bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for long‐term changes in base cations in the atmospheric aerosol
Authors: Lee David S. , Espenhahn Sarah E. , Baker Steven
Published: September 2002

Data on concentrations of base cations in air and precipitation are important in calculating the net deposited acidity to ecosystems. Measurements of many trace metals in air have been made at three rural sites in the United Kingdom over the past 20 years. Measurements of the concentrations of the base cations, Ca2+, Mg2+, K+, and Na+ have also been made but not routinely reported nor considered. Some data were missing for Ca2+ for the period between 1985 and 1989, and a large number of “less than” values were present. Despite these uncertainties, these data represent the only long‐term record of their kind in the United Kingdom. An examination of the data revealed that concentrations of non‐sea‐salt Ca2+ in air at these three sites have declined over the past 20 years by between approximately 40 and 60%. Concentrations of Mg2+ and K+ have also declined, and Ca2+, Mg2+, and K+ all show greater variability in earlier years. Concentrations of Na+ in air showed no detectable long‐term trend. These declines of base cations in air are similar to those observed in precipitation elsewhere in North America and mainland Europe, and these trends are similar to declines in emissions of sulphur dioxide. The estimated emissions of calcium from particles deriving from fossil fuel combustion was 21 kt in 1991 and 67 kt in 1970, a decline of 67%. Present‐day rates of non‐sea‐salt Ca2+ deposition to the United Kingdom from wet and dry deposition are estimated to be 86 and 27 kt yr−1, respectively. It is clear that these calculated emissions of Ca from fossil fuel combustion alone cannot adequately explain the estimated deposition nor the decline of concentrations in air. The observed decline of scandium, a “crustal” element, provides good evidence that the decline in industrial particle emissions partly explains the decline in base cations in air. It is necessary to consider the possible implications of the trends revealed in this work as the declines in concentrations of base cations in air, and thus deposition may offset some of the benefits resulting from emissions control of acidic gases, if acid‐sensitive receptors are to show stabilization or recovery.
Volatile organic compound concentration patterns at the New Hendersonville monitoring site in the 1995 Southern Oxidants Study in the Nashville, Tennessee, area
Authors: McClenny William A. , Daughtrey E. Hunter , Adams Jeffrey R. , Oliver Karen D. , Kronmiller Keith G.
Published: September 2002

Ambient gaseous organic compounds were monitored on an hourly basis with an automated gas chromatograph from June 15 to 27, 1995, at the New Hendersonville site near Nashville, Tennessee, as part of the Southern Oxidants Study (SOS). These compounds and their estimated average contributions to the total were as follows: isoprene (2.1 ppbC), methyl vinyl ketone (1.1 ppbC), methacrolein (0.6 ppbC), α‐pinene plus β‐pinene (1.3 ppbC), and those nonmethane hydrocarbons, minus isoprene, monitored routinely in the Photochemical Assessment Monitoring Stations (44.6 ppbC). The sum of n‐aldehydes from butanal through nonanal averaged 12.6 ppbC, where a conservative estimate of artifact n‐aldehydes has been subtracted. Strong diurnal variations in the concentrations of n‐aldehydes and the apparent influence of wind shifts on concentration support the existence of n‐aldehydes at significant levels in the ambient air. The empirical fit to data as developed by Jobson et al. [1994] was the upper bound to the loci of maximum isoprene concentrations as a function of temperature and the diurnal variation of the ratio of methyl vinyl ketone to methacrolein was similar to that in studies by Montzka et al. [1993] in the rural southeastern United States. The α‐pinene and β‐pinene concentrations were proportional and α‐pinene concentrations always less than 2 ppbC. In supplemental experiments at a rural site in North Carolina, the α‐pinene concentrations showed a distinctive diurnal pattern with high nighttime values and low midday values. Patterns of concentration for the anthropogenic hydrocarbons benzene, toluene, and o‐xylene versus wind direction showed the impact of a major toluene emitting source as well as the influence of emissions from the direction of Nashville.
Microwave ozone and lidar aerosol profile observations at Table Mountain, California, following the Pinatubo eruption
Authors: Parrish A. , Connor B. J. , Tsou J. J. , Beyerle G. , McDermid I. S. , Hollandsworth S. M.
Published: September 2002

Ozone profiles measured with a ground‐based microwave instrument in years from 1989 through 1992 at latitude 34°N. were searched for effects arising from the eruption of Mount Pinatubo in 1991. Between 20 and 24 km, ozone values after November 1991 were systematically less than in earlier years, and the deviation generally grew with time through May 1992. The minimum was 11 to 15% below values in earlier years, and occurred later than minima observed with ozonesondes at higher latitudes or predicted by some models. Although there was a steady increase in ozone levels in the 18–10 hPa range between February and May 1992, the highest values were not significantly above normal. Effects of the quasi‐biennial oscillation on ozone values are much smaller than the observed changes. Colocated lidar observations show that stratospheric aerosol levels were steadily elevated from November 1991 through at least March 1992, with some intermittent activity in late August through October 1991. The main aerosol cloud thus arrived at the same time as depletion first appeared.
Airborne retrieval of cirrus cloud optical and microphysical properties using Airborne Remote Earth Sensing System 5.1–5.3 and 3.7‐μm channel data
Authors: Ou S. C. , Liou K. N. , Yang P. , Rolland P. , Caudill T. R. , Lisowski J. , Morrison B.
Published: September 2002

We present an airborne retrieval algorithm to infer cirrus cloud temperature, optical depth, and mean effective sizes using the Airborne Remote Earth Sensing System (ARES) hyperspectral spectrometer data for the 5.1–5.3 and 3.7 μm channels. The algorithm, development and the selection of the channels are based on the principle and parameterization of radiative transfer involving cirrus clouds and the associated atmospheric and surface properties. It has been applied to a selected case of the ARES data collected over the western Boston area on September 16, 1995. Validation of the retrieved parameters was carried out using the collocated and coincident ground‐based 8.6‐mm radar data and ice crystal size distribution measurements obtained from the 2D‐P probe on board the high‐altitude reconnaissance platform (HARP). We show that the retrieved cirrus cloud temperature, mean effective ice crystal size, and optical depth match closely with those derived from the observations.
An overview of the University of Washington airborne measurements and results from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)
Authors: Hobbs Peter V.
Published: September 2002

During the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) conducted off the East Coast of the United States in July 1996, the University of Washington research aircraft facility was used to obtain comprehensive in situ and remote sensing measurements of the physical and chemical nature of the aerosol and its effects on direct radiative forcing. This paper describes the airborne instrumentation used for this purpose, the sampling strategy, the times and locations of the 18 research flights, and a summary of the highlights of the results obtained to date.
Influence of air mass history on black carbon concentrations and regional climate forcing in southeastern United States
Authors: Bahrmann C. P. , Saxena V. K.
Published: September 2002

Atmospheric black carbon (BC) mass concentrations in the southeastern United States have been measured at a regionally representative site near Mount Mitchell, North Carolina (35°44′05″N, 82°17′15″W, 2038 m elevation), the highest peak in the eastern United States, during a 9 month period from June to October 1996 and March to June 1997. BC concentrations are measured by an aethalometer, which operates by measuring the attenuation of light through a sample. All measured BC concentrations are reported in terms of air mass histories determined from back trajectory analysis using the Hybrid Single‐Particle Lagrangian Integrated Trajectory (HY‐SPLIT) model. Air masses influencing the site have been classified as polluted, marine, and continental according to SOx and NOx. emission inventories. The average BC mass concentrations for each sector are 216.6±47.8 ng m−3 for polluted air masses, 65.6±23.5 ng m−3 for marine air masses, and 169.9±50.6 ng m−3 for continental air masses. A positive relationship between cloud condensation nuclei and BC concentrations suggest at times the BC measured at the site may be internally mixed. The average BC concentration found in cloud water is 74.2 μg kg−1. Derived BC to sulfate mass ratios ranged from 0.01 to 0.06.
A simple analytical model of aerosol properties with account for hygroscopic growth: 2. Scattering and absorption coefficients
Authors: Khvorostyanov Vitaly I. , Curry Judith A.
Published: September 2002

A new microphysical model of aerosol size spectra accounting for hygroscopic growth is used to calculate the aerosol scattering and absorption coefficients of solar and longwave radiation. Dependence of the extinction coefficient is explored theoretically, starting from theJunge[1963] power spectra of the dry aerosol and the Kohler equation [Khvorostyanov and Curry, this issue]. It is shown that the general dependence of the aerosol scattering and absorption coefficients on λ andHcan be presented in the form σ∼λ−γ(1 −H)R. This model explains both the empirical angstrom wavelength law andKasten[1969]Hanel[1976] humidity law and identifies a functional relationship between them. The empirical coefficients of these laws are related to the aerosol microstructure and to each other by a very simple relationship. An explanation is offered for the spectral behavior of the scattering coefficient and its variation with relative humidity for various types of atmospheric hazes. It is shown that at very high humidities a dense haze with visibility less than 1 km may form under subsaturated conditions and without activated droplets. Application of this model to the longwave spectrum allows us to explain quantitatively the negative temperature dependence of atmospheric absorption in the atmospheric window without depending on the presence of water vapor dimers. Recommendations for aerosol optical and microphysical measurements are given. This simple model can be used as a tool in remote sensing for evaluation of aerosol scattering and absorption optical thicknesses and for parameterization of aerosol optical properties in general circulation and cloud models.
Volatile halogenated hydrocarbons over the western Pacific between 43°and 4°N
Authors: Quack Birgit , Suess Erwin
Published: September 2002

A spectrum of halogenated hydrocarbon compounds in marine air masses were surveyed over an area in the western Pacific between 43°N, 150°E and 4°N, 113°E in September 1994. The ship's track between northern Japan and Singapore traversed three climatic zones of the northern hemisphere. Recently polluted air, clean marine air derived from the central Pacific Ocean from different latitudes, and marine air from the Indonesian archipelago were collected. Tetrachloroethene and trichloroethene of anthropogenic origin, brominated halocarbons as tribromomethane, dibromochloromethane and bromodichloromethane of anthropogenic and natural sources, and other trace gases were measured in the air samples. Very sparse data on the distribution of these compounds exist for the western Pacific atmosphere. The distribution patterns of the compounds were related to synoptic‐scale meteorology, spatial conditions, and origin of the air masses. Anthropogenic and natural sources for both chlorinated and brominated substances were identified. Tetrachloroethene and trichloroethene concentrations and their ratios identify anthropogenic sources. Their mixing ratios were quite low compared to previously published data. They are in agreement with expected low concentrations of photochemically active substances during autumn, with an overall decrease in concentrations toward lower latitudes, and with a decrease of emissions during recent years. Strong evidence for a natural source of trichloroethene was discovered in the tropical region. The concentrations of naturally released brominated species were high compared to other measurements over the Pacific. Gradients toward the coasts and elevated concentrations in air masses influenced by coastal emissions point to significant coastal sources of these compounds. The trace gas composition of anthropogenic and natural compounds clearly identified the air masses which were traversed during the cruise.
Loss of volatile acid species from upper firn layers at Vostok, Antarctica
Authors: Wagnon P. , Delmas R. J. , Legrand M.
Published: September 2002

Significant natural artifacts in ice chemical records have been pointed out in recent preliminary glaciochemical studies carried out in central Antarctic areas with very low snow accumulation rates (generally less than 5 g cm−2 yr−1). Several deep drilling operations are underway in these regions for long‐term paleoclimatic reconstructions. A detailed glaciochemical study has been carried out at Vostok Station in order to investigate post deposition changes of ion concentrations in the snow and firn layers. The results show that, in general, concentration profiles of species such as Cl, F, and NO3, partly deposited as gases, exhibit a rapid decrease in the first few meters, indicating that a fraction, sometimes major, of these compounds is expelled back in the atmosphere after deposition. Some redeposition process of the gases is likely in the upper firn layers. Surprisingly, a similar effect is found for methanesulfonate (MS), suggesting that this compound could have a gaseous component in central Antarctic regions. The data also show that Cl, F, NO3, and MSA may be slowly but significantly displaced in the firn layers by high sulfuric acid levels of volcanic origin. The drastic changes observed in the surface snow layers may severely question current interpretations of certain chemical data recovered in these areas and point out an urgent need for new field and laboratory experiments on the air‐to‐ice transfer processes prevailing under central Antarctic conditions.
MHD simulations of Io's interaction with the plasma torus
Authors: Linker Jon A. , Khurana Krishan K. , Kivelson Margaret G. , Walker Raymond J.
Published: September 2002

We compare results from magnetohydrodynamic computations of Io's interaction with the plasma torus with observations from the Galileo flyby. Both conducting and intrinsically magnetized models of Io are considered. Both models can reproduce many observed features of the interaction, including a high plasma density, a low plasma temperature, and a significant depression in magnetic field magnitude in Io's wake. The high plasma density in the wake is produced by ion pickup and concomitant slowing of the flow and is not of ionospheric origin. The models also show important quantitative differences with the data. In particular, neither model reproduces large‐scale structure on the flanks of the geometric wake. Neither model can be ruled out at the present time, but intrinsically magnetized models most easily match the magnitude of the maximum observed magnetic field depression in the wake. Comparison of results with future Galileo flybys past Io (planned for 1999) may help to clarify whether Io is magnetized.
A comparison of different polarization schemes for the radar sensing of precipitation
Authors: Torlaschi Enrico , Holt Anthony R.
Published: September 2002

The equations of the radar covariances and cross covariances for linear vertical and horizontal polarization, slant linear +45° and −45° polarization, and left‐hand and right‐hand circular polarization are presented for a model medium containing spheroidal particles.This model takes into account the distribution of canting angles but assumes the uniformity of the distribution function along the propagation path. Assuming the particles to be locally equioriented, equations for the intrinsic differential reflectivity and the mean canting angle are derived. Furthermore, for particles having the same orientations throughout the region of precipitation, the total differential phase shift is obtained. Reflectivity and depolarization ratios are also considered. A comparison of the three polarization schemes from a theoretical point of view is made and illustrated with data from the DLR C band Doppler and polarimetric weather radar. Since the DLR radar did not record the magnitude of the covariances and cross covariances, the comparison is only partially complete. The data confirm the theoretical prediction that depolarization is stronger in circular and slant linear polarization than in linear horizontal/vertical polarization.
Some statistical properties of power averages for lognormal samples
Authors: Jensen Jerry L.
Published: September 2002

Power averages are often used to estimate the effective permeability of a region based on sample measurements. Since the average is computed from a limited number of samples, it may suffer bias and sampling variation. Expressions for bias and sampling variation are derived here for averages having any exponent value between +1 (arithmetic average) and −1 (harmonic average). The derivations assume independent, lognormally distributed samples. The expressions agree with known results for the arithmetic, geometric, and harmonic averages. Estimator bias is generally smaller than 15% for common levels of permeability variability and sample numbers. Sampling variability, however, may be a considerable fraction of the true mean. If sampling schemes aim to collect sufficient data to keep the harmonic average within acceptable tolerances, other averages will meet or better that tolerance.
A low‐dimensional model for concentration‐discharge dynamics in groundwater stream systems
Authors: Duffy Christopher J. , Cusumano Joseph
Published: September 2002

In this paper we investigate the physical basis and validity of a dynamical model for environmental tracer response for a groundwater‐dominated stream reach or small catchments. The dynamical model is formed by volume averaging of the local equations of saturated flow and solute transport. The approach interprets the empirical concentration‐discharge C‐Q as a pair of integrated state variables from an underlying state space (or phase space) for the hillslope or catchment response. The inputs represent episodic, seasonal, and random recharge rate and concentration time series. A closed form solution is found for constant inputs. Results are compared with numerical solutions of the governing partial differential equations, and agreement is found for a full range of initial states and levels of forcing. For pulse‐type or piecewise constant recharge events, the phase plane trajectories for C‐Q are shown to exhibit looping behavior, without the need for an assumption of hysteresis in the model. The orientation and looping direction of these solutions are shown to be controlled by the dimensionless ratio of solute residence time to hydraulic relaxation time and the relative phase lag between recharge and recharge concentration. The closed form solution is extended to the case of piecewise constant, random, input sequences resulting in a “random map” for C‐Q. An application is presented for seasonal storage and flushing of SO−4 in runoff for a small catchment in central Pennsylvania.
Practical Scheffé‐type credibility intervals for variables of a groundwater model
Authors: Cooley Richard L.
Published: September 2002

Simultaneous Scheffé‐type credibility intervals (the Bayesian version of confidence intervals) for variables of a groundwater flow model calibrated using a Bayesian maximum a posteriori procedure were derived by Cooley [1993b]. It was assumed that variances reflecting the expected differences between observed and model‐computed quantities used to calibrate the model are known, whereas they would often be unknown for an actual model. In this study the variances are regarded as unknown, and variance variability from observation to observation is approximated by grouping the data so that each group is characterized by a uniform variance. The credibility intervals are calculated from the posterior distribution, which was developed by considering each group variance to be a random variable about which nothing is known a priori, then eliminating it by integration. Numerical experiments using two test problems illustrate some characteristics of the credibility intervals. Nonlinearity of the statistical model greatly affected some of the credibility intervals, indicating that credibility intervals computed using the standard linear model approximation may often be inadequate to characterize uncertainty for actual field problems. The parameter characterizing the probability level for the credibility intervals was, however, accurately computed using a linear model approximation, as compared with values calculated using second‐order and fully nonlinear formulations. This allows the credibility intervals to be computed very efficiently.
Study blazing new trails into effects of aviation and rocket exhaust in the atmosphere
Authors: Ross Martin N. , Friedl Randall R. , Anderson Donald E. , Ash Gary , Berman Michael R. , Gandrud Bruce , Rawlins Wilson T. , Richard Erik C. , Tuck Adrian F.
Published: September 2002

A new study may help resolve uncertainties in the impact of aviation and rocket exhaust on the atmosphere. Results of the project are expected to serve the aviation and rocket communities in their propulsion system choices and fleet operations in the 21st century. The study, known as the Atmospheric Chemistry of Combustion Emissions near the Tropopause (ACCENT) project, follows the lead of two other programs motivated by continuing concern over the impact such emissions are having on upper troposphere and lower stratosphere (UT/LS) ozone and climate. ACCENT in effect combines those two programs, one of which concerns aviation, the other rockets.
Pharmacological analysis for mechanisms of GPI‐80 release from tumour necrosis factor‐α‐stimulated human neutrophils
Authors: Nitto Takeaki , Araki Yoshihiko , Takeda Yuji , Sendo Fujiro
Published: September 2002

GPI‐80, a glycosylphosphatidylinositol (GPI)‐anchored protein initially identified on human neutrophils, plays a role(s) in the regulation of β2 integrin function. Previous studies have shown that GPI‐80 is sublocated in secretory vesicles. It is also found in soluble form in the synovial fluid of rheumatoid arthritis patients, and in the culture supernatant of formyl‐methionyl‐leucyl‐phenylalanine‐stimulated neutrophils. To understand the behaviour of GPI‐80 under conditions of stimulation, we investigated the effects of tumour necrosis factor (TNF)‐α on its expression and release. We also probed the mechanism of its release with various pharmacologic tools.

TNF‐α induced the release of GPI‐80 from human neutrophils in a concentration‐ and time‐dependent manner (in the range of 1–100 u ml−1 and 30–120 min, respectively), but did not affect surface GPI‐80 levels.

Cytochalasin B, genistein, and SB203580 but not PD98059 inhibited TNF‐α‐stimulated GPI‐80 release and neutrophil adherence at the same concentration. In addition, TNF‐α‐induced GPI‐80 release was inhibited by blocking monoclonal antibodies specific to components of Mac‐1 (CD11b and CD18).

Antioxidants (pyrrolidine dithiocarbamate and N‐acetyl‐L‐cysteine) inhibited GPI‐80 release by TNF‐α stimulation, but superoxide dismutase did not. Antioxidants but not superoxide dismutase reduced an intracellular oxidation state.

These findings indicate that TNF‐α‐stimulated GPI‐80 release from human neutrophils depends upon adherence via β2 integrins. They also suggest that cytochalasin B, genistein, and SB203580 inhibit GPI‐80 release by suppressing signals for cell adherence, rather than by a direct effect on its secretion. Finally, we suggest that GPI‐80 release involves an intracellular change in a redox state.

British Journal of Pharmacology (2002) 137, 353–360. doi:10.1038/sj.bjp.0704860
Oral single high‐dose aspirin results in a long‐lived inhibition of anodal current‐induced vasodilatation
Authors: Durand S , Fromy B , Koïtka A , Tartas M , Saumet J L , Abraham P
Published: September 2002

Acetyl salicyclic acid (aspirin) irreversibly blocks cyclo‐oxygenase (COX). This effect is short‐lived in endothelial or smooth muscle cells due to resynthesis but long‐lived in platelets devoid of synthesis ability. Aspirin blocks the anodal current‐induced vasodilatation, suggesting participation by prostaglandin (PG). We analysed the time course of the effect of aspirin as an indirect indicator of the origin of the PG possibly involved in anodal current‐induced vasodilatation.

In healthy volunteers, vasodilatation, estimated from the peak cutaneous vascular conductance (CVCpeak), was recorded in the forearm during and in the 20 min following 5 min, 0.10 mA transcutaneous anodal current application, using deionized water as a vehicle. CVCpeak was normalized to 44°C heat‐induced maximal vasodilatation and expressed in per cent values. Experiments were performed before and at 2 and 10 h, 3, 7, 10 and 14 days after blinded 1‐g aspirin or placebo treatment.

CVCpeak (mean±s.d.mean) after aspirin vs placebo was 13.6±14.5 vs 65.0±32.1 (P<0.05) 14.7±4.2 vs 87.5±31.9 (P<0.05), 18.1±10.2 vs 71.6±26.8 (P<0.05), 42.5±23.4 vs 73.3±26.8 (non significant, NS), 60.2±24.3 vs 75.2±26.9 (NS), 52.1±18.5 vs 67.9±32.1 (NS) at 2 and 10 h and at days 3, 7, 10 and 14 respectively.

Aspirin inhibition of anodal current‐induced vasodilatation persists long after endothelial and smooth muscle cyclo‐oxygenases are assumed to be restored. This suggests that the PG involved in this response are not endothelial‐ or smooth muscle‐derived. The underlying mechanism of this unexpected long‐lived inhibition of vasodilatation by single high dose aspirin remains to be studied.

British Journal of Pharmacology (2002) 137, 384–390. doi:10.1038/sj.bjp.0704868
The effect of age on the light scattering characteristics of the eye
Authors: Hennelly M. L. , Barbur J. L. , Edgar D. F. , Woodward E. G.
Published: September 2002

The rising mean age of our population has increased the need for understanding the physiologic consequences of ageing on visual function. Changes due to age were evaluated using a new scatter test implemented on theP_SCAN 100 pupillometer apparatus (Barbur, 1991). The test yields the full scatter function of the eye and also permits simultaneous measurement of pupil size (Barbur et al., 1995). In addition, contrast sensitivity was measured using sine wave gratings. The 28 subjects had a spherical refractive error between +0.50 DS and −0.25 DS, and astigmatism of less than −0.50 DC, V.A. of at least 6/6, and were ophthalmologically normal. To facilitate statistical analysis, subjects were classified into five groups according to age. For younger subjects (under 45 years),k′, the integrated straylight parameter, varied little with age. For this group,k′ ranged from 4.9 to 8.1. For subjects aged over 45 years,k′ increased with age, ranging from 10.7 to 19.7. One way analysis of variance showed Group 5 (60 year olds) to have significantly greaterk′ than 20, 30, 40 and 50 year olds (P=0.000). A slight downward shift in the contrast sensitivity function was seen over the age of 45. Significant differences between older and younger subjects were found at spatial frequencies of 3, and 10 cpd (P=0.081,P=0.002, respectively). Pupil diameter was found to reduce with age, but there was no significant difference between groups. Therefore, above 45 years, the ageing eye reveals a more rapid increase in forward scatter, and a reduction in contrast sensitivity, despite apparently good visual acuity.
Reliability of and comparisons among three variations of the alternating cover test
Authors: Rainey Bill B. , Schroeder Tracy L. , Goss David A. , Grosvenor Theodore P.
Published: September 2002

One of the most commonly used methods for measuring heterophoria is the alternating cover test. Differences in specific procedures and observational criteria used by examiners may result in different measurements of heterophoria on the same patient. This study evaluated the inter‐examiner reliability of three different cover test techniques: the estimated cover test, the prism neutralized objective cover test, and the prism neutralized subjective cover test. Two examiners performed each technique on each of 72 subjects. Reliability was assessed using correlational methods and mean difference calculations. Although there were some inter‐examiner differences for the different techniques, all of these differences were within previously determined minimum detectable eye movement ranges. Therefore, when used by experienced clinicians, each of these techniques appears to be a reliable method of heterophoria determination, and their results are comparable.
Comparison of the tolerability and efficacy of unit‐dose, preservative‐free topical ocular anaesthetics
Authors: Lawrenson J. G. , Edgar D. F. , Tanna G.K. , Gudgeon A.C.
Published: September 2002

Several topical ocular local anaesthetics are available in preservative‐free unit‐dose applicators. There is little comparative data as to the efficacy and tolerability of these drugs. The purpose of this study was to compare the tolerability, and the depth and duration of corneal anaesthesia following instillation of one drop of 0.4% oxybuprocaine (benoxinate), 0.5% amethocaine, or 0.5% proxymetacaine. The tolerability of each anaesthetic was assessed using a linear ten point arbitrary comfort scale. A group of 14 healthy male subjects, with a wide variation in iris pigment levels, participated in the study (mean age 26.6 years, range 18–40 years). Corneal sensitivity was measured using a slit‐lamp mounted Cochet–Bonnet aesthesiometer prior to instillation, and at 1, 2, 5, 10, 15, 20 and 30 min after instillation, and continued if necessary until corneal sensitivity had returned to pre‐instillation levels. For each anaesthetic, complete anaesthesia occurred within 1 min of instillation and a return to baseline sensitivity levels occurred by 45 min. No significant difference in anaesthesia was found between the drugs at each time point. Tolerability profiles indicated that proxymetacaine was significantly better tolerated than either amethocaine (p<0.01) or oxybuprocaine (benoxinate) (p<0.001). There was considerable inter‐subject variability in the duration of anaesthesia, and practitioners should be alert to this when allowing patients to leave the practice following the production of corneal anaesthesia. There seems little to choose clinically between the three active agents as regards clinical effectiveness. Proxymetacaine was significantly better tolerated than either amethocaine or oxybuprocaine.
Assessment of a new through‐the‐eyelid technique for ‘A’ scan ultrasound ocular axial length measurement
Authors: Laws Fiona , Laws David , Wood Ivan , Clark David
Published: September 2002

This study evaluated the repeatability both within one session and between two sessions of a new technique of axial length measurement using ‘A’ scan ultrasound through the eyelids. The validity of the technique was assessed by comparing the results to those taken through the cornea. The new technique was very reliable, the mean difference between two readings at the first visit being 0.01 mm and between the two visits being 0.01 mm with 95% of differences between two readings in both cases being less than two standard deviations. The axial length measurements through the lid were a mean of 0.05 mm longer than the corneal measurements. The standard deviation of the difference between the two forms of measurement was 0.16 mm and 95% of axial length readings through the eyelid were within two standard deviations (±=0.32 mm) of the corneal measurement. Providing strict criteria are applied to the quality of the ‘A’ scan images we believe that satisfactory axial length values may be obtained using this technique.
An optical explanation of the entoptic phenomenon of ‘clouds’ in posterior vitreous detachment
Authors: Serpetopoulos Christos N. , Korakitis Romylos A.
Published: September 2002

The purpose of this work is to investigate in detail the optics of the shadow cast by vitreous opacities and its effects in the perception of related entoptic phenomena. The optics of the eclipse has been used as a model. The various parameters affecting the shadow, i.e. the diameter of the opacity, its distance from the retina and the overall distance between the pupillary plane and the retina, have been taken into account in the calculations. A mathematical function has been derived and curves defining the density of the penumbra have been plotted for various distances of an opacity from the retina. An area of uniform partial illumination of the retina behind the opacity has been defined, outside of which the density of the penumbra falls rapidly. It is concluded that the sensation of ‘cloud’ or ‘smoke’ reported by the patient stems from this uniform area of penumbra behind the opacity, whose extent depends on the above mentioned parameters. Thus, the optics of the eclipse explains this entoptic phenomenon. Of course, ‘clouds’ can also be due to semi‐transparent vitreous floaters.
Kinematics of eye movement
Authors: Bolina Oscar , Monteiro L.H.A.
Published: September 2002

In a simplified fashion, the motion of the eyeball in its orbit consists of rotations around a fixed point. Therefore, this motion can be described in terms of Euler's angles of rigid body dynamics. However, there is a physiological constraint in the motion of the eye which reduces to two its degrees of freedom, so that one of Euler's angles is not an independent variable. This paper reviews the basic features of the kinematics of the eye and the laws governing its motion.
The ageing effect on the central posterior corneal radius
Authors: Lam Andrew K. C. , Douthwaite William A.
Published: September 2002

The posterior corneal radii along the vertical and horizontal meridians were measured using the Purkinje image technique. Two‐hundred and forty subjects were recruited and divided into four different age groups (mean age of 20, 33, 41 and 50 years, respectively). Male and female subjects were nearly equally distributed in each group. A significant correlation was found between the anterior and posterior corneas, along both the vertical (r=0.83, P<0.01) and horizontal (r=0.89, P<0.01) meridians. Ageing has a significant effect on the horizontal meridian but not on the vertical meridian. The radii reduced with age and this phenomenon applied to both the anterior and posterior corneas, gives rise to a more spherical cornea in advancing age. The posterior cornea has a surface power around 13% of the anterior corneal surface, which indicates that the use of keratometer index 1.3375 is valid in estimating the total corneal power from the anterior corneal radius. More information about the anterior and posterior corneas could be useful in the proposal of a four‐surface schematic eye.
Improving the reliability of visual acuity measures in young children
Authors: McGraw Paul V. , Winn Barry , Gray Lyle S. , Elliott David B.
Published: September 2002

Whilst the methodology of adult letter acuity measurement has been substantially refined over the last two decades, relatively little development has occurred in methods for quantifying letter acuity in young children. This study compares a recently developed visual acuity test (Glasgow Acuity Cards), which incorporates several key design features used in adult test charts to improve the sensitivity and reliability of visual acuity measurements. The equivalence of acuity measurements made with Glasgow Acuity Cards were compared with the Bailey–Lovie logMAR chart and Snellen chart in adults, and with traditional Single Letter Acuity and a modified Single Letter Acuity test in children. The test–retest reliability of acuity measurements made with Glasgow Acuity Cards and the Single Letter Acuity tests were also assessed in a large group of visually normal children. In addition, the ability of the pre‐school letter acuity tests to detect differences in acuity between the two eyes, and to detect amblyopia were examined. Ninety‐five percent of vision measurements made with the Bailey–Lovie chart and Glasgow Acuity Cards differ by less than 0.07 log unit. Furthermore, the sensitivity of Glasgow Acuity Cards to detecting changes in acuity longitudinally and inter‐ocular differences in acuity is considerably greater as compared with traditional Single Letter Acuity tests. Improvements in paediatric acuity chart design are important for the effective detection and management of children with amblyopia.
An introduction to analysis of variance (ANOVA) with special reference to data from clinical experiments in optometry
Authors: Armstrong R. A. , Slade S. V. , Eperjesi F.
Published: September 2002

This article is aimed primarily at eye care practitioners who are undertaking advanced clinical research, and who wish to apply analysis of variance (ANOVA) to their data. ANOVA is a data analysis method of great utility and flexibility. This article describes why and how ANOVA was developed, the basic logic which underlies the method and the assumptions that the method makes for it to be validly applied to data from clinical experiments in optometry. The application of the method to the analysis of a simple data set is then described. In addition, the methods available for making planned comparisons between treatment means and for making post hoc tests are evaluated. The problem of determining the number of replicates or patients required in a given experimental situation is also discussed.
The three point vernier alignment or acuity test (3Pt VA test): an analysis of variance
Authors: Fang Michelle Shih‐Ming , Enoch Jay M. , Lakshminarayanan Vasudevan , Kim Eunice , Kono Momoyo , Strada Elisabetta , Srinivasan Ranjani
Published: September 2002

A very useful clinical vernier acuity or vernier alignment test has been developed in this and associated laboratories over a span of two decades. We seek to refine further this test, to seek internal inconsistencies and to optimize parameters used in a variety of devices and environments. Vernier testing, and many aspects of this work have been considered by numerous able scientists over a long time period (not reviewed here), but none have encountered conditions faced by this group, particularly in the developing world.

The three point vernier alignment (acuity) threshold test (3Pt VeA test) employed here has broad applications; it can be used as a clinical test of vision status, for triage, and as a reference standard for vision testing (in general). As one example, if sufficient luminance is employed, the test is applicable in the presence of truly dense media disorders, even advanced leucomas, mature cataracts, intraocular bleeds, as well as combinations of these disorders, with or without a window to the retina. Only retinal and centrally‐based neural disorders, eccentricity from fixation, and about 50% of hypermature cataracts affect outcomes. With minor alterations, this test can be employed to assess the visual field. An analysis of variance (ANOVA) was performed on a defined set of parameters, to enable us to understand better the special properties and requirements associated with this test. Results are not significantly altered between ages 10–94 years (not assessed here). Employing settings well above threshold for test spot detection and well separated individual test spots, changes in test spot luminance, or background luminance (or adaptation level), contrast, veiling glare, test spot size, clear and variously degraded images, seem not to affect meaningfully measured outcomes. If an observer can define well a center of gravity for each test spot viewed, he can align the three points with remarkable precision.
The effect of prism adaptation on the response AC/A ratio
Authors: Rainey Bill B.
Published: September 2002

Vergence adaptation, also known as prism adaptation, is a phenomenon in which a patient's heterophoria changes after prolonged viewing through prism. The effect of prism adaptation on the accommodation–convergence relationship, quantified by the AC/A ratio, is not known. Previous studies of AC/A ratio stability and alterability have used only stimulus AC/A ratio calculations, or have measured accommodative responses to only one or two stimuli. The ideal study of AC/A ratio stability and alterability would measure accommodative responses to several accommodative stimuli, and use these along with vergence responses to calculate response AC/A ratios, rather than stimulus AC/A ratios. In addition, the gradient method should be used to avoid any effect of proximal vergence resulting from changes in target distance. This paper describes a project which investigated the effect of vergence (prism) adaptation on the gradient response AC/A ratio, using accommodative responses measured for five different accommodative stimuli. The response AC/A ratio did not significantly change following a period of adaptation to base‐in prism for six of the eight subjects in this study. In addition, the response AC/A ratio did not significantly change following a period of adaptation to base‐out prism for six of the eight subjects.
Aging, perception, and visual short‐term memory for luminance‐defined form
Authors: Sara Mona , Faubert Jocelyn
Published: September 2002

The sensory, perceptual, and visual short‐term memory (VSTM) capacity of young and older observers for processing luminance‐defined shape information was assessed in a series of experiments. The following were assessed: each individual's threshold necessary to detect a square from its background as measured by luminance thresholds; the capacity for making simultaneous size discriminations when compensating for individual differences in sensory input; the capacity for making sequential size discriminations; and the capacity for remembering size differences over time. The results show a selective deficit for simultaneous perceptual processing for older subjects, which cannot be attributed to differences in sensory input, task difficulty, interhemispheric transfer, or VSTM.
Inhibition of hypochlorous acid-induced cellular toxicity by nitrite
Authors: Whiteman Matthew , Hooper D. Craig , Scott Gwen S. , Koprowski Hilary , Halliwell Barry
Published: September 2002

Chronic inflammation results in increased nitrogen monoxide (⋅NO) formation and the accumulation of nitrite (NO

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). Neutrophils stimulated by various inflammatory mediators release myeloperoxidase to produce the cytotoxic agent hypochlorous acid (HOCl). Exposure of chondrocytic SW1353 cells to HOCl resulted in a concentration- and time-dependent loss in viability, ATP, and glutathione levels. Treatment of cells with NO

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but not nitrate (NO

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) substantially decreased HOCl-dependent cellular toxicity even when NO

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was added at low (μM) concentrations. In contrast, NO

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alone (even at 1 mM concentrations) did not affect cell viability or ATP and glutathione levels. These data suggest that NO

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accumulation at chronic inflammatory sites, where both HOCl and ⋅NO are overproduced, may be cytoprotective against damage caused by HOCl. We propose that this is because HOCl is removed by reacting with NO

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to give nitryl chloride (NO
2
Cl), which is less damaging in our cell system.
Inhibition of amyloid-β aggregation and caspase-3 activation by the
Ginkgo biloba
extract EGb761
Authors: Luo Yuan , Smith Julie V. , Paramasivam Vijaykumar , Burdick Adam , Curry Kenneth J. , Buford Justin P. , Khan Ikhlas , Netzer William J. , Xu Huaxi , Butko Peter
Published: September 2002

Standardized extract from the leaves of the
Ginkgo biloba
tree, labeled EGb761, has been used in clinical trials for its beneficial effects on brain functions, particularly in connection with age-related dementias and Alzheimer's disease (AD). Substantial experimental evidence indicates that EGb761 protects against neuronal damage from a variety of insults, but its cellular and molecular mechanisms remain unknown. Using a neuroblastoma cell line stably expressing an AD-associated double mutation, we report that EGb761 inhibits formation of amyloid-β (Aβ) fibrils, which are the diagnostic, and possibly causative, feature of AD. The decreased Aβ fibrillogenesis in the presence of EGb761 was observed both in the conditioned medium of this Aβ-secreting cell line and in solution
in vitro
. In the cells, EGb761 significantly attenuated mitochondrion-initiated apoptosis and decreased the activity of caspase 3, a key enzyme in the apoptosis cell-signaling cascade. These results suggest that (
i
) neuronal damage in AD might be due to two factors: a direct Aβ toxicity and the apoptosis initiated by the mitochondria; and (
ii
) multiple cellular and molecular neuroprotective mechanisms, including attenuation of apoptosis and direct inhibition of Aβ aggregation, underlie the neuroprotective effects of EGb761.
Optimizing grain yields reduces CH
4
emissions from rice paddy fields
Authors: Denier van der Gon H. A. C. , Kropff M. J. , van Breemen N. , Wassmann R. , Lantin R. S. , Aduna E. , Corton T. M. , van Laar H. H.
Published: September 2002

Microbial production in anoxic wetland rice soils is a major source of atmospheric CH
4,
the most important non-CO
2
greenhouse gas. Much higher CH
4
emissions from well managed irrigated rice fields in the wet than in the dry season could not be explained by seasonal differences in temperature. We hypothesized that high CH
4
emissions in the wet season are caused by low grain to biomass ratios. In a screenhouse experiment, removing spikelets to reduce the plants' capacity to store photosynthetically fixed C in grains increased CH
4
emissions, presumably via extra C inputs to the soil. Unfavorable conditions for spikelet formation in the wet season may similarly explain high methane emissions. The observed relationship between reduced grain filling and CH
4
emission provides opportunities to mitigate CH
4
emissions by optimizing rice productivity.