Academic literature on the topic 'Optimum Replacement Fraction'

Background: Available evidence suggest that the optimum prothrombin time-international normalised ratio (PT-INR) intensities recommended for anticoagulation of patients with mechanical heart valve prosthesis may not apply to all race groups. Optimal PT-INR target ranges and effectiveness of warfarin oral anticoagulation were determined among black South African patients fitted with St Jude bileaflet mechanical heart valve prosthesis (SJBMHVP) at Dr George Mukhari Academic Hospital (DGMAH). Methods: A convenience sample of 95 medical records of patients fitted with SJBMHVP from 1994 until 2013 was reviewed. Optimum PT-INR target ranges were estimated using two different methods: the classical two PT-INR target level method and the alternative, PT-INR specific incident rate method. The quality of warfarin anticoagulation was assessed using the fraction in therapeutic range method.Results: Optimum PT-INR target ranges for all participants fitted with SJBMHVP in the aortic position was estimated to be 2.0–3.5 and 2.6–3.5, respectively, by the classical and alternative methods. That of the patients with mitral valve replacement was estimated to be in the range 2.6–3.5 by the classical method and that of patients with double heart valve replacement was estimated to be 3.5 by both methods. The quality of warfarin anticoagulation of participants with SJBMHVP replacement was found to be inadequate as indicated by percentage time in treatment range (TTR) of 49.7% for all study participants compared with the ideal TTR of 70% and above.Conclusion: Optimum Caucasian-based PT-INR intensities recommended for oral anticoagulation of patients fitted with mechanical heart valve prosthesis are applicable to black patients fitted with SJBMHVP at DGMAH.

Economic and environmental factors call for increased resource productivity. Partial or full replacement of Portland cement by wastes and by-products, and natural aggregates by construction and demolition wastes, are two prominent routes of achieving circular economy in construction and related industries. Municipal solid waste incineration (MSWI) bottom ashes have been found to be suitable to be used as a supplementary cementitious material (SCM) after various treatments. This paper reports a brief literature review on optimum use of recycled aggregates in concrete and an experimental study using replacement of natural aggregate by demolished concrete having MSWI bottom ash as partial replacement of Portland cement, and compares its properties to that of completely natural aggregate concrete. Additional water was added as a compensation for the water absorption by the recycled aggregate during the first 30 min of water contact during concrete mixing. Also the fine fraction of crushed concrete (<250 µm) was removed to reduce the ill-effects of using recycled aggregate. The replacement of aggregates was limited to 23% by weight of natural aggregate. The results prove environmentally safe and comparable performance of concrete including recycled aggregate with bottom ash to that of natural aggregate concrete.

This study investigates the influence of silane-treated aluminum hydroxide on the mechanical performance of flame-retardant composites. These composites have potential applications for luggage bags, as a replacement for conventional plastics, offering more durability and lighter weight. Glass fabric was used as the reinforcement, while epoxy was used as the matrix material. To impart flame retardancy, aluminum hydroxide nanoparticles were used as fillers in different weight % age (5%, 10% and 15%). As these are inorganic particles and have compatibility issues with the matrix material, silane-coupling agents (Dynasylan® 6490 and Dynasylan Glymo) were used to treat these filler particles. Both the silane-coupling agents fraction used for treatment and the fillers fraction added to the composites were varied to determine the most optimum combination. The mechanical properties of the developed composites such as tensile, flexural, and short beam shear strength were investigated. The best results were exhibited by 10% aluminum hydroxide fillers treated with 1% (by weight) coupling agent (Dynasylan Glymo).

The results of studying the influence of boiler ash slags with a circulating fluidized bed on the freeze-thaw resistance of heavy concretes are presented. The following materials were used in the studies: Portland cement PPC 500 N, sand with the fineness modulus Mf =1.05, crushed granite fraction 5-10 mm, boiler ashes with circulating fluidized bed, hyperplasticizer «Fluid Premia-196». The study was performed using mathematical planning of the experiment. It is proved that with the replacement of sand with ashes, the freeze-thaw resistance is somewhat reduced, but the hyperplasticizer compensates the reduction of freeze-thaw resistance by reducing the W/C ratio, resulting in the formation of super-fine pore structure of concrete. Fine pores in the concrete structure compensate the ice formation stress at low ambient temperatures. The optimal cement consumption has been established in terms of freeze-thaw resistance, both at full and partial replacement of sand with ash. It was also determined that the optimum should be considered the consumption of a hyperplasticizer in the amount of 1.2-1.4% of the cement mass.

The pore structure is one of the major factors affecting the mechanical properties of waste fiber recycled concrete. In this article, the pore structure and strength performance of waste fiber recycled concrete are experimentally studied. The design variables are water–cement ratio, recycled aggregate replacement rate, waste fiber length, and volume fraction of waste fibers. The pore structure characteristic parameters of waste fiber recycled concrete are investigated using mercury intrusion porosimetry test and fractal theory. The complex distribution of pore structure in space is quantitatively described by fractal dimension, and the pore structure is comprehensively evaluated. The results show that the water–cement ratio has the largest influence on the pore structure, and the fiber length has the least influence. The optimum volume fraction of waste fibers is 0.12%. There is an obvious linear relationship between the pore volume fractal dimension and strength. With the increase in the fractal dimensions, the compressive and splitting tensile strengths increase. Macroscopic mechanical properties of waste fiber recycled concrete can be predicted by the pore structure.

Abstract The study deals with the examination of the rheological behaviour of rubber blends which were filled with bentonite. The filler - polymer as well as the filler - filler interactions were studied and determined from the frequency sweep and strain sweep rheological measurements. The used natural bentonite was extracted from the locality called Jelsovy Potok. The natural bentonite had a fine fraction with a particle size of 15μm a 45 μm and it was added into rubber blends as a partial replacement of commonly used filler. The rubber blends were characterised on the basis of curing characteristics (minimum torque ML, maximum torque MH, optimum time of cure t(c90), processing safety of blend ts,). Moreover, the complex viscosity and Payne effect were also specified. The required measurements were done by using PRPA 2000.

The objective of this study is to investigate the flexural behavior of M30 grade PSCC, GFRSCC, SFRSCC and HFRSCC beams made with PF=1.12 and s/a=0.53 and PF=1.14 and s/a=0.57 to understand the effect of copper slag as partial replacement of fine aggregate on its deflection characteristics and cracking behaviour. The yield and ultimate load taken by HFRSCC beams made with optimum PF and s/a ratios are higher than the conventional RCC beam elements. The deflections at centre at failure in HFRSCC beams made with optimum PF and s/a ratios were more than that of conventional beams. This shows improvement in ductility of HFRSCC beams. First crack formation was delayed in M30 grade HFRSCC beams due to dense micro structure with low pore fraction and reduced pore size due to which fatigue strength is increased which in turn increases the time taken for first crack occurrence and thereby increasing the load carrying capacity. The deflection at the mid span decreased in HFRSCC beams which shows that the flexural stiffness of the elements increases thereby reducing the structural member’s deformability, increasing strength and hence controlling deflection.

Due to the ozone depletion issue, R-502, which had long been used as the refrigerant of an ice cream refrigerator, has been replaced by R-404A. However, global warming potential (GWP) of R-404A is high, and thus, a replacement refrigerant is necessary in the long term. Natural refrigerants, such as R-290 or DME (dimethylether), could be a choice. In this study, an ice cream refrigerator cycle was optimized using R-290/DME mixture (mass fraction 65/35). The optimization was accomplished through a search for the proper refrigerant charge amount and the opening of the expansion valve. For the present ice cream refrigerator having 2.8[Formula: see text]L freezer volume, the optimum charge amount was 900[Formula: see text]g, and the optimum valve opening was [Formula: see text]120[Formula: see text]. At this configuration, the ice cream formation time was 3[Formula: see text] 6[Formula: see text] and COP was 2.0. The ice cream formation time was much shorter than when R-404A was used, and the COP was increased by more than 100%. For actual usage of the refrigerant, however, the flammability issue of the R-290/DME mixture should be cleared.

Even though TIMETAL-54M (Ti-5Al-4V-0.6Mo-0.4Fe or Ti54M) has been commercially available for over 10 years, further study of its superplastic properties is still required in order to assess its applicability within the aerospace industry as a potential replacement for other commercial titanium alloys such as Ti-6Al-4V (Ti64). Ti54M is expected to obtain superplastic characteristics at a lower temperature than Ti64 due to its lower beta-transus temperature. The superplastic forming (SPF) capability of alloys that can be formed at lower temperatures has always attracted the interest of industry as it reduces the grain growth and alpha-case formation, leading to longer life for costly high temperature resistant forming tools. In this work, the SPF characteristics of both Ti54M and Ti64 have been examined by conducting tensile tests according to the ASTM E2448 standard within a range of temperatures and strain values at a fixed strain rate of 1 × 10-4/S. A high strain rate sensitivity and uniform deformation at high strains are key indicators in selecting the optimum superplastic temperature. This was observed at 815˚C and 925˚C for Ti54M and Ti64 respectively. The tensile samples were water quenched to freeze their respective microstructure evolution following superplastic deformation and SEM images were captured for grain size and volume fraction of alpha-phase analyses. A slightly higher alpha-grain growth rate was observed during superplastic deformation of Ti64. The initial fine-grain microstructure of Ti54M (~1.6 micron) resulted in a final microstructure with an average grain size of ~3.4 micron and optimum the alpha/beta ratio. Both the fine-grained microstructure and increased amount of beta-volume fraction promotes the superplastic behaviour of Ti54M by grain boundary sliding (GBS). Thus superplastic properties were observed for Ti54M at a lower temperature (~100˚C) than for Ti64.

Abstract: Concrete is one of the most widely used construction material in today’s world. Cement being one of the essential constituent of the concrete. Environmental issues are also playing a vital role in today’s world, the production of cement one of the major constituent of concrete leads to release the of significant amount of carbon dioxide a greenhouse gas contributing 7% of greenhouse gas emission to the earth atmosphere, beside deforestation and burning of fossil fuels. Safe disposal of glass waste generated in day to day life due to limited life span and after use it is either stock piled or sent to land fill is also a challenging task. There is now a significant world-wide interest to solve the environmental problem caused by industrial waste and other material by including such material in the manufacture of concrete. Effort have been made in concrete industry to use waste glass in concrete production not only provide significant environmental benefits but also enhances performances of concrete when used at optimum amounts. Efforts have been made in the concrete industry to use fly ash & waste glass as partial replacement of cement, fine & coarse aggregates. Recently the research has shown that the waste glass can be effectively used in concrete as several alternatives for the constituent of concrete under proper fraction and grade. Waste glass when ground to a very fine powder show pozzolanic properties as it contains high SiO2 and therefore to some extent can replaced cement in concrete and contributes strength development. In this study, glass fibers in different volume fraction with 20%, 30% and 40% replacement of cement by fly ash has been to study the effect on compressive strength, split tensile strength, of concrete and compared it to the conventional concrete. The overall test result shows glass fiber could be utilized in concrete. The result indicates that the maximum strength of concrete occurs at around 20% glass powder. Beyond 20% glass fiber the strength of concrete reduces and is lower than that of the control.

Liver was always considered to be ‘highly sensitive’ to radiation therapy (RT) and was not considered ‘safe’ for radiation therapy treatment. The most significant radiation induced liver toxicity was described by Ingold et al. as “Radiation hepatitis.” Historically, radiation to liver lesions with curative intent or incidental exposure during adjacent organ treatment or total body irradiation implied whole organ irradiation due to lack of high precision technology. Whole organ irradiation led to classic clinical picture termed as “Radiation Induced Liver Disease (RILD).” In conventional fractionation, the whole liver could be treated only to the doses of 30–35Gy safely, which mostly serves as palliation rather than cure. With the advent of technological advancements like IMRT, especially stereotactic radiation therapy (SBRT), the notion of highly precise and accurate treatment has been made practically possible. The toxicity profile for this kind of focused radiation was certainly different from that of whole organ irradiation. There have been attempts made to characterize the effects caused by the high precision radiation. Thus, the QUANTEC liver paper distinguished RILD to ‘classic’ and ‘non-classic’ types. Classic RILD is defined as ‘anicteric hepatomegaly and ascites’, and also can also have elevated alkaline phosphatase (more than twice the upper limit of normal or baseline value). This is the type of clinical picture encountered following irradiation of whole or greater part of the organ. Non-classic RILD is defined by elevated liver transaminases more than five times the upper limit of normal or a decline in liver function (measured by a worsening of Child-Pugh score by 2 or more), in the absence of classic RILD. In patients with baseline values more than five times the upper limit of normal, CTCAE Grade 4 levels are within 3 months after completion of RT. This is the type of RILD that is encountered typically after high-dose radiation to a smaller part of liver. It is commonly associated with infective etiology. Emami et al. reported the liver tolerance doses or TD 5/5 (5% complication rate in 5 years) as 50 Gy for one-third (33%) of the liver, 35 Gy for two-thirds (67%) of the liver, and 30 Gy for the whole liver (100%). Liver function (Child Pugh Score), infective etiology, performance status and co-morbidities influence the radiation induced toxicity. Lyman–Kutcher–Burman (LKB)-NTCP model was used to assess dose-volume risk of RILD. Lausch et al. at London Regional Cancer Program (LRCP), developed a logistic TCP model. Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) reported recommendations that mean normal liver dose should be <18 Gy for baseline CP-A patients and < 6 Gy for those with CP-B, for a 6-fraction SBRT regimen. The University of Colorado phase 1 clinical trial of SBRT for liver metastases described the importance of the liver volume spared, that is, ‘critical volume model.’ It is estimated that a typical normal liver volume is approximately 2000 mL and specified that a minimum volume of 700 mL or 35% of normal liver should remain uninjured by SBRT i.e. at least 700 mL of normal liver (entire liver minus cumulative GTV) had to receive at total dose less than 15 Gy. In treatment regimen of 48 Gy in 3 fractions, CP-A patients were required to either limit the dose to 33% of the uninvolved liver (D33%) < 10 Gy and maintain the liver volume receiving <7 Gy to <500 cc. In more conservative treatment regimen, such as in 40 Gy in 5 fractions schedule, CP-B7 patients had to meet constraints of D33% < 18 Gy and/or > 500 cc receiving <12 Gy. The concept of body surface area (BSA) and Basal Metabolic Index (BMI) guided estimation of optimal liver volume is required to estimate the liver volume need to be spared during SBRT treatment. Radiation induced liver injury is potentially hazardous complication. There is no definitive treatment and a proportion of patient may land up in gross decompensation. Usually supportive care, diuretics, albumin supplement, and vitamin K replacement may be useful. Better case selection will avert incidence of RILD. Precise imaging, contouring, planning and respecting normal tissue constraints are critical. Radiation delivery with motion management and image guidance will allow delivery of higher dose and spare normal liver and hence will improve response to treatment and reduce RILD.

This paper presents a theoretical study on optimizing the mixing ratios of hydrocarbon blends to be used as refrigerants in existing refrigeration equipment. The primary objective is to maximize the coefficient of performance. The gas blending optimization problem is posed in a multi-objective framework, where the optimization seeks to generate Pareto optimal solutions that span the trade-off frontier between coefficient of performance versus deviation from a desired volumetric refrigeration capacity, while adhering to a maximum compression ratio. Design variables in the optimization are the mass fractions of hydrocarbon gases in the blend. A domain reduction scheme is introduced, which allows for efficient conduction of exhaustive search, with up to three hydrocarbon gases in the blend. While exhaustive search guarantees that the obtained solutions are global optima, the computational resources it requires scale poorly as the number of design variables increase. Two alternative approaches, (multi-start SQP) and (NSGA-II) are also tested for solving the optimization problem. Numerical simulation case studies for replacement of R12, R22 and R134a with hydrocarbon blends of isobutane, propane and propylene show agreement between solution methods that good compromises are possible to achieve, but a small loss in coefficient of performance is inevitable.

Abstract Waterfloods are amongst the most widely implemented methods for oil field development. Despite their vast implementation, operational bottlenecks such as lack of surveillance and optimization tools to guide fast paced decisions render most of these sub-optimal. This paper presents a novel machine-learning, reduced-physics approach to optimize an exceptionally complex off-shore waterflood in the Gulf of Suez. Leveraging a hybrid data-driven and physics approach, the water flooding scheme in Nezzezat reservoir was optimized to improve reservoir voidage replacement, increase oil production, and reduce water production by identifying potential in wells. As a by-product of the study, a better understanding of the complex fault system was also achieved. Including the geological understanding and its uncertainty is one of the key elements that must be preserved. All geological attributes, along with production rates are used to solve for pressure and inter-well communication. This is later supplemented by machine-learning algorithm to solve for the fractional flow of inter-well connections. Combining the inter-well connectivity and fractional flow, an optimization was performed to reach the best possible conditions for oil gains and water-cut reduction. A global optimization is possible thanks to the low computational demand of this approach, as thousands to millions of realizations must be run to reach the best solution while satisfying all constraints. This is all done in a fraction of the time it takes to run a traditional reservoir simulation. For the present case, the paper will present the underlying physics and data-driven algorithms, along with the blind tests performed to validate the results. In addition to the method's inner workings, the paper will focus more on the results to guide operational decisions. This is inclusive of all the complex constraints of an offshore field, as well as the best reservoir management practices, when reaching optimal production and injection rates for each well. An increase in production was achieved with some reduction in water-cut, while honoring well and platform level limitations. While these represent the gains for a particular month, optimization scenarios can be run weekly or monthly to capture the dynamic nature of the problem and any operational limitations that might arise. The ability to update the models and run optimization scenarios effortlessly allows pro-active operational decisions to maximize the value of the asset. The approach followed in this paper solves for the critical physics of the problem and supplements the remaining with machine learning algorithms. This novel and extremely practical approach facilitate the decision making to operate the field optimally.

Abstract Production and Injection rate target optimization plays an important role in waterflooded field management in order to ensure hydrocarbon recovery. In line with ADNOC Digital transformation and waterflood excellence initiatives CRM and Optimization technology has been progressed to maximize opportunities in oil recovery increase. The optimization means that producing well delivers a maximum amount of oil with minimal water production along with maintaining proper Voidage Replacement Ratio (VRR) to support reservoir pressure. To reach such goal, the optimization procedure needs to run multiple rate scenarios to calculate the objective function value. The conventional way is to perform multiple runs on simulation model, which can be very time-consuming. The data driven approach described in this paper suggests faster and convenient methodology to solve this problem. The process applied to this approach consists of data preparation/ data cleansing stage, CRM (Capacitance Resistance Model) and optimization procedure based on the objective function with a penalty to imbalanced VRR at the pattern level. The CRM algorithm can calculate fraction of injection distributed from each injecting well to connected producing wells at any timestep. These calculated injection allocation factors are considered in the rate optimization procedure in order to define optimal injection and production rates along with balancing of VRR at the pattern level. The method also considers 3-phase flow across wells and reservoir intervals. The objective function calculates overall profit from oil production, costs for water and gas handling, and the penalty for the production injection difference at the producing well level. At the end, the output of this optimization process is to recommend production and injection rates targets for each well and short term forecast of the production based on fractional flow model. The data driven approach shows quite good efficiency in terms of time and efforts, the injection allocation factors based on CRM model are comparatively same as it is calculated in streamline simulation model but with better granularity at the pattern level. The optimization procedure works quite fast, and the results have shown decrease of water production rate and increase of recovery factor due to maintaining VRR close to the target level. The data driven approach described in the paper implements a new way to apply CRM in fields with waterflooding and gas injection with the enhancement of managing 3-phase flow. The in-house developed optimization function and its implementation is a novel approach in terms of practical application to the fields in Abu Dhabi area.

Abstract Westinghouse has recently completed the evaluation and optimization of nuclear fuel cycles for both 18-month (520 EFPD) and 24-month (700 EFPD) fuel cycle lengths in high power density Westinghouse plants with 17 × 17 fuel, including enrichments and burnup above the current licensed limits. Westinghouse has developed a comprehensive levelized cost of electricity (LCOE) methodology to compare the different fuel cycle and plant operational scenarios on an equivalent net present value basis. This method realistically accounts for the expenses related to fuel procurement, manufacturing, in-core utilization and disposal as well as the plant operational aspects of outage cost and site staffing, capital expense, construction recovery, major modifications, uprates and load follow. The resulting LCOE gives a single figure merit allowing comparison of scenarios on a consistent basis to evaluate potential economic benefits of various fuel and plant operational options. These options include the use of Intermediate Enriched Uranium (IEU), various fuel cycle lengths, pre-operational interest, incore carrying charges, used fuel storage, used fuel disposal, plant operations, plant capitalization, maintenance, outages, replacement power, generation revenue, capital improvement, licensing transition costs, uranium transition costs and others are explicitly accounted and discounted back to a common reference time irrespective of the fuel cycle length or plant design options with higher 235U enrichment and discharge burnup than the current prevalent fuel designs. Where appropriate, assumptions have also been made to incorporate reactor operational and other cost aspects. This paper presents the methodology used to evaluate the LCOE of a power reactor that is independent of the reactor design and applies that methodology to sample fuel management cases of arbitrary fuel cycle length. These evaluations make a number of conclusions that are dependent on the power density of the plant. In general, many nuclear power plants operating within reasonable US cost models are generally at minimum LCOE when operated on 24-month cycles within the current licensing regime of peak rod burnup &lt; 62 GWD/TU and fuel enrichment &lt; 5 w/o 235U, hereafter referred to as “LEU”. The exception to this conclusion comes for the high-power density 17 × 17 Westinghouse units where the current licensing regime of 18-month LEU fuel cycles results in minimum LCOE thereby making cycle length extension to 24 month cycles economically unattractive with the current fuel products. The reason is that these Westinghouse plants, when operating on 24-month cycles, require feed batch fractions well above 50% of the core loading resulting in low fuel utilization and steep fuel cycle cost penalties that cannot be compensated by operating cost savings or additional generation revenue arising from 24-month cycle operation. Westinghouse has explored scenarios where the current licensing regime restrictions on enrichment and burnup are removed and has found that, when Intermediate Enriched Uranium (IEU) (5 w/o 235U &lt; IEU &lt; 20 w/o 235U) and high burnup (HBU) in which lead rod burnup in the range of 75 GWD/TU are allowed, the optimal cycle length for these Westinghouse plants changes from 18-months to 24-months. This conclusion holds true over a wide range of input economic assumptions. Westinghouse has also evaluated 18-month cycles for Westinghouse units using current enrichment and burnup licensing paradigm and for the case where IEU is enabled and HBU is licensed. Westinghouse concludes that the IEU and HBU for 18-month cycle option for Westinghouse units results in a significant penalty when compared to both the 24-month HBU, which is the most economical, and the 18-month cycle under the LEU paradigm.