Longitudinal flow evolution and turbulence structure of dynamically similar, sustained, saline density and turbidity currents

Experimental results are presented concerning flow evolution and turbulence structure of sustained saline and turbidity flows generated on 0°, 3°, 6°, and 9° sloping ramps that terminate abruptly onto a horizontal floor. Two-component velocity and current density were measured with an ultrasonic Doppler velocity profiler and siphon sampler on the slope, just beyond the slope break and downstream on the horizontal floor. Three main factors influence longitudinal flow evolution and turbulence structure: sediment transport and sedimentation, slope angle, and the presence of a slope break. These controls interact differently depending on flow type. Sediment transport is accompanied by an inertial fluid reaction that enhances Reynolds stresses in turbidity flows. Thus turbidity flows mix more vigorously than equivalent saline density flows. For saline flows, turbulent kinetic energy is dependent on slope, and rapid deceleration occurs on the horizontal floor. For turbidity flows, normalized turbulent kinetic energy increases downstream, and mean streamwise deceleration is reduced compared with saline flows. The slope break causes mean bed-normal velocity of turbidity flows to become negative and have a gentler gradient compared with other locations. A reduction of peak Reynolds normal stress in the bed-normal direction is accompanied by an increase in turbulent accelerations across the rest of the flow thickness. Thus the presence of particles acts to increase Reynolds normal stresses independently of gradients of mean velocity, and sediment transport increases across the break in slope. The experiments illustrate that saline density currents may not be good dynamic analogues for natural turbidity currents

Rapid spatiotemporal variations in rift structure during development of the Corinth Rift, central Greece

The Corinth Rift, central Greece, enables analysis of early rift development as it is young (<5Ma) and highly active and its full history is recorded at high resolution by sedimentary systems. A complete compilation of marine geophysical data, complemented by onshore data, is used to develop a high-resolution chronostratigraphy and detailed fault history for the offshore Corinth Rift, integrating interpretations and reconciling previous discrepancies. Rift migration and localization of deformation have been significant within the rift since inception. Over the last circa 2Myr the rift transitioned from a spatially complex rift to a uniform asymmetric rift, but this transition did not occur synchronously along strike. Isochore maps at circa 100kyr intervals illustrate a change in fault polarity within the short interval circa 620-340ka, characterized by progressive transfer of activity from major south dipping faults to north dipping faults and southward migration of discrete depocenters at ~30m/kyr. Since circa 340ka there has been localization and linkage of the dominant north dipping border fault system along the southern rift margin, demonstrated by lateral growth of discrete depocenters at ~40m/kyr. A single central depocenter formed by circa 130ka, indicating full fault linkage. These results indicate that rift localization is progressive (not instantaneous) and can be synchronous once a rift border fault system is established. This study illustrates that development processes within young rifts occur at 100kyr timescales, including rapid changes in rift symmetry and growth and linkage of major rift faults

The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy

Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations. Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves. Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p  90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score. Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care

Synclinal-horst basins: Examples from the southern Rio Grande rift and southern transition zone of southwestern New Mexico, USA

In areas of broadly distributed extensional strain, the back-tilted edges of a wider than normal horst block may create a synclinal-horst basin. Three Neogene synclinal-horst basins are described from the southern Rio Grande rift and southern Transition Zone of southwestern New Mexico, USA. The late Miocene-Quaternary Uvas Valley basin developed between two fault blocks that dip 6-8° toward one another. Containing a maximum of 200 m of sediment, the Uvas Valley basin has a nearly symmetrical distribution of sediment thickness and appears to have been hydrologically closed throughout its history. The Miocene Gila Wilderness synclinal-horst basin is bordered on three sides by gently tilted (10°, 15°, 20°) fault blocks. Despite evidence of an axial drainage that may have exited the northern edge of the basin, 200-300 m of sediment accumulated in the basin, probably as a result of high sediment yields from the large, high-relief catchments. The Jornada del Muerto synclinal-horst basin is positioned between the east-tilted Caballo and west-tilted San Andres fault blocks. Despite uplift and probable tilting of the adjacent fault blocks in the latest Oligocene and Miocene time, sediment was transported off the horst and deposited in an adjacent basin to the south. Sediment only began to accumulate in the Jornada del Muerto basin in Pliocene and Quaternary time, when an east-dipping normal fault along the axis of the synclinc created a small half graben. Overall, synclinal-horst basins are rare, because horsts wide enough to develop broad synclines are uncommon in extensional terrains. Synclinal-horst basins may be most common along the margins of extensional terrains, where thicker, colder crust results in wider fault spacing

Modern flood deposition, erosion, and fan-channel avulsion on the semiarid Red Canyon and Palomas Canyon alluvial fans in the Southern Rio Grande Rift, New Mexico, U.S.A

In the summer of 2006, large floods occurred on the Red Canyon (footwall-derived) and Paloinas Canyon (hanging-wall-derived) alluvial fans, which are located on opposite sides of the Rio Grande floodplain in the Palomas half graben of the southern Rio Grande rift. The initial phase of the Red Canyon flood took place on the active central fan lobe, but subsequent avulsion of the main channel shifted the flood to the south, where it eroded all but two small relicts of the former inactive, toe-cut lobe before depositing up to 2 in of coarse gravel. Deposition of 0.5 m of gravel-size detritus by the Palomas Canyon flood was largely confined to the active, incised channel and to gravel bars that built into the river, although floodwater spilled over the southern bank of the channel near its mouth, depositing a thin (< 15 cm) veneer of fine sand on the floodplain. Measurements of mean and maximum grain size of the flood deposits, channel-bed slopes, and flood depth based on vegetative high-water marks allow estimates of mean flood velocity (Red Canyon = 8.6 m s-1; Palomas Canyon = 7.4 m s-1), flood-water discharge (Red Canyon = 971 m3 s-1; Palomas Canyon = 179 m3 s-1), and volume -of flood deposits (Red Canyon = 3.19 × 105 m3; Palomas Canyon = 1.72 × 104 m3). Mapping of the modern floodplain and outcrop analysis of the Palomas Formation (Pliocene-lower Pleistocene) in the Palomas basin provide insight into facies architecture in half grabens. Footwall-derived alluvial-fan detritus consists principally of shallow, multistory gravel-conglomerate channels produced by channel avulsion across the surface of the small fans. Asymmetrical basin tilting causes toe-cutting of the footwall-derived fans by the axial river and incision of hanging-wall-derived alluvial-fan channels, the latter resulting in ribbon-shaped gravel-conglomerate channels interbedded with finer-grained, distal-fan sediment. The Red Canyon and Palomas Canyon floods changed the location, width, and depth of the Rio Grande, causing flooding of the western floodplain for ~ 1 km upstream of the constriction. Because the Rio Grande has been dammed since 1916, it no longer has the stream power to ffectively redistribute large volumes of fan detritus and must be dredged in order to avoid upstream flooding by the river

Building up or out? Disparate sequence architectures along an active rift margin-Corinth rift, Greece

Early Pleistocene synrift deltas developed along the southern Corinth rift margin were deposited in a single, dominantly lacustrine depocenter and were subject to the same climate-related base-level and sediment supply cyclicity. Two synrift deltas, just 50 km apart, show markedly different sequence geometry and evolution related to their location along the evolving border fault. In the west, strongly aggradational fan deltas (>600 m thick; 2–4 km radius) deposited in the immediate hanging wall of the active border fault comprise stacked 30–100 m thick stratal units bounded by flooding surfaces. Each unit evolves from aggradational to progradational with no evidence for abrupt subaerial exposure or fluvial incision. In contrast, in the central rift, the border fault propagated upward into an already deep lacustrine environment, locating rift-margin deltas 15 km into the footwall. The deltas here have a radius of >9 km and comprise northward downstepping and offlapping units, 50–200 m thick, that unconformably overlie older synrift sediments and are themselves incised. The key factors driving the marked variation in sequence stratigraphic architecture are: (1) differential uplift and subsidence related to position with respect to the border fault system, and (2) inherited topography that influenced shoreline position and offshore bathymetry. Our work illustrates that stratal units and their bounding surfaces may have only local (<10 km) extent, highlighting the uncertainty involved in assigning chronostratigraphic significance to systems tracts and in calculating base-level changes from stratigraphy where marked spatial variations in uplift and subsidence occur

A pre-operative elevated neutrophil: lymphocyte ratio does not predict survival from oesophageal cancer resection

Background: Elevated pre-operative neutrophil: lymphocyte ratio (NLR) has been identified as a predictor of survival in patients with hepatocellular and colorectal cancer. The aim of this study was to examine the prognostic value of an elevated preoperative NLR following resection for oesophageal cancer. Methods: Patients who underwent resection for oesophageal carcinoma from June 1997 to September 2007 were identified from a local cancer database. Data on demographics, conventional prognostic markers, laboratory analyses including blood count results, and histopathology were collected and analysed. Results: A total of 294 patients were identified with a median age at diagnosis of 65.2 (IQR 59-72) years. The median pre-operative time of blood sample collection was three days (IQR 1-8). The median neutrophil count was 64.2 × 10-9/litre, median lymphocyte count 23.9 × 10-9/litre, whilst the NLR was 2.69 (IQR 1.95-4.02). NLR did not prove to be a significant predictor of number of involved lymph nodes (Cox regression, p = 0.754), disease recurrence (p = 0.288) or death (Cox regression, p = 0.374). Furthermore, survival time was not significantly different between patients with high (≥ 3.5) or low (< 3.5) NLR (p = 0.49). Conclusion: Preoperative NLR does not appear to offer useful predictive ability for outcome, disease-free and overall survival following oesophageal cancer resection