bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of paired histogram, maximum likelihood, class elimination, and neural network approaches for daylight global cloud classification using AVHRR imagery
Authors: Berendes T. A. , Kuo K. S. , Logar A. M. , Corwin E. M. , Welch R. M. , Baum B. A. , Pretre A. , Weger R. C.
Published: September 2002

The accuracy and efficiency of four approaches to identifying clouds and aerosols in remote sensing imagery are compared. These approaches are as follows: a maximum likelihood classifier, a paired histogram technique, a hybrid class elimination approach, and a back‐propagation neural network. Regional comparisons were conducted on advanced very high resolution radiometer (AVHRR) local area coverage (LAC) scenes from the polar regions, desert areas, and regions of biomass‐burning, areas which are known to be particularly difficult. For the polar, desert, and biomass burning regions, the maximum likelihood classifier achieved 94–97% accuracy, the neural network achieved 95–96% accuracy, and the paired histogram approach achieved 93–94% accuracy. The primary advantage to the class elimination scheme lies in its speed; its accuracy of 94–96% is comparable to that of the maximum likelihood classifier. Experiments also clearly demonstrate the effectiveness of decomposing a single global classifier into separate regional classifiers, since the regional classifiers can be more finely tuned to recognize local conditions. In addition, the effectiveness of using composite features is compared to the simpler approach of using the five AVHRR channels and the reflectance of channel 3 treated as a sixth channel as the elements of the feature vector. The results varied, demonstrating that the features cannot be chosen independently of the classifier to be used. It is also shown that superior results can obtained by training the classifiers using subclass information and collapsing the subclasses after classification. Finally, ancillary data were incorporated into the classifiers, consisting of a land/water mask, a terrain map, and a computed sunglint probability. While the neural network did not benefit from this information, the accuracy of the maximum likelihood classifier improved by 1%, and the accuracy of the paired histogram method increased by up to 4%.
Multiannual simulations with a three‐dimensional chemical transport model
Authors: Chipperfield M. P.
Published: September 2002

An off‐line three‐dimensional stratospheric chemical transport model (CTM) has been developed and integrated in a series of 6‐year experiments covering 1991 to 1997. The model has a detailed chemistry scheme and is forced by the meteorological analyses for the temperatures and horizontal winds, while the vertical motion is diagnosed using a radiation scheme. By using the meteorological analyses, the model captures the interannual variability in chlorine activation in the Arctic winter lower stratosphere, as well as the much more regular, strong activation in the Antarctic. The model fields show generally good agreement with long time series of ground‐based observations. In particular, the model simulations of column O3 are excellent in terms of capturing the magnitude and day‐to‐day, seasonal, and interannual variations at all latitudes. However, a large model/observation discrepancy for O3 occurs at high latitudes during the summer, when the model overestimates the O3 profile throughout the lower and mid‐stratosphere. The model also reproduces many features in ground‐based observations of HCl, ClONO2, HNO3, and NO2, such as short‐term variability, the seasonal cycles, and winter/spring enhancements of ClONO2 at northern midlatitudes. By running the model without cold, chlorine activating heterogeneous reactions the effect of polar (and subpolar) processing on midlatitudes has been estimated. Polar processing results in 2–3% less O3 at 50°N throughout the year, and around 5% less O3 at 50°S. Direct chlorine activation on enhanced midlatitude aerosol contributes 1% to column ozone depletion at mid and low latitudes in early 1992. The enhanced aerosol also caused column ozone reductions of around 3% at 45°N throughout 1992 and 1993. However, the CTM runs confirm the suggestion interannual dynamical variability (which may be partly driven by the radiative effects of the aerosols) contributed to the large negative ozone anomaly in northern midlatitudes in 1992/1993.
Detection of Kelvin‐Helmholtz instability with the Indian mesosphere‐stratosphere‐troposphere radar: A case study
Authors: Singh Sachchidanand , Mahajan K. K. , Choudhary R. K. , Nagpal O. P.
Published: September 2002

Measurements with the Indian mesosphere‐stratosphere‐troposphere (MST) radar at Gadanki (13.5°N, 79.2°E) on May 26, 1994, revealed the presence of a Kelvin‐Helmholtz instability (KHI) in between two stratified shear layers. The KHI occurred at the shear maximum, at 17.7 km, just above the meteorological tropopause. The characteristic period for the KH wave was found to be 12 min with a billow wavelength of 7.2 km. At the critical level, 17.7 km, the wave showed a sudden change of phase of the order of 160°. In addition to the characteristic high‐signal power bursts, it also exhibited enhanced Doppler width during the occurrence of KHI. This indicates the generation of 3 m scale turbulence in the region where KHI is observed. A detailed investigation of the Doppler width structure reveals that the KH billows undergo breakdown in between the shear layers, causing peaked structure in the Doppler width profile.
Galileo observes electromagnetically coupled dust in the Jovian magnetosphere
Authors: Grün E. , Krüger H. , Graps A. L. , Hamilton D. P. , Heck A. , Linkert G. , Zook H. A. , Dermott S. , Fechtig H. , Gustafson B. A. , Hanner M. S. , Horányi M. , Kissel J. , Lindblad B. A. , Linkert D. , Mann I. , McDonnell J. A. M. , Morfill G. E. , Polanskey C. , Schwehm G. , Srama R.
Published: September 2002

Measurements of dust coupled to the Jovian magnetosphere have been obtained with the dust detector on board the Galileo spacecraft. We report on data obtained during the first four orbits about Jupiter that had flybys of the Galilean satellites: Ganymede (orbits 1 and 2), Callisto (orbit 3), and Europa (orbit 4). The most prominent features observed are highly time variable dust streams recorded throughout the Jovian system. The impact rate varied by up to 2 orders of magnitude with a 5 and 10 hour periodicity, which shows a correlation with Galileo's position relative to the Jovian magnetic field. Around 20 RJ (Jupiter radius, RJ = 71,492 km) in bound a dip in the impact rate has been found consistently. At the same times, reversals by 180° in impact direction occurred. This behavior can be qualitatively explained by strong coupling of nanometer‐sized dust to the Jovian magnetic field. At times of satellite flybys, enhanced rates of dust impacts have been observed, which suggests that all Galilean satellites are sources of ejecta particles. Inside about 20 RJ impacts of micrometer‐sized particles have been recorded that could be particles on bound orbits about Jupiter.
A two‐dimensional model of plasma transport and chemistry in the Jovian magnetosphere
Authors: Schreier Ron , Eviatar Aharon , Vasyliūnas Vytenis M.
Published: September 2002

A two‐dimensional model of plasma transport and chemistry in the Jovian inner magnetosphere that enables us to calculate ion and electron densities and temperatures as well as their radiative emission properties is presented. As input data, the model uses (assumed) neutral densities, arbitrary initial ion densities, and ion and electron (both thermal and hot) temperatures given by the published empirical model derived from Voyager data. Six thermal ion species, three hot ion species, and both thermal and hot electrons are included. The calculated ion partitioning is similar to the results of previous numerical models (rather than the empirical model). The observed general increase in temperature of both the ions and electrons versus distance can be accounted for by a distributed neutral source. Model electron temperature (and thus torus emission) was found to be less than expected. Of three proposed mechanisms that might account for the observed electron heating, namely, (1) an increase in the temperature of the thermal ions, resulting in electron heating via Coulomb collisions, (2) hot ions, presumably of ring current origin, diffusing inward and heating the thermal electrons, and (3) a flux of suprathermal electrons, alternative (2) is most strongly supported by our model.
Recent results from EUVE observations of the Io plasma torus and Jupiter
Authors: Gladstone G. Randall , Hall Doyle T.
Published: September 2002

Between 1993 and 1996 the Extreme Ultraviolet Explorer (EUVE) satellite has observed Jupiter and the Io plasma torus (IPT) for a total of over 380 hours. The data consist of time‐tagged photons at wavelengths in the 7–76 nm range. By using appropriate ephemerides for Jupiter and EUVE, these data can be made into spectral images, or “overlappograms,” of the IPT. Most of the emissions from the IPT appear in the bandpass of the long‐wavelength (LW) spectrograph (28–76 nm), which has 0.2 nm spectral resolution and spatial resolutions of 60 arc sec full width at half maximum (FWHM) in the dispersion direction and 24 arc sec FWHM in the direction perpendicular to dispersion. Presented here is a subset of the EUVE data, comprising 83 consecutive orbits during June 19–24, 1996. The dusk (west on the sky) half of the IPT is, on average, ∼25–30% brighter than the dawn half of the IPT, in the most prominent EUV emission features. In addition, there is no noticeable correlation of total IPT brightness with Io orbital phase during this time period. On Jupiter, the brightness of the reflected He I 58.4 nm emission was measured in June 1996 to be 1.3±0.5 R. This level is substantially less than the 4–5 R measured during the Voyager flybys and is attributed to solar cycle variability of the Sun's He I 58.4 nm emission.
Uranus' magnetic field and particle drifts in its inner magnetosphere
Authors: Gao Shan , Ho C. Wing , Huang Tian‐Sen , Alexander Claudia J.
Published: September 2002

Both the Q3 model (dipole and quadrupole) and OCT model (Q3 plus octupole) of Uranus' magnetic field within 5 RU are expressed in α and β (Euler potentials) coordinate systems. By using the α and β coordinates of magnetic fields, we calculate the drift paths and velocities for the zero second invariant (J = 0) charged particles with different total energies. Many aspects of Uranus' magnetic field are similar to those of Neptune [Ho et al., 1997], such as a warped zero magnetic scalar potential surface and a region of local distorted magnetic field lines that gives rise to a large “open” area on the planetary surface when the field lines are mapped from this region. It is found that the OCT model gives a map of magnetic field coordinates on the planetary surface that better explains the Voyager 2 ultraviolet spectrometer (UVS) data of Herbert and Sandel [1994] than the Q3 model. The grossly distorted α and β contours on the planetary surface may explain the incomplete aurora circles around both magnetic poles, and weak UV emissions are found lying along a belt that coincides remarkably well with the OCT magnetic equator. In addition, tracing of drift paths of J = 0 charged particles shows that the weak emission along the magnetic equator is due to the precipitation of J = 0 particles, or particles with a large equatorial pitch angle. In particular, the low‐energy J = 0 particles tend to drift toward a planet in three concentrated regions where UV emissions are observed.
Observations at the Mars Pathfinder site: Do they provide “unequivocal” evidence of catastrophic flooding?
Authors: Chapman Mary G. , Kargel Jeffrey S.
Published: September 2002

After Mars Pathfinder landed at the mouth of Ares Valus, a large channel that drains into the Chryse Planitia basin, the mission reports unanimously supported the interpretation that the lander site is the locus of catastrophic flooding by noting that all aspects of the scene are consistent with this interpretation. However, alternatives cannot be ruled out by any site observations, as all aspects of the scene are equally consistent with other interpretations of origin, namely, ice and mass‐flow processes subsequently modified by wind erosion. The authors discuss alternative explanations for the geologic history of the channel based on a regional view of the circum‐Chryse channels from Viking images (our best broad‐scale information to date) and the local view from the recent Pathfinder landing site. Mega‐indicators of channel origin, the regional geomorphology, geology, and planetary climatic conditions, taken together suggest some combination of flood, mass flow, glacial, and eolian processes. The macro‐indicators of channel origin (sedimentologic) are also not indicative of one process of emplacement, either as single criteria or taken cumulatively. Finally, the micro‐indicators of channel origin (geochemical and mineralogic composition) do not provide very tight constraints on the deposits' possible origins other than that water was in some way involved.
Open‐ocean convection: Observations, theory, and models
Authors: Marshall John , Schott Friedrich
Published: September 2002

We review what is known about the convective process in the open ocean, in which the properties of large volumes of water are changed by intermittent, deep‐reaching convection, triggered by winter storms. Observational, laboratory, and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales, the large‐scale circulation of the ocean, and the prevailing meteorology. Two aspects make ocean convection interesting from a theoretical point of view. First, the timescales of the convective process in the ocean are sufficiently long that it may be modified by the Earth's rotation; second, the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability. Moreover, the convective and geostrophic scales are not very disparate from one another. Detailed observations of the process in the Labrador, Greenland, and Mediterranean Seas are described, which were made possible by new observing technology. When interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection, great progress in our description and understanding of the processes at work is being made.
Neural networks for the retrieval of water vapor and liquid water from radiometric data
Authors: Frate Fabio Del , Schiavon Giovanni
Published: September 2002

This paper investigates the potentiality of neural networks for the retrieval of integrated water vapor and integrated liquid water from data simulating the measurements of different groundbased microwave radiometers, with the optional addition of a laser ceilometer. The reliability of the neural network algorithms was evaluated comparing their performance with that achievable by linear regression techniques with the same data sets. The obtained results showed that the neural inversion provides a more accurate estimation of the parameters to be retrieved, especially in the case of strong nonlinearities. In addition, neural networks succeed in exploiting the information given by the ceilometer significantly better than linear regression. The advantages shown by the neural inversion led the investigation further, aiming at the optimization of the architecture of the net and focusing on the number of processing units and connections. An optimum range for the choice of the number of neurons to be inserted in the net has been determined, and ineffective connections have been removed via pruning algorithms. A fault tolerance analysis was also performed, which pointed out other interesting properties of the neural retrieval procedure. In conclusion, the results of this simulation indicate that neural networks, if compared with linear regressions, are more suitable for cases with stronger nonlinearities and are more flexible and robust algorithms. Moreover, their performance can improve when the number of units and connections is optimized.
Corrections functions for digital correlators with two and four quantization levels
Authors: Kogan Leonid
Published: September 2002

The function that relates the true correlation of analog signals to the measured correlation of digitized signals has been analyzed for two and four quantization levels. The analysis has been carried out for both XF and FX correlators, including a mixed two‐four case when a two‐level digitizer is used for one input signal and a four‐level digitizer is used for the other input signal. It is shown that the same parameters of a four‐level digitizer optimize both the two‐four case and the four‐four case. The signal‐to‐noise ratio of the two‐four case is ∼17% worse than that of the four‐four. The fringe stopping procedure, which is typical for the interferometry application of a correlator, linearizes the correction function. So different correction functions should be used for autocorrelation and cross correlation.
Prediction of fingering in porous media
Authors: Wang Zhi , Feyen Jan , Elrick David E.
Published: September 2002

Immiscible displacement, involving two fluids in a porous medium, can be unstable and fingered under certain conditions. In this paper, the original linear instability criterion of Chuoke et al. [1959] is generalized, considering wettability of two immiscible fluids to the porous medium. This is then used to predict 24 specific flow and porous medium conditions for the onset of wetting front instability in the subsurface. Wetting front instability is shown to be a function of the driving fluid wettability to the medium, differences in density and viscosity of the fluids, the magnitude of the interfacial tension, and the direction of flow with respect to gravity. Scenarios of water and nonaqueous‐phase liquid infiltration into the vadose zone are examined to predict preferential flow and contamination of groundwater. The mechanisms of finger formation, propagation, and persistence in the vadose zone are reviewed, and the existing equations for calculating the size, the number and velocity of fingers are simplified for field applications. The analyses indicate that fingers initiate and propagate according to spatial and temporal distribution of the dynamic breakthrough (water‐ or air‐entry) pressures in the porous medium. The predicted finger size and velocity are in close agreement with the experimental results.
Bowen Ratio estimates of evapotranspiration for Tamarix ramosissima stands on the Virgin River in southern Nevada
Authors: Devitt D. A. , Sala A. , Smith S. D. , Cleverly J. , Shaulis L. K. , Hammett R.
Published: September 2002

A Bowen ratio energy balance was conducted over a Tamarix ramosissima (saltcedar) stand growing in a riparian corridor along the Virgin River in southern Nevada. Measurements in two separate years were compared and contrasted on the basis of changes in growing conditions. In 1994, a drought year, record high temperatures, dry winds, and a falling water table caused partial wilt of outer smaller twigs in the canopy of many trees in the stand around the Bowen tower. Subsequently, evapotranspiration (ET) estimates declined dramatically over a 60‐day period (11 mm d−1 to <1 mm d−1). In 1995, the Virgin River at the Bowen tower area changed its course, hydrologically isolating the Tamarix stand in the vicinity of the tower. In 1996, a 25% canopy loss was visually estimated for the Tamarix growing in the area of the tower. Higher soil temperatures relative to air temperatures were recorded in 1996 in response to this loss in canopy. With a more open canopy, thermally induced turbulence was observed in 1996. On day 160 of 1996, a 28°C rise over a 9‐hour period was correlated with increased wind speeds of greater than 4 m s−1. Subsequently, higher ET estimates were made in 1996 compared to 1994 (145 cm versus 75 cm). However, the energy balance was dominated by advection in 1996, with latent energy flux exceeding net radiation 65% of the measurement days compared to only 11% in 1994. We believe this advection was on a scale of the floodplain (hundreds of meters) as opposed to regional advection, since the majority of wind (90%) was in a N–S direction along the course of the river, and that a more open canopy allowed the horizontal transfer of energy into the Tamarix stand at the Bowen tower. Our results suggest that Tamarix has the potential to be both a low water user and a high water user, depending on moisture availability, canopy development, and atmospheric demand, and that advection can dominate energy balances and ET in aridland riparian zones such as the Virgin River.
Structure, flow, and generalized conductivity scaling in fracture networks
Authors: Margolin Gennady , Berkowitz Brian , Scher Harvey
Published: September 2002

We present a three‐dimensional (3‐D) model of fractures that within the same framework, allows a systematic study of the interplay and relative importance of the two key factors determining the character of flow in the system. The two factors of complexity are () the geometry of fracture plane structure and interconnections and (2) the aperture variability within these planes. Previous models have concentrated on each separately. We introduce anisotropic percolation to model a wide range of fracture structures and networks. The conclusion is that either of these elements, fracture geometry and aperture variability, can give rise to channeled flow and that the interplay between them is especially important for this type of flow. Significant outcomes of our study are (1) a functional relationship that quantifies the dependence of the effective hydraulic conductivity on aperture variability and on the network structure and fracture element density, (2) a relation between aperture variability and the Peclet number, and (3) a basis for a new explanation for the field‐length dependence of permeability observed in fractured and heterogeneous porous formations.
Annual hysteresis in bed load rating curves
Authors: Moog Douglas B. , Whiting Peter J.
Published: September 2002

The relationship between flow and bed load transport measured for 10 years in six gravel‐bed streams in Idaho exhibits annual hysteresis. At a given flow rate, more bed load is carried by discharges preceding the first annual occurrence of a “threshold” rate, which is characteristic of each stream. Incorporating the effect of hysteresis leads to a small improvement in the fit of the bed load–flow regression. As the turning point for hysteresis, a constant threshold discharge is found to work better than the annual peak discharge. This bimodal hysteresis model is also found to out perform one with a more gradual transition, based on cumulative discharge. These results are interpreted to reflect a buildup of readily moved sediment supplies during the low‐flow periods from late summer to early spring, supplies which are then exhausted by rising springtime discharges up to the threshold. The threshold is greater than mean annual discharge and about one‐half bank‐full discharge.
Susceptibility and predictability of conditions for preferential flow
Authors: Wang Zhi , Feyen Jan , Ritsema Coen J.
Published: September 2002

Preferential flow in the field might be caused by various factors and is difficult to observe in situ. This experimental study was designed to identify the combined effects of air entrapment, surface desaturation (suction head), soil layering, and water repellency (hydrophobicity) of the porous media on unstable preferential flow (or fingering) in the vadose zone. The predictability of unstable flow was studied on the basis of two existing criteria for gravity fingering: (1) a velocity criterion proposed by Hill and Parlange [1972] and (2) a pressure head criterion by Raats [1973] and Philip [1975]. Two‐dimensional transparent chambers (60 cm high, 41.5 cm wide, and 2.8 cm thick and 90 cm deep, 74.5 cm wide, and 1.8 cm thick) were used to visualize water infiltration into a water‐wettable sand, a water‐wettable loam, differently layered sand and loam, and a water‐repellent sand. The results suggested that infiltration into the homogeneous sand and a sand‐over‐loam system, without the effects of air entrapment and surface desaturation, was unconditionally stable. Infiltration into the loam was also stable as observed in the limited chambers. The flow was unconditionally unstable in a fine‐over‐coarse stratified sublayer and conditionally unstable in the homogeneous sand under the effects of air entrapment and surface desaturation. In multiple‐layered systems, infiltration flow was semiunstable; fingers developed in the sand layer and were stabilized in the loam. In the repellent sand the wetting front was unstable under low ponding conditions; however, it was stabilized when the ponding depth exceeded the water‐bubbling (entry) value of the hydrophobic medium. Both the velocity and pressure head criteria predicted fingering in the sand (layers) with the effects of gravity. However, the criteria failed to predict stable flow in the loam, indicating that the capillary (stabilizing) effects on the flow need to be included in theoretical developments. Finally, the observed width and speed of the fingers and the system flux were found to be always higher under air‐draining fingering conditions than with fingering under air‐confined conditions.
Controls of sediment transport capacity in laminar interrill flow on stone‐covered surfaces
Authors: Li Gary , Abrahams Athol D.
Published: September 2002

Sediment transport capacity is an important control on soil erosion and deposition by overland flow. To investigate the controls of transport capacity in laminar interrill overland flow on stone‐covered surfaces, 357 flume experiments were performed using a single sediment size. Multiple regression analyses reveal that transport capacity is positively related to excess flow power ω − ωc, but the slope of the relation is steeper where ω < 0.3 W m−2 than where ω ≥ 0.3 W m−2. Transport capacity is positively related to rainfall intensity where ω < 0.3 W m−2 and negatively related to rainfall intensity where ω ≥ 0.3 W m−2. Transport capacity is negatively related to stone concentration and positively related to stone size irrespective of the value of ω. Finally, transport capacity is negatively related to fluid viscosity where ω < 0.3 W m−2 and unrelated to viscosity where ω ≥ 0.3 W m−2.
Markov switching time series models with application to a daily runoff series
Authors: Lu Zhan‐Qian , Berliner L. Mark
Published: September 2002

We consider a class of Bayesian dynamic models that involve switching among various regimes. As an example we produce a model for a runoff time series exhibiting pulsatile behavior. This model is a mixture of three autoregressive models which accommodate “rising,” “falling,” and “normal” states in the runoff process. The mechanism for switching among regimes is given by a three‐state Markov chain whose transition probabilities are modeled on the basis both of past runoff values and of a time series of rainfall data. We adopt the Bayesian approach and use the Gibbs sampler in the numerical analyses. A study of a daily runoff series from Lake Taupo, New Zealand, is given.
Permeability of shaly sands
Authors: Revil A. , Cathles L. M.
Published: September 2002

The permeability of a sand shale mixture is analyzed as a function of shale fraction and the permeability of the two end‐members, i.e., the permeability of a clay‐free sand and the permeability of a pure shale. First, we develop a model for the permeability of a clay‐free sand as a function of the grain diameter, the porosity, and the electrical cementation exponent. We show that the Kozeny‐Carman‐type relation can be improved by using electrical parameters which separate pore throat from total porosity and effective from total hydraulic radius. The permeability of a pure shale is derived in a similar way but is strongly dependent on clay mineralogy. For the same porosity, there are 5 orders of magnitude of difference between the permeability of pure kaolinite and the permeability of pure smectite. The separate end‐members' permeability models are combined by filling the sand pores progressively with shale and then dispersing the sand grains in shale. The permeability of sand shale mixtures is shown to have a minimum at the critical shale content at which shale just fills the sand pores. Pure shale has a slightly higher permeability. Permeability decreases sharply with shale content as the pores of a sand are filled. The permeability of sand shale mixtures thus has a very strong dependence on shale fraction, and available data confirm this distinctive shale‐fraction dependence. In addition, there is agreement (within 1 order of magnitude) between the permeabilities predicted from our model and those measured over 11 orders of magnitude from literature sources. Finally, we apply our model to predict the permeabilities of shaly sand formations in the Gulf Coast. The predictions are compared to a data set of permeability determination made on side‐wall cores. The agreement between the theoretical predictions and the experimental data is very good.
Images may show start of European‐African plate collision
Authors: Mascle J. , Huguen C. , Benkhelil J. , Chamot‐Rooke N. , Chaumillon E. , Foucher J. P. , Griboulard R. , Kopf A. , Lamarche G. , Volkonskaia A. , Woodside J. , Zitter T.
Published: September 2002

Aspects of the initial stages of a collision between European and African plates may have been documented in a geophysical survey of the central Mediterranean Ridge (MR) conducted last year. The idea of an incipient collision was first suggested by Finetti [1976],and details of the seafloor and tectonic deformation along the MR, revealed for the first time in the survey, seem to point in that direction.

A unique opportunity may therefore exist for studying the beginnings of such a collision—between the passive margin of a major plate (Africa) acting as a continental indenter against the active margin of another plate (Europe). More wide angle data, deep penetrating multichannel seismic data, and drilling data are crucial to better assess the nature and the architecture of the underlying lithosphere, the styles of sedimentary deformation, and the consequences on fluid releases. Such data will make it possible to establish, or reject, a geodynamic collision model.
Risk factors for the development of invasive fungal infections in allogeneic blood and marrow transplant recipients
Authors: De La Rosa G.R. , Champlin R.E. , Kontoyiannis D.P.
Published: September 2002

Abstract: Blood and marrow transplantation (BMT) is increasingly used to treat malignant and nonmalignant diseases. Despite significant advances in the management of transplant recipients, however, fungal infections remain important life‐threatening complications of BMT. Over the past two decades, the incidence of fungal infections in this population has continued to rise. Several factors predispose BMT recipients to invasive fungal infections. These include but are not limited to use of intensive myeloablative chemotherapy and radiation therapy combined with prolonged granulocytopenia; development of acute and chronic graft‐versus‐host disease; administration of immunosuppressive therapy, particularly using corticosteroids; use of central venous catheters; and prolonged impairment of cell‐mediated immunity secondary to the underlying disease and post‐transplant immunodeficiency. Environmental factors also play a key part in the pathogenesis of fungal infections. Therefore, infection‐control measures are critical to the prevention of such infections. In addition, although Candida and Aspergillus species are still the major culprits, other opportunistic fungi have emerged in recent years.
Pharmacology and potential therapeutic applications of nitric oxide‐releasing non‐steroidal anti‐inflammatory and related nitric oxide‐donating drugs
Authors: Keeble J E , Moore P K
Published: September 2002

This review examines the biological significance, therapeutic potential and mechanism(s) of action of a range of nitric oxide‐releasing non‐steroidal anti‐inflammatory drugs (NO‐NSAID) and related nitric oxide‐releasing donating drugs (NODD). The slow release of nitric oxide (NO) from these compounds leads to subtle changes in the profile of pharmacological activity of the parent, non‐steroidal anti‐inflammatory drugs (NSAID). For example, compared with NSAID, NO‐NSAID cause markedly diminished gastrointestinal toxicity and improved anti‐inflammatory and anti‐nociceptive efficacy. In addition, nitroparacetamol exhibits hepatoprotection as opposed to the hepatotoxic activity of paracetamol. The possibility that NO‐NSAID or NODD may be of therapeutic benefit in a wide variety of disease states including pain and inflammation, thrombosis and restenosis, neurodegenerative diseases of the central nervous system, colitis, cancer, urinary incontinence, liver disease, impotence, bronchial asthma and osteoporosis is discussed.

British Journal of Pharmacology (2002) 137, 295–310. doi:10.1038/sj.bjp.0704876
Eye problems and visual display terminals—the facts and the fallacies
Authors: Thomson W. David
Published: September 2002

Estimates of the prevalence of eye problems associated with using visual display terminals (VDTs) vary enormously depending on the sample tested and the research methods employed. However, most authors agree that eye problems are common among VDT users. In this paper, the relative contributions of the nature of VDT displays, workstation design, work‐practices and optometric factors are discussed, drawing from the substantial body of literature which now exists on this subject.
Early ocular and non‐ocular indications of diabetes mellitus
Authors: North Rachel V.
Published: September 2002

This article aims to review the early indications of diabetes, both ocular and non‐ocular. Epidemiological data is showing an increase in both non‐insulin dependent and insulin dependent diabetes mellitus. It is therefore important that diabetes mellitus is detected early so that regular screening and good metabolic control can be encouraged. Strict glycaemic control is important in order to delay the onset or slow the progression of diabetic complications.
The aging eye and vision appliances
Authors: Rumney Nicholas J.
Published: September 2002

This paper describes some of the potential impact the aging population may have on routine optometric practice from the perspective of the aging normal patient as opposed to the low vision patient. The significance of social aspects, criteria for change and the importance of effective communication are emphasised. The implications of the major aging diseases (stroke, Parkinson's disease and Alzheimer's disease) on the optometric examination is included.
Current trends in modern orthokeratology
Authors: Dave Trusit , Ruston David
Published: September 2002

The present article describes the basic concepts and principles of modern orthokeratology. Early investigators postulated a variety of theories. However, controlled clinical studies have shown these methods to be both unpredictable and also modest in their ability to correct myopia. These traditional techniques involved fitting lenses according to a `rule‐of‐thumb' and clinicians had no means of accurately evaluating corneal topography. More recently, with the significant advances in corneal topography systems and the application of reverse geometry lenses (lenses where the secondary curve steepens) certain investigators have concluded that the technique can rapidly reduce greater levels of myopia with greater predictability. The procedure involves a more scientific sagitta based fitting philosophy and predictability is defined according to corneal asphericity.
Accommodation to perceived depth in stereotests
Authors: Koh L‐H. , Charman W. N.
Published: September 2002

The question of whether the eye may accommodate to the stimulus provided by apparent depth in stereograms is considered theoretically in relation to the magnitudes of the disparities and viewing distances found in typical clinical stereotests. It is concluded that, for the relevant range of disparities (≤2000 arc sec), any shift in accommodation is likely to be small (≤0.15 D). An experimental study with two different clinical stereotests (Lang, TNO) confirms this prediction.
Repeatability and comparability of automated keratometry: the Nikon NRK‐8000, the Nidek KM‐800 and the Bausch and Lomb keratometer
Authors: Elliott Michelle , Simpson Trefford , Richter Doris , Fonn Desmond
Published: September 2002

This study assessed the repeatability of the Nikon NRK‐8000, the Nidek KM‐800 and the Bausch and Lomb keratometer. In addition, the comparability of the Nikon NRK‐8000 and the Nidek KM‐800 are evaluated relative to the Bausch and Lomb keratometer. Measurements were taken with all three techniques on two separate occasions with a test–retest separation of at least 24 hr. The right eyes of 30 normal subjects were used. Repeatability and comparability statistics and plots were generated using matrix representations of dioptric power. The Nidek KM‐800 coefficient of repeatability values were found to be 0.345, 0.187, and 0.321 in the vertical, torsional, and horizontal meridians while the Nikon NRK‐8000 values were 0.346, 0.232, and 0.276 respectively.
Variability in glaucomatous visual fields: implications for shared care schemes
Authors: Henson David B. , Spry Paul G. , Spencer Ian C. , Sparrow John M.
Published: September 2002

The purpose of this study was to establish the extent of variability in the visual fields of patients with glaucoma using a suprathreshold perimetric test strategy. The visual fields of 104 patients (126 eyes) were measured twice, on separate days, with a Henson CFA3000 central visual field analyser. All eyes had a diagnosis of glaucoma and had a minimum of three stimuli missed at 12 dB above their threshold estimate derived at the beginning of the first suprathreshold examination. The perimeter tested 132 locations within the central 25 degrees with a multiple stimulus suprathreshold strategy. Data were analysed on the basis of the difference in the number of recorded missed stimuli between the two visits. Large amounts of variability were found in the visual field results. Variability was largest when all levels of defect were included (>=5 dB) and was found to be independent of the overall extent of loss. Results from the superior hemifield were found to be more variable than those from the inferior hemifield. The results highlight the problem of differentiating real change in visual field status from the enhanced variability seen in patients with glaucomatous visual field loss. The results from this study can be used to establish return‐referral criteria for shared care schemes. The advantages of duplicate measures of the visual field are highlighted.
The effect of different forms of monocular occlusion on measures of central visual function
Authors: Wildsoet Christine , Wood Joanne , Maag Helene , Sabdia Safira
Published: September 2002

The purpose of this study was to determine whether clinically used measures of central visual function were influenced by the method of monocular occlusion used. Twenty young visually normal subjects were tested both monocularly and binocularly using an Australian Vision Chart No. 5 (which includes high and low contrast letters) and the Pelli–Robson letter chart. During monocular assessments, the non‐tested eye was occluded with either a translucent (frosted) diffuser, a +1.50 D (fogging) lens, or a white opaque occluder. A significant difference in monocular sensitivity between the three occluder types was found for Pelli–Robson contrast sensitivity, and the high and low contrast letter acuities, with poorest performance being recorded with the opaque occluder in all cases. The same trend was evident in the derived binocular summation ratios which were found to vary with the type of occluder used before the non‐tested eye, as well as with the visual function measured. The data imply that binocular interactions occur during ‘monocular’ testing of central visual function and that these interactions vary with the method of occlusion used. The clinical ramifications of these results are discussed.
Transverse chromatic aberration and colour‐defined motion
Authors: Faubert Jocelyn , Bilodeau Lynda , Simonet Pierre
Published: September 2002

A number of recent studies have explored the role of the chromatic system in motion processes using the isoluminance paradigm. A major concern when using such methodological procedures is potential artefacts produced by chromatic aberrations. In the present study we address the problem of optically induced luminance artefacts produced by transverse chromatic aberrations (TCA), which may contaminate the results obtained in chromatic motion‐nulling experiments. Results show that different TCA levels artificially increase chromatic motion sensitivity values to varying degrees above 0.5 cpd for red/green gratings. The data also suggest the notion that naturally occurring TCA can decrease motion‐nulling thresholds for chromatic gratings at high spatial frequencies. Furthermore, our data show that the motion‐nulling paradigm for chromatic gratings may in fact be an efficient functional method for assessing the amount of TCA produced by optical factors.
Iris color and age‐related changes in lens optical density⋆
Authors: Hammond Billy R. , Nanez Jose E. , Fair Christine , Snodderly D. Max
Published: September 2002

Purpose: Epidemiologic evidence indicates that dark iris color increases risk of age‐related cataract. No information is currently available, however, on the effects of iris color on the lens prior to cataract development. In this study, we relate iris color to lens optical density (OD) in individuals without frank cataract.

Methods: 90 subjects with blue or green irises (light color) were compared with 87 subjects having hazel, brown, or black irises (dark color). Lens OD was measured psychophysically by comparing scotopic thresholds obtained at 410 (measuring) and 550 nm (reference). Stimuli were presented in Maxwellian view.

Results: The groups with light and with dark iris color did not differ significantly in smoking habits, dietary patterns, or age. Despite other similarities between the groups, lens OD was significantly(p<0.024) higher in the group with dark irises. The higher OD of the dark iris group was due to differences in the older subjects (>45 years,p<0.005), rather than the younger subjects (20–45 years) who showed no differences in lens OD.

Conclusion: Our data indicate that iris pigmentation may be directly related to age‐associated increases in lens OD.
Mechanism by which 2,2,2-trifluoroethanol/water mixtures stabilize secondary-structure formation in peptides: A molecular dynamics study
Authors: Roccatano Danilo , Colombo Giorgio , Fioroni Marco , Mark Alan E.
Published: September 2002

Molecular dynamics simulation techniques have been used to investigate the effect of 2,2,2-trifluoroethanol (TFE) as a cosolvent on the stability of three different secondary structure-forming peptides: the α-helix from Melittin, the three-stranded β-sheet peptide Betanova, and the β-hairpin 41–56 from the B1 domain of protein G. The peptides were studied in pure water and 30% (vol/vol) TFE/water mixtures at 300 K. The simulations suggest that the stabilizing effect of TFE is induced by the preferential aggregation of TFE molecules around the peptides. This coating displaces water, thereby removing alternative hydrogen-bonding partners and providing a low dielectric environment that favors the formation of intrapeptide hydrogen bonds. Because TFE interacts only weakly with nonpolar residues, hydrophobic interactions within the peptides are not disrupted. As a consequence, TFE promotes stability rather than inducing denaturation.
Trojan particles: Large porous carriers of nanoparticles for drug delivery
Authors: Tsapis N. , Bennett D. , Jackson B. , Weitz D. A. , Edwards D. A.
Published: September 2002

We have combined the drug release and delivery potential of nanoparticle (NP) systems with the ease of flow, processing, and aerosolization potential of large porous particle (LPP) systems by spray drying solutions of polymeric and nonpolymeric NPs into extremely thin-walled macroscale structures. These hybrid LPPs exhibit much better flow and aerosolization properties than the NPs; yet, unlike the LPPs, which dissolve in physiological conditions to produce molecular constituents, the hybrid LPPs dissolve to produce NPs, with the drug release and delivery advantages associated with NP delivery systems. Formation of the large porous NP (LPNP) aggregates occurs via a spray-drying process that ensures the drying time of the sprayed droplet is sufficiently shorter than the characteristic time for redistribution of NPs by diffusion within the drying droplet, implying a local Peclet number much greater than unity. Additional control over LPNPs physical characteristics is achieved by adding other components to the spray-dried solutions, including sugars, lipids, polymers, and proteins. The ability to produce LPNPs appears to be largely independent of molecular component type as well as the size or chemical nature of the NPs.
Complete genome sequence and comparative genomic analysis of an emerging human pathogen, serotype VStreptococcus agalactiae
Authors: Tettelin Hervé , Masignani Vega , Cieslewicz Michael J. , Eisen Jonathan A. , Peterson Scott , Wessels Michael R. , Paulsen Ian T. , Nelson Karen E. , Margarit Immaculada , Read Timothy D. , Madoff Lawrence C. , Wolf Alex M. , Beanan Maureen J. , Brinkac Lauren M. , Daugherty Sean C. , DeBoy Robert T. , Durkin A. Scott , Kolonay James F. , Madupu Ramana , Lewis Matthew R. , Radune Diana , Fedorova Nadezhda B. , Scanlan David , Khouri Hoda , Mulligan Stephanie , Carty Heather A. , Cline Robin T. , Van Aken Susan E. , Gill John , Scarselli Maria , Mora Marirosa , Iacobini Emilia T. , Brettoni Cecilia , Galli Giuliano , Mariani Massimo , Vegni Filippo , Maione Domenico , Rinaudo Daniela , Rappuoli Rino , Telford John L. , Kasper Dennis L. , Grandi Guido , Fraser Claire M.
Published: September 2002

The 2,160,267 bp genome sequence ofStreptococcusagalactiae, the leading cause of bacterial sepsis, pneumonia, and meningitis in neonates in the U.S. and Europe, is predicted to encode 2,175 genes. Genome comparisons amongS. agalactiae,Streptococcus pneumoniae,Streptococcus pyogenes, and the other completely sequenced genomes identified genes specific to the streptococci and toS. agalactiae. Thesein silicoanalyses, combined with comparative genome hybridization experiments between the sequenced serotype V strain 2603 V/R and 19S. agalactiaestrains from several serotypes using whole-genome microarrays, revealed the genetic heterogeneity amongS. agalactiaestrains, even of the same serotype, and provided insights into the evolution of virulence mechanisms.