Andrzej J. Nowak

Heat transfer analysis of the continuous casting process by the front tracking BEM

Abstract Heat transfer problem in the strand during continuous casting is considered in the paper. Steady state temperature field in a coordinate system attached to the mould has been analyzed. Phase change is assumed to take place at constant temperature. The nonlinearity in this problem is caused by the unknown location of the solid–liquid interface. To determine both, this location and the resulting temperature field in the strand, a novel BEM front tracking algorithm has been developed. Numerical examples like one-dimensional (1D) phase change benchmark (modeled as two-dimensional (2D)) and several 2D problems of continuous casting of copper are included and discussed.

Seroprevalence of Helicobacter pylori infection in Polish children and adults depending on socioeconomic status and living conditions

PURPOSE Helicobacter pylori (H. pylori) is one of the causes of gastritis, peptic ulcer disease, gastric cancer and MALT-lymphoma. The frequency of H. pylori infection is different in various regions of the world and dependent on age, socioeconomic and hygiene status. The objective of this study was to assess seroprevalence and the associated socioeconomic and sociodemographic characteristics influencing H. pylori infection in children and adults in Polish population. MATERIAL/METHODS In multicenter epidemiological studies, H. pylori infection occurrence was assessed in Poland in the years 2002 and 2003. The seroprevalence of H. pylori infection diagnosis was based on IgG anti-H. pylori antibodies concentration above 24 UI/ml, which was measured using ELISA test. The study included 6565 subjects: 3307 adults (50.37%) and 3258 children (49.63%). RESULTS Positive result was observed in 3827 subjects (58.29%), i.e. 1043 children (32.01%) and 2784 adults (84.19%). H. pylori infection prevalence was greater in children of poor economic status, who were born in a rural area, lived in crowded houses with no running tap water and with toilet outside the house, and who did not observe hygiene rules. In adults, the factors predisposing to higher probability of being H. pylori infected included: being born in a rural area, having low family income and elementary education, smoking tobacco, drinking high proof alcohols as well as not observing of hygiene rules. CONCLUSIONS Improvement of socioeconomic status, sanitary and hygienic conditions and the education of the society might decrease H. pylori infection prevalence in children and in adults.

The dynamics of the oxidant-antioxidant balance in the early phase of human acute biliary pancreatitis.

Background/Aim: Reactive oxygen species play an important role in the pathogenesis of acute pancreatitis (AP) in animal models. Data on the oxidant-antioxidant balance in humans are scanty. The present study was undertaken to evaluate the dynamics of changes in the oxidant-antioxidant balance in the early phase of human AP. Methods: 74 consecutive patients with acute biliary pancreatitis (16 with severe, 58 with mild pancreatitis), treated endoscopically, were included in the study. Serum concentrations of sulfhydryl groups (SH; main nonenzymatic antioxidant; 73 patients) and thiobarbituric acid reactive substances (TBARS; markers of reactive oxygen species-mediated tissue damage; 56 patients) were determined on admission and on each of 10 successive days. The analysis comprised the comparison of results in patients with mild and severe outcome of pancreatitis. Results: Serum SH dropped by 27%, reaching the trough level on day 4 of hospitalization, whereas serum TBARS rose by 28%, reaching a peak 1 day later. Neither SH nor TBARS returned to initial values at the end of observation. The most dynamic changes in both SH and TBARS concentrations occurred in the first 3 days of hospitalization. The changes were significantly greater in patients with complicated pancreatitis in comparison to patients with mild disease, and were most pronounced in patients who developed infected pancreatic necrosis and who subsequently died. Conclusions: The oxidant-antioxidant balance changes rapidly in the early phase of human AP, confirming the role of oxidative stress in the pathogenesis of AP. The degree of changes correlates with the clinical severity of pancreatitis.

Identification of phase change fronts by Bezier splines and BEM

Abstract This paper discusses the identification of the phase change front in continuous casting. The problem is formulated and solved as a geometry inverse problem. Sensitivity analysis and boundary element method are used for the estimation of the identified values. The interface between solid and liquid phases in the process is modelled by Bezier curves. The measured temperatures required to solve the problem are always affected by measurement errors. Extensive calculations allow us to determine the influence of measurement errors on the accuracy of the phase change front location.

Shape Optimization of Coils and Cooling Ducts in Dry-Type Transformers Using Computational Fluid Dynamics and Genetic Algorithm

In this paper, shapes of cooling ducts in dry-type transformers are optimized using computational fluid dynamics (CFD) and the Genetic Algorithm (GA). The GA is used to optimize diameters of both ducts and coils. Constraints in the optimization process are the minimum distance between the high-voltage (HV) and the low-voltage (LV) windings and the outer diameter of coils. Since the investigated transformer is a special unit, two objective functions (OF) were applied to minimize the average and the maximum temperature of the windings, and thus the coil power losses. The OF value is determined using a CFD model that accounts for all three heat transfer modes. The local total heat fluxes are specified on the model external boundaries. The thermal properties of the coils and core are treated as anisotropic and temperature-dependent quantities, while the power losses are treated as heat sources and are computed based on the coupled CFD-EMAG model. Both coil properties and losses vary with each generated coil configuration. The results show that the nonuniform positioning of the wires and air ducts can significantly improve the heat dissipation. Consequently, the coil losses are substantially reduced.

Inverse analysis of continuous casting processes

This paper discusses an algorithm for phase change front identification in continuous casting. The problem is formulated as an inverse geometry problem, and the solution procedure utilizes temperature measurements inside the solid phase and sensitivity coefficients. The proposed algorithms make use of the boundary element method, with cubic boundary elements and Bezier splines employed for modelling the interface between the solid and liquid phases. A case study of continuous casting of copper is solved to demonstrate the main features of the proposed algorithms.

Solving Heat Transfer Problems by the Dual Reciprocity BEM

The impressive success of the Boundary Element Method [1],[2] in the last decade has been mainly due to the fact that the technique became applicable to a wide range of engineering problems e.g. [3–8]. The boundary value problems of heat transfer are among those which can be effectively solved by BEM. For many practical cases, e.g. linear and non-linear steady-state heat conduction, some problems of thermal radiation and many others, BEM can result in a simple and elegant formulation. However, some heat transfer problems lead to an integral equation with domain integrals. The presence of these integrals diminishes the efficiency of the method and makes the data preparation needed for the computer codes much more difficult.

Application of Bezier surfaces to the 3-D inverse geometry problem in continuous casting

In this article, a three-dimensional (3-D) numerical solution of the inverse geometry problem for a continuous casting process of an aluminium alloy is presented. In particular, an accurate determination of the interface location between the liquid and solid phases based on temperature measurements at several internal points of the body is discussed. This problem is crucial for the design and control of the casting process. To solve it, an algorithm was proposed that is an extension into 3-D of the solution procedure developed for the two-dimensional (2-D) geometrical inverse problem. Namely, in the solution algorithm, the Bezier splines for the 2-D procedures were replaced with the Bezier surfaces for the 3-D phase change boundary approximation. In the inverse procedure, a sensitivity analysis was used to estimate the location of the Bezier surface control points. While the measured temperatures required to solve the problem always contain measurement errors, a comparison of the numerically measured and retrieved values showed a very high computational accuracy. Consequently, the average percentage error of the control point locations is very satisfactory compared with the reference phase change solution. In addition, the computationally effective method was independent of the maximum error of measurements used for calculations.

Multivariate Analysis of Risk Factors for Development of Duodenal Ulcer in Helicobacter pylori-Infected Patients

Background: Although Helicobacter pylori is a significant etiologic factor of peptic ulcer disease, it remains unknown why ulcers develop only in the minority of infected individuals. Aim: The aim of this cross-sectional study was to evaluate the association between the presence of duodenal ulcer in H. pylori-infected patients and different risk factors. Methods: A total of 122 H. pylori-infected patients were enrolled; 79 had duodenal ulcer and 43 gastritis. Univariate analysis was conducted using either Fisher’s exact test or exact Cochrane-Armitage trend test. In multivariate analysis the logistic model was used. Results: Univariate analysis indicated six factors (male sex, smoking, antral H. pylori density, cagA presence in antrum, and vacA s1a presence in antrum and corpus). Four factors (sex, smoking-alcohol index, H. pylori density index, and cagA index) were found to be significant in multivariate analysis. The best model predicting duodenal ulcer included male sex, smoking, presence of H. pylori on histopathology in antrum and cagA presence in corpus. Conclusion: Although several risk factors were significantly associated with duodenal ulcer, we failed in the identification of either a single risk factor or a set of factors that can unequivocally differentiate patients with ulcer from those with gastritis.

Diagnostic and therapeutic guidelines for gastro-entero-pancreatic neuroendocrine neoplasms (recommended by the Polish Network of Neuroendocrine Tumours)

An increased interest in gastro-entero-pancreatic neuroendocrine neoplasms (GEP NENs) has recently been observed. These are rare neoplasms and their detection in recent years has improved. Over 50% of GEP NENs are carcinoids, and they are usually found incidentally during surgery in the small intestine and appendix and at diagnosis in distant metastases, mainly to the liver. There is a need for co-operation between specialists in various disciplines of medicine in order to work out the diagnostic and therapeutic guidelines. In this publication, we present general recommendations of the Polish Network of Neuroendocrine Tumours for the management of patients with GEP NENs, developed at the Consensus Conference which took place in Kamień Śląski in April 2013. Members of the guidelines working groups were assigned sections of the 2008 guidance to update. In the subsequent parts of this publication, we present the rules of diagnostic and therapeutic management of: - neuroendocrine neoplasms of the stomach and duodenum (including gastrinoma); - pancreatic neuroendocrine neoplasms; - neuroendocrine neoplasms of the small intestine and the appendix; - colorectal neuroendocrine neoplasms. The proposed recommendations by Polish and foreign experts representing different fields of medicine (endocrinology, gastroenterology, surgery, oncology, nuclear medicine and pathology) will be helpful in the diagnosis and treatment of GEP NENs patients.