bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of Sweep Test for Emulsion and Hot Asphalt Chip Seals: Laboratory and Field Evaluation
Authors: Wasiuddin Nazimuddin M. , Marshall Amanda , Saltibus Nibert E. , Saber Aziz , Abadie Christopher , Mohammad Louay N.
Published: February 2013

Currently, the scope of the standard test method for sweep test of bituminous emulsion surface treatment samples (ASTM D7000) is limited to emulsion-based chip seals only. To this end, the objective of this study is to evaluate the sensitivity of the sweep test for both emulsions and hot asphalts, with respect to aggregate mineralogical types, aggregate precoating, aggregate moisture content, asphaltic materials type, and application rates of asphaltic materials. For the field evaluation, fifteen chip seal test sections were prepared with three asphaltic materials and five aggregates in a 9-acre parking lot. Two years after construction, each of the 15 sections were visually inspected for aggregate loss and bleeding. Each section was given a distress rating. The % aggregate loss from the sweep test was then compared with the field distress rating. Both laboratory and field tests indicate that overall, expanded shale lightweight aggregate is better than any crushed stone, whereas clay lightweight performed the worst among the six aggregates tested in this study. Precoated expanded shale lightweight aggregates performed better than uncoated shale lightweight aggregates, with respect to % aggregate loss. Between the two hot asphalts, PAC-15 performed better than AC20-5TR. In the case of hot asphalt, the % aggregate loss increases as moisture content increases in oven dry, air dry, and saturated surface dry aggregates. However, for emulsion, air dry aggregates performed the best. For both emulsion and hot asphalt, an increase in asphaltic materials application rate reduces the % aggregate loss significantly. Distress rankings in all 15 sections, except for one PAC-15 section, matched sweep test rankings. Overall, the results indicate that the sweep test using both emulsion and hot asphalt can be an effective tool for evaluation of performance of chip seals.
Exploration of a Performance Test for Emulsion Treated Asphalt Surfaces
Authors: Braham Andrew , Howard Isaac L. , Barham Jason
Published: February 2013

Asphalt emulsions are a key material used for pavement preservation. Over time, asphalt concrete pavements become oxidized, which can lead to cracking and other surface deterioration. The addition of pavement maintenance treatments, such as scrub seals, chip seals, or fog seals, can rejuvenate the pavement surface as the asphalt emulsion penetrates the oxidized layer of pavement. However, most existing test methods for asphalt emulsions are empirical in nature and do not directly address field performance. With the aim of improving material characterization and testing so as to better capture field properties, this research explored using a bending beam rheometer (BBR) to measure the stiffness and rate of change of the stiffness (or m-value) of asphalt concrete mixture beams treated with asphalt emulsions. There were three components of this study. First, procedures for fabricating BBR beams from field asphalt concrete samples were developed, as the top portion of pavement is often brittle after field aging and oxidation. It was determined that beams could be successfully fabricated with reasonable geometric variability. Second, asphalt concrete BBR specimens compacted and fabricated in the laboratory were sawn and tested, with and without asphalt emulsion, to determine whether the addition of emulsion could be detected. Third, the same emulsion applied to the laboratory fabricated specimens was applied to field mixes to determine the influence of asphalt emulsion on candidate materials for pavement preservation. Overall, beam fabrication was repeatable, and coefficient of variation values for test results were lower for the laboratory compacted plant mix (10 % to 25 %) than for the field mixtures (9 % to 57 %). Emulsion addition increased the m-value and decreased the stiffness of all pavements, which indicates rejuvenation of the asphalt concrete. BBR mixture beams appear to be able to capture the effect of adding emulsion to both lab produced and field specimens, but more types of emulsions, a more comprehensive conditioning regime, and more asphalt concrete mixtures should be examined in order to determine the effectiveness of the measured performance properties of asphalt concrete with the addition of asphalt emulsion.
Method for Assessing Applicability of an Artificial Flaw as a Small Initial Crack for Fatigue Limit Evaluation and Its Application to a Drill Hole and an FIB Processed Sharp Notch in Annealed 0.45% Carbon Steel
Authors: Sakamoto Junji , Takahashi Yoshimasa , Aono Yuuta , Noguchi Hiroshi
Published: February 2013

In this study, we propose a method for assessing the applicability of an artificial flaw as a small initial crack for fatigue limit evaluation. The proposed method is applied to drill holes and sharp notches introduced using a focused ion beam (FIB) technique in annealed 0.45% carbon steel. It is found that under rotating bending fatigue, an FIB notch can be used as a small initial crack for fatigue limit evaluation, whereas a drill hole cannot, for √area of ∼50 μm. Here, √area is the square root of the area obtained by projecting the defect onto a plane perpendicular to the load axial direction. The results indicate that an FIB notch can be used as a small initial crack for fatigue limit evaluation in a greater number of materials than those in which a drill hole can be used.
The Damage Investigation of Wedge-Shaped Electromagnetic Riveting Structure of CFRP/Aluminium Alloy
Authors: Liu Shengwang , Zhang Weifang , Wu Yufeng , Chen Yu
Published: February 2013

In the aircraft industry, electromagnetic riveting is now widely used in the riveting of wedge-shaped aluminium-alloy structure and carbon-fibre-reinforced polymer (CFRP), but damages to the CFRP often happen. To investigate the reason for the damages, methods of C-scan, x ray, Compton backscatter scanning (CBS), metallography, and thermal deply were applied to study the wedge-shaped riveting structures. The study indicates that the composites by the tail of the rivets, which are close to the edge of the structure, are almost comminuted, and those rivets expand uniformly along the shaft and interference fit with the structure, and at the same time curve toward the edge. The composites around the rivets, which are away from the edge of the structure, are slightly damaged, and these rivets deformed not so uniformly, most of them clearance fit with the structure, and in some joints interference fit and clearance fit occur alternatively. The investigation shows that, in the joints close to the edge, the balance of constraints from the aperture to the rivet is broken by the slope around the tail of the rivet, results in a rightward force working on the rivet tail. The integration of this force and the riveting force curves the rivet instantaneously, which comminutes the right-side composites of the rivet tail. For the rivets away from the edge, the deformation becomes more buckled the longer the rivet, which causes the instability of the fit situation and reduces the damage to the composites.
A Study on the Fitting Accuracy of CMOD Compliance Equations
Authors: Wang Enyang , Zhou Wenxing , Shen Guowu
Published: February 2013

The maximum error of the inverse fitting of Tada et al.’s equation of the a/W–crack mouth opening displacement (CMOD) compliance equation proposed by Joyce and adopted in ASTM E1820-11 for single edge bend [SE(B)] specimens with shallow cracks (0.05 ≤ a/W < 0.45) is observed to be 2.03 % for 0.05 < a/W < 0.1. A new a/W–CMOD compliance equation with the same fifth-order polynomial fitting applicable for SE(B) specimens with 0.05 ≤ a/W ≤ 0.7 is therefore proposed. The maximum fitting error of the proposed equation is approximately 0.19 %.
Expanding the Availability of Extracorporeal Cardiopulmonary Resuscitation
Authors: McMullan D. Michael
Published: February 2013

A healthy 14-year-old presented to an emergency department in Alaska, complaining of shortness of breath, chest pain, and 72 hours of malaise and headache. On admission, her blood pressure was 80/50 mm Hg, and she had cool extremities. Electrocardiography revealed wide-complex ventricular tachycardia. She underwent synchronized electrical cardioversion. Although she initially converted to sinus rhythm, she subsequently became pulseless, with electrocardiographic evidence of ventricular tachycardia. Despite cardiopulmonary resuscitation, she failed to achieve a perfusing rhythm. Cardiovascular surgery consultation was obtained, and she was placed on partial cardiopulmonary bypass during 2 hours of ongoing chest compressions. Cardiopulmonary bypass flow was limited by the small size of her femoral arteries. She remained in refractory ventricular tachycardia. The cardiopulmonary bypass circuit was modified for transportation of the patient via air ambulance 1500 miles to a tertiary medical center that specializes in pediatric heart failure and mechanical cardiopulmonary support. Upon arrival at the tertiary medical center, she underwent carotid artery cannulation to improve total cardiopulmonary support and percutaneous balloon atrial septostomy to facilitate left ventricular decompression. Intravenous immunoglobulin and steroids were administered to treat presumed acute fulminant viral myocarditis. Extracorporeal life support was support was successfully discontinued after 14 days, but she experienced a thromboembolic stroke. The patient was discharged on hospital day 65 with moderate generalized left-sided weakness, but she was able to ambulate with minimal assistance. She subsequently returned to school and is progressing appropriately with her peers. Cardiac function has normalized, and she remains in normal sinus rhythm.
Health Information Technology in Screening and Treatment of Child Obesity: A Systematic Review
Authors: Smith Anna Jo , Skow Áine , Bodurtha Joann , Kinra Sanjay
Published: February 2013

BACKGROUND AND OBJECTIVES:

Childhood obesity is a major problem in the United States, yet screening and treatment are often inaccessible or ineffective. Health information technology (IT) may improve the quality, efficiency, and reach of chronic disease management. The objective of this study was to review the effect of health IT (electronic health records [EHRs], telemedicine, text message or telephone support) on patient outcomes and care processes in pediatric obesity management.

METHODS:

Medline, Embase, and the Cochrane Registry of Controlled Trials were searched from January 2006 to April 2012. Controlled trials, before-and-after studies, and cross-sectional studies were included if they used IT to deliver obesity screening or treatment to children aged 2 to 18 and reported impact on patient outcomes (BMI, dietary or physical activity behavior change) or care processes (BMI screening, comorbidity testing, diet, or physical activity counseling). Two independent reviewers extracted data and assessed trial quality.

RESULTS:

Thirteen studies met inclusion criteria. EHR use was associated with increased BMI screening rates in 5 of 8 studies. Telemedicine counseling was associated with changes in BMI percentile similar to that of in-person counseling and improved treatment access in 2 studies. Text message or telephone support was associated with weight loss maintenance in 1 of 3 studies.

CONCLUSIONS:

To date, health IT interventions have improved access to obesity treatment and rates of screening. However, the impact on weight loss and other health outcomes remains understudied and inconsistent. More interactive and time-intensive interventions may enhance health IT's clinical effectiveness in chronic disease management.
Readiness of Primary Care Practices for Medical Home Certification
Authors: Zickafoose Joseph S. , Clark Sarah J. , Sakshaug Joseph W. , Chen Lena M. , Hollingsworth John M.
Published: February 2013

OBJECTIVES:

To assess the prevalence of medical home infrastructure among primary care practices for children and identify practice characteristics associated with medical home infrastructure.

METHODS:

Cross-sectional analysis of restricted data files from 2007 and 2008 of the National Ambulatory Medical Care Survey. We mapped survey items to the 2011 National Committee on Quality Assurance’s Patient-Centered Medical home standards. Points were awarded for each “passed” element based on National Committee for Quality Assurance scoring, and we then calculated the percentage of the total possible points met for each practice. We used multivariate linear regression to assess associations between practice characteristics and the percentage of medical home infrastructure points attained.

RESULTS:

On average, pediatric practices attained 38% (95% confidence interval 34%–41%) of medical home infrastructure points, and family/general practices attained 36% (95% confidence interval 33%–38%). Practices scored higher on medical home elements related to direct patient care (eg, providing comprehensive health assessments) and lower in areas highly dependent on health information technology (eg, computerized prescriptions, test ordering, laboratory result viewing, or quality of care measurement and reporting). In multivariate analyses, smaller practice size was significantly associated with lower infrastructure scores. Practice ownership, urban versus rural location, and proportion of visits covered by public insurers were not consistently associated with a practice’s infrastructure score.

CONCLUSIONS:

Medical home programs need effective approaches to support practice transformation in the small practices that provide the vast majority of the primary care for children in the United States.
A Novel Multispecialty Surgical Risk Score for Children
Authors: Rhee Daniel , Salazar Jose H. , Zhang Yiyi , Yang Jingyan , Yang Jessica , Papandria Dominic , Ortega Gezzer , Goldin Adam B. , Rangel Shawn J. , Chrouser Kristin , Chang David C. , Abdullah Fizan
Published: February 2013

BACKGROUND AND OBJECTIVE:

There is a lack of broadly applicable measures for risk adjustment in pediatric surgical patients necessary for improving outcomes and patient safety. Our objective was to develop a risk stratification model that predicts mortality after surgical operations in children.

METHODS:

The model was created by using inpatient databases from 1988 to 2006. Patients younger than 18 years who underwent an inpatient surgical procedure as identified by using the International Classification of Diseases, Ninth Revision, Clinical Modification, coding were included. A 7-point scale was developed with 70 variables selected for their predictive value for mortality using multivariate analysis. This model was evaluated with receiver operating characteristic (ROC) analysis and compared with the Charlson Comorbidity Index (CCI) in two separate validation data sets.

RESULTS:

A total of 2 087 915 patients were identified in the training data set. Generated risk scores positively correlated with inpatient mortality. In the training data set, the ROC was 0.949 (95% confidence interval [CI]: 0.947, 0.950). In the first validation data set, the ROC was 0.959 (95% CI: 0.952, 0.967) compared with the CCI ROC of 0.596 (95% CI: 0.575, 0.616). In the second validation data set, the ROC was 0.901 (95% CI: 0.885, 0.917) and the CCI ROC was 0.587 (95% CI: 0.562, 0.611).

CONCLUSIONS:

This study depicts creation of a broadly applicable model for risk adjustment that predicts inpatient mortality with more reliability than current risk indexes in pediatric surgical patients. This risk index will allow comorbidity-adjusted outcomes broadly in pediatric surgery.
Developmental Trends in Peer Victimization and Emotional Distress in LGB and Heterosexual Youth
Authors: Robinson Joseph P. , Espelage Dorothy L. , Rivers Ian
Published: February 2013

OBJECTIVES:

This study had 2 objectives: Our first objective was to provide the first evidence of developmental trends in victimization rates for lesbian, gay, and bisexual (LGB)- and heterosexual-identified youth, both in absolute and relative terms, and to examine differences by gender. Our second objective was to examine links between victimization, sexual identity, and later emotional distress.

METHODS:

Data are from a nationally representative prospective cohort study of youth in England were collected annually between 2004 and 2010. Our final analytic dataset includes 4135 participants with data at all 7 waves; 4.5% (n = 187) identified as LGB. Analyses included hierarchical linear modeling, propensity score matching, and structural equation modeling.

RESULTS:

LGB victimization rates decreased in absolute terms. However, trends in relative rates were more nuanced: Gay/bisexual-identified boys became more likely to be victimized compared with heterosexual-identified boys (wave 1: odds ratio [OR] = 1.78, P = .011; wave 7: OR = 3.95, P = .001), whereas relative rates among girls approached parity (wave 1: OR = 1.95, P = .001; wave 7: OR = 1.18, P = .689), suggesting different LGB–heterosexual relative victimization rate trends for boys and girls. Early victimization and emotional distress explained about 50% of later LGB–heterosexual emotional distress disparities for both boys and girls (each P < .015).

CONCLUSIONS:

Victimization of LGB youth decreases in absolute, but not necessarily relative, terms. The findings suggest that addressing LGB victimization during adolescence is critical to reducing LGB–heterosexual emotional distress disparities but additional support may be necessary to fully eliminate these disparities.
Modeling Silicon-Based Periodic Waveguides for Optical Interconnects
Authors: Shih Meng-Mu
Published: February 2013

To assist the precision and stability of wavelength at 1550 nm and 1300 nm in planar optical waveguides, hybrid semiconductor-metal corrugated gratings with nanometer period are integrated into silicon-based optical interconnects. This work utilizes multi-parametric optical waveguide models to compute the mode-coupling coefficients in the silicon photonic devices. For such a semiconductor-metal hybrid structure, a proper photonic technique needs to be utilized to solve this computational complexity. The optical method and the photonic method are used to compute coupling coefficients. Both methods have close numerical values shown in figures. Numerical results demonstrate how the normalized corrugation amplitudes of metal gratings can affect the coupling coefficients. Further physical interpretation and discussion can support and explain the above results. The modeling results can help engineers decide the values of parameters used in the design and fabrication of optical waveguides.
Nonlinear optical properties related to intersubband transitions in asymmetrical double δ-doped GaAs; effects of an applied electric field
Authors: Rodríguez-Magdaleno K. A. , Martínez-Orozco J. C. , Rodríguez-Vargas I. , Mora-Ramos M. E. , Duque C.A.
Published: February 2013

In this work, we calculated the ground and first excited states of an electron confined in an asymmetric double DDQW system within a Gallium Arsenide (GaAs) matrix. The two-dimensional impurities density (N2d) considered in our calculation are within the range of 1012 to 1013 cm−2. We obtain the linear and nonlinear optical properties related to intersubband transitions as a function of the spacing between δ-doped wells, two-dimensional impurities concentrations as well as in presence of electric field. We reported results for the linear and nonlinear optical absorption coefficient and in the relative refractive index changes. Our results show that the asymmetry induced in the double δ-doped well system gives rise to values that are several orders of magnitude higher in the resonant peaks intensity.
Electrodeposited Cobalt Alloys as Materials for Energy Technology
Authors: Glushkova Maryna , Bairachna Tetiana , Ved Maryna , Sakhnenko Mykola
Published: February 2013

The influence of electrodeposition parameters on chemical composition, morphology and functional properties of such binary cobalt alloys as CoAg, CoW, and CoFe has been investigated. The alloys are shown to possess catalytic properties. Catalytic activity was preliminary estimated in the electrolytic hydrogen evolution reaction and tested by CO to CO2 conversion during the catalytic benzene oxidation.
Oligothiophene-Based Organic Thin-Film Transistors: A Kelvin Probe Force Microscopy Study of the Electronic Properties
Authors: Afsharimani N.S. , Nysten B.
Published: February 2013

In the past decades organic thin film transistors (OTFTs) have been notably studied due to their interesting properties. Not only they can be processed by simple methods such as inkjet printing but also open the doors to new applications for cheap plastic electronics including electronic tags, biosensors, flexible screens,… However, the measured field-effect mobility in OTFTs is relatively low compared to inorganic devices. Generally, such low field-effect mobility values result from extrinsic effects such as grain boundaries or imperfect interfaces with source and drain electrodes. It has been shown that reducing the number of grain boundaries between the source and drain electrodes improves the field effect mobility.1-3 Therefore, it is important to understand the transport mechanisms by studying the structure of organic thin films and local electrical properties within the channel and at the interfaces with source and drain electrodes in order to improve the field-effect mobility in OTFTs. Kelvin probe force microscopy (KPFM) is an ideal tool for that purpose since it allows to simultaneously investigation of the local structure and the electrical potential distribution in electronic devices. In this work, the structure and the electrical properties of OTFTs based on dioctylterthiophene (DOTT) were studied. The transistors were fabricated by spin-coating of DOTT on the transistor structures with treated (silanized) and untreated channel oxide. The potential profiles across the channel and at the metal-electrode interfaces were measured by KPFM. The effect of surface treatment on hysteresis effects was also studied. Smaller crystals and a lower threshold voltage were observed for the silanized devices. Hysteresis effects appeared to be less important in modified devices compared to the untreated ones.
Transparent Conductive Oxide Less Flexible Dye-sensitized Solar Cells with Flat and Cylinder Shapes
Authors: Usagawa Jun , Park Byung-wook , Ogomi Yuhei , Pandey Shyam S. , Hayase Shuzi
Published: February 2013

Transparent conductive oxide less flexible dye-sensitized solar cells (TCO-less DSC) with flat and cylinder shapes are reported. The cell consists of a plastic cover, a flexible titania/dye sheet back contacted with a metal mesh sheet, a gel electrolyte sheet, and Pt layer on a Ti sheet. How to increase the efficiency were discussed. We concluded that making a titania/dye layer on a metal mesh sheet thinner and using a thinner electrolyte layer were effective for increasing the efficiency. A flat TCO-less DSC with 6.1 % efficiency and a cylindrical TCO-less DSC with 5.1 % efficiency are reported.
Investigation of Nanometric Thin-Film Bismuth Piezoresistors Deposited on Silicon Substrates
Authors: Estrada Horacio V.
Published: February 2013

Thin film bismuth piezoresistors, defined on oxidized silicon wafers, are investigated as a function of their orientation for their eventual integration on micro-electro-mechanical (MEMS) microsensors. Bismuth’s piezoresistance (or elasto-resistance) is experimentally investigated to accurately determine its longitudinal and transverse strain sensitivities. Whisker-shaped resistive elements defined on different orientations (from 0o, the beam’s main strain axis, to 90o, perpendicular to that axis) undergo changes of resistance (ΔR), associated with the induced strains on silicon cantilevers beam’s surface when these are mechanically loaded under pure bending stress conditions. For Bi-resistors, the traditional gage factor concept, (ΔR/Ro)/εl, is found to be equal to +16 and +33, for elements oriented along 0 and 90o, respectively, considerably larger than those for metals or metal alloys. These high sensitivity values and the “unusual” positive, higher value for the 90o (perpendicular) resistors can be of considerable interest for microsensors applications. The results of this study enable us to precisely determine the bismuth’s longitudinal and transverse strain sensitivities that are calculated to be equal to +26 and +40.5 respectively. This experimental study is extended to explore the Bi-films’ response to bi-axial strain fields.
Sputtered Bismuth thin films as trace metal electrochemical sensors
Authors: Baron J. , Silva-Bermudez P. , Rodil S.E.
Published: February 2013

This work studies the performance of sputtered bismuth films as disposable working electrodes for stripping voltammetry. The electrodes were produced by coating a glass substrate with a bismuth film using DC magnetron sputtering under different conditions of power and time. The Bi-based sensors were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Electrochemical evaluation included linear sweep voltammetry using different buffer solution and pHs to observe the effect of the deposition conditions and thickness on the potential window accessible for stripping analysis. Subsequently, the electrodes were tested for the detection of low concentrations of trace metals (Cd(II) and Pb(II)) by square wave anodic stripping voltammetry (SWASV). Clear and reproducible stripping peaks were observed for trace concentrations in the 50 - 450 ppb range of the target analytes. The detection limit of the Bi electrodes were quantitatively estimated from the analyses of SWASV, demonstrating that even using simple sensor geometry, detection limits in the 14-20 ppb range could be obtained. The reproducibility of the measurements is good (relative standard deviations about 4%) after 10 consecutive measurements which define the maximum number of times that the sensor can be used.
Piezoresponse Force Microscopy Studies of pc-BiFeO3 Thin Films Produced by the Simultaneous Laser Ablation of Bi and FeO3
Authors: Enriquez-Flores C. I. , Gervacio-Arciniega J. J. , Flores-Ruiz F. J. , Cardona D. , Camps E. , Muñoz-Saldaña J. , Espinoza-Beltrán F.J.
Published: February 2013

Bismuth iron oxide BFO films were produced by the pulsed laser deposition technique. These films are a mixture of BiFeO3 ferroelectrical and Bi25FeO40 piezoelectrical phases. The ferroelectrical domain structure of these films was studied via contact resonance piezoresponse force microscopy (CR-PFM) and resonance tracking PFM (RT-PFM). The proportions of area of these BFO phases were derived from the PFM images. The ferroelectrical domain size corresponds to the size of the BiFeO3 crystals. The CR-PFM and RT-PFM techniques allowed us to be able to distinguish between the ferroelectric domains and the piezoelectric regions existing in the polycrystalline films.
Thermoelectrical properties of α phase and γ phase NaxCo2O4 ceramics prepared by spark plasma sintering method
Authors: Mikami Natsuko , Nishio Keishi , Arai Koya , Sakamoto Tatsuya , Minowa Masahiro , Nakamura Tomoyuki , Hirayama Naomi , Kogo Yasuo , Iida Tsutomu
Published: February 2013

The thermoelectrical properties of α and γ phases of NaxCo2O4 having different amounts of Na were evaluated. The γ NaxCo2O4 samples were synthesized by thermal decomposition in a metal-citric acid compound, and the α NaxCo2O4 samples were synthesized by self-flux processing. Dense bulk ceramics were fabricated using spark plasma sintering (SPS), and the sintered samples were of high density and highly oriented. The thermoelectrical properties showed that γ NaxCo2O4 had higher electrical conductivity and lower thermal conductivity compared with α NaxCo2O4 and that α NaxCo2O4 had a larger Seebeck coefficient. These results show that γ NaxCo2O4 has a larger power factor and dimensionless figure of merit, ZT, than α NaxCo2O4.
Dependent vs. independent juvenile survival: contrasting drivers of variation and the buffering effect of parental care
Authors: Dybala Kristen E. , Gardali Thomas , Eadie John M.
Published: February 2013

Juvenile survival is often found to be more sensitive than adult survival to variation in environmental conditions, and variation in juvenile survival can have significant impacts on population growth rates and viability. Therefore, understanding the population‐level effects of environmental changes requires understanding the effects on juvenile survival. We hypothesized that parental care will buffer the survival of dependent juveniles from variation in environmental conditions, while the survival of independent juveniles will respond more strongly to environmental variation and, in turn, drive the overall variation in annual juvenile survival. We tested this parental‐care hypothesis using a 30‐year mark–recapture data set to model the survival of juvenile Song Sparrows (Melospiza melodia) during the dependent and independent stages. We examined the effects of weather, density, and cohort mean fledge date and body mass on annual variation in survival during the first 12 weeks after fledging, as well as effects of individual fledge date and body mass on individual variation in survival. The primary driver of annual variation in juvenile survival was precipitation during the previous rainy season, consistent with an effect on food availability, which had a strong positive effect on the survival of independent juveniles, but no effect on dependent juveniles. We also found strong support for effects of body mass and fledge date on individual survival probability, including striking differences in the effect of fledge date by stage. Our results provided evidence that different mechanisms influence juvenile survival during each stage of fledgling development, and that parental care buffers the survival of dependent juveniles from variation in environmental conditions. Consequently, variation in juvenile survival was driven by independent juveniles, not dependent juveniles, and studies focused only on survival during the dependent stage may not be able to detect the major drivers of variation in juvenile survival. We recommend that future efforts to understand or project the population‐level effects of environmental change not only examine the effects on juvenile survival, but specifically consider the survival of independent juveniles, as well as how the drivers of variation in juvenile survival may vary by stage.
Prediction of SRV and Optimization of Fracturing in Tight Gas and Shale Using a Fully Elasto-Plastic Coupled Geomechanical Model
Authors: Nassir M. , Settari A. , Wan R.
Published: February 2013

Hydraulic fracturing is essential for economical development of tight gas and shale gas reservoirs. Current techniques are unable to predict the SRV dependence on frac job and rock mechanics parameters, which precludes any meaningful optimization. In our previous work on the SRV propagation prediction by means of combined tensile/shear fracturing model, the applications showed relatively narrow, focused SRV that resembled behavior dominated by a single fracture. In this work, we significantly improved the model by implementing rigorous full Newton elasto-plastic solution of fracturing problems by pseudo-continuum technique. The results reveal interesting features of complex fracturing occurring in tight formations, which are in broad agreement with the shapes of SRV’s obtained from microseismic imaging.

Flexibility of the code to select either tensile or shear fracturing mechanism or combination of both allows various scenarios to be examined. Different cases of 2-D and 3-D simulations will be presented which demonstrate some important features of the process. First, it is found that a wide SRV can result in cases where initial reservoir conditions are close to shear fracturing point such as in formations with microfractures, partially cemented natural fractures and abnormally high initial pore pressure. The SRV width is found to depend on the horizontal stress contrast as expected. Second, wide SRV growth is associated with constant or increasing pumping pressure for further failed zone growth due to the loss of elastic coupling by off-planar failure propagation. Further, under high injection pressure, an efficient fracture elasto-plastic constitutive model developed can drive both maximum and minimum effective stresses to zero or tensile and therefore creation of tensile fracture can be predicted simultaneously with shear fracturing. This will then provide means of modeling proppant transport. The new model is a significant step towards development of an integrated predictive tool for the optimization of shale gas development.
Interpretation of Closure Stress in the Montney Shale Using PTA Based Techniques
Authors: Hawkes Robert V. , Anderson Irene , Bachman R. C. , Settari A.
Published: February 2013

The Montney formation In NE British Columbia and NW Alberta is one of the largest economically feasible resource plays in North America. It contains both gas and liquids rich light ends. Horizontal multi-staged fracturing is the method for developing this vast resource. Prior to hydraulically fracturing the wellbore, the toe stage is frequently mini-fraced to obtain reservoir and geomechanical properties. Interpreting these mini-fracs, commonly referred to as DFIT’s (Diagnostic Fracture Injection Tests), has proved to be a challenge using traditional combination G Function and square root plots. It is always important to ensure that all data being analyzed is associated with a reservoir response and not wellbore behavior, surface operational interruptions or data quality issues. Some of these challenges can be overcome when using some new techniques for mini-frac Fall-off analysis, which will be discussed in this paper.

Various pressure transient analyses (PTA) based interpretation techniques have been introduced to the industry over the last couple of years for the determination of closure pressure (Bachman et al. 2012, Mohamed et al. 2011 and Marongiu-Porcu et al. 2011). From a theoretical viewpoint, unification of the fields of traditional PTA and mini-frac interpretation has been achieved.

We recommend that the standard PTA based log-log derivative plot using equivalent time is included in the analysis of mini-frac / fall-off tests. This plot is rarely, if ever, used in current interpretations. For mini-frac interpretation, the starting point should now be the standard PTA based log-log derivative plot. The primary pressure derivative (dp/dt) curve should also be added to the log-log derivative plot as an independent flow regime identification technique. This now gives two independent flow regime identification techniques in one plot. The power of the primary pressure derivative to enhance the interpretation of closure and flow regime identification will be illustrated. Subsequently, flow regime specific plots can be constructed to enhance the interpretation.

A number of field examples from the Montney formation in the Farrell Creek area of NE British Columbia are illustrated using a systematic PTA interpretation methodology demonstrating multiple closure events, high fracture extension pressure gradients of 34.0 kPa/m, non-Darcy pressure derivative diagnostics and observation of complex fracture orientation.
Breaking Up is Hard to Do: Creating Hydraulic Fracture Complexity in the Bakken Central Basin
Authors: Pearson C. Mark , Griffin Larry , Wright Chris , Weijers Leen
Published: February 2013

The Bakken drilling boom in North Dakota has seen a frenzy of activity over the past several years as operators sought to hold acreage and create value with the drill bit. This has been particularly true in the Central Basin portion of the Williston Basin where initial wells drilled prior to 2008 were uneconomic. However, advances in completion technology caused such a fundamental shift in economics that the whole Central Basin area of over 2500 square miles has been opened to economic development with ~100 rigs currently drilling in the region.

The most fundamental change in completion design has been the incorporation of "high-intensity" multi-stage fracturing. What makes Bakken completion design fundamentally different from recent shale gas developments has been the widespread use of uncemented liners with external packers in the open-hole lateral in order to create the multi-stage zonal isolation.

As operators have advanced the application of multi-stage completion techniques there has been a wide variety of completion equipment used and stimulation designs that have been pumped. This operator decided to employ a completion design that comprised: An open-hole "uncemented" liner section;Annular zonal isolation created by swell packers;The use of "plug and perf" technology to individually open successive zones to stimulation;The pumping of slickwater fracture treatment fluids at high rate;The use of high-quality ceramic proppant to generate the required fracture conductivity.

Production data are presented from 58 wells in which this completion and stimulation design has been conducted, which show that the use of this approach has resulted in well performance that is 25-45% superior to any other Bakken completion technique.
Development of the Brittle Shale Fracture Network Model
Authors: M. Nejad Amir , Shelley Robert F. , Lehman Lyle V. , Shah Koras , Gusain Deepak , Conway Matthew T.
Published: February 2013

This paper discusses the workflow for the development of a brittle shale model using a data mining approach. A database of more than 1,000 fracture stages and associated microseismic mapping results in the Barnett Shale was assembled. The fracture database is comprised of fracture design parameters including treatment volumes, rates, proppant mass and size, perforation length, fracture pressure, surface pressure trend and fracture dimensions on horizontal well bores. The goal of this analysis is to establish the relationship between frac design, pressure and frac network geometry. Data mining techniques are used on this complex database to find possible hidden relationships to explain the nature of the data. The outcome of this study is to develop a predictive model for fracture networks in shale. Also, using the predictive model, improvements in the current fracture design in Barnett shale are made.

Various aspects of this dataset are examined using data modeling and mining techniques including self-organizing maps (SOM). SOMs are unsupervised artificial neural networks that can cluster large amounts of data into two dimensional maps. Using SOM, frac design parameters are clustered and studied in depth. Then, a forward predictive neural network model is trained with fracture design parameters as inputs and fracture network length, width, height, and fracture volume as outputs. The network is trained with the help of genetic algorithm (GA). Sensitivity study on the trained network demonstrates the effect of different parameters on the fracture geometry. For example, an increase in slick-water volume will have a positive effect on fracture network width and length and negative effect on height. On the other hand, higher injection rates tend to accelerate height growth. Perforation length is also having a negative impact on the total stimulated or affected reservoir volume and tighter perforation designs are preferred. The results of this work potentially helps understanding of the development of fracture networks in shale reservoirs and the recommendations on improving stimulated reservoir volume. This will potentially help operators on more effective treatment designs and reducing the operational costs associated with fracturing in a brittle shale environment.
Impact of Liquid Loading in Hydraulic Fractures on Well Productivity
Authors: Agrawal Samarth , Sharma Mukul M.
Published: February 2013

One of the major challenges in fracturing low permeability gas formations is the loss of well productivity due to fluid entrapment in the matrix or fracture. Field results have indicated that only 15-30% of the frac fluid is recovered at the surface after flow back. Past studies have suggested that this water is trapped in the rock matrix near the fracture face and remains trapped due to the high capillary pressure in the matrix. Significant efforts have been made in the past to understand the impact of liquid blocking in hydraulically fractured conventional gas wells. This study shows that when considering hydraulic fractures in horizontal wells, the fluid may also be trapped within the fracture itself and may impact the cleanup as well as productivity. Under typical gas flow rates in tight / shale gas formations, liquid loading of both the fractures and the matrix is very likely to occur. This paper presents the results of 3D simulations of liquid loading in hydraulic fractures in horizontal wells, including gravity and capillary pressure effects. The impact of drawdown, fracture and reservoir properties on liquid loading and well productivity is presented. Results show that low drawdown, low matrix permeability or low initial gas rates aggravate the liquid loading problem inside the fracture and thereby impact the gas productivity during initial production.
Production Review of Current Stimulation Techniques in the Jonah Field
Authors: Paterniti Melanie , Kundert Donald , Ramurthy Muthukumarappan , Craig David
Published: February 2013

Since the discovery of the Jonah field in 1977, many styles of hydraulic fracturing treatments have been employed to stimulate the Lance formation. Commercial production was not established in the field until the early 1990s, and technological improvements have permitted increased production since that time. Further trials of fracturing techniques, including slickwater fracs, induced stress diversion, and flow-through composite fracture plugs, continued over time. Since March 2010, channel fracturing treatments have been employed in the Lance formation in conjunction with more traditional, conventional fracturing treatments.

For the purpose of this paper, conventional fracturing treatments consist of either crosslinked gel or slickwater fracturing treatments. The proppant is added in a continuous manner with an increasing proppant concentration. For crosslinked gel treatments, the typical proppant is 20/40 -mesh white sand added up to a maximum of 6 lbm/gal. For the slickwater treatments, the typical proppant is 40/70- or 30/50- mesh white sand added up to a maximum of 3 lbm/gal. The channel fracturing treatments use a pulsed method of adding the proppant to the fluid. Instead of adding the proppant continuously, the proppant is turned on and off in approximately 15-second time intervals. This concept is intended to provide high-conductivity, unpropped open flow paths through hydraulic fractures held open by the proppant pillars.

To assess the effectiveness of the channel fracturing method in the Jonah field compared to conventional fracturing treatments, a spatial sampling technique was used. Spatial sampling is a documented method for comparing large groups of wells with their direct offsets. The original intent of the spatial sampling method was to identify underperforming wells; however, the method has also been employed as a way to compare various completion or stimulation techniques. In this case, spatial sampling was applied in an attempt to evaluate the effectiveness of the channel fracturing technique compared to conventional fracturing techniques using continuous proppant addition during the treatment. Five discrete areas of the Jonah field were included in the study. Only wells completed in the same time frame as the channel fractured wells were included. The treatment and production data for all wells were obtained from public sources. There might also be differences in production among the conventionally fractured wells, depending on whether a crosslinked or slickwater treatment was used; however, the effect of slickwater treatments, as opposed to crosslinked treatments, was not considered in this study.
Development of a Three-Dimensional Three-Phase Fully Coupled Numerical Simulator for Modeling Hydraulic Fracture Propagation in Tight Gas Reservoirs
Authors: Jahromi Mohamad Zeini , Wang John Yilin , Ertekin Turgay
Published: February 2013

Conventional fracture propagation models predict fracture geometry based on fracture fluid mechanics, rock mechanics, petrophysical properties, and analytical leak-off models. Reservoir flow simulators are then used to evaluate post-fracture well performances. This approach is called de-coupled modeling. It is a major challenge to couple these two processes, particularly when dealing with large amount of input data. Furthermore decoupled modeling is a time-intensive job that requires a coordinated effort from stimulation and reservoir engineers. This approach may not work in low-permeability reservoirs because the hydraulic fracture propagation is complex, fracture fluid leak-off is pressure/reservoir/fracture dependent, and there are changes in in-situ stress and permeability during and after fracturing. Therefore, a new model is needed to include all of these influences.

This paper describes a three-dimensional, three-phase coupled numerical model which takes into consideration the mutual influence between dynamic fracture propagation and reservoir flow. The model is capable of fully simulating reservoir flow, fluid leak off, fracture propagation and resulted stress change through a stationary reservoir/stress grid system.

The model uses a three-dimensional, three-phase finite difference reservoir flow simulator coupled with finite difference geomechanics model where both are applied on the same grid system. Using an iterative procedure, changes in pressure, in-situ stress and fracture propagation boundaries are determined during and after the fracture treatment.

The model has been validated with the most recent available data. The results show that the model predicts fracture parameters accurately and match the history of injections and change in fracture /matrix area pressure/stress. This model could help one optimize completion and fracture design and evaluate pre-fracture and post fracture well performances.