bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of the stochastic distorted-wave Born approximation model with broad bandwidth total target strength measurements of Antarctic krill
Authors: Demer David A. , Conti Stéphane G.
Published: June 2003

Total-scattering cross-sections (σt) of Antarctic krill (Euphausia superba) were measured over a broad bandwidth (36–202 kHz) using a new technique based on acoustical reverberation in a cavity. From 18 February to 9 March 2002, mean total target strengths (TTS = 10 log(σt/4π)), were measured from groups of 57–1169 krill (average standard length=31.6 mm; standard deviation=6.6 mm) at the Cape Shirreff field station, Livingston Island, Antarctica, and aboard RV “Yuzhmorgeologiya”. Chirp pulses were transmitted sequentially by an omni-directional emitter into one of three glass carboys containing groups of krill swimming in 9.3, 19.3, or 45.9 liters of seawater (0.6°C≤temperature≤4.0°C). Between each pulse the krill moved within the fixed-boundary tank and the modulated reverberations were sensed bi-statically with three omni-directional receivers. At each center frequency (fc), the coherent energy in 200-pulse ensembles identified sound scattered by the tank. The incoherent energy described total sound scattering from the krill. Thus, the TTS at each fc was extracted from a correlation analysis of energy reverberated in the tank. Measurement bias was determined to be ±0.4 dB from an experiment using metal sphere reference targets, and the precision was estimated as ±0.8 dB from the variability in the krill TTS (fc) measurements. The empirical estimates of mean σt corroborated a krill-scattering model based on the distorted-wave Born approximation (DWBA), enhanced by the authors to account for the stochastic nature of sound scattering (SDWBA), integrated over all scattering angles and averaged over all incident angles (SDWBATTS). The SDWBA, solved for target strength of Antarctic krill, may be the best predictor of backscatter for this important species and may also provide backscattering spectra for improving their acoustic identification. These advances may help to reduce uncertainty in krill-biomass estimation using multi-frequency echosounder data and echo-integration methods.
Mitotic activity in the growing red deer antler
Authors: Matich Jessica , Nicholson Louise Frances Basford , Barling Peter Michael
Published: June 2003

Antlers grow rapidly through the coordinated development of both osseocartilage and skin (velvet). The regional patterns of cell division in these two compartments were assessed by immunochemical detection of proliferating cell nuclear antigen (PCNA) in antlers from one‐year‐old red deer. The whole antler integument was in a state of growth and/or renewal, particularly the keratinocytes of the basal cell layer of the epidermis near the tip, and hair bulbs and sebaceous glands. More proximally, a zone of weaker mitotic activity was detected. Within the osseocartilagenous compartment, rapid mitosis was particularly apparent within the distal mesenchyme, visible as a dome‐shaped band of staining. Mitotic activity of chondrocytes and osteoblasts was more extensive in peripheral areas of developing bone than in the centre. We conclude that the antler tip is the site of most active epidermal growth, and hypothesise that other mechanisms in addition to mechanical stretching play a role in growth of the integument.
Monopolar spindles in meiosis of intergeneric cereal hybrids
Authors: Shamina N.V. , Silkova O.G. , Seriukova E.G.
Published: June 2003

Monopolar spindles in pollen mother cells of cereal wide F1 hybrids are described; details of the formation of anastral spindles are discussed.
A prognostic index to predict long‐term mortality in patients with mild to moderate chronic heart failure stabilised on angiotensin converting enzyme inhibitors
Authors: Kearney Mark T. , Nolan James , Lee Amanda J. , Brooksby Paul W. , Prescott Robin , Shah Ajay M. , Zaman Azfar G. , Eckberg Dwain L. , Lindsay H. Stephen , Batin Philip D. , Andrews Richard , Fox Keith A.A.
Published: June 2003

Background:

Mortality in patients with mild to moderate chronic heart failure remains high. At present there is no easy way of identifying patients within this population at increased risk of death in the medium to long term.

Aims:

To develop a prognostic index to identify outpatients with mild to moderate chronic heart failure at increased risk of death.

Methods and results:

Five hundred and fifty‐three outpatients mean (S.D.) age 63(±10) years with symptoms of chronic heart failure (mean New York Heart Association functional class, 2.3(±0.5)), were recruited between December 1993 and April 1995. By April 2000, 201 patients had died. Using data from non‐invasive measurements of cardiac size, electrical and autonomic function, renal function and plasma biochemistry we identified eight independent predictors of mortality (allP<0.01). To develop a prognostic index, predictors were dichotomised by group median and awarded 0 or 1 point accordingly. Serum sodium≤140 mmol/l (1 point), creatinine≥111 μmol/l (1 point), cardiothoracic ratio≥0.52 (1 point), SDNN≤112 ms (1 point), maximum corrected QT interval≥487 ms (1 point), QRS dispersion≥42.7 ms (1 point), the presence of non‐sustained ventricular tachycardia (1 point) and voltage criteria for left ventricular hypertrophy on 12‐lead ECG (1 point). We calculated risk scores for patients by adding the points of each independent risk factor. In the low‐risk group (0–3 points) mortality at 5 years was 20% and in the high‐risk group (4–8 points) 53%. The area under the receiver–operator characteristic curve using dichotomised variables was 0.74 and for continuous model 0.78.

Conclusions:

Our prognostic index which uses eight non‐invasive measurements and a straightforward additive points system, has good discrimination and stratifies outpatients with chronic heart failure into high and low risk. This index may be useful in clinical care and risk stratification.
The crustal structure from the Altai Mountains to the Altyn Tagh fault, northwest China
Authors: Wang Youxue , Mooney Walter D. , Yuan Xuecheng , Coleman Robert G.
Published: June 2003

We present a new crustal section across northwest China based on a seismic refraction profile and geologic mapping. The 1100‐km‐long section crosses the southern margin of the Chinese Altai Mountains, Junggar Accretional Belt and eastern Junggar basin, easternmost Tianshan Mountains, and easternmost Tarim basin. The crustal velocity structure and Poisson's ratio (σ), which provide a constraint on crustal composition, were determined fromPandSwave data. Despite the complex geology, the crustal thickness along the entire profile is nearly uniform at 50 km. The thickest crust (56 km) occurs at the northern end of the profile beneath the Altai Mountains and the thinnest (46 km) crust is beneath the Junggar basin. Beneath surficial sediments, the crust is found to have three layers withPwave velocities (Vp) of 6.0–6.3, 6.3–6.6, and 6.9–7.0 km/s, respectively. The southern half of the profile, including the eastern Tianshan Mountains and eastern margin of the Tarim basin, shows lowPwave velocities and σ = 0.25 to a depth of 30 km, which suggests a quartz‐rich, granitic upper crustal composition. The northern half of the profile below the Altai Mountains and Junggar Accretional Belt has a higher Poisson's ratio of σ = 0.26–0.27 to a depth of 30 km, indicative of an intermediate crustal composition. The entire 1100‐km‐long profile is underlain by a 15–30 km thick high velocity (6.9–7.0 km/s; σ = 0.26–0.28) lower‐crustal layer that we interpret to have a bulk composition of mafic granulite. At the southern end of the profile, a 5‐km‐thick midcrustal low‐velocity layer (Vp= 5.9 km/s,σ= 0.25) underlies the Tianshan and the region to the south, and may be indicative of a near‐horizontal detachment interface.Pnvelocities are ∼7.7–7.8 km/s between the Tianshan and the Junggar basin, and ∼7.9–8.0 km/s below the Altai Mountains and eastern margin of the Tarim basin. We interpret the consistent three‐layer stratification of the crust to indicate that the crust has undergone partial melting and differentiation after Paleozoic terrane accretion. The thickness (50 km) of the crust appears to be related to compression resulting from the Indo‐Asian collision.
Effects of wood on debris flow runout in small mountain watersheds
Authors: Lancaster Stephen T. , Hayes Shannon K. , Grant Gordon E.
Published: June 2003

Debris flows have typically been viewed as two‐phase mixtures of sediment and water, but in forested mountain landscapes, wood can represent a sizable fraction of total flow volume. The effects of this third phase on flow behavior are poorly understood. To evaluate whether wood can have a significant effect on debris flow runout in small mountainous watersheds, we used a landscape‐scale model combining empirical, stochastic, and physical submodels of storms, fires, forest growth, tree fall, wood decay, soil production and diffusion, landslide initiation, debris flow runout, and fluvial sediment transport. We examined changes in the cumulative distribution function of debris flow runout lengths in a small (2 km2) watershed in the Oregon Coast Range due to presence or absence of two hypothesized effects of wood: (1) velocity reduction due to entrainment of wood in the runout path and (2) velocity reduction due to changes in flow direction angle. The model was calibrated such that the distribution for simulations including both effects was similar to that measured in the study basin, and amounts of wood in the simulation and the field, both fallen in small valleys and incorporated by debris flows, were comparable. Removal of either effect, or both, significantly shifted runout length distributions to longer lengths. Simulations and field observations indicate that with wood, fluvial transport is a significant source of sediment output, few debris flows reach the outlet, and debris flow deposits are widely distributed throughout the network. Simulations indicate that without wood, basin sediment yield greatly increases, that yield is dominated by longer‐runout debris flows, and that debris flow deposits are concentrated in the low‐gradient reach near the outlet.
Equatorial evening prereversal electric field enhancement and sporadic E layer disruption: A manifestation of E and F region coupling
Authors: Abdu M. A. , MacDougall J. W. , Batista I. S. , Sobral J. H. A. , Jayachandran P. T.
Published: June 2003

An investigation of the evening prereversal enhancement in the equatorial zonal electric field (PRE) based on ionosonde data show that the PRE development process is coupled with the sporadic E layer formation in the evening over Fortaleza. Larger PRE amplitudes are associated with disruption of the Es layer, whereas for smaller PRE amplitudes such disruption does not occur, in general. The Es layer disruption does not occur also when the PRE amplitude decreases or is inhibited under a disturbance dynamo electric field. The disruption of these layers is followed by their reconstitution after a break of ∼3 hours. An examination of the relative role of the electric field and winds on ion velocity convergence process shows that the Es layer formation from a shearing (or height‐independent and westward) zonal wind is directly influenced by a vertical electric field (but not by zonal electric field). Measurements of the Es patch zonal drift velocities by a digital ionosonde seem to support the role of a westward wind in the Es layer formation. The observed association between the PRE and Es layer disruption/formation is shown to arise from sunset‐related vertical electric field development originating from the E and F region electrodynamic coupling processes. The results demonstrate the competing influences of the vertical electric field and the zonal wind in the evening Es layer processes. Since the PRE is responsible for the equatorial spread F (ESF) development, its relationship with the Es layer is discussed in the context of the day‐to‐day variability of the ESF.
Demagnetization of transmitted electrons through a quasi‐perpendicular collisionless shock
Authors: Lembège B. , Savoini P. , Balikhin M. , Walker S. , Krasnoselskikh V.
Published: June 2003

Physical processes responsible for the electron demagnetization within the front of a quasiperpendicular collisionless shock are analyzed via a comparative study between theoretical calculations and computer simulations. Herein, simulation results of a shock in supercritical regime are based on the use of a 2‐D full particle self‐consistent code. Present statistics on the spatial widths of the magnetic field (LBr) and electric field (LEr) within the ramp show that their ratio R = LEr/LBr is around 1; this value is appropriate to demagnetize electrons and to provide a resulting deviation from adiabaticity [Balikhin et al., 1998]. In order to verify this theoretical expectation, two complementary approaches are used. First, the deviation of the full electron gyroperiod from the magnetic gyroperiod is analyzed from the trajectories of “marked” self‐consistent electrons crossing the shock ramp. In such a case, nonstationary and nonuniformity effects of the shock front are fully involved. Second, such effects are removed and test particles simulations are used in order to determine the strength of electron demagnetization when effects of width shock along the shock normal are included only. Both approaches confirm that demagnetization takes place within the first half of the ramp, that is, where the gradient dElx/dx seen by transmitted electrons is positive. Statistical results performed using test particles simulations show that a noticeable number of demagnetized electrons are formed within the ramp even for a moderate supercritical Mach number and that the relative percentage of demagnetized/magnetized electrons varies according to the nonstationary behavior of the shock front (self‐reformation).
Tail‐dominated storm main phase: 31 March 2001
Authors: Skoug R. M. , Thomsen M. F. , Henderson M. G. , Funsten H. O. , Reeves G. D. , Pollock C. J. , Jahn J.‐M. , McComas D. J. , Mitchell D. G. , Brandt P. C. , Sandel B. R. , Clauer C. R. , Singer H. J.
Published: June 2003

On 31 March 2001 a fast solar wind transient with strong southward interplanetary magnetic field Bz produced a large geomagnetic storm at Earth, with a drop in the Dst index to −350 nT between 0400 and 0900 UT. The Earth's magnetosphere was very compressed during this interval, with the bow shock crossing geosynchronous orbit on at least two occasions. Here we present space‐based and ground‐based observations demonstrating that tail currents, rather than ring currents, were the dominant contributor to the Dst index during the main phase of this storm. The plasma sheet during this interval was exceptionally dense and penetrated very deeply towards the Earth, leading to extremely strong tail currents flowing quite close to the Earth. These tail currents produced a very distorted magnetosphere, with strong stretching of the magnetic field lines in the nightside plasma sheet. Energetic neutral atom (ENA) images from the MENA and HENA instruments on IMAGE show a very narrow spatial distribution, with ENAs confined to the nightside until a magnetic field dipolarization at ∼0630 UT when Dst was −250 nT. Ground magnetometer measurements confirm that the disturbance was localized on the nightside and dominated by tail currents up until the field dipolarization. Following the dipolarization, higher energy ENAs began to drift toward dusk, forming a partial ring current. Even at that time, low‐energy ENAs were not observed on the dayside, either due to inhibited access or to strong charge exchange losses.
On the role of thermohaline advection and sea ice in glacial transitions
Authors: Kravtsov S. , Dewar W. K.
Published: June 2003

A two‐dimensional, one‐basin thermohaline oceanic circulation (THC) model coupled to an atmospheric energy balance model (EBM) with land ice albedo effect and a thermodynamic sea ice model is used to study global climate on centennial, and longer, timescales. The model is interpreted to represent the effect of the global ocean, rather than the Atlantic, as is commonly done. It is forced by symmetric insolation and includes a diagnostic parameterization of the hydrologic cycle. Here the strength of the ocean's haline forcing is controlled by a parameter, which reflects the effect of river runoff. This parameter is varied in a set of experiments, which also differ by the magnitude of solar insolation. In wide ranges of the hydrologic cycle, multiple climatic equilibria exist, consisting of circulations with different degrees of asymmetry. More symmetric states have a higher global atmospheric temperature, characteristic of modern climate, whereas less symmetric states are colder and resemble glacial conditions. The maximum global atmospheric temperature difference between such states is consistent with proxy‐data‐derived temperature drop of about 4°C during the glacial, in contrast to EBM‐only sensitivity of about 0.4°C. The mechanics of climate transitions in the model are due to amplification of the orbitally induced global heat budget changes by a major reorganization of the oceanic heat transport. In our model this reorganization is caused by the nonlinear dynamics of the ocean's THC, whose stability regime shifts subject to variable external forcing. Sea ice enhances model climate sensitivity by anchoring deep‐ocean temperature to be near freezing [Kravtsov, 2000] and by affecting atmospheric temperature and land ice extent near the poles because of sea ice insulating properties.
Evaluating the first‐order effect of intraannual temperature variability on urban air pollution
Authors: Aw Jeremy , Kleeman Michael J.
Published: June 2003

The direct effect of intraannual temperature variability on ozone and PM2.5 concentrations at the urban scale was simulated using a high‐resolution air quality model that tracks the temperature‐dependant formation of secondary organic and inorganic aerosol components. Calculations show that the concentration of ozone and non‐volatile secondary particulate matter will generally increase at higher temperatures due to increased gas‐phase reaction rates. The concentration of semi‐volatile reaction products also will increase at higher temperatures, but the amount of this material that partitions to the particle‐phase may decrease as equilibrium vapor pressures rise. Calculations performed for Southern California on September 25, 1996 predict that intraannual temperature variability may cause peak ozone and PM2.5 concentrations to fluctuate by up to 16% and 25% respectively. 24‐hour average PM2.5 concentrations will decrease with increasing temperatures for inland portions of the South Coast air basin during most of the day. Slight increases in 24‐hour average PM2.5 concentrations were predicted for coastal regions. The majority of the predicted shift in PM2.5 concentrations was related to increased production rates for nitric acid and condensable organic compounds balanced against increased volatilization of these products. Semi‐volatile particulate ammonium nitrate concentrations are most sensitive to volatilization losses at hotter temperatures and when the ratio of gas‐phase ammonia to nitric acid concentrations is approximately unity. Background sulfate particles and particles released from non‐catalyst equipped gasoline‐powered engines, diesel engines, and food cooking were shifted to smaller sizes as ammonium nitrate volatilized at hotter temperatures.
A unified, long‐term, high‐latitude stratospheric aerosol and cloud database using SAM II, SAGE II, and POAM II/III data: Algorithm description, database definition, and climatology
Authors: Fromm Michael , Alfred Jerome , Pitts Michael
Published: June 2003

A 22 year, high‐latitude, stratospheric aerosol and cloud database has been formed in a “unified” manner by combining the Stratospheric Aerosol Measurement (SAM) II, Stratospheric Aerosol and Gas Measurement (SAGE) II, Polar Ozone and Aerosol Measurement (POAM) II, and POAM III 1 μm aerosol extinction profiles. The database is “unified” in that it embodies similar aerosol extinction measurements, uses a single meteorological data set, and employs a single algorithm for calculating background extinction and cloud detection thresholds. Latitude is constrained to poleward of 45° in each hemisphere. The Unified cloud detection algorithm and database are designed for the straightforward addition of new data when other compatible data sets (e.g., SAGE III) become available. “Unified” cloud detection is similar to, but a refinement of, earlier attempts to identify polar stratospheric clouds (PSCs) with SAM II and POAM II data. The Unified algorithm is instrument‐independent and circumvents fundamental cloud detection pitfalls. The database contains over 73,000 (36,000) polar vortex‐region profiles in the Antarctic (Arctic) and over 21,000 (2000) PSC observations. An introductory climatology of Unified “background” extinction is presented. It is seen that volcanic effects dominate the evolution of outside‐vortex background extinctions, but perturbations apparently not related to volcanoes are seen as well. Interannual variations of background extinction inside the austral vortex are seen to be nearly decoupled from volcanic effects, while in the Arctic, inside‐vortex extinctions show a considerable volcanic influence. An analysis of long‐term PSC sighting is presented. Midwinter (July and January) PSC and clear‐sky measurements at 20 km, in a fixed temperature range, are used for computing PSC probability. The grand average PSC probability calculated this way is nearly identical between hemispheres. In the Antarctic the interannual PSC probability pattern is distinctly cyclic but is convoluted by volcanic perturbations in background aerosol. In the Arctic the PSC probability has much less temporal coherence than in the Antarctic but is similarly impacted by volcanic background increases. An explanation for the variation in PSC probabilities, in terms of interannual differences in denitrification, is discussed. Finally, a statistical analysis of tropopause height in relation to PSC formation is also presented. PSC observations are seen to be strongly associated with elevated tropopause heights, indicating that tropospheric, synoptic‐scale flow perturbations are the primary forcing mechanism for Arctic PSC formation, as evidenced in this long‐term satellite record.
Validation of POAM III ozone: Comparisons with ozonesonde and satellite data
Authors: Randall C. E. , Rusch D. W. , Bevilacqua R. M. , Hoppel K. W. , Lumpe J. D. , Shettle E. , Thompson E. , Deaver L. , Zawodny J. , Kyrö E. , Johnson B. , Kelder H. , Dorokhov V. M. , König‐Langlo G. , Gil M.
Published: June 2003

This paper describes the validation of ozone profiles from the Polar Ozone and Aerosol Measurement (POAM) III instrument. POAM III O3 is measured with 1‐km vertical resolution throughout most of the stratosphere and random errors of ∼5%. It is shown that sunspots do not significantly affect the POAM O3 retrievals, nor do polar stratospheric clouds, except under rarely encountered, extreme conditions of very low O3 and exceptionally high aerosol extinction. A statistical analysis is presented of comparisons between coincident measurements from POAM III and ozonesondes, the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiment (SAGE) II. On average, POAM III O3 profiles agree to within ±5% with these correlative data from 13 to 60 km. There is a suggestion that from 30 to 60 km POAM III sunrise data might be biased slightly low (<5%) relative to POAM sunset data. There is evidence that POAM III has a high bias of up to ∼0.1 ppmv from 10 to 12 km, and that this bias might stem, in part, from errors in the retrieval of aerosol extinction at 0.6 μm, the primary O3 absorption wavelength in the POAM retrievals. Below 10 km the POAM III data agree with coincident sonde measurements to better than 0.05 ppmv on average, which can correspond to large relative differences of more than +30% at 8–9 km and −100% at 5 km. We conclude that the POAM III profiles are highly accurate and adequate for quantitative scientific studies.
Why small? The use of small inorganic clusters to understand mineral surface and dissolution reactions in geochemistry
Authors: Casey William H. , Swaddle Thomas W.
Published: June 2003

Geochemical reactions commonly fall into two classes: (1) ligand exchange reactions where one of the atoms bonded to a metal is exchanged for another and (2) electron exchange reactions where the valence state of a metal changes. Electron exchange reactions cannot be understood without first addressing the role of the coordinated ligands, and we review the use of small aqueous oligomers and complexes to understand mechanisms of ligand exchange reactions at the surfaces of minerals such as metal‐(hydr)oxides in soil.
On the porous continuum‐scale modeling of gravity‐driven fingers in unsaturated materials: Numerical solution of a hypodiffusive governing equation that incorporates a hold‐back‐pile‐up effect
Authors: Eliassi Mehdi , Glass Robert J.
Published: June 2003

We consider the use of a hypodiffusive governing equation (HDE) for the porous‐continuum modeling of gravity‐driven fingers (GDF) as occur in initially dry, highly nonlinear, and hysteretic porous media. In addition to the capillary and gravity terms within the traditional Richards equation, the HDE contains a hypodiffusive term that models an experimentally observed hold‐back‐pile‐up (HBPU) effect and thus imparts nonmonotonicity at the wetting front. In its dimensionless form the HDE contains the dimensionless hypodiffusion number, NHD. As NHD increases, one‐dimensional (1D) numerical solutions transition from monotonic to nonmonotonic. Considering the experimentally observed controls on GDF occurrence, as either the initial moisture content and applied flux increase or the material nonlinearity decreases, solutions undergo the required transition back to monotonic. Additional tests for horizontal imbibition and capillary rise show the HDE to yield the required monotonic response but display sharper fronts for NHD > 0. Finally, two‐dimensional (2D) numerical solutions illustrate that in parameter space where the 1D HDE yields nonmonotonicity, in 2D it forms nonmonotonic GDF.
Calibration of regional groundwater flow models: Working toward a better understanding of site‐specific systems
Authors: Castro Maria Clara , Goblet Patrick
Published: June 2003

This work highlights the lack of unique solutions for regional groundwater flow models and quantifies the degree of freedom concerning hydraulic conductivities for models calibrated on measured hydraulic heads. The potential of 4He as an independent tracer at reducing the nonuniqueness problem is tested. Four different calibrated groundwater flow scenarios are presented for the Carrizo aquifer and surrounding formations in Texas. It is shown that variations of hydraulic conductivities up to 2 orders of magnitude in the Carrizo aquifer and overlying confining layer lead to similar calculated hydraulic heads. No clear‐cut arguments are present to invalidate one groundwater flow scenario over a different one. In contrast, when tested with a 4He transport conceptual model, all groundwater flow scenarios except one failed to reproduce a coherent 4He transport behavior in the system. This study exemplifies possible future contributions of 4He at discerning which model most closely replicates natural conditions.
A monthly and latitudinally varying volcanic forcing dataset in simulations of 20th century climate
Authors: Ammann Caspar M. , Meehl Gerald A. , Washington Warren M. , Zender Charles S.
Published: June 2003

A new monthly volcanic forcing dataset is included in a coupled GCM for a more physically consistent treatment of the stratospheric sulfate aerosol history from explosive volcanism. The volcanic forcing is different from previous versions in that there is an individual evolution of the aerosol for each event. Thus the seasonal and latitudinal dependence of the volcanic aerosol can affect global climate in a more realistic way prior to the satellite period, compared to earlier volcanic forcing datasets. Negative radiative forcing from volcanic activity is greatest in the early 20th century prior to 1915 and in the late 20th century after 1960. The combination of volcanic and solar forcing contributes to an early‐20th century warming, followed by relative cooling in late 20th century. Consequently, the addition of natural forcing factors to the anthropogenic GHG forcing in late 20th century is required to simulate the observed late 20th century warming.
Real‐time measurement of volcanic H2S and SO2 concentrations by UV spectroscopy
Authors: O'Dwyer M. , Padgett M. J. , McGonigle A. J. S. , Oppenheimer C. , Inguaggiato S.
Published: June 2003

Sulphur speciation in volcanic gases acts as a major redox buffer, and H2S/SO2 ratios represent a valuable indicator of magmatic conditions and interactions between magmatic and hydrothermal fluids. However, measurement of H2S/SO2 even by direct sampling techniques, is not straightforward. We7 report here on application of a small ultraviolet spectrometer for real‐time field measurement of H2S and SO2 concentrations, using open‐path and extractive configurations. The device was tested at fumaroles on Solfatara and Vulcano, Italy, in November 2002. H2S concentrations of up to 220 ppmm (400 ppmv) were measured directly above the Bocca Grande fumarole at Solfatara, and H2S/SO2 molar ratios of 2 and 2.4, respectively, were determined for the ‘F11’ and ‘F0’ fumaroles at Vulcano. In comparison with other optical techniques capable of multiple volcanic gas measurements, such as laser and FTIR spectroscopy, this approach is considerably simpler and cheaper, with the potential for autonomous, sustained high‐time resolution operation.
Experimental observations of fracture dissolution: The role of Peclet number on evolving aperture variability
Authors: Detwiler Russell L. , Glass Robert J. , Bourcier William L.
Published: June 2003

Dissolution of the surfaces of rock fractures can cause significant alteration of the fracture void space (aperture) and fracture permeability (k). Both surface reaction rates and transport of reactants within the fracture can limit local dissolution. We investigated the role of Peclet number (Pe), a measure of the relative importance of advective and diffusive transport of reactants, on fracture dissolution in two identical transparent analog fractures with different initial values of Pe (Peo). High‐resolution light‐transmission techniques provided direct measurements of the evolving aperture field during each experiment. For Peo = 54 distinct dissolution channels formed, while for Peo = 216 we measured minimal channeling and a reduction in short wavelength aperture variability. The nature of the dissolution patterns strongly influenced the relative increase in k. A 110% increase in the mean aperture due to dissolution resulted in estimated permeability increases of 440% and 640% for the Peo = 54 and Peo = 216 experiments, respectively.
Evaluation of the parameterization‐simulation‐optimization approach for the control of reservoir systems
Authors: Koutsoyiannis Demetris , Economou Athanasia
Published: June 2003

Most common methods used in optimal control of reservoir systems require a large number of control variables, which are typically the sequences of releases from all reservoirs and for all time steps of the control period. In contrast, the less widespread parameterization‐simulation‐optimization (PSO) method is a low‐dimensional method. It uses a handful of control variables, which are parameters of a simple rule that is valid through the entire control period and determines the releases from different reservoirs at each time step. The parameterization of the rule is linked to simulation of the reservoir system, which enables the calculation of a performance measure of the system for given parameter values, and nonlinear optimization, which enables determination of the optimal parameter values. To evaluate the PSO method and, particularly, to investigate whether the radical reduction of the number of control variables might lead to inferior solutions or not, we compare it to two alternative methods. These methods, namely, the high‐dimensional perfect foresight method and the simplified “equivalent reservoir” method that merges the reservoir system into a single hypothetical reservoir, determine “benchmark” performance measures for the comparison. The comparison is done both theoretically and by investigation of the results of the PSO against the benchmark methods in a large variety of test problems. Forty‐one test problems for a hypothetical system of two reservoirs are constructed and solved for comparison. These refer to different objectives (maximization of reliable yield, minimization of cost, maximization of energy production), water uses (irrigation, water supply, energy production), characteristics of the reservoir system and hydrological scenarios. The investigation shows that PSO yields solutions that are not inferior to those of the benchmark methods and, simultaneously, it has several theoretical, computational, and practical advantages.
InterRing: A Visual Interface for Navigating and Manipulating Hierarchies
Authors: Yang Jing , Ward Matthew O. , Rundensteiner Elke A. , Patro Anilkumar
Published: June 2003

Radial, space-filling (RSF) techniques for hierarchy visualization have several advantages over traditional node–link diagrams, including the ability to use the display space efficiently while effectively conveying the hierarchy structure. Several RSF systems and tools have been developed to date, each with varying degrees of support for interactive operations such as selection and navigation. In this paper, we describe what we believe to be a complete set of desirable operations on hierarchical structures. We then present InterRing, an RSF hierarchy visualization system that supports a significantly more extensive set of these operations than prior systems. In particular, InterRing supports multifocus distortions, interactive hierarchy reconfiguration, and both semiautomated and manual selection. We show the power and utility of these and other operations, and describe our ongoing efforts to evaluate their effectiveness and usability.
Beamtrees: Compact Visualization of Large Hierarchies
Authors: van Ham Frank , van Wijk Jarke J.
Published: June 2003

Beamtrees are a new method for the visualization of large hierarchical data sets, such as directory structures and organization structures. Nodes are shown as stacked circular beams such that both the hierarchical structure as well as the size of nodes are depicted. The dimensions of beams are calculated using a variation of the treemap algorithm. Both a two-dimensional and a three-dimensional variant are presented. A small user study indicated that beamtrees are significantly more effective than nested treemaps and cushion treemaps for the extraction of global hierarchical information.
Visual Unrolling of Network Evolution and the Analysis of Dynamic Discourse
Authors: Brandes Ulrik , Corman Steven R.
Published: June 2003

We introduce a method for visualizing evolving networks. In addition to the intermediate states of the network, it conveys the nature of change between states by unrolling the dynamics of the network. Each modification is shown in a separate layer of a three-dimensional representation, where the stack of layers corresponds to a time line of the evolution. We focus on networks of dynamic discourse as the driving application, but the method extends to any type of networks evolving in similar ways.
Data-Mining and Uncertain Reasoning: An Integrated Approach
Authors: Hu Xiaohua
Published: June 2003

By Z Chen, published by John Wiley, New York, 2001 Hardback, ISBN 0471388785
Room temperature nanocrystalline silicon single-electron transistors
Authors: Tan Y. T. , Kamiya T. , Durrani Z. A. K. , Ahmed H.
Published: June 2003

Single-electron transistors operating at room temperature have been fabricated in 20-nm-thick nanocrystalline silicon thin films. These films contain crystalline silicon grains 4 – 8 nm in size, embedded in an amorphous silicon matrix. Our single-electron transistor consists of a side-gated 20 nm×20 nm point contact between source and drain electrodes. By selectively oxidizing the grain boundaries using a low-temperature oxidation and high-temperature argon annealing process, we are able to engineer tunnel barriers and increase the potential energy of these barriers. This forms a “natural” system of tunnel barriers consisting of silicon oxide tissues that encapsulate sub-10 nm size grains, which are small enough to observe room-temperature single-electron charging effects. The device characteristics are dominated by the grains at the point contact. The material growth and device fabrication process are compatible with silicon technology, raising the possibility of large-scale integrated nanoelectronic systems.
The fluid–solid equilibrium for a charged hard sphere model revisited
Authors: Vega Carlos , Abascal José L. F. , McBride Carl , Bresme Fernando
Published: June 2003

The global phase diagram of a system of charged hard spheres, composed of positive and negative ions of the same size, is obtained by means of computer simulations. Thermodynamic integration and Einstein crystal calculations are used to determine the free energies of the different possible solid structures. In this way, the fluid–solid and solid–solid phase transitions are located. Gibbs–Duhem integration is used to trace the full coexistence curves between the different phases involved. Three different solid structures are found to be stable for the model considered; namely, a cesium chloride structure (CsCl), a substitutionally disordered close packed structure which is faced centered cubic (fcc), and a tetragonal ordered structure with a fcc arrangement of atoms if the charge of the ions is not considered. At high temperatures, freezing leads to the substitutionally disordered close packed structure. This solid structure undergoes an order–disorder transition at low temperatures transforming into the tetragonal solid. At low temperatures freezing leads to the cesium chloride structure (CsCl) which undergoes a phase transition to the tetragonal structure at high pressures. The tetragonal solid is the stable solid phase at low temperatures and high densities. In a narrow range of temperatures direct coexistence between the fluid and the tetragonal solid is observed. Three triple points are found for the model considered. The usual vapor–liquid–CsCl solid triple point occurs at T*=0.0225. In addition, a fluid-fcc disordered-tetragonal triple point is located at T*=0.245 and, finally, a fluid-CsCl-tetragonal triple point appears at T*=0.234. The results presented here can be used to test the performance of the different theoretical treatments of freezing available in the literature.
Non-Markovian effects on quantum optimal control of dissipative wave packet dynamics
Authors: Ohtsuki Yukiyoshi
Published: June 2003

Optimal control within the density matrix formalism is applied to the creation of a specified superposition state in condensed phases. The primary system modeled by a displaced harmonic oscillator is surrounded by a boson heat bath, the dynamics of which is described by a non-Markovian master equation. A newly developed monotonically convergent algorithm is used to solve the pulse design equations. The control mechanisms are strongly dependent on the bath correlation time that is characterized by the inverse of an exponential decay constant, γ. If the correlation time is shorter than the temporal width of a typical subpulse involved in an optimal pulse, the solution is reduced to that in the Markovian case. If we assume a longer correlation time, by weighing less physical significance on the penalty due to pulse fluence, an optimal pulse with high intensity is obtained, the temporal width of which approaches ∼1/γ. We also see considerable changes in the shape of the optimal pulse with increasing intensity, suggesting that strong fields open up control mechanisms that are qualitatively different from those in weak fields.
Inhomogeneous model of an Ar–Hg direct current column discharge
Authors: Petrov G. M. , Giuliani J. L.
Published: June 2003

The inhomogeneous electron Boltzmann equation is solved for an Ar–Hg positive column direct current glow discharge with properties similar to the standard fluorescent lamp. The inhomogeneity arises from the ambipolar potential and requires the inclusion of the spatial gradient term in the Boltzmann equation. The electron kinetics is coupled to a collisional–radiative equilibrium model for various states of Ar and Hg subject to a reaction set with electron and heavy particle collisions. The axial electric field and space-charge potential are solved self-consistently. The calculated electron distribution function satisfies neither the local nor nonlocal approaches, but rather is found to be a function of both the electron energy and radial position. The radial dependence produces an energy flow from one part of the discharge to another, which results in nonuniform ultraviolet radiative power. Results are given for global properties of the discharge such as power per unit length and axial electric field, as well as spatially averaged quantities (densities, electron and gas temperatures, and emission powers) as a function of the wall temperature and the current. Extensive comparisons are presented with experimental data and previous homogeneous Boltzmann models of the discharge. The optimum current and fill pressures are determined and the general trends of varying the input parameters are established. There is general agreement between the present model and data, except that the calculated average electron density is larger than the measured values.
One-step processing of spinel ferrites via the high-energy ball milling of binary oxides
Authors: Harris V. G. , Fatemi D. J. , Cross J. O. , Carpenter E. E. , Browning V. M. , Kirkland J. P. , Mohan Amitabh , Long Gary J.
Published: June 2003

MnZn ferrites have been produced via the high-energy ball milling of binary oxide precursors. The milled ferrites have a nonequilibrium cation site distribution, with an unusually high population of Zn cations on the octahedral sites. The particle size distribution drops precipitously with milling time from 60±1 to ∼14±1 nm at 10 h, but increases to 18.5±1 nm after long durations (20–40 h) concurrent with the formation of nearly pure ferrite. A 1 h anneal at 673 K facilitates a redistribution of cations to their near equilibrium sites. This processing approach circumvents the need for deleterious high-temperature heat treatments that often lead to nonstoichiometries in the resulting ferrites.
Optical response functions with semiclassical dynamics
Authors: Noid W. G. , Ezra Gregory S. , Loring Roger F.
Published: June 2003

Observables in nonlinear spectroscopic measurements may be calculated from response functions, which have the form of averages of nested commutators involving the operator governing the radiation–matter interaction. We present a semiclassical formulation of the optical nonlinear response function, employing the Herman–Kluk frozen Gaussian approximation to the quantum propagator in the coherent states representation. This semiclassical approximation permits the response function to be computed from classical trajectories and stability matrices, and provides insight into the relationship between nonlinear response in classical and quantum mechanics. Linear response calculations for an anharmonic oscillator illustrate that the semiclassical approach reproduces the significant differences between quantum and classical results.
Phonon-assisted cooperative energy transfer and frequency upconversion in a Yb3+/Tb3+ codoped fluoroindate glass
Authors: de S. Menezes L. , Maciel G. S. , de Araújo Cid B. , Messaddeq Y.
Published: June 2003

We report large thermal enhancement of the frequency upconversion (UC) process due to cooperative energy transfer (CET) in a Yb3+/Tb3+ codoped fluoroindate glass obtained by heating the sample from 308 to 530 K. To study the influence of multiphonon transitions in the UC process we chose anti-Stokes quasiresonant excitation of Yb3+ ions which were used as sensitizers. UC of radiation at 1064 nm into blue and green light was obtained. Various emission lines of Tb3+ were observed between 400 and 700 nm due to CET from Yb3+ to Tb3+ ions. A rate equation model was used to describe the temperature dependence of the UC emission intensities and the theoretical results are in good agreement with the experimental data.
Defect density and recombination lifetime in microcrystalline silicon absorbers of highly efficient thin-film solar cells determined by numerical device simulations
Authors: Brammer T. , Stiebig H.
Published: June 2003

The absorber layers of microcrystalline silicon thin-film solar cells with p-i-n structure deposited by plasma-enhanced chemical vapor deposition at 200 °C are characterized regarding the defect density and the recombination lifetime. The characterization is based on a comparison of experimentally determined solar cell characteristics with results from numerical device simulations. Evaluation of the dark reverse saturation current indicates a strong dependence of the recombination lifetime τ on the hydrogen dilution during the deposition. Close to the transition region to amorphous growth, where the highest solar cell efficiencies are observed, τ is maximum within the crystalline deposition regime and equals around 80 ns. The aspect of a spatially varying defect density within the absorber layer is also addressed by numerical simulations. The results from the analysis of the dark current are compared with electron spin resonance data determined on single layers, which allows conclusions to be drawn regarding the capture cross section of the dominant recombination site in microcrystalline silicon.
X-ray detection by an on-chip coil integrated superconducting tunnel junction
Authors: Maehata Keisuke , Ariyoshi Tetsuya , Hora Akihito , Mori Naoto , Ishibashi Kenji , Taino Tohru , Sato Hiromi , Nakagawa Hiroshi , Kikuchi Katsuya , Aoyagi Masahiro , Akoh Hiroshi , Matsumoto Yuzuru
Published: June 2003

An on-chip coil integrated superconducting tunnel junction (OC2-STJ) was used for x-ray detection by applying the magnetic field produced by a superconducting microstrip coil integrated into the superconducting tunnel junction chip. The fabricated OC2-STJ chip was mounted in a cooling capsule attached to the mixing chamber of a compact He3–4He dilution refrigerator. The OC2-STJ chip was held at a constant temperature in the capsule against the Joule heat generated in the current feed line of the strip coil during the detection operation. Stable operation of the OC2-STJ was demonstrated without using the usual external electromagnets.