forcing the model with a spatially uniform wind field constructed from a single station resulted in poor agreement with the observed currents, indicating the importance of the wind field spatial pattern.
Validation of Aura Microwave Limb Sounder water vapor by balloon‐borne Cryogenic Frost point Hygrometer measurements
Authors: Vömel H. , Barnes J. E. , Forno R. N. , Fujiwara M. , Hasebe F. , Iwasaki S. , Kivi R. , Komala N. , Kyrö E. , Leblanc T. , Morel B. , Ogino S.‐Y. , Read W. G. , Ryan S. C. , Saraspriya S. , Selkirk H. , Shiotani M. , Valverde Canossa J. , Whiteman D. N.
Published: December 2007

Here we present extensive observations of stratospheric and upper tropospheric water vapor using the balloon‐borne Cryogenic Frost point Hygrometer (CFH) in support of the Aura Microwave Limb Sounder (MLS) satellite instrument. Coincident measurements were used for the validation of MLS version 1.5 and for a limited validation of MLS version 2.2 water vapor. The sensitivity of MLS is on average 30% lower than that of CFH, which is fully compensated by a constant offset at stratospheric levels but only partially compensated at tropospheric levels, leading to an upper tropospheric dry bias. The sensitivity of MLS observations may be adjusted using the correlation parameters provided here. For version 1.5 stratospheric observations at pressures of 68 hPa and smaller MLS retrievals and CFH in situ observations agree on average to within 2.3% ± 11.8%. At 100 hPa the agreement is to within 6.4% ± 22% and at upper tropospheric pressures to within 23% ± 37%. In the tropical stratosphere during the boreal winter the agreement is not as good. The “tape recorder” amplitude in MLS observations depends on the vertical profile of water vapor mixing ratio and shows a significant interannual variation. The agreement between stratospheric observations by MLS version 2.2 and CFH is comparable to the agreement using MLS version 1.5. The variability in the difference between observations by MLS version 2.2 and CFH at tropospheric levels is significantly reduced, but a tropospheric dry bias and a reduced sensitivity remain in this version. In the validation data set a dry bias at 177.8 hPa of −24.1% ± 16.0% is statistically significant.
Validation of middle‐atmosphere carbon monoxide retrievals from the Microwave Limb Sounder on Aura
Authors: Pumphrey H. C. , Filipiak M. J. , Livesey N. J. , Schwartz M. J. , Boone C. , Walker K. A. , Bernath P. , Ricaud P. , Barret B. , Clerbaux C. , Jarnot R. F. , Manney G. L. , Waters J. W.
Published: December 2007

The Microwave Limb Sounder on Aura has produced an extensive set of measurements of CO in the middle atmosphere. The measurements are usable for scientific studies from the upper troposphere up to 90 km altitude. We describe these measurements and validate them by demonstrating their internal consistency and by comparing them to other remotely sounded measurements and to 2‐D model simulations. Comparisons with other measurements suggest that MLS has a positive bias of 25–50% in the mesosphere and a negative bias of up to 70% in the (almost CO‐free) lower stratosphere. The geophysical features observed in the MLS CO field show excellent qualitative agreement with other measurements.
Global modeling analysis of tropospheric ozone and its radiative forcing from biomass burning emissions in the twentieth century
Authors: Ito Akinori , Sudo Kengo , Akimoto Hajime , Sillman Sanford , Penner Joyce E.
Published: December 2007

This work evaluates the sensitivity of tropospheric ozone (O3) and its radiative forcing (RF) from 1890 to 1990 to different biomass burning (BB) emissions using a global tropospheric climate‐chemistry model (CCM) with a modified chemical mechanism for anthropogenic volatile organic compounds (AVOC). The use of the most efficient simplified chemical scheme among three chemical mechanisms with different degrees of complexity is acceptable for global scale simulations of the radiative effects of tropospheric O3 changes in the CCM, since the differences in the results are small. The CCM model with simplified chemistry is implemented to study various aspects of the impact of BB emissions on tropospheric O3 and its RF. The backward emission model results are in good agreement with the present‐day observations for regions downwind of BB sources, while the forward emission model may reasonably produce the distributions of regional emissions in the preindustrial period. The global mean RF due to tropospheric O3 increase from 1890 to 1990 is 0.41 W m−2 on a global average. When no anthropogenic emissions in the preindustrial period are considered, this forcing reaches 0.47 W m−2. We find that the global mean BB forcing due to tropospheric O3 changes from 1890 to 1990 is 0.15 W m−2 on a global average. The preindustrial BB emissions need to be represented realistically when evaluating controls on the emissions of trace gases and aerosols for a sustainable society, because there are significant open biomass burning emissions in the preindustrial period. The significant regional differences in the surface O3 concentrations among three different BB data sets are found in the United States for 1890 and in Brazil for 1990. In these regions during the periods, the most common land uses in the forests are logging and conversion of primary or secondary forests to cattle pasture or shifting cultivation. Improvement in the data sets of historical land use changes and accurate representation of carbon dynamics are needed for improving the model calculation of biomass burning emissions.
Aerosols and surface UV products from Ozone Monitoring Instrument observations: An overview
Authors: Torres Omar , Tanskanen Aapo , Veihelmann Ben , Ahn Changwoo , Braak Remco , Bhartia Pawan K. , Veefkind Pepijn , Levelt Pieternel
Published: December 2007

We present an overview of the theoretical and algorithmic aspects of the Ozone Monitoring Instrument (OMI) aerosol and surface UV algorithms. Aerosol properties are derived from two independent algorithms. The nearUV algorithm makes use of OMI observations in the 350–390 nm spectral region to retrieve information on the absorption capacity of tropospheric aerosols. OMI‐derived information on aerosol absorption includes the UV Aerosol Index and absorption optical depth at 388 nm. The other algorithm makes use of the full UV‐to‐visible OMI spectral coverage to derive spectral aerosol extinction optical depth. OMI surface UV products include erythemally weighted daily dose as well as erythemal dose rate and spectral UV irradiances calculated for local solar noon conditions. The advantages and limitations of the current algorithms are discussed, and a brief summary of several validation and evaluation analysis carried out to assess the current level of uncertainty of these products is presented.
Sensitivity of MOPITT observations to carbon monoxide in the lower troposphere
Authors: Deeter M. N. , Edwards D. P. , Gille J. C. , Drummond James R.
Published: December 2007

The sensitivity of Measurements of Pollution in the Troposphere (MOPITT) observations to carbon monoxide (CO) concentrations in the lower troposphere (LT) varies widely as the result of variability in thermal contrast conditions. This effect is evident in both the MOPITT weighting functions and averaging kernels, particularly after these quantities are properly normalized to remove grid effects. Comparisons of simulated weighting functions and averaging kernels with operational data confirm the significance of thermal contrast effects. Retrieval sensitivity to LT CO is greatest in daytime observations over land, particularly in tropical and midlatitude regions exhibiting large diurnal variations in surface temperature. Nighttime observations over land typically exhibit poor sensitivity to LT CO. On the global scale, analysis of MOPITT averaging kernels for 1 month indicates that daytime MOPITT observations offer useful sensitivity to LT CO over large areas of most continents. Exceptions include tropical rainforests in Africa and South America, where thermal contrast conditions are relatively weak.
Paleoceanography of the southern Agulhas Plateau during the last 150 ka: Inferences from benthic foraminiferal assemblages and multispecies epifaunal carbon isotopes
Authors: Diz Paula , Hall Ian R. , Zahn Rainer , Molyneux Elizabeth G.
Published: December 2007

Benthic foraminiferal assemblages and the carbon isotope composition of the epifaunal benthic foraminifera Epistominella exigua and Fontbotia wuellerstorfi have been investigated along core MD02‐2589 located at the southern Agulhas Plateau (41°26.03′S, 25°15.30′E, 2660 m water depth). This study aims to evaluate changes in the benthic paleoenvironment and its influence on benthic δ13C with a notable focus on E. exigua, a species associated with phytodetritus deposits and poorly studied in isotope paleoceanographic reconstructions. The benthic foraminiferal assemblages (>63 μm) show large fluctuations in species composition suggesting significant changes in the pattern of ocean surface productivity conceivably related to migrations of the Subtropical Convergence (STC) and Subantarctic Front (SAF). Low to moderate seasonality and relatively higher food supply to the seafloor are indicated during glacial marine isotope stages (MIS) 6, 4, and 2 and during MIS 3, probably associated with the northward migration of the SAF and confluence with the more stationary STC above the southern flank of the Agulhas Plateau. The lowest organic carbon supply to the seafloor is indicated from late MIS 5b to MIS 4 as a consequence of increased influence of the Agulhas Front (AF) and/or weakening of the influence of the STC over the region. Episodic delivery of fresh organic matter, similar to modern conditions at the core location, is indicated during MIS 5c–MIS 5e and at Termination I. Comparison of this paleoenvironmental information with the paired δ13C records of E. exigua and F. wuellerstorfi suggests that organic carbon offsets δ13C of E. exigua from ambient bottom water δ13CDIC, while its δ13C amplitude, on glacial‐interglacial timescales, does not seem affected by changes of organic carbon supply to the seafloor. This suggests that this species calcifies preferentially during the short time span of the year when productivity peaks and phytodetritus is delivered to the seafloor. Therefore E. exigua, while offset from δ13CDIC, potentially more faithfully records the amplitude of ambient bottom water δ13CDIC changes than F. wuellerstorfi, notably in settings such as the Southern Ocean that experienced substantial changes through time in the organic carbon supply to the seafloor.
Multifractal analysis of flow velocity simulated with the lattice model approach in idealized three‐dimensional porous media
Authors: Jiménez‐Hornero F. J. , Giráldez J. V. , Laguna A. M.
Published: December 2007

The strange attractor formalism has been used to check whether the flow velocity in idealized three‐dimensional porous media could be described by the multifractal approach. The flow velocity magnitude was simulated with a lattice model in six media with different porosities. The results obtained from the analysis of the mass exponent functions and the multifractal and generalized dimensions spectra show that the velocity of the simulated flows has a multifractal type of scaling that becomes stronger as the porosity decreases. A correlation analysis has been performed showing the relationships between the statistical properties and the multifractal parameters of the velocity magnitude distribution.
Analysis of DNA structure as a 2D random walk by complex wavelet transform
Authors: Postnikov Eugene , Loskutov Alexander , Larionov Sergey , Ryadchenko Evgeny , Kiseliov Roman
Published: December 2007

We propose the original method of the time-scale wavelet analysis of DNA sequence represented as a 2D walk on a complex plane. Namely, we consider the mapping of two irreducible A − T and G − C sequences into a walk trajectory in the plane AGTC (firstly proposed by M. Gates) as a unique complex-valued function. This function is processed with the new algorithm of the continuous wavelet transform with the Morlet wavelet. This method is based on the representation of the transform’s result as a solution of the specific Cauchy problem for the system of PDE. As an example, we applied the described algorithm to a part of the telomer region of the 22 human chromosome and demonstated the high exactness. Moreover, it is very fast and it provides wide opportunities for the analysis of large genome data samples.
Fast Point-Feature Label Placement for Dynamic Visualizations
Authors: Mote Kevin
Published: December 2007

This paper describes a fast approach to automatic point label de-confliction on interactive maps. The general Map Labeling problem is NP-hard and has been the subject of much study for decades. Computerized maps have introduced interactive zooming and panning, which has intensified the problem. Providing dynamic labels for such maps typically requires a time-consuming pre-processing phase. In the realm of visual analytics, however, the labeling of interactive maps is further complicated by the use of massive datasets laid out in arbitrary configurations, thus rendering reliance on a pre-processing phase untenable. This paper offers a method for labeling point-features on dynamic maps in real time without pre-processing. The algorithm presented is efficient, scalable, and exceptionally fast; it can label interactive charts and diagrams at speeds of multiple frames per second on maps with tens of thousands of nodes. To accomplish this, the algorithm employs a novel geometric de-confliction approach, the ‘trellis strategy,’ along with a unique label candidate cost analysis to determine the “least expensive” label configuration. The speed and scalability of this approach make it well-suited for visual analytic applications.
Biatomic substrates for bulk-molecule interfaces: The PtCo-oxygen interface
Authors: Sotelo Juan C. , Seminario Jorge M.
Published: December 2007

We develop an ab initio procedure for materials participating in electron transfer reactions, to consider biatomic backgrounds (e.g., substrates, catalysts, electrodes), thus the precise effects of the continuum and long-range interactions as well as the effects of the discrete and local nature of the chemistry can be combined to study molecules under such biatomic backgrounds. We test this new procedure by studying the reactivity of molecular oxygen on bimetallic clusters of platinum and cobalt. The reaction of molecular oxygen on the surface of the L12 phase of Co3Pt yields three distinct chemisorbed precursors, two of which are energetically almost degenerate. One precursor is formed across a bridge site with the molecule parallel to the surface, the second one is formed at the bridge with the molecule again parallel to the surface, and the third is formed in the threefold fcc hollow site, with the molecule slightly tilted in a top-hollow-bridge geometry.
Nature of the metal–nonmetal transition in metal–ammonia solutions. I. Solvated electrons at low metal concentrations
Authors: Chuev Gennady N. , Quémerais Pascal , Crain Jason
Published: December 2007

Using a theory of polarizable fluids, we extend a variational treatment of an excess electron to the many-electron case corresponding to finite metal concentrations in metal–ammonia solutions (MAS). We evaluate dielectric, optical, and thermodynamical properties of MAS at low metal concentrations. Our semianalytical calculations based on a mean-spherical approximation correlate well with the experimental data on the concentration and temperature dependencies of the dielectric constant and the optical absorption spectrum. The properties are found to be mainly determined by the induced dipolar interactions between localized solvated electrons, which result in the two main effects: the dispersion attractions between the electrons and a sharp increase in the static dielectric constant of the solution. The first effect creates a classical phase separation for the light alkali metal solutes (Li, Na, K) below a critical temperature. The second effect leads to a dielectric instability, i.e., polarization catastrophe, which is the onset of metallization. The locus of the calculated critical concentrations is in a good agreement with the experimental phase diagram of Na-NH3 solutions. The proposed mechanism of the metal–nonmetal transition is quite general and may occur in systems involving self-trapped quantum quasiparticles.
Nonadiabatic dynamics of charge transfer in diatomic anion clusters
Authors: Cho Eunseog , Shin Seokmin
Published: December 2007

We have studied the photodissociation and recombination dynamics of the diatomic anions X2− and XY− designed to mimic I2− and ICl−, respectively, by using a one-electron model in size-selected N2O clusters. The one-electron model is composed of two nuclei and an extra electron moving in a two-dimensional plane including the two nuclei. The main purpose of this study is to explain the salient features of various dynamical processes of molecular ions in clusters using a simple theoretical model. For heteronuclear diatomic anions, a mass disparity and asymmetric electron affinity between the X and Y atoms lead to different phenomena from the homonuclear case. The XY− anion shows efficient recombination for a smaller cluster size due to the effect of collision-mediated energy transfer and an inherent potential wall on excited state at asymptotic region, while the recombination for the X2− anion is due to rearrangement of solvent configuration and faster nonadiabatic transitions. The results of the present study illustrate the microscopic details of the electronically nonadiabatic processes which control the photodissociation dynamics of molecular ions in clusters.
Electronic polarization effect on low-frequency infrared and Raman spectra of aprotic solvent: Molecular dynamics simulation study with charge response kernel by second order Møller–Plesset perturbation method
Authors: Isegawa Miho , Kato Shigeki
Published: December 2007

Low-frequency infrared (IR) and depolarized Raman scattering (DRS) spectra of acetonitrile, methylene chloride, and acetone liquids are simulated via molecular dynamics calculations with the charge response kernel (CRK) model obtained at the second order Møller–Plesset perturbation (MP2) level. For this purpose, the analytical second derivative technique for the MP2 energy is employed to evaluate the CRK matrices. The calculated IR spectra reasonably agree with the experiments. In particular, the agreement is excellent for acetone because the present CRK model well reproduces the experimental polarizability in the gas phase. The importance of interaction induced dipole moments in characterizing the spectral shapes is stressed. The DRS spectrum of acetone is mainly discussed because the experimental spectrum is available only for this molecule. The calculated spectrum is close to the experiment. The comparison of the present results with those by the multiple random telegraph model is also made. By decomposing the polarizability anisotropy time correlation function to the contributions from the permanent, induced polarizability and their cross term, a discrepancy from the previous calculations is observed in the sign of permanent-induce cross term contribution. The origin of this discrepancy is discussed by analyzing the correlation functions for acetonitrile.
Two-photon absorption of [2.2]paracyclophane derivatives in solution: A theoretical investigation
Authors: Ferrighi Lara , Frediani Luca , Fossgaard Eirik , Ruud Kenneth
Published: December 2007

The two-photon absorption of a class of [2.2]paracyclophane derivatives has been studied using quadratic response and density functional theories. For the molecules investigated, several effects influencing the two-photon absorption spectra have been investigated, such as side-chain elongation, hydrogen bonding, the use of ionic species, and solvent effects, the latter described by the polarizable continuum model. The calculations have been carried out using a recent parallel implementation of the polarizable continuum model in the DALTON code. Special attention is given to those aspects that could explain the large solvent effect on the two-photon absorption cross sections observed experimentally for this class of compounds.
Infrared spectra of SF6−∙(H2O)n (n=1–3): Incipient reaction and delayed onset of water network formation
Authors: Schneider Holger , Weber J. Mathias
Published: December 2007

We present data on the microsolvation of an extended charge distribution with SF6− as a model system. Infrared spectroscopy, aided by ab initio calculations, shows that the first two water molecules attach to the ion by a combination of single ionic H bonds, sharing one of the F atoms, and weak electrostatic interactions with other F atoms in the ion. No water-water bonds are formed at the dihydrate level, which is an unusual observation, given the strong propensity of water to form H-bonded networks. The onset of water networks occurs with the addition of the third water molecule. Moreover, the attachment of the first two water molecules considerably weakens the SF bond of the F atom involved in bonding to both ligands, indicating a possible mechanism for water-induced reactions.
Comment on “Enhanced optical field intensity distribution in organic photovoltaic devices using external coatings” [Appl. Phys. Lett. 89, 233502 (2006)]
Authors: Song Q. L. , Li C. M.
Published: December 2007

O’Connor et al.1 reported the enhancement of light intensity at a donor-acceptor (D-A) interface in organic solar cells, in which an external coating of an aluminum hydroxiquinoline (Alq3) cap layer was used. Since the enhancement of light intensity at the D-A interface is periodic with the thickness of Alq3 and the lifetime of an organic solar cell based on copper phthalocyanine (CuPc)–C60 is sensitive to air,2,3 the suggestion of protecting the cells by external coating of Alq3 seems like a great idea that not only improves the cell photocurrent but also protects the cells from the ambient, particularly with the use of thick Alq3. However, as the discussion in this letter later, this may be not true.
Base-pair interactions in the gas-phase proton-bonded complexes of C+G and C+GC
Authors: Han Sang Yun , Lee Sang Hak , Chung Jayong , Oh Han Bin
Published: December 2007

Interactions involved in the formation of gas-phase proton-bonded molecular complexes of cytosine (C) and guanine (G) were theoretically investigated for the case of C+G and C+GC using B3LYP density functional theory. In this study, particular focus was on the dimeric interaction of proton-bonded C+G, where a proton bond and a hydrogen bond are cooperatively involved. The dimer interaction energy in terms of dissociation energy (De) was predicted to be 41.8kcal∕mol. The lowest (frozen) energy structure for the C+G dimeric complex was found to be CH+⋯G rather than C⋯H+G in spite of the lower proton affinity of the cytosine moiety, which was more stable by 3.3kcal∕mol. The predicted harmonic vibrational frequencies and bond lengths suggest that the combined contributions of proton and hydrogen bonding may determine the resultant stability of each complex structure. In contrast to the dimer case, in the case of the isolated C+GC triplet, the two minimum energy structures of CH+⋯GC and C⋯H+GC were predicted to be almost equivalent in total energy. The dissociation energy (De) for the C+G pairing in the C+GC triplet was 43.7kcal∕mol. Other energetics are also reported. As for the proton-transfer reaction in the proton-bond axis, the forward proton-transfer barriers for the dimer and trimer complexes were also predicted to be very low, 3.6 and 1.5kcal∕mol (ΔEePT), respectively.
Spatiotemporal correlation functions in beam-driven plasmas with fluctuations
Authors: Tyshetskiy Yu. , Roberts J. A. , Robinson P. A. , Cairns I. H. , Li B.
Published: December 2007

Using a reduced-parameter model of wave-particle interactions in a beam-driven plasma, the linear spatiotemporal correlation functions of wave and particle quantities are derived. These are found to have an oscillatory structure with characteristic spatial and temporal scales reflecting the dynamics of energy exchange between particles and waves. The effects of various system parameters on these characteristic scales and the correlation functions are investigated. The correlation scales are shown to diverge in some limiting cases, implying the possibility of criticality in the system. A comparison with fully nonlinear numerical simulations is carried out, and the criterion for validity of the linear correlation functions is derived and verified. The nonlinear simulation results are shown to converge to the linear prediction in appropriate limits dictated by this criterion. The correlation functions obtained provide a useful tool for studying dynamical properties of beam-driven plasma-wave systems with fluctuating parameters.
Boron 1s photoelectron spectrum of B11F3: Vibrational structure and linewidth
Authors: Thomas T. Darrah , Püttner Ralph , Fukuzawa Hironobu , Prümper Georg , Ueda Kiyoshi , Kukk Edwin , Sankari Rami , Harries James , Tamenori Yusuke , Tanaka Takahiro , Hoshino Masamitsu , Tanaka Hiroshi
Published: December 2007

The boron 1s photoelectron spectrum of B11F3 has been measured at a photon energy of 400eV and a resolution of about 55meV. The pronounced vibrational structure seen in the spectrum has been analyzed to give the harmonic and anharmonic vibrational frequencies of the symmetric stretching mode, 128.1 and 0.15meV, as well as the change in equilibrium BF bond length upon ionization, −5.83pm. A similar change in bond length has been observed for PF3 and SiF4, but a much smaller change for CF4. Theoretical calculations for BF3 that include the effects of electron correlation give results that are in reasonable accord with the experimental values. The Lorentzian (lifetime) width of the boron 1s core hole in BF3 is found to be 72meV, comparable to the value of 77meV that has been reported for CF4.
Uniqueness of the iterative solution of the optimized effective potential equation
Authors: Joubert D. P.
Published: December 2007

The optimized effective potential (OEP) equation can be used in a numerically efficient self-consistent form to solve for the density functional exchange and correlation potentials, as shown in a recent paper of Kümmel and Perdew [Phys. Rev. Lett. 90, 43004 (2003)]. The uniqueness of an iterative solution of the OEP equation has not yet been adequately addressed. In this paper, it is shown that no nonconstant multiplicative potentials that can contaminate an iterative solution of the OEP equation exist and, hence, that formally the exact exchange-correlation potential determined form of the OEP equation is unique to within a constant.
Resonance enhanced turbulent transport
Authors: Newton Andrew P. L. , Kim Eun-jin
Published: December 2007

The effect of oscillatory shear flows on turbulent transport of passive scalar fields is studied by numerical computations based on the results provided by E. Kim [Physics of Plasmas 13, 022308 (2006)]. Turbulent diffusion is found to depend crucially on the competition between suppression due to shearing and enhancement due to resonances, depending on the characteristic time and length scales of shear flow and turbulence. Enhancements in transport occur for turbulence with finite memory time either due to Doppler or parametric resonances. Scalings of turbulence amplitude and transport are provided in different parameter spaces. The results suggest that oscillatory shear flows are not only less efficient in regulating turbulence, but also can enhance the value of turbulent diffusion, accelerating turbulent transport.
Cerium oxide nanocrystals for nonvolatile memory applications
Authors: Yang Shao-Ming , Chien Chao-Hsin , Huang Jiun-Jia , Lei Tan-Fu , Tsai Ming-Jinn , Lee Lurng-Shehng
Published: December 2007

The characteristics of silicon-oxide-nitride-oxide-silicon-type memories embedded with cerium oxide nanocrystals were demonstrated. They were fabricated by depositing a thin CeO2 film on the SiO2 tunneling layer and subsequently rapid-thermal annealing process. The mean size and aerial density of the CeO2 nanocrystals embedded in SiO2 are estimated to be about 8–10nm and (3–7)×1011∕cm−2 after a high-temperature annealing with different ambients on 900°C. The program/erase behaviors and data retention characteristics were described to demonstrate its advantages for nonvolatile memory device applications.