Small Extension Research Articles

Parameters of Sand-Tyre Chips Mixture for Hardening Soil Small Constitutive Model

Hardening Soil model with the small strain extension (HSS) is lately one of the most popular constitutive models to describe soil behaviour. It is versatile – includes the phenomena of shear strength, stress history, dilatancy, volumetric and shear hardening, hyperbolic stress-strain relationship in axial compression, stiffness dependency on stress and its degradation with strain, as well as the regain of the high stiffness after sharp loading reversals. Even though the model is advanced and complex, accordingly to its authors, it is relatively easy to calibrate based on results of standard tests and empirical formulas. In this paper an attempt was undertaken to estimate the parameters of untypical anthropogenic soils – mixtures of sand and scrap tyre rubber in order to build a database for future numerical analyses. A literature review was conducted and, eventually, the material parameters were determined based on results of a series of laboratory tests (cyclic and monotonic triaxial with bender elements, direct shear) published by researchers of Wollongong University of Australia.

Functions-as-constructors higher-order unification: extended pattern unification

Unification is a central operation in constructing a range of computational logic systems based on first-order and higher-order logics. First-order unification has several properties that guide its incorporation in such systems. In particular, first-order unification is decidable, unary, and can be performed on untyped term structures. None of these three properties hold for full higher-order unification: unification is undecidable, unifiers can be incomparable, and term-level typing can dominate the search for unifiers. The so-called pattern subset of higher-order unification was designed to be a small extension to first-order unification that respects the laws governing λ-binding (i.e., the equalities for α, β, and η-conversion) but which also satisfied those three properties. While the pattern fragment of higher-order unification has been used in numerous implemented systems and in various theoretical settings, it is too weak for many applications. This paper defines an extension of pattern unification that should make it more generally applicable, especially in proof assistants that allow for higher-order functions. This extension’s main idea is that the arguments to a higher-order, free variable can be more than just distinct bound variables. In particular, such arguments can be terms constructed from (sufficient numbers of) such bound variables using term constructors and where no argument is a subterm of any other argument. We show that this extension to pattern unification satisfies the three properties mentioned above.

Numerical Simulation and Linearized Theory of Vortex Waves in a Viscoelastic, Polymeric Fluid

In a high viscosity, polymeric fluid initially at rest, the release of elastic energy produces vorticity in the form of coherent motions (vortex rings). Such behavior may enhance mixing in the low Reynolds number flows encountered in microfluidic applications. In this work, we develop a theory for such flows by linearizing the governing equations of motion. The linear theory predicts that when elastic energy is released in a symmetric manner, a wave of vorticity is produced with two distinct periods of wave motion: (1) a period of wave expansion and growth extending over a transition time scale, followed by (2) a period of wave translation and viscous decay. The vortex wave speeds are predicted to be proportional to the square root of the initial fluid tension, and the fluid tension itself scales as the viscosity. Besides verifying the predictions of the linearized theory, numerical solutions of the equations of motion for the velocity field, obtained using a pseudo-spectral method, show that the flow is composed of right- and left-traveling columnar vortex pairs, called vortex waves for short. Wave speeds obtained from the numerical simulations are within 1.5% of those from the linear theory when the assumption of linearity holds. Vortex waves are found to decay on a time scale of the order of the vortex size divided by the solution viscosity, in reasonable agreement with the analytical solution of the linearized model for damped vortex waves. When the viscoelastic fluid is governed by a nonlinear spring model, as represented by the Peterlin function, wave speeds are found to be larger than the predictions of the linear theory for small polymer extension lengths.

Lineament mapping in the Ikniouen area (Eastern Anti-Atlas, Morocco) using Landsat-8 Oli and SRTM data

The present work focuses on the use of remote sensing techniques and Geographical Information Systems (GIS), to Automatic extraction and geospatial analysis of lineaments, in the district of Ikniouen located in the eastern Moroccan Anti Atlas. To achieve this objective, we relied on the processing of Landsat-8 OLI spectral bands and SRTM data covering the study site. In the first instance, essential pre-processing was carried out on our spatial data for the automatic extraction of lineaments by applying the mathematical algorithm Line Module from PCI's Geomatica 2016 software. Some of the treatments used included Principal Component Analysis, Shaded relief of SRTM data from different angles, 7 × 7 matrix directional filters, and finally the automatic extraction of lineaments. The results obtained from lineament extraction from the PC1 image, the seven spectral bands with a spatial resolution of 30 m, and the digital elevation models (DEM) SRTM proved that each map produced had a strong similarity in terms of density and orientation with two major directions – NE-SW and E-W – with high densities in areas well known to be fractured, namely the Oussilkane granites in the northeast, the Ikniouen granites in the west, and the rhyolites and ignimbrites of the Amtatouch-Yadawdane formations in the south of the study area. The results from the automatic extraction of the lineaments revealed 2680 lineaments, whose size varied from a few metres to 3.4 km, with an average length of 534 m. The lineaments of small extensions were the most numerous, as they had an interval comprising almost between 30 and 1158 m. The projection of these lineaments on a Rose diagram showed a predominance of the NE-SW direction. Multi-source data, such as lithological factors, slope factors, and calibrated, high-resolution ESRI field imagery basemap, were used to validate potential results of this automatic lineament mapping. The automatic extraction allowed a better mapping of the structural lineaments; it add information to geological data, but the geological meaning of the linear feature have to be investigated. This technique is usefull to preliminary identify areas with a probable difference in potential lineament density together with their main directions.

New insights into the daily and symbolic use of plants during initial occupations of Formentera (Balearic Islands, Spain)

The island of Formentera, with its small extension and flat orography, was settled relatively late in Mediterranean prehistory between the third and second millennium BC. The sites presented in this paper, Cova des Fum and Cova des Riuets, offer evidence of the island’s first occupation. Cova des Fum comprises a necropolis of the Bronze Age and two sanctuary spaces (used, at least, from 2035 cal BC), with hearths and water management structures. Cova des Riuets is a habitation site from the beginning of the Bronze Age (available dates ranging from 2030 to 1760 cal BC). This landscape study, among the first on the ancient occupation of the island, focuses on the plant macro-remains from both sites, providing new data on the vegetation of the surrounding areas and the use of both wild and domesticated plant resources for various daily and ritual tasks. The firewood came from evergreen thermo-Mediterranean formations well adapted to drought and summer heat, as well as rocky environments, and could have been collected in the vicinity of the sites. The autochthonous character of some species, such as the fig tree, has also been investigated and has provided the oldest existing date for this species on the island. This study reveals some peculiarities in the island’s subsistence strategy that are relevant to the study of small islands more generally.

Investigating Thaw and Plant Productivity Constraints on Old Soil Carbon Respiration From Permafrost

AbstractIsotopic radiocarbon (Δ14C) signatures of ecosystem respiration (Reco) can identify old soil carbon (C) loss and serve as an early indicator of permafrost destabilization in a warming climate. Warming also stimulates plant productivity causing plant respiration to dominate Reco Δ14C signatures and potentially obscuring old soil C loss. Here, we investigate how a wide spatio‐temporal gradient of permafrost thaw and plant productivity affects Reco Δ14C patterns and isotopic partitioning. Spatial gradients came from a warming experiment with doubling thaw depth and variable biomass, and a vegetation removal manipulation to eliminate plant contributions. We sampled in August and September to capture transitions from high to low plant productivity, decreased surface soil temperature, and relatively small seasonal thaw extensions. We found that surface processes dominate spatial variation in old soil C loss and a process‐based partitioning approach was crucial for constraining old soil C loss. Resampling the same plots in different times of the year revealed that old soil C losses tripled with cooling surface temperature, and the largest old soil C losses were detected when the organic‐to‐mineral soil horizons thawed (∼50–60 cm). We suggest that the measured increase in old soil respiration over the season and when the organic‐to‐mineral horizon thawed, may be explained by mobilization of nitrogen that stimulates microbial decomposition at depth. Our results suggest that soil C in the organic to mineral horizon may be an important source of soil C loss as the entire Arctic region warms and could lead to nonlinearities in projected permafrost climate feedbacks.

Vulnerability of Farmers to Crop Farming Risks in Ethiopia: An Integrated Vulnerability Analysis Approach Using Social-Ecological System Framework

Crop production under a smallholder system is challenged by several (a)biotic risks those resulted in livelihood insecurity. This study assesses farmers’ perceived vulnerability level to the crop farming risks and identifies its determinants using an integrated vulnerability analysis approach. Survey data collected from 393 sample households in West Shewa Zone, Ethiopia, were analyzed using PCA and ordered probit regression. Results indicate that 13 percent of the sampled households are highly vulnerable, 73.5 percent are moderately vulnerable and 13.5 percent are less vulnerable where 77 percent of the highly vulnerable groups faced more than 3 months lean season and 72 percent of the less vulnerable groups faced less than 3 months of lean season. Moreover, farming experience and education level of household head, livestock owned, farm size, on-farm diversification, access to credit, small scale irrigation, off-farming income, extension contact, and social capital are significantly affecting the perceived vulnerability level. These calls for need-based government and/or non-government intervention plans focusing on improving rural infrastructure and facilities and devising an effective and responsive institutional setup for enhancing the responsive capacities of smallholder farmers in the short-run and minimizing the likelihood of exposure and sensitivity in the long-run.

Simultaneous high Q/V-ratio and optimized far-field emission pattern in diamond slot-bridge nanobeam cavity

We present a design for a slot-bridge nanobeam cavity that supports ultrahigh Q/V and optimized far-field emission pattern, and operates at the zero-phonon transition (637nm) of the nitrogen-vacancy color centers in diamond. The slot-bridge cavity is formed by introducing a diamond bridge at the center of the air region of a slotted cavity. As a result of the boundary condition on the parallel component of the electric field, the electric field in the bridge region is the same as that in the slot. This results in a further reduction of the mode volume. Optimized slot-bridge cavities with a calculated Q factor of 6×106 and mode volume of Veff=0.28(λ/n)3have been realized. In comparison to nanobeam cavities, the mode volume is reduced by a factor of 139. The far-field pattern of a slot-bridge cavity is optimized by using the band folding method and by adding small air-slot extensions to the two closest air-holes surrounding the cavity. A high Q of 9.8×105 and a small mode volume of Veff=0.011(λ/n)3 is realized for this design. Therefore, this type of cavities would allow for the realization of efficient single-photon sources. Our results are important for fundamental studies, like cavity quantum electrodynamics, as well as applications in quantum information processing based on diamond where high quality-factor and ultrasmall mode volume are required.

Determinants of healthcare worker turnover in intensive care units: A micro-macro multilevel analysis.

BackgroundHigh turnover among healthcare workers is an increasingly common phenomenon in hospitals worldwide, especially in intensive care units (ICUs). In addition to the serious financial consequences, this is a major concern for patient care (disrupted continuity of care, decreased quality and safety of care, increased rates of medication errors, …).ObjectiveThe goal of this article was to understand how the ICU-level nurse turnover rate may be explained from multiple covariates at individual and ICU-level, using data from 526 French registered and auxiliary nurses (RANs).MethodsA cross-sectional study was conducted in ICUs of Paris-area hospitals in 2013. First, we developed a small extension of a multi-level modeling method proposed in 2007 by Croon and van Veldhoven and validated its properties using a comprehensive simulation study. Second, we applied this approach to explain RAN turnover in French ICUs.ResultsBased on the simulation study, the approach we proposed allows to estimate the regression coefficients with a relative bias below 7% for group-level factors and below 12% for individual-level factors. In our data, the mean observed RAN turnover rate was 0.19 per year (SD = 0.09). Based on our results, social support from colleagues and supervisors as well as long durations of experience in the profession were negatively associated with turnover. Conversely, number of children and impossibility to skip a break due to workload were significantly associated with higher rates of turnover. At ICU-level, number of beds, presence of intermediate care beds (continuous care unit) in the ICU and staff-to-patient ratio emerged as significant predictors.ConclusionsThe findings of this research may help decision makers within hospitals by highlighting major determinants of turnover among RANs. In addition, the new approach proposed here could prove useful to researchers faced with similar micro-macro data.

Clinicoradiological Features and Treatment Outcome of Supratentorial Intraparenchymal Epidermoid Cyst: A Report of Five Cases and Literature Review.

Objectives Intraparenchymal epidermoid cysts (IECs) are rare lesions. They represent less than 1% of the intracranial epidermoid cysts. The supratentorial IEC is a clinically and prognostically distinct subset. Given the rarity, most of the articles are case reports. We present a series of five cases of supratentorial IEC to characterize their clinical presentation and outcome, with emphasis on the surgical features. Materials and Methods We searched our database for all cases of intracranial epidermoid cysts operated between January 2005 and January 2020. Five patients were identified having IEC from the hospital information system and the neurosurgical operation record book. Standard craniotomy and decompression of the lesion were performed in all these patients. Standard postoperative care includes computed tomography scan of head on the day of surgery and magnetic resonance imaging of brain after 6 weeks to look for the residual lesion, if any. Subsequent follow-up visits in outpatient department to look for resolution of the presurgical symptoms. Results The mean age of the patients in our series was 28.8 years (range: 28–40 years.). All the five patients were male. Four patients had IEC involving frontal lobe and one in parietal lobe with a small occipital lobe extension. Seizure was the most common presenting complaint followed by headache. Complete excision was achieved in all the cases. All the three patients with seizure attained seizure freedom postlesionectomy. Focal neurological deficits resolved gradually in postoperative period. There was no recurrence of lesion during follow-up. Conclusion Supratentorial IEC most commonly affects young males, involve frontal lobe and present clinically with seizure. Complete surgical excision offers best outcome in the form of remission of seizure disorder.

Abordagem cirúrgica para cisto periapical de tamanho atípico em idosa: Relato de caso

Os cistos periapicais, são formados pelo processo inflamatório do epitélio no ápice de dentes não vitais. Normalmente apresenta características de crescimento lento, assintomático e de pequena extensão. Nesse estudo, objetiva-se reportar um caso de cisto periapical com tamanho atípico, submetido à abordagem cirúrgica. Aqui, trata-se de um estudo qualitativo, descritivo, retrospectivo e realizado pela da técnica da observação direta, respeitando todos os protocolos éticos. Paciente 74 anos, feminina, compareceu ao serviço de Cirurgia e Traumatologia Buco-maxilo-facial do Hospital da Restauração Governador Paulo Guerra - Recife, encaminhada por um cirurgião-dentista após análise de exame de imagem de rotina sugestivo de lesão cística em mandíbula. Ao exame físico apresentou discreto abaulamento em cortical vestibular de corpo mandibular direito, assintomático ao toque. Através da tomografia computadorizada se constatou uma área hipodensa, unilocular, circunscrita por uma linha hiperdensa, abrangendo região de dentes 42,43,44,e 45. Com base no exame clínico, foi estabelecida a hipótese diagnóstica de cisto periapical, confirmada após análise histopatológica. Como abordagem terapêutica optou-se por realizar sob anestesia geral a enucleação, osteotomia periférica e exodontias dos dentes envolvidos. Em 08 meses de acompanhamento não apresenta sinal de recidivas. Desse modo, fica claro a importância do correto diagnóstico, bem como a eficácia da intervenção cirúrgica como tratamento de lesão periapical de grande extensão.

Stakeholders role in economy creative development of maritime culture in Alor Regency

Culture-based creative economy development policies need to have a broader impact on the acceptance of benefits, by the community, local and central governments. Furthermore, these policies need the support of various stakeholders to determine their roles and functions. Therefore, this study examines each stakeholder’s roles and influences in the creative economy development based on the maritime culture in the Alor Regency. The snowball sampling method was used to obtain data from government, private, community, and non-governmental organizations. Besides, the analytical method used is descriptive and stakeholder analyzed comprising the mactor program (Matrix of Alliances and Conflicts: Tactics, Objectives, and Recommendations). The results showed that the main stakeholders that play important roles in the formulation of maritime culture-based creative economy development policies in the Alor Regency are the Industries Extensions, Cooperatives Small and Medium Enterprises Extensions, Empowerment Community Extensions, Fisheries Extensions, District Tourism Office, and Kabola Fishers Communication Forum. These stakeholders are achieved in collaboration with those with high power and interests and increase academics’ role as a part of Penta helix process.

Mohs micrographic surgery: a review of indications, technique, outcomes, and considerations

Mohs micrographic surgery is a specialized form of skin cancer surgery that has the highest cure rates for several cutaneous malignancies. Certain skin cancers can have small extensions or “roots” that may be missed if an excised tumor is serially cross-sectioned in a “bread-loaf” fashion, commonly performed on excision specimens. The method of Mohs micrographic surgery is unique in that the dermatologist (Mohs surgeon) acts as both surgeon and pathologist, from the preoperative considerations until the reconstruction. Since Dr. Mohs’s initial work in the 1930s, the practice of Mohs micrographic surgery has become increasingly widespread among the dermatologic surgery community worldwide and is considered the treatment of choice for many common and uncommon cutaneous neoplasms. Mohs micrographic surgery spares the maximal amount of normal tissue and is a safe procedure with very few complications, most of them managed by Mohs surgeons in their offices. Mohs micrographic surgery is the standard of care for high risks basal cell carcinomas and cutaneous squamous cell carcinoma and is commonly and increasingly used for melanoma and other rare tumors with superior cure rates. This review better familiarizes the dermatologists with the technique, explains the difference between Mohs micrographic surgery and wide local excision, and discusses its main indications.

Effect of polymer chains entanglements, crosslinks and finite extensibility on the nonlinear dynamic oscillations of dielectric viscoelastomer actuators

Soft materials exhibiting large deformation under external stimuli have gained an increasing attention in the recent past because of their potential applications in soft transducers aimed at achieving biomimetic actuation. This paper theoretically analyzes the effect of internal properties, including entanglements, crosslinks and finite extensibility of polymer chains along with inherent viscoelastic properties of polymers on the performance of Dielectric Elastomer actuator (DEA) in dynamic modes of actuation. A physics based nonaffine material model proposed by Davidson and Goulbourne is used to model the polymer chains entanglements, crosslinks and finite extensibility. To incorprate the viscoelastic properties, a rheological material model based on the additive decomposition of the isotropic strain energy density into equilibrium and viscous parts is implemented. A computationally efficient method, which relies on the principle of least action is used for extracting the governing equation representing the dynamic motion of the DE actuator. The results demonstrate that DEAs with strong entanglements and crosslinks along with small finite extensibility of polymer chains exhibits lower deformation level in DC dynamic modes of actuation. It is inferred that the strong entanglements and crosslinks in polymer chains enhances the resonant frequency, but debilitate the intensity of vibration of viscoelastic DEAs. Further, the periodicity and stability of the nonlinear oscillations exhibited by the viscoelastic DEAs are assessed by employing the Poincare maps and phase portraits. The results of the present investigation can be applied effectively in bridging the mechanism between the microcosmic polymer chains and macroscopic dynamic behavior of viscoelastic DE actuators.

Evolution of internal pores within AlSi10Mg manufactured by laser powder bed fusion under tension: As-built and heat treated conditions

The optimisation of processing parameters to produce high densification AlSi10Mg parts by laser powder bed fusion (LPBF) has received considerable attention in recent years. Nonetheless, it is important to consider the potential presence of as-built large pores in real world applications, e.g. due to limitations of the available LPBF system, time and cost constraints associated with producing near-perfect density and so on. In this work, recycled powder was used to fabricate AlSi10Mg specimens with sub-optimal densification by LPBF and an experimental investigation into the evolution of specimen porosity occurring under increasing tensile load was performed. A combination of high-resolution X-ray micro computed tomography (XμCT) and an in-situ micro-testing stage was employed to acquire 3D images at different loading stages. Specimens were tested in the as-built condition and following hot isostatic pressing (HIPping) or HIPping with T6. As-built porosity did not change markedly in the lead-up to brittle-like fracture. Pores within ductile HIPped specimens were uniformly elongated up to the onset of damage propagation and pore coalescence. Pore shape change occurred largely without volume change at small extension. HIPping plus T6 produced a compromise between as-built and HIPped conditions in terms of the extent of pore modification observed prior to failure.

Determination of predisposing scapular anatomy with a statistical shape model-Part II: shoulder osteoarthritis.

Shoulder osteoarthritis can be divided into different glenoid types (A, B, C, and D) and subtypes. The aim of this study was to investigate if there is an association between the prearthropathy scapular anatomy, shoulder osteoarthritis, and different glenoid types and subtypes. Using principal components analysis, a statistical shape model (SSM) of the scapula was constructed from a data set of 110 computed tomographic (CT) scans. These subjects formed the control group. Next, CT scan images of 117 patients with osteoarthritis were classified according to the modified Walch classification. A complete 3-dimensional (3D) scapular bone model was created for every patient, and using the SSM, a reconstruction of their prearthropathy scapular anatomy was performed. Automated 3D measurements were performed in both the patient and control group to obtain glenoid version and inclination, critical shoulder angle (CSA), posterior acromial slope (PAS), lateral acromion angle, scapular offset, and the rotational alignment of the coracoacromial complex. These parameters were compared between controls, patients with osteoarthritis, and glenoid types and subtypes. Mean version and inclination for the control group was 6° retroversion and 8° superior inclination (both SD 4°). The mean CSA, PAS, coracoid-posterior acromion angle, posterior acromion-scapular plane angle, and fulcrum axis ratio were 30° (SD 4°), 64° (SD 8°), 116° (SD 9°), 55° (SD 7°), and 46% (SD 4%), respectively. Patients with osteoarthritis had a significant lower CSA, posterior acromion-scapular plane angle, coracoid-posterior acromion angle, and fulcrum axis ratio (27°, 50°, 111°, and 44%, all P < .001). We found a significant difference between the control group and the respective glenoid types for the following parameters: mean CSA and coracoid-posterior acromion angle for A glenoids (27°, P = .001, and 111°, P = .007); mean version, CSA, PAS, coracoid-posterior acromion angle, posterior acromion-scapular plane angle, and fulcrum axis ratio for B glenoids (11°, 27°, 71°, 111°, 49°, and 43%, all P< .001); and mean version, CSA, and posterior acromion-scapular plane angle for D glenoids (2°, P = .002, 26°, P = .003, and 48°, P= .007). There seems to be an association between prearthropathy scapular anatomy and shoulder osteoarthritis. A small lateral extension and less posterior rotation of the acromion is associated with shoulder osteoarthritis and is present in almost all types and subtypes of glenoid morphology. Furthermore, B and D glenoids are associated with, respectively, a more and less pronounced prearthropathy glenoid retroversion.

Measuring and benchmarking the benefits of Athens metro extension using an ex-post cost benefit analysis

The development of metro projects is an essential step for the establishment of a high level of mobility, especially in urban areas, where traffic congestion is a major issue to tackle. Nevertheless, underground projects of this scale require major investments and often become the objects of skepticism regarding the associated expenditures. Cost-benefit analysis (CBA) is the tool to assess such projects and provide support in the decision process. Such tools are examined in the present paper, where a relatively small extension of the Athens metro is evaluated. The analysis is being made as an ex-post CBA, utilizing the retrospective experience and the available data from the project’s construction period and its operation until now. The findings of the current analysis are then compared to a respective ex-ante CBA that was made during the initial phase of the construction phase revealing a considerable positive change in valuation having twice as much more ENPV (€153 million vs. €340 million). By comparing the results of both the ex-ante and the ex-post approach the main differentiating factors, similarities and shortcomings are identified, especially in the cost aspects of the development and the accurate assessment and valuation of benefits that render the whole extension even more socially desirable than it was initially perceived.

Development of the Miocene Guangle Carbonate Platform in the South China Sea: Architecture and Controlling Factors

AbstractThis study investigates the evolution of the Miocene Guangle carbonate platform (or Triton Horst) of the northwestern South China Sea margin. The platform is located at a junction area surrounded by Yinggehai basin, Qiongdongnan basin and Zhongjiannan basin. Well and regional geophysical data allow the identification of the morphologic and stratigraphic patterns. The Guangle carbonate platform was initiated on a tectonic uplift during the Early Miocene. The early platform was limited at Mesozoic granitic basement, pre‐Paleogene sediments localized tectonic uplift and was small extension at the beginning stage. While during the Middle Miocene, the carbonate buildup flourished, and grow a thrived and thick carbonate succession overlining the whole Guangle Uplift. The isolated platforms then united afterward and covered an extensive area of several tens of thousands of square kilometers. However, it terminated in the Late Miocene. What are the control factors on the initiation, growth and demise of the Guangle carbonate platform? The onset of widespread carbonate deposits largely reflected the Early Miocene transgression linked with early post‐rift subsidence and the opening of the South China Sea. Stressed carbonate growth conditions on the Guangle carbonate platform probably resulted from increased inorganic nutrient input derived from the adjacent uplifted mainland, possibly enhanced by deteriorated climatic conditions promoting platform drowning. Therefore, tectonics and terrigenous input could be two main controlling factors on the development of the Guangle carbonate platforms and main evolution stages.

Modeling and analyzing evaluation cost of CUDA kernels

General-purpose programming on GPUs (GPGPU) is becoming increasingly in vogue as applications such as machine learning and scientific computing demand high throughput in vector-parallel applications. NVIDIA's CUDA toolkit seeks to make GPGPU programming accessible by allowing programmers to write GPU functions, called kernels, in a small extension of C/C++. However, due to CUDA's complex execution model, the performance characteristics of CUDA kernels are difficult to predict, especially for novice programmers. This paper introduces a novel quantitative program logic for CUDA kernels, which allows programmers to reason about both functional correctness and resource usage of CUDA kernels, paying particular attention to a set of common but CUDA-specific performance bottlenecks. The logic is proved sound with respect to a novel operational cost semantics for CUDA kernels. The semantics, logic and soundness proofs are formalized in Coq. An inference algorithm based on LP solving automatically synthesizes symbolic resource bounds by generating derivations in the logic. This algorithm is the basis of RaCuda, an end-to-end resource-analysis tool for kernels, which has been implemented using an existing resource-analysis tool for imperative programs. An experimental evaluation on a suite of CUDA benchmarks shows that the analysis is effective in aiding the detection of performance bugs in CUDA kernels.

Fracturing With Height Control Extends the Life of Mature Reservoirs in the Pannonian Basin

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 200588, “Fracturing With Height Control Extends the Life of Mature Reservoirs: Case Studies From the Pannonian Basin,” by Ruslan Malon, SPE, Independent, and Jonathan Abbott, SPE, and Ludmila Belyakova, SPE, Schlumberger, et al., prepared for the 2020 SPE Europec featured at the 82nd EAGE Conference and Exhibition, originally scheduled to be held in Amsterdam, 1-3 December. The paper has not been peer reviewed. Hydraulic proppant fracturing is an effective tool in mature, low-permeability reservoirs found in the Pannonian Basin. However, for wells already producing with high water cut, even a small fracture extension into a water-bearing zone offsets the gains in hydrocarbon production. Fracture-geometry-control (FGC) techniques limit increases in water cut. The complete paper describes the first implementation of a solution to control fracture height for conventional wells in the Pannonian Basin. An integrated engineering approach was applied, including a new proppant-transport model to predict fracture geometry improvement using the FGC solution. Decreased Recovery in A and B Fields Oilfield A began producing in 1984. In addition to an interruption by the war in Yugoslavia in the 1990s, production has been in decline, and most wells are at risk of being shut in because of low production rates. During the last 10 years, propped fracturing was integrated into the production strategy for this mature field. Field A comprises Lower Pontian (Miocene) sandstones. Another sandstone formation exists between 5 and 15 m below the production target reservoir, with high water saturation as confirmed by log analysis and well testing. The proximity of the oil target to the water-bearing interval still presents a risk to production considering that hydraulic fracturing is required to extend field life. An impermeable shale streak that may act as a geomechanical barrier exists below the target formation. With a lower risk of fracture propagation into the water zone, Field A was one of the first candidate fields for propped fracturing and was later considered for advanced fracture-height-control techniques to prevent the increase of water cut after stimulation. Hydraulic fracturing would not be trialed in Field B—the characteristics of which are provided in the complete paper—until the advanced height-control techniques had been proved on the basis of experience with Field A. Oilfield A: Early Fracturing Results Early campaigns proved the economic feasibility of propped fracturing, resulting in a 2.1-fold average increase in oil production during the first 6 months of production. Unfortunately, production after this early period declined rapidly. Increases in water cut, seen in several fracturing campaigns, clearly were related to hydraulic fracture growth. Although the resulting uplift in oil production warranted continued fracturing, avoiding water was a key issue to address before expansion of propped fracturing further in this field and to other fields with an even higher risk of water.