Rollover Point Research Articles

Impact of wave, tides and fluid mud on fluvial discharge across a compound clinoform (Pliocene Orinoco Delta)

AbstractCompound clinoforms are well‐recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net‐to‐gross, thickness and facies association evaluation show overall coarsening‐upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The subaqueous clinothem records a lower, relatively muddy coarsening‐upward interval, 112 m thick, with net‐to‐gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated subaqueous platform (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near‐bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid‐mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid‐mud carpet. The shoreline clinothem (<8 m thick) has high net‐to‐gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net‐to‐gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop.

Enhancement of detachment control with simplified real-time modelling on the KSTAR tokamak

Detachment control based on ion saturation current I sat measurements from Langmuir probes (LPs) is implemented in the KSTAR tokamak and shown to be capable of following dynamic and constant target trajectories with good accuracy, in H-mode, by moderating the flow rate of nitrogen or deuterium. I sat controllers normalize I sat in order to form attachment fraction (A frac ) as their control parameter. The KSTAR implementation of A frac control differs from previous work in that it continuously calculates a model for attached I sat and uses that as the denominator in A frac , whereas prior implementations either record peak I sat at rollover as they pass it or take estimated as a manual input prior to the shot. The KSTAR controller therefore does not need to keep track of rollover status and keep separate targets for pre- and post-rollover states, and it can automatically adapt to changes in scenario at any time. It is also less vulnerable to noise as it will not lock in an outlier as a rollover point.

Palaeo-Shoreline Configuration of the Adventure Plateau (Sicilian Channel) at the Last Glacial Maximum

The Adventure Plateau, located in the NW sector of the Sicilian Channel, experienced several episodes of exposure/erosion and subsequent drowning, with the most recent occurring after the Last Glacial Maximum (LGM). Unlike other parts of the Sicilian Channel, the Adventure Plateau is relatively tectonically stable and is therefore best suitable for reconstructing its coastal configuration before the post-LGM marine transgression. Here, we use high-resolution seismic data to identify and map the palaeo-coastline at the LGM on the basis of the internal architecture of the prograding wedges (i.e., the location of the subaqueous clinoform rollover point) and the erosional markers such as the subaerial unconformities and the wave ravinement surfaces. These data, which show an extreme variability in the palaeo-morphology of the coastal margins of the Adventure Plateau, have been complemented with vintage seismic profiles in order to entirely cover its perimeter. The mapped LGM coastline has then been compared to predictions from glacial isostatic adjustment (GIA) modeling, which considers the horizontal migration of the shorelines in response to sea level rise and to Earth’s rotational and deformational effects associated with deglaciation. The two shorelines (i.e., the coastline derived from the marine data interpretation and the one derived from the GIA model) are in good agreement at 21 kyears BP, although some discrepancies occur in the southern part of the plateau, where the seabed slope is extremely gentle, which makes the clinoform rollover points and the buried erosional unconformities difficult to detect. After 20 kyears BP, an acceleration in the rate of the sea level rise occurred. The results of this study indicate the importance of comparing experimental data with model predictions in order to refine and calibrate boundary parameters and to gain a better picture of the evolution of sea level rise over various time scales.

Top-emitting 940-nm thin-film VCSELs transferred onto aluminum heatsinks

Thin-film vertical cavity surface emitting lasers (VCSELs) mounted onto heatsinks open up the way toward low-power consumption and high-power operation, enabling them to be widely used for energy saving high-speed optical data communication and three-dimensional sensor applications. There are two conventional VCSEL polarity structures: p-on-n and n-on-p polarity. The former is more preferably used owing to the reduced series resistance of n-type bottom distributed Bragg reflection (DBR) as well as the lower defect densities of n-type GaAs substrates. In this study, the p-on-n structures of thin-film VCSELs, including an etch stop layer and a highly n-doped GaAs ohmic layer, were epitaxially grown in upright order by using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The p-on-n structures of thin-film VCSELs were transferred onto an aluminum heatsink via a double-transfer technique, allowing the top-emitting thin-film VCSELs to keep the p-on-n polarity with the removal of the GaAs substrate. The threshold current (Ith) and voltage (Vth) of the fabricated top-emitting thin-film VCSELs were 1 mA and 2.8 V, respectively. The optical power was 7.7 mW at a rollover point of 16.1 mA.

A Recurrent Neural Network Model for Battery Capacity Fade Curve Prediction Using Early Life Data

Batteries are often considered the most performance and reliability-limiting component of any electronic and electrical assembly. Thus their degradation trend characterization through extensive testing and development of life prediction algorithms using testing data have been at the forefront of battery research. However, battery testing is also time-consuming, and it can take at least few months, even years, to test a battery for cycle life performance under normal operating conditions. Hence, there is a need to develop tools for battery life and degradation trend prediction using limited cycle data. Early life prediction tools can facilitate battery qualification, timely replacement of batteries in critical applications, and even the secondary use market. In this study, we present a recurrent neural network-linear network model to predict the entire battery capacity fade curve using less than 100 cycles of data (~ 1 month of testing). The discharge voltage-capacity curves have been used as input to the model. Our approach is also able to predict the rollover point (knee point) in the capacity fade curve of the battery, which indicates the onset of increased capacity fade rate. We use the publicly available MIT dataset to show the validity of the approach and extend the previous work from Severson et al. [1] on the end-of-life prediction to the entire capacity fade trend prediction. The recurrent neural network can capture the sequential changes in discharge voltage-capacity curves with cycles and provide flexibility in terms of the input data size.

Clinoforms and clinothems: Fundamental elements of basin infill

AbstractThis special issue dealing with the recent advances on modern and ancient clinoform‐stratified sedimentary successions arises from a European Geoscience Union (EGU) session “Clinoform drivers and stratigraphic products in siliciclastic and carbonate successions”, Vienna, April 2018. Clinoforms and clinothems represent a dominant architectural style of strata in many sedimentary environments, including deltaic and nondeltaic shorelines in both marine and lacustrine settings, and are one of the key building blocks of the sedimentary record. This Special Issue in Basin Research aspires to represent a step forward in understanding formation and preservation of these fundamental stratigraphic elements. As this Special Issue documents, a comprehensive understanding of clinoformal strata requires a multidisciplinary and multi‐scale approach. Sixteen papers present case studies from a variety of tectonic settings worldwide, investigated with an array of methods, including seismo‐stratigraphy, well logs, cores, high‐resolution biostratigraphy, outcrop studies and modern bathymetric data. While observations document sedimentary processes and products in sedimentary basins, numerical models are necessary to provide a quantitative basis for the extrapolation of these processes and strata at different temporal and spatial scales. The papers highlight at least five main research avenues that we briefly introduce and discuss below: (a) clinoforms and clinothems as sedimentary archives; (b) the nested nature of clinoformal strata and implications for the trajectory of the rollover point(s); (c) quantitative clinoform parameters and dynamic indices; (d) architecture, growth and sequence stratigraphy of marine versus lacustrine clinoformal strata; and (e) clinoforms and geological time. This introduction also contains brief descriptions of each paper of the Special Issue.

Ephemeral rollover points and clinothem evolution in the modern Po Delta based on repeated bathymetric surveys

AbstractReconstructions of ancient delta systems rely typically on a two‐dimensional (2D) view of prograding clinothems but may miss their three‐dimensional (3D) stratigraphic complexity which can, instead, be best documented on modern delta systems by integrating high‐resolution geophysical data, historical cartography, core data and geomorphological reconstructions offshore. We quantitatively compare three precisely positioned, high‐resolution multi‐beam bathymetry maps in the delta front and pro delta sectors (0.3 to 10 m water depth) of Po di Pila, the most active of the modern Po Delta five branches. By investigating the detailed morphology of the prograding modern Po Delta, we shed new light on the mechanisms that control the topset to foreset transition in clinothems and show the temporal and spatial complexity of a delta and its pro delta slope, under the impact of oceanographic processes. This study documents the ephemeral nature of the rollover point at the transition between sandy topset (fluvial, delta plain to mouth‐bar) and muddy seaward‐dipping foreset deposits advancing, in this case, in >20 m of water depth. Three multibeam surveys, acquired between 2013 and 2016, document the complexity in space and time of the topset and foreset regions and their related morphology, a diagnostic feature that could not be appreciated using solely 2D, even very high‐resolution, seismic profiles. In addition, the comparison of bathymetric surveys gathered with one‐year lapses shows the migration of subaqueous sand dunes on the clinothem topset, the formation of ephemeral cut‐and‐fill features at the rollover point (few m below mean sea level), the presence of collapse depressions derived by sagging of sediments and fluid expulsion (possibly induced by storm waves) on the foreset, and splays of sand likely reflecting gravity flows on the lower foreset. Though the modern Po Delta is anthropogenic in many respects, its subaqueous clinothem can be studied as a scale model for ancient clinothems that are less resolved geometrically and far less constrained chronologically.

Exploring the DBR superlattice effect on the thermal performance of a VECSEL with the finite element method.

The design criterion of thermal conductivity for the GaAs/AlAs distributed Bragg reflector (DBR) superlattice structure was thoroughly investigated to precisely analyze the thermal behaviors of the optically pumped vertically external cavity surface-emitting laser (VECSEL). A finite element model with detailed configuration of a VECSEL gain chip was constructed to fulfill the analysis. A 1060nm VECSEL with different pump conditions was further demonstrated to verify the finite element analysis. At the VECSEL thermal rollover point, the analysis results show that the model with the superlattice property predicts more precise temperature values than that using a bulk composite property. It reveals that the accurate determination of the thermal conductivity of the DBR superlattice is significantly important for the VECSEL thermal analysis.

Factors controlling landslide frequency–area distributions

AbstractA power‐law relation for the frequency–area distribution (FAD) of medium and large landslides (e.g. tens to millions of square meters) has been observed by numerous authors. But the FAD of small landslides diverges from the power‐law distribution, with a rollover point below which frequencies decrease for smaller landslides. Some studies conclude that this divergence is an artifact of unmapped small landslides due to lack of spatial or temporal resolution; others posit that it is caused by the change in the underlying failure process. An explanation for this dilemma is essential both to evaluate the factors controlling FADs of landslides and power‐law scaling, which is a crucial factor regarding both landscape evolution and landslide hazard assessment. This study examines the FADs of 45 earthquake‐induced landslide inventories from around the world in the context of the proposed explanations. We show that each inventory probably involves some combination of the proposed explanations, though not all explanations contribute to each case. We propose an alternative explanation to understand the reason for the divergence from a power‐law. We suggest that the geometry of a landslide at the time of mapping reflects not just one single movement but many, including the propagation of numerous smaller landslides before and after the main failure. Because only the resulting combination of these landslides can be observed due to a lack of temporal resolution, many smaller landslides are not taken into account in the inventory. This reveals that the divergence from the power‐law is not necessarily attributed to the incompleteness of an inventory. This conceptual model will need to be validated by ongoing observation and analysis. Also, we show that because of the subjectivity of mapping procedures, the total number of landslides and total landslide areas in inventories differ significantly, and therefore the shapes of FADs also differ considerably. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Gas generation and its isotope composition during coal pyrolysis: Potential mechanism of isotope rollover

Recent studies on both conventional (thermogenic gas) and unconventional (shale gas) gases show comparable carbon/hydrogen isotope rollover, i.e., before the rollover point, carbon/hydrogen isotope increases with increasing thermal maturity (or decreasing gas wetness), while after the rollover point, the gas component (i.e., ethane, propane, etc.) becomes more depleted in 13C or 2H with increasing thermal maturity. In order to further investigate potential mechanism of the isotope rollover, combined with previous researches on isotope rollover, this study carried out two batches of pyrolysis experiments on a low mature coal sample from the Songliao Basin, China at constant temperatures for about 72 h under the condition with added water and without added water. The results demonstrate that carbon and hydrogen isotope rollover of ethane and propane started at 500 °C, no matter with added water or without added water. Combined with previous studies on gases of various origins, it is found that such isotopic anomalies were a common phenomenon at high thermal mature stage, despite of what kind of the source rocks and whether adding water or not under the laboratory condition. This is likely caused by the mixing of gases directly from the decomposition of macromolecule of kerogen and those from the tightly entrapped straight-chain species in kerogen at relatively high thermal mature stage. These straight-chain species are normally entrapped in the kerogen, and will probably be released at high thermal maturation stage. Marine facies source rocks from southern China also demonstrate the existence of such tightly entrapped hydrocarbons at very high thermal maturity. The results may have important significance on the gas exploration at relatively high mature stage and have a guidance on the gas production changes during the exploration.

Dynamic controls on shallow clinoform geometry: Mekong Delta, Vietnam

Compound deltas, composed of a subaerial delta plain and subaqueous clinoform, are common termini of large rivers. The transition between clinoform topset and foreset, or subaqueous rollover point, is located at 25–40-m water depth for many large tide-dominated deltas; this depth is controlled by removal of sediment from the topset by waves, currents, and gravity flows. However, the Mekong Delta, which has been classified as a mixed-energy system, has a relatively shallow subaqueous rollover at 4–6-m depth. This study evaluates dynamical measurements and seabed cores collected in Sep 2014 and Mar 2015 to understand processes of sediment transfer across the subaqueous delta, and evaluate possible linkages to geometry. During the southwest rainy monsoon (Sep 2014), high river discharge, landward return flow under the river plume, and regional circulation patterns facilitated limited sediment flux to the topset and foreset, and promoted alongshore flux to the northeast. Net observed sediment fluxes in Sep 2014 were landward, however, consistent with hypotheses about seasonal storage on the topset. During the northeast rainy monsoon, low river discharge and wind-driven currents facilitated intense landward and southwestward fluxes of sediment. In both seasons, bed shear velocities frequently exceeded the 0.01–0.02m/s threshold of motion for sand, even in the absence of strong wave energy. Most sediment transport occurred at water depths <14m, as expected from observed cross-shelf gradients of sedimentation. Sediment accumulation rates were highest on the upper and lower foreset beds (>4cm/yr at <10m depth, and 3–8cm/yr at ~10–20m depth) and lowest on the bottomset beds. Physically laminated sediments transitioned into mottled sediments between the upper foreset and bottomset regions. Application of a simple wave-stress model to the Mekong and several other clinoforms illustrates that shallow systems are not necessarily energy-limited, and thus rollover depths cannot be predicted solely by bed-stress distributions. In systems like the subaqueous Mekong Delta, direction of transport may have a key impact on morphology.

The Future Prediction of the One-Dimensional Topography of the Estuary Delta of the Shirakawa River

Predicting the long-term topographical change based on results of a time-slice experiment using a General Circulation Model (GCM) is difficult because actual change is a result of the continuum of events occurring in succession leading from the past to the future. We developed a one-dimensional topographical model of an estuary delta as the first step of assessing climate change effects. Three major effects, i.e. tidal flow, waves and sediment supply from the river, were included in this model. In order to estimate the sensitivity of these effects, simulations with virtual conditions were conducted. These simulations show equilibrium profiles that are close to the results of Roberts et al. [2000] “Predicting the profile of intertidal mudflats formed by cross-shore tidal currents,” Proc. Marine Sci. 3, 263–285.]. The simulation results were validated with observation data from the Shirakawa River delta. As a long-term prediction (about 37 years), the propagation of the rollover point was less than the actual data showed. The gradient of the subtidal zone was gentler than that observed. However, the short-term prediction (about 17 years) agrees with the observation data. These results show that old, unreliable, observation data used as a boundary condition significantly affects the reproducibility of the actual tidal flat profile. Finally, the effect of continuous Sea Level Rise (SLR) over 100 years from the present was investigated. As expected, the simulation results show a shift of the shoreline landward. The water depths in the intertidal and subtidal zones increase compared to a no-SLR condition. Therefore, the topset area grows as a consequence of SLR. Additionally, it was shown that future accumulation in the subtidal zone is reduced with SLR.

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)

AbstractHigh‐resolution swath bathymetry data collected in fjord‐lakes Pentecôte, Walker and Pasteur (eastern Québec, Canada) allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes. The morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows. The shape of the bedforms, mostly crescentic, and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps. The crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore (and decreasing slopes) are compatible with a cyclic step origin. At the rollover point, the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms. Further downslope, decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms. The wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump. Bedform morphometry and morphology are used to reconstruct density flow behaviour downslope. Froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler. Conversely, the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment. The supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta‐front slope failures is also observed. The differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology, but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front.

Ramp sedimentation across a middle Albian, Arctic embayment: Influence of subsidence, eustasy and sediment supply on stratal architecture and facies distribution, Lower Cretaceous, Western Canada Foreland Basin

AbstractRegional mapping of Middle Albian, shallow‐marine clastic strata over ca 100 000 km2 of the Western Canada Foreland Basin was undertaken to investigate the relationship between large‐scale stratal architecture and lithology. Results suggest that, over ca 5 Myr, stratal geometry and facies were dynamically linked to tectonic activity in the adjacent Cordillera. Higher frequency modulation of accommodation is most reasonably ascribed to eustasy. The Harmon and Cadotte alloformations were deposited at the southern end of an embayment of the Arctic Ocean. The Harmon alloformation, forming the lower part of the succession, constitutes a wedge of marine mudstone that thickens westward over 400 km from &lt;5 m near the forebulge to &gt;150 m in the foredeep. Constituent allomembers are also wedge‐shaped but lack distinct clinothems, a rollover point or downlapping geometry. Ubiquitous wave ripples indicate that the sea floor lay above storm wave base. Deposition took place on an extremely low‐gradient ramp, where accommodation was limited by effective wave base. Lobate, river‐dominated deltas fringed the southern margin of the basin. The largest deltas are stacked in the same area, suggesting protracted stability of the feeder river. A buried palaeo‐valley on the underlying sub‐Cretaceous unconformity may have influenced compaction and controlled river location for ca 3 Myr. Adjacent to the western Cordillera, a predominantly mudstone succession is interbedded with abundant storm beds of very fine‐grained sandstone and siltstone that reflect supply from the adjacent orogen. Bioturbation indices in the Harmon alloformation range from zero to six which reflects the influence of stressors related to river‐mouth proximity. Harmon alloformation mudstone grades abruptly upward into marine sandstone and conglomerate of the overlying Cadotte alloformation. The Cadotte is composed of three allomembers ‘CA’ to ‘CC’, that represent the deposits of prograding strandplains 200 × 300 km in extent. Allomembers ‘CA’ and ‘CB’ are strongly sandstone‐dominated, whereas allomember ‘CC’ contains abundant conglomerate in the west. The dominantly aggradational wedge of Harmon alloformation mudstone records flexural subsidence driven by active thickening in the adjacent orogen: the high accommodation rate trapped coarser clastic detritus close to the basin margin. In contrast, the tabular, highly progradational sandstone and conglomerate bodies of the Cadotte alloformation record a low subsidence rate, implying tectonic quiescence in the adjacent orogen. Erosional unloading of the orogen through Cadotte time steepened rivers to the extent that they delivered gravel to the shore. These observations support an ‘anti‐tectonic’ model of gravel supply proposed previously for the United States portion of the Cretaceous foreland basin. Because Cadotte allomembers do not thicken appreciably into the foredeep, accommodation changes that controlled these transgressive–regressive successions were probably of eustatic origin.

Shelf-to-canyon connections: Transport-related morphology and mass balance at the shallow-headed, rapidly aggrading Swatch of No Ground (Bay of Bengal)

The Swatch of No Ground (SoNG) canyon in the Bay of Bengal is a shelf-incising submarine canyon that is actively aggrading in its upper reaches despite regular gravity-driven transport and mass wasting. Although the canyon lies 150km downdrift of its main sediment source, the Ganges–Brahmaputra–Meghna (GBM) river mouth, high sedimentation rates (5–50cmyear−1) are sustained by both progradation of the subaqueous delta into the canyon head and the conveyance of shelf-generated hyperpycnal flows to the canyon floor. This rapid accretion appears to be largely balanced by mass failures triggered by regularly occurring storms, and less frequently by major earthquakes. Here we use high-resolution sub-bottom sonar data to elucidate dominant sediment-dispersal pathways and their transport-related morphology at the canyon head; these include: 1) a laterally prograding clinoform that intersects the canyon head at water depths of 20–120m; 2) several shelf-incising bypass gullies that originate in <20m water depth above the rollover point and connect the inner shelf to the canyon floor, and 3) numerous U-shaped slide valleys formed by deep-seated mass failures initiating at water depths >50m. The clinoform deposits reflect westward progradation of the GBM subaqueous delta into the upper canyon, where its axis-normal orientation leaves it dissected by cross-cutting gullies and mass failures. The morphology and acoustic stratigraphy of the gullies, coupled with strong bed shear and high suspended sediment concentrations on the inner shelf, suggest that these features are sustained by the regular conveyance of gravity-driven fluid muds that are formed in shallow water (<20m) where the gullies originate. The downslope termination of the gullies coincides with a break in slope at the canyon floor, indicating that gullies serve as sediment conduits linking shallow water processes with sediment deposition in the lower canyon. Together these locally interacting shelf, clinoform, and canyon features form a unique composite morphodynamic system that more broadly defines the highstand connection between this large fluvial delta system and its shelf-indenting canyon.

Isotope rollover in shale gas observed in laboratory pyrolysis experiments: Insight to the role of water in thermogenesis of mature gas

Pyrolysis experiments on type II kerogen with maturities equivalent to vitrinite reflectance (Ro) between 0.7% and 1.4% were conducted in the presence and absence of added water to determine whether the isotope rollover effect observed in natural highly productive shale gas plays can be reproduced in the laboratory. Isotope rollover occurs when isotope δ values (i.e. measures of the abundance of heavy stable isotopes 2H or 13C) initially become less negative, as expected, with increasing thermal maturity but later display a reversal in trend becoming more negative with increasing maturity. It was found that H2O had a pronounced influence on the composition, yields and carbon and hydrogen isotopic ratios of thermogenic gases. Compared to gases from confined pyrolysis experiments without added water, lower overall quantities of hydrocarbon gases were generated from experiments with water added, although the relative abundance of methane among other gas species was higher in the experiments with water introduced. Methane, ethane and CO2 generated from pyrolysis experiments with added water exhibited the carbon isotope rollover while the corresponding gases produced from pyrolysis experiments without added water did not show carbon isotope rollover. The rollover point was observed after 7days of heating (Easy Ro=1.49%) of the least mature kerogen but shifted to nearly 15days (Easy Ro=1.65%) when heating more mature kerogens. The least mature kerogen was able to generate the largest amount of late gas in the presence of H2O. In contrast to carbon, hydrogen isotope rollover was not observed in either methane or ethane generated during the pyrolysis experiments no matter if water was added or not. Confined pyrolysis experiments with added water generally yielded more negative δ2HCH4 values than pyrolysis experiments without added water, indicating that water promoted the secondary cracking of C2+ hydrocarbons to methane. Our results confirm that (1) carbon isotope rollover in productive shale gas plays is not an oddity but can be reproduced in the laboratory and can be explained by chemical mechanisms operating at elevated temperatures, and (2) the presence of H2O promotes secondary cracking of C2+ hydrocarbons to methane and generates isotopically lighter gas accumulatively to present isotope rollover in a closed system.

Cost-Effective Thermally-Managed 1.55-$\mu{\rm m}$ VECSEL With Hybrid Mirror on Copper Substrate

An electroplated copper substrate was evaluated for heat dissipation in 1.55-μ.m optically pumped vertical extended cavity surface emitting lasers (OP-VECSELs). It is a cost-effective and flexible solution compared with the previously proposed chemical vapor deposition diamond substrate assembled by metallic bonding. Continuous-wave (CW) lasing operation was demonstrated from a device (with copper electroplated substrate) under optical pumping with pump spot diameter of 100 μm and a maximum output power of 260 mW at 0°C; heatsink temperature was achieved. Room-temperature CW operation with an output power of 75 mW and an external quantum efficiency of 35% was achieved in an optimized plane-concave cavity. The thermal resistance and the maximum output power of VECSEL chips assembled with bonded bulk copper and electroplated copper substrates were measured and compared. A value of ~50 K/W was estimated for both devices, and a similar rollover point was observed, which indicates that the electroplated copper solution leads to similar thermal properties as a bonded bulk copper substrate.

Contrasting slope channel styles on a prograding mud-prone margin

The Pleistocene slope clinoform succession of the Pescara Basin foredeep (Central Adriatic Basin, Italy) has been investigated combining the analysis of the rollover point trajectories with 2D seismic facies analysis and 3D seismic geomorphology approach and visualization techniques. The study documents two different types of slope clinoforms, each of which is characterized by a specific slope turbidite system with distinctive morphologies, internal geometries and architectural elements.Type 1 clinoforms are characterized by rectilinear, slope-confined gullies which develop during a phase of margin growth. Type 1 clinoforms are characterized by a rise of the trajectories of the rollover points, which can be indicative of intervals of relative sea level rise. In type 1 clinoforms most of the coarse-grained sediments are stored in the shelf. The slope-confined gullies barely indent the shelf break, are not connected to rivers, and develop thin (<30 m) frontal splays at the base of the slope. All these evidences indicate that the gullies are inefficient pathways to transfer sandy sediment basinward. The gully depressions are net-erosional and also the inter-gully sectors are sites of dominant sediment bypass. The infill deposit of the gullies consists of channel-wide high-amplitude reflectors (HARs) wedging-out downslope. The origin of the slope-confined gullies is interpreted to be linked to mass wasting processes affecting the upper slope and the shelf-edge during conditions of relative sea level rise. Longshore drifts and storm-driven turbidity currents rework the outer shelf, promoting the maintenance of gully systems, which become filled during the ensuing high-stand of the sea level.Type 2 clinoforms are characterized by a negative trajectory of the rollover points, and develop during a lowering of the sea level and during lowstand periods. Type 2 clinoforms develop sinuous, aggradational slope channels which are river-connected, with incised valleys that supply sediment directly to the head of the slope channel. The slope channels are fed through sustained turbidity currents possibly associated with hyperpycnal flows. Type 2 slope channels develop in a net-aggradational setting, forming erosive based channel-fill deposits about 150 m thick which are characterized by high-amplitude reflectors (HARs). Type 2 slope channels are able to transfer larger amount of sediment to the basin, comparing with type 1 gullies, as the presence of thick (∼150 m) channelized frontal–splay complexes seems to confirm. The combination of 2D and 3D data analysis has lead to the reconstruction of a sedimentological model which has the potential to be applied as analogue for seismic or outcrop-based studies of slope channels in supply-dominated, mud-prone margins.

Sediment transport processes from the topset to the foreset of a crenulated clinoform (Adriatic Sea)

Crenulated clinoforms of complex and uncertain origin characterize large portions of the Late-Holocene prograding mud wedge in the western Adriatic continental shelf. Sediment failure was originally postulated as the most plausible mechanism for the formation of the crenulations. Subsequent work has shown that, although the origin of the crenulations may have been related to deformation processes, their maintenance through time seems to be better explained by different sediment accumulation rates in the flat and steep flanks. In order to establish relationships between active sediment dynamics, across-shelf transport and sediment accumulation in these crenulated clinoforms, two tripods and a mooring were deployed off the Pescara River during autumn and winter 2002–2003 as part of the EuroSTRATAFORM program, and in combination with the Po and Apennine Sediment Transport and Accumulation (PASTA) study. The tripods were placed on the shallow topset region and close to the clinoform roll-over point (i.e., offlap break), at 12 and 20-m water depth, respectively, and the mooring was located at 50-m depth, in the crenulated foreset region. Several sediment-resuspension events were recorded, mainly related to Bora and Sirocco storms, during which wave–orbital and current velocities increased considerably. Sediment transport in the topset region was predominantly towards the SE, following the direction of the coastal current and the bathymetry, but showing a significant offshore component at the roll-over point that was intensified during storm events. Currents at the foreset region were also directed to the SE. In mid-waters they were clearly aligned with the local bathymetry, whereas near the bottom they had an important and persistent offshore component. This current behavior seems to be associated with an intense bottom Ekman transport that causes the near-bottom current to be deflected to the left (i.e., offshore) with respect to the direction of the surface current. This mechanism enhances the suspended-sediment transport from the topset down the foreset region along the Adriatic prograding mud wedge, contributing to the basinward clinoform progradation and controlling the depth of the clinoform roll-over point. In addition, activity of near-inertial internal waves was also recorded by the near-bottom instrument deployed in the foreset region. During periods characterized by a strong near-inertial signal, increases of the water turbidity clearly coincided with an intensified offshore velocity component, which suggest that this mechanism also contributes to the transport of suspended sediment across the clinoform. Both the bottom Ekman transport and the internal waves are mechanisms that could be responsible for the formation/maintenance of the Adriatic seafloor crenulations until present-day, although several arguments suggest that the latter likely plays the major role.

Characterization and analysis of single-mode high-power continuous-wave quantum-cascade laser

We measured and modeled the performance characteristics of a distributed-feedback quantum-cascade laser exhibiting high-power continuous-wave (CW) operation in a single spectral mode at λ≈4.8μm and temperatures up to 333K. The sidemode suppression ratio exceeds 25dB, and the emission remains robustly single mode at all currents and temperatures tested. CW output powers of 99mW at 298K and 357mW at 200K are obtained at currents well below the thermal rollover point. The slope efficiency and subthreshold amplified spontaneous emission spectra are shown to be consistent with a coupling coefficient of no more than κL≈4–5, which is substantially lower than the estimate of 9 based on the nominal grating fabrication parameters.