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The problem of on‐line optimization of a model IV fluidized catalytic cracking (FCC) unit is analyzed. The “process” was modeled by combining a model IV FCC unit dynamic simulator (McFarlane et al, 1993; Khandalekar, 1993) with a ten‐lump yield model (Jacob et al, 1976; Arbel et al., 1995) for the reactor section. The steady‐state optimization model consisted of macroscopic steady‐state models of the regenerator and reactor, a simplified reactor yield model, and models of the various process constraints. The steady‐state optimization problem was solved using successive quadratic programming software (NPSOL, Gill et al., 1986) and the optimum process set points were implemented on the process simulator using a nonlinear constraint controller (Kandalekar and Riggs, 1995). The relative performance of constraint control, off‐line optimization, and on‐line optimization is compared for different feed characteristics and product pricing structures.

Modeling and optimization of a semiregenerative catalytic naphtha reformer has been carried out considering most of its key constituent units. A detailed kinetic scheme involving 35 pseudocomponents connected by a network of 36 reactions in the C5–C10 range was modeled using Hougen‐Watson Langmuir‐Hinshelwood‐type reaction‐rate expressions. Deactivation of the catalyst was modeled by including the corresponding equations for coking kinetics. The overall kinetic model was parameterized by bench‐marking against industrial plant data using a feed‐characterization procedure developed to infer the composition of the chemical species in the feed and reformate from their measured ASTM distillation data. For the initial optimization studies, a constant reactor inlet temperature configuration that would lead to optimum operation over the entire catalyst life cycle was identified. The analysis was extended to study the time‐optimal control profiles of decision variables over the run length. In addition, the constant octane case was also studied. The improvement in the objective function achieved in each case was determined. Finally, the sensitivity of the optimal results to uncertainty in reactor‐model parameters was evaluated.

This paper is an evidence based study of freshman engineering based on a number of interview with course coordinators as well as a theoretical analysis of the problems. The one common denominator for freshman engineering courses is that they are all different. They range from a single class taught by single professor in an engineering department to 2000 to 3000 students from an engineering college broken into a number of very large sections each year. The emphasis of these classes ranges from teaching a programming language to teaching design using a team environment to engineering analysis. Many times programming languages are a primary emphasis of these courses with a single platform or a combination of platforms being taught, including MATLAB, C, C++, Fortran, Excel, visual basic, Java and Python. There is clearly no consensus on what or how freshman should be taught. By examining the goals of these courses we can better understand how the current state evolved and where we can go from here. The goals of these course in general involve preparing the freshman student for the remainder of their academic and professional career and take the form of teaching students what engineering really is and why it is important to society, how to work in teams, how to implement design, how to program a computer, how to solve engineering equations, how to solve problems and how to develop models. While these are noble goals, most students fail to understand the significance of what they have been exposed to and how it relates to the courses that they will be taking in their sophomore, junior and senior years. Moreover, the emphasis of these courses can distort the student’s perspective of what engineering is, e.g., many times the students that take classes that primarily emphasize design leave these classes thinking that design is the primary activity that engineers perform regardless of the type of engineer. To the professor that understands the full extent of design, the design experiences in these classes are perfectly logical, but the uninitiated student lacks the overall perspective to appreciate what they have been exposed to. Based on this perspective, we will examine the full range of engineering fundamentals (i.e., ethics, problem solving, modeling, analysis, design, economics and communications) in an effort to layout an approach that prepares freshman students for their future careers in a manner that is consistent with their current knowledge and experience. That is, in a general sense engineering reduces to either engineering analysis or engineering design both of which rely on problem solving and modeling. Engineering economics provides a means to consistently evaluate the performance of an engineering project by using optimization while engineering communications allows for the effective dissimilation of the engineer’s results. Finally, engineering ethics provides a means for navigating complex legal, social and ethical issues. Moreover, we will demonstrate how this approach can be applied and still expose the student to teamwork, design, programming, etc. This approach provides a simple, but powerful structure with which to understand engineering and its practice. In this manner, the student will be able to understand how each class that they take in the future relates to their overall goal of becoming a successful engineer and after they graduate and become practicing engineers, they can continue to effectively use this structure to build they base of knowledge.

Manifolds collect or disperse flows and are characterized as dividing, combining, reverse, or parallel. The engineer's objective is to make the flows approximately the same through all the branches without excessive capital cost or wasteful pressure drops. In presenting a more direct procedure for designing a manifold, it is assumed that: 1. the manifold headers and laterals are cylindrical pipe of constant cross section, 2. the fluids are incompressible, and 3. the flow is turbulent. The pressure drop in the header, due to frictional losses and the pressure changes in the header due to pressure recovery are the 2 factors primarily controlling flow distribution in a manifold. Pressure recovery is the result of a drop in flow velocity in the header. In a dividing manifold, not all of the momentum is converted into static pressure due to the fact that some of it is carried into the laterals. Taking this into account is the momentum correction factor, 0.

[This corrects the article DOI: 10.1371/journal.pone.0329874.].

In the United States, taper and discontinuation of opioids prescribed for long-term pain have emerged as statistical correlates of suicidal events. Suicide is a complex and multidetermined event reflecting a combination of risks occurring over time in a particular narrative context. Prevention of suicides should be informed by a detailed understanding of life events, pain-related and other risk factors contributing to these tragedies. To date, there have been no efforts to qualitatively profile these suicides through interview of bereaved survivors or review of medical records. This method is usually termed \"psychological autopsy.\". This paper summarizes the protocol for the Clinical Context of Suicide Following Opioid Transitions (CSI:OPIOIDs) study. The study seeks to qualitatively characterize patient and clinical context factors associated with suicide among persons who died by suicide in the context of opioid stoppage or reduction, and to compare findings between Veteran and non-Veteran decedents. In the United States, there is no master list for suicide deaths linked to an antemortem health care event. For this reason, recruitment requires public advertising followed by screening of bereaved individuals who wish to participate. Data collection and interpretation are guided by the Social-Ecological Model for suicide. The study involves a collaboration of persons with lived experience and disciplinary experts in suicide, primary care, pain, health services, and medical anthropology. This study aims to deliver the first in-depth analysis of suicide events occurring in persons with chronic pain who died by suicide in the context of a prescription opioid reduction or stoppage. The results should provide insights that can guide alterations to care by health systems and by individual practitioners.

There is a lack of data for how the viability of biological agents may degrade over time in different environments. In this study, experiments were conducted to determine the persistence of Bacillus anthracis and Bacillus subtilis spores on outdoor materials with and without exposure to simulated sunlight, using ultraviolet (UV)-A/B radiation. Spores were inoculated onto glass, wood, concrete, and topsoil and recovered after periods of 2, 14, 28, and 56 days. Recovery and inactivation kinetics for the two species were assessed for each surface material and UV exposure condition. Results suggest that with exposure to UV, decay of spore viability for both Bacillus species occurs in two phases, with an initial rapid decay, followed by a slower inactivation period. The exception was with topsoil, in which there was minimal loss of spore viability in soil over 56 days, with or without UV exposure. The greatest loss in viable spore recovery occurred on glass with UV exposure, with nearly a four log10 reduction after just two days. In most cases, B. subtilis had a slower rate of decay than B. anthracis, although less B. subtilis was recovered initially.

The paralogous iron-responsive transcription factors Aft1 and Aft2 (a̱activators of f̱errous ṯransport) regulate iron homeostasis in Saccharomyces cerevisiae by activating expression of iron-uptake and -transport genes when intracellular iron is low. We present the previously unidentified crystal structure of Aft2 bound to DNA that reveals the mechanism of DNA recognition via specific interactions of the iron-responsive element with a Zn2+-containing WRKY-GCM1 domain in Aft2. We also show that two Aft2 monomers bind a [2Fe-2S] cluster (or Fe2+) through a Cys-Asp-Cys motif, leading to dimerization of Aft2 and decreased DNA-binding affinity. Furthermore, we demonstrate that the [2Fe-2S]-bridged heterodimer formed between glutaredoxin-3 and the BolA-like protein Fe repressor of activation-2 transfers a [2Fe-2S] cluster to Aft2 that facilitates Aft2 dimerization. Previous in vivo findings strongly support the [2Fe-2S] cluster-induced dimerization model; however, given the available evidence, Fe2+-induced Aft2 dimerization cannot be completely ruled out as an alternative Aft2 inhibition mechanism. Taken together, these data provide insight into the molecular mechanism for iron-dependent transcriptional regulation of Aft2 and highlight the key role of Fe-S clusters as cellular iron signals.