Average Thickness Values Research Articles

Single Crystals of Chain-Folded Copolyterephthalamides

Crystallization of copolyaramides composed of rigid poly(p-phenylene terephthalamide) segments (containing 3−11 aromatic cycles) and short amine aliphatic chains (5−10 CH2 groups) was studied. Crystallization was induced at room temperature by slow saturation with methanol vapors of sulfuric acid solutions. In electron diffraction, the 3AR6DA, which has monodisperse rigid blocks, exhibits weak but typical single crystal diffraction, with relatively sharp diffraction spots. Other wARnDAs, for which the rigid blocks are polydisperse, show a similar diffraction diagram albeit with lower resolution and considerable peak broadening, indicating that considerable disruption of the crystal phase has taken place. All observed diagrams correspond to the hk0 level, and chains are perpendicular to the lamellar plane. Atomic force microscopy observations show that most crystals are multilamellar, the thickness of each lamella increasing regularly with the number of aromatic groups in the rigid segment. The average lamellar thickness value is in agreement with the expected rigid segment length. It is therefore concluded that the addition of a short aliphatic chain fragment allows chain folding to occur.

Retinal nerve fiber layer thickness measured by optical coherence tomography and its correlation with visual field defects in early glaucoma.

To study the relationship between retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) and visual field defects in early glaucomatous eyes and to study the diagnostic ability of OCT in distinguishing early glaucomatous eyes from normal eyes. We studied 68 eyes from primary open-angle glaucoma patients with early visual field defect (mean deviation > -6 dB), and 94 normal eyes from healthy age- and gender- matched individuals. All participants underwent 3.4-mm diameter circular OCT scans and Humphrey 30-2 mode visual field testing. The average and segmental RNFL thickness values were compared between the 2 groups. The correlation between the mean deviation in the visual field examination and RNFL thickness was evaluated. The area under the receiver operating characteristic (ROC) curve was used to distinguish normal eyes from early glaucomatous eyes. There was a significant difference in RNFL thickness between the 2 groups based on the following parameters: average thickness; superior, inferior, and nasal quadrant thickness; and 1-7, 11, 12 o'clock hour segment thickness (p < 0.05). In the glaucoma group, superior and inferior quadrant thicknesses and average RNFL thickness significantly correlated with the visual field index (superior quadrant thickness, r = 0.36; inferior quadrant thickness, r = 0.32; average RNLF thickness, r = 0.35; p < 0.05). The average RNFL and inferior quadrant thickness of early glaucomatous eyes had the widest areas under the ROC curves (0.812 and 0.793, respectively). Measurement of average and inferior quadrant RNFL thickness by OCT is useful in detecting early glaucomatous change.

Evaluation of the Orssengo-Pye IOP corrective algorithm in LASIK patients with thick corneas

The objective of this study was to evaluate the Orssengo-Pye central corneal thickness (CCT) Goldmann applanation tonometry (GAT) corrective algorithm by observing changes in GAT and CCT before and after laser in situ keratomileusis (LASIK) surgery in patients with CCT that remains greater than 545 microm postoperatively. Tonometric and pachymetric measurements were made on 14 patients (28 eyes) before and after LASIK surgery. The selected patients were required to have average or above average postoperative central corneal thickness values in both eyes (not less than 545 microm). Preoperatively, all patients had CCT and GAT measurements taken. Postoperatively patients had CCT, GAT, and dynamic contour tonometric (DCT) measurements taken. Preoperatively, median CCT values were 589.536 microm. Median GAT values were 16.750 mmHg. Median corrected preoperative GAT values were 14.450 mmHg. After LASIK treatment, median CCT values were 559.417 microm. The decrease in median CCT was 30.119 microm. Median postoperative GAT values were 11.500 mmHg (decrease, 5.250 mmHg). Median corrected postoperative GAT values were 10.775 mmHg (decrease, 3.675 mmHg). Median postoperative DCT values were 17.858 mmHg. LASIK treatment causes a significant reduction in measured GAT intraocular pressure (IOP) values. The Orssengo-Pye formula, which attempts to correct for GAT error associated with individual variation in CCT, appears to yield misleading results in these circumstances. An unexpected 3.675-mmHg decrease in "corrected IOP" by the Orssengo-Pye method seen in this study may be attributed to some limitation or error in the formula. After adjusting for the approximate1.7-mmHg difference, which has been demonstrated between DCT and GAT, postoperative DCT values were similar to preoperative measured GAT values.

Protective Effects of Antithrombin III on Retinal Ischemia/Reperfusion Injury in Rats: A Histopathologic Study

Purpose To investigate the effect of antithrombin III (AT III) on retinal ischemia/reperfusion (I/R) injury in rats. Methods The study was carried out on 10 Wistar albino rats (20 eyes) and four-vessel occlusion method was employed to induce retinal ischemia in this study. Rats were divided into two groups: Group I (control group, 10 eyes) and Group II (AT III, 10 eyes). In both groups, vertebral arteries were occluded bilaterally an electric needle coagulator under an operating microscope. A total of 48 hours after the initial procedure, the rats were re-anesthetized and both common carotid arteries were clamped to interrupt blood flow. In Group II, rats were injected intravenously with 250 U/kg of AT III 5 minutes before the induction of ischemia. Duration of ischemia was 30 minutes. At the end of this period, clamp was removed for the reperfusion of the eye for 4 hours. Following the reperfusion period, the animals were killed by decapitation. Retinal sections were evaluated under light and electron microscope. The signs of l/R injury at the microscopic level, i.e., cellular degeneration, vacuolization between retinal layers, increase in the retinal thickness due to edema, mononuclear cell infiltration, and apoptotic cells, were recorded for each group. Results Retinal sections obtained from the rats in the AT III group revealed a well preserved retinal structure. When average thickness values of the two groups were compared to each other, the difference was significant with respect to inner nuclear and inner plexiform layers indicating increased retinal thickness values in Group I due to tissue edema resulting from l/R injury. Similarly, mononuclear cell infiltration and apoptotic cell counts were found to be significantly higher in control group compared to AT III group showing the inhibitory effect of AT III on leukocyte infiltration and apoptotic cell death in rat retina. Conclusions Antithrombin III attenuated l/R injury in rat retina.

Protective effects of antithrombin III on retinal ischemia/reperfusion injury in rats: A histopathologic study.

To investigate the effect of antithrombin III (AT III) on retinal ischemia/reperfusion (I/R) injury in rats. The study was carried out on 10 Wistar albino rats (20 eyes) and four-vessel occlusion method was employed to induce retinal ischemia in this study. Rats were divided into two groups: Group I (control group, 10 eyes) and Group II (AT III, 10 eyes). In both groups, vertebral arteries were occluded bilaterally an electric needle coagulator under an operating microscope. A total of 48 hours after the initial procedure, the rats were re-anesthetized and both common carotid arteries were clamped to interrupt blood flow. In Group II, rats were injected intravenously with 250 U/kg of AT III 5 minutes before the induction of ichemia. Duration of ischemia was 30 minutes. At the end of this period, clamp was removed for the reperfusion of the eye for 4 hours. Following the reperfusion period, the animals were killed by decapitation. Retinal sections were evaluated under light and electron microscope. The signs of I/R injury at the microscopic level, i.e., cellular degeneration, vacuolization between retinal layers, increase in the retinal thickness due to edema, mononuclear cell infiltration, and apoptotic cells, were recorded for each group. Retinal sections obtained from the rats in the AT III group revealed a well preserved retinal structure. When average thickness values of the two groups were compared to each other, the difference was significant with respect to inner nuclear and inner plexiform layers indicating increased retinal thickness values in Group I due to tissue edema resulting from I/R injury. Similarly, mononuclear cell infiltration and apoptotic cell counts were found to be significantly higher in control group compared to AT III group showing the inhibitory effect of AT III on leukocyte infiltration and apoptotic cell death in rat retina. Antithrombin III attenuated I/R injury in rat retina.

Slurry Distribution in Soil as influenced by Slurry Application Micro-rate and Injection Tool Type

The study of slurry distribution in soil following slurry injection is important for the design of an efficient injection tool, for the selection of injection tool spacing and for the reduction of slurry nutrient losses. In this research, two types of injection tools (sweep & furrower) were studied in laboratory conditions, and the same furrower and another type of injection tool (disc) were studied in field conditions over 3 years. For each injection tool, experiments were conducted with three slurry application micro-rates: r1 of 1·2×10−3 m3 m−1 tool−1; r2 of 2·4×10−3 m3 m−1 tool−1; and r3 of 3·6×10−3 m3 m−1 tool−1. To quantify slurry distribution in the soil following injection, image analysis technique was used in the laboratory study, while a manual tracing method was used in the field study. Slurry distribution in the soil was characterised by the parameters: lateral spread, vertical thickness and area of the slurry-soil mix zone. The lateral spread for a tool was recommended as the minimum tool spacing. A slurry distribution index was developed as an indicator of injection tool performance. The average values of the area of the slurry-soil mix zone, ranging from 6·5×103 to 18·0×103 mm2 tool−1, increased significantly with an increased micro-rate, as did for the average values of lateral spread and vertical thickness. The laboratory study showed that the sweep and the furrower resulted in similar characteristics of slurry-soil mix zone. The field studies showed the furrowers resulted in greater values of lateral spread, while the discs resulted in greater values of vertical thickness. The slurry distribution index indicated that at the low rate r1, the disc mixed slurry with the soil better, while at the higher rates r2 and r3, the furrower had a better performance.

Optical coherence tomography detects characteristic retinal nerve fiber layer thickness corresponding to band atrophy of the optic discs

To analyze retinal nerve fiber layer (RNFL) thickness in eyes with band atrophy by use of optical coherence tomography (OCT) and to evaluate the ability of OCT to detect this characteristic pattern of RNFL loss. Cross-sectional, retrospective study. Thirty-four eyes of 18 patients with bitemporal hemianopia caused by optic chiasm compression by chiasmal tumors were studied. All eyes were divided into 3 groups according to visual field loss grading after Goldmann perimetry. Retinal nerve fiber layer thickness measurements with OCT. Retinal nerve fiber layer thickness around the optic disc was measured by OCT (3.4-mm diameter circle). Calculation of the changes in OCT parameters, including the horizontal (nasal + temporal quadrant RNFL thickness) and vertical values (superior + inferior quadrant RNFL thickness) was based on data from 160 normal eyes. Comparison between the 3 visual field grading groups was done with the analysis of variance test. The receiver operating characteristic (ROC) curve for the horizontal and vertical value were calculated, and the areas under the curve (AUC) were compared. Retinal nerve fiber layer thickness in eyes with band atrophy decreased in all OCT parameters. The reduction rate in average and temporal RNFL thickness and horizontal value was correlated with visual field grading. The AUC of horizontal value was 0.970+/-0.011, which was significantly different from AUC of vertical value (0.903+/-0.022). The degree of RNFL thickness reduction correlated with that of visual field defects. Optical coherence tomography was able to identify the characteristic pattern of RNFL loss in these eyes.

Structural parameters of amylopectin clusters and semi-crystalline growth rings in wheat starches with different amylose content

Small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) were used to investigate the internal structure of wheat starch granules with different amylose content. Different approaches were used for treatment (interpretation) of SAXS data to assess the values of structural parameters of amylopectin clusters and the size of crystalline and amorphous lamella in different wheat starches. The average values of the semi-crystalline growth rings thickness in starches have been determined and the relationship between structural characteristics and thermodynamic melting parameters is discussed.

Reduction of posterior pole retinal thickness in glaucoma detected using the Retinal Thickness Analyzer

Objectives To report evidence of changes in posterior pole retinal thickness in glaucoma and preperimetric glaucoma. Design Cross-sectional study. Participants One hundred forty participants (140 eyes): 31 normal subjects, 33 with ocular hypertension, 43 with primary open-angle glaucoma (POAG), and 33 with preperimetric glaucoma. Intervention Posterior pole retinal thickness measurements using the Retinal Thickness Analyzer (RTA; Talia Technology Ltd., Neve-Ilan, Israel). Main outcome measures The mean foveola average thickness (VAV), foveola minimum thickness (VMI), perifoveal average thickness (PFAV), perifoveal minimum thickness (PFMI), posterior pole average thickness (PPAV), and posterior pole minimum thickness (PPMI) were compared among the groups. The correlation between RTA values and visual field values was evaluated. The area under the receiver operator characteristic (AROC) curve, the optimal cut values, and the predictability values were estimated statistically between normal and the other groups using RTA values. Results Results from 91 eyes (65%) were included. Perifoveal average thickness values in preperimetric glaucoma (190.4±15.6 μm; mean±standard deviation) and POAG (185.7±16.8 μm) were significantly less than in normal controls (211.4±16.8 μm) and in eyes with ocular hypertension (211.6±15.9 μm). Perifoveal minimum thickness, PPAV, and PPMI were significantly less in preperimetric glaucoma and in POAG than in normal controls; VAV and VMI were not significantly different among groups. Perifoveal average thickness, PFMI, PPAV, and PPMI significantly correlated with visual field mean defect ( R = −0.38, −0.42, −0.36, and −0.41, respectively) and loss of variance ( R = −0.29, −0.30, −0.26, and −0.17, respectively). The AROC using PFAV, PFMI, PPAV, and PPMI was significantly larger than 0.5 between normal and preperimetric glaucoma (0.83, 0.92, 0.82, and 0.87, respectively) and between normal and POAG eyes (0.86, 0.97, 0.83, and 0.93, respectively). When using the PFMI, the sensitivities at the minimum specificity cutoffs of 90% were highest in comparisons between normal and preperimetric glaucoma (sensitivity, 75%) and between normal and POAG eyes (sensitivity, 95%). By the logistic regression analysis, PFAV, PFMI, PPAV, and PPMI distinguished between normal and preperimetric glaucoma ( R 2 = 0.30, 0.49, 0.27, and 0.37, respectively) and between normal and POAG ( R 2 = 0.37, 0.59, 0.31, and 0.51, respectively). Conclusions Posterior pole retinal thickness decreases in early- and moderate-stage glaucoma. Reduction of perifoveal retinal thickness is correlated with visual field loss. In vivo measurements of posterior pole retinal thickness may help distinguish between normal and glaucomatous eyes.

The influence of a lateral basin-slope on the depositional patterns of natural and experimental turbidity currents

Abstract Understanding topographic effects upon the depositional processes of turbidity currents and the resulting deposit characteristics is key to producing reliable depositional models for turbidity currents. In this study, the effect on depositional patterns of a lateral slope whose strike is parallel to the principal direction of flow is explored using field and experimental results. This type of basin topography is commonly found in confined turbidite systems. Field data from the Peïra Cava turbidite system of the Tertiary Alpine Foreland Basin (SE France) and experimental data show that a characteristic depositional pattern is produced by surge-type waning flows that interact with a lateral slope. This pattern comprises beds that thin (and fine in the field study) not only downstream but also markedly away from the lateral slope (Type I beds). In the Peïra Cava system, this pattern is also observed in average values of sandstone bed thickness, sandstone percentage and grain-size, derived from measured sections, demonstrating that the processes responsible for this pattern also control gross properties within this sheet system. The characteristic thinning-away-from-slope deposit geometry is interpreted as an effect of the lateral slope via its influence on spatial variations in flow properties and on the suspended load fallout rate (SLFR) from currents. Flow velocity non-uniformity cannot explain thinning into the basin because flow has a higher deceleration along streamlines away from the slope that should cause higher SLFR and thicker deposits away from the slope instead of close to the slope. A concentration non-uniformity mechanism is invoked that has the effect of maintaining relatively high flow concentrations and hence SLFR in medial and distal locations close to the slope. Experiments suggest that this may arise due to different rates of flow expansion on the obstructed and unobstructed sides of the current in proximal regions. Velocity non-uniformity can, however, explain the geometry of deposits that thicken away from slope. Beds of this type do occur occasionally in the Peïra Cava system (Type II beds). Flow velocity non-uniformity patterns have been used previously to successfully explain the spatial distributions of depositional facies of turbidity currents that have interacted with topography. The analysis in this study demonstrates that velocity non-uniformity, by itself, cannot explain depositional patterns in all basin settings. Future depositional models need to incorporate the effects of spatial changes in other flow properties, such as flow concentration, upon deposition to be able to predict turbidite facies in many different types of basin setting.

Carotid intima-media thickness and coronary artery disease: an Indian perspective.

To determine whether carotid intima-media thickness is associated with coronary artery disease and cardiovascular risk factors in the Indian population, carotid intima-media thickness was measured using high-resolution B-mode ultrasonography in 101 patients with coronary artery disease and 140 control subjects. Carotid intima-media thickness was measured at 3 predefined sites on each side. The maximum carotid intima-media thickness was significantly higher in the coronary disease group compared to the controls (1.02 vs. 0.80 mm). The average intima-media thickness was also significantly higher in the coronary disease group (0.82 vs. 0.67 mm). On multivariate logistic regression analysis, carotid intima-media thickness was the only factor found to be an independent predictor of coronary artery disease. There was a significant association between risk factor count and the average and maximum intima-media thickness values in the combined study population. These results indicate that raised values of average and maximum carotid intima-media thickness are significantly associated with the presence of coronary artery disease and this association is independent of the presence of other conventional cardiovascular risk factors.

The Effect of Blood Glucose Regulation on Retinal Nerve Fiber Layer Thickness in Diabetic Patients

Purpose: To evaluate the effect of blood glucose (BG) regulation on the retinal nerve fiber layer (RNFL) in diabetic patients by using a scanning laser polarimeter (NFA-GDx). Methods: We prospectively assessed RNFL thickness in diabetic patients and an age-matched control group. Patients without diabetic retinopathy, with BG >250 mg/dl, HbA1c >8%, fructosamine >285 µmol/l and triglyceride >200 mg/dl were included in the study. RNFL assessment was performed before and after metabolic regulation of diabetes. Symmetry, superior maximum, ellipse modulation and the average thickness variables of NFA-GDx were used for the assessment. Mann-Whitney U and Wilcoxon tests were used for the statistical analysis. Results: A total of 40 diabetic patients were included in the study and a repeat RNFL examination could be performed in 22 of them following regulation of BG levels. None of the GDx variables were significantly different between pre- and postregulation measurements (p > 0.05, Wilcoxon test). The mean superior maximum, ellipse modulation and average thickness values of the diabetic group were significantly lower than the control group (p < 0.05, Mann-Whitney U-test). Conclusions: Poor metabolic control of diabetes mellitus adversely affects the thickness of RNFL and this effect does not seem to be acute since it was not reversed by short-term BG regulation. This issue needs to be kept in mind when assessing glaucomatous progress in diabetic patients.

A study of annular flow film characteristics in microgravity and hypergravity conditions

Annular flow is an important flow regime in many industrial applications. The need for a better understanding of this flow regime is driven by the desire to improve the design of many terrestrial and space-based systems. Gravity is a complicating factor in the studies and modeling of two-phase flows on earth. Experimental data on the annular flow film characteristics was collected in microgravity aboard the Novespace Zero-G Airbus microgravity simulator. The gravitational effect on the film thickness characteristics was examined by collecting data using an air-water mixture during the microgravity and pull-up (hypergravity) portions of each parabolic flight. Previously reported trends in annular flow average film thickness values for normal gravity are observed in microgravity and hypergravity conditions. The change in gravitational acceleration has little effect on the average film thickness and the film thickness time trace. However, the wave characteristics vary significantly.

Evaluation of the glaucomatous damage on retinal nerve fiber layer thickness measured by optical coherence tomography

Purpose To evaluate the relationship between visual field and retinal nerve fiber layer (RNFL) thickness measured by optical coherent tomography (OCT) and to assess the diagnostic ability of OCT to distinguish between early glaucomatous or glaucoma-suspect eyes from normal eyes. Design Retrospective, non-randomized, cross-sectional study. Methods A total of 160 eyes of 120 normal Japanese adults, 23 eyes of 16 patients with ocular hypertension, 38 eyes of 35 glaucoma-suspect patients, and 237 glaucomatous eyes of 140 glaucoma patients were enrolled in the study. The glaucoma group included 89 early glaucomatous eyes. Thickness of the RNFL around the optic disk was determined with three 3.4-mm diameter circle OCT scans. Average and segmental RNFL thickness values were compared among all groups. The correlation between mean deviation and RNFL thickness in glaucomatous eyes was also analyzed. Receiver operating characteristic (ROC) curve area was calculated to discriminate normal eyes from early glaucomatous or glaucoma-suspect eyes. Results A significant relationship existed between the mean deviation and RNFL thickness in all parameters excluding the 3-o’clock area. The average RNFL thickness had the strongest correlation in all parameters (r = −0.729, P < .001). Retinal nerve fiber layer thickness at the 7-o’clock inferotemporal segment had the widest areas under the ROC curves in all parameters for early glaucomatous eyes (0.873). Conclusion Measurement of RNFL thickness by OCT is useful in detecting early RNFL damage. Furthermore, OCT measurements of RNFL thickness may provide clinically relevant information in monitoring glaucomatous changes.

Assessment of nerve fiber layer in diabetic patients with scanning laser polarimetry

To evaluate the effects of diabetes mellitus, diabetic retinopathy and degree of blood glucose (BG) regulation on retinal nerve fiber layer (RNFL) thickness by using a scanning laser polarimeter (NFA-GDx). We prospectively assessed RNFL thickness in four groups of patients, who were all age matched. Diabetic patients without diabetic retinopathy were grouped according to their BG regulation level into two, as: BG-regulated group (BG <140 mg/dl, HbA1c <8%, fructosamine <285 micromol/l, TG <200 mg/dl, n = 50), and BG-non-regulated group (BG = 140-250 mg/dl, HbA1c >8%, fructosamine >285 micromol/l, TG >200 mg/dl, n = 44). A group of patients with nonproliferative diabetic retinopathy (NPDR) formed the 3rd group (n = 41). The 4th group consisted of healthy subjects and acted as a control group (n = 50). Symmetry, superior maximum, ellipse modulation and the average thickness variables of NFA-GDx were used for the assessment. ANOVA test was used for the statistical analysis of variables between groups. The mean superior maximum and ellipse modulation values were statistically significantly lower than the control group in BG-non-regulated and NPDR groups (P < 0.05). The average thickness value was also statistically significantly lower than the control group in NPDR group. These values in the BG-regulated group were not statistically significantly different from the control group (P > 0.05). This is the first clinical study demonstrating the effects of diabetic glucose regulation level on RNFL by using NFA-GDx. RNFL thickness was seen to decrease with development of diabetic retinopathy and with impairment of metabolic regulation. This issue should be taken into account while assessing RNFL in diabetic glaucomatous patients.

Correction for corneal polarization axis improves the discriminating power of scanning laser polarimetry

PURPOSE: Corneal polarization axis (CPA) has been reported to affect retardation measurements obtained with scanning laser polarimetry (SLP). The purpose of this investigation was to prospectively determine whether correction for CPA improves the discriminating power of SLP for detection of mild-to-moderate glaucoma.DESIGN: Cross-sectional analysis of normal and glaucomatous eyes.METHODS: We constructed a noninvasive slit-lamp-mounted device incorporating two crossed linear polarizers and an optical retarder to measure the slow axis of corneal polarization. Complete ocular examination, standard automated perimetry, SLP imaging, and CPA measurements were performed on normal and glaucomatous eyes. One eye/subject was enrolled; if both eyes of a patient were eligible for the study, the right eye was selected. For each of the 13 SLP parameters, logistic regression was used to determine if including CPA in the model influenced the ability to discriminate between normal and glaucomatous eyes.RESULTS: Forty-three normal eyes (average visual field mean defect, −0.53 ± 1.4 dB) and 33 glaucomatous eyes (average visual field mean defect, −5.93 ± 6.5 dB) were enrolled. CPA was significantly correlated with summary retardation parameters (average thickness and integral values) in normal (r = 0.72–0.83, P < .001 for all values) and glaucomatous eyes (r = 0.43–0.62, P = .013 to < .001). Including CPA in the model improved the ability to discriminate between normal and glaucomatous eyes for five retardation parameters quantifying retinal nerve fiber layer (RNFL) thickness (range of P values: 0.045–0.001). For inferior average thickness, area under the receiver operating characteristic (ROC) curve increased significantly (P = .002) from 0.70 to 0.78 after accounting for CPA; with a sensitivity set at 80% specificity improved from 33% to 72%. Correlations between visual field corrected pattern standard deviation and average thickness, ellipse average, superior average, and inferior average significantly increased (range of P values, .018–.001) after adjustment for CPA (r = −0.35 and −0.45, −0.38 and −0.47, −0.46 and −0.57, and −0.42 and −0.49, respectively).CONCLUSIONS: Correction for CPA significantly increases the correlation between retinal nerve fiber layer structural damage and visual function and significantly improves the discriminating power of SLP for detection of mild-to-moderate glaucoma.

Pelagic sedimentation on rough seafloor topography 2. Inversion results from the North Atlantic Acoustic Reverberation Corridor

Seafloor slope distributions are sensitive to basement topography, the surface shape of sediment distributions, and the average thickness of sediment within a region. By comparing slope distributions computed from bathymetric data to distributions from realistic models of sedimented topography, we determine how characteristic values of average sediment thickness (L), RMS basement variability (H), and apparent diffusivity (κ) vary throughout the Office of Naval Research Acoustic Reverberation Corridor, located on the western flank of the Mid‐Atlantic Ridge north of the Kane Fracture Zone (25.5°–27.25°N, 44.5°–49°W). Values of L from basin‐centered subregions show thinner sediments near the axis, thickening westward with maximum values found on 10–20 Ma seafloor. Lower values of L are found for older (late Oligocene/early Miocene) seafloor. Values of L on young seafloor suggest a sediment accumulation rate of 6.5±2.3 m/m.y. since ∼10 Ma. Values of H computed from hill‐centered regions range from 217 to 306 m, with an average of 267±27 m. Hills are generally larger to the north of a low running through the study area. Values of κ range from 0.12 to 0.77 m2/yr, with an average of 0.32±0.19 m2/yr. Lower values of Kbetter describe the surface shapes of individual high‐standing ponds, while higher values are needed to model the surface shapes of thick deposits in regional lows. This difference in κ with geological setting is probably due to variations in sediment transport mechanisms.

Geostatistical Reserve Estimation: A Case Study in the Canakci Coal Seam of Ermenek Basin, Turkey

The Ermenek Basin in the central Taurus Region, southern part of Turkey, is a Neogene coal basin superimposed on the Late Cretaceous-Late Eocene nappe system of the Taurus mountains. The basin contains a mineable coal seal which extends to the different parts of the basin. In this study, for the reserve estimation of the Canakci coal seam, variogram calculation, a spherical-type geostatistical model and its validation, and kriging were used. The data used in the study were obtained from 31 vertical drillholes. The results of the data and variogram analysis indicate that the coal seam thicknesses display a mean of 11.37 m with 120.56 variance and 0.97 coefficient of variation. After the estimation of the average thickness values of the blocks by kriging, the total volume of 4,757,441 m3 was calculated and the mean density of coal was taken as 1.30 t/m3, and the coal tonnage in the Canakci area was determined as 6,184,673 by block kriging technique.

Vegetation detection through smoke‐filled AVIRIS images: An assessment using MODIS band passes

Radiometrically calibrated, Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) images acquired during the Smoke, Clouds and Radiation in Brazil (SCAR‐B) experiment were processed to simulate vegetation index (VI) imagery with the Moderate Resolution Imaging Spectroradiometer (MODIS) band passes. Data sets were extracted from tropical forested areas, burned fields, and shrub/grassland areas over both clear and variable smoke conditions with average aerosol optical thickness (AOT) values at 0.67 μm of 0.14, 1.1, and 1.9, respectively. The atmospheric resistant VIs and various middle‐infrared (MIR) derived VIs were then analyzed with respect to their ability to minimize atmospheric “smoke” contamination. The atmospheric resistant VIs utilized the blue band for correction of the red band, while the MIR‐derived VIs used the MIR region (1.3–2.5 μm) as a substitute for the red band since it is relatively transparent to smoke, yet remains sensitive to green vegetation. The performance of these indices were assessed and compared with the normalized difference vegetation index (NDVI) and the soil‐adjusted vegetation index (SAVI). Over the tropical forests the NDVI and SAVI had high relative errors over all smoke‐filled atmospheric conditions (50–80% error), while the atmospheric resistant VIs resulted in a 50–80% relative error only over thick levels of smoke. Over optically thin levels (AOT at 0.67 μm &lt;1.1) they performed much better with a 20–40% relative error. The MIR‐derived VIs, on the other hand, outperformed all other VIs over forested areas (≤ 5% error). However, over burned fields with minimal amounts of green biomass the MIR‐derived VIs had the highest levels of error due to smoke (&gt;40%), while all other indices had errors below 20%. In the shrub/grassland site, the atmospheric resistant indices behaved similarly with the MIR‐derived indices, with both less sensitive to smoke than the NDVI and SAVI. We conclude that the MIR indices, particularly with MODIS band 7 (2.13 μm), are useful in vegetation monitoring over forested areas during the burning season. However, they did not perform well in areas outside of forests such as burned areas and shrub/grassland.

A pilot survey of radiation doses received in the United Kingdom Breast Screening Programme.

A survey of radiation dose and compressed breast thickness was conducted in samples of women undergoing mammography in the United Kingdom National Health Service breast screening programme. The aims were to determine the average value and distribution of dose and thickness, and to identify technical difficulties in carrying out such a survey. Values of breast thickness and mean glandular dose, calculated from exposure factors and measured X-ray beam parameters, were collected for 4633 women in 92 screening units in 1994 and 1995. The median (lower quartile, upper quartile) dose per film was 1.7 (1.2, 2.4) mGy for the mediolateral oblique view (mean thickness 57 mm) and 1.4 (1.1, 2.0) mGy for the craniocaudal view (mean thickness 52 mm). The median dose per woman was 1.8 (1.3, 2.5) mGy for a one-view examination and 3.3 (2.3, 4.6) mGy for a two-view examination. The dose per film showed an exponential relationship to breast thickness, but no relationship was found between median dose and median breast thickness in the different screening units, possibly because of errors in breast thickness measurement. The values of breast thickness and dose were generally consistent with those in other published surveys, allowing for differences in radiographic technique. No relationship between breast dose and standard optical density was demonstrated. Some recommendations for the conduct of future surveys of breast dose in the UK are proposed.