Marek Krawczyk and Piotr Arkuszewski
Piotr Arkuszewski and Marek Krawczyk
Surgical Management of Injuries of the Hepatic Veins and Retrohepatic Inferior Vena Cava
Andrzej Krawczyk and Marek Krąpiec
The Permutation Test for Testing the Statistical Significance of the Power Spectrum Estimation in Dendrochronological Analysis
The study presents a proposal of application of the statistical permutation test, known from other applications, for searching for the symptoms of cyclicity, in particular related to solar activity, in the annual growth sequences of trees. The test consists in generation of random sequences of the increment widths observed and comparison of their periodograms with the periodogram of the sequence analysed. This allows for evaluation of the significance of the individual frequencies in the total variability. The model calculations carried out indicate that in the studies on cyclicity in dendrochronological sequences satisfactory results could be obtained in the analysis of sets of the individual sequences (but not the chronologies produced from them). It is important to generate sufficiently high numbers (1000 and more) of random sequences and to apply relatively low significance levels (at 0.05, or even 0.01).
Dorota Krawczyk-Stańdo and Marek Rudnicki
Regularization Parameter Selection in Discrete Ill-Posed Problems — The Use of the U-Curve
To obtain smooth solutions to ill-posed problems, the standard Tikhonov regularization method is most often used. For the practical choice of the regularization parameter α we can then employ the well-known L-curve criterion, based on the L-curve which is a plot of the norm of the regularized solution versus the norm of the corresponding residual for all valid regularization parameters. This paper proposes a new criterion for choosing the regularization parameter α, based on the so-called U-curve. A comparison of the two methods made on numerical examples is additionally included.
Jarosław Sowiński, Marek Krawczyk and Marek Dziubiński
Comparison of experimental data and numerical simulation of two-phase flow pattern in vertical minichannel
The aim of the study was the implementation of a numerical simulation of the air-water two-phase flow in the minichannel and comparing results obtained with the values obtained experimentally. To perform the numerical simulations commercial software ANSYS FLUENT 12 was used. The first step of the study was to reproduce the actual research installation as a three-dimensional model with appropriate and possible simplifications - future computational domain. The next step was discretisation of the computational domain and determination of the types of boundary conditions. ANSYS FLUENT 12 has three built-in basic models with which a two-phase flow can be described. However, in this work Volume-of-Fluid (VOF) model was selected as it meets the established requirements of research. Preliminary calculations were performed for a simplified geometry. The calculations were later verified whether or not the simplifications of geometry were chosen correctly and if they affected the calculation. The next stage was validation of the chosen model. After positive verification, a series of calculations was performed, in which the boundary conditions were the same as the starting conditions in laboratory experiments. A satisfactory description of the experimental data accuracy was attained.
Oskar Kornasiewicz, Piotr Hevelke and Marek Krawczyk
Split Liver Transplantation (SLT) - Practical Introduction to Technical Aspects of Liver Splitting
Marek Krawczyk, Kamil Kamiński and Jerzy Petera
Experimental and numerical investigation of electrostatic spray liquid-liquid extraction with ionic liquids
A new concept of an electrostatic spray column for liquid-liquid extraction was investigated. An important problem for separation processes is the presence of azeotropic or close-boiling mixtures in their production, for example heptane with ethanol, since the separation is impossible by ordinary distillation. The use of ionic liquids (IL) as a dispersed solvent specially engineered for any specific organic mixture in terms of selectivity is a key factor to successful separation. As IL present particularly attractive combination of favorable characteristics for the separation of heptane and ethanol, in this work we use 1-butyl-3-methylimidazolium methyl sulfate [BMIM][MeSO4]. Because of high viscosity and relatively high cost of IL a new technique was introduced, consisting in the electrostatically spray generation to enhance the mass transport between the phases. In order to optimally design the geometry of the contactor a series of numerical simulation was performed. Especially multi-nozzle variants for better exploitation of contactor volume were investigated. Experiments showed excellent possibility of control of the dispersion characteristics by applied voltage and thus control of the rate of extraction. The preliminary simulations based on our mathematical model for a three nozzle variant exhibited visual agreement with the theory of electrostatics.
Łukasz Nazarewski, Waldemar Patkowski, Ryszard Pacho, Maja Marczewska and Marek Krawczyk
Lymphangiomas are rare benign lesions of the lymphatic vessels that are most commonly diagnosed in childhood. Intraperitoneal localization is unusual as, typically, they are located in the head and neck areas. In general, abdominal lymphangiomas seem to be asymptomatic, however, patients may occasionally suffer from acute abdominal symptoms, due to intestinal obstruction or peritonitis.
The study presented a case of a 41-year-old female patient, clinically asymptomatic, who was accidentally diagnosed with a multiseptated cystic lesion of the right liver lobe surrounding the gall-bladder fossa in a routine ultrasound examination. Further examinations including computed tomography and magnetic resonance (MR) aroused suspicion of a polycystic lesion of the gall-bladder and hepatoduodenal ligament. The cystic lesion of the gall-bladder and hepatoduodenal ligament filled with lymphatic fluid was diagnosed intraoperatively. Simultaneous cholecystectomy and radical resection of the cystic lesion was undertaken. The histopathological examination revealed the presence of a lymphangioma. Additionally, the authors of the study reviewed literature data concerning gall-bladder lymphangiomas.
Michał Grąt, Wacław Hołówko, Karolina Grzegorczyk, Michał Skalski and Marek Krawczyk
Long-Term Results of Liver Resection in the Treatment of Patients with Hepatocellular Carcinoma
The aim of the study was the analysis of the results of liver resection in the treatment of patients with hepatocellular carcinoma, taking into consideration the selected factors based on the department's material.
Material and methods. Data of 122 patients subject to liver resection due to hepatocellular carcinoma at the Department of General, Transplantation and Liver Surgery, Medical University of Warsaw, were subject to retrospective analysis.
The influence of selected factors on the long-term treatment results was determined, and the patient survival depending on the tumor stage as per the TNM scale was compared. The statistical significance threshold was set at p = 0.05.
Results. 1- and 3-year overall survival and recurrence-free survival in the whole patient group was 82.1% and 56.3%, and 57.7% and 20.1%, respectively. The perioperative mortality rate was 1.6%. The neoplasm advancement exceeding the first stage on the TNM scale was associated with lower values of overall survival (p = 0.001, HR = 3.7) and recurrence-free survival (p = 0.00008, HR = 3.8). Elevation of AFP was the only independent prognostic factor for overall survival (p = 0.04, HR = 1.04 at alpha-fetoprotein levels > 1000 ng/ml), while the presence of neoplastic emboli in small blood vessels was an independent risk factor for HCC recurrence (p = 0.02, HR = 2.24).
Conclusions. The alpha-fetoprotein levels and presence in the histopathological examination of neoplastic emboli in small blood vessels are independent prognostic factors for outcome of patients operated for hepatocellular carcinoma. The diagnosis of neoplasm at stage 1 as per TNM significantly improves long-term results of resective treatment.
Rafał Stankiewicz, Bogusław Najnigier and Marek Krawczyk
Resection of the gall-bladder is still the most common surgical procedure performed at general surgery departments. The laparoscopic method used in the majority of cases offers considerable benefits but at the same time is associated with an increased rate of bile duct complications. So far, a slim female aged 25-50 years was a typical patient with a iatrogenic bile duct injury.
The aim of the study was to identify the age of patients with iatrogenic bile duct injuries as well as the clinical course observed in recent years.
Material and methods. Gender and age structure of patients admitted to the Department of General, Transplant and Liver Surgery between the beginning of 2011 and June 2014 and treated for iatrogenic bile duct injuries, complications of laparoscopic cholecystectomy, were analysed. The patients were referred to the department as a reference centre.
Results. In the group of 186 patients, females predominated (69.4%) and the mean age was 52 years. A considerable increase in the mean age of patients treated in 2014 as compared with previous years was seen. This was related to an increased rate of bile duct injuries in patients aged over 70 years, who accounted for about 25% of the group. In previous years, bile duct injuries in patients of such an advanced age happened considerably less frequently.
Conclusions. A iatrogenic bile duct injury in an elderly person may prove a fatal complication. A repair surgery, i.e. the biliary-enteric anastomosis, is a major and burdensome procedure, particularly in the case of patients aged over 70 years. Special caution during laparoscopic cholecystectomy is advised in this population, and the slightest doubts should lead to conversion.