bluuebunny/crossref_metadata_2025 huggingface dataset:
Occurrence of pharmaceuticals and personal care products in fish: Results of a national pilot study in the united states
Authors: Ramirez Alejandro J. , Brain Richard A. , Usenko Sascha , Mottaleb Mohammad A. , O'Donnell John G. , Stahl Leanne L. , Wathen John B. , Snyder Blaine D. , Pitt Jennifer L. , Perez-Hurtado Pilar , Dobbins Laura L. , Brooks Bryan W. , Chambliss C. Kevin
Published: March 2009

Pharmaceuticals and personal care products are being increasingly reported in a variety of biological matrices, including fish tissue; however, screening studies have presently not encompassed broad geographical areas. A national pilot study was initiated in the United States to assess the accumulation of pharmaceuticals and personal care products in fish sampled from five effluent-dominated rivers that receive direct discharge from wastewater treatment facilities in Chicago, Illinois; Dallas, Texas; Orlando, Florida; Phoenix, Arizona; and West Chester, Pennsylvania, USA. Fish were also collected from the Gila River, New Mexico, USA, as a reference condition expected to be minimally impacted by anthropogenic influence. High performance liquid chromatography-tandem mass spectrometry analysis of pharmaceuticals revealed the presence of norfluoxetine, sertraline, diphenhydramine, diltiazem, and carbamazepine at nanogram-per-gram concentrations in fillet composites from effluent-dominated sampling locations; the additional presence of fluoxetine and gemfibrozil was confirmed in liver tissue. Sertraline was detected at concentrations as high as 19 and 545 ng/g in fillet and liver tissue, respectively. Gas chromatography-tandem mass spectrometry analysis of personal care products in fillet composites revealed the presence of galaxolide and tonalide at maximum concentrations of 2,100 and 290 ng/g, respectively, and trace levels of triclosan. In general, more pharmaceuticals were detected at higher concentrations and with greater frequency in liver than in fillet tissues. Higher lipid content in liver tissue could not account for this discrepancy as no significant positive correlations were found between accumulated pharmaceutical concentrations and lipid content for either tissue type from any sampling site. In contrast, accumulation of the personal care products galaxolide and tonalide was significantly related to lipid content. Results suggest that the detection of pharmaceuticals and personal care products was dependent on the degree of wastewater treatment employed.
Challenges, Lessons Learned, and Successful Implementations of Multilateral Completion Technology Offshore Abu Dhabi
Authors: Kikuchi Shuichi , Fada'q Abdulla S.
Published: March 2009

Zakum Development Company (ZADCO), with the support from shareholders and the cooperation of Abu Dhabi Marine Operating Company (ADMA-OPCO), successfully completed the final design of the multilateral completion (MLC) system for Reservoirs A and B through the Multilateral Tie Back System (MLTBS) project. Well T-2 in the Upper Zakum field was recompleted as dual lateral/dual producer using a re-entry drilling system (RDS) Version 2 and a dual bore deflector (DBD) oriented and set on a latch coupling in the 7-in. liner hanger assembly.

According to Technology Advancement Multilateral (TAML) level specification, the final MLC is categorized as TAML Level-4 E-2-PN-D/4-TR-SEP (Level-4, existing well application, two junction, producer with natural lift, dual completion, tubing reentry, separated flow). The multilateral liner hanger (MLLH) system (i.e., accommodating a latch coupling in 7-in. liner hanger assembly to have a certain access to the upper lateral) was the first successful application of that kind in the world.

The teamwork and integrated approach for the trial planning and implementation, as well as lessons learned from a predesign trial (TAML Level-4 E-2-PN-D-TR-SEP using straddle assembly) for Well T-1 completed in 2000, have led to reaching the final goal of the MLC in Well T-2, which provides ZADCO with the following reservoir benefits: -Independent coiled tubing access to the upper (Reservoir A) and lower laterals (Reservoir B) through a dual completion to perform effective stimulation and reservoir monitoring.-Full bore access to each lateral immediately after pulling out the completion, which is an additional feature to the predesign of an MLC for Well T-1.-Allow selective water shutoff to cope with water breakthrough into the upper-cased lateral.-Possibility of extending well life by drilling a secondary lateral through a window joint installed in the upper-cased lateral.

Moreover, another MLC trial, installed in the quadrant multilateral well RL-2 in 2005, has been successfully implemented by using mechanically selective through tubing re-entry equipment. This success was largely because of the lessons learned from a similar MLC design implemented in well RL-1 in 2001.

These successful trial implementations proved the MLC system is applicable for any new/re-entry wells in ZADCO reservoirs, which provides new methods of reservoir management, and creates new completion strategies for ZADCO field development.

This paper covers the MLC strategies, lessons learned through the successes and failures and the additional challenges planned for the future of the MLTBS project.
Cement-Shrinkage Measurement in Oilwell Cementing—A Comparative Study of Laboratory Methods and Procedures
Authors: Reddy B. R. , Xu Ying , Ravi Kris , Gray Dennis , Pattillo P. D.
Published: March 2009

Cement-sheath shrinkage after placing the cement slurry in the annulus has been of concern in oilwell cementing because of the potential detrimental effects that shrinkage can have on long-term zonal isolation.

This paper compares several methods for measuring cement shrinkage under a variety of conditions including those downhole. Using the various methods, cement shrinkage in environments where the cement slurry is either closed to or open to external water sources was measured, and the values were compared. The methods used for measurement under atmospheric conditions were based on American Petroleum Institute (API) test apparatus (balloon and ring mold) and flask methods currently used in laboratories. Measurements under pressure were performed using the balloon and ring-mold methods, in-house designed equipment, and commercial equipment.

The values obtained by the different methods are discussed. Procedure modifications are proposed for measuring volume changes to cement slurries on the basis of placement time, shear history, and gel-strength development.

The results presented in this work can be used to test shrinkage characteristics of cement slurries in the laboratory under downhole conditions and to select a cement system that is fit for purpose.
Evaluation of Sand-Control Completions in the Duri Steamflood, Sumatra, Indonesia
Authors: Underdown David , Chan Henky
Published: March 2009

The Duri field in Sumatra, Indonesia, shown in Fig. 1 and operated by Chevron Pacific Indonesia (CPI), is one of the largest onshore steamflood operations in the world. Producing heavy oil (approximately 25°API) from an essentially unconsolidated reservoir with a depth that ranges from 300 to 700 ft using steam injection at 300 to 400°F poses a unique challenge in designing an effective, yet economic, completion. One of the biggest problems associated with the production of the crude oil in this environment is the production of massive amounts of solids. In addition to the cost of the recompletions, problems associated with disposing of this amount of sand—and the effect the produced solids have on the facilities, such as stabilization of emulsions—are a large cost to operations.

A program was initiated in 2002 to evaluate the effectiveness of the completions in the Duri field. This effort involved evaluated field data, such as the frequency and type of workovers, the amount and size of produced solids, the nature and number of failed liners, and the frequency of stuck sucker-rod pumps, to understand the efficiency of the sand-control completions better. Local sand-control gravel used in the completions was evaluated for steam dissolution and adherence to American Petroleum Institute (API) gravel-pack-sand standards. An audit of the primary sand-control-screen manufacturer was also conducted to evaluate the quality of the sand-control screens used in the completions. In addition, on-site inspections of the operational aspects of the completions were completed. The results of the program showed that the completion designs and sand-control screens were up to industry standards. However, several operational aspects were identified as opportunities for improvement. The results of the program are presented, and items for improvement of the completion for thermal wells in the Duri field are discussed in this paper.
Magnolia Deepwater Experience—Frac Packing Long, Perforated Intervals in Unconsolidated Silt Reservoirs
Authors: Eaton Luke F. , Reinhardt W. Randall , Bennett J. Scott , Blake Kenyon , Morales Hugo
Published: March 2009

ConocoPhillips is developing the Magnolia field with a tension-leg platform (TLP) in 4,674 ft of water at Garden Banks Block 783 in the Gulf of Mexico. The wells target multiple zones, resulting in complex directional wells with 50–60 maximum hole angles. The wells are completed using dry trees from the TLP and are produced primarily from massive, fine-grained, Pleistocene reservoirs.

These reservoirs require sand control to prevent sand production at the expected drawdowns planned during the life of the wells. To help ensure high-rate, long-life completions, the producing zones are frac packed. The average perforated interval during the initial completion program was 310 ft, with a maximum perforated interval of 571 ft.

The typical production-casing string for the wells consists of 10¾-in. casing with an 8116-in. production liner. Drift diameter through the tapered production casing is 9½ and 6½ in., respectively. The 6½-in. drift diameter allows using common-sized screens and packers. The wells are generally completed with a 4½ × 3½ -in. tapered-tubing string.

Premium screens with shunt tubes are used on the wells because of the long deviated intervals. The "frac-pack" stimulation treatments are pumped at rates of 27 to 40 bbl/min with a viscoelastic-surfactant (VES) carrier fluid. Washpipe-conveyed downhole-pressure and -temperature gauges and radioactive tracers are used to help analyze the treatment results.

This paper will discuss screen-selection philosophy in silt/ very-fine-sand reservoirs, carrier-fluid selection, perforation strategy, and ability to frac across shale intervals. The paper also will cover the effectiveness of achieving a frac pack with premium screens with shunt tubes, on the basis of downhole-pressure and – temperature and radioactive-tracer information, and will discuss revised operational practices that resulted in zero- to negative-skin completions across long, perforated intervals, which continue to produce sand-free after extreme reservoir depletion.
Hydraulic Predictions for Polymer-Thickened Foam Flow in Horizontal and Directional Wells
Authors: Chen Z. , Duan M. , Miska S. Z. , Yu M. , Ahmed R. M. , Hallman J.
Published: March 2009

Foam has proved to be effective and economical in underbalanced operations (UBO) and is gaining wider applications in many areas. It provides the desired flexibility in controlling pressure profile and equivalent circulating density (ECD). However, the knowledge of rheology and hydraulics of polymer-thickened foams is still limited. This paper summarizes the significant effects of polymer on foam rheology and presents a hydraulic model that simulates aqueous and polymer-based foam flow in directional and horizontal wellbores.

Experimental studies on the rheology of polymer-enhanced foam were conducted using a specially designed flow-through rotational viscometer and pipe viscometers with different concentrations of hydroxyethylcellulose (HEC) polymer. Correlations have been developed for rheological parameters of aqueous- and polymer-based drilling foams.

On the basis of the experimental results of foam rheology and a steady-state momentum balance equation, a foam-flow hydraulics model was developed to predict pressure profile, ECD, foam velocity, and foam quality along a vertical/inclined/horizontal wellbore. For practical applications, a simulator has been developed and validated by experimental flow-loop data obtained from the Advanced Cuttings Transport Facility of Tulsa University Drilling Research Project. The effects of polymer concentration, backpressure, and wellbore trajectory on foam hydraulics were studied extensively using the simulator. Results show significant impact of polymer on foam hydraulics. When 0.5% volume to volume (v/v) HEC polymer is added to aqueous foam, bottomhole pressure (BHP) and foam density are significantly increased, while foam quality and velocity are greatly decreased. The polymer effects are more pronounced in vertical wells than in horizontal wells.

Simulation results also indicate that it is possible to use foam to create a pressure profile within the narrow window between continuously changing pore-pressure and facture pressure gradients, which is not possible with conventional fluids. Those responsible for hydraulic optimization and well control in managed-pressure drilling/UBO where foam is used will find this paper useful for practical design applications.
Optimization of Deep-Drilling Performance—Benchmark Testing Drives ROP Improvements for Bits and Drilling Fluids
Authors: Judzis Arnis , Bland Ronald G. , Curry David A. , Black Alan D. , Robertson Homer A. , Meiners Matthew J. , Grant Timothy C.
Published: March 2009

A critical cost in future deep-oil and -gas recovery is the cost to drill a well. This cost is dominated by the rate of penetration (ROP) that becomes increasingly important with increasing depth. Improving the technology of drilling and increasing the ROP was the object of full-scale laboratory testing conducted under a joint industry and Department of Energy (DOE) program titled "Improving Deep Drilling Performance" (Black and Judzis 2003). Simulations of deep-well drilling in the Arbuckle play and the Tuscaloosa trend were accomplished during 16 full-scale, high-pressure tests using four different 6-in. drill bits, three types of rock, and five different drilling fluids.

This paper describes what is believed to be the first set of full-scale laboratory drilling tests yet performed at bottomhole pressures in excess of 10,000 psi. Accomplishments of the testing and analysis include the following: Laboratory data was compared with field data to confirm that the simulated laboratory conditions provided similar results to what would be expected in the field.ROP reductions were significant when "mudding up" at high bottomhole pressures.Polycrystalline-diamond-compact (PDC) bits provided substantially higher ROP performance than impregnated or roller-cone bits in the environment of this study.The relationship between ROP and confined-rock strength is not a simple function of bottomhole pressure alone.The mechanical specific energy (MSE) when drilling at high bottomhole pressure is often substantially higher than the rock's compressive strength, even when the bit is drilling efficiently.Fluid invasion of intact rock and of rock broken up by the bit's cutting structure seems to play a major role in controlling ROP at these high bottomhole pressures.Drilling-fluid compositions and properties that promote invasion without provoking formation damage, and bit-design features that facilitate the removal of rock debris from the hole bottom, hold promise for improving drilling efficiency in hard rock drilled at high bottomhole pressures.
Special Issues in the Stress Analysis of Casing Strings in Steam-Injection Wells: Mathematical Development and Design
Authors: Garside R. , Pattillo P. D. , Pattillo II P. D. , Sathuvalli U. B
Published: March 2009

The design and development of steam-injection fields is a mature subject. Because the tubulars in these wells invariably experience inelastic loading, issues such as the effects of temperature on the static and cyclic (fatigue) material properties become important. The original papers that address steam-injection casing-design issues date back to the 1960s. These studies include temperature prediction (Leutwyler and Bigelow 1965), casing-stress analysis (Willhite and Dietrich 1967), and development of design guidelines (Holliday 1969). Though these works acknowledge the role of temperature on the static and cyclic material properties, data on the cyclic thermal properties of oil-country tubular-goods steels rarely appear in oilfield literature (Placido et al. 1997; Maruyama et al. 1990).

This paper presents a mathematical model of casing strings subjected to thermal loads in steam-injection wells. The model includes the effects of temperature on material properties and the effects of wellbore curvature and prestress during the heating cycle. Several counterintuitive aspects of the casing-stress state during cooling/unloading are examined. Further, the general equations are shown, with appropriate simplifications, to reproduce the earlier work (Willhite and Dietrich 1967; Holliday 1969). Example calculations are used throughout to illustrate key insights.
Sand Exclusion and Management in the Okwori Subsea Oil Field, Nigeria
Authors: Guinot Frédéric , Douglass Stuart , Duncan Jim , Orrell Martin , Stenger Bruno
Published: March 2009

Several downhole-sand-control failures in Okwori subsea oil producers triggered a significant overhaul of the downhole-sand-control method and a review of topside sand management. Because the eventuality of further downhole-sand-control failures in existing producers could not be ignored, a surface-sand-handling and -management facility was designed. For the future development producers, the downhole-sand-control method was re-engineered to increase its reliability. The initial multizone, fully selective sand-control-completion system, with expanded sand screens inside the casing, was abandoned. A revised openhole sand control was designed with similar completion selectivity. The new completion system implied a change in drilling practices, in reservoir drill-in fluid, and in filter-cake-cleanup techniques that required simultaneous engineering. These revisions were validated and implemented only a few months after encountering the first major sand-control failure. The Okwori floating production, storage, and offloading (FPSO) vessel was not expected to deal with sand production. Temporary sand traps were installed to minimize production downtime and to determine flow regimes that minimized sand production. Severe-service adjustable chokes were introduced to avoid valve erosion and stabilize production rates. Finally, a long-term topside-sand-management solution was designed and recommended for implementation.
Evaluation of the Potential for Gas and CO2 Leakage Along Wellbores
Authors: Watson Theresa L. , Bachu Stefan
Published: March 2009

Implementation of carbon dioxide (CO2) storage in geological media requires a proper assessment of the risk of CO2 leakage from storage sites. Leakage pathways may exist through and along wellbores, which may penetrate or be near to the storage site. One method of assessing the potential for CO2 leakage through wells is by mining databases that usually reside with regulatory agencies. These agencies collect data concerning wellbore construction, oil and gas production, and other regulated issues for existing wells. The Alberta Energy Resources Conservation Board (ERCB), the regulatory agency in Alberta, Canada, collects and stores information about more than 315,000 oil, gas, and injection wells in the province of Alberta. The ERCB also records well leakage at the surface as surface-casing-vent flow (SCVF) through wellbore annuli and gas migration (GM) outside casing, as reported by the industry.

The evaluation of a leakage pathway through wellbore casing or annuli and what causes these wellbore leaks are the first step in determining what factors may contribute to wellbore leakage from CO2-storage sites. By using available data, major factors that contribute to wellbore leakage were identified.

Data analysis shows that there is a correlation between these SCVF/GM and economic activity, technology changes, geographic location, and regulatory changes regarding well completion and abandonment. Further analysis indicates a relationship between low-annular-cement top, external corrosion, casing failure, and wellbore leakage (SCVF/GM). Other factors that could affect the presence of wellbore leakage, such as wellbore deviation, surface-casing depth, and wellbore density, were also investigated.

This paper presents the findings of the data analysis and a method to evaluate the potential for leakage along wells in an area where CO2 storage is intended. This information is useful not only for future operations of CO2 storage in geological media, but also for current operations relating to the exploration and production of hydrocarbons.
Finite-Element Studies of Near-Wellbore Region During Cementing Operations: Part I
Authors: Gray K. E. , Podnos E. , Becker E.
Published: March 2009

A wellbore cement sheath is expected to provide zonal isolation and borehole integrity during well construction and well life. Mechanical interactions of the cement sheath to existing and operationally induced stresses, along with other elements in proximity to the wellbore, have increasingly large technical, economic, and environmental ramifications.

Staged-finite-element procedures during well construction consider sequentially the stress states and displacements at and near the wellbore. The model replicates complicated stress states arising from simultaneous action of far-field stresses, overburden pressure, cement hardening and shrinkage, debonding at the interfaces, and plastic flow of cement sheath and rock formation. At present, temperature, flow, and poroelasticity effects are not included. The technique tracks the time-dependent behavior of cement slurry, curing (with or without shrinkage), and hardened cement during the critical period after slurry placement.

Material models for casing, cement, and rock formation and failure criteria for cement, formation, and interface bonds were calibrated using published information and experimental data. Calculations were conducted for various loading and unloading scenarios, geometric configurations, properties of rock formations, and cement-slurry formulations. Results are discussed in terms of field implication;, for example: (1) Interface microchan-nels may or may not develop, depending upon shrinkage magnitudes; and (2) simplifying modeling assumptions that are often used, such as 2D stresses and/or deformations, may obscure critical casing, cement, and formation behavior in the wellbore region and in the producing horizon.

This paper, part of a series quantifying the interacting physical components and processes at and near the wellbore region, initiates useful comparisons of analytical results and field realities. The series illustrates and compares results and practical implications from simple to increasingly complex, but more realistic, assumptions, such as isotropic/directional-stress states and isotropic/anisotropic casing, cement, and formation-material parameters.
Policies to Deal with the Implosion in the Mortgage Market
Authors: Shiller Robert J.
Published: March 2009

This paper relates the 2006-2008 meltdown in mortgage markets to falling asset prices, excessive psychological reaction to the burst bubble, and new mortgage vehicles incapable of accommodating sudden changes in asset values. A combination of market-based and regulatory innovations are proposed. The paper suggests placing greater reliance on innovative futures markets in real estate, inducing the flow of capital to vehicles having self-regulatory features and cultivating resiliency in the market. The bankruptcy law also might come to include circuit breaker" delays in finalizing settlements during turbulent market settings. Some of the fundamental premises underlying mortgage finance should also be reconsidered. Stakes in individual residences could be combined with stakes in regional property portfolios. Finally, the paper promotes a system of continuous workout mortgages" regularly readjusting loan balances to reflect economic conditions. These contracts could provide needed flexibility; they also offer systematic advantages over the various sector-based bailout strategies inherent in current loan-modification proposals.
The Mortgage Market Meltdown and House Prices
Authors: Hubbard R. Glenn , Mayer Christopher J
Published: March 2009

This paper argues that the U.S. mortgage debacle must be analyzed in the broader setting of global real estate markets. Recent U.S. home price growth closely tracked increases in other developed economies. The analysis distinguishes among market regions in terms of supply elasticity and localized transactions-costs. A series of user-cost models are presented which imply that interest rate fluctuations must figure prominently in any explanation of movements in price/rent ratios. National factors such as the expansion of subprime credit must also be accounted for. The paper concludes with policy prescriptions addressing rapid price declines and elevated interest-rate spreads. We argue that the federal government should play a leading role in helping to reduce interest rates on new mortgages and cushion against underwriting losses on the existing balance sheets of lenders.
Three Initiatives Enhancing the Mortgage Market and Promoting Financial Stability
Authors: Hancock Diana , Passmore Wayne
Published: March 2009

In recent years, the government has greatly extended its reach into the mortgage markets with the goals of (1) mitigating the deadweight losses associated with mortgage foreclosures, (2) promoting affordable homeownership, and (3) providing low cost mortgage financing. In this paper, we identify three innovations-one in each of these areas-that could be made to the American mortgage market that would help obtain the government's objectives while enhancing financial market stability-particularly if all are done together. These three innovations are: (1) buy your own mortgage" options, (2) variable maturity mortgages, and (3) creation of a government mortgage bond insurer, with an emphasis on insuring covered bonds as well as GSE debt. The first innovation would allow homebuyers to repurchase their mortgage at the market value" of their homes when they move, thereby helping society avoid some of the deadweight losses associated with unnecessary foreclosures. The second innovation would provide a mortgage that could promote affordable housing without unduly raising the default risks of low- and moderate-income families. The third innovation would help create a variety of financing options for mortgages in the United States. Moreover, it could be integrated into the current system of mortgage financing, which would include government-sponsored enterprises (GSEs), in a manner that would help the government manage the systemic risks associated with the quasi-government backing of mortgage credit and mortgage insurance. In particular, we propose that the government explicitly insure pre-designated financial instruments used to fund mortgage credit (such as covered bonds and GSE debt) by creating a government-backed insurance fund similar to that currently used for deposits.
Homes and Cars: Why are the Cycles in Homes and Consumer Durables so Similar?
Authors: Leamer Edward E
Published: March 2009

This paper reports three sets of facts: 1) Declines in housing are very good predictors of oncoming recessions in the U.S.; 2) Housing and consumer durables are the most important components of GDP that are soft prior to the official beginnings of recessions, and these two contribute substantially to weakness during recessions; and 3) The cycles in homes and consumer durables are very close, raising the prospect that a monetary rule that targeted housing would alleviate the cycle in consumer durables as well; this is confirmed in an econometric exercise with rates set to stabilize housing starts.These facts are used to argue in favor of monetary policy that prevents excessive building of homes and cars with preemptive rate increases in the middle of expansions when housing starts are above normal and growing higher. This contrasts with the traditional approach which is to raise rates late in expansions when inflation is apparent, but when the markets for homes and durables are very fragile because of excessive building earlier.
The Emerging Low-dose Therapy for Advanced Cancers
Authors: Satti Jahangir
Published: March 2009

Generally minute doses of drugs have been prescribed in biotherapies, homeopathy, immunization and vaccinations for centuries. Now the use of low doses of drugs is on the rise to combat serious diseases such as advanced cancers around the world. This new therapeutic approach to address solid tumors and other advanced diseases is a departure from the conventional use of maximum dose protocol. A small dose of the prescribed drug is frequently administered in a continuous fashion, at regular intervals, either as a standard treatment or as a maintenance therapy for a long time. However, this new treatment method lacks any standard for drug quantization, dose fractionation, repetition frequency and duration of a treatment course for an individual patient. This paper reviews literature about metronomic therapy and discusses hormesis: both phenomena occur in low dose ranges. Better mathematical models, computer simulations, process optimization and clinical trials are warranted to fully exploit the potential of low dose metronomic therapy to cure chronic and complicated diseases. New protocols to standardize metronomic dosimetry will answer the age old questions related to hormesis and homeopathy. It appears that this new low-dose metronomic therapy will have far reaching effects in curing chronic diseases throughout the world.
A Synthesis of Reading Interventions and Effects on Reading Comprehension Outcomes for Older Struggling Readers
Authors: Edmonds Meaghan S. , Vaughn Sharon , Wexler Jade , Reutebuch Colleen , Cable Amory , Tackett Kathryn Klingler , Schnakenberg Jennifer Wick
Published: March 2009

This article reports a synthesis of intervention studies conducted between 1994 and 2004 with older students (Grades 6–12) with reading difficulties. Interventions addressing decoding, fluency, vocabulary, and comprehension were included if they measured the effects on reading comprehension. Twenty-nine studies were located and synthesized. Thirteen studies met criteria for a meta-analysis, yielding an effect size (ES) of 0.89 for the weighted average of the difference in comprehension outcomes between treatment and comparison students. Word-level interventions were associated with ES = 0.34 in comprehension outcomes between treatment and comparison students. Implications for comprehension instruction for older struggling readers are described.
A Review of Empirical Evidence About School Size Effects: A Policy Perspective
Authors: Leithwood Kenneth , Jantzi Doris
Published: March 2009

This review examined 57 post-1990 empirical studies of school size effects on a variety of student and organizational outcomes. The weight of evidence provided by this research clearly favors smaller schools. Students who traditionally struggle at school and students from disadvantaged social and economic backgrounds are the major benefactors of smaller schools. Elementary schools with large proportions of such students should be limited in size to not more than about 300 students; those serving economically and socially heterogeneous or relatively advantaged students should be limited in size to about 500 students. Secondary schools serving exclusively or largely diverse and/or disadvantaged students should be limited in size to about 600 students or fewer, while those secondary schools serving economically and socially heterogeneous or relatively advantaged students should be limited in size to about 1,000 students.
Cultural Explanations for Racial and Ethnic Stratification in Academic Achievement: A Call for a New and Improved Theory
Authors: Warikoo Natasha , Carter Prudence
Published: March 2009

In this article we assess the literature on cultural explanations for ethno-racial differences in K–12 schooling and academic performance. Some cultural arguments problematically define certain ethno-racial identities and cultures as subtractive from the goal of academic mobility while defining the ethnic cultures and identities of others as additive and oriented toward this goal. We review two prevailing schools of thought that compare immigrant and native minority students: cultural–ecological theory and segmented assimilation theory. Second, we examine empirical research that highlights the complexity of culture, focusing on four domains: (a) the school’s cultural environment; (b) variation in identities and cultural practices within ethnic and racial groups; (c) the multidimensional nature of culture and its variable impact on students; and (d) the intersections of race, ethnicity, class, and gender. This literature—when synthesized—suggests that a coherent theory of culture’s impact on ethnic and racial differences in schooling outcomes must unpack the multiple influences of identity and context more deliberately than previous literature has done. Finally, we call for studies that employ comparative research across groups and understand race and ethnicity contextually, not as mere dummy variables, thereby equipping researchers with the tools to better explain how culture influences schooling and achievement.
Microstructure of a ternary Al–Pd–Rh alloy
Authors: Svoboda Milan , Buršík Jiří , Janovec Jozef , Kriška Martin , Kusý Martin , Švec Peter
Published: March 2009

The characterization of phases in a ternary Al – Pd – Rh complex metallic alloy annealed at 1100 °C for 49 h before (original state) and after differential thermal analysis was performed. In the investigation, light microscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, wavelength-dispersive X-ray spectroscopy, and differential thermal analysis were used. The dominant constituent in the original state was characterized as ∊6-phase. The minor constituent was attributed to the additionally solidified liquid co-existing with the ∊6-phase at 1100 °C. After differential thermal analysis, the microstructure of the alloy was composed of the matrix ∊6-phase and areas of the creek-type morphology.
High-temperature mechanical properties of Fe-40 at.% Al based intermetallic alloys with C or Ti addition
Authors: Karlík Miroslav , Haušild Petr , Šíma Vladimír , Málek Přemysl , Vlasák Tomáš
Published: March 2009

Tensile and creep properties of vacuum-induction-melted and cast Fe-40Al-1C and Fe-40Al-1Ti (at.%) were studied. The ingots were hot-rolled at 1200 °C to plates of 12.5 mm thickness using a stainless steel sheath and cooled in air. The alloys showed microstructures with coarse elongated grains having diameters up to 500 and 300 m in the direction of rolling, respectively. Tensile tests were carried out at temperatures 20, 400, 600, 700, and 800 °C. The creep tests were performed under constant load of 100 MPa and 150 MPa at temperatures 550, 600, 650, and 670 °C. Fracture surfaces of tensile specimens tested up to 700 °C exhibited mainly intergranular decohesion. With increasing temperature, the proportion of ductile dimpled fracture increased, and at 800 °C the fracture surfaces of both alloys were practically completely covered by ductile dimples. In comparison to tensile test specimens, fracture surfaces of creep specimens showed an increased fraction of intergranular ductile fracture.
Phase composition and morphology development in WE-type alloys modified by high Zn content
Authors: Smola Bohumil , Stulíková Ivana , Žaludová Nad'a , Hnilica František , Janík Vít , Očenášek Vladivoj
Published: March 2009

Quasicrystalline icosahedral equilibrium phase was found in Mg – Y – Nd (WE43) alloys with the addition of 12 wt.% and 25 wt.% Zn constituting grain boundary eutectic phases. In response to the isochronal annealing, morphologically similar precipitates of phases with the same structure as those developing during heat treatment of binary Mg-8 wt.% Zn alloy at temperatures higher than 150 °C were observed, namely β (b-centered monoclinic crystal structure a = 2.596 nm, b = 1.428 nm, c = 0.524 nm, = 102.5°) and β (hexagonal MgZn2). The evolution of the resistivity and microhardness during isochronal annealing corresponds to the phase transformations and the morphology changes of the phases observed. Dislocations with the c Burgers vector component generated due to the presence of icosahedral phase are responsible for the improved formability as compared to the WE43 alloy.
Influence of titanium volume fraction on the mechanical properties of Mg–Ti composites
Authors: Pérez Pablo , Garcés Gerardo , Adeva Paloma
Published: March 2009

The influence of titanium volume fraction on the mechanical properties of Mg – Ti composites prepared through a powder metallurgy route has been evaluated. Titanium was added as particles smaller than 25 m and volume fractions ranging from 5 to 15 %. The increase in the volume fraction of titanium particles results in a slight decrease in the maximum strength. In contrast to this, the ductility of all composites was significantly enhanced by titanium additions. The mechanical properties can be explained on the basis of texture changes induced by the presence of titanium particles. The decrease in the basal texture along the extrusion direction as the amount of titanium is progressively increased accounts for the decrease in the maximum strength.
Bauschinger effect in thin metal films simulated by the continuum dislocation-based model
Authors: Sedláček Radan , Schwarz Cornelia , Wesenjak Robert , Bensimon Adrien
Published: March 2009

The continuum dislocation-based model is applied to cyclic deformation of thin constrained crystalline strips. The simulated size effect upon loading as well as the size-dependent Bauschinger effect upon unloading are caused by the line tension of the curved dislocations that bow out between the impenetrable edges of the strip.
Alloying behaviour of binary transition metal systems
Authors: Paidar Václav , Duparc Olivier Hardouin
Published: March 2009

The properties of A – B binary alloys are controlled by the mixed AB interaction potentials. The interfaces between two different metals are investigated for fictive mixed potentials spreading from A-type to B-type nature. The elemental AA and BB potentials are fixed. The tendencies towards formation of ordered structures on one side, and separation of phases on the other side are discussed. A description of interatomic forces respecting metallic bonding character in many-body potentials is used. This approach can be helpful for applications of alloy potentials in models with complex structures of extended defects such as dislocations and grain boundaries and in the assessment of their behaviour.
Surface composition of a Ag-5.1Cu (mass%) alloy
Authors: Vaníčková Jaroslava , Kovač Janez , Děd Jirí , Lejček Pavel , Samardžija Zoran , Zalar Anton
Published: March 2009

X-ray photoelectron spectroscopy was applied to study the evolution of surface composition in a polycrystalline Ag-5.1Cu mass% alloy during in-situ annealing in ultra-high vacuum at temperatures ranging between 300 °C and 600 °C. The results show an enrichment of copper on the free surface. The results imply that the compositional changes at the surface of this alloy are dominated by copper segregation at grain boundaries.
Quantitative characterization of the orientation spread within individual grains in copper after tensile deformation
Authors: Krog-Pedersen Stine , Bowen Jacob R. , Pantleon Wolfgang
Published: March 2009

By means of electron backscatter diffraction, orientations are determined on a regular grid on a polished section of a copper specimen after tensile deformation to 25 %. Individual grains separated by boundaries with disorientation angles above 7 are identified and the microtexture in the form of the orientation distribution function of each individual grain is analyzed. Extent and shape of the disorientation distribution in orientation space are quantified by the tensor of the second-order central moments, its principal values and directions. The latter characterize the main rotation axes of the orientation spread and the former the extent of the distribution in orientation space along these principal axes allowing a classification of the disorientation distribution into archetypical shapes. The disorientation distributions developed in grains with tensile axes close to [001] or [011] are more anisotropic than expected from their eight possibly activated slip systems indicating a mutual suppression of possibly activated slip systems.
Comparative study of the high-temperature behaviour of Mg–Al and Mg–Zn wrought alloys
Authors: Mehtedi Mohamad El , Spigarelli Stefano , Evangelista Enrico , Rosen Gady
Published: March 2009

The high-temperature workability of AZ31 has been extensively investigated in recent years, since this alloy is considered the best candidate for production of wrought components in Mg. While peak flow stresses, and thus working loads during rolling, extrusion or forging, seem to weakly depend on the initial microstructure, the same conclusion does not hold for the ductility of the alloy. Fewer studies have considered the high temperature workability of Mg – Zn alloys. This study aims at relating the mechanical response of the materials, in term of flow stresses and strain to fracture, with the chemical composition and the prior microstructure. The results of mechanical testing in torsion, carried out in the same regime of temperature and strain rates were then analysed and discussed. Constitutive equations relating flow stresses to straining conditions were obtained for each tested alloy, and the differences in strain-to-fracture were closely analysed.
Influence of the dynamic crystallization conditions on the martensitic transformation in the Ti40.7Hf9.5Ni39.8Cu10 shape memory alloy
Authors: Resnina Natalia , Belyaev Sergey , Shelyakov Alexander
Published: March 2009

The article deals with the problem of the influence of the dynamic crystallization conditions on the structure and on the martensitic transformation in amorphous Ti40.7 Hf9.5 Ni39.8 Cu10 thin ribbons. The crystallization was realized in a DSC apparatus by heating the samples at different heating rates. DSC and X-ray diffraction were employed to study the martensitic transformation and the structure of the crystallized ribbons. The data show that increasing heat rate resulted in an increase in the crystallization temperature, a decrease in the B2 ↔ B19′ transformation temperature and an extension of the halfwidth of (110) reflections of the B2 phase. It is concluded that the increase in the heating rate decreases the grain size of the crystalline phase. As the temperature of the B2 ↔ B19′ transition depends sensitively on the grain size the heating rate could be used for controlling the characteristics of the phase transformations.
Very high cycle fatigue behaviour of as-extruded AZ31, AZ80, and ZK60 magnesium alloys
Authors: Nový František , Janeček Miloš , Škorík Viktor , Müller Julia , Wagner Lothar
Published: March 2009

The very high cycle fatigue properties of extruded AZ31, AZ80, and ZK60 magnesium alloys were investigated. Fatigue tests were performed at ultrasonic cyclic frequency and at a load ratio of R = – 1 at ambient temperature using smooth electropolished specimens. Fatigue failures were observed at lifetimes above 109 cycles. The fatigue life was found to increase with decreasing stress amplitude. The fracture surfaces and fracture profiles of selected specimens cycled until failure were examined. The purpose of the study was to determine the role of the microstructure on the fatigue crack nucleation and growth. Furthermore, the fatigue properties were discussed on the basis of microstructure and the presence of inclusions which are known as crack initiation sites. In AZ31 and AZ80 alloys only surface-induced fatigue cracks were observed. On the other hand, in the ZK60 alloy both surface- and interior-induced fatigue cracks were observed. Both mechanisms operate in the ZK60 also at a lifetime of around 1010 cycles. Interior-induced fatigue cracks were accompanied by clear fish-eye marks on the fracture surfaces of the ZK60 alloy.
Isostructural phase transition in hexagonal Ce1–x
Y
x
PdAl compounds
Authors: Rusňák Martin , Prchal Jiří , Daniš Stanislav
Published: March 2009

The Ce1 – x
Y
x
PdAl pseudoternaries belong to the ternary RTX compounds (where R stands for rare-earth, T for transition metal, X for a p-metal). We have studied three compounds with compositions x = 0.2, 0.5, and 0.8 by means of X-ray diffraction at room temperature. Moreover, Ce0.5 Y0.5 PdAl was also studied in the temperature range from 70 K to 500 K. The existence of a gap of forbidden values of the c/a ratio was confirmed. The compounds with x = 0.2 and 0.8 have different phases. The compound with x = 0.5 exhibits coexistence of both the x = 0.2 and x = 0.8 phases. The diffraction patterns and the calculated lattice parameters indicate that the Ce0.5 Y0.5 PdAl sample undergoes a phase transition towards the single-phased state at both high and low temperatures.
Temperature and strain rate dependent flow criterion for bcc transition metals based on atomistic analysis of dislocation glide
Authors: Gröger Roman , Vitek Vaclav
Published: March 2009

1/2111 screw dislocations that possess non-planar cores and thus a high lattice friction (Peierls) stress control the plastic deformation of pure bcc metals. In this paper we formulate an analytical flow criterion based on the recognition that at finite temperatures the screw dislocations glide via formation and subsequent propagation of pairs of kinks. This development employs first an atomistically calculated dependence of the Peierls stress on the applied loading to construct the Peierls potential that depends on the applied stress tensor. This Peierls potential is then used to evaluate the activation enthalpy for the kink-pair formation employing mesoscopic dislocation models and its dependence on the applied stress tensor is then approximated by a relatively simple analytical form. Using the standard transition state theory to ascertain the dislocation velocity and related strain rate allows us to formulate the temperature and strain rate dependent flow criterion. Implications of this criterion are then compared with available experimental data demonstrating its excellent predictive value.
Deformation behaviour of microcrystalline magnesium reinforced by alumina nano- and microparticles
Authors: Drozd Zdeněk , Trojanová Zuzanka
Published: March 2009

Mg-based micro- and nanocomposites were prepared by the powder metallurgical route. Specimens were deformed in tension and in compression at temperatures between RT and 300 °C at a constant crosshead speed giving an initial strain rate of 5.5 × 10– 5 s– 1. Both a yield stress and an ultimate stress improvement were observed in the composites in comparison with the unreinforced microcrystalline Mg. A different deformation behaviour in tension and in compression was observed. The changes in the deformation behaviour can be attributed, among others, to twinning, which occurs in the composites at higher stages of deformation. Various contributions to the composite strengthening are discussed.