bluuebunny/crossref_metadata_2025 huggingface dataset:
River and floodplain process simulation for subsurface characterization
Authors: Gross Lori Juergens , Small Mitchell J.
Published: September 2002

Subsurface heterogeneity is characterized with a method based on facies delineation and process modeling. A geologic process model is formulated to simulate the development of four facies: channel fill, levee, splay, and floodplain, which commonly form in a meandering river and its floodplain. The model accounts for meandering, cutoff, flooding, and crevasse‐splay processes and links these formational processes to the statistical properties of the resulting facies. The model is utilized in a case study to simulate the horizontal pattern of deposition and facies distributions of the Stratton field, part of the Middle Frio Formation of southeast Texas, using known or estimated relationships and historical information for the Stratton field region. The simulated distributions of longitudinal and transverse facies dimensions and corresponding transition probabilities among facies are compared to those determined from sampling an observed section of the field, yielding similar results though some differences. Similarities and differences are related to the model processes and sampling procedures. Model sensitivity is investigated by changing selected model variables and analyzing the change in the facies distributions. The application of the geologic process model to the Stratton field demonstrates the viability of linking process understanding and modeling of complex meandering stream processes to characterization of subsurface heterogeneity.
Simulations of cobble structure on a gravel streambed
Authors: Tribe Selina , Church Michael
Published: September 2002

We present a two‐dimensional, time independent, kinematic simulation of a gravel streambed that models impacts between clasts as elastic collisions without momentum transfer between discrete, circular disks. The prototype bed forms that we seek to simulate are the “stone cells” observed in Harris Creek, south central British Columbia. The basic algorithm causes simulated stones to cluster into longitudinal structures that resemble such gravel bed forms as imbricate clusters and cluster bed forms. A modified algorithm incorporating programming rules such as stone rotation, entrainment probability inversely proportional to stone size, and the shielding effects of neighbors causes simulated stones to cluster into structures that resemble transverse ribs. Trials incorporating the rotation rule, with or without additional rules, produce a cobble structure most similar to the prototype. Of all the parameters in the simulation, the number of stones seems to have the most control on the development of an extended surface structure.
Observations of measured hydraulic conductivity in two artificial, confined aquifers with boundaries
Authors: Silliman Stephen E. , Caswell Stephen
Published: September 2002

Recent theoretical efforts have provided strong evidence that the effective conductivity varies with distance between monitoring wells and a point source. In the present study, two artificial confined aquifers were subjected to steady state pumping tests. Analysis of these experimental results indicates dependence of the estimated hydraulic conductivity on distance from the pumping well and the form of the physical heterogeneity present. As the precision of the measured hydraulic heads within the experimental apparatus was limited to ∼0.5 mm, the experimental results were reproduced numerically. Although some minor discrepancies were noted between the numerical and experimental results, the primary observations were consistent. In all cases the Thiem equation was used in combination with image well theory (to account for the boundary conditions) to analyze the response at 25 observation points (87 observation points used in the numerical experiments), providing a number of estimates of the hydraulic conductivity. Within each experiment it was observed that the variance of the conductivity estimate decreased with the distance between the two observation wells used in the calculation. Further, the mean conductivity varied with distance from the pumping well. In an experiment in which the medium was constructed to mimic a second‐order stationary random field the mean conductivity approached, at large distance from the pumping well, the conductivity for a random, anisotropic medium under mean uniform flow. In an experiment in which the medium was constructed to mimic a structured (scaled) medium the mean conductivity decreased, at large distance from the pumping well, below the geometric mean and approached a value between the geometric and the harmonic means of the conductivity field. While the boundary conditions make it difficult to fully analyze the large‐dimension behavior of these two media, it is clear from the results that the structured medium performs quite differently than the random field at large‐measurement scale.
Field study and simulation of diurnal temperature effects on infiltration and variably saturated flow beneath an ephemeral stream
Authors: Ronan Anne Dudek , Prudic David E. , Thodal Carl E. , Constantz Jim
Published: September 2002

Two experiments were performed to investigate flow beneath an ephemeral stream and to estimate streambed infiltration rates. Discharge and stream‐area measurements were used to determine infiltration rates. Stream and subsurface temperatures were used to interpret subsurface flow through variably saturated sediments beneath the stream. Spatial variations in subsurface temperatures suggest that flow beneath the streambed is dependent on the orientation of the stream in the canyon and the layering of the sediments. Streamflow and infiltration rates vary diurnally: Streamflow is lowest in late afternoon when stream temperature is greatest and highest in early morning when stream temperature is least. The lower afternoon Streamflow is attributed to increased infiltration rates; evapotranspiration is insufficient to account for the decreased Streamflow. The increased infiltration rates are attributed to viscosity effects on hydraulic conductivity from increased stream temperatures. The first set of field data was used to calibrate a two‐dimensional variably saturated flow model that includes heat transport. The model was calibrated to (1) temperature fluctuations in the subsurface and (2) infiltration rates determined from measured Streamflow losses. The second set of field data was to evaluate the ability to predict infiltration rates on the basis of temperature measurements alone. Results indicate that the variably saturated subsurface flow depends on downcanyon layering of the sediments. They also support the field observations in indicating that diurnal changes in infiltration can be explained by temperature dependence of hydraulic conductivity. Over the range of temperatures and flows monitored, diurnal stream temperature changes can be used to estimate streambed infiltration rates. It is often impractical to maintain equipment for determining infiltration rates by traditional means; however, once a model is calibrated using both infiltration and temperature data, only relatively inexpensive temperature monitoring can later yield infiltration rates that are within the correct order of magnitude.
Mapping surface energy flux partitioning at large scales with optical and microwave remote sensing data from Washita '92
Authors: Kustas William P. , Zhan Xiwu , Jackson Thomas J.
Published: September 2002

A model evaluating the energy balance of the soil/substrate and vegetation (i.e., two‐source) was applied to remotely sensed near‐surface soil moisture maps generated from passive microwave data collected during the Washita '92 experiment. Model parameters were derived from a soil texture and a land‐use/land cover database along with a normalized difference vegetation index map created from a SPOT satellite image. The Bowen ratio (BO, ratio of sensible to latent heat flux) was used for investigating the temporal and spatial variability in model output. Comparisons between predicted and observed heat fluxes were made with values summed over the daytime period. Daily maps of midday BO indicated areas with low vegetation cover or bare soil and senescent vegetation were drying out significantly (i.e., dramatic increases in BO), while other areas with higher vegetation cover showed smaller increases in BO in response to a drying soil surface. This result agrees with the profile soil moisture and surface flux observations indicating adequate moisture was available to the vegetation for meeting atmospheric demand. The predicted daytime fluxes agreed to within 1 mm of the observations with ≈25% difference between modeled and observed daytime evapotranspiration. Differences between modeled and measured surface temperatures averaged ≈2 K. The discrepancies between model output and observations are similar to the uncertainty in these measurements, indicating that the model provided reliable daytime energy flux maps for the Washita '92 study area using remotely sensed near‐surface soil moisture.
A model for stripping multicomponent vapor from unsaturated soil with free and trapped residual nonaqueous phase liquid
Authors: Ng Chiu‐On , Mei Chiang C. , Ostendorf David W.
Published: September 2002

We present a model for the multicomponent vapor transport due to air venting in an unsaturated zone in the presence of free and trapped phases of residual nonaqueous phase liquid (NAPL). On the microscale the soil particles are assumed to form spherical aggregates with micropores filled with immobile water, trapped phases of NAPL and air. The interaggregate space is occupied with mobile air, and a thin film of free NAPL adheres on the aggregate surface. While the free NAPL can readily be in equilibrium with macropore vapor, the mass transfer from immobile phases in aggregates is rate‐limited by aqueous diffusion. This model enables us to predict the vapor concentrations of various chemical species and the free NAPL saturation over the macroscale, based on the detailed understanding of the aqueous concentrations of the species and the trapped NAPL saturation within the aggregates. The model is compared favorably with some experimental data of sparging multicomponent vapor out of an intact core taken from a contaminated site. The distinctive features of multicomponent transport, clearly exhibited by the data, are further examined in the simulations of a hypothetical case of three‐aromatic vapor transport under a radial flow field. It is found that while the vapor concentration of the most volatile component drops monotonically with time, those of the less volatile may rise as their mole fractions in the NAPL increase. The vapor concentration of a heavy component may have a local maximum at the evaporation front of the free NAPL. In the case of radial flow the free NAPL has two receding evaporation fronts. Condensation of the heavy component downstream of the far front causes a temporary increase of its total concentration there. With trapped NAPL and soil aggregation the macroscale transport is retarded, and the effluent concentrations end up in noticeable tailing.
Relationship between geomorphic settings and unsaturated flow in an arid setting
Authors: Scanlon Bridget R. , Langford Richard P. , Goldsmith Richard S.
Published: September 2002

Because geomorphology can readily be mapped, our ability to characterize unsaturated flow over large areas would be greatly enhanced if relationships between geomorphic settings and unsaturated flow could be identified. The purpose of this study was to evaluate relationships between geomorphic settings and spatial and temporal variability in unsaturated flow at a field site in the Chihuahuan Desert of Texas. This study differs from most previous studies in the variety of geomorphic settings studied, including drainage areas (Blanca Draw and Grayton Lake playa) and interdrainage areas (basin‐fill deposits, eolian sheets, alluvial fans, and a fissure), density of data (∼50 sampled boreholes 3–31 m deep), and variety of techniques (physical, chemical, and electromagnetic) used to quantify unsaturated flow. Spatial variability in unsaturated flow parameters is related to geomorphic settings. The various geomorphic settings form distinct groups on a plot of chloride versus water potential. Interdrainage areas have low water potentials and high chloride concentrations, indicating low water fluxes. Mean water fluxes estimated from chloride data ranged from 0.02 to 0.05 mm yr−1. In contrast, localized topographic depressions (fissure, gully, and borrow pit) have high water potentials and low chloride concentrations which indicate high mean water flux (∼100 mm yr−1). These topographic depressions occupy <1% of the basin area. Drainage areas have low water potentials, which indicate low water fluxes and low to moderate chloride concentrations, which indicate higher water fluxes in the past (≤40 mm yr−1). Short‐term variability in response to precipitation events was only monitored in topographic depressions. The age of the pore water in the interdrainage areas spanned paleoclimatic variations (≤136,000 years at 25 m depth); however, most interdrainage profiles show negligible response to past climate fluctuations. Some profiles in eolian sheets showed increased water flux in response to Pleistocene climate change. The findings from this study indicate that geomorphology can provide valuable information on unsaturated flow and underscore the importance of localized topographic depressions for focusing unsaturated flow.
Outstanding student paper awards
Authors: Anonymous
Published: September 2002

The Hydrology Section presented five outstanding student paper awards at the 1999 Spring Meeting in Boston, Massachusetts, last June.

Maneesha Joshi presented a poster titled “Estimation of the Extent and Duration of Melt on the Greenland Ice Sheet using an Edge Detection Technique on Passive Microwave Data.” She received her B.Tech. in civil engineering from the Indian Institute of Technology, Bombay in 1991, and a M.S. in environmental engineering from State University of New York, Buffalo in 1994. Maneesha expects to complete her Ph.D. in civil engineering (remote sensing) in September 1999, under the supervision of Carolyn Merry (Department of Civil and Environmental Engineering & Geodetic Science), Ken Jezek, and John Bolzan (Byrd Polar Research Center) at the Ohio State University, Columbus, Ohio. Her thesis focuses on estimating the extent of melt, melt season, and duration, and absorbed radiation on the Greenland ice sheet from passive microwave and SAR data. Maneesha's other interests include image processing, issues related to global climate change, and photogrammetry.
Tides: A Scientific History
Authors: Agnew Duncan
Published: September 2002

If you ask most oceanographers what a Proudman function or a Doodson number is, you are likely to be met with blank looks—and yet these are terms central to the oldest concern of oceanography, the tides. Indeed, at one time tidal science was sufficiently prominent that those who studied it were called “tidalists,” a term coined by the same person (William Whewell) who invented the term “scientist,” and who was himself a tidalist.

The long and varied history of this part of geophysics has been examined by its leading expert, David Cartwright, in a narrative that extends from ancient Greek and Chinese ideas (already based on an impressive amount of empirical knowledge) to the latest results from satellite altimetry. As Cartwright points out, satellite data have essentially solved the long‐standing problem of mapping the global ocean tides, and thus have in some ways brought tidal studies, if not to an end, to a point from which a retrospective look is appropriate.
Assembly fetes world climate research area and its leader
Authors: McGuffie Kendal
Published: September 2002

Both a relatively new world‐climate research area and a person instrumental in bringing it about were feted at the International Union of Geodesy and Geophysics (IUGG) Assembly this past July. The research area has been embodied in the Project for Intercomparison of Land‐Surface Parameterization Schemes (PILPS), which actually began in 1992. Its leader, Ann Henderson‐Sellers, was awarded a doctor of science degree in recognition of her 21 years of work in climate model predictions.

Said Henderson‐Sellers: “I am very pleased to be able to look back on an era in which this discipline's research develops from the simplest conceivable land‐surface scheme, literally a hole in the soil, to today's highly complex schemes, which include leaves, stomates, roots, and even ecological transitions.”
Advances in varved sediment studies help paleoclimate reconstructions
Authors: Francus Pierre , Saarinen Timo
Published: September 2002

Recent interest in varved sediments has expanded considerably, since they can provide an accurate chronology for paleoclimatic reconstruction and can be found in various environments around the globe. A varve is a lamina or a sequence of laminae deposited in a body of still water within a year's time. Proxy data, such as pollen, diatoms, stable isotope geochemistry and microchemical analysis, retrieved from such laminated records can be temporarily constrained. Also, the varves themselves contain climatic information.

Generally in order to validate climate models, especially in terms of their ability to simulate short‐term environmental changes such as El Niño, it is important to test them against the past climate record. Such testing is usually restricted to instrumental climate data. However, high‐resolution records (such as tree rings, banded corals, and ice cores, as well as varved sediments) can provide annually resolved paleoclimatic information for longer periods of time.
New seismic study of deep sea gas hydrates results in greatly improved resolution
Authors: Gettrust J. , Wood W. , Lindwall D. , Chapman R. , Walia R. , Hannay D. , Spence G. , Louden K. , MacDonald R. , Hyndman R. D.
Published: September 2002

A multichannel seismic survey has resulted in greatly improved resolution of structural details of deep sea gas hydrates off the west coast of Canada, revealing numerous geological features not before evident. The survey using the Naval Research Laboratory deep‐towed acoustic/geophysics system (DTAGS), provided high‐resolution images and layer velocities more than 10 times better than those obtained in the past using conventional systems. Vertical resolution within 2 m and horizontal resolution within 20 m were achieved.

The work demonstrates that high‐resolution seismic surveys with deep towed multichannel systems can provide important new information about pathways of fluid and gas migration that control the formation of gas hydrates. Conventional surface‐towed seismic systems are unable to do this.
Climate change and greenhouse gases
Authors: Ledley Tamara S. , Sundquist Eric T. , Schwartz Stephen E. , Hall Dorothy K. , Fellows Jack D. , Killeen Timothy L.
Published: September 2002

Infrared (IR) active gases, principally water vapor (H2O), carbon dioxide (CO2), and ozone (O3), naturally present in the Earth's atmosphere, absorb thermal IR radiation emitted by the Earth's surface and atmosphere. The atmosphere is warmed by this mechanism and, in turn, emits IR radiation, with a significant portion of this energy acting to warm the surface and the lower atmosphere. As a consequence the average surface air temperature of the Earth is about 30°C higher than it would be without atmospheric absorption and reradiation of IR energy [Kellogg, 1996; Peixoto and Oort, 1992; Henderson‐Sellers and Robinson, 1986].

This phenomenon is popularly known as the “greenhouse effect,” and the IR active gases responsible for the effect are likewise referred to as “greenhouse gases.” The rapid increase in concentrations of greenhouse gases since the industrial period began has given rise to concern over potential resultant climate changes.
The Victorian Amateur Astronomer: Independent Astronomical Research in Britain, 1820–1920
Authors: Malin Stuart
Published: September 2002

Though astronomy is not without its practical applications (to navigation, for example), the main motivation for its study has always been intellectual and aesthetic stimulation. It has therefore appealed to a much wider audience than its relatively few professionals. In our time such professionals conduct nearly all of its research, backed by a large body of serious amateurs who provide support, interest, and help in disseminating the results. But in Victorian Britain it was the other way around, with the amateurs leading the way in instrumentation, observation, and interpretation. Thus The Victorian Amateur Astronomer: Independent Astronomical Research in Britain, 1820–1920 is of considerably broader interest for the history of astronomy than might be gathered from the title.
Pharmacological characterization of CGP 12177 at the human β2‐adrenoceptor
Authors: Baker Jillian G , Hall Ian P , Hill Stephen J
Published: September 2002

It has recently been reported that CGP 12177 can act as an agonist at a novel secondary site within the human β1‐adrenoceptor. The aim of this study was to undertake a detailed pharmacological study of the effects of CGP 12177 on the human β2‐adrenoceptor.

CGP 12177 acted as a potent partial agonist of 3H‐cyclic AMP accumulation (log EC50−8.90±0.06) and CRE‐mediated reporter gene transcription (log EC50−9.66±0.04) in CHO‐K1 cells expressing the human β2‐adrenoceptor. These CGP‐induced responses were antagonized by the β2‐selective antagonist ICI 118551 (apparent log KD values of −8.84±0.15 and −9.51±0.02 for the cyclic AMP and reporter gene responses respectively).

CGP 12177 was also able to antagonize both cyclic AMP and reporter gene responses to more efficacious β2‐agonists with similar log KD values (e.g. −9.57±0.15 and −10.04±0.096 respectively with salbutamol as agonist).

3H‐CGP 12177 binding to β2‐adrenoceptors in intact CHO‐β2 cells yielded a log KD value of −9.84±0.06, but indicated that the ligand dissociates very slowly from the receptor (t½ for dissociation=65 min). However, studies with a Green Fluorescent Protein (GFP)‐tagged β2‐adrenoceptor indicated that CGP 12177 does not stimulate β2‐adrenoceptor internalization.

This study demonstrates that CGP 12177 is a high affinity partial agonist of both cAMP accumulation and CRE‐mediated gene transcription at the human β2‐adrenoceptor. It provides no evidence that CGP 12177 can discriminate a secondary site on the β2‐adrenoceptor analogous to that observed for the human β1‐adrenoceptor. However, despite its very weak actions on cAMP accumulation, the potent agonist effects of CGP 12177 on CRE‐mediated gene transcription at the human β2‐adrenoceptor, coupled with its long duration of action, offers a potential lead for drug development for the treatment of chronic inflammatory airway diseases.

British Journal of Pharmacology (2002) 137, 400–408. doi:10.1038/sj.bjp.0704855
An overview of the current drugs scene
Authors: Edgar D. F.
Published: September 2002

Ophthalmic drugs, both diagnostic and therapeutic, play a central role in new developments in optometry, particularly as practitioners extend their involvement in primary care. Optometrists now dilate more patients in routine practice, and this brings increasing concern about the risk of provoking acute closed angle glaucoma (CAG) attacks. It would seem that the risk of inducing acute CAG is far outweighed by the potential benefit of examining the eye through a dilated pupil. Driving difficulties, reported subjectively to be the result of glare, are frequently encountered by patients after dilation, and advice from the College of Optometrists is welcomed. The local anaesthetic proxymetacaine 0.5% is now marketed in the UK in preservative‐free unit‐dose applicators both alone and in combination with fluorescein, and is a more comfortable alternative to existing anaesthetics in unit‐dose form. The second half of this paper includes a summary of the background to recent developments, as the UK profession takes its first steps towards the use of ocular therapeutic agents. Finally, some exciting new therapeutic preparations for use in the treatment of glaucoma, allergic eye disease, and dry eye conditions are discussed.
New developments in retinal drusen
Authors: Gibson J. M.
Published: September 2002

Retinal drusen are an important manifestation of age‐related maculopathy, and increase with ageing. Recent studies have shown that gentle laser photocoagulation can lead to resolution of soft drusen and may lessen the high risk of development of choroidal neovascularisation in these cases. Laser induced regression of retinal drusen appears to be a safe technique, but no long term results are yet available. Retinal drusen may also occur as a dominantly inherited disorder and current evidence suggests that these represent more than one disorder. Misclassification of retinal drusen as retinal exudates is an important cause of false positive referral in diabetic retinopathy screening programmes.
Investigating and managing the child with special needs
Authors: Woodhouse J. Margaret
Published: September 2002

Children with disabilities are much more at risk of eye and vision problems than are able children. These problems can take the form of ‘optical’ defects such as refractive errors and poor accommodation. Thus children with all forms of special needs not only have a right to Optometric services, but have a greater need than the rest of the population. This paper presents recent data on the defects found specifically in children with Down's Syndrome, (but likely to occur in other children) and provides general guidelines for Optometrists working with children with special needs.
Contrast and glare sensitivity in diabetic patients with and without pan‐retinal photocoagulation
Authors: Mackie S. W. , Walsh G.
Published: September 2002

Patients with diabetes mellitus often have ophthalmic dysfunction, as diabetic eye disease can affect the majority of the ocular structures. The present study investigated contrast sensitivity (experiment 1) and glare sensitivity (experiment 2) using Pelli‐Robson and Bailey‐Lovie charts in normal and diabetic patients with a range of degrees of ischaemic retinopathy (n=220). Contrast sensitivity thresholds reduced and glare sensitivity progressively increased throughout the range from normal to advanced stages of diabetic eye disease. However, the reduction in contrast sensitivity between adjacent groups was not significant (P>0.10). Conversely, glare sensitivity was found to be greater in those diabetic patients who had received laser treatment (P=0.001). The potential use of both tests is discussed.
Contrast restoration model for contrast matching of cosine gratings of various spatial frequencies and areas
Authors: Näsänen Risto , Tiippana Kaisa , Rovamo Jyrki
Published: September 2002

The purpose of the model presented in this paper is to explain the well known fact that perceived contrast becomes independent of optical low‐pass and neural high‐pass filtering as well as areal integration with increasing stimulus contrast. In the model we assume that perceived contrast is computed by two different parallel mechanisms. One of them integrates signal information across space to improve the signal‐to‐noise ratio and is affected by the optical low‐pass and neural high‐pass filtering. The other mechanism estimates external local contrast by using inverse filtering. These two factors are combined by a ‘restoration’ mechanism so that the first mechanism affects the perception of low contrast and the latter that of high contrast stimuli. The behaviour of the model was tested against experimental results obtained with normal human observers. At low contrast levels, contrast matching curves were similar in shape to the detection threshold curves both as a function of the spatial frequency and area of the grating. At high contrast levels, contrast matches became physically correct. The model described the experimental results accurately.
Vergence control across saccades in dyslexic adults
Authors: Moores Elisabeth , Frisby John P. , Buckley David , Reynolds Emma , Fawcett Angela
Published: September 2002

Many aspects of vision have been investigated in developmental dyslexia. Some research suggests deficits in vergence control (e.g. Buzzelli, 1991,Optom. Vision Sci.68, 842–846), although ability to control vergence across saccades has not yet been investigated. We have explored this question indirectly using Enright's (1996Vision Res.36, 307–312.) sequential stereopsis task. The task requires observers to set two adjacent targets (whose textures cannot be resolved simultaneously if either is fixated) to appear equi‐distant. Enright has argued that sequential stereopsis stereoacuity thresholds offer an indication of vergence control across saccades. We report two experiments using a total of 17 dyslexic and 18 control adults. Performance was measured on a sequential stereopsis task and an ordinary ‘simultaneous’ stereopsis task. No significant differences between groups were found. However, whereas practice of the sequential task lowered control group thresholds on the simultaneous task, for the dyslexic group it significantly raised thresholds, suggesting that visual fatigue is especially important in investigations of visual functions in dyslexia. Although the small samples used limit conclusions at this stage, the main sequential stereopsis results suggest that, if Enright is correct, dyslexic adults can show normal vergence control across saccades.
Errors in determining the direction of the visual axis in the presence of defocus
Authors: Atchison David A. , Smith George , Charman W. Neil
Published: September 2002

The visual axis is the ray path from the fixation point to the fovea by way of the nodal points. Such a ray path does not exist in unaccommodated vision when the fixation point does not coincide with the far point of the eye because of induced or natural defocus. Nevertheless an approximation to the visual axis can be obtained by the position of a small pupil close to the cornea for which a bichromatic vernier target appears correctly aligned. When the visual axis is determined, an eye rotation from the usual fixation position must occur, which is reversed upon removing the small pupil. Upon engaging in any experiments for which the visual axis is then used as a reference, there is an error in this reference position. We develop simple paraxial equations to estimate this error. We show that these equations have good accuracy. The error associated with locating the visual axis at the cornea is 0.002 mm per dioptre of defocus, which is small enough to be ignored.
Vergence adaptation and the clinical AC/A ratio
Authors: Rosenfield Mark , Rappon Joseph M. , Carrel Meredith F.
Published: September 2002

The accuracy of the gradient technique for measuring the clinical accommodative convergence to accommodation (AC/A) ratio is dependent upon obtaining veridical heterophoria measurements. However, previous studies have demonstrated that the sustained output of slow fusional vergence, which may take several minutes or even hours to decay, can bias heterophoria assessment. In the clinical setting, it is usual to estimate the AC/A ratio after just a few seconds of dissociation. This study investigated whether the slow fusional vergence response alters this crosslink ratio by comparing values of AC/A measured both before and immediately after a 1‐hr period of continuous monocular occlusion. Sustained occlusion produced a significant change in near heterophoria in 10 out of the 21 subjects examined, but no significant change in AC/A was observed in either the adapting or non‐adapting subgroups. Accordingly, while the sustained output of slow fusional vergence will influence clinical measurements of heterophoria, its presence does not alter the stimulus AC/A ratio significantly.
Characteristics of a paediatric low vision population in a private eye hospital in India
Authors: Gothwal Vijaya K. , Herse Peter
Published: September 2002

While private hospitals provide an important access point for low vision services for children in urban India, little is known about this service delivery route. A cross sectional survey was done of consecutive records of 220 children presenting at a newly opened paediatric low vision centre in a private eye hospital in Hyderabad. On presentation, 49% of the children were classified as moderately visually impaired, 31% were severely visually impaired and 20% were blind. The four major causes of visual impairment were the hereditary/genetic conditions of congenital glaucoma, hereditary macular degeneration, retinitis pigmentosa and albinism. Approach magnification was sufficient for required near tasks in all pre‐school children and about 50% of school children. Provision of a distance refraction decreased the prevalence of severe visual impairment and blindness by 31%. The most commonly prescribed low vision devices were spectacles indicating a key role for optometry in the management of visual impairment in Indian children. Establishment of low vision clinics in existing Indian eye hospitals using associated optometric staff would be a cost effective method to minimise visual impairment in Indian children.
Spatial location studies on the chemical composition of human tear ferns
Authors: Pearce E. Ian , Tomlinson Alan
Published: September 2002

Tear ferns are the patterns formed when tears are allowed to dry on a clean smooth surface. The patterns have been categorised according to confluence of pattern,with less confluent ferns indicative of tear film abnormalities. Little is known about the mechanism that gives rise to this phenomenon. Previous work has concentrated on correlation of alterations in tear film composition on the ferning phenomenon. The present study takes a new approach by analysing the locations of chemical elements in the fern to understand how the ferns form. By means of SEM coupled with EDXA, Na, K and Cl were detected within the fern. Sulphur, indicative of the presence of macromolecules such as mucins and proteins, was only found at the very periphery of the dry tear drop. The results suggest that macromolecules do not play a direct role in the formation of the ferns. A model is put forward to explain the observation whereby proteins and mucins are precipitated selectively by increasing salt concentration at the drop margin.
Oral and silent reading performance with macular degeneration
Authors: Lovie‐Kitchin Jan E. , Bowers Alex R. , Woods Russell L.
Published: September 2002

Previous studies have shown that reading rate for very large print (6°, 1.86 logMAR character size) is a strong predictor of oral reading rate with low vision devices (LVDs). We investigated whether this would apply using large print sizes more readily available in clinical situations (e.g. 2°, 1.4 logMAR), for subjects with macular degeneration. We assessed rauding rates—reading for understanding. A combination of near word visual acuity and large print reading rate (without LVDs) provided the best prediction of oral rauding rates (with LVDs). However, near word visual acuity alone was almost as good. Similarly, silent rauding rate was predicted best by near word visual acuity alone. We give near visual acuity limits as a clinical guide to expected oral and silent reading performance with LVDs for patients with macular degeneration.
Effects of prediction on timing and dynamics of vergence eye movements
Authors: Yuan Weihong , Semmlow John L. , Munoz Paula
Published: September 2002

Periodic square waves were used to generate predictable vergence eye movement responses. The timing and dynamic characteristics of vergence eye movement responses to predictable and non‐predictable stimuli were compared. Results showed significant changes in timing characteristics along with a highly characteristic anticipatory movement in the early part of predictable vergence responses. This phenomenon is similar to that seen in saccadic eye movements and appears to influence the timing and dynamics of the subsequent vergence response. A model‐based analysis of dynamics showed that the pulse width, pulse gain, and step gain of the motor command signal did not show major differences between predictable and non‐predictable response. However, other model parameters related to the acceleration of the response showed a substantial decrease when the movements were predictive.
Optical Fourier filtering for whole lens assessment of progressive power lenses
Authors: Spiers T. , Hull C. C.
Published: September 2002

Four binary filter designs for use in an optical Fourier filtering set‐up were evaluated when taking quantitative measurements and when qualitatively mapping the power variation of progressive power lenses (PPLs). The binary filters tested were concentric ring, linear grating, grid and “chevron” designs. The chevron filter was considered best for quantitative measurements since it permitted a vernier acuity task to be used for measuring the fringe spacing, significantly reducing errors, and it also gave information on the polarity of the lens power. The linear grating filter was considered best for qualitatively evaluating the power variation. Optical Fourier filtering and a Nidek automatic focimeter were then used to measure the powers in the distance and near portions of five PPLs of differing design. Mean measurement error was 0.04 D with a maximum value of 0.13 D. Good qualitative agreement was found between the iso‐cylinder plots provided by the manufacturer and the Fourier filter fringe patterns for the PPLs indicating that optical Fourier filtering provides the ability to map the power distribution across the entire lens aperture without the need for multiple point measurements. Arguments are presented that demonstrate that it should be possible to derive both iso‐sphere and iso‐cylinder plots from the binary filter patterns.
Spectral filters in low‐vision correction
Authors: Rosenblum Y.Z. , Zak P.P. , Ostrovsky M.A. , Smolyaninova I.L. , Bora E.V. , Dyadina U.V. , Trofimova N.N. , Aliyev A.‐G.D.
Published: September 2002

Coloured filters are used to protect the lens, retina and other ocular tissues against the hazard of light damage and to improve the quality of vision mainly in cases of ocular media opacities.

Four types of yellow, amber and orange filters have been designed as tinted glasses, shields and colour covering of spectacles. They were tested on 15 adult patients with partial cataract and on 80 children with congenital pathology (i.e. macular hypoplasia, albinism, aphakia after congenital cataract). The majority of the children had nystagmus. The filters with particular spectral characteristics provide reduction of light intensity in the light‐damaging range by at least a factor of five. Optimal filters were selected by examination of visual acuity, contrast frequency sensitivity, glare sensitivity and subjective selection by the patients. The effects of filters were: 11–43% increase in corrected visual acuity, 27–34% increase in contrast sensitivity function (CSF) for all frequencies and a marked reduction in glare sensitivity. All patients reported subjective improvement including reduction of photophobia, eye‐strain and eye discomfort. It is concluded that coloured filters are able to contribute substantially to rehabilitation of low‐vision patients.
Heterozygous α
2A
-adrenergic receptor mice unveil unique therapeutic benefits of partial agonists
Authors: Tan Christopher M. , Wilson Matthew H. , MacMillan Leigh B. , Kobilka Brian K. , Limbird Lee E.
Published: September 2002

Genetic manipulation of the α
2A
-adrenergic receptor (α
2A
-AR) in mice has revealed the role of this subtype in numerous responses, including agonist-induced hypotension and sedation. Unexpectedly, α
2
-agonist treatment of mice heterozygous for the α
2A
-AR (α

2A

-AR
+/−
) lowers blood pressure without sedation, indicating that more than 50% of α
2A
-AR must be activated to evoke sedation. We postulated that partial activation of α
2A
-AR in wild-type α

2A

-AR
+/+
animals could be achieved with partial agonists, agents with variable ability to couple receptor occupancy to effector activation, and might elicit one versus another pharmacological response.
In vitro
assays reveal that moxonidine is a partial agonist at α
2A
-AR. Although moxonidine was developed to preferentially interact with imidazoline binding sites, it requires the α
2A
-AR to lower blood pressure because we observe no hypotensive response to moxonidine in α
2A
-AR-null (α

2A

-AR
−/−
) mice. Moreover, we observe that moxonidine lowers blood pressure without sedation in wild-type mice, consistent with the above hypothesis regarding partial agonists. Our findings suggest that weak partial agonists can evoke response-selective pathways and might be exploited successfully to achieve α
2A
-AR pharmacotherapy where concomitant sedation is undesirable, i.e., in treatment of depression or attention deficit hyperactivity disorder, in suppression of epileptogenesis, or enhancement of cognition. Furthermore, rigorous physiological and behavioral assessment of mice heterozygous for particular receptors provides a general strategy for elucidation of pathways that might be selectively activated by partial agonists, thus achieving response-specific therapy.
Cytochrome
c
folding pathway: Kinetic native-state hydrogen exchange
Authors: Hoang Linh , Bédard Sabrina , Krishna Mallela M. G. , Lin Yan , Englander S. Walter
Published: September 2002

Native-state hydrogen exchange experiments under EX1 conditions can distinguish partially unfolded intermediates by their formation rates and identify the amide hydrogens exposed and protected in each. Results obtained define a cytochrome
c
intermediate seen only poorly before and place it early on the major unfolding pathway. Four distinct unfolding steps are found to be kinetically ordered in the same pathway sequence inferred before.
M-FISH analysis shows that complex chromosome aberrations induced by α-particle tracks are cumulative products of localized rearrangements
Authors: Anderson Rhona M. , Stevens David L. , Goodhead Dudley T.
Published: September 2002

Complex chromosome aberrations are characteristically induced after exposure to low doses of densely ionizing radiation, but little is understood about their formation. To address this issue, we irradiated human peripheral blood lymphocytes
in vitro
with 0.5 Gy densely ionizing α-particles (mean of 1 α-particle/cell) and analyzed the chromosome aberrations produced by using 24-color multiplex fluorescence
in situ
hybridization (M-FISH). Our data suggest that complex formation is a consequence of direct nuclear α-particle traversal and show that the likely product of illegitimate repair of damage from a single α-particle is a single complex exchange. From an assessment of the “cycle structure” of each complex exchange we predict α-particle-induced damage to be repaired at specific localized sites, and complexes to be formed as cumulative products of this repair.
Topical applications of caffeine or (−)-epigallocatechin gallate (EGCG) inhibit carcinogenesis and selectively increase apoptosis in UVB-induced skin tumors in mice
Authors: Lu Yao-Ping , Lou You-Rong , Xie Jian-Guo , Peng Qing-Yun , Liao Jie , Yang Chung S. , Huang Mou-Tuan , Conney Allan H.
Published: September 2002

SKH-1 hairless mice were irradiated with ultraviolet B (UVB) twice weekly for 20 weeks. These tumor-free mice, which had a high risk of developing skin tumors during the next several months, were then treated topically with caffeine (6.2 μmol) or (−)-epigallocatechin gallate (EGCG; 6.5 μmol) once a day 5 days a week for 18 weeks in the absence of further treatment with UVB. Topical applications of caffeine to these mice decreased the number of nonmalignant and malignant skin tumors per mouse by 44% and 72%, respectively. Topical applications of EGCG decreased the number of nonmalignant and malignant tumors per mouse by 55% and 66%, respectively. Immunohistochemical analysis showed that topical applications of caffeine or EGCG increased apoptosis as measured by the number of caspase 3-positive cells in nonmalignant skin tumors by 87% or 72%, respectively, and in squamous cell carcinomas by 92% or 56%, respectively, but there was no effect on apoptosis in nontumor areas of the epidermis. Topical applications of caffeine or EGCG had a small inhibitory effect on proliferation in nonmalignant tumors as measured by BrdUrd labeling (16–22%), and there was also a similar, but nonsignificant, inhibitory effect on proliferation in malignant tumors. The results suggest a need for further studies to determine whether topical applications of caffeine or EGCG can inhibit sunlight-induced skin cancer in humans.
Multiple thyroid hormone-induced muscle growth and death programs during metamorphosis in
Xenopus
laevis
Authors: Das Biswajit , Schreiber Alexander M. , Huang Haochu , Brown Donald D.
Published: September 2002

Xenopus
laevis
tadpole tails contain fast muscle fibers oriented in chevrons and two pairs of slow muscle “cords” along the length of the tail. When tail resorption is inhibited by a number of different treatments, fast muscle but not the slow cord muscle still is lost, demonstrating that the fast tail muscle is a direct target of the thyroid hormone-induced death program. Expression of a dominant negative form of the thyroid hormone receptor (TRDNα) was restricted to tadpole muscle by means of a muscle-specific promoter. Even though the transgene protects fast tail muscle from thyroid hormone (TH)-induced death, the tail shortens, and the distal muscle chevrons at the tail tip are degraded. This default pathway for muscle death is probably caused by the action of proteolytic enzymes secreted by neighboring fibroblasts. Non-muscle tissues that are sensitive to TH, such as the fibroblasts, are not protected by the transgene when it is expressed solely in muscle. If allowed to develop to metamorphosis, these transgenic animals die at the climax of metamorphosis before tail resorption has begun. Their limbs have very little muscle even though the rest of limb morphology is normal. Thus, fast tail muscle and limb muscle have their own cell autonomous death and growth programs, respectively, that are independent of the fate of the other neighboring cell types. In contrast, death of the slow muscle is controlled by the other cell types of the tail.
Ethyl pyruvate prevents lethality in mice with established lethal sepsis and systemic inflammation
Authors: Ulloa Luis , Ochani Mahendar , Yang Huan , Tanovic Mahira , Halperin Daniel , Yang Runkuan , Czura Christopher J. , Fink Mitchell P. , Tracey Kevin J.
Published: September 2002

Sepsis, a potentially fatal clinical syndrome, is mediated by an early (e.g., tumor necrosis factor and IL-1) and late [e.g., high mobility group B-1 (HMGB1)] proinflammatory cytokine response to infection. Specifically targeting early mediators has not been effective clinically, in part because peak mediator activity often has passed before therapy can be initiated. Late-acting downstream effectors, such as HMGB1, that mediate sepsis lethality may be more relevant therapeutic targets. Ethyl pyruvate (EP) recently was identified as an experimental therapeutic that significantly protects against lethal hemorrhagic shock. Here, we report that EP attenuates lethal systemic inflammation caused by either endotoxemia or sepsis even if treatment begins after the early tumor necrosis factor response. Treatment with EP initiated 24 h after cecal puncture significantly increased survival (vehicle survival = 30% vs. EP survival = 88%,
P
< 0.005). EP treatment significantly reduced circulating levels of HMGB1 in animals with established endotoxemia or sepsis. In macrophage cultures, EP specifically inhibited activation of p38 mitogen-activated protein kinase and NF-κB, two signaling pathways that are critical for cytokine release. This report describes a new strategy to pharmacologically inhibit HMGB1 release with a small molecule that is effective at clinically achievable concentrations. EP now warrants further evaluation as an experimental “rescue” therapeutic for sepsis and other potentially fatal systemic inflammatory disorders.