bluuebunny/crossref_metadata_2025 huggingface dataset:
A near‐real‐time model‐assisted ionosphere electron density retrieval method
Authors: Nava B. , Radicella S. M. , Leitinger R. , Coïsson P.
Published: August 2006

NeQuick is a three‐dimensional and time‐dependent quick run electron density model specifically designed for transionospheric propagation applications. It allows calculation of electron concentration values at any location in the ionosphere and the total electron content (TEC) along any ground station–to–satellite ray path. After specific adaptations, the model has been used to develop a near‐real‐time nontomographic electron density retrieval technique able to provide the electron density of the ionosphere above the geographic area of interest. The technique relies on the knowledge of the model driving parameter Az (ionization level) for the location considered. In the present study, the necessary Az values have been obtained through direct ingestion of Global Positioning System (GPS)–derived slant TEC data in two different ways: using data from a single GPS receiver and using data from multiple ground stations. Statistical comparisons between experimental and reconstructed slant TEC values and between experimental and retrieved maximum electron concentration values are shown.
Nonlinear reflection of a high‐frequency radio wave by the ionospheric grating created by another wave
Authors: Kumar Ashok , Uma R. , Tripathi V. K.
Published: August 2006

A powerful O‐mode radio wave of frequency ω0, launched from a ground‐based transmitter into the equatorial ionosphere, forms a standing wave pattern below the critical layer, heating the electrons with spatial periodicity. Subsequent ambipolar redistribution of plasma creates a density ripple. When another radio wave, of higher‐frequency ω, is launched into the ripple region, the oscillatory electron velocity due to the ω wave couples to the density ripple to produce a nonlinear current that resonantly drives a reflected wave toward the Earth at frequency ω when k matching condition is satisfied. By this scheme one may reflect radio waves of frequency 20 times the maximum plasma frequency ωpmax of the ionosphere. In the case when the heater wave is mode converted into a plasma wave with Airy function profile, the nonuniform heating of electrons forms a nonuniform density grating of much shorter periodicity length. This grating may cause reflection of much higher frequency waves, however, with lesser amplitude.
Seismotectonics of the southern Apennines and Adriatic foreland: Insights on active regional E‐W shear zones from analogue modeling
Authors: Di Bucci Daniela , Ravaglia Antonio , Seno Silvio , Toscani Giovanni , Fracassi Umberto , Valensise Gianluca
Published: August 2006

The active tectonics at the front of the southern Apennines and in the Adriatic foreland is characterized by E‐W striking, right‐lateral seismogenic faults, interpreted as reactivated inherited discontinuities. The best studied among these is the Molise‐Gondola shear zone. The interaction of these shear zones with the Apennines chain is not yet clear. To address this open question, we developed a set of scaled analogue experiments, aimed at analyzing (1) how dextral strike‐slip motion along a preexisting zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge; (2) the propagation of deformation as a function of displacement; and (3) any insights on the active tectonics of southern Italy. Our results stress the primary role played by these inherited structures when reactivated and confirm that regional E‐W dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the southern Apennines.
Uncertainty quantification of satellite precipitation estimation and Monte Carlo assessment of the error propagation into hydrologic response
Authors: Hong Yang , Hsu Kuo‐lin , Moradkhani Hamid , Sorooshian Soroosh
Published: August 2006

The aim of this paper is to foster the development of an end‐to‐end uncertainty analysis framework that can quantify satellite‐based precipitation estimation error characteristics and to assess the influence of the error propagation into hydrological simulation. First, the error associated with the satellite‐based precipitation estimates is assumed as a nonlinear function of rainfall space‐time integration scale, rain intensity, and sampling frequency. Parameters of this function are determined by using high‐resolution satellite‐based precipitation estimates and gauge‐corrected radar rainfall data over the southwestern United States. Parameter sensitivity analysis at 16 selected 5° × 5° latitude‐longitude grids shows about 12–16% of variance of each parameter with respect to its mean value. Afterward, the influence of precipitation estimation error on the uncertainty of hydrological response is further examined with Monte Carlo simulation. By this approach, 100 ensemble members of precipitation data are generated, as forcing input to a conceptual rainfall‐runoff hydrologic model, and the resulting uncertainty in the streamflow prediction is quantified. Case studies are demonstrated over the Leaf River basin in Mississippi. Compared with conventional procedure, i.e., precipitation estimation error as fixed ratio of rain rates, the proposed framework provides more realistic quantification of precipitation estimation error and offers improved uncertainty assessment of the error propagation into hydrologic simulation. Further study shows that the radar rainfall‐generated streamflow sequences are consistently contained by the uncertainty bound of satellite rainfall generated streamflow at the 95% confidence interval.
Improvements in large‐scale drainage networks derived from digital elevation models
Authors: Paz Adriano Rolim , Collischonn Walter , Lopes da Silveira André Luiz
Published: August 2006

This paper presents an improved algorithm for deriving drainage networks for coarse‐gridded distributed hydrological models based on relatively fine resolution digital elevation models. The proposed algorithm aims to reproduce actual drainage networks more closely when applied in regions with meandering rivers running in parallel and for cell sizes of the order of 10 kilometers. To achieve this goal, the COTAT algorithm of Reed (2003) was improved, introducing another parameter related to the minimum upstream flow path into the cell besides the area threshold. The proposed algorithm was tested by applying it to the catchments of the rivers Tapajos (530,000 km2) and Grande (145,000 km2) in South America. Results show that drainage networks are generally improved by the proposed algorithm, needing only minor manual corrections.
Ecohydrological controls on soil moisture fluxes in arid to semiarid vadose zones
Authors: Sandvig Renee M. , Phillips Fred M.
Published: August 2006

Overlying vegetation plays a key role in the hydrodynamics of desert vadose zones. To investigate the roles of vegetation and climate on vadose zone dynamics, eleven 5–10 m boreholes were drilled under ponderosa pine, juniper, grassland, and creosote vegetation communities along a transect ranging in elevation from 1470 to 2380 m in central New Mexico and were analyzed for soil water content and potential and environmental tracers. The results indicate that there has been no downward liquid movement past the root zone under the creosote sites over the past ∼20 kyr. There have been periodic, downward fluxes past the root zone under the grass and juniper sites (<0.4 mm yr−1) as well as preferential flow, but under ponderosa pine, downward fluxes are appreciable (2.3 mm yr−1). Fluxes were similar within vegetation communities, even at sites separated by considerable distance and elevation (and thus climate), but differed markedly over short distances across ecotones, demonstrating that vegetation ecology strongly modulates the influence of climate and that characteristic vadose zone hydrological regimes are associated with the various vegetation communities.
Soil moisture and vegetation controls on evapotranspiration in a heterogeneous Mediterranean ecosystem on Sardinia, Italy
Authors: Detto Matteo , Montaldo Nicola , Albertson John D. , Mancini Marco , Katul Gaby
Published: August 2006

Micrometeorological measurements of evapotranspiration (ET) can be difficult to interpret and use for validating model calculations in the presence of land cover heterogeneity. Land surface fluxes, soil moisture (θ), and surface temperatures (Ts) data were collected by an eddy correlation‐based tower located at the Orroli (Sardinia) experimental field (covered by woody vegetation, grass, and bare soil) from April 2003 to July 2004. Two Quickbird high‐resolution images (summer 2003 and spring 2004) were acquired for depicting the contrasting land cover components. A procedure is presented for estimating ET in heterogeneous ecosystems as the residual term of the energy balance using Ts observations, a two‐dimensional footprint model, and the Quickbird images. Two variations on the procedure are successfully implemented: a proposed two‐source random model (2SR), which treats the heat sources of each land cover component separately but computes the bulk heat transfer coefficient as spatially homogeneous, and a common two‐source tile model. For 2SR, new relationships between the interfacial transfer coefficient and the roughness Reynolds number are estimated for the two bare soil–woody vegetation and grass–woody vegetation composite surfaces. The ET versus θ relationships for each land cover component were also estimated, showing that that the woody vegetation has a strong tolerance to long droughts, transpiring at rates close to potential for even the driest conditions. Instead, the grass is much less tolerant to θ deficits, and the switch from grass to bare soil following the rainy season had a significant impact on ET.
Particle acceleration at a dynamic termination shock
Authors: Florinski V. , Zank G. P.
Published: August 2006

We investigate the effects of a large‐scale interplanetary disturbance, such as a merged interaction region (MIR), on the properties of the heliospheric termination shock and particle population accelerated at the shock. The interaction process between transient structures and the shock is reflected in energetic particle spectra through variability in shock location, its compression ratio, and particle mean free paths that control their acceleration rate. It is shown that particle distributions observed at a specific moment of time exhibit features, such as spectral breaks, from earlier acceleration stages with lowest energy particles produced most recently and the more energetic anomalous cosmic rays (ACRs) accelerated at earlier times. We also show that a MIR collision can produce an extended period of anomalously low radial velocity in the heliosheath if density and velocity variations are correlated within a MIR and a following rarefaction.
Influence of the rupture initiation on the intersonic transition: Crack‐like versus pulse‐like modes
Authors: Festa G. , Vilotte J.‐P.
Published: August 2006

We numerically investigate the supershear transition of inplane rupture under slip weakening friction and tectonic loading, using a non‐smooth spectral element method. Nucleation of the rupture in the vicinity of an initial stress concentration is consistently solved together with the dynamic propagation. Nucleation is shown to influence the transition to the supershear propagation and, depending upon the initiation process and the level of the stress out of the nucleating asperity, crack‐like or pulse‐like solutions can be selected in the intersonic regime. Pulses are triggered by dynamic unloading of the traction ahead of the Rayleigh wave and tend to become metastable. The asymptotic numerical solution is always a crack propagating close to P wave speed. The rupture front and the arrest velocities are numerically characterized. We argue that the nucleation phase introduces a trade‐off with the state of the stress, in determining the distance at which supershear appears.
The apparently isotropic Australian upper mantle
Authors: Heintz Maggy , Kennett Brian L. N.
Published: August 2006

We investigate shear wave splitting measurements performed on two years of data recorded at stations deployed in the TASMAL experiment, a network of 20 broadband seismological stations designed to record data on each side of the controversial Tasman Line in Australia. Whereas a subset of measurements previously performed on one year of data exhibited a curvilinear pattern similar to that of the Tasman Line, suggesting anisotropy frozen in the lithosphere, considering the whole data set drastically changes the situation: apparent isotropy in the Australian upper mantle is observed at numerous stations. This apparent isotropy together with the EW or NS orientations of the polarization plane of the fast S wave (ϕ) observed at some stations is consistent with a two‐layer anisotropic system underneath the Australian continent, with a perpendicular orientation of ϕ in each layer. From the latest tomographic results, the transition between the Precambrian western and Phanerozoic eastern Australia appears to define blocks of various thickness. Unlike the situation across the TESZ in Europe, these blocks do not seem to be correlated with a different behavior in terms of seismic anisotropy.
Magnesium isotopic composition of olivine from the Earth, Mars, Moon, and pallasite parent body
Authors: Norman M. D. , Yaxley G. M. , Bennett V. C. , Brandon A. D.
Published: August 2006

To investigate the nebular history of material contributing to the terrestrial planets, and search for evidence of a high‐temperature origin of the Moon, we measured Mg isotopic compositions of primitive olivines from the Earth, Moon, Mars, and pallasite parent body using laser‐ablation multi‐collector ICPMS. No temporal variation in the Earth's mantle since at least 3.8 Ga, and only limited variations in the compositions of mantle sources from diverse tectonic settings were found. Earth, Moon, Mars, and differentiated asteroids appear to have formed from a nebular reservoir that was homogeneous with respect to Mg isotopes. This implies either a minor role for evaporation‐condensation in the inner solar system, or a limited variation in the proportion of refractory CAI‐like material contributing to the terrestrial planets. The Mg isotopic composition of the Moon is identical to the Earth's mantle, placing strong constraints on any volatility‐related fractionation that occurred during formation of the Moon.
Future winter extreme temperature and precipitation events in the Arctic
Authors: Saha S. K. , Rinke A. , Dethloff K.
Published: August 2006

This study investigates the possible changes in future winter temperature and precipitation extremes in the Arctic using the regional climate model HIRHAM4. Under the B2 emission scenario conditions, frequency and intensity of future (2037–2051) extremes have changed significantly compared to the present‐day (1981–1995) extremes. Extreme precipitations have intensified and the number of extreme events has changed significantly over East Siberia and Barents Sea. Extreme warm and extreme cold temperatures have become warmer with maxima over Barents Sea and Central Eurasia. Changes in the mean climate and its variability are modulating the future winter extreme events.
Testing the silica leakage hypothesis with sedimentary opal records from the eastern equatorial Pacific over the last 150 kyrs
Authors: Kienast S. S. , Kienast M. , Jaccard S. , Calvert S. E. , François R.
Published: August 2006

We have measured 230Th‐normalized opal fluxes in several cores from the eastern equatorial Pacific (EEP) to test the validity of the “silica leakage” hypothesis, which purports that redistribution of silicic acid from the Southern Ocean to the low latitudes was responsible for a significant portion of the reduction in atmospheric carbon dioxide (CO2) during the last glacial period. The silica leakage hypothesis predicts higher opal fluxes in the EEP and lower opal fluxes in the Southern Ocean during periods of low atmospheric CO2. These predictions are not borne by the sedimentary record during glacial oxygen isotope stage 2 (OIS 2, 13–27 kyrs B.P.). However, we find a prominent opal flux maximum in the EEP in the middle of OIS 3 (ca. 40–60 kyrs BP) coinciding with low opal fluxes in several cores from the subantarctic zone. This observation is consistent with silica leakage from the Southern Ocean to the equatorial upwelling region during OIS 3, when both low dust flux and extended sea ice could have contributed to limiting diatom productivity in the Southern Ocean. Since this event is not associated with a clear minimum in the Vostok ice record of CO2, its impact on atmospheric CO2 appears to be small.
Direct test of static stress versus dynamic stress triggering of aftershocks
Authors: Pollitz Fred F. , Johnston Malcolm J. S.
Published: August 2006

Aftershocks observed over time scales of minutes to months following a main shock are plausibly triggered by the static stress change imparted by the main shock, dynamic shaking effects associated with passage of seismic waves from the main shock, or a combination of the two. We design a direct test of static versus dynamic triggering of aftershocks by comparing the near‐field temporal aftershock patterns generated by aseismic and impulsive events occurring in the same source area. The San Juan Bautista, California, area is ideally suited for this purpose because several events of both types of M ∼ 5 have occurred since 1974. We find that aftershock rates observed after impulsive events are much higher than those observed after aseismic events, and this pattern persists for several weeks after the event. This suggests that, at least in the near field, dynamic triggering is the dominant cause of aftershocks, and that it generates both immediate and delayed aftershock activity.
Tidal dynamics and rainfall control N2O and CH4 emissions from a pristine mangrove creek
Authors: Barnes J. , Ramesh R. , Purvaja R. , Nirmal Rajkumar A. , Senthil Kumar B. , Krithika K. , Ravichandran K. , Uher G. , Upstill‐Goddard R.
Published: August 2006

Dissolved CH4, N2O, O2, and inorganic nitrogen nutrients (NH4+, NO3− and NO2−) were measured over tidal cycles in pristine Wright Myo mangrove creek waters during dry and wet seasons. Dissolved CH4 and N2O showed no seasonality (dry season; 491 ± 133 nmol CH4 l−1, 9.0 ± 2.3 nmol N2O l−1, wet season; 466 ± 94 nmol CH4 l−1, 8.6 ± 1.3 nmol N2O l−1). Creek water dissolved gas and inorganic nitrogen distributions reflect sediment porewater release during hydrostatic pressure drop toward low water. Creek water CH4 emission was suppressed by oxidation during rainfall, consistent with changes to dissolved nitrogen speciation, although N2O emissions were unaffected. Scaling up emissions flux estimates from mangrove creek waters and intertidal sediment gives worldwide mangrove emissions ∼1.3 × 1011 mol CH4 yr−1 and 2.7 × 109 mol N2O yr−1; mangrove ecosystems are thus small contributors to coastal N2O emissions but could dominate coastal CH4 emissions. Comparing our data with mangrove CO2 fluxes, mangrove ecosystems could be small net contributors of atmospheric greenhouse gases.
Interaction between iron and post‐perovskite at core‐mantle boundary and core signature in plume source region
Authors: Sakai Takeshi , Kondo Tadashi , Ohtani Eiji , Terasaki Hidenori , Endo Noriaki , Kuba Toshiko , Suzuki Toshiaki , Kikegawa Takumi
Published: August 2006

Interaction between the lower mantle and core is essential for understanding the nature of D″ layer at the core‐mantle boundary (CMB). Here, we report the reaction between post‐perovskite (PPv) and metallic iron under the condition of the CMB, for example, 139 GPa and 3000 Kelvin. Analytical transmission electron microscope (ATEM) analysis revealed that significant amount of oxygen up to 6.3 weight percent (wt.%) and silicon up to 4.0 wt.% can be dissolved into molten iron. The dihedral angle between PPv and molten iron is 67 degrees. Thus, a small amount of core metal of about 2 volume percent (vol.%) can be trapped without separation in the PPv region at the CMB. The amount of core metal trapped by this mechanism can produce the isotopic signature of the outer core in the plume source at the base of the lower mantle.
Ice shelf grounding zone structure from ICESat laser altimetry
Authors: Fricker Helen Amanda , Padman Laurie
Published: August 2006

We present a technique for investigating the grounding zone (GZ) of Antarctic ice shelves using laser altimetry from the Ice, Cloud and land Elevation Satellite (ICESat). Most surface height variability in the GZ is easily resolved by the ICESat laser's ∼65 m footprint and ∼172 m along‐track spacing. Comparisons of repeated tracks sampled at different phases of the ocean tide identify the landward and seaward limits of tide‐forced ice flexure, providing GZ location and width information for each track. Using ICESat data in the Institute Ice Stream region of southern Ronne Ice Shelf, we demonstrate that the location of the GZ based on feature identification in satellite imagery or digital elevation models may be in error by several km. Our results show that ICESat will contribute significantly to improving knowledge of GZ structure and to studies requiring accurate GZ locations, e.g., ice mass balance calculations and ice‐sheet/ocean modeling.
Chemical ozone loss in a chemistry‐climate model from 1960 to 1999
Authors: Lemmen Carsten , Dameris Martin , Müller Rolf , Riese Martin
Published: August 2006

In the recent WMO assessment of ozone depletion, the minimum ozone column is used to assess the evolution of the polar ozone layer simulated in several chemistry‐climate models (CCMs). The ozone column may be strongly influenced by changes in transport and is therefore not well‐suited to identify changes in chemistry. The quantification of chemical ozone depletion can be achieved with tracer‐tracer correlations (TRAC). For forty Antarctic winters (1960–1999), we present the seasonal chemical depletion simulated with the ECHAM4.L39(DLR)/CHEM model. Analyzing methane–ozone correlations, we find a mean chemical ozone loss of 80 ± 10 DU during the 1990s, with a maximum of 94 DU. Compared to ozone loss deduced from HALOE measurements the model underestimates chemical loss by 37%. The average multidecadal trend in loss from 1960 to 1999 is 17 ± 3 DU per decade. The largest contribution to this trend comes from the 62 ± 11 DU ozone loss increase between the 1970s and 1990s.
A novel human artificial chromosome gene expression system using herpes simplex virus type 1 vectors
Authors: Moralli Daniela , Simpson Kirsty M , Wade‐Martins Richard , Monaco Zoia Larin
Published: August 2006

Human artificial chromosome (HAC) vectors are an important gene transfer system for expression and complementation studies. We describe a significant advance in HAC technology using infectious herpes simplex virus type 1 (HSV‐1) amplicon vectors for delivery. This highly efficient method has allowed gene‐expressing HACs to be established in glioma‐, kidney‐ and lung‐derived cells. We also developed an HSV‐1 hypoxanthine phosphoribosyltransferase (HPRT) HAC vector, which generated functional HPRT‐expressing HACs that complemented the genetic deficiency in human cells. The transduction efficiency of the HSV‐1 HAC amplicons is several orders of magnitude higher than lipofection‐mediated delivery. Studies on HAC stability between cell types showed important differences that have implications for HAC development and gene expression in human cells. This is the first report of establishing gene‐expressing HACs in human cells by using an efficient, high‐capacity viral vector and by identifying factors that are involved in cell‐type‐specific HAC instability. The work is a significant advance for HAC technology and the development of HAC gene expression systems in human cells.
Formation of GW bodies is a consequence of microRNA genesis
Authors: Pauley Kaleb M , Eystathioy Theophany , Jakymiw Andrew , Hamel John C , Fritzler Marvin J , Chan Edward K L
Published: August 2006

GW bodies (GWBs), or mammalian P bodies, proposed to be involved in messenger RNA storage and/or degradation, have recently been linked to RNA interference and microRNA (miRNA) processing. We report that endogenous let‐7 miRNA co‐precipitates with the GW182 protein complex. In addition, knockdown of two proteins, Drosha and its protein partner DGCR8, which are vital to the generation of mature miRNA, results in the loss of GWBs. Subsequent introduction of short interference RNA specific to lamin A/C is accompanied by reassembly of GWBs and concurrent knockdown of lamin A/C protein. Taken together, these studies show that miRNAs are crucial components in GWB formation.
Aβ42‐driven cerebral amyloidosis in transgenic mice reveals early and robust pathology
Authors: Radde Rebecca , Bolmont Tristan , Kaeser Stephan A , Coomaraswamy Janaky , Lindau Dennis , Stoltze Lars , Calhoun Michael E , Jäggi Fabienne , Wolburg Hartwig , Gengler Simon , Haass Christian , Ghetti Bernardino , Czech Christian , Hölscher Christian , Mathews Paul M , Jucker Mathias
Published: August 2006

We have generated a novel transgenic mouse model on a C57BL/6J genetic background that coexpresses KM670/671NL mutated amyloid precursor protein and L166P mutated presenilin 1 under the control of a neuron‐specific Thy1 promoter element (APPPS1 mice). Cerebral amyloidosis starts at 6–8 weeks and the ratio of human amyloid (A)β42 to Aβ40 is 1.5 and 5 in pre‐depositing and amyloid‐depositing mice, respectively. Consistent with this ratio, extensive congophilic parenchymal amyloid but minimal amyloid angiopathy is observed. Amyloid‐associated pathologies include dystrophic synaptic boutons, hyperphosphorylated tau‐positive neuritic structures and robust gliosis, with neocortical microglia number increasing threefold from 1 to 8 months of age. Global neocortical neuron loss is not apparent up to 8 months of age, but local neuron loss in the dentate gyrus is observed. Because of the early onset of amyloid lesions, the defined genetic background of the model and the facile breeding characteristics, APPPS1 mice are well suited for studying therapeutic strategies and the pathomechanism of amyloidosis by cross‐breeding to other genetically engineered mouse models.
Eddy viscosity for gravity waves propagating over turbulent surfaces
Authors: Garnier Josselin , Nachbin André
Published: August 2006

This article analyzes (one-dimensional) nonlinear wave propagation over a disordered fluid body having a small viscosity. The lower boundary is disordered and modeled by a random process. As a pulse shaped nonlinear wave propagates over this turbulent boundary, the velocity and wave elevation are viewed as random fields. Starting from first principles the eddy viscosity is characterized and shown to depend on different scales. This is captured as the leading order pseudodifferential operator resulting from the asymptotic analysis of stochastic differential equations. A discussion is provided showing that mean-field theory would have not captured the correct attenuation rate for the large scale object. Numerical results are provided illustrating the accuracy of the eddy viscosity expression.
High-accuracy extrapolated ab initio thermochemistry. II. Minor improvements to the protocol and a vital simplification
Authors: Bomble Yannick J. , Vázquez Juana , Kállay Mihály , Michauk Christine , Szalay Péter G. , Császár Attila G. , Gauss Jürgen , Stanton John F.
Published: August 2006

The recently developed high-accuracy extrapolated ab initio thermochemistry method for theoretical thermochemistry, which is intimately related to other high-precision protocols such as the Weizmann-3 and focal-point approaches, is revisited. Some minor improvements in theoretical rigor are introduced which do not lead to any significant additional computational overhead, but are shown to have a negligible overall effect on the accuracy. In addition, the method is extended to completely treat electron correlation effects up to pentuple excitations. The use of an approximate treatment of quadruple and pentuple excitations is suggested; the former as a pragmatic approximation for standard cases and the latter when extremely high accuracy is required. For a test suite of molecules that have rather precisely known enthalpies of formation {as taken from the active thermochemical tables of Ruscic and co-workers [Lecture Notes in Computer Science, edited by M. Parashar (Springer, Berlin, 2002), Vol. 2536, pp. 25–38; J. Phys. Chem. A 108, 9979 (2004)]}, the largest deviations between theory and experiment are 0.52, −0.70, and 0.51kJmol−1 for the latter three methods, respectively. Some perspective is provided on this level of accuracy, and sources of remaining systematic deficiencies in the approaches are discussed.
Relative Boltzmann entropy, evolution equations for fluctuations of thermodynamic intensive variables, and a statistical mechanical representation of the zeroth law of thermodynamics
Authors: Chan Eu Byung
Published: August 2006

Generalized thermodynamics or extended irreversible thermodynamics presumes the existence of thermodynamic intensive variables (e.g., temperature, pressure, chemical potentials, generalized potentials) even if the system is removed from equilibrium. It is necessary to properly understand the nature of such intensive variables and, in particular, of their fluctuations, that is, their deviations from those defined in the extended irreversible thermodynamic sense. The meaning of temperature is examined by means of a kinetic theory of macroscopic irreversible processes to assess the validity of the generalized (or extended) thermodynamic method applied to nonequilibrium phenomena. The Boltzmann equation is used for the purpose. Since the relative Boltzmann entropy has been known to be intimately related to the evolution of the aforementioned fluctuations in the intensive thermodynamic variables, we derive the evolution equations for such fluctuations of intensive variables to lay the foundation for investigating the physical implications and evolution of the relative Boltzmann entropy, so that the range of validity of the thermodynamic theory of irreversible processes can be elucidated. Within the framework of this work, we examine a special case of the evolution equations for the aforementioned fluctuations of intensive variables, which also facilitate investigation of the molecular theory meaning of the zeroth law of thermodynamics. We derive an evolution equation describing the relaxation of temperature fluctuations from its local value and present a formula for the temperature relaxation time.
Rotational spectra of 1-chloro-2-fluoroethylene. I. Main isotopologues and deuterated species of the trans isomer
Authors: Cazzoli Gabriele , Puzzarini Cristina , Gambi Alberto , Gauss Jürgen
Published: August 2006

Guided by theoretical predictions, the rotational spectra of the mono- and bideuterated species of trans-1-chloro-2-fluoroethylene, CHCl35CDF, CHCl37CDF, CDCl35CHF, CDCl37CHF, CDCl35CDF, and CDCl37CDF, have been recorded for the first time. Assignment of the ΔJ=0 and ΔK−1=+1 bands with K−1=3,4,5,… (all isotopic species) as well as of several ΔJ=±1 and ΔK−1=+1 transitions (all isotopic species except CHCl37CDF, CDCl37CHF, and CDCl37CDF) led to the accurate determination of the ground-state rotational constants, the quartic, and some sextic centrifugal distortion constants, as well as the nuclear quadrupole coupling constants for both Cl35 and Cl37 in good agreement with corresponding theoretical predictions based on high-level coupled-cluster calculations. Inconsistencies of the present spectroscopic parameters with respect to those reported earlier for the two main isotopologues, i.e., CHCl35CHF and CHCl37CHF, necessitated a reinvestigation of the rotational spectra for these two isotopic species. Supported by quantum chemical calculations, the previously recorded spectra are reassigned to a vibrationally excited state, while analysis of the ΔJ=0 and ΔK−1=+1 as well as some ΔJ=±1 and ΔK−1=+1 transitions provided a revised set of spectroscopic parameters for the vibrational ground state of these two isotopic species.
Mapping a homopolymer onto a model fluid
Authors: Pasquali S. , Percus J. K.
Published: August 2006

We describe a linear homopolymer using a grand canonical ensemble formalism, a statistical representation that is very convenient for formal manipulations. We investigate the properties of a system where only next neighbor interactions and an external, confining, field are present and then show how a general pair interaction can be introduced perturbatively, making use of a Mayer expansion. Through a diagrammatic analysis, we shall show how constitutive equations derived for the polymeric system are equivalent to the Ornstein-Zernike and Percus-Yevick equations for a simple fluid and find the implications of such a mapping for the simple situation of Van der Waals mean field model for the fluid.
Tuning the structural, electronic, and optical properties of BexZn1−xTe alloys
Authors: de Almeida J. S. , Ahuja R.
Published: August 2006

A series of first principles calculations have been carried out to investigate structural, electronic, and optical properties of BexZn1−xTe alloys for five beryllium compositions. Our results show that the lattice constant scales linearly with beryllium composition and there is a direct-to-indirect band gap crossover nearly at the composition of 20%. It is also found that no bowing effect in the absorption edge is observed unlike other II-VI semiconductor alloys. Our results are in good qualitative agreements with experimental observations.
Molecular hydrogen adsorption at surface adatoms
Authors: Bellman J. , Svensson K. , Andersson S.
Published: August 2006

Using electron-energy-loss spectroscopy, we have measured preferential adsorption of molecular hydrogen at Cu and Au adatoms deposited on a cold Cu(100) surface. We show, with particular attention to the D2–Au system, that the molecules adsorb at the adatoms, with an enhanced binding energy. The adsorption state is not of chemisorption character, the D2 rotational and internal vibrational transition energies are close to the corresponding gas phase values, a characteristic property of a physisorbed state. A revealing signature of the D2–Au interaction is an induced dipole activity of the rotational transition, which discriminates molecules adsorbed at the adatoms from those adsorbed on the bare substrate surface. The average number of molecules per Au atom depends on the Au coverage and increases at lower coverages, for example, at 4% of an adatom monolayer, there are approximately six D2 molecules per Au adatom. In this limit, Au monomers prevail, and a cluster of six D2 around a single Au adatom appears to be an optimal dense two-dimensional configuration.
Engineering patterns of Co nanoclusters on thin film Al2O3∕NiAl(100) using scanning tunneling microscopy manipulation techniques
Authors: Sartale Shrikrishina D. , Lin Ku-Liang , Chiang Chou-I , Luo Meng-Fan , Kuo Chien-Cheng
Published: August 2006

We present precise engineering of patterns of Co nanoclusters grown on ordered Al2O3∕NiAl(100) surface using the scanning tunneling microscopy (STM) manipulation technique. The clusters are attracted to the STM tip by lowering the bias below a threshold value and translated and relocated to another position by reversing the polarity. This facile manipulation technique in combination with the self-organized patterning on this system reported earlier might play a decisive role in nanotechnology for various applications where patterned nanoclusters are desired.
Wigner molecules: Natural orbitals of strongly correlated two-electron harmonium
Authors: Cioslowski Jerzy , Buchowiecki Marcin
Published: August 2006

Explicit asymptotic expressions for natural orbitals and their occupancies are derived for the harmonium atom at the strong-correlation limit at which the confinement strength ω tends to zero. Unlike in systems with moderate correlation effects, the occupancies at the ω→0 limit (derived from occupation amplitudes with alternating sign patterns) are vanishingly small and asymptotically independent of the angular momentum, forming a geometric progression with the scale factor proportional to ω1∕3 and the common ratio of ca. 0.0186. The radial components of the natural orbitals are given by products of polynomials and Gaussian functions that, as expected, peak at approximately half of the equilibrium interelectron distance.
Wigner molecules: The strong-correlation limit of the three-electron harmonium
Authors: Cioslowski Jerzy , Pernal Katarzyna
Published: August 2006

At the strong-correlation limit, electronic states of the three-electron harmonium atom are described by asymptotically exact wave functions given by products of distinct Slater determinants and a common Gaussian factor that involves interelectron distances and the center-of-mass position. The Slater determinants specify the angular dependence and the permutational symmetry of the wave functions. As the confinement strength becomes infinitesimally small, the states of different spin multiplicities become degenerate, their limiting energy reflecting harmonic vibrations of the electrons about their equilibrium positions. The corresponding electron densities are given by products of angular factors and a Gaussian function centered at the radius proportional to the interelectron distance at equilibrium. Thanks to the availability of both the energy and the electron density, the strong-correlation limit of the three-electron harmonium is well suited for testing of density functionals.
Critical point estimation of the Lennard-Jones pure fluid and binary mixtures
Authors: Pérez-Pellitero Javier , Ungerer Philippe , Orkoulas Gerassimos , Mackie Allan D.
Published: August 2006

The apparent critical point of the pure fluid and binary mixtures interacting with the Lennard-Jones potential has been calculated using Monte Carlo histogram reweighting techniques combined with either a fourth order cumulant calculation (Binder parameter) or a mixed-field study. By extrapolating these finite system size results through a finite size scaling analysis we estimate the infinite system size critical point. Excellent agreement is found between all methodologies as well as previous works, both for the pure fluid and the binary mixture studied. The combination of the proposed cumulant method with the use of finite size scaling is found to present advantages with respect to the mixed-field analysis since no matching to the Ising universal distribution is required while maintaining the same statistical efficiency. In addition, the accurate estimation of the finite critical point becomes straightforward while the scaling of density and composition is also possible and allows for the estimation of the line of critical points for a Lennard-Jones mixture.
Zero energy resonance and the logarithmically slow decay of unstable multilevel systems
Authors: Miyamoto Manabu
Published: August 2006

The long time behavior of the reduced time evolution operator for unstable multilevel systems is studied based on the N-level Friedrichs model in the presence of a zero energy resonance. The latter means the divergence of the resolvent at zero energy. Resorting to the technique developed by Jensen and Kato [Duke Math. J. 46, 583 (1979)], the zero energy resonance of this model is characterized by the zero energy eigenstate that does not belong to the Hilbert space. It is then shown that for some kinds of the rational form factors the logarithmically slow decay proportional to (logt)−1 of the reduced time evolution operator can be realized.
Calculation of zero-field splitting parameters: Comparison of a two-component noncolinear spin-density-functional method and a one-component perturbational approach
Authors: Reviakine Roman , Arbuznikov Alexei V. , Tremblay Jean-Christophe , Remenyi Christian , Malkina Olga L. , Malkin Vladimir G. , Kaupp Martin
Published: August 2006

Two different sets of approaches for the density-functional calculation of the spin-orbit contributions to zero-field splitting (ZFS) parameters of high-spin systems have been implemented within the same quantum chemistry code ReSpect and have been validated and compared for a series of model systems. The first approach includes spin-orbit coupling variationally in a two-component calculation, using either an all-electron Douglas-Kroll-Hess ansatz or two-component relativistic pseudopotentials. The ZFS parameters are computed directly from energy differences between different relativistic states. Additionally, an approximate second-order perturbation theory approach has been implemented, based on nonrelativistic or scalar relativistic wave functions. For a series of group 16 triplet diatomics and for the octet GdH3 molecules, two-component density functional calculations underestimate the zero-field splitting D systematically by a factor of 2. This may be rationalized readily by the incomplete description of states with ∣MJ∣<J by a single-determinantal wave function built from two-component spinors. In the case of two 3d transition metal complexes and for GdH3, the results depend furthermore sensitively on exchange-correlation functional. Results of the alternative one-component approach agree strikingly with the two-component data for systems with small spin-orbit effects and start to deviate from them only for heavier systems with large spin-orbit effects. These results have fundamental implications for the achievable accuracy of one-component density-functional approaches used widely to compute ZFS parameters in the field of molecular magnetism. Possible refinements of both one-and two-component approaches are discussed.
The first layer of water on Rh(111): Microscopic structure and desorption kinetics
Authors: Beniya Atsushi , Yamamoto Susumu , Mukai Kozo , Yamashita Yoshiyuki , Yoshinobu Jun
Published: August 2006

The adsorption states and growth process of the first water (D2O) layer on Rh(111) were investigated using infrared reflection absorption spectroscopy, temperature programed desorption, and spot-profile-analysis low energy electron diffraction. Water molecules wet the Rh(111) surface intact. At the early stage of first layer growth, a (√3×√3)R30° commensurate water layer grows where “up” and “down” species coexist; the up and down species represent water molecules which have free OD, pointing to a vacuum and the substrate, respectively. The up domain was a flatter structure than an icelike bilayer. Water desorption from Rh(111) was a half-order process. The activation energy and the preexponential factor of desorption are estimated to be 60kJ∕mol and 4.8×1016ML1∕2∕s at submonolayer coverage, respectively. With an increase in water coverage, the flat up domain becomes a zigzag layer, like an ice bilayer. At the saturation coverage, the amount of down species is 1.3 times larger than that of the up species. In addition, the activation energy and the preexponential factor of desorption decrease to 51kJ∕mol and 1.3×1014ML1∕2∕s, respectively.
Strong and weak adsorptions of polyelectrolyte chains onto oppositely charged spheres
Authors: Cherstvy A. G. , Winkler R. G.
Published: August 2006

We investigate the complexation of long thin polyelectrolyte (PE) chains with oppositely charged spheres. In the limit of strong adsorption, when strongly charged PE chains adapt a definite wrapped conformation on the sphere surface, we analytically solve the linear Poisson-Boltzmann equation and calculate the electrostatic potential and the energy of the complex. We discuss some biological applications of the obtained results. For weak adsorption, when a flexible weakly charged PE chain is localized next to the sphere in solution, we solve the Edwards equation for PE conformations in the Hulthén potential, which is used as an approximation for the screened Debye-Hückel potential of the sphere. We predict the critical conditions for PE adsorption. We find that the critical sphere charge density exhibits a distinctively different dependence on the Debye screening length than for PE adsorption onto a flat surface. We compare our findings with experimental measurements on complexation of various PEs with oppositely charged colloidal particles. We also present some numerical results of the coupled Poisson-Boltzmann and self-consistent field equation for PE adsorption in an assembly of oppositely charged spheres.
Effective stochastic dynamics on a protein folding energy landscape
Authors: Yang Sichun , Onuchic José N. , Levine Herbert
Published: August 2006

We present an approach to protein folding kinetics using stochastic reaction-coordinate dynamics, in which the effective drift velocities and diffusion coefficients are determined from microscopic simulation data. The resultant Langevin equation can then be used to directly simulate the folding process. Here, we test this approach by applying it to a toy two-state dynamical system and to a funnellike structure-based (Gō-type) model. The folding time predictions agree very well with full simulation results. Therefore, we have in hand a fast numerical tool for calculating the folding kinetic properties, even when full simulations are not feasible. In addition, the local drift and diffusion coefficients provide an alternative way to compute the free energy profile in cases where only local sampling can be achieved.
Inversion vibration of PH3+(X̃A2″2) studied by zero kinetic energy photoelectron spectroscopy
Authors: Yang Jie , Li Juan , Hao Yusong , Zhou Chang , Mo Yuxiang
Published: August 2006

We report the first rotationally resolved spectroscopic studies on PH3+(X̃A2″2) using zero kinetic energy photoelectron spectroscopy and coherent VUV radiation. The spectra about 8000cm−1 above the ground vibrational state of PH3+(X̃A2″2) have been recorded. We observed the vibrational energy level splittings of PH3+(X̃A2″2) due to the tunneling effect in the inversion (symmetric bending) vibration (ν2+). The energy splitting for the first inversion vibrational state (0+∕0−) is 5.8cm−1. The inversion vibrational energy levels, rotational constants, and adiabatic ionization energies (IEs) for ν2+=0–16 have been determined. The bond angles between the neighboring P–H bonds and the P–H bond lengths are also obtained using the experimentally determined rotational constants. With the increasing of the inversion vibrational excitations (ν2+), the bond lengths (P–H) increase a little and the bond angles (H–P–H) decrease a lot. The inversion vibrational energy levels have also been calculated by using one dimensional potential model and the results are in good agreement with the experimental data for the first several vibrational levels. In addition to inversion vibration, we also observed firstly the other two vibrational modes: the symmetric P–H stretching vibration (ν1+) and the degenerate bending vibration (ν4+). The fundamental frequencies for ν1+ and ν4+ are 2461.6 (±2) and 1043.9 (±2)cm−1, respectively. The first IE for PH3 was determined as 79670.9 (±1)cm−1.
The use of quadratic forms in the calculation of ground state electronic structures
Authors: Keller Jaime , Weinberger Peter
Published: August 2006

There are many examples in theoretical physics where a fundamental quantity can be considered a quadratic form ρ=∑iρi=∣Ψ∣2 and the corresponding linear form Ψ=∑iψi is highly relevant for the physical problem under study. This, in particular, is the case of the density and the wave function in quantum mechanics. In the study of N-identical-fermion systems we have the additional feature that Ψ is a function of the 3N configuration space coordinates and ρ is defined in three-dimensional real space. For many-electron systems in the ground state the wave function and the Hamiltonian are to be expressed in terms of the configuration space (CS), a replica of real space for each electron. Here we present a geometric formulation of the CS, of the wave function, of the density, and of the Hamiltonian to compute the electronic structure of the system. Then, using the new geometric notation and the indistinguishability and equivalence of the electrons, we obtain an alternative computational method for the ground state of the system. We present the method and discuss its usefulness and relation to other approaches.