Significant Thickness Variations Research Articles

Analysis Of Fluvial Architecture In the Blackhawk Formation, Wasatch Plateau, Utah, U.S.A., Using Large 3D Photorealistic Models

Abstract There are numerous allocyclic and autocyclic factors which influence fluvial sandbody geometry. Unraveling the relative importance of such factors is challenging because fluvial systems can migrate and avulse across significant distances on the floodplain, so that collecting datasets that cover a large enough area with sufficient detail is difficult. This problem has been addressed by acquiring an oblique helicopter-mounted lidar survey over 16 km of exposed sections from Cretaceous coastal-plain deposits cropping out in the Wasatch Plateau of east-central Utah. The exposures of the Blackhawk Formation occur in steep cliffs, which are continuous for several tens of kilometers, and have been previously inaccessible for study. The recorded lidar data were used to build detailed photorealistic models (virtual outcrops) from which quantitative dimensional data on fluvial architectural elements (mostly sandstone channel bodies) were collected. Those channelized bodies show significant variation in width and thickness. 26% of the sandbodies were identified as being multistory channel bodies, with a thickness of 9.1 m (± 4.67 m; 1 σ) and a width of 142.6 m (± 180.7 m), which are significantly larger than the measured single-story sandbodies (5.9 m and 96.9 m, respectively). 50% of all sandbodies have aspect ratios smaller 13∶1 and the highest values reach 78∶1. The spatial constraint of the 397 fluvial sandbodies enabled the recognition of a series of vertical trends within the dataset. These trends include a subtle upward increase in width and thickness of both the mean and maximum values. This is coupled with a general upward decrease in the number of sandbodies and results in a broadly constant channel-to-overbank ratio. A clear correlation between wider channels with increased distance to the shoreline could also be documented. These observations can be explained by considering the entire Blackhawk Formation as the deposits of a large distributive fluvial system. In this model the key control on channel architecture is the distance to the shoreline, contrasting with previous interpretations of the Blackhawk depositional system in which the rate of accommodation creation in the coastal plain was thought to be the key control on channel geometry and stacking patterns.

Evaluation of choroidal and retinal thickness measurements in haemodialysis patients

We read with interest the article by Ulas et al. [1] which reported a statistically significant reduction in choroidal thickness following haemodialysis in nondiabetic patients, and ‘‘concluded that ultrafiltrationinduced hypovolemia and increased plasma colloid osmotic pressure caused the IOP decrease and choroidal thinning’’ [1]. While this paper contributes to our understanding of how haemodynamic changes may potentially affect the choroidal vasculature, there are relevant considerations that we will like to highlight. It is important to consider the potential effects of normal diurnal variation of choroidal thickness on the reported results [2–4]. The haemodialysis treatments lasted between 3.5 to 4 hours, with choroidal thickness measurements obtained using spectral-domain optical coherence tomography (OCT) scans performed just before and after haemodialysis. While this is an unavoidable feature of the study design, earlier studies have reported significant diurnal variation in choroidal thickness throughout the day, with amplitudes (the difference between the maximum and minimum choroidal thickness) of up to 67 lm [2, 4]. In addition, one study has reported that choroidal thickness decreases progressively during the period from 9:00 am to 5:00 pm [2], which is presumably when the haemodialysis treatments were performed. Therefore, while the observed differences in choroidal thickness could possibly be accounted for by haemodynamic changes occurring during haemodialysis, the effect of normal changes in choroidal thickness also needs to be considered. An additional consideration is the inherent accuracy of point thickness choroidal measurements. Studies have reported significant intra-observer and inter-observer differences in choroidal thickness assessment of up to 32 lm [5]. The reported changes in choroid thickness in this study ranged from 16.57 lm to 21.90 lm [1], which lie within the reported ranges of both diurnal variation and intraobserver repeatability. It will also be interesting to know whether the initial OCT scan was set as a reference for the followup OCT scan after haemodialysis. Without the use of eye tracking and reference scans, a single-line scan may have minor changes in position. Since the choroid has significant topographic variation [3], a slight displacement of the follow-up scan may result in differences of choroidal thickness measurements, which may be sufficient to account for the changes in choroidal thickness that were observed. On the other hand, a review of Fig. 1 in the article by Ulas et al. shows very good consistency of the vascular landmarks between successive OCT scans. The authors also found no significant differences in retinal C. S. H. Tan (&) K. X. Cheong Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, Singapore e-mail: Colintan_eye@yahoo.com.sg

An assessment of the Top Khuff reflectivity: Central Saudi Arabia

The Top Khuff is a major regional seismic marker in Saudi Arabia with an apparent strong and consistent amplitude interpreted as a large impedance contrast between the Khuff carbonate and the overlying Sudair shale. However, the effective Top Khuff response is, in fact, a complex reflection of a stack of thin beds of highly contrasting impedance with significant lateral variations in reflectivity and thickness. Interference among these reflected waves disturbs the amplitude strength and effective reflection time of the Top Khuff and alters the phase and frequency bandwidth of the reflection wavelet. Variations in the Top Khuff amplitude and reflection wavelet were quantified using a Ricker wavelet and solved as an inverse problem with four model parameters: reflection coefficient, reflection time, phase, and frequency. These model parameters are interrelated, and the effective seismic response in a complex situation is a compromise among them. The fit of the Ricker wavelet with the Top Khuff amplitude revealed significant variations in these parameters and verified the Top Khuff is not a simple reflector and may not be a suitable reference horizon for seismic amplitude processing.

Regional and Hemispheric Variation in Cortical Thickness in Chimpanzees (Pan troglodytes)

Recent advances in structural magnetic resonance imaging technology and analysis now allows for accurate in vivo measurement of cortical thickness, an important aspect of cortical organization that has historically only been conducted on postmortem brains. In this study, for the first time, we examined regional and lateralized cortical thickness in a sample of 71 chimpanzees for comparison with previously reported findings in humans. We also measured gray and white matter volumes for each subject. The results indicated that chimpanzees showed significant regional variation in cortical thickness with lower values in primary motor and sensory cortex compared with association cortex. Furthermore, chimpanzees showed significant rightward asymmetries in cortical thickness for a number of regions of interest throughout the cortex and leftward asymmetries in white but not gray matter volume. We also found that total and region-specific cortical thickness was significantly negatively correlated with white matter volume. Thus, chimpanzees with greater white matter volumes had thinner cortical thickness. The collective findings are discussed within the context of previous findings in humans and theories on the evolution of cortical organization and lateralization in primates.

Characterizing the Main Himalayan Thrust in the Garhwal Himalaya, India with receiver function CCP stacking

We use common conversion point (CCP) stacking of Ps receiver functions to image the crustal structure and Moho of the Garhwal Himalaya of India. Our seismic array of 21 broadband seismometers spanned the Himalayan thrust wedge at 79–80°E, between the Main Frontal Thrust and the South Tibet Detachment, in 2005–2006. Our CCP image shows the Main Himalayan Thrust (MHT), the detachment at the base of the Himalayan thrust wedge, with a flat-ramp-flat geometry. Seismic impedance contrasts inferred from geologic cross-sections in Garhwal imply a negative impedance contrast (velocity decreasing downward) for the upper flat, located beneath the Lower Himalaya, and a positive impedance contrast (velocity increasing downward) for the ramp, located beneath the surface trace of the Munsiari Thrust (or MCT-I). At the lower flat, located beneath the Higher Himalaya, spatially coincident measurements of very high electrical conductivities require the presence of free fluids, and we infer a negative impedance contrast on the MHT caused by ponding of these fluids beneath the detachment. Our seismic image indicates that the upper flat of the MHT is ∼10km below sea level and dips north at ∼2°, connecting to a mid-crustal ramp which is ∼10km high and dips at ∼16°. The lower flat is 20–25km below sea level and dips at ∼4°. The Main Central Thrust (MCT) appears as a negative impedance contrast, dipping at ∼16°. The Moho is nearly horizontal at 35–45km depth beneath the Sub-Himalaya and Lower Himalaya, deepening to 50km or more beneath the Higher Himalaya. This depth is 10–25km shallower than in the NW Indian Himalaya and 5–10km shallower than in central Nepal, requiring significant along-strike variations in crustal thickness. The observed thickness of subducted Indian crust in Garwhal is 20–28km.

Effects of Temperature and Time on the Morphology, pH, and Buffering Capacity of Bast and Core Kenaf Fibres

This study investigated the effects of heating on the morphology, pH, and buffering capacity of bast and core kenaf fibre. The bast material yielded longer and thinner fibres (with a higher aspect ratio) compared to the core. Changes in fibre morphology were clearly visible when the temperature of pulping was increased. The morphology of the bast fibre displayed significant variations following treatment at different pulping temperature (150, 160, 170, and 180 °C), time (1, 2, and 3 hours), and with the interaction between both parameters. Core fibre also exhibited significant variation in length, width, and wall thickness in all parameters, but lumen diameter and aspect ratio were not significantly affected by the same processing conditions. The pH value of both fibres was reduced as the temperature increased; core fibre was more acidic compared to bast fibre. Bast fibre exhibited greater acid buffering capacity and core fibre greater alkaline buffering capacity.

The cuticle micromorphology of in situ Erica arborea L. exposed to long-term volcanic gases

Epidermis micromorphology of in situ Erica arborea L. exposed for generations to long-term effect of volcanic gases in Pisciarelli and Solfatara di Pozzuoli areas have been studied by X-ray analyses, SEM and TEM observations. In particular, the aim of this study is to investigate the effects of volcanic gases on extant and possibly fossil plants. Plants of the same species living in a nearby control site were also studied for comparison. SEM coupled with EDX analysis was used to localize different elements within the leaves (mesophyll, cell wall and cuticle). After conventional and cryo preparation, SEM of mature leaves ascertained that the abaxial side is more serrate in fumigated leaves and hairs, epicuticular wax alterations have also been noted. Leaves experiencing chronic fumigation display stomata more sunken with respect to the epidermal surface. TEM of transverse and longitudinal sections of cuticle showed an outer A2 granular amorphous layer and external to a B1 fibrillous layer. Significant statistical variations of ultrastructural components of the cuticle revealed a response of E. arborea to this extreme environment. At the ultrastructural level, significant variations in thickness of the cell wall plus cuticle, cell wall and A2 layer among fumigated and non-fumigated leaves have been found. In the studied localities a positive correlation between atmospheric CO2 concentration and the thickness of A2 layer also exists. The results are of interest being applicable in the understanding of plant cuticle responses during periods of normal vs. volcanic activity.

Geologic Setting, Sedimentary Architecture, and Paragenesis of the Mesoproterozoic Sediment-Hosted Sheep Creek Cu-Co-Ag Deposit, Helena Embayment, Montana

The northern margin of the Helena Embayment contains extensive syngenetic to diagenetic massive pyrite horizons that extend over 25 km along the Volcano Valley-Buttress fault zone and extend up to 8 km basinward (south) within the Mesoproterozoic Newland Formation. The Sheep Creek Cu-Co deposit occurs within a structural block along a bend in the fault system, where replacement-style chalcopyrite mineralization is spatially associated mostly with the two stratigraphically lowest massive pyrite zones. These mineralized pyritic horizons are intercalated with debris flows derived from synsedimentary movement along the Volcano Valley-Buttress fault zone. Cominco American Inc. delineated a geologic resource of 4.5 Mt at 2.5% Cu and 0.1% Co in the upper sulfide zone and 4 Mt at 4% Cu within the lower sulfide zone. More recently, Tintina Resources Inc. has delineated an inferred resource of 8.48 Mt at 2.96% Cu, 0.12% Co, and 16.4 g/t Ag in the upper sulfide zone. The more intact upper sulfide zone displays significant thickness variations along strike thought to represent formation in at least three separate subbasins. The largest accumulation of mineralized sulfide in the upper zone occurs as an N-S–trending body that thickens southward from the generally E trending Volcano Valley Fault and probably occupies a paleograben controlled by normal faults in the hanging wall of the Volcano Valley Fault. Early microcrystalline to framboidal pyrite was accompanied by abundant and local barite deposition in the upper and lower sulfide zones, respectively. The sulfide bodies underwent intense (lower sulfide zone) to localized (upper sulfide zone) recrystallization and overprinting by coarser-grained pyrite and minor marcasite that is intergrown with and replaces dolomite. Silicification and paragenetically late chalcopyrite, along with minor tennantite in the upper sulfide zone, replaces fine-grained pyrite, barite, and carbonate. The restriction of chalcopyrite to inferred synsedimentary E- and northerly trending faults and absence of definitive zonation with respect to the Laramide Volcano Valley Fault in the lower sulfide zone suggest a diagenetic age related to basin development for the Sheep Creek Cu-Co-Ag deposit.

Regional cartilage properties of three quadruped tibiofemoral joints used in musculoskeletal research studies

Quadruped joints are commonly used in musculoskeletal studies as a surrogate for human joints despite inherent differences in tissue properties. Although concerns exist regarding model validity, relatively few studies comparing the mechanical properties of quadruped tissue exist. This study aimed to characterise the regional intrinsic mechanical properties and thickness of tibiofemoral cartilage from three quadrupeds used in modern musculoskeletal research. Osteochondral plugs were removed from the major weight-bearing regions of porcine (6 months), bovine (18-24 months) and ovine (approximately 5 years) tibiofemoral joints. The equilibrium elastic modulus and permeability of the cartilage were derived by combining the creep indention deformation results and calculated tissue thickness within an in-silica model. Results showed significant interspecies and regional variation in cartilage thickness. Cartilage was thickest on porcine femoral condyles whereas ovine cartilage was consistently thinner across all sites. Furthermore, porcine tissue had a significantly lower equilibrium elastic modulus and significantly higher permeability than ovine cartilage. The results highlight the importance of considering the interspecies and regional variation in quadruped tissue properties when selecting animal joints for musculoskeletal investigations.

Influence of volcanic gases on the epidermis of Pinus halepensis Mill. in Campi Flegrei, Southern Italy: A possible tool for detecting volcanism in present and past floras

Cuticle micromorphology together with epidermal and epistomatal wax, in both current- and first-year-old needles of conifer Pinus halepensis (Aleppo pine) trees growing under volcanic gas fumigation was analysed in Pisciarelli area, Campi Flegrei, Southern Italy. As a control, current- and first-year-old needles growing far from volcanic gas emission were also sampled. Using a multidisciplinary approach with SEM, TEM and X-ray, volcanic gases were shown to cause degradation on epicuticular and epistomatal waxes. Significant statistical variations of ultrastructural components of the cuticle, with 30 measurements, including total thickness of the cuticle, and details and proportions of all different layers, and use of confidence interval, revealed a high degree of sensitivity of Aleppo pine to this extreme environment. In the present study, non-significant thickness variations of the cell wall plus cuticle among current- and first-year-old needles of both fumigated and non fumigated trees have been found. However, at the ultrastructural level, significant variations in cell wall and total cuticle thickness, especially within the three zones of B1 fibrillar layer, revealed different equilibria for each of the four types of material. Using energy dispersive X-ray microanalysis, no sulphur was found in either cuticle or epidermal cells, but the presence of H2S in the fumarole gas is suspected to cause indirect and/or direct cuticle alterations of wax structure. Ultrastructural characters of plant cuticles related to emission of volcanic gases during the geological past are also discussed. Among these considerations, an identification key enabling distinction between non fumigated and fumigated materials with 9 characters, provides a good tool detecting the influence of volcanism for extant and fossil plants.

Variations in bark thickness and sapwood density of Calophyllum inophyllum provenances in Australia and in Sri Lanka

Sapwood density and bark thickness of Calophyllum inophyllum L. (a multipurpose durable timber species) were studied in various locations in Northern Australia and in Sri Lanka. Measurements were taken non-destructively by using core sampling and bark gauge. From each provenance, 4–15 mature trees having girth at breast height over bark (GBHOB) at 100–150 cm were selected on the basis of the population size. Significant (p<0.05) hemispheric and provenance variations in bark thickness were found. Variations in the bark thickness are influenced by environmental variables. Variations in sapwood density were less pronounced compared to that of bark thickness. Variations in sapwood density are likely to be governed by genotypic variations.

Interpretation of channelized architecture using three-dimensional photo real models, Pennsylvanian deep-water deposits at Big Rock Quarry, Arkansas

Mapping geological details and interpreting three-dimensional geometries in a highly heterogeneous outcrop such as the exposure at Big Rock Quarry has been a continuous challenge especially because high vertical cliffs make access to most of the rocks difficult for direct geological observations. Previous interpretations of facies architecture were derived from gamma–ray profiles, a core and measurements made on two-dimensional photomosaics. This paper represents the first attempt of three-dimensional interpretation of the geometry and facies pattern of the Jackfork nested channel complex deposited at the base-of-slope. Examination of the photo real model of the outcrop with assigned lithologies allowed extraction of accurate 3-D qualitative, as well as quantitative (channel dimensions) geometric information. This facilitated interpretation and reconstruction of the submarine channel complex architecture making possible correlations of strata exposed on the two sides of the quarry. Most of the exposed vertically and laterally stacked channels are large, aggradational with well-defined axial regions overlain by matrix-supported breccia which grades upward into amalgamated sandstones. The thickness of the sandstone decreases toward the southeastern end of the quarry where more shale is present. The channel infill consists of thin-bedded sandstones interlayered with shale which overlain the breccia. The upper part of the quarry is made up of smaller, lateral migrating channels. Significant channel width and thickness variation can be recognized at outcrop scale. Thirty-eight identified channels are characterized by a relatively low aspect ratio (4:1 to 32:1) with channel dimensions ranging from 25 m to 314 m wide and 2 m–24 m deep. Bed thickness distributions of various facies show that the sandstone comprises a significant proportion (83%) of the total channel thickness, while shale and breccia represent about 8%, and 17% respectively. This yields a high net-to gross ratio of more than 80%. Compared to previous reconstructions our 3-D photo real model is more accurate and it can be used to calibrate simulation of processes in deep-water environments.

Assessing debris flows using LIDAR differencing: 18 May 2005 Matata event, New Zealand

The town of Matata in the Eastern Bay of Plenty (New Zealand) experienced an extreme rainfall event on the 18 May 2005. This event triggered widespread landslips and large debris flows in the Awatarariki and Waitepuru catchments behind Matata. The Light Detection and Ranging technology (LIDAR) data sets flown prior to and following this event have been differenced and used in conjunction with a detailed field study to identify the distribution of debris and major sediment pathways which, from the Awatarariki catchment, transported at least 350,000 ± 50,000 m 3 of debris. Debris flows were initially confined to stream valleys and controlled by the density and hydraulic thrust of the currents, before emerging onto the Awatarariki debris fan where a complex system of unconfined sediment pathways developed. Here, large boulders, clasts, logs and entire homes were deposited as the flows decelerated. Downstream from the debris fan, the pre-existing coastal foredune topography played a significant role in deflecting the more dilute currents that in filled lagoonal swale systems in both directions. The differenced LIDAR data have revealed several sectors characterised by significant variation in clast size, thickness and volume of debris as well as areas where post-debris flow cleanup and grading operations have resulted in man-made levees, sediment dumps, scoured channels and substantial graded areas. The application of differenced LIDAR data to a debris flow event demonstrates the techniques potential as a precise and powerful tool for hazard mapping and assessment.

Sedimentation styles and variability of organic matter types in the Triassic, non-marine half-grabens of west Argentina: implications for petroleum systems in rift basins

ABSTRACT Extensional relaxation due to the collapse of the active margin of Gondwanaland during the Triassic led to rapidly subsiding, fault-bounded half-grabens in west Argentina. The Cuyo rift basin was the largest of these fault-bounded troughs. Two linked asymmetrical half-grabens have been identified in the Cuyo basin: Cacheuta in the south and Las Penas-Tamberias in the north. Their stratigraphy exhibits a classic tripartite internal organization with a basal alluvial and fluvial section followed by a lacustrine interval which in turn is overlain by fluvial deposits. The basin fill in both half-grabens shows significant lateral thickness variations that reflect the contrasting subsidence rates on the fault and flexural margins. The lacustrine shales in the Cacheuta half-graben have an average total organic carbon (TOC) content of 4%, locally reaching 20%, dominated by type I, amorphous, algal organic matter and high hydrogen index (HI) values. The shales are associated with parasequences in river-dominated deltas. Oils derived from these source rocks are waxy and with low sulphur content. The oil shales are associated with sandstones arranged in parasequences deposited in river-dominated Gilbert-type deltas. This interval in the Cacheuta half-graben can be assigned to a slightly overfilled to balanced-fill lake type. In Las Penas-Tamberias, the dominant source rock facies in the lacustrine section is made up of calcareous shales with oil-prone, type I(II) kerogen and TOC values up to 13% and high HI values. The presence of gammacerane and b-carotane, common in saline conditions, is conspicuous. The presence of oolitic and bioclastic grainstones and microstromatolitic limestones on the ramp margin and clastic facies on the border fault suggests a slightly underbalanced to balanced lake type. The Cuyo rift basin branches to the NE into the Ischigualasto-Villa Union half-graben. Lacustrine shales along the fault margin of this half-graben are dominated by type III, gas-prone organic matter with TOC values up to 4% and low HI values. Parasequences with a strong progradational stacking pattern and steep front slopes are interpreted as mouth bars in a Gilbert-type delta. These characteristics are consistent with an overfilled lake basin type where sedimentation rate exceeds subsidence rate. The Triassic rift system of west Argentina shows the gamut of lacustrine source rocks that, combined with the analysis of diagnostic associated facies, allow the discrimination of lake basin types and their influence in the resulting hydrocarbon phase.

Variations in chondrocyte apoptosis may explain the increased prevalence of osteoarthritis in some joints

To investigate whether there are any variations in chondrocyte susceptibility to an apoptotic stimulus between cells of articular cartilage (AC) from equine joints that differ in prevalence of osteoarthritis (OA). Cartilage from macroscopically normal equine metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints was used. Prior to culture, chondrocyte viability was assessed using the fluorescein diacetate (FDA) and propidium iodide paravital staining method. AC explants were subsequently treated with tumour necrosis factor-α (TNF-α) in combination with Actinomycin D to induce apoptosis. Apoptosis of chondrocytes in cartilage sections was assessed by expression of active caspase-3 using indirect immunohistochemistry and sections also histologically graded using a 'modified' Mankin scoring system. Prior to culture (mean±standard deviation) chondrocyte viability was 80.7% (3.5). The extent of chondrocyte apoptosis induced by TNF-α/Actinomycin D varied markedly according to the joint type that the cartilage was sampled from. For MCP joints, the extent of overall chondrocyte apoptosis was significantly higher (P<0.001) in stimulated explants (26.7%, 10.3) than that observed in unstimulated control samples (9.6%, 7.5). Conversely, chondrocytes from PIP and DIP joint cartilage did not respond significantly to apoptotic stimulation (P>0.05). Significant variations in cellularity and thickness were also evident between cartilages of different joint types. Data in this study demonstrate that chondrocytes from three equine joint types with varying prevalences of OA differ significantly in terms of susceptibility to apoptosis induction. This may provide a possible explanation for the joint-specific nature of the disease.

Dimensions of the human sclera: Thickness measurement and regional changes with axial length

Scleral thickness, especially near the region of the optic nerve head (ONH), is a potential factor of interest in the development of glaucomatous optic neuropathy. Our goal was to characterize the scleral thickness distribution and other geometric features of human eyes. Eleven enucleated human globes (7 normal and 4 ostensibly glaucomatous) were imaged using high-field microMRI, providing 80 μm isotropic resolution over the whole eye. The MRI scans were segmented to produce 3-D corneoscleral shells. Each shell was divided into 15 slices along the anterior–posterior axis of the eye, and each slice was further subdivided into the anatomical quadrants. Average thickness was measured in each region, producing 60 thickness measurements per eye. Hierarchical clustering was used to identify trends in the thickness distribution, and scleral geometric features were correlated with globe axial length. Thickness over the whole sclera was 670 ± 80 μm (mean ± SD; range: 564 μm–832 μm) over the 11 eyes. Maximum thickness occurred at the posterior pole of the eye, with mean thickness of 996 ± 181 μm. Thickness decreased to a minimum at the equator, where a mean thickness of 491 ± 91 μm was measured. Eyes with a reported history of glaucoma were found to have longer axial length, smaller ONH canal dimensions and thinner posterior sclera. Several geometrical parameters of the eye, including posterior scleral thickness, axial length, and ONH canal diameter, appear linked. Significant intra-individual and inter-individual variation in scleral thickness was evident. This may be indicative of inter-individual differences in ocular biomechanics.

Deep crustal structure of the Indian shield from joint inversion of P wave receiver functions and Rayleigh wave group velocities: Implications for Precambrian crustal evolution

The S wave velocity structure of the crust and uppermost mantle of the Indian shield has been investigated by jointly inverting P wave receiver functions and Rayleigh wave group velocities at 38 broadband stations in the subcontinent. The Indian shield is an amalgamation of several terranes of Archean and Proterozoic age that were partly flooded by Deccan Trap volcanism during Cenozoic times and that make up a natural laboratory for assessing models of Precambrian crustal evolution. Our results reveal significant variations in crustal thickness and deep crustal velocities: 45–50 km thick under the Archean West Dharwar craton and Southern Granulite Terrane, with lower crustal velocities around 4.1 km/s; 32–35 km thick beneath the Archean East Dharwar and Bundelkhand cratons, with lower crustal velocities around 3.8–3.9 km/s; 50–65 km thick under the Proterozoic Bhandara craton, with lower crustal velocities around 4.2–4.3 km/s; and ∼55 km thick under the Proterozoic Aravalli‐Delhi belt, with lower crustal velocities around 4.2 km/s. S velocities in the 4.1–4.3 km/s range in the deep crust can be attributed to mafic lithologies, suggesting there has been no secular change in the Precambrian evolution of the south Indian shield. Moreover, pervasive mafic dike swarming throughout the Indian shield suggests that the layer of mafic cumulates is 2.5–1.6 Ga old and that it delaminated from some Archean terranes. Our interpretation is that mafic underplating of the terranes making up the Indian shield occurred in Proterozoic times and that a refractory root developed under the Archean terranes after the Proterozoic event.

Seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western North China Craton

We have migrated teleseismic S-receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the North China Craton (NCC). Our images show that in contrast to the eastern NCC where significantly thinned lithosphere (60–100 km) is widespread, the central and western NCC are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere. The thick lithosphere (> 200 km) is present beneath the stable Ordos Plateau and the thinned lithosphere (up to 80 km) is found in the late Cenozoic Yinchuan–Hetao and Shaanxi–Shanxi rift areas, with sharp changes occurring over a lateral distance of < 200–400 km. Near the boundary between the eastern and central NCC, a rapid thickening of the lithosphere by 20–40 km over ~ 100 km laterally is observed, concordant with abrupt changes in surface topography and roughly coincident with the North–South Gravity Lineament (NSGL). Together with petrological and geochemical data these structural features suggest that lithospheric remobilization and thinning may have affected the NCC much further to the west than previously thought. Compared to the widespread reactivation and destruction of lithospheric mantle in the eastern NCC, lithospheric modification of the central and western NCC may have been less intensive and spatially more localized. Rifting and lithospheric reactivation probably occurred at mechanically weak boundary zones, but the cratonic nucleus of the Ordos block (which forms the western part of NCC) seems to have retained its rigidity, thickness, and stability over long periods of geological time. The long-term survival of such lateral contrasts suggests that the thick lithosphere is compositionally distinct from the convecting upper mantle.

Thickness Measurements of Donor Posterior Disks After Descemet Stripping Endothelial Keratoplasty With Anterior Segment Optical Coherence Tomography

To evaluate donor posterior disk thickness measured with anterior segment optical coherence tomography after Descemet stripping endothelial keratoplasty. Fifteen patients (17 eyes) after Descemet stripping endothelial keratoplasty, using manually dissected donor posterior disks, were measured with the Visante anterior segment optical coherence tomography (Carl Zeiss Meditec Inc, Dublin, CA). Optical coherence tomography scans were made in a radial pattern, 45 degrees apart, starting in the horizontal axis. Thickness measurements of the donor posterior disks were taken centrally and at fixed radii toward the periphery and were correlated to postoperative change in spherical equivalent (SE), best-corrected visual acuity (BCVA, in Snellen), and improvement in BCVA. Median BCVA was 20/30 (range 20/60-20/20) postoperatively. Median postoperative improvement in BCVA was 4 lines (range 1-11). Median follow-up time was 15.5 months (range 6-32 months). Median postoperative change in SE was -0.25 diopters (range -4.25 to +3.00 diopters). Median central disk thickness was 128.3 microm (range 55-181 microm) and increased significantly toward the periphery: median disk thickness at the 1.5 mm radius was 140.8 microm (range 72-199 microm) and at the 3.0 mm radius was 161.5 microm (range 102-245 microm). No correlation was found between (central) donor disk thickness and postoperative BCVA or change in SE. A nonstatistically significant trend was seen toward more improvement in BCVA with thinner donor disks. Optical coherence tomography measurements of the manually dissected donor posterior disk showed significant variation in thickness, without a statistically significant effect on postoperative BCVA or improvement thereof. Central thickness varied significantly from the peripheral thickness within donor posterior disk.

Influence of polymeric fluid additives in EHL rolling/sliding line contacts

The effect of polymeric fluid additives on EHL behavior of rolling/sliding line contacts is investigated numerically at low as well as high loads. The polymer-modified oil is represented by a homogeneous mixture of Newtonian base oil and power law fluid with varying concentration, viscosity ratio and power law index. The Reynolds equation incorporating the mixed rheological fluid model is derived using perturbation method. The EHL characteristics computed for polymer-modified oils are found to depend upon the effective viscosity of the lubricant mixture which is governed by the superposition of shear thinning behavior and piezo-thickening effect of the polymeric fluid additive. Since the reference viscosity of polymeric fluid additives is much higher than that of base oil, therefore, polymer-modified oils are shown to yield thicker fluid films in most of the cases. The results show a significant variation in maximum fluid pressure and minimum fluid film thickness with the volume fraction, reference viscosity ratio and power law index of the polymeric fluid additive.