bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term observations of VHF scintillation and total electron content near the crest of the equatorial anomaly in the Indian longitude zone
Authors: Chakraborty S. K. , DasGupta A. , Ray S. , Banerjee S.
Published: September 2002

Ionospheric VHF scintillation (SI ≥ 3 dB and saturated level) and total electron content (TEC) data obtained at Calcutta (subionospheric 21°N, 92.7°E geographic, 27°N dip) and ionosonde data at Kodaikanal ( 10.2°N, 77.5°E geographic, 3.5°N dip) for the period 1977‐1990 have been analysed to show the importance of electrodynamic drift near the magnetic equator in controlling nighttime ionospheric F region ionization and irregularities in the equatorial region. Such long‐term observations extending over a period of more than 13 years are possibly being reported for the first time from a location situated near the equatorial anomaly crest. Frequent and intense VHF scintillations near the equatorial anomaly crest during equinoctial and December solstice months around solar maximum years, have been identified with the equatorial F region irregularities. Simultaneous measurement of TEC at the same location shows that during solar maximum years the high F region ambient ionization is sustained for several hours in the postsunset period, often showing secondary enhancements during equinoctial months. Under solar minimum epoch, when scintillation is sparse, TEC in the above period shows a rapid decrease. At Kodaikanal, situated near the magnetic equator, during the equinoctial and December solstice months of solar maximum years, h/F values rise by more than 100 km in about an hour around sunset. These features are seldom observed during solar minimum epoch. A causative connection among h/F variation near the magnetic equator and the maintenance of high ambient ionization and occurrence of scintillation near the anomaly crest is established. Further, scintillation occurrence during the May‐July months shows a remarkable hysteresis effect with solar activity level.
Extinction pulse and resonance annihilation filter: Two methods for radar target discrimination
Authors: Ruiz Diego P. , Gallego Antolino , Carrión María C.
Published: September 2002

A comparison of the resonance annihilation filter (RAF) method and the extinction pulse (E‐pulse) technique for radar target discrimination is presented in this paper. It is theoretically demonstrated that the RAF synthesized using finite impulse‐response digital filters is a particular forced E‐pulse waveform expanded using impulse‐basis functions. This fact reveals the RAF method to be a very poor technique for discrimination in a noisy environment. Improvement is possible with suitable data windowing equivalent to using E‐pulse waveforms synthesized with continuous and smooth basis functions. Numerical simulations are employed to compare the two techniques when different levels of additive white Gaussian noise are present in the target response. This comparison shows that the use of the Gaussian window originally proposed in the RAF method produces results comparable to rectangular E‐pulses. However, these results can be improved by the introduction of alternative smoothing windows or subsectional‐polynomial E‐pulses.
Stomatal control of transpiration: Examination of Monteith's Formulation of canopy resistance
Authors: Lhomme J.‐P. , Elguero E. , Chehbouni A. , Boulet G.
Published: September 2002

The stomatal response to air humidity has been recently reinterpreted in the sense that stomata seem to respond to the rate of transpiration rather to air humidity per se. Monteith suggested that the relation between canopy stomatal resistance rs and canopy transpiration E can be written as rs/rsn=1/(1 − E/Ex), where rsn is a notional minimum canopy resistance, obtained by extrapolation to zero transpiration, and Ex is a notional maximum transpiration rate, obtained by extrapolation to infinite resistance. The exact significance and possible values of these parameters have not been specified yet. In this study we show that this apparently new relation can be inferred from the common Jarvis‐type models, in which canopy stomatal resistance is expressed in the form of a minimal resistance multiplied by a product of independent stress functions (each one representing the influence of one factor). This is made possible by replacing leaf water potential in the corresponding stress function by its dependence on transpiration and soil water potential. The matching of the two formulations (Monteith and Jarvis) allows one to express the two parameters rsn and Ex in terms of the functions and parameters making up the Jarvis‐type models; rsn appears to depend upon solar radiation and soil water potential: it represents the canopy stomatal resistance when the leaf water potential is equal to the soil water potential, all other conditions being equal. Ex depends upon soil water potential and represents the maximum flux of water which can be extracted from the soil by the canopy.
Instabilities during liquid migration into superheated geothermal reservoirs
Authors: Fitzgerald Shaun D. , Woods Andrew W.
Published: September 2002

We examine the stability of a vaporizing liquid front migrating through a permeable rock. We show that such liquid‐vapor fronts may become unstable if a sufficient fraction of the liquid vaporizes. This instability is a result of the different speed of the fluid on each side of the front. We also identify that short‐wavelength perturbations are stabilized by thermal conduction, while long‐wavelength perturbations are stabilized as a result of the compressibility of the vapor. Furthermore, under conditions typical of geothermal reservoirs, where the pressure is ∼10 atm and the temperature is ∼200°–300°C, we find that if the permeability of the system is smaller than ∼10−15 m 2, then these two stabilizing mechanisms overlap and the system becomes stable to perturbations of any wavelength. We also examine the role of gravity in suppressing the instability of an ascending front and promoting the instability of a descending front. We apply our results to the vapor‐dominated geothermal reservoirs at Larderello, Italy, and the Geysers, California, to predict conditions under which liquid fronts, advancing into superheated vapor, are stable.
Numerical modeling of observed effective flow behavior in unsaturated heterogeneous sands
Authors: Wildenschild D. , Jensen K. H.
Published: September 2002

The concept of effective parameters has been introduced in recent years to represent the spatial variability of natural soils in numerical simulation models. In the present study, effective hydraulic properties of unsaturated flow were investigated for the case of a two‐dimensional heterogeneous laboratory tank. Hydraulic parameter estimates obtained from simple statistical averages, inverse procedures, and a stochastic theory were compared to effective retention and hydraulic conductivity characteristics measured for the whole tank at steady state. The applicability of the effective parameter estimates was investigated by comparing transient flow events monitored in the laboratory tank with simulated results based on those estimates. Capillary suction measurements were simulated reasonably well using several straightforward arithmetic and geometric statistical averaging approaches, whereas most averaging approaches simulated too slow a response in the outflow rate. An alternative approach involving a combination of arithmetic and geometric averaging of the measured values more closely simulated the observed relatively fast changes in outflow rate. Generally, the simulations based on the measurements of effective properties performed quite well, indicating that the fundamental concept of effective parameters may be valid for this type of heterogeneous soil system.
Some properties of currents and mixing in a shallow ice‐covered lake
Authors: Malm Joakim
Published: September 2002

A study on characteristics of currents and mixing in a shallow ice‐covered Russian lake is presented. The current velocity data are separated into four main components, mean velocity, uninodal longitudinal and transverse seiche currents, and “high”‐frequency velocity fluctuations, using digital filters. The analysis of components shows that mean currents are most pronounced in early winter and are of the order of 1–10 mm s−1. All three oscillatory components are, on average, of the same magnitude, 0.1–1 mm s−1, and about the same as mean currents in midwinter, and do not show any pronounced differences during winter. Mean currents increase during the convective period in late winter up to several millimeters per second. Apart from possible local hydrodynamic instability, induced by salt fluxes at the ice and bottom boundaries, and local turbulence near the boundaries in early winter, the vertical mixing in early winter and midwinter in the lake appears to be determined solely by molecular processes.
Horizontal and vertical self‐organization of braided rivers toward a critical state
Authors: Sapozhnikov Victor B. , Foufoula‐Georgiou Efi
Published: September 2002

Self‐organization in an experimental braided river is studied. It is shown that the experimental braided river self‐organizes into a critical state where it shows dynamic scaling; that is, small and large parts of the river evolve statistically identically after proper renormalization of space and time. The dynamic scaling emerges during the process of approaching the critical state which involves self‐adjustment of both profile (vertical self‐organization) and braiding pattern (horizontal self‐organization). The obtained result corroborates the hypothesis suggested by the authors earlier [Sapozhnikov and Foufoula‐Georgiou, 1997] that braided rivers are self‐organized critical systems. The results are also important for understanding and statistically predicting the behavior of natural braided rivers because, owing to external conditions (e.g., sudden streamflow changes), some of them may be driven out of the critical state and therefore may show deviation from dynamic scaling.
Surface water quality management using a multiple‐realization chance constraint method
Authors: Takyi Andrews K. , Lence Barbara J.
Published: September 2002

Traditional chance‐constrained programming (CCP) and simulation‐optimization methods of incorporating input information uncertainty in pollution management models are unsuitable for complex river systems with several critical water quality segments. Using the CCP method, characterization of the joint probability distribution of coefficients of the management model is often difficult because stream information is limited and the model formulation is generally difficult to understand and solve. For the simulation‐optimization method most of the solutions produced are inferior. The multiple realization model, which includes several scenarios of design conditions simultaneously in an optimization model, overcomes such weaknesses by not requiring the joint probability distribution of the stochastic model coefficients and by producing noninferior solutions. Heuristic and neural network techniques are developed to reduce the computational time required to solve the multiple realization model, through identification and utilization of only potentially important stream and water quality information that influence the optimal solution. These techniques are applied to develop trade‐off relationships between waste treatment cost and reliability of achieving dissolved oxygen objectives for an example river basin. Results show that the heuristic technique is computationally efficient when <1000 realizations are included in the model, while the neural network method is suitable when several thousand realizations are needed to adequately represent the stochastic water quality system.
Dispersionless injection simulations explore auroral substorm origins
Authors: Li Xinlin , Baker D. N. , Temerin M. , Reeves G. D. , Belian R. D.
Published: September 2002

The “driving engine” of auroral substorms is rather far out in the magnetotail and then propagates inward, a recent study suggests. The results are based on test particle simulations of dispersionless particle injections and indicate an origin distance of more than 15 Earth radii (RE) away (1 RE = 6380 kilometer). The work is also showing how such dispersionless injections can, in principal, be produced.

Dispersionless particle injection is one of the characteristic features of substorm onset and refers to the sudden appearance of energetic ions and electrons over a broad range of energies (tens to hundreds of keV) in the Earth's magnetosphere. Such injection events are often seen near midnight on satellites in geosynchronous orbit in association with substorm onset.
Ocean management plan includes array of recommendations
Authors: Showstack Randy
Published: September 2002

When U.S. President Bill Clinton and Vice President Al Gore appeared in Monterey, California in June 1998 for a National Oceans Conference, some of the salt water spray from the Pacific Ocean must have clung to them.

As a follow‐up to the conference, the Clinton Administration on September 2 issued an interagency report to help guide federal efforts in establishing a comprehensive ocean policy.The report, which touches upon a number of global issues including the United Nations Convention on the Law of the Sea, contains nearly 150 recommendations.
Outstanding student paper awards
Authors: Anonymous
Published: September 2002

The Space Physics & Aeronomy Section presented seven outstanding student paper awards at the 1999 Spring Meeting in Boston, Massachusetts, last June.

Jerry Goldsteinpresented a paper titled “Simulation and Detection of Plasmaspheric Cavity Modes.” Jerry received a B.S. in physics from Brooklyn College in 1993. He is presently at Dartmouth College working toward completion of his Ph.D. under the direction of Professor Mary Hudson. Before coming to Dartmouth, Jerry participated in theoretical quantum mechanics research at Penn State, and instrumentation development at Brookhaven National Laboratory Jerry's current research is an observational/numerical study of ULF cavity mode resonances in the plasmasphere and outer magnetosphere. Using an MHD wave simulation code that incorporates in situ electron density measurements to specify a background plasma density, Jerry has been examining electric and magnetic field observations made by the Polar and CRRES satellites for evidence of cavity modes. He has also been working on a simple analytical MHD wave model of the magnetospheric cavity, in order to study wave leakage and ionospheric Joule heating effects due to realistic boundary conditions.
Outstanding student paper awards
Authors: Anonymous
Published: September 2002

The Ocean Sciences Section presented three outstanding student paper awards at the 1999 AGU Spring Meeting in Boston, Mass., last June

Susan C. Bates presented a paper titled “The Effect of Subsurface Temperature Variability on the Predictability of Tropical Atlantic SST.” Susan obtained her bachelor of science degree in geology at Duke University while focusing on coastal/barrier island processes. After receiving her degree in 1995, she worked for 2 years as a geologist for an environmental consulting company in Raleigh, North Carolina. She is currently pursuing a master's degree at Texas A&M University under the advisement of Ping Chang. Although her research focuses on statistical analysis of tropical Atlantic SST, she is also interested in the broader topic of the effect of ocean processes on global climate and local/regional weather phenomena.
Augmentation of allergic inflammation in prostanoid IP receptor deficient mice
Authors: Takahashi Yoshimasa , Tokuoka Shota , Masuda Taisei , Hirano Yousuke , Nagao Masafumi , Tanaka Hiroyuki , Inagaki Naoki , Narumiya Shuh , Nagai Hiroichi
Published: September 2002

To evaluate the role of prostaglandin I2 (PGI2) in allergic inflammation, allergic responses in the airway, skin and T cells were studied in mice lacking the receptor for PGI2 (the prostanoid IP receptor) through gene disruption.

Three inhalations of antigen caused an increase in plasma extravasation, leukocyte accumulation and cytokine (interleukin (IL)‐4 and IL‐5) production in the airway of sensitized mice. These airway inflammatory responses were significantly greater in IP receptor deficient mice than in wild‐type mice.

The vascular leakage caused by passive cutaneous anaphylaxis, substance P and 5‐hydroxytryptamine was markedly increased in the skin of IP receptor deficient mice, compared with comparably treated wild‐type mice.

The inhalation of antigen in sensitized mice resulted in increased serum antigen specific IgE, total IgE and IgG levels. The magnitude of the elevations of each immunoglobulin level in IP receptor deficient mice is notably higher than that in wild‐type mice. To elucidate the mechanism of an enhancement of immunoglobulin production, the activity of T cells in sensitized and non‐sensitized mice was studied by means of the production of cytokines. The antigen‐induced IL‐4 production by spleen cells from sensitized IP receptor deficient mice was almost three times greater than that in wild‐type mice. On the contrary, the anti‐CD3 antibody‐induced interferon‐γ production by CD4+ T cells from non‐sensitized IP receptor deficient mice was significantly lower than that in wild‐type mice.

The present data indicate that IP receptor deficiency reinforced an allergic airway and skin inflammation by augmentation of vascular permeability increase and the T helper 2 cell function. These findings suggest a regulatory role of PGI2 in allergic inflammation.

British Journal of Pharmacology (2002) 137, 315–322. doi:10.1038/sj.bjp.0704872
Metformin enhances insulin signalling in insulin‐dependent and ‐independent pathways in insulin resistant muscle cells
Authors: Kumar Naresh , Dey Chinmoy S
Published: September 2002

Metformin lowers blood glucose levels in type 2 diabetic patients. To evaluate the insulin sensitizing action of metformin on skeletal muscle cells, we have used C2C12 skeletal muscle cells differentiated in chronic presence or absence of insulin.

Metformin was added during the last 24 h of differentiation of the C2C12 myotubes. Insulin‐stimulated tyrosine phosphorylation of insulin receptor (IR) and insulin receptor substrate‐1 (IRS‐1) was determined.

Chronic insulin treatment resulted in 60 and 40% reduction in insulin‐stimulated tyrosine phosphorylation of IR and IRS‐1, respectively. Treatment with metformin was able to increase the tyrosine phosphorylation of IR and IRS‐1 by 100 and 90% respectively.

Chronic insulin treatment drastically reduced (45%) insulin‐stimulated phosphatidyl inositol 3‐kinase (PI 3‐kinase) activity. Metformin treatment restored PI 3‐kinase activity in insulin‐resistant myotubes.

Insulin‐stimulated glucose uptake was impaired in chronically insulin‐treated myotubes. Metformin increased basal glucose uptake to significant levels (P<0.05), but metformin did not increase insulin‐stimulated glucose transport.

All the three mitogen‐activated protein kinases (MAPK) were activated by insulin in sensitive myotubes. The activation of p38 MAPK was impaired in resistant myotubes, while ERK and JNK were unaffected. Treatment with metformin enhanced the basal activation levels of p38 in both sensitive and resistant myotubes, but insulin did not further stimulate p38 activation in metformin treated cells.

Treatment of cells with p38 inhibitor, SB203580, blocked insulin‐ and metformin‐stimulated glucose uptake as well as p38 activation.

Since the effect of metformin on glucose uptake corresponded to p38 MAPK activation, this suggests the potential role p38 in glucose uptake.

These data demonstrate the direct insulin sensitizing action of metformin on skeletal muscle cells.

British Journal of Pharmacology (2002) 137, 329–336. doi:10.1038/sj.bjp.0704878
Protective effect of relaxin in cardiac anaphylaxis: involvement of the nitric oxide pathway
Authors: Masini E , Zagli G , Ndisang J F , Solazzo M , Mannaioni P F , Bani D
Published: September 2002

Relaxin (RLX) is a multifunctional hormone best known for its role in pregnancy and parturition, that has been also shown to influence coronary perfusion and mast cell activation through the generation of endogenous nitric oxide (NO). In this study we report on the effects of RLX on the biochemical and mechanical changes of ex vivo perfused hearts isolated from ovalbumin‐sensitized guinea‐pigs induced by challenge with the specific antigen. The possible involvement of NO in the RLX action has been also investigated.

A 30‐min perfusion with RLX (30 ng ml−1) before ovalbumin challenge fully abated the positive chronotropic and inotropic effects evoked by anaphylactic reaction to the antigen. RLX also blunted the short‐term coronary constriction following to antigen challenge. Conversely, perfusion with chemically inactivated RLX had no effect.

The release of histamine in the perfusate and the accumulation of calcium in heart tissue induced by antigen challenge were significantly decreased by RLX, while the amounts of nitrites in the perfusate were significantly increased, as were NO synthase activity and expression and cGMP levels in heart tissue.

These findings indicate that RLX has a protective effect in cardiac anaphylaxis which involves an up‐regulation of the NO biosynthetic pathway.

British Journal of Pharmacology (2002) 137, 337–344. doi:10.1038/sj.bjp.0704879
Interaction of different potassium channels in cardiac repolarization in dog ventricular preparations: role of repolarization reserve
Authors: Biliczki Péter , Virág László , Iost Norbert , Papp Julius Gy , Varró András
Published: September 2002

The aim of this study was to investigate the possible role of the interaction of different potassium channels in dog ventricular muscle, by applying the conventional microelectrode and whole cell patch‐clamp techniques at 37°C.

Complete block of IKr by 1 μM dofetilide lengthened action potential duration (APD) by 45.6±3.6% at 0.2 Hz (n=13). Chromanol 293B applied alone at 10 μM (a concentration which selectively blocks IKs) did not markedly lengthen APD (<7%), but when repolarization had already been prolonged by complete IKr block with 1 μM dofetilide, inhibition of IKs with 10 μM chromanol 293B substantially delayed repolarization by 38.5±8.2% at 0.2 Hz (n=6).

BaCl2, at a concentration of 10 μM which blocks IKl without affecting other currents, lengthened APD by 33.0±3.1% (n=11), but when IKr was blocked with 1 μM dofetilide, 10 μM BaCl2 produced a more excessive rate dependent lengthening in APD, frequently (in three out of seven preparations) initiating early afterdepolarizations.

These findings indicate that if only one type of potassium channels is inhibited in dog ventricular muscle, excessive APD lengthening is not likely to occur. Dog ventricular myocytes seem to repolarize with a strong safety margin (‘repolarization reserve’). However, when this normal ‘repolarization reserve’ is attenuated, otherwise minimal or moderate potassium current inhibition can result in excessive and potentially proarrhythmic prolongation of the ventricular APD. Therefore, application of drugs which are able to block more than one type of potassium channel is probably more hazardous than the use of a specific inhibitor of one given sort of potassium channel, and when simultaneous blockade of several kinds of potassium channel may be presumed, a detailed study is needed to define the determinants of ‘repolarization reserve’.

British Journal of Pharmacology (2002) 137, 361–368. doi:10.1038/sj.bjp.0704881
A novel system for the objective classification of iris colour and its correlation with response to 1% tropicamide
Authors: German Emma J. , Hurst Mark A. , Wood Diana , Gilchrist Jim
Published: September 2002

Iris colour can provide an enormous amount of information about an individual. In addition to changes with pathological conditions, the colour of the iris can be a particularly useful indicator of how well a person will respond to a topically applied ocular drug. Until recently, classification of iris colour has been subjective, ranging from a basic description (‘light’ and ‘dark’) to more detailed grading systems, such as a comparison with preset photographic standards. However, variability within observers and differences in the interpretation between observers can influence the results. Objective techniques, in this respect, possess several advantages. They are able to detect differences in colour that subjective techniques are incapable of and they provide continuous data rather than discrete categories, thus improving the accuracy of drug response predictions. This study assessed iris colour by objective means. Slit‐lamp photographs of various coloured irides were taken under standardised conditions. The slides were then scanned into a computer and the colour analysed using a calibrated software package. To establish the optimum colour parameter to be used for predictions of drug response, several parameters were calculated and compared with the subject response to 1% tropicamide (maximum change in pupil size, time to maximum change and total duration of effect). Many parameters had strong correlations with drug response, but the parameters ‘z’, ‘b’ (the proportion of blue in the image) and ‘y’ (the proportion of yellow in the image) were found to exhibit the highest correlations. They also showed better correlations with drug response than did a current iris colour grading system.
A study of the accuracy of lens measures
Authors: Hilton Owen , Obstfeld Henri
Published: September 2002

The accuracy of 26 aged and three new lens measures was investigated. Instruments were applied to surfaces of known curvature employing the conventional, hand‐held method as well as while rigged on an optical bench. In addition, using the latter method, a controlled amount of surface tilt was introduced. A large inter‐instrument variation in accuracy was encountered. In general, hand‐held lens measures were found to provide equally accurate measurements on convex and concave surfaces, with the exception of the −20 D surface, and inclinations from 0° to 5° did not result in erroneous measurements. Results for inclinations of 15° became unreliable. The different usages of the instrument are discussed.
The infant patient
Authors: McCulloch Daphne L.
Published: September 2002

The infant patient presents a challenge to the optometrist who must structure an examination within the infant's limited capabilities and then manage a rapidly developing visual system. The present paper provides an overview of infant visual development and the visually guided behaviours expected during normal development. Techniques for assessing vision in infant are reviewed and a recommendation is given for the optometric examination of infants. Some important urgencies, emergencies and causes of visual impairment are highlighted.
The influence of cognition and age on accommodation, detection rate and response times when using a car head‐up display (HUD)
Authors: Wolffsohn J. S. , McBrien N. A. , Edgar G. K. , Stout T.
Published: September 2002

Car head‐up displays (HUDs), which portray information in the form of a virtual image reflected off a combiner, allow the viewing of complex information, such as route guidance, without the need for the driver to look away from the road ahead. The cognitive demand required by the HUD task may distract drivers from the outside world scene and cause reaction times to slow. Cognitive capacity also decreases with age. The aim of the present study was to determine the effect of cognitive demand and age on the use of a car HUD. Subjects (young, middle or older age drivers, each groupn=8) performed a HUD‐assisted driving task, with three levels of cognitive demand, whilst accommodation was simultaneously measured using a dynamically recording infra‐red optometer. Response times to, and the detection rate of, changes in both the HUD image and the outside world scene were analysed. Increasing the cognitive demand associated with the HUD image increased over‐accommodation (greatest in the young, 0.34±0.05 D,p<0.001). Response times to and detection of changes in the HUD image and outside world scene were significantly worse with increased cognitive demand. Response times to and detection of changes in the HUD image and outside world scene also increased with age. The implication of the results with respect to car HUD design and safety are discussed.
Imaging in the 21st century
Authors: Charman W. N.
Published: September 2002

Methods which are likely to become increasingly common in the next century for producing images of the eye and related structures are briefly reviewed. Although techniques based on reflected visible light will continue to be of importance, improved versions of methods based on other physical principles will come into increasingly widespread use. Digital image recording will probably play a dominant role and it is concluded that a key feature that will be common to almost all the methods will be their capacity to provide quantitative data on the state of the eye.
Positional acuity in amblyopia: does a perceptual consequence of neural recruitment exist?
Authors: McGraw Paul V. , Winn Barry , Whitaker David , McFadzean Robert
Published: September 2002

Animal models of amblyopia have shown that visual deprivation for even brief periods can result in dramatic changes in cortical architecture. Active neural recruitment mechanisms present the possibility that the non‐deprived eye of amblyopes may show enhanced visual capacity. This idea was tested by measuring a form of positional acuity which we have termed alignment threshold. Three subject groups were examined, adults, visually normal children, and children with amblyopia in which the non‐deprived eye was tested. Alignment thresholds in adults were significantly better (∼0.3 log unit) than the thresholds for visually normal children. No significant difference was found in thresholds between the visually normal children and the non‐deprived eye of the amblyopic children. The results of this study suggest that subjects with unilateral amblyopia do not show enhanced visual alignment performance in their non‐deprived eye.
Intraocular pressure and pulse rate measurements by the OBF tonograph — comparison to reference instruments
Authors: Yang Y. C. , Illango B. , Cook A. , Batterbury M.
Published: September 2002

The purpose of this study was to evaluate the accuracy of intraocular pressure (IOP) and ocular pulse rate (OPR) measurements obtained by the Ocular Blood Flow (OBF) tonograph (OBF Labs, Wiltshire, UK). Measurements of IOP and OPR by the OBF tonograph were compared to those of reference instruments. For IOP evaluation, measurements were obtained on patients with normal and abnormal pressures using the OBF tonograph and the Goldmann applannation tonometer in random alternate order. For the OPR evaluation, measurements were obtained using the OBF tonograph with simultaneous heart rate monitoring by ECG on patients with normal IOP. The validity of the OBF tonograph measurements was quantified in terms of 95% limits of agreement and their relationships to measurements by reference instruments was determined by linear regression analyses. 102 patients were recruited for IOP measurements. Mean IOP obtained by the Goldmann tonometer was 20.7 mmHg (7–42 mmHg, SD 6.98) whilst mean IOP obtained by the OBF tonograph was 20.1 mmHg (8.1–40.2, SD 6.1). Goldmann IOP and OBF tonograph IOP readings were well correlated (r=0.945). Analysis of the difference in IOP measurements between two instruments (tonograph minus Goldmann tonometer) showed the mean bias to be 0.26 mmHg (−7.8 to +6.1 mmHg) and the 95% limits of agreement to be −4.35 to +4.87 mmHg. Agreement between two instruments appeared to be dependent on the IOP; at IOP lower than 20.6 mmHg there was an overall tendency for the tonograph IOP to be higher than Goldmann IOP and vice versa when IOP was above 20.6 mmHg. 47 patients were recruited for OPR and ECG measurements. Mean pulse rates were 74.8 beats per min (mean 43–110) by ECG and 73.9 beats per min (43–110) by tonography. Analysis of the difference in pulse rate between instruments (tonograph OPR minus ECG pulse rate) against the average pulse rate showed the mean bias to be −0.8 beats and the 95% limits of agreement to be between −7 to +5 beats. Ocular pulse rate values obtained by the OBF tonograph were very accurate when compared to ECG pulse rate. This indicates that there is unlikely to be a systematic lag in continuous ocular pulse waveform recording. Intraocular pressure measurements by the OBF tonograph correlated very well with Goldmann readings over a wide range of pressures and should be valid in the clinical setting.
Response of the human visual system to variable illuminant conditions: An analysis of opponent‐colour mechanisms in colour constancy
Authors: Nieves J.L. , Garcı´a‐Beltrán A. , Romero J.
Published: September 2002

Illuminant changes in a scene generally cause displacements in the chromaticity and luminance of the objects of which the scene is composed; however, the visual system is capable of maintaining a constant object colour appearance independently of the illuminant. This is the phenomenon traditionally known as colour constancy. A classical asymmetric colour‐matching experiment is reported to address two aspects of colour constancy: successive colour constancy and the role of opponent mechanisms in it. To this end, colour matches are made with chromatically complex backgrounds under different illuminants and with an equal‐energy light source as standard. The results are analysed in the cone‐excitation space, separately along the L‐2M and S dimensions.Data are presented showing that colour‐vision mechanisms respond differently to illuminant changes when colour constancy is considered at both receptoral and post‐receptoral levels. The L‐ and M‐cones tend to adapt so as to support colour constancy, whereas S‐cones are strongly influenced by the illuminant changes. In addition, the data suggest good approaches to colour constancy linked particularly to the yellow‐blue mechanism.
Accommodation microfluctuations and pupil size during sustained viewing of visual display terminals
Authors: Gray L.S. , Gilmartin B. , Winn B.
Published: September 2002

Accommodation microfluctuations comprise two dominant frequencies; a low frequency component (LFC0.6 Hz) and a high frequency component (1.0 Hz<HFC<2.1 Hz). In the present experiment we examine accommodation microfluctuations and steady‐state pupil responses during sustained viewing of visual display terminals (VDTs). Steady‐state accommodation and pupil responses were measured continuously and simultaneously using a modified Canon Autoref R‐1 infra‐red objective optometer and an Hamamatsu C3160 Perceptscope Video Area Analyser. Measurements were obtained at three time intervals (0, 10 and 20 min) during a 20 min reading task presented on five different displays. With the displays placed at 50 cm, the task was to locate and identify typographical errors in one of five sets of standard text. Five young visually‐normal emmetropic subjects with a mean age of 22.5±3.0 years participated in the study. Two‐way ANOVA revealed no significant variation in the magnitude of the accommodation microfluctuations with either display or task duration, nor was there any significant interaction between these two factors. There was no significant variation in mean pupil diameter with either display or task duration. These measures may have the potential to provide objective information about visual display quality.
Astigmatism
Authors: Harris W.F.
Published: September 2002

The quantitative representation and analysis of astigmatism present difficulties for the researcher. The case is made that the difficulties arise because of the way astigmatism is conceived and defined. In most cases astigmatism is regarded as cylinder. Cylinder, however, is not invariant under spherocylindrical transposition and, hence, cannot strictly be regarded as meaningful. The purpose of the paper is to find a rational, context‐free, invariant and universally‐applicable definition of astigmatism for all quantitative analyses. One is led to definitions of astigmatism and its components some of which have already appeared in the literature but which are not in use in analyses of astigmatism. Astigmatism is defined with respect to pure sphere. In the case of thin systems (including keratometric measurements and refraction) astigmatism turns out to be Jacksonian power, that is, the power of a Jackson crossed cylinder. The power of every thin system can be regarded as consisting of two orthogonal components, sphere and astigmatism. The astigmatism of thin systems itself further decomposes naturally into two orthogonal components called ortho‐ and oblique astigmatism. In the case of thick systems, like the eye itself, astigmatism decomposes naturally into three orthogonal components, ortho‐, oblique and antisymmetric astigmatism. The approach is based on the general definition of power in paraxial optics, the dioptric power matrix, and leads to useful graphical representations. Because of its mathematical foundation the analysis can claim completeness and contextual independence. Furthermore it is also directly applicable to the four fundamental paraxial properties of optical systems.
Mutagenesis and repair by low doses of α radiation in mammalian cells
Authors: Puck Theodore T. , Johnson Robert , Webb Patricia , Cui Helen , Valdez Joseph G. , Crissman Harry
Published: September 2002

Low doses of α radiation in basements have been causally implicated in lung cancer. Previous studies have concentrated on high dose effects, for which no significant repair was found. In the present study, the methodology for measuring mutation by quantitating mitotic breaks and gaps was found to be applicable to G
2
-phase Chinese hamster ovary cells irradiated with 10–50 cGy of α radiation. The mutation yield in such cells closely resembles that of γ irradiation. Caffeine, which inhibits repair, produces the same straight line increase of α and γ mutation yields plotted against the dose. In the absence of caffeine, the repair of α radiation lesions is almost twice as great as for γ radiation. Mitotic index changes substantiate these interpretations. It is proposed that the higher ion density associated with α radiation may result in fewer lesions being missed by the repair processes. The quantitation of chromosomal lesions for G
2
cells exposed to low doses of α radiation, γ radiation, or chemical mutagens in the presence and absence of caffeine is a rapid and reproducible methodology. Protection from mutational disease in a fashion similar to the use of sanitation for infectious disease appears practical.
Tumor necrosis factor-α regulation of CD4+C25+T cell levels in NOD mice
Authors: Wu Ava J. , Hua Hong , Munson Sibyl H. , McDevitt Hugh O.
Published: September 2002

The mechanism by which tumor necrosis factor-α (TNF) differentially modulates type I diabetes mellitus in the nonobese diabetic (NOD) mouse is not well understood. CD4+CD25+T cells have been implicated as mediators of self-tolerance. We show (i) NOD mice have a relative deficiency of CD4+CD25+T cells in thymus and spleen; (ii) administration of TNF or anti-TNF to NOD mice can modulate levels of this population consistent with their observed differential age-dependent effects on diabetes in the NOD mouse; (iii) CD4+CD25+T cells from NOD mice treated neonatally with TNF show compromised effector function in a transfer system, whereas those treated neonatally with anti-TNF show no alteration in ability to prevent diabetes; and (iv) repeated injection of CD4+CD25+T cells into neonatal NOD mice delays diabetes onset for as long as supplementation occurred. These data suggest that alterations in the number and function of CD4+CD25+T cells may be one mechanism by which TNF and anti-TNF modulate type I diabetes mellitus in NOD mice.
Cortical representation of first and second pain sensation in humans
Authors: Ploner Markus , Gross Joachim , Timmermann Lars , Schnitzler Alfons
Published: September 2002

Single painful stimuli evoke two successive and qualitatively distinct sensations referred to as first and second pain sensation. Peripherally, the neural basis of this phenomenon is a dual pathway for pain with Aδ and C fibers mediating first and second pain, respectively. Yet, the differential cortical correlates of both sensations are largely unknown. We therefore used magnetoencephalography to record and directly compare first and second pain-related cortical responses to cutaneous laser stimuli in humans. Our results show that brief painful stimuli evoke sustained cortical activity corresponding to sustained pain perception comprising early first pain-related and late second pain-related components. Cortical activity was located in primary (S1) and secondary (S2) somatosensory cortices and anterior cingulate cortex. Time courses of activations disclosed that first pain was particularly related to activation of S1 whereas second pain was closely related to anterior cingulate cortex activation. Both sensations were associated with S2 activation. These results correspond to the different perceptual characteristics of both sensations and probably reflect different biological functions of first and second pain. First pain signals threat and provides precise sensory information for an immediate withdrawal, whereas second pain attracts longer-lasting attention and motivates behavioral responses to limit further injury and optimize recovery.
Isolation of an
Arabidopsis
mutant lacking vitamin E and identification of a cyclase essential for all tocopherol biosynthesis
Authors: Porfirova Svetlana , Bergmüller Eveline , Tropf Susanne , Lemke Rainer , Dörmann Peter
Published: September 2002

Tocopherol (vitamin E) is a plant chloroplast lipid presumed to be involved in the response to oxidative stress. A tocopherol-deficient mutant (
vte1
) was isolated from
Arabidopsis thaliana
by using a TLC-based screening approach. Mutant plants lacked all four tocopherol forms and were deficient in tocopherol cyclase activity. Genetic mapping of
vte1
and a genomics-based approach led to the identification of the ORF At4g32770 as a candidate gene for tocopherol cyclase. In
vte1
, At4g32770 contains a splicing site mutation and the corresponding mRNA expression is reduced. Expression of VTE1 in
Escherichia coli
resulted in the production of a protein with high tocopherol cyclase and tocotrienol cyclase activity. The
VTE1
sequence shows no similarities to genes with known function, but is similar to that of
SXD1
, a gene that was recently isolated based on the availability of the
sucrose export defective1
maize mutant (
sxd1
). Growth of the
vte1
mutant, chlorophyll content, and photosynthetic quantum yield were similar to wild type under optimal growth conditions. Therefore, absence of tocopherol has no large impact on photosynthesis or plant viability, suggesting that other antioxidants can compensate for the loss of tocopherol. During photo-oxidative stress, chlorophyll content and photosynthetic quantum yield were slightly reduced in
vte1
as compared with wild type indicating a potential role for tocopherol in maintaining an optimal photosynthesis rate under high-light stress.
Rapid atmospheric CO
2
changes associated with the 8,200-years-B.P. cooling event
Authors: Wagner Friederike , Aaby Bent , Visscher Henk
Published: September 2002

By applying the inverse relation between numbers of leaf stomata and atmospheric CO
2
concentration, stomatal frequency analysis of fossil birch leaves from lake deposits in Denmark reveals a century-scale CO
2
change during the prominent Holocene cooling event that occurred in the North Atlantic region between 8,400 and 8,100 years B.P. In contrast to conventional CO
2
reconstructions based on ice cores from Antarctica, quantification of the stomatal frequency signal corroborates a distinctive temperature–CO
2
correlation. Results indicate a global CO
2
decline of ≈25 ppm by volume over ≈300 years. This reduction is in harmony with observed and modeled lowering of North Atlantic sea-surface temperatures associated with a short-term weakening of thermohaline circulation.
A p5 integration efficiency element mediates Rep-dependent integration into AAVS1 at chromosome 19
Authors: Philpott Nicola J. , Gomos Janette , Berns Kenneth I. , Falck-Pedersen Erik
Published: September 2002

Adeno-associated virus (AAV) undergoes site-specific integration into human chromosome 19 through a deletion-substitution mechanism at the well characterized AAVS1 site. We have shown previously that a cis element within the left end of the AAV genome enhances the efficiency of Rep-mediated site-specific integration into chromosome 19 when present in inverted terminal repeat-containing recombinant AAV (rAAV) plasmids. We now demonstrate that a 138-bp cis element, the p5 integration efficiency element (p5IEE), mediates efficient integration. The p5IEE is not only required for efficient site-specific integration, it is also sufficient. Integration mediated by the p5IEE occurs in the absence of the AAV inverted terminal-repeat elements. The data presented in this study demonstrate that the p5IEE is a multifunctional element, serving as the highly regulatable Rep promoter and the primary substrate for targeted integration.
Convergent evolution sheds light on the anti-β-elimination mechanism common to family 1 and 10 polysaccharide lyases
Authors: Charnock Simon J. , Brown Ian E. , Turkenburg Johan P. , Black Gary W. , Davies Gideon J.
Published: September 2002

Enzyme-catalyzed β-elimination of sugar uronic acids, exemplified by the degradation of plant cell wall pectins, plays an important role in a wide spectrum of biological processes ranging from the recycling of plant biomass through to pathogen virulence. The three-dimensional crystal structure of the catalytic module of a “family PL-10” polysaccharide lyase, Pel10Acm from
Cellvibrio japonicus
, solved at a resolution of 1.3 Å, reveals a new polysaccharide lyase fold and is the first example of a polygalacturonic acid lyase that does not exhibit the “parallel β-helix” topology. The “Michaelis” complex of an inactive mutant in association with the substrate trigalacturonate/Ca
2+
reveals the catalytic machinery harnessed by this polygalacturonate lyase, which displays a stunning resemblance, presumably through convergent evolution, to the tetragalacturonic acid complex observed for a structurally unrelated polygalacturonate lyase from family PL-1. Common coordination of the −1 and +1 subsite saccharide carboxylate groups by a protein-liganded Ca
2+
ion, the positioning of an arginine catalytic base in close proximity to the α-carbon hydrogen and numerous other conserved enzyme–substrate interactions, considered in light of mutagenesis data for both families, suggest a generic polysaccharide
anti
-β-elimination mechanism.