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Partial physeal bars may develop after injury to the growth plate in children, eventually leading to disturbance of normal growth. Clinical presentation, age of the patient, and the anticipated growth will dictate the best treatment strategy. The ideal treatment for a partial physeal bar is complete excision to allow growth resumption by the remaining healthy physis. There are countless surgical options, some technically challenging, that must be weighted according to each case’s particularities. We reviewed the current literature on physeal bars while reporting the challenging case of a short stature child submitted to a femoral physeal bar endoscopic-assisted resection with successful growth resumption. This case dares surgeons to consider all options when treating limb length discrepancy, such as the endoscopic-assisted resection which might offer successful results.

Perilunate injuries are complex and rare lesions with circumferential carpal bones, ligamentous and cartilage involvement. Despite optimal surgical treatment, poor prognosis is expected and usually gets worse over time. Our aim was to address clinical and radiological outcomes after 2 years of follow-up. Seven wrists were revised with average age of 35.59 ± 14.01 (range 21–56) years old and mean follow-up of 44.10 ± 14.24 (range 25.60–68.63) months. At the latest follow-up, mean postoperative VAS score for pain was 2.71 ± 3.40 and DASH score was 10.48 ± 10.54. Patients returned to work in 5.00 ± 3.15 months. Strength and Range of Motion (ROM) parameters were ∼80% of the contralateral side, with exception for extension (61%) and radial deviation (73%). After 2 years of follow-up, radiographic arthrosis was observed in 29% of the cases. One of these patients was symptomatic and was proposed for arthrodesis. Mean carpal height was 1.51 ± 0.81 and scapholunate angle was 41.58 ± 22.82°. A correlation was observed between arthritis found at final follow-up and grip (r = −0.8660; p

Foreign bodies in the external ear are very common. The same cannot be said about foreign bodies in the Eustachian tube (ET). We report the case of a 63-year-old woman with a history of painless left side otorrhea and hearing loss. She reported a left ear surgery when she was 30-year-old but she did not know the diagnosis that was made at that time neither the kind of surgery performed. Otoscopic examination revealed an inferior perforation of the eardrum. Audiologic evaluation demonstrated a unilateral, moderate-severe mixed hearing loss. Computed tomography scan showed, in left ear, a soft tissue density filling the middle ear cavity and a foreign body in ET. The patient underwent middle ear exploration which required endoscopic assistance to visualize and remove the foreign body. It appeared to be a stapes prothesis of Robinson type. The displacement of a stapes prosthesis to the ET has not been reported in the literature. Surgeries in this region are challenging. This case highlights the importance of the integration of endoscopy into otologic surgery.

Introduction: Central venous stenosis can be the main obstacle to the creation of an autologous vascular access in the upper limbs. The Hemodialysis Reliable Outflow graft was developed to provide an upper limb vascular access option to such patients, avoiding alternative, less advantageous options, such as lower limb vascular accesses or central venous catheters. Its advantages include catheter avoidance and, in case of lower limbs accesses, reduction of the ischemic risk and iliac vein thrombosis, potentially compromising a future kidney transplant. Patients and methods: Revision of the clinical files of the four patients who were placed a Hemodialysis Reliable Outflow device in our Center, including demographic variables, implantation technique characteristics, surgical complications, episodes of infection and thrombosis of the access, and need to place a transitory central venous catheter to undergo hemodialysis treatment. Results: Four Hemodialysis Reliable Outflow grafts were placed, which resulted in a significant improvement in the dialysis efficacy in all patients, with a median raise in the Kt/V of 36.7%. Two cases needed thrombectomy, one of which was unsuccessful. The actual time of patency varies between 3 and 28 months. Conclusion: Our experience with the Hemodialysis Reliable Outflow device showed that it was a safe option for patients with central venous stenosis and was associated with good clinical and analytic outcomes.

Atypical hemolytic uremic syndrome (aHUS) is one of the most challenging diseases for a nephrologist, with high rates of progression to end- -stage kidney disease (ESKD) and post-transplant recurrence. Complement dysregulation has been found in up to 70% of cases, which can be hereditary or acquired. Over the last few years, knowledge of the pathogenesis of aHUS has greatly increased, with the unravelling of the complement’s role, providing not only the chance for individualized post-transplant recurrence risk assessment, but also the possibility of a highly effective treatment through pharmacological C5-9 blockade with eculizumab. The overall outcome and prognosis of patients with aHUS has dramatically improved since the approval of this drug in 2011, allowing renal transplant to be a much safer option for these patients. Our aim was to present a proposal for the management of patients with aHUS, candidates for renal transplantation, in the light of the most recent studies.

The optimal design of experiments for the parameters of the differential equations arising in many kinetic and pharmacodynamic models requires the numerical maximization of a function of the numerical solutions of sets of differential equations, the solutions depending on the experimental design. This problem in the design of experiments is solved as a dynamic optimization problem, using a simultaneous approach. The time horizon of the experiments is discretized in finite elements and orthogonal collocation on finite elements is used to parameterize the solution. The solution in each finite element is described by cubic Lagrange polynomials and the control action is represented by piecewise constant polynomials. We find D-optimum designs for two- and three-compartment models with Michaelis–Menten elimination rate kinetics. We consider three different design problems including both dynamic and static experiments. Single- and multi-experiment designs are addressed. Importantly, our algorithm allows the calculation of designs with constraints not only on the design region but also on the concentrations of the components in the compartments and on the rates of change of the design variables and of the resulting concentrations.

The linear time invariant state–space model representation is common to systems from several areas ranging from engineering to biochemistry. We address the problem of systematic optimal experimental design for this class of model. We consider two distinct scenarios: (i) steady-state model representations and (ii) dynamic models described by discrete-time representations. We use our approach to construct locally D–optimal designs by incorporating the calculation of the determinant of the Fisher Information Matrix and the parametric sensitivity computation in a Nonlinear Programming formulation. A global optimization solver handles the resulting numerical problem. The Fisher Information Matrix at convergence is used to determine model identifiability. We apply the methodology proposed to find approximate and exact optimal experimental designs for static and dynamic experiments for models representing a biochemical reaction network where the experimental purpose is to estimate kinetic constants.

In this paper we propose a framework for Model-based Sequential Optimal Design of Experiments to assist experimenters involved in Vapor-Liquid equilibrium characterization studies to systematically construct thermodynamically consistent models. The approach uses an initial continuous optimal design obtained via semidefinite programming, and then iterates between two stages (i) model fitting using the information available; and (ii) identification of the next experiment, so that the information content in data is maximized. The procedure stops when the number of experiments reaches the maximum for the experimental program or the dissimilarity between the parameter estimates during two consecutive iterations is below a given threshold. This methodology is exemplified with the D-optimal design of isobaric experiments, for characterizing binary mixtures using the NRTL and UNIQUAC thermodynamic models for liquid phase. Significant reductions of the confidence regions for the parameters are achieved compared with experimental plans where the observations are uniformly distributed over the domain.

Explicit models representing the response variables as functions of the control variables are standard in virtually all scientific fields. For these models, there is a vast literature on the optimal design of experiments (ODoE) to provide good estimates of the parameters with the use of minimal resources. Contrarily, the ODoE for implicit models is more complex and has not been systematically addressed. Nevertheless, there are practical examples where the models relating the response variables, the parameters and the factors are implicit or hardly convertible into an explicit form. We propose a general formulation for developing the theory of the ODoE for implicit algebraic models to specifically find continuous local designs. The treatment relies on converting the ODoE problem into an optimization problem of the nonlinear programming (NLP) class which includes the construction of the parameter sensitivities and the Cholesky decomposition of the Fisher information matrix. The NLP problem generated has multiple local optima, and we use global solvers, combined with an equivalence theorem from the theory of ODoE, to ensure the global optimality of our continuous optimal designs. We consider D- and A-optimality criteria and apply the approach to five examples of practical interest in chemistry and thermodynamics. Supplementary materials for this article are available online.

Background and Aims Arteriovenous fistula is the optimal vascular access for hemodialysis as it has the best long-term patency rate and the lowest complication rate among hemodialysis vascular accesses. However, its occasional delayed maturation poses a challenge. Surgery has been advocated as the best treatment option. We proposed to evaluate the results of endovascular approach of arteriovenous fistula’s maturation delay in our hospital. Method We conducted a retrospective study, selecting patients referenced to our diagnostic and therapeutic angiography unit due to arteriovenous fistula delayed maturation, between April 2017 and October 2019. Physical examination and echography were used to confirm arteriovenous fistula delayed maturation. Results Thirty patients were referenced. Nine were excluded as maturation delay was not confirmed. Three patients were excluded due to extensive outflow stenosis since they were proposed to new vascular access creation. The other 18 patients were subjected to percutaneous endovascular treatment. Mean patient’s age was 65 years old. Twelve patients (66,7%) had forearm fistulas and the remaining (33,3%) had arm fistulas. Fourteen patients (77,7%) had maturation delay due to peri-anastomotic stenosis. The mean follow-up time was 14 months, (minimum - 3 months; maximum - 33 months). Seventeen fistulas (94,4%) were salvaged, although 3 (16,7%) needed a second intervention. Primary and secondary patencies at 3, 6 and 12 months were 77,8% vs. 94,4%, 69,2% vs. 92,3% and 75% vs. 100%, respectively. Arm fistulas had 83,3% of primary and secondary patencies. Forearm fistula’s primary and secondary patencies were 66,7% vs. 91,6%, 57,1% vs. 100% and 60% vs. 100%, at 3, 6 and 12 months, respectively. When maturation failure was due to peri-anastomotic stenosis, primary and secondary patencies were 71,4% vs. 92,9%, 66,7% vs. 100% and 66,7% vs. 100% at 3, 6 and 12 months, respectively. Conclusion Even though we are still lacking consensus about the best treatment option for fistula’s maturation delay, current guidelines suggest that, at least in delayed maturation due to peri-anastomotic stenosis, surgery may be the best treatment. Our results point out that endovascular treatment is a good treatment option for arteriovenous fistulas with maturation delay, mainly in the arm fistulas. Even though surgical treatment appears to have better primary patency, a step by step approach seems to be a valid approach, as our secondary patency shows.

This study addresses the glyceride transesterification (TE) kinetics, a crucial step in biodiesel production from vegetable oils. An nth order reversible model is considered to describe the TE reaction rate, using experimental data gathered from different authors for a broad range of conditions. An incremental model-building strategy is used, consisting of the following sequence of steps: (a) structural identifiability analysis; (b) outliers detection using a robust M-estimator; (c) parameter estimation and subsequent construction of the respective confidence intervals; and (d) practical identifiability analysis. The methodology is applied to the glyceride TE reaction with sodium methoxide as catalyst, using a data set comprising 144 points collected from literature, and comparing the results for a five (5P) and a six (6P) parameters’ model. Although the results show that both kinetic models are structurally nonidentifiable, the former is practically identifiable for the case study analyzed. Furthermore, ...

Mixture models of the Scheffe polynomial class are standard in several scientific fields. For these models there is a vast literature on the optimal design of experiments to provide good estimates of the parameters with the use of minimal resources. Contrarily, the optimal design of experiments for general blending models, extending the class of Becker, have not been systematically addressed. Nevertheless, there are practical examples where the models relating the response variables, the parameters and the factors including nonlinear blending effects fall into a general form. We propose a general formulation to find continuous and exact D– and A–optimal designs for general blending models. First, we consider designs to estimate the regression coefficients, and then extend the formulations to find locally optimal continuous designs for estimating both the coefficients and the power exponents. The treatment relies on converting the Optimal Experimental Design (OED) problem into an optimization problem of the Nonlinear Programming (or Mixed Integer Nonlinear Programming) class. We apply this approach to quadratic and special cubic general blending models of the H2 class of polynomials introduced by Becker, and to three examples of practical interest in combustion science and in the characterization of fuel properties.

Soybean is currently recognized as a high value crop, allowing the manufacture of a broad range of products. This contribution investigates the synergies resulting from coupling the production of biodiesel with soybean processing facilities, defining the core structure of a soy-based biorefinery. Simulations in Aspen Plus® were performed, employing a detailed modeling framework. A base case scenario was established, allowing a detailed economic assessment of the process, a profitability and risk analysis, as well as the identification of plant integration opportunities. Increased process integration leads to an 18% decrease of the biodiesel production costs, corresponding to a 9% reduction of the break-even price (from 875 to 798 $/t of biodiesel). This is accompanied by an overall decrease of hot and cold utilities consumption of 20%, with a heat exchanger network that performs closely to the energy recovery targets determined through pinch technology. The need for fresh water in biodiesel production is also completely eliminated and the generation of wastewater is mitigated by 9%. The risk analysis, carried out through Monte Carlo simulations, shows that the new plant configuration becomes more robust to variations in the key economic factors considered.

•Modelling and design of reactive distillation systems.•Economic evaluation of reactive distillation systems.•Comparison of conventional and RD-based processes for the production of ethyl tert-butyl ether.

Liquid&ndash, liquid equilibria (LLE) characterization is a task requiring considerable work and appreciable financial resources. Notable savings in time and effort can be achieved when the experimental plans use the methods of the optimal design of experiments that maximize the information obtained. To achieve this goal, a systematic optimization formulation based on Semidefinite Programming is proposed for finding optimal experimental designs for LLE studies carried out at constant pressure and temperature. The non-random two-liquid (NRTL) model is employed to represent species equilibria in both phases. This model, combined with mass balance relationships, provides a means of computing the sensitivities of the measurements to the parameters. To design the experiment, these sensitivities are calculated for a grid of candidate experiments in which initial mixture compositions are varied. The optimal design is found by maximizing criteria based on the Fisher Information Matrix (FIM). Three optimality criteria (D-, A- and E-optimal) are exemplified. The approach is demonstrated for two ternary systems where different sets of parameters are to be estimated.

A 72-year-old woman was admitted to the hospital because of dorsal, lumbar and lower abdomen pain that had started 4 days before. She had a history of age-related macular degeneration (treated with intraocular bevacizumab). Blood tests showed anaemia, thrombocytopaenia, acute kidney injury, elevated liver enzymes and total bilirubin (mainly because of the indirect fraction). Viral serologies and ADAMTS13 activity levels were normal, and stool testing was negative for Escherichia coli-producing Shiga toxins. E. coli was isolated in urine. Atypical haemolytic uremic syndrome triggered by a urinary tract infection or by the vascular endothelial growth factor-inhibitor bevacizumab were the most likely hypothesis. The patient started urgent plasmapheresis and dialysis that lasted for a total of 18 days. There was complete remission and recovery of kidney function allowing for treatment discontinuation, and she was discharged home. After 6 months of follow-up, she shows no signs of relapse.

Spontaneous umbilical cord haematoma (SUCH) is a rare complication of delivery, associated with high mortality and causing fetal distress and stillbirth. Perinatal loss rate is about 50% and its incidence in live births is approximately one in 11 000 pregnancies.[1][1] It occurs from the rupture

Introduction: Vascular access for hemodialysis is a key factor in every patient dependent on this treatment. Maintaining a central venous catheter can be a good choice when all the other options have been exhausted, but unwanted and rare complications may arise from longer catheter dwell time. Case report: We describe a case of a 65-year-old woman undergoing hemodialysis treatment since 1986 after a bilateral nephrectomy due to complicated nephrolithiasis. Her last access, two Tesio® tunneled cuffed catheters implanted via the right internal jugular vein functioned correctly for 14 years without complications, and so, was not replaced in the meantime. She was referred to our hospital due to a rupture in a catheter lumen, which was corrected conservatively by creating a more proximal tunnel and excising the affected area. A few weeks later, a new rupture in the same lumen was identified, so the catheter was replaced with angiographic control. The catheter was frail, so upon its removal, the tip fractured and remained in the right ventricle, being swiftly removed by an endovascular snare without complications. Discussion: This case reports two rare complications associated with catheter handling and identifies a possible technique for conservative resolution of a lumen rupture.

The synthesis of hydrogen distribution networks has been an active area of research over the last two decades. The concept of hydrogen management based on an economic cost-driven analysis appeared late in the 1990s and was followed up by numerous insight-based and mathematical optimisation approaches in the 2000s. More recently, several superstructure-based optimisation methods have been proposed to accommodate pressure restrictions, additional equipment and other practical constraints when finding the optimal flowsheet configuration. This paper provides a state-of-the-art review of different process integration technologies adopted for the assessment of hydrogen resources in refineries and petrochemical plants, published from late in the 1990s to the present time. Both targeting and design methods are reviewed. An effective hydrogen management strategy can only be achieved by combining different insight-based approaches with detailed mathematical programming.

Staphylococcus aureus is a troublesome pathogen, responsible for a broad range of clinical manifestations, ranging from benign skin infections to life-threatening conditions such as endocarditis and osteomyelitis. The kidney can be affected through a rapidly progressive glomerulonephritis mediated by an inflammatory reaction against a superantigen deposited in the glomerulus during the infection’s course. This glomerulopathy has a poor prognosis, often leading to chronically impaired kidney function, eventually progressing to end-stage renal disease. Treatment rests on antibiotherapy. Despite the inflammatory role in this disease’s pathophysiology, most authors discourage a simultaneous immunosuppressive approach given the concomitant infection. However, there are some reports of success after administration of systemic corticosteroids in these patients. We present a 66-year-old man with a staphylococcus-induced glomerulonephritis brought on by a vascular graft infection, with rapidly deteriorating kidney function despite extraction of the infected graft and 3 weeks of antibiotherapy with achievement of infection control. Kidney function improved after the introduction of corticosteroids. This case highlights the potential role of corticosteroids in selected cases of staphylococcus-induced glomerulonephritis, particularly those in which the infection is under control.

This work addresses the production of gasohol using gasoline as a separation agent, an alternative approach to processes that recover and dehydrate ethanol before its blending with gasoline. Experimental data was used to build the thermodynamic model used to predict phase equilibrium and thermophysical properties. Two configurations for the direct manufacture of E10 gasohol were analyzed. Process I is extraction-based whereas Process II is extractive distillation-based. The processes were compared with each other in terms of energy needs as well as with a state-of-art process where ethanol dehydration is performed with molecular sieves (Process MS). The results show that Processes I and II are energetically favorable, and consume, after process optimization and heat integration, 30% less heat than Process MS, for ethanol concentrations in fermentation broths between 2 and 10 wt%. Furthermore, estimated ethanol separation costs are approximately $0.19/kg-ethanol for a 5 wt% feed.

Superior semicircular canal dehiscence is caused by a bone defect on the roof of the superior semicircular canal. The estimated prevalence when unilateral varies between 0.4% and 0.7% and is still unknown when bilateral. Patients may present with audiologic and vestibular symptoms that may vary from asymptomatic to disabling. We report a case of a 72-year-old Caucasian woman presented to otolaryngology department reporting imbalance, bilateral pulsatile tinnitus, hypoacusis while being very sensitive to certain sounds. Physical examination was unremarkable, except for the Rinne test that was negative in both sides. The patient underwent an audiometry revealing a mild bilateral conductive hearing loss. A temporal bone CT scan was performed which evidenced bilateral superior semicircular canal dehiscence. Cervical vestibular evoked myogenic potentials and electrocochleography confirmed diagnosis. Although rare, superior semicircular canal dehiscence shall be considered in conductive hearing loss with vestibular symptoms.

Mulher, de 55 anos, com antecedentes de obesidade mórbida, dislipidemia e diabetes mellitus não insulino-tratada, recorreu ao serviço de urgência por quadro de queixas álgicas e sinais inflamatórios na região perianal direita com uma semana de evolução.

A formulation for quality management programs for discrete time scenarios.A formulation for quality management programs for continuous scenarios.Explicit integration of the uncertainty in the formulations.The optimal improvement policies concentrate the efforts in the initial stages. The problem of determining the optimal improvement programme quality effort in an organization over a given time horizon is posed as a dynamic optimization problem. The advantage of such approach with respect to a static scenario is discussed. The quality level is modeled as a function of the improvement investment, and of the costs of quality accounting for both prevention-appraisal and failure costs. The uncertainty on the quality level and failure cost variables is modeled by Ito processes. Two formulations of the dynamic quality improvement problem are described: one using a discrete time representation of the quality level dynamics and another using a continuous time representation. The application of these strategies is demonstrated by simulation of an illustrative example of a given organization. The optimal improvement policy results indicate the need to invest as soon as possible in order to reduce the failure cost, since it dominates the overall quality cost. Furthermore, the results are consistent with the fact that the improvement effort required is higher for firms with lower efficacy in converting that effort in terms of quality level.

The worldwide increase in biodiesel production has created a major market for sodium methoxide, as a catalyst in the transesterification of vegetable oils. This work evaluates different methods for the manufacture of sodium methoxide, diluted in methanol. Alternative process designs are reviewed, and the most promising solutions are modeled in Aspen Plus, including their phase and chemical equilibria. Economic indicators are incorporated in a comparative profitability analysis that includes a risk evaluation with Monte Carlo simulations. The results show that the methods of manufacturing sodium methoxide from sodium metal (process II) and from sodium hydroxide (process III) are the most competitive alternatives, although each can be preferred in different contexts. Process III has a better chance of profitability (41%) than process II (34%), where the latter can be affected by higher raw-material costs and the first is more sensitive to variations in the utility and capital costs.

In this work, experimental values of gas solubility of hydrofluorocarbons (CHF 3 , CH 2 F 2 and CH 3 F) in three room-temperature ionic liquids (RTILs) were determined within the temperature range 288 K to 308 K and at atmospheric pressure. The RTILs used were trihexyltetradecylphosphonium chloride ([P 6,6,6,14 ][Cl]), tributyl(methyl)phosphonium methylsulfate ([P 4,4,4,1 ][C 1 SO 4 ]), and tributyl(ethyl)phosphonium diethylphosphate ([P 4,4,4,2 ][(C 2 ) 2 PO 4 ]). The data gathered have been modelled using two approaches: the Cubic plus Association equation of state (CPA EoS) and the regular-solution theory (RST). The experimental measurements were then discussed critically and the modelling results compared.

This work addresses the design of reactive distillation columns to produce ETBE, based on a detailed first-principles model that considers equilibrium and kinetic information, rigorous physical property data, and catalyst deactivation. An evolutionary algorithm is used to generate a sequence of feasible designs with improved characteristics in a sequential solution/optimisation strategy, by specifying the design variables (both integer and continuous) that characterise a particular column configuration. Two classes of optimisation algorithms are compared: genetic algorithms and particle swarm optimisation. The objective function considered is the gross annual profit. The results demonstrate that both algorithms are adequate to solve this design problem. The effect of catalyst deactivation included in the design stage played a determinant role in the optimal column specification. A post-design sensitivity analysis is developed to assess the quality of the solutions obtained, together with the individual effects of each design variable in the optimal configuration identified.

This paper describes our experience at the University of Coimbra in introducing discrete optimization topics in an Operations Management (OM) course and how those topics and associated tools are then exploited in subsequent senior courses, namely Process Integration and Intensification, Product Design and Process Design. We believe our methodology in the OM course to be reasonably efficient, providing students with valuable skills in problem formulation and solution. Simultaneously, results relative to the subsequent application in the senior design projects are encouraging, although there is scope for more extensive usage, as the tools to implement these techniques become more effective and widely available.

This work describes the inclusion of energetic constraints in a step-wise methodology to develop kinetic models, spanning all stoichiometric consistent reaction networks. The task of generating reaction networks is formulated as a combinatorial optimization problem, identifying sets of reactions that link all species and allow a consistent flux balance analysis. The Gibbs free energy variations of the system, considered in the entire time domain, is used as the main criterion for selecting feasible candidates. This is illustrated with the α -pinene isothermal liquid isomerization.

This study addresses the glyceride transesterification (TE) kinetics, a crucial step in bio-diesel production from vegetable oils. To overcome common limitations of the existing kinetic models, a n th order reversible model with a broader domain of application is fitted to experimental data gathered from different authors. We consider the glyceride TE employing sodium methoxide (NaOCH 3 ), and use a general four-step model building approach, including (i) structural identifiability analysis; (ii) outlier detection using a robust M-estimator; (iii) parameter estimation (PE) and subsequent construction of the respective confidence intervals; and (iv) practical identifiability analysis. The results show that although the kinetic models with five (5P) and six (6P) parameters are structurally non-identifiable, the former (5P) can be shown to be practically identifiable and fit accurately the data, with an average relative deviation (ARD) of 6.5 %.

The recent environmental restrictions to cut down pollutant gas emissions, along with the increasing drive to process heavy and sour crude oils, and the refining market trends toward gasoline and middle distillate fuels, have led to increased hydrogen demands associated with hydrotreating and hydrocracking processes. This manuscript addresses the synthesis of optimal hydrogen distribution systems bearing in mind both economic and operational issues. The optimal flowsheet configuration is established following a deterministic optimisation approach. One practical case study is provided to highlight the importance of an effective hydrogen management strategy amongst other production planning and scheduling decisions. This work was carried out within an industrial research project in close collaboration with Galp Energia and it is focused on a Petrogal’s refinery located near Sines, Portugal.

We use mathematical programming tools, such as Semidefinite Programming (SDP) and Nonlinear Programming (NLP)-based formulations to find optimal designs for models used in chemistry and chemical engineering. In particular, we employ local design-based setups in linear models and a Bayesian setup in nonlinear models to find optimal designs. In the latter case, Gaussian Quadrature Formulas (GQFs) are used to evaluate the optimality criterion averaged over the prior distribution for the model parameters. Mathematical programming techniques are then applied to solve the optimization problems. Because such methods require the design space be discretized, we also evaluate the impact of the discretization scheme on the generated design. We demonstrate the techniques for finding D-, A- and E-optimal designs using design problems in biochemical engineering and show the method can also be directly applied to tackle additional issues, such as heteroscedasticity in the model. Our results show that the NLP formulation produces highly efficient D-optimal designs but is computationally less efficient than that required for the SDP formulation. The efficiencies of the generated designs from the two methods are generally very close and so we recommend the SDP formulation in practice.

This work considers the development and validation of a first-principles dynamic model for the production of ethyl tert-butyl ether (ETBE) in the presence of the coproducts diisobutene (DIB) and tert-butyl alcohol (TBA). Desulfonation is assumed to be the main deactivation mechanism of the catalyst used, an acidic ion-exchange resin. Operational data from an industrial ETBE production plant, taken over the period of 1 year, were used to estimate both the deactivation and DIB kinetic constant parameters. A data reconciliation strategy was employed to convert the raw data into a consistent data set, representing the most likely process operation data. The parameters estimated were incorporated in a set of detailed mass and energy balances, together with additional kinetic and physical information from the literature, to originate a distributed parameter model capable of accurately describing the operation of two industrial reactors used for the production of ETBE. Model development and validation were perfo...

Two types of deactivation functions are usually employed when modelling catalytic cracking: the time-based models and the coke-on-catalyst models. In this paper, a comparison is made between these two types of deactivation functions in the simulation of an industrial UOP fluid catalytic cracking (FCC) unit with high-efficiency regenerator. For this purpose, a FCC mathematical dynamic model, previously presented and validated, is used. The dynamic responses to perturbations of +10% increase in the combustor air mass flowrate and +5% in the feedstock flow, were studied. The results for these perturbations show that the slight differences observed were due to the fact that the coke-on-catalyst approach takes into account the coke content present at the riser inlet.

This paper focuses on the fluid catalytic cracking (FCC) process and reviews recent developments in its modeling, monitoring, control, and optimization. This challenging process exhibits complex behavior, requiring detailed models to express the nonlinear effects and extensive interactions between input and control variables that are observed in industrial practice. The FCC models currently available differ enormously in terms of their scope, level of detail, modeling hypothesis, and solution approaches used. Nevertheless, significant benefits from their effective use in various routine tasks are starting to be widely recognized by the industry. To help improve the existing modeling approaches, this review describes and compares the different mathematical frameworks that have been applied in the modeling, simulation, control, and optimization of this key downstream unit. Given the effects that perturbations in the feedstock quality and other unit disturbances might have, especially when associated with fr...

The need to develop the capacity for autonomous and critical thinking in students and introduce practical approaches that complement the scientific background, have been acting as driving-forces that motivate engineering educators to develop new teaching methodologies. The Chemical Engineering Departments of both the Universities of Coimbra and Porto have been experimenting in this area and addressing these concerns. Recently, they have been engaged in a broader project, involving a large group of academics with complementary competencies. This project is aimed at developing a virtual platform directed towards the learning of Chemical Processes with a wide scope. From the functional point of view the platform is organized into four main areas: Chemical Engineering, Chemical Processes, Virtual Experiments and Simulators. The Chemical Processes area is further divided into four different sections: Unit Operations and Separations, Chemical Reaction, Process Systems Engineering and Biological Processes. These sections include simulators, applications and case studies to better understand the chemical/biochemical processes. The Virtual Experiments area considers both the laboratory visualization of the basic phenomena related to the processes in the other four sections, and the remote monitoring of laboratory experiments. This platform, constructed around a dynamic Web Portal, allows discussion forums and is also aimed at sharing experiences with other schools. This paper describes the different subjects included in the web platform, as well as the simulation strategies and the web methodologies used for its construction, and also presents examples of application in the classroom.

Introducao: A proteinuria e um achado laboratorial comum em adultos assintomaticos, que em circunstância alguma deve ser menosprezado. A utilizacao de tiras teste e o metodo mais utilizado na deteccao da proteinuria, mas, como apresenta uma elevada taxa de falsos positivos, impoe-se a utilizacao de outros metodos na sua confirmacao/monitorizacao. Objectivos: Efectuar uma revisao dos principais mecanismos fisiopatologicos de proteinuria e dos metodos actualmente utilizados na sua deteccao e quantificacao. Discutir a sua importância clinica e apresentar um possivel protocolo de abordagem diagnostica. Rever as terapeuticas especificas disponiveis, principalmente no contexto da Doenca Renal Cronica (DRC). Metodologia: Foi realizada uma pesquisa na Pubmed de artigos originais, de artigos de revisao e de meta-analises ate Abril de 2007 e foram consultadas fontes documentais de referencia, nas areas da Nefrologia e da Medicina Interna. Foram ao todo incluidos 63 artigos. Conclusoes: A utilizacao de um algoritmo diagnostico ajuda na distincao entre as causas benignas (doenca febril, exercicio fisico, desidratacao...) de outras causas menos frequentes, mas mais graves (glomerulopatias, gamapatias monoclonais...). A presenca de proteinuria deve ser confirmada obrigando a estudo complementar, nomeadamente com analises quantitativas (proteinuria das 24 horas ou razao proteina/creatinina em amostra aleatoria de urina). Os doentes com proteinuria persistente e cuja causa para a mesma nao se identifica apos investigacao clinica, devem referenciados a consulta de Nefrologia. Nos doentes renais cronicos, a deteccao e o tratamento precoces da proteinuria melhoram o prognostico a curto e a longo prazo. Considerando o aumento da prevalencia da DRC na populacao geral, o Medico de Familia tem um papel preponderante na identificacao dos individuos em risco de doenca renal e na vigilância dos factores de risco a ela associados, designadamente da proteinuria.

In the context of the application of systematic methodologies for the incremental development of mechanistic kinetic models, various regularization techniques have been explored to allow the estimation of rate phenomena as the derivatives of sparse data sets. Through a combination of a numerical approach with aspects of qualitative analysis, this work proposes a novel method to obtain smoothed concentration profiles that allow their reliable differentiation. Two different case studies are considered to illustrate the performance of the method.

Hydrogen management practices in the petroleum industry aim at maximising refining gross margins while addressing environmental and production planning issues. A novel pinch analysis software tool – H2TT – establishes targets for the minimum hydrogen utility consumption prior to detailed network design. H2TT is an interactive spreadsheet-based software programmed in Visual Basic for Applications that analyses the potential for reusing hydrogen across the refinery based on pinch analysis principles. This software identifies the existence of bottlenecks in the hydrogen distribution system and gives valuable insights into the appropriate placement of additional purification units within the hydrogen network. Moreover, it can be used to assess the availability of hydrogen at different purity levels. One example is provided to illustrate the applicability of H2TT for the integration hydrogen resources in refineries and petrochemical plants. This work was carried out within an industrial research project in close collaboration with Galp Energia and is focused on a Petrogal refinery located near Sines, Portugal.

This paper addresses the nitrogen oxides absorption process in nitric acid plants. A mechanistic model is developed for this gas-liquid reactive absorption system, able to predict the unit behaviour and support its optimization during regular and transient operating regimes. A rigorous rate-based model was adopted, and a new modelling strategy is proposed to assure the compatibility of mass transfer limitations and equilibrium kinetics. The model has the form of a DAE system, and is solved with an algebraic solver combined with an integration algorithm. This study was focused on the analysis of the unit steady state. The acid strength through the whole column was analysed and a good agreement with industrial data is observed.

The possibility of existence of multiple steady states in fluid catalytic cracking (FCC) units has a major impact in the supervision of these systems. The origins of these behaviours are usually due to the exothermicity of the catalyst regeneration reactions and to the strong interactions between the reactor and the regenerator system. Prior work has focused on modelling and control problems of different operating FCC units. However, none of these studies have considered a high-efficiency regenerator. This paper presents an analysis of the existence of output and input multiple steady states in an UOP FCC unit with a high-efficiency regenerator. The influence of unit disturbances and model uncertainties, such as coke composition and cracking enthalpy, in the output multiplicity, was studied and the results show that the high-efficiency regenerator exhibits at least three multiple output steady states and a maximum of five output steady states, in the operating range considered. Moreover, the state multiplicity analysis revealed that input multiplicity can be present in this FCC unit, depending on the choice of the control structure, and that operating the unit in full combustion mode can prevent instabilities due to input and output multiplicities. Therefore, these results can be used to guide the design of the most appropriate control structures in industrial applications. For the FCC unit with high-efficiency regenerator the most appropriate control structure corresponds to the control of the riser reactor temperature and the oxygen level in the flue gas, with the catalyst circulation rate and the combustion air flow rate, respectively.

The aim of this study is to obtain a model that can simulate the performance of an industrial fluid catalytic cracking (FCC) unit in steady and dynamic state, and which will subsequently be used in studies of control and real time optimisation. In this paper, a dynamic model for a R2R type FCC unit is presented. The model includes the riser, the stripper/disengager, the regeneration system and the catalyst transport lines. Mass, energy and pressure balances are performed for each of these sections. Simulation results for steady state are presented and compared qualitatively to those obtained from previous FCC models. The dynamic behaviour of the system is explored through two perturbations in open loop, one on the fresh feed flow rate and one on the air flow rate to the first regenerator. The results illustrate the consistency of the model and are in agreement with what has been observed in studies available in the open literature.

This paper presents an approach to estimate the outputs and the uncertainty associated to the forecast for discrete dynamic systems represented by state-space models. The complete strategy includes three steps: 1. process identification based on a data sample; 2. estimation of the current process state based on the information available during a moving past horizon, which may contain lack of observations; 3. forecast of process states, process outputs and uncertainty along the future horizon. This procedure can be incorporated in control strategies that explicitly consider model uncertainty.

This work introduces a strategy for the optimal design of distillation systems based on continuous optimization. The approach is similar to the one proposed earlier by [Lang, Y. -D., & Biegler, L. T. (2002). A distributed stream method for tray optimization. AIChE Journal, 48, 582], avoiding the need of solving extremely large and non-linear discrete optimization problems. When used with complex distillation units, it can identify interesting design configurations not considered by other continuous formulations, and also relieve some of the numerical difficulties associated with the use of distribution functions for the optimal location of feed and side-streams. The method considers a relaxation of the original problem, where the streams are initially split to several trays in the column, not necessarily adjacent. The optimal location of each stream is converged by constraining the optimization problem, using adjustable parameters that control the minimum amount of aggregation allowed. The methodology is illustrated with the application to several industrial case studies, including sets of distillation columns. Models up to 17,000 variables/equations were solved, revealing large economic benefits in the design of new units and optimization of sets of existing ones. http://www.sciencedirect.com/science/article/B6TFT-4FPX2PR-2/1/3f5cfa384d0e1815a6bb4f3f2a808ec0

A pilot plant for the continuous adiabatic nitration of benzene was constructed, reproducing the industrial operating conditions, in order to identify the reaction regime prevailing in this industrial process. Important process parameters were tested covering a wide range of operating conditions: reaction temperature (80–135 ◦ C), benzene to nitric acid molar feed ratio (0.96–1.15) and stirring speed (390–1700 rpm). The residence time and the sulphuric acid strength were fixed at 2 min and 68%, respectively. The data from a large number of experiments show a good agreement with the results of a mathematical model of the reactor. In the range of operating conditions tested, it was shown that the prevailing reaction regime is the intermediate one (0.3 < Ha < 2). The film model used to predict the mononitrobenzene production according to the intermediate regime achieved a good accuracy. The asymptotic solutions for the fast and slow reaction regimes were compared with the full solution model and it was clearly shown that the last led to improved results. Since the film model is a simple approach to describe the mass transfer with simultaneous chemical reaction, the results achieved confirmed the adequacy of this modelling approach. © 2004 Elsevier B.V. All rights reserved.

The film and the Danckwerts penetration models were used to model the heterogeneous liquid-liquid reaction of benzene nitration. Analytical solutions were developed for both models considering a pseudo-first order reaction. Models were confronted with experimental results showing good predictions in the intermediate reaction regime (0.3