bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of aerosols on the wavelength dependence of atmospheric transmission in the ultraviolet and visible: 2. Continental and urban aerosols in clear skies
Authors: Erlick Carynelisa , Frederick John E.
Published: September 2002

In this study we model the effects of continental and urban aerosols and their variation with humidity on the transmission of ultraviolet and visible radiation to the Earth's surface. Normalizing the transmission to that of an aerosol‐free atmosphere, we examine the mechanisms behind two wavelength‐dependent aerosol effects. The first is a dip in the normalized transmission at wavelengths below around 320 nm, which is caused by a coupling between multiple scattering by the aerosol particles and absorption by ozone and by the rapidly increasing absorption coefficient of tropospheric water‐soluble aerosols below 340 nm, based on limited available refractive index data in the UV. The second effect is an increase in normalized transmission with wavelength from 320 nm through the visible, which is caused by the decrease with wavelength in the Mie scattering coefficients of tropospheric water‐soluble, soot, and stratospheric sulfate aerosols. Using our continental aerosol model, at 0% relative humidity we compute aerosol optical depths of 0.72 at 310 nm and 0.35 at 550 nm, which reduce atmospheric transmission by 12.8% at 310 nm and by 7.9% at 550 nm. With our urban aerosol model we compute aerosol optical depths of 1.82 at 310 nm and 0.87 at 550 nm, which reduce transmission by 34.5% at 310 nm and by 21.1% at 550 nm. Absorption by the aerosols is a significant contributor to this, reducing transmission by 20.9% at 310 nm and by 8.6% at 550 nm beyond nonabsorbing aerosols. For average summer humidity conditions our continental aerosol model predicts an increase in optical depth to 1.26 at 310 nm and to 0.65 at 550 nm, leading to a reduction in transmission of 15.2% at 310 nm and 9.7% at 550 nm, as compared with an aerosol‐free atmosphere. For average summer humidity conditions our urban aerosol model predicts an increase in optical depth to 3.22 at 310 nm and to 1.65 at 550 nm, leading to a reduction in transmission of 40.0% at 310 nm and 25.3% at 550 nm, as compared with an aerosol‐free atmosphere. Comparison with ground‐based data indicates that our estimated optical depths are toward the high end of values seen for continental aerosols, being more typical of industrial than rural areas.
Measurements of ship‐induced tracks in clouds off the Washington coast
Authors: Ferek Ronald J. , Hegg Dean A. , Hobbs Peter V. , Durkee Philip , Nielsen Kurt
Published: September 2002

In situ cloud microphysical measurements are presented for two ship tracks detected off the Washington coast in three successive satellite images from the advanced very high resolution radiometer (AVHRR) channel 3 (3.7 μm). Aerosol and cloud water chemical data suggest that the tracks were produced by effluents from ship stacks. Cloud droplet spectra measured in the ship tracks had effective radii about one half of those measured in the ambient clouds. A drizzle mode was present in the ambient cloud, but this was largely suppressed in the ship tracks. Analysis of cloud condensation nucleus (CCN) and total particle spectra in and around the ship tracks suggest that the stability of the tracks could have been due to a feedback between the lowering of CCN concentrations as the ship plumes diluted, consequent increases in peak supersaturations in the cloud, and a modest amount of particle growth by gas‐to‐particle conversion.
Thunderstorm activity over India and the Indian southwest monsoon
Authors: Manohar G. K. , Kandalgaonkar S. S. , Tinmaker M. I. R.
Published: September 2002

This paper describes the results of monthly latitudinal (8°–30°N) and latitude belts (8° –10°, 10° –15°, 15° –20°, 20° –25°, and 25° –30° N) averaged seasonal thunderstorm activity over India by using monthly data from a large number of Indian stations from 1970 to 1980. The latitudinal variation in the premonsoon (March‐April‐May) and monsoon season (June‐September) months is described and the results are discussed. An examination of the seasonal thunderstorm day activity in the first four belts indicated systematic changes in their signals of semiannual oscillation. These changes are noted to be a function of latitude and season and appear to be consistent with the seasonal migration of the Intertropical Convergence Zone and solar heating of the Indian landmass. We compare the thunderstorm day activity with the monthly mean maximum values of the surface wet‐bulb (Tw) temperatures in the five latitude belts over the Indian region. By using rainfall data for the same period of study, the relationship between seasonal rainfall and number of thunderstorm days over the 11 year period is examined. The results of variation of the ratio of monthly rainfall to thunderstorm days (RTR) during different phases of the southwest monsoon are also presented. Results of the monthly mean electrical conditions of mesoscale and isolated deep convective storms at Pune are summarized. It is noted that the electrification of the premonsoon season thunderstorms dominated by a factor of 3–4 over the monsoon ones. We have examined at length the possible influence of the El Nino on the occurrence and electrification of thunderstorms over the Indian region.
Effect of air‐sea‐ice interaction on winter 1996 Southern Ocean subpolar storm distribution
Authors: Yuan Xiaojun , Martinson Douglas G. , Liu W. Timothy
Published: September 2002

Air‐sea‐ice interaction processes in the Southern Ocean are investigated utilizing space‐observed surface winds, sea ice concentration, and sea surface temperature (SST) from September through December, 1996. The sea ice edge (SIE) shows three ice‐extent maxima around the Antarctic during September and October when sea ice coverage is maximum. They are located in the central Indian Ocean, east of the Ross Sea, and in the eastern Weddell Gyre. During September and October, most of the strong and long lasting storms initiate northeast of the three sea ice maxima. Such spatial distributions of storms and sea ice reflect coupling processes of the air‐sea‐ice interaction. A relatively stable, wave number 3 atmospheric circulation pattern that is believed to be fixed by the land‐ocean distribution prevails during the ice maximum season. The ice‐extent maxima coincide with strong southerlies and divergent wind fields associated with this pattern, which suggests that the mean atmospheric circulation determines the ice distribution. The ice‐extent maxima can enhance the regional meridional surface pressure gradient and therefore strengthen the westerly winds north of the ice edge. The decreasing ice extent east of the ice maxima creates a local zonal thermal gradient which enhances local southerlies. This positive feedback between the wave pattern in the mean atmospheric circulation and ice distribution partially causes the eastward propagation of the ice maxima and also provides a favorable condition for cyclogenesis northeast of the ice‐extent maxima. The mechanism of the cyclogenesis is the baroclinic instability caused by the cold air blown from the ice pack to the warm open‐ocean waters. Where the SST is warmest off the SIE and the southerlies are the strongest, the potential for cyclogenesis is most likely. This is consistent with the observations.
Laboratory study of NO flux from agricultural soil: Effects of soil moisture, pH, and temperature
Authors: Ormeci Banu , Sanin Selim L. , Peirce J. Jeffrey
Published: September 2002

Unique laboratory test chambers with attendant procedures are described, and the results of a comprehensive test protocol are discussed in terms of the mechanical, chemical and biological factors contributing to NO flux from agricultural soil to the lower levels of the troposphere. Soil moisture content, pH, and temperature are investigated to determine the effects of these important variables on NO flux. The flux is seen to increase with temperature and is greatest at pH <5 and pH >8 for the ranges studied. Further, NO flux is seen to decrease as soil moisture content is <1% or >45% water filled pore space. Mechanical, chemical, and biological factors in the soil which contribute to these observed fluxes are addressed.
Location and shape of the Jovian magnetopause and bow shock
Authors: Huddleston D. E. , Russell C. T. , Kivelson M. G. , Khurana K. K. , Bennett L.
Published: September 2002

Following Galileo's arrival at Jupiter in fall 1995, a total of six spacecraft have now sampled the Jovian magnetosphere. Using these data sets to investigate the average location and shape of the Jovian boundaries, we fit ellipse profiles to the observations, allowing for the disk‐like shape of the magnetosphere and taking account of variable solar wind pressure. We find that the subsolar magnetopause location varies with solar wind dynamic pressure to power between −1/5 and −1/4, in contrast to the terrestrial −1/6 power; this is a well‐known difference attributed to the presence of hot plasma and centrifugal stretching in the Jovian magnetodisk that lessens the pressure gradients in the outer magnetosphere, resulting in its unusual responsiveness to compression. The magnetopause is less flared than the bow shock as expected, and the magnetopause shape is especially streamlined (least flared and more bullet‐like) during the higher solar wind dynamic pressure conditions encountered. The average subsolar shock‐to‐magnetopause standoff ratio is approximately 6/5, while at low incident solar wind dynamic pressure the ratio rises to around 4/3 suggesting a blunter Earth‐type magnetopause shape under these conditions. In particular, our analysis confirms that the magnetopause boundary shape is influenced by the radially inflated magnetodisk, as has been previously inferred from the stretched magnetic field lines seen within the magnetosphere. Our fits to the observations reveal that the average magnetopause boundary is indeed contracted on the north‐south axis about the magnetic equator. The bow shock is not found to be so asymmetric in shape, suggesting that there is little effect of external magnetic field direction, and supporting our conclusion that the internal magnetodisk shape is the cause of the magnetopause polar flattening.
Galileo orbiter ultraviolet observations of Jupiter aurora
Authors: Ajello Joseph , Shemansky Donald , Pryor Wayne , Tobiska Kent , Hord Charles , Stephens Stuart , Stewart Ian , Clarke John , Simmons Karen , McClintock William , Barth Charles , Gebben Jeremy , Miller Deborah , Sandel Bill
Published: September 2002

In 1996 during the first four orbits of the satellite tour the Galileo ultraviolet spectrometer (UVS) (1130–4320 Å) and extreme ultraviolet spectrometer (EUVS) (540–1280 Å) performed near‐simultaneous observations of the Jupiter aurora in both the north and south polar regions. These observations are modeled to provide the absolute surface brightness of the aurora from the H2 Rydberg Systems (B, B′, B″, C, D, D′ → X band systems). The spectral distribution and brightness of the EUV aurora are sensitive to H2 abundance, H2 temperature, and CH4 abundance. Analysis of the emission spectra indicates that the EUV aurora (800–1200 Å) are produced over a range of altitudes corresponding to slant column abundances of H2 from 1016 to 1020 cm−2 or greater. The UVS spectra of the far ultraviolet (FUV) from 1130 to 1700 Å are optically thin in H2, but highly sensitive to the CH4 column abundance and to the secondary electron energy distribution. The slant column abundance of CH4 absorbers found from models of the FUV spectra varied in the range 0–10 × 1016 cm−2, indicating the presence of both high altitude aurora, at or above the homopause, and deep aurora. The FUV spectra show C2H2 absorption bands near 1520 Å. The surface brightness of the aurora from the H2 Rydberg Systems ranged from 100 to 600 kR and of H Lyman α was 60 to 130 kR for a 2000 km wide oval. The total power input to the atmosphere from particle deposition is estimated to be ∼1×1014 W.
The plasmasphere of Neptune
Authors: Huang Tian‐Sen , Ho C. Wing , Alexander Claudia J.
Published: September 2002

We examine the plausible existence of Neptune's plasmasphere and study the drift of particles inside it. Using the O8 magnetic field model [Connerney et al., 1991] and assuming a uniform solar wind convection electric field, the plasma convection time and refilling time are calculated in a Euler potential coordinate system [Ho el al., 1997]. The plasma density and refilling time at the equilibrium state are first calculated, and the location of the plasmapause is set to be where the refilling time and convection time are equal. The refilling time as a function of ion speed is then recalculated along field lines, and the plasma density and temperature are obtained by directly integrating the local ion distribution function over the range of speeds for which the refilling time is less than the convection time. The density calculated using this model shows sharp drop‐offs at approximately 3.25 to 4.5 RN on the zero magnetic scalar potential surface, a boundary taken to be the plasmapause. Our calculated density compares fairly with the observed density along the Voyager trajectory within about 5 RN. Ion temperature is also calculated along the field line with results which indicate that high‐speed tails of the distribution function might be needed to explain the high observed temperature measured along the Voyager 2 trajectory. Drift trajectories and speeds of 90° pitch angle particles inside the plasmapause are calculated. Particles of energy above tens of eV are gradient drift dominated, and the drift paths of this class of particles are essentially the minimum B contours that are similar to Acuña et al.'s [1993] calculations. Atmospheric precipitation of the J = 0 particles may provide an explanation for the UV emissions, as an alternative to the “monoprecipitation” suggested by Paranicas and Cheng [1994]. Drifts of low‐energy particles are strongly affected by the gravitational and centrifugal forces, and because of the largely tilted dipole and the large higher components of magnetic field, the resultant drift is nonaxisymmetric and quite complicated.
Geology of Xanthe Terra outflow channels and the Mars Pathfinder landing site
Authors: Nelson David M. , Greeley Ronald
Published: September 2002

The Mars Pathfinder landing site (MPLS) was selected for its location at the mouths of Ares and Tiu Valles outflow channels on Mars, where sediments from a variety of geologic units could have accumulated in a lacustrine environment. Recent geologic mapping at 1:2 M scale of the Xanthe Terra channels and Chryse Planitia near MPLS reveals a progression of fluvial erosion and deposition throughout the Hesperian period. From the geology, the watersheds of the channels were inferred, and a sequence of paleogeologic maps was produced. Three outflow episodes are recognized: (1) broad sheetwash during the early Hesperian, emanating from eastern Valles Marineris and equatorial chaos regions, with initial erosion into highland plateau basement, (2) early channel formation, and (3) subsequent flooding which deepened the channels to their current morphologies. The most recent flooding issued from Simud and Tiu Valles during the late Hesperian, indicated by stratigraphic superposition, striations along the floor of the channel, and the orientation of streamlined islands in the flood direction. This suggests that surface sediments deposited at MPLS are most likely to have come from these channels, and to a lesser extent from Ares Vallis. A ranking scheme was developed to assess the potential origins for the sediments found at MPLS. The most abundant materials are inferred to have come from the Noachian and Hesperian highland plains and reworked sediments from previous floods. Underlying materials from earlier floods could also be found at MPLS as ejecta from nearby impact craters.
Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting?
Authors: Savage M. K.
Published: September 2002

Shear wave splitting measurements now allow us to examine deformation in the lithosphere and upper asthenosphere with lateral resolution <50 km. In an anisotropic medium, one component of a shear wave travels faster than the orthogonal component. The difference in speed causes the waves to separate; this phenomenon is called shear wave splitting. The polarization of the fast component and the time delay between the components provide simple measurements to characterize the anisotropy. Strain aligns highly anisotropic olivine crystals in the mantle, which is the most likely cause of splitting measured from records of distant earthquakes. The seismic community is in the fundamental stages of determining the relations between strain and anisotropy, measuring anisotropy around the world, and determining how much is formed by past and present lithospheric deformation and how much is formed by crustal and asthenospheric sources. The mantle appears isotropic between 600 km depth and the D″ layer at the top of the core‐mantle boundary. Shear wave anisotropy of up to 4% is ubiquitous in the upper 200 km of the crust and mantle. Evidence for stronger and deeper anisotropy is less common. Anisotropy in the transition zone between 400 and 600 km and in the D″ layer may be patchy. Transcurrent deformation at plate boundaries appears to be one of the best mechanisms for causing splitting on nearly vertically traveling waves by aligning foliation planes and the fast axes of olivine within the lithosphere parallel to the boundary and in the most favorable orientation for splitting. Similar deformation may also contribute to anisotropy observed at convergent margins. Shear wave splitting data are challenging conventional beliefs about mantle flow. Simple models of asthenosphere diverging at spreading centers and flowing downward beneath subduction zones appear to be only part of the story, with significant components of flow parallel to ridges and trenches. Parallelism between fast polarizations of waves passing through the deep mantle beneath cratons and surficial geological strain indicators has been used to suggest that the mantle at depths of several hundred kilometers beneath the cratons may have been stable since the initial deformation in the Archean. New paths of investigation include testing a wider range of anisotropic symmetry systems and more complicated models by examining variations in splitting as a function of earthquake arrival angle and distance and by numerical modeling of waveforms and of proposed deformation scenarios.
Angular resolution of two‐dimensional, hexagonally sampled interferometric radiometers
Authors: Bará J , Camps A. , Torres F. , Corbella I.
Published: September 2002

A theoretical analysis of the angular resolution of two‐dimensional interferometric radiometers for Earth observation from low‐orbit satellites and its degradation due to spatial decorrelation effects is presented. The analysis extends basic effects known in the context of radio astronomy (application with narrow field of view, very few baselines) and in one dimension (ESTAR L band, few baselines interferometric radiometer) to the wide‐field‐of‐view, many‐baseline, high‐resolution two‐dimensional system required by Earth observation applications and computes beam width, encircled energy (or main beam efficiency), and side lobe level as a function of windowing (apodization) to allow for an optimum angular versus radiometric resolution trade‐off. It is found that the extension of the Barlett window (which has a poor performance in one dimensional signal processing) to two dimensions produces high‐quality results, comparable or better than those of Gaussian and Blackmann windows. Theory is extended to hexagonally sampled systems based on a Δ or Y‐shaped instrument, with hexagonal‐ and star‐shaped support regions in the visibility space, respectively. The superior performance of the latter over the former for the same number of antennas and correlators is quantified and details of the angular resolution of one instrument of this kind, MIRAS, under development by the European Space Agency, are presented. For this radiometer Gaussian or Barlett windows should be used for good radiometric sensitivity or spatial resolution, respectively. In both cases the effects of decorrelation within the small alias‐free field of view are negligible. It is also found that the impact of hardware imperfections which exist within the strict requirements of the specifications have a negligible effect on the angular resolution. Finally, experimental angular resolution results with a laboratory breadboard in a focused near‐field setup are presented and compared to the theoretical predictions.
Phase compensation experiments with the paired antennas method: 2. Millimeter‐wave fringe correction using centimeter‐wave reference
Authors: Asaki Yoshiharu , Shibata Katsunori M. , Kawabe Ryohei , Roh Duk‐Gyoo , Saito Masao , Morita Ko‐Ichiro , Sasao Tetsuo
Published: September 2002

An experiment for compensating interferometer phase fluctuations due to the turbulent troposphere was conducted with the paired antennas method (PAM) using different sky frequencies for a target and reference source. A celestial source 3C279 was observed at 146.81 GHz with the Nobeyama millimeter array (NMA), while a geostationary satellite was observed as a reference source at 19.45 GHz with commercially available antennas. Each of the antennas was installed near one of the NMA antennas, thus giving us 10 pairs of nearly parallel baselines up to 316 m. Large fluctuations in the interferometer phase of 3C279 were mostly eliminated on almost all baselines by subtracting the reference phase multiplied by a ratio of the observing frequencies. The standard deviations of the compensated interferometer phase were under the level of 20° where the angular separation between the two sources was within 2°, while those of the original phase were typically at the level of 40°–50°. The phase compensation was much improved to the level of the differential excess path length of 0.06‐mm rms (11° at 146.81GHz) in inserting a time lag proportional to the separation angle to the reference phase time series. These results have practical significance for the millimeter or submillimeter wave interferometry because there is rarely a suitable reference source in the vicinity of scientifically interesting sources at such high frequencies. The present experiment shows that it is quite effective in the PAM to use the reference phase at centimeter wave for compensating the millimeter‐wave phase for future large millimeter‐wave arrays.
Atmospheric modulation of microwave backscatter from the ocean surface
Authors: Zamora R. J. , Kropfli R. A.
Published: September 2002

During a month‐long experiment near San Clemente Island, California, the San Clemente Ocean Probing Experiment (SCOPE), unusual radar echoes were observed from an X‐band Doppler radar operated by the National Oceanic and Atmospheric Administration Environmental Technology Laboratory from a cliff 573 m above mean sea level. These radar images were often obtained whenever a strong marine inversion was observed below the level of the radar. The unusual characteristics of the specific event analyzed here were the observed wavelength of the periodic pattern, about 2 km, and its lack of movement during the 15‐min period during which specific features of the pattern, for example, the “wave” crest, could be identified. Several explanations were considered but rejected because of their conflict with the observations and known characteristics of ocean waves. The simplest explanation consistent with all of the observations was that of microwave propagation through a marine inversion which was supporting a low‐amplitude standing wave in the lee of the island. The plausibility of this hypothesis was supported by a simple ray‐trace calculation that simulated propagation through an analytical two‐dimensional field of modified refractive index that represented the essential characteristics of the observed refractive index profile.
A study of the generalized Faraday effect in several media
Authors: Yeh K. C. , Chao H. Y. , Lin K. H.
Published: September 2002

The Faraday effect has been investigated in various fields of study since 1845. In this paper, we provide a unified formulation of the effect for several media. In the classical case, the direction of propagation is parallel to the magnetic field. Here we generalize to any direction of propagation. When describing the state of wave polarization, we find it convenient to use the complex polarization ratio R plane. On the complex R plane, the change of polarization as the wave propagates follows a circle. The resulting polarization loci are illustrated for three different lossless media: a biaxial medium, a chiral medium, and a magnetoionic medium. Through the analysis of the patterns of these loci, we can visualize the generalized Faraday effect on the polarization state diagram and also gain some physical insights into these media in terms of their wave polarization characteristics.
Evaluation of in situ cosolvent flushing dynamics using a network of spatially distributed multilevel samplers
Authors: Sillan Randall K. , Annable Michael D. , Rao P. Suresh C. , Dai Dongping , Hatfield Kirk , Graham Wendy D. , Wood A. Lynn , Enfield Carl G.
Published: September 2002

A network of multilevel samplers was used to evaluate the spatial patterns in contaminant extraction during an in situ cosolvent flushing field test. The study was conducted in an isolation test cell installed in a fuel contaminated site at Hill Air Force Base, Utah. Partitioning tracer tests, conducted before and after the cosolvent flush, were used to estimate the spatial distribution of nonaqueous phase liquids (NAPL) and the effectiveness of cosolvent flushing for removing NAPL. Samples collected during the cosolvent flushing test were used to visualize the extraction process. The results of these two analyses showed similar spatial trends in mass removal and were in general agreement with observations based on soil core data. In general, the cosolvents were more effective in the upper portion of the flow domain and had slightly lower mass removal effectiveness in the lower portion of the flow domain. In this region, tracers indicated slower transport rates and higher NAPL saturations. The spatial analysis also indicated that cosolvent was trapped in the capillary fringe increasing the time required to displace the cosolvent from the aquifer. These results demonstrate the value of spatial information for performance assessment and improving in situ flushing design strategies.
Modeling river flows with heavy tails
Authors: Anderson Paul L. , Meerschaert Mark M.
Published: September 2002

Recent advances in time series analysis provide alternative models for river flows in which the innovations have heavy tails, so that some of the moments do not exist. The probability of large fluctuations is much larger than for standard models. We survey some recent theoretical developments for heavy tail time series models and illustrate their practical application to river flow data from the Salt River near Roosevelt, Arizona. We also include some simple diagnostics that the practitioner can use to identify when the methods of this paper may be useful.
Comparison of soil moisture penetration depths for several bare soils at two microwave frequencies and implications for remote sensing
Authors: Owe Manfred , Van de Griend Adriaan A.
Published: September 2002

Microwave brightness temperature measurements were made over three different bare soils at frequencies of 5 GHz (λ=6 cm) and 1.67 GHz (λ=18 cm) to compare differences in penetration depth according to texture, soil moisture, and wavelength. The soil plots were wetted, and circularly polarized microwave measurements were made during the dry‐down cycle. Soil profile temperature and profile moisture content were monitored continuously for the duration of the experiment. Laboratory analyses of soil physical properties such as texture and bulk density were conducted to aid theoretical calculations of the soil dielectric constants. Laboratory measurements of the soil dielectric constants were also made. Two commonly used soil dielectric models were compared. Theoretical values of soil dielectric constant were calculated with the Dobson model and the Wang‐Schmugge model, and both compared reasonably well with laboratory measurements and also to values reported in the literature. Calculated soil emissivities derived from the field measurements also compared well with emissivities calculated from both the modeled dielectrics and those measured in the laboratory. Emissivities were compared with the average soil moisture for surface profiles of varying thickness. It was found that the observed effective penetration depth appeared to exceed the theoretically defined values.
Experimental analysis of size and distance of travel of unconstrained particles in interrill flow
Authors: Parsons Anthony J. , Stromberg Simon G. L.
Published: September 2002

The travel distances of particles ranging in size from 2.88 mm to 10.63 mm were investigated in laboratory simulations of interrill overland flow. Using travel distances scaled for differences among the experiments in flow and rainfall energy, a relationship between distance traveled and particle size is obtained that shows a steep reduction in travel distance with increase in particle size. Travel distance is the outcome of two probabilities: that of moving and that of coming to rest. In interrill flow, the former is controlled by rainfall energy, but the latter is controlled by flow energy. Analysis of subsets of the data in which only rainfall or flow energy varied shows that the steep reduction in travel distance with particle size is primarily due to sensitivity to flow energy. Although particle movement (entrainment) by rainfall energy does vary with particle size, the sensitivity is less.
Validation of Braided‐Stream Models: Spatial state‐space plots, self‐affine scaling, and island shapes
Authors: Sapozhnikov Victor B. , Murray A. Brad , Paola Chris , Foufoula‐Georgiou Efi
Published: September 2002

We present a comprehensive approach for validating braided‐stream models and apply it to a specific cellular braided‐stream model. The approach involves quantitative comparison of modeled and natural braided streams in terms of two main aspects: the sequential organization of their plan patterns studied using their state‐space characteristics and the hierarchical organization of their patterns studied in the framework of self‐affine scaling. These two aspects of braided streams are complementary to each other and taken together provide a sensitive test of the validity of a model of braided streams. The simple model we examine produces patterns that are similar to those of natural braided rivers in terms of both sequential organization and self‐affine scaling. This finding supports the conclusion that the nonlinear interactions between water and sediment in the model are the primary mechanisms responsible for shaping braided rivers in nature.
A new method for estimation of sensible heat flux from air temperature
Authors: Wang Jingfeng , Bras Rafael L.
Published: September 2002

A new method has been proposed for estimating sensible heat flux from single‐level measurement of air temperature. When turbulent transfer of heat in the lower atmosphere over a homogeneous surface is modeled by a one‐dimensional diffusion equation with a constant diffusivity, heat flux can be expressed as a weighted average (half‐order derivative) of the time history of air temperature. This formula provides an approximate solution of the diffusion equation where the (eddy) diffusivity characterizing the turbulent flow is not constant. Eddy diffusivity has been formulated based on Monin‐Obukhov similarity theory with Businger‐Dyer stability functions or determined by an empirical equation. The knowledge of surface parameters including friction velocity sometimes is needed to apply this method. The method was tested against observations collected during two field experiments, FIFE and ABRACOS. The close agreement between the estimated sensible heat flux and observations suggests that this novel approach is a potentially powerful tool in evaluating the energy balance at the land surface.
Matching objective and subjective information in groundwater inverse analysis by Akaike's Bayesian information criterion
Authors: Honjo Yusuke , Kashiwagi Nobuhisa
Published: September 2002

In order to overcome the illposedness of groundwater inverse analysis it is inevitable to introduce prior information of some form and thus Bayesian statistics. One of the essential problems in Bayesian inverse formulation is the optimum matching between the objective information (i.e., the observation) and the subjective information (i.e., the prior information). In this study, Akaike's Bayesian Information Criterion (ABIC) is introduced to overcome this problem. ABIC is also effective in the model identification problem, and this aspect is also emphasized. The effectiveness of the method is illustrated by analyses on an actual aquifer system. Both steady and transient state analyses are carried out. The paper also provides the background of ABIC in some detail.
Asymptotic solutions for solute transport: A formalism for tracer tomography
Authors: Vasco D. W. , Datta‐Gupta Akhil
Published: September 2002

An asymptotic approach to the solution of the transport equation, in the limit of rapid spatial and temporal variation, produces an extremely efficient formalism for the inversion of tracer data. The technique provides tracer concentration sensitivities to porosity, permeability, and pressure gradient variations in just a single simulation run. The calculated sensitivities compare well with those derived using a numerical perturbation method, at a fraction of the computational requirements. An application to a conservative tracer test at Hill Air Force Base in Utah indicates the efficiency and utility of the approach for characterizing three‐dimensional variations in flow properties. On the basis of tracer concentration histories at 12 multilevel samplers and three extraction wells, some 44 tracer curves in all, significant small‐scale variability in permeability is inferred. In general, the permeability is found to decrease as the lower boundary of the aquifer is approached. The permeability trends we find are consistent with tracer swept volume calculations based upon a moment analysis.
Geophysicists
Authors: Anonymous
Published: September 2002

Industrial pollution declined 2.3% in the United States and Canada in 1996, continuing a dip during the previous 2 years, according to the Commission for Environmental Cooperation's (CEC) August 10 report, “Taking Stock 1996.” The report says the decline also continues beyond 1996.

Large manufacturing facilities in the United States and Canada that reported information to CEC produced 1.225 billion kg of pollution in 1996, compared to 1.254 billion kg in 1995, the report says.
Group calls for protecting Great Lakes water
Authors: Showstack Randy
Published: September 2002

Neither Canadian nor United States governments should allow any surface or groundwater removals from the Great Lakes Basin that endanger the region and its ecosystem, an intergovernmental body recommended on August 18.

In addition, the governments should lower substantially the trigger point for proposed new or increased water use that require notice, consultation, and the seeking of consent and concurrence, said the International Joint Commission (IJC).
Bioenergy and biobased products hold promise of reducing pollution emissions
Authors: Showstack Randy
Published: September 2002

Trees and other plants have, of course, long been useful for the wood and agricultural benefits they provide. Now, this organic matter is gaining new cachet as “biomass.”

Some scientists hope that this stuff can be converted into practically a panacea of goods, including transportation fuels, electricity, commercial products such as chemicals, glues, and paints, and other materials—reducing societal dependence on petrochemical products.
Remembering Robert Goddard's vision 100 years later
Authors: Stern David P.
Published: September 2002

“Life, liberty, and the pursuit of happiness” —such are the goals of most of us.Yet a few always exist who feel called by a higher purpose. Society often owes them a great deal.

Robert Hutchins Goddard, whose work made spaceflight possible, found his vision 100 years ago this October as a youth of 17. His family was staying on the farm of a relative, when he was asked to trim the branches of a cherry tree behind the barn.
Inhibition of neuronal nicotinic acetylcholine receptors by the abused solvent, toluene
Authors: Bale Ambuja S , Smothers Corigan T , Woodward John J
Published: September 2002

Toluene is a representative example of a class of industrial solvents that are voluntarily inhaled as drugs of abuse. Previous data from this lab and others has shown that toluene modulates the function of N‐methyl‐D‐aspartate (NMDA), γ‐aminobutyric acid (GABA) and glycine receptors at concentrations that do not affect non‐NMDA receptors.

We utilized two‐electrode voltage‐clamp and whole cell patch‐clamp techniques to assess the effects of toluene on neuronal nicotinic acetylcholine receptors expressed in oocytes and cultured hippocampal neurons. Toluene (50 μM to 10 mM) produced a reversible, concentration‐dependent inhibition of acetylcholine‐induced current in Xenopus oocytes expressing various nicotinic receptor subtypes. The α4β2 and α3β2 subunit combinations were significantly more sensitive to toluene inhibition than the α4β4, α3β4 and α7 receptors.

Receptors composed of α4 and β2(V253F) subunits showed α4β4‐like toluene sensitivity while those containing α4 and β4(F255V) subunits showed α4β2‐like sensitivity.

In hippocampal neurons, toluene (50 μM to 10 mM) dose‐dependently inhibited ACh‐mediated responses with an IC50 of 1.1 mM.

Taken together, these results suggest that nicotinic receptors, like NMDA receptors, show a subunit‐dependent sensitivity to toluene and may represent an important site of action for some of the neurobehavioural effects of toluene.

British Journal of Pharmacology (2002) 137, 375–383. doi:10.1038/sj.bjp.0704874
Recent trends in progressive power lenses
Authors: Fowler Colin
Published: September 2002

Despite having been first marketed in the 1950s, new designs of progressive addition spectacle lens continue to appear. Some of the recent patent literature is reviewed on the design of such lenses. As well as a number of improvements to general purpose designs, specifically to include aspheric surfaces for the distance portion of progressive lenses, the literature includes a recent patent on an improved version of the Alvarez lateral translation lens system. The optimisation of single vision lens forms in order to extend the depth of field for early presbyopes is also discussed.
The pharmacological basis of anterior segment therapy
Authors: Vale Janet
Published: September 2002

The main concerns in anterior segment therapy are allergy, inflammation and infection. Allergic reactions can be divided into four types with differing etiologies. Although all types may be manifested in ocular inflammatory states, Type I, involving the release of histamine is probably the most common, being involved in responses to pollen, drugs and in GPC and VKC. Inflammation is a complex, multicomponent, protective response involving the synthesis, release and actions of many chemical mediators, including prostaglandins which are synthesised from cell membrane components. Drugs used act through a number of mechanisms: decongestants act directly on dilated vessels to cause constriction and decreased permeability; antihistamines block the access of histamine to its receptors in the target tissues and mast cell stabilisers prevent the release of mediators including histamine in response to the antigen/antibody interaction. Both the non‐steroidal anti‐inflammatory drugs and steroids decrease the production of the prostaglandins by inhibiting the action of cyclo‐oxygenase and phospholipase respectively. Most infections are bacterial and the majority of drugs used are antibacterial. However, many of the principles of antibacterial therapy can be applied to the other classes of drugs. The basic principle in the treatment of any infection is that of selective toxicity, which is the ability to effect harm to the infecting cells (e.g. bacteria) without a similar effect being exerted on the host cells. This selectivity may be qualitative, at no drug concentration is the host cell affected in the same way as the invading cell, or quantitative where the separation of effect is dose dependent. The selectivity may have a biochemical or distributional basis, and the effects may be, in the case of bacteria, bactericidal or bacteriostatic. Most antibiotics used in anterior segment therapy show quantitative biochemical selectivity and are bacteriostatic in action. The antiviral compound (aciclovir) shows quantitative biochemical selectivity because it is a pro‐drug activated in infected cells.
Prevalence of ‘non‐hexagonal’ cells in the corneal endothelium of young Caucasian adults, and their inter‐relationships
Authors: Doughty Michael J.
Published: September 2002

The corneal endothelium is often described as a mosaic of hexagonal cells, despite numerous reports that the relative number of ‘hexagonal’ cells is often only around 65%. Such estimates also cannot define the relative area contribution to the cell mosaic of either these cells, or those that are not 6‐sided. Specular micrographs were therefore taken of 20 healthy young Caucasian adults aged 21 to 34 years and the apical surface areas of at least 105 contiguous cells from each central corneal endothelium measured by planimetry. The numbers of each cell type and their surface areas were assessed so that the summated area occupied by each cell type could be calculated. The results reveal that endothelia that show only modest variance in cell areas are usually composed of 4‐, 5‐, 6‐, 7‐ and 8‐sided cells. Assessments of relative contribution of each cell type to the mosaic indicates that the 6‐sided cells can be expected to constitute just over 60% of the total cell area. Increases in the variance in the areas across all the cells can be strongly correlated with a reduction in the 6‐sided cells and increases in the 5‐ and 7‐sided cells. Each cell type (4‐, 5‐, 6‐sided etc) has a preferred area that is proportional to other cells. The results firmly indicate that the mosaic is not random and follows a specific order that is presumably dictated by the physics of cell packing. These methods of comparing endothelia should allow distinctions to be made between endothelia that are different, versus being abnormal (i.e. with disease).
Modelling adaptation effects in vergence and accommodation after exposure to a simulated Virtual Reality stimulus
Authors: Eadie A. S. , Gray L. S. , Carlin P. , Mon‐Williams M.
Published: September 2002

Natural viewing conditions place equal demands on the vergence and accommodation systems. The two responses are co‐ordinated via the interactive components which couple the two systems: accommodative vergence and vergence accommodation. The crosslink components are usually quantified by the AC/A and CA/C ratios. Whether these ratios are stable entities, genetically determined, or modifiable by experience has been the subject of some debate. A ‘Virtual Reality’ stimulus was used to place unequal demands on the vergence and accommodation systems. Pre‐task and post‐task measures of AC/A and CA/C were objectively determined. The changes in the post‐task measures are discussed with reference to a dual interactive model of vergence and accommodation. Model simulations suggest that adaptation of the vergence and accommodative controllers (tonic adaptation) may also play a part by altering the open loop bias. The results therefore support the idea that vergence accommodation and accommodative vergence are capable of adaptation.
Towards a colorimetric characterization of the human iris
Authors: Melgosa M. , Rivas M. J. , Gómez L. , Hita E.
Published: September 2002

We propose a new approach to the quantitative determination of the iris colour through the spectroradiometric measurement of a set of 72 artificial irises under controlled illumination and geometry. The spread of these samples in the CIELAB colour space indicates no clearly distinguished groups within the set analysed. Colour measurements for different points of these irises and for the overall irises (pupil and specular image of the light source included) are well correlated. Complementary colour measurements were also performed for the irises of 25 ocular prostheses and 40 real observers. All these colour measurements appear to be quite consistent, the average standard deviation of any of the three a*, b*, L* co‐ordinates being lower than 1.0 units. In a visual experiment where 11 normal observers matched the 25 ocular prostheses using the 72 artificial irises, the results indicate that a simple criterion based on the lowest colour‐difference agreed with the observers’judgements in only 18% of the cases. This result suggests that, although colour appears to be a major parameter in the overall characterization of the human iris, additional factors such as patterns or textures should also be considered.
Further analysis of the size and shape of cells obtained by impression cytology from the exposed portion of the human bulbar conjunctiva
Authors: Doughty Michael J. , Blades Kenneth , Button Norman F. , Wilson Graeme
Published: September 2002

Purpose: To assess whether the size of the cells obtained by conjunctival impression cytology can be quantitatively assessed by measurement of the longest dimension of the cells.

Methods: Under topical benoxinate anaesthesia, cells were removed from the normally exposed nasal bulbar conjunctival surface using a 0.4 μm pore diameter filter (Biopore® filter; type Millcell®‐CM). The filters were stained with haematoxylin after ethanol denaturation, photographed at 40× magnification, and 35 mm slides prepared. An optical overlay method was used to outline the borders of sets of 30–35 contiguous cells on each image. The cell area, longest and shortest dimensions were measured by planimetry to an accuracy of ±3%.

Results: Analyses of 20 sets of samples, from individuals aged 21 to 48 years and without clinically significant ocular surface disease, revealed a median cell area of 133 μm2 (n=621, range 46–1602 μm2; average 212 μm2), a median longest dimension of 13.9 μm (range 6.6–68.8 μm; average 16.9 μm) and a shorter dimension of 10.0 μm (range 4.7–43.0 μm; average 11.9 μm); the distributions of values indicated bimodality. Most cells had a long:short ratio (L:S ratio) value between 1.00 and 1.80, but 11.9±6.1% of the cells had L:S ratios between 1.80 and 4.60. The overall relationship between the longest dimension and the area of the cells was non‐linear, with cells having larger L:S ratios having disproportionately smaller areas.

Conclusions: The superficial conjunctival cells are small, and their longest dimensions are systematically related to area. Analyses of cell shape indicate further possible ways of identifying different cells on the bulbar conjunctiva. Compared to literature values, there is a substantial overlap in longest dimensions of the conjunctival cells with those of cells that can be collected off the corneal surface. This means that superficial conjunctival and corneal cells cannot be distinguished simply on the basis of measurements of the long dimension.