Ross procedure: is the root replacement technique superior to the sub-coronary implantation technique? Long-term results.

There is controversy over the use of the Ross procedure with regard to the sub-coronary and root replacement technique and its long-term durability. A systematic review of the literature may provide insight into the outcomes of these two surgical subvariants. A systematic review of reports between 1967 and February 2013 on sub-coronary and root replacement Ross procedures was undertaken. Twenty-four articles were included and divided into (i) sub-coronary technique and (ii) root replacement technique. The 10-year survival rate for a mixed-patient population in the sub-coronary procedure was 87.3% with a 95% confidence interval (CI) of 79.7-93.4 and 89.1% (95% CI, 85.3-92.1) in the root replacement technique category. For adults, it was 94 vs 95.3% (CI, 88.9-98.1) and in the paediatric series it was 90 vs 92.7% (CI, 86.9-96.0), respectively. Freedom from reoperation at 10 years was, in the mixed population, 83.3% (95% CI, 69.9-93.4) and 93.3% (95% CI, 89.4-95.9) for sub-coronary versus root replacement technique, respectively. In adults, it was 98 vs 91.2% (95% CI, 82.4-295.8), and in the paediatric series 93.3 vs 92.0% (95% CI, 86.1-96.5) for sub-coronary versus root replacement technique, respectively. The Ross procedure arguably has satisfactory results over 5 and 10 years for both adults and children. The results do not support the advantages of the sub-coronary technique over the root replacement technique. Root replacement was of benefit to patients undergoing reoperations on neoaorta and for long-term survival in mixed series.

Field Evaluation of Elliptical Fiber Reinforced Polymer Dowel Performance, June 2005

Fiber reinforced polymer (FRP) composite materials are making an entry into the construction market in both buildings and pavements. The application to pavements so far has come in the form of joint reinforcement (dowels and tie bars). FRP resistance to salt corrosion in dowels has made it an alternative to standard epoxy-coated steel dowels for pavements. Iowa State University has completed a large amount of laboratory research to determine the diameter, spacing, and durability of FRP dowels. This report documents the performance of elliptical FRP dowels installed in a field situation. Ten joints were monitored in three consecutive test sections, for each of three dowel spacings (10, 12, and 15 inches) including one instrumented dowel in each test section. The modulus of dowel bar support was determined using falling weight deflectometer (FWD) testing and a loaded crawl truck. FWD testing was also used to determine load transfer efficiency across the joint. The long-term performance and durability of the concrete was also evaluated by monitoring faulting and joint opening measurements and performing visual distress surveys at each joint. This report also contains similar information for standard round, medium elliptical, and heavy elliptical steel dowels in a portion of the same highway. In addition, this report provides a summary of theoretical analysis used to evaluate joint differential deflection for the dowels.

Evaluating Properties of Blended Cements for Concrete Pavements, December 2003

The addition of supplementary cementitious materials (SCMs), such as fly ash (FA) and slag, generally improves concrete workability, durability, and long-term strength. New trends in sustainable development of concrete infrastructure and in environmental regulations on waste disposal are spurring use of SCMs in concrete. However, use of SCM concrete is sometimes limited due to a lack of understanding about material behaviors and lack of proper specifications for its construction practice. It is believed that SCM concrete performance varies significantly with the source and proportion of the cementitious materials. SCM concrete often displays slower hydration, accompanied by slower setting and lower early-age strength, especially under cold weather conditions. The present research was conducted to have a better understanding of SCM concrete behaviors under different weather conditions. In addition to the study of the effect of SCM content on concrete set time using cementitious materials from different sources/manufacturers, further research may be needed to investigate the effects of SCM combinations on concrete flowability, air stability, cracking resistance, and durability.

Sustainable Development and Concrete Technology, May 2004

For a variety of reasons, the concrete construction industry is not sustainable. First, it consumes huge quantities of virgin materials. Second, the principal binder in concrete is portland cement, the production of which is a major contributor to greenhouse gas emissions that are implicated in global warming and climate change. Third, many concrete structures suffer from lack of durability which has an adverse effect on the resource productivity of the industry. Because the high-volume fly ash concrete system addresses all three sustainability issues, its adoption will enable the concrete construction industry to become more sustainable. In this paper, a brief review is presented of the theory and construction practice with concrete mixtures containing more than 50% fly ash by mass of the cementitious material. Mechanisms are discussed by which the incorporation of high volume of fly ash in concrete reduces the water demand, improves the workability, minimizes cracking due to thermal and drying shrinkage, and enhances durability to reinforcement corrosion, sulfate attack, and alkali-silica expansion. For countries like China and India, this technology can play an important role in meeting the huge demand for infrastructure in a sustainable manner.

Two-Lift Portland Cement Concrete Pavements to Meet Public Needs, September 2004

The report reviews the past work in the United States and internationally in the development of two-lift pavements. It points out the strengths and limitations in the construction of such portland cement concrete pavements. Certain cost, mix design, and construction problems are inhibiting the growth of this product. Changes in the availability of aggregates, knowledge of materials and new construction equipment, and the desire for specific surfaces to meet noise, durability, and safety are prompting the need to reconsider this type of construction.

Using the Air Void Anal Analyzer for Real-Time Quality Control Adjustments in the Field, November 2004

The air void analyzer (AVA) with its independent isolation base can be used to accurately evaluate the air void system—including volume of entrained air, size of air voids, and distribution of air voids—of fresh portland cement concrete (PCC) on the jobsite. With this information, quality control adjustments in concrete batching can be made in real time to improve the air void system and thus increase freeze-thaw durability. This technology offers many advantages over current practices for evaluating air in concrete.

Field Evaluation of Elliptical Fiber Reinforced Polymer Dowel Performance, June 2003

Fiber composite materials (FRP) are making an entry into the construction market in both buildings and pavements. The application to pavements comes in the form of joint reinforcement (dowels and tie bars) to date. FRP resistance to salt corrosion in dowels has made it an alternative to standard epoxy coated dowels for pavements. Iowa State University has completed a large amount of laboratory research into the determination of diameter, spacing, and durability of FRP dowels. This report documents the installation of a series of FRP elliptical-shaped dowel joints (including instrumented units) in a field situation and the beginning of a two-year study to compare laboratory results to in-service pavements. Ten joints were constructed for each of three dowel spacings of 10, 12, and 15 inches ( 254, 305, and 381 mm) with one instrumented joint in each test section. The instrumented bars will be load tested with a loaded truck and FWD testing.

Material and Construction Optimization for Prevention of Premature Pavement Distress in PCC Pavements, September 2004

The chemistry of today’s concrete mixture designs is complicated by many variables, including multiple sources of aggregate and cements and a plethora of sometimes incompatible mineral and chemical admixtures. Concrete paving has undergone significant changes in recent years as new materials have been introduced into concrete mixtures. Supplementary cementitious materials such as fly ash and ground granulated blast furnace slag are now regularly used. In addition, many new admixtures that were not even available a few years ago now have widespread usage. Adding to the complexity are construction variables such as weather, mix delivery times, finishing practices, and pavement opening schedules. Mixture materials, mix design, and pavement construction are not isolated steps in the concrete paving process. Each affects and is affected by the other in ways that determine overall pavement quality and long-term performance. Equipment and procedures commonly used to test concrete materials and concrete pavements have not changed in decades, leaving serious gaps in our ability to understand and control the factors that determine concrete durability. The concrete paving community needs tests that will adequately characterize the materials, predict interactions, and monitor the properties of the concrete.

Development of Performance Properties of Ternary Mixes: Scoping Study, June 2005

Pozzolans and slag extend the market for concrete products by improving specific properties of the products, which allows the products to be constructed with materials or placed in environments that would have precluded the use of portland cement alone. In properly formulated concrete mixes, pozzolans and slag have been shown to enhance long-term strength, decrease permeability, increase durability, reduce thermal cracking of mass concrete, minimize or eliminate cracking related to alkali-silica reaction (ASR), and minimize or eliminate cracking related to sulfate attack. The purpose of this research project was to conduct a scoping study that could be used to evaluate the need for additional research in the area of supplementary cementitious materials (SCMs) that are used in concrete for highway applications. Special emphasis was given to the concept of using two or more SCMs in a single concrete mixture. The scope of the study was limited to a literature survey and panel discussions concerning issues relevant to the project. No laboratory work was conducted for this project. A problem statement with research plan was created that could be used to guide a pooled fund project.

Two Lift Portland Cement Concrete Pavements to Meet Public Needs, September 2004

The report reviews the past work in the United States and internationally in the development of two-lift pavements. It points out the strengths and limitations in the construction of such portland cement concrete pavements. Certain cost, mix design, and construction problems are inhibiting the growth of this product. Changes in the availability of aggregates, knowledge of materials and new construction equipment, and the desire for specific surfaces to meet noise, durability, and safety are prompting the need to reconsider this type of construction.

Sähkökoneen staattorikäämityksen kehittäminen

Tämä insinöörityö tehtiin ABB:n Pitäjänmäen konetehtaalle Tahtikoneet-tulosyksikölle. Työssä tutkittiin mahdollisuuksia valmistaa murtovakovyyhtejä kestomagneettituuligeneraattoreihin, joissa vakoluku on alle yhden. Työ tehtiin tutustumalla aluksi Pitäjänmäen konetehtaan käytössä oleviin vyyhden valmistus- ja käämintämenetelmiin. Lisäksi tutkittiin erilaisia mahdollisia murtovakovyyhden valmistusmenetelmiä, joista lupaavimpia myös kokeiltiin. Saatujen kokemusten pohjalta valittiin vyyhden valmistusmenetelmä, jonka mukaan valmistettiin koe-erä. Koe-erälle suoritettiin mittauksia, joilla varmistettiin niiden sähköinen kestävyys Työn tuloksena valitulla valmistusmenetelmällä valmistettiin vyyhdet prototyyppi tuuligeneraattorin.

Field Experiments of Current Concrete Pavement Surface Characteristics Practices: Iowa Data Collection and Analysis, December 2005

One of the most important issues in portland cement concrete pavement research today is surface characteristics. The issue is one of balancing surface texture construction with the need for durability, skid resistance, and noise reduction. The National Concrete Pavement Technology Center at Iowa State University, in conjunction with the Federal Highway Administration, American Concrete Pavement Association, International Grinding and Grooving Association, Iowa Highway Research Board, and other states, have entered into a three-part National Surface Characteristics Program to resolve the balancing problem. As a portion of Part 2, this report documents the construction of 18 separate pavement surfaces for use in the first level of testing for the national project. It identifies the testing to be done and the limitations observed in the construction process. The results of the actual tests will be included in the subsequent national study reports.

Strategic Plan for Improved Concrete Pavement Surface Characteristics, July 2006

Surface characteristics represent a critical issue facing pavement owners and the concrete paving industry. The traveling public has come to expect smoother, quieter, and better drained pavements, all without compromising safety. The overall surface characteristics issues is extremely complex since all pavement surface characteristics properties, including texture, noise, friction, splash/spray, rolling resistance, reflectivity/illuminance, and smoothness, are complexly related. The following needs and gaps related to achieving desired pavement surface characteristics need to be addressed: determined how changes in one surface characteristic affect, either beneficially or detrimentally, other characteristics of the pavement, determine the long-term surface and acoustic durability of different textures, and develop, evaluate, and standardize new data collection and analysis tools. It is clear that an overall strategic and coordinated research approach to the problem must be developed and pursued to address these needs and gaps.

Dynamic adverse selection and debt

This paper argues that the strategic use of debt favours the revelationof information in dynamic adverse selection problems. Our argument is basedon the idea that debt is a credible commitment to end long term relationships.Consequently, debt encourages a privately informed party to disclose itsinformation at early stages of a relationship. We illustrate our pointwith the financing decision of a monopolist selling a good to a buyerwhose valuation is private information. A high level of (renegotiable)debt, by increasing the scope for liquidation, may induce the highvaluation buyer to buy early at a high price and thus increase themonopolist's expected payoff. By affecting the buyer's strategy, it mayreduce the probability of excessive liquidation. We investigate theconsequences of good durability and we examine the way debt mayalleviate the ratchet effect.

Nouveautés en chirurgie vasculaire [New treatments in vascular diseases]

In superficial venous insufficiency, surgery remains the treatment of choice. Endovenous therapies are a minimal invasive alternative, whose long-term results are not demonstrated yet. In the treatment of abdominal aortic aneurysm, endovascular repair (EVAR) and laparoscopic approach are comparatively studied with open repair, to define their precise indications. In occlusive arterial disease, endovascular treatment offers inferior results in term of durability and patency, however with a decrease in morbidity and mortality.