bluuebunny/crossref_metadata_2025 huggingface dataset:
Extending Values of a PDHMS System to Production Optimization
Authors: Mei Ken
Published: March 2015

Over the last decade, many permanent downhole pressure and temperature gauges (PDG), also called permanent downhole monitoring systems (PDHMS), have been installed globally in many oilfields. One primary objective of installing permanent downhole gauges in a wellbore is to avoid field trips with a wireline unit for pressure surveys. Additionally the system can turn any well “shut-in” time into a valuable opportunity for both a pressure survey and a build-up testing, significantly improving the reservoir surveillance frequency. Only a few authors have conducted a systematic analysis and explored the potential application of a PDHMS system.

This paper briefly describes the elements of a typical PDHMS monitoring system. A detailed systematic analysis is presented for the first time, including factors affecting the application of such a system. Our analysis reveals that the accuracy of the pressure gauges, gauge installation, depth and the distance between the two pressure gauges have a significant impact on the application of a PDHMS system. Improperly choosing the accuracy of pressure gauges, randomly placing the pressure gauges in a wellbore, or improperly setting a distance between two pressure gauges could result in little benefits from such practice. The analysis presented in this paper enables petroleum engineers to make the sound engineering decisions during the planning of PDHMS installation.

Our study presented in this paper extensively includes an investigation of the specific requirements of such a system in different types of wells (producers and injectors) and explores their potential applications. This study extends the application of a PDHMS system to a new horizon in terms of production optimization and reservoir surveillance. Also presented in this paper are some cases showing how real time PDHMS data is utilized for continuously monitoring reservoir pressure changes, and optimizing both testing frequency and wellhead sampling requirements in a Saudi Arabia field.
Application of Fast Reservoir Simulation Methods to Optimize Production by Reallocation of Water Injection Rates in an Omani Field
Authors: Al Saidi A. , Pourafshary P. , Al Wadhahi M.
Published: March 2015

There are wide and crucial applications of the reservoir simulation to develop, manage and monitor reservoirs. However, the traditional simulation methods have different limitations such as noticeable necessary time to prepare and model data and uncertainties in the available data. Therefore, new approaches are developed to offer rapid reservoir simulation with lower and more reliable data to manage and optimize production from hydrocarbon reservoirs and provide us a quick estimation of the performance of the reservoirs. One of these approaches is the Capacitance-Resistive Model (CRM).

CRM is a quantitative technique based on material balance that uses only injection/production rates and well coordinates to identify and quantify reservoir model parameters, which are well connectivity and time constant values. In CRM, the reservoir is assumed as a system where the injection rates are the input signals and the production rates are the output signals. The injection performance over a period of time can be identified by estimating fractions of injected fluid to each producer and the time taken for a producer to sense the injections. With CRM, it is possible to optimize a waterflooding operation in a field by reallocating the water injection rates to optimize the oil production. This tool is preferred due to its simplicity, the short computation time and the use of available field data.

In this study, we developed a new approach to use the Capacitance Resistive method to optimize the waterflooding process in an Omani oil field by a ranking approach for the injectors. By reallocation of the available water to injectors, the future oil production was optimized for the next three years. This method showed that the optimized scenario leads to 29.90% increase in future oil production compared to the current injection rates profile. This was achieved by injecting 59% of available water for most effective wells and the remaining amount for other wells.
A Full Scale Two-Phase Flow Loop Test of Downhole Permanent Multiphase Flow Meter
Authors: Saeed Abubaker , Noui-Mehidi Mohamed N. , Black Michael J. , Abbad Mustapha , Shafiq Muhammad
Published: March 2015

This work presents a joint collaboration effort between Saudi Aramco and Schlumberger for the qualification of a new generation of downhole permanent multiphase flow meter. We report the validation test of a new permanent completion tool, which is planned to be deployed in horizontal and multi-lateral wells. The field deployment requires the installation of several stations of the tool for an efficient zonal monitoring and control of the reservoir. Each metering station has a miniature flow meter, water cut sensor and an electro-valve which can be controlled by the operator to prevent the water breakthrough in the production tubing and optimize the oil production. Before the field installation, a unique full scale two-phase flow loop was built in Saudi Arabia specifically to test the accuracy of the metering devices. A complete physical modeling campaign was designed to model the flow of oil and water in downhole conditions through appropriate matching of defined flow non-dimensional numbers. The experimental tests showed excellent results with accurate monitoring of the produced fluids and a smooth control of the oil production.
Drilling Professional Development Program (DPDP)
Authors: Mohammad Rahman , Mamdouh Agawani , Eiman Hazza
Published: March 2015

Shortage of qualified, experienced and competent drilling professionals is worldwide, especially among Saudis within the Kingdom. Visualizing the Saudi Aramco management intension to develop home-grown talent, the D&WO HR Training Division has taken up an accelerated and challenging training initiative “Drilling Professional Development Program” (DPDP) to develop the fresh engineers and prepare them to be professional drilling foremen and drilling engineers. This paper outlines how the Training Division has planned and implemented this unique program to tackle technical manpower requirements through a comprehensive, structured, and knowledge-based competency program utilizing the diverse training methods.

Executing such a training program is expensive in short-run but provides multiple returns on the investment in the long-run. This will be felt when the Saudi talent takes over D&WO operations, and the dependency on expatriates begin to diminish. The impact on the targeted Saudization not only can be cost effective but also ensure high level of competent professionals. This paper explains the DPDP program development, challenges, results and the lessons learned.
Heavy Oil Characterization: Lessons Learned During Placement of a Horizontal Injector at a Tar/Oil Interface
Authors: Lyngra Stig , Hursan Gabor G. , Palmer Richard G. , Zeybek Murat , Ayyad Hazim A. , Qureshi Ahmed
Published: March 2015

A case history is presented for a horizontal injector drilled at the base of a moveable oil column on top of a tar mat in a carbonate oil reservoir in the Middle East. The well was placed utilizing real-time Logging-While-Drilling (LWD) Nuclear Magnetic Resonance (NMR) oil viscosity correlations and formation tester mobility data.

As a pilot water injector, placed at an oil/tar interface with restricted historic oil viscosity versus depth data, obtaining calibration oil samples was considered critical. Both LWD and pipe-conveyed (TLC) formation tester data sets were acquired, which made direct comparisons of LWD and TLC acquired formation pressures and formation mobilities possible. The comparison proves the reliability of the LWD formation mobilities. The LWD measured formation pressures were supercharged while the TLC formation tester formation pressures were largely in line with expected formation pressures.

The oil viscosity results from the TLC formation tester in-situ viscosity fluid analyzer and the NMR viscosity correlation compared favorably with the laboratory results from the acquired TLC formation tester fluid samples. This indicates that accurate real-time in-situ fluid property determination is possible with modern formation tester and NMR tools.

In this reservoir, at an early phase of acquiring oil/tar transition zone oil viscosity versus depth data, the main lesson learned was that the deeper section of the case study well contained higher asphaltene content than expected, which caused wellbore plugging that prevented reservoir access after suspending the well for tie-in. A clean-out operation was unsuccessful as plugging reoccurred. The well is now planned to be re-sidetracked in 3-20 centiPoise (cP) oil at the top portion of the oil/tar transition zone.
Wellbore Stability Analysis in Depleted Deepwater Reservoirs: A Case Study from Australia
Authors: Asadi M.S. , Khaksar A. , White A. , Yao Z
Published: March 2015

The formation fracture gradient (FG) in deepwater environments is lower, compared to that in shallow water and onshore fields. Consequently, narrow margin drilling is generally a challenge in deepwater fields. The FG is sometimes different from the principal minimum horizontal stress (Shmin). The FG may be determined from the fracture initiation pressure (FIP) or from the pressure required for the fluid to leak off through conductive natural fractures. In contrast to the Shmin, the FIP is a function of wellbore trajectory.

In this study, we present data from a deepwater gas field in Australia. The Shmin profile was calibrated against extended leak-off tests (XLOTs), microfrac, and injectivity tests in 12 offset wells using log-based poro-elastic and effective stress ratio (ESR) methodologies. We then constrained and calibrated the geomechanical model using a range of well logs, drilling data, and core experiments. The geomechanical model was used to calculate the FIP and its variation with borehole trajectory for a number of horizontal wells under initial and depleted conditions. The results show, for particular well trajectories, the mud weight window (MWW) is extremely narrow if the FG is considered to be equivalent to the FIP. In addition, Shmin tends to be low in reservoir sandstones, which will make the drilling of high-angled wells in the depleted zones challenging. If natural fractures exist in the reservoir, fluid may leak through the fractures in which conductivity could be enhanced by shear slip with a hole pressure less than both Shmin and FIP. We used the Mohr-Coulomb sliding criterion to identify the population of fractures in the reservoir most susceptible to shear slip. The results indicated that high-angled fractures that strike NE-SW may become critically stressed during drilling, meaning they are prone to slip and may lead to fluid losses with the bottomhole pressure (BHP) less than the FIP. The results of this study led to revisions to the planned well trajectories. We optimized the trajectories to take advantage of higher FIP (relative to Shmin) to reduce the risk of fluid losses into natural fractures. In addition, we considered depletion in the reservoirs for optimization.
Technology-driven Approach to Develop Shale Gas in Saudi Arabia
Authors: Bartko Kirk M. , Coffin Brian , Tineo Roberto
Published: March 2015

Early in the 1980s, efforts started to be made to develop the now famous Barnet Shale. It required 20+ years of drilling and completion innovations to make it commercially viable. The Barnett was the starting point to develop other plays in North America such as at Fayetteville, Marcellus, Haynesville, Woodford, and New Albany. It is important to note that success in shale production has been the result of years of work of many companies (mostly small independent operators) drilling thousands of wells, learning from each other, and ultimately developing the so-called factory approach to drilling and completions.

Unlike the U. S., Saudi Arabia does not have the luxury of thousands of penetrations through its shale gas plays; particularly critical is the absence of other operators to share experiences and risks. Therefore, Saudi Aramco decided to explore its shale gas resources in the Kingdom by adopting a “technology driven” approach against the U.S.-based “factory” or “statistical” approach.

The “technology-driven” approach and the customized workflow applied in this project have minimized the time required to understand the reservoir and apply technologies appropriate for their completion. To date, this workflow has been utilized and calibrated with single well analysis. As sufficient amounts of data, especially 3D seismic data, which is currently being shot in the northern region of Saudi Arabia, becomes available, this workflow can be further enhanced and calibrated with a three-dimensional regional model. A wellbore calibrated workflow based on the pilot hole data, learnings from surrounding holes, and North American organic industry experience can substantially shorten the learning curve in Saudi Arabia.

This paper demonstrates a customized workflow developed for Saudi Arabian shale gas plays and shares the preliminary results of the project.
Standardising Petroleum Engineering Education in Brazil: Preparing The Next Generation
Authors: Mendes G. D. , Souza A. F. , Terrazas R. R. , Lacerda R. F.
Published: March 2015

During the past years, Brazil has been experiencing a significant oil boom, mainly due to its successful and technologically challenging deep offshore exploration campaign, namely the “pre-salt” area. Furthermore, after a five-year halt on bidding rounds, Brazil held two bidding rounds last year: one aimed at on-shore unconventional exploration, as an attempt to stay current on the abroad shale revolution, the other being the first pre-salt PSC bidding for the super-giant field of “Libra”. In fact, Brazilian authorities have stated that they expect to nearly double its domestic production within the next five years [1].

Both of these exploration frontiers represent not only innumerous financial, technological and logistical challenges, but the success will be dependent and profoundly driven by the availability of the country's petroleum-industry workforce resources involved; specifically, its ability to supply the sudden and critically arising demand. In addition, turning the scenario even more complex is the fact that Brazilian law [1] requires a substantial share of local content, including workforce, must be employed in any of those projects.

In face of such a scenario, the SPE Brazil Section, along with several nation-wide company and university representatives, developed and proposed a new unified petroleum engineering program course, aimed at all Brazilian universities. It is on such report that this paper is based.

The extensive report indicates that existing academic programs must undergo some changes, if they are to adapt to modern industry requirements and standards. For instance, it concluded that only one-third of a program should be composed of basic courses, with more than half of them on specific-petroleum-oriented courses, together with one-tenth on professional-applied courses. In summary, the report indicates that the Brazilian approach on scientific education must be improved and re-thought, combining a theoretical approach and practical considerations.
World Record Longest and Deepest 7" Turbine Reaming Liner: Application and Challenges
Authors: Al-Jamal Abdulrahman A. , Hanafi Machmud X. , Al-Dhafeeri Bader N. , Al-Saggaf Hatem M. , Dias Pradeep , El-Debais Jamal
Published: March 2015

One of world's longest cemented 7″ turbine reaming liners, 5.1 km long, was successfully deployed in the Manifa field located in Saudi Arabia. The 7″ liner was effectively aided in reaching the liner point (LP) below the 9⅝ casing using turbine reamer technology installed at the end of string and was then successfully cemented. The reaming operation was performed by activating the turbine reamer shoe by pumping drilling fluid when a borehole restriction was encountered while running in the hole (RIH).

The turbine reamer is a high speed reaming tool and the main benefits of using this technology in such a long horizontal section is to ream and remove obstructions (debris, cuttings, ledges, excessive filter cake) and successfully deploy the liner to the target depth (TD).

The process of utilizing the turbine reamer technology to deploy the 5.1 km liner to the TD was successfully executed in a horizontal producer well in the Manifa Increment Project, resulting in reduced risk of stuck casings and liners. This paper will present a case study of the turbine reaming operation, lessons learned and challenges encountered during the running and cementing the 16,758 ft (5.1 km) of a 7″ liner in the 8½″ hole section. It also provides focus on potential enhancements for future utilization of the technology.
Pre-Drill and Real-Time Pore Pressure Prediction: Lessons from a Sub-Salt, Deep Water Wildcat Well, Red Sea, KSA
Authors: Brown John P. , Fox Adam , Sliz Krzysztof , Hanbal Ibrahim , Planchart Carlos , Davies Graham , Bradford Charles , McCrossan John , McFarlane Mark
Published: March 2015

Saudi Aramco's first deepwater exploration well targeted a sub-salt Miocene syn-rift section located in over 2,000 ft of water and beneath 9,000 ft of halite and evaporites. Offset well information from previous shallow exploration wells was limited; therefore, calibration for pre-drill pore pressure and fracture gradient prediction (PPFG) was performed using a single shallow water well completed two months prior to spuding the well. Pre-drill PPFG predictions presented a very high degree of uncertainty, which translated into uncertainty in well design and mud weight planning. Pre-drill pore pressure prediction relied on seismic velocities extracted from a wide azimuth 3D survey and used Residual Normal Move Out (RNMO) and seismic inversion to extract velocities that were presumed to represent shale velocities. Real-time pore pressure monitoring was based on a comprehensive program that included logging while drilling (LWD), multiple look-ahead vertical seismic profiles (VSPs), velocity model updating and rapid remigration (pre-stack depth migration) around the wellbore to produce simultaneous improvements in imaging and depth estimates that were tied back to an evolving geological pore pressure model. Significant differences between the pre-drill pore pressure model and measured well pressures highlight the critical importance of the pre-stack depth migration (PSDM) velocity model and the necessity to be able to modify the seismic velocity model and calculated pore pressures in real time to provide accurate information to drilling operations. An integrated team of technical professionals from nine separate departments was required to successfully carry out this project, which resulted in the successful drilling of a deepwater well in a high overpressure — low fracture gradient environment with minimal operational downtime.
Innovative, Cost Effective and Simpler Technology to Recover Flare Gas
Authors: Peeran Syed , Beg Dr Najam
Published: March 2015

According to the Global Gas Flaring Reduction Initiative (GGFR) – more than 140 billion cubic metres (4.9 trillion ft3) is flared annually and the same amount is probably vented. There is a growing awareness in the oil and gas industry to reduce flaring and on utilising Flare Gas Recovery Systems (FGRS).

Conventional Flare Gas Recovery systems usually comprise of one or more compressors, which compress the collected flare gas and route it for further processing. The compressor design is critical and determines the system’'s capacity and turndown capability. However compressor based solutions can be physically large, complex and have relatively high capital and operating costs. They can also be very sensitive to changes in gas composition and MW.

Surface jet pumps (SJPs) are simple, low cost passive devices that can also be used to recover flare or vent gas. They use a high pressure (HP) fluid as the motive force to capture and boost the pressure of the low pressure LP flare / vent gas and deliver it for processing. The high pressure fluid that is needed as the source of energy for the SJP is usually a portion of gas taken from the discharge of an existing compressor or from the export gas line. However HP liquids, such as oil or injection water can also be used as the motive sources for the SJP. Advantages of using SJPs include using already available fluid energy within a process stream, no moving parts, zero maintenance, zero power or fuel gas usage, small footprint and varying layout configurations. SJPs are well suited to liquid ingestion and to changes in process conditions (without affecting performance).

This paper looks briefly at the designs of FGRS currently used, their location in a plant and in particular discusses the use of Surface Jet Pumps as an alternative to compressors dedicated for flare gas recovery. It cites several case studies of where this technology has been successfully utilised. The design and operational criteria of SJPs, as well as the economics are also highlighted.
Assessing EOR Potential from Partitioning Tracer Data
Authors: Huseby Olaf , Hartvig Sven K. , Jevanord Kjersti , Dugstad Øyvind
Published: March 2015

In development of mature oil fields using enhanced oil recovery (EOR) techniques, one of the challenges is to quantify remaining oil and to evaluate the potential gain of EOR in pilot studies. One of the proven technologies to estimate remaining amounts of oil is the single-well chemical tracer test (SWCTT). During such push-and-pull tests, oil/water partitioning ester partially hydrolyses to a non-partitioning water tracer. A time-lag in back-production time between the injected ester and the alcohol generated in-situ yields remaining oil saturation (ROS) through a simple relation. A similar time-lag technique is used in partitioning inter-well tracer tests (PITTs), where tracers are injected into injectors and sampled in producers. New and stable, oil-water partitioning tracers suitable for oil reservoir PITTs have been recently developed and field tested (SPE164059), allowing measurement of remaining oil saturation in inter-well regions.

This paper reviews methodology to assess oil saturation in both near-well and inter-well regions of an oil reservoir, and highlights the differences and similarities of partitioning near-well and inter-well tracer tests that can be used to evaluate the potential gain from an EOR-operation.

SWCTTs and PITTs target different scales of an oil field, as a SWCTT explores the near well zone, up to a few meters, and a PITT explore an inter-well region. In order to assess information on both these scales we propose a systematic procedure for oil saturation measurement, using partitioning tracers. The procedure involves use of PITTs and systematic residence time distribution (RTD) interpretation of tracer production curves to extract information about remaining oil saturation and the distribution of this saturation in an oil field. The procedure is validated using the tracer data recently reported by Viig et al. (SPE164059).
Performance of upflow gravel filtration in multi-stage filtration plants
Authors: Sánchez L. D. , Visscher J. T. , Rietveld L. C.
Published: March 2015

This paper presents the results of a study of four full-scale upflow gravel filters that are part of full-scale multi-stage filtration. The study explored the design criteria, the operation and maintenance (O&M) practices, and the performance of the systems. Findings showed that most design criteria and O&M procedures are following the recommendations as presented in the literature but several diversions were also identified. Performance data showed that removal efficiencies were on the low side when compared to the literature, possibly because of the good influent quality water that was treated. Cleaning efficiency was analyzed and the overall conclusion is that an adjustment of the design criteria and O&M procedures is needed to enhance system performance. This includes drainage system design, surface cleaning by weir, and filter bed cleaning to allow a reduction in cleaning cycles and an improvement in operation control.
Methodological approach for the optimization of drinking water treatment plants' operation: a case study
Authors: Sorlini Sabrina , Collivignarelli Maria Cristina , Castagnola Federico , Crotti Barbara Marianna , Raboni Massimo
Published: March 2015

Critical barriers to safe and secure drinking water may include sources (e.g. groundwater contamination), treatments (e.g. treatment plants not properly operating) and/or contamination within the distribution system (infrastructure not properly maintained). The performance assessment of these systems, based on monitoring, process parameter control and experimental tests, is a viable tool for the process optimization and water quality control. The aim of this study was to define a procedure for evaluating the performance of full-scale drinking water treatment plants (DWTPs) and for defining optimal solutions for plant upgrading in order to optimize operation. The protocol is composed of four main phases (routine and intensive monitoring programmes – Phases 1 and 2; experimental studies – Phase 3; plant upgrade and optimization – Phase 4). The protocol suggested in this study was tested in a full-scale DWTP placed in the North of Italy (Mortara, Pavia). The results outline some critical aspects of the plant operation and permit the identification of feasible solutions for the DWTP upgrading in order to optimize water treatment operation.
Full-scale phosphorus recovery from digested wastewater sludge in Belgium – part II: economic opportunities and risks
Authors: Geerts Sam , Marchi Adrien , Weemaes Marjoleine
Published: March 2015

One of the options to recycle phosphorus (P) in the wastewater sector is to recover it as struvite crystals from digested sludge. Measurements on a full-scale demonstration plant in Leuven, Belgium, yielded a first indication of the profitability of struvite recovery, in function of different variables such as incoming PO43− concentration, MgCl2 dosing, improved dewaterability, etc. An uncertainty and sensitivity analysis was carried out. Although possible improvement in sludge dewaterability when recovering struvite from digested sludge has a positive economic amortization effect, it is at the same time the largest source of financial risk. A theoretical exercise showed that for struvite recovery from centrate, uncertainty would be lower, and the largest sensitivity would be attributed to ingoing PO43− concentration. Although struvite recovery from digested sludge is riskier, it is an investment with potentially a higher return than investment in struvite recovery from centrate. The article provides information for possible financial incentive schemes to support P-recovery.
Developing a demand model integrating end uses of water (DMEUW): structure and process of integration
Authors: Sarker R. C. , Gato-Trinidad S.
Published: March 2015

The process of developing an integrated water demand model integrating end uses of water has been presented. The model estimates and forecasts average daily water demand based on the end-use pattern and trend of residential water consumption, daily rainfall and temperature, water restrictions and water conservation programmes. The end-use model uses the latest end-use data set collected from Yarra Valley Water, Australia. A computer interface has also been developed using hypertext markup language and hypertext pre-processor. The developed model can be used by water authorities and water resource planners in forecasting water demand and by household owners in determining household water consumption.
Protection of biomass from snail overgrazing in a trickling filter using sponge media as a biomass carrier: down-flow hanging sponge system
Authors: Onodera Takashi , Syutsubo Kazuaki , Yoochatchaval Wilasinee , Sumino Haruhiko , Mizuochi Motoyuki , Harada Hideki
Published: March 2015

This study investigated down-flow hanging sponge (DHS) technology as a promising trickling filter (TF) using sponge media as a biomass carrier with an emphasis on protection of the biomass against macrofauna overgrazing. A pilot-scale DHS reactor fed with low-strength municipal sewage was operated under ambient temperature conditions for 1 year at a sewage treatment plant in Bangkok, Thailand. The results showed that snails (macrofauna) were present on the surface of the sponge media, but could not enter into it, because the sponge media with smaller pores physically protected the biomass from the snails. As a result, the sponge media maintained a dense biomass, with an average value of 22.3 gVSS/L sponge (58.1 gTSS/L sponge) on day 370. The snails could graze biomass on the surface of the sponge media. The DHS reactor process performance was also successful. The DHS reactor requires neither chemical treatments nor specific operations such as flooding for snail control. Overall, the results of this study indicate that the DHS reactor is able to protect biomass from snail overgrazing.
Communication practices and preferences between orthodontists and general dentists
Authors: Bibona Kevin , Shroff Bhavna , Best Al M. , Lindauer Steven J.
Published: March 2015

Objective: 

To evaluate similarities and differences in orthodontists' and general dentists' perceptions regarding their interdisciplinary communication.

Materials and Methods: 

Orthodontists (N  =  137) and general dentists (N  =  144) throughout the United States responded to an invitation to participate in a Web-based and mailed survey, respectively.

Results: 

The results indicated that orthodontists communicated with general dentists using the type of media general dentists preferred to use. As treatment complexity increased, orthodontists shifted from one-way forms of communication (letters) to two-way forms of communication (phone calls; P < .05). Both orthodontists and general dentists reported that orthodontists' communication regarding white spot lesions was inadequate. When treating patients with missing or malformed teeth, orthodontists reported that they sought input from the general dentists at a higher rate than the general dentists reported (P < .005).

Conclusions: 

Orthodontists' and general dentists' perceptions of how often specific types of media were used for interdisciplinary communication were generally similar. They differed, however, with regard to how adequately orthodontists communicated with general dentists and how often orthodontists sought input from general dentists. The methods and extent of communication between orthodontists and general dentists need to be determined on a patient-by-patient basis.
An improved model for tidally modulated grounding-line migration
Authors: Tsai Victor C. , Gudmundsson G. Hilmar
Published: March 2015

Understanding grounding-line dynamics is necessary for predictions of long-term ice-sheet stability. However, despite growing observations of the tidal influence on grounding-line migration, this short-timescale migration is poorly understood, with most modeling attempts assuming beam theory to calculate displacements. Here we present an improved model of tidal grounding-line migration that treats migration as an elastic fracture problem, forced by the additional ocean water pressure from the tide. This new model predicts that the grounding line cannot be assumed to be in hydrostatic equilibrium and, furthermore, that migration is inherently asymmetric and nonlinear, with migration distances that are not proportional to the tidal load. Specifically, for constant surface slope, the grounding line migrates upstream approximately ten times further as the tide rises from mean sea level to high tide than it migrates downstream as the tide falls from mean sea level to low tide, and migration distances are substantially larger than simple flotation arguments suggest. Numerical tests also show that the dependence of migration distance on elastic moduli and ice-sheet thickness are inconsistent with predictions of beam theory for a range of realistic values. Finally, applying the new model to observations in Antarctica results in new estimates of bed slopes, though these estimates remain uncertain due to imperfect knowledge of the relevant rheological parameters.
Marine ice-sheet profiles and stability under Coulomb basal conditions
Authors: Tsai Victor C. , Stewart Andrew L. , Thompson Andrew F.
Published: March 2015

The behavior of marine-terminating ice sheets, such as the West Antarctic ice sheet, is of interest due to the possibility of rapid grounding-line retreat and consequent catastrophic loss of ice. Critical to modeling this behavior is a choice of basal rheology, where the most popular approach is to relate the ice-sheet velocity to a power-law function of basal stress. Recent experiments, however, suggest that near-grounding line tills exhibit Coulomb friction behavior. Here we address how Coulomb conditions modify ice-sheet profiles and stability criteria. The basal rheology necessarily transitions to Coulomb friction near the grounding line, due to low effective stresses, leading to changes in ice-sheet properties within a narrow boundary layer. Ice-sheet profiles ‘taper off’ towards a flatter upper surface, compared with the power-law case, and basal stresses vanish at the grounding line, consistent with observations. In the Coulomb case, the grounding-line ice flux also depends more strongly on flotation ice thickness, which implies that ice sheets are more sensitive to climate perturbations. Furthermore, with Coulomb friction, the ice sheet grounds stably in shallower water than with a power-law rheology. This implies that smaller perturbations are required to push the grounding line into regions of negative bed slope, where it would become unstable. These results have important implications for ice-sheet stability in a warming climate.
Weakest-Link Scaling and Extreme Events in Finite-Sized Systems
Authors: Hristopulos Dionissios , Petrakis Manolis , Kaniadakis Giorgio
Published: March 2015

Weakest-link scaling is used in the reliability analysis of complex systems. It is characterized by the extensivity of the hazard function instead of the entropy. The Weibull distribution is the archetypical example of weakest-link scaling, and it describes variables such as the fracture strength of brittle materials, maximal annual rainfall, wind speed and earthquake return times. We investigate two new distributions that exhibit weakest-link scaling, i.e., a Weibull generalization known as the κ-Weibull and a modified gamma probability function that we propose herein. We show that in contrast with the Weibull and the modified gamma, the hazard function of the κ -Weibull is non-extensive, which is a signature of inter-dependence between the links. We also investigate the impact of heterogeneous links, modeled by means of a stochastic Weibull scale parameter, on the observed probability distribution.
Two-Step Lasso Estimation of the Spatial Weights Matrix
Authors: Ahrens Achim , Bhattacharjee Arnab
Published: March 2015

The vast majority of spatial econometric research relies on the assumption that the spatial network structure is known a priori. This study considers a two-step estimation strategy for estimating the n(n-1) interaction effects in a spatial autoregressive panel model where the spatial dimension is potentially large. The identifying assumption is approximate sparsity of the spatial weights matrix. The proposed estimation methodology exploits the Lasso estimator and mimics two-stage least squares (2SLS) to account for endogeneity of the spatial lag. The developed two-step estimator is of more general interest. It may be used in applications where the number of endogenous regressors and the number of instrumental variables is larger than the number of observations. We derive convergence rates for the two-step Lasso estimator. Our Monte Carlo simulation results show that the two-step estimator is consistent and successfully recovers the spatial network structure for reasonable sample size, T.
Tetraspanin 8-Rictor-Integrin α3 Complex Is Required for Glioma Cell Migration
Authors: Pan Si-Jian , Zhan Shi-Kun , Pan Yi-Xin , Liu Wei , Bian Liu-Guan , Sun Bomin , Sun Qing-Fang
Published: March 2015

The malignant glioma remains one of the most aggressive human malignancies with extremely poor prognosis. Glioma cell invasion and migration are the main causes of death. In the current study, we studied the expression and the potential functions of tetraspanin 8 (Tspan8) in malignant gliomas. We found that Tspan8 expression level is high in both malignant glioma tissues and in several human glioma cell lines, where it formed a complex integrin α3 and rictor, the latter is a key component of mammalian target of rapamycin (mTOR) complex 2 (mTORC2). Disruption of this complex, through siRNA-mediated knockdown of anyone of these three proteins, inhibited U251MG glioma cell migration in vitro. We further showed that Tspan8-rictor association appeared required for mTORC2 activation. Knockdown of Tspan8 by the targeted siRNAs prevented mTOR-rictor (mTORC2) assembly as well as phosphorylation of AKT (Ser-473) and protein kinase C α (PKCα) in U251MG cells. Together, these results demonstrate that over-expressed Tspan8 in malignant glioma forms a complex with rictor and integrin α3 to mediate mTORC2 activation and glioma cell migration. Therefore, targeting Tspan8-rictor-integrin α3 complex may provide a potential therapeutic intervention for malignant glioma.
Different Apoptotic Pathways Activated by Oxaliplatin in Primary Astrocytes vs. Colo-Rectal Cancer Cells
Authors: Zanardelli Matteo , Micheli Laura , Nicolai Raffaella , Failli Paola , Ghelardini Carla , Di Cesare Mannelli Lorenzo
Published: March 2015

Oxaliplatin-based chemotherapy improves the outcomes of metastatic colorectal cancer patients. Its most significant and dose-limiting side effect is the development of a neuropathic syndrome. The mechanism of the neurotoxicity is unclear. The limited knowledge about differences existing between neurotoxic and antitumor effects hinders the discovery of effective and safe adjuvant therapies. In vitro, we suggested cell-specific activation apoptotic pathways in normal nervous cells (astrocytes) vs. colon-cancer cells (HT-29). In the present research we compared the apoptotic signals evoked by oxaliplatin in astrocytes and HT-29 analyzing the intrinsic and extrinsic apoptotic pathways. In astrocytes, oxaliplatin induced a mitochondrial derangement measured as cytosolic release of cytochrome C, increase in superoxide anion levels and decreased expression of the antiapoptotic protein Bcl-2. Caspase-8, a main initiator of the extrinsic process remained unaltered. On the contrary, in HT-29 oxaliplatin increased caspase-8 activity and Bid expression, thus activating the extrinsic apoptosis, while the Bcl-2 increased expression blocked the mitochondrial damage. Data suggest the preferred activation of the intrinsic apoptosis as oxaliplatin damage signaling in normal nervous cells. The extrinsic pathway prevails in tumor cells indicating a possible strategy for planning new molecules to treat oxaliplatin-dependent neurotoxicity without negatively influence chemotherapy.
A Calibration Report for Wireless Sensor-Based Weatherboards
Authors: Masinde Muthoni , Bagula Antoine
Published: March 2015

Sub-Saharan Africa contains the highest number of people affected by droughts. Although this can easily be mitigated through the provision of timely, reliable and relevant weather forecasts, the sparse network of weather stations in most of these countries makes this difficult. Rapid development in wireless sensor networks has resulted in weatherboards capable of capturing weather parameters at the micro-level. Although these weatherboards offer a viable solution to Africa’s drought, the acceptability of such data by meteorologists is only possible if these sensors are calibrated and their field readiness scientifically evaluated. This is the contribution of this paper; we present results of a calibration exercise that was carried out to: (1) measure and correct lag, random and systematic errors; (2) determine if Perspex was an ideal material for building sensor boards’ enclosures; and (3) identify sensor boards’ battery charging and depletion rates. The result is a calibration report detailing actual error and uncertainty values for atmospheric pressure, humidity and temperature sensors, as well as the recharge and discharge curves of the batteries. The results further ruled out the use of Perspex for enclosing the sensor boards. These experiments pave the way for the design and implementation of a sensor-based weather monitoring system (SenseWeather) that was piloted in two regions in Kenya.
Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals
Authors: Ribeiro Adolfo , Fabre Guillaume , Guermond Jean-Luc , Aurnou Jonathan
Published: March 2015

Planets and stars are often capable of generating their own magnetic fields. This occurs through dynamo processes occurring via turbulent convective stirring of their respective molten metal-rich cores and plasma-based convection zones. Present-day numerical models of planetary and stellar dynamo action are not carried out using fluids properties that mimic the essential properties of liquid metals and plasmas (e.g., using fluids with thermal Prandtl numbers Pr < 1 and magnetic Prandtl numbers Pm ≪ 1). Metal dynamo simulations should become possible, though, within the next decade. In order then to understand the turbulent convection phenomena occurring in geophysical or astrophysical fluids and next-generation numerical models thereof, we present here canonical, end-member examples of thermally-driven convection in liquid gallium, first with no magnetic field or rotation present, then with the inclusion of a background magnetic field and then in a rotating system (without an imposed magnetic field). In doing so, we demonstrate the essential behaviors of convecting liquid metals that are necessary for building, as well as benchmarking, accurate, robust models of magnetohydrodynamic processes in Pm ≪ Pr < 1 geophysical and astrophysical systems. Our study results also show strong agreement between laboratory and numerical experiments, demonstrating that high resolution numerical simulations can be made capable of modeling the liquid metal convective turbulence needed in accurate next-generation dynamo models.
Correction: Chapman, E.; et al. Inhibitors of the AAA+ Chaperone p97. Molecules 2015, 20, 3027-3049
Authors: Chapman Eli , Maksim Nick , De la Cruz Fabian , La Clair James
Published: March 2015

The authors wish to make the following correction to paper [1], doi:10.3390/molecules20023027, website: http://www.mdpi.com/1420-3049/20/2/3027/. [...]
“In-plant” NMR: Analysis of the Intact Plant Vesicularia dubyana by High Resolution NMR Spectroscopy
Authors: Kutyshenko Viktor , Beskaravayny Peter , Uversky Vladimir
Published: March 2015

We present here the concept of “in-plant” NMR and show that high-resolution NMR spectroscopy is suitable for the analysis of intact plants and can be used to follow the changes in the intraorganismal molecular composition over long time periods. The NMR-based analysis of the effect of different concentrations of heavy water on the aquatic plant Vesicularia dubyana revealed that due to the presence of specific adaptive mechanisms this plant can sustain the presence of up to 85% of D2O. However, it dies in 100% heavy water.
Phytochemicals and Other Characteristics of Croatian Monovarietal Extra Virgin Olive Oils from Oblica, Lastovka and Levantinka Varieties
Authors: Šarolić Mladenka , Gugić Mirko , Friganović Emilija , Tuberoso Carlo , Jerković Igor
Published: March 2015

Virgin olive oils from the fruits of Croatian autochthonous varieties Oblica, Lastovka and Levantinka were characterized for the first time. Headspace volatiles were analyzed by HS-SPME/GC-FID/MS. The main volatiles were C6 compounds. The most abundant was (E)-hex-2-enal (62.60%–69.20%). (Z)-Hex-3-enal was not found in Lastovka oil, while Levantinka oil did not contain hexanal. Tocopherols, chlorophylls and carotenoids were determined by HPLC-FL. Levantinka oil was characterized by the highest α-tocopherol level (222.00 mg/kg). Total phenolic contents (TPs), as well as antioxidant activity (DPPH assay) of the oils hydrophilic fractions (HFs) were assessed by spectroscopic methods. The antioxidant activity of Oblica oil HF was the most pronounced (0.91 mmol TEAC/kg) and the HF contained the highest TPs amount (212.21 mg/kg). HFs phenolic composition was determined by HPLC-DAD. The main identified phenols were secoiridoids dominated in Oblica oil: decarboxymethyl ligstroside aglycone (p-HPEA-EDA up to 158.5 mg/kg), oleuropein aglycone (3,4-HPEA-EA up to 96.4 mg/kg) and decarboxymethyl oleuropein aglycon (3,4-DHPEA-EDA up to 93.5 mg/kg).
Magnetization Reversal and Magnetic Anisotropy in Ordered CoNiP Nanowire Arrays: Effects of Wire Diameter
Authors: Van Thiem Luu , Tu Le , Phan Manh-Huong
Published: March 2015

Ordered CoNiP nanowires with the same length of 4 µm and varying diameters (d = 100 nm–600 nm) were fabricated by electrodeposition of CoNiP onto polycarbonate templates. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy confirmed the quality of the fabricated nanowires. Magnetic measurements and theoretical analysis revealed that the magnetization reversal and magnetic anisotropy were significantly influenced by varying of the diameters of the nanowires. There existed a critical wire diameter (dc ≈ 276 nm), below which the magnetization reversal occurred via a coherent rotation mode, and above which the magnetization reversal occurred via a curling rotation mode. The easy axis of the magnetization tended to change in direction from parallel to perpendicular with respect to the wire axis as the wire diameter exceeded dc ≈ 276 nm. With increasing wire diameter, the coercive field (Hc) and the remanent to saturation magnetization ratio (Mr/Ms) were also found to rapidly decrease in the range d = 100–400 nm and gradually decrease for d > 400 nm.
Optical Sensing of the Fatigue Damage State of CFRP under Realistic Aeronautical Load Sequences
Authors: Zuluaga-Ramírez Pablo , Arconada Álvaro , Frövel Malte , Belenguer Tomás , Salazar Félix
Published: March 2015

We present an optical sensing methodology to estimate the fatigue damage state of structures made of carbon fiber reinforced polymer (CFRP), by measuring variations on the surface roughness. Variable amplitude loads (VAL), which represent realistic loads during aeronautical missions of fighter aircraft (FALSTAFF) have been applied to coupons until failure. Stiffness degradation and surface roughness variations have been measured during the life of the coupons obtaining a Pearson correlation of 0.75 between both variables. The data were compared with a previous study for Constant Amplitude Load (CAL) obtaining similar results. Conclusions suggest that the surface roughness measured in strategic zones is a useful technique for structural health monitoring of CFRP structures, and that it is independent of the type of load applied. Surface roughness can be measured in the field by optical techniques such as speckle, confocal perfilometers and interferometry, among others.