bluuebunny/crossref_metadata_2025 huggingface dataset:
Singularities in elasticity and their treatment with Fourier series
Authors: Nkemzi B.
Published: March 2004

This paper analyses the regularity of the weak solution of the linear elasticity system in three‐dimensional axisymmetric domains with reentrant edges under prescribed traction on the boundary by means of Fourier series. Using partial Fourier analysis with respect to one space direction (rotational angle), the three‐dimensional boundary value problem (BVP) is decomposed into a sequence of decoupled two‐dimensional boundary value problems on the meridian of the axisymmetric domain. The splitting of the 2D solutions near corners of the meridian domain into regular and singular parts provides coefficients from which the 3D edge singularity functions (generalized stress intensity factors) are derived. Two types of singularity functions are presented, namely, a tensorial type, which needs more smoothness assumption on the right hand side and a non‐tensorial type, which does not demand any further smoothness assumptions.
On the boundary conditions for EG methods applied to the two‐dimensional wave equation system
Authors: Lukáčová‐Medvid'ová M. , Warnecke G. , Zahaykah Y.
Published: March 2004

The subject of the paper is the study of several nonreflecting and reflecting boundary conditions for the evolution Galerkin (EG) methods which are applied for the two‐dimensional wave equation system. Different known tools are used to achieve this aim. Namely, the method of characteristics, the method of extrapolation, the Laplace transformation method, and the perfectly matched layer (PML) method. We show that the absorbing boundary conditions which are based on the use of the Laplace transformation lead to the Engquist‐Majda first and second order absorbing boundary conditions, see [3]. Further, following Bérenger [1] we consider the PML method. We discretize the wave equation system with the leap‐frog scheme inside the PML while the evolution Galerkin schemes are used inside the computational domain. Numerical tests demonstrate that this method produces much less unphysical reflected waves as well as the best results in comparison with other techniques studied in the paper.
Modelling in vehicle dynamics of automobiles
Authors: Lugner P. , Plöchl M.
Published: March 2004

A general problem formulation and the resulting scheme of modelling dynamical system behaviour is introduced before a specification with respect to automobiles is done. An essential component for the vehicle behaviour is the tyre. Models of different complexity with respect to its mathematical‐mechanical formulation are presented. Simple models of the automobile itself allow a separation of longitudinal, lateral, and vertical dynamics and a partially analytical derivation of corresponding equations of motion. These models are usually also the approximations used for the design of a state observer and controller to influence the vehicle behaviour. For a more detailed representation of the vehicle 3D‐models are assembled by their individual components, e.g. suspensions, drive train, and steering system. In this way a good agreement between measurements and simulation results can be realized up to the nonlinear range of vehicle behaviour. Nowadays MBS‐models, established with professional software packages, are applied. They integrate all essential components, taking into account different linkages, e.g. bushings and joints. For component strength design, a rough road surface description can be implemented additionally. To improve by simulation the active safety or handling of the vehicle, these models represent the controlled complex vehicle in the global control loop whereas linearized models as mentioned above are applied for the controller design. As an example the design of an extended ESP‐controller and its consequences for severe braking conditions during cornering are discussed showing the necessary steps in modelling and their mathematical formulation.
A physical basis for fractional derivatives in constitutive equations
Authors: Pfitzenreiter T.
Published: March 2004

In good coincidence with experimental data the damping properties of viscoelastic media can be described by fractional derivatives. We present a model, which under certain assumptions on the interactions between macromolecules leads to a macroscopic stress strain relation with fractional derivatives in the damping term. For this purpose we use the Kubo formula of nonequilibrium thermodynamics.
Glutaminyl cyclases unfold glutamyl cyclase activity under mild acid conditions
Authors: Schilling Stephan , Hoffmann Torsten , Manhart Susanne , Hoffmann Matthias , Demuth Hans-Ulrich
Published: March 2004

N‐terminal pyroglutamate (pGlu) formation from glutaminyl precursors is a posttranslational event in the processing of bioactive neuropeptides such as thyrotropin‐releasing hormone and neurotensin during their maturation in the secretory pathway. The reaction is facilitated by glutaminyl cyclase (QC), an enzyme highly abundant in mammalian brain. Here, we describe for the first time that human and papaya QC also catalyze N‐terminal glutamate cyclization. Surprisingly, the enzymatic Glu1 conversion is favored at pH 6.0 while Gln1 conversion occurs with an optimum at pH 8.0. This unexpected finding might be of importance for deciphering the events leading to deposition of highly toxic pyroglutamyl peptides in amyloidotic diseases.
Feline Vestibular Disorders. Part I: Anatomy and Clinical Signs
Authors: LeCouteur R A , Vernau K M
Published: March 2004

An understanding of the anatomy of the feline vestibular system is essential for interpretation of the clinical signs associated with vestibular dysfunction, for precise lesion localisation, and for accurate interpretation of results of diagnostic imaging. Appropriate recognition and interpretation of the clinical signs of vestibular disease is also an essential aspect of the precise diagnosis of the cause of vestibular dysfunction in cats. The objectives of this review are to provide an overview of the anatomy of the feline vestibular system, and to review the clinical signs of peripheral and central vestibular dysfunction of cats.
Feline Vestibular Disorders. Part II: Diagnostic Approach and Differential Diagnosis
Authors: Vernau K M , LeCouteur R A
Published: March 2004

Results of a neurological examination usually permit localisation of a vestibular disorder to either the central or peripheral parts of the vestibular system. Many different disorders located in the same part of the vestibular system will produce similar clinical signs. Therefore, additional diagnostic tests beyond a neurological examination are required in order to make an accurate diagnosis. The objectives of this review are to outline a diagnostic approach for disorders affecting the feline vestibular system, and to summarise the clinically important features of frequently diagnosed diseases affecting the vestibular system of cats.
Two Cases of Feline Visceral and Cutaneous Leishmaniosis in Spain
Authors: Hervás J , De Lara F Chacón-M , Sánchez-Isarria M A , Pellicer S , Carrasco L , Castillo J A , Gómez-Villamandos J C
Published: March 2004

This paper describes clinical signs and lesions in two cases of leishmaniosis—one visceral and one cutaneous in the cat ( Felis catus domesticus). The diagnosis was achieved by a combination of serology, light and electron microscopic studies. The vague nature of the clinical signs observed in both cases was particularly striking, and clinical features were similar to many other diseases commonly found in cats. Therefore, the use of various investigations to detect leishmaniosis (serum chemistry, serology and histopathology) is highly recommended in cases where clinical signs do not respond to conventional treatment.
Insulin Sensitivity in Normal and Diabetic Cats
Authors: Feldhahn J R , Rand J S , Martin G
Published: March 2004

Estimates of in vivo insulin sensitivity (SI) can be derived from minimal model analysis of a frequently sampled intravenous glucose tolerance test (FSIVGTT). Modification of the FSIVGTT by the injection of insulin allows insulin sensitivity to be measured in diabetics. To establish and compare reference values for insulin sensitivity in clinically normal and diabetic cats, we subjected 10 clinically normal cats and five diabetic cats to the insulin-modified FSIVGTT with minimal model analysis. Diabetic cats had a significantly lower insulin sensitivity than clinically normal cats ( P <0.05). Mean insulin sensitivity in clinically normal cats was 3.22 × 10−4/min/μU/ml (range 1.71–5.23 × 10−4/min/μU/ml). In contrast, the mean insulin sensitivity in diabetic cats was 0.58 × 10−4/min/μU/ml (range 0.136–0.88 × 10−4/min/μU/ml), or approximately six times less insulin sensitive than clinically normal cats. Mean glucose effectiveness in clinically normal cats was 0.030/min (range 0.021–0.045/min). Mean glucose effectiveness in diabetic cats was 0.014/min (range 0.008–0.021/min). Our data demonstrate that insulin resistance is a feature of feline diabetes mellitus and that diabetic cats have a similar relative decrease in insulin sensitivity to humans with type 2 diabetes.
Inversion of diurnally varying synthetic CO2: Network optimization for an Australian test case
Authors: Law R. M. , Rayner P. J. , Wang Y. P.
Published: March 2004

Hourly CO2 fluxes, generated from a biosphere model applied to the Australian region, are used to produce synthetic CO2 atmospheric concentration data. The concentration data are inverted using a Bayesian synthesis method, to test whether the CO2 fluxes can be successfully retrieved at monthly temporal resolution. The inversion is performed globally (with a base network of about 100 sites), but the tests focus on the Australian continent, subdivided into 12 regions. The inversion is tested using dense networks of approximately 40 new sites in and around Australia. Land‐based and offshore networks are compared. The land‐based network produces biased source estimates, for regions with large diurnal source variability, if the inversion only solves for a constant flux throughout the month. The bias is eliminated when we solve for two fluxes for each region, a constant monthly flux and a daytime‐only flux. The offshore network gives large uncertainties and biases for inland regions of Australia. These latter biases are not significantly improved by solving for the daytime flux. The inversion that includes daytime fluxes is used to design a network to minimize the average annual mean uncertainty for Australian sources. Networks designed using incremental optimization are compared with some reference networks. Site locations are found to be sensitive to the data uncertainty applied to each site. The incremental optimization method appears to be most effective for networks of fewer sites than about half the number of regions being solved for.
Nitrous oxide emissions from temperate grassland ecosystems in the Northern and Southern Hemispheres
Authors: Müller Christoph , Sherlock Robert R.
Published: March 2004

Nitrogen (N) fertilized or grazed grasslands in temperate regions of the Northern and Southern Hemisphere are important sources for atmospheric nitrous oxide (N2O). Following synthetic urine applications in a New Zealand grassland ecosystem, and ammonium (NH4+) and nitrate (NO3−) applications to a German grassland ecosystem, approximately 31, 16, and 5%, respectively, of the total emitted N2O (N2Otot) was produced by nitrification (N2Onit) with the rest being produced by denitrification (N2Oden). Analyses of the combined data set showed that 75% of all N2O emissions occurred above 60% water filled porosity (WFPS) and that more than 80% of all N2O emissions occurred at soil temperatures between 10° and 15°C. N2Oden emissions were associated with a WFPS value at around 80% at relatively low NO3− concentrations, while N2Onit emissions only occurred at high NH4+ levels shortly after N application at soil temperatures around 10°C. To increase the accuracy of predictions with simple mathematical models, such as the “hole‐in‐the‐pipe‐model,” long‐term validation data sets are needed where driving variables are related to measured N2Onit and N2Oden data.
Effect of plasticity on elastic modulus measurements
Authors: Weidner Donald J. , Li Li , Davis Maria , Chen Jiuhua
Published: March 2004

Recent developments in high‐pressure X‐ray studies enable the measurement of the elastic strain anisotropy induced by a macroscopic differential stress in an aggregate sample. Such data are commonly used to constrain the single‐crystal elastic moduli under the assumptions of the Reuss‐Voigt state. We find this procedure is valid only for samples that have not been plastically deformed. Measured elastic strain anisotropy for MgO at stress levels below the yield point agree well with the Reuss elastic model. Plastic deformation effects a change in the stress field for subpopulations of grains that represent different crystallographic orientations with respect to the applied stress field. Our data for the plastically deformed sample are consistent with the predictions of a self‐consistent aggregate model for deforming polycrystals. Such models may be useful as a guide to define the elastic properties in light of the active slip systems.
An analytical expression for predicting the critical radius in the autoconversion parameterization
Authors: Liu Yangang , Daum Peter H. , McGraw Robert
Published: March 2004

An analytical expression for the critical radius associated with Kessler‐type parameterizations of the autoconversion process is derived. The expression can be used to predict the critical radius from the cloud liquid water content and the droplet number concentration, eliminating the need to prescribe the critical radius as an empirical constant in numerical models. Data from stratiform clouds are analyzed, indicating that on average continental clouds have larger critical radii than maritime clouds. This work further suggests that anthropogenic aerosols affect the autoconversion process by increasing the critical radius and decreasing the characteristic radius, which in turn inhibits the initiation of embryonic raindrops, and by decreasing the autoconversion rate after the initiation process. The potential impact of this work on the evaluation of the second indirect aerosol effect is discussed.
DNAPL mass transfer and permeability reduction during in situ chemical oxidation with permanganate
Authors: Li X. David , Schwartz Franklin W.
Published: March 2004

This study utilized a series of laboratory experiments to examine the DNAPL mass removal rate and permeability reduction during ISCO using permanganate (MnO4−). Results show that MnO4− oxidation is effective in removing residual DNAPL from a porous medium. The DNAPL mass removal rate correlated positively with both the hydraulic stress and the oxidant load. A power relationship model of DNAPL mass removal under ISCO was proposed. Results also show that oxidation by‐products CO2(g) and Mn oxide can cause pore plugging and flow by‐passing. The reduction in hydraulic conductivity due to the Mn oxide precipitates was quantified. Hydraulic conductivity reduction as high as 80% was observed for oxidizing a small quantity of TCE.
Direct wind measurements of Saharan dust events from Terra and Aqua satellites
Authors: Koren Ilan , Kaufman Yoram J.
Published: March 2004

Wind speed and direction, during Saharan dust episodes are calculated by estimating the movement of the dust plume between the morning observations from Terra and the afternoon observations from Aqua by the MODerate resolution Imaging Spectroradiometer (MODIS). The difference in the position of the dust front (easily identified both near the dust sources and over the ocean) between the Terra and Aqua observations is used to derive the actual wind field of the dust layer. The analysis is used to estimate the near‐surface wind properties needed for dust mobilization in the Bodele depression. Comparison with NCEP reanalysis winds shows that NCEP underestimated by factor 2 the actual speed of the dust front progression near the sources and produced an azimuthal spread, three times wider than the measured one. Over the seashore, with more numerous meteorological observations, the NCEP wind field did match very well the dust measurements.
Perspicacious indicators of atmospheric blocking
Authors: Schwierz C. , Croci‐Maspoli M. , Davies H. C.
Published: March 2004

A novel dynamically‐based approach is introduced to identify, describe and diagnose atmospheric blocking events. The approach is based upon the potential vorticity perspective and takes into account the three‐dimensional structure of the phenomenon. It is argued that the essence of a blocking anomaly is located in the upper troposphere, just below the tropopause. The associated novel blocking indicators are derived from two‐dimensional fields at 6‐hourly temporal resolution, and provide information on the spatial scale, shape, amplitude and movement of blocks. A northern hemisphere winter (DJF) climatology for the ERA15 period (1979–1993) is presented and comments are made on the relationship between the indicators and previous blocking indices.
Compression of iron hydride to 80 GPa and hydrogen in the Earth's inner core
Authors: Hirao Naohisa , Kondo Tadashi , Ohtani Eiji , Takemura Kenichi , Kikegawa Takumi
Published: March 2004

Here we report a new data on the equation of state of iron hydride up to 80 GPa measured by an in situ X‐ray diffraction method. We observed anomalous compression behavior at 30 to 50 GPa, and found that iron hydride might be less compressible above 50 GPa than at lower pressures. The bulk modulus above 50 GPa is larger than that of pure hcp‐iron. Our data support the ab initio calculation suggesting a magnetic transition of iron hydride at around 60 GPa. The density deficit of the Earth's inner core could be explained by dissolution of smaller amount of hydrogen than previously suggested.
The O+ density trough at 5000 km altitude in the polar cap
Authors: Zeng W. , Horwitz J. L. , Craven P. D. , Rich F. J. , Moore T. E.
Published: March 2004

At altitudes near 5000 km over the southern polar cap region of the terrestrial magnetosphere/ionosphere, the Thermal Ion Dynamics Experiment (TIDE) on board the Polar satellite has observed O+ ion density trough regions, in which the O+ densities were at least one order of magnitude lower than the surrounding O+ densities. In the O+ density trough regions, the estimated O+ densities were generally lower than 0.01 per cc. The boundaries between normal density level regions and the trough density regions were usually abrupt transitions. From 1 December 1997 to 30 November 1998, polar cap O+ troughs in Polar/TIDE observations occurred at a frequency of about 48%. Statistical examination of the Polar perigee observations from 1 December 1997 to 30 November 1998 shows that the Polar perigee passes evenly covered the southern polar cap region, while the O+ density trough was always located on the nightside portion of the polar cap magnetosphere/ionosphere, and that invariant latitude spans of such troughs could be as large as 23° in extent. The trough occurrence displayed a strong seasonal dependence; in the winter season (e.g., for July in the Southern Hemisphere) the O+ ion density trough occurrence frequency ranged up to 92%, while in the summer season (e.g., for January in the Southern Hemisphere) it decreased to as low as 15%. Our statistical results show that the trough occurrence was generally anticorrelated with solar wind dynamic pressure in the solar wind dynamic pressure range 0.8–2.6 nanopascal. The O+ ion density trough occurrence appeared relatively independent of the geomagnetic Kp index, IMF Bz, and By conditions. However, as suggested by the seasonal dependence, the O+ ion density trough occurrence was strongly related to the solar zenith angle (SZA). In the SZA range 50° to 125°, the trough occurrence increased monotonically with SZA. In addition, we sought to determine consistent density and velocity signatures at lower altitudes associated the O+ ion density trough at 5000 km by examining the near‐simultaneous O+ densities and vertical velocities observed by the DMSP satellite group orbiting at 840 km altitude. However, consistent correlations between the dual altitudes were not reliably established from the present examinations.
Satellite evidence of hurricane‐induced phytoplankton blooms in an oceanic desert
Authors: Babin S. M. , Carton J. A. , Dickey T. D. , Wiggert J. D.
Published: March 2004

The physical effects of hurricanes include deepening of the mixed layer and decreasing of the sea surface temperature in response to entrainment, curl‐induced upwelling, and increased upper ocean cooling. However, the biological effects of hurricanes remain relatively unexplored. In this paper, we examine the passages of 13 hurricanes through the Sargasso Sea region of the North Atlantic during the years 1998 through 2001. Remotely sensed ocean color shows increased concentrations of surface chlorophyll within the cool wakes of the hurricanes, apparently in response to the injection of nutrients and/or biogenic pigments into the oligotrophic surface waters. This increase in post‐storm surface chlorophyll concentration usually lasted 2–3 weeks before it returned to its nominal pre‐hurricane level.
Observations of low‐frequency current fluctuations in deep water of the Eastern Gotland Basin/Baltic Sea
Authors: Hagen E. , Feistel R.
Published: March 2004

In the deep Eastern Gotland Basin of the Baltic Sea, multiday fluctuations could be analyzed based on hourly sampled current and temperature measurements from August 31, 1999, to October 23, 2002. Data were continuously recorded in layers beneath the perennial pycnocline over a stagnation period of the hydrographic regime which lasted more than 3 years. At a water depth of 204 m, records were realized at 20 m above the seabed in the northeast of this basin (57°23′N, 20°19.6′E). Overall averages show vanishing east‐west motions, but a permanent northward velocity of 3 cm/s. The results obtained from daily means suggest that current fluctuations with periods longer than about 18 days are energetically decoupled from those of shorter timescales. Quasi‐cycles of 100–150 days characterize along‐slope currents while fluctuations typically occur in two period ranges of 40–65 and 25–37 days in both current components. Corresponding fluctuations also occur in sea level anomalies recorded at the coastal station Landsort/Sweden. Shorter timescales involve periods around 10 and 3.5 days at the synoptic scale. There is a positive correlation between daily values of the along‐slope current and corresponding variances with strengthening during the winter season. This suggests an enhanced flux of kinetic energy from the daily current field toward more turbulent fluctuations to maintain mixing processes via enhanced vertical current shear within thin near‐bottom layers. Results are discussed in the context of previous observations and existing working hypotheses.
Some observations of nonlinearly modified internal wave spectra
Authors: van Haren Hans
Published: March 2004

Four examples are discussed of different internal wave band kinetic energy spectra from moored instruments at middle and high latitudes (38° < ϕ < 61°) in the eastern Atlantic Ocean and the western Mediterranean Sea. It is observed that for N ≫ f, where N is the buoyancy frequency and f is the inertial frequency, the spectral falloff rate with frequency σ for internal waves tends to σ−3. Either spectra are dominated at tidal and/or inertial nonlinear higher harmonics superposed on a nearly white (noise) spectral continuum, the latter extending to supertidal frequencies up to N (it is hypothesized that such a spectrum is found near the source of nonlinear interactions), or the spectrum is smooth, showing a σ−3 falloff rate for most of the internal wave band continuum outside an inertial peak. Such a spectrum may be typical for regions well away from the sources for interaction, although governed by the same nonlinear advection dynamics. The present observations contrast with a recently proposed model for the internal wave spectrum, similar to the canonical Garrett and Munk [1972] model, showing a σ−2 falloff rate, except for a nearly white continuum in the range between f and the solar semidiurnal tidal frequency (S2) for latitudes ∣ϕ∣ < 20°.
Impact of ocean roughness and bogus typhoons on summertime circulation in a wave‐atmosphere coupled regional climate model
Authors: Lee Dong‐Kyou , Ahn Young‐In , Kim Chun‐Ji
Published: March 2004

In order to examine the impact of ocean roughness and bogus typhoons on the east Asian summer monsoon circulation, three runs with a regional climate model (RegCM2) for 1994 summertime simulation were conducted: a control run (CTRL), a run with RegCM2 coupled to an ocean‐wave model (WAVE), and a run with RegCM2 coupled to a wave model and a bogus typhoon scheme (WBGS). The National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalyses were used for initial and lateral boundary conditions. The regional climate model with a fixed value of roughness length over the ocean (CTRL) did not adequately simulate the extreme anomalous summer monsoon of 1994. However, the simulation of the atmosphere‐wave coupled model (WAVE) produced better anomalous features than CTRL, closer to the 1994 extreme summer climate. In WAVE the roughness length over the ocean was increased to over twice the fixed value. The maximum values of roughness length were found in the active monsoon regions. Increased ocean roughness length resulted in more changes over land rather than over the ocean due to more moisture supplies from the ocean, such that the maximum changes of surface climate occurred over China. In particular, the differences between CTRL and WAVE were relatively large over areas of warmer ground temperature, such as central China. In WBGS the roughness length over the ocean was increased by about 20% relative to that of WAVE under the high wind conditions induced by bogus typhoons. It was also found that the seasonal march of the east Asian summer monsoon was better reproduced in WBGS than in the other two simulations. The bogus typhoons in east Asia played an important role in simulating the variations of surface climate and lower troposphere circulations associated with storms, including typhoons, by the transport of heat and moisture toward the midlatitude land areas. However, the precipitation in WBGS was degraded comparing to that of CTRL. This study suggests that proper simulation of east Asian summer monsoon circulations, especially during an active typhoon season, requires the proper representation of ocean roughness length and typhoons.
Remote sensing of net ecosystem productivity based on component spectrum and soil respiration observation in a boreal forest, interior Alaska
Authors: Kushida Keiji , Kim Yongwon , Tanaka Noriyuki , Fukuda Masami
Published: March 2004

We built a remote‐sensing method for determining leaf area index (LAI) and ground cover mosses/lichens in boreal forests by field component spectral observation and radiative transfer modeling based on the spectrum. The method was applied to evaluate annual net ecosystem productivity (NEP) distribution in a boreal forest, interior Alaska, by accounting for net primary productivity (NPP) of the vegetation compositions and soil respiration observation synchronized to the spectral observation. Spectral reflectance and soil respiration were observed in two 30‐m × 30‐m plots in black spruce stands, central Alaska. Spectral characteristics of the forest floor and the needle leaves were used as input parameters of a radiative transfer model to evaluate nadir reflectances of spruce communities in relation to varying upper layer LAI, forest floor bryophyte types, and leaf spectral characteristics. Using the relationship, we obtained LAI and bryophyte area ratios for each pixel that corresponds to spruce forest on Landsat ETM+ imagery. The LAI‐NPP relationship of spruce forest was estimated from Plonski's [1981] normal yield table data and specific leaf area, and NPP was calculated from LAI. Observations of daily respiration were extrapolated to annual timescales using soil temperature. On the basis of the annual soil respiration and NPP of the upper layer and forest floor, annual NEP geographical distribution in a recent normal year was estimated from remotely sensed LAI and forest floor bryophyte area ratios. The annually estimated NEP was 51 g C/m2/yr, which corresponds to the value (55 g C/m2/yr) for 150‐year‐old black spruce forest in the Boreal Ecosystem‐Atmosphere Study (BOREAS) region, Canada.
Effects of multiple reflection and albedo on the net radiation in the pack ice zones of Antarctica
Authors: Wendler G. , Moore B. , Hartmann B. , Stuefer M. , Flint R.
Published: March 2004

Radiative and meteorological measurements were collected continuously during a cruise from Australia to Antarctica in austral summer 2000. On the average, the amount of fractional cloud cover was high (81%), reducing the incoming solar radiation. The albedo varied widely from over 80% for snow‐covered undisturbed sea ice to below 10% for open water. In general, sea ice concentration was the strongest determining factor for the reflectivity. However, different ice types and snow cover also had a substantial influence on the reflectivity. When a highly reflecting surface was present (total snow‐covered undisturbed ice pack with an albedo of 81%), the incoming global radiation under overcast conditions was 85% higher than for a water surface due to multiple reflections. The net radiation was found to be a strong function of both fractional cloud cover and surface albedo. For low albedo values, the net radiation increases with decreasing cloudiness, e.g., for a water surface (albedo 8%) the mean daily value increased from 88 Wm−2 for total cloud cover to 226 Wm−2 for clear skies. For highly reflecting surfaces, the net radiation decreases with decreasing cloud amount for most of the day. The mean daily value was slightly negative for clear skies (−7 Wm−2), but somewhat positive (23 Wm−2) for overcast conditions.
Stable isotopic composition of water vapor in the tropics
Authors: Lawrence James Robert , Gedzelman Stanley David , Dexheimer Darielle , Cho Hye‐Khung , Carrie Gordon D. , Gasparini Robert , Anderson Casey R. , Bowman Kenneth P. , Biggerstaff Mike I.
Published: March 2004

Water vapor samples collected during tropical field experiments at Puerto Escondido, Mexico, near Kwajalein (KWAJEX), and near Key West, Florida (CAMEX 4), were analyzed for their stable isotope contents, 1H218O:1H216O and 2H1H16O:1H216O. Highest δ18O values approached isotopic equilibrium with seawater during quiescent weather or in regions of isolated or disorganized convection. Lowest δ18O values occurred in or downwind from regions of organized mesoscale weather disturbances and ranged as low as 15‰ below isotopic equilibrium with seawater. The mean δ18O value of vapor over the sea surface therefore decreases as storm activity and organization increases.
Monitoring of observation errors in the assimilation of satellite ozone data
Authors: Stajner Ivanka , Winslow Nathan , Rood Richard B. , Pawson Steven
Published: March 2004

Ozone observations from the Solar Backscatter UltraViolet/2 (SBUV/2) instruments and/or the Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) have been assimilated in near‐real time at NASA's Data Assimilation Office (DAO) since January 2000. The ozone data assimilation system was used as a tool for detecting and characterizing changes in the observation errors. The forecast model captures the geophysical variability. A change in the observed‐minus‐forecast (O‐F) residuals, which are defined as differences between the incoming ozone observations and the collocated short‐term model forecast, indicates a change in the assimilation system. If the model and the statistical analysis scheme are stable, then it points to a modification in instrument characteristics or a retrieval algorithm. However, sometimes a change in the ozone O‐F residuals is caused by differences in the availability of the meteorological observations or modifications in the meteorological assimilation system whose winds are used to drive the ozone transport model. The O‐F residuals are routinely produced and monitored in the assimilation process. Using examples from the NOAA 14 and NOAA 16 SBUV/2 instruments, and the EP TOMS, we demonstrate that the monitoring of time series of O‐F residual statistics is an effective, sensitive, and robust method for identifying time‐dependent changes in the observation‐error characteristics of ozone. In addition, the data assimilation system was used to assist in the validation of updated calibration coefficients for the NOAA 14 SBUV/2 instrument. This assimilation‐based monitoring work is being extended to ozone data from instruments on new satellites: Environmental satellite (Envisat), Earth Observing System (EOS) Aqua, and EOS Aura.
Radiation Transfer Model Intercomparison (RAMI) exercise: Results from the second phase
Authors: Pinty B. , Widlowski J.‐L. , Taberner M. , Gobron N. , Verstraete M. M. , Disney M. , Gascon F. , Gastellu J.‐P. , Jiang L. , Kuusk A. , Lewis P. , Li X. , Ni‐Meister W. , Nilson T. , North P. , Qin W. , Su L. , Tang S. , Thompson R. , Verhoef W. , Wang H. , Wang J. , Yan G. , Zang H.
Published: March 2004

The Radiation Transfer Model Intercomparison (RAMI) initiative is a community‐driven exercise to benchmark the models of radiation transfer (RT) used to represent the reflectance of terrestrial surfaces. Systematic model intercomparisons started in 1999 as a self‐organized, open‐access, voluntary activity of the RT modeling community. The results of the first phase were published by Pinty et al. [2001]. The present paper describes the benchmarking protocol and the results achieved during the second phase, which took place during 2002. This second phase included two major components: The first one included a rerun of all direct‐mode tests proposed during the first phase, to accommodate the evaluation of models that have been upgraded since, and the participation of new models into the entire exercise. The second component was designed to probe the performance of three‐dimensional models in complex heterogeneous environments, which closely mimic the observations of actual space instruments operating at various spatial resolutions over forest canopy systems. Phases 1 and 2 of RAMI both confirm not only that a majority of the radiation transfer models participating in RAMI are in good agreement between themselves for relatively simple radiation transfer problems but also that these models exhibit significant discrepancies when considering more complex but nevertheless realistic geophysical scenarios. Specific recommendations are provided to guide the future of this benchmarking program (Phase 3 and beyond).
Granular avalanches across irregular three‐dimensional terrain: 2. Experimental tests
Authors: Iverson Richard M. , Logan Matthew , Denlinger Roger P.
Published: March 2004

Scaling considerations indicate that miniature experiments can be used to test models of granular avalanches in which the effects of intergranular fluid and cohesion are negligible. To test predictions of a granular avalanche model described in a companion paper, we performed bench top experiments involving avalanches of dry sand across irregular basal topography that mimicked the complexity of natural terrain. The experiments employed a novel method of laser‐assisted cartography to map the three‐dimensional morphology of rapidly moving avalanches, thereby providing high‐resolution data for comparison with model output. Model input consisted of two material properties (angles of internal and basal Coulomb friction of the sand), which were measured in independent tests, and of initial and boundary conditions that characterized the geometry of the experimental apparatus. Experimental results demonstrate that the model accurately predicts not only the gross behavior but also many details of avalanche motion, from initiation to deposition. We attribute this accuracy to a mathematical and computational formulation that conserves mass and momentum in three‐dimensional physical space and satisfies the Coulomb equation in three‐dimensional stress space. Our results support the hypothesis that a Coulomb proportionality between shear and normal stresses applies in moderately rapid granular flows and that complicated constitutive postulates are unnecessary if momentum conservation is strictly enforced in continuum avalanche models. Furthermore, predictions of our Coulomb continuum model contrast with those of a Coulomb point mass model, illustrating the importance of multidimensional modeling and model testing.
Geoid displacement about Greenland resulting from past and present‐day mass changes in the Greenland Ice Sheet
Authors: Fleming K. , Martinec Z. , Hagedoorn J.
Published: March 2004

Predictions are presented of secular changes in the geoid arising from glacial‐isostatic adjustment (GIA) following the Last Glacial Maximum and from present‐day mass changes in the Greenland Ice Sheet (GIS). Geoid displacement from ongoing GIA is dominated by ice‐load changes outside of Greenland at lower spherical‐harmonic degrees (<30), and modified at higher degrees by the recent (last few thousand years) GIS history. Ice‐margin mass changes dominate the present‐day GIS geoid response, although comparable signals are obtained when considering the uncertainty range in the higher‐elevation changes (>2000 m). Spatial variability is noted when the present‐day GIS response is expanded to degree and order 32. This is detectable by GRACE when assuming an optimistic accuracy, but is too small by a factor of ca. 3 for an alternate accuracy estimate. Present‐day GIS geoid displacement rates are generally less than the equivalent response from ice‐mass changes in Antarctica, Patagonia and Alaska.
Quantum dynamics in simple fluids
Authors: Lawrence C. P. , Nakayama A. , Makri N. , Skinner J. L.
Published: March 2004

We use quantum-correction factors to calculate approximately the quantum velocity time-correlation function (TCF) of supercritical Lennard-Jones argon from the classical TCF. We find that for this quite classical system, several different quantum-correction schemes yield essentially identical results for the real and imaginary parts of the quantum TCF, and also agree well with the recent forward–backward semiclassical dynamics (FBSD) results of Wright and Makri [J. Chem. Phys. 119, 1634 (2003)]. We also consider a more quantum-mechanical fluid of lighter atoms (neon) at a lower temperature. In this case different quantum-correction schemes give different results. FBSD calculations show that the harmonic quantum correction factor works the best for this system.
Kinetic theory and hydrodynamics of dense, reacting fluids far from equilibrium
Authors: Lutsko James F.
Published: March 2004

The kinetic theory for a fluid of hard spheres which undergo endothermic and/or exothermic reactions with mass transfer is developed. The exact balance equations for concentration, density, velocity, and temperature are derived. The Enskog approximation is discussed and used as the basis for the derivation, via the Chapman–Enskog procedure, of the Navier–Stokes reaction equations under various assumptions about the speed of the chemical reactions. It is shown that the phenomenological description consisting of a reaction–diffusion equation with a convective coupling to the Navier–Stokes equations is of limited applicability.
Exit interaction effect on nascent product state distribution of O(1D)+N2O→NO+NO
Authors: Kawai Shinnosuke , Fujimura Yo , Kajimoto Okitsugu , Takayanagi Toshiyuki
Published: March 2004

We have determined the rotational state distributions of NO(v′=0,1,2) products produced from the reaction O(1D)+N2O. This is the first full characterization of the product rotational distribution of this reaction. The main part of each rotational distribution (up to j′≈80) has rotational temperature ≈20 000 K and all these distributions are quite near to those predicted by the phase space theory (PST). This observation and previously reported vibrational distribution indicate that the most part of the energy partitioning of the reaction products is at least apparently statistical although the intermediate of this reaction is not so stable as to ensure the long lifetime. On the other hand, the distributions in the high rotational levels (j′=80–100) are found to decrease more sharply as j′ increases than the PST predictions. The origin of the observed decrease of the distribution is discussed with quasiclassical trajectory (QCT) calculations on a five-dimensional ab initio potential energy surface (PES). The observed near-statistical distribution and the sharp decrease in the high-j′ levels are well reproduced by a “half-collision” QCT calculation, where statistical distribution at the reaction intermediate is assumed. This agreement shows the rotation–translation interaction in the exit region has an effect of yielding small high-j′ populations. However, a little bias of the calculated distribution toward lower rotational excitation than the observed one indicates that the combination of the statistical intermediate and the exit interaction on the current PES does not completely describe the real system. It is suggested that the reaction intermediate is generated with the distribution which is close to statistical but a little biased toward yielding high-j′ products, and that the interaction in the exit region of the PES results in the sharp decrease in the high-j′ levels.
Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. II. Furo-furan Isomers
Authors: Cuesta I. Garcı́a , Jartı́n R. Soriano , Sánchez de Merás A. , Lazzeretti P.
Published: March 2004

Magnetic susceptibility and nuclear magnetic shielding at the nuclei of bis-heteropentalenes formed by two furan units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been computed by several approximated techniques and a large Gaussian basis set to achieve near Hartree–Fock estimates. Ab initio models of the ring currents induced by a magnetic field normal to the molecular plane were obtained for the three isomeric systems of higher symmetry, showing that the π electrons give rise to intense diamagnetic circulation. The π currents are responsible for enhanced magnetic anisotropy and strong out-of-plane proton deshielding. The theoretical findings are used to build up a “diatropicity matrix” for two fused five-membered heterocyclic systems.
Raman spectra of ionic liquids: Interpretation via computer simulation
Authors: Madden Paul A. , Wilson Mark , Hutchinson Francis
Published: March 2004

Theoretical Raman spectra of the complex-forming ionic liquids LaCl3 and ScCl3, derived from molecular dynamics computer simulations, are presented. These simulations, which use polarizable ion interaction models, have previously been shown to predict structural properties in excellent agreement with diffraction experiments. The dependence of the polarizability of the melt on the ionic positions, which determines the Raman spectrum through the time dependence of the polarizability correlation function, is modeled on the basis of ab initio electronic structure calculations carried out on alkali chlorides. New simulation techniques are introduced in order to allow the spectrum to be calculated with acceptable statistics. The calculated spectra are in semiquantitative agreement with experimental data. The distinctive bands which appear in the spectra of such complex melts are linked to the vibrations of the transient coordination complexes which form in these melts and new interpretations for the origin of several well-known features are proposed. The simulations thus enable a link between the structure of a melt as perceived through Raman spectroscopy and through diffraction experiments to be made.
Thermal decomposition of ethanol. III. A computational study of the kinetics and mechanism for the CH3+C2H5OH reaction
Authors: Xu Z. F. , Park J. , Lin M. C.
Published: March 2004

The mechanism for the CH3+C2H5OH reaction has been investigated by the modified Gaussian-2 method based on the geometric parameters of the stationary points optimized at the B3LYP/6-311+G(d,p) level of theory. Five transition states have been identified for the production of CH4+CH3CHOH (TS1), CH4+CH3CH2O (TS2), CH4+CH2CH2OH (TS3), CH3OH+CH3CH2 (TS4), and CH3CH2OCH3+H (TS5) with the corresponding barriers 12.0, 13.2, 16.0, 44.7, and 49.9 kcal/mol, respectively. The predicted rate constants and branching ratios for the three lower-energy H-abstraction reactions were calculated using the conventional and variational transition state theory with quantum-mechanical tunneling corrections for the temperature range 300–3000 K. The predicted total rate constant, kt=8.36×10−76 T20.00 exp(5258/T) cm3 mol−1 s−1 (300–600 K) and 6.10×10−25 T4.10exp(−4058/T) cm3 mol−1 s−1 (600–3000 K), agrees closely with existing experimental data in the temperature range 403–523 K. Similarly, the predicted rate constants for CH3+CH3CD2OH and CD3+C2H5OD are also in reasonable agreement with available low temperature kinetic data.
Gas phase infrared spectroscopy of mono- and divanadium oxide cluster cations
Authors: Asmis Knut R. , Meijer Gerard , Brümmer Mathias , Kaposta Cristina , Santambrogio Gabriele , Wöste Ludger , Sauer Joachim
Published: March 2004

The vibrational spectroscopy of the mono- and divanadium oxide cluster cations VO1−3+ and V2O2−6+ is studied in the region from 600 to 1600 wave numbers by infrared photodissociation of the corresponding cluster cation-helium atom complexes. The comparison of the experimental depletion spectra with the results of density functional calculations on bare vanadium oxide cluster cations allows for an unambiguous identification of the cluster geometry in most cases and, for VO1−3+ and V2O5,6+, also of the electronic ground state. A common structural motif of all the studied divanadium cluster cations is a four-membered V–O–V–O ring, with three characteristic absorption bands in the 550–900 wave number region. For the V–O–V and V=O stretch modes the relationship between vibrational frequencies and V–O bond distances follows the Badger rule.
Thermodynamics of lattice heteropolymers
Authors: Bachmann Michael , Janke Wolfhard
Published: March 2004

We calculate thermodynamic quantities of hydrophobic-polar (HP) lattice proteins by means of a multicanonical chain-growth algorithm that connects the new variants of the Pruned-Enriched Rosenbluth Method and flat histogram sampling of the entire energy space. Since our method directly simulates the density of states, we obtain results for thermodynamic quantities of the system for all temperatures. In particular, this algorithm enables us to accurately simulate the usually difficult accessible low-temperature region. Therefore, it becomes possible to perform detailed analyses of the low-temperature transition between ground states and compact globules.
Aspects of prewetting at nonplanar surfaces
Authors: Bohlen Holger , Schoen Martin
Published: March 2004

We employ Monte Carlo simulations in the grand canonical ensemble (GCEMC) to investigate the impact of nonplanarity of a solid substrate on the locus of the prewetting phase transition. The substrate is modelled as a periodic sequence of furrows of depth D and periodicity sx in the x direction; the furrows are infinitely long in the y direction. Our results indicate that a necessary prerequisite for a prewetting transition is the formation of a(n approximately) planar interface between molecularly thin films and an adjacent (bulk) gas. Thus, in general the prewetting transition is shifted to larger chemical potentials because the formation of a planar film–gas interface is more difficult next to a nonplanar compared with a planar solid surface. However, this shift turns out to be nonmonotonic depending on D on account of subtle packing effects manifested in the deviation of the local density Δρ(x,Δz;D) at the nonplanar solid surface from that at a planar substrate. If D becomes sufficiently large prewetting as a discontinuous phase transition is suppressed because inside the furrow a highly ordered film forms that prevents a planar film–gas interface from forming.