Organic matter identifies the nano-mechanical properties of native soil aggregates.

Localized variations at the nanoscale in soil aggregates and in the spatial organisation of soil organic matter (SOM) are critical to understanding the factors involved in soil composition and turnover. However soil nanoscience has been hampered by the lack of suitable methods to determine soil biophysical properties at nanometre spatial resolution with minimal sample preparation. Here we introduce for the first time an Atomic Force Microscopy (AFM)-based Quantitative Nano-Mechanical mapping (QNM) approach that allows the characterisation of the role of SOM in controlling surface nano-mechanical properties of soil aggregates. SOM coverage resulted in an increased roughness and surface variability of soil, as well as in decreased stiffness and adhesive properties. The latter also correlates with nano- to macro-wettability features as determined by contact angle measurements and Water Drop Penetration Time (WDPT) testing. AFM thus represents an ideal quantitative tool to complement existing techniques within the emerging field of soil nanoscience.

Modelling the shrinkage in pigmented coatings during drying: a stick-slip mechanism.

Pigmented coatings, used to improve optical and printing properties, are applied to fibrous paper substrates as slurry, which then dries. We have elucidated the mechanism of the shrinkage which occurs during drying. The void space of the dry coating layers and their effective solid skeletal elements were modelled using the porous network simulation software Pore-Cor. The water-filled porous structures at the beginning of the shrinking process were modelled by creating simulated structures with the same effective skeletal element size distribution as the dry ones, but with higher given porosity to account for the water present. The capillary forces acting on the surface of the drying coating were calculated for the model structures and found to be orders of magnitude larger than the experimentally measured shrinkage forces. The shrinkage process was therefore postulated as resulting from the effect of capillary forces resisted by a discrete stick-slip process. The differences in the visco-elastic properties of the slurries also supported this postulate, as did further experimental evidence.

High-resolution laboratory lysimeter for automated sampling of tracers through a 0.5 m soil block.

A computer-controlled, automated sample collection from a 0.5-m lysimeter, designed to give superior temporal and spatial resolution for monitoring the movement of chemical tracers through a large undisturbed soil block, is described. The soil block, 0.5 x 0.5 x 0.5 m, was monitored for saturation using eight time domain reflectometry probes. Rainfall was applied at approximately 1600 ml h(-1) using a 12212 array of 23-gauge (0.318 mm internal diameter) hypodermic needles. Soil leachates were collected at the base of the soil block using a machined aluminium collection plate with a 10 x 10 grid of funnels that passed leachates to sample collection palettes. Sample collection was automated using a personal computer equipped with National Instruments LabVIEW software and linked to sensors for palette tracking. The automation of the lysimeter allowed sample collection and storage over a user-defined period with no human interaction. As an example of the use of the automated lysimeter, results show the distribution of phosphate within the soil. The eluted phosphate showed an initial and secondary peak, and only emerged from preferential flow channels.

The epidemiology of serious eye injuries from the United States Eye Injury Registry.

BACKGROUND: Trauma remains a major problem throughout the world. The prognosis of severe eye injuries is commonly bleak. This paper focuses on the epidemiology of eye trauma, the role of ocular epidemiology, and identification and reduction of risk factors. METHODS: An analysis of the first 8,952 patients reported with severe eye injuries, defined as those eye injuries resulting in permanent and significant (measurable and observable on routine eye examination) structural and/or functional changes to the eye, from the United States Eye Injury Registry as of 31 July 1998. RESULTS: The age of patients entered was from the 1st year of life to 103 years. Fifty-eight percent of those injured were less than 30 years of age. The male to female ratio was 4.6:1, reaching 7.4:1 in the fourth decade of life. Almost half of the injuries involved the retina, and 77% of the injured eyes required one or more surgical procedures, including a large proportion which have undergone vitreoretinal surgical procedures. CONCLUSION: Injuries remain the most serious public health problem facing developed nations. Yet, a persistent inadequacy exists both in the standardized documentation of eye injuries and in their treatment. With appropriate surgical and medical intervention, a majority of the reported injured eyes recovered functional levels of visual acuity. It appears that glasses, including prescription glasses and even non-prescription sunglasses, can offer measurable protection which results in a lower incidence of severe eye injuries to those wearing glasses.

Pneumatic buckle for the repair of primary rhegmatogenous retinal detachment.

OBJECTIVES: This prospective study examines the effectiveness of the pneumatic buckle procedure (nondrainage scleral buckle with pneumatic retinopexy) for repair of primary rhegmatogenous retinal detachments. METHODS: We studied 58 consecutive patients with primary rhegmatogenous retinal detachments who underwent a pneumatic buckle with air or SF6. The procedures were performed at 2 centers. Retinal reattachment and visual acuity were examined. RESULTS: The single operation reattachment rate for patients undergoing a pneumatic buckle procedure was 95%. Eighty eight percent of patients with macula-on detachment had unchanged or improved final visual acuity. Sixty seven percent of patients with macula-off detachments had a final visual acuity between 20/20 and 20/50. Twenty nine percent had final visual acuity between 20/60 and 20/200. Two patients developed a new retinal hole postoperatively. CONCLUSION: Pneumatic buckle is an effective technique for repair of primary rhegmatogenous retinal detachments caused by breaks in the superior 8 o'clock segment. This technique avoids the complications associated with the drainage portion of the traditional scleral buckle operation and results in a high rate of retinal reattachment and stable or improved visual acuity. The rate of new retinal hole formation in this study is much lower than those reported for pneumatic retinopexy.

Visual outcome and ocular survival in patients with retinal detachments secondary to open- or closed-globe injuries.

BACKGROUND AND OBJECTIVE: A retrospective study was undertaken to establish predictive clinical features for final visual outcome and ocular survival for patients who have sustained traumatic retinal detachments (RDs). PATIENTS AND METHODS: The authors reviewed 191 cases of RD following open- or closed-globe trauma. The clinical features that were analyzed included the initial visual acuity, the location of the wound, the mechanism of injury (blunt, sharp, or projectile), and the number of quadrants of RD. RESULTS: The significant predictive factors for good visual outcome (1/200 or better) included an initial visual acuity of hand motions or better, wounds located anterior to the equator, closed-globe injuries, sharp injury in open globes, and three or fewer quadrants of RD. The factors that predicted enucleation included an initial visual acuity of light perception or no light perception, wounds located posterior to the equator, and four quadrants of RD. CONCLUSION: The significant predictive factors for final visual outcome in patients with traumatic RD were the initial visual acuity, the location of the wound, the mechanism of injury, and the number of quadrants of RD.

Modelling of the void space of tablets compacted over a range of pressures.

A previously developed computer model, named Pore-Cor, has been used to simulate the changes in the void-space dimensions which occur during the compaction of tablets over a range of pressures. The tablets were made by mixing pharmaceutical grade crystalline lactose and an anti-inflammatory compound in the proportion 4:1. Compacts were made by placing a weighed amount of the mixed powder into a stainless-steel die and applying pressure with a hand-operated calibrated hydraulic press. Compacts were prepared at eight pressures over the hydraulic pressure range 1 to 8 ton in-2 (15.4-123.2 MPa) in 1 ton in-2 increments. Mercury-intrusion curves were measured for the eight samples by use of a porosimeter and the Pore-Cor package was then used to simulate the mercury-intrusion curves and generate void-space models of the correct porosity. The experimental and simulated characteristic throat diameter, the experimental and simulated porosity, and the simulated permeability of the tablets have all been shown to follow expected trends. The successful modelling of void-structure parameters, which are difficult or impossible to measure experimentally, opens the way to an improved understanding of the strength of compacts.

Rapid determination of dissolved organic phosphorus in soil leachates and runoff waters by flow injection analysis with on-line photo-oxidation.

A rapid method suitable for the determination of dissolved organic phosphorus (DOP) in soil leachates and runoff waters is presented. The flow injection (FI) manifold contains an in-line PTFE reaction coil wrapped around a low power UV lamp and is based on the spectrophotometric determination of dissolved reactive phosphorus (DRP) and mineralised DOP at 690 nm after reduction of phosphomolybdate to molybdenum blue with tin(II) chloride. The linear range was 0-1.5 mg 1(-1) PO(4)-P, with a detection limit (3 s) of 7 mug 1(-1) and a sample throughput of 40 h(-1). Tolerance to potential matrix interferences in soil pore waters, particularly Al(III), Si(IV), Fe(II) and Fe(III), was achieved using a combination of on-line sample pre-treatment by a strong acid ion exchange column, low photoreactor pH and acid induced control of the kinetics of the molybdenum blue reaction. The results obtained with this manifold were in good agreement with those obtained by a batch spectrophotometric reference method.

Dense vitreous hemorrhages predict poor visual and neurological prognosis in infants with shaken baby syndrome.

OBJECTIVE: A retrospective study was performed to examine the relationship between the severity of vitreous hemorrhages and the severity of neurological injury in infants with shaken baby syndrome, and the result of early vitrectomy in these infants. METHODS: Five infants, ages 3 to 8 months, with confirmed child abuse underwent ocular examination and neurological testing to identify varying degrees of vitreoretinal changes and neurological dysfunction. Pars plana vitrectomy was performed on one or both eyes in each infant to remove the vitreous hemorrhage. RESULTS: The three infants with bilateral dense vitreous hemorrhage and multiple subarachnoid hemorrhage and cerebral contusions had poor postoperative ocular and neurological outcomes including light perception (LP) or no light perception (NLP) vision, large retinal holes or tears, retinal ischemia, and severe encephalopathy. The other two infants presented with bilateral subhyaloid and retinal hemorrhages without dense vitreous involvement, along with mild subarachnoid hemorrhage and minimal neurological findings. Following vitrectomy, visual acuities in these infants improved to or remained at the fix and follow state, and both infants improved neurologically. CONCLUSIONS: The presence of dense vitreous hemorrhage in infants with shaken baby syndrome has a poor visual prognosis, due to the frequent concomitant occurrence of significant retinal and visual cortical pathology. In contrast, infants with only intraretinal or subhyaloid hemorrhage tend to have a much better prognosis, with less disruption of both intraocular and intracranial structures.

Retinal tolerance to intravitreal perfluoroethylcyclohexane liquid in the rabbit.

To evaluate the use of perfluoroethylcyclohexane (PFE) liquid during vitreoretinal surgery, retinal tolerance was tested by electroretinographic (ERG) and histologic study of rabbit eyes undergoing intravitreal placement of PFE for 48 hours. When PFE occupied the vitreous cavity, ERG amplitudes were decreased, probably because of electrical insulation by the liquid. Immediately after removal of the liquid, elevations of a and b waves occurred. Further improvements in the waveforms were recorded when tested between 5 days and 2 months after PFE removal, such that the eyes injected with PFE exhibited ERG amplitudes comparable to contralateral control eyes and preoperative eyes. Histologic examination of the eyes 2 months after PFE removal also revealed normal morphologic features. Small residual amounts of PFE produced no adverse histologic changes after 6 months. When PFE remained intravitreally for longer than 1 week, dispersion of the liquid and preretinal accumulation of macrophages occurred, and in inferior retina, distortions of photoreceptor outer segments and narrowing of outer plexiform layer were observed in the rabbit model.

Foveal cone electroretinograms in patients with central visual loss of unexplained etiology.

Foveal cone electroretinograms (ERGs) were recorded in five patients (aged 24 to 66 years) referred because of central visual loss of unexplained etiology. These patients had no family history of visual loss and no diagnostic fundus abnormalities seen on ophthalmoscopy or fluorescein angiography. Foveal cone ERGs were elicited with a 4 degrees white stimulus flickering at 42 Hz centered within a steady 10 degrees white surround presented through the dilated pupil to the fovea by a hand-held, dual-beam stimulator-ophthalmoscope. All five patients showed reduced foveal cone ERG amplitudes. Their abnormal responses were similar to those previously reported in cases of clinically apparent macular degeneration and contrasted with previously reported normal responses in patients with optic atrophy or strabismic amblyopia. The progressive loss of central vision as determined by history and these subnormal foveal cone ERG amplitudes suggest that these patients have a form of macular degeneration.

Relationship of oscillatory potential amplitude to A-wave slope over a range of flash luminances in normal subjects.

The effect of flash luminance on the relationship of oscillatory potential (OP) amplitude, as a measurement of inner retinal function, to a-wave slope, as a measurement of photoreceptor function, was evaluated in full-field electroretinograms recorded from normal subjects. The ratio of OP amplitude to a-wave slope was found to be independent of flash luminance over a 3000-fold luminance range. This finding raises the possibility that a reduction in the ratio of OP amplitude to a-wave slope in eyes with media opacities may be used as a sign of inner retinal malfunction. Selected cases are presented to illustrate application of this approach.

Effects of 2-amino-4-phosphonobutyric acid (APB) and glycine on the oscillatory potentials of the rat electroretinogram.

Oscillatory potentials of the electroretinogram were monitored in dark-adapted rats following intravitreal injection of 2-amino-4-phosphonobutyric acid (APB), a glutamate analog that preferentially blocks the light response of depolarizing bipolar cells, or glycine, a known endogenous inhibitory neurotransmitter that suppresses the light response of cells in the inner retina postsynaptic to glycinergic neurons. Oscillatory potentials were abolished in conjunction with the b-wave with APB and selectively reduced or eliminated by glycine: neither agent attenuated the a-wave. The results are compatible with the idea that light-induced depolarizing bipolar cell, hyperpolarizing bipolar cell, and glycinergic amacrine cell responses are all necessary for the generation of oscillatory potentials in the rat. The results also suggest that hyperpolarizing bipolar cells do not contribute to b-wave generation.

Chromograms of color normals and multiple sclerosis patients.

The Gunkel chromograph was tested on 81 volunteers with normal color vision as indicated by screening with Ishihara plates and the panel D-15. Most of these color normals located their neutral area superior to the geometric center of the chromogram. A minority located their neutral area at the geometric center. Recognition of this variation may prevent misdiagnosis of chromographs of patients suspected of having color vision defects. All 29 eyes with history and VEP findings consistent with optic nerve demyelinization had enlargement of the neutral area, even though visual acuity could be corrected to 20/20.