bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accurate Frequency Estimation Based On Three-Parameter Sine-Fitting With Three FFT Samples
Authors: Liu Xin , Ren Yongfeng , Chu Chengqun , Fang Wei 
Published: September 2015

Abstract
This paper presents a simple DFT-based golden section searching algorithm (DGSSA) for the single tone frequency estimation. Because of truncation and discreteness in signal samples, Fast Fourier Transform (FFT) and Discrete Fourier Transform (DFT) are inevitable to cause the spectrum leakage and fence effect which lead to a low estimation accuracy. This method can improve the estimation accuracy under conditions of a low signal-to-noise ratio (SNR) and a low resolution. This method firstly uses three FFT samples to determine the frequency searching scope, then – besides the frequency – the estimated values of amplitude, phase and dc component are obtained by minimizing the least square (LS) fitting error of three-parameter sine fitting. By setting reasonable stop conditions or the number of iterations, the accurate frequency estimation can be realized. The accuracy of this method, when applied to observed single-tone sinusoid samples corrupted by white Gaussian noise, is investigated by different methods with respect to the unbiased Cramer-Rao Low Bound (CRLB). The simulation results show that the root mean square error (RMSE) of the frequency estimation curve is consistent with the tendency of CRLB as SNR increases, even in the case of a small number of samples. The average RMSE of the frequency estimation is less than 1.5 times the CRLB with SNR = 20 dB and N = 512.
The Analysis Of Accuracy Of Selected Methods Of Measuring The Thermal Resistance Of IGBTs
Authors: Górecki Krzysztof , Górecki Paweł 
Published: September 2015

Abstract
In the paper selected methods of measuring the thermal resistance of an IGBT (Insulated Gate Bipolar Transistor) are presented and the accuracy of these methods is analysed. The analysis of the measurement error is performed and operating conditions of the considered device, at which each measurement method assures the least measuring error, are pointed out. Theoretical considerations are illustrated with some results of measurements and calculations.
Optical properties of defects in nitride semiconductors
Authors: Tischer Ingo , Hocker Matthias , Neuschl Benjamin , Madel Manfred , Feneberg Martin , Schirra Martin , Frey Manuel , Knab Manuel , Maier Pascal , Wunderer Thomas , Leute Robert A.R. , Wang Junjun , Scholz Ferdinand , Biskupek Johannes , Bernhard Jörg , Kaiser Ute , Simon Ulrich , Dieterle Levin , Groiss Heiko , Müller Erich , Gerthsen Dagmar , Thonke Klaus 
Published: September 2015

Abstract
Cobalt Sulfide-Graphene (CoSG) Composite based Electrochemical Double Layer Capacitors
Authors: Ramachandran R , Nirmala Grace A , Subramaniam Chittur K 
Published: September 2015

ABSTRACTElectrochemical Double Layer Capacitors, EDLC, using Cobalt sulfide- Graphene (CoSG) composite electrodes, were fabricated and the storage process was studied. CoSG composite was prepared by a simple chemical route. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Field Emission Scanning Electron microscopy (FESEM) were used to characterized the as prepared composites which indicated formation of Co S phase. Solutions of perfluorosulfonic acid and Polyvinylidene Fluoride (PVDF) were used as electrode binding material. The storage capacitance of the composites were studied in 1M KCl and 6M KOH electrolytes using standard electrochemical techniques like cyclic voltammetry, CV, electrochemical impedance spectroscopy, EIS, and discharge profiles. The capacitance was estimated for various binder concentrations for both the electrolytes. The concentration of perflurosulfonic acid binder of 0.8 wt% and PVDF of 0.04 wt% showed optimized specific capacitances of 657.8 F/gm and 1418.8 F/g, respectively. Some of the problems in storage density in activated carbon, like varying micro or meso pores, poor ion mobility due to varying pore distribution, low electrical conductivity, can be overcome by using Graphene and composites of Graphene. Graphene in various structural nomenclatures have been used by different groups for charge storage. Optimization of the electrode structure in terms of blend percentage, binder content and interface character in the frequency and time domain provides insights to the double layer interface structure.
An Important Episode in the Evolution of Romanian Identity in the 18ᵗʰ Century: from Uniatism to the Transylvanian School
Authors: Untea Ionut 
Published: September 2015

The article focuses on the process, events and attempts from the end of the 17ᵗʰ and the beginning of the 18ᵗʰ century to unite the Romanian Orthodox Church or rather a part of it belonging to the Orthodox Metropolitan of Transylvania with the Roman Catholic Church. The author analyzes the challenges and consequences of such a union for the Romanian identity. To overcome the controversies and strengthen a common Romanian identity, the cultural program of the Transylvanian School movement was initiated.
The Position of Palestinian Jerusalem Christians and Patriarchates on the Status of Jerusalem – comparison and analysis of research findings
Authors: Buśko Michał 
Published: September 2015

The paper discusses a question of Palestinian Jerusalem Christian (PJCh) position on the problem of Jerusalem status. It presents a part of findings of a research that was undertaken to investigate PJCh preferable solution to Jerusalem problem. The main aim of the paper is to discuss similarities and differences of official and common level perspective of the problem. The problem has been approached through the analysis of written sources issued by Jerusalem patriarchates and analysis of the questionnaire that had been used to investigate common PJCh position of Jerusalem status.
Maximizing Information through Data Driven Analytics in Petrophysical Evaluation of Well Logs
Authors: Jain Vikas , Gzara Kais , Makarychev Gennady , Minh Chanh Cao , Heliot Denis 
Published: September 2015

Abstract
Modern logging data are characterized by abundance and multiple dimensions: spatial, temporal, and physical. Traditional interpretation workflows for logging data are often limited in their scope and flexibility and use only a subset of the data dimensions, either by choice or necessity. Furthermore, the various deterministic or stochastic workflows typically rely on preconceived rock and fluid models. When those a priori models do not fit the data, confusion can ensue, whereas it is obvious that the correct model is buried somewhere in the “big logging data.”
To overcome these limitations, new symbiotic approaches using domain expertise and data analytics (“domain-analytics”) have been developed. Domain experts use those novel approaches to develop data-driven workflows to explore and mine complex logging datasets for latent but interpretable information. Once validated to be idempotent, the expert workflows that respect both the acquired data and domain knowledge can be packaged into new classes of answers products.
In this paper, the novel approaches, along with the examples of new answer products, are presented. These include 1) the automated spatial search for common modes and repeated patterns in the single or multi-well nuclear magnetic resonance (NMR) data, 2) the generation of a data-driven fluid model using time-lapse logging data acquired during multiple passes over the same formation, and 3) the creation of interpretive class-based models using definitive core data that could be propagated to continuous log data for a richer petrophysical interpretation.
Drilling Depleted Sands: Geomechanics, Challenges and Mitigations
Authors: Majidi Reza , Edwards Stephen , Zhang Jianguo , Sant Randall , Last Nigel 
Published: September 2015

Abstract
When hydrocarbons are produced from a subsurface reservoir, pore pressure in the reservoir is reduced. This reduction (termed depletion) causes a redistribution of stress in the reservoir and surrounding rocks, leading to a variety of potential issues such as compaction and subsidence, fault reactivation and other forms of strain localization. It generally also leads to a reduction in the minimum horizontal stress (Sh) and therefore to a potential reduction in the fracture gradient (FG) in the depleted interval. The reduction in FG can be one of the most notable challenges when attempting to drill and complete new wells and is the focus of this paper.
The level of depletion at which the reduced FG becomes an operational issue is a function of the geomechanical properties of the reservoir and surrounding rocks. It is also a function the effectiveness of so called “wellbore strengthening” techniques which aim to locally increase the FG by the addition of an appropriately sized concentration of lost circulation material (LCM). Within BP, reservoirs with depleted sand drilling challenges range from just a few hundred psi of depletion (for example in deep water Angola fields with shallow reservoirs) to several thousand psi (in deeper reservoirs as in the Gulf of Mexico) and in some cases to 10,000 psi or more of depletion in certain High Pressure/High Temperature settings.
Quantifying the FG of the depleted interval and the effectiveness of wellbore strengthening techniques is key to field development planning and safe drilling operations. For a safe and successful development, several issues need to be considered. These include the variation of original (prior to depletion) FG across a field (where experience has shown that traditional 1-D models are inadequate for the complex structures drilled today), the change of FG with depletion (is the “Stress Path” linear and uniform across the field, or is structure and potential stress arching important?), and by how much we can increase the near-wellbore FG using wellbore strengthening techniques such as StressCage.
In this paper, we present an integrated workflow undertaken to mitigate the risks of drilling depleted sands. Field examples are used to demonstrate the utilization of multiple sources of information including drilling data, rock mechanics, and stress analysis, along with the size distribution and concentration of particulate materials in the mud to achieve an optimum solution.
Successful Application of a New Fracturing Fluid with Supramolecular Complex Structure
Authors: Yang Jiang , Cui Weixiang , Duan Yaoyao , Yang Zhanwei , Qiu Xiaohui , Guan Baoshan , Lu Yongjun , Zhai Wen , Liu Ping , Ding Yunhong , Bai Jianwen 
Published: September 2015

Abstract
A new fracturing fluid based on supramolecular complex of associative polymer and wormlike micelle was developed and applied in a gas well in China. The crosslink complex gel was based on weak physical attractive force such as van der waals, hydrogen bonding and electrostatic interaction between associative polymer and wormlike micelle. The fluid contained much less surfactant than that of conventional viscoelastic surfactant. The associative polymer is used at less than 0.25% by weight. The gel is reversible, and has 50% lower formation damage than that of conventional guar. The mixture of the two fluids synergistically enhances the viscosity ten times more than individually combined. The viscosity of fluid can maintain at the test temperature and suspend proppant up under static condition. The dynamic proppant transport test in flow tube also showed good proppant suspension ability. The fluid was simple to prepare with less additives, and formed gel instantly upon mixing in the field. The gel can be completely broken with no residue by an internal breaker. Field application of the new fracturing fluid in a gas well of Sulige basin in China showed the enhancement of gas production over 100%. The fracture height is also well controlled. The fluid also has 20% lower friction pressure than that of guar fluid. Hence, the supramolecular complex gel provides a new fracturing fluid system with less formation damage for fracturing operation.
Assessing Diverse Variables and Technologies and Their Impact on Sustained Gas Production in Carbonate Reservoirs – Field Examples
Authors: Rahim Zillur , Al-Anazi Hamoud , Al-Kanaan Adnan , Kayumov Rifat , Al-Jalal Ziad 
Published: September 2015

Abstract
Using well performance as the primary determining factor, a systematic study and evaluation was conducted on numerous vertical and horizontal wells drilled in the high-pressure/high temperature heterogeneous carbonate reservoirs to assess effectiveness of stimulation treatments and benefits of using novel technologies. Numerous variables analyzed to determine impact on production include well type, wellbore length, drilling azimuth, number of stimulation stages per well, chemistry and volumes of treatment fluids, pumping rates and pressures, fracture dimensions (half-length and width), and applied drawdown. A comprehensive database for stimulated wells was created that included reservoir parameters, completion data, minifrac and main stimulation treatment parameters (fluid types, volumes, rates and pressures), computed fracture geometry, and normalized well performance data. The variables were grouped and arranged according to their similarities and impact on well productivity. Correlations were drawn using the Pearson correlation coefficient to compute upward and downward data trend, ensure use of good quality data, and discard few nonaligned data. Numerous, very useful plots are constructed and presented that show the different trends of the variables evaluated and how they affect the productivity index (PI) of a well.
Results have been drawn based on completion parameters, design and execution variables, treatment evaluation results, and well production. The results demonstrate the importance of real-time application of geomechanics to achieve borehole stability and drilling laterals toward the minimum in-situ stress σmin) direction to achieve sustained post-treatment gas rates. Trends also highlight improved well performance with the increase in stimulation stage count and maintaining isolation between producing intervals. The influence of different fluid types and their volume on post-fracturing productivity was analyzed. Normalized PI was used to assess optimum pump rates and pressures. Some important conclusions were made regarding targeted etched fracture half-length and width. The analyses identified the key post-fracturing production drivers in the gas reservoirs and their impact on long-term well performance.
Walking the Walk – Industry Support of Natural Resource High School Education
Authors: Tobin John , Todd Jennifer 
Published: September 2015

Abstract
Until recently the Energy Industry has only passively supported high school education in the natural resource field. At the same time this industry continually expresses concerns over its future work force and the public's appreciation of the role energy plays in our daily lives.
This paper discusses two examples where the industry is truly “walking-the-walk” with programs aimed at stimulating interest and preparing high school students for college and eventual careers in the industry. The Energy Institute Magnet High School in Houston is an example of an existing effort that came into existence in the fall of 2013 with the enthusiastic support of the industry. The other example that will be discussed is an embryonic effort in Colorado that is trying to capture similar support.
These education models and their support by the industry can be applied nationally. This will require not only similar enthusiastic support, but also a real effort to get the hundreds of existing educational programs to work together. Only through such collaboration can this overall goal be achieved.
Innovative Process for Formation Damage Removal in Sandstone Reservoir Based on Real-Time Downhole Monitoring: A Malaysia Case History
Authors: Riyanto Latief , Musa Mohd Nizar , Deris Nurul Asyikin , Yaakub Mohd Yuzmanizei , Ghazali Rohaizat , Hamidon Zahaezuani Rafiq , Wijoseno Danny Aryo , Jenie John Rizal , Parapat Arthur , Kasim Mohamed Heikal 
Published: September 2015

Abstract
Many retrograde condensate gas wells in field A, located offshore Malaysia, are underperforming or even idle because of calcium carbonate scale deposition and near-wellbore condensate banking. Previous treatments were performed without any adjustment of fluid placement across the multiple fractured zones due to the lack of technology enabling real-time downhole monitoring. Fluids could, therefore, be lost into depleted or high-water-cut intervals, leading to suboptimal treatment.
Distributed temperature sensing (DTS) technology through optical fiber installed inside coiled tubing strings mitigates the risks related to blind acid pumping. The technology makes it possible in real time to monitor and adjust fluid placement and diversion efficiency to squeeze acid into target zones and maximize the treatment success.
The first worldwide implementation of sandstone matrix acidizing using the DTS technology was performed on a well completed with four perforated and propped fractured zones. The main treatment fluid was designed to remove both types of formation damage: organic acid would attack the scale and alcohol would eliminate the condensate banking. The first challenge was the cleanout of hard carbonate scale from the wellbore, which was performed with a bottomhole assembly composed of a high-pressure rotating jetting tool and a real-time fiber-optic tension-compression sub enabling the coiled tubing unit operator to maximize the slack-off on scale and facilitate its removal. The second challenge was the depleted upper perforated and propped fracture interval detected by the DTS. If diversion was inefficient, all fluids would get lost into the upper zone. A diverter fluid system formulated with degradable fiber blended into viscoelastic-surfactant-based fluid was optimized based on expected downhole conditions, and two stages were successively squeezed into the highly permeable (130-Darcy) depleted upper interval before getting a good signature on the DTS surveys showing that this zone was temporarily plugged and that the main treatment fluid would be squeezed into the lower target zones.
The post-treatment gas production was double what was expected. A memory production logging tool was run after the job. This confirmed the crossflow to the upper depleted zone during shut-in and showed 86% gas production from the two bottom intervals, which demonstrates the effectiveness of both the innovative stimulation process with DTS and the diversion with degradable fiber.
Fracture Gradient Prediction Using the Viscous Relaxation Model and Its Relation to Out-of-Zone Microseismicity
Authors: Yang Yi , Sone Hiroki , Zoback Mark. D. 
Published: September 2015

Abstract
During hydraulic fracture stimulation of the Middle Bakken Formation, many out-of-zone microseismic events are observed in the Mission Canyon Formation located ~ 800 ft above the Middle Bakken. These microseismic events follow an abnormal sequence, where the events are first located ~800 ft above the perforation location, followed by subsequent events moving downwards towards to the perforation location along an interpreted fault. We predict frac gradient variation in the vertical depth direction to investigate its relation to the unusual microseismicity. Using laboratory observed time-dependent behavior of rocks from the study field, we apply the viscous relaxation model to predict horizontal differential stress accumulation from geophysical logs. We further calculate two horizontal stress magnitude profiles from knowledge of the tectonic faulting constraint within the reservoir. The predicted least principal stress magnitude indicates that the Upper and Lower Bakken Formations are acting as weak frac barriers during hydraulic fracture stimulation in the Middle Bakken, while the Lodgepole and the Three Forks Formations above and below the Bakken Formation are not frac barriers. To compare the predicted stress values with the depth at which the out-of-zone seismicity occurs, we calculate the pore pressure perturbation (ΔP) required to cause slip along well-oriented fractures and faults as a function of depth. We find that the calculated ΔP values match the microseismicity sequence: that is, the events occur first at depths that require the smallest values of pore pressure perturbation, and events of later stages are located at depths that require a much higher pressure perturbation. The stress profile calculated using a modified Eaton model does not capture the characters of the microseismicity. The calculated stress and ΔP profiles indicate that the out-of-zone microseismic events are related to a combined contribution from preexisting fault and the lack of frac barrier above the Bakken Formation, while the abnormal sequence of these events are caused by variations of the stress state within the formations.
Analytical Model to Estimate the Directional Tendency of Point and Push-the-Bit BHAs
Authors: Zhang Yuan , Samuel Robello 
Published: September 2015

Abstract
Over the past few decades, drilling engineers have developed two types of rotary-steerable systems (RSS) as directional drilling tools: push-the-bit and point-the-bit bottomhole assemblies (BHAs). Some eccentric components are used in these RSS BHAs to control the drilling direction. For these RSS, side forces on bits are important factors that change drilling direction. However, because of the complex structure of BHA and wellbore environments, there is not a good analytical industry model currently available, so experience-based methods are commonly used to estimate BHA tendencies.
In this paper, an analytical method is proposed to calculate side force on the bit and the dog leg severity (DLS) of a wellbore to help predict the drilling direction. In this method, a drillstring is taken as a continuous beam, which is supported by components installed on the string. Side forces and bend angles induced by the eccentric component are solved with the continuous beam theory. After force analysis is completed, drilling engineers can use new equations proposed in this paper to calculate the DLS of the wellbore.